Functional Materials for Next-Generation Rechargeable Batteries

The following sections are included:

• Preface
• Contents

Lithium rechargeable batteries have witnessed significant technical advances in the electrochemical performance and stability, together with success in penetrating into every corner of our lives. This success also leads to the 2019 Nobel Prize in Chemistry being awarded to three scientists for the development of lithium-ion batteries. In this chapter, the principles and fundamentals of lithium rechargeable batteries are reviewed, aiming to provide a beginner’s guide to researchers going into battery communities. The basic concepts and characteristics of batteries are expounded, showing how lithium rechargeable batteries are developed and assessed. A brief summary of battery material is then provided, highlightling some key cathode and anode components, whose discovery and optimization finally leads to the success of commercial batteries. Topics discussed also include the battery design and manufacture and offer insights into the future development of lithium rechargeable batteries. The knowledge deposited in this chapter is expected to stimulate the design of functional materials in multiple dimensions and scales required for future battery applications.

In rechargeable lithium-sulfur (Li-S) batteries, the conductive carbon materials with high surface areas can greatly enhance the electrical conductivity of sulfur cathode, and metal oxides can restrain the dissolution of lithium polysulfides within the electrolyte through strong chemical bindings. The rational design of carbon-metal oxide nanocomposite cathodes has been considered as an effective solution to increase the sulfur utilization and improve cycling performance of Li-S batteries. Here, we summarize the recent progresses in the carbon-metal oxide composites for Li-S battery cathodes. Some insights are also offered on the future directions of carbon-metal oxide hybrid cathodes for high performance Li-S batteries.

Lithium sulfur batteries (LSBs) have been one of the most promising second batteries for energy storage. However, the commercialization of LSBs is still hindered by low sulfur utilization and poor cycling stability, resulting from shuttle effect and low redox kinetics of lithium polysulfides (LiPSs). Significant progress has been made over the years in enhancing the batteries performances and tap density with the transition-metal sulfides as sulfur host or additive in LSBs. In this review, we present the recent advances in the use of various nanostructured transition-metal sulfides applied in LSBs, and also focus on the interaction mechanisms of polar transition-metal sulfides with LiPSs and its catalysis for the redox of LiPSs. It may provide avenues for the application of transition-metal sulfides in LSBs. The challenges and perspectives of transition-metal sulfides are also addressed.

Lithium-sulfur batteries are considered as a promising candidate for the next-generation high energy density storage devices. However, they are still hindered by serious capacity decay on cycling caused by the dissolution of redox intermediates. Here, we designed a unique structure with polypyrrole (ppy) inserting into the graphene oxide (GO) sheet for accommodating sulfur. Such a sulfur host not only exhibits a good electronic and ionic conductivity, but also can suppress polysulfide dissolution effectively. With this advanced design, the composite cathode showed a high specific capacity of 548.4 mA⋅h⋅g^–1 at 5.0 C. A stable Coulombic efficiency of ~99.5% and a capacity decay rate as low as 0.089% per cycle along with 300 cycles at 1.0 C were achieved for composite cathodes with 78 wt.% of S. Besides, the interaction mechanism between PPy and lithium polysulfides (LPS) was investigated by density-functional theory (DFT), suggesting that only the polymerization of N atoms can bind strongly to Li ions of LPS rather than single N atoms. The 3D structure GO-PPy host with high conductivity and excellent trapping ability to LPS offered a viable strategy to design high-performance cathodes for Li–S batteries.

It is of great importance to develop high-quality carbon/sulfur cathode for lithium-sulfur batteries (LSBs). Herein, we report a facile strategy to embed sulfur into interconnected carbon nanoflake matrix forming integrated electrode. Interlinked carbon nanoflakes have dual roles not only as a highly conductive matrix to host sulfur, but also act as blocking barriers to suppress the shuttle effect of intermediate polysulfides. In the light of these positive characteristics, the obtained carbon nanoflake/S cathode exhibits good LSBs performances with high capacities (1117 mAh g^–1 at 0.2°C, and 741 mAh g^–1 at 0.6°C) and good high-rate cycling performance. Our synthetic method provides a novel way to construct enhanced carbon/sulfur cathode for LSBs.

Recent results have shown that sodium-ion batteries complement lithium-ion batteries well because of the low cost and abundance of sodium resources. Hard carbon is believed to be the most promising anode material for sodium-ion batteries due to the expanded graphene interlayers, suitable working voltage and relatively low cost. However, the low initial coulombic efficiency and rate performance still remains challenging. The focus of this review is to give a summary of the recent progresses on hard carbon for sodium-ion batteries including the impact of the uniqueness of carbon precursors and strategies to improve the performance of hard carbon, and highlight the advantages and performances of the hard carbon. Additionally, the current problems of hard carbon for sodium-ion batteries and some challenges and perspectives on designing better hard-carbon anode materials are also provided.

