Stabilizing Solid-state Lithium Metal Batteries through In Situ Generated Janus-heterarchical LiF-rich SEI in Ionic Liquid Confined 3D MOF/Polymer Membranes

Pursuing high power density lithium metal battery with high safety is essential for developing next-generation energy-storage devices, but uncontrollable electrolyte degradation and the consequence formed unstable solid-electrolyte interface (SEI) make the task really challenging. Herein, an ionic liquid (IL) confined MOF/Polymer 3D-porous membrane was constructed for boosting in situ electrochemical transformations of Janus-heterarchical LiF/Li₃N-rich SEI films on the nanofibers. Such a 3D-Janus SEI-incorporated into the separator offers fast Li⁺ transport routes, showing superior room-temperature ionic conductivity of 8.17×10⁻⁴ S cm⁻¹ and Li⁺ transfer number of 0.82. The cryo-TEM was employed to visually monitor the in situ formed LiF and Li₃N nanocrystals in SEI and the deposition of Li dendrites, which is greatly benefit to the theoretical simulation and kinetic analysis of the structural evolution during the battery charge and discharge process. In particular, this membrane with high thermal stability and mechanical strength used in solid-state Li||LiFePO₄ and Li||NCM-811 full cells and even in pouch cells showed enhanced rate-performance and ultra-long life spans.     

Reforming the Uniformity of Solid Electrolyte Interphase by Nanoscale Structure Regulation for Stable Lithium Metal Batteries

The stability of high-energy-density lithium metal batteries depends on the uniformity of solid electrolyte interphase (SEI) on lithium metal anodes. Rationally improving SEI uniformity is hindered by poorly understanding the effect of structure and components of SEI on its uniformity. Herein, a bilayer structure of SEI formed by isosorbide dinitrate (ISDN) additives in localized high-concentration electrolytes was demonstrated to improve SEI uniformity. In the bilayer SEI, LiN_xO_y generated by ISDN occupies top layer and LiF dominates bottom layer next to anode. The uniformity of lithium deposition is remarkably improved with the bilayer SEI, mitigating the consumption rate of active lithium and electrolytes. The cycle life of lithium metal batteries with bilayer SEI is three times as that with common anion-derived SEI under practical conditions. A prototype lithium metal pouch cell of 430 Wh kg⁻¹ undergoes 173 cycles. This work demonstrates the effect of a reasonable structure of SEI on reforming SEI uniformity.     

Solubilization of SEI lithium salts in alkylcarbonate solvents

The SEI (Solid Electrolyte Interphase) at the surface of electrodes in lithium-ion batteries is composed of various lithium compounds, organic or mineral, which have a direct impact on cycling performance. The main lithium species constituting the SEI and selected in this study are lithium fluoride LiF, lithium carbonate Li₂CO₃, lithium hydroxide LiOH, lithium oxide Li₂O, lithium methoxide LiOCH₃ and lithium ethoxide LiOC₂H₅. Their solubilities were determined in ethylene, propylene, dimethyl, diethyl and vinylene carbonates (EC, PC, DMC, DEC and VC) and in one of their mixtures commonly used in lithium-ion batteries (EC/PC/3DMC) by mean of atomic absorption spectroscopy (AAS). These solutions were also investigated by EIS (Electrochemical Impedance Spectroscopy) and conductimetry measurements. Results show that while solubilization properties differ between LiF and other lithium compounds considered, their association pattern in solution is identical and solutions are mainly constituted of quadrupolar aggregates.     

A Sustainable Solid Electrolyte Interphase for High-Energy-Density Lithium Metal Batteries Under Practical Conditions

High-energy-density Li metal batteries suffer from a short lifespan under practical conditions, such as limited lithium, high loading cathode, and lean electrolytes, owing to the absence of appropriate solid electrolyte interphase (SEI). Herein, a sustainable SEI was designed rationally by combining fluorinated co-solvents with sustained-release additives for practical challenges. The intrinsic uniformity of SEI and the constant supplements of building blocks of SEI jointly afford to sustainable SEI. Specific spatial distributions and abundant heterogeneous grain boundaries of LiF, LiN_xO_y, and Li₂O effectively regulate uniformity of Li deposition. In a Li metal battery with an ultrathin Li anode (33 μm), a high-loading LiNi_0.5Co_0.2Mn_0.3O₂ cathode (4.4 mAh cm⁻²), and lean electrolytes (6.1 g Ah⁻¹), 83 % of initial capacity retains after 150 cycles. A pouch cell (3.5 Ah) demonstrated a specific energy of 340 Wh kg⁻¹ for 60 cycles with lean electrolytes (2.3 g Ah⁻¹).     

