Lithium Ion Transport Number Research Articles

Amorphous solid electrolytes in the system Li2S-Al2S3-SiS2prepared by mechanical milling

Amorphous solid electrolytes in the ternary system Li2S-Al2S3-SiS2 were successfully prepared by mechanical milling. The ambient temperature conductivity of the 60Li2S·10AlS1.5·30SiS2 (mol%) sample reached over 10−4 S cm−1 with amorphization by mechanical milling for 40 h. The binary Li2S-Al2S3 amorphous electrolytes, which have not been synthesized by a conventional melt-quenching technique, were also obtained by mechanical milling. The 60Li2S·40AlS1.5 (mol%) amorphous electrolyte exhibited lower conductivity and higher activation energy for conduction than the 60Li2S·40SiS2 (mol%) amorphous electrolyte. The addition of SiS2 to Li2S-Al2S3 system monotonically increased electrical conductivity and decreased activation energy for conduction. The amorphous 60Li2S·10AlS1.5·30SiS2 material showed favorable features as a solid electrolyte such as unity of lithium ion transport number and wide electrochemical window.

LiMOB, an Unsymmetrical Nonaromatic Orthoborate Salt for Nonaqueous Solution Electrochemical Applications

Synthesis, characterization, ionic conductivity, electrochemical stability, and lithium-ion transport number of an asymmetric version of the successful orthoborate lithium salt lithium bis(oxalato)borate (LiBOB), are described. The salt, lithium (malonato oxalato) borate (LiMOB), is thermally stable up to 273°C. It is poorly soluble in common organic solvents such as 1,2-dimethoxyethane, tetrahydrofuran, acetonitrile, dimethyl carbonate, and propylene carbonate, but has moderate solubility in γ-butyrolactone (GBL) and N,N-dimethylformamide (DMF), and high solubility in dimethyl sulfoxide (DMSO). The 0.5 M solutions of LiMOB in GBL, DMSO, and DMF show high conductivities and at 25°C, respectively) relative to most 0.5 M nonaqueous solutions. Even the room temperature conductivity of the 0.08 M LiMOB-PC solution is close to The conductivities of LiMOB solutions are close to those of LiBOB solutions, which has been demonstrated in recent studies to be a successful substitute for in lithium-ion batteries. The cyclic voltammograms show that LiMOB solutions in PC and GBL have electrochemical stability as high as 4.3 V vs. The lithium-ion transport number at room temperature for 0.5 M LiMOB in was 0.36, obtained from self-diffusivity measurement by the pulsed field gradient spin echo nuclear magnetic resonance technique. The highest occupied molecular orbital energy, which is usually correlated with electrochemical stability has been calculated, and electrostatic potential maps for the new anion and its fluorinated derivatives are presented. They suggest that the fluorinated analogue of LiMOB should be more stable and more soluble, and may have unique properties. © 2004 The Electrochemical Society. All rights reserved.

リチウムイオン伝導性Ｌｉ２Ｓ‐ＧｅＳ２系非晶質材料のメカニカルミリング法による合成

Lithium-ion-conducting amorphous materials in the system Li2S-GeS2 were prepared by use of a high-energy ball-milling process. The amorphous materials were obtained over the wide composition range up to 66.7mol%Li2S content. The composition range in which the amorphous materials were obtained by the ball-milling process was much wider than the glass-forming region by conventional melt-quenching methods. The lithium-ion conductivities of the obtained amorphous materials increased with an increase in the Li2S content. The activation energies for conduction correspondingly decreased with increasing the Li2S content. The 66.7Li2S⋅33.3GeS2(mol%) sample showed the maximum conductivity 1.1×10-4Scm-1 at 298 K.DC polarization measurements suggested that a lithiumion transport number was almost unity for the obtained amorphous materials.

