A PEO / garnet solid-state composite electrolyte using plasma technology and its preparation method and application

Abstract

The application discloses a kind of PEO / garnet type solid composite electrolyte prepared using plasma technology and its preparation method and application, belong to solid battery technical field.The method includes: PEO, lithium salt, succindinitrile and garnet type solid electrolyte filler are dissolved in organic solvent, and precursor solution is formed;Solution is placed in plasma equipment;Under the condition of vacuum, low temperature, gas excitation liquid is introduced and plasma is excited, and precursor is treated for a short time, and one step realizes the thorough removal of organic solvent and in-situ crosslinking solidification of PEO matrix.The application utilizes the double effect of plasma technology, fundamentally solves the difficult problem of solvent residue and filler uneven dispersion in traditional method, and the prepared composite electrolyte has high ionic conductivity, high lithium ion transference number and excellent stability to lithium metal.The method is simple, efficient and energy-saving, suitable for preparing high-performance solid-state battery, and has wide industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of solid-state battery materials technology, and in particular to a method for preparing and applying a PEO / garnet-type solid-state composite electrolyte synthesized using plasma technology. Background Technology

[0002] With the rapid development of electric vehicles and large-scale energy storage technologies, the demand for high-energy-density and high-safety lithium batteries is becoming increasingly urgent. Traditional lithium-ion batteries use organic liquid electrolytes, which pose safety hazards such as easy leakage, flammability, and explosion, severely restricting their further development. Solid-state electrolytes are considered key materials for solving these safety problems and are expected to be matched with high-capacity lithium metal anodes, thereby achieving a leapfrog improvement in battery energy density. Currently, the mainstream solid-state electrolytes mainly include three categories: oxides, sulfides, and polymers. Among them, garnet-type oxide electrolytes, especially Li7La3Zr2O... 12 And its doped materials, such as LLZTO, are due to their high ionic conductivity (up to 10). -4 ~ 10 -3 LLZTO has attracted much attention due to its excellent stability to lithium metal (S / cm), wide electrochemical window, and high interfacial impedance. However, as a rigid ceramic material, its intrinsic brittleness leads to point contact with the electrode, resulting in high interfacial impedance, complex and costly molding process, which limits its large-scale application.

[0003] To overcome the shortcomings of single materials, researchers have turned their attention to composite electrolyte systems. Introducing LLZTO ceramic filler into a polymer matrix (such as polyethylene oxide (PEO)) to construct an LLZTO / PEO composite electrolyte is considered a promising technological approach. This composite system theoretically combines the advantages of both: PEO provides good flexibility and interfacial contact, reducing interfacial impedance; LLZTO not only improves the overall ionic conductivity of the system but also inhibits PEO crystallization through Lewis acid-base interactions and enhances its mechanical strength to suppress lithium dendrite growth. Currently, common PEO polymerization methods employ solution casting, where the organic solvents used in the polymerization process are difficult to completely evaporate, filler agglomeration easily occurs, deteriorating interfacial stability, and high-temperature processing leads to polymer degradation. These processes are complex and have certain limitations. To address this, CN114221029A discloses a method for UV-curing PEO solid polymer electrolytes that does not require the addition of organic solvents. Curing with ultraviolet light can effectively reduce the crystallinity of PEO, but the preparation process is relatively complex.

[0004] Based on this, the present invention proposes a method for preparing LLZTO / PEO composite electrolyte using plasma technology. By using plasma technology to completely remove the solvent at low temperature and simultaneously complete the polymerization and crosslinking of PEO, this method effectively combines the advantages of solution method and dry method to prepare a high-performance composite solid electrolyte. Summary of the Invention

[0005] To address the problems of residual organic solvents, uneven dispersion of LLZO fillers, high interfacial impedance between phases, and polymer degradation caused by high-temperature processing in the preparation of PEO / garnet-type solid composite electrolytes in existing technologies, this invention provides a method for preparing PEO / garnet-type solid composite electrolytes using plasma technology. In a low-temperature environment, plasma initiates cross-linking polymerization of PEO monomers or oligomers, thoroughly removing the organic solvents used in the mixing process and promoting uniform dispersion of LLZO fillers.

