Polymer solid electrolyte, and preparation method and application thereof

Abstract

The application discloses a kind of polymer solid electrolyte and its preparation method and application, the polymer solid electrolyte includes hydroxyapatite nanowire, fluorine-containing polymer and lithium salt;The hydroxyapatite nanowire is intertwined with each other to form three-dimensional network structure, the fluorine-containing polymer and lithium salt are distributed in three-dimensional network structure;The fluorine-containing polymer is connected between the hydroxyapatite nanowire by hydrogen bond.This polymer solid electrolyte in the application has better stress strain performance, excellent thermal stability, higher ionic conductivity, more ion transference number, wider electrochemical window and other advantages, so that it can be applied in lithium metal battery, and the battery containing it has excellent cycle performance, rate performance, coulomb efficiency and capacity retention rate.

Description

Technical Field

[0001] This invention belongs to the field of batteries, specifically relating to a polymer solid electrolyte, its preparation method, and its application. Background Technology

[0002] In the research of new energy sources, lithium metal batteries, with their advantages of long cycle life, high energy density, large capacity, and light weight, have emerged in the public eye. The electrolyte, playing a crucial role in lithium metal battery materials, has become a focal point of attention. Currently, commercially available lithium batteries generally use liquid electrolytes based on carbonate organic solvents and lithium salts, which suffer from problems such as flammability, leakage, and short lifespan, becoming a major barrier to the high-performance development of lithium batteries. Compared to liquid electrolytes, solid electrolytes can effectively overcome these defects, exhibiting good safety and stability, thus becoming a key issue in the development of lithium metal batteries. Solid electrolytes are mainly divided into inorganic solid electrolytes and polymer solid electrolytes. Inorganic solid electrolytes have high melting points and low ion migration rates, resulting in poor ionic conductivity at low temperatures. Furthermore, their preparation process is complex and costly, limiting their application. Polymer solid electrolytes, on the other hand, have good contact with the electrode interface and are easy to process, giving them a significant advantage in realizing the industrialization of high-energy-density solid-state lithium batteries. However, they also have some shortcomings, specifically:

[0003] (1) Unsatisfactory mechanical properties: Polymer electrolytes have low flexibility and poor mechanical properties, such as poor mechanical properties. When applied to fields such as foldable electronic products and aerospace, their performance is not ideal, leading to the growth of lithium dendrites. The formation of lithium dendrites will threaten many aspects of battery performance. Lithium dendrites are tiny dendritic lithium metal structures on the negative electrode of lithium metal batteries. They may cause battery safety problems, reduced cycle life, decreased battery efficiency and reduced energy density. Their presence can lead to internal short circuits in the battery, increase the risk of explosion, and affect battery performance and lifespan.

[0004] (2) Adverse reactions between electrolyte and electrode materials can easily occur inside the battery, leading to a decline in battery performance. Currently, commercially available lithium metal battery separators are mainly polyolefin organic separators. However, due to their poor wettability to electrolytes, low porosity, poor thermal stability, and tendency to shrink or melt at high temperatures, they pose safety hazards.

[0005] (3) Battery performance is easily affected by temperature changes: Polymer solid electrolytes are sensitive to temperature changes and often suffer from dehydration, decomposition and melting at high temperatures, which reduces the reliability and life of the battery and limits its application under extreme temperature conditions.

[0006] (4) Low battery conductivity: The battery conductivity is low due to the poor conductivity of the polymer solid electrolyte and the insufficient conductivity of the electrode materials. The limited conductivity of the polymer solid electrolyte hinders the smooth transport of ions. This limitation hinders the efficient energy transfer during charging and discharging, resulting in decreased battery performance, shortened cycle life, and a tendency to overheat at high current densities, thus limiting the battery's application prospects in some high-performance applications.

[0007] (5) Low ion transport number: The impedance problem of polymer solid electrolytes limits the rapid transport of lithium ions in the battery, which leads to limited charge and discharge rate, affecting battery performance, cycle life and charging speed. It is one of the limiting factors for improving the energy density and efficiency of lithium batteries.

[0008] (6) Narrow electrochemical window: The limited electrochemical stability of polymer solid electrolytes restricts the width of the electrochemical window of lithium batteries. At higher or lower voltages, irreversible chemical reactions may occur between the solid electrolyte and the electrodes, leading to a decline in battery performance and an increase in safety risks. This limits the reliability and lifespan of batteries in high energy density and wide voltage range applications, and is a key challenge in the development of lithium battery technology.

[0009] (7) Poor cycle and rate performance: Currently, polymer solid electrolytes are subject to degradation, which leads to shortened battery life and reduced energy density, limiting their reliability and efficiency in fast charging and high-power applications.

[0010] Therefore, in order to solve at least one technical problem of polymer solid electrolytes in the prior art, the present invention has developed a new polymer solid electrolyte. Summary of the Invention

[0011] In order to overcome at least one of the problems existing in the prior art, one of the objectives of the present invention is to provide a polymer solid electrolyte.

[0012] The second objective of this invention is to provide a method for preparing a polymer solid electrolyte.

[0013] The third objective of this invention is to provide a lithium metal battery.

[0014] The fourth objective of this invention is to provide an application of a polymer solid electrolyte in batteries.

[0015] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0016] A first aspect of the present invention provides a polymer solid electrolyte comprising hydroxyapatite nanowires, a fluoropolymer, and a lithium salt; wherein the hydroxyapatite nanowires are intertwined to form a three-dimensional network structure, and the fluoropolymer and lithium salt are distributed in the three-dimensional network structure; the fluoropolymer and the hydroxyapatite nanowires are connected by hydrogen bonds.

[0017] Preferably, the mass ratio of the fluoropolymer to the lithium salt is 1:(1 to 1.2).

[0018] Preferably, the fluoropolymer is selected from at least one of polyvinylidene fluoride-hydrofluoric acid copolymer, polytetrafluoroethylene, polychlorotrifluoroethylene, and polyvinylidene fluoride.

