Tailoring a fluorophosphate as a novel 4 V cathode for lithium-ion batteries

Abstract

Lithium-ion batteries, which have been widely used to power portable electronic devices, are on the verge of being applied to new automobile applications. To expand this emerging market, however, an electrode that combines fast charging capability, long-term cycle stability, and high energy density is needed. Herein, we report a novel layered lithium vanadium fluorophosphate, Li1.1Na0.4VPO4.8F0.7, as a promising positive electrode contender. This new material has two-dimensional lithium pathways and is capable of reversibly releasing and reinserting ~1.1 Li+ ions at an ideal 4 V (versus Li+/Li) to give a capacity of ~156 mAh g−1 (energy density of 624 Wh kg−1). Moreover, outstanding capacity retentions of 98% and 96% after 100 cycles were achieved at 60°C and room temperature, respectively. Unexpectedly high rate capability was delivered for both charge and discharge despite the large particle size (a few microns), which promises further enhancement of power density with proper nano-engineering.

Fluoro-polyanionic Compounds

“…Experimentally, LiNiPO 4 F discharge voltage is demonstrated to be close to 5.3 V [88]. Khasanova et al [89] have investigated the electrochemical performance and structural properties of the high-voltage cathode material Li 2 CoPO 4 F. The cyclic voltammetry and coulometry under potential step mode in the voltage range 3.0-5.1 V vs. Li revealed a structural transformation at potentials above 4.8 V. This transformation occurring upon Li-extraction appears to be irreversible: the subsequent Li-insertion does not result in restoration of the initial structure, but takes place within a new "modified" framework. According to the structure refinement, this modification involves the mutual rotations of (CoO 4 F 2 ) octahedra and (PO 4 ) tetrahedra accompanied by the considerable unit cell expansion, which is expected to enhance the Li transport upon subsequent cycling.…”

“…The Li 2 MPO 4 F (M ¼ Fe, Co, Mn, Ni) crystallize in three different structures types; triclinic (tavorite) and two-dimensional orthorhombic (Pbcn S.G.) and tunnel-like monoclinic (P2 1 /n S.G.) [85]. In their prior work, Ellis et al [41] [13,42,89]. Dumont Botto et al [85] have pointed out that, contrary to the Na phases which are quite simple to obtain, the synthesis of Li 2 MPO 4 F remains difficult and requires either the ion exchange of the Na-counterparts or a lengthy solid-state reaction (at least 10-h heat treatment) [83].…”

“…Park et al [89] have prepared the Li 1.1 Na 0.4 VPO 4.8 F 0.8 phase from the pseudo-layered structure Na 1.5 VPO 5 F 0.5 using an ion-exchange process between Na + and Li + in 1-hexanol at its boiling point (160 C) under reflux with LiBr as the lithium source. The lattice is made up of VO 5 F octahedral and PO 4 tetrahedra units, where two VO 5 F are linked by a bridging fluorine ion to form V 2 O 10 F bi-octahedron.…”

Na1+yVPO4F1+y (0 ≤ y≤ 0.5) as Cathode Materials for Hybrid Na/Li Batteries

“…When y exceeded 0.5, new weak reflections appeared, which could be assigned to other impurity phases such as Na 3 directions for the construction of new high-energy rechargeable batteries. However, the mechanism of alkali ion insertion/deinsertion in these systems is not yet well understood [4,20,21,[24][25][26]. We report here the energy-efficient mechanochemically-assisted solid-state synthesis of sodium vanadium fluorophosphates Na1+yVPO4F1+y (0 ≤ y ≤ 0.75) and the results of the comparative study of their crystal structure and electrochemistry in hybrid-ion cells.…”

“…Tetragonal NaVPO 4 F is structurally related to the known Na-ion for the construction of new high-energy rechargeable batteries. However, the mechanism of alkali ion insertion/deinsertion in these systems is not yet well understood [4,20,21,[24][25][26].…”