CN114649587A - Quasi-solid electrolyte based on boron nitride nanosheets and preparation method and application thereof - Google Patents

Quasi-solid electrolyte based on boron nitride nanosheets and preparation method and application thereof Download PDF

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CN114649587A
CN114649587A CN202210250223.8A CN202210250223A CN114649587A CN 114649587 A CN114649587 A CN 114649587A CN 202210250223 A CN202210250223 A CN 202210250223A CN 114649587 A CN114649587 A CN 114649587A
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boron nitride
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solid electrolyte
lithium
pvca
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宫勇吉
左璟涵
翟朋博
王蕾
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Beihang University
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
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    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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Abstract

The invention provides a quasi-solid electrolyte based on boron nitride nanosheets and a preparation method and application thereof, and belongs to the technical field of solid electrolytes. In the quasi-solid electrolyte provided by the invention, the inorganic filler boron nitride nanosheet and the liquid-phase component can improve the poor intrinsic lithium ion conductivity of an organic framework, improve the mechanical property and improve the lithium ion transmission capability of the electrolyte, so that the quasi-solid electrolyte has higher lithium ion conductivity and higher lithium ion migration number; the organic framework (the poly (ethylene carbonate)) has better mechanical property and stability, and the organic framework and the liquid phase component can improve interface contact and improve the toughness and processability of electrolyte; the inorganic filler and the organic framework can improve the safety and stability of the liquid phase component, and the three components are coordinated and cooperated, so that the construction of a high-performance electrolyte system is realized.

Description

Quasi-solid electrolyte based on boron nitride nanosheets and preparation method and application thereof
Technical Field
The invention relates to the technical field of solid electrolytes, in particular to a quasi-solid electrolyte based on boron nitride nanosheets and a preparation method and application thereof.
Background
With the popularization of personal mobile electronic devices and the popularization of new energy automobiles in recent years, lithium batteries are becoming an indispensable part of life. However, the liquid organic electrolyte used in the conventional lithium ion battery has potential safety hazards such as flammability, easy leakage, poor thermal stability and the like, and is one of the main causes of deflagration and explosion of the lithium battery. Therefore, the development of solid electrolytes has become one of the most promising approaches for improving the safety and overall performance of lithium batteries.
The solid electrolyte has no liquid flowing characteristic, has higher thermal stability and better mechanical property, is not easy to burn and leak, and is one of the research hotspots in the energy storage system based on the lithium battery at present. At present, solid electrolytes can be mainly classified into inorganic solid electrolytes and organic solid electrolytes. The inorganic solid electrolyte mainly includes oxides and sulfides. Wherein the oxide includes, for example, Li3xLa2/3-xTiO3(LLTO), NASICON type Li1+ xAlxTi2-x(PO4)3(LATP)、Li1+xAlxGe2-x(PO4)3(LAGP), garnet type Li7La3Zr2O12(LLZO) and the like, which generally have advantages of high lithium ion conductivity and high hardness, but have disadvantages of poor toughness, poor contact with electrodes, high processing difficulty, and the like. Sulfides mainly include, for example, Li3.25Ge0.25P0.75S4、Li9.54Si1.74P1.44S11.7Cl0.3And the like, but the lithium ion battery is usually sensitive to air and water, has poor stability and brings adverse effects on processing, assembly and practical use. The most mature organic solid electrolyte is PEO (polyethylene oxide), which has good film forming property and good interface contact, but has low lithium ion conductivity at room temperature and narrower electrochemical working window; besides the similar advantages and disadvantages of the organic solid electrolytes based on PAN (polyacrylonitrile) and PVDF (polyvinylidene fluoride), the performance influence caused by solvent residue also hinders the practical application of the organic solid electrolytes [ SCHNELLJ, GuntHERT, KNOCH ET, ETum-ionandlithiummetalbatteries-pavingthewaytolarge-scaleproduction[J].2018,382(160-75).]。
In general, various types of solid electrolytes have considerable drawbacks and disadvantages. Therefore, the development of solid electrolytes with high safety, high ionic conductivity and high performance of battery performance is still the research target and discussion of researchers.
Disclosure of Invention
The quasi-solid electrolyte has good mechanical property, proper flame retardance, high lithium ion conductivity, high lithium ion migration number and wide electrochemical working window.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a quasi-solid electrolyte, which comprises poly (ethylene carbonate), a liquid component and boron nitride nanosheets; the liquid component comprises vinylene carbonate and lithium salt; the liquid component and the boron nitride nanosheets are dispersed in the backbone of the poly (ethylene carbonate).
Preferably, the quasi-solid electrolyte comprises, by mass, 74.8-84.8 wt% of the poly (ethylene carbonate), 15-25 wt% of the liquid component and 0.2-0.8 wt% of the boron nitride nanosheet.
Preferably, the boron nitride nanosheet is hexagonal boron nitride, and the particle size of the boron nitride nanosheet is 20 nm-5000 nm.
