High Electrolyte Concentrations Research Articles

Localized high-concentration electrolytes for lithium metal batteries: progress and prospect

Localized high-concentration electrolytes for lithium metal batteries: progress and prospect

Reversible Li Plating on Graphite Anodes through Electrolyte Engineering for Fast-Charging Batteries.

The difficulties to identify the rate-limiting step cause the lithium (Li) plating hard to be completely avoided on graphite anodes during fast charging. Therefore, Li plating regulation and morphology control are proposed to address this issue. Specifically, a Li plating-reversible graphite anode is achieved via a localized high-concentration electrolyte (LHCE) to successfully regulate the Li plating with high reversibility over high-rate cycling. The evolution of solid electrolyte interphase (SEI) before and after Li plating is deeply investigated to explore the interaction between the lithiation behavior and electrochemical interface polarization. Under the fact that Li plating contributes 40 % of total lithiation capacity, the stable LiF-rich SEI renders the anode a higher average Coulombic efficiency (99.9 %) throughout 240 cycles and a 99.95 % reversibility of Li plating. Consequently, a self-made 1.2-Ah LiNi0.5 Mn0.3 Co0.2 O2 | graphite pouch cell delivers a competitive retention of 84.4 % even at 7.2 A (6 C) after 150 cycles. This work creates an ingenious bridge between the graphite anode and Li plating, for realizing the high-performance fast-charging batteries.

Adsorption and quantitative fluorescence-based measurement of ammonium ions using a chitosan-based hydrogel combined with p-hydroxybenzoic acid

Ammonium removal in high-density fish cultures is highly reliant on time-consuming and costly biological treatment methods. Therefore, the development of cheap and rapid chemical methods has recently garnered increasing attention. Our study developed a dissolved ammonium removal method using a chitosan-based hydrogel (Cht-HG) modified with 0.3 mM of p-hydroxybenzoic acid (Cht-0.3PHBA-HG). Our proposed method enabled the adsorption and measurement of dissolved ammonium via fluorescence detection. In the ammonium adsorption test, the maximum adsorption capacities (qm) of Cht-HG and Cht-0.3PHBA-HG were 11.6 mg g−1 and 19.9 mg g−1, respectively. Cht-0.3PHBA-HG exhibited a relatively elevated adsorption capacity (i.e., 1.71-fold higher adsorption efficiency) due to the morphological and chemical modifications attributed to p-hydroxybenzoic acid (PHBA). These findings were confirmed by our chemical characterization and adsorption test results. Particularly, the adsorbed ammonium atomic percentages (at.%) of Cht-HG-NH4 and Cht-0.3PHBA-HG-NH4 were 6.33 % and 15.2 %, respectively. Compared to Cht-HG, the adsorption properties of Cht-0.3PHBA-HG were more stable in a pH range of 2–8. Moreover, we quantitatively analyzed the oxidation of the combined PHBA at different dissolved ammonium concentrations (0.1–5.0 mM) using fluorescence detection. The fluorescence sensitivity of ammonium was maintained, even in high concentrations of common electrolytes (Ca2+, K+, Mg2+, Na+, and PO43-). The ammonium adsorption mechanisms of Cht-0.3PHBA-HG were strongly consistent with the pseudo-first order (PFO), pseudo-second order (PSO), and Langmuir models. In addition to its role as an adsorbent, Cht-0.3PHBA-HG could also be used to detect ammonium in real time.

Manganese-based flow battery based on the MnCl2 electrolyte for energy storage

Manganese-based flow batteries are attracting considerable attention due to their low cost and high safe. However, the usage of MnCl2 electrolytes with high solubility is limited by Mn3+ disproportionation and chlorine evolution reaction. Herein, the reversible Mn2+/MnO2 reaction without the generation of Mn3+ and Cl2 in the manganese-based flow batteries with the MnCl2 electrolyte is successfully achieved by adding amino acid additives. The effect and the function mechanism of a series of amino acid additives are discussed in detail via the experiment and theoretical calculation. Benefiting from the hydrogen bond between Cl- and amino acid, the chlorine evolution reaction is effectively avoided. In addition, the interaction of the Mn2+ and amino acid boosts the Mn2+/MnO2 reaction and inhibits the production of unstable Mn3+. As a result, the zinc-manganese flow battery with high-concentration MnCl2 electrolyte exhibits an outstanding performance of 82 % EE with a low capacity decay rate (1.45% per cycle over 1000 cycles) and wide temperature adaptability (from −10 ℃ to 65 ℃). This study opens a new opportunity for the application of flow batteries with high-concentration chloride electrolytes.

