Aerogel-reinforced composite electrolyte thin film for solid-state lithium batteries and method of making the same

Abstract

The application provides an aerogel reinforced composite electrolyte film for a solid lithium battery and a preparation method thereof, and belongs to the technical field of composite electrolytes. The film comprises a three-dimensional porous aerogel framework, a solid electrolyte composite and lithium salt nanocrystals. The three-dimensional porous aerogel framework is prepared from inorganic oxide nanoparticles and polymer precursors by a sol-gel method. The solid electrolyte composite is filled in the pores of the three-dimensional porous aerogel framework. The solid electrolyte composite comprises lithium lanthanum zirconium oxide nanowires and a polyethylene oxide-lithium salt composite matrix. The lithium lanthanum zirconium oxide nanowires are arranged in the thickness direction of the film. The lithium salt nanocrystals are in-situ grown on the surface of the three-dimensional porous aerogel pore wall. The mass ratio of the aerogel framework to the solid electrolyte composite is 1:3-1:15. The film of the application significantly improves the ionic conductivity, mechanical strength and interface stability of the electrolyte.

Description

Technical Field

[0001] This invention belongs to the field of composite electrolyte technology, and more specifically, relates to an aerogel-reinforced composite electrolyte film for solid-state lithium batteries and its preparation method. Background Technology

[0002] With the rapid growth of energy demand and the increasing severity of environmental pollution, the development of high-energy-density and high-safety energy storage technologies has become a research hotspot. Solid-state lithium batteries, due to their high theoretical energy density and inherent safety, are considered an important development direction for next-generation energy storage devices. However, the low ionic conductivity, high interfacial impedance, and insufficient mechanical properties of solid-state electrolytes severely restrict their practical application. Traditional polymer-based solid-state electrolytes, while possessing flexibility and processing advantages, have low room-temperature ionic conductivity and insufficient mechanical strength to suppress lithium dendrite growth. Inorganic solid-state electrolytes, although exhibiting high ionic conductivity and mechanical strength, are brittle, have poor interfacial contact, and are difficult to form a tight contact with the electrodes.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] The primary objective of this invention is to provide an aerogel-reinforced composite electrolyte film for solid-state lithium batteries, which achieves high ionic conductivity, excellent mechanical strength, and interfacial stability through the synergistic effect of a unique three-dimensional porous aerogel framework, a solid electrolyte composite, and lithium salt nanocrystals.

[0005] The second objective of this invention is to provide a method for preparing an aerogel-reinforced composite electrolyte film for solid-state lithium batteries, which solves the long-standing dilemma in the field of composite electrolytes of achieving both high conductivity, good mechanical properties, and excellent interface stability.

[0006] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

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

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

[0009] The solid electrolyte composite fills the pores of the three-dimensional porous aerogel framework. The solid electrolyte composite includes 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.

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

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

[0012] This invention provides an aerogel-reinforced composite electrolyte film for solid-state lithium batteries. It achieves high ionic conductivity, excellent mechanical strength, and interfacial stability primarily through the synergistic effect of a unique three-dimensional porous aerogel framework, a solid electrolyte composite, and lithium salt nanocrystals. The three-dimensional porous aerogel framework serves as the supporting structure of the composite electrolyte film and is mainly prepared from inorganic oxide nanoparticles and polymer precursors via a sol-gel method. A gradient distribution of the pore size within the three-dimensional porous aerogel framework effectively controls the ion transport path, reducing resistance during ion transport and thus improving ionic conductivity. Furthermore, the larger pore sizes in the three-dimensional porous aerogel framework facilitate electrolyte filling and rapid ion transport, while the smaller pore sizes enhance mechanical strength and prevent lithium dendrite penetration. In addition, the high porosity of the aerogel provides ample space for the solid electrolyte composite, ensuring the film's lightweight and flexibility.

