NL8003521A - ELECTROCHEMICAL CELL. - Google Patents

Description

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Electrochemical cell.

The invention relates to glass-metal sealing and cell barrier structures for electrochemical cells, and more particularly to those cells containing lithium anodes and corrosive materials.

In recent times, the preferred glass types for the construction of glass-metal seals * in electrochemical cells and capacitors requiring stringent hermeticity, such as those described in U.S. Pat. Nos. 4,053,692 and 3,646,405, 10, are those referred to as borosilicate glass. Such glasses include Corning 7052 and Fusite GC, and have the general composition:

Qxyde Approx.%

SiO2 70-75 15 B203 20 A12'03 4-8

Na20 4-7 K206

BaO 0-2 20 Suitable borosilicate glasses are and are extensively used in the construction of glass-metal seals because of their relatively low operating temperatures and the good glass-metal seals that can be obtained therewith. Accordingly, such glasses are used in a wide variety of glass-metal sealing applications. However, it has been found that while such glass metal seals are considered suitable for sealing cell holders, in certain cases, especially when used as cell seals in cells containing lithium anodes, such glass metal seals are subject to deterioration with resulting loss of elasticity, and possibly electrical insulation, especially under high temperature storage conditions. Said glasses are particularly subject to deterioration when used in the glass-metal seals of cells containing lithium anodes 800 3 5 21: λ - 2 -ν 'and in particular corrosive liquid depolarizer electrolytes such as thionyl chloride and sulfur dioxide . Glass metal seals in electrochemical cells have the typical configuration of an external and internal metal member separated by and sealed to the glass therebetween by fusion to the glass metal interfaces. Seals of this type are described in more detail in U.S. Pat. No. 4,053,692. Typically, the metal members function as opposed terminals 10 of the cell with electrical connection to the electrodes within the cell. The glass member between the metal members therefore functions both as a hermetic seal and as an electrical insulator.

In lithium cells, the metal member, which is used as the conductor from the lithium anode, and the immediately adjacent glass attract lithium ions from the electrolyte solution. The attracted lithium has been found to penetrate the neighboring glass, making it an electrical conductor. This conductive-20 glass then becomes part of the anode conductor, which thus extends into the glass, increasingly reducing the insulator width. This lithium-impregnated glass further has a larger volume than the original glass, inducing glass breakage, and in some clamping configurations separation of the glass from the adjacent metal.

This mechanical damage directly degrades the glass-metal seal and affects the degree of insulation loss due to the substitution of conductive glass.

As the lithium permeation of the glass increases and spreads across the glass to the opposite cathode conductor, a conductive bridge can be formed over the original insulating glass with resulting reduction of cell capacity by self-discharge.

It is now an object of the invention to provide improved glass-metal seals for use in lithium electrochemical cells, wherein the glass of the seals has improved deterioration resistance even under misuse conditions.

800 35 21 * ί'- - 3 -

According to the invention, an electrochemical cell (especially one with a lithium anode) has a metal-glass-metal sealing assembly, in which the glass insulator or a glass is charged with particles of aluminum oxide (A 2 O 3) or other stable metal oxides, or a aluminosilicate or like glass with or without such dispersed particles therein.

Aluminosilicate glasses contain relatively large amounts (about 15-35% by weight) of dissolved aluminum oxide (Al2C> 3). This alumina in aluminosilicate glasses is part of the molecular structure of the glass, and is incorporated into and modifies the glass structure of pure SiO2. The typical aluminosilicate glasses include Corning 1720 and 1723, which have the following general compositions: 1723 1720

Si02 57 60 A1203 15 17 B2 ° 3 5 5 20 MgO 7 7-8

CaO 10 7-8

BaO 6

Na20 - 1

Aluminosilicate glasses have been found to be more resistant to lithium ion intrusion, and therefore provide more stable glass-metal seals than the above-described borosilicate glasses. However, aluminosilicate glasses are not used in the construction of glass-metal seals for use in electrochemical cells, in part because of the high temperature (typically 1200 ° C) required to process or soften the glass. The predominant maximum temperature for equipment used in the continuous manufacture of glass-metal seals is around 1200 ° C. Due to the high softening temperatures, low thermal expansion, and suitability for seals adapted to tungsten (W) and molybdenum (Mo), aluminosilicate glasses have mainly found use in high temperature applications including projection lamps, 800 35 21 - 4 - high temperature thermometers, combustion tubes, and household roasting and cooking utensils, to be used directly over flames or other heating units.

