Electrolyte design combining fluoro- with cyano-substitution solvents for anode-free Li metal batteries.

Fluoro-substitution solvents have achieved great success in electrolyte engineering for high-energy lithium metal batteries, which, however, is beset by low solvating power, thermal and chemical instability, and possible battery swelling. Instead, we herein introduce cyanogen as the electron-withdrawing group to enhance the oxidative stability of ether solvents, in which cyanogen and ether oxygen form the chelating structure with Li+ not notably undermining the solvating power. Cyano-group strongly bonds with transition metals (TMs) of NCM811 cathode to attenuate the catalytic reactivity of TMs toward bulk electrolytes. Besides, a stable and uniform cathode-electrolyte interphase (CEI) inhibits the violent oxidation decomposition of electrolytes and guarantees the structural integrity of the NCM811 cathode. Also, a N-containing and LiF-rich solid-electrolyte interphase (SEI) in our electrolyte facilitates fast Li+ migration and dense Li deposition. Accordingly, our electrolyte enables a stable cycle of Li metal anode with Coulombic efficiency of 98.4% within 100 cycles. 81.8% capacity of 4.3 V NCM811 cathode remains after 200 cycles. Anode-free pouch cells with a capacity of 125 mAh maintain 76% capacity after 100 cycles, corresponding to an energy density of 397.5 Wh kg-1.

A Recyclable and Scalable High-Capacity Organic Battery.

Redox organic electrode materials (OEMs) have attracted extensive attention for batteries due to the possibility to be designed with high performance. However, the practical application of OEMs requires rigor criteria such as low cost, recyclability, scalability and high performance etc. and hence seems still far away. Here, we demonstrate an OEM for high performance aqueous organic batteries. Quantification of the charge storage confirmed the storage of protons with fast reaction kinetics, thereby enabling the high performance at high mass loading. As a result, the laminated pouch cells delivered Ampere-hour-scale capacity with excellent cycling performance. Benefited from the small molecular nature and the stable both charged and discharged states, the electrodes can be recycled at any states of charge with high yields (more than 90 %). This work provides a substantial step in the practical applications of OEMs for the future sustainable batteries.

Storing Mg Ions in Polymers: A Perspective.

The electrochemical performance of rechargeable Mg batteries (RMBs) is primarily determined by the cathodes. However, the strong interaction between highly polarized Mg2+ and the host lattice is a big challenge for inorganic cathode materials. While endowed with weak interaction with Mg2+ , organic polymers are capable of fast reaction kinetics. Besides, with the advantages of light weight, abundance, low cost, and recyclability, polymers are deemed as ideal cathode materials for RMBs. Although polymer cathodes have remarkably progressed in recent years, there are still significant challenges to overcome before reaching practical application. In this perspective, the challenges faced by polymer cathodes are critically focused, followed by the retrospection of efforts devoted to design polymers. Some feasible strategies are proposed to explore new structures and chemistries for the practical application of polymer cathodes in RMBs.

A Small Molecular Symmetric All-Organic Lithium-Ion Battery.

The structural designability of organic electrode materials makes them attractive for symmetric all-organic batteries (SAOBs) by virtue of different plateaus. However, quite a few works have reported all-organic batteries and it is still challenging to develop a high-performance organic material for SAOBs. Herein, a small molecule, 2,3,7,8-tetraaminophenazine-1,4,6,9-tetraone (TAPT), is reported for SAOBs. The rich C=O and C=N groups ensure the high capacity at both plateaus for C=O/C-O and C=N/C-N redox reactions, which are hence utilized as cathodic and anodic active centers respectively. Moreover, the presence of C=O, C=N and NH2 groups resulted in plentiful strong intermolecular interactions, leading to layered structures, insolubility and high stability. The rich functional groups also facilitated the chelation of N and O with Li cations and hence benefited the storage of Li cations. The electrochemical performances of TAPT-based SAOBs outperformed all of the previously reported SAOBs.

Joint Cationic and Anionic Redox Chemistry for Advanced Mg Batteries.

Lack of appropriate cathodes severely restrains the development of high-energy Mg batteries. In this work, we proposed joint cationic and anionic redox chemistry of transition-metal (TM) sulfides as the most promising way out. A series of solid-solution pyrite FexCo1-xS2 (0 ≤ x ≤ 1) was specially designed, in which S 3p electrons pour into the d bands of Fe and Co, generating redox-active dimerized (S2)2-. The Fe0.5Co0.5S2 sample is highlighted to deliver a high specific energy of 240 Wh/kg at room temperature involving both cationic (Fe and Co) and anionic (S) redox. The highly delocalized electronic clouds in pyrite structures comfortably accommodate the charge of Mg2+, contributing to the fast kinetics and the superior cycling stability of the Fe0.5Co0.5S2. It is anticipated that the joint cationic and anionic redox chemistry proposed in this work would be the ultimate answer for designing high-energy cathodes for advanced Mg batteries.

