Kristian Nikolowski

Changes in the crystal and electronic structure of LiCoO2 and LiNiO2 upon Li intercalation and de-intercalation

Li(x)CoO(2) and Li(x)NiO(2) (0.5 < x < 1) are used as prototype cathode materials in lithium ion batteries. Both systems show degradation and fatigue when used as cathode material during electrochemical cycling. In order to analyze the change of the structure and the electronic structure of Li(x)CoO(2) and Li(x)NiO(2) as a function of Li content x in detail, we have performed X-ray diffraction studies, photoelectron spectroscopy (PES) investigations and band structure calculations for a series of compounds Li(x)(Co,Ni)O(2) (0 < x < or = 1). The calculated density of states (DOS) are weighted by theoretical photoionization cross sections and compared with the DOS gained from the PES experiments. Consistently, the experimental and calculated DOS show a broadening of the Co/Ni 3d states upon lithium de-intercalation. The change of the shape of the experimental PES curves with decreasing lithium concentration can be interpreted from the calculated partial DOS as an increasing energetic overlap of the Co/Ni 3d and O 2p states and a change in the orbital overlap of Co/Ni and O wave functions.

Thermal Stability of LiCoPO4 Cathodes

The thermal stability of LiCoPO 4 cathodes charged to different lithium contents was studied by synchrotron diffraction and differential thermal analysis. Both olivine-like phases Li Z COPO 4 (z = 0.6) and CoPO 4 appearing during the delithiation of LiCoPO 4 are unstable upon heating, and decompose readily in the range 100-200°C. The decomposition of lithium-poor phases leads to gas evolution and the crystallization of CO 2 P 2 O 7 . The role of carbon present in the electrochemically delithiated samples is discussed. The significantly lower stability of charged LiCoPO 4 in comparison with LiFePO 4 is a serious challenge for the application of this material in rechargeable Li-ion batteries.

Synchrotron Diffraction Study of Lithium Extraction from LiMn0.6Fe0.4PO4

Electrochemical lithium extraction from LiMn0.6Fe0.4PO4 was revealed to proceed through two two-phase regions in contrast to the mechanism earlier reported. All phases appearing during charging of the cell have the same olivine-like structure with different cell parameters.

Advances in in situ powder diffraction of battery materials - a case study of the new beamline P02.1 at DESY Hamburg

A brief review of in situ powder diffraction methods for battery materials is given. Furthermore, it is demonstrated that the new beamline P02.1 at the synchrotron source PETRA III (DESY, Hamburg), equipped with a new electrochemical test cell design and a fast two-dimensional area detector, enables outstanding conditions for in situ diffraction studies on battery materials with complex crystal structures. For instance, the time necessary to measure a pattern can be reduced to the region of milliseconds accompanied by an excellent pattern quality. It is shown that even at medium detector distances the instrumental resolution is suitable for crystallite size refinements. Additional crucial issues like contributions to the background and available q range are determined.

A Swagelok‐type in situ cell for battery investigations using synchrotron radiation

An in situ cell designed for synchrotron X-ray diffraction during electrochemical cycling of battery materials is presented. The cell operates in transmission mode and can be oscillated with the dedicated sample holder to improve powder statistics. It allows fast data acquisition, provides hermetic sealing and high-quality diffraction data, and is easy to assemble, since a commercially available Swagelok junction is used as the cell body. Diffraction data from the cycling of a battery using LixNi0.8Co0.2O2 (0 ≤ x ≤ 1) as the cathode material are presented.

Revisiting the layered LiNi0.4Mn0.4Co0.2O2: a magnetic approach

Layered LiNi0.4Mn0.4Co0.2O2 has been synthesized by the co-precipitation method, and the structural, electrochemical and magnetic properties were comprehensively studied by Rietveld analysis, charge–discharge potential profiles, X-ray photoelectron spectroscopy, and dc and ac susceptibilities. The material shows initial discharge capacities of 166 and 206 mA h g−1 in potential windows of 2.5–4.4 V and 2.5–4.6 V, respectively, and a better capacity retention of 95% at 2.5–4.4 V after 50 cycles. The effective paramagnetic moment is calculated to be 3.02(3) μB/f.u. by fitting to the Curie–Weiss law, which is consistent with the averaged value, based on the specific contributions, as quantified by an analysis of the X-ray photoelectron spectroscopy data. The dc magnetization curves show irreversibility and spin freezing behavior at 77 K and 18 K, respectively. The evolution of irreversibility temperature under different applied fields indicates a spin-glass-like transition. The ac susceptibility data and the fitting using the frequency dependent spin-freezing temperatures also confirm this magnetic transition. In comparison with the previous results, the co-precipitation prepared sample shows a big difference in the magnetic parameters, coming from the different microscopic exchange interactions or the formation of a different scale of spin clusters, which is sensitive to the preparation procedure.

In Situ XRD of Highly Charged and Discharged Li x Ni0.8Co0.2O2 ( x close to 0)

Lithium has been electrochemically extracted and inserted from LixNi0.8Co0.2O2 (0{less than or equal to}xLi{less than or equal to}1) using a dedicated electrochemical cell. The behavior of this cathode material for lithium batteries was studied by in situ-X-ray diffraction using synchrotron radiation and analyzed by Rietveld refinement. Besides the accurate determination of the lattice parameters during cycling, an anisotropic broadening of specific reflections, most pronounced around xLi=0.1, is observed and attributed to reversible microstructural changes at this high degree of lithium extraction.

Fatigue processes in commercial LiCoO 2 batteries: In situ neutron diffraction and electrochemical study

In situ high-resolution neutron powder diffraction along with electrochemical analysis was used to study fatigue processes in commercial LiCoO2 (18650-type) batteries. The electrochemical and structural behavior of cathode and anode materials in fully charged and discharged states has been studied for cells exhibiting different cycling at 25°C and 50°C. High-resolution neutron powder diffraction leads us to observe simultaneous changes in LiCoO2 cathode and graphitic anode, which are related to lithium de-/intercalation processes during the battery operation. Detailed features of the battery organization and details of its evolution on a micrometer scale have been visualized using neutron radiography and tomography.