A Systematic Study on the Effects of Solvating Solvents and Additives in Localized High-Concentration Electrolytes over Electrochemical Performance of Lithium-Ion Batteries.

Localized high-concentration electrolytes (LHCEs) based on five different types of solvents were systematically studied and compared in lithium (Li)-ion batteries (LIBs). The unique solvation structure of LHCEs promotes the participation of Li salt in forming solid electrolyte interphase (SEI) on graphite (Gr) anode, which enables solvents previously considered incompatible with Gr to achieve reversible lithiation/delithiation. However, the long cyclability of LIBs is still subject to the intrinsic properties of the solvent species in LHCEs. Such issue can be readily resolved by introducing a small amount of additive into LHCEs. The synergetic decompositions of Li salt, solvating solvent and additive yield effective SEIs and cathode electrolyte interphases (CEIs) in most of the studied LHCEs. This study reveals that both the structure and the composition of solvation sheaths in LHCEs have significant effect on SEI and CEI, and consequently, the cycle life of energetically dense LIBs.

Gold Nanotriangle-Assembled Nanoporous Structures for Electric Field-Assisted Surface-Enhanced Raman Scattering Detection of Adenosine Triphosphate.

A reliable, rapid, cost-effective, and simple method for the detection of biomolecules would greatly promote the research of analytical detection of single molecules. A nanopore-based analytical technique is promising for detecting biomolecules. Conventional electrochemical nanopores cannot distinguish biomolecules precisely because of their fast translocation speed and limited electrochemical information. Therefore, it is highly desirable to develop electrochemical surface-enhanced Raman scattering (SERS) nanopores to obtain multidimensional information. Herein, we designed and fabricated gold nanotriangle (AuNT)-assembled porous structures at the tip of a glass capillary using dithiol adenosine triphosphate (ATP) aptamers as cross-linking molecules. The AuNTs exhibited an edge length of 57.3 ± 6.2 nm and thickness of about 15 nm. The gold nanoporous structure (GPS) showed a strong ion rectification even at a high concentration of electrolyte (2 M) and a high SERS activity. Based on these designed structures, SERS and electrochemistry techniques were combined to control the rapid movement of ATP to the vicinity of the GPS by an applied potential of +1 V, where ATP was concentrated by ATP aptamers and the molecular signals were amplified by SERS. As a result, the GPS successfully detected ATP at a concentration as low as 10-7 M.

Characterizing the Impact of Mg-Doped Li Metal Anode and Excess Electrons on High Concentration Electrolyte Interfacial Stability: A Theoretical Study

Characterizing the Impact of Mg-Doped Li Metal Anode and Excess Electrons on High Concentration Electrolyte Interfacial Stability: A Theoretical Study

Outstanding performances of graphite||NMC622 pouch cells enabled by a non-inert diluent

Although high salt concentration electrolyte (HCE) can construct effective LiF-rich interphase film and solve the interphasial instability issue of graphite anode, its high cost, high viscosity and poor wettability with electrode materials limit its large-scale application. Generally, localized high concentration electrolyte (LHCE) is obtained by introducing an electrochemically inert diluent into HCE to avoid the above-mentioned problems while maintaining the high interphasial stability of HCE with graphite anode. Unlike traditional inert diluents, 1, 1, 2, 2-tetrafluoroethyl-2, 2, 3, 3-tetrafluropropyl ether (TTE) with electrochemical activity is introduced into propylene carbonate (PC)-based HCE to obtain LHCE-2 (1 M LiPF6, PC:DMC:TTE = 1:1:6.1) herein. Experimental and theoretical simulation results show that TTE participates in the oxidation decomposition and film-forming reaction at the NCM622 cathode surface, conducting a cathode electrolyte interphase (CEI) rich in organic fluorides with excellent electron insulation ability, high structural stability and low interphasial impedance. Thanks to the outstanding interphasial properties induced by LHCE-2, the graphite||NMC622 pouch cell reaches a capacity retention of 80% after 500 cycles at 1 C under room temperature. While at sub-zero temperatures, the capacity released by the cell with LHCE-2 electrolyte is significantly higher than that of HCE and conventional EC-based electrolytes. Meanwhile, the LHCE-2 electrolyte inherits the advantages of TTE flame-resistant, thus improving the safety of the battery.

