Energy storage devices that can deliver high powers have many applications, including hybrid vehicles and renewable energy. Much research has focused on increasing the power output of lithium batteries by reducing lithium-ion diffusion distances, but outputs remain far below those of electrochemical capacitors and below the levels required for many applications. Here, we report an alternative approach based on the redox reactions of functional groups on the surfaces of carbon nanotubes. Layer-by-layer techniques are used to assemble an electrode that consists of additive-free, densely packed and functionalized multiwalled carbon nanotubes. The electrode, which is several micrometres thick, can store lithium up to a reversible gravimetric capacity of approximately 200 mA h g(-1)(electrode) while also delivering 100 kW kg(electrode)(-1) of power and providing lifetimes in excess of thousands of cycles, both of which are comparable to electrochemical capacitor electrodes. A device using the nanotube electrode as the positive electrode and lithium titanium oxide as a negative electrode had a gravimetric energy approximately 5 times higher than conventional electrochemical capacitors and power delivery approximately 10 times higher than conventional lithium-ion batteries.

High-Power Lithium Batteries from Functionalized Carbon Nanotube Electrodes

Noticeable pseudo-capacitance behavior out of charge storage mechanism (CSM) has attracted intensive studies because it can provide both high energy density and large output power. Although cyclic voltammetry is recognized as the feasible electrochemical technique to determine it quantitatively in the previous works, the results are inferior due to uncertainty in the definitions and application conditions. Herein, three successive treatments, including de-polarization, de-residual and de-background, as well as a non-linear fitting algorithm are employed for the first time to calibrate the different CSM contribution of three typical cathode materials, LiFePO4 , LiMn2 O4 and Na4 Fe3 (PO4 )2 P2 O7 , and achieve well-separated physical capacitance, pseudo-capacitance and diffusive contributions to the total capacity. This work can eliminate misunderstanding concepts and correct ambiguous results of the pseudo-capacitance contribution and recognize the essence of CSM in electrode materials.

Understanding and Calibration of Charge Storage Mechanism in Cyclic Voltammetry Curves

Prussian blue analogue (PBA)-type metal hexacyanoferrates are considered as significant cathodes for zinc batteries (ZBs). However, these PBA-type cathodes, such as cyanogroup iron hexacyanoferrate (FeHCF), suffer from ephemeral lifespan (≤1000 cycles), and inferior rate capability (1 A g-1 ). This is because the redox active sites of multivalent iron (Fe(III/II)) can only be very limited activated and thus utilized. This is attributed to the spatial resistance caused by the compact cooperation interaction between Fe and the surrounded cyanogroup, and the inferior conductivity. Here, it is found that high-voltage scanning can effectively activate the C-coordinated Fe in FeHCF cathode in ZBs. Thanks to this activation, the Zn-FeHCF hybrid-ion battery achieves a record-breaking cycling performance of 5000 (82% capacity retention) and 10 000 cycles (73% capacity retention), respectively, together with a superior rate capability of maintaining 53.2% capacity at superhigh current density of 8 A g-1 (≈97 C). The reversible distortion and recovery of the crystalline structure caused by the (de)insertion of zinc and lithium ions is revealed. It is believed that this work represents a substantial advance on PBA electrode materials and may essentially promote application of PBA materials.

Activating C‐Coordinated Iron of Iron Hexacyanoferrate for Zn Hybrid‐Ion Batteries with 10 000‐Cycle Lifespan and Superior Rate Capability

Hard carbon (HC) is recognized as a promising anode material with outstanding electrochemical performance for alkali metal-ion batteries including lithium-ion batteries (LIBs), as well as their analogs sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs). Herein, a comprehensive review of the recent research is presented to interpret the challenges and opportunities for the applications of HC anodes. The ion storage mechanisms, materials design, and electrolyte optimizations for alkali metal-ion batteries are illustrated in-depth. HC is particularly promising as an anode material for SIBs. The solid-electrolyte interphase, initial Coulombic efficiency, safety concerns, and all-climate performances, which are vital for practical applications, are comprehensively discussed. Furthermore, commercial prototypes of SIBs based on HC anodes are extensively elaborated. The remaining challenges and research perspectives are provided, aiming to shed light on future research and early commercialization of HC-based SIBs.

Hard carbon anodes: fundamental understanding and commercial perspectives for Na-ion batteries beyond Li-ion and K-ion counterparts

Revealing the Intercalation Mechanisms of Lithium, Sodium, and Potassium in Hard Carbon

Hard carbon is considered as one of the most promising anodes in sodium-ion batteries due to its high capacity, low cost, and abundant resources However, the available capacity and low initial Coulombic efficiency (ICE) limits the practical application of hard carbon anode This issue results from the unclear understanding of the Na+ storage mechanism in hard carbon In this work, a series of hard carbons with different microstructures are synthesized through an "up to down" approach by using a simple ball-milling method to illustrate the sodium-ion storage mechanism The results demonstrate that ball-milled hard carbon with more defects and smaller microcrystalline size shows less low-potential-plateau capacity and lower ICE, which provides further evidence to the "adsorption-insertion" mechanism This work might give a new perspective to design hard carbon material with a proper structure for efficient sodium-ion storage to develop high-performance sodium-ion batteries

Exploring Sodium-Ion Storage Mechanism in Hard Carbons with Different Microstructure Prepared by Ball-Milling Method.

A rechargeable aqueous Zn/Mn battery is a promising device for large-scale energy storage because of its abundant resources, low cost, and high safety. However, its application is plagued by a poor life cycle because of the electrochemical instability of MnO2 in aqueous electrolytes. Here, an alkaline Zn-Na0.44MnO2 dual-ion battery (denoted AZMDIB) is developed for the first time using Na0.44MnO2 as the cathode, a zinc metal sheet as the anode, and a 6 M NaOH aqueous solution as the electrolyte. When the discharge cutoff voltage is lowered to 0.3 V (vs Zn/Zn2+), the Na0.44MnO2 cathode delivers a high capacity of 345.5 mA h g-1 but with a poor cycling performance. The charge-discharge mechanism and structural evolution of the Na0.44MnO2 cathode in an extended potential window (1.95-0.3 V) are also explored. The Na0.44MnO2 electrode experiences two different electrochemical processes: Na+ ions insert/extract reversibly in the potential range of 1.95-1.1 V, and a phase transition occurs from Na0.559MnO2 to Mn(OH)2 below 1.1 V. The latter irreversible reaction is probably due to proton insertion, leading to a severe capacity fade. Nevertheless, in a narrower voltage range (2.0-1.1 V), the AZMDIB full cell exhibits a high reversible capacity (80.2 mA h g-1 at 0.5 C), high rate capability (32 mA h g-1 at 50 C), and excellent cycling stability (73% capacity retention over 1000 cycles at 10 C). Benefiting from the merits of environmental friendliness, cost-effectiveness, and high electrochemical performance, the rechargeable AZMDIB is a promising contender for grid-scale energy storage applications.

Novel Alkaline Zn/Na0.44MnO2 Dual-Ion Battery with a High Capacity and Long Cycle Lifespan.

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Exploring Sodium-Ion Storage Mechanism in Hard Carbons with Different Microstructure Prepared by Ball-Milling Method.

Novel Alkaline Zn/Na0.44MnO2 Dual-Ion Battery with a High Capacity and Long Cycle Lifespan.