Ionic Liquid Electrolyte with Weak Solvating Molecule Regulation for Stable Li Deposition in High-Performance Li-O2 Batteries

Upcycling Spent Lithium-Ion Batteries: Constructing Bifunctional Catalysts Featuring Long-Range Order and Short-Range Disorder for Lithium-Oxygen Batteries

Upcycling of high-value metals (M = Ni, Co, Mn) from spent ternary lithium-ion batteries to the field of lithium-oxygen batteries is highly appealing, yet remains a huge challenge. In particular, the alloying of the recovered M components with Pt and applied as cathode catalysts have not yet been reported. Herein, a fresh L12-type Pt3 M medium-entropy intermetallic nanoparticle is first proposed, confined on N-doped carbon matrix (L12-Pt3(Ni1/3Co1/3Mn1/3)@N-C) based on spent 111 typed LiNi1-x-yMnxCoyO2 cathode. This well-defined catalyst combines both features of long-range order L12 face-centered cubic structure and short-range disorder in M sites. The former contributes to enhancing the structural stability, and the latter further facilitates deeply activating the catalytic activity of Pt sites. Experiments and theoretical results demonstrate that the local coordination environment and electronic distribution of Pt are both fundamentally modulated via surrounding disordered Ni, Co, and Mn atoms, which greatly optimize the affinity toward oxygen-containing intermediates and facilitate the deposition/decomposition kinetics of the thin-film Li2O2 discharge products. Specifically, the L12-Pt3(Ni1/3Co1/3Mn1/3)@N-C catalyst exhibits an ultra-low overpotential of 0.48 V and achieves 220 cycles at 400 mA g-1 under 1000 mAh g-1. The work provides important insights for the recycling of spent lithium-ion batteries into advanced catalyst-related applications.

Machine Learning-Guided Modulation of Li+ Solvation Structures towards Optimal Electrolyte Systems for High-Performance Li-O2 Battery

As the "blood" of Li-O2 batteries (LOBs), electrolytes with various solvation structures of Li+ can greatly influence the composition of solid electrolyte interphase (SEI) on anode and the growth kinetics of Li2O2 on cathode, and further the battery performance. However, achieving delicate modulation of the multi-composition electrolytes remains significantly challenging to simultaneously give consideration to both the anode and cathode reactions. In this work, we employed Bayesian optimization to develop advanced electrolytes for LOBs, enabling the formation of a stable inorganic-rich SEI, and modulation of Li2O2 morphologies. Thus obtained LOBs using the optimized dual-solvent electrolyte could deliver a discharge capacity of 14,063 mAh g-1 at a current density of 500 mA g-1, which is far higher than those using the single-solvent electrolytes. This study not only highlights the critical role of the solvation structure for improving the battery performance, but also provides new insights and important theoretical guidance for delicate modulation of electrolyte compositions.

Research Progress in Ionic Liquid-Based Electrolytes for Electrochromic Devices

Electrochromic (EC) technology has become one of the smart technologies with the most potential for development and application at this stage. Based on electrochromic devices (ECDs), this technology has shown extraordinary potential in the fields of smart windows, display devices, and sensing systems. With the optimization and iteration of various core components in ECDs, the electrolyte layer, a key component, evolved from its initial liquid state to a quasi-solid state and solid state. As driven by increasing application demands, the development trend indicates that all-solid-state, transparent electrolytes will likely become the future form of the electrolyte layer. Recently, the application of ionic liquid (IL)-based electrolytes in the field of electrochromism attracted a lot of attention due to their ability to bring outstanding EC cycling stability, thermal stability, and a wider operating voltage range to ECDs, and they are regarded as the new generation of electrolyte materials with the most potential for application. Although compared with conventional electrolytes, IL-based electrolytes have the characteristics of high price, high viscosity, and low conductivity, they are still considered the most promising electrolyte materials for applications. However, so far, there has been a lack of comprehensive analysis reports on "Research progress in ionic liquid-based electrolytes for electrochromic devices" within the EC field. In this article, the research progress of IL-based electrolytes in ECDs will be summarized from three perspectives: liquid, quasi-solid, and solid state. The future development directions of IL-based electrolytes for ECDs are discussed.

