NL8104075A - RECHARGEABLE, FULLY INORGANIC NON-AQUEOUS LI / SO2 CELL WITH ELECTROLYT SALT LIGACL4. - Google Patents

Description

* ** Λ- Ν.Ο.5Ο.364

Rechargeable, fully inorganic non-aqueous Li / SO4 cell with the electrolyte salt LiGaCl.

The invention relates to charging at room temperature, bare, non-aqueous cells provided with active metal anodes such as lithium, and more particularly to such cells with sulfur dioxide electrolyte solvent / cathode depolarizers.

5 Significant efforts have been made in the past to develop a practically usable and commercially acceptable room temperature rechargeable lithium cell which, over conventional rechargeable lead acid and nickel cadmium batteries, has the advantages of higher efficiency, lower weight and longer primary 10 have a service life so that more time between charge cycles is available. These attempts have had varying degrees of success, however, saline cells seldom have a recharge efficiency of more than 80% over a large number of charge and discharge cycles. bit cycle efficiency is very different from the very high efficiency when depositing lithium, since lithium is deposited from the electrolyte solution commonly used in lithium cells with an efficiency approaching 100% (the reverse current of the reaction hi Ii + + e ~ "is very high, on the order of" 1 x 10 × 10 / cm). The recycling efficiency, on the other hand, is related to the subsequent anodic orydation of the deposited lithium, generally involving the effectiveness of the deposited lithium as anode material decreases rapidly with the number of charge and discharge cycles despite the high sales efficiency.

Several reasons can be given for explaining the inefficiency of the deposited lithium on repeated anodic oxidation and of cells containing such anodes. One reason given is that lithium is dendritically deposited and, especially at the small contact point with the anode substrate, is covered with an insulating layer that electrically insulates the anode substrate despite its physical presence on the anode, deposited lithium dendrites. because they are electrically insulated, they are no longer available for efficient anodic oxidation during discharge, moreover, the precipitated lithium dendrites are brittle and can easily become mechanically detached from the anode substrate. The loosened lithium is then lost to discharge and further deposition because it is insoluble 8104075 4; ΐ 2 in the electrolyte. The efficiency is therefore reduced by depletion of lithium available for repeated completion of the charge and discharge cycle.

Electrically isolated lithium generally results from the interaction of lithium with the organic solvent (s) used in the cells. When the cell is reused, the lithium metal is deposited in the form of large-area dendrites, which thereby increasingly react with the electrolyte solvent, especially on the precipitate side, thereby forming isolated surface layers of increasing surface, and the lithium thus deposited is increasingly electrically isolated from the anode. These layers, when extensively formed, also tend to limit the rate at which the lithium cations dissolve and thus also decrease the capacity of the cell. In addition, the reaction products of lithium and the commonly used electrolyte solvents (especially with respect to the solvent) are not naturally reversible. Therefore, the electrolyte solvents themselves become depleted during repeated cycle cycles with loss of conductivity and cell power.

The reaction products resulting from the solvents also tend to act as harmful impurities, further reducing the capacity of the cell. Moreover, even the lithium contained in such reaction products can also be lost, further decreasing the amount of lithium available for reuse.

For example, fropylene carbonate will react with lithium to form an insulating layer of lithium carbonate and propylene gas that cannot be reversed to get the original solvent.

Although some of the lithium can be recovered during charging, the lithium carbonate is not efficiently reversible to its constituent elements. As a result, part of the lithium is lost for further cycles. Similarly, other solvents such as tetrahydrofuran and acetonitrile form complex reaction products with lithium which are also not reversible. By their nature, the organic solvents must indeed react with the lithium anode. In order to dissolve the electrolyte salts required for conductivity, the organic electrolytes must be slightly polar, and it is precisely this property that causes such solvents to react with lithium to form non-reversible reaction products.