Lithium Nitrate Regulated Sulfone Electrolytes for Lithium Metal Batteries

The electrolytes in lithium metal batteries have to be compatible with both lithium metal anodes and high voltage cathodes, and can be regulated by manipulating the solvation structure. Herein, to enhance the electrolyte stability, lithium nitrate (LiNO₃) and 1,1,2,2-tetrafuoroethyl-2′,2′,2′-trifuoroethyl(HFE) are introduced into the high-concentration sulfolane electrolyte to suppress Li dendrite growth and achieve a high Coulombic efficiency of >99 % for both the Li anode and LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) cathodes. Molecular dynamics simulations show that NO₃⁻ participates in the solvation sheath of lithium ions enabling more bis(trifluoromethanesulfonyl)imide anion (TFSI⁻) to coordinate with Li⁺ ions. Therefore, a robust LiN_xO_y−LiF-rich solid electrolyte interface (SEI) is formed on the Li surface, suppressing Li dendrite growth. The LiNO₃-containing sulfolane electrolyte can also support the highly aggressive LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) cathode, delivering a discharge capacity of 190.4 mAh g⁻¹ at 0.5 C for 200 cycles with a capacity retention rate of 99.5 %.     

Electrochemical and in-situ X-ray diffraction studies of Ti3C2Tx MXene in ionic liquid electrolyte

2D titanium carbide (Ti₃C₂T_x MXene) showed good capacitance in both organic and neat ionic liquid electrolytes, but its charge storage mechanism is still not fully understood. Here, electrochemical characteristics of Ti₃C₂T_x electrode were studied in neat EMI-TFSI electrolyte. A capacitive behavior was observed within a large electrochemical potential range (from − 1.5 to 1.5 V vs. Ag). Intercalation and de-intercalation of EMI⁺ cations and/or TFSI⁻ anions were investigated by in-situ X-ray diffraction. Interlayer spacing of Ti₃C₂T_x flakes decreases during positive polarization, which can be ascribed to either electrostatic attraction effect between intercalated TFSI⁻ anions and positively charged Ti₃C₂T_x nanosheets or steric effect caused by de-intercalation of EMI⁺ cations. The expansion of interlayer spacing when polarized to negative potentials is explained by steric effect of cation intercalation.     

三维多孔碳负载氧化锡并协同氟化锂制备高性能锂离子阳极

新型多孔碳纳米片/碳纳米管（PC/CNT）材料表现出丰富的分级孔隙结构,具有较高的氧化锡（SnO₂）负载量。通过PC和CNT交联形成的三维结构能够有效地提高锂离子传输速率和电子的传导。此外,在电极中掺杂的氟化锂（LiF）不仅能够降低SnO₂-PC/CNT-LiF电极的电荷转移电阻,而且还能补充SEI膜形成时消耗的Li⁺,降低不可逆容量,增强SEI膜的稳定性。研究表明,SnO₂-PC/CNT-LiF电极在电流密度为100 mA·g^-1时,首次可逆比容量达到1 642.98 mAh·g^-1,活性物质的利用率高达90.12%,循环100次后,放电比容量仍然达到745.11 mAh·g^-1,且库仑效率仍然保持在95.1%以上,显示出优异的倍率和循环性能。     

三维多孔碳负载氧化锡并协同氟化锂制备高性能锂离子阳极

新型多孔碳纳米片/碳纳米管(PC/CNT)材料表现出丰富的分级孔隙结构,具有较高的氧化锡(SnO₂)负载量。通过PC和CNT交联形成的三维结构能够有效地提高锂离子传输速率和电子的传导。此外,在电极中掺杂的氟化锂(LiF)不仅能够降低SnO₂-PC/CNT-LiF电极的电荷转移电阻,而且还能补充SEI膜形成时消耗的Li+,降低不可逆容量,增强SEI膜的稳定性。研究表明,SnO₂-PC/CNT-LiF电极在电流密度为100 mA·g^-1时,首次可逆比容量达到1642.98 mAh·g^-1,活性物质的利用率高达90.12%,循环100次后,放电比容量仍然达到745.11 mAh·g^-1,且库仑效率仍然保持在95.1%以上,显示出优异的倍率和循环性能。     

Polymérisation anionique des diènes. V. Configurations des oligopolyisoprènyl–lithium en milieu benzènique et en présence de dioxanne. Étude par résonance magnétique protonique: Haute résolution (RMP-HR)

