JPS6043631B2 - Composite negative electrode structure for secondary batteries - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates generally to electrical energy storage devices, and more particularly to lithium electrode structures.

Two methods are generally used to manufacture lithium electrodes for use in electrical energy storage devices such as rechargeable batteries, particularly batteries using molten salt electrolytes.

In one method, lithium is alloyed with another metal, such as aluminum, to form a solid electrode at the battery's operating temperature.

In other methods, liquid lithium is held in a porous metal substrate by capillary action. Traditionally, the latter method is preferred as it provides higher operating cell voltage and therefore potentially higher cell energy density. However, certain problems arise when attempting to retain molten lithium in a porous metal substrate. More specifically, the metals that are easily wetted by lithium are: Most metals that are structurally resistant to lithium attack are poorly wetted by lithium when placed in a molten salt electrolyte. It has been reported that metals that are structurally resistant to attack by molten lithium can become wettable by maintaining the molten lithium in which they are immersed at high temperatures.

However, structures that are so wetted by lithium at those higher temperatures are normally used as negative electrodes in secondary batteries containing molten salt electrolytes held at substantially lower temperatures at which the batteries operate. Wetting becomes worse gradually. It has therefore been found that after a number of cycles of battery operation, the lithium no longer preferentially wets the substrate and the electrode gradually loses capacity. Various methods have been proposed in an attempt to solve this problem. See, eg, US Pat. Nos. 3,409,465 and 3,634,144.

Both methods proposed by Tsutsumi have proven to be unsatisfactory. The use of solid lithium alloys, as taught by the prior art, is also not without problems.

More specifically, for example, a lithium-aluminum alloy is about 300 mv more positive than liquid lithium. Therefore, electrochemical cells using lithium-aluminum alloys as electrodes cannot achieve the same potential as cells using liquid lithium electrodes. Furthermore, in a molten salt electrolyte, the lithium-aluminum electrode expands and contracts significantly during charging and discharging of an electrochemical cell. For example, it has been reported that lithium-aluminum electrodes can change volume by as much as 200% during charging and discharging of a battery. Additionally, lithium-aluminum alloys generally have a lithium content of about 30 Wt. % or less. Various other materials have been suggested for use as alloys with lithium to make solid electrodes.

For example, in U.S. Patent No. 35064,
It has been suggested to alloy lithium with aluminum, indium, tin, lead, silver or copper. However, none of these materials has been found to be completely satisfactory. More specifically, these other suggested materials, such as tin and lead, tend to form alloys with less lithium than aluminum, thus further reducing the capacity per unit weight (amp hours) of the alloy. Furthermore, the potentials of alloys of these other materials relative to liquid lithium are more positive than the potentials of lithium-aluminum alloys;
Alloys of such other materials are therefore less desirable. Other patents relating to solid lithium cathodes include US Pat. Nos. 3,506,492 and 3,508,967. Therefore, when used as a negative electrode in an electrochemical cell, it retains its capacity over repeated cycling, preferably has substantially the same potential as liquid lithium, and maintains dimensional stability during charging and discharging of the battery. There remains a need for lithium electrodes that

Generally speaking, the present invention provides an improved lithium electrode.

The improved electrode consists of an alloy of lithium and silicon in intimate contact with a supporting current collecting matrix. Lithium is present in the alloy at approximately 80-28 Wt. Present in an amount of 1%. The improved electrical energy storage device includes a rechargeable lithium battery in which the positive and negative electrodes are spaced apart from each other and in contact with a suitable lithium ion-containing electrolyte, preferably a molten salt electrolyte. The improved lithium electrode of the present invention is used as a negative electrode and functions as a circular battery cathode in the discharge mode of the battery. The present invention relates to lithium electrodes.

The lithium electrode of the present invention consists of an alloy of lithium and silicon in intimate contact with a supporting current collecting matrix, thereby generally providing a single or composite electrode structure.

