A Two-dimensional Metal-Organic Framework as Promising Cathode for Advanced Lithium Storage.

Anthraquinone electrode materials are promising candidates for lithium-ion batteries (LIBs) due to the abundance of anthraquinone and the high theoretical capacity, and good reversibility of the anthraquinone electrodes. However, the active anthraquinone materials are soluble in organic electrolytes, resulting in a sharp decay of capacity during the charge and discharge processes. Herein, we report on a two-dimensional calcium anthraquinone 2,3-dicarboxy metal-organic framework (2D CaAQDC MOF) fabricated using a simple hydrothermal method. The 2D CaAQDC MOF not only effectively inhibits the dissolution of active electrode substances into the electrolyte, but also promotes the diffusion of lithium ion into the pores of the MOF. When used as a cathode for the LIBs, the resulting CaAQDC electrode delivers a high specific capacity of ~100 mAh g-1 at a current density of 50 mA g-1 after 200 cycles, demonstrating its good cycle stability. Even at a high current density of 200 mA g-1 , the CaAQDC electrode exhibits a specific capacity of ~60 mAh g-1 . The fabricated 2D coordination polymers effectively restrains the dissolution of anthraquinone into the organic electrolyte and enhances the structural stability, which greatly improves the electrochemical performance of anthraquinone. These research results offer a rational molecular design strategy to address the dissolution of this and other active organic electrode materials.

Advanced 1D Metal-Organic Coordination Polymer for Lithium-Ion Batteries: Designing, Synthesis, and Working Mechanism.

Anthraquinone (AQ) and its derivatives have been attracting more attention as promising electrode materials for lithium storage because of their high specific capacity, structural diversity, and environmental friendliness. The dissolution and poor electrical conductivity of AQ, however, limit its practical application. Here, a novel metal-organic coordination polymer with a one-dimensional (1D) chain ([C14H6O4Cu]n denoted as Cu-DHAQ; DHAQ, 1,5-dihydroxyl anthraquinone) and its composite with graphene (Cu-DHAQ/G; G, graphene) are developed by the introduction of graphene and copper ion into DHAQ. The fabricated polymer with a 1D chain not only well inhibits the dissolution of DHAQ in organic electrolytes but also facilitates lithium-ion insertion/extraction on carbonyl groups and shortens the migration path of lithium ions. Furthermore, the addition of the conductive network of graphene provides fast transfer rates of electrons. As a result, Cu-DHAQ/G delivers a high discharge capacity, long cycle life, and excellent rate capability. The lithium storage mechanism shows lithium ion insertion/extraction on two carbonyl groups of Cu-DHAQ in the range of 1.6-2.0 V and the redox reaction of Cu+/Cu2+ between 2.8 and 3.0 V, and Cu2+ and Cu+ coexist in the Cu-DHAQ/G electrode during the charge/discharge process. This study provides meaningful guidance to develop metal-organic coordination polymer electrodes for high-performance Li-ion batteries.