A Moisture‐ and Oxygen‐Impermeable Separator for Aprotic Li‐O₂ Batteries

Abstract

Despite the unparalleled theoretical gravimetric energy, Li-O 2 batteries are still under a research stage because of their insuffi cient cycle lives. While the reversibility in air-cathodes has been lately improved signifi cantly by the deepened understanding on the electrode-electrolyte reaction and the integration of diverse catalysts, the stability of the Li metal interface has received relatively much less attention. The destabilization of the Li metal interface by crossover of water and oxygen from the air-cathode side can indeed cause as fatal degradation for the cycle life as the irreversibility of the air-cathodes. Here, it is reported that cheap poreless polyurethane separator can effectively suppress this crossover while allowing Li ions to diffuse through selectively. The polyurethane separator also protects Li metal anodes from redox mediators used for enhancing the reversibility of the air-cathode reaction. Based on the Li metal protection, a persistent capacity of 600 mAh g −1 is preserved for more than 200 cycles. The current approach can be readily applicable to many other rechargeable batteries that suffer from similar interfacial degradation by side products from the other electrode.

Advances in Lithium-Containing Anodes of Aprotic Li-O2Batteries: Challenges and Strategies for Improvements

“…The design of specific functional separators is an effective anode protection strategy to block hazardous O 2 and H 2 O from reaching a lithium‐based anode. For example, Kim et al reported a poreless polyurethane (PU) separator, as a simple and effective solution, to overcome the problem of O 2 and H 2 O attacking lithium‐metal anodes . The poreless nature of the PU separator means O 2 and H 2 O could be prevented from reaching the lithium‐anode surface yet still facilitates lithium‐ion diffusion by the high electrolyte uptake of the separator compared with conventional PE separators, as shown in Figure b,d.…”

“…d) SEM images of the PU separator (anode side) in the PU cell during 100 cycles. Reproduced with permission . Copyright 2016, Wiley‐VCH.…”

Strategies Toward Stable Nonaqueous Alkali Metal–O2 Batteries

“…Moisture and oxygen-impermeable membrane composed of poreless polyurethane (PU) polymer was proposed as separator for the Li-O 2 battery by Kim et al [56] The PU separator contains 4, 4-diphenylmethane diisocyanate, polyethylene oxide (PEO), and polytetramethylene glycol units, which enable its high mechanical rigidity and wettability in the electrolyte. Moisture and oxygen-impermeable membrane composed of poreless polyurethane (PU) polymer was proposed as separator for the Li-O 2 battery by Kim et al [56] The PU separator contains 4, 4-diphenylmethane diisocyanate, polyethylene oxide (PEO), and polytetramethylene glycol units, which enable its high mechanical rigidity and wettability in the electrolyte.…”

Optimized Concentration of Redox Mediator and Surface Protection of Li Metal for Maintenance of High Energy Efficiency in Li–O2 Batteries

“…[10,11] Alternatively, liquid catalysts, called redox mediators (RMs), [10][11][12][13][14][15][16] have been added to the electrolyte as electron-hole transfer agents to promote reversible Li 2 O 2 formation/ decomposition. [20,[22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] However, reported Li protection materials and Li-protective layers mainly consist of polymers, which have insufficient stiffness to suppress the growth of Li dendrites. However, it has recently been reported that RMs can be deactivated during cycling through chemical reduction at the Li metal electrode (self-discharge of the electrochemically oxidized RM) and attack by oxygen species at the cathode.…”

“…[20,[22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] However, reported Li protection materials and Li-protective layers mainly consist of polymers, which have insufficient stiffness to suppress the growth of Li dendrites. [20,[22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] However, reported Li protection materials and Li-protective layers mainly consist of polymers, which have insufficient stiffness to suppress the growth of Li dendrites.…”