Stable Solid Electrolyte Interface Layer Research Articles

Control of interfacial layers for high-performance porous Si lithium-ion battery anode.

We demonstrate a facile synthesis of micrometer-sized porous Si particles via copper-assisted chemical etching process. Subsequently, metal and/or metal silicide layers are introduced on the surface of porous Si particles using a simple chemical reduction process. Macroporous Si and metal/metal silicide-coated Si electrodes exhibit a high initial Coulombic efficiency of ∼90%. Reversible capacity of carbon-coated porous Si gradually decays after 80 cycles, while metal/metal silicide-coated porous Si electrodes show significantly improved cycling performance even after 100 cycles with a reversible capacity of >1500 mAh g(-1). We confirm that a stable solid-electrolyte interface layer is formed on metal/metal silicide-coated porous Si electrodes during cycling, leading to a highly stable cycling performance.

Low temperature process modified MCMB for lithium ion batteries

The negative electrode of a lithium-ion battery should have the characteristics of large charge capacity, excellent charge and discharge cycle, steady discharge voltage, low irreversible charge capacity, and stable electrolyte. Natural graphite and mesocarbon microbeads (MCMB) are the most common materials used for the negative electrodes of such batteries. This study examines the effect of the use of homemade non-modified MCMB (HMM), modified MCMB (HMMQ), and natural graphite (NG) to produce electrodes on the batteries' high current charge–discharge behavior. In this experiment, the charge–discharge results showed that the voltage plateaus of HMM and HMMQ sloped due to short-range structural order, which enabled the intercalation and deintercalation of lithium ions to occur at different voltages. When HMMQ was charging and discharging high current at a rate of 2C, the battery's charge capacity reached 160mAh·g−1 and the coulometric efficiency exceeded 96%. Following the start of charging and discharging, a stable solid electrolyte interface (SEI) layer formed on HMMQ. The charge capacity of HMMQ was approximately 167mAh·g−1 after 100 charge–discharge cycles at 1C, and the cycles were stable. According to FTIR analysis, the content of the SEI layer produced within HMMQ consisted of Li2CO3 and (CH2OCOLi)2, and was stable, non-soluble, and passive. Negative electrodes made using modified material displayed good stability throughout many cycles when charging and discharging at a high current.

High-Voltage Electrolyte Additive for High-Energy Lithium-Ion Batteries

Increasing demand of high-energy lithium-ion batteries for being adopted in electric vehicles and energy storage systems drives the development of high-voltage and high-capacity cathode together with functional electrolyte with high anodic and thermal stabilities. Lithium-rich layered material of xLi2MnO3-(1-x)Li(Ni, Co, Mn)O2 is an attractive cathode material because of their higher capacity than 200 mAh/g. Its performance however is often difficult to be achieved, in particular, at high voltage operation (> 4.3 V vs. Li/Li+), due to severe oxidative decomposition of conventional electrolyte consisting of LiPF6 salt and non-aqueous carbonate-based organic solvents. Operation of the cathode at higher voltage than 4.6 V can lead to a further increase in the capacity. Extensive research efforts have been made to develop appropriate electrolyte components with high anodic stability but yet to be established. We have been screening and evaluating a number of fluorinated carbonates as electrolyte additives for high-performance operation of 4.8 V Li1.2Mn0.525Ni0.175Co0.1O2 cathode. The use of a low fraction additive comprises low cost, compared to solvent. Here we present the first report on a new fluorinated carbonate as a high-performance electrolyte additive for 4.8 V Li1.2Mn0.525Ni0.175Co0.1O2 cathode operated at a wide temperature range. The SEI formation mechanism, composition and stability, and their relation to high-voltage cycling performance, and cycling performance of full-cells are discussed.The Li1.2Mn0.525Ni0.175Co0.1O2 cathode material was synthesized at 900 oC in air using the carbonate coprecipitate precursor. The crystal structure of coprecipitate precursor and cathode material were identified by X-ray diffraction analysis, measured in the 2θ range of 10 - 80o with the scan rate of 2o/min. Lithium coin cells, consisted of Li1.2Mn0.525Ni0.175Co0.1O2 as a working electrode, a lithium foil as counter electrode and the electrolyte of 1M LiPF6/EC:EMC (3:7 volume ratio) with 5 wt% additive of fluorinated carbonate was assembled in the Ar-filled glove box. The 2016 coin half- and full-cells were evaluated for their cycling ability at C/5 rate between 2.5 and 4.8 V. AC impedance spectra were also collected during cycling. For characterization of solid electrolyte interface (SEI) composition, attenuated total reflection FTIR combined with X-ray photoelectron spectroscopic (XPS) analyses were conducted.Figure 1a compares the cycling ability of Li1.2Mn0.525Ni0.175Co0.1O2 cathode without and with additive. With additive, the initial charge and discharge capacities are 350 and 256 mAh/g, respectively, with initial coulombic efficiency of 73%. The cathode delivers the capacity retention of 89% with the discharge capacity of 227 mAh/g at the 50th cycle. On the contrary, without additive, inferior capacities of 222 – 156 mAh/g and capacity retention of 70% over 50 cycles are observed. The use of additive is found to be very effective in enabling high-voltage cycling performance of Li1.2Mn0.525Ni0.175Co0.1O2 cathode. Our spectroscopic surface chemistry studies suggest that with additive, the cathode surface is effectively passivated with a stable SEI layer with maintained surface cathode structure (Figure 1b-iii), leading to a suppressed change in charge transfer resistance with cycling. On the contrary, the occurrence of surface structural degradation by the formation of dissolvable Mn2+proably followed by oxygen loss is observed when cycled without additive (Figure 1b-ii). Further discussion of the SEI formation mechanism and stability, their correlation to interfacial resistance and cycling performance, and the cycling performance of full-cells would be presented in the meeting. Acknowledgements: This research was financially supported by the Korean Ministry of Education and National Research Foundation (2012026203) and by the Ministry of Trade, Industry & Energy (A0022-00725).

