Aerogel reinforced composite electrolyte film for solid-state lithium battery and preparation method of aerogel reinforced composite electrolyte film

Abstract

The invention provides an aerogel reinforced composite electrolyte thin film for a solid-state lithium battery and a preparation method of the aerogel reinforced composite electrolyte thin film, and belongs to the technical field of composite electrolytes.The thin film comprises a three-dimensional porous aerogel skeleton, a solid-state electrolyte compound and lithium salt nanocrystals; wherein the three-dimensional porous aerogel skeleton is prepared from inorganic oxide nanoparticles and a polymer precursor through a sol-gel method; pores of the three-dimensional porous aerogel skeleton are filled with the solid electrolyte compound, the solid electrolyte compound comprises lithium lanthanum zirconium oxide nanowires and a polyoxyethylene-lithium salt composite matrix, and the lithium lanthanum zirconium oxide nanowires are directionally arranged in the thickness direction of the film; the lithium salt nanocrystals grow on the surface of the pore wall of the three-dimensional porous aerogel in situ; the mass ratio of the aerogel skeleton to the solid electrolyte compound is (1: 3)-(1: 15). According to the thin film, the ionic conductivity, the mechanical strength and the interface stability of the electrolyte are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of composite electrolyte, and particularly relates to an aerogel reinforced composite electrolyte film for a solid-state lithium battery and a preparation method thereof. BACKGROUND

[0002] With the rapid growth of energy demand and the increasingly serious environmental pollution problem, developing high-energy density and high-safety energy storage technology has become a research hotspot. Among them, the solid-state lithium battery is considered as an important development direction of the next generation of energy storage devices due to its high theoretical energy density and intrinsic safety. However, the low ionic conductivity of the solid-state electrolyte, the large interface impedance and the insufficient mechanical properties seriously restrict its practical application. Although the traditional polymer-based solid-state electrolyte has the advantages of flexibility and processing, it has low room temperature ionic conductivity and insufficient mechanical strength to inhibit lithium dendrite growth. Although the inorganic solid-state electrolyte has high ionic conductivity and mechanical strength, it is brittle and has poor interface contact, which is difficult to form a close contact with the electrode.

[0003] In view of this, the present application is proposed. SUMMARY

[0004] The first object of the present application is to provide an aerogel reinforced composite electrolyte film for a solid-state lithium battery, which realizes high ionic conductivity, excellent mechanical strength and interface stability of the electrolyte film through the synergistic effect of a unique three-dimensional porous aerogel skeleton, a solid-state electrolyte composite and lithium salt nanocrystals.

[0005] The second object of the present application is to provide a preparation method of the above-mentioned aerogel reinforced composite electrolyte film for a solid-state lithium battery, which solves the long-standing dilemma in the field of composite electrolyte that high conductivity, good mechanical properties and excellent interface stability are difficult to be considered together.

[0006] In order to achieve the above-mentioned objects of the present application, the following technical solutions are adopted:

[0007] An aerogel reinforced composite electrolyte film for a solid-state lithium battery, the film comprising a three-dimensional porous aerogel skeleton, a solid-state electrolyte composite and lithium salt nanocrystals;

[0008] The three-dimensional porous aerogel skeleton is prepared from inorganic oxide nanoparticles and polymer precursors by sol-gel method, and the pore size of the three-dimensional porous aerogel skeleton is gradient distributed;

[0009] The solid-state electrolyte composite is filled in the pores of the three-dimensional porous aerogel skeleton, and the solid-state electrolyte composite comprises lithium lanthanum zirconium oxide nanowires and a polyethylene oxide-lithium salt composite matrix, wherein the lithium lanthanum zirconium oxide nanowires are arranged in the direction of the film thickness;

[0010] The lithium salt nanocrystals are in-situ grown on the surface of the pore wall of the three-dimensional porous aerogel;

[0011] The mass ratio of the aerogel framework to the solid-state electrolyte compound is 1:3-1:15.

[0012] The present application provides an aerogel reinforced composite electrolyte film for solid-state lithium battery, which realizes high ionic conductivity, excellent mechanical strength and interface stability of the electrolyte film mainly through the synergistic effect of unique three-dimensional porous aerogel framework, solid-state electrolyte compound and lithium salt nanocrystals, wherein the three-dimensional porous aerogel framework is the supporting structure of the composite electrolyte film of the present application, which is mainly prepared by inorganic oxide nanoparticles and polymer precursor through sol-gel method, at the same time, the pore size of the three-dimensional porous aerogel framework adopts gradient distribution mode to effectively control the ion transmission path and reduce the resistance of ions in the transmission process, thereby improving the ionic conductivity; further, the larger pore size area in the three-dimensional porous aerogel framework is beneficial to the filling of electrolyte and the rapid transmission of ions, while the smaller pore size area can enhance the mechanical strength and prevent the penetration of lithium dendrites. In addition, the high porosity of the aerogel can provide sufficient space for the filling of the solid-state electrolyte compound, ensuring the lightweight and flexibility of the film.

