Two-Plateau Li-Se Chemistry for High Volumetric Capacity Se Cathodes

For Li-Se batteries, ether- and carbonate-based electrolytes are commonly used. However, because of the “shuttle effect” of the highly dissoluble long-chain lithium polyselenides (LPSes, Li₂Se_n, 4≤n≤8) in the ether electrolytes and the sluggish one-step solid-solid conversion between Se and Li₂Se in the carbonate electrolytes, a large amount of porous carbon (>40 wt % in the electrode) is always needed for the Se cathodes, which seriously counteracts the advantage of Se electrodes in terms of volumetric capacity. Herein an acetonitrile-based electrolyte is introduced for the Li-Se system, and a two-plateau conversion mechanism is proposed. This new Li-Se chemistry not only avoids the shuttle effect but also facilitates the conversion between Se and Li₂Se, enabling an efficient Se cathode with high Se utilization (97 %) and enhanced Coulombic efficiency. Moreover, with such a designed electrolyte, a highly compact Se electrode (2.35 g_Se cm⁻³) with a record-breaking Se content (80 wt %) and high Se loading (8 mg cm⁻²) is demonstrated to have a superhigh volumetric energy density of up to 2502 Wh L⁻¹, surpassing that of LiCoO₂.     

Wintersweet‐Flower‐Like CoFe2O4/MWCNTs Hybrid Material for High‐Capacity Reversible Lithium Storage

CoFe₂O₄/multiwalled carbon nanotubes (MWCNTs) hybrid materials were synthesized by a hydrothermal method. Field emission scanning electron microscopy and transmission electron microscopy analysis confirmed the morphology of the as‐prepared hybrid material resembling wintersweet flower “buds on branches”, in which CoFe₂O₄ nanoclusters, consisting of nanocrystals with a size of 5–10 nm, are anchored along carbon nanotubes. When applied as an anode material in lithium ion batteries, the CoFe₂O₄/MWCNTs hybrid material exhibited a high performance for reversible lithium storage. In particular, the hybrid anode material delivered reversible lithium storage capacities of 809, 765, 539, and 359 mA h g^?1 at current densities of 180, 450, 900, and 1800 mA g^?1, respectively. The superior performance of CoFe₂O₄/MWCNTs hybrid materials could be ascribed to the synergistic pinning effect of the wintersweet‐flower‐like nanoarchitecture. This strategy could also be applied to synthesize other metal oxide/CNTs hybrid materials as high‐capacity anode materials for lithium ion batteries.     

Wet‐Chemical Synthesis of Phase‐Pure FeOF Nanorods as High‐Capacity Cathodes for Sodium‐Ion Batteries

It is challenging to prepare phase‐pure FeOF by wet‐chemical methods. Furthermore, nanostructured FeOF has never been reported. In this study, hierarchical FeOF nanorods were synthesized through a facile, one‐step, wet‐chemical method by the use of just FeF₃?3H₂O and an alcohol. It was possible to significantly control the FeOF nanostructure by the selection of alcohols with an appropriate molecular structure. A mechanism for the formation of the nanorods is proposed. An impressive high specific capacity of approximately 250 mAh g^?1 and excellent cycling and rate performances were demonstrated for sodium storage. The hierarchical FeOF nanorods are promising high‐capacity cathodes for SIBs.     

Porous Co3O4 Nanosheets with Extraordinarily High Discharge Capacity for Lithium Batteries

Cobalt and battery charge : Porous Co₃O₄ with a hexagonal sheetlike structure has been synthesized through precursor Co(OH)₂ hexagonal nanosheets (see figure). The as‐prepared nanosheets exhibit excellent Li‐battery performance with a good cycle life and high capacity (1450 mAh g^?1).

