An official website of the United States government
Conventional lithium ion battery separators are microporous polyolefin membranes that play a passive role in the electrochemical cell. Next generation separators should offer significant performance enhancements, while being fabricated through facile, low cost approaches with the ability to readily tune physicochemical properties. This study presents a single-step manufacturing technique based on UV-initiated polymerization-induced phase separation (PIPS), wherein microporous separators are fabricated from multifunctional monomers and ethylene carbonate (EC), which functions as both the pore-forming agent (porogen) and electrolyte component in the electrochemical cell. By controlling the ratio of the 1,4-butanediol diacrylate (BDDA) monomer to ethylene carbonate, monolithic microporous membranes are readily prepared with 25 μm thickness and pore sizes and porosities ranging from 6.8 to 22 nm and 15.4% to 38.5%, respectively. With 38.5% apparent porosity and an average pore size of 22 nm, the poly(1,4-butanediol diacrylate) (pBDDA) separator takes up 127% liquid electrolyte, resulting in an ionic conductivity of 1.98 mS cm −1 , which is greater than in conventional Celgard 2500. Lithium ion battery half cells consisting of LiNi 0.5 Mn 0.3 Co 0.2 O 2 cathodes and pBDDA separators were shown to undergo reversible charge/discharge cycling with an average discharge capacity of 142 mA h g −1 and a capacity retention of 98.4% over 100 cycles – comparable to cells using state-of-the-art separators. Moreover, similar discharge capacities were achieved in rate performance tests due to the high ionic conductivity and electrolyte uptake of the film. The pBDDA separators were shown to be thermally stable to 374 °C, lack low temperature thermal transitions that can compromise cell safety, and exhibit no thermal shrinkage up to 150 °C.
more »
« less
Self-limiting electrospray deposition (SLED) of porous polyimide coatings as effective lithium-ion battery separator membranes
Electrospray deposition (ESD) is employed to produce separator membranes for coin-cell lithium-ion batteries (LIBs) using off-the-shelf polyimide (PI). The PI coatings are deposited directly onto planar LiNi0.6Mn0.2Co0.2O2 (NMC) electrodes via self-limiting electrospray deposition (SLED). Scanning electron microscopy (SEM), optical microscopy, and spectroscopic microreflectometry are implemented in combination to evaluate the porosity, thickness, and morphology of sprayed PI films. Furthermore, ultraviolet-visual wavelength spectroscopy (UV vis) is utilized to qualitatively assess variation in film porosity within a temperature range of 20-400oC, to determine the stable temperature range of the separator. UV vis results underscore the ability of the SLED PI separator to maintain its porous microstructure up to ~350oC. Electrochemical performance of the PI separators is analyzed via charge/discharge cycle rate tests. Discharge capacities of the SLED PI separators are within 83-99.8% of commercial Celgard 2325 PP/PE/PP separators. This study points to the unique possibility of SLED as a separator manufacturing technique for geometrically complex energy storage systems. Further research is needed to optimize the polymer-solvent system to enhance control of porosity, pore size, and coating thickness. This can lead to significant improvement in rate and cycle life performance in more advanced energy storage devices.
