High Energy Density Rechargeable Batteries Research Articles

Sulfone-based high-voltage electrolytes for high energy density rechargeable lithium batteries: Progress and perspective

Further enhancement in the energy density of rechargeable lithium batteries calls for high-voltage cathode materials and stable anodes, as well as matched high-voltage electrolytes without compromising the overall property of batteries. Sulfone-based electrolytes have aroused great interest in recent years owing to their wide electrochemical window and high safety. However, significant challenges such as the complexity of synthesis, high melting point (typically above room temperature), high viscosity, and their poor compatibility with graphite-based anodes have drastically impeded their practical applications. In this review, recent progress of sulfone solvents in high energy density rechargeable lithium batteries is summarized theoretically and experimentally. More importantly, general improvement methods of sulfone-based electrolytes, such as adding additives and cosolvents, structural modifications of sulfone, superconcentrated salt strategy are briefly discussed. We expect that this review provides inspiration for the future developments of sulfone-based high-voltage electrolytes (SHVEs) and their widespread applications in high specific energy lithium batteries.

Electrochemistry of Electrode Materials Containing S-Se Bonds for Rechargeable Batteries.

Sulfur (S) and selenium (Se) have been considered as promising high capacity cathode materials for rechargeable batteries. They have differences in their physical properties (e.g., electronic conductivity) but the same number of electrons in their outermost shells, which leads to similarity in their electrochemical behavior in batteries. In recent years, some efforts have been taken to combine them in electrodes in the hope of improved battery performance. The S-Se bonds of these electrode materials lead to unusual properties and intriguing electrochemical behavior, which have attracted increasing interest. In this Minireview, electrode materials containing S-Se bonds are summarized, including inorganic Sx Sey solid solutions, organic compounds, and organic-inorganic hybrid materials. Our understanding in these materials is still premature, but they have shown unique properties to be electrode materials. We hope this Minireview could provide a new insight into the design, synthesis, and understanding of these materials, which could enable high energy density rechargeable batteries.

In Situ Formed LiZn Alloy Skeleton for Stable Lithium Anodes

Lithium metal is the most promising anode for developing high-energy density rechargeable batteries because of its ultrahigh theoretical capacity and extremely low reduction potential. However, the formation of dendritic lithium and the huge volume change of the anode during the charge/discharge process severely hinder the practical application of the lithium anode. Obtaining high-performance, simple methods that can simultaneously modify the interface and restrict the volume change of the Li anode are highly required. Herein, the lithiophilic Zn nanoparticles are introduced into molten lithium directly to obtain a composite anode filled with in situ formed LiZn alloy rods. These micrometer-sized alloy rods can serve as a skeleton to provide a large number of lithium deposition sites as well as volume suppression for lithium deposition. Benefiting from these two aspects, the composite anode exhibits superior electrochemical performance by means of lowering the overpotential and prolonging the cycle life of symmetrical cells. Furthermore, the full cell paired with this composite anode and LiFePO4 cathode also demonstrates a better capacity retention than its counterpart with raw Li anode.

Localized High Concentration Electrolytes for High Voltage Lithium-Metal Batteries: Correlation between Salt, Solvent, and Diluent Contents, and Reductive Stability of the Electrolytes

