Modification of bismuth oxyiodide-based composite solid-state polymer electrolyte and method of constructing lithium battery therefrom

Abstract

The application discloses a modified bismuth oxyiodide-based composite solid-state polymer electrolyte and a lithium battery construction method thereof, and the method comprises the following steps: preparing a metal bismuth oxyiodide compound or a bismuth oxyiodide compound with defects, and preparing the bismuth oxyiodide-based composite solid-state polymer electrolyte by taking the compound as a filler. The electrolyte has the characteristics of high ionic conductivity and high mechanical strength, the bismuth oxyiodide can react in situ with a lithium negative electrode to form an SEI with lithium iodide, and the growth of dendrites is inhibited; through modification of the bismuth oxyiodide, the interface contact between a polymer and inorganic fillers can be improved, and the ionic conductivity of the composite electrolyte is improved. The composite electrolyte can match a lithium iron phosphate, NCM811 and sulfur positive electrode, and a high-conductivity and high-stability solid-state battery is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new energy battery materials, and particularly relates to a modification method of an iodine bismuth oxide-based composite solid-state polymer electrolyte and a construction method of a lithium battery thereof. BACKGROUND

[0002] A lithium ion battery is a common secondary battery and is widely used in various portable electronic devices, electric tools, electric vehicles, and energy storage systems. It is widely favored due to its high energy density, lightweight, no memory effect, low self-discharge rate, and long cycle life. However, the traditional lithium ion battery uses a liquid electrolyte, which has the risk of combustion and explosion under high temperature or high pressure, and is prone to leakage during the cycle process, reducing the safety and stability of the battery.

[0003] Therefore, it is necessary to replace the traditional liquid electrolyte with a high-safety solid-state electrolyte. As an electrolyte material, the solid-state polymer electrolyte has many advantages compared to the traditional liquid electrolyte. First, the solid-state electrolyte has higher safety because it does not leak or volatilize, reducing the risk of accidents in the battery. Second, the solid-state electrolyte has higher chemical stability and can withstand a wider voltage range, making the cycle life of the battery longer. In addition, the solid-state electrolyte also has higher ion transmission rate and lower internal resistance, which can improve the energy density and power density of the battery.

[0004] The research on solid-state polymer electrolytes began in the 1960s, initially focusing on the synthesis method and performance control of polymer electrolytes. With the development of material science and electrochemistry, the synthesis method of solid-state polymer electrolytes has been continuously innovated, including solution impregnation, in-situ polymerization, and interfacial polymerization. At the same time, researchers have also continuously improved the ion conductivity, mechanical properties, and chemical stability of solid-state polymer electrolytes to meet the needs of different electrochemical devices.

[0005] However, there are still some defects in the solid-state polymer electrolyte, such as the lower ion conductivity compared to the liquid electrolyte. Although some progress has been made, it is still necessary to further improve its ion conductivity to meet the requirements of high-power and high-energy density batteries. In addition, the interface stability between the solid-state electrolyte and the electrode is one of the key factors affecting the performance of the battery. The lack of electrochemical stability of the interface may lead to electrolysis of the electrolyte, dissolution of the electrode material, and formation of a solid-state interface, which in turn affects the cycle life and safety of the battery. To address these issues, current research focuses on finding new polymer materials, optimizing electrolyte structure design, improving preparation processes, and improving battery interface engineering. SUMMARY

[0006] The present application aims at the current technical situation that solid-state electrolyte ion conductivity and interface electrochemical stability cannot meet the use requirements, and provides a modification method of iodine bismuth oxide-based composite solid-state polymer electrolyte and a lithium battery construction method thereof.

[0007] The solid-state polymer electrolyte of the present application is composed of an ion-conducting polymer and a metal iodine oxide, and the modification process is summarized as follows: first, modified bismuth iodine oxide is prepared by using a hydrothermal synthesis method, and the metal iodine oxide is modified by doping, calcination and the like; then, the modified bismuth iodine oxide is dispersed in an organic solvent, lithium salt is added, and the polymer matrix is dispersed into the solvent, stirred until uniform, cast into a film, and vacuum dried to obtain a composite solid-state polymer electrolyte.

