Preparation And Investigation Of Key Materials For Lithium/Air Batteries Application

Rechargeable Lithium-air(or Li/O2) batteries have been considered a promising power source candidate due to their impressive high theoretical energy density(11,400 Wh kg-1 based on the mass of active materials, O2), which is 5~10 times higher than the conventional lithium ion batteries. However, the development of lithium-air batteries are still in their infancy stage and many scientific and technological challenges and obstacles must be addressed before its practical application, including, the unstable catalytic electrode structure, liquid electrolyte solvent volatility, and the corrosion and passivation of lithium anode etc.To address above issues, we launched a series of research works for the Li/O2 battery, including, i) the development of a novel polymer gel electrolyte and applied in li/O2 battery, and systematicly investigated the correlation between material structure and the battery performance; ii) the design and construct of a series of high effective/stable catalytic materials and evaluated their ORR/OER properties and cell performance. Moreover, we further investigated the correlation between materials structure and their catalytic activity, and explored the working mechanism of Li/O2 battery by all kinds of characterization techniques. The details of the works and the important results are described as below:Firstly, we developed a novel polymer gel electrolyte membrane(PGE) based on a blend of cellulose acetate(CA) and P(VDF-HFP) using a solution casting technique followed by impregnation with liquid electrolyte solution, and investigated the performance of Li/O2 battery with PGE. It was found that the PGE membrane has good electrolyte uptake and shows high ionic conductivity as well as excellent electrochemical stability, and low air permeability compared with the conventional liquid electrolyte(LE) system assembled with commercial PE separator. Furthermore, a Li/O2 battery based on PGE exhibits superior cycling stability compared to a battery using LE system under the same testing conditions. The enhanced cycling performance of PGE battery was verified by SEM analysis, which maybe restrain the diffusion of oxygen from the air cathode to corrode and passivate the Li metal anode. In a word, this study may provide a promising pathway for resolving the problem of oxygen crossover in Li/O2 batteries which result in lithium metal anode corrosion and passivation.Secondly, inspired by the concept of “carbon/binder-free electrode” design, we constructed and prepared a 3D, porous Co3O4 nanowire clusters decorated with Pd nanoparticles(Pd/Co3O4/NF) cathode and used in Li/O2 battery, which exhibited excellent low polarization and superior cycling performance. The catalytic cell can operate stably for 240 cycles(1280 h, with a fixed capacity of 500 mAh g-1 at 0.1 mA cm-2) with terminal charge voltage below 4.2 V all through battery cycling, and significantly better than the previous reported Li/O2 cell performance with Co3O4 catalyst. Verified the morphology, structure and composition of different states cathodes employed with SEM/XRD/XPS, we found that its enhanced electrochemical performance may be attributed to(i) the homogeneous distribution of Pd nanoparticles on the surface of Co3O4 nanowires, which could tailor the structure and morphology of the formation of Li2O2 on the Pd/Co3O4/NF cathode to facilitate the decomposition of Li2O2 and finally improve the rechargeability;(ii) employed with the free-standing Pd/Co3O4/NF electrode can effectively avoid the degradation reaction of carbon/binder-induced, thus leading to battery performance decline.Thirdly, we synthesized an ultrafine LiMn2O4(LMO) nanoparticles homogeneously grown on nitrogen-doped reduced graphene oxide nanosheets(N-rGO) via a one-step hydrothermal treatment. Due to the large surface area and high electronic conductivity of N-rGO and a synergetic effect from the spinal LMO nanoparticles and N-rGO, the LMO@N-rGO catalyzed cell possessed superior cycling stability(obtained 6005 mAh g-1 after 4 cycles with capacity retention ratio of 93.7%) than that of N-rGO catalyst at 375 mA g-1 with voltage between 2.0 and 4.4 V. In addition, a uniformly dispersed Pd or bimetallic PdM(M = Fe, Co, Ni) alloy nanoparticles in-situ anchored on N-rGO was prepared by a NaBH4 reduction method, and act as an efficient bifunctional catalyst for ORR/OER in Li/O2 battery. Because of the change in the electronic properties of Pd by alloyed with the cheap transition metal, which lead to a strong interaction between PdM and N-rGO supporter, and the as-prepared PdM/N-r GO catalysts exhibited greatly enhanced activity and stability. It was found that the PdFe/N-r GO catalyzed battery can significantly maintained long time stable cycling(400 cycles, 2000 h) with a limited capacity of 1000 mAh g-1 at 400 mA g-1.Finally, we firstly fabricated 3D ordered, porous TiN nanorod arrays through the nitridation of TiO2 nanorod arrays on carbon fiber paper(CP), which is the oxide arrays were synthesized by a hydrothermal process. Then, we modified the nitride arrays by loading manganese oxide nanosheets or Ir nanoparticles. The batteries with two kinds of modified nitride arrays as cathode exhibited excellent cycling stability, which is much superior to that of the battery with commercial Pt/C catalyst as cathode. With a controlling capacity of 500 mAh g-1 at a current density of 100 mA g-1, the TiN@MnO2/CP and TiN@Ir/CP-based batteries can operate stably 200 cycles for 2000 h, respectively. The excellent cycling performance of modified cathodes could be ascribed to:(i) the highly stable TiN nanorod arrays supporter decorated with MnO2 nanosheets or Ir nanoparticles catalysts has large open space and high surface area,(ii) providing abundant lithium ion and oxygen transport path and favorable catalytic activities for the formation and decomposition of Li2O2. In addition, we explored the effect of LiI additive with different concentration in electrolyte on the performance of Li/O2 battery and found that the addition appropriate amount LiI(~0.05 M) in electrolyte can obviously decrease discharge/charge overpotentials and restrain lithium metal corrosion and improve cell cycling(or rechargebility) stability.