A Comprehensive Approach toward Stable Lithium–Sulfur Batteries with High Volumetric Energy Density

A comprehensive approach is reported to construct stable and high volumetric energy density lithium–sulfur batteries, by coupling a multifunctional and hierarchically structured sulfur composite with an in‐situ cross‐linked binder. Through a combination of first‐principles calculations and experimental studies, it is demonstrated that a hybrid sulfur host composed by alternately stacking graphene and layered graphitic carbon nitride embraces high electronic conductivity as well as high polysulfide adsorptivity. It is further shown that the cross‐linked elastomeric binder empowers the hierarchical sulfur composites—multi‐microns in size—with the ability to form crack‐free and compact high‐loading electrodes using traditional slurry processing. Using this approach, electrodes with up to 14.9 mg cm^?2 sulfur loading and an extremely low electrolyte/sulfur ratio as low as 3.5: 1 µL mg^?1 are obtained. This study sheds light on the essential role of multifaceted cathode design and further on the challenges facing lithium metal anodes in building high volumetric energy density lithium–sulfur batteries.     

Elastic Sandwich‐Type rGO–VS2/S Composites with High Tap Density: Structural and Chemical Cooperativity Enabling Lithium–Sulfur Batteries with High Energy Density

Driven by increasing demand for high‐energy‐density batteries for consumer electronics and electric vehicles, substantial progress is achieved in the development of long‐life lithium–sulfur (Li–S) batteries. Less attention is given to Li–S batteries with high volume energy density, which is crucial for applications in compact space. Here, a series of elastic sandwich‐structured cathode materials consisting of alternating VS₂‐attached reduced graphene oxide (rGO) sheets and active sulfur layers are reported. Due to the high polarity and conductivity of VS₂, a small amount of VS₂ can suppress the shuttle effect of polysulfides and improve the redox kinetics of sulfur species in the whole sulfur layer. Sandwich‐structured rGO–VS₂/S composites exhibit significantly improved electrochemical performance, with high discharge capacities, low polarization, and excellent cycling stability compared with their bare rGO/S counterparts. Impressively, the tap density of rGO–VS₂/S with 89 wt% sulfur loading is 1.84 g cm^?3, which is almost three times higher than that of rGO/S with the same sulfur content (0.63 g cm^?3), and the volumetric specific capacity of the whole cell is as high as 1182.1 mA h cm^?3, comparable with the state‐of‐the‐art reported for energy storage devices, demonstrating the potential for application of these composites in long‐life and high‐energy‐density Li–S batteries.     

Metal‐Air Batteries: Metal–Air Batteries with High Energy Density: Li–Air versus Zn–Air (Adv. Energy Mater. 1/2011)

In the past decade, there have been exciting developments in the field of lithium ion batteries as energy storage devices, resulting in the application of lithium ion batteries in areas ranging from small portable electric devices to large power systems such as hybrid electric vehicles. However, the maximum energy density of current lithium ion batteries having topatactic chemistry is not sufficient to meet the demands of new markets in such areas as electric vehicles. Therefore, new electrochemical systems with higher energy densities are being sought, and metal‐air batteries with conversion chemistry are considered a promising candidate. More recently, promising electrochemical performance has driven much research interest in Li‐air and Zn‐air batteries. This review provides an overview of the fundamentals and recent progress in the area of Li‐air and Zn‐air batteries, with the aim of providing a better understanding of the new electrochemical systems.     

Metal–Air Batteries with High Energy Density: Li–Air versus Zn–Air

In the past decade, there have been exciting developments in the field of lithium ion batteries as energy storage devices, resulting in the application of lithium ion batteries in areas ranging from small portable electric devices to large power systems such as hybrid electric vehicles. However, the maximum energy density of current lithium ion batteries having topatactic chemistry is not sufficient to meet the demands of new markets in such areas as electric vehicles. Therefore, new electrochemical systems with higher energy densities are being sought, and metal‐air batteries with conversion chemistry are considered a promising candidate. More recently, promising electrochemical performance has driven much research interest in Li‐air and Zn‐air batteries. This review provides an overview of the fundamentals and recent progress in the area of Li‐air and Zn‐air batteries, with the aim of providing a better understanding of the new electrochemical systems.     

