“Water-in-Salt” for Supercapacitors: A Compromise between Voltage, Power Density, Energy Density and Stability

Lannelongue, Pierre; Bouchal, Roza; Mourad, Eléonore; Bodin, Charlotte; Olarte, Marco; Vot, Steven Le; Favier, Frèdéric; Fontaine, Olivier

doi:10.1149/2.0951803jes

Cited by 143 publications

(99 citation statements)

References 33 publications

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“…[81] Since the ratio of water to the lithium salt is smaller than unity, the electrolyte is considered as a water-in-salt in lieu of saltin-water (similar to the terminology quoted in Section 2.2). Albeit, the idea of water-in-salt has been used for the fabrication of supercapacitors [88,89] sodium-ion batteries (SIBs), [85,90,91] and potassium-ion batteries (KIBs) [92] too. Unfortunately, this brilliant approach has not appropriately attracted the attention of researchers in the field, and the majority of available papers are still by the same research group.…”

Section: Water-in-saltmentioning

confidence: 99%

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High‐Energy Aqueous Lithium Batteries

Eftekhari¹

2018

Advanced Energy Materials

152

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research, aqueous electrolytes were occasionally employed for the investigation of cathode materials instead of the conventional nonaqueous electrolytes. [9,10] It was discussed that the simplicity of an aqueous electrolyte provides a better opportunity for the fundamental studies of the process of intercalation/deintercalation of Li-ions as opposed to the nonaqueous electrolytes. For instance, although the formation of solid electrolyte interphase (SEI) is of utmost importance for the cyclability of LIB, the significant role of the electrolyte does not allow to exclusively study the electrochemical behavior of the electrode material under consideration. The current research has specifically targeted the development of ARLBs, but in practice, most of the recent papers have followed the same line of research in investigating a limited range of cathode and anode materials in the same aqueous electrolytes. [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] A possible reason is that the key advantage of ARLBs was low cost, and thus, the focus was limited to a few inexpensive materials (e.g., lithium salts). Aqueous electrolytes are definitely excellent choices for the fundamental studies of electrode materials, but the practical development of ARLBs needs overcoming the key obstacles rather than finding more cathode materials.In any case, aqueous electrolytes were occasionally used during the 2000s by various research groups, but there was no vivid plan for the development of ARLBs. These works have been extensively reviewed before, [29][30][31][32][33] and it is not aimed to repeat the general works on aqueous electrolytes here. During the recent years, new opportunities have been introduced, which can extend the stable potential window of aqueous electrolyte to the range of 3-4 V. Upon this advancement, aqueous electrolytes can fairly compete with the conventional nonaqueous electrolytes for the fabrication of cheaper and safer LIBs. On the other hand, novel designs such as self-healing [34] or flexible [16,35,36] ARLBs have paved the path for new practical potentials of aqueous electrolytes. The present paper specifically focuses on the recent advancements and attempts to foster the strategy of research to shed light on the pathway of this emerging area of research. Two factors are directly responsible for achieving a high energy density, the specific capacity, and the cell voltage. Since the former is not massively controlled by the electrolyte and the specific capacity of most electroactive Owing to the high voltage of lithium-ion batteries (LIBs), the dominating electrolyte is non-aqueous. The idea of an aqueous rechargeable lithium battery (ARLB) dates back to 1994, but it had attracted little attention due to the narrow stable potential window of aqueous electrolytes, which results in low energy density. However, aqueous electrolytes were employed during the 2000s for the fundamental studies of electrode materials in the absence of side reactions such as the decomposition of organic spec...

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Section: Water-in-saltmentioning

confidence: 99%

“…[89,92] The key feature of this novel class of ARLB electrolytes is the capability of forming a protective SEI on the electrode surface, which can defer the evolution reactions. The stable potential window widens by the molality of the salt.…”

Section: Water-in-saltmentioning

confidence: 99%

High‐Energy Aqueous Lithium Batteries

Eftekhari¹

2018

Advanced Energy Materials

152

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“…[17] In addition, ah igh concentration of the pseudocapacitive component of 0.5 m 4hT in the electrolyte deterioratest he performance. These values are much highert han those of a previously reported concentrated aqueous LiTFSI electrolyte, [23] and also higher than those with ionic liquid ([EMIm][TFSI]) in acetonitrile as electrolyte and porous biomass-derived graphene-based carbon (BGC, with as urface area of 3657 m 2 g À1 ) electrodes. [6] Remarkably,amaximum energy density of 110Whkg À1 with ap owerd ensity of 3kWkg À1 was observed in this study for the 20 m[ BMIm]Cl/H 2 Oe lectrolyte with 0.1 m 4hT.…”

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confidence: 69%

“…Am aximum power density of 16.4 kW kg À1 was observed, with an energy density of 28.5 Wh kg À1 .C ompared to the power performance of the BGC electrode (a maximum of 408 kW kg À1 ), the low powerd ensity in this study is probably relatedt ot he non-optimized electrode materialsi nt he surface area, porosity,a nd wettability.C arbon materials with suitable channel and pore size that allow fast ion transport and adsorption are desirable. [23] At an even lower temperature of À32 8C, the electrolyte remains al iquid form and exhibits as pecific capacitance of 97 Fg À1 at 20 mV s À1 (Figure 3b). [2] To date, the low temperature application of supercapacitors has mostly been limitedt oo rganic solvents or ionic liquidbased electrolytes.…”