[0008] The electrolyte has the characteristics of high ionic conductivity and high mechanical strength, the bismuth iodine oxide can react in situ with the lithium negative electrode to form an SEI with lithium iodide, and the growth of dendrites is inhibited; through modification of the bismuth iodine oxide, the interface contact between the polymer and the inorganic filler can be improved, and the ionic conductivity of the composite electrolyte can be improved. The composite electrolyte can match lithium iron phosphate, NCM811, sulfur positive electrode, and realize high ionic conductivity and high stability of the solid-state battery.

[0009] Specifically, the technical solutions adopted by the present application are as follows:

[0010] In the first aspect of the present application, a modification method of bismuth iodine oxide-based composite solid-state polymer electrolyte is provided, comprising the following steps:

[0011] (1) Solution mixing

[0012] Bismuth nitrate pentahydrate is added to an organic solvent, and optionally other metal-doped salt hydrates are added according to different proportions, and the mixture is heated and stirred uniformly at 50℃ until fully dissolved to obtain a clear solution; iodide is added to the organic solvent, heated and stirred until fully dissolved, and then slowly added to the clear solution of the bismuth metal salt;

[0013] (2) Preparation of metal bismuth iodine oxide compound

[0014] After the mixed solution is fully stirred, a one-step solvothermal synthesis method is used, the mixed solution is placed in a reaction kettle, and hydrothermal synthesis is carried out at 120-240℃ for 2-24 hours, and the mixed solution after reaction is washed with ethanol and deionized water for multiple times, and then dried at 80℃ to obtain a metal bismuth iodine oxide compound;

[0015] (3) Preparation of bismuth iodine oxide compound with defects

[0016] The prepared metal bismuth oxy-iodide compound is placed in a tube furnace, and is gradiently heated under air or hydrogen atmosphere, and is annealed at a temperature of 200-500℃ for 2h, and a bismuth oxy-iodide compound with defects is obtained after annealing;

[0017] (4) solid-state polymer electrolyte preparation

[0018] After vacuum drying the polymer matrix at 60℃, the polymer matrix and lithium salt are mixed by stirring in an organic solvent; the metal bismuth oxy-iodide compound or the bismuth oxy-iodide compound with defects is added to the mixed solution in different mass ratios and is magnetically stirred to obtain a slurry; the slurry is poured into a mold, and after vacuum drying at 60℃, a composite solid-state polymer electrolyte film is obtained.

[0019] The preferred scheme of the above steps is as follows:

[0020] In step (1), the concentration of bismuth nitrate pentahydrate is 0.1-0.5mol / L, and the concentration of iodide is 0.1-0.5mol / L;

[0021] The organic solvent is selected from ethylene glycol, propylene glycol or butanediol;

[0022] The dissolved salt hydrate of other metals for doping includes any one or a combination of cerium nitrate, lanthanum nitrate, titanium chloride, iron chloride, zinc nitrate hexahydrate, zirconium chloride octahydrate, molybdenum chloride, antimony chloride, and tungsten chloride;

[0023] The iodide is selected from any one of potassium iodide and sodium iodide;

[0024] The molar ratio between bismuth nitrate pentahydrate and other metal dissolved salts is 9:1;

[0025] After adding the iodide, heating and stirring at 50℃ for 20min.

[0026] In step (4), the polymer matrix is selected from any one of polyethylene oxide, polyvinylidene-hexafluoropropylene, and polyacrylonitrile;

[0027] The lithium salt is selected from any one of lithium trifluoromethanesulfonate, lithium nitrate, lithium hexafluorophosphate, and lithium borohydride;

[0028] The organic solvent is selected from any one of acetonitrile, methanol, and N-methylpyrrolidone;

[0029] The proportion of the metal bismuth oxy-iodide compound or the bismuth oxy-iodide compound with defects to the polymer matrix is 0.01-30wt%;

[0030] The molar ratio between the polymer matrix and the lithium salt is 20:1-10:1,

[0031] The thickness of the composite solid-state polymer electrolyte film is 30-150 mu m.

[0032] In a second aspect, the application provides a bismuth oxyiodide-based composite solid-state polymer electrolyte film prepared by the method described above.