Preferential decomposition of the major anion in a dual-salt electrolyte facilitates the formation of organic-inorganic composite solid electrolyte interphase.

The performance of a lithium metal battery (LMB) with liquid electrolytes depends on the realization of a stable solid electrolyte interphase (SEI) on the Li anode surface. According to a recent experiment, a high-concentrated (HC) dual-salt electrolyte is effective in modulating the SEI formation and improving the battery performance. However, the underlying reaction mechanism between this HC dual-salt electrolyte and the lithium metal anode surface remains unknown. To understand the SEI formation mechanism, we first performed 95ps ab initio Molecular Dynamics (AIMD) simulation and then extend this AIMD simulation to another 1ns by using Hybrid ab Initio and Reactive Molecular Dynamics (HAIR) to investigate the deep reactions of such dual-salt electrolytes consists of lithium difluorophosphate and lithium bis(trifluoromethanesulfonyl)imide in dimethoxyethane (DME) solvent at lithium metal anode surface. We observed the detailed reductive decomposition processes of DFP- and TFSI-, which include the formation pathway of CF3 fragments, LiF, and LixPOFy, the three main SEI components observed experimentally. Furthermore, after extending the simulation to 1.1ns via the HAIR scheme, the decomposition reactions of DME solvent molecules were also observed, producing LiOCH3, C2H4, and precursors of organic oligomers. These microscopic insights provide important guidance in designing the advanced dual-salt electrolytes for developing high-performance LMB.

Design of Localized High-Concentration Electrolytes via Donor Number

Salt-concentrated electrolytes offer properties beyond conventional dilute electrolytes yet suffer from high cost and viscosity which hinder their practical applications. Introducing a secondary solvent as a diluent could reduce the salt content while maintaining the local solution structure of salt-concentrated electrolytes, giving rise to localized high-concentration electrolytes (LHCEs). Through a comprehensive investigation involving over 500 samples, we find that the dielectric constant of solvent, a widely used parameter for electrolyte design, does not serve as a useful screening criterion for diluents; instead, donor number (DN) is an effective design parameter to achieve LHCE structure─i.e., the primary solvent must have DN > 10 and the diluent must have DN ≤ 10. Based on this simple rule, a new LHCE using low-cost m-fluorotoluene diluent is formulated, enabling high-voltage (>4.6 V) and wide-temperature (−40–100 °C) operation of lithium batteries.

(Localized) Highly Concentrated Electrolytes for Calcium Batteries

AbstractThe concept of non‐aqueous highly concentrated electrolytes (HCEs) for modern rechargeable batteries has recently evolved further by also adding a non‐coordinating solvent, i. e., a diluent, to create localized HCEs (LHCEs). LHCEs rely on a charge carrier design similar to that of HCEs in synergy with tailored macroscopic properties, especially reduced viscosity. LHCEs have now been extensively investigated for monovalent Li+ and Na+ based batteries, but here we investigate both HCEs and LHCEs for divalent Ca2+ conducting systems. Here we systematically map both molecular and macroscopic features as function of composition of Ca(TFSI)2 (calcium bis(trifluoromethane)sulfonimide) in PC (propylene carbonate) based HCEs as well as the corresponding LHCEs created using TTE (1,1,2,2‐tetrafluoroethyl‐2,2,3,3‐tetrafluoropropyl ether) as diluent. Some unique HCE properties arise already at ca. 2.00 m, which is at a lower salt concentration than for monovalent systems, and in addition the local structure of the HCE can be maintained even within a nominal 0.45 m LHCE (starting from a 3.26 m parent HCE). The combined observations made at molecular and macro levels pave the way for further optimization of important physico‐chemical properties, proper design of electrochemical investigations, and eventually a better understanding of how to best improve the desolvation kinetics at e. g., the electrolyte/electrode interfaces of a Ca metal anode.

