真乄科技業的頂尖投資團隊

鋰離子電池雖然被認為是當今電動車(EV)的電源首選，但它其實存在明顯的缺點：不防火。更糟的是，他們在過載和短路的情況下十分易於著火，甚至可能引發嚴重事故的後果。

為此，美國史丹佛大學(Stanford University)的研究人員開發出可望克服這個難題的解決方案。

鋰離子電池如此容易自燃的原因在於電池陽極與陰極之間進行電子交換時必要的電解質，它是一種高度活性的物質，而且十分易燃。史丹佛大學研究員Kai Liu表示，儘管電池製造商試圖以內部保護層或增加阻燃劑使起火燃燒的風險降至最低，但鋰電池仍然免不了發生這些風險。此外，這些保護措施也帶來了副作用：可能降低能量密度與鋰離子遷移率，造成電池性能退化。

因此，史丹佛大學的研究團隊在電池上增加了一層隔離層。該隔離層是由兩個一般隔離元件組成，其作用是在電池過熱時釋放阻燃劑。在正常的作業期間，這種阻燃劑是被密封住的，因而不至於影響電池性能。這種元件取代了通常採用一層微孔薄膜的傳統隔離層。

該技術由Kai Liu和他的同事共同開發，他們也一樣採用微孔材料，只不過這種材料是由微纖維複合均衡組織製造而成的。這種組織的每一根纖維包含一個磷酸三苯酯(TPP)核心——這是一種廣泛被採用的阻燃劑。

而在此核心周圍的是一層用於隔離其與電解質的聚合物層。該聚合物的熔點低，不過在正常的電池作業期間都能維持穩定。因此，在正常的作業期間，這種新的隔離層具有與傳統聚乙烯隔離器類似的電特性。當達到聚合物的熔點時，這種纖維也隨之熔融，從而釋放出被封包住的TPP。

史丹佛大學的研究人員們並為進行測試，在達到攝氐160度溫度時觸發阻燃劑完全釋放到電解質中。研究人員們並嘗試點燃阻燃劑與電解質的混合物，結果火焰立刻熄滅了。研究人員指出，「大約在0.4秒內，火就完全熄滅了。」

編譯：Susan Hong

(參考原文：Separator layer makes lithium-ion batteries fire-proof，by Christoph Hammerschmidt)

A powerful flame retardant added to lithium-ion batteries that only gets released when the devices get too hot could help keep them from catching on fire, a new study finds.

When lithium-ion batteries overheat, they can burn through clothing, burst into flames and even explode. Such "thermal runaways" have led some engineers to explore the creation of lithium-ion batteries with their own fire alarms or chemical additives that can prevent short circuits.

Researchers previously tried adding flame retardants directly into the batteries’ electrolytes, which connect the electrodes of the energy storage devices. However, these approaches significantly reduced battery performance.

Now researchers have designed a lithium-ion battery in which the separator, the component that keeps the battery's positive and negative electrodes apart, contains a cheap, powerful, and commonly used flame retardant known as triphenyl phosphate.

During normal battery operation, the flame retardant stays encapsulated within plastic fibers. If the separator gets hotter than 150 degrees C, the plastic melts, releasing the flame retardant. In experiments, the chemical completely quenched flaming electrolyte in 0.4 seconds. The scientists detailed their findings online in the 13 January edition of the journal Science Advances.

“Using our ‘smart’ separators, battery electrochemical performance will not be affected by the flame retardant under normal conditions," says study senior author Yi Cui, a materials scientist at Stanford University in California. “However, once there is a potential thermal runaway, the flame retardant will be activated and nip the fire or explosion in the bud.”

Future research can explore how well this separator responds to electrical abuse such as overcharging or discharging too deeply, or physical abuse such as crushing or penetration, Cui says. “We believe our safe separator should find broad applications, considering that more and more fires and explosions of lithium-ion batteries have been reported recently.”

Source:IEEE