The stability of the SEI layer, surface composition and the oxidation state of transition metals at the electrolyte–cathode interface impacted by the electrochemical cycling: X-ray photoelectron spectroscopy investigation

Abstract

The stability of the valence state of the 3d transition metal ions and the stoichiometry of LiMO(2) (M = Co, Ni, Mn) layered oxides at the surface-electrolyte interface plays a crucial role in energy storage applications. The surface oxidation/reduction of the cations caused by the contact of the solids to air or to the electrolyte results in the blocking of the Li-transport through the interface that leads to the fast batteries deterioration. The influence of the end-of-charge voltage on the chemical composition and the oxidation state of 3d transition metal ions, as well as the stability of the solid-electrolyte interface formed during the electrochemical Li-deintercalation/intercalation of the LiCoO(2) and Li(Ni,Mn,Co)O(2), have been investigated by X-ray photoelectron spectroscopy. While the chemical composition of the solid-electrolyte interface is similar for both layered oxide surfaces, the electrochemical cycling to some critical voltage values leads to the disappearance of the interface. By the analysis of the shape of the 2p and 3s photoelectron emissions we show that the formation of the solid-electrolyte interface layer correlates with the partial reduction of the trivalent Co ions at the electrolyte-LiCoO(2) interface and the amount of the Co(2+) ions is increased as the solid-electrolyte interface vanishes. In contrast, the Mn(4+), Co(3+) and Ni(2+) ions of the Li(Ni,Mn,Co)O(2) are stable at the interface under the electrochemical cycling to higher end-of-charge voltage. A correlation between deterioration of the LiCoO(2) and Li(Ni,Mn,Co)O(2) batteries and the change of electronic structure at the surface/interface after the electrochemical cycling has been found. The dissolution of the solid-electrolyte interface layer might be the reason for the fast deterioration of the Li-ion batteries.

Olivine-LiNiPO4Thin Films: Chemical Compatibility with Liquid Electrolyte and Interface Stability at High Potential

“…SEI dissolution accompanied by Co 3+ ion reduction was already observed in the NMC layered cathode material charged to a high potential, which was explained by the lattice expansion followed by the weakening and breaking of the chemical bonds of organic molecules constituting the SEI layer. 23 One plausible reason for the different sustainability of the LNP-electrolyte interfaces at a high potential is assigned to the surface defects of the pristine LNPs, the amount of which, as well as their nature are defined by the film preparation conditions. Among possible non-stoichiometric phases in olivine-LNP films grown at lower temperatures are the inclusions of amorphous phase or/and phosphor-oxygen groups, which do not belong to the olivine structure.…”

Utilization of heavy alkali dopants as a beacon to study the cathode electrolyte decomposition layer in lithium-ion batteries

“…Thẽ 56 eV fitted peak represents LiF and LiP x F y O z (55.9 eV) [36], and possibly LiCl (56.3 eV) [37]. After 60 s of ion milling, a signal appears at approximately 54.5 eV which is characteristic of lattice lithium in n-LiCoO 2 [36]. Figure 2d is the depth profile for the Cs 3d 5/2 and 3d 3/2 peaks near 725 and 738 eV, respectively.…”

“…Figure 2c shows the lithiated species identified by the Li 1 s (~56-54.5 eV) peaks along with the Co 3p (~61 eV). Thẽ 56 eV fitted peak represents LiF and LiP x F y O z (55.9 eV) [36], and possibly LiCl (56.3 eV) [37]. After 60 s of ion milling, a signal appears at approximately 54.5 eV which is characteristic of lattice lithium in n-LiCoO 2 [36].…”

Laser ablation of electrodes for Li-ion battery remanufacturing

“…10a, b). The peaks can be attributed to the presence of LiF and LiPF 6 on surface of the cathode [41,42]. For the XPS survey of postlaser-treated cathode, the plots show decrease in the peaks for both P and F. P peak shifted to 132 eV while F peaks at 684 eV.…”

“…11a, b), the peaks originate from Li salt of organic carbonates [41][42][43]. The high binding energy peaks found in the XPS of O and C are results of polymeric compounds.…”