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In order to optimize the electrolyte system of lithium difluoro (oxalato) borate (LiDFOB)-ethyl methyl carbonate (EMC)/ethylene carbonate (EC)/adiponitrile (ADN) to overcome the drawback of low discharge capacity at room temperature and the easily decomposition of ADN under lower potential, three sulfur-containing solvents, ethylene sulfite (ES), dimethyl sulfite (DMS) and sulfolane (SL) are introduced. AC impedances, cycling performance, cyclic voltammetry tests as well as compatibilities between electrolytes and positive/negative electrodes are evaluated, respectively. Both of the solution systems of 0.7 M LiDFOB-EMC/ES/ADN (49: 49: 2, vol. % ratio) and 0.7 M LiDFOB-EMC/SL/ADN (65.3: 32.7: 2, vol. % ratio) are recommended as alternative electrolytes for 5 V high-voltage lithium ion batteries, benefitting from the synergistic effect between LiDFOB salt and sulfur-containing solvents. Besides, the effect on the performance of sulfur-containing solvents on the positive and negative electrodes is studied by theoretical calculation. This paper provides a promising candidate for improving the electrochemical performance of the battery by optimization of electrolyte formula, especially by a combination of lithium salt and solvent mixture. [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]

The longevity of lithium-ion batteries is determined by the rate of chemical and electrochemical side reactions that limit their charge storage capacity. In particular, dissolution of transition metals from the cathode accelerates the blockage of Li x C 6 anodes, but few direct dissolution studies have been made to date. Although LiMn 2 O 4 (LMO) has been frequently used as a model electrode for dissolution studies, the cause and nature of dissolution and dissolution-free states are still unclear. By online inductively coupled plasma analysis, we detect dissolution from LMO electrodes in real time to reveal the role of surface versus bulk structure effects, electrode potential and degree of lithiation on Mn dissolution. We find that fully lithiated LMO, with an average Mn redox state of 3.5, readily dissolves when brought in contact with 0.2 M Li 2 SO 4 , but that on initial charging a dissolution–passivation event preceding delithiation abruptly stops further detectable dissolution, until well past fully delithiated λ-MnO 2. Dissolution reactivates on returning to the initial potential of pristine LMO, and increases exponentially in the overlithiation region. Our results provide access to much more detailed dissolution information than post-mortem battery analysis allows, enabling targeted materials screening and informing best practices in charging/discharging profiles. In particular, our data suggests that suitable potential conditioning of electrodes may mitigate dissolution, as an alternative or additional measure to the use of protective surface films or incorporation of dopants. [ABSTRACT FROM AUTHOR]

The development of high energy density and power density battery is of increasing importance for new generation energy storage system. However, interface instability between cathode and electrolyte remains a challenge for taking advantage of battery consistency. The use of commercial LiPF 6 -based electrolyte still has the limitations in optimizing interface stability to reduce material performance degradation. Here, self-developed synthetic lithium difluorobis (oxalato) phosphate (LiDFBOP) additive acts as "interface modifier" is adopted in the traditional electrolyte system. The resulting optimized electrolyte formulation exhibits improved electrochemical properties and self-discharge inhibition at high temperatures. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) and density functional theory (DFT) calculation is applied to detect the LiDFBOP effect mechanism and distribution of main components of the interface film. It can be demonstrated that the participation of LiDFBOP can lead to a change in the composition of the interface film, which increases the number of components that facilitate the transport of lithium ions. The analytical means for additive effect obtained from this work offer a new opportunity to make an in-depth analysis of film components between cathode and electrolyte. Image 1 • LiDFBOP as a novel additive is firstly synthesized and characterized. • LiDFBOP as film reconstructor can optimize the performance of LNMO/Li cells. • CEI film composition distribution is proven by the TOF-SIMS. • The effect mechanism of LiDFBOP is verified by the DFT calculation in detail. [ABSTRACT FROM AUTHOR]