Surface analysis of the solid electrolyte interface formed by additives on graphite electrodes in Li‐ion batteries using XPS, FE‐AES, and XHR‐SEM techniques

We investigate the formation and distribution of the solid electrolyte interface (SEI) layer on a graphite anode with two additives [vinylethylene carbonate (VEC) and vinylene carbonate (VC)] in a formation process using XPS, field emission AES, and extreme high‐resolution SEM (XHR‐SEM) techniques, and we studied what factors play an important role in determining the formation of the SEI layer. The VEC‐derived SEI behaviors (morphology, thickness, compound, and balance over electrode position) on a graphite anode largely depend on the elevated temperature. The VC‐derived SEI layer is mostly formed in the initial charging step, showing simple growth (formation) behavior. It is suggested that the properties of the additives are important for SEI bonding configurations at the nanoscale film surface, and to achieve the stable SEI layer, there appears to be an effective formation process for the additive properties. This research highlights the challenges of developing a stable SEI layer with additives in the formation process for electric vehicle batteries and would make a contribution to the understanding of how formation conditions affect an SEI layer with respect to additive properties. Copyright © 2014 John Wiley & Sons, Ltd.

Interfacial Origin of Performance Improvement and Fade for 4.6 V LiNi0.5Co0.2Mn0.3O2 Battery Cathodes

The interfacial origin of performance improvement and fade of high-voltage cathodes of LiNi0.5Co0.2Mn0.3O2 for high-energy lithium-ion batteries has been investigated. Performance improvement was achieved through interfacial stabilization using 5 wt % methyl (2,2,2-trifluoroethyl) carbonate (FEMC) of fluorinated linear carbonate as a new electrolyte additive. Cycling with the FEMC additive at 3.0–4.6 V versus Li/Li+ results in the formation of a stable solid electrolyte interface (SEI) layer and effective passivation of cathode surface, leading to improved cycling performance delivering enhanced discharge capacities to 205–182 mAhg–1 and capacity retention of 84% over 50 cycles. The SEI layer notably includes plenty of metal fluorides and −CF-containing species formed by additive decomposition. On the contrary, the origin of performance fade in electrolyte only was ineffective surface passivation and dissolution of metal elements, which leads to oxygen loss, surface structural degradation and crack formation at the LiNi0.5Co0.2Mn0.3O2 particles. The data provide a basic understanding of the interfacial stabilization mechanism on high-voltage layered oxide cathodes.

Characterization of a P2-type chelating-agent-assisted Na2/3Fe1/2Mn1/2O2 cathode material for sodium-ion batteries

A chelating-agent-assisted Na2/3Fe1/2Mn1/2O2 material showed enhanced electrochemical performance due to the formation of a thin and stable solid-electrolyte interface layer.

