Mixed ion conductor layer for lithium metal negative electrode, preparation method of mixed ion conductor layer and all-solid-state battery

Abstract

The invention discloses a mixed ion conductor layer for a lithium metal negative electrode, a preparation method of the mixed ion conductor layer and an all-solid-state battery, and belongs to the technical field of sulfide all-solid-state batteries. The preparation method comprises the following steps: synthesizing a sulfide electrolyte 70 (0.75 Li2S-0.25 P2S5)-30LiI through a liquid phase, introducing graphene oxide and a lithium salt precursor 2, 5-dihydroxy-1, 4-benzene diphosphate in the electrolyte preparation process, and carrying out heat treatment and pressing to obtain a mixed ion conductor layer; the graphene oxide can isolate the sulfide electrolyte layer from the lithium metal negative electrode, interface reaction is avoided, and a special porous and interlayer structure provides a transverse growth space for lithium metal deposition. And meanwhile, the lithium diphosphate-based MOF among the graphene layers ensures the rapid movement of lithium ions, enhances the bulk diffusion of lithium at the negative electrode end, reduces the local current density, plays a role in dredging the distribution of the lithium ions, and remarkably prolongs the cycle life of the sulfide all-solid-state battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sulfide full solid-state batteries, and particularly relates to a mixed ion conductor layer for a lithium metal negative electrode, a preparation method thereof and a full solid-state battery. BACKGROUND

[0002] There is an urgent need for secondary batteries with high safety and higher energy density in large-scale energy storage devices and electric vehicle applications. However, there are serious safety problems in the current lithium-ion batteries using organic electrolyte, and the frequent battery fire and explosion incidents in recent years have caused public concern. The full solid-state battery using non-flammable solid-state electrolyte is expected to fundamentally solve the safety problem and improve the energy density, and is one of the ideal next-generation energy storage devices.

[0003] For example, the invention with the publication number CN118156593A discloses a sulfide solid-state electrolyte film, a preparation method and application thereof. The sulfide solid-state electrolyte film is composed of an ion-conducting polymer binder and a sulfide solid-state electrolyte, and the sulfide solid-state electrolyte is uniformly wrapped by the ion-conducting polymer binder. Organic polymer A, lithium salt B and ionic liquid C are added to organic solvent D for mixing to obtain a uniform solution, and then the organic solvent is dried to remove the organic solvent to obtain the ion-conducting polymer binder. The organic polymer A is a thermoplastic polymer electrolyte with a melting range of 40-140℃. The organic polymer A has a polar group in its chemical structure. The sulfide solid-state electrolyte powder and the ion-conducting polymer binder are mixed and then a dry process is used to obtain the sulfide solid-state electrolyte film.

[0004] For another example, the invention with the publication number CN114914422A also discloses a composite negative electrode suitable for a sulfide full solid-state battery, a preparation method and a lithium battery. The composite negative electrode includes a mixture of a sulfide solid-state electrolyte and an inert protective layer type core-shell lithium alloying negative electrode. The preparation method includes: first sintering lithium-storing metal and metal lithium at a proper ratio to obtain a pre-lithiated lithium alloying negative electrode material; ball milling the pre-lithiated lithium alloying negative electrode for granulation treatment; uniformly mixing and dispersing the granulated pre-lithiated lithium alloying negative electrode and the sulfide solid-state electrolyte at a proper ratio to obtain a composite negative electrode precursor; and placing the composite negative electrode precursor in an oxygen atmosphere for second sintering to obtain the required composite negative electrode.

[0005] However, there are still some challenges in using sulfide solid-state electrolytes, mainly including: (1) the electrolyte reacts with lithium metal, and the production of interface products increases the interface resistance and leads to low storage efficiency; (2) lithium dendrites can grow along the pores, cracks and grain boundaries inside the sulfide solid-state electrolyte, and eventually penetrate the entire electrolyte, leading to battery failure. Therefore, developing a new type of lithium metal negative electrode protective layer has become the current research focus. SUMMARY

[0006] Based on the deficiencies in the prior art, the application provides a mixed ion conductor layer for a lithium metal negative electrode, a preparation method thereof and a full solid-state battery. A sulfide electrolyte 70 (0.75Li2S-0.25P2S5)-30LiI is synthesized by a liquid phase, and in the process of preparing the electrolyte, graphene oxide (GO) and a lithium salt precursor 2,5-dihydroxy-1,4-benzenediol lithium phosphate are introduced. After heat treatment and pressing, the mixed ion conductor layer is obtained. The GO can isolate the sulfide electrolyte layer from the lithium metal negative electrode, and avoid interface reaction. The unique porous and interlayer structure provides a horizontal growth space for lithium metal deposition. At the same time, the lithium phosphate-based MOF between the graphene layers ensures the rapid movement of lithium ions, enhances the bulk diffusion of lithium at the negative electrode, reduces the local current density and plays a role in dredging the distribution of lithium ions, and significantly improves the cycle life of the sulfide full solid-state battery.