The so-called solid-electrolyte interface (SEI) derived from the interaction between electrolyte and electrode plays a decisive role in Li-ion battery performance. Lithium difluoro(bisoxalato) phosphate (LiDFBOP) as the derivative of LiPF 6 has caused great attention among the researchers. However, the mechanism of effect for LiDFBOP salt has not yet revealed, which limits the findings for the fundamental cause of performance improvement. In this work, the effect of LiDFBOP on the mesocarbon microbead (MCMB) anode electrode has been investigated with aid of surface analysis technique, such as scanning electron microscope (SEM), X-ray photoelectron spectrum (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). On the basis of the modification with LiDFBOP, the long-term cycling and degradation resistance of Li/MCMB half cells have been achieved, which results from the preferential decomposition of LiDFBOP regulating the decomposition law of the electrolyte system. The SEI film with layer structure has different composition distribution under the obstruction of LiDFBOP of the decomposition of LiPF 6. The more organic ingredients are distributed in the SEI film on the electrolyte side, which leads to low impedance and fast transportation of lithium ions. The special ingredient distribution is ascribed to the obstruction of LiDFBOP on the decomposition of LiPF 6. This work signifies the research of the effect of SEI film distribution on the battery performance. [ABSTRACT FROM AUTHOR]

Bismuth(III) sulfide (Bi 2 S 3) is a promising cathode material for aqueous zinc ion batteries (ZIBs), yet suffers from serious capacity issues due to its poor electrical conductivity and microstructural degradations. In this work, Bi 2 S 3 anchored on reduced graphene oxide (rGO) is prepared through hydrothermal reaction and is used as cathode material for aqueous ZIBs. Raman and XPS characterizations confirmed that the oxygen bridge in Bi–O–C heterostructures is successfully created during the hydrothermal synthesis. These oxygen bridges are energy favourable in the Bi 2 S 3 /rGO composite materials and serve as the electron transfer channels for rapid charge compensation during Zn2+ incorporation/extraction. Rotating ring–disc electrode (RRDE) measurements demonstrate improved electrochemical stability of the Bi 2 S 3 /rGO composite material compared to pristine Bi 2 S 3. As a result of these improved characteristics, Bi 2 S 3 /rGO composite shows notably better rate performance and cycling stability than unsupported Bi 2 S 3. Ex-situ X-ray diffraction and XPS characterizations indicate that Zn2+ undergoes a reversible conversion reaction with Bi 2 S 3 to form ZnS/Bi0, rather than being intercalated into Bi 2 S 3 crystal interlayers. The rGO substrate forms chemical bonds with bismuth in the composite material, and the strongly anchored bismuth on the rGO through a Bi–O–C bridge enables a highly reversible conversion reaction. As a result, the Bi 2 S 3 /rGO composite with 8 wt% rGO can deliver a reversible capacity of ∼186 mAh g−1 at the current density of 500 mA g−1 after 150 cycles, showing high promise as Zn-ion battery material. [ABSTRACT FROM AUTHOR]

• The elements of Li, Ni, Co and Mn in Li-rich Mn-based cathode materials were replacing with Al. • Al-doped materials display different electrochemical performances. • The relationship between electrochemical characteristics and structure evolution has been systematically studied. Layered Li-rich Mn-based cathode materials have attracted immense interest for using in lithium-ion batteries, owing to their high energy density. However, the severe degradation of cycle and rate performances has impeded the actual commercial application. Herein, Al was selected as doping element to substitute for the metal elements of Li, Ni, Co and Mn in Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O 2 material to promote electrochemical performances and optimize element proportion. Results indicate that when replacing Li with Al, it displays outstanding initial coulombic efficiency of 80.06%. Besides, Al-substitution for Co shows excellent rate performance of 147.3 mAh g−1 at 5.0 C. Particularly, the replacement of Mn not only shows the highest capacity and voltage retention within the potential range from 2.0 to 4.8 V, but also presents superior capacity retention up to the potential of 5.0 V. Unfortunately, the substitution of Ni displays the worst balanced electrochemical performance among Al-doped materials, which shows lower voltage retention than that of pristine. The reasons why Al-substitution for various cations displays difference on electrochemical performance were discussed from the perspective of migration, dissolution and valence reduction of transition metal ions to the structure evolution in detail. The proposed method and detected action mechanisms can provide guidance on how to optimize materials structure and composition for cathode materials in lithium-ion batteries to obtain electrode materials with excellent comprehensive electrochemical performance. [Display omitted] [ABSTRACT FROM AUTHOR]

