CN111799506B - Composite gel polymer electrolyte applying polymer nano-filler, preparation method and solid-state lithium battery using electrolyte - Google Patents

Composite gel polymer electrolyte applying polymer nano-filler, preparation method and solid-state lithium battery using electrolyte Download PDF

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CN111799506B
CN111799506B CN202010242250.1A CN202010242250A CN111799506B CN 111799506 B CN111799506 B CN 111799506B CN 202010242250 A CN202010242250 A CN 202010242250A CN 111799506 B CN111799506 B CN 111799506B
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electrolyte
lithium
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filler
composite gel
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CN111799506A (en
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廖开明
叶飞
周嵬
邵宗平
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Nanjing Tech University
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0565—Polymeric materials, e.g. gel-type or solid-type
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0065—Solid electrolytes
    • H01M2300/0082—Organic polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0085—Immobilising or gelification of electrolyte
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02E60/10—Energy storage using batteries

Abstract

The invention discloses a composite gel polymer electrolyte applying polymer nano-filler, a preparation method and a solid-state lithium battery using the electrolyte. The composite gel polymer electrolyte comprises a polyurethane polymer, a polyquinone nanosheet filler and a lithium electrolyte salt. The polymer nano-filler provided by the invention has lithium affinity, so that the composite gel polymer electrolyte has flexibility, high room temperature ionic conductivity and good electrochemistry and interface stability, and can obviously inhibit the formation of lithium dendrite; when the lithium ion battery electrolyte is used as a lithium battery electrolyte, the problems of liquid leakage and solvent volatilization of the traditional liquid electrolyte can be solved, and internal short circuit caused by the fact that lithium dendrite pierces a diaphragm can be prevented.

Description

Composite gel polymer electrolyte applying polymer nano-filler, preparation method and solid-state lithium battery using electrolyte
Technical Field
The invention belongs to the field of preparation of gel polymer electrolytes, and relates to preparation of a composite gel polymer electrolyte which takes a mixture of a high-molecular polymer matrix and an organic polymer nano filler (namely, a thermoplastic polyurethane polymer and a polypolyquinone nanosheet) as main components and application of the composite gel polymer electrolyte to a solid lithium battery.
Background
Metallic lithium is considered to be a promising battery negative electrode material due to its ultra-high theoretical specific capacity and extremely low oxidation-reduction potential. However, lithium dendrites are easily formed on the surface of the lithium metal during the charge-discharge cycle to pierce the diaphragm, which causes great potential safety hazard to the conventional liquid lithium battery. Therefore, practical application of metallic lithium negative electrodes faces a great technical bottleneck.
Gel polymer electrolytes are considered to be the most promising alternative liquid electrolytes for constructing high-safety solid lithium batteries due to their good processability, good interfacial compatibility with electrodes, higher mechanical strength and ionic conductivity, compared to liquid electrolytes. From the current research situation, high room temperature ionic conductance and good working condition adaptability are the key for determining whether the polymer electrolyte can realize industrial application, especially in an energy storage system using lithium metal. Therefore, it is of great significance to design and optimize the material composition of the polymer electrolyte to obtain a novel polymer electrolyte with high performance, and the polymer electrolyte is an important key technology which is expected to solve the practical application of the lithium metal battery.
The use of fillers is generally required in the prior art to improve the mechanical strength and room temperature ionic conductivity of the gel polymer electrolyte. However, the fillers reported at present are all inorganic, and these inorganic fillers can mechanically block lithium dendrites to a certain extent, but cannot fundamentally solve the problem of non-uniform deposition of lithium ions at the interface of electrode/electrolyte. Thus, lithium dendrites remain a key problem that is difficult to overcome with gel polymer electrolytes.
Disclosure of Invention
The invention provides a method for introducing lithium-philic polymer nano-filler into a gel polymer electrolyte, which can effectively control the uniform deposition of lithium ions on an electrode/electrolyte interface, fundamentally eliminate the threat of lithium dendrite on the safety of a battery and provide an important technical guarantee for the practicability of a lithium metal battery.
In a first aspect of the present invention, there is provided:
a composite gel polymer electrolyte is prepared from lithium electrolyte salt, polyurethane (TPU) polymer and polyquinone nanosheets.
In one embodiment, the lithium electrolyte salt in the composite gel polymer electrolyte is lithium hexafluorophosphate.