[0033] In a third aspect, the application provides a method for constructing a bismuth oxyiodide-based composite solid-state lithium battery, comprising the following steps:

[0034] (1) 75wt% positive active material, 10wt% carbon black and 15wt% PVDF are dispersed into N-methylpyrrolidone solvent, and then coated on aluminum foil paper after uniform stirring; then the solvent is removed at 60 DEG C under vacuum, and the film is cut into a certain diameter of round sheet;

[0035] (2) a suitable type of battery shell is selected, the current collector is a 1mm stainless steel sheet, and the battery is assembled in the order of lithium sheet, bismuth oxyiodide-based composite solid-state polymer electrolyte film, positive sheet and current collector from negative to positive.

[0036] Preferably, the positive active material is selected from any one of lithium iron phosphate, NCM811 and carbon / sulfur composite positive material;

[0037] The loading capacity of the positive sheet is 2-4 mg / cm 2 .

[0038] In a fourth aspect, the application provides a corresponding bismuth oxyiodide-based composite solid-state lithium battery constructed by the method described above.

[0039] The experimental test results show that the ionic conductivity of the battery constructed by the method of the application is higher than that of the battery without adding metal bismuth oxyiodide compound filler, and the lowest increase is 1.84 times.

[0040] The beneficial technical effects of the application are:

[0041] (1) The modified bismuth oxyiodide filler solid-state polymer electrolyte prepared by the application has high ionic conductivity and high mechanical strength. By adding bismuth oxyiodide filler, the glass transition temperature of the polymer is reduced, so that the conductivity of the composite solid-state polymer electrolyte at room temperature is increased. Inorganic fillers can adsorb trifluoromethanesulfonic acid anions, promote the dissociation of lithium salt, and improve the ionic conductivity of the solid-state electrolyte; at the same time, the addition of inorganic fillers also improves the mechanical strength of the composite solid-state polymer electrolyte, and improves the disadvantage that the solid-state polymer electrolyte is difficult to process due to poor mechanical strength.

[0042] (2) The modified bismuth oxyiodide filler solid-state polymer electrolyte can improve the interface contact between the electrolyte and the lithium negative electrode, and the lithium negative electrode and the bismuth oxyiodide can form a hard lithium iodide in situ at the interface, which can effectively inhibit the growth of dendrites and improve the cycle life of the solid-state battery.

[0043] (3) The modified bismuth oxyiodide filler solid-state polymer electrolyte can improve the cycle performance of the battery, and the CEI buffer layer formed at the interface between the positive electrode and the polymer can effectively inhibit the structural damage and capacity decay of the positive electrode material at high temperature, thereby improving the stability of the battery under long cycle.

[0044] The project relied on by the present application is as follows: Project type: Shanghai Municipal Science and Technology Commission, basic research special zone plan; Project number: 22T01400100-18; Project name: Design, preparation and application of key materials for solid-state batteries. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 It is a field emission scanning electron microscope photo of bismuth oxyiodide prepared from Example 1;

[0046] Figure 2 It is a scanning electron microscope photo of the composite solid-state polymer electrolyte prepared from Example 2;

[0047] Figure 3 It is an EPR spectrum of oxygen-deficient bismuth oxyiodide prepared from Example 3;

[0048] Figure 4 It is the cycle performance of the doped bismuth oxyiodide composite solid-state electrolyte symmetrical battery prepared from Example 3;

[0049] Figure 5 It is a voltammetry characteristic curve diagram of the bismuth oxyiodide composite solid-state polymer electrolyte lithium iron phosphate full battery constructed from Example 5;

[0050] Figure 6 It is a flowchart diagram of the composite solid-state electrolyte constructed by the present application. DETAILED DESCRIPTION

[0051] In order to more clearly illustrate the present application, the present application will be further described below in conjunction with preferred embodiments. Those skilled in the art should understand that the specific description below is illustrative rather than limiting, and should not limit the protection scope of the present application.

[0052] Example 1

[0053] A, modification and construction of bismuth oxyiodide-based composite solid-state polymer electrolyte

[0054] (1) 4.85 g of bismuth nitrate pentahydrate (BiNO3·5H2O) was added into 30 ml of ethylene glycol, 1.66 g of potassium iodide was added into 30 ml of ethylene glycol, after being fully stirred and dissolved, the ethylene glycol solution of potassium iodide was slowly poured into the ethylene glycol solution of bismuth nitrate pentahydrate and fully mixed, heating and stirring was carried out at a temperature of 50°C for 20 min, and then the mixed solution was transferred into an autoclave. The hydrothermal reaction was carried out at a temperature of 180°C for 2 h.

