A Direct Real-Time Observation of Anion Intercalation in Graphite Process and Its Fully Reversibility by SAXS/WAXS Techniques

The process of anion intercalation in graphite and its reversibility plays a crucial role in the next generation energy-storage devices. Herein the reaction mechanism of the aluminum graphite dual ion cell by operando X-ray scattering from small angles to wide angles is investigated. The staging behavior of the graphite intercalation compound (GIC) formation, its phase transitions, and its reversible process are observed for the first time by directly measuring the repeated intercalation distance, along with the microporosity of the cathode graphite. The investigation demonstrates complete reversibility of the electrochemical intercalation process, alongside nano- and micro-structural reorganization of natural graphite induced by intercalation. This work represents a new insight into thermodynamic aspects taking place during intermediate phase transitions in the GIC formation.

Enhanced Li+ Transport in Ionic Liquid-Based Electrolytes Aided by Fluorinated Ethers for Highly Efficient Lithium Metal Batteries with Improved Rate Capability

FSI^- -based ionic liquids (ILs) are promising electrolyte candidates for long-life and safe lithium metal batteries (LMBs). However, their practical application is hindered by sluggish Li⁺ transport at room temperature. Herein, it is shown that additions of bis(2,2,2-trifluoroethyl) ether (BTFE) to LiFSI-Pyr₁₄ FSI ILs can effectively mitigate this shortcoming, while maintaining ILs' high compatibility with lithium metal. Raman spectroscopy and small-angle X-ray scattering indicate that the promoted Li⁺ transport in the optimized electrolyte, [LiFSI]₃ [Pyr₁₄ FSI]₄ [BTFE]₄ (Li₃ Py₄ BT₄ ), originates from the reduced solution viscosity and increased formation of Li⁺ -FSI^- complexes, which are associated with the low viscosity and non-coordinating character of BTFE. As a result, Li/LiFePO₄ (LFP) cells using Li₃ Py₄ BT₄ electrolyte reach 150 mAh g^-1 at 1 C rate (1 mA cm^-2 ) and a capacity retention of 94.6% after 400 cycles, revealing better characteristics with respect to the cells employing the LiFSI-Pyr₁₄ FSI (operate only a few cycles) and commercial carbonate (80% retention after only 218 cycles) electrolytes. A wide operating temperature (from -10 to 40 °C) of the Li/Li₃ Py₄ BT₄ /LFP cells and a good compatibility of Li₃ Py₄ BT₄ with LiNi_0.5 Mn_0.3 Co_0.2 O₂ (NMC532) are demonstrated also. The insight into the enhanced Li⁺ transport and solid electrolyte interphase characteristics suggests valuable information to develop IL-based electrolytes for LMBs.

Cathode-Electrolyte Interphase in a LiTFSI/Tetraglyme Electrolyte Promoting the Cyclability of V2O5

V₂O₅, one of the earliest intercalation-type cathode materials investigated as a Li⁺ host, is characterized by an extremely high theoretical capacity (441 mAh g^-1). However, the fast capacity fading upon cycling in conventional carbonate-based electrolytes is an unresolved issue. Herein, we show that using a LiTFSI/tetraglyme (1:1 in mole ratio) electrolyte yields a highly enhanced cycling ability of V₂O₅ (from 20% capacity retention to 80% after 100 cycles at 50 mA g^-1 within 1.5-4.0 V vs Li⁺/Li). The improved performance mostly originates from the V₂O₅ electrode itself, since refreshing the electrolyte and the lithium electrode of the cycled cells does not help in restoring the V₂O₅ electrode capacity. Electrochemical impedance spectroscopy (EIS), post-mortem scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, and X-ray photoelectron spectroscopy (XPS) have been employed to investigate the origin of the improved electrochemical behavior. The results demonstrate that the enhanced cyclability is a consequence of a thinner but more stable cathode-electrolyte interphase (CEI) layer formed in LiTFSI/tetraglyme with respect to the one occurring in 1 M LiPF₆ in EC/DMC (1:1 in weight ratio, LP30). These results show that the cyclability of V₂O₅ can be effectively improved by simple electrolyte engineering. At the same time, the uncovered mechanism further reveals the vital role of the CEI on the cyclability of V₂O₅, which can be helpful for the performance optimization of vanadium-oxide-based batteries.

