Solid electrolyte using electrostatic spinning fiber membrane as matrix, and preparation method and application thereof

Abstract

The invention discloses a solid electrolyte using an electrostatic spinning fiber membrane as a matrix and a preparation method and application thereof, and the preparation method of the solid electrolyte specifically comprises the following steps: (1) sequentially dissolving PVDF powder and commercial tetragonal phase BaTiO3 (BTO) powder in a mixed solvent of DMF and THF, and uniformly stirring with a magnetic stirrer to obtain a PVDF / BTO solution; and (2) carrying out electrostatic spinning on the PVDF / BTO solution to prepare a fiber membrane, drying, and carrying out a solution pouring method to prepare the composite solid electrolyte film. Compared with the prior art, the prepared solid electrolyte has excellent cycle performance, the ion transference number of the solid electrolyte is greatly increased, and the solid electrolyte has good lithium metal negative electrode compatibility.

Description

TECHNICAL FIELD

[0001] The present application relates to battery materials and preparation methods, in particular to a static electrospinning fiber membrane as a matrix for the preparation and application of a solid-state electrolyte. BACKGROUND

[0002] In this context, traditional fuel vehicles are gradually being replaced by new energy vehicles. Among them, the power battery system as the core component of new energy vehicles directly affects the endurance mileage, safety and fast charging capacity. The power battery widely used in new energy vehicles is mainly based on lithium ion batteries with liquid organic electrolyte. However, the flammability of organic electrolyte makes such battery system have inherent safety hazards. In addition, the application of high-capacity negative electrode materials (such as lithium metal and silicon-based negative electrode) in liquid lithium batteries is limited, mainly due to the continuous chemical evolution at the interface between the liquid electrolyte and these materials and the formation of lithium dendrites, which seriously restricts the energy density of the battery. In order to solve this problem, the use of solid-state electrolyte instead of liquid electrolyte and the development of solid-state battery are considered as an effective strategy to improve the safety of battery system and achieve high energy density. Therefore, solid-state battery is widely regarded as the most potential power battery system of the next generation.

[0003] In composite solid-state electrolyte (CSEs), strong organic-inorganic interfacial interactions are constructed to make inorganic nanowire fillers form a close combination with the polymer matrix, thereby creating efficient Li + transport channels, which is considered as an effective strategy to improve the Li + transport efficiency. Thanks to this strategy, the problem of "non-ion conductive area" formed by traditional inert nanowire fillers due to the lack of Li + conductivity has been cleverly avoided. Since the functionalized surface of inorganic nanowire fillers accounts for only a small part of the overall material, reducing the size of nanowire fillers can effectively increase their contact area with the polymer matrix, thereby significantly expanding the Li + transport channel, reducing the non-ion conductive area and improving the overall ion conductivity. However, inorganic nanowire fillers with smaller size often have higher surface energy and are prone to agglomeration, which hinders their uniform dispersion in the polymer matrix. This phenomenon not only limits the effective construction of the inorganic nanowire and polymer interface, but also inevitably increases the non-conductive area, which has a negative impact on Li + transport and inhibits the improvement of the ionic conductivity of CSEs. Therefore, achieving a balance between size regulation and agglomeration inhibition of nanowire fillers to construct large-scale, uniform and efficient interfaces is the key to improving the Li + transport efficiency. SUMMARY

[0004] Invention purposes: The purpose of the present application is to provide a electrospun fiber membrane as a substrate for the preparation and application of solid-state electrolyte, solve the above-mentioned inorganic filler agglomeration, Li + Transmission channel short-range disorder, low electrolyte ion conductivity and other problems, the prepared electrolyte has a high 0.57 lithium ion transference number, a high limit current density of 2.2mAcm -2 , And show good cycle stability in NCM811 / Li battery.

[0005] Technical scheme: The present application provides a method for preparing a solid-state electrolyte using the electrospun fiber membrane as a substrate, comprising the following steps:

[0006] (1) Dissolve PVDF powder and commercial tetragonal BTO powder in a mixed solvent of DMF and THF in turn, and stir uniformly with a magnetic stirrer to obtain a PVDF / BTO solution;

[0007] (2) The PVDF / BTO solution is prepared into a fiber membrane by electrospinning, and after drying, a composite solid-state electrolyte film is prepared by solution casting method.

[0008] Further, in step (1), the volume ratio of DMF and THF is 1.3-1.7.

[0009] Further, in step (1), the mass fraction of BTO in the PVDF / BTO solution is 1.5-3wt%.

[0010] Further, in step (2), the electrospinning uses a positive high voltage of 17kV and a negative high voltage of 2kV, a flow rate of 0.5mL / h, and the distance between the needle and the drum collector is 14-16cm.

[0011] Further, in step (2), the prepared fiber membrane is stored in vacuum at 70℃ to remove excess solvent, leaving about 12%-20%.

[0012] Further, in step (2), the specific process of solution casting is: preparing LiFSI / PVDF / DMF electrolyte, casting onto the fiber membrane, standing in Ar gas environment, and then drying in vacuum.