In this case, an alloy is an intimate mixture of two metals that can form a mixed crystal, solid solution, or chemical compound. Also, metals can exist in one or more of these states in the same alloy. The alloy is about 80-28 Wt. % lithium and about 20-72 Wt. % silicon is an essential feature of the present invention. The preferred alloy is about 60-40
Wt. % lithium and the remainder essentially silicon. In this case, the weight percentages refer to electrodes in a chemically formed or fully charged state. This is because apparently in the operating state of the battery the lithium is discharged and an alloy containing substantially less lithium or no lithium is formed. The alloy may also contain small amounts of impurities such as iron, calcium, magnesium and aluminum. The reason why the amount of lithium is limited to 28-8% is as follows.

If the alloy contains more than about 8 weight percent lithium, it will behave more like a liquid or pure lithium electrode. The disadvantages of pure lithium electrodes have already been mentioned. On the other hand, if the lithium content of the alloy is less than about 2% by weight, the electrode capacity will be so small as to be of little practical use. The lithium-alloy electrode structure further includes a supporting current collection matrix in intimate contact with the alloy.

Suitable materials for the supporting current collector matrix are materials that are resistant to attack by lithium or lithium-silicon mixtures. Examples of such materials include iron, steel, stainless steel,
Mention may be made of nickel, titanium, tantalum and zirconium. The purpose of providing the matrix in intimate contact with the alloy is to provide a substantially uniform current density throughout the alloy and to provide structural support for the alloy. The lithium-silicon alloy used in the present invention is an electrical energy storage device,
It has been found that it lacks structural integrity when used as a unitary member of the negative electrode, especially at high operating temperatures in molten salt electrolytes. Therefore, it is essential to provide the lithium alloy with a support matrix in order to function for a significant period of time without disintegration.
It is contemplated and preferred within the scope of the present invention that support and current collection capability be provided by a single structure; however, the support may be provided in one structure and the current collection capability provided in another, separate structure. Can be set up. The matrix can be in the form of an electronically conductive porous substrate having an apparent density of about 1-30% of that of the base material.

Advantageously, the substrate has a mesopore size of about 20-500 microns, preferably about 50-200 microns. A particularly preferred form of such a substrate is formed from woven or non-woven wires that are pressed together to the desired apparent density and then sintered. Such pressed and sintered wire structures are well known and commercially available as felt metal. The porous substrate is then impregnated with the alloy, for example, by immersing the substrate in a molten bath of the alloy, removing it, and cooling it. Alternatively, the alloy may be cast around a matrix formed from wire mesh or expanded metal. In other variations, the matrix can be in the form of a perforated container formed from wire mesh or the like and containing only the alloy therein.

Alternatively, the alloy is preferably brought into intimate contact with a porous substrate housed in a perforated container, with the container and substrate being in electrical contact with each other. This latter variation is particularly useful when the porous substrate is made from very fine woven or non-woven wire meshes pressed together to form the object. More specifically, at least when iron is used as the substrate material, the wire used to form the porous substrate is approximately 10 microns in diameter, and the substrate is repeatedly charged and discharged by placing the electrode in a molten salt electrolyte. It was found that there is a tendency for the material to deteriorate and break down.

It is not known with certainty whether such fractures are the result of imperceptible expansion and contraction of the electrodes or chemical interactions between the lithium-silicon alloy and the iron. Therefore, when selecting the material to be used as a substrate, consideration must be given to possible chemical reactions or corrosion as a result of the particular electrolyte or matrix material used. Further, when the matrix is comprised of woven or woven wires pressed into a porous substrate, the wires are at least about
It is necessary to have a diameter of 0 microns. Advantageously, the diameter of the wire is from about 10 to about 500 microns, preferably from about 10 to 200 microns. In a preferred embodiment of the invention, the electrode is formed by encircling the molten alloy around the matrix, for example by immersing the porous substrate in the melt of the alloy.

