The electrolyte of the lithium-air battery is the medium which supports the reactions at the cathode and the anode. Four types of electrolytes can be used in the design of lithium-air cells. These include aqueous acidic, non-aqueous aprotic, aqueous alkaline and aprotic.
LITHIUM-AIR BATTERY TECHNOLOGY 9 Acidic electrolyte The use of acidic electrolyte results in the following half equations pf the reactions at the cathode and the anode: 2Li + ½ O 2 + 2H + → 2Li + + H 2 O In this case, a conjugate base is involved in the reaction. The maximum specific energy if an acidic electrolyte is used is 1400 W·h/kg. The corresponding energy density of this design is 1680 W·h/l. Aqueous electrolyte In this design arrangement of the Lithium-air cell, an aqueous electrolyte, a lithium metal anode and a mesoporous carbon cathode make up the Lithium-air battery. This electrolyte reacts with the lithium salts and then dissolves in water. This design criterion is advantageous as it avoids cathode clogging because the reactions end products are soluble in water. The discharge potential associated with this type of design is much higher compared to aprotic based lithium-air cells. However, due to the use of a lithium anode, water reacts violently with it, necessitating the use of a solid electrolyte interface Aprotic based electrolyte The aprotic based design of the lithium-air battery involves the use of a lithium anode, a carbon cathode and an organic electrolyte. The organic electrolyte used must have the capability to dissolve lithium salts which are produced during the working of the battery. The carbon cathode must be made such that it has a large surface area and covered by non-structured metal oxides, which work as catalysts (Zhang et al., 2016). This results in the formation of an analogous barrier between the anode and the electrolyte, which is advantageous to the working of the battery. However, the lithium peroxide that is produced at the cathode is insoluble in the
LITHIUM-AIR BATTERY TECHNOLOGY 10 organic electrolyte medium, meaning that the aprotic based lithium-air battery is prone to clogging at the cathode, which is detrimental to its effective working. Aqueous alkaline For the aqueous alkaline electrolyte based design, the theoretical values of specific energy and energy density are 1300 W·h/kg and 1520 W·h/l. As seen in the following half-cell reactions, a new compound, lithium hydroxide is produced, meaning that suitable protection for the cathode should be applied, together with the use of catalysts. 2Li + ½ O 2 + H 2 O → 2LiOH Benefits of Lithium-Air Batteries One of the key benefits of the development of Lithium-air batteries with theoretical specific energy capabilities lies in the electric cars industry. The conventional Lithium-ion batteries are some of the costliest constituents of the electric cars, and hence the adoption of Lithium-air batteries could be a game-changer in the industry. This is so because the specific energy of power output of
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