[0019] Preferably, the lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, and lithium tetrafluoroborate.

[0020] Preferably, the mass ratio of the hydroxyapatite nanowires to the fluoropolymer is (1-15):100; more preferably, the mass ratio of the hydroxyapatite nanowires to the fluoropolymer is (5-15):100.

[0021] Preferably, the hydroxyapatite nanowires have a length of 500–600 nm and a diameter of 10–12 nm.

[0022] Preferably, the polymer solid electrolyte has an ionic conductivity of 0.9–2.2 × 10⁻⁶. -4 S / cm.

[0023] Preferably, the polymer solid electrolyte has an ion transference number of 0.45 to 0.65.

[0024] Preferably, the electrochemical window of the polymer solid electrolyte is 4.7–4.8 V.

[0025] Preferably, the tensile strength of the polymer solid electrolyte is 0.9 to 1 MPa.

[0026] Preferably, the fracture strain of the polymer solid electrolyte is 114-120%; more preferably, the fracture strain of the polymer solid electrolyte is 114-116%.

[0027] Preferably, the self-extinguishing time of the polymer solid electrolyte after combustion does not exceed 3 seconds; more preferably, the self-extinguishing time of the polymer solid electrolyte after combustion does not exceed 2.5 seconds.

[0028] The second aspect of the present invention provides a method for preparing the polymer solid electrolyte provided in the first aspect of the present invention, comprising the following steps:

[0029] S1: Mix oleate, calcium salt and dihydrogen phosphate, and then hydrothermally react at 190-210℃ for 30-40h to obtain hydroxyapatite nanowires;

[0030] S2: The hydroxyapatite nanowires are dispersed in a solvent and then mixed with a fluorinated polymer and a lithium salt to prepare an electrolyte solution;

[0031] S3: Form the electrolyte solution into a film to obtain the polymer solid electrolyte.

[0032] Step S1 can prepare ultra-long hydroxyapatite nanowires, and the preparation method is simple and easy to operate. The prepared hydroxyapatite nanowires have better mechanical properties, and their morphology is closer to the microstructure of natural bone, which can provide better mechanical properties.

[0033] Preferably, the oleate is selected from sodium oleate, potassium oleate, or a combination thereof.

[0034] Preferably, the calcium salt is selected from calcium chloride, calcium nitrate, or a combination thereof.

[0035] Preferably, the dihydrogen phosphate is selected from potassium dihydrogen phosphate, sodium dihydrogen phosphate, or a combination thereof.

[0036] Preferably, in step S2, the solvent is selected from DMF.

[0037] Preferably, the mixing temperature in step S2 is 55–65°C.

[0038] Preferably, in step S2, the dispersion step employs ultrasonic dispersion.

[0039] Preferably, step S3 involves coating the electrolyte solution by scraping or spin coating it into a film, and then drying it to obtain the polymer solid electrolyte.

[0040] A third aspect of the present invention provides a lithium metal battery comprising a positive electrode, a negative electrode, and a polymer solid electrolyte provided in the first aspect of the present invention.

[0041] Preferably, the positive electrode is made of NCM811 material.

[0042] The fourth aspect of the present invention provides the application of the polymer solid electrolyte provided in the first aspect of the present invention in batteries.

[0043] The beneficial effects of this invention are as follows: The polymer solid electrolyte of this invention has advantages such as good stress-strain performance, excellent thermal stability, high ionic conductivity, high ion transport number, and wide electrochemical window, making it suitable for lithium metal batteries and enabling batteries containing it to have excellent cycle performance, rate performance, coulombic efficiency, and capacity retention. Specifically, the polymer solid electrolyte of this invention has the following advantages:

[0044] (1) Better stress-strain performance. With the addition of hydroxyapatite nanowires (HAP), the interaction of molecules within the electrolyte leads to an improvement in the electrolyte's stress-strain capacity, giving the electrolyte good bending and stretching recovery performance. The pressure required to stretch to the same strain is about twice that of electrolytes without hydroxyapatite nanowires. This is beneficial for the battery to work in harsh environments, allowing the battery to continue to work normally even if it undergoes partial deformation.

[0045] (2) Good thermal resistance. HAP is an inorganic filler with good thermal stability. The addition of HAP increases the decomposition temperature of the polymer electrolyte, making the electrolyte more thermally stable, and also gives it a certain flame retardant ability. The electrolyte self-extinguishes within 2.5s, providing a great guarantee for battery safety.

[0046] (3) It has a high ionic conductivity, ranging from 0.9 to 2.2 × 10⁻⁶. -4 S / cm, where the ionic conductivity of the electrolyte reaches 2.18 × 10⁻⁶ when the amount of HAP added reaches 10%. -4 S / cm. Because the hydroxyl groups in HAP form hydrogen bonds with -CF3 in LiTFSI, they establish lithium-ion transport channels and synergistically bind TFEI. - Anions, so much so that Li + It is easier to dissociate. The addition of HAP also disrupts the crystallization of the polymer chains, effectively reducing crystallinity, which is beneficial to Li + Moving along the polymer chain, causing Li + The increased transfer rate can reduce Li + The impedance during transmission facilitates the achievement of higher ionic conductivity.

[0047] (4) Significantly increased ion transport number. The fraction of charge transported by ions in the total charge passing through the solution is called the ion transport number. When the amount of HAP added reaches 10%, the ion transport number of the electrolyte reaches 0.61. This is because the hydroxyl groups in HAP form hydrogen bonds with -CF3 in LiTFSI, establishing lithium-ion transport channels and synergistically binding TFEI. - Anions make Li + Li is easier to dissociate. +As the concentration increases, the ion transport number in the electrolyte changes with the concentration, thus increasing the ion transport number.

[0048] (5) Wider electrochemical window. The electrochemical window of the electrolyte reached 4.73V after the addition of 10% HAP. A wider electrochemical window means that the material or electrolyte can operate at higher or lower voltages, thus providing greater electrochemical stability and higher voltage output.

