Suppression of Co(Ⅱ)ion deposition and hazards:Regulation of SEI film composition and structure

Despite the presence of Li F components in the solid electrolyte interphase(SEI)formed on the graphite anode surface by conventional electrolyte,these Li F components primarily exist in an amorphous state,rendering them incapable of effectively inhibiting the exchange reaction between lithium ions and transition metal ions in the electrolyte.Consequently,nearly all lithium ions within the SEI film are replaced by transition metal ions,resulting in an increase in interphacial impedance and a decrease in stability.Herein,we demonstrate that the SEI film,constructed by fluoroethylene carbonate(FEC)additive rich in crystalline Li F,effectively inhibits the undesired Li^(+)/Co^(2+)ion exchange reaction,thereby suppressing the deposition of cobalt compounds and metallic cobalt.Furthermore,the deposited cobalt compounds exhibit enhanced structural stability and reduced catalytic activity with minimal impact on the interphacial stability of the graphite anode.Our findings reveal the crucial influence of SEI film composition and structure on the deposition and hazards associated with transition metal ions,providing valuable guidance for designing next-generation electrolytes.

Tackling application limitations of high-safetyγ-butyrolactone electrolytes:Exploring mechanisms and proposing solutions

Developing wide-temperature and high-safety lithium-ion batteries(LIBs)presents significant challenges attributed to the absence of suitable solvents possessing broad liquid range and non-flammability properties.γ-Butyrolactone(GBL)has emerged as a promising solvent;however,its incompatibility with graphite anode has hindered its application.This limitation necessitates a comprehensive investigation into the underlying mechanisms and potential solutions.In this study,we achieve a molecular-level understanding of the perplexing interphase formation process by employing in-situ spectroelectrochemical techniques and density function calculations.Our findings reveal that,even at high salt concentrations,GBL consistently occupies the primary Li^(+)solvation sheath,leading to extensive GBL decomposition and the formation of a high-impedance and inorganic-poor solid-electrolyte interphase(SEI)layer.Contrary to manipulating solvation structures,our research demonstrates that the utilization of filmforming additives with higher reduction potential facilitates the pre-establishment of a robust SEI film on the graphite anode.This approach effectively inhibits GBL decomposition and significantly enhances the battery's lifespan.This study provides the first reported intrinsic understanding of the unique GBLgraphite incompatibility and offers valuable insights for the development of wide-temperature and high-safety LIBs.

Stabilizing electrode-electrolyte interface for high-performance SiO_(x) anode by dual electrolyte additive

Macro-and micro-interface instability of SiO_(x)anode caused by its dramatic volume variation during cycling will result in low Coulombic efficiency and rapid capacity degradation.In this work,an organic-inorganic composite interfacial layer rich in benzene ring groups,polyisocyanates,and LiF was obtained on SiO_(x)anode by the introduction of 4-fluorophenyl isocyanate(FPI)and fluoroethylene carbonate(FEC)co-additives in electrolyte.The SiO_(x)anode material shows a capacity retention of 69.2%after 100 cycles at a current density of 1 A g^(-1)and rate capacity of 523 m A h g^(-1)at the current density of 3A g^(-1),while the SiO_(x)anode cycling in reference electrolyte has almost no capacity.

Boosting the cell performance of the SiO_(x)@C anode material via rational design of a Si-valence gradient

Relieving the stress or strain associated with volume change is highly desirable for high-performance SiOx anodes in terms of stable solid electrolyte interphase(SEI)-film growth.Herein,a Si-valence gradient is optimized in SiOx composites to circumvent the large volume strain accompanied by lithium insertion/extraction.SiO_(x)@C annealed at 850℃ has a gentle Si-valence gradient along the radial direction and excellent electrochemical performances,delivering a high capacity of 506.9 mAh g^(−1) at 1.0 A g^(−1) with a high Coulombic efficiency of~99.8%over 400 cycles.Combined with the theoretical prediction,the obtained results indicate that the gentle Si-valence gradient in SiO_(x)@C is useful for suppressing plastic deformation and maintaining the inner connection integrity within the SiO_(x)@C particle.Moreover,a gentle Si-valence gradient is expected to form a stress gradient and affect the distribution of dangling bonds,resulting in local stress relief during the lithiation/delithiation process and enhanced Li-ion kinetic diffusion.Furthermore,the lowest interfacial stress variation ensures a stable SEI film at the interface and consequently increases cycling stability.Therefore,rational design of a Si-valence gradient in SiOx can provide further insights into achieving high-performance SiOx anodes with large-scale production.