[0013] And the selection of inorganic oxide nanoparticles can further optimize the performance of the framework, the present application uses SiO2 as the core to provide stable structural support, and Al2O3 as the shell and through surface modification to enhance the interface compatibility with the solid-state electrolyte compound and reduce the interface impedance, the present application through the design of this core-shell structure not only improves the thermal stability of the framework, but also promotes the in-situ growth of lithium salt nanocrystals through the introduction of surface functional groups.

[0014] The solid-state electrolyte composite is composed of lithium lanthanum zirconium oxide nanowires and a polyethylene oxide-lithium salt composite matrix, and is filled in the pores of the three-dimensional porous aerogel framework. The lithium lanthanum zirconium oxide nanowires are well-known for high ionic conductivity and excellent chemical stability, and are ideal lithium ion transmission channels. The polyethylene oxide-lithium salt composite matrix serves as a flexible matrix, fills the gaps between the lithium lanthanum zirconium oxide nanowires, and promotes the migration of lithium ions through the chain segment movement. In the application, the lithium lanthanum zirconium oxide nanowires are grown on the surface of the aerogel pore wall by chemical vapor deposition, and are arranged in the thickness direction of the film, so that the tortuosity of ion transmission can be significantly reduced, and the ionic conductivity of the film can be further improved. The directional arrangement is realized by applying an axial magnetic field, and the magnetic field direction is consistent with the thickness of the film. In addition, ultrasonic treatment at 20-40 kHz is used to effectively overcome the problem of random distribution of the nanowires. In the application, the mass ratio between the three-dimensional porous aerogel framework and the solid-state electrolyte composite is further limited, so that the prepared film has excellent performance. When the ratio is less than 1:3, the electrolyte content is insufficient, and the ionic conductivity is significantly reduced. When the ratio is higher than 1:15, the supporting effect of the framework is weakened, and the mechanical properties of the film cannot meet the actual application requirements.

[0015] In addition, the lithium salt nanocrystals in the application are grown in situ on the surface of the three-dimensional porous aerogel pore wall, and the particle size is controlled in the range of 10-50 nm, so that the small size and high specific surface area of the nanocrystals provide more active sites, which is beneficial to the rapid deintercalation of lithium ions. In-situ growth ensures the close contact between the lithium salt and the aerogel framework, and reduces the interface impedance. The uniform distribution of the lithium salt nanocrystals avoids the local concentration of the lithium salt nanocrystals, which leads to the electrochemical inhomogeneity. The particle size range of 10-50 nm balances the ion transmission rate and the interface stability. A too small particle size may lead to agglomeration, and a too large particle size may reduce the effective contact area.

[0016] Preferably, as a further specific embodiment, the lithium lanthanum zirconium oxide nanowires are coated with a Li3PO4 interface layer, and the thickness of the Li3PO4 interface layer is 1-5 nm.

[0017] The cross-section performance of the lithium lanthanum zirconium oxide nanowire is further optimized in the application, and the performance of the prepared thin film is further optimized by coating a 1-5 nm thick Li 3 PO 4 interface layer on the surface of the lithium lanthanum zirconium oxide nanowire, wherein Li 3 PO 4 is a material with high lithium ion conductivity and excellent chemical stability, which can effectively reduce the interface impedance between the lithium lanthanum zirconium oxide nanowire and the composite matrix, and the thickness range of 1-5 nm is strictly considered, and an excessively thin coating layer may lead to incomplete coverage and cannot effectively inhibit the interface side reaction; and an excessively thick coating layer will increase the ion transmission distance and reduce the overall conductivity, in addition, the coating of Li 3 PO 4 can also inhibit the side reaction between lithium lanthanum zirconium oxide and lithium metal negative electrode, and improve the cycle stability of the battery.

[0018] Preferably, as a further specific embodiment, the lithium salt nanocrystal has a particle size of 10-50 nm; and the lithium salt nanocrystal is any one of LiTFSI or LiFSI.

[0019] In the application, the lithium salt nanocrystal in the composite electrolyte thin film is also limited, and its particle size range and specific type are specified, wherein when the particle size of the lithium salt nanocrystal is controlled in the range of 10-50 nm, its specific surface area increases significantly, providing more active sites for lithium ion migration, and the nanometer size effect makes the crystal boundary diffusion possible, and this diffusion mechanism has lower activation energy than bulk diffusion; and for the application, the particle size of the lithium salt nanocrystal should not be too small, and if it is less than 10 nm, it is easy to agglomerate due to excessively high surface energy, which will block the ion transmission channel; and if it is more than 50 nm, the advantages of nanometer materials will be lost, resulting in insufficient interface contact area.

[0020] In the selection of the type of lithium salt nanocrystal, LiTFSI (lithium bis-trifluoromethanesulfonimide) and LiFSI (lithium bis-fluorosulfonimide) are both high-performance lithium salts selected with care, and both of them contain strong electron-withdrawing groups and flexible carbon chains, and such a structure endows them with excellent dissociation ability and thermal stability, specifically, the larger anion volume in LiTFSI effectively reduces the lattice energy, promoting the dissociation of lithium ions; LiFSI has better oxidation resistance stability while maintaining high conductivity, and the melting points of the two lithium salts are relatively low, which enables them to form a uniform composite matrix with a polyethylene oxide matrix under relatively mild conditions.

