JPH0337262B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of the Invention] The present invention relates to an electrochemical cell cathode made of an intermediate heat-resistant hard metal compound activated by halogenation, and an electrochemical cell using the cathode. [Prior Art] Recently, there has been increasing interest in the development of electrochemical energy storage pores. However, these developments are often delayed due to the difficulty in effectively immobilizing, isolating, and controlling electrochemically active substances that are easily dispersed. Proposals to overcome these problems, for example by using solid electrolytes acting as electrode separators, or by using compounds which are electrochemically active substances, have not yet met with complete success; Particularly with certain electrochemically active substances, success has not been achieved. Solid electrolytes such as β-alumina have been proposed, but they have been associated with several disadvantages. Since beta-alumina is a solid ceramic, it is sensitive to shock and typically has a higher internal resistance in the battery than the electrolyte, which is a liquid at the battery's operating temperature. Furthermore, depending on the conditions in which the battery is placed, β-alumina is extremely susceptible to corrosion, causing cracks and flaws, thereby limiting the service life of the battery. The most promising efforts to overcome some of the above problems are those related to electrochemically active materials for the anode. These developments include, for example, the use of alloys of lithium with aluminum or silicon in the anode. These alloys are solid at the operating temperatures of cells using such anodes, thereby providing effective immobilization of electropositive substances. However, similar attempts to overcome the problem of effectively immobilizing electronegative substances have not yet been completely successful. The most successful attempts known to the applicant in this regard have attempted to solve the problem of sulfur immobilization by using iron sulfides, such as FeS or FeS ₂ . However, this proposal is based on the fact that the FeS ₂ cathode is very susceptible to corrosion, that although the FeS ₂ cathode is less corroded than the FeS 2 cathode, its theoretical energy density is much lower than that of the FeS ₂ cathode, and that the FeS ₂ cathode has a two-step discharge reaction. The disadvantages include that sulfur may fall off and dissolve into the electrolyte, and that both FeS and FeS ₂ may expand during charge/discharge cycles, leading to mechanical damage to the cathode. Accompany. The applicant is also aware of attempts to immobilize electrochemically active substances by forming intercalation compounds with graphite. In such charging compounds, graphite exists in the form of strong aromatic carbon planes, e.g.
An electrocatholytic material such as FeCl ₃ or CrO ₃ is located between the planes in molecular form. During the insertion process, the spacing of the graphite planes widens to accommodate molecules of electronegative material. In intercalated graphite compounds, the metal compound maintains a stable molecular form and is weakly bonded to the graphite structure. Once such an insertion type compound is electrochemically discharged as a cathode, it cannot be restored to its original structure at the time of discharge. This is also illustrated by the fact that such cathodes are not rechargeable and are therefore typically used as cathodes for primary batteries, but not for secondary batteries. Furthermore, intercalated graphite compounds are unstable even at temperatures below 400° C., and when heated, the intercalated material falls off from the graphite substrate. Therefore, the present invention aims to solve the above-mentioned problems by providing a stable and electrochemically active material that can be used in the cathode of a secondary battery. [Structure of the Invention] The material suitable for the cathode for an electrochemical cell of the present invention is one or more metals selected from the group consisting of chromium, manganese, iron, cobalt, and nickel, and carbon, boron, nitrogen, and silicon. and one or more non-metals selected from the group consisting of
compound) by halogenation. The term "heat-resistant hard metal compound" as used in this invention refers to a compound that has a sufficiently high melting point to be used as an electrode in a high-temperature battery such as one that uses a molten electrolyte, and also maintains its shape as an electrode by itself. It should be understood that it refers to a metal compound that can be used as an electrode in a battery and has sufficient mechanical strength to be used as an electrode in a battery.Usually, transition metal carbides, nitrides, borides,
Heat-resistant hard metal compounds consisting of silicides and phosphides are extremely chemically inert, and although many of these heat-resistant hard metal compounds exhibit high electrical conductivity, they are not electrochemically active. It is usually not expected to show activity. In fact, refractory hard metal compounds such as interstitial carbides of titanium, vanadium, molybdenum, tantalum and tungsten exhibit little or no electrochemical activity. However, despite the above facts, the present applicant has discovered that heat-resistant hard metal compounds of chromium, manganese, iron, cobalt, and nickel exhibit sufficient electrochemical activity when halogenated, and have achieved the present invention. This is what I did. In this specification, specific heat-resistant hard metal compounds that exhibit electrochemical activity due to such halogenation, namely chromium, manganese,
The compound of one or more metals selected from the group consisting of iron, cobalt, and nickel and one or more nonmetals selected from the group consisting of carbon, boron, nitrogen, silicon, and phosphorus is collectively referred to as "intermediate". The term "heat-resistant hard metal compound" is used. (More details on this later in [Logical Background])
