BATT Research Highlight: Electrode Fabrication and Materials Benchmarking

December 4, 2014

The Batteries for Advanced Transportation Technologies (BATT) Program is the premier fundamental research program in the U.S. for developing high-performance, rechargeable batteries for electric vehicles (EVs) and hybrid-electric vehicles (HEVs). BATT is supported by the U.S. Department of Energy Office of Vehicle Technologies. BATT investigators in top research universities and institutions work on the following task areas: Anodes, Cathodes, Liquid Electrolytes, Solid Electrolytes, Cell Analysis, Diagnostics, Modeling, lithium-air batteries and sodium-ion batteries. BATT funds research at institutions throughout the U.S. The BATT program publishes a quarterly report, from which the following research highlight is adapted.

Electrode Fabrication and Materials Benchmarking

Although a successful energy storage technology, rechargeable lithium-ion batteries face some critical challenges before they can reach their full potential for transportation applications. The Environmental Energy Technologies Division's (EETD's) Vince Battaglia heads one of the groups that address these challenges for the U.S. Department of Energy's Batteries for Advanced Transportation Technologies (BATT) program. Battaglia's group conducts cell analysis work at Lawrence Berkeley National Laboratory, specializing in battery design and electrode development. The group's primary focus is electrode fabrication and identifying sources of electrode failure.

A current project focuses on identifying and providing quality materials, electrodes, and cell performance data that can be used as a benchmark for the rest of the BATT program. The goal is to advance lithium-ion (Li-ion) chemistry through the analysis of state-of-the-art materials. One focus of the project is to compare silicon (Si) anodes provided by an EETD group headed by Gao Liu with matching cathodes of lithium iron phosphate (LiFePO4) developed for this project, to benchmark the effect of side reactions at the anode on cell capacity fade. Because silicon's side reactions are a major material flaw, it is critical to quantify the effect of these reactions in a full cell. Another focus involves benchmarking (i.e., measuring reversible capacity, rate performance, and cycle efficiency) the latest nickel manganese oxide (NMO) material from NEI Corporation and a nickel cobalt manganese (NCM) material for comparative testing. The project also is a hub for testing new materials developed in the BATT program, and this project is key to demonstrating progress within the program against industry standards.

Recent Progress

The NCM baseline material that was developed into an electrode experienced some capacity fade under the present testing conditions. Researchers are continuing to test the material until a half-cell can be constructed with negligible capacity- and energy-fade.

The team fabricated two laminates of NCM with different levels of inactive material. One electrode consisted of the standard level of carbon and binder and the other with half of these inactive components. Electrodes of each composition were constructed and tested, and they both displayed the same rate capability, indicating that the lower level of inactive materials was sufficient for discharging and charging the cells at rates equivalent to the standard inactive material loadings. The test also showed that the top charge rate for this cathode material at loadings above 1 mAh/cm2 is C/2 and that its top discharge rate is 2C.

The electrodes were also evaluated for cycling ability. For a cell of 1.4 mAh/cm2, the capacity demonstrated a slight cycling decline to about 60 cycles, where it declined precipitously with erratic coulombic efficiency. Also during the first 60 cycles, the efficiency steadily dropped. The next step will be to test electrodes of loadings below 1 mAh/cm2 with a new electrolyte in Li half-cells to cutoff voltages below 4.2 V until an electrode composition, loading, and cutoff voltage can be identified that leads to negligible capacity fade over more than 100 cycles.

Author

Mark WIlson