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Lithium salt‐type additives have triggered widespread concern because of their excellent film‐forming properties to construct a solid electrolyte interphase (SEI) with high stability and low impedance. However, little attention has been paid to enhancing the utilization efficiency of the expensive lithium salt‐type additives. Herein, the main factor limiting the decomposition of lithium difluoro bis(oxalate) phosphate (LiDFBOP) during the initial SEI formation is clarified. Combining the electrochemical analysis results and quantum chemistry calculations, it is inferred that LiDFBOP preferentially decomposes and generates soluble products accumulating on the graphite surface due to diffusion control kinetics. The excessive aggregation of these products on the electrode inhibits the subsequent continuous decomposition of LiDFBOP. An ultrasound auxiliary method is developed to accelerate the soluble product diffusion and promote the reduction decomposition of LiDFBOP increasing the inorganics content of Li2C2O4 and LiF in the formed SEI. Accordingly, the cell performance is greatly improved compared with that without ultrasound: Li/graphite cells with ultrasound can retain 60.60% of initial capacity after 500 cycles at 1C. This work not only pioneers the study of improving the utilization efficiency of additives contributing to reducing the electrolytes cost but also has direct guiding significance in the targeted regulation of interface properties. [ABSTRACT FROM AUTHOR]

• Directly introducing LiNO 3 into the Gr slurry overcomes its solubility limit. • Sustained releasing LiNO 3 from the Gr reservoir constitutes a virtuous circle in LCE. • Stronger bind of NO 3 –-Li+ weakens shielding effect, inhibiting solvents decomposition. • Increased interaction between anions and Li+ generates a Li 3 N&LiF-rich SEI. • Expanding the LCEs application by regulating the solvation and stabilizing interface. The high de-solvation energy derived from the solvent-rich Li+ solvation sheath and the resultant porous organic-rich electrode/electrolyte interface has hindered the commercialization of low-concentration electrolytes (LCEs). Here, unlike the common method so far reported, we invent an approach of sustained releasing LiNO 3 from the graphite (Gr) anode reservoir to optimize the solvation structure and form a stable interface in LCEs. The solubility limit can be overcome by introducing LiNO 3 directly in the Gr slurry. Moreover, the stronger binding energy between NO 3 – and Li+ drives NO 3 – enter the Li+ solvation sheath, weakening the shielding effect of solvent on Li+, and surprisingly increasing the coordination of PF 6 - to Li+. Thermodynamically, the corresponding lowest unoccupied molecular orbital energy levels of anions decrease, reducing the de-solvation energy of Li+ and forming a Li 3 N&LiF-rich solid electrolyte interface (SEI). This inorganic-rich SEI demonstrates advantages of inhibiting the decomposition of solvent and facilitating the transmission of Li+. As a result, the cell with Gr anode containing 1 wt% LiNO 3 exhibits superior cycle performance in LCE, almost no degradation within 200 cycles, even higher than that in conventional concentration electrolyte. More importantly, the continuous consumption of NO 3 – in turn promotes its sustained redissolution from the anode, constituting a virtuous circle of regulating solvation structure, stabilizing interface and improving battery performance. This work blazes a new trail to revive lithium salt additives with low solubility, and expands the design strategy and application prospect of LCEs by building the bridges between regulating the solvation structure and constructing favorable electrode/electrolyte interface. [ABSTRACT FROM AUTHOR]

The prevailing account attributes the positive effects of boron-based additives on solid electrolyte interface (SEI) layers to its solid products by prior decomposition. However, this study proves the BOF2− anion, a soluble product of film formation additive of lithium difluoro(oxalato)borate, plays a crucial role in improving the SEI layer. Specifically, BOF2− suppresses the excessive decomposition of salt anions by aggregating on the electrode surface. Meanwhile, it catalyzes the reduction of ethylene carbonate, leading to improving the stability of the interface. In the end, ultrasound shaking is used to generate more BOF2− anion and increase the cycle performance of cells at a high rate as excepted. This work helps to understand the effects of soluble products on the SEI forming process and provides new insights for improving the stability of electrode electrolyte interfaces. [Display omitted] • An effect mechanism of SEI formation is proved from the view of soluble product. • The soluble product of LiDFOB prevents its excessive decomposition. • The soluble product catalyzes the reduction of EC. [ABSTRACT FROM AUTHOR]

