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This study aims to develop high-capacity hard carbon anode materials for alkali-ion batteries by controlling the microstructures of non-graphitic hard carbon through an annealing protocol and investigating the effects on the alkali-ion storage mechanisms using physical, chemical, and electrochemical analytical techniques. The hard carbon materials were synthesized at temperatures ranging from 900 °C to 1600 °C. Those synthesized at 1100 °C with high surface area and abundant defects exhibited the highest reversible capacity in Li- and K-ion systems, with the storage dominated by surface-adsorption mechanisms. In contrast, the hard carbon compounds prepared at 1400 °C with numerous curve-featured pores delivered the highest reversible capacity in the Na-ion system, indicating that these pores are the preferred Na-ion storage sites, particularly in low-voltage plateau regions. This study provides a comprehensive understanding of the relationship between microstructures and alkali-ion storage mechanisms in non-graphitic hard carbon and highlights the importance of tailoring the microstructures of hard carbon to achieve high specific capacity for the desired alkali-ion species.

The micrometer-scale reticulated structure of highly sulfur-philic nitrogen-doped graphene oxide (NrGO) that is achieved by chemically controlling the nitrogen-doping degree improves the chemical and electrochemical stability of the active sulfur while providing sufficient sulfur/electrolyte interface for a facile electrochemical process so that a high specific energy of 325 W h kg-1 can be achieved.

To date, Li2S has drawn significant attention as a positive electrode active material for rechargeable lithium cells due to its high theoretical specific capacity and capability of pairing with a lithium-free anode which can obviate any safety concern of the lithium metal anode when using sulfur. In recent years, various approaches have been employed to develop Li/Li2S rechargeable cells for commercialization that meet the performance goals for high energy/power applications. It is expected that high lithium sulfide-loading cells with long cycle life, an excellent capacity delivery and low electrolyte:sulfur weight ratio (E/S ratio) can be achieved. Here, we report a Li2S electrode comprised of a novel Li2S/KB@Cf nanocomposite which delivers an areal capacity of 7.56 mAh cm-2 and good cycling stability with a mass loading of 11.29 mg cm-2 and a robust 3-dimensional (3D) aluminum foam current collector with a high open area. The high conductivity and scalability of the active material, the availability of 3D current collection for the active material and the control of the electrolyte/sulfur ratio offer the potential of realization of practical Li/S cells.

Rational design of sulfur electrodes is exceptionally important in enabling a high-performance lithium/sulfur cell. Constructing a continuous pore structure of the sulfur electrode that enables facile lithium ion transport into the electrode and mitigates the reconstruction of sulfur is a key factor for enhancing the electrochemical performance. Here, we report a three-dimensionally (3D) aligned sulfur electrode cast onto conventional aluminum foil by directional freeze tape casting. The 3D aligned sulfur-graphene oxide (S-GO) electrode consisting of few micron thick S-GO layers with 10-20 μm interlayer spacings demonstrates significant improvement in the performance of the Li/S cell. Moreover, the freeze tape cast graphene oxide electrode exhibits homogeneous reconfiguration behavior in the polysulfide catholyte cell tests and demonstrated extended cycling capability with only 4% decay of the specific capacity over 200 cycles. This work emphasizes the critical importance of proper structural design for sulfur-carbonaceous composite electrodes.

A novel ionic liquid-containing electrolyte has been demonstrated to improve charging efficiency, lifetime and safety of Li/S cells. However, the high viscosity of the ionic liquid can reduce the kinetics of the electrochemical process and degrade the wettability the S electrode by the electrolyte, which limits electrochemical utilization of the active S. To realize the advantages of the ionic liquid in the electrolyte, while maintaining good cell performances, we have investigated the critical properties of polymeric binders such as polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA) and lithium polyacrylate (LiPAA) for the S electrode operated in ionic liquid-containing electrolytes. The PAA binder electrode showed the most promising cell performance which is attributed to its good physical stability and wettability. Moreover, the cell performance of the PAA binder electrode was further improved by combining the PAA binder with the PVDF binder, which enhances the specific capacity up to 1.3 times higher than that of the PAA binder electrode.

