High-conductivity sulfide solid electrolyte as well as preparation method and application thereof

Abstract

The invention discloses a high-conductivity sulfide solid electrolyte as well as a preparation method and application thereof. The high-conductivity sulfide solid electrolyte comprises the following components in percentage by mass: 70-85wt% of a lithium source and a network forming body, the doping element accounts for 10-40 wt%; and 1-5 wt% of an additive. The high-conductivity sulfide solid electrolyte provided by the invention has excellent ionic conductivity, thermal stability and chemical stability, and can meet the requirements of high-performance solid-state batteries.

Description

Technical Field

[0001] The invention relates to a high-conductivity sulfide solid electrolyte and a preparation method and application thereof, belonging to the technical field of batteries. Background Art

[0002] With the increasing demand for electric vehicles and renewable energy storage, and the popularity of portable devices (such as mobile phones and computers), people's demand for high-capacity energy storage devices continues to grow. Lithium batteries are currently the chemical power source with high energy density and good cycle stability among rechargeable and dischargeable batteries, and lithium batteries are being used on a large scale. However, organic liquid electrolyte lithium-ion batteries contain a large amount of organic solvents, so they will cause prominent safety hazards during use, and the safety issues they present cannot be ignored. On the one hand, organic electrolytes are volatile and flammable. When the battery is overcharged, over-discharged, and at high temperatures, it will swell, and electrolyte leakage and other problems will easily cause safety problems such as fire. On the other hand, when the battery is overcharged, overcharged, and overcharged, lithium ions are easily grown on the surface of the negative electrode during the shuttle conduction in the electrolyte to produce lithium dendrites. Lithium dendrites will penetrate the diaphragm and cause direct contact between the positive and negative electrodes of the battery, resulting in a short circuit, which will cause safety hazards. Therefore, the research of safe and reliable new lithium-ion batteries has become a very urgent task at present.

[0003] Solid electrolyte is an electrolyte that transfers charge between positive and negative electrodes in a solid form. For all-solid-state lithium secondary batteries, in order to ensure that they have good electrochemical properties and safety performance, solid electrolytes are usually required to have high ionic conductivity and low electronic conductivity, that is, lithium ions can be transferred in solid electrolytes, but electrons cannot be transferred. The ionic conductivity of solid electrolytes is the diffusion phenomenon of ions under the action of an electric field, including the embodiment of ion movement in solid electrolytes, which reflects the migration ability of ions, and is related to the charge level of mobile ions in solid electrolytes and the crystal structure of solid electrolytes. Generally, lithium ions, as monovalent cations, have little charge, low activation energy, and high ionic conductivity. At the same time, in tightly structured ionic crystals, due to the small gaps available for ion movement and the difficulty of interstitial ion migration, the activation energy of ion migration is high and the ionic conductivity is low. Therefore, if a solid electrolyte wants to have high ionic conductivity, it must have a large concentration of ionic lattice defects, and these lattice defects must participate in ionic conductivity, that is, the generation of ionic lattice defects and their concentration are the key to determining the size of the ionic conductivity of solid electrolytes.

[0004] All-solid-state lithium secondary batteries have safety performance that cannot be matched by liquid lithium secondary batteries, and are expected to completely eliminate potential safety hazards during use. They are more in line with the future development needs of electric vehicles and large-scale energy storage, and have become a research and development hotspot for researchers from various countries. Up to now, all-solid-state lithium secondary batteries have not yet been widely used, and the bottleneck is the research and development of high-performance solid electrolyte materials. The research directions of solid electrolyte materials currently mainly include: polymers, oxides, sulfides and other categories. Among them, the conductivity of polymer solid electrolytes at room temperature is extremely low (usually <10 -6 S / cm), so it is difficult to play its advantages; oxide solid electrolytes also have low conductivity, and their hardness is usually large, which makes it difficult to adapt to the changes in electrode size during charging and discharging, and thus prone to matching failure problems; sulfide solid electrolytes have high room temperature conductivity (up to 10 -3 S / cm to 10 -2 S / cm) and good contact with the electrode interface, so it has attracted widespread attention from researchers as the preferred solid electrolyte for all-solid-state lithium secondary batteries.

[0005] However, sulfide solid electrolytes still have some problems and shortcomings. The conductivity of solid electrolytes still needs to be further improved. Secondly, the composition of sulfide solid electrolytes is unstable, and it is easy to react with water and oxygen. The stability at high temperature and compatibility with electrode materials are still insufficient. Therefore, sulfide solid electrolytes still need further research and optimization. Summary of the invention

[0006] In view of this, the present invention provides a high-conductivity sulfide solid electrolyte and a preparation method and application thereof. The technical problem to be solved is to provide a high-conductivity sulfide solid electrolyte with excellent ionic conductivity, thermal stability and chemical stability, which can meet the needs of high-performance solid-state batteries.

[0007] The purpose of the present invention and the technical problems solved therein are achieved by adopting the following technical measures. The present invention proposes a highly conductive sulfide solid electrolyte, which comprises, by mass percentage:

[0008] Lithium source and network former 70-85wt%;

[0009] Doping elements 10-40wt%;

[0010] Additives 1-5wt%.

[0011] The purpose of the present invention and the technical problems to be solved can be further achieved by adopting the following technical measures.

[0012] Preferably, in the aforementioned highly conductive sulfide solid electrolyte, the lithium source is Li2S; and the network former is P2S5.

[0013] Preferably, in the aforementioned highly conductive sulfide solid electrolyte, the doping element is selected from at least one of Al2S3, ZnS, CdS2 and MnS2.

