A method of modifying the interface of a lithium negative electrode and a solid-state electrolyte

Abstract

This invention discloses a method for modifying the interface between a lithium anode and a solid electrolyte. The lithium anode is prepared using a simple punching method. During battery assembly, ionic liquids are applied at both the interface between the positive electrode and the solid electrolyte, and at the interface between the anode and the solid electrolyte. This invention solves the problems of high process requirements, easy contamination of ceramic sheet surface, and battery short circuits associated with existing molten lithium anode preparation processes. By using only a punching method for anode preparation, combined with interface modification of the anode, the battery can achieve excellent performance. Furthermore, the process is simple, can be mass-produced, and has excellent market potential.

Description

Technical Field

[0001] This invention relates to all-solid-state lithium-ion batteries, and particularly to a method for modifying the interface between the lithium anode and the solid electrolyte. Background Technology

[0002] Traditional rechargeable lithium batteries use organic liquid electrolytes or gel-type polymer electrolytes, which are prone to leakage and combustion under certain conditions, posing significant safety hazards. Furthermore, their complex structure limits further improvements in energy density. Replacing the electrolyte with a solid-state electrolyte promises to significantly improve battery safety and energy density. Among various solid-state electrolytes, the garnet-type structure Li7La3Zr2O... 12 (LLZO) has attracted much attention due to its advantages such as high conductivity and good electrochemical stability.

[0003] Compared to other solid-state electrolytes, LLZO solid-state electrolytes have higher hardness and exhibit rigid point-to-point contact with electrode materials, resulting in high interfacial resistance. To address the positive electrode interface problem, researchers utilize liquid electrolytes with high ionic conductivity to wet the positive electrode interface, transforming the discontinuous point-to-point solid / solid contact into a better planar contact, thus reducing interfacial resistance. Lithium metal, due to its outstanding properties, is considered a key material for achieving high-energy-density batteries and is often used as the negative electrode in all-solid-state batteries. When lithium is used as the negative electrode in LLZO solid-state electrolytes, its solid / solid contact leads to high interfacial impedance. Molten lithium is often used to mitigate this issue, but the molten lithium process is demanding. Molten lithium must be handled entirely in a glove box, and lithium tends to adhere around the ceramic sheet. Polishing also requires a glove box, making the process difficult and prone to surface contamination. Incomplete polishing can cause short circuits. Furthermore, molten lithium has a large contact angle on the LLZO solid-state electrolyte surface, making the electrolyte lithium-repellent. Simultaneously, the unevenness of the interfacial contact can easily lead to lithium dendrite growth, ultimately damaging the battery structure. Summary of the Invention

[0004] To address the aforementioned problems in the existing molten lithium method for preparing anodes, this invention provides a method for modifying the interface between the lithium anode and the solid electrolyte. The anode is prepared using a simple punching method, and the interface is improved using ionic liquids, thereby achieving good performance.

[0005] The technical solution of the present invention is as follows:

[0006] A method for modifying the interface between a lithium anode and a solid electrolyte involves applying an ionic liquid at both the interface between the positive electrode and the solid electrolyte and the interface between the negative electrode and the solid electrolyte during battery assembly.

[0007] Furthermore, the battery is composed of a positive electrode, a negative electrode, and a solid electrolyte, wherein the negative electrode is prepared by a punching method.

[0008] Furthermore, the negative electrode is preferably a lithium negative electrode.

[0009] Furthermore, the solid electrolyte is preferably a garnet-type solid electrolyte ceramic sheet.

[0010] Furthermore, the preparation method of the ionic liquid is as follows:

[0011] N-propyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl)imine salt ionic liquid (PY 13 Using a volumetric metric of NTF2 ionic liquid, add lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) at a concentration of 1.2-2 mol / L, mix thoroughly, and then add PY 13 Add 10 vol% to 15 vol% of commercial carboxylic acid ester electrolyte to the NTF2 ionic liquid volume meter.

[0012] Furthermore, the commercial carboxylic acid ester electrolyte can be selected as 1 mol / L LiClO4, with a solvent MF (methyl formate):MA (methyl acetate) volume ratio of 1:1.

[0013] Furthermore, the preparation method of the garnet-type solid electrolyte ceramic sheet is as follows:

[0014] (1) Lithium hydroxide monohydrate, lanthanum oxide, zirconium oxide and aluminum oxide were prepared according to stoichiometric ratio, solvent was added, and then ball milling was performed;

[0015] (2) The powder obtained by ball milling in step (1) is sintered at 800-1000℃ for 4-8h to obtain cubic garnet-type solid electrolyte, i.e. LLZAO ceramic powder.

[0016] (3) Press the LLZAO ceramic powder obtained in step (2) to obtain a blank, and embed the blank with the LLZAO ceramic powder obtained in step (2), then calcine it at 1000-1400℃ for 6-10h, and then grind and polish it to obtain LLZAO ceramic sheet.

