Ion Diffusion Kinetics Research Articles

Promising electrochemical performance of pristine SnO2 anodes for lithium and sodium-ion batteries

Sustainable materials with nanostructured architecture have made great strides in today’s energy storage technology. In this context, sustainable, environment-friendly SnO2 are synthesised by hydrothermal method and its electrochemical performance as anode material for lithium and sodium-ion batteries are investigated. Structural analysis such as X-ray diffraction and Raman measurement validates the formation of the tetragonal rutile structure of pristine SnO2. Scanning electron microscope image shows mixed, hollow spherical and rod- shape morphology. The Li+ and Na+ ion diffusion kinetics are conferred using cyclic voltammetry. The rate capability of pristine SnO2 anodes are tested using charge–discharge measurements. SnO2/Li half-cell shows the initial discharge capacity of 982 mAh/g at 0.1C rate and delivers the specific capacity of 219 mAh/g and 72 mAh/g at 10C and 20C rates. The SnO2/Na half-cell delivers the initial discharge capacity of 600 mAh/g and maintains the specific capacity of 110 mAh/g (1C-rate) after 500 charge–discharge cycles. The mixed spherical and rod shape morphology increases the surface area and facilitates the Li+ and Na+-ion diffusion and minimizes pulverization. Post-mortem microstructural studies are performed after 500 cycles, confirming the formation of inert oxide phases and degradation of electrolyte by-products in both LIB and SIB.

Integrated solution for a stable and high-performance zinc-ion battery using an electrolyte additive

Owing to their excellent safety, high capacity, eco-friendliness, and low cost, aqueous zinc-ion batteries (ZIBs) consisting of Zn anode and vanadium pentoxide cathode are considered as an attractive candidate for large-scale energy storage systems. However, the non-uniform dendrite growth and hydrogen evolution at the anode, as well as metal-ion dissolution at the cathode, caused by the utilization of acid electrolytes limit the capacity and cycle life of ZIBs. To address this, this study demonstrated the use of a stable and high-performance active material as the anode/cathode and vanadium (IV) oxide sulfate (VOSO4) as an electrolyte additive to fabricate high-energy performance ZIBs via a one-step process. The self-assembled passive layer on the anode surface enabled improved ion diffusion kinetics; thus, the ZIBs exhibited increased capacity (590 mAh g − 1 at 1 A g − 1) and rate capability (420 mAh g − 1 at 5 A g − 1). In addition, the inhibition of vanadium dissolution at the cathode extended the cycling performance of the battery for up to 400 cycles with a capacity retention of 77%. This strategy is a facile and feasible method to address the anode and cathode issues of ZIBs, thus providing new opportunities for the realization of stable and high-performance ZIBs.

Sm2O3 coating to suppress electrode/electrolyte side reactions of single crystal materials at high voltage

Coating modification of single-crystal materials was studied to improve the electrochemical properties of the materials by suppressing the electrode/electrolyte side reactions. The commercial LiNi0·6Co0·1Mn0·3O2 was used as the base material and Sm2O3 coating was applied on its surface. The Sm2O3-coated NCM613 single-crystal material was synthesized. The structure and morphology of the electrode materials were characterized by XRD, FESEM, and TEM. The results showed that Sm2O3 was successfully coated on the surface of the particles without damaging the original structure of the material. Meanwhile, the lithium ions diffusion kinetics of the material was analyzed by cyclic voltammetry. The results show that the coated cathode material has a more excellent lithium ions diffusion coefficient, which provides a kinetic basis for charging and discharging the battery at high voltage. At 25 °C, 3.0−4.5 V, and 1 C current density, the capacity retention of the coated cathode material after 100 cycles was 87.5% (182.8−159.9 mAh g−1), which was much higher than that of the original material at 77% (177−136.3 mAh g−1). SEM and other characterizations of the electrode sheets after cycling showed that the Sm2O3 coating layer effectively prevented the direct contact between the cathode material and the electrolyte, which played a positive role in suppressing the occurrence of side reactions, and inhibits the formation of microcracks during the cycling process. In general, this method contributed to the stability of the electrode/electrolyte interface and electrochemical performance.