(Page 38 of the present invention). ) The compound of the present invention can be provided with electrochemical activity that can be used as a cathode of an electrochemical cell by halogenating the intermediate heat-resistant metal compound, and this is referred to as activation by halogenation. It is something to do. When the compound of the present invention is used as a battery cathode, the battery reaction at the cathode is, for example, M(Hal) _x +xe ^- M+xHal ^- . However, M is the intermediate type heat-resistant hard metal compound, Hal is a halogen, and x is a positive integer. The intermediate heat-resistant hard metal compounds used in the present invention are, for example, iron, chromium, manganese, nickel or cobalt carbides, iron borides, nitrides, silicides or phosphides, cobalt, nickel or chromium borides, chromium or nickel silicide,
It may be a phosphide of cobalt, a nitride of manganese or kelom, or the like. The intermediate heat-resistant hard metal compound may be formed of metals and non-metals of various different stoichiometries, e.g. Cr ₃ C ₂ , Cr ₇ C ₃ , where the metal is chromium and the non-metal is carbon. Compounds such as _Cr23C6 may be used _. Further, the intermediate heat-resistant hard metal may be a compound of one or more of the above metals and a plurality of the above nonmetals. Examples of such compounds include:
Examples include Mn ₈ Si ₂ C, Fe ₈ SiC, Mn ₅ SiC, and the like. Further, the intermediate type heat-resistant hard metal compound may be a compound of a plurality of the above-mentioned metals and one or more of the above-mentioned non-metals. Such a compound is formed as a compound of an alloy or mixture of multiple metals and a nonmetal. When two transition metals are alloyed or alloyed, it is preferred that one transition metal makes up a minor portion of the alloy or mixture, such as up to about 30% of the other metal, preferably about
It may account for 10-20% or less. Examples of such heat-resistant hard metal compounds include:
Examples include molybdenum-nickel carbide, tungsten-cobalt carbide, ferrochrome carbide, ferromanganese carbide, and the like. As mentioned above, the use of an intermediate type heat-resistant hard metal compound as a compound consisting of three or more components is particularly useful for improving the stability when the compound is used as a cathode in a battery, the electrical conductivity of the compound, etc. Useful. It is believed that the compounds of the present invention can generally be used as cathodes even if they contain excess nonmetals. This is because even if there is an excess of non-metals, they are chemically and electrochemically inert and therefore do not cause any harm to the battery environment as long as they do not significantly reduce the electrical conductivity. be. However, extreme excess of non-metals, even though they are chemically and electrochemically inert during use, can unnecessarily damage the cathode without contributing in any way to the capacity of a battery equipped with such a cathode. It will add weight. It is therefore practical to avoid the use of extreme excess non-metals, unless the excess non-metal contributes to the electrical conductivity of the cathode or to the anchoring of said metal to the cathode structure. If the compound of the present invention contains a considerable amount of excess metal, it should be subjected to a preliminary tempering treatment before use,
It may be necessary to separate out metal components that are susceptible to decomposition or shedding as a result of excess. This preliminary tempering treatment can be carried out, for example, by charging and discharging in a separate electrochemical cell to sufficiently remove excess metal. However, excess metal is acceptable if it is small and does not significantly interfere with the operation of the cell if it separates during use in the cell. When a significant excess of metal is present, the compound structure tends to collapse during its activation, leaving behind a stable framework. However, there is little geometrical and crystallographic relationship between this structure and the original compound lattice. In extreme cases, the concept can become completely amorphous while remaining electrically and physically continuous, but still retaining the ability to immobilize active metals. This type of structure is believed to be particularly unaffected by initial impurities or initial crystallographic defects. The intermediate heat-resistant hard metal compound used in the present invention is selected in consideration of the following points. (1) From the viewpoint of service life (number of cycles), carbon materials having a larger carbon/metal ratio are preferred. This is because after activation by halogenation, the metal is more likely to be fixed to the carbon/metal structure during use, and there is less risk of cathode collapse or electrolyte contamination during use. (2) From the perspective of capacity and cathode current density,
Due to its high active metal content, metal/
Compounds with a large nonmetal ratio are preferred. (3) From the viewpoint of service life and microstructure, carbides that can form a stable skeleton through bonds between adjacent carbon atoms or bonds between metal and carbon atoms are preferred. This is because such a framework can maintain the structural integrity of the cathode. The cathode of the present invention can be formed by preparing an intermediate heat-resistant hard metal compound of one or more metals and one or more non-metals by conventional methods and further activating it by halogenation. Halogenation can be carried out chemically or electrochemically. For example, the intermediate heat-resistant hard metal compound may be halogenated in the gas phase in heated powder or porous form with a halogen gas stream or a dilute halogen gas stream, or treated with other suitable halogenating agents. can be chemically activated by Further, the intermediate heat-resistant hard metal compound is molded into an appropriate shape and used as an electrode of an electrochemical cell, and an appropriate electrode and an electrolyte capable of supplying appropriate halogen ions for activation by halogenation are used.
It can be electrochemically halogenated and activated by performing multiple charge/discharge cycles. In this case, the electrolyte must be selected so that the electrolytic threshold voltage of the electrolyte itself is higher than the halogenation threshold voltage of the intermediate type heat-resistant hard metal compound, and halogenation must be performed at a voltage intermediate between both threshold voltages.
