CaLi2 as an Anode in Li-Ion Batteries

Report No. ARL-TN-201
Authors: Jeff Wolfenstine
Date/Pages: April 2003; 12 pages
Abstract: This technical note summarizes the work on CaLi2 as a potential anode for use in Li-ion batteries. CaLi2 was studied for two reasons: (1) CaLi2 has a theoretical gravimetric capacity of 3.6 times the theoretical value of the currently used graphite, and (2) The melting temperature of CaLi2 is 503 K. The ratio of the testing temperature (room temperature), T, to the melting temperature, Tm, for CaLi2 is equal to 0.59. This is significant because it is known that as the ratio of T/Tm > 0.4, diffusion processes become important allowing time-dependent plastic deformation to occur, which can accommodate the stresses generated as a result of Li insertion. In contrast, most Li alloys are tested in the region T/Tm < 0.4, where no plastic deformation occurs and hence, rapid failure with high capacity fade is observed. It was expected that CaLi2 should exhibit low capacity fade compared to most other Li alloys. A CaLi2 alloy with micron-sized particles exhibited a rapid loss of capacity with increasing number of cycles. Its rapid failure and capacity fade can be correlated with its low-fracture toughness (KIC ~ 1 MPa-m1/2). It is anticipated if the particle/grain size can be reduced from the micron to the nanoscale that the material will switch from a dislocation to a grain-sliding deformation mechanism, which will lead to increased ductility and reduced capacity fade. A high ratio of the testing temperature to the melting temperature (T/Tm > 0.4) is a necessary but not sufficient condition for an alloy to exhibit low capacity fade. The microstructure must also be considered.
Distribution: Approved for public release
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Last Update / Reviewed: April 1, 2003