In-situ growth of nitrogen-doped carbon nanotubes on MXene nanosheets for efficient sodium/potassium-ion storage

For game changing for future of large-scale energy storage technologies, sodium-ion and potassium-ion batteries provide a substitute to lithium-ion batteries. As an excellent candidate anode, MXene still suffers from the blockage of active sites caused by restacking of sheets. Herein, an in-situ decoration of MXene nanosheets with nitrogen-doped carbon nanotubes (CNTs) is introduced, to yield MXene@CNTs. The modification of nitrogen-doped CNTs not only prevents the restacking of MXene and increases ion accessibility but also improves the electrode’s overall conductivity, thereby enhancing electron conduction and ion diffusion kinetics significantly. Therefore, MXene@CNTs exhibits superior sodium/potassium-ion storage performance than pure MXene nanosheets. At 0.05 A g-1, it can deliver reversible capacities of 286 mAh g-1 for SIBs and 250 mAh g-1 for PIBs. This research illustrates the significance of the electrode architecture for electrochemical performances, and the in-situ growth strategy could provide some insight on searching for high-performance MXene-based anodes for SIBs and PIBs.

Self-lithiation electrode with improved lithium-ion transport kinetics enables fast-charging SiOx-based anode for lithium-ion batteries

As an important component of lithium-ion battery anodes, SiOx (0 < x < 2) has received lots of attention in the past few years. However, poor electrical conductivity and huge volume expansion (∼200%) result in an unsatisfied electrochemical kinetics process, which severely hinders the further development of SiOx-based anode materials. In this work, a concept of self-lithiation electrode was proposed, and MoS2 was chosen as a proof-of-concept to construct a core–shell structured composite (SC@M−0.3). The coated MoS2 delivers a high lithiation potential and fast ion diffusion kinetics, which could rapidly provide extra Li ions to SiOx-based core materials based on self-lithiation behavior. The superior structural stability of MoS2 could additionally inhibit the huge volume change of the composite. Impressively, the prepared SC@M−0.3 electrode achieves stable long-term cycling and a high specific capacity of 1007 mAh g−1 even after 400 cycles at a demanding current of 5 A g−1. This study provides a new direction for the design of functional composite materials with fast ion diffusion kinetics and superior cycling stability for pursuing fast-charging secondary ion batteries.

Accelerated Li+ Desolvation for Diffusion Booster Enabling Low‐Temperature Sulfur Redox Kinetics via Electrocatalytic Carbon‐Grazfted‐CoP Porous Nanosheets

AbstractLithium–sulfur (Li–S) batteries are famous for their high energy density and low cost, but prevented by sluggish redox kinetics of sulfur species due to depressive Li ion diffusion kinetics, especially under low‐temperature environment. Herein, a combined strategy of electrocatalysis and pore sieving effect is put forward to dissociate the Li+ solvation structure to stimulate the free Li+ diffusion, further improving sulfur redox reaction kinetics. As a protocol, an electrocatalytic porous diffusion‐boosted nitrogen‐doped carbon‐grafted‐CoP nanosheet is designed via forming the NCoP active structure to release more free Li+ to react with sulfur species, as fully investigated by electrochemical tests, theoretical simulations and in situ/ex situ characterizations. As a result, the cells with diffusion booster achieve desirable lifespan of 800 cycles at 2 C and excellent rate capability (775 mAh g−1 at 3 C). Impressively, in a condition of high mass loading or low‐temperature environment, the cell with 5.7 mg cm−2 stabilizes an areal capacity of 3.2 mAh cm−2 and the charming capacity of 647 mAh g−1 is obtained under 0 °C after 80 cycles, demonstrating a promising route of providing more free Li ions toward practical high‐energy Li–S batteries.

