Electrodes For Rechargeable Lithium Batteries Research Articles

Mechanism of Electrochemical Activity in Li2MnO3

Lithium intercalation compounds based on lithium manganese oxides are of great importance as positive electrodes for rechargeable lithium batteries. It is widely accepted that Li+ may be extracted (deintercalated) from such lithium manganese oxides accompanied by oxidation of Mn up to a maximum oxidation state of +4. However, it has been suggested recently that further Li+ removal may be possible. Among the mechanisms that have been proposed to charge balance the removal of Li+ are Mn oxidation beyond +4 or loss of O2-. To investigate this phenomenon we have selected Li2MnO3, a layered compound Li[Li1/3Mn2/3]O2 with a ready supply of mobile Li+ ions but with all Mn already in the +4 oxidation state. We show that a substantial quantity of Li (at least 1.39 Li) may be removed. At 55 °C this occurs exclusively by oxidation of the nonaqueous electrolyte, thus generating H+ which exchange one-for-one with Li+ to form Li2-xHxMnO3. The presence of H+ between the oxide layers results in a change of the layer stac...

Poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene): a new organic polymer as positive electrode material for rechargeable lithium batteries

A new organic polymer as positive electrode material is presented. Poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene) (PDBM) has oxocarbon cycles which are part of the polymer backbone and exhibit redox properties. Composite materials with acetylene black were investigated as positive electrodes for rechargeable lithium batteries. A specific capacity of 150 mAh g −1 was reached with 40% acetylene black. The composite electrodes showed moderately good cyclability with less than 10% degradation in the first 100 cycles.

Ce–Sn intermetallic compounds as new anode materials for rechargeable lithium batteries

To increase the volumetric discharge capacity of negative electrode for rechargeable lithium batteries, a new intermetallic compound including rare earth element, CeSn 3, was synthesized by mechanical alloying (MA), and the performance of the electrode was investigated. The CeSn 3 electrode was found to have a volumetric discharge capacity of over 2000 mA h cm −3 based on the theoretical volume of CeSn 3, which is three times larger than that of graphite electrode. The electrochemical reaction of the CeSn 3 electrode with Li may not obey the well-known mechanism of Li x Sn formation in the other tin-based electrodes because of lower potential plateaus in comparison with those of pure tin electrode. Although the CeSn 3 electrode exhibited very poor cycle life, performance could be improved significantly if the CeSn 3 was reacted with lithium using MA in advance. The resulting Li 3.8CeSn 3 electrode showed an excellent performance not only on the cyclability, but also on the reversibility at the first cycle.

LiMn 2O 4-based composites processed by a chemical-route : Microstructural, electrical, electrochemical, and mechanical characterization

Composites of positive electrodes for rechargeable lithium batteries have been prepared from LiMn 2O 4 as electrochemically active material, carbon black (CB) as good electronic conductor, and polyvinylidenefluoride (PVDF) as binder. The composites having different contents in LiMn 2O 4 and CB, and nearly the same content in PVDF have been processed by a route that is currently used. The microstructure of the composites, as followed by scanning electron microscopy (SEM), is heterogeneous showing extended regions of PVDF–CB, and clusters of LiMn 2O 4. The electrical conductivity shows a sharp increase at the CB content of 3 vol.% (2 wt.%) in accordance with a percolation process. The capacity shows also a sharp increase at that content. A maximum in capacity at ca. 10 wt.% of CB is observed when the overall weight of the composite is taken into account. Both features, sharp increase in capacity and maximum of capacity, have been found in discharge experiments made at different currents. The composites show an elastic behavior up to a stress of ca. 6 MPa. Above this, the composites breaks down through a crack that propagates slowly according to a ductile behavior. The microstructure as well as the electrical, electrochemical, and mechanical properties of the composites are compared with those reported on composites having the same three components but processed by a different route.

Attempts to Improve the Behavior of Li Electrodes in Rechargeable Lithium Batteries [Journal of The Electrochemical Society, 149, A1267 (2002)

© 2003 The Electrochemical Society. All rights reserved.

