Dual-salt Electrolyte Research Articles

Trace Dual-Salt Electrolyte Additive Enabling a LiF-Rich Solid Electrolyte Interphase for High-Performance Lithium Metal Batteries.

The composition and physiochemical properties of the solid electrolyte interphase (SEI) significantly impact the electrochemical cyclability of the Li metal. Here, we introduce a trace dual-salt electrolyte additive (TDEA) that accelerates LiF production from FEC decomposition and improves the LiF distribution, resulting in earlier LiF precipitation and the formation of a LiF-rich SEI on the Li anode. TDEA at a millimolar-level concentration was found to alter the morphology of deposited Li, suppress Li dendrite formation, and increase the cycling time and operating current density for Li anodes. Li∥NCM811 full cells using TDEA-based electrolytes exhibited approximately two times longer lifespan than those without additives. Additionally, the TDEA-based electrolytes enabled a high energy density of 347 Wh kg-1 for 500-mAh pouch cells, maintaining stable cycling over 180 cycles under stringent conditions (N/P = 1.26 and E/C = 2.2 g A h-1). Our findings suggest that the proposed TDEA strategy offers a promising path to achieving high-performance Li metal batteries.

Long-duration aqueous Zn-ion batteries achieved by dual-salt highly-concentrated electrolyte with low water activity

Aqueous Zn-ion batteries have attracted much attention due to their unique high safety and low-cost merits. However, their practical applications are at a slow pace due to their short cycle life, which fundamentally results from the instability of the positive/negative electrode interface in the traditional dilute aqueous electrolytes with high water activity. Developing highly concentrated electrolyte (HCE) has been considered as an effective solution. Unlike previous studies of single salt-based HCE (SS-HCE), herein, a new dual-salt HCE (15 m ZnCl2 + 10 m NH4NH2SO3 DS-HCE) was proposed for the first time. DS-HCE was proven to simultaneously possess higher conductivity than traditional dilute electrolytes and ultralow water activity of SS-HCE by the regulation of dual high-concentration salts on the solvation structure, which renders the Zn||Zn symmetric cell the record-long cycling life of 2200 h compared with those with SS-HCE (30 m ZnCl2, 300 h) and other reported HCEs. Additionally, the Zn||NH4V4O10 full cell with DS-HCE demonstrated impressed rate capability within a wide-range current densities from 0.1 to 10 A g−1. Moreover, at the high current density of 5 A g−1, the full cell shows almost 100% capacity retention after 4000 cycles, which indicates the promising future of the DS-HCE system for long-duration aqueous Zn-ion batteries.

Engineering the solvent-anion interactions of LiTFSI-based dual-salt electrolytes to sustain high-performance NCM622 cathodes

Electrolytes play a vital role in determining the performances of lithium-ion batteries (LIBs), especially the high-voltage LiNi0.6Co0.2Mn0.2O2 (NCM622) cathode in LiTFSI-based electrolytes. Herein, we report a high-capacity and stable NCM622 cathode that can be realized in LiTFSI-based (named T) carbonate electrolytes by tuning the intermolecular interactions using the added LiDFOB (named D). In the 1 M dual-salt electrolyte, the cathode failure and Al corrosion are suppressed in the 4.5 V-NCM622||Li batteries, because a uniform interfacial layer and weaker Li+-solvent interactions are built to inhibit the parasitic reactions. As a result, the capacity retention reaches 94.68% after 200 cycles and the 10 C-rate capacity is about 160 mA h g-1 in the 1 M T + D dual-salt electrolyte. Unlike the commonly used electrolyte, the FEC additive increases the de-solvation barrier and disturbs the cycle stability in (T + D) dual-salt systems. Density functional theory (DFT) calculation and nuclear magnetic resonance (NMR) spectra reveal that the additive FEC changes the solvent-solvent and solvent-anion interactions in the presence of T + D, which weakens the electrolyte-cathode compatibility. This work indicates that regulating the solvation structure and interfacial chemistry from solvent-solvent/anion interactions is promising for designing high-performance LIBs by using dual‐salt electrolytes.

