The authors acknowledge financial support from the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy.

1. Stripping Copper/Tin Wires
<ol>
	<li>Heat commercially obtained stripping solution.
	<ol>
		<li>Pour commercial industrial grade stripping solution into a stainless steel beaker (7.6 cm in diameter and 8.5 cm in height) to a depth of about 5 mm from the bottom. Place the beaker on to a hot plate. Begin heating a slow rate of about 5 &#176;C/min.</li>
		<li>Immerse a portable thermocouple into the solution to closely monitor the temperature ramp of the solution and adjust the heating rate of the hot plate to maintain...

<ol>
	<li>Ma, D., Cao, Z., Hu, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Si-Based+Anode+Materials+for+Li-Ion+Batteries:+A+Mini+Review.">Si-Based Anode Materials for Li-Ion Batteries: A Mini Review.</a> Nano-Micro Letters. 6 (4), (2014).</li><li>Jung, S. -. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Understanding+the+Degradation+Mechanisms+of+LiNi0.5Co0.2Mn0.3O2+Cathode+Material+in+Lithium+Ion+Batteries.">Understanding the Degradation Mechanisms of LiNi0.5Co0.2Mn0.3O2 Cathode Material in Lithium Ion Batteries.</a> Advanced Energy Materials. 4 (1), 1300787 (2014).</li><li>Streipert, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+LiPF6+on+the+Aluminum+Current+Collector+Dissolution+in+High+Voltage+Lithium+Ion+Batteries+after+Long-Term+Charge/Discharge+Experiments.">Influence of LiPF6 on the Aluminum Current Collector Dissolution in High Voltage Lithium Ion Batteries after Long-Term Charge/Discharge Experiments.</a> Journal of The Electrochemical Society. 164 (7), A1474-A1479 (2017).</li><li>Gilbert, J. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cycling+Behavior+of+NCM523/Graphite+Lithium-Ion+Cells+in+the+3-4.4+V+Range:+Diagnostic+Studies+of+Full+Cells+and+Harvested+Electrodes.">Cycling Behavior of NCM523/Graphite Lithium-Ion Cells in the 3-4.4 V Range: Diagnostic Studies of Full Cells and Harvested Electrodes.</a> Journal of The Electrochemical Society. 164 (1), A6054-A6065 (2017).</li><li>Shim, J., Kostecki, R., Richardson, T., Song, X., Striebel, K. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrochemical+analysis+for+cycle+performance+and+capacity+fading+of+a+lithium-ion+battery+cycled+at+elevated+temperature.">Electrochemical analysis for cycle performance and capacity fading of a lithium-ion battery cycled at elevated temperature.</a> Journal of Power Sources. 112 (1), 222-230 (2002).</li><li>Peled, E., Menkin, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Review-SEI:+Past,+Present+and+Future.">Review-SEI: Past, Present and Future.</a> Journal of The Electrochemical Society. 164 (7), A1703-A1719 (2017).</li><li>Nadimpalli, S. P. V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantifying+capacity+loss+due+to+solid-electrolyte-interphase+layer+formation+on+silicon+negative+electrodes+in+lithium-ion+batteries.">Quantifying capacity loss due to solid-electrolyte-interphase layer formation on silicon negative electrodes in lithium-ion batteries.</a> Journal of Power Sources. 215, 145-151 (2012).</li><li>Ender, M., Weber, A., Ellen, I. -. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+Three-Electrode+Setups+for+AC-Impedance+Measurements+on+Lithium-Ion+Cells+by+FEM+simulations.">Analysis of Three-Electrode Setups for AC-Impedance Measurements on Lithium-Ion Cells by FEM simulations.</a> Journal of The Electrochemical Society. 159 (2), A128-A136 (2011).</li><li>Zhou, J., Notten, P. H. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+Reliable+Lithium+Microreference+Electrodes+for+Long-Term+In+Situ+Studies+of+Lithium-Based+Battery+Systems.">Development of Reliable Lithium Microreference Electrodes for Long-Term In Situ Studies of Lithium-Based Battery Systems.</a> Journal of The Electrochemical Society. 151 (12), A2173-A2179 (2004).</li><li>Klink, S., H&#246;che, D., La Mantia, F., Schuhmann, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=FEM+modelling+of+a+coaxial+three-electrode+test+cell+for+electrochemical+impedance+spectroscopy+in+lithium+ion+batteries.">FEM modelling of a coaxial three-electrode test cell for electrochemical impedance spectroscopy in lithium ion batteries.</a> Journal of Power Sources. 240 (Supplement C), 273-280 (2013).</li><li>B&#252;nzli, C., Kaiser, H., Nov&#225;k, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Important+Aspects+for+Reliable+Electrochemical+Impedance+Spectroscopy+Measurements+of+Li-Ion+Battery+Electrodes.">Important Aspects for Reliable Electrochemical Impedance Spectroscopy Measurements of Li-Ion Battery Electrodes.</a> Journal of The Electrochemical Society. 162 (1), A218-A222 (2015).