钠电池过放的危害有哪些？

What hazards are caused by over-discharging sodium-ion batteries?

钠电池过放指放电电压低于 2.5V 截止阈值，负极钠离子大量脱出、晶格空置，会带来不可逆材料损伤、界面膜破坏、性能永久衰减，多次深度过放后容量大幅跳水，严重时电芯直接报废无法修复。第一类负极界面膜毁灭性损伤：正常放电保留少量钠离子维持 SEI 膜稳定，深度过放负极完全脱钠，SEI 固态钝化膜整体破裂、脱落；再次充电时只能重新生成残缺不均匀的 SEI 膜，内阻永久性大幅上升，充放电效率持续走低。第二类负极晶格结构损伤：硬碳微孔完全失去钠离子支撑，微观结构坍塌、微孔堵塞，储钠位点永久消失，电池标称容量不可逆下降，单次深度过放即可造成 5%-15% 固定容量损失。第三类正极金属溶出损伤：过放低电位下正极过渡金属（铁、锰、钒）大量溶入电解液，金属离子迁移至负极表面沉积，持续破坏新生 SEI 膜，形成恶性循环，每次充放电副反应成倍增加，循环寿命快速缩短。第四类电气与安全次生隐患：多串电池包中单芯过放会拉大整包压差，其余电芯充放电区间失衡，整包一致性持续劣化；长期过放电芯内阻飙升，大电流放电局部剧烈发热，叠加界面破损短路风险，轻微撞击即可诱发热失控。对比锂电池，钠电池耐轻度过放，但连续、长时间放空至 2.0V 以下，损伤依旧不可逆；短期轻微过放补电后可恢复 80% 左右容量，若静置数天深度亏电，负极微孔永久堵塞，修复率不足 50%，电芯达不到储能、动力设备使用标准，只能淘汰更换，大幅增加设备运维与更换成本。

Over-discharging occurs when cell voltage drops below the 2.5V cut-off limit with massive sodium extraction from anodes, triggering irreversible material damage, interface film breakdown and permanent performance decay. Repeated deep over-discharge leads to sharp capacity loss and permanent cell scrappage in severe cases. First, catastrophic SEI film damage: minor residual sodium sustains stable passivation under normal discharge; full sodium removal during deep over-discharge cracks and peels off complete SEI layers. Regenerated uneven defective SEI after recharge permanently raises internal resistance and reduces charge-discharge efficiency. Second, anode lattice collapse: hard carbon micropores lose sodium support to block storage sites permanently, causing 5%-15% irreversible capacity loss per deep over-discharge cycle. Third, cathode metal dissolution: low over-discharge potential dissolves iron, manganese and vanadium into electrolyte. Dissolved metals migrate and deposit on anodes to damage regenerated SEI in a vicious cycle, multiplying side reactions and shortening cycle life rapidly. Fourth, secondary electrical & safety risks: single-string over-discharge widens pack voltage difference and degrades overall cell consistency. Long-term over-discharge raises cell resistance to generate severe local heat under high current, with latent short-circuit risks from broken films that trigger thermal runaway under minor impact. Sodium cells tolerate mild over-discharge better than lithium cells, yet prolonged discharge below 2.0V still creates irreversible damage. Short slight over-discharge recovers around 80% capacity after recharge; if left fully depleted for days, blocked microparticles only restore less than 50% capacity, failing storage and power standards and requiring costly replacement.