Conventional Carbonate Electrolytes Research Articles

Fast‐Charging Electrolyte: A Multiple Additives Strategy with 1,3,2‐Dioxathiolane 2,2‐Dioxide and Lithium Difluorophosphate for Commercial Graphite/LiFePO4 Pouch Battery

AbstractSafe fast‐charging lithium‐ion batteries (LIBs) can be achieved by using LiFePO4 electrode and optimized electrolyte for the rapid development of electric vehicles. However, conventional carbonate electrolyte suffers resistive solid electrolyte interphase (SEI) that hampering the fast‐charging for LIBs. Herein, a multiple additive strategy, the combination of 1,3,2‐Dioxathiolane 2,2‐dioxide (DTD) and lithium difluorophosphate (DFP), is proposed to optimize the electrode interface for graphite (Gr)/LiFePO4(LFP) pouch cells under fast‐charging. Combining DTD with DFP can significantly reduce the charge transfer resistance of anode and greatly extend the lifespan of cells with >2400 cycles at a 2 C rate, which is much better than that of baseline and single additive based electrolytes with <1000 cycles. Further mechanistic studies revealed that proper sulfurized and phosphatized species are involved in the SEI film, which stabilizes lithium carbonate in the middle of SEI to avoid being attacked by Lewis acids. Multiple additive strategies optimize the interfacial structure and provide valuable guidance for the development of safe fast‐charging engineering.

A sulfone-based crystalline organic electrolyte for 5 V solid-state potassium batteries

Solid-state potassium batteries are promising energy storage systems, but their wide use requires suitable solid electrolytes to ensure high ionic conductivity, electrochemical stability, and contacting ability with composite electrodes. For this purpose, this study introduces sulfone-based crystalline organic electrolytes (SCOEs) consisting of dimethyl sulfone (DMS) and potassium bis(fluorosulfonyl)imide (KFSI). One solid-state SCOE, KFSI/DMS 1:9 by mol, exhibits high ionic conductivity (4.0 × 10−4 S cm−1 at 25 °C), oxidation stability (∼5.8 V vs. K+/K), and negligible flammability. Moreover, owing to its optimal melting point (94 °C), the SCOE enables seamless contact with the composite electrodes through the melt-casting process, which has been challenging for other solid-state electrolytes. K||KVPO4F cells filled with this SCOE show improved cycle performance (capacity retention 88.8% after 100 cycles vs. 77.6% after 74 cycles at 25 °C) with high Coulombic efficiency (asymptotic value 99.6% vs. 92.0%) compared to cells with a conventional carbonate electrolyte. With these results, the developed SCOE paves the way to room-temperature operable, 5 V solid-state potassium batteries.

Improved Low‐Temperature Performance of Rocking‐Chair Sodium‐Ion Hybrid Capacitor by Mitigating the De‐Solvation Energy and Interphase Resistance

AbstractHybrid capacitors, which bear the advantages of secondary batteries and supercapacitors, can deliver high power with a relatively fair amount of energy. However, its kinetic performance, especially at low temperatures, is strongly limited by the battery‐type electrode and electrolyte. In this work, Na‐ion, which has a lower solvation energy than Li‐ion, is chosen as the charge carrier to build the hybrid capacitor. A sodium‐ion hybrid capacitor is built with an activated carbon cathode and a pre‐sodiated hard carbon anode. To achieve a better kinetic performance, the de‐solvation energy and interphase resistance is decreased through replacing conventional carbonate electrolyte with a diethylene glycol dimethyl ether (DEGDME) based electrolyte. As a result, the sodium‐ion capacitor delivers an energy density of 42 Wh kg–1 and a high power of 4565 W kg–1 for 3000 cycles at 2.5 A g–1. Furthermore, this capacitor could sustain an energy density of 36 Wh kg–1 at the low temperature of −30 °C and maintain 70% of the capacity after 500 cycles. The strategies of reducing de‐solvation energy and optimizing the solid electrolyte interphase property offers a clear path for developing electrochemical energy storage devices at lower temperatures.

