A metal lithium secondary battery anode containing an alloy protective layer prepared by physical deposition and a preparation method

Abstract

This invention relates to a lithium metal secondary battery anode containing an alloy protective layer prepared by physical deposition and its preparation method. A lithium strip used as the anode of the lithium metal secondary battery is cut and sampled, and then a lithium-tin alloy thin film with a thickness of 30nm to 50nm is physically deposited by magnetron sputtering, thereby forming a thin film interface protective layer on the surface of the anode. The lithium battery containing this interface protective layer achieves uniform dissolution and deposition of lithium metal during cycling. Furthermore, the anode with the lithium-tin alloy protective layer can be used in lithium metal secondary batteries. The lithium-tin alloy protective layer can improve the interface stability of the battery anode, resulting in better stability of the lithium metal secondary battery, thereby achieving battery cycle interface stability and a long cycle life.

Description

Technical Field

[0001] This invention belongs to the field of chemical power source technology, and in particular relates to a lithium metal secondary battery anode containing an alloy protective layer prepared by physical deposition and its preparation method. Background Technology

[0002] In recent years, with the diversification of energy demands, higher requirements have been placed on energy storage systems with high energy density and long cycle life. Despite research progress, the actual energy density of commercial batteries has only increased sixfold from the first-generation lead-acid batteries (~40Wh / kg) to the current lithium-ion batteries (~240Wh / kg and 640Wh / L), with the energy density growth rate of lithium-ion batteries only reaching 7%-8% annually. Lithium-ion batteries were once considered suitable candidates for energy storage, but their energy density is now close to theoretical values. Lithium metal, with its ultra-high capacity (3860mAh / g) and the lowest negative electrochemical potential (-3.040V relative to the standard hydrogen electrode), is considered the "holy grail" electrode and has attracted widespread research attention. Compared with existing lithium-ion battery anode materials, lithium metal anodes have enormous potential in meeting the demand for high energy density. Lithium metal secondary batteries with lithium metal anode systems can achieve energy densities of 450–600 Wh / kg. Despite the superior theoretical capacity and energy density of lithium metal anodes, various safety issues have prevented lithium metal secondary batteries from entering the commercial market. These include instability at the lithium metal / liquid electrolyte interface caused by dendrite growth during lithium deposition / stripping, the risk of short circuits leading to thermal runaway due to dendritic lithium crystal growth, and the risk of explosions. Therefore, for the past 40 years, lithium battery researchers have been studying strategies to suppress dendrite growth. Summary of the Invention

[0003] To address the cycle stability issue in novel battery system applications, this invention proposes an innovative method for preparing an alloy protective layer by physical deposition, and a lithium metal secondary battery anode containing an alloy protective layer prepared by physical deposition, and its preparation method.

[0004] The technical solution adopted in this invention is: a method for preparing a lithium metal secondary battery anode containing an alloy protective layer prepared by physical deposition, wherein a lithium-tin alloy thin film layer is deposited on the surface of a cut lithium strip by DC magnetron sputtering physical deposition to obtain a battery anode containing a lithium-tin alloy protective layer.

[0005] Preferably, the thickness of the lithium-tin alloy protective layer is 30nm to 50nm, and the thickness of the lithium-tin alloy protective layer is controlled by controlling the magnetron sputtering deposition time.

[0006] Preferably, the lithium strip is cut, copper tabs are pressed onto the lithium strip, and the sample is placed on a magnetron sputtering stage, with the chamber vacuum reduced to 10. -4Pa, turn on the DC power supply, and deposit a lithium-tin alloy thin film layer with a thickness of 30nm to 50nm on the surface of the lithium anode by controlling the magnetron sputtering deposition time.

[0007] A battery anode containing a lithium-tin alloy protective layer was prepared by a method for preparing a battery anode containing an alloy protective layer by physical deposition.

[0008] A lithium metal secondary battery includes a lithium metal secondary battery negative electrode containing a lithium-tin alloy protective layer.

[0009] Preferably, it is a lithium-lithium symmetrical button cell battery or a lithium metal rechargeable soft-pack battery.

[0010] Preferably, the specific preparation method is as follows:

[0011] Step 1: The positive electrode active material, conductive agent, and binder are uniformly dispersed in an appropriate amount of NMP solvent using a homogenizer; the uniformly dispersed slurry is coated onto an aluminum foil current collector to prepare a positive electrode, which is then rolled, slit, and die-cut to obtain the positive electrode sheet;

[0012] Step 2: After cutting and fixing the lithium strip, use a hydraulic press to press the copper tabs onto the lithium sheet. Then, use DC magnetron sputtering physical deposition to deposit a lithium-tin alloy thin film on the surface of the cut lithium strip to obtain a negative electrode sheet containing a lithium-tin alloy protective layer.

