A modified sepiolite fiber and its preparation method and a flame-retardant composite polymer solid electrolyte membrane and its preparation method and application

Abstract

The present invention provides a modified sepiolite fiber, a preparation method thereof, a flame-retardant composite polymer solid electrolyte membrane, a preparation method thereof and an application, relating to the technical field of lithium-ion batteries. In the present invention, sepiolite fiber, aluminum hydroxide, phosphoric acid and water are mixed to carry out a heterogeneous precipitation reaction under the condition that the pH value is 4-5 to obtain sepiolite fiber coated with aluminum phosphate; the sepiolite fiber coated with aluminum phosphate is surface-modified with calcium stearate in an alcohol solvent to obtain the modified sepiolite fiber. The composite polymer solid electrolyte membrane prepared from the prepared modified sepiolite fiber and polyethylene oxide has good electrochemical performance, and its ionic conductivity can reach up to 2.39×10<supgt;‑5< / supgt; S·cm<supgt;‑1< / supgt>. At the same time, the flame-retardant performance of the composite polymer solid electrolyte membrane is improved, that is, the obtained polyethylene oxide-based composite solid electrolyte membrane has both good electrochemical performance and flame-retardant performance, and is a high-safety composite polymer solid electrolyte membrane.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a modified sepiolite fiber and a preparation method thereof, and a flame retardant composite polymer solid electrolyte membrane and a preparation method and application thereof. Background Art

[0002] In recent years, solid polymer electrolytes have attracted much attention due to their convenient processing, good flexibility, and low contact resistance. However, they have low production, high cost, low ionic conductivity, and flammable organic components, which pose safety risks. Polyethylene oxide (PEO) is considered to be an ideal matrix material for building composite polymer electrolytes because it is non-toxic, has strong negative electrode stability of ether groups, and is not easy to react with negative ions in lithium salts. However, as a polymer matrix material, PEO still has problems such as low ionic conductivity, narrow electrochemical stability window, and poor mechanical strength. In addition, its main component is polyether chain forging. Theoretically calculated limiting oxygen index (LOI) of PEO is about 17.5%, which is a flammable organic polymer, which seriously limits its application range. Summary of the invention

[0003] In view of this, the present invention aims to provide a modified sepiolite fiber and a preparation method thereof, and a flame-retardant composite polymer solid electrolyte membrane and a preparation method and application thereof. The polyethylene oxide solid electrolyte membrane prepared from the modified sepiolite fiber provided by the present invention has both good electrochemical properties and flame retardant properties and high safety.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The present invention provides a method for preparing modified sepiolite fiber, comprising the following steps:

[0006] The sepiolite fiber, aluminum hydroxide, phosphoric acid and water are mixed, and a heterogeneous precipitation reaction is carried out at a pH value of 4 to 5 to obtain the aluminum phosphate-coated sepiolite fiber;

[0007] The aluminum phosphate coated sepiolite fiber, calcium stearate and an alcohol solvent are mixed to carry out a surface modification reaction to obtain the modified sepiolite fiber.

[0008] Preferably, the mass ratio of the sepiolite fiber, aluminum hydroxide and phosphoric acid is (4-10): (0.5-1): (5-15).

[0009] Preferably, the specific operation of the homogeneous precipitation reaction is:

[0010] mixing sepiolite fibers with water to obtain a sepiolite fiber dispersion;

[0011] Adding hydrochloric acid dropwise into the sepiolite fiber dispersion to adjust the pH value to 2-3 to obtain an acidified sepiolite fiber dispersion;

[0012] Aluminum hydroxide, phosphoric acid and water are mixed, and the obtained mixed solution is added into the acidified sepiolite fiber dispersion; then ammonia water is added dropwise to carry out a heterogeneous precipitation reaction under the condition of pH value of 4-5.

[0013] Preferably, the heterogeneous precipitation reaction time is 30 to 50 minutes; the heterogeneous reaction is carried out under stirring conditions, and the stirring rate is 800 to 1000 r / min.

[0014] Preferably, the mass ratio of the aluminum phosphate-coated sepiolite fiber to calcium stearate is (4-5): (0.02-0.1).

[0015] Preferably, the temperature of the surface modification reaction is 70-80° C., and the time is 30-50 min; the surface modification reaction is carried out under stirring, and the stirring rate is 500-800 r / min.

[0016] The present invention provides modified sepiolite fibers prepared by the preparation method described in the above technical solution, wherein the modified sepiolite fibers are coated sepiolite fibers modified by calcium stearate, and the coated sepiolite fibers are aluminum phosphate coated sepiolite fibers.

[0017] The present invention provides a flame-retardant composite polymer solid electrolyte membrane, the components of which include modified sepiolite fiber, lithium salt and polyethylene oxide, wherein the modified sepiolite fiber is the modified sepiolite fiber described in the above technical solution;

[0018] The ratio of the molar number of EO in the polyethylene oxide to the molar number of lithium ions in the lithium salt is 16-20:0.5-1; the mass of the modified sepiolite fiber is 1-20% of the mass of the polyethylene oxide.

[0019] The present invention provides a method for preparing the flame-retardant composite polymer solid electrolyte membrane described in the above technical solution, comprising the following steps:

[0020] The modified sepiolite fiber, lithium salt, polyethylene oxide and an organic solvent are mixed to obtain a glue solution;

[0021] The glue solution is subjected to film-forming to obtain the flame-retardant composite polymer electrolyte membrane.

[0022] The present invention provides the use of the flame-retardant composite polymer solid electrolyte membrane described in the above technical solution or the flame-retardant composite polymer solid electrolyte membrane prepared by the preparation method described in the above technical solution in a lithium ion battery.

