A method for integrated interface cleaning and optimization of oxide solid state electrolytes

Abstract

This invention belongs to the field of battery materials technology, specifically disclosing an integrated method for cleaning and optimizing the interface of an oxide solid electrolyte. The invention involves exposing a polished oxide solid electrolyte to air, causing a Li₂CO₃-containing surface contamination layer to form on its surface. Then, the oxide solid electrolyte with this surface contamination layer is immersed in a weakly acidic ionic liquid to perform an interfacial reaction, achieving cleaning and optimization of the oxide solid electrolyte interface, resulting in an oxide solid electrolyte with a flexible interface layer. The weakly acidic ionic liquid contains acidic functional groups, including one or more of carboxyl groups, sulfonamide groups, and sulfonylimide groups. The processing method disclosed in this invention has the advantages of mild conditions, simple process, and integration, and can improve the electrolyte / electrode interface contact state, reduce interfacial impedance, and enhance the electrochemical performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to an integrated treatment method for cleaning and optimizing the interface of oxide solid electrolytes. Background Technology

[0002] As the energy density of traditional lithium-ion batteries gradually approaches its theoretical limit, and the demand for high-safety and high-energy-density energy storage systems continues to grow, all-solid-state batteries based on solid-state electrolytes have become an important development direction for next-generation battery technology due to their excellent safety performance and potential high energy density. Currently, common solid-state electrolytes mainly include three types: oxide-type, sulfide-type, and polymer-type.

[0003] Oxide solid electrolytes (OSEs) are considered one of the most promising solid electrolytes due to their high ionic conductivity and good chemical stability. However, during actual preparation and storage, the surface of OSEs readily reacts with H₂O and CO₂ in the air, forming a contamination layer such as lithium carbonate (Li₂CO₃). This Li₂CO₃ contamination layer has poor ionic conductivity, significantly increasing the interfacial impedance at the electrolyte / electrode interface, hindering effective lithium-ion transport, and leading to problems such as poor interfacial contact, increased battery polarization, decreased electrochemical performance, and deteriorated cycle stability.

[0004] For the treatment of contamination layers, existing technologies mainly focus on the following types of methods: (1) Mechanical treatment methods: such as polishing and grinding to remove the surface contaminant layer. This method is simple to operate, but after treatment, the electrolyte surface is prone to regenerating Li2CO3 in the air, and it is difficult to maintain the long-term stability of the interface; (2) Heat treatment method: Li2CO3 layer is separated by high temperature sintering or annealing, but this method usually requires a high temperature, which can easily lead to lithium loss and cause changes in crystal phase structure, reducing the ionic conductivity of the electrolyte sheet; (3) Acidic solution treatment method: Using acidic solutions (such as organic or inorganic acids) to remove the Li2CO3 layer can effectively remove surface contamination, but strong acids often react with the oxide solid electrolyte body, corrode it and cause damage to the surface structure, reducing the stability of the material.

[0005] (4) Interface modification method: By introducing metal layers (such as Au, Al, Bi) and oxide layers to construct interface buffer layers, the interface impedance can be reduced. However, this buffer layer cannot eliminate the adverse effects of Li2CO3 on interface ion transport, and the interface structure is mainly physical coating. In the long-term cycling process, the performance may still degrade due to interface contact decay or structural mismatch.

[0006] In summary, although existing technologies have improved the interface problem of oxide solid electrolytes to some extent, they still have the following shortcomings: the Li2CO3 removal process and interface construction are usually carried out in steps, which is complex; the interface layer is mostly a physical coating structure, and is mainly composed of rigid or semi-rigid materials, which makes it difficult to effectively buffer the volume change stress of lithium metal during charging and discharging, resulting in limited interface stability.