A Nanocrystalline Ferric Oxide Cathode for Rechargeable Lithium Batteries

Lithium intercalation hosts as the positive electrode (cathode) are central to the chemistry and key to the energy density of rechargeable lithium batteries. The high cost and toxicity of the commercially used LiCoO 2 cathode have prompted extensive searches for alternatives. While manganese oxides have been investigated most extensively, iron oxides are even more attractive from cost and environmental standpoints. However, search for iron oxides of conventional crystalline structures and micrometer particle sizes as lithium intercalation cathodes has been greeted with disappointing results. Here we report a nanocrystalline ferric oxide that simultaneously exhibits very high lithium intercalation capacity, excellent rate capability and capacity retention upon cycling. These properties reveal thermodynamics and kinetics of the nanocrystalline material inherently different from those of its microcrystalline counterpart, and suggest promise of nanostructured intercalation compounds as electrodes for rechargeable lithium batteries.

LiCoO2 and LiMn2 O 4 Thin-Film Electrodes for Rechargeable Lithium Batteries: Preparation Using PVP Sol-Gel to Produce Excellent Electrochemical Properties

and thin-film electrodes for rechargeable lithium batteries were prepared by a sol-gel method with poly(vinylpyrrolidone) (PVP). The Li-Co-O and Li-Mn-O sols were successfully prepared by using PVP. The sol coated on an Au substrate by a spin coater was converted to a gel film through the spin-coating process. The gel films were heated at 800°C for 1 h. The prepared thin films were characterized with both the X-ray diffraction method and scanning electron microscopy. From these results, it was found that the films prepared from Li-Co-O and Li-Mn-O sols were with a rock-salt-like structure and with a spinel structure, respectively. Electrochemical properties of the prepared films were evaluated with charge and discharge tests and cyclic voltammetry in a mixed solvent of ethylene carbonate and diethyl carbonate (1:1 in volume) with These results showed that these thin-film electrodes have excellent electrochemical properties. © 2002 The Electrochemical Society. All rights reserved.

Lithium intercalated compounds

Abstract Numerous channel- or tunnel-structured compounds are interesting materials in which lithium intercalation occurs primarily without destruction of the host lattice assuming a complete charge transfer. In many cases, the rigid-band model (RBM) is a useful first approximation for describing the changes in electronic properties of the host material with intercalation. The applicability of the rigid-band model is taken as a test for the properties most desirable in a good intercalation material. This review paper presents experimental results, namely optical and electrical measurements, obtained on various intercalation materials such as dichalcogenides, trichalcogenides and oxides to probe the validity of the RBM. The impact of the lithium intercalation is discussed for various structural forms, from well-crystallised to amorphous compounds. We observed, nevertheless, that the rigid-band model is not applicable to all of the layered intercalation materials. This needs yet to be more extensively documented for their promising application as insertion electrode in rechargeable lithium batteries. Compounds such as TiS 2 , TaS 2 , MoS 2 , NiPS 3 , MoO 3 , V 2 O 5 , V 6 O 13 , LiCoO 2 , LiNiO 2 , LiMn 2 O 4 and LiNiVO 4 are tested in this work. Some guidelines are established for improving the performances of these materials in their most eminent applications.

Spinel - ramsdellite transition: A new synthesis route to materials useful as electrodes in rechargeable lithium batteries

