A PEO-based enhanced LLZO composite solid electrolyte membrane, a preparation method and applications thereof

Abstract

The application discloses a PEO-based reinforced LLZO composite solid electrolyte film, a preparation method and application. Firstly, nano ceramic particles are prepared; then, PVDF, LLZO and PEO are uniformly dispersed in N, N-dimethylformamide solvent; an organic-inorganic composite nanofiber film (LLZO NF) is prepared through electrospinning technology; finally, an organic-inorganic system (PEO / SN / ZnO) mixed solution is poured on the LLZO NF through a solution pouring method to obtain a PEO-based reinforced LLZO composite solid electrolyte film with double additives (SN and ZnO). The material has good tensile flexibility and can be bent and folded. When the material is used as a solid electrolyte material of a full solid-state lithium metal battery, the material has good ion transmission capacity and can meet the demand of a long-life lithium metal battery.

Description

Technical Field

[0001] This invention relates to a method for preparing energy storage system device materials, and particularly to a PEO-based enhanced LLZO composite solid electrolyte membrane with dual additives SN and ZnO, its preparation method and application, belonging to the field of energy storage system device material preparation technology. Background Technology

[0002] Solid-state lithium metal batteries have emerged over decades to address the growing demand for environmentally friendly and safer high-energy-density storage systems. While plastic crystalline electrolytes are among the most promising candidates for practical applications due to their high environmental ionic conductivity and excellent stability over a wide temperature range, they exhibit high activity upon contact with the Li anode and are prone to severe parasitic reactions, leading to significant damage to the electrode-electrolyte interface. These severe interface problems also make it difficult for lithium-ion batteries to achieve long-term cycle stability, failing to meet the ecological requirements of green sustainability.

[0003] To address the environmental problems caused by poor electrolytes, inorganic-polymer composite solid electrolytes have attracted widespread attention as a promising option for solid-state lithium metal batteries due to their high mechanical properties and excellent stability against Li. Solid electrolytes are non-flammable, offering a significant improvement in safety compared to plastic crystalline electrolytes. Furthermore, the use of solid electrolytes allows for the achievement of the highest theoretical capacity (3860 mAh g / g). -1 This makes it possible to directly use lithium metal, with its lowest chemical potential (-3.04V), as the negative electrode. Solid-state electrolytes are currently mainly classified into three categories: inorganic solid-state electrolytes, polymer solid-state electrolytes, and inorganic-polymer composite solid-state electrolytes. Among them, inorganic solid-state electrolytes have high ionic conductivity (10⁻⁶V) at room temperature. -2 S cm -1 This has attracted attention; however, its poor mechanical properties cause inconvenience for mass production and commercial use. Furthermore, the high interfacial resistance between the electrode and electrolyte fails to meet the requirements for flexibility; polymer solid electrolytes have superior mechanical properties, but poor ion transport capacity (10...). -5 S cm -1 However, these methods cannot meet the requirements for high-performance lithium metal batteries. Therefore, using non-conductive oxide nanoparticles as fillers and bridges to form a dense and continuous ionic conductivity network and orderly ion channels on the electrolyte surface, followed by composite with polymer solutions to improve electrochemical performance, is an ideal choice for preparing high-performance inorganic-polymer composite solid electrolytes that combine the advantages of both organic and inorganic solid electrolytes.

[0004] Inorganic-polymer composite solid electrolytes are typically prepared by dispersing conductive / non-conductive inorganic nanoparticles within an organic polymer matrix to improve the overall ionic conductivity of the solid electrolyte, while the polymer imparts mechanical flexibility. However, interfacial degradation between the polymer and the lithium anode in composite solid electrolytes can lead to interfacial instability. To date, constructing self-reinforcing interfacial films to promote ion transport and improve the cycle life of lithium metal batteries has become a comprehensive strategy. Summary of the Invention

[0005] This invention provides a PEO-based reinforced LLZO composite solid electrolyte membrane with dual additives SN and ZnO, which has good tensile flexibility and can be bent and folded. When used as a solid electrolyte material for all-solid-state lithium metal batteries, it has good ion transport capability and can meet the requirements of long-life lithium metal batteries.

[0006] The present invention also provides a method for preparing the PEO-based reinforced LLZO composite solid electrolyte membrane with dual additives SN and ZnO.

