2.4 Electrochemical tests
To prepare LFP electrodes, first, CNTs were pre-dispersed in NMP to form a slurry containing 0.4 wt% CNTs. Then, LFP (89 wt%), polyvinylidene fluoride (7 wt%, using a solution in NMP), CNTs (1 wt%, using the CNTs slurry) and carbon black (3 wt%) were mixed with a small amount of NMP to adjust the viscosity and stirred for 12 h. The work electrode was prepared by casting the as-obtained LFP slurry onto an Al foil. The coated Al foil was cut into disks (13 mm in diameter), and the active materials mass loading of each disks was about 4~5 mg. Similar process was used in an aqueous fabrication of LFP electrodes except using water as solvent and 7 wt% aqueous solution of acrylonitrile multicomponent copolymer (LA133) as binder.
The electrochemical properties of the as-prepared materials were tested via assembling coin-type cells in an Ar-filled glove box, with Li metal discs as the counter electrode, Celgard 2400 membrane as separator, and 1 M LiPF6 dissolved in a mixture of ethylene carbonate and dimethyl carbonate (1:1, volume ratio) as electrolyte. Furthermore, the charge/discharge measurement was performed on a battery tester (BTS3000, Neware) in a voltage range of 2.0-4.2V. Electrochemical impendence spectroscopy (EIS) was tested on a Zahner Zennium E electrochemical workstation at a potential of open circuit potentials from 0.01 to 100 kHz.