Richard S. Baldwin

Glenn Research Center, Cleveland, Ohio

A Review of State-of-the-Art Separator Materials

for Advanced Lithium-Based Batteries for

Future Aerospace Missions

NASA/TM—2009-215590

March 2009
NASA STI Program . . . in Profi le

Since its founding, NASA has been dedicated to the 

advancement of aeronautics and space science. The 

NASA Scientifi c and Technical Information (STI) 

program plays a key part in helping NASA maintain 

this important role.

The NASA STI Program operates under the auspices 

of the Agency Chief Information Offi cer. It collects, 

organizes, provides for archiving, and disseminates 

NASA’s STI. The NASA STI program provides access 

to the NASA Aeronautics and Space Database and 

its public interface, the NASA Technical Reports 

Server, thus providing one of the largest collections 

of aeronautical and space science STI in the world. 

Results are published in both non-NASA channels 

and by NASA in the NASA STI Report Series, which 

includes the following report types:

• TECHNICAL PUBLICATION. Reports of 

completed research or a major signifi cant phase 

of research that present the results of NASA 

programs and include extensive data or theoretical 

analysis. Includes compilations of signifi cant 

scientifi c and technical data and information 

deemed to be of continuing reference value. 

NASA counterpart of peer-reviewed formal 

professional papers but has less stringent 

limitations on manuscript length and extent of 

graphic presentations.

• TECHNICAL MEMORANDUM. Scientifi c 

and technical fi ndings that are preliminary or 

of specialized interest, e.g., quick release 

reports, working papers, and bibliographies that 

contain minimal annotation. Does not contain 

extensive analysis.

• CONTRACTOR REPORT. Scientifi c and 

technical fi ndings by NASA-sponsored 

contractors and grantees.

• CONFERENCE PUBLICATION. Collected 

papers from scientifi c and technical 

conferences, symposia, seminars, or other 

meetings sponsored or cosponsored by NASA.

• SPECIAL PUBLICATION. Scientifi c, 

technical, or historical information from 

NASA programs, projects, and missions, often 

concerned with subjects having substantial 

public interest.

• TECHNICAL TRANSLATION. Englishlanguage translations of foreign scientifi c and 

technical material pertinent to NASA’s mission.

Specialized services also include creating custom 

thesauri, building customized databases, organizing 

and publishing research results.

For more information about the NASA STI 

program, see the following:

• Access the NASA STI program home page at 

http://www.sti.nasa.gov

• E-mail your question via the Internet to help@

sti.nasa.gov

• Fax your question to the NASA STI Help Desk 

at 301–621–0134

• Telephone the NASA STI Help Desk at

 301–621–0390

• Write to:

 NASA Center for AeroSpace Information (CASI)

 7115 Standard Drive

 Hanover, MD 21076–1320
Richard S. Baldwin

Glenn Research Center, Cleveland, Ohio

A Review of State-of-the-Art Separator Materials

for Advanced Lithium-Based Batteries for

Future Aerospace Missions

NASA/TM—2009-215590

March 2009

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135
Available from

NASA Center for Aerospace Information

7115 Standard Drive

Hanover, MD 21076–1320

National Technical Information Service

5285 Port Royal Road

Springfi eld, VA 22161

Available electronically at http://gltrs.grc.nasa.gov

Trade names and trademarks are used in this report for identifi cation 

only. Their usage does not constitute an offi cial endorsement, 

either expressed or implied, by the National Aeronautics and 

Space Administration.

Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2009-215590 1

A Review of State-of-the-Art Separator Materials 

for Advanced Lithium-Based Batteries for 

Future Aerospace Missions 

Richard S. Baldwin 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Abstract 

As NASA embarks on a renewed human presence in space, safe, human-rated, electrical 

energy storage and power generation technologies, which will be capable of demonstrating 

reliable performance in a variety of unique mission environments, will be required. To address 

the future performance and safety requirements for the energy storage technologies that will 

enhance and enable future NASA Constellation Program elements and other future aerospace 

missions, advanced rechargeable, lithium-ion battery technology development is being pursued 

with an emphasis on addressing performance technology gaps between state-of-the-art 

capabilities and critical future mission requirements. The material attributes and related 

performance of a lithium-ion cell’s internal separator component are critical for achieving overall 

optimal performance, safety and reliability. This review provides an overview of the general 

types, material properties and the performance and safety characteristics of current separator 

materials employed in lithium-ion batteries, such as those materials that are being assessed 

and developed for future aerospace missions. 

