Feasible engineering of cathode electrolyte interphase enables the profoundly improved electrochemical properties in dual-ion battery

Dual-ion battery(DIB) composed of graphite cathode and lithium anode is regarded as an advanced secondary battery because of the low cost, high working voltage and environmental friendliness. However,DIB operated at high potential(usually ≥ 4.5 V versus Li+/Li) is confronted with severe challenges including electrolyte decomposition on cathode interface, and structural deterioration of graphite accompanying with anions de-/intercalation, hinder its cyclic life. To address those drawbacks and preserve the DIB virtues, a feasible and scalable surface modification is achieved for the commercial graphite cathode of mesocarbon microbead. In/ex-situ studies reveal that, such an interfacial engineering facilitates and reconstructs the formation of chemically stable cathode electrolyte interphase with better flexibility alleviating the decomposition of electrolyte, regulating the anions de-/intercalation behavior in graphite with the retainment of structural integrity and without exerting considerable influence on kinetics of anions diffusion. As a result, the modified mesocarbon microbead exhibits a much-extended cycle life with high capacity retention of 82.3% even after 1000 cycles. This study demonstrates that the interface modification of electrode and coating skeleton play important roles on DIB performance improvement, providing the feasible basis for practical application of DIB owing to the green and scalable coating procedures.

Unique double-layer solid electrolyte interphase formed with fluorinated ether-based electrolytes for high-voltage lithium metal batteries

Li metal batteries using high-voltage layered oxides cathodes are of particular interest due to their high energy density.However,they suffer from short lifespan and extreme safety concerns,which are attributed to the degradation of layered oxides and the decomposition of electrolyte at high voltage,as well as the high reactivity of metallic Li.The key is the development of stable electrolytes against both highvoltage cathodes and Li with the formation of robust interphase films on the surfaces.Herein,we report a highly fluorinated ether,1,1,1-trifluoro-2-[(2,2,2-trifluoroethoxy)methoxy]ethane(TTME),as a cosolvent,which not only functions as a diluent forming a localized high concentration electrolyte(LHCE),but also participates in the construction of the inner solvation structure.The TTME-based electrolyte is stable itself at high voltage and induces the formation of a unique double-layer solid electrolyte interphase(SEI)film,which is embodied as one layer rich in crystalline structural components for enhanced mechanical strength and another amorphous layer with a higher concentration of organic components for enhanced flexibility.The Li||Cu cells display a noticeably high Coulombic efficiency of 99.28%after 300 cycles and Li symmetric cells maintain stable cycling more than 3200 h at 0.5 mA/cm^(2) and 1.0m Ah/cm^(2).In addition,lithium metal cells using LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2) and Li CoO_(2) cathodes(both loadings~3.0 m Ah/cm^(2))realize capacity retentions of>85%over 240 cycles with a charge cut-off voltage of 4.4 V and 90%for 170 cycles with a charge cut-off voltage of 4.5 V,respectively.This study offers a bifunctional ether-based electrolyte solvent beneficial for high-voltage Li metal batteries.

Synergistic interphase modification with dual electrolyte additives to boost cycle stability of high nickel cathode for all-climate battery

B-containing electrolyte additives are widely used to enhance the cycle performance at low temperature and the rate capability of lithium-ion batteries by constructing an efficient cathode electrolyte interphase(CEI)to facilitate the rapid Li+migration.Nevertheless,its wide-temperature application has been limited by the instability of B-derived CEI layer at high temperature.Herein,dual electrolyte additives,consisting of lithium tetraborate(Li_(2)TB)and 2,4-difluorobiphenyl(FBP),are proposed to boost the widetemperature performances of LiNi_(0.6)Co_(0.2)Mn_(0.2)O_(2)(NCM)cathode.Theoretical calculation and electrochemical performances analyses indicate that Li_(2)TB and FBP undergo successive decomposition to form a unique dual-layer CEI.FBP acts as a synergistic filming additive to Li_(2)TB,enhancing the hightemperature performance of NCM cathode while preserving the excellent low-temperature cycle stability and the superior rate capability conferred by Li_(2)TB additive.Therefore,the capacity retention of NCM‖Li cells using optimal FBP-Li_(2)TB dual electrolyte additives increases to 100%after 200 cycles at-10℃,99%after 200 cycles at 25℃,and 83%after 100 cycles at 55℃,respectively,much superior to that of base electrolyte(63%/69%/45%).More surprisingly,galvanostatic c ha rge/discharge experiments at different temperatures reveal that NCM‖Li cells using FBP-Li_(2)TB additives can operate at temperatures ranging from-40℃to 60℃.This synergistic interphase modification utilizing dual electrolyte additives to construct a unique dual-layer CEI adaptive to a wide temperature range,provides valuable insights to the practical applications of NCM cathodes for all-climate batteries.