[0013] Further, in step (2), the preparation method of LiFSI / PVDF / DMF electrolyte is: dissolving 0.4g LiFSI and 0.2g PVDF in 10ml DMF solution, and stirring and dissolving for 10-12h.

[0014] Further, in step (2), the specific process of solution casting is as follows: configuring LiFSI / PVDF / DMF electrolyte, then casting on the fiber membrane, standing for 10 h in Ar gas environment, and then drying in vacuum at 55 DEG C for 12 h;

[0015] Further, in step (2), the specific ratio of LiFSI / PVDF / DMF electrolyte is as follows: dissolving 0.4 g of LiFSI and 0.2 g of PVDF in 10 ml of DMF solution, and stirring for 10 h at 25 DEG C for dissolution.

[0016] The preparation principle process of the application is as follows:

[0017] ① DMF has strong polarity and can effectively dissolve PVDF, THF has good solubility and volatility, and the use of mixed solvents can adjust the solvent evaporation rate and viscosity, thereby affecting the diameter and morphology of the fiber;

[0018] ② The electrospinning process can effectively stretch and orient the PVDF molecular chain under the action of the electric field, significantly enhancing the mobility and freedom of the molecular chain. In this process, the interaction between the polymer chain segments is weakened, causing the molecular chain to undergo phase transition, especially the formation of beta phase. Beta phase PVDF has a larger dipole moment and a looser molecular chain arrangement, so it can provide higher ion conductivity.

[0019] ③ The internal electric field generated by the spontaneous polarization of tetragonal barium titanate optimizes the ion migration path and reduces the migration energy barrier; its high dielectric constant enhances the electric field effect and promotes ion transmission; the structural order provides a stable channel, improving the ion conductivity and mechanical properties of the composite solid electrolyte;

[0020] ④ The surface charge and local electric field effect of BTO can act on the PVDF molecular chain, helping it to be more easily oriented during the spinning process and promoting the stability of the beta phase structure. Compared with traditional polymer fillers, BTO not only enhances the ordered arrangement of PVDF chain segments, but also improves the ion conductivity of the electrolyte material. In addition, the incorporation of BTO filler leads to the formation of more amorphous regions, reducing the crystallinity and thereby enhancing the mechanical strength of the material. Higher amorphous regions enable the material to better adapt to volume changes during charging and discharging, helping to improve its cycle stability and mechanical properties;

[0021] In another aspect, the present application provides an electrospun fiber membrane as a matrix for a solid-state electrolyte, which is prepared by the preparation method described above. The PVDF nanofiber (S-PVBT) filled with uniformly dispersed BTO inside the polymer solid-state electrolyte creates a continuous and efficient lithium ion transmission path. The XRD and infrared tests prove that the strong polarization BTO further increases the proportion of beta-phase PVDF in the S-PVBT fiber membrane, thus further increasing the dielectric properties and ferroelectric properties of S-PVBT. The calculation shows that the S-PVBT electrolyte has a low ion migration activation energy of 0.14eV and a high ion conductivity of 0.57.

[0022] The electrospinning process is used to prepare S-PVDF nanowires from PVDF powder with high crystallinity, which has lower crystallinity and higher dielectric properties. More importantly, the filler BTO dispersed on the nanowires overcomes the problem of uneven dispersion and agglomeration of fillers caused by directly adding fillers in the electrolyte slurry, and the presence of BTO further enhances the ferroelectricity of the fiber membrane. Subsequently, the electrolyte slurry containing lithium salt is poured into the 3D network structure to form a structure similar to "reinforced concrete". The electrolyte with such a network structure has better toughness and tensile properties. In particular, we found that the ferroelectric polarization of BTO at very high voltage can effectively promote the phase transition of PVDF, improve the dielectric properties of the electrolyte, dissociate lithium salt through stronger ferroelectric effect, and improve the interface stability of the electrode and electrolyte.

[0023] In still another aspect, the present application also provides an electrospun fiber membrane prepared by the method of any one of claims 1-7, and a battery prepared by using the electrospun fiber membrane.

[0024] The electrospun fiber membrane is used in a solid-state lithium metal battery, and NCM811 is used as a positive electrode material and lithium sheet is used as a negative electrode material.

[0025] Compared with the prior art, the present application has the following advantages:

[0026] 1. The electrospun fiber membrane (S-PVBT) of the present application as a matrix for a solid-state electrolyte greatly improves the dielectric and ferroelectric properties of the polymer matrix, and improves the ion transmission performance and high-voltage performance of the composite solid-state electrolyte. The preparation method is simple to operate, low in cost, and uses non-toxic raw materials, which meets the production requirements of environmental protection.