Operando pH Measurements Decipher H+/Zn2+ Intercalation Chemistry in High-Performance Aqueous Zn/δ-V2O5 Batteries

Vanadium oxides have been recognized to be among the most promising positive electrode materials for aqueous zinc metal batteries (AZMBs). However, their underlying intercalation mechanisms are still vigorously debated. To shed light on the intercalation mechanisms, high-performance δ-V₂O₅ is investigated as a model compound. Its structural and electrochemical behaviors in the designed cells with three different electrolytes, i.e., 3 m Zn(CF₃SO₃)₂/water, 0.01 M H₂SO₄/water, and 1 M Zn(CF₃SO₃)₂/acetonitrile, demonstrate that the conventional structural and elemental characterization methods cannot adequately clarify the separate roles of H⁺ and Zn²⁺ intercalations in the Zn(CF₃SO₃)₂/water electrolyte. Thus, an operando pH determination method is developed and used toward Zn/δ-V₂O₅ AZMBs. This method indicates the intercalation of both H⁺ and Zn²⁺ into δ-V₂O₅ and uncovers an unusual H⁺/Zn²⁺-exchange intercalation-deintercalation mechanism. Density functional theory calculations further reveal that the H⁺/Zn²⁺ intercalation chemistry is a consequence of the variation of the electrochemical potential of Zn²⁺ and H⁺ during the electrochemical intercalation/release.

A Lithium-Ion Battery using a 3 D-Array Nanostructured Graphene-Sulfur Cathode and a Silicon Oxide-Based Anode

An efficient lithium-ion battery was assembled by using an enhanced sulfur-based cathode and a silicon oxide-based anode and proposed as an innovative energy-storage system. The sulfur-carbon composite, which exploits graphene carbon with a 3 D array (3DG-S), was synthesized by a reduction step through a microwave-assisted solvothermal technique and was fully characterized in terms of structure and morphology, thereby revealing suitable features for lithium-cell application. Electrochemical tests of the 3DG-S electrode in a lithium half-cell indicated a capacity ranging from 1200 to 1000 mAh g^-1 at currents of C/10 and 1 C, respectively. Remarkably, the Li-alloyed anode, namely, Li_y SiO_x -C prepared by the sol-gel method and lithiated by surface treatment, showed suitable performance in a lithium half-cell by using an electrolyte designed for lithium-sulfur batteries. The Li_y SiO_x -C/3DG-S battery was found to exhibit very promising properties with a capacity of approximately 460 mAh g_S^-1 delivered at an average voltage of approximately 1.5 V over 200 cycles, suggesting that the characterized materials would be suitable candidates for low-cost and high-energy-storage applications.

Low-Polarization Lithium-Oxygen Battery Using [DEME][TFSI] Ionic Liquid Electrolyte

The room-temperature molten salt mixture of N,N-diethyl-N-(2-methoxyethyl)-N-methylammonium bis(trifluoromethanesulfonyl) imide ([DEME][TFSI]) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt is herein reported as electrolyte for application in Li-O₂ batteries. The [DEME][TFSI]-LiTFSI solution is studied in terms of ionic conductivity, viscosity, electrochemical stability, and compatibility with lithium metal at 30 °C, 40 °C, and 60 °C. The electrolyte shows suitable properties for application in Li-O₂ battery, allowing a reversible, low-polarization discharge-charge performance with a capacity of about 13 Ah g-1carbon in the positive electrode and coulombic efficiency approaching 100 %. The reversibility of the oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) is demonstrated by ex situ XRD and SEM studies. Furthermore, the study of the cycling behavior of the Li-O₂ cell using the [DEME][TFSI]-LiTFSI electrolyte at increasing temperatures (from 30 to 60 °C) evidences enhanced energy efficiency together with morphology changes of the deposited species at the working electrode. In addition, the use of carbon-coated Zn_0.9 Fe_0.1 O (TMO-C) lithium-conversion anode in an ionic-liquid-based Li-ion/oxygen configuration is preliminarily demonstrated.