[0007] The technical solution adopted by this invention to solve its technical problem is:

[0008] A method for preparing a PEO-based reinforced LLZO composite solid electrolyte membrane with dual additives SN and ZnO, the method comprising the following steps:

[0009] S1. Preparation of organic-inorganic composite nanofiber membranes

[0010] Polyvinylidene fluoride (PVDF), inorganic ceramic filler (LLZO), and polyethylene oxide (PEO) are added to the solvent N,N-dimethylformamide (DMF) and stirred thoroughly at 35-45°C to obtain a uniformly mixed spinning precursor solution; wherein, the weight ratio of PVDF to LLZO is 0.08-0.2:1, and the amount of PEO added is 4-6% of the mass of PVDF;

[0011] The spinning precursor solution was electrospun to prepare LLZO nanofiber membrane, and after vacuum drying at 45±5℃, an organic-inorganic composite nanofiber membrane was obtained.

[0012] S2, Preparation of electrolyte solution

[0013] Polyethylene oxide (PEO), conductive lithium salt, and additive inorganic ZnO nanoparticles and succinic anion (SN) were vacuum dried within a suitable temperature range and then put into use.

[0014] The polymer and conductive lithium salt were stirred uniformly in a solvent until completely dissolved. Inorganic ZnO nanoparticles were added and stirred until dissolved. Succinate (SN) was then added and stirred until uniformly dispersed to obtain an electrolyte solution containing an organic-inorganic (PEO / SN / ZnO) mixture.

[0015] Based on the total mass of all solutes in the electrolyte solution being 100%, the amount of inorganic ZnO nanoparticles used is 3-8%; the total solutes refer to polyethylene oxide (PEO), conductive lithium salt, inorganic ZnO nanoparticles, and succinic anionyl nitrile (SN); based on the mass of PEO being 100%, the amount of SN used is 50-80%.

[0016] S3. Preparation of composite solid electrolyte membranes

[0017] The organic-inorganic composite nanofiber membrane described in S1 is placed on a mold, and an electrolyte solution obtained in S2 is poured onto its surface. After the solvent has completely evaporated, it is vacuum dried at 40-50°C to obtain a PEO-based reinforced LLZO composite solid electrolyte membrane with dual additives SN and ZnO.

[0018] This invention first prepares nano-ceramic particles; then, PVDF, LLZO, and PEO are uniformly dispersed in N,N-dimethylformamide solvent; an organic-inorganic composite nanofiber membrane (LLZONF) is prepared by electrospinning; finally, an organic-inorganic system (PEO / SN / ZnO) mixture is cast onto LLZONF by solution casting to obtain a PEO-based reinforced LLZO composite solid electrolyte membrane with dual additives (SN, ZnO). This material can be applied to the energy storage field of flexible lithium-ion batteries.

[0019] The PEO-based reinforced LLZO composite solid electrolyte membrane material with dual additives SN and ZnO prepared by this invention can be applied in flexible solid-state lithium-ion batteries. By complexing Zn atoms in ZnO with N atoms in SN, ineffective SN molecules are successfully fixed in the SEI layer, and the SN self-polymerization reaction is promoted, causing the cyano group to be converted into -C=N-, so as to prevent the generation of LiCN from hindering charge transfer and effectively improve the lithium-ion transport capacity.

[0020] The stirring temperature of the electrospinning precursor solution is 35-45℃. This temperature range allows PVDF to dissolve completely, resulting in a homogeneous solution.

[0021] Preferably, the electrospinning parameters are: electrostatic voltage 12-14kV, spinning distance 8-10cm, flow rate of electrospinning precursor solution 0.7-0.9mL / h, and spinning drum speed 270-330rpm.

[0022] Preferably, the PVDF in S1 needs to be dried at a temperature of 70-80℃. The raw material PVDF must be dried before preparing the spinning solution; if the raw material absorbs water, the spinning solution cannot be prepared and spinning cannot be carried out.

[0023] Preferably, the preparation method of the inorganic ceramic filler is as follows: dissolve a metal ion precursor salt in water, add an appropriate amount of heteroatom precursor salt as a dopant, stir uniformly at 50-60℃ until dissolved, dry at 200-250℃, and calcine at 750-850℃ to obtain LLZO ceramic filler; the metal ion precursor salt is selected from Li salt, La salt, and Zr salt, and the heteroatom precursor salt is selected from Al salt and Nb salt. The purpose of heating in the preparation method of the inorganic ceramic filler is to dissolve the metal salt, and the temperature is generally controlled at 50±5℃. Inorganic ceramic fillers also include several phases, such as garnet type, perovskite type, and NASICON type, etc., and the above types of inorganic ceramic fillers can be prepared by doping.

