J.O. Besenhard

Will advanced lithium-alloy anodes have a chance in lithium-ion batteries?

Abstract The high packing density of lithium is a significant advantage of lithium insertion into metallic matrices that can be achieved in lithium alloys compared with lithium intercalation into carbonaceous materials. Moreover, the operating voltage of lithium-alloy anodes may be chosen well-above the potential of metallic lithium and the solvent co-intercalation has not been observed at lithium-alloy electrodes. On the other hand, the volume changes related with insertion/removal of lithium into/ from the metallic matrices cause pulverization and rapid failure of lithium-alloy anodes. This paper demonstrates the dramatic effect of the morphology of the metallic host matrix on the performance of the lithium-alloy anodes. Two component host matrices with ultrasmall (submicro- or nanoscale) particle size show an impressive cycling performance. This is related with the small absolute changes of the dimensions of the individual particles and also with the fact that in the first charging step the more reactive particles are allowed to expand in a ductile surrounding of still unreacted material.

Small particle size multiphase Li-alloy anodes for lithium-ionbatteries

An impressive improvement of the cycling performance of Li-alloy anodes (M + Li+ +e− ⇆ LixM) in rechargeable organic electrolyte lithium batteries can be achieved by replacing compact or large particle size metallic host matrices M (e.g. Sn or Sb) with small particle size (micro- or nano-scale) multiphase metallic host materials like SnSnSbn or SnSnAgn. Electrochemical alloy deposition is a convenient way to prepare sub-micrometer particles of Sn and SnSbn or Sn and SnAgn. During the first lithium insertion these small particle size multiphase matrix materials are expanded to a porous material, however, without formation of major cracks. This seems not only to be related with the small absolute changes in the size of the individual particles, but also with the fact that the more reactive particles are allowed to expand in a soft and ductile surrounding of still unreacted material.

Filming mechanism of lithium-carbon anodes in organic and inorganic electrolytes

Abstract To study the filming mechanism of graphite-based LiCn electrodes, electrochemical reduction of graphite materials was carried out in 1 M LiClO4/ethylene carbonate (EC)-1,2-dimethoxyethane (DME) (1:1 by volume). Due to film forming a peak at potentials around 0.8 V versus Li Li + was observed during the first reduction. The reversibility of this peak was examined by cyclic voltammetry; in addition, the crystal expansion/contraction was checked by means of dilatometry. The results indicate that ternary solvated graphite-intercalation compounds (GICs) were formed at those potentials leading to drastic expansion of the graphite matrix (>150%). These Li(EC)y1(DME)y2Cn-GICs decompose and build up a protective layer on the graphite that prevents further solvent co-intercalation. The beneficial effect of EC-containing electrolytes on the stability of lithium-carbon anodes seems to be related to inorganic films formed via secondary chemical decomposition of electrochemically formed EC-GICs. The key-role of inorganic films is also demonstrated by the fact that inorganic additives, such as carbon dioxide, suppress the formation of solvated GICs. Furthermore, it can be seen that lithium-carbon negatives can even be operated in inorganic electrolytes such as SO2 and SOCl2.

Ethylene Sulfite as Electrolyte Additive for Lithium‐Ion Cells with Graphitic Anodes

A liquid organic electrolyte system for lithium-ion cells with graphitic anodes containing the solvents ethylene sulfite (ES) and propylene carbonate (PC) has been studied. Even in additive amounts (5 vol %) ES is suppressing cointercalation of PC into graphite. The PC-ES electrolytes are characterized by a high oxidation stability allowing the cycling of a LiMn{sub 2}O{sub 4} cathode with good reversibility. Moreover, the good low temperature performance compared to ethylene carbonate-dimethyl carbonate electrolytes may favor PC-ES electrolytes for special applications.