[0014] Preferably, in the aforementioned highly conductive sulfide solid electrolyte, the additive comprises a halide and lithium oxide; the halide is selected from at least one of LiCl, LiF and LiI.

[0015] Preferably, the aforementioned highly conductive sulfide solid electrolyte, wherein the ionic conductivity of the highly conductive sulfide solid electrolyte is greater than 1.3 mS / cm; the interface impedance is less than 40 Ω·cm 2 ; Thermal decomposition temperature>400℃.

[0016] The purpose of the present invention and the technical problem to be solved are achieved by adopting the following technical solutions. A method for preparing a highly conductive sulfide solid electrolyte proposed in the present invention comprises the following steps:

[0017] S1: mixing the lithium source, the network former, the doping element and the additive in proportion to obtain a mixed powder;

[0018] S2 sintering the mixed powder obtained in step S1 at a high temperature to obtain a crude electrolyte;

[0019] S3 annealing the crude electrolyte obtained in step S2 to obtain a solid electrolyte;

[0020] S4: ball-milling the solid electrolyte obtained in step S3 into solid electrolyte powder to obtain the highly conductive sulfide solid electrolyte.

[0021] The purpose of the present invention and the technical problems to be solved can be further achieved by adopting the following technical measures.

[0022] Preferably, in the aforementioned method for preparing a highly conductive sulfide solid electrolyte, in step S1, the lithium source is Li2S; the network former is P2S5; the doping element is selected from at least one of Al2S3, ZnS, CdS2 and MnS2; the additive includes a halide and lithium oxide; and the halide is selected from at least one of LiCl, LiF and LiI.

[0023] Preferably, in the aforementioned method for preparing a highly conductive sulfide solid electrolyte, in step S2, the sintering temperature is 200-600° C.; and the sintering time is 1-16 hours.

[0024] Preferably, in the aforementioned method for preparing a highly conductive sulfide solid electrolyte, in step S2, the annealing temperature is 100-400° C.; and the annealing time is 1-10 h.

[0025] Preferably, in the aforementioned method for preparing a highly conductive sulfide solid electrolyte, in step S4, the particle size range of the powder is 1-40 μm.

[0026] The purpose of the present invention and the solution of its technical problems can also be achieved by the following technical measures. An all-solid-state lithium secondary battery proposed in the present invention comprises a positive electrode sheet, a negative electrode sheet and a solid electrolyte membrane, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode membrane sheet disposed on the positive electrode current collector, and the solid electrolyte membrane is composed of the above-mentioned high-conductivity sulfide solid electrolyte; the high-conductivity sulfide solid electrolyte comprises, by mass percentage:

[0027] Lithium source and network former 70-85wt%;

[0028] Doping elements 10-40wt%;

[0029] Additives 1-5wt%.

[0030] The purpose of the present invention and the technical problems to be solved can be further achieved by adopting the following technical measures.

[0031] Preferably, the aforementioned all-solid-state lithium secondary battery, wherein the first-week specific capacity of the all-solid-state lithium secondary battery is greater than 100 mAh / g; the capacity retention rate after 1000 cycles is greater than 85%; the battery cycle life at room temperature is greater than 5000 times; and the battery energy density is greater than 300 Wh / kg.

[0032] The purpose of the present invention and the solution to the technical problem thereof can also be achieved by adopting the following technical measures. A method for preparing an all-solid-state lithium secondary battery proposed in the present invention comprises the following steps:

[0033] The positive electrode active material and the highly conductive sulfide solid electrolyte are mixed uniformly in proportion and then pressed into a layer to obtain a positive electrode membrane;

[0034] The positive electrode current collector, the positive electrode membrane, the high-conductivity sulfide solid electrolyte and the negative electrode plate are assembled into an all-solid-state lithium secondary battery by pressure molding.

[0035] Compared with the prior art, the highly conductive sulfide solid electrolyte and its preparation method and application described in the present invention have the following beneficial effects:

[0036] 1. The highly conductive sulfide solid electrolyte of the present invention has excellent ionic conductivity, thermal stability and chemical stability, and can meet the requirements of high-performance solid-state batteries;

[0037] 2. The all-solid-state lithium secondary battery prepared using the sulfide solid electrolyte, cathode and anode of the present invention has high first-cycle specific capacity, high first-cycle coulombic efficiency and good cycle performance.

[0038] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the preferred embodiments of the present invention are described in detail as follows. DETAILED DESCRIPTION

[0039] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following is a detailed description of a highly conductive sulfide solid electrolyte and its preparation method and application according to the present invention, its specific implementation method, structure, characteristics and effects in combination with the preferred embodiment. In the following description, different "one embodiment" or "embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures or characteristics in one or more embodiments may be combined in any suitable form.

[0040] Unless otherwise specified, the materials, reagents, etc. involved below are all commercially available products well known to those skilled in the art; unless otherwise specified, the methods described are all methods known in the art. Unless otherwise defined, the technical terms or scientific terms used should have the usual meanings understood by ordinary technicians in the field to which the present invention belongs. If no specific experimental steps or conditions are specified below, the operations or conditions of the conventional experimental steps described in the literature in the field can be followed.

[0041] Some embodiments of the present invention provide a highly conductive sulfide solid electrolyte, which comprises, by mass percentage:

[0042] Lithium source and network former 70-85wt%;

[0043] Doping elements 10-40wt%;

[0044] Additives 1-5wt%.

[0045] In some embodiments, optionally, the lithium source is Li2S; the network former is P2S5. Preferably, the total content of the lithium source and the network former (Li2S+P2S5) is 72-82wt%. Preferably, the mass ratio of Li2S to P2S5 is 0.3-0.7. Further preferably, the mass ratio of Li2S to P2S5 is 0.4-0.5.

