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Metal dissolution from the positive electrode and redeposition on the negative electrode is one of the well-known failure processes in lithium-ion batteries (LIBs). And it is necessary to take effective measures to prevent this kind of issue from happening. This study examines the Mn tolerance of electrolytes based upon lithium bis(oxalato)borate (LiBOB) and LiPF 6 . Results show that compared with LiPF 6 -based cell, the one based on LiBOB is impacted less by dissolved Mn 2+ ions. When Mn concentration in electrolyte is less than 50 ppm, the adverse effect of additive Mn 2+ ions is tolerable, due to the excellent film-forming properties of LiBOB itself. However, when Mn concentration in LiBOB-based electrolyte is higher than 50 ppm, a small amount of Mn ions are detected on the graphite electrode. Subsequently, continuous decomposition products of the electrolyte induced by the deposited Mn compounds may hinder the intercalation of lithium into the graphite, thereby reducing the reversibility of the lithium intercalation. This study suggests that LiBOB-based electrolyte is an alternative electrolyte for relatively low-cost manganese-based electrodes by improving Mn tolerance to some extent. [ABSTRACT FROM AUTHOR]

Cathode materials LiNiMnO and LiNiLaMnO ( x = 0.04, 0.1, 0.14) were successfully prepared by the sol-gel self-combustion reaction (SCR) method. The X-ray diffraction (XRD) patterns indicated that, a few of doping La ions did not change the structure of LiNiMnO material. The scanning electronic microscopy (SEM) showed that the sample heated at 800°C for 12 h and then annealed at 600°C for 10 h exhibited excellent geometry appearance. A novel electrolyte system, 0.7 mol L lithium bis(oxalate)borate (LiBOB)-propylene carbonate (PC)/dimethyl carbonate (DMC) (1: 1, v/v), was used in the cycle performance test of the cell. The results showed that the cell with this novel electrolyte system performed better than the one with traditional electrolyte system, 1.0 mol L LiPF-ethylene carbonate (EC)/DMC (1: 1, v/v). And the electrochemical properties tests showed that LiNiLaMnO/Li cell performed better than LiNiMnO/Li cell at cycle performance, median voltage, and efficiency. [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]

Abstract: To seek the promising candidate for 5 V electrolytes, fluorine-free lithium bis(oxalato)borat (LiBOB) is chosen as the lithium salt, γ-butyrolactone (GBL) as well as sulfolane (SL) with the property of stability against oxidative decomposition is chosen as supporting electrolyte solvents, and linear diethyl carbonate (DMC) is chosen as the third supporting electrolyte solvent to lower viscosity. After systematical analytical studies, it indicates that SL solvent is the main and key reason for the improvement of electrochemical performance, which not only improves the stability of electrolyte system against oxidative decomposition, but also decreases the electrode polarization resistance. More than that, 1.0molL−1 LiBOB–SL/GBL/DMC electrolyte shows good compatibilities with both intercalation hosts as LiNi0.5Mn1.5O4 cathode and carbonaceous anode. It suggests that this novel electrolyte would be an alternative electrolyte for 5 V high-voltage rechargeable lithium-ion batteries based upon LiNi0.5Mn1.5O4 cathode. [Copyright &y& Elsevier]

Highlights: [•] LiBF2SO4 was investigated as a novel electrolyte salt for advanced high-temperature LIBs. [•] At 80°C, LiBF2SO4-EC/DMC electrolyte favourably facilitates the formation of a thermal stable, effective and conductive interface film on the surface of carbonaceous anode. [•] At 80°C, LiBF2SO4-EC/DMC electrolyte exerts several advantages, such as stable cycling performance, low polarization resistance, and good rate performance in LiFePO4/Li cells. [ABSTRACT FROM AUTHOR]