The alloy can be formed by mixing particulate lithium and silicon and heating the mixture to a temperature high enough to form a melt. However, according to a preferred method, lithium is first heated in an inert atmosphere to a temperature above the melting point of lithium, and then silicon is added in an amount to give the desired weight percent of the alloy. In these latter methods, the exothermic reaction between the lithium and silicon provides substantially all of the heat necessary to form the alloy melt.
It will be appreciated that the production of lithium-silicon alloys is known per se.

The existence of such alloys and exemplary methods of making them is described, for example, in U.S. Pat.
Reported in the eel specification. For additional information regarding the temperatures required to form a substantially homogeneous alloy of lithium and silicon, see 1 Construction of Binary Alloys (CON
stitutlOnOfBinaryA]10ys)J
See Supplement 2, Matsukugrow Hill Book Company, New York (1969).

Lithium electrodes can be formed electrochemically in a molten salt electrolyte using the same methods commonly used to form known lithium-aluminum electrodes.

In particular, silicon in intimate contact with a supporting current collector matrix is immersed in a molten salt electrolyte containing a source of lithium ions;
Lithium is introduced into the electrode in an amount that forms the desired alloy. The present invention also provides an electrical energy storage device, particularly a secondary battery or storage battery, comprising the lithium electrode of the present invention as an electrically renewable negative electrode.

The electrical energy storage device also includes a positive electrode and an electrolyte, generally referred to as a non-aqueous lithium ion-containing electrolyte. The positive electrode, or anode, contains an active material that is an electron acceptor and is an electrical anode with respect to the lithium electrode.

The active material of the anode is sulfur or metal halide, sulfide,
It can be an oxide or a selenide. Suitable metals include copper, iron, tungsten, chromium, molybdenum,
Mention may be made of titanium, nickel, cobalt and tantalum. Iron and copper sulfides are particularly preferred for use in molten salt electrolytes. The anode can be formed entirely of active material or can consist of a composite structure, such as a graphite holder containing an active material body. The lithium ion-containing non-aqueous electrolyte used in preferred cell embodiments is a molten salt electrolyte; alternatively, solid electrolytes or organic solvent electrolytes can be used.

In this case, the molten salt electrolyte refers to a lithium halide-containing salt that is maintained at a temperature above its melting point during operation of the electrical energy storage device.

The molten salt can be a single lithium halide, a mixture of lithium halides, or a eutectic mixture of one or more lithium halides and other alkali metal or alkaline earth metal halides. Common examples of binary eutectic salts are lithium chloride-potassium chloride, lithium chloride-magnesium chloride, lithium chloride-sodium chloride, lithium bromide-potassium bromide, lithium fluoride-rubidium fluoride, lithium iodide-potassium iodide, and mixtures thereof. It is.

Two preferred binary salt eutectics are a eutectic mixture of lithium chloride and potassium chloride (melting point 357C) and a eutectic mixture of lithium bromide and rubidium bromide (melting point 278C).
℃).

Examples of ternary eutectics useful as molten salt electrolytes are calcium chloride-lithium chloride-potassium chloride, lithium chloride-potassium chloride-barium chloride, calcium chloride-lithium chloride-barium chloride, and lithium bromide, barium monobromide-lithium chloride.

A preferred ternary eutectic mixture contains lithium chloride, lithium fluoride and lithium iodide. eutectic mixture (melting point 3
4rc) and a eutectic mixture (melting point 260°C) containing lithium chloride, lithium iodide and potassium iodide. Suitable alkali or alkaline earth metal ions are very close to the lithium ion deposition potential in the electrolyte! It is necessary to have a deposition potential of about 50% or preferably more than 100%.

Lithium halide salts can be easily combined with potassium, barium, and strontium halides. Halides of metals such as cesium, rubidium, calcium or sodium can be used, but
However, a substantial proportion of these metals can co-deposit with lithium when charging the electrode, resulting in a small loss of potential. Although ternary eutectic salt mixtures, especially those containing iodide, give lower melting points, the binary lylium chloride-potassium chloride eutectic mixture is particularly useful for large-scale applications due to its lower cost and availability. Preferred for storage batteries used in bulk energy storage for vehicles and electric utilities.

