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[Shoichi Matsuda](https://orcid.org/0000-0002-0640-3404), Shin Kimura, Misato Takahashi

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[Automated Robotic Cell Fabrication Technology for Stacked‐Type Lithium‐Oxygen Batteries](https://mdr.nims.go.jp/datasets/4f32b61b-2994-4bc7-969f-8cdec1df001a)

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Automated Robotic Cell Fabrication Technology for Stacked‐Type Lithium‐Oxygen BatteriesAutomated Robotic Cell Fabrication Technology forStacked-Type Lithium-Oxygen BatteriesShoichi Matsuda,*[a, b, c] Shin Kimura,[a] and Misato Takahashi[a]Rechargeable lithium-oxygen batteries (LOBs) are gaininginterest as next-generation energy storage devices due to theirsuperior theoretical energy density. While recent years haveseen successful operation of LOBs with high cell-level energydensity, the technology for cell fabrication is still in its infancy.This is because the cell fabrication procedure for LOBs is quitedifferent from that of conventional lithium-ion batteries. Thestudy presents a fully automated sequential robotic experimen-tal setup for the fabrication of stacked-type LOB cells. Thisapproach allows for high accuracy and high throughputfabrication of the cells. The developed system enables thefabrication of over 80 cells per day, which is 10 times higherthan conventional human-based experiments. In addition, thehigh alignment accuracy during the electrode stacking andelectrolyte injection process results in improved batteryperformance and reproducibility. The effectiveness of thedeveloped system was also confirmed by investigating a multi-component electrolyte to maximize battery performance. Webelieve the methodology demonstrated in the present study isbeneficial for accelerating the research and development ofLOBs.IntroductionLithium-oxygen batteries (LOBs) are a promising candidate fornext-generation energy storage devices due to their extremelyhigh theoretical energy density.[1–4] In LOBs, metallic lithium,which has a low redox potential of � 3.04 V (vs. SHE) and hightheoretical capacity of 3860 mAh/g, is utilized as the activematerial for the negative electrode, while atmospheric oxygenis utilized for the positive electrode. For example, a theoreticalenergy density of 3150 Wh/kg can be achieved by multiplyingan assumed operating voltage of 2.7 V with the specific capacityof 1168 mAh/g based on the reaction 2Li+O2=Li2O2.[1] At thecell level, LOBs can achieve an energy density two to five timeshigher than that of Li-ion batteries. In fact, LOBs with a 500 Wh/kg energy density have already been demonstrated,[5,6] demon-strating the high energy density potential of LOBs.While there have been numerous studies investigatingmaterials for LOBs, such as self-standing porous carbonelectrodes,[7–10] stable electrolytes,[11–16] and protective layers forlithium metal electrodes,[6,17] research on cell fabricationtechniques for LOBs is still in its early stages. From a practicalstandpoint, multiple LOB cells must be densely stacked, similarto conventional lithium-ion batteries (LiBs), to achieve highenergy density at the cell level. In stacked situations, it isnecessary to have a proper cell configuration to ensure effectiveoxygen transfer throughout the positive electrode via the gas-diffusion layer. A 4 cm×5 cm sized 10-cell stacked LOB wasfabricated and exhibited stable discharge/chargeperformance.[18] The effective cell area was 200 cm2, which is100 times larger than that of conventional coin-type cells (S=2 cm2). To maximize the cell-level energy density of LOBs, it isimportant to quantitatively control the amount of electrolyte inthe porous carbon electrode. The surface of the porous carbonelectrode should ideally be completely wetted with the electro-lyte to enable efficient transfer of Li ions. It is crucial to maintaina balance between wetting and filling of the electrode withelectrolyte. Additionally, the voids in the electrode should notbe completely filled with the electrolyte to ensure oxygentransport channels from a gas diffusion layer. Several electrolyteinjection techniques have been demonstrated to improve theperformance of LOBs.[19] These techniques include the ’inkjetmethod’, which uses a piezoelectric element to emit nanoliter-scale electrolyte droplets, and the ’stamping method’, whichuses two highly hydrophilic filters as electrolyte transfer agentsto uniformly spread the electrolyte onto the carbon electrodesandwiched between them. Notably, the previous studiesrevealed the importance of the quality of the cell, such asinhomogeneity of electrolyte in porous carbon electrode, formaximizing the battery performance as well as the design ofthe cell.