DE2817776A1 - POSITIVE ELECTRODE FOR SOLID LITHIUM ELEMENTS - Google Patents

Description

1817776

DIPL-ΙΝΘ. R. LEMCKE
DR.-IN6. HJ BROMMER

PATENT LAWYERS KARLSRUHE 1

PR MALLORY & GO. INC., 3029 East Washington Street, Indianapolis, Indiana 46206, USA

Positive electrode for solid-state lithium elements

809843/1022

The invention relates to electrochemical cells with high energy density using solid electrolysis, solid negative electrodes made of an active metal and novel solid positive electrodes. It relates in particular to such cells in which _t the positive electrodes contain an active material that conducts both ions and electrons.

In the recent past, electronics in particular has with regard to integrated circuits for quartz watches, calculators, cameras, pacemakers and the like went through a stormy development. The miniaturization of these components, the low energy drain and the long service life require power sources that are durable thanks to their robust construction Storage time, high reliability and energy density as well as readiness for use over a wide temperature range distinguish. In addition, the alimeasurements of this power source are also as small as possible should fail. These requirements are in the conventional cells, whose electrolytes in dissolved or in pasty form, difficult to meet, especially with regard to the storage time. The electrode materials react with time the electrolyte solution and tend to self-discharge, the self-discharge time being relatively short compared to the potential life of solid-state batteries. Gas can also develop, which forces the electrolyte out of the battery seal and other I ^ achbar parts are damaged, which is very expensive, especially with high-quality devices. Increasing the reliability of the cell closures increases both their size and cost and yet does not eliminate the problem of self-discharge. On top of that, cells that come with solutions

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operate within a temperature-limited operating range, depending on where the freezer and the boiling point of the solution contained in the cell is.

The problems outlined above were caused by cells Solved with solid electrolytes and electrodes that do not have the disadvantages of working with dissolved electrolytes Have cells. There is also no evolution of gas or self-discharge during long storage periods and nor to problems with the sealing of the electrolyte. However, these have solid cells in turn special disadvantages or limitations that do not exist in cells with dissolved electrolytes.

A cell with high voltage and high energy density would be ideal and high performance. The known plague cells, however, are in at least one of these Poor points.

A major consideration for the operation of a pesticide cell is the choice of solid electrolyte. To ensure high performance, the solid electrolyte should have a high ion conductivity, which allows the ion transport through Defects in the crystalline electrolyte structure of the electrode-electrolyte system made possible. An additional and a very important aspect for the solid electrolyte is that it is almost exclusively must be an ion conductor. The conductivity due to the mobility of electrons must be negligibly small otherwise there would be a partial internal short circuit and the electrode materials would used up despite the open circuit at the pole terminals

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will. Therefore, cells usually contain solute Electrolyte a separator between the electrodes that does not conduct any electrons and thus prevents a short circuit, while in solid cells the solid electrolyte acts both as an electron barrier and as an ion conductor Tung i ert.

The achievement of higher currents was "in solid cells through the use of" to ff er. that are exclusively ionic conductors, such as RbAg. "T _r (0.27 Ohm" cm ~ conductivity at room temperature). These conductors can only be used for electrolysis, however, if the cells are low voltage and low energy density cells . For example, the solid cell Ag / fibAg ^ lp. / Rbl- can be discharged at 40 ir.A / 'cm below room temperature, but only brings about 0.012 vvh / cm (0.2 Wh / in) and an open terminal voltage of Q66 V. Materials for the negative electrode with high energy density and high voltage, such as lithium, begin to react chemically with such conductors, which is why this combination is not possible. Electrolytes that are chemically compatible with substances of high energy density and high voltage for the negative electrode, such as Lit, only have a conductivity of 5.10 0hm cm at room temperature, even if they are doped for the purpose of higher conductivity. That is, cells with high energy density, which is 0.3 to 0.6 Wh / cm ⁵ (5 to 10 Wh / in ⁵ ) and with a voltage of about 1.9 V, as in the type currently being produced Lil / PbX, PbS, Pb is present, cannot achieve a performance higher than about 50 iiA / cm at room temperature. Another disadvantage in addition to the low current strength in cells with high energy density is the low conductivity (both in terms of electrons and ions) of the active substances for the positive electrode. The increase in conductivity through, for example, graphite for electron conduction or through the

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Electrolytes for the ionic conduction, the current strength depending on the conductivity of the electrolyte Maximum value can be increased, leads to the fact that the energy density of the cell decreases because of the added coming volumes.

