Preparation method and application of ceramic-based composite solid electrolyte

Abstract

The invention belongs to the technical field of solid electrolyte, and particularly relates to a preparation method and application of ceramic-based composite solid electrolyte. The ceramic-based composite solid electrolyte composition is prepared from the following components in parts by weight: 1.2 to 4.6 parts of lithium titanium aluminum phosphate, 0.5 to 0.7 part of polyvinylidene fluoride-hexafluoropropylene copolymer, 0.1 to 0.3 part of lithium bis (trifluoromethanesulfonimide) and 3.0 to 12 parts of N, N-dimethylformamide, and the number-average molecular weight of the polyvinylidene fluoride-hexafluoropropylene copolymer is 200000 to 500000. The prepared ceramic-based composite solid electrolyte has the characteristics of mechanical flexibility, high lithium ion conductivity, large lithium ion transference number, wide electrochemical stability window and the like, and has a wide application prospect in quasi-solid-state and all-solid-state lithium batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid electrolytes, and in particular relates to a preparation method and application of a ceramic-based composite solid electrolyte. Background Art

[0002] As electric vehicles become increasingly common, battery energy density, electrochemical stability, and safety continue to attract attention. Most commercial lithium-ion batteries use liquid electrolytes as a transmission medium. Liquid electrolytes are often volatile and flammable, making them prone to battery-related safety incidents that seriously impact people's daily lives. Furthermore, liquid lithium-ion batteries are prone to lithium dendrites, which can cause short circuits. If used improperly, they can even cause fires, explosions, and other safety incidents. In contrast, solid-state batteries offer the advantages of higher energy density, greater electrochemical stability, and improved safety.

[0003] Composite solid electrolytes can be categorized as polymer-based and ceramic-based based on the matrix material. Polymer-based composite solid electrolytes use a polymer matrix (such as PEO and PVDF), with the polymer amorphous regions dominating and fillers assisting in the formation of fast channels. These electrolytes exhibit flexibility, good interfacial contact, and ease of processing, but generally exhibit low ionic conductivity and a narrow electrochemical window (approximately 4V for PEO-based electrolytes). These electrolytes are suitable for flexible batteries and consumer electronics. Ceramic-based composite solid electrolytes use a ceramic matrix (such as LLZO and LATP), with the ceramic phase dominating and interface modification optimizing contact. These electrolytes exhibit high ionic conductivity and provide efficient ion transport pathways. Ceramic fillers promote lithium salt dissociation through interfacial interactions (such as Lewis acid-base interactions) and form fast interfacial channels. These electrolytes exhibit a wide electrochemical window (>5V) and excellent chemical stability across a wide range of temperatures and chemical environments, making them suitable for high-energy-density solid-state lithium metal batteries. However, these electrolytes are difficult to process, requiring high-pressure and high-temperature processing, which increases manufacturing costs. High-pressure and high-temperature processing can lead to increased brittleness and cracking, potentially shortening their service life.

[0004] In the prior art, although a polymer-based composite solid electrolyte is disclosed, which is a layered structure composed of multiple polymer electrolyte layers, each polymer electrolyte layer is obtained by spin coating an electrolyte solution, wherein the electrolyte solution includes: polymer, lithium salt and active filler. However, the thermal stability of the polymer-based composite solid electrolyte is poor, the preparation process is complicated and tedious, and the added polymer is dominant (volume share> 30%), and the ceramic filler is added to reduce the crystallinity of the polymer and provide additional Li + Transmission channel, etc.; Li + The transmission mainly relies on the amorphous region of the polymer matrix. It can be seen that there are significant differences between ceramic-based composite solid electrolytes and polymer-based composite solid electrolytes in terms of material composition, structural design, performance characteristics and applicable scenarios. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing and applying a ceramic-based composite solid electrolyte, thereby overcoming the shortcomings of the prior art. The ceramic-based composite solid electrolyte, prepared by mixing high-content solid electrolyte lithium aluminum titanium phosphate, lithium bis(trifluoromethanesulfonylimide) and polyvinylidene fluoride-hexafluoropropylene copolymer, has the characteristics of mechanical flexibility, high lithium ion conductivity, large lithium ion migration number, and wide electrochemical stability window, and can be applied to quasi-solid-state and all-solid-state lithium batteries.