[0023] The present invention provides a method for preparing modified sepiolite fiber, comprising the following steps: mixing sepiolite fiber, aluminum hydroxide, phosphoric acid and water, and performing a heterogeneous precipitation reaction under a pH value of 4 to 5 to obtain aluminum phosphate coated sepiolite fiber; mixing the aluminum phosphate coated sepiolite fiber, calcium stearate and an alcohol solvent to perform a surface modification reaction to obtain the modified sepiolite fiber. In the present invention, the sepiolite fiber has a large ion channel. On the one hand, the filler interacts with the polymer, especially the nano-scale particles can be dispersed between the polymer molecules, affecting the phase composition of the polymer electrolyte at room temperature, increasing the amorphous phase content of the system, and improving the creeping ability of the molecular chain segment; on the other hand, the filler acts as a Lewis acid and lithium salt anion X - and react with Lewis bases such as O in PEO to reduce Li + -X - ion pairs, increasing the number of free carriers and weakening the O-Li + The interaction makes it easier for lithium ions to be transmitted, thereby increasing the ionic conductivity, and can effectively improve the ionic conductivity of the polyethylene oxide solid electrolyte membrane; and the sepiolite fiber has excellent properties of high temperature resistance and flame retardancy, and can significantly improve the flame retardancy of the polymer composite material. The present invention can further improve the flame retardancy by coating the sepiolite fiber with aluminum phosphate, and give full play to the excellent properties of aluminum phosphate and sepiolite fiber respectively; but sepiolite is hydrophilic and oleophobic, and has poor compatibility with polyethylene oxide. The present invention uses calcium stearate to perform surface organic modification on the aluminum phosphate-coated sepiolite fiber to improve the compatibility of the sepiolite fiber with polyethylene oxide.

[0024] The present invention provides a modified sepiolite fiber prepared by the preparation method described in the above technical solution, wherein the modified sepiolite fiber is a coated sepiolite fiber modified by calcium stearate, and the coated sepiolite fiber is an aluminum phosphate coated sepiolite fiber. The polyethylene oxide polymer solid electrolyte membrane prepared by the modified sepiolite fiber provided by the present invention has good electrochemical properties, and its ionic conductivity can reach up to 2.39×10 -5 S cm -1 , and at the same time improves the flame retardant properties of the composite polymer electrolyte membrane, that is, the obtained polyethylene oxide polymer solid electrolyte membrane has both good electrochemical properties and flame retardant properties, and is a high-safety composite polymer solid electrolyte membrane. The button-type lithium ion battery assembled using the polyethylene oxide polymer solid electrolyte membrane not only has a high initial capacity, but also has high charge and discharge efficiency and good cycle performance. The present invention provides a new approach and idea for the preparation of solid electrolytes and high-safety lithium ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1The pure sepiolite fiber (SEP) and the aluminum phosphate coated sepiolite fiber (SEP@AlPO 4 ) scanning electron microscopy (SEM), transmission electron microscopy (TEM) and elemental analysis diagrams; Figure 1 (a) is the SEM image of pure SEP, (b) is the SEP@AlPO 4 SEM image of (c) SEP@AlPO 4 TEM image of (d) SEP@AlPO 4 Elemental analysis diagram of

[0026] Figure 2 The pure sepiolite fiber (SEP) and the aluminum phosphate coated sepiolite fiber (SEP@AlPO 4 )’s XPS spectrum;

[0027] Figure 3 For different Al(OH) in Examples 1 to 3 3 and H 3 PO 4 XRD curve of mass ratio coated sepiolite fiber;

[0028] Figure 4 Pure SEP, calcium stearate (CaSt 2 ) and SEP@AlPO before and after calcium stearate modification in Example 6 4 Infrared spectrum of

[0029] Figure 5 The pure PEO film in Comparative Example 1, the PEO / LiTFSI composite film in Comparative Example 2, and the PEO / LiTFSI / m-SEP@AlPO in Examples 7 to 10 4 XRD spectrum and DSC curve of composite electrolyte membrane, Figure 5 (a) is the XRD spectrum, (b) is the DSC curve;

[0030] Figure 6 The AC impedance spectra of the electrolyte membranes prepared in Examples 7 to 10 and Comparative Example 2 are shown in FIG. Figure 6 (a) is the AC impedance spectrum of the blocked cell, and (b) is the AC impedance spectrum of the full cell;

[0031] Figure 7 Microcalorimeter curves of the PEO electrolyte membranes prepared in Examples 7 to 10 and Comparative Examples 1 to 2;

[0032] Figure 8 The PEO / LiTFSI electrolyte membrane prepared in Comparative Example 2 and the PEO / LiTFSI / m-SEP@AlPO prepared in Example 8 4 10 SEM photos of electrolyte membranes, Figure 8 (a) is the SEM image of PEO / LiTFSI electrolyte membrane, (b) is the SEM image of PEO / LiTFSI / m-SEP@AlPO 4 10 SEM images of electrolyte membranes, (c) PEO / LiTFSI / m-SEP@AlPO 4 10 Cross-sectional photo of the electrolyte membrane. DETAILED DESCRIPTION

[0033] The present invention provides a method for preparing modified sepiolite fiber, comprising the following steps:

[0034] The sepiolite fiber, aluminum hydroxide, phosphoric acid and water are mixed, and a heterogeneous precipitation reaction is carried out at a pH value of 4 to 5 to obtain the aluminum phosphate-coated sepiolite fiber;

[0035] The aluminum phosphate coated sepiolite fiber, calcium stearate and an alcohol solvent are mixed to carry out a surface modification reaction to obtain the modified sepiolite fiber.

[0036] In the present invention, unless otherwise specified, the raw materials involved are commercially available products well known to those skilled in the art.