Development of PFAS-Free Locally Concentrated Ionic Liquid Electrolytes for High-Energy Lithium and Aluminum Metal Batteries

ConspectusLithium-ion batteries (LIBs) based on graphite anodes are a widely used state-of-the-art battery technology, but their energy density is approaching theoretical limits, prompting interest in lithium-metal batteries (LMBs) that can achieve higher energy density. In addition, the limited availability of lithium reserves raises supply concerns; therefore, research on postlithium metal batteries is underway. A major issue with these metal anodes, including lithium, is dendritic formation and insufficient reversibility, which leads to safety risks due to short circuits and the use of flammable electrolytes.Ionic liquid electrolytes (ILEs), composed of metal salts and ionic liquids, offer a safer alternative due to their nonflammable nature and high thermal stability. Moreover, they can enable high Coulombic efficiency (CE) for lithium metal anodes (LMAs) and allow reversible stripping/plating of various post-lithium metals for battery application, e.g., aluminum metal batteries (AMBs). Despite these advantages, ILEs suffer from high viscosity, which impairs ion transport and wettability. To resolve these challenges, researchers have developed locally concentrated ionic liquid electrolytes (LCILEs) by adding low-viscosity nonsolvating cosolvents, e.g., hydrofluoroether, to ILEs. These cosolvents do not coordinate with cationic charge carriers, thereby reducing viscosity and improving ion transport without compromising the compatibility of electrolytes with metal anodes. However, due to the inherent difference of molecular organic solvents and ionic liquids full of charged species, the most used nonsolvating cosolvents, i.e., hydrofluoroether, are less effective for ILEs with respect to concentrated electrolytes based on conventional organic solvents. Moreover, hydrofluoroether contains environmentally problematic -CF3 and/or -CF2- groups, i.e., per- and polyfluoroalkyl substances (PFAS), with their use subject to restrictions.In this Account, we provide an overview of the endeavors of our research group on the development of PFAS-free LCILEs for high-energy LMBs and AMBs. First, aromatic organic cations and aromatic less/nonfluorinated cosolvents are proposed to weaken the organic cation-anion interaction and strengthen the organic cation-cosolvent interaction, respectively. This is with consideration of the uncovered phase nanosegregation structure of LCILEs that effectively reduces the viscosity and promotes the Li+ transport ability with respect to the conventional nonaromatic organic cations and highly fluorinated PFAS cosolvents. Then, the effect of electrolyte components that do not coordinate to Li+, including organic cations and nonsolvating cosolvents, on the SEI composition and LMA reversibility is presented, which confirms the feasibility of reaching a high lithium stripping/plating CE up to 99.7% in the developed PFAS-free LCILEs. In the subsequent discussion on cathode compatibility, we present that in addition to LiFePO4 with high cyclability but inferior energy density, nickel-rich layered oxide and sulfurized polyacrylonitrile (SPAN) can be employed to construct high-energy LMBs for PFAS-free LCILEs with different anodic stability. Additionally, the feasible application of the LCILE strategy to promote the kinetics of AMBs relying on a different anode chemistry is demonstrated. Lastly, future research directions with an emphasis on nonsolvating component optimization, electrolyte dynamics, and electrode/electrolyte interphase formation are provided.

Host-Guest Interactions of Metal-Organic Framework Enable Highly Conductive Quasi-Solid-State Electrolytes for Li-CO2 Batteries

High-energy lithium (Li)-based batteries, especially rechargeable Li-CO2 batteries with CO2 fixation capability and high energy density, are desirable for electrified transportation and other applications. However, the challenges of poor stability, low energy efficiency, and leakage of liquid electrolytes hinder the development of Li-CO2 batteries. Herein, a highly conductive and stable metal-organic framework-encapsulated ionic liquid (IL@MOF) electrolyte system is developed for quasi-solid-state Li-CO2 batteries. Benefiting from the host-guest interaction of MOFs with open micromesopores and internal IL, the optimized IL@MOF electrolytes exhibit a high ionic conductivity of 1.03 mS cm-1 and a high transference number of 0.80 at room temperature. The IL@MOF electrolytes also feature a wide electrochemical stability window (4.71 V versus Li+/Li) and a wide working temperature (-60 °C ∼ 150 °C). The IL@MOF electrolytes also enable Li+ and electrons transport in the carbon nanotubes-IL@MOF (CNT-IL@MOF) solid cathodes in quasi-solid-state Li-CO2 batteries, delivering a high specific capacity of 13,978 mAh g-1 (50 mA g-1), a long cycle life of 441 cycles (500 mA g-1 and 1000 mAh g-1), and a wide operation temperature of -60 to 150 °C. The proposed MOF-encapsulated IL electrolyte system presents a powerful strategy for developing high-energy and highly safe quasi-solid-state batteries.

