A modified MOFs filler, a preparation method and a composite solid electrolyte of a lithium ion battery

Abstract

The application discloses a modified MOFs filler, a preparation method and a composite solid electrolyte of a lithium ion battery, the preparation method of the modified MOFs filler is that a cerium salt is added when a MOF material is prepared to obtain a cerium-doped MOF material, or the MOF material is etched after being prepared to obtain an etched MOF material. The preparation method of the composite solid electrolyte is that the prepared MOF material is dispersed in a solvent under the protection of an inert gas, electrolyte lithium salt and PEO are added, a colloidal suspension is obtained after stirring, and then the colloidal suspension is poured into a mold and dried to be formed. After the obtained modified MOFs filler is added to the composite solid electrolyte, the conductivity of the composite solid electrolyte can be effectively improved, the composite solid electrolyte has a wide electrochemical stability window, and a lithium ion battery assembled by using the composite solid electrolyte has excellent electrochemical performance.

Description

Technical Field

[0001] This invention relates to a modified MOF filler, its preparation method, and a composite solid electrolyte for lithium-ion batteries, belonging to the field of solid-state battery materials technology. Background Technology

[0002] A lithium-ion battery is a chemical power source that stores and releases energy through the reversible lithium-ion insertion and extraction process between the positive and negative electrode materials. Since the concept of lithium-ion batteries was proposed in the late 1970s and Sony successfully commercialized them in 1991, these batteries have become the preferred energy storage device in many fields, including portable electronic devices, electric vehicles, and large-scale energy storage systems, due to their significant advantages such as high energy density, long lifespan, and low self-discharge rate. As one of the world's largest lithium-ion battery producers, China has established a complete industrial chain from raw material mining and processing to battery manufacturing and application promotion.

[0003] However, the liquid electrolytes currently used in lithium batteries pose a flammable risk, potentially leading to overheating and safety incidents. The continued development of battery technology not only demands improved energy density and cycle stability but also urgently requires addressing safety issues to achieve comprehensive optimization of lithium-ion battery technology. Compared to traditional liquid electrolyte lithium batteries, all-solid-state lithium batteries offer higher safety, longer cycle life, and higher energy density, making them an effective strategy for balancing high safety and high specific energy, and a viable means to address the aforementioned safety concerns.

[0004] Solid-state electrolytes, named in contrast to liquid electrolytes, are solid materials with ionic conductivity. Currently, solid-state electrolytes can be classified into three types based on their material properties: inorganic electrolytes, polymer electrolytes, and composite electrolytes. The concept of polymer electrolytes (PEs) was first proposed in the 1970s, and their application in lithium-ion batteries was subsequently explored, thus initiating the research and development of polymer electrolytes for lithium-ion batteries. Compared to inorganic solid-state electrolytes, polymer electrolytes are easier to process, lighter, and less expensive. Furthermore, their high flexibility can buffer the volume expansion of the electrodes to some extent during battery cycling, which helps maintain the stability of the battery structure. However, most polymers have high crystallinity at room temperature and poor chain segment mobility, resulting in very low room-temperature conductivity.

[0005] The most studied matrices for polymer electrolytes include ether polymers (ethylene oxide, PEO), fluorinated polymers (polyvinylidene fluoride, PVDF; polyvinylidene fluoride-hexafluoropropylene, PVDF-HFP), carbonate polymers (polymethyl methacrylate, PMMA), and nitrile polymers (polyacrylonitrile, PAN). PEO is currently one of the most widely studied polymer matrices due to its low cost and environmental friendliness. The PEO molecular chain exhibits excellent flexibility, which facilitates rapid lithium-ion transport. It is generally believed that the fluidity of cation transport is related to the movement of the complexed segments of the PEO chain.

[0006] Because ion transport depends on the segmented movement of the main chain, this movement weakens rapidly with decreasing temperature and increasing crystallinity. Due to the presence of crystalline domains, the PEO-lithium salt system provides relatively low ionic conductivity (10⁻⁶) at ambient temperature. -7 S·cm -1 Therefore, reducing the crystallinity of PEO to promote chain segment movement is crucial, and the continuous movement of amorphous segments above the glass transition temperature (Tg) plays a decisive role in ion transport. Furthermore, with increasing temperature, the increase in amorphous regions within the PEO matrix can improve ionic conductivity and even interfacial stability with electrode materials. However, operation at high temperatures may lead to decreased mechanical properties and a limited electrochemical stability window, resulting in lithium dendrite growth and reduced safety performance of the polymer electrolyte system.