Ultralight Electrolyte for High-Energy Lithium-Sulfur Pouch Cells.

The high weight fraction of the electrolyte in lithium-sulfur (Li-S) full cell is the primary reason its specific energy is much below expectations. Thus far, it is still a challenge to reduce the electrolyte volume of Li-S batteries owing to their high cathode porosity and electrolyte depletion from the Li metal anode. Herein, we propose an ultralight electrolyte (0.83 g mL-1 ) by introducing a weakly-coordinating and Li-compatible monoether, which greatly reduces the weight fraction of electrolyte within the whole cell and also enables Li-S pouch cell functionality under lean-electrolyte conditions. Compared to Li-S batteries using conventional counterparts (≈1.2 g mL-1 ), the Li-S pouch cells equipped with our ultralight electrolyte could achieve an ultralow electrolyte weight/capacity ratio (E/C) of 2.2 g Ah-1 and realize a 19.2 % improvement in specific energy (from 329.9 to 393.4 Wh kg-1 ) under E/S=3.0 µL mg-1 . Moreover, more than 20 % improvement in specific energy could be achieved using our ultralight electrolyte at various E/S ratios.

High-Energy-Density Rechargeable Mg Battery Enabled by a Displacement Reaction.

Because of its high theoretical volumetric capacity and dendrite-free stripping/plating of Mg, rechargeable magnesium batteries (RMBs) hold great promise for high energy density in consumer electronics. However, the lack of high-energy-density cathodes severely constrains their practical applications. Herein, for the first time, we report that a CuS cathode can fully reversibly work through a displacement reaction in CuS/Mg pouch cells at room temperature and provide a high capacity of ∼400 mA h/g in a MACC electrolyte, corresponding to the gravimetric and volumetric energy density of 608 W h/kg and1042 W h/L, respectively. Even after 80 cycles, CuS/Mg pouch cells can maintain a high capacity of 335 mA h/g. Detailed mechanistic studies reveal that CuS undergoes a displacement reaction route rather than a typical conversion mechanism. This work will provide a guide for more discovery of high-performance cathode candidates for RMBs.

Antimony Nanorod Encapsulated in Cross-Linked Carbon for High-Performance Sodium Ion Battery Anodes.

Antimony- (Sb) based materials have been considered as one of promising anodes for sodium ion batteries (SIBs) owing to their high theoretical capacities and appropriate sodium inserting potentials. So far, the reported energy density and cycling stability of the Sb-based anodes for SIBs are quite limited and need to be significantly improved. Here, we develop a novel Sb/C hybrid encapsulating the Sb nanorods into highly conductive N and S codoped carbon (Sb@(N, S-C)) frameworks. As an anode for SIBs, the Sb@(N, S-C) hybrid maintains high reversible capacities of 621.1 mAh g-1 at 100 mA g-1 after 150 cycles, and 390.8 mAh g-1 at 1 A g-1 after 1000 cycles. At higher current densities of 2, 5, and 10 A g-1, the Sb@(N, S-C) hybrid also can display high reversible capacities of 534.4, 430.8, and 374.7 mAh g-1, respectively. Such impressive sodium storage properties are mainly attributed to the unique cross-linked carbon networks providing highly conductive frameworks for fast transfer of ions and electrons, alleviating the volume expansion and preventing the agglomeration of Sb nanorods during the cycling.

A critical review of cathodes for rechargeable Mg batteries.

Benefiting from a higher volumetric capacity (3833 mA h cm-3 for Mg vs. 2046 mA h cm-3 for Li) and dendrite-free Mg metal anode, reversible Mg batteries (RMBs) are a promising chemistry for applications beyond Li ion batteries. However, RMBs are still severely restricted by the absence of high performance cathodes for any practical application. In this review, we provide a critical and rigorous review of Mg battery cathode materials, mainly reported since 2013, focusing on the impact of structure and composition on magnesiation kinetics. We discuss cathode materials, including intercalation compounds, conversion materials (O2, S, organic compounds), water co-intercalation cathodes (V2O5, MnO2etc.), as well as hybrid systems using Mg metal anode. Among them, intercalation cathodes are further categorized by 3D (Chevrel phase, spinel structure etc.), 2D (layered structure), and 1D materials (polyanion: phosphate and silicate), according to the diffusion pathway of Mg2+ in the framework. Instead of discussing every published work in detail, this review selects the most representative works and highlights the merits and challenges of each class of cathodes. Advances in theoretical analysis are also reviewed and compared with experimental results. This critical review will provide comprehensive knowledge of Mg cathodes and guidelines for exploring new cathodes for rechargeable magnesium batteries.

