A lithium negative electrode double-layer interface modification layer based on welding area segregation and its preparation method and application

Abstract

A double-layer interface modification layer for lithium negative electrodes based on weld zone segregation, and its preparation method and application, belong to the field of solid-state battery technology. The scheme includes the following steps: step 1, grinding and polishing the surface of the solid electrolyte sheet; step 2, modifying bismuth halide on the polished surface of the solid electrolyte sheet to obtain a solid electrolyte sheet modified with bismuth halide; step 3, compounding the lithium negative electrode with the surface of the solid electrolyte sheet modified with bismuth halide, heating the reaction at 220-240°C for 15-30 minutes, and controlling the cooling rate to achieve regulation of the interface layer structure, thereby obtaining a double-layer interface modification layer comprising lithium halide and lithium bismuth alloy, wherein the lithium halide is close to one side of the solid electrolyte sheet and the lithium bismuth alloy is close to the lithium negative electrode side. The operation method of the present invention is simple, efficient and reliable, does not require the use of complex precision instruments, and has excellent improvement effects, making it easy to promote and apply on a large scale.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid-state batteries, and specifically relates to a method for modifying the interface of a solid-state lithium battery negative electrode, and more particularly to a lithium negative electrode double-layer interface modification layer based on welding area segregation, and a preparation method and application thereof. Background Art

[0002] All-solid-state lithium batteries (ASSLBs) have attracted much attention due to their high safety and high energy density. Among the many solid electrolytes reported, garnet-type Li 6.5 La3Zr2O 12 (LLZO) has high ionic conductivity at room temperature (10 -4 ~10 -3 S cm -1 ) and excellent chemical / electrochemical stability, showing broad application prospects. Unfortunately, lithium metal easily forms dendrites during repeated deposition / stripping processes, penetrating the electrolyte and causing short circuits, which seriously hinders the practical application of solid-state lithium batteries. As a result, various strategies have been proposed to enhance the interfacial contact between LLZO and lithium metal, such as removing surface contaminants, using composite negative electrodes, introducing lithiophilic intermediate layers, and increasing pressure. Although these methods improve the wettability of the material to a certain extent, lithium dendrites are still unavoidable with the increase of current density or the extension of cycle time. Therefore, how to design an interface modification strategy that can achieve close contact between the electrode and the electrolyte and inhibit the growth of lithium dendrites has become a difficult problem. Summary of the Invention

[0003] The present invention addresses the problems of poor interface contact between garnet-type solid electrolyte and lithium negative electrode, high interface impedance, and growth of lithium dendrites at the interface and inside the electrolyte. It provides a lithium negative electrode double-layer interface modification layer based on welding area segregation, as well as its preparation method and application.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A double-layer interface modification layer for a lithium negative electrode based on welding area segregation, wherein the double-layer interface modification layer is located between a solid electrolyte sheet and a lithium negative electrode, and comprises a lithium halide layer and a lithium-bismuth alloy layer, wherein the lithium halide layer is close to one side of the solid electrolyte sheet, and the lithium-bismuth alloy layer is close to one side of the lithium negative electrode.

[0006] Furthermore, the solid electrolyte is a garnet-type solid electrolyte Li 7-x La3Zr 2-x M x O 12 , and at least one of its doped compounds, wherein M is Nb or Ta, wherein 0≤x<2.

[0007] A method for preparing a double-layer interface modification layer for a lithium negative electrode based on welding zone segregation comprises the following steps:

[0008] Step 1: grinding and polishing the surface of the solid electrolyte sheet;

[0009] Step 2: modifying the polished surface of the solid electrolyte sheet with bismuth halide to obtain a solid electrolyte sheet modified with bismuth halide;

[0010] Step 3: Composite the lithium negative electrode with the surface of the solid electrolyte sheet modified with bismuth halide, heat the reaction at 220-240°C for 15-30 minutes, and control the cooling rate to achieve regulation of the interface layer structure to obtain a double-layer interface modification layer containing lithium halide and lithium bismuth alloy, wherein the lithium halide is close to one side of the solid electrolyte sheet and the lithium bismuth alloy is close to the lithium negative electrode side.

[0011] Furthermore, in step 3, the temperature is lowered at a cooling rate of less than 3°C / min. The cooling rate can be adjusted according to actual conditions. A slower cooling rate makes the interface layer easier to delaminate, while a faster cooling rate makes the intermediate layer a mixed conductive layer.

[0012] Furthermore, in step 2, the method for modifying the bismuth halide on the surface of the polished solid electrolyte sheet is: coating the surface of the polished solid electrolyte sheet with a bismuth halide dispersion, wherein the bismuth halide dispersion includes a bismuth halide solution or a bismuth halide suspension, and the bismuth halide is already in a molten state at 220-240°C. The purpose of using the dispersion is to evenly disperse the bismuth halide.