Unlocking the critical roles of N, P Co-Doping in MXene for Lithium-Oxygen Batteries: Elevated d-Band center and expanded interlayer spacing

The design and fabrication of bifunctional catalysts with high electrocatalytic activity and stability are critical for developing highly reversible Li-O2 batteries (LOBs). Herein, the N, P co-doped MXene (NP-MXene) is prepared by one-step annealing method and evaluated as bifunctional catalyst for LOBs. The results suggest that the P doping plays a crucial role in increasing interlayer distance of MXene, thereby effectively providing more active sites, fast mass transfer, and ample space for the deposition/decomposition of Li2O2. Moreover, the N doping can significantly elevate the d-band center of Ti, thereby remarkably improving the adsorption of reaction intermediates and accelerating the deposition/decomposition of Li2O2 films. Consequently, the MXene-based LOBs deliver an ultrahigh specific capacity of 13,995 mAh/g at 500 mA g-1, a discharge/charge voltage gap of 0.89 V, and a cycle life up to 523 cycles with a limited capacity of 1000 mAh/g at 500 mA g-1. Impressively, the as-fabricated flexible LOBs with NP-MXene cathode display excellent cycling stability and ability to continuously power LEDs even after bending. Our findings pave the road of heteroatom doped MXenes as next-generation electrodes for high-performance energy storage and conversion systems.

Dual-Steric Hindrance Modulation of Interface Electrochemistry for Potassium-Ion Batteries

Electrolyte chemistry regulation is a feasible and effective approach to achieving a stable electrode-electrolyte interface. How to realize such regulation and establish the relationship between the liquid-phase electrolyte environment and solid-phase electrode remains a significant challenge, especially in solid electrolyte interphase (SEI) for metal-ion batteries. In this work, solvent/anion steric hindrance is regarded as an essential factor in exploring the electrolyte chemistry regulation on forming ether-based K+-dominated SEI interface through the cross-combination strategy. Theoretical calculation and experimental evidence have successfully indicated a general principle that the combination of increasing solvent steric hindrance with decreasing anion steric hindrance indeed prompts the construction of an ideal anion-rich sheath solvation structure and guarantees the cycling stability of antimony-based alloy electrode (Sb@3DC, Sb nanoparticles anchored in three-dimensional carbon). These confirm the critical role of electrolyte modulation based on molecular design in the formation of stable solid-liquid interfaces, particularly in electrochemical energy storage systems.

Counterintuitive Isomerization of TFSI- and TFSI--Cation Correlated Isomerization: Insights into the Low Melting Points of TFSI--Based Ionic Liquids

Ionic liquids (ILs), particularly bis(trifluoromethane)sulfonamide (TFSI-)-based ILs, have attracted substantial attention in electrochemical energy storage, ionic gating for superconductivity, and iontronic sensing. However, underestimating TFSI- isomerization and overlooking TFSI--cation correlation make the origin of their most characteristic property, low melting points (Tm), ambiguous. Traditional static electronic structure calculations assume that C2-symmetric trans enantiomers of TFSI- easily isomerize into cis enantiomers through four symmetrically equivalent pathways over a barrier of 7.1 kJ mol-1. Herein, ab initio molecular dynamics (AIMD) simulations combined with metadynamics reveal that the unusual oscillation of the central nitrogen atom promotes TFSI- to undergo complex isomerization. Specifically, asymmetric trans-to-cis diastereomers of TFSI- experience restricted interconversion (20-52 kJ mol-1) through four distinct asymmetric pathways. The adaptive oscillation and hybridization of chiral nitrogen boost nN → σ*S-C negative hyperconjugation for stabilizing conformational structures and enlarging energy barriers. The orientational distortion of oxygen atoms' lone pairs enhances conjugation but breaks the C2-symmetry. The coexistence of both helicity and chiral nitrogen breaks the enantiomeric relationship. Furthermore, Raman characterization and AIMD simulations confirm the positive correlation between the relative stability of cis-TFSI- and its countercation's polarity. TFSI- and countercations make a mutual conformational selection instead of free isomerization. Surprisingly, Tm increases with the cation-dependent conformational rigidity of TFSI-, offering new fundamental insights into the low Tm of ILs. This descriptor encoding the dependence of thermal property on cation-anion correlated isomerization provides material design guidelines and property prediction capability.