Here, the electrolysis threshold voltage of the electrolyte itself is the lowest voltage at which electrolysis occurs in the electrolyte itself when voltage is applied to the battery configured as above, and it is the halogenation threshold voltage of the intermediate type heat-resistant hard metal compound. Similarly, is the lowest voltage at which halogenation of the metal compound occurs. Therefore, by selecting the electrolyte as described above, only halogenation of the intermediate heat-resistant hard metal compound is caused without electrolysis of the electrolyte. If the halogenation threshold voltage of the metal compound is higher than the electrolysis threshold voltage of the electrolyte, halogenation cannot occur without electrolysis of the electrolyte. Once such a battery has been subjected to sufficient charge and discharge cycles, the intermediate type refractory hard metal compound becomes sufficiently activated for use as a cathode within the battery. Experiments conducted by the applicant have shown that the compound is sufficiently activated by 2 to 20 charge/discharge cycles. The threshold voltage for halogenation depends on the types of metals and nonmetals that constitute the compound. but,
It is thought that it also depends on the types of halogen ions and alkali metal ions contained in the electrolyte used for activation. Furthermore, the electrolytic threshold voltage of the electrolyte itself depends on the type of alkali metal or alkaline earth metal contained in the electrolyte, but in the case of alkali metal halides, the threshold voltage is generally lowest for iodide and for fluoride. Become the best. Fluorides and chlorides are most preferred for producing the highest energy density and lightest batteries. Electrolytes that could be used to supply suitable halide ions include alkali metal and/or alkaline earth metal halide molten salt electrolytes;
It was LiAlCl type ₄ electrolyte. When the halogenation threshold voltage of the intermediate heat-resistant hard metal compound is not very high, the compound is halogenated and installed as a cathode in an electrochemical cell using an electrolyte with a sufficiently high electrolytic threshold voltage to be used as a cathode. can be activated in situ within the battery. Therefore, in such cases, the cathode is installed in the electrochemical cell in its inactive state. On the other hand, if the initial halogenation threshold voltage of the intermediate heat-resistant hard metal compound is too high relative to the electrolysis threshold voltage of the electrolyte itself of the secondary battery in which it is intended to be used as a cathode, a sufficiently high electrolysis threshold The compound can be activated by use as an electrode in another suitable battery using an electrolyte with a voltage. In such an activation process, an electrode refining process for separating and removing the excess metal when the metal compound contains an excess metal as described above can be performed at the same time. If the metal compound is activated in a separate cell, it can then be incorporated into the electrochemical cell in which it is to be used. Once the metal compound is sufficiently activated at a certain voltage, it can effectively act as a cathode at lower voltages. Therefore, if the compound is activated in a very stable electrolyte (usually one with a high melting point), electrochemistry using that electrolyte or a less stable electrolyte with a substantially lower melting point It can be said that it can be used as a cathode in a battery. It will be appreciated that an activated cathode according to the invention will be halogenated in its charged state and dehalogenated in its discharged state. The cathode according to the invention can be suitably compression molded, suitably compression molded or supported with a binder, supported on a support structure or matrix, or contained within a porous cathode holder. This allows for the formation of a self-supporting structure or matrix. For example, the cathode may be contained within a porous, corrosion-resistant cathode holder, such as a porous graphite cup or container. Compression molding of the cathode improves interparticle contact and increases electronic conductivity. However, it can reduce the porosity of the cathode and affect the diffusion of electrolyte into the cathode during use. Compression molding therefore meets the requirements of improved mechanical strength and electronic conductivity, as well as the need for the electrolyte to have sufficient access and penetration into the cathode during use so that it can act as a three-dimensional cathode and provide sufficient current density. It is necessary to strike a good balance between the requirements of The invention further relates to an electrochemical cell comprising a cathode as described above. The anode used in such a battery may be any anode that can be used to construct a battery using the cathode and a suitable electrolyte. Examples of anodes used in the batteries of the invention include alkali metals, combinations of alkali metals, alkaline earth metals, combinations of alkaline earth metals, combinations or alloys of alkali metals and alkaline earth metals, or alkali and/or alkaline earth metals. or an alloy or composition containing an alkaline earth metal. When the anode consists of an alkali metal, the alkali metal is preferably lithium or sodium.
In addition, when it is composed of an alkaline earth metal, the alkaline earth metal is preferably calcium or magnesium. When the anode is made of an alloy or composition containing an alkali metal and/or an alkaline earth metal, it can be an alloy or composition containing one or more alkali metals and/or alkaline earth metals, and the remaining component is the alkali metal. It may be any metal or similar material that can form suitable alloys or compositions with metals and/or alkaline earth metals. The remaining component may thus be, for example, silicon, aluminum, boron or the like. Since the mass of the anode is often an important factor, a light metal or material such as aluminum or silicon may then be suitable for the remaining component. Examples of anodes for use in the cells of the invention include those consisting of or containing aluminum or a suitable aluminum alloy, in the form of a suitable electrochemically active material sorbed onto a molecular sieve carrier. There are things like that. In the latter case, the molecular sieve carrier is obtained as a zeolite or zeolitic material. The electrolyte used in the battery of the present invention may be any electrolyte that can constitute the battery together with the cathode and anode described above. The electrolyte may be a solid electrolyte, but since the electrochemically active metal of the intermediate refractory hard metal compound of the cathode will be trapped in the cathode during use in the cell, the electrolyte should be in a liquid state at the cell operating temperature. It can be assumed that there is. The electrolyte can also be a combination of a solid electrolyte and a molten or liquid electrolyte between the solid electrolyte and the cathode. Examples of solid electrolytes include conventional solid electrolytes such as β-alumina, nasicon (Na ₃ Zr ₂ Si ₂ PO ₁₂ ), and the like. The electrolyte used in the battery of the present invention may be a source of desorbed metal and halogen ions. Thus, the electrolyte may include an alkali metal or alkaline earth metal halide salt, such as, for example, sodium chloride, calcium chloride, calcium fluoride, magnesium chloride, lithium boride, and the like. The electrolyte may also be composed of a binary or ternary salt mixture of alkali metal and/or alkaline earth metal halide salts. The electrolyte may therefore be, for example, lithium iodide.
