The tortoise and the hare

龜兔賽跑

How to hybridize batteries and supercapacitors

如何將電池與超級電容器合二為一

The offspring will give electric cars more range and power

混合裝置將使電動汽車續航更遠、動力更強


When it comes to putting on pace, some electric vehicles rely not only on a battery to deliver the necessary wattage, but also on a second source of power called a supercapacitor. The battery serves as a marathon runner, providing a steady discharge over a long distance. The supercapacitor is a sprinter, unleashing a large amount of energy rapidly.

提到汽車加速,有些電動汽車不僅依靠電池產生足夠的功率,還依靠另一種被稱為超級電容器的動力源。電池猶如馬拉松賽跑運動員,在遠距離行駛中穩定放電。超級電容器猶如短跑運動員,快速釋放大量電能。



Batteries store their energy chemically, in the form of reactive substances in their two electrodes. These electrodes are held physically apart, but are connected by a material called an electrolyte through which charged atoms, known as ions, can pass from one to the other, in order to permit a reaction to proceed. That, though, happens only when the ion flow is balanced by a flow of electrons through an external circuit between the electrodes. This electron flow is the electric current which is the reason for the battery’s existence.

電池是以化學方式和電極內活性物質形式儲存電能。兩電極以物理方式分隔,但被電解質材料相連,俗稱離子的帶電原子通過電解質從一極遷移到另一極,從而發生化學反應。但只有當通過兩極間外部電路的電子流與電池內的離子流等當量時才會發生這一過程。電子流就是電流,這正是電池存在的原因。



Making the leap from a basic capacitor to the super variety involves two things. One is to coat the plates with a porous material such as activated carbon, to increase the surface area available for energy storage. The other is to soak them in an electrolyte. This creates yet more storage area in the form of the electrolyte’s boundary with the plates. But adding an electrolyte to the mix also brings the possibility of adding a bit of battery-like electrochemistry at the same time. And Skeleton Technologies, an Estonian supercapacitor firm, plans to do just that.

簡單電容器升級為超級電容器需要兩樣東西。一是在導電板表面鍍上一層活性炭等多孔材料,以增大儲能表面積。二是將導電板侵入電解質中,通過電解質與導電板之間形成的帶電界面來進一步增大儲能表面積。但加入電解質的同時,增添一些類似于電池的電化學儲能也成為可能。愛沙尼亞的一家超級電容器公司Skeleton Technologies打算這么做。

Plate tectonics
Skeleton has already developed plates composed of what it calls “curved” graphene, for a new range of straightforward supercapacitors. Ordinary graphene is a single layer of carbon atoms arranged in a hexagonal grid. It is highly conductive. Skeleton’s curved variety consists of crumpled sheets of the stuff. The consequent increase in surface area will, the firm hopes, push the energy density of its new products to 10-15wh/kg—a good fraction of the theoretical maximum for a supercapacitor of 20-30wh/kg.

導電板的構造
Skeleton公司已研發出一種由“弧形”石墨烯構成的導電板,用于一系列新型簡單的超級電容器。普通石墨烯是由六角網格狀的單層碳原子構成,導電性強。Skeleton公司采用的“弧形”石墨烯是由褶皺的多層碳原子構成。該公司希望,增大的儲能表面積使新產品的能量密度達到10-15瓦時/千克——這是相當高的,超級電容器的理論最大值為20-30瓦時/千克。


Other groups, too, are working on ways to add chemical-energy storage to a supercapacitor. Researchers at Graz University of Technology in Austria, for example, have developed a version that has its electrical contacts coated with carbon which is pierced by tiny pores. One contact operates like a capacitor plate, the other like a battery electrode. Unlike Skeleton, the Graz group are open about their approach to electrolyte chemistry. They are using aqueous sodium iodide (ie, a solution of sodium ions and iodine ions). At the electrode, the iodide turn into elemental iodine, which crystallises within the pores during discharge. This process then reverses itself when the device is charging. The pores in the plate serve to accommodate sodium ions similarly.