Electrolyte Engineering with TFA- Anion-Rich Solvation Structure to Construct Highly Stable Zn2+/Na+ Dual-Salt Batteries.

Electrolyte engineering is recognized as an effective technique for high-performance aqueous zinc-ion rechargeable batteries, addressing difficulties such as free water decomposition, zinc anode corrosion, and zinc dendrite growth. Different from traditional strategies in aqueous electrolyte systems, this work focuses on organic electrolytes involving zinc trifluoroacetate hydrate (Zn(TFA)2·xH2O), sodium trifluoroacetate (NaTFA) dual-salt and acetonitrile (AN) solvent, in which trifluoroacetate anions (TFA- anions) have strong affinity toward zinc ions to form anion-rich solvates, thus inducing an inorganic-rich solid electrolyte interphase (SEI) to protect Zn from dendrite growth and side reactions. The Zn anode manifests long-term cycling over 2400h at a current density of 0.5mAcm-2 with a high Coulombic efficiency (CE) of 99.75%, showing an areal capacity as high as 5mAhcm-2. Owing to the high reversibility of the sodium ions intercalation/deintercalation process in Na2MnFe(CN)6, the Zn//Na2MnFe(CN)6 full cells with the dual-salt electrolyte perform much better in terms of capacity retention than a device with Zn(TFA)2/AN electrolyte. This approach may open a new avenue for efficient zinc-ion rechargeable batteries via developing organic electrolytes.

Achieving the Inhibition of Aluminum Corrosion by Dual-Salt Electrolytes for Sodium-Ion Batteries.

Sodium bis(fluorosulfonyl)imide (NaFSI) electrolytes are renowned for their superior physicochemical and electrochemical properties, making them ideal for high-performance sodium-ion batteries (SIBs). However, severe oxidative dissolution of aluminum current collectors (commonly known as Al corrosion) in NaFSI-based electrolytes occurs at high potentials. To address this challenge, aiming to understand the Al corrosion mechanism and develop strategies to inhibit corrosion, we propose dual-salt electrolytes using 0.8 mol L-1 (M) NaFSI and 0.2 M of a second fluorine-containing sodium salt dissolved in EC/PC solutions (1:1, v/v) to construct an insoluble deposits layer on the Al. Dual-salt electrolytes adopting a second sodium salt capable of passivating the Al collector have been extensively investigated through various techniques, such as cyclic voltammetry, scanning electron microscopy, chronoamperometry, X-ray photoelectron spectroscopy, and charge-discharge tests. Our findings demonstrate that introducing sodium difluoro(oxalato)borate (NaDFOB) into the NaFSI electrolytes inhibits Al corrosion, which is attributed to the formation of insoluble deposits of Al-F (AlF3) and B-F containing polymers. Moreover, the capacity retention of Na||Na3V2(PO4)3 (NVP) cells using the NaFSI-NaDFOB dual-salt electrolyte reaches 99.2% along with a Coulombic efficiency over 99.3% at a 1 C rate after 200 cycles. This research provides a practical solution for passivating Al collectors in SIBs with NaFSI electrolytes and promotes the development of sodium batteries with long calendar lifetimes.

Dual-Salt aqueous electrolyte for enhancing Charge-Storage properties of VO2 polymorphic cathodes for Zn-Ion batteries