Superlithiation Performance of Pyridinium Polymerized Ionic Liquids with Fast Li+ Diffusion Kinetics as Anode Materials for Lithium-Ion Battery.

Polymerized ionic liquids (PILs) with super ion diffusion kinetics have aroused considerable attention in rechargeable batteries, which are very promising to solve the problem of the slow ion diffusion kinetics in organic electrode materials. Theoretically, PILs incorporated redox groups are very suitable as anode materials to realize "superlithiation" performance, achieving high lithium storage capacity. In this study, redox pyridinium-based PILs (PILs-Py-400) have been synthesized through trimerization reactions by pyridinium ionic liquids with cyano groups under an appropriate temperature (400 °C). The positively charged skeleton, extended conjugated system, abundant micropores, and amorphous structure for PILs-Py-400 can boost the utilization efficiency of redox sites. A high capacity of 1643 mAh g-1 at 0.1 A g-1 (96.7% of the theoretical capacity) has been obtained, indicating intriguing 13 Li+ redox reactions in per repeating unit of one pyridinium ring, one triazine ring, and one methylene. Moreover, PILs-Py-400 exhibit excellent cycling stability with a capacity of around 1100 mAh g-1 at 1.0 A g-1 after 500 cycles, and the capacity retention is 92.2%.

In Situ Formed Gradient Composite Solid Electrolyte Interphase Layer for Stable Lithium Metal Anodes.

Lithium (Li) metal anode (LMA) is highly considered as a desirable anode material for next-generation rechargeable batteries because of its high specific capacity and the lowest reduction potential. However, uncontrollable growth of Li dendrites, large volume change, and unstable interfaces between LMA and electrolyte hinder its practical application. Herein, a novel in situ formed artificial gradient composite solid electrolyte interphase (GCSEI) layer for highly stable LMAs is proposed. The inner rigid inorganics (Li2 S and LiF) with high Li+ ion affinity and high electron tunneling barrier are beneficial to achieve homogeneous Li plating, while the flexible polymers (poly(ethylene oxide) and poly(vinylidene fluoride)) on the surface of GCSEI layer can accommodate the volume change. Furthermore, the GCSEI layer demonstrates fast Li+ ion transport capability and increased Li+ ion diffusion kinetics. Accordingly, the modified LMA enables excellent cycling stability (over 1000h at 3mA cm-2 ) in the symmetric cell using carbonate electrolyte, and the corresponding Li-GCSEI||LiNi0.8 Co0.1 Mn0.1 O2 full cell demonstrates 83.4% capacity retention after 500 cycles. This work offers a new strategy for the design of dendrite-free LMAs for practical applications.

Two-dimensional dumbbell silicene as a promising anode material for (Li/Na/K)-ion batteries

Rechargeable ion batteries require anode materials with excellent performance, presenting a key challenge for researchers. This paper explores the potential of using two-dimensional dumbbell silicene as an anode material for alkali metal ion batteries through density functional theory (DFT) calculations. Our findings demonstrate that alkali metal ions have negative adsorption energies on dumbbell silicene, and the energy barriers for Li/Na/K ion diffusion are as low as 0.032 eV/0.055 eV/0.21 eV, indicating that metal ions can easily diffuse across the entire surface of dumbbell silicene. Additionally, the average open circuit voltages of dumbbell silicene as anode for Li-ion, Na-ion, and K-ion batteries are 0.42 V, 0.41 V, and 0.60 V, respectively, with corresponding storage capacities of 716 mAh/g, 622 mAh/g, and 716 mAh/g. These results suggest that dumbbell silicene is an ideal anode material for Li-ion, Na-ion, and K-ion batteries, with high capacity, low open circuit voltage, and high ion diffusion kinetics. Moreover, our calculations show that the theoretical capacities obtained using DFT-D2 are higher than those obtained using DFT-D3, providing a valuable reference for subsequent theoretical calculations.

