DE19646682C2 - Electrolytic cell and treated electrode - Google Patents

Description

The present invention relates to a treated electrode and an electrolytic cell containing this electrode.

The use of additives / surfactants within an elec trolytic cell and especially within secondary lithium batteries in the prior art as a possible measure for possible improvements in Morphology and the Coulomb effectiveness of an electrode made of an alkali metal source (such as lithium) identified during cell cycling. During this State of the art with the hopeful results of Additives / surfactants in, for example, rechargeable Li concerned the teaching of this research of the state of the art nik to lie in a direction that focuses on surfactants, which are soluble in the associated electrolyte and / or those with the special one Alkali metal (lithium) electrode are reactive. (See e.g. publications with the title: "THE US NAVY'S LITHIUM RECHARGEABLE BATTERY PROGRAM PART II RESEARCH INTO NEW OR IMPROVED CHEMISTRIES ", by S. James, P. Smith, T. Murphy and D. Cason-Smith, published on pages 238-243 in Progress in Batteries & Solar Cells, Vol. 9 (1990); and "FLUORINATED SURFACTANTS AS ADDITIVES FOR LITHIUM BATTERIES ", by D. Lemordant, A. Tudela Ribes and P. Willmann, published on pages 69-80 in Power Sources, Vol. 14 (1992)).

EP-A-0 715 366 describes a rechargeable lithium battery with an anode coating, the coating comprising a film with a metal oxide material with a standard electrode potential difference or potential difference with respect to lithium of 1.5 or less. The metal oxide material is in a high molecular weight organic material, which organic material may contain hydroxyl groups. Other organic materials of high molecular weight, such as silicone resins, fluororesins and polyolefins, which have inherent solubility in the electrolyte solution, are also possible. US-A-5 437 942 describes a lithium secondary battery comprising a positive electrode, an electrolyte layer with a solid polymer electrolyte and a negative electrode using metallic lithium or a lithium alloy as an active material. The electrolyte layer includes a first layer and a second layer. The electrolyte of one layer is formed by polymerizing a polyether that has no functional groups at the end of a main chain, but includes an ionic salt. The electrolyte of the other layer is a high-molecular compound which is formed by polymerizing a polyether having a functional group at the end of the main chain and including an ionic salt. In the examples, the polymer electrolyte is a copolymer of ethylene oxide with propylene oxide and is solid. US-A-5 387 479 describes a battery that includes a layer between the major surface of the electrode and the electrolyte to reduce passivation of the electrode body, this layer containing carbon particles retained in a binder matrix material. The binder can be a thermoplastic resin that can be blended with carbon black to form a film. Furthermore, the binder has transport properties for ions, in particular Li ⁺ ions, in that it has SO ₃ groups. US-A-5 314 765 describes a lithium battery with a layer of lithium phosphorus oxynitride on the lithium anode.

Although attempts have been made to assess the effects of additives / upper to use surface active agents in secondary lithium cells and completely understand the research and experiments carried out in the state of the art Technique, such surfactants are shown to be specific have chemical properties. Unfortunately, such have chemical Features so far have not been proven to be a rechargeable battery  lead, which has the assumed advantages, which such additives / upper surface active agents theoretically (according to this research of the state of the tech nik) deliver.

It is therefore an object of the present invention to provide an electrolytic cell or to provide an electrode, wherein the on the alkali metal electrode (which in a rechargeable battery to be used) additive applied to a predominant additive interface, which among other things leads to a considerable increase in interfacial capacity and a significant decrease in Interfacial resistance leads to the cyclability and the effectiveness of the Increase cell.

This object is achieved by the electrolytic cell according to claim 1 and solved the electrode according to claim 7.

Advantageous embodiments of the invention are contained in the subclaims ten.

These and other objects of the present invention are presented in the light of lying description, claims and drawings.