</li><li>Delacourt, C., Ridgway, P. L., Srinivasan, V., Battaglia, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurements+and+Simulations+of+Electrochemical+Impedance+Spectroscopy+of+a+Three-Electrode+Coin+Cell+Design+for+Li-Ion+Cell+Testing.">Measurements and Simulations of Electrochemical Impedance Spectroscopy of a Three-Electrode Coin Cell Design for Li-Ion Cell Testing.</a> Journal of The Electrochemical Society. 161 (9), A1253-A1260 (2014).</li><li>Hoshi, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optimization+of+reference+electrode+position+in+a+three-electrode+cell+for+impedance+measurements+in+lithium-ion+rechargeable+battery+by+finite+element+method.">Optimization of reference electrode position in a three-electrode cell for impedance measurements in lithium-ion rechargeable battery by finite element method.</a> Journal of Power Sources. 288 (Supplement C), 168-175 (2015).</li><li>La Mantia, F., Wessells, C. D., Deshazer, H. D., Cui, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reliable+reference+electrodes+for+lithium-ion+batteries.">Reliable reference electrodes for lithium-ion batteries.</a> Electrochemistry Communications. 31 (Supplement C), 141-144 (2013).</li><li>Aurbach, D., Zinigrad, E., Cohen, Y., Teller, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+short+review+of+failure+mechanisms+of+lithium+metal+and+lithiated+graphite+anodes+in+liquid+electrolyte+solutions.">A short review of failure mechanisms of lithium metal and lithiated graphite anodes in liquid electrolyte solutions.</a> Solid State Ionics. 148 (3), 405-416 (2002).</li><li>Klett, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrode+Behavior+RE-Visited:+Monitoring+Potential+Windows,+Capacity+Loss,+and+Impedance+Changes+in+Li1.03(Ni0.5Co0.2Mn0.3)0.97O2/Silicon-Graphite+Full+Cells.">Electrode Behavior RE-Visited: Monitoring Potential Windows, Capacity Loss, and Impedance Changes in Li1.03(Ni0.5Co0.2Mn0.3)0.97O2/Silicon-Graphite Full Cells.</a> Journal of The Electrochemical Society. 163 (6), A875-A887 (2016).</li><li>Zhang, W. -. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+review+of+the+electrochemical+performance+of+alloy+anodes+for+lithium-ion+batteries.">A review of the electrochemical performance of alloy anodes for lithium-ion batteries.</a> Journal of Power Sources. 196 (1), 13-24 (2011).</li><li>Klett, M., Gilbert, J. A., Pupek, K. Z., Trask, S. E., Abraham, D. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Layered+Oxide,+Graphite+and+Silicon-Graphite+Electrodes+for+Lithium-Ion+Cells:+Effect+of+Electrolyte+Composition+and+Cycling+Windows.">Layered Oxide, Graphite and Silicon-Graphite Electrodes for Lithium-Ion Cells: Effect of Electrolyte Composition and Cycling Windows.</a> Journal of The Electrochemical Society. 164 (1), A6095-A6102 (2017).</li><li>Ma, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Guide+to+Ethylene+Carbonate-Free+Electrolyte+Making+for+Li-Ion+Cells.">A Guide to Ethylene Carbonate-Free Electrolyte Making for Li-Ion Cells.</a> Journal of The Electrochemical Society. 164 (1), A5008-A5018 (2017).</li><li>Michan, A. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fluoroethylene+Carbonate+and+Vinylene+Carbonate+Reduction:+Understanding+Lithium-Ion+Battery+Electrolyte+Additives+and+Solid+Electrolyte+Interphase+Formation.">Fluoroethylene Carbonate and Vinylene Carbonate Reduction: Understanding Lithium-Ion Battery Electrolyte Additives and Solid Electrolyte Interphase Formation.</a> Chemistry of Materials. 28 (22), 8149-8159 (2016).</li><li>Rahmoun, A., Loske, M., Rosin, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+the+Impedance+of+Lithium-ion+Batteries+Using+Methods+of+Digital+Signal+Processing.">Determination of the Impedance of Lithium-ion Batteries Using Methods of Digital Signal Processing.</a> Energy Procedia. 46, 204-213 (2014).</li><li>Jiang, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrochemical+Impedance+Spectra+for+Lithium-ion+Battery+Ageing+Considering+the+Rate+of+Discharge+Ability.">Electrochemical Impedance Spectra for Lithium-ion Battery Ageing Considering the Rate of Discharge Ability.</a> Energy Procedia. 105, 844-849 (2017).</li><li>Andre, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+high-power+lithium-ion+batteries+by+electrochemical+impedance+spectroscopy.+I.+Experimental+investigation.">Characterization of high-power lithium-ion batteries by electrochemical impedance spectroscopy. I. Experimental investigation.</a> Journal of Power Sources. 196 (12), 5334-5341 (2011).</li><li>Li, S. E., Wang, B., Peng, H., Hu, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+electrochemistry-based+impedance+model+for+lithium-ion+batteries.">An electrochemistry-based impedance model for lithium-ion batteries.</a> Journal of Power Sources. 258, 9-18 (2014).</li></ol>