[0013] The selection of inorganic oxide nanoparticles can further optimize the performance of the framework. This invention uses SiO2 as the core, which provides stable structural support, while Al2O3 is used as the shell and its surface modification enhances the interfacial compatibility with the solid electrolyte complex and reduces interfacial impedance. This core-shell structure design not only improves the thermal stability of the framework, but also promotes the in-situ growth of lithium salt nanocrystals by introducing surface functional groups.

[0014] The solid electrolyte composite consists of lithium lanthanum zirconium oxide nanowires and a polyethylene oxide-lithium salt composite matrix, which fill the pores of a three-dimensional porous aerogel framework. Lithium lanthanum zirconium oxide nanowires are renowned for their high ionic conductivity and excellent chemical stability, making them ideal lithium-ion transport channels. The polyethylene oxide-lithium salt composite matrix, as a flexible matrix, not only fills the gaps between the lithium lanthanum zirconium oxide nanowires but also promotes lithium-ion migration through their chain segment movement. This invention grows lithium lanthanum zirconium oxide nanowires on the surface of the aerogel pore walls using chemical vapor deposition and controls their directional alignment along the film thickness direction, thereby significantly reducing the tortuosity of ion transport. This further enhances the ionic conductivity of the film. The directional alignment relies on the application of an axial magnetic field, with the magnetic field direction aligned with the film thickness. Simultaneously, ultrasonic treatment at 20-40 kHz effectively overcomes the problem of random nanowire distribution. Furthermore, this invention further limits the mass ratio between the three-dimensional porous aerogel framework and the solid electrolyte composite, resulting in a film with superior performance. This is because when the ratio is less than 1:3, the electrolyte content is insufficient, and the ionic conductivity decreases significantly; while when the ratio is greater than 1:15, the supporting effect of the framework weakens, and the mechanical properties of the film cannot meet the requirements of practical applications.

[0015] Furthermore, the lithium salt nanocrystals in this invention are grown in situ on the surface of the pore walls of a three-dimensional porous aerogel, and their particle size is controlled within the range of 10-50 nm. This allows the small size and high specific surface area of ​​the nanocrystals to provide more active sites, which is beneficial for the rapid insertion and extraction of lithium ions. In situ growth also ensures close contact between the lithium salt and the aerogel framework, reducing interfacial impedance. At the same time, the uniform distribution of lithium salt nanocrystals avoids electrochemical inhomogeneity caused by excessively high local concentrations. The 10-50 nm particle size range balances ion transport rate and interfacial stability. Too small a particle size may lead to agglomeration, while too large a particle size will reduce the effective contact area.

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

[0017] In this invention, the cross-sectional properties of lithium lanthanum zirconium oxide nanowires are further optimized by coating their surface with a 1-5 nm thick Li3PO4 interfacial layer, thereby further optimizing the performance of the prepared film. Li3PO4 is a material with high lithium-ion conductivity and excellent chemical stability, which can effectively reduce the interfacial impedance between lithium lanthanum zirconium oxide nanowires and the composite matrix. The 1-5 nm thickness range is carefully considered. Too thin a coating layer may lead to incomplete coverage and failure to effectively suppress interfacial side reactions; while too thick a coating layer will increase the ion transport distance and reduce the overall conductivity. In addition, the Li3PO4 coating can also suppress the side reactions between lithium lanthanum zirconium oxide and lithium metal anode, and improve the cycle stability of the battery.

[0018] Preferably, as a further specific embodiment, the lithium salt nanocrystals have a particle size of 10-50 nm; the lithium salt nanocrystals are either LiTFSI or LiFSI.

[0019] In this invention, the lithium salt nanocrystals in the composite electrolyte film are further defined, specifying their particle size range and specific types. When the particle size of the lithium salt nanocrystals is controlled within the range of 10-50 nm, their specific surface area increases significantly, providing more active sites for lithium ion migration. At the same time, the nanoscale effect makes grain boundary diffusion possible, and this diffusion mechanism has a lower activation energy compared to bulk diffusion. Furthermore, for this invention, the particle size of the lithium salt nanocrystals should not be too small. If it is less than 10 nm, it is easy to agglomerate due to excessively high surface energy, which will block the ion transport channels. If it exceeds 50 nm, it will lose the advantages of nanomaterials, resulting in insufficient interfacial contact area.