[0007] The object of the application can be achieved by the following technical solutions: The application provides a preparation method of a mixed ion conductor layer for a lithium metal negative electrode, comprising the following steps: (1) preparing graphene oxide powder; (2) mixing the graphene oxide powder, an organic solvent, a 2,5-dihydroxy-1,4-benzenediol lithium phosphate precursor, Li2S, P2S5 and LiI to form a slurry, and reacting to obtain a precursor; (3) annealing the precursor of step (2) to obtain the mixed ion conductor layer; Preferably, the preparation method of the GO is an improved Hummer method, and the specific steps are as follows:

[0008] Preferably, the preparation method of the GO is an improved Hummer method, and the specific steps are as follows: Step (1) of preparing graphene oxide powder comprises the following steps: (1.1) pre-oxidation treatment: adding sodium nitrate and graphite in a concentrated sulfuric acid system and reacting at constant temperature; (1.2) step-by-step oxidation: adding potassium permanganate to the system of step (1.1) in multiple times, and after the addition is completed, continuing to react by heating; (1.3) high-temperature hydrolysis: (1.3.1) adding water to the system of step (1.2), and then continuing to react by heating; (1.3.2) adding water and hydrogen peroxide to the system of step (1.3.1) to terminate the reaction, and filtering the filter cake while hot; (1.4) purification treatment: washing the filter cake with dilute hydrochloric acid and water in sequence, then dispersing in water for dialysis, and drying to obtain the graphene oxide powder.

[0009] In some embodiments of the present application, in step (1.1), the molar ratio of the concentrated sulfuric acid, sodium nitrate and graphite is 4-5:0.05-0.06:0.4-0.5; The temperature of the constant temperature reaction is -5-30℃, and the time is 20-40 min; In step (1.2), the potassium permanganate is added for 10-30 times, and the total mass of the potassium permanganate added is 1:2.5-3.5 times the mass of the graphite in step (1.1); In the temperature rising reaction, the temperature is raised to 30-50℃ and the reaction is continued for 20-40 min.

[0010] In some embodiments of the present application, in step (1.3), in step (1.3.1), the mass ratio of the water added to the concentrated sulfuric acid system in step (1.1) is 1:0.5-1, and the temperature is raised to 95-100℃ and the reaction is continued for 50-70 min; In step (1.3.2), when the reaction is terminated, 500-1000 ml of water is added, and the amount of 5wt% hydrogen peroxide is determined according to the actual reaction phenomenon (slowly add hydrogen peroxide until no bubbles are generated, and the residual potassium permanganate is completely reacted, and the reaction liquid finally becomes a golden yellow transparent dispersion liquid); In step (1.4), the concentration of the dilute hydrochloric acid is 5wt%, the mass ratio of the dilute hydrochloric acid to water in a single washing is 10-20:20-30, and the washing is repeated for 3-5 times; The washed filter cake is dispersed in 1000-2000 parts by mass of water, stirred at room temperature for 1-2 days, and then dialyzed for 5-10 days; The drying temperature is 120℃.

[0011] Preferably, in step (2), the mass ratio of the graphene oxide powder, 2,5-dihydroxy-1,4-benzenediol lithium phosphate, lithium sulfide Li2S, phosphorus pentasulfide P2S5 and lithium iodide LiI is 0.1-0.4:0.01-0.03:0.1-0.25:0.2-0.6:0.1-0.31; In the examples of the present application, the mass ratio of the graphene oxide powder, 2,5-dihydroxy-1,4-benzenediol lithium phosphate, lithium sulfide Li2S, phosphorus pentasulfide P2S5 and lithium iodide LiI is 0.1-0.3:0.03:0.21-0.27:0.22-0.29:0.24-0.31; The organic solvent is anhydrous n-hexane, which accounts for 40%-80% of the total mass of the slurry; The preparation method of the 2,5-dihydroxy-1,4-benzenediol lithium phosphate precursor is as follows: 2,5-dihydroxy-1,4-benzene diphosphonic acid, lithium nitrate, 200-300 ml of water, the reaction temperature is 35 DEG C, the reaction time is 60 min, water is removed by distillation under reduced pressure, and 2,5-dihydroxy-1,4-benzene diphosphonic acid lithium precursor is obtained; wherein the molar ratio of 2,5-dihydroxy-1,4-benzene diphosphonic acid to lithium nitrate is 0.5-1:1, and the mass ratio is 1.96-3.92:1.

