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Publication numberUSH723 H
Publication typeGrant
Application numberUS 07/215,664
Publication date2 Jan 1990
Filing date6 Jul 1988
Priority date6 Jul 1988
Also published asCA1306001C
Publication number07215664, 215664, US H723 H, US H723H, US-H-H723, USH723 H, USH723H
InventorsEdward J. Plichta, Steven M. Slane
Original AssigneeThe United States Of America As Represented By The Secretary Of The Army
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Lithium electrochemical cell containing diethylcarbonate as an electrolyte solvent additive
US H723 H
Abstract
An electrochemical cell comprising lithium as the anode, the lithium intelating compound Lix CoO2 (O<X<1) as the cathode, and a solution of a lithium salt in a mixed organic solvent of methylformate and diethylcarbonate as the electrolyte.
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Claims(5)
What is claimed is:
1. An electrochemical cell comprising lithium as the anode, the lithium intercalating compound Lix CoO2 (0<x<1) as the cathode, and a solution of a lithium salt in a mixed organic solvent of methylformate and diethylcarbonate as the electrolyte.
2. An electrochemical cell according to claim 1 wherein the mass percent of the diethylcarbonate in the mixed organic solvent of methylformate and diethylcarbonate can vary from about 10 to 100 mass percent in the electrolyte.
3. An electrochemical cell according to claim 2 wherein the solution of lithium salt is 1-2 mol dm-3 LiAsF6 in methylformate.
4. An electrochemical cell according to claim 1 wherein the Lix CoO2 cathode consists of a mixture of about 80 weight percent Lix CoO2, about 10 weight percent carbon diluent and about 10 weight percent Teflon binder roll pressed onto aluminum substrates and sintered in a vacuum oven at 280 C. for 1 hour.
5. An electrochemical cell according to claim 4 wherein the mass percent of the diethylcarbonate in the mixed organic solvent of methylformate and diethylcarbonate can vary from about 10 to 100 mass percent in the electrolyte and wherein the solution of lithium salt is 1-2 mol dm-3 LiAsF6 in methylformate.
Description

The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without the payment to us of any royalty thereon.

This invention relates in general to a lithium electrochemical cell and in particular, to a lithium electrochemical cell including lithium as the anode, the lithium intercalating compound Lix CoO2 (0<x<1) as the cathode, and a solution of a lithium salt in a mixed organic solvent of methyl formate (MF) and diethylcarbonate (DEC) as the electrolyte.

BACKGROUND OF THE INVENTION

This application is copending with U.S. patent application Ser. No. 125,642, filed Nov. 1, 1987, now U.S. Pat. No. 4,786,499 for "Lithium Electrochemical Cell Including Aprotic Solvent-Dialkyl Carbonate Solvent Mixture" and assigned to a common assignee. In that application, there is described and claimed a lithium electrochemical cell including lithium as the anode, non-stoichiometric (NS)-V6 O13 as the cathode, and a solution of a lithium salt in a mixed organic solvent of methyl formate and diethylcarbonate as the electrolyte.

Another lithium intercalating compound, to wit, Lix CoO2 (0<x<1) is particularly attractive for battery applications because of its inherently high energy content. However, the known Lix CoO2 cathode material/solvent combinations are susceptible to oxidation during charge and reduction during discharge that results in losses in cell capacity and cycle-life. In addition to oxidation and reduction of the electrolyte, both the cathode and anode are subject to reaction with the solvent and electrolyte. This can result in poor lithium cyclability and structural rearrangement of the active material which may limit rechargeability.

SUMMARY OF THE INVENTION

The general object of this invention is to provide an improved lithium electrochemical cell including Lix CoO2 (0<x<1) as the cathode active material. A more particular object of the invention is to provide an intercalating solvent system for Lix CoO2 (0<x<1) that produces higher energy lithium cells also characterized by increased resistance to solvent oxidation and improved lithium cycling efficiencies.

It has now been found that the aforementioned objects can be attained by employing a system including lithium as the anode, Lix CoO2 (0<x<1) as the cathode, and a solution of a lithium salt in a mixed organic solvent of MF and DEC as the electrolyte.

