Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Reexamination Certificate
1998-09-23
2002-07-09
Chaney, Carol (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
C429S306000, C429S212000
Reexamination Certificate
active
06416905
ABSTRACT:
The present invention relates to mixtures which are e.g. suitable for solid electrolytes or separators for electrochemical cells containing lithium-containing electrolytes, their use for example in solid electrolytes, separators and electrodes; solid electrolytes, separators, electrodes, sensors, electrochromic windows, displays, capacitors and ion-conducting films which respectively comprise such a mixture; electrochemical cells containing such solid electrolytes, separators and/or electrodes; and the use of the solids being comprised in the mixtures in electrochemical cells for improving the cycle stability.
Electrochemical cells, especially rechargeable cells, are generally known, for example from “Ullmann's Encyclopedia of Industrial Chemistry”, 5th edition, volume A3, VCH Verlagsgesellchaft mbH, Weinheim, 1985, pages 343-397.
Among these cells, the lithium and lithium ion batteries are particularly important, especially as secondary cells, owing to their high specific energy storage density.
As is described among others in the above citation taken from “Ullmann”, the cathode of such cells includes lithiated mixed oxides containing manganese, cobalt, vanadium or nickel, such as those which, in the stoichiometrically simplest case, may be described as LiMn
2
O
4
, LiCoO
2
, LiV
2
O
5
or LiNiO
2
.
These mixed oxides undergo a reversible reaction with compounds capable of incorporating the lithium ions into their lattice, such as graphite, with removal of the small lithium ions from the crystal lattice; in the course of this procedure the metal ions, such as manganese, cobalt or nickel ions, are oxidized. This reaction can be utilized for current storage in an electrochemical cell by separating the compound which receives the lithium ions, i.e. the anode material, and the lithium-containing mixed oxide, i.e. the cathode material by an electrolyte, through which the lithium ions migrate from the mixed oxide to the anode material.
In this arrangement, the compounds suitable for reversible storage of lithium ions are usually fixed to discharge electrodes using a binder.
When the cell is charged, electrons flow through an external voltage source and lithium cations through the electrolyte to the anode material. When the cell is used, the lithium cations flow through the electrolyte while the electrons flow through a useful resistance from the anode material to the cathode material.
In order to avoid a short circuit within the electrochemical cell, there is a layer located between the two electrodes which is electrically insulating but is conductive for the lithium cations. This layer may be a solid electrolyte or a customary separator.
Solid electrolytes and separators consist, as is known, of a carrier material into which there are incorporated a dissociatable compound containing lithium cations, whose purpose is to increase the lithium ion conductivity, and, customarily, further additives such as solvents.
Carrier materials proposed to date include highly resistant polymers (U.S. Pat. No. 5,296,318, U.S. Pat. No. 5,429,891), for example a copolymer of vinylidene difluoride and hexafluoropropene. The use of these high performance (co)polymers has several disadvantages.
Such polymers are not only expensive but are also difficult to dissolve. Furthermore, they increase the resistance of the cell, owing to their comparably low lithium cation conductivity, so that the electrolyte, which usually consists of a compound containing lithium cations, such as LiPF
6
, LiAsF
6
or LiSbF
6
, and an organic solvent, such as ethylene carbonate or propylene carbonate, has to be added as early as during the preparation of the insulating layer (U.S. Pat. No. 5,296,318, U.S. Pat. No. 5,429,891). Moreover, such polymers are only processible by adding high quantities of plasticizers, for example di-n-butyl phthalate, and of pyrogenic silicic acids in order, on the one hand, to ensure adequate film formation and cohesion of the electrolyte layer, and the capacity for bonding with the electrode layers, and, on the other hand, to ensure an adequate conductivity and permeability for lithium cations. It is subsequently necessary to remove the plasticizer quantitatively from the composite consisting of anode, solid electrolyte layer or separator layer and cathode layer, which is, on the industrial scale, an extremely difficult and expensive extraction step and must be carried out before the batteries are operated. Even if only small traces of the plasticizer remain in the composite, it is not possible to achieve adequate cycle stability in the battery.
Furthermore, known are solid electrolytes on the basis of polyalkylene oxides which are e.g. described in EP-A 559 317, EP-A 576 686, EP-A 537 930, EP-A 585 072 and U.S. Pat. No. 5,279,910. The polyether, as described therein, are modified at their end or functional groups, respectively, e.g. by means of (meth)acryloyl groups and are cross-linked by energy (heat, light) prior to use. Furthermore they generally comprise a conducting salt, e.g. LiPF
6
, for improving their conductivity. The use of a solid for improving the mechanical, thermal and electrical strength of the solid electrolyte is not described therein. Conclusively, the systems as described therein, although cross-linked, do not always exhibit satisfactory characteristics with respect to the mechanical strength, the porosity of the obtained films and the short circuit resistance.
Accordingly, it is an object of the present invention to remedy these disadvantages and to provide a mixture being especially suitable for the preparation of solid electrolytes and separators, but which may be also used for preparing electrodes in electrochemical cells and for other application as is described hereinafter.
Due to especially the presence of a solid III, as described later herein, the use of the mixture according to the invention results in solid electrolytes, separators or electrodes which exhibit an improved short circuit resistance, an increased pressure resistance, especially at elevated temperatures of above 120° C. and a larger porosity, compared to already known systems, and which are furthermore capable to suppress the formation of lithium dendrites. In addition thereto, the presence of the solid yields an improved cycle strength and an increased ampacity in an electrochemical cell. When using the preferably used basic solids, a neutralization or capture of the acid formed during the operation of an electrochemical cell takes place.
Thus, in one embodiment thereof, the present invention relates to a mixture Ia which comprises a composition IIa consisting of
a) 1 to 95% by weight of a solid III, preferably a basic solid III, having a primary particle size of 5 nm to 20 microns, and
b) 5 to 99% by weight of a polymeric mass IV obtainable by polymerizing
b1) 5 to 100% by weight, based on the mass IV of a condensation product V of
&agr;) at least one compound VI which is capable to react with a carboxylic acid or a sulfonic acid or a derivative thereof or a mixture of two or more thereof, and
&bgr;) at least one mole per mole of the compound VI of a carboxylic acid or a sulfonic acid VII which exhibits at least one radically polymerizable functional group, or a derivative thereof or a mixture of two or more thereof
and
b2) 0 to 95% by weight, based on the mass IV, of a further compound VIII having an average molecular weight (number average) of at least 5000 and having polyether segments in the main or side chain,
wherein the proportion by weight of the composition IIa in the mixture Ia is 1 to 100% by weight.
Preferably, the above mixture Ia is a mixture comprising a composition IIa consisting of
a) 1 to 95% by weight of a solid III, preferably a basic solid III, having a primary particle size of 5 nm to 20 microns and
b) 5 to 99% by weight of a polymeric mass IV obtainable by polymerizing
b1) 5 to 100% by weight, based on the mass IV, of a condensation product V consisting of
&agr;) a polyhydric alcohol VI whose main chain contains carbon and oxygen atoms,
and
&bgr;) at least one mole per mol
Bronstert Bernd
Möhwald Helmut
BASF - Aktiengesellschaft
Chaney Carol
Keil & Weinkauf
LandOfFree
Mixtures suitable as solid electrolytes or separators for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Mixtures suitable as solid electrolytes or separators for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Mixtures suitable as solid electrolytes or separators for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2868848