[0013] Preferably, the solvent for bismuth halide includes anhydrous ethanol, acetone or other solvents with high solubility for bismuth halide.

[0014] Furthermore, the mass of bismuth halide used per unit area of ​​the solid electrolyte sheet surface is 0.005-0.05 mg / cm 2 .

[0015] Furthermore, the coating method includes at least one of drop coating, spin coating, and sputtering.

[0016] Furthermore, the halogen element in the bismuth halide includes at least one of chlorine (Cl) and bromine (Br). Because bismuth chloride and bismuth bromide have relatively low melting points, both below 240°C, they can fully contact and react with molten lithium in liquid form at relatively low temperatures. The bismuth halide may be partially oxidized to form bismuth oxyhalide. The lithium halide layer in the reaction product will contain lithium oxide, which can also transport lithium ions without affecting the transport of ions at the interface.

[0017] An application of the lithium negative electrode double-layer interface modification layer based on welding area segregation in a solid-state lithium battery.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] After the molten bismuth halide and molten lithium metal have fully reacted, the cooling rate is controlled to allow them to cool slowly. As the bismuth halide crystals continue to grow, they push the lithium halide impurities to the electrolyte side. After complete cooling, a lithium bismuth alloy / lithium halide interlayer with a double-layer structure is formed. On the one hand, lithium halide has extremely low electronic conductivity, which can block electrons and prevent the electrolyte from being attacked. On the other hand, the lithium bismuth alloy adjusts the local current distribution, achieves uniform deposition / stripping of lithium, and avoids the formation of dendrites at the interface. It should be noted that although the presence of inorganic salt impurities will reduce the welding effect, because the interlayer is very thin (<500nm), this preparation method can achieve a close connection between the metal electrode and the ceramic electrolyte. Therefore, this solid-state lithium battery with a multifunctional double-layer interlayer shows stable long-cycle performance and high limiting current density at room temperature.

[0020] The operation method of the present invention is simple, efficient and reliable, does not require the use of complex precision instruments, has excellent improvement effects, and is easy to promote and apply on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 For the comparative example, unmodified Li 6.5 La3Zr 1.5 Ta 0.5 O 12 Impedance diagram of the assembled symmetrical battery;

[0022] Figure 2 Li modified with BiCl3 in Example 1 6.5 La3Zr 1.5 Ta 0.5 O 12 Impedance diagram of the assembled symmetrical battery. MDL in the figure is the abbreviation of Multifunctional Double Layer, which means multifunctional double layer.

[0023] Figure 3 Li modified with BiCl3 in Example 1 6.5 La3Zr 1.5 Ta 0.5 O 12 The limiting current density diagram of the assembled symmetrical battery. MDL in the figure is the abbreviation of Multifunctional Double Layer, which means multifunctional double layer.

[0024] Figure 4 Li modified with BiCl3 in Example 1 6.5 La3Zr 1.5Ta 0.5 O 12 Time-current curve of the assembled blocking battery. MDL in the figure is the abbreviation of Multifunctional Double Layer, which means multifunctional double layer.

[0025] Figure 5 Li modified with BiCl3 in Example 1 6.5 La3Zr 1.5 Ta 0.5 O 12 The long-cycle performance diagram of the assembled symmetrical battery. In the figure, MDL is the abbreviation of Multifunctional Double Layer, which means multifunctional double layer. DETAILED DESCRIPTION

[0026] The technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0027] Example 1

[0028] A method for preparing a double-layer interface modification layer for a lithium negative electrode based on welding zone segregation comprises the following steps:

[0029] Step 1: Solid electrolyte sheet Li 6.5 La3Zr 1.5 Ta 0.5 O 12 Grind and polish the two surfaces;

[0030] Step 2: Spin coat 5 μl of a 0.2% by mass BiCl3 anhydrous ethanol solution onto the surface of a polished solid electrolyte sheet with a diameter of 12 mm using a spin coater to obtain a BiCl3-modified solid electrolyte sheet;

[0031] Step 3: Place lithium sheets on the upper and lower surfaces of the BiCl3-modified solid electrolyte sheet to build a solid-state lithium symmetrical battery, then place it on a heating table, heat it at 240°C for 20 minutes, and then cool it to room temperature at a cooling rate of 2°C / min to obtain a double-layer interface modification layer of solid electrolyte / lithium negative electrode containing lithium chloride (LiCl) and lithium bismuth alloy (BiLi3), wherein the lithium bismuth alloy is close to the lithium negative electrode side, and the lithium chloride is close to the solid electrolyte sheet side.