Another important consideration in making clay plague cells is the suitability of the electrolyte material. The physical properties of electrolytes such as BaMg ₁ -S ₁ - and Bai-igpSe, -, which are compatible with a negative electrode made of magnesium but not lithium, and of sodium beta-alumina such as NapO.11 AIpO- , which is compatible with a sodium negative electrode, makes it possible to produce cells with high energy density even if expensive production measures are taken. This is because these electrolytes have ceramic properties that make them very difficult to work with, especially if the material is to be ground and pelletized in the course of production, and firing is generally necessary to give the material the desired structure. In addition, the glazed material produced in this way prevents good surface contact with the electrodes, which results in poor conductivity and thus low cell performance. These electrolytes are therefore mainly used in cells with molten electrodes.

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Proceeding from this, the object of the present invention is to determine the conductivity of the positive electrode to increase in pesticide elements, with substances of high energy density and the negative electrode electrolysis compatible with this should be used, so that an increase in the energy density is obtained, without the performance decreasing. The chemical stability between the components of the element should be guaranteed.

According to the invention is an electrochemical pesticide element provided which has a solid, negative lithium electrode, furthermore a body electrolyte with one or more lithium salts and an ion conductivity above 10 ^ ohm cm at room temperature as well as a positive plague electrode with an ion and electron conducting metal chalcogenide,

its ion and electron conductivity between

-10 +2 -1 -1
10 and 10 ohm cm is at room temperature and the cathodically reacts actively with the said negative lithium electrode, the positive electrode still containing sulfur, selenium, tellurium, bromine and / or iodine as the second active positive electrode material.

The present invention is based on the use of a material for the positive electrode of a pesticide element, which is characterized by the fact that it conducts both ions and electrons and that is equally suitable as an active material for the positive electrode. Usually the positives require Electrodes the addition of a not inconsiderable amount (for example over 20 percent by weight) of one Ion conductor, such as is used as an electrolyte,

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to promote the flow of ions in the positive electrode during the reaction of the element. this applies especially if the material of the positive electrode is an electron conductor, otherwise a reduction product at the contact surface of the positive electrode with the electrolyte, the would possibly make the flow of ions considerably more difficult during the discharge. In the previously known elements However, the added ion conductors were generally not active substances of the positive electrode - with the Result of a significant loss of capacity. In addition, substances suitable for the positive electrode with poor electron conductivity require the addition of good electronic conductors, which results in the Capacity of the elements further reduced. The inventive combination of the electron and the Ion conduction with the activity of the positive electrode becomes a higher energy density and at the same time also a higher amperage can be achieved without the need for space for additional conductor materials.

Examples of materials that have the desired ion and electron conductivity and which serve as active material for the positive electrode and also with those in elements of high energy density Electrolytes used are compatible, show the

following connections ₂ , MoS 2 ' MoSe ₂ , : CoTe , NbS 2 ^pp ₃ , HfS ₂ , HfSe ₂ , HfTe ₂ , IrTe ₂ , PtS 2 ' PtSe ₂ , MoTe ₂ , SnS 2 ' NbSe ₂ , NbSe ₂ , NbTe ₂ , NiTe , TaTe 2 » TiS ₂ , PtTe ₂ TiTe 2 ' SnSSe , SnSe ₂ , TaS ₂ , TaSe ₂ WTe ₂ , ZrS TiSe ₂ , ZrTe 2 ' vs ₂ , VSe ₂ , VTe ₂ , WS ₂ , WSe ₂ , ₂ , ZrSe ₂ and 2 ' whereby the Chal-

cogenide is a sulfide, selenide, telluride, or a combination thereof.

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Also suitable are non-stoichiometric metal chalcogenides such as Li TiS ₉ , where ^ x 1, which to some extent contains the complex form of one of the positive electrode materials with the negative electrode cation and which are believed to be intermediate reaction products during the element discharge.