Diffusion kinetics of CuCo2O4 nanorods for next‐generation solid state sodium‐ion hybrid supercapacitor

AbstractIn the current study, we report a straightforward and affordable sol‐gel preparation approach for the fabrication of spinel CuCo2O4 nanorods for sodium ion‐based hybrid supercapacitor. The morphological and structural analysis shows that appropriate purity nanorods of CuCo2O4 are formed with good stoichiometry. The electrochemical study of CuCo2O4 nanorods reveals that the electrode has highest specific capacitance of 367 F g−1 at 1 A g−1 in 1 M Na2SO4 electrolyte. Evaluation of the diffusion kinetics of sodium ions through detailed electrochemical evaluations of cyclic voltammogram (CV) showing the charge storage kinetics of CuCo2O4 is primarily performed through the diffusive limited mechanisms, suggesting the battery‐like behavior of CuCo2O4 electrode. Hybrid supercapacitor (HSC) device is fabricated by utilizing CuCo2O4 for positive and reduced graphene oxide (rGO) for negative electrodes material. The polymer gel electrolyte is used in the form of hydrogel membrane made of PVA and Na2SO4, and the HSC device (rGO || CuCo2O4) exhibits energy density of 9.18 Wh kg−1. Therefore, sodium‐ion hybrid supercapacitor electrode materials for this investigation are established using a comprehensive electrochemical kinetics.

Phase engineering of nickel-based sulfides toward robust sodium-ion batteries

Nickel-based sulfides are considered promising materials for sodium-ion batteries (SIBs) anodes due to their abundant resources and attractive theoretical capacity. However, their application is limited by slow diffusion kinetics and severe volume changes during cycling. Herein, we demonstrate a facile strategy for the synthesis of nitrogen-doped reduced graphene oxide (N-rGO) wrapped Ni3S2 nanocrystals composites (Ni3S2-N-rGO-700 °C) through the cubic NiS2 precursor under high temperature (700 ℃). Benefitting from the variation in crystal phase structure and robust coupling effect between the Ni3S2 nanocrystals and N-rGO matrix, the Ni3S2-N-rGO-700 °C exhibits enhanced conductivity, fast ion diffusion kinetics and outstanding structural stability. As a result, the Ni3S2-N-rGO-700 °C delivers excellent rate capability (345.17 mAh g−1 at a high current density of 5 A g−1) and long-term cyclic stability over 400 cycles at 2 A g−1 with a high reversible capacity of 377 mAh g−1 when evaluated as anodes for SIBs. This study open a promising avenue to realize advanced metal sulfide materials with desirable electrochemical activity and stability for energy storage applications.

Mott-Schottky Effect in Core-Shell W@Wx C Heterostructure: Boosting Both Electronic/Ionic Kinetics for Lithium Storage.

The dynamics rate of traditional metal carbides (TMCs) is relatively slow, severely limiting its fast-charging capacity for lithium-ion batteries (LIBs). Herein, the core-shell W@Wx C heterostructure is developed to form Mott-Schottky heterostructure, thereby simultaneously accelerating the electronic and ionic transport kinetics during the charging/discharging process. The W nanoparticles are partially reduced into Wx C to form a particular core-shell structure with abundant heterogeneous interfaces. Benefiting from the Mott-Schottky effect, the electrons at the metal/semiconductor heterointerface can migrate spontaneously to realize an equal work function on both sides. In addition, the independent nanoparticle as well as the unique core-shell structure facilitate the ionic diffusion kinetics. As expected, the W@Wx C electrode exhibits excellent electrochemical stability for LIBs, whose capacity can be maintained at 173.8mA h g-1 after 1600 cycles at a high current density of 5 A g-1 . When assembled into a full cell, it can achieve an energy density of 360.2Wh kg-1 . This work presents a new avenue to promote the electronic and ionic kinetics for LIBs anodes by constructing the unique Mott-Schottky heterostructure.

