GB2149197A

GB2149197A - Electrochemical cell manufacture

Info

Publication number: GB2149197A
Application number: GB08426369A
Authority: GB
Inventors: Dr Alan Hooper; John Malcolm North
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1983-11-01
Filing date: 1984-10-18
Publication date: 1985-06-05
Also published as: DK518584A; FR2554278A1; GB8426369D0; DK518584D0; JPS60112261A; GB8329116D0; DE3439327A1; GB2149197B

Abstract

A solid state electrochemical cell is made by assembling together in electrical contact an anode having lithium as its active material, a polymeric electrolyte (e.g. based on poly(ethylene oxide) and LiF3CSO3), and a cathode in the form of a composite of an insertion electrode material (e.g. V6O13) or similarly active material in combination with a polymeric material. Either before or during assembly the anode, electrolyte and cathode are heated together under pressure. This removes the necessity for applying an external pressure to the cell during cycling.

Description

SPECIFICATION Electrochemical cell manufacture This invention relates to a method of making a solid state electrochemical cell by assembling together in electrical contact an anode having lithium as its active material, a polymeric electrolyte, and a cathode in the form of a a composite of an insertion electrode material or similarly active material in combination with a polymeric material.

A solid state electrochemical cell comprising a Li or Li-based anode, a lithium ion conducting polymeric electrolyte, and a cathode based on an insertion electrode material is known.

See, for example, European Patent Application Publication No 0 013 199 (corresponding to US Patent No. 4 303 748). In order to achieve high active cathode utilizations at realistic current densities, the cathode may be constructed as a composite structure comprising the insertion electrode material (active catholyte), the polymer electrolyte and, if required, an electronically conducting medium such as graphite. Examples of preferred proportions are: 20% to 70% polymer electrolyte, 30% to 80% active catholyte and, if required, 1% to 20% of an electronically conduting medium, where all percentages are by volume.

It has hitherto been believed that it is necessary to apply an external pressure (e.g.

1 to 3 Kg/cm2) during cycling in order to hold the individual cell components in intimate contact and thereby ensure good performance of such cells. Provision of the means for applying such pressure has, however, imposed constraints on cell design. A way of ameliorating the problem has now been devised; this comprises subjecting the cell components to a thermal pre-treatment under pressure.

Thus, in one aspect, the invention provides a a method of making a solid state electrochemical cell by assembling together in electrical contact an anode having lithium as its active material, a polymeric electrolyte, and a cathode in the form of a composite of an insertion electrode material or similarly active material in combination with a polymeric material, characterised in that said anode, electrolyte and cathode are heated together in intimate contact under pressure either before or during assembly of said cell.

It has been found that, if a cell made according to the invention is cycled under little or no external pressure, it has a performance comparable to that of a cell cycled under a a substantial external pressure. The invention would therefore enable simpler, more flexible and lighter encapsulation cases to be used in the manufacture of such cells. Also, complete, pre-formed cells comprising current collector, cathode, electrolyte and anode could be made for subsequent assembly into a series/parallel array as required. For example, cell components in sheet form could be fed between a pair of hot rollers to give a pre-formed cell or cells. If desired, an outer polymeric encapsulant could be incorporated to give a complete "ribbon" battery.

An example of the temperature at which the anode, cathode and electrolyte are heated together in the invention is a temperature in the range of 90 C to 1 40 C. The pressure may, for example, be of the order of a few Kg/cm2 The electrolyte may be a complex of a macromolecular material such as poly(ethylene oxide), referred to hereinafter as PEO, or poly(propylene oxide), referred to hereinafter as PPO, with a lithium salt, the anion of which may, for example, be I-. Br-, ClO4-, SCN- or F3CSO3-. The composite cathode may contain as an insertion electrode material, a material known in the art such as V60,3, V205 or TiS2, and, as a polymeric material, a material such as PEO or PPO.If required, the composite cathode may also contain an electronically conducting medium such as graphite or other forms of carbon.

The assembly of the cell may be effected by methods known in the art, for example by stacking, rolling or folding into a required configuration and containment within a suitable cell casing.

One way of carrying out the invention will now be described, by way of example only, as follows.

Example 1 Three films each of 1 cm diameter and consisting respectively of a Li metal foil of thickness 300 zm (anode), (PEO)9LiF3CSO3 of thickness 50 ym (electrolyte) and 50% PEO, 45% V6013 and 5% acetylene black of thickness 50 #m (composite cathode; all percentages by volume) were stacked and heated to C. 1 35 C under a spring load of C.

1.5 Kg/cm2 and kept at this temperature and pressure for an hour. The load was then reduced to a minimum which was estimated to be C. 100/g/cm2.

The resulting eletrochemical cell was found to exhibit no difference in performance in cycling tests in comparison with a cell made of the same components and maintained under an externally applied pressure of 1 to 3 Kg/cm2 during cycling, the comparison cell not having been subjected to the above-mentioned heat treatment.

Claims

1. A method of making a solid state electrochemical cell by assembling together in electrical contact an anode having lithium as its active material, a polymeric electrolyte, and a cathode in the form of a composite of an insertion electrode material or similarly active material in combination with a polymeric material, wherein the anode, electrolyte and cathode are heated together in intimate contact under pressure either before or during assembly of the cell.

2. A method as claimed in claim 1 wherein the heating gives rise to a temperature in the range of 90 C to 140"C.

3. A method as claimed in either of the preceding claims wherein the pressure is up to 5 Kg/cm2.

4. A method as claimed in any of the preceding claims wherein the anode, electrolyte and cathode are each in sheet form and are fed between hot rollers thereby to produce the assembled cell.

5. A method as claimed iin any of the preceding claims wherein the electrolyte is a complex of poly(ethylene oxide) or poly(propylene oxide) with a lithium salt.

6. A method as claimed in any of the preceding claims wherein the cathode comprises a composite of an insertion electrode material in combination with poly(ethylene oxide) or poly(propylene oxide).

7. A method of making a solid state electrochemical cell substantially as described herein with reference to the example.

8. A solid state electrochemical cell made by a method as claimed in any of the preceding claims.