Abstract: Lithium bis(oxalate)borate (LiBOB) has many unique properties, such as thermal stability and the formation of a stable passivation layer on the surface of carbonaceous anode. In this work, the electrochemical behaviors of sulfolane (SL) with LiBOB were studied by employment of dimethyl sulfite (DMS) and diethyl sulfite (DES) as mixed solvents, respectively. When used in Li/MCMB (mesophase carbon microbeads) cells at 60°C, only LiBOB-SL/DMS electrolyte exhibits not only excellent film-forming characteristics, but also good thermal stability of the interface film on the surface of MCMB. Besides, when used in LiFePO4/Li cells at 60°C, only LiBOB-SL/DMS electrolyte simultaneously exerts several advantages, such as good thermal stability of the interface film on the surface of LiFePO4, stable cycling performance, high mean voltage, and excellent discharge rate performance. It suggests that LiBOB-SL/DMS electrolyte is an excellent candidate electrolyte for high-temperature lithium ion batteries. [Copyright &y& Elsevier]

Lithium-rich layered oxide is a promising cathode material for high-energy density lithium ion batteries. Generally, it is essential to develop high-voltage electrolyte because electrolyte is one of the key factors that determines the capacity of cathode materials. In this work, lithium difluoro(oxalato) borate (LiODFB) is introduced as a novel lithium-salt for lithium-rich cathodes. The investigation reveals that the LiODFB modifies the surface film and forms a uniform and electrochemical stable cathode electrolyte interface (CEI) on the lithium-rich cathode. The LiODFB-derived CEI layer effectively suppresses severe electrolyte decomposition at high voltages and hinders undesirable phase transformation from layered to spinel-like phases during cycling. Furthermore, the Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O 2 /Li cell with the LiODFB-based electrolyte exhibits high capacity retention of 91.73% after 50 cycles and better rate capability of 195 mAh g −1 at 2 C. The unique function of the LiODFB on the surface chemistry of lithium-rich cathodes is confirmed through X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy analyses. [ABSTRACT FROM AUTHOR]

• Formation of lif-rich cathode-electrolyte interphase via potentiostatic reduction. • The lif-rich CEI inhibits the corrosion of FSI− anion on aluminum collector. • The electrochemical performances of l -std-F reach the level of 1.0 m LiPF6-DEC/EC. The low concentration electrolyte shows the advantages of low viscosity and low cost, but the formation of porous and soluble organic cathode-electrolyte interphase (CEI) limits its performance. Herein, the electrochemical performance of the low concentration electrolyte of 0.45 M LiPF 6 ‑diethyl carbonate (DEC)/ ethylene carbonate (EC) (1:1, in volume ratio) is improved by 0.05 M bis(fluorosulfonyl)imide (LiFSI) additive, aided by the antecedent process of potentiostatic reduction at a low potential of 1.5 V. Results show that LiFSI is preferentially reduced via breaking the structure of FSI− anion to form a robust LiF-rich CEI on the surface of LiFePO 4 (LFP) cathode, solving the problem that it is difficult to form inorganic LiF on the cathode surface. In the subsequent cycling of LFP/Li half-battery, the as-formed CEI inhibits the corrosion of aluminum collector, suppresses the excessive decomposition of the electrolyte and improves the diffusion of Li+, resulting in a much-enhanced cycle stability of the cathode. Therefore, the cyclic performance of the LFP/Li half-battery using the modified low concentration electrolyte with the antecedent process of potentiostatic reduction is on a par with that using the standard electrolyte (1.0 M LiPF 6 -DEC/EC). Compared with the traditional electrolyte engineering of constructing a LiF-rich CEI by the direct oxidation defluorination of fluorinated anions, this strategy needs a lower reaction energy and can play a positive role at a lower reaction potential. This work provides an effective way to construct LiF-rich CEI which helps to improve the performance of low concentration electrolytes. [Display omitted] [ABSTRACT FROM AUTHOR]

To satisfy the need of 5 V high-voltage cathode materials, lithium difluoro(oxalato)borate (LiDFOB) with excellent film-forming property has been chosen as lithium salt, and adiponitrile (ADN) with stable electrochemical performance has been evaluated as functional additive. An electrochemical investigation of this novel electrolyte solution shows a wide electrochemical oxidation window of nearly 6.0 V vs Li + /Li. Due to the positive effect of ADN on the cathode/electrolyte interface, LiNi 0.5 Mn 1.5 O 4 /Li half-cell with ADN-adding electrolyte exhibits prominent rate capability and cyclability. It is believed that the improvement of electrochemical performances has benefitted greatly from interfacial impedance reducing. Two modeling hypotheses have been used to explain interfacial interaction between ADN and LiNi 0.5 Mn 1.5 O 4 , by the means of analysis of X-ray photoelectron spectroscopy and theoretical calculation. Results show that ADN can enrich the surface of cathode material to hinder the further decomposition of the electrolyte, and contribute to the formation of a cathode-electrolyte interface passivation film with protective and conductive properties. [ABSTRACT FROM AUTHOR]