其他企業集團也在研究超級電容器如何利用化學儲能的方式。例如,奧地利格拉茨技術大學的研究人員研發出一種超級電容器,其電觸頭表面鍍有一層布滿細孔的碳,其中一個觸頭相當于電容器導電板,另一個相當于電池電極。不像Skeleton公司,格拉茨團隊公開了電解質的化學成分。他們使用的是碘化鈉溶液(即鈉離子與碘離子的混合溶液)。電極一端的碘離子變成元素碘,放電時在細孔內形成結晶,此過程在充電中是逆向的。導電板上的細孔以同樣的方式聚集鈉離子。

According to a paper its inventors published recently in Nature Communications, the Graz cell’s performance exceeds that of a Li-ion battery. It is able, for example, to cope with up to 1m charge and discharge cycles, says Qamar Abbas, a member of the team. A Li-ion equivalent might be expected to manage a couple of thousand cycles.

發明者最近在《自然通訊》雜志上發表的論文中提到,格拉茨電池的性能超過了鋰離子電池。例如,研究團隊成員卡馬爾·阿巴斯說,充放電周期可達100萬次。等量的鋰離子電池的充放電周期可能是幾千次。

Both Skeleton and the Graz group, then, are taking modified supercapacitor architecture and adding some bespoke electrochemistry. By contrast, although the offering from nawaTechnologies does indeed also employ modified supercapacitor plates as its electrodes, it uses tried and trusted Li-ion ingredients for the chemical donkey work.

Skeleton公司和格拉茨團隊都在使用改進的超級電容器架構,并增添了獨家定制的電化學儲能。相比之下,盡管nawaTechnologies公司的產品也使用改進的超級電容器導電板作為電極,但使用的是經過檢驗、可靠的鋰離子來完成單調的化學工作。

Like Skeleton, nawa already manufactures supercapacitors. The plates for these are created using a process which the firm calls vacnt (vertically aligned carbon nanotubes). This arranges those tubes in an array that resembles, in miniature, the bristles on a brush. Extreme miniature. A square centimetre contains about 100bn of them, all standing to attention. That greatly increases the surface area available to hold an electric charge.

與Skeleton公司一樣,nawa公司已在生產超級電容器。導電板的制造工藝被公司稱為“垂直定向碳納米管陣列”(vacnt),排列成陣列的納米管微觀上像刷子毛。它們極其微小,每平方厘米包含1000億個豎立的納米管,大幅增加儲存電荷的表面積。

To adapt vacnt plates to operate also as battery-like electrodes, nawa’s engineers have thinned the nanotube forest to make room for coatings of the chemicals which batteries employ for their reactions, and also for the movement of lithium ions into and out of the spaces between the tubes. This freedom of movement, the company reckons, will boost the arrangement’s power density by a factor of ten.

為了使vacnt導電板能像電池電極一樣工作,nawa公司的工程師們已將納米管簇變薄,一來為電池發生反應所需的化學涂層留出空間,二來允許鋰離子進出納米管之間的空隙,公司認為這種自由運動能將該裝置的功率密度提高十倍。

To start with, the nanotubes of the invention’s cathode (the positive electrode in a battery) will be coated with nickel, manganese and cobalt, a mixture already widely used to make such cathodes. Conventional anodes (the negative electrodes) are already carbon based, so using that element in the form of nanotubes is not a big departure. Other, less commercially developed battery chemistries should, though, also work with vacnt electrodes. These include lithium-sulphur and lithium-silicon, both of which have the potential to increase energy densities.

首先,該項發明的陰極納米管(電池正極)表面有鎳、錳、鈷混合物涂層,該涂層已被廣泛應用于這種陰極。常規的陽極(電池負極)原本就以碳材料為主,所以使用碳納米管不足為奇。不過,商業化程度較低的其他電池化學材料也可用于vacnt電極,包括鋰硫、鋰硅,兩者都有潛力提高能源密度。

Silicon is particularly promising, but it swells as it absorbs ions, and that can rupture a battery. The thicket of nanotubes in a vacnt electrode should operate like a cage to keep the silicon in check, says Pascal Boulanger, a physicist who helped found nawa in 2013. The new electrode material could also be used with solid rather than liquid electrolytes, to make “solid-state” batteries. These are powerful and robust, but are proving tricky to commercialise.

