Advanced Materials Characterization and Processing of Gen II Materials Based Lithium Ion Battery

Abstract

The purpose of this Cooperative Research and Development Agreement (CRADA) between Oak Ridge National Laboratory (ORNL) and Dow Kokam, LLC was to investigate the microstructure and materials processing on long-term performance of Dow Kokam’s Gen II anodes and cathodes for lithium ion batteries. The findings were implemented into Dow Kokam’s new U.S. based production line, which has a capacity of 600 MWh/yr in total battery output. A principal need for automotive energy storage applications is the ability of the battery pack to satisfy a 10-15 year calendar life in addition to improved safety, high charge-discharge rate capability, high energy density, and high power density. Current cathode chemistries such as those based on LiNixMnyCo1-x-yO2 (NMC) metal oxides are limited to approximately 1500 cycles (or 5-7 year equivalent automotive calendar life). Dow Kokam Gen II technology has shown a 2× cycle life over conventional NMC based materials, while also improving by similar metrics the charge-discharge limits. The impact of this improvement is significant in terms of launching pure electric vehicles and plug-in hybrid electric vehicles with lifetimes comparable to those of the traditional IC engine. However, in order to scale the technology and achieve substantial market penetration, the electrode structure and processing based on the new Gen II material in comparison to that of the traditional NMC needs to be better understood. As the microstructure and chemistry of the new electrode type have been elucidated by this project, scaling and mass production has become the focus. Electrode dispersion formulations, coating parameters, and methods of energy savings were subsequently investigated. The capabilities of ORNL were implemented to assist in these efforts in terms of quality control, materials characterization, and electrochemical testing. Dow Kokam provided raw materials and electrodes, as well as background IP and technical expertise. The current state-of-the-art for NMC cathode durability is 1500 cycles to 100% depth of discharge (DOD) at 1C/-1C charge/discharge rates. This cycle lifetime only satisfies about half of the lifetime requirement for plug-in hybrid electric vehicles (PHEVs) and electric vehicles (EVs). Dow Kokam’s Gen II modified NMC cathode increases cycle life by 2×, depending on the charge/discharge rates, and will be capable of meeting the full 15 year lifetime once scaled to mass production. This improvement will allow PHEV and EV manufacturers to use only one battery pack per vehicle and will result in approximately 50% reduction in energy required to produce battery packs on a per vehicle basis. This further translates into a significantly reduced cost of ownership for PHEVs and EVs based on lithium ion battery technology. However, the chemical and microstructural changes of the modified Gen II anodes and cathodes during long-term operation are not well understood, as well as the effects of the starting material modifications to anode and cathode active material performance (i.e., nanoscale coatings deposited on the surfaces of graphite and NMC). Effects of processing variables related to mixing and coating of the electrode materials on cell performance and durability were also studied. To supplement these materials characterization and processing variable experiments, thorough electrochemical testing was completed by Dow Kokam.