Interfacial nitrogen engineering of robust silicon/MXene anode toward high energy solid-state lithium-ion batteries

Replacing the conventional carbonate electrolyte by solid-state electrolyte (SSE) will offer improved safety for lithium-ion batteries. To further improve the energy density, Silicon (Si) is attractive for next generation solid-state battery (SSB) because of its high specific capacity and low cost. High energy density and safe Si-based SSB, however, is plagued by large volume change that leads to poor mechanical stability and slow lithium ions transportation at the multiple interfaces between Si and SSE. Herein, we designed a self-integrated and monolithic Si/two dimensional layered T3C2Tx (MXene, Tx stands for terminal functional groups) electrode architecture with interfacial nitrogen engineering. During a heat treatment process, the polyacrylonitrile not only converts into amorphous carbon (a-C) that shells Si but also forms robust interfacial nitrogen chemical bonds that anchors Si and MXene. During repeated lithiation and delithiation processes, the robust interfacial engineered Si/MXene configuration enhances the mechanical adhesion between Si and MXene that improves the structure stability but also contributes to form stable solid-electrolyte interphase (SEI). In addition, the N-MXene provides fast lithium ions transportation pathways. Consequently, the Si/MXene with interfacial nitrogen engineering (denoted as Si-N-MXene) deliveres high-rate performance with a specific capacity of 1498 mAh g−1 at a high current of 6.4 A g−1. A Si-N-MXene/NMC full cell exhibited a capacity retention of 80.5% after 200 cycles. The Si-N-MXene electrode is also applied to SSB and shows a relative stable cycling over 100 cycles, demonstrating the versatility of this concept.

Coexistence of (O2)n- and Trapped Molecular O2 as the Oxidized Species in P2-Type Sodium 3d Layered Oxide and Stable Interface Enabled by Highly Fluorinated Electrolyte.

The interface stability of cathode/electrolyte for Na-ion layered oxides is tightly related to the oxidized species formed during the electrochemical process. Herein, we for the first time decipher the coexistence of (O2)n- and trapped molecular O2 in the (de)sodiation process of P2-Na0.66[Li0.22Mn0.78]O2 by using advanced electron paramagnetic resonance (EPR) spectroscopy. An unstable interface of cathode/electrolyte can thus be envisaged with conventional carbonate electrolyte due to the high reactivity of the oxidized O species. We therefore introduce a highly fluorinated electrolyte to tentatively construct a stable and protective interface between P2-Na0.66[Li0.22Mn0.78]O2 and the electrolyte. As expected, an even and robust NaF-rich cathode-electrolyte interphase (CEI) film is formed in the highly fluorinated electrolyte, in sharp contrast to the nonuniform and friable organic-rich CEI formed in the conventional lowly fluorinated electrolyte. The in situ formed fluorinated CEI film can significantly mitigate the local structural degeneration of P2-Na0.66[Li0.22Mn0.78]O2 by refraining the irreversible Li/Mn dissolutions and O2 release, endowing a highly reversible oxygen redox reaction. Resultantly, P2-Na0.66[Li0.22Mn0.78]O2 in highly fluorinated electrolyte achieves a high Coulombic efficiency (CE) of >99% and an impressive cycling stability in the voltage range of 2.0-4.5 V (vs Na+/Na) under room temperature (147.6 mAh g-1, 100 cycles) and at 45 °C (142.5 mAh g-1, 100 cycles). This study highlights the profound impact of oxidized oxygen species on the interfacial stability of cathode/electrolyte and carves a new path for building stable interface and enabling highly stable oxygen redox reaction.

Decomposition Reactivities of Carbonate Electrolyte Vs. Localized High Concentration Electrolytes on NaNiO2 Cathode Surface

