什么是钠电池的 SEI 膜？

What is the SEI film of sodium-ion batteries?

SEI 膜全称固体电解质界面膜，仅生成于负极硬碳表面，是电芯首次化成充电时电解液还原分解形成纳米级致密固态钝化层。该膜电子绝缘、只允许钠离子单向穿透，隔绝负极与电解液直接接触，抑制电解液持续消耗、延缓负极腐蚀，是电池稳定循环基础。若无 SEI 膜，每次充放电都会大量分解电解液，容量快速下滑。膜品质由化成电流、温度、电解液添加剂共同决定；优质 SEI 薄均匀、阻抗低、韧性强；劣质膜疏松厚薄不均，负极膨胀易开裂，裸碳持续消耗钠离子，不可逆损耗不断增加。电解液成膜添加剂是调控 SEI 核心手段，也是各材料企业核心技术壁垒。

SEI stands for Solid Electrolyte Interphase film, a nano-scale dense solid passivation layer formed only on hard carbon anodes via reductive decomposition of electrolytes during initial cell formation charging. Electronically insulating yet unidirectionally permeable to sodium ions, it isolates anodes from direct electrolyte contact, restrains continuous electrolyte consumption and slows anode corrosion, laying the foundation for stable battery cycling. Without SEI films, electrolytes decompose heavily every cycle with rapid capacity decay. Film quality is jointly determined by formation current, temperature and electrolyte additives. High-quality SEI is thin, uniform, low-impedance and tough; inferior loose uneven films crack easily under anode expansion, exposing carbon to continuous sodium loss. Film-forming electrolyte additives are the core method to regulate SEI and constitute key technical barriers for material manufacturers.