Distinguishing Li⁺ Charge Transfer Kinetics at 1. NCA/Electrolyte and Graphite/Electrolyte Interfaces and 2. NCA/Electrolyte and LFP/Electrolyte Interfaces in Li-ion Cells

Abstract

In examining the Li + charge transfer kinetics at the graphite anode and the lithium nickel cobalt aluminum oxide, LiNi 0.80 Co 0.15 Al 0.05 O 2 (NCA), cathode in a complete cell, we found that the activation energy, E a , for the charge transfer at the graphite/electrolyte interface is about 68 kJ/mol, which is consistent with the recently reported values. However, the E a for the charge transfer at the NCA/electrolyte interface is about 50 kJ/mol, which is lower than that at the graphite anode. With desolvation as the predominate step for limiting the kinetics and both of the electrodes were subject to the same electrolyte, the difference in E a suggests that the E a is influenced greatly with respect to the nature of electrode materials and their associated SEIs. This is further confirmed by the examination of the LiFePO 4 (LFP)/electrolyte and the graphite/electrolyte interfaces using a LFP/graphite complete cell.

Li+-Desolvation Dictating Lithium-Ion Battery’s Low-Temperature Performances

“…It has been well established that the energy barrier or resistance determines how fast and how much Li + can be extracted out or intercalated back into the electrodes. 20,22 A complete pathway of Li + transfer during a discharge process in a graphite∥NCA full cell can be broken down into the following steps (as shown in Figure 2). All of these steps will possibly affect the discharge capacity at low temperatures.…”

“…The overall cell resistance consists of the bulk electrolyte (R b ), SEI (R SEI ), and charge transfer (R ct ), 22 among which R ct is considered as the most significant factor affecting the lowtemperature performance of the batteries, 17,18 and Xu et al suggested that the desolvation resistance of Li + before it enters the interlayer of materials (R desolvation ) is a main section of R ct . 20 Having excluded the Li + migration across SEI and its solid− solid diffusion as the limiting factors that affects the lowtemperature performance, the stripping of a solvated Li + (step 7) becomes the only possible main energy-consuming step at low temperature.…”

Interfacial Structure and Dynamics of the Lithium Alkyl Dicarbonate SEI Components in Contact with the Lithium Battery Electrolyte

“…Further separate analysis of the positive and negative electrodes indicated significant differences in both the prefactors and the activation energies of the interfacial impedance. 23,24 Specifically, the interfacial impedance at the graphite anode was found 23,24 to have an activation energy of 0.64 eV, which is 0.14 eV higher than the activation energy for the LiNi 0.8 Co 0.15 Al 0.05 O 2 cathode side. The activation energy for the interfacial impedance was also dependent on the electrolyte composition 14,25−29 as well as on the cathode and anode-surface modification.…”

Molecular Dynamics Simulations and Experimental Study of Lithium Ion Transport in Dilithium Ethylene Dicarbonate

“…11 Interfacial resistance at the anode side with the thick SEI and a cathode with a much thinner passivation layer were also reported to have different activation energies. 10,12 For example, the interfacial impedance at the graphite anode was found 10,12 to have an activation energy of ΔE = 64 kJ/mol, which is noticeably higher than the activation energy for the LiNi 0.80 Co 0.15 Al 0.05 O 2 cathode side (ΔE = 50 kJ/mol). These results suggest that the chargetransfer process and diffusion through the SEI formed on the anode might influence low-temperature battery power density to a larger extent than the cathode passivation layer.…”

“…9 Battery impedance is typically the sum of the bulk electrolyte resistance (R bulk ), resistance of the SEI (R SEI ), and a charge transfer resistance (R ct ) that is associated with the Li + desolvation from the electrolyte or SEI and intercalation into the electrode and electrode resistance. 10 The electrolyte resistance is usually associated with the high frequency of the impedance spectrum; R ct is associated with the lowest frequency of the impedance spectrum; while R SEI is attributed to the intermediate frequency processes. Analysis of the temperature dependence of the impedance spectra indicated the following order to the activation energies associated with these resistance contributionsΔE(R ct ) > ΔE(R SEI ) > ΔE(R bulk ) with the charge transfer resistance dominating at low temperatures and limiting cell power capabilities.…”