Preferably, the lithium salt comprises lithium difluorooxalato borate or lithium perchlorate.
The invention provides a preparation method of the quasi-solid electrolyte in the technical scheme, which comprises the following steps:
mixing lithium salt, vinylene carbonate and boron nitride nanosheets to obtain a polymeric precursor;
and mixing the polymerization precursor and an initiator, and carrying out thermal polymerization to obtain the quasi-solid electrolyte.
Preferably, the mixture of lithium salt, vinylene carbonate and boron nitride nanosheets comprises: first mixing lithium salt and vinylene carbonate to obtain a liquid component; and secondly, mixing the liquid component and the boron nitride nanosheet to obtain a polymerization precursor.
Preferably, the ratio of the mass of the lithium salt to the volume of the vinylene carbonate is (0.4-1.7) g, (8-12) mL; the ratio of the mass of the boron nitride nanosheet to the volume of the liquid component is (18-25) mg (3-4) mL.
Preferably, the initiator comprises azobisisobutyronitrile, and the ratio of the mass of the initiator to the volume of the polymerization precursor is (6-8.5) mg:3.5 mL.
Preferably, the pressure of the thermal polymerization is 30-50 kPa, the temperature is 55-65 ℃, and the time is 700-900 min.
The invention provides the application of the quasi-solid electrolyte in the technical scheme or the quasi-solid electrolyte prepared by the preparation method in the technical scheme in a lithium battery.
The invention provides a quasi-solid electrolyte, which comprises poly (ethylene carbonate), a liquid component and boron nitride nanosheets; the liquid component comprises vinylene carbonate and lithium salt; the liquid component and the boron nitride nanosheets are dispersed within the backbone of the poly (ethylene carbonate).
In the quasi-solid electrolyte provided by the invention, the liquid-phase component has higher capability of transmitting lithium ions, and the boron nitride nanosheets can promote the rapid transmission of the lithium ions, so that the inorganic filler boron nitride nanosheets and the liquid-phase component can improve the poor intrinsic lithium ion conductivity of an organic framework, improve the transmission capability of the electrolyte to the lithium ions, and enable the quasi-solid electrolyte to have higher lithium ion conductivity and higher lithium ion migration number; the organic framework (the poly (ethylene carbonate)) has better mechanical property and stability, and the organic framework and the liquid phase component can improve interface contact and improve the toughness and processability of electrolyte; the inorganic filler and the organic framework can improve the safety and stability of the liquid phase component, and the three components are coordinated and cooperated, so that the construction of a high-performance electrolyte system is realized. The boron nitride nanosheet filler in the quasi-solid electrolyte provided by the invention has a rapid transmission mechanism for lithium ions, reduces the transmission barrier of the lithium ions and improves the diffusion coefficient of the lithium ions, so that the quasi-solid electrolyte has a high lithium ion transfer number (the ratio of the charge transferred by the lithium ions to the total charge), the closer the lithium ion transfer number is to 1, the better the deposition effect of the lithium ions on a negative electrode is, the fewer side reactions between the electrode and the electrolyte are, the longer the cycle life of the electrolyte can be maintained, and the better the cycle performance of the battery is.
The quasi-solid electrolyte provided by the invention has a wide electrochemical working window, can stably circulate within 0-5V, can be well compatible with commercial lithium iron phosphate anodes and ternary anodes, and has a stable working state, because the electrochemical stability windows of the poly (ethylene carbonate) and the vinylene carbonate are wide, the oxidation resistance is good, and in addition, the chemical stability of the boron nitride nanosheet is high, so that the stability of the electrolyte is further improved.
The quasi-solid electrolyte provided by the invention has quasi-solid characteristics, the liquid phase component improves the elasticity of the electrolyte, so that a quasi-solid system with an organic framework and a liquid phase component coexisting has better elasticity, and thus, the quasi-solid electrolyte has higher elongation at break and deformation recovery capability, so that the quasi-solid electrolyte has excellent mechanical properties, the elongation at break of stretching is more than 200%, and the quasi-solid electrolyte can be folded and twisted at 180 degrees without damage; the cutting tool has good processability, and can be easily cut by a common cutter; has the capability of mass production, and the size of the mould can be changed according to the size change of the forming mould.
The quasi-solid electrolyte provided by the invention has high lithium ion conductivity and high lithium ion migration number, and the boron nitride nanosheets are beneficial to constructing a good electrolyte-electrode contact layer, a lithium nitride contact layer can be formed at a contact interface, the lithium nitride has high mechanical strength and high lithium ion conductivity, and is beneficial to stabilizing the surface of a lithium metal cathode so as to reduce side reactions, inhibit the growth of lithium dendrites, improve the safety and cycle life, balance the surface charge distribution so as to avoid the uneven deposition of lithium, and further improve the electrical property of the lithium battery: the cycling stability is good, and the cycling can be stably carried out for more than 5600 hours in the lithium-lithium symmetric battery; the rate capability is good, and the lithium iron phosphate electrode can be supported by the rate of 2CThe charge and discharge are carried out rapidly, and the specific capacity is kept at 100mAh g-1Above; the capacity retention rate is high, and after the assembled lithium iron phosphate full battery is cycled for 120 circles, the capacity retention rate is as high as 96%.
