Strain-Induced Stabilization of Charged State in Li-Rich Layered Transition-Metal Oxide for Lithium-Ion Batteries

Abstract

Li-rich layered oxide (LLO) is a promising cathode material for lithium-ion batteries because of its large capacity in comparison with conventional layered rock-salt structure materials. In contrast to the conventional materials, it is known that LLO of 3d transition metal has a nanodomain microstructure; however, roles of each domain and effects of strain, induced by the microstructure, on electrode properties are still unclear. In this study, the influence of the strain on an electronic structure is studied to elucidate the stabilization mechanism of LLO material Li­[Li0.2Ni0.2Mn0.6]­O2 in the charged state by using resonant X-ray diffraction spectroscopy (RXDS), X-ray diffraction, and X-ray absorption spectroscopy (XAS) in combination with ab initio calculation. RXDS of a superlattice peak and XAS at Mn and Ni K-edges unveil that this material has a microstructure consisting of Mn-rich and Ni-rich domains, whose structures are similar to Li2MnO3 and LiNiO2, respectively. In the Ni-rich domain, trigonal distortion in the NiO6 octahedral cluster is induced by an elastic constraint due to the microstructure. Hybridization between oxygen p- and nickel d-orbitals is enhanced by the distortion as revealed both by XAS and by ab initio calculation, accounting for stabilization of the charged state by alleviating the direct hole formation on oxygen p-orbital that usually destabilizes the charged material.

Synergistically Enhanced Electrochemical Performance of Ni-rich Cathode Materials for Lithium-ion Batteries by K and Ti Co-modification

“…19,20 The corresponding potential difference (ΔV) between the anodic and cathodic peak results from the formation of a solid electrolyte interface (SEI) film or the occurrence of side reactions on the electrode surfaces, which represents the degree of electrochemical reversibility. 48 The value of ΔV at 3.8 V for NCM-K-Ti is 0.172 V, lower than those for NCM-K, NCM-Ti. and NCM-0 (0.234, 0.195, and 0.277 V), hinting that the reactivity and reversibility of NCM could be improved by K and Ti comodification (Table S2).…”

“…Although the diffraction lines show their layered structures, the diffraction peaks for both NCM-0 and NCM-K-Ti gradually broaden and decrease with the increase of cycles. Compared with NCM-K-Ti, the peaks of pristine NCM-0 weaken more, indicating that the NCM-0 electrodes suffer from larger degrees of structural damage and particles pulverization. , The (003) peaks of both samples move toward lower diffraction angles, but the slip angle of NCM-K-Ti is 0.06°, much smaller than 0.22° of NCM-0 from the 50th to 100th cycle. The results suggest that NCM-K-Ti electrodes possess better structural stability during Li + deintercalation/intercalation process.…”

“…As shown in Figure , all CV curves possess quite similar profiles with three pairs of peaks, i.e ., a large anodic peak at ∼3.8 V, and two small anodic peaks at ∼4.05 and ∼4.25 V during the delithiation processes, corresponding to the large cathodic peak at ∼3.7 V and other two small cathodic peaks at ∼3.95 V and ∼4.2 V during the lithiation processes. The large oxidation peak at 3.8 V is attributed to the oxidation of Ni 2+ to Ni 3+ and/Ni 4+ , and the small pair of peaks at 4.05 and 4.25 V are caused by the phase transition of M to H2 and H2 to H3 respectively. , The corresponding potential difference (Δ V ) between the anodic and cathodic peak results from the formation of a solid electrolyte interface (SEI) film or the occurrence of side reactions on the electrode surfaces, which represents the degree of electrochemical reversibility . The value of Δ V at 3.8 V for NCM-K-Ti is 0.172 V, lower than those for NCM-K, NCM-Ti.…”

“…Thermal stability of NCM materials will be significantly improved by comodification of K and Ti, which may delay the formation of cubic spinel phase and reduce the release of oxygen from the host structure in delithiated Ni-rich compounds. 22,48 To further illustrate the structural stability, XRD measurements of NCM-0 and NCM-K-Ti after different cycles at 1 C under a cutoff voltage of 4.35 V were carried out as shown in Figure S8. Although the diffraction lines show their layered structures, the diffraction peaks for both NCM-0 and NCM-K-Ti gradually broaden and decrease with the increase of cycles.…”

Strain analysis from M-edge resonant inelastic X-ray scattering of nickel oxide films

“…In particular, epitaxial strain between the nano-layers and substrate surfaces provides a powerful strategy to manipulate (atomic-scale) physical properties by shortening or extending their chemical bonds via lattice-mismatch, commonly referred to as strain engineering. This strain engineering has become a key tactic for improving material properties of graphene and similar materials, 1,2 high-T c superconductors, 3 energy storage materials, 4 quantum materials 5 and solid heterogeneous (electro-)catalysts. [6][7][8][9][10] Lattice strain is typically measured through the analysis of lattice peak positions measured with hard X-ray diffraction.…”