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] In a first aspect, the present invention provides a ceramic-based composite solid electrolyte composition, which is composed of the following components, calculated by weight: 1.2-4.6 parts of lithium aluminum titanium phosphate, 0.5-0.7 parts of polyvinylidene fluoride-hexafluoropropylene copolymer, 0.1-0.3 parts of lithium bis(trifluoromethanesulfonyl)imide, and 3.0-12 parts of N,N-dimethylformamide;

[0008] The number average molecular weight of the polyvinylidene fluoride-hexafluoropropylene copolymer is 200,000 to 500,000.

[0009] In some other embodiments, the composition is composed of the following components, by weight: 1.2-3.2 parts of lithium titanium aluminum phosphate, 0.55-0.65 parts of polyvinylidene fluoride-hexafluoropropylene copolymer, 0.15-0.25 parts of lithium bis(trifluoromethanesulfonyl)imide, and 3.5-8.5 parts of N,N-dimethylformamide;

[0010] The number average molecular weight of the polyvinylidene fluoride-hexafluoropropylene copolymer is 250,000 to 350,000.

[0011] In some other embodiments, the composition is composed of the following components, in parts by weight: 3.2 parts of lithium titanium aluminum phosphate, 0.6 parts of polyvinylidene fluoride-hexafluoropropylene copolymer, 0.2 parts of lithium bis(trifluoromethanesulfonyl)imide, and 8 parts of N,N-dimethylformamide;

[0012] The number average molecular weight of the polyvinylidene fluoride-hexafluoropropylene copolymer is 300,000.

[0013] In some other embodiments, the particle size of the lithium aluminum titanium phosphate is 200-400 nm;

[0014] The purity of the lithium bis(trifluoromethanesulfonyl)imide is greater than 99%.

[0015] In a second aspect, the present invention provides a ceramic-based composite solid electrolyte membrane made from the ceramic-based composite solid electrolyte composition described in the first aspect.

[0016] In some other embodiments, the thickness of the ceramic-based composite solid electrolyte membrane is 15-60 μm;

[0017] Lithium ion transference number> 0.434, lithium ion conductivity> 0.418mS / cm;

[0018] In the ceramic-based composite solid electrolyte membrane, lithium titanium aluminum phosphate is filled in a polyvinylidene fluoride-hexafluoropropylene copolymer.

[0019] In a third aspect, the present invention provides a method for preparing the ceramic-based composite solid electrolyte membrane according to the second aspect,

[0020] The dried lithium aluminum titanium phosphate, lithium bis(trifluoromethanesulfonyl imide), polyvinylidene fluoride-hexafluoropropylene copolymer and a dispersant are uniformly mixed, coated on a substrate, and vacuum-dried to obtain the product.

[0021] In some other embodiments, the drying is vacuum drying at 45-55° C. for 20-30 h;

[0022] The vacuum drying is to first stand at room temperature for 20-30 minutes under vacuum, and then heat to 55-65° C. and dry for 10-12 hours.

[0023] In a fourth aspect, the present invention provides the use of the ceramic-based composite solid electrolyte membrane described in the second aspect in quasi-solid-state and all-solid-state lithium batteries.

[0024] In a fifth aspect, the present invention provides a lithium battery comprising the ceramic-based composite solid electrolyte membrane described in the second aspect, a lithium iron phosphate positive electrode, and a metallic lithium negative electrode;

[0025] Preferably, the lithium iron phosphate positive electrode includes a positive electrode current collector, a conductive material, a binder and a catalyst;

[0026] Further preferably, the conductive material is one of conductive carbon black, carbon nanotubes, acetylene black and Ketjen carbon;

[0027] More preferably, the binder is one of polyvinylidene fluoride and polytetrafluoroethylene.