Solid electrolytes contemplated in this) include mixtures of lithium sulfate and lithium halides, such as lithium chloride or lithium bromide, or mixtures thereof.
The composition of the mixed salt solid electrolyte can vary from 10 to 95 mole % lithium sulfate. A solid electrolyte having such a composition is electrically conductive at a low temperature of about 400° C. in a state considered to be a solid phase. Lithium iodide and silver halide, mercuric silver halide, lead halide, copper halide,
Combinations with ammonium halides or combinations thereof are also suitable for solid electrolytes. The lithium electrode of the present invention is also useful in electrical energy storage devices that use a lithium ion source in an organic solvent.

1. Organic electrolyte means a non-aqueous electrolyte containing an organic solvent and a solute.

The solute is a source of lithium ions. Of course, the solute may be miscible or dissolved in the organic solvent. The solvent is one that does not attack the electrode material and is not affected by the material. Obviously, the solute needs to be stable in the environment at the intended operating temperature and potential. Organic electrolyte batteries generally operate at temperatures below about 125°C, more specifically between about 0 and 8°C.
Designed to operate at temperatures of 0°C. It is important that the solute and solvent be such as to provide a lithium ion-containing conductive medium that is mobile or liquid under these conditions. It is generally preferred that the solute be of high purity. The solutes that most closely meet these requirements are lithium halide salts.

For conductivity purposes, other metal halides, such as aluminum chloride, are often combined with lithium halide. The halide is selected from the group consisting of chlorine, fluorine, bromine, iodine and mixtures thereof. It is conceivable that double anionic complexes could also be used. Examples of suitable solutes are:
These are lithium bromide, lithium chloride, lithium fluoride, sodium chloride, sodium fluoride, and potassium chloride. The lithium salt can also be lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium tetrachloroaluminate or lithium hexafluoroborate. Preferably, the lithium ion-containing conductive medium used is saturated or supersaturated.

It is necessary that the ion-containing conductive medium have a sufficient salt concentration to allow the most economical operation of the cell. It is necessary that the ion-containing conductive medium have a volumic concentration of about 0.5 molar or greater. The selection of organic solvent for the ion-containing conductive medium is governed by many considerations, including volume. The solvent of the ion-containing conductive medium is any polar substance that meets the requirements of acting as a transport medium for the solute and with which the solute is miscible or dissolved. The solvent also needs to be a material that is inert to the electrolyte.
Preferably, the solvent is liquid at about 0-125°C. Operating conditions dictate such requirements. For example, dimethyl sulfoxide is an excellent solvent above its melting point of about 18.5°C. It is desirable that the solvent does not easily release hydrogen ions. Solvents with high dielectric setpoints and low viscosity coefficients are preferred. Suitable solvents are, for example, nitriles such as acetonitrile, probionitrile; sulfoxides such as dimethyl, diethyl, ethylmethyl and benzylmethyl sulfoxide; pyrrolidones such as N-
Methylpyrrolidone, and carbonates such as propylene carbonate.

In addition to the aforementioned representative representations of suitable electrolytes and cathode materials, many others will be apparent to those skilled in the art.

Therefore, the present invention is not limited to what has been particularly pointed out. Referring to FIG. 1, curve A shows a typical discharge plot of the electrode of the present invention (60 Wt% Li-40 wt% Sj) relative to a liquid lithium counter electrode.

This plot shows that virtually 100% of the theoretical capacity (in ampere hours) can be obtained from the electrode of the present invention. It will also be observed that the potential relative to liquid lithium changes during discharge. Specifically, the electrode of the present invention discharges through five different voltage plateaus. The first plateau is at substantially the same potential as liquid lithium.

