Cycling performance of low-cost lithium ion batteries with natural graphite and LiFePO4

Low-cost lithium ion batteries with LiFePO4 and natural graphite were cycled in 1 M LiBF4 + EC/DEC at 100% depth of discharge and 25 degreesC in order to investigate cycle performance and diagnostics for capacity fading. The 12 cm(2) pouch cell showed 65% of capacity retention at 5C compared to that at C/25. The cell showed 80% of initial capacity after 80 cycles and its capacity fade rate was 11.3 muA h/cycle during constant C/2 cycling. In hybrid pulse power characterization, the discharge resistance of this cell was higher than commercial graphite/LiCoO2 cell because of low lithium diffusivity in LiFePO4. Slow rate cycling in pouch full cell showed almost 40% of capacity fade after 100 cycles. However, the 100-cycled cathode and anode did not show any capacity fading in half-cell test after disassembling full cell, suggesting that capacity fade in the full cell is caused by loss of cycleable Li. (C) 2003 Elsevier Science B.V. All rights reserved.