Preparation of hyperbranched polymer for sulfide electrolyte film formation and application to all-solid-state battery

Abstract

The application relates to a kind of preparation of hyperbranched polymer for sulfide electrolyte film forming and all-solid-state battery application;Including: the preparation of hyperbranched polymer;The preparation of sulfide electrolyte film based on hyperbranched polymer binder;The preparation of all-solid-state lithium battery based on sulfide electrolyte film.Compared with prior art, the hyperbranched polymer prepared in the application has excellent film forming property and mechanical property, as the binder of sulfide electrolyte, realizes the good lithium ion conductivity of sulfide electrolyte film, and has good application prospect in the field of all-solid-state lithium battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new energy, and particularly relates to a preparation of a hyperbranched polymer for forming a sulfide electrolyte and application of the hyperbranched polymer to a full solid-state battery. BACKGROUND

[0002] Lithium ion batteries have the advantages of high energy density, high open-circuit voltage, large output power, wide working temperature range, fast charging / discharging speed, etc., and have been widely used in small intelligent electronic products, smart home facilities, robots, electric vehicles, etc. At present, large-scale commercial lithium ion batteries generally use liquid electrolytes of organic carbonates, which have safety problems such as easy leakage, easy combustion and easy explosion. Therefore, developing full solid-state lithium batteries with high energy density and high safety is the future development direction, and the solid electrolyte is a key component. Sulfide solid electrolytes have the advantages of good safety performance, wide working temperature range, high lithium ion conductivity, etc. Moreover, they have low hardness, good interface contact, can effectively reduce the interface impedance, and can inhibit the growth of lithium dendrites. However, sulfide solid electrolytes have the disadvantages of chemical instability and poor compatibility with solvents and binders, which are the biggest factors hindering the commercialization of sulfide electrolyte-based full solid-state lithium batteries.

[0003] By adding a certain amount of polymer binder, the sulfide electrolyte can be prepared into a film, which not only improves the processability, but also reduces the interface resistance between the electrode and the electrolyte. The selection of the binder is usually a linear polymer material with weak polarity, such as poly(styrene-co-butylene), polytetrafluoroethylene, polyisobutylene, butacryl rubber, etc. However, linear polymers have the problems of easy crystallization and poor solubility. Compared with linear polymers, hyperbranched polymers are a kind of highly branched three-dimensional macromolecules. Hyperbranched polymers have many branching points and the molecular chains are not easy to entangle. They are applied in the fields of coatings, drug carriers, environmental remediation and oil exploitation. More importantly, the topological structure and end functional groups of hyperbranched polymers can be effectively adjusted by monomer structure and polymerization conditions. The application adjusts the topological structure and end functional groups of hyperbranched polymers through monomer structure and polymerization conditions, which is conducive to the coating of sulfide electrolytes, thereby constructing a new type of self-supporting solid electrolyte film. SUMMARY

[0004] The polymer structure prepared by end group chemical modification or crosslinking reaction of hyperbranched polymer is often uncontrollable. The structure of hyperbranched polymer can be effectively controlled by using a bottom-up synthesis strategy, so as to establish the structure-activity relationship between the structure of polymer material and the application performance. In order to overcome the shortcomings of the prior art, the present application provides a kind of hyperbranched polymer preparation and all-solid-state battery application for sulfide electrolyte film forming. The present application prepares a kind of novel hyperbranched polymer by means of efficient Michael addition click chemistry, and adjusts the reactivity of amine group and double bond by using the proton content of mixed solvent, so as to adjust the topological structure of hyperbranched polymer. The polymer as a binder for sulfide solid electrolyte not only has high adhesion to sulfide electrolyte, but also shows excellent lithium ion conductivity. In the application of all-solid-state lithium battery, the sulfide electrolyte film based on hyperbranched polymer binder has good flexibility and high lithium ion conductivity, and shows excellent specific capacity and good cycle stability in all-solid-state lithium battery test, and has broad application prospect in the field of all-solid-state lithium battery application.

[0005] The purpose of the present application is achieved by the following technical solutions:

[0006] In a first aspect, the present application relates to a preparation method of hyperbranched polymer, comprising the following steps:

[0007] S1, under the condition of organic solvent, in the nitrogen environment, N-aminoethyl piperazine and divinyl compound react;

[0008] S2, after the reaction is completed, the solution is concentrated and poured into a precipitant, the precipitate is recovered, the dissolution-precipitation is repeated for several times, finally the precipitate is collected and vacuum dried.