Introduction 

As NASA embarks on a renewed human presence in space as part of the “U.S. Space 

Exploration Policy”, we will require safe, human-rated, electrical energy storage and power 

generation technologies that will be able to demonstrate reliable performance in a variety of 

unique mission environments. NASA Constellation Program elements include the Crew 

Exploration Vehicle (Orion), crew and cargo launch vehicles (Ares I and Ares V, respectively), 

the Lunar Surface Access Module (Altair), extravehicular activity (EVA) surface suits and 

extraterrestrial rovers and habitats (Ref. 1). To address the future performance and safety 

requirements for the energy storage technologies that will enhance and enable these and other 

future aerospace missions, advanced rechargeable, lithium-ion battery technology development 

is being pursued with an emphasis on addressing performance technology gaps between stateof-the-art capabilities and critical future mission requirements. 

Lithium-ion batteries have not been fully space-qualified for use as a main energy storage 

element for manned, human-rated aerospace missions. Currently, both cell and cell component 

development efforts are focused on improving the overall safety, as well as the electrochemical 

attributes, of such battery systems in order to optimize such for manned space applications. A 

key cell component of a lithium-ion battery which significantly impacts both of these 

performance features is the battery separator. 

The function and reliability of the separator is critical for the optimal performance and safety 

of a lithium-ion cell. In nonaqueous, liquid-electrolyte cells that exemplify a lithium-ion cell 

chemistry, the separator is typically a nonelectrically-conducting porous electrolyte-filled media 

or membrane, which is sandwiched between and in contact with the two active, solid electrodes. 

Its roles are to prevent direct electronic contact between the two electrodes that would result in 
NASA/TM—2009-215590 2

a short-circuit, to allow the flow of ionic species within the cell and certain separator materials 

can function as an internal cell safety device. The separator affects the internal cell resistance, 

stability, cycle-life, operating temperature range and cell kinetic parameters such as discharge 

and charge rates. By its ability to regulate the electrolyte distribution between the active 

electrodes, as a result of its morphology and permeability characteristics, the separator limits 

ionic diffusion and recombination rates, and, thus, impacts the cell capacity, power and 

available energy. With respect to the inherent safety of a lithium-ion cell, the separator may 

afford passive protection and tolerance to cell abuse conditions that may arise, and it can 

enhance the overall cell safety by providing another level of internal redundancy. 

Battery Separators 

The structural and physiochemical properties of the separator material strongly influence the 

overall cell performance, although the separator does not “actively” participate in the battery 

operation. The mere presence of the separator component within a cell adversely affects the 

overall cell performance, as it adds electrical resistance and occupies limited space. For 

electrochemical cell chemistries in which the liquid electrolyte solution serves only as an ionic 

conductor, the separator should be as thin as possible and porous, but yet possesses the 

required physical strength to maintain the mechanical and electrical separation between the 

solid electrodes. These characteristics are essential in order to achieve high energy and power 

densities for applications requiring such performance attributes. Thus, the practical design of a 

separator is an art, as there is a compromise between the degree of porosity of the material and 

its mechanical strength. For battery safety, a state-of-the-art battery separator for utilization with 

lithium-based cell chemistries should have the inherent ability to shut the battery down if 

overheating occurs. Several comprehensive reviews of battery separators in general (Refs. 2 

and 3) have appeared in the literature, as well as some with a primary emphasis on lithiumbased cell technologies (Refs. 4 and 5). 

Primary Separator Properties and Characteristics 

for Rechargeable Lithium-Based Cells 

A minimal separator thickness is required for high energy and high power applications; 

however, this can have a negative impact on mechanical strength and on safety. Presently, 

commercial separators for lithium-ion cells are nominally <30 μm in thickness. 

