Operando Observations and First‐Principles Calculations of Reduced Lithium Insertion in Au‐Coated LiMn₂O₄

Abstract

The deposition of protective coatings on the spinel LiMn2O4 (LMO) lithium‐ion battery cathode is effective in reducing Mn dissolution from the electrode surface. Although protective coatings positively affect LMO cycle life, much remains to be understood regarding the interface formed between these coatings and LMO. Using operando powder X‐ray diffraction with Rietveld refinement, it is shown that, in comparison to bare LMO, the lattice parameter of a model Au‐coated LMO cathode is significantly reduced upon relithiation. Less charge passes through Au‐coated LMO in comparison to bare LMO, suggesting that the reduced lattice parameter is associated with decreased Li+ solubility in the Au‐coated LMO. Density functional theory calculations show that a more Li+‐deficient near‐surface is thermodynamically favorable in the presence of the Au coating, which may further stabilize these cathodes through suppressing formation of the Jahn–Teller distorted Li2Mn2O4 phase at the surface. Electronic structure and chemical bonding analyses show enhanced hybridization between Au and LMO for delithiated surfaces leading to partial oxidation of Au upon delithiation. This study suggests that, in addition to transition metal dissolution from electrode surfaces, protective coating design must also balance potential energy effects induced by charge transfer at the electrode‐coating interface.

High-Rate Spinel LiMn2O4 (LMO) Following Carbonate Removal and Formation of Li-Rich Interface by ALD Treatment

“…We propose that Li is pushed away from the external LMO surface upon TMA exposure due to electrostatic repulsion from Al 3+ incorporated into the surface of the LMO, as well as positively charged −CH 3 groups bound to surface O . This is analogous to the observation of positively charged Au coatings leading to lithium depletion at the LMO surface Figure a presents DFT + U -calculated Li vacancy formation energy vs depth into the LMO(111) surface.…”

“…44 This is analogous to the observation of positively charged Au coatings leading to lithium depletion at the LMO surface. 46 Figure 5a presents DFT + U-calculated Li vacancy formation energy vs depth into the LMO(111) surface. The Li vacancy formation energy in pristine LMO (black data series in Figure 5a) is predicted to be ∼3.9 eV in the bulk and 4.4 eV at the LMO surface (depth of ∼0 Å in Figure 5a).…”

Tailoring Interfaces in Solid-State Batteries Using Interfacial Thermochemistry and Band Alignment

“…These effects have been demonstrated recently, where indirect decomposition reaction pathways can lead to larger stability windows than predicted by bulk thermodynamics . Previous computational studies have analyzed the stability of solid electrolyte surface phases, − and the construction of solid/solid interfacial models have been applied in previous studies of various energy storage systems. ,,− In concert with experimental characterization, such computational analyses can be used to gain a more comprehensive understanding of interfacial reactivity in solid-state batteries and develop rational strategies to control it.…”

“…Furthermore, X-ray photoelectron spectroscopy experiments have shown that LLTO is unstable against Li metal and cyclic voltammetry experiments indicated that LLTO undergoes a reduction reaction with lithium around 1.5–1.7 V vs Li/Li + . − These material instabilities at low voltages make the Li/LLTO interface a compelling model system to understand and control aspects of solid/solid interfacial chemistry. In addition to an understanding of the bulk LLTO thermochemistry, analysis of surface and interfacial thermodynamics and metal–semiconductor band alignment ,,, can aid in forming a more comprehensive understanding of the driving forces for interfacial decomposition.…”

The effect of niobium doping on lithium manganese oxide surfaces, LiMn2-xNbxO4: DFT study

“…However, the spinel LiMn 2 O 4 -based Li-ion batteries suffer from capacity fading mainly due to manganese (Mn 2+ ) ion dissolution (Hunter, 1981;Park et al, 2011), electrolyte oxidation, and the formation of Jahn-Teller distorted Li 2 Mn 2 O 4 tetragonal phases (Arora et al, 1998;Dai et al, 2013) upon cycling. It's believed that manganese dissolution is the major cause of deterioration since Jahn-Teller distortion and electrolyte oxidation can be controlled by cycling at restricted voltages (Bassett et al, 2019;Xia et al, 1997).…”