Facilitating an Ultrastable O3-Type Cathode for 4.5 V Sodium-Ion Batteries via a Dual-Reductive Coupling Mechanism.

O3-type layered oxides for sodium-ion batteries (SIBs) have attracted extensive attention due to their inherently sufficient Na content, which have been considered as one of the most promising candidates for practical applications. However, influenced by the irreversible oxygen loss and the phase transition of O3-P3, the O3-type cathodes are always limited by low cutoff voltages (typically <4.2 V), restraining the full release of the capacity. In this study, we originally propose a dual-reductive coupling mechanism in a novel O3-type Na0.8Li0.2Fe0.2Ru0.6O2 cathode with the suppressed O3-P3 phase transition, aiming at improving the reversibility of oxygen redox at high voltage regions. Consequently, thanks to the formation of the strong covalent Fe/Ru-(O-O) bonding and inhibited slab gliding from the O to P phase, the cathode delivers the preeminent cyclic stability among the numerous O3-type cathodes within a high voltage of 4.5 V (a capacity retention of 95.4% after 100 cycles within 1.5-4.5 V). More importantly, HAADF-STEM and 7Li solid-state NMR results reveal the absence of transition metal migration and the presence of reversible Li migration during cycling, which further contributes to the improved structural robustness of the cathode. This study proposes an innovative strategy to boost the reversibility of anionic redox and to achieve stable high-voltage O3-type layered oxides, promoting the further development of SIBs.

A Rechargeable "Rocking Chair" Type Zn-CO2 Battery.

Rising global temperatures and critical energy shortages have spurred researches into CO2 fixation and conversion within the realm of energy storage such as Zn-CO2 batteries. However, traditional Zn-CO2 batteries employ double-compartment electrolytic cells with separate carriers for catholytes and anolytes, diverging from the "rocking chair" battery mechanism. The specific energy of these conventional batteries is constrained by the solubility of discharge reactants/products in the electrolyte. Additionally, H2O molecules tend to trigger parasitic reactions at the electrolyte/electrode interfaces, undermining the long-term stability of Zn anodes. In this report, we introduce an innovative "rocking chair" type Zn-CO2 battery that utilizes a weak-acidic Zn(OTf)2 aqueous electrolyte compatible with both cathode and anode. This design minimizes side reactions on the Zn surface and leverages the high catalytic activity of the cathode material, allowing the battery to achieve a substantial discharge capacity of 6734 mAh g-1 and maintain performance over 65 cycles. Moreover, the successful production of pouch cells demonstrates the practical applicability of Zn-CO2 batteries. Electrode characterizations confirm superior electrochemical reversibility, facilitated by solid discharge products of ZnCO3 and C. This work advances a "rocking chair" Zn-CO2 battery with enhanced specific energy and a reversible pathway, providing a foundation for developing high-performance metal-CO2 batteries.

A Bio-Inspired Trehalose Additive for Reversible Zinc Anodes with Improved Stability and Kinetics.

The moderate reversibility of Zn anodes, as a long-standing challenge in aqueous zinc-ion batteries, promotes the exploration of suitable electrolyte additives continuously. It is crucial to establish the absolute predominance of smooth deposition within multiple interfacial reactions for stable zinc anodes, including suppressing side parasitic reactions and facilitating Zn plating process. Trehalose catches our attention due to the reported mechanisms in sustaining biological stabilization. In this work, the inter-disciplinary application of trehalose is reported in the electrolyte modification for the first time. The pivotal roles of trehalose in suppressed hydrogen evolution and accelerated Zn deposition have been investigated based on the principles of thermodynamics as well as reaction kinetics. The electrodeposit changes from random accumulation of flakes to dense bulk with (002)-plane exposure due to the unlocked crystal-face oriented deposition with trehalose addition. As a result, the highly reversible Zn anode is obtained, exhibiting a high average CE of 99.8 % in the Zn/Cu cell and stable cycling over 1500 h under 9.0 % depth of discharge in the Zn symmetric cell. The designing principles and mechanism analysis in this study could serve as a source of inspiration in exploring novel additives for advanced Zn anodes.

Dual Honeycomb-Superlattice Enables Double-High Activity and Reversibility of Anion Redox for Sodium-Ion Battery Layered Cathodes.

