Electronics

Lithium metal battery prototype boasts 3 times the capacity of lithium-ions

Lithium metal battery prototyp...
Could a new material involving a carbon nanotube and graphene hybrid put an end to the dendrite problem in lithium batteries?
Could a new material involving a carbon nanotube and graphene hybrid put an end to the dendrite problem in lithium batteries?
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Due to the low density and high surface area of the nanotube forest, the lithium metal is able to coat the carbon nanotube evenly when charged
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Due to the low density and high surface area of the nanotube forest, the lithium metal is able to coat the carbon nanotube evenly when charged
Close-up of the lithium metal coating the graphene-nanotube anode
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Close-up of the lithium metal coating the graphene-nanotube anode
Close-up of a carbon nanotube that is evenly coated with lithium
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Close-up of a carbon nanotube that is evenly coated with lithium
Could a new material involving a carbon nanotube and graphene hybrid put an end to the dendrite problem in lithium batteries?
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Could a new material involving a carbon nanotube and graphene hybrid put an end to the dendrite problem in lithium batteries?

The high energy capacity of lithium-ion batteries has led to them powering everything from tiny mobile devices to huge trucks. But current lithium-ion battery technology is nearing its limits and the search is on for a better lithium battery. But one thing stands in the way: dendrites. If a new technology by Rice University scientists lives up to its potential, it could solve this problem and enable lithium-metal batteries that can hold three times the energy of lithium-ion ones.

Dendrites are microscopic lithium fibers that form on the anodes during the charging process, spreading like a rash till they reach the other electrode and causing the battery to short circuit. As companies such as Samsung know only too well, this can cause the battery to catch fire or even explode.

"Lithium-ion batteries have changed the world, no doubt," says chemist James Tour, who led the study. "But they're about as good as they're going to get. Your cellphone's battery won't last any longer until new technology comes along."

So until scientists can figure out a way to solve the problem of dendrites, we'll have to put our hopes for a higher capacity, faster-charging battery that can quell range anxiety on hold. This explains why there's been no shortage of attempts to solve this problem, from using Kevlar to slow down dendrite growth to creating a new electrolyte that could lead to the development of an anode-free cell. So how does this new technology from Rice University compare?

For a start, it's able to stop dendrite growth in its tracks. Key to it is a unique anode made from a material that was first created at the university five years ago. By using a covalent bond structure, it combines a two-dimensional graphene sheet and carbon nanotubes to form a seamless three-dimensional structure. As Tour explained back when the material was first unveiled:

"By growing graphene on metal (in this case copper) and then growing nanotubes from the graphene, the electrical contact between the nanotubes and the metal electrode is ohmic. That means electrons see no difference, because it's all one seamless material."

Close-up of the lithium metal coating the graphene-nanotube anode
Close-up of the lithium metal coating the graphene-nanotube anode

Envisioned for use in energy storage and electronics applications such as supercapacitors, it wasn't until 2014, when co-lead author Abdul-Rahman Raji was experimenting with lithium metal and the graphene-nanotube hybrid, that the researchers discovered its potential as a dendrite inhibitor.

"I reasoned that lithium metal must have plated on the electrode while analyzing results of experiments carried out to store lithium ions in the anode material combined with a lithium cobalt oxide cathode in a full cell," says Raji. "We were excited because the voltage profile of the full cell was very flat. At that moment, we knew we had found something special."

Closer analysis revealed no dendrites had grown when the lithium metal was deposited into a standalone hybrid anode – but would it work in a proper battery?

To test the anode, the researchers built full battery prototypes with sulfur-based cathodes that retained 80 percent capacity after more than 500 charge-discharge cycles (i.e. the rough equivalent of what a cellphone goes through in a two-year period). No signs of dendrites were observed on the anodes.

Close-up of a carbon nanotube that is evenly coated with lithium
Close-up of a carbon nanotube that is evenly coated with lithium

How it works

The low density and high surface area of the nanotube forest allow the lithium metal to coat the carbon hybrid material evenly when the battery is charged. And since there is plenty of space for the particles to slip in and out during the charge and discharge cycle, they end up being evenly distributed and this stops the growth of dendrites altogether.

According to the study, the anode material is capable of a lithium storage capacity of 3,351 milliamp hours per gram, which is close to pure lithium's theoretical maximum of 3,860 milliamp hours per gram, and 10 times that of lithium-ion batteries. And since the nanotube carpet has a low density, this means it's able to coat all the way down to substrate and maximize use of the available volume.