Figure 2a is the voltage profile of the full cell while Figure 2b and 2c show voltage profiles corresponding to the positive and the negative electrode vs Li/Li+ couple while the full cell is cycled between 3 and 4.4 V. It can be seen that as the full cell scans between 3 and 4.4 V, the positive electrode experiences voltages between 3.65 V and 4.45 V and the negative electrode between 0.65 V and 0.05 V vs. Li/Li+ ...

The demand for high energy densities from Li-ion batteries (LIBs) is driving research towards understanding fundamental factors that limit Li- ion cell performance1. High voltage operation of cells containing a new generation of layered transition metal oxide cathodes, graphite anodes and organic carbonate electrolytes is associated with several parasitic reactions2,3. Some of these reactions consume Li - ion inventory and often result in significant impedance rise of the cell4,5,6,7. Loss of Li- ion also results in a net shift of the surface potentials of electrodes. Monitoring of voltage changes on an individual electrode in a full cell versus a reference electrode (RE) can be performed in commercial 3-electrode cell designs8,9,10,11,12,13,14. Information pertaining to voltage profiles and the impedance changes on individual electrodes promotes a deeper understanding of the fundamental degradation mechanisms of a LIB. Conventional 3-electrode cells contain Li metal as a reference electrode, which facilitates a distinct understanding of the electrochemical processes at each electrode. Li-metal in contact with the organic electrolyte undergoes spontaneous surface modification and the contribution of this surface layer on Li cannot be quantified15. Several 3-electrode configurations such as (a) T-model, (b) a micro-RE positioned coaxial to both the working and the counter electrode, (c) a coin cell with an RE at the back of the counter electrode, etc. have been proposed earlier. Most of these cell configurations have the RE positioned away from the cell sandwich, generating significant drift in the impedance data due to low conductivity of the electrolyte. It has been proven that a RE with a stable potential throughout the measurement must be stationed in the center of the sandwich to ensure reliable impedance data.
In order to address these discrepancies, we have designed a cell setup involving a fourth RE16. An ultra-thin Sn plated Cu wire is sandwiched in between the electrodes of a battery that can be electrochemically lithiated in situ to form a LixSn alloy. As Sn undergoes lithiation, the voltage of the reference wire drops and a completely lithiated wire has a potential close to 0 V vs. Li+/Li17. The lithiated composition has a potential comparable to Li metal and the metastable alloys facilitate a stable potential during the time period of the measurement. A Li metal exposed to the electrolyte is prone to electrolyte decomposition products forming surface layers. An EIS measurement to probe the impedance of individual electrodes by collecting spectra between one of the electrodes and the Li metal reference as coupled have not been reliable due to the contribution of these layers on the impedance. Although electrolyte reduction is inevitable also on the Li-Sn surface, an in situ lithiated reference wire has the following advantages: (a) no constant electrolyte decomposition products as the voltage is always above the decomposition potential of the electrolyte unless lithiated ,implying no loss of Li inventory in the system to interfacial layers; (b) layers formed during lithiation of the Sn wire are over a very small area, providing negligible contribution to the EIS data; and (c) the formed products degrade as the Sn wire loses Li and the potential of the wire increases, resulting in lithiation of fresh Sn wire during every lithiation and thus formation of very thin interfacial layers every time instead of increased thickness of these layers. Spectra recorded with these alloys as reference provide more accurate and reliable data of the electrode impedance. We conducted tests with standard 2032-type coin cells and 4-electrode RE cells to validate our design. Results from these tests and our interpretation of the data will be used as a representative result to explain the efficacy of our protocol. The 3-4.4 V cycling followed a standard protocol, which included formation cycles, aging cycles, and periodic AC impedance measurements during the cycling. The coin cell measurements provide valuable information on the parameters such as cycle life, capacity retention, AC impedance changes, etc. RE cells enable monitoring voltage changes and impedance rise on individual electrodes. Our mechanistic understanding into the capacity fade and impedance rise can provide guidelines for the development of electrolyte systems and understand contributions for capacity loss from each electrode during high-voltage cell operation.
Our cells contained Li1.03 (Ni0.5Co0.2Mn0.3)0.97O2 (denoted here as NMC532)-based positive electrodes, graphite-based negative electrodes (denoted here as Gr) and a 1.2 M solution of LiPF6 in Fluoroethylene Carbonate (FEC):Ethyl Methyl Carbonate (EMC) (5:95 w/w) as the electrolyte. The electrodes used in this study are standard electrodes fabricated at the Cell Analysis, Modeling and Prototyping (CAMP) Facility at Argonne National Laboratory. The positive electrode consists of NMC532, conductive carbon additive (C-45) and polyvinylidene fluoride (PVdF) binder in a weight ratio of 90:5:5 on a 20 &#181;m thick Al current collector. The negative electrode consists of graphite, mixed with C-45, and PVdF binder in a weight ratio of 92:2:6 on a 10 &#181;m thick Cu current collector. Circular discs of 5.08 cm diameter were punched from the electrode laminates and the separators were punched with a 7.62 cm die for use in fixtures with 7.62 cm inner diameter. These electrodes were dried at 120 &#176;C and the separators at 75 &#176;C in a vacuum oven for at least 12 h prior to the cell assembly. A schematic representation of the fixture design is represented in Figure 1. Large fixtures and electrodes ensure minimum inhomogeneities in current distributions per unit area, thus, providing the least distortions in the impedance spectra. The 3-4.4 V cycling followed a standard protocol, which included two formation cycles at a C/20 rate, 100 ageing cycles at a C/3 rate and two diagnostic cycles at C/20. All battery tests were conducted at 30 &#176;C. Electrochemical cycling data was measured using a battery cycler and the electrochemical impedance spectroscopy (EIS) is performed using a potentiostat system.