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confidence: 99%

“…Aqueouse lectrolytes for supercapacitors couldenabletheir assembly and operation under atmosphericc onditions. [23] Recently,X ia and co-workers reported a2 .6 Va symmetric supercapacitor with a1 m Na 2 SO 4 aqueouse lectrolyte and Na 0.5 MnO 2 // Fe 3 O 4 @C electrodes, with al arge energy density up to 81 Wh kg À1 . [19] It has been reported that the operating voltage of water-based electrolytes is generally limited to 1.2 Vi na symmetric supercapacitoro r2Vi na na symmetrics upercapacitor.…”

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High‐Voltage and Low‐Temperature Aqueous Supercapacitor Enabled by “Water‐in‐Imidazolium Chloride” Electrolytes

2018

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Symmetric aqueoush igh voltage supercapacitors up to 3V have been demonstrated using concentrated aqueous 1-butyl-3-methylimidazolium chloride ([BMIm]Cl), namely," water-inimidazolium chloride", as working electrolytes, andg raphene nanoplatelets-coated carbon paper as electrodes. Performance enhancement was furthera chieved either through adding redox speciess uch as 4-hydroxy-2,2,6,6-tetramethylpiperidin-1oxyl (4hT) into the electrolytes (110 Wh kg À1 for a2 0m [BMIm]Cl/H 2 Ow ith 0.1 m 4hT) or by pre-inserting ClO 4 À anions into the graphene platelets. Moreover,t he newly studied aqueous electrolytes allow low-temperature operation at À20 8C and even at À32 8C, retaining competitive energy storage capability (maximum energy densities of 36 and 21 Wh kg À1 ,r espectively).With ultrafastc harge-discharge rates through building up electricald ouble layers on porous electrodes with at ypical timescale of seconds, supercapacitors can generally realize high power densities of about 10 kW kg À1 and energy densities of about 5Whkg À1 . [1,2] They exhibit excellent cyclingr eversibility,w ithoutc ausingi nherent structural changes in electrodes and electrolytes. Thus,s upercapacitors are promising for rapid response in peak shavinga nd grid stabilization. [3,4] To facilitate their practical application,i ssues of low energy density,s afety, and high cost need to be solved. Besides the selection and optimization of electrode materials towards high availablesurface areas and porosities, [5][6][7][8][9][10] great efforts have been made to tailor the electrolyte formulation including the selection of types of solvents and electrolyte ions. [11][12][13] The amount of stored energy in supercapacitors can be increased by increasing the ion-accessible surfacea rea of the electrode materials. Another way to increase the energy density of supercapacitors is to increase the operating potential range of the system, as energy density is proportionaltot he square of the voltage.Organics olvents and room-temperature ionic liquidsa re commonlyu sed as workingm edia for high operating-voltage (> 2V)s upercapacitors. [14] However,t hey typically have poor ion conductivities, from about af ew mS cm À1 for ionic liquids to tens of mS cm À1 for conventionalo rganic electrolytes at room temperature. [15] By adding molecular solvents, such as water or acetonitrile, into ionic liquids, [16][17][18] the viscosity can be greatly reduced and the ion conductivity can be accordingly enhanced with as acrifice in the electrochemical stability window of the electrolytes. Water as an atural alternative to the flammable organic solvents or highly viscous room-temperaturei onic liquidsi si deal for use as aw orking medium for electrochemical devices with the merits of intrinsic safety and fast transport for ionic species. Aqueouse lectrolytes for supercapacitors couldenabletheir assembly and operation under atmosphericc onditions. However,i th as been al ongstanding challenge that water has an arrow electrochemical stability window (a sum of the thermo...

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Optimization of Organic/Water Hybrid Electrolytes for High‐Rate Carbon‐Based Supercapacitor

Xiao

Dou

Zhang

et al. 2019

Adv Funct Materials

119

107

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Water-in-salt" (WIS) electrolytes with wide electrochemical stability windows (ESWs) have made a breakthrough in energy density of aqueous batteries and supercapacitors (SCs), but the sluggish ion diffusion limits their widespread application. Although the ion diffusion of WIS electrolytes can be improved by the addition of organic co-solvents, the effects of types and amounts of added organic solvents on the physicochemical properties of hybrid electrolytes are not clear. Here, the conductivity, ESW, and flammability of a series of hybrid electrolytes prepared by adding different organic solvents to a typical lithium bis(trifluoromethane sulfonyl) imide (LiTFSI)-based WIS electrolyte are systematically studied. The results show that acetonitrile (ACN) is the best one to improve ion diffusion while maintaining high-level safety and wide ESW. Furthermore, a ternary phase diagram of LiTFSI/H 2 O/ACN is drawn to comprehensively show the relationship among the conductivity, flammability, and solubility of the hybrid electrolytes. According to the guidance of this phase diagram, an optimal hybrid electrolyte (LiTFSI/H 2 O/(ACN) 3.5 ) is obtained, and the carbon-based symmetric SC using such hybrid electrolyte is able to fully work at 2.4 V with superior rate capability and excellent cycling stability over 40 000 cycles.

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“Water-in-Salt” for Supercapacitors: A Compromise between Voltage, Power Density, Energy Density and Stability

Cited by 143 publications

References 33 publications

High‐Energy Aqueous Lithium Batteries

High‐Energy Aqueous Lithium Batteries

High‐Voltage and Low‐Temperature Aqueous Supercapacitor Enabled by “Water‐in‐Imidazolium Chloride” Electrolytes

Optimization of Organic/Water Hybrid Electrolytes for High‐Rate Carbon‐Based Supercapacitor

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