The quasi-solid electrolyte provided by the invention has excellent flame retardance, is directly ignited by a lighter, has a self-extinguishing phenomenon, improves the stability of a fire source, and is beneficial to improving the safety of a battery. The quasi-solid electrolyte provided by the invention has the quasi-solid characteristic, the organic framework is less prone to ignition relative to a liquid phase, meanwhile, the boron nitride inorganic filler has high thermal stability and high thermal conductivity, is beneficial to uniform dispersion of local high heat, is not flammable, plays a decisive role in improving the overall flame retardance of the electrolyte, has remarkably improved safety and stability relative to a simple liquid phase component or a traditional organic electrolyte, and has a higher ignition point.
According to the invention, the boron nitride nanosheet is used as an inorganic filler, the poly (ethylene carbonate) is used as an organic framework, and the vinylene carbonate is used as a liquid phase component, so that the high-performance quasi-solid electrolyte with good mechanical property, proper flame retardance, high lithium ion conductivity, high lithium ion migration number and wide electrochemical working window can be obtained, and the development of a solid electrolyte system for improving the actual performance of the lithium battery is facilitated.
The results of the examples show that the boron nitride nanosheets used in the present invention are hexagonal (PDF # 45-0894); the lithium ion conductivity of the quasi-solid electrolyte is 1.1mS cm-1The lithium ion transfer number is 0.78, the electrochemical working window is 0-5V, and the tensile elastic modulus>7MPa, elongation at tensile break>230％。
Drawings
Figure 1 is an XRD pattern of boron nitride nanoplates used in example 1;
fig. 2 is a raman spectrum of the boron nitride nanosheet used in example 1;
fig. 3 is a TEM image of boron nitride nanoplates used in example 1;
FIG. 4 shows 50X 50mm obtained in example 12Quasi solid electrolyte membrane (PVCA-BNNF QS)E) The photograph of (a);
FIG. 5 is a photograph of the PVCA-BNNF QSE prepared in example 1 taken from the original and in the twisted, stretched and folded condition;
FIG. 6 is a cross-sectional SEM picture of PVCA-BNNF QSE prepared in example 1;
FIG. 7 is a photograph of PVCA-BNNF QSE prepared in example 1 after it was ignited by a lighter;
FIG. 8 is an electrochemical impedance spectrum of PVCA-BNNF QSE prepared in example 1;
FIG. 9 is the transient current test results of the PVCA-BNNF QSE prepared in example 1, with built-in electrochemical impedance spectra before and after polarization;
FIG. 10 is a graph of the full battery performance of the PVCA-BNNF QSE prepared in example 1;
FIG. 11 is a graph of the electrochemical stability tests of the PVCA-BNNF QSE prepared in example 1 and the PVCA QSE prepared in comparative example 1;
fig. 12 is a TEM image of boron nitride nanoplates used in example 2;
FIG. 13 is a digital photograph of PVCA-BNNF QSE prepared in example 2;
FIG. 14 is a photograph of the PVCA-BNNF QSE prepared in example 2 and the PVCA QSE prepared in comparative example 1 after they were ignited using a lighter;
FIG. 15 is a plot of voltage at different current densities for the PVCA-BNNF QSE prepared in example 2 and the PVCA QSE prepared in comparative example 1;
FIG. 16 shows the PVCA-BNNF QSE prepared in example 2 and the PVCA QSE prepared in comparative example 1 at 0.5mA cm-2Current density of 0.5mAh cm-2Voltage curve at face volume of (a);
FIG. 17 is a full cell performance curve for the PVCA-BNNF QSE and NCM811, lithium sheet assembly prepared in example 2;
FIG. 18 is a digital picture after folding PVCA-BNNF QSE prepared in example 3;
FIG. 19 is a graph of the symmetric cell cycle performance of PVCA-BNNF QSE prepared in example 3;
FIG. 20 is a graph showing the rate performance of a full cell assembled by the PVCA-BNNF QSE prepared in example 3 and the PVCA QSE prepared in comparative example 1 with a lithium iron phosphate pole piece and a lithium piece respectively;
FIG. 21 is the charge-discharge curves at 0.1C after the PVCA-BNNF QSE prepared in example 3 and the PVCA QSE prepared in comparative example 1 are respectively assembled with lithium iron phosphate into a full cell;
FIG. 22 is a stress-strain curve of PVCA-BNNF QSE prepared in example 3;
fig. 23 is a photograph of PVCA QSE direct lighter ignition prepared from comparative example 1.