The solution can be, for example, 1 to 2 mol dm-3 LiAsF6 in the mixed organic solvent. Though the use of LiAsF6 as the electrolyte salt is preferred, other electrolyte salts can be used such as the soluble salts of light metals, for example, tetrafluoroborates, tetrachloroaluminates, perchlorates, hexafluorophosphates, and halides of lithium.

The mass percent of the DEC in the mixed organic solvent can vary from 10 to 100 mass percent. The instant invention identifies and demonstrates that the addition of DEC to ester containing electrolytes, such as LiAsF6 in MF, results in significant improvements in the electrolytes resistance to electrochemical oxidation and improved lithium cycling efficiencies. In addition, when these electrolytes containing the DEC additives are used in Li/Lix CoO2 electrochemical cells, there is significant improvements in the cell cycling behavior over cells without the DEC additive.

DESCRIPTION OF THE DRAWING AND THE PREFERRED EMBODIMENT

The drawing compares cycling results obtained for additions of DEC and dimethylcarbonate (DMC) to LiAsF6 in MF electrolyte in a Li/Lix CoO2 electrochemical cell.

The drawing shows the dramatic improvement in cycling behavior for the electrolyte containing DEC as opposed to DMC. The Li/Lix CoO2 cells are cycled between either 4.3 V to 3.5 V or 4.3 V to 2.5 V where the charging rate is 0.5 mAcm2, the discharge rate is 2 0 mAcm2, and the temperature is 25 C. The Lix CoO2 cathodes include a mixture of 80 weight percent Lix CoO2, 10 weight percent carbon diluent, and 10 weight percent Teflon binder. The cathode mixture is roll pressed onto aluminum substrates and sintered in a vacuum oven at 280 C. for 1 hour. The cycling is performed on identically prepared cells consisting of flag electrodes sealed in a glass pressure vessel where Celgard 2400 is used as separators and a glass fiber wick for drawing electrolyte in between the electrode.

Interestingly, homologues of DEC such as DMC have been utilized in lithium cells and are known to be sufficiently stable towards lithium. However, although DMC and DEC show structural similarities, they behave very differently in the presence of lithium, both chemically and electrochemically. DMC produces a high cycling efficiency of 80 percent as compared to DEC which is 0 percent. This is due to the reactive nature of DEC with lithium as opposed to the more stable DMC solvent. However, even though DMC is more stable with lithium, its addition to the LiAsF6 -MF electrolyte does not result in the improved results observed with DEC. Therefore, where the successful use of DMC as a solvent in lithium cells may imply the possible use of a similar solvent such as DEC, this is not made obvious due to the lack of lithium stability of the neat DEC electrolyte, thus precluding such applications. Furthermore, one would not find obvious the discovery that a mixture of the unstable solvent DEC with another solvent would produce an improved mixture suitably stable for use in a lithium cell. It is only through its addition to other ester electrolytes that the use of DEC in lithium cells is possible.

The use of DEC as a solvent additive in electrolytes for use in either primary, rechargeable, or reserve electrochemical cells is not considered to be limited to the instance where lithium is the anode. That is, other light metals or composites may be applicable as the anode such as sodium, potassium and aluminum, or any conductively doped polymeric material or similar compound. Moreover, the positive electrode or cathode, may be any oxide, sulfide or combinations of titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum, hafnium, tantalum, or tungsten or any conductively doped polymeric material or similar compound.

We wish it to be understood that we do not desire to be limited to the exact details as described for obvious modifications will occur to a person skilled in the art.