[0007] Therefore, there is an urgent need to develop a method that can gently remove Li2CO3 and construct flexible composite interfaces in situ to achieve synergistic optimization of interface structure and electrochemical performance. Summary of the Invention

[0008] In view of this, the present invention provides an integrated treatment method for cleaning and optimizing the interface of oxide solid electrolytes, in order to solve the problems of complex processes and limited interface stability of existing treatment methods.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A method for integrated cleaning and optimization of oxide solid electrolyte interfaces includes the following steps: 1) Polish the oxide solid electrolyte and place the polished oxide solid electrolyte in the air to react, so that a surface contamination layer containing Li2CO3 is formed on the surface of the oxide solid electrolyte. 2) The oxide solid electrolyte with a surface contamination layer is immersed in a weakly acidic ionic liquid to carry out the reaction, thereby cleaning and optimizing the oxide solid electrolyte interface and obtaining an oxide solid electrolyte with a flexible interface layer. The weakly acidic ionic liquid contains acidic functional groups, including one or more of carboxyl groups, sulfonamide groups, and sulfonylimide groups.

[0010] Preferably, the cations in the weakly acidic ionic liquid include one or more of imidazoles, pyridines, or quaternary ammonium salts; The anions in the weakly acidic ionic liquid include one or more of the following: bis(trifluoromethanesulfonyl)imide anion, bis(fluorosulfonyl)imide anion, hexafluorophosphate anion, tetrafluoroborate anion, and trifluoromethanesulfonate anion.

[0011] Preferably, the oxide solid electrolyte in step 1) includes NASICON type oxide solid electrolyte, garnet type oxide solid electrolyte or perovskite type oxide solid electrolyte.

[0012] Preferably, the oxide solid electrolyte has a diameter of 5-50 mm and a thickness of 0.5-10 mm.

[0013] Preferably, the polished oxide solid electrolyte described in step 1) has an ionic conductivity of 1×10⁻⁶ at room temperature. -4 ~1×10 -3 S cm -1 .

[0014] Preferably, the endpoint of the reaction in step 1) is the formation of a surface contamination layer with a thickness of 0.01~5 μm on the surface of the oxide solid electrolyte.

[0015] Preferably, the reaction temperature in step 2) is 10~80℃ and the reaction time is 2~7h.

[0016] Preferably, the atmosphere for the reaction in step 2) is an anhydrous atmosphere.

[0017] This invention utilizes the selective reactivity between the tunable weakly acidic functional groups in a weakly acidic ionic liquid and Li₂CO₃ to achieve controlled removal of the Li₂CO₃ contamination layer on the surface of an oxide solid electrolyte under mild conditions. Simultaneously, the ionic liquid components can undergo adsorption and coordination behavior on the electrolyte surface, constructing a flexible composite interface layer in situ while removing the contamination layer. This flexible composite interface layer possesses certain ion transport capabilities and structural tunability, effectively buffering the volume change stress of lithium metal during charging and discharging, thereby improving the interfacial contact state.

[0018] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects: 1. This invention uses a weakly acidic ionic liquid to effectively remove the Li2CO3 contamination layer on the surface of oxide solid electrolytes under mild conditions, and simultaneously constructs a flexible composite interface in situ, realizing an integrated process of interface cleaning and interface optimization, which significantly simplifies the interface engineering steps.

[0019] 2. The constructed flexible composite interface has good ion transport capability and structural adaptability, which can effectively buffer the volume change stress of lithium metal during charging and discharging, improve the electrolyte / electrode interface contact state, and reduce interface impedance.

[0020] 3. This invention significantly improves the electrochemical performance of solid-state batteries through interface structure optimization, resulting in a marked reduction in interface impedance and a significant improvement in cycle stability and rate performance.

