Battery Science 101


What is a battery?

ARGONNE NATIONAL LABORATORY

Batteries power our lives by transforming energy from one type to another.

Whether a traditional disposable battery (e.g. AA) or a rechargeable lithium-ion battery (used in cell phones, laptops and cars), a battery stores chemical energy and releases electrical energy.

There are four key parts in a battery — the cathode (positive side of the battery), the anode (negative side of the battery), a separator that prevents contact between the cathode and anode and a chemical solution known as an electrolyte that allows the flow of electrical charge between the cathode and anode.

Lithium-ion batteries that power cell phones, for example, typically consist of a cathode made of cobalt, manganese, and nickel oxides and an anode made out of graphite, the same material found in many pencils. The cathode and anode store the lithium.

When a lithium-ion battery is turned on, positively charged particles of lithium (ions) move through the electrolyte from the anode to cathode. Chemical reactions occur that generate electrons and convert stored chemical energy in the battery to electrical current.

When you plug in your cell phone to charge the lithium-ion battery, the chemical reactions go in reverse: the lithium ions move back from the cathode to the anode.

As long as lithium ions shuttle back and forth between the anode and cathode, there is a constant flow of electrons. This provides the energy to keep your devices running. Since this cycle can be repeated hundreds of times, this type of battery is rechargeable.

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HOW DOES A LITHIUM-ION BATTERY WORK?

Lithium-based batteries power our daily lives, from consumer electronics to national defense

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A lithium-ion battery is a type of rechargeable battery. It has four key parts:

  • 1The cathode (the positive side), typically a combination of nickel, manganese and cobalt oxides.
  • 2The anode (the negative side), commonly made out of graphite, the same material found in many pencils.
  • 3separator that prevents contact between the anode and cathode.
  • 4A chemical solution known as an electrolyte that moves lithium ions between the cathode and anode. The anode and cathode store lithium.

When the battery is in use, positively charged particles of lithium (ions) move through the electrolyte from the anode to cathode. Chemical reactions occur that generate electrons and convert stored chemical energy in the battery to electrical current.

When the battery is charging, the chemical reactions go
in reverse: the lithium ions move back from the cathode to the anode.

How does an X-ray light source work?
Batteries and the U.S. Department of Energy’s (DOE) Argonne National Laboratory

Argonne is recognized as a global leader in battery science and technology. Over the past sixty years, the lab’s pivotal discoveries have strengthened the U.S. battery manufacturing industry, aided the transition of the U.S. automotive fleet toward plug-in hybrid and electric vehicles, and enabled greater use of renewable energy, such as wind and solar power.

The lab’s research spans every aspect of battery development, from the breakthrough fundamental science of the Argonne-led Joint Center for Energy Storage Research, a DOE Energy Innovation Hub, to the Argonne Collaborative Center for Energy Storage Science, a cross-lab collective of scientists and engineers that solves complex battery problems through multidisciplinary research.

Argonne researchers are also exploring how to accelerate the recycling of lithium-ion batteries through the DOE’s ReCell Center, a collaboration led by Argonne that includes the National Renewable Energy Laboratory, Oak Ridge National Laboratory, as well as Worcester Polytechnic Institute, University of California at San Diego and Michigan Technological University.

For another take on “Batteries 101,” check out DOE Explains.

Eliminating the bottlenecks in performance of lithium-sulfur batteries


Graphical abstract. Credit: Chem (2022). DOI: 10.1016/j.chempr.2022.03.001

Energy storage in lithium-sulfur batteries is potentially higher than in lithium-ion batteries but they are hampered by a short life. Researchers from Uppsala University in Sweden have now identified the main bottlenecks in performance.

Lithium-sulfur batteries are high on the wish-list for future batteries as they are made from cheaper and more environmentally friendly materials than lithium-ion batteries. They also have higher energy storage capacity and work well at much lower temperatures. However, they suffer from short lifetimes and energy loss. An article just published in the journal Chem by a research group from Uppsala University has now identified the processes that are limiting the performance of the sulfur electrodes that in turn reduces the current that can be delivered. Various different materials are formed during the discharge/charge cycles and these cause various problems. Often a localized shortage of lithium causes a bottleneck.

“Learning about problems allows us to develop new strategies and materials to improve battery performance. Identifying the real bottlenecks is needed to take the next steps. This is big research challenge in a system as complex as lithium-sulfur,” says Daniel Brandell, Professor of Materials Chemistry at Uppsala University who works at the Ångström Advanced Battery Centre.

The study combined various radiation scattering techniques: X-ray analyses were made in Uppsala, Sweden and neutron results came from a large research facility, the Institut Laue Langevin, in Grenoble, France.

“The study demonstrates the importance of using these infrastructures to tackle problems in materials science,” says Professor Adrian Rennie. “These instruments are expensive but are necessary to understand such complex systems as these batteries. Many different reactions happen at the same time and materials are formed and can disappear quickly during operation.”

The study was carried-out as part of a co-operation with Scania CV AB.

