Stepwise optimization of single-ion conducting polymer electrolytes for high-performance lithium-metal batteries

Single-ion conducting polymer electrolytes(SIPEs)are promising candidates for high-energy and highsafety lithium-metal batteries(LMBs).However,their insufficient ionic conductivity and electrochemical stability hinder their practical application.Herein,three new SIPEs,i.e.,poly(1,4-phenylene ether ether sulfone)-Li(PEES-Li),polysulfone-Li(PSF-Li),and hexafluoropolysulfone-Li(6FPSF-Li),all containing covalently tethered perfluorinated ionic side chains,have been designed,synthesized,and compared to investigate the influence of the backbone chemistry and the concentration of the ionic group on their electrochemical properties and cell performance.Especially,the trifluoromethyl group in the backbone and the concentration of the ionic function appear to play an essential role for the charge transport and stability towards oxidation,and the combination of both yields the best-performing SIPE with high ionic conductivity of ca.2.5×10^(-4)S cm^(-1),anodic stability of more than 4.8 V,and the by far highest capacity retention in Li‖LiNi0.6Co0.2Mn0.2O2cells.

Electrochemical Kinetic Modulators in Lithium–Sulfur Batteries:From Defect-Rich Catalysts to Single Atomic Catalysts

Lithium–sulfur batteries exhibit unparalleled merits in theoretical energy density(2600 W h kg^(-1))among next-generation storage systems.However,the sluggish electrochemical kinetics of sulfur reduction reactions,sulfide oxidation reactions in the sulfur cathode,and the lithium dendrite growth resulted from uncontrollable lithium behaviors in lithium anode have inhibited high-rate conversions and uniform deposition to achieve high performances.Thanks to the“adsorption-catalysis”synergetic effects,the reaction kinetics of sulfur reduction reactions/sulfide oxidation reactions composed of the delithiation of Li_(2)S and the interconversions of sulfur species are propelled by lowering the delithiation/diffusion energy barriers,inhibiting polysulfide shuttling.Meanwhile,the anodic plating kinetic behaviors modulated by the catalysts tend to uniformize without dendrite growth.In this review,the various active catalysts in modulating lithium behaviors are summarized,especially for the defect-rich catalysts and single atomic catalysts.The working mechanisms of these highly active catalysts revealed from theoretical simulation to in situ/operando characterizations are also highlighted.Furthermore,the opportunities of future higher performance enhancement to realize practical applications of lithium–sulfur batteries are prospected,shedding light on the future practical development.

Towards an enhanced understanding of the particle size effect on conversion/alloying lithium-ion anodes

Conversion/alloying materials(CAMs)represent a potential alternative to graphite as a Li-ion anode active material,especially for high-power applications.So far,however,essentially all studies on CAMs have been dealing with nano-sized particles,leaving the question of how the performance(and the de-/lithiation mechanism in general)is affected by the particle size.Herein,we comparatively investigate four different samples of Zn_(0.9)Co_(0.1)O with a particle size ranging from about 30 nm to a few micrometers.The results show that electrodes made of larger particles are more susceptible to fading due to particle displacement and particle cracking.The results also show that the conversion-type reaction in particular is affected by an increasing particle size,becoming less reversible due to the formation of relatively large transition metal(TM)and alloying metal nanograins upon lithiation,thus hindering an efficient electron transport within the initial particle,while the alloying contribution remains essentially unaffected.The generality of these findings is confirmed by also investigating Sn_(0.9)Fe_(0.1)O_(2) as a second CAM with a substantially greater contribution of the alloying reaction and employing Fe instead of Co as a TM dopant.