[0055] (2) The reacted mixed solution was centrifuged and washed three times in ethanol and deionized water respectively, and then dried at a temperature of 80°C for 10 hours to obtain a bismuth oxyiodide filler. The constructed bismuth oxyiodide filler was observed under a microscope to obtain the field emission scanning electron microscope image as shown in FIG. 2, which shows that the prepared bismuth oxyiodide filler is in a flower ball shape and is self-assembled by stacked nanosheets. Figure 1

[0056] (3) A PEO-based composite solid-state electrolyte film was prepared by using PEO as a polymer matrix, bismuth oxyiodide as a filler, and LiTFSI as a lithium salt by a solution casting method: first, PEO was vacuum dried at 60°C for 2 h, 2 g of PEO and 0.725 g of LiTFSI were added into a stirring bottle and mixed with an appropriate amount of acetonitrile. 0.1 g of bismuth oxyiodide was added to the mixed solution and magnetically stirred for 12 h. After stirring, the obtained slurry was cast into a polytetrafluoroethylene mold in a glove box, and then placed in a vacuum drying oven and dried at 60°C for 24 h to obtain a composite solid-state polymer electrolyte film.

[0057] B, Construction of bismuth oxyiodide composite solid-state polymer electrolyte full cell

[0058] The flow chart is shown in FIG. 1. Figure 6 The main steps are as follows:

[0059] (1) 240 mg of NCM811 active material, 30 mg of carbon black and 30 mg of PVDF were dispersed into N-methyl pyrrolidone solvent, and then coated on an aluminum foil after being uniformly stirred. Subsequently, the NMP solvent was removed at a temperature of 60°C in a vacuum, and then cut into a circular sheet with a diameter of 8 mm, and the active material loading was about 2.4 mg / cm 2 .

[0060] (2) A 2032 type battery shell was used, and a 1 mm stainless steel sheet was used as a current collector. The battery was assembled in the order of lithium sheet, polymer electrolyte sheet, positive electrode sheet and current collector, and the electrochemical performance was tested.

[0061] Example 2

[0062] A, Modification and construction of bismuth oxyiodide-based composite solid-state polymer electrolyte

[0063] ​(1) 4.85 g of bismuth nitrate pentahydrate (BiNO3·5H2O) was added into 30 ml of ethylene glycol, 1.66 g of potassium iodide was added into 30 ml of ethylene glycol, after being fully stirred and dissolved, the ethylene glycol solution of potassium iodide was slowly poured into the ethylene glycol solution of bismuth nitrate pentahydrate and fully mixed, heating and stirring was performed at a temperature of 50°C for 20 min, and then the mixed solution was transferred into an autoclave. Hydrothermal reaction was performed at a temperature of 120°C for 24 h.

[0064] (2) The reacted mixed solution was centrifuged and washed three times in ethanol and deionized water respectively, and then dried at a temperature of 80°C for 10 h to obtain bismuth oxyiodide filler;

[0065] (3) The bismuth oxyiodide filler was placed in a tube furnace and annealed by calcination at a temperature of 500°C for 2 h in an air atmosphere to obtain oxygen-deficient bismuth oxyiodide.

[0066] (4) PVDF-HFP was used as a polymer matrix, bismuth oxyiodide was used as a filler, and LiTFSI was used as a lithium salt to prepare a PVDF-HFP-based composite solid electrolyte membrane by a solution casting method: first, PVDF-HFP was vacuum dried at 60°C for 2 h, 2 g of PVDF-HFP and 1 g of LiTFSI were added into a stirring bottle, and an appropriate amount of acetonitrile was added for mixing. 0.2 g of bismuth oxyiodide was added to the mixed solution and magnetically stirred for 12 h. After stirring was completed, the obtained slurry was cast into a polytetrafluoroethylene mold in a glove box, and then placed in a vacuum drying box and dried at 60°C for 24 h to obtain a composite solid polymer electrolyte membrane.