In one embodiment, the polypolyquinone nanosheet filler has an average thickness of 20 to 40 nm.
In a second aspect of the present invention, there is provided:
the preparation method of the composite gel polymer electrolyte comprises the following steps:
a first step of dissolving a polyurethane (TPU) polymer in a first solvent;
step 2, dispersing polyquinone nanosheet filler in the solution obtained in the step 1 to obtain gel sol;
step 3, preparing the gel sol obtained in the step 2 into a film in a mould, and drying the film to form a polymer matrix;
and 4, soaking the polymer matrix in a liquid electrolyte containing lithium electrolyte salt for adsorption, taking out, and drying to obtain the composite gel polymer electrolyte.
In one embodiment, the weight ratio of the lithium electrolyte salt, The Polyurethane (TPU) polymer and the polypolyquinone nanosheet filler is (8-3) to (8-3) 10.
In one embodiment, the first solvent is N-methylpyrrolidone; the concentration of The Polyurethane (TPU) polymer dissolved in the organic solvent is 10 to 20 wt%.
In one embodiment, the polypolyquinone nanosheet filler is polymerized from anthraquinone and pyromellitic dianhydride.
In one embodiment, the adsorption time in the 4 th step is 5-10 h.
In a third aspect of the present invention, there is provided:
the use of the composite gel polymer electrolyte in a solid state lithium battery.
In one embodiment, the solid state lithium battery includes a positive electrode and a negative electrode with a composite gel polymer electrolyte enclosed therebetween.
In one embodiment, the positive electrode material is NCM622 and the negative electrode material is lithium foil.
In a fourth aspect of the present invention, there is provided:
use of polypolyquinone nanoplates to improve the performance of a gel polymer electrolyte for a solid state lithium battery.
In one embodiment, the properties are: the surface compactness of the gel electrolyte membrane is improved, the strength of the gel electrolyte membrane is improved, the crystallinity of a matrix is reduced, the ionic conductivity of the gel electrolyte membrane is improved, the lithium ion transfer number is improved, the thermal stability of the gel electrolyte membrane is improved, the generation of lithium dendrites is inhibited, and the stability after cyclic charge and discharge is improved.
Advantageous effects
1. The invention provides composite gel polymer electrolysisIon conductivity of matter at room temperature is as high as 3.78X 10-3S·cm-1Obviously higher than the ion conductivity (less than or equal to 10) of the traditional PEO-based gel polymer electrolyte-4～10-5S·cm-1) And PAN-based gel polymer electrolyte (less than or equal to 10)-4S·cm-1)；
2. The lithium ion transference number of the composite gel polymer electrolyte provided by the invention is as high as 0.74.
3. The composite gel polymer electrolyte provided by the invention is applied to a lithium symmetric battery, has good stability in a cycle performance test at room temperature, and basically has no lithium dendrite.
4. The composite gel polymer electrolyte provided by the invention is applied to a solid-state lithium battery, and has good stability in a cycle performance test at room temperature and high coulombic efficiency.
5. The composite gel polymer electrolyte has simple process, is environment-friendly and has the possibility of practical application.
Drawings
Fig. 1 is a schematic diagram of the beneficial effects of the present invention.
Fig. 2 is a synthetic scheme of a polypolyquinone nanosheet filler.
FIG. 3 is a poly-polyquinone nanosheet filler13C solid state nuclear magnetic spectrum.
Fig. 4 is a characterization spectrum of the polypoquinone nanosheet filler, wherein the a region is an X-ray electron energy spectrum total spectrum, the b region is a high resolution C1s spectrum, and the C region is a raman spectrum.
Fig. 5 is a high resolution transmission electron micrograph of a polypolyquinone nanosheet filler.
FIG. 6 is a characterization map of polypolyquinone nanosheet filler, wherein regions a-C are C and O element mapping scanning transmission electron micrographs, (d) region is a selected area diffraction image, region e is an X-ray diffraction image, region f is an atomic force microscope image, and region g is an infrared spectrum.
Fig. 7 is a nitrogen adsorption and desorption curve and a pore size distribution of a polypolyquinone nanosheet filler.
