Synthesis And Electrochemical Properties Of Tin-Based Micro/Nano Structure Materials

Lithium-ion batteries（LIBs）,benefited of high energy density and good rate performance,are the most widely applied commercial energy storage devices,and especially have achieved tremendous success as power sources for small electronic devices,wearable electronic devices,and power tools.However,the expanding Lithium-ion battery market has brought about problems such as the shortage of lithium resources and the increase of cost,which would hinder the further development of LIBs.Sodium-ion batteries（SIBs）are emerging as a promising alternative to LIBs,owing to abundance in natural resources,low price as well as the similar energy storage mechanism to LIBs.Nevertheless,the larger radius of Na⁺than Li⁺makes that graphite,as the anode of commercial LIBs,exhibits poor rather than equally excellent electrochemical performance in SIBs system.Hence,it is crucial to develop high performance anode materials for promoting the commercial application of SIBs.The electrochemistry performance of existing anode materials of SIBs is hard to satisfy the demands of high specific capacity,long cycle life and high rate concurrently.Carbon anode materials have excellent cycle stability,but show low capacity.The alloy-based anode materials have high theoretical capacity thanks to alloy reaction mechanism,but cycle stability and rate performance are poor as a result of the severe volume expansion during the electrochemical cycle.Considering the different advantages of carbon and alloy-based anode materials,the composites of two type materials were prepared in this thesis.On the basis that the performance of carbon materials directly affects composite materials,various organic compounds were selected as carbon sources to obtain a series of carbon composite materials.The specific research work is as follows:（1）Sn/C composite was prepared based on Sn-MOFs precursor and subsequent heat treatment.Firstly,terephthalic acid（PTA）acted as the carbon source,and～1μm cubic particles（Sn/C-1）was prepared as anode of SIBs.Compared with tin electrode,cycle performance has improved slightly,and the capacity degradation is still serious.The capacity after 10 cycles decreases to 55%（0-2 V）and 45%（0-3 V）of the initial reversible capacity at 100 m A·g^-1.In order to enhance cycle stability,2-aminoterephthalic acid was selected as the carbon source to prepare～700 nm polyhedral particles（Sn/C-2）.The introduction of nitrogen could improve the conductivity of the composite,provide more defects and enhance the adsorption of Na⁺.The capacity and cycle performance improved slightly,but capacity degradation remained severe.The capacity after 10 cycles decreases to 73%（0-2 V）and 77%（0-3 V）of the initial reversible capacity at 100 m A·g^-1.（2）Replacing carbon source with tartaric acid（TA）,a composite of Sn particles confined in three-dimensional porous carbon framework（3D Sn@C）was synthesized by means of Na Cl template-assisted in-situ freeze-drying treatment and subsequent thermal reduction method as anode of SIBs.TA also affected as a complexing agent to coordinate with Sn⁴⁺.The well-interconnected porous honeycomb structure network could not only act as a buffer layer to alleviate structural degradation and restrain aggregation of tin particles,but also increase the effective contact area between electrode and electrolyte.The capacity fading remarkably reduced and cycle stability significantly enhanced.The capacity reduction was relatively obvious in first five cycles（only 90%of the initial reversible capacity was retained）,but the capacity remained stable in the subsequent cycles.（3）In order to achieve further higher cycle stability,introducing Sb element(TA could coordinate with Sn⁴⁺and Sb³⁺at same time and form stable complex),an efficient composite of Sn Sb alloy particles confined in three-dimensional porous carbon framework（Sn Sb@C）was fabricated with Na Cl template and subsequent thermal reduction method.The theoretical capacity of Sn Sb alloy is also considerable owing to high theoretical capacity of antimony result from Na–Sb alloying reaction.Based on the different sodium insertion potentials of Sn and Sb,Sn Sb alloy has self-buffering effect.Both metal element to each other could affect as buffering materials to alleviate the volume variation in electrochemical process.3D Sn Sb@C delivered a high initial reversible capacity of 457 m A·h·g^-1 at 100 m A·g^-1,and excellent cycling stability with capacity retention of 84%after 200 cycles（little capacity decrease after 5 circles）,showing great potential of high energy SIBs.