With regard to the ion and electron conductive active material for the positive electrode, it should be be usable in elements with a high output voltage, for example in elements with negative electrodes made of lithium, and there should be an open terminal voltage of at least 1.3 V with the lithium and preferably over 2 V.

The working voltage of the ion and electron conductive positive electrode active material should preferably be by and large the voltage of the non-conductive, active positive electrode material is higher Energy density that is mixed with it to avoid detrimental voltage losses.

Another criterion for the material of the positive electrode is that both the ion and

the electron conductivity of the active material between

-10 +2 -1 -1
see 10 and 20 ohm cm should be where

the ion conductivity preferably above 10 ~ and the electron conductivity preferably above 10 should be at room temperature.

Furthermore, it is important that the active material of the positive electrode, which is both ion and electron conductive is, is also compatible with the pesticide electrolyte, which is usually found in elements of higher

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Energy density is used.

The solid electrolytes for lithium elements of high energy density are mostly lithium salts, which are an ionic

—Q —I —I

Conductivity above 10 ohm cm "at room temperature exhibit. These salts can either be in pure form or with additives that increase conductivity "to improve cell performance. Examples of lithium salts with the required conductivity are lithium iodide (LiJ) and lithium;) odid, that with lithium hydroxide (LiOH) and Alumina (AlpO,) is mixed, the latter being the latter The mixture is referred to as LLA and is described in U.S. Patent 3,713,897.

It is believed that the aforementioned positive electrode active material which is both ionic and also conducts electrons, with the ions of the negative electrode (e.g. lithium cations) will react to form a non-stoichiometric complex during the element discharge. These Complex formation of the cations allows them to shift their seat and thereby the desired ionic conductivity bring about. In addition, the above-mentioned compounds provide free electrons that are used to conduct electrons are necessary.

The aforementioned ingredients are mixed with other ingredients or elements, in particular Sulfur, selenium, tellurium, iodine and bromine, which ensure a higher energy density, but not alone can be used because they are not able to serve as ion and / or electron conductors. Included increases the inclusion of ions and electrons

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conductive, positive, active electrode material reduces the capacitance of the element by avoiding the need non-discharging conductor material. In addition, when the conductive active material is mixed, it is more homogeneous Form with the material of higher energy density the realizable usability of an element designed in this way approximately equal to the theoretical value. A limiting factor in solid state elements is that Conductivity of the reaction product of the element. A product with low conductivity results from a large one internal loss of resistance, which permanently limits the usefulness of the element. For elements that have the have the aforementioned ion- and electron-conductive, active, positive electrode material obtained Complex reaction products increase the conductivity, thereby allowing them to fully utilize the other active psitiven Ensure electrode material that is in their vicinity.

Accordingly, high energy density positive electrode materials such as sulfur and iodine, as well as other solid chalcogenides, Se and Te, and halogens such as bromine, can be effectively used for increasing potential. Solid elements with sulfur in connection with negative lithium electrodes and an electrolyte made of lithium salt made great promises with regard to the achievable voltage and the overall energy density. One of the disadvantages was the formation of low ion conductivity lithium sulfide (Li ₂ S) as a reaction product of the element, especially at the point of contact between the positive electrode and the electrolyte. This phenomenon permanently blocked the further use of such elements. The inclusion of ion and electron conductive, active, positive electrode

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However, materials ensures a more even distribution of the reaction products over the entire structure the positive electrode due to its ion-conducting property. Since the reaction products of the ion-conducting Maintaining the conductivity of the material, the further usability of the element is as well with the Non-conductive active material possible in conductive proximity to the conductive active material.

In addition, a small amount of electrolyte may be included in the positive electrode structure to bridge the boundary area between positive electrode and electrolyte by creating a more intimate electrical Contact between positive electrode and electrolyte is thereby established. This makes it possible for the element to work for longer periods of time at higher power outputs. In addition, the electrolyte inclusion can increase the ion conductivity increase the positive electrode in the event that the ion conductivity of the active, positive Electrode material has a lower conductivity than the electrolyte. This inclusion should however, when made, do not exceed 10 percent by weight as larger proportions only increase energy density it would reduce the element while at the same time only increasing it slightly, if at all the current delivery capability.