[0024] More preferably, the raw material formula of the nano-ceramic filler is: 0.0078mol C6H8O7·H2O, 0.007mol LiOH, 0.003mol La(NO3)3·6H2O, 0.00175mol ZrO(NO3)2·xH2O, and 0.00024mol Al(NO3)3·9H2O.

[0025] Preferably, in S2, the amount of inorganic ZnO nanoparticles is 3g, based on the total mass of the solute in the electrolyte solution being 100%. .5 -5%; all solutes refer to polyethylene oxide (PEO), conductive lithium salt, inorganic ZnO nanoparticles and succinic anionyl nitrile (SN); based on PEO mass of 100%, the amount of SN is 50-60%.

[0026] Preferably, the conductive lithium salt is selected from one or more of lithium halides (LiX, X=F,Cl,Bt,I), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), or lithium tetrafluoroborate (LiBF4).

[0027] Preferably, the solvent in S2 is acetonitrile or N,N-dimethylformamide, and the stirring time when PEO is mixed with conductive lithium salt is 12-18h; the drying time of the composite solid electrolyte membrane in S3 is 8-12h.

[0028] Preferably, the amount of PEO added is 5% of the mass of PVDF.

[0029] Preferably, the total thickness of the composite solid electrolyte membrane is generally maintained at 90μm-110μm.

[0030] A PEO-based reinforced LLZO composite solid electrolyte membrane with dual additives SN and ZnO prepared by the method of the present invention.

[0031] The present invention relates to the application of a PEO-based enhanced LLZO composite solid electrolyte membrane with dual additives SN and ZnO in the preparation of flexible solid-state lithium-ion batteries.

[0032] The method of this invention is easy to implement and can be mass-produced. The resulting organic-inorganic composite nanofiber membrane can form a three-dimensional ion-conducting pathway. The final PEO-based reinforced LLZO composite solid electrolyte membrane with dual additives SN and ZnO has good tensile flexibility and can be bent and folded. When used as a solid electrolyte material for all-solid-state lithium metal batteries, it has good ion transport capabilities and can meet the requirements of long-life lithium metal batteries.

[0033] To achieve high ionic conductivity and excellent mechanical flexibility in composite solid-state electrolytes, an organic-inorganic composite nanofiber membrane (LLZO NF) can be prepared using electrospinning technology. This membrane is then combined with an organic-inorganic system (PEO / SN / ZnO) mixture to obtain a PEO-based reinforced LLZO composite solid-state electrolyte membrane with dual additives, SN and ZnO. The continuous 3D ion-conducting pathway of the organic-inorganic composite nanofiber membrane enhances the overall ion-conducting effect of the solid-state electrolyte, while the PEO polymer matrix provides overall mechanical flexibility. Selecting appropriate additives enhances polymer chain kinetics, improves ionic conductivity, and enhances electrode-electrolyte interface compatibility. Furthermore, during the charge-discharge process of lithium metal batteries, uniform lithium deposition is achieved, resulting in stable ion transport. This composite solid-state electrolyte, possessing both excellent electrochemical performance and mechanical flexibility, has broad application prospects in solid-state batteries.

[0034] This invention adds a small amount of ZnO nanoparticles and SN polymer to a PEO-based casting solution to achieve a high-quality LLZO composite solid electrolyte membrane. Through multiple experiments, the inventors have verified that when the organic-inorganic mixed electrolyte solution described in this invention is supplemented with dual additives SN and ZnO, SN can open PEO chain segments, reduce crystallinity, and improve ionic conductivity; however, the presence of ineffective SN molecules will hinder ion transport. By utilizing the complexation of Zn atoms in ZnO with N atoms in SN, we successfully immobilized the ineffective SN molecules in the SEI layer and promoted SN self-polymerization, converting cyano groups to -C=N- to prevent the generation of LiCN from hindering charge transfer and affecting electrochemical performance. Experiments have verified that good electrochemical performance can only be achieved when the amount of SN added is 50-60% of PEO and the amount of ZnO nanoparticles added is 3.5-5% of the total solute weight.

