Application of operando X-ray diffraction and Raman spectroscopies in elucidating the behavior of cathode in lithium-ion batteries

With the advances in characterization techniques, various operando/in-situ methods were applied in studying rechargeable batteries in order to improve the electrochemical properties of electrode materials, prolonging the battery life and developing new battery materials. In the present review, we focus on the characterization of electrode materials with operando/in-situ X-ray diffraction and Raman spectroscopies. By correlating the results obtained via these two techniques in different electrode chemistry: (a) intercalation materials, such as layered metal oxides and (b) conversion materials, such as elemental sulfur. We demonstrate the importance of using operando/in-situ techniques in examining the microstructural changes of the electrodes under various operating conditions, in both macro and micro-scales. These techniques also reveal the working and the degradation mechanisms of the electrodes and the possible side reactions involved. The comprehension of these mechanisms is fundamental for ameliorating the electrode materials, enhancing the battery performance and lengthening its cycling life

Discovering the influence of lithium loss on Garnet Li7La3Zr2O12 Electrolyte Phase Stability

Garnet-type lithium lanthanum zirconate (Li7La3Zr2O12, LLZO) based ceramic electrolyte has potential for further development of all-solid-state energy storage technologies including Li metal batteries, Li-S and Li-O2 chemistries. The essential prerequisites such as LLZO’s compactness, stability and ionic conductivity for this development are nearly achievable via solid-state reaction route (SSR) at high temperatures but it involves a trade-off between LLZO’s caveats owing to Li loss via volatilization. For example, SSR between lithium carbonate, lanthanum oxide and zirconium oxide is typically supplemented by dopants (e.g. gallium or aluminum) to yield the stabilized cubic phase (c-LLZO) that is characterized by ionic conductivity an order of magnitude higher than the other polymorphs of LLZO. Whilst the addition of dopants as phase stabilizing agent and supplying extra Li precursor for compensating Li loss at high temperatures become common practice in solid-state process of LLZO, the exact role of dopants and stabilization pathway is still poorly understood, which leads to several manufacturing issues. By following LLZO’s chemical phase evolution in relation to Li loss at high temperatures, we here show that stabilized c-LLZO can directly be achieved by an in-situ control of lithium loss during SSR and without needing dopants. In light of this, we demonstrate that dopants in the conventional SSR route also play a similar role, i.e., making more accessible Li to the formation and phase stabilization of c-LLZO, as revealed by our in-situ X-ray diffraction analysis. Further microscopic (STEM, EDXS, and EELS) analysis of the samples obtained under various SSR conditions provides insights into LLZO phase behavior. Our study can contribute to the development of more reliable solid-state manufacturing routes to Garnet-type ceramic electrolytes in preferred polymorphs exhibiting high ionic conductivity and stability for all-solid-state energy storage

Measuring Spatially Resolved Collective Ionic Transport on Lithium Battery Cathodes Using Atomic Force Microscopy

One of the main challenges in improving fast charging lithium-ion batteries is the development of suitable active materials for cathodes and anodes. Many materials suffer from unacceptable structural changes under high currents and/or low intrinsic conductivities. Experimental measurements are required to optimize these properties, but few techniques are able to spatially resolve ionic transport properties at small length scales. Here we demonstrate an atomic force microscope (AFM)-based technique to measure local ionic transport on LiFePO₄ to correlate with the structural and compositional analysis of the same region. By comparing the measured values with density functional theory (DFT) calculations, we demonstrate that Coulomb interactions between ions give rise to a collective activation energy for ionic transport that is dominated by large phase boundary hopping barriers. We successfully measure both the collective activation energy and the smaller single-ion bulk hopping barrier and obtain excellent agreement with values obtained from our DFT calculations