According to the present invention, an electrolytic cell 10 is provided, comprising a first electrode ( 12 ) which can give off alkali metal ions, a second electrode ( 14 ) and an electrolyte ( 16 ), the first electrode ( 12 ) being connected to the electrolyte ( 16 ) includes an adjacent surface ( 13 ), onto which - at least a part - an additive ( 18 ) that is practically insoluble in the electrolyte ( 16 ) is applied in such a way that an additive interface between the surface ( 13 ) of the first electrode ( 12 ) and the electrolyte ( 16 ), and in an amount such that the interfacial capacity of the first electrode ( 12 ) is increased beyond 10 µF / cm ² , the additive for the alkali metal ion of the first electrode ( 12 ) being ionically conductive; is non-ionic; and is not reactive with the alkali metal of the first electrode ( 12 ). Although the term additive is used, it will be understood by those of ordinary skill in the art that such an expression may as well be a surfactant.

According to the present invention there is further provided a treated electrode ( 12 ) obtainable by a process comprising the following steps:

• - Applying carbon particles ( 21 ) to at least part of the surface ( 13 ) of the electrode ( 12 ); and
• - Applying an additive ( 18 ) on the carbon particles ( 21 ) and also on the surface ( 13 ) of the electrode ( 12 ), which is not covered by the carbon particles ( 21 ), so that there is an additive / carbon interface adjacent to the surface ( 13 ) of the electrode ( 12 ) and at least part of the electrolyte ( 16 ) results, the additive ( 18 ) being applied in an amount such that the interface capacity of the first electrode ( 12 ) is increased beyond 10 μF / cm ² , wherein the additive for the alkali metal ion of the first electrode ( 12 ) is ionically conductive; is non-ionic; and is not reactive with the alkali metal of the first electrode ( 12 ).

Brief description of the drawings

Fig. 1 is a diagram of the secondary electrolytic cell of the present invention.

Fig. 2 is a diagram of another preferred embodiment of the se ondary electrolytic cell of the present invention.

Fig. 3 is a chemical structure.

Fig. 4 is a photomicrograph of a lithium electrode, and

Fig. 5 is a microphotograph of a lithium electrode.

Embodiments in many different ways during this invention are accessible are specific in the drawings and here in detail Embodiments described with the intent that the present disclosure is to be regarded as an exemplary representation of the principle of the invention and the  The invention is not intended to limit the embodiments shown.

The electrolytic cell 10 is shown in FIG. 1 as having a first electrode 12 with the surface 13 , a second electrode 14 , the electrolyte 16 and a surface-active agent / additive 18 . In a preferred embodiment, the first electrode 12 releases lithium ions, although other alkali metal sources are correspondingly contemplated for use. In addition, although not intended to limit, the present invention is described in the context of a rechargeable lithium battery provided that other types of electrolytic cells are also contemplated by the present description.

The additive 18 is made of a material that has several desired properties. First, the alkali metal ion additive 18 of the first electrode must be ionically conductive with respect to the particular ions associated with the source of alkali metal ion of the first electrode 12 , which are preferably lithium ions. Accordingly, such ion conductivity serves to allow the practically unimpeded permeation / movement of the lithium ions during the cycling of the battery.

The additive 18 is also non-ionic, so that the additive is relatively unaffected by electrical fields that are continuously applied within the electrolytic cell 10 . In fact, one of the objectives of the present invention is to prevent the additive 18 from migrating away from the surface 13 of the first electrode 12 ; a goal that would be bypassed if the additive were ionic due to the nature of an ionic material to migrate towards an electric field and / or as a result of polarization.

The additive 18 is also practically insoluble in the associated electrolyte, so that accidental absorption in the electrolyte is avoided. In addition, since various alkali metals can be quite reactive, it is also desirable that the additive be practically inert with respect to the particular source of alkali metal.