Polyacrylonitrile Separator for High-Performance Aluminum Batteries with Improved Interface Stability

Herein we report, for the first time, an overall evaluation of commercially available battery separators to be used for aluminum batteries, revealing that most of them are not stable in the highly reactive 1-ethyl-3-methylimidazolium chloride:aluminum trichloride (EMIMCl:AlCl₃) electrolyte conventionally employed in rechargeable aluminum batteries. Subsequently, a novel highly stable polyacrylonitrile (PAN) separator obtained by the electrospinning technique for application in high-performance aluminum batteries has been prepared. The developed PAN separator has been fully characterized in terms of morphology, thermal stability, and air permeability, revealing its suitability as a separator for battery applications. Furthermore, extremely good compatibility and improved aluminum interface stability in the highly reactive EMIMCl:AlCl₃ electrolyte were discovered. The use of the PAN separator strongly affects the aluminum dissolution/deposition process, leading to a quite homogeneous deposition compared to that of a glass fiber separator. Finally, the applicability of the PAN separator has been demonstrated in aluminum/graphite cells. The electrochemical tests evidence the full compatibility of the PAN separator in aluminum cells. Furthermore, the aluminum/graphite cells employing the PAN separator are characterized by a slightly higher delivered capacity compared to those employing glass fiber separators, confirming the superior characteristics of the PAN separator as a more reliable separator for the emerging aluminum battery technology.

An Overview and Future Perspectives of Aluminum Batteries

A critical overview of the latest developments in the aluminum battery technologies is reported. The substitution of lithium with alternative metal anodes characterized by lower cost and higher abundance is nowadays one of the most widely explored paths to reduce the cost of electrochemical storage systems and enable long-term sustainability. Aluminum based secondary batteries could be a viable alternative to the present Li-ion technology because of their high volumetric capacity (8040 mAh cm(-3) for Al vs 2046 mAh cm(-3) for Li). Additionally, the low cost aluminum makes these batteries appealing for large-scale electrical energy storage. Here, we describe the evolution of the various aluminum systems, starting from those based on aqueous electrolytes to, in more details, those based on non-aqueous electrolytes. Particular attention has been dedicated to the latest development of electrolytic media characterized by low reactivity towards other cell components. The attention is then focused on electrode materials enabling the reversible aluminum intercalation-deintercalation process. Finally, we touch on the topic of high-capacity aluminum-sulfur batteries, attempting to forecast their chances to reach the status of practical energy storage systems.

A Long-Life Lithium Ion Battery with Enhanced Electrode/Electrolyte Interface by Using an Ionic Liquid Solution

In this paper, we report an advanced long-life lithium ion battery, employing a Pyr14 TFSI-LiTFSI non-flammable ionic liquid (IL) electrolyte, a nanostructured tin carbon (Sn-C) nanocomposite anode, and a layered LiNi1/3 Co1/3 Mn1/3 O2 (NMC) cathode. The IL-based electrolyte is characterized in terms of conductivity and viscosity at various temperatures, revealing a Vogel-Tammann-Fulcher (VTF) trend. Lithium half-cells employing the Sn-C anode and NMC cathode in the Pyr14 TFSI-LiTFSI electrolyte are investigated by galvanostatic cycling at various temperatures, demonstrating the full compatibility of the electrolyte with the selected electrode materials. The NMC and Sn-C electrodes are combined into a cathode-limited full cell, which is subjected to prolonged cycling at 40 °C, revealing a very stable capacity of about 140 mAh g(-1) and retention above 99 % over 400 cycles. The electrode/electrolyte interface is further characterized through a combination of electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) investigations upon cell cycling. The remarkable performances reported here definitively indicate that IL-based lithium ion cells are suitable batteries for application in electric vehicles.