[0006] To achieve the above-mentioned objectives, the technical solution of the present invention is as follows:

[0007] This invention provides a method for preparing a PEO / garnet-type solid composite electrolyte using plasma technology, comprising the following steps:

[0008] Preparation of electrolyte precursor: PEO, lithium salt, succinic acid, garnet-type solid electrolyte filler and organic solvent are mixed to obtain precursor solution;

[0009] Preparation of composite electrolyte: The precursor solution is transferred into a polytetrafluoroethylene mold, placed in a plasma device, the plasma reaction chamber is evacuated to a vacuum, a gas excitation source is introduced, the radio frequency power is adjusted, and after ignition, the reaction is carried out under the reaction vacuum for a certain period of time to obtain the PEO / garnet type solid composite electrolyte polymerized by plasma technology.

[0010] Preferably, in step (1), the garnet-type solid electrolyte filler includes at least one garnet-type inorganic solid electrolyte LLZO with or without doping elements; the doping element is selected from at least one of Ta, Al, and Nb; more preferably, the garnet-type solid electrolyte filler is LLZTO, which is a Ta-doped garnet-type inorganic solid electrolyte Li 6.4 La3Zr 1.4 Ta 0.6 O 12 More preferably, the LLZTO filler is synthesized by a high-temperature solid-state method and has a particle size of 0.5-1 μm.

[0011] Preferably, in step (1), the organic solvent is anhydrous acetonitrile, and the molar ratio of PEO, lithium salt, and SN is 15-20:1:4-8, more preferably 20:1:4; the mass percentage of garnet-type solid electrolyte filler in the solid material (including PEO, lithium salt, SN, and garnet-type solid electrolyte filler) is 5%-15%, more preferably 15%; the solid-liquid mass ratio is 1:4-6, more preferably 1:5. More preferably, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LITFSI).

[0012] Preferably, in step (1), the mixing refers to stirring evenly at room temperature, more preferably at 15-40℃, more preferably at 20-30℃, more preferably at 4-48h, more preferably at 24h, and the speed of the magnetic stirrer is 400-650rpm, more preferably at 500rpm.

[0013] Preferably, in step (2), the precursor solution needs to be allowed to stand before transfer to remove air bubbles; more preferably, the standing time is not less than 4 hours, and more preferably 10 hours.

[0014] Preferably, in step (2), after placing the mold in the reaction chamber, the vacuum is evacuated to 5-20 Pa and maintained continuously, more preferably 5-10 Pa. After introducing the gas excitation source, the gas flow rate is 20-70 sccm, and the vacuum is maintained at 30-50 Pa, more preferably 20-50 sccm, and preferably 30-40 Pa.

[0015] Preferably, in step (2), the gas excitation source is at least one of SF6, N2, NF3, and CF4, more preferably SF6.

[0016] Preferably, in step (2), the reaction conditions after ignition are: the RF power after ignition is 35-100 W, the reaction temperature is room temperature, preferably 15-40℃, the reaction time is 90-350 s, and / or the system vacuum degree is 30-50 Pa. More preferably, the RF power is 40-100 W, the reaction time is 100-350 s, and more preferably 100-200 s.

[0017] More preferably, in step (1), the solid-liquid mass ratio is 1:5, in step (2), the RF power after ignition is 40 W, the reaction temperature is room temperature, the reaction time is 150 s, and / or the system vacuum degree is 30 Pa. Using the above technical solution, the obtained electrochemical performance is even more superior.

[0018] The present invention also provides a PEO / garnet type solid composite electrolyte prepared by any of the above preparation methods.

[0019] The present invention also provides an application of the PEO / garnet type solid-state composite electrolyte prepared by any of the above preparation methods in the field of batteries.

