Palladium-Filled Carbon Nanotubes Cathode for Improved Electrolyte Stability and Cyclability Performance of Li-O₂Batteries

Abstract

Li-oxygen (Li-O 2 ) cathodes using palladium-coated and palladium-filled carbon nanotubes (CNTs) were investigated for their battery performance. The full discharge of batteries in the 2-4.5 V range showed 6-fold increase in the first discharge cycle of the Pd-filled over the pristine CNTs and 35% increase over their Pd-coated counterparts. The Pd-filled also exhibited improved cyclability with 58 full cycles of 500 mAh · g −1 at current density of 250 mA · g −1 versus 35 and 43 cycles for pristine and Pd-coated CNTs, respectively. In this work, the effect of encapsulating the Pd catalysts inside the CNTs proved to increase the stability of the electrolyte during both discharging and charging. Voltammetry, Raman spectroscopy, FTIR, XRD, UV/Vis spectroscopy and visual inspection of the discharge products using scanning electron microscopy confirmed the improved stability of the electrolyte due to this encapsulation and suggest that this approach could lead increasing the Li-O 2 battery capacity and cyclability performance. High energy density batteries have garnered much attention in recent years due to their demand in electric vehicles. Lithium oxygen (Li-O 2 ) batteries have nearly 10 times the theoretical specific energy of common lithium-ion batteries and in that respect have been regarded as the batteries of the future. and other forms of carbons 13,14 have been commonly used as cathode materials in Li-O 2 batteries. Among carbon-based materials, carbon nanotubes (CNTs) have been widely used in Li-O 2 cathodes due to their high specific surface area, good chemical stability, high electrical conductivity, and large accessibility of active sites. 15,16 Zhang et al. reported one of the early uses of CNT (single-walled) as cathode materials in Li-O 2 batteries in which discharge specific capacities as high as 2540 mAh · g −1 were obtained at 0.1 mA · cm −2 discharge current density.8 Although many research studies have been done to improve the performance metrics of Li-O 2 batteries, they are still in their early stages and many technical challenges have to be addressed before their practical applications. 17,18 The most common problems impeding the development of Li-O 2 batteries have been low rate capability, poor recyclability and low round-trip efficiency.19,3 All of these issues are originally stemmed from sluggish kinetics and irreversible characteristic of the OER and ORR reactions which causes high overpotentials in discharging/charging process. Hence, increasing the efficiency of OER/ORR reactions and minimizing the overpotentials during the = These authors contributed equally to this work. 21 Alternatively, the use of different noble metals and metal oxide catalysts has also been integrated in the cathodes of Li-O 2 batteries. [22][23][24][25] The catalyst may influence the performance of Li-O 2 batteries by destabilizing the oxidizing species which decreases the charging overpotential.26,27 They may also increase the surface active sites and facilitate charge transport from oxidized reactants to the e...

Poly(Ionic Liquid)‐Based Composite Gel Electrolyte for Lithium Batteries

“…A number of research has been going on to replace the electrolyte with a non‐flammable, both chemically and thermally stable electrolyte . Polymer electrolyte (PE) as electrolyte shows a safer route to LIB technology as there is no issue of leakage, flammability, chemical instability problems as associated with liquid electrolyte . PEs for LIBs mainly consist of a polymer dissolved in a high concentration of lithium salts.…”

“…[8] Polymer electrolyte (PE) as electrolyte shows a safer route to LIB technology as there is no issue of leakage, flammability, chemical instability problems as associated with liquid electrolyte. [9][10][11] PEs for LIBs mainly consist of a polymer dissolved in a high concentration of lithium salts. Although PEs have advantages over liquid electrolytes, poor room temperature ionic conductivity (~10 À 8 À 10 À 5 S cm À 1 ) due to ion diffusion restrictions causing a major problem for them to be applied in LIBs.…”

Hybrid Polymer Electrolyte for Lithium-Oxygen Battery Application

“…Therefore, stabilizing the cathode-electrolyte interfacial resistance contributed to improving the charge capacity of cGPE-1% over GPE and cGPE containing cells, as can be observed in voltage profiles of Figure 3-11. Moreover, it is noteworthy that the poor rechargeability of all Li-O2 batteries using GPE and cGPEs (Figure 3-10) was mainly due to the low OER activity of MWCNT cathodes as previously observed [88,129]. Various catalysts and redox mediators have been proposed to improve the OER and rechargeability of Li-O2 batteries [130,131].…”

“…As mentioned earlier in this dissertation, the Li-O2 batteries suffer from poor cyclability due to the reactivity of lithium anode with oxygen crossover, cathode decomposition, and electrolyte evaporation and decomposition [11,22,30,46,[86][87][88]. Electrolyte decomposition has been previously reported to yield the formation of solid by-products covering gradually the surface of electrodes and causing rapid capacity fading in Li-O2 batteries [31,48].…”

“…According to recent reports, the electrolyte remains as the leading cause for rapid capacity fading and poor cyclability in Li-O2 batteries [136][137][138]. Commonly carbonate-based solvents used in Li-ion batteries have been shown to be unstable during the ORR process [47].…”