[0037] The present invention mixes sepiolite fiber, aluminum hydroxide, phosphoric acid and water, and performs a heterogeneous precipitation reaction under the condition of pH value of 4 to 5 to obtain aluminum phosphate coated sepiolite fiber. In the present invention, the specification of the phosphoric acid is preferably analytical grade; the mass ratio of the sepiolite fiber, aluminum hydroxide and phosphoric acid is preferably (4 to 10): (0.5 to 1): (5 to 15), and more preferably (4 to 8.5): 1: (6 to 8).

[0038] In the present invention, the specific operation of the heterogeneous precipitation reaction is preferably:

[0039] (a) mixing sepiolite fibers with water to obtain a sepiolite fiber dispersion;

[0040] (b) adding hydrochloric acid dropwise to the sepiolite fiber dispersion to adjust the pH value to 2-3 to obtain an acidified sepiolite fiber dispersion;

[0041] (c) mixing aluminum hydroxide, phosphoric acid and water, and adding the resulting mixed solution into the acidified sepiolite fiber dispersion; then dripping ammonia water to carry out a heterogeneous precipitation reaction at a pH value of 4 to 5.

[0042] In the present invention, the sepiolite fiber is preferably washed, dried and ground in sequence before use; the washing is preferably carried out with deionized water under ultrasonic oscillation to remove impurities; the drying temperature is preferably 50-60°C, and the drying time is based on drying to constant weight; the grinding is based on grinding to powder. In the present invention, the dosage ratio of sepiolite fiber to water in the step (a) is preferably 10g:160mL, and the mixing of the sepiolite fiber and water is preferably carried out at room temperature and under stirring, based on the uniform dispersion of the sepiolite fiber in the water. In the present invention, the mass fraction of hydrochloric acid in the step (b) is preferably 37%. In the present invention, the ratio of the total mass of aluminum hydroxide and phosphoric acid to the volume of water in the step (c) is preferably (9.84-19.66)g:10mL; the mixing of aluminum hydroxide, phosphoric acid and water is preferably carried out at room temperature and under stirring. In the present invention, the time of the heterogeneous precipitation reaction is preferably 30 to 50 minutes, more preferably 30 to 40 minutes; the heterogeneous precipitation reaction is preferably carried out under stirring, and the stirring rate is preferably 800 to 1000 r / min. The present invention slowly precipitates aluminum phosphate on the surface of sepiolite fiber by carrying out heterogeneous precipitation reaction under vigorous stirring. The present invention utilizes the characteristics of easy condensation and dehydration of P-OH in the molecular structure of aluminum phosphate, and adopts heterogeneous precipitation method to coat aluminum phosphate precipitate on the surface of nano-fibrous sepiolite.

[0043] In the present invention, after the heterogeneous precipitation reaction is completed, the obtained reaction system is preferably subjected to solid-liquid separation, solid phase water washing, drying and grinding in sequence; the solid-liquid separation method is preferably vacuum filtration, the water washing is preferably carried out with deionized water, the drying temperature is preferably 60-80°C; the grinding is based on grinding to powder.

[0044] After obtaining the aluminum phosphate coated sepiolite fiber, the present invention mixes the aluminum phosphate coated sepiolite fiber, calcium stearate and an alcohol solvent for surface modification reaction to obtain the modified sepiolite fiber. In the present invention, the alcohol solvent is preferably anhydrous ethanol; the mass ratio of the aluminum phosphate coated sepiolite fiber and calcium stearate is preferably (4-5): (0.02-0.1), more preferably 4: (0.02-0.08); the mass ratio of the aluminum phosphate coated sepiolite fiber and the alcohol solvent is preferably 4g: 30mL. In the present invention, the temperature of the surface modification reaction is preferably 70-80°C, more preferably 70-75°C, the time is preferably 30-50min, more preferably 30-40min; the surface modification reaction is carried out under stirring, and the stirring rate is preferably 500-800r / min. After the surface modification reaction, the present invention preferably sequentially performs solid-liquid separation, solid-phase alcohol washing, drying and grinding on the obtained modified liquid to obtain modified sepiolite fiber; the solid-liquid separation method is preferably suction filtration; the alcohol reagent used in the alcohol washing is preferably anhydrous ethanol, and the number of alcohol washings is preferably 2 to 3 times; the drying temperature is preferably 50 to 70°C, more preferably 60°C, and the drying time is preferably 10 to 15h, more preferably 12h; and the grinding is based on grinding to a fine powder.

[0045] The present invention provides a modified sepiolite fiber prepared by the preparation method described in the above technical solution, wherein the modified sepiolite fiber is a coated sepiolite fiber modified by calcium stearate, and the coated sepiolite fiber is an aluminum phosphate coated sepiolite fiber. In the present invention, the sepiolite fiber has a large ion channel. On the one hand, the filler interacts with the polymer, especially the nano-scale particles can be dispersed between the polymer molecules, affecting the phase composition of the polymer electrolyte at room temperature, increasing the amorphous phase content of the system, and improving the creeping ability of the molecular chain segment; on the other hand, the filler acts as a Lewis acid and lithium salt anion X - and react with Lewis bases such as O in PEO to reduce Li + -X - The ion pairs increase the number of free carriers and weaken the O-Li + The interaction makes it easier for lithium ions to be transmitted, thereby increasing the ionic conductivity, and can effectively improve the ionic conductivity of the polyethylene oxide polymer solid electrolyte membrane, and the sepiolite fiber has excellent high temperature resistance and flame retardant properties, which can significantly improve the flame retardancy of the polymer composite material; the present invention can further improve the flame retardant property by coating the sepiolite fiber with aluminum phosphate, and give full play to the excellent properties of aluminum phosphate and sepiolite fiber; but sepiolite exhibits hydrophilicity and oleophobicity, and has poor compatibility with polyethylene oxide. The present invention uses calcium stearate to perform surface organic modification on the aluminum phosphate-coated sepiolite fiber to improve the compatibility of the sepiolite fiber with polyethylene oxide.