FIG. 8 is a representation of a polymer gel electrolyte, wherein the a region is a scanning electron micrograph of a polyurethane polymer without a polyquinone nanosheet filler added thereto, and the b-d regions are scanning electron micrograph images of a polymer gel electrolyte with different amounts of polyquinone nanosheet filler added thereto; the e-region is the corresponding stress strain curve and the f-region is the corresponding X-ray diffraction pattern.
Fig. 9 is a cross-sectional electron microscope image of a polymer gel electrolyte. Wherein the a area is a polyurethane polymer substrate without polypolyquinone nanosheet filler, and the b-d areas are cross-sectional scanning electron microscope images of polymer gel electrolytes with different amounts of polypolypolyquinone nanosheet filler added.
FIG. 10 is a potentiostatic polarization curve for a polymer gel electrolyte, where regions a-c are before gelation and regions d-f are after gelation.
FIG. 11 is the results of the relevant electrochemical performance tests of the polymer gel electrolyte, wherein the (a) region is the room temperature electrochemical impedance spectrum; (b) zone is a temperature-ionic conductivity map of the polymer gel electrolyte without addition of poly-polyquinone nanosheet filler and different poly-polyquinone nanosheet filler content; the c-j region is the constant potential polarization curve and the alternating current impedance spectrum of the corresponding gel polymer electrolyte.
FIG. 12 is a temperature mapping-AC impedance spectrum of a polymer gel electrolyte in which (a) the regions are reacted with a polyurethane polymer that does not contain a polypolyquinone nanosheet filler, and (b-d) the regions are reacted with a polymer gel electrolyte of different polyquinone nanosheet filler content.
Figure 13 thermogravimetric analysis curves of polymer gel electrolytes containing polyquinone nanosheet fillers.
Fig. 14 is used to illustrate the cycling performance of a symmetric cell. Wherein region (a) is a comparison of the cycling stability of lithium-lithium symmetric batteries using a polymer gel electrolyte containing a polypyroquinone nanosheet filler and a polyurethane polymer. (b) Regionally reacted is the rate capability of a lithium-lithium symmetric battery using a polymer gel electrolyte containing polyquinone nanosheet filler.
Fig. 15 is a graph of cell operational stability of polymer gel electrolytes of different polypolyquinone nanosheet filler content.
Fig. 16 is used to illustrate the cycling stability of lithium symmetric cells with polymer gel electrolytes of different polypolypolyquinone nanosheet filler content.
Fig. 17 is a cross-sectional sem image of a lithium metal anode after cycling in a symmetric cell for 100 hours and 300 hours, where (a) the region is a liquid electrolyte, (b) the region is a polyurethane polymer electrolyte, and (c) the region is a polymer gel electrolyte containing a polypyroquinone nanosheet filler.
Fig. 18 is an in situ optical microscope photograph of a continuous 3 hour process of lithium deposition wherein (a) region is a liquid electrolyte and (b) region is a polymer gel electrolyte containing a polypaquinone nanoplate filler.
Fig. 19 is an X-ray electron spectrum of the surface of the lithium electrode after 50 hours of cycling of the liquid electrolyte battery.
Fig. 20 is an X-ray electron spectrum of the surface of a lithium electrode after 50 hours cycling of a polymer gel electrolyte battery containing a polypyroquinone nanosheet filler.
Fig. 21 is a scanning electron micrograph of a lithium electrode after a certain time of cyclic discharge in a symmetric cell. Wherein (a) the region is cycled in the liquid electrolyte battery for 100 hours; (b) the area is the polyurethane polymer electrolyte battery cycle for 100 hours; (c) the region is cycled for 300 hours in a polymer gel electrolyte battery containing the polyquinone nanosheet filler; (d) the region is an acyclic lithium electrode; (e) the area is a scanning electron microscope image of a cross-section of the polymer gel electrolyte containing the polypyroquinone nanosheet filler cycled for 300 hours.
