| The growing exhaustion of fossil fuels as well environmental concerns leads to high attraction for renewable energy sources such as wind and solar energy systems.The utilization of these renewable energy sources is highly dependent on the availability of large-scale energy storage system（ESS）.In the last few decades,lithium ion batteries（LIBs）have played an important role in devices such as portable electronic devices and electric vehicles.However,the rareness of lithium source and its high cost greatly limit the large-scale application of LIBs.Nowadays,sodium ions batteries（NIBs）are considered as one of the most important next-generation rechargeable batteries due to earth abundance,cost-effectiveness and widespread reserves of sodium salt.In the last few years,many achievements have been made for NIBs.However,advanced electrode materials of high performance and low cost are still the key factor to impede the practical application of NIBs.For anode materials,although graphite can be efficiently used in LIBs,it can hardly deliver high capacity in NIBs.Therefore,one of the most important research topic of electrode materials is advanced,high-performance anode materials.Alloy-type materials are able to meet the requirements of high capacity,low cost,low pollution as well as others,and thus can be used as high-performance anode materials in NIBs,showing great potential in research and future application.Among various advanced anode materials,phosphorous（P）,tin（Sn）etc.have very high theoretical capacity.However,problems including high volume expansion,low conductivity and so on lead to the poor cycling performance of such materials.To efficiently improve the overall electrochemical performance of these materials,many strategies can be used including:（1）.Preparation of alloy anodes to change the physical/chemical performance of the materials;（2）.Controlling crystalline domain structure,spacial relationship between components and interface structures;（3）.Preparation of composites to improve the conductivity and impress the volume expansion.In this Doctoral thesis,we focused on the phosphorous based anode materials,applied the strategies together,and developed several series high-performance anode materials,as listed below.（1）By using low-cost high-energy ball milling approach,SiP2 and SiP2/C composite materials have been made.By controlling the milling parameters,the SiP2 crystallites can be well prepared and tuned,the crystallites can be well dispersed in the super P carbon,and the tight interface structure can be obtained.As a result,the conductivity of the composite was greatly enhanced,and the volume expansion of SiP2 was largely compressed,leading to the improved cyclability in the sodiation/desodiation reaction.The overall performance of the materials,especially the long cycle performance,was thus greatly improved.Furthermore,various ex-situ/in-situ techniques were applied to monitor the structure transformation of SiP2/C composite in the electrochemical reaction,and the reaction products of Na3P and NaSi6 were confirmed.（2）By using high energy ball milling techniques,Sn4P3 crystallites have been synthesized.Further, by using composition approach with carbon materials and tuning the structure transformation of Sn4P3 using milling rotation rates,a series of binary Sn4P3/C,quaternary Sn4P3/Sn/P/C and ternary Sn/P/C composites have been made.The crystalline domain/amorphous structure distribution of active materials was thus been produced in these materials.Electrochemical test showed that the quaternary Sn4P3/Sn/P/C composites have the best electrochemical performance.Analysis including in-situ XRD demonstrate that the co-existence and tuning of multiple active materials,the spacial configuration of crystalline domain distribution in amorphous P materials are key factors for the high performance of the quaternary Sn4P3/Sn/P/C composites.It showed that tuning the local structure of anode materials is an efficiently strategy for enhancing the electrochemical performance.（3）A series of Sn/P/C composites was prepared using high energy ball milling techniques by tuning the ratio of P,Sn and C.It was found that the different ratios can be used to tune the amorphous structures and ratios/spacial distributions of active materials.By using multiple structure analysis and electrochemical test,the influence of material ratios and structures on the electrochemical performance was investigated.Furthermore,by using in-situ characterization techniques,the Na storage mechanism was revealed.Based on the above studies,we systemically established the low-cost and efficient synthesis and composition techniques of P-based materials including P-Si,P-Sn and Sn-P-C alloy materials.By tuning the crystalline/amorphous structure,size control and spacial distribution,tight interface structure and so on,the electrochemical performance of these materials have been efficiently improved.Further,by using diverse in-situ/ex-situ characterization techniques,the structural evolution of anode materials in the electrochemical reactions was monitored,and the reaction mechanism was revealed.The studies provide important insights into the development of high-performance alloy anode materials for secondary batteries. |