To discuss the source of sulfolane (SL) in decreasing the interface resistance of Li/mesophase carbon microbeads cell with lithium bis(oxalate)borate (LiBOB)-based electrolyte, the morphology and the composition of the solid electrolyte interphase (SEI) layer on the surface of carbonaceous anode material have been investigated. Compared with the cell with 0.7 mol l−1 LiBOB-ethylene carbonate/ethyl methyl carbonate (EMC) (1 : 1, v/v) electrolyte, the cell with 0.7 mol l−1 LiBOB-SL/EMC (1 : 1, v/v) electrolyte shows better film-forming characteristics in SEM (SEI) spectra. According to the results obtained from Fourier transform infrared spectroscopy, XPS, and density functional theory calculations, SL is reduced to Li2SO3 and LiO2S(CH2)8SO2Li through electrochemical processes, which happens prior to the reduction of either ethylene carbonate or EMC. It is believed that the root of impedance reduction benefits from the rich existence of sulfurous compounds in SEI layer, which are better conductors of Li+ ions than analogical carbonates. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Because of the higher delithiation capacity, Li 5 FeO 4 (LFO) can be used as sacrificial prelithiation additive to compensate the initial capacity loss caused by the formation of solid electrolyte interphase in lithium-ion batteries (LIBs). However, the extremely poor air stability and severe phase transition after Li+ deintercalation make it difficult for LFO to be applied in prelithiation engineering practice. Herein, the residual alkali layer generated on the LFO due to air exposure is directly converted into a Li 3 PO 4 layer by a one-pot solid–liquid reaction. The as-obtained surface phosphorylated LFO (LP-LFO) ensures high air stability and effective prelithiation capability. Introducing only 3 wt% LP-LFO to the LiFePO 4 /Li half-cell can maximally replenish the active Li+ loss and the initial coulombic efficiency, displaying a 9.9 % increase in the initial charge capacity. Moreover, the Li 3 PO 4 coating enables LP-LFO to be a fast ionic conductor, not only inhibiting the phase transition of LFO, but also improving the electronic and ionic conductivity of the electrode, which is confirmed by the complementary tests of galvanostatic intermittent titration technique and electrochemical impedance spectroscopy, as well as the structure and morphology characterization. As a result, the LiFePO 4 /Li half-cell with LP-LFO additive exhibits a higher rate capability (144 mAh g−1 at 2 C) and cycle stability (157 mAh g−1 after 100 cycles at 0.1 C). And a 17.4 % increase in the discharge capacity and a 12.7 % increase in energy density after 200 cycles for the 3 wt% LP-LFO-added LiFePO 4 ||graphite full cell is also achieved. This work provides a facile and efficient conversion strategy for the air-instable electrode additives, and furtherly broadens their industrial application prospect in high energy density LIBs. [ABSTRACT FROM AUTHOR]

Silicon(Si)-based anodes exhibit higher energy density than traditional graphite anodes but suffer from significant volume changes during lithiation/delithiation, destabilizing the solid electrolyte interface (SEI) and reducing cycle stability. This study explores the effect of 1,3,6-hexane trinitrile (HTCN) on mitigating Si@C electrode expansion. The inclusion of HTCN modifies the original solvation structure of Li+, and the HTCN additive undergoes preferential coordination with Li+ because its binding energy with Li+ is larger than that of ethylene carbonate (EC). This lowers the lowest unoccupied molecular orbital (LUMO) of the HTCN-containing solvation structure, promoting preferential reduction decomposition on the anode surface. This process increases inorganic Li 3 N formation and produces a rich carbon-organic SEI film, effectively reducing electrolyte decomposition and Si@C anode expansion from 72.98 % to 4.46 %. Adding 1 % HTCN to Si@C/Li half-cells enhances capacity retention to 72.4 % after 100 cycles at 0.2C, significantly outperforming cells without HTCN (50.9 %). This study provides a new idea for constructing high-performance SEI films to inhibit electrode expansion by adjusting the solvation structure of Li+. •HTCN preferentially coordinates with Li+, altering the solvation structure. •The STD+1 % HTCN electrolyte preferentially reduces to form Li(PF 6) 1 (HTCN) 3. •1 % HTCN addition boosts SEI's inorganic Li 3 N, enhancing Li+ diffusion regulation. •HTCN boosts carbon-rich components, reducing expansion and interfacial cracking. [ABSTRACT FROM AUTHOR]