[0021] 4. The method of the present invention is simple to operate, has mild conditions, and is widely applicable. It is suitable for a variety of oxide solid electrolyte systems and has good repeatability and potential for large-scale application. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0023] Figure 1 This is a schematic diagram illustrating the mechanism of the integrated treatment for cleaning and optimizing the interface of oxide solid electrolytes according to the present invention. Figure 2 The XRD diffraction pattern of the garnet-type oxide solid electrolyte sheet prepared in this invention; Figure 3 The XRD diffraction pattern of the garnet-type oxide solid electrolyte sheet prepared in this invention after 7 days of storage. Figure 4 Here is a SEM image of the garnet-type oxide solid electrolyte sheet prepared according to the present invention, wherein, Figure 4 In the image, 'a' corresponds to the SEM image after polishing, 'b' corresponds to the SEM image after being placed in air for 1 day, and 'c' corresponds to the SEM image after being placed in air for 7 days. Figure 5 The EIS impedance diagram of the garnet-type oxide solid electrolyte sheet prepared according to the present invention is shown below. Figure 5 In the diagram, 'a' corresponds to the EIS impedance diagram after polishing, 'b' corresponds to the EIS impedance diagram after being placed in air for 1 day, and 'c' corresponds to the EIS impedance diagram after being placed in air for 7 days. Figure 6 AFM atomic force microscope image of the garnet-type oxide solid electrolyte sheet prepared in this invention after 7 days of storage; Figure 7 This is a SEM image of the solid electrolyte after interface modification in Example 1 of the present invention; Figure 8 This is an AFM atomic force microscope image of the solid electrolyte after interface modification in Example 1 of the present invention; Figure 9 EIS impedance diagram of the solid electrolyte after interface modification in Example 1 of this invention; Figure 10 This is a CCD test image of the solid electrolyte after interface modification in Example 1 of the present invention; Figure 11 This is a CCD test image of the solid electrolyte after interface modification in Comparative Example 1 of this invention. Among them, Intensity is the strength, Voltage is the voltage, and Current density is the current density. Detailed Implementation

[0024] This invention provides an integrated method for cleaning and optimizing the interface of oxide solid electrolytes, comprising the following steps: 1) Polish the oxide solid electrolyte and place the polished oxide solid electrolyte in the air to react, so that a surface contamination layer containing Li2CO3 is formed on the surface of the oxide solid electrolyte. 2) The oxide solid electrolyte with a surface contamination layer is immersed in a weakly acidic ionic liquid to carry out the reaction, thereby cleaning and optimizing the oxide solid electrolyte interface and obtaining an oxide solid electrolyte with a flexible interface layer.

[0025] In this invention, the weakly acidic ionic liquid contains acidic functional groups, which include one or more of carboxyl groups, sulfonamide groups, and sulfonylimide groups.

[0026] In this invention, the cations in the weakly acidic ionic liquid include one or more of imidazoles, pyridines, or quaternary ammonium salts.

[0027] In this invention, the anions in the weakly acidic ionic liquid include one or more of bis(trifluoromethanesulfonyl)imide anion, bis(fluorosulfonyl)imide anion, hexafluorophosphate anion, tetrafluoroborate anion, and trifluoromethanesulfonate anion.

[0028] In this invention, the weakly acidic ionic liquid includes one or more of 1-carboxymethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-carboxyethyl-3-methylimidazolium trifluoromethanesulfonate, and 1-sulfonamide ethyl-3-methylimidazolium trifluoromethanesulfonate.

[0029] In this invention, the oxide solid electrolyte in step 1) includes NASICON type oxide solid electrolyte, garnet type oxide solid electrolyte or perovskite type oxide solid electrolyte.

[0030] In this invention, the general chemical formula of the NASICON-type oxide solid electrolyte is Li. 1+x Al x Z 2-x (PO4)3, where Z is one or more of Ti, Ge, and Zr, 0 ≤ x ≤ 3, specifically 0.5, 1, 1.5, 2, 2.5; the chemical formula of the garnet-type oxide solid electrolyte is Li. 7-x La3Zr 2-x A x O 12 Wherein, A is one or more elements selected from Ta, Nb, Sn, Hf, Sc, and Ge, and 0 ≤ x ≤ 0.75, specifically 0.1, 0.2, 0.4, 0.5, 0.6, and 0.7; the general chemical formula of the perovskite oxide solid electrolyte is Li.3x La 0.66-x TiO3, where 0 < x ≤ 0.16, specifically 0.02, 0.05, 0.08, 0.1, 0.12, and 0.15.

