Preparation And Properties Of High-Safety Composite Separator For Lithium/Sodium Battery

Lithium-ion batteries are widely used in electric vehicles,mobile digital devices and backup power supplies for large base stations with their excellent comprehensive performance.Wide application prospects have promoted the development of the lithium-ion battery industry,and people also put forward higher requirements for lithium-ion batteries in terms of cycle stability,capacity,and safety.As an important part of the lithium-ion battery,the separator does not directly participate in the electrochemical reaction of the battery,but it blocks the contact between the cathodes and anodes of the battery and can also conduct ions.Therefore,the material selection and structural composition of the separator have a profound impact on the performance of the battery.At present,polyolefin separators are widely used in lithium-ion batteries.The overall performance of this type of separators is relatively excellent,but there are also some disadvantages such as poor thermal stability,low safety,poor wettability to electrolyte,and poor performance under high-voltage battery systems,this series of problems restrict the development of lithium-ion batteries.Therefore,improving the electrochemistry and safety performance of lithium-ion batteries from the perspective of separators has become a hot research topic.In this work,in order to improve the performance of lithium/sodium batteries,we select specific substrate and coating materials to prepare composite separators by suction filtration,dip-coating and other methods.The results are as follows:1.The restricted functional separator(PX)for high-voltage additive system batteries was prepared by coating polyacrylonitrile(PAN)on one side of the PP separator by the suction filtration method,and the performance of the PX separator with SN was tested.The research results show that the introduction of electrolyte additive SN significantly promoted the film formation on the cathode side,and since SN can be restricted to the cathode side by PAN,the introduction of PX separator on this basis can reduce the corrosion of the additive SN on the lithium metal.Therefore,in the battery system with 2wt%SN added,the Li||Li Co O2 batteries assembled with PX separator has a capacity retention of 89.7%after 240 cycles at 1 C,while that of the batteries assembled with the PP separator is only 75.4%.2.A PAN non-woven fabric with high porosity and excellent heat resistance was selected to replace the PP separator as the substrate material,and boehmite(Al OOH)was coated on the surface of the non-woven fabric to prepare a composite separator(PNA).Thus,the performance of PNA separator was investigated.The research results show that the pore size distribution on the surface of the non-woven fabric is effectively improved by coating Al OOH on the surface of the non-woven PAN.Secondly,the introduction of Al OOH improves the thermal stability,ionic conductivity and flame retardancy of the composite separator.PNA separator shows excellent safety performance,and the discharge capacity of the Li||Li Fe PO4 battery assembled with PNA separator is 165 m Ah g^-1 after 100 cycles at 1 C,while the discharge capacity of the battery assembled with PE separator is 150 m Ah g^-1.3.Considering the current development trend of the battery industry,in order to reduce pollution and costs,we introduced composite separators into the sodium system battery system,and selected low-cost,safety and environmentally friendly dust-free paper instead of PAN non-woven fabric as the composite separator substrate material.At the same time,the coating material was upgraded from 0-D nanoparticles to 2-D material,and the paper-based/g-C3N4 composite separator(PCG)was prepared by the dip-coating method.The research results show that coating g-C3N4 on the surface of dust-free paper can effectively improve the pore size distribution and size of the substrate,so that it can be successfully used in batteries;Secondly,thanks to the self-stacking properties of 2-D material(g-C3N4),the preparation of PCG separator requires less binder than 0-D particles(too much binder will block ion conduction),so PCG separator exhibits better ionic conductivity.Thirdly,because the substrate material of the composite separator is paper,PCG separator shows high safety performance.Meanwhile,the Na||Na3V2(PO4)3 battery assembled with PCG separator is about 15 m Ah g^-1 higher than that assembled with PE separator in each cycle at 1 C and its rate performance is also better than that assembled with PE separator.