By PMR, three dioxane–Li⁺ complexes have been detected for the oligopolyisoprenyl–lithium–dioxane mixtures in benzene solution. The (4-1) living end isomerizes into the cis configuration when the sample temperature or the dioxane concentration is increased, but the isomerization phenomenon is reversible only if dioxane/Li⁺ ratios are smaller than unity. The specificity of the vinyl addition (86%), mainly (4-3) (70%), due to the stronger negative charge at the C_γ carbon atom is effective only at low temperature (+15°C). At higher temperature, because of the steric hindrance of the methyl group, this stereospecificity decreases.     

Effects of Solid Electrolyte Interphase Components on the Reduction of LiFSI over Lithium Metal

The use of a lithium metal anode still presents a challenging chemistry and engineering problem that holds back next generation lithium battery technology. One of the issues facing lithium metal is the presence of the solid electrolyte interphase (SEI) layer that forms on the electrode creating a variety of chemical species that change the properties of the electrode and is closely related to the formation and growth of lithium dendrites. In order to advance the scientific progress of lithium metal more must be understood about the fundamentals of the SEI. One property of the SEI that is particularly critical is the passivating behavior of the different SEI components. This property is critical to the continued formation of SEI and stability of the electrolyte and electrode. Here we report the investigation of the passivation behavior of Li₂O, Li₂CO_3, LiF and LiOH with the lithium salt LiFSI. We used large computational chemistry models that are able to capture the lithium/SEI interface as well as the SEI/electrolyte interface. We determined that LiF and Li₂CO₃ are the most passivating of the SEI layers, followed by LiOH and Li₂O. These results match previous studies of other Li salts and provide further examination of LiFSI reduction.     

Charge Density Overcomes Steric Hindrance of Ferrocene Surfactant in Switchable Oil-in-Dispersion Emulsions

A ferrocene surfactant can be switched between single and double head form (FcN⁺C₁₂/Fc⁺N⁺C₁₂) triggered by redox reaction. FcN⁺C₁₂ can neither stabilize an O/W emulsion alone nor an oil-in-dispersion emulsion in combination with alumina nanoparticles due to the steric hindrance of the ferrocene group. However, such steric hindrance can be overcome by increasing the charge density in Fc⁺N⁺C₁₂, so that oil-in-dispersion emulsions can be co-stabilized by Fc⁺N⁺C₁₂ and alumina nanoparticles at very low concentrations (1×10⁻⁷ M (≈50 ppb) and 0.001 wt %, respectively). Not only can reversible formation/destabilization of oil-in-dispersion emulsions be achieved by redox reaction, but also reversible transformation between oil-in-dispersion emulsions and Pickering emulsions can be obtained through reversing the charge of alumina particles by adjusting the pH. The results provide a new protocol for the design of surfactants for stabilization of smart oil-in-dispersion emulsions.     

富钴多孔碳制备高性能氧化锡阳极

通过一步碳化法制备富含氧化钴(CoO)的多孔碳(PC(Co))材料作为氧化锡(SnO_2)的载体。PC(Co)材料具有丰富的多孔结构,能够高效承载SnO_2。不仅如此,PC(Co)材料中的氧化钴能够作用于电化学反应,有效降低LiO_2的生成。但CoO参与反应会消耗大量的锂离子,所以选择添加氟化锂(LiF),在补锂的同时能够增强SEI膜的稳定性。SnO_2-PC(Co)/LiF电极活性物质的负载量高达1.51 mg·cm~(-2)。电化学测试表明,在电流密度为100 mAh·g~(-1)时,SnO_2-PC(Co)/LiF电极首次放电比容量达到1 653.63mAh·g~(-1),活性物质的利用率高达93.14%。循环100次后,放电比容量仍然达到1 070.68 mAh·g~(-1),且库仑效率仍然保持在99.81%。     

Reconstruction of Solid Electrolyte Interphase with SrI2 Reactivates Dead Li for Durable Anode-Free Li-Metal Batteries

Without excess Li, anode-free Li-metal batteries (AFLMBs) have been proposed as the most likely solution to realizing highly-safe and cost-effective Li-metal batteries. Nevertheless, short cyclic life puzzles conventional AFLMBs due to anodic dead Li accumulation with a local current concentration induced by irreversible electrolyte depletion, insufficient active Li reservoir and slow Li⁺ transfer at the solid electrolyte interphase (SEI). Herein, SrI₂ is introduced into carbon paper (CP) current collector to effectively suppress dead Li through synergistic mechanisms including reversible I⁻/I₃⁻ redox reaction to reactivate dead Li, dielectric SEI surface with SrF₂ and LiF to prevent electrolyte decomposition and highly ionic conductive (3.488 mS cm⁻¹) inner layer of SEI with abundant LiI to enable efficient Li⁺ transfer inside. With the SrI₂-modified current collector, the NCM532/CP cell delivers unprecedented cyclic performances with a capacity of 129.2 mAh g⁻¹ after 200 cycles.     

