LATP solid electrolyte membrane ultrathin protection layer and preparation method thereof

Abstract

The invention relates to the technical field of solid electrolyte membrane protection, in particular to an LATP solid electrolyte membrane ultrathin protection layer and a preparation method thereof.The preparation method comprises the steps that an LATP solid electrolyte membrane is placed in a vacuum plasma equipment cavity, process gas or mixed gas is introduced, plasma is excited at the frequency of 40 kHz or 13.56 MHz, and the LATP solid electrolyte membrane is prepared; and the process gas is polymerized and deposited on the surface of the LATP to form a submicron protection layer. The protective layer is composed of a polymer containing a carbon, fluorine or ether group structure, has high ionic conductivity and excellent mechanical properties, can physically isolate LATP from being in contact with metal lithium, and inhibits interface side reaction and lithium dendrite penetration. The thickness and uniformity of the protection layer can be accurately controlled under the condition of room temperature, and the preparation method is suitable for substrates with complex shapes, has industrial amplification potential and provides key technical support for all-solid-state lithium batteries.

Description

Technical Field

[0001] This invention relates to the field of solid-state battery technology, and in particular to an ultrathin protective layer for an LATP solid electrolyte membrane and its preparation method. Background Technology

[0002] Li 1+x Al x Ti 2-x (PO4)3 (0≤x≤0.5, abbreviated as LATP) is a typical NASICON structure oxide solid electrolyte with advantages such as high room temperature ionic conductivity (0.1-1mS / cm), wide electrochemical window (>4.5V), good chemical stability in humid air, low raw material cost and easy sintering. Therefore, it is widely regarded as one of the most promising inorganic solid electrolytes in high energy density all-solid-state lithium batteries (ASSB).

[0003] However, there is a severe thermodynamic instability between LATP and metallic lithium. Under direct contact conditions, Ti 4+ It will be reduced to Ti by metallic lithium at the interface. 3+ The formation of this phase leads to the formation of a Li-Ti-PO mixed conductive phase (MCI) with electronic conductivity. This phase induces continuous interfacial side reactions, grain boundary cracks, and a sharp increase in interfacial impedance, ultimately resulting in increased battery polarization and even short-circuit failure. Therefore, stabilizing the LATP / Li interface has become a key scientific and engineering challenge limiting the practical application of LATP.

[0004] To address the aforementioned interface instability, there are currently three main types of modification strategies: Element doping control strategies: For example, partially replacing Ti with Ge can improve lattice ion migration and suppress lithium dendrite growth to some extent. However, Ge is still easily reduced by lithium, is expensive, and has limited doping capacity, making it difficult to maintain long-term stability at the interface.

[0005] Constructing an artificial SEI to protect the lithium metal surface: Forming an artificial SEI on the lithium surface using chemical or electrochemical methods can mitigate the corrosion of lithium by LATP. However, artificial SEIs are prone to cracking or fracturing during cycling, and failure can still lead to lithium degradation. 4 The irreversible restoration of ⁺ cannot fundamentally solve the problem of interface instability.

[0006] Constructing a protective layer on the LATP surface: Achieving physical isolation through the construction of a barrier layer is currently the more effective strategy. However, the protective layer must simultaneously possess high ionic conductivity, excellent mechanical stability, and dendrite suppression capabilities, placing extremely high demands on thickness controllability and material compatibility. While dense films can be obtained using methods such as ALD, CVD, or magnetron sputtering, these methods suffer from complex processes, high costs, and limitations in scalability. Wet processes such as casting and spin coating are difficult to control at the nanoscale, and issues with interfacial adhesion and chemical compatibility are prominent.

[0007] Therefore, there is an urgent need to develop an ultrathin LATP solid electrolyte membrane protective layer and its preparation method, which can take into account high ion conduction, interfacial chemical stability and preparation feasibility, and is expected to break through the bottleneck of LATP / Li interface stability, providing key technical support for the realization of a new generation of high energy density all-solid-state lithium batteries. Summary of the Invention