Potassium iodide, lithium chloride-potassium chloride,
Lithium chloride - magnesium chloride, lithium bromide - potassium bromide, lithium fluoride - rubidium fluoride, lithium chloride, lithium fluoride, calcium chloride - lithium chloride, lithium fluoride - lithium chloride - lithium bromide, etc. obtain. The electrolyte can also be an alkali metal or alkaline earth metal halide electrolyte dissolved in an aprotic solvent. The aprotic solvent may be any suitable solvent such as, for example, propylene carbonate. The electrolytes, such as the molten alkali metal halide salts mentioned above, may be doped with aluminum halides (eg AlCl ₃ ) or other dopants to lower their melting points. The electrolyte may therefore be, for example, an alkali metal halide-aluminum halide mixture or double salt, or an alkaline earth metal halide-aluminum halide mixture or double salt, or a mixture thereof, in particular _NaAlCl4 ,
_LiAlCl4 , _KAlCl4 , _NaAlBr4 , _LiAlBr4 ,
_KAlBr4 , _NaAlI4 , _LiAlI4 , _KAlI4 , Mg
( _AlCl4 ) ₂ , Ca( _AlCl4 ) ₂ , Mg( _AlBr4 ) ₂ , Ca
(AlBr ₄ ) ₂ , Mg(AlI ₄ ) ₂ , Ca(AlI ₄ ) ₂ , etc. When the electrolyte is a mixture or a melt, it is preferably a eutectic mixture or a melt. A cathode according to the invention can also be used as an active cathode current collector. That is, it is the active material that performs the function of current collection and at the same time contributes to the battery capacity. Such an active cathode current collector may be used as a current collector in a suitable battery with a suitable cathode;
Alternatively, it may be used as a current collector with the cathode of the invention in the battery of the invention. Such cathodic current collectors may be in the form of polymeric current collectors consisting of a core of chromium, manganese, iron, cobalt, or nickel with a protective surface layer of an activated intermediate type refractory hard metal compound. The cathode current collector may also be in the form of a laminated current collector consisting of a core of an electrically conductive substrate coated with a protective surface layer of a heat resistant hard metal compound intermediate. The core of the electrically conductive substrate can be selected from any suitable electrically conductive material, such as copper, aluminum, copper-clad aluminum, iron, steel, or alloys thereof. The composite and laminated cathode current collectors of the present invention have a protective surface layer that is continuous to protect the core and has sufficient thickness to prevent scraping, cracking, and penetration. This is very important. The composite and laminated current collectors of the invention have the advantage that said protective surface layer can be easily formed to the required thickness. A further advantage is that the substrate or core material is flexible and can be easily formed into wires, sheets, nets, etc., and the protective surface layer is hard and rigid. The laminated current collector also has the advantage of being flexible, highly conductive, lightweight and inexpensive, or by forming a hard corrosion-resistant layer of the required thickness around the core to protect the core. have In both the composite and laminated current collectors of the present invention, the protective surface layer is sufficiently thick to prevent the protective surface layer from being fully activated when the battery is fully charged. is important. If not, the substrate or core may undergo chemical attack or degradation during use. As mentioned above, the active cathode current collector of the present invention can be used with other types of conventional cathodes, but again the active cathode current collector contributes to battery capacity while maintaining resistance to aging for the reasons discussed above. can do. [Theoretical background] Intermediate heat-resistant hard metal compound used in the present invention,
That is, some further explanations regarding the compound of one or more metals selected from the group consisting of chromium, manganese, iron, cobalt, and nickel and one or more nonmetals selected from the group consisting of carbon, boron, nitrogen, silicon, and phosphorus. Add. As already mentioned, refractory hard metal compounds consisting of carbides, nitrides, borides, silicides and phosphides of transition metals are characterized by their high degree and generally extreme chemical inertness. Therefore, although many such heat-resistant hard metal compounds exhibit high electrical conductivity, they are usually not expected to exhibit electrochemical activity. Indeed, experiments carried out by the applicant using heat-resistant hard metal compounds such as interstitial carbides of titanium, vanadium, molybdenum, tantalum and tungsten have confirmed the above fact. These experiments were conducted using refractory hard metal compounds of the transition metals as cathodes of suitable electrochemical cells, using anodes such as lithium-aluminum alloy anodes, and using multiple salts of alkali and/or alkaline earth metal halides. This was done using a mixture of electrolytes. In these experiments, no or almost no electrochemical activity was shown under conditions up to the upper charge voltage of 2.8V. As mentioned above, although heat-resistant hard metal carbides such as titanium and vanadium do not exhibit electrochemical properties, heat-resistant hard metal compounds such as chromium, manganese, iron, cobalt, and nickel can be sufficiently halogenated. This is based on the finding that they exhibit electrochemical properties and can be used as cathodes in electrochemical cells. The reason why heat-resistant hard metal compounds of specific metals as described above form a unique group that commonly exhibits characteristics not found in compounds of other transition metals will be discussed. According to Van Nostrand's Scientific Encyclopedia, binary carbides are defined as ionic or salt carbides, and intermediate carbides.