[0007] For PEO electrolytes, there are two urgent problems to be solved. On the one hand, the high crystallinity at room temperature leads to poor conductivity, while the mechanical properties are poor at high temperatures. On the other hand, PEO-based solid electrolytes have a narrow electrochemical window and lack stability under high voltage, which limits the application of PEO in high-voltage solid-state batteries. Summary of the Invention

[0008] The purpose of this invention is to provide a modified MOFs filler, a preparation method, and a composite solid electrolyte for lithium-ion batteries. When the modified MOFs filler is added to the composite solid electrolyte, it can effectively improve the conductivity of the composite solid electrolyte and has a wide electrochemical stability window. The assembled lithium battery exhibits excellent discharge capability.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A modified MOFs packing material, wherein the MOFs packing material refers to one of the following two types:

[0011] The first type: In the MIL series of MOF materials, some metal nodes are replaced by cerium metal;

[0012] The second type is the MIL series of MOF materials, whose surface contains pores formed by etching.

[0013] The metal in question is one of Fe, V, Cr, and Ni.

[0014] The MIL series MOF materials mentioned refer to one or more of MIL-53, MIL-68, MIL-88A, MIL-88B, MIL-100, MIL-101, and MIL-125.

[0015] Cerium accounts for 0.1-0.45% of all metals.

[0016] The pore size ranges from 10 to 200 nm.

[0017] The above-mentioned method for preparing modified MOFs fillers, for the first type of filler, includes the following steps: dissolving the metal source salt, cerium salt and ligand in water, and after crystallization reaction, centrifuging, washing and drying are performed.

[0018] For the second type of filler, the following steps are included: dissolving the metal source salt and ligand in water, crystallizing the reaction, centrifuging, washing, and drying to obtain MOF particles; dispersing the obtained MOF particles and phytic acid in water, heating, washing, centrifuging, and drying.

[0019] The ligand is fumaric acid, the metal source salt is FeCl3·6H2O, and the cerium salt is Ce(NO3)3·6H2O.

[0020] For the first type of filler, the molar ratio of cerium salt to metal source salt ranges from 0.1 to 0.45; the ratio of the total molar amount of metal source salt and cerium salt to the molar amount of added ligand is 1:(0.8-1.2).

[0021] The conditions for the crystallization reaction are: 60-90℃, 10-15h;

[0022] The drying conditions are: vacuum conditions, 90-120℃, 20-48h.

[0023] For the second type of filler, the molar ratio of the metal source salt to the ligand is 1:(0.8-1.2);

[0024] The conditions for the crystallization reaction are: 60-90℃, 10-15h;

[0025] The drying conditions are: vacuum conditions, 90-120℃, 20-48h.

[0026] Preferably, the ratio of MOF particles to phytic acid is (80-120) mg:(40-150) μl;

[0027] The heating conditions are: under vacuum, 80-110℃, for 2-8 hours;

[0028] The drying conditions are: vacuum conditions, 50-80℃, 4-9h.

[0029] A method for preparing a composite solid electrolyte involves dispersing any of the modified MOF fillers prepared by the above methods in a solvent under inert gas protection, then adding organic electrolyte lithium salt and PEO, stirring to obtain a colloidal suspension, and finally pouring it into a mold for drying and shaping.

[0030] Preferably, the molar ratio of the organic electrolyte lithium salt to the EO in PEO is 1:(18-25); the organic electrolyte lithium salt is selected from lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4) or lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2).

[0031] The amount of modified MOF filler added is 5-20 wt% of the total amount of PEO and modified MOF filler.

[0032] Preferably, the drying and molding conditions are: 50-70℃, 30-50h.

[0033] Application of composite solid electrolytes prepared by any of the above methods in lithium-ion batteries.

[0034] The beneficial effects of this invention are as follows:

[0035] By adding cerium salt during MOF preparation, cerium-doped MOF materials are obtained. PEO-based composite solid electrolytes prepared using these materials as fillers exhibit high mechanical strength, good thermal stability, a wide electrochemical stability window, improved interfacial properties, significantly enhanced ionic conductivity, and Li+. + The number of lithium transfers is significantly reduced, and the formation of dendritic lithium during cycling is significantly eliminated; the assembled lithium battery exhibits excellent discharge capability, coulombic efficiency, and capacity retention.

[0036] Simultaneously, by etching the prepared MOF, an etched MOF material was obtained. This material, used as a filler, was used to prepare a PEO-based composite solid electrolyte, which exhibited significantly improved ionic conductivity and Li... + Increased transfer number and a wider electrochemical stability window; the corresponding lithium batteries exhibit excellent discharge capability and lower polarization. Attached Figure Description

[0037] Figure 1SEM images of (a) MIL-88A; (b) MIL-88A 0.1Ce; (c) MIL-88A 0.2Ce; (d) MIL-88A 0.1Ce; and (e) XRD images of MIL-88A and MIL-88A xCe.

[0038] Figure 2 (a) XPS spectra of MIL-88A and MIL-88AxCe; (b) Py-FTIR spectra.

