Aluminium-ion battery

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Aluminium-ion batteries are a class of rechargeable battery in which aluminium ions provide energy by flowing from the negative electrode of the battery, the cathode, to the positive electrode, the anode. When recharging, aluminium ions return to the anode, and it can exchange three redox electrons per cation. This means that insertion of one Al³⁺
is equivalent to three Li⁺
ions in conventional intercalation cathodes. Thus, since the ionic radii of Al³⁺
(0.54 A) and Li⁺
(0.76 A) are similar, significantly higher models of electrons and Al³⁺
ions can be accepted by the cathodes without much pulverization. The trivalent charger carrier, Al³⁺
is both the advantage and disadvantage of this battery.. While transferring 3 units of charge by one ion significantly increase the energy storage capacity but the electrostatic intercalation of the host materials with a trivalent cation is too strong for a well-defined electrochemical behavior.

Rechargeable aluminium-based batteries offer the possibilities of low cost and low flammability, together with three-electron-redox properties leading to high capacity. The inertness of aluminum and the ease of handling in an ambient environment is expected to offer significant safety improvements for this kind of battery. In addition, aluminum possesses a higher volumetric capacity than Li, K, Mg, Na, Ca and Zn owning to its high density (2.7g cm^-3 at 25°C) and ability to exchange three electrons. This again means that the energy stored in aluminum-batteries on a per volume basis is higher than that in other metal-based batteries. Hence, aluminum-batteries are expected to be smaller in size.

Video Aluminium-ion battery

Design

Like all other batteries, the basic structure of aluminium-ion batteries includes two electrodes connected by an electrolyte, an ionically (but not electrically) conductive material acting as a medium for the flow of charge carriers. Unlike lithium-ion batteries, where the mobil ion is Li⁺
, aluminum forms a complex with chloride in most electrolytes and generates an anionic mobile charge carrier, usually AlCl
₄^-
or Al
₂Cl
₇^-
.

The amount of energy or power that a battery can release is dependent on factors including the battery cell's voltage, capacity and chemical composition. A battery can maximize its energy output levels by:

• Increasing chemical potential difference between the two electrodes
• Reducing the mass of reactants
• Preventing the electrolyte from being modified by the chemical reactions

Maps Aluminium-ion battery

Research

Various research teams are experimenting with aluminium and other chemical compounds to produce the most efficient long lasting and safe battery.

Oak Ridge National Laboratory

Around 2010 the Oak Ridge National Laboratory (ORNL) developed and patented a high energy density device, producing 1,060 Wh/kg versus 406 Wh/kg for lithium-ion batteries. ORNL used an ionic electrolyte, instead of the typical aqueous electrolyte which can produce hydrogen gas during operation and corrode the aluminium anode. The electrolyte was made of 3-ethyl-1-methylimidazolium chloride with excess aluminium trichloride. However, ionic electrolytes are less conductive, reducing power density. Reducing anode/cathode separation can offset the limited conductivity, but causes heating. ORNL devised a cathode made up of spinel manganese oxide further reducing corrosion.

Cornell University

In 2011 at Cornell University, a research team used the same electrolyte as ORNL, but used vanadium oxide nanowires for the cathode. Vanadium oxide displays an open crystal structure, allowing greater surface area for an aluminium structure and reduces the path between cathode and anode, maximizing energy output levels. The device produced a large output voltage during operation. However, the battery had a low coulombic efficiency.

Stanford University

In April 2015 researchers at Stanford University claimed to have developed an aluminum-ion battery with a recharge time of about one minute (for an unspecified battery capacity). They claimed that their battery has no possibility of catching fire, offering a video of a hole being drilled into the battery while it was generating electricity. Their cell provides about 2 volts. Connecting 2 cells in a series circuit will provide 4 volts. The prototype lasted over 7,500 charge-discharge cycles with no loss of capacity.

The "ultrafast rechargeable aluminum-ion battery" is made of an aluminum anode, liquid electrolyte, isolation foam, and a graphite cathode. During the charging process, AlCl
₄^-
ions intercalates among the graphene stacked layers. While discharging, AlCl
₄^-
ions are rapidly de-intercalated through the graphene stacked layers. The features of Al-ion batteries include:

• Fast charging: a charge dis-charge cycle can be completed in one minute
• High durability: the Al-ion battery withstands more than 10,000 cycles without a capacity decay
• High safety: the thin battery cell is stable, nontoxic, and bendable. It will not catch fire even if damaged by drilling
• Low cost: the acquisition cost of raw materials are relatively cheap. In addition to powering 3C electronic devices, the Al-ion batteries can also be used in electric bikes and motorcycles, golf carts, lift trucks, wind turbines, solar cells etc.

In 2016, the lab tested these cells through collaborating with Taiwan's Industrial Technology Research Institute (ITRI) to power a motorbike. However, that version of the battery had one major drawback: it involved an expensive electrolyte. In 2017, the newest version includes a urea-based electrolyte and is about 100 times cheaper than the 2015 model, with higher efficiency and a charging time of 45 minutes. It's the first time urea has been used in a battery. The battery exhibits ~99.7% Coulombic efficiency and a substantial rate capability, with a cathode capacity of 73 mAg^-1 at 100 mAg^-1 (1.4°C).