carbides), interstitial carbides
carbon compounds) and covalent binary carbon compounds. The same document further states that intermediate carbide refers to a compound that exhibits properties intermediate between ionic carbide and interstitial carbide. This intermediate carbide, a carbide of chromium, manganese, iron, cobalt, and nickel, is similar to ionic oxides in that it reacts with water or dilute acids to generate carbon hydrogen, and is electrically conductive and opaque. and similar to interstitial carbides in terms of metallic luster. Because of the above properties, these five types of carbides form a unique group, and it is thought that the borides, nitrides, silicides, and phosphides of these metals also form a unique group. The group of metals consisting of chromium, manganese, iron, cobalt, and nickel is based on the atomic radius of Goldschmit and Pauling (“Refractory Hard Metals” (1953)).
Schmarzkopf and Kiffer pp12, 13) from 1.24
It is unique in that it is in the 1.27 Å range. These atomic radii are considerably smaller than those of other metals that make up heat-resistant hard metals. The same document also mentions Hagg's observation that because the atomic radii of these five metals are small, the radius ratio of their carbides (carbon radius: metal radius) is slightly larger than 0.59, and therefore they have a complex structure. mentioned. For other transition metals where this radius ratio is less than 0.59, the observed structures are all carbon atoms in the interstitial spaces of a close packed arrangement of metal atoms. The most important assumption of Linus Pauling's theory of metallic bonding is that the interatomic distance is a measure of the bonding force, and thus of the number of electron pairs resonating between available positions in the metal crystal. That's what it means. From the radius observed in each metal crystal in the first long period of the periodic table, the number of resonant bonds (and therefore the metallic valence of the atom according to Pauling's theory) is determined by K, Ca, Sc. ,Ti,V,
Cr and series increase from 1 to 5.78, Mn,
It remains at 5.78 for Fe, Co, and Ni, and it is shown that it gradually decreases from Cu. Moreover, Cr,
Only Mn, Fe, Co and Ni have excess electrons available to occupy the d-orbitals of the atoms after subtracting the required bonding electrons from the total out-of-shell electrons. Pauling proposed the above theory for Cr, Mn, Fe, Co and Ni.
applied it to explain the unusual structure of monosilicides, and reasoned that these metals constitute a series of progressively increasing d-characteristics of the metal orbitals that form metal-silicon bonds. . Thermodynamic data on metal borides, silicides, and phosphides is sparse, but enough data is available to detect simple trends in heat of formation and melting point. The values for chromium, manganese, iron, cobalt and nickel are much lower than those for titanium and vanadium and are less variable. Since various theoretical hypotheses have been made regarding the electronic configuration and bonding in heat-resistant hard metals, and their crystal chemistries vary, intermediate heat-resistant hard metal compounds of chromium, manganese, iron, cobalt, and nickel are From purely theoretical considerations, we can definitively state the reason why there are heat-resistant hard metal compounds of transition metals that exhibit sufficient electrochemical activity when used as cathodes but do not function under similar experimental conditions. It is impossible to explain it. However, even if a logical explanation is given, the characteristics of the metal compounds described above are clear from the several evidences obtained so far, and it is clear that these metals can be classified as one group.
In fact, in experiments conducted by the applicant, the intermediate type heat-resistant hard metal compound used in the present invention shows electrochemical activity, but heat-resistant hard metal compounds of several other transition metals do not show electrochemical activity under the same conditions. It has been shown that it does not exhibit sufficient electrochemical properties and cannot be used as a cathode for electrochemical cells. For the above reasons, in this specification, one or more metals selected from the group consisting of chromium, manganese, iron, cobalt, and nickel used in the present invention,
A heat-resistant hard metal compound that is a compound with one or more nonmetals selected from the group consisting of carbon, boron, nitrogen, silicon, and phosphorus is defined as an intermediate heat-resistant hard metal compound as a group of compounds that exhibit common properties. It refers to them collectively. Furthermore, the following was found regarding the structure of the intermediate heat-resistant hard metal compound of the present invention. The cathode of the present invention composed of two chromium carbides (Cr ₃ C ₂ and Cr ₅ C ₂ - mixed carbide) and the aluminum anode are used as electrodes in an electrochemical cell with LiAlCl ₄ as the electrolyte, and this cell Several charge/discharge cycles were performed for the battery. Subsequent X-ray diffraction analysis of the cathode showed that the carbon structure was completely or mostly intact. This means that the role of non-metallic carbon in the cathode is to participate with metal atoms to form a skeleton, which maintains the integrity of the cathode, contributes to the electronic conductivity of the cathode, and during use. This shows that it plays the important role of effectively retaining metallic chromium within the cathode. Therefore, chromium does not desorb from the activated cathode and contaminate the electrolyte, thereby adversely affecting the operation of the cell. Instead, it is possible that an entirely new layer is formed, but this point cannot be clarified theoretically. Also, CERAC INC. (Milwaukee,
325U.S. purchased from Wisconsin)
