page_title: Lithium–air battery
section_title: Mixed aqueous–aprotic
hierarchical_section_title: Lithium–air battery / Design and operation / Electrolyte / Mixed aqueous–aprotic
caption_attribution_description: English: Schematic of a fully solid-state type Lithium-air battery design
context_page_description: The lithium–air battery is a metal–air electrochemical cell or battery chemistry that uses oxidation of lithium at the anode and reduction of oxygen at the cathode to induce a current flow.
  Pairing lithium and ambient oxygen can theoretically lead to electrochemical cells with the highest possible specific energy. Indeed, the theoretical specific energy of a non-aqueous Li–air battery, in the charged state with Li₂O₂ product and excluding the oxygen mass, is ~40.1 MJ/kg. This is comparable to the theoretical specific energy of gasoline, ~46.8 MJ/kg. In practice, Li–air batteries with a specific energy of ~6.12 MJ/kg at the cell level have been demonstrated. This is about 5 times greater than that of a commercial lithium-ion battery, and is sufficient to run a 2,000 kg EV for ~500 km on one charge using 60 kg of batteries. However, the practical power and life-cycle of Li–air batteries need significant improvements before they can find a market niche.
  Significant electrolyte advances are needed to develop a commercial implementation. Four approaches are active: aprotic, aqueous, solid state and mixed aqueous–aprotic.
context_section_description: The aqueous–aprotic or mixed Li–air battery design attempts to unite advantages of the aprotic and aqueous battery designs. The common feature of hybrid designs is a two-part (one part aqueous and one part aprotic) electrolyte connected by a lithium-conducting membrane. The anode abuts the aprotic side while the cathode is in contact with the aqueous side. A lithium-conducting ceramic is typically employed as the membrane joining the two electrolytes.
  The use of a solid electrolyte (see Fig. 3) is one such alternative approaches that allows for a combination of a lithium metal anode with an aqueous cathode. Ceramic solid electrolytes (CSEs) of the NASICON family (e.g., Li1−xAₓM2−x(PO₄)₃ with A ∈ [Al, Sc, Y] and M ∈ [Ti, Ge]) has been studied. Compatible with water at alkaline pH and having a large electrochemical window (see Figs. 3,4), their low Li+ ion conductivity near room temperature (< 0.005 S/cm, >85 Ω cm²) makes them unsuitable for automotive and stationary energy storage applications that demand low cost (i.e., operating current densities over 100 mA/cm²). Further, both Ti and Ge are reduced by metallic Li, and an intermediate layer between the ceramic electrode and the negative electrode is required. In contrast, solid polymer electrolytes (SPEs) can provide a higher conductivity at the expense of a faster crossover of water and of other small molecules that are reactive toward metallic Li. Among the more exotic membranes considered for Li-O₂ batteries is single-crystal silicon.
  In 2015 researchers announced a design that used highly porous graphene for the anode, an electrolyte of lithium bis(trifluoromethyl) sulfonylimide/dimethoxyethane with added water and lithium iodide for use as a "mediator". The electrolyte produces lithium hydroxide (LiOH) at the cathode instead of lithium peroxide (Li
  ₂O
  ₂). The result offered energy efficiency of 93 percent (voltage gap of .2) and cycled more than 2,000 times with little impact on output. However, the design required pure oxygen, rather than ambient air.
caption: Schematic of solid-state type Li–air battery design
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