The following examples illustrate the high energy density and usefulness of a sulfur containing one positive electrode in a solid element connected with the said ion- and electron-conducting, active, positive electrode metal chalcogenide is combined. Sulfur cannot be used alone as a positive electrode in a solid state element if it is not

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Contains a substantial proportion of ion and electron conductive material making up $ 60 or more of the total positive electrode weight. Therefore, the inclusion of an ion and electron conductive metal chalcogenide, such as titanium disulfide, in a positive sulfur electrode enables the use of sulfur without the hitherto simultaneous great loss of energy capacity. Titanium disulfide is a good ionic

and electron conductors (1 0 0hm ~ cm "ion conductivity

-2 -1 -1 hours at room temperature and more than 10 ohm cm Electron conductivity at room temperature) and it also acts as a reagent in the reaction of the element with the lithium cations to form the non-stoichiometric L. TiS «, which is also ion and electron conductive, and in this way the other Problem of non-conductive reaction products is improved, which block a further reaction of the element. In addition, TiSp basically discharges at a voltage similar to that of sulfur; H. 2.3 V, and on in this way the tension of the element is stable without any loss of tension.

The following examples are as well as in the whole. Description and in the claims all proportions and percentages based on weight, unless otherwise stated. The examples are given for illustration purposes only, so that details are not to be regarded as a limitation of the invention.

Example I:

A plague body element was attached to a lithium metal

2 slices made with a surface of about 1.47 cm

and had a thickness of 0.01 cm. Plus a positive one

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ρ Electrode disk about 1.82 cm in surface and about 0.02 cm thick, which consisted of 80 $> _{TiS 2} and 20 <fo S with a weight of 100 mg. Furthermore, a solid electrolyte therebetween with the same dimensions as the positive electrode and consisting of IiJ, LiOH and

Al ₀ O, in a ratio of 4: 1: 2. The electrolyte was

8/2

first pressed at a pressure of 6.8 × 10 N / m with the positive electrode and then the negative electrode was pressed on with a pressure of 3.4 × 10 E / m. The element thus obtained was discharged at room temperature with a load of 100 kilohms. The element delivered 26 mAH at 2 V, about 41 mAH at 1.5 V, and greater than 46 mAH at 1 Y. The element had a realizable capacity of greater than 0.73 Whrs / cc (12 watt hours / in ').

The following table illustrates the results that were achieved with elements that basically correspond to Example I, but had different weights of the positive electrode, the contact area between positive electrode and electrolyte or the relative percentage of TiSp to S, tested at different loads or temperatures which resulted in capacity limits of 2, 1.5 and 1 V.

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Example no.

% TiS ₂ : S.

Surface (cm ² )

Weight ■ - (mg)

Discharge load

- Temperature mAH: around 2 V / olt

80:20
80:20
80:20
80:20
80:20
80:20
60:40
60:40
80:20
80:20
80:20
80:20
80:20
80:20
80:20
80:20
80:20
80:20
80:20
80:20
80:20
80:20

1.82

1.82

1.82

1.71

1.71

1.71

1.82

1.82

1.82

1.82

1.82

1.82

1.82

1.82

1.82

1.82

1.82

1.82

1.82

1.82

1.82

1.82

100 100 100 100 100 100 100 100 700 700 700 700 700 700 700 700 700 700 700 200 200 200

100 50 20 '50 20 10

18 / ΛΙ 10 200 100 77.5 50 30 20 200 100 77.5 50 30 270 100 52

Room 26th Room 16 Room 6th 72 ° C 32 72 ^O C 27 72 ° C 18th ) Room 11th 72 ° C 9 37 ° C 110 + 37 ° C 55 37 ° C 40 37 ° C 25th 37 ° C 8th 3 7 ° C 5 Room 72 Room 38 Room '28 Room 12th Room 5 37 ° C 50 ·; 37 ° C 35 37 ° C 25th

1.5 volts 1 volt 41 46 34 40 24 30th 39 42 37 40 35 41 28 31 19th 21

UO + 90 55 26 21

110+ 80. 55 39 15

52

45

■ ¹⁰⁺ V

, 3 31

102 65 50

18th

(54 55

From the table it can be seen that discharged at 37 ° C Elements even have a greater capacity than identical elements with the same load were discharged at room temperature. Therefore, elements according to the present invention, since 37 ° C the human body temperature is, in pacemakers, with a usefulness that lasts over ten years lasts, eliminating the need for new batteries to be surgically installed is reduced.

