FR2472278A1 - ELECTROCHEMICAL CATHODE ACCUMULATOR COMPRISING A HALOALCAN AND A HALOACIDE - Google Patents

Abstract

ELECTROCHEMICAL ACCUMULATOR IT INCLUDES AN ALKALINE METAL ANODE 7, AN 11 IONIC SOLID ELECTROLYTE, A LIQUID CATHOLYTE 9 CONSISTING OF SULFUR, HALOSULFAN, SUCH AS SULFUR AND HALOACID MONOCHLORIDE SUCH AS ALUMINUM CHLORIDE. ELECTRODES 3 AND 15 ARE CONNECTED RESPECTIVELY TO THE ANODE AND THE CATHODE. THE ACCUMULATOR IS HEATED AND IS SEALED BY FLANGES 5, 17, 19 AND 21. AUTOMOTIVE INDUSTRY.

Description

The present invention relates to electronic accumulators

  chemical. There has been considerable interest

  years, to electrochemical accumulators of advanced technology

  because of their potentially high energy density

  per unit weight and per unit volume. Among the applications

  Potential sources of such accumulators include sources of backup energy, regulating the load on equipment, storing solar photovoltaic energy and

  propelling vehicles. These applications can be completed

  mentary. For example, electric vehicles

  that draw their energy from accumulators can contribute to

  equalize the equipment load, because we can recharge

  accumulators during the night, when the equipment

  have an excess capacity. The classic lead-acid battery

  traditionally does not seem to be suitable for the moment for these applications. It is not practical for equalizing charges, because it is unable to withstand the large number of desired deep discharge cycles, if it is not

  required for such use. The relatively low ratio

  the energy density at about 20 watts per hour

  kg limit, but it does not prevent it, the use of such

  emateurs for the propulsion of vehicles.

  Several systems that can be used to test

  Advanced technology emateurs. The systems examined

  Many different materials are available to form the electrodes and the electrolyte. One of the systems that has been a lot

  studied uses the alkali-sulfur metal pair for electro-

  of. The alkali metal is typically lithium or sodium.

  Other alkali metals could be used, but their higher atomic weight would lower the energy densities theoretically achievable. These couples are attractive

  as electrodes because of their theoretical specific energy-

  high of 2600 and 750 watts respectively.

  hour / kilogram for lithium-sulfur and sodium-

  sulfur. The basic configuration of a sodium-sulfur accumulator is a molten metal sodium anode, a molten sulfur cathode and a sodium ion conducting electrolyte disposed between the anode and the cathode. In this arrangement, the accumulator

  operates at a relatively high temperature. This temperature

  high operating temperature is typically between 300 and 4000C and is necessary to maintain the materials

  components of the anode and the cathode, as well as the

  cathode reaction products, such as polysulfides of

  sodium, in the molten state. As expected, the temperature

  High operating temperature leads to complications and problems. Thus, for example, an external energy source and thermal insulation are required to maintain the reactants in the molten state. In addition, both sulfur

  sodium polysulfides are very corrosive to the temperatures

  high batteries and well-designed accumulators require

  materials constituting the structure and particulate

  sought after if one wants to achieve safe operation. Lithium-sulfur accumulators have the same arrangement of

  base as sodium-sulfur accumulators.

  To avoid these problems and others that have arisen,

  the aim has been to reduce the operating temperature range.

  Sodium-sulfur or lithium-sulfur accumulators, while retaining as much as possible desirable provisions of the high-temperature arrangement. But several considerations

  limit the possibility of lowering the operating temperature

  sodium-sulfur accumulators and the operating temperature of

  minimally, which is useful for such accumulators

  is about 1000C. This minimum is imposed by two

  practices. Sodium metal is not in the molten state below 980C and the conductivity of typical solid electrolytes driving the sodium ion is generally too low below this temperature to have accumulators

  suitable for the applications mentioned above.