A pentafluorophenylboron oxalate additive in non-aqueous electrolytes for lithium batteries

A novel compound named pentafluorophenylboron oxalate (PFPBO) has been synthesized. PFPBO has a unique molecular structure containing a boron atom center with electron deficiency and an oxalate group. It is found that when PFPBO is used as additive, the solubility of lithium fluoride (LiF) or lithium oxide (Li₂O, Li₂O₂) in propylene carbonate (PC) and dimethyl carbonate (DMC) solvents can be increased dramatically. The new electrolytes show high ionic conductivity, high lithium ion transference number and good compatibility with LiMn₂O₄ cathode and MCMB anode. PFPBO was synthesized with the designed structure to act as a bi-functional additive: boron-based anion receptor (BBAR) additive and stable solid electrolyte interphase (SEI) formation additive in PC-based electrolytes. The results show it does possess these two desired functionalities.     

Fluoroethylene Carbonate Enabling a Robust LiF‐rich Solid Electrolyte Interphase to Enhance the Stability of the MoS2 Anode for Lithium‐Ion Storage

As a high‐capacity anode for lithium‐ion batteries (LIBs), MoS₂ suffers from short lifespan that is due in part to its unstable solid electrolyte interphase (SEI). The cycle life of MoS₂ can be greatly extended by manipulating the SEI with a fluoroethylene carbonate (FEC) additive. The capacity of MoS₂ in the electrolyte with 10 wt % FEC stabilizes at about 770 mAh g^?1 for 200 cycles at 1 A g^?1, which far surpasses the FEC‐free counterpart (ca. 40 mAh g^?1 after 150 cycles). The presence of FEC enables a robust LiF‐rich SEI that can effectively inhibit the continual electrolyte decomposition. A full cell with a LiNi_0.5Co_0.3Mn_0.2O₂ cathode also gains improved performance in the FEC‐containing electrolyte. These findings reveal the importance of controlling SEI formation on MoS₂ toward promoted lithium storage, opening a new avenue for developing metal sulfides as high‐capacity electrodes for LIBs.     

Ordered and Fast Ion Transport of Quasi-solid-state Electrolyte with Regulated Coordination Strength for Lithium Metal Batteries

Polymer based quasi-solid-state electrolyte (QSE) has attracted great attention due to its assurance for high safety of rechargeable batteries including lithium metal batteries (LMB). However, it faces the issue of low ionic conductivity of electrolyte and solid-electrolyte-interface (SEI) layer between QSE and lithium anode. Herein, we firstly demonstrate that the ordered and fast transport of lithium ion (Li⁺) can be realized in QSE. Due to the higher coordination strength of Li⁺ on tertiary amine (−NR₃) group of polymer network than that on carbonyl (−C=O) group of ester solvent, Li⁺ can diffuse orderly and quickly on −NR₃ of polymer, significantly increasing the ionic conductivity of QSE to 3.69 mS cm⁻¹. Moreover, −NR₃ of polymer can induce in situ and uniform generation of Li₃N and LiN_xO_y in SEI. As a result, the Li||NCM811 batteries (50 μm Li foil) with this QSE show an excellent stability of 220 cycles at ≈1.5 mA cm⁻², 5 times to those with conventional QSE. LMBs with LiFePO₄ can stably run for ≈8300 h. This work demonstrates an attractive concept for improving ionic conductivity of QSE, and also provides an important step for developing advanced LMB with high cycle stability and safety.     