Revealing the critical effect of solid electrolyte interphase on the deposition and detriment of Co(Ⅱ) ions to graphite anode

"Dissolution,migration,and deposition"of transition metal ions (TMIs) result in capacity degradation of lithium-ion batteries (LIBs).Understanding such detrimental mechanism of TMIs is critical to the development of LIBs with long cycle life.In most previous works,TMIs were directly introduced into the electrolyte to investigate such a detrimental mechanism.In these cases,the TMIs are deposited directly on the fresh anode surface.However,in the practical battery system,the TMIs are deposited on the anode covered with solid electrolyte interphase (SEI) film.Whether the pre-presence of SEI film on anode surface influences the deposition and detriment of TMIs is unclear.In this work,the deposition of Co element on graphite anode with and without SEI film were systematically studied.The results clearly show that,in comparison with that of fresh graphite (SEI-free),the presence of SEI film aggravates the deposition of Co ions due to the Li^(+)–Co^(2+) ion exchange between the SEI and Co^(2+)-containing electrolyte without the driving of the electric field,leading to faster capacity fading of graphite anode.Therefore,how to regulate electrolytes and film-forming additives to design the components of SEI and prevent its exchange with TMIs,is a crucial way to inhibit the deposition and detriment of TMIs on graphite anode.

Impedance Studies of Spinel LiMn_2O_4 Electrode/electrolyte Interfaces

The formation process of solid electrolyte interphase（SEI） film on spinel LiMn2O4 electrode surface was studied by electrochemical impedance spectroscopy（EIS） during the initial storage in 1 mol/L LiPF6-EC：DMC：DEC electrolyte and in the subsequent first charge-discharge cycle. It has been demonstrated that the SEI film thickness increased with the increase of storage time and spontaneous reactions occurring between spinel LiMn2O4 electrode and electrolyte can be prevented by the SEI film. In the first charge-discharge cycle succeeding the storage, the electrolyte oxidation coupled with Li-ion insertion is evidenced as the main origin to increase the resistance of SEI film. The results also confirm that the variations of the charge transfer resistance（Rot） with the electrode potential（E） can be well described using a classical equation.

Lithiophilic Cu-Li_(2)O matrix on a Cu Collector to Stabilize Lithium Deposition for Lithium Metal Batteries

Lithium metal anode is the most ideal candidate for next-generation energy storage system.However,the uncontrolled dendrite growth,infinite volume expansion,and undesired side reactions lead to serious safety issues and hinder their potential application.Herein,a pre-lithiation strategy is proposed to construct a high-lithiophilic Cu-Li_(2)O matrix on commercial Cu foil.The in situ-generated Li_(2)O promises adequate nucleation sites and strengthens solid electrolyte interphase and lateral lithium deposition.Meanwhile,the existence of 3D matrix reduces the local current density.The synergy effect of Li_(2)O and Cu suppresses the growth of lithium dendrites.As a result,Cu-Li_(2)O matrix reveals an enhanced lithium plating/stripping behavior with Coulombic efficiency of 98.46%after 270 cycles.The symmetrical cell assembled by Li-plated electrodes displays a prolonged lifespan of 1400 h.The work demonstrates a scalable and effective approach for modified current collectors toward stable Li metal anode.

二维sp^(2)碳连接共价有机框架作为无枝晶锂金属电池的人工SEI膜

锂金属负极(LMA)具有前所未有的理论比容量和超低的氧化还原电位,因此锂金属电池(LMBs)得到了广泛的研究.然而,不可控的锂枝晶生长和易碎的固体电解质界面相(SEI)严重阻碍了LMBs的实际商业应用.本文制备了二维sp^(2)碳连接的共价有机框架sp^(2)c-COF,并在LMA表面构建了人工SEI膜,以抑制锂枝晶的形成,并调节界面稳定性.sp^(2)c-COF被设计成沿x和y方向全π共轭的高导电性的结构,从而起到降低界面阻抗、促进Li^(+)通量均匀分布的作用.因此,sp^(2)c-COF改性的对称电池Li^(+)迁移数高达0.85,并且在5mA cm^(-2)电流密度下具有较长的循环寿命(4000 h)和极低的过电位(10 mV).此外还利用原位光学显微镜研究了锂沉积行为,结果表明sp^(2)c-COF能显著提高LMA的界面稳定性.该策略对抑制锂枝晶的形成具有重要的应用价值,可促进COF人工SEI膜的发展.