more »
« less
- Award ID(s):
- 2019849
- PAR ID:
- 10561644
- Publisher / Repository:
- The Royal Society of Chemistry
- Date Published:
- Journal Name:
- RSC Applied Polymers
- Volume:
- 2
- Issue:
- 6
- ISSN:
- 2755-371X
- Page Range / eLocation ID:
- 1074 to 1081
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Zinc metal anodes are attracting much attention to enable more economical and sustainable energy storage devices. However, like other metal anodes, dendritic growths and penetrations of porous separators are still challenging to eliminate. Introducing negative surface charges on the pore walls of separators have been exploited to enforce a uniform incoming Zn-ion flux toward more uniform electrodeposition, but penetrations induced by localized high current densities still remain in available systems. In this work, we report, for the first time, a bipolar separator that exploits the distinct electroosmotic effects of the negative and the positive surface charges. The surface charge effects on Zn dendrite growths were first verified in transparent capillary cells viaoperandovideo microscopy. By stacking the positively charged separator over the negatively charged separator as our proof-of-concept, the system offers preemptively a uniform Zn-ion flux through the negative layer yet starve-stops local metal growths that already penetrated the negative layer autonomously. Chronopotentiometry experiments with the symmetric cells reveal extended short-circuit time compared to control cells. Galvanostatic cycle-life experiments of full cells with the bipolar separator showed excellent cycle life of 5,000 cycles at the rate of 10 C, without signs of metal penetration.more » « less
-
The development of high-performance battery technologies necessitates ultrathin separators with superior mechanical strength and electrochemical properties. We present an innovative 1 µm thick, pinhole-free zeolitic imidazolate framework-8 (ZIF-8) layer, cathodically deposited on an 8 µm thick commercial polypropylene (PP) film in a rapid process, resulting in a ZIF-8@8-µm PP flexible membrane. This crack-free ZIF-8 layer, featuring angstrom-scale pores and chemical polar groups, functions as a Li+ sieve, regulating Li+ transport, controlling Li deposition, and blocking dissolved active cathode materials. It also enhances Li+ diffusion and transference number, extending the Sand’s time for Li dendrite formation. Consequently, the ZIF-8@8-µm PP separator addresses polysulfide shuttling in Li-S batteries and Li dendrite formation in Li-metal batteries, significantly improving their performance compared to conventional separators. Our findings indicate that while the 8-μm PP alone is unsuitable as a battery separator, the ZIF-8@8-μm PP, possesses the mechanical strength and electrochemical properties necessary for developing both Li-S and Li-metal batteries, as well as application in conventional Li-ion batteries with enhanced volumetric energy densities.more » « less
-
null (Ed.)Abstract Electrospray deposition (ESD) applies a high voltage to liquids flowing through narrow capillaries to produce monodisperse generations of droplets down to hundreds of nanometers in diameter, each carrying a small amount of the delivered solute. This deposition method has been combined with insulated stencil masks for fabricating micropatterns by spraying solutions containing nanoparticles, polymers, or biomaterials. To optimize the fabrication process for micro-coatings, a self-limiting electrospray deposition (SLED) method has recently been developed. Here, we combine SLED with a pre-existing patterned polymer film to study SLED’s fundamental behavior in a bilayer geometry. SLED has been observed when glassy insulating materials are sprayed onto conductive substrates, where a thickness-limited film forms as charge accumulates and repels the arrival of additional charged droplets. In this study, polystyrene (PS), Parylene C, and SU-8 thin films of varying thickness on silicon are utilized as insulated spraying substrates. Polyvinylpyrrolidone (PVP), a thermoplastic polymer is sprayed below its glass transition temperature (T g ) to investigate the SLED behavior on the pre-deposited insulating films. Furthermore, to examine the effects of in-plane confinement on the spray, a microhole array patterned onto the PS thin film by laser dewetting was sprayed with dyed PVP in the SLED mode. This was then extended to an unmasked electrode array showing that masked SLED and laser dewetting could be used to target microscale regions of conventionally-patterned electronics.more » « less
-
Abstract We establish a sample‐ and data‐processing pipeline that allows for high‐throughput optical microscope measurement of porous films, provided they are sufficiently optically scattering. Here, self‐limiting electrospray deposition (SLED) is used to manufacture scattering films of different morphologies. This technique compensates for the scattering of the films through background subtraction of the reflection image with the transmission image. This process is implemented through a combination of an ImageJ and MATLAB data pipeline; the Canny edge‐detector is used as the image‐processing algorithm to identify the boundaries of the film. This process is verified against manually measured images; a comparative study between cross‐sectional scanning electron microscopy (where scattering effects are diminished) and optical microscopy also verifies that our optical microscopy technique can be used to consistently, non‐destructively measure film thickness regardless of film morphology. In addition, this technique can be used in combination with dense film measurements to measure film porosity.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D4LP00192C