Three VO2 polymorphs, namely monoclinic VO2 (B), monoclinic VO2 (M), and tetragonal VO2 (A), are synthesized, and their microstructures and electrochemical properties are studied for application in Zn-ion batteries (ZIBs). A cost-effective ZnSO4-based aqueous electrolyte with various concentrations (3 − 7 m) of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) additive is developed. The optimal ZnSO4/LiTFSI ratio in the electrolyte for superior Zn//VO2 battery properties is examined. The coordination structures of various electrolytes are investigated using wide-angle X-ray scattering. The incorporation of LiTFSI impairs the hydrogen-bonded network of H2O molecules and causes solvated-TFSI and TFSI‧‧‧TFSI structures to form, altering the electrolyte properties (such as electrochemical stability window, ionic conductivity, and Zn(OH)2)3(ZnSO4)·xH2O byproduct formation tendency). It is found that an excessive LiTFSI concentration leads to the formation of ion aggregates in the electrolyte and thus deterioration of electrode specific capacity and rate capability. Operando transmission X-ray microscopy observations confirm the high dimensional stability of the VO2 cathode during charging and discharging; the length variation of the VO2 (B) rods is approximately 10 %. The electrolyte composition also affects the Zn2+/Zn redox behavior at the anode side. The incorporation of LiTFSI into the electrolyte affects the Zn plating/stripping Coulombic efficiency, morphology of the deposited Zn, dead Zn amount, and anode cycle life. The constructed Zn//VO2 (B) cell with 1 m ZnSO4/5 m LiTFSI dual-salt electrolyte shows 90 % capacity retention after 1000 cycles. The proposed electrode material and electrolyte composition have great potential for applications in high-performance and high-stability rechargeable ZIBs.

A Sodium Bis(fluorosulfonyl)imide (NaFSI)-based Multifunctional Electrolyte Stabilizes the Performance of NaNi1/3Fe1/3Mn1/3O2/hard Carbon Sodium-ion Batteries.

A sodium bis(fluorosulfonyl)imide (NaFSI)-based multifunctional electrolyte is developed by partially replacing NaPF6 salt in the electrolyte to improve the wide temperature range working capability of NaNi1/3Fe1/3Mn1/3O2/hard carbon (NNFM111/HC) sodium-ion batteries (SIBs). The capacity retention of the SIBs with NaFSI-NaPF6 dual salt electrolyte increases from 47.2 % to 75.5 % after 250 cycles at 25 °C, and from 51.0 % to 82.3 % after 80 cycles at 45 °C, and the 1 C discharge capacity retention at the low temperature of -20 °C also increases 26.8 %. In the single salt system, NaPF6 effectively passivate the aluminum foil and NaFSI passivate the electrode/electrolyte interface. The synergistic effect of NaPF6 and NaFSI greatly improves the battery performance in a wide temperature range. This NaFSI-based dual salt electrolyte also effectively overcomes the flaws when the SIBs using NaFSI or NaPF6 independently, and makes it more suitable for SIBs, indicating promising prospects in the commercial application of NNFM111/HC SIBs.

Revealing the alkali ions effects in potential shift and Zn dendrites suppression via electrolyte concentration regulation in aqueous zinc ion batteries

The energy density of aqueous reachable batteries (ARBs) is limited by the output voltage in the aqueous electrolyte. Herein, low-cost aqueous hybrid electrolytes composed of ZnSO4 and K2SO4 dual salts effectively improve the output voltage and suppress the zinc dendrites. The aqueous full cells assembled with potassium zinc hexacyanoferrate (KZnHCF) cathodes and zinc foil anodes reach an output voltage of 1.92 V and an energy density of 107.6 Wh kg−1. It is demonstrated the reversible insertion/extraction of K+ at the cathodes and uniform zinc deposition/striping at the anode in hybrid electrolyte via a series in-situ and ex-situ investigation. The dual salt electrolyte can not only satisfy the reversible capacitive dominated process at the cathodes but also suppress the zinc dendrite. Density functional theory (DFT) calculation demonstrates the K+ preferential intercalation mechanism of KZnHCF in hybrid electrolyte and the inhibition effect of K+ insertion on Zn2+ insertion. This strategy presents a promising approach for development of high performance and low-cost aqueous electrolyte.

Upgrading Gel Electrolytes Through Electrostatic-Induced Dual-Salt Paradigm for Superior Zn-Ion Battery Performance.