For longevity, the cell separator must have a high degree of chemical stability to resist 

degradation and/or loss of mechanical strength due to reactivity with or dissolution by the 

electrolyte. Also, it must have electrochemical stability to the highly oxidative or reductive 

environments posed by the active electrode cell components. Coupled with analyses of the 

separator material, cycle life and calendar life testing data can yield qualitative and quantitative 

measures of the material stability; both conditions can degrade the separator material 

properties, and such can be reflected by an observed degradation in cell performance. 

Optimal separator porosity, which is the ratio of void volume to apparent geometric volume, 

is critical for optimal performance and safety, as sufficient liquid electrolyte must be absorbed 

and retained within the pores in order to maintain a high level of ionic conductivity. Porosity can 

be measured using liquid or gas absorption methods. Typical commercial separators for lithiumion cells have a porosity of ~40 percent. A uniform pore size distribution is desirable within the 

total area of a separator film in order to achieve a uniform current distribution within a cell. In 

addition, small, submicron pore size dimensions have proven effective in reducing the possibility 

of an internal short circuit by preventing the penetration of larger active electrode material 

particles or by dendritic lithium metal. Pore structure and distribution can be characterized by 

modern analytical porosimetry techniques (Ref. 6) and/or scanning electron microscopy (SEM). 
NASA/TM—2009-215590 3

The separator should also possess characteristics for a high degree of wettability in the 

electrolyte. 

A critical functional separator property is its permeability, as the presence of a solid 

separator material significantly increases the effective resistance of the ion-conducting 

electrolyte. Permeability is a measure of the ability of a porous material to transmit a fluid, i.e., 

the liquid electrolyte solution in a lithium-ion cell. The permeability is related to the material’s 

porosity and tortuosity, (Ref. 7) which is the ratio of mean effective capillary length to the 

separator thickness. Although an air permeability method could be used to characterize the 

separator permeability, electrical resistance (Ref. 3) or modern ac impedance measurements 

are more comprehensive for the separator in an actual electrochemical cell environment. Data 

from such measurements are useful performance indicators, as they describe a voltage loss 

within the cell during discharge and afford a measure of rate capabilities. The air permeability 

method is most useful for quality control purposes where rapid determination of lot-to-lot 

variability is the principal concern. 

The overall mechanical strength of the separator is characterized in terms of several factors, 

with each possessing desired requirements and performance metrics. Tensile strength and 

properties are strongly dependent upon the material manufacturing process. Uniaxially-oriented 

separator films are generally preferred for material dimensional stability, as they exhibit a 

minimal tendency to shrink at elevated temperatures or when exposed to electrolyte. High 

puncture strength, which can be measured with a tensile tester, is important to prevent the 

penetration of particulate electrode material through the separator, especially during cell 

assembly, which could lead to an electrical short circuit. High mechanical strength is important, 

especially in a uniaxially-oriented separator film’s machine direction, as the material is subjected 

to considerable tension in this direction during the winding operation of a spiral-wound battery 

fabrication procedure, and contraction of the width during the operation would be undesirable. 

Biaxially-oriented films are more uniformly strong in both the machine and transverse directions. 

The chemical composition and structure/morphology attributes of the separator material, 

which significantly impact the optimization of the properties and characteristics summarized 

above, can be qualitatively and quantitatively assessed and characterized by a host of analytical 

spectroscopic, microscopic, thermal and mechanical methodologies that are available within a 

modern, state-of-the-art materials R&D infrastructure. Most of the separator properties 

described above can be measured or characterized by established American Society for Testing 

and Materials (ASTM) standard methods. Separator material manufactured for either specific 

aerospace-battery applications or for high-volume terrestrial markets should also be defect-free, 

should have uniform properties and should be capable of forming a good interface with the cell 

electrode components. Separator thermal properties and related characteristics will be 

discussed in a subsequent section of this review. 

General Types of Separator Materials for Rechargeable Lithium-Based Cells 

Generally, battery separators for lithium-based cells can be classified into three major types, 

with respect to their structure, composition and related properties (1) nonwoven fiber mats, (2) 

microporous polymeric membranes, and (3) inorganic composite membranes (Ref. 5). In most 

commercial liquid-electrolyte lithium-based cells, microporous membrane separators are 

employed, and this class will be the subject of a subsequent section. 