[0032] Example 2

[0033] A method for preparing a double-layer interface modification layer for a lithium negative electrode based on welding zone segregation comprises the following steps:

[0034] Step 1: Solid electrolyte sheet Li 6.5 La3Zr 1.5 Ta 0.5 O 12 Grind and polish the two surfaces;

[0035] Step 2: Spin coat 6 μl of a 0.2% by mass BiBr3 anhydrous ethanol solution onto the surface of a polished solid electrolyte sheet with a diameter of 12 mm using a spin coater to obtain a BiBr3-modified solid electrolyte sheet;

[0036] Step 3: Place lithium sheets on the upper and lower surfaces of the BiBr3-modified solid electrolyte sheet to build a solid-state lithium symmetrical battery, then place it on a heating table, heat it at 220°C for 30 minutes, and then cool it to room temperature at a cooling rate of 2°C / min to obtain a double-layer interface modification layer of solid electrolyte / lithium negative electrode containing lithium chloride (LiBr) and lithium bismuth alloy (BiLi3), wherein the lithium bismuth alloy is close to the lithium negative electrode side, and the lithium chloride is close to the solid electrolyte sheet side.

[0037] Example 3

[0038] A method for preparing a double-layer interface modification layer for a lithium negative electrode based on welding zone segregation comprises the following steps:

[0039] Step 1: Solid electrolyte sheet Li 6.5 La3Zr 1.5 Ta 0.5 O 12 Grind and polish the two surfaces;

[0040] Step 2: Spin coat 5 μl of a 0.2% by mass BiOCl solution in anhydrous ethanol on the surface of a polished solid electrolyte sheet with a diameter of 12 mm using a spin coater to obtain a BiOCl-modified solid electrolyte sheet;

[0041] Step 3: Lithium sheets are placed on the upper and lower surfaces of the BiOCl-modified solid electrolyte sheet to build a solid-state lithium symmetrical battery, which is then placed on a heating table, heated at 230°C for 15 minutes, and then cooled to room temperature at a cooling rate of 2°C / min to obtain a double-layer interface modification of the solid electrolyte / lithium negative electrode comprising lithium chloride / lithium oxide (LiCl / Li2O) and lithium bismuth alloy (BiLi3), wherein the lithium bismuth alloy is close to the lithium negative electrode side, and the lithium chloride / lithium oxide is close to the solid electrolyte sheet side.

[0042] Example 4

[0043] A method for preparing a double-layer interface modification layer for a lithium negative electrode based on welding zone segregation comprises the following steps:

[0044] Step 1: Solid electrolyte sheet Li 6.5 La3Zr 1.5 Ta 0.5 O 12 Grind and polish the two surfaces;

[0045] Step 2: Spin coat 5 μl of a 0.2% by mass BiCl3 acetone solution onto the surface of a polished solid electrolyte sheet with a diameter of 12 mm using a spin coater to obtain a BiCl3-modified solid electrolyte sheet;

[0046] Step 3: Place lithium sheets on the upper and lower surfaces of the BiCl3-modified solid electrolyte sheet to build a solid-state lithium symmetrical battery, then place it on a heating table, heat it at 240°C for 20 minutes, and then cool it to room temperature at a cooling rate of 2°C / min to obtain a double-layer interface modification layer of solid electrolyte / lithium negative electrode containing lithium chloride (LiCl) and lithium bismuth alloy (BiLi3), wherein the lithium bismuth alloy is close to the lithium negative electrode side, and the lithium chloride is close to the solid electrolyte sheet side.

[0047] Example 5

[0048] A method for preparing a double-layer interface modification layer for a lithium negative electrode based on welding zone segregation comprises the following steps:

[0049] Step 1: Solid electrolyte sheet Li 6.5 La3Zr 1.5 Ta 0.5 O 12 Grind and polish the two surfaces;

[0050] Step 2: 5 μl of a 0.2% by mass BiCl3 anhydrous ethanol solution was drop-coated on the surface of a polished solid electrolyte sheet with a diameter of 12 mm to obtain a BiCl3-modified solid electrolyte sheet;

[0051] Step 3: Place lithium sheets on the upper and lower surfaces of the BiCl3-modified solid electrolyte sheet to build a solid-state lithium symmetrical battery, then place it on a heating table, heat it at 240°C for 20 minutes, and then cool it to room temperature at a cooling rate of 2°C / min to obtain a double-layer interface modification layer of solid electrolyte / lithium negative electrode containing lithium chloride (LiCl) and lithium bismuth alloy (BiLi3), wherein the lithium bismuth alloy is close to the lithium negative electrode side, and the lithium chloride is close to the solid electrolyte sheet side.