Detailed Description
The invention provides a quasi-solid electrolyte, which comprises poly (ethylene carbonate), a liquid component and boron nitride nanosheets; the liquid component comprises vinylene carbonate and lithium salt; the liquid component and the boron nitride nanosheets are dispersed in the backbone of the poly (ethylene carbonate).
In the present invention, unless otherwise specified, all the starting materials or reagents required for the preparation are commercially available products well known to those skilled in the art.
The quasi-solid electrolyte provided by the invention comprises poly (ethylene carbonate); the polyethylene carbonate is polymerized by vinylene carbonate, and the molecular weight of the polyethylene carbonate is preferably 20-80 ten thousand, and more preferably 40 ten thousand.
The quasi-solid electrolyte provided by the invention comprises a liquid component, wherein the liquid component comprises vinylene carbonate and lithium salt. In the present invention, the vinylene carbonate is preferably pure>96 percent; the lithium salt preferably comprises lithium difluorooxalato borate (LiODFB, purity)>97%) or lithium perchlorate (LiClO)4Purity of>97%). In the present invention, the lithium salt is dissolved in vinylene carbonate to form a liquid component. In the present invention, the concentration of the liquid component (i.e., the concentration of the lithium salt in the vinylene carbonate) is preferably 0.3 to 1.5mol L-1More preferably 0.95 to 1mol L-1。
The quasi-solid electrolyte provided by the invention comprises boron nitride nanosheets. In the present invention, the boron nitride nanosheet is preferably hexagonal boron nitride (h-BN, purity > 98%), and the particle size of the boron nitride nanosheet is preferably 20nm to 5000nm, and more preferably 100nm to 1000 nm. The hexagonal boron nitride has various excellent characteristics, and has the advantages of small density, high chemical stability, good thermal conductivity, incombustibility, good mechanical properties and the like, and has improvement potential on the interface of an electrolyte and lithium ion transmission in the electrolyte.
In the invention, the quasi-solid electrolyte preferably comprises, by mass, 74.8-84.8 wt% of poly (ethylene carbonate), 15-25 wt% of liquid components and 0.2-0.8 wt% of boron nitride nanosheets, the poly (ethylene carbonate) more preferably comprises 71.8-87.8 wt% and further preferably comprises 75.2-79.9 wt%, the liquid components preferably comprise 12-24.2 wt%, more preferably comprises 19.7-22.3 wt%, and the boron nitride nanosheets preferably comprise 0.4-0.6 wt% and further preferably comprises 0.5 wt%.
The invention provides a preparation method of the quasi-solid electrolyte in the technical scheme, which comprises the following steps:
mixing lithium salt, vinylene carbonate and boron nitride nanosheets to obtain a polymeric precursor;
and mixing the polymerization precursor and an initiator, and carrying out thermal polymerization to obtain the quasi-solid electrolyte.
According to the invention, lithium salt, vinylene carbonate and boron nitride nanosheets are mixed to obtain a polymeric precursor.
In the present invention, the mixture of lithium salt, vinylene carbonate and boron nitride nanosheets preferably includes: first mixing lithium salt and vinylene carbonate to obtain a liquid component; and secondly, mixing the liquid component and the boron nitride nanosheet to obtain a polymerization precursor. In the invention, the first mixing is preferably carried out under stirring, and the temperature of the first mixing is preferably 15-40 ℃, and more preferably 25 ℃; the time is preferably 1 to 24 hours, and more preferably 12 to 15 hours. The stirring rate is not particularly limited in the present invention, and the lithium salt may be completely dissolved according to a process well known in the art.
In the present invention, the ratio of the mass of the lithium salt to the volume of vinylene carbonate is preferably (0.4-1.7) g, (8-12) mL, more preferably (1.06-1.42) g, (10-12) mL, and still more preferably 1.37g, (10-12) mL; when the lithium salt is lithium difluoro oxalato borate, the ratio of the mass of the lithium salt to the volume of vinylene carbonate is preferably (0.5-1.7) g, (8-12) mL; more preferably 1.42g (8-12) mL; when the lithium salt is lithium perchlorate, the ratio of the mass of the lithium salt to the volume of the vinylene carbonate is preferably (0.4-1.5) g, (8-12) mL; more preferably 1.06g (8-12) mL.
In the present invention, the ratio of the mass of the boron nitride nanosheet to the volume of the liquid component is preferably (18-25) mg (3-4) mL, more preferably (20-22) mg:3.5mL, and even more preferably 21mg:3.5 mL.
In the invention, the temperature of the second mixing is preferably 15-40 ℃, and more preferably 25 ℃; the time is preferably 1 to 10 hours, and more preferably 2 to 4 hours; the second mixing is preferably carried out under ultrasonic conditions; the time of the second mixing is preferably adjusted according to the mass and the particle size of the boron nitride nanosheets, so that the boron nitride nanosheets are uniformly dispersed. The conditions of the ultrasound are not particularly limited in the present invention, and the boron nitride nanosheets are uniformly dispersed according to a process well known in the art.
