Enabling Aqueous Processing of Cathode Materials for Li-Ion Batteries

Abstract

Nowadays, Li-ion batteries have become the most promising power source for hybrid and electric vehicles. Considering their environmental friendliness, recycling issues and therefore cost issues, one approach towards greener batteries is the substitution of fluorinated binders like polyvinylidene difluoride (PVdF) that require the use of toxic and highly volatile solvents (e.g. N-methyl-2-pyrrolidone (NMP)), with aqueous binders such as sodium carboxymethyl cellulose (sodium CMC) [1]. Nevertheless, there is a significant drawback associated aqueous processing: slurries become strongly basic due to the reaction of the cathode material with water. This leads to aluminium corrosion of the current collector [2] in addition to the active material degradation. One strategy to overcome material degradation and aluminium corrosion is the preliminary coating of the active material to prevent its reaction with water. It is then of paramount importance that the active material is not damaged upon coating process and the coating layer itself does not affect negatively the capacity or rate performance of the active material [3-5]. Here, the properties of coated Li-NMC are investigated using different coating approaches and materials. The coated Li-NMC materials were analysed by XRD to study their structure. The positive influence of the coating on the composite Li-NMC electrodes prepared with the aqueous binder is demonstrated, in particular with regard to the prevention of aluminium corrosion. SEM and TEM were used to characterize the composite electrodes, while elemental analysis and TGA were used to investigate the coating, quantitatively. Electrodes of coated and uncoated materials were prepared using the aqueous binder and investigated in terms of their capacity and rate performance to establish the influence of the active material coating. [1] G.T. Kim, S.S. Jeong, M. Joost, E. Rocca, M. Winter, S. Passerini, A. Balducci, Journal of Power Sources, 196 (2011) 2187-2194. [2] S.F. Lux, F. Schappacher, A. Balducci, S. Passerini, M. Winter, Journal of The Electrochemical Society, 157 (2010) A320-A325. [3] M. Bettge, Y. Li, B. Sankaran, N.D. Rago, T. Spila, R.T. Haasch, I. Petrov, D.P. Abraham, Journal of Power Sources, 233 (2013) 346-357. [4] B. Lin, Z. Wen, J. Han, X. Wu, Solid State Ionics, 179 (2008) 1750-1753. [5] J. Ni, L. Gao, L. Lu, Journal of Power Sources, 221 (2013) 35-41. Figure 1