[0046] In some embodiments, optionally, the doping element is selected from at least one of Al2S3, ZnS, CdS2 and MnS2 to improve the ionic conductivity of the electrolyte. Preferably, the composition of the doping element in terms of mass percentage is: Al2S34-15wt%, ZnS2-15wt%, CdS2

[0047] 0.5-10wt%, MnS2 2-10wt%. Preferably, the masses of Al2S3, ZnS, CdS2 and MnS2 satisfy the following relationship: CdS2 / (Al2S3+ZnS+CdS2+MnS2)<0.25.

[0048] In some embodiments, optionally, the additive includes a halide and lithium oxide (Li2O) to enhance the ionic conductivity and thermal stability of the electrolyte; the halide is selected from at least one of LiCl, LiF and LiI. Preferably, the masses of LiCl, LiF and LiI satisfy the following relationship: LiF / (LiCl+LiF+LiI)=0.5-1.0. Preferably, the masses of Li2O, LiCl, LiF and LiI satisfy the following relationship: Li2O / (LiCl+LiF+LiI+Li2O)=0.2-0.6. Further preferably, the masses of Li2O, LiCl, LiF and LiI satisfy the following relationship: Li2O / (LiCl+LiF+LiI+Li2O)=0.3-0.5.

[0049] According to the test, the ionic conductivity of the highly conductive sulfide solid electrolyte is greater than 1.3 mS / cm. Preferably, it is greater than 1.7 mS / cm. More preferably, it is greater than 2.0 mS / cm; the interface impedance is less than 40 Ω·cm 2 (Contact surface with electrode); thermal decomposition temperature>400℃.

[0050] In the above technical solution, a solid electrolyte in which amorphous and crystalline states are uniformly mixed can be obtained by mixing Li2S, P2S5, Al2S3, ZnS, CdS2, MnS2, LiCl, LiF, LiI, and Li2O, i.e., the highly conductive sulfide solid electrolyte. Among them, Li2S is a glassy network modified sulfide, P2S5 is a glassy network forming sulfide, Al2S3 is a glassy network intermediate sulfide, and ZnS, CdS2, MnS2, LiCl, LiF, LiI, and LiO are dopants.

[0051] As the main ion conductor, Li2S's excellent ionic conductivity is the basis of solid electrolytes. Li2S exhibits good ionic conductivity at room temperature, which helps to improve the overall performance of the battery. P2S5 acts as a network former in the electrolyte. The introduction of P2S5 can reduce the lattice energy of sulfides, enhance the migration ability of lithium ions, improve conductivity, and enhance the structural stability of the material. By forming a sulfide network, the composite effect of Li2S and P2S5 can optimize the ion migration path and improve the overall ionic conductivity. If the content of Li2S and P2S5 is too small, on the one hand, the source of lithium ions in the sulfide solid electrolyte is less, which will reduce the ionic conductivity of the sulfide solid electrolyte. On the other hand, it will also cause the final sulfide solid electrolyte to contain more bridging sulfur, which is not conducive to the rapid transmission of lithium ions therein, and will also reduce the ionic conductivity of the sulfide solid electrolyte. If the content of Li2S and P2S5 is too high, the content of bridging sulfur in the final sulfide solid electrolyte is too low, and the content of non-bridging sulfur is high. Non-bridging sulfur easily captures lithium ions and makes it difficult for them to move, so it is not conducive to improving the ionic conductivity of the sulfide solid electrolyte. By limiting the total content of Li2S+P2S5 to 70-85wt% and optimizing its ratio to Li2S:P2S5=0.3~0.7, a highly conductive sulfide solid electrolyte is obtained. The electrolyte is prepared by a high-temperature solid-phase reaction method to ensure its structural uniformity and relatively high mechanical strength.

[0052] Al2S3 is a network intermediate, which can further expand the three-dimensional spatial network structure, interact with the network former to form a special glass phase network, and improve the electrochemical stability of the sulfide solid electrolyte. Since sulfur has a large ionic radius and a small electronegativity, it has a weak binding effect on lithium ions. At the same time, the long-range disordered glass phase network also provides a large transmission channel for lithium ions, which is convenient for the transmission of lithium ions and makes the sulfide solid electrolyte have a higher ionic conductivity overall. If the content of Al2S3 is too small, it cannot form an expanded spatial network structure with Li2S+P2S5, which is not conducive to the rapid transmission of lithium ions. If the content of Al2S3 is too large, the three-dimensional spatial network structure of the glass phase is dense, resulting in excessive viscosity of the glass phase. At the same time, the content of Li2S+P2S5 is relatively small, and it is impossible to effectively break some sulfur bridges in the molecular chain, which is not conducive to the rapid transmission of lithium ions. Preferably, the content of Al2S3 is 4-15wt%.

[0053] The use of ZnS, CdS2, and MnS2 doping can improve the ionic conductivity and electrolyte compatibility of sulfide solid electrolytes by constructing gaps and changing the size of lithium ion transmission channels. By changing the electronic structure of the material, expanding the size of lithium ion channels in the crystal, and enhancing the migration ability of ions in the lattice, multi-doped sulfide solid electrolytes can obtain higher lithium ion conductivity.2+ The structural stability of multi-doped sulfide solid electrolytes can be improved and their thermal stability can be increased. Cd ions can effectively inhibit phase change under high temperature conditions and maintain the stability of the electrolyte. Manganese doping helps to optimize the crystal structure of the electrolyte and enhance its ionic conductivity. At the same time, manganese ions can form stable complexes with lithium ions to further improve conductivity. Preferably, ZnS is 2-15wt%, CdS2 is 0.5-10wt%, and MnS2 is 2-10wt%. Further preferably, the doping amount of Al2S3, ZnS, CdS2, and MnS2 is 10-30wt% in total.