Constructing sulfur and oxygen co-doped carbon nanosheets by tailoring poly tannic acid for fast and stable potassium storage

Carbonaceous material with excellent structural stability and low cost has always been deemed focus of pursuer, nevertheless it showed the sluggish dynamics and large volume expansion as the anode materials for potassium-ion batteries (PIBs). Herein, S, O co-doped ultra-thin carbon nanosheets (S/O-CNS) with enlarged interlayer spacing was synthesized through pyrolysis poly tannic acid with a sulfur-assisted carbonization strategy. Under the unique synthesis process, sulfur acts as a dopant and intercalating agent to acquire few-layer carbon nanosheets with large interlayer spacing (0.42 nm), while oxygen was in-situ doped into the carbon lattice and provides sites for sulfur doping. With the synergistic effects of the co-doping effect and heterostructure, S/O-CNS delivers an excellent reversible capacity of 375.6 mA h g−1 at 0.1 A g−1, an impressive rate performance of 159.9 mA h g−1 even at 10 A g−1 as well as outstanding cycle stability of 198.9 mA h g−1 after 700 cycles at 1.0 A g−1. Kinetics analysis indicates that the capacitance-controlled process plays a dominant role in K+ storage. The results prove that the enlarged interlayer spacing and abundant edge defects accelerate the ion diffusion kinetics. This dual-doping strategy provides a way to design high-performance carbonaceous materials for PIBs.

Electronic structure engineering on NiSe2 micro-octahedra via nitrogen doping enabling long cycle life magnesium ion batteries

Multivalent ion batteries have attracted great attention because of their abundant reserves, low cost and high safety. Among them, magnesium ion batteries (MIBs) have been regarded as a promising alternative for large-scale energy storage device owing to its high volumetric capacities and unfavorable dendrite formation. However, the strong interaction between Mg2+ and electrolyte as well as cathode material results in very slow insertion and diffusion kinetics. Therefore, it is highly necessary to develop high-performance cathode materials compatible with electrolyte for MIBs. Herein, the electronic structure of NiSe2 micro-octahedra was modulated by nitrogen doping (N-NiSe2) through hydrothermal method followed by a pyrolysis process and this N-NiSe2 micro-octahedra was used as cathode materials for MIBs. It is worth noting that N-NiSe2 micro-octahedra shows more redox active sites and faster Mg2+ diffusion kinetics compared with NiSe2 micro-octahedra without nitrogen doping. Moreover, the density functional theory (DFT) calculations indicated that the doping of nitrogen could improve the conductivity of active materials on the one hand, facilitating Mg2+ ion diffusion kinetics, and on the other hand, nitrogen dopant sites could provide more Mg2+ adsorption sites. As a result, the N-NiSe2 micro-octahedra cathode exhibits a high reversible discharge capacity of 169 mAh g−1 at the current density of 50 mA g−1, and a good cycling stability over 500 cycles with a maintained discharge capacity of 158.5 mAh g−1. This work provides a new idea to improve the electrochemical performance of cathode materials for MIBs by the introduction of heteroatom dopant.

Rationally designed NASICON-type Na3.75V1.25Mn0.75(PO4)3 cathode towards long life-span sodium ion batteries

