(Invited) Development of Most Important Cathodes for Li Ion Batteries that can Promote the Electro-Mobility Revolution

Abstract

Electro-mobility is the major challenge today in the field of electrochemical power sources. However, we encounter too many unsupported promises, too much noise! Examples: Many publications on ‘novel’ nano-materials, not suitable for practical battery applications. Nanomaterials may mean high surface area and pronounced side reactions. For instance - thousands of papers on conversion reactions anodes (nanomaterials), none of them show performance at elevated temperatures, why? Also nano-materials have puffy structure (difficult to process into electrodes). A lot of words (recently also conferences) on “ beyond Li-ion batteries”. Beyond… for what purposes? Hard to see what can be relevant for electrochemical propulsion beyond Li-ion batteries. In fact, the only relevant partner may be H2/O2 fuel cells, which are becoming highly relevant power sources because hydrogen can be stored in EVs at high pressure. The renaissance of Li metal based batteries is interesting, fully justified, but not for cars! Is the progress in Li-S batteries relevant to EVs? Practically, safety concerns are not being addressed well enough. The main theme of this presentation is to examine what is the true horizons for advance Li ion batteries that can promote the electro-mobility revolution. The limiting factor in Li-ion batteries in terms of energy density, cost, potential, durability and cycling efficiency are the cathode materials used. Over the years many types of cathode materials for Li-ion batteries were examined, including olivine phosphates (LiMPO4) , spinel structures (LiMn2O4,LiMn0.15Ni0.5O2) , Li and Mn rich layered oxides (Li1+x[MnNiCo]1-xO2 and layered Li[NiCoMn]O2 compounds The most promising cathode materials for advanced Li-ion batteries are lithiated transition metal oxides with a layered structure, in which the main transition metal is nickel. As the amount of Ni in lithiated transition metal cathode materials is higher, the specific capacity is higher as well, yet can be extracted at relatively low potentials (< 4.3 V vs. Li) which do not endanger the anodic stability of the electrolyte solutions used in these batteries. For instance, The specific capacity of LiNiO2 cathodes can reach 240 mAh/g upon charging to 4.3 V. However, as the content of Ni is higher, these cathode materials are less stable mechanically, thermally and electrochemically. The capacity fading mechanisms involve stresses with are formed in the particles when their full capacity is realized by charging to 4.3 V. Cracks are formed, increase the specific surface area and allow detrimental reactions of components from the electrolyte solutions with the cathode materials within their cracks. These side reactions lead to exfoliation and destruction of the active mass. Using judicious doping and/or surface coating, it is possible to fully mitigate these detrimental situation. After gaining enough experience, it is possible to develop computational routes that can suggest optimal doping and coating processes. This presentation reports about our ongoing work in the field. Accumulated results by us and by many others indicate that developing advanced Li-ion batteries, fully suitable for long range electric vehicles, is real and fruitful.