ALION Project

In June 2015 a European Horizon 2020 research project on aluminium-ion batteries was launched at the technological research center LEITAT. The project aims at developing a prototype with the help of various European industries and research institutes. The project entitled High Specific Energy Aluminium-Ion Rechargeable Batteries for Decentralized Electricity Generation Sources, or ALION for short, pursues an integral approach comprising electroactive materials based on "rocking chair" mechanism, robust ionic liquid-based electrolytes as well as novel cell and battery concepts, finally resulting in a technology with much lower cost, improved performance, safety and reliability with respect to current energy storage solutions (e.g. Pumped hydro storage, Compressed air energy storage, Li-ion battery, Redox flow battery etc.). The project covers the whole value chain from materials and component manufacturers, battery assembler, until the technology validation in specific electric microgrid system including renewable energy source (i.e. mini wind turbine, photovoltaic system, etc.). Thus, the final objective of this project is to obtain an Al-ion battery module validated in a relevant environment, with a specific energy of 400 Wh/kg, a voltage of 48 V and a cycle life of 3000 cycles.

University Of Maryland

In 2016, a University of Maryland team reported a rechargeable aluminium/sulfur battery that utilizes a sulfur/carbon composite as the cathode material. The chemistry is able to provide a 1340 Wh/kg energy density in theory. The team made a prototype cell which demonstrated an energy density of 800 Wh/kg for over 20 cycles.

Zhejiang University Department of Polymer Science

In December 2017 a team, led by professor Gao Chao, from Department of Polymer Science and Engineering of Zhejiang University, announced the design of a battery using graphene films as anode and metallic aluminium as cathode.

The 3H3C (Trihigh Tricontinuous) design results in a graphene film cathode with excellent electrochemical properties. The arrangement of graphene liquid crystals result in a highly oriented structure. A process of high temperature annealing under gas pressure produces a high quality and high channelling graphene structure. This 3H3C design creates an aluminium-graphene battery (Al-GB) which has impressive properties:

• The battery works well after quarter-million cycles retaining 91.7 percent of its original capacity.
• The battery can be fully charged in 1.1 seconds.
• The assembled battery works well across a temperature range of minus 40 to 120 degrees Celsius.
• It offers a high current capacity (111 mAh / g 400 A / g based on the cathode).
• It can be folded.
• It does not explode when exposed to fire and the materials used are non flammable.

However, the aluminum-ion battery cannot compete with commonly-used Li-ion batteries in terms of energy density, or the amount of power you can store in a battery in relation to the size, according to Gao.

Clemson University

In 2017, researchers at Clemson Nanomaterials Institute built a prototype Al-ion battery that uses a graphene electrode to intercalate tetrachloroaluminate (AlCl
₄^-
). Their new battery technology uses aluminum foil and thin sheets of graphite called few-layer graphene (FLG) as the electrode to store electrical charge from aluminum ions present in the electrolyte. The team constructed batteries with aluminum anodes, pristine or modified FLG cathodes, and an ionic liquid with AlCl3 salt as the electrolyte . They claimed that the battery can operate over 10,000 cycles and the energy density is 200 Wh/kg. Their hope is to make aluminum batteries with higher energy to ultimately displace lithium-ion technology .

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Electrochemistry

Anode half reaction:

Cathode half reaction:

Combining the two half reactions yields the following reaction:

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Lithium-ion comparison

Aluminium-ion batteries are conceptually similar to lithium-ion batteries, but possess an aluminum anode instead of a lithium anode. While the theoretical voltage for aluminium-ion batteries is lower than lithium-ion batteries, 2.65 V and 4 V respectively, the theoretical energy density potential for aluminium-ion batteries is 1060 Wh/kg in comparison to lithium-ion's 406 Wh/kg limit..

Today's lithium ion batteries have high power density (they recharge fast) and high energy density (they stay charged a long time). But lithium is rare, expensive and toxic. It can also develop dendrites, like splinters, that can short-circuit a battery and lead to a fire. Aluminum also transfers energy more efficiently. Inside a battery, the element -- lithium or aluminum -- give up some of their electrons, which flow through external wires to power a device. Because of their atomic structure, lithium ions can only provide one electron at a time; aluminum can give three at a time. Aluminum is also more abundant than lithium, lowering material costs.

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Challenges

Aluminium-ion batteries have a relatively short shelf life. The combination of heat, rate of charge, and cycling can dramatically decrease energy capacity. When metal ion batteries are fully discharged, they can no longer be recharged. Ionic electrolyte materials are expensive. In addition, current breakthroughs are only limited in laboratory settings where a lot more work needs to be done on scaling up the production in commercial settings.

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See also

• Aluminium-air battery
• Comparison of battery types
• List of battery types
• Energy density

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References

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External links

• Stanford unveils aluminum-ion battery on YouTube
• Cathode materials for rechargeable aluminum batteries: current status and progress

Source of the article : Wikipedia