High-performance Si anodes with a highly conductive and thermally stable titanium silicide coating layer

We report a simple route for synthesizing titanium silicide-coated Si anodes via the silicothermic reduction process of TiO2-coated Si. The titanium silicide enhances the electrical conductivity of Si nanoparticles and provides a highly stable solid electrolyte interface layer during the cycling, resulting in excellent electrochemical performances and significantly improved high thermal stability.

Methyl Methacrylate (MMA)-Grafted Polypropylene (PP) Separator for Rechargeable Lithium Metal Battery

In this article the polypropylene (PP) separator grafted by methyl methacrylate (MMA) functional groups with plasma technique has been primarily investigated. The MMA groups are expected to form a stable interface with lithium metal electrode. In addition, the effect of the surface functional group MMA on the graphite and the LiFePO4 electrode has been also primarily examined. The cyclic voltammetry (CV) tests have exhibited faster deposition/dissolution reaction kinetics of lithium on stainless steel electrode. The impedance measurements have shown a smaller interface resistance between the electrolyte (PP-MMA separator) and the lithium metal electrode. The interface reaction kinetics of the electrolyte (separator)/lithium electrode can be effectively enhanced by the MMA surface functional groups. It is also found that the existence of the MMA-groups at the separator surface can increase the reversible capacity of both LiFePO4 and graphite electrode. Rechargeable secondary batteries with lithium metal as the negative electrode have a relatively high energy density in comparison with those with carbon-based materials as the negative electrode due to the high theoretical capacity of 3860 mAh/g. In the early stage of the researches on lithium battery systems, many attempts had been made to improve the cycle life of the lithium metal electrode. Later researchers paid their attention on the splendid appearance of the graphite-based carbon materials. As well-known, the carbon-based materials have been successfully used as the negative electrode in the commercial rechargeable Li-ion batteries nowadays. In fact, lithium metal electrode still has potential in the rechargeable lithium-based micro-batteries and the all-solid-state lithium batteries, etc. 1–6 For some devices such as the implantable medicine devices and microchips, the output power of the batteries is relatively small, but the cycle life must be long enough. Safety is the most important factor to the commercial applications; the solution leakage is absolutely not allowed in such systems. This type of battery is named as energy-type battery. The issue that the lithium metal anode faces is that the formation of the lithium dendrites leads to two main consequences. Firstly, the electrically isolated lithium is not to be used and will shed. Secondly, the penetration of fine lithium particles into the separator will cause the internal short. There are three main strategies that are used to improve the cyclic performance of the lithium metal electrode. The first strategy has been extensively investigated by researchers and is just on Li-alloys and Li-intermetallics. 2 The improvement of the cycle stability of the lithium electrode is expected by modifying the solid electrolyte interface (SEI) or by buffering the volume expansion. The second one is focused on the electrolyte additives, such as HF, CO2, sulfides and surfactants. 7 The additives play the role of decreasing the content of the deleterious impurities in SEI layers, stabilizing the SEI, modifying the morphology of SEI and weakening or delaying the formation of the lithium dendrites by the specific adsorption of these surfactants on the convex points of the surface that has a relatively high surface energy. Ishikawa and Morita 8 have compiled the related results. We thought that the first strategy came from the lithium metal itself; the second one originated from the electrolyte. There also exists the third strategy which is on the separator. After being assembled, the lithium metal electrode is in close contact with the separator. A more stable SEI layer can be constructed by modifying the surface of the separator and by grafting some functional groups into the separator surface. These functional groups are expected to improve the stability of the interface between the liquid electrolyte (separator) and the lithium metal electrode. In commercial lithium ion batteries, the separator is also in contact with the positive

Quaternary Ammonium Ionic Liquid Electrolyte for a Silicon Nanowire-Based Lithium Ion Battery

The performance of a silicon nanowire battery anode was investigated in electrolytes consisting of butyl-trimethyl ammonium bis(trifluoromethylsulfonyl)imide (QATFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The lithiation capacity of silicon nanowires in 1 M LiTFSI/QATFSI was low due to the lack of a stable solid–electrolyte interface (SEI) layer. The addition of 10 wt % propylene carbonate to the ionic liquid electrolyte promoted the formation of a stable SEI layer and resulted in substantially higher lithiation capacity. Galvanostatic cycling at a rate of C/20 for silicon half-cells and Si/LiCoO2 full cells showed good performance with a discharge capacity of ∼2000 mAh/g and Coulombic efficiency of 97% after 50 cycles. The effect of electrolyte additives, including ethylene carbonate and vinylene carbonate, was investigated by chronopotentiometry and electrochemical impedance spectroscopy. Results are discussed in terms of the SEI layer and its influence on battery capacity as well as cycle life.