[0046] The present invention provides a flame-retardant composite polymer solid electrolyte membrane, the components of which include modified sepiolite fiber, lithium salt and polyethylene oxide, wherein the modified sepiolite fiber is the modified sepiolite fiber described in the above technical solution. In the present invention, the lithium salt is preferably lithium bis(trifluoromethanesulfonyl imide); the ratio of the molar number of EO in the polyethylene oxide to the molar number of lithium ions in the lithium salt is 16 to 20:0.5 to 1, preferably 20:1; the mass of the modified sepiolite fiber is 1 to 20% of the mass of the polyethylene oxide, preferably 5 to 20%, and more preferably 10 to 15%. The polyethylene oxide polymer solid electrolyte membrane provided by the present invention has good electrochemical properties, and its ionic conductivity can reach up to 2.39×10 -5 S cm -1 , and at the same time has improved flame retardant properties, that is, the obtained polyethylene oxide polymer solid electrolyte membrane has both good electrochemical properties and flame retardant properties, and is a high-safety composite polymer solid electrolyte membrane.

[0047] The present invention provides a method for preparing the flame-retardant composite polymer electrolyte membrane described in the above technical solution, comprising the following steps:

[0048] The modified sepiolite fiber, lithium salt, polyethylene oxide and an organic solvent are mixed to obtain a glue solution;

[0049] The glue solution is subjected to film-forming to obtain the flame-retardant composite polymer electrolyte membrane.

[0050] In the present invention, the organic solvent is preferably acetonitrile; the mixing is preferably: the modified sepiolite fiber is first mixed with the organic solvent, and lithium salt and polyethylene oxide are added to the obtained dispersion for second mixing; the first mixing is preferably carried out under ultrasonic conditions; the second mixing is preferably carried out under stirring conditions, and a uniform glue solution is obtained after the second mixing. In the present invention, the film forming method is preferably: pouring the glue solution into a polytetrafluoroethylene mold, standing until the organic solvent is completely volatilized, and then demolding to obtain a flame-retardant composite polymer electrolyte membrane. In the present invention, the thickness of the flame-retardant composite polymer electrolyte membrane is preferably 50 to 80 μm, more preferably 70 to 80 μm.

[0051] The present invention provides the use of the flame-retardant composite polymer electrolyte membrane described in the above technical solution or the flame-retardant composite polymer electrolyte membrane prepared by the preparation method described in the above technical solution in a lithium-ion battery. The present invention has no special requirements for the type of the lithium-ion battery; the present invention has no special requirements for the application method, and the application method familiar to those skilled in the art can be used. The lithium-ion battery assembled using the flame-retardant composite polymer electrolyte membrane not only has a high initial capacity, but also has a high charge and discharge efficiency and good cycle performance.

[0052] The modified sepiolite fiber and its preparation method and the flame-retardant composite polymer solid electrolyte membrane and its preparation method and application provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0053] Example 1

[0054] Preparation of aluminum phosphate coated sepiolite fibers:

[0055] Weigh a certain amount of sepiolite fiber, disperse it evenly with deionized water by ultrasonic oscillation, filter and wash it several times to remove some impurities; dry the washed sepiolite in a 60°C oven, and then grind it into powder for use. Weigh 10g of sepiolite powder and disperse it in 160mL of deionized water, stir it evenly with magnetic stirring to obtain a sepiolite fiber dispersion; then use 37% hydrochloric acid to adjust the pH value of the dispersion to about 2 to obtain an acidified sepiolite fiber dispersion for use. Weigh 2.33gAl(OH) 3 and 17.33 g H 3 PO 4 Pour into a beaker, add 10 mL of ultrapure water, add the resulting mixture to the acidified sepiolite fiber dispersion, then add ammonia solution dropwise by magnetic stirring to adjust the pH value to about 4.8 to produce phosphate precipitate, filter, wash with deionized water, and dry at 60 ° C to obtain aluminum phosphate-coated sepiolite fibers (denoted as SEP@AlPO 4 Ⅰ).

[0056] The aluminum phosphate-coated sepiolite fiber prepared in Example 1 was subjected to scanning electron microscopy (SEM), transmission electron microscopy (TEM), elemental analysis and X-ray photoelectron spectroscopy (XPS) analysis. The test results are as follows: Figure 1 and Figure 2 shown.

[0057] Pure sepiolite fiber (SEP) and aluminum phosphate coated sepiolite fiber SEP@AlPO prepared in Example 1 4 The scanning electron microscope pictures are as follows Figure 1 As shown in (a) and (b), SEP@AlPO 4 Transmission electron microscopy (TEM) Figure 1 As shown in (c). Figure 1 As shown in (a), sepiolite is fibrous and has a relatively smooth surface. After the introduction of aluminum phosphate, Figure 1 As can be seen from (b) and (c), a large number of aluminum phosphate particles are evenly dispersed on the SEP surface, indicating that aluminum phosphate has successfully coated the sepiolite fiber. 4 The elemental analysis of Figure 1As shown in (c), elemental analysis shows that AlPO also exists on the surface of SEP. 4 The content of Al and P in the particles is 19%. Figure 2 Pure SEP and SEP@AlPO 4 The XPS spectrum of SEP@AlPO 4 The electron energy spectrum peaks of P2p (134 eV) and Al2p (75 eV) appeared, indicating that AlPO 4 Successfully coated on sepiolite fiber.