Electron energy levels determining cathode electrolyte interphase formation

Cathode electrolyte interphase(CEI)has a significant impact on the performance of rechargeable batteries and is gaining increasing attention.Understanding the fundamental and detailed CEI formation mechanism is of critical importance for battery chemistry.Herein,a diverse of characterization tools are utilized to comprehensively analyze the composition of the CEI layer as well as its formation mechanism by LiCoO_(2)(LCO)cathode.We reveal that CEI is mainly composed of the reduction products of electrolyte and it only parasitizes the degraded LCO surface which has transformed into a disordered spinel structure due to oxygen loss and lithium depletion.Based on the energy diagram and the chemical potential analysis,the CEI formation process has been well explained,and the proposed CEI formation mechanism is further experimentally validated.This work highlights that the CEI formation process is nearly identical to that of the anode-electrolyte-interphase,both of which are generated due to the electrolyte directly in contact with the low chemical potential electrode material.This work can deepen and refresh our understanding of CEI.

Durable semi-crystalline interphase engineering to stabilize high voltage Ni-rich cathode in dilute ether electrolyte

Ethers are promising electrolyte solvents for secondary Li metal batteries because of their excellent reduction stability.However,their oxidation stability has been mostly relying on the high concentration approach,and limited progress has been made on building effective interphase to protect the cathode from the corrosion of the electrolyte.In this work,we construct a semi-crystalline interfacial layer on the surface of Li(Ni_(0.8)Co_(0.1)Mn_(0.1))O_(2)cathode that can achieve improved electrochemical stability in the highly corrosive chemical environment formed by the decomposition of ether molecules.Different from traditional brittle crystalline interphases,the optimized semi-crystalline layer with low modulus and high ionic conductivity can effectively relieve electrode strain and maintain the integrity of the interface layer.Due to this design,the continuous oxidation decomposition of ether-based electrolytes could be significantly suppressed and the battery shows outstanding cycling stability(84%capacity retention after 300 cycles).This article provides a solution to address the oxidation instability issue of ether-based electrolytes.

Achieving long-cycling sodium-ion full cells in ether-based electrolyte with vinylene carbonate additive

Application of sodium-ion batteries is suppressed due to the lack of appropriate electrolytes matching cathode and anode simultaneously.Ether-based electrolytes,preference of anode materials,cannot match with high-potential cathodes failing to apply in full cells.Herein,vinylene carbonate(VC)as an additive into NaCF_(3) SO_(3)-Diglyme(DGM)could make sodium-ion full cells applicable without preactivation of cathode and anode.The assembled FeS@C||Na3 V2(PO_(4))_(3)@C full cell with this electrolyte exhibits long term cycling stability and high capacity retention.The deduced reason is additive VC,whose HOMO level value is close to that of DGM,not only change the solvent sheath structure of Na^(+),but also is synergistically oxidized with DGM to form integrity and consecutive cathode electrolyte interphase on Na3 V2(PO_(4))_(3)@C cathode,which could effectively improve the oxidative stability of electrolyte and prevent the electrolyte decomposition.This work displays a new way to optimize the sodium-ion full cell seasily with bright practical application potential.

Electrolyte perspective on stabilizing LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)cathode for lithium-ion batteries

Nickel-rich LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM811)is regarded as the promising cathode for lithium-ion batteries(LIBs).However,the challenges such as safety issues and poor cycling performance have seriously hindered its commercial applications.In order to overcome these difficulties,there has been extensive research and development of electrolyte modifications for high-energy-density LIBs with Ni-rich cathodes.Herein,this review introduces the research progress based on solvent additives,salt type additives and other electrolytes for LIBs with NCM811cathode materials and discusses how they control the interface stability.In particular,some recommendations for further modification of enhancing electrolyte stability and improving NCM811 electrochemical properties are summarized and proposed,which put forward new design rules for the screening and customizing ideal electrolyte additives for high performance NCM811 cathode-based LIBs.