     

Poly(2,5‐dimercapto‐1,3,4‐thiadiazole) as a Cathode for Rechargeable Lithium Batteries with Dramatically Improved Performance

Organosulfur compounds with multiple thiol groups are promising for high gravimetric energy density electrochemical energy storage. We have synthesized a poly(2,5‐dimercapto‐1,3,4‐thiadiazole) (PDMcT)/poly(3,4‐ethylenedioxythiophene) (PEDOT) composite cathode for lithium‐ion batteries with a new method and investigated its electrochemical behavior by charge/discharge cycles and cyclic voltammetry (CV) in an ether‐based electrolyte. Based on a comparison of the electrochemical performance with a carbonate‐based electrolyte, we found a much higher discharge capacity, but also a very attractive cycling performance of PDMcT by using a tetra(ethylene glycol) dimethyl ether (TEGDME)‐based electrolyte. The first discharge capacity of the as‐synthesized PDMcT/PEDOT composite approached 210 mAh g^?1 in the TEGDME‐based electrolyte. CV results clearly show that the redox reactions of PDMcT are highly reversible in this TEGDME‐based electrolyte. The reversible capacity remained around 120 mAh g^?1 after 20 charge/discharge cycles. With improved cycling performance and very low cost, PDMcT could become a very promising cathode material when combined with a TEGDME‐based electrolyte. The poor capacity in the carbonate‐based electrolyte is a consequence of the irreversible reaction of the DMcT monomer and dimer with the solvent, emphasizing the importance of electrolyte chemistry when studying molecular‐based battery materials.     

Electrochemical Oxidation of Lithium Carbonate Generates Singlet Oxygen

Solid alkali metal carbonates are universal passivation layer components of intercalation battery materials and common side products in metal‐O₂ batteries, and are believed to form and decompose reversibly in metal‐O₂/CO₂ cells. In these cathodes, Li₂CO₃ decomposes to CO₂ when exposed to potentials above 3.8 V vs. Li/Li⁺. However, O₂ evolution, as would be expected according to the decomposition reaction 2 Li₂CO₃→4 Li⁺+4 e^?+2 CO₂+O₂, is not detected. O atoms are thus unaccounted for, which was previously ascribed to unidentified parasitic reactions. Here, we show that highly reactive singlet oxygen (¹O₂) forms upon oxidizing Li₂CO₃ in an aprotic electrolyte and therefore does not evolve as O₂. These results have substantial implications for the long‐term cyclability of batteries: they underpin the importance of avoiding ¹O₂ in metal‐O₂ batteries, question the possibility of a reversible metal‐O₂/CO₂ battery based on a carbonate discharge product, and help explain the interfacial reactivity of transition‐metal cathodes with residual Li₂CO₃.     

Formulation of Blended‐Lithium‐Salt Electrolytes for Lithium Batteries

Blended‐salt electrolytes showing synergistic effects have been formulated by simply mixing several lithium salts in an electrolyte. In the burgeoning field of next‐generation lithium batteries, blended‐salt electrolytes have enabled great progress to be made. In this Review, the development of such blended‐salt electrolytes is examined in detail. The reasons for formulating blended‐salt electrolytes for lithium batteries include improvement of thermal stability (safety), inhibition of aluminum‐foil corrosion of the cathode current collector, enhancement of performance over a wide temperature range (or at a high or low temperature), formation of favorable interfacial layers on both electrodes, protection of the lithium metal anode, and attainment of high ionic conductivity. Herein, we highlight key scientific issues related to the formulation of blended‐salt electrolytes for lithium batteries.     

Elastic and Wearable Wire‐Shaped Lithium‐Ion Battery with High Electrochemical Performance

A stretchable wire‐shaped lithium‐ion battery is produced from two aligned multi‐walled carbon nanotube/lithium oxide composite yarns as the anode and cathode without extra current collectors and binders. The two composite yarns can be well paired to obtain a safe battery with superior electrochemical properties, such as energy densities of 27 Wh kg^?1 or 17.7 mWh cm^?3 and power densities of 880 W kg^?1 or 0.56 W cm^?3, which are an order of magnitude higher than the densities reported for lithium thin‐film batteries. These wire‐shaped batteries are flexible and light, and 97 % of their capacity was maintained after 1000 bending cycles. They are also very elastic as they are based on a modified spring structure, and 84 % of the capacity was maintained after stretching for 200 cycles at a strain of 100 %. Furthermore, these novel wire‐shaped batteries have been woven into lightweight, flexible, and stretchable battery textiles, which reveals possible large‐scale applications.     

