High-Potential Reversible Li Deintercalation in a Substituted Tetrahydroxy-p-benzoquinone Dilithium Salt: An Experimental and Theoretical Study

Efficient organic Li-ion batteries require air-stable lithiated organic structures that can reversibly deintercalate Li at sufficiently high potentials. To date, most of the cathode materials reported in the literature are typically synthesized in their fully oxidized form, which restricts the operating potential of such materials and requires use of an anode material in its lithiated state. Reduced forms of quinonic structures could represent examples of lithiated organic-based cathodes that can deintercalate Li+ at potentials higher than 3 V thanks to substituent effects. Having previously recognized the unique electrochemical properties of the C6O6-type ring, we have now designed and then elaborated, through a simple three-step method, lithiated 3,6-dihydroxy-2,5-dimethoxy-p-benzoquinone, a new redox amphoteric system derived from the tetralithium salt of tetrahydroxy-p-benzoquinone. Electrochemical investigations revealed that such an air-stable salt can reversibly deintercalate one Li+ ion on charging with a practical capacity of about 100 mAh?g-1 at about 3 V, albeit with a polarization effect. Better capacity retention was obtained by simply adding an adsorbing additive. A tetrahydrated form of the studied salt was also characterized by XRD and first-principles calculations. Various levels of theory were probed, including DFT with classical functionals (LDA, GGA, PBEsol, revPBE) and models for dispersion corrections to DFT. One of the modified dispersion-corrected DFT schemes, related to a rescaling of both van der Waals radii and s6 parameter, provides significant improvements to the description of this kind of crystal over other treatments. We then applied this optimized approach to the screening of hypothetical frameworks for the delithiated phases and to search for the anhydrous structure.