Cathode electrolyte interphase (CEI) layers formed by the electrolyte decomposition on the positive electrode have been thought to be critical for the electrochemical performance of sodium-ion batteries. The conventional carbonate electrolyte decomposition often leads to unstable CEI layers, which are one of the known causes of capacity loss and structural degradation over repeated charging cycles. To solve this obstacle, the conception of localized high concentration electrolyte (LHCE) was proposed to maintain localized solvation structure of active electrolyte salts by using hydrofluoroethers as diluents. However, the cathode decomposition mechanisms of LHCE electrolytes have been rarely studied and the formation of CEI layers at cathode-LHCE interfaces are still unclear. Here, density functional theory is applied to investigate the oxidative decompositions of carbonate electrolyte and LHCE electrolyte on layered NaNiO2 surface. We compared the oxidation potentials of electrolyte molecules, reactions mechanisms of bulk electrolytes and decomposition reactions on (0 0 2) and (1 0 -2) surfaces of NaNiO2. Our results indicated that H-transfer reactions were prone to occur during carbonate electrolyte decomposition, while solvent(diluent) dissociation reactions were the primary pathways for LHCE decomposition. The proton transfer reactions with cathode surface oxygen atoms contribute to the formation of hydroxyl group (-OH). We predicted that the charge reduction of surface nickel atoms bonded with -OH groups is the main reason for the capacity fading and structural transformation of NaNiO2 cathode.

(Invited) Tuning the Formation and Structure of the Silicon Electrode/Electrolyte Interphase in Superconcentrated Ionic Liquids

In order to push further the development of next generation Li-ion batteries (LiBs), high energy density, good capacity retention and increased safety are key features that need to be taken into account when designing energy storage devices. To this date, commercial batteries for portable devices mainly use graphite as anode. However, with the advent of electric vehicles and intelligent power grids, there is an increasing demand for high capacity materials to meet the energy and power requirement of these applications. More recently, Si anode has received considerable attention because of its natural abundance and its ability to deliver high energy density, with a gravimetric capacity of 3579 mAhg-1 which is almost 10 times that of graphite (372 mAhg-1) [1-2].Bearing in mind that commercial LiBS use carbonate electrolytes which are recognized to pose safety issues and have been identified to suffer from degradation during charge-discharge cycles, we explored in this study the performance of Si anode in ionic liquid electrolytes based on phosphonium and pyrrolidinium cations, systems that are currently the most studied in the field of Li batteries [3-4]. Ionic liquid electrolytes are an appealing alternative to carbonates mainly because of their low volatility and better stability.In the recent years, good electrochemical behavior has been observed in ionic liquids with high salt concentration [3-5]. In this work, we were able to demonstrate better electrochemical performance of Si anode in ionic liquid electrolytes with 3.2 M LiFSI compared to conventional carbonate electrolytes in terms of capacity and capacity retention at 50°C. Our recent study using superconcentrated electrolytes revealed the superior electrochemical behaviour of triethyl(methyl)phosphonium bis(fluorosulfonyl)imide (P1222FSI) in a half-cell investigation of Si negative electrodes (Fig. 1). This result was linked to the stability of the electrolyte upon cycling and to improved lithium ion transport which is facilitated at high Li salt content [6]. Moreover, initial investigation of the SEI using NMR and XPS spectroscopy revealed that less degradation products are formed upon cycling in ionic liquid electrolytes compared to usual carbonates electrolytes. In the present work, we report the importance of tuning the Si/IL electrolyte interface as a function of IL cation nature and salt concentration. Experimental techniques such as 7Li, 19F MAS-NMR, SEM, and STEM-EDX were used to determine the SEI composition and morphology in order to further investigate its influence on the electrochemical performance as well as the relationship of the electrolyte chemistry (P1222FSI, N-methyl-N-propylpyrrolidinium (C3mpyr) FSI-based electrolytes and carbonate-based electrolyte) to the SEI properties. In addition, computational methods and differential capacitance (DC) experiments using AC impedance were applied to gain a better understanding of the SEI formation by examining the structuring at the electrode/electrolyte interphase.

High-Li+-fraction ether-side-chain pyrrolidinium–asymmetric imide ionic liquid electrolyte for high-energy-density Si//Ni-rich layered oxide Li-ion batteries