Dense Graphene Monolith for High Volumetric Energy Density Li–S Batteries

Despite the outstanding gravimetric performance of lithium–sulfur (Li–S) batteries, their practical volumetric energy density is normally lower than that of lithium‐ion batteries, mainly due to the low density of nanostructured sulfur as well as the porous carbon hosts. Here, a novel approach is developed to fabricate high‐density graphene bulk materials with “ink‐bottle‐like” mesopores by phosphoric acid (H₃PO₄) activation. These pores can effectively confine the polysulfides due to their unique structure with a wide body and narrow neck, which shows only a 0.05% capacity fade per cycle for 500 cycles (75% capacity retention) for accommodating polysulfides. With a density of 1.16 g cm^?3, a hybrid cathode containing 54 wt% sulfur delivers a high volumetric capacity of 653 mA h cm^?3. As a result, a device‐level volumetric energy density as high as 408 W h L^?1 is achieved with a cathode thickness of 100 µm. This is a periodic yet practical advance to improve the volumetric performance of Li–S batteries from a device perspective. This work suggests a design principle for the real use Li–S batteries although there is a long way ahead to bridge the gap between Li–S batteries and Li–ion batteries in volumetric performance.     

Carbon Quantum Dots–Modified Interfacial Interactions and Ion Conductivity for Enhanced High Current Density Performance in Lithium–Sulfur Batteries

Significant progress has achieved for developing lithium–sulfur (Li–S) batteries with high specific capacities and excellent cyclic stability. However, some critical issues emerge when attempts are made to raise the areal sulfur loading and increase the operation current density to meet the standards for various industrial applications. In this work, polyethylenimine‐functionalized carbon dots (PEI‐CDots) are designed and prepared for enhancing performance of the Li–S batteries with high sulfur loadings and operation under high current density situations. Strong chemical binding effects towards polysulfides and fast ion transport property are achieved in the PEI‐CDots‐modified cathodes. At a high current density of 8 mA cm^?2, the PEI‐CDots‐modified Li–S battery delivers a reversible areal capacity of 3.3 mAh cm^?2 with only 0.07% capacity decay per cycle over 400 cycles at 6.6 mg sulfur loading. Detailed analysis, involving electrochemical impedance spectroscopy, cyclic voltammetry, and density functional theory calculations, is done for the elucidation of the underlying enhancement mechanism by the PEI‐CDots. The strongly localized sulfur species and the promoted Li⁺ ion conductivity at the cathode–electrolyte interface are revealed to enable high‐performance Li–S batteries with high sulfur loading and large operational current.     

Recent Progress in High Donor Electrolytes for Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries continue to be considered promising post‐lithium‐ion batteries owing to their high theoretical energy density. In pursuit of a Li–S cell with long‐term cyclability, most studies thus far have relied on using ether‐based electrolytes. However, their limited ability to dissolve polysulfides requires a high electrolyte‐to‐sulfur ratio, which impairs the achievable specific energy. Recently, the battery community found high donor electrolytes to be a potential solution to this shortcoming because their high solubility toward polysulfides enables a cell to operate under lean electrolyte conditions. Despite the increasing number of promising outcomes with high donor electrolytes, a critical hurdle related to stability of the lithium‐metal counter electrode needs to be overcome. This review provides an overview of recent efforts pertaining to high donor electrolytes in Li–S batteries and is intended to raise interest from within the community. Furthermore, based on analogous efforts in the lithium‐air battery field, strategies for protecting the lithium metal electrode are proposed. It is predicted that high donor electrolytes will be elevated to a higher status in the field of Li–S batteries, with the hope that either existing or upcoming strategies will, to a fair extent, mitigate the degradation of the lithium–metal interface.