Se han investigado las posibles transformaciones a alta temperatura de diversas espinelas del tipo LiTi2-xMxO4 con M = V, Cr, Fe y Co, habiendose determinado que es posible la obtencion de nuevas rasmdellitas LiTi2-xVxO4 y LiTi2-xCrxO4 con 0 . x . 1. La caracterizacion estructural mediante difraccion de rayos X y las medidas de susceptibilidad magnetica realizadas para el caso del cromo, en union de los datos aportados por el estudio electroquimico realizado, han permitido establecer que la sustitucion cationica lleva a compuestos del tipo Li(Ti3+)1-xMx(Ti4+)O4 con M = V3+ o Cr3+. El comportamiento electroquimico de LiTi2- xVxO4 permite proponer su posible uso como electrodo negativo en baterias de ion litio, ya que estos nuevos electrodos desarrollan capacidades de 160 mAh/g a un potencial medio de 1.5 V, valores que resultan similares a los del compuesto sin sustituir, la ramsdellita LiTi2O4 (166 mAh/g). Hay que destacar el comportamiento versatil de una nueva familia de ramsdellitas, LiTi2-xCrxO4. El estudio presentado sobre el miembro de esta familia con x = 1, la composicion que se ha considerado mas relevante, ha permitido proponer a este nuevo material como un buen candidato a electrodo negativo en baterias recargables de litio. Ademas de poder desarrollar en reduccion, una capacidad maxima de 157 mAh/g a un potencial medio de 1.5 V, el material puede desarrollar en oxidacion una capacidad de unos 90 mAh/g bajo una densidad de corriente de 0.1 mA/cm2 , por lo que podria actuar como el electrodo positivo, ya que en este caso el potencial medio de trabajo seria de 4 V.

Attempts to Improve the Behavior of Li Electrodes in Rechargeable Lithium Batteries

In this work we studied properties of modified lithium electrodes in an attempt to improve the high rate performance of rechargeable Li (metal) batteries containing liquid electrolyte solutions. Li (metal)- AA batteries with solutions containing 1,3-dioxolane (DN), and a basic stabilizer became commercial several years ago but failed to compete with Li-ion battery technology because of a very limited cycle life at high charging rates. The problem relates to intensive reactions between Li deposited at high rates and the electrolyte solutions, which dry the batteries. The lithium-solution reactivity was modified through several approaches. Li anodes doped by Al, and Mg were tested, as well as solutions containing derivatives of DN that are expected to be less reactive toward lithium than DN. It was concluded that reduction of the Li anode-solution reactivity by these approaches cannot solve the problem, because it is impossible to modify the rough morphology, high surface of lithium electrodes when charging (Li deposition) rates are high (>1 mA/cm2). Since there is no hermetic passivation of any Li surface in liquid electrolyte solutions, the high-surface-area Li deposits react with solution components. Therefore, upon charge-discharge cycling of practical Li (metal) batteries, the electrolyte solution is consumed in these reactions. Hence, the future of Li (metal) rechargeable batteries lies either in the use of solid electrolyte matrices instead of the liquid solutions, or in applications where low charging rates are tolerable. © 2002 The Electrochemical Society. All rights reserved.

LiCo 1− yM yO 2 positive electrodes for rechargeable lithium batteries : I. Aluminum doped materials

Several substituted layered cobaltates of formula LiCo 1− y Al y O 2 (0.05≤ y≤0.30) were synthesized and investigated as cathode materials in rechargeable lithium batteries. These materials were investigated by X-ray powder diffraction, spectroscopic measurements (Raman and FTIR), and galvanostatic cycling. Structural data have shown that single phase impurity free can be made through careful selection of precursors. The voltage profiles of electrochemical cells including substituted oxides were monitored against lithium electrode. The overall capacity of the oxides have been reduced due to the sp metal substitution, however, a more stable charge–discharge cycling performances have been observed when electrodes are charged to 4.4 V as compared with the performances of the native oxides. At this cut-off voltage, the charge capacity of the Li//LiCo 0.80Al 0.20O 2 cell is ca. 128 mAh g −1. Kinetics were characterized by the galvanostatic intermittent titration technique. Al substitution also provides an increase of the chemical diffusion coefficients of Li ions in the LiCo 1− y Al y O 2 matrix.