<table border="0" cellpadding="0" cellspacing="0" width="645">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Insulstrip 220</td>
			<td style="width:143px;">Ambion Corporation</td>
			<td style="width:119px;">081607-1</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Sodium Hydroxide (23 wt%)</td>
			<td style="width:143px;">Ambion Corporation</td>
			<td>1310-73-2</td>
			<td>Contents of Insulstrip 220</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Furfuryl Alcohol (10 wt%)</td>
			<td style="width:143px;">Ambion Corporation</td>
			<td style="width:119px;">98-00-0</td>
			<td>Contents of Insulstrip 220</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">NCM523</td>
			<td>TODA America</td>
			<td style="width:119px;">NM4100</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">C-45&#160;</td>
			<td>Timcal Inc.</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">polyvinylidene fluoride (PVdF)</td>
			<td>Sigma Aldrich</td>
			<td style="width:119px;">427152</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Sn over Cu wire</td>
			<td style="width:143px;">Kanthal</td>
			<td style="width:119px;">MELT # 24633</td>
			<td>Custom ordered</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Battery cycler</td>
			<td style="width:143px;">Maccor USA</td>
			<td style="width:119px;">Series 2300&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Potentiostat</td>
			<td style="width:143px;">Solartron Analytical</td>
			<td style="width:119px;">1470 E</td>
			<td></td>
		</tr>
	</tbody>
</table>

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.

Figure 2 is a representative profile of the voltages of individual electrodes with 1.2M LiPF6 in (FEC):EMC (5:95 w/w) as the electrolyte during the first and second cycles of formation. Figure 3 shows the EIS spectra of the cell after three formation cycles and at the end of the cycle life ageing protocol. The ability to re-lithiate the RE to obtain EIS data aids in precise tracking of the impedance changes in individu...

Watch this Scientific Journal Video about In Situ Lithiated Reference Electrode: Four Electrode Design for In-operando Impedance Spectroscopy at JoVE.com