“Electric power is needed for the heavy truck business and not just personal vehicles. They must keep up with developments of a range of different batteries that may soon become highly relevant,” says Daniel Brandell.

Scientists discover new electrolyte for solid-state lithium-ion batteries


Chlorine-based electrolytes like the one shown here are offering improved performance for solid-state lithium-ion batteries. Credit: Linda Nazar/University of Waterloo

In the quest for the perfect battery, scientists have two primary goals: create a device that can store a great deal of energy and do it safely. Many batteries contain liquid electrolytes, which are potentially flammable.

As a result, solid-state lithium-ion batteries, which consist of entirely solid components, have become increasingly attractive to scientists because they offer an enticing combination of higher safety and increased energy density—which is how much energy the battery can store for a given volume.

Researchers from the University of Waterloo, Canada, who are members of the Joint Center for Energy Storage Research (JCESR), headquartered at the U.S. Department of Energy’s (DOE) Argonne National Laboratory, have discovered a new solid electrolyte that offers several important advantages.

This electrolyte, composed of lithium, scandium, indium and chlorine, conducts lithium ions well but electrons poorly. This combination is essential to creating an all-solid-state battery that functions without significantly losing capacity for over a hundred cycles at high voltage (above 4 volts) and thousands of cycles at intermediate voltage.

The chloride nature of the electrolyte is key to its stability at operating conditions above 4 volts—meaning it is suitable for typical cathode materials that form the mainstay of today’s lithium-ion cells.

“The main attraction of a solid-state electrolyte is that it can’t catch fire, and it allows for efficient placement in the battery cell; we were pleased to demonstrate stable high-voltage operation,” said Linda Nazar, a Distinguished Research Professor of Chemistry at UWaterloo and a long-time member of JCESR. 

Current iterations of solid-state electrolytes focus heavily on sulfides, which oxidize and degrade above 2.5 volts. Therefore, they require the incorporation of an insulating coating around the cathode material that operates above 4 volts, which impairs the ability of electrons and lithium ions to move from the electrolyte and into the cathode.

“With sulfide electrolytes, you have a kind of conundrum—you want to electronically isolate the electrolyte from the cathode so it doesn’t oxidize, but you still require electronic conductivity in the cathode material,” Nazar said.

While Nazar’s group wasn’t the first to devise a chloride electrolyte, the decision to swap out half of the indium for scandium based on their previous work proved to be a winner in terms of lower electronic and higher ionic conductivity. “Chloride electrolytes have become increasingly attractive because they oxidize only at high voltages, and some are chemically compatible with the best cathodes we have,” Nazar said. “There’s been a few of them reported recently, but we designed one with distinct advantages.

One chemical key to the ionic conductivity lay in the material’s crisscrossing 3D structure called a spinel. The researchers had to balance two competing desires—to load the spinel with as many charge carrying ions as possible, but also to leave sites open for the ions to move through. “You might think of it like trying to a host a dance—you want people to come, but you don’t want it to be too crowded,” Nazar said.

According to Nazar, an ideal situation would be to have half the sites in the spinel structure be lithium occupied while the other half remained open, but she explained that creating that situation is hard to design.

In addition to the good ionic conductivity of the lithium, Nazar and her colleagues needed to make sure that the electrons could not move easily through the electrolyte to trigger its decomposition at high voltage. “Imagine a game of hopscotch,” she said. “Even if you’re only trying to hop from the first square to the second square, if you can create a wall that makes it difficult for the electrons, in our case, to jump over, that is another advantage of this solid electrolyte.”

Nazar said that it is not yet clear why the electronic conductivity is lower than many previously reported chloride electrolytes, but it helps establish a clean interface between the cathode material and solid electrolyte, a fact that is largely responsible for the stable performance even with high amounts of active material in the cathode.

A paper based on the research, “High areal capacity, long cycle life 4 V ceramic all-solid-state Li-ion batteries enabled by chloride solid electrolytes,” appeared in the January 3 online edition of Nature Energy.

Other authors of the paper include Nazar’s graduate student, Laidong Zhou, a JCESR member who was responsible for the majority of the work, and Se Young Kim, Chun Yuen Kwok and Abdeljalil Assoud, all of UWaterloo. Additional authors included Tong-Tong Zuo and Professor Juergen Janek of Justus Liebig University, Germany and Qiang Zhang of the DOE’s Oak Ridge National Laboratory.

Explore further

New solid electrolyte promises cheaper, better all-solid-state lithium batteries

More information: Laidong Zhou et al, High areal capacity, long cycle life 4 V ceramic all-solid-state Li-ion batteries enabled by chloride solid electrolytes, Nature Energy (2022). DOI: 10.1038/s41560-021-00952-0

Journal information: Nature Energy 

Provided by Argonne National Laboratory

Stanford University: Lithium/graphene “foil” makes for a great battery electrode – 2X current Energy Density


Graphene handles the issues that come with an electrode’s lithium moving elsewhere.