Anion redox contributes to the anomalous capacity exceeding the theoretical limit of layered oxides. However, double-high activity and reversibility is challenging due to the structural rearrangement and potential oxygen loss. Here, we propose a strategy for constructing a dual honeycomb-superlattice structure in Na2/3 [Li1/7 Mn5/14 ][Mg1/7 Mn5/14 ]O2 to simultaneously realize high activity and reversibility of lattice O redox. Theoretical simulation and electrochemical tests show that [Li1/7 Mn5/14 ] superlattice units remarkably trigger the anion redox activity and enable the delivery of a record capacity of 285.9 mA g-1 in layered sodium-ion battery cathodes. Nuclear magnetic resonance and in situ X-ray diffraction reveal that [Mg1/7 Mn5/14 ] superlattice units are beneficial to the structure and anion redox reversibility, where Li+ reversibly shuttles between Na layers and transition-metal slabs in contrast to the absence of [Mg1/7 Mn5/14 ] units. Our findings underline the importance of multifunctional units and provide a path to advanced battery materials.

Fluorinated Rocksalt Cathode with Ultra-high Active Li Content for Lithium-ion Batteries.

The key to increasing the energy density of lithium-ion batteries is to incorporate high contents of extractable Li into the cathode. Unfortunately, this triggers formidable challenges including structural instability and irreversible chemistry under operation. Here, we report a new kind of ultra-high Li compound: Li4+x MoO5 Fx (1≤x≤3) for cathode with an unprecedented level of electrochemically active Li (>3 Li+ per formula), delivering a reversible capacity up to 438 mAh g-1 . Unlike other reported Li-rich cathodes, Li4+x MoO5 Fx presents distinguished structure stability to immunize against irreversible behaviors. Through spectroscopic and electrochemical techniques, we find an anionic redox-dominated charge compensation with negligible oxygen release and voltage decay. Our theoretical analysis reveals a "reductive effect" of high-level fluorination stabilizes the anionic redox by reducing the oxygen ions in pure-Li conditions, enabling a facile, reversible, and high Li-portion cycling.

Disproportionation of Sodium Superoxide in Metal-Air Batteries.

The sodium oxygen battery is a promising metal-air battery; however, the discharge process is not well understood and the major discharge product is still under debate. The discharge products determined the theoretical specific energy and electrochemical performance of the battery. Now it is demonstrated that NaO2 spontaneously disproportionates to Na2 O2 , no matter whether it is dissolved in solution or stays on the surface. The behaviors of NaO2 in solution and on the surface are different. Solvents play a crucial effect on the disproportionation of dissolved NaO2 species, which is fast in low donor number (DN) solvents such as acetonitrile but sluggish in high DN solvents such as DMSO. In situ XRD results exhibited the different product growing processes in various solvents. Surface NaO2 would slowly disproportionate to Na2 O2 anyway, but this process is relatively slow compared to the time span of discharge process and it does not affect the major product on discharge.

Boosting a practical Li-CO2 battery through dimerization reaction based on solid redox mediator.

Li-CO2 batteries offer a promising avenue for converting greenhouse gases into electricity. However, the inherent challenge of direct electrocatalytic reduction of inert CO2 often results in the formation of Li2CO3, causing a dip in output voltage and energy efficiency. Our innovative approach involves solid redox mediators, affixed to the cathode via a Cu(II) coordination compound of benzene-1,3,5-tricarboxylic acid. This technique effectively circumvents the shuttle effect and sluggish kinetics associated with soluble redox mediators. Results show that the electrochemically reduced Cu(I) solid redox mediator efficiently captures CO2, facilitating Li2C2O4 formation through a dimerization reaction involving a dimeric oxalate intermediate. The Li-CO2 battery employing the Cu(II) solid redox mediator boasts a higher discharge voltage of 2.8 V, a lower charge potential of 3.7 V, and superior cycling performance over 400 cycles. Simultaneously, the successful development of a Li-CO2 pouch battery propels metal-CO2 batteries closer to practical application.

A solid-state lithium-ion battery with micron-sized silicon anode operating free from external pressure.