[0017] The beneficial effects of this invention are as follows:

[0018] This invention modifies the battery by applying a specific ionic liquid to the interface between the negative electrode and the solid electrolyte, and uses only a punching method to prepare the negative electrode, which enables the battery to achieve excellent performance. The process is simple, can be mass-produced, and has excellent market potential. Attached Figure Description

[0019] Figure 1 The image shows the XRD pattern of the solid electrolyte ceramic sheet after sintering at 1200℃ in Example 1.

[0020] Figure 2This is a graph showing the long-cycle performance of the lithium symmetric battery with an interface modified by ionic liquid in Example 1.

[0021] Figure 3 The graph shows the performance of the full battery during cyclic charging and discharging obtained in Example 1.

[0022] Figure 4 The impedance test diagram is shown for the assembled battery in Example 1. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited thereto.

[0024] Example 1

[0025] Step 1: Preparation of Garnet-type Solid Electrolyte (LLZAO) Ceramic Powder. Raw materials used included lithium hydroxide monohydrate, lanthanum oxide, zirconium oxide, and alumina. The raw materials were prepared according to stoichiometric ratios and placed in a nylon container. Zirconia grinding beads were added, along with 15 mL of isopropanol. The mixture was ball-milled using a high-energy ball mill at 400 rpm for at least 12 hours. The milled powder was then placed in a magnesium oxide crucible and sintered in a muffle furnace at 900℃ with a heating rate of 5℃ / min for 6 hours. The final product was cubic LLZAO ceramic powder.

[0026] Step 2: Preparation of LLZAO solid electrolyte (LLZAO) ceramic sheets includes: taking 0.6 g of the prepared LLZAO ceramic powder, placing it in a 13 mm pressing mold, applying pressure of 15-20 MPa, and holding for at least 10 minutes to obtain an LLZAO ceramic sheet preform. Then, the pressed preform is placed in a magnesium oxide crucible, and the LLZAO preform is buried in the ceramic powder obtained in Step 1. The crucible is then placed in a muffle furnace, with the temperature set at 1200℃, a heating rate of 5℃ / min, and held for 6 hours. The sintered LLZAO ceramic sheets are then successively polished using 320-mesh, 1000-mesh, 3000-mesh, and 5000-mesh sandpaper to remove impurities such as lithium carbonate and lithium hydroxide from the surface. The polished LLZAO ceramic sheets are then set aside.

[0027] Step 3: Preparation of positive and negative electrodes and assembly of coin cells

[0028] Preparation of the positive electrode: Commercially available LiFePO4 was selected as the active material for preparing the positive electrode.

[0029] Preparation of negative electrode: The lithium negative electrode is prepared by punching, and a thin lithium sheet with a diameter of 9 mm is cut out using a punch.

[0030] Battery Assembly: Assemble a full cell with LiFePO4 as the positive electrode and a lithium-symmetric cell. During assembly, add 5 μL of ionic liquid between the electrode and the solid electrolyte. The ionic liquid is prepared as follows: Take 1 mL of N-propyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl)imide salt ionic liquid (PY). 13 NTF2); with PY 13 Using a volumetric metric of NTF2 ionic liquid, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added at a concentration of 1.2 mol / L and mixed thoroughly. Then, PY was used as the final volumetric metric. 13 Add 10 vol% of commercial electrolyte (1 mol / L LiClO4, solvent MF:MA volume ratio = 1:1) to the NTF2 ionic liquid volume meter.

[0031] Example 2

[0032] The only difference from Example 1 is the third step: preparation of positive and negative electrodes and assembly of coin cells.

[0033] Preparation of the positive electrode: LiFePO4 was selected as the active material for preparing the positive electrode.

[0034] Negative electrode preparation: The negative electrode is prepared by punching, using a punch to cut out thin lithium sheets with a diameter of 9 mm.

[0035] Battery Assembly: Assemble a full cell with LiFePO4 as the positive electrode and a lithium-symmetric cell. During assembly, add 5 μL of ionic liquid between the electrode and the solid electrolyte. The preparation process of the ionic liquid is as follows: Take 1 mL of N-propyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl)imide salt ionic liquid (PY). 13 NTF2); with PY 13 Using a volumetric metric of NTF2 ionic liquid, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added at a concentration of 2 mol / L and mixed thoroughly. Then, PY was used as the final volumetric metric. 13 The volumetric sample of NTF2 ionic liquid was filled with 10 vol% commercial electrolyte (1 mol / L LiClO4, solvent MF:MA volume ratio = 1:1).

[0036] Example 3

[0037] The only difference from Example 1 is the third step: preparation of positive and negative electrodes and assembly of coin cells.

[0038] Preparation of the positive electrode: Commercially available LiFePO4 was selected as the active material for preparing the positive electrode.

[0039] Negative electrode preparation: The negative electrode is prepared by punching, using a punch to cut out thin lithium sheets with a diameter of 9 mm.