Owning to non-toxic and high working potential, Mn-substituted NASICON-type Na3+xMnxV2-x(PO4)3 cathodes have promising application in sodium ion batteries (SIBs). However, the poor cycling stability limits their further practical applications. Herein, a succession of carbon coated Na3.75Mn0.75V1.25(PO4)3 cathodes are constructed via a sol–gel combining with heating treatment. The effects of carbon content on the structure, electrochemical properties and sodium ion diffusion kinetics are investigated. The optimal composition, Na3.75Mn0.75V1.25(PO4)3/2VitC, displays an outstanding specific capacity and long-cycling stability. It releases a discharge capacity of 105.6 mAh g-1 with a high initial Coulombic efficiency of 97.5% at 0.2C. It can also deliver a high capacity of 92.6 mAh g-1 with a capacity retention of 88.3% at 5C over 2000 cycling, and the reversible capacity can achieve to 79.1 mAh g-1 with 78% capacity retention after 4000 cycles at high rate of 10C. Ex-situ X-ray diffraction and X-ray photoelectron spectroscopy reveal a biphasic reaction process and high structural reversibility during sodium ion insertion/extraction. The good multiplicity performances, excellent long cycle stability and low cost of the optimized Na3.75Mn0.75V1.25(PO4)3 composite indicate that it is a promising cathode material for SIBs.

Boosting aqueous zinc-ion storage by synergistically coupling sodium manganese oxides with MXene nanosheets

Aqueous zinc ion batteries (ZIBs) are regarded as a promising battery mainly due to their high safety and environmental friendliness, but suffer from low capacity and energy density. Herein, a pre-intercalated manganese oxide (Na0.55Mn2O4·1.5 H2O)/MXene hybrid (NMO/MXene) is successfully proposed for high-performance ZIBs, in which synergistic effect between MXene and NMO greatly improves the structural stability of NMO and facilitates fast charge transfer and ion diffusion kinetics. Therefore, the resulting NMO/MXene cathodes deliver high-rate capacity of 180 mAh g−1 at 10 C (3.08 A g−1) and long cycling life over 2500 times at 5 C, outperforming most reported Mn-base cathodes. The MXene-mediated strategy for advanced Mn-based cathodes developed here paves a new way to construct high-performance Zn-MnO2 batteries.

Ti3C2Tx MXenes bonded MoS2 nanosheets for superior sodium-ion batteries

Sodium-ion batteries (SIBs) have evolved into the most potential alternatives to lithium-ion batteries (LIBs) especially for large-scale energy storage applications. However, the large radius of sodium ion inevitably causes large volume change and sluggish ion diffusion kinetics. Molybdenum disulfide (MoS2) as a rising star of anode for SIBs has raised concern because of its high theoretical capacity. Nevertheless, MoS2 suffers from low electronic conductivity and serious re-stacking, resulting in declined cycling stability and poor rate capability. Herein, we reported an electrostatic self-assembly process to synthesize three-dimensional (3D) crumpled MXene-bonded MoS2 nanosheets. The MoS2/MXene heterostructure not only avoids the serious self-aggregation of MoS2 nanoparticles but only maintains the chemical and mechanical stability of MoS2/MXene hybrids during sodiation and desodiation. Strong chemical interactions were validated on the interface of MXene and MoS2, favoring fast charge transfer kinetics and durable structural stability. The developed MoS2/MXene electrode exhibits a high specific capacity (509 mAh g−1 at 0.05 A g−1) and considerable cyclability (326 mAh g−1 at 1 A g−1 after 900 cycles), manifesting a promising application prospect for SIBs. Our work can provide a rational strategy for the electrode design strategy for SIBs.

Triggering Mixed Cationic‐Anionic Redox in Cu2‐xSe Cathodes via Tailored Charge‐Carrier for High Energy Density Aqueous Zn Batteries

