New additives to improve the first-cycle charge-discharge performance of a graphite anode for lithium-ion cells

We tested the effect of two new additives, cyclo hexane (CH) and 1-methyl-2-pyrrolidinone (NMP), on the cycling performance of a carbon-coated artificial graphite (AG) anode on a lithium-ion cell to investigate suppression of irreversible capacity loss of the graphite anode during the first-cycle charge. Both CH and NMP additives effectively increased the coulombic efficiency of the graphite anode during the first cycle. We attribute this phenomenon to the dissolution of the poly(vinylidene fluoride) (PVdF) binder of the AG anode due to CH or NMP addition, which improved the PVdF elasticity and reduced the contact area between the AG particles and the electrolyte. Consequently, adding CH or NMP reduced the loss of lithium ions in the first-cycle charge. Cycle-performance testing of the Li/AG half-cell indicated that we could achieve maximum discharge capacity and coulombic efficiency by applying an additive amount ranging from 2 to 5% for both CH and NMP. The cycling performance testing of the LiCoO2 half-cell suggested that these two additives also have good oxidation stability and are therefore worth applying in lithium-ion cells with graphite anodes. (c) 2005 The Electrochemical Society.