[0020] Using the technical solution described in this invention, the matrix PEO and succinate undergo efficient cross-linking and in-situ solidification reactions under the action of plasma excited by gases such as SF6 and N2. The resulting three-dimensional network polymer acts as the rigid skeleton of the composite electrolyte, which can stably confine the lithium salt and ion transport medium within the polymer network without introducing any chemical cross-linking agents. During the rapid solidification process, LLZO is uniformly dispersed, resulting in a dense and uniformly dispersed PEO / garnet-type solid composite electrolyte. Achieving in-situ solidification without initiators through plasma such as SF6 fundamentally solves the persistent problems of solvent residue and filler agglomeration in traditional methods. This not only significantly improves the interfacial stability of the electrolyte with lithium metal and battery safety but also simplifies the process and reduces costs. The entire reaction process is rapid, efficient, and energy-efficient, greatly improving production efficiency. The prepared electrolyte has significantly optimized interfacial ion transport capabilities. Tests show that the plasma-polymerized PEO / garnet-type solid composite electrolyte obtained by this invention exhibits significantly improved ionic conductivity, a significantly increased lithium-ion transference number, and excellent cycle stability, demonstrating great potential for commercial application.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] (1) A green polymerization process without initiators is achieved, eliminating the interfacial side reactions of residual organic solvents and chemical initiators on lithium metal anodes from the source, which significantly improves the safety and cycle stability of the battery.

[0023] (2) This method is efficient and simple, with mild reaction conditions and low energy consumption. The entire process does not require complicated post-processing, showing excellent potential for process scale-up and cost advantages for large-scale production, and is suitable for large-scale industrial production.

[0024] (3) The LLZO filler in the prepared plasma-polymerized PEO / garnet type solid composite electrolyte is uniformly dispersed, which is conducive to the uniform passage of lithium ions, thereby greatly improving the rate performance and cycle life of the battery.

[0025] (4) The plasma-polymerized PEO / garnet type solid composite electrolyte has high ionic conductivity and dense microstructure, which can significantly reduce the battery internal resistance and heat accumulation during charging and discharging, thereby effectively reducing the risk of battery thermal runaway and broadening its application range in high-power and high-safety scenarios.

[0026] In summary, this invention relates to a method for preparing PEO / garnet-type solid-state composite electrolytes using plasma technology and its application in solid-state batteries. Its innovation lies in achieving optimization and solidification of the composite electrolyte in one step through the synergistic dual effect of plasma: on the one hand, the high-energy bombardment and cleaning action of plasma thoroughly removes organic solvents from the precursor, fundamentally solving the solvent residue problem; on the other hand, through plasma-induced active group reactions, in-situ cross-linking polymerization of the PEO matrix is ​​achieved at low temperatures, and a stable interfacial bond is formed by its interaction with the LLZO filler surface, such as LLZTO. This method, for the first time, combines the excellent dispersibility of solution methods with the high efficiency of dry plasma technology. Through extremely short plasma treatment, the solvent can be removed while the uniformly dispersed LLZO structure in the solution mixture is "fixed in situ," thereby achieving a three-dimensional uniform distribution of the filler in the final product, significantly improving the ionic conductivity of the electrolyte and its interfacial stability with lithium metal. Furthermore, this method features simple process, short processing time, no need for initiators, low energy consumption, and high efficiency, making it suitable for the industrial manufacturing of high-performance solid-state batteries and possessing broad market and industrial application prospects. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the plasma reaction device and a digital photograph of the electrolyte membrane in this invention;

[0028] Figure 2 The XRD patterns of Example 1 and Comparative Example 1 in this invention are shown below.

[0029] Figure 3 These are digital scanning electron microscope images of Embodiment 1 and Comparative Example 1 in this invention;

[0030] Figure 4 The graph shows the long-cycle performance of the assembled lithium symmetric batteries of Example 1 and Comparative Example 1 in this invention at a current density of 0.1 c.