[0039] Figure 3 (a) Surface SEM; (b) Cross-sectional SEM of PEO; (c) Surface SEM; (d) Cross-sectional SEM of MIL-88A@CSPE; (e) Surface SEM; (f) Cross-sectional SEM of MIL-88A0.2Ce@CSPE;

[0040] Figure 4 (a) FTIR spectra of MIL-88AxCe@CSPE and PEO; (b) FTIR spectra of MIL-88A@CSPE and MIL-88A; (c) FTIR spectra of MIL-88A0.2Ce@CSPE and MIL-88A0.2Ce.

[0041] Figure 5 (a) Comparison of stress-strain curves; (b) TG curves of MIL-88AxCe@CSPE and PEO; (c) DSC curves;

[0042] Figure 6 (a) Ionic conductivity of MIL-88A@CSPE with different MIL-88A loadings; (b) Ionic conductivity of MIL-88AxCe@CSPE and PEO; (c) Linear sweep voltammetry of MIL-88AxCe@CSPE and PEO at 60 °C.

[0043] Figure 7 The ion transport numbers of different solid electrolytes at 60 °C are: (a) PEO; (b) MIL-88A@CSPE.

[0044] (c)MIL-88A0.2Ce@CSPE;

[0045] Figure 8 Storage time dependence of resistance of different batteries at 60°C (a) PEO; (b) MIL-88A@CSPE;

[0046] (c) MIL-88A0.2Ce@CSPE; (d) Li||PEO||Li, Li||MIL-88A@CSPE||Li and

[0047] Li||MIL-88A0.2Ce@CSPE||Li battery at 60℃ and 0.1mA / cm 2 The charge / discharge voltage curves are as follows;

[0048] Figure 9 (a) Rate performance and (b) Cycling performance of full cells assembled for PEO, MIL-88A@CSPE and MIL-88A0.2Ce@CSPE at 60°C;

[0049] Figure 10 SEM images of (ab)MIL-88A; (cd)MIL-88A-50μl; (ef)MIL-88A-100μl;

[0050] Figure 11 TEM images of (ab)MIL-88A; (cd)MIL-88A-50μl; (ef)MIL-88A-100μl;

[0051] Figure 12 (ab)SEM of PEO; (cd)SEM of PEO-MIL-88A; (ef)SEM of PEO-MIL-88A-50μl; (gh)SEM of PEO-MIL-88A-100μl;

[0052] Figure 13 The ionic conductivity of the composite solid electrolyte;

[0053] Figure 14 (a) Linear scan voltammograms of full cells assembled for PEO, PEO-MIL-88A, PEO-MIL-88A-50μl and PEO-MIL-88A-100μl at 60 °C; (b) Rate performance. Detailed Implementation

[0054] Composite solid electrolytes typically consist of a polymer matrix, inorganic fillers, lithium salts, and ionic liquid additives. Introducing inorganic fillers into polymer electrolytes makes it possible to simultaneously obtain composite polymer electrolytes with high ionic conductivity and high mechanical strength. The improved ionic conductivity is mainly due to the filler's reduced crystallinity of PEO, enhanced interfacial stability, and promoted lithium salt dissociation, thus increasing the lithium-ion concentration in the electrolyte. Each material in the composite retains its own properties; therefore, the addition of fillers can significantly improve the mechanical properties of the electrolyte.

[0055] MOFs (Metal-Organic Facility Materials) are a class of materials with regular porous structures, large specific surface areas, and both organic and inorganic properties, and have been widely used in various fields. Recently, MOFs have become a hot research topic in polymer electrolytes due to their insulating properties and inherent characteristics. Factors such as the composition, structure, and internal environment of MOFs offer possibilities for achieving high-performance polymer electrolytes. MOFs possess high surface polarity, enabling them to control Lewis acid-base interactions within the system, thereby improving its electrochemical performance. Furthermore, the diverse structures of MOFs allow them to adapt to different materials, making it easy to composite them with various electrolyte materials and utilize their excellent electrochemical properties to modify solid-state electrolytes, thereby improving the ionic conductivity, ion migration, and other electrochemical properties of solid-state electrolytes.

[0056] In this invention, the performance of PEO is optimized by modifying it with MOFs (Metal-Oxide-Factory) fillers. First, a series of bimetallic MIL-88A materials were prepared by Ce doping (also known as substitution) and used as fillers. MIL-88A materials with different Ce doping amounts exhibited different Lewis acidities. Experiments showed that the ionic conductivity and electrochemical properties of PEO solid electrolytes are positively correlated with the Lewis acidity of the MOFs. The solid electrolyte prepared with 0.2Ce MIL-88A exhibited the highest Lewis acidity, with a maximum ionic conductivity of 4.47 × 10⁻⁶. - 4 Scm -1 On the other hand, defect sites in MOFs can be constructed through acid etching to expand their active sites. High specific surface area, high porosity, and high thermal stability facilitate ion entry into Lewis acid centers on the inner surface of MOFs. These sites undergo strong Lewis acid-base interactions with the ether oxygen (EO) bond of PEO and the anion of Li salt, generating higher Li content. + Transfer number and conductivity. This CSPE exhibits 4.7 × 10⁻⁶ at 60 °C. -4 S cm -1 High ionic conductivity.

