DEVELOPMENT OF NON-AQUEOUS ASYMMETRIC HYBRID SUPERCAPACITORS BASED ON Li-ION INTERCALATED COMPOUNDSGUIDEDr.D.KALPANA, SCIENTIST, BYEEC DIVISION, NAKKIRAN.A,CECRI,KARAIKUDI.
An overview of previous presentations Introduction Hybrid supercapacitors Synthesis of LiMn2O4 and the same multidoped with Ni, Co and Cu Physical characterization - XRD, SEM, FTIR Cell Fabrication Electrochemical characterizations Comparison of their performances
Study of supercapacitors Having LiCo1-xAlxO2 as cathodes (where x=0,0.2,0.4 and 0.6)
Lithium Cobaltate(LiCoO2) Commercially successful The layered structure of LiCoO2 enables easy diffusion of Li-ions in and out of the structure
Why Aluminum There has recently been considerable interest in Al- doping of lithium intercalation oxides. Al substitution of the transition-metal cation has been shown theoretically and experimentally to increase the cell voltage. Some other advantages of Al are that it is light, non- toxic, and inexpensive
Advantage The similarity of Al and Co ions in these lithium metal oxides makes Al an attractive choice for doping The end members, a-LiAlO2 and LiCoO2, have the same crystal structure, layered a-NaFeO2 and the metal ions are close in size. These similarities remove the complications of phase transitions and lattice strain when varying doping content.
Synthesis Of Cathode Material Two cathode materials synthesized are, i) Pure LiCoO2 ii) LiCoO2 doped with Al - LiCo1-xAlxO2 ( x = 0.2, 0.4,0.6 ) The cathode material was synthesized by soft combustion method Compositions were taken on a stoichometric ratio based on following equations, LiNO3 + Co(NO3)2.6H2O LiCoO2 (for pure substance) LiNO3 + (1-x) Co(NO3)2.6H2O + xAl(NO3)2.9H2O LiCo1-xAlxO2 (for doped substance)
Composition of precursors required for synthesis Basis : 0.2 moles of product Weight of the material Precursor X=0 X=0.2 X=0.4 X=0.6 LiNO3 13.8g 13.8 g 13.8g 13.8 Al(NO3)2.9H2O - 15 g 30g 45g Co(NO3)2.6H2O 58.2g 46.56 g 34.92g 23.28gGlycine(C2H5NO2) 30g 30 g 30g 30g Distilled Water 100ml 100 ml 100ml 100mlX= Fraction of Aluminium
The Soft Combustion Process Weighing of required chemicals Dissolve in 100ml distilled water Stir well at 600C Heat the mixture at 1000C for 8 hours Product is formed following a soft combustion
Thermal Analysis TGA is used to find the optimum temperature ranges for drying a sample to remove the moisture and impurities from it. In DTA phase transitions or chemical reactions are followed through observation of heat absorbed or liberated.
TGA Curves The initial weight drop from 300C-1500C is due to moisture removal from the sample. the subsequent weight loss from 1500C to 3000Ccorresponds to elimination of organic compounds from samples. Next weight drop in the temperature range of 3000C-5000C is formed as a result of the reaction of unreacted precursors to give the final product. The stabilization temperature for these samples mostly lay after 8000C. So the samples are heated at 8000C for 4 hours.
These are the FTIR spectroscopes of LiCoO2, LiCo0.8Al0.2O2, LiCo0.6Al0.4O2, and LiCo0.4Al0.6O2 respectively For high level of Al substitution, the broadening of the infrared peaks can be interpreted as an increase in CoO6 distortion due to the incorporation of Al3+ in the Co3+ site.
All samples are single phase and have the α-NaFeO2 structure (space group R3m). Miller indices (hkl) are indexed in the hexagonal setting. No impurity phase was detected in the XRD patterns of LiAlyCo1−yO2 On Al doping, the (108) peak shifts towards lower 2θ and the (110) peak shifts towards higher 2θ value
Results of Galvanostatic Charge-Discharge Analysis Properties Composition Specific Power density Energy density capacitance (kW/kg) (kWh/kg) (F/g) 0 11.17 312.5 12.41 0.2 0.415 303.03 0.44Before cycles 0.4 11.41 333.3 12.68 0.6 1.53 322.58 1.075 0 1.8 312.5 2.01 0.2 0.303 303.03 0.336After cycles 0.4 3.83 333.33 4.25 0.6 0.88 322.58 0.986
Conclusion LiCoO2 is a good cathode material for hybrid supercapacitor since it is having specific capacitance of 11 F/g. In the doped cathode materials, LiCo0.6Al0.4O2 is having good capacitance and cycle behaviour.