Electrospinning Preparation, Modification And Electrochemical Performance Of LiFePO₄ Nanofiber Cathode Materials

With the development of wind power, smart grid and electric vehicle technology,fast charge and discharge storage equipment may have been the bottleneck for those new industries. Cathode material has been one of the key issues inhibiting lithium-ion batteries?LIBs? widely using in above areas. Presently, as one of the most potential cathode material for LIBs, LiFe PO₄ has been widely concerned. However, because of its low electrical conductivity, the rate performance of LiFePO₄ is difficult to meet the actual requirements. In this paper, we successfully prepared LiFe PO₄/C and new structured LiFe PO₄/Ni nanofiber composites for LIBs using electrospinning and thermal treatment. Different kinds of properties of the materials were characterized and tested.The main contents and results includes the following aspects:?1? LiFe PO₄/C composites were prepared for LIBs via electrospinning and we discussed the effect of electrospinning and thermal treatment process parameters for the fiber structure and electrochemical properties. It was found that preparing a precursor solution as DMF: PAN = 9: 1, setting the high voltage 25 kV, the syringe pump speed 6ml/h, the roller speed of 200 r/min, keeping the distance 15 cm, than stabilizing at280 ?for 2 h with a heating rate of 1 ?·min-1 in air and carbonizing at 750 ? for 10 hours with a heating rate of 2 ?·min-1 in argon, can maintain the nanofiber composites with good morphology and membrane structures, which can be directly cut as self-supporting cathode electrode material. It showed the best electrochemical properties in terms of higher first discharge capacity?116 mAh g-1, 0.1 C?, more stable cycling performance?dropped from 85 mAh g-1 to 75 mAh g-1 after 500 cycles at 5 C?, and better rate capabilities?116, 109, 129, 103, and 85 mAh g-1 at rates of 0.1 C, 0.5 C, 1 C, 3 C and 5C?.?2? The effects of fibrous nickel?Ni? additives on the electrochemical performance of LiFe PO₄ as a lithium-ion battery cathode were investigated by a simple mixing process of LiFe PO₄ powders and porous nickel fibers. The electrode with optimal fiber content of 10 wt% has the best surface topography and possesses a good rate capability of 85mAh·g-1 even at 5 C. It also shows pretty good cycling performance with initialdischarge capacity of 131.1 mAh g-1 at 1 C, and remains 119.8 mAh g-1 after 100 cycles.?3? Combined with heat treatment process, we had tried to prepare a novel structure LiFe PO₄/Ni composites cathode material with adding nothing binder and conductive agents by coaxial and layered electrospinning technique. For the coaxial structured LiFe PO₄ /Ni composites, after calcined for 10 h at 750 ?in nitrogen, the LiFe PO₄ and Ni do not occur any two-phase chemical reaction; The composites, instead of the expected coaxial structure, actually is a irregular mixture of nickel and LiFe PO₄; The released capacity mostly attributed to the wetness and weight of each electrode; The LiFePO₄/Ni composites prepared as 1:1.4 molar ratio combines good pure crystalline phase LiFe PO₄, Ni phase and amorphous carbon composite coexistence characteristics and the first discharge capacity is 110.2 mAh g-1 and remains 75.56 % after 5000 cycles at 1 C. In addition, for the layered electrospun nanofiber composites handled in the same thermal treatment process, the LiFe PO₄/Ni/LiFe PO₄ structured sample has a relatively optimal cycling and rate performance, the discharge capacity is 49.8 mAh·g-1and remains 93.57 % after 1000 cycles at 1 C.