Origin of Capacity Fade of pure layered P2-NaxMnyNi1-yO2 Cathode Materials with Controlled Particle Architecture


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With increasing share of energy from renewable sources, an increasing demand for energy storage evolves. Today, lithium-ion batteries are dominating mobile drive-trains and also play a key role in stationary energy storage. Lithium-ion batteries are incorporating critical raw materials in view of availability and economic importance, such as cobalt, lithium and graphite.
Sodium-based batteries, in which Lithium is replaced by Sodium have a couple of strong benefits among that the use of cobalt-free host lattices. Furthermore, aluminium can replace copper in anode current collector foils. The wide availability and cost-effectiveness of Sodium makes sodium-ion batteries (SIB) a promising complementary technology to lithium-ion batteries [1].
Among various known cathode materials for sodium-ion batteries, the family of layered sodium transition metal oxides (NaxMO2, 1>x>0) offers the most promising electrochemical performance [2]. These compounds show a wide structural variety (O3, P3, P2) due to the ionic radius of sodium and the tendency for Na+/vacancy ordering [3].
In our work, we developed manganese-based, cobalt-free layered NaxMnyNi1-yO2 active cathode materials with P2-type structure. The chosen synthesis route enables to control electrochemically important factors such as crystallite size, particle size and particle architecture. The influence of the Na/M-stoichiometry and synthesis temperature is analysed over a broad range. Under optimized conditions phase-pure P2 materials form.
We characterized such cathode materials by ICP-OES, XRD, SEM and EDX. The materials provide reversible discharge capacities in excess of 200 mAh g-1 at 17 mA g-1 in the voltage window between 1.5 – 4.3 Volt in half-cell configuration. Capacity fade was investigated using electrochemical methods and ex-situ characterization of the electrodes. The poster will discuss the influence of crystallographic structure and chemical composition on the electrochemical performance. It will also comment on the processability of such materials in electrode manufacturing under ambient air conditions.
The selected synthesis process of such cathode materials can be easily scaled-up and the product can be used in commercial battery manufacturing processes.

[1] Vaalma, Buchholz, Weil, Passerini, Nature Rev. Mater. 2018, 3, 18013
[2] Ortiz-Vitoriano, Drewett, Gonzalo, Rojo, Energy Environ. Sci. 2017, 10, 1051
[3] Kubota, Kumakura, Yoda, Kuroki, Komaba, Adv. Energy Mater. 2018, 8, 1703415

The German Federal Ministry of Education and Research (BMBF) supported this work within the project TRANSITION (03XP0186C).

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