[20–23]In recent years, fundamental technology related to thefabrication of practical LOB cells has been developed at thelaboratory level. However, these techniques rely on human-based experiments involving manual handling of cell compo-[a] S. Matsuda, S. Kimura, M. TakahashiCenter for Green Research on Energy and Environmental Materials, NationalInstitute for Material Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, JapanE-mail: MATSUDA.Shoichi@nims.go.jp[b] S. MatsudaCenter for Advanced Battery Collaboration, National Institute for MaterialScience, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan[c] S. MatsudaNIMS-SoftBank Advanced Technologies Development Center, NationalInstitute for Material Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, JapanSupporting information for this article is available on the WWW underhttps://doi.org/10.1002/batt.202400509© 2024 The Authors. Batteries & Supercaps published by Wiley-VCH GmbH.This is an open access article under the terms of the Creative CommonsAttribution Non-Commercial NoDerivs License, which permits use and dis-tribution in any medium, provided the original work is properly cited, the useis non-commercial and no modifications or adaptations are made.Wiley VCH Donnerstag, 05.12.20242412 / 375923 [S. 168/175] 1Batteries & Supercaps 2024, 7, e202400509 (1 of 8) © 2024 The Authors. Batteries & Supercaps published by Wiley-VCH GmbHBatteries & Supercapswww.batteries-supercaps.orgResearch Articledoi.org/10.1002/batt.202400509http://orcid.org/0000-0002-0640-3404https://doi.org/10.1002/batt.202400509http://crossmark.crossref.org/dialog/?doi=10.1002%2Fbatt.202400509&domain=pdf&date_stamp=2024-10-28nents. Therefore, a series of process technologies for handling,stacking cell components, and electrolyte injection should bedeveloped in an automated manner. Given the differencesbetween the current lithium-ion battery cell production processand the process required for LOB-specific cell fabrication, it isessential to establish appropriate technology. This studypresents the development of an automated cell fabricationsystem for stacked-type LOB cells. By coordinating theoperations of electrode handling, electrode stacking, andelectrolyte injection processes, we have constructed a LOB cellfabrication equipment that can continuously create more than80 LOB cells per day.Results and DiscussionTo develop an automated cell fabrication robotic system, it isimportant to consider the differences between LiB and LOB inthe cell fabrication procedure. In conventional LiB cell fabrica-tion, a composite electrode consisting of LiCoO2 active materialwith binder and conductive additives coated on an aluminummetal foil is used as the positive electrode. The negativeelectrode utilized a composite of graphite active material withbinder coated on copper metal foil. Both electrodes have aporosity of approximately 30%. A separator made of apolyolefin-based membrane with a porosity of 50% was used.The electrode materials were stacked and laminated as apouch-type cell. The cell was then filled with electrolyte using avacuum impregnation process. The electrolyte spreads through-out the pore space in electrodes and separators. However, it isimportant to note that the electrode materials and cellfabrication procedure of LOB differ significantly from those ofLiB. In the case of LOB, a porous carbon membrane with aporosity of about 90% serves as the positive electrode, while ametal lithium foil is used as the negative electrode (Figure 1a).The separator is similar to that used for LiB. A membrane madeof carbon fiber with a porosity of about 80% is typically used asa gas-diffusion layer. This layer functions as an oxygen transportchannel from outside of the cell.Before stacking these electrode materials, a controlledamount of electrolyte should be injected properly. This isbecause the void spaces in the carbon electrode and GDLshould not be filled with electrolyte in order to maintain aninterconnected oxygen transport pathway. Therefore, it isimportant to satisfy these requirements during the electrolyteinjection process for LOB. Additionally, special attention shouldbe paid to the handling of the electrodes during LOB cellfabrication. Porous carbon electrodes can become distortedwhen they contain electrolyte (Figures 1b and c) and can beeasily damaged during electrode handling and stacking proc-esses. Similarly, the lithium metal foil is also susceptible todamage when handled with typical ceramic-based tweezers(Figures 1d and e). To minimize damage to