[0021] Preferably, as a further specific embodiment, the inorganic oxide nanoparticle is a SiO 2 -Al 2 O 3 core-shell structure; the SiO 2 is the inner core, and has a particle size of 20 nm; and the Al 2 O 3 is the outer shell, and has a thickness of 5 nm.

[0022] Wherein the inorganic oxide nanoparticles are further limited in the application, and are limited to have a core-shell structure feature, which realizes the synergistic optimization of multiple functions, wherein the SiO2 inner core provides a stable mechanical support skeleton, and the particle size of 20 nm is selected to not only ensure sufficient specific surface area to enhance the interaction with the polymer matrix, but also avoid the agglomeration problem caused by high surface energy due to too small particle size; at the same time, the thickness of the Al2O3 shell is in the range of 5 nm, which is sufficient to form a complete coating layer to effectively isolate the adverse interaction between the SiO2 inner core and the electrolyte, and at the same time will not increase unnecessary mass burden due to being too thick.

[0023] At the same time, the Al2O3 shell has abundant surface hydroxyl groups, which provide an ideal reaction platform for subsequent modification of fluorine-containing silane coupling agents; secondly, the isoelectric point of Al2O3 is higher than that of SiO2, which makes the Al2O3 surface maintain a moderate positive charge under near-neutral preparation conditions, which is beneficial to the adsorption and uniform distribution of the negatively charged lithium salt precursor; in addition, the difference in the thermal expansion coefficient of Al2O3 and SiO2 is precisely matched so that beneficial interfacial compressive stress can be generated when the temperature changes, thereby enhancing the bonding strength of the nanoparticles and the polymer matrix.

[0024] Preferably, as a further specific embodiment, the surface of the Al2O3 shell is modified by a fluorine-containing silane coupling agent, and the grafting density is 1.2-2.5 per nm 2 .

[0025] In the application, the surface of the Al2O3 shell in the composite electrolyte thin film is also modified by a fluorine-containing silane coupling agent, and the grafting density is 1.2-2.5 per nm 2 . Wherein the grafting density of the fluorine-containing silane coupling agent on the surface of Al2O3 is less than 1.2 per nm 2 , at which time the surface modification is insufficient to effectively improve the interfacial compatibility; and more than 2.5 per nm 2 will cause an increase in intermolecular steric hindrance, causing defects in the structure of the modified layer. Therefore, by using the surface modification technology of the fluorine-containing silane coupling agent, the grafting density is accurately controlled in the range of 1.2-2.5 per nm 2 , thereby realizing the synergistic optimization of interfacial compatibility, ion transport performance and mechanical strength. This method not only solves the key problems of high interfacial impedance and poor stability of inorganic / organic phases in traditional composite electrolytes, but also provides a solution for performance improvement of solid-state lithium batteries.

[0026] The application also provides a preparation method of the aerogel reinforced composite electrolyte thin film, comprising the following steps:

[0027] The inorganic oxide nanoparticles are dispersed in a polymer precursor solution, and after a sol-gel reaction, a three-dimensional porous aerogel skeleton with gradient pore size is formed by a supercritical CO2 drying method;

[0028] Subsequently, lithium lanthanum zirconium oxide nanowires are grown on the pore wall surface of the three-dimensional porous aerogel skeleton by a chemical vapor deposition method, and the growth temperature is controlled to be 600-800℃;

[0029] After the polyethylene oxide-lithium salt composite matrix is melted and injected into the aerogel pores, and an axial magnetic field is applied, the lithium lanthanum zirconium oxide nanowires are arranged in the thickness direction of the film.

[0030] Subsequently, after rolling and annealing, the product is obtained.

[0031] In the preparation method of the present application, the inorganic oxide nanoparticles are first dispersed in a polymer precursor solution, and a three-dimensional network structure is constructed by a sol-gel reaction. When the mass ratio of inorganic oxide nanoparticles to polymer precursor is controlled to be in the range of 1:5 to 1:8, the sol formed has the best rheological properties, which can ensure the smooth progress of the subsequent forming process and also ensure the ideal proportion of inorganic phase and organic phase in the final product.

[0032] In addition, the supercritical CO2 drying process is a key step for constructing the gradient-pore aerogel skeleton in the present application. In the supercritical state, the surface tension disappears, and the collapse of the pore structure caused by conventional drying can be avoided.

[0033] In the process of growing lithium lanthanum zirconium oxide nanowires by chemical vapor deposition, the growth temperature is very important for the present application. This is because when the growth temperature is lower than 600℃, the precursor decomposition is not complete, resulting in a decrease in product purity; and when the temperature exceeds 800℃, lithium volatilization is easily caused, which destroys the stoichiometric ratio. Within the optimized temperature range, by controlling the carrier gas flow rate and growth time, LLZO nanowires with suitable diameter and length can be obtained, and the growth rate can be stabilized at 100-200nm / min.

