National Aeronautics and Space Administration

Glenn Research Center

Developing Techniques for Evaluating Separator Materials for Lithium-Ion Batteries

By: MaryBeth Lewton

Principle Investigator: Dr. Richard Baldwin

ETDP Mission Objectives and Overview

Proper electrical energy storage and power generation technologies are needed as the human presence in space is renewed through future NASA Exploration Missions and the Constellation Program. These directives include the Orion (Crew Exploration Vehicle, CEV), Ares I (Crew Launch Vehicle, CLV), and subsequently Ares V (Cargo Launch Vehicle, CaLV), Altair (Lunar Lander), Extravehicular Activities (EVA) and Lunar Surface Systems such as surface suits, extraterrestrial rovers and habitats. The Exploration Technology Development Program (ETDP) concentrates on future performance and safety requirements necessary for the energy storage technologies that will enhance and enable these future aerospace missions. Advanced lithium-ion battery technology development is being pursued to address existing technology gaps between state-of-the-art capabilities and critical future mission requirements. From a scientific standpoint, ETDP seeks to improve the performance of lithium-based cells for integration into battery modules to meet the energy storage requirements for Constellation customers. Lithium-ion batteries have not yet been fully approved for use as a main energy storage element for manned, human-rated aerospace missions due to general safety and electrochemical concerns.

The lithium-ion battery separator plays an important role in the electrochemical attributes as well as the overall safety of the cell. The separator is typically a non-electrically-conducting, porous, electrolyte-filled media sandwiched between and in contact with the two active electrodes in a non-aqueous environment. The separator does not allow direct contact between the anode and cathode, which prevents a short circuit, but still allows the flow of ionic species, and it functions as an internal safety device. The structure and physiochemical properties of the separator influence overall cell performance through stability, internal cell resistance, cycle life and more, even though the separator does not “actively” partake in battery operation (Baldwin). For the duration of the summer I will be developing in-house test profiles for advanced lithium-ion cell-level components and full lithium-ion cells, focusing on battery separator component materials. The profiles will examine standard performance and abuse conditions to determine the limitations of lithium-ion battery separators. Profiles include baseline material composition/morphology, thermal performance, electrical performance and mechanical performance. A formal portfolio of test profiles will be drafted after tests and procedures are fully developed and baseline materials are characterized. From this portfolio of standard procedures, optimal components for the evolving lithium-ion cell development project will be selected.
My Role as an ETDP Research Associate

The majority of the work in prepping for the new ETDP tasks within the Electrochemistry branch is the design and the implementation of characterization and screening procedures. These procedures or profiles will define and validate appropriate cell components which will be optimized for use in meeting future NASA customer mission needs. It is the goal of my PI, Dr. Richard Baldwin, and myself that I play an important role in developing a specific profile or parts of various profiles to ultimately assess the best material for a separator that works ideally in lithium-ion batteries. I will also be tasked with analyzing data to see how different properties affect one another. For example, separator resistivity is dependent upon thickness, permeability, porosity, etc.

Specific goals I have for myself this summer include:

1. Acquire knowledge and understanding of practical electrochemistry, specifically, lithium-ion cells

2. Study how components are integrated in a battery to be evaluated and developed to obtain optimal desired performance

3. Gain exposure to various thermal, mechanical and electrochemical laboratory methods and how they are used diagnostically

4. Deliver appropriate documentation pertaining to the personally developed laboratory procedures in a formal template form to be used by RPC staff members

5. Provide significant impact or contribution to the ETDP project schedule and milestones

NASA’s current directive is to go back to space using manned missions to the Moon and to Mars, but before that can be done alternative power sources and energy storage such as lithium-ion batteries need to be perfected. This is exactly what the ETDP project is going to do. It is an honor to be working with my PI, Dr. Baldwin, and the Glenn Electrochemistry branch staff. I hope that in addition to learning a great deal, I can apply my past experiences in chemistry to help the NASA researchers make progress towards the big objective. To say the least I am very excited about the opportunity I have this summer to be a part of this technology for space applications.