Perspective on ultramicroporous carbon as sulphur host for Li-S batteries

Lithium-sulphur(Li-S)batteries are currently considered as next-generation battery technology.Sulphur is an attractive positive electrode for lithium metal batteries,mainly due to its high capacity(1675 m Ah g^(-1))and high specific energy(2600 Wh kg^(-1)).The electrochemical reaction of lithium with sulphur in non-aqueous electrolytes results in the formation of electrolyte soluble intermediate lithium-polysulphides.The dissolved polysulphides shuttle to the anode and get reduced at the anode resulting in Li metal corrosion.The solubility of polysulphide gradually reduces the amount of sulphur in the cathode,thereby limiting the cycle life of Li-S batteries.Several strategies have been proposed to improve the cycling stability of Li-S batteries.A unique approach to eliminate the polysulphide shuttle is to use ultramicroporous carbon(UMC)as a host for sulphur.The pore size of UMC which is below 7A,is the bottleneck for carbonate solvents to access sulphur/polysulphides confined in the pores,thereby preventing the polysulphide dissolution.This perspective article will emphasise the role of UMC host in directing the lithiation mechanism of sulphur and in inhibiting polysulphide dissolution,including the resulting parasitic reaction on the lithium anode.Further,the challenges that need to be addressed by UMC-S based Li-S batteries,and the strategies to realise high power density,high Coulombic efficiency,and resilient Li-S batteries will be discussed.

Oxygen-Containing Functional Groups Regulating the Carbon/Electrolyte Interfacial Properties Toward Enhanced K^(+)Storage

Oxygen-containing functional groups were found to e ectively boost the K^(+)storage performance of carbonaceous materials,however,the mechanism behind the performance enhancement remains unclear.Herein,we report higher rate capability and better long-term cycle performance employing oxygen-doped graphite oxide(GO)as the anode material for potassium ion batteries(PIBs),compared to the raw graphite.The in situ Raman spectroscopy elucidates the adsorption-intercalation hybrid K^(+)storage mechanism,assigning the capacity enhancement to be mainly correlated with reversible K^(+)adsorption/desorption at the newly introduced oxygen sites.It is unraveled that the C=O and COOH rather than C-O-C and OH groups contribute to the capacity enhancement.Based on in situ Fourier transform infrared(FT-IR)spectra and in situ electrochemical impedance spectroscopy(EIS),it is found that the oxygen-containing functional groups regulate the components of solid electrolyte interphase(SEI),leading to the formation of highly conductive,intact and robust SEI.Through the systematic investigations,we hereby uncover the K^(+)storage mechanism of GO-based PIB,and establish a clear relationship between the types/contents of oxygen functional groups and the regulated composition of SEI.

Manipulating dielectric property of polymer coatings toward highretention-rate lithium metal full batteries under harsh critical conditions

Lithium(Li)metal batteries(LMBs)can potentially deliver much higher energy density but remain plagued by uncontrollable Li plating with dendrite growth,unstable interfaces,and highly abundant excess Li(>50 mAh·cm^(-2)).Herein,different from the artificial layer or three-dimensional(3D)matrix host constructions,various dielectric polymers are initially well-comprehensively investigated from experimental characterizations to theoretical simulation to evaluate their functions in modulating Li ion distribution.As a proof of concept,a 3D interwoven high dielectric functional polymer(HDFP)nanofiber network with polar C-F dipole moments electrospun on copper(Cu)foil is designed,realizing uniform and controllable Li deposition capacity up to 5.0 mAh·cm^(-2),thereby enabling stable Li plating/stripping cycling over 1400 h at 1.0 mA·cm^(-2).More importantly,under the highcathode loading(~3.1 mAh·cm^(-2))and only 0.6×excess Li(N/P ratio of 1.6),the full cells retain capacity retention of 97.4%after 200 cycles at 3.36 mA·cm^(-2)and achieve high energy density(297.7 Wh·kg^(-1)at cell-level)under lean electrolyte conditions(15μL),much better than ever-reported literatures.Our work provides a new direction for designing high dielectric polymer coating toward high-retention-rate practical Li full batteries.