Sub‐Microcrystalline Sn and Sn ‐ SnSb Powders as Lithium Storage Materials for Lithium‐Ion Batteries

The cycling behaviors of and powders, which were synthesized by chemical reduction and combined with a binder and a conductive additive to produce composite electrodes, are presented. The cycling stability of the electrode increased with decreasing particle size, and was higher for the multiphase material than for the single‐phase material of comparable particle size. The higher cycling stability of is explained by the subsequent reaction of the constituent phases and the mechanism of the reaction of with , and is discussed with respect to other multiphase materials which have been reported in the literature. The best‐performing material was of particle size , yielding about 200 cycles for galvanostatic, charge‐limited cycling. ©1999 The Electrochemical Society

XPS studies of graphite electrode materials for lithium ion batteries

Abstract Surface pre-treatment of graphitic electrode materials for lithium ion cells has recently been shown to significantly reduce the irreversible consumption of material and charge due to the formation of the so-called solid electrolyte interphase (SEI) during battery charging. In this paper, we compare graphite powders and carbon fibres as model materials for X-ray photoemission spectroscopy (XPS) studies of the effects of surface pre-treatments. For carbon fibres, the surface carbon percentage was found to vary from 70–95% depending on the surface treatment, with corresponding changes in the relative proportion of graphitic compared to CO bonds, as determined from C 1s curve fits. In contrast, results from the graphite powders show very little change in surface chemical composition and an essentially constant C 1s lineshape dominated by graphitic carbon. SEM data show the carbon fibre cross-section to be composed of a radial array of layered graphite, leaving a surface consisting largely of prismatic planes, while the graphite powder consists of graphite platelets with the surface area predominantly of basal planes. We conclude that the chemical modification occurs at the prismatic planes, and that the powders are unsuitable as models for XPS studies of electrode surface modification, while the fibres are very well suited.

Propylene sulfite as film-forming electrolyte additive in lithium ion batteries

Propylene sulfite (PS) has been studied as a film-forming electrolyte additive for use in lithium ion battery electrolytes. Even small amounts in the order of 5 vol.% PS suppress propylene carbonate (PC) co-intercalation into graphite. In addition, a 1 M LiClO4/PC/PS (95:5 by volume) electrolyte is characterised by a high oxidation stability at a LiMn2O4 cathode.

Electron microscopical characterization of Sn/SnSb composite electrodes for lithium-ion batteries

Abstract Lithium storage alloys such as Sn/SnSb are promising new anode materials for Li-ion batteries. Due to a proper design of the active Sn/SnSb material as well as the composite electrode, capacities exceeding 500 mAh g −1 have been achieved with this system for more than 30 cycles. The observation of micro- and nano-structural changes in the composite electrode during charge/discharge cycling is of immense importance for a further improvement of the cycling performance. Electron microscopy (SEM and TEM) in combination with analytical techniques (EFTEM, EDXS and EELS) has been used for the characterization of Sn/SnSb raw powder as well as the Sn/SnSb composite electrodes. The pristine morphology and the changes of morphology during cycling of the electrode material have been studied. Furthermore, the chemical composition and particularly compositional fluctuations within the composite material have been investigated using EFTEM and EDXS. The electron microscopy results indicate that parts of the active material get finer during the initial cycles. Moreover, amorphous regions are detected in the cycled material. The experimental results are discussed with regard to the reaction mechanism of SnSb with Li.

Acrylic acid nitrile, a film-forming electrolyte component for lithium-ion batteries, which belongs to the family of additives containing vinyl groups

We present results on the electrolyte additive acrylic acid nitrile (AAN), which allows the use of propylene carbonate (PC)-based electrolytes together with graphitic anodes. This report will focus on the basic electrochemical properties and on XPS results of the films formed in the presence of AAN. Further data on in situ investigations of AAN is presented in another paper of this proceedings. The combination of both reports gives strong evidence, that the initiative step for solid electrolyte interphase (SEI) formation is a cathodic, i.e. by reduction induced electro-polymerisation of the vinyl-group. It is concluded that this electro-polymerisation may also be a main reduction mechanism of other vinyl compounds such as vinylene carbonate (VC), vinylene acetate and others.

Fluorinated organic solvents in electrolytes for lithium ion cells

A novel partly fluorinated solvent for lithium ion batteries, N,N-dimethyl trifluoracetamide (DTA), is presented. The physical properties and the electrochemical behaviour of this compound are investigated. With its low viscosity and high boiling point and flash point it could replace low viscosity solvents (thinners) such as dimethyl carbonate or diethyl carbonate currently used in lithium ion battery electrolytes to achieve the demand for safer lithium ion batteries. The outstanding filming properties allow to use the DTA even in mixtures with PC in amounts of 10%. With both solvents having a freezing point below −40°C, the mixture is promising as low temperature electrolyte.