[0028] The ceramic-based composite solid electrolyte composition of the present invention is composed of an inorganic solid electrolyte, lithium titanium aluminum phosphate, lithium bis(trifluoromethanesulfonyl imide), and polyvinylidene fluoride-hexafluoropropylene copolymer. It can better adhere to the lithium negative electrode and the lithium iron phosphate positive electrode, reducing the interfacial impedance, thereby directly improving the thermal stability and electrochemical performance of the solid-state battery. Among them, the addition of a high content of lithium titanium aluminum phosphate gives the composite solid electrolyte strong mechanical strength, which, from a physical perspective, better suppresses the formation of lithium dendrites and increases the conductivity of the composite solid electrolyte. It also improves the mechanical strength and stability in high temperature and high pressure environments, avoiding its possible deformation, decomposition, or failure.

[0029] Beneficial effects of the present invention:

[0030] (1) The present invention combines inorganic filler lithium titanium aluminum phosphate, lithium bis(trifluoromethanesulfonyl imide) and polyvinylidene fluoride-hexafluoropropylene copolymer (high-density lithium titanium aluminum phosphate is precipitated and the upper polymer is stable to obtain a polymer layer) thin layer to obtain a ceramic-based composite solid electrolyte with high ionic conductivity, high ion migration number, wide electrochemical stability window, good heat resistance and flexibility, so that it can be used in quasi-solid-state and all-solid-state lithium batteries. The polymer thin layer is close to the lithium negative electrode to protect the active metal.

[0031] (2) The present invention produces a ceramic-based composite solid electrolyte by adding a high content of inorganic filler, improving its room temperature conductivity and lithium ion transference number, and widening its electrochemical stability window. The ceramic-based composite solid electrolyte also exhibits excellent thermal stability and a simple preparation process. The high mechanical modulus of the ceramic component in the ceramic-based composite solid electrolyte effectively inhibits lithium dendrite penetration, improving battery safety.

[0032] (3) The polyvinylidene fluoride-hexafluoropropylene copolymer of the present invention provides support and wrapping for lithium aluminum titanium phosphate, solving the problem of Ti in the traditional LiSICON inorganic solid electrolyte lithium aluminum titanium phosphate (LATP). 4+ Regarding the problem of attacks on the active metal negative electrode of metal batteries; lithium bis(trifluoromethanesulfonyl imide) has high ionic conductivity. In the ceramic-based composite solid electrolyte, it can provide a good channel for the migration of lithium ions, so that lithium ions can be conducted more quickly between the positive and negative electrodes during the battery charging and discharging process; and lithium aluminum titanium phosphate is filled in polyvinylidene fluoride-hexafluoropropylene copolymer, which increases the conductivity of the polymer electrolyte; improves the mechanical strength and stability in high temperature and high pressure environments, and avoids possible deformation, rupture, decomposition or failure.

[0033] (4) The preparation method of the present application is simple and the preparation conditions are mild. The raw materials are cheap and easily available, which is conducive to promoting the industrialization and application of ceramic-based composite solid electrolytes in lithium batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0035] Figure 1 is an optical photograph of the ceramic-based composite solid electrolyte prepared in Example 1 of the present invention;

[0036] Figure 2 are scanning electron microscope images of Examples 1-3 of the present invention and Comparative Example 1;

[0037] Figure 3 is the X-ray diffraction pattern of the ceramic-based composite solid electrolyte prepared in Examples 1-3 of the present invention;

[0038] Figure 4 Figures 1-3 and 2 show the fire test results of the ceramic-based composite solid electrolytes prepared in Examples 1-3 and Comparative Example 1, as well as Comparative Example 2. Figure a shows the fire test results after 10 minutes of fire at room temperature and 200°C, b shows the thermogravimetric test, c shows the extreme fire test results of the commercial Celgard 2400 separator in Comparative Example 2, d shows the extreme fire test results of Comparative Example 1, and e.g. show the extreme fire test results of Examples 1-3.

