US20100136426A1

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Publication number: US20100136426A1
Application number: US12/683,514
Authority: US
Inventors: Donald R. Merritt; Craig L. Schmidt
Original assignee: Medtronic Inc
Current assignee: Medtronic Inc
Priority date: 2006-01-31
Filing date: 2010-01-07
Publication date: 2010-06-03
Also published as: WO2007089978A2; WO2007089978A3; US20070178378A1; US7807300B2; EP1992039A2

Abstract

A resistance-stabilizing additive to an electrolyte for a battery cell in an implantable medical device is presented. At least one resistance-stabilizing additive is selected from a group comprising an electron withdrawing group, an aromatic diacid salt, an inorganic salt, an aliphatic organic acid, an aromatic diacid, and an aromatic monoacid.

Description

RELATED APPLICATION

This application is related to, and claims the benefit of, U.S. patent application Ser. No. 10/876,003 filed Feb. 13, 2003 entitled “Liquid Electrolyte For An Electrochemical Cell, Electrochemical Cell And Implantable Medical Device”, which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to an electrochemical cell and, more particularly, to an additive in an electrolyte for a battery.

BACKGROUND OF THE INVENTION

Implantable medical devices (IMDs) detect and treat a variety of medical conditions in patients. IMDs include implantable pulse generators (IPGs) or implantable cardioverter-defibrillators (ICDs) that deliver electrical stimuli to tissue of a patient. ICDs typically comprise, inter alia, a control module, a capacitor, and a battery that are housed in a hermetically sealed container. When therapy is required by a patient, the control module signals the battery to charge the capacitor, which in turn discharges electrical stimuli to tissue of a patient.

The battery includes a case, a liner, and an electrode assembly. The liner surrounds the electrode assembly to prevent the electrode assembly from contacting the inside of the case. The electrode assembly comprises an anode and a cathode with a separator therebetween. In the case wall or cover is a fill port or tube that allows introduction of electrolyte into the case. The electrolyte is a medium that facilitates ionic transport and forms a conductive pathway between the anode and cathode. An electrochemical reaction between the electrodes and the electrolyte causes charge to be stored on each electrode. The electrochemical reaction also creates a solid electrolyte interphase (SEI) or passivation film on a surface of an anode such as a lithium anode. The passivation film is ionically conductive and prevents parasitic loss of lithium. However, the passivation film increases internal resistance which reduces the power capability of the battery. It is desirable to reduce internal resistance associated with the passivation film for a battery.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a cutaway perspective view of an implantable medical device (IMD);

FIG. 2 is a cutaway perspective view of a battery in the IMD ofFIG. 1;

FIG. 3 is an enlarged view of a portion of the battery depicted inFIG. 2 and designated byline4.

FIG. 4 is a cross-sectional view of an anode and a passivation film;

FIG. 5 is graph that compares discharge and resistance for a conventional and exemplary additive in an electrolyte;

FIG. 6 is graph that compares resistance over time for exemplary additives to an electrolyte;

FIG. 7 is a flow diagram for forming an electrolyte for a battery; and

FIG. 8 is a flow diagram for autoclaving a battery.

DETAILED DESCRIPTION

The following description of embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers are used in the drawings to identify similar elements.

The present invention is directed to an additive for an electrolyte. The additive stabilizes resistance of the battery during storage, thermal processing, and throughout discharge. A resistance-stabilizing additive is defined as one or more chemical compounds, added to an electrolyte, that causes a battery to exhibit low resistance (i.e. generally below 500 ohm centimeter (cm)²) throughout the battery's useful life. In one embodiment, the additive is characterized by an electron withdrawing group. Exemplary chemical compounds containing electron withdrawing group include 2,2,2-trifluoroacetamide, and benzoyl acetone. In another embodiment, an organic acid serves as a resistance-stabilizing additive. Exemplary organic acids include benzoic acids, carboxylic acids, malic acid, tetramethylammonium (TMA) hydrogen phthalate and hexafluoroglutaric acid.

A battery that includes an exemplary additive may be autoclaved at 125° C. for a half an hour, defined as one cycle, performed three times without adversely affecting the battery. The additives may be used in low, medium, or high capacity batteries.