A Pyrazine-Based Polymer for Fast-Charge Batteries.

The lack of high-power and stable cathodes prohibits the development of rechargeable metal (Na, Mg, Al) batteries. Herein, poly(hexaazatrinaphthalene) (PHATN), an environmentally benign, abundant and sustainable polymer, is employed as a universal cathode material for these batteries. In Na-ion batteries (NIBs), PHATN delivers a reversible capacity of 220 mAh g-1 at 50 mA g-1 , corresponding to the energy density of 440 Wh kg-1 , and still retains 100 mAh g-1 at 10 Ag-1 after 50 000 cycles, which is among the best performances in NIBs. Such an exceptional performance is also observed in more challenging Mg and Al batteries. PHATN retains reversible capacities of 110 mAh g-1 after 200 cycles in Mg batteries and 92 mAh g-1 after 100 cycles in Al batteries. DFT calculations, X-ray photoelectron spectroscopy, Raman, and FTIR show that the electron-deficient pyrazine sites in PHATN are the redox centers to reversibly react with metal ions.

Nitrogen, Fluorine, and Boron Ternary Doped Carbon Fibers as Cathode Electrocatalysts for Zinc-Air Batteries.

Zinc-air batteries with high-density energy are promising energy storage devices for the next generation of energy storage technologies. However, the battery performance is highly dependent on the efficiency of oxygen electrocatalyst in the air electrode. Herein, the N, F, and B ternary doped carbon fibers (TD-CFs) are prepared and exhibited higher catalytic properties via the efficient 4e- transfer mechanism for oxygen reduction in comparison with the single nitrogen doped CFs. More importantly, the primary and rechargeable Zn-air batteries using TD-CFs as air-cathode catalysts are constructed. When compared to batteries with Pt/C + RuO2 and Vulcan XC-72 carbon black catalysts, the TD-CFs catalyzed batteries exhibit remarkable battery reversibility and stability over long charging/discharging cycles.

Pipe-Wire TiO2-Sn@Carbon Nanofibers Paper Anodes for Lithium and Sodium Ion Batteries.

Metallic tin has been considered as one of the most promising anode materials both for lithium (LIBs) and sodium ion battery (NIBs) because of a high theoretical capacity and an appropriate low discharge potential. However, Sn anodes suffer from a rapid capacity fading during cycling due to pulverization induced by severe volume changes. Here we innovatively synthesized pipe-wire TiO2-Sn@carbon nanofibers (TiO2-Sn@CNFs) via electrospinning and atomic layer deposition to suppress pulverization-induced capacity decay. In pipe-wire TiO2-Sn@CNFs paper, nano-Sn is uniformly dispersed in carbon nanofibers, which not only act as a buffer material to prevent pulverization, but also serve as a conductive matrix. In addition, TiO2 pipe as the protection shell outside of Sn@carbon nanofibers can restrain the volume variation to prevent Sn from aggregation and pulverization during cycling, thus increasing the Coulombic efficiency. The pipe-wire TiO2-Sn@CNFs show excellent electrochemical performance as anodes for both LIBs and NIBs. It exhibits a high and stable capacity of 643 mA h/g at 200 mA/g after 1100 cycles in LIBs and 413 mA h/g at 100 mA/g after 400 cycles in NIBs. These results would shed light on the practical application of Sn-based materials as a high capacity electrode with good cycling stability for next-generation LIBs and NIBs.

Hofmeister Effects in Supramolecular Chemistry for Anion-Modulation to Stabilize Zn Anode.