Examples of additives / surfactants that are acceptable for practicing the claimed and described invention include, but are not limited to, E-10 (Me) ₂ (t-BuMe ₂ Si) ₂ , the chemical structure of which is shown in FIG. 3 is shown; Polyethylene glycol (with an average molecular weight of 400) dimethyl ether; PLURONIC-L-92 dimethyl ether, which is produced using the commercially available PLURONIC L-92 from BASF Corp. of Parsi panny, NJ, is synthesized as a starting material; and a surfactant sold under the tradename SILWET L7602 and commercially available from OSi Specialties Inc. of Danbury Conn. is available. Although not necessary, it is contemplated that additive 18 may be polymerizable after being applied to surface 13 of first electrode 12 .

As can be seen in Fig. 1, the additive 18 is effectively applied to the surface 13 of the first electrode 12 , so that a predominant additive interface adjacent to the electrolyte 16 is formed. As will be explained in more detail, the additive interface, which has the properties mentioned above (other than the ability to be polymerizable), will in fact serve to increase the capacity of the first electrode 12 over the known ordinary capacity of an electrode which e.g. . B. lithium ions can be constructed, namely over 10 uF / cm ² .

Another preferred embodiment of the electrolytic cell 20 is shown in FIG. 2, where carbon particles 21 are effectively applied to the surface 23 of the first electrode 22 . In this preferred embodiment, the carbon particles are applied to the surface 13 in a non-continuous / discontinuous orientation and additive 28 (which has the same properties as previously described for additive 18 of FIG. 1) is effective on the carbon particles 21 and also on the Surface 23 of the first electrode 22 brought up. Such discontinuous orientation of the deposited carbon particles helps to suppress dentritic growth on the first electrode, while the additive serves to increase the capacitance and decrease the resistance to it. The actual application of the carbon particles to the surface 23 of the first electrode 22 can be effected by various methods, such as argon spraying, brushing or vacuum coating, to name just a few.

After the carbon particles have been effectively applied to the surface of the first electrode, the additive can then be applied in various ways. For example, the additive can be applied / coated directly over the carbon particles and also over the areas of the surface 23 that are not covered by the carbon particles, or additive can be added to the electrolyte, whereupon it is on the carbon particles and not on carbon covered areas of the surface of the first electrode after the initial cycling of the electrolytic cell 20 is absorbed. As will be explained in more detail, it is also contemplated that the carbon particles and the additive are mixed together and then applied to the upper surface of the electrode together.

The electrolyte 26 and the second electrode 24 are also shown in FIG. 2. It is contemplated that the electrolyte in the embodiment of FIG. 2 and in FIG. 1 comprises a gel, a liquid, or even a polymer. Any number of different electrodes can be used in the electrolytic cell and are easily determined by one of ordinary skill in the art having the present description in mind.

In support of the advantages of the electrolytic cell 10 ( FIG. 1) and the electrolytic cell 20 ( FIG. 2) and in particular the advantages associated with the new application of the claimed and described electrolytic cell which uses an additive which has the chemical properties identified above, ten experiments were carried out. In each of these experiments, it was found that the additive resulted in a predominant additive interface that increased the interface capacity of the first electrode well beyond 10 µF / cm ² while also serving to greatly reduce the interface resistance. The results and summaries of these experiments are shown below.

Initially, it should be noted that Experiments Nos. 1 through 5 used a three-electrode electrolytic cell that had the following common features:

• a working electrode constructed from a 4 mil (0.1 mm) piece of lithium foil with an area of 4.9 cm ² ;
• - a lithium counter electrode;
• - a lithium reference electrode; and
• a glass fiber separator which separated the electrodes and which was filled with an electrolyte consisting of 1 M LiClO ₄ in propylene carbonate.

In addition, interfacial resistance was used in each of these first five experiments between the lithium working electrode and the special electrolyte by changing current impedance spectroscopy using a Solartron frequency Response analyzer 1250 measured using a Solartron electrochemical Interface was connected in 1286. The change in the interface resistance and the capacity for each cell in each of Run Nos. 1 through 5 were then observed and recorded. The results of such tests are shown in Table 1 shown, which follows the information relating to experiments Nos. 1 to 5.