FIG. 1 depicts an implantable medical device (IMD)10. IMD10 includes acase50, acontrol module52, a battery54 (e.g. organic electrolyte battery) and capacitor(s)56.Control module52 controls one or more sensing and/or stimulation processes fromIMD10 via leads (not shown).Battery54 includes aninsulator58 disposed therearound.Battery54 charges capacitor(s)56 andpowers control module52.

FIGS. 2 and 3 depict details of an exemplaryorganic electrolyte battery54.Battery54 includes acase70, ananode72,separators74, acathode76, aliquid electrolyte78, and a feed-through terminal80.Cathode76 is wound in a plurality of turns, withanode72 interposed between the turns of the cathode winding.Separator74

insulates anode

72 fromcathode76 windings.Case70 contains theliquid electrolyte78 to create a conductive path betweenanode72 andcathode76.Electrolyte78, which includes an additive, serves as a medium for migration of ions betweenanode72 andcathode76 during an electrochemical reaction with these electrodes.

Anode

72 is formed of a material selected from Group IA, IIA or IIIB of the periodic table of elements (e.g. lithium, sodium, potassium, etc.), alloys thereof or intermetallic compounds (e.g. Li—Si, Li—B, Li—Si—B etc.).Anode72 comprises an alkali metal (e.g. lithium, etc.) in metallic or ionic form.

Cathode

76 may comprise metal oxides (e.g. vanadium oxide, silver vanadium oxide (SVO), manganese dioxide (MnO₂) etc.), carbon monofluoride and hybrids thereof (e.g., CF_x+MnO₂), combination silver vanadium oxide (CSVO) or other suitable compounds.

Electrolyte

78 chemically reacts withanode72 to form an ionicallyconductive passivation film82 onanode72, as shown inFIG. 4.Electrolyte78 includes a base liquid electrolyte composition and at least one resistance-stabilizing additive selected from Table 1 presented below. The base electrolyte composition typically comprises 1.0 molar (M) lithium tetrafluoroborate (1-20% by weight), gamma-butyrolactone (50-70% by weight), and 1,2-dimethoxyethane (30-50% by weight). In one embodiment, resistance-stabilizing additives are directed to chemical compounds that include electron withdrawing groups. An exemplary chemical compound with an electron withdrawing group includes 2,2,2-trifluoroacetamide. In another embodiment, the additive is a proton donor such as an organic acid. One type of organic acid is benzoic acid (e.g. 3-hydroxy benzoic acid or 2-4 hydroxy benzoic acid etc.). Every combination of benzoic acid and hydroxyl benzoic acids that exists may be used as a resistance-stabilizing additive composition. Malic acid and tetramethylammonium hydrogen phthalate are other organic acids that may serve as a resistance-stabilizing additive.

Tables 1 and 2 list some exemplary resistance-stabilizing additives. In particular, Table 1 ranks each additive as to its effectiveness with a rank of 1 being the highest or best additive and rank6 being the lowest ranked additive. Table 1 also briefly describes the time period in whichbattery54, which included the specified additive in theelectrolyte78, exhibited resistance-stabilizing characteristics.

TABLE 1

List of exemplary additive resistance-stabilizing additives

	Chemical	Exemplary additive
Rank	class	compound	Chemical Structure	Notes

3	Aromatic diacid salts	Tetramethyl- ammonium (TMA) hydrogen phthalate		Battery exhibited excellent resistance- stabilizing characteristic during storage Battery exhibited good to neutral resistance- stabilizing characteristic during discharge

6	Inorganic acid salts	Tetrabutyl- ammonium (TBA) hydrogen sulfate		Battery exhibited good resistance- stabilizing characteristic during storage Battery exhibited neutral resistance- stabilizing characteristic duringdischarge

5	Aliphatic organic acids	Phosphonoacetic acid		Battery exhibited excellent resistance- stabilizing characteristic during storage Battery exhibited good to neutral resistance- stabilizing characteristic during discharge

1	(*)	2,2,2- Trifluoroacetamide		Battery exhibited excellent resistance- stabilizing characteristic during storage and discharge

	(*)	Trifluoromethyl vinyl acetate		Battery exhibited very good resistance- stabilizing characteristic duringdischarge

4	Aromatic diacids	Phthalic acid		Battery exhibited good resistance- stabilizing characteristic during storage and discharge