[0020] In terms of lithium salt nanocrystal selection, LiTFSI (lithium bis(trifluoromethanesulfonyl)imide) and LiFSI (lithium bis(fluorosulfonyl)imide) are both carefully selected high-performance lithium salts. Both lithium salts contain strong electron-withdrawing groups and flexible carbon chains. This structure endows them with excellent dissociation ability and thermal stability. Specifically, the larger anion volume in LiTFSI effectively reduces the lattice energy and promotes the dissociation of lithium ions; while LiFSI maintains high electrical conductivity while having better antioxidant stability. Moreover, both lithium salts have low melting points, which allows them to form a uniform composite matrix with polyethylene oxide under relatively mild conditions.

[0021] Preferably, as a further specific embodiment, the inorganic oxide nanoparticles have a SiO2-Al2O3 core-shell structure; the SiO2 is the core with a particle size of 20 nm; and the Al2O3 is the outer shell with a thickness of 5 nm.

[0022] In this invention, the inorganic oxide nanoparticles are further defined as having a core-shell structure. This core-shell structure achieves synergistic optimization of multiple functions. The SiO2 core provides a stable mechanical support framework, and its 20nm particle size ensures sufficient specific surface area to enhance the interaction with the polymer matrix while avoiding the aggregation problem caused by high surface energy due to excessively small particle size. At the same time, the 5nm thickness of the Al2O3 shell is sufficient to form a complete coating layer, effectively isolating the adverse interaction between the SiO2 core and the electrolyte, without adding unnecessary mass burden due to excessive thickness.

[0023] Meanwhile, the Al2O3 shell has abundant surface hydroxyl groups, and these active sites provide an ideal reaction platform for subsequent modification with fluorinated silane coupling agents. Secondly, the isoelectric point of Al2O3 is higher than that of SiO2, which allows the Al2O3 surface to maintain a moderate positive charge under near-neutral preparation conditions, which is beneficial for the adsorption and uniform distribution of negatively charged lithium salt precursors. In addition, the difference between the thermal expansion coefficient of Al2O3 and that of SiO2 is precisely matched, which generates beneficial interfacial compressive stress when the temperature changes, enhancing the bonding strength between nanoparticles and the polymer matrix.

[0024] Preferably, as a further specific embodiment, the surface of the Al2O3 shell is modified with a fluorinated silane coupling agent, and the grafting density is 1.2-2.5 grafts / nm. 2 .

[0025] In this invention, the surface of the Al2O3 shell in the composite electrolyte film is modified with a fluorinated silane coupling agent, and the grafting density is specified to be 1.2-2.5 grafts / nm. 2 The grafting density of the fluorinated silane coupling agent on the Al2O3 surface is less than 1.2 grafts / nm. 2 At this point, the surface modification is insufficient and cannot effectively improve interface compatibility; while exceeding 2.5 per nm 2 This can lead to increased steric hindrance between molecules, causing structural defects in the modified layer. Therefore, this invention utilizes a fluorinated silane coupling agent surface modification technique, precisely controlling the grafting density to 1.2-2.5 grafts / nm. 2 Within this range, synergistic optimization of interfacial compatibility, ion transport performance, and mechanical strength is achieved. This approach not only solves key problems such as high interfacial impedance and poor stability of inorganic / organic phases in traditional composite electrolytes, but also provides a solution for improving the performance of solid-state lithium batteries.

[0026] The present invention also provides a method for preparing the above-mentioned aerogel-reinforced composite electrolyte film, comprising the following steps:

[0027] Inorganic oxide nanoparticles were dispersed in a polymer precursor solution, and after a sol-gel reaction, a three-dimensional porous aerogel framework with gradient pore sizes was formed by supercritical CO2 drying.

[0028] Subsequently, lithium lanthanum zirconium oxide nanowires were grown on the pore wall surface of the three-dimensional porous aerogel framework by chemical vapor deposition, with the growth temperature controlled at 600-800℃.

