Reverse Ragone vs. Direct Ragone plots: a comparative study for ultra-fast charging lithium-ion batteries

Abstract

A new concept of “Reverse” Ragone plots (RevRg) is introduced as opposed to the well-known “Direct” Ragone plots (DirRg). RevRg typically addresses the question of how much energy a lithium-ion battery (LIB) delivers according to the charging time. In contrast, DirRg predicts the amount of energy a LIB delivers from the initial full charge state according to the discharging time. In both RevRg and DirRg tests, the energy during discharge converts to the energy density E_d (W h kg⁻¹), whereas the charging and discharging times convert to the power densities _c and _d (W kg⁻¹), leading to the RevRg and DirRg plots. The constant current-constant voltage (CCCV) charging method and a newly developed non-linear voltammetry (NLV) charging method are used for RevRg and DirRg tests on LIB cells. It is found that the NLV method occasionally enables full charging as fast as in 10 minutes, achieving much higher E_d than CCCV does in the same charging time.