Flexible Aqueous Lithium‐Ion Battery with High Safety and Large Volumetric Energy Density

A flexible and wearable aqueous lithium‐ion battery is introduced based on spinel Li_1.1Mn₂O₄ cathode and a carbon‐coated NASICON‐type LiTi₂(PO₄)₃ anode (NASICON=sodium‐ion super ionic conductor). Energy densities of 63 Wh kg^?1 or 124 mWh cm^?3 and power densities of 3 275 W kg^?1 or 11.1 W cm^?3 can be obtained, which are seven times larger than the largest reported till now. The full cell can keep its capacity without significant loss under different bending states, which shows excellent flexibility. Furthermore, two such flexible cells in series with an operation voltage of 4 V can be compatible with current nonaqueous Li‐ion batteries. Therefore, such a flexible cell can potentially be put into practical applications for wearable electronics. In addition, a self‐chargeable unit is realized by integrating a single flexible aqueous Li‐ion battery with a commercial flexible solar cell, which may facilitate the long‐time outdoor operation of flexible and wearable electronic devices.     

Sucrose‐Assisted Loading of LiFePO4 Nanoparticles on Graphene for High‐Performance Lithium‐Ion Battery Cathodes

A simple approach for loading LiFePO₄ (LFP) nanoparticles on graphene (G) that could assemble amorphous LiFePO₄ nanoparticles into a stable, crystalline, graphene‐modified layered materials (G‐S‐LFP, S=sucrose) by using graphene as building block and sucrose as a linker has yet to be developed. On the basis of differential scanning calorimetric and transmission electron microscopy analysis of the samples from controlled experiment, a possible mechanism was proposed to explain the “linker” process of LFP and graphene with sucrose as the linker. The electrochemical properties of the samples as cathode material for lithium‐ion batteries were studied by cyclic voltammogrametry and galvanostatic methods. Results showed that G‐S‐LFP displayed superior lithium‐storage capability with current density changes randomly form 0.5 to 10 C. The significant improvement for rate and cycle performance could be attributed to the high conductivity of the graphene host, the high crystallinity, and the layered structure.     

A Biodegradable Polydopamine‐Derived Electrode Material for High‐Capacity and Long‐Life Lithium‐Ion and Sodium‐Ion Batteries

Polydopamine (PDA), which is biodegradable and is derived from naturally occurring products, can be employed as an electrode material, wherein controllable partial oxidization plays a key role in balancing the proportion of redox‐active carbonyl groups and the structural stability and conductivity. Unexpectedly, the optimized PDA derivative endows lithium‐ion batteries (LIBs) or sodium‐ion batteries (SIBs) with superior electrochemical performances, including high capacities (1818 mAh g^?1 for LIBs and 500 mAh g^?1 for SIBs) and good stable cyclabilities (93 % capacity retention after 580 cycles for LIBs; 100 % capacity retention after 1024 cycles for SIBs), which are much better than those of their counterparts with conventional binders.     

Synergistic Dual‐Additive Electrolyte Enables Practical Lithium‐Metal Batteries

A rechargeable Li metal anode coupled with a high‐voltage cathode is a promising approach to high‐energy‐density batteries exceeding 300 Wh kg^?1. Reported here is an advanced dual‐additive electrolyte containing a unique solvation structure and it comprises a tris(pentafluorophenyl)borane additive and LiNO₃ in a carbonate‐based electrolyte. This system generates a robust outer Li₂O solid electrolyte interface and F‐ and B‐containing conformal cathode electrolyte interphase. The resulting stable ion transport kinetics enables excellent cycling of Li/LiNi_0.8Mn_0.1Co_0.1O₂ for 140 cycles with 80 % capacity retention under highly challenging conditions (≈295.1 Wh kg^?1 at cell‐level). The electrolyte also exhibits high cycling stability for a 4.6 V LiCoO₂ (160 cycles with 89.8 % capacity retention) cathode and 4.95 V LiNi_0.5Mn_1.5O₄ cathode.     

