Overview of Lithium-Air (Lithium-Oxygen) Batteries By: Dixit Chhatbar and Tak Hung Kwan

Overview Overall structure of Li-Air (Li-O2) battery Electrochemistry of Li-Air (Li-O2) battery Energy Density of Li-Air (Li-O2) battery Types of Electrolyte used in Li-Air (Li-O2) battery and their strengths and weaknesses Weaknesses of the electrodes used in Li-Air (Li-O2) battery

General Information Lithion-ion batteries have been the most suitable for utility storage Energy Density Lithium-ion batteries ~400 Wh-kg-1 Lead-acid batteries 30-40 Wh-kg-1 Nickel-cadmium batteries 40-60 Wh-kg-1 Within Li-ion batteries, lithium-air (lithium-oxygen) batteries attracts the most attention

Structure of Li-Air (Li-O2) Battery

Electrochemistry of Li-Air (Li-O2) Battery Anodic reaction Li → Li+ + e⁻ Cathodic reaction O2 + 2e⁻ + 2Li+ → Li2O2 (non-aqueous) 4Li+ + 4OH- → 4Li + O2 + 2H2O (aqueous and hybrid non-aqueous/ aqueous) 2Li+ + 2O- → Li2O2 (solid-state)

Energy Density of Li-Air (Li-O2) Battery Non-aqueous Li-Air (Li-O2) battery At Voc = 2.96V 11,680 Wh-kg-1 for the charged state Closed to energy density of gasoline (13,000 Wh- kg-1) 10 times higher than other Li-ion battery 3,460 Wh-kg-1 for the discharge state

Energy Density of Li-Air (Li-O2) Battery

Energy Density of Li-Air (Li-O2) Battery Aqueous Li-Air (Li-O2) Battery At VOC = 3.0V 1,910 Wh-kg-1 for the charged state 5 times higher than Li-ion batteries 2,004 Wh-kg-1 for the discharge state

Types of Electrolytes in Li-Air (Li-O2) Battery There are four types of electrolytes currently being used in lithium-air (lithium- oxygen) batteries which are: Non-aqueous Aqueous Hybrid non-aqueous/ aqueous Solid state.

Non-aqueous Li-Air (Li-O2) Battery Composed of an electrode made of lithium metal on one side Air electrode on the other side- a saturated non-aqueous electrolyte made up of lithium salt that is dissolved in non-aqueous solvent A liquid electrolyte in the middle Strength high ionic conductivity, good chemical and electrochemical stability, high boiling point, low vapor pressure, and high oxygen solubility, high specific energy density(charged and discharged) Weakness stability issues for both the solvent and the lithium salt

Aqueous Li-Air (Li-O2) Battery Anode- lithium metal Cathode- a porous air electrode Elctrolyte- lithium salt and water as the aqueous solvent in the middle In this battery, the lithium metal needs to be protected by placing a solid-state lithium ion conducting membrane on the metal This is done as to get rid of the blockage of the porous air electrode by the discharge product that the non-aqueous and solid-state lithium-air batteries have with the soluble LiOH. Weakness low specific energy density and low stability towards the solid-state membrane

Hybrid non-aqueous/ aqueous Li-Air (Li-O2) Battery Anode- a non-aqueous electrolyte Cathode- an aqueous electrolyte Electrolyte- a non-aqueous electrolyte membrane Strength Increases the lithium ion conductivity and allow the lithium and the solid electrolyte membrane to be in no direct contact. Weakness Similar to weaknesses of the aqueous lithium-air

Solid state Li-Air (Li-O2) Battery The anode and the cathode are same as that of non-aqueous lithium-air but the electrolyte is solid-state lithium ion conducting membrane Strength High lithium ion conductivity, very low diffusion coefficient for other species such as O2 and H2O, and a high resistance towards the direction reaction with the lithium metal Weakness Lies at the solid-state lithium ion membrane, which causes a low stability towards the electrolyte and the lithium metal

Weaknesses of Air Electrode of Li-Air (Li-O2) Battery The reaction pathways among oxygen, lithium ions, and the electrons for the lithium-air (lithium-oxygen) batteries needs to be maintained as long as possible in order to have a high practical capacity. Also they use carbon materials as the catalysts, instability occurs, thus, minimizing the cycling life for the air electrodes. Also carbon materials are used as catalysts for the air electrode, carbon dioxide (CO2) gas occurs during the reactions, where CO2 gas can further pollute the environment, thus, increasing the danger of global warming.

Weaknesses of Lithium Electrode of Li-Air (Li-O2) Battery Oxygen and other side products have caused the reactions between the lithium metal anode and the electrolyte to be extremely complicated, thus, creating a thick passivation layer on the lithium surface. Increases the lithium ion transport resistance, leading to the decay of the battery performance and to the battery failure.

But I’ll use it anyhow because!!! The battery’s high specific energy density, these lithium-air (lithium- oxygen) batteries have been considered as the possible power sources for the electric vehicles (EVs). These batteries can serve as the solar energy storage for PV utility systems.