[0054] As modifiers, LiCl, LiF, LiI, and Li2O can reduce the interfacial impedance between the electrolyte and the electrode by optimizing the interfacial interaction, improve the interfacial properties of the electrolyte, form a better conductivity path, reduce the interfacial resistance of the electrolyte material, and further improve the chemical stability, thermal stability, and ionic conductivity. As an additive, Li2O can enhance the ionic conductivity of the electrolyte, improve its thermal stability, and inhibit the degradation of the electrolyte. Preferably, the doping content is 1-5wt% in total.

[0055] The “high conductivity” in the above-mentioned “highly conductive sulfide solid electrolyte” means that the ionic conductivity of the sulfide solid electrolyte is greater than or equal to 1.87 mS / cm.

[0056] Some embodiments of the present invention also provide a method for preparing a highly conductive sulfide solid electrolyte, comprising the following steps:

[0057] S1: The lithium source and the network former, the doping element and the additive are mixed uniformly in proportion to obtain a mixed powder; specifically, a high-purity lithium source and the network former, the doping element and the additive are used as raw materials, mixed in proportion, and mixed uniformly by ball milling; wherein the lithium source is Li2S; the network former is P2S5; the doping element is selected from at least one of Al2S3, ZnS, CdS2 and MnS2; the additive includes a halide and lithium oxide; the halide is selected from at least one of LiCl, LiF and LiI;

[0058] Preferably, in an argon dry atmosphere (water content is less than or equal to 1ppm, oxygen content is less than or equal to 1pmm. Excessive moisture and oxygen content will seriously affect the performance and life of the electrolyte), analytically pure Li2S, P2S5, Al2S3, ZnS, CdS2, MnS2, halides and lithium oxide are weighed in proportion and placed in a mortar for manual premixing to obtain a premixed initial material. The premixed initial material is then placed in a ball mill, and the ball mill is sealed after adding cyclohexane organic solvent, and high-energy ball milling is performed at a speed of 200 to 1000rpm for 10 to 20h to obtain an initial wet material. In an argon dry atmosphere (water content is less than or equal to 1ppm, oxygen content is less than or equal to 1ppm), the initial wet material is decompressed and drained to remove the organic solvent to obtain a uniform initial dry powder, the powder uniformity is >95%, preferably >98% (the greater the uniformity, the better), and the test method is the conductivity method.

[0059] S2: Sintering the mixed powder obtained in step S1 at high temperature to obtain a crude electrolyte (forming a dense solid electrolyte); the sintering temperature is 200-600°C; specifically, the primary dry powder is formed into a sheet material at a pressure of >10MPa, preferably, the pressure is >15MPa, and more preferably, 50MPa>pressure>20MPa. The sheet material is placed in an argon dry atmosphere (water content is less than 1ppm, oxygen content is less than 1ppm), heated to 200-600°C at a heating rate of 1-5°C / min for heat treatment, kept warm for 0.5-20h, cooled to room temperature with the furnace and then discharged, ground and crushed to an average particle size of 20μm, to obtain a sulfide solid electrolyte. Preferably, the sintering temperature is 250-550°C. More preferably, the sintering temperature is 400-500°C. Preferably, the insulation time is 1-16h. More preferably, the insulation time is 2-14h.

[0060] S3: annealing the crude electrolyte obtained in step S2 to improve its microstructure and ionic conductivity to obtain a sintered dense solid electrolyte; preferably, the annealing temperature is 100-400°C, more preferably, the annealing temperature is 230-360°C, and the annealing time is 1-10h. More preferably, the annealing time is 2-5h.

[0061] S4: solid-phase ball milling the solid electrolyte obtained in step S3 into solid electrolyte powder to obtain the highly conductive sulfide solid electrolyte. The particle size of the powder is in the range of 1-40 μm.

[0062] The existing solid-phase ball milling process is difficult to achieve the preparation of sulfide solid electrolyte particles with smaller particle sizes. The gaps between the sulfide solid electrolyte particles in the pressed solid electrolyte membrane are large, and the solid electrolyte film is not dense enough, which increases the solid-phase diffusion energy barrier of lithium ions and reduces the cycle performance of all-solid-state lithium secondary batteries. In addition, negative electrode lithium dendrites are more likely to pierce the solid electrolyte membrane to reach the positive electrode, causing internal short circuits and triggering safety problems for all-solid-state lithium secondary batteries.

[0063] Preferably, the grinding balls used in the solid phase ball mill are made of zirconium oxide.

[0064] Preferably, the weight ratio of grinding balls to materials is 30:1 to 50:1. Further preferably, the weight ratio of grinding balls to materials is 40:1 to 45:1.

[0065] Preferably, the particle size range of the powder is 2-35 μm, the weight content of particles larger than 30 μm is less than 1%, and the weight content of particles smaller than 3 μm is less than 1%, which is to control the particle size range and uniformity of the powder. The fewer particles larger than 30 μm and smaller than 3 μm, the better the uniformity of the particles.

[0066] Preferably, the powder particles have a D50 of 5-10 μm.

[0067] Some embodiments of the present invention also provide an all-solid-state lithium secondary battery, comprising a positive electrode plate, a negative electrode plate and a solid electrolyte membrane, wherein the positive electrode plate comprises a positive electrode collector and a positive electrode membrane arranged on the positive electrode collector, and the solid electrolyte membrane is composed of the above-mentioned high-conductivity sulfide solid electrolyte.

[0068] In some optional embodiments, the positive electrode membrane includes a positive electrode active material and the above-mentioned high-conductivity sulfide solid electrolyte, and the mass ratio of the two is (65-75):30.

