What is the holy grail of lithium batteries?

23 Sep.,2024

 

Solid-state battery: The Holy Grail in battery research

&#;the year when decisions have to be made

According to the Solid-State Battery study from Yole Développement, the first batteries could be available from and by , production could increase to 2.36 GWh&#;which, however, is still a small volume compared to overall demand for lithium-ion batteries. Mass production of vehicles with solid-state batteries is not expected before . According to IDTechex, the market could grow to USD 8 billion by . A market which will no longer be mainly an &#;Asian&#; issue but will have become a global affair with regional interests and government subsidies. However, analysts do not expect to see a major swing to solid-state batteries quite as soon.

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The pioneers

But in some cases, things do seem to be moving at a faster pace. For instance, BMW recently promised the first prototypes of electric cars with solid-state batteries &#;well before &#;. The Solid Power partners plan to deliver the first qualification tests with 100-Ah cells already in . With conventional lithium-ion processes, multi-layer solid-state batteries already run with 20 ampere hours (Ah) capacity from a roll-to-roll production line.

Chinese startup NIO is more advanced and has announced that the ET7&#;the first mass-produced vehicle with a solid-state battery&#;will be launched on the Chinese market at the end of . The company claims that the solid-state battery installed in the top-of-the-range model, with an energy density of 360 Wh/kg, will give the vehicle a range of kilometers. However, the CEO recently stated in an interview that it is actually a &#;semi-solid-state battery&#;.

Twenty-one Mercedes-Benz eCitaro electric buses have been in use at ESWE Verkehr, the public transport provider in Wiesbaden, Germany, with &#;complete&#; solid-state batteries since the beginning of February. The batteries were supplied by the Bolloré subsidiary Blue Solutions. They are based on a solid electrolyte, a lithium-metal anode and a standard cathode, as in conventional Li-ion batteries &#; apart from the fact that iron phosphate is used instead of NMC (lithium-nickel-cobalt-manganese). However, depending on the application, the LMP batteries have to be operated at temperatures between 50 and 80 degrees Celsius.

At CES , another pioneer, Taiwan-based battery cell producer ProLogium, presented a solid-state battery for electric cars, electric buses, and electric two-wheeled vehicles. Its partners are the Chinese automaker Nio and EnovatE.

And what is Tesla doing? Elon Musk is backing better lithium-ion batteries with liquid electrolytes such as those from CATL&#;at least that is the official statement. However, Martin Eberhard, co-founder and former CEO of Tesla, recently observed that the solid-state electrolyte technology from ProLogium was the most exciting new development that he had seen in this area.

The Holy Grail Of Lithium Batteries

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Building a Better Lithium Battery

Last year I wrote about A Battery That Could Change The World, which addressed the development of a solid-state lithium battery that won't catch fire if damaged. More recently, I wrote about a different approach to the problem of fires in lithium-ion batteries, which quickly dissipates the heat released from a fire in a cell before it can spread.

Development of better batteries is critical as more electric vehicles hit the roads, and as electric utilities seek better options for storing power from intermittent renewables. In addition, lithium-ion batteries have become ubiquitous in our lives through any number of consumer electronics.

Three key issues that companies are working to address are safety, energy density, and cost. Safety mainly concerns the possibility that lithium-ion batteries can catch fire if damaged. The two aforementioned stories are mostly focused on that aspect of the problem.

The problem of energy density concerns the ability to store energy in a specific volume (or weight). Batteries have low energy density compared to liquid fuels. Gasoline, for example, has about 100 times the volumetric energy density of a Li-ion battery pack. However, the greater efficiency of an electric motor versus a combustion engine substantially narrows the gap for usable energy.

Finally, batteries have historically been an expensive way to store energy. According to the Energy Information Administration, in recent years the cost to install large-scale battery storage systems was typically thousands of dollars per kilowatt (kW). In comparison, the capital costs of producing electricity by power plants can be under $1,000/kW. Importantly, lower battery storage costs would be a critical enabler for utilities seeking to incorporate higher levels of intermittent renewables into the power mix.

It isn't surprising that companies are working to solve each of these battery challenges. But the solution to one problem can create another.

Consider energy density. Lithium-metal batteries allow for much higher energy density than lithium-ion batteries by using lithium-metal electrode instead of graphite electrode. But lithium deposits called dendrites can spontaneously grow from the lithium metal electrodes whenever the battery is being charged. If these dendrites bridge the gap between the anode and cathode (the two opposite electrodes in a battery), a short circuit results. This can cause the battery to fail, which may result in a fire or explosion.