[0058] Example 2

[0059] Preparation of aluminum phosphate coated sepiolite fibers:

[0060] Weigh a certain amount of sepiolite fiber, disperse it evenly with deionized water by ultrasonic oscillation, and filter and wash it several times to remove some impurities. Dry the washed sepiolite in a 60°C oven, and then grind it into powder for use. Weigh 10g of sepiolite powder and disperse it in 160mL of deionized water, stir it evenly with magnetic stirring to obtain a sepiolite fiber dispersion; then adjust the pH value of the dispersion to about 2 with 37% hydrochloric acid to obtain an acidified sepiolite fiber dispersion for use. Weigh 1.75gAl(OH) 3 and 13g H 3 PO 4 Pour into a beaker, add 10 mL of ultrapure water, add the resulting mixture to the acidified sepiolite fiber dispersion, then add ammonia solution dropwise by magnetic stirring to adjust the pH value to about 4.8 to produce phosphate precipitate, filter, wash with deionized water, and dry at 60 ° C to obtain aluminum phosphate-coated sepiolite fibers (denoted as SEP@AlPO 4 Ⅱ).

[0061] Example 3

[0062] Weigh a certain amount of sepiolite fiber, disperse it evenly with deionized water by ultrasonic oscillation, and filter and wash it several times to remove some impurities. Dry the washed sepiolite in a 60°C oven, and then grind it into powder for use. Weigh 10g of sepiolite powder and disperse it in 160mL of deionized water, stir it evenly with magnetic stirring to obtain a sepiolite fiber dispersion; then adjust the pH value of the dispersion to about 2 with 37% hydrochloric acid to obtain an acidified sepiolite fiber dispersion for use. Weigh 1.17gAl(OH) 3 and 8.67 g H 3 PO 4Pour into a beaker, add 10 mL of ultrapure water, add the resulting mixture to the acidified sepiolite fiber dispersion, then add ammonia solution dropwise by magnetic stirring to adjust the pH value to about 4.8 to produce phosphate precipitate, filter, wash with deionized water, and dry at 60 ° C. Grind to obtain aluminum phosphate-coated sepiolite fibers (denoted as SEP@AlPO 4 Ⅲ).

[0063] Figure 3 For example 1, example 2, example 3 different Al (OH) 3 and H 3 PO 4 XRD curve of the mass ratio-coated sepiolite fiber. Figure 3 It can be seen that SEP has a characteristic diffraction peak at 2θ=10.5°, and AlPO 4 The characteristic diffraction peak of AlPO is 2θ=13.7°, and with the 4 The corresponding SEP@AlPO 4 The peak intensity of AlPO increases, which further indicates that 4 The particles were successfully coated on the SEP surface.

[0064] Example 4

[0065] Preparation of modified coated sepiolite fiber:

[0066] Weigh 4 g of SEP@AlPO prepared in Example 1 4 , 30 mL of anhydrous ethanol and 0.02 g of calcium stearate were added to a three-necked flask, and then the three-necked flask was placed in an oil bath, stirred at 70 ° C for 30 min, then cooled to room temperature, taken out and vacuum filtered, the filter cake was washed with anhydrous ethanol 2 to 3 times, and the filter cake was placed in a 60 ° C oven for 12 h. After drying, it was ground into fine powder with a mortar to obtain modified coated sepiolite fiber (denoted as m-SEP@AlPO 4 ), put it in a sealed bag for storage.

[0067] Example 5

[0068] Weigh 4 g of SEP@AlPO prepared in Example 1 4 , 30 mL of anhydrous ethanol and 0.04 g of calcium stearate were added to a three-necked flask, and then the three-necked flask was placed in an oil bath, stirred at 70 ° C for 30 min, then cooled to room temperature, taken out and vacuum filtered, the filter cake was washed with anhydrous ethanol 2 to 3 times, and the filter cake was placed in a 60 ° C oven for 12 h. After drying, it was ground into fine powder with a mortar to obtain modified coated sepiolite fiber (denoted as m-SEP@AlPO 4 ), put it in a sealed bag for storage.

[0069] Example 6

[0070] Weigh 4 g of SEP@AlPO prepared in Example 1 4 , 30 mL of anhydrous ethanol and 0.08 g of calcium stearate were added to a three-necked flask, and then the three-necked flask was placed in an oil bath, stirred at 70 ° C for 30 min, then cooled to room temperature, taken out and vacuum filtered, the filter cake was washed with anhydrous ethanol 2 to 3 times, and the filter cake was placed in a 60 ° C oven for drying for 12 h. After drying, it was ground into fine powder with a mortar to obtain modified coated sepiolite fiber (denoted as m-SEP@AlPO 4 ), put it in a sealed bag for storage.

[0071] Figure 4 Pure SEP, calcium stearate (CaSt 2 ) and SEP@AlPO before and after calcium stearate modification in Example 6 4 Infrared spectrum of Figure 4 It can be seen that pure sepiolite is at 3673cm -1 The stretching vibration peak of sepiolite hydroxyl (-OH) appears; 900cm -1 ~1100cm -1 1030cm of the spectrum -1 、972cm -1 、930cm -1 The asymmetric stretching diffraction peak of Si-O-Si bond appears at 765cm -1 With 798cm -1 Symmetrical stretching vibration of Si-O-Si bond occurs. Calcium stearate has a peak at 1541 cm -1 、1575cm -1 By comparing the spectra before and after coating, it was found that after aluminum phosphate coated sepiolite, the peak at 3673 cm -1 The characteristic peak intensity of -OH and Si-O-Si bond of sepiolite at the modified SEP@AlPO 4 Calcium stearate 1541cm -1 、1575cm -1 The characteristic peaks at , indicating that calcium stearate successfully 4 Modified.

