真乄科技業的頂尖投資團隊

鋰電池應用廣泛，但充電時間較長、循環次數等限制仍難以突破。美國史丹佛大學華裔科學家就研發了一款新型的鋁電池，號稱能在極短時間內充電完成，充電週期遠超過鋰電池，而且還更加安全。

研發團隊的華人教授戴宏傑表示，這種新型鋁電池與舊型鋁電池不同，用鋁作為正極、石墨為負極，電解液是等離子液體，充電只需要一分鐘，且經過7500個充放電週期測試也沒有影響電容量，比現有鋰電池約1000個充放電週期更耐用。

這種新型鋁電池採用的新材料成本低廉，可彎曲且不易燃燒，有望成為既有電器產品之鋰電池與鹼性電池的替代品。在測試時，研發團隊還在電池上鑽孔，電池並未因此爆炸或立即毀損。不過，戴宏傑指出這種電池的能量密度不夠高，僅有約鋰電池一半，未來還需精進改良，因此距離量產上市還有一段時間。相關研究已發表在《Nature》期刊上。

A new kind of flexible aluminum-ion battery holds as much energy as lead-acid and nickel metal hydride batteries but recharges in a minute. The battery also boasts a much longer cycle life than today’s battery technologies.

The battery’s low cost, long cycle life and stability are appealing for grid-scale storage, says Hongjie Dai, a professor of chemistry at Stanford University. The technology could also be developed to power wearable devices. Dai and his colleagues reported the details regarding the new device in the journal Nature.

Aluminum-ion batteries are an attractive alternative to lithium-ion batteries for a few reasons. For one, aluminum is abundant and hence cheap. It is less reactive, which would mean safer, less-flammable batteries. In a video, the researchers drill into the batteries and they continue working for a while without catching fire. For the same reasons, many teams are also working on alternatives to lithium batteries that feature potassium, sodium and manganese.

Delving into chemistry, aluminum has three valence electrons compared to lithium’s one. So charge-discharge reactions transfer three electrons per atom, which means an aluminum battery could pack almost three times as much energy as its lithium-ion counterpart, and in a smaller, lighter package.

But scientists have been trying, unsuccessfully, for over three decades to develop an effective aluminum-ion battery chemistry. Most designs have used solid aluminum anodes, aluminum-containing ionic liquid electrolytes, and various cathode materials such as manganese oxide, vanadium nanowires and doped polymers.

The best of these systems have low discharge voltages, cycle lives shorter than 100 cycles, and large decays in energy-storage capacity. Their cathode materials also quickly disintegrate.

Dai and his colleagues say they have found a cathode that works much better than ones used before. The cathode is a flexible 3-D graphite foam, a highly porous and lightweight spongelike carbon material that they made in their lab. The airy material can hold a large number of aluminum ions. The ions also move through the material quickly, enabling fast charge and discharge.

The researchers packed the graphite cathode along with a thin aluminum foil anode and an ionic liquid electrolyte in a flexible pouch.

The pouch cell could be charged at a current density of 5 amperes per gram in about a minute. It could be discharged over 34 minutes at a specific capacity of close to 70 milliampere-hours per gram.

The energy density of the battery (40 watt-hours per kilogram) is comparable to lead-acid and NiMH batteries. But it has a much more impressive cycle life than competing technologies; it lasted for up to 7,500 charge cycles without any loss in capacity. Typical lithium-ion batteries last for only about 1,000 cycles.

Further, the new battery has a power density of 3000 W/kg, very high relative to that of supercapacitors. What makes this a battery and not a supercapacitor, though, is that it has a voltage plateau. “Supercapacitors do not show voltage plateaus and the discharge voltage would decrease continuously,” Dai says.

The Stanford team is still working to refine the energy storage breakthroughs. While the electrodes are made of very cheap materials, the ionic liquid electrolyte will have to be replaced with a more cost-effective electrolyte to make the battery market competitive. The research team is also trying to increase the energy storage capacity of the graphite foam cathode.

Several companies are trying to license the technology from Stanford, Dai says.