A material approach to efficient lithium-ion and aluminum batteries: from electrode to current collector

Abstract

Rechargeable batteries are deeply integrated into the present green energy economy, which becomes an integral part of human life. Smartphones, tablets, laptops, electric cars, buses, bikes, home energy storage systems, and electrical grids are only a few examples from a long list of the possible application of batteries. This shows the broad diversification of battery applications and indicates on the needs for the development of different energy storage technologies. For instance, to design the battery for portable electronics or mobility, it requires high energy and power density. On the other hand, a major requirement for stationary batteries is low capital costs of stored energy per cycle (¢ kW−1 h−1 cycle−1). The latter presumes that stationary batteries should be exclusively composed of inexpensive, Earth‐abundant, easy‐to‐produce components. Apart from that, for all battery applications, there are numerous other important electrochemical characteristics that have to be considered such as long-term cycling performance (cycle life), calendrical life, Coulombic efficiency (measure for charge loss due to irreversible side reactions), energy efficiency and the performance at different charge/discharge rates or at different temperatures. In this context, aiming to fulfill versatile requirements in the energy storage sector, researchers are constantly exploring new materials for existing battery technologies (Li-ion, Na-S, etc.) as well as new electrochemical energy concepts. In this doctoral project, towards the increase of energy density of Li-ion batteries, the utility of Sn-based anode materials which possess the high gravimetric and volumetric capacity of up to 992 mAh g−1 and 7296 mAh cm−3 has been first explored. In particular, Sn was combined with Co or Fe, which are two metals that do not form alloys with Li. On the basis of bulk phase diagrams and earlier studies on microcrystalline materials, the synthesis of CoSn2 and FeSn2 nanocrystals (NCs) was targeted to determine whether uniform CoSn2 and FeSn2 nanoalloys, composed of mixed elements with atomic homogeneity, exhibit advantageous electrochemical performances compared with those of elemental Sn NCs and their mixtures with Co (Fe) NCs (obtained by simple mechanical mixing). This study shows that monodisperse CoSn2 alloyed NCs possess considerably improved cycling stability over pure Sn NCs and mixtures of Co or Fe and Sn NCs. Notably, CoSn2 delivered a stable average capacity of 650 mAh g−1 for 5000 cycles at a high current density of 1984 mA g−1, which is among the highest reported cycling stabilities for Sn-based anode materials. The last two decades have witnessed a surge of reports on Li-ion-free batteries. For instance, other single and multivalent cations are being utilized in place of Li-ions in the conventional rocking-chair-type battery concept as Na, K, Mg, and Al-ion batteries. Further to this, other concepts commonly referred to as hybrid or dual-ion batteries draw increasing attention for stationary energy storage applications, wherein electroactive (inserted) ionic species are based on abundant metals. In particular, much attention has been paid to the development of aluminum-carbon/graphite dual-ion batteries based on chloroaluminate ionic liquids (AlCl3-carbon/graphite batteries). These batteries work as non-rocking-chair systems utilizing the reversible adsorption/intercalation of AlCl4− ions into the carbon/graphite cathode during charging (oxidation of carbon network) while Al electroplating takes place on the anode side. In an effort to improve AlCl3-carbon batteries, this work presents the use of a microporous, sp2-hybridized zeolite-templated carbon (ZTC) as a cathode material that exhibits a high specific surface area as well as the highest density of pores capable of accommodating AlCl4– ions. Its ultrahigh surface area and a dense, conductive network of homogeneous channels (12 Å in width) make ZTC suitable for the fast, dense storage of AlCl4– ions (6 Å in ionic diameter). Full cells being composed of ZTC cathode and Al anode exhibited high specific energy density (up to 64 Wh kg–1, 30 Wh L–1), highly stable cycling performance, and complete reversibility within the potential range of 0.01–2.20 V. In order to gain insight into the electrochemical performance of AlCl3-graphite battery, most basic and inexpensive forms of natural graphite-graphite flakes, and synthetic (kish) graphite flakes, have been tested as cathode materials. This work shows that the major factors that govern the efficient uptake of AlCl4– ions are the flaky morphologies and high atomistic structural quality of graphite particles. One reason for the beneficial effect of the flake geometry relates to the drastic expansion of graphite by up to 148% upon the insertion of large AlCl4– ions, which is easily accommodated by increasing the flake thickness, and much harder to accommodate by folded or corrugated graphite layers. In addition to this form factor, the structural atomic or crystalline disorder, which is probed by Raman spectroscopy and X-ray diffraction (XRD), has been shown to a profound effect on the uptake of AlCl4– ions. With respect to the electrochemical performance, the AlCl3-graphite battery using graphite flake cathode exhibited high energy and power densities of 72 Wh kg–1 and 4363 W kg–1. The latter indicates that this battery may find use as a nontoxic alternative to the primary battery technologies of similar energy densities: lead–acid (30–50 Wh kg–1; 50–80 Wh L–1) and vanadium redox-flow batteries (VRB; 10–30 Wh kg–1; 50–80 Wh L–1).Apart from carbonous cathodes, the oxidatively stable and inexpensive current collectors for AlCl3-carbon/graphite batteries were explored that can be operated in chloroaluminate ionic liquids and are composed of Earth-abundant elements. This work presents the use of titanium nitride (TiN) as a compelling material exhibiting high oxidative stability in AlCl3/1-ethyl-3-methylimidazolium chloride ionic liquid. TiN current collectors can be easily fabricated by magnetron sputtering on stainless steels or polyimide surfaces on a large scale. Moreover, its high oxidative stability has been assessed with a high-voltage LiMn1.5Ni0.5O4 cathode for high voltage Li-ion batteries. TiN/LiMn1.5Ni0.5O4 half cells comprising lithium fluorosulfonylimide-based electrolytes demonstrated high Coulombic efficiency of 98.5% at a low C-rate of 0.2 C after 100 cycles. The last part of this doctoral project focused on the use of anatase TiO2 nanorods (NRs) as a cathode material for Al-ion batteries. This material delivers high capacities of 112-165 mAh g–1 at a current density of 50 mA g–1 in AlCl3/1-ethyl-3-methylimidazolium chloride ionic liquid electrolyte of various acidities. The mechanism of aluminum intercalation into anatase TiO2 nanorods and the related crystal structure changes were assessed by density functional theory, ex situ X-ray photoelectron and energy-dispersive X-ray spectroscopies.