[0031] Figure 5 This is an electrochemical window test diagram of Example 1 and Comparative Example 1 in this invention. Detailed Implementation

[0032] To facilitate understanding, the technical solutions and implementation methods of the present invention will be further described clearly, completely, and in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the embodiments described herein are implemented based on the technical solutions of the present invention, providing detailed implementation methods and specific operating procedures, but are only some embodiments of the present invention, not all embodiments. The specific implementation methods described are limited to illustrating and explaining the present invention and do not limit the present invention. Based on the embodiments of the present invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Unless otherwise specified, the experimental methods and conditions used in the following embodiments are conventional methods and conditions. The materials, reagents, instruments, and equipment used in the embodiments, unless otherwise specified, are all conventional substances or equipment known to those skilled in the art and are commercially available. The reaction conditions described in the invention can all achieve the reactions and obtain the desired products. Due to space limitations, only some embodiments are listed below to further illustrate the advantages of the technical solution of the present invention.

[0034] This invention provides a method for preparing PEO / garnet-type solid-state composite electrolytes using plasma technology. This method is applicable to various types of garnet-type electrolytes, specifically LLZO. In some embodiments of this invention, LLZO is used as an example to further illustrate the relevant technical solutions. The preparation method includes the following steps:

[0035] PEO, lithium salt, SN, LLZTO and organic solvent are mixed and stirred evenly at room temperature. The preferred organic solvent is anhydrous acetonitrile.

[0036] The well-stirred LLZTO / PEO composite electrolyte precursor solution was transferred to a polytetrafluoroethylene mold and placed in a plasma device. Copper rings were then connected to both ends of the plasma reaction device, and wires were used to connect the copper rings to the generator of the radio frequency power supply. The device was then evacuated to a vacuum level of 5-20 Pa, and a gas excitation source was introduced. The reaction time, vacuum level, and radio frequency power were adjusted. After ignition, the vacuum level was maintained at 30-40 Pa. After a certain reaction time, the radio frequency power supply was turned off, and the LLZTO / PEO composite electrolyte polymerized by plasma technology was obtained.

[0037] Example 1

[0038] PEO, lithium salt, SN, LLZTO, and anhydrous acetonitrile were mixed at a solid-liquid ratio of 1:5. The molar ratio of PEO, lithium salt (lithium bis(trifluoromethanesulfonylimide)), and SN was 20:1:4. The mass of PEO was fixed at 1 g. The mixture was stirred at 500 rpm at room temperature until homogeneous and allowed to stand for 10 hours to remove foam. The homogeneous LLZTO / PEO composite electrolyte precursor solution was transferred to a polytetrafluoroethylene mold and placed in a plasma device. Copper rings were then connected to both ends of the plasma reaction apparatus and wired to the generator of the RF power supply. The apparatus was then evacuated to a vacuum of 10 Pa, and an SF6 gas excitation source was introduced, raising the vacuum to 30 Pa. The RF power supply was turned on, and the RF power was adjusted to 40 W, while maintaining the vacuum at 20 Pa. After ignition, the vacuum was maintained at 30 Pa, and the reaction was allowed to proceed for 150 seconds. The RF power supply was then turned off, yielding the plasma-polymerized LLZTO / PEO composite electrolyte.

[0039] Example 2

[0040] PEO, lithium salt, SN, LLZTO, and anhydrous acetonitrile were mixed at a solid-liquid ratio of 1:5. The molar ratio of PEO, lithium salt (lithium bis(trifluoromethanesulfonylimide)) and SN was 20:1:4. The mixture was stirred at 500 rpm at room temperature until homogeneous. The homogeneous LLZTO / PEO composite electrolyte precursor solution was transferred to a polytetrafluoroethylene mold and placed in a plasma device. Copper rings were then connected to both ends of the plasma reaction apparatus and wired to the generator of the radio frequency power supply. The apparatus was then evacuated to a vacuum level of 10 Pa, and an N2 gas excitation source was introduced, raising the vacuum level to 30 Pa. The radio frequency power switch was turned on, and the radio frequency power was adjusted to 40 W, while maintaining the vacuum level of 20 Pa. After ignition, the vacuum level was maintained at 30 Pa, and the reaction was allowed to proceed for 150 s. The radio frequency power supply was then turned off, yielding the plasma-polymerized LLZTO / PEO composite electrolyte.

