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Titanium-based potassium-ion battery positive electrode

Small energy storage devices (like the ones used in cell phones, tablets, and laptops) based on the mature Lithium-ion technology have become a key element of our daily life. Facing the pressing challenges posed by Global Warming, the increasing demand of storage systems for the large-scale automotive industry will soon clash with the sparse provision of lithium in the Earth’s crust.
In this panorama, the development of economically feasible emerging battery technologies based on alternative, earth-abundant, elements, is thus highly desirable.
Potassium-ion batteries could represent a viable substitute to Lithium-ion technology in a large-scale green economy. However, the key problem preventing the success of the K-ion technology is linked to the low efficiency of cathode materials. 

Recently, the group of prof. Stanislav Fedotov from the Skoltech Center for Energy Science and Technology (Moscow, Russia) developed a novel titanium-based K-ion fluoride-phosphate material with the perspective to set an important milestone in the design of future storage systems based on this metal.
In this work, published in Nature Communications, this material, KTiPO4F, was found to adopt a KTiOPO4-(KTP)-type orthorhombic crystal structure that boosts the Ti4+/Ti3+transition to extraordinarily high electrode potentials approaching 3.6–3.7 V vs. K+/K with unprecedented stability at high discharge rates. Understanding the structural evolution of the positive electrode during its charge/discharge is extremely important to explain this unique electrochemical performance. With access to X-ray powder diffraction at the MCX beamline the structural transformation was successfully studied in operando (see data shown in Figure 1). 
According to the diffraction data, the structural transformation of KTiPO4F starts with a two-phase transition leading to a lower (monoclinic) symmetry. The further K+deintercalation tentatively proceeds via a solid-solution mechanism, as no changes in symmetry are observed, and is followed by another two-phase transition. The potassium depleted material was charged up to 4.2 V reaching the K0.2TiPO4F composition without undergoing amorphization, preserving the integrity of the polyhedral framework.
Compared to isostructural compounds, KTiOPOand KVPO4F, the new material contains slightly larger interstitial voids resulting in the splitting of K ions over several energetically equivalent sites, which ultimately promotes the ionic diffusion.
The work by S. Fedotov et al. shows that the titanium redox activity traditionally considered as “reducing” can be upshifted to near-4V electrode potentials thus offering a playground to design sustainable and cost-effective titanium-containing positive electrode materials with promising electrochemical characteristics.
Overall, this earth-abundant, easily scalable, and thermally stable KTiPO4F material reveals exciting electrochemical performance outperforming many benchmarked potassium-ion cathode materials. 

Figure 1.    Structural evolution of KTiPO4F. (a) Initial crystal structure (b) In operando SXPD: phase transformations. (c) Corresponding charge-discharge profile
 

 

This research was conducted by the following research team:

Stanislav S. Fedotov1, Nikita D. Luchinin2, Dmitry A. Aksyonov1, Anatoly V. Morozov1, Sergey V. Ryazantsev1,2, Mattia Gaboardi3, Jasper R. Plaisier3,Keith J. Stevenson1, Artem M. Abakumov1, Evgeny V. Antipov1,2.

Skoltech Center for Energy Science and Technology, Skolkovo Institute of Science and Technology, Russian Federation.
Department of Chemistry, Lomonosov Moscow State University, Russian Federation. 
Elettra - Sincrotrone Trieste SCpA, Trieste, Italy.



Contact persons:

Stanislav S. Fedotov, email: s.fedotov@skoltech.ru
 

Reference

Stanislav S. Fedotov, Nikita D. Luchinin, Dmitry A. Aksyonov, Anatoly V. Morozov, Sergey V. Ryazantsev, Mattia Gaboardi, Jasper R. Plaisier, Keith J. Stevenson, Artem M. Abakumov, Evgeny V. Antipov, “Titanium-based potassium-ion battery positive electrode with extraordinarily high redox potential”, Nature Communications 11, 1484 (2020); DOI: 10.1038/s41467-020-15244-6



Last Updated on Wednesday, 08 April 2020 09:15