Lithium Nitrate/Amide-Based Localized High Concentration Electrolyte for Rechargeable Lithium–Oxygen Batteries under High Current Density and High Areal Capacity Conditions

Lithium Nitrate/Amide-Based Localized High Concentration Electrolyte for Rechargeable Lithium–Oxygen Batteries under High Current Density and High Areal Capacity Conditions

4.2V polymer all-solid-state lithium batteries enabled by high-concentration PEO solid electrolytes

Polyethylene oxide (PEO) solid electrolytes (SEs) are practicable in all-solid-state lithium batteries (ASSLBs) with high safety for driving electric vehicles. However, the low oxidative decomposition potential (below 4 V) of normal PEO SEs rules out high-voltage (≥4.2 V) cathodes in PEO-based ASSLBs with sacrificed energy densities. Herein, high-concentration PEO SEs (EO:Li+ ≤ 6:1) possessing high oxidation potentials (>5 V vs. Li/Li+) are designed based on concentrated-salt chemistry with oxidation potential surging incessantly with increasing the degree of coordinated EO. Thereby, double-layered heterogenous SEs with PEO(EO:Li=4:1) on the cathode side and PEO(EO:Li=16:1) on the anode side are designed to resist oxidation and bate interfacial impedance. Coupled with 4.2 V-class LiCoO2 and LiNi0.6Co0.2Mn0.2O2, the ASSLBs using heterogenous SEs exhibit enhanced stable cycling performances when charged to 4.2 V and 4.4 V at 60°C. As revealed by the Wagner-type model and Raman spectra, high-concentration PEO SE could suppress the interfacial degradation kinetics, the production of electronic conduction in the cathode electrolyte interphase (CEI) and the irreversible phase-change of LiCoO2 to Co3O4. All these contribute to the improved electrochemical performance of PEO/LiCoO2 system with high-volage, offering a potential pathway toward high-voltage stable polymer electrolytes for high-energy-density lithium batteries.

Synergistic-effect of diluent to reinforce anion-solvation-derived interfacial chemistry for 4.5 V−class Li||LiCoO2 batteries

Electrolyte engineering-controlled interfacial chemistries on both lithium metal anode (LMA) and high-voltage cathode are key to stable lithium-metal batteries (LMBs). Here, we demonstrate that a kind of local high concentrated electrolyte (LHCE) by introducing an active difluoroethylene carbonate (DFEC) co-solvent can contribute to excellent interfacial chemistries. Unlike the conventional LHCEs, DFEC with lower LUMO energy serves as both additive and diluent, and reinforces the anion-solvation-derived interfacial layers, leading to the suppression of side reactions/dendrite lithium growth and the acceleration of Li+ desolvation/transfer kinetics. Consequently, the assembled high-capacity Li||LiCoO2 full cell (1.836 mAh cm−2) holds a high retention of > 80% over 1000 cycles at 0.3 C under a high cut-off voltage of 4.5 V. More impressively, the addition of DFEC leads to a significant improvement of cycle stability for ∼265 mAh Li||LiCoO2 pouch cells. Designing functional diluent with a synergistic effect that heightens interfacial chemistries to control anion-solvation is very promising and paves a bright way to develop rechargeable LMBs.

Regulating solid electrolyte interphases on phosphorus/carbon anodes via localized high-concentration electrolytes for potassium-ion batteries

Regulating solid electrolyte interphases on phosphorus/carbon anodes via localized high-concentration electrolytes for potassium-ion batteries

Mechanism of high-concentration electrolyte inhibiting the destructive effect of Mn(II) on the performance of lithium-ion batteries

Mechanism of high-concentration electrolyte inhibiting the destructive effect of Mn(II) on the performance of lithium-ion batteries

Localized High-Concentration Electrolyte (LHCE) for Fast Charging Lithium-Ion Batteries