Interface engineering of MXene-based heterostructures for lithiumsulfur batteries

High energy density and low cost make lithium-sulfur(Li-S)batteries as one of the next generation's promising energy storage systems.However,the following problems need to be solved before commercialization:(i)the shuttling effect and sluggish redox kinetics of lithium polysulfides in sulfur cathode;(ii)the formation of lithium dendrites and the crack of solid electrolyte interphase;(iii)the large volume changes during charge and discharge processes.MXenes,as newly emerging two-dimensional transition metal carbides/nitrides/carbonitrides,have attracted widespread attention due to their abundant active surface terminals,adjustable vacancies,and high electrical conductivity.Designing MXene-based heterogeneous structures is expected to solve the stacking problem induced by hydrogen bonds or Van der Waals force and to provide other charming physiochemical properties.Herein,we generalize the design principles of MXene-based heterostructures and their functions,i.e.,adsorption and catalysis in advanced conversion-based Li-S batteries.Firstly,the physiochemical properties of MXene and MXene-based heterostructures are briefly introduced.Secondly,the catalytic functions of MXene-based heterostructures with the compositional constituents including carbon materials,metal compounds,organic frameworks,polymers,single atoms and special high-entropy MXenes are comprehensively summarized in sulfur cathodes and lithium anodes.Finally,the challenges of MXene-based heterostructure in current Li-S batteries are pointed out and we also provide some enlightenments for future developments in high-energy-density Li-S batteries.

Enhanced interfacial compatibility of FeS@N,S-C anode with ester-based electrolyte enables stable sodium-ion full cells

The development of sodium-ion full cells is seriously suppressed by the incompatibility between electrodes and electrolytes. Most representatively, high-voltage ester-based electrolytes required by the cathodes present poor interfacial compatibility with the anodes due to unstable solid electrode interphase(SEI). Herein, Fe S@N,S-C(spindle-like Fe S nanoparticles individually encapsulated in N,S-doped carbon) with excellent structural stability is synthesized as a potential sodium anode material. It exhibits exceptional interfacial stability in ester-based electrolyte(1 M NaClO_(4) in ethylene carbonate/propylene carbonate with 5% fluoroethylene carbonate) with long-cycling lifespan(294 days) in Na|Fe S@N,S-C coin cell and remarkable cyclability in pouch cell(capacity retention of 82.2% after 170 cycles at 0.2 A g^(-1)).DFT calculation reveals that N,S-doping on electrode surface could drive strong repulsion to solvated Na_(2) and preferential adsorption to ClO_(4)^(-) anion, guiding the anion-rich inner Helmholtz plane.Consequently, a robust SEI with rich inorganic species(NaCl and Na_(2)O) through the whole depth stabilizes the electrode–electrolyte interface and protects its integrity. This work brings new insight into the role of electrode’s surface properties in interfacial compatibility that can guide the design of more versatile electrodes for advanced rechargeable metal-ion batteries.

Assessing n-type organic materials for lithium batteries:A techno-economic review

The high demand for critical minerals such as lithium,copper,nickel,and cobalt,required for lithium-ion batteries,has raised questions regarding the feasibility of maintaining a steady and affordable supply of raw materials for their production.In the last years,researchers have shifted their attention toward organic materials,which are potentially more widely available,affordable,and sustainable due to the ubiquitous presence of the constituent organic elements.The n-type materials have a redox mechanism analogous to that of lithium-ion cathodes and anodes,hence they are suitable for a meaningful comparison with the state-of-the-art technology.While many reviews have evaluated the properties of organic materials at the material or electrode level,herein,the properties of n-type organic materials are assessed in a complex system,such as a full battery,to evaluate the feasibility and performance of these materials in commercial-scale battery systems.The most relevant cathode materials for organic batteries are reviewed,and a detailed cost and performance analysis of n-type material-based battery packs using the BatPaC 5.0 software is presented.The analysis considers the influence of electrode design choices,such as the conductive carbon content,active material mass loading,and electrode density,on energy density and cost.The potential of n-type organic materials as a low-cost and sustainable solution for energy storage applications is highlighted,while emphasizing the need for further advancements of organic materials for energy storage applications.

