NA/S AND LI/S BATTERIES DEVELOPED IN OTHER PROJECTS IN THIS PROGRAMME OPERATE AT 350 AND 450 DEGREES RESPECTIVELY. ALTHOUGH A LIMITED NUMBER OF THERMAL CYCLES IS POSSIBLE WITHOUT IMPAIRING THE OPERATION OF THE BATTERIES, THIS REMAINS A SERIOUS DISADVANTAGE. THEREFORE THIS PART OF THE EC PROGRAMME TRIES TO DEVELOP HIGH ENERGY AND POWER DENSITY BATTERIES AT LOWER TEMPERATURES. THE RESEARCH IS CARRIED OUT BY THE ANGLO-DANISH PROJECT (A CLOSE COLLABORATION BETWEEN FOUR BRITISH AND THREE DANISH RESEARCH INSTITUTES).

THE ANGLO-DANISH GROUP STARTED IN A FIRST PROJECT (1977-1979) WITH MATERIAL RESEARCH FOR BATTERIES. THIS RESULTED IN THE IDENTIFICATION OF SUITABLE AND PROMISING MATERIALS FOR ELECTROLYTES AND ELECTRODES. IN THE SECOND PHASE (1980-1983) COMBINATIONS OF DIFFERENT ELECTRODE AND ELECTROLYTE MATERIALS ARE BEING TESTED IN ORDER TO IDENTIFY GOOD CELLS. IN THE CELLS INVESTIGATED, ALKALI METAL ATOMS WILL GIVE UP AN ELECTRON AT THE NEGATIVE ELECTRODE, MOVE THROUGH THE SOLID ELECTROLYTE (WHICH SHOULD HAVE A HIGH ION CONDUCTIVITY) AND SETTLES IN A POSITIVE ELECTRODE, MADE OF MATERIAL WHOSE CHRYSTAL AND ELECTRONIC BAND STRUCTURE IS SUCH THAT IT CAN ACCOMMODATE ALKALI METALS (INSERTION ELECTRODE). THE POWER DENSITY OF A BATTERY INCREASES WITH THE ION CONDUCTIVITY OF THE ELECTROLYTE, AND THE ENERGY DENSITY OF A BATTERY IS LARGER WHEN MORE ALKALI METAL IONS CAN BE ACCOMMODATED IN THE POSITIVE ELECTRODE. DURING CHARGING, THE PROCESS IS RESERSED. IN THIS PROJECT SOLIDS ARE USED FOR BOTH THE ELECTRODES AND ELECTROLYTES, THIS RESULTS IN INTERFACE PROBLEMS WHICH FORM AN IMPORTANT PART OF THE R & D CARRIED OUT.

IN THE FIRST PHASE OF THE EC PROGRAMME SEVERAL INTERESTING ELECTROLYTE MATERIALS HAVE BEEN IDENTIFIED WHICH WHERE FURTHER STUDIED IN THE SECOND PHASE (1980-1983). LI3N HAS A HIGH ION CONDUCTIVITY BUT MAY BE TOO HARD MECHANICALLY TO ENABLE AN INTIMATE CONTACT WITH A SOLID ELECTRODE. THE COMPOSITE LIL/AL2O3 HAS A HIGH ION CONDUCTIVITY BUT AN EXPLANATION HAS NOT YET BEEN GIVEN. FURTHER STUDY IS THEREFORE NEEDED IN ORDER TO OPTIMIZE THE ION CONDUCTIVITY. MIXTURES OF POLYMERS AND LITHIUM SALTS GAVE GOOD ION CONDUCTIVITIES AND HAVE UNIQUE MECHANICAL PROPERTIES : THEY ARE SOFT, CAN BE FORMED IN THIN LAYERS, ARE DURABLE TOWARDS REPEATED DEFORMATION AND HAVE EXCELLENT BINDING PROPERTIES. THIS WILL ASSURE GOOD CONTACTS WITH THE ELECTRODE AND REDUCE INTERFACE PROBLEMS.

TABLE 1 : CONDUCTIVITY OF THREE ELECTROLYTES IN OHM EXP-1 CM EXP-1 AT 140 DEGREES C

POLYMERIC : 3.4 10EXP-4

LI/AL2O3 : 1.5 10EXP-3

LI3N : 5. 10EXP-3

FOR POSITIVE ELECTRODES TIS2 AND V6O13 ARE USED. THEY HAVE VERY FAVOURABLE INSERTION PROPERTIES FOR LI+. ALSO COMPOSITES OF THESE MATERIALS WITH POLY;ERS WITH A GOOD ION CONDUCTIVITY HAVE BEEN STUDIED. A COMBINATION OF AN ELECTRODE AND ELECTROLYTE WITH BOTH CONTAIN LI+ CONDUCTING POLYMERS HAS THE ADVANTAGE THAT IONS CAN EASILY MOVE FROM THE ELECTROLYTE INTO THE ELECTRODE WITHOUT INTERFACE PROBLEMS.(SUITE VOUR "RESULTS")