| Research and development of large-scale electrical energy storage systems are vitally important for the utilization of renewable energies and smart grid.Sodium-ion batteries?SIBs?show great promise due to the abundant sodium resources and low cost.So far,a variety of electrode materials have been investigated for SIBs,such as hard carbon and alloys as anode materials;layered metal oxides,polyanion compounds as cathode materials.However,there are still several problems need to be conquered before their commercialization.For layered transition metal oxides cathodes,although they exhibit high specific capacity,most of these materials are not stable against moisture and display multiple redox charge/discharge plateau due to the successive phase transformations.These behaviors undoubtedly increase the storage cost and lead to capacity fading.A post spinel-type NaMn2O4 shows an ultra-stable cycle performance both at room temperature and 55°C,but the synthesis conditions are harsh and the capacity is low.Therefore,the systematic research is urgently needed regarding to explore facile synthesis methods,enhance the air stability and structural stability of these materials.Among anode materials,the tin-based alloy type anode is attractive due to its high theoretical capacity of 847 mAh g-1 in SIBs.However,the Sn-based anodes experience severe volume expansion and low conductivity.Therefore,overcome the volume expansion and improve the conductivity are vitally important for alloy electrodes.In this paper,to address these challenges,we have done the following studies:Firstly,we fabricated a TiMn mixed oxides and studied its air storage performance.The effects of different synthetic methods,the proportion of elements and the sintering temperature on the structure and properties of the materials have been studied.The experimental results show that the materials synthesized by sol-gel method with Na:Mn:Ti=1:1:1 and calined at 750?have good electrochemical performance and air stability.The titanium element plays a critical role in both positive and negative electrodes,i.e.,served as electrochemical active center during the low voltage window when using as anode,it also enhanced the structural and cycling stability when using as cathodes;Secondly,Na4Mn4Ti5O188 has been synthesized under ambient pressure by using solid state method,which have high stability and cycle performance.The structure,morphology and electrochemical properties of the materials were characterized by XRD,ICP,SEM,XPS and charge/discharge tests.It demonstrated a specific capacity and cycle stability.It delivers a charge/discharge capacity of 261.2/131.9 mAh g-1.After 200 repeated cycles,the capacity was still 132.4/130.0 mAh g-1.Both of the capacity and stability have been improved compared with the previous reports.The introduction of Ti stabilized the cathode structure during cycles.Finally,a novel CuSn alloy composite with three-dimensional nanoporous structure was prepared by the dealloying method.The as-prepared nanoporous CuSn alloy composite delivers a capacity of 573.2 mAh g-1.After 100 repeated cycles,the capacity was still 233.2mAh g-1.This result is much superior to that of pure Sn particles,and the nanoporous structure is well maintained after discharge.The bi-continuous structure promotes the electrolyte permeation and accommodates the volume expansion.The Cu components enhance the conductivity of the electrode composite. |
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