Abstract:
AIn the past 25 years lithium ion batteries have changed the way we communicate with cell phones and in the next 25 years electric vehicles are expected to change our everyday mobility with the electric car. If lithium will enable renewable energy storage lithium extraction should be sustainable. In this presentation we will focus on the electrochemical sustainable extraction of lithium chloride form natural brine.
The spontaneous electrochemical extraction of lithium chloride from natural brine of high altitude salt flats in northwest Argentina and recovery in a dilute electrolyte has been demonstrated in two experiments.
- A highly selective LiMn2O4 insertion cathode and polypyrrole anion selective anode (salt capturing).
- An LiMn2O4 anode and lithium deficient Li1-xMn2O4 cathode separated by anion selective membrane (selective ion exchange).
The entropy driven transfer of LiCl from concentrated brine to a dilute recovery electrolyte has been experimentally studied by ion pumping and the LiCl activity measured in natural brine.
An electrochemical reactor for the extraction of lithium from natural brine has been designed. It comprises two 3D porous packed bed electrodes and (i) a porous separator filled with electrolyte or (2) an anion selective membrane. The electrodes are filled with conducting petroleum coke particles covered respectively with LiMn2O4 selective to chloride ions and (i) polypyrrole selective to anions or (ii) Li+ deficient Li1-xMn2O4. The reactor operates (i) in two steps: First the porous electrode and separator are filled with natural brine to extract Li+ and Cl- by intercalation and adsorption, respectively. Then, after rinsing with water the reactor is filled with a dilute LiCl recovery solution and LiCl is recovered by reversing the electrical current. While the first step is spontaneous, the second one requires energy from solar panels to drive the electrolysis. Alternatively, in (ii) a continuous process of lithium extraction at the Li1-xMn2O4 cathode and lithium release at the LiMn2O4 separated by the anion selective membrane takes place. After completion, and rising with water the brine and recovery solutions are exchanged and the lithiated electrode becomes anode while the delithiated electrode is the cathode to continue the extraction.
The evolution of lithium chloride concentration in the recovery electrolyte has been followed by a lithium selective electrode, while the reactor total voltage and each electrode potential with respect to a Ag/AgCl; 3 M KCl reference electrode were continuously monitored by high impedance potential followers.
The effect of lithium chloride concentration in natural brine, applied current density and reactor geometry have been studied in scalling up the lithium chloride extracting reactor, while the extraction efficiency and charge capacity were evaluated.
A mathematical model for the reactor comprising the Nernst-Planck equation and the battery intercalation model has been developed. The model was solved using the finite element method under the COMSOL multiphysics environment in order to obtain the electrostatic potential and the ion currents and concentrations across the systems. Unlike the asymmetric LiMn2O4 /activated carbon supercapacitor, in the lithium extracting reactor the total LiCl concentration decreases in the extraction step and increases in the recovery step. A good agreement between the experimental and simulated potential difference vs. time at constant current validates the model of the reactor.
References
- V.C.E. Romero, M. Tagliazucchi, V. Flexer and E.J. Calvo, J. Electrochem. Soc., 165. (10), A2294-A2302, 2018).
- 2. F. Marchini, F.J. Williams, E.J. Calvo, J. Electrochem. Soc., 165,(14), A3292-A3298, (2018).
Hosted by Dino Tonti, Solid State Chemistry Group