[0041] Based on Examples 1 and 2, the solid-liquid ratio, type of plasma excitation source, plasma reaction power, reaction vacuum degree, and reaction time were changed. The reaction conditions are shown in Table 1 below:

[0042]

[0043] Comparative Example 1

[0044] PEO, lithium salt, SN, LLZTO, and anhydrous acetonitrile were mixed at a solid-liquid ratio of 1:10, with a molar ratio of PEO, lithium salt, and SN of 20:1:4. The mixture was stirred at 500 rpm at room temperature until homogeneous. The homogeneous LLZTO / PEO composite electrolyte precursor solution was transferred to a polytetrafluoroethylene mold and allowed to stand at room temperature for 12 hours, followed by placement at 60°C. o After standing in a vacuum oven for 24 hours, the polymerized LLZTO / PEO composite electrolyte is obtained by transferring it to a glove box and standing for 12 hours.

[0045] Performance testing

[0046] Electrochemical tests were conducted on the LLZTO / PEO composite electrolyte assembled batteries successfully prepared in the above embodiments. The batteries were assembled in the order of positive electrode shell, lithium sheet, electrolyte membrane, lithium sheet, and negative electrode shell, and then sealed using a sealing machine. After the batteries were allowed to stand for 24 hours, electrochemical tests were performed using a Newway testing system and an electrochemical workstation. All electrochemical tests were conducted within 30 minutes. o The tests were conducted under constant temperature conditions (C), primarily focusing on critical current density, interfacial impedance, and lithium stability. The critical current density test procedure was: rest for 5 min – constant current discharge – rest for 5 min – constant current charging, with the current increasing by 0.5 mA per cycle. The interfacial impedance test procedure was: test range 0.1 Hz to 1 MHz, test amplitude 20 mV. The lithium stability test procedure was: rest for 5 min – constant current discharge – rest for 5 min – constant current charging, each charge / discharge cycle lasting 1 h, with a current density of 0.1 mA cm⁻¹. -2 .

[0047] The performance test results are shown in Table 2 below:

[0048]

[0049] Table 2 shows the performance test results of the successful film-forming examples. Examples 1 and 2, using a 1:5 solid-liquid ratio, 40 W RF power, 150 s reaction time, and 30 Pa reaction vacuum, prepared electrolyte membranes that met mechanical performance standards and exhibited excellent electrochemical performance. However, Examples 3-10 failed to form membranes due to excessive organic solvent addition, which prevented complete solvent evaporation during polymerization. Examples 11 and 12, with excessively long reaction times, resulted in poor mechanical properties of the polymerized membranes, leading to fragmentation and making them unsuitable for application. Examples 13-28 were also successfully prepared, and the combined battery's electrochemical performance was comparable to Comparative Example 1, demonstrating a significant advantage in efficiency. However, compared to the optimal conditions of Examples 1 and 2, their electrochemical performance was slightly inferior.

[0050] Figure 1This is a schematic diagram of the plasma reaction device and a digital photograph of the electrolyte membrane in this invention; Figure 1 (a) in the figure represents the glow phenomenon generated when SF6 plasma is successfully excited during the plasma polymerization process in this invention. Figure 1 (b) is a schematic diagram of the composite electrolyte membrane successfully prepared by plasma technology in Example 1 of this invention;

[0051] Figure 2 The XRD patterns of the composite solid electrolyte membranes of Example 1 and Comparative Example 1 in this invention are compared; no change in crystal structure was found, indicating that the plasma polymerization method does not cause deterioration of the membrane.