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

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 demand for better performing lithium ion batteries is driving research towards understanding factors causing degradation. The method described here can precisely guage the behavior of individual battery components. The wealth of information that this technique provides amplifies the reach of diagnostic analysis in lithium ion batteries, and provides valuable input into the optimization of individual cell components.To begin, obtain a four centimeter wide seven centimeter long jig made of two millimeter thick copper wire. With flat loops to stabilize the jig at one end, and a handle at the other end. Then, pour about 23 milliliters of industrial grade stripping solution into a 7.6 centimeter diameter stainless steel beaker to obtain a solution depth of about five millimeters.Immerse a thermo couple in the solution, keeping the tip away from the bottom of the beaker. Start heating the beaker on a hot plate to 85 degrees celsius. While the solution heats, carefully wind 60 centimeters of 25.4 micron polyurethane coated tin plated copper wire length wise around the jig.Gently tape the ends of the wire to the handles. Once the solution reaches 85 degrees celsius, turn off the heat and place the jig vertically in the solution to immerse one side of the wrapped wire. Leave the jig in the solution for 15 seconds, and then rinse the wire and jig in deionized water for 15 seconds.Inspect the wire for exposed tin, which will appear as a silvery white material. Repeat the immersion in stripping solution and rinsing until one side of the wrapped wire has been completely stripped to the tin layer. Be careful not to etch away the plated tin.Then, rinse the jig and wire in deionized water and allow them to dry in air at room temperature. Once dry, cut the wire in the center of each stripped area to obtain approximately 10 centimeter long wires with exposed tin plated ends. To begin preparing a reference wire, cut about 10 centimeters of insulated two millimeter wide electrical circuit wire.Strip about two centimeters of insulation from each end of the wire. Then, gently lay one stripped end of a tin plated copper wire on the stripped electrical wire. Solder the junction to form an electrical contact between the wires.Confirm that the resistance across the newly formed tin reference electrode is between six and eight ohms. Assemble a second reference electrode with an exposed copper end in the same way, and bring the wires into an argon filled glove box. Next, cut a piece of 200 micron thick lithium metal no larger than five millimeters by five millimeters, and place it on a PTFE platform.Use a roller covered with polymer tape to flatten the metal to 25 microns thick. Then, bend the metal into a U shape, and lay the exposed tip of the copper wire in the bend. Carefully press the lithium around the wire to completely encapsulate the exposed copper.This will be the lithium metal reference electrode. Place an anode in a lithium cell fixture so that the center of the electrode is slightly offset from the center of the fixture. Place an insulating separator made of a trilayer of polyethylene and polypropylene on the anode.Use a PTFE sweep to gently remove trapped air bubbles between the anode and the separator. Ensure that the separator is firmly seated in the fixture. Then, apply a 10 microliter drop of the electrolyte on the separator two millimeters form the edge of the anode.Apply a second drop over the center of the anode. Position the exposed tin plated tip of the tin reference electrode in the drop at the center of the anode. Position the tip of the lithium reference electrode in the drop two millimeters away from the anode.Apply another 10 microliter drop of electrolyte to the lithium encapsulated tip, and remove air bubbles between the lithium metal and the separator with the sweep. Then, apply 400 microliters of electrolyte to the separator. Place