the electrode, thecell fabrication process should be designed to avoid handlingthe electrolyte after it has been injected.Based on these considerations, we investigated the LOB cellfabrication procedure, which can be applied to an automatedrobotic process. The procedure is shown in Figure 2. First, thelithium metal foil with copper metal foils is transported to thecell folder. Then, the separator is also transported and stackedon top of it, and the electrolyte is injected. After that, theporous carbon-based positive electrode is also moved andplaced on top of it. The proper amount of electrolyte is injectedinto the porous carbon-based positive electrode. The gas-diffusion layer, made of carbon fiber, is placed on top. Thisprocedure allows for the fabrication of LOB cells with properelectrolyte injection conditions, ensuring high reproducibilitywhile minimizing damage to the electrode materials.We fabricated the automated LOB cell fabrication roboticsystem. Figure 3 showed the over-view of the automated LOBcell fabrication equipment developed in the present study. Thephotographic images are also shown in Figures S1 and S2. Thedevice consists of a total of 9 parts: 5 units and 4 transport armsthat connect each unit.Figure 1. (a) Schematic illustration of stacked type LOB cell. Photographic images of porous carbon electrode (b) before and (c) after electrolyte injectionprocess. Photographic images of lithium metal foil (d) before and (e) after handling by ceramic tweezers.Wiley VCH Donnerstag, 05.12.20242412 / 375923 [S. 169/175] 1Batteries & Supercaps 2024, 7, e202400509 (2 of 8) © 2024 The Authors. Batteries & Supercaps published by Wiley-VCH GmbHBatteries & SupercapsResearch Articledoi.org/10.1002/batt.202400509 25666223, 2024, 12, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/batt.202400509 by National Institute For, Wiley Online Library on [11/12/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons LicenseUnit 1 Cell holder unit: PEEK based cell folder (Figure S3a) isutilized for stacking LOB cells and 80 holders can bestored in cell folder unit. Glass based plate is utilized assubstrate for stacking electrode materials.Unit 2 Electrode store unit: Porous carbon membrane aspositive electrode (20 mm×20 mm), lithium metal foil(20 mm×20 mm) attached with copper metal foil(20 mm×30 mm) as negative electrode, carbon fiber-based gas-diffusion layer (20 mm×30 mm) are placed oneach plate and stored in the electrode uni. The separatoris stored as roll and cut into individual pieces(22 mm×22 mm).Unit 3 Stacking unit: Electrode materials are transferred fromelectrode storing unit to stacking unit and stacked. Tominimize the damage to electrode materials, thevacuum type handling system is adopted (green line inFigure S3b). In case, electrolyte is necessary to beinjected into electrode materials, cell folder is transferredto the electrolyte injection unit. For minimizing themisalignment of electrodes material during stacking andelectrolyte injection process, electrode materials areholed of their edge position (red line in Figure S3b).Figure 2. Schematic illustration of cell fabrication procedure by automated robotic system developed in the present study.Figure 3. Photographic and schematic images of automated robotic system developed in the present study. (a) Stacking unit, (b) Electrolyte injection unit, (c)Fabricated cell stored unit, (d) Electrode stored unit, (e) Cell holder unit.Wiley VCH Donnerstag, 05.12.20242412 / 375923 [S. 170/175] 1Batteries & Supercaps 2024, 7, e202400509 (3 of 8) © 2024 The Authors. Batteries & Supercaps published by Wiley-VCH GmbHBatteries & SupercapsResearch Articledoi.org/10.1002/batt.202400509 25666223, 2024, 12, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/batt.202400509 by National Institute For, Wiley Online Library on [11/12/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons LicenseUnit 4 Electrolyte injection unit: Cell folder is transferred fromstacking unit to electrolyte injection unit. Non-contact-ing type dispenser is utilized for electrolyte injectionprocess. Inject a total of 400 droplets of electrolyte intoa 20 mm×20 mm sized electrode at 1 mm intervals. Theamount of one droplet of electrolyte can be quantita-tively controlled.Unit 5 Cell store unit: When all the stacking and electrolyteinjection process is completed, cells are labeled their QRcode and moved to cell store unit (Figure S3c). At most,80 cells can be stored.These five kinds of units are connected by four transport armsin following.Transport 1 Folder transport arm: The rack at left holds platescontaining positive electrodes, negative electrodeand