The quest for energy storage devices with high energy densities leads researches to drift away from conventional electrodes for novel architectures able to withstand high lithium loadings and deliver high discharge voltages. Two of the most promising electrode architectures to achieve these goals are the lithium metal anodes and the so-called high-Ni LiNixCoyMn1-x-yO2 (x ≥ 0.6) (NMC) cathodes based on mixed transition metal oxides. These electrodes, however, produce strong reducing/oxidizing environments at the interface with the electrolyte. Dilute electrolyte formulations (dominant in conventional lithium-ion batteries) are inadequate to resist uncontrolled electrolyte decomposition, triggering Li dendritic growth, and prompting low Coulombic efficiency (CE).There is an urgent need to work on new electrolyte formulations. In this sense, high concentrated electrolytes (HCE) gained attention due to their enhanced reductive and oxidative stability and high carrier density but still suffer from low ionic conductivity, high viscosity, and poor wettability. A promising strategy to overcome these drawbacks is diluting the electrolyte without affecting the original lithium salt – solvent coordination from the HCE, which has proven effective in increasing the CE and producing thinner lithium deposition patterns on the anode compared to dilute electrolytes.In this work, we examine the liquid structure and electronic properties in dilute, HCE, and localized high concentration electrolytes (LHCE), in an attempt to uncover changes in the solvated complexes based on salt, solvent, and diluent contents, focusing on an electrolyte formulation proven effective in experiments with lithium bis(fluorosulfonyl)imide (LiFSI), dimethyl carbonate (DMC), and bis(2,2,2-triflouroethyl) ether (BTFE) as the diluent. In our calculations, we modeled the liquid electrolytes within a unit cell with periodic boundaries along the x-, y-, and z-coordinates, and followed the formation of solvated structures performing ab-initio molecular dynamics (AIMD).Examining the dilute and the HCE formulations, besides the depletion of free solvent DMC molecules, we found a change in the coordination behavior of the FSI- anions that trigger the formation of a three-dimensional solution structure. Each FSI- anion coordinates with multiple lithium-ions, shifting the anion LUMO levels lower than the solvent molecules, which explains the improved reductive stability of the HCE formulation and the salt-dominant composition of the SEI films in experiments. Different from previous explanations, however, we do not attribute this improvement to the depletion of free solvent molecules but to lithium-salt pairing mechanisms modified in HCE electrolytes.For the LHCE formulations, we found that dilution does not influence the three-dimensional solution structure from the equivalent HCE. However, we found there should be a limit beyond which the solvation complexes that exist in the equivalent HCE formulation disappear. In summary, our approach allows for the development of a screening methodology that allows finding a correlation between the salt, solvent, and diluent contents, and the reductive properties of the electrolyte formulation. We believe this methodology constitutes an effective tool to explore further LHCE electrolyte formulations for a new generation of high energy density rechargeable batteries.

Porous Silicon-Cobalt Silicide-Carbon Composites for Reversible Lithium Storage

With increasing use of portable electronic devices and electric vehicles, demand for development of high-energy density rechargeable batteries is rising. To meet the market demand for long-lasting rechargeable batteries, energy density of Li-ion batteries (LIBs) should be increased. The energy density of batteries is determined by the capacities of electrodes. Carbonaceous materials have been used as negative electrodes (anodes) in commercial LIBs because of their low operating potential and reasonable cycle life. However, the theoretical capacity of graphite anodes is relatively low, which is 372 mAh g-1 for the fully intercalated LiC6 phase. To increase the capacity, different types of materials using alloying or conversion reaction should be developed. Li-alloy-based materials can store several Li ions with an atom by electrochemical alloying reactions and therefore, high capacity can be obtained. In particular, Si has a high theoretical capacity of 3580 mAh g-1 for Li15Si4 and low operating potential. However, serious capacity fading usually occurs because of huge volume changes during cycling and their low electric conductivity. To address this problem, many strategies have been developed through changes in materials design. For example, incorporation of carbon is the most famous method to solve the capacity fading of Li-alloy-based materials upon cycling. The existence of carbon in Si matrix can buffer the volume expansion of Si materials with increased electric conductivity, thus simultaneously improving both cycling and rate performance. Porous structure can be another strategy to relieve the volume expansion by using the internal pores. However, the process is generally time and energy consuming. In this study, we report a simple preparation process of porous Si-CoSi2-C composites as anode materials for LIBs. The porous composite was synthesized through cheap starting materials and cost-effective methods. Si, magnesium silicide, and cobalt oxide were mixed using high energy mechanical milling (HEMM). Then, a carbon material was incorporated by HEMM. To produce porous structure, MgO formed by HEMM was removed by a wet etching process. As a result, porous Si-CoSi2-C composites were prepared. These composites exhibited a reversible capacity of 1100 mAh g-1 and good capacity retention after 100 cycles. The porous structure and the amorphous carbon matrix alleviated the volume change to allow the enhanced electrochemical performance.

Binder-Free V2O5 Cathode for High Energy Density Rechargeable Aluminum-Ion Batteries.

Nowadays, research on electrochemical storage systems moves into the direction of post-lithium-ion batteries, such as aluminum-ion batteries, and the exploration of suitable materials for such batteries. Vanadium pentoxide (V2O5) is one of the most promising host materials for the intercalation of multivalent ions. Here, we report on the fabrication of a binder-free and self-supporting V2O5 micrometer-thick paper-like electrode material and its use as the cathode for rechargeable aluminum-ion batteries. The electrical conductivity of the cathode was significantly improved by a novel in-situ and self-limiting copper migration approach into the V2O5 structure. This process takes advantage of the dissolution of Cu by the ionic liquid-based electrolyte, as well as the presence of two different accommodation sites in the nanostructured V2O5 available for aluminum-ions and the migrated Cu. Furthermore, the advanced nanostructured cathode delivered a specific discharge capacity of up to ~170 mAh g−1 and the reversible intercalation of Al3+ for more than 500 cycles with a high Coulomb efficiency reaching nearly 100%. The binder-free concept results in an energy density of 74 Wh kg−1, which shows improved energy density in comparison to the so far published V2O5-based cathodes. Our results provide valuable insights for the future design and development of novel binder-free and self-supporting electrodes for rechargeable multivalent metal-ion batteries associating a high energy density, cycling stability, safety and low cost.