Referenced by
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US5147739 *1 Aug 199015 Sep 1992Honeywell Inc.High energy electrochemical cell having composite solid-state anode
US5284721 *1 Aug 19908 Feb 1994Alliant Techsystems Inc.High energy electrochemical cell employing solid-state anode
US733701029 Oct 200426 Feb 2008Medtronic, Inc.Medical device having lithium-ion battery
US756354129 Oct 200421 Jul 2009Medtronic, Inc.Lithium-ion battery
US758238729 Oct 20041 Sep 2009Medtronic, Inc.Lithium-ion battery
US763554127 Oct 200522 Dec 2009Medtronic, Inc.Method for charging lithium-ion battery
US764199229 Oct 20045 Jan 2010Medtronic, Inc.Medical device having lithium-ion battery
US764201329 Oct 20045 Jan 2010Medtronic, Inc.Medical device having lithium-ion battery
US766250929 Oct 200416 Feb 2010Medtronic, Inc.Lithium-ion battery
US768274529 Oct 200423 Mar 2010Medtronic, Inc.Medical device having lithium-ion battery
US774098523 Apr 200922 Jun 2010Medtronic, Inc.Lithium-ion battery
US779486929 Jul 200914 Sep 2010Medtronic, Inc.Lithium-ion battery
US780348125 Sep 200928 Sep 2010Medtronic, Inc,Lithium-ion battery
US780729929 Oct 20045 Oct 2010Medtronic, Inc.Lithium-ion battery
US781170529 Oct 200412 Oct 2010Medtronic, Inc.Lithium-ion battery
US785823628 Jul 200928 Dec 2010Medtronic, Inc.Lithium-ion battery
US787538921 May 200925 Jan 2011Medtronic, Inc.Lithium-ion battery
US787949529 Oct 20041 Feb 2011Medtronic, Inc.Medical device having lithium-ion battery
US788379022 Sep 20098 Feb 2011Medtronic, Inc.Method of preventing over-discharge of battery
US792774229 Sep 200819 Apr 2011Medtronic, Inc.Negative-limited lithium-ion battery
US793198727 May 201026 Apr 2011Medtronic, Inc.Lithium-ion battery
US810571413 Jul 200731 Jan 2012Medtronic, Inc.Lithium-ion battery
US898045330 Apr 200817 Mar 2015Medtronic, Inc.Formation process for lithium-ion batteries
US906514513 Jul 200723 Jun 2015Medtronic, Inc.Lithium-ion battery
US90770226 Dec 20107 Jul 2015Medtronic, Inc.Lithium-ion battery
US928758027 Jul 201115 Mar 2016Medtronic, Inc.Battery with auxiliary electrode
US958732131 Mar 20157 Mar 2017Medtronic Inc.Auxiliary electrode for lithium-ion battery
US20060093871 *29 Oct 20044 May 2006Medtronic, Inc.Lithium-ion battery
US20060093872 *29 Oct 20044 May 2006Medtronic, Inc.Medical device having lithium-ion battery
US20060093873 *29 Oct 20044 May 2006Medtronic, Inc.Lithium-ion battery
US20060093913 *29 Oct 20044 May 2006Medtronic, Inc.Medical device having lithium-ion battery
US20060093916 *29 Oct 20044 May 2006Medtronic, Inc.Lithium-ion battery
US20060093917 *29 Oct 20044 May 2006Medtronic, Inc.Medical device having lithium-ion battery
US20060093918 *29 Oct 20044 May 2006Medtronic, Inc.Lithium-ion battery
US20060093921 *29 Oct 20044 May 2006Medtronic, Inc.Lithium-ion battery
US20060093923 *29 Oct 20044 May 2006Medtronic, Inc.Medical device having lithium-ion battery
US20080020278 *13 Jul 200724 Jan 2008Medtronic, Inc.Lithium-ion battery
US20080020279 *13 Jul 200724 Jan 2008Medtronic, Inc.Lithium-ion battery
US20090208845 *23 Apr 200920 Aug 2009Medtronic, Inc.Lithium-ion battery
US20090274849 *30 Apr 20085 Nov 2009Medtronic, Inc.Formation process for lithium-ion batteries
US20090286158 *28 Jul 200919 Nov 2009Medtronic, Inc.Lithium-ion battery
US20100009245 *29 Jul 200914 Jan 2010Medtronic,Inc.Lithium-ion battery
US20100015528 *25 Sep 200921 Jan 2010Medtronic, Inc.Lithium-ion battery
US20100076523 *22 Sep 200925 Mar 2010Medtronic, Inc.Method of preventing over-discharge of battery
US20100239908 *27 May 201023 Sep 2010Medtronic, Inc.Lithium-ion battery
Classifications
U.S. Classification429/326, 429/231.2
International ClassificationH01M10/0569, H01M10/05
Cooperative ClassificationH01M10/0569, H01M10/05, H01M4/02
European ClassificationH01M10/0569, H01M10/05, H01M4/02