[0031] In this invention, the diameter of the oxide solid electrolyte is 5~50mm, specifically 10mm, 15mm, 20mm, 25mm, 30mm, 35mm, 40mm, 45mm; the thickness is 0.5~10mm, specifically 0.8mm, 1mm, 2mm, 4mm, 5mm, 6mm, 8mm.

[0032] In this invention, the polished oxide solid electrolyte described in step 1) has an ionic conductivity of 1×10⁻⁶ at room temperature. -4 ~1×10 -3 S cm -1 Specifically, it can be 1.8 × 10 -4 S cm -1 2×10 -4 S cm -1 4×10 -4 S cm -1 5×10 -4 Scm -1 6×10 -4 S cm -1 8×10 -4 S cm -1 .

[0033] In this invention, the endpoint of the reaction in step 1) is the formation of a surface contamination layer with a thickness of 0.01~5μm on the surface of the oxide solid electrolyte; the specific thickness of the surface contamination layer can be 0.02μm, 0.05μm, 0.08μm, 0.1μm, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, or 4.5μm.

[0034] In this invention, the reaction temperature in step 2) is 10~80℃, specifically 20℃, 30℃, 40℃, 50℃, 60℃, or 70℃; the reaction time is 2~7h, specifically 3h, 4h, 5h, or 6h.

[0035] In this invention, the atmosphere of the reaction in step 2) is an anhydrous atmosphere, specifically an argon and / or nitrogen atmosphere with low water content (≤0.1wt%).

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0037] The oxide solid electrolyte described in this embodiment of the invention uses garnet-type Li 6.5 La3Zr 1.5 Ta 0.5 O 12 We will use (LLZTO) as an example for analysis and explanation.

[0038] LLZTO electrolyte sheets are synthesized using a solid-state method: First, LiOH·H2O (Aladdin, 99.99%), La2O3 (Aladdin, 99.99%), ZrO2 (Aladdin, 99.9%), and Ta2O5 (Aladdin, 99.99%) are weighed according to the stoichiometric ratio of LLZTO. An excess of 15 wt% of LiOH·H2O is added to compensate for the volatilization of Li-containing components at high temperature. Isopropanol is used as the solvent, and the mixture is ball-milled at 800 rpm for 10 hours to obtain a homogeneous slurry. After drying, the slurry is calcined at 900℃ in a muffle furnace for 10 hours. The calcined powder is then ball-milled again for 2 hours to obtain finer LLZTO powder. A certain mass of the powder is then weighed into a 16mm diameter stainless steel mold and pressed into raw blank discs. Finally, the raw wafer was covered with an appropriate amount of precursor powder in an MgO crucible and sintered at 1180℃ for 8 hours. This yielded an LLZTO electrolyte sheet with a diameter of 14 mm, which was then mechanically ground and polished to a thickness of 800 μm to eliminate surface scratches, reduce surface roughness, and obtain a flat, mirror-like surface (compared to a polishing step with interface cleaning optimization).

[0039] The garnet-type oxide solid electrolyte sheet LLZTO prepared above was characterized and analyzed. The XRD diffraction pattern is shown below. Figure 2 As shown, by Figure 2 As can be seen, the diffraction peak positions of the LLZTO solid electrolyte sheet are consistent with those of the standard PDF card, and no obvious impurity peaks were detected, indicating that the obtained sample has a pure-phase garnet structure. The XRD diffraction pattern after being placed in air for 7 days is shown below. Figure 3 As shown, through Figure 3 The presence of characteristic diffraction peaks of Li2CO3 in the sample indicates that during placement in air, the surface of the electrolyte sheet reacts with CO2 and H2O to generate a Li2CO3 contamination layer.

