Examining the Role of Electrolyte and Binders in Determining Discharge Product Morphology and Cycling Performance of Carbon Cathodes in Li-O₂Batteries

Abstract

In this report we examine the influence of electrode binder and electrolyte solvent on the electrochemical response of carbon based Li-O 2 battery cathodes. Much higher discharge capacities were noted for cathodes discharged in DMSO compared to TEGDME. The increased capacities were related to the large spherical discharge products formed in DMSO. Characteristic toroids which have been noted in TEGDME electrolytes previously were not observed due to the low water content of the electrolyte. Linear voltage sweeps were used to investigate ORR in both of the solvents for each of the binder systems (PVDF, PVP, PEO and PTFE) and related to the Li 2 O 2 formed on the cathode surfaces. Galvanostatic tests were also conducted in air as a comparison with the pure O 2 environment typically used for Li-O 2 battery testing. Interestingly, tests for the two electrolytes showed opposite trends in terms of discharge capacity values with capacities increased in TEGDME (compared to those seen in O 2 ) and decreased in DMSO. The report highlights the key roles of electrolyte and cathode composition in determining the stability of Li-O 2 batteries and highlights the importance of identifying more stable electrolyte/cathode pairings. Li-O 2 batteries are an exciting class of energy storage devices with exceptional theoretical capacities which could facilitate longrange electrical vehicles if fully optimized systems are realized. [1][2][3][4][5] Energy storage in Li-O 2 batteries proceeds via different mechanisms to those associated with conventional Li-ion batteries, necessitating detailed studies into the fundamental processes associated with discharge and charge.6-8 It has been shown in a number of studies that the energy storage mechanism for Li-O 2 batteries involves the reversible formation/decomposition of Li 2 O 2 upon discharge and charge respectively.9-13 While the O 2 required to form Li 2 O 2 during discharge can theoretically be provided from ambient air, the majority of systems investigated to date have used pure O 2 to avoid unwanted side-reactions due to the ingress of atmospheric CO 2 and H 2 O.14,15 The formation of parasitic by-products in Li-O 2 batteries (which have been found to form extensively on charging due to cathode and electrolyte instabilities) is a major hurdle to their widespread implementation. 16,17 The nature of Li 2 O 2 (i.e morphology, crystallinity, size and location on the cathode) formed during discharge, and its impact on capacity, cycle life and charging behavior has attracted recent research interest.18-20 A number of reports have presented the formation of Li 2 O 2 toroids on cathode surfaces during discharge in a variety of cathode/electrolyte systems. 7,8,12,19,[21][22][23][24][25] Adams et al. showed that the formation of these toroids was related to the applied current for a given system (TEGDME/LiTFSI electrolyte and Super P carbon cathode). 26Their results suggested that low applied currents tend to favor the formation of large crystalline Li 2 O 2 toroids on the cathode surface with ...

Structure and Catalyst Effects on the Electrochemical Performance of Air Electrodes in Lithium‐Oxygen Batteries

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Cobalt-doped mesoporous carbon nanofibres as free-standing cathodes for lithium–oxygen batteries

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