Journal
SMALL
Volume 16, Issue 20, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/smll.202001090
Keywords
first-principles calculations; insertion; KTi2(PO4)(3); potassium-ion batteries
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Funding
- Basic Science Research Program through the National Research Foundation of Korea (NRF) - Ministry of Education, Science, and Technology of Korea [NRF 2015M3D1A1069713, NRF 2017R1E1A2A01079404, NRF 2017M2A2A6A01070834, NRF 2017K1A3A1A30084795]
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In this work, rhombohedral KTi2(PO4)(3) is introduced to investigate the related theoretical, structural, and electrochemical properties in K cells. The suggested KTi2(PO4)(3) modified by electro-conducting carbon brings about a flat voltage profile at approximate to 1.6 V, providing a large capacity of 126 mAh (g-phosphate)(-1), corresponding to 98.5% of the theoretical capacity, with 89% capacity retention for 500 cycles. Structural analyses using electrochemical performance measurements, first-principles calculations, ex situ X-ray absorption spectroscopy, and operando X-ray diffraction provide new insights into the reaction mechanism controlling the (de)intercalation of potassium ions into the host KTi2(PO4)(3) structure. It is observed that a biphasic redox process by Ti4+/3+ occurs upon discharge, whereas a single-phase reaction followed by a biphasic process occurs upon charge. Along with the structural refinement of the electrochemically reduced K3Ti2(PO4)(3) phase, these new findings provide insight into the reaction mechanism in Na superionic conductor (NASICON)-type KTi2(PO4)(3). The present approach can also be extended to the investigation of other NASICON-type materials for potassium-ion batteries.
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