Research at Argonne National Laboratory was funded by U.S. Department of Energy, FreedomCAR and Vehicle Technologies Office. Use of the Advanced Photon Source and research carried out in the Electron Microscopy Center at Argonne National Laboratory was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

Please consult all relevant Material Safety Data Sheets (MSDS) before use. Several of the chemicals used in these syntheses are acutely toxic and carcinogenic. Nanomaterials may have additional hazards compared to their bulk counterpart. Please use all appropriate safety practices when performing a nanocrystal reaction including the use of engineering controls (fume hood, glovebox) and personal protective equipment (safety glasses, gloves, lab coat, full length pants, closed-toe shoes). Portions of the following procedures involve standard air-free handling techniques.
1. Synthesis of Cathode Materials
Note: Cathode materials can be synthesized by either atomic layer deposition or wet chemistry reaction.
<ol>
	<li>Atomic Layer Deposition (ALD)
	<ol>
		<li>Disperse 5 g of porous carbon in 100 ml 1 M KMnO4 solution under magnetic stirring for 12 hr.</li>
		<li>Spread 100 mg of the oxidized carbon powder onto a stainless steel tray of the ALD instrument, and clamp a stainless steel mesh cover over the tray.</li>
		<li>Hold the carbon powder in the tray at 200 &#176;C under continuous flow of 300 sccm ultra-high-purity nitrogen carrier gas at 1 Torr pressure for 30 min.</li>
		<li>Treat the carbon powder with a complete ALD cycle as follows. 
		Note: Take Pd nanoparticles as an example of the electrocatalysts in this protocol. Reagents can be changed according to specific requirements. All reagents are used as-received without any further purification.
		<ol>
			<li>Expose the carbon substrate (100 mg) to palladium hexafluoroacetylacetonate (Pd(hfac)2, 99.9%) at 200 &#176;C for 100 min.</li>
			<li>Purge the tray with continuous flow of 300 sccm ultra-high-purity nitrogen carrier gas at 1 Torr pressure for 300 min.</li>
			<li>Expose the carbon substrate to formalin (HCHO 37 wt. % in H2O) at 200 &#176;C for 100 min.</li>
			<li>Purge the tray with continuous flow of 300 sccm ultra-high-purity nitrogen carrier gas at 1 Torr pressure for 300 min.</li>
		</ol>
		</li>
		<li>Repeat ALD cycle as necessary. Usually 3-10 repetitions.</li>
	</ol>
	</li>
	<li>Wet-chemistry Reaction 
	Note: Take Fe nanoparticles as an example of the electrocatalyst in this protocol. Reagents can be changed according to specific requirements. All reagents are used as-received without any further purification.
	<ol>
		<li>Disperse 5 g of porous carbon in 100 ml 1 M KMnO4 solution under magnetic stirring for 12 hr.</li>
		<li>Wash the oxidized carbon with deionized water.</li>
		<li>Filter the washed carbon with a filter flask fitted with a glass fiber, and then dry it in an oven at 110 &#176;C for 12 hr.</li>
		<li>Disperse the dried carbon in 100 ml deionized water, then add 1 g of FeCl3 under magnetic stirring.</li>
		<li>Adjust the pH value to about 9, using 1 M NaOH solution.</li>
		<li>Stir the resulting slurry for 5 hr, and then filter the slurry with a filter flask fitted with a glass fiber.</li>
		<li>Wash the product with deionized water and ethanol. Then dry it in an oven at 110 &#176;C for overnight.</li>
		<li>Heat-treat the product at 450 &#176;C with continuous flow of H2/Ar mixture (4% H2) in a quartz tube furnace. Use a flow rate of 100 ml/min for 5 hr.</li>
	</ol>
	</li>
</ol>
2. Preparation of Electrodes and Electrolyte
<ol>
	<li>Cathode
	<ol>
		<li>Mix the as-prepared cathode material and binder poly(vinylidene fluoride) (PVDF) in a 4:1 weight ratio. 
		Note: The total of the mixture depends on the amount of the cathodes. The loading of cathode material on each piece is in the range of 0.1-1 mg.</li>
		<li>Add 1-methyl-2-pyrrolidinone (NMP) to the mixture, and stir well to make an even-textured slurry. Add NMP at about three times the weight of the mixture.</li>
		<li>Coat the slurry onto carbon paper by a doctor blade with a thickness around 100 &#181;m.</li>
		<li>Dry the laminate in a vacuum oven at 100 &#176;C for overnight.</li>
		<li>Punch the laminate into disks with a hole puncher to a diameter of 7/16 inches, and weigh it.</li>
	</ol>
	</li>
	<li>Aprotic Electrolyte
	<ol>
		<li>Dry lithium trifluoromethanesulfonate (LiCF3SO3) in a vacuum oven at 100 &#176;C for overnight.</li>
		<li>Add dried LiCF3SO3 in tetraethylene glycol dimethyl ether (TEGDME; H2O ~ 10 ppm) with a concentration of 1 mol/L, then stir the solution with magnetic stirring until the salt is dissolved.</li>
		<li>Keep the electrolyte in a glovebox filled with Ar.</li>
	</ol>
	</li>
	<li>Anode
	<ol>
		<li>Punch the lithium foil/chips into disks with a hole puncher to a diameter of 7/16 inches.</li>
	</ol>
	</li>
</ol>
3. Electrochemical Testing
<ol>
	<li>Assembly of Swagelok Cell 
	Note: All the steps of the assembly are operated in a glovebox filled with Ar, except 3.1.9.
	<ol>
		<li>Assemble the Swagelok set as shown in Figure 1a. Tighten the anode end, and loosen the cathode end.</li>
		<li>Put a piece of lithium metal chip (diameter 7/16 inches) on the top of the stainless steel rod of the anode end.</li>
		<li>Put a piece of glass fiber separator (diameter 1/2 inches) on the top of the lithium metal anode.</li>