The intrinsic behavior of lithium fluoride in solid electrolyte interphases on lithium

Lithium is the most attractive anode material for high-energy density rechargeable batteries, but its cycling is plagued by morphological irreversibility and dendrite growth that arise in part from its heterogeneous "native" solid electrolyte interphase (SEI). Enriching the SEI with lithium fluoride (LiF) has recently gained popularity to improve Li cyclability. However, the intrinsic function of LiF-whether chemical, mechanical, or kinetic in nature-remains unknown. Herein, we investigated the stability of LiF in model LiF-enriched SEIs that are either artificially preformed or derived from fluorinated electrolytes, and thus, the effect of the LiF source on Li electrode behavior. We discovered that the mechanical integrity of LiF is easily compromised during plating, making it intrinsically unable to protect Li. The ensuing in situ repair of the interface by electrolyte, either regenerating LiF or forming an extra elastomeric "outer layer," is identified as the more critical determinant of Li electrode performance. Our findings present an updated and dynamic picture of the LiF-enriched SEI and demonstrate the need to carefully consider the combined role of ionic and electrolyte-derived layers in future design strategies.

High-Voltage Resistant Ionic Liquids for Lithium-Ion Batteries.

With the growing demand for high energy and high power density rechargeable lithium-ion batteries, increasing research is focused on improving the output voltage of these batteries. Herein, a series of pyrrolidinium and piperidinium cations with various N-substituents (including cyanomethyl, benzyl, butyl, hexyl, and octyl groups) were synthesized and investigated with respect to their electrochemical stability under high voltages. The influence of substitutions at the N-position of pyrrolidinium and piperidinium cations on their high-voltage resistance was studied by both theoretical and experimental approaches. The voltage resistance was enhanced as the electron-donating ability of the substitutes increased. Furthermore, 1-hexyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide ([C6Py][TFSI]) exhibited the highest decomposition voltage at approximately 5.12 V and showed promising potential in a lithium-ion battery.

Inducing the Formation of In Situ Li3N-Rich SEI via Nanocomposite Plating of Mg3N2 with Lithium Enables High-Performance 3D Lithium-Metal Batteries.

Lithium metals fit the growing demand of high-energy density rechargeable batteries because of their high specific capacity and low redox potential. However, the lithium-metal anodes are abandoned because of various defects. In this study, we apply composite plating into the protection of lithium-metal anodes. We confirmed that the Mg3N2 nanoparticle dispersed in the ether electrolyte can be easily composite-plated with lithium, resulting in a flat, dense, and dendrite-free lithium deposition layer during the electrodeposition process. In addition, the Mg3N2 plated in the lithium metal phase would react with lithium and then generate a Li3N-rich solid electrolyte interphase (SEI) layer, mitigating continuous side reactions of the electrolyte on the Li metal. In addition, another product of the reaction is Mg which can work as lithiophilic sites in electrodeposition. The combined effect of the two fields can effectively improve the performance of lithium metal anodes. The Li3N-rich SEI layer would grow well on the surface of the three-dimensional (3D) lithium anode by composite plating. Furthermore, composite plating with the Mg3N2-containing electrolyte is a viable route that can be used for various 3D current collectors easily with a small volume effect. Here, we show that the composite plating 3D lithium metal anode is successfully applied in the Li-S battery with a long lifetime.

Hierarchical Nanosheet Arrays of Metal Oxides Guide Uniform Deposition for Lithium Anodes

Lithium metal, regarded as the “Holy Grail” of lithium battery anodes, has been considered as the most promising material for high-energy density rechargeable batteries. However, its practical application has been hindered by the uncontrolled dendrite growth of the lithium metal during charge–discharge cycles. Guiding uniform deposition of lithium during cycling is an effective route to solve the problem. In this contribution, nanosheet arrays of lithiophilic metal oxides with a hierarchical structure, that is, primary vertical thin arrays coupled with secondary grid-like ones, were constructed on a Cu current collector to regulate lithium nucleation and growth. It was found that the primary vertical thin nanosheet arrays could reduce the current density and provide adequate lithiophilic sites with a lower nucleation barrier, while the secondary grid-like nanosheet arrays offered facile Li-ion diffusion and a large volume for lithium deposition. Owing to the uniform deposition behavior and stable electrod...

