Metal-ion Batteries Research Articles

Ordered Vacancies as Sodium Ion Micropumps in Cu-Deficient Copper Indium Diselenide to Enhance Sodium Storage.

Unordered vacancies engineered in host anode materials cannot well maintain the uniform Na+ adsorbed and possibly render the local structural stress intense, resulting in electrode peeling and battery failure. Here, the indium is first introduced into Cu2Se to achieve the formation of CuInSe2. Next, an ion extraction strategy is employed to fabricate Cu0.54In1.15Se2 enriched with ordered vacancies by spontaneous formation of defect pairs. Such ordered defects, compared with unordered ones, can serve as myriad sodium ion micropumps evenly distributing in crystalline host to homogenize the adsorbed Na+ and the generated volumetric stress during the electrochemistry. Furthermore, Cu0.54In1.15Se2 is indeed proved by the calculations to exhibit smaller volumetric variation than the counterpart with unordered vacancies. Thanks to the distinct ordered vacancy structure, the material exhibits a highly reversible capacity of 428mAhg-1 at 1C and a high-rate stability of 311.7mAhg-1 at 10C after 5000 cycles when employed as an anode material for Sodium-ion batteries (SIBs). This work presents the promotive effect of ordered vacancies on the electrochemistry of SIBs and demonstrates the superiority to unordered vacancies, which is expected to extend it to other metal-ion batteries, not limited to SIBs to achieve high capacity and cycling stability.

Optimizing the performance of a graphite anode for innovative metal-ion batteries and hybrid capacitors

Herein, we present an optimum method for maximizing the electrochemical performance of graphite anodes using two heat treatment methods involving graphite intercalated compound (GIC) group within graphite, namely, thermal shock (TS; directly input target temperature) and gradual heating (GH; including ramping time). Different heating methods for preparing expanded graphite (EG) involve different reactions, relaxation times, and diffusion pathways for the diffusion of metal ions into EG. We find that rapidly shocking the layered structure can facilitate faster lithium and potassium ion diffusion from EG (TS) (heated for 30 min) via different intercalation/deintercalation processes compared to that from EG (GH). Consequently, EG (TS) exhibits the most significantly improved electrochemical performance among the lithium and potassium ion half-cells. For full lithium-ion hybrid capacitors (LIHCs), EG (TS)||activated carbon (AC) shows reasonable values of maximum power density (2.8 kW kg−1 with 59.12 Wh kg−1) and energy density (196.41 Wh kg−1), demonstrating its ultrahigh durability (capacity retention: 70.01%) over 12000 cycles at 2.0 A g−1. In addition, for potassium-ion hybrid capacitors (PIHCs), reasonable performance is achieved (average capacity of 82.02 mAh g−1 at 1.0 A g−1 over 2000 cycles with 94.35% capacity retention), demonstrating the high efficiency of PIHCs for substituting LIHCs without any systematic alterations.

Trigger a multi-electron reaction by tailoring electronic structure of VO2 toward more efficient aqueous zinc metal batteries

VO2 (B) is recognized as a promising cathode material for aqueous zinc metal batteries (AZMBs) owing to its remarkable specific capacity and its unique, expansive tunnel structure, which facilitates the reversible insertion and extraction of Zn2+. Nonetheless, challenges such as the inherent instability of the VO2 structure, poor ion/electron transport and a limited capacity due to the low redox potential of the V3+/V4+ couple have hindered its wider application. In this study, we present a strategy to replace vanadium ions by doping Al3+ in VO2. This approach activates the multi-electron reaction (V4+/V5+), to increase the specific capacity and improve the structural stability by forming robust V5+O and Al3+O bonds. It also induces a local electric field by altering the local electron arrangement, which significantly accelerates the ion/electron transport process. As a result, Al-doped VO2 exhibits superior specific capacity, improved cycling stability, and accelerated electronic transport kinetics compared to undoped VO2. The beneficial effects of heterogeneous atomic doping observed here may provide valuable insights into the improvement electrode materials in metal-ion battery systems other than those based on Zn.