Sodium-ion batteries (SIB) play a promising role in the area of energy storage device researching. MoS₂-based materials are considered as one of the most attractive materials for high-performance SIBs owing to their high capacity, high cycle stability and excellent Coulomb effect. This review has summarized the synthesis of MoS₂-based materials (MoS₂, MoS₂/carbon-based materials, MoS₂/metal oxides, MoS₂/metal sulfides) to emphasize their electrochemical behaviors in SIBs.

The sharp increase in the cost of lithium resource has driven the research on sodium-ion batteries (SIBs) as sodium shares a similar electrochemical property as lithium. Carbonaceous materials are important anodes for rechargeable batteries, but the prevailing graphite only shows a limited activity towards sodium storage. Herein, we demonstrate that carbon nanoflakes serve as an efficient anode material for SIBs, exhibiting a stable capacity of 148 mAh g^–1 over 600 continuous cycles at 150 mA g^–1 and an excellent rate capability of 120 mAh g^–1 at 1500 mA g^–1. More importantly, sodium storage in carbon nanoflakes exhibits a pseudocapacitive behavior, possibly due to their larger interlayer spacing and less-ordered structure vs. crystallized carbon.

The biomass carbons with highly developed porosity were prepared by carbonization of phoenix tree leaves (PTLs) followed by activation with KOH. The as-prepared carbons possess large interlayer spacing, abundant oxygen-containing functional groups and high degree of structural disorder. The PTLs derived carbons were firstly employed as anodes for sodium-ion batteries, with the optimized material delivering an initial discharge capacity as high as 602 mAh g^–1 and a reversible capacity of 134 mAh g^–1 after 300 cycles at 100 mA g^–1. Electrochemical mechanism analysis reveals a capacitive dominating Na⁺ storage process.

With the rise of flexible electronics, flexible rechargeable batteries have attracted widespread attention as a promising power source in new generation flexible electronic devices. In this work, α-Fe₂O₃ nanorods grown on carbon cloth have been synthesized through a facile hydrothermal method as binder-free electrode material. The electrochemical performance measurements show that α-Fe₂O₃3 nanorods possess high specific capacitance and specific capacity retention of 119% after 100 cycles. The combination of low cost and excellent electrochemical performance makes α-Fe₂O₃ nanorods promising anode materials for sodium-ion batteries.

In this work, nanosized polythiophene (PTh) was synthesized via a green and facile method. The obtained nanosized PTh was characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), Brunauer–Emmett–Teller theory (BET) and scanning electron microscopy (SEM). The results indicated that a nanosized, porous and amorphous PTh was synthesized. As an organic anode material for potassium ion battery, the PTh shows excellent performance with a reversible capacity of 58 mAh g^–1 at 30 mA g^–1.

The development of manganese dioxide (MnO₂) as the cathode for aqueous Zn-MnO₂ batteries is hindered by poor capacity. Herein, we propose a high-capacity MnO₂ cathode constructed by engineering it with N-doping (N-MnO₂) for a high-performance Zn-MnO₂ battery. Benefiting from N element doping, the conductivity of N-MnO₂ nanorods (NRs) electrode has been improved and the dissolution of the cathode during cycling can be relieved to some extent. The fabricated Zn-N-MnO₂ battery based on the N-MnO₂ cathode and a Zn foil anode presents a real capacity of 0.31 mAh cm^–2 at 2 mA cm^–2, together with a remarkable energy density of 154.3 Wh kg^–1 and a peak power density of 6914.7 W kg^–1, substantially higher than most recently reported energy storage devices. The strategy of N doping can also bring intensive interest for other electrode materials for energy storage systems.

Metal-organic frameworks (MOFs) have attracted great attention as versatile precursors or sacrificial templates for the preparation of novel porous structures. Due to their tunable compositions, structures and porosities as well as high surface area, MOF-derived materials have revealed promising performance for energy storage devices. In this mini review, the recent progress of MOF-derived materials as electrodes of next-generation rechargeable batteries was summarized. We briefly introduce the preparation methods, various design strategies and the structure-dependent performance of recently reported MOF-derived materials as electrodes of post-lithium-ion batteries, focusing on lithium-sulfur (Li-S) batteries, sodium-ion batteries (SIBs) and metal–air batteries. Finally, we give the conclusion with some insights into future development of MOF-derived materials for next-generation rechargeable batteries.

Solid-state polymer lithium-ion batteries with better safety and higher energy density are one of the most promising batteries, which are expected to power future electric vehicles and smart grids. However, the low ionic conductivity at room temperature of solid polymer electrolytes (SPEs) decelerates the entry of such batteries into the market. Creating polymer-in-salt solid electrolytes (PISSEs) where the lithium salt contents exceed 50 wt.% is a viable technology to enhance ionic conductivity at room temperature of SPEs, which is also suitable for scalable production. In this review, we first clarify the structure and ionic conductivity mechanism of PISSEs by analyzing the interactions between lithium salt and polymer matrix. Then, the recent advances on polyacrylonitrile (PAN)-based PISSEs and polycarbonate derivative-based PISSEs will be reviewed. Finally, we propose possible directions and opportunities to accelerate the commercializing of PISSEs for solid polymer Li-ion batteries.