Highlights: [•] LiBOB–SL/DMC electrolyte has good compatibility with LiNi0.5Mn1.5O4 cathode. [•] It is an attractive electrolyte for 5V high voltage lithium-ion batteries based upon LiNi0.5Mn1.5O4 cathode. [•] It has characteristic of good stability against oxidative decomposition (5.3V, vs. Li/Li+) and satisfactory safety performance. [•] When used in LiNi0.5Mn1.5O4/Li cells, this electrolyte exhibits stable cycle performance, low cell resistance, and good rate performance. [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]

Abstract: Lithium bis(oxalato)borate (LiBOB) is a promising salt for lithium ion batteries. However, to achieve better electrochemical performance of LiBOB, the development of appropriate electrolytes is essential. In this work, the electrochemical behaviors of sulfolane (SL) with LiBOB were studied by employment of dimethyl sulfite (DMS) and diethyl sulfite (DES) as mixed solvents, respectively. Both of the LiBOB-based electrolytes show high oxidation potentials (>5.5V), and good conductivities. When used in Li/MCMB (mesophase carbon microbeads) cells, these two kinds of novel electrolytes exhibit not only excellent film-forming characteristics, but also low impedances of the interface films. Besides, when used in LiFePO4/Li cells, compared to the cell with the electrolyte system of 1M LiPF6-EC/DMC (1:1, v/v), both of the LiBOB-based electrolytes exhibit several advantages, such as more stable cycle performance even at elevated temperature, and higher mean voltage. [Copyright &y& Elsevier]

Abstract: Lithium bis(oxalato)borate (LiBOB) is a promising salt for lithium ion batteries. However, before applying in lithium ion batteries, it is necessary to prepare high purity LiBOB with a simple method, and find more appropriate solvent systems to exert the perfect electrochemical performance of LiBOB. In this paper, LiBOB is synthesized by the compressing dry granulation method, with the yield of 97%. Moreover, the electrochemical performances of LiBOB-sulfolane (SL)/diethyl carbonate (DEC) electrolyte are investigated. It shows high oxidation potentials (>5.3V) and satisfactory conductivities, also the temperature dependence of the conductivity is well in accord with the Vogel–Tamman–Fulcher (VTF) behavior. When used in Li/MCMB (mesophase carbon microbeads) cells, this novel electrolyte exhibits not only excellent film-forming characteristics, but also low impedances of the interface films. When used in LiFePO4/Li cells, compared to the cell with the electrolyte system of LiBOB-EC/DEC electrolyte, LiBOB-SL/DEC electrolyte exhibit several advantages, such as more stable cycle performance, and higher discharge voltage plateau (>3.35V). [Copyright &y& Elsevier]

A blank comparison group of lithium salt-free electrolyte system, replacing the lithium salt of electrolyte with a redox shuttle agent, is constructed to give targeted research on the single role of lithium bis(oxalate)borate (LiBOB) salt, especially of bis(oxalate)borate anions (BOB−) in the film-forming process. By combining and comparing all available studies, such as attenuated total reflectance (IR-ATR), X-Ray photoelectron diffraction spectrum (XPS), electrochemical impedance spectrum (EIS), scanning electron microscopy (SEM) tests and quantum chemical calculation, the formation mechanism of the solid electrolyte interphase (SEI) film is proposed. Results reveal that the prior reduction of BOB− anions can postpone the reduction potential and hinder the decomposition rate of carbonate solvents, but promote the formation of a dense, conductive and effective SEI film. This work provides a novel way to investigate the film-forming mechanism and has guiding significance for revealing the effect of other kinds of lithium salts on the surface film formation. • A lithium salt-free electrolyte is constructed. • Single role of BOB− anions on SEI film-forming process is revealed. • The reduction of BOB− postpones the reduction potential of solvents. • The initial SEI film from LiBOB hinders the decomposition rate of solvent. [ABSTRACT FROM AUTHOR]