Liquid‐Free Lithium–Oxygen Batteries

Abstract

Non-aqueous lithium-oxygen batteries are considered as most advanced power sources, albeit they are facing numerous challenges concerning almost each cell component. Herein, we diverge from the conventional and traditional liquid-based non-aqueous Li-O 2 batteries to a Li-O 2 system based on a solid polymer electrolyte (SPE-) and operated at a temperature higher than the melting point of the polymer electrolyte, where useful and most applicable conductivity values are easily achieved. The proposed SPE-based Li-O 2 cell is compared to Li-O 2 cells based on ethylene glycol dimethyl ether (glyme) through potentiodynamic and galvanostatic studies, showing a higher cell discharge voltage by 80 mV and most significantly, a charge voltage lower by 400 mV. The solid-state battery demonstrated a comparable dischargespecific capacity to glyme-based Li-O 2 cells when discharged at the same current density. The results shown here demonstrate that the safer PEO-based Li-O 2 battery is highly advantageous and can potentially replace the contingent of liquid-based cells upon further investigation.Rechargeable Li-O 2 batteries based on non-aqueous electrolytes attracted much attention in recent years due to their outstanding theoretical energy density of about 3500 W h kg À1 . [1][2][3][4] However, there are some critical challenges regarding the electrolyte, hindering the actualization of a Li-O 2 battery as a high-energy storage device: 1) Most common organic liquid electrolytes are volatile and hence, are less suited for the Li-O 2 battery, which is in essence an open system. 2) The Achilles heel of most organic electrolytes is their long-term stability as they are prone to autoxidation under oxygenated radicals (formed during cell operation), being converted into unstable peroxide species. [5][6][7][8][9][10][11] 3) Low surface tension between the carbon surface of the air cathode and most organic electrolytes results in flooding of the air electrode and hence, only dissolved [11] O 2 participates in the actual oxygen reduction reaction (ORR) and the associated charge-transfer reaction, occurring in the two-phase boundary reaction zone. [12] One approach to tackle all of the above problems is to design a liquid-free Li-O 2 cell which is safer and is based on a solid polymer electrolyte (Scheme 1). Polymers are expected to exhibit higher chemical, thermal, and electrochemical stabilities (see Figure S1 in the Supporting Information). Moreover, not only that the polymer can ensure safe cell operation, but it would also minimize oxygen crossover towards the anode and would totally eliminate the use of a separator in the cell. Despite the advantages pointed out, SPE has high internal resistance at room temperature, resulting from a low ionic mobility, high degree of polymer matrix crystallinity, and low degree of charge separation in addition to ion association, preventing their practical use as electrolyte in Li-O 2 batteries, unless inorganic fillers such as ZrO 2 , Al 2 O 3 , SiO 2 , TiO 2 , and/or anion traps are used. [13][...

Electrolytes for Rechargeable Lithium–Air Batteries

“…The crystallization of polymer chains can be suppressed by synthetic approaches such as cross‐linking and copolymerization or by raising the temperature. For example, a Li–O 2 battery containing PEO‐based electrolytes operated at 80 °C showed a low overpotential of 480 mV and a comparable discharge specific capacity to that of glyme‐based Li–air batteries …”

Lithium Ion Pathway within Li7La3Zr2O12‐Polyethylene Oxide Composite Electrolytes

“…In addition, Li dendrite growth across liquid‐based electrolytes causes safety issues and limits the utilization of Li metal as anodes . To overcome these challenges, non‐flammable solid‐state electrolytes are suitable alternatives to organic‐solvent‐based electrolytes . Inorganic ceramics and organic polymers are two general classes of materials used as solid electrolytes for LIBs.…”

Lithium Ion Pathway within Li7La3Zr2O12‐Polyethylene Oxide Composite Electrolytes

“…In addition, Li dendrite growth across liquid‐based electrolytes causes safety issues and limits the utilization of Li metal as anodes . To overcome these challenges, non‐flammable solid‐state electrolytes are suitable alternatives to organic‐solvent‐based electrolytes . Inorganic ceramics and organic polymers are two general classes of materials used as solid electrolytes for LIBs.…”