[0057] Comparative Example 1: Synthesis of MIL-88A

[0058] 6.67 mmol of ferric chloride hexahydrate (FeCl3·6H2O) and 6.67 mmol of fumaric acid were dissolved separately in 25 mL of ultrapure water. The salt solutions were mixed in a polytetrafluoroethylene reactor and stirred for 5 minutes. A crystallization reaction was then carried out at 70 °C for 12 h. Finally, the precipitated powder was collected by centrifugation, washed several times with ethanol, and then dried under vacuum at 100 °C for 24 h to obtain MIL-88A.

[0059] Example 1: Synthesis of MIL-88AxCe

[0060] Ce-doped MIL-88A (labeled MIL-88AxCe, where x represents the substitution ratio) was prepared using a partial substitution method. MIL-88A0.2Ce was prepared using the same method, except that 1.3 mmol of cerium nitrate hexahydrate (Ce(NO3)3·6H2O) was added to replace an equal amount of FeCl3·6H2O. Other doped MIL-88A catalysts, including MIL-88A0.1Ce and MIL-88A0.3Ce, were also prepared with different Ce substitution ratios.

[0061] Characterization of MIL-88A and MIL-88AxCe

[0062] Scanning electron microscope (SEM) images Figure 1 The XRD pattern (in the mid-ad region) shows that both MIL-88A and MIL-88A0.2Ce are rod-shaped with a relatively uniform length distribution of approximately 10 μm. The morphology of MIL-88A did not change significantly after Ce doping. The crystal structures of the original doped and Ce-doped MIL-88A were analyzed by XRD, as shown below. Figure 1 The region in the middle is shown. The original MIL-88A shows two distinct peaks at 10.4° and 12.1°, corresponding to the (101) and (002) crystal planes, respectively, which is consistent with the characteristic peaks of the standard card of MIL-88A. As for the XRD pattern of MIL-88AxCe, it can be observed that the peak of the (101) crystal plane shifts to a higher angle. In addition, the peak of the (101) plane gradually broadens and splits into two peaks. Its intensity changes significantly with the increase of Ce substitution ratio. This is due to the long-distance distortion / destruction of MIL-88A and the formation of crystal defects caused by Ce doping.

[0063] XPS analysis was performed to further analyze the chemical composition and electronic structure of MIL-88A and MIL-88AxCe. The XPS spectra were obtained from the results. Figure 2 As can be seen in region a) of all prepared MOF materials, at approximately 725 eV (Fe 2p 1 / 2 716 eV (satellite) and 712 eV (Fe 2p) 3 / 2 A clear signal of Fe(III) presence was detected at the binding energy (BE) of Fe. With increasing Ce doping content, all Fe 2p and O1s peaks in the XPS spectrum shifted slightly to lower BE. This indicates that the Ce-O-Fe bond is formed through Ce doping, as Ce has a lower electronegativity than Fe. Combining the XRD and XPS results, Ce(III) was successfully doped into MIL-88A, forming Ce-O-Fe at the nodes. Pyridine infrared spectroscopy was also performed, and the signal was obtained in the Py-FTIR spectrum. Figure 2Pyridine molecules coordinated with tetrahedral unsaturated metal sites (Ce or Fe centers) in the middle b region are at ~1069 cm⁻¹ -1 and ~1040cm -1 The two distinct peaks in the band confirm the presence of Lewis acid sites.

[0064] Lewis acidity (i.e., the amount of LAS, denoted as LA) for each MOF was calculated according to the formula. Table 1 summarizes the LAS amounts for MIL-88A and MIL-88AxCe. As the Ce substitution amount increases to 0.20, the number of strong acidic sites steadily increases, and the acidity begins to decrease with further substitution.