[0027] 2. The BTO-loaded PVDF nanowire (S-PVBT) of the present application as a new type of composite polymer matrix has the following advantages in the application of composite solid-state electrolyte:

[0028] ① Electrospinning process prepares the originally high crystallinity PVDF powder into S-PVDF nanowires with lower crystallinity and higher dielectric properties;

[0029] ② The filler BTO dispersed on the nanowires overcomes the problem of uneven dispersion and agglomeration of fillers caused by directly adding fillers in the electrolyte slurry;

[0030] ③ The presence of BTO further enhances the dielectric and ferroelectric properties of the fiber membrane;

[0031] ④ The S-PVBT electrolyte has a low activation energy of 0.14eV;

[0032] ⑤ The S-PVBT electrolyte has a lithium ion transference number of 0.57;

[0033] ⑥ The S-PVBT electrolyte has an ultimate current density of 2.2mAcm -2

[0034] ⑦ Assemble NCM811 / CSE / Li and perform long cycle test at 1C, the battery can have a capacity retention rate of 76.1% after 1200 cycles.

[0035] 3. The electrospun fiber membrane of the application is used as a substrate for a solid-state electrolyte, and by filling the polymer solid-state electrolyte with uniformly dispersed BTO PVDF nanofibers (S-PVBT), a continuous and efficient lithium ion transmission path is created.

[0036] 4. The electrospun fiber membrane of the application is used as a substrate for a solid-state electrolyte, and through the synergistic effect of electrospinning process and polarization BTO, the transformation of PVDF from alpha phase to beta phase is promoted, greatly improving the dielectric properties of the polymer solid-state electrolyte. XRD and infrared tests prove that the strong polarization BTO further increases the proportion of beta phase PVDF in the S-PVBT fiber membrane, thus the dielectric and ferroelectric properties of S-PVBT are further increased.

[0037] 5. The electrospun fiber membrane of the application is used as a substrate for a solid-state electrolyte, and the S-PVBT electrolyte optimizes the ion conductivity of PVDF, improves the mechanical strength, and improves the interface stability, which is the key reason for improving the ultimate current density. In addition, the PVDF electrolyte has accumulated too much lithium dendrite and byproduct during the long-term high current density cycle process, while the S-PVBT electrolyte exhibits a low overpotential of 0.18V at a current density of 1mA cm -2

[0038] ​​6. The electrospun fiber membrane of the present invention is used as a matrix for solid electrolyte, and the NCM811 / S-PVBT / Li battery shows a performance of more than 165mAh g -1 The initial discharge specific capacity of NCM811 / S-PVDF / Li and NCM811 / PVDF / Li batteries still has a capacity retention rate of 76.1% after 1200 cycles. However, in sharp contrast, the capacity of NCM811 / S-PVDF / Li and NCM811 / PVDF / Li batteries decayed significantly after 300 cycles. This is because even if PVDF powder is prepared into a 3D network nanofiber structure, the intrinsically narrow electrochemical window of PVDF cannot be changed. Lithium ion transport still relies on slow polymer chain transport, and limited β-phase PVDF alone is not enough to support rapid ion transport during long cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 : a is an optical photograph of the PVDF solid electrolyte obtained in Comparative Example 1; b is an optical photograph of the electrospun S-PVBT nanofiber membrane obtained in Example 1; c is an optical photograph of the S-PVBT composite solid electrolyte obtained in Example 1;

[0040] Figure 2 : a is a scanning electron microscope (SEM) image of the electrospun S-PVBT nanofiber membrane obtained in Example 1, wherein the scale is 10 μm; b is a scanning electron microscope (SEM) image of the electrospun S-PVBT nanofiber membrane obtained in Example 1, wherein the scale is 1 μm; c is a fiber diameter distribution diagram of the electrospun S-PVBT nanofiber membrane obtained in Example 1 obtained by Image J software;

[0041] Figure 3 : a is the effect of different BTO filler contents on the impedance of the S-PVBT electrolyte in Examples 1-5; b is the ionic conductivity of the S-PVBT electrolyte under different BTO filler contents in Examples 1-5;

[0042] Figure 4 : a is the XRD pattern of the S-PVBT fiber membrane in Example 1, the S-PVDF fiber membrane in Comparative Example 2, and the PVDF powder in Comparative Example 1; b is the infrared spectrum test pattern of the S-PVBT fiber membrane in Example 1, the S-PVDF fiber membrane in Comparative Example 2, and the PVDF powder in Comparative Example 1;

[0043] Figure 5: a is the ion conductivity graph of S-PVBT in Example 1, S-PVDF in Comparative Example 2, and PVDF in Comparative Example 1; b is the variable temperature impedance test of the PVDF electrolyte in Comparative Example 1; c is the variable temperature impedance test of the S-PVDF electrolyte in Comparative Example 2; d is the variable temperature impedance test of the S-PVBT electrolyte in Example 1; e is the Arrhenius curve of the S-PVBT electrolyte in Example 1, the S-PVDF electrolyte in Comparative Example 2, and the PVDF electrolyte in Comparative Example 1; f is the ion migration activation energy of the S-PVBT electrolyte in Example 1, the S-PVDF electrolyte in Comparative Example 2, and the PVDF electrolyte in Comparative Example 1;

