Iron-Doped ZnO for Lithium-Ion Anodes: Impact of the Dopant Ratio and Carbon Coating Content

Abstract

Herein, an investigation of the impact of the dopant and carbon content in iron-doped zinc oxide/carbon composites is presented. For this purpose, a comprehensive morphological, structural, and electrochemical characterization of a series of different compounds is reported, including techniques like X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma optical emission spectroscopy (ICP-OES), thermogravimetric analysis (TGA), specific surface area using the Brunauer-EmmettTeller (BET) algorithm, pycnometry, small-angle X-ray scattering (SAXS), cyclic voltammetry (CV), and galvanostatic cycling. The obtained results reveal an impact of the iron-dopant content on the crystallite and particle size as well as the detailed de-/lithiation mechanism. The effect on the cycling stability, however, appears to be rather minor. The carbon coating content, on the contrary, has a significant influence on the cycling stability and rate capability. According to these results, a carbon content of about 10 wt% is sufficient to achieve stable cycling at lower current densities, while a carbon content of 15-20 wt% allows for specific capacities of 425-500 mAh g −1 , when applying a specific current of 1 A g −1 , for instance. Despite the tremendous commercial success of lithium-ion batteries for a wide variety of applications -ranging from small-scale portable electronics to electric bikes and scooters and, recently, electric vehicles -further enhanced energy and power densities are needed for the realization of a fully electrified public and private transport. [1][2][3][4] While optimized cell designs and battery engineering have a great impact on such improvement, the next great leap forward will require the implementation of new battery chemistries. With regard to the anode side, most research activities within the past years have focused on replacing graphite by alloying or conversion materials, which commonly allow for substantially higher specific capacities. [5][6][7] However, both material classes suffer intrinsic challenges like dramatic volume variations upon de-/lithiation (particularly in case of alloying materials) and relatively wide lithium reaction potentials, accompanied by a substantial voltage hysteresis between charge and discharge (especially in case of conversion materials), resulting in rapid capacity fading of the corresponding electrodes, comparably lower specific energies, and improvable energy storage efficiencies, respectively. [5][6][7] In an attempt to overcome these challenges, we have recently reported a new class of materials -transition metal-doped metal oxides -for which the reduced transition metal (i.e., upon lithiation) enables the reversible formation of Li 2 O, i.e., the conversion reaction. Additionally, the metal itself can form a lithium alloy. [8][9][10][11][12] Within this materials' class a particular focus was, so far, set on Fedoped ZnO with a Zn:Fe ratio of 9:1, providing a theoretical specific capacity of 966 mAh g -1 . 8,9,12 While the nanopart...

3D Porous Cu–Zn Alloys as Alternative Anode Materials for Li‐Ion Batteries with Superior Low T Performance

“…This proves that similarly to Co and Fe, Cu enhances the reversibility of Li 2 O. [30,32] When increasing the Zn content to 86%, the "activation" is not observed, and a stable capacity around 150 mAh g −1 is provided by the alloying mechanism already from the first cycle. However, the reversibility of the conversion process decreases, resulting in an overall reduced capacity over the first 10 cycles.…”

In‐Situ Electrochemical SHINERS Investigation of SEI Composition on Carbon‐Coated Zn0.9Fe0.1O Anode for Lithium‐Ion Batteries

“…Improvement in energy and power densities can be achieved by substituting the graphite with other negative electrode materials with much higher capacity values. This is attainable with the combination of a conversion reaction, which leads to the reversible formation of Li 2 O, and an alloying reaction with lithium, thus transition metal‐doped metal oxides are of great interest . Zinc ferrite (ZnFe 2 O 4 ) has a theoretical specific capacity of 1001 mAh g −1 which is almost three times higher than the theoretical specific capacity of graphite (C=372 mAh g −1 ) ,.…”

“…Fe‐doped ZnO (Zn 1−x Fe x O) materials also have high capacity values due to conversion‐alloying processes, with practical capacities of 900 mAh g −1 after the first cycle and a stabilised capacity of 735 mAh g −1 upon cycling at 48 mA g −1 . The amount of iron dopant in the structure has an influence on the (de)lithiation mechanism ,. Higher iron content leads to higher capacities at high potentials due to the reduction of Fe 3+ to Fe 2+ at 1.5 V and 1.2 V, resulting in cationic vacancies that allows the insertion of lithium cations prior to the conversion reaction .…”

“…However, these transition metal oxides suffer from large volume changes during cycling that result in nanoparticle contact loss with poor electronic conductivity leading to capacity fading and low cyclability ,. These issues can be overcome by encapsulating the metal oxide nanoparticles inside of a carbon coating ,,,. The amount of carbon content has an impact on the material stability during cycling and on the rate capability …”

“…These issues can be overcome by encapsulating the metal oxide nanoparticles inside of a carbon coating ,,,. The amount of carbon content has an impact on the material stability during cycling and on the rate capability …”