Aqueous Zn-ion batteries (AZIBs) are considered as promising candidates for the next-generation large-scale energy storage, which, however, is facing the challenge of instable Zn anodes. The anion is pivotal in the stability of anodes, which are not being paid enough attention to. Herein, the modulation of anions is reported using the Hofmeister series in supramolecular chemistry to boost the stability of Zn anodes. It is found that the right-side anions in the Hofmeister series (e.g., OTf-) can enhance the Zn2+ transference number, increase the Coulombic efficiency, facilitate uniform Zn deposition, reduce the freezing point of electrolytes, and thereby stabilize the Zn anodes. More importantly, the right-side anions can form strong interaction with ß-cyclodextrin (ß-CD) compared to the left-side anions, and hence the addition of ß-CD can further enhance the stability of Zn anodes in OTf--based electrolytes, showing enhancement of cycling lifespan in the Zn//Zn symmetric cells more than 45.5 times with ß-CD compared with those without ß-CD. On the contrary, the left-side anions show worse rate performance after the addition of ß-CD. These results provide an effective and novel approach for choosing anions and matching additives to stabilize the anodes and achieve high-performance AZIBs through the Hofmeister effect.

The Proof-of-Concept of Anode-Free Rechargeable Mg Batteries.

The desperate pursuit of high gravimetric specific energy leads to the ignorance of volumetric energy density that is one of the basic requirements for batteries. Due to the high volumetric capacity, less-prone formation of dendrite, and low reduction potential of Mg metal, rechargeable Mg batteries are considered with innately high volumetric energy density. Nevertheless, the substantial elevation in energy density is compromised by extremely excessive Mg metal anode. Herein, the proof-of-concept of anode-free Mg2 Mo6 S8 -MgS/Cu batteries is proposed, in which MgS as the premagnesiation additive constantly decomposes to replenish Mg loss by electrolyte corrosion over cycling, while both Mg2 Mo6 S8 and MgS acts as the active material to reversibly provide high capacities. Besides, Mg2 Mo6 S8 shows superior catalytic activity on the decomposition of MgS and provides the strong affinity to polysulfides to restrain their dissolution. Consequently, the anode-free Mg2 Mo6 S8 -MgS/Cu batteries deliver a high reversible capacity of 190 mAh g-1 with the capacity retention of 92% after 100 cycles, corresponding to the highly competitive energy density of 420 Wh L-1 . The proposed anode-free Mg battery here spotlights the great promise of Mg batteries in achieving high volumetric energy densities, which will significantly expedite the advances of Mg batteries in practice.

Mobile energy storage technologies for boosting carbon neutrality.

Carbon neutrality calls for renewable energies, and the efficient use of renewable energies requires energy storage mediums that enable the storage of excess energy and reuse after spatiotemporal reallocation. Compared with traditional energy storage technologies, mobile energy storage technologies have the merits of low cost and high energy conversion efficiency, can be flexibly located, and cover a large range from miniature to large systems and from high energy density to high power density, although most of them still face challenges or technical bottlenecks. In this review, we provide an overview of the opportunities and challenges of these emerging energy storage technologies (including rechargeable batteries, fuel cells, and electrochemical and dielectric capacitors). Innovative materials, strategies, and technologies are highlighted. Finally, the future directions are envisioned. We hope this review will advance the development of mobile energy storage technologies and boost carbon neutrality.

Framework Dimensional Control Boosting Charge Storage in Conjugated Coordination Polymers.

Conjugated coordination polymers (CCPs) with extended π-d conjugation, which can effectively promote long-range delocalization of electrons and enhance conductivity, are superior to traditional metal-organic frameworks (MOFs) and attracted great attention for potential applications in chemical sensors, electronics, energy conversion/storage devices, etc. However, the precise construction of CCPs is still challenging due to the complex and uncontrollable reactions of CCPs. Herein, two different framework dimensions of CCPs are controllably realized by employing the same ligand (2,3,5,6-tetraaminobenzoquinone (TABQ)) and the same metal (copper) as center ions. The manipulation of reaction leads to different valences of ligands and metal ions, different coordination geometries, and thereby 1D-CuTABQ and 2D-CuTABQ frameworks, respectively. High performance of charge storage is hence achieved involving the storage of both cations and anions, and therein, 2D-CuTABQ shows a high reversible capacity of ≈305 mAh g-1 , good rate capability and high capacity retention (≈170 mAh g-1 after 2000 cycles at 5 A g-1 with 0.01% decay per cycle), which outperforms 1D-CuTABQ and almost all of the reported MOFs as cathodes for batteries. These results highlight the delicate structural control of CCPs for high-performance batteries and other various applications.

Anion-enrichment interface enables high-voltage anode-free lithium metal batteries.