New lithium organic salts for promising polymer electrolytes

In the plasticized and gel-like polymer, electrolytes containing such aprotic solvents as plasticizers, cations and anions of lithium salts are mobile. As a rule the transport number of lithium ions in these systems is far less than 1 (usually 0.5). Such a situation can result from the possibility of cation binding by polymer matrix polar groups (e.g., -Oin polyethylene oxide, -CN in polyacrylonitrile, -NR in polyamide, etc). In this case, an anion can contribute more to the conductivity than a cation can. The problems of the undesirable participation of anions in ion transport and decreasing reactivity of polymer electrolytes relative to the electrode materials can be solved by using lithium organic salts with large anions. This is illustrated by the increased interest in the application of new organic and inorganic lithium salts in the composition of polymer electrolytes:

Structures of Orthoborate Anions and Physical Properties of Their Lithium Salt Nonaqueous Solutions

We compare the physical properties and solution conductivities of three new lithium orthoborate salts with those of the well-known salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The three new lithium salts are lithium bis(perfluoropinacolato)borate (LiBPFPB), lithium bis(oxalato)borate, and lithium bis(malonato)borate (LiBMB). Computational models of the three orthoborate anions show that the borate oxygens in anion are the least exposed. The oxygens are electronically identical in but not in the other anions. The three new lithium salts show conductivities that closely approach those of LiTFSI but show surprising and solvent-dependent orderings. The conductivity is nearly independent of the salt content in the salt concentration range of which is advantageous for their applications. Self-diffusivity measurements for and are presented and are consistent with the very high ionic dissociation levels proposed for these salts based on other evidence. The lithium-ion transport number at room temperature for LiBPFPB in nonaqueous solutions exceeds 0.5 and for LiBMB is about 0.4. © 2002 The Electrochemical Society. All rights reserved.

Mechanochemical Synthesis of High Lithium Ion Conducting Materials in the System Li3N—SiS2.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Ionic mobilities of PVDF-based polymer gel electrolytes as studied by direct current NMR

In order to estimate the ionic transference number precisely the equipment of the direct current (DC) NMR measurement (the pulsed-gradient spin-echo (PGSE) NMR by applying a direct electric field) was improved with an electric field control technique using a four-terminal electrophoretic sample cell. It was found that this technique was appropriate to achieve the constant electric field condition at the NMR detected section. The ionic mobilities of the cation and anion of the lithium gel electrolyte, 1 M LiN(CF 3SO 2) 2–EC/DEC–PVdF-HFP, were measured individually using the modified apparatus. The transport number of lithium ion obtained from the ionic mobilities of lithium ion and counter anion group was different from the apparent value estimated from the diffusion coefficients of the lithium and anion species. This disagreement was due to the ion-pair component in diffusion coefficients. It indicated that the DC-NMR was more precise technique for estimating the transference number of ions than the simple PGSE-NMR.

Mechanochemical Synthesis of High Lithium Ion Conducting Materials in the System Li3N−SiS2

High lithium ion conducting materials were mechanochemically synthesized using Li 3 N and SiS 2 as starting materials. The obtained Li 3 N-SiS 2 materials were almost amorphous; the amorphous phases consisted of SiS 4 tetrahedral units with no edge sharing and the local structure was very similar to that of mechanically milled Li 2 S-SiS 2 amorphous materials. High lithium ion conducting Li 3 N-SiS 2 materials could be synthesized in very short milling periods, around 20 min, since explosive reactions occurred in this system. The mechanically milled 40L1 3 N60SiS 2 (mol %) material exhibited excellent properties as solid electrolytes such as high conductivity around 10 -4 S cm -1 at room temperature, unity of lithium ion transport number, and a wide electrochemical window of about 10 V vs Li + /Li.

Characterization of Li 2S–SiS 2–Li xMO y (M=Si, P, Ge) amorphous solid electrolytes prepared by melt-quenching and mechanical milling

The oxysulfide amorphous materials in the systems 95(0.6Li 2S·0.4SiS 2)·5Li x MO y (M=Si, P, and Ge) were prepared by melt-quenching and mechanical milling techniques. These amorphous materials exhibited high conductivity over 10 −4 S cm −1 at room temperature, a lithium transport number of unity, and a wide potential window of 10 V. The solid-state cells with the oxysulfide amorphous materials as solid electrolytes worked as lithium secondary batteries and exhibited excellent cycling performance over 100 times. The local structure of the mechanically milled amorphous materials containing Li 4SiO 4 was similar to that of the corresponding melt-quenched glasses, in which the SiS 4 and SiOS 3 tetrahedral units were mainly present. The SiO n S 4− n ( n=1, 2, 3) tetrahedral units were formed in the case of the addition of Li 4SiO 4 and Li 4GeO 4 to the base sulfide system, while these units were not present in the addition of Li 3PO 4. We have concluded that the reactivity of Li x MO y derived from its basicity affected the structure and formation process of the oxysulfide materials prepared by mechanical milling.