The lithium-ion battery was a solution to this problem. The dendrite problem can be resolved by replacing the lithium-metal electrode with a carbon electrode that has a layered sheet structure (i.e., graphite), which hosts discrete tiny lithium ions between the layers. However, the result is a lower lithium storage capacity than a battery utilizing a solid, continuous lithium-metal electrode.

Solving the Dendrite Problem

An ideal battery would contain solid lithium electrodes while avoiding the dendrite problem. A company called Zeta Energy, using technology licensed from a top university, believes it has created just such a solution.

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I recently spoke to Zeta Energy CEO Charles Maslin, who explained that Zeta is the sixth Greek letter and corresponds to carbon, the sixth element in the periodic table. Zeta potential is also a measure of the effective electric charge on a nanoparticle surface.

In an interview I conducted with Maslin, he provided a description of the new battery along with peer-reviewed data from the 10+ years of research and testing that led to its development.

The key innovation in the Zeta battery is a hybrid anode created from graphene and carbon nanotubes. The resulting three-dimensional carbon anode approaches the theoretical maximum for storage of lithium metal &#; about 10 times the lithium storage capacity of graphite used in lithium-ion batteries.

According to published research, the hybrid anode is one of the best-known conductors of electricity, and when the battery is charged, lithium metal is deposited on the sidewalls of the carbon nanotubes and in the pores between the nanotubes. These are chemically bonded to the surface of the graphene that is in turn chemically bonded to a copper substrate. The graphene-carbon nanotube-copper connections introduce no additional electrical resistance that is typically generated at the interface when electrode materials are coated on copper in batteries. This means no heat is generated at this interface.

The combination of a dendrite-free electrode with the seamless interface enables fast charging and discharging of the Zeta battery, unlike in a graphite-based lithium-ion battery where very fast charging can cause lithium dendrites to form on top of graphite. No resistance at the interface means electrons can travel to the electrode much more rapidly. The Zeta battery can thus be charged safely within a few minutes.

More Energy, Less Cost

Despite the breakthrough, building the ideal battery requires more than perfecting the anode. A cathode that matches the high capacity anode is required to unleash the boost in energy density, but current cathodes do not have enough capacity to match the lithium metal anode.

Zeta&#;s second key innovation is a hybrid cathode created from sulfur and carbon, which has 8 times the capacity of current cathodes based on metal oxide. Thus, Zeta&#;s anode-cathode combination means a packaged lithium-sulfur battery with three times the energy storage capacity of lithium-ion batteries.

Further, Zeta has eliminated the use of expensive metals such as cobalt in its battery. That translates to a significant reduction in battery cost. Though others have been trying to develop sulfur-based cathode for decades, they just could not get it to cycle well, and the battery dies after just a couple of hundred cycles at most. Maslin explained that Zeta has succeeded in stabilizing the sulfur cathode and pointed to test results that show it can be cycled with minimal capacity loss over thousands of cycles.

Furthermore, the Zeta lithium-sulfur battery does not self-discharge to any appreciable extent and holds charge for a significantly long time, thus boasting a superb shelf life. A major battery performance concern is self-discharge &#; you charge the battery then store it, but when you use it later, only a fraction of the stored battery capacity is left.

Based on Zeta&#;s measurements, it is estimated that more than 90% of its battery capacity will remain after 10 years of storage at full charge, unlike regular lithium-ion batteries that will have at best 10% capacity over the same period of storage. That means the Zeta battery is ready to work after virtually any period of storage.

In summary, the Zeta battery addresses both energy density and safety. Test results published in several scientific journals including Nature Magazine show that the Zeta battery has:

  • Up to 3 times the energy storage capacity of lithium-ion batteries

  • Faster charge time (minutes instead of hours)

  • Lower battery temperature

  • Little degradation over charge/recharge cycles

  • Outstanding shelf life

  • Significantly lighter than lithium-ion batteries

  • Zero cobalt

  • Significantly lower cost than lithium-ion batteries

Conclusions

If their research and test results are accurate, Zeta Energy may hold the new gold standard in energy storage. The technology appears to address multiple shortcomings of current lithium-ion batteries and has done so at a lower price point. These are exactly the kinds of breakthroughs that are needed if battery storage is to be adopted widely by utilities seeking to smooth out the intermittency of renewables like wind and solar power.

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