Lithium Hexamethyldisilazide Endows Li||NCM811 Battery with Superior Performance

The construction of stable cathode electrolyte interphase(CEI)is the key to improve the NCM811 particle structure and interfacial stability via electrolyte engineering.In He’s work,lithium hexamethyldisilazide(LiHMDS)as the electrolyte additive is proposed to facilitate the generation of stable CEI on NCM811 cathode surface and eliminate H_(2)O and HF in the electrolyte at the same time,which boosts the cycling performance of Li||NCM811 battery up to 1000 or 500 cycles with 4.5 V cut-off voltage at 25 or 60℃.

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.

Improved cyclic stability of LiNi_(0.8)Mn_(0.1)Co_(0.1O2)cathode enabled by a novel CEI forming additive

The undesired side reactions at electrode/electrolyte interface as well as the irreversible phase evolution during electrochemical cycling significantly affect the cyclic performances of nickel-rich NMCs electrode materials.Electrolyte optimization is an effective approach to suppress such an adverse side reaction,thereby enhancing the electrochemical properties.Herein,a novel boron-based film forming additive,tris(2,2,2-trifluoroethyl)borate(TTFEB),has been introduced to regulate the interphasial chemistry of LiNi0.8Mn0.1Co0.1O2(NMC811)cathode to improve its long-term cyclability and rate properties.The results of multi-model diagnostic study reveal that formation lithium fluoride(LiF)-rich and boron(B)containing cathode electrolyte interphase(CEI)not only stabilizes cathode surface,but also prevents electrolyte decomposition.Moreover,homogenously distributed B containing species serves as a skeleton to form more uniform and denser CEI,reducing the interphasial resistance.Remarkably,the Li/NMC811 cell with the TTFEB additive delivers an exceptional cycling stability with a high-capacity retention of 72.8%after 350 electrochemical cycles at a 1 C current rate,which is significantly higher than that of the cell cycled in the conventional electrolyte(59.7%).These findings provide a feasible pathway for improving the electrochemical performance of Ni-rich NMCs cathode by regulating the interphasial chemistry.

Calcium-and sulfate-functionalized artificial cathode–electrolyte interphases of Ni-rich cathode materials

Ni-rich lithium nickel–cobalt-manganese oxides(NCM) are considered the most promising cathode materials for lithium-ion batteries(LIBs);however, relatively poor cycling performance is a bottleneck preventing their widespread use in energy systems. In this work, we propose the use of a dually functionalized surface modifier, calcium sulfate(CaSO_(4), CSO), in an efficient one step method to increase the cycling performance of Ni-rich NCM cathode materials. Thermal treatment of LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM811) cathode materials with a CSO precursor allows the formation of an artificial Ca-and SO_(x)-functionalized cathode–electrolyte interphase(CEI) layer on the surface of Ni-rich NCM cathode materials. The CEI layer then inhibits electrolyte decomposition at the interface between the Ni-rich NCM cathode and the electrolyte. Successful formation of the CSO-modified CEI layer is confirmed by scanning electron microscopy(SEM) and Fourier transform infrared(FTIR) spectroscopy analyses, and the process does not affect the bulk structure of the Ni-rich NCM cathode material. During cycling, the CSO-modified CEI layer remarkably decreases electrolyte decomposition upon cycling at both room temperature and 45 ℃, leading to a substantial increase in cycling retention of the cells. A cell cycled with a 0.1 CSO-modified(modified with 0.1% CSO)NCM811 cathode exhibits a specific capacity retention of90.0%, while the cell cycled with non-modified NCM811 cathode suffers from continuous fading of cycling retention(74.0%) after 100 cycles. SEM, electrochemical impedance spectroscopy(EIS), X-ray photoelectron spectroscopy(XPS), and inductively coupled plasma mass spectrometry(ICP-MS) results of the recovered electrodes demonstrate that undesired surface reactions such as electrolyte decomposition and metal dissolution are well controlled in the cell because of the artificial CSO-modified CEI layer present on the surface of Ni-rich NCM811 cathodes.

