Due to their numerous advantages, such as high specific capacity, lithium–sulfur batteries (Li–S batteries) have attracted much attention as next‐generation energy storage systems. To meet future ...needs for commercial application, Li–S batteries will require both improved cycle life and high energy density. It is of critical importance to understand the fundamental mechanisms in Li–S systems to further improve the overall battery performance. Various advanced characterization techniques, over the past few years, have proven their important role in promoting the mechanism understanding for Li–S batteries. Here, the recent progress of mechanism understanding, including redox reactions, Li polysulfides dissolution, etc., in Li–S systems based on the advanced characterization techniques is reviewed. Special focus is placed on how these advanced characterization techniques are being employed and what characteristic or capability they possess. The importance of the combination of multiple characterization techniques, differences between ex situ and in situ experimental methods, as well as effects of characterization conditions in Li–S batteries are also discussed.
Various advanced characterization techniques tremendously promote the progress of mechanism understanding in Li–S batteries, providing guidance for the optimization of overall battery performances. This review highlights the importance, and presents the basic principles as well as characteristics of different characterization techniques employed in Li–S systems, which is helpful for the research of Li–S batteries in the future.
The irreversible consumption of sodium at the anode side during the first cycle prominently reduces the energy density of Na‐ion batteries. Different sacrificial cathode additives have been recently ...reported to address this problem; however, critical issues such as by‐products (e.g., CO2) release during cycling and incompatibility with current battery fabrication procedures potentially deteriorate the full‐cell performance and prevent the practical application. Herein, an additive‐free self‐presodiation strategy is proposed to create lattice‐coherent but component‐dependent O3‐NaxTMMnO2 (TM = transition metal ion(s)) cathodes by a quenching treatment rather than the general natural cooling. The quenching material preserves higher Mn3+ and Na+ content, which is able to release Na+ via Mn3+ oxidation to compensate for sodium consumption during the initial charge while adopting other TM to provide the capacity in the following cycles. Full cells fabricated with hard carbon anode and this material as both cathode and sodium supplement reagent have a nearly 9.4% cathode mass reduction, around 9.9% energy density improvement (from 233 to 256 Wh kg−1), and 8% capacity retention enhancement (from 76% to 84%) after 300 cycles. This study presents the route to rational design cathode materials with sodium reservoir property to simplify the presodiation process as well as improve the full‐cell performance.
An additive‐free self‐presodiation strategy is proposed for the rational design of Na‐ion battery (NIB) cathode materials to compensate for the irreversible consumption of sodium at the anode side during the first cycle of NIBs. The as‐prepared O3‐NaxTMO2 cathodes preserve higher Na+ and Mn3+ content by a quenching treatment, rendering it not only the cathode but also a sodium donor.
The energy density presents the core competitiveness of lithium (Li)‐ion batteries. In conventional Li‐ion batteries, the utilization of the gravimetric/volumetric energy density at the electrode ...level is unsatisfactory (<84 wt% and <62 vol%, respectively) due to the existence of non‐electrochemical active parts among the 3D porous electrodes, including electrolytes, binders, and carbon additives. These are regarded as indispensable and irreducible components of the electronic and ionic transport network. Here, a dense “all‐electrochem‐active” (AEA) electrode for all‐solid‐state Li batteries is proposed, which is entirely constructed from a family of superior mixed electronic–ionic‐conducting cathodes, to minimize the energy density gap between the accessible and theoretical energy density at the electrode level. Furthermore, with the ionic–electronic‐conductive network self‐supported from the AEA cathode, the dense hybrid sulfur (S)‐based AEA electrode exhibits a high compacted filling rate of 91.8%, which indicates a high energy density of 777 W h kg−1 and 1945 W h L−1 at the electrode level based on the total cathodes and anodes when at 70 °C.
A new family of cathodes with superior ionic/electronic conductivities is demonstrated for all‐solid‐state Li‐metal batteries. No carbon and electrolyte additives are needed in such an “all‐electrochem‐active” (AEA) cathode so the space and mass of the electrode are fully utilized and high mass/volume energy density are obtained.
Hard carbon anode materials for sodium-ion batteries (SIB) have usually been tested in half-cells by cycling between 0–2V, and is believed to exhibit low rate capability. However, we find that the ...specific capacity, the rate performance, and the cycling performance may all be severely underestimated with the traditional half-cell cycling evaluation method, due to premature truncation of part II of the capacity (part I is “sloping”, part II is “plateauing”, while part III is Na metal deposition). Here we introduce a sodium-matched SIB full-cell architecture, with newly developed hard carbon derived from macadamia shell (MHC) as anode and NaCu1/9Ni2/9Fe1/3Mn1/3O2 (NCNFM) as the cathode material, with anode/cathode areal capacity ratio of 1.02–1.04. Our carefully balanced full-cells exhibit a cell-level theoretical specific energy of 215Whkg−1 at C/10 and 186Whkg−1 at 1C based on cathode-active and anode-active material weights, and an outstanding capacity retention of 70% after 1300 cycles (∼2000h). Traditional half-cell test (THT) of MHC using superabundant Na metal counter electrode shows only 51.7mAhg−1 capacity at 1C, and appears to die in no more than 100h due to low open-circuit voltage slope and large polarization. A revised half-cell test (RHT) which shows much better agreements with full-cell test results, delivers a specific capacity of 314mAhg−1, with an initial Coulombic efficiency of ∼91.4%, which is comparable to that of graphite anode in lithium-ion batteries.