Nonwoven separator mats, which are prepared by bonding either natural or synthetic fibers 

together by various methods, possess the attributes of high porosity and large pore sizes, but 

thin structures generally lack the physical properties required for utilization in lithium-based 

cells. Such porous structures can usefully serve as mechanical support structures for gel 

polymer electrolytes, which can be impregnated into the fibrous mat (Ref. 8). A gel polymer 

electrolyte cell component can be inherently safer than a flammable organic liquid electrolyte, as 
NASA/TM—2009-215590 4

a result of decreased volatility. Depending upon the specific chemistry, a gel polymer electrolyte 

could possess sufficient mechanical integrity on its own to serve as both electrolyte and 

separator, such as was the case for the “Bellcore” cell technology (Ref. 9) of the mid-1990’s. 

An inorganic composite or ceramic membrane, formed by bonding highly hydrophilic/ 

wettable, nano-sized inorganic particles such as alumina, silica or zirconia together would 

possess the additional desirable properties of exceptional thermal stability and dimensional 

stability. However, it would be difficult for a thin film of such material to have the mechanical 

integrity necessary for cell winding and assembly. This may not be as significant of an issue for 

a prismatic cell design. Recently, Evonik Degussa Corporation has introduced a series of 

Separion separator materials into the marketplace which combine the desirable properties of 

both ceramic and polymeric nonwoven materials (Ref. 10). Possessing both excellent cell 

performance and thermal safety and abuse characteristics, this separator material is currently 

being developed further for hybrid electric vehicle applications (Ref. 11). 

Microporous Polymeric Membranes 

Presently, most commercially-available lithium-ion spiral-wound cells containing a liquid 

organic electrolyte employ a microporous polymeric membrane separator due to advantages of 

performance, safety and cost (Refs. 3 and 5). These separators are based on polyolefin 

materials, such as polyethylene (PE), polypropylene (PP) and blends of such. Such polyolefinbased separators, which afford both excellent chemical stability and mechanical properties, are 

manufactured by either a wet or a dry process, both of which employ orientation steps to impart 

porosity and increase tensile strength. 

The dry process involves no use of solvents, which could be a source of separator material 

contamination, and involves (1) melting a polyolefin resin, (2) extruding the resin into a film, (3) 

thermal annealing, and (4) stretching under controlled thermal conditions to create desired 

structural micropores (Ref. 4). Commercial polyethylene and polypropylene films prepared by 

this process are available from Celgard, LLC (Ref. 3). Celgard 2730 and Celgard 2400 are 

single layer PE and PP separators, respectively, while Celgard 2320 and 2325 are PP/PE/PP 

trilayer separator materials. As will be discussed in a subsequent section, the trilayer material 

structure can function in a lithium-ion cell as a “thermal fuse” for enhanced inherent cell safety, 

as well as providing exceptional puncture strength. The Celgard microporous separator 

materials have been extensively characterized as a lithium-ion cell component. Single-layer 

materials made from a blend of PE and PP have also been patented to afford enhanced cell 

safety characteristics (Ref. 12). Upon heating this blended material, which contains microporous 

regions of PE and PP, the separator impedance increases near the melting point of the PE and 

remains high until beyond the melting point of PP. 

The wet process, or phase inversion process, (Refs. 13 and 14) involves mixing a polyolefin 

resin with a hydrocarbon liquid or low molecular oil, melting the mixture, extruding the melt into 

a sheet, orientating the sheet and extracting the liquid phase. Polyolefin battery separators 

made by the wet process are available from several sources, such as a widely used 

polyethylene-based material from ExxonMobil Chemical and its Japanese affiliate Tonen 

Chemical. 