  We tried to reduce the operating temperatures

  Sodium-sulfur accumulators in several ways.

  One of them makes use of catholytes in which organic solvents dissolve sulfur in accumulators

  having solid electrolytes. This seems to give accumula-

  in the temperature range between 2000C and 2000C. But the catholytes of these systems present

  currently the disadvantages of having marginal solubilities

  for the reagents, excessive polarization and poor reversibility. These disadvantages limit flow rate capacity and cycle time, respectively. Although these accumulators actually operate at fairly low temperatures, their characteristics do not allow them to compete in a manner currently favorable with sodium-sulfur accumulators operating at high temperature. Cathodes have also been used in which the reagents are dissolved in molten salts. For example, a system uses cathodic reagents dissolved in molten salts of sodium chloride and aluminum chloride, with solid electrolytes driving the sodium ion, and anodes made of liquid sodium to form accumulators operating between 1750C and 3000C. But sulfur is not very soluble in molten sodium tetrachloroaluminate. As a result, the practical utility of this system as a battery cathode is limited. Another system using this technology is described in U.S. Patent No. 4,063,005. Sulfur 'tetravalent is the active ingredient

  cathode and is used in a chlorinated solvent

  aluminate formed from a mixture of AlCl 3 and NaCl, having molar ratios greater than 1: 1 and less than 4: 1. The tetravalent sulfur is contained in the compound SC13: AlCl4, and

  it is reversibly reduced to elemental sulfur and chlorine

  Sodium in the acid solvent of molten salts, while the elemental sodium is oxidized on the other side of a solid electrolyte driving the sodium ion. Typical temperatures of

  operation of this accumulator are approximately 2000C.

  The subject of the invention is an accumulator comprising an alkali metal anode, a cathode, a solid ionic electrolyte separating the anode and the cathode, characterized in that,

  when the battery is charged, the cathode includes a halo

  sulfonamide and a haloacid, halosulfane and haloacid having

  molar ratios between 2: 1 and 1: 2.

  It has been found that an alkali metal-sulfur accumulator having a liquid alkali metal anode, a solid electrolyte driving the alkali metal ion and active cathodic reagents including dissolved / complexed salts can be constructed.

  by liquid mineral solvents. If necessary, the

  Ionicity of the mineral liquid is increased by dissolving inorganic salts. Active cathodic reagents, or the

  catholyte, CanPrEnnentX at least one halosulfane, at least one

  acid, such as a Lewis halo acid and, where appropriate, molten sulfur (S8). In a preferred variant, the alkali metal is sodium, halosulfane. sulfur monochloride (S2ci2), and haloacid aluminum chloride (AlCM3). The molar ratio of sulfur monochloride to aluminum chloride in the catholyte is, initially or when the accumulator is charged, between 2: 1 and 1: 2. The mole fraction of sulfur in the catholyte is greater than 0% and less than about%. In another variant, the catholyte consists solely of aluminum chloride and sulfur monochloride,

  the initial molar ratio being between 2: 1 and 1: 2.

  In the attached drawings, given solely for the purpose of

example

  FIG. 1 is a sectional view of an accumulator

  sensing a variant of the invention; FIG. 2 is a graph showing the voltage of

  the accumulator in ordinates according to the capacity of this

  ci in abscissas for a constant discharge current in a first accumulator according to the invention; and FIG. 3 is a graph showing the voltage of the accumulator on the ordinate as a function of the capacity of the accumulator on the abscissa for a constant discharge current.

  in a second accumulator according to the invention.

  Fig. 1 is a sectional view of an alkali metal-sulfur accumulator shown generally at 1. A container 3 having a rim 5 provides a chamber 7 for the alkali metal anode. The cathodic mixture or catholyte is contained inside a tube 11 which is placed in the container 3. The tube 11 is ionically conductive and it is convenient to constitute it in a material conducting the alkali metal ion such that alumina and sodium. The tube It separates

  also the anode and the cathode. In tube 11, there is a collection

  13 of the current and an electrode 15. The anode of alkali metal

  lin is between the tube II and the container 3. The accumula-

  is closed by a head 17 and by flanges 19 and 21.

