The Process Reaction Kinetics of Synthesis and Capacitance Performance of LiNiPO<sub<4</sub< from a Precursor via Solid-State Reaction

The nano-crystallite LiNiPO<sub<4</sub< powder was synthesized via solid-state reaction of the precursor NH<sub<4</sub<NiPO<sub<4</sub< using raw materials LiOH, NH<sub<3</sub<H<sub<2</sub<PO<sub<4</sub< and NiAc<sub<2</sub<·4H<sub<2</sub<O by adding surfactant PEG-400. The results showed that the process kinetics mechanism of LiNiPO<sub<4</sub< crystals was two-dimensional interface diffusion and the reaction activation energy <em<E</em< was 81.08 kJ·mol<sup<-1</sup<. The formation of amorphous LiNiPO<sub<4</sub< from the precursor consists with the interfacial reaction mechanism of the index nucleation which the activation energy <em<E</em<<sub<1</sub< was 11.82 kJ·mol<sup<-1</sup< and logarithm of exponential factor ln <em<A</em< was 13.82. The process of crystal LiNiPO<sub<4</sub< growth had smaller activation energy <em<E</em<<sub<2</sub< of 17.73 kJ·mol<sup<-1</sup<. The key controllable steps in whole prepared processes are the conversion reaction and crystallization of LiNiPO<sub<4</sub<. LiNiPO<sub<4</sub<+Nafion/C composite electrode in sulfuric acid solution (0.5 mol·L<sup<-1</sup<) has typical capacitance properties and the specific discharge capacity was 214 F·g<sup<-1</sup<. After 1 000 times discharge and charge cycling, the electrode discharge capacity increased slightly instead of attenuation. Results show that the LiNiPO<sub<4</sub<+Nafion/C composite could be applied as the potential material for capacitor.