Regulating lithium nucleation and growth by zinc modified current collectors

Lithium metal is commonly regarded as the “Holy Grail” anode material for high energy density rechargeable batteries. However, the uncontrollable growth of Li dendrites has posed safety concerns and thus greatly hindered its large-scale application. Here we have modified the surface of a commercial anode current collector, Cu foil, with a thin layer of Zn by a facile electroplating method, in order to regulate the Li nucleation and the following growth processes. Because of the formation of a solid solution buffer layer and Li-Zn alloy phases, the Li nucleation overpotential was dramatically reduced, realizing a uniform Li nucleation and a smooth Li plating morphology. As a result, significantly improved long-term cycling performance with a high Coulombic efficiency was achieved by the lithiophilic Zn coated Cu foil as a current collector. Full cells of Li–LiFePO4 and Li–S using the Li deposited on the Zn modified Cu as the anode, showed increased capacity with low voltage hysteresis and greatly enhanced cycling stability, ascribed to the uniform Li deposition and formation of a stable SEI layer. This work demonstrates the feasibility of employing lithiophilic modified Cu foils as Li metal current collectors for practical applications.

Dual Storage Mechanism Induced High Capacity Cathode for Rechargeable Aluminium Ion Battery

Rechargeable energy storage devices have attained much interest in the society as it provides solution to energy crisis. The excessive use of lithium due to ever increasing demand of lithium ion battery in stationary energy storage and portable electronic devices coupled with restricted availability, urges to move towards alternative low cost energy storage device. Developing a new type of sustainable electrochemical energy storage device depends on the exploration of electrochemistry of other alkali metals. Looking for the low cost energy storage device, Al is the third most abundant element in the Earth’s crust and can be used as low cost energy storage device. Moreover, it can exchange three redox electrons per cations so that the energy density of the battery is high compared to lithium based storage system. But the lack of suitable cathode material is the major draw back of aluminium ion battery not reaching the level of commercialization. Carbon based materials like graphite and reduced graphene oxide have been probed as a cathode material where the charge storage occurs by the in intercalation of AlCl4 - anion into the graphite interlayer which limits the specific capacity in the range of 80 to 100 mAh g-1. Cathode materials, which can also intercalate trivalent aluminium ions, can enhance the specific capacity. This work aims to design a cathode material, which can react with both Al3+ and AlCl4 – ions. Sulfur, a cost effective material, embedded in distorted multiwalled carbon nanotubes (DCNT) provides a new concept of both intercalation of AlCl4 – ions in DCNT as well as conversion reaction of sulfur with trivalent aluminium ions. This design of cathode delivers a specific capacity of 500 mAh g-1 at a current density of 50 mA g-1 with a stable cycling of about 600 cycles and can lead to the development of high energy density rechargeable aluminium ion battery.

Selenium Nanocomposite Cathode with Long Cycle Life for Rechargeable Lithium‐Selenium Batteries

AbstractSelenium (Se) is a potential cathode material for high energy density rechargeable lithium batteries. In this study, a binder‐free Se‐carbon nanotube (CNT) composite electrode has been prepared by a facile chemical method. At initial state, Se is present in the form of branched nanowires with a diameter of <150 nm and a length of 1–2 μm, interwoven with CNTs. After discharge and re‐charge, the Se nanowires are converted to nanoparticles embedded in the CNT network. This synthesis method provides a path for fabricating the Se cathodes with controllable mass loading and thickness. By studying the composite electrodes with different Se loading and thickness, we found that the electrode thickness has a critical impact on the distribution of Se during repeated cycling. Promising cycling performance was achieved in thin electrodes with high Se loading. The composite electrode with 23 μm thickness and 60 % Se loading shows a high initial capacity of 537 mAh g−1 and stable cycling performance with a capacity of 401 mAh g−1 after 500 cycles at 1 C rate. This study reports a synthesis strategy to obtain Se/CNT composite cathode with long cycle life for rechargeable Li−Se batteries.