In addition to the common elements and test procedures above, these were following characteristics unique in each respective experiment.

Trial No. 1

In this experiment, neither the electrolytic cell nor the working electrode were used treated with some kind of additive. The results of this experiment are in  Table 1 shown below under the name of the additive "none".

Trial No. 2

In this experiment, an E-10 (Me) ₂ (t-BuMe ₂ Si) ₂ additive (as shown in Fig. 3) of about 5% by volume of the electrolyte was added to the electrolyte. The results of this experiment are shown in Table 1 below under the name of the additive "EMBSi".

Trial No. 3

In this experiment, a Pluronic-L-92 dimethyl ether additive of about 5% by volume of the electrolyte was added to the electrolyte. The results of this test are shown in Table 1 below under the additive designation "Me ₂ L-92".

Experiment No. 4

In this trial, a surfactant that was commercially available as Silwet L7602 is known, with about 5 vol .-% of the electrolyte added to the electrolyte. The results of this experiment are shown in Table 1 below under the additive designation "L7602" shown.

Trial No. 5

In this experiment, a polyethylene glycol (with a molecular weight of 400) dimethyl ether from about 5% by volume of the electrolyte to the electrolyte set. The results of this experiment are listed in Table I below under the Additive designation "PEG (400) DME" shown.  

Table I

As can be clearly seen from Table I, an additive which has the claimed and described chemical characteristics when used in combination with an alkali metal electrode and in particular a lithium source electrode leads to a considerable increase in the interfacial capacity and a considerable decrease in the interfacial resistance of the lithium electrode compared to that of an untreated electrode. As can also be observed, the interfacial capacity in each case where the additive was used is well over 10 µ / cm ² .

In Experiments Nos. 6 to 8, a cell with three electrodes was built similar to that used in Experiment No. 1, but in each of these three experiments the lithium surface of the working electrode was modified to include carbon particles to suppress dentritic growth. In particular, the lithium surface in each of these experiments was coated with 0.03 mg / cm ^{2 of} a non-continuous / interrupted layer of 100% compressed carbon black particles (available from Chevron Chemical Co. of Houston, Texas, under the trade name CHEVRON C-100). the coating being applied from a suspension of 1.5 g of the carbon in about 200 g of heptane using known argon spraying techniques.

The change in interfacial resistance and capacity for each cell in each of Experiments 6 through 8 were then observed (as was the case with Experiments No. 1 to 5 was made) and recorded. The results of this Experiments are shown in Table II which of the information related to the experiments Nos. 6 to 8 follow.

In addition to the common elements and attachments above, those were following characteristics once for each respective experiment.

Trial No. 6

In this experiment, neither the electrolytic cell nor the working electronics were used trode treated with some kind of additive. The results of this experiment are shown in Table II below under the additive designation "none".

Trial No. 7

In this experiment, about 1 g of E-10 (Me) ₂ (t-BuMe ₂ Si) _{2 was} also suspended in the heptane together with the carbon particles and then sprayed together on the lithium surface. The results of this test are shown in Table II below under the additive designation "EMBSi".

Trial No. 8

In this experiment, about 1 g of polyethylene glycol (with a molecular weight weight of 400) dimethyl ether also in heptane, together with the coals particles, suspended and then applied together on the lithium surface sprays. The results of this experiment are shown in Table II below under the  Additive designation "PEG (400) DME" shown.

Table II

As can be seen from Table II, the use of an additive with the chemical features claimed and described in combination with the carbon particles also resulted in a significant increase in interfacial capacity and a significant decrease in interfacial resistance of a lithium electrode compared to that of an untreated electrode. As can also be observed, the interfacial capacitance was well over 10 µF / cm ² in each case where the additive was used.

In experiments Nos. 9 and 10, a cell with two electrodes was put together built.