[0035] In summary, the method of the present invention has the following characteristics:

[0036] 1. This invention is simple to operate, the reaction conditions are easy to control and achieve, and it can be mass-produced;

[0037] 2. PEO-based reinforced LLZO composite solid electrolyte membranes with dual additives (SN, ZnO) have continuous 3D ion conduction paths and ion channels;

[0038] 3. SN molecules open the PEO polymer chain, reduce crystallinity, and increase ionic conductivity; at the same time, ZnO inhibits ineffective SN molecules from escaping to the lithium anode surface and undergoing severe parasitic reactions, thus promoting ion transport.

[0039] 4. The obtained PEO-based enhanced LLZO composite solid electrolyte membrane with dual additives (SN, ZnO) can be applied to lithium metal batteries. During charging and discharging, due to the anchoring effect of ZnO on TFSI-, electrolyte decomposition can be inhibited, interface stability can be improved, and the cycle life of the battery can be increased.

[0040] 5. Creatively introducing dual additives to realize the practical application value of flexible pouch batteries. Attached Figure Description

[0041] Figure 1 This is a scanning electron microscope (SEM) image of the surface of the PEO-based reinforced LLZO composite solid electrolyte membrane with dual additives (SN, ZnO) prepared in Example 1.

[0042] Figure 2 This is a polarization curve of a Li / solid electrolyte / Li symmetric cell with a PEO-based enhanced LLZO composite solid electrolyte membrane with dual additives (SN, ZnO) prepared in Example 1.

[0043] Figure 3 The image shows a scanning electron microscope (SEM) image of the lithium anode surface after cycling of a Li / solid electrolyte / Li symmetric battery with a PEO-based enhanced LLZO composite solid electrolyte membrane with dual additives (SN, ZnO) prepared in Example 1.

[0044] Figure 4 This is the electrochemical impedance (EIS) diagram of a stainless steel / solid electrolyte / stainless steel symmetric cell with a PEO-based enhanced LLZO composite solid electrolyte membrane with dual additives (SN, ZnO) prepared in Example 1.

[0045] Figure 5 The polarization curves of the Li / solid electrolyte / Li symmetric cell of the PEO-based enhanced LLZO composite solid electrolyte membrane without additives prepared in Comparative Example 1 are shown.

[0046] Figure 6 This is a scanning electron microscope (SEM) image of the surface of the PEO-based reinforced LLZO composite solid electrolyte membrane containing only ZnO prepared in Comparative Example 2.

[0047] Figure 7 The polarization curves of the Li / solid electrolyte / Li symmetric cell with PEO-based enhanced LLZO composite solid electrolyte membrane containing only SN prepared in Comparative Example 3 are shown.

[0048] Figure 8 This is a polarization curve of a Li / solid electrolyte / Li symmetric cell with a PEO-based enhanced LLZO composite solid electrolyte membrane containing 8% ZnO prepared in Comparative Example 4.

[0049] Figure 9 This is a scanning electron microscope (SEM) image of the surface of the PEO-based reinforced LLZO composite solid electrolyte membrane containing 40% SN prepared in Comparative Example 5.

[0050] Figure 10 This is a scanning electron microscope (SEM) image of the surface of the PEO-based reinforced LLZO composite solid electrolyte membrane containing 80% SN prepared in Comparative Example 6.

[0051] Figure 11 This is an application diagram of the pouch cell with the PEO-based enhanced LLZO composite solid electrolyte membrane with dual additives (SN, ZnO) prepared in Example 1. Detailed Implementation

[0052] The technical solution of the present invention will be further described in detail below through specific embodiments. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any modifications and / or alterations made to the present invention will fall within the protection scope of the present invention.

[0053] In this invention, unless otherwise specified, all parts and percentages are by weight, and the equipment and raw materials used are commercially available or commonly used in the art. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0054] Unless otherwise specified, the reagents used in the following examples can be purchased from a regular biochemical reagent store.