[0029] After melting the polyethylene oxide-lithium salt composite matrix and lithium salt nanocrystals, the mixture was injected into the aerogel pores. At the same time, an axial magnetic field was applied to orient the lithium lanthanum zirconium oxide nanowires along the thickness direction of the film.

[0030] The product is then obtained through rolling and annealing.

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

[0032] In addition, the supercritical CO2 drying process is a key step in constructing the gradient pore size aerogel framework for this invention. In the supercritical state, the surface tension disappears, which can avoid the collapse of the pore structure caused by conventional drying.

[0033] Subsequently, the growth temperature is crucial in the chemical vapor deposition process for growing lithium lanthanum zirconium oxide nanowires. This is because when the growth temperature is below 600°C, the precursor decomposes incompletely, leading to a decrease in product purity; while temperatures exceeding 800°C easily cause lithium volatilization, disrupting the stoichiometry. Within the optimized temperature range, by controlling the carrier gas flow rate and growth time, LLZO nanowires with suitable diameters and lengths can be obtained, and their growth rate can be stabilized at 100-200 nm / min.

[0034] When the PEO-LiTFSI composite matrix reaches the molten state, applying an axial magnetic field can induce the LLZO nanowires to align along the magnetic field direction. Simultaneous ultrasonic treatment generates a microscale flow field, which can further promote the orientation alignment of the nanowires. This multi-field coupling assembly strategy makes the ionic conductivity of the composite electrolyte exhibit significant anisotropy, perfectly matching the ion transport requirements in the thickness direction of solid-state batteries.

[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 as the carrier gas, and the growth rate is 100-200 nm / min.

[0036] In this invention, the precursors used for the growth of lithium lanthanum zirconium oxide nanowires are 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 unique advantages as a lanthanum source, as its decomposition temperature matches that of tetrabutyl zirconate, ensuring that the two metal precursors can release active components simultaneously. At the same time, the chelating effect of the acetylacetonate ligand can effectively reduce the diffusion rate of lanthanum ions, avoiding component segregation caused by local overconcentration. The choice of lithium foil as a 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 contamination of the deposition system. Choosing high-purity argon as the carrier gas can prevent the precursor from being oxidized during transport, especially protecting tetrabutyl zirconate from hydrolysis. When the argon flow rate is below 50 sccm, insufficient precursor transport leads to uneven nanowire growth; while exceeding 100 sccm will cause turbulence, resulting in disordered nanowire orientation. In addition, when the growth rate is below 100 nm / min, although the crystal integrity is good, the production efficiency is too low to meet the needs of practical applications; and when the rate exceeds 200 nm / min, a large number of grain boundary defects will be introduced, resulting in a decrease in ionic conductivity of more than 30%.

[0037] Preferably, as a further specific embodiment, the magnetic field is applied in the same direction as the film thickness direction, and ultrasonic treatment of 20-40 kHz is applied simultaneously to promote the directional alignment of lithium lanthanum zirconium oxide nanowires.

[0038] Preferably, as a further specific implementation, the supercritical CO2 drying adopts a gradient pressure reduction method: first, the temperature is increased to 50-60℃ at 2-5℃ / min, the pressure is maintained at 10-15MPa for 2 hours, and then the pressure is reduced at a rate of 0.1-0.5MPa / min.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] (1) This invention provides an aerogel-reinforced composite electrolyte film for solid-state lithium batteries. Through the synergistic effect of a unique three-dimensional porous aerogel framework, solid electrolyte composite and lithium salt nanocrystals, the electrolyte film achieves high ionic conductivity, excellent mechanical strength and interface stability.

[0041] (2) The present invention provides a method for preparing the above-mentioned aerogel-reinforced composite electrolyte film for solid-state lithium batteries. This preparation method solves the long-standing dilemma in the field of composite electrolytes that it is difficult to simultaneously achieve "high conductivity, good mechanical properties and excellent interface stability". Detailed Implementation

[0042] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] To more clearly illustrate the technical solutions in this invention, specific embodiments are described below.

