Improving Lithium-Ion Battery Performance of Metal Oxide Nanoparticles By Organic Hybridization Using Anchoring Carbon Precursor Polymers

Designing new electrode materials is a promising way to solve several issues, which currently exist in state-of-the-art lithium-ion batteries. These issues comprise especially a safety issue caused by the degradation of commonly used electrolytes due to the high cell voltage.^[1] Moreover, current commercial batteries suffer from low specific capacities,^[2] which makes the application of current batteries to electric vehicles not reasonable.

Promising alternative materials, which might substitute the currently used graphite on the anode side and which might solve the previously mentioned issues, are transition metal oxides.^[1] However, using these materials requires commonly also a down-sizing approach to nanometer-sized particles to ensure short diffusion distances for lithium-ions and electrons.^[2] Introducing a conductive coating on the surface of such kind of nanoparticles increases on the one hand the conductivity of the otherwise hardly conducting inorganic nanoparticles and prevents on the other hand side reactions related to the high surface. ^[3]

In this contribution, a carbon coating approach is introduced using carbon precursor polymers, that contain besides well carbonizable repeating units also anchoring units, which can effectively coordinate onto the metal oxide surface (see Figure 1a).^[4] This approach ensures, that the carbonization takes place exclusively on the surface of the particles yielding a homogeneous carbon coating.

The carbon coating approach is applied to different nanostructured anatase titanium dioxide particles, whereas the purpose of using titanium dioxide is to solve the safety issue. Our electrochemical investigation proves that the introduced carbon coating enhances the battery with respect to cycling stability and to the energy efficiency (see Figure 2b), since the carbon coating prevents a structural degradation of anatase nanoparticles observed for uncoated particles.^[3] Increasing the surface area of nanostructured TiO₂by variation of the morphology could in addition improve the high C-rate performance.

Furthermore, the carbon coating approach was applied to gold/zinc oxide hetero-nanoparticles, which work as an alloying compound during the reaction with lithium and offers theoretically higher specific capacities (ZnO: 987 mAh g^-1) compared to graphite (372 mAh g^-1). In this case the positive influence of the carbon coating expresses in a dramatically enhanced specific capacity during the lithiation/delithiation process compared to uncoated particles demonstrating again the importance of surface coating for the battery performance of nano-sized inorganic nanoparticles.

[1]     B. Scrosati, J. Garche, J. Power Sources, 195, 2419 (2010).

[2]     A. S. Aricò, P. Bruce, B. Scrosati, J.-M. Tarascon, W. van Schalkwijk, Nat. Mater. 4, 366 (2005).

[3]     D. Bresser, B. Oschmann, M. N. Tahir, W. Tremel, R. Zentel, S. Passerini, Journal of Power Sources, 248, 852 (2014).

[4]     B. Oschmann, D. Bresser, M. N. Tahir, K. Fischer, W. Tremel, S. Passerini, R. Zentel, Macromol. Rapid Commun., 34, 1693 (2013).