While the solid electrolyte interphase (SEI) film in carbonate-based lithium-ion batteries (LIBs) has been extensively studied, less is known about the formation of SEI due to the complexity and instability of interfacial chemical reactions between Li+ and solvent. This study presents new insights into the formation mechanism of SEI film on graphite anode in ethylene carbonate (EC) and dimethyl carbonate (DMC) co-solvent-based electrolytes. The potential-resolved in-situ electrochemical impedance spectroscopy technology and density functional theory calculations combined with multi-sweep cyclic voltammetry are utilized to confirm that EC prefers to solvate with Li+. Then, a large amount of Li+-EC and a small amount of Li+-DMC solvent molecules undergo solvent migration process and de-solvation at the electrode/electrolyte interface. It was found that Li+-DMC is preferentially de-solvation and reduced to form an unstable SEI film, while Li+-EC inhibits the reduction of DMC and turns the reduction process to be diffusion-controlled. This work provides a fresh perspective on the formation of SEI film by Li+-solvent interaction, which could guide the construction of a stable interface by regulating the Li+-solvation kinetic for high-performance LIBs. [ABSTRACT FROM AUTHOR]

Lithium-ion batteries (LIBs) suffering from severe performance degradation because of the unstable solid electrolyte interphase (SEI) on the anode at low temperature restricts their practical applications. Herein, lithium difluorophosphate (LiDFP) as the additive is introduced into lithium bis(fluorosulfonyl) imide (LiFSI) based electrolyte to improve the electrochemical performance of graphite/Li half-cells at low temperature. Contrary to the popular perception, we reveal at low temperature that LiDFP attenuates the decomposition of LiFSI by competing the hydrolysis reaction with LiFSI to generate a SEI film rich in LiF and Li 3 PO 4 during prolonged cycling, rather than preferential decomposition. Additionally, the possible reaction equations and the interaction mechanism between LiDFP and LiFSI are proposed by combining in situ electrochemical impedance electrochemical (PRIs-EIS) tests, spectroscopic characterization techniques and density functional theory (DFT) calculations. It is demonstrated that the strong binding energy between LiF (from the decomposition of LiFSI) and LiDFP makes LiDFP easier deposit on the electrode surface. This work demonstrates the synergistic role combining the complementary advantage of film-forming additives and main lithium salts to improve the interfacial stability of LIBs at low temperature. Additionally, it can also pave the new pathway for the design of low temperature electrolytes in LIBs. [Display omitted] • The synergy effect of additive LiDFP and LiFSI improves the interface stability. • The competitive hydrolysis reaction of LiDFP and LiFSI is elucidated. • The strong binding energy between LiF and LiDFP enables LiDFP easier deposit. • The stable and robust interface can avoid the aggregation of organics. [ABSTRACT FROM AUTHOR]

[Display omitted] • A potential resolved in-situ electrochemical impedance technique was built. • The solid electrolyte interface layer still be formed and decomposed after long cycle. • The contribution of the interface layer compounds to impedance was distinguished. An understanding of the formation and evolution of the solid electrolyte interface (SEI) layer is still a challenge for lithium ion batteries due to its complexity and non-uniformity. Herein, an in-situ electrochemical technique, named potential resolved in-situ electrochemical impedance spectroscopy (PRIs-EIS), have developed to correlate the Nyquist and Bode plot changes with the voltammetric scan, which is then used to determine the correspondence between circuit components and SEI layer composition. Moreover, the formation and re-oxidation of organic compounds in the SEI layer are studied in conjunction with the electrochemical quartz crystal microbalance characteristics. In particular, it is shown that more inorganic compounds accumulate in the SEI layer as the cycle continues, repairing the pore structure, but decreasing the toughness of the SEI layer. The PRIs-EIS technique is shown to be a powerful, useful and cost-effective tool to illuminate the interfacial reaction mechanism, and the results from this technique aid in the evaluation and design of electrolyte systems. [ABSTRACT FROM AUTHOR]

Abstract: As a promising salt for lithium-ion batteries, lithium difluoro(oxalate)borate (LiODFB) has become a research hotspot in recently. In this work, LiODFB-based electrolytes are studied. When used in Li/MCMB (mesophase carbon microbeads) cells, cell with 0.9 M LiODFB–ethyl methyl carbonate (EMC)/sulfolane (SL) (1:1, v/v) electrolyte shows lower impedance than ones with 0.9 M LiODFB–EMC/ethylene carbonate (EC) (1:1, v/v) electrolyte. Reduction of impedance mainly dues to the fitting nature of solid electrolyte interphase (SEI) film on carbon electrode of lithium-ion battery. The changing morphologies of SEI films with increased circulation numbers were analyzed by scanning electron microscope (SEM). And C2H5OLi, C2H5CO3Li, Li2CO3, RSO3Li, Li2SO3, LiF, C2H5F and some complicated mesh compounds based on >B–O– bond, were found in SEI film by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). It was believed that the root of impedance reduction benefits from both the rich existence of sulfurous compounds and the low content of LiF in SEI film. [Copyright &y& Elsevier]