Detailed Description
The invention provides a composite gel polymer electrolyte, which is prepared from lithium electrolyte salt, polyurethane polymer and polyquinone nanosheet filler. After the materials are compounded, the electrolyte material applied to the solid lithium battery can be prepared. In the technical scheme of the invention, the gel polymer electrolyte containing the polymer filler is prepared by using the polyquinone polymer as the filler and the thermoplastic polyurethane as the polymer electrolyte matrix. The new conceptual design of gel polymer electrolytes containing polymer fillers is expected to offer a number of advantages, such as: (1) the ionic conductivity is high, and the mechanical strength is strong; the polymer matrix is polyurethane polymer, and the macromolecular chain contains rich ether groupsFunctional groups such as ester group, carbamido group and amido group, so hydrogen bonds are easily generated among macromolecules, and the macromolecules have better toughness; meanwhile, the adopted organic filler is polyquinone nanosheets, molecular chains of the organic filler contain a large number of carbonyl groups, and the carbonyl groups can interact with carbamido groups, amide groups and the like of the polyurethane polymer to form N … H-O hydrogen bonds, so that the filler is uniformly dispersed, and the excellent characteristic of high ionic conductivity is shown; the rigid chain structure of the organic filler effectively improves the mechanical strength of the composite polymer electrolyte membrane; (2) a large number of carbonyl groups on the molecular chain of the organic filler effectively guide lithium ions to be uniformly deposited on the surface of the lithium metal negative electrode, and the generation of lithium dendrites is inhibited; (3) the polymer nanosheet filler can rapidly consume lithium dendrites after the lithium dendrites permeate into electrolyte, and further ensures stable and safe operation of the lithium-based battery in long-term circulation. In addition, the polymer nanosheet filler with the two-dimensional nanostructure can provide a larger surface-to-mass ratio, increase the contact area of the filler and an electrolyte, and is beneficial to the diffusion of lithium ions. With these advantages, a small and stable plating/stripping overpotential of about 25mV can be achieved within 700 hours when applied to a lithium symmetric cell. Using LiNi0.6Co0.2Mn0.2O2(NCM622) cathode material, the coulomb efficiency can reach about 99% after 100 cycles, and the cathode material has good commercial prospect.
Synthesis of polypolyquinone nanosheet filler:
polypolyquinone is synthesized by taking pyromellitic dianhydride and anthraquinone as raw materials and anhydrous zinc chloride as a catalyst by a molten salt polycondensation method. The starting materials and the catalyst were mixed in a molar ratio of 1:1:1, ground in a glove box filled with argon for several minutes, then transferred to a glass vial, sealed and calcined at 330 ℃ for 12 hours. After calcination, the zinc chloride catalyst was removed using 50 ml of 10% mass fraction hydrochloric acid. Then, the obtained crude product was ground in a mortar, washed with deionized water, ethanol and toluene in this order for 24 hours, and further ground at 400 rpm for 2 hours. After drying in vacuum at 100 ℃ for 12 hours, a polypolyquinone nanosheet filler was obtained and stored for later use.
Characterization of polyquinone nanosheets:
by using13C crossAnd identifying the structural change of the sample by polarization/magic angle rotation solid-state nuclear magnetic resonance spectrum, Fourier transform infrared spectrum and Raman spectrum. The phase structure of the sample was characterized using an X-ray diffractometer. The chemical composition of the sample was characterized by X-ray photoelectron spectroscopy. And (4) carrying out morphology and energy spectrum analysis on the sample by using a transmission electron microscope. The specific surface area of the sample was determined using an adsorption-desorption isotherm of nitrogen.
Synthesis of polymeric membrane containing polyquinone nanosheets:
firstly, polyurethane powder is dissolved in N-methyl-2-pyrrolidone (1/10, w/w) at 70 ℃ to form transparent solution, then the prepared poly-quinone nanosheet filler (the addition amounts are 30%, 50% and 80% respectively) is added, and then the solution is fully mixed under ultrasonic dispersion to form uniform slurry. The slurry was cast onto a polytetrafluoroethylene film and then dried in an oven at 70 ℃ overnight to form a film. For the purpose of control experiments, polyurethane films were prepared in the same manner.
Characterization of polymeric membranes containing polyquinone nanoplates:
the thermal stability in air was evaluated by thermogravimetric analysis. And observing the surface appearance and the cross section appearance of the film by using a field emission scanning electron microscope. The phase structure of the film was analyzed by X-ray diffraction. The mechanical strength of the polymer films was tested on a universal tester.
The electrochemical performance test method comprises the following steps:
and respectively soaking the prepared polymer containing the polyquinone nanosheets and the polyurethane film into 1M lithium hexafluorophosphate electrolyte (EC/DMC, 1:1, w/w) to obtain the polymer containing the polyquinone nanosheets and the polyurethane electrolyte film. The lithium ion conductivity (σ) of the electrolyte membrane was calculated by the ac impedance method based on the stainless steel sheet symmetric cell according to the following equation.