[0008] The purpose of this invention is to provide an ultrathin protective layer for LATP solid electrolyte membranes and its preparation method, aiming to overcome the problem of thermodynamic instability at the LATP-lithium metal interface in existing technologies. By depositing a submicron-scale dense film in situ on the LATP surface, direct contact between LATP and lithium metal is physically isolated, while simultaneously endowing the protective layer with high ionic conductivity and excellent mechanical properties, thereby solving the problems of interfacial side reactions, grain boundary crack propagation, and increased interfacial impedance.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: An ultrathin protective layer for LATP solid electrolyte membrane and its preparation method are described below: S1. Place the LATP solid electrolyte membrane inside the vacuum plasma equipment chamber and evacuate the chamber to 5 Pa to 100 Pa; the chemical formula of the LATP solid electrolyte membrane is Li. 1+x Al x Ti 2-x (PO4)3, where x takes values ​​in the range 0 ≤ x ≤ 0.5; S2. Introduce process gas or a mixture of process gas and carrier gas into the cavity, with a total gas flow rate of 50 sccm to 350 sccm. When the process gas is in a gaseous state at room temperature, it is selected from hydrocarbons, halogenated hydrocarbons, or cyclic ethers with ≤4 carbon atoms. When the process gas is in a liquid state at room temperature, it is selected from compounds with a boiling point ≤200℃, and enters the cavity after being vaporized by heating and carried by the carrier gas. S3. Turn on the plasma power supply and generate plasma at a frequency of 40kHz or 13.56MHz to cause the process gas to polymerize and deposit on the LATP surface, forming a submicron-level protective layer. When the plasma power supply frequency is 40kHz, the power supply power is 100W to 2000W and the processing time is 1min to 120min. When the plasma power supply frequency is 13.56MHz, the power supply power is 50W to 600W and the processing time is 1min to 120min.

[0010] The prepared protective layer comprises polymers containing carbon, fluorine, or ether groups, with a thickness on the submicron scale. After absorbing the liquid electrolyte, it exhibits high ionic conductivity, exceeding 10⁻⁶. -5 S / cm.

[0011] The protective layer inhibits Ti by physically isolating LATP from direct contact with metallic lithium. 4+ Reduced to Ti 3+ This process avoids the formation of a Li-Ti-PO mixed conductive phase. Furthermore, the density and insulation of the protective layer prevent lithium dendrites from penetrating and contacting LATP, further reducing the risk of interface failure.

[0012] After absorbing the liquid electrolyte, the protective layer forms an ionic conductivity channel that allows lithium ions to migrate, ensuring efficient lithium ion transport at the interface. The protective layer formed by the fluorine-containing monomer reacts with fresh metallic lithium to generate a LiF-containing passivated interface, further enhancing interface stability.

[0013] As a preferred technical solution, the process gas is preferably ethylene, tetrafluoroethylene, or ethylene oxide; when the process gas is liquid, diethylene glycol dimethyl ether is preferred as the process gas, and argon is preferred as the carrier gas.

[0014] As a preferred technical solution, the vacuum degree inside the vacuum plasma equipment cavity is preferably 5Pa to 30Pa, and the total gas flow rate is preferably 50sccm to 250sccm.

[0015] As a preferred technical solution, when the plasma power supply frequency is 40kHz, the power supply power is preferably 800W to 1500W, and the processing time is preferably 10min to 30min; when the plasma power supply frequency is 13.56MHz, the power supply power is preferably 200W to 500W, and the processing time is preferably 10min to 30min.

[0016] As a preferred technical solution, the LATP solid electrolyte membrane needs to be cleaned before entering the cavity to remove surface impurities and oxide layers, ensuring good adhesion between the protective layer and the LATP surface.

[0017] The beneficial effects of this invention are: This invention solves the thermodynamic instability problem between LATP and metallic lithium by in-situ deposition of a submicron-sized protective layer with a cross-linked structure on the LATP surface using plasma polymerization technology. The density and insulation of the protective layer effectively prevent lithium dendrites from penetrating and contacting LATP, avoiding interfacial side reactions. Furthermore, the protective layer exhibits high ionic conductivity after absorbing liquid electrolyte, ensuring efficient lithium-ion transport at the interface. Its ultra-thin nature reduces the impact on the cell's internal resistance and energy density. The chemical composition and surface energy of this film can be precisely controlled by adjusting the type and flow rate of the process gas and plasma parameters.

[0018] The protective layer formed by the fluorine-containing monomer can also react with fresh lithium metal to form a LiF-containing SEI layer passivation interface, which further reduces the possibility of LATP being destroyed.

[0019] The preparation method of this invention is simple in steps, easy to automate, and significantly improves manufacturing efficiency. Furthermore, the plasma polymerization technology equipment has a simple structure and low energy consumption, possessing excellent potential for industrial scale-up, providing key technical support for the realization of a new generation of high-energy-density all-solid-state lithium batteries. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 shows the appearance of Sample 1, Sample 2 and Sample 3; Figure 2 shows the lithium symmetric battery of sample 2 at 1 mA / cm². 2 At a current density of 3 mAh / cm 2 Electron micrograph of the LATP solid electrolyte membrane protective layer after 500 cycles under the specified conditions; Figure 3 shows the results of samples 1, 2, and 3 at 1 mA / cm². 2 At a current density of 3 mAh / cm 2 Circular data graph under certain conditions. Detailed Implementation

[0022] The following description is intended to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art.