	(*)	Benzoylacetone		Battery exhibited good resistance- stabilizing characteristic during storage and discharge

	(*)	Benzoyltrifluoro- acetone		Battery exhibited good resistance- stabilizing characteristic during storage and discharge

2	Aromatic mono- acids	Benzoic acid		Battery exhibited excellent resistance- stabilizing characteristic during storage and discharge

(*) These compounds include a chemical structure that is characterized by one or more electron-withdrawing groups (e.g. —CF₃, —C₆H₅located one or two carbon atoms from a double-bonded oxygen atom (i.e. a ketone group)). Additionally, the listed additives may be added to the base electrolyte composition in the range of about 0.001M to 0.5M.

TABLE 2

Exemplary resistance-stabilizing composition additives

	Additive compositions	Quantity of each additive

	TMA hydrogen phthalate +	About 0.001 M to about 0.5M
	2,2,2-Trifluoroacetamide
	TMA hydrogen phthalate +	About 0.001 M to about 0.5M
	Trifluoromethyl vinyl acetate
	TMA hydrogen phthalate +	About 0.001 M to about 0.5M
	Acetone
	TMA hydrogen phthalate +	About 0.001 M to about 0.05M
	Xylitol
	Phosphonoacetic acid +	About 0.001 M to about 0.5M
	2,2,2-Trifluoroacetamide
	Phosphonoacetic acid +	About 0.001 M to about 0.5M
	Trifluoromethyl vinyl acetate
	Phosphonoacetic acid +	About 0.001 M to about 0.5M
	Acetone
	Phosphonoacetic acid +	About 0.001 M to about 0.5M
	Xylitol

FIGS. 5-6 graphically depict the resistance-stabilizing superiority ofelectrolyte78 over acontrol electrolyte88.Electrolyte78 includes 2,2,2-trifluoroacetamide as the resistance-stabilizing additive and the base electrolyte composition previously described.Control electrolyte88 is the base electrolyte composition without any additive.Passivation layer82 initially possesses similar discharge to passivation layer formed bycontrol electrolyte88. However, later in the discharge (e.g. about 0.90 ampere·hour(Ah)), the passivation layer formed bycontrol electrolyte88 exhibits resistance that substantially increases. In contrast,electrolyte78 that includes the additive causesbattery54 to exhibit resistance that remains substantially below the resistance ofcontrol electrolyte88 late in discharge. For example,electrolyte78 results inbattery54 having 30 ohms lower resistance thancontrol electrolyte88, as show inFIG. 5.

If the resistance increases in the area between 1 and 1.2 Ah of the curve andIMD10 records the voltage after a high current event (e.g. telemetry event etc.), a recommended replacement time (RRT) signal may be generated. Preferably, desirable resistance is kept low as long as possible to increase efficiency ofbattery54.

FIG. 7 depicts a method for forming a resistance-stabilizing additive composition. Atoperation200, a first resistance stabilizing additive is selected. Atoperation210, the first resistance stabilizing additive is combined with a second resistance stabilizing additive to create a resistance stabilizing composition.

FIG. 8 depicts a method for autoclavingbattery cell54.Battery cell54 is inserted into a chamber of an autoclave atoperation300.Battery cell54 includes an electrolyte and a first resistance-stabilizing additive combined with the electrolyte. Atblock310, heat is applied to the chamber of the autoclave. Generally, the autoclaving process occurs at a temperature of 125° C. for a half an hour per cycle. The autoclave cycle is repeated at least three times. After three cycles of autoclaving,battery cell54 adequately operates.

The following patent application is incorporated by reference in its entirety. Co-pending U.S. patent application Ser. No. XXXXXXXX, entitled “ELECTROLYTE ADDITIVE FOR PERFORMANCE STABILITY OF BATTERIES”, filed by Kevin Chen, Donald Merritt and Craig Schmidt and assigned to the same Assignee of the present invention, describes resistance-stabilizing additives for electrolyte.

Although various embodiments of the invention have been described and illustrated with reference to specific embodiments thereof, it is not intended that the invention be limited to such illustrative embodiments. For example, while an additive composition is described as a combination of two additives, it may also include two or more additives selected from Table 1. The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.