Understanding underlying mechanisms of charge-discharge behaviour of batteries, especially the intercalation Li-ion and Na-ion ones, is obligatory to develop and design the energy storage devices. The behaviour of the voltage-capacity/time...
This paper proposes a mathematic relationship between obtained capacity and the corresponding current rate for the Li-S and Na-S conversion batteries.Using experimental data on different conditions of the Li/Na-S batteries, taken from literature, it is established that the inverse value of obtained capacity is changing linearly with respect to square root of the corresponding applied current rate. The theoretical-based relationship has been established for the Li-ion and Na-ion batteries. Therefore, this paper proposes similar behavior for the conversion and intercalation batteries. The proposed relationship and its beyond approach proffer estimations of: alteration of capacity by rate, optimal cathode mass, corresponding reaction components, and fraction of (in)active particles. Also, they offer a quantitative criterion for performance and ratecapability, the capability to justify observed phenomena, and also qualification of the powder, preparation, and assembling of the cell.
As a high-capacity cathode material with a considerable cycle life, lithium metal orthosilicates have attracted much attention. In this paper, Li 2 FeSiO 4 , Li 2-FeSiO 4-x Cl x and Li 2 FeSiO 4-x F x are successfully synthesized via solid-state method. Li 2 FeSiO 4-x F x is also composited with reduced graphene oxide (rGO). The X-ray diffraction patterns show 0.2% expansion in the lattice volume of Li 2 FeSiO 4-x F x and 0.7% shrinkage for Li 2 FeSiO 4-x Cl x due to the doping effect. Fourier-transform infrared spectroscopy also indicates a frequency shift for [SiO 4 ] 4and [LiO 4 ] functional groups due to ion doping. The SEM images confirm that rGO surrounded Li 2 FeSiO 4-x F x microparticles. The electrochemical performance illustrates a reversible ox/red reaction of Fe 2? /Fe 3? couple at the potential of 3/2.6 V for Li 2 FeSiO 4 , 3.5/2.9 V for Li 2 FeSiO 4-x F x , and 3.3/2.3 V for Li 2 FeSiO 4-x Cl x . Lithiation curves at 0.05C rate show the first specific capacity of 168 mAh g -1 for Li 2 FeSiO 4 with 84% retention after 25th cycles, 190 mAh g -1 for Li 2 FeSiO 4-x F x with 100% retention, and 120 mAh g -1 for Li 2 FeSiO 4-x Cl x with 73% retention. Li 2 FeSiO 4-x F x /rGO cathode delivers 265 mAh g -1 with 88% retention after 25th cycles.
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