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- ItemStructural and Electrochemical Properties of Layered P2-Na0.8Co0.8Ti0.2O2 Cathode in Sodium-Ion Batteries(Basel : MDPI, 2022) Pohle, Björn; Gorbunov, Mikhail V.; Lu, Qiongqiong; Bahrami, Amin; Nielsch, Kornelius; Mikhailova, DariaLayered Na0.8Co0.8Ti0.2O2 oxide crystallizes in the β-RbScO2 structure type (P2 modification) with Co(III) and Ti(IV) cations sharing the same crystallographic site in the metal-oxygen layers. It was synthesized as a single-phase material and characterized as a cathode in Na- and Na-ion batteries. A reversible capacity of about 110 mA h g−1 was obtained during cycling between 4.2 and 1.8 V vs. Na+/Na with a 0.1 C current density. This potential window corresponds to minor structural changes during (de)sodiation, evaluated from operando XRD analysis. This finding is in contrast to Ti-free NaxCoO2 materials showing a multi-step reaction mechanism, thus identifying Ti as a structure stabilizer, similar to other layered O3- and P2-NaxCo1−yTiyO2 oxides. However, charging the battery with the Na0.8Co0.8Ti0.2O2 cathode above 4.2 V results in the reversible formation of a O2-phase, while discharging below 1.5 V leads to the appearance of a second P2-layered phase with a larger unit cell, which disappears completely during subsequent battery charge. Extension of the potential window to higher or lower potentials beyond the 4.2–1.8 V range leads to a faster deterioration of the electrochemical performance. After 100 charging-discharging cycles between 4.2 and 1.8 V, the battery showed a capacity loss of about 20% in a conventional carbonate-based electrolyte. In order to improve the cycling stability, different approaches including protective coatings or layers of the cathodic and anodic surface were applied and compared with each other.
- ItemProgress and challenges in using sustainable carbon anodes in rechargeable metal-ion batteries(Amsterdam [u.a.] : Elsevier, 2021) Soltani, Niloofar; Bahrami, Amin; Giebeler, Lars; Gemming, Thomas; Mikhailova, DariaRechargeable lithium-ion batteries (LIBs) are one of the most promising alternatives to effectively bypass fossil fuels. However, long-term energy application of LIBs could be restricted in the future due to the increased production cost of LIB arising from the shortage and inaccessibility of Li in the Earth's crust. Na or K have been considered as substitutes for Li but in spite of their natural abundance, they suffer from low gravimetric/volumetric energy density. An alternative to increase the efficiency of sodium-ion battery (SIBs) and potassium-ion battery (KIBs) is to focus on finding the high‐performing negative electrode, the anode. The large volume changes of alloying and conversion type anodes for KIBs and SIBs make hard carbons to a better option on this regard than usual graphitic carbons, but a key obstacle is the reliance on unsustainable sources. Thus, biomass-derived carbon could offer a promising alternative, and it has indeed been in the focus of much recent work. This review highlights the recent advances in using carbon extracted from various biomass sources in rechargeable Li-, Na-, and K-ion batteries. Maximizing the energy and power densities as well as the lifetime of carbon anodes require an exploration of the right balance between carbon structures, pore morphology, chemical composition and alkali metal-ion storage. Thus, in this review, first, we take stock of key challenges and opportunities to extract carbon from various plants structural components and identify the extracted carbon structure compared to graphite-like structure. Then, we provide an overview on morphological and structural modification of the extracted carbons. Finally, we show how the physicochemical properties, structural alignment and morphological variation of the biomass-derived carbon can affect the storage mechanism and electrochemical performance. The extensive overview of this topic provided here is expected to stimulate further work on environmentally friendly battery design and towards the optimization of the battery performance. Electrode materials in alkali-metal-ion batteries that are based on biomass-derived carbon may allow not only a technical breakthrough, but also an ethically and socially acceptable product.