[0049] (6) Good cycle and rate performance. The electrolyte has good capacity retention and long cycle life, which is beneficial to improving the service life of lithium metal batteries.

[0050] The polymer solid electrolyte of this invention has a simple synthesis method, mild reaction conditions, and inexpensive and readily available raw materials, making it suitable for mass production. Attached Figure Description

[0051] Figure 1 The above is a process flow diagram of the preparation process of the polymer solid electrolyte in Examples 1 to 3 of the present invention.

[0052] Figure 2 This is a SEM image of the hydroxyapatite nanowires from Example 1.

[0053] Figure 3 The images shown are cross-sectional SEM images of the polymer solid electrolytes in Example 2 and Comparative Example 1.

[0054] Figure 4 The images shown are planar SEM images of the polymer solid electrolytes in Example 2 and Comparative Example 1.

[0055] Figure 5 The electron diffraction pattern and TEM image of the hydroxyapatite nanowires in Example 1 are shown.

[0056] Figure 6 The image shows the XRD pattern of the hydroxyapatite nanowires in Example 1.

[0057] Figure 7 The image shows the XRD pattern of the polymer solid electrolyte in Comparative Example 1.

[0058] Figure 8 The image shows the XRD pattern of the polymer solid electrolyte in Example 1.

[0059] Figure 9 The image shows the XRD pattern of the polymer solid electrolyte in Example 2.

[0060] Figure 10 The image shows the XRD pattern of the polymer solid electrolyte in Example 3.

[0061] Figure 11This is the EDS image of the hydroxyapatite nanowires in Example 1.

[0062] Figure 12 This is the EDS diagram of the polymer solid electrolyte in Example 2.

[0063] Figure 13 The image shows the DSC test results of the polymer solid electrolyte in Comparative Example 1.

[0064] Figure 14 The image shows the DSC test results of the polymer solid electrolyte in Example 2.

[0065] Figure 15 The TGA and DTG test results are shown for the polymer solid electrolyte in Comparative Example 1.

[0066] Figure 16 The TGA and DTG test results are shown for the polymer solid electrolyte in Example 2.

[0067] Figure 17 The stress-strain test results are shown for the polymer solid electrolyte in Comparative Example 1.

[0068] Figure 18 The stress-strain test diagram is shown for the polymer solid electrolyte in Example 2.

[0069] Figure 19 The figure shows the AC impedance test results of the polymer solid electrolyte in Comparative Example 1.

[0070] Figure 20 The image shows the AC impedance test results of the polymer solid electrolyte in Example 1.

[0071] Figure 21 The image shows the AC impedance test results of the polymer solid electrolyte in Example 2.

[0072] Figure 22 The image shows the AC impedance test results of the polymer solid electrolyte in Example 3.

[0073] Figure 23 The graph shows the linear voltammetry of the polymer solid electrolyte in Comparative Example 1.

[0074] Figure 24 The graph shows the linear voltammetry of the polymer solid electrolyte in Example 1.

[0075] Figure 25 The graph shows the linear voltammetry of the polymer solid electrolyte in Example 2.

[0076] Figure 26 The graph shows the linear voltammetry of the polymer solid electrolyte in Example 3.

[0077] Figure 27 The graph shows the change in ionic conductivity of the polymer solid electrolyte in Comparative Example 1 as a function of temperature.

[0078] Figure 28 The graph shows the change in ionic conductivity of the polymer solid electrolyte in Example 1 as a function of temperature.

[0079] Figure 29 The graph shows the change in ionic conductivity of the polymer solid electrolyte in Example 2 as a function of temperature.

[0080] Figure 30 The graph shows the change in ionic conductivity of the polymer solid electrolyte in Example 3 as a function of temperature.

[0081] Figure 31 The graph shows the charge-discharge cycle test results of the polymer solid electrolyte in Comparative Example 1 under 1C conditions.

[0082] Figure 32 This is a charge-discharge cycle test diagram of the polymer solid electrolyte in Example 2 under 1C conditions.

[0083] Figure 33 This is a charge-discharge cycle test diagram of the polymer solid electrolyte in Example 2 under 0.5C conditions.

[0084] Figure 34 The graph shows the cycle performance of a Li / PVHLi-10HAP / Li symmetric cell.

[0085] Figure 35 XPS analysis of the lithium sheet surface after 50 cycles of a Li / PVHLi-10HAP / Li symmetric cell. Detailed Implementation

[0086] The specific implementation of the present invention will be further described in detail below with reference to the accompanying drawings and examples, but the implementation and protection of the present invention are not limited thereto. It should be noted that any processes not specifically described below are those that can be implemented or understood by those skilled in the art by referring to the prior art. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0087] The main instruments and materials used in the embodiments and comparative examples of this invention are as follows:

[0088] Instrument names: ① Magnetic stirrer, ② Hydrothermal reactor, ③ Ultrasonic instrument, ④ Constant temperature stirring pot, ⑤ Glove box, ⑥ Glass bottle, ⑦ Glass plate, ⑧ Vacuum drying oven, ⑨ Slicer / press

[0089] Material names: N,N-dimethylformamide (DMF); polyvinylidene fluoride-hydrofluoric acid copolymer (PVDF-HFP); lithium bis(trifluoromethanesulfonylimide) (LiTFSI).

[0090] The process flow diagrams for preparing the polymer solid electrolytes in Examples 1-3 of this invention are as follows: Figure 1 As shown.