[0023] Example 1: This example provides an ultrathin LATP solid electrolyte membrane protective layer, using Li1+ x Al x Ti 2-x A LATP solid electrolyte ceramic membrane with a thickness of approximately 300 μm and a (PO4)3 (x=0.4) oxide content was prepared. Surface impurities were removed through polishing, alcohol cleaning, high-temperature annealing, or argon plasma cleaning. The LATP solid electrolyte membrane was placed in a vacuum plasma chamber, and the chamber was evacuated to 5 Pa. Ethylene process gas was introduced into the chamber at 200 sccm. The plasma power supply was turned on, with a frequency set to 13.56 MHz and a power output of 450 W. After 15 minutes of operation, a protective layer was obtained, approximately 0.43 μm thick, of ethylene plasma polymerization. This layer continuously, densely, and uniformly covered the LATP surface, its pores, and edges. This is designated as Sample 1.

[0024] Performance characterization: SEM showed that the film surface was smooth and free of pores. EIS test showed that the interfacial impedance was reduced by approximately 40% compared to sample 3. The Li / LATP / Li symmetric cell showed stable cycling for 280 hours without short circuit.

[0025] Example 2: This example provides an ultrathin LATP solid electrolyte membrane protective layer. The difference from Example 1 is that the LATP solid electrolyte membrane is placed inside a vacuum plasma equipment chamber, the chamber is evacuated to 5 Pa, and tetrafluoroethylene process gas is introduced into the chamber at 150 sccm. The plasma power supply is turned on, the frequency is set to 13.56 MHz, the power supply is 450 W, and the running time is 15 minutes. A fluorinated plasma polymerized protective layer with a thickness of approximately 0.30 μm is obtained, and the membrane layer is uniform and dense. This is designated as Sample 2.

[0026] Performance and Mechanism Verification: XPS analysis revealed the formation of an FC cross-linked structure, enabling the generation of LiF upon initial contact with lithium metal. After 24 hours of direct contact with Li, LATP showed no significant Ti formation. 3+ The increased peak size indicates that the interfacial reduction reaction is suppressed. Symmetric cells can achieve this at 0.1 mA·cm⁻¹. -2 The stable cycle time exceeded 320 hours.

[0027] Example 3: This example provides an ultrathin LATP solid electrolyte membrane protective layer. The LATP solid electrolyte membrane is placed in the vacuum plasma equipment chamber, and the chamber is evacuated to 5 Pa. Process gas and carrier gas are introduced into the chamber at 150 sccm. The process gas is diethylene glycol dimethyl ether, which is heated and vaporized (boiling point 160℃ → can be slightly depressurized and vaporized) and then enters the chamber under the carry of argon carrier gas. The plasma power supply is turned on, the frequency is set to 13.56MHz, the power supply is 450W, and the running time is 15min to obtain an ether-based plasma polymerized membrane layer with a thickness of 90nm-160nm.

[0028] Interfacial properties: The ether-based structure exhibits high ion channel capacity after liquid absorption, and the interfacial impedance decreases by approximately 50%; no obvious blackening or cracking is observed after 48 hours of contact with Li, indicating weak interfacial side reactions; the symmetric cell can operate stably for over 260 hours.

[0029] Comparative Example 1: An untreated LATP solid ceramic film, without any surface modification or protective layer deposition, was directly used for electrochemical testing and designated as Sample 3. After 12-24 hours of contact with Li, significant blackening appeared on the surface, and XPS analysis revealed Ti… 3+ The peak was significantly enhanced; the symmetrical cell showed a sharp rise in voltage and short-circuit failure within 2-3 hours; the interface impedance tested by EIS was about 200 times higher than that of samples 1 and 2.

[0030] The comparison reveals that the ultrathin protective layer constructed on the LATP surface using plasma polymerization technology in this invention effectively blocks direct contact between metallic lithium and LATP. The inorganic-organic cross-linked structure of the protective layer is dense and exhibits excellent electronic insulation, inhibiting the reaction between Li and Ti. 4+ The direct reaction significantly reduces Ti 4+ →Ti 3+ The irreversible reduction process. XPS depth profiling verifies the Ti content of samples 1, 2, and 3. 3+ Peak ratio, Ti of the protective layer sample 3+ The peak decreased significantly, proving that the interfacial side reactions were effectively suppressed.

