电解液添加剂硫酸亚乙酯对锂离子电池性能的影响

在1 mol/L LiPF₆/碳酸乙烯酯+碳酸二甲酯+碳酸甲乙酯（体积比1∶1∶1）电解液中,采用恒流充放电测试、循环伏安法（CV）、扫描电子显微镜（SEM）、能量散射光谱（EDS）、电化学阻抗谱（EIS）等测试技术,研究了添加剂硫酸亚乙酯（DTD）对锂离子电池性能及石墨化中间相碳微球（MCMB）电极/电解液界面性质的影响。 结果表明,在电解液中引入体积分数0.01%DTD后,MCMB/Li电池可逆放电容量从300 mA·h/g提高至350 mA·h/g,电池总阻抗降低,循环稳定性提高。CV测试发现,在首次还原过程中,DTD在电极电位1.4 V左右（vs Li/Li⁺）发生电化学还原,参与了MCMB电极表面固体电解质相界面膜（SEI膜）的形成过程。 同时,DTD对LiMn₂O₄电极性能无不良影响。     

Electrochemical performances of two kinds of ternary electrolyte mixtures with lithium bis(oxalate)borate

Conductivities (??) of PC (propylene carbonate)/EMC (ethyl methyl carbon ate)/DMC (dimethyl carbonate) and EC (ethylene carbonate)/EMC/DMC solutions of lithium bis(oxalate)borate (LiBOB) were experimentally determined at a temperature (??) range from ?40.0 to 60.0°C. Under such experimental conditions, the effect factors on the ??, such as the salt molar concentrations (m), and the volume ratio of solvent compositions, were also investigated. The results showed that, in wide ?? range, the higher ?? were obtained with 0.7 mol L^?1 LiBOB in PC/EMC/DMC and 0.6 mol L^?1 LiBOB in EC/EMC/DMC and with a volume ratio of 1: 1: 1 and 1: 1: 2, respectively. When used in LiFePO₄/Li cells, compared to the cell with the electrolyte system of 1.0 mol L^?1 LiPF₆-EC/EMC/DMC (1: 1: 1), LiBOB cells with PC/EMC/DMC and EC/EMC/DMC electrolyte systems with the same volume mixture solvent compositions exhibit several advantages, such as more stable cycle performance, higher mean voltage, excellent large current discharge capability, more capacity retention at high temperature, and more stable storage performance, etc. This study not only shows that LiBOB is a very promising alternative salt for lithium ion chemistry, but also provides appropriate solvent to improve LiBOB??s electrochemical performance.     

A Liquid/Liquid Electrolyte Interface that Inhibits Corrosion and Dendrite Growth of Lithium in Lithium‐Metal Batteries

A proof‐of‐concept study on a liquid/liquid (L/L) two‐phase electrolyte interface is reported by using the polarity difference of solvent for the protection of Li‐metal anode with long‐term operation over 2000 h. The L/L electrolyte interface constructed by non‐polar fluorosilicane (PFTOS) and conventionally polar dimethyl sulfoxide solvents can block direct contact between conventional electrolyte and Li anode, and consequently their side reactions can be significantly eliminated. Moreover, the homogeneous Li‐ion flow and Li‐mass deposition can be realized by the formation of a thin and uniform solid‐electrolyte interphase (SEI) composed of LiF, Li_xC, Li_xSiO_y between PFTOS and Li anode, as well as the super‐wettability state of PFTOS to Li anode, resulting in the suppression of Li dendrite formation. The cycling stability in a lithium–oxygen battery as a model is improved 4 times with the L/L electrolyte interface.     

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).     

In situ analysis of interfacial reactions between negative MCMB,lithium electrodes,and gel polymer electrolyte

The interfacial properties of mesocarbon-microbeads (MCMB) and lithium electrodes during charge process in poly (vinylidenefluoride-co-hexafluoropropylene)-based gel electrolyte were investigated by in situ Raman microscopy, in situ Fourier transform-infrared (FTIR) spectroscopic methods, and charge–discharge, electrochemical impedance spectroscopy techniques. For MCMB electrode, the series phase transitions from initial formation of the dilute stage 1 graphite intercalation compound (GIC) to a stage 4 GIC, then through a stage 3 to stage 2, and finally to stage 1 GIC was proved by in situ Raman spectroscopic measurement. The formation of solid electrolyte interface (SEI) films formed on MCMB and metal lithium electrode was studied by in situ reflectance FTIR spectroscopic method. At MCMB electrode surface, the solvent (mostly ethylene carbonate) decomposed during charging process and ROCO₂Li may be the product. ROCO₂Li, ROLi, and Li₂CO₃ were the main composites of SEI film formed on lithium electrode, not on electrodeposited lithium electrode or lithium foil electrode.     