Determinants of the Surface Film during the Discharging Process in Lithium-Oxygen Batteries

Lithium-oxygen batteries have one of the highest theoretical capacities and specific energies, but several challenges remain. One of them is premature death caused by a passivation layer with poor conductivities (both electronic and ionic) on the electrode surface during the discharge process. Once this thin layer forms on the surface of the catalyst and substrate, the overpotential significantly increases and causes early cell death. Therefore, understanding this thin layer is crucial to achieving high specific energy lithium-oxygen batteries. Herein, we quantitatively compared the ratio of lithium carbonate to lithium peroxide during the discharge process in a flow cell at different potentials. We found that the ratio rapidly increased at low potential and high flow rates. The surface route led to significant byproducts on the Au electrodes, and consequently, a 3 nm thick discharge product film passivates the electrode surface in a flow cell.

Regulating Intramolecular Electron Transfer of Nickel-Based Coordinations through Ligand Engineering for Aqueous Batteries

The integration of electronic effects into complexes for the construction of novel materials has not yet attracted significant attention in the field of energy storage. In the current study, eight one-dimensional (1D) nickel-based salicylic acid  complexes (Ni-XSAs, X = pH, pMe, pMeO, mMe, pBr, pCl, pF, and pCF3 ), are prepared by ligand engineering. The coordination environments in the Ni-XSAs are explored using X-ray absorption fine structure spectroscopy. The charge transfer of the complexes is modulated according to the difference in the electron-donating ability of the substituents, in combination with frontier orbital theory. Furthermore, density functional theory is used to investigate the effect of the substituent position on the electronic properties of the complexes. Ni-mMeSA exhibits better electrical conductivity than Ni-pMeSA. The electrochemical performance of Ni-mMeSA as an aqueous battery cathode is remarkably improved with a maximum energy density of 0.30 mWh cm-2 (125 Wh kg-1 ) and a peak power density of 33.72 mW cm-2 (14.03 kW kg-1 ). This study provides ideas for the application of new coordination chemistry in the field of energy materials science.

Sabatier Relations in Electrocatalysts Based on High-entropy Alloys with Wide-distributed d-band Centers for Li-O2 Batteries

Li-O2 battery (LOB) is a promising "beyond Li-ion" technology with ultrahigh theoretical energy density (3457 Wh kg-1 ), while currently impeded by the sluggish cathodic kinetics of the reversible gas-solid reaction between O2 and Li2 O2 . Despite many catalysts are developed for accelerating the conversion process, the lack of design guidance for achieving high performance makes catalysts exploring aleatory. The Sabatier principle is an acknowledged theory connecting the scaling relationship with heterogeneous catalytic activity, providing a tradeoff strategy for the topmost performance. Herein, a series of catalysts with wide-distributed d-band centers (i.e., wide range of adsorption strength) are elaborately constructed via high-entropy strategy, enabling an in-depth study of the Sabatier relations in electrocatalysts for LOBs. A volcano-type correlation of d-band center and catalytic activity emerges. Both theoretical and experimental results indicate that a moderate d-band center with appropriate adsorption strength propels the catalysts up to the top. As a demonstration of concept, the LOB using FeCoNiMnPtIr as catalyst provides an exceptional energy conversion efficiency of over 80 %, and works steadily for 2000 h with a high fixed specific capacity of 4000 mAh g-1 . This work certifies the applicability of Sabatier principle as a guidance for designing advanced heterogeneous catalysts assembled in LOBs.