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Triclinic α-LiVOPO 4 that was prepared at 500 • C by citric acid assisted sol-gel technique revealed uniform carbon coating and interagglomerate voids/pore-like morphologies from XRD, TG/DTA, SEM, FE-TEM and BET studies. When tested for Li-ion insertion properties, α-LiVOPO 4 /C cathode delivered an initial discharge capacity of 163 mAh/g (98% of theoretical value) at C/20 rate with impressive capacity retentions until 50 cycles attributed to the combined contributions of surface coating and porous structure that serve as facile electrical conduits for ion/electron transport.Lithium metal phosphates have invoked great interest as cathodes for rechargeable Li-ion batteries. 1 The stable structural framework of phosphate units promotes cathode safety, high theoretical capacities and facile ion insertion/de-insertion at suitably high operating voltages versus Li. Among metal phosphates, the feasibility of vanadium to exist in three different oxidation states (III, IV, V) and polymorphs make vanadium phosphates attractive for Li-intercalation hosts. 2 Lithium vanadium phosphate cathodes including LiVOPO 4 , LiVPO 4 F, 3 and Li 3 V 2 (PO 4 ) 3 4 display merits of stable framework, relatively high voltage, good lithium-ion transport, and large theoretical capacities. In particular, the high theoretical specific capacity (166 mAhg −1 ), reversible Li-ion intercalation at appropriately high potentials (∼4 V) of LiVOPO 4 , which exists as α-LiVOPO 4 (triclinic, space group P-1) and β-LiVOPO 4 (orthorhombic, space group Pnma), can ensure scaling up of Li-ion battery potentials. Among these phases, the orthorhombic-phase has been extensively investigated due to its better ion-intercalation properties. 5,6 Traditionally α-LiVOPO 4 electrode was known for its poor electrochemical reactivity with lithium. 7 However, recently, enhanced Li-storage capacities in this cathode were demonstrated by strategies of morphology tailoring and mixing electrical additives. 6,8 Alternatively, nano-sizing, carbon nano-coating and porous structures have also improved electrochemical properties in insulating Li-ion battery electrodes. 9,10 In light of these aspects, we demonstrate the sol-gel synthesis of a triclinic-LiVOPO 4 using citric-acid that offers unique multiadvantages of serving as a chelating agent, pore-forming template, combustion agent, and also acts as a carbon source that prevents metal ion oxidation and affords an electrical conduction network which ultimately enhances α-LiVOPO 4 cathode performance. 4,10,11 Synthesis and ExperimentalLiVOPO 4 cathode was prepared by citric acid assisted sol-gel technique. Briefly, appropriate stoichiometric ratios (1:1:1) of lithium nitrate (LiNO 3 ), ammonium metavanadate (NH 4 VO 3 ) and ammonium dihydrogen phosphate (NH 4 H 2 PO 4 ) were dissolved in de-ionized water and subsequently citric acid, equivalent to molar ratio of metal ion, was added and stirred at 80 • C. The resultant homogenous solution dried at 120 • C for 12 h produced a xerogel before sintering at 500 • C for 8 h in air to ...

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In order to investigate the effect of single doping and co-doping on the enhancement of ionic conductivity in ceria (CeO 2 ), CeO 2 and a few compositions in the system Ce 0.85 Sm 0.15−x Gd x O 1.925 (x=0.00, 0.06, 0.09, and 0.15) were prepared using citrate-nitrate auto-combustion method. Gels were characterized by simultaneous differential thermal analysis and thermogravimetric analysis to confirm the formation of end product from the precursor. All the compositions were found to be single-phase solid solution from their X-ray diffraction pattern. Complex plane impedance analysis clearly revealed the contribution of grains, grain boundaries, and electrode specimen interface to the total value of the resistance. The value of activation energy, E a , of conduction shows that the conduction process is mainly due to diffusion of O 2− ions through oxygen vacancies. Effect of doping has been analyzed using the concept of radius mismatch and effective index reported earlier in the literature.

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