钠电池内部短路的原因有哪些？

What causes internal short circuits in sodium-ion batteries?

钠电池内部短路是正负极在电芯壳体内部直接接触形成导电通路，分为生产制造原生缺陷、外力机械破坏、长期循环老化三大类诱因，每类诱因包含多种细分场景，也是诱发热失控的核心前置故障。第一类制造原生缺陷，生产工序管控疏漏留下永久隐患：极片裁切、焊接产生超长金属毛刺，辊压分切未打磨去除，电芯卷绕 / 叠片时毛刺刺穿隔膜；隔膜原料存在微孔、出厂检测漏检，隔膜本身无法隔绝正负极；浆料杂质混入硬质金属颗粒，循环过程戳破隔膜；注液、封装工序带入金属碎屑，沉积在极片表面形成导电桥；电芯化成分容阶段局部过热微损伤，长期使用逐步扩大隔膜破损。第二类外力机械破坏，电芯受外部物理冲击直接造成隔膜失效：针刺、尖锐硬物戳穿外壳与隔膜；仓储运输堆叠挤压、叉车重压导致极片形变，隔膜撕裂；车辆行驶持续剧烈震动，极片位移错位，边缘刺破隔膜；电池跌落撞击，内部结构松散，正负极碎屑脱落搭接导通。第三类长期循环老化带来的次生短路：数千次充放电后电极材料粉化脱落，微小导电碎屑游离在电解液中，游动造成局部微短路；SEI、CEI 膜过度增厚开裂，脱落碎片形成导电介质；电芯长期过充过放加速材料粉化，碎屑持续累积；PACK 内部温差过大，单芯膨胀变形挤压隔膜，出现持续性微孔破损。额外配套系统诱因：BMS 均衡失效，单串长期压差过大，部分电芯持续过充加速粉化；散热不良电芯长期高温运行，隔膜热收缩露出导电通道，最终形成稳定内部短路故障。

Internal short circuits of sodium-ion batteries form conductive paths when positive and negative electrodes contact inside cells, divided into inherent manufacturing defects, external mechanical damage and long-term cycle aging, all primary precursors of thermal runaway. First, inherent factory defects from loose process control: overlong metal burrs generated during electrode cutting and welding pierce separators after winding/stacking; separators with undetected inherent micropores fail to isolate electrodes; hard metal impurities mixed in slurry puncture films over cycles; metal debris introduced during liquid injection and packaging deposit on electrodes to build conductive bridges; minor separator damage from local overheating during formation expands after long operation. Second, external mechanical damage breaks separators physically: needle puncture penetrates shell and film; stacking squeeze and forklift pressure deform electrodes and tear separators; continuous vehicle vibration shifts electrode edges to cut separators; cell drop loosens internal structures with fallen electrode fragments bridging poles. Third, secondary short circuits from long cycle aging: electrode pulverization after thousands of cycles releases conductive particles floating in electrolyte to form micro shorts; over-thickened cracked SEI/CEI fragments act as conductive media; repeated overcharge/over-discharge accelerates material powder accumulation; excessive PACK temperature difference causes cell expansion to squeeze separators and create permanent holes. Auxiliary system triggers: failed BMS equalization leads to long-term string voltage deviation and overcharge-induced pulverization; poor heat dissipation causes separator thermal shrinkage to expose conductive paths and form stable internal short circuits.