Self-discharge mechanism of high-voltage KVPO4F for K-ion batteries

Romain Wernert (1, 2, 3) , Long H.B. Nguyen (1, 2, 3) , Antonella Iadecola (3) , François Weill (1, 4, 3) , François Fauth (5) , Laure Monconduit (2, 4, 3) , Dany Carlier (1, 4, 3) , Laurence Croguennec (1, 4, 3)

1 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux
2 ICGM - Institut Charles Gerhardt Montpellier - Institut de Chimie Moléculaire et des Matériaux de Montpellier
3 RS2E - Réseau sur le stockage électrochimique de l'énergie
4 ALISTORE-ERI - Advanced Lithium Energy Storage Systems - ALISTORE-ERI
5 CELLS ALBA - CELLS ALBA synchroton = ALBA Synchrotron

Current performances of Li-, Na-, or K-ion batteries are mainly limited by the specific capacity of the positive electrode. Therefore, it is important to reach the highest capacity possible for a given electrode material. Here, we investigate the performance limitation of KVPO4F, a prospective material for K-ion batteries, which can deliver only 80% of its theoretical capacity. We discover that the capacity limitation of KVPO4F is related to a kinetic competition between K+ deinsertion and side reactions ascribed to the electrolyte degradation at high potentials. Homeotypic VPO4F can be obtained from KVPO4F through a chemical deintercalation process, which disproves a possible structural limitation or instability. The deintercalated compound was characterized by electron and X-ray diffraction, X-ray absorption spectroscopy, and nuclear magnetic resonance spectroscopy. Despite the structural stability, a spontaneous reaction occurs between the deintercalated KxVPO4F (x < 0.5) and the electrolyte (0.8 M KPF6 in ethylene carbonate/diethylene carbonate), with an electron transfer to vanadium compensated by K+ intercalation. This reaction leads to self-discharge until the open circuit potential is lower than 4.7 V versus K+/K, corresponding to the K0.5VPO4F composition.

Mots clés: Vanadium phosphate fluoride; Potassium-ion battery; Chemical deintercalation; Self-discharge mechanism; Side reactions

Domaines: Matériaux

Romain Wernert, Long H.B. Nguyen, Antonella Iadecola, François Weill, François Fauth, et al.. Self-discharge mechanism of high-voltage KVPO4F for K-ion batteries. ACS Applied Energy Materials, 2022, 5 (12), pp.14913-14921. ⟨10.1021/acsaem.2c02379⟩. ⟨hal-03857373⟩