Lithium-ion batteries introduced in the early 1990s are the energy storage backbone of the present generations of portable power products. While the characteristics of the LiCoO2/Graphite electrochemical system are acceptable for the portable electronics market, significant improvements in the safety and lifetime of lithium-ion must be achieved in order for large-scale lithium-ion batteries to become a viable solution for vehicle propulsion.
At this time, the LiFePO4/Graphite electrochemical couple offers the most promise, as it provides beneficial power, safety and cycle life over the most mature cobalt-based systems. Although LiFePO4 has many advantages, it suffers from low potential (3.45V vs. Li+/Li), and low material density (3.6 g cm−3). Batteries based on this cathode have relatively low energy-density - approximately 50% that of the cobalt-based system. New battery systems that have the positive attributes of the LiCoO2 and the LiFePO4 systems, while overcoming their respective deficits, are in great demand.
High voltage spinel oxides are promising candidates. This type of cathode chemistry has been studied for a number of years. However, the high voltage has the following detrimental effects, which have thwarted its implementation in commercial batteries:
(1) Oxidation of the electrolyte solvent - results in the damage of the anode and cathode SEI structures, mechanical blockage of electrode active sites and parasitic reactions.
(2) PPM concentrations of HF due to residual moisture in the electrolyte - results in partial dissolution of metal ions in the cathode and damage of the anode and cathode SEI structures.
The resultant LMNS cathode may be coupled with a range of anodes. ETV is working on two cell chemistries: LMNS/Graphite to form a 4.7V cell; and LMNS/LiTiO to form a 3.2V cell.