Mechanochemical Synthesis of the High Lithium lon Conductive Amorphous Materials in the Systems Li2S-SiS2 and Li2S-SiS2-Li4SiO4.

Amorphous materials in the system xLi2S⋅(100-x)SiS2, where x ranged from 50 to 70mol%, and (100-y)(0.6Li2S⋅0.4SiS2)⋅yLi4SiO4, where y ranged from 0 to 10mol%, were synthesized by mechanical milling of crystalline starting materials, Li2S, SiS2 and Li4SiO4. At the compositions with large amounts of Li+ ions, a part of crystalline Li2S used as a starting material remained in the milled powder samples. It was found that the milled powder samples in both systems obtained by mechanical milling exhibited high conductivities in the order of 10-4S·cm-1 at room temperature in spite of the presence of small amounts of Li2S crystals. The conductivity values of the pelletized samples of xLi2S⋅(100-x)SiS2 powders maximized at the composition of about x=60. On the other hand, the conductivities in the composition range with y≤5 in the system (100-y)(0.6Li2S⋅0.4SiS2)⋅yLi4SiO4 were nearly the same values in the measured temperature range and higher by a half order of magnitude than those at the composition with y=10. The transport number of lithium ions of the amorphous materials after mechanically milled was almost unity and the potential window was wider than 10V at room temperature.

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.

Mechanochemical Synthesis of New Amorphous Materials of 60Li2S·40SiS2 with High Lithium Ion Conductivity

New amorphous materials were mechanochemically synthesized by use of crystalline starting materials of Li2S and SiS2. The conductivity of a mechanochemically prepared sample of 60Li2S40SiS2(mol%) after a milling for 20 h was around 10‐4 Scm‐1 at room temperature. This conductivity was comparable to that of the corresponding glassy powders prepared by twin‐roller rapid quenching of melt and then pulverizing. The transport number of lithium ions in the mechanochemically prepared sample was nearly unity. Mechanochemical synthesis is a promising way to produce new solid electrolytes for solid‐state lithium secondary batteries.

High lithium ionic conductivity of poly(ethylene oxide)s having sulfonate groups on their chain ends

Poly(ethylene oxide) oligomers having sulfonate groups on one or both chain ends [PEO–(SO 3 M) n (n=1 or 2); M=Li, Na, K, Rb or Cs] with different PEO molecular masses (150–2000) have been prepared as new single-ion conductive matrices. High lithium ionic conductivity (4.45×10 -6 S cm -1 , at 30 °C) was obtained in PEO–SO 3 Li with PEO molecular mass of 350, the transport number of lithium ion (t Li+ ) was ca. 0.75 at 20 °C. The glass transition temperature (T g ) of these hybrid salts depended significantly on the molecular mass of the PEO and its molecular structure. The PEO oligomers containing a sulfonate group on only one end showed higher ionic conductivity than those containing sulfonate groups on both ends at the same salt fraction up to 50% per OE unit (i.e. M w >500). In both types of hybrid salts, the PEO–sulfonate with relatively high molecular mass around 2000 showed a crystalline phase at room temperature reflecting the crystallinity of the PEO component. On the other hand, the hybrid having PEO with low molecular mass of ca. 200 showed an amorphous phase but had a very high T g , considerably reflecting the characteristics of the salt unit. PEO–sulfonates with molecular masses of PEO between 350 and 1000 were confirmed not only to show an amorphous phase over a wide temperature range but also to have low glass transition temperatures at ca. -40 °C.

Studies on the lithium ion conduction in Ca0.95Li0.10WO4 using cold neutron radiography

Cold neutron radiography (CNR) was applied to study the lithium ion conduction in the substituted scheelite-type oxide of Ca0.95Li0.10WO4. The lithium ion distribution profiles were obtained from a set of neutron radiography (NR) images of the electrolyzed oxides having different 6Li/7 ratios. They showed that the lithium ion transport number of the oxide is 0.99, which coincided with the value derived from the EMF measurement of an oxygen gas concentration cell. Furthermore, they denoted that the lithium ion conduction was preferably ascribed to lithium ions in the interstitial sites.

