The current research hotspots of lithium-ion batteries are mainly focused on lithium-air batteries and lithium-sulfur batteries, both of which are considered to be the new generation of lithium batteries with the most development potential. They are very different from the previous lithium-ion battery cathode materials in structure and reaction mechanism.

　　1. Lithium-air battery

　　Lithium-air battery is a kind of metal-air battery, because it uses the lowest molecular weight lithium metal as the active material, its theoretical specific energy is very high. If the oxygen mass is not calculated, it is 11140Wh/kg. In fact, the usable energy density can reach 1700Wh/kg, which is much higher than other battery systems. The basic structure and working mechanism of the lithium-air battery are shown in the figure below.

　　Lithium-air batteries can be divided into water system, organic system, water-organic hybrid system and all-solid-state lithium-air battery according to the state of electrolyte used. When the organic system lithium-air battery is working, the raw material O2 enters the battery through the porous air electrode, and is catalyzed to O2- or O22- on the surface of the electrode, and then combines with the Li+ in the electrolyte to generate lithium peroxide (Li2O2) or lithium oxide ( Li2O), the product is deposited on the surface of the air electrode. When all the air holes in the air electrode are blocked by the product, the battery discharge is terminated. The electrode reaction is as follows:

　　Cathode: O2+2e-+2Li+?Li2O2;O2+4e-+4Li+?2Li2O

　　negative electrode: Li? Li++e-

　　Total reaction: 2Li+O2?Li2O2(2.96V); 4Li+O2?2Li2O(2.91V)

　　Li-air battery has unparalleled advantages of ultra-high energy density, environmental friendliness and low price, but its research is still in its infancy and there are many thorny problems, mainly including:

　　(1) The positive electrode reaction requires a catalyst. During the discharge process, in the absence of a catalyst, the oxygen reduction is very slow; during the charging process, the voltage plateau is about 4V, which is likely to cause side reactions such as the decomposition of the electrolyte. Need to use appropriate catalyst to help the battery reaction.

　　(2) Lithium-air battery is an open system, which will cause a series of fatal problems such as electrolyte volatilization, electrolyte oxidation, moisture in the air and the reaction of CO2 with lithium metal.

　　(3) The air electrode channel is blocked. Li2O and Li2O2 that are insoluble in the electrolyte generated by the discharge will accumulate in the air electrode and block the air pores, leading to inactivation of the air electrode and termination of the discharge.

　　In summary, there are many problems in lithium-air batteries that need to be solved urgently: including the catalysis of the oxygen reduction reaction, the oxygen permeability and hydrophobicity of the air electrode, and the deactivation of the air electrode. Although lithium-air batteries have made some progress, there is still a long way to go before they are truly applied.　　2. Lithium-sulfur battery

　　The research on lithium-sulfur batteries first originated in the 1970s, but the actual capacity of lithium-sulfur batteries has been low and the attenuation has been serious, so they have not received much attention. In 2009, LindaF.Nazar's research group reported that sulfur-carbon composites used as lithium-sulfur battery cathode materials to obtain better cycle performance and very high discharge capacity, which set off an upsurge in lithium-sulfur battery research. Lithium-sulfur batteries mainly use elemental sulfur or sulfur-based compounds as the battery's positive electrode material, and the negative electrode mainly uses metal lithium. The battery structure is shown in the figure.