Lithium transport within the solid electrolyte interphase

A LiClO₄ SEI film grown on copper was examined with time-of-flight secondary ion mass spectrometry. The SEI porosity profile and Li⁺ transport processes within the SEI were studied with isotopically labeled ⁶LiBF₄ electrolyte. An ~ 5 nm porous region, into which electrolytes can easily diffuse, was observed at the electrolyte/SEI interface. Below the porous region, a densely packed layer of Li₂O and/or Li₂CO₃ prevents electrolyte diffusion, but Li⁺ transports through this region via ion exchange.     

Dendrite‐Free Epitaxial Growth of Lithium Metal during Charging in Li–O2 Batteries

Lithium (Li) dendrite formation is one of the major hurdles limiting the development of Li‐metal batteries, including Li‐O₂ batteries. Herein, we report the first observation of the dendrite‐free epitaxial growth of a Li metal up to 10‐μm thick during charging (plating) in the LiBr‐LiNO₃ dual anion electrolyte under O₂ atmosphere. This phenomenon is due to the formation of an ultrathin and homogeneous Li₂O‐rich solid‐electrolyte interphase (SEI) layer in the preceding discharge (stripping) process, where the corrosive nature of Br^? seems to give rise to remove the original incompact passivation layer and NO₃^? oxidizes (passivates) the freshly formed Li surface to prevent further reactions with the electrolyte. Such reactions keep the SEI thin (<100 nm) and facilitates the electropolishing effect and gets ready for the epitaxial electroplating of Li in the following charge process.     

Solvent Molecule Cooperation Enhancing Lithium Metal Battery Performance at Both Electrodes

Developing electrolytes compatible with efficient and reversible cycling of electrodes is critical to the success of rechargeable Li metal batteries (LMBs). The Coulombic efficiencies and cycle lives of LMBs with ethylene carbonate (EC), dimethyl carbonate, ethylene sulfite (ES), and their combinations as electrolyte solvents show that in a binary‐solvent electrolyte the extent of electrolyte decomposition on the electrode surface is dependent on the solvent component that dominates the solvation sheath of Li⁺. This knowledge led to the development of an EC‐ES electrolyte exhibiting high performance for Li||LiFePO₄ batteries. Carbonate molecules occupy the solvation sheath and improve the Coulombic efficiencies of both the anode and cathode. Sulfite molecules lead to desirable morphology and composition of the solid electrolyte interphase and extend the cycle life of the Li metal anode. The cooperation between these components provides a new example of electrolyte optimization for improved LMBs.     

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.     

Model Studies on the Formation of the Solid Electrolyte Interphase: Reaction of Li with Ultrathin Adsorbed Ionic-Liquid Films and Co3O4(111) Thin Films

In this work we aim towards the molecular understanding of the solid electrolyte interphase (SEI) formation at the electrode electrolyte interface (EEI). Herein, we investigated the interaction between the battery-relevant ionic liquid (IL) 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMP-TFSI), Li and a Co₃O₄(111) thin film model anode grown on Ir(100) as a model study of the SEI formation in Li-ion batteries (LIBs). We employed mostly X-ray photoelectron spectroscopy (XPS) in combination with dispersion-corrected density functional theory calculations (DFT-D3). If the surface is pre-covered by BMP-TFSI species (model electrolyte), post-deposition of Li (Li⁺ ion shuttle) reveals thermodynamically favorable TFSI decomposition products such as LiCN, Li₂NSO₂CF₃, LiF, Li₂S, Li₂O₂, Li₂O, but also kinetic products like Li₂NCH₃C₄H₉ or LiNCH₃C₄H₉ of BMP. Simultaneously, Li adsorption and/or lithiation of Co₃O₄(111) to Li_nCo₃O₄ takes place due to insertion via step edges or defects; a partial transformation to CoO cannot be excluded. Formation of Co⁰ could not be observed in the experiment indicating that surface reaction products and inserted/adsorbed Li at the step edges may inhibit or slow down further Li diffusion into the bulk. This study provides detailed insights of the SEI formation at the EEI, which might be crucial for the improvement of future batteries.     

Electrochemical Performance of PEO10LiX-Li2TiO3 Composite Polymer Electrolytes

Introduction Recently, polymer electrolytes have attracted much attention for their potential use in replacing flammable organic solvent electrolytes currently used in lith-ium-ion batteries, thus improving the safety of re-chargeable lithium batteries. Moreover, the batteries with PE can be made in any shape, which make fully use of the space of electronic devices. PEO is a linear polymer with helix structure, and its structure makes it have much higher dissolution ability for salt even tho…     

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.     