laminate sheets. A separator – the long roll ofwhite material at right – is automatically dispensedand cut into individual pieces.Transport 2 Electrode transport arm: The arm lifts a materialfrom the electrode rack using a suction cup andtransports it to the stacking area at the center. Thesuction strength of the arm is controllable, ensur-ing safe transfer of even extremely thin electrodematerials.Transport 3 Stacked electrode transport arm:Transport 4 Fabricated cell transport arm: This arm transferssealed cells to the battery cell holder.The system developed has dimensions of approximately 5 m inlength, 3 m in width, and 2 m in height, and is installed inside adry room (Figure S3d). The cell fabrication procedure depictedin Figure 2 is executed by each unit and transport arm duringspecific time periods. It is important to note that by selectingappropriate electrode materials or electrolyte solutions, it ispossible to create various types of LOB cells with differentelectrode materials and/or electrolytes. Movies for the auto-mated cell fabrication process carried out by the developedsystem can be found in supporting information andelsewhere.[24]The cell fabrication proceeds as shown in Figure 2, whichconsist by following eight steps. The details of cell componentsare described in experimental method section in Supplemen-tary Information file.Step 1 In Unit 1 (Cell holder unit), glass plate is placed on thetop of PEEK based cell folder. Then, the cell folder ismoved to Unit 3 (Stacking unit) by Transport arm 1(Folder transport arm).Step 2 Transport 2 (Electrode transport arm) and placed on theglass plate.Step 3 Separator is cut into suitable size and moved to Unit 3and placed on the Li foil.Step 1–3 proceeds parallelly and found in Movie: 0 : 00–1 :55.Step 4 The cell folder is moved to Unit 4 (Electrolyte injectionunit) by Transport 3 (Stacked electrode transport arm)and controlled amount of electrolyte was injected intoseparator (Movie: 1 : 56–2 :57).Step 5 The cell folder returns back to Unit 3. The porous carbonelectrode is moved from Unit 2 to Unit 3 by Transport 2and placed on the top of separator (Movie: 2 : 58–3 :10).Step 6 The cell folder is moved to Unit 4 and controlledamount of electrolyte was injected into porous carbonelectrode (Movie: 3 :11–3 :46).Step 7 The cell returns back to Unit 3. The gas-diffusion layer ismoved from Unit 2 to Unit 3 by Transport 2 and placedon the top of porous carbon electrode.Step 8 Glass plate is placed on gas diffusion layer. The cell ismoved to Unit 5 by transport 1 and 4.The developed system can fabricate one LOB cell within10 minutes and can continuously operate to fabricate 80 cells,completing the process within 14 hours. In case, same LOB cellswere fabricated by manually, it takes almost one day forfabricating the eight cells. Therefore, the developed system hasa cell fabrication throughput that is 10 times higher thanstandard human-based experiments. In addition, the developedautomated system fabricates the LOB cells with high accuracy,with an alignment error of less than 0.1 mm. This is beneficialfor improving the reproducibility of battery performance tests.To evaluate the effectiveness of the developed automatedcell fabrication system, we compared the battery performanceof the cell fabricated using the developed system with the cellfabricated manually. For this experiment, three independentcells were fabricated, and battery performance tests wereperformed at a current density of 0.4 mA/cm2, an areal capacityof 4.0 mAh/cm2, and a cutoff voltage of 2.0 V/4.5 V. The positiveelectrode utilized a KB-based self-standing membrane with amass loading of 4.8 mg/cm2, and the electrolyte solutioncontained 0.5 M LiTFSI, 0.5 M LiNO3, and 0.2 M LiBr. To minimizethe undesired effect of chemical crossover between electrodes,a ceramic-based separator was introduced by sandwiching itbetween two pieces of polyolefin-based separators. Beforecycling test, the fabricated cells are firstly subjected toconditioning process, in which the cells are subjected to threerepeated discharge/charge cycle with limited capacity(0.1 mAh/cm2) and current density (0.1 mAh/cm2), in order toimprove the uniform electrolyte distribution in the cell.Figure 4a–c shows the discharge/charge profile of LOB cells.Both manually and robotically fabricated LOB cells exhibited arepresentative voltage profile of LOB, consistent with previousstudies using the same cell contents.