The cation positions in dehydrated synthetic faujasite (zeolite 13Y, with a unit cell content approximately represented by NasTSiissA^Osst, Fd3m, a0 = 24.71 ± 0.02 A) and the analogous Kand Ag-exchange compounds (K57SÍ135AI57O384, 0 = 24.80 ± 0.02 A; Ag57Sii35-AI57O384, Oo = 24.85 ± 0.03 A) were determined with X-ray powder diffraction data by means of three-dimensional Fourier syntheses and the structures were refined by least squares. The cations Na+, K+, and Ag+ were found to occupy three different kinds of sites (I, II, III) on the threefold symmetry axes of the faujasite framework structure. These sites are associated with two sets of tetrahedrally arranged (Si, Al)eOe rings which with additional oxygen atoms define the "sodalite unit." Site I approaches, from outside of the sodalite unit, the center of the six-membered ring that faces the large absorption cavity of the structure; site II, from inside of the sodalite unit, approaches the second sixmembered ring which faces the center of symmetry. Site III is at the center of symmetry. A cation in site I or II has three nearest oxygen neighbors forming a regular triangle; in site III it is surrounded by six equidistant oxygens forming a moderately distorted octahedron. In all cases, site II has the smallest occupancy factor. The occupancy factor is close to unity for site I with Na+ and K+ and for site III with Ag+. For site I, the distances Na-0 2.33 A, K-0 2.72 A, and Ag-0 2.32 A were observed.

In this paper we introduce a pseudo two-dimensional (P2D) model for a common lithium-nickel-cobalt-manganese-oxide versus graphite (NCM/graphite) cell with solid electrolyte interphase (SEI) growth as the dominating capacity fade mechanism on the anode and active material dissolution as the main aging mechanism on the cathode. The SEI implementation considers a growth due to non-ideal insulation properties during calendar as well as cyclic aging and a re-formation after cyclic cracking of the layer during graphite expansion. Additionally, our approach distinguishes between an electronic (σ SEI ) and an ionic (κ SEI ) conductivity of the SEI. This approach introduces the possibility to adapt the model to capacity as well as power fade. Simulation data show good agreement with an experimental aging study for NCM/graphite cells at different temperatures introduced in literature. © The Author Lithium-ion batteries are one of the most promising candidates for energy storage in future stationary storage systems and electric vehicles.1-3 Enormous research efforts have been conducted to get a thorough understanding of the system "lithium-ion cell" and to further develop it for higher energy and power density, higher safety standards as well as longer cycle life. 4 The aging behavior of lithium-ion batteries has been a focus issue of battery research since the introduction of lithium-ion cells by Sony in 1991. 5 Reviews by Agubra et al., 6,7 Arora et al., 8 Aurbach et al., 9,10 Birkl et al., 11 Broussely et al., 12 Verma et al. 13 and Vetter et al. 14 are just a few examples of the extensive literature regarding aging behavior. Commonly accepted and experimentally verified aging phenomena as mentioned in the previously cited literature are electrolyte decomposition leading to solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) growth, solvent co-intercalation, gas evolution with subsequent cracking of particles, a decrease of accessible surface area and porosity due to SEI growth, contact loss of active material particles due to volume changes during cycling, binder decomposition, current collector corrosion, metallic lithium plating and transition-metal dissolution from the cathode. The listed aging mechanisms can be assigned to three different categories that are a loss of lithium-ions (LLI), an impedance increase and a loss of active material (LAM). 12,[15][16][17][18] The LLI is synonymous to a decrease in the amount of cyclable lithium-ions as they are trapped in a passivating film on either of the electrodes or in plated metallic lithium. Due to the growth of the passivating layers and/or the formation of rock-salt in the cathode (residue of the cathode active material after transition-metal dissolution), kinetic transport of lithium-ions through those inactive areas is limited and results in an impedance rise. An LAM can be caused by the dissolution of transition-metal-ions from the cathode bulk material, changes in the electrode composition and/or changes in crystal structure of the a...

We present an electrochemical aging model with solid electrolyte interphase (SEI) formation, SEI re-formation due to cracking of the layer during graphite expansion, lithium plating when the potential of the negative electrode becomes negative vs Li/Li+, and subsequent lithium stripping once the potential becomes positive again. The model considers the transition from an early stage, linear to a later stage, nonlinear capacity fade. While SEI re-/formation define linear aging, the onset and slope of nonlinear aging is simulated based on the ratio of reversibly and irreversibly plated lithium. With ongoing aging, more lithium is plated irreversibly so that less lithium is stripped. The simulation data agree very well with experimental data on commercial 18 650-type lithium-nickel-cobalt-manganese-oxide vs graphite (NCM/C) cells.

In this paper, we present an aging study of commercial 18650-type C/LiNi 0.33 Mn 0.33 Co 0.33 O 2 lithium-ion cells. The test procedure comprises varying charging currents, discharging currents and resting times between cycles. The cells show a nonlinear capacity fade after a few hundred equivalent full cycles, if cycled with a standard charging and discharging rate of almost 1C, and different resting times. By increasing the discharging current or decreasing the charging current, the lifetime improves and results in a linear capacity fade. The neutron diffraction experiment reveals a loss of lithium inventory as the dominant aging mechanism for both linearlyand nonlinearly-aged cells. Other aging mechanisms such as the structural degradation of anode or cathode active materials, or the deactivation of active materials, cannot be confirmed. With ongoing aging, we observe an increasing capacity loss in the edge area of the electrodes. Whereas the growth of the solid electrolyte interphase defines the early stage, linear aging, marginal lithium deposition is supposed to cause the later stage, nonlinear aging. Capacity recovery caused by lithium stripping and chemical intercalation is shown to be dependent on the cell's state of health.

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Inhomogeneity within lithium-ion battery modules can occur due to variations in capacity and impedance of the connected cells as well as due to thermal gradients or cell connector design. We present a model for describing xSyP battery modules during operation, which is able to study these effects. The multidimensional multiphysics model includes a physicochemical model describing the electrochemical behavior of each cell. The electrical model accounts for the conservation of electric charge and energy between the cells to reach electrical consistency according to the respective module topology and cell interconnections. The model is capable of investigating the influence of defective and asymmetric cell connectors on the inhomogeneity of module operation. To evaluate this electrical influence, the observed inhomogeneities are compared to the influence of thermal gradients between the cells. The resulting inhomogeneous current distribution is presented for a module of two parallel connected lithium iron phosphate-graphite cells under constant current discharge operation for variations in cell capacity, cell impedance and ambient temperature at different module contact scenarios. From the observed impact of both, electrical and thermal variations between parallel connected cells, a matching strategy is derived and discussed which can enhance a module's performance during e.g. second life applications.

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