A lithium-air battery is a battery that uses metallic lithium as the negative electrode and oxygen in the air as the positive electrode reactant. Discharge process: Lithium in the negative electrode releases electrons to become lithium ions (Li+), Li+ passes through the electrolyte material, combines with oxygen at the positive electrode and electrons flowing from the external circuit to form lithium oxide (Li2O) or lithium peroxide (Li2O2), and stay positive. The open circuit voltage of the Li-air battery is 2.91V, as shown in Figure 1.
Electrode reaction during discharge:
Negative electrode: Li→Li++e–
Metal lithium is dissolved in the organic electrolyte in the form of lithium ions (Li+), and electrons are supplied to the external circuit. Dissolved lithium ions (Li+) move through the solid electrolyte into the aqueous electrolyte of the positive electrode.
Positive electrode: O2+2H2O+4e–→4OH–
By supplying electrons through wires, oxygen in the air and water react on the surface of the micronized carbon to generate hydroxide ions (OH–). It combines with lithium ions (Li+) in the aqueous electrolyte of the positive electrode to form water-soluble lithium hydroxide (LiOH).
Electrode reaction during charging:
Negative electrode: Li++e–→Li
Electrons are supplied through wires, and lithium ions (Li+) are passed from the aqueous electrolyte of the positive electrode through the solid electrolyte to the surface of the negative electrode, and react on the surface of the negative electrode to form metallic lithium.
Positive electrode: 4OH–→O2+2H2O+4e–
The reaction generates oxygen, and the generated electrons are supplied to the external circuit.
Li-air batteries have higher energy density than Li-ion batteries because the cathode (mainly porous carbon) is light, and oxygen is obtained from the environment instead of being stored in the battery. Limited, the capacity of this battery depends only on the lithium electrode, and its specific energy is 5.21 kW h/kg (including oxygen mass) or 11.1 kW h/kg (excluding oxygen).
There are many research projects underway for lithium-air batteries, including the Japan Institute of Industrial Technology, IBM’s Almaden Laboratory, and the University of Dayton. On May 3-4, 2010, the Argonne National Laboratory in the United States held a seminar to discuss lithium-air batteries used in the field of transportation. It was believed that lithium-ion batteries were only a transitional technology, but there were still many technical problems to be solved. To achieve the popularization of electric autos, the energy density needs to reach 6 to 7 times that of current lithium-ion batteries. Lithium-air batteries, which theoretically have a much higher energy density than lithium-ion batteries, have attracted much attention.
Lithium-air batteries also have a fatal defect, that is, the solid reaction product lithium oxide (Li2O) will accumulate on the positive electrode, blocking the contact between the electrolyte and the air, thus causing the discharge to stop, February 2009, Japan Institute of Industrial Technology Research Zhou Haoshen, head of the Energy Interface Technology Research Group of the Energy Technology Research Department, and Wang Yonggang, a foreign researcher at the Japan Society for the Promotion of Science (JSPS), jointly developed a lithium-air battery with a new structure. They solved the above problem by splitting the electrolyte into two types. An organic electrolyte is used on the negative electrode (metal lithium) side, and an aqueous electrolyte is used on the positive electrode (air) side. A trapped electrolyte membrane through which only lithium ions pass through is placed between the two electrolytes to separate them. This prevents the electrolytes from mixing and encourages the battery to react. Since the discharge reaction does not generate solid Li2O, but LiOH (potassium hydroxide) that is easily dissolved in the aqueous electrolyte, lithium oxide will not stop working after the accumulation of lithium oxide on the air electrode. Water, nitrogen, etc. also do not pass through the partition walls of the solid electrolyte, so there is no danger of reacting with the lithium metal of the negative electrode. In addition, the researchers are also considering using a different method of use from a simple rechargeable battery, that is, without charging the battery, but by replacing the aqueous electrolyte of the positive electrode of the battery, and replenishing the metal lithium of the negative electrode by means of cartridges, etc. charging function. Then, the used aqueous electrolyte is recovered to regenerate metal lithium, which can continue to be recycled as a battery anode fuel. Then, the lithium-air battery can be said to be a new type of fuel cell with metal lithium as the fuel, and its principle is shown in Figure 2.
Many laboratories around the world are researching and developing lithium-air battery technology. Since there are many major technical difficulties that have not yet been broken through, it may take more than 10 years to achieve commercial use.
IBM launched a sustainable transportation project in 2009 to develop a lithium-air battery suitable for home electric autos. In this project, IBM and other partners, such as the US National Laboratory, will make full use of the current leading technology in the fields of chemistry, physics, nanotechnology and supercomputer modeling.
According to IBM announced in May 2012, Japan’s Asahi Kasei (Asahi Kasei) and Central Glass (Central Glass) will join IBM’s “lithium-air battery” project team, and carry out long-term cooperative research. Asahi Kasei Corporation, Japan’s leading chemical manufacturer and one of the leading global suppliers of membrane separators for lithium-ion batteries, will leverage its experience in innovative membrane technology to develop a key component for lithium-air batteries. Central Glass, one of the world’s leading producers of lithium-ion battery electrolytes, will use its experience in chemistry to research new electrolytes and high-performance additives to improve air batteries.
IBM expects to produce the first samples in five years, while other researchers are cautiously predicting that such a research protocol could take decades.