| Lithium-ion batteries(LIBs)have been branded one of the most promising electric energy storage systems(ESSs)because of their long cycle life,high energy density and operation voltage.Nevertheless,with the widespread application of LIBs all over the world in recent decades,lithium resources are faced with the risk of drying up,which has turned current research focus towards high safety,cost-effective and environmental-friendly beyond-LIBs systems.Aluminum-ion batteries(AIBs)have lately aroused great concern among researchers because aluminum owns advantages including rich reserves,low cost,unrestricted distribution and high stability compared with lithium.Moreover,Al can transmit three electrons during the redox reaction and provide ultrahigh volumetric capacity(8.05 Ah cm-3),which is roughly four-fold and two-fold than that of monovalent lithium(2.06 Ah cm-3)and divalent magnesium(3.83 Ah cm-3),respectively.Hence,it is reasonable to conclude that the AIBs will have a great application prospect and value in use for large-scale smart grid energy storage systems and car batteries that prone to have the risk of collision and explosion.However,the development of AIBs is now confined by cathodic performance such as low capacity and insufficient cycling stability,hence finding a high-performance cathode material for AIBs and exploring the electrochemical reaction mechanism are of vital importance.In this work,the morphology,phase structure and electrochemical performance of Li3VO4@C and Cu2-xSe were intensively investigated by a series of physical and electrochemical characterizations.Moreover,an extensive research was dedicated to investigating the detailed electrochemical reaction mechanism of Al/Li3VO4@C battery and Al/Cu2-xSe battery,which can solidly enrich the in-depth understanding of the electrochemical process of rechargeable AIBs.The main results are listed as follow.(1)The mesoporous Li3VO4@C and Li3VO4 hollow spheres were prepared by a spray drying process and succeeding heat treatment in argon atmosphere.It is concluded that the Li3VO4@C electrode exhibits better electrochemical performance.The initial discharge capacity is 137 mAh g-1 and remains at 48 mAh g-1 after 100 cycles with the Coulombic efficiency of near 100%.It may attribute to the structural superiority of Li3VO4@C composite,the carbon layer covered the spheres not only can promote the electronic conductivity of material but can regulate the size of sphere particles,furthermore,the geometric structure of mesoporous hollow sphere can enlarge the contact area between electrolyte and active material and reduce the ion diffusion distance.On the other hand,the detailed intercalation mechanism of Al3+ into the orthorhombic Li3VO4 was characterized by several ex-situ measurements,and the first-principle calculations also elucidated Al3+ mainly inserts into a-site of Li3VO4,and there were scarcely any structural changes after intercalation.(2)One dimensional Cu2-xSe nanorods material was fabricated by a facile water evaporation process.The Cu2-xSe electrode manifests excellent electrochemical performance,the initial charge capacity is 241 mAh g-1 even at high current density of 200 mA g-1 and maintains a high reversible capacity of 100 mAh g-1 after 100 cycles with a coulombic efficiency of 96.1%.The prominent electrochemical performance can be attributed to the ultrahigh electronic conductivity,the large enough cell volume and one-dimensional structure of Cu2-xSe.Besides,the electrochemical reaction mechanism of the Cu2-xSe/Al battery also had been intensively investigated.It is reasonable to conclude that primarily AICl4-ions are intercalated and de-intercalated in the tunnel structure of Cu2-xSe during the charge/discharge processes,and the redox reactions rely on the conversion between Al2Cl7-and AlCl4-. |
PDF Full Text Request