The solid electrolyte interphase (SEI) significantly influences the electrochemical performance of lithium-ion batteries. Traditional electrolytes, particularly ether electrolytes, make it challenging to form a stable SEI film, and the corresponding lithium-ion batteries frequently exhibit poor electrochemical performance. In this paper, we develop a stable SEI film to improve fast charging and cycle performance using a localized high concentration electrolyte (LHCE). A unique solvation sheath formed by the coordination of Li+, anion, and solvent in the LHCE caused the anion to migrate quickly to the surface of the graphite anode and decompose to form a LiF-rich SEI. A LHCE enabled the Li||C battery to maintain a capacity of 124 mAh g−1 at a rate of 5 C, and the capacity remained at 289 mAh g−1 after 150 cycles at a rate of 0.1 C, with a capacity retention rate of 73% and an average coulomb efficiency of about 99.8%, thus demonstrating excellent long-cycle performance. The LFP||Li battery capacity at a 5 C rate can also be maintained at 102 mAh g−1.

Electrophilically Trapping Water for Preventing Polymerization of Cyclic Ether Towards Low-Temperature Li Metal Battery.

Cyclic ether, such as 1,3-dioxolane (DOL), are promising solvent for low-temperature electrolytes because of the low freezing point. Their use in electrolytes, however, is severely limited since it easily polymerizes in the presence of lithium inorganic salts. The trace water plays a key role via providing the source (proton) for chain initiation, which has, unfortunately, been neglected in most cases. In this work, we present an electrophile, trimethylsilyl isocyanate (Si-NCO), as the water scavenger, which eliminates moisture by a nucleophilic addition reaction. Si-NCO allows DOL to maintain liquid over a wide temperature range even in high-concentration electrolyte. Electrolyte with Si-NCO additive shows promising low-temperature performance. Our finding expands the use of cyclic ether solvents in the presence of inorganic salts and highlights a large space for unexplored design of water scavenger with electrophilic feature for low-temperature electrolytes.

Ion Transport in Glyme- and Sulfolane-Based Highly Concentrated Electrolytes.

Highly concentrated electrolytes (HCEs) have a similarity to ionic liquids (ILs) in high ionic nature, and indeed some of HECs are found to behave like an IL. HCEs have attracted considerable attention as prospective candidates for electrolyte materials in future lithium secondary batteries owing to their favorable properties both in the bulk and at the electrochemical interface. In this study, we highlight the effects of the solvent, counter anion, and diluent of HCEs on the Li+ ion coordination structure and transport properties (e. g., ionic conductivity and apparent Li+ ion transference number measured under anion-blocking conditions, ). Our studies on dynamic ion correlations unveiled the difference in the ion conduction mechanisms in HCEs and their intimate relevance to values. Our systematic analysis of the transport properties of HCEs also suggests the need for a compromise to simultaneously achieve high ionic conductivity and high values.

Anionic Effects on Li-Ion Activity and Li-Ion Intercalation Reaction Kinetics in Highly Concentrated Li Salt/Propylene Carbonate Solutions

Certain highly concentrated electrolytes (HCEs) enhance the charge-transfer reaction rate at the electrode/electrolyte interface in Li-ion batteries. The solvation structure of Li+ in HCEs significantly affects the electrochemical interfacial reaction kinetics. However, the effects of different anions on these kinetics have not yet been fully understood. Therefore, in this study, we investigated the effects of anionic species on the liquid structure and electrochemical reactions of HCEs composed of various Li salts and propylene carbonate (PC). Raman spectra revealed that both PC and anions were coordinated to Li+ ions in HCEs and that the concentration of uncoordinated (free) PC changed depending on the anionic species. Consequently, the activity of Li+ in the electrolyte changed depending on the anionic species. The use of Li salts with weakly Lewis basic anions increased the activity of Li+ and decreased the concentration of free PC in HCEs. The activity of Li+ in the electrolyte significantly affected the Li+ intercalation/deintercalation reaction rate of the LiCoO2 thin-film electrode. Electrochemical impedance spectroscopy revealed that the interfacial reaction rate of LiCoO2 was enhanced in the HCEs with anions having weaker Lewis basicity owing to the higher Li+ ion activity.