The impact of calendering process on the geometric characteristics and electrochemical performance of LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC) electrode was investigated in this study. The geometric properties of NMC electrodes with different calendering conditions, such as porosity, pore size distribution, particle size distribution, specific surface area and tortuosity were calculated from the computed tomography data of the electrodes. A synchrotron transmission X-ray microscopy tomography system at the Advanced Photon Source of the Argonne National Laboratory was employed to obtain the tomography data. The geometric and electrochemical analysis show that calendering can increase the electrochemically active area, which improves rate capability. However, more calendering will result in crushing of NMC particles, which can reduce the electrode capacity at relatively high C rates. This study shows that the optimum electrochemical performance of NMC electrode at 94:3:3 weight ratio of NMC:binder:carbon black can be achieved by calendering to 3.0 g/cm 3 NMC density.

To investigate geometric and electrochemical characteristics of Li ion battery electrode with different packing densities, lithium cobalt oxide (LiCoO 2 ) cathode electrodes were fabricated from a 94:3:3 (wt%) mixture of LiCoO 2 , polymeric binder, and super-P carbon black and calendered to different densities. A synchrotron X-ray nano-computed tomography system with a spatial resolution of 58.2 nm at the Advanced Photon Source of the Argonne National Laboratory was employed to obtain three dimensional morphology data of the electrodes. The morphology data were quantitatively analyzed to characterize their geometric properties, such as porosity, tortuosity, specific surface area, and pore size distribution. The geometric and electrochemical analysis reveal that high packing density electrodes have smaller average pore size and narrower pore size distribution, which improves the electrical contact between carbon-binder matrix and LiCoO 2 particles. The better contact improves the capacity and rate capability by reducing the possibility of electrically isolated LiCoO 2 particles and increasing the electrochemically active area. The results show that increase of packing density results in higher tortuosity, but electrochemically active area is more crucial to cell performance than tortuosity at up to 3.6 g/cm 3 packing density and 4 C rate.

An in situ formed, super-ionically conductive, and inactive network in high capacity anode particles can improve the performance of Li-ion batteries.

A synchrotron transmission X-ray microscopy tomography system with a spatial resolution of 58.2 nm at the Advanced Photon Source was employed to obtain three-dimensional morphological data of all-solid Li-ion battery electrodes. The three-phase electrode was fabricated from a 47:47:6 (wt %) mixture of Li(NiMnCo)O as active material, LiTiAl(PO) as Li-ion conductor, and Super-P carbon as electron conductor. The geometric analysis show that particle-based all-solid Li-ion battery has serious contact interface problem which significantly impact the Li-ion transport and intercalation reaction in the electrode, leading to low capacity, poor rate capability and cycle life.

The electrode of Li-ion batteries is required to be chemically and mechanically stable in the electrolyte environment for in situ monitoring by transmission X-ray microscopy (TXM). Evidence has shown that continuous irradiation has an impact on the microstructure and the electrochemical performance of the electrode. To identify the root cause of the radiation damage, a wire-shaped electrode is soaked in an electrolyte in a quartz capillary and monitored using TXM under hard X-ray illumination. The results show that expansion of the carbon-binder matrix by the accumulated X-ray dose is the key factor of radiation damage. For in situ TXM tomography, intermittent X-ray exposure during image capturing can be used to avoid the morphology change caused by radiation damage on the carbon-binder matrix.