Effects of vinylene carbonate on high temperature storage of high voltage Li-ion batteries

The effects of vinylene carbonate (VC) on high temperature storage of high voltage Li-ion batteries are investigated. 1.3 M of LiPF 6 dissolved in ethylene carbonate (EC), ethylmethyl carbonate (EMC) and dimethyl carbonate (DMC) of 3:3:4 volume ratio is used as original electrolyte for 18650 cylindrical cells with LiCoO 2 cathode and graphite anode. VC is then added to electrolyte. At the initial stage of the high temperature storage, higher open-circuit voltage (OCV) is maintained when increasing the VC concentration. As the storage time increases, OCV of higher VC concentration drops gradually, and then the gas evolution takes place abruptly. Gas analysis shows methane (CH 4) decreases with increase of the VC concentration due to formation of stable solid electrolyte interface (SEI) layer on the graphite. Since the residual VC after formation of the SEI layer decomposes on the cathode surface, carbon dioxide (CO 2) dramatically increases on the cathode with the VC concentration, leaving poly(VC) film at the anode surface, as suggested by XPS test results.

Effect of activation at elevated temperature on Li-ion batteries with flame-retarded electrolytes

The effect of activation temperature on Li-ion batteries with flame-retarded electrolytes containing 5 wt.% dimethyl methyl phosphonate (DMMP) and trimethyl phosphate (TMP) is investigated respectively. It is found that activation at elevated temperature promotes the formation of a stable solid electrolyte interface layer on the graphite electrode, which may significantly suppress the reductive decomposition of DMMP and TMP and avoid graphite exfoliation. But fierce oxidation of the electrolytes on the LiCoO 2 electrode at elevated temperature is harmful to the cell performance. A procedure of so-called altered temperature activation (ATA) is adopted for LiCoO 2/graphite full-cells. It can compromise the contradictive effects on the separate electrodes at the elevated temperature. High capacity and good rate capability are obtained for the cells with the flame-retarded electrolytes, especially for the TMP-containing electrolyte.

New electrolytes for lithium ion batteries using LiF salt and boron based anion receptors

The thermal and electrochemical stability, as well as compatibility with various bench mark cathode and anode materials of two new lithium fluoride salt (LiF) based electrolytes have been studied. These two new electrolytes are formed by using boron-based anion receptors, tris(pentafluorophenyl) borane (TPFPB), or tris(2H-hexafluoroisopropyl) borate (THFPB) as additives, which were designed and synthesized at Brookhaven National Laboratory (BNL), to dissolve the LiF salt in carbonate solvents. The transference number of Li + for these electrolytes is as high as 0.7 and the room-temperature conductivity is around 2 × 10 −3 S cm −1. The electrolytes containing propylene carbonate (PC) show superior low-temperature conductivity properties. The electrochemical window is approaching 5.0 V. It was also found that the new electrolytes work well with LiCoO 2 or LiMn 2O 4 cathodes. However, when PC containing electrolytes were used, PC co-intercalation is still a problem for graphite anodes. The formation of a stable solid electrolyte interface layer on the surface of anode in this type of electrolyte needs to be studied further.

Raman scattering and short range order in amorphous germanium : J. S. Lannin, N. Maley and S. T. Kshirsagar. Solid St. Commun.53 (11) 939 (1985)

Tin-antimony/phosphorus nanocomposite thin films have been successfully prepared by pulsed laser deposition and are studied as anode materials for sodium ion batteries. The thin films exhibit a specific capacity of about 252 mAh g−1 over 100 cycles at a rate of 250 mA g−1, which is much higher than those for tin-antimony alloy, antimony or tin thin films. The improved electrochemical performance is attributed to the introduced phosphorus, which plays a key role in forming a stable solid electrolyte interface layer, thus enhances the reversibility. Phase separation is revealed after the initial cycle by forming the metallic tin and antimony nanoparticles. In addition, introducing phosphorus into tin-antimony alloy film can reduce the interfacial resistance between the electrode and electrolyte, as well as facilitate sodium-ion diffusion in the electrode.