[0091] Example 1

[0092] The polymer solid electrolyte in this example was prepared using the following method, with the specific steps as follows:

[0093] (1) First, 2.4 g of sodium oleate was dissolved in 25 mL of deionized water, and then 25 mL of aqueous solution containing CaCl2 (0.22 g) was added. After stirring magnetically for about 1 hour, 25 mL of aqueous solution containing NaH2PO4·2H2O (0.28 g) was added. After stirring for about half an hour, the solution was transferred to a 100 mL hydrothermal reactor, sealed and heated to 200 °C, and kept at that temperature for 36 hours to obtain hydroxyapatite nanowires (HAP). After washing with ethanol and deionized water three times each, the nanowires were redispersed in deionized water at a mass ratio of 100:1 to construct a hydroxyapatite nanowire network. The length of the hydroxyapatite nanowires was 500–600 nm and the diameter was 10–12 nm.

[0094] (2) Weigh 1.5g of DMF, and then weigh 5% of the pre-constructed hydroxyapatite nanowires (i.e., the mass ratio of PVDF-HFP to HAP is 100:5). Dissolve the weighed hydroxyapatite nanowires in the weighed DMF and disperse them ultrasonically. Transfer the prepared solution to a glove box, and weigh 0.300g of PVDF-HFP and 0.330g of LiTFSI into the glove box, then add them to the solution to obtain a new prepared solution. (The ratio of lithium salt LiTFSI to polymer PVDF-HFP is controlled at 1:1.1 to form a high-salt system.)

[0095] (3) The newly prepared solution was stirred overnight in a 60°C water bath to initially form a high-salt polymer system. After the solution was stirred evenly, an electrolyte precursor solution was obtained. It was placed in a glove box and vacuumed to remove air bubbles (the purpose of removing air bubbles is to prevent the electrolyte precursor solution from having an uneven electrolyte surface and causing excessively high interfacial impedance). It was then poured onto a clean glass plate and coated into a film using a stainless steel scraper with a height of 400 μm. The glass plate was then immediately placed in a constant temperature and humidity chamber at 25°C and 80% humidity for 3 hours to obtain a preliminarily formed electrolyte film. The film was peeled off the glass plate and placed in a vacuum drying oven at 60°C for 24 hours to obtain an electrolyte film with a thickness of about 100 μm. After drying, the electrolyte was quickly removed and cut into round slices with a radius of 8 mm or the required size using a slicer. The slices were then sealed and stored to prevent the electrolyte from absorbing water, thus obtaining the polymer solid electrolyte in this example, denoted as: PVHLi-5HAP.

[0096] Example 2

[0097] The polymer solid electrolyte in this example was prepared using the following method, with the specific steps as follows:

[0098] (1) Weigh 1.500g of DMF, and then weigh 10% of the hydroxyapatite nanowires with the constructed network from Example 1 (i.e., the mass ratio of PVDF-HFP to HAP is 100:10, and the preparation method of the hydroxyapatite nanowires is the same as in Example 1). Dissolve the weighed hydroxyapatite nanowires in the weighed DMF and disperse them by ultrasonication. Then transfer the prepared solution to a glove box, and weigh 0.300g of PVDF-HFP and 0.330g of LiTFSI in the glove box, and then add them to the solution to obtain a new prepared solution. (The ratio of lithium salt LiTFSI to polymer PVDF-HFP is controlled at 1:1.1 to form a high-salt system.)

[0099] (2) The newly prepared solution was stirred overnight in a 60°C water bath to initially form a high-salt polymer system. After the solution was stirred evenly, an electrolyte precursor solution was obtained. It was placed in a glove box and vacuum-sealed to remove air bubbles (the purpose of removing air bubbles is to prevent the electrolyte precursor solution from having an uneven electrolyte surface and causing excessively high interfacial impedance). It was then poured onto a clean glass plate and coated into a film using a stainless steel scraper with a height of 400 μm. The glass plate was then immediately placed in a constant temperature and humidity chamber at 25°C and 80% humidity for 3 hours to obtain a pre-formed electrolyte membrane. The membrane was peeled off the glass plate and placed in a vacuum drying oven at 60°C for 24 hours to obtain an electrolyte membrane with a thickness of approximately 100 μm. After drying, the electrolyte was quickly removed and cut into round slices with a radius of 8 mm or the required size using a slicer. The slices were then sealed and stored to prevent the electrolyte from absorbing water, thus obtaining the polymer solid electrolyte in this example, denoted as: PVHLi-10HAP.

[0100] Example 3

[0101] The polymer solid electrolyte in this example was prepared using the following method, with the specific steps as follows:

[0102] (1) Weigh 1.500g of DMF, and then weigh 15% of the hydroxyapatite nanowires with the constructed network from Example 1 (the method for preparing the hydroxyapatite nanowires is the same as in Example 1, i.e., the mass ratio of PVDF-HFP to HAP is 100:15). Dissolve the weighed hydroxyapatite nanowires in the weighed DMF and disperse them by ultrasonication. Transfer the prepared solution to a glove box, and weigh 0.300g of PVDF-HFP and 0.330g of LiTFSI into the glove box, and then add them to the solution to obtain a new prepared solution. (The ratio of lithium salt LiTFSI to polymer PVDF-HFP is controlled at 1:1.1 to form a high-salt system.)

[0103] (2) The newly prepared solution was stirred overnight in a 60°C water bath to initially form a high-salt polymer system. After the solution was stirred evenly, an electrolyte precursor solution was obtained. It was placed in a glove box and vacuum-sealed to remove air bubbles (the purpose of removing air bubbles is to prevent the electrolyte precursor solution from having an uneven electrolyte surface and causing excessively high interfacial impedance). It was then poured onto a clean glass plate and coated into a film using a stainless steel scraper with a height of 400 μm. The glass plate was then immediately placed in a constant temperature and humidity chamber at 25°C and 80% humidity for 3 hours to obtain a preliminarily formed electrolyte film. The film was peeled off the glass plate and placed in a vacuum drying oven at 60°C for 24 hours to obtain an electrolyte film with a thickness of approximately 100 μm. After drying, the electrolyte was quickly removed and cut into round slices with a radius of 8 mm or the required size using a slicer. The slices were then sealed and stored to prevent the electrolyte from absorbing water, thus obtaining the polymer solid electrolyte in this example, denoted as: PVHLi-15HAP.