Each of the four successive plateaus is at an increasingly positive potential with respect to liquid lithium, i.e. approximately 70,1
70, 250 and 310rr1v are positive. The reason for such a series of different potentials is not known with certainty, and the invention is not limited by any particular theory. However, it is believed that the first plateau, which is substantially the same for liquid lithium, occurs during discharge of unalloyed lithium, with each subsequent plateau representing a particular lithium-silicon compound species. However, there are two known lithium-silicon phase diagrams, namely Li4Si and L
It must be understood that only i2Si is shown. Therefore, it is not known whether Figure 1 points to the existence of an as-yet-unidentified lithium-silicon species or whether some other mechanism is involved. Obviously, knowledge of the precise mechanisms involved is unnecessary to the practice of the invention. For comparison purposes, Figure 1 also shows a typical lithium-aluminum electrode (30 wt% Li-
Discharge curve B for 70 wt% Al) is shown. A comparison of curves A and B shows that the lithium electrode of the present invention has a substantially higher capacity than the corresponding prior art lithium-aluminum electrode. Such capacity is achieved due to the large amount of lithium that can be included in the lithium-silicon alloy. Prior art lithium-aluminum alloys are generally limited to a maximum amount of lithium of no more than about 30 wt%. In practice, lithium-aluminum alloys containing more than about 20 wt% lithium are rarely used. This is because alloys with a higher proportion of lithium are more likely to release free lithium into the electrolyte, resulting in a loss of coulombic efficiency much like that of prior art liquid lithium electrodes. When comparing two curves, 2
It will be appreciated that the two alloys start at substantially the same potential as liquid lithium.

At such potentials, release of free lithium into the electrolyte could possibly occur. If it is desired to eliminate this possibility, the electrode can be discharged against a liquid lithium counterelectrode until the potential reaches a second plateau (approximately 70 rnv for lithium-silicon and 300 rr1v for lithium-aluminum). is advantageous. Even after the initial discharge of the electrode, which lowers the electrode to a second plateau, the electrode of the present invention has a more favorable potential than the lithium-aluminum electrode and still retains a substantially greater capacity (amp hours). . Furthermore, after such an initial discharge,
Even if the electrode of the present invention is fully discharged to the end of the last plateau (310n1v), the time-averaged potential will be substantially closer to that of liquid lithium compared to the prior art lithium-aluminum electrode. The two comparative curves in FIG. 1 demonstrate the superiority and advantage of the lithium electrode of the present invention over the prior art lithium-aluminum electrode. Referring to FIG. 2, a lithium electrode 10 of the present invention is shown.

Electrode 10 includes a matrix consisting of a cage or perforated container made of conductive wire 12 and wire mesh 14, and a porous substrate impregnated with lithium silicon alloy 16. In Figure 3,
The present invention shows an electrical energy storage device 20 that uses lithium alloy electrodes.

Storage device 20 includes a positive electrode 22 and a negative electrode 24, the latter consisting of a porous metal substrate impregnated with a lithium-silicon alloy. Electrodes 22 and 24 have electrical connections 26 and 28.
are provided for each. The electrical energy storage device also includes a housing 30 and a cover 32. Cover 32 is provided with eyelets for passing electrical connections 26 and 28 therethrough. A non-conductive insulator 34 is positioned inside the eyelet. The electrical energy storage device also contains a non-aqueous electrolyte 36. If the non-aqueous electrolyte is a solid electrolyte or a molten monosalt electrolyte (both of which must operate at relatively high temperatures), the housing 30 may be provided with heating means, such as an electrical resistance heater 38. The following examples are presented to further illustrate the invention. For convenience, most examples are of the invention! The present invention relates to the use of electrodes in preferred molten salt electrolytes. However, the present invention is not limited to electrical energy storage devices using a molten salt electrolyte as described above, but three electrical energy storage devices using a solid electrolyte or an organic electrolyte (ordinary dry batteries or (including rechargeable secondary batteries or storage batteries)
It is equally useful for Example 1 The following example demonstrates the production and testing of lithium electrodes of the present invention.