High nickel LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) cathode material has become one of the most promising cathode materials in the field of power batteries, but the side reaction between the conventional LiPF 6 -based electrolyte and the surface of the NCA material results in poor material interface stability. In this work, a compatible lithium difluoro(oxalate)borate (LiDFOB)-based electrolyte by the employment of sulfolane (SL) as a representative sulfur-containing solvent has been built to enhance the interfacial stability of NCA electrode. The composition, morphology and electrochemical properties are studied by X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy et al. Results show that the decomposition of LiDFOB on the surface of the positive electrode material contributes to forming a uniform cathode electrolyte interface (CEI) film, which subsequently reduces the dissolution of metal ions and hinders the structure transition of the material from the layered structure to spinel or rock-salt phases. Besides, the sulfur-containing products resulted from the decomposition of SL promote the conductivity of Li+ ions for CEI film, which makes up for shortcomings of LiDFOB. Moreover, more LiF has been formed due to the synergistic action between LiDFOB salt and SL solvent, improving the stability and density of CEI film, reducing the thickness of CEI film, and further improving the cycle performance of the battery. [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]

The Al-doped modification strategy by substituting Al for different transition metal ions (TMs, TM = Mn, Ni, Co) has achieved excellent results in improving the cyclic performance of Li-rich Mn-based cathode materials (LRMs). However, the traditional explanation known as "pegging effect" is hard to distinguish how Al works in different TM substitutions. Herein, the electrochemical performances of Li 1.2 Mn 0.52 Ni 0.13 Co 0.13 Al 0.02 O 2 (LRM-Mn), Li 1.2 Mn 0.54 Ni 0.11 Co 0.13 Al 0.02 O 2 (LRM-Ni) and Li 1.2 Mn 0.54 Ni 0.13 Co 0.11 Al 0.02 O 2 (LRM-Co) are studied, and LRM-Mn shows the superior long-term cycling stability, especially at the high temperature of 55 °C. Density functional theory (DFT) reveals that LRM-Mn crystal structure has higher thermodynamic stability than any other sample, which is advantageous for inhibiting the transition of LRMs to low-energy stable phases during cycling (e.g., spinel phase and rock salt phase). Combined with density of states and Bader charge analyses, we think that the increased thermodynamic stability of LRM-Mn results from the reduction of the charge transfer of Mn and Co ions in a single delithiation process, which lowers the reactivity of TMs, alleviates the Li/TM mixing and inhibits the irreversible oxygen release. In addition, the biggest volume change during the delithiation process was observed when Al was substituted for Co, which results in the materials' premature production of fatigue stresses and intergranular cracking. This work comprehensively explains the modification mechanism of Al-doped in LRMs. It demonstrates practical significance for both the rational design of materials and the electrode electrochemical performance prediction. [Display omitted] [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]

Water has a fatal influence on the performance of lithium ion batteries. In this work, Lithium hexafluoro phosphate(LiPF 6 )-ethylene carbonate (EC)/diethyl carbonate (DEC) and lithium bis(oxalato)borate (LiBOB)-tetramethylene sulfone (SL)/DEC are taken as examples to investigate the influences of water concentration for electrochemical window, acidity, impedance and cycling performance for lithium ion batteries by adjusting water concentrations in the electrolytes. Results show that LiBOB-based electrolyte has better water tolerance compared with LiPF 6 -based system, due to the formation of LiBOB·xH 2 O compounds by consuming the additive trace water. Besides, inductively coupled plasma test result shows that Mn ion dissolution in LiPF 6 systems is extremely severe, which is mainly caused by the corrosive reaction between LiMn 2 O 4 and by-product HF acid. And we believe that Mn ion dissolution and the following deposition should be responsible for failure work of LiPF 6 -based cells. But for LiBOB-based cells, stable SEI layers and good electrochemical performances have been obtained, benefitting from the synergistic effect between LiBOB salt and SL solvent. And the presence of high-resistance B(C 2 O 4 ) (OH) and LiB(C 2 O 4 ) (OH) 2 products on surface of graphite electrode is the main reason for a small number of capacity fading. [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]

The dissolution, migration, and deposition of transition metal (TM) ions are the main reasons for the capacity degradation of lithium-ion batteries, which significantly affect their comprehensive electrochemical performance and safety. In this work, the effects of different TM ions (Mn2+, Co2+, and Ni2+) on the electrochemical performance of lithium/mesocarbon microbeads half-cell were compared, and the mechanism was discussed. It is found that Mn2+ ions inhibit the decomposition of lithium salt and promote the decomposition of solvents, resulting in the crack of electrode material and solid electrolyte interface (SEI) film and the increase of capacity degradation. In contrast, Ni2+ ions promote the decomposition of lithium salts to a certain extent, thus inhibiting the excessive damage to the SEI film and electrode material. This study can provide theoretical support and research direction for the design of the electrolytes that can alleviate the damage of TM ions to the anode and the SEI film. [Display omitted] [ABSTRACT FROM AUTHOR]