Hydrated Iron Phosphates FePO4 ⋅ n H 2 O and Fe4 ( P 2 O 7 ) 3 ⋅ n H 2 O as 3 V Positive Electrodes in Rechargeable Lithium Batteries

Hydrated phosphates were investigated as positive electrode materials in lithium batteries. Reversible lithium insertion into amorphous and crystalline and compositions was found at potentials between 3.5 and 2.5 V vs. The roles of (i) specific surface area, amorphous vs. crystalline state, content, and electronic contact between particles in the composite positive electrode, on the electrochemical performances of these materials are discussed. Very stable cycling was obtained for optimized and electrodes at an average voltage of 3.0 and 3.2 V vs. respectively. © 2002 The Electrochemical Society. All rights reserved.

Combinatorial computational chemistry approach to the design of cathode materials for a lithium secondary battery

Combinational chemistry is an efficient technique to find materials with novel properties by synthesizing and screening a large number of compounds in a short time. Recently, we introduced the concept of combinational approach into computational chemistry and proposed a novel approach, “combinatorial computational chemistry”. In the present study, we applied combinatorial computational chemistry to investigate the structural properties of lithium transition metal oxides, LiMO 2 (M=3d transitional metal), with a layered rocksalt structure. LiMO 2 is a promising material as positive electrodes in rechargeable lithium batteries. Density functional calculations on periodic models were performed to investigate the structural properties of LiCoO 2, LiNiO 2, and doped LiNiO 2, revealing that the poor charge–discharge cyclic reversibility of LiNiO 2 resulted from the large change in the structure due to the difference in the bond length between Ni 3+–O and Ni 4+–O. The analysis of the structural properties of Li 0.66Ni 0.5Me 0.5O 2 (Me=dopant) revealed that doping with Co decreased the change in the structure of LiNiO 2 during cycling. Doping of Ni with Al was also found to stabilize LiNiO 2.

First-Principles Study of the Lithium Interaction with Polycyclic Aromatic Hydrocarbons

We have performed first-principles calculations in order to understand the binding mechanism of Li atoms in disordered carbon materials that are used for negative electrodes of rechargeable lithium batteries. We used pyrene, anthracene, and phenanthrene molecules as parts of disordered carbon. We examined several binding sites for two Li atoms in these aromatics and found that they are bound with substantial negative binding energies. The most negative one was −142.8 kJ/mol for Li-containing pyrenes, −211.0 kJ/mol for anthracenes, and −146.2 kJ/mol for phenanthrenes at the B3LYP/6-31G*//HF/6-31G* level of calculation. Li atoms are bound to interstitial (ring-over) and edge sites. In addition to these binding mechanisms, we found that Li atoms could be bound, forming a Li dimer in anthracene and phenanthrene. Their binding energies are −200.5 and −146.2 kJ/mol, respectively, being larger in magnitude than Li2 dissociation energy. These aromatics lose their planarity when they accommodate Li atoms. We found...

Electrophoretic fabrication of LiCoO 2 positive electrodes for rechargeable lithium batteries

LiCoO 2 composite electrodes for rechargeable lithium batteries were fabricated by an electrophoretic deposition (EPD) method. LiCoO 2 oxide particles were deposited on an Al current collector with appropriate amounts of Ketjen black and polytetrafluoroethylene (PTFE) by applying a high dc voltage between two electrodes in an EPD suspension. The density of the composite electrode was comparable with that for an electrode prepared by a conventional process. The LiCoO 2 electrode exhibited an initial discharge capacity of 142 mAh g −1. The cycleability of the LiCoO 2 electrode prepared by the EPD was also equivalent to those of pellet type electrodes. From these results, it is concluded that the EPD method can be applied as the practical electrode fabrication process for a rechargeable lithium battery.

Surface film formation on graphite negative electrodes in rechargeable lithium batteries

The choice of solvent is quite important to obtain good protecting surface film on graphite negative electrodes in rechargeable lithium batteries. A subtle difference of the molecular structure of solvent greatly affects the easiness of surface film formation. In order to understand the solvent effects and to elucidate the mechanism of surface film formation, morphology changes of the basal plane of highly oriented pyrolytic graphite were studied using electrochemical scanning tunneling microscopy (EC-STM). In this article, our recent results of EC-STM observation in different solvent systems are reviewed.