[0069] In some optional embodiments, the positive electrode current collector may be an aluminum foil; and the negative electrode plate may be a metal lithium plate.

[0070] In some optional embodiments, the positive electrode active material may be selected from at least one of lithium iron phosphate, lithium cobalt phosphate, lithium nickel phosphate, lithium manganese phosphate and corresponding double salts. When the positive electrode active material is the above-mentioned lithium salt positive electrode active material, the corresponding negative electrode active material may be selected from at least one of graphite, soft carbon, hard carbon, silicon carbon, metallic lithium and lithium alloy.

[0071] In some optional embodiments, the positive electrode plate may further include a conductive agent and a binder, and the types of the conductive agent and the binder are not specifically limited.

[0072] After testing, the first-week specific capacity of the all-solid-state lithium secondary battery is greater than 100mAh / g; further preferably, the first-week specific capacity is greater than 130mAh / g; further preferably, the first-week specific capacity is greater than 160mAh / g. The capacity retention rate after 1000 cycles is greater than 85%; further preferably, the capacity retention rate after 1000 cycles is greater than 90%; further preferably, the capacity retention rate after 1000 cycles is greater than 95%. The battery cycle life is greater than 5000 times (at room temperature); further preferably, the battery cycle life is greater than 10000 times (at room temperature). The battery energy density is greater than 300Wh / kg; further preferably, the battery energy density is greater than 350Wh / kg.

[0073] Some embodiments of the present invention also provide a method for preparing an all-solid-state lithium secondary battery, comprising the following steps:

[0074] The positive electrode active material and the above-mentioned highly conductive sulfide solid electrolyte are mixed uniformly in proportion and then pressed into a layer to obtain a positive electrode membrane;

[0075] The positive electrode current collector, the positive electrode membrane, the above-mentioned high-conductivity sulfide solid electrolyte and the negative electrode plate are assembled into an all-solid-state lithium secondary battery by pressure molding.

[0076] Furthermore, the positive electrode current collector may be an aluminum foil; and the negative electrode plate may be a metal lithium plate.

[0077] Specifically, the mass ratio of the positive electrode active material to the above-mentioned highly conductive sulfide solid electrolyte is (65-75):30.

[0078] The performance tests described in the present invention are all conventional test methods in the field of this technology. For example, the peak current ratio of the anode peak to the cathode peak of the multi-doped sulfide solid electrolyte and the ionic conductivity are tested by an electrochemical workstation (Donghua Test: DH7001) to test its AC impedance and then calculate its ionic conductivity; the thermal decomposition temperature of the electrolyte is measured by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) to evaluate thermal stability; chemical stability test: the chemical stability test is carried out in the environment where the electrolyte material is in contact with the electrode material to observe the phase change and degradation of the electrolyte; the first week specific capacity, first week coulomb efficiency, and capacity retention rate after 100 cycles of the all-solid-state lithium secondary battery are tested by (New Will Battery Tester: CT-4008) for battery performance, and the assembled all-solid-state lithium secondary battery is subjected to constant current charge and discharge test, the charge and discharge voltage range is -0.5V~6V, and the test temperature is 25°C.

[0079] The present invention is further described below in conjunction with specific embodiments.

[0080] Example 1

[0081] This embodiment provides a method for preparing a highly conductive sulfide solid electrolyte, comprising the following steps:

[0082] In an argon dry atmosphere (water content of 0.1ppm, oxygen content less than 0.2ppm), analytically pure Li2S, P2S5, Al2S3, ZnS, CdS2, MnS2 and LiCl, LiF, LiI, Li2O were weighed in a mass ratio of 24:56:8:3:1:3:1:2:1:1 and placed in a mortar for manual premixing to obtain a premixed initial material. Then, 5g of the premixed initial material was taken and placed in a 60ml ZrO2 ball mill (the mass ratio of the ball mill was 40:1), and 15ml of commercially available cyclohexane organic solvent was added and the ball mill was sealed, and high-energy ball milling was performed at a speed of 900rpm for 10h to obtain an initial wet material. In an argon dry atmosphere (water content of 0.1ppm, oxygen content of 0.2ppm), the initial wet material is decompressed to 0.1Pa to remove the organic solvent to obtain an initial dry powder, and then the initial dry powder is formed into a sheet material at a pressure of 25MPa. The sheet material is placed in an argon dry atmosphere (water content of 0.1ppm, oxygen content of 0.2ppm), heated to 450°C at a heating rate of 1°C / min, kept warm for 3h, cooled to room temperature with the furnace, discharged, ground and crushed to D50 of 20μm, to obtain a multi-doped sulfide solid electrolyte 24Li2S-56P2S5-8Al2S3-3ZnS-1CdS2-3MnS2-1LiCl-2LiF-1LiI-1Li2O, that is, the highly conductive sulfide solid electrolyte is obtained.

[0083] A positive electrode membrane is obtained by uniformly mixing the positive electrode active material and the multi-doped sulfide solid electrolyte prepared above at a mass ratio of 70:30 and then pressing the mixture into a layer with a thickness of 0.05 mm at a pressure of 20 MPa, wherein the positive electrode active material is solid LiNiO2, the positive electrode collector is aluminum foil, and a metal lithium sheet is used as the negative electrode pole piece. The positive electrode collector, the positive electrode membrane, the multi-doped sulfide solid electrolyte prepared above and the negative electrode pole piece are assembled into an all-solid-state lithium secondary battery by pressure forming (20 MPa).

