Preparation And Electrochemical Characteristics Of Cathode Catalysts For Li-Air Rechargeable Batteries

As a novel electrochemical energy storage device, rechargeable Li-Air(O2) battery has attracted great interest for its ultrahigh energy density up to 11400 Wh Kg-1(excluding the mass of O2),which is close to the energy density of gasoline about 13000 Wh Kg-1. The rechargeable Li-Air batteries based on organic electrolyte, as an important one of the Li-Air battery system, have attracted much attention and develope rapidly, recently.However, several challenging problems in the current rechargeable Li-Air battery system should be resolved before its practical use. Firstly, effective cathode catalysts are needed to realize the reversible reduction and generation(ORR and OER) of the oxygen in the Li-Air battery. Secondly, the problems in the anode, such as the instability of lithium metal and the lithium dendrites formed in the discharge-charge process, are needed to be resolved in the batteries. At Last, the stable electrolyte is needed to improve the cyling stability of Li-Air batteries.This paper mainly focuses on solving the problems in the cathode catalyst for the Li-Air battery, and the content of this paper are listed as follows:1) Preparation and electrochemical investigation of α-Mn O2 and α-Mn O2/Ni O cathode catalysts. The urchin’s spherical α-Mn O2 and α-Mn O2/Ni O materials were prepared by a simple liquid method in acid solutions. With the help of α-Mn O2 cathode catalyst, the first discharge capacity of Li-Air battery reached 950.6m Ah gcat.-1 at a current density of 0.2m A cm-2, and the capacity retention ratio was about 56% after 3rd discharge-charge cycle. Furthermore, under the same condition, the α-Mn O2/Ni O cathode catalyst displayed better cycling stability than that for α-Mn O2 cathode catalyst; After 8th discharging-charging cycle the capacity retention ratio of the batteries with α-Mn O2/Ni O catalyst was 32.3%, higher than 8% for α-Mn O2 cathode catalyst. The Ni O component can be favorable to the ORR and OER process due to its 3D track structure, which improves the electrocatalytic activities of α-Mn O2/Ni O cathode catalyst. However, the low discharge capacity, poor rate capacity and cyling stability of the α-Mn O2 and α-Mn O2/Ni O catalyst limit their application in the Li-Air battery.2) Preparation and electrochemical investigation of nanofibrous Mn Ni/CNF cathode catalyst. In order to further improve the electrochemical performance of the batteries, Mn Ni/CNF(Mn O-Ni/CNF) cathode catalyst was prepared by electrospun technique. It was found that the Mn Ni/CNF cathode catalyst displayed a discharge capacity of 3850 m Ah gcat.-1 in the first discharging-charging cycle at 0.1m A cm-2 current density, and the capacity retention ratio was about 70% after 8th cycle, which was much better than that for the α-Mn O2 and α-Mn O2/Ni O cathode catalysts. The excellent catalytic activity of Mn O-Ni component, superior electronic conductivity of metal Ni and carbon fiber in the Mn Ni/CNF composite have greatly improved the electrochemical performance of Li-Air batteries. However, the rate capacity, cycling stability and energy efficiency of the batteries based on Mn Ni/CNF catalyst, are still needed to be improved before practical use.3) Preparation and electrochemical investigation of porous nanofibrous Co O/CNFs cathode catalyst. The Co O/CNFs cathode catalyst was prepared by electrospun technique and controlled thermal treatment. With the help of the Co O/CNFs cathode catalyst, the rate capacity and cycling stability are much better than that for the Mn Ni/CNF catalyst, and the capacity retention ratio was above 85% after 8th cycle at a current density of 0.2 m A cm-2. More importantly, the cycling stability of Co O/CNFs based Li-Air battery can be maintained over 50 cycles at a fixed discharge-charge capacity of 1000 m Ah gcat.-1. The RDE and BET test results demonstrate that the excellent catalytic activity of Co O component and superior electronic conductivity of carbon fiber, as well as the unique porous structure in the Co O/CNFs composite has greatly improved the electrochemical performance of Li-Air batteries. However the low discharge capacity about 3882.5m Ah gcat.-1 still needs to be improved before the practical application of Li-Air batteries.4) Preparation and electrochemical investigation of Co-Co O/r GO(Graphene) cathode catalyst. The Co-Co O/r GO cathode catalyst was prepared by solution self-assembly method and hydrothermal treatment. With the help of the Co-Co O/r GO cathode catalyst, the first discharge capacity of Li-Air battery reached 6841.1 m Ah gcat.-1 at a current density of 0.2 m A cm-2, and the capacity was maintained about 3896.7 m Ah gcat.-1 after 8th discharge-charge cycle, which was much better than that for the Mn Ni/CNF, Co O/CNFs and r GO cathode catalysts, Furthermore, the cycling stability of Co-Co O/r GO based Li-Air battery can be maintained over 30 cycles at fixed capacity of 1000 m Ah gcat-1. The dimension tuning of Co and Co O, as well as the synergistic effects among Co, Co O and r GO(G-metal) are the main factors to improve the electrocatalytic activity of Co-Co O/r GO catalyst. The electrochemical tests, such as CV and RDE test, demonstrate that Co-Co O/r GO is an effective cathode catalyst for the Li-Air battery.