"Many people doing battery research only make the anode, because to do the whole package is much harder," says Tour. "We had to develop a commensurate cathode technology based upon sulfur to accommodate these ultrahigh-capacity lithium anodes in first-generation systems. We're producing these full batteries, cathode plus anode, on a pilot scale, and they're being tested."

The study was published in ACS Nano.

Source: Rice University

8 comments
highlandboy
10 times the density with no dendrites spells the end of range anxiety for electric vehicles. Even half this would be outstanding.
wle
what would they cost per kwh? how fast can they charge?
DaveWesely
This is impressive. I just wish we could get past this "range anxiety" issue. It is a non-issue. Think about it: if you needed to compete in a long range race with an electric vehicle - how would you refuel? Gas race car crews have figured out how to completely service their cars within a matter of seconds. How would an electric car completely recharge in a matter of seconds in order to compete? It most certainly wouldn't try to fast charge the batteries. Instead the electric car crew would figure out a way to swap out the batteries within a matter of seconds. The answer to "range anxiety" then, is not to figure out how to fast charge batteries. That is hard on the electric infrastructure as well as the batteries. The answer is to create a standard battery type that can be effectively swapped out and leased during those occasional road trips.
StWils
More to the point and far more important is that this makes better use of lithium. While lithium is a very common element in the Earth's crust there are only Two known significant sources of ore with useful amounts of lithium. Recovering lithium from most other rocks & soils is hard to do. Also, the graphene carpet structure may well enable using other elements than lithium that would remove any cost or environmental constraints. While the pinheads currently vandalizing the American government and specifically, the EPA, may not have the attention span or IQ bandwidth to understand or believe terms like "environmental impact" these folks are only temps. They will go in time and hopefully be replaced by people with skill, intellect, and a strong concern for everyone else AND our future. It would be great if newer, better batteries were available to fill a wide array of applications, from vehicles to stationary uses.
Future3000
I agree StWils: The "dirtiest to produce" car worldwide was Toyota Prius, then came Tesla and overthrow Prius easily! This batteries are very dirty to produce! This shown report means "please give us more money for R&D!"... and provide Goldman Sachs, which owns over 90% of all worldwide put and call certificates for Lithium trade till 2025! It's all about money, nothing else! Let me tell you a small fairytale, happen in Germany since 2003: a small group of independent engineers built a solid state Electric-Double-Layer-Capacitor, made of Silicone (sand) and Carbon (charcoal). Today we would say Graphene Battery. Cheap raw materials, cheap in mass production, non-inflammable, 100.000s charging cycles, recharging within a minute, 20 years minimum lifetime. It had a energy storage density over 1.5 KWh/kg (in this time 12 times more than best Li-Batteries, 400 times of other EDLC). So they tried to sell it in the last 14 years to big battery manufacturers like Bosch, Siemens, LG and Panasonic... as the "we need electric cars"-hype came, they offered this technology to Mercedes, VW, Porsche, GM, BYD, Honda, Toyota... and Tesla. Without any testing the answer of ALL this companies was: "We have other plans". So I ask you: WHAT are their "other plans"? With this EDLC technology a Tesla S would have a range of 5.500 km with one single charge, or, if 1.500 km range is enough, reduce 600 kg overweight of this 2.3 ton heavy Tesla! Sad story!
YuraG
@StWils – exactly!!!, @Future3000 - I hope you are wrong;-)
BrandonVirgin
@Future3000 I am skeptical that they really had something. If they had the goods, why not build a demo battery? You could replace the batteries of an existing phone or electric car. After that, they could demo it to Newatlas or another publisher with a similar reach. Why didn't something like this happen? 1.)Maybe Newatlas and all of the other publications in the world are also in on the protecting the profits of Gold Slacks. JPMorgan Chase would also have to be in on the conspiracy. If Goldman owns 90% of the market JPMorgan Chase could have no more than 10%. That kind of market imbalance would give JP a strong incentive to invest. For the conspiracy to continue, JP Morgan must now hate money. Additionally, all of the electric car startups must be in on the conspiracy and they are more interested in protecting Goldman's profits than their own success. 2.) Of course, a simpler explanation exists and Occam's razor dictates that it must, therefore, be true. Newatlas would report on any such battery that was demoed to them, JP still likes money, startup electric car companies want to succeed and the Electric-Double-Layer-Capacitor was not fully baked.
SaysMe
Every battery, even lead acid, has this dendrite problem!