Low-temperature performance of Li-ion batteries: The behavior of lithiated graphite

Safety issues along with the substantially reduced energy and power capabilities of Li-ion cells, operated at low temperatures, pose a technical barrier limiting their use in electric vehicles and aerospace applications. A combined in situ high-resolution neutron powder diffraction and electrochemical study on Li-ion cells of the 18650-type over a temperature range from 230 K to 320 K is reported with a focus on the graphite anode and the low temperature performance of the cell. Instead of a quasi-continuous behavior as observed at ambient temperatures, an anomalous behavior occurs upon discharge at low temperature, primarily reflected in the abrupt character of the LiC12 – to – graphite phase transformation and the unusual temperature dependence of the amount of LiC6. An instability of lithiated graphite phases at temperatures below 250 K is observed, which affects the performance of Li-ion batteries at low temperatures.