[0072] Example 7

[0073] Preparation of composite polymer electrolyte membrane:

[0074] 0.025 g (5%) of the modified coated sepiolite fiber prepared in Example 6 was weighed and dispersed in 20 mL of acetonitrile solution. After ultrasonic oscillation for 0.5 h, the fiber was transferred to a glove box and stirred for 1 h. Then, 0.16 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 0.5 g of polyethylene oxide (PEO) (n(EO): n(Li + )=20:1) was added to the above solution and stirred for 5 hours to form a uniform glue solution; the obtained glue solution was poured into a polytetrafluoroethylene mold and allowed to stand for 12 hours until the acetonitrile was completely volatilized, and the prepared electrolyte membrane was removed from the mold with a thickness of about 70-80 μm, which was recorded as PEO / LiTFSI / m-SEP@AlPO 4 5.

[0075] Example 8

[0076] Preparation of composite polymer electrolyte membrane:

[0077] 0.05 g (10%) of the modified coated sepiolite fiber prepared in Example 6 was weighed and dispersed in 20 mL of acetonitrile solution. After ultrasonic oscillation for 0.5 h, the fiber was transferred to a glove box and stirred for 1 h. Then, 0.16 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 0.5 g of polyethylene oxide (PEO) (n(EO): n(Li + )=20:1) was added to the above solution and stirred for 5 hours to form a uniform glue solution; the obtained glue solution was poured into a polytetrafluoroethylene mold and allowed to stand for 12 hours until the acetonitrile was completely volatilized, and the prepared electrolyte membrane was removed from the mold with a thickness of about 70-80 μm, which was recorded as PEO / LiTFSI / m-SEP@AlPO 4 10.

[0078] Example 9

[0079] Preparation of composite polymer electrolyte membrane:

[0080] 0.075 g (15%) of the modified coated sepiolite fiber prepared in Example 6 was weighed and dispersed in 20 mL of acetonitrile solution. After ultrasonic oscillation for 0.5 h, the fiber was transferred to a glove box and stirred for 1 h. Then, 0.16 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 0.5 g of polyethylene oxide (PEO) (n(EO): n(Li + )=20:1) was added to the above solution and stirred for 5 hours to form a uniform glue solution; the obtained glue solution was poured into a polytetrafluoroethylene mold and allowed to stand for 12 hours until the acetonitrile was completely volatilized, and the prepared electrolyte membrane was removed from the mold with a thickness of about 70-80 μm, which was recorded as PEO / LiTFSI / m-SEP@AlPO 4 15.

[0081] Example 10

[0082] Preparation of composite polymer electrolyte membrane:

[0083] 0.1 g (20%) of the modified coated sepiolite fiber prepared in Example 6 was weighed and dispersed in 20 mL of acetonitrile solution. After ultrasonic oscillation for 0.5 h, the fiber was transferred to a glove box and stirred for 1 h. Then, 0.16 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 0.5 g of polyethylene oxide (PEO) (n(EO): n(Li + )=20:1) was added to the above solution and stirred for 5 hours to form a uniform glue solution; the obtained glue solution was poured into a polytetrafluoroethylene mold and allowed to stand for 12 hours until the acetonitrile was completely volatilized, and the prepared electrolyte membrane was removed from the mold with a thickness of about 70-80 μm, which was recorded as PEO / LiTFSI / m-SEP@AlPO 4 20.

[0084] Comparative Example 1

[0085] Preparation of PEO membrane:

[0086] Weigh 0.5 g of polyethylene oxide (PEO) and add it to 20 mL of acetonitrile. Stir in a glove box for 5 h to form a uniform glue solution. Pour the obtained glue solution onto a polytetrafluoroethylene mold and let it stand for 12 h until the acetonitrile is completely evaporated. Remove the prepared electrolyte membrane from the mold. The thickness is about 70 to 80 μm. Put it into a sealed bag and place it in the glove box for use.

[0087] Comparative Example 2

[0088] Preparation of PEO / LiTFSI composite membrane:

[0089] Weigh 0.16 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 0.5 g of polyethylene oxide (PEO) (n(EO): n(Li + )=20:1) was added into 20mL acetonitrile and stirred in a glove box for 5h to form a uniform glue solution; the obtained glue solution was poured into a polytetrafluoroethylene mold and allowed to stand for 12h until the acetonitrile was completely evaporated, and the prepared electrolyte membrane was removed from the mold with a thickness of about 70-80μm.

[0090] The electrolyte membranes prepared in Examples 7 to 10 and Comparative Example 2 were assembled into button cells:

[0091] Use a manual punching machine to cut the electrolyte membrane into discs with a diameter of 18 mm and 15 mm, put them into a sealed bag and place them in a glove box for standby use. In the glove box, place the positive electrode shell flat on the insulating table, place the positive electrode sheet on the upper layer of the positive electrode shell, then place the electrolyte membrane on the positive electrode sheet, place the metal lithium sheet on the electrolyte membrane, and then place the steel sheet, spring sheet in turn and finally cover the negative electrode shell. Use a paper towel to test the surface of the battery, and finally use tweezers to clamp the battery with the positive electrode facing up into the mold of the battery sealing machine, adjust the pressure to 900Pa, press for 5s, and use tweezers to clamp the assembled battery out to obtain a CR2032 full battery. At the same time, place the cut electrolyte membrane between the gaskets, encapsulate it with the positive and negative electrode shells to obtain a blocked battery, and store the assembled battery in the glove box for standby use. For the assembled blocked battery, the electrochemical performance and charge and discharge characterization tests of the full battery are carried out.