		<li>Add 5-7 drops of electrolyte to fully wet the glass fiber separator. Gently press the separator to remove bubbles.</li>
		<li>Put a piece of cathode on the top of the wetted separator, with the active material facing the anode.</li>
		<li>Cover the cathode with a piece of aluminum mesh (diameter 7/16 inches).</li>
		<li>Press the above mentioned layers with the aluminum tube, then tighten the cathode end.</li>
		<li>Seal the whole Swagelok cell in a glass chamber, and fix the chamber with a clamp, as shown in Figure 1.</li>
		<li>Take the whole cell out of glovebox. Connect the glass chamber to an ultra-high-purity oxygen tank, and purge it with continuous oxygen flow at 1 atm pressure for 30 min.</li>
	</ol>
	</li>
	<li>Battery Performance Testing
	<ol>
		<li>Set a thermostat to 25 &#176;C.</li>
		<li>Put cells and electrodes (electronic clips connected to the equipment by a cable) into the thermostat, and fix them.</li>
		<li>Clip the cathode and anode on glass chamber with corresponding electronic clips.</li>
		<li>Open the operating software of the battery test system, and select the channel connected with the cable.</li>
		<li>Set a procedure of the electrochemical testing. 
		Note: Set the current density of 100 mA/gactive material, and voltage range of 2.2-4.5 V.
		<ol>
			<li>Set the discharge cut-off voltage of 2.2 V for discharge test.</li>
			<li>Set the discharge/charge step-time of 5 or 10 hr for capacity-controlled cycling test.</li>
			<li>Set the discharge cut-off voltage of 2.2 V and charge cut-off voltage of 4.5 V for voltage-controlled cycling test.</li>
		</ol>
		</li>
		<li>Run the procedure by clicking the &#34;run&#34; button on the software interface.</li>
	</ol>
	</li>
	<li>Disassembly and cleaning of the cell
	<ol>
		<li>Disassemble cells in a glovebox.</li>
		<li>Keep the electrodes in glass vials for the following characterizations. Transfer other cell parts out of the glovebox.</li>
		<li>Put the Swagelok parts, stainless steel rods, aluminum tubes, and aluminum meshes in acetone solution (~ 20%) or deionized water in a beaker, and clean them with ultrasonication for 15-30 min.</li>
		<li>Dry the parts and glass chambers in a thermostat set to 60-80 &#176;C.</li>
	</ol>
	</li>
</ol>
4. Preparation of Characterization Specimens
Note: Specimens are prepared in a hood (for as-prepared materials) or a glovebox filled with Ar (for air-sensitive specimens).
<ol>
	<li>Specimens for SEM and XPS
	<ol>
		<li>Stick a carbon tape on the sample stage. The carbon tape can be as large as the sample stage, or as small as the specimen piece.</li>
		<li>Cut a piece of specimen about 5 mm2, and stick it on the carbon tape. 
		Note: The specimen can be any non-magnetic samples. For the specimens after electrochemical tests, wash them with the electrolyte solvent before stick to the carbon tape.</li>
		<li>Seal the air-sensitive specimens in a Mason jar before measurement.</li>
		<li>Operate the SEM34-36 or XPS37,38 according to the manufacturer&#39;s instructions.</li>
	</ol>
	</li>
	<li>Specimens for TEM
	<ol>
		<li>Mill 1 mg of the sample powder. 
		Note: For electrode specimens, scrape the active materials off carbon paper before milling.</li>
		<li>Load the sample powder onto a copper grid, and remove the loose powder.</li>
		<li>Load the copper grid to the sample holder of TEM. 
		Note: Get this step done as fast as possible for air-sensitive samples.</li>
		<li>Perform TEM.39-41</li>
	</ol>
	</li>
	<li>Specimens for High-energy XRD
	<ol>
		<li>Powder specimens
		<ol>
			<li>Seal one end of a polyimide tubing by clay or glue.</li>
			<li>Load the powder into the tubing.</li>
			<li>Seal the other end of the tubing.</li>
		</ol>
		</li>
		<li>Disk specimens 
		Note: To measure the active materials on electrode, another option is to scrape them off carbon paper and follow step 4.3.1.
		<ol>
			<li>Seal the sample pieces with a piece of polyamide tape. Seal by putting the samples in the middle of one piece of tape, and covering them with another piece of tape. 
			Note: For the specimens after electrochemical tests, wash them with the electrolyte solvent before sealing.</li>
		</ol>
		</li>
		<li>Operate the high-energy XRD42-44 in Advanced Photon Sources in Argonne National Laboratory.</li>
	</ol>
	</li>
	<li>Specimens for XANES
	<ol>
		<li>Powder samples
		<ol>
			<li>Dilute the samples if the concentration of the measured elements is high, using either boron nitride (BN) or carbon black as the dilute agent. Here, dilute to 3-5 wt. %.</li>
			<li>Press the powder into disk with the diameter of 7 mm and the thickness of around 1 mm, using a KBr Press Kit and 7 mm Die Set.</li>
			<li>Seal the disk with window film.</li>
		</ol>
		</li>
		<li>Disk specimens
		<ol>
			<li>Seal the specimen with window film.</li>
		</ol>
		</li>
		<li>Operate the high-energy XANES45-47 in Advanced Photon Sources in Argonne National Laboratory.</li>
	</ol>
	</li>
	<li>Specimens for ATR-FTIR
	<ol>
		<li>Clean the diamond attenuated total reflection (ATR) unit before and after measurement.</li>
		<li>Put specimens on the diamond unit for all samples interested.</li>
		<li>Perform ATR-FTIR spectrometry.48,49</li>
	</ol>
	</li>
	<li>Specimens for Raman Spectra
	<ol>
		<li>Put the specimen on a flat board (glass, stainless steel, etc.).</li>
		<li>Cover the specimen with a cover slide.</li>
		<li>Seal the set for air-sensitive samples.</li>
		<li>Perform Raman spectrometry.50,51</li>
	</ol>
	</li>
</ol>