[0012] In the embodiment of the application, the molar ratio of 2,5-dihydroxy-1,4-benzene diphosphonic acid to lithium nitrate is preferably 1:1 as an example.

[0013] Further, in step (2), the reaction temperature is 30-60 DEG C, and the reaction time is 60-84 hours. After the reaction, a suspension is obtained, and the suspension is evaporated to obtain the precursor, wherein the evaporation temperature is 50-100 DEG C, and the evaporation time is 10-14 hours.

[0014] The reaction mechanism of the application is as follows: 1. Reactivity of hydroxyl and isocyanate: under appropriate reaction conditions, the hydroxyl (-OH) in the 2,5-dihydroxy-1,4-benzene diphosphonic acid lithium precursor attacks the carbon atom of the isocyanate (-NCO) in the isocyanate propyl graphene oxide. Because the isocyanate has strong electrophilicity, it is easy to react with the hydroxyl, which is the starting step of the entire condensation reaction.

[0015] Formation of intermediate: after the reaction of the hydroxyl and the isocyanate, an intermediate containing a new C-O-N bond is formed. This step is the key to the entire reaction chain and lays the foundation for the formation of more complex structures.

[0016] Formation of final product: this intermediate is finally converted into stable lithium diphosphate MOF modified graphene oxide through a series of internal rearrangement and dehydration reactions. In this process, the metal-organic framework (MOF) structure self-assembles on the surface of graphene oxide, forming a composite structure.

[0017] Self-assembly of MOF structure: in this process, metal ions and organic ligands self-assemble into MOF structures through coordination bonding. The key to this process is to control the reaction conditions to ensure the regularity and uniformity of MOFs, which has a decisive influence on the functional performance of the final material.

[0018] Role of graphene oxide: as a base material, graphene oxide not only provides a reaction site, but its rich functional groups may also participate in the reaction to enhance the overall functionality of the material, such as providing additional chemical active sites or enhancing electron transport capacity, and the porous and interlayer structure provides lateral space for the growth of lithium metal; The role of the mixed conductor GO-MOF-LPSI: the mixed ionic conductor has good affinity with lithium metal, and can react with lithium to form a stable interface, blocking the growth of lithium dendrites. The lithium diphosphate-based MOF can selectively induce the deposition of lithium ions, reduce the local current density, and prevent local interface fluctuations.

[0019] Preferably, in step (3), the annealing temperature is 200-300℃, and the time is 0.5-2 hours.

[0020] The application also provides a mixed ionic conductor layer prepared by the preparation method.

[0021] The application also provides a lithium metal composite negative electrode, comprising: a lithium metal substrate and the mixed ionic conductor layer covering the surface of the lithium metal substrate.

[0022] The application also provides a full solid-state battery, comprising a positive electrode, a negative electrode, and a solid-state electrolyte. The positive electrode is NCM811, the solid-state electrolyte is sulfide electrolyte lithium phosphorus sulfur chloride, and the negative electrode is the lithium metal composite negative electrode.

[0023] The application has the following beneficial effects: (1) Because GO has high structural strength, it can inhibit the side reaction between the sulfide electrolyte layer LPSC and the negative electrode Li metal and the uneven deposition of lithium at the negative electrode, and the layered structure and porous structure provide sufficient space for the volume expansion caused by lithium ion deposition, preventing the unrestricted longitudinal growth of lithium dendrites; (2) The sulfide LPSI in the mixed ionic conductor layer reacts with lithium metal to further form a stable interface, blocking the growth of lithium dendrites; (3) The lithium diphosphate-based MOF uses the functional groups on the surface of graphene oxide as anchor points, further enhancing the interlayer strength of graphene oxide. The lithium diphosphate-based MOF has a certain lithium ion conductivity, improving the transfer speed of lithium ions and the local current density. At the same time, the lithium diphosphate-based MOF has a lower interface energy with lithium metal, and has better wettability on the surface of lithium metal, which can improve the critical current density during charging, so that the full solid-state lithium metal battery can achieve higher charging capacity. In summary, the lithium diphosphate-based MOF modified graphene oxide material not only improves the overall performance of the battery through its unique chemical and physical properties, but also significantly improves the cycle performance of the battery system using a sulfur-based solid-state electrolyte through the improvement of electrical conductivity, the enhancement of structural stability, and the optimization of interface performance. These characteristics make the material have great application potential in the field of high-performance batteries, and it is expected to play an important role in electric vehicles and other high-demand battery applications in the future. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 A schematic diagram of a full solid-state battery. DETAILED DESCRIPTION

[0025] To further illustrate the technical means and effects adopted by the present application to achieve the predetermined inventive purposes, the specific embodiments and effects according to the present application are described in detail below in combination with examples.