Applying high stack pressure (often up to tens of megapascals) to solid-state Li-ion batteries is primarily done to address the issues of internal voids formation and subsequent Li-ion transport blockage within the solid electrode due to volume changes. Whereas, redundant pressurizing devices lower the energy density of batteries and raise the cost. Herein, a mechanical optimization strategy involving elastic electrolyte is proposed for SSBs operating without external pressurizing, but relying solely on the built-in pressure of cells. We combine soft-rigid dual monomer copolymer with deep eutectic mixture to design an elastic solid electrolyte, which exhibits not only high stretchability and deformation recovery capability but also high room-temperature Li-ion conductivity of 2×10-3 S cm-1 and nonflammability. The micron-sized Si anode without additional stack pressure, paired with the elastic electrolyte, exhibits exceptional stability for 300 cycles with 90.8% capacity retention. Furthermore, the solid Li/elastic electrolyte/LiFePO4 battery delivers 143.3 mAh g-1 after 400 cycles. Finally, the micron-sized Si/elastic electrolyte/LiFePO4 full cell operates stably for 100 cycles in the absence of any additional pressure, maintaining a capacity retention rate of 98.3%. This significantly advances the practical applications of solid-state batteries.

Perspective on High-Stability Single-Crystal Li-Rich Cathode Materials for Li-Ion Batteries.

Benefiting from anionic and cationic redox reactions, Li-rich materials have been regarded as next-generation cathodes to overcome the bottleneck of energy density. However, they always suffer from cracking of polycrystalline (PC) secondary particles and lattice oxygen release, resulting in severe structural deterioration and capacity decay upon cycling. Single-crystal (SC) design has been proven as an effective strategy to relieve these issues in traditional Li-rich cathodes with PC morphology. Herein, we first reviewed the main synthesis routes of SC Li-rich materials including solid-state reaction, molten salt-assisted, and hydrothermal/solvothermal methods, in which the differences in grain morphology, electrochemical behaviors, and other properties induced by various routes were analyzed and discussed. Furthermore, the distinct characteristics were compared between SC and PC cathodes from the aspects of irreversible capacity, structural stability, capacity/voltage degradation, and gas release. Besides, recent advances in layered SC Li-rich oxide cathodes were summarized in detail, where the unique structural designs and modification strategies could greatly promote their structural/electrochemical stability. At last, challenges and perspectives for the emerging SC Li-rich cathodes were proposed, which provided an exceptional opportunity to achieve high-energy-density and high-stability Li-ion/metal batteries.

Bifunctional electrolyte additive MgI2 for improving cycle life in high-efficiency redox-mediated Li-O2 batteries.

Here, MgI2 is introduced as a bifunctional self-defense redox mediator into dimethyl sulfoxide-based Li-O2 batteries. During charging, I- is first oxidized to I3-, which facilitates the decomposition of Li2O2, and thus reduces overpotential. In addition, Mg2+ spontaneously reacts with the Li anode to form a very stable SEI layer containing MgO, which can resist the synchronous attack by the soluble I3- and improve the interface stability between the Li anode and the electrolyte. Therefore, a Li-O2 battery containing MgI2 exhibits an extended cycling life span (400 cycles) and a quite low overpotential (0.6 V).

Trifunctional imidazolium bromide: a high-efficiency redox mediator for high-performance Li-O2 batteries.

In this work, 1-aminopropyl-3-methylimidazolium bromide (APMImBr) is introduced in dimethyl sulfoxide-based Li-O2 batteries. The Br- functions as a redox mediator to catalyze the decomposition of the Li2O2 products. Meanwhile, the APMIm+ serves as a scavenging agent for superoxide radicals as well as protects the lithium metal anodes via an in situ formed Li3N-rich solid electrolyte interface layer. As a result, the Li-O2 batteries containing APMImBr delivered an enlarged discharge capacity, a reduced charge overpotential of around 0.61 V and a prolonged cyclic life of over 200 cycles.

Binuclear Cu complex catalysis enabling Li-CO2 battery with a high discharge voltage above 3.0 V.

Li-CO2 batteries possess exceptional advantages in using greenhouse gases to provide electrical energy. However, these batteries following Li2CO3-product route usually deliver low output voltage (<2.5 V) and energy efficiency. Besides, Li2CO3-related parasitic reactions can further degrade battery performance. Herein, we introduce a soluble binuclear copper(I) complex as the liquid catalyst to achieve Li2C2O4 products in Li-CO2 batteries. The Li-CO2 battery using the copper(I) complex exhibits a high electromotive voltage up to 3.38 V, an increased output voltage of 3.04 V, and an enlarged discharge capacity of 5846 mAh g-1. And it shows robust cyclability over 400 cycles with additional help of Ru catalyst. We reveal that the copper(I) complex can easily capture CO2 to form a bridged Cu(II)-oxalate adduct. Subsequently reduction of the adduct occurs during discharge. This work innovatively increases the output voltage of Li-CO2 batteries to higher than 3.0 V, paving a promising avenue for the design and regulation of CO2 conversion reactions.