In order to provide a highly efficient rechargeable cell, in accordance with the present invention, the deposited lithium must have a reduced dendrite character and not be covered with a non-reversible insulating layer. It is also essential that virtually all active components of the oil complete the loading and reloading cycle without introducing or creating additional reaction in products that are not naturally reversible. Accordingly, free organic solvents or cosolvents from the cells of the present invention are excluded. Although the recharge efficiency problem has further been described as being inherent in the lithium cells with organic solvents, the cells with only inorganic constituents such as a lithium cell with an inorganic thionyl-15 chloride solvent / cathode depolarizer exhibit the same problems in inefficient reuse . The reaction of thionyl chloride with lithium produces the reaction products lithium chloride and an unstable SO1 which cannot be effectively combined with the original starting materials. Thus, the electrolyte solvent and cathode depolarizer, even if inorganic, must only react with the anode metal only to the extent that totally reversible reaction products are formed.

Recently, cathode depolarizing materials have been found that are highly rechargeable themselves. Examples of such materials include the layered metal chalcogenide compounds as described in US Patent 4 * 009 * 052, which insert lithium ions into the space between the layers that do not participate in the full reaction. This property makes them effectively reversible and rechargeable. However, when these materials are used in lithium cells at ambient temperature with organic electrolytes, the cell as a whole remains inefficiently rechargeable.

Various attempts have been made to improve the efficiency and rechargeable of the lithium anodes in non-aqueous cells. Attempts have generally been made to minimize the dendritic deposition of the lithium by using various means such as additives, alloying the lithium anode, use of certain electrolyte salts and solvents and the like. U.S. Pat. Nos. 3 * 953 * 302 and 4 * 091 * 152 disclose the use of metal salt additives, which consist of metals that can be reduced by lithium jugs 40 and which together with lithium 81 0 4 0 75.

* N> 4 are deposited during charging and form lithium-rich metals or alloys. The use of polyalkylene glycol ethers is described in U.S. Pat. No. 3,928,067 as improving the reuse properties of the lithium cells by improving the morphology of the deposited lithium. While such efforts have led to improved rechargeable, such cells still contain organic elements which, as described, prevent truly efficient recharging of cells. The dendritic deposition of lithium in secondary cells is described in U.S. Patent 4 * 139,680 and could be effectively prevented through the use of clovoborate electrolyte salts. However, such electrolyte salts are difficult to produce by synthesis and are accordingly very expensive. United States Patent 3-580,828 describes the concentrations and current density limits of a particular electrolyte salt which, if taken into account, improve lithium deposition properties. Other methods of improving the reloadability of deposited lithium include the initial use of alloyed lithium anodes, particularly with aluminum, as described in U.S. Patent 4,002,492.

General improvements in rechargeable cells include the use of complex inorganic lithium salts as charge transfer agents (US Patent 3,746,585) and the judicious use of organic cosolvents with SOg to improve the solubility of the electrolyte salts (US Patent 3,953,234) The use of solvents that are relatively stable to the lithium anode is described per se in, for example, U.S. Pat. No. 3,540,988 as being necessary to obtain increased cell rechargeable power.

Various systems require external mechanical parts such as molten lithium cells (not simply subject to dendritic deposition) requiring extensive heating and shielding parts but which are the most efficient lithium cells available because there are no dendrites or layers on the molten lithium. Other systems include cyclic electrolytes as described in U.S. Pat. No. 4,154 * 902 that require complicated circulators.

Electrolytic lithium deposition processes generally require organic solvent carriers for the electrolyte salt, 8104075 for high conductivity and efficient deposition of the lithium metal. Examples of such lithium deposition processes are known from U.S. Pat. Nos. 5,791,945 and 5,530,828. Cells as described above (except those containing electrolyte clovoborate salts 5) also require organic solvents for high conductivity and efficient deposition of lithium.

The electrolytic deposition of lithium in an electrolyte consisting of lithium and sodium tetrachloroaluminate or lithium and sodium tetrabromoaluminate dissolved in pure sulfur dioxide (without organic auxiliary solvents) is described in U.S. Patent 5 * 495 * 453. However, the discharge behavior of such cells is very limited because the discharge capacity is considerably less than the theoretical capacity. Since these salts are disclosed therein as the only salts that have sufficient solubility and conductivity in pure SO2 for efficient deposition, in cells with other salts in liquid SO2, further organic co-solvents are as mentioned above and described in U.S. Patent 3 * 953 * 234 needed.

One of the objects of the present invention is to provide a highly efficient, room temperature rechargeable inorganic lithium cell or other alkali or alkaline earth metal cell which contains mainly only reversible reaction products and is both efficiently discharged and substantially rechargeable during long periods of charge and discharge cycles.