[25,26] The standard devia-tion of the average discharge voltage and the average chargevoltage was evaluated, and it was found to be less than 5 mV inboth cases (Figure 4d and e). Associated with the progress ofthe cycle, there can be an increase in the variation of bothaverage discharge and charge voltage. As a result, the valuereached over 15 mV at the 5th cycle. In sharp contrast, for thecells fabricated by the robotic setup, the variation is less than5 mV even at the 5th cycle. Such a difference is considered toWiley VCH Donnerstag, 05.12.20242412 / 375923 [S. 171/175] 1Batteries & Supercaps 2024, 7, e202400509 (4 of 8) © 2024 The Authors. Batteries & Supercaps published by Wiley-VCH GmbHBatteries & SupercapsResearch Articledoi.org/10.1002/batt.202400509 25666223, 2024, 12, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/batt.202400509 by National Institute For, Wiley Online Library on [11/12/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licenseoriginate from building quality of the cell. Namely, experimentalvariation factors during the cell fabrication process; mainly fromthe electrode alignment error, have influence of the perform-ance variation of LOB. Notably, the other technical factors,including the amount of electrolyte and stacking pressure areessentially same for both manually and robotically fabricatedLOB cells. The results demonstrate the effectiveness of theautomated cell fabrication system in minimizing the validationof battery performance of LOBs, given the positional accuracyof electrode stacking of the robotic arm is less than 0.5 mm andthe accuracy of electrolyte injection by the dispensing unit isless than 0.1 μL.It should be noted that the robotically fabricated LOB cellsexhibited superior battery performance compared to themanually fabricated LOB cells. In the case of the manuallyfabricated cells, the average charging voltage increased witheach cycle and reached over 3.65 V (Figure 4f). In contrast, theaverage charge voltage of the robotically fabricated LOB cellsremained below 3.6 V. During the 5th charging process, therobotically fabricated cells exhibited a lower voltage at the endof the process compared to the manually fabricated LOB cells.At the 8th cycle, the discharge voltage of the manuallyfabricated LOB cells had decreased significantly, falling below2.5 V. On the other hand, the robotically fabricated cells exhibita stable discharge process with a plateau of 2.6 V, revealing thenovelty of the automated cell fabrication system in improvingbattery performance.To demonstrate the effectiveness of the developed auto-mated cell fabrication system in accelerating the discovery ofnew materials to improve the battery performance of LOB, wefocus on using this setup to search for a multi-componentelectrolyte. In this study, we direct our research towardsdiscovering the ideal combination of redox mediator (RM)compounds that maximize LOB performance. The use of RM is awell-known approach for improving the performance of LOBsby enhancing the Li2O2 decomposition reaction during thecharging process.[1] In our experiment, we selected LiI, LiBr,LiNO3, and TEMPO as model systems, as they are known asRM.[27–33] We manually prepared eight types of solutions listed inTable S1 and selected one to three types of solution from theseeight types to mix, resulting in various kinds of electrolytescontaining different combinations of RM with different concen-trations. A total of 92 types of electrolytes were prepared,namely 8 C1=8, 8 C2=28, and 8 C3=56. These 92 cells werefabricated using a developed automated robotic system. Batteryperformance tests were conducted at a current density of0.2 mA/cm2, an areal capacity of 2.0 mAh/cm2, and a cutoffvoltage of 2.0 V/4.5 V. The ratio of electrolyte amount to arealcapacity (E/C, g/Ah), which is a technological parameter of LOB,was measured. In the following cell investigation, the value ofE/C is 12 g/Ah, which is relatively smaller compared to thestandard LOB cell reported in the literature.[2]Here, compared to the experiment in Figure 4, we set thehalf value of current density and areal capacity. Under such lowE/C condition, it is reported that the sever degradation reactionproceeds in LOB cell, including the decomposition of carbonelectrode and electrolyte movement phenomenon.