[0009] As an embodiment of the present application, the molar ratio of N-aminoethyl piperazine and divinyl compound is 1:1-1:2.

[0010] As an embodiment of the present application, in step S1, the reaction temperature is 25-60℃.

[0011] As an embodiment of the present application, in step S1, the reaction time is 2-5 days.

[0012] As an embodiment of the present application, in step S2, the precipitant is diethyl ether.

[0013] As an embodiment of the present application, in step S2, the precipitation times is 3-6 times.

[0014] As an embodiment of the present application, the organic solvent, also called polymerization solvent, is a mixture of tetrahydrofuran and ethanol with a volume ratio of 1:0-0:1. More preferably, the solvent is one of the three mixtures of ethanol / tetrahydrofuran with a volume ratio of 1:0, 0.5:0.5 and 0:1.

[0015] As an embodiment of the present application, the divinyl compound is one or several of p-phenylene divinyl, diethylene glycol divinyl ether and 1,8-nonadiene.

[0016] The hyperbranched polymer prepared by the above method also falls within the protection scope of the present application.

[0017] In the second aspect, the present application also relates to the use of the hyperbranched polymer as a binder in the preparation of a sulfide electrolyte membrane.

[0018] In the third aspect, the present application relates to a sulfide electrolyte membrane. A sulfide electrolyte powder is dispersed in an acetonitrile solution of a hyperbranched polymer, and a sulfide electrolyte slurry is prepared by stirring in an inert environment; the slurry is coated on a planar substrate by doctor blading, and the electrolyte membrane is peeled off after drying to remove the organic solvent.

[0019] As an embodiment of the present application, the stirring is performed at 25±2℃ for 20-25 hours. Preferably, the stirring is performed at 25±2℃ for 24 hours.

[0020] As an embodiment of the present application, the drying is performed at 55-65℃ for 20-26 hours. Preferably, the drying is performed at 60℃ for 24 hours.

[0021] As an embodiment of the present application, the sulfide electrolyte includes glass type, glass-ceramic type, argyrodite type, thio-LISICON type and lithium-germanium-phosphorus-sulfur type.

[0022] As an embodiment of the present application, the content of the hyperbranched polymer in the acetonitrile solution of the hyperbranched polymer is 1wt%-10wt%.

[0023] As an embodiment of the present application, the solid content of the sulfide electrolyte slurry is 20wt%-40wt%.

[0024] As an embodiment of the present application, the planar substrate is selected from a glass plate, a metal plate, a polytetrafluoroethylene plate and a PET film.

[0025] As an embodiment of the present application, the thickness of the sulfide electrolyte membrane is 100-1000μm.

[0026] In the fourth aspect, the present application also relates to the use of the aforementioned sulfide electrolyte membrane in the preparation of a full-solid-state lithium battery.

[0027] In a fifth aspect, the present application relates to an all-solid-state lithium battery, comprising a positive electrode layer, a sulfide electrolyte film and a negative electrode layer.

[0028] As an embodiment of the present application, the positive electrode layer is composed of a ternary positive electrode, a sulfide electrolyte and conductive carbon.

[0029] As an embodiment of the present application, the negative electrode layer is selected from at least one of the following: metal lithium, metal lithium alloy, silicon, silicon carbon.

[0030] Compared with the prior art, the present application has the following beneficial effects:

[0031] 1) The present application constructs a new type of hyperbranched polymer by means of efficient Michael addition click chemistry, and uses it as an adhesive for the preparation of a sulfide solid electrolyte film. This strategy not only has a high adhesion to the sulfide electrolyte, showing good flexibility, but also has excellent lithium ion conductivity.