[0026] Example 1 A preparation method of a mixed ionic conductor layer GO-MOF-LPSI applied to a sulfide full solid-state battery lithium metal negative electrode, comprising the following steps: (1) Preparation of graphene oxide (GO): The preparation method of GO is an improved Hummer method, and the specific preparation method is completed according to the following steps.

[0027] 1) Pour 230 mL of concentrated sulfuric acid into a three-necked glass flask and stir at 0°C.

[0028] 2) Gradually add 5 g of sodium nitrate and 5 g of graphite into the system of step 1) at 0°C, and react for 30 min.

[0029] 3) Slowly add 15 g of potassium permanganate into the system of step 2) in 15 times, and after complete addition, increase the temperature of the system to 40°C and continue to react for 30 min.

[0030] 4) Slowly add 500 mL of deionized water into the system of 3), and then increase the temperature of the system to 98°C and continue to react for 60 min.

[0031] 5) Add 1200 mL of deionized water and 500 mL of 5 wt% hydrogen peroxide solution into the system of 4) respectively, filter under high temperature to obtain a solid filter cake.

[0032] 6) Wash the obtained solid with 15 mL of 5% dilute hydrochloric acid solution and 25 mL of deionized water respectively for four times to obtain a filter cake.

[0033] 7) Redisperse the filter cake of step 6) in 1500 mL of deionized water, and then stir at room temperature for 1 day. Then, pack the suspension into a dialysis bag and put it into water for dialysis, and the dialysis time is 5 days. After dialysis is completed, the suspension in the dialysis bag is the GO suspension.

[0034] 8) Collect the suspension obtained in 7) into a container for high-temperature drying at 120°C to obtain graphene oxide GO powder.

[0035] (2) Preparation of ionic conductor mixture GO-MOF-LPSI: The preparation method of the lithium 2,5-dihydroxy-1,4-benzenephosphonic acid precursor is as follows: 27 g of 2,5-dihydroxy-1,4-benzenephosphonic acid, 6.9 g of lithium nitrate, and 250 ml of water are reacted at a reaction temperature of 35°C for 60 min, and water is removed by distillation under reduced pressure to obtain the lithium 2,5-dihydroxy-1,4-benzenephosphonic acid precursor; The mass ratio of graphene oxide: lithium 2,5-dihydroxy-1,4-benzenephosphonic acid: lithium sulfide: phosphorus pentasulfide: lithium iodide is 0.15:0.03:0.25:0.27:0.3, that is, 4.5 g of GO is dispersed in 100 ml of anhydrous n-hexane, and the mixture is stirred, 7.5 g of lithium sulfide Li2S, 0.9 g of lithium 2,5-dihydroxy-1,4-benzenephosphonic acid precursor, 9 g of lithium iodide LiI, and 8.1 g of phosphorus pentasulfide P2S5 are fully ground and added to the above graphene oxide dispersion. The above mixed solution is stirred at 50°C for 72h until the reaction is complete. Then the solvent is evaporated at 80°C for 12h to obtain the electrolyte precursor, and the obtained powder is uniformly ground and annealed at 250°C for 1h to finally obtain the ion conductor mixture GO-MOF-LPSI, and all the preparation processes are carried out in an argon-filled glove box.

[0036] (3) Preparation of lithium metal negative electrode coated with mixed ion conductor layer 1) The ion mixture GO-MOF-LPSI obtained in (2) is added to a container containing anhydrous acetonitrile, and homogenized by vacuum stirring defoaming machine; 2) The mixture slurry of 1) is spread on a lithium-copper composite sheet, and the slurry is uniformly coated on the surface of the lithium metal using a four-sided film maker, and the sheet is placed in a vacuum oven for drying to remove the solvent, thereby obtaining a lithium metal negative electrode coated with a mixed ion conductor layer; all the preparation processes are carried out in an argon-filled glove box.

[0037] In order to study the effect of the mixed ion conductor layer on the cycle performance of the lithium metal full solid-state battery, NCM811 is used as the positive electrode, lithium phosphorus sulfur chloride LPSC is used as the sulfide solid-state electrolyte layer, and NCM811 / LPSC / GO-MOF-LPSI / Li full solid-state battery is assembled. At a current density of 0.1C, the initial discharge capacity of NCM811 / LPSC / GO-MOF-LPSI / Li battery is as high as 160.0 mAhg -1 , and the capacity retention rate is still 82.7% after 100 cycles.

