No abstract

Purposely plating lithium metal on a graphite anode in an optimized electrolyte enables hybrid lithium-ion/lithium metal cells that deliver 20% increased energy density compared with conventional lithium-ion cells. Hybrid cells can be operated highly reversibly in lithium-ion mode for low capacity utilization and charged fully to harness the extra capacity of the lithium metal for extended operation.

A new "hot formation" protocol is proposed to improve lower temperature cycling of lithium metal batteries. The cycling stability of anode-free pouch cells under low pressure (75 kPa) is shown to decline significantly as the cycling temperature is decreased from 40°C to 20°C. At low pressure and 40°C the initial morphology of the lithium anode is dense and columnar, far superior to that plated at 20°C. For "hot formation" two initial 40°C cycles (C/10 charge C/2 discharge) are conducted prior to extended low temperature (20°C) cycling. These two initial cycles have a surprisingly large impact; capacity retention to 80% is increased from only 18 cycles without hot formation to 60 cycles with hot formation at low pressure. When the applied pressure is increased to 1200 kPa, the hot formation (20°C cycling) cells show 85% capacity retention at 100 cycles. The benefits established during these two initial formation cycles are apparently carried forward to improve the longer term performance of lithium metal cells tested at room temperature.

Eagle-Picher Technologies, LLC (EPT) has been involved in the design, development and production of special purpose batteries since the late 1940's. Among these niche markets, EPT has been the supplier of choice for the majority of all satellite applications. As energy density requirements for the aerospace industry batteries have increased, the chemistry of these batteries has evolved from nickel-cadmium (NiCd) to nickel-hydrogen (NiH2). Most recently, the lithium-ion technology has proven to be the next generation of choice. With cell voltages more than 3 times that of nickel-hydrogen and a very low volume configuration, these high energy density, lithium-ion secondary cells are very attractive for use on future spacecraft. This paper summarizes the past and present activities of EPT in the quest to develop the lithium-ion technology for spacecraft applications, as well as environmental issues and future development work. Specific technical challenges include the ability of lithium-ion secondary cells to achieve the hgh cycle life and long calendar life required for use on highreliability spacecraft, and the difficulties in scaling up cell technology (15 Ah) to larger sizes (100 Ah) required for spacecraft power systems. With significant improvements over existing cell technology, the lithium-ion system will provide tremendous savings in lift-off cost as well as package flexibility. Cycle life, mechanical and thermal designs are discussed.