A long-life fast charging lithium-ion energy storage device

Abstract

A long cycle-life high-power energy storage device is prototyped where the fast charge capability is focused on rather than the fast discharge capability. Instead of using a supercapacitor device, the reworking and engineering of a Li-ion device is prototyped. The aim of the work was to be able to charge in a matter of minutes without excessive degradation in capacity and without a significant increase in device resistance with continued cycling. To achieve these goals, a Lithium Iron Phosphate – Lithium titanate (LFP-LTO) chemistry was selected, with a number of modifications, such as reduced electrode loadings, lowering the active material content to 70%, while increasing the conducting carbon content including carbon fibre additives. These measures overall reduce the energy density to about 42 Wh kg −1 . Other measures are incorporated to improve the cycle life and power. More than 85% capacity retention is achieved at 20C or 3-min charging. Also, a long cycle life of over 27,000 full State-of-Charge cycles at high rate 15C/5C charge/discharge with little increase in resistance (<10%) concurrent with the capacity fade to 80% is achieved with a prototype device. Consequently, at CSIRO-Australia, we have designed a long-life high-power energy storage device ideal for a range of applications.