Electrolytes For Lithium Rechargeable Batteries Research Articles

Recent Progress and Perspectives of Solid Electrolytes for Lithium Rechargeable Batteries

현재 상용화되어 있는 리튬이온전지에 사용하고 있는 비수계 유기 전해액은 가연성, 부식성, 고휘발성, 열적 불안정성 등의 단점 때문에 더욱 안전하고 장수명을 보이는 고체 전해질로 대체하는 연구가 진행되고 있으며, 이것은 전기자동차 및 에너지저장 시스템과 같은 중대형 이차전지에도 효율적으로 활용될 수 있다. 다양한 형태의 고체 전해질 중에서 현재 고분자 매트릭스에 활성 무기 충진재가 포함되어 있는 복합 고체 전해질이 고이온전도도와 전극과의 탁월한 계면접촉을 이루는데 가장 유리한 것으로 알려졌다. 본 총설에서는 우선 고체 전해질의 종류와 연혁에관해 간단히 소개하고, 고분자 및 무기 충진재 (불활성 및 활성)로 구성되는 고체 고분자 전해질 및 무기 고체 전해질의 기본적 물성 및 전기화학적 특성을 개괄한다. 또한 이 소재들의 형상을 기준으로 입자형 (0D), 섬유형 (1D), 평판형 (2D), 입체형 (3D)의 형식으로 구성된 복합고체 전해질과 이에 따른 전고체 전지의 전기화학적 특성을 논의한다. 특히 리튬금속 음전극을사용하는 전고체 전지에 있어서 양전극-전해질 계면, 음전극-전해질 계면, 입자간 계면의 특성에관해 소개하고, 마지막으로 현재까지 보고된 관련 총설들을 참조하여 복합 고체 전해질 기술의현재 요구조건 및 미래 전망을 알아본다.

High-throughput design and optimization of fast lithium ion conductors by the combination of bond-valence method and density functional theory.

Looking for solid state electrolytes with fast lithium ion conduction is an important prerequisite for developing all-solid-state lithium secondary batteries. By combining the simulation techniques in different levels of accuracy, e.g. the bond-valence (BV) method and the density functional theory (DFT), a high-throughput design and optimization scheme is proposed for searching fast lithium ion conductors as candidate solid state electrolytes for lithium rechargeable batteries. The screening from more than 1000 compounds is performed through BV-based method, and the ability to predict reliable tendency of the Li+ migration energy barriers is confirmed by comparing with the results from DFT calculations. β-Li3PS4 is taken as a model system to demonstrate the application of this combination method in optimizing properties of solid electrolytes. By employing the high-throughput DFT simulations to more than 200 structures of the doping derivatives of β-Li3PS4, the effects of doping on the ionic conductivities in this material are predicted by the BV calculations. The O-doping scheme is proposed as a promising way to improve the kinetic properties of this materials, and the validity of the optimization is proved by the first-principles molecular dynamics (FPMD) simulations.

Fast lithium ion conducting solid state thin-film electrolytes based on lithium thio-germanate materials

In this study, lithium thio-germanate thin-film electrolytes for lithium rechargeable batteries have been successfully prepared by radio-frequency (RF) magnetron sputtering deposition in Ar gas atmospheres. The targets for RF sputtering were prepared by melting, milling and pressing the appropriate amounts of the starting materials in the nLi2S+GeS2, n=1–4, binary system. 2mm wide×18mm long Au electrodes with a parallel configuration of 2mm spacing were sputtered to ∼100nm thick at a sputtering rate at ∼5nmmin−1 on Al2O3 single crystal substrates. Thin-film electrolytes were grown on this electrode assembly at 50W power and 25mtorr in Ar gas pressure. The ionic conductivities of the thin-film electrolytes were measured from −25°C to 100°C with 25°C increments over the frequency range 0.1Hz–1MHz. The d.c. ionic conductivities determined from complex plane plots of the impedance of the Li2GeS3, Li4GeS4, Li6GeS5, and Li8GeS6 amorphous thin films at 25°C were found to be 1.1×10−4Scm−1, 7.5×10−4Scm−1, 1.7×10−3Scm−1, and 7.0×10−5Scm−1, respectively. As the Li2S content in the thin film increases, the ionic conductivities of the thin films increase from n=1 to n=3. However, for the n=4 Li8GeS6 thin film, the ionic conductivity decreased and the activation energy increased. The maximum in the conductivity for the n=3 film is among the highest ever reported for an amorphous solid state Li+ ion conductor.