Trimethoxyboroxine as an electrolyte additive to enhance the 4.5​V cycling performance of a Ni-rich layered oxide cathode

Ni-rich layered oxides are attractive cathode materials for advanced lithium-ion batteries(LIBs)due to their high energy density.However,their large-scale application is seriously hindered by their interfacial instability,especially at a high cut-off potential.Here,we demonstrate that trimethoxyboroxine(TMOBX)is an effective film-forming additive to address the interfacial instability of LiNi0.8Co0.1Mn0.1O_(2)(NCM811)material at a high cut-off voltage of 4.5​V.We find that TMOBX decomposes before carbonate solvent and forms a thin cathode electrolyte interphase(CEI)layer on the surface of the NCM811 material.This TMOBX-formed CEI significantly suppresses electrolyte decomposition at a high potential and inhibits the dissolution of transition metals from NCM811 during cycling.In addition,electron-deficient borate compounds coordinate with anions(PF6^(−),F^(-) etc.)and H2O in the battery,further improving the battery's stability.As a result,adding 1.0​wt%of TMOBX boosts the capacity retention of a Li||NCM811​cell from 68.72%to 86.60%after 200 cycles at 0.5C in the range of 2.8–4.5​V.

In situ analysis of dynamic evolution of the additive-regulated cathode processes in quasi-solid-state lithium-metal batteries

The implementation of high-energy-density storage devices can be facilitated by the built-in situ cathode electrolyte interphase(CEI)between Ni-rich cathodes and gel polymer electrolytes,as it improves interfacial compatibility and enhances security.Understanding the interphase processes of cathode materials,including the structural evolution and the formation of cathode electrolyte interphase upon charging/discharging,is crucial for the design of solid-state lithium batteries.Here,we employed in situ atomic force microscopy(AFM)to investigate the effects of lithium difluoro(oxalato)borate(Li DFOB)on the dynamic evolution of the cathode interphase.In the presence of Li DFOB,the adhesion of nanoparticles and a thin amorphous film on the cathode surface resulted in the formation of a homogeneous CEI,inducing the production of LixPFyas byproducts.Furthermore,the stable CEI formed between the cathode and electrolyte helps maintain the integrity of the composition and structure,reduces interfacial resistance,and improves the cycle stability of the batteries.The visualization of in situ AFM in quasi-solid-state lithium-metal batteries provides valuable insights into the distinct nanostructures and growth dynamics of Li DFOB-mediated CEI on the LiNi_(6)Co_(2)Mn_(2)O_(2) cathode,thus offering a universal and convenient technique for interfacial analysis and a mechanistic understanding of solid-state batteries.

Mechanism of interfacial effects in sodium-ion storage devices

Rechargeable sodium-ion batteries(SIBs)are considered as the next-generation secondary batteries.The performance of SIB is determined by the behavior of its electrode surface and the electrode–electrolyte interface during charging and discharging.Thus,the characteristics of these surfaces and interfaces should be analyzed to realize large-scale energy storage systems with high energy density and long-cycle stability.Although various studies have investigated the properties of electrode materials,few studies have focused on the construction of stable and efficient SIB interfaces,and even fewer have explored the mechanisms of interfacial effects;however,the strategies of regulating interfacial effects are yet to be completely developed.Moreover,the results obtained thus far are insufficient to draw systematic conclusions.The present study reviews the literature on the mechanism of interfacial effects in Na+storage devices.The interfaces in a sodium-ion storage device include a heterogeneous interface between electrode materials,a solid electrolyte interphase,and a cathode electrolyte interphase.The interfacial effects during the intercalation,transformation,and alloy reactions and the resulting overall battery performance were theoretically analyzed.In this review,we aim to provide a theoretical basis for optimizing the structures of electrode surface and electrode–electrolyte interface to optimize the performance of SIBs.In addition,the challenges of investigating interfacial effects and several possible helpful methods and opportunities for studying the mechanisms of interfacial effects in SIBs will be presented.

Stabilizing High-voltage Cathode Materials for Next-generation Li-ion Batteries

The pressing demand for high-energy/power lithium-ion batteries requires the deployment of cathode materials with higher capacity and output voltage.Despite more than ten years of research,high-voltage cathode mate-rials,such as high-voltage layered oxides,spinel LiNi0.5Mn1.5O4,and high-voltage polyanionic compounds still cannot be commercially viable due to the instabilities of standard electrolytes,cathode materials,and cathode electrolyte interphases under high-voltage operation.This paper summarizes the recent advances in addressing the surface and interface issues haunting the application of high-voltage cathode materials.The understanding of the limitations and advantages of different modification protocols will direct the future endeavours on advancing high-energy/power lithium-ion batteries.