[0055] Example 1 (Best Practice)

[0056] A method for preparing a PEO-based reinforced LLZO composite solid electrolyte membrane with dual additives SN and ZnO, the specific steps of which are as follows:

[0057] (1) Preparation of inorganic ceramic filler: 0.0078 mol C6H8O7·H2O, 0.007 mol LiOH, 0.003 mol La(NO3)3·6H2O, 0.00175 mol ZrO(NO3)2·xH2O, and 0.00024 mol Al(NO3)3·9H2O were dissolved in 10 ml of deionized water and a homogeneous solution was obtained under stirring and heating (55℃, the same below). After drying the sol at 250℃ for 3 h, a brown porous gel was obtained. The dried gel was calcined in a muffle furnace (under air conditions) at 850℃ for 2 h to obtain the inorganic ceramic filler;

[0058] (2) Preparation of organic-inorganic composite nanofiber membrane: 0.8g polyvinylidene fluoride, 0.1g inorganic ceramic filler and 0.04g polyoxyethylene oxide (PEO) were dissolved in 9.2g N,N-dimethylformamide solvent and stirred at 50℃ for 24h to obtain electrospinning precursor solution; the precursor solution was spun into nanofiber membrane under the spinning conditions of electrostatic voltage of 13kV, spinning distance of 8cm, spinning solution flow rate of 0.6mL / h and drum speed of 310rpm, and then vacuum dried at 50℃ for 24h. The membrane was then placed in a glove box filled with argon for later use to obtain organic-inorganic composite nanofiber membrane (LLZO NF);

[0059] (3) Preparation of organic-inorganic system mixture: First, polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were vacuum dried at 40°C with dual additives SN and ZnO at 50°C for 24 h for later use; then, PEO and LiTFSI were dissolved in acetonitrile at a molar ratio of EO∶Li=20∶1, with inorganic ZnO nanoparticles accounting for 3.5 wt% of the total solute and SN accounting for 60% of the mass of PEO; finally, the mixture was stirred at room temperature for 48 h to form a homogeneous mixed solution, thus obtaining the electrolyte mixture solution of the organic-inorganic (PEO / SN / ZnO) system.

[0060] (4) Preparation of PEO-based reinforced LLZO composite solid electrolyte membrane with dual additives SN and ZnO: First, the organic-inorganic (PEO / SN / ZnO) mixed solution from step (3) was drawn up with a syringe; then, the organic-inorganic composite nanofiber membrane (LLZONF) obtained in step (2) was placed on a polytetrafluoroethylene mold, and another layer of organic-inorganic (PEO / SN / ZnO) mixed solution was poured until it was completely permeated; finally, after the acetonitrile in the organic-inorganic (PEO / SN / ZnO) mixed solution had completely evaporated, the PEO-based reinforced LLZO composite solid electrolyte membrane with dual additives SN and ZnO was removed and vacuum dried at 50°C for 24 h to obtain the final composite solid electrolyte. The total thickness of the composite solid electrolyte membrane was controlled at 90-110 μm.

[0061] The scanning electron microscope (SEM) surface morphology of the PEO-based reinforced LLZO composite solid electrolyte membrane with dual additives SN and ZnO is shown in [reference needed]. Figure 1 The observable surface is flat, smooth, and wrinkle-free, and the ZnO nanoparticles are uniformly distributed, indicating that phase separation has not occurred, which is beneficial for stable ion transport at the interface. The polarization test curves of the PEO-based reinforced LLZO composite solid electrolyte membrane with dual additives SN and ZnO for the Li / solid electrolyte / Li symmetric battery are shown below. Figure 2 The ion mobility reaches 0.88 at 50℃; and during charging and discharging, the organic-inorganic (PEO / SN / ZnO) mixed solution enables the electrolyte to suppress the formation of lithium dendrites. Figure 3 The electrochemical impedance spectroscopy (EIS) of the stainless steel / solid electrolyte / stainless steel battery with the PEO-based reinforced LLZO composite solid electrolyte membrane containing dual additives SN and ZnO is shown in [reference needed]. Figure 4 The calculated ionic conductivity at room temperature reaches 10. -4 This improves the electrochemical performance of solid-state lithium metal batteries.

[0062] Comparative Example 1

[0063] The difference from Example 1 is:

[0064] Step (3) Preparation of casting solution: First, polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) are vacuum dried at 50°C for 24 hours for later use; then, PEO and LiTFSI are dissolved in acetonitrile at a molar ratio of EO:Li = 20:1; finally, the mixture is stirred at room temperature for 48 hours to form a homogeneous mixed solution, thus obtaining the organic polymer solution of “PEO-LiTFSI”.