[0034] The axial magnetic field applied when the PEO-LiTFSI composite matrix reaches the melting state can induce the arrangement of LLZO nanowires along the magnetic field direction, and the simultaneous application of ultrasonic treatment generates a micro-scale flow field, which can further promote the orientation and arrangement of the nanowires. This multi-field coupling assembly strategy makes the ionic conductivity of the composite electrolyte exhibit significant anisotropy, which perfectly matches the ion transport requirements in the thickness direction of the solid-state battery.

[0035] Preferably, as a further specific embodiment, the growth of the lithium lanthanum zirconium oxide nanowires uses lanthanum acetylacetonate, tetrabutyl zirconate and lithium foil as precursors, high-purity argon gas as the carrier gas, and the growth rate is 100-200nm / min.

[0036] In the present application, the precursor used for the growth of lithium lanthanum zirconium oxide nanowires is lanthanum acetylacetonate, tetrabutyl zirconate and lithium foil, the carrier gas is high-purity argon, and the growth rate is 100-200 nm / min. Lanthanum acetylacetonate has a unique advantage as a lanthanum source. Its decomposition temperature matches that of tetrabutyl zirconate, ensuring that the two metal precursors can release active components synchronously. At the same time, the chelation of the acetylacetonate ligand can effectively reduce the diffusion rate of lanthanum ions, avoiding composition segregation caused by local over-concentration. The choice of lithium foil as the lithium source takes into account the need for vapor pressure control. Within the growth temperature range of 600-800℃, the equilibrium vapor pressure of lithium can ensure sufficient lithium supply while avoiding excessive lithium vapor pollution of the deposition system. The selection of high-purity argon as the carrier gas can prevent the precursors from being oxidized during transportation, especially protecting tetrabutyl zirconate from hydrolysis. At this time, when the argon flow rate is less than 50 sccm, insufficient precursor transportation leads to uneven nanowire growth. When the flow rate exceeds 100 sccm, turbulence causes disorder in the orientation of the nanowires. In addition, when the growth rate is less than 100 nm / min, although the crystal integrity is good, the production efficiency is too low to meet the actual application requirements. When the rate exceeds 200 nm / min, a large number of grain boundary defects are introduced, resulting in a decrease in ionic conductivity of more than 30%.

[0037] Preferably, as a further specific embodiment, the direction of application of the magnetic field is consistent with the thickness direction of the thin film, and ultrasonic treatment of 20-40 kHz is applied synchronously to promote the directional arrangement of the lithium lanthanum zirconium oxide nanowires.

[0038] Preferably, as a further specific embodiment, the supercritical CO2 drying adopts a gradient pressure reduction method: first, increase the temperature to 50-60℃ at a rate of 2-5℃ / min, maintain the pressure at 10-15 MPa for 2 h, and then reduce the pressure at a rate of 0.1-0.5 MPa / min.

[0039] Compared with the prior art, the present application has the following beneficial effects:

[0040] (1) The present application provides an aerogel-reinforced composite electrolyte thin film for solid-state lithium batteries, which realizes high ionic conductivity, excellent mechanical strength and interface stability of the electrolyte thin film through the synergistic effect of a unique three-dimensional porous aerogel skeleton, a solid-state electrolyte composite and lithium salt nanocrystals.

[0041] (2) The present application provides a preparation method of the above-mentioned aerogel-reinforced composite electrolyte thin film for solid-state lithium batteries, which solves the long-standing dilemma in the field of composite electrolytes that high conductivity, good mechanical properties and excellent interface stability are difficult to balance. DETAILED DESCRIPTION

[0042] The technical solutions of the present application will be described clearly and completely in combination with specific embodiments below, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the present application, not all the embodiments, and are only used to illustrate the present application, and should not be regarded as limiting the scope of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

[0043] In order to more clearly illustrate the technical solutions in the present application, the following will be described in the form of specific embodiments.

[0044] Embodiment 1

[0045] Raw material preparation:

[0046] Inorganic oxide nanoparticles: SiO2-Al2O3 core-shell structure (wherein the diameter of the SiO2 inner core is 20 nm, and the thickness of the Al2O3 outer shell is 5 nm);

[0047] Polymer precursor: tetraethyl orthosilicate (TEOS) and polyvinyl alcohol (PVA) mixed solution (mass ratio 1:3) precursor: lanthanum acetylacetone (99.9%), tetrabutyl zirconate (99.9%), lithium foil (thickness 25 μm)

[0048] Lithium salt nanocrystals: LiTFSI (particle size 10 nm)

[0049] Composite matrix: polyethylene oxide-lithium salt composite matrix, wherein the lithium salt is LiTFSI

[0050] Modifier: heptadecafluorodecyltrimethoxysilane (purity ≥98%);

[0051] Preparation process:

[0052] Step 1: Preparation of three-dimensional porous aerogel skeleton

[0053] Disperse the SiO2-Al2O3 core-shell nanoparticles (10 g) in 200 mL of ethanol / water mixed solvent (volume ratio 4:1) and ultrasonic treat for 30 minutes (power 300 W);