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•A sodium-ion battery full-cell architecture with great stability and good rate performance is demonstrated.•A novel hard carbon with a high initial Coulombic efficiency of 91.4% is delivered.•The traditional half-cell test protocol is suggested to be revised.
Na-ion batteries (NIBs) have attracted significant attention owing to Na being an abundant resource that is uniformly distributed in the Earth’s crust. Several 3d transition metal (TM) ions have been ...thoroughly investigated as charge compensators in single or multiple composition systems to enhance the electrochemical performance of cathodes for the practical applications. In this review, the composition-structure-property relationship of Ni-based cathodes has been reviewed as a design perspective for NIB’s cathodes. The typical Ni-based cathode materials have been systematically summarized and comparatively analyzed, and it is demonstrated that Ni ions can be used to provide charge compensation. Moreover, Ni-based cathodes present high reversible capacity owing to the multi-electron redox reactions and suitable redox potential of Ni-ions redox. However, considering the abundance, cost, and hygroscopic properties of Ni element, the content of 0.15–0.35 per formula can be optimal for enhancing the performance of cathodes. Lastly, further perspectives on designing Ni-containing cathodes, including Ni-rich layered cathodes, have been discussed, which could promote the practical applications of NIBs for grid-scale energy storage in future.
Na superionic conductor structured Na3V2(PO4)3 cathodes have attracted great interest due to their long cycling lifespan and high thermal stability rendered by the robust 3D framework. However, their ...practical application is still hindered by the high cost of raw materials and limited energy density. Herein, a doping strategy with low‐cost Fe2+ is developed to activate V4+/V5+ redox, in an attempt to increase the energy density of phosphate cathodes. It is also revealed that reversible activation of V4+/V5+ redox is related to the Na positions (Na1, 6b; Na2, 18e). Only the V‐based compounds with enough Na2 content can activate the V4+/V5+ reversibly. More importantly, without presodiation treatment and addition of any sodiation agent, Na3.4V1.6Fe0.4(PO4)3 is delicately designed as both cathode and the Na self‐compensation agent in full cells, allowing a promising energy density of ≈260 Wh kg−1. This work sheds light on enhancing the energy density, and designing Na self‐compensation for practical Na‐ions batteries.
Na3.4V1.6Fe0.4(PO4)3 is delicately designed as both cathode and the Na self‐compensation agent in full cells, which can supplement the Na+ consumption during the formation of the solid electrolyte interphase layer on the hard carbon by sacrificing the capacity from the low‐voltage Fe2+/Fe3+ and achieve a promising energy density of 260 Wh kg−1 contributed to by the reversible V3+/V4+/V5+ redox couples.
Sodium–ion batteries (NIBs), due to the advantages of low cost and relatively high safety, have attracted widespread attention all over the world, making them a promising candidate for large‐scale ...energy storage systems. However, the inherent lower energy density to lithium–ion batteries is the issue that should be further investigated and optimized. Toward the grid‐level energy storage applications, designing and discovering appropriate anode materials for NIBs are of great concern. Although many efforts on the improvements and innovations are achieved, several challenges still limit the current requirements of the large‐scale application, including low energy/power densities, moderate cycle performance, and the low initial Coulombic efficiency. Advanced nanostructured strategies for anode materials can significantly improve ion or electron transport kinetic performance enhancing the electrochemical properties of battery systems. Herein, this Review intends to provide a comprehensive summary on the progress of nanostructured anode materials for NIBs, where representative examples and corresponding storage mechanisms are discussed. Meanwhile, the potential directions to obtain high‐performance anode materials of NIBs are also proposed, which provide references for the further development of advanced anode materials for NIBs.
Advanced nanostructured strategies, including morphology/structure engineering, heteroatom doping, and conductive/framework materials coating, are confirmed to be the potential choices to improve the performance of anode materials for sodium–ion batteries on the low initial coulombic efficiency, poor cycle performance, and power density due to sluggish sodiation kinetics.
Aggressive chemistry involving Li metal anode (LMA) and high-voltage LiNi
Mn
Co
O
(NCM811) cathode is deemed as a pragmatic approach to pursue the desperate 400 Wh kg
. 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 (LiBF
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 LiCoO
cathode. Accordingly, industrial anode-free pouch cells under harsh testing conditions deliver a high energy of 442.5 Wh kg
with 80% capacity retention after 100 cycles.
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