In this study, Si nanoparticles with interweaving carbon nanotubes are wrapped by graphitic sheets to achieve high conductivity and high dimensional stability of a composite anode (denoted as Si/CNT/G) for Li-ion batteries. In addition, an ionic liquid (IL) electrolyte that consists of ether-side-chain pyrrolidinium, asymmetric imide, and a high Li+ fraction is prepared. This electrolyte is for the first time employed for Si-based Li-ion batteries. Decomposition of the ether groups creates organic components in the solid electrolyte interphase (SEI). The high Li+ concentration promotes decomposition of the (fluorosulfonyl)(trifluoromethanesulfonyl)imide (FTFSI−) anions, leading to a LiF- and Li3N-rich SEI. The organic-inorganic balanced SEI is responsible for the excellent charge-discharge properties of the Si/CNT/G anode. The FTFSI− anions exhibit low corrosivity toward the Al current collector and high compatibility with the LiNi0.8Co0.1Mn0.1O2 (NCM-811) cathode. With a charging voltage of 4.5 V, remarkable reversible capacities and cycling stability of NCM-811 in the high-Li+-fraction N-methoxyethyl-N-methylpyrrolidinium/FTFSI IL electrolyte are observed. Differential scanning calorimetry is used to examine the interfacial exothermic reactions between the delithiated NCM-811 and various electrolytes. After 300 charge-discharge cycles, the capacity retention of a Si/CNT/G||NCM-811 full cell with the proposed IL electrolyte is 80% with a Coulombic efficiency of ∼99.9%. These values are significantly higher than those of the conventional carbonate electrolyte cell.

Role of Electrolyte in Stabilizing the Solid Electrolyte Interface of Hard Carbon As an Anode for Sodium-Ion Batteries

Hard carbon (HC) is an attractive anode material for sodium-ion batteries (NIBs) because it can be made from biomass or plastic, has a high capacity of ~300 mAh/g, and an extremely low average voltage near 0V. When fabricated with cathodes free of Li, Ni, and Co, NIBs using HC anodes are a promising approach for grid storage because they are energy-dense, sustainable, and have a low cost of energy. In order for these batteries to become a practical long-life solution, the issues of low first coulombic efficiency and poor rate performance of HC in conventional carbonate electrolytes need to be addressed. Two mechanisms that potentially cause these issues to occur are changes to the HC structure affecting sodium storage and the formation of the solid electrolyte interface (SEI). The proper selection of electrolyte is critical for controlling these mechanisms. To observe and characterize these mechanisms, we compared HC using a conventional carbonate electrolyte, 1M NaPF6 in propylene carbonate (PC), with a high performing glyme based electrolyte, 1M NaBF4 in tetraethylene glycol dimethyl ether (TEGDME). Compared to the poor rate capability of HC in PC electrolyte, HC in TEGDME electrolyte shows an excellent rate capability of ~265 mAh/g at C/20 and ~260 mAh/g at C/3. Titration gas chromatography and Raman spectroscopy were used to show that the HC with either electrolyte had the same sodium storage mechanism with no “stuck” sodium in the HC structure after the first cycle. These observations suggest that SEI formation is responsible for the irreversible capacity differences. The SEI formation was explored with scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), and x-ray photoelectron spectroscopy (XPS). The PC electrolyte’s SEI is found to be thick, fluffy, irregular and composed of polyesters, alkyl carbonates, NaxPFyOz, and NaF. The TEGDME electrolyte’s SEI is found to be thin, conformal, uniform, and composed of polyethers, sodium alkoxides, NaxBFyOz, and NaF. Additionally, the PC electrolyte’s SEI is rate dependent with more unstable products formed at high rates whereas the TEGDME electrolyte’s SEI is not rate dependent. These findings show that HC anode’s rate capability is controlled by the quality of the SEI formed by the electrolyte rather than the HC material structure. This model of rate and electrolyte dependent SEI indicates that SEI engineering is a pathway to improve HC as an anode for long-life grid-level NIBs. Figure 1

Efficient Lithium Metal Cycling at a Wide Range of Pressures from an Anion-Derived Solid-Electrolyte Interphase Framework

Novel electrolytes have been developed to improve the cyclability of lithium (Li) metal anodes, yet their working mechanisms remain unclear. The dependence of the performance on the operational pressure can provide valuable insights on the Li plating mechanisms in different electrolytes. Here, we study Li cycling performance evolution against pressure in 1 M LiFSI/fluorinated 1,4-dimethoxylbutane (FDMB) electrolyte, one of the highest-performing electrolytes for Li metal to date. We show that it enables excellent Coulombic efficiency (CE) in a pouch cell format under a wide range of initial pressures (30-600 psi). We discover that this is due to a completely different Li plating mode with superior deposition morphologies compared to that in a conventional carbonate electrolyte, which exhibits increasing cycle stability with increased pressure. We show that this is enabled by the properties of an anion-derived residual solid-electrolyte interphase (rSEI) framework on the electrode surface, an undercharacterized structure with profound implications for Li metal cycling. The plating morphology enabled by this anion-derived rSEI chemistry is likely the key to a prolonged cycle life in high performance electrolytes for Li metal.