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X-Ray Photoelectron Spectrometer Operation Procedure Available from: <a target="_blank" href="https://nanofabrication.4dlabs.ca">https://nanofabrication.4dlabs.ca</a> (2015)</li><li>Haasch, R. T., Sardela, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Practical Materials Characterization. , 93-132 (2014).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> JEM-2100F Field Emission Transmission Electron Microscope. , (2015).</li><li>Wen, J. -. G., Sardela, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Practical Materials Characterization. , 189-229 (2014).</li><li>Williams, D. B., Carter, C. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Transmission Electron Microscopy. , (2009).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Beamline 11-ID-C: High-energy Diffraction Beamline. , (2015).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Beamline 11-ID-D: Sector 11 - Time Resolved X-ray Spectroscopy and Scattering. , (2015).</li><li>Sardela, M. R., Sardela, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Practical Materials Characterization. , 1-41 (2014).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Beamline 9-BM-B,C: X-ray Absorption Spectroscopy Beamline. , (2015).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Beamline 20-BM-B: X-ray Absorption Spectroscopy Beamline. , (2015).</li><li>Bunker, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Introduction to XAFS: A Practical Guide to X-ray Absorption Fine Structure Spectroscopy. , (2010).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Nicolet FT-IR User's Guide. , (2015).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Nicolet iS5 User Guide. , (2015).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Renishaw inVia Raman Microscope Training Notebook. , (2015).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Renishaw InVia Quick Operation Summary. , (2015).</li><li>Mitchell, R. R., Gallant, B. M., Thompson, C. V., Shao-Horn, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=All-carbon-nanofiber+electrodes+for+high-energy+rechargeable+Li-O2+batteries.">All-carbon-nanofiber electrodes for high-energy rechargeable Li-O2 batteries.</a> Energy Environ. Sci. 4, 2952-2958 (2011).</li></ol>

The authors have nothing to disclose.

Considering the sensitivity of Li-O2 battery system to air, especially CO2 and moisture, lots of steps in the protocol are necessary in order to reduce the interferents and to avoid side reactions. For example, the Swagelok-type cell is assembled in a glovebox filled with Ar with O2 &#60; 0.5 ppm and H2O &#60; 0.5 ppm; and all the cathode materials, electrolyte solvent and salt, glass fiber, Swagelok parts, and the glass chambers are dried before assembly to reduce the moisture contamination. The anode end is a stainless steel rod in order to avoid the direct contact between lithium metal and O2 and to protect the lithium anode. The whole Swagelok setup is placed into a pure-oxygen-filled glass chamber which guarantees a leak-proof container by sealing with O-ring and vacuum greases. Moreover, Al-mesh, the current-collector, can help to protect the brittle carbon cathode.
The electrochemical test demonstrate that the as-prepared cathode materials showed a superior electrochemical behavior in Li-O2 battery. Due to that, the catalyst nanoparticles were uniformly dispersed over the high surface area carbon support, and that the porous structure and surface area were well persevered by the catalysts deposition methods used in this protocol. The overall reaction of nonaqueous Li-O2 battery is 2Li+ + O2 + 2e- &#8594; Li2O2.2,3,7 Side reactions, such as electrolyte decomposition, are also likely to occur due to the activity of the materials and intermediates used in a cell. However, in the research at the present stage, the side reactions and byproducts (LiOH, Li2CO3, etc.) have been significantly reduced with the improvement of materials and synthesis technologies. As shown in Figure 2d, although there might be a small amount of byproducts, the amount is too low to be detected by XRD. Some surface-sensitive techniques, such as XPS, FT-IR, and Raman spectroscopy, are, therefore, used to detect the minor products, especially on the surface region. There is no doubt that the stability of the electrolytes is very critical in oxygen environment and electrochemical reactions. Ether-based electrolytes (e.g., TEGDME) are relatively stable at the present stage of Li-O2 battery research. However, their behavior still needs to be investigated during long-term cycling; and searching for stable electrolytes is the research priority presently.
There are some other characterization methods to establish the discharge yield, or byproducts, such as mass spectrometry (MS) and titration. However, in the current research stage, the battery system is much more stable and reversible, and the byproducts have been significantly reduced by the development of electrolyte and cathode materials which have been more stable to oxygen and the discharge products.3,13,15 In this case, MS and titration are not sensitive enough to estimate the discharge yield. Besides, LiO2, the intermediate product, cannot be detected by titration either, due to its extreme activity.
In this article, we have demonstrated a systematic and efficient protocol of routine tests of aprotic Li-O2 battery, including the performance test and characterization of battery materials and reaction products. The approaches of catalyst loading result in a uniform distribution of catalyst nanoparticles with preservation of the surface structure of carbon substrate. Appropriate assembly protocol optimizes the active materials and ensures the pure-O2 environment for the electrochemical reactions.

