Lithium batteries began with the pioneering work of G.N and Lewis in the 1910s. The first Li/(CF)n lithium primary battery was sold in the 1970s, and its cathode material (CF)n is a compound of fluorine and carbon that can intercalate and desorb lithium. American researchers have tried to develop Li/Mn02 batteries, but they were unsuccessful due to problems in humidity control, battery structure, and assembly technology. In 1973, Japan became the first country to commercialize Li/MnO2 batteries. The batteries used organic solvents instead of water solvents to achieve a working voltage of up to 3v, and soon gained universal recognition. These works laid the foundation for the birth of the first lithium secondary battery in Japan.
According to different cathode materials, the early development of lithium primary batteries include Li/(CF)n batteries, Li/MnO2 batteries, Li/SO2 batteries and Li/SOCL2 batteries. Among them, Li/MnO2 batteries are the most widely used. Although Li/SO2 batteries and Li/SOCl2 batteries have excellent low-temperature performance and durability, due to the presence of harmful substances, these two batteries are limited to military use.
With the discovery of (CF)n cathode materials with a layered structure that can intercalate lithium in primary batteries in the 1970s, a large number of studies have focused on finding intercalable compounds with both high conductivity and high electrochemical reactivity. . The study found that chalcogenide compounds such as TiS2 can undergo interlayer intercalation and desorption reactions. This discovery laid the foundation for the development of lithium secondary battery commercial technology. as the picture shows,
TiS2 is a light semi-metal with a layered structure and can be directly used as an electrode material without adding a conductive agent. Because its structure can remain unchanged during battery charging and discharging, the insertion and extraction of lithium are reversible. However, the material is difficult to synthesize and the cost is high, which limits its commercial development. In 1989, Moli Energy of Canada developed a metal lithium secondary battery using MoS2 as the positive electrode material, but the dendritic growth of the lithium negative electrode would bring safety problems such as internal short circuit and combustion.
In addition to low-potential sulfides, some oxides have also been considered as cathode materials for lithium batteries, but they have not been commercialized. Until 1991, after the successful commercialization of lithium secondary batteries with LiCoO2 as the positive electrode and carbon as the negative electrode, a large amount of research and development on cathode materials was initiated. When LiCoO2 is used as a positive electrode, the carbon of the negative root can form LixC6 compound through the intercalation of lithium ions, thus avoiding the problem of internal short circuit caused by dendritic growth caused by using lithium metal as the negative electrode. The reduction potential of carbon is 0.1-0.3V higher than that of lithium metal, but the high potential of LiCoO2 can offset this effect. The average voltage of carbon/LiCoO2 batteries can reach 3.7 V, and the potassium ion diffusion coefficient of LiCoO2 is 5×10﹣9cm2/s , Which is similar to LiTis2 (10 ﹣8cm2/s). Its electronic conductivity is related to the amount of lithium inserted, which is between semiconductors and metals.
With the commercialization of LiCoO2, various types of cathode materials have been widely studied. Among them, materials with higher capacity include: LiMn2O4 with a stable spinel structure and LiNi02 which can insert and release 70% of lithium. However, the relative capacity of spinel LiMn2O4 is low, and at the same time, the dissolution of manganese at high temperature will cause performance degradation; while LiMn2O4 has safety problems. In order to solve these problems, the advantages of LiCoO2, LiNiO2 and LiMn2O4 are integrated in the ternary material Li[Ni, Mn, Co] O2. The iron-containing olivine-type LiFePO4 has also been widely studied. The figure shows the relationship between the potential and capacity of the material between 3~4V.
