The main challenges facing rechargeable batteries today are: (1) increasing the electrode capacity; (2) prolonging the cycle life; (3) enhancing the rate performance and (4) insuring their safety. Significant efforts have been devoted to improve the present electrode materials as well as to develop and design new high performance electrodes. All of the efforts are based on the understanding of the materials, their working mechanisms, the impact of the structure and reaction mechanism on electrochemical performance. Various operando/in-situ methods are applied in studying rechargeable batteries to gain a better understanding of the crystal structure of the electrode materials and their behaviors during charge-discharge under various conditions. In the present review, we focus on applying operando X-ray techniques to investigate electrode materials, including the working mechanisms of different structured materials, the effect of size, cycling rate and temperature on the reaction mechanisms, the thermal stability of the electrodes, the degradation mechanism and the optimization of material synthesis. We demonstrate the importance of using operando/in-situ XRD and its combination with other techniques in examining the microstructural changes of the electrodes under various operating conditions, in both macro and atomic-scales. These results reveal the working and the degradation mechanisms of the electrodes and the possible side reactions involved, which are essential for improving the present materials and developing new materials for high performance and long cycle life batteries.

We report the analysis of comb-like polymers by solid-state NMR. The polymers were previously evaluated as solid-polymer-electrolytes (SPE) for lithium-polymer-metal batteries that have suitable ionic conductivity at 60 °C. We propose to develop a correlation between ¹³C solid-state NMR measurements and phase segregation. ¹³C solid-state NMR is a perfect tool for differentiating polymer phases with fast or slow motions. ⁷Li was used to monitor the motion of lithium ions in the polymer, and activation energies were calculated.

In situ X-ray diffraction was employed to investigate the crystal structure changes in Cr/Si co-doped Li(Co,Fe)PO₄ cathode material during a galvanostatic charge/discharge process at a slow rate of C/30. The evolution of the X-ray patterns revealed that the phase transformation between the Cr/Si-Li(Co,Fe)PO₄ and Cr/Si-(Co,Fe)PO₄ is a two-step process, which involves the formation of an intermediate compound of Cr/Si-Li_0.62(Co,Fe)PO₄ upon the extraction of Li ions from the pristine phase. Different from the previously reported two biphasic transition steps, the phase transformation of the Cr/Si-Li(Co,Fe)PO₄ followed a solid solution and a biphasic reaction pathway at different stages of the delithiation/lithiation process, respectively.