Layered LixMn1 − yNiyO2 intercalation electrodes

Synthesis of the layered lithium intercalation compound LixMn1 − yNiyO2, with the O3 (α-NaFeO2) structure is reported and it is shown to exhibit amongst the highest capacity to cycle lithium (charge) on intercalation/deintercalation (220 mA h g−1 between potential limits of 2.4 to 4.8 V) of any such material and at a relatively high charge/discharge rate; the ion exchange conditions used in the synthesis have an important influence on the defect chemistry of the host structure and this in turn influences the performance of the compound as an electrode in rechargeable lithium batteries.

Spinel Electrodes for Lithium Batteries

This article gives a historical account of the development of spinel electrodes for rechargeable lithium batteries. Research in the late 1970s and early 1980s on high‐temperature Li/Fe3O4 cells led to the evaluation of lithium spinels Li[B2]X4 at room temperature (B = metal cation). This work highlighted the importance of the [B2]X4 spinel framework as a host electrode structure and the ability to tailor the cell voltage by selection of various B cations. Examples of lithium‐ion cells that operate with spinel anode/spinel cathode couples are provided. Particular attention is given to spinels within the solid‐solution system Li1+xMn2‐xO4 (0 lessthan equal to x lessthan equal to 0.33).

Electrochemical characterization of various tin-based oxides as negative electrodes for rechargeable lithium batteries

Tin oxide and tin-based composite electrodes are examined in both bulk and thin-film form for prospective use as negative electrodes for lithium rechargeable batteries. For bulk electrodes, tin oxides and Sn–Zn–P–O composite materials are compared by charge–discharge testings. Thin films of oxides and composite thin-film electrodes prepared by heat treatment (temperature and time) are characterized by X-ray diffraction analysis, Auger electron spectroscopy, and scanning electron microscopy. The characteristics of thin films are found to depend on the heat-treatment temperature, which influences the structure, the grain size, and adhesion to the substrate. Capacities higher than 350 mA h g −1 are found for bulk electrodes beyond 20 cycles, and beyond 100 cycles for thin-film electrodes.

The Layered Intercalation Compounds Li(Mn1−yCoy)O2: Positive Electrode Materials for Lithium–Ion Batteries

The layered intercalation compounds Li(Mn1−yCoy)O2; 0≤y≤0.5 cannot be prepared by conventional solid state reaction but have been synthesized using a solution-based route coupled with ion exchange. A continuous range of solid solutions with rhombohedral symmetry exists for 0.1≤y≤0.5. Consideration of transition metal to oxygen bond lengths indicates that Mn3+ is replaced by cobalt in the trivalent state. Localized high spin Mn3+ (3d4) induces a cooperative Jahn–Teller distortion in layered LiMnO2, lowering the symmetry from rhombohedral R3m to monoclinic (C2/m). Substitution of as little as 10% Mn by Co is sufficient to suppress the distortion in Li0.9(Mn0.9Co0.1)O2, whereas half the Li must be extracted from LiMnO2 to achieve a single undistorted rhombohedral phase. On removing and reinserting Li in LiMnO2 only half the quantity of Li (equivalent to a specific charge of 130 mAhg−1) may be reinserted on the first cycle; this substantial drop in capacity is eliminated with only 10% Co substitution. The latter material can sustain a large capacity on cycling (200 mAhg−1). Higher Co contents have somewhat lower capacities but fade less at higher cycle numbers. The marked improvement in capacity retention of the Co-doped materials compared with pure LiMnO2 may be related in part to the absence of the Jahn–Teller distortion. Electrochemical data indicate conversion to a spinel-like structure on cycling. Such conversion is progressively slower with increasing Co content. Cycling of this spinel-like material is significantly better than Co-doped spinel of the same composition. These materials are of interest as electrodes in rechargeable lithium batteries.