轉基因病毒大幅提升電池性能

MIT researchers have found a way to boost lithium-air battery performance, with the help of modified viruses.

Lithium-air batteries have become a hot research area in recent years: They hold the promise of drastically increasing power per battery weight, which could lead, for example, to electric cars with a much greater driving range. But bringing that promise to reality has faced a number of challenges, including the need to develop better, more durable materials for the batteries' electrodes and improving the number of charging-discharging cycles the batteries can withstand.

Now, MIT researchers have found that adding genetically modified viruses to the production of nanowires -- wires that are about the width of a red blood cell, and which can serve as one of a battery's electrodes -- could help solve some of these problems.

The new work is described in a paper published in the journal Nature Communications, co-authored by graduate student Dahyun Oh, professors Angela Belcher and Yang Shao-Horn, and three others. The key to their work was to increase the surface area of the wire, thus increasing the area where electrochemical activity takes place during charging or discharging of the battery.

The researchers produced an array of nanowires, each about 80 nanometers across, using a genetically modified virus called M13, which can capture molecules of metals from water and bind them into structural shapes. In this case, wires of manganese oxide -- a "favorite material" for a lithium-air battery's cathode, Belcher says -- were actually made by the viruses. But unlike wires "grown" through conventional chemical methods, these virus-built nanowires have a rough, spiky surface, which dramatically increases their surface area.

Belcher, the W.M. Keck Professor of Energy and an affiliate of MIT's Koch Institute for Integrative Cancer Research, explains that this process of biosynthesis is "really similar to how an abalone grows its shell" -- in that case, by collecting calcium from seawater and depositing it into a solid, linked structure.

The increase in surface area produced by this method can provide "a big advantage," Belcher says, in lithium-air batteries' rate of charging and discharging. But the process also has other potential advantages, she says: Unlike conventional fabrication methods, which involve energy-intensive high temperatures and hazardous chemicals, this process can be carried out at room temperature using a water-based process.

Also, rather than isolated wires, the viruses naturally produce a three-dimensional structure of cross-linked wires, which provides greater stability for an electrode.

A final part of the process is the addition of a small amount of a metal, such as palladium, which greatly increases the electrical conductivity of the nanowires and allows them to catalyze reactions that take place during charging and discharging. Other groups have tried to produce such batteries using pure or highly concentrated metals as the electrodes, but this new process drastically lowers how much of the expensive material is needed.

Altogether, these modifications have the potential to produce a battery that could provide two to three times greater energy density -- the amount of energy that can be stored for a given weight -- than today's best lithium-ion batteries, a closely related technology that is today's top contender, the researchers say.

Belcher emphasizes that this is early-stage research, and much more work is needed to produce a lithium-air battery that's viable for commercial production. This work only looked at the production of one component, the cathode; other essential parts, including the electrolyte -- the ion conductor that lithium ions traverse from one of the battery's electrodes to the other -- require further research to find reliable, durable materials. Also, while this material was successfully tested through 50 cycles of charging and discharging, for practical use a battery must be capable of withstanding thousands of these cycles.

While these experiments used viruses for the molecular assembly, Belcher says that once the best materials for such batteries are found and tested, actual manufacturing might be done in a different way. This has happened with past materials developed in her lab, she says: The chemistry was initially developed using biological methods, but then alternative means that were more easily scalable for industrial-scale production were substituted in the actual manufacturing.

In addition to Oh, Belcher, and Shao-Horn, the work was carried out by MIT research scientists Jifa Qi and Yong Zhang and postdoc Yi-Chun Lu. The work was supported by the U.S. Army Research Office and the National Science Foundation.據外媒11月13日報道，麻省理工學院(MIT)研究人員發現，轉基因病毒可以大大提升電池的性能。

鋰空氣電池近年來一直是研究熱點，它的容電量有潛力大幅提高。不過，科學家需要先找到更加耐用的電極材料，增加電池的可充電次數，這個想法才能實現。

麻省理工學院研究人員讓轉基因病毒參與到納米線的生產中，解決了一些技術難題。納米線的寬度類似紅細胞，在電池中可以用作電極。技術的關鍵在於增加納米線的表面積，增加充電和用電過程中電極的活躍範圍。這一研究成果已經在學術雜誌《自然通訊》上發表。

一種名叫M13的轉基因病毒能夠抓取水中的金屬分子，組成穩定的結構。科學家用M13病毒收集製作電池陰極的極佳材料——氧化錳，製造大約80納米寬的氧化錳納米線。和傳統化學方法制造的納米線相比，病毒納米線表面粗糙不平，表面積顯著增大。最後還要加入少量鈀等金屬元素，提升電極的導電性，促進充電和放電時的化學反應。

麻省理工學院能源教授貝爾徹說，M13的生物合成過程和鮑魚長殼差不多。鮑魚就是從海水中收集鈣，再組成堅固的外殼。

有了病毒的幫助，新型電池的能量密度能夠達到目前頂尖鋰離子電池的2到3倍，並且在諸多方面優勢明顯。新電池電極表面積更大，充電和放電效率更高。其製造工藝更加簡單、安全，病毒於常溫狀態下就能在水中完成工作，傳統方法必須的高溫條件和危險化學品已經沒有用武之地。病毒製造的納米線相互交錯關聯，製成的電極更加穩定。另外，電池對電極的金屬材質要求降低，成本也更加合理。

貝爾徹強調說，研究還處於早期階段，只做出了陰極，而電解液等關鍵部分仍然有待開發。此外，新型電池經測試可以充電50次，要真正應用，這個數字得上千才行。

貝爾徹還表示，目前在實驗中雖然利用生物技術，通過病毒收集金屬分子，但可能不是長久之計。如果將來找到最合適的材料，並且通過測試，工業生產中可能會採用別的辦法，方便定量控制。

多年來，科學家一直熱衷於病毒電池的研究。2010年，馬里蘭大學科學家讓菸草花葉病毒(TMV)幫助電池進行化學反應，收集電流，增強電池的儲電能力。同年，麻省理工學院科學家馬克•艾倫也提出，可以利用M13病毒製造氟化鐵陰極，希望製造輕巧持久的可充電池。