[0040] The SEM images of the garnet-type oxide solid electrolyte sheet LLZTO prepared above are as follows: Figure 4 As shown, where, Figure 4 In this diagram, 'a' represents a polished solid electrolyte sheet, denoted as a fresh electrolyte sheet; 'b' represents a solid electrolyte sheet left in air for 1 day, denoted as left in air for 1 day; and 'c' represents a solid electrolyte sheet left in air for 7 days, denoted as left in air for 7 days. Figure 4 It can be seen that the surface of the freshly prepared LLZTO solid electrolyte sheet is relatively dense and flat, with tightly bonded grains, and no obvious Li2CO3 contamination layer was observed. After 1 day, a black coating layer formed on the surface of the LLZTO electrolyte sheet. After 7 days, a coating layer formed on the surface of the LLZTO electrolyte sheet, and the surface changed from the original dense and flat to a relatively rough and loose morphology.

[0041] EIS impedance diagram as follows Figure 5 As shown, where, Figure 5 In this diagram, 'a' represents a polished solid electrolyte sheet, denoted as a fresh electrolyte sheet; 'b' represents a solid electrolyte sheet left in air for 1 day, denoted as left in air for 1 day; and 'c' represents a solid electrolyte sheet left in air for 7 days, denoted as left in air for 7 days. Figure 5 It can be seen that the ionic conductivity of the freshly prepared solid electrolyte sheet, calculated through fitting, is 1.8 × 10⁻⁶ at room temperature. -4 S cm -1 After being left for one day, the ionic conductivity decreased from 1.8 × 10⁻⁶ to the value immediately after preparation. -4 S cm -1 Reduced to 4.5×10 -8 S cm -1 After 7 days, the concentration decreased to 5.3 × 10⁻⁶. -9 S cm -1 .

[0042] Example 1

[0043] AFM atomic force microscope image of LLZTO solid electrolyte sheet placed for 7 days is shown below. Figure 6 As shown, through Figure 6 It can be seen that the surface of the electrolyte sheet has obvious undulating structure, and the surface roughness Ra is 264.2 nm, indicating that a relatively rough Li2CO3 coating layer has been formed on its surface.

[0044] The LLZTO electrolyte sheet containing a Li₂CO₃ contamination layer (80 nm thick) that had been stored for 7 days was immersed in a weakly acidic ionic liquid of 1-carboxymethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt for 2 hours in an Ar atmosphere at 30°C with a water content of 0.01 wt%, resulting in an interface-modified LLZTO solid electrolyte sheet. Its SEM image is shown below. Figure 7 AFM atomic force microscope image (see) Figure 8 EIS impedance see Figure 9 CCD testing is available. Figure 10 .Depend on Figure 7 It is evident that after treatment with a weakly acidic ionic liquid, the coating layer on the electrolyte sheet surface is significantly reduced or disappears, and the surface tends to become denser and smoother; from Figure 8 It can be seen that the surface roughness Ra of the electrolyte decreased to 28.4 nm, significantly lower than before treatment, indicating that the surface contaminant layer was effectively removed and a uniform interface layer was formed on the electrolyte surface; Figure 9 It can be seen that, based on fitting calculations, its ionic conductivity is 2.1 × 10⁻⁶. -3 S cm -1 ;Depend on Figure 10 The CCD test results show that its critical current density reaches 2.5 mA cm⁻¹. -2 .

[0045] Example 2

[0046] The LLZTO electrolyte sheet containing a 20 nm thick Li₂CO₃ contamination layer, which had been left to stand for one day, was immersed in a weakly acidic ionic liquid of 1-carboxyethyl-3-methylimidazolium trifluoromethanesulfonate for 5 hours in an environment of 30°C, N₂ atmosphere, and 0.1 wt% water content. This yielded an interface-modified LLZTO solid electrolyte sheet with a structure and properties similar to that of Example 1, exhibiting an ionic conductivity of 2.0 × 10⁻⁶. -3 S cm -1 The critical current density is 2.8 mA cm⁻¹. -2 .

