Preparation And Properties Of Carbon Coating Lithium Iron Phosphate Flexible Electrode

The fast-growth of technology and extended demand for high-tech products have inspired the development of portable or wearable electronic devices featuring light weight,miniaturization and flexibility,hence,there are identical requirements for energy storage equipments.However,available current conventional power sources are too bulky and rigid to be integrated into flexible devices,it is urgent to develop novel and advanced flexible power source.In this paper,a new type of flexible lithium-ion battery was designed and fabricated,which adopted a film-type and current-collector-free cathode to render the battery’s flexibility and excellent electrochemical properties,carbon coating-modified lithium iron phosphate was employed as active cathode material.And the XRD,SEM and other methods were used to characterize the structure and morphology while the galvanostatic charge/discharge test and electrochemical impedance spectroscopy were carried out to characterize the electrochemical performance.1.The nano-sized lithium iron phosphate was synthesised by sol-gel method using ferrous sulfate（heptahydrate）,phosphoric acid and lithium hydroxide（monohydrate）as raw materials.And the LiFePO₄ crystal particles exhibited perfect homogeneity,which can be infered from the SEM images.For bare LiFePO₄,the electrochemical properties was inferior,the initial discharge capacity is 102mAh/g at 0.1C and 30mAh/g at 10C.2.Carbon coating modification for lithium iron phosphate was conducted by two different strategies:glucose was employed as carbon source,the sintered sample or the reaction product soaking in glucose water solution,in these two strategies,lithium iron phosphate were all first dipping into glucose water solution,but dried by filtering and centrifugation,respectively.And then these two samples were sintered at 600^oC for 3h under H₂ and Ar atmosphere to yield the final composite.Both methods are effective to improve the battery’s discharge capacity at high rates.Samples obtained from reaction product soaking in glucose solution of concentration 75%and volume 80 ml（labeled as LFP/C-75%-80）have the optimum electrochemical performance:specific capacity154 mAh/g at 0.2C and maintenance of 130 mAh/g at 10C.3.Flexible current collector-free LiFePO₄/C films with good flexibility and mechanical strength were prepared by simple drop-coating on sapphire substrate.The films can endure a tensile strength of as high as 0.71 Mpa with a strain of 0.65%.After500 cycles of charging and discharging at 10C,it still exhibit excellent structure stability and no obviously decay of the specific capacity.This results also show that the flexible film have good rate performance and stable long cycle life.