Lithium/Sulfur (Li/S) cells are a promising chemistry with potential to deliver a step-change in energy density compared to state-of-the-art Li-ion batteries. To minimize the environmental impact of the Li/S cell manufacturing and to compete with Li-ion cells in both performance and cost, electrodes cast using an aqueous process are highly desirable. Here we describe the discovery and application of a lithiated redox-mediating supramolecular binder based on the well-known n-type semiconductor, perylene bisimide, that forms high-fidelity sulfur electrodes from water-processed slurries. A 1.4-fold improvement in sulfur utilization at 3.0 C and 58% increase in capacity retention after 250 cycles at 1.5 C are reported for the prelithiated, supramolecular binder compared to control samples. These improvements are attributed to the self-assembly of lithiated perylene bisimide binders in water to yield nanowire web morphologies that increase interfacial area between electrode components and exhibit enhanced electrode-current collector adhesion.

The ambient-temperature rechargeable lithium/sulfur (Li/S) cell is a strong candidate for the beyond lithium ion cell since significant progress on developing advanced sulfur electrodes with high sulfur loading has been made. Here we report on a new sulfur electrode active material consisting of a cetyltrimethylammonium bromide-modified sulfur-graphene oxide-carbon nanotube (S-GO-CTA-CNT) nanocomposite prepared by freeze-drying. We show the real-time formation of nanocrystalline lithium sulfide (Li2S) at the interface between the S-GO-CTA-CNT nanocomposite and the liquid electrolyte by in situ TEM observation of the reaction. The combination of GO and CNT helps to maintain the structural integrity of the S-GO-CTA-CNT nanocomposite during lithiation/delithiation. A high S loading (11.1 mgS/cm2, 75% S) S-GO-CTA-CNT electrode was successfully prepared using a three-dimensional structured Al foam as a substrate and showed good S utilization (1128 mAh/g S corresponding to 12.5 mAh/cm2), even with a very low electrolyte to sulfur weight ratio of 4. Moreover, it was demonstrated that the ionic liquid in the electrolyte improves the Coulombic efficiency and stabilizes the morphology of the Li metal anode.

π-Stacked perylene bisimide (PBI) molecules are implemented here as highly networked, redox-active supramolecular polymer binders in sulfur cathodes for lightweight and energy-dense Li-S batteries. We show that the in operando reduction and lithiation of these PBI binders sustainably reduces Li-S cell impedance relative to nonredox active conventional polymer binders. This lower impedance enables high-rate cycling in Li-S cells with excellent durability, a critical step toward unlocking the full potential of Li-S batteries for electric vehicles and aviation.

Fully lithiated lithium sulfide (Li2S) has become a promising cathode material for Li/S cells due to its high theoretic capacity (1166 mA h g-1) and specific energy (2600 W h kg-1). However, low utilization of sulfur and poor rate capability still hinder the practical application of Li/S cells. In this paper, a carbon coated Li2S/graphene composite (Li2S/G@C) was developed by incorporating Li2S nano spheres with single-layered graphene and further forming a durable protective carbon layer on the surface of the Li2S particles using a facile CVD method. The high rate capability and remarkable cycle life of the Li2S/G@C cathode were demonstrated, which was mainly attributed to the unique structure of the Li2S/G@C that can significantly improve not only the electrical conductivity, but also the mechanical stability of the sulfur cathode.

In recent years, lithium/sulfur (Li/S) cells have attracted great attention as a candidate for the next generation of rechargeable batteries due to their high theoretical specific energy of 2600 W·h kg(-1), which is much higher than that of Li ion cells (400-600 W·h kg(-1)). However, problems of the S cathode such as highly soluble intermediate species (polysulfides Li2Sn, n = 4-8) and the insulating nature of S cause poor cycle life and low utilization of S, which prevents the practical use of Li/S cells. Here, a high-rate and long-life Li/S cell is proposed, which has a cathode material with a core-shell nanostructure comprising Li2S nanospheres with an embedded graphene oxide (GO) sheet as a core material and a conformal carbon layer as a shell. The conformal carbon coating is easily obtained by a unique CVD coating process using a lab-designed rotating furnace without any repetitive steps. The Li2S/GO@C cathode exhibits a high initial discharge capacity of 650 mA·h g(-1) of Li2S (corresponding to the 942 mA·h g(-1) of S) and very low capacity decay rate of only 0.046% per cycle with a high Coulombic efficiency of up to 99.7% for 1500 cycles when cycled at the 2 C discharge rate.