钠电池过充的危害有哪些？

What hazards are caused by overcharging sodium-ion batteries?

过充是钠电池高频危险电气故障，指充电电压持续超过单体 3.4V 上限，钠离子过量从正极脱嵌，会对电芯材料、内部结构、整体安全造成多层不可逆永久性损伤，同时大幅缩短循环使用寿命，严重时直接触发热失控起火。第一层材料损伤：持续过充让正极晶格大量脱钠，晶体骨架失去钠离子支撑快速坍塌、粉化，正极活性物质永久失效，电池额定容量断崖式下跌；过量游离钠离子无法全部嵌入负极，负极表面析出金属钠枝晶，尖锐枝晶持续穿刺隔膜，诱发内部微短路隐患。第二层电解液与界面膜损伤：过充高电压加速电解液氧化分解，大量甲烷、一氧化碳、可燃烷烃气体生成，电芯内部气压持续升高出现鼓包变形；正极 CEI 膜、负极 SEI 膜在高电位下持续破损、反复重建，不断消耗电解液与钠离子，库仑效率快速下滑，每一次深度过充都会永久性增加电芯内阻。第三层结构与密封损伤：内部产气持续累积冲破电芯铝塑膜 / 钢壳密封焊缝，出现电解液漏液；泄漏电解液具备弱腐蚀性，腐蚀 PACK 汇流排、线束金属接头，造成接触不良、局部发热。第四层连锁安全风险：多次轻度过充累积多重损伤后，单次重度过充极易触发链式放热反应，电芯温度快速突破 150℃热失控临界值，喷射可燃电解液并起火；多串电池包中单芯持续过充会不断拉大整包压差，其余电芯同步加速老化，整套储能或动力电池包寿命折损一半以上。日常使用中单次短时轻微过充可修复少量容量，但反复、长时间深度过充带来的晶格坍塌、枝晶、鼓包损伤完全不可逆，即便后续正常充放电，电池容量、安全性、循环寿命也无法恢复出厂标准，只能提前报废更换。

Overcharging, a frequent dangerous electrical fault where cell voltage exceeds the 3.4V upper limit, causes multi-layer irreversible permanent damage to cell materials, internal structures and overall safety, shortens cycle life drastically and may trigger thermal runaway and fire in severe cases. First, material damage: excessive sodium deintercalation collapses cathode crystal frameworks and pulverizes active materials to lead sharp capacity drop; surplus free sodium precipitates into sharp dendrites on anodes to puncture separators and form latent micro short circuits. Second, electrolyte and interface film damage: high overcharge voltage accelerates electrolyte oxidation to generate massive flammable gas and raise internal pressure for cell swelling. CEI and SEI films rupture and reconstruct repeatedly under high potential to consume electrolyte and sodium ions permanently, lifting internal resistance and lowering Coulomb efficiency after each deep overcharge. Third, structural and sealing damage: accumulated gas breaks cell shell welds to leak weakly corrosive electrolyte, eroding PACK busbars and wiring to create poor contact and local heat. Fourth, cascading safety risks: accumulated minor overcharge damage plus one severe overcharge easily cross the 150℃ thermal runaway threshold with flammable electrolyte ejection and fire. Continuous overcharge of a single string widens pack voltage difference and accelerates aging of all cells, cutting full pack service life by over half. Short mild overcharge can recover partial capacity, yet repeated long-term deep overcharge causes irreversible lattice collapse, dendrite formation and swelling damage. Even under normal subsequent cycling, capacity, safety and cycle life never return to factory standards, requiring early scrapping and replacement.