In Figure 1, the microstructures of microporous polyolefin separators made by the dry 

process (a) and the wet process (b) are compared. In general, separators made by the dry 

process exhibit a high orientation-dependent tensile strength, while membranes made by the 

wet process are nonoriented with respect to both pore structure and mechanical strength. A dryprocess produced separator appears to be more suited for a high power density lithium-ion cell 

due to its open and straight porous structure, while the tortuous and interconnected porous 

structure of a wet-process made material is more suitable for a cell with a long cycle life 

requirement (Ref. 5). 
NASA/TM—2009-215590 5

For practical lithium-ion cell performance most microporous separators have a thickness 

below 50 μm and average pore diameters below 1 μm. For high energy density applications, 

separator thicknesses of <25 μm are desirable in order to achieve a lower internal resistance, 

however, the safety concern with respect to mechanical integrity and penetration must be 

considered. 

Lithium-ion Cell Performance and Safety: Separator Effects 

Although classified as an inactive cell component, the separator properties play a critical 

role in obtaining practical and optimal cell-level performance and the inherent safety of the cell. 

In addition to initially possessing optimal properties for meeting the requirements for a specific 

application, the material properties must be uniform and stable over the desired application/ 

mission life. The topic of separator performance degradation will be addressed in a subsequent 

section. With respect to cell and battery-level safety, the internal cell separator can complement 

safety control circuits possessing redundant safety features (e.g., CID, PTC, vent, etc.). 

As mentioned earlier, the separator should possess a uniform pore structure and exhibit 

desired dimensional stability (e.g., low shrinkage) and a low electrical resistance in order to 

achieve good performance. The separator property of a low electrical resistance, which is a 

function of multiple material properties, has a pronounced effect upon such cell properties as 

capacity, rate performance, fast charge capability, overall cell resistance and cycle life. For 

safety concerns, the advantages of utilizing a thin separator must be weighed against the 

reduction in mechanical integrity, and the cell design should reflect such. External mechanical 

abuse (e.g., “nail” penetration or crush) or an internal short circuit could result in an abnormal 

increase in cell temperature, which, as discussed below, could seriously compromise safety. If 

an undesirable cell overcharge condition occurs, dendritic lithium metal could form, which could 

penetrate the separator as well as causing a drastic reduction in thermal stability. 

Thermal Properties and Separator Shutdown Performance 

If a lithium-ion cell is accidentally overcharged or abused, heat can be generated that could 

seriously compromise cell and battery-level safety, which is especially critical for manned, 

human-rated applications. Above a threshold temperature, a “self-heating” condition could occur 

due to exothermic reactions occurring internally within the cell (Ref. 15). Such reactions may 

include reactions between lithium and electrolyte and the thermal decomposition of internal cell 
NASA/TM—2009-215590 6

components. If the internal heat generation is allowed to continue, a catastrophic cell “thermal 

runaway” condition could occur, which would be a serious safety concern for a manned 

application. 

The shutdown property of a polymeric separator material can internally provide a margin of 

safety against an external short circuit, accidental overcharge or an abuse condition resulting in 

an elevated cell temperature. Near the melting temperature of the specific polymeric material, 

the pores collapse, and this is accompanied by a significant increase in the separator and 

overall cell impedances, resulting in a termination of electrochemical activity and current flow. 

The shutdown property of a separator material can be characterized by monitoring the 

electrolyte-saturated separator material impedance while the temperature is ramped (Ref. 16). 

Optimization of the shutdown response and efficiency may be achievable by tailoring material 

properties and processing methods, and by employing additives to remove impurities. The 

shutdown mechanism would provide very little protection from an internal short circuit 

accompanied by a rapid internal heating rate. 

The separator material should also possess high-temperature melt integrity and exhibit 

mechanical robustness above the shutdown temperature. After a separator shutdown 

occurrence, the cell temperature is likely to continue to increase. The separator must maintain 

mechanical integrity and a high impedance as a function of time at elevated temperatures in 

order to prevent the electrodes from making physical contact and creating the safety hazard of 

an internal short circuit. Thermal mechanical analysis (TMA) can provide a measure of a 

material’s melt integrity. 