[0032] 2) Electrochemical test data show that the initial capacity of the prepared all-solid-state lithium battery under 1C cycle for 200 cycles is 114 mAh g -1 , and the capacity retention rate after 200 cycles is 82.5%. BRIEF DESCRIPTION OF DRAWINGS

[0033] Other features, objects and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments, made with reference to the accompanying drawings:

[0034] Figure 1 Schematic diagram for synthesizing polymers

[0035] Figure 2 NMR hydrogen spectrum of No. 1 hyperbranched polymer;

[0036] Figure 3 GPC chart and test results of No. 1 hyperbranched polymer;

[0037] Figure 4 Photo of sulfide electrolyte film prepared in Example 1;

[0038] Figure 5 Performance test curve of all-solid-state lithium battery of Examples 1-5 and comparative examples;

[0039] Figure 6 Stress-strain curve of electrolyte film prepared in Example 1 and comparative examples. DETAILED DESCRIPTION

[0040] The present invention will be described in detail below with reference to embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several adjustments and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0041] In the embodiments, the structure and composition of the polymer were characterized using an AAANCEⅢAA 500AA nuclear magnetic resonance spectrometer; the performance of the all-solid-state lithium battery was measured using a LANA-CT2001A battery charge-discharge tester at a test temperature of 25°C.

[0042] Example 1

[0043] (1) Preparation of the first hyperbranched polymer: such as Figure 1 As shown, the hyperbranched polymer was prepared by synthesizing N-aminoethylpiperazine and a divinyl compound as monomers via a highly efficient Michael addition reaction. Specifically, N-aminoethylpiperazine and terephthalene (molar ratio 1:1) were weighed and placed in a flask, and 20 mL of ethanol was added. The mixture was stirred at 60 °C for 3 days under nitrogen atmosphere to prepare a hyperbranched polymer with a branching degree in the range of 0.31–0.45. After the reaction was completed, the solution was concentrated and poured into diethyl ether. The precipitate was recovered, and the dissolution-precipitation process was repeated three times. The final precipitate was collected and dried under vacuum. The 1H NMR spectrum of the prepared hyperbranched polymer is shown below. Figure 2 GPC charts and test results are shown below. Figure 3 .

[0044] (2) Li6PS5Cl powder was dispersed in an acetonitrile solution of hyperbranched polymer No. 1 (polymer content 2 wt%), and stirred at room temperature under nitrogen atmosphere for 48 hours to obtain a sulfide electrolyte slurry (solid content 30%). The slurry was spread evenly on an aluminum sheet using a scraper technique, dried at 60°C for 24 hours to remove organic solvents, and the electrolyte membrane was peeled off (e.g. Figure 4 The electrolyte membrane thickness is 89 μm, made of... Figure 4 It can be seen that it is extremely flexible. Stress-strain tests show that the maximum tensile force reaches 0.45 MPa. Figure 6 The ratio was higher than that of the control group, indicating stronger adhesion and flexibility of the adhesive.

[0045] (3) Under an argon atmosphere in a glove box, a pressure cell was assembled sequentially using a 10mm diameter positive electrode layer (NCM811, Li6PS5Cl, super P mass ratio of 77.5:20:2.5), an electrolyte membrane, and a negative electrode lithium indium sheet. The cell was then placed under 10MPa pressure and subjected to electrochemical performance testing at room temperature (25℃). The positive electrode NCM811 loading was 10mg / cm³. -2 The measured cycle performance is as follows:Figure 5 The initial capacity at 0.1C cycle 2 times and 1C cycle 200 times is 114 mAh g -1 , and the capacity retention rate after 200 cycles is 82.5%.

[0046] Example 2

[0047] (1) Preparation of the second hyperbranched polymer: N-aminoethylpiperazine and diethylene glycol divinyl ether (molar ratio 1:1) were weighed into a flask, ethanol (20 mL) was added, and the mixture was stirred at 60°C for 3 days under a nitrogen atmosphere to prepare a hyperbranched polymer with a branching degree in the range of 0.31-0.45. After the reaction was completed, the solution was concentrated and poured into diethyl ether, the precipitate was recovered, and the dissolution-precipitation process was repeated three times. The final precipitate was collected and vacuum dried.

[0048] (2) Li6PS5Cl powder was dispersed in an acetonitrile solution of the hyperbranched polymer (polymer content 2 wt%), and the mixture was stirred at room temperature for 48 hours under a nitrogen atmosphere to obtain a sulfide electrolyte slurry (solid content 30%). The slurry was spread on an aluminum sheet using a doctor blade technique, and the organic solvent was removed by drying at 60°C for 24 hours. The electrolyte membrane was peeled off. The thickness of the electrolyte membrane was 100 μm.

[0049] (3) In an argon atmosphere glove box, a positive electrode layer (NCM811, Li6PS5Cl, super P, mass ratio 77.5:20:2.5) with a size of 10 mm in diameter, an electrolyte membrane, and a lithium indium sheet negative electrode were sequentially assembled into a pressure battery, which was subjected to electrochemical performance testing under a pressure of 10 MPa at room temperature 25°C. The positive electrode NCM811 loading was 10 mg cm -2 . The measured cycle performance is shown in Figure 5 , and the capacity retention rate after 200 cycles at 1C was 81.5%.