[0039] Figure 5 Schematic diagram of the structural assembly of lithium metal batteries assembled with ceramic-based composite solid electrolytes prepared in Examples 1-3 and Comparative Example 1 of the present invention;

[0040] Figure 6 The ion migration number test results and constant voltage polarization curves of the ceramic-based composite solid electrolytes prepared in Examples 1-3 and Comparative Example 1, as well as the EIS results before and after constant voltage polarization (inset), are shown in Figures a and b, respectively, for Comparative Example 1, c and d, respectively, for Example 2 and 3.

[0041] Figure 7 The conductivity test results of the ceramic-based composite solid electrolytes prepared in Examples 1-3 and Comparative Example 1 are as follows;

[0042] Figure 8 is the mechanical flexibility of Inventive Examples 1-3;

[0043] Figure 9 This is the electrochemical window test of the ceramic-based composite solid electrolytes prepared in Examples 1-3 and Comparative Example 1;

[0044] Figure 10 The ceramic-based composite solid electrolyte lithium symmetric batteries prepared in Examples 1-3 and Comparative Example 1 were subjected to SEM characterization tests after cycling for 650 h.

[0045] Among them, Figure 2-Figure 4 、 Figure 6-10 CSE-1, CSE-2, CSE-3, and CSE-0 correspond to the ceramic-based composite solid electrolytes prepared in Example 1, Example 2, Example 3, and Comparative Example 1, respectively. DETAILED DESCRIPTION

[0046] The PVDF-HFP, LATP, LITFSI and N,N-dimethylformamide used in the embodiments of the present invention are all commercially available products, wherein the purity of PVDF-HFP is 99.9 wt.%, and the purity of LITFSI is greater than 99%.

[0047] Example 1

[0048] (1) Drying of raw materials:

[0049] PVDF-HFP, LATP, and LITFSI were placed in a vacuum drying oven at 50°C for 24 hours to remove moisture, and then placed in a glove box for later use. The number average molecular weight of PVDF-HFP was 300,000, and the particle size of LATP was 300 nm.

[0050] (2) Preparation of lithium aluminum titanium phosphate, lithium bis(trifluoromethanesulfonyl imide) and polyvinylidene fluoride-hexafluoropropylene copolymer slurry:

[0051] Weigh 1.2g of LATP, 0.6g of PVDF-HFP, and 0.2g of LITFSI and dissolve them in 4g of N,N-dimethylformamide. Ultrasonicate for 1 hour to completely disintegrate any LATP clumps and obtain a slurry. Stir the slurry at 800 rpm for 24 hours. During stirring, add N,N-dimethylformamide frequently until the slurry clearly adheres to the wall of the cup when gently shaken and still maintains some fluidity.

[0052] (3) Slurry coating and film formation

[0053] The stirred slurry was coated onto a thin glass slide using an infrared flatbed coater to a coating height of 300 μm. The slide was then placed in a vacuum drying oven at room temperature for 30 minutes, then heated to 60°C and dried for 10 hours to remove the solvent, resulting in a ceramic-based composite solid electrolyte film. The film was then gently removed with tweezers. A hydraulic slicer was used to cut the film into discs with a diameter of 16 mm and a thickness ranging from 15 μm to 60 μm. The discs were then placed in a glove box with a water and oxygen concentration of less than 0.1 ppm for further use. The prepared ceramic-based composite solid electrolyte was designated CSE-1.

[0054] The optical photos taken of the prepared ceramic-based composite solid electrolyte are as follows: Figure 1 As shown, the surface is white.