[0065] Step (4) Preparation of PEO-based reinforced LLZO composite solid electrolyte membrane with dual additives SN and ZnO: First, the organic polymer solution of the “PEO-LiTFSI” system in step (3) is drawn with a syringe; then, the organic-inorganic composite nanofiber membrane (LLZO NF) obtained in step (2) is placed on a polytetrafluoroethylene mold, and a layer of electrolyte solution of the “PEO-LiTFSI” system is poured until it is completely permeated; finally, after the acetonitrile in the electrolyte solution has completely evaporated, the composite solid electrolyte membrane is removed and vacuum dried at 50°C for 24 h to obtain the PEO-based reinforced LLZO composite solid electrolyte membrane with dual additives SN and ZnO, with the total thickness controlled at 100-120 μm;

[0066] The polarization test curves of the Li / solid electrolyte / Li symmetric cell with the additive-free PEO-based enhanced LLZO composite solid electrolyte membrane are shown in the figure. Figure 5 At 50℃, the ion mobility is only 0.61, indicating poor ion transport capability.

[0067] Comparative Example 2

[0068] The difference from Example 1 is:

[0069] Step (3) Preparation of organic polymer electrolyte solution: First, polyethylene oxide (PEO), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and inorganic ZnO nanoparticles were vacuum dried at 50°C for 24 h for later use; then, PEO and LiTFSI were dissolved in acetonitrile at a molar ratio of EO∶Li=20∶1, and the inorganic ZnO nanoparticles accounted for 3.5wt% of the total solute; finally, the mixture was stirred at room temperature for 48 h to form a homogeneous mixed solution, thus obtaining the organic solution of the “PEO-LiTFSI-ZnO” system.

[0070] Preparation of PEO-based reinforced LLZO composite solid electrolyte membrane with dual additives SN and ZnO in step (4): First, the electrolyte solution of the PEO-LiTFSI-ZnO system in step (3) is drawn up with a syringe; then, the organic-inorganic composite nanofiber membrane (LLZO NF) obtained in step (2) is placed on a polytetrafluoroethylene mold, and another layer of PEO-LiTFSI-ZnO electrolyte solution is poured; finally, after the acetonitrile in the PEO-LiTFSI-ZnO electrolyte solution has completely evaporated, the composite solid electrolyte membrane is removed and vacuum dried at 50°C for 24 h to obtain the final PEO-based reinforced LLZO composite solid electrolyte membrane with dual additives SN and ZnO. The total thickness of the composite solid electrolyte membrane is controlled at 100-120 μm;

[0071] The Li / solid electrolyte / Li symmetric battery with a PEO-based enhanced LLZO composite solid electrolyte membrane containing dual additives SN and ZnO exhibits an uneven lithium anode surface during charge and discharge processes. Figure 6 Uneven lithium deposition.

[0072] Comparative Example 3

[0073] The difference from Example 1 is:

[0074] Step (3) Preparation of electrolyte solution for organic-inorganic system: First, polyethylene oxide (PEO), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and succinate (SN) are vacuum dried at 50°C for 24 h for later use; then, PEO and LiTFSI are dissolved in acetonitrile at a molar ratio of EO∶Li=20∶1, with the SN polymer accounting for 60wt% of the PEO solute; finally, the mixture is stirred at room temperature for 48 h to form a homogeneous mixed solution, thus obtaining the electrolyte solution of the “PEO-LiTFSI-SN” system;

[0075] Step (4) Preparation of PEO-based reinforced LLZO composite solid electrolyte membrane with dual additives SN and ZnO: First, the electrolyte solution of the PEO-LiTFSI-SN system in step (3) is drawn up with a syringe; then, the organic-inorganic composite nanofiber membrane (LLZO NF) obtained in step (2) is placed on a polytetrafluoroethylene mold, and another layer of PEO-LiTFSI-SN system electrolyte solution is poured until it is completely permeated; finally, after the acetonitrile in the PEO-LiTFSI-SN system electrolyte solution has completely evaporated, the composite solid electrolyte membrane is removed and vacuum dried at 50°C for 24 h to obtain the final PEO-based reinforced LLZO composite solid electrolyte membrane with dual additives SN and ZnO. The total thickness of the composite solid electrolyte membrane is controlled at 100-120 μm;

[0076] The polarization test curves of the Li / solid electrolyte / Li symmetric cell with the PEO-based enhanced LLZO composite solid electrolyte membrane with dual additives SN and ZnO are shown in the figure. Figure 7 At 50℃, the ion mobility is only 0.46, indicating poor ion transport capability.