[0050] Example 3

[0051] (1) Preparation of the third hyperbranched polymer: N-aminoethylpiperazine and 1,8-nonadiene (molar ratio 1:1) were weighed into a flask, ethanol (20 mL) was added, and the mixture was stirred at 60°C for 3 days under a nitrogen atmosphere to prepare a hyperbranched polymer with a branching degree in the range of 0.31-0.45. After the reaction was completed, the solution was concentrated and poured into diethyl ether, the precipitate was recovered, and the dissolution-precipitation process was repeated three times. The final precipitate was collected and vacuum dried.

[0052] (2) Li6PS5Cl powder was dispersed in the acetonitrile solution of hyperbranched polymer (polymer content 2 wt%), stirred for 48 hours at room temperature under nitrogen atmosphere, to obtain the sulfide electrolyte slurry (solid content 30%). The slurry was spread on an aluminum sheet using a doctor blade technique, dried at 60°C for 24 hours to remove the organic solvent, and the electrolyte film was peeled off. The thickness of the electrolyte film was 100 pm.

[0053] (3) The positive electrode layer (NCM811, Li6PS5Cl, superP with a mass ratio of 77.5:20:2.5), the electrolyte film, and the negative electrode lithium indium sheet were sequentially assembled into a pressure battery under an argon atmosphere in a glove box, and the electrochemical performance test was carried out at room temperature 25°C under a pressure of 10 MPa. The positive electrode NCM811 loading was 10 mg cm -2 . The measured cycle performance is shown in Figure 5 , and the capacity retention rate was 73.4% after 200 cycles at 1C.

[0054] Example 4

[0055] (1) Preparation of the fourth hyperbranched polymer: N-aminoethylpiperazine and p-phenylenediamine (molar ratio 1:1) were weighed into a flask and added to a mixed solvent of tetrahydrofuran / ethanol (v / v = 1:1, 20 mL), and stirred at 60°C under a nitrogen atmosphere for 3 days to prepare a hyperbranched polymer with a branching degree in the range of 0.15-0.30. After the reaction was completed, the solution was concentrated and poured into diethyl ether, and the precipitate was recovered, and the dissolution-precipitation process was repeated 3 times. The final precipitate was collected and vacuum dried.

[0056] (2) Li6PS5Cl powder was dispersed in the acetonitrile solution of hyperbranched polymer (polymer content 2 wt%), stirred for 48 hours at room temperature under nitrogen atmosphere, to obtain the sulfide electrolyte slurry (solid content 30%). The slurry was spread on an aluminum sheet using a doctor blade technique, dried at 60°C for 24 hours to remove the organic solvent, and the electrolyte film was peeled off. The thickness of the electrolyte film was 100 pm.

[0057] (3) The positive electrode layer (NCM811, Li6PS5Cl, superP with a mass ratio of 77.5:20:2.5), the electrolyte film, and the negative electrode lithium indium sheet were sequentially assembled into a pressure battery under an argon atmosphere in a glove box, and the electrochemical performance test was carried out at room temperature 25°C under a pressure of 10 MPa. The positive electrode NCM811 loading was 10 mg cm -2 . The measured cycle performance is shown in Figure 5 , and the capacity retention rate was 73.3% after 200 cycles at 1C.

[0058] Example 5

[0059] (1) Preparation of No. 5 hyperbranched polymer: N-aminoethylpiperazine and p-phenylenediamine (molar ratio 1:1) were weighed into a flask, tetrahydrofuran (20 mL) was added, and stirring was carried out at 60°C for 3 days under a nitrogen atmosphere to prepare a hyperbranched polymer with a branching degree in the range of 0.05-0.12. After the reaction was completed, the solution was concentrated and poured into diethyl ether, the precipitate was recovered, and dissolution-precipitation was repeated 3 times, finally the precipitate was collected and vacuum dried.

[0060] (2) Li6PS5Cl powder was dispersed in an acetonitrile solution of the hyperbranched polymer (polymer content 2 wt%), stirring was carried out at room temperature for 48 hours under a nitrogen atmosphere to obtain a sulfide electrolyte slurry (solid content 30%). The slurry was spread on an aluminum sheet using a doctor blade technique, and the organic solvent was removed by drying at 60°C for 24 hours, and the electrolyte film was peeled off. The thickness of the electrolyte film was 100 μm.

