Electrolyte-dependent formation of solid electrolyte interphase and ion intercalation revealed by in situ surface characterizations

The formation of solid electrolyte interphase(SEI) and ion intercalation are two key processes in rechargeable batteries, which need to be explored under dynamic operating conditions. In this work, both planar and sandwich model lithium batteries consisting of Li metal | ionic liquid electrolyte | graphite electrode have been constructed and investigated by a series of in situ surface analysis platforms including atomic force microscopy, Raman and X-ray photoelectron spectroscopy. It is found that the choice of electrolyte, including the concentration and contents, has a profound effect on the SEI formation and evolution, and the subsequent ion intercalation. A smooth and compact SEI is preferably produced in highconcentration electrolytes, with FSI^(-) salt superior to TFSI^(-) salt, facilitating the lithiation/delithiation to achieve high capacity and excellent cycle stability, while suppressing the co-intercalation of electrolyte solvent ions. The innovative research scenario of well-defined model batteries in combination with multiple genuinely in situ surface analysis methods presented herein leads to insightful results, which provide valuable strategies for the rational design and optimization of practical batteries, and energy storage devices in general.

Transforming a Two-Dimensional Layered Insulator into a Semiconductor or a Highly Conductive Metal through Transition Metal Ion Intercalation

Atomically thin two-dimensional(2D) materials are the building bricks for next-generation electronics and optoelectronics, which demand plentiful functional properties in mechanics, transport, magnetism and photoresponse.For electronic devices, not only metals and high-performance semiconductors but also insulators and dielectric materials are highly desirable. Layered structures composed of 2D materials of different properties can be delicately designed as various useful heterojunction or homojunction devices, in which the designs on the same material(namely homojunction) are of special interest because preparation techniques can be greatly simplified and atomically seamless interfaces can be achieved. We demonstrate that the insulating pristine ZnPS_3, a ternary transition-metal phosphorus trichalcogenide, can be transformed into a highly conductive metal and an n-type semiconductor by intercalating Co and Cu atoms, respectively. The field-effect-transistor(FET) devices are prepared via an ultraviolet exposure lithography technique. The Co-ZnPS_3 device exhibits an electrical conductivity of 8 × 10^(4) S/m, which is comparable to the conductivity of graphene. The Cu-ZnPS_3 FET reveals a current ON/OFF ratio of 1-05 and a mobility of 3 × 10^(-2 )cm^(2)·V^(-1)·s^(-1). The realization of an insulator, a typical semiconductor and a metallic state in the same 2D material provides an opportunity to fabricate n-metal homojunctions and other in-plane electronic functional devices.

Tuning the local coordination environment of silver(Ⅰ) coordination networks with counterions for enhanced electrocatalytic CO_(2) reduction

Very recently, the local coordination environment of active sites has been found to strongly influence their performance in electrocatalytic CO_(2) reduction by tuning the intrinsic kinetics of CO_(2) activation and intermediate stabilization. It is imperative to elucidate the mechanism for such an influence towards the rational design of efficient catalysts;however, the complex interactions between the multiple factors involved in the system make it challenging to establish a clear structure–performance relationship. In this work, we chose ion-intercalated silver(I)-based coordination networks(AgCNs) with a well-defined structure as a model platform, which enables us to understand the regulation mechanism of counterions as the counterions are the only tuning factor involved in such a system. We prepared two isostructural Ag CNs with different intercalation ions or counterions of BF_(4)^(-) and ClO_(4)^(-)(named as AgCNs-BF_(4) and AgCNs-ClO_(4)) and found that the former has a more competitive CO_(2) electroreduction performance than the latter. AgCNs-BF_(4) achieves the highest Faradaic efficiency for CO_(2) to CO of 87.1% at-1.0 V(vs. RHE) with a higher partial current density, while AgCNs-ClO_(4) exhibits only 77.2% at the same applied potential.Spectroscopic characterizations and theoretical calculation reveal that the presence of BF_(4)^(-)is more favorable for stabilizing the COOH^(*) intermediate by weakening hydrogen bonds, which accounts for the superior activity of Ag CNs-BF_(4).

Hierarchical CoNi-LDH nanosheet array with hydrogen vacancy for high-performance aqueous battery cathode

Aqueous rechargeable multiple metal-ion storage battery (ARSB) has a large potential in energy storage devices due to their safe usage, low cost and high rate capability. Nevertheless, the performance of practical ARSB is largely restricted by low capacity and limited cathode materials. Herein, we demonstrate an efficient cathode material based on Co Ni-layered double hydroxide (LDH) nanosheets arrays with abundant hydrogen vacancy induced by electrochemical activation process for high performance of cations storage. Consequently, the electrochemical activated Co Ni-LDH (ECA-Co Ni-LDH) nanosheets arrays exhibit high metal ion (Li^(+), Na^(+), Zn^(2+), Mg^(2+) and Ca^(2+)) storage capacities, which is 9 times and 3 times higher that of unactivated Co Ni-LDH arrays and ECA-Co Ni-LDH without hierarchical structure, respectively.Moreover, the ECA-Co Fe-LDH also shows the possibility for practical applications in actual batteries.By coupling with a Fe_(2)O_(3)/C anode, the assembled aqueous battery delivered a large energy density of 184.4 Wh kg^(-1)at power density of 4 Wh kg^(-1) in high voltage range of 0–2 V. To our best knowledge, such high energy density and large working window of our assembled aqueous battery is exceeded other LDH-based aqueous battery or supercapacitor, and the energy density almost comparable than that of commercial Li-ion batteries. Moreover, almost no measurable capacitance losses can be detected even after 10000 cycles. In addition, this work also provides a strategy to develop a high energy density cathode for multiple metal-ion storage batteries.