Preparation and Characterization of Fast Ion Conducting Lithium Thio-Germanate Thin-Films Grown by RF Magnetron Sputtering

In this study, amorphous lithium thio-germanate thin-films were prepared as electrolytes for lithium rechargeable batteries by RF sputtering deposition in Ar atmospheres. For the first time, new high quality lithium germanium sulfide, nLi2S + GeS2(n = 1, 2, and 3) thin-films have been successfully made by RF sputtering and synthesized as new solid state electrolytes. Although these materials are unstable in air the starting materials, target materials, and thin-films were thoroughly characterized by XRD, Raman, SEM, XPS, and impedance spectroscopy using special setups to prevent contamination. Thin-films did not show any cracks and pits on the surface and the ionic conductivities of the thin-films are ~1000 times higher than reported values for oxide thin-films. In this way, this work may provide a new way for developing new thin-film electrolytes for solid state lithium ion batteries.

Cation−Anion Interactions in 1-Ethyl-3-Methylimidazolium Trifluoromethanesulfonate-Based Ionic Liquid Electrolytes

An important step in developing ionic-liquid-based electrolytes for lithium rechargeable batteries is obtaining a molecular-level understanding of the ionic interactions that occur in these systems. In this study, 1-ethyl-3-methylimidazolium trifluoromethansulfonate ([C2mim]CF3SO3) is complexed with LiCF3SO3, and the local structures of the CF3SO3- and [C2mim]+ ions are investigated with infrared and Raman spectroscopy. The isolation and subsequent refinement of a Li[C2mim](CF3SO3)2 crystal provides further insight into the structure of the [C2mim]CF3SO3-LiCF3SO3 solutions. Minor changes are observed in the infrared and Raman spectra of dilute [C2mim]CF3SO3-LiCF3SO3 solutions compared to pure [C2mim]CF3SO3. However, a suspension of very small Li[C2mim](CF3SO3)2 crystallites forms at a solution composition of [C2mim]CF3SO3:LiCF3SO3 = 10:1 (mole ratio), placing an upper limit on the solubility of LiCF3SO3. Essentially no changes are observed in the vibrational modes of the [C2mim]+ cations over the entire range of LiCF3SO3 compositions studied, suggesting that the addition of these compounds does not significantly perturb the local structure of the [C2mim]+ cations. The salt used in this study has a common anion with the ionic liquid; thus, the ion cloud surrounding the [C2mim]+ ions, which must be primarily composed of CF3SO3- anions, is not significantly altered with the addition of LiCF3SO3.

Electrical properties of plasticized chitosan-lithium imide with oleic acid-based polymer electrolytes for lithium rechargeable batteries

Solid polymer electrolytes (SPEs) were prepared and their electrochemical characteristics were characterized. The composition of SPEs containing chitosan, lithium trifluoromethane sulfonimide (LiN(CF3SO2)2) and oleic acid (OA) was optimized employing ac impedance measurements at various temperatures. The electrical conductivity of the SPEs with OA shows the highest value and the presence of OA does not change the structure of the polymer.