[0031] The protective layer possesses high cross-linking density and low electronic conductivity, forming a mechanically stable barrier at the interface to block the growth of lithium dendrites into the LATP, thereby preventing short-circuit failure. Long-term electroplating experiments on symmetrical cells (Li / protective layer-LATP-protective layer / Li) showed that samples 1 and 2 exhibited similar performance at 0.1 mA·cm⁻¹. -2 Under 300h cycling conditions, there was no significant increase in polarization, while sample 3 showed a short circuit after 2h.

[0032] The protective layer, with a thickness on the submicron scale, offers minimal obstruction to ion migration. Furthermore, upon absorbing the liquid electrolyte, the protective layer forms ion channel structures rich in ether / fluorinated groups, enhancing interfacial ion conductivity. EIS testing shows that the interfacial impedance (R0) of samples 1 and 2 is... eax The levels of LATP were reduced by 30–60% compared to naked LATP (sample 3), confirming the protective layer's role in promoting ion transport.

[0033] For tetrafluoroethylene or some ether monomers (Examples 2 and 3), the protective layer can undergo limited surface chemical reactions when in contact with metallic lithium, generating a uniform LiF composition, forming a stable SEI passivation interface, and improving the reduction resistance of LATP.

[0034] Compared to high-cost processes such as ALD and CVD, the protective layer thickness obtained by this invention can be controlled within the range of tens to hundreds of nanometers, without significantly increasing the film thickness and film resistance, and greatly preserving the energy density advantage brought by the high ionic conductivity of LATP.

[0035] The plasma polymerization method of the present invention has low sensitivity to substrate morphology and can form continuous and dense film layers on porous, rough, curved or even complex structures. It does not require high-temperature sintering or high-vacuum equipment and is suitable for large-scale industrial applications.

[0036] Table 1: Thickness changes of Samples 1, 2, and 3 before and after treatment sample Total thickness μm Protective layer thickness (μm) Sample 1 301.7 0.3 Sample 2 301.8 0.4 Sample 3 301.4 / The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. An ultrathin protective layer for an LATP solid electrolyte membrane, characterized in that, The protective layer is a submicron-scale dense film formed by in-situ deposition on the surface of the LATP solid electrolyte membrane via plasma polymerization. The protective layer is used to physically isolate LATP from direct contact with metallic lithium and has ionic conductivity channels that allow lithium ions to migrate after absorbing the electrolyte.

2. The ultrathin LATP solid electrolyte membrane protective layer according to claim 1, characterized in that, The protective layer comprises a polymer containing carbon, fluorine, or ether groups.

3. The ultrathin LATP solid electrolyte membrane protective layer according to claim 1, characterized in that, The protective layer exhibits high ionic conductivity after absorbing the liquid electrolyte, with an ionic conductivity greater than 10. -5 S / cm.

4. A method for preparing the ultrathin LATP solid electrolyte membrane protective layer according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Place the LATP solid electrolyte membrane in the plasma device and pump the chamber to 5Pa~100Pa. S2. Introduce process gas or a mixture of process gas and carrier gas into the cavity, with a total gas flow rate of 50 sccm to 350 sccm. S3. Turn on the plasma power supply and generate plasma at a frequency of 40kHz or 13.56MHz to cause the process gas to polymerize and deposit on the LATP surface, forming a submicron-level protective layer.

5. The preparation method according to claim 4, characterized in that, The process gas, when in a gaseous state at room temperature, is selected from hydrocarbons, halogenated hydrocarbons, or cyclic ethers with ≤4 carbon atoms.

6. The preparation method according to claim 5, characterized in that, The process gas is ethylene, tetrafluoroethylene, or ethylene oxide.

7. The preparation method according to claim 4, characterized in that, When the process gas is in a liquid state at room temperature, it is selected with a boiling point ≤200℃. After being heated and vaporized, it enters the reaction chamber under the carry of the carrier gas.

8. The preparation method according to claim 7, characterized in that, The process gas is diethylene glycol dimethyl ether, and the carrier gas is argon.

9. The preparation method according to claim 4, characterized in that, The chemical formula of the LATP solid electrolyte membrane is Li 1+ x Al x Ti 2-x (PO4)3, 0≤x≤0.

5.

10. The preparation method according to claim 4, characterized in that, When the plasma power supply frequency is 40kHz, the power supply power is 100W to 2000W; when the plasma power supply frequency is 13.56MHz, the power supply power is 50 to 600W; the processing time is 1 to 120 minutes.

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