Aggressive chemistry involving Li metal anode (LMA) and high-voltage LiNi0.8Mn0.1Co0.1O2 (NCM811) cathode is deemed as a pragmatic approach to pursue the desperate 400 Wh kg-1. Yet, their implementation is plagued by low Coulombic efficiency and inferior cycling stability. Herein, we propose an optimally fluorinated linear carboxylic ester (ethyl 3,3,3-trifluoropropanoate, FEP) paired with weakly solvating fluoroethylene carbonate and dissociated lithium salts (LiBF4 and LiDFOB) to prepare a weakly solvating and dissociated electrolyte. An anion-enrichment interface prompts more anions' decomposition in the inner Helmholtz plane and higher reduction potential of anions. Consequently, the anion-derived interface chemistry contributes to the compact and columnar-structure Li deposits with a high CE of 98.7% and stable cycling of 4.6 V NCM811 and LiCoO2 cathode. Accordingly, industrial anode-free pouch cells under harsh testing conditions deliver a high energy of 442.5 Wh kg-1 with 80% capacity retention after 100 cycles.

In Situ Synthesis of Organopolysulfides Enabling Spatial and Kinetic Co-Mediation of Sulfur Chemistry.

Li-S batteries have been regarded as one of the most promising alternatives of the next-generation Li batteries. However, the dissolution and shuttling of lithium polysulfides lead to low cycle stability and low Coulombic efficiency, which intensively hinder the practical application of Li-S batteries. Herein, we propose a strategy to simultaneously promote the redox kinetics and inhibit the shuttle of lithium polysulfides, through in situ synthesis of insoluble organopolysulfides by adding a special additive. Attractively, the thus-formed insoluble organopolysulfides in the form of nanoparticle aggregates are also capable of adsorbing unconverted lithium polysulfides and hence effectively spatially suppress the shuttle effect. Furthermore, the organopolysulfides served as active redox mediators, showing faster redox kinetics of S chemistry than that of lithium polysulfides. As a result, the Li-S batteries showed impressive capacity, improved rate performance, and long cycling stability even under lean-electrolyte and high sulfur loading conditions.

Rational design of a topological polymeric solid electrolyte for high-performance all-solid-state alkali metal batteries.

Poly(ethylene oxide)-based solid-state electrolytes are widely considered promising candidates for the next generation of lithium and sodium metal batteries. However, several challenges, including low oxidation resistance and low cation transference number, hinder poly(ethylene oxide)-based electrolytes for broad applications. To circumvent these issues, here, we propose the design, synthesis and application of a fluoropolymer, i.e., poly(2,2,2-trifluoroethyl methacrylate). This polymer, when introduced into a poly(ethylene oxide)-based solid electrolyte, improves the electrochemical window stability and transference number. Via multiple physicochemical and theoretical characterizations, we identify the presence of tailored supramolecular bonds and peculiar morphological structures as the main factors responsible for the improved electrochemical performances. The polymeric solid electrolyte is also investigated in full lithium and sodium metal lab-scale cells. Interestingly, when tested in a single-layer pouch cell configuration in combination with a Li metal negative electrode and a LiMn0.6Fe0.4PO4-based positive electrode, the polymeric solid-state electrolyte enables 200 cycles at 42 mA·g-1 and 70 °C with a stable discharge capacity of approximately 2.5 mAh when an external pressure of 0.28 MPa is applied.

Electronic Conductive Inorganic Cathodes Promising High-Energy Organic Batteries.

The electrochemical utilization of organic electrode materials (OEMs) is highly dependent on an excess amount of inactive carbon at the expense of low packing density and energy density. In this work, the challenges by substituting inactive carbon with electronic conductive inorganic cathode (ECIC) materials, which are endowed with high electronic conductivity to transport electrons for redox reactions of the whole electrodes, high ion-storage capacity to act as secondary active materials, and strong affinity with OEMs to inhibit their dissolution, are addressed. Combining representative ECICs (TiS2 and Mo6 S8 ) with organic electrode materials (perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) and hexaazatrinaphthalene (HATN)) simultaneously achieves high capacity, low porosity, lean electrolyte, and thus high energy density. High gravimetric and volumetric energy densities of 153 Wh kg-1 and 200 Wh L-1 are delivered with superior cycling stability in a 30 mA h-level Li/PTCDA-TiS2 pouch cell. The proof-of-concept of organic-ECIC electrodes is also successfully demonstrated in monovalent Na, divalent Mg, and trivalent Al batteries, indicating their feasibility and generalizability. With the discovery of more ECIC materials and OEMs, it is anticipated that the proposed organic-ECIC system can result in further improvements at cell level to compete with transition metal-based Li-ion batteries.