Theoretical investigation of Mo2C and Mo2CO2 as anodes for sodium/magnesium-ion batteries

Due to the rapid evolution of the global electronic product industry, the limited availability of lithium resources has prompted extensive research into alternative metal ion batteries that can substitute for lithium batteries. The exceptional potentiality for MXenes as electrode materials in energy storage batteries is demonstrated by excellent conductivity, expansive surface area, and mechanical strength. The performance of Na and Mg on Mo2C and Mo2CO2 monolayers have been investigated employing first-principles calculations, including geometry configurations, electronic structures, ion diffusion properties, open-circuit voltages, and theoretical specific capacities. The conductivity of stable anodes is superior both before and after ion adsorption. Additionally, the formation energies of Na/Mg on the monolayer are negative, indicating a strong binding between metal atoms and the substrate. The migration energy barriers of Na and Mg on Mo2C are estimated to be 0.017 eV and 0.070 eV, respectively, suggesting a significant level of mobility and reversibility for Mo2C. The predicted range of average open-circuit voltages for Na/Mg-ion battery anodes is approximately 0.05–1.00 V in the case of Mo2C and Mo2CO2. The highest concentrations of Na and Mg atoms on Mo2C and Mo2CO2 are achieved through multilayer adsorption up to Mo2CNa3.3, Mo2CMg2, Mo2CO2Na3.3, and Mo2CO2Mg1.8, resulting in corresponding theoretical capacities of 438, 526, 379 and 411 mA·h/g, respectively. In conclusion, the outstanding electrochemical performance of Mo2C and Mo2CO2 anode materials in sodium-ion batteries (SIBs) and magnesium-ion batteries (MIBs) has prompted the exploration of other MXenes electrodes with advantageous characteristics for ion battery applications, contributing to the advancement of renewable energy technology.

Two-dimensional copper vanadate intercalated vanadium carbide MXene nanoplates as a high-performance cathode for aqueous Zn-ion batteries

Cathode materials play a crucial role in the energy-storage performances of zinc ion battery (ZIB). In this paper, the two-dimensional vanadium carbide MXene (V2C-MXene) nanoplates intercalated by Cu3V2O7(OH)2·2 H2O (CuVO) are synthesized. The intercalation of CuVO in the interlayers of V2C-MXene overcomes self-aggregation of CuVO and improves its structural stability. Meanwhile, the enlarged interlayer spacing of highly conductive V2C-MXene upgrades the electron transfer within the composite. As the cathode electrode of ZIB, the CuVO intercalated V2C-MXene (CuVO@V2C-MXene) battery shows capacity as high as 551.8 mAh g−1 when discharged at 0.5 A g−1. The capacity retention rate reaches 91.8% after 3000 cycles at high current density of 6.0 A g−1. As a comparison, the CuVO//Zn battery has capacity only 193.3 mAh g−1 at 0.5 A g−1, with the capacity retention of just 43.1% after 3000 cycles at 6.0 A g−1. Simultaneously, the CuVO@V2C-MXene//Zn illustrates greatly improved rate capability compared with CuVO//Zn. The CuVO@V2C-MXene composite nanoplates in this work show promise in fabrication of high capacity metal ion batteries.

Pyrazinoquinoxaline graphdiyne: A novel high-capacity anode material for metal-ion batteries

