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In a collaborative effort, Lithion and NASA/JPL developed a lithium ion battery capable of meeting the physical and electrochemical requirements for the 2003/2004 Mars Exploration Rover (MER) missions. The cells provide up to 145 Wh/kg, while the specific energy at the battery level, including wiring harnesses, thermal hardware and mounting hardware is approximately 90 Wh/kg. This paper discusses the specific requirements of the mission and how those requirements were met. Furthermore, an overview of the technique used to select cells for batteries is presented. The cell selection criteria resulted in cell to cell variation of approximately ± 0.6% in the first qualification unit.

NASA requires lightweight rechargeable batteries for future missions to Mars and the outer planets that are capable of operating over a wide range of temperatures, with high specific energy and energy densities. Due to the attractive performance characteristics, lithium-ion batteries have been identified as the battery chemistry of choice for a number of future applications, including Mars rovers and landers. The Mars 2001 Lander (Mars Surveyor Program MSP 01) will be among one of the first missions which will utilize lithium-ion technology. This application will require two lithium-ion batteries, each being 28 V (eight cells), 25 Ah and 8 kg. In addition to the requirement of being able to supply at least 200 cycles and 90 days of operation upon the surface of Mars, the battery must be capable of operation (both charge and discharge) at temperatures as low as -20°C.

In contrast to the primary batteries (lithium thionyl chloride) on the Sojourner Mars Rover and the upcoming 2001 Mars Rover, the Mars Sample Return (MSR) Athena Rover will utilize rechargeable lithium ion batteries, following the footsteps of MSP 2001 Lander. The MSR Athena Rover will contain a rechargeable lithium ion battery of 16 V and a total energy of 150 Wh. The mass and volume of the projected power system will be a maximum of 3 kg and 2 liters, respectively. Each battery consists of twelve cells (6-7 Ah), combined in three parallel strings of four cells (16 V) each, such that the capability of the Rover shall be maintained even in the event of one string failure. In addition to usual requirements of high specific energy and energy density and long cycle life (100 cycles), the battery is required to operate at wide range of temperatures, especially at sub-zero temperatures down to -20°C.

NASA requires lightweight rechargeable batteries for future missions to Mars and the outer planets that are capable of operating at low temperatures. Due to the attractive performance characteristics, lithium-ion batteries have been identified as the battery chemistry of choice for a number of future applications, including Mars Rovers and Landers. Under an Interagency program, lithium-ion cells of varying capacity are being developed for NASA and DOD applications. JPL, in collaboration with Wright Patterson Laboratory (Air Force), is currently evaluating a number of lithium-ion cells varying in capacity from 3 Ah to 50 Ah for future aerospace applications. The Mars Lander and Rover applications require a rechargeable, high energy density system capable of operation at temperatures as low as -20°C.

Lithium-ion rechargeable batteries have been demonstrated to have high energy density, high voltage, and excellent cycle life which make this technology more attractive than competing systems such as Ni-Cd and Ni-H2. However, the SOA cells fail to meet certain requirements necessary for various future NASA missions, such as good low temperature performance. Under a program sponsored by the Mars Exploration Program we have developed an organic non-aqueous electrolyte which has been demonstrated to result in improved low temperature performance of lithium-ion cells. The electrolyte formulation which has resulted in excellent low temperature performance, as well as good cycle life performance at both ambient and low temperatures, consists of a 1.0M solution of a lithium salt, lithium hexafluoro-phosphate (LiPF6), dissolved in a mixture of carbonates: ethylene carbonate + dimethyl carbonate + diethyl carbonate (1:1:1).