Al³⁺/Cl^- Hybrid Battery And Its Cathode Materials

Rechargeable aluminium-based batteries are considered to be promising new energy storage devices because of their high specific capacity,low cost and high safety.Among the numerous cathode materials reported for aluminum-based batteries,graphite,graphene,and conductive polymers were those exhibit better electrochemical performance.Typically,the electrolytes used are electrochemical stable ionic liquids.Moreover,the charge carriers are much complex than the state-of-the-art lithium ion batteries in which Li⁺is the only charge carrier shuttling between anode and cathode:it is AlCl₄^-ions that intercalates into/deintercalates from the cathode materials,while Al₂Cl₇^-ions play the decisive role in the process of aluminum deposition/stripping at the anode.From this perspective,rechargeable aluminium-based batteries using graphite,graphene,conductive polymers cathode materials can be considered as hybrid batteries.Therefore,hybrid aluminium-based batteries are expedient way to solve the dilemma of rechargeable aluminium-based batteries.Considering the high content of Cl^-ion in the electrolyte solutions of rechargeable aluminium-based batteries,we try to construct a novel hybrid battery,namely Al³⁺/Cl^-hybrid battery.The main work of this thesis is summarized as follows:Firstly,the concept of Al³⁺/Cl^-hybrid ions battery?ACHB?is proposed,which works on the bases of the reversible deposition/stripping of Al at the anode and intercalation/de-intercalation of Cl^-at the cathode.BiOCl,a typical cathode material for chloride ion battery,was chosen here to demonstrate the working principle of ACHB.BiOCl particles were ball-milled uniformly dispersible to beneficial to the movement of chloride ions.The molar ratio of AlCl₃to[EMIm]Cl in the ionic liquid electrolyte was set to 1.3:1.The electrochemical performance of ACHB were then tested.At the rate of 0.05 C,the initial specific discharge capacity of Al/BiOCl battery reached to 142 mAh g^-1,which was much higher than its theoretical value.Two stable discharge platforms were observed near 1.0 V and 0.8 V.Intensive studies on the element compositions of the BiOCl electrode were carried out by energy spectrometer?EDS?.EDS measurements revealed the shuttle of Cl^-ions in the BiOCl electrode during discharge and recharge.It was also tested by tracing the oxidation state change of Bi element in BiOCl electrode.XPS results prove the feasibility of our ACHB.Secondly,in spite of the discharge capacity as high as 142 mAh g^-1,BiOCl delivered a large irreversible capacity and showed poor cycle performances.So another attempt was made by using MCl_x-GICs as the cathode material of Al³⁺/Cl^-hybrid batteries.As is known to us,MCl_x has a high theoretical chloride ion storage capacity,and is low-cost,readily available,and environmentally benign.However,as Lewis acid,it can react with the chloride ions in the electrolyte solutions and generate soluble complex ions,leading to the loss of active materials and capacity fade.MCl_x-GIC is of regularly stacked structure where MCl_x is sandwiched by a certain number of graphene layers.Graphene layers can provide unique electronic conductivity and buffer the volume change of MCl_x during chlorination.CuCl₂-GIC was used as the first example to study the chloride storage performance of MCl_x-GIC.CuCl₂-GIC was synthesized at 528 ^oC in vacuum.Galvanostatic charge-discharge tests demonstrated MCl_x-GIC owned much better cycling stability and rate capability compared with pure MCl_x cathode materials.By means of XPS,the valence change of Cu element in the CuCl₂-GIC electrodes was traced.The chloride storage behavior of CuCl₂-GIC was first proved,which also further proved the practicability of ACHB.