[0067] The composite solid polymer electrolyte constructed in this embodiment was observed under a microscope, and a field emission scanning electron microscope image as shown in FIG. 6 was obtained. The results show that the prepared composite solid polymer electrolyte is smooth, indicating that the filler is uniformly dispersed in the polymer membrane. Figure 2

[0068] B. Construction of bismuth oxyiodide composite solid polymer electrolyte full cell

[0069] (1) 240 mg of lithium iron phosphate active material, 30 mg of carbon black and 30 mg of PVDF were dispersed into N-methyl pyrrolidone solvent, and then uniformly stirred and coated on an aluminum foil. Subsequently, the NMP solvent was removed at a temperature of 60°C in a vacuum, and then cut into a circular sheet with a diameter of 8 mm. The active material loading was about 2.4 mg / cm 2 .

[0070] (2) A 2032 type battery shell was used, and a 1 mm stainless steel sheet was used as a current collector. The battery was assembled in the order of lithium sheet, polymer electrolyte sheet, positive electrode sheet and current collector for electrochemical performance test.

[0071] Example 3​

[0072] Modification and construction of bismuth oxyiodide-based composite solid-state polymer electrolyte

[0073] (1) 4.85 g of bismuth nitrate pentahydrate (BiNO3·5H2O) was added to 30 ml of ethylene glycol, and 1.66 g of potassium iodide was added to 30 ml of ethylene glycol. After being fully stirred and dissolved, the potassium iodide ethylene glycol solution was slowly poured into the bismuth nitrate pentahydrate ethylene glycol solution and fully mixed. Heating and stirring were performed at a temperature of 50°C for 20 min, after which the mixed solution was transferred to an autoclave. Hydrothermal reaction was performed at a temperature of 180°C for 2 h.

[0074] (2) The reacted mixed solution was washed three times by centrifugation in ethanol and deionized water, respectively, and then dried at a temperature of 80°C for 10 hours to obtain bismuth oxyiodide filler;

[0075] (3) The bismuth oxyiodide filler was placed in a tube furnace and annealed by calcination under a hydrogen atmosphere at a temperature of 300°C for 2 hours to obtain defect-type bismuth oxyiodide.

[0076] The bismuth oxyiodide prepared in this example was subjected to EPR testing, and the results are shown in Figure 3 The bismuth oxyiodide reduced by hydrogen appeared a characteristic peak of oxygen vacancy at g = 2.003, indicating that oxygen vacancies were successfully introduced on the surface of bismuth oxyiodide by hydrogen reduction. The oxygen vacancies, as Lewis acids, can adsorb trifluoromethanesulfonate anions, which are Lewis bases, to promote the dissociation of lithium salt.

[0077] (4) PAN was used as the polymer matrix, bismuth oxyiodide was used as the filler, and LiNO3 was used as the lithium salt,

[0078] A PEO-based composite solid-state electrolyte membrane was prepared by solution casting. First, PEO was vacuum dried at 60°C for 2 h, and 2 g of PAN and 0.725 g of LiNO3 were added to a stirring bottle and mixed with an appropriate amount of acetonitrile. 0.2 g of bismuth oxyiodide was added to the mixed solution and magnetically stirred for 12 h. After stirring was completed, the obtained slurry was cast into a polytetrafluoroethylene mold in a glove box, and then placed in a vacuum drying oven at 60°C for 24 h to obtain a composite solid-state polymer electrolyte membrane.

[0079] B. Construction of bismuth oxyiodide composite solid-state polymer electrolyte full cell

[0080] (1) 240 mg of sulfur / carbon active material, 30 mg of carbon black, and 30 mg of PVDF were dispersed in an N-methylpyrrolidone solvent, and then uniformly stirred and coated on an aluminum foil. Subsequently, the NMP solvent was removed at a temperature of 60°C under vacuum, and then cut into a circular sheet with a diameter of 8 mm. The active material loading was about 2.4 mg / cm 2 .

[0081] (2) The battery shell of type 2032 was used, the current collector was 1 mm stainless steel sheet, and the lithium sheet, polymer electrolyte sheet, positive electrode sheet, and current collector were sequentially assembled into a battery for electrochemical performance test.