[0044] Figure 6 : a is the polarization curve and impedance test before and after polarization and the calculated ion migration number of the PVDF electrolyte in Comparative Example 1; b is the polarization curve and impedance test before and after polarization and the calculated ion migration number of the S-PVBT electrolyte in Example 1;

[0045] Figure 7 : a is the limiting current density test of the S-PVBT electrolyte in Example 1 and the PVDF electrolyte in Comparative Example 1, wherein the charging and discharging time in each cycle is 1 h; b is the variable current density test of the S-PVBT electrolyte in Example 1 and the PVDF electrolyte in Comparative Example 1, wherein the charging and discharging time in each cycle is 10 h;

[0046] Figure 8 is the performance of the NCM811 / Li battery assembled by the S-PVBT electrolyte in Example 1, the S-PVDF electrolyte in Comparative Example 2, and the PVDF electrolyte in Comparative Example 1 at a 1C rate. DETAILED DESCRIPTION

[0047] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be further described below.

[0048] In the present application, the electrochemical performance is tested by an electrochemical workstation. The electrochemical workstation used is a CHI660E electrochemical workstation from Chenhua Electrochemical Workstation.

[0049] The instrument for the charge and discharge test of the battery is a new MIHW-200-160CH from Xinwei Electronic Co., Ltd. of Shenzhen;

[0050] The electrochemical performance test method in each example is as follows:

[0051] Assembly of NCM811 / Li battery: negative shell - lithium sheet - composite solid electrolyte - NCM811 positive sheet - gasket - spring - positive shell. Among them, the NCM811 positive electrode is made of NCM811 active material, PVDF, carbon black, which are mixed in a ratio of 8:1:1 into an appropriate amount of NMP solvent, and then coated on a carbon-coated aluminum foil and dried. Figure 8 The NCM811 / Li battery was assembled for testing in the middle.

[0052] Assembly of Li / Li symmetric lithium battery: negative shell - lithium sheet - composite solid electrolyte - lithium sheet - thin gasket - spring - positive shell. Figure 6 ,The lithium battery was assembled for testing in the middle. Figure 7

[0053] Assembly of SS / SS symmetric steel battery: negative shell - gasket (steel sheet) - composite solid electrolyte - gasket (steel sheet) - spring - positive shell. Figure 3 ,The symmetric steel battery was assembled for testing in the middle. Figure 5

[0054] Example 1

[0055] An electrospun fiber membrane as a substrate for a solid-state electrolyte is prepared by a method comprising the following steps:

[0056] (1) Dissolve PVDF powder and commercial tetragonal BTO powder in a mixed solvent of DMF and THF in sequence, and stir uniformly with a magnetic stirrer to obtain a PVDF / BTO solution:

[0057] Specifically, 18 ml of DMF and 12 ml of THF are mixed to form a solvent, then 1.92 g of PVDF is added to form a 15wt% PVDF solution, and then 0.592 g of BTO is added to form a BTO / PVDF solution, wherein the BTO accounts for 3wt% in the total solution. At the same time, perform sufficient magnetic stirring to uniformly disperse the BTO and PVDF.

[0058] (2) The PVDF / BTO solution is prepared into a fiber membrane by electrospinning, and after drying, a composite solid electrolyte thin film is prepared by a solution casting method:

[0059] Specifically, the prepared solution was loaded into a 20 ml syringe and connected to the spinneret with a 21G needle. The electrospinning was performed with a positive voltage of 17 kV, a flow rate of 0.5 mL / h for the syringe, and a distance of 15 cm between the needle and the drum collector. The drum collector was covered with aluminum foil, and the negative voltage was 2 kV, and the rotation speed was 1500 rpm. Subsequently, the electrospun membrane was dried in a vacuum oven at 70 °C for 10 h to remove excess residual solvent. Then, the LiFSI / PVDF / DMF electrolyte was configured, and then cast onto the fiber membrane, and placed in an Ar gas environment for 10 h, and then dried in a vacuum at 55 °C for 12 h to obtain the S-PVBT electrolyte.

[0060] The S-PVBT fiber membrane obtained in step (1) of Example 1 was scanned by a scanning electron microscope (model FEI XL 30 SEM-FEG, produced by Japan JEOL Electronics Corporation) at magnifications of 3000 and 20000, and the obtained scanning electron microscope images are shown in Figure 2 a and 2b, it can be seen from Figure 2 As can be seen from a, 2b and 2c, the diameter distribution of the S-PVBT fiber membrane is uniform, and the average diameter reaches 615 nm.

[0061] The S-PVBT fiber membranes with different BTO contents obtained in step (1) of Examples 1-5 and the PVDF powder of Comparative Example 1 and the S-PVDF fiber membrane of Comparative Example 2 were measured by an X-ray diffractometer (model: D8 advance, produced by Germany Bruker Corporation). The obtained XRD graphs are shown in Figure 4 a, Figure 4 In a, the abscissa is the 2θ angle, and the ordinate is the diffraction peak intensity. As can be seen from the figure, the relative intensity of the characteristic peaks of the α and β phases of PVDF is observed, as shown in Table 1.

