文章信息
钠离子电池初始库仑效率研究进展
董春伟,孔俊丽,苏志江,梁文斌
(北京低碳清洁能源研究院,北京 102211)
摘要:锂离子电池主导了便携式电子产品和电动汽车市场、储能市场,锂的成本和资源可用性也越来越受到关注。钠离子电池被认为是电网级能量存储系统的理想选择。然而,在钠离子电池实现商业化应用之前,仍有各种挑战需要克服,其中,初始库仑效率低是制约钠离子全电池实际能量密度提升的关键问题。分析了钠离子电池低初始库仑效率的影响因素,包括在初始循环过程中因电解液分解形成的固体电解液界面膜、较差的钠离子嵌入/脱出可逆性、缺陷和表面官能团影响等。总结了结构/形貌设计、表面改性、电解液优化等提高钠离子电池初始库仑效率的策略,对于推动与实现高能量密度钠离子电池的实际应用具有重要意义。
关键词:钠离子电池;负极;初始库仑效率;改性策略
1钠离子电池的工作机理
考虑到实际应用,ICE是SIBs组装成全电池时影响能量密度的一个重要参数。进一步深入认识其根源、制定相应的对策、提高ICE等对于实现SIBs的实际应用是十分必要的。
2钠离子电池初始库仑效率的影响因素
2.1电解液的不可逆分解
图1 代表性的钠基电解质的离子电导率与温度的关系
图2 玻璃碳(a)和石墨(b)负极分别以0.5 mol/L NaPF6、1 mol/L NaClO4 和 0.5 mol/L NaOTf为电解液时的循环伏安曲线
2.2负极材料的缺陷和表面官能团
图3 钠离子半电池中HC-0.5、HC-1、HC-2和HC-5电极在20 mA/g电流密度下的首次库仑效率
2.3嵌钠/脱钠过程的差可逆性
(a)不同温度下的比容量以及库仑效率;(b)平均电压
图4 CuO/Na在25 ℃(蓝色)和50 ℃(红色)下的结果
2.4未知的副反应
3提高负极初始库仑效率的策略
3.1电极结构设计
(a)碳化温度分别为1 200、1 400和1 600 ℃时三个样品在0.1 C电流密度下的首次充放电曲线;(b)循环性能曲线[22];(c)硬碳纸负极的SEM照片;(d)20 mA/g电流密度下硬碳纸负极的充放电曲线[23];(e)空心碳球负极的TEM照片;(f) 50 mA/g电流密度下空心碳球负极的充放电曲线[25]
图5 不同无定形碳负极材料及对应的电化学性能
3.2表面改性
(a)CoSx@NSC-1的SEM照片;(b) 在1 A/g电流密度下CoSx@NSC-1电极的充放电曲线;(c)P@RGO复合材料的SEM照片;(d)在1 593.9 mA/g电流密度下P@RGO复合材料电极的充放电曲线;(e)α-Fe2O3@TiO2的TEM照片;(f)α-Fe2O3@TiO2电极的充放电曲线
图6 表面改性获得的不同负极材料形貌及其对应的充放电曲线
3.3电解液优化
图7 不同电解液中SEI膜的不同成分及其与钠存储的相关性[34]
4 结论
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