Fe ₃ C powder was halogenated in two ways. (1) The samples were electrochemically activated in a cell with LiAlCl ₄ electrolyte and Al anode. This electrochemically activated compound was used as a cathode in a battery and was subjected to 20 consecutive charge/discharge cycles over 30 days, with no significant capacity loss observed. The cathode was removed in a charged state for analysis. (2) Another sample was vapor-phase chlorinated using a 50/50 volume argon-chlorine mixture at 170°C for 4 hours. When powder X-ray diffraction was performed on these two compounds and the starting material iron carbide, similar results were obtained as in the case of the chromium carbide. These analytical results show that the carbide compounds according to the invention bear no resemblance to intercalated graphite compounds such as iron chloride intercalated graphite. Although the analysis was performed only on the carbides used in the present invention, the experimental results showed that the mechanism estimated for them also applies to the borides, nitrides, silicides, and phosphides used in the present invention. ing. In fact, experimental results show that even if one nonmetal does not retain a certain metal well in a given battery environment, another nonmetal that retains the same metal well in the same power supply environment will. has been shown to exist. However, as for the non-metal included in the intermediate heat-resistant hard metal compound according to the present invention, carbon may be preferred in terms of cost and availability, depending on the specific battery environment. Examples Embodiments of the invention are described below by way of example with reference to the accompanying drawings and some experiments. The drawing is a schematic structural diagram of a typical electrochemical cell according to the present invention used in the conducted experiments. Referring to the drawings, numeral 10 generally indicates an electrochemical cell according to the present invention, comprising an anode 12, a cathode 14, and an electrolyte 16 contained within an outer casing 18. The outer casing 18 has a sealing lid 20 which is clamped to the casing 18 and sealed by an annular sealing ring 22 . Cell 10 includes an anode current collector 24 in the form of a stainless steel bar. The free end of anode current collector 24 is enclosed within a glass rod 26. Cell 10 further includes a cathode current collector 28 in the form of a tungsten wire. The free end of cathode current collector 28 is also encapsulated in glass rod 30. The glass rods 26 and 30 pass through the sealing lid 20 and through a positioning sleeve 32 that projects from the sealing lid 20. The cell further includes two polytetrafluoroethylene (PTFE) sealing rings 34, two annular sealing rings 36, and two locking nuts 38 that sealingly fit the glass rods 26 and 30. The locking nut 38 has a threaded hole formed therein, and the positioning sleeve 32 is threaded on its outer surface to cooperate with the threaded hole. Therefore, by tightening the locking nut 38 onto the locating sleeve 32, the sealing ring 36 and
The PTFE sleeve 34 can be compressed, thereby sealing the glass rods 26 and 30. The cell further includes an alumina cylinder 40 surrounding the anode, cathode and electrolyte. Anode 12 is tightly packed within a stainless steel anode housing 42 that is integral with anode current collector 24 . Cathode 14 is tightly packed within a porous graphite cathode housing 44 that communicates with cathode current collector 28 . The anode 12 has an annular alumina spacer 46
and an alumina collar body 47 around the anode 12, which separates it from the cathode 14 and holds it above. A simple 40 zirconia felt separator 48 isolates the anode 12 from the cathode 14.
crossing. In the experiments carried out, the cathode 14 was the cathode according to the invention, and the anode 12 was of a lithium-aluminum alloy for high temperature experiments and of aluminum for low temperature experiments. Electrolytes for high temperature experiments are LiF/LiCl/KCl or
It was a eutectic consisting of LiCl/KCl. The electrolyte for the low temperature experiments was in the form of _LiAlCl4 . Utilizing the cell structure of electrochemical cell 10, several experiments have been conducted, and some experiments are currently ongoing, using various electrochemical cells according to the present invention. In the experiments conducted, a refractory hard metal compound was formed by conventional means and then assembled into an electrochemical cell using an anode and an electrolyte having a sufficiently high electrolytic threshold voltage as described above and capable of supplying halogen ions during use. The compound was placed as a cathode inside the cell and activated by charging and discharging cycles to become a cathode. The cathode, anode and electrolyte were all maintained under inert argon conditions. In the first series of experiments, various heat-resistant hard metal carbides were tested at an operating temperature of 400° C., using a lithium-aluminum alloy anode, and a molten LiF/LiCl/KCl electrolyte at that temperature. The results of the first series of experiments (average results in some cases) are shown in the table below. The abbreviations in the table below and are as follows. VP (ch/di) - Voltage plateau - (charge/discharge) EN - Experiment number dc - Intermediate heat-resistant hard metal compound DC - Discharge capacity (amp hours/g) SCC - Short circuit current (ampere) OCV - Open circuit voltage ( Volt) CE - Coulometric efficiency (%) L (cy/da) - Usage life when continuously charging and discharging (cycles/day)

[Table] Experiments 1 and 2 were discontinued because sufficient data were obtained. Experiments 3 and 5 were terminated due to internal shots. Experiment 4 was terminated due to sudden capacity loss. From these experiments it was determined that the effective operating voltage range during charging was up to about 3 volts, above which corrosion of the dungsten wire field-through occurred. Similar experiments using tantalum carbide (TaC), tungsten carbide (WC and W ₂ C), and titanium carbide (TiC) electrodes at a maximum charging voltage of approximately 3 volts did not result in any electrochemical activity. Nakatsuta. Also, similar experiments using vanadium carbide (VC) and molybdenum carbide (Mo ₂ C) did not result in significant electrochemical activity. In the second series of experiments conducted, the operating temperature using an aluminum anode and LiAlCl ₄ electrolyte was
Chromium carbide and other carbides were tested as cathodes in low temperature batteries at 200°C. The results of the second series of experiments (in some cases average results) are shown in the table below.