[0104] Comparative Example 1

[0105] The polymer solid electrolyte in this example was prepared using the following method, with the specific steps as follows:

[0106] (1) First, weigh 1.500g of DMF and 0.330g of LiTFSI into a bottle in a glove box. Shake gently until LiTFSI dissolves, then add 0.300g of PVDF-HFP and shake well to obtain a freshly prepared solution. (The ratio of lithium salt LiTFSI to polymer PVDF-HFP is controlled at 1:1.1 to form a high-salt system.)

[0107] (2) The newly prepared solution was stirred overnight in a 60°C water bath to initially form a high-salt polymer system. After the solution was stirred evenly, an electrolyte precursor solution was obtained. It was placed in a glove box and vacuum-sealed to remove air bubbles (the purpose of removing air bubbles is to prevent the electrolyte precursor solution from having an uneven electrolyte surface and causing excessively high interfacial impedance). It was then poured onto a clean glass plate and coated into a film using a stainless steel scraper with a height of 400 μm. The glass plate was then immediately placed in a constant temperature and humidity chamber at 25°C and 80% humidity for 3 hours to obtain a preliminarily formed electrolyte film. The film was peeled off the glass plate and placed in a vacuum drying oven at 60°C for 24 hours to obtain an electrolyte film with a thickness of approximately 100 μm. After drying, the electrolyte was quickly removed and cut into round slices with a radius of 8 mm or the required size using a slicer. The slices were then sealed and stored to prevent the electrolyte from absorbing water, thus obtaining the polymer solid electrolyte in this example, denoted as: PVHLi.

[0108] Comparative Example 2

[0109] The polymer solid electrolyte in this example was prepared using the following method, with the specific steps as follows:

[0110] (1) Oleic acid (105 mL), methanol (60 mL) and deionized water (135 mL) were stirred to obtain mixed solution 0; sodium hydroxide (10.5 g) was dissolved in deionized water (150 mL) to obtain solution 1; anhydrous calcium chloride (3.33 mL) was dissolved in deionized water (120 mL) to obtain solution 2; disodium hydrogen phosphate (9.36 g) was dissolved in deionized water (180 mL) to obtain solution 3; under mechanical stirring, solutions 1, 2 and 3 were added to mixed solution 0 respectively, and after mixing evenly, the mixture was transferred to a 1 L high-pressure reactor and heated in a forced-air oven at 180 °C for 24 hours. After cooling to room temperature, the hydrothermal products were washed with ethanol and deionized water respectively to obtain an aqueous suspension of hydroxyapatite nanowires. After vacuum drying by filtration, hydroxyapatite nanowires were obtained. The length of the hydroxyapatite nanowires was 200-250 nm and the diameter was 5-6 nm.

[0111] (2) Hydroxyapatite composite solid polymer electrolyte was prepared by casting film formation method. Hydroxyapatite nanowires (0.025 g) and acetonitrile (10 mL) were stirred and sonicated to obtain a uniformly dispersed hydroxyapatite suspension. Then, PEO (0.5 g), lithium salt (0.1632 g), and EO / Li were added respectively. +The mixture was stirred for 24 hours under an inert gas atmosphere at a ratio of 20 / 1 to obtain a mixed solution. The solution was then transferred to a specific polytetrafluoroethylene (PTFE) disc mold (80 mm inner diameter) and heated in a vacuum drying oven at 60°C for 10 hours. After cooling to room temperature, the solid polymer electrolyte membrane was peeled off and cut into 16 mm diameter circular separators using a manual button cell slicer. These were then placed in a glove box for later use, yielding the polymer solid electrolyte in this example, denoted as PEHLi.

[0112] Performance testing:

[0113] (1) SEM analysis and TEM analysis

[0114] The size and microstructure of the hydroxyapatite nanowires prepared in Example 1 were tested, specifically as follows: Figure 2 As shown, where, Figure 2 a is a SEM image of hydroxyapatite nanowires. Figure 2 b is Figure 2 A magnified view of the area within the box; by Figure 2 It can be seen that the hydroxyapatite nanowires prepared in Example 1 are continuous long linear shapes. The hydroxyapatite nanowires of Comparative Example 2 have a length of 200-250 nm and a diameter of 5-6 nm. The hydroxyapatite nanowires of Example 1 have a length of 500-600 nm and a diameter of 10-12 nm. Therefore, it can be seen that Example 1 of the present invention does not use methanol and alkaline solution, and the hydroxyapatite nanowires prepared are longer, thicker, have a larger surface area, contain more hydroxyl groups, and require fewer raw materials. The reaction conditions are milder, the reaction steps are shorter, and side reactions are reduced, which is more conducive to the formation of longer hydroxyapatite nanowires. The reduced use of alkaline solution is more conducive to the formation and protection of hydroxyl groups, thereby obtaining more hydroxyl groups and a longer structure, which is beneficial for their combination into a three-dimensional network. At the same time, hydroxyl groups can also form hydrogen bonds with polymers to transport lithium ions and improve the electrochemical performance of the electrolyte.

[0115] Cross-sectional SEM images of the polymer solid electrolytes in Example 2 and Comparative Example 1 were obtained, as shown below. Figure 3 As shown, where, Figure 3 (a) Figure 3 (b) and Figure 3 (c) Cross-sectional SEM images of PVHLi in Comparative Example 1 with scale bars of 20 μm, 10 μm, and 5 μm, respectively; Figure 3 (d) Figure 3 (e) and Figure 3 (f) Cross-sectional SEM images of PVHLi-10HAP in Example 2, with scale bars of 20μm, 10μm, and 5μm, respectively; Figure 3It can be seen that, compared with Comparative Example 1, the electrolyte membrane in Example 2 has a denser and smoother cross-section in the microscopic state, and more micropores, which has more lithium ion channels and is beneficial to improving ionic conductivity.