Enhanced cycle stability of aprotic Li-O_(2) batteries based on a self-defensed redox mediator

LiBr as a promising redox mediator(RM)has been applied in Li-O_(2)batteries to improve oxygen evolution reaction kinetics and reduce overpotentials.However,the redox shuttle of Br_(3)^-can induce the unexpected reactions and thus cause the degradation of LiBr and the corrosion of Li anode,resulting in the poor cyclability and the low round-trip efficiency.Herein,MgBr_(2)is firstly employed with dual functions for Li-O_(2)batteries,which can serve as a RM and a SEI film-forming agent.The Br^(–)is beneficial to facilitating the decomposition of Li_(2)O_(2)and thus decreasing the overpotential.Additionally,a uniform SEI film containing Mg and MgO generates on Li anode surface by the in-situ spontaneous reactions of Mg^(2+)and Li anode in an O_(2)environment,which can suppress the redox shuttle of Br_(3)^-and improve the interface stability of Li anode and electrolyte.Benefiting from these advantages,the cycle life of Li-O_(2)battery with MgBr_(2)electrolyte is significantly extended.

Uniform lithium deposition induced by copper phthalocyanine additive for durable lithium anode in lithium-sulfur batteries

Copper phthalocyanine(CuPc)is adopted as an electrolyte additive to stabilize lithium anode for lithiumsulfur(Li-S)batteries.CuPc with a planar molecular structure and lithiophilic N-containing group,is likely to be adsorbed on the surface of Li anode to form a coating layer,which can restrict the direct contact between Li anode and solvents,and guide the uniform deposition of Li^(+)ions.The Li||Li symmetric cells demonstrate a stable cycle performance,and Li||Cu cells show high Coulombic efficiencies.In Li-S batteries,the formed stable solid-electrolyte interface(SEI)film containing copper sulfides can protect Li anode from the polysulfide corrosion and side reactions with the electrolyte,leading to the compact and smooth surface morphology of Li anode.Therefore,the Li-S batteries with CuPc additive deliver much higher capacity,better cycle performance and rate capability as compared to the one without CuPc additive.

Secondary electron emission characteristics of graphene films with copper substrate

For modern and future circular accelerators, especially high-intensity proton synchrotrons or colliders, the electron cloud effect is a key issue. So, in order to reduce the electron cloud effect, exploring very low secondary electron yield （SEY） material or coating used in vacuum tubes becomes necessary. In this article, we studied the SEY characteristics of graphene films with different thicknesses which were deposited on copper substrates using chemical vapor deposition. The SEY tests were done at temperatures of 25 ℃and vacuum pressure of （2-6）x 10-9 torr. The properties of the deposited graphene films were investigated by X-ray photoelectron spectroscopy （XPS） and Raman spectroscopy. The SEY curves show that the number of graphene layers has a great effect on the SEY of graphene films. The maximum SEY of graphene films decreases with the increase of the number of layers. The maximum SEY of 6-8 layers of graphene film is 1.25. These results have a great significance for next-generation particle accelerators.

Gel electrolyte via in situ polymerization to promote durable lithium-air batteries

Aprotic lithium-air batteries(LABs)have been known as the holy grail of energy storage systems due to their extremely high energy density.However,their real-world application is still hindered by the great challenges from the Li anode side,like dendrite growth and corrosion reactions,thus a pure oxygen atmosphere is usually adopted to prolong the lifetime of LABs,which is a major obstacle to fully liberate the energy density advantages of LABs.Here,a gel polymer electrolyte has been designed through in-situ polymerization of 1,3-dioxolane(DOL)by utilizing the unique semi-open nature of LABs to protect the Li anode to conquer its shortcomings,enabling the high-performance running of LABs in the ambient air.Unlike common liquid electrolytes,the in-situ formed gel polymer electrolyte could facilitate constructing a gradient SEl film with the gradual decrease of organic components from top to bottom,preventing the Li anode from dendrite growth and air-induced corrosion reactions and thus realizing durable Li repeated plating/stripping(2000h).Benefiting from the anode protection effects of the gradient SEI film,the LABs display a long lifetime of 17o cycles,paving an avenue for practical,long-term,and high-efficiency operation of LABs.