[0092] In the preparation process of the composite polymer electrolyte membrane and button cell thereof, the positive electrode material of the lithium ion battery in the embodiment and the comparative example is lithium iron phosphate (LiFePO 4 ), the assembly order is: negative electrode shell / shrapnel / stainless steel sheet / lithium sheet / polyethylene oxide solid electrolyte / LiFePO 4 / Positive electrode shell.

[0093] The ionic conductivity was tested by AC impedance method: AC impedance test was performed at 60°C using an electrochemical workstation; the ionic conductivity σ of the polyoxyethylene solid electrolyte was calculated using the formula σ=t / RA through the AC impedance spectrum obtained by the test. Among them, t is the thickness of the electrolyte membrane, R is the resistance of the electrolyte membrane, and A is the cross-sectional area of ​​the electrolyte membrane.

[0094] Figure 5 The pure PEO film in Comparative Example 1, the PEO / LiTFSI composite film in Comparative Example 2, and the PEO / LiTFSI / m-SEP@AlPO in Examples 7 to 10 4 XRD spectrum and DSC curve of composite electrolyte membrane, Figure 5 (a) is the XRD spectrum, (b) is the DSC curve. Figure 5 As can be seen in (a), the PEO molecular chains are arranged in a spiral shape to form a single crystal. The PEO characteristic peaks of pure PEO and lithium salt film are basically consistent. PEO characteristic peaks appear at 2θ = 19° and 23°, where 19° corresponds to the (120) crystal plane and 23° corresponds to the (032) and (112) crystal planes, indicating that the PEO structure has not changed. By comparing PEO / LiTFSI with different m-SEP@AlPO 4 From the XRD spectrum of the electrolyte membrane with a content of 2.5, it can be found that after adding inorganic fillers, strong sepiolite characteristic diffraction peaks appear at 2θ=10.3°, 11.5°, 28.3° and 30.8°, which are the main components of sepiolite, Mg 4 Si 6 O15 (OH) 2 6H 2 O diffraction peaks, these diffraction peaks increase with the increase of m-SEP@AlPO 4 At the same time, at 2θ = 19° and 23°, it can be found that with the increase of m-SEP@AlPO 4 As the filling amount increases, the characteristic peak here attenuates, which indicates that m-SEP@AlPO 4 The interaction with PEO reduced the characteristic peak intensity of PEO. In addition, the addition of m-SEP@AlPO 4 The increase of its relative content will not cause a significant change in the position of the characteristic peak of PEO. 4 The introduction of significantly changes the crystallization characteristics of PEO, which may lead to changes in the physicochemical properties of the film.

[0095] Figure 5 (b) and Table 1 are different m-SEP@AlPO 4 PEO / LiTFSI / m-SEP@AlPO 4 DSC curves and data of composite electrolyte membrane. Figure 5 In (b), it can be seen that the glass transition temperature of each composite film is around -50°C and the melting temperature is around 60°C; the difference between the composite film with added lithium salt and the one without added lithium salt is obvious. 4 The melting temperature of the composite membrane was partially reduced. 4 As the content of m-SEP@AlPO increases, the melting temperature does not change much. From the crystallinity data in Table 1, it can be seen that when m-SEP@AlPO 4 When the addition content is 10%, m-SEP@AlPO 4 The inhibition of the crystallization of the composite film is most obvious. m-SEP@AlPO 4 The addition of has a certain inhibitory effect on the crystallization of the composite film.

[0096] Table 1 DSC data of composite polymer electrolyte membrane

[0097]

[0098] Figure 6 Table 2 shows the AC impedance spectra and ionic conductivity of the electrolyte membranes prepared in Examples 7 to 10 and Comparative Example 2 at 60°C. Figure 6 (a) is the AC impedance spectrum of the blocked battery, and (b) is the AC impedance spectrum of the full battery. Figure 6 As can be seen from (a) and Table 2, adding different contents of m-SEP@AlPO 4The impedance value of the post-blocking battery has a tendency to decrease within a certain range, thereby improving the ionic conductivity. By comparing with PEO / LiTFSI, it is not difficult to see that the addition of inorganic fillers effectively improves the ionic conductivity of the composite electrolyte film. 4 When the addition amount of increases to 10%, the ionic conductivity of the composite electrolyte membrane is the largest. Figure 6 The impedance spectrum analysis of the whole cell assembled with PEO composite membrane in (b) and Table 2 shows that the addition of m-SEP@AlPO 4 After adding m-SEP@AlPO, the overall impedance of the whole battery has a decreasing trend, and the ionic conductivity is improved compared with PEO / LiTFSI, which is consistent with the conclusion of the blocked battery. 4 The ionic conductivity of the composite electrolyte film was effectively improved. This shows that increasing the content of the coated sepiolite fiber within a certain range is beneficial to reducing the impedance of the composite electrolyte membrane, thereby improving the ionic conductivity, effectively reducing the resistance of lithium ion transmission in the electrolyte, and reducing the internal resistance of the battery.

[0099] Table 2 PEO / LiTFSI / m-SEP@AlPO 4 Blocking cell impedance and ionic conductivity

[0100]

[0101] The CR2032 button cells (referred to as cells 1 to 5, respectively) assembled with the electrolyte membranes prepared in Examples 7 to 10 and Comparative Example 2 were subjected to constant current charge-discharge cycle tests, with a discharge rate of 0.2C, and the test results are shown in Table 3. As can be seen from Table 3, the lithium-ion battery prepared using the polyethylene oxide solid electrolyte provided by the present invention not only has a high initial capacity, but also has a high charge-discharge efficiency and good cycle performance.

