Title:	Exploring Organic Cocrystals as Electrode Materials for Sustainable Batteries
DNr:	NAISS 2023/5-243
Project Type:	NAISS Medium Compute
Principal Investigator:	Cleber Marchiori <cleber.marchiori@kau.se>
Affiliation:	Karlstads universitet
Duration:	2023-05-26 – 2024-06-01
Classification:	10304 10302 10402
Keywords:

Abstract

Organic electrode materials (OEM) are emerging as a promising alternative to develop greener and more sustainable battery technologies. However, significant improvements are still required in their cycling stability, rate capability, and energy density to become a competitive alternative. This can only be achieved through a fundamental understanding of electrochemistry at the molecular level establishing the structure-properties relationships. One of the hurdles to be overcome is the low electronic conductivity of organic materials, which forces one to use considerable amounts of additives. However, this strategy compromises significantly the electrode performance as the additives do not contribute to the energy storage, being dead-weight in the device. The concept of donor-acceptor cocrystals can contribute to circumventing this problem. By selecting the materials that compose the cocrystal, one can tailor the electronic structure by a selective choice of the donor and acceptor molecules. This strategy enables the generation of different systems from charge-transfer complexes to doped structures with electronic mobility improved by several orders of magnitude in comparison to the pristine materials.[1] So far this strategy is not fully explored for energy storage purposes. The cocrystallization strategy brings complexity to the electronic structure making the understanding of the Me-ions insertion non-trivial. To achieve this knowledge, the modeling of such materials in what concerns the crystal structure determination and assessment of the thermodynamics and kinetics of the Me-ion insertion is needed. To contribute to this end, we developed theoretical methodologies based on evolutionary algorithms (EA) [2,3] and potential-mapping algorithms (MAP) [4] to resolve the crystal structure of the different lithiated (or sodiated) phases. These methods unveil different lithiation pathways, which help exploring the formation of metastable phases and one or multi-electron reactions, which constitute phenomena that are still poorly understood for organic intercalation electrodes. When comparing to experimental outcomes, it is demonstrated that metastable phases with specific molecular features are more likely to be controlling the redox reactions thermodynamics, and consequently the battery voltage. The MAP showed to be a promising methodology to assess the metastable phases during Metal-ion insertion in OEM. The use of the EA as implemented in the USPEX code demands the use of advanced computational resources as it can take up to 5000 DFT calculations to resolve one crystal structure. The goal of this project is i) to screen candidate molecules for cocrystallization by assessing their redox potentials, ii) determine the cocrystal structure and assess their electronic structure and thermodynamics of Li(Na)-ion insertion, iii) assess the electronic mobility in those cocrystals, iv) design novel donor-acceptor pairs for cocrystals to be used as OEM in the next-generation of sustainable batteries. [1] L. Sun et al., Adv. Mater. 2019, 31, 1902328 [2] C. Marchiori et al., J. Phys. Chem. C 2019, 123, 4691−4700 [3] R. P. Carvalho et al., Mater. Adv., 2021,2, 1024-1034 [4] R. P. Carvalho et al., ChemSusChem 2022, e202200354