锂离子电池隔膜物理及电化学性能评价及对比

Evaluation and comparison of the physical and electrochemical properties of lithiumion battery separators

对目前被广泛使用的聚乙烯隔膜、聚丙烯隔膜、聚丙烯/聚乙烯/聚丙烯三层复合隔膜和氧化铝涂覆聚乙烯隔膜的物理性能和电化学性能进行了详细的分析对比.研究表明:氧化铝涂覆聚乙烯隔膜相比于其他三种隔膜,除拉伸强度略低于聚丙烯/聚乙烯/聚丙烯三层复合隔膜外,在耐穿刺性、热稳定性、润湿性及离子电导率等方面均具有更突出的性能.其穿刺强度达到了426.91 N·mm^(-1),并且在140℃下热处理1 h基本没有热收缩.氧化铝颗粒的亲水性提高了隔膜与电解液之间的润湿性,使得隔膜具有优异的离子电导率(0.719 mS·cm^(-1)),并且100次循环后容量保持率为91.19%,优于聚乙烯隔膜、聚丙烯隔膜、聚丙烯/聚乙烯/聚丙烯三层复合隔膜.表明氧化铝涂覆聚乙烯隔膜与其他三种隔膜相比在长循环、高功率和高安全性的锂离子电池中具有最好的应用前景.

The separator is one of the core inner components of the lithium-ion battery,and its performance directly affects the electrochemical properties,life,and safety performance of the battery.In this research,the physical and electrochemical properties of polyethylene(PE),polypropylene(PP)/PE/PP multilayer,(PP),and aluminum oxide ceramic-coated PE(PE-Al_(2)O_(3))separators were analyzed and compared in detail.Among the separators,the PE-Al_(2)O_(3)separator exhibited better performance pertaining to puncture strength,thermal stability,wettability,and ionic conductivity.However,its tensile strength is slightly lower than that of the PP/PE/PP separator.The surface of the PE,PP,and PP/PE/PP separators exhibited a large number of submicron pores.Alumina particles were uniformly distributed on the surface of the PE-Al_(2)O_(3)separator,and a large number of clear pores were presented between the alumina particles.The PP/PE/PP separator exhibited the best tensile properties among the separators in the mechanical direction;the tensile strength of the PP/PE/PP separator was 247.53 MPa,which is higher than that of the PE-Al_(2)O_(3)(197.58 MPa),PP(119.06 MPa),and PE(147.69 MPa)separators.Meanwhile,the puncture strength of the PE separator was the lowest among the separators at 144.26 N·mm^(-1)whereas that of the PE-Al_(2)O_(3)separator was the highest at 426.91 N·mm^(-1),which was attributed to the high hardness of alumina particles.The melting temperature of the PE-Al_(2)O_(3)separator was 140.9℃,which is lower than that of the PP and PP/PE/PP separators but higher than that of the PE separator.Further,it exhibited no heat shrinkage with heat treatment at 140℃for 1 h.Accordingly,thePE-Al_(2)O_(3)separator exhibited the best thermal stability compared to the PP,PP/PE/PP,and PE separators.The unique hydrophilic properties of alumina particles improved the wettability between the separator and electrolyte;the wetting angle between the PE-Al_(2)O_(3)separator and the electrolyte was 12.3°,which was considerably smaller than that for the PP(35.9°),PE(38.3°),and PP/PE/PP(35.3°)separators.The electrolyte wettability of the PE-Al_(2)O_(3)separator effectively reduced the transmission resistance of lithium ions between the anode and cathode,enabling the separator to exhibit an excellent ionic conductivity(0.719 mS·cm^(-1)).After 100 cycles at 1 C,the capacity retention rate of the PE Al_(2)O_(3)separator was 91.19%,which was considerably better than the other three types of separators.To summarize,this study reveals that the PE-Al_(2)O_(3)separator has the best application prospect in high power,long-term stability,and highsafety lithium-ion batteries.