[0013] Step 3: Preparation of lithium-lithium symmetrical coin cell batteries: The coin cell spring sheet, coin cell pad, lithium anode with lithium-tin alloy protective layer, separator, electrolyte, and lithium sheet are placed into the coin cell casing in sequence to form a secondary lithium metal coin cell battery.

[0014] Alternatively, a soft-pack battery can be prepared by repeatedly stacking lithium metal secondary battery electrode groups in the order of separator, lithium anode with lithium-tin alloy protective layer, separator, and positive electrode, injecting electrolyte, and then performing a formation and degassing process to produce a lithium metal secondary soft-pack battery.

[0015] Preferably, the positive electrode active material comprises 97 wt% high-nickel ternary material, 1 wt% conductive carbon black and 0.5 wt% conductive carbon nanotubes as conductive agents, and 1.5 wt% PVDF as binder, wherein the proportion of PVDF in NMP solvent is 5 wt%.

[0016] The advantages and positive effects of this invention are: by physically depositing a lithium-tin alloy thin film interface protective layer through magnetron sputtering, the protective layer improves the non-uniform structure of the electrode surface and has high ionic conductivity to reduce the diffusion resistance of lithium ions through the film; the protective layer has excellent mechanical properties and can adapt to the impact and non-uniform volume changes during repeated lithium deposition / stripping processes.

[0017] Lithium batteries containing this interface protective layer achieve uniform dissolution and deposition of metallic lithium during cycling, thereby achieving battery cycle interface stability and long cycle life. The physical deposition preparation method of lithium alloy protective layer has high uniformity and excellent performance, and has broad application prospects in the field of metallic lithium secondary batteries. Attached Figure Description

[0018] Figure 1 This is a comparison diagram of the cycle overpotential of Example 1 and the comparative example lithium-ion symmetrical coin cell;

[0019] Figure 2 This is a comparison chart of the cycle capacity retention rates of Example 1 and the comparative example lithium metal secondary soft-pack batteries. Detailed Implementation

[0020] The embodiments of the present invention will now be described with reference to the accompanying drawings.

[0021] This invention relates to a lithium metal secondary battery anode containing an alloy protective layer prepared by physical deposition and its preparation method. A lithium strip used as the battery anode is cut, and a lithium-tin alloy layer is then physically deposited by magnetron sputtering, thereby forming a thin film interface protective layer on the surface of the anode. Furthermore, it can be used in lithium metal battery systems with higher energy density. For example, using an anode with a lithium-tin alloy protective layer in a lithium metal secondary battery can improve the interface stability of the battery anode, resulting in better stability of the lithium metal secondary battery.

[0022] When preparing a negative electrode containing a lithium-tin alloy protective layer, the lithium strip is cut and fixed on the magnetron sputtering sample stage using a fixture. After closing the magnetron sputtering vacuum chamber door, the chamber is evacuated until the vacuum level drops to 10. -4 Pa, turn on the DC power supply, and by controlling the magnetron sputtering deposition time to 0.5h, deposit a lithium-tin alloy thin film layer with a thickness of 30nm to 50nm on the surface of the lithium anode. The tin content in the lithium-tin alloy is 1% to 5%. Then, the anode containing the alloy protective layer is cut into the required size by a die-cutting tool.

[0023] The lithium-tin alloy protective layer improves the non-uniform structure of the electrode surface and has high ionic conductivity to reduce the diffusion resistance of lithium ions through the film. The protective layer has excellent mechanical properties, which can withstand the impact and non-uniform volume changes during repeated lithium deposition / stripping processes. The protective layer has remarkable stability in morphology, structure and chemical properties during long-term cycling, which improves the stability of the battery anode interface, thereby achieving more uniform lithium dissolution / deposition during cycling and inhibiting the growth of dendritic / granular lithium dendrites to a certain extent.

[0024] A lithium-metal secondary battery can be fabricated using a negative electrode containing a lithium-tin alloy protective layer. The positive electrode active material can be a high-nickel ternary (NCM) material. The electrolyte consists of a lithium difluorosulfonylimide electrolyte and ester and ether organic solvents. The separator is a ceramic-coated composite separator. After preparing all battery components, they are assembled using conventional methods to obtain a lithium-metal secondary battery including a negative electrode with a lithium-tin alloy protective layer. Specifically, this can be a lithium-lithium symmetrical coin cell battery or a lithium-metal secondary pouch battery. During the cycling process of lithium-lithium symmetrical coin cells and lithium-metal secondary pouch batteries, the lithium-tin alloy protective layer achieves uniform dissolution and deposition of lithium metal on the negative electrode surface, thereby achieving stable cycling interfaces and a long cycle life.