[0065] Table 1. Lewis acidity of MIL-88A and MIL-88AxCe

[0066]

[0067]

[0068] Preparation of PEO-based composite solid electrolytes

[0069] The PEO-based composite SPE (labeled MIL-88AxCe@CSPE) was obtained via solution casting. Pre-dried PEO (molecular weight = 6 × 10⁻⁶) was used. 6 MIL-88A and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were prepared. First, MIL-88A was sonicated in acetonitrile for 30 min. Then, LiTFSI was added to the above MOF dispersion and stirred for 2 h. PEO was then dissolved in the suspension and stirred for 24 h. The homogenized colloidal suspension was poured into a polytetrafluoroethylene mold and dried at 60 °C for 48 h to form a CSPE film. The mass percentages of MIL-88A, MIL-88A0.1Ce, MIL-88A0.2Ce, and MIL-88A0.3Ce in the total PEO and MOF were 10 wt%, and the Li / EO molar ratio was 1:20. All preparation processes were carried out in an argon-filled glove box.

[0070] Characterization of composite solid electrolytes

[0071] SEM images of pure PEO solid electrolyte and composite solid electrolyte, such as Figure 3 As shown, the prepared composite solid electrolyte is translucent, freestanding, and flexible. The composite solid electrolyte can also adhere firmly to the electrode. Figure 3 As shown in region c, the interface resistance is reduced due to its smooth and flat surface. Furthermore, Figure 3Cross-sectional SEM images of the composite solid electrolyte in region d show a thickness of approximately 50 μm, with MOF particles uniformly distributed within the PEO polymer. Similarly, the prepared composite solid electrolyte ( Figure 3 The central cf region is relatively flat, with few defects or clusters.

[0072] The crystallinity of PEO has a significant impact on the ionic conductivity of PEO-based solid electrolytes. This was determined by analyzing the XRD data of the prepared CSPE. Figure 4 The crystallization trend of PEO can be clearly understood by examining region a. In the XRD pattern of PEO, there are two distinct peaks at 19.5° and 23.6°, assigned to the (120) and (112) crystal planes, respectively. After the addition of MIL-88AxCe, the relative intensity and width of these PEO characteristic peaks changed to some extent. The peak intensity of the characteristic peaks decreased with the increase of Lewis acidity of the added MOF. These changes indicate that MIL-88AxCe can interact with the PEO matrix and increase its amorphous degree, which is beneficial to the transport of lithium ions in the electrolyte.

[0073] The structure of CSPE was further characterized by FTIR testing. Figure 4 (Middle b region). First, at 1396cm -1 The nearby peaks correspond to the symmetrical stretching of C=O, and can be observed in the FTIR spectra of both MIL-88A and MIL-88A@CSPE, confirming the presence of MIL-88A in MIL-88A@CSPE. Secondly, the FTIR spectrum of the pure PEO film ( Figure 4 In region b), 1356 and 1346 cm -1 The peak values ​​at 1144, 1113, and 1061 cm⁻¹ correspond to the bending vibrations of -CH₂-, while those at 1144, 1113, and 1061 cm⁻¹... -1 The peak at [value missing] belongs to the stretching of -COC-. It is noteworthy that this bending bimodality of -CH2- and the stretching ternary peak of -COC- are considered to be related to crystallized PEO. With the addition of MIL-88A, the bending vibration of -CH2- only [value missing] at 1356 cm⁻¹. -1 A peak appears at a certain point, with decreasing intensity, indicating a weakening of the intensity of the stretched ternary peak -COC-. This clearly demonstrates that the addition of MIL-88A disrupts the crystallinity of PEO. Finally, all characteristic peaks in the MIL-88AxCe@CSPE spectrum are similar to those of PEO electrolyte.

[0074] Mechanical strength is an important objective of electrolyte membranes, and its improvement is effectively achieved through the addition of MOFs. Tensile strength test results ( Figure 5Region a) shows that the maximum strength of the PEO electrolyte membrane is 1.29 MPa, while the maximum strengths of MIL-88A@CSPE and MIL-88A0.2Ce@CSPE can be increased to 2.93 and 3.83 MPa, respectively. The enhanced mechanical strength is attributed to the physical cross-linking between the active surface of MIL-88A and the PEO chains. When the polymer chains are subjected to external forces, MIL-88A can act as a cross-linking point, dispersing and transferring stress to other polymer chains, thereby reducing stress concentration and increasing the polymer strength. This high mechanical strength characteristic gives the composite electrolyte an advantage in suppressing lithium dendrite growth when applied to lithium metal batteries.

[0075] Thermogravimetric analysis (TG) is one of the most important parameters in practical applications of solid polymer electrolytes. Figure 5 The middle b region shows that the thermal decomposition temperature of PEO is approximately 373.6 °C, which increases slightly with increasing MIL-88AxCe doping concentration. PEO decomposes at around 350 °C, with the final residual amount remaining at ~3.3 wt%. When the temperature rises to 600 °C, the residual amount of MIL-88AxCe@CSPE is higher than that of PEO. These results indicate that the introduction of MIL-88AxCe particles can slightly improve the thermal stability of the electrolyte. Differential scanning calorimetry (DSC) measurements were performed to investigate the glass transition and crystallinity of the prepared PEO and MIL-88AxCe@CSPE. Figure 5 (Region c). It can be seen that adding MIL-88AxCe to PEO lowers the glass transition temperature from -32℃ to -34℃, indicating that MIL-88AxCe disrupts the PEO chains, thereby reducing the crystallinity of CSPE. This means that MIL-88AxCe@CSPE possesses significantly more amorphous regions than PEO. Increased amorphization will enhance the segmentation of the PEO chains.