[0044] Example 1

[0045] Raw material preparation:

[0046] Inorganic oxide nanoparticles: SiO2-Al2O3 core-shell structure (where the SiO2 core has a diameter of 20nm and the Al2O3 shell has a thickness of 5nm);

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

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

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

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

[0051] Preparation process:

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

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

[0054] The ultrasonically treated SiO2-Al2O3 core-shell nanoparticles were added to a TEOS / PVA mixed solution at a mass ratio of 1:2, the pH was adjusted to 5.0, and the mixture was stirred at 60°C for 6 hours to obtain the initial gel product.

[0055] The initial gel sample was transferred to a supercritical drying vessel, heated to 50°C at a rate of 2°C / min, maintained at 10 MPa pressure for 2 hours, and then gradually depressurized to atmospheric pressure at a rate of 0.1 MPa / min to obtain a three-dimensional porous aerogel framework with gradient pore sizes (30 nm pore size on the surface and 150 nm pore size in the core region).

[0056] Step 2: Al2O3 surface modification

[0057] A three-dimensional porous aerogel framework was immersed in an ethanol solution containing 1.5 vol% heptadecafluorodecyltrimethoxysilane and reacted at 90 °C for 3 hours, achieving a grafting density of 1.2 grafts / nm. 2 ;

[0058] Nitrogen purging to remove residual reagents, followed by vacuum drying at 80°C for 12 hours.

[0059] Step 3: LLZO nanowire growth

[0060] The modified three-dimensional porous aerogel framework was placed in the CVD reaction chamber.

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

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

[0063] After obtaining LLZO nanowires with a diameter of 70±5nm and a length of 6±1μm, a sample was obtained, wherein 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 1 hour to form a Li3PO4 coating layer with a thickness of 1nm.

[0066] Step 5: Electrolyte Recombination

[0067] A polyethylene oxide-lithium salt composite matrix was melt-mixed with LiTFSI at 120°C. After melting, the mixture was injected into the pores of a three-dimensional porous aerogel, while a 0.8T axial magnetic field and 20kHz ultrasound (power density 6W / cm³) were applied simultaneously. 2 )

[0068] Maintain field-assisted conditions for 30 minutes to align LLZO nanowires along the thickness direction, wherein the mass ratio of the three-dimensional porous aerogel framework to the solid electrolyte complex is 1:3.

[0069] Step 6: Post-processing

[0070] Densification was achieved through three-stage rolling (0.5MPa→2MPa→5MPa), followed by annealing at 90℃ for 3 hours to obtain the final film.

[0071] Example 2

[0072] Raw material preparation:

[0073] Inorganic oxide nanoparticles: SiO2-Al2O3 core-shell structure (where the SiO2 core has a diameter of 20nm and the Al2O3 shell has a thickness of 5nm);

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

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

[0076] Composite matrix: Polyoxyethylene-lithium salt composite matrix, wherein the lithium salt is LiFSI.

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

[0078] Preparation process:

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

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

[0081] The ultrasonically treated SiO2-Al2O3 core-shell nanoparticles were added to a TEOS / PVA mixed solution at a mass ratio of 1:2, the pH was adjusted to 5.0, and the mixture was stirred at 60°C for 6 hours to obtain the initial gel product.

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

[0083] Step 2: Al2O3 surface modification

[0084] A three-dimensional porous aerogel framework was immersed in an ethanol solution containing 1.5 vol% heptadecafluorodecyltrimethoxysilane and reacted at 90 °C for 3 hours, achieving a grafting density of 2.5 grafts / nm. 2 ;

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

[0086] Step 3: LLZO nanowire growth

[0087] The modified three-dimensional porous aerogel framework 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℃

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

[0090] A sample was obtained after LLZO nanowires with a diameter of 70±5 nm and a length of 6±1 μm, wherein the growth rate of 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℃ for 1 hour to form a Li3PO4 coating layer with a thickness of 5nm.