[0077] Comparative Example 4

[0078] The difference from Example 1 is:

[0079] Step (3) Preparation of organic-inorganic system mixture: First, polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) are vacuum dried at 40°C with dual additives SN and ZnO at 50°C for 24 hours for later use; then, PEO and LiTFSI are dissolved in acetonitrile at a molar ratio of EO∶Li=20∶1, with inorganic ZnO nanoparticles accounting for 8wt% of the total solute and SN accounting for 60% of the mass of PEO; finally, the mixture is stirred at room temperature for 48 hours to form a homogeneous mixed solution, thus obtaining the electrolyte mixed solution of the organic-inorganic (PEO / SN / ZnO) system.

[0080] The SEM images of the PEO-based reinforced LLZO composite solid electrolyte membrane with dual additives SN and ZnO are shown below. Figure 8The presence of numerous surface pores indicates that severe phase separation occurs when the ZnO content reaches 8%, resulting in high crystallinity, which is detrimental to ion transport.

[0081] Comparative Example 5

[0082] The difference from Example 1 is:

[0083] Step (3) Preparation of organic-inorganic system mixture: First, polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) are vacuum dried at 40°C with dual additives SN and ZnO at 50°C for 24 hours for later use; then, PEO and LiTFSI are dissolved in acetonitrile at a molar ratio of EO∶Li=20∶1, with inorganic ZnO nanoparticles accounting for 3.5wt% of the total solute and SN accounting for 40% of the mass of PEO; finally, the mixture is stirred at room temperature for 48 hours to form a homogeneous mixed solution, thus obtaining the electrolyte mixed solution of the organic-inorganic (PEO / SN / ZnO) system.

[0084] The SEM images of the PEO-based reinforced LLZO composite solid electrolyte membrane with dual additives SN and ZnO are shown below. Figure 9 The severe surface wrinkles indicate that phase separation occurs when the SN content reaches 40%, which is not conducive to ion transport.

[0085] Comparative Example 6

[0086] The difference from Example 1 is:

[0087] Step (3) Preparation of organic-inorganic system mixture: First, polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) are vacuum dried at 40°C with dual additives SN and ZnO at 50°C for 24 hours for later use; then, PEO and LiTFSI are dissolved in acetonitrile at a molar ratio of EO∶Li=20∶1, with inorganic ZnO nanoparticles accounting for 3.5wt% of the total solute and SN accounting for 80% of the mass of PEO; finally, the mixture is stirred at room temperature for 48 hours to form a homogeneous mixed solution, thus obtaining the electrolyte mixed solution of the organic-inorganic (PEO / SN / ZnO) system.

[0088] The SEM images of the PEO-based reinforced LLZO composite solid electrolyte membrane with dual additives SN and ZnO are shown below. Figure 10 The presence of wrinkles and pores on the surface indicates that when the SN content reaches 80%, phase separation is severe, which is not conducive to the transport of ions between the interfaces.

[0089] Application example: Packaging of pouch batteries

[0090] Prepare a LiFePO4-coated positive electrode (larger than the lithium sheet), and cut a 3×3cm lithium sheet in a glove box. Prepare two electrode sheets and heat the two tabs on the electrode sheets to tightly bond the electrodes to the composite solid electrolyte, then encapsulate them together in aluminum foil (heating times: 3-5 times). It is particularly important to ensure that the vacuum in the aluminum foil is completely removed during the encapsulation process (vacuuming times: 5-7 times) to prevent lithium sheet oxidation. To demonstrate the cycle stability of the PEO-based enhanced LLZO composite solid electrolyte membrane with dual additives SN and ZnO provided by this invention in a pouch battery, first connect the two electrode sheets to the positive and negative terminals of an LED light, thereby lighting it. Then, test its safety performance by puncturing a hole in the pouch. Photos from the scene are shown below. Figure 11 As shown, the brightness of the LED light was not affected, proving that the composite solid electrolyte has good cycle stability.

[0091] The above experiments fully demonstrate that the PEO-based enhanced LLZO composite solid electrolyte membrane with dual additives SN and ZnO can greatly improve the electrochemical performance of solid lithium metal batteries and can be practically applied to the preparation of flexible solid lithium batteries.

[0092] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the method section.