These and other objects, features and advantages of the present invention will now be further elucidated with reference to the following description and the figure: ...

The figure represents the voltage variation in the charge and discharge cycle of a cell according to the present invention.

The present invention mainly relates to a fully inorganic, non-aqueous, efficiently rechargeable cell with an IftM-nm or other active metal (generally alkali or earth alkali metals or alloys thereof) for the anode and an exclusively inorganic electrolyte solvent consisting essentially of sulfur dioxide 35, which can also serve as a cathode depolarizer (with an inert usually carbon cathode) and an inorganic gallium salt such as gallium halide with anode metal cations and LiGaCl 2 (with a lithium cation and a GaCl 2 anion in a lithium anode cell) in particular, dissolved in said sulfur dioxide electrolyte solvent. Other 40 gallium salts such as Li20 (GaCl ^) 2 and Li2S (GaClj) 2 (with 8104075 6 * "2 _2 lithium cations and 0 (GaCl ^) 2" and S (GaCl ^) 2 "anions, respectively) are described in patent application M -5465 · A fully reversible solid cathode depolarizer such as an intercalation compound can be additionally used with the SO 2 electrolyte solvent. Examples of such solid cathode depolarizers are chromium oxide (Seloxette), titanium disulfide, magnesium dioxide, etc. The cell is efficient to recharge because all the reactions going on therein, including the internal reactions between the cell components, such as between the lithium anode and the SO 2 solvent and the electrochemical cell reaction products give essentially only reversible products of, for example, lithium disulfide which is 100% reversible on recharge or intercalated or reactive lithium, which is also fully reversible. In addition, the use of gallium salts also significantly reduces dendritic deposition.

In general, any co-solvents normally used in non-aqueous lithium / SQ2 cells such as propylene carbonate, acetonitrile, tetrahydrofuran, dioxolane, / -butrolactone and the like are detrimental as co-solvents in the present invention as they tend to complex non-reversible reaction. 20 to form products on the active metal anodes such as lithium. Thus, a requirement of the present invention is that the electrolyte solvent be completely inorganic. However, it is not sufficient for the electrolyte solvent to be completely inorganic since the most commonly used inorganic solvent in fully inorganic cells, thionyl chloride, as described above, also forms irreversible reaction products with an active metal anode such as lithium. Accordingly, the inorganic solvent of the present invention is specifically SO 2 which reacts with lithium by forming fully reversible lithium dithionite. Sulfur dioxide, however, is a relatively poor solvent for lithium salts since it is an acceptor solvent that interacts primarily with the electrolyte salt anion rather than the cation. Accordingly, in order to improve solubility and conductivity, organic solvents (normally donor solvents) are invariably coupled thereto to obtain a complete solution, the organic solvents sulfating the electrolyte salt cations as described in U.S. Pat. The only salts generally described as sufficiently soluble in SO 2 alone are the above 40 lithium and sodium tetrachloroaluminates and borates and 8104075 7 clovoborates. Although, however, the salt in SCL can be soluble hair? it must also yield a cathodically conductive (greater than 1 x 10 ohm cm) ion before it can be considered an acceptable electrolyte. Thus, materials such as LiAlCl 2 which are soluble and electrically conductive in SO 2 are nevertheless unsuitable for the cells of the present invention due to the low cathodic conductivity of the electrolyte. However, the clovaborate salts that are soluble and cathodically conductive are very expensive. The electrolyte salts of the present invention, which are in particular gallium salts such as halides with anode metal cations, are found to be soluble and to provide high cathodic conductivity in pure SO2. Moreover, they are relatively inexpensive compared to the clovoborate salts.

It is preferred that the pendant metal rest on a metal foil substrate. A preferred substrate for a lithium anode is a copper foil with the lithium in the form of a sandwich applied to both sides of the copper.

In an SO2 cathode depolarizer, the cathode consists of an inert material such as carbon, supported by a generally metal substrate such as an expanded metal, for example aluminum.

The most preferred gallium halide salt that has the required conductivity in SO4, without the need for organic cosolvents, is a salt with a gallium tetrachloride anion such as a HiGaCl salt for use in a lithium anode cell as described in U.S. Patent 4,177 529 However, in said patent, the gallium salts are specifically described for use in a cell containing inorganic SOClg and not rechargeable in accordance with the present invention.