After obtaining the polymerization precursor, the invention mixes the polymerization precursor and the initiator for thermal polymerization to obtain the quasi-solid electrolyte. In the present invention, the initiator preferably includes azobisisobutyronitrile (AIBN, purity > 99%), and the ratio of the mass of the initiator to the volume of the polymerization precursor is preferably (6 to 8.5) mg:3.5mL, more preferably (7.2 to 7.7) mg:3.5mL, and further preferably 7.5mg:3.5 mL.
In the invention, the polymerization precursor and the initiator are preferably mixed by adding the initiator into the polymerization precursor and carrying out ultrasonic treatment for 10min to 1h until the initiator is completely dissolved. The conditions for the sonication are not particularly limited in the present invention, and the initiator may be completely dissolved according to a procedure well known in the art.
After the mixing is completed, the invention preferably adds the obtained mixed solution into a polytetrafluoroethylene mold, and the mold is placed under pressure condition for thermal polymerization. The polytetrafluoroethylene mold and the size thereof are not specially limited and can be selected according to actual requirements; in an embodiment of the invention, the dimensions of the polytetrafluoroethylene mold are specifically 5cm by 0.1 cm.
In the present invention, the pressure of the thermal polymerization is preferably 30 to 50kPa, more preferably 35 to 40kPa, and still more preferably 37 to 38 kPa; the temperature is preferably 55-65 ℃, and more preferably 58-60 ℃; the time is preferably 700 to 900min, and more preferably 850 to 860 min. The manner in which the pressure is applied is not particularly limited and any manner known in the art to achieve the above pressures may be used.
In the thermal polymerization process, vinylene carbonate monomers are polymerized to form a poly (ethylene carbonate) polymer skeleton, and the liquid component and the boron nitride nanosheets are physically mixed in the poly (ethylene carbonate) polymer skeleton.
After the thermal polymerization is finished, the obtained product is preferably naturally cooled to room temperature, and after demolding, the quasi-solid electrolyte is obtained; the quasi-solid electrolyte is in the form of a membrane. The demolding process is not particularly limited in the present invention, and may be performed according to a process known in the art.
The invention provides the application of the quasi-solid electrolyte in the technical scheme or the quasi-solid electrolyte prepared by the preparation method in the technical scheme in a lithium battery. The method of the present invention is not particularly limited, and the method may be applied according to a method known in the art.
The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It should be apparent that the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
Composition of quasi-solid electrolyte membrane: 77.2 wt% of poly (ethylene carbonate) (molecular weight is about 42 ten thousand), 22.3 wt% of liquid component and 0.5 wt% of boron nitride nanosheet;
at room temperature (25 ℃), 1.37g of lithium difluorooxalato borate (LiODFB, purity)>97%) was added to 10mL of vinylene carbonate monomer (purity)>96%) for 12h, to give a concentration of 0.95mol L-1The monomer-lithium salt solution of (a);
under the condition of room temperature (25 ℃), adding 22mg of boron nitride nanosheet (h-BN, the purity is more than 98%, and the particle size is 100nm) into 3.5mL of monomer-lithium salt solution, and ultrasonically dispersing for 2h to obtain a polymerization precursor;
adding 7.5mg of azobisisobutyronitrile (AIBN, the purity is more than 99%) into the polymerization precursor, ultrasonically dissolving for 10min, adding 3mL of the obtained solution into a polytetrafluoroethylene mold with the pressure of 5cm multiplied by 0.1cm, placing the mold in an environment with the pressure of 40kPa and the temperature of 60 ℃, preserving the temperature for 850 min, naturally cooling to room temperature, and demolding to obtain a quasi-solid electrolyte membrane which is marked as PVCA-BNNF QSE.
Example 2
Composition of quasi-solid electrolyte membrane: 75.2 wt% of polyethylene carbonate (molecular weight is about 37 ten thousand), 24.2 wt% of liquid component and 0.6 wt% of boron nitride nanosheet;
under room temperature conditions (25 ℃), 1.06g of lithium perchlorate (LiClO)4Purity of>97%) was added to 10mL of vinylene carbonate monomer (purity)>96%) for 15h, to give a concentration of 1mol L-1The monomer-lithium salt solution of (a);
under the condition of room temperature (25 ℃), adding 21mg of boron nitride nanosheet (h-BN, the purity is more than 98%, and the particle size is 100nm) into 3.5mL of monomer-lithium salt solution, and ultrasonically dispersing for 4h to obtain a polymerization precursor;
adding 7.7mg of azobisisobutyronitrile (AIBN, the purity is more than 99%) into the polymerization precursor, carrying out ultrasonic dissolution for 10min, adding 3.1mL of the obtained solution into a 5cm × 5cm × 0.1cm polytetrafluoroethylene mold, placing the mold in an environment with the pressure of 35kPa and the temperature of 60 ℃, carrying out heat preservation for 850 min, naturally cooling to room temperature, and demoulding to obtain the quasi-solid electrolyte membrane PVCA-BNNF QSE.