In 1996, Abraham and Jiang1 reported the first reversible non-aqueous Li-O2 battery consisting of a porous carbon cathode, an organic electrolyte, and a Li-metal anode. Since then, due to its extremely high theoretical energy density exceeding that of any other existing energy storage systems, the Li-O2 battery, which induces a current flow by the oxidation of lithium at the anode and the reduction of oxygen at the cathode (overall reaction Li+ + O2 + e- &#8596; Li2O2), has received significant interest recently.1-8
A cathode material with the following requirements would be able to cater for the needs of high performance of Li-O2 battery: (1) fast oxygen diffusion; (2) good electric and ionic conductivity; (3) high specific surface area; and (4) stability. Both the surface area and porosity of the cathode are critical for the electrochemical performance of Li-O2 batteries.9-12 The porous structure allows the deposition of solid discharge products generated from the reaction of Li cations with O2; and larger surface areas provide more active sites to accommodate electrocatalytic particles that accelerate the electrochemical reactions. Such electrocatalysts are added to the cathode material by certain deposition methods, which provide strong adhesion to the substrate and good control of the catalyst particles, with preservation of the original porous surface structure of the substrate.13-17 The as-prepared materials are tested in Swagelok-type cells as the cathode of aprotic Li-O2 battery. However, the performance of the cell not only depends on the nature of cathode materials, but also on the type of the aprotic electrolyte18-22 and Li-metal anode.23-26 More influences include the amount and concentration of the materials and the procedure used in the charge/discharge tests. Proper conditions and protocols would optimize and improve the overall performance of battery materials.
In addition to the results of the electrochemical test, the battery performance can be also evaluated by characterizing the pristine materials and the reaction products.27-33 Scanning electron microscopy (SEM) is used to investigate the surface microstructure of the cathode material and the morphology evolution of the discharge products. Transmission electron microscopy (TEM), X-ray absorption near edge structure (XANES), and X-ray photoelectron spectroscopy (XPS) can be used to determine the ultrastructure, chemical state, and component of elements, especially for that of catalyst nanoparticles. High-energy X-ray diffraction (XRD) is used for directly identifying the crystalline discharge products. Possible electrolyte decomposition can be determined by attenuated total reflection Fourier transform infrared (ATR-FTIR) and Raman spectra.
This article is a protocol that demonstrates a systematic and efficient arrangement of routine tests of the aprotic Li-O2 battery, including the preparation of battery materials and accessories, the electrochemical performance test, and characterization of pristine materials and reaction products. The detailed video protocol is intended to help new practitioners in the field avoid many common pitfalls associated with the performance testing and characterization of Li-O2 batteries.

<table><tbody><tr><td>1-Methyl-2-pyrrolidinone (NMP), 99.5%</td><td>Sigma-Aldrich</td><td>328634</td><td></td></tr><tr><td>Battery test system</td><td>MACCOR</td><td>Series 4000 Automated Test System</td><td></td></tr><tr><td>Dimethyl carbonate (DMC), &amp;ge;99%</td><td>Sigma-Aldrich</td><td>517127</td><td></td></tr><tr><td>Ethyl alcohol, &amp;ge;99.5%</td><td>Sigma-Aldrich</td><td>459844</td><td></td></tr><tr><td>Formaldehyde solution, 37 wt. % in H&lt;sub&gt;2&lt;/sub&gt;O</td><td>Sigma-Aldrich</td><td>252549</td><td></td></tr><tr><td>Graphitized Carbon black, &gt;99.95%</td><td>Sigma-Aldrich</td><td>699632</td><td></td></tr><tr><td>Iron(III) chloride (FeCl&lt;sub&gt;3&lt;/sub&gt;), 97%</td><td>Sigma-Aldrich</td><td>157740</td><td></td></tr><tr><td>Kapton polyimide tubing</td><td>Cole-Parmer</td><td>EW-95820-09</td><td></td></tr><tr><td>Kapton polymide tape</td><td>Cole-Parmer</td><td>EW-08277-80</td><td></td></tr><tr><td>Kapton window film</td><td>SPEX Sample Prep</td><td>3511</td><td></td></tr><tr><td>Lithium Chip (99.9% Lithium)</td><td>MTI Corporation</td><td>EQ-Lib-LiC25</td><td></td></tr><tr><td>Lithium trifluoromethanesulfonate (LiCF&lt;sub&gt;3&lt;/sub&gt;SO&lt;sub&gt;3&lt;/sub&gt;)</td><td>Sigma-Aldrich</td><td>481548</td><td></td></tr><tr><td>Palladium hexafluoroacetylacetonate (Pd(hfac)&lt;sub&gt;2&lt;/sub&gt;), 99.9%</td><td>Aldrich</td><td>401471</td><td></td></tr><tr><td>Poly(vinylidene fluoride) (PVDF)</td><td>Aldrich</td><td>182702</td><td></td></tr><tr><td>Potassium permanganate (KMnO&lt;sub&gt;4&lt;/sub&gt;), &amp;ge;99.0%&amp;nbsp;</td><td>Sigma-Aldrich</td><td>223468</td><td></td></tr><tr><td>Sodium hydroxide (NaOH), &amp;ge;97.0%</td><td>Sigma-Aldrich</td><td>221465</td><td></td></tr><tr><td>Tetraethylene glycol dimethyl ether (TEGDME), &amp;ge;99%</td><td>Aldrich</td><td>172405</td><td></td></tr><tr><td>Toray 030 carbon paper</td><td>ElectroChem Inc.</td><td>590637</td><td></td></tr></tbody></table>

protocol of electrochemical test and characterization of aprotic li-o2 battery

We demonstrate a method for electrochemical testing of an aprotic Li-O2 battery. An aprotic Li-O2 battery is made of a Li-metal anode, an aprotic electrolyte, and an O2-breathing cathode. The aprotic electrolyte is a solution of lithium salt with aprotic solvent; and porous carbon is commonly used as the cathode substrate. To improve the performance, an electrocatalyst is deposited onto the porous carbon substrate by certain deposition methods, such as atomic layer deposition (ALD) and wet-chemistry reaction. The as-prepared cathode materials are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray absorption near edge structure (XANES). A Swagelok-type cell, sealed in a glass chamber filled with pure O2, is used for the electrochemical test on a battery test system. The cells are tested under either capacity-controlled mode or voltage controlled mode. The reaction products are investigated by electron microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, and Raman spectroscopy to study the possible pathway of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). This protocol demonstrates a systematic and efficient arrangement of routine tests of the aprotic Li-O2 battery, including the electrochemical test and characterization of battery materials.