Glasses, which contain only oxides such as alumina and oxides, which are even more stable than aluminum oxide (which have free energies of more negative formation than about -125 Kcal / gm oxygen atom), such as a calcium aluminate glass, and which satisfy the thermal contraction, work and metal bonding requirements for glass to metal seals are generally similarly considered to resist lithium attack and serve as a durable end clamp insulator, glasses, and are therefore within the scope of the invention.

The deterioration resistant characteristics of aluminosilicate and stable oxide glasses can be further enhanced by the mechanical inclusion or addition therein by mixing specific metal oxide additives therein, especially alumina, in amounts sufficient to prevent harmful cracking, which typically comes down at least 10 wt. %. It has further been found that the incorporation of metal oxides such as aluminum oxide into the existing borosilicate glasses used in glass-metal seals also significantly reduce the degradation of such glasses into glass-metal seals used in lithium cells.

The dispersion of hard particles of metal oxides such as aluminum oxide in a glass can prevent the propagation of cracks through the glass structure.

It is believed that if particles contained in the glass, which are more contractile than the glass, remain bound to the glass during contraction, compressive stresses within the glass surrounding each particle will counteract the propagation stress at the top of a approaching crack. If the glass surrounding the particle separates from the particle during the contraction, a cavity forms between the glass and the particle. This cavity serves to stop a 40 expanding crack by a redistribution stress in 800 3 5 21 - 5 - the glass. Metal oxide particles, which contract to the same extent as the glass, if weakly bonded to the surrounding glass, will similarly provide such cavity inhibition of crack propagation, while if strongly bonded to the glass they will prevent crack propagation alone, when they are more mechanically resistant to cracking than the glass itself.

Metal oxides other than alumina, which are suitable for incorporation into the glasses of glass-metal seals used in lithium electrochemical cells to reduce their deterioration include CaO, BeO, MgO, SrO, BaO, CeC ^, SC2O2, Ce2 ^ 3 'ZrO 2 / TiO 2 / and the like, which have high thermodynamic stability even when used in 15 corrosive lithium cell environments. Suitable metal oxides generally have a more negative free energy of formation than aluminum oxide (about -125 Kcal / gm oxygen atom) and are therefore thermodynamically more stable than aluminum oxide. For the sake of manufacturing simplicity, it is preferred that the amount of metal oxide including the glassware temperature does not increase above 1100 ° C. The alumina or other stable particles including are generally obtained by mechanically mixing appropriate amounts of dried powdered glass and alumina, pressing this mixture into a brittle compact form of desired configuration, and heating this compact form to coalesce the glass particles by locally flow around the still rigid particles of aluminum oxide. It is preferable that the glass compact form is sintered (typically from about 800 ° C to 1000 ° C for the alumina-aluminosilicate glass and from about 600 ° C to 800 ° C for the alumina prior to melting into a terminal clamp assembly. borosilicate glass) for a short period of time to reduce porosity and minimize flow required for sealing.

It is also preferred that after melting the glass mixture is annealed to provide increased mechanical strength of the glass and to release pressures 40 in the glass when used in 800 3 5 21 * 6 glass-metal seal. In the formation of the metal-glass-metal seal, the glass preform structure is placed between the two metal members and heated to a high temperature sufficient to soften the glass, whereby a metal-glass-metal seal is established according to known glass-metal sealing technology. The temperature used in forming the glass-metal seals generally depends on the amount of undissolved alumina inclusion, with higher percentages of alumina requiring a lower glass viscosity and thus a slightly higher operating temperature.

In order to facilitate the relative movement of the alumina particles as the glass flows, the alumina particles are preferably as free from asferites as much as practically possible. The preferred particle size is in the diameter range between 1 and 30 microns.

