A Synergistic Approach to Reduce the Hysteresis in Conversion Reactions

Keywords:Lithium-ion battery, conversion reaction, hysteresis, composite material

In order to expand the Li-ion battery (LIB) technology and to enlarge energy demanded applications such as the electrical vehicle, an increase in their energy storage density is needed. An alternative to common intercalation materials are the so-called conversion materials which undergo a multi-electron redox process [1]. Instead of inserting Li, these materials undergo reversible reduction to form metal nanoparticles M⁰ and binary Li compounds: Mⁿ⁺X_y + nLi⁺+ ne^- ↔ M⁰ + yLi_z/yX [2]. Transition metal oxides such as Fe₂O₃ or Fe₃O₄are examples of this type of materials and have largely been studied these last years due to their high capacity values, good cycleability, capacity retentions and low toxicity and cost [2]. However, they present some drawbacks such as large voltage hysteresis between charge and discharge, which would lead to an enormous loss of energy efficiency of the battery.

In this work we present a synergistic approach to reduce the hysteresis in conversion materials. To do so, C- FeO_xcomposites with tailored microstructure are prepared using low cost methods. In the literature, carbon-metal oxide nanocomposites has already been used as a strategy to improve the cycleablity of conversion materials but no hysteresis reduction effect was previously observed [2, 3]. In our work, a significant hysteresis voltage reduction ( ≥ 0.3 V) will be shown through the combination of two materials reacting through different mechanisms (intercalation and conversion). The reduction of polarisation through a dual mechanism has been observed in the nanocomposite formed during the electrochemical reaction of titanium hydroxyfluoride [4] and is herein applied to abundant and low cost materials able to deliver much higher capacities. Insights about the electrochemical reactions and mechanisms taking place in these composite materials will be shown by means of TEM, XPS and in-situ Raman spectroscopy data.

References

[1]   Armand, M.; Tarascon, J.-M. Nature 2008, 451, 652.

[2]   Cabana, J.; Monconduit, L.; Larcher, D. ; Palacin, M. R. Adv. Mater. 2010, 22, E170.

[3]   Zhang W.M. ; Wu X.L. ; Hu J.S. ; Guo Y.G : Wan L.J. Adv. Funct. Mater. 2008, 18, 3941.

[4]   Dambournet, D. ; Chapman, K. W. ; Chupas P.J. ; Gerald, R.E.; Penin, N.; Labrugere, C.; Demourgues, A.; Tressaud, A.; Amine, K. J. Am. Chem. Soc. 2011, 133, 13240.