Electrospinning Preparation And Properties Of High-safety Composite Separator For Lithium Battery

Lithium ion battery has been widely used in electronic products,electric vehicles and large energy storage equipments because of its high energy density,long life and no memory effect.It is regarded as one of the most promising batteries.Separator is one of the most important components of battery,and is called the"third electrode".Although the separator does not directly participate in the electrochemical reactions,its structure and performance will affect the electrochemical kinetic process.Thus directly affects the performance of the battery.Currently,the most widely used separators are polyolefin membranes.Nevertheless,the polyolefin separators exist a series of problems,such as bad electrolyte wettability,weak thermal stability and low ionic conductivity.Consequently,the polyolefin membrane is difficult to meet the large current of power lithium battery and high operation temperature.Especially,the safety issue restricts the development of lithium battery in electric vehicle and energy storage system.How to improve the performance of lithium batteries has been becoming the current hot topic in the perspective of the separator.While non-woven mats are supposed to be the best choice of the lithium ion battery separators due to their high porosity and good electrolyte wettability.Therefore,we adopt an electrospinning technique to make non-woven separator,which can improve the safety and electrochemical performance of lithium batteries.The results are as follows:1.Sb₂O₃-modified poly(vinylidene fluoride-co-chlorotrifluoroethylene)(PVDF-CTFE)fibrous organic-inorganic composite membranes(SPCF)were prepared via a sequential electrospinning technique.Compared with the PE separator,the SPCF separator had good thermal stability,electrolyte wettability and the synergistic flame retardancy performance of sb and cl.Thus the SPCF separator possessed excellent safety performance.The SPCF composite membrane was used as lithium ion battery separator,which shows low impedance,high ionic conductivity and good electrochemical stability that makes the Li||Li Fe PO₄ cell exhibit good cycle stability and rate performance.Specifically the Li||Li Fe PO₄ cell held discharge capacity 167 m Ah g^-1 after 100 cycles at 1 C.At 32 C,the cell containing the SPCF separator has the discharge capacity of 93 m Ah g^-1,which is higher than the cell with PE separator(19 m Ah g^-1).2.Polyacrylonitrile(PAN)has good heat resistance,mechanical properties,electrochemical stability and electrode compatibility.We introduced PAN and studied the effects of different proportions of PAN and PVDF-CTFE on the basis of the first part of the experiments.The results show that the composite separator exhibited the best comprehensive performance when the PAN and PVDF-CTFE was made at the ratio of 5:5,which possessed the most excellent porosity,electrolyte uptake,relatively excellent mechanical properties and thermal stability.Meanwhile,the previous chapter shows synergistic flame retardancy of sb and cl,which greatly improves the safety of the battery.Moreover,the composite separator with a ratio of 5:5 has the best ionic conductivity and electrochemical stability.Thus the Li||Li Ni_0.6Co_0.2Mn_0.2O₂cell showed good cycle stability and rate performance.3.We used the 3d PAN nanofiber as the substrate,which holds good flexibility.Then compounded a layer of PAN nanofiber with CNT and studied its properties.The results show that the composite membrane exhibited excellent thermal stability and electrolyte wettability.Meanwhile,the double PAN/CNT composite separator not only had high ionic conductivity and good electrochemical stability,but also can effectively inhibit the growth of lithium dendrite,which makes the high voltage nickel manganese lithium battery show higher energy density,good cycle stability and rate performance.In addition,the cell with PAN/CNT composite separator has the discharge capacity of 88 m Ah g^-1,which is higher than the cell with PE separator(26m Ah g^-1).