Redox Intercalation and Electrochemical Reactions of Metal-Organic Frameworks and a Mixed Transition Metal Oxide with Applications in Lithium and Magnesium Batteries

Abstract

This dissertation focuses on the redox properties of metal-organic frameworks and a microporous mixed transition metal oxide. The study is divided into two main areas: an intercalation of a redox active molecular guest into host single crystals, and an intercalation of reactive alkali and alkaline earth metals, Li and Mg, by solid state electrochemical reactions into the microporous compounds with applications in lithium and magnesium rechargeable batteries. A metal-organic framework [VIV(O)(bdc)](H2bdc)0.71 (1) was synthesized. This solid was activated to remove the guest molecules, and an empty framework of [VIV(O)(bdc)] (2) was obtained. 2 was used as a host to undergo a vapor-phase redox intercalation of an electroactive organic guest, hydroquinone. In ambient atmosphere, [VIII(OH)(bdc)]•{(O-C6H4-O)(HO-C6H4-OH)}0.76•(H2O)0.48 (3) was formed, whereas under anhydrous conditions, the product was [VIII(O-C6H4-O)(bdc)] (4). Structural deformations as a function of temperature of 2 and 4 were also studied. [VIV(O)(bdc)] (2) was used in solid state electrochemical reaction with lithium. The Li cells with 2 as the cathode material were reversibly cycled with good rate capability and specific capacity. The cell performance and electrochemical profiles at various current conditions were discussed. Structural evolution associated with the electrochemical lithiation was characterized. A metal-organic framework, [NH2(CH3)2][FeIIIFeII(HCOO)6] (FeFOR), was used as cathode in secondary lithium batteries. The electrochemical profiles suggested that FeFOR reacted reversibly with Li. The mechanism involved in the electrochemical reaction was proposed to be intercalation-based and conversion-based with LiHCOO being the matrix involved. A microporous molybdenum-vanadium oxide with large open 1D channels, Mo2.5+yVO9+δ, was used as an intercalation positive electrode material in lithium batteries. The electrochemical profiles showed good specific capacity at high current densities. The cells were found to be reversible even without conducting additives. The structural changes taking place during Li-ion insertion were described, and the chemical deintercalation of lithium was also performed to demonstrate the reversibility. Mo2.5+yVO9+δ was found to reversibly undergo not only lithium insertion in Li-based batteries, but also magnesium intercalation. The compound was used as cathode material, and reversibly cycled with magnesium as the counter electrode with good specific capacity. The effect of varying current densities on the discharge profiles was included.Chemistry, Department o