最近，研究人員從一種野生菌類中發(fā)現(xiàn)了一種新型碳纖維材料。這種材料經(jīng)過納米顆粒改性，與鋰離子電池中最為常見的石墨電極相比，可以呈現(xiàn)出更佳的表現(xiàn)。
據(jù)了解，這種野生菌類名為硫磺干酪菌（Tyromyces Fissilis），美國普渡大學(xué)(Purdue University)的研究人員正是以這種菌類為原材料，成功制造了一種新型電極。
“為了滿足未來電動汽車和電網(wǎng)的儲能需求，即使現(xiàn)階段最為先進的鋰離子電池也必須從能量密度與功率輸出兩個方面進行優(yōu)化。”普度大學(xué)化學(xué)工程與材料工程學(xué)院副教授Vilas Pol表示，“因此，現(xiàn)在急需開發(fā)擁有更高性能的新型電極材料。”
鋰電池中的鋰離子存在于電解質(zhì)之中，但在充電階段，鋰離子是存儲在電極中的，而目前絕大多數(shù)鋰離子電池采用的電極材料均為石墨。
Pol教授與博士生Tang Jialiang發(fā)現(xiàn)，從硫磺干酪菌中提取的碳纖維材料，經(jīng)過氧化鈷納米顆粒的改性后，性能優(yōu)于傳統(tǒng)石墨電極材料。Pol教授表示，這種混合設(shè)計的優(yōu)異表現(xiàn)是一種協(xié)同作用的結(jié)果。
他說，“碳纖維和氧化鈷顆粒均具有電化學(xué)活性，兩者都能參與到反應(yīng)之中，因此可以提高電極的容量。”
這種新型混合電極的容量很穩(wěn)定，約為530毫安/克，比石墨電極的容量高1.5倍。
為了提高電池的性能，一種方法是通過添加特定的金屬對碳纖維進行改性，比如合金或金屬氧化物就允許電極在電池充電時，存儲更多的鋰離子。據(jù)了解，在讀博士Tang一直在尋找碳纖維的替代材料，并在探索的過程中發(fā)現(xiàn)了這種菌類原材料。
Tang表示，“現(xiàn)階段，生產(chǎn)電池所需碳纖維材料的過程過于依賴化學(xué)過程，而且成本高昂。”
他發(fā)現(xiàn)自家后院中一截腐爛的樹樁上長出了一種菌類，并決定探索以這種菌類為原材料，生產(chǎn)碳纖維的可能性。
“我對這種菌類的結(jié)構(gòu)很好奇，所以把它切了開來，然后發(fā)現(xiàn)這種菌類的屬性非常有趣。”他說。“這種菌類很類似橡膠，但同時也非常結(jié)實。最有趣的是，當(dāng)你把它切開后，會發(fā)現(xiàn)這種菌類擁有一種纖維性的網(wǎng)狀結(jié)構(gòu)。”
與其他菌類相比，硫磺干酪菌中的纖維非常豐富，而這些纖維可以在高溫氬氣室中發(fā)生熱解反應(yīng)，生成真菌纖維狀的純碳。
這些纖維交纏在一起，并沒有什么順序，就像一盤意大利面一樣。
Pol表示，“這些纖維可以構(gòu)成一個導(dǎo)電的互聯(lián)網(wǎng)絡(luò)。”
由于這個網(wǎng)絡(luò)傳輸電子的速度更快，因此可以提高電池的充電速度。
作者：Jean L. Broge
來源：SAE《航空工程》雜志
翻譯：SAE 上海辦公室
Fungus-inspired improvements in battery performance
Carbon fibers derived from a sustainable source, a type of wild mushroom, and modified with nanoparticles have been shown to outperform conventional graphite electrodes for lithium-ion batteries.
Researchers at Purdue University have created electrodes from a species of wild fungus called Tyromyces fissilis.
"Current state-of-the-art lithium-ion batteries must be improved in both energy density and power output to meet the future energy storage demand in electric vehicles and grid energy-storage technologies," said Vilas Pol, an Associate Professor in the School of Chemical Engineering and the School of Materials Engineering. "So there is a dire need to develop new anode materials with superior performance."
The anodes in most of today's lithium-ion batteries are made of graphite. Lithium ions are contained in an electrolyte, and those ions are stored in the anode during recharging.
Pol and doctoral student Jialiang Tang have found that carbon fibers derived from Tyromyces fissilis and modified by attaching cobalt oxide nanoparticles outperform conventional graphite in the anodes. The hybrid design has a synergistic result, Pol said.
"Both the carbon fibers and cobalt oxide particles are electrochemically active, so your capacity number goes higher because they both participate," he said.
The hybrid anodes have a stable capacity of 530 mAh/g, which is one and a half times greater than graphite's capacity.
One approach for improving battery performance is to modify carbon fibers by attaching certain metals, alloys or metal oxides that allow for increased storage of lithium during recharging. Tang got the idea of tapping fungi for raw materials while researching alternative sources for carbon fibers.
"The methods now used to produce carbon fibers for batteries are often chemical heavy and expensive," Tang said.
He noticed a mushroom growing on a rotting wood stump in his backyard and decided to study its potential as a source for carbon fibers.
"I was curious about the structure so I cut it open and found that it has very interesting properties," he said. "It's very rubbery and yet very tough at the same time. Most interestingly, when I cut it open it has a very fibrous network structure."
Comparisons with other fungi showed the Tyromyces fissilis was especially abundant in fibers. The fibers are processed under high temperatures in a chamber containing argon gas using a procedure called pyrolysis, yielding pure carbon in the original shape of the fungus fibers.
The fibers have a disordered arrangement and intertwine like spaghetti noodles.
"They form a conductive interconnected network," Pol said.
The interconnected network brings faster electron transport, which could result in faster battery charging.
Author: Jean L. Broge
Source: SAE Aerospace Engineering Magazine
我們可以在顯微鏡下看到野生菌類（如圖）內(nèi)部“錯綜復(fù)雜”的纖維網(wǎng)絡(luò)，這使其成為了一種非常理想的電極材料。（普渡大學(xué)/Jialiang Tang）