Halide‐Based Materials and Chemistry for Rechargeable Batteries

Rechargeable batteries are considered one of the most effective energy storage technologies to bridge the production and consumption of renewable energy. The further development of rechargeable batteries with characteristics such as high energy density, low cost, safety, and a long cycle life is required to meet the ever‐increasing energy‐storage demands. This Review highlights the progress achieved with halide‐based materials in rechargeable batteries, including the use of halide electrodes, bulk and/or surface halogen‐doping of electrodes, electrolyte design, and additives that enable fast ion shuttling and stable electrode/electrolyte interfaces, as well as realization of new battery chemistry. Battery chemistry based on monovalent cation, multivalent cation, anion, and dual‐ion transfer is covered. This Review aims to promote the understanding of halide‐based materials to stimulate further research and development in the area of high‐performance rechargeable batteries. It also offers a perspective on the exploration of new materials and systems for electrochemical energy storage.     

Hexagonal‐Shaped Tin Glycolate Particles: A Preliminary Study of Their Suitability as Li‐Ion Insertion Electrodes

Tin glycolate particles were prepared by a simple, one‐step, polyol‐mediated synthesis in air in which tin oxalate precursor was added to ethylene glycol and heated at reflux. Hexagonal‐shaped, micron‐sized tin glycolate particles were formed when the solution had cooled. A series of tin oxides was produced by calcination of the synthesized tin glycolate at 600–800 °C. It was revealed that the micron‐sized, hexagonal‐shaped tin glycolate now consisted of nanosized tin‐based particles (80–120 nm), encapsulated within a tin glycolate shell. XRD, TGA, and FT‐IR measurements were conducted to account for the three‐dimensional growth of the tin glycolate particles. When applied as an anode material for Li‐ion batteries, the synthesized tin glycolate particles showed good electrochemical reactivity in Li‐ion insertion/deinsertion, retaining a specific capacity of 416 mAh g^?1 beyond 50 cycles. This performance was significantly better than those of all the other tin oxides nanoparticles (<160 mAh g^?1) obtained after heat treatment in air. We strongly believe that the buffering of the volume expansion by the glycolate upon Li–Sn alloying is the main factor for the improved cycling of the electrode.     

Iron Fluoride Hollow Porous Microspheres: Facile Solution‐Phase Synthesis and Their Application for Li‐Ion Battery Cathodes

Iron fluoride cathodes have been attracting considerable interest due to their high electromotive force value of 2.7 V and their high theoretical capacity of 237 mA h g^?1 (1 e^? transfer). In this study, uniform iron fluoride hollow porous microspheres have been synthesized for the first time by using a facile and scalable solution‐phase route. These uniform porous and hollow microspheres show a high specific capacity of 210 mA h g^?1 at 0.1 C, and excellent rate capability (100 mA h g^?1 at 1 C) between 1.7 and 4.5 V versus Li/Li⁺. When in the range of 1.3 to 4.5 V, stable capacity was achieved at 350 mA h g^?1 at a current of 50 mA g^?1.     

Solvated Graphene Frameworks as High‐Performance Anodes for Lithium‐Ion Batteries

A solvent‐exchange approach for the preparation of solvated graphene frameworks as high‐performance anode materials for lithium‐ion batteries is reported. The mechanically strong graphene frameworks exhibit unique hierarchical solvated porous networks and can be directly used as electrodes with a significantly improved electrochemical performance compared to unsolvated graphene frameworks, including very high reversible capacities, excellent rate capabilities, and superior cycling stabilities.