Figure RE-GDA0002669879780000061
Where D is the thickness of the film, A is the actual contact area between the film and the barrier electrode, and RbIs an electrolyte membrane bodyAnd (4) resistance.
The transfer number of lithium ions is calculated by Bruce-Vincent-Evans equation as follows:
Figure RE-GDA0002669879780000062
in which Δ V is a constant potential step of 20mV, I0And IsIs the initial and steady state current, R0And RsIs the interface resistance before and after polarization. The deposition/peeling behavior was studied using lithium symmetrical cells and the electrochemical performance of the electrolyte membrane in NCM622 single cells was tested with CR2025 type button cells. The cell assembly was carried out in an argon-filled glove box with a cathode having an active mass weight of about 3mg cm-2. The performance of all cells was evaluated in room temperature constant current mode with a computer controlled galvanostat.
FIG. 2 shows the reaction mechanism of the synthesis of poly-quinone nanosheet filler, mainly a Friedel-crafts polycondensation reaction catalyzed by Lewis acid. Successful formation of carbonyl-rich and highly conjugated polypolyquinone nanosheet fillers is demonstrated by a combination of solid-state nuclear magnetic, X-ray electron spectroscopy, and infrared spectroscopy characterization. From the solid-state nmr spectrum, characteristic chemical shifts of aliphatic, aromatic carbon and carbonyl groups were observed at around 20-50, 136 and 168ppm as shown in fig. 3. The XPS spectrum in the range of 200-600eV shows that the sample contained C and O elements (region a in FIG. 4). The high resolution spectrum of C1s in the polypolyquinone nanosheet filler sample (region b in fig. 4) shows three major peaks centered at 284.5, 286.5 and 288.3eV, corresponding to sp p2Hybrid graphitic carbon (C-C/C ═ C), enolyl (C-O), and carbonyl (C ═ O).
Fig. 5 is a high resolution transmission electron microscope image of a polypolypolyquinone nanosheet filler, confirming the lamellar morphology of the polypolyquinone nanosheet filler. The a-region of fig. 6 shows the scanning transmission electron microscope image and the energy dispersive X-ray spectral mapping corresponding to the elements C (region b of fig. 6) and O (region C of fig. 6). The region d of fig. 6 shows the corresponding selected region electron diffraction pattern of the polypolyquinone nanosheet filler sample, indicating the amorphous structure of the sample, which is shown in region e of fig. 6The results of X-ray diffraction are consistent, and in the X-ray diffraction pattern, the wide diffraction peaks of 26.5 degrees and 44 degrees are equivalent to the (002) and (100) diffraction planes of the carbon or graphite-like structure. The stacking height of the atomic force microscope surface two-dimensional nano-structured polypolyquinone nanosheet filler is about 30nm (region f of fig. 6). Raman spectroscopy was further used to study the graphite-like structure of the polypolyquinone nanosheet filler, as shown in region c of FIG. 6, at 1395cm-1And 1600cm-1Two distinct characteristic peaks were observed, similar to the characteristic D and G bands of the carbon-based material. The region g in FIG. 6 shows the infrared spectrum of the polyquinone nanosheet filler, with characteristic peaks of 1570-1650cm-1Has an aromatic C ═ C tensile vibration absorption peak of 1240cm-1C-C tensile vibration absorption peak of (600--1Has an out-of-plane absorption peak of C-H of 1042cm-1Peak value of C-H in-plane bending vibration of 1720cm-1The tensile vibration peak of the carbonyl group of (1).
Figure 7 shows the nitrogen adsorption-desorption isotherms of polypolyquinone nanosheet fillers. At a lower relative pressure (p/p)0< 0.001), the isotherm showed a high nitrogen uptake, indicating the presence of a microporous structure. Meanwhile, in the isotherm, the absorption of nitrogen is in p/p0>0.8, which is likely due to the interparticle porosity associated with the complex structure of the polypyroquinone nanosheet filler. Thus, the polypolyquinone nanosheet filler has a relatively high specific surface area (288 m)2·g-1) And pore volume (0.3014 cm)3 g-1) This facilitates electrolyte absorption, increases the contact area of the filled electrolyte, forms a uniform gel electrolyte, and facilitates diffusion of lithium ions.