[0082] Example 4

[0083] A, Modification and construction of bismuth oxyiodide-based composite solid-state polymer electrolyte

[0084] (1) 4.365 g of bismuth nitrate pentahydrate (BiNO3·5H2O) and 0.326 g of cerium nitrate (CeNO3) were added to 30 ml of ethylene glycol, 1.66 g of potassium iodide was added to 30 ml of ethylene glycol, and after being fully stirred and dissolved, the ethylene glycol solution of potassium iodide was slowly poured into the ethylene glycol solution of bismuth nitrate pentahydrate and fully mixed, heated and stirred at a temperature of 50°C for 20 min, and then the mixed solution was transferred to an autoclave. Hydrothermal reaction was carried out at a temperature of 180°C for 2h;

[0085] (2) The reacted mixed solution was washed with ethanol and deionized water three times by centrifugation, and then dried at a temperature of 80°C for 10 hours to obtain a cerium-doped bismuth oxyiodide filler;

[0086] (3) PEO was used as the polymer matrix, bismuth oxyiodide was used as the filler, and LiTFSI was used as the lithium salt. A PEO-based composite solid-state electrolyte membrane was prepared by solution casting method: first, PEO was vacuum dried at 60°C for 2h, 2g of PEO and 0.725g of LiTFSI were added to a stirring bottle, and an appropriate amount of acetonitrile was added for mixing. 0.1 g of bismuth oxyiodide was added to the mixed solution and magnetically stirred for 12h. After stirring, the obtained slurry was cast into a polytetrafluoroethylene mold in a glove box, and then placed in a vacuum drying oven at 60°C for 24h to obtain a composite solid-state polymer electrolyte membrane.

[0087] B, Construction of bismuth oxyiodide composite solid-state polymer electrolyte full battery

[0088] (1) 240 mg of lithium iron phosphate active material, 30 mg of carbon black, and 30 mg of PVDF were dispersed in N-methyl pyrrolidone solvent, and then coated on aluminum foil paper after uniform stirring. Subsequently, the NMP solvent was removed at a vacuum of 60°C, and it was cut into a circular sheet with a diameter of 8 mm. The active material loading was about 2.4 mg / cm 2 .

[0089] (2) The battery shell of type 2032 was used, the current collector was 1 mm stainless steel sheet, and the lithium sheet, polymer electrolyte sheet, positive electrode sheet, and current collector were sequentially assembled into a battery for electrochemical performance test.

[0090] The full battery was tested by volt-ampere curve at different scan rates, and Figure 4 As shown in FIG. 2, the volt-ampere characteristic curves at different scan rates all appeared standard redox peaks, indicating that the full battery assembled by the solid composite polymer electrolyte had good electrochemical performance.

[0091] Example 5

[0092] Modification and construction of A, bismuth oxyiodide-based composite solid-state polymer electrolyte

[0093] (1) 8.73 g of bismuth nitrate pentahydrate (BiNO3·5H2O), 0.378 g of zinc nitrate (ZnNO3) were added to 30 ml of ethylene glycol, 3.32 g of potassium iodide was added to 30 ml of ethylene glycol, after fully stirring and dissolving, the potassium iodide ethylene glycol solution was slowly poured into the bismuth nitrate pentahydrate ethylene glycol solution and fully mixed, and heating and stirring was performed at a temperature of 50°C for 20 min, and then the mixed solution was transferred to an autoclave. Hydrothermal reaction was performed at a temperature of 180°C for 2 h;

[0094] (2) The reacted mixed solution was washed with ethanol and deionized water respectively by centrifugation for three times, and then dried at a temperature of 80°C for 10 hours to obtain a zinc-doped bismuth oxyiodide filler;

[0095] (3) A PEO-based composite solid-state electrolyte film was prepared by using PAN as a polymer matrix, bismuth oxyiodide as a filler, and LiPF6 as a lithium salt by a solution casting method: first, PAN was vacuum dried at 60°C for 2 h, 2 g of PAN and 0.9 g of LiPF6 were added to a stirring bottle, and 40 ml of methanol was added for mixing. 0.1 g of zinc-doped bismuth oxyiodide was added to the mixed solution and magnetically stirred for 12 h. After stirring, the obtained slurry was cast into a polytetrafluoroethylene mold in a glove box, and then placed in a vacuum drying box and dried at 60°C for 24 h to obtain a composite solid-state polymer electrolyte film.