Lithium ion batteries, as the name implies, work by shuffling lithium atoms between a battery’s two electrodes. So, increasing a battery’s capacity is largely about finding ways to put more lithium into those electrodes. These efforts, however, have run into significant problems.

If lithium is a large fraction of your electrode material, then moving it out can cause the electrode to shrink. Moving it back in can lead to lithium deposits in the wrong places, shorting out the battery.

Now, a research team from Stanford has figured out how to wrap lots of lithium in graphene. The resulting structure holds a place open for lithium when it leaves, allowing it to flow back to where it started.

Tests of the resulting material, which they call a lithium-graphene foil, show it could enable batteries with close to twice the energy density of existing lithium batteries.

Lithium behaving badly

One obvious solution to increasing the amount of lithium in an electrode is simply to use lithium metal itself. But that’s not the easiest thing to do. Lithium metal is less reactive than the other members of its column of the periodic table (I’m looking at you, sodium and potassium), but it still reacts with air, water, and many electrolyte materials.

In addition, when lithium leaves the electrode and returns, there’s no way to control where it re-forms metal. After a few charge/discharge cycles, the lithium electrode starts to form sharp spikes that can ultimately grow large enough to short out the battery.

To have better control over how lithium behaves at the electrode, the Stanford group has looked into the use of some lithium-rich alloys. Lithium, for example, forms a complex with silicon where there are typically over four lithium atoms for each atom of silicon. When the lithium leaves the electrode, the silicon stays behind, providing a structure to incorporate the lithium when it returns on the other half of the charge/discharge cycle.

While this solves the problems with lithium metal, it creates a new one: volume changes. The silicon left behind when the lithium runs to the other electrode simply doesn’t take up as much volume as it does when the same electrode is filled with the lithium-silicon mix.

As a result, the electrode expands and contracts dramatically during a charge-discharge cycle, putting the battery under physical stress. (Mind you, a lithium metal electrode disappears entirely, possibly causing an even larger mechanical stress.)

And that would seem to leave us stuck. Limiting the expansion/contraction of the electrode material would seem to require limiting the amount of lithium that moves into and out of it. Which would, of course, mean limiting the energy density of the battery.

Between the sheets

In the new work, the researchers take their earlier lithium-silicon work and combine it with graphene. Graphene is a single-atom-thick sheet of carbon atoms linked together, and it has a number of properties that make it good for batteries. It conducts electricity well, making it easy to shift charges to and from the lithium when the battery charges and discharges. It’s also extremely thin, which means that packing a lot of graphene molecules into the electrode doesn’t take up much space. And critically for this work, graphene is mechanically tough.

To make their electrode material, the team made nanoparticles of the lithium-silicon material. These were then mixed in with graphene sheets in an eight-to-one ratio. A small amount of a plastic precursor was added, and the whole mixture was spread across a plastic block. Once spread, the polymer precursor created a thin film of polymer on top of the graphene-nanoparticle mix. This could be peeled off, and then the graphene-nanoparticle mix could be peeled off the block as a sheet.

The resulting material, which they call a foil, contains large clusters of the nanoparticles typically surrounded by three to five layers of graphene. Depending on how thick you make the foil, there can be several layers of nanoparticle clusters, each separated by graphene.

The graphene sheets make the material pretty robust, as you can fold and unfold it and then still use it as a battery electrode. They also help keep the air from reacting with the lithium inside. Even after two weeks of being exposed to the air, the foil retained about 95 percent of its capacity as an electrode. Lower the fraction of graphene used in the starting mix and air becomes a problem, with the electrode losing nearly half of its capacity in the same two weeks.

And it worked pretty well as an electrode. When the lithium left, the nanoparticles did shrink, but the graphene sheets held the structure together and kept it from shrinking. And it retained 98 percent of its original capacity even after 400 charge-discharge cycles. Perhaps most importantly, when paired with a vanadium oxide cathode, the energy density was just over 500 Watt-hours per kilogram. Current lithium-ion batteries top out at about half that.

Normally, work like this can take a while to get out of an academic lab and have a company start looking into it. In this case, however, the head of the research group Yi Cui already has a startup company with batteries on the market. So, this could take somewhat less time for a thorough commercial evaluation. The biggest sticking point may be the cost of the graphene. A quick search suggests that graphene is still thousands of dollars per kilogram, although it has come down, and lots of people are looking for ways to make it even less expensive.

If they succeed, then the rest of the components of this electrode are pretty cheap. And the process for making it seems pretty simple.

Nature Nanotechnology, 2017. DOI: 10.1038/NNANO.2017.129  (About DOIs).

Rice U: New Lithium metal battery prototype boasts 3X the capacity of current lithium-ions ~ Dendrite Problem Solved?


graphene-nanotube-lithium-battery-4

Could a new material involving a carbon nanotube and graphene hybrid put an end to the dendrite problem in lithium batteries? (Credit: Tour Group/Rice University)

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 Dr. 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.”

Rice logo_rice3So 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 (Credit: Tour Group/Rice University)

 

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.

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