Gel electrolytes are gaining attention for rechargeable Zn-ion batteries because of their high safety, high flexibility, and excellent comprehensive electrochemical performances. However, current gel electrolytes still perform at mediocre levels due to incomplete Zn salts dissociation and side reactions. Herein, an electrostatic-induced dual-salt strategy is proposed to upgrade gel electrolytes to tackle intrinsic issues of Zn metal anodes. The competitive coordination mechanism driven by electrostatic repulsion and steric hindrance of dual anions promotes zinc salt dissociation at low lithium salt addition levels, improving ion transport and mechanical properties of gel electrolytes. Li+ ions and gel components coordinate with H2O, reducing active H2O molecules and inhibiting associated side reactions. The dual-salt gel electrolyte enables excellent reversibility of Zn anodes at both room and low temperatures. Zn||Polyaniline cells using the dual-salt gel electrolyte exhibit a high discharge capacity of 180mAhg-1 and long-term cycling stability over 180 cycles at -20°C. The dual-salt strategy offers a cost-effective approach to improving gel electrolytes for high-performance flexible Zn-ion batteries.

Retarding anion migration for alleviating concentration polarization towards stable polymer lithium-metal batteries

Traditional dual-ion lithium salts have been widely used in solid polymer lithium-metal batteries (LMBs). Nevertheless, concentration polarization caused by uncontrolled migration of free anions has severely caused the growth of lithium dendrites. Although single-ion conductor polymers (SICP) have been developed to reduce concentration polarization, the poor ionic conductivity caused by low carrier concentration limits their application. Herein, a dual-salt quasi-solid polymer electrolyte (QSPE), containing the SICP network as a salt and traditional dual-ion lithium salt, is designed for retarding the movement of free anions and simultaneously providing sufficient effective carriers to alleviate concentration polarization. The dual salt network of this designed QSPE is prepared through in-situ crosslinking copolymerization of SICP monomer, regular ionic conductor, crosslinker with the presence of the dual-ion lithium salt, delivering a high lithium-ion transference number (0.75) and satisfactory ionic conductivity (1.16 × 10−3 S cm−1 at 30 °C). Comprehensive characterizations combined with theoretical calculation demonstrate that polyanions from SICP exerts a potential repulsive effect on the transport of free anions to reduce concentration polarization inhibiting lithium dendrites. As a consequence, the Li||LiFePO4 cell achieves a long-cycle stability for 2000 cycles and a 90% capacity retention at 30 °C. This work provides a new perspective for reducing concentration polarization and simultaneously enabling enough lithium-ions migration for high-performance polymer LMBs.

Low-Temperature and Fast-Charge Sodium Metal Batteries.

Low-temperature operation of sodium metal batteries (SMBs) at the high rate faces challenges of unstable solid electrolyte interphase (SEI), Na dendrite growth, and sluggish Na+ transfer kinetics, causing a largely capacity curtailment. Herein, low-temperature and fast-charge SMBs are successfully constructed by synergetic design of the electrolyte and electrode. The optimized weak-solvation dual-salt electrolyte enables high Na plating/stripping reversibility and the formation of NaF-rich SEI layer to stabilize sodium metal. Moreover, an integrated copper sulfide electrode is in situ fabricated by directly chemical sulfuration of copper current collector with micro-sized sulfur particles, which significantly improves the electronic conductivity and Na+ diffusion, knocking down the kinetic barriers. Consequently, this SMB achieves the reversible capacity of 202.8mAhg-1 at -20°C and 1C (1C = 558mAg-1). Even at -40°C, a high capacity of 230.0mAhg-1 can still be delivered at 0.2C. This study is encouraging for further exploration of cryogenic alkali metal batteries, and enriches the electrode material for low-temperature energy storage.

Dual-Salt Electrolyte Additive Enables High Moisture Tolerance and Favorable Electric Double Layer for Lithium Metal Battery.