[0096] B, construction of a bismuth oxyiodide composite solid-state polymer electrolyte full battery

[0097] (1) 240 mg of NCM811 active material, 30 mg of carbon black and 30 mg of PVDF were dispersed in N-methyl pyrrolidone solvent, and then coated on aluminum foil paper after uniform stirring. Subsequently, the NMP solvent was removed at a vacuum of 60°C, and then cut into a circular sheet with a diameter of 8 mm. The active material loading was about 2.4 mg / cm 2 .

[0098] (2) A 2032 type battery shell was used, the current collector was a 1 mm stainless steel sheet, and the battery was assembled in the order of lithium sheet, polymer electrolyte sheet, positive electrode sheet and current collector for electrochemical performance test.

[0099] Comparative Example 1

[0100] The composite solid-state polymer electrolyte was prepared and the battery was constructed by the method of Example 1, except that no modified bismuth oxyiodide composite was added in this comparative example 1.

[0101] A. Modification of the composite solid-state polymer electrolyte and construction

[0102] (1) PEO-based solid-state electrolyte film was prepared by solution casting method using PEO as polymer matrix and LiTFSI as lithium salt. First, 2 g of PEO and 0.1 g of LiTFSI were added to a stirring bottle with 40 ml of acetonitrile and stirred. After stirring, the obtained slurry was cast into a polytetrafluoroethylene mold in a glove box, and then placed in a vacuum drying oven at 60°C for 24 h to obtain a composite solid-state polymer electrolyte film.

[0103] B. Construction of composite solid-state polymer electrolyte full battery

[0104] (1) 240 mg of lithium iron phosphate active material, 30 mg of carbon black and 30 mg of PVDF were dispersed in N-methyl pyrrolidone solvent, and then coated on aluminum foil paper after stirring. Then the NMP solvent was removed at 60°C in vacuum, and cut into a round piece with a diameter of 8 mm. The active material loading was about 2.4 mg / cm 2 .

[0105] (2) The battery was assembled in the order of lithium sheet, polymer electrolyte sheet, positive electrode sheet, current collector, and the current collector was assembled into a 2032 type battery shell with 1 mm stainless steel sheet as the current collector, and the electrochemical performance was tested.

[0106] The PEO solid-state electrolyte prepared in Examples 1-5 and Comparative Example 1 was tested for conductivity under the same conditions, and the results are shown in Table 1. The conductivity of the PEO solid-state electrolyte in Examples 1-5 with the addition of the modified bismuth oxyiodide composite filler was significantly better than that of Comparative Example 1. The defect type bismuth oxyiodide composite improved the conductivity of the PEO solid-state electrolyte better than the bismuth oxyiodide composite without defect type improvement, and the oxygen defect type bismuth oxyiodide had the best improvement effect, followed by the zinc doped bismuth oxyiodide.

[0107] Table 1. Test results of PEO solid-state electrolyte conductivity prepared in Examples 1-5 and Comparative Example 1

[0108]

[0109] In summary, after adding bismuth oxyiodide filler, the ionic conductivity of the PEO solid-state polymer electrolyte is obviously improved, and targeted modification design of bismuth oxyiodide can improve the interface contact between bismuth oxyiodide and PEO, further improving the ionic conductivity.

[0110] The above merely describes preferred embodiments of the present application and is not intended to limit the present application in any form. Although the present application has been disclosed with the above preferred embodiments, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above-mentioned technical content without departing from the technical solution range of the present application, and equivalent embodiments with equivalent changes are equivalent. Any simple modification, equivalent change and modification of the above embodiments made according to the technical essence of the present application are still within the scope of the present application.