A scanning electron micrograph of the surface and cross-section of the polymer film containing the polypyroquinone nanosheet filler is shown in fig. 8. According to region a of fig. 8, the original polyurethane film exhibits a smooth but discontinuous surface. After the polypoquinone nanosheet filler was introduced into the matrix, the film surface (region b-d of fig. 8) became dense, but with increasing content of the polypoquinone nanosheet filler (30%, 50%, 80%), a large number of cracks appeared on the film surface. From the cross-sectional image (fig. 9), again, the higher the polypolyquinone nanosheet filler content, the rougher the film cross-section. The thickness of the polymer film is about 100-120 μm. The compact structure of the prepared film shows that the polyquinone nanosheet filler and the polyurethane matrix have good mixing performance. Region e of fig. 8 shows the stress-strain curves for a polyurethane film without a polypolypolyquinone nanosheet filler and a polymer film with a different polypolyquinone nanosheet filler, and it can be found that as the polypolyquinone nanosheet filler content increases, the strength and stiffness of the film increases. This phenomenon can be attributed to the specific structure of the polypyroquinone nanosheet filler; meanwhile, due to the existence of rich carbonyl groups, the polyquinone nanosheet filler can be well dispersed in the polyurethane matrix, so that the mechanical strength of the film is improved.
Region f of fig. 8 shows the X-ray diffraction patterns of polyurethane films without the addition of the polypyroquinone nanosheet filler and polymer electrolyte membranes containing varying amounts of the polypyroquinone nanosheet filler. For the polyurethane film without the polyquinone nanosheet filler, an obvious diffraction peak is formed at about 20.5 degrees, and the intensity of the diffraction peak is obviously attenuated along with the increase of the using amount of the polyquinone nanosheet filler, so that the crystallinity of the polyurethane matrix is reduced. The fact that the poly-polyquinone nanosheet filler is added into the polymer matrix can effectively reduce the crystallinity of the polymer, so that higher ionic conductivity is obtained.
Low electronic conductivity is a fundamental requirement of battery electrolytes, and too high electronic conductivity can introduce internal leakage current and increase self-discharge rate. To evaluate the electronic conductivity of the polymer electrolyte containing polyquinone nanosheet filler, a classical potentiostatic polarization test was used, with the results shown in fig. 10. The calculated electronic conductivities corresponding to polymer electrolytes containing different amounts (30%, 50%, 80%) of polypolyquinone nanosheet filler were 1 × 10-11、2.2×10-11And 4.4X 10-11S cm-1Indicating that it meets the battery electrolyte standard.
Fig. 11 shows electrochemical impedance spectra of stainless steel symmetric cells employing polyurethane electrolytes without polypolyquinone nanosheet filler and polymer electrolytes with varying amounts of polypolyquinone nanosheet filler, and their ionic conductivities were calculated. The result shows that the ionic conductivity of the polyurethane electrolyte without the polypolyquinone nanosheet filler is 0.18 mS-cm-1The ionic conductivities of the polymer electrolytes containing different amounts of polypolyquinone nanosheet fillers are respectively 1.75, 3.78 and 1.9 mS-cm-1The ionic conduction of the electrolyte is obviously improved by adding the polyquinone nanosheet filler. The improvement in ionic conductivity of the polymer electrolyte containing the polypyroquinone nanosheet filler can be attributed to the following aspects. Firstly, the introduction of the polyquinone nanosheet filler expands the amorphous region of the polyurethane matrix, thereby facilitating the transfer of lithium ions on the polymer chain. Secondly, the rich carbonyl groups in the polypyroquinone nanosheet filler can effectively increase the dissociation of lithium salt and release more lithium ion carriers. Third, the carbonyl group is superior to the lithium ion transport capability of the carbon-oxygen bond.
The temperature-dependent ionic conductivities of the polyurethane electrolytes and polymer electrolytes containing polyquinone nanosheet fillers are shown in region b of fig. 11, with the corresponding temperature-dependent ac impedance spectra and calculated ionic conductivities as shown in fig. 12 and the following table.
Figure RE-GDA0002669879780000081
At low temperatures, the free volume in the electrolyte is filled by the aggregated polymer chains, and the reduction in space impedes the transfer of lithium ions, resulting in a decrease in ionic conductivity. In contrast, at high temperatures, the enhanced segmental motion of the polymer chains can accelerate the transfer of lithium ions. Therefore, the ionic conductivity is positively correlated with the temperature.