[0054] Add the ultrasonic treated SiO2-Al2O3 core-shell nanoparticles into the TEOS / PVA mixed solution according to a mass ratio of 1:2, adjust the pH to 5.0, and stir at 60°C for 6 hours to obtain a gel product;

[0055] The gel precursor was transferred into a supercritical drying vessel, heated to 50℃ at 2℃ / min, maintained at 10MPa for 2h, and depressurized to ambient pressure at a gradient of 0.1MPa / min, to obtain a three-dimensional porous aerogel skeleton with gradient pore size (30nm in the surface layer, 150nm in the core region)

[0056] Step 2: Al2O3 surface modification

[0057] The three-dimensional porous aerogel skeleton was immersed in an ethanol solution containing 1.5vol% heptadecafluorodecyltrimethoxysilane and reacted at 90℃ for 3h, with a grafting density of 1.2 / nm 2 ;

[0058] The residual reagent was removed by nitrogen blowing and vacuum dried at 80℃ for 12h

[0059] Step 3: LLZO nanowire growth

[0060] The modified three-dimensional porous aerogel skeleton was placed in a CVD reaction chamber

[0061] Precursor feeding: lanthanum acetylacetonate 0.5g / min, tetrabutyl zirconate 0.3g / min, lithium foil evaporation zone temperature 480℃

[0062] Carrier gas: high-purity argon (80sccm), reaction temperature 700℃, growth time 40min

[0063] After obtaining the LLZO nanowires with a diameter of 70±5nm and a length of 6±1μm, the growth rate of the LLZO nanowires was 100nm / min;

[0064] Step 4: Li3PO4 interface layer coating

[0065] The sample was immersed in a 0.1M Li3PO4 precursor solution and heat treated at 150℃ for 1h to form a Li3PO4 coating layer with a thickness of 1nm;

[0066] Step 5: electrolyte compounding

[0067] The polyethylene oxide-lithium salt composite matrix was mixed with LiTFSI at 120℃, and after the melt was completed, it was injected into the three-dimensional porous aerogel pores, while a 0.8T axial magnetic field and 20kHz ultrasound (power density 6W / cm 2 )

[0068] The field-assisted condition was maintained for 30min, and the LLZO nanowires were arranged in the thickness direction, with a mass ratio of the three-dimensional porous aerogel skeleton to the solid-state electrolyte composite of 1:3;

[0069] Step 6: post-processing

[0070] The final film was obtained by three-stage rolling (0.5 MPa→2 MPa→5 MPa) densification and annealing at 90°C for 3 hours.

[0071] Example 2

[0072] Raw material preparation:

[0073] Inorganic oxide nanoparticles: SiO2-Al2O3 core-shell structure (with a 20 nm diameter SiO2 core and a 5 nm thick Al2O3 shell);

[0074] Polymer precursor: tetraethyl orthosilicate (TEOS) and polyvinyl alcohol (PVA) mixed solution (mass ratio 1:3) precursor: lanthanum acetylacetonate (99.9%), tetrabutyl zirconate (99.9%), lithium foil (thickness 25 μm)

[0075] Lithium salt nanocrystals: LiFSI (50 nm)

[0076] Composite matrix: polyethylene oxide-lithium salt composite matrix, with the lithium salt being LiFSI

[0077] Modifier: heptadecafluorodecyltrimethoxysilane (purity ≥ 98%);

[0078] Preparation process:

[0079] Step 1: Preparation of three-dimensional porous aerogel skeleton

[0080] The SiO2-Al2O3 core-shell nanoparticles (10 g) were dispersed in 200 mL of an ethanol / water mixed solvent (volume ratio 4:1) and ultrasonically treated for 30 minutes (power 300 W);

[0081] The ultrasonically treated SiO2-Al2O3 core-shell nanoparticles were added to the TEOS / PVA mixed solution in a mass ratio of 1:2, the pH was adjusted to 5.0, and the gel was obtained by stirring at 60°C for 6 hours;

[0082] The gel was transferred to a supercritical drying oven, heated to 60°C at a rate of 5°C / min, maintained at a pressure of 15 MPa for 2 hours, and then gradually reduced to atmospheric pressure at a rate of 0.5 MPa / min to obtain a three-dimensional porous aerogel skeleton with a gradient pore size (30 nm in the surface layer and 150 nm in the core region)

[0083] Step 2: Surface modification of Al2O3

[0084] The three-dimensional porous aerogel skeleton was immersed in an ethanol solution containing 1.5 vol% heptadecafluorodecyltrimethoxysilane and reacted at 90°C for 3 hours, with a grafting density of 2.5 per nm 2 ;

[0085] Nitrogen purging to remove residual reagents, vacuum drying at 80°C for 12 hours

[0086] Step 3: LLZO nanowire growth

[0087] The modified three-dimensional porous aerogel skeleton was placed in the CVD reaction chamber

[0088] Precursor feed: lanthanum acetylacetonate 0.5 g / min, tetrabutyl zirconate 0.3 g / min, lithium foil evaporation zone temperature 480°C

[0089] Carrier gas: high-purity argon (80 seem), reaction temperature 700°C, growth time 40 minutes