The glass-metal seals according to the invention comprise both adapted expansion seals and compression seals. In a modified expansion seal, the selected alumino-silicate glass or the glass filled with alumina (or other stable particles) is used with a pure metal, or alloy of metals, which has a substantially equal coefficient of thermal expansion when the glass is rigid. The metal used in the modified expansion seal is usually given a surface coating of its oxide prior to assembly, whereby an intimate and hermetic bond can be obtained between the oxide glass and the metal or metal alloy with its oxide. Generally, an external compression seal contains glass, surrounded by an external metal member, which has an expansion coefficient greater than that of the glass to compress the glass, as cooling continues after the glass sets, but not large enough to cause inelastic stresses or glass cracks. An internal compression seal contains a less expanding metal surrounded by glass.

The seals according to the invention are particularly suitable for cells containing lithium anodes 800 3 5 21 - 7 - Λ. Anode metals other than lithium for use in non-aqueous electrolyte cells include the alkalis alkaline earth metals such as sodium, potassium, magnesium and calcium; and aluminum.

Cathodes used in lithium cells include cathode active materials such as silver chromate or carbon fluoride (CF) or a carbonaceous substrate

λ XI

for soluble active cathode materials such as liquid oxyhalides, non-metal oxides, or non-metal halides.

Such soluble active cathode materials include sulfur dioxide (SC ^) and thionyl chloride (SOC ^), as well as phosphorus oxychloride ((POCl ^) / selenium oxychloride (SeOC ^) / sulfur trioxide (SO ^), vanadium oxytrichloride (VOCl ^), chromyl chloride (CRO2CI2) / sulfur oxychloride (SO2CI2), 15 nitryl chloride (NO2CI), nitrosyl chloride (NOC1), nitrogen dioxide (NC ^), sulfur monochloride (S2CI2), sulfur monobromide (S2Br2), and mixtures thereof Other active cathode materials include ΜηΟχ (where x is about 2 ), HgÓrO ^,

HgO, and generally metal halides, oxides, chromates, and dichromates, permanganates, periodates, molybdates, vanadates, chalcogenides, and mixtures thereof.

Electrolyte solvents used in lithium cells include organic solvents such as tetrahydrofuran, propylene carbonate, dimethyl sulfate, dimethyl sulfoxide, N-nitrosodimethylamine, gamma-butyrolactone, dimethyl carbonate, methylfomate, butyl format, dimethoxyethane, acetonitrile, and N: N-dimethyl. Electrolyte salts for such cells include light metal salts such as perchlorates, tetrachloroaluminates, tetrafluoroborates, halides, hexafluorophosphates, hexafluoroarsenates, and clovohorates.

Examples of specific metals, which can be used in such seals, and are compatible with various components in cells, containing lithium anodes, include the following:

In suitable electrolytes, metals usable for contact with lithium include copper, iron, steel, stainless steels of all kinds, nickel, titanium, tantalum, molybdenum, vanadium, niobium, tungsten, 40, and metal alloys such as Kovar, Inconel, and Monel (trade 80 0 3 5 21 - 8 brands).

Examples of metals and metal alloys that are stable at sulfur dioxide cathode potential include aluminum, titanium, tantalum, vanadium, tungsten, niobium, and molybdenum.

Examples of metals compatible with silver chromate include titanium, tantalum, molybdenum, vanadium, chrome, tungsten, and stainless steel.

Examples of metals and metal alloys that are stable at cathode potentials with the strong oxidizing thionyl chloride include titanium, molybdenum, niobium, tantalum, tungsten, Kovar, Inconel, Monel, nickel, and stainless steel.

The following examples illustrate seals 15 manufactured in accordance with the invention, and which have been tested in lithium cell environments, making the stability more apparent. All parts specified are parts by weight unless otherwise indicated. The examples are intended to illustrate the invention only, and the details provided are not intended to limit the invention thereto.

EXAMPLE I

An amount of Buehler "1 micron" alumina swarf was heated to transform any remaining alumina hydrate into anhydrous alpha alumina. The dried alumina was mixed with powdered and dried Corning 1723 alumino-silicate glass in an amount sufficient to form a 10% alumina mixture. Annular pellets or "preforms" were pressed at 226 MN / m from the mixture and sintered in air from 850 ° C to 1050 ° C, gradually increasing the temperature in steps of 50 ° C at 10 min intervals. A metal-glass-metal end clamp was assembled with the bead in the annular space 35 between an external cold rolled steel (low carbon) metal member and an molybdenum internal member to provide external compression and an internally matched seal. The seals were prepared in an argon atmosphere by passing for 15 min.