Stabilization effect of solid-electrolyte interphase by electrolyte engineering for advanced Li-ion batteries

Sn-based materials have been highlighted as promising anodes for next-generation batteries; however, such alloying-based anodes suffer from gradual cell degradation caused by the associated large volume changes, leading to particle pulverization and an unstable solid electrolyte interphase (SEI). A key to constructing a stable SEI as well as effectively buffering the large volume expansion is to establish appropriate electrolyte conditions. In this work, to induce the formation of a favorable SEI layer, a Sn anode is paired with an electrolyte composed of eutectic succinonitrile (SN) combined with fluoroethylene carbonate (FEC) for the first time. Whereas conventional electrolytes are prone to form organic SEI components, which are vulnerable to large volume changes, the combination of SN and FEC enables the formation of a mechanically rigid SEI that is mainly composed of favorable inorganics such as LiF and Li3N. The synergistic effects of SN and FEC result in superior cycle performance of the Sn anode with improved efficiency compared with that achieved using conventional carbonate electrolytes. The modified SEI layer was closely investigated using various surface analysis techniques, with the individual effects of SN and FEC extracted. The rational design of the electrolyte provides a simple yet effective approach to enhance the electrochemical performance of Sn anodes and can be further extended to other alloying-based anode materials.

Reversible Mn/Cr dual redox in cation-disordered Li-excess cathode materials for stable lithium ion batteries

Cation-disordered Li-excess oxides/oxyfluorides have opened the door for designing alternative, high energy cathodes. However, achieving long cycle life and high rate capability represents a major challenge for disordered rocksalt cathodes (DRX). Herein, we develop Li2Mn3/4Cr1/4O2F (LMCOF) DRX materials through a distinct redox mechanochemical method. The LMCOF contains trivalent Cr3+ and Mn3+, which allows for simultaneously accessing stable Mn/Cr dual redox at a narrow voltage window acceptable for conventional carbonate electrolytes. Coupled with the mitigated and reversible oxygen chemical changes, the LMCOF delivers high capacity, rate capability, as well as long cycle life upon extensive 1,000 cycles at various current densities. The multiscale synchrotron and neutron scattering, spectroscopic, and imaging analyses demonstrate that the capacity originates from the Mn/Cr dual redox with minimal contribution from oxygen redox, and that the good cycle life is attributed to the stable global crystal structure and local oxygen chemical environment.

A crystalline organic electrolyte for safe, room-temperature operable all-solid-state sodium batteries

Owing to their mitigated safety risk and high energy density, all-solid-state sodium batteries are promising post-Li batteries. However, current solid-state electrolytes have insufficient ionic conductivity, electrochemical stability, and contacting ability with porous electrodes. To overcome these issues, this study presents sulfone-based crystalline organic electrolytes (SCOEs) composed of dimethyl sulfone (DMS) and sodium bis(fluorosulfonyl)imide (NaFSI). One particular SCOE (NaFSI/DMS, 2:8 by mol) has high ionic conductivity (7.0 × 10−4 S cm−1) at 25 °C and excellent oxidative stability (>5.5 V vs. Na+/Na). Importantly, the SCOE displays an optimum melting point (66 °C), enabling intimate contact with porous composite electrodes via the melt-casting process. Na||Na3V2(PO4)3 cells employing this SCOE show better cyclability than do cells employing a conventional carbonate electrolyte (capacity retention 91.1% vs. 60.3% after 200 cycles at 25 °C). Additionally, the SCOE has negligible flammability, unlike carbonate electrolytes, thus holding great promise as an electrolyte for safe, room-temperature operable all-solid-state sodium batteries.

