While lithium-ion batteries have emerged as a leading energy-storage option, aluminum has captured interest for its potential low cost, intrinsic safety, and abundance in the Earth's crust.
Researchers from Cornell University have redesigned the battery so that aluminum more easily integrates into a cell's electrodes. The new aluminum arrangement resulted in rechargeable batteries that offer up to 10,000 error-free cycles.
In previous attempts to use aluminum in batteries, the metal reacts chemically with the glass fiber separator, which physically divides the anode and the cathode, causing the battery to short circuit and fail.
The Cornell researchers instead designed a substrate of interwoven carbon fibers that forms an even stronger chemical bond with aluminum. While electrodes in conventional rechargeable batteries are only two dimensional, the Cornell-developed technique uses a three-dimensional – or nonplanar – architecture and creates a deeper, more consistent layering of aluminum..
When the battery is charged, the aluminum is deposited into the carbon structure via covalent bonding, or the sharing of electron pairs between aluminum and carbon atoms.
“Basically we use a chemical driving force to promote a uniform deposition of aluminum into the pores of the architecture, the electrode is much thicker and it has much faster kinetics.” said lead author Jingxu (Kent) Zheng, Ph.D. ’20, who is currently a postdoctoral researcher at the Massachusetts Institute of Technology.
The aluminum anode batteries can be reversibly charged and discharged one or more orders of magnitude more times than other aluminum rechargeable batteries under practical conditions.
The team's paper, “Regulating Electrodeposition Morphology in High-Capacity Aluminium and Zinc Battery Anodes Using Interfacial Metal–Substrate Bonding ,” was published on April 5 in Nature Energy.
Cornell researchers led by Professor of Engineering Lynden Archer , have been exploring the use of low-cost materials to create rechargeable batteries that will make energy storage more affordable.
In a short Q&A below, Archer explains how he envisions the role of aluminum anode batteries in the future.
Tech Briefs: If aluminum is low‐cost and abundant, why has it not been used in a mainstream way in batteries?
Prof. Lynden Archer: Aluminum has a lot going for it as a metal anode. It is not only Earth abundant (actually the third most abundant element in the Earth's crust) and cost-effective, but is trivalent, meaning that reduction of the metal at a battery anode can store 3 electrons per Al, which yields a very high storage capacity on either a volumetric or gravimetric basis.
The principal barriers to building practical batteries that utilize aluminum anodes are:
1) The metal readily forms a high electrical bandgap, Al2O3, passivation layer which prevents ready electrochemical access — drastically lowering reversibility of the plating and stripping reactions that must occur repeatedly during battery charge and discharge.
2) Like all reactive metals, aluminum forms patchy, mossy, and dendritic deposits that grow out from the plane of the anode during cycling. This process, loosely termed dendritic growth, causes premature battery failure either when the fragile deposits physically break away from the anode and become electrically disconnected from the external current source in a process termed orphaning, or when the out-of-plane growth causes the battery to short-circuit internally by bridging the anode and cathode.
3) The aluminum ion is large, trivalent, and forms strongly solvated complexes in typical liquid electrolytes used in batteries. This means that it is difficult to find cathodes that achieve the high levels of reversibility needed to match the charge-storage capacity, cost, and lifetime of the aluminum anode. Our contribution is important because it addresses all three of these problems in a battery framework that appears scalable.
Tech Briefs: What applications do you envision for aluminum‐anode batteries? What are the most exciting possibilities?
Prof. Archer: Aluminum anode batteries offer comparable storage capacity to lithium anode batteries on either a volumetric or mass basis. They are therefore, in principle, good candidates as next-generation storage technology in any of the applications where Li-ion batteries are being used.
Aluminum batteries, of course, bring the added advantages of low cost, an abundant supply, and lower sensitivity to moisture and oxygen in air, which makes manufacturing more straightforward. These traits mean that it may be easier to produce these batteries at the scales needed if electric power generation from renewable sources (e.g., wind and solar) and electrification of transportation progress at the pace needed to meet the growing global appetite for these transformations.
Our technology translation plan will focus on applications in the electric-power and grid-storage sector where cost, lifetime, and power are crucial. I believe if we can create battery systems that are successful in this space, it will create opportunities later on to address the scaling issues that are likely to emerge as electrification in the transportation sector make deeper inroads globally.
Tech Briefs: What will you and your team be working on next, in regards to this research?
Prof. Archer: The areal capacities and lifetime of the Al anodes reported in our recent paper are 10 to 100 times larger than any previous report, which is what makes the results promising. However, the full-cell battery studies reported in the paper employ relatively small (mWh-scale) CR2032 coin- and small pouch-cell modules as proof-of-concept type demonstration platforms.
The next step is to demonstrate larger (Wh to kWh) scale batteries that preserve the beneficial performance and cost features of the smaller cells. This will also require scale-up of our electrode making processes and detailed analysis of the supply chain and cost for the ionic liquid electrolyte components used in the cell.
Tech Briefs: How does the look of this battery differ from conventional designs? And is the battery challenging to make?
Prof. Archer: We are intentionally targeting the now standard cylindrical 18650 and planar pouch cell form factors in designing the larger versions of our Al batteries. The goal is to create cells that can be deployed in existing systems designed to accept 18650 or pouches. We would like to quickly get these cells into the hands of third parties able to evaluate them in real-world scenarios to more efficiently identify gaps and wring out risks in the technology.
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