[0062] The S-PVBT fiber membranes with different BTO contents obtained in step (1) of Example 1 and the PVDF powder of Comparative Example 1 and the S-PVDF fiber membrane of Comparative Example 2 were measured by a Fourier infrared spectrometer (model: IS10, produced by Japan Shimadzu). The obtained Fourier infrared spectra are shown in Figure 4 b, Figure 4 In b, the abscissa is the wave number, and the ordinate is the transmittance. The relative intensity of the characteristic peaks of the α and β phases is obtained by infrared testing and the relative proportion is calculated, as shown in Table 2.

[0063] The S-PVBT electrolyte obtained in step (2) of Example 1, the PVDF electrolyte of Comparative Example 1, and the S-PVDF electrolyte of Comparative Example 2 were tested using an electrochemical workstation (Model: CHI760E, manufacturer: Shanghai Chenhua). As the temperature increased, the impedance of the electrolytes all decreased. This is because the increased temperature increases the movement ability of the polymer chain segments, thereby promoting the migration of lithium ions. The movement of the polymer chain segments provides more "jumping" sites for ions, allowing the ions to move more freely, thereby reducing the impedance of the electrolyte. Notably, as shown in Figure 5 Fig. a, the ionic conductivity of the S-PVBT electrolyte at each temperature is higher than that of the S-PVDF and PVDF electrolytes, which is due to the synergistic effect of the 3D network fibrous PVDF and the polarized BTO prepared by electrospinning, which improves the dielectric properties of the composite polymer electrolyte. As shown in Figure 5 Fig. f, the S-PVBT electrolyte has the lowest ion migration activation energy (0.14 eV), while the activation energies of the S-PVDF and PVDF electrolytes are 0.22 eV and 0.19 eV, respectively. Ion migration activation energy is a key parameter for measuring the ease of ion migration. Lower activation energy means that the ion needs to overcome a smaller energy barrier when migrating in the material, making it easier to move under the driving action of the electric field.

[0064] The S-PVBT electrolyte obtained in step (2) of Example 1 and the S-PVDF electrolyte of Comparative Example 2 were tested using an electrochemical workstation (Model: CHI760E, manufacturer: Shanghai Chenhua). The polarization current curves and the impedance before and after polarization of the PVDF and S-PVBT electrolytes were determined. As shown in Figure 6 Figs. a and b, the lithium ion transference number of PVDF is only 0.35, while the lithium ion transference number of the S-PVBT electrolyte is as high as 0.57. A high lithium ion transference number means that the lithium ion has a stronger migration ability in an electric field, allowing it to complete charge transfer in a shorter time. This allows the battery to reduce the charging time when charging at a high rate, while also reducing the concentration polarization.

[0065] The composite solid electrolyte membranes obtained in step (2) of Examples 1-5 were tested using an electrochemical workstation (Model: CHI760E, manufacturer: Shanghai Chenhua). As shown in Figure 3 Fig. a, the bulk impedance of the electrolyte was tested by assembling a steel battery. Among them, the S-PVBT fiber membrane prepared from the BTO / PVDF spinning solution containing 3.0 wt% BTO has the lowest impedance, and its corresponding ionic conductivity is as high as 0.58 mS cm -1 . Therefore, no matter how the filler is doped (directly added or dispersed through nanofibers) into the CPE, there is a most suitable doping content.

[0066] Li / Li battery performance test

[0067] The S-PVBT obtained in step (2) of Example 1 and the PVDF electrolyte of Comparative Example 1 were tested on symmetrical lithium batteries using a Xinwei charge and discharge tester. Figure 6 As shown in a, the limiting current density of the S-PVBT electrolyte is as high as 2.2 mA cm -2 , even at 2.0mA cm -2 At high current densities near 1.5 V, the overpotential is only about 0.42 V. In comparison, the limiting current density of PVDF electrolyte is only 1.4 mA cm -2 , and then a short circuit occurred. The limiting current density of PVDF electrolyte is low, which is mainly attributed to its low ionic conductivity, limited segment motion due to high crystallinity, interface polarization effect, uneven distribution of lithium salt and other factors. In addition, during the test, factors such as lithium dendrite penetration, interface instability, electrolyte degradation and mechanical damage will cause battery short circuit. Therefore, the key reason for the improvement of limiting current density is that S-PVBT electrolyte optimizes the ionic conductivity of PVDF, improves mechanical strength and improves interface stability. Figure 6 As shown in b, PVDF and S-PVBT electrolytes were tested with variable current density to observe their performance in the actual battery operation process. -2 The S-PVBT electrolyte showed an overpotential of more than 0.24 V at a current density of 1 mA cm and short circuited when the current density was subsequently reduced. This was because the PVDF electrolyte had accumulated too many lithium dendrites and side reaction products during the long-term high current density cycle. -2 The S-PVBT electrolyte exhibited a low overpotential of 0.18 V at a current density of 1.5 V, and no short circuit occurred under conditions of changing current density, maintaining a good polarization potential. Therefore, the S-PVBT electrolyte is expected to be able to cycle for a long time at a higher current density.

