context: In the last few decades, the demand for batteries has rapidly increased in various application fields. Although rechargeable batteries (such as lithium-ion batteries) have become a focus of attention, primary batteries still occupy a large market share in many civilizations and military applications such as portable power sources, signal lights, and space and ocean exploration. As a result, efforts to develop primary batteries with high energy density, high power density, and low cost have never stopped ever since the invention of volt batteries in 18th century. Especially in recent years, large number of batteries with high energy density have been developed, such as the Zn–O2, Mg–O2, Al–O2, Na–O2, and Li–O2 systems. In addition, primary batteries, such as the currently developed Li–SO2, Li–SOCl2, Li–MnO2, and Li-CFx systems, have also been developed under isolated conditions for applications such as ocean and out space. Primary batteries are usually required to have high energy density, long shelf life, stable discharge voltage, and low self-discharge rate and should be readily available for use. Currently, the Li/MnO2 batteries account for more than 80% share of the lithium primary battery market due to their low cost, high safety, and natural abundance of Li and Mn. Moreover, the Li/MnO2 batteries possess a high practical specific energy of 308 W h kg−1 and a long shelf life of about 10 years. However, the application of Li/MnO2 batteries is limited by their poor electrochemical performance at high power output and low temperature, which is ascribed to several issues including low electronic conductivity, low lithium diffusion coefficient, and structural susceptibility of the MnO2 cathode. To address these issues, numerous methods, such as structural design and composite, coating, and metal cation doping, have been studied to optimize the performance of the MnO2 cathode. In addition, to overcome the intrinsic limitations of the current cathode materials, exploring novel cathode materials is a potential strategy for promoting the performance of lithium primary batteries.
answer: MnO2 