[0025] The present invention will now be described with reference to the accompanying drawings. Experimental methods not specifically described in terms of operation steps are performed in accordance with the corresponding product manuals. Unless otherwise specified, the instruments, reagents, and consumables used in the embodiments can be purchased from commercial companies.

[0026] Example 1:

[0027] Positive electrode preparation: 97 wt% of high-nickel ternary (NCM) positive electrode active material, 1 wt% conductive carbon black and 0.5 wt% conductive agent composed of carbon nanotubes, and 1.5 wt% binder PVDF are uniformly dispersed in an appropriate amount of NMP solvent using a homogenizer, wherein the proportion of PVDF in the NMP solvent is 5 wt%; the uniformly dispersed slurry is coated on an aluminum foil current collector to prepare a positive electrode, and the positive electrode sheet is obtained after rolling, slitting and die cutting.

[0028] Lithium anode fabrication: After cutting a 0.06mm thick lithium strip to a suitable size, a copper tab is pressed onto the lithium sheet using a hydraulic press at a fixed position. A lithium alloy anode protective layer is prepared on the surface of the lithium anode. After cutting the lithium strip, it is fixed on the magnetron sputtering sample stage using tooling. After closing the magnetron sputtering vacuum chamber door, the chamber is evacuated until the vacuum level drops to 10. - 4 Pa, turn on the DC power supply, and deposit a lithium-tin alloy thin film layer with a thickness of 30nm to 50nm on the lithium anode surface by controlling the magnetron sputtering deposition time to 0.5h. Then, the anode containing the alloy protective layer is cut into the required size by a die-cutting tool.

[0029] Button cell battery fabrication and testing: The button cell spring sheet, button cell gasket, lithium anode with lithium-tin alloy protective layer, separator, electrolyte, and lithium sheet are sequentially placed into the button cell casing. The button cell is then placed in a battery packaging machine and sealed under constant pressure to produce a lithium-lithium symmetrical button cell battery. A charge / discharge device is used at 2.5 mA / cm². 2 The current density is 2.5 mAh / cm³. 2 The capacity density is used for charge-discharge cycles.

[0030] Soft-pack battery preparation and testing: A lithium secondary battery electrode assembly was obtained by stacking lithium metal anode, lithium battery separator, and positive electrode in a lamination manner. The assembly was then encapsulated using an aluminum-plastic film for lithium batteries, followed by processes such as electrolyte injection, aging, formation, and degassing / removal of the gas chamber to prepare the lithium secondary soft-pack battery. Charge-discharge cycle performance was tested using a charge-discharge apparatus at a rate of 0.2CC / 0.5CD, with a charging cutoff voltage of 4.35V and a discharging cutoff voltage of 3.0V.

[0031] Comparative example:

[0032] In this embodiment, the positive electrode is prepared in the same manner as in Example 1; however, no protective layer is prepared for the negative electrode. The battery preparation and testing methods are the same as in Example 1.

[0033] The test results of Example 1 and the comparative example were compared and analyzed. The comparison results are shown in [the table below]. Figure 1 and Figure 2 .

[0034] Figure 1 For the comparison of the cycling overpotential of Example 1 and the comparative example lithium-ion symmetrical coin cell, the overpotential was as high as 2.5 mA / cm. 2 Current density, 2.5 mAh / cm 2 Under the same charge / discharge regime and capacity density, the coin cell with a lithium alloy protective layer (Example 1) exhibits lower overpotential and superior cycle stability compared to the coin cell without the protective layer. The battery with the lithium alloy protective layer exhibits lower overpotential during cycling. During 200 lithium deposition / stripping cycles, after 400 hours, the battery with the lithium alloy protective layer also achieved a stable voltage profile, with the overpotential remaining stable at 0.15V for 300 hours and 0.20V for 400 hours. The battery without the protective layer failed after only 80 hours of cycling. This phenomenon indicates that the lithium alloy thin-film protective layer effectively achieves uniform deposition at the interface during cycling, suppresses the formation of dendritic lithium during lithium deposition, promotes the deposition of effective active lithium, and thus improves the cycle stability of the battery.