The supporting current collecting matrix used was 4 fine low carbon steel fibers (
Approximately 10 microns in diameter) on a flat porous plate (32C7
It was a commercially available material known as felt metal, which is made by packing and sintering the metal. The matrix has a surface area of approximately 6.45c7j per side and an apparent density of 10
%. The mesopore size was about 50-150 microns. The matrix is weighed and then added to an alloy consisting of 45 Wt% lithium and 55 Wt% silicon.
The lithium alloy was impregnated by dipping for about one time at a temperature of 820°C. The matrix was then removed from the molten lithium alloy bath, cooled, and weighed again. The matrix is approximately 1
．． 32y alloy was measured, thus forming a lithium electrode with a total theoretical capacity of 2.29 amp hours. The electrodes were tested in a molten salt bath containing 58.8 mole % lithium chloride and 41.2 mole % potassium chloride.

The molten salt electrolyte was maintained at about 400° C. and the test electrode was alternately charged and discharged at a constant current of about 600 n1A against a larger liquid lithium counter electrode gate. The voltage and current between the two electrodes were recorded continuously over time on a strip chart recorder.

From the chart, it was determined that the average coulombic efficiency over four charge/discharge cycles was approximately 100%. Here, the coulombic efficiency is defined by the following equation. When the amount of electricity (in ampere-hours, coulombs) of a battery at a time is the same as the amount of electricity recovered by discharging the battery, the coulombic efficiency is 1.
It becomes 00%.

The potential and discharge characteristics for the liquid lithium counter electrode were substantially the same as in FIG.

The test was stopped after 4 cycles when the fine individual fibers of the support matrix broke. This is because the destruction caused a loss in Coulombic efficiency. Example 2 The above procedure of Example 1 was repeated, except that the matrix was a porous substrate of titanium metal and the alloy was 60 Wt. %Li and 40W
t. %Si.

The titanium substrate had fibers of approximately 100 microns in diameter, an apparent density of 19%, and a mesopore size of 400-500 microns. The electrodes were tested in substantially the same manner as previously described, with the tests being terminated spontaneously after cycling. , thus demonstrating the advantage of larger fiber dimensions and the usefulness of titanium as a matrix material.
Example 3 Apparent density 10% made of iron fibers with a diameter of approximately 10 microns
and a porous substrate having a medium pore size of 50 to 150 microns.

Porous substrate with diameter 230 microns and mesh size 6
0 (US standard sieve size) to form a matrix (same as in FIG. 2). Form an electrode and apply 60Wt. %Li-40wt. %S
Tests were conducted in substantially the same manner as described above, except that the i-alloy was used. Coulombic efficiencies of 95-100% were again obtained and the discharge characteristics were substantially the same as those in FIG. This test also terminated spontaneously after 17 cycles, thus demonstrating the utility of a two-structure combined version of the support current collection matrix, ie separate support structure and current collection structure. Example 4 The following example is presented to demonstrate the applicability and effectiveness as a cathode of an electrical energy storage device using the lithium 6 silicon alloy electrode and organic electrolyte of the present invention.

60wt. %Li-40wt. A lithium-silicon alloy negative electrode was prepared in substantially the same manner as the electrode of Example 1, except that a %Si alloy was used.

The positive electrode consisted of a porous carbon structure impregnated with iron sulfide and held in a high-density graphite holder. The organic electrolyte consisted essentially of propylene carbonate containing 100y of lithium perchlorate per e of solvent. The electrical energy storage device was alternately charged and discharged at a given current for a defined time.

The potential and current between the two electrodes were recorded continuously over time on a strip chart recorder.

It was determined from the chart that a Coulombic efficiency of approximately 95-100% was achieved. The time-averaged voltage during discharge of an electrical energy storage device using the electrode of the present invention was about 2.1 volts, while for the comparative lithium aluminum electrode the time-averaged voltage was only about 1.8 volts. Furthermore, no significant change or degradation in electrode performance was observed, thus demonstrating the utility of fine woven iron fibers as a supporting current collection matrix for use in organic electrolytes.
Example 5 The following example is presented to demonstrate the applicability and effectiveness of the electrode of the present invention when used as a negative electrode in an electrical energy storage device.