[Table] *Experiments with this indication are still in progress at the time of writing this specification.
Experiments 2 and 3 were stopped when samples for analysis were needed. Experiment 5 was terminated because no electrochemical activity occurred. Corresponding experiments were performed using chromium and iron as cathodes. In these experiments, a decline in activity over time due to metal desorption from the cathode and contamination of the electrolyte was observed. The two different open circuit voltages in the chromium series can be reasonably explained from the different oxidation states of chromium. Cr ₇ C ₃ above 1 volt
discharges 30% _{and Cr3C2} discharges 60%. Therefore,
It is presumed that most of the chromium in these two carbides has been oxidized to Cr4 ⁺ .
For Cr ₂₃ C ₆ most discharges are lower than 0.5 volts, so Cr is up to Cr ²⁺ or at most Cr ³⁺
Take up to. In the case of the Fe ₃ C cathode, the coulometric efficiency decreased from about 100% to about 30% during about one year of continuous cell operation.
The applicant believes that this is due to the formation of dendrites, which causes internal shoots and lowers the coulometric efficiency. In all experimental series conducted, the table ~
It should be noted that most cells are susceptible to internal shoots and dendrite formation, which causes loss of coulometric efficiency, as shown in Figure 2.
This is mainly a problem of battery structure and can be improved by a suitable structure or by taking appropriate measures to suppress dendrite formation. Therefore, if care is taken to suppress dendrite formation, as in experiment number 4 in the table, where a Cr ₃ C ₂ cathode was used and a sintered glass disk was used to isolate the electrodes,
High coulometric efficiency (approximately 90%) was maintained for three months. In all experiments in Tables, and, all cells were subjected to continuous charge-discharge cycles. Experiments were generally terminated due to mechanical failure or internal leakage due to dendrite formation at the anode. This was more important since the cathode was activated at that location. The fact that Mn _x C _y exhibits cathodic activity in the high temperature electrolyte shown in the table but not in the low temperature electrolyte shown in the table is due to the theoretical em
It can be easily explained based on f. That is, the theoretical emf for the Li/Mn (chloride electrolyte) electrode pair is 1.66 volts, while the theoretical emf for the Al/Mn (chloride electrolyte) electrode pair is -0.11 volts. In a third series of experiments, various metal borides, nitrides, silicides, and phosphides were tested as cathodes in low-temperature cells with an operating temperature of 200 °C using aluminum anodes and _LiAlCl4 electrolytes.
The results of these experiments are shown in the table below.

【table】

[Table] * Experiments with this indication began relatively recently and are still ongoing at the time of writing this specification.
Nuclear tests numbered 1, 6, 11, and 12 were terminated because sufficient data was obtained or cathode analysis was required. Run number 2 was terminated due to internal shoots and run number 5 was terminated due to no electrochemical activity. Charge and discharge current densities were in the range of 10 mA/cm ² for all cells. Most batteries are susceptible to internal shoots and dendrite formation, which causes reduced coulometric efficiency. With proper cell construction and proper precautions to suppress dendrite formation, coulometric efficiency can be significantly improved and maintained at a sufficiently high level. It will be noted above and from above that the open circuit voltage is relatively low. However, this may be due to the aluminum anode used in these experiments. If an electrically positive material is used as the anode, a much higher open circuit voltage may be obtained. In some cases, the open circuit voltage will increase by more than a factor of two. This is verified from the circuit voltages obtained in the high temperature experiments shown in the table. Based on the experimental results shown in Tables to Tables, it can be said that if the coulometric efficiency and open circuit voltage are increased, various batteries that can effectively operate as off-peak energy storage and secondary batteries for electric vehicles can be obtained. . A fourth series of experiments was conducted using various intermediate heat-resistant hard metal compounds according to the present invention as cathodes. In this fourth series of experiments, a lithium-aluminum alloy was used as an anode, and LiCl/
The battery was used as a high temperature battery at a temperature of 400°C using KCl electrolyte. The results of these experiments (in some cases average results) are shown in the table below.

【table】

[Table] *Experiments with this indication are still in progress at the time of writing this specification.