五种1-烷基-2,3-二甲基咪唑型离子液体的合成及作为Li/LiFeO_4电池电解液的研究

合成了五种新的1-烷基-2,3-二甲基咪唑二(三氟甲基磺酰)亚胺离子液体(alkyl-DMimTFSI).以离子液体作为Li/LiFeO4电池电解液,分别考察不同烷基(正丁基、正戊基、正辛基、异辛基和正癸基)对电解液理化性质、界面性质和电池行为的影响.结果表明离子液体的电化学窗口都可以达到5.6V(-0.4～5.2Vvs.Li+/Li),显示它们具有较好的电化学稳定性.加入碳酸亚乙烯酯作为添加剂后,离子液体电解液在Li负极形成稳定的固体电解质相界面膜(SEI),从而提高了Li负极的稳定性,保护了Li片不受腐蚀.电化学阻抗和循环伏安分析进一步揭示LiFeO4正极与离子液体电解液也有良好的兼容性.此外,研究还表明离子液体中烷基种类严重影响它们的电池行为.采用butyl-DMimTFSI和amyl-DMimTFSI电解液体系的电池充放电容量和可逆性明显优于另外三种离子液体,它们的首次放电容量分别达到145和152.6mAh/g,并表现出良好的充放电循环性能.因粘度最大,采用isooctyl-DMimTFSI电解液的电池首次放电容量仅为8.3mAh/g,但添加碳酸丙烯酯(质量比1∶1)稀释后首次放电容量上升至132.4mAh/g.     

Fluorine‐Doped Antiperovskite Electrolyte for All‐Solid‐State Lithium‐Ion Batteries

A fluorine‐doped antiperovskite Li‐ion conductor Li₂(OH)X (X=Cl, Br) is shown to be a promising candidate for a solid electrolyte in an all‐solid‐state Li‐ion rechargeable battery. Substitution of F^? for OH^? transforms orthorhombic Li₂OHCl to a room‐temperature cubic phase, which shows electrochemical stability to 9 V versus Li⁺/Li and two orders of magnitude higher Li‐ion conductivity than that of orthorhombic Li₂OHCl. An all‐solid‐state Li/LiFePO₄ with F‐doped Li₂OHCl as the solid electrolyte showed good cyclability and a high coulombic efficiency over 40 charge/discharge cycles.     

The understanding of solid electrolyte interface (SEI) formation and mechanism as the effect of flouro-o-phenylenedimaleimaide (F-MI) additive on lithium-ion battery

Solid electrolyte interface (SEI) is a critical factor that influences battery performance. SEI layer is formed by the decomposition of organic and inorganic compounds after the first cycle. This study investigates SEI formation as a product of electrolyte decomposition by the presence of flouro-o-phenylenedimaleimaide (F-MI) additive. The presence of fluorine on the maleimide-based additive can increase storage capacity and reversible discharge capacity due to high electronegativity and high electron-withdrawing group. The electrolyte containing 0.1 wt% of F-MI-based additive can trigger the formation of SEI, which could suppress the decomposition of remaining electrolyte. The reduction potential was 2.35 to 2.21 V vs Li/Li⁺ as examined by cyclic voltammetry (CV). The mesocarbon microbeads (MCMB) cell with F-MI additive showed the lowest SEI resistance (Rsei) at 5898 Ω as evaluated by the electrochemical impedance spectroscopy (EIS). The morphology and element analysis on the negative electrode after the first charge-discharge cycle were examined by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS). XPS result showed that MCMB cell with F-MI additive provides a higher intensity of organic compounds (RCH₂OCO₂Li) and thinner SEI than MCMB cell without an additive that provides a higher intensity of inorganic compound (Li₂CO₃ and Li₂O), which leads to the performance decay. It is concluded that attaching the fluorine functional group on the maleimide-based additive forms the ideal SEI formation for lithium-ion battery.     

Monitoring electrode/electrolyte interfaces of Li-ion batteries under working conditions: A surface-enhanced Raman spectroscopic study on LiCoO2 composite cathodes

Lithium-ion batteries are commonly used for electrical energy storage in portable devices and are promising systems for large-scale energy storage. However, their application is still limited due to electrode degradation and stability issues. To enhance the fundamental understanding of electrode degradation, we report on the Raman spectroscopic characterization of LiCoO₂ cathode materials of working Li-ion batteries. To facilitate the spectroscopic analysis of the solid electrolyte interface (SEI), we apply in situ surface-enhanced Raman spectroscopy under battery working conditions by using Au nanoparticles coated with a thin SiO₂ layer (Au@SiO₂). We observe a surface-enhanced Raman signal of Li₂CO₃ at 1090 cm⁻¹ during electrochemical cycling as an intermediate. Its formation/decomposition highlights the role of Li₂CO₃ as a component of the SEI on LiCoO₂ composite cathodes. Our results demonstrate the potential of Raman spectroscopy to monitor electrode/electrolyte interfaces of lithium-ion batteries under working conditions thus allowing relations between electrochemical performance and structural changes to be established.     

