Crystal structure evolution via operando neutron diffraction during long-term cycling of a customized 5 V full Li-ion cylindrical cell LiNi 0.5 Mn 1.5 O 4 vs. graphite

International audienceDisordered spinel LiNi0.5Mn1.5O4 (d-LNMO) is the cathode material of choice for next generation batteries based on 5 V systems. Unfortunately, once cycled under real conditions i.e. in a full-cell configuration (versus graphite), it displays a quite pronounced fading of the electrochemical performance, even under optimized cycling conditions, and about a half of the specific charge is ‘lost’ after 500 cycles. Thus, we intensively investigated the crystal structure evolution of a full-cell d-LNMO vs. graphite by means of operando neutron diffraction. For this purpose, a new cylindrical electrochemical cell was designed, suitable for operando neutron diffraction studies and allowing for precise Rietveld refinement analyses. During the first cycle, lithium content in the electrode materials (graphite and d-LNMO) could be determined, thus, allowing an estimation of the lithium consumption in side reactions. The neutron diffraction data obtained after long-term cycling (100 cycles) show that the fading of the electrochemical performance can be attributed to an insufficient amount of lithium in the system, which presumably is consumed by side reactions since no structural damage was observed in the positive and negative electrodes

Stroboscopic neutron diffraction applied to fast time-resolved operando studies on Li-ion batteries (d-LiNi 0.5 Mn 1.5 O 4 vs. graphite)

International audienceThe high penetration ability of neutrons and dramatic character of crystal structure modifications occurring in battery materials during electrochemical cycling make neutron powder diffraction an obvious method to study the reaction mechanisms in rechargeable cells. Unfortunately, a typical balance of the available intensities of neutron beams and the amounts of active materials in commercial battery systems often limits the area of study to slow cycling rates or forces the use of too large amounts of materials, which in turn is incompatible with reliable electrochemistry. Herein we present a practical implementation of stroboscopic operando neutron diffraction to allow studying the structural changes occurring in a battery composed of a next generation 5 V disordered LiNi0.5Mn1.5O4 spinel cathode versus graphite during repetitive cycles at incredibly fast rates (up to 15C). We demonstrate that the graphite lithiation mechanisms at fast rates are different from those observed at reasonable rates. In particular, the earlier appearance and disappearance of lithiated graphite stages 1 and 2 in the charge and discharge processes, and also the suppression of the formation of the LiC18 phase can be associated with cell degradation at fast charge rates. This result is in agreement with the theoretical ‘shrinking-annuli’ model developed to simulate the electrochemical processes occurring during graphite lithiation at fast rates

Versatile Approach Combining Theoretical and Experimental Aspects of Raman Spectroscopy To Investigate Battery Materials: The Case of the LiNi_0.5Mn_1.5O₄ Spinel

We report a correlation between experimental and theoretical Raman spectra. Using density functional theory calculations, we resolve the last bottleneck in the understanding of Raman spectra by simulating and coupling the Raman vibrational modes to their calculated intensities of the promising 5-V LiNi_0.5Mn_1.5O₄ spinel cathode. The origin of the simulated Raman intensities is elucidated thanks to a careful analysis of the electronic structure performed on the vibrating atoms in a solid compound. This novel approach leads to correctly assigning the main vibrational modes to Li–O bond motions that are indirectly linked to Mn or Ni (or both), contrary to what has been reported in the literature so far. This methodology will lead to a better understanding of the reaction mechanisms of active materials used for energy applications

Versatile Approach Combining Theoretical and Experimental Aspects of Raman Spectroscopy To Investigate Battery Materials: The Case of the LiNi_0.5Mn_1.5O₄ Spinel

We report a correlation between experimental and theoretical Raman spectra. Using density functional theory calculations, we resolve the last bottleneck in the understanding of Raman spectra by simulating and coupling the Raman vibrational modes to their calculated intensities of the promising 5-V LiNi_0.5Mn_1.5O₄ spinel cathode. The origin of the simulated Raman intensities is elucidated thanks to a careful analysis of the electronic structure performed on the vibrating atoms in a solid compound. This novel approach leads to correctly assigning the main vibrational modes to Li–O bond motions that are indirectly linked to Mn or Ni (or both), contrary to what has been reported in the literature so far. This methodology will lead to a better understanding of the reaction mechanisms of active materials used for energy applications

Operando Neutron Powder Diffraction Using Cylindrical Cell Design: The Case of LiNi_0.5Mn_1.5O₄ vs Graphite

In order to follow the structural changes correlated to the evolution of the lithium content in high voltage battery systems (based on a disordered LiNi_0.5Mn_1.5O₄ (d-LNMO) and a graphite electrode), we developed a new cylindrical cell suitable for operando neutron diffraction measurements. The cell, containing two grams of electroactive materials, is able to cycle at a fast rate (1C) with reliable electrochemical performance. The operando neutron diffraction measurements revealed the evolution of the lattice parameters of both the d-LNMO and graphite phases, notably showing the transitions between graphite lithiation stages. Furthermore, as a result of Rietveld refinements, the lithium consumption could be attributed mainly to the formation of a solid electrolyte interphase (SEI) layer on the graphite surface. This approach provides important insights helping to optimize the loading of the electroactive materials in batteries, especially for high voltage systems in which side reactions and lithium consumption can occur during cycling