The rapid expansion of the electronics industry and the growing need for advanced energy storage solutions have driven the quest for rechargeable batteries with improved capacity and prolonged lifetimes. In this context, significant attention has been directed towards the exploration of two-dimensional (2D) materials, particularly carbon nanosheets such as Graphdiyne, owing to their compelling electrical, optical, mechanical, and chemical properties. The recent achievement in producing pyrazinoquinoxaline graphdiyne (PQ-GDY) nanosheets, distinguished by their remarkable stability and exceptional physical properties, has ignited our research curiosity, prompting an exploration of their potential suitability as anode materials for lithium (Li), sodium (Na), calcium (Ca), and magnesium (Mg) ion batteries. This investigation is conducted using first-principle electronic structure simulations. Drawing from our rigorous theoretical analysis, pyrazinoquinoxaline graphdiyne (PQ-GDY) has demonstrated favorable electrode properties, positioning it as a promising candidate for potential utilization in Li, Na, and Ca ion batteries. Notably, the pyrazinoquinoxaline graphdiyne rectangular (PQ-GDY-Rec) material demonstrates remarkable storage capacities for Li, Na, and Ca ions, reaching values of 1938 mAh/g, 1716 mAh/g, and 830.60 mAh/g, respectively. These findings position PQ-GDY-Rec as a highly promising material for application in metal-ion batteries, suggesting new avenues for the advancement of rechargeable batteries with significantly enhanced storage capabilities.

Dynamic Molecular Interphases Regulated by Trace Dual Electrolyte Additives for Ultralong-Lifespan and Dendrite-Free Zinc Metal Anode.

Metallic zinc is a promising anode material for rechargeable aqueous multivalent metal-ion batteries due to its high capacity and low cost. However, the practical use is always beset by severe dendrite growth and parasitic side reactions occurring at anode/electrolyte interface. Here we demonstrate dynamic molecular interphases caused by trace dual electrolyte additives of D-mannose and sodium lignosulfonate for ultralong-lifespan and dendrite-free zinc anode. Triggered by plating and stripping electric fields, the D-mannose and lignosulfonate species are alternately and reversibly (de-)adsorbed on Zn metal, respectively, to accelerate Zn2+ transportation for uniform Zn nucleation and deposition and inhibit side reactions for high Coulombic efficiency. As a result, Zn anode in such dual-additive electrolyte exhibits highly reversible and dendrite-free Zn stripping/plating behaviors for >6400 hours at 1 mA cm-2, which enables long-term cycling stability of Zn||ZnxMnO2 full cell for more than 2000 cycles.

Ultra‐Long Lifespan Ni Based Porphyrin Complex Cathode for Organic Alkali Metal Batteries

AbstractThe high solubility and low intrinsic electronic conductivity are the key challenges for application of organic materials in electrochemical energy storage. Herein, a functionalized porphyrin complex of [5,15‐Bis(ethynyl)‐10,20‐diphenylporphinato]nickel(II) (NiDEPP) is proposed as new cathode material for alkali metal ion batteries. Owing to the in‐situ electropolymerization, NiDEPP became extremely stable after initial cycling. Therefore, the NiDEPP electrode delivers remarkable reversible capacity of 153 mAh g−1 at 1 A g−1, a high specific energy density of 459 Wh kg−1 and extremely stable cyclability for 4000 cycles with negligible capacity decay in organic lithium batteries. It can further be cycled upto 10000 cycles. Due to the bipolar capability of porphyrin ring, this cathode can also be extended in both sodium and potassium based organic cells. Similar charge storage mechanism enables highly reversible capacity and long‐term cycling stability. This study would open a pathway toward new organic electrodes with long cycling life and high energy densities for renewable charge storage devices.

Antiperovskite active materials for metal-ion batteries: Expected advantages, limitations, and perspectives

Metal-ion batteries, particularly lithium-ion (Li-ion) and sodium-ion (Na-ion) batteries, are currently among the most compelling technologies for energy storage. However, the growing demands driven by wide implementation of batteries in multiple applications call for further improvements of energy and power densities. Despite the incredible developments in this field observed over the past decades, the innovation of new active materials for metal-ion batteries has seen only modest progress, with primary focus on the optimization of already existing materials. The recent discovery of cathode materials with antiperovskite structure signals a promising direction for the creation of relatively simple materials geared towards electrochemical energy storage. These materials can be synthesized through relatively simple chemical processes using abundant elements and could offer stable electrochemical performance. Even though the number of reported examples is still limited, the structural flexibility of these materials offers multiple possibilities for tuning the chemical stability, operating voltage and capacity. This perspective provides a summary of the latest advancements in the field of antiperovskite active materials, highlighting both the advantages and the challenges associated with their integration into metal-ion batteries, and suggests possible future research directions towards practical implementation of this promising yet underexplored class of materials.