A review on electrode and electrolyte for lithium ion batteries under low temperature

Under low temperature (LT) conditions (−80 °C∼0 °C), lithium-ion batteries (LIBs) may experience the formation of an extensive solid electrolyte interface (SEI), which can cause a series of detrimental effects such as Li⁺ deposition and irregular dendritic filament growth on the electrolyte surface. These issues ultimately lead to the degradation of the LT performance of LIBs. As a result, new electrode/electrolyte materials are necessary to address these challenges and enable the proper functioning of LIBs at LT. Given that most electrochemical reactions in lithium-ion batteries occur at the electrode/electrolyte interface, finding solutions to mitigate the negative impact caused by SEI is crucial to improve the LT performance of LIBs. In this article, we analyze and summarize the recent studies on electrode and electrolyte materials for low temperature lithium-ion batteries (LIBs). These materials include both metallic materials like tin, manganese, and cobalt, as well as non-metallic materials such as graphite and graphene. Modified materials, such as those with nano or alloying characteristics, generally exhibit better properties than raw materials. For instance, Sn nanowire-Si nanoparticles (SiNPs−In-SnNWs) and tin dioxide carbon nanotubes (SnO₂@CNT) have faster Li⁺ transport rates and higher reversible capacity at LT. However, it′s important to note that when operating under LT, the electrolyte may solidify, leading to difficulty in Li⁺ transmission. The compatibility between the electrolyte and electrode can affect the formation of the solid electrolyte interphase (SEI) and the stability of the electrode/electrolyte system. Therefore, a good electrode/electrolyte system is crucial for successful operation of LIBs at LT.     

Enhanced electrochemical performance of LiFePO4 cathode with the addition of fluoroethylene carbonate in electrolyte

The effect of the fluoroethylene carbonate (FEC) addition in electrolyte on LiFePO₄ cathode performance was investigated in low-temperature electrolyte LiPF₆/EC/PC/EMC (0.14/0.18/0.68). Cyclic voltammetry, electrochemical impedance spectroscopy, and charge/discharge tests were conducted in this work. In the presence of FEC, the polarization of LiFePO₄ electrode decreased both at room and low temperatures. Meanwhile, the exchange current density increased. The rate capability of LiFePO₄ electrode was greatly enhanced as well. The morphology of the solid electrolyte interphase (SEI) on LiFePO₄ surface was modified with the addition of FEC as confirmed by scanning electron microscopy measurement. A compact film with small impedance was formed on LiFePO₄ surface compared to the case of FEC-free. The compositions of the film were analyzed by X-ray photoelectron spectroscopic measurement. The contents of Li _x PO _y F _z , LiF, and the carbonate species generated from solvents decomposition were reduced. The modified SEI promoted the migration of lithium ion through the electrode/electrolyte interphase and enhanced the electrochemical performance of the cathode.     

Electrochemical SPM investigation of the solid electrolyte interphase film formed on HOPG electrodes

Solid electrolyte interphase (SEI) film formation on graphite electrodes was studied on highly oriented pyrolytic graphite (HOPG) in nonaqueous electrolyte by in situ electrochemical atomic force microscopy (AFM). For potentials negative to 0.7 V versus Li|Li⁺ a SEI film is formed on the HOPG electrode surface. After the first cycle the film is rough and covers the surface of the HOPG electrode only partially. After the second cycle the HOPG surface is fully covered by a compact film. The thickness of the SEI film was measured by increasing the pressure of the AFM tip and thus scraping a part of the electrode surface. In this way a thickness of about 25 nm was found for the SEI film formed after two scan cycles between 3 and 0.01 V versus Li|Li⁺.     

Synergistic Dual‐Additive Electrolyte Enables Practical Lithium‐Metal Batteries

A rechargeable Li metal anode coupled with a high‐voltage cathode is a promising approach to high‐energy‐density batteries exceeding 300 Wh kg^?1. Reported here is an advanced dual‐additive electrolyte containing a unique solvation structure and it comprises a tris(pentafluorophenyl)borane additive and LiNO₃ in a carbonate‐based electrolyte. This system generates a robust outer Li₂O solid electrolyte interface and F‐ and B‐containing conformal cathode electrolyte interphase. The resulting stable ion transport kinetics enables excellent cycling of Li/LiNi_0.8Mn_0.1Co_0.1O₂ for 140 cycles with 80 % capacity retention under highly challenging conditions (≈295.1 Wh kg^?1 at cell‐level). The electrolyte also exhibits high cycling stability for a 4.6 V LiCoO₂ (160 cycles with 89.8 % capacity retention) cathode and 4.95 V LiNi_0.5Mn_1.5O₄ cathode.