Thermal shutdown separators have been fabricated for commercial lithium-ion cells, typically 

as multilayer polyolefin structures (Ref. 17). The Celgard trilayer PP/PE/PP separator material, 

for example, functions as such an inherent safety device due to the difference in the PE and PP 

melting points (~130 to 140, and ~165 °C, respectively) (Refs. 5 and 18). The inner PE layer is 

capable of melting and filling the pores to inhibit ionic conduction at a temperature lower that 

that associated with an uncontrollable thermal runaway, while the outer PP layers continue to 

provide mechanical strength up to its melting temperature. If a “nail” penetration or an accidental 

overcharge at a high current density were to occur, such a structure would provide little 

protection from rapid localized overheating. Figure 2 is a DSC plot of a Celgard 2325 trilayer 

separator, which shows the melting temperatures of the PE and PP component layers. 
NASA/TM—2009-215590 7

With both U.S. Department of Energy’s (DOE) and NASA Small Business Innovative 

Research (SBIR) program support, Policell Technologies, Inc. focused on the development of a 

novel separator material possessing a selectable thermal shutdown temperature which would 

be significantly lower than that of available commercial separator products in order to enhance 

large format, lithium-ion cell safety attributes (Ref. 20). The family of separator materials, which 

were engineered with respect to composition, could also be bonded via heat activation to the 

cell electrode surfaces for enhanced interfacial contact. 

In support of the DOE Advanced Technology Development (ATD) Program for electric 

vehicle applications, Sandia National Laboratory (SNL) maintains an infrastructure dedicated to 

assessing and improving the thermal abuse tolerance of lithium-ion cells and cell components 

(Ref. 21). Employing a variety of experimental methodologies, responses of separator materials 

to abuse conditions are characterized and correlated with observed cell behavior (Ref. 22). 

Studies include shutdown performance, upper integrity temperature and separator breakdown 

leading to a cell thermal runaway condition. 

Separator Degradation 

Lithium-ion battery performance degradation and failure can often be attributed to the 

degradation of the separator component. Primary causes of separator degradation, excluding 

the previously-discussed thermal melting scenarios, are typically (Ref. 1) chemical attack by the 

electrolyte, (Ref. 2) electrochemical oxidation, (Ref. 3) dendritic growth of electrode material 

through the separator pores, (Ref. 4) structural degradation as a result of high temperature or 

cycling or (Ref. 5) clogging of separator pores during cycling. With respect to chemical stability, 

polyolefins exhibit excellent resistance to degradation in typical lithium-ion cell electrolytes. 

During extended cycling, especially at elevated temperatures, the separator should be 

stable to the strongly oxidizing electrochemical environment on the surface facing the positive 

electrode and to the strongly reducing environment on the surface facing the negative electrode. 

Poor oxidation resistance can result in both poor high-temperature storage performance and 

long-term cycling behavior (Ref. 3). The superior oxidative resistance of polypropylene as 

compared to polyethylene results in a PP/PE/PP trilayer separator being more stable to an 

oxidative cell environment. Separator tolerance to an electrochemically oxidative environment 

will become more critical in the future, as a need for higher cell specific energies is addressed 

by employing higher positive voltage cathode materials. The superior mechanical integrity of the 

polypropylene outer layers of the trilayer material also affords puncture resistance. 

When aged and/or cycled at elevated temperatures, lithium-ion cells may demonstrate a 

power loss that is partially attributed to a deterioration in separator performance (Ref. 23). It was 

shown that the cell impedance increased significantly, with a significant contribution being 

attributed to a loss in the ionic conductivity of the separator as a result of pores being blocked 

by electrolyte decomposition products. 

Also in support of the DOE ATD Program for electric vehicle applications, extensive 

diagnostic studies were performed on aged, cycled and/or abused polyolefin separators in order 

to elucidate the causes and mechanisms of material degradation (Ref. 24). Dramatic changes in 

the separator surface morphology were observed; porosity losses, which were accompanied by 

increased separator resistance, were attributed to a clogging of the pores by solid deposits. The 

deposits resulted from electrolyte decomposition processes occurring at the electrode/ 

electrolyte interfaces. 