In addition, the 80:20 weight ratio of TiSp to S, which essentially corresponds to the molar ratio, for greater usable capacity than the 60:40 ratio despite the increased proportion of sulfur with higher energy density. With the molar ratio, three lithium components can be used in the element reaction react stoichiometrically, d, h, 2 Li + S- ^ Li "S and Li + TiSp "^ LiTiSp. These reactions lead to a Three-electron exchange at both high voltage and high capacity. The molar ratio of TiSp to S leads to complete stoichiometric utilization and is therefore extremely preferable.

Example XXIII:

An element comprising the materials of claim 1 having an outside diameter of 3.195 cm and a thickness of 0.216 cm and a positive electrode weighing 1.5 g was used as the back cover of a tritium-illuminated Demonstration watch made with liquid crystal. A limit resistance of 330 kilo ohms limited the voltage with which the watch was supplied. The working current for this watch ranged between 1 and

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3 / uA. With a stoichiometric capacity of 750 mAH and provided that 2/3 of the capacity can be used, this element is theoretically capable of operating the watch with a continuous discharge of 2 Alk and a voltage of around 2.2 V for 98.5 years to supply. The lifespan of such elements is thus longer than the lifespan of clocks usually manufactured. As a result of the stability of solid elements in general and the performance of the element described in particular, batteries can be used as a built-in component of electrical devices, such as clocks, instead of as such a component that is permanent or needs to be replaced from time to time.

Example XXIV:

An element according to Example I was produced, but with tantalum _{disulfide (TaS 2} ) instead of titanium disulfide (TiSp) and a weight ratio to sulfur of 87.5: 12.5. When the element was discharged at 72 ° C with a load of 10 kiloohms, the element delivered 6 mAH at 2 V, 18 mAH at 1.5 V and 24 mAH at 1 V.

Example XXV:

An element was produced according to Example XXIV and ^{discharged at 72 °} C. with a load of 20 kiloohms. The element provided Η mAH at 2 V, 25 mAH at 1.5 V, and approximately 28 mAH at 1 V.

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Claims (7)

Pat ent calls ' 1/. Pesticide element with a fixed lithium negative electrode, a solid electrolyte containing one or more lithium salts and with an ion-conducting —9 —1 —1 ability of more than 1x10 ohm cm at room temperature as well as a fixed positive electrode, characterized in that that the positive electrode contains an ion and electron conductive metal chalcogenide, its ion and -10 2 -1 -1 electron conductivity between 10 and 10 ohm cm is at room temperature and that is cathode-active with said negative lithium electrode, and that the positive electrode furthermore as a second cathode-active material is sulfur, selenium, tellurium, bromine and / or Contains iodine. 2. Solid element according to claim 1, characterized in that that the lithium salt is lithium iodide. 3. Solid element according to claim 2, characterized in that that the electrolyte contains lithium hydroxide and aluminum oxide. 4. Solid element according to claim 1, 2 or 3 »thereby characterized in that the metal chalcogenide has an ionic conductivity of more than at room temperature - f> -1 -1 10 "ohms" cm "and an electron conductivity at room temperature greater than 10 "^ ohms" cm " 809843/102 and that it has a clamping voltage associated with the lithium negative electrode of more than 1.5V. 5. pesticide element according to claim 1, 2, 3 or 4, ä thereby characterized in that the metal chalcogenide is titanium disulfide. 6. Solid element according to claim 5, characterized in that that said second positive electrode active material is sulfur. 7. solid element according to claim 6, characterized in that that the titanium disulphide is in an equal molar ratio with the sulfur ". 809843/1022