Example 3
Composition of quasi-solid electrolyte membrane: 79.9 wt% of polyethylene carbonate (molecular weight is about 48 ten thousand), 19.7 wt% of liquid component and 0.4 wt% of boron nitride nanosheet;
under room temperature conditions (25 ℃), 1.42g of lithium difluorooxalato borate (LiODFB, purity)>97%) was added to 10mL of vinylene carbonate monomer (purity)>96％) Stirring for 15h in the liquid to obtain a concentration of 1mol L-1The monomer-lithium salt solution of (a);
under the condition of room temperature (25 ℃), adding 20mg of boron nitride nanosheet (h-BN, the purity is more than 98%, and the particle size is 100nm) into 3.5mL of monomer-lithium salt solution, and ultrasonically dispersing for 4h to obtain a polymerization precursor;
adding 7.2mg of azobisisobutyronitrile (AIBN, the purity is more than 99%) into a polymerization precursor, carrying out ultrasonic dissolution for 10min, adding 3mL of the obtained solution into a 5cm × 5cm × 0.1cm polytetrafluoroethylene mold, placing the mold in an environment with the pressure of 37kPa and the temperature of 58 ℃, carrying out heat preservation for 860min, naturally cooling to room temperature, and demolding to obtain the quasi-solid electrolyte membrane PVCA-BNNF QSE.
Comparative example 1
Composition of quasi-solid electrolyte membrane: 76.4 wt% of polyethylene carbonate (molecular weight about 40 ten thousand), 23.6 wt% of liquid component;
under room temperature conditions (25 ℃), 1.43g of lithium difluorooxalato borate (LiODFB, purity)>97%) was added to 10mL of vinylene carbonate monomer (purity)>96%) for 15h, to give a concentration of 1mol L-1The monomer-lithium salt solution of (a);
adding 7.5mg of azobisisobutyronitrile (AIBN, the purity is more than 99%) into the monomer-lithium salt solution, ultrasonically dissolving for 10min, adding 3mL of the obtained solution into a 5cm multiplied by 0.1cm polytetrafluoroethylene mold, placing the mold in an environment with the pressure of 35kPa and the temperature of 60 ℃, preserving the temperature for 850 min, naturally cooling to room temperature, and demolding to obtain a quasi-solid electrolyte membrane, which is marked as PVCA QSE.
Characterization and Performance testing
In the following test procedures, when the batteries were assembled, C2032 coin batteries were assembled in a glove box, which was filled with argon gas so that the contents of water and oxygen were both less than 0.1 ppm.
1) XRD testing was performed on the boron nitride nanosheets used in example 1, and the resulting pattern is shown in FIG. 1; as can be seen from fig. 1, the boron nitride nanosheet is hexagonal boron nitride, and has high purity and good crystallinity.
2) The boron nitride nanosheets used in example 1 were subjected to raman testing, and the resulting spectra are shown in fig. 2; byAs can be seen from FIG. 2, at 1370cm-1The peak indicates that the boron nitride nanosheet is hexagonal boron nitride, and the boron nitride nanosheet is small in layer number and thin as a whole.
3) The boron nitride nanosheets used in example 1 were subjected to TEM testing, and the resulting spectra are shown in fig. 3; as can be seen from fig. 3, the boron nitride nanosheets exhibit a platelet morphology, and the diameter of the boron nitride nanosheets is about 100 nm.
4) FIG. 4 shows 50X 50mm obtained in example 12The photo of the quasi-solid electrolyte membrane (PVCA-BNNF QSE) is shown, and the insert picture at the upper right corner in FIG. 4 is an SEM picture of the upper surface of the quasi-solid electrolyte membrane, and as can be seen from FIG. 4, the prepared quasi-solid electrolyte membrane has high overall uniformity, smooth surface, clear edge and good formability.
5) FIG. 5 shows the original photographs of PVCA-BNNF QSE prepared in example 1 and photographs under the conditions of twisting, stretching and folding, and it can be seen from FIG. 5 that the quasi-solid electrolyte has high bending and stretching ability, strong processability, potential application in flexible electronic devices, and convenient production and transfer.
6) FIG. 6 is a SEM image of the cross-section of PVCA-BNNF QSE prepared in example 1. As can be seen from FIG. 6, the quasi-solid electrolyte has a thickness of about 500 μm and a relatively uniform thickness.
7) FIG. 7 is a photograph of PVCA-BNNF QSE prepared in example 1 after being ignited by a lighter; as can be seen from fig. 7, the self-extinguishing of the flame within 0.2 seconds proves that the quasi-solid electrolyte has self-extinguishing property and better flame retardance, and the higher safety is proved because the boron nitride nanosheet BNNF has better thermal conductivity and thermal stability.
