EFFECT OF ELECTRODE POROSITY ON THE PERFORMANCE OF NATURAL BRAZILIAN GRAPHITE-ELECTRODES

Natural Brazilian graphite has been investigated as a reversible Li+-i ntercalating electrode for lithium-ion cells. Its performance is great ly influenced by the electrode preparation technique. A short compacti ng time (1 s or less), when pressing the powders, increases the specif ic capacity because the porosity remains sufficiently high. Low pressu res (< 200 kg/cm(2)), which create higher porosities, give limited cap acities due to poor inter-particle electrical contact. Excellent resul ts have been obtained by substituting pressed powders with slurry-deri ved electrodes. In this case, an electrode porosity of 25-30% can be m easured from compacting pressures between 20 and 200 kg/cm(2). With th is technique, it is possible to obtain: (i) an efficiency of 85% in th e first cycle; () a high rate capability, and (iii) a high and constan t capacity upon cycling, i.e. 340 mAh/g at 0,4 mA/cm(2). Cycling produ ces an increase in graphite surface area, a phenomenon which deserves a closer attention in view of possible safety problems.