[34,35] In theexperiment in Figure 5, we set relatively mild conditions, toevaluate the influence of electrolyte composition on the LOBperformance. For this experiment, we set charging cutoffFigure 4. Voltage profile of LOB cells fabricated by manually (black curves) and by robotically (blue curves) at (a) 1st and (b) 5th, and (c) 8th cycle. Standarddeviation of (d) average discharge voltage and (e) average charge voltage for LOB cells. (f) Average voltage in charge process.Wiley VCH Donnerstag, 05.12.20242412 / 375923 [S. 172/175] 1Batteries & Supercaps 2024, 7, e202400509 (5 of 8) © 2024 The Authors. Batteries & Supercaps published by Wiley-VCH GmbHBatteries & SupercapsResearch Articledoi.org/10.1002/batt.202400509 25666223, 2024, 12, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/batt.202400509 by National Institute For, Wiley Online Library on [11/12/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensevoltage of 4.5 V. Of course, setting lower voltage is beneficialfor minimizing the oxidative side reaction that proceeds inpositive electrode side. However, setting lower cutoff voltageresults in the uncomplete decomposition of solid-state products(Li2O2 and/or Li2CO3) in carbon electrode.[34] As results, poreclogging of carbon electrode easily occurs, resulting in thedecrease of discharge voltage. Although the details are notclarified yet, it looks, high voltage condition is necessary forfully decompose these solid products. For these reasons, in thepresent study we set charging cutoff voltage of 4.5 V.Figure 5 shows the discharge/charge performance of theLOB cell with an electrolyte containing only one type of RM(8 C1). The results of cycle life of LOB cell with equipped withsingle kinds of RM were summarized in Table S2. When usingan electrolyte with 1 M LiI+0.2 M LiTFSI in TEGDME, the cellexhibited the typical voltage profile of LOB containing LiI(Figure 5a). During the first discharge process, there are twodistinct plateaus at 2.9 V and 2.6 V. The first discharge plateaucan be assigned to reduction reaction of redox couple of I� /I3�and the second plateau is assigned to Li2O2 formationassociated with the oxygen reduction reaction. During thecharging process, the cell voltage increased from 3.0 V to 3.5 V,which is a typical profile of LOB containing LiI. As the cycleprogressed, the charging voltage gradually increased. Finally,the cell voltage reached the cutoff voltage of 2.0 V during the32th discharging process (purple curve in Figure 5a). Duringcharging process when I3� is electrochemically generated, thisI3� can react with Li2O2, generating I� and O2. Ideally only suchreaction should proceed in the cell. However, several kinds ofside reaction are reported, in which I3� /I� redox involved.[36]Such side reaction is one of the reasons for increase of over-potential both in discharge/charge process with progress ofcycle. When using an electrolyte with 1 M LiBr+0.2 M LiTFSI inTEGDME, the cell exhibited the representative voltage profile ofLOB containing LiBr. During the first discharge process, a two-stage plateau can be observed at 3.4 V and 2.6 V, respectively(Figure 5b). The first discharge plateau can be attributed toreduction reaction of redox couple of Br� /Br3� , while the secondplateau is associated with the formation of Li2O2 resulting fromthe oxygen reduction reaction. During the charging process, avoltage plateau of 3.5 V is observed. As the cycle progresses,the voltage at the end of the charging process increases, whilethe discharge voltage decreases. As a result, the cell voltagereached the cutoff condition of 2.0 V at the 21th dischargingprocess. When using an electrolyte with 1 M LiTFSI+1 MTEMPO in TEGDME, a unique voltage profile was observed.Although the cell exhibited a representative LOB voltage profileduring the 1st discharge/charge cycle, there was a sharpincrease in voltage during the 7th charging process (Figure 5c).The discharge voltage rapidly decreased during the 8thdischarge process and reached the cutoff voltage. This chargingprofile has been reported in previous studies of LOB with leanelectrolyte and high areal capacity conditions, and the move-ment of electrolytes in the carbon electrode is considered apossible mechanism.[31] In contrast, this unique chargingbehavior was not observed in the case of electrolyte containing1 M LiTFSI+0.1 M TEMPO in TEGDME (Figure 5d). The resultsindicate a complex degradation mechanism of LOB under lowE/C conditions in the cell with electrolyte containing a highconcentration of TEMPO. For clarifying the detailed mechanismof unique cell degradation phenomenon, in which the chargingvoltage quickly increase at the begging of charging process, theuse of non-destructive analytical methods is crucial.