8) The PVCA-BNNF QSE prepared in example 1 is assembled into a blocking battery, stainless steel gaskets are arranged on two sides of a quasi-solid electrolyte membrane for alternating current impedance test, the obtained spectrogram is shown in figure 8, and the lithium ion conductivity of the PVCA-BNNF QSE at room temperature (25 ℃) is 1.1mS cm-1。
9) A lithium sheet was placed on one side of the PVCA-BNNF QSE prepared in example 1, and a stainless steel gasket was placed on the other side, and the transference number of lithium ions was measured by a transient current method, and the obtained result is shown in fig. 9; FIG. 9 is an inset of the electrochemical impedance spectrum of the corresponding cell before and after polarization; the lithium ion transport number of the PVCA-BNNF QSE measured by a transient current method is 0.78, which is larger than the lithium ion transport number (<0.5) in the conventional liquid electrolyte, because of the addition of the boron nitride nanosheet. The larger the lithium ion transport number is, the more stable performance can be brought.
10) The PVCA-BNNF QSE electrolyte membrane prepared in example 1 is respectively matched with a lithium metal negative electrode and a lithium iron phosphate positive electrode, wherein the surface volume density of the lithium iron phosphate positive electrode is 2mAh cm-2Then, a new power battery test system is used for carrying out constant current charge and discharge tests on the battery within a matched test voltage interval and under different charge and discharge multiplying powers, the performance of the whole battery is tested, and the obtained result is shown in a figure 10; as can be seen from fig. 10, the current density of 0.1C stably cycled for 100 cycles, and the capacity retention rate was as high as 96.8%, which showed excellent cycling stability.
11) Performing electrochemical stability test on the PVCA-BNNF QSE prepared in the example 1 and the PVCA QSE prepared in the comparative example 1, wherein the test method is linear sweep voltammetry, the sweep speed is 1mV/s, the voltage interval is 0-6.3V, and the obtained result is shown in a figure 11; as can be seen from FIG. 11, the electrochemical working windows of both are larger than 5V, and the electrochemical oxidation resistance of the PVCA-BNNF QSE is improved to a certain extent after the boron nitride nanosheet is added.
12) Fig. 12 is a TEM image of the boron nitride nanosheets used in example 2, from which fig. 12 it can be determined that the interplanar spacing of the (002) crystal plane is 0.34nm, which is in good agreement with the parameters of hexagonal boron nitride, and that the single nanosheet consists of only four layers of hexagonal boron nitride, confirming that it has lamellar properties.
13) FIG. 13 is a digital photograph of the PVCA-BNNF QSE electrolyte prepared in example 2, showing sharp edges, dimensions up to 50mm by 50mm, and uniform dispersion of inorganic filler.
14) FIG. 14 is a photograph of the PVCA-BNNF QSE prepared in example 2 and the PVCA QSE prepared in comparative example 1 after they were ignited using a lighter; as can be seen from FIG. 14, the PVCA-BNNF QSE is not ignited, and the PVCA is ignited and continuously burnt, which shows that the flame retardant property of the electrolyte is obviously improved after the boron nitride nanosheet is added.
15) FIG. 15 is a diagram of PVCA-BNNF QSE prepared in example 2 and PVC prepared in comparative example 1Voltage curves for QSE at different current densities. As can be seen from fig. 15, at the same low current density, PVCA exhibits a higher overpotential; with the increase of current density, the PVC is 3mA cm-2About, the voltage value overflowed, while the PVCA-BNNF QSE was at 5mA cm-2The current density of the current source is kept to be over-potential of not more than 2V, and the current is cycled smoothly. The result shows that after the boron nitride nanosheet is added, the PVCA-BNNF QSE has strong lithium ion transmission capability and high-rate charge and discharge capability.
16) Lithium plates are respectively placed on two sides of the PVCA-BNNF QSE prepared in the example 2 and the PVCA QSE prepared in the comparative example 1, and the symmetrical batteries are assembled; FIG. 16 shows PVCA-BNNF QSE prepared in example 2 and PVCA QSE symmetric cell prepared in comparative example 1 at 0.5mA cm-2Current density of 0.5mAh cm-2Voltage curve at face volume of (a). As can be seen from fig. 16, the PVCA QSE symmetric cell failed after about 500 hours of cycling, while the PVCA-BNNF QSE could be stably cycled for over 1800 hours with an overpotential not exceeding 0.4V, which shows excellent cycling stability of the PVCA-BNNF QSE for large current and large capacity.
17) FIG. 17 is a full cell performance curve for the PVCA-BNNF QSE and NCM811, lithium sheet assembly prepared in example 2. As can be seen from FIG. 17, the medium and high capacity (3mAh cm)-2) After the high-nickel anode NCM811 is matched, the PVCA-BNNF QSE electrolyte still shows stable performance, which shows that the high-nickel anode NCM can normally work in a high-voltage range (4V-5V), and shows good compatibility with the anodes of two main-stream lithium batteries and a potential application prospect.
18) Figure 18 is a folded digital picture of the PVCA-BNNF QSE prepared in example 3, showing good flexibility and processability.
