A modified Doyle-Fuller-Newman model for the physical simulation of dual-ion batteries

Lithium-ion batteries are the currently dominant electrochemical energy storage technology, but the forecasted battery demand and the uncertainty on the supply of raw materials for their production call for the search of alternatives and complementary solutions.&nbsp“;“In the variety of proposals along this direction, dual-ion batteries are characterized by the involvement of both the electrolyte’s cations and anions in the redox reactions allowing the storage and the release of energy.&nbsp“;“The positive electrode (cathode) of a dual-ion battery uptakes anions during charge while the negative electrode (anode) stores the cations, and vice versa during the discharge. The electrolyte plays then a fundamental role, becoming an active component in the cell as the only source of both the anions and cations for the proper functioning of the dual-ion battery.

In a moment when the technology is coming out of laboratories and the first commercialization attempts are made, a physics-based model that can describe and simulate the dual-ion battery behavior is necessary to have a deeper understanding of this novel system and to help the design of practical batteries. The model proposed here is based on the standard pseudo-2D Doyle-Fuller-Newman model developed for lithium-ion batteries, which is then modified to account for the radically different redox reaction that occurs at the cathode and the anode of the dual-ion battery.

This modified model is able to simulate the variation of salt concentration in the electrolyte during charge and discharge of the dual-ion battery, including the concentration gradients that are formed along the battery length, as well as experimental data of dual-ion batteries up to moderate current rates. The parameters of the model were adjusted to simulate a lab-scale coin cell with poly(2,2,6,6-tetramethyl- piperidenyloxyl-4-yl methacrylate) (PTMA) as cathode, a thick glass fiber separator, a lithium metal anode, and 1M LiPF₆ in EC:DEC 1:1 as electrolyte.

The proposed model can reproduce the mechanistic behavior of dual-ion batteries, and it can be adapted easily to other anion-hosting materials as graphite and other p-type organic electrode materials. Such a tool can be used to support the design of dual-ion batteries, and help in achieving the delicate balance between electrolyte quantity, salt concentration and amount of cathode active material that this type of battery requires.