[0038] Example 2 A preparation method of a mixed ion conductor layer GO-MOF-LPSI applied to a lithium metal negative electrode of a sulfide full solid-state battery, comprising the following steps: (1) Preparation of graphene oxide (GO): The preparation method of GO is improved Hummer method, and the specific preparation method is completed according to the following steps.

[0039] 1) Pour 230 mL of concentrated sulfuric acid into a three-necked glass flask and stir at 0°C.

[0040] 2) Gradually add 5 g of sodium nitrate and 5 g of graphite into the system of step 1) at 0°C, and react for 30 min.

[0041] 3) Slowly add 15 g of potassium permanganate into the system of step 2) in 15 times, and after complete addition, increase the temperature of the system to 40°C and continue to react for 30 min.

[0042] 4) Slowly add 500 mL of deionized water into the system of 3), and then increase the temperature of the system to 98°C and continue to react for 60 min.

[0043] 5) Add 1200 mL of deionized water and 500 mL of 5 wt% hydrogen peroxide solution into the system of 4) respectively, and filter under high temperature to obtain a solid filter cake.

[0044] 6) Wash the obtained solid with 15 mL of 5% dilute hydrochloric acid solution and 25 mL of deionized water respectively for four times to obtain a filter cake.

[0045] 7) Redisperse the filter cake of step 6) in 1500 mL of deionized water, and then stir at room temperature for 1 day. Then, put the suspension into a dialysis bag and put it into water for dialysis, and the dialysis time is 5 days. After dialysis, the suspension in the dialysis bag is the GO suspension.

[0046] 8) Collect the suspension obtained in 7) into a container for high-temperature drying at 120°C to obtain graphene oxide GO powder.

[0047] (2) Preparation of ion conductor mixture GO-MOF-LPSI: The preparation method of the 2,5-dihydroxy-1,4-benzene diphosphonic acid lithium precursor is: React 27 g of 2,5-dihydroxy-1,4-benzene diphosphonic acid, 6.9 g of lithium nitrate, and 250 ml of water at a reaction temperature of 35°C for 60 min, and remove water by reduced pressure distillation to obtain the 2,5-dihydroxy-1,4-benzene diphosphonic acid lithium precursor; The mass ratio of graphene oxide: 2,5-dihydroxy-1,4-benzene lithium diphosphate: lithium sulfide: lithium iodide: phosphorus pentasulfide: lithium iodide is 0.3:0.03:0.21:0.22:0.24, that is, 4.5 g of GO is dissolved in 20 mL of anhydrous n-hexane, and the mixture is stirred, 3.15 g of lithium sulfide, 0.45 g of 2,5-dihydroxy-1,4-benzene lithium diphosphate precursor, 3.6 g of lithium iodide and 3.3 g of phosphorus pentasulfide are added to the above graphene oxide solution after being ground. The above mixed solution is stirred at 40°C for 60h until the reaction is complete. Then the solvent is evaporated at 50°C for 10h to obtain an electrolyte precursor, and the obtained powder is uniformly ground and annealed at 200°C for 0.5h to finally obtain an ion conductor mixture GO-MOF-LPS. The above process is carried out in an argon-filled glove box.

[0048] (3) Preparation of lithium metal negative electrode coated with mixed ion conductor layer 1) The ion mixture GO-MOF-LPSI obtained in (2) is added to a container containing anhydrous acetonitrile, and homogenized by vacuum stirring defoaming machine; 2) The mixture slurry of 1) is spread on a lithium-copper composite sheet, and the slurry is uniformly coated on the surface of the lithium metal using a four-sided film maker. The sheet is placed in a vacuum oven for drying and solvent removal to obtain a lithium metal negative electrode coated with a mixed ion conductor layer. All preparation processes are carried out in an argon-filled glove box.

[0049] In order to study the effect of the mixed ion conductor layer on the cycle performance of the lithium metal full solid-state battery, NCM811 is used as the positive electrode, lithium phosphorus sulfur chloride LPSC is used as the sulfide solid-state electrolyte layer, and NCM811 / LPSC / GO-MOF-LPSI / Li full solid-state battery is assembled. At a current density of 0.1C, the initial discharge capacity of NCM811 / LPSC / GO-MOF-LPSI / Li battery is as high as 158.0mAhg -1 , and the capacity retention rate is still 72.7% after 100 cycles.

[0050] Example 3 The preparation method of graphene oxide GO and 2,5-dihydroxy-1,4-benzene lithium diphosphate in Example 3 is the same as that in Example 1.