[0090] After obtaining LLZO nanowires with a diameter of 70±5 nm and a length of 6±1 μm, the sample was obtained, wherein the growth rate of the LLZO nanowires was 200 nm / min;

[0091] Step 4: Li3PO4 interface layer coating

[0092] The sample was immersed in a 0.1M Li3PO4 precursor solution and heat treated at 150°C for 1 hour to form a Li3PO4 coating layer with a thickness of 5 nm;

[0093] Step 5: electrolyte compounding

[0094] The polyethylene oxide-lithium salt composite matrix was mixed with LiTFSI at 120°C, and after the melt was completed, it was injected into the three-dimensional porous aerogel pores, while a 0.8T axial magnetic field and 40 kHz ultrasound (power density 6 W / cm 2 )

[0095] The field-assisted condition was maintained for 30 minutes, and the LLZO nanowires were arranged in the thickness direction, wherein the mass ratio of the three-dimensional porous aerogel skeleton to the solid-state electrolyte composite was 1:15;

[0096] Step 6: post-processing

[0097] Densification was achieved using three-stage rolling (0.5 MPa→2 MPa→5 MPa), and a final film was obtained by annealing at 90°C for 3 hours.

[0098] Example 3

[0099] Raw material preparation:

[0100] Inorganic oxide nanoparticles: SiO2-Al2O3 core-shell structure (with a SiO2 core diameter of 20 nm and an Al2O3 shell thickness of 5 nm);

[0101] Polymer precursor: TEOS / PVA mixed solution (mass ratio 1:3) precursor: lanthanum acetylacetonate (99.9%), tetrabutyl zirconate (99.9%), lithium foil (thickness 25 pm)

[0102] Lithium salt nanocrystals: LiFSI (30 nm)

[0103] Composite matrix: polyethylene oxide-lithium salt composite matrix, wherein the lithium salt is LiFSI

[0104] Modification agent: heptadecafluorodecyltrimethoxysilane (purity > 98%);

[0105] Preparation process:

[0106] Step 1: Preparation of three-dimensional porous aerogel skeleton

[0107] The SiO2-Al2O3 core-shell nanoparticles (10 g) were dispersed in 200 mL of ethanol / water mixed solvent (volume ratio 4:1) and ultrasonicated for 30 minutes (power 300 W);

[0108] The ultrasonicated SiO2-Al2O3 core-shell nanoparticles were added to the TEOS / PVA mixed solution in a mass ratio of 1:2, the pH was adjusted to 5.0, and the reaction was stirred at 60°C for 6 hours to obtain the gel product;

[0109] The gel product was transferred to a supercritical drying oven, heated to 56°C at a rate of 3°C / min, maintained at a pressure of 10 MPa for 2 hours, and then reduced to atmospheric pressure at a gradient of 0.4 MPa / min to obtain a three-dimensional porous aerogel skeleton with gradient pore size (30 nm in the surface layer and 150 nm in the core region)

[0110] Step 2: Al2O3 surface modification

[0111] The three-dimensional porous aerogel skeleton was immersed in an ethanol solution containing 1.5 vol% heptadecafluorodecyltrimethoxysilane and reacted at 90°C for 3 hours, with a grafting density of 2 / nm 2 ;

[0112] The residual reagents were removed by nitrogen purging and vacuum dried at 80°C for 12 hours

[0113] Step 3: Growth of LLZO nanowires

[0114] The modified three-dimensional porous aerogel skeleton was placed in a CVD reaction chamber

[0115] Precursor feed: lanthanum acetylacetonate 0.5 g / min, tetrabutyl zirconate 0.3 g / min, lithium foil evaporation zone temperature 480°C

[0116] Carrier gas: high purity argon gas (80 sccm), reaction temperature 700℃, growth time 40 minutes

[0117] After obtaining the LLZO nanowires with a diameter of 70±5nm and a length of 6±1μm, the sample was obtained, wherein the growth rate of the LLZO nanowires was 150nm / min;

[0118] Step 4: Li3PO4 interface layer coating

[0119] The sample was immersed in a 0.1M Li3PO4 precursor solution and heat treated at 150℃ for 1 hour to form a Li3PO4 coating layer with a thickness of 3nm;

[0120] Step 5: electrolyte compounding

[0121] The polyethylene oxide-lithium salt composite matrix was mixed with LiTFSI at 120℃, and after the melt blending was completed, it was injected into the pores of the three-dimensional porous aerogel, while a 0.8T axial magnetic field and 30kHz ultrasound (power density 6W / cm 2 )

[0122] The field-assisted condition was maintained for 30 minutes, and the LLZO nanowires were arranged along the thickness direction, wherein the mass ratio of the three-dimensional porous aerogel skeleton to the solid-state electrolyte composite was 1:10;

[0123] Step 6: post-processing

[0124] Densification was achieved by three-stage rolling (0.5MPa→2MPa→5MPa), and a final film was obtained by annealing at 90℃ for 3 hours.