[0093] Step 5: Electrolyte Recombination

[0094] A polyethylene oxide-lithium salt composite matrix was melt-mixed with LiTFSI at 120°C. After melting, the mixture was injected into the pores of a three-dimensional porous aerogel, while a 0.8T axial magnetic field and 40kHz ultrasound (power density 6W / cm³) were applied simultaneously. 2 )

[0095] Maintain the field-assisted conditions for 30 minutes to align the LLZO nanowires along the thickness direction, wherein the mass ratio of the three-dimensional porous aerogel framework to the solid electrolyte complex is 1:15.

[0096] Step 6: Post-processing

[0097] Densification was achieved through three-stage rolling (0.5MPa→2MPa→5MPa), followed by annealing at 90℃ for 3 hours to obtain the final film.

[0098] Example 3

[0099] Raw material preparation:

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

[0101] Polymer precursor: a mixed solution of tetraethyl orthosilicate (TEOS) and polyvinyl alcohol (PVA) (mass ratio 1:3). Precursors: lanthanum acetylacetonate (99.9%), tetrabutyl zirconate (99.9%), lithium foil (25 μm thickness).

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

[0103] Composite matrix: Polyoxyethylene-lithium salt composite matrix, wherein the lithium salt is LiFSI.

[0104] Modifier: Heptadecafluorodecyltrimethoxysilane (purity ≥98%);

[0105] Preparation process:

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

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

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

[0109] The initial gel sample was transferred to a supercritical drying vessel, heated to 56°C at a rate of 3°C / min, maintained at 10 MPa for 2 hours, and then gradually depressurized to atmospheric pressure at a rate of 0.4 MPa / min to obtain a three-dimensional porous aerogel framework with gradient pore sizes (30 nm pore size on the surface and 150 nm pore size in the core region).

[0110] Step 2: Al2O3 surface modification

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

[0112] Nitrogen purging to remove residual reagents, followed by vacuum drying at 80°C for 12 hours.

[0113] Step 3: LLZO nanowire growth

[0114] The modified three-dimensional porous aerogel framework was placed in the CVD reaction chamber.

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

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

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

[0121] A polyethylene oxide-lithium salt composite matrix was melt-mixed with LiTFSI at 120°C. After melting, the mixture was injected into the pores of a three-dimensional porous aerogel, while a 0.8T axial magnetic field and 30kHz ultrasound (power density 6W / cm³) were applied simultaneously. 2 )

[0122] Maintain the field-assisted conditions for 30 minutes to align the LLZO nanowires along the thickness direction, wherein the mass ratio of the three-dimensional porous aerogel framework to the solid electrolyte complex is 1:10.

[0123] Step 6: Post-processing

[0124] Densification was achieved through three-stage rolling (0.5MPa→2MPa→5MPa), followed by annealing at 90℃ for 3 hours to obtain the final film.

[0125] Comparative Example 1

[0126] The specific implementation steps are the same as in Example 3, except that the mass ratio of the three-dimensional porous aerogel framework to the solid electrolyte complex in Example 3 is adjusted to 1:1.

[0127] Comparative Example 2

[0128] The specific implementation steps are the same as in Example 3, except that the mass ratio of the three-dimensional porous aerogel framework to the solid electrolyte complex in Example 3 is adjusted to 1:20.

[0129] Comparative Example 3

[0130] The specific implementation steps are the same as in Example 3, except that the lithium salt nanocrystal particle size in Example 3 is adjusted to 1 nm.

[0131] Comparative Example 4

[0132] The specific implementation steps are the same as in Example 3, except that the lithium salt nanocrystal particle size in Example 3 is adjusted to 100 nm.

[0133] Comparative Example 5

[0134] The specific implementation steps are the same as in Example 3, except that the grafting density in Example 3 is adjusted to 0.1 grafts / nm. 2 .

[0135] Comparative Example 6

[0136] The specific implementation steps are the same as in Example 3, except that the grafting density in Example 3 is adjusted to 10 grafts / nm. 2 .