[0052] Example 6

[0053] A method for preparing a double-layer interface modification layer for a lithium negative electrode based on welding zone segregation comprises the following steps:

[0054] Step 1: Solid electrolyte sheet Li 6.5 La3Zr 1.5 Ta 0.5 O 12 Grind and polish the two surfaces;

[0055] Step 2: BiCl3 is modified on the surface of a polished solid electrolyte sheet with a diameter of 12 mm by magnetron sputtering to obtain a BiCl3-modified solid electrolyte sheet;

[0056] Step 3: Place lithium sheets on the upper and lower surfaces of the BiCl3-modified solid electrolyte sheet to build a solid-state lithium symmetrical battery, then place it on a heating table, heat it at 240°C for 20 minutes, and then cool it to room temperature at a cooling rate of 2°C / min to obtain a double-layer modified interface of solid electrolyte / lithium negative electrode containing lithium chloride (LiCl) and lithium bismuth alloy (BiLi3), wherein the lithium bismuth alloy is close to the lithium negative electrode side, and the lithium chloride is close to the solid electrolyte side.

[0057] Comparative Example

[0058] The difference between this comparative example and Example 1 is that: 6.5 La3Zr 1.5 Ta 0.5 O 12 Lithium sheets are placed on the upper and lower surfaces of the solid electrolyte sheet to assemble a solid-state lithium symmetrical battery.

[0059] Figure 2 and Figure 1 The comparison shows that the impedance of the symmetrical battery modified with bismuth halide is significantly reduced. Figure 3 It is shown that the symmetrical battery modified with bismuth halide has a high limiting current density and can effectively inhibit the growth of lithium dendrites. Figure 4 Calculations show that the electronic conductivity is nearly two orders of magnitude lower than that of the unmodified LLZTO, indicating that the modified layer has excellent insulation properties and can effectively inhibit the growth of lithium dendrites inside the electrolyte. Figure 5 It shows that the symmetrical battery modified with bismuth halide has excellent long-cycle performance and good resistance to lithium dendrite growth.

[0060] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for preparing a double-layer interface modification layer for a lithium negative electrode based on weld zone segregation, wherein the double-layer interface modification layer is located between a solid electrolyte sheet and a lithium negative electrode, characterized in that: The double-layer interface modification layer includes a lithium halide layer and a lithium-bismuth alloy layer, wherein the lithium halide layer is close to the solid electrolyte sheet side, and the lithium-bismuth alloy layer is close to the lithium negative electrode side; the preparation method of the lithium negative electrode double-layer interface modification layer based on welding area segregation includes the following steps: Step 1: grinding and polishing the surface of the solid electrolyte sheet; Step 2: modifying the polished surface of the solid electrolyte sheet with bismuth halide to obtain a solid electrolyte sheet modified with bismuth halide; Step 3: Composite the lithium negative electrode with the surface of the solid electrolyte sheet modified with bismuth halide, heat the reaction at 220-240°C for 15-30 minutes, and cool it down at a cooling rate of less than 3°C / min to achieve regulation of the interface layer structure, thereby obtaining a double-layer interface modification layer comprising lithium halide and lithium bismuth alloy, wherein the lithium halide is close to one side of the solid electrolyte sheet and the lithium bismuth alloy is close to the lithium negative electrode side.

2. The preparation method according to claim 1, wherein: The solid electrolyte is garnet-type solid electrolyte Li 7-x La3Zr 2-x M x O 12 , and at least one of its doped compounds, wherein M is Nb or Ta, wherein 0≤x<2.

3. The preparation method according to claim 1, wherein: In step 2, the method for modifying the bismuth halide on the polished surface of the solid electrolyte sheet is: coating the bismuth halide dispersion on the polished surface of the solid electrolyte sheet.

4. The preparation method according to claim 3, wherein: The solvent of the bismuth halide dispersion includes anhydrous ethanol or acetone solvent.

5. The preparation method according to claim 1, wherein: The mass of bismuth halide used per unit area on the surface of the solid electrolyte sheet is 0.005-0.05 mg / cm 2 .

6. The preparation method according to claim 3, wherein: The coating method includes at least one of drop coating, spin coating, and sputtering.

7. The preparation method according to claim 1, wherein: The halogen element in the bismuth halide includes at least one of chlorine and bromine.

8. Use of a lithium negative electrode double-layer interface modification layer based on weld zone segregation prepared by the preparation method according to any one of claims 1 to 7 in a solid-state lithium battery.

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