[0055] Example 2

[0056] Unlike Example 1, in step (2), 1.87 g of LATP, 0.6 g of PVDF-HFP, and 0.2 g of LITFSI were weighed and dissolved in 5.4 g of N,N-dimethylformamide solution. The solution was ultrasonically treated for 1 hour to completely crush the bulk LATP to obtain a slurry. The slurry was stirred at 800 rpm for 24 hours. During the stirring process, N,N-dimethylformamide was added at regular intervals until the slurry adhered to the wall of the cup when lightly shaken and still had a certain degree of fluidity.

[0057] The other steps are the same as those in the embodiment and will not be repeated here. The prepared ceramic-based composite solid electrolyte is labeled CSE-2.

[0058] Example 3

[0059] Unlike Example 1, in step (2), 3.2 g of LATP, 0.6 g of PVDF-HFP, and 0.2 g of LITFSI were weighed and dissolved in an 8 g N,N-dimethylformamide solution. The solution was ultrasonically treated for 1 hour to completely crush the bulk LATP to obtain a slurry. The slurry was stirred at 800 rpm for 24 hours. During the stirring process, N,N-dimethylformamide was added at regular intervals until the slurry adhered to the wall of the cup when lightly shaken and still had a certain degree of fluidity.

[0060] The other steps are the same as those in the embodiment and will not be repeated here. The prepared ceramic-based composite solid electrolyte is labeled CSE-3.

[0061] Example 4

[0062] Unlike Example 1, in step (2), 4.53 g of LATP, 0.6 g of PVDF-HFP, and 0.2 g of LITFSI were weighed and dissolved in an N,N-dimethylformamide solution (11 g). The solution was ultrasonically treated for 1 hour to completely crush the bulk LATP to obtain a slurry. The slurry was stirred at 800 rpm for 24 hours. During the stirring process, N,N-dimethylformamide was added at regular intervals until the slurry adhered to the wall of the cup when lightly shaken and still had a certain degree of fluidity.

[0063] In step (3), since the proportion of filler LATP is too large, there is too little polymer to form a film, and the whole is in powder form. The reason may be that part of PVDF-HFP loses its polymer properties during the doping reaction.

[0064] The other steps are the same as those in the embodiment and will not be repeated here.

[0065] Comparative Example 1

[0066] The difference from Example 1 is that LATP is not added. The preparation process is as follows:

[0067] (1) Drying of raw materials:

[0068] PVDF-HFP and LITFSI were placed in a vacuum drying oven at 60°C for 24 hours to remove moisture, and then placed in a glove box for later use. The polyvinylidene fluoride-hexafluoropropylene copolymer had a number average molecular weight of 300,000, and the purity of LITFSI was greater than 99%.

[0069] (2) Preparation of lithium bis(trifluoromethanesulfonyl)imide and polyvinylidene fluoride-hexafluoropropylene copolymer slurry:

[0070] Dissolve lithium bis(trifluoromethanesulfonylimide) and poly(vinylidene fluoride-hexafluoropropylene) in N,N-dimethylformamide (DMF). Stir the slurry at 800 rpm for 24 hours. Add DMF frequently during stirring until the slurry adheres to the wall of the cup when gently shaken and retains some fluidity.

[0071] (3) Slurry coating and film formation

[0072] The stirred slurry was coated onto a thin glass slide using an infrared flatbed coater to a coating height of 300 μm. The slide was then placed in a vacuum drying oven at room temperature for 30 minutes, then heated to 60°C and dried for 10 hours to remove the solvent, resulting in a polymer solid electrolyte film. The film was then gently removed with tweezers. A hydraulic slicer was used to cut the film into discs with a diameter of 16 mm and a thickness ranging from 15 μm to 60 μm. The discs were then stored in a glove box with a water and oxygen concentration of less than 0.1 ppm until ready for use. The resulting ceramic-based composite solid electrolyte is designated CSE-0.

[0073] Comparative Example 2

[0074] Commercial Celgard 2400 diaphragm.

[0075] Comparative Example 3

[0076] Commercially available lithium aluminum titanium phosphate electrolyte (Kulude LATP lithium aluminum titanium phosphate solid electrolyte sheet, Dongguan Kulude New Energy Technology Co., Ltd.).