a second separator on the assembly so that the reference electrode wires are sandwiched between the separators.To avoid applying excessive tension to the wires, leave some slack in the wires between the separators. Remove air bubbles between the separators with the sweep. Then, wet a cathode with 400 microliters of the electrolyte solution.Place the cathode on the upper separator aligned with the anode. Carefully place a stainless steel spacer on the cathode without disturbing the alignment of the cell stack. Put two stainless steel wave springs on the spacer to accommodate cell volume changes and pressure build up, and then close the fixture.Connect the cathode and anode of the battery cell to the corresponding battery cycler terminals. Connect the lithium reference electrode to the auxiliary terminal. Generate voltage profiles for each electrode with respect to the lithium couple.Apply a constant current of five microamperes for six hours between the cathode and the tin reference electrode with an upper voltage cutoff of four volts to electrochemically lithiate the tin. When finished, disconnect the cell from the battery cycler terminals, and allow the lithiated wire to equilibrate for two hours. To confirm successful lithiation, connect the lithium reference electrode to the auxiliary terminal, and the lithiated tin electrode to the negative terminal.The potential difference between them should be close to zero volts. To obtain spectra for the full cell, first, connect the negative voltage and current terminals of a potentia stat to the anode, and the positive terminals to the cathode. Cycle the electrochemical couple over a small voltage amplitude below five millivolts using alternating current or varying frequencies, with the impedance response plotted as the imaginary component versus the real component.Next, switch the negative voltage and current terminals from the anode to the lithium tip alloy electrode, and acquire a spectrum of the cathode versus the lithium tin alloy electrode. Lastly, connect the negative voltage and current terminals to the anode, and the positive terminals to the lithium tin alloy electrode. Voltage profiles were obtained of the full cell, and of each electrode with respect to the lithium couple.The increasing potential of the positive electrode during charge indicated delithiation. And the decreasing potential of the negative electrode correspondingly indicated lithiation. Electrochemical impedance spectroscopy showed a significant increase in impedance of the positive electrode with respect to the lithiated tin reference electrode after the battery had been cycled 100 times, but a minimal increase in impedance of the negative electrode.This implied that the overall increase in impedance was predominantly driven by the increase in positive impedance. Cycling at extreme voltage conditions increases the chances of lithium plating onto the negative electrode, causing intense safety challenges. Additional experiments are under way to understand the occurrence of lithium plating by developing protocols to probe the onset of lithium deposition.This approach can be used to obtain insider information about electrode behavior during the aging of a battery. Align tin wire with metals such as sodium or magnesium can widen the application of this technique to new generation batteries.

in-situ-lithiated-reference-electrode-four-electrode-design-for

Research

JoVE Journal

Chemistry

8.6K Views.  Argonne National Laboratory. The demand for better performing lithium ion batteries is driving research towards understanding factors causing degradation. The method described here can precisely guage the behavior of individual battery components. The wealth of information that this technique provides amplifies the reach of diagnostic analysis in lithium ion batteries, and provides valuable input into the optimization of individual cell components.To begin, obtain a four centimeter wide seven centimeter long jig m...