What is a 1.2V NiMH battery? What is the principle of a 1.2V NiMH battery?

What is a 1.2V NiMH battery?

A 1.2V NiMH battery is a battery that uses lithium as the anode and oxygen in the air as the cathode reactant. Lithium-air batteries have a higher energy density than lithium-ion batteries because their cathodes (mainly porous carbon) are very light and oxygen is obtained from the environment instead of being stored in the battery. In fact, lithium-air batteries are metal fuel-powered lithium batteries, which are generally lithium-ion batteries that use metallic lithium as the negative electrode and oxygen as the positive electrode. The advantage of lithium-air batteries is that they have a high specific energy (specific energy, in simple terms, is the amount of electrical energy released when a unit mass of electrode material participates in a reaction), which is theoretically close to gasoline.

Although lithium-air batteries have a high specific energy, their disadvantage is that the reaction reversibility is poor and a catalyst is required. The 2D materials mentioned here are also called two-dimensional materials. When they are used as catalysts, they can increase the chemical reaction rate inside the battery, making lithium-air batteries more efficient and more rechargeable, and greatly improving the battery's ability to store and supply energy.

Discharge process: The lithium at the anode releases electrons to become lithium cations (Li+). Li+ passes through the electrolyte material and combines with oxygen and electrons flowing from the external circuit at the cathode to form lithium oxide (Li2O) or lithium peroxide (Li2O2), and remains at the cathode. The open circuit voltage of the 1.2V NiMH battery is 2.91V.

What is the principle of lithium-air batteries?

Lithium-air batteries use lithium as the negative electrode active material and a porous gas diffusion layer electrode as the positive electrode material. According to the electrolyte system, they are mainly divided into organic electrolyte liquid (non-aqueous electrolyte system), aqueous electrolyte system, mixed electrolyte system and all-solid electrolyte system.

4Li+O2+2H2O→4LiOH (1-1)

During the discharge process, Li, H2O and O2 are consumed, and a protective film is formed on the surface of Li, which hinders the rapid progress of the electrochemical reaction. In the open circuit or low power state, the self-discharge rate of Li is very high, accompanied by the corrosion reaction of Li:

Li+H2O→LiOH+1/2H2（1-2）

In the aqueous electrolyte, metal Li reacts easily with water, so there are high requirements for the water resistance of the lithium ion diaphragm, and there is no commercial product yet. Considering the practicality and safety, aqueous lithium-air batteries are not the first choice for actual use.

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