硅頗有前景,但吸收離子會膨脹,可能導致電池破裂。物理學家帕斯卡爾·布朗熱曾在2013年為nawa公司的創建提供過幫助,他說Vacnt電極中的納米管簇能像籠子一樣鎖住硅。這種新型電極材料也可使用固態而非液態電解質來制造“固態”電池。這些材料都很強大,但事實證明難以實現商業化。

Bristling to work
In tests with a number of unnamed battery companies, Dr Boulanger says vacnt electrodes achieved an energy density of 500wh/kg in one battery and up to 1,400 watt-hours per litre in another. This is roughly double what a typical Li-ion battery can manage in terms of weight and volume respectively. “We have done that very easily,” he adds, “so we believe there is more room for improvement.”

急于干活
布朗熱博士說,在許多匿名電池公司的試驗中,vacnt電極在一塊電池中的能源密度達到500瓦時/千克,在另一塊電池中達到1400瓦時/升。分別以重量和容積來計算,比典型鋰電池的能源密度高出近一倍?!拔覀冚p而易舉地做到了”,他補充道,“所以我們相信還有更大的改進空間”。

One firm that nawa does admit to working with is Saft, a large batterymaker owned by Total, a French oil giant keen to diversify from fossil fuels. Among Saft’s customers are several Formula 1 teams which use some electric power in their racing cars. Saft has also teamed up with psa group, a big European carmaker, to manufacture batteries for electric vehicles.

Nawa公司承認合作的一家企業是大型電池制造商“帥福得”,它是法國石油巨頭“道達爾”旗下的公司,后者渴望從化石燃料轉向多元化發展?!皫浉5谩钡目蛻舭ǘ嘀б患壏匠淌劫愜囮?,其賽車使用一部分電力驅動?!皫浉5谩边€與歐洲大型汽車制造商“標致雪鐵龍集團”合作,為電動汽車制造電池。

Naturally, the new device’s success will depend on the cost of manufacturing it. nawa is already constructing a mass-production line to make vacnt plates for its latest supercapacitors. The process used, which grows nanotubes on both sides of a roll of aluminium foil, would, says Ulrik Grape, nawa’s chief executive, transfer easily to an existing battery-production line and might even reduce battery-making costs. He expects the first versions of the supercapacitor-battery hybrids to be in production by 2023.

當然,這種新型裝置能否成功將取決于生產成本。Nawa公司正在建造一條量產線,為新型超級電容器制造vacnt導電板。所用工藝是在一卷鋁箔的兩面種植納米管,據Nawa公司總裁烏爾里克·格拉佩透露,這種工藝能輕而易舉地用于現有的電池生產線,甚至可能降低電池生產成本。他預計首款超級電容器-電池混合裝置將于2023年投產。

Whether such hybrid storage will be able to compete with conventional Li-ions remains to be seen. Li-ion batteries have the advantage of incumbency, and batterymakers have invested billions of dollars in huge “gigafactories” to turn them out in droves. Yet, for all the hype surrounding electric cars, doubts about Li-ions linger in many customers’ minds. Range-anxiety, recharge rate and cost all combine to induce a hesitation to reach for the credit card. Mixing the spice of a supercapacitor with the stamina of a battery might overcome at least the first two of these obxtions, and thus, at last, truly launch an era of carefree electric motoring.

這種混合儲能裝置能否與鋰電池相媲美有待于觀察。鋰電池有在位優勢,電池制造商向龐大的“超級工廠”投資了數十億美元,用于大批量生產鋰電池。然而,雖然電動汽車充斥著種種炒作,但許多消費者對鋰電子心存疑慮。里程焦慮、充電速度、成本使他們在買與不買之間猶豫不決。超級電容器的速度與電池的耐力相結合,至少可能打消前兩點疑慮,最終真正開啟無憂無慮的電動汽車時代。