[0093] The foregoing has provided a detailed description of the PEO-based reinforced LLZO composite solid electrolyte membrane, its preparation method, and its applications. Specific examples have been used to illustrate the principles and implementation methods of the invention. These examples are merely illustrative to aid in understanding the method and core concepts of the invention. It should be noted that those skilled in the art can make various improvements and modifications to the invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims.

Claims

1. A method for preparing a PEO-based reinforced LLZO composite solid electrolyte membrane with dual additives SN and ZnO, characterized in that... The method includes the following steps: S1. Preparation of organic-inorganic composite nanofiber membranes Polyvinylidene fluoride (PVDF), inorganic ceramic filler (LLZO), and polyethylene oxide (PEO) were added to the solvent N,N-dimethylformamide and stirred thoroughly at 35-45 °C to obtain a uniformly mixed spinning pretreatment solution; wherein the weight ratio of PVDF to LLZO was 0.08-0.2:1, and the amount of PEO added was 4-6% of the mass of PVDF; The spinning precursor solution was electrospun to prepare LLZO nanofiber membrane, and after vacuum drying at 45±5℃, an organic-inorganic composite nanofiber membrane was obtained. S2, Preparation of electrolyte solution PEO, conductive lithium salt, and additive inorganic ZnO nanoparticles and succinic acid (SN) are vacuum dried within a suitable temperature range and then put into use. The polymer and conductive lithium salt are stirred uniformly in a solvent until completely dissolved. Inorganic ZnO nanoparticles are added and stirred until dissolved. Then, SN is added and stirred until uniformly dispersed to obtain an electrolyte solution containing an organic-inorganic mixture. Based on the total mass of all solutes in the electrolyte solution being 100%, the amount of inorganic ZnO nanoparticles used is 3.5-5%; all solutes refer to PEO, conductive lithium salt, inorganic ZnO nanoparticles, and SN; based on the mass of PEO being 100%, the amount of SN used is 50-60%. S3. Preparation of composite solid electrolyte membranes The organic-inorganic composite nanofiber membrane described in S1 is placed on a mold, and an electrolyte solution obtained in S2 is poured onto its surface. After the solvent has completely evaporated, it is vacuum dried at 40-50°C to obtain a PEO-based reinforced LLZO composite solid electrolyte membrane with dual additives SN and ZnO.

2. The preparation method according to claim 1, characterized in that: The electrospinning parameters are: electrostatic voltage 12-14 kV, spinning distance 8-10 cm, electrospinning precursor solution flow rate 0.7-0.9 mL / h, and spinning drum speed 270-330 rpm.

3. The preparation method according to claim 1, characterized in that: The PVDF in S1 needs to be dried at a temperature of 70-80℃.

4. The preparation method according to claim 1, characterized in that: The preparation method of the inorganic ceramic filler is as follows: dissolve the metal ion precursor salt in water, add an appropriate amount of heteroatom precursor salt as a dopant, stir evenly at 50-60℃ until dissolved, dry at 200-250℃, and calcine at 750-850℃ to obtain LLZO ceramic filler; the metal ion precursor salt is selected from Li salt, La salt and Zr salt, and the heteroatom precursor salt is selected from Al salt and Nb salt.

5. The preparation method according to claim 1, characterized in that: The raw material formula of the inorganic ceramic filler is: 0.0078 mol C6H8O7•H2O, 0.007 mol LiOH, 0.003 mol La(NO3)3•6H2O, 0.00175 mol ZrO(NO3)2•xH2O, and 0.00024 mol Al(NO3)3•9H2O.

6. The preparation method according to claim 1, characterized in that: The conductive lithium salt is selected from one or more of lithium halides, lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium hexafluorophosphate, or lithium tetrafluoroborate.

7. The preparation method according to claim 1, characterized in that: The solvent in S2 is acetonitrile or N,N-dimethylformamide, and the stirring time when PEO is mixed with conductive lithium salt is 12-18 h; the drying time of the composite solid electrolyte membrane in S3 is 8-12 h.

8. A PEO-based reinforced LLZO composite solid electrolyte membrane with dual additives SN and ZnO prepared by the preparation method of claim 1.

9. The application of the PEO-based enhanced LLZO composite solid electrolyte membrane with dual additives SN and ZnO as described in claim 8 in the preparation of flexible solid-state lithium-ion batteries.

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