[0051] The difference is that the mass ratio of graphene oxide: 2,5-dihydroxy-1,4-benzene lithium diphosphate: lithium sulfide: lithium iodide: phosphorus pentasulfide in the mixed ionic conductor mixture is adjusted to 0.1:0.03:0.27:0.29:0.31, that is, 4.5 g of GO is dissolved in 100 mL of anhydrous n-hexane, and the mixture is stirred, 12.15 g of lithium sulfide, 1.35 g of 2,5-dihydroxy-1,4-benzene lithium diphosphate precursor, 13.95 g of lithium iodide and 13.05 g of phosphorus pentasulfide are fully ground and added to the above graphene oxide solution. The above mixed solution is stirred at 40°C for 60h until the reaction is complete. Then the solvent is evaporated at 50°C for 10h to obtain an electrolyte precursor, and the obtained powder is uniformly ground and annealed at 200°C for 0.5h to finally obtain the ion conductor mixture GO-MOF-LPS, and the above process is carried out in an argon-filled glove box.

[0052] (3) Preparation of lithium metal negative electrode coated with mixed ion conductor layer 1) The ion mixture GO-MOF-LPSI obtained in (2) is added to a container containing anhydrous acetonitrile, and homogenized by vacuum stirring defoaming machine; 2) The mixture slurry of 1) is spread on a lithium-copper composite sheet, and the slurry is uniformly coated on the surface of the lithium metal using a four-sided film applicator. The sheet is placed in a vacuum oven for drying and solvent removal to obtain a lithium metal negative electrode coated with a mixed ion conductor layer; all preparation processes are carried out in an argon-filled glove box.

[0053] In order to study the effect of the mixed ion conductor layer on the cycle performance of the lithium metal full solid-state battery, NCM811 is used as the positive electrode, lithium phosphorus sulfur chloride LPSC is used as the sulfide solid-state electrolyte layer, and NCM811 / LPSC / GO-MOF-LPSI / Li full solid-state battery is assembled. At a current density of 0.1C, the initial discharge capacity of NCM811 / LPSC / GO-MOF-LPSI / Li battery is as high as 155.0mAhg -1 , and the capacity retention rate is still 70.7% after 100 cycles.

[0054] Comparative Example 1 A method for preparing an ion conductor mixture GO-Li7P3S 11 , comprising the following steps: (1) Preparation of graphene oxide (GO): The steps are the same as in Example 1.

[0055] (2) Preparation of ion conductor mixture GO-LPSI: The mass ratio of graphene oxide: lithium sulfide: diphosphorus pentasulfide: lithium iodide is 0.4:0.19:0.2:0.21. 1.86 g of lithium sulfide, 1.98 g of diphosphorus pentasulfide and 2.16 g of lithium iodide are thoroughly ground and added to the 4 g graphene oxide-water n-hexane dispersion solution of Example 1. The above mixed solution is stirred at 50°C for 72 h until the reaction is complete. Then the solvent is evaporated at 80°C for 12 h to obtain an electrolyte precursor. The obtained powder is uniformly ground and annealed at 250°C for 1 h to finally obtain the ion mixed conductor mixture GO-LPSI. All preparation processes are carried out in an argon-filled glove box.

[0056] (3) Preparation of lithium metal negative electrode coated with mixed ion conductor layer: 1) The obtained ion mixture GO-LPSI is added to a container containing anhydrous acetonitrile and uniformly grinded by vacuum stirring defoaming machine; 2) The mixture slurry of 1) is spread on a lithium-copper composite sheet, and the slurry is uniformly coated on the surface of the lithium metal by using a four-sided film applicator. The sheet is placed in a vacuum oven for drying and solvent removal to obtain a lithium metal negative electrode coated with a mixed ion conductor layer. All preparation processes are carried out in an argon-filled glove box.

[0057] In order to study the effect of the mixed ion conductor layer on the cycle performance of the lithium metal full solid-state battery, NCM811 is used as the positive electrode, lithium phosphorus sulfur chloride LPSC is used as the sulfide solid-state electrolyte layer, and NCM811 / LPSC / GO-LPSI / Li full solid-state battery is assembled. At a current density of 0.1C, the initial discharge capacity of NCM811 / LPSC / GO-LPSI / Li battery is as high as 105.0 mAh g -1 , and the capacity retention rate is still 63.7% after 100 cycles.

[0058] Comparative Example 2 A method for preparing an ion conductor mixture GO-MOF, comprising the following steps: (1) Preparation of graphene oxide (GO): The steps are the same as in Example 1.

