| With the change of the times,various types of new energy storage systems are gradually put into use.With the rapid development of electric vehicles and large-scale energy storage systems,research and development of a new generation of batteries with high energy density has become an urgent task.Among many battery anode materials,sodium metal anodes are considered as the ideal next-generation anode materials due to their lower redox potential and higher capacity.However,sodium metal has high reactivity and is easy to react with the electrolyte.In addition,sodium metal anode will generate sodium dendrites during the cycle of the battery.The generation of sodium dendrites will cause the battery capacity to decrease and the volume to expand,which may cause the battery to explode and cause safety hazards.The generation of sodium dendrites is also the most prominent problem of sodium metal anodes at present,which greatly hinders the practical application of sodium metal batteries.Studies have shown that constructing a stable and uniform artificial solid electrolyte interphase is an effective method to improve the generation of sodium dendrites.Based on the idea,this paper studies the effect of copper current collectors with double-layer protective layers on the performance of sodium metal anodes.This article uses a simple and easy-to-operate spin coating method to prepare two different protective layers on the surface of a commercial copper current collector.The bottom layer is an Al2O3 layer and the top layer is a PVDF polymer layer(referred to as Cu@APDL).For the double-layer composite protective layer,the underlying Al2O3 layer has a high hardness,which can effectively inhibit the growth of sodium dendrites.The flexible PVDF layer on the top layer can alleviate the volume change of the anode.The two protective layers work together to protect sodium metal anode.In this paper,the ratio of raw materials and the speed of spin coating were screened.After testing,Al2O3: PVDF = 4: 1 is the best ratio,and 4000 rpm is the best speed.However,the copper current collector modified by the one-step spin coating method has the problem of uneven surface.In this paper,the spin coating method is optimized.Compared with the blade coating method and the one-step spin coating method,the two-step spin coating method is the best coating method.The copper current collector modified by this method has a uniform surface and excellent cycle performance.In this paper,the electrochemical performance of a copper current collector(Cu@APDL)with a double-layer composite protective layer modified by a two-step spin coating method is investigated.Under the capacity of 1 m Ah cm-2 and the current density of 1 m A cm-2,Cu@APDL can stably cycle up to 1600 hours,and its cycle life is far longer than that of copper current collector.In addition,under high current density(5 m A cm-2),Cu@APDL can be stably cycled for nearly 400 hours.In the test of Coulomb efficiency,after the Cu@APDL was circulated over 600 times at a current density of 1 m A cm-2,its Coulomb efficiency was still maintained at 99.88%.In this paper,by testing the Cu@APDL current collector after cycling,the protective mechanism of the double-layer protective layer on the current collector was explored.After 50 cycles,the solid electrolyte interphase of Cu@APDL is mainly composed of Na2CO3,Na F,Na2 O,and ROCO2 Na.A variety of inorganic components greatly improve the density and rigid modulus of the solid electrolyte interphase,which can effectively protect the sodium anode and improve battery performance.The modification process of the Cu@APDL current collector is easy to operate,and the Cu@APDL current collector exhibits excellent electrochemical performance,which highlights the advantages of the modification strategy of using the spin coating method to build a double protective layer and provides a new method to protective sodium metal anode. |
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