[0040] Battery Assembly: Assemble a full cell with LiFePO4 as the positive electrode and a lithium-symmetric cell. During assembly, add 5 μL of ionic liquid between the electrode and the solid electrolyte. The preparation process of the ionic liquid is as follows: Take 1 mL of N-propyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl)imide salt ionic liquid (PY). 13 NTF2); with PY 13 Using a volumetric metric of NTF2 ionic liquid, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added at a concentration of 1.2 mol / L and mixed thoroughly. Then, PY was used as the final volumetric metric. 13 The volumetric liquid NTF2 was measured, and then 15 vol% of commercial electrolyte (1 mol / L LiClO4, solvent MF:MA volume ratio = 1:1) was added.

[0041] Example 4

[0042] The only difference from Example 1 is the third step: preparation of positive and negative electrodes and assembly of coin cells.

[0043] Preparation of the positive electrode: Commercially available LiFePO4 was selected as the active material for preparing the positive electrode.

[0044] Negative electrode preparation: The negative electrode is prepared by punching, using a punch to cut out thin lithium sheets with a diameter of 9 mm.

[0045] Battery Assembly: Assemble a full cell with LiFePO4 as the positive electrode and a lithium-symmetric cell. During assembly, add 5 μL of ionic liquid between the electrode and the solid electrolyte. The preparation process of the ionic liquid is as follows: Take 1 mL of N-propyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl)imide salt ionic liquid (PY). 13 NTF2); with PY 13 Using a volumetric metric of NTF2 ionic liquid, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added at a concentration of 2 mol / L and mixed thoroughly. Then, PY was used as the final volumetric metric. 13 The volumetric liquid NTF2 was measured, and then 15 vol% of commercial electrolyte (1 mol / L LiClO4, solvent MF:MA volume ratio = 1:1) was added.

[0046] Electrochemical tests were performed on the assembled symmetrical cells and full cells.

[0047] Example 1: XRD tests were performed on a solid electrolyte ceramic sheet sintered at 1200℃ for 6 hours. The test results are as follows: Figure 1 As shown.

[0048] In Example 1, a lithium symmetric battery with a solid electrolyte modified with an ionic liquid was subjected to long-cycle testing at a current density of 0.1C. The test results are as follows: Figure 2 As shown. Figure 2This indicates that the lithium symmetric battery modified with ionic liquid exhibits excellent long-cycle performance.

[0049] In Example 1, the assembled LiFePO4 battery was activated for 5 cycles at a current density of 0.1C, and then subjected to a cyclic charge-discharge test at a current density of 0.2C, with a voltage range of 2.5-4.0V. The cycle graph is shown below. Figure 3 As shown. By Figure 3 It can be seen that the initial discharge capacity of the LiFePO4 battery is 162.3 mAh / g, and the discharge capacity after 120 cycles is 144.5 mAh / g, with the coulombic efficiency consistently remaining above 99%.

[0050] The impedance test diagram of the assembled LiFePO4 battery in Example 1 is shown below. Figure 4 As shown. Figure 4 This indicates that ionic liquid modification can significantly enhance the contact effect between the solid electrolyte and the lithium metal anode, improve the interface performance, and thus effectively improve the ability of solid-state batteries to suppress dendrites.

Claims

1. A method for modifying the interface between a lithium anode and a solid electrolyte, characterized in that, When assembling the battery, ionic liquids are applied at both the interface between the positive electrode and the solid electrolyte and the interface between the negative electrode and the solid electrolyte. The negative electrode is a lithium negative electrode; The solid electrolyte is a garnet-type solid electrolyte ceramic sheet; The preparation method of the ionic liquid is as follows: With PY 13 Using a volumetric meter for NTF2 ionic liquid, add LiTFSI at a concentration of 1.2-2 mol / L, mix thoroughly, and then add PY. 13 Add 10 vol%-15 vol% of commercial carboxylic acid ester electrolyte to the NTF2 ionic liquid volume meter; The carboxylic acid ester electrolyte is 1 mol / L LiClO4, and the volume ratio of solvent MF to MA is 1:

1.

2. The method for modifying the interface between the lithium anode and the solid electrolyte according to claim 1, characterized in that, The battery is composed of a positive electrode, a negative electrode, and a solid electrolyte, wherein the negative electrode is prepared by a punching method.

3. The method for modifying the interface between the lithium anode and the solid electrolyte according to claim 1 or 2, characterized in that, The preparation method of the garnet-type solid electrolyte ceramic sheet is as follows: (1) Prepare a mixture of lithium hydroxide monohydrate, lanthanum oxide, zirconium oxide and aluminum oxide in stoichiometric ratio, add solvent, and then ball mill; (2) The powder obtained by ball milling in step (1) is sintered at 800-1000℃ for 4-8h to obtain cubic garnet-type solid electrolyte, i.e. LLZAO ceramic powder. (3) Press the LLZAO ceramic powder obtained in step (2) to obtain a blank, and then embed the blank with the LLZAO ceramic powder obtained in step (2), and then calcine it at 1000-1400℃ for 6-10h, and then grind and polish it to obtain LLZAO ceramic sheet.

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