It has been found that such salts can be formed in situ in a pure SOg solvent by the reaction between, for example, LiCl and GaCl 2 to form LiGaCl 2. Hit is added to the locally formed salt in a SOClg solvent as described in said patent.

The LiGaCl. salt can also be prepared by a direct fusion of LiCl and GaCl, by melting these materials in stoichiometric amounts and allowing the melt to crystallize.

As indicated in Table 1, the electrolyte salt LiGaCl 4 has a high conductivity over a wide temperature range even if it has decomposed into a relatively lean electrolyte solvent 40 consisting of pure SO 4.

8104075! \ ƒ 8

TABLE A

Temperature Conductivity (1H LiGaCl ^ -SOg) (ohm cm) "1 40 ° C 5.32 x 10" 2 30 ° C 5.27 x 10 "2 20 ° C 5.17 X 10'2 io ° c 5, 05 x 10 "2 0 ° c 4.76 x 10" 2 -10 ° C 4.45 x 10 "2 -16.8 ° C 4.19 X 10” 2

It has also been found that the above LiGaCl 2 salt reduces the dendritic deposition of anode materials such as lithium since no lithium particles enter the electrolyte solutions or partially insoluble precipitates even after 5 repeated cycles. Since the electrolyte solution remains free of such particles, the LiGaCl 2 is also believed to form cleaning or removing particles during charging which clean or remove loosened lithium dendrites and lithium from lithium reaction products on both the anode and cathode. Therefore, even when isolated from the anode or cathode substrates, the products produced by the cell reaction return to the liquid to improve both the anode metal and the electrolyte solvent.

In order to illustrate the effectiveness of the present invention for an efficiently rechargeable cell, the following examples and similar results are given (relative to other materials which are part of the prior art). Unless otherwise indicated, all parts are parts by weight. Basic I

A format D cell is made of spirally wound lithium foil (50.8 x 4.15 x 0.03 cm) and porous carbon electrodes (an expanded aluminum substrate) (50.8 x 4.4 x 0.063) with a intermediate polypropylene separator. The cell is filled with a solution of 1M LiGaCl 2 in pure SO 2 (about 40 g).

The theoretical capacity of the lithium anode is about 13. Ah and the capacity of the SOg is about 14 Ah. The cell goes through the charge and discharge cycles at 0.5A during a 2-hour discharge followed by a 2-hour charge. The voltage levels of the 81 0Λ075 9 second and the sixty-ninth cycle (the cell failed after the 69th cycle) are shown in the figure. There is an almost negligible change in the discharge and charging voltage, indicating a reuse efficiency of almost 100% <5 h rechargeable, however, is not a sufficient criterion for the usefulness of the cell. The cell must also have good primary cell properties. 33rd following examples II-IV show the possibilities of the cells of the present invention.

Example II

A 'D * cell, manufactured as in Example 1, is polarized at room temperature (55 ° C) and at -30 ° C with the results as shown in Table 33.

TABLE 33

i (λ) _Volt bi.i 25 ° C_Volt bi.i -50 ° C

15 unloaded 2.91 2.97 .026 2.89 2.85 .050 2.89 2.80 0.10 2.87 2.75 0.25 2.84 20 0.55 ---. 2.58 0.50 2.79 2.53 1.0 2.63 1.5 2.58 2.32 2.0 2.53 2.27 25 3.0 2.47 2.15 5.0 - 1.85 3 The relatively high voltages at currents above 1 ampere show the high conductivity of the electrolyte salt and good charging capabilities of the oil both at room temperature and low temperatures.

Example III-IV

Two "33n cells were run as in Example I and discharged at different rates and temperatures under conditions 35 and with the results given in Table C.

TABLE C

föorbeeLd temperature discharge load capacity up to 2v III -30 ° C 4.4 ohm 3.5 Ah IV 25 ° C 0.25 A 9.5 Ah 8104075 /: &

Since the cell has a theoretical capacity of 10 Ah (limited by C), the capacity (90%) obtained at room temperature at a discharge current of 0.25 A reflects a very good behavior as a primary cell. The 5.5 -Ah achieved at -50 ° C is also an excellent low temperature performance.

