Long-Life, High-Rate Lithium-Organic Batteries Based on Naphthoquinone Derivatives

We report the facile synthesis of new naphthoquinone (NQ) derivatives for use in lithium-organic batteries to improve performance. The rational design of these NQ derivatives is based on theoretical calculations. Our lithium-organic batteries demonstrate remarkable chargedischarge properties, for example, a high discharge capacity of 250 mAh g(-1) (363 mAh cm(-3)), discharge potential plateaus in the range of 2.3-2.5 V, and 99% capacity retention after 500 cycles at 0.2C. In particular, the batteries had excellent rate performance up to 50C with reversible redox behavior, unlike most other organic cathode materials. The key to success was a simple molecular substitution, addition of amino groups at the 2- and 3- positions of the NQ ring, yielding 2,3-diamino-1,4-naphthoquinone (DANQ). DANQ has an exceptionally low band gap of 2.7 eV and greater than 20-fold enhancement in the lithium diffusion rate compared to unmodified NQ. The fundamental shortcoming of the organic molecules, i.e., their solubility in the electrolyte, was resolved by covalent linking of the amino groups to the surfaces of the cathode framework. The cyclization of amino groups in DANQ yielded 1H-naphtho[2,3-d]imidazole-4,9-dione (IMNQ), enabled us to achieve a 0.15 V enhancement in the redox potential owing to the delocalized electron distribution in the heteroaromatic ring. Our work suggests that NQ derivatives with modulated charge/ion transport properties are a viable alternative to the more widely studied lithium metal oxides.