AbstractThe further application of promising transition‐metal chalcogenides (TMCs) cathodes in dilute neutral aqueous Zn batteries (AZBs) is mainly plagued by unsatisfactory working voltages (usually &lt;1 V vs Zn2+/Zn) and their conventional cationic redox centers reaching theoretical capacity limit. Hence, to break the confinement, a novel Zn‐Cu2‐xSe battery is developed in dilute neutral‐aqueous electrolyte by introducing a tailored charge‐carrier, which not only alters the intercalation potential of ions embedded into Cu2‐xSe (vs Zn2+/Zn, working voltage from ≈0.4 to ≈1.2 V) but also activates the anionic redox centers of Cu2‐xSe (capacity release from 143.4 to 323.2 mAh g−1 at 0.4 A g−1). In situ synchrotron X‐ray diffraction (SXRD) and substantial ex situ characterizations reveal the multi‐step phase conversion undergone by cathode and triggered additional Se‐based anionic (Sen2−/Se2−) reversible redox reaction. A multi‐electron synergistic transfer process established on the cationic‐anionic redox centers circumvents the slow relaxation of single‐ion charge compensation achieving high‐capacity and enhanced ion diffusion kinetics. As a result, an extraordinary energy density of up to 406.2 Wh kg−1 at 240 W kg−1 is implemented (calculated based on the mass of Cu2‐xSe cathode), which is ≈8.4 times higher than that of conventional Zn‐Cu2‐xSe batteries, representing an advanced development toward energetic AZBs.

Tuning nickel cobalt sulfides embedded in hierarchical porous carbon nanosheets/carbon nanotubes interpenetrating frameworks by in situ bimetallic MOF-derived engineering towards exceptional lithium storage

A Ni/Co-MOF-engaged bimetallic nickel cobalt sulfide nanoparticles encapsulating into a 3D interpenetrating hierarchical porous ultrathin carbon nanosheets/carbon nanotubes framework (NiCo2S4 @HPCS/CNTs) have been designed and fabricated via carbonization under the reducing atmosphere and further sulfurization processes. The in situ development of extruded CNTs from organic ligands in MOF templates is autocatalyzed by the metal nanoparticles created during the reduction process. Intriguingly, MOFs serve as periodically atom-dispersed self-sacrificial templates for the in situ formation of hierarchical porous carbon-encapsulated micro/nano heterostructure materials. NiCo2S4 nanocrystals are uniformly dispersed into the 1D CNTs/2D carbon nanosheets/3D carbon spheres conductive networks in this special compositional and hierarchical structure, effectively inhibiting volume expansion, enhancing the electronic conductivity, and further enabling ultrafast lithium ion diffusion kinetics. When used as anode materials of lithium-ion battery (LIB), the NiCo2S4 @HPCS/CNTs electrode delivers outstanding cycling stability with capacity retention of 782.4 mAh g−1 after 800 cycles at 1 A g−1 and excellent rate capability of 584.9 mAh g−1 at a high current density of 4 A g−1. This study provides a novel approach for preparing multi-metallic sulfide generated from MOF precursors with surprisingly heterostructures as the advanced anode materials for LIBs.

High‐Power and Ultrastable Aqueous Calcium‐Ion Batteries Enabled by Small Organic Molecular Crystal Anodes

AbstractCalcium ion batteries (CIBs) are pursued as potentially low‐cost and safe alternatives to current Li‐ion batteries due to the high abundance of calcium element. However, the large and divalent nature of Ca2+ leads to strong interaction with intercalation hosts, sluggish ion diffusion kinetics and low power output. Herein, a small molecular organic anode is reported, tetracarboxylic diimide (PTCDI), involving carbonyl enolization (CO↔CO−) in aqueous electrolytes, which bypasses the diffusion difficulties in intercalation‐type electrodes and avoid capacity sacrifice for polymer organic electrodes, thus manifesting rapid and high Ca storage capacities. In an aqueous Ca‐ion cell, the PTCDI presents a reversible capacity of 112 mAh g−1, a high‐capacity retention of 80% after 1000 cycles and a high‐power capability at 5 A g−1, which rival the state‐of‐the‐art anode materials in CIBs. Experiments and simulations reveal that Ca ions are diffusing along the a axis tunnel to enolize carbonyl groups without being entrapped in the aromatic carbon layers. The feasibility of PTCDI anodes in practical CIBs is demonstrated by coupling with cost‐effective Prussian blue analogous cathodes and CaCl2 aqueous electrolyte. The appreciable Ca storage performance of small molecular crystals will spur the development of green organic CIBs.