[0125] Comparative Example 1

[0126] The specific implementation steps were consistent with those of Example 3, except that the mass ratio of the three-dimensional porous aerogel skeleton to the solid-state electrolyte composite in Example 3 was adjusted to 1:1.

[0127] Comparative Example 2

[0128] The specific implementation steps were consistent with those of Example 3, except that the mass ratio of the three-dimensional porous aerogel skeleton to the solid-state electrolyte composite in Example 3 was adjusted to 1:20.

[0129] Comparative Example 3

[0130] The specific implementation steps were consistent with those of Example 3, except that the lithium salt nanocrystal particle size in Example 3 was adjusted to 1nm.

[0131] Comparative Example 4

[0132] The specific implementation steps were consistent with those of Example 3, except that the lithium salt nanocrystal particle size in Example 3 was adjusted to 100nm.

[0133] Comparative Example 5

[0134] The specific implementation steps are consistent with Example 3, except that the grafting density in Example 3 is adjusted to 0.1 per nm 2 .

[0135] Comparative Example 6

[0136] The specific implementation steps are consistent with Example 3, except that the grafting density in Example 3 is adjusted to 10 per nm 2 .

[0137] Comparative Example 7

[0138] The specific implementation steps are consistent with Example 3, except that the growth rate of lithium lanthanum zirconium oxide nanowires in Example 3 is adjusted to 10 nm / min.

[0139] Comparative Example 8

[0140] The specific implementation steps are consistent with Example 3, except that the growth rate of lithium lanthanum zirconium oxide nanowires in Example 3 is adjusted to 500 nm / min.

[0141] Comparative Example 9

[0142] The specific implementation steps are consistent with Example 3, except that the surface of the lithium lanthanum zirconium oxide nanowires is not coated with Li3PO4.

[0143] Comparative Example 10

[0144] The specific implementation steps are consistent with Example 3, except that the inorganic oxide nanoparticles only use nano-silicon dioxide particles instead of core-shell structures.

[0145] Comparative Example 11

[0146] The specific implementation steps are consistent with Example 3, except that the surface of the Al2O3 shell is not modified with a fluorine-containing silane coupling agent.

[0147] Experimental Example 1: Performance Test of Aerogel Reinforced Composite Electrolyte Film

[0148] 1 Test Method

[0149] Ion conductivity test: using alternating current impedance method (EIS), the film samples obtained in Examples 1-3 and Comparative Examples 1-11 are placed between two stainless steel blocking electrodes, the frequency range is 0.1 Hz-1 MHz, the amplitude is 10 mV, and the test is carried out at 25°C, the bulk resistance (Rb) is obtained by Nyquist plot fitting, and the ion conductivity is calculated;

[0150] Mechanical strength test: using a universal material testing machine to stretch the film to break at a rate of 1 mm / min, recording the maximum tensile strength (MPa) and elongation at break (%);

[0151] Interface stability test: assemble Li / film / Li symmetrical battery, 0.5mA / cm 2 Cycling 100 times at a current density, recording the interface impedance growth rate;

[0152] Electrochemical window test: linear sweep voltammetry (LSV), scan rate 1 mV / s, range 2.5-6V vs. Li+ / Li, record the oxidation onset potential;

[0153] Table 1 test results

[0154]

[0155] From the above experimental table, it can be seen that the aerogel reinforced composite electrolyte film designed by the application has significant advantages in ion conductivity, mechanical strength and interface stability, and the embodiment 3 is the optimal scheme, wherein the influence of the mass ratio of the three-dimensional porous aerogel skeleton and the solid-state electrolyte composite in the comparative examples 1-2 is investigated, when the ratio of the two in the comparative example 1 is adjusted to 1:1, the insufficient electrolyte content leads to the decrease of the ion conductivity, at the same time, the mechanical strength is improved to 15.2MPa, but the elongation at break is greatly reduced to 45%, indicating that the flexibility is poor; and when the ratio in the comparative example 2 is increased to 1:20, the ion conductivity is further improved, but the tensile strength is suddenly reduced to 6.4MPa, and the interface impedance growth rate is increased to 25.7%, indicating that the skeleton support function is weakened, which affects the stability of the film;

[0156] And the comparative examples 3-4 investigate the influence of the lithium salt nanocrystalline particle size on the performance of the finally prepared film, when the particle size is reduced to 1nm in the comparative example 3, the ion conductivity is reduced to 7.3×10 -4 , and the interface impedance growth rate is 12.6%, indicating that too small particle size is easy to cause agglomeration and hinder ion transmission. When the particle size is increased to 100nm in the comparative example 4, the ion conductivity is further reduced, and the interface impedance growth rate is increased to 18.4%, indicating that too large particle size leads to the reduction of active sites and the deterioration of interface contact;

[0157] And the comparative examples 5-6 study the influence of the grafting density on the performance of the finally prepared film, when the grafting density is reduced to 0.1 / nm 2 in the comparative example 5, the ion conductivity and mechanical properties are significantly reduced, and the interface impedance growth rate is as high as 22.1%, indicating that insufficient modification leads to poor interface compatibility; and when the grafting density is increased to 10 / nm 2At this time, the performance is slightly better than that of Comparative Example 5, but still not as good as that of Example 3, indicating that too high grafting density can introduce steric hindrance, affecting the modification effect;