Number of lithium ion transfer (t)Li+) Is another important parameter of the electrolyte. The number of lithium ion transfers for polyurethane electrolytes without poly-polyquinone nanosheet filler and polymer electrolytes of varying amounts of poly-polyquinone nanosheet filler were determined using chronoamperometry in conjunction with the ac impedance test (region c-j in fig. 11). The number of lithium ion transfer of the polyurethane electrolyte without the polypolyquinone nanosheet filler was 0.45, and the number of lithium ion transfer of the polymer electrolyte at different amounts of polypolyquinone nanosheet filler was 0.67, 0.74 and 0.82, respectively, from which it can be seen that the addition of the polyquinone nanosheet filler is beneficial to the effective transfer of lithium ions and the suppression of space charge. Study by thermogravimetric analysisThe thermal stability of the polymer electrolyte containing the poly-quinone nanosheet filler is 10 ℃ min from air-1The temperature rise rate of (a) was increased from room temperature to 900c, as shown in fig. 13, showing good thermal stability.
The prepared gel electrolyte is subjected to long-term cycling stability test by adopting a constant current charge-discharge cycling method. As shown in the a region of fig. 14, the polymer electrolyte containing the poly-quinone nanosheet filler amount was stable over 700 hours without any internal short-circuit poling voltage variation within ± 25 mv. The excellent cycling stability shows that the polymer electrolyte containing the polypolyquinone nanosheet filler has good inhibition capability on dendritic growth or dendritic perforation. In contrast, the polyurethane electrolyte without the polypyroquinone nanosheet filler has a large change in the polarization voltage of the symmetric battery, and becomes unstable after 50 hours of cycling, indicating that the interface between the electrode and the electrolyte is broken. Region b of fig. 14 shows rate performance of a lithium symmetric battery with a polymer electrolyte containing a polypyroquinone nanosheet filler.
The electrochemical performance of the polymer electrolyte containing the polypolyquinone nanosheet filler was examined in a half-cell system with NCM622 as the cathode, and compared with a polyurethane electrolyte without the polyquinone nanosheet filler, the results are shown in fig. 16. It can be clearly observed that the addition of the polypyroquinone nanosheet filler effectively increases the reversible capacity of the battery. After 100 cycles, the maximum specific capacity of the battery is 145mAh g-1The stable coulombic efficiency was close to 99%. In comparison, the output capacity of the cell without the polyurethane electrolyte of the polypolyquinone nanosheet filler was from 150mA · h · g-1Sharply decreases to 50mA · h · g-1And there is a large fluctuation in coulombic efficiency.
In order to evaluate the dendritic crystal inhibition effect of the polyquinone nanosheet filler, the surface morphology of a lithium metal cathode polarized by applying a liquid electrolyte, a polyurethane electrolyte and a polymer electrolyte containing the polyquinone nanosheet filler is researched by using a scanning electron microscope. As shown in regions a-c in fig. 21, after 100 hours of deposition, the lithium metal surface using both the liquid electrolyte and the polyurethane electrolyte without the addition of the polyquinone nanosheet filler changed from a smooth morphology (region d in fig. 21) to a typical moss and dendritic structure. In contrast, after 300 hours of cycling, little lithium dendrite was seen at the surface of the lithium metal negative electrode with the polymer electrolyte containing the polypyroquinone nanosheet filler (region c of fig. 21). As can be seen from the cross-sectional sem images, the lithium metal negative electrodes of the liquid electrolyte and polyurethane electrolyte without addition of the polyquinone nanosheet filler exhibited a rough porous morphology (see regions a and b of fig. 17), indicating that lithium dendrites were generated during cycling due to uneven lithium exfoliation/plating. The polymer electrolyte containing the polypyroquinone nanosheet filler keeps the lithium metal negative electrode smooth and dense after cycling for 300 hours under the same conditions (see highlighted in region c of fig. 17 and region e of fig. 21). The growth process of dendrites on a polymer electrolyte lithium electrode using a liquid electrolyte and a polypyroquinone-containing nanosheet filler was observed using an in situ optical microscope. Initially, the two lithium electrode surfaces were flat without any protrusions; after 3h of deposition, the lithium electrode edge using the polymeric electrolyte containing the polyquinone nanosheet filler remained smooth without any lithium dendrites or dead lithium (region a of fig. 18), while significant dendrites were observed with the lithium metal edge using the liquid electrolyte (region b of fig. 18), consistent with the conclusions of the sem images.