[0137] Comparative Example 7

[0138] The specific implementation steps are the same as in 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 the same as in 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 the same as in Example 3, except that Li3PO4 is not coated on the surface of the lithium lanthanum zirconium oxide nanowires.

[0143] Comparative Example 10

[0144] The specific implementation steps are the same as in Example 3, except that the inorganic oxide nanoparticles only use nano-silica particles instead of a core-shell structure.

[0145] Comparative Example 11

[0146] The specific implementation steps are the same as in Example 3, except that the Al2O3 shell surface is not modified with a fluorinated silane coupling agent.

[0147] Experimental Example 1: Performance Testing of Aerogel-Reinforced Composite Electrolyte Films

[0148] 1. Testing Method

[0149] Ionic conductivity test: The electrochemical impedance spectroscopy (EIS) method was used. The thin film samples obtained in Examples 1-3 and Comparative Examples 1-11 were placed between two stainless steel blocking electrodes. The frequency range was 0.1 Hz-1 MHz, the amplitude was 10 mV, and the test was carried out at 25 °C. The bulk resistance (Rb) was obtained by fitting the Nyquist plot, and the ionic conductivity was calculated.

[0150] Mechanical strength test: Using a universal testing machine, the film was stretched to break at a rate of 1 mm / min, and the maximum tensile strength (MPa) and elongation at break (%) were recorded.

[0151] Interface stability test: Assembled Li / thin-film / Li symmetric cell, 0.5 mA / cm 2 Cycle 100 times at current density and record the growth rate of interface impedance.

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

[0153] Table 1 Test Results

[0154]

[0155] As can be seen from the experimental tables above, the aerogel-reinforced composite electrolyte film designed in this invention exhibits significant advantages in terms of ionic conductivity, mechanical strength, and interfacial stability. Among them, Example 3 is the optimal solution. In Comparative Examples 1-2, the effect of the mass ratio of the three-dimensional porous aerogel framework to the solid electrolyte composite was investigated. When the ratio of the two in Comparative Example 1 was adjusted to 1:1, the insufficient electrolyte content led to a decrease in ionic conductivity. At the same time, although the mechanical strength increased to 15.2 MPa, the elongation at break decreased significantly to 45%, indicating a deterioration in flexibility. When the ratio in Comparative Example 2 was increased to 1:20, although the ionic conductivity was further improved, the tensile strength dropped sharply to 6.4 MPa, and the interfacial impedance growth rate increased to 25.7%, indicating that the support of the framework was weakened, affecting the stability of the film.

[0156] Comparative Examples 3-4 investigated the effect of lithium salt nanocrystal size on the properties of the final prepared film. When the particle size in Comparative Example 3 was reduced to 1 nm, the ionic conductivity decreased to 7.3 × 10⁻⁶. -4 The interfacial impedance growth rate was 12.6%, indicating that excessively small particle size easily leads to aggregation and hinders ion transport. In contrast, when the particle size in Comparative Example 4 increased to 100 nm, the ionic conductivity further decreased, and the interfacial impedance growth rate increased to 18.4%, indicating that excessively large particle size leads to a reduction in active sites and a deterioration in interfacial contact.

[0157] Comparative Examples 5-6 investigated the effect of grafting density on the properties of the final prepared thin film. In Comparative Example 5, the grafting density was reduced to 0.1 grafts / nm. 2 At this point, both ionic conductivity and mechanical properties decreased significantly, and the interfacial impedance increased by as much as 22.1%, indicating that insufficient modification led to poor interfacial compatibility; while in Comparative Example 6, when the grafting density was increased to 10 grafts / nm... 2While the performance was slightly better than that of Comparative Example 5, it was still inferior to that of Example 3, indicating that excessively high grafting density would introduce steric hindrance and affect the modification effect.

[0158] Comparative Examples 7-8 investigated the effect of nanowire growth rate on the properties of the final prepared film. When the growth rate in Comparative Example 7 was too slow, 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 in Comparative Example 8 was too fast, although the ionic conductivity was slightly improved compared to Comparative Example 7, the tensile strength and interfacial stability both decreased, indicating that rapid growth introduced grain boundary defects.