[0059] (2) Preparation of ion conductor mixture GO-MOF: The preparation method of the lithium 2,5-dihydroxy-1,4-benzenediol phosphate precursor is as follows: 27 g of 2,5-dihydroxy-1,4-benzenediol phosphate, 6.9 g of lithium nitrate and 250 ml of water are reacted at a reaction temperature of 35°C for 60 min. Water is removed by vacuum distillation to obtain the lithium 2,5-dihydroxy-1,4-benzenediol phosphate precursor; The 4.5 g of GO was dispersed in 20 mL of anhydrous n-hexane, and stirred and mixed, and 0.45 g of lithium 2,5-dihydroxy-1,4-benzene diphosphonate precursor was added to the above graphene oxide dispersion. The above mixed solution was stirred at 40°C for 60 h until the reaction was complete. Then the solvent was evaporated at 50°C for 10 h to obtain an electrolyte precursor, and the obtained powder was uniformly ground and annealed at 300°C for 2 h to finally obtain an ion conductor mixture GO-MOF, and the above process was carried out in an argon-filled glove box.

[0060] (3) Preparation of lithium metal negative electrode coated with mixed ion conductor layer: 1) The obtained ion mixture GO-MOF was added to a container containing anhydrous acetonitrile, and homogenized by vacuum stirring and degassing machine; 2) The mixture slurry of 1) was spread on a lithium-copper composite sheet, and the slurry was uniformly scraped on the surface of the lithium metal by using a four-sided film applicator. The sheet was placed in a vacuum oven for drying and solvent removal to obtain a lithium metal negative electrode coated with a mixed ion conductor layer; all the preparation processes were carried out in an argon-filled glove box.

[0061] In order to study the influence of the mixed ion conductor layer on the cycle performance of the lithium metal full solid-state battery, NCM811 was used as the positive electrode, lithium phosphorus sulfur chloride LPSC was used as the sulfide solid-state electrolyte layer, and NCM811 / LPSC / GO-MOF / Li full solid-state battery was assembled. At a current density of 0.1C, the initial discharge capacity of NCM811 / LPSC / GO-MOF / Li battery was as high as 145.0 mAh g -1 , and after 100 cycles, the capacity retention rate was 50.7%.

[0062] Comparative Example 3 Different from Example 1, the sulfide electrolyte type LPSI was replaced by LPSC; (1) Preparation of graphene oxide (GO): The preparation method was the same as that of Example 1; (2) Preparation of ion conductor mixture GO-MOF-LPSC: The preparation method of lithium 2,5-dihydroxy-1,4-benzene diphosphonate precursor was the same as that of Example 1; 4.5 g of GO was dispersed in 100 mL of anhydrous n-hexane, and stirred and mixed, and 36.76 g of Li2S, 8.1 g of 2,5-dihydroxy-1,4-benzene lithium diphosphate precursor, 17 g of lithium chloride LiCl and 177.8 g of phosphorus pentasulfide P2S5 were added to the above graphene oxide dispersion after being ground sufficiently. The above mixed solution was stirred at 40°C for 60 h until the reaction was complete. Then the solvent was evaporated at 50°C for 10 h to obtain an electrolyte precursor, and the obtained powder was ground uniformly and annealed at 300°C for 2 h to finally obtain an ion conductor mixture GO-MOF-LPSC. The above process was carried out in an argon-filled glove box.

[0063] (3) Preparation of lithium metal negative electrode coated with mixed ion conductor layer: 1) The ion mixture GO-MOF-LPSC obtained in (2) was added to a container containing anhydrous acetonitrile, and homogenized by vacuum stirring and defoaming machine; 2) The mixture slurry of 1) was spread on a lithium-copper composite sheet, and the slurry was uniformly scraped on the surface of the lithium metal using a four-sided film applicator. The sheet was placed in a vacuum oven for drying and solvent removal to obtain a lithium metal negative electrode coated with a mixed ion conductor layer. All the preparation processes were carried out in an argon-filled glove box.

[0064] In order to study the effect of the mixed ion conductor layer on the cycle performance of the lithium metal full solid-state battery, NCM811 was used as the positive electrode, lithium phosphorus sulfur chloride LPSC was used as the sulfide solid-state electrolyte layer, and NCM811 / LPSC / GO-MOF-LPSC / Li full solid-state battery was assembled. At a current density of 0.1C, the initial discharge capacity of the NCM811 / LPSC / GO-MOF-LPSC / Li battery was as high as 145.0 mAhg -1 , and after 100 cycles, the capacity retention rate was still 65.4%.