  Between the flanges 5 and 19 there are provided O-rings.

  Between the flanges 19 and 21 are provided-seals 27, 29 and 25 toric. External electrical contacts (not shown) go to the alkali metal electrode and electrode according to conventional and well-known techniques. The accumulator is surrounded by a heating element (not shown) and by insulating material (not shown) which are conventional and which keep the accumulator at the desired temperature. The accumulators are intended to operate at temperatures of at least 140 ° C. This temperature should only be high enough to hold the alkali metal and the catholyte

in the liquid state.

  The container 3 is conveniently made of stainless steel. The

  current collector 13 is made of graphite felt and the elec-

  trode 15 is typically made of stainless steel. Although the dimensions

  are not critical, the tube 11 typically has a

  wall thickness of between 1 mm and 2 mm and a resis-

  from about 5 ohms-cm to 3000C. The head 17 can be in

  alumina a. The flanges 19 and 21 may be stainless steel.

  The alkali metal anode will typically include a liquid alkali metal. But the anode may also have alkali metal in a solution, for example cesium,

  gallium, indium or mercury. According to a preferred variant

  The alkali metal is sodium, although potassium and lithium can also be used. Sodium is preferred because of stable ionically conductive solid electrolytes

which are known for sodium.

  The catholyte comprises dissolved salts complexed with inorganic solvents. Active reagents are halosulfane, halo acid (Lewis) and elemental sulfur melt. A Lewis acid is an acceptor of a pair of electrons. A halo acid is a compound capable of serving as an acceptor

halide ion in solution.

  The halosulfane or halosulfanes have the formula X2Sn, wherein X is a halogen selected from group VII of the Periodic Table of Elements and n is

  greater than or equal to 1 and less than or equal to 8. In a

  Preferably, X is Cl, and n is 2. This Cl2S2 compound is

  commonly referred to as sulfur monochloride. Methods of pre-

  Halosulfane pares are well known to those skilled in the art. It is

  for example, that processes for the preparation of dichloro-

  Sulfane is described in Handbook of Preparative Inorganic Chemistry, Vol. 1, pp. 270-376, Academic Press, New York, 1963. The amount of elemental sulfur in the catholyte is from about 0 mol% to about 75 mol%. The

  The initial molar ratio of halosulfane to haloacid is

taken between 2: 1 and 1: 2.

  Some of the mixtures of sulfur and halosulfane are not electrically conductive and will not solubilize the sodium chloride that forms when the chlorine is reduced. The electrical conductivity and solubility of sodium chloride are improved to acceptable levels by the halo acid of the melt. In a preferred embodiment, the halo acid is

  a chloro acid, for example aluminum chloride. Chlorine

  acid forms an ionic compound with sodium chloride,

  which is the product that is formed during the discharge.

  The elemental sulfur melts at 120C and is a mobile liquid up to about 1580C. At this temperature, it becomes extremely viscous and both electrical conductivity and mass transfer decrease. The polymerization, when sulfur is present, is prevented by the presence of halosulfane, such as sulfur monochloride. Sulfur is solubilized by forming polysulfide-like chains that are protected by chlorine atoms. Sulfur need not be present in elemental form in the catholyte. he

  may alternatively be present only in halosulfane.

  Starting materials, including sodium alumina tubes, are commercially available. We describe

  now examples of accumulators according to the invention.

  We will also review the reactions that we make the hypothesis

that they occur.

EXAMPLE 1

  The accumulator is manufactured using a catholyte con-

  in monochloride of sulfur, in aluminum chloride and

  in sulfur, in relative molar ratios of 1: 0.65: 4.56.