[0047] Example 3

[0048] The freshly prepared and polished LLZTO electrolyte sheet was placed in air for 3 days for characterization analysis. The structure and performance were similar to those in Example 2.

[0049] The resulting LLZTO electrolyte sheet containing a Li₂CO₃ contamination layer (50 nm thick) was then immersed in a weakly acidic ionic liquid of 1-sulfonamide ethyl-3-methylimidazolium trifluoromethane sulfonate at 30°C in an Ar atmosphere with a water content of 0.1 wt% for 7 h, yielding an interface-modified LLZTO solid electrolyte sheet with a structure and properties similar to those in Example 1, exhibiting an ionic conductivity of 2.1 × 10⁻⁶. -3 S cm -1 The critical current density is 2.5 mA cm⁻¹. -2 .

[0050] Comparative Example 1

[0051] This comparative example involved placing freshly prepared LLZTO electrolyte sheets in air for one day, resulting in a 20 nm thick Li₂CO₃ contamination layer on the surface. The sheets were then immersed in a weakly acidic ionic liquid without further treatment. The resulting comparative sample was assembled into a symmetrical cell and subjected to CCD testing. Figure 11 ,Depend on Figure 11 The CCD test results show that its critical current density is 1.2 mA cm⁻¹. -2 .

[0052] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0053] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for integrated cleaning and optimization of oxide solid electrolyte interfaces, characterized in that, Includes the following steps: 1) Polish the oxide solid electrolyte and place the polished oxide solid electrolyte in the air to react, so that a surface contamination layer containing Li2CO3 is formed on the surface of the oxide solid electrolyte. 2) The oxide solid electrolyte with a surface contamination layer is immersed in a weakly acidic ionic liquid to carry out the reaction, thereby cleaning and optimizing the oxide solid electrolyte interface and obtaining an oxide solid electrolyte with a flexible interface layer. The weakly acidic ionic liquid contains acidic functional groups, including one or more of carboxyl groups, sulfonamide groups, and sulfonylimide groups.

2. The integrated treatment method for cleaning and optimizing the interface of oxide solid electrolytes according to claim 1, characterized in that, The cations in the weakly acidic ionic liquid include one or more of imidazole, pyridine, or quaternary ammonium salts; The anions in the weakly acidic ionic liquid include one or more of the following: bis(trifluoromethanesulfonyl)imide anion, bis(fluorosulfonyl)imide anion, hexafluorophosphate anion, tetrafluoroborate anion, and trifluoromethanesulfonate anion.

3. The integrated treatment method for cleaning and optimizing the interface of oxide solid electrolytes according to claim 2, characterized in that, The oxide solid electrolyte mentioned in step 1) includes NASICON type oxide solid electrolyte, garnet type oxide solid electrolyte or perovskite type oxide solid electrolyte.

4. The integrated treatment method for cleaning and optimizing the interface of oxide solid electrolytes according to claim 3, characterized in that, The oxide solid electrolyte has a diameter of 5-50 mm and a thickness of 0.5-10 mm.

5. A method for integrated cleaning and optimization of oxide solid electrolyte interfaces according to any one of claims 1 to 4, characterized in that, The polished oxide solid electrolyte described in step 1) has an ionic conductivity of 1×10⁻⁶ at room temperature. -4 ~1×10 -3 S cm -1 .

6. The integrated treatment method for cleaning and optimizing the interface of oxide solid electrolytes according to claim 5, characterized in that, The endpoint of the reaction described in step 1) is the formation of a surface contamination layer with a thickness of 0.01~5 μm on the surface of the oxide solid electrolyte.

7. The integrated treatment method for cleaning and optimizing the interface of oxide solid electrolytes according to claim 6, characterized in that, The reaction in step 2) is carried out at a temperature of 10~80℃ for 2~7 hours.

8. The integrated treatment method for cleaning and optimizing the interface of oxide solid electrolytes according to claim 6 or 7, characterized in that, The reaction atmosphere described in step 2) is an anhydrous atmosphere.

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