Extended light absorption and accelerated charge migration in ultrathin twisted carbon nitride nanoplates for efficient solar hydrogen production

Polymeric carbon nitride has been widely developed as a promising photocatalyst for solar hydrogen production via photocatalytic water splitting.However,pristine carbon nitride prepared by traditional solid-state polymerization usually encounters issues such as rapid carrier recombination and insufficient absorption of visible light below 460 nm.Herein,poly(heptazine imide)with a distinctive nanoplate structure was synthesized in a binary molten salt of NaCl–CaCl_(2).The salt template allows the formation of the thin nanoplate structure,which promotes the charge separation and migration.Besides,the intercalation of Ca^(2+)ions between the conjugated layers endows the activation of n–π*electron transition due to the distortion of in-plane heptazine layers.Accordingly,the optimized poly(heptazine imide)nanoplates achieve an apparent quantum efficiency of up to 17.3%at 500 nm for photocatalytic hydrogen production from water.This work shares new idea for rational control of the optical absorption and charge carrier dynamics of poly(heptazine imide).

MoS2 as a long-life host material for potassium ion intercalation

Electrochemical potassium ion intercalation into two-dimensional layered MoS2 was studied for the first time for potential applications in the anode in potassium-based batteries. X-ray diffraction analysis indicated that an intercalated potassium compound, hexagonal K0.4MoS2, formed during the intercalation process. Despite the size of K^＋, MoS2 was a long-life host for repetitive potassium ion intercalation and de-intercalation with a capacity retention of 97.5% after 200 cycles. The diffusion coefficient of the K^＋ ions in KxMoS2 was calculated based on the Randles-Sevcik equation. A higher K^＋ intercalation ratio not only encountered a much slower K^＋ diffusion rate in MoS2, but also induced MoS2 reduction. This study shows that metal dichalcogenides are promising potassium anode materials for emerging K-ion, K-O2, and K-S batteries.

Intercalation-deintercalation design in MXenes for high-performance supercapacitors

MXene is a new intercalation pseudocapacitive electrode material for supercapacitor application.Intensifying fast ion diffusion is significantly essential for MXene to achieve excellent electrochemical performance.The expansion of interlayer void by traditional spontaneous species intercalation always leads to a slight increase in capacitance due to the existence of species sacrificing the smooth diffusion of electrolyte ions.Herein,an effective intercalation-deintercalation interlayer design strategy is proposed to help MXene achieve higher capacitance.Electrochemical cation intercalation leads to the expansion of interlayer space.After electrochemical cation extraction,intercalated cations are deintercalated mostly,leaving a small number of cations trapped in the interlayer silt and serving as pillars to maintain the interlayer space,offering an open,unobstructed interlayer space for better ion migration and storage.Also,a preferred surface with more-O terminations for redox reaction is created due to the reaction between cations and-OH terminations.As a result,the processed MXene delivers a much improved capacitance compared to that of the original Ti_(3)C_(2)T_(x)electrode(T stands for the surface termination groups,such as-OH,-F,and-O).This study demonstrates an improvement of electrochemical performance of MXene electrodes by controlling the interlayer structure and surface chemistry.

Visualizing surface-enriched Li storage with a nanopore-array model battery

The coupling of model batteries and surface-sensitive techniques provides an indispensable platform for interrogating the vital surface/interface processes in battery systems.Here,we report a sandwich-format nanopore-array model battery using an ultrathin graphite electrode and an anodized aluminum oxide(AAO)film.The porous framework of AAO regulates the contact pattern of the electrolyte with the graphite electrode from the inner side,while minimizing contamination on the outer surface.This model battery facilitates repetitive charge-discharge processes,where the graphite electrode is reversibly intercalated and deintercalated,and also allows for the in-situ characterizations of ion intercalation in the graphite electrode.The ion distribution profiles indicate that the intercalating Li ions accumulate in both the inner and outer surface regions of graphite,generating a high capacity of~455 mAh·g^(-1)(theory:372 mAh·g^(-1)).The surface enrichment presented herein provides new insights towards the mechanistic understanding of batteries and the rational design strategies.

Non-aqueous Al-ion batteries:cathode materials and corresponding underlying ion storage mechanisms

Aluminum-ion batteries(AIBs)are recognized as one of the promising candidates for future energy stor-age devices due to their merits of cost-effectiveness,high voltage,and high-power operation.Many efforts have been devoted to the development of cathode materials,and the progress has been well summarized in this review paper.Moreover,in addition to materials,the intercalation mechanism also plays a key role in determining cell per-formance.Here,the research progress of cathode materials and corresponding ion intercalation mechanism in AIBs are summarized,including intercalation of AlCl_(4)-,intercala-tion of Al^(3+),and coordination of AlCl_(2)^(+)/AlCl^(2+).This minireview provides comprehensive guidance on the design of cathode materials for the development of high-performance AIBs.