Porous Materials Applied in Nonaqueous Li–O₂ Batteries: Status and Perspectives

Abstract

Li-O 2) batteries with high theoretical energy densities offer considerable potential for a new generation of energy storage technology. [1] In 1996, the first nonaqueous Li-O 2 battery was introduced with a polymer organic electrolyte and a carbon-cobalt composite cathode by Abraham and Jiang. [2] This was followed by the verification of the rechargeability of Li-O 2 batteries with manganese dioxide-super S cathodes for over 50 cycles by Bruce and co-workers, [3] after which nonaqueous Li-O 2 batteries received substantial research attention worldwide. A typical nonaqueous Li-O 2 battery includes a Li metal anode, an aprotic electrolyte and an O 2 cathode. It operates according to the reaction 2Li + O 2 ↔ Li 2 O 2 (2.96 V vs Li/Li +), in which O 2 is reduced to form Li 2 O 2 on the cathode during discharging and Li 2 O 2 is decomposed to O 2 and Li + through a reversible charging process. In this way, the battery delivers exceptional theoretical energy density of ≈3600 Wh kg −1. [4] This report is centered on nonaqueous Li-O 2 batteries, and the use of the term "Li-O 2 batteries" mentioned below represents "nonaqueous Li-O 2 batteries." To date, enormous progress has been achieved in the understanding and application of high-performance Li-O 2 batteries, however, their low practical discharge capacity, poor rate capability, low round-trip efficiency, and inferior cycling stability have greatly blocked their practical applications. The current major scientific and technical challenges of Li-O 2 batteries can be summarized as follows. 1) The slow kinetics of formation and decomposition of the discharge products lead to poor rate capability and low round-trip efficiency. 2) Cathode corrosion and electrolyte decomposition due to the attack by the discharge intermediates such as superoxide species, giving rise to poor cycling stability. 3) Pore clogging on the cathode arising from the stacking of insulated, insoluble discharge products blocks the mass transfer and oxygen/Li + diffusion, limiting the capacity and degrading the cycling performance. 4) The inevitable side reactions between the highly reactive Li anode and the organic electrolyte, crossover O 2 , CO 2 , etc., and the redox mediators (RMs), give rise to premature battery death. [1a,5] 5) The unavoidable Li dendrites caused by uncontrollable deposition of lithium, as well as the risk of collapse of the lithium anode due to the volume change during iterative plating/stripping processes, increase the probability of safety problems. [6] Consequently, the slow kinetics of Li 2 O 2 Porous materials possessing high surface area, large pore volume, tunable pore structure, superior tailorability, and dimensional effect have been widely applied as components of lithium-oxygen (Li-O 2) batteries. Herein, the theoretical foundation of the porous materials applied in Li-O 2 batteries is provided, based on the present understanding of the battery mechanism and the challenges and advantageous qualities of porous materials. Furthermore, recent progress in porous material...

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