Claims

1. A method for modifying a bismuth oxyiodide-based composite solid-state polymer electrolyte, characterized by, Comprising the following steps: (1) Solution mixing Bismuth nitrate pentahydrate is added to an organic solvent, and other metal-doped dissolved salt hydrates are added according to different proportions. After being heated and stirred uniformly at 50°C, a clear solution is obtained. Iodide is added to the organic solvent, and after being heated and stirred to dissolve completely, it is slowly added to the clear solution of the bismuth metal salt, Wherein, the concentration of bismuth nitrate pentahydrate is 0.1-0.5mol / L; the concentration of iodide is 0.1-0.5mol / L, the iodide is selected from any one of potassium iodide, sodium iodide, after adding iodide, heating and stirring at 50°C for 20min; The organic solvent is selected from ethylene glycol, propylene glycol or butanediol; the other metal-doped dissolved salt hydrate includes any one or combination of cerium nitrate, lanthanum nitrate, titanium chloride, iron chloride, zinc nitrate hexahydrate, zirconium chloride octahydrate, molybdenum chloride, antimony chloride, tungsten chloride; the molar ratio between bismuth nitrate pentahydrate and other metal-doped dissolved salt is 9:1; (2) Preparation of metal bismuth oxyiodide compound After the mixed solution is fully stirred, a one-step solvothermal synthesis method is used. The mixed solution is placed in a reaction kettle and hydrothermally synthesized at 120-240°C for 2-24 hours. The mixed solution after the reaction is completed is washed with ethanol and deionized water several times and dried at 80°C to obtain a metal bismuth oxyiodide compound. (3) Preparation of bismuth oxyiodide compound with defects The prepared metal bismuth oxyiodide compound is placed in a tube furnace and gradient heated in air or hydrogen atmosphere, and annealed at a temperature of 200-500°C for a certain time to obtain a bismuth oxyiodide compound with defects. (4) Preparation of solid-state polymer electrolyte After the polymer matrix is vacuum dried at 60°C, the polymer matrix and lithium salt are stirred and mixed in an organic solvent. The bismuth oxyiodide compound with defects is added to the mixed solution in different mass ratios and magnetically stirred to obtain a slurry. The slurry is poured into a mold and vacuum dried at 60°C to obtain a composite solid-state polymer electrolyte film, Wherein, the polymer matrix is selected from any one of polyethylene oxide, polyvinylidene-hexafluoropropylene, and polyacrylonitrile; the lithium salt is selected from any one of lithium trifluoromethanesulfonate, lithium nitrate, lithium hexafluorophosphate, and lithium borohydride; the organic solvent is selected from any one of acetonitrile, methanol, and N-methyl pyrrolidone, The proportion of the bismuth oxyiodide compound with defects to the polymer matrix is 0.01-30%wt; the molar ratio between the polymer matrix and the lithium salt is 20:1 ~ 10:

1.

2. The modification method of the bismuth oxyiodide-based composite solid-state polymer electrolyte according to claim 1, characterized in that: wherein In step (3), the annealing time is 2h.

3. The modification method of the bismuth oxyiodide-based composite solid-state polymer electrolyte according to claim 1, characterized in that: wherein The thickness of the composite solid-state polymer electrolyte film is 30-150 μm.

4. A bismuth oxyiodide-based composite solid-state polymer electrolyte membrane, characterized by, Prepared by the method of any one of claims 1-3.

5. A method of constructing a bismuth oxyiodide-based composite solid-state lithium battery, characterized by, Comprising the following steps: (1) 75wt% positive electrode active material, 10wt% carbon black and 15wt% PVDF are dispersed in N-methyl pyrrolidone solvent, uniformly stirred and coated on aluminum foil paper; then the solvent is removed at 60°C under vacuum, and it is cut into a certain diameter of round sheet; (2) Select a battery shell, and use a 1mm stainless steel sheet as the current collector. From the negative electrode to the positive electrode, the battery is assembled in the order of lithium sheet, iodine bismuth oxide-based composite solid-state polymer electrolyte film, positive electrode sheet and current collector. The iodine bismuth oxide-based composite solid-state polymer electrolyte film is as shown in claim 4.

6. The construction method of the iodine bismuth oxide-based composite solid-state lithium battery according to claim 5, characterized in that: The positive electrode active material is selected from any one of lithium iron phosphate, NCM811 and carbon / sulfur composite positive electrode material; The method is constructed by using the method of claim 5 or 6. wherein, ​ The positive electrode sheet has a loading amount of 2 to 4 mg / cm 2 .

7. A bismuth oxyiodide-based composite solid-state lithium battery, characterized by ​

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