Emerging trends and prospects in aqueous electrolyte design: Elevating energy density and power density of multivalent metal-ion batteries

Aqueous batteries, using multivalent metallic charge carriers (Zn2+, Mg2+, Ca2+, Al3+), show promise as next-generation electrochemical energy storage due to their adequate energy density, high power density, and cost-effectiveness. The electrolyte, serving as a bridge between the cathode and anode, plays a crucial role in functionality. However, the use of aqueous electrolytes introduces issues such as limited voltage range, slow kinetics of multivalent cations, and side reactions on metal surfaces. Electrolyte engineering has emerged as a key solution to overcome major challenges in multivalent metal-ion batteries. This innovative approach involves optimizing factors such as electrolyte concentration, specific additives, pH management, and manipulating the ligand effect of cation salts. Additionally, incorporating anti-freezing agents is crucial. A systematic review of this domain is crucial for further development and refinement of electrolyte engineering strategies. This review should primarily focus on assessing how these modifications can enhance energy and power densities, broaden the operational range of the batteries (by adjusting water activity and LUMO/HOMO energy levels), improve cation transport (via enhanced ion conductivity, dielectric constant, transference number, and solvation structure), and effectively mitigate detrimental side reactions, such as metal deposition, interphase formation, and hydrogen bonding regulation. The electrolyte design strategies in multivalent metal-ion systems are outlined in terms of their effectiveness in smoothing metal dendrites, managing solvation shells and free water molecules, and minimizing side reactions between the metal surface and electrolyte. The article proposes future innovation directions and development prospects for enhancing electrolyte design engineering in these systems.

Facile Fabrication of FePO4–V2O5–Graphene Oxide Recovered From Spent LiFePO4 Batteries as High‐Performance Cathode for Lithium/Sodium‐Ion Batteries

AbstractThe resource scarcity and pollution leakage risk caused by discarding the spent power lithium‐ion batteries has aroused growing concern. Recovering and regenerating the cathode material from spent power lithium‐ion batteries in an easy and environmentally friendly manner remains a significant challenge and an area of focus in battery research. Hence, a green and convenient method to recover FePO4 from spent LiFePO4 cathode powder by using Na2S2O8 as an oxidizer and as cathode materials for lithium/sodium‐ion batteries (LIBs/SIBs) is reported. Benefiting from the remarkable graphene oxide (GO) and vanadium oxide (V2O5) coating, the regenerated FePO4–V2O5–graphene oxide (FePO4–V2O5–GO) is suitable for Li/Na storage (153 mAh g−1 at 0.2C/118 mAh g−1 at 0.5C). The high capacity retention, that stable for 300 cycles in LIBs and 300 cycles for SIBs, is also realized due to the stable structure. This work provides a green strategy for regenerating the cathode of spent lithium‐ion batteries and designing cathodes of alkali metal ion batteries.

Outer Sphere Electron Transfer Enabling High-Voltage Aqueous Electrolytes.

Aqueous electrolytes with a low voltage window (1.23 V) and prone side reactions, such as hydrogen evolution reaction and cathode dissolution, compromise the advantages of high safety and low cost of aqueous metal-ion batteries. Herein, introducing catechol (CAT) into the aqueous electrolyte, an outer sphere electron transfer mechanism is initiated to inhibit the water reactivity, achieving an electrochemical window of 3.24 V. In a typical Zn-ion battery, the outer sphere electrons jump from CAT to Zn2+-H2O at a geometrically favorable situation and between the solvation molecules without breaking or forming chemical bonds as that of the inner sphere electron transfers. The excited state π-π stacking further leads to the outer sphere electron transfer occurring at the electrolyte/electrode interface. This high-voltage electrolyte allows achieving an operating voltage two times higher than that of the usual aqueous electrolytes and provides almost the highest energy density and power density for the V2O5-based aqueous Zn-ion full batteries. The Zn//Zn symmetric battery delivers a 4000 h lifespan, and the Zn//V2O5 full battery achieves a ∼380 W h kg-1 energy density and a 92% capacity retention after 3000 cycles at 1 A g-1 and a 2.4 V output voltage. This outer sphere electron transfer strategy paves the way for designing high-voltage aqueous electrolytes.