Interphase Evolution of a Lithium-Ion/Oxygen Battery

A novel lithium-ion/oxygen battery employing Pyr14TFSI-LiTFSI as the electrolyte and nanostructured LixSn-C as the anode is reported. The remarkable energy content of the oxygen cathode, the replacement of the lithium metal anode by a nanostructured stable lithium-alloying composite, and the concomitant use of nonflammable ionic liquid-based electrolyte result in a new and intrinsically safer energy storage system. The lithium-ion/oxygen battery delivers a stable capacity of 500 mAh g(-1) at a working voltage of 2.4 V with a low charge-discharge polarization. However, further characterization of this new system by electrochemical impedance spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy reveals the progressive decrease of the battery working voltage, because of the crossover of oxygen through the electrolyte and its direct reaction with the LixSn-C anode.

A Polymer Lithium-Oxygen Battery

Herein we report the characteristics of a lithium-oxygen battery using a solid polymer membrane as the electrolyte separator. The polymer electrolyte, fully characterized in terms of electrochemical properties, shows suitable conductivity at room temperature allowing the reversible cycling of the Li-O2 battery with a specific capacity as high as 25,000 mAh gC(-1) reflected in a surface capacity of 12.5 mAh cm(-2). The electrochemical formation and dissolution of the lithium peroxide during Li-O2 polymer cell operation is investigated by electrochemical techniques combined with X-ray diffraction study, demonstrating the process reversibility. The excellent cell performances in terms of delivered capacity, in addition to its solid configuration allowing the safe use of lithium metal as high capacity anode, demonstrate the suitability of the polymer lithium-oxygen as high-energy storage system.

A lithium-ion oxygen battery using a polyethylene glyme electrolyte mixed with an ionic liquid

An efficient, safe lithium-ion oxygen battery is formed by combining an oxygen cathode and a lithium-alloy anode in a glyme-based ionic liquid-containing electrolyte.

An advanced lithium-air battery exploiting an ionic liquid-based electrolyte

A novel lithium-oxygen battery exploiting PYR14TFSI-LiTFSI as ionic liquid-based electrolyte medium is reported. The Li/PYR14TFSI-LiTFSI/O2 battery was fully characterized by electrochemical impedance spectroscopy, capacity-limited cycling, field emission scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. The results of this extensive study demonstrate that this new Li/O2 cell is characterized by a stable electrode-electrolyte interface and a highly reversible charge-discharge cycling behavior. Most remarkably, the charge process (oxygen oxidation reaction) is characterized by a very low overvoltage, enhancing the energy efficiency to 82%, thus, addressing one of the most critical issues preventing the practical application of lithium-oxygen batteries.

A new, high energy Sn-C/Li[Li(0.2)Ni(0.4)/3Co(0.4)/3Mn(1.6/3)]O2 lithium-ion battery

In this paper we report a new, high performance lithium-ion battery comprising a nanostructured Sn-C anode and Li[Li0.2Ni0.4/3Co0.4/3Mn1.6/3]O2 (lithium-rich) cathode. This battery shows highly promising long-term cycling stability for up to 500 cycles, excellent rate capability, and a practical energy density, which is expected to be as high as 220 Wh kg(-1) at the packaged cell level. Considering the overall performance of this new chemistry basically related to the optimized structure, morphology, and composition of the utilized active materials as demonstrated by XRD, TEM, and SEM, respectively, the system studied herein is proposed as a suitable candidate for application in the lithium-ion battery field.