[0077] Performance Testing:

[0078] 1. Scanning Electron Microscope:

[0079] The ceramic-based composite solid electrolyte films prepared in Examples 1 to 3 of the present invention and Comparative Example 1 were observed under a scanning electron microscope at a scale of 1 μm. Figure 2 As shown. Figure 2It can be seen that the surface of the ceramic-based composite solid electrolytes of Examples 1 to 3 is uniformly loaded with LATP, the LATP interconnection provides angular contact, and the internal phosphorus-oxygen tetrahedron provides high lithium ion migration efficiency; while in Comparative Example 1, which is composed of pure polymer PVDF-HFP and lithium salt, lithium ion transport mainly relies on the movement of PVDF-HFP chain segments and the dissociation of lithium salt.

[0080] 2. X-ray diffraction:

[0081] The X-ray diffraction results of the ceramic-based composite solid electrolytes prepared in Examples 1 to 3 of the present invention and Comparative Example 1 are as follows: Figure 3 As shown. Figure 3 It can be seen that the ceramic-based composite solid electrolytes of Examples 1 to 3 are free of impurity peaks, have high crystallinity, and exhibit good suppression of the amorphous region. In contrast, the XRD pattern of Comparative Example 1 shows characteristic amorphous peaks of PVDF-HFP at 2θ values of 18.25° and 20.02°, indicating that the relative intensity of the amorphous peaks decreases with increasing LATP content.

[0082] 3. Fire performance:

[0083] The fire performance of the solid electrolytes of Examples 1 to 3 of the present invention and Comparative Examples 1 and 2 is shown in FIG. Figure 4 As shown, a is a fire test diagram after burning for 10 minutes at a temperature from room temperature to 200°C; b is a thermogravimetric test; c is the extreme fire test of the commercial Celgard2400 diaphragm of comparative example 2, d is the extreme fire test of comparative example 1; eg are the extreme fire tests of Examples 1-3.

[0084] Depend on Figure 4 It can be seen that from Figure 4 It can be seen from a, c, d and eg in that Examples 1 to 3 have better overall stability than Comparative Examples 1 and 2 when burning with the external flame of an alcohol lamp, without any ignition phenomenon, and have stable performance at high temperatures. This is because the main components of Comparative Examples 1 and 2 are polyethylene and polypropylene organic substances, which are extremely flammable and unsafe in extreme conditions of the battery. This is consistent with the Figure 4 The thermogravimetric test results in Figure b remain consistent. For Comparative Example 1, the main components are a polymer and an organic lithium salt. Under the high temperature of the flame, the polymer's molecular chains break, triggering a thermal decomposition reaction. The organic lithium salt also decomposes, resulting in curling. For Example 3, the solid electrolyte with a high lithium aluminum titanium phosphate content did not ignite itself during the 10-second fire test, but only partially turned black. This is because the PVDF-HFP partially carbonized. Therefore, Example 3 exhibits the best extreme fire performance.

[0085] 4.Battery assembly:

[0086] The structural assembly diagram of ceramic-based composite solid electrolyte (CSE) applied to lithium metal batteries is shown as follows: Figure 5 The entire process is performed in a glove box (Ar atmosphere, H2O / O2 <0.1ppm). From bottom to top, the negative electrode shell, spring, steel sheet, lithium sheet, CSE (ceramic composite solid electrolyte), lithium iron phosphate (LFP) positive electrode sheet, and positive electrode shell are placed in the order shown. The assembled battery is placed in a manual pressing clamp or mold, and gentle pressure is applied to seal it.