Claims

1. A method for preparing a mixed ionic conductor layer for lithium metal anodes, characterized in that, Includes the following steps: (1) Preparation of graphene oxide powder; (2) The graphene oxide powder, organic solvent, lithium 2,5-dihydroxy-1,4-phenyl diphosphate precursor, Li2S, P2S5 and LiI are mixed to form a slurry, and the mixture is reacted to obtain the precursor. (3) Anneal the precursor from step (2) to obtain the mixed ion conductor layer; Steps (2) and (3) are carried out under an inert atmosphere.

2. The method for preparing the mixed ion conductor layer according to claim 1, characterized in that, The preparation of graphene oxide powder in step (1) includes the following steps: (1.1) Pre-oxidation treatment: Sodium nitrate and graphite are added to a concentrated sulfuric acid system and reacted at a constant temperature; (1.2) Stepwise oxidation: Potassium permanganate was added to the system of step (1.1) in multiple portions, and the temperature was raised to continue the reaction after the addition was completed; (1.3) High-temperature hydrolysis: (1.3.1) Add water to the system of step (1.2), and then raise the temperature to continue the reaction; (1.3.2) Add water and hydrogen peroxide to the system in step (1.3.1) to terminate the reaction, and filter the mixture while it is hot to obtain a filter cake; (1.4) Purification treatment: The filter cake was washed with dilute hydrochloric acid and water in sequence, then dispersed in water for dialyzing, and dried to obtain the graphene oxide powder.

3. The method for preparing the mixed ion conductor layer according to claim 2, characterized in that, In step (1.1), the molar ratio of concentrated sulfuric acid, sodium nitrate and graphite is 4-5:0.05-0.06:0.4-0.5; The isothermal reaction is carried out at a temperature of -5 to 30°C for 20 to 40 minutes. In step (1.2), the potassium permanganate is added 10-30 times, and the total mass added is in a mass ratio of 1:2.5 to 3.5 with the mass of graphite in step (1.1). The reaction continues at 30-50℃ for 20-40 minutes.

4. The method for preparing the mixed ion conductor layer according to claim 2, characterized in that, In step (1.3), the mass ratio of water added in step (1.3.1) to the mass ratio of concentrated sulfuric acid added in step (1.1) is 1:0.5~1, and the temperature is raised to 95-100℃ and the reaction is carried out for 50-70 min. In step (1.4), the concentration of the dilute hydrochloric acid is 5 wt%, the mass ratio of dilute hydrochloric acid to water in a single wash is 10-20:20-30, and the washing is repeated 3-5 times. Disperse the washed filter cake in 1000-2000 parts by weight of water, stir at room temperature for 1-2 days, and then dialyze for 5-10 days; The drying temperature is 120℃.

5. The method for preparing the mixed ion conductor layer according to claim 1, characterized in that, In step (2), the mass ratio of the graphene oxide powder, lithium 2,5-dihydroxy-1,4-phenylenediphosphate, Li2S, P2S5, and LiI is 0.1~0.4∶0.01~0.03∶0.1~0.25∶0.2~0.6∶0.1~0.31; The organic solvent is anhydrous n-hexane, accounting for 40% to 80% of the total mass of the slurry; The preparation method of the lithium 2,5-dihydroxy-1,4-phenylenediphosphate precursor is as follows: 2,5-Dihydroxy-1,4-phenylenediphosphoric acid, lithium nitrate, and 200-300 ml of water were reacted at 35°C for 60 min. The water was removed by vacuum distillation to obtain a lithium 2,5-dihydroxy-1,4-phenylenediphosphoric acid precursor. The molar ratio of 2,5-dihydroxy-1,4-phenylenediphosphoric acid to lithium nitrate was 0.5-1:

1.

6. The method for preparing the mixed ion conductor layer according to claim 1 or 5, characterized in that, In step (2), the reaction temperature is 30-60℃ and the reaction time is 60-84 hours; After the reaction, a suspension is obtained. The suspension is then evaporated to dryness to obtain the precursor. The evaporation temperature is 50-100℃ and the time is 10-14 hours.

7. The method for preparing the mixed ion conductor layer according to claim 1, characterized in that, In step (3), the annealing temperature is 200-300℃ and the time is 0.5-2 hours.

8. The mixed ion conductor layer prepared by the preparation method according to any one of claims 1-7.

9. A lithium metal composite anode, characterized in that, include: The lithium metal substrate and the mixed ion conductor layer of claim 8 covering the surface of the lithium metal substrate.

10. An all-solid-state battery, the all-solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte, characterized in that, The positive electrode is NCM811, the solid electrolyte is a sulfide electrolyte lithium-phosphorus-sulfur-chlorine, and the negative electrode is the lithium metal composite negative electrode as described in claim 9.

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