Figure 1a shows the setup of the Swagelok-type cell of the Li-O2 battery test. A piece of lithium film is placed on a stainless steel rod at the anode end. The porous cathode is open to pure O2 through an aluminum tube. Glass fiber is used as a separator and an absorber of aprotic electrolyte; and Al-mesh is used as a current-collector. The whole Swagelok-type cell is sealed in a glass chamber filled with ultra-high purity oxygen. For in-depth study, multiple characterization methods are applied to examine the battery system, including the as-prepared electrode materials and the reaction products. SEM and TEM images present the microstructure of the samples. SEM images of the carbon powder before (Figure 1c) and after (Figure 1d) the catalyst loading demonstrate a well preservation of the porous surface structure. TEM images (Figure 1e) shows the electrocatalyst nanoparticles uniformly distribute on the carbon substrate; and well crystallized nanoparticles are shown in the high-resolution TEM image in Figure 1f. Although electron microscopy images show the detail morphology and structure of the electrocatalysts, other X-ray based characterization techniques can provide more information on their chemical composition and valance state. As shown in Figure 1b,13 XANES spectra, which are applied to determine the valence states, show that the electrocatalyst nanoparticles are partly oxidized due to the preparation of cathodes in air.
As-prepared cathode materials are tested in Swagelok-type cells in a voltage window of 2.2-4.5 V (vs Li+/Li). Typical voltage profiles for discharge and discharge-charge cycles are shown in Figure 2a and b. With the presence of the electrocatalyst loaded by ALD, the discharge specific capacity increased to over 4,000 mAh/g when the cell is discharged to 2.2 V, compared to that of the cathode without the electrocatalysts (905 mAh/g). The charge potential reduced to 3.4 V when the cell capacity is controlled at 500 mAh/g (Figure 2b), which are significant improvements comparing with charge potential of 4 V (Figure 2b) for bare carbon cathodes. To better evaluate the battery performance and understand the electrochemical reaction mechanism, the samples at different discharge/charge stages are subjected to the characterization using multiple advanced techniques. In the SEM image of discharged cathode as shown in Figure 2c, the discharge products have the toroidal shape, which are widely accepted as the primary morphology of Li2O2 in a Li-O2 cell.15,52 XRD pattern is used as a direct evidence to identify crystalline products. There are only peaks of Li2O2 and carbon in the XRD pattern of the discharged cathode (Figure 2d), suggesting that the side reactions are minimized in the cell.
XPS and Raman spectra are used to identify the surface composition on electrodes at different charge/discharge status. According to the XPS spectra (Figure 3a), Li2O2 and LiOH form on the cathode surface after discharging; and by charging, Li2O2 is reduced but the irreversible product LiOH remains on the surface. A slight amount of LiO2, an intermediate product of the one-electron transfer ORR, is detected by Raman spectroscopy (Figure 3b). LiO2 is metastable due to its easy disproportionation, which makes only detected by surface-sensitive characterization technique like Raman spectroscopy. The vibration signal of O-H and C=O bond in the FT-IR spectra (Figure 3c and d) indicates the presence of the ether electrolyte as well as other hydroxide, carbonate, or carbonyl species on the surface of Li anode or the glass fiber separator, which form in the side reactions such as the electrolyte decomposition and oxygen crossover effect.
<img alt="Figure 1" src="/files/ftp_upload/53740/53740fig1.jpg" /> 
Figure 1. Swagelok-type cell and as-prepared materials. (a) Schematics of a Swagelok-type cell sealed in a glass chamber. (b) Pd K-edge XANES spectra of the as-prepared cathode material, reprinted from ref. 13. (c, d) SEM images of the carbon powder before and after electrocatalyst loading, respectively. (e, f) TEM and HRTEM images of the carbon powder with electrocatalyst, respectively. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53740/53740fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/53740/53740fig2.jpg" /> 
Figure 2. Voltage Profiles of the discharge/charge process and characterization of the discharged cathodes. (a, b) Voltage profile of a discharge to 2.2 V and a capacity-controlled discharge-charge cycle, respectively. (c, d) SEM image and high-energy XRD pattern of the cathode discharged in Swagelok-type Li-O2 battery, respectively. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53740/53740fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/53740/53740fig3.jpg" /> 
Figure 3. Characterization results. (a) XPS spectra of Li 1s peaks at different charge/ discharge status, reprinted from ref. 13. (b) Raman spectra of the carbon cathodes discharged to 2.5 V. (c, d) FTIR spectra of the anode and separator after discharge-charge cycles, respectively. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53740/53740fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Protocol of Electrochemical Test and Characterization of Aprotic Li-O2 Battery at JoVE.com

Protocol of Electrochemical Test and Characterization of Aprotic Li-O2 Battery

A protocol for the electrochemical testing of an aprotic Li-O2 battery with the preparation of electrodes and electrolytes and an introduction of the frequently used methods of characterization is presented here.