Zinc ion storage abilities of Mo3WOx nano-ceramic under extreme-cold environments

It is imperative to develop new electrode materials for aqueous multivalent metal ion batteries with electrochemistry abilities at extreme-low temperatures due to the possible extreme-cold operating conditions of batteries in the present or the future. Herein, as a proof-of-concept experiment, a new orthorhombic molybdenum-tungsten oxide (Mo3WOx) is synthesized by a wet-chemical method and tested as anode material for aqueous zinc ion batteries at extreme-cold temperatures (−40, −60 and −75 °C) for the first time. Two anti-freezing electrolytes are selected to examine the related half-cell performances, and 7.5 m ZnCl2 aqueous solution is more suitable for Mo3WOx half-cells than 2 m Zn(BF4)2 aqueous solution. At −40 °C, Mo3WOx exhibits reversible charge capacity of 104.1 mAh g−1 at 100 mA g−1 and the charge capacity can still maintain 82.3 mAh g−1 after 100 cycles; and under further test at 5000 mA g−1, Mo3WOx shows a high initial charge capacity of 42.5 mAh g−1 together with a capacity retention ratio of 81.6 % after 10,000 cycles. It is worth highlighting that the high capacities of Mo3WOx delivered at −40 °C are even comparable with the capacities of some “new-type” anode materials for aqueous zinc ion batteries exhibited at ambient temperature. At colder temperatures of −60 and −75 °C, the as-prepared compound still owns certain zinc ion storage abilities, especially high discharge/charge capacities of 48.9/48.7 mAh g−1 can be still achieved in the 100th cycle at −75 °C (100 mA g−1). Furthermore, a full-cell with operational capability at −40 °C is also built here, and it can exhibit discharge capacity of 66.1 mAh g−1 (coulombic efficiency of 99.7 %) in the 3rd cycle and discharge capacity of 48.2 mAh g−1 (coulombic efficiency of 99.7 %) in the 50th cycle.

Principles and Requirements of Battery Membranes: Ensuring Efficiency and Safety in Energy Storage

This critical review highlights the latest improvements and special features regarding the membrane separators available for lead-acid, alkaline, metal-metal, metal-gas, and metal-ion batteries such as lithium-ion. In the recent years, there has been a surge in the intensive work aimed at developing innovative separators for rechargeable lithium-ion batteries, for example, electric vehicles (EVs), portable electronics and for energy storage in power grid. The separator finds itself in a very important place as it provides physical separation between two electrodes. It also acts as an electrical insulator. This separator is known as an electrolyte gateway which helps the movement of ions during charge/discharge cycles. This review addresses the requirements for battery separators and explains the structure and properties of various types of membrane separators; there are several types of membranes such as microporous membranes, modified microporous membranes, nonwoven mats, composite membranes and electrolyte membranes. Similarly, each type of separator has inherent advantages and disadvantages which in turn directly affects the performance of batteries. This review article systematically deals with the structures and working principle of separators, properties and main requirements and their characterization method of separators, generation, improvements, and function assessments of these separators. Furthermore, this study also enlightens the emerging research path and future prospects.