[0158] Comparative Examples 7-8 were used to investigate the influence of nanowire growth rate on the performance of the finally prepared thin film. When the growth rate was too slow in Comparative Example 7, the ionic conductivity dropped sharply, the interfacial impedance increased by as much as 30.5%, and the production efficiency was also limited. When the growth rate was too fast in Comparative Example 8, the ionic conductivity was slightly improved compared with that of Comparative Example 7, but the tensile strength and interfacial stability were both decreased, indicating that fast growth introduced grain boundary defects;

[0159] In the comparative examples of the present application, Comparative Examples 9-11 further verified the key design of the present application. Comparative Example 9 did not coat a Li3PO4 interfacial layer, and the interfacial impedance increased by as much as 35.6%, and the electrochemical window narrowed to 4.3V, indicating that the interfacial layer is crucial for inhibiting side reactions. Comparative Example 10 used SiO2 nanoparticles with a non-core-shell structure, and the ionic conductivity and mechanical properties were both significantly reduced, highlighting the contribution of the core-shell structure to the optimization of the interface. Comparative Example 11 did not perform surface modification, and the interfacial impedance increased by 38.7%, further proving the necessity of fluorine-containing silane coupling agent modification for improving the interfacial stability.

[0160] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. An aerogel-reinforced composite electrolyte film for solid-state lithium batteries, characterized in that: The film comprises a three-dimensional porous aerogel skeleton, a solid electrolyte composite and lithium salt nanocrystals; The three-dimensional porous aerogel skeleton is prepared by a sol-gel method from inorganic oxide nanoparticles and polymer precursors, and the pore size of the three-dimensional porous aerogel skeleton is distributed in a gradient manner; The solid electrolyte composite is filled in the pores of the three-dimensional porous aerogel skeleton, and the solid electrolyte composite comprises lithium lanthanum zirconium oxide nanowires and a polyethylene oxide-lithium salt composite matrix, wherein the lithium lanthanum zirconium oxide nanowires are oriented along the thickness direction of the film; The lithium salt nanocrystals are in-situ grown on the surface of the pore walls of the three-dimensional porous aerogel; The mass ratio of the three-dimensional porous aerogel skeleton to the solid electrolyte composite is 1:3-1:

15.

2. The aerogel-reinforced composite electrolyte membrane according to claim 1, characterized in that: The surface of the lithium lanthanum zirconium oxide nanowire is coated with a Li3PO4 interface layer, and the thickness of the Li3PO4 interface layer is 1-5 nm.

3. The aerogel-reinforced composite electrolyte membrane according to claim 1, characterized in that: The particle size of the lithium salt nanocrystal is 10-50 nm; the lithium salt nanocrystal is any one of LiTFSI or LiFSI.

4. The aerogel-reinforced composite electrolyte membrane according to claim 1, characterized in that: The inorganic oxide nanoparticles are of SiO2-Al2O3 core-shell structure; the SiO2 is the core with a particle size of 20 nm; the Al2O3 is the shell with a thickness of 5 nm.

5. The aerogel-reinforced composite electrolyte membrane according to claim 4, characterized in that: The surface of the Al2O3 shell is modified with a fluorine-containing silane coupling agent, and the grafting density is 1.2-2.5 per nm. 2 .

6. A method for preparing an aerogel-reinforced composite electrolyte membrane according to any one of claims 1 to 5, characterized in that: The following steps are involved: Inorganic oxide nanoparticles are dispersed in a polymer precursor solution, and after a sol-gel reaction, a supercritical CO2 drying method is used to form a three-dimensional porous aerogel skeleton with gradient pore sizes. Then, lithium lanthanum zirconium oxide nanowires are grown on the pore wall surface of the three-dimensional porous aerogel skeleton by chemical vapor deposition, and the growth temperature is controlled to be 600-800°C; The polyethylene oxide-lithium salt composite matrix and lithium salt nanocrystals are melted and injected into the aerogel pores. At the same time, an axial magnetic field is applied to orient the lithium lanthanum zirconium oxide nanowires along the thickness direction of the film. It is then rolled and annealed.

7. The preparation method according to claim 5, characterized in that The growth of the lithium lanthanum zirconium oxide nanowires uses lanthanum acetylacetonate, tetrabutyl zirconate and lithium foil as precursors, high-purity argon as the carrier gas, and a growth rate of 100-200 nm / min.

8. The preparation method according to claim 5, characterized in that The direction of applying the magnetic field is consistent with the thickness direction of the film, and ultrasonic treatment of 20-40 kHz is applied simultaneously to promote the directional arrangement of the lithium lanthanum zirconium oxide nanowires.

9. The preparation method according to claim 5, characterized in that The supercritical CO2 drying adopts a gradient pressure reduction method: first, the temperature is raised to 50-60°C at a rate of 2-5°C / min, the pressure is maintained at 10-15MPa for 2h, and then the pressure is reduced at a rate of 0.1-0.5MPa / min.

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