Urchin‐like CoSe2 assembled by nanorods has been synthesized via simple solvothermal route and has been first applied as an anode material for sodium‐ion batteries (SIBs) with ether‐based electrolytes. The CoSe2 delivers excellent sodiation and desodiation properties when using 1 m NaCF3SO3 in diethyleneglycol dimethylether as an electrolyte and cycling between 0.5 and 3.0 V. A high discharge capacity of 0.410 Ah g−1 is obtained at 1 A g−1 after 1800 cycles, corresponding to a capacity retention of 98.6% calculated from the 30th cycle. Even at an ultrahigh rate of 50 A g−1, the capacity still maintains 0.097 Ah g−1. The reaction mechanism of the as‐prepared CoSe2 is also investigated. The results demonstrate that at discharged 1.56 V, insertion reaction occurs, while two conversion reactions take place at the second and third plateaus around 0.98 and 0.65 V. During the charge process, Co first reacts with Na2Se to form NaxCoSe2 and then turns back to CoSe2. In addition to Na/CoSe2 half cells, Na3V2(PO4)3/CoSe2 full cell with excessive amount of Na3V2(PO4)3 has been studied. The full cell exhibits a reversible capacity of 0.380 Ah g−1. This work definitely enriches the possibilities for anode materials for SIBs with high performance.

Manganese based layered oxides have received increasing attention as cathode materials for sodium ion batteries due to their high theoretical capacities and good sodium ion conductivities. However, the Jahn–Teller distortion arising from the manganese (III) centers destabilizes the host structure and deteriorates the cycling life. Herein, we report that zinc-doped Na0.833[Li0.25Mn0.75]O2 can not only suppress the Jahn–Teller effect but also reduce the inherent phase separations. The reduction of manganese (III) amount in the zinc-doped sample, as predicted by first-principles calculations, has been confirmed by its high binding energies and the reduced octahedral structural variations. In the viewpoint of thermodynamics, the zinc-doped sample has lower formation energy, more stable ground states, and fewer spinodal decomposition regions than those of the undoped sample, all of which make it charge or discharge without any phase transition. Hence, the zinc-doped sample shows superior cycling performance, demonstrating that zinc doping is an effective strategy for developing high-performance layered cathode materials.

such as elements, alloys, and oxides, have been investigated for anodic use in Li-ion batteries. [ 5,6 ] Among these materials, elemental Si has received distinctive attention because of its huge theoretical capacity coming up to 4200 mA h g −1 , which is greater than those of any other materials. [ 7,8 ] Improving the Li storage properties of Si has been of great signifi cance for commercializing high energy-density batteries incorporating Si-based anodes. However, the enormous volume change during lithiation/delithiation induces a critical mechanical strain on Si particles, thus causing pulverization and the loss of electrical contact, which have been recognized as the major reasons for the rapid capacity fading of Si-based anodes.Extensive efforts have been made to solve the aforementioned problems and obtain highly reversible Si-based anodes. One effective approach is to utilize an electronically conductive carbon matrix, [ 9,10 ] which not only helps to maintain the electrical conductivity around Si parts but also reduces or relieves its huge volume change. Recent studies have shown that graphene can greatly improve cycling stability and rate capability of Li-ion battery electrodes as a conducting and buffering matrix. [11][12][13] However, it is well known that graphene has been diffi cult to be utilized in Si-based anodes [14][15][16] because of its complex, expensive, and non-environment friendly synthetic route. Luo et al. [ 17 ] prepared micrometer-sized Si nanoparticles (NPs) wrapped in graphene shells by a one-step rapid capillary-driven assembly route with improved cycling stability and descent initial coulombic effi ciency. However, an ultrasonic atomizer was used to disperse Si NPs onto the graphene layer, thus rendering the process complex and costly. Zhou et al. [ 18 ] developed nitrogen-doped carbon-coated graphene/Si NPs composites using ionic liquid 1-ethyl-3-methylimidazolium dicyanamide as a carbon precursor. It showed a decent reversible capacity of 902 mA h g −1 after 100 cycles but a very low initial coulombic effi ciency of 57.3%, which renders it not suitable for the commercial full cell application. Although Yi et al. [ 19 ] recently reported an initial coulombic effi ciency of over 60% for graphene/Si-carbon composite and an impressive areal capacity Improving the lithium (Li) storage properties of silicon (Si)-based anode materials is of great signifi cance for the realization of advanced Li-ion batteries. The major challenge is to make Si-based anode materials maintain electronic conduction and structural integrity during cycling. Novel carboncoated Si nanoparticles (NPs)/reduced graphene oxides (rGO) composites are synthesized through simple solution mixing and layer-by-layer assembly between polydopamine-coated Si NPs and graphene oxide nanosheets by fi ltration, followed by a thermal reduction. The anodic properties of this composite demonstrate the potency of the novel hybrid design based on two dimensional materials for extremely reversible energy conversion and storage. A high...

