Start Date: August 2008
Jean-Marie Tarascon, Michel Armand, G. Demailly, Franck Dolhem, Philippe Poizot, University of Picardie Jules Verne, France
While inorganic lithium-ion battery approaches have achieved reasonable energy density, radical new approaches are required to enable batteries with the high energy density, low cost, and the environmental compatibility required to penetrate the transportation sector. This effort seeks to develop a new class of organic battery electrodes with outstanding properties in each of these three respects.
Battery performance in electric vehicles has improved primarily from increased penetration and development of lithium-ion technology within the field of electrochemical energy storage. Nevertheless, today’s Li-ion electro-active components, such as LiCoO2 and LiMn2O4, are not produced through renewable resources but from ores that can be limited or hazardous. The raw materials extraction and electrode processing techniques require large amounts of energy. Additionally, the rechargeable batteries must be recycled from regular solid wastes. A thermal recovery process reclaims the metals and prepares them for use in new products. Supplementary energy consumption and CO2 gas emissions are associated with this process, which would not be negligible for a foreseeable annual production of 10 billion cells. Thus high performing, battery electrodes composed of organic materials would avoid many of the energy costs associated with processing and recovering inorganic cathode materials. Additionally preliminary data on oxocarbon molecules shows the feasibility of reacting up to four electrons per molecule which could have a significant impact on battery capacity.
There are two main components to this program; 1) Creating a new bank of scientific knowledge in designing and synthesizing organic molecules and polymers electrochemically active towards Li, and 2) Practical integration of these materials into laboratory test cells for increased performance and evaluation. To accomplish these objectives, the research tasks are set up around innovative, rapid, and efficient synthesis processes using cheap and clean methods.
Task 1: Synthesis of new electrochemically active organic molecules
Preliminary data on a new electrochemical active organic molecule, Li2C6O6, shows that it can react with four electrons per molecule (see Figure 1). The electroactivity of carbonyl groups to be reduced or oxidized makes Li2C6O6 organic salts attractive for use as electrode materials. Other concepts will also be investigated by searching for alternative electroactive functions to evaluate the feasibility of an attractive Li-ion cell with both positive and negative organic electrodes. A wide variety of single and multiple ring molecules, which could contain electrochemically active C=O functions with the possible addition or substitution of various heteroatoms (N, S, etc.) will also be considered. The objective will be to further increase the theoretical capacities, tune electron-transfer (e.g., electrode power rate) and ensure stability of the organic molecules in Li-based electrolytes (e.g., increase the electrode lifetime). This activity requires a survey of various chemical functions with an ultimate goal of achieving electrodes operating around 0.5V.
Task 2: Theoretical Analysis
Theoretical guidance will aid the search for new suitable organic redox molecules by providing a systematic approach to calculating redox potentials. Existing computer modeling methods using Density Function Theory (DFT) procedures have proven to be successful in describing and calculating many properties of organic molecules, including their stability and redox features. Such computational modeling will allow a molecular-level understanding of features, such as the structural relationships associated with the geometrical degrees of freedom that dictate the properties of redox active species.
Task 3: Learning from bio-inspired materials
Besides chemical intuition and theoretical guidance from the first two tasks, bio-inspired materials will be considered to take advantage of the fact that nature has been optimizing organic molecular structures for millions of years. For example cell membranes establish a steady potential responsible for controlling the fluxes of charged species (e.g.; H+, Na+ and Cl-). They are made from organic elements (C, H, N, O and P) with other trace elements in a cascade of redox reactions, which are fast (electro)chemical reactions that make energy available for various biological processes. The results of analysis of biological systems will be fed back to Task 2.
Task 4: Electrochemical characterization: Cell Performance
The newly synthesized organic materials (both monomers and polymers) will be characterized for their electrochemical reactivity towards lithium. The electrochemical characterization will use various cell configurations and Li-based electrolytes (gel, liquid or polymer) in order to test whether the organic molecule is effectively electroactive and chemically compatible with the classical Li-based battery materials. If the tests are positive, subsequent experiments will be carried out to identify the electrochemical properties of the organic material and to gain a comprehensive understanding of the electrochemical mechanisms. This method enables a step-wise evolution towards creating other molecules with enhanced performance.