Surface Modification of