Interfacial Speciation Determines Interfacial Chemistry: X-ray-Induced Lithium Fluoride Formation from Water-in-salt Electrolytes on Solid Surfaces

Super-concentrated “water-in-salt” electrolytes recently spurred resurgent interest for high energy density aqueous lithium-ion batteries. Thermodynamic stabilization at high concentrations and kinetic barriers towards interfacial water electrolysis significantly expand the electrochemical stability window, facilitating high voltage aqueous cells. Herein we investigated LiTFSI/H₂O electrolyte interfacial decomposition pathways in the “water-in-salt” and “salt-in-water” regimes using synchrotron X-rays, which produce electrons at the solid/electrolyte interface to mimic reductive environments, and simultaneously probe the structure of surface films using X-ray diffraction. We observed the surface-reduction of TFSI⁻ at super-concentration, leading to lithium fluoride interphase formation, while precipitation of the lithium hydroxide was not observed. The mechanism behind this photoelectron-induced reduction was revealed to be concentration-dependent interfacial chemistry that only occurs among closely contact ion-pairs, which constitutes the rationale behind the “water-in-salt” concept.     

酯加氢反应中影响羧基活化的因素

通过浸渍法制备4%Ru-9%La/γ-Al2O3催化剂,采用X射线衍射(XRD),X射线光电子能谱(XPS)和透射电子显微镜(TEM)对其结构进行表征.将该催化剂用于丙酸甲酯的加氢反应,分别考察了溶剂、无机盐添加剂、底物空间因素及电子因素对酯加氢反应的影响.发现以水为溶剂以及添加Co(NO3)2对丙酸甲酯加氢都显示出明显的促进作用,底物的转化率及丙醇的选择性随之增加.这是由于水及适量Co2+的引入能极化底物分子的C=O键,有利于活化氢对羧基碳原子的进攻,改善催化剂的性能.此外,底物分子中吸电子基团能提高羧基碳原子的正电性,也有利于加氢反应的进行;而增大底物分子空间位阻,不利于底物在催化剂上的吸附,催化反应速率下降.     

First-principles study of the effect of mechanical strength on ion transport in La-doped LiF-SEI on the Li (001) surface

The solid electrolyte interface (SEI) plays an important role in the lithium–sulfur battery system. It not only protects the stability of the lithium metal anode interface but also inhibits the growth of lithium dendrites during charge and discharge. The relationship between the shape of the SEI and the transport behavior of lithium ions affects the homogeneity of lithium dendrites. In this work, first-principles calculations are used to determine the stable structure and transport properties of the La-doped LiF solid electrolyte interface (La–LiF SEI) on the Li substrate. For the vertical transport of Li ions within the La–LiF SEI, the transport of Li ions in the grain boundary and that in the crystal grain was calculated separately. Regarding the plane diffusion behavior of Li ions between the La–LiF SEI and the lithium anode, the diffusion of Li ions on the surface and interface of the lithium anode were calculated. The effect of critical tensile strain on the diffusion of Li ions on the surface and interface was investigated. The results show that doping with La solves the problem of excessive periodic grain boundary gaps caused by the difference between LiF and Li lattices during the deposition process. The periodic gap is reduced from 0.478 nm to 0.306 nm after La doping. By comparing the migration energy barriers of each path, it is found that lithium ions are more likely to be inserted and extracted at the La–LiF SEI grain boundary. The reason is that the existence of the rare earth element La causes the grain boundary to have a more stable vacancy structure and a smaller transport energy barrier (0.789 eV). The critical tensile strain reduces the diffusion energy barrier (0.813 eV) of Li ions on the surface of the lithium metal anode, which promotes the fast diffusion and uniform deposition of Li ions between the interfaces. The establishment of SEI transport characteristics under the coupling conditions of mechanical stretching and ion transport is expected to improve the Li deposition behavior.     

In-Situ Constructing A Heterogeneous Layer on Lithium Metal Anodes for Dendrite-Free Lithium Deposition and High Li-ion Flux

Constructing efficient artificial solid electrolyte interface (SEI) film is extremely vital for the practical application of lithium metal batteries. Herein, a dense artificial SEI film, in which lithiophilic Zn/Li_xZn_y are uniformly but nonconsecutively dispersed in the consecutive Li⁺-conductors of Li_xSiO_y, Li₂O and LiOH, is constructed via the in situ reaction of layered zinc silicate nanosheets and Li. The consecutive Li⁺-conductors can promote the desolvation process of solvated-Li⁺ and regulate the transfer of lithium ions. The nonconsecutive lithiophilic metals are polarized by the internal electric field to boost the transfer of lithium ions, and lower the nucleation barrier. Therefore, a low polarization of ≈50 mV for 750 h at 2.0 mA cm⁻² in symmetric cells, and a high capacity retention of 99.2 % in full cells with a high lithium iron phosphate areal loading of ≈13 mg cm⁻² are achieved. This work offers new sights to develop advanced alkali metal anodes for efficient energy storage.