The effect of plasticizers on transport and electrochemical properties of PEO-based electrolytes for lithium rechargeable batteries

The effect of plasticizers (or solvent additives) on the transport and electrochemical properties of polymer electrolytes has been examined. First, the mobility of cations and anions of LiN(CF 3SO 2) 2 (LiTFSI) was increased by doping the PEO-based electrolytes with ethylene carbonate and poly(ethylene glycol dimethyl) ether. However, the cation mobility in PEO-based electrolytes doped with propylene carbonate was suppressed resulting in a lower cation transference number. Nevertheless, all the plasticized electrolytes have higher bulk conductivity than the non-plasticized, even in the case the cation transference number decreased. This is due to increased ion mobilities and/or higher degree of ion dissociation upon the introduction of plasticizers. A study of the electrochemical stability of the electrolytes, by linear sweep voltammetry, shows that the plasticizers have a negligible effect on the electrolyte stability windows. Finally, the electrolyte/lithium metal electrode interfacial impedance was monitored by A.C. impedance as a function of storage time. The formation and growth rate of the passivation layer was diminished in the presence of the plasticizers.

Composite Electrolytes for Lithium Rechargeable Batteries

The paper reviews and presents attributes of emerging polymer-ceramic composite electrolytes for lithium rechargeable batteries. The electrochemical data of a diverse range of composite electrolytes reveal that the incorporation of a ceramic component in a polymer matrix leads to enhanced conductivity, increased lithium transport number, and improved electrode-electrolyte interfacial stability. The conductivity enhancement depends upon the weight fraction of the ceramic phase, annealing parameters, nature of polymer-ceramic system, and temperature. The ceramic additive also increases the effective glass transition temperature and thus decouples structural and electrical relaxation modes which in turn increases the lithium transport number. The ceramic additives also provide a range of free energy of reactions with lithium. A few of the ceramic materials (MgO, CaO, Si3N4) have positive free energy of reaction and they should not passivate lithium electrodes.

Chemical properties of various organic electrolytes for lithium rechargeable batteries: 1. Characterization of passivating layer formed on graphite in alkyl carbonate solutions

The characteristics and reaction mechanisms of the passivating film formed on the surface of graphite were investigated in ethylene carbonate-diethyl carbonate solutions containing LiClO 4, LiPF 6 and LiN(SO 2CF 3) 2. The electron consumption resulting on the irreversible capacity of graphite was almost equivalent to that used in the one-electron reduction of Li + found in the film. The electrochemical reactions in the first discharge process may be divided into the following steps: (i) ‘initial film formation step’ from 1.4 to 0.55 V; (ii) ‘main film formation step’ from 0.55 to 0.2 V, and (iii) 'lithium intercalation step from 0.2 to 0.0 V. Most of the passivating film is formed together with the lithium intercalation reaction at step (ii). The passivating film formed at this step contained a significant amount of organic film such as EtOCO 2Li, (CH 2OCO 2Li) 2, etc. Through the consecutive formation of passivating film at steps (i) and (ii), lithium intercalation into graphite proceeds smoothly without further decomposition of the organic electrolyte.

Development of ion‐conducting polymer electrolytes for use in high‐energy lithium rechargeable batteries

AbstractPolymers based on poly(thylene oxide) (PEO) are a very promising new type of stable electrolytes for lithium rechargeable batteries. Their relatively low ionic conductivities can be more than compensated by the very small electrolyte thicknesses that can be used. Specific energies of 100 Wh/kg at sustained specific powers of 70 W/kg, have been obtained at Hydro‐Québec with 100 μm of PEO electrolyte at 100°C. In an electric vehicle, this would give a driving range of over 300 km at 80 km/h, more than three times as much as lead‐acid batteries. PEO‐related polymers have been developed for lower temperature applications such as computers or portable appliances. Advantages over competitive Ni‐Cd batteries are higher energy densities and absence of self‐discharge, with expected shell lifes of 10 years. Laboratory prototypes (3600 cm2, 10 Wh) demonstrate the absence of scale‐up effects and excellent cycling capability (over 300 charge‐discharge cycles).