煅烧对空气电极的多孔结构和电化学性能的影响

Effect of calcination on porous structure and electrochemical properties of air electrode

优化空气电极的孔道结构对提升电极的电化学性能至关重要。通过电极多孔结构的重组,可以提高氧气的传输速率,从而实现金属空气电池的高能量密度和长放电寿命。采用扫描电镜、差热分析仪、比表面积测试仪、润湿角测试仪和电化学测试仪等检测技术,研究了不同煅烧温度(200、250、300、350、400℃)对空气电极的表观形貌、微孔结构和电化学性能的影响,并进一步测试了镁基空气电池的放电性能。结果表明,随着煅烧温度升高,电极中黏结剂聚四氟乙烯(PTFE)的纤维熔融状态改变了其微孔结构分布(包括气孔和液孔),从而影响了电极的氧还原电化学性能和放电寿命。尤其在接近PTFE相变点(343℃)的煅烧温度350℃下制备的空气电极,具有均匀的孔径分布和最佳疏水特性(包含疏水点和气体扩散孔道)。因此,空气电极表现出最小电极极化(-0.45 V极化电位下,电极电流密度为159.1 mA/cm^(2))、最长放电寿命(15 mA/cm^(2)电流密度下,放电时长为39.0 h),较大的容量及功率密度(分别为37.4 A·h和13.05 mW/cm^(2))。

The optimization of the pore structure for the air electrode plays a crucial role in enhancing electrochemical performance of the electrode.The oxygen transmission rate can be enhanced,leading to achieve high energy density and long discharge life of metal air batteries by the recombination of the porous electrode structure.In the forming process of air electrode,the effects of calcination temperatures(200,250,300,350,400 ℃) on the apparent morphology,micropore structure,and electrochemical performance of the air electrode were investigated using scanning electron microscopy,differential thermal analysis,specific surface area measurement,wetting angle determination,and electrochemical testing.Additionally,the discharge performance of the Mg-based air battery was further evaluated.The results showed that the fiber melting state of PTFE binder in air electrode changed the distribution of micropore structure(including air inlet and liquid inlet) via the increase of heat treatment temperature,which affected the oxygen reduction electrochemical performance and the discharge life of air electrode.In particular,the air electrode prepared at a calcination temperature of 350 ℃,which was close to the PTFE phase transition point(343 ℃),exhibited the uniform pore size distribution and the optimal hydrophobic characteristics(including hydrophobic points and gas diffusion channels).As a result,the air electrode demonstrated the minimum electrode polarization(with an electrode current density of 159.1 mA/cm^(2) at a polarization potential of-0.45 V),the longest discharge lifespan(with a discharge time of 39.0 h at a current density of 15 mA/cm^(2)),as well as high capacity and power density(37.4 A·h and 13.05 mW/cm^(2),respectively).