[0068] NCM811 / Li battery performance test

[0069] The S-PVBT obtained in step (2) of Example 1, the PVDF electrolyte of Comparative Example 1, and the S-PVDF electrolyte of Comparative Example 2 were tested on NCM811 / Li batteries using a Xinwei charge and discharge tester. Figure 7As shown, NCM811 / CPEs / Li full cells were assembled with NCM811 cathode for long cycle test. It is worth noting that NCM811 / S-PVDF / Li and NCM811 / PVDF / Li batteries have a significant capacity decay after 300 cycles, which is due to the fact that even if the PVDF powder is prepared into a 3D network nanofiber structure, it cannot change the relatively narrow electrochemical window of PVDF itself. Lithium ion transport still depends on the slow polymer chain segment transport, and only limited β-phase PVDF is not enough to support fast ion transport during long cycle process. However, in sharp contrast, the NCM811 / S-PVBT / Li battery showed an initial discharge specific capacity of more than 165 mAh g -1 After 1200 cycles, it still has a capacity retention rate of 76.1%. This is not only due to the dissociation of lithium salt by the intrinsic ferroelectric polarization properties of BTO, but also due to the Lewis acid-base interaction between PVDF and BTO, which enhances the electrochemical stability of S-PVBT. In addition, the strong polarization BTO further increases the generation of β-phase PVDF, making β-phase PVDF dominate in the PVDF-based electrolyte, optimizing the composition and performance of the electrolyte.

[0070] The above results show that the improvement of the performance of the composite solid-state electrolyte is due to the creation of a continuous and efficient lithium ion transport path inside the polymer solid-state electrolyte. The synergistic effect of electrospun PVDF and polarized BTO improves the dielectric and ferroelectric properties of the electrolyte film, thereby greatly improving the battery performance.

[0071] Example 2

[0072] An electrospun fiber membrane as a substrate for a solid-state electrolyte is prepared by a method comprising the following steps:

[0073] (1) Dissolve PVDF powder and commercial tetragonal phase BTO powder in a mixed solvent of DMF and THF in turn, and obtain a PVDF / BTO solution after uniform stirring with a magnetic stirrer:

[0074] Specifically, 18 ml of DMF and 12 ml of THF are mixed into a solvent, then 1.92 g of PVDF is added to form a 15wt% PVDF solution, and then an appropriate amount of BTO is added to form a BTO / PVDF solution, wherein the BTO accounts for 1.5wt% in the total solution. At the same time, sufficient magnetic stirring is carried out to uniformly disperse BTO and PVDF.

[0075] (2) The PVDF / BTO solution is prepared into a fiber membrane by electrospinning, and after drying, a composite solid-state electrolyte film is prepared by a solution casting method:

[0076] Specifically, the prepared solution was loaded into a 20 ml syringe and connected to the spinneret with a 21G needle. The electrospinning used a positive high voltage of 17 kV, the syringe used a flow rate of 0.5 mL / h, and the distance between the needle and the drum collector was 15 cm. The drum collector was covered with aluminum foil, with a negative voltage of 2 kV and a rotation speed of 1500 rpm. Subsequently, the electrospun film was dried in a vacuum oven at 70°C for 10 h to remove excess residual solvent. Then, the LiFSI / PVDF / DMF electrolyte was configured, and then poured onto the fiber film, and placed in an Ar gas environment for 10 h, and then dried in a vacuum at 55°C for 12 h to obtain the S-PVBT electrolyte.

[0077] The S-PVBT electrolyte obtained in step (2) of Example 2 was subjected to electrochemical performance testing of impedance and ionic conductivity, and the method was the same as in Example 1. The results showed that the ionic conductivity of the electrolyte obtained in Example 2 was lower than that of the electrolyte obtained in Example 1, and the reason may be that the incorporation of 3wt% BTO in Example 1 increased the dielectric properties of the electrolyte and improved the interaction between BTO and PVDF.

[0078] Example 3

[0079] An electrospun fiber membrane as a substrate for a solid-state electrolyte is prepared by a method comprising the following steps:

[0080] (1) PVDF powder and commercial tetragonal BTO powder were sequentially dissolved in a mixed solvent of DMF and THF, and a magnetic stirrer was used to stir until a PVDF / BTO solution was obtained:

[0081] Specifically, 18 ml of DMF and 12 ml of THF were mixed to form a solvent, then 1.92 g of PVDF was added to form a 15wt% PVDF solution, and then an appropriate amount of BTO was added to form a BTO / PVDF solution, wherein the BTO accounted for 2.0wt% of the total solution. At the same time, the BTO and PVDF were uniformly dispersed by thorough magnetic stirring.

