Micro/Nano Structure Manipulation And Electrochemical Performance Of Sn-Based Chalcogenide Anodes For Lithium/Sodium-ion Batteries

Lithium-ion batteries?LIBs?have the advantages of high energy density,long cyclic life and etc.,and have been widely applied in mobile electronic devices and electric vehicles.However,with the development of new energy storage devices,such as electric vehicles and large-scale energy storage stations,it is necessary to develop the next generation electrode materials to improve the overall performance of LIBs.On the other hand,with wide application of those devices,the lithium resources will be excessively consumed,and the price of lithium resources rises continuously.Thus,the sodium-ion batteries?SIBs?,having the advantages of abundant resources and low cost,have attracted increasing attentions.However,the commercial application of SIBs also depends on high-performance electrode materials.As one of the key components of LIBs/SIBs,the anode can significantly influence the overall electrochemical performance.Sn-based chalcogenides?Sn_aX_b,X=O,S,Se?,delivering high theoretical capacities through combination of conversion and alloying reactions,have been considered as one of the most promising anode materials for LIBs/SIBs.However,the realization of high-performance Sn-based chalcogenide anode has been hindered mainly by the low electric conductivity,large volume change by Li/Na intercalation,and inferior reversibility.Herein,we focus on the micro-nano structural design and fabrication of Sn-based chalcogenide composites to improve the electrochemical performance,and a series of anode materials of high electrochemical performance have been obtained by simple plasma milling?P-milling?.The main results are as follows:First,the?SnO_x-Sn?@FLG composite were synthesized by using Sn powder and expanded graphite?EG?as raw materials via oxygen plasma milling.Owing to the synergistic effect of rapid plasma heating and ball mill grinding,SnO₂ nanoparticles were generated from the reaction of Sn with oxygen and were tightly wrapped by the few-layer graphene?FLG?which is simultaneously exfoliated from EG.Furthermore,compared with the conventional milling,the P-milling shows unique advantages in preparing the SnO₂/C composite:The SnO₂nanoparticles,in-situ formed by P-milling,have characteristic of small size,which can offer more active sites for sodium storage;The P-milling can effectively exfoliate the EG to conductive FLG matrix,which can not only improve the electrical conductivity of composite and enable the fast kinetics for Na⁺transfer,but also alleviate the volume change of SnO₂ and inhibit the disintegration of electrode during cycling.Second,based on the above work,the SnSe/FLG and SnS/FLG composite were in-situ synthesized by replacing oxygen with selenium and sulfur,as high-performance anodes.For the SnSe/FLG system,the P-milling can not only more effectively exfoliate the EG to FLG,but also induce more carbon vacancy defects in the carbon matrix compared with the conventional milling,which leads to the forming of Sn-C and Se-C co-bonding.The co-bonding can enable the strong affinity between SnSe nanoparticles and FLG matrix,preventing SnSe from aggregating and detaching even after long-term cycling.As anode for LIBs,the SnSe/FLG composite exhibits ultra-long cyclic life,with a high capacity retention of 92.8%after 2000 cycles,corresponding to the capacity decay of only 0.0036%per cycle.As anode for SIBs,it shows a high capacity retention of 91.6%after 1000 cycles.For the SnS/FLG system,the combination of microstructure and nanostructure can promote the volumetric capacity of electrode without sacrificing the rate capability and cycling stability.The microsized secondary granules enable the SnS/FLG composite a high tap density up to1.98 g cm^-3,which leads to a high volumetric lithium/sodium storage of 1926.5 mAh cm^-3/1051.8 mAh cm^-3.Inside the nanosized building blocks,the combination of SnS nanoparticles and conductive FLG matrix can not only enhance the overall electron and ion conductivity,but also effectively accommodate the large volume expansion of SnS,and thus improve the rate performance and cycling performance of electrode.As SnS shows better prospects for application compared with other Sn-based chalcogenide anodes,which is demonstrated by its better initial coulombic efficiency than SnO₂ and SnSe,and the nontoxic and environmentally friendly synthesis shown above.Therefore,the multi-phase structured?SnS-SnS₂-S?/FLG composite anode was created,based on the result on SnS/FLG,to achieve the ultra-long cyclic life?thousands of cycles?of SnS.The step-wise electrochemical reactions of S,SnS₂ and SnS can offer nano-spatially confined effects to accommodate the volume expansion and particle aggregation of SnS.Meanwhile,the FLG matrix can serve as a robust layer to further maintain the structural stability of electrode.On the other hand,the high-density grain/phase boundary in the multi-phase structure can not only offer substantial active site for the ion and charge storage,but also shorten the ion diffusion length and facilitate the ion diffusion.As anode for LIBs,the?SnS-SnS₂-S?/FLG composite shows ultra-high rate(842 mAh g^-1 and 756 mAh g^-1 even at5.0 A g^-11 and 10.0 A g^-1)and ultra-long cyclic life(almost no capacity fading after 1000 cycles at 1.0 A g^-1 and 10.0 A g^-1).As anode for SIBs,it also demonstrates superb comprehensive performance.Finally,aiming at settling the inferior cycling reversibility of SnS,the SnS/Mo/FLG composite was successfully synthesized by P-milling,and the crucial role of transition metal Mo was revealed for the electrochemical process of composite:The Mo can act as inactive matrix to alleviate the large volume expansion of SnS,and inhibit the breakdown of Sn/Li₂S structure and the agglomeration of Sn grains,thus enables highly reversible conversion reaction during cycling.As anode for LIBs,at the current density of 0.2 A g^-1,the SnS/Mo/FLG composite exhibits a high initial reversible capacity of 1125.6 mAh g^-1,high initial coulombic efficiency of 86.1%,and high capacity retention of 1045 mAh g^-1 after 200cycles.Even at the high current density of 1.0 A g^-1,it still maintains high capacity retention of 830 mAh g^-1 after 600 cycles.As anode for SIBs,it also demonstrates excellent cycling reversibility and stability.