In-situ X-ray electron spectroscopy testing (without air contact) of the symmetrical lithium electrode surfaces after 50 hours cycling using liquid electrolytes, polyurethane electrolytes, and polymer electrolytes containing polyquinone nanoplate fillers studied the composition of the SEI layer. From the results, the SEI layer compositions of both were similar (fig. 19 and fig. 20). In the spectrum of C1s, the diffraction peaks at 284.5, 286.3, 288.5 and 289.9eV are assigned to C-C (or C ═ C), C-O, C ═ O and CO respectively3 2-. In the Li 1s spectrum, peaks at 54.9, 55.7 and 56.2eV correspond to C-O-Li, respectively2CO3And LiF. The F1 s spectrum shows two peaks at 684.8 and 686.8eV, LiF and Li respectivelyxPOyFz. In fact, the addition of the polypaquinone nanosheet filler can slightly increase the relative content of LiF, which is beneficial to forming a stable and uniform SEI layer and inhibiting the growth of lithium dendrites. Nevertheless, the compositions of the two SEI layers are very similar, indicating polyThe polyquinone nanosheet filler plays other important roles in inhibiting dendritic growth. Since the formation of dendrites is closely related to the initial nucleation mode, which is determined by the surface chemistry of the electrolyte. To inhibit dendritic growth, the lithium-philic centers in the matrix need to be sufficiently uniform to ensure uniformity of the nucleation centers. The abundance of carbonyl groups on the polypolyquinone nanosheet filler allows it to be uniformly dispersed in the base polymer electrolyte matrix, resulting in high lithium ion transfer number (0.74) and ionic conductivity (3.78mS cm) at room temperature-1) Thereby effectively reducing the space charge at the electrode/electrolyte interface. More importantly, the abundant carbonyl groups on the polypoquinone nanosheet filler are lithium-philic, allowing for uniform deposition of lithium at the interface. Meanwhile, due to the lithium-philic nature of the polyquinone nanosheet filler, highly active lithium dendrites can be consumed and eliminated. Thus, the polypyroquinone nanosheet filler as an organic filler can effectively suppress lithium dendrites.

Claims (7)

1. The composite gel polymer electrolyte is characterized by being prepared from lithium electrolyte salt, polyurethane polymer and polyquinone nanosheets; the weight ratio of the lithium electrolyte salt to the polyurethane polymer to the polyquinone nanosheet filler is (8-3) to (8-3) and (10);
the preparation method of the composite gel polymer electrolyte comprises the following steps:
step 1, dissolving a polyurethane polymer in a solvent;
step 2, dispersing polyquinone nanosheet filler in the solution obtained in the step 1 to obtain gel sol;
step 3, preparing the gel sol obtained in the step 2 into a film in a mould, and drying the film to form a polymer matrix;
step 4, soaking the polymer matrix in a liquid electrolyte containing lithium electrolyte salt for adsorption, taking out the polymer matrix, and drying the polymer matrix to obtain a composite gel polymer electrolyte;
the polyquinone nanosheet filler is synthesized by taking pyromellitic dianhydride and anthraquinone as raw materials and anhydrous zinc chloride as a catalyst through a molten salt polycondensation method.
2. The composite gel polymer electrolyte of claim 1 wherein the lithium electrolyte salt is lithium hexafluorophosphate.
3. The composite gel polymer electrolyte of claim 1, wherein the average thickness of the polypolyquinone nanosheet filler is 20-40 nm.
4. The composite gel polymer electrolyte of claim 1 wherein said solvent is N-methyl pyrrolidone; the concentration of the polyurethane polymer dissolved in the solvent is 10-20 wt%.
5. The composite gel polymer electrolyte as claimed in claim 1, wherein the adsorption time in the 4 th step is 5 to 10 hours.
6. Use of the composite gel polymer electrolyte of claim 1 in the preparation of a solid state lithium battery.
7. The use according to claim 6, wherein the solid state lithium battery comprises a positive electrode and a negative electrode, and the composite gel polymer electrolyte is enclosed between the positive electrode and the negative electrode.
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