Real Time Observation of LiFePO4:V Cathode and (Ti,Sn)O2 Anode for a Lithium Ion Battery By Synchrotron X-Ray and Neutron Methods

Real time observations on a lithium ion battery containing (Sn,Ti)O₂ anode and LiFePO₄:V cathode are performed by in situ synchrotron X-ray and neutron methods. To meet the requirements of real applications to the electric vehicles, storage devices,...etc., the new electrode materials exploration and current materials modification are very important to achieve such a goal. In situ techniques could provide real time structural changes during charging and discharging. Whether working on new material exploration or current materials modification, the obtained information from structural changes could provide a correct direction to develop a more suitable battery for real applications.

(Sn, Ti)O₂ is newly developed [1] for next general anode material. To combine the good characteristics of TiO₂ and high specific capacity of SnO₂, we could have a good and interesting material. The synthesized (Sn,Ti)O₂ is rutile-type solid solution after annealing. We have chosen the sample after annealing under 550°C, which has the best electrochemical properties to be the anode material. From the neutron and X-ray powder diffraction (XPD) patterns, we are certainly sure the formation of (Sn,Ti)O₂ with a part of amorphous components in the produced samples. The in situ XPD will provide more detail structural changes during the electro-chemical cycling. From X-ray absorption data, we find the extended X-ray absorption find structure (EXAFS) spectra of Sn are changed but no changes of Ti spectra as the annealing temperatures changes. That means Si-O-Ti bindings formed. From the in-situ measurement of Sn EXAFS curves, these spectra won’t be changed according to the changes of charging and discharging conditions. That means the local environment of Sn didn’t changed. That fits to expect on that Ti plays the most important role during lithiation and delithiation process. In situ EXAFS spectra of Ti will prove this assumption.    

LiFePO₄:V cathode is produced by modifying the pristine LiFePO₄ by adding a small amount of V. After adding V into LiFePO₄, the mechanism of enhancing the capacity of the LiFePO4 cathodes is due to the location of V is at the lithium site and then to induce lithium vacancies in the crystal structure [2]. From the in situ X-ray data, whether in XPD or X-ray absorption near edge structure (XANES), which reveals the parts of amorphous components of the pristine LiFePO_4, are increased as the electrochemical cycles increase. After adding V, the speed to form the amorphous parts is reduced. As the increase of the amorphous part, the electrochemical properties become poor. That means the added V could effectively prolong the cycling life through reducing production of amorphous components. To observe the (Sn, Ti)O₂ anode and LiFePO₄:V cathode in a battery at the same time is worth expect.

References:

[1] Y. C. Chen et al., Nanoscale 5 (2013) 2254.

[2] C. Y. Chiang et al., J. Phys. Chem. C 116 (2012) 24424.