[0084] The operating voltage range of the all-solid-state lithium secondary battery is set to 2.5V to 5V, and a constant current charge and discharge method is used to perform a cycle test to obtain the first-cycle discharge specific capacity, first-cycle coulomb efficiency, and capacity retention rate after 1000 cycles of the all-solid-state lithium secondary battery. The test current is 0.1C (current density is 0.13mA / cm 2 ), the test temperature is 25℃.

[0085] 0.2g of the multi-doped sulfide solid electrolyte prepared in the above steps was pressed into a solid electrolyte film with a diameter of 15mm at a pressure of 25MPa, and a symmetrical cell was formed with stainless steel as a blocking electrode to test the impedance of the sulfide solid electrolyte at 25°C. The ionic conductivity of the sulfide solid electrolyte is calculated by the formula δ=L / (R·S), where δ is the ionic conductivity, L is the thickness of the solid electrolyte film, R is the impedance value of the sulfide solid electrolyte, and S is the effective cross-sectional area of ​​the solid electrolyte film.

[0086] 0.2 g of the sulfide solid electrolyte prepared in the above steps was pressed into a solid electrolyte membrane with a diameter of 15 mm at a pressure of 25 MPa. Then, metallic lithium was used as the working electrode and stainless steel as the counter electrode to test the electrochemical stability of the sulfide solid electrolyte. The scanning potential range was -0.5 V to 6 V, and the process was set to scan from the open circuit potential to -0.5 V at a scanning speed of 1 mV / s, then the potential was reversed and scanned to 6 V, and finally scanned back to the open circuit potential.

[0087] The test results show that the peak current ratio of the anode peak to the cathode peak of the multi-doped sulfide solid electrolyte prepared above is 0.87; the ionic conductivity is 2.14mS / cm; the interface impedance is 32.7Ω·cm 2 (Contact surface with electrode); decomposition temperature is 480°C; in the environment in contact with electrode materials, the electrolyte exhibits excellent chemical stability and can effectively inhibit the degradation of electrode materials.

[0088] After testing, the all-solid-state lithium secondary battery prepared above has a first-week specific capacity of 184mAh / g; the first-week coulomb efficiency is 91.6%; the capacity retention rate after 1000 cycles is 94.2%; the battery cycle life is greater than 10,000 times (at room temperature); and the battery energy density is 385Wh / kg.

[0089] Example 2

[0090] The difference between this embodiment and embodiment 1 is that, in this embodiment, the mass ratio of Li2S, P2S5, Al2S3, ZnS, CdS2, MnS2, LiCl, LiF, LiI, and Li2O is 29:43:14:6:2:2.5:0.4:1.8:0.3:1; the remaining steps and parameters are the same as those in embodiment 1, and a multi-doped sulfide solid electrolyte 29Li2S-43P2S5-14Al2S3-6ZnS-2CdS2-2.5MnS2-0.4LiCl-1.8LiF-0.3LiI-1Li2O is obtained, that is, the highly conductive sulfide solid electrolyte is obtained.

[0091] A positive electrode membrane is obtained by uniformly mixing the positive electrode active material and the multi-doped sulfide solid electrolyte prepared above at a mass ratio of 70:30 and then pressing the mixture into a layer with a thickness of 0.05 mm at a pressure of 20 MPa, wherein the positive electrode active material is solid LiNiO2, the positive electrode collector is aluminum foil, and a metal lithium sheet is used as the negative electrode pole piece. The positive electrode collector, the positive electrode membrane, the multi-doped sulfide solid electrolyte prepared above and the negative electrode pole piece are assembled into an all-solid-state lithium secondary battery by pressure forming (20 MPa).

[0092] The operating voltage range of the all-solid-state lithium secondary battery is set to 2.5V to 5V, and a constant current charge and discharge method is used to perform a cycle test to obtain the first-cycle discharge specific capacity, first-cycle coulomb efficiency, and capacity retention rate after 1000 cycles of the all-solid-state lithium secondary battery. The test current is 0.1C (current density is 0.13mA / cm 2 ), the test temperature is 25℃.

[0093] 0.2g of the multi-doped sulfide solid electrolyte prepared in the above steps was pressed into a solid electrolyte film with a diameter of 15mm at a pressure of 25MPa, and a symmetrical cell was formed with stainless steel as a blocking electrode to test the impedance of the sulfide solid electrolyte at 25°C. The ionic conductivity of the sulfide solid electrolyte is calculated by the formula δ=L / (R·S), where δ is the ionic conductivity, L is the thickness of the solid electrolyte film, R is the impedance value of the sulfide solid electrolyte, and S is the effective cross-sectional area of ​​the solid electrolyte film.

[0094] 0.2 g of the sulfide solid electrolyte prepared in the above steps was pressed into a solid electrolyte membrane with a diameter of 15 mm at a pressure of 25 MPa. Then, metallic lithium was used as the working electrode and stainless steel as the counter electrode to test the electrochemical stability of the sulfide solid electrolyte. The scanning potential range was -0.5 V to 6 V, and the process was set to scan from the open circuit potential to -0.5 V at a scanning speed of 1 mV / s, then the potential was reversed and scanned to 6 V, and finally scanned back to the open circuit potential.

[0095] The test results show that the peak current ratio of the anode peak to the cathode peak of the multi-doped sulfide solid electrolyte prepared above is 0.84; the ionic conductivity is 1.93mS / cm; the interface impedance is 33.8Ω·cm 2 (Contact surface with electrode); decomposition temperature is 515°C; in the environment in contact with electrode materials, the electrolyte exhibits excellent chemical stability and can effectively inhibit the degradation of electrode materials.