Although cell capacity was not perfect for all cells tested, coulometric efficiency could be improved considerably by effective cell construction or by reducing the extent of shoots due to dendrite formation. Experiments 1, 2 and 5 were terminated due to internal leakage. Experiment 3 was terminated due to mechanical fracture and shoot. From the experimental results shown in the table above, it can be said that the optimized battery of the present invention can effectively operate as a secondary battery useful for electric vehicles and off-peak energy storage systems. Experimental results show that the cathode according to the invention exhibits good electronic conductivity in both charging and discharging states of the battery. The electronic conductivity of the cathode is determined by the cathode metal-carbide, metal-boride, metal-nitride,
It is believed to be provided by a metal-silicide or metal-phosphide network or lattice. It is believed that during battery reactions, only atoms of metals (or metal compounds) and alkali metals undergo a change in their oxidation state. The results of the experiments conducted further indicate that under suitable conditions the metal component of the activated refractory hard metal compound remains entrapped within the cathode during operation of the cell. Accordingly, the preferred embodiment of the present invention, as shown in the experiments, is that the metal is retained at the activated cathode to inhibit desorption and consequent electrolyte contamination during use; This has the advantage of eliminating limitations on the useful life of cathode-based batteries. That is, the electrochemical cell of the present invention using the cathode of the present invention is characterized in that, under appropriate conditions, the activated cathode is stable, inexpensive, and exhibits good electronic conductivity in both charged and discharged states. It has the advantage that it can be used with a low melting point electrolyte and that the electrochemically active metal is captured during use, and that the metal remains accessible and available for electrochemical activity. Furthermore, experimental results show that the cathode according to the present invention
It has been shown that it is possible to act as a dimensional cathode, thereby significantly increasing the capacity of a battery equipped with such a cathode. Furthermore, the optimized cell of the invention can offer the advantages of ease of operation, simple construction, good energy density and good power to weight ratio. The power to weight ratio can be improved, especially when using low melting point electrolytes. This is because a lighter battery casing (for example made of synthetic plastic material) can be used than would otherwise be possible and a less complex heating system is required. Although some of the cells according to the invention can provide only relatively moderate energy densities, such energy densities are sufficient to demonstrate the effectiveness of the cells. This is because these cells have various advantages over high energy density cells, such as those with sulfur-based cathode systems.

[Brief explanation of drawings]

The drawing is a cross-sectional view of the electrochemical cell of the present invention. 10... Electrochemical cell, 12... Anode, 1
4... cathode, 18... external casing.

Claims (1)

[Claims] 1. An electrochemically active cathode material that is halogenated during charging and dehalogenated during discharge, and the cathode material includes chromium, manganese, iron,
An electrochemical cell cathode which is a compound of one or more metals selected from the group consisting of cobalt and nickel and one or more non-metals selected from the group consisting of carbon, boron, nitrogen, silicon and phosphorous, the cathode comprising: the compound is an intermediate heat-resistant hard metal compound activated by halogenation, the cathode can be used in an electrochemical cell operating at temperatures from room temperature to 400°C, and the metal and non-metal Said cathode, characterized in that the atomic ratio is substantially constant during charging and discharging. 2. The cathode according to claim 1, wherein the intermediate heat-resistant hard metal compound is a carbide of iron, chromium, or manganese. 3. The cathode according to claim 1, wherein the intermediate heat-resistant hard metal compound is a carbide of cobalt or nickel. 4 The intermediate heat-resistant hard metal compound is iron boride,
2. The cathode according to claim 1, wherein the cathode is a nitride, a silicide, or a phosphide. 5. The cathode according to claim 1, wherein the intermediate heat-resistant hard metal compound is a boride of cobalt, nickel, or chromium. 6. The cathode according to claim 1, wherein the intermediate heat-resistant hard metal compound is a silicide of chromium or nickel, a phosphide of cobalt, or a nitride of manganese or chromium. 7. The cathode according to any one of claims 1 to 6, wherein the intermediate heat-resistant hard metal compound is composed of a compound of one or more metals and a plurality of nonmetals. 8. The cathode according to any one of claims 1 to 6, wherein the intermediate heat-resistant hard metal compound is composed of a compound of a plurality of metals and one or more nonmetals. 9 Formed in an inactive state, a plurality of electrolytes can be arranged as electrodes in an electrochemical cell using an electrolyte capable of supplying adequate halogen ions and having an electrolytic threshold voltage higher than the halogenation threshold voltage of the cathode. 9. The cathode according to claim 1, wherein the cathode is activated by subjecting it to charge and discharge cycles. 10 consisting of a cathode, a suitable anode and a suitable electrolyte, said cathode comprising chromium, manganese, manganese, chromium, manganese,
An electrochemical cell comprising a compound of one or more metals selected from the group consisting of iron, cobalt and nickel and one or more non-metals selected from the group consisting of carbon, boron, nitrogen, silicon and phosphorus, the compound is an intermediate heat-resistant hard metal compound and is activated by halogenation;
The electrochemical cell is stable at temperatures up to 400° C., characterized in that the atomic ratio of the metal to the non-metal remains substantially constant during charging and discharging. 11 An electrolytic threshold voltage higher than the threshold voltage of the cathode for the cathode to be in a non-activated state and for the electrolyte to be a source of suitable halogen ions and to activate the cathode in situ by halogenation. 11. The battery according to claim 10, characterized in that the battery has: 12. The battery according to claim 10, wherein the anode is an alkali metal anode. 13. The battery according to claim 10, wherein the anode comprises an alkali metal alloy anode. 14. The battery according to claim 13, wherein the anode is made of an alkali metal, aluminum or silicon alloy. 15. The battery according to claim 10, wherein the anode comprises an aluminum anode. 16. Claim 10 or 1, characterized in that the electrolyte consists of a mixture of a plurality of alkali and/or alkaline earth metal halide salts.
The battery according to item 1. 17. The battery according to claim 10 or 11, wherein the electrolyte comprises an alkali metal halide-aluminum halide mixture. 18 Claim 1 comprising an active cathode current collector corresponding to the cathode.
The battery according to any one of items 0 to 17.