The cell included:

• two lithium electrodes, each having an area of about 5.14 cm ² ;
• - a polypropylene ring with a thickness of about 5 mm, which the two Electrodes separated; and
• - An electrolyte consisting of 1 M LiClO ₄ in propylene carbonate.

However, no additive was used with respect to Experiment No. 9, while in Experiment No. 10 an E-10 (Me) ₂ (t-BuMe ₂ Si) ₂ additive (see FIG. 3) contained about 5% by volume of the electrolyte Electrolyte was added.

Both cells (in Experiment Nos. 9 and 10) were then cycled using an alternating current of +/- 4.290 mA at one hour intervals. After ten complete cycles, the cells were disassembled and the electrodes washed three times with dimethyl carbonate. After the washes, the electrodes were vacuum dried. The morphology of both cells was then observed through a scanning electron microscope. Photographs of these observations, ie, the cell from Run # 9 (no additive) is shown in Fig. 4 and the cell from Run # 10 (with additive) is shown in Fig. 5 clearly show much less degradation of the Electrode treated with the additive claimed and described.

The foregoing description and drawings are only intended to illustrate the invention explain and explain, and the invention is not thereby limited except insofar as the appended claims are limited, since the person skilled in the art who Description has before it is able to make modifications and changes to be made therein without departing from the scope of the invention.

Claims (11)

1. Electrolytic cell containing:
a first electrode which can give off alkali metal ions, a second electrode and an electrolyte, the first electrode comprising a surface adjacent to the electrolyte, to which - at least in part - a practically non-soluble additive is applied in such a way that there is an additive interface between the surface of the first electrode and the electrolyte, and in an amount so that the interface capacity of the first electrode is increased beyond 10 µF / cm ² , the additive for the alkali metal ion of the first electrode being ionically conductive; is non-ionic; and is not reactive with the alkali metal of the first electrode. 2. Electrolytic cell according to claim 1, characterized in that the electrode can release lithium ions. 3. Electrolytic cell according to claim 1 or 2, characterized in that it further comprises means for polymerizing the additive after which the additive on at least part of the surface of the first electrode is applied. 4. Electrolytic cell according to claim 1, characterized in that it continues to include funds to curb dendritic growth to suppress the first electrode practically.   5. Electrolytic cell according to claim 4, characterized in that the means to suppress dendritic growth of coal comprise particles of matter that are at least a portion of the source of the Alkali metal ion of the first electrode are applied. 6. Electrolytic cell according to claim 1, characterized in that the first electrode comprises a lithium metal anode. 7. Treated electrode, obtainable by a process comprising the following steps:

• Applying carbon particles to at least part of the surface of the electrode; and
• - Application of an additive on the carbon particles and also on the surface of the electrode, which is not covered by the carbon particles, so that there is an additive / carbon interface adjacent to the surface of the electrode and at least part of the electrolyte, the additive in one Amount is applied so that the interfacial capacity of the first electrode is increased beyond 10 uF / cm ² , the additive for the alkali metal ion of the first electrode being ionically conductive; is non-ionic; and is not reactive with the alkali metal of the first electrode.

8. Treated electrode according to claim 7, wherein the method thereby is characterized in that the step of applying an additive the carbon particle the stage of coating the carbon part prior to the step of applying the carbon particles to the Surface of the electrode includes. 9. Treated electrode according to claim 7, wherein the method is characterized in that the step of applying an additive to the carbon particles comprises the following steps:

• Adding the additive to the electrolyte; and
• Adsorbing the additive on the carbon particles after the initial cycling of the electrolytic cell.

10. Treated electrode according to claim 7, wherein the method thereby is characterized in that it further comprises the step of polymerizing the Additive after the step of applying the additive to the Carbon particles and then onto the surface of the electrode. 11. Treated electrode according to claim 7, wherein the method thereby is characterized that it continues the stage of construction of the electrode made of lithium metal.