[0096] After testing, the all-solid-state lithium secondary battery prepared above has a first-week specific capacity of 176mAh / g; the first-week coulomb efficiency is 92.3%; the capacity retention rate after 1000 cycles is 92.2%; the battery cycle life is greater than 10,000 times (at room temperature); and the battery energy density is 407Wh / kg.

[0097] Example 3

[0098] The difference between this embodiment and embodiment 1 is that, in this embodiment, the mass ratio of Li2S, P2S5, Al2S3, ZnS, CdS2, MnS2, LiCl, LiF, LiI, and Li2O is 31:45:7:9:2:1.5:0.4:2.8:0.2:1.1; the remaining steps and parameters are the same as those in embodiment 1, and a multi-doped sulfide solid electrolyte 31Li2S-45P2S5-7Al2S3-9ZnS-2CdS2-1.5MnS2-0.4LiCl-2.8LiF-0.2LiI-1.1Li2O is obtained, that is, the highly conductive sulfide solid electrolyte is obtained.

[0099] A positive electrode membrane is obtained by uniformly mixing the positive electrode active material and the multi-doped sulfide solid electrolyte prepared above at a mass ratio of 70:30 and then pressing the mixture into a layer with a thickness of 0.05 mm at a pressure of 20 MPa, wherein the positive electrode active material is solid LiNiO2, the positive electrode collector is aluminum foil, and a metal lithium sheet is used as the negative electrode pole piece. The positive electrode collector, the positive electrode membrane, the multi-doped sulfide solid electrolyte prepared above and the negative electrode pole piece are assembled into an all-solid-state lithium secondary battery by pressure forming (20 MPa).

[0100] The operating voltage range of the all-solid-state lithium secondary battery is set to 2.5V to 5V, and a constant current charge and discharge method is used to perform a cycle test to obtain the first-cycle discharge specific capacity, first-cycle coulomb efficiency, and capacity retention rate after 1000 cycles of the all-solid-state lithium secondary battery. The test current is 0.1C (current density is 0.13mA / cm 2 ), the test temperature is 25℃.

[0101] 0.2g of the multi-doped sulfide solid electrolyte prepared in the above steps was pressed into a solid electrolyte film with a diameter of 15mm at a pressure of 25MPa, and a symmetrical cell was formed with stainless steel as a blocking electrode to test the impedance of the sulfide solid electrolyte at 25°C. The ionic conductivity of the sulfide solid electrolyte is calculated by the formula δ=L / (R·S), where δ is the ionic conductivity, L is the thickness of the solid electrolyte film, R is the impedance value of the sulfide solid electrolyte, and S is the effective cross-sectional area of ​​the solid electrolyte film.

[0102] 0.2 g of the sulfide solid electrolyte prepared in the above steps was pressed into a solid electrolyte membrane with a diameter of 15 mm at a pressure of 25 MPa. Then, metallic lithium was used as the working electrode and stainless steel as the counter electrode to test the electrochemical stability of the sulfide solid electrolyte. The scanning potential range was -0.5 V to 6 V, and the process was set to scan from the open circuit potential to -0.5 V at a scanning speed of 1 mV / s, then the potential was reversed and scanned to 6 V, and finally scanned back to the open circuit potential.

[0103] The test results show that the peak current ratio of the anode peak to the cathode peak of the multi-doped sulfide solid electrolyte prepared above is 0.82; the ionic conductivity is 1.87mS / cm; the interface impedance is 32.1Ω·cm 2 (Contact surface with electrode); decomposition temperature is 510℃; in the environment in contact with electrode materials, the electrolyte exhibits excellent chemical stability and can effectively inhibit the degradation of electrode materials.

[0104] After testing, the all-solid-state lithium secondary battery prepared above has a first-week specific capacity of 170mAh / g; the first-week coulomb efficiency is 90.8%; the capacity retention rate after 1000 cycles is 90.6%; the battery cycle life is greater than 10,000 times (at room temperature); and the battery energy density is 391Wh / kg.

[0105] Comparative Example 1

[0106] The difference between this comparative example and Example 1 is that in this comparative example, the mass ratio of Li2S, P2S5, Al2S3, ZnS, CdS2, MnS2, LiCl, LiF, LiI, and Li2O is 35:11:13:14:4:14:2:1:4:2; the remaining steps and parameters are the same as those in Example 1, and a multi-doped sulfide solid electrolyte 35Li2S-11P2S5-13Al2S3-14ZnS-4CdS2-14MnS2-2LiCl-1LiF-4LiI-2Li2O is obtained, that is, the highly conductive sulfide solid electrolyte is obtained.

[0107] A positive electrode membrane is obtained by uniformly mixing the positive electrode active material and the multi-doped sulfide solid electrolyte prepared above at a mass ratio of 70:30 and then pressing the mixture into a layer with a thickness of 0.05 mm at a pressure of 20 MPa, wherein the positive electrode active material is solid LiNiO2, the positive electrode collector is aluminum foil, and a metal lithium sheet is used as the negative electrode pole piece. The positive electrode collector, the positive electrode membrane, the multi-doped sulfide solid electrolyte prepared above and the negative electrode pole piece are assembled into an all-solid-state lithium secondary battery by pressure forming (20 MPa).

[0108] The operating voltage range of the all-solid-state lithium secondary battery is set to 2.5V to 5V, and a constant current charge and discharge method is used to perform a cycle test to obtain the first-cycle discharge specific capacity, first-cycle coulomb efficiency, and capacity retention rate after 1000 cycles of the all-solid-state lithium secondary battery. The test current is 0.1C (current density is 0.13mA / cm 2 ), the test temperature is 25℃.

