Research

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    Lithium-based battery technologies have dominated the past decades, which fueled modern technologies from electric transportation to mobile devices. However, the ever-evolving industry requires better battery along with new battery materials and mechanisms. Our research interests in lithium-ion batteries covers a variety of topics such as conventional layered oxides cathodes, lithium-rich layered oxides and anionic redox, conversion-type anodes, lithium dendrites growth mechanism, electrolyte design, and battery recycling.

    Our group specialize in using cutting edge characterizations to probe the structural evolution of electrode materials during battery operations. We used multi-length-scale X-ray spectroscopic to reveal the root reason of voltage decay in lithium- and manganese-rich (LMR) layered material to be oxygen release from the material and the resultant lower valence redox couple chemistry. For Ni-rich layered oxides, we managed to track the volume variation associated with anisotropic lattice strain and stress during lithium (de)intercalation via synchrotron-based spectroscopic imaging combined with x-ray absorption near edge structures, and proposed the “rivet” strategy to efficiently retard the strain. We also dedicate our efforts to the Lithium metal anode, where we quantified the solid-electrolyte interphase component and demonstrated an effective strategy of rejuvenating the dead Li metal via iodine redox chemistry.

01 Lithium ion battery

02 Characterizations

   Our group is experienced in using the spherical aberration corrected scanning transmission electron microscope (AC-STEM) to reveal the atomic structure of electrode materials. By transmitting a beam of electrons through a specimen, it is capable of imaging down to atomic level, which helps us understanding the charge-discharge mechanism of electrodes.

    In one of our recent works, we are able to clarify the debating charge-discharge mechanism of α-MnO2 in an aqueous ZnSO4 solution and unveil the charge carrier. By directly looking at the un-tilted α-MnO2 tunnel structure with the absence of any “heavy atom” at the center of tunnels, we propose that H  instead of Zn   to be the charge carrier in aqueous systems.

Building...

Ref：

Liu, T., Liu, J., Li, L. et al. Origin of structural degradation in Li-rich layered oxide cathode. Nature, 2022, 606, 305–312.

Wang, L., Liu, T., Wu, T. et al. Strain-retardant coherent perovskite phase stabilized Ni-rich cathode. Nature, 2022, 611, 61–67.

Li, M., Lu, Jun., Cobalt in lithium-ion batteries, Science, 2020, 367, 6481, 979-980.

Jin, C., Liu, T., Sheng, O. et al. Rejuvenating dead lithium supply in lithium metal anodes by iodine redox. Nat. Energy, 2021, 6, 378–387.

Wang, L., Dai, A., Xu W., Structural Distortion Induced by Manganese Activation in a Lithium-Rich Layered Cathode, J. Am. Chem. Soc., 2020, 142, 35, 14966–14973.

2.1 Spherical aberration corrected scanning transmission electron microscope (AC-STEM)

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Ref：

Yuan, Y., Sharpe, R., He, K. et al. Understanding intercalation chemistry for sustainable aqueous zinc–manganese dioxide batteries. Nat Sustain, 2022, 5, 890–898.

2.2 In-situ X-ray diffraction studies

  Our group has access to synchrotron beamline and is adept at in operando characterizations using synchrotron. The high intensity of the beamline greatly shortens the signal-collecting time and made operando measurement possible. Such in operando measurement presents valuable information because it avoids any complication caused by battery disassembling and provides us with first-hand information about the battery.

    We have used in-situ X-ray diffraction studies to observe the structural evolution of many cathode materials, and valuable information such as phase transition, lattice strain build-up, structure collapse, etc., have been extracted before. Recently, we use it to observe the structural evolution of Ni-rich layered oxides intertwined with a perovskite phase, which shows significant retarded strain and excellent structural reversibility during the battery operation.

Ref：

Wang, L., Liu, T., Wu, T. et al. Strain-retardant coherent perovskite phase stabilized Ni-rich cathode. Nature, 2022, 611, 61–67.

  Other than diffraction, X-rays are also absorbed by an atom at energies near and above the core-level binding energies of that atom, and Synchrotron gives us such spectral characterizations as in operando XANES and EXAFS. By monitoring an atom’s x-ray absorption probability, we can evaluate the chemical and physical state of the atom, and extract valuable information such as the formal oxidation state, coordination chemistry, interatomic distance, and coordination number. From different regimes in an X-ray absorption spectrum, XANES gives us the oxidation states of the atom and EXAFS shows us the bond length information.

     In one of our group’s works, we used such techniques to evaluate the structural reversibility of lithium-rich manganese-based layered oxides, whose high voltage anionic redox and structural distortion mechanism have long been elusive. Via in operando XANES and EXAFS measurements on Ni, we observed perfect reversibility of Ni   <-> Ni   with no oxidation state change over 4.4 V, indicating that Ni is not an active player both in structural distortion and high voltage capacity.

Ref：

Wang, L., Dai, A., Xu W., Structural Distortion Induced by Manganese Activation in a Lithium-Rich Layered Cathode, J. Am. Chem. Soc., 2020, 142, 35, 14966–14973.

2.3 In operando X-ray absorption near edge structure (XANES) & Extended X-ray absorption fine structure (EXAFS) 

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    Coherent X-ray diffraction imaging hits the sample with a highly coherent beam of X-rays, which gets scattered by the object and produce a diffraction pattern on X-ray CCD detectors. The reciprocal space diffraction pattern is used in the reconstruction of real space images via an iterative feedback algorithm, and the penetrative nature of X-rays enables a 3D reconstruction of the particles in electrodes. With such a technique, we are able to directly monitor the electrode evolution of lattice displacement and nanoscale strain in battery operation, which is non-viable by surface characterization techniques before.

    We managed to track the lattice displacement and strain evolution of Li- and Mn-rich oxides (LMR) cathodes with this technique and realize that the strain reached its maximum at 4.43 V during the de-lithiation. Combined with the In situ differential electrochemical mass spectroscopy measurements, we propose the heterogeneous composite structures with different electrochemical activities to be the root reason for lattice strain, which also destabilize structures and trigger Li2MnO3 decomposition with oxygen release.

Ref：

Liu, T., Liu, J., Li, L. et al. Origin of structural degradation in Li-rich layered oxide cathode. Nature, 2022, 606, 305–312.

2.4 In operando Bragg coherent X-ray diffraction imaging (BCDI)

    Transmission X-ray microscopy generates images contrasted by the adsorption difference of X-ray from the different components in the materials. A focused X-ray beam is transmitted through the sample and a CCD detector records the transmitted X-ray intensity as a function of the sample position. Such a technique can provide richly detailed information about electrode particles, such as the particle size and homogeneity of the composition. By combining with XANES technique, the color-coded images provide valuable information such as electronic, atomic, and mechanochemical structural changes of electrode particles during the battery operation, and help evaluate the material’s redox stability and reversibility, also predicting the cycling life.

    We manifested the practicality of such a technique in one of our recent works, where we stabilized the Ni-rich layered oxides (LiNixCoyMn1−x−yO2, x > 0.5) by introducing a perovskite phase into the layered structure (D-NCM). The cycled D-NCM showed much similar homogeneous color distribution on the mapping than the pristine one without the perovskite (P-NCM), indicating superior stability of the material.

Ref：

Wang, L., Liu, T., Wu, T. et al. Strain-retardant coherent perovskite phase stabilized Ni-rich cathode. Nature, 2022, 611, 61–67.

2.5 2D full-field transmission X-ray microscopy (TXM)– XANES mappings