[37] Althoughthe understanding of such details is quite important, werecognize this is the out of scope of the present study. Webelieve the use of such advanced analytical techniques clarifiedFigure 5. Voltage profile of LOB cells with electrolyte of (a) 1 M LiI+1 M LiTFSI in TEGDME, (b) 1 M LiBr+1 M LiTFSI in TEGDME, (c) 1 M LiTFSI+1 M TEMPO,(d) 1 M LiTFSI+0.1 M TEMPO in TEGDME, (e) 0.33 M LiNO3+0.07 M LiBr+0.07 M LiI+0.71 M LiTFSI in TEGDME, and (f) 0.33 M LiNO3+0.33 M LiBr+0.33 M LiI+0.2 M LiTFSI in TEGDME.Wiley VCH Donnerstag, 05.12.20242412 / 375923 [S. 173/175] 1Batteries & Supercaps 2024, 7, e202400509 (6 of 8) © 2024 The Authors. Batteries & Supercaps published by Wiley-VCH GmbHBatteries & SupercapsResearch Articledoi.org/10.1002/batt.202400509 25666223, 2024, 12, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/batt.202400509 by National Institute For, Wiley Online Library on [11/12/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensethe unique cell degradation phenomenon observed in thepresent study.The discharge and charge performance tests were alsoconducted on the other LOB cells using electrolytes 8 C2 and8 C3. Figure S4 summarizes the distribution table of cycle lifefor all 92 LOB cells evaluated in this study, revealing an averagecycle life of 28 cycles. Most cells exhibited a cycle life betweenthe 20 and 36 cycle. Table S3 shows the details of theelectrolyte composition of the top 10 samples with the highestcycle life. Of the samples investigated, the cell containing anelectrolyte of 0.33 M LiNO3, 0.07 M LiBr, 0.07 M LiI, and 0.71 MLiTFSI, which consists by the electrolyte No.1, No.6 and No.7,exhibited the best cycle life, lasting 41 cycles (Figure 5e). InFigure 5f, the profile of LOB cell containing an electrolyte of0.33 M LiNO3, 0.33 M LiBr, 0.33 M LiI, and 0.2 M LiTFSI, whichconsists by the electrolyte No. 1, No. 2 and No. 3, was alsoshown. Although at the beginning of cycle, the cell exhibitedrelatively low charging voltage, there can be seen the gradualincrease of voltage with progress of cycle. At 25th dischargeprocess, the voltage showed sudden decrease and reached tocutoff condition. Both electrolytes are consisted by four kinds ofchemicals, LiNO3, LiBr, LiI and LiTFSI. Only the difference is theconcentration of LiBr and LiI. Notably, the LOB cell with lowerRM concentration results in higher cycle life. This resultsuggests that the high concentration level of RM is more likelyto cause new side reactions, resulting in the negative influenceon the cycle life, although high concentration level of RM haspositive have the positive effect of lowering the chargingvoltage and suppressing side reactions.The negative effect of high concentration level RM also canbe found in Table S3. Among the 10 kind of electrolyte, 9electrolyte do not contain the solution No. 2 and No. 4, whichcorrespond to high concentration LiBr solution and highconcentration TEMPO solution. Of course, the optimum electro-lyte composition can be change by the choice of batteryevaluation conditions, including charging cutoff voltage, cur-rent density, areal capacity, the results obtained in the presetstudy revealed the existence of complicated synergetic effect ofRMs. In a multi-component electrolyte system, the relationshipbetween electrolyte composition and battery performance iscomplex and difficult to predict. To evaluate their performanceexperimentally, the use of a high-throughput experimentalsetup is beneficial.ConclusionsIn this study, we developed an automated robotic system forfabricating stacked-type lithium-oxygen batteries. The systemcan fabricate 80 LOB cells within 14 hours, which is 10 timesfaster than standard human-based experiments. The systemalso ensures high alignment accuracy during the electrodestacking and electrolyte injection processes, resulting inimproved reproducibility of battery performance. To demon-strate the effectiveness of the developed system in acceleratingthe discovery of new materials to improve the battery perform-ance of LOB, we attempted to identify the ideal combination ofredox mediator (RM) compounds that would maximize LOBperformance. Through investigation of 92 different electrolytecompositions, including various combinations of RM and theirconcentrations, it was determined that LOB cells with anelectrolyte consisting of 0.33 M LiNO3, 0.07 M LiBr, 0.07 M LiI,and 0.71 M LiTFSI exhibited the best cycle life. These resultsdemonstrate the effectiveness of multi-component electrolytediscovery for LOB with long cycle life. The automated roboticcell fabrication technology is believed to be beneficial foraccelerating the research and development of LOBs with longcycle life and high energy density.Supporting Information SummaryExperimental details, photographic image of automated LOBcell fabrication robotic system, distribution table of cycle life ofLOB cells are provided in the Supporting Information.AcknowledgementsThe present work was partially supported by JST COI-NEXTGrant Number JPMJPF2016. 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