Example 7

A cell manufactured in accordance with Example Γ but with an anode consisting of two (0.025 cm) films of lithium sandwiched between a copper foil substrate, passes at 0.10 A cycles of 10 hours of discharge and 10 hours of charging. The cell gives about 104 Ah, about 5 times the original lithium capacity. Example 71

A glass cell is made using a 2 cm x 0.5 cm li anode and a 2.0 x 0.5 cm catalytic carbon cathode with about 20 cc of 1M LigaCl. in pure SO4 electrolyte. The cell is discharged at 4 mA at 1 mA / cm for 5 hours and then charged at 2

1 mA / cm for 5 hours, Ha 15 cycles, the lithium surface is clean and free from dendrites and the electrolyte remains clear. Example VII

Two cells are manufactured according to example I, but one of which has an electrolyte consisting of 1M LiAlCl 2 in pure SO 2. as described in U.S. Pat. No. 3 * 493,433 * \

The cells are discharged with the results as given in Table D.

25 TABLE · D

Electrolyte 0CV Capacity at 0.25 A.

discharge current 1 M IiGaCl4 2.94V 9.0 Ah 1 M MAICI 3.26 0.38 Ah 30 It is clear from the above equation that the prior art electrolyte salt LiAlCl 2 provides only a minimal primary cell behavior in pure SOg and is certainly unsuitable for secondary or rechargeable cells of the present invention. It should also be noted that LiAlCl 2 electrolyte-55 salt is selected in fully inorganic cells with lithium anodes and thionyl chloride electrolyte solvent / cathode depolarizers.

The following examples are given to further illustrate for the present invention the reloading power of cells 40 under different cycle conditions.

8104075

V

11

Examples 7ΙΙΙ-Σ

Three cells made in accordance with Example V and cycling under the conditions of Table E provide the results as set forth in Table V.

✓

5 TABLE E

Example Test conditions Capacity (Ah) Application (charging and discharging) Li SOg VIII 0.5 A x 2 hours 73 360% 570% discharging / charging IX 0.25 A x 4 hours 66 330% 500% 10 X 0.5 A ( discharge 80 400% 600% to 2.5 V charge at 3 »5 V

It goes without saying that these examples do not limit the scope of protection requested.

8104075

Claims (15)

Rechargeable, non-aqueous electrochemical cell consisting of an active metal anode and an electrolyte salt containing a cation of the anode metal and an anion, characterized in that the anion contains gallium and halogen atoms and the salt is decomposed into a total inorganic solvent consisting essentially of sulfur dioxide. Cell according to claim 1, characterized in that the anode consists of lithium or alloys thereof. Cell according to claim 2, characterized in that the lithium or alloys thereof is supported by a metal substrate. 4. Cell according to claim 3, characterized in that the metal substrate consists of a metal foil enclosed between lithium or alloys thereof. 5. Cell according to claim 4, characterized in that the metal substrate consists of copper. 6. Cell according to claims 1 to 5, characterized in that the sulfur dioxide also comprises the cathode depolarizer 20 of the cell. Cell according to claim 6, characterized in that it contains an inert carbon cathode. 8. Cell according to claim 7, characterized in that the carbon is carried by an expanded aluminum substrate. 9. Cell according to claims 1 to 5, characterized in that the cell contains a solid cathode depolarizer which, upon reaction with cations of the active metal anode, forms a fully reversible product during the discharge of the cell. 30 loading the cell. 10. Cell according to claim $, characterized in that the fixed cathode depolarizer is an intercalation compound. Cell according to claim 10, characterized in that the cathode depolarizer is selected from the group formed by 35 TiS2 '^^ 2 and cllroomoxi <ae Gel according to claims 1 to 11, characterized in that the salt has anions selected from the group formed GaCl ", 0 (GaCl5.r22, and StGaCl ^)" 2 ^ 13. Method for improving the rechargeable ability of a 40 non-aqueous rechargeable cell containing an active metal anode, 81. A 0 7 5 comprising the decomposition of a salt containing the cation of the anode metal and an anion containing gallium and halogen atoms in a solution, characterized in that said solution is wholly inorganic and consists essentially of sulfur dioxide. 8104075