Thus, practical applications of Li batteries have been limited over the past 50 years.We have gained a substantial amount of information about the nucleation and growth process of Li dendrites and the SEI fi lm over time, [5][6][7][8] and many attempts have been made to inhibit Li dendrites and improve cycling performance. This has led to a revival of Li metal batteries. [9][10][11][12][13] According to previous studies, Li dendrite originates from uneven Li deposition and dissolution. When ionic concentrations at the anode surface becomes zero at Sand's time, cations and anions in the liquid electrolyte show different behaviors, leading to excessive Li + ions at the surface. [ 14,15 ] At this point, lithium nucleates and grows dendritically as a function of current density and interfacial elastic strength. [ 5 ] Initial growth of Li dendrites promotes interfacial contacts between the Li anode, the separator, and the electrolyte, which decreases cell resistance. [ 15 ] However, further growth of Li dendrites may puncture the separator, leading to a short circuit of a cell. It is very important, therefore, to constrain the growth of dendrites in order to eliminate safety hazards associated with the Li anode.From decades of research, it is known that low current density, fl exible SEI fi lm, high Li + transference number (t Li + ), and large shear modulus of electrolytes can suppress the growth of Li dendrite. Many methods have been adopted enabling to increase the surface area of the Li anode to reduce the effective current density, use a single ion conductor (SIC) as an electrolyte to enhance t Li + , form a suitable SEI fi lm, employ quasi-solid or all-solid state electrolytes to promote the shear modulus, and coat the Li anode to avoid direct contact between the anode and the electrolyte. [ 1,3,16 ] Now, it is required to systematically summarize them to gain insights for better and more creative solutions. This review summarizes recent studies about the modifi cation of the electrolyte and the Li anode for Li batteries. Their design concepts and preparation methods are introduced, and the resulting effects on electrochemical performance are discussed in details. Simultaneously, challenges and future perspectives of Li batteries are also outlined. Electrolyte Modifi cationElectrolytes can be divided into three states: liquid, quasi-solid, and all-solid. [ 17 ] Quasi-solid and all-solid state electrolytes have Over the last 40 years, metallic lithium as an anode material has been of great interest owing to its high energy density. However, dendritic lithium growth causes serious safety issues. Awareness and understanding of the Li deposition and stripping processes have grown rapidly especially in recent years, and consequently, there have been many attempts to suppress the Li dendrites. Recent developments that have modifi ed the electrolytes and the Li anode in order to inhibit the growth of Li dendrite and improve cycling performance are summarized. It has been shown that current density, solid-electrolyte in...

The development of next-generation energy-storage devices with high power, high energy density, and safety is critical for the success of large-scale energy-storage systems (ESSs), such as electric vehicles. Rechargeable sodium-oxygen (Na-O ) batteries offer a new and promising opportunity for low-cost, high-energy-density, and relatively efficient electrochemical systems. Although the specific energy density of the Na-O battery is lower than that of the lithium-oxygen (Li-O ) battery, the abundance and low cost of sodium resources offer major advantages for its practical application in the near future. However, little has so far been reported regarding the cell chemistry, to explain the rate-limiting parameters and the corresponding low round-trip efficiency and cycle degradation. Consequently, an elucidation of the reaction mechanism is needed for both lithium-oxygen and sodium-oxygen cells. An in-depth understanding of the differences and similarities between Li-O and Na-O battery systems, in terms of thermodynamics and a structural viewpoint, will be meaningful to promote the development of advanced metal-oxygen batteries. State-of-the-art battery design principles for high-energy-density lithium-oxygen and sodium-oxygen batteries are thus reviewed in depth here. Major drawbacks, reaction mechanisms, and recent strategies to improve performance are also summarized.

The increasing demand to efficiently store and utilize the electricity from renewable energy resources in a sustainable way has boosted the request for sodium-ion battery technology due to the high abundance of sodium sources worldwide. Na superionic conductor (NASICON) structured cathodes with a robust polyanionic framework have been intriguing because of their open 3D structure and superior thermal stability. The ever-increasing demand for higher energy densities with NASICON-structured cathodes motivates us to activate multielectron reactions, thus utilizing the third sodium ion toward higher voltage and larger capacity, both of which have been the bottlenecks for commercializing sodium-ion batteries. A doping strategy with Cr inspired by first-principles calculations enables the activation of multielectron redox reactions of the redox couples V2+/V3+, V3+/V4+, and V4+/V5+, resulting in remarkably improved energy density even in comparison to the layer structured oxides and Prussian blue analogues. This work also comprehensively clarifies the role of the Cr dopant during sodium storage and the valence electron transition process of both V and Cr. Our findings highlight the importance of a broadly applicable doping strategy for achieving multielectron reactions of NASICON-type cathodes with higher energy densities in sodium-ion batteries.

Considering that the high capacity,l ong-term cycle life,and high-rate capability of anode materials for sodium-ion batteries (SIBs) is abottleneckcurrently,aseries of Co-doped FeS 2 solid solutions with different Co contents were prepared by afacile solvothermal method, and for the first time their Nastorage properties were investigated. The optimized Co 0.5 Fe 0.5 S 2 (Fe0.5) has discharge capacities of 0.220 Ah g À1 after 5000 cycles at 2Ag À1 and 0.172 Ah g À1 even at 20 Ag À1 with compatible ether-based electrolyte in av oltage windowo f 0.8-2.9 V. The Fe0.5 sample transforms to layered Na x Co 0.5 Fe 0.5 S 2 by initial activation, and the layered structure is maintained during following cycles.T he redoxr eactions of Na x Co 0.5 Fe 0.5 S 2 are dominated by pseudocapacitive behavior, leading to fast Na + insertion/extraction and durable cycle life. AN a 3 V 2 (PO 4 ) 3 /Fe0.5 full cell was assembled, delivering an initial capacity of 0.340 Ah g À1 .

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