[0052] Figure 3 Image (a) shows the planar scanning electron microscope (SEM) morphology of Example 1. Figure 3 (b) shows the planar scanning electron microscope (SEM) morphology of Comparative Example 1. In Example 1, plasma technology was used for polymerization, and the LLZTO filler was uniformly dispersed. In contrast, in Comparative Example 1, the conventional polymerization method was used, and the LLZTO filler showed obvious agglomeration.

[0053] Figure 4 The lithium symmetric battery assembled with the composite solid electrolyte membrane of Example 1 and Comparative Example 1 of this invention was tested at 0.1 mA cm⁻¹. -2 0.1 mAh cm -2 Comparison charts of long-cycle performance tests; the electrolyte using plasma polymerization shows significantly better performance than the electrolyte using traditional polymerization;

[0054] Figure 5 This is a comparison chart of the electrochemical window performance of stainless steel-lithium batteries assembled with composite solid electrolyte membranes in Example 1 and Comparative Example 1 of this invention. It can be found that the electrolyte using plasma polymerization has a higher electrochemical window, indicating that it has excellent high voltage resistance and stronger electrochemical stability.

[0055] The plasma technology method for preparing LLZTO / PEO composite electrolytes provided in this application is simple, has a short processing time, and can significantly improve the overall electrochemical performance of the electrolyte. Button batteries assembled based on this electrolyte exhibit low interfacial impedance and excellent cycle stability, showing broad application prospects in small mobile electronic devices, electric vehicles, large-scale energy storage, and aerospace.

[0056] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications may be made without departing from the technical solutions described in the claims.

Claims

1. A method for preparing a PEO / garnet-type solid-state composite electrolyte using plasma technology, characterized in that, Includes the following steps: (1) Preparation of electrolyte precursor: PEO, lithium salt, succinate, garnet-type solid electrolyte filler and organic solvent are mixed to obtain precursor solution, and the solid-liquid mass ratio is 1:5~6; the organic solvent is anhydrous acetonitrile; (2) Preparation of composite electrolyte: The precursor solution is transferred to the plasma device, the plasma reaction chamber is evacuated to a vacuum, a gas excitation source is introduced, the radio frequency power is adjusted, and the reaction is carried out under the reaction vacuum after ignition to obtain PEO / garnet type solid composite electrolyte; the reaction conditions after ignition are: the radio frequency power after ignition is 35-100 W, the reaction temperature is room temperature, the reaction time is 90-350 s, the system vacuum degree is 30-50 Pa, and the gas excitation source is at least one of SF6, N2, NF3, and CF4.

2. The method for preparing a PEO / garnet-type solid composite electrolyte using plasma technology according to claim 1, characterized in that, In step (1), the garnet-type solid electrolyte filler includes at least one garnet-type inorganic solid electrolyte with or without doping elements; the doping element is selected from at least one of Ta, Al, and Nb.

3. The method for preparing a PEO / garnet-type solid composite electrolyte using plasma technology according to claim 1, characterized in that, In step (1), the molar ratio of PEO, lithium salt and succinic acid is 15~20:1:4~8, and the mass percentage of garnet-type solid electrolyte filler in the solid material is 5%-15%.

4. The method for preparing a PEO / garnet-type solid composite electrolyte using plasma technology according to claim 1, characterized in that, In step (1), the mixing refers to stirring evenly at room temperature, with a stirring speed of 400-650 rpm and a stirring time of 4-48 h.

5. The method for preparing a PEO / garnet-type solid composite electrolyte using plasma technology according to claim 1, characterized in that, In step (2), the precursor solution needs to be allowed to stand before being transferred to remove air bubbles.

6. The method for preparing a PEO / garnet-type solid composite electrolyte using plasma technology according to claim 1, characterized in that, In step (2), the vacuum level is 5-20 Pa, and after the gas excitation source is introduced, the vacuum level is maintained at 30-50 Pa.

7. A solid-state composite electrolyte of PEO / garnet type prepared by the preparation method according to any one of claims 1-6 using plasma technology.

8. The application of a plasma-polymerized PEO / garnet type solid composite electrolyte prepared by the preparation method according to any one of claims 1-6 in the field of batteries.

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