Beneficial impact of lithium bis(oxalato)borate as electrolyte additive for high-voltage nickel-rich lithium-battery cathodes

High-voltage nickel-rich layered cathodes possess the requisite,such as excellent discharge capacity and high energy density,to realize lithium batteries with higher energy density.However,such materials suffer from structural and interfacial instability at high voltages(>4.3 V).To reinforce the stability of these cathode materials at elevated voltages,lithium borate salts are investigated as electrolyte additives to generate a superior cathode-electrolyte interphase.Specifically,the use of lithium bis(oxalato)borate(LiBOB)leads to an enhanced cycling stability with a capacity retention of 81.7%.Importantly,almost no voltage hysteresis is detected after 200 cycles at 1C.This outstanding electrochemical performance is attributed to an enhanced structural and interfacial stability,which is attained by suppressing the generation of micro-cracks and the superficial structural degradation upon cycling.The improved stability stems from the formation of a fortified borate-containing interphase which protects the highly reactive cathode from parasitic reactions with the electrolyte.Finally,the decomposition process of LiBOB and the possible adsorption routes to the cathode surface are deduced and elucidated.

Synthesis,Structure,Electrochemical Mechanisms,and Atmospheric Stability of Mn-Based Layered Oxide Cathodes for Sodium Ion Batteries

CONSPECTUS:The commercialization of lithium ion batteries(LIBs)triggered a new era of portable electronics and electric vehicles,which changed our daily life remarkably.Meanwhile,LIBs are promising as large-scale storage batteries in green electric grids by using renewable energy as the primary energy source.Driven by the concerns of lithium depletion and the turbulent price of Li,Ni,and Co mineral resources,sodium ion batteries(NIBs)have been intensively investigated and are becoming a strong competitor for large-scale energy storage,such as in national grids.

Unlocking the potential of weberite-type metal fluorides in electrochemical energy storage

Sodium-ion batteries(NIBs)are a front-runner among the alternative battery technologies suggested for substituting the state-ofthe-art lithium-ion batteries(LIBs).The specific energy of Na-ion batteries is significantly lower than that of LIBs,which is mainly due to the lower operating potentials and higher molecular weight of sodium insertion cathode materials.To compete with the high energy density of LIBs,high voltage cathode materials are required for NIBs.Here we report a theoretical investigation on weberitetype sodium metal fluorides(SMFs),a new class of high voltage and high energy density materials which are so far unexplored as cathode materials for NIBs.The weberite structure type is highly favorable for sodium-containing transition metal fluorides,with a large variety of transition metal combinations(M,M’)adopting the corresponding Na_(2)MM’F_(7) structure.A series of known and hypothetical compounds with weberite-type structure were computationally investigated to evaluate their potential as cathode materials for NIBs.Weberite-type SMFs show two-dimensional pathways for Na^(+)diffusion with surprisingly low activation barriers.The high energy density combined with low diffusion barriers for Na+makes this type of compounds promising candidates for cathode materials in NIBs.

P2-type layered high-entropy oxides as sodium-ion cathode materials

P2-type layered oxides with the general Na-deficient composition Na_(x)TMO_(2)(x<1,TM:transition metal)are a promising class of cathode materials for sodium-ion batteries.The open Na+transport pathways present in the structure lead to low diffusion barriers and enable high charge/discharge rates.However,a phase transition from P2 to O2 structure occurring above 4.2 V and metal dissolution at low potentials upon discharge results in rapid capacity degradation.In this work,we demonstrate the positive effect of configurational entropy on the stability of the crystal structure during battery operation.Three different compositions of layered P2-type oxides were synthesized by solid-state chemistry,Na_(0.67)(Mn_(0.55)Ni_(0.21)Co_(0.24))O_(2),Na_(0.67)(Mn_(0.45)Ni_(0.18)Co_(0.24)Ti_(0.1)Mg_(0.03))O_(2) and Na_(0.67)(Mn_(0.45)Ni_(0.18)Co_(0.18)Ti_(0.1)Mg_(0.03)Al_(0.04)Fe_(0.02))O_(2) with low,medium and high configurational entropy,respectively.The high-entropy cathode material shows lower structural transformation and Mn dissolution upon cycling in a wide voltage range from 1.5 to 4.6 V.Advanced operando techniques and post-mortem analysis were used to probe the underlying reaction mechanism thoroughly.Overall,the high-entropy strategy is a promising route for improving the electrochemical performance of P2 layered oxide cathodes for advanced sodium-ion battery applications.