[0102] Table 3 Constant current charge and discharge cycle test results of the batteries prepared in Examples 7 to 10 and Comparative Example 2

[0103]

[0104]

[0105] Figure 7 Table 4 shows the microcalorimeter curves and values ​​of the PEO electrolyte membranes prepared in Examples 7 to 10 and Comparative Examples 1 to 2. Figure 7 It can be seen that the peak heat release rate (PHRR) of the PEO composite film is higher than that of m-SEP@AlPO after adding lithium salt. 4 After that, there was a significant decrease. The total heat release (THR) increased with the increase of lithium salt and m-SEP@AlPO 4The addition of lithium salt and m-SEP@AlPO decreased to a certain extent, indicating that the coated sepiolite fiber improved the flame retardancy of PEO. The peak temperature of heat release rate (TPHRR) was significantly lower than that of m-SEP@AlPO. 4 The flame retardant properties of PEO film were effectively improved by 5% and 10% of m-SEP@AlPO. 4 The flame retardant properties of the electrolyte membrane decreased with the increase of the addition amount, indicating that the proper addition of m-SEP@AlPO 4 It is beneficial to improve the flame retardant properties of the electrolyte membrane and provides a new idea and theoretical basis for high-safety composite polymer electrolyte membranes.

[0106] Table 4 Microcalorimetric data of electrolyte membranes of Examples 7 to 10 and Comparative Examples 1 to 2

[0107]

[0108] Figure 8 The PEO / LiTFSI electrolyte membrane prepared in Comparative Example 2 and the PEO / LiTFSI / m-SEP@AlPO prepared in Example 8 4 10 SEM photos of electrolyte membranes, Figure 8 (a) is the SEM image of PEO / LiTFSI electrolyte membrane, (b) is the SEM image of PEO / LiTFSI / m-SEP@AlPO 4 10 SEM images of electrolyte membranes, (c) PEO / LiTFSI / m-SEP@AlPO 4 10 Cross-sectional photo of the electrolyte membrane. Figure 8 As can be seen from (a) and (b), the surface of the PEO / LiTFSI electrolyte membrane is smooth and uniform. 4 After the electrolyte membrane was exposed, fibrous sepiolite appeared on the surface, and the distribution was relatively uniform, and the surface was relatively uniform and flat. Figure 8 As can be seen in (c), the electrolyte membrane interface is uniform and the thickness of the prepared electrolyte membrane is about 70 μm.

[0109] It can be seen from the above examples that the polyethylene oxide polymer solid electrolyte membrane prepared by using the modified sepiolite fiber provided by the present invention has both good electrochemical properties and flame retardant properties and high safety.

[0110] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A flame retardant composite polymer solid electrolyte membrane, It is characterized in that The components include modified sepiolite fiber, lithium salt and polyethylene oxide, wherein the modified sepiolite fiber is a coated sepiolite fiber modified by calcium stearate, and the coated sepiolite fiber is an aluminum phosphate coated sepiolite fiber; The ratio of the molar number of EO in the polyethylene oxide to the molar number of lithium ions in the lithium salt is 16-20:0.5-1; The mass of the modified sepiolite fiber is 1 to 20% of the mass of polyethylene oxide; The preparation method of the modified sepiolite fiber comprises the following steps: The sepiolite fiber, aluminum hydroxide, phosphoric acid and water are mixed, and a heterogeneous precipitation reaction is carried out at a pH value of 4 to 5 to obtain the aluminum phosphate-coated sepiolite fiber; The aluminum phosphate coated sepiolite fiber, calcium stearate and an alcohol solvent are mixed to carry out a surface modification reaction to obtain the modified sepiolite fiber.

2. The flame-retardant composite polymer solid electrolyte membrane according to claim 1, It is characterized in that The mass ratio of the sepiolite fiber, aluminum hydroxide and phosphoric acid is (4-10): (0.5-1): (5-15).

3. The flame-retardant composite polymer solid electrolyte membrane according to claim 1 or 2, It is characterized in that The specific operation of the heterogeneous precipitation reaction is: mixing sepiolite fibers with water to obtain a sepiolite fiber dispersion; Adding hydrochloric acid dropwise into the sepiolite fiber dispersion to adjust the pH value to 2-3 to obtain an acidified sepiolite fiber dispersion; Aluminum hydroxide, phosphoric acid and water are mixed, and the obtained mixed solution is added into the acidified sepiolite fiber dispersion; then ammonia water is added dropwise to carry out a heterogeneous precipitation reaction under the condition of pH value of 4-5.

4. The flame-retardant composite polymer solid electrolyte membrane according to claim 3, It is characterized in that The heterogeneous precipitation reaction is carried out for 30 to 50 minutes; the heterogeneous precipitation reaction is carried out under stirring conditions, and the stirring rate is 800 to 1000 r / min.

5. The flame-retardant composite polymer solid electrolyte membrane according to claim 1, It is characterized in that The mass ratio of the aluminum phosphate-coated sepiolite fiber to calcium stearate is (4-5):(0.02-0.1).

6. The flame-retardant composite polymer solid electrolyte membrane according to claim 1 or 5, It is characterized in that The temperature of the surface modification reaction is 70-80° C., and the time is 30-50 min. The surface modification reaction is carried out under stirring, and the stirring rate is 500-800 r / min.

7. The method for preparing the flame-retardant composite polymer solid electrolyte membrane according to any one of claims 1 to 6, It is characterized in that The following steps are involved: The modified sepiolite fiber, lithium salt, polyethylene oxide and an organic solvent are mixed to obtain a glue solution; The glue solution is subjected to film-forming to obtain the flame-retardant composite polymer solid electrolyte membrane.

8. Use of the flame-retardant composite polymer solid electrolyte membrane according to any one of claims 1 to 6 or the flame-retardant composite polymer solid electrolyte membrane prepared by the preparation method according to claim 7 in lithium-ion batteries.

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