The electrodes used were made using a commercially available substrate as a matrix. The substrate consisted of a plurality of 16 micron diameter woven nickel wires compressed and sintered to an apparent density of 15%. Melt the electrode matrix (700℃
) Lithium-silicon alloy (60Wt.% lithium-40W
t. % silicon). Next, the electrode is +70rr1v against the liquid lithium counter electrode.
It was discharged to the potential plateau (see Figure 1). The positive electrode, or anode, consisted of a dense graphite holder containing an amount of iron sulfide as the active material. This was covered with a porous graphite separator to hold the active material in the holder while allowing the free passage of charged ions. The negative electrode and the positive electrode were immersed in a molten salt electrolyte containing 58.8 mol% lithium chloride and 41.2 mol% potassium chloride. The electrolyte was maintained at about 40 (something). The electrical energy storage device was alternately charged and discharged at a given current for a defined period of time.

The voltage and current between the two electrodes were recorded continuously over time on a strip chart recorder.

It was determined from the chart that a Coulombic efficiency of approximately 96-100% was obtained. Furthermore, the time-averaged voltage during discharge of the electrical energy storage device using the electrode of the present invention using the second and third plateaus is 1.48 volts, while for the comparative lithium-aluminum electrode the time-averaged voltage is 1.48 volts. It was only about 1.3 volts. Also,) virtually no dimensional changes in the lithium-silicon electrode were perceptible during cycling. Furthermore, no lithium lost to the electrolyte was detected. The test was stopped after 4 cycles due to failure of one of the cathode components. Nevertheless, the results clearly demonstrate the effectiveness of the lithium electrode of the present invention and the benefits obtained thereby. It is, of course, recognized that various changes may be made in the design and operation of the lithium electrodes and batteries of the present invention without departing from the spirit of the invention.
It will be.

Accordingly, lithium electrode structures are described with respect to certain preferred constructions and materials of supporting current collector matrices, and preferred embodiments of secondary batteries employing molten salt electrolyte electrolytic metal sulfide anodes are described. Although described, it will be understood that the invention may be practiced otherwise than as specifically described and within the scope of the invention. Embodiments of the present invention are shown below. (1) The negative electrode structure according to claim 1, wherein the alloy consists of about 40 to 6 weight percent lithium and about 40 to 60 weight percent silicon, and the matrix consists of a porous metal substrate.

(2) The negative electrode structure according to claim 1, wherein the supporting current collecting matrix includes a porous substrate obtained from metal fibers.

(3) A negative electrode structure according to claim 1, wherein the supporting current collecting matrix comprises a porous metal substrate impregnated with the above-mentioned alloy, and further includes a perforated container surrounding the porous metal substrate.

(4) The negative electrode structure according to item 2 above, wherein the metal fiber is an iron fiber having a diameter of about 10 to 200 microns.

(5) The negative electrode structure according to item 2 above, wherein the metal fiber is a nickel fiber having a diameter of about 10 to 200 microns.

(6) The negative electrode structure according to item 2 above, wherein the metal fiber is a titanium fiber having a diameter of about 10 to 200 microns.

[Brief explanation of drawings]

FIG. 1 is a comparison graph of the curved discharge characteristics of two lithium alloy electrodes, FIG. 2 is a perspective view of the electrode of the present invention, and FIG. 3 is a schematic diagram of the electrical energy storage device of the present invention.

Claims (1)

[Claims] 1 An alloy of lithium and silicon, in which lithium is present in the alloy in an amount of 28 to 80% by weight, and silicon is present in the alloy in an amount of 28 to 80% by weight.
A composite negative electrode structure for a secondary battery with a lithium-containing electrolyte, characterized in that it consists of a supporting current collector matrix in intimate contact with an alloy present in an amount of 0 to 72% by weight.