[0061] (3) A pressure battery was assembled by sequentially arranging a positive electrode layer (NCM811, Li6PS5Cl, super P mass ratio 77.5:20:2.5) with a size of 10 mm in diameter, an electrolyte film, and a negative electrode lithium indium sheet in a glove box under an argon atmosphere, and the electrochemical performance was tested at room temperature 25°C under a pressure of 10 MPa. The positive electrode NCM811 loading was 10 mg cm -2 . The measured cycle performance is shown in Figure 5 , and the capacity retention rate after 1C cycling for 200 cycles was 82.1%.

[0062] Comparative Example

[0063] Li6PS5Cl powder was dispersed in an acetonitrile solution of polytetrafluoroethylene (polymer content 2 wt%), stirring was carried out at room temperature for 48 hours under a nitrogen atmosphere to obtain a sulfide electrolyte slurry (solid content 30%). The slurry was spread on an aluminum sheet using a doctor blade technique, and the organic solvent was removed by drying at 60°C for 24 hours, and the electrolyte film was peeled off. The thickness of the electrolyte film was 100 μm. The stress-strain curve was tested. As can be seen from Figure 6 , the maximum tensile force in the stress-strain test was only 0.28 MPa, which was less than the mechanical properties of the sulfide electrolyte prepared by using the hyperbranched polymer as the binder. A pressure battery was assembled by sequentially arranging a positive electrode layer (NCM811, Li6PS5Cl, super P mass ratio 77.5:20:2.5) with a size of 10 mm in diameter, an electrolyte film, and a negative electrode lithium indium sheet in a glove box under an argon atmosphere, and the electrochemical performance was tested at room temperature 25°C under a pressure of 10 MPa. The positive electrode NCM811 loading was 10 mg cm -2 . The measured cycle performance is shown in Figure 5 , and the capacity retention rate after 1C cycling for 200 cycles was 71.4%.

[0064] The specific embodiments of the present application are described above. It needs to be understood that the present application is not limited to the specific embodiments described above, and various modifications or changes can be made by those skilled in the art within the scope of the claims, which do not affect the essence of the present application.

Claims

1. A sulfide solid electrolyte membrane, characterized in that, The sulfide electrolyte powder is dispersed in an acetonitrile solution of a hyperbranched polymer, and stirred under an inert environment to obtain a sulfide electrolyte slurry. The slurry is then coated onto a planar substrate, dried to remove the acetonitrile, and the electrolyte membrane is peeled off. The hyperbranched polymer is prepared according to a method comprising the following steps: S1. N-aminoethylpiperazine and a divinyl compound react in the presence of an organic solvent under a nitrogen atmosphere; the organic solvent is a tetrahydrofuran / ethanol mixture with a volume ratio of 1:0 to 0:1; the divinyl compound is one or more of terephthalene, diethylene glycol divinyl ether, and 1,8-nonadiene. S2. After the reaction is complete, concentrate the solution and pour it into the precipitant. After the precipitate is recovered, repeat the dissolution-precipitation process several times. Collect the final precipitate and dry it under vacuum.

2. The sulfide solid electrolyte membrane according to claim 1, characterized in that, The molar ratio of N-aminoethylpiperazine to the divinyl compound is 1:1 to 1:

2.

3. The sulfide solid electrolyte membrane according to claim 1, characterized in that, In step S1, the reaction temperature is 25–60°C and the reaction time is 2–5 days.

4. The sulfide solid electrolyte membrane according to claim 1, characterized in that, In step S2, the precipitant is diethyl ether, and the precipitation is performed 3 to 6 times.

5. The sulfide solid electrolyte membrane according to claim 1, characterized in that, The hyperbranched polymer content in the acetonitrile solution is 1 wt% to 10 wt%; the solid content of the sulfide electrolyte slurry is 20 wt% to 40 wt%.

6. The sulfide solid electrolyte membrane according to claim 1, characterized in that, The thickness of the sulfide solid electrolyte membrane is 100–1000 μm.

7. An all-solid-state lithium battery, characterized in that, It includes a positive electrode layer, a sulfide solid electrolyte membrane as described in claim 1, and a negative electrode layer.

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