Calendering effect on the electrochemical performances of the thick Li-ion battery electrodes using a three dimensional Ni alloy foam current collector

High surface area and a three dimensional NiCrAl alloy foam current collector was used for two kinds of thick lithium iron phosphate electrodes. One kind of electrodes were compressed after the slurry of active material in the metal foam was dried and then annealed at 140 °C for half a day whereas the other kind of electrodes were prepared without pressing. When the addition of carbon black was 4 wt% for the two kinds of electrodes, a charge-discharge test revealed that the capacity of the cell using the pressed electrode faded much more although the voltage-drop was much smaller at the plateau region. For example, the capacity of the pressed electrode exhibited 85 mA h g−1, while it was 135 mA h g−1 for the unpressed electrode although the voltage-drop at the plateau region was 250 mV higher at 0.5C-rate for the unpressed electrode. The AC impedance analysis showed that the charge transfer resistance of the pressed electrode was only 15 Ω whereas it was 4 times higher for the unpressed electrode. The results illustrated that the effective redox area was much larger for the unpressed electrode since the cell using the unpressed electrode exhibited much higher capacity even at the condition of poor electronic conductivity. To solve the low electronic conductivity issue for the unpressed electrode, the addition of carbon black was further increased to 14 wt% and as a result, there was almost no difference in voltage drop at plateau region or charge transfer resistance between the two kinds of electrodes. Obviously, the capacity of unpressed electrode exhibited much higher at higher current rate due to the larger effective redox area.