Protocol of Electrochemical Test and Characterization of Aprotic Li-O2 Battery

We demonstrate a method for electrochemical testing of an aprotic Li-O2 battery. An aprotic Li-O2 battery is made of a Li-metal anode, an aprotic ...

protocol-electrochemical-test-characterization-aprotic-li-o2

Nanyang Technological University

Research

JoVE Journal

Engineering

11.4K Views.  Argonne National Laboratory. A protocol for the electrochemical testing of an aprotic Li-O2 battery with the preparation of electrodes and electrolytes and an introduction of the frequently used methods of characterization is presented here. 

Video: Protocol of Electrochemical Test and Characterization of Aprotic Li-O2 Battery

Construction and Testing of Coin Cells of Lithium Ion Batteries

Rechargeable lithium ion batteries have wide applications in electronics, where customers always demand more capacity and longer lifetime. Lithium ion batteries have also been considered to be used in electric and hybrid vehicles1 or even electrical grid stabilization systems2. All these applications simulate a dramatic increase in the research and development of battery materials3-7, including new materials3,8, doping9, nanostructuring10-13, coatings or surface modifications14-17 and novel binders18. Consequently, an increasing number of physicists, chemists and materials scientists have recently ventured into this area. Coin cells are widely used in research laboratories to test new battery materials; even for the research and development that target large-scale and high-power applications, small coin cells are often used to test the capacities and rate capabilities of new materials in the initial stage. 
 In 2010, we started a National Science Foundation (NSF) sponsored research project to investigate the surface adsorption and disordering in battery materials (grant no. DMR-1006515). In the initial stage of this project, we have struggled to learn the techniques of assembling and testing coin cells, which cannot be achieved without numerous help of other researchers in other universities (through frequent calls, email exchanges and two site visits). Thus, we feel that it is beneficial to document, by both text and video, a protocol of assembling and testing a coin cell, which will help other new researchers in this field. This effort represents the "Broader Impact" activities of our NSF project, and it will also help to educate and inspire students.
In this video article, we document a protocol to assemble a CR2032 coin cell with a LiCoO2 working electrode, a Li counter electrode, and (the mostly commonly used) polyvinylidene fluoride (PVDF) binder. To ensure new learners to readily repeat the protocol, we keep the protocol as specific and explicit as we can. However, it is important to note that in specific research and development work, many parameters adopted here can be varied. First, one can make coin cells of different sizes and test the working electrode against a counter electrode other than Li. Second, the amounts of C black and binder added into the working electrodes are often varied to suit the particular purpose of research; for example, large amounts of C black or even inert powder were added to the working electrode to test the "intrinsic" performance of cathode materials14. Third, better binders (other than PVDF) have also developed and used18. Finally, other types of electrolytes (instead of LiPF6) can also be used; in fact, certain high-voltage electrode materials will require the uses of special electrolytes7.

A protocol to construct and test coin cells of lithium ion batteries is described. The specific procedures of making a working electrode, preparing a counter electrode, assembling a cell inside a glovebox and testing the cell are presented.

Rechargeable lithium ion batteries have wide applications in electronics, where customers always demand more capacity and longer lifetime.  Lithium ion ...

Characterization of Electrode Materials for Lithium Ion and Sodium Ion Batteries Using Synchrotron Radiation Techniques

Intercalation compounds such as transition metal oxides or phosphates are the most commonly used electrode materials in Li-ion and Na-ion batteries. During insertion or removal of alkali metal ions, the redox states of transition metals in the compounds change and structural transformations such as phase transitions and/or lattice parameter increases or decreases occur. These behaviors in turn determine important characteristics of the batteries such as the potential profiles, rate capabilities, and cycle lives. The extremely bright and tunable x-rays produced by synchrotron radiation allow rapid acquisition of high-resolution data that provide information about these processes. Transformations in the bulk materials, such as phase transitions, can be directly observed using X-ray diffraction (XRD), while X-ray absorption spectroscopy (XAS) gives information about the local electronic and geometric structures (e.g.&#160;changes in redox states and bond lengths). In situ experiments carried out on operating cells are particularly useful because they allow direct correlation between the electrochemical and structural properties of the materials. These experiments are time-consuming and can be challenging to design due to the reactivity and air-sensitivity of the alkali metal anodes used in the half-cell configurations, and/or the possibility of signal interference from other cell components and hardware. For these reasons, it is appropriate to carry out ex situ experiments (e.g.&#160;on electrodes harvested from partially charged or cycled cells) in some cases. Here, we present detailed protocols for the preparation of both ex situ and in situ samples for experiments involving synchrotron radiation and demonstrate how these experiments are done.

We describe the use of synchrotron X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) techniques to probe details of intercalation/deintercalation processes in electrode materials for Li-ion and Na-ion batteries. Both in situ and ex situ experiments are used to understand structural behavior relevant to the operation of devices

Intercalation compounds such as transition metal oxides or phosphates are the most commonly used electrode materials in Li-ion and Na-ion batteries. ...

Failure Analysis of Batteries Using Synchrotron-based Hard X-ray Microtomography

Imaging morphological changes that occur during the lifetime of rechargeable batteries is necessary to understand how these devices fail. Since the advent of lithium-ion batteries, researchers have known that the lithium metal anode has the highest theoretical energy density of any anode material. However, rechargeable batteries containing a lithium metal anode are not widely used in consumer products because the growth of lithium dendrites from the anode upon charging of the battery causes premature cell failure by short circuit. Lithium dendrites can also form in commercial lithium-ion batteries with graphite anodes if they are improperly charged. We demonstrate that lithium dendrite growth can be studied using synchrotron-based hard X-ray microtomography. This non-destructive imaging technique allows researchers to study the growth of lithium dendrites, in addition to other morphological changes inside batteries, and subsequently develop methods to extend battery life.

