In situ neutron diffraction on commercial batteries has been used to provide structural information of electrodes at various states of charge [179, 180], under overcharge (or overdischarge) conditions [181], with fresh and fatigued or used batteries [182, 183], and at different temperatures and electrochemical conditions (applied currents) [180, 183—187]. In situ NPD allows structural snapshots of electrodes within a battery to be obtained, and depending on the diffractometer, these snapshots can be extremely fast such that the time-resolved structural evo­lution can be captured. Notably, new aspects of the graphitic anode and LiCoO2 cathode that were commercialised in the 1990s are being discovered with this probe. Such insights include the existence of a small quantity of a spinel phase in
the previously-thought layered LiCoO2 cathode, an apparent lack of staged Li insertion into graphite to form LiC12 with low current rates [180], and the transfor­mation of the graphite anode to a wholly LiC6 anode with voltages around 4.5 V— above and beyond the recommend limits applied by manufacturers [181]. Figure 7.26 shows LiCoO2 and LixC6 reflections and their evolution as a function of time. Structural changes are a function of the applied charge/discharge rates, with faster structural evolution occurring at higher rates. Importantly, higher rates produce a lower capacity which is directly related to a lower quantity of the LiC6 (charged anode phase) being formed.

This information explains the processes in electrodes that are well known and in situ neutron diffraction can be used to explore a wide variety of battery-function parameters ranging from current, voltage, and lifetime. Kinetic processes in bat­teries can be probed with time-resolved data, where rates of structural changes are determined for electrode materials and related to the applied current. In most cases [184, 188, 189] the rate of structural change is directly proportional to the applied current. The rate of lattice expansion and contraction can be used to determine the

viability of electrode materials for higher power applications. However, the rela­tionship between kinetic structural parameters and the electrochemical capabilities of the battery are yet to be explored in detail. This is an active research area that may yield valuable information with more advanced experiments.