[0087] 5. Lithium ion migration number test:

[0088] The ion migration number of the ceramic-based composite solid electrolyte prepared in Examples 1-3 and Comparative Example 1 was tested using a classic ion migration number test method. The test process is as follows:

[0089] (1) Assemble a lithium sheet-solid electrolyte-lithium sheet symmetrical battery and add 5 μL of electrolyte (1M LiPF6EC:DEC=1:1Vo1%) to ensure good contact;

[0090] (2) EIS test was performed using an electrochemical workstation with a scanning rate of 5 mV·s and a test condition of 100000 Hz-10 Hz. -1 , record the impedance data;

[0091] (3) Using an electrochemical workstation, perform constant voltage polarization on the battery with a perturbation voltage of 10 mV and a perturbation time of 3600 s. Stop after observing the current equilibrium.

[0092] (4) Test EIS again with the same parameters as in step (2) and calculate the ion mobility using formula (1).

[0093]

[0094] Among them, I ss is the current after constant voltage polarization; I0 is the current before constant voltage polarization; ΔV is the polarization voltage; R ss is the impedance before constant voltage polarization; R0 is the impedance after constant voltage polarization.

[0095] The test results are as follows Figure 6 As shown in a to d in FIG, as the content of lithium aluminum titanium phosphate increases, the lithium ion migration number calculated according to formula (1) also increases. This is because the phosphorus-oxygen tetrahedron inside the lithium aluminum titanium phosphate contacts and transmits lithium ions.

[0096] 6. Conductivity test:

[0097] A symmetrical steel sheet-solid electrolyte-steel sheet cell was assembled, with a test frequency set between 100,000 Hz and 10 Hz, and a test rate of 5 mV / s. Bulk impedance was measured using an electrochemical workstation (no fitting required). Lithium ion conductivity was calculated by substituting the electrolyte thickness L, effective area S, and measured bulk impedance R into the ionic conductivity formula.

[0098]

[0099] Wherein, σ is the ionic conductivity; L is the thickness of the solid electrolyte; R is the resistance of the solid electrolyte; and S is the effective area of the solid electrolyte in contact with the steel sheet.

[0100] The test results are as follows Figure 7 As shown, from Figure 7 As can be seen in a and b, as the content of lithium aluminum titanium phosphate increases, the lithium ion conductivity gradually increases. This is because the phosphorus-oxygen tetrahedron inside the lithium aluminum titanium phosphate contacts and transmits lithium ions.

[0101] The properties of the mixed solid electrolytes of Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 1 below.

[0102] Table 1 Properties of ceramic-based composite solid electrolytes

[0103]

[0104] “-” in Table 1 means not tested

[0105] As shown in Table 1, Comparative Example 1 does not add lithium titanium aluminum phosphate polymer electrolyte, and both the ion conductivity and the ion migration number are the lowest. After adding the inorganic solid electrolyte in Examples 1-3, the high ion flux polymer coating connects the inorganic solid electrolyte lithium titanium aluminum phosphate to form a channel for lithium ion transmission efficiency. It can be seen that as the content of lithium titanium aluminum phosphate increases, the overall performance increases. This is because the internal structure has been converted from the polymer in Comparative Example 1 as the main body to the inorganic filler as the main body of the solid electrolyte. During the constant voltage polarization process, the directional migration of lithium ions will cause a concentration gradient to appear inside the electrolyte, thereby triggering concentration polarization. This polarization will significantly increase the interfacial impedance, which is manifested as an increase in impedance after polarization.

[0106] Figure 8 The mechanical flexibility of the invention examples 1-3 was tested by the bending flexibility test method. Figure 8 It can be seen that the ceramic-based composite solid electrolyte has a certain flexibility.

[0107] Figure 9 The electrochemical window test of the ceramic-based composite solid electrolyte prepared in Examples 1-3 and Comparative Example 1 was performed, and the electrochemical window test was performed on the assembled lithium-steel battery. Figure 9It can be seen that CSE-3 with high inorganic filler content has a wider electrochemical window.

