Development of Aluminum-ion Batteries

Introduction

Fig. 1: A Japan Airlines Boeing 787 lithium-ion battery that caught fire in 2013. (Source: Wikimedia Commons)

Batteries convert stored chemical energy into electrical energy. They consist of two electrodes with different chemical potentials, an anode and cathode, connected by an ionically conductive material known as an electrolyte. Because of the difference in chemical potentials, the electrons spontaneously flow from the more negative anode to the more positive cathode. [1] The transportation of ions through the electrolyte maintains the charge balance, and the electrical energy generated by the movement of the electrons can be accessed through an external circuit. Batteries power the electronics that pervade contemporary society, but their development has stalled due to difficulties in finding and designing more effective electrodes and electrolytes.

Lithium-ion Batteries

Lithium-ion batteries power most portable electronic devices like phones, laptops, and cameras and consist of graphite as the anode and a lithiated transition metal oxide (Li-T^MO₂) as the cathode. During the first charging of the cell, the oxidation and delithiation of the cathode occurs, which reversibly intercalates lithium with the graphitic anode to form LiC₆ as the final anode material. [2] The massive production of lithium ion batteries is unsustainable because the most common transition metal used in the cathode is cobalt, a depletable element that must be mined. Furthermore, there are significant safety risks involved with lithium ion batteries due to the presence of both combustible materials and an oxidizing agent, leading to the possibility of uncontrolled reactions resulting in explosions and fires. [2]

Despite their risks, lithium-ion batteries are currently the most effective commercial batteries available for consumer electronics due to a number of factors. They possess a high mass energy density of 180 Wh/kg that is significantly higher than older batteries such as rechargeable nickel cadmium batteries (80 Wh/kg) or nickel metal hydride batteries (60 Wh/kg). [3] Furthermore, lithium ion batteries produce an average of 3.8 V, which is five times higher than the older lead-acid batteries and three times higher than the rechargeable nickel cadmium or nickel metal hydride batteries. [1,3] Finally, the lithium ion batteries lack the memory effect observed in rechargeable nickel cadmium batteries where the apparent discharge capacity is lowered when it is incompletely discharged and then recharged. [3]

The lithium-ion battery redox reactions are: [4]

Aluminum-ion Batteries

Aluminum is a promising anode material in the development of aluminum-ion batteries that may be an alternative to lithium-ion batteries. Aluminum has a low atomic weight (26.98 g/mol) that is still higher than lithium (6.941 g/mol), but aluminum's trivalence compared to lithium's single valence electron allows aluminum-ion batteries to have a higher energy density potential threshold. [3] Aluminum (2.98 Ah/g) has a lower mass electrochemical equivalent than lithium (3.86 Ah/g), but the volume electrochemical equivalent of aluminum (8.04 Ah/cm³) is nearly a factor of four greater than lithium (2.06 Ah/cm³). [3] However, the development of aluminum ion batteries over the past 30 years has stalled due to a number of issues: cathode material disintegration, low discharge voltage of 0.55 V, low cycle life of less than 100 cycles, and rapid discharge capacity decay of 26-85% over only 100 cycles. [5]

In 2014, Lin et al. developed an ultrafast rechargeable aluminum-ion battery that consisted of an aluminum metal anode and a three dimensional graphitic foam cathode. [5] This aluminum-ion battery operates through the dissolution of aluminum at the anode and the subsequent intercalation of chloroaluminate anions in the graphite cathode. Unlike previous iterations of aluminum ion batteries, their new battery can undergo up to 7500 charge cycles without discharge capacity decay even at ultrahigh current densities. [5] The three dimensional graphitic foam cathode permitted ultrafast chloroaluminate anion diffusion and intercalation, resulting in charging times of approximately one minute with current density of nearly 4000 mA/g. [5] Although the battery is only 2 V with an energy density of 40 Wh/kg, which is comparable to lead acid and Ni-MH batteries, its stability and ultrafast charging capabilities are unmatched by lithium-ion batteries. [5]

The aluminum-ion battery redox reactions are: [5]

Conclusion

Lithium-ion batteries are omnipresent in modern consumer electronics due to their high energy density and voltage compared to older lead-acid and nickel-cadmium batteries and lack of memory effect. However, further improvements to battery technology must be developed in order to create better energy storage; one possible avenue is through aluminum-ion batteries. Despite stalled development over the past 30 years, Lin et. al have successfully developed a rechargeable aluminum-ion battery with ultrafast recharge times and high charge cycle lifetime. Despite lower voltage and energy density compared to lithium-ion batteries, aluminum-ion batteries are a promising alternative.

© Jeremy Uang. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.

References

[1] M. Armand and J.M. Tarascon, "Building Better Batteries," Nature 451, 652 (2008).

[2] V. Etacheri et al., "Challenges in the Development of Advanced Li-Ion Batteries: A Review," Energy Environ. Sci. 4, 3243 (2011).

[3] "Overview of Lithium Ion Batteries," Panasonic, January 2007.

[4] "Lithium Ion Technical Handbook," Gold Peak Industries, December 2000.

[5] M.-C. Lin et al., "An Ultrafast Rechargeable Aluminium-Ion Battery," Nature 520, 324 (2014).