Evolutionary prediction of novel biphenylene networks as an anode material for lithium and potassium-ion batteries

The discovery of novel materials with compelling properties is more accessible with the help of advanced computational algorithms. Recent experimental synthesis of the biphenylene network (C6) motivated us to discover new BN-doped biphenylene networks (C4BN, C2B2N2, and B4N4) and their applications in Li(K)-ion batteries using an evolutionary algorithm and the first-principles calculations. The thermodynamic, thermal, and mechanical stability calculations and decomposition energy suggest the experimental synthesis of predicted biphenylene networks. Adding BN in the biphenylene networks shows a transition from metal to semimetal to semiconductor. The BN biphenylene network shows an HSE06 band gap of 3.06 ​eV, smaller than h-BN. The C4BN and C2B2N2 biphenylene networks offer Li(K) adsorption energy of −0.56 ​eV (−0.81 ​eV) and −0.14 ​eV (−0.28 ​eV), respectively, with a low diffusion barrier of 178 ​meV (58 ​meV) and 251 ​meV (79 ​meV), and a large diffusion constant of 8.50 ​× ​10−5cm2/s (8.78 ​× ​10−3cm2/s) and 5.33 ​× ​10−6cm2/s (4.12 ​× ​10−3cm2/s), respectively. The calculated Li(K) theoretical capacity of C4BN and C2B2N2 biphenylene networks is 940.21 ​mA ​h ​g−1 (899.01 ​mA ​h ​g−1) and 768.08 ​mA ​h ​g−1 (808.47 ​mA ​h ​g−1), with a low open circuit voltage of 0.34 ​V (0.23 ​V), and 0.17 ​V (0.13 ​V), resulting in very high energy density of 2576.18 ​mW ​h ​g−1 (2445.31 ​mW ​h ​g−1) and 2181.35 ​mW ​h ​g−1 (2263.72 ​mW ​h ​g−1), respectively. Only a slight volume change of 1.6% confirms the robustness of BN-doped carbon-based biphenylene networks. Our findings present novel 2D BN-doped biphenylene networks and a pathway toward their applications in metal-ion batteries.

The structural, electronic, optical, and mechanical properties of carbon-based halides: An ab initio DFT approach

In the present work, we choose the carbon-based halides CX4 (X = Br, Cl) to conduct a study on the ground-state properties using first-principles calculations based on density functional theory. We provide a comparative study for bromide and chloride materials using standard generalized gradient approximation functionals. A total of 80 atoms have been simulated on a single unit cell. A direct bandgap energy of 3.28 (4.64) eV for X = Br (X = Cl) with Z–Z transition is found on the studied materials. According to our partial density of states plot, a hybridization of s orbitals on C and X atoms is observed. Metallic properties have also been identified. A low reflectivity of 6% (12%) has been measured, which presents excellent material absorption. Such a material is also determined to be brittle, based on the calculated Pugh’s ratio. The reflectivity (ductility) tends to increase as the X element increases down the Period Table. The negative Poisson’s ratio found also suggests that the materials could be used as an electrode for metal-ion (e.g., Li, K, and Na) batteries.

Unfolding the potassium storage mechanism of tin selenides

Tin selenides have attracted great attention as anode materials for alkali metal ion batteries in recent years because of the high theoretical capacity. However, there is currently few literatures on the application of tin selenides in potassium ion battery, and the comparative research on the actual potassium storage mechanism of different tin selenides is rarely reported. Herein, tin selenides including SnSe2@C and SnSe@C are synthesized by regulating the selenization temperature, and their potassium storage performance and the mechanism have been comparatively investigated with various physicochemical techniques as well as operando synchrotron X-ray diffraction (SXRD) and density functional theory (DFT) calculations. It is revealed that the better potassium storage performance of SnSe2@C is mainly due to the generation of highly conductive Se during the first depotassiation process, which not only participates in the subsequent potassiation/depotassiation process, but also improves the conductivity of electrode and facilitates the kinetics of K+. While the sluggish kinetics and partial irreversible decomposition of KxSe lead to the inferior potassium storage performance of SnSe@C.

Ligand-channel-enabled ultrafast Li-ion conduction.