[0076] Electrochemical performance testing

[0077] To investigate the effect of MIL-88AxCe on the ion transport behavior of PEO-based CSPE, the ionic conductivity of MIL-88A@CSPE with different MIL-88A loadings was first measured by electrochemical impedance spectroscopy (EIS) in the temperature range of 30–80 °C. Figure 6 The optimal MOF loading was determined to be 10% in the middle a region. The ionic conductivity of MIL-88AxCe@CSPE was then tested at 30–80 °C. Figure 6(Middle b region). The ionic conductivity of MIL-88AxCe@CSPE increases and then decreases with increasing Ce doping concentration, reaching a maximum at x = 0.2. Similarly, the results show that the ionic conductivity of CSPE increases with increasing Lewis acidity. The ionic conductivity of MIL-88A0.2Ce@CSPE at 60 °C reaches 4.47 × 10⁻⁶. -4 Scm -1 The ionic conductivity of PEO is 1.63 × 10⁻⁶. -4 S cm -1 It is about two orders of magnitude higher.

[0078] Electrochemical stability is a key factor in evaluating the performance of solid polymer electrolytes and their potential for practical application in batteries. The effect of MIL-88AxCe on the electrochemical stability window of CSPE was investigated using linear sweep voltammetry (LSV). Figure 6 As shown in region c, the LSV curves of SS||PEO||Li and SS||MIL-88AxCe@CSPE||Li measured at 60 °C show that the latter exhibits a more stable voltage than the former. This indicates that the electrochemical stability of the PEO-based solid electrolyte is enhanced by the addition of MIL-88AxCe. The improved electrochemical stability window is attributed to the effective trapping ability of MIL-88AxCe for small molecules and the strong interaction between MIL-88AxCe nanoparticles and PEO chains.

[0079] To characterize Li + The effect on total ionic conductivity was measured by impedance potential polarization analysis after 4000 seconds of polarization at 10 mV, and the lithium-ion transfer number (t) was determined. Li+ ),like Figure 7 The ac region is shown. The tLi of PEO + Only 0.25, while the tLi of MIL-88A@CSPE + Increased to 0.49. Li+ The enhancement can be attributed to the Lewis acid-base interaction between MOFs and PEO, which increases the concentration of mobile lithium ions.

[0080] Furthermore, the Li||SPE||Li symmetric cell was stored at 60°C for 6 days. Figure 8 The interfacial stability of PEO-based SPE was further investigated in the middle AC region. The initial resistance was much higher than that after high-temperature storage, because heat treatment can effectively improve the contact between Li and SPE. In addition, compared with PEO, MIL-88AxCe@CSPE showed much less interfacial reaction with lithium. This is because MIL-88AxCe has a strong affinity for small molecules and can effectively absorb trace solvents or small molecules in the homogeneous nanocomposite polymer electrolyte membrane.

[0081] At 0.1 mA / cm 2 The long-term lithium plating / stripping performance of the Li||SPE|||Li symmetric cell was further characterized at 60℃. Figure 8 (Middle d region). The Li||MIL-88A@CSPE||Li symmetric cell operates for over 450 hours, significantly longer than the Li|PEO||Li cell (only 120 hours before short circuit). These results indicate that MIL-88A@CSPE exhibits a stronger ability to suppress lithium dendrite growth than PEO.

[0082] The prepared CSPE exhibits high mechanical strength, good thermal stability, a wide electrochemical stability window, improved interfacial properties, significantly enhanced ionic conductivity, and Li... + The transfer number is significantly reduced, and the formation of dendritic lithium during cycling is significantly eliminated. In particular, thanks to the high Lewis acidity of MIL-88AxCe, the prepared MIL-88AxCe@CSPE also exhibits significantly enhanced ionic conductivity and Li-transfer rate. + Transition number.