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The energy and power capabilities of Li ion batteries (LIBs) have been considered critical factors to determine the commercial values of the LIB powered applications. Many efforts have been done to improve the energy density and rate capability of LIBs. In addition to intrinsic material properties of anode and cathode active materials, the structure of electrode at micro and nano scales also plays a critical role in determining the energy density and rate capability of a LIB (1-3). Calendering is a process in battery manufacturing to lower the porosity of the electrode and increase electrical contact. Increased calendering can increase the packing density of active materials in LIB electrodes, thereby increasing the volumetric energy density. The specific energy density is also increased by calendering via decreasing the percentage of inactive materials, such as current collector and separator. However, higher fraction of active materials in LIB electrodes can change electrodes’ structural properties significantly, such as porosity, specific surface area, pore size distribution and tortuosity (4). To this end, there are few reports on the geometric characteristics and their impact on the electrochemical performance of LIB electrodes with different calendering conditions due to the inhomogeneity, complexity, and three-dimensional (3D) nature of the electrode’s microstructure (5, 6). Recently, porous electrode microstructures have been reconstructed by advanced tomography techniques such as X-ray nano-computed tomography (nano-CT) and focused ion beam scanning electron microscope (FIB-SEM) (7, 8). The reconstructed microstructures have been employed to investigate the geometric characteristics and spatial inhomogeneity of porous electrodes. In this study, we investigated real 3D Li[Ni1/3Mn1/3Co1/3]O2 (NMC) electrode microstructures under different calendering conditions and the effect of calendering on the performance of LIBs (4). To investigate geometric characteristics of porous microstructures, cathode electrodes were fabricated from a 94:3:3 (weight %) mixture of NMC, PVDF, and super-P carbon black. To change the calendering condition, initial thickness of the electrodes was set 50µm, 80um, 90um, 100um. Then all electrodes were pressed down to 50 µm by using a rolling press machine. A synchrotron X-ray nano-CT at the Advanced Photon Source of Argonne National Lab was employed to obtain morphological data of the electrodes, with voxel size of 58.2 × 58.2 × 58.2 nm3. The morphology data sets were quantitatively analyzed to characterize their geometric properties. The geometric analysis showed that high packing density can result in smaller pore size and more uniform pore size distribution. The specific surface area and tortuosity of different electrodes will be reported. The charge/discharge experiments were also conducted for these electrodes. The geometric properties and cell testing results will be analyzed and reported. Acknowledgments: This work was supported by US National Science Foundation under Grant No. 1335850. References: 1.      R. E. García and Y.-M. Chiang, J. Electrochem. Soc., 154, A856 (2007). 2.      J. B. Goodenough and Y. Kim, Chem. Mater., 22, 587 (2009). 3.      C.-W. Wang and A. M. Sastry, J. Electrochem. Soc., 154, A1035 (2007). 4.      C. Lim, B. Yan, L. Yin and L. Zhu, Energies, 7, 2558 (2014). 5.      G. M. Goldin, A. M. Colclasure, A. H. Wiedemann and R. J. Kee, Electrochim. Acta, 64, 118 (2012). 6.      M. Smith, R. E. García and Q. C. Horn, J. Electrochem. Soc., 156, A896 (2009). 7.      M. Ebner, F. Geldmacher, F. Marone, M. Stampanoni and V. Wood, Advanced Energy Materials, 3, 845 (2013). 8.      T. Hutzenlaub, S. Thiele, R. Zengerle and C. Ziegler, Electrochem. Solid-State Lett., 15, A33 (2011).

Germanium (Ge) has been studied as an anode active material for high energy density lithium ion batteries (LIBs) (1, 2), due to its high volumetric capacity, low operation voltage, fast bulk Li diffusion, and high electrical conductivity. Similar to other high capacity lithium alloys (Si and Sn), Ge electrode accompanies large volume change of the active material during (de)lithiation processes. The repeated volume change causes fractures, pulverizations, and delamination of the electrode. The mechanical degradation reduces the reversible capacity and shortens the cycle life of the Ge anode LIBs. Klavetter et al. introduced micron sized selenium-doped germanium (Ge0.9Se0.1) as an active material, and reported higher reversible capacity and longer cycle life of a Ge0.9Se0.1 electrode than a Ge electrode (3). They proposed that the additional superionically conductive inactive phase (Li-Se-Ge) buffered the volumetric change of the active phase (Ge) and increased the rate of Li diffusion during the cell operation and it enhanced mechanical stability of the Ge0.9Se0.1 electrode. Thus, it is necessary to investigate mechanical stability of the lithium alloy electrodes for high performance LIBs. Recently, in-situ transmission X-ray microscopy (TXM) tomography was introduced to investigate 3D volume change of anode electrodes (4-6). The non-invasive X-ray imaging technique provides practical visual electrode information to understand the impact of the electrode’s microstructure change on LIB performance. In this study, a novel approach is used to investigate mechanical stability of Ge and Ge0.9Se0.1 electrodes by in-situ and in-operando monitoring the microstructure change. An X-ray transparent LIB cell was designed to capture the microstructure of high capacity anode electrodes with the synchrotron TXM technique at the beamline 32-ID-C of the Advanced Photon Source at the Argonne National Lab. In-operando TXM scan was implemented to monitor structural evolution of the Ge and Ge0.9Se0.1 electrodes under galvanostatic cell operation. Moreover, in-situ TXM tomography captured 3D microstrures of the electrodes at pristine, lithiated, and delithiated states. The obtained 2D dynamics and 3D volume changes of the Ge and Ge0.9Se0.1 electrodes contribute to understand mechanical stability and degradation mechanism of high capacity lithium alloy anode. Acknowledgments: This work was supported by US National Science Foundation under Grant No. 1603847. References: 1. J. Graetz, C. Ahn, R. Yazami and B. Fultz, J. Electrochem. Soc., 151, A698 (2004). 2. C.-Y. Chou and G. S. Hwang, J. Power Sources, 263, 252 (2014). 3. K. C. Klavetter, J. P. de Souza, A. Heller and C. B. Mullins, J. Mater. Chem. A, 3, 5829 (2015). 4. M. Ebner, F. Marone, M. Stampanoni and V. Wood, Science, 342, 716 (2013). 5. J. Wang, Y. c. K. Chen‐Wiegart and J. Wang, Angew. Chem., 126, 4549 (2014). 6. J. N. Weker, N. Liu, S. Misra, J. Andrews, Y. Cui and M. Toney, Energy Environ. Sci., 7, 2771 (2014).