[0082] (2) The PVDF / BTO solution was prepared into a fiber membrane by electrospinning, and after drying, a composite solid-state electrolyte film was prepared by a solution pouring method:

[0083] Specifically, the prepared solution was loaded into a 20 ml syringe and connected to the spinneret with a 21G needle. The electrospinning used a positive high voltage of 17 kV, the syringe used a flow rate of 0.5 mL / h, and the distance between the needle and the drum collector was 15 cm. The drum collector was covered with aluminum foil, with a negative voltage of 2 kV and a rotation speed of 1500 rpm. Subsequently, the electrospun film was dried in a vacuum oven at 70°C for 10 h to remove excess residual solvent. Then, the LiFSI / PVDF / DMF electrolyte was configured, and then poured onto the fiber film, and placed in an Ar gas environment for 10 h, and then dried in a vacuum at 55°C for 12 h to obtain the S-PVBT electrolyte.

[0084] The S-PVBT electrolyte obtained in step (2) of Example 3 was subjected to electrochemical performance testing of impedance and ionic conductivity, and the method was the same as that of Example 1. The results showed that the ionic conductivity of the electrolyte obtained in Example 3 was lower than that of the electrolyte obtained in Example 1, and the reason may be that the incorporation of 3wt% BTO in Example 1 increased the dielectric properties of the electrolyte and improved the interaction between BTO and PVDF.

[0085] Example 4

[0086] An electrospun fiber membrane as a substrate for a solid-state electrolyte is prepared by a method comprising the following steps:

[0087] (1) PVDF powder and commercial tetragonal BTO powder were sequentially dissolved in a mixed solvent of DMF and THF, and a magnetic stirrer was used to stir uniformly to obtain a PVDF / BTO solution:

[0088] Specifically, 18 ml of DMF and 12 ml of THF were mixed to form a solvent, then 1.92 g of PVDF was added to form a 15wt% PVDF solution, and then an appropriate amount of BTO was added to form a BTO / PVDF solution, wherein the BTO accounted for 2.5wt% in the total solution. At the same time, sufficient magnetic stirring was performed to uniformly disperse the BTO and PVDF.

[0089] (2) The PVDF / BTO solution was prepared into a fiber membrane by electrospinning, and after drying, a composite solid-state electrolyte film was prepared by a solution pouring method:

[0090] Specifically, the prepared solution was loaded into a 20 ml syringe and connected to the spinneret with a 21G needle. The electrospinning used a positive high voltage of 17 kV, the syringe used a flow rate of 0.5 mL / h, and the distance between the needle and the drum collector was 15 cm. The drum collector was covered with aluminum foil, with a negative voltage of 2 kV and a rotation speed of 1500 rpm. Subsequently, the electrospun film was dried in a vacuum oven at 70°C for 10 h to remove excess residual solvent. Then, the LiFSI / PVDF / DMF electrolyte was configured, and then poured onto the fiber film, and placed in an Ar gas environment for 10 h, and then dried in a vacuum at 55°C for 12 h to obtain the S-PVBT electrolyte.

[0091] The S-PVBT electrolyte obtained in step (2) of Example 4 was subjected to electrochemical performance tests of impedance and ionic conductivity, and the method was the same as that of Example 1. The results showed that the ionic conductivity of the electrolyte obtained in Example 4 was lower than that of the electrolyte obtained in Example 1, and the reason may be that the incorporation of 3wt% BTO in Example 1 increased the dielectric properties of the electrolyte and improved the interaction between BTO and PVDF.

[0092] Example 5

[0093] An electrospun fiber membrane as a substrate for a solid-state electrolyte is prepared by a method comprising the following steps:

[0094] (1) PVDF powder and commercial tetragonal BTO powder were sequentially dissolved in a mixed solvent of DMF and THF, and a magnetic stirrer was used to stir uniformly to obtain a PVDF / BTO solution:

[0095] Specifically, 18 ml of DMF and 12 ml of THF were mixed to form a solvent, then 1.92 g of PVDF was added to form a 15wt% PVDF solution, and then an appropriate amount of BTO was added to form a BTO / PVDF solution, wherein the BTO accounted for 3.5wt% in the total solution. At the same time, sufficient magnetic stirring was performed to uniformly disperse the BTO and PVDF.

[0096] (2) The PVDF / BTO solution was prepared into a fiber membrane by electrospinning, and after drying, a composite solid-state electrolyte film was prepared by a solution pouring method:

[0097] Specifically, the prepared solution was loaded into a 20 ml syringe and connected to the spinneret with a 21G needle. The electrospinning was performed with a positive high voltage of 17 kV, the syringe was operated at a flow rate of 0.5 mL / h, and the distance between the needle and the drum collector was 15 cm. The drum collector was covered with aluminum foil, and the negative voltage was 2 kV, and the rotation speed was 1500 rpm. Subsequently, the electrospun membrane was dried in a vacuum oven at 70 °C for 10 h to remove excess residual solvent. Then, the LiFSI / PVDF / DMF electrolyte was configured, and then poured onto the fiber membrane, and placed in an Ar gas environment for 10 h, and then dried in a vacuum at 55 °C for 12 h to obtain the S-PVBT electrolyte.