  The total mass is 2.35 grams. The anode is sodium and has a large excess of Na on the outside of the S-alumina tube. The accumulator is operated at temperatures of about 1550C and at a constant current of 1 mA / cm 2. Typical curves Charging and discharging are given in Figure 2, the voltage of the accumulator in volts being plotted on the ordinate, while the capacity of the accumulator in mAH is plotted on the abscissa. The charge limit is 4.1 volts. The numbers are the numbers of cycles. The scale, especially for low capacities, is compressed and some details are difficult to see. There are nevertheless three voltage stages at 3.65, 3.55 and 2.65 volts. There is also a plateau of tension

minimal at 1.5 volts.

EXAMPLE 2

  An accumulator is manufactured as described in connection with FIG. 1. It has a catholyte consisting of sulfur monochloride and aluminum chloride. The molar ratio of these two components is 1: 1.03 and the catholyte has a total mass of 7.73 grams. The anode is sodium. The accumulator is cycled at different constant currents

  and at different voltage limits, as well as

  different types. The initial open circuit voltage at 1550C is 4.21 volts. With constant current densities of 2.5 mA / cm2 and voltage limits of 1.7 volts and 4.1 volts, the total capacitance is about 2.16 ampere hours and voltage levels are observed. at 3.65, 3.55 and 2.65 volts. The accumulator is also operated in cycles between the smaller voltage limits of 2.25 volts and 3.1 volts, i.e. on the lower level. Figure 3

  is a graph giving there battery voltage in ordon-

  depending on the capacity of this one in milliamperes hours, mAH, for cycles on the lower bearing. For the cycles indicated (67 and 70), the temperature is 1750C and the current density is 2.5 mA / cm. At the 67-th

  discharge, the accumulator has a capacity of 970 mAH approximately.

  For this accumulator, as well as for that of example 1, the

  2.7 volt bearing is extremely reversible.

  It is assumed that the reactions are the following

  for the first accumulator. For the first step, that is, the 3.65-volt plateau, the reaction is thought to be Na + AlCl3 + S2C12 <SI + [(S2c2) + NaAlCl4. The reaction at the plateau of 3, 55 volts is Na + [S] + 2 (S2Cl2) + NaAlCl4 <2 [S] + NaCl + NaAlCl It is believed that the 2.7 volt step reaction is: 2Na + 2 [S] + NaCl + NaAlCl 4 2 [S] + 3NaCl + NaAlSC12 The reactions in the accumulator are similar for

the accumulator of Example 2.

  It is believed that the initial discharge, that is, 3.65 volts, removes most of the acid and gives a basic melt which is less corrosive than the initial acidic melt. Accumulators that have undergone cycles on the 2.7 volts stage have specific energies exceeding 200 WH / kg on this level. Overload protection is provided

  3.65 volts and the protection against

  discharge is provided by the bearing at 1.5 volts.

Claims (9)

  1. Electrochemical accumulator comprising an anode   alkali metal, a cathode and a separate solid ionic electrolyte   the anode and the cathode, characterized in that, when the accu-   the cathode comprises a halosulfane and a haloacid, the halosulfane and the haloacid having molars between 2: 1 and 1: 2.   Accumulator according to Claim 1, characterized   in that the alkali metal is sodium.   3. Accumulator according to claim 1 or 2, characterized   in that the electrolyte is alumina and sodium.   4. Accumulator according to claim 1, 2 or 3, characterized in that the halosulfane has the formula C12Sn, n   being greater than or equal to 1 and less than or equal to 8.   Accumulator according to Claim 4, characterized in that n is 2.   Accumulator according to one of Claims 1 to 5,   characterized in that the halo acid is a chloro acid.   Accumulator according to Claim 6, characterized   in that the chloro acid is aluminum chloride.   8. Accumulator according to one of the preceding claims   characterized in that the cathode further comprises   up to 75 mol% of elemental sulfur.   9. Accumulator according to one of the preceding claims   dentes, characterized in that it is in the unloaded state.