Synchrotron-based hard X-ray microtomography is used to image the electrochemical growth of dendrites from a lithium metal electrode through a solid polymer electrolyte membrane.

Imaging morphological changes that occur during the lifetime of rechargeable batteries is necessary to understand how these devices fail. Since the advent ...

Non-aqueous Electrode Processing and Construction of Lithium-ion Coin Cells

Research into new and improved materials to be utilized in lithium-ion batteries (LIB) necessitates an experimental counterpart to any computational analysis. Testing of lithium-ion batteries in an academic setting has taken on several forms, but at the most basic level lies the coin cell construction. In traditional LIB electrode preparation, a multi-phase slurry composed of active material, binder, and conductive additive is cast out onto a substrate. An electrode disc can then be punched from the dried sheet and used in the construction of a coin cell for electrochemical evaluation. Utilization of the potential of the active material in a battery is critically dependent on the microstructure of the electrode, as an appropriate distribution of the primary components are crucial to ensuring optimal electrical conductivity, porosity, and tortuosity, such that electrochemical and transport interaction is optimized. Processing steps ranging from the combination of dry powder, wet mixing, and drying can all critically affect multi-phase interactions that influence the microstructure formation. Electrochemical probing necessitates the construction of electrodes and coin cells with the utmost care and precision. This paper aims at providing a step-by-step guide of non-aqueous electrode processing and coin cell construction for lithium-ion batteries within an academic setting and with emphasis on deciphering the influence of drying and calendaring.

Non-aqueous electrode processing is central to the construction of coin cells and the evaluation of new electrode chemistries for lithium-ion batteries. A step-by-step guide to the basic practices needed as an electrochemical engineer working with batteries in an academic experimental setting is furnished.

Research into new and improved materials to be utilized in lithium-ion batteries (LIB) necessitates an experimental counterpart to any computational ...

A Protocol for Electrochemical Evaluations and State of Charge Diagnostics of a Symmetric Organic Redox Flow Battery

Redox flow batteries have been considered as one of the most promising stationary energy storage solutions for improving the reliability of the power grid and deployment of renewable energy technologies. Among the many flow battery chemistries, non-aqueous flow batteries have the potential to achieve high energy density because of the broad voltage windows of non-aqueous electrolytes. However, significant technical hurdles exist currently limiting non-aqueous flow batteries to demonstrate their full potential, such as low redox concentrations, low operating currents, under-explored battery status monitoring, etc. In an attempt to address these limitations, we recently reported a non-aqueous flow battery based on a highly soluble, redox-active organic nitronyl nitroxide radical compound, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO). This redox material exhibits an ambipolar electrochemical property, and therefore can serve as both anolyte and catholyte redox materials to form a symmetric flow battery chemistry. Moreover, we demonstrated that Fourier transform infrared (FTIR) spectroscopy could measure the PTIO concentrations during the PTIO flow battery cycling and offer reasonably accurate detection of the battery state of charge (SOC), as cross-validated by electron spin resonance (ESR) measurements. Herein we present a video protocol for the electrochemical evaluation and SOC diagnosis of the PTIO symmetric flow battery. With a detailed description, we experimentally demonstrated the route to achieve such purposes. This protocol aims to spark more interests and insights on the safety and reliability in the field of non-aqueous redox flow batteries.

We present the protocols for electrochemically evaluating a symmetric non-aqueous organic redox flow battery and for diagnosing its state of charge using FTIR.

Redox flow batteries have been considered as one of the most promising stationary energy storage solutions for improving the reliability of the power grid ...

Chemistry

Synthesis of Ionic Liquid Based Electrolytes, Assembly of Li-ion Batteries, and Measurements of Performance at High Temperature

The chemical instability of the traditional electrolyte remains a safety issue in widely used energy storage devices such as Li-ion batteries. Li-ion batteries for use in devices operating at elevated temperatures require thermally stable and non-flammable electrolytes. Ionic liquids (ILs), which are non-flammable, non-volatile, thermally stable molten salts, are an ideal replacement for flammable and low boiling point organic solvent electrolytes currently used today. We herein describe the procedures to: 1) synthesize mono- and di-phosphonium ionic liquids paired with chloride or bis(trifluoromethane)sulfonimide (TFSI) anions; 2) measure the thermal properties and stability of these ionic liquids by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA); 3) measure the electrochemical properties of the ionic liquids by cyclic voltammetry (CV); 4) prepare electrolytes containing lithium bis(trifluoromethane)sulfonamide; 5) measure the conductivity of the electrolytes as a function of temperature; 6) assemble a coin cell battery with two of the electrolytes along with a Li metal anode and LiCoO2 cathode; and 7) evaluate battery performance at 100 &#176;C. We additionally describe the challenges in execution as well as the insights gained from performing these experiments.

Here, we describe protocols to prepare phosphonium-based ionic liquid and lithium bis(trifluoromethane)sulfonimide salt electrolytes, and assemble a non-flammable and high temperature functioning lithium-ion coin cell battery.

The chemical instability of the traditional electrolyte remains a safety issue in widely used energy storage devices such as Li-ion batteries. Li-ion ...

Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing

Solid-state electrolytes are a promising replacement for current organic liquid electrolytes, enabling higher energy densities and improved safety of lithium-ion (Li-ion) batteries. However, a number of setbacks prevent their integration into commercial devices. The main limiting factor is due to nanoscale phenomena occurring at the electrode/electrolyte interfaces, ultimately leading to degradation of battery operation. These key problems are highly challenging to observe and characterize as these batteries contain multiple buried interfaces. One approach for direct observation of interfacial phenomena in thin film batteries is through the fabrication of electrochemically active nanobatteries by a focused ion beam (FIB). As such, a reliable technique to fabricate nanobatteries was developed and demonstrated in recent work. Herein, a detailed protocol with a step-by-step process is presented to enable the reproduction of this nanobattery fabrication process. In particular, this technique was applied to a thin film battery consisting of LiCoO2/LiPON/a-Si, and has further been previously demonstrated by in situ cycling within a transmission electron microscope.

Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing

A protocol for the fabrication of electrochemically active LiPON-based solid-state lithium-ion nanobatteries using a focused ion beam is presented.

Solid-state electrolytes are a promising replacement for current organic liquid electrolytes, enabling higher energy densities and improved safety of ...

In Situ Lithiated Reference Electrode: Four Electrode Design for In-operando Impedance Spectroscopy

Extending operating voltage of Li-ion batteries results in higher energy output from these devices. High voltages, however, may trigger or accelerate multiple processes responsible for long-term performance decay. Given the complexity of physical processes occurring inside the cell, it is often challenging to achieve a full understanding of the root causes of this performance degradation. This difficulty arises in part from the fact that any electrochemical measurement of a battery will return the combined contributions of all components in the cell. Incorporation of a reference electrode can solve part of the problem, as it allows the electrochemical reactions of the cathode and the anode to be individually probed. A variation in the voltage range experienced by the cathode, for example, can indicate alterations in the pool of cyclable lithium ions in the full-cell. The structural evolution of the many interphases existing in the battery can also be monitored, by measuring the contributions of each electrode to the overall cell impedance. Such wealth of information amplifies the reach of diagnostic analysis in Li-ion batteries and provides valuable input to the optimization of individual cell components. In this work, we introduce the design of a test cell able to accommodate multiple reference electrodes, and present reference electrodes that are appropriate for each specific type of measurement, detailing the assembly process in order to maximize the accuracy of the experimental results.

The incorporation of reference electrodes in a Li-ion battery provides valuable information to elucidate degradation mechanisms at high voltages. In this article, we present a cell design that accommodates multiple reference electrodes, along with the assembly steps to assure maximum accuracy of the data obtained in electrochemical measurements.

Extending operating voltage of Li-ion batteries results in higher energy output from these devices. High voltages, however, may trigger or accelerate ...

The Effect of Charging and Discharging Lithium Iron Phosphate-graphite Cells at Different Temperatures on Degradation

The effect of charging and discharging lithium iron phosphate-graphite cells at different temperatures on their degradation is evaluated systematically. The degradation of the cells is assessed by using 10 charging and discharging temperature permutations ranging from -20 &#176;C to 30 &#176;C. This allows an analysis of the effect of charge and discharge temperatures on aging, and their associations. A total of 100 charge/discharge cycles were carried out. Every 25 cycles a reference cycle was performed to assess the reversible and irreversible capacity degradation. A multi-factor analysis of variance was used, and the experimental results were fitted showing: i) a quadratic relationship between the rate of degradation and the temperature of charge, ii) a linear relationship with the temperature of discharge, and iii) a correlation between the temperature of charge and discharge. It was found that the temperature combination for charging at +30 &#176;C and discharging at -5 &#176;C led to the highest rate of degradation. On the other hand, the cycling in a temperature range from -20 &#176;C to 15 &#176;C (with various combinations of temperatures of charge and discharge), led to a much lower degradation. Additionally, when the temperature of charge is 15 &#176;C, it was found that the degradation rate is nondependent on the temperature of discharge.

This article describes the effect of dissimilar charging/discharging temperatures on the degradation of lithium iron phosphate-graphite pouch cells, aiming at simulating close to real case scenarios. In total, 10 temperature combinations are investigated in the range -20 to 30 &#176;C in order to analyze the impact of temperature on degradation.

The effect of charging and discharging lithium iron phosphate-graphite cells at different temperatures on their degradation is evaluated systematically. ...

Three-electrode Coin Cell Preparation and Electrodeposition Analytics for Lithium-ion Batteries

As lithium-ion batteries find use in high energy and power applications, such as in electric and hybrid-electric vehicles, monitoring the degradation and subsequent safety issues becomes increasingly important. In a Li-ion cell setup, the voltage measurement across the positive and negative terminals inherently includes the effect of the cathode and anode which are coupled and sum to the total cell performance. Accordingly, the ability to monitor the degradation aspects associated with a specific electrode is extremely difficult because the electrodes are fundamentally coupled. A three-electrode setup can overcome this problem. By introducing a third (reference) electrode, the influence of each electrode can be decoupled, and the electrochemical properties can be measured independently. The reference electrode (RE) must have a stable potential that can then be calibrated against a known reference, for example, lithium metal. The three-electrode cell can be used to run electrochemical tests such as cycling, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). Three-electrode cell EIS measurements can elucidate the contribution of individual electrode impedance to the full cell. In addition, monitoring the anode potential allows the detection of electrodeposition due to lithium plating, which can cause safety concerns. This is especially important for the fast charging of Li-ion batteries in electric vehicles. In order to monitor and characterize the safety and degradation aspects of an electrochemical cell, a three-electrode setup can prove invaluable. This paper aims to provide a guide to constructing a three-electrode coin cell setup using the 2032-coin cell architecture, which is easy to produce, reliable, and cost-effective.

Three-electrode cells are useful in studying the electrochemistry of lithium-ion batteries. Such an electrochemical setup allows the phenomena associated with the cathode and anode to be decoupled and examined independently. Here, we present a guide for construction and use of a three-electrode coin cell with emphasis on lithium plating analytics.

As lithium-ion batteries find use in high energy and power applications, such as in electric and hybrid-electric vehicles, monitoring the degradation and ...

Protocol of Electrochemical Test and Characterization of Aprotic Li-O₂ Battery

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