[0098] The S-PVBT electrolyte obtained in Example 5 step (2) was subjected to electrochemical performance test of impedance and ionic conductivity, and the method was the same as that in Example 1. The results showed that the ionic conductivity of the electrolyte obtained in Example 5 was lower than that of the electrolyte obtained in Example 1. The reason may be that the excess BTO in Example 5 made it difficult to completely adhere to the surface of PVDF, causing the agglomeration of part of the BTO, and the agglomerated BTO was not ionically conductive, thus reducing the ionic conductivity.

[0099] Comparative Example 1:

[0100] Compared with Example 1, no electrospinning process was performed, and no BTO was added. The specific process was as follows:

[0101] 0.4 g of LiFSI and 0.6 g of PVDF were dissolved in 10 ml of DMF, stirred at 25 °C for 12 h, then placed in an Ar gas environment for 10 h, and then dried in a vacuum at 55 °C for 12 h to obtain a PVDF electrolyte

[0102] Without performing the electrospinning process and adding BTO, the Figure 1 a, the obtained PVDF electrolyte showed a semi-transparency. And through the test of Figures 5-8 , it was found that in terms of ionic conductivity, ion activation energy, ion transference number, limiting current density, lithium metal compatibility, and long cycle performance, the PVDF electrolyte was not as good as the S-PVBT electrolyte obtained in Example 1 and the PVDF electrolyte in Comparative Example 2.

[0103] Comparative Example 2:

[0104] Compared with Example 1, most of them were the same, but no BTO was added, and the S-PVDF electrolyte was obtained.

[0105] Without adding BTO, the Figures 5-8The test can know that, no matter in ionic conductivity, ion activation energy, ion transfer number, limiting current density, lithium metal compatibility, long cycle performance, all are not as good as S-PVBT electrolyte obtained in example 1, but still due to the PVDF electrolyte in comparative example 1. This is due to the lack of high dielectric BTO incorporation leads to the reduction of electrolyte dielectric properties, however, the S-PVDF fiber matrix obtained by spinning still has higher β phase PVDF content, and provides long-range ordered ion transport channel, so the performance is improved compared with PVDF electrolyte.

[0106] Table 1 is Figure 4 a. The relative intensity of α and β phase characteristic peaks is obtained by XRD test.

[0107] Table 1

[0108]

[0109] Table 2 is Figure 4 b. The relative intensity of α and β phase characteristic peaks is obtained by infrared test.

[0110] Table 2

[0111]

[0112] The above is only the preferred embodiment of the present application, and does not limit the present application in any way. Any person skilled in the art, without departing from the scope of the technical solutions of the present application, makes any form of equivalent replacement or modification of the technical solutions and technical contents disclosed by the present application, etc. change, all belong to the content of the technical solutions of the present application, still belong to the protection scope of the present application.

Claims

1. A method for preparing a solid electrolyte using an electrospun fiber membrane as a matrix, characterized in that: The following steps are involved: (1) Dissolving PVDF powder and tetragonal BaTiO3 powder in a mixed solvent of DMF and THF in sequence, and stirring to obtain a PVDF / BTO solution; (2) The PVDF / BTO solution was electrospinned to obtain a fiber membrane, which was then dried and cast into a composite solid electrolyte film.

2. The method for preparing a solid electrolyte using the electrospun fiber membrane as a matrix according to claim 1, characterized in that: In step (1), the volume ratio of DMF to THF is 1.3 to 1.

7.

3. The method for preparing a solid electrolyte using the electrospun fiber membrane as a matrix according to claim 1, characterized in that: In step (1), the mass fraction of BTO in the PVDF / BTO solution is 1.5-3 wt %.

4. The method for preparing a solid electrolyte using the electrospun fiber membrane as a matrix according to claim 1, characterized in that: In step (2), electrospinning adopts a positive high voltage of 17 kV and a negative high voltage of 2 kV, and a flow rate of 0.5 mL / h, and the distance between the needle and the roller collector is 14 to 16 cm.

5. The method for preparing a solid electrolyte using the electrospun fiber membrane as a matrix according to claim 1, characterized in that: In step (2), the prepared fiber membrane is stored in a vacuum at 70° C. to remove excess solvent.

6. The method for preparing a solid electrolyte using the electrospun fiber membrane as a matrix according to claim 1, characterized in that: In step (2), the specific process of solution casting is: preparing LiFSI / PVDF / DMF electrolyte, casting it onto the fiber membrane, letting it stand in an Ar gas environment, and then drying it in a vacuum.

7. The method for preparing a solid electrolyte using the electrospun fiber membrane as a matrix according to claim 6, characterized in that: In step (2), the LiFSI / PVDF / DMF electrolyte was prepared by dissolving 0.4 g of LiFSI and 0.2 g of PVDF in 10 ml of DMF solution and stirring for 10 to 12 hours.

8. An electrospun fiber membrane, prepared by the method according to any one of claims 1 to 7.

9. A battery prepared using the electrospun fiber membrane according to claim 8.

10. The electrospun fiber membrane according to claim 8, characterized in that Used in solid-state lithium metal batteries, NCM811 is used as the positive electrode material and lithium sheet is used as the negative electrode material.

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