The carbonate electrolyte chemistry is a primary determinant for the development of high-voltage lithium metal batteries (LMBs). Unfortunately, their implementation is greatly plagued by sluggish electrode interfacial dynamics and insufficient electrolyte thermodynamic stability. Herein, lithium trifluoroacetate-lithium nitrate (LiTFA-LiNO3 ) dual-salt additive-reinforced carbonate electrolyte (LTFAN) is proposed for stabilizing high-voltage LMBs. We reveal that 1) the in situ generated inorganic-rich electrode-electrolyte interphase (EEI) enables rapid interfacial dynamics, 2) TFA- preferentially interacts with moisture over PF6 - to strengthen the moisture tolerance of designed electrolyte, and 3) NO3 - is found to be noticeably enriched at the cathode interface on charging, thus constructing Li+ -enriched, solvent-coordinated, thermodynamically favorable electric double layer (EDL). The superior moisture tolerance of LTFAN and the thermodynamically stable EDL constructed at cathode interface play a decisive role in upgrading the compatibility of carbonate electrolyte with high-voltage cathode. The LMBs with LTFAN realize 4.3 V-NCM523/4.4 V-NCM622 superior cycling reversibility and excellent rate capability, which is the leading level of documented records for carbonate electrode.

Dual-Salt Mixed Electrolyte for High Performance Aqueous Aluminum Batteries.

A dual-salt electrolyte with 5 M Al(OTF)3 and 0.5 M LiOTF is proposed for aqueous aluminum batteries, which can effectively prevent the corrosion caused by the hydrogen evolution reaction. With the addition of LiOTF in the electrolyte, the solvation phenomenon has changed with the coordination mode of Al3+ conversion from an all octahedral structure to a mixed octahedral and tetrahedral structure. This change can reduce the hydrogen bond between water molecules, which will minimize the occurrence of hydrogen evolution reactions. Moreover, the new electrolyte improves the cycle life of the battery. With MnO as the cathode, 2.1 V high charging platform and 1.5 V high discharge platform can be obtained. The electrochemical stability window (ESW) has been improved to 3.8 V. The first cycle capacity is up to 437 mAh g-1, which can be maintained at 103 mAh g-1 after 100 cycles. This work provides solutions for the future development of electrolyte for aqueous aluminum batteries.

Solvation Engineering via Fluorosurfactant Additive Toward Boosted Lithium-Ion Thermoelectrochemical Cells

HighlightsSolvation engineering toward dual-salt electrolyte by fluorosurfactant additive is proposed, which implements the stable interface of electrode/electrolyte coupled with fast ion thermodiffusion, improving the durability and capability of lithium-ion thermoelectrochemical cell.By combining the optimized electrolyte with functional electrodes, as-constructed device exhibits high Seebeck coefficient and energy density based on hybrid mechanisms, which can be extended as self-power supply for smart electronics.

Long-stable lithium metal batteries with a high-performance dual-salt solid polymer electrolyte

A high-performance dual-salt solid polymer electrolyte, consisting of cross-linked NPGDA-VEC copolymer interpenetrated in a PVDF-HFP nanofiber matrix, with LiTFSI and LiBOB as Li+ sources, was prepared for lithium metal battery applications.

Lithium Nitrate as Salt Additive for Solid Electrolyte Interphase Formation in Dual‐Ion Battery

AbstractTuning the solid electrolyte interphase (SEI) formation in dual‐ion batteries is important for improving their long‐term stability. In this context, salt additives have gained importance which can sacrificially undergo reduction thereby protecting the working salt. Herein, we have considered dual salt electrolyte models of LiNO3 additive with LiPF6 and LiFSI salt to carry out ab initio molecular dynamics (AIMD) simulations and witness the evolution of SEI layer. Various contact ion pair and solvent separated ion pair models of the dual salt electrolytes have been considered to further understand the role played by solvation shells of the ions. The small size and quicker diffusion of anions through the electrolyte results in its decomposition at the electrode surface irrespective of the anion being in contact ion pair or solvated by solvent molecules. Overall, along with underlining the role of salt additives in SEI formation, this detailed study also provides insights regarding the factors beyond solvation characteristics of salt that determines the SEI growth process.