[0108] Figure 10 The ceramic-based composite solid electrolyte assembled lithium symmetric batteries prepared in Examples 1-3 and Comparative Example 1 were subjected to SEM characterization tests after 650 hours of cycling to detect the inhibition of lithium dendrites. Figure 10 It can be seen that the surface of CSE-3 with a high inorganic filler content is smooth and has a good inhibitory effect on the growth of lithium dendrites. The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A ceramic-based composite solid electrolyte composition, characterized in that: The invention is composed of the following components in parts by weight: 1.2-4.6 parts of lithium titanium aluminum phosphate, 0.5-0.7 parts of polyvinylidene fluoride-hexafluoropropylene copolymer, 0.1-0.3 parts of lithium bis(trifluoromethanesulfonyl)imide, and 3.0-12 parts of N,N-dimethylformamide; The number average molecular weight of the polyvinylidene fluoride-hexafluoropropylene copolymer is 200,000-500,000.

2. A ceramic-based composite solid electrolyte composition according to claim 1, characterized in that: The invention is composed of the following components in parts by weight: 1.2-3.2 parts of lithium titanium aluminum phosphate, 0.55-0.65 parts of polyvinylidene fluoride-hexafluoropropylene copolymer, 0.15-0.25 parts of lithium bis(trifluoromethanesulfonyl)imide, and 3.5-8.5 parts of N,N-dimethylformamide; The number average molecular weight of the polyvinylidene fluoride-hexafluoropropylene copolymer is 250,000-350,000.

3. The ceramic-based composite solid electrolyte composition according to claim 1, characterized in that: The invention is composed of the following components in parts by weight: 3.2 parts of lithium aluminum titanium phosphate, 0.6 parts of polyvinylidene fluoride-hexafluoropropylene copolymer, 0.2 parts of lithium bis(trifluoromethanesulfonyl)imide, and 8 parts of N,N-dimethylformamide; The number average molecular weight of the polyvinylidene fluoride-hexafluoropropylene copolymer is 300,000.

4. The ceramic-based composite solid electrolyte composition according to claim 1, characterized in that: The particle size of the lithium aluminum titanium phosphate is 200-400 nm; The purity of the lithium bis(trifluoromethanesulfonyl)imide is greater than 99%.

5. A ceramic-based composite solid electrolyte membrane made from the ceramic-based composite solid electrolyte composition according to any one of claims 1 to 4.

6. The ceramic-based composite solid electrolyte membrane according to claim 5, characterized in that: The thickness of the ceramic-based composite solid electrolyte membrane is 15-60 μm; Lithium ion transference number> 0.434, lithium ion conductivity> 0.418mS / cm; In the ceramic-based composite solid electrolyte membrane, lithium titanium aluminum phosphate is filled in a polyvinylidene fluoride-hexafluoropropylene copolymer.

7. A method for preparing a ceramic-based composite solid electrolyte membrane according to claim 5 or 6, characterized in that: The dried lithium aluminum titanium phosphate, lithium bis(trifluoromethanesulfonyl imide), polyvinylidene fluoride-hexafluoropropylene copolymer and N,N-dimethylformamide are uniformly mixed, coated on a substrate, and vacuum-dried to obtain the product.

8. The method for preparing a ceramic-based composite solid electrolyte membrane according to claim 7, wherein: The drying is performed by vacuum drying at 45-55° C. for 20-30 hours; The vacuum drying is to first stand at room temperature for 20-30 minutes under vacuum, and then heat to 55-65° C. and dry for 10-12 hours.

9. Use of the ceramic-based composite solid electrolyte membrane according to claim 5 or 6 in quasi-solid-state and all-solid-state lithium batteries.

10. A lithium battery, characterized in that: It comprises the ceramic-based composite solid electrolyte membrane according to claim 5 or 6, a lithium iron phosphate positive electrode and a metallic lithium negative electrode; Preferably, the lithium iron phosphate positive electrode includes a positive electrode current collector, a conductive material, a binder and a catalyst; Further preferably, the conductive material is one of conductive carbon black, carbon nanotubes, acetylene black and Ketjen carbon; More preferably, the binder is one of polyvinylidene fluoride and polytetrafluoroethylene.

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