[0109] 0.2g of the multi-doped sulfide solid electrolyte prepared in the above steps was pressed into a solid electrolyte film with a diameter of 15mm at a pressure of 25MPa, and a symmetrical cell was formed with stainless steel as a blocking electrode to test the impedance of the sulfide solid electrolyte at 25°C. The ionic conductivity of the sulfide solid electrolyte is calculated by the formula δ=L / (R·S), where δ is the ionic conductivity, L is the thickness of the solid electrolyte film, R is the impedance value of the sulfide solid electrolyte, and S is the effective cross-sectional area of ​​the solid electrolyte film.

[0110] 0.2 g of the sulfide solid electrolyte prepared in the above steps was pressed into a solid electrolyte membrane with a diameter of 15 mm at a pressure of 25 MPa. Then, metallic lithium was used as the working electrode and stainless steel as the counter electrode to test the electrochemical stability of the sulfide solid electrolyte. The scanning potential range was -0.5 V to 6 V, and the process was set to scan from the open circuit potential to -0.5 V at a scanning speed of 1 mV / s, then the potential was reversed and scanned to 6 V, and finally scanned back to the open circuit potential.

[0111] The test results show that the peak current ratio of the anode peak to the cathode peak of the multi-doped sulfide solid electrolyte prepared above is 0.47; the ionic conductivity is 0.81mS / cm; the interface impedance is 106.3Ω·cm 2 (Contact surface with electrode); decomposition temperature is 335°C; in the environment in contact with electrode materials, the electrolyte exhibits excellent chemical stability and can effectively inhibit the degradation of electrode materials.

[0112] After testing, the all-solid-state lithium secondary battery prepared above has a first-week specific capacity of 78mAh / g; the first-week coulomb efficiency is 78.4%; the capacity retention rate after 1000 cycles is 45.7%; the battery cycle life is greater than 10,000 times (at room temperature); and the battery energy density is 178Wh / kg.

[0113] The above embodiments are only used to explain the content of the present invention, and are not intended to limit the present invention. Simple technical variations within the technical concept of the present invention should be considered to be covered by the content disclosed by the present invention and belong to the protection scope of the present invention.

[0114] In the specification of the present invention, a lot of specific details are described. However, it is understood that embodiments of the present invention can be practiced without these specific details. In some embodiments, well-known methods, structures and techniques are not shown in detail so as not to obscure the understanding of this specification.

[0115] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0116] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

[0117] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A highly conductive sulfide solid electrolyte, characterized in that: In terms of mass percentage, it includes: Lithium source and network former 70-85wt%; Doping elements 10-40wt%; Additives 1-5wt%.

2. The highly conductive sulfide solid electrolyte according to claim 1, characterized in that The lithium source is Li2S; the network former is P2S5; the doping element is selected from at least one of A12S3, ZnS, CdS2 and MnS2; the additive includes a halide and lithium oxide; the halide is selected from at least one of LiCl, LiF and LiI.

3. The highly conductive sulfide solid electrolyte according to claim 1, characterized in that The ionic conductivity of the highly conductive sulfide solid electrolyte is greater than 1.3 mS / cm; the interface impedance is less than 40 Ω·cm 2 ; Thermal decomposition temperature>400℃.

4. A method for preparing a highly conductive sulfide solid electrolyte, characterized in that: The following steps are involved: S1: mixing the lithium source, the network former, the doping element and the additive in proportion to obtain a mixed powder; S2 sintering the mixed powder obtained in step S1 at a high temperature to obtain a crude electrolyte; S3 annealing the crude electrolyte obtained in step S2 to obtain a solid electrolyte; S4: ball-milling the solid electrolyte obtained in step S3 into solid electrolyte powder to obtain the highly conductive sulfide solid electrolyte.

5. The method for preparing a highly conductive sulfide solid electrolyte according to claim 4, characterized in that: In step S1, the lithium source is Li2S; the network former is P2S5; the doping element is selected from at least one of Al2S3, ZnS, CdS2 and MnS2; the additive includes a halide and lithium oxide; the halide is selected from at least one of LiCl, LiF and LiI.

6. The method for preparing a highly conductive sulfide solid electrolyte according to claim 4, characterized in that: In step S2, the sintering temperature is 200-600°C; the sintering time is 1-16 hours; the annealing temperature is 100-400°C; and the annealing time is 1-10 hours.

7. The method for preparing a highly conductive sulfide solid electrolyte according to claim 4, characterized in that: In step S4, the particle size range of the powder is 1-40 μm.

8. An all-solid-state lithium secondary battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet and a solid electrolyte membrane, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode membrane sheet arranged on the positive electrode current collector, and the solid electrolyte membrane is composed of the above-mentioned high-conductivity sulfide solid electrolyte; the high-conductivity sulfide solid electrolyte comprises, by mass percentage: Lithium source and network former 70-85wt%; Doping elements 10-40wt%; Additives 1-5wt%.

9. The all-solid-state lithium secondary battery according to claim 8, characterized in that: The first-week specific capacity of the all-solid-state lithium secondary battery is greater than 100 mAh / g; the capacity retention rate after 1000 cycles is greater than 85%; the battery cycle life at room temperature is greater than 5000 times; and the battery energy density is greater than 300 Wh / kg.

10. A method for preparing an all-solid-state lithium secondary battery, characterized in that: The following steps are involved: The positive electrode active material and the highly conductive sulfide solid electrolyte are mixed evenly in proportion and then pressed into a layer to obtain a positive electrode membrane; The positive electrode active material and the highly conductive sulfide solid electrolyte are mixed evenly in proportion and then pressed into a layer to obtain a positive electrode membrane; The positive electrode current collector, the positive electrode membrane, the high-conductivity sulfide solid electrolyte and the negative electrode plate are assembled into an all-solid-state lithium secondary battery by pressure molding.