[0035] Figure 2A comparison of the cycle capacity retention performance of Example 1 and the comparative example lithium metal secondary batteries shows that, under the same charge-discharge regime, Example 1, with its lithium alloy protective layer, exhibits superior cycle stability and slower capacity decay compared to the comparative example without the protective layer. At week 76, Example 1 retained 98.71% of its capacity, while the comparative example retained 81.37%. Furthermore, after 140 cycles, the capacity retention of Example 1 dropped below 80%. These results indicate that the lithium alloy protective layer (Example 1) stabilizes the negative electrode interface film, preventing repeated consumption and regeneration. The stable negative electrode interface film reduces the reaction between the electrolyte and lithium metal, effectively weakening side reactions between the lithium metal negative electrode and the electrolyte, inhibiting lithium dendrite growth, and improving the cycle stability of the lithium metal negative electrode.

[0036] The experimental data above show that the lithium alloy anode protective layer has a significant effect on improving the interface stability of lithium metal anodes. The capacity retention rate of a lithium metal secondary soft-pack battery with the lithium alloy protective layer can still reach over 80% after 139 stable cycles, while the capacity retention rate of a battery without the protective layer drops below 80% after only 76 cycles. The lithium alloy protective layer, applied to lithium metal secondary batteries, provides excellent mechanical properties, reduces the volume expansion of the lithium anode during cycles, and has a homogenizing and densifying effect on lithium deposition during the first charge, thereby improving the battery's subsequent cycle stability. This provides an engineeringable solution for the practical application of lithium metal anodes, significantly improves the overall performance of lithium metal secondary batteries, and is beneficial to enhancing the market application prospects of batteries, possessing significant practical production value.

[0037] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A method for preparing a lithium metal secondary battery anode containing an alloy protective layer prepared by physical deposition, characterized in that: A lithium-tin alloy thin film was deposited on the cut lithium strip surface using DC magnetron sputtering physical deposition. The tin content in the lithium-tin alloy was 1%~5%, and the thickness of the lithium-tin alloy protective layer was 30-50nm. The thickness of the lithium-tin alloy protective layer was controlled by controlling the magnetron sputtering deposition time, thus obtaining a battery negative electrode containing a lithium-tin alloy protective layer.

2. The method for preparing a lithium metal secondary battery anode containing an alloy protective layer prepared by physical deposition according to claim 1, characterized in that: Cut the lithium strip, press the copper tabs onto the lithium strip, place it on the magnetron sputtering sample stage, and set the chamber vacuum to 10. -4 Pa, turn on the DC power supply, and deposit a lithium-tin alloy thin film layer with a thickness of 30nm~50nm on the surface of the lithium anode by controlling the magnetron sputtering deposition time.

3. The battery anode containing a lithium-tin alloy protective layer prepared by the method for preparing a lithium secondary battery anode containing an alloy protective layer prepared by physical deposition as described in claim 1 or 2.

4. A lithium metal secondary battery, characterized in that: The negative electrode of a secondary lithium metal battery containing a lithium-tin alloy protective layer as described in claim 3.

5. The lithium metal secondary battery according to claim 4, characterized in that: Specifically, it is a lithium-lithium symmetrical button cell battery or a lithium metal secondary soft-pack battery.

6. The lithium metal secondary battery according to claim 5, characterized in that: The specific preparation method is as follows: Step 1: The positive electrode active material, conductive agent, and binder are uniformly dispersed in an appropriate amount of NMP solvent using a homogenizer; the uniformly dispersed slurry is coated onto an aluminum foil current collector to prepare a positive electrode, which is then rolled, slit, and die-cut to obtain the positive electrode sheet; Step 2: After cutting and fixing the lithium strip, use a hydraulic press to press the copper tabs onto the lithium sheet. Then, use DC magnetron sputtering physical deposition to deposit a lithium-tin alloy thin film on the surface of the cut lithium strip to obtain a negative electrode sheet containing a lithium-tin alloy protective layer. Step 3: Preparation of lithium-lithium symmetrical coin cell batteries: The coin cell spring sheet, coin cell pad, lithium anode with lithium-tin alloy protective layer, separator, electrolyte, and lithium sheet are placed into the coin cell casing in sequence to form a lithium-lithium symmetrical coin cell battery. Alternatively, a soft-pack battery can be prepared by repeatedly stacking lithium metal secondary battery electrode groups in the order of separator, lithium anode with lithium-tin alloy protective layer, separator, and positive electrode, injecting electrolyte, and then performing a formation and degassing process to produce a lithium metal secondary soft-pack battery.

7. The lithium metal secondary battery according to claim 6, characterized in that: The positive electrode active material includes 97wt% high-nickel ternary material, 1wt% conductive carbon black and 0.5wt% conductive carbon nanotubes as conductive agents, and 1.5wt% PVDF as binder, wherein the proportion of PVDF in NMP solvent is 5wt%.

Images