The high voltage stability of the separator material at an elevated temperature following a 

successful thermally-induced shutdown is an important requirement for series-connected cells 

(Ref. 22). A high-impedance cell in a series string could be subjected to high voltages from the 
NASA/TM—2009-215590 8

remaining cells, leading to a voltage breakdown of the separator caused by local currents 

through pinhole defects. Such a mechanism could result in localized heating and an internal 

short, which could ultimately result in thermal runaway and explosive cell failure. 

Future Direction 

Historically, only within the past decade have lithium-based cell separator materials been a 

strong focus of attention for enhanced development and optimization efforts, in order to address 

specific battery application performance requirements. As emphasized in this review, the 

separator component of advanced lithium-ion and lithium-based cells for high specific energy 

and/or high power density applications will play an important role in realizing optimal levels of 

performance and safety. It will be important to optimize all cell and battery/system-level 

components to enhance performance and reliability while maintaining and enhancing the safety 

of the technology. As lithium-based cell technology continues to become more advanced and 

mature, the requirements for and function of the separator will become more demanding and 

complex. Eventually, the goal of realizing an infinitely thin separator with negligible resistance 

will be met by a future generation of lithium-based cell technology that will practically employ 

polymeric or solid-state electrolytes. 

As mentioned, energy storage needs and requirements for future NASA manned aerospace 

missions will demand high performance, high reliability and exceptional safety from battery 

technologies earmarked or selected for specific applications. The separator cell component will 

need to meet all of the key criteria necessary to be qualified for a particular battery type, and it 

will be critical that all components are assessed, characterized and qualified in appropriate 

multi-component and system-level configurations. Fortunately, at this point in time when NASA 

is investing resources in technology development for future human-rated aerospace missions, 

other governmental entities, coupled with the commercial sector, are also investing resources in 

similar technologies to address their unique future needs. Thus, viable opportunities for 

interagency collaborations and technology leveraging currently exist. 

In similarity to addressing the technical challenges being addressed by NASA for achieving 

enhanced safety, reliability and performance of lithium-ion cells for human-rated mission 

applications, the U.S. Department of Energy has invested heavily in developing and maturing 

advanced electrochemical and battery technologies, particularly for future manned hybrid and 

all-electric vehicle applications. To meet future terrestrial consumer needs, it is highly 

recognized that “the cell separator component is the key to the safety of the battery” (Ref. 25). 

To address the future technical performance and safety requirements that will be required 

for the advanced lithium-ion battery technologies that will eventually enhance and enable future 

NASA Exploration Mission and Constellation Program aerospace missions, the NASA 

Exploration Technology Development Program (ETDP) is currently supporting the Lithiumbased Battery Development element of the Energy Storage Project (Ref. 26), which also 

includes an advanced proton-exchange membrane fuel cell development element. Lithium-ion 

cell component development subtasks, which are focused on achieving necessary cell-level 

performance and safety goals, are a critical part of this program. A focused separator 

development subtask is a key part of this NASA program, and it will address technology gaps 

between contemporary material performance and needs to meet future aerospace mission 

requirements. The programmatic approach for this subtask will emphasize the leveraging of 

current government and private-sector technology development activities. 
NASA/TM—2009-215590 9

References 

1. M.A. Manzo, et al., Energy Storage: Batteries and Fuel Cells for Exploration, 45th 

Aerospace Sciences Meeting and Exhibit, Reno, NV (2007). 

2. W. Boehnstedt, in Handbook of Battery Materials, Besenhard, J.O., Ed., VCH Wiley, 

Amsterdam and New York, 1999. 

3. P. Arora and Z. Zhang, Chem. Rev., 104, 4419 (2004). 

4. R. Spotnitz, in Handbook of Battery Materials, Besenhard, J.O., Ed., VCH Wiley, Amsterdam 

and New York, 1999. 

5. S. Zhang, J. Power Sources, 164, 351 (2007). 

6. G. Venugopal, et al., J. Power Sources, 77, 34 (1999). 

7. K.M. Abraham, Electrochim. Acta, 38, 1233 (1993). 

8. K.M. Abraham, et al., J. Electrochem. Soc., 142, 3 (1995). 

9. A.S. Gozdz, et al., U. S. Patent 5,456,000 (1995). 

10. S. Augustin, Advanced Automotive Battery & Ultracapacitor Conference, Baltimore, MD, 

May, 2006. 