Li-ion batteries (LIBs) for electric vehicles and aviation demand high energy density, fast charging and awide operating temperature range, which are virtually impossible because they require electrolytes to simultaneously have high ionic conductivity, low solvation energyand low melting point and form ananion-derived inorganic interphase1-5. Here we report guidelines for designing such electrolytes by using small-sized solvents with low solvation energy. The tiny solvent in the secondary solvation sheath pulls out the Li+ in the primary solvation sheath to form a fast ion-conduction ligand channel to enhance Li+ transport, while the small-sized solvent with low solvation energy also allows the anion to enter the first Li+ solvation shell to form aninorganic-rich interphase. The electrolyte-design concept is demonstrated by using fluoroacetonitrile (FAN) solvent. The electrolyte of 1.3 M lithium bis(fluorosulfonyl)imide (LiFSI) in FAN exhibits ultrahigh ionic conductivity of 40.3 mS cm-1 at 25 °C and 11.9 mS cm-1 even at -70 °C, thus enabling 4.5-V graphite||LiNi0.8Mn0.1Co0.1O2 pouch cells (1.2 Ah, 2.85 mAh cm-2) to achieve high reversibility (0.62 Ah) when the cells are charged and discharged even at -65 °C. The electrolyte with small-sized solvents enables LIBs to simultaneously achieve high energy density, fast charging and awide operating temperature range, which is unattainable for the current electrolyte design but is highly desired for extreme LIBs. This mechanism is generalizable and can be expanded to other metal-ion battery electrolytes.

Graphene-like BGe monolayer as anode material for metal-ions batteries: Computational predictions

Magnesium-, calcium- and potassium-ion batteries (MIBs, CIBs and PIBs) have attracted extraordinary attention as alternative batteries of lithium-ion batteries, due to their due to their abundancies, the low cost, safety. Herein, we investigated the suitability of BGe monolayer as anode material for MIBs, CIBs, and PIBs by using first-principles calculations in framework of density functional theory (DFT). The energy adsorption calculations and the charge transfer analysis show that the hollow site is the most favorable site for Mg, Ca, and K atoms adsorption on the BGe monolayer. In addition, the BGe monolayer has remained the same, preserving its metallic behavior after Mg, Ca and K atoms adsorption, which is suitable for batteries applications. The open circuit voltage ranges from 1.03 V to 1.02, 1.86 V to 1.67 V, and 2.85 V to 2.28 V for Mg, Ca, and K, respectively. Especially, the BGe monolayer exhibits a high theoretical specific capacity, up to 1284.63 mAhg−1 for Mg and Ca, and 642.31 mAhg−1 for K, which are higher than other monolayers. In addition, the BGe monolayer can provide a good charging-discharging processes with a low diffusion barrier of 0.80, 0.52, and 0.17 eV for Mg, Ca, and K-ion, respectively. All these properties indicate that the BGe monolayer is promising anode material for Mg/Ca/K ion batteries.

Tandem Chemistry with Janus Mesopores Accelerator for Efficient Aqueous Batteries.

A reliable solid electrolyte interphase (SEI) on the metallic Zn anode is imperative for stable Zn-based aqueous batteries. However, the incompatible Zn-ion reduction processes, scilicet simultaneous adsorption (capture) and desolvation (repulsion) of Zn2+(H2O)6, raise kinetics and stability challenges for the design of SEI. Here, we demonstrate a tandem chemistry strategy to decouple and accelerate the concurrent adsorption and desolvation processes of the Zn2+ cluster at the inner Helmholtz layer. An electrochemically assembled perforative mesopore SiO2 interphase with tandem hydrophilic -OH and hydrophobic -F groups serves as a Janus mesopores accelerator to boost a fast and stable Zn2+ reduction reaction. Combining in situ electrochemical digital holography, molecular dynamics simulations, and spectroscopic characterizations reveals that -OH groups capture Zn2+ clusters from the bulk electrolyte and then -F groups repulse coordinated H2O molecules in the solvation shell to achieve the tandem ion reduction process. The resultant symmetric batteries exhibit reversible cycles over 8000 and 2000 h under high current densities of 4 and 10 mA cm-2, respectively. The feasibility of the tandem chemistry is further evidenced in both Zn//VO2 and Zn//I2 batteries, and it might be universal to other aqueous metal-ion batteries.