Flowable polymer electrolytes for lithium metal batteries

Solid polymer electrolytes (SPEs) are currently attracting extensive interest as Li-ion conducting materials for building safe and high energy density rechargeable lithium metal batteries due to their low flammability and ease in process. The structural design of polymer matrices could effectively regulate the physicochemical and electrochemical properties of SPEs, thereby enhancing the performance of rechargeable all solid-state lithium metal batteries (ASSLMBs). Herein, we report a new type of flowable polymer electrolyte (FPE), containing a liquid-like polymer with highly conductive polyether side chains and sulfonimide lithium salts [i.e., lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI)]. The high amorphicity and segmental mobility of the liquid-like polymer matrices facilitate fast ionic transport, thus leading to the highest ionic conductivity reported (6.6 × 10−4 S cm−1 at 70 °C and 1.4 × 10−4 S cm−1 at 30 °C). The introduction of FPE as a buffer layer between Li metal (Li°) electrode and poly(ethylene oxide)-based SPE decreases the interfacial resistivity of Li°/electrolyte and improves remarkably cyclability and coulombic efficiency of the Li° || LiFePO4 cell. These results suggest that the FPEs are promising candidates for lithium metal protection in ASSLMBs.

Ni3N Nanocrystals Decorated Reduced Graphene Oxide with High Ionic Conductivity for Stable Lithium Metal Anode

Lithium (Li) metal is the ultimate choice of anode material for high energy density rechargeable Li batteries, yet its practical application has been seriously hindered due to fast capacity decay, ...

Metal-organic frameworks for energy storage devices: Batteries and supercapacitors

Abstract The rise of metal-organic frameworks (MOFs) that are distinctive class of porous materials has attained enormous consideration during the last decades owing to their controllable structures, high surface areas and tunable pore sizes. The applications of MOFs range from the traditional gas separation and storage, drug delivery, sensors and catalysis to the emerging field of energy storage devices, such as high energy density rechargeable batteries and supercapacitors. Metal-organic frameworks are excellent candidates for electrode materials in electrochemical energy storage devices due to their irreplaceable morphology, appropriate functional linkers, high specific surface area and metal sites. Herein, a brief review is carried out on recent development in the utilization of metal-organic framework based materials for rechargeable batteries and supercapacitors, which would be the prevailing guidance to the materials design and optimization for battery community and electrochemical energy storage applications.

Organic positive-electrode material utilizing both an anion and cation: a benzoquinone-tetrathiafulvalene triad molecule, Q-TTF-Q, for rechargeable Li, Na, and K batteries

This study highlights the design concept of a positive electrode material which can accommodate both cations and anions during the charge/discharge process for realizing high energy density rechargeable batteries.

Aqueous Lithium Rechargeable Battery with a Tin(II) Chloride Aqueous Cathode and a Water-Stable Lithium-Ion Conducting Solid Electrolyte

Electrical vehicles (EVs) have enjoyed extensive focus this decade as next-generation vehicles. However, high specific energy, high power density and low-cost batteries are essential for EVs to replace vehicles with internal combustion engines. Here, we propose a novel high specific energy and power density rechargeable aqueous lithium battery with an aqueous SnCl2 cathode and a lithium metal anode, where the lithium anode and the aqueous cathode are separated by a water-stable high lithium-ion conductivity solid electrolyte of Li1.4Al0.4Ge0.2Ti1.4(PO4)3. The theoretical specific energy density of this battery was 681 Wh kg−1, which is around 1.8 times higher than that of conventional lithium-ion batteries. The cell was successfully cycled at 1.5 mA cm−2 and 25°C for a specific areal capacity of 15 mAh cm−2.

Graphene network nested Cu foam for reducing size of lithium metal towards stable metallic lithium anode

Metallic lithium anode has attracted immense attention for high energy density rechargeable batteries. However, the infinity volume change and safety issues caused by the uncontrollable growth of lithium dendrites during long-term cycling hinder its practical applications. Herein, we explore an effective strategy to solve these problems by building a secondary conductive graphene network inside the macropores of copper foam as a three-dimensional host to fabricate metallic lithium (CuFG@Li) anode. The graphene network, nested in the Cu foam, can further split the large pores of Cu foam to form micron-sized cages. After the molten lithium being infused inside the host, this graphene conductive network can be used as a deposition matrix for lithium metal in the pores and minimize the local size of lithium metal to enhance the reversibility of plating/stripping of lithium and maintain the constant volume of anode during the long cycles. The CuFG@Li anode displays stable cycling for more than 1300 h at a current density of 1 mA/cm2, and exhibits high Coulombic efficiency of 98% over 200 cycles at 1 mA/cm2, which is much better than bare Li foil anode. The CuFG@Li/LiFePO4 full cell is also fabricated and displays excellent rate performance. This strategy presents a general approach to suppress the growth of lithium dendrites and regulate the volume changes for long-lifespan lithium metal batteries.

Growth of Lithium Dendrites and Globules through a Solid Block Copolymer Electrolyte as a Function of Current Density

The uncontrollable nonplanar electrodeposition of lithium is a significant barrier to the widespread adoption of high energy density rechargeable batteries with a lithium metal anode. A promising a...