Constructing stable interfaces for wide-temperature and high-rate aqueous zinc metal batteries by dual-salt cosolvent electrolyte

Rechargeable aqueous zinc metal batteries are large-scale new energy storage system due to their low cost and high safety. Nonetheless, a series of problems faced by zinc anode at wide temperatures will also limit its development, such as serious zinc dendrites and parasitic reactions. Herein, we report a dual-salt cosolvent electrolyte in which the addition of zinc perchlorate and 2-methyltetrahydrofuran assists the formation of stable SEI on the Zn anode surface. The ZnF2-rich SEI was constructed in-situ, which effectively inhibited the growth of zinc dendrite and exacerbation of parasitic reaction. Meanwhile, such solvents break the hydrogen bond network between the water molecules and change the solvation structure of Zn2+. Consequently, the Zn||Zn symmetric cells could remain stable during cycling for 9200 min at −20 °C and 6000 min at 60 °C (5 mA cm−2). Significantly, AZMBs exhibited an ultrahigh cumulative cycling capacity of 2250 mAh cm−2 at 20 °C. The PANI@V2O5 full cells maintained a capacity of 78.80 mAh/g after 250 cycles at −20 °C (2 A/g) and exhibited a long cycle life at 60 °C (more than 200 cycles). This study demonstrates a promising pathway for the future exploitation of high-rate AZMBs for operation under wide temperature.

Poly(vinylidene fluoride)-based dual-salt composite polymer electrolytes for superior room-temperature solid-state lithium batteries

Polymer electrolytes are one of the most promising candidates for advancing the development of solid-state lithium metal batteries (SLMBs) due to their easy preparation process, high flexibility, and lightweight. However, the low ionic conductivity at room temperature limits their practical applications. In this study, we propose a strategy of dual-salt modification of polyvinylidene fluoride (PVDF)-based polymer electrolytes to enhance lithium ion transport channels, specifically through the introduction of Lithium bis(trifluoromethanesulphonyl)imide (LiTFSI), lithium bis(oxalate)borate (LiBOB), and Li6.4La3Zr1.4Ta0.6O12 (LLZTO) into polyvinylidene fluoride-polyvinyl acetate (PVDF-PVAC) polymer chain to form a dual-salt composite polymer electrolyte (DS-CPE), which effectively control the dehydrofluorination of the PVDF skeleton and eliminate the PVDF gel discoloration phenomenon. The newly developed DS-CPE shows high ionic conductivity at room temperature (4.96 × 10−4 S cm−1), sufficient Li+ transference number (tLi+ = 0.57), excellent oxidation resistance (5.4 V vs. Li/Li+), and favorable interfacial compatibility. Moreover, Li|DS-CPE|Li symmetric cell stably cycles 1300 h at 0.1 mA cm−1, and the Li|DS-CPE|LFP cell delivers excellent rate performance, maintaining a capacity retention of 91.4 % over 450 cycles.

Flame-Retardant Gel Electrolyte toward High-Safety Lithium Metal Batteries with High-Mass-Loading Cathodes

Gel electrolytes are an important transitional state in developing lithium-ion conductors from the liquid state to the solid state. However, very few gel electrolytes have been realized to enable the long-term operation of high-safety lithium metal batteries (LMBs) with high-mass-loading cathodes. Here, we propose a dual-salt gel electrolyte with a flame-retardant plasticizer (denoted as PVC/TEP electrolyte) for LMBs. Flame-retardant molecules were encapsulated into the PVC matrix via in situ polymerization of a vinylene carbonate monomer. The resultant PVC/TEP electrolyte possesses a high ionic conductivity of ∼3.1 × 10–3 S cm–1 at 30 °C, a wide electrochemical window of ∼4.85 V, and low self-extinguishing times of less than 0.3 s g–1 due to the homogeneous distribution of flame-retardant and fluorine-rich dual salts. Consequently, gel electrolyte-based LMBs with high-mass-loading cathodes (8.49 mg cm–2) achieve comparable rate performance to liquid electrolyte-based LMBs and long cycle life well beyond them.

Enabling good interfacial stability by dual-salt composite electrolyte for long cycle lithium metal batteries

Enabling good interfacial stability by dual-salt composite electrolyte for long cycle lithium metal batteries