Application of NR for research in electrochemical systems

The neutron radiography (NR) technique has been applied to high temperature ion conducting materials such as Li 1.33 Ti 1.67O 4 and Ca 0.95 Li 0.1 WO 4 in order to visualize the movement of lithium ions within the material. After electrolysis DC current was passed through these oxides prepared with different isotope ratios ( 6Li/ 7Li), a set of NR images was obtained which verified the lithium ion conduction in the oxides. It was also clearly shown that the transport number of lithium ions in such oxides can be accurately determined by digitizing and analyzing the NR images. In addition, some investigation was carried out using the NR technique to see the lithium distribution in a lithium battery before and after discharge. The results indicated that NR can be used to clarify the local discharging efficiency in a battery and/or to investigate the reversibility of lithium rechargeable batteries.

Application of Neutron Radiography to Visualize the Motion of Lithium Ions in Lithium‐Ion Conducting Materials

Neutron radiography (NR) has been applied to a lithium in conducting spinel‐type oxide in order to visualize the movement of lithium ions. After dc current was passed for electrolysis through specially prepared oxides with different isotope ratios , a set of NR images was obtained that illustrate the lithium ion conduction in the oxide. Analysis of the NR images determined that the transport number of lithium ions in the spinel‐type is 0.99 at 900°C, which is almost the same as that measured by the oxygen concentration cell method. Further detailed analysis was carried out to investigate which kind of lithium ion in the oxide ion array of the spinel‐type structure contributes to the electric conduction, the tetrahedral A site lithium, the octahedral B site, or both of these. As a result, the contribution of A site lithium to ionic conduction was confirmed.

Conductivity and thermal studies of solid polymer electrolytes prepared by blending poly(ethylene oxide), poly(oligo[oxyethylene]oxysebacoyl) and lithium perchlorate

Blend-based polymer electrolytes composed of poly(ethylene oxide)(PEO), poly(oligo[oxyethylene]oxysebacoyl)(PES) and lithium perchlorate have been prepared. The characteristics of these polymer electrolytes were investigated in terms of blend composition and salt concentration. The addition of PEO to PES/LiClO 4 complex significantly improved the dimensional stability with a slight decrease in the latter's ionic conductivity. The PEO(40)/PES(60)/LiClO 4 electrolyte at [LiClO 4] [EO] = 0.10 exhibited an ionic conductivity of 3 × 10 −5 S/cm at 25 °C, and was an elastomeric material with dimensional stability. The lithium transport number in this system was determined to be about 0.37 at 40 °C.

A New Class of Advanced Polymer Electrolytes and Their Relevance in Plastic‐like, Rechargeable Lithium Batteries

The synthesis, properties, and application of a new class of polymer electrolytes, are here reported and discussed. The electrolytes have a very high ionic conductivity, an acceptable lithium ion transport number, and a wide electrochemical stability window. The members of the family which appear most promising in terms of stability of the lithium electrode interface have been tested as electrolyte separators in high voltage, thin layer, laminated rechargeable batteries. Preliminary results provided indications of promising performance in terms of voltage output and cyclability.

Ion‐conduction of lithium fluoroalkylsulfonates in oligo(oxyethylene)‐branched poly(phosphazene)

AbstractNovel organic‐soluble lithium salts, lithium 1,1,2‐trifluoro‐4‐methoxy‐1‐butanesulfonate (I) and lithium 3‐(2‐methoxyethoxy)‐1‐propanesulfonate (II), were synthesized. Their ionic conductivities were examined in a solid polymer matrix of endo‐methoxy oligo(oxyethylene)‐branched poly(phosphazene) (III) and compared with the ordinary hybrids of LiCIO4/III or LiSO3CF3/III. The ionic conductivity of I/III hybrid was as high as 2,2.10−5 S. cm−1 at 25°C, which is comparable to that of LiCIO4/III or LiSO3CF3/III hybrids. Although anions are the major carrier ions in the LiCIO4/III or LiSO3CF3/III hybrids, the lithium transport number of I/III hybrid was about 0.5 due to the larger size of the counter anion.

Ionic transport number of network PEO electrolytes

The temperature dependence of the ionic transport numbers of Li + was determined by means of the combination of the complex impedance and potentiostatic polarization measurements of the crosslinked poly(ethylene oxide) (PEO) electrolytes containing dissolved lithium perchlorate (LiClO 4). The ionic conductivity and lithium ion transport number showed dependence on the temperature and LiClO 4 content of the network PEO electrolytes, namely its Tg. The lithium ion transport number of the network PEO complexes was lower than 0.5. The lithium ion which has a solvated radius migrates with the segmental motion of the polymer.