Structure Design And Performance Study Of Lithium Ion Battery Electrode

Lithium-ion batteries have continued to evolve in terms of electrochemical performance,increased safety and cost reduction.For a long time,researchers have focused on the material of each component in LIB.And most of the research on electrode materials have a mass loading less than 3 mg cm-2.However,in commercial lithium-ion battery cells,the mass loading of electrode is 8-30 mg cm-2.The easiest way to increase the proportion of active material is to thicken the electrode coating.However,simply increasing the thickness of the electrode greatly limits the transmission of electrons and ions in the thick electrode,resulting in a sharp deterioration in battery performance.Whether the performance of the battery is good or not is the result of the synergy of various parts of the battery system,and each component together forms a charge transfer system inside the battery The charge transport system not only connects the active materials,but also controls the transport process of ions and electrons,which determines the electrochemical performance and safety of the battery.Therefore,indepth understanding of the effect of electrode structure on battery performance;To construct an excellent charge transfer system inside the lithium-ion battery based on the scientific and rational electrode structure design;development of low-cost production of high-efficiency charge transport system electrode preparation process,to achieve the improvement of energy density,power density,cycle and safety is an important direction and urgent need.(1)The effect of electrode thickness on the performance of LFP and LTO was studied by measuring the battery performance and the AC/DC internal resistance.The effect of electrode thickness on charge diffusion in the electrode is discussed.The application and limitation of EIS and HPPC in analyzing battery internal resistance are discussed.The improved GITT test was used to verify the rule of Rion increasing with electrode thickness.(2)In terms of the structural design of active electrode materials,this paper synthesized WO3-SnO2 hollow nano sphere materials as the cathode active materials by a simple hydrothermal method,and compared them with WO3,SnO2 and WO3-Sn02 particle materials to explore the influence of hollow sphere structure active materials on the performance of batteries.The hollow sphere structure material showed good electrochemical properties:the specific capacity reached 883.9 mAh g-1 at 50 mA g-1;after 500 cycles at 1000 mA g-1,the specific capacity was still 50.8%of the theoretical capacity.(3)In terms of ion conductive network,the low-cost porosity controllable preparation of thick electrode was realized by using the NaCl particle template pore-forming method based on the traditional coating process.The effect of porosity on the transport effect of lithium ion in porous electrode with high mass loading was investigated.The 12 mg cm-2 LTO electrode had a specific capacity of 120 mAh g-1 at 5C discharge rate,and had no significant attenuation after 500 cycles.The concept of gradient porous electrode was proposed,and the LTO electrode with active material loading of 20 mg cm-2 and 30 mg cm-2 was prepared.The feasibility of the gradient porous electrode for high mass loading electrode was verified(4)In terms of electronic conductive network,a multi-walled carbon nanotube was used to prepare a self-supporting LFP electrode with a three-dimensional conductive network.The mechanism of the three-dimensional conductive network on the battery performance improvement was discussed.There is no attenuation in 3 mg cm-2 3D-CNT-LFP after 500 cycles at 1C rate.After 200 cycles the capacity of 13 mg cm-2 3D-CNT-LFP specific capacity maintained above 98%at 1C rate.In order to reduce the mass ratio of battery inactive materials,we designed and fabricated a separator/three-dimensional conductive network integrated electrode by using PAN nano fiber.The cell specific capacity is 44 mAh g-1,which is nearly twice the traditional coating electrode cell of 24 mAh g-1.(5)In terms of electrode preparation technology,a novel electrode preparationprocess which combining electrospinning and air spray was proposed.A three-dimensional conductive network structure formed by PAN nanofiber interlacing gap and carbon nanotube-covered active material particles was prepared.The LFP electrode(13 mg cm-2)specific capacity maintained above 85%after 200 cycles at 1C rate.LFP electrode with active material loading>75 mg cm-2 and area specific capacity of 12.3 mAh cm-2 was prepared.At the same time,the process is a general electrode preparation method.