[0116] Planar SEM images of the polymer solid electrolytes in Example 2 and Comparative Example 1 were obtained, as shown below. Figure 4 As shown, where, Figure 4 (a) is a planar SEM image of PVHLi in Comparative Example 1; Figure 4 (b) and Figure 4 (c) Planar SEM images of PVHLi-10HAP in Example 2, with scale bars of 50 μm and 5 μm, respectively. Figure 4 It can be seen that, compared with Comparative Example 1, the electrolyte membrane in Example 2 has a greater number of micropores, which provides Li + The transport provides a channel, thereby improving the conductivity of the electrolyte membrane at room temperature, which also explains the high conductivity of the PVHLi-10HAP electrolyte membrane from a microscopic perspective.

[0117] Transmission electron microscopy (TEM) was used to examine the hydroxyapatite nanowires in Example 1, and their selected area electron diffraction (SED) images were also measured. Specific test results are as follows: Figure 5 As shown, where, Figure 5 (a) is the selected area electron diffraction pattern of the hydroxyapatite nanowires in Example 1. Figure 5 (b) is a TEM image of the hydroxyapatite nanowires in Example 1. Figure 5 It can be seen that the hydroxyapatite nanowires prepared in Example 1 of the present invention are uniform and have good morphology; the electron diffraction pattern shows that they are polycrystalline structures, and the disordered polycrystalline structure is conducive to lithium ion transport (ordered crystal structures are not conducive to ion transport).

[0118] (2) XRD analysis and EDS energy dispersive spectroscopy analysis

[0119] X-ray diffraction (XRD) was used to test the XRD patterns of the hydroxyapatite nanowires in Example 1, and the polymer solid electrolytes in Examples 1-3 and Comparative Example 1. Specific test results are as follows: Figures 6-10 As shown, where, Figure 6 , Figure 7 , Figure 8 , Figure 9 and Figure 10 The figures show the XRD patterns of hydroxyapatite nanowires, PVHLi, PVHLi-5HAP, PVHLi-10HAP, and PVHLi-15HAP, respectively. Figure 6 It can be seen that HAP belongs to the hexagonal crystal system, and its pattern is typical of HAP. From... Figures 7-10It can be seen that, compared with Comparative Example 1, after introducing hydroxyapatite nanowire filler in Example 1, the crystallinity of the polymer decreased, lithium ions were more easily transported in the polymer matrix, and the ionic conductivity of the polymer was increased to a certain extent.

[0120] The EDS elemental distribution map of the hydroxyapatite nanowires in Example 1 is shown in the figure below. Figure 11 As shown, where, Figure 11 (a) is the EDS elemental distribution diagram of the hydroxyapatite nanowires in Example 1. Figure 11 (b) Figure 11 (c) and Figure 11 (d) EDS plots showing the distribution of Ca, P, and O elements, respectively. Figure 11 It can be seen that the Ca, P and O elements are relatively evenly distributed in the hydroxyapatite nanowires.

[0121] The EDS diffraction pattern of the PVHLi-10HAP composite electrolyte membrane in Example 2 was tested, and the test results are as follows: Figure 12 As shown, where, Figure 12 (a) Figure 12 (b) Figure 12 (c) and Figure 12 (d) are EDS diagrams of Ca, P, C, and N elements in the electrolyte membrane of Example 2. Figure 12 It can be seen that Ca, P, C and N elements are uniformly distributed in the PVHLi-10HAP composite electrolyte membrane, indicating that HAP is uniformly distributed in the PVHLi matrix.

[0122] (3) Thermal stability and flame retardant performance test

[0123] The DSC curves of the polymer solid electrolytes in Comparative Example 1 and Example 2 were tested respectively, and the test results are as follows: Figure 13 and Figure 14 As shown. By Figures 13-14 It can be seen that, compared with Comparative Example 1, the introduction of hydroxyapatite nanowire filler in Example 2 reduced the glass transition temperature (the glass transition temperature of Comparative Example 1 is about 100°C, and the glass transition temperature of Example 2 is about 80°C) and melting point (the melting point of Example 2 is 77.7°C, and the melting point of Comparative Example 1 is 80.9°C), enhanced the creep ability of polymer segments, and facilitated the transport of lithium ions in the polymer matrix.

[0124] The TGA and DTG curves of the polymer solid electrolytes in Comparative Example 1 and Example 2 were tested respectively, and the test results are as follows: Figure 15 and Figure 16 As shown. By Figures 15-16It is known that in Example 2, the hydroxyl groups on the surface of the hydroxyapatite nanowire filler form a hydrogen bond network with the fluorine on the polymer, which increases the decomposition temperature of the polymer matrix (the decomposition temperature is increased to 332.5℃), thus improving the thermal stability of the electrolyte.

[0125] The flame retardant properties of the polymer solid electrolytes in PVHLi, PVHLi-5HAP, PVHLi-10HAP and PVHLi-15HAP were tested respectively, and the self-extinguishing time of the electrolytes during combustion was recorded. The specific test results are shown in Table 1.

[0126] Table 1. Flame retardant performance test results of electrolyte combustion in Examples 1-3 and Comparative Example 1.

[0127]

[0128] As shown in Table 1, compared with PVHLi, the present invention introduces HAP filler into PVHLi-5HAP, PVHLi-10HAP and PVHLi-15HAP electrolytes, which makes the prepared electrolytes have excellent flame retardant effect and excellent thermal stability. The electrolytes can achieve self-extinguishing within 2.5s, and the self-extinguishing time gradually shortens with the increase of HAP content.

[0129] (4) Mechanical property testing

[0130] Stress-strain tests were conducted on the electrolytes in PVHLi and PVHLi-10HAP using an electronic tensile testing machine. The specific test results are as follows: Figure 17 , Figure 18 As shown in the figure, the test results of the tensile strength and fracture strain are recorded in Table 2 below.

