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Abstract: The structural response to electrochemical cycling of the components within a commercial Li-ion battery (LiCoO2 cathode, graphite anode) is shown through in situ neutron diffraction. Lithuim insertion and extraction is observed in both the cathode and anode. In particular, reversible Li incorporation into both layered and spinel-type LiCoO2 phases that comprise the cathode is shown and each of these components features several phase transitions attributed to Li content and correlated with the state-of-charge of the battery. At the anode, a constant cell voltage correlates with a stable lithiated graphite phase. Transformation to de-lithiated graphite at the discharged state is characterised by a sharp decrease in both structural cell parameters and cell voltage. In the charged state, a two-phase region exists and is composed of the lithiated graphite phase and about 64% LiC6. It is postulated that trapping Li in the solid|electrolyte interface layer results in minimal structural changes to the lithiated graphite anode across the constant cell voltage regions of the electrochemical cycle. [ABSTRACT FROM AUTHOR]

The reaction evolution and kinetics of the LiFePO 4 positive electrode material is dependent on the synthesis method and cycling conditions. In operando neutron powder diffraction is used investigate the structure-electrochemistry relationship of the electrode materials in a Valence Technology Inc. 18650 Energy cell (IFR18650EC) containing a graphite negative electrode and a Mg-doped LiFePO 4 (Li(MgFe)PO 4 ) positive electrode. Two cells were studied at ambient (298 K) and elevated (323 K) temperature, and higher temperatures were found to improve reaction kinetics and hence capacity. Rietveld refinement of structural models against the diffraction data revealed information about the nucleation of the lithiated and delithiated phases in the Li(MgFe)PO 4 positive electrode material as a function of each cell's state of charge. Polarisation was indicated by a shift in the potential at which the lithiated and delithiated (MgFe)PO 4 phases nucleate during cycling, the extent of which was found to be linearly proportional to the applied current. This work provides new evidence for polarisation of the positive electrode material in a Li-ion battery system. [ABSTRACT FROM AUTHOR]

Ex situ and time-resolved in operando neutron powder diffraction (NPD) has been used to study the structural evolution of the graphite negative electrode and LiFePO 4 positive electrode within ANR26650M1A commercial batteries from A123 Systems, in what to our knowledge is the first reported NPD study investigating a 26650-type battery. Batteries with different and accurately-known electrochemical and storage histories were studied, enabling the tell-tale signs of battery degradation to be elucidated using NPD. The ex-situ NPD data revealed that the intensity of the graphite/lithiated graphite (Li x C 6 or Li y C) reflections was affected by battery history, with lower lithiated graphite (LiC 12 ) reflection intensities typically corresponding to more abused batteries. This indicates that the lithiation of graphite is less progressed in more abused batteries, and hence these batteries have lower capacities. In operando NPD allows the rate of structural evolution in the battery electrode materials to be correlated to the applied current. Interestingly, the electrodes exhibit different responses to the applied current that depend on the battery cycling history, with this particularly evident for the negative electrode. Therefore, this work illustrates how NPD can be used to correlate a battery history with electrode structure. [ABSTRACT FROM AUTHOR]