[0083] To further evaluate the electrochemical performance of MIL-88AxCe@CSPE, an LFP||SPE|||Li battery was assembled and tested at 60°C. Figure 9 The middle region (a) shows the rate performance of the LFP||PEO||Li and LFP||MIL-88AxCe@CSPE||Li full cells. As shown in the figure, the discharge capacities of the LFP||PEO||Li battery at 0.05, 0.1, 0.2, 0.5, 1, and 2C rates are 158.3, 157, 153.2, 144.7, 118.6, and 56.9 mAh g, respectively. -1 The LFP||MIL-88AxCe@CSPE|Li battery exhibits a higher discharge capacity. High ionic conductivity and tLi + It can alleviate the polarization effect inside the battery, thereby reducing the increase in internal polarization voltage. Specifically, MIL-88A0.2Ce@CSPE has the highest ionic conductivity, providing 127.5 mAh g at 2C. -1 The highest discharge capacity was observed. When the current density recovered to 0.1C, the LFP||MIL-88A0.2Ce@CSPE||Li battery also exhibited a higher discharge capacity than the LFP||PEO||Li battery. Similarly, the cycle performance of the full cell was tested, such as... Figure 9 As shown in region b, an increase in battery discharge capacity was observed during the initial cycling due to the activation process. After 100 cycles, the LFP||MIL-88A0.2Ce@CSPE||Li capacity remained at 113.3 mAh g⁻¹.-1 The discharge capacity is only 76.6 mAh g for LFP||PEO||Li batteries. -1 During cycling, LFP||MIL-88A0.2Ce@CSPE||Li showed significant improvements over LFP||PEO||Li in terms of stabilizing the electrode / electrolyte interface and exhibiting lower interfacial reactions. Based on these results, LFP||MIL-88A0.2Ce@CSPE||Li demonstrated excellent discharge capability, coulombic efficiency, and capacity retention.

[0084] Example 2: Synthesis of Etching MIL-88A

[0085] 100 mg of the synthesized MIL-88A and 50 μl of phytic acid were dispersed in 25 ml of water, sonicated, stirred, and then transferred to a 50 ml screw-top glass bottle. The mixture was heated in a vacuum oven at 90 °C for 3 hours, and then allowed to cool naturally to room temperature to obtain a pale orange product. The product was washed with water and ethanol, and centrifuged twice to obtain a relatively pure product. Finally, the product was dried in a vacuum oven at 60 °C for 6 hours to obtain 50 μl of modified MIL-88A.

[0086] Characterization of MIL-88A and etched MIL-88Ax

[0087] Scanning electron microscopy (SEM) images were taken of MIL-88A raw material, 50 μl of phytic acid-etched MIL-88A, and 100 μl of phytic acid-etched MIL-88A, respectively (see [link to SEM image]). Figure 10 The surface of the unetched MOF material is relatively dense, but as the amount of phytic acid increases, pores begin to appear on the surface of the material.

[0088] Further analysis of its structure, as shown in the TEM image ( Figure 11 The MOF structure is not significantly damaged, and increasing the acidity can increase the number of etched holes without destroying the overall basic framework.

[0089] Preparation of PEO-based composite solid electrolytes

[0090] The PEO-based composite SPE was obtained by solution casting. Pre-dried PEO (molecular weight = 6 × 10⁻⁶) was used. 6MIL-88A and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were prepared. First, MIL-88A was sonicated in acetonitrile for 30 min. Then, LiTFSI was added to the above MOF dispersion and stirred for 2 h. PEO was then dissolved in the suspension and stirred for 24 h. The homogenized colloidal suspension was poured into a polytetrafluoroethylene mold and dried at 60 °C for 48 h to form a CSPE film. The mass percentage of MIL-88A and etched MIL-88A in the total PEO and MOF was 10 wt%, and the Li / EO molar ratio was 1:20. All preparation processes were performed in an argon-filled glove box.

[0091] Characterization of composite solid electrolytes

[0092] A composite electrolyte was obtained by combining acid-etched MIL-88A with PEO and LiTFSI. Surface and cross-sectional SEM images of the CSPE are shown. Figure 12 The morphology and structure of the electrolyte were shown. Compared to the rough surface of the PEO sample, the introduction of MIL-88A and modified MIL-88A resulted in a relatively smoother surface for all composite electrolytes. SEM images showed that the MOFs were tightly encapsulated by the PEO matrix, and no obvious cracks or pinholes were observed on the electrolyte surface, indicating a high affinity between MIL-88A and PEO. Cross-sectional SEM images revealed the dense structure of the prepared composite solid electrolyte, with MOFs uniformly distributed within the PEO matrix. Further verification confirmed that the film thickness was approximately 50 μm.

[0093] Electrochemical performance testing

[0094] To investigate the effect of acid-etched MIL-88A on the ion transport behavior of PEO-based CSPE, the ionic conductivity of the composite solid electrolyte was tested at 30–80 °C. Figure 12 The ionic conductivity of CSPE increases with the degree of MOF acid etching. MIL-88A-100μL-PEO achieves an ionic conductivity of 4.7 × 10⁻⁶ at 60 °C. -4 S·cm -1 The ionic conductivity of PEO is 1.63 × 10⁻⁶. -4 S·cm -1 The ionic conductivity is approximately two orders of magnitude higher than that of MIL-88A-100μL-PEO. This is attributed to the ability of MIL-88AMOF to capture anions (TFSI) after etching. - The ability to reduce the crystallinity of electrolytes after addition.