[0131] Table 2 shows the stress-strain test results of the electrolytes in Example 2 and Comparative Example 1.

[0132]

[0133] Depend on Figures 17-18 As shown in Table 2, compared with PVHLi in Comparative Example 1, the electrolyte in PVHLi-10HAP in Example 2 has excellent mechanical properties and can effectively suppress lithium dendrite growth. The mechanical properties of the polymer solid electrolytes in Examples 1 and 3 were tested and found to be basically the same as those in Example 2.

[0134] (5) AC impedance and linear voltammetry test

[0135] PVHLi, PVHLi-5HAP, PVHLi-10HAP, and PVHLi-15HAP were assembled into batteries according to their respective testing requirements for performance testing. The positive electrode was an NCM811 electrode. Batteries for ion electrochemical impedance spectroscopy (ELS) were assembled using the following components: anode shell, spring, gasket, electrolyte membrane, gasket, and cathode shell. Lithium-ion batteries for measuring the electrochemical window were assembled using the following components: anode shell, spring, gasket, electrolyte membrane, lithium sheet, and cathode shell. Lithium-ion batteries for measuring cycle performance were assembled using the following components: anode shell, spring, gasket, positive electrode, electrolyte membrane, lithium sheet, and cathode shell. All batteries were pressurized to 50N and subjected to linear voltammetry (LSV) and electrochemical impedance spectroscopy (ELS) using a CHI660E electrochemical workstation. The voltage range for LSV testing was 2V-5.5V, and the scan rate was 0.1mV / s. -1 The EIS frequency was 106 Hz and the amplitude was 5 mV. All tests were conducted at 25℃. Ionic conductivity was calculated from the measured impedance value using the following formula:

[0136]

[0137] Where R is the AC impedance of the electrolyte membrane obtained from the impedance diagram, L is the thickness of the electrolyte membrane, and S is the effective contact area between the electrolyte and the electrode. Considering that the membrane will thin under pressure during battery assembly, the actual L of the membrane needs to be measured after disassembling the test battery.

[0138] The ion transport number is calculated as the fraction of the charge transported by ions in the total charge passing through the solution.

[0139] All the above experimental steps were carried out in a glove box under an argon atmosphere to avoid the influence of water and oxygen on the experimental results.

[0140] Following the above test methods, AC impedance spectroscopy (ELS), linear voltammetric scanning (LSV), and flame retardant performance tests were performed on PVHLi, PVHLi-5HAP, PVHLi-10HAP, and PVHLi-15HAP respectively. Specific test results are as follows: Figures 19-30 As shown in the figure, Figure 19 , Figure 20 , Figure 21 , Figure 22 These are the AC impedance test diagrams for PVHLi, PVHLi-5HAP, PVHLi-10HAP, and PVHLi-15HAP, respectively. Figure 23 , Figure 24 , Figure 25 , Figure 26 The linear voltammetric test diagrams are for PVHLi, PVHLi-5HAP, PVHLi-10HAP, and PVHLi-15HAP, respectively. Figure 27, Figure 28 , Figure 29 , Figure 30 The graphs show the changes in ionic conductivity of PVHLi, PVHLi-5HAP, PVHLi-10HAP, and PVHLi-15HAP as a function of temperature. The test data for ion transport number, ionic conductivity, and electrochemical window are then recorded in Table 3 below.

[0141] Table 3 shows the electrochemical performance test results of the electrolytes in Examples 1-3 and Comparative Example 1.

[0142]

[0143] Depend on Figures 19-30 As shown in Table 3, compared with PVHLi-5HAP and PVHLi-15HAP, PVHLi-10HAP has better ion transference number, ionic conductivity and electrochemical window, with an ion transference number of 0.61 and an ionic conductivity of 2.18 × 10⁻⁶. -4 S / cm, electrochemical window is 4.73V. (From...) Figures 27-30 It can be seen that, compared with PVHLi-5HAP and PVHLi-15HAP, the ionic conductivity of PVHLi-10HAP changes the most with temperature. The addition of HAP filler significantly enhances the thermal stability of the electrolyte.