Reduced Gassing In Lithium-Ion Batteries With Organosilicon Additives

The release of gases through electrolyte decomposition is a problem of prominent concern in the Li-ion battery industry, due to the negative impact of gassing on cell safety and performance. The development of new electrolytes and additives is essential in enabling low-gassing batteries. Organosilicon (OS) molecules, which merge a silane with a Li+ coordinating functionality, have been developed by Silatronix® as additions to conventional carbonate electrolytes, demonstrating critical high thermal and voltage stability to enable next-generation Li-ion batteries. In this study we report performance testing and fundamental mechanistic studies to investigate gassing phenomena in advanced Li-ion chemistries under storage test conditions. Novel organosilicon nitriles developed by Silatronix® as well as common gas reducing additives (i.e. 1,3-propanesultone, succinonitrile) were evaluated in a 4.35 V Graphite/NMC622 (LiNi0.6Mn0.2Co0.2O2) multi-layer pouch cell. Potential synergies between OS materials and these additives were investigated. The dependence of gassing on electrolyte composition and test conditions was investigated, and connections between gassing behavior and electrode surface chemistry are also reported. Key experimental results show that all OS concentrations reduce gas generation during 60 °C storage, and higher OS content provides greater benefit. Overall, we show that organosilicon additives substantially reduce gassing from carbonate-based electrolytes while maintaining cell performance.

Thermal Stability Analysis of Lithium-Ion Battery Electrolytes Based on Lithium Bis(trifluoromethanesulfonyl)imide-Lithium Difluoro(oxalato)Borate Dual-Salt.

Lithium-ion batteries with conventional LiPF6 carbonate electrolytes are prone to failure at high temperature. In this work, the thermal stability of a dual-salt electrolyte of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium difluoro(oxalato)borate (LiODFB) in carbonate solvents was analyzed by accelerated rate calorimetry (ARC) and differential scanning calorimetry (DSC). LiTFSI-LiODFB dual-salt carbonate electrolyte decomposed when the temperature exceeded 138.5 °C in the DSC test and decomposed at 271.0 °C in the ARC test. The former is the onset decomposition temperature of the solvents in the electrolyte, and the latter is the LiTFSI-LiODFB dual salts. Flynn-Wall-Ozawa, Starink, and autocatalytic models were applied to determine pyrolysis kinetic parameters. The average apparent activation energy of the dual-salt electrolyte was 53.25 kJ/mol. According to the various model fitting, the thermal decomposition process of the dual-salt electrolyte followed the autocatalytic model. The results showed that the LiTFSI-LiODFB dual-salt electrolyte is significantly better than the LiPF6 electrolyte in terms of thermal stability.

Insight into bulk charge transfer of lithium metal anodes by synergism of nickel seeding and LiF-Li3N-Li2S co-doped interphase

Cycling lithium (Li) metal anode with a low negative/positive capacity (N/P) ratio is critical to build high-energy-density Li metal batteries (LMBs). Many strategies focusing on interfacial protection are limited to shallow conditions using excessive Li with a high negative/positive capacity (N/P) ratio > 50. Herein, we demonstrate a deeply enhanced charge transfer kinetic by a rational incorporation of nickel (Ni) seeds in the Li anodes with a tailored interfacial chemistry. The Ni seeds in the bulk Li anode not only act as well-dispersed nucleation sites to enable Ni-seeded growth of granular Li deposits, but also adsorb acetonitrile (AN) molecules when the Ni-seeded Li anodes are paired with an AN-based electrolyte using lithium bis-(fluorosulfonyl)imide as salt, forming a fast Li+ conducting interphase with co-produced LiF, Li3N and Li2S components. These benefits conduct an exchange current density ~ 20 times higher than that of the bare Li in conventional carbonate electrolytes. Stable cycling of LMBs with a practical cathode loading (~ 5 mAh cm−2) and a low N/P capacity ratio of 2 is also demonstrated, showing the prominence of this remedy for developing high-energy-density LMBs.