11. J. Tarabocchia, Evonik Industries, private communication, February 2008. 

12. H. Higuchi, et al., U. S. Patent 5,385,777 (1995). 

13. M. Weighall, J. Power Sources, 34, 257, 1991. 

14. K. Yagi, et al., European Patent Application 0683196A2 (1995). 

15. J. Dahn, et al., Solid State Ionics, 69, 265 (1994). 

16. F. Laman, et al., J. Electrochem. Soc., 140, L51 (1993). 

17. J. Lundquist, et al., U. S. Patent 4,731,304 (1988). 

18. R. Callahan, et al., U. S. Patent 6,602,593 (2003). 

19. E. Wong, NASA Glenn Research Center, private communication, 2008. 

20. L. Sun, et al., 42nd Power Sources Conference, Philadelphia, PA, June 2006. 

21. E.P. Roth, DOE Vehicle Technologies Peer Review, Bethesda, MD, February 2008. 

22. E.P. Roth, et al., J. Power Sources, 174, 579 (2007). 

23. R. Kostecki, et al., Electrochem. Solid State Lett., 5, A67 (2002). 

24. R. Kostecki, et al., J. Electrochem. Soc., 151, A522 (2004). 

25. A. Tullo, Chemical and Engineering News, 22 (February 18, 2008). 

26. M. Manzo, et al., Space Technology and Applications International Forum, Albuquerque, 

NM, February 2008. 
REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188 

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the 

data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this 

burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. 

Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB 

control number. 

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 

1. REPORT DATE (DD-MM-YYYY)

01-03-2009 

2. REPORT TYPE

Technical Memorandum 

3. DATES COVERED (From - To)

4. TITLE AND SUBTITLE

A Review of State-of-the-Art Separator Materials for Advanced Lithium-Based Batteries for 

Future Aerospace Missions 

5a. CONTRACT NUMBER

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Bladwin, Richard, S. 

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

WBS 038957.04.07.02.01.03 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration 

John H. Glenn Research Center at Lewis Field 

Cleveland, Ohio 44135-3191 

8. PERFORMING ORGANIZATION

 REPORT NUMBER

E-16879 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration 

Washington, DC 20546-0001 

10. SPONSORING/MONITORS

 ACRONYM(S)

NASA 

11. SPONSORING/MONITORING

 REPORT NUMBER

NASA/TM-2009-215590 

12. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified-Unlimited 

Subject Categories: 23, 24, 27, and 44 

Available electronically at http://gltrs.grc.nasa.gov 

This publication is available from the NASA Center for AeroSpace Information, 301-621-0390

13. SUPPLEMENTARY NOTES

14. ABSTRACT

As NASA embarks on a renewed human presence in space, safe, human-rated, electrical energy storage and power generation technologies, 

which will be capable of demonstrating reliable performance in a variety of unique mission environments, will be required. To address the 

future performance and safety requirements for the energy storage technologies that will enhance and enable future NASA Constellation 

Program elements and other future aerospace missions, advanced rechargeable, lithium-ion battery technology development is being pursued 

with an emphasis on addressing performance technology gaps between state-of-the-art capabilities and critical future mission requirements. 

The material attributes and related performance of a lithium-ion cell’s internal separator component are critical for achieving overall optimal 

performance, safety and reliability. This review provides an overview of the general types, material properties and the performance and 

safety characteristics of current separator materials employed in lithium-ion batteries, such as those materials that are being assessed and 

developed for future aerospace missions. 

15. SUBJECT TERMS

Electrochemistry; Energy storage; Lithium battery; Polymer; Membrane 

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF

 ABSTRACT

UU 

18. NUMBER

 OF 

 PAGES

15 

19a. NAME OF RESPONSIBLE PERSON

STI Help Desk (email:help@sti.nasa.gov) 

a. REPORT

U 

b. ABSTRACT

U 

c. THIS 

PAGE

U 

19b. TELEPHONE NUMBER (include area code)

301-621-0390 

Standard Form 298 (Rev. 8-98)

Prescribed by ANSI Std. Z39-18