40 to melt at 1200 ° C, followed by a 15 min. Annealing 800 35 21 - 9 -

V

Λ period at 712 ° C. The completed end clamp was then assembled in a "D" sized Li / SC4 cell with its external metal member attached to the lithium anode. The cell was filled with an electrolyte consisting of a 3/4 molar solution of lithium bromide in a mixture of 74 wt. % sulfur dioxide and 26 wt. % acetonitrile, and was stored in the clamp down position at 72 ° C. After six months, there was no leakage of electrolyte or deterioration of the insulation IQ (a "D" size cell is a cylinder with a diameter of 33.3 mm and a length of 60.2 mm).

EXAMPLE II

A glass-to-metal seal was prepared according to the procedure of Example 1, but the surrounding metal member was made of molybdenum to form a custom seal. The seal was then placed in a sealed glass vial containing an electrolyte solution of the above components, but with 40% SO 2, with the metal member of the seal being lithium polarized. The vials were stored at 72 ° C for five months.

At the end of the storage period, only slight corrosion was visible, indicating only very slight adjustment. Borosilicate glass seals, tested in a similar manner, showed extensive corrosion after only six weeks of storage.

EXAMPLE III

A Fusite borosilicate glass, which contains 30.8 wt. % alumina, was bonded in custom 3Q glass-metal seals with Kovar conductors. The internal metal member or lead-through was lithium polarized, and the seal was exposed to boiling refluxed 1 molar LiAlCl 2 -thionyl chloride electrolyte solution for 32 days. Only a slight blackening of the internal seal was found after this time.

A seal of similar construction, using such a Fusite borosilicate glass, but only with the addition of 5% aluminum oxide, developed extensive cracking under corresponding 4Q test conditions.

800 3 5 21 y '- 10 -

The above examples were intended only to illustrate the invention. Changes and modifications are possible without departing from the scope of the invention.

- conclusions - 800 35 21

Claims (12)

1. Electrochemical cell 7 hermetically sealed with a metal-glass-metal seal, characterized in that the glass is selected from the group consisting of: aluminosilicate glass, glass containing alumina and oxides more stable than aluminum oxide, and glass incorporating particles of metal oxides in sufficient amounts to substantially prevent cracking of the glass, said particles having free energies per µm oxygen atom which are at least as negative as those of aluminum oxide. Electrochemical cell according to claim 1, characterized in that the glass contains particles selected from CaO, BeO, Ba2 <0, MgO, SrO, BaO, Cet ^, SC2O3 ' 15 Zri ^, TiC> 2, and Ί ^ Ο ^ · Electrochemical cell according to claim 1, characterized in that the glass contains alumina particles. Electrochemical cell according to claim 3, characterized in that the glass is a borosilicate glass. Electrochemical cell according to claim 3 or 4, characterized in that the alumina particles are substantially free of sharp parts. Electrochemical cell according to claim 3, 4 or 5, characterized in that the particles have diameters between 1 and 30 microns. Electrochemical cell according to any one of the preceding claims, characterized in that the amount of the particles is at least 10 wt. % of the glass. Electrochemical cell according to any one of the preceding 800 3 5 21 - 12 -f claims, characterized in that the metal oxide particles, including the glass processing temperature, do not increase above 1100 ° C. Electrochemical cell according to claim 1, 5, characterized in that the glass, which contains aluminum oxide and oxides which are more stable than aluminum oxide, consists of calcium aluminate. 10. An electrochemical cell according to any one of the preceding claims, characterized in that the cell has a lithium anode. Electrochemical cell according to claim 10, characterized in that the cell contains sulfur dioxide or thionyl chloride as a cathode depolarizer. Electrochemical cell according to claim 11, 15, characterized in that the metal-glass-metal seal contains an aluminosilicate or borosilicate glass in which at least 10 wt. % of alumina particles are included. * T 800 3 5 21