In Situ Electrolyte Gelation to Prevent Chemical Crossover in Li Metal Batteries

AbstractChemical crossover is one of the key factors affecting the stable cycling of Li metal batteries using conventional carbonate electrolyte. Solid state electrolyte can help solve this problem, but has serious electrolyte/electrode problems that may cause non‐uniform Li deposition. Herein, a simple strategy to balance the chemical crossover and interfacial problems by employing composite gel electrolyte composed of PEO‐based polymer electrolyte and liquid LiPF6 electrolyte, is reported. The high viscosity of the gel polymer can effectively prevent side reaction products and also ensures good contact between electrolyte and electrode. Meanwhile, Li+ migration number of the colloidal polymer electrolyte is as high as 0.67, allowing the cells to be operated at room temperature. The full battery assembled with commercial high‐capacity LiFePO4 (12 mg cm–2) has a specific capacity of 110 mAh g–1 after 160 cycles along with high Coulombic efficiency. Further structural analyses confirm the LiFePO4 cathodes are well maintained after long‐term cycling, indicating the simple cell engineering process is effective to prevent the shuttling of undesired ions and thus protects LiFePO4 cathode from corrosion due to chemical crossover.

Strategies to Enable Reversible Magnesium Electrochemistry: From Electrolytes to Artificial Solid–Electrolyte Interphases

AbstractThe first prototype of a rechargeable magnesium (Mg) battery demonstrated two decades ago sparked tremendous interest in the electrochemical community due to their potential low cost, high volumetric energy density. However, the development of rechargeable Mg batteries has been hampered by the incompatibility between the Mg‐metal anode and conventional carbonate electrolytes. Research has focused on electrolytes that are thermodynamically stable against reduction at the expense of low oxidation potential at the cathode side. Alternatively, the use of an artificial solid–electrolyte interphase (SEI) via surface coating presents promising results to address the Mg/electrolyte incompatibility and significantly broaden the selection of electrolytes. This minireview discusses the limitations of electrolyte development and strategies for the design of artificial interphases in magnesium‐ion batteries. Future perspectives in the development of artificial interphases for rechargeable magnesium batteries are also discussed.

Strategies to Enable Reversible Magnesium Electrochemistry: From Electrolytes to Artificial Solid-Electrolyte Interphases.

The first prototype of a rechargeable magnesium (Mg) battery demonstrated two decades ago sparked tremendous interest in the electrochemical community due to their potential low cost, high volumetric energy density. However, the development of rechargeable Mg batteries has been hampered by the incompatibility between the Mg-metal anode and conventional carbonate electrolytes. Research has focused on electrolytes that are thermodynamically stable against reduction at the expense of low oxidation potential at the cathode side. Alternatively, the use of an artificial solid-electrolyte interphase (SEI) via surface coating presents promising results to address the Mg/electrolyte incompatibility and significantly broaden the selection of electrolytes. This minireview discusses the limitations of electrolyte development and strategies for the design of artificial interphases in magnesium-ion batteries. Future perspectives in the development of artificial interphases for rechargeable magnesium batteries are also discussed.

X-ray photoelectron spectroscopy as a probe for understanding the potential-dependent impact of fluoroethylene carbonate on the solid electrolyte interface formation in Na/Cu2Sb batteries

The solid electrolyte interface (SEI) forms from electrolyte decomposition during the initial discharge of half-cell batteries and is affected by the presence of electrolyte additives. Breaking down the initial discharge into stages, defined by voltage cut offs, can help discover the role of additives in SEI growth. In this study, X-Ray Photoelectron Spectroscopy (XPS) is used to analyze the SEI formed on electrodeposited, binder free Cu2Sb thin films in sodium ion half-cell batteries. The presence of fluoro-ethylene carbonate (FEC), an electrolyte additive known to enhance battery lifetime, has a significant effect on the carbon 1s XPS spectra. The concentration of oxygenated carbon environments are dramatically decreased when FEC is added to the system. These environments were present in samples without FEC before significant electrochemistry was observed, potentially displaying the reactivity of sodium metal with conventional carbonate electrolytes to form the initial components of the SEI before the battery is cycled. The differences observed when FEC is added are likely the chemical environments of the SEI that have the dramatic effect on battery performance. Interestingly, these results suggest that the critical aspects of SEI formation are determined before the active material is sodiated, with FEC playing an integral role.