什么是钠电池的热失控？

What is thermal runaway of sodium-ion batteries?

钠电池热失控是电芯内部链式放热化学反应引发的极端安全故障，指电池内部多种放热副反应连续触发，温度与内部压力呈指数级快速上升，超出电池结构承受极限，最终出现鼓包、漏液、喷射可燃电解液，严重时起火甚至爆燃，是储能与动力电池最需防控的重大安全隐患。正常充放电工况下，钠电池内部化学反应温和，产热速度小于散热速度，温度维持稳定；一旦出现过充、内部短路、高温烘烤、外力穿刺挤压等异常诱因，电极、电解液之间会快速发生不可逆放热反应，正极分解、SEI 膜破损、电解液燃烧多重反应叠加，热量持续堆积无法散出，形成自加速放热循环。钠电池热失控烈度显著低于三元锂电池，因正负极热分解温度更高、可燃产气更少，极少发生剧烈爆炸，但持续高温仍会引燃周边电芯，造成电池簇连锁火情。热失控存在清晰发展阶段：第一阶段预升温，异常工况下电芯温度缓慢上升至 120℃以上，SEI 膜开始分解产气；第二阶段自加速放热，温度突破临界阈值，各类放热反应连锁爆发，每分钟温升可达数十摄氏度；第三阶段产气膨胀，内部压力冲破密封外壳，电解液喷出；第四阶段燃烧阶段，可燃气体遇高温引燃。热失控无法自行终止，仅能依靠外部喷淋、干粉灭火等手段干预，因此电芯 BMS、PACK 热管理、储能舱消防三重防护体系必须配套，从源头规避触发条件，大幅降低热失控发生概率。

Thermal runaway refers to an extreme safety hazard triggered by chain exothermic reactions inside sodium-ion cells. When consecutive heat-generating side reactions are activated, internal temperature and pressure rise exponentially beyond structural limits, resulting in swelling, electrolyte leakage, flammable liquid ejection, fire or even deflagration, the top safety risk for storage and power batteries. Under normal charge-discharge conditions, mild internal reactions generate less heat than dissipated heat to maintain stable temperature. Abnormal triggers including overcharge, internal short circuit, high-temperature baking, puncture or squeeze initiate irreversible exothermic reactions between electrodes and electrolytes. Cathode decomposition, SEI film rupture and electrolyte combustion stack to trap heat and form self-accelerating heating cycles. Sodium batteries deliver far milder thermal runaway than ternary lithium cells thanks to higher thermal decomposition temperatures and less flammable gas generation, with rare violent explosions, yet sustained high temperatures ignite adjacent cells to trigger cluster fire spread. Thermal runaway follows four clear phases: preheating (temperature rises above 120℃ with SEI decomposition and gas generation); self-accelerating heating (crossing critical threshold with dozens of degrees temperature rise per minute from chained reactions); gas expansion (internal pressure ruptures the shell to eject electrolyte); combustion (flammable gas ignites by high heat). Thermal runaway cannot stop spontaneously and requires external dry powder or water mist intervention. Therefore triple protection including cell BMS, PACK thermal management and storage cabin fire control must be equipped to eliminate triggering risks fundamentally.