19) FIG. 19 is a graph of the symmetric cell cycle performance of the PVCA-BNNF QSE prepared in example 3. As can be seen from FIG. 19, the current density was 0.1mA cm-2Current density of 0.1mAh cm-2The surface capacity of the PVCA-BNNF QSE can be stably circulated for more than 5600 hours, and a high-rate test is added in the circulation process, when the current density is increased to 1mA cm-2Then reduced to 0.1mA cm-2Then, the circuit can still be kept circulating at a low overpotentialOver 2500h and over 0.2V. The excellent cycling stability and high rate performance of PVCA-BNNF QSE are proved.
20) Fig. 20 is a rate performance test of the PVCA-BNNF QSE prepared in example 3 and the PVCAQSE prepared in comparative example 1 after being assembled with a lithium iron phosphate pole piece and a lithium piece to form a full cell. As can be seen from FIG. 20, the PVCA-BNNF QSE can support better capacity release in each multiplying factor relative to PVCA without adding boron nitride nanosheets, when the charge-discharge multiplying factor is improved, the capacity retention rate of the PVCA-BNNF QSE is higher, and can still be kept above 100mAh g-1 at 2C, so that good quick-charging and quick-releasing potential is embodied.
21) Fig. 21 is a charge-discharge curve at 0.1C for the PVCA-BNNF QSE prepared in example 3 and the PVCA QSE prepared in comparative example 1, respectively, after they were assembled with lithium iron phosphate into a full cell. As can be seen in fig. 21, PVCA-BNNF QSE has a flat platform, demonstrating a good reaction process with few side reactions; meanwhile, the voltage difference of the PVCA-BNNF QSE between the charging and discharging curve platforms is obviously smaller than that of the PVCA, and the PVCA-BNNF QSE is proved to have higher lithium ion transmission capability.
22) FIG. 22 is a stress-strain curve of the PVCA-BNNF QSE prepared in example 3. from FIG. 22, it can be seen that the prepared PVCA-BNNF QSE has a higher tensile modulus of 7.3MPa and an elongation at break of 230%, and shows better device performance and processability.
23) Fig. 23 is a picture of the direct ignition of the PVCA QSE lighter prepared in comparative example 1, and it can be seen from fig. 23 that the direct ignition is maintained until the combustion is complete after the direct ignition is contacted with flame, which shows the flammability, and represents the great improvement of the flame retardancy of the PVCA-BNNF QSE after the boron nitride nanosheet is added.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims (10)

1. A quasi-solid electrolyte is characterized by comprising poly (ethylene carbonate), a liquid component and boron nitride nanosheets; the liquid component comprises vinylene carbonate and lithium salt; the liquid component and the boron nitride nanosheets are dispersed in the backbone of the poly (ethylene carbonate).
2. The quasi-solid electrolyte according to claim 1, wherein the quasi-solid electrolyte comprises, by mass, 74.8-84.8 wt% of poly (ethylene carbonate), 15-25 wt% of liquid components, and 0.2-0.8 wt% of boron nitride nanosheets.
3. The quasi-solid electrolyte of claim 1, wherein the boron nitride nanoplates are hexagonal boron nitride, and the boron nitride nanoplates have a particle size of 20nm to 5000 nm.
4. The quasi-solid electrolyte of claim 1, wherein the lithium salt comprises lithium difluorooxalato borate or lithium perchlorate.
5. A method for preparing a quasi-solid electrolyte as claimed in any one of claims 1 to 4, comprising the steps of:
mixing lithium salt, vinylene carbonate and boron nitride nanosheets to obtain a polymeric precursor;
and mixing the polymerization precursor and an initiator, and carrying out thermal polymerization to obtain the quasi-solid electrolyte.
6. The method of claim 5, wherein the mixing of the lithium salt, vinylene carbonate, and boron nitride nanoplates includes: first mixing lithium salt and vinylene carbonate to obtain a liquid component; and secondly, mixing the liquid component and the boron nitride nanosheet to obtain a polymerization precursor.
7. The method according to claim 6, wherein the ratio of the mass of the lithium salt to the volume of vinylene carbonate is (0.4-1.7) g (8-12) mL; the ratio of the mass of the boron nitride nanosheet to the volume of the liquid component is (18-25) mg (3-4) mL.
8. The method according to claim 5, wherein the initiator comprises azobisisobutyronitrile, and the ratio of the mass of the initiator to the volume of the polymerization precursor is (6-8.5) mg:3.5 mL.
9. The method according to claim 5, wherein the thermal polymerization is carried out under a pressure of 30 to 50kPa at a temperature of 55 to 65 ℃ for 700 to 900 min.
10. Use of the quasi-solid electrolyte according to any one of claims 1 to 4 or the quasi-solid electrolyte prepared by the preparation method according to any one of claims 5 to 9 in a lithium battery.
CN202210250223.8A 2022-03-15 2022-03-15 Quasi-solid electrolyte based on boron nitride nanosheets and preparation method and application thereof Pending CN114649587A (en)

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