Therefore, driven by the development of lithium primary batteries, research began on lithium primary batteries that could almost simultaneously charge and discharge lithium secondary batteries. With the increasing population—reaching 6.5 billion as of February 25, 2006, and estimated to reach 7 billion by October 18, 2012—and the finite nature of Earth's resources, it is imperative to improve resource utilization. Using rechargeable batteries is one effective method to promote the research and development of lithium secondary batteries. With increasing environmental awareness, the use of toxic metals such as lead and cadmium is becoming increasingly restricted, necessitating the search for new rechargeable batteries to replace traditional lead-acid and nickel-cadmium batteries. Lithium secondary batteries are a natural choice. The continuous development of electronic technology has driven the miniaturization of various electronic products, such as mobile phones, miniature cameras, and laptops. Miniaturization inevitably leads to the miniaturization of power supplies. For example, traditional lead-acid batteries have limited capacity, thus necessitating the search for new battery systems. Their advantages make lithium-ion secondary batteries a strong candidate.
Before the 1980s, the main focus was on lithium-ion rechargeable battery systems using lithium resistive metal and alloy cathodes. However, during charging, the uneven surface of the lithium metal electrode derivatives led to uneven potential distribution, resulting in uneven lithium deposition. This uneven deposition process caused lithium to deposit too quickly in some areas, forming dendritic crystals (dendritic protrusions). When the dendrites developed to a certain extent, they broke off, resulting in dead lithium and forming small, reversible lithium. More seriously, the dendrites connected the positive and negative electrodes through the separator, causing a short circuit, generating a large amount of heat, and potentially leading to battery fire or even explosion, thus posing a serious safety hazard. The most representative example is the Li//TiS2 system researched by ExxonMobil in the late 1970s. Although ExxonMobil failed to commercialize the lithium-ion rechargeable battery system, it greatly promoted the research and development of lithium-ion rechargeable batteries. Then MoLi was founded in Canada, using MoS2 as its cathode material. Despite initially having good financial lessons, an explosion in 1989 led to its bankruptcy, and it was later acquired by a Japanese company. These companies are unable to gain a basic market because there is no fundamental solution to the cycle life and safety issues of lithium metal or its alloy anode lithium secondary batteries. This is because (1) as mentioned above, during the charging process, the lithium and water can be very uniform, which is impossible to fundamentally solve the problem of dendrite rise, and therefore cannot fundamentally solve the safety issue; lithium metal is more active and it is easy to react with non-aqueous liquid electrolytes, resulting in high pressure and danger.