[0144] (6) Charge-discharge cycle test

[0145] Following the test methods described in section (5) on AC impedance and linear volt-ampere testing, a lithium battery for measuring cycle performance was assembled from an anode shell, spring plate, gasket, positive electrode (NCM811), electrolyte membrane, lithium sheet, and cathode shell. The batteries in Example 2 and Comparative Example 1 were designated as NCM811 / PVHLi-10HAP / Li and NCM811 / PVHLi / Li, respectively. The charge-discharge cycle performance of the polymer solid electrolytes in Comparative Example 1 and Example 2 at 1C was tested, and the specific test results are as follows: Figure 31 and Figure 32 As shown, the charge-discharge cycle performance of the polymer solid electrolyte in Example 2 at 0.5C was then tested, and the test results are as follows. Figure 33 As shown. By Figure 31 It can be seen that the NCM811 / PVHLi / Li in Comparative Example 1 has a first-cycle coulombic efficiency of 69.7% and a first-cycle discharge specific capacity of 114.2 mAh g under 1C conditions. -1 After 50 cycles, the energy density stabilized at 104.0 mAh g. -1 It remained at around 57.6 mAh g after 500 cycles. -1 The Coulomb efficiency remains stable at around 99.0%. Figure 32 It can be seen that, in Example 2, the PVHLi-10HAP electrolyte containing 10% HAP has a first-cycle coulombic efficiency of 59.0% and a first-cycle discharge specific capacity of 79.4 mAh g under 1C conditions. -1 After 50 cycles, the energy density increased to 130 mAh g. -1 After approximately 100 cycles, the coulombic efficiency is 99.2%, and the discharge specific capacity is 140.1 mAh g. -1 It can still maintain 91mAh g after 500 cycles. -1 The Coulomb efficiency remains stable at around 99.0%. Figure 33 It can be seen that under 0.5C conditions, the coulombic efficiency of the first cycle is 71.8%, stabilizing at around 99%, and the specific capacity of the first cycle discharge is 124.0 mAh g. -1 After 50 cycles, the discharge specific capacity increased to 145.0 mAh g. -1 After 500 cycles, the discharge specific capacity is 98.7 mAh g. -1 The capacity retention rate was 79.5%. This further demonstrates that the PVHLi-10HAP in this invention performs normally under long-term operation, is not prone to overheating, and has good thermal conductivity. The polymer solid electrolytes in Examples 1 and 3 were tested and found to have essentially the same charge-discharge cycle performance as in Example 2. For ease of comparison, the polymer solid electrolyte in Comparative Example 2 was assembled into a lithium battery for cycle performance measurement, consisting of an anode shell, spring, gasket, positive electrode (LiFePO4), electrolyte membrane, lithium sheet, and cathode shell. This battery was denoted as LiFePO4 / PEHLi / Li. The charge-discharge cycle performance of LiFePO4 / PEHLi / Li at 1C was then tested. According to the test results, when using lithium iron phosphate (positive electrode) in Comparative Example 2, the first-cycle coulombic efficiency was 61.7%, and the first-cycle discharge specific capacity was 144.4 mAh g. -1 After 100 cycles, the coulombic efficiency was around 98.0%, and the discharge specific capacity continued to decrease to 122.4 mAh g. -1 After 500 cycles, the coulombic efficiency was 98.4%, and the discharge specific capacity was 64.7 mAh g. -1The operating voltage range of NCM811 is 2.6-4.3V, while that of lithium iron phosphate is 2.5-3.7V, a difference of 0.5V. This invention uses NCM811, which can improve the energy density, application range, and safety stability of the applied battery. Furthermore, NCM811 possesses high specific capacity, high cycle performance, and high safety performance. More importantly, under the same conditions, the cycle performance of a battery using NCM811 as the positive electrode is significantly lower than that using lithium iron phosphate as the positive electrode. The electrolyte provided in Example 2 of this invention, when used with NCM811, exhibits higher cycle time, capacity retention, and coulombic efficiency than Comparative Example 2, which uses lithium iron phosphate, further demonstrating that the performance of the electrolyte in Comparative Example 2 is significantly inferior to that of the electrolyte in Example 2.

[0146] The PVHLi-10HAP from Example 2 was assembled into a battery according to the structure of anode shell, spring, gasket, lithium sheet, electrolyte membrane, lithium sheet, and cathode shell, denoted as Li / PVHLi-10HAP / Li symmetric battery. The battery's cycle performance was then tested at 0.1 mA / cm². 2 The current density was charged and discharged at a temperature of 35℃, and the specific test results are as follows: Figure 34 As shown. By Figure 34 It can be seen that the polarization voltage of the PVHLi-10HAP electrolyte remained at around 15mV throughout the 800-hour cycle, and the voltage remained relatively stable with increasing cycle charge-discharge time. Under the same test conditions, the polarization voltage of Comparative Example 2 was 47mV, and it failed after about 700 hours of cycling. Therefore, it can be concluded that the PVHLi-10HAP electrolyte in Example 2 of this invention has stable lithium ion insertion and extraction on the electrode surface, which helps to improve the cycle life of lithium batteries.

[0147] (7) XPS Analysis

[0148] XPS analysis was performed on the lithium sheet surface of the above-mentioned Li / PVHLi-10HAP / Li symmetric battery after 50 cycles. The specific test results are as follows: Figure 35 As shown. By Figure 35 It can be seen that other elements were detected on the lithium sheet after 50 cycles of the Li / PVHLi-10HAP / Li symmetric battery, indicating that the electrolyte and electrode have good compatibility.

[0149] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A polymer solid electrolyte, characterized in that: It is composed of hydroxyapatite nanowires, fluoropolymers, and lithium salts; the hydroxyapatite nanowires are intertwined to form a three-dimensional network structure, and the fluoropolymers and lithium salts are distributed in the three-dimensional network structure; the fluoropolymers and the hydroxyapatite nanowires are connected by hydrogen bonds. The mass ratio of the fluoropolymer to the lithium salt is 1:(1~1.2). The mass ratio of the hydroxyapatite nanowires to the fluoropolymer is (1~15):100; The hydroxyapatite nanowires have a length of 500-600 nm and a diameter of 10-12 nm. The polymer solid electrolyte has the following characteristics: (a) Ionic conductivity is 0.9~2.2×10 -4 S / cm; (b) Ion transport number is 0.45–0.65; (c) The electrochemical window is 4.7~4.8V; (d) Tensile strength is 0.9~1MPa; (e) The fracture strain is 114~120%; (f) The self-extinguishing time after combustion shall not exceed 3 s.

2. The polymer solid electrolyte according to claim 1, characterized in that: The fluoropolymer is selected from at least one of polyvinylidene fluoride-hydrofluoric acid copolymer, polytetrafluoroethylene, polychlorotrifluoroethylene, and polyvinylidene fluoride; And / or, the lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, and lithium tetrafluoroborate.

3. The method for preparing the polymer solid electrolyte according to any one of claims 1 to 2, characterized in that: Includes the following steps: S1: Mix oleate, calcium salt and dihydrogen phosphate, and then hydrothermally react at 190~210℃ for 30~40h to obtain hydroxyapatite nanowires; S2: The hydroxyapatite nanowires are dispersed in a solvent and then mixed with a fluorinated polymer and a lithium salt to prepare an electrolyte solution; S3: Form the electrolyte solution into a film to obtain the polymer solid electrolyte.

4. A lithium metal battery, characterized in that: Includes a positive electrode, a negative electrode, and a polymer solid electrolyte as described in any one of claims 1 to 2.

5. The lithium metal battery according to claim 4, characterized in that: The positive electrode is made of NCM811 material.

6. The application of the polymer solid electrolyte according to any one of claims 1 to 2 in a battery.

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