[0095] The effect of etching MIL-88A on the electrochemical stability window of CSPE was investigated using linear sweep voltammetry (LSV). Figure 13Compared to PEO with a stable voltage of ~5.2 V, MIL-88A-PEO and etched MIL-88A-PEO exhibit a wider electrochemical window (~5.6 V), indicating improved electrochemical stability of the electrolyte. This significant improvement in the electrochemical stability window is due to the effective trapping ability of MIL-88A for small molecules and the strong interaction between MIL-88A nanoparticles and PEO chains. The additional porosity of the etched MIL-88A further adsorbs organic molecules.

[0096] LFP||SPE||Li cells were assembled and tested at 60°C to investigate electrochemical cycling and rate performance. Figure 14 It can be seen that the LFP||PEO||Li battery exhibits 158.3, 157, 153.2, 144.7, 118.6, and 56.9 mAh g⁻¹ at 0.05, 0.1, 0.2, 0.5, 1, and 2C, respectively. -1 The discharge capacity of all LFP||etched MIL-88A-PEO||Li batteries is higher and the polarization is lower than that of LFP||PEO||Li batteries. Specifically, the etched MIL-88A-100μL-PEO with the highest ionic conductivity provides 138.1 mAh g at 2C. -1 The highest discharge capacity. When the current density returns to 0.1C, the LFP||etched MIL-88A-100μL-PEO||Li battery also exhibits better performance than the LFP||PEO||Li battery (150.8mAh g). -1 ) Higher 157.2mAh g -1 The discharge capacity was measured. The results show that the LFP||etched MIL-88A-100μL-PEO||Li full cell exhibits good transport dynamics.

[0097] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. The application of a composite solid electrolyte prepared from modified MOFs fillers in lithium-ion batteries, characterized in that, The preparation method of composite solid electrolyte is to disperse modified MOF fillers in solvent under inert gas protection, then add organic electrolyte lithium salt and PEO, stir to obtain colloidal suspension, and then pour it into mold to dry and shape. The molar ratio of Li in the organic electrolyte lithium salt to EO in PEO is 1:(18-25); the amount of modified MOF filler added is 5-20 wt% of the total amount of PEO and modified MOF filler. Modified MOF fillers refer to one of the following two types: The first type: In the MIL series of MOF materials, some metal nodes are replaced by cerium metal; The preparation method includes the following steps: dissolving the metal source salt, cerium salt and ligand in water, followed by crystallization reaction, centrifugation, washing and drying; The molar ratio of cerium salt to metal source salt ranges from 0.1 to 0.

45. The ratio of the total molar amount of the metal source salt and cerium salt to the molar amount of the added ligand is 1:(0.8-1.2); The second type: MIL series MOF materials, with etched holes on the surface; The preparation method includes the following steps: dissolving the metal source salt and ligand in water, followed by crystallization reaction, centrifugation, washing, and drying to obtain MOF particles; dispersing the obtained MOF particles and phytic acid in water, heating, and then washing, centrifuging, and drying. The molar ratio of the metal source salt to the ligand is 1:(0.8-1.2); The ratio of MOF particles to phytic acid is (80-120) mg:(40-150) μl.

2. The application according to claim 1, characterized in that, Metal refers to one of the following: Fe, V, Cr, and Ni; The MIL series of MOF materials refers to one or more of MIL-53, MIL-68, MIL-88A, MIL-88B, MIL-100, MIL-101, and MIL-125.

3. The application according to claim 1, characterized in that, Cerium accounts for 0.1-0.45% of all metals; the pore size ranges from 10-200 nm.

4. The application according to claim 1, characterized in that, The ligand is fumaric acid, the metal source salt is FeCl3⋅6H2O, and the cerium salt is Ce(NO3)3⋅6H2O.

5. The application according to claim 1, characterized in that, For the first type of filler, the crystallization reaction conditions are: 60-90℃, 10-15h; the drying conditions are: under vacuum, 90-120℃, 20-48h.

6. The application according to claim 1, characterized in that, For the second type of filler, the crystallization reaction conditions are: 60-90℃, 10-15h; the drying conditions are: under vacuum, 90-120℃, 20-48h.

7. The application according to claim 1, characterized in that, For the second type of packing, the heating conditions are: under vacuum, 80-110℃, for 2-8 hours; The drying conditions are: vacuum conditions, 50-80℃, 4-9h.

8. The application according to claim 1, characterized in that, The organic electrolyte lithium salt is selected from lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, or lithium bis(trifluoromethanesulfonyl)imide.

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