[0159] In the comparative examples of this invention, Comparative Examples 9-11 further verified the key design of this invention. Comparative Example 9, without the Li3PO4 interface layer, showed a high interface impedance growth rate of 35.6% and a narrowed electrochemical window to 4.3V, indicating that the interface layer is crucial for suppressing side reactions. Comparative Example 10, using SiO2 nanoparticles with a non-core-shell structure, showed a significant reduction in ionic conductivity and mechanical properties, highlighting the contribution of the core-shell structure to interface optimization. Comparative Example 11, without surface modification, showed an interface impedance growth rate of 38.7%, further demonstrating the necessity of fluorinated silane coupling agent modification for improving interface stability.

[0160] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An aerogel-reinforced composite electrolyte film for solid-state lithium batteries, characterized in that, The thin film comprises a three-dimensional porous aerogel framework, a solid electrolyte complex, and lithium salt nanocrystals; The three-dimensional porous aerogel framework is prepared by inorganic oxide nanoparticles and polymer precursors via a sol-gel method, and the pore size of the three-dimensional porous aerogel framework is gradient distributed. The solid electrolyte composite fills the pores of the three-dimensional porous aerogel framework. The solid electrolyte composite includes 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 grown in situ on the surface of the pore walls of the three-dimensional porous aerogel. The mass ratio of the three-dimensional porous aerogel framework to the solid electrolyte complex is 1:3-1:15; The surface of the lithium lanthanum zirconium oxide nanowire is coated with a Li3PO4 interface layer, the thickness of which is 1-5 nm. The lithium salt nanocrystals have a particle size of 10-50 nm; the lithium salt nanocrystals are either LiTFSI or LiFSI. The inorganic oxide nanoparticles have a SiO2-Al2O3 core-shell structure; the SiO2 is the core with a particle size of 20 nm; and the Al2O3 is the outer shell with a thickness of 5 nm.

2. The aerogel-reinforced composite electrolyte film according to claim 1, characterized in that, The surface of the Al2O3 shell is modified with a fluorinated silane coupling agent, and the grafting density is 1.2-2.5 grafts / nm. 2 .

3. A method for preparing an aerogel-reinforced composite electrolyte film as described in any one of claims 1-2, characterized in that, Includes the following steps: Inorganic oxide nanoparticles were dispersed in a polymer precursor solution, and after a sol-gel reaction, a three-dimensional porous aerogel framework with gradient pore sizes was formed by supercritical CO2 drying. Subsequently, lithium lanthanum zirconium oxide nanowires were grown on the pore wall surface of the three-dimensional porous aerogel framework by chemical vapor deposition, with the growth temperature controlled at 600-800℃. After melting the polyethylene oxide-lithium salt composite matrix and lithium salt nanocrystals, the mixture was injected into the aerogel pores. At the same time, an axial magnetic field was applied to orient the lithium lanthanum zirconium oxide nanowires along the thickness direction of the film. The product is then obtained through rolling and annealing.

4. The preparation method according to claim 3, characterized in that, The lithium lanthanum zirconium oxide nanowires were grown using lanthanum acetylacetonate, tetrabutyl zirconate, and lithium foil as precursors, with high-purity argon as the carrier gas, and a growth rate of 100-200 nm / min.

5. The preparation method according to claim 3, characterized in that, The magnetic field is applied in the same direction as the film thickness, and ultrasonic treatment of 20-40 kHz is applied simultaneously to promote the directional alignment of lithium lanthanum zirconium oxide nanowires.

6. The preparation method according to claim 3, characterized in that, The supercritical CO2 drying adopts a gradient pressure reduction method: first, the temperature is increased to 50-60℃ at 2-5℃ / min, and the pressure is maintained at 10-15MPa for 2 hours, and then the pressure is reduced at a rate of 0.1-0.5MPa / min.

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