Cathode and Anode Materials for Na-Ion Battery - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 401

Fig. 15 a TEM images of the Na 3 V 2 (PO 4 ) 3 /C prepared by pyro-synthetic reaction. b The
voltage profiles and c the discharge capacities obtained at various C-rates in the voltage range
3.8-2.5 V [ 32 ]

at 3.6 and 4.1 V, high rate capability (100 mAh g -1

at 1 C) and good cyclability

(98 % capacity retention for 30 cycles).
Olivine LiFePO 4 has been widely investigated as cathode for Li-ion batteries.
Unfortunately, NaFePO 4 does not present an olivine phase through conventional
high temperature preparation conditions. NaFePO 4 usually shows a maricite
structure, [ 40 , 41 ] which is electrochemically inactive [ 30 ]. Moreau et al. syn-
thesized olivine FePO 4 through chemical oxidation in acetonitrile with NO 2 BF 4
[ 42 ]. FePO 4 is electrochemically active and can allow reversible Na-ion interca-
lation/deintercalation. In order to obtain electrochemically active olivine-type
phosphate compound, Nazar et al. prepared metastable Na[Mn 1-x Fe x ]PO 4 nano-
rods by a low-temperature solid-state method [ 41 ]. This material showed a sloping
voltage profile, indicating a single-phase reaction, which was different from the
two-phase reaction of olivine LiFePO 4 [ 25 ].