Modulation of Local Charge Distribution Stabilized the Anionic Redox Process in Mn-Based P2-Type Layered Oxides.

An anionic redox reaction is an extraordinary method for obtaining high-energy-density cathode materials for sodium-ion batteries (SIBs). The commonly used inactive-element-doped strategies can effectively trigger the O redox activity in several layered cathode materials. However, the anionic redox reaction process is usually accompanied by unfavorable structural changes, large voltage hysteresis, and irreversible O2 loss, which hinders its practical application to a large extent. In the present work, we take the doping of Li elements into Mn-based oxide as an example and reveal the local charge trap around the Li dopant will severely impede O charge transfer upon cycling. To overcome this obstacle, additional Zn2+ codoping is introduced into the system. Theoretical and experimental studies show that Zn2+ doping can effectively release the charge around Li+ and homogeneously distribute it on Mn and O atoms, thus reducing the overoxidation of O and improving the stability of the structure. Furthermore, this change in the microstructure makes the phase transition more reversible. This study aimed to provide a theoretical framework for further improve the electrochemical performance of similar anionic redox systems and provide insights into the activation mechanism of the anionic redox reaction.

Achieving long cycle life for all-solid-state rechargeable Li-I2 battery by a confined dissolution strategy.

Rechargeable Li-I2 battery has attracted considerable attentions due to its high theoretical capacity, low cost and environment-friendliness. Dissolution of polyiodides are required to facilitate the electrochemical redox reaction of the I2 cathode, which would lead to a harmful shuttle effect. All-solid-state Li-I2 battery totally avoids the polyiodides shuttle in a liquid system. However, the insoluble discharge product at the conventional solid interface results in a sluggish electrochemical reaction and poor rechargeability. In this work, by adopting a well-designed hybrid electrolyte composed of a dispersion layer and a blocking layer, we successfully promote a new polyiodides chemistry and localize the polyiodides dissolution within a limited space near the cathode. Owing to this confined dissolution strategy, a rechargeable and highly reversible all-solid-state Li-I2 battery is demonstrated and shows a long-term life of over 9000 cycles at 1C with a capacity retention of 84.1%.

Diagnosing the SEI Layer in a Potassium Ion Battery Using Distribution of Relaxation Time.

Understanding the solid electrolyte interphase (SEI) formation process in novel battery systems is of primary importance. Alongside increasingly powerful in situ techniques, searching for readily accessible, noninvasive, and low-cost tools to probe battery chemistry is highly demanded. Here, we applied distribution of relaxation time analysis to interpret in situ electrochemical impedance spectroscopy results during cycling, which is able to distinguish various electrochemical processes based on their time constants. By building a direct link between the SEI layer and the cell performances, it allows us to track the formation and evolution process of the SEI layer, diagnose the failure of the cell, and unveil the reaction mechanisms. For instance, in a K-ion cell using a SnS2/N-doped reduced graphene oxide composite electrode, we found that the worsened mass transport in the electrolyte phase caused by the weak SEI layer is the main reason for cell deterioration. In the electrolyte with potassium bis(fluorosulfonyl)imide, the porous structure of the composite electrode was reinforced by rapid formation of a robust SEI layer at the SnS2/electrolyte interface, and thus, the cell delivers a high capacity and good cyclability. This method lowers the barrier of in situ EIS analysis and helps public researchers to explore high-performance electrode materials.

A ß-FeOOH/MXene sandwich for high-performance anodes in lithium-ion batteries.

FeOOH is one of the earth abundant and high-capacity anode materials for lithium-ion batteries (LIBs), but faces problems of inevitable structure collapse and thus poor capacity retention. Herein, we report a composite of ß-FeOOH/Ti3C2Tx MXene sandwich by an intercalation of ß-FeOOH nanorods within single-layer Ti3C2Tx MXene flakes. After 100 cycles, the ß-FeOOH/Ti3C2Tx composite retains a capacity of 937.5 mA h g-1 at 200 mA g-1, and 671.4 mA h g-1 at 1 A g-1. The composite as an anode in LIB delivers improved cyclability and better high-rate performance compared to pristine ß-FeOOH, which result from the excellent conductivity of single-layer MXene, facilitating mass transport by the sandwich structure. This work provides a strategy for the design of electrodes, particularly in Na-ion and K-ion batteries, which involve active materials that experience volume change and structural damage during cycling.