An energy storage and power generation system for planetary exploration missions is described in which lithium metal is the fuel. At high enough temperatures, lithium will spontaneously and exothermically react with several planetary atmospheres, such as on Venus, as well as with in situ water that may be present on bodies such as Mars, our own moon, or Jupiter’s watery companion, Europa. This proposed energy source fills a niche for exploration missions in regions where there is little or no access to solar energy, and where integral days of data collection and operation are sufficient for mission success, and which therefore do not require very long-lived and expensive nuclear options. The proposed lithium energy system has a much greater system specific energy than primary battery systems. Like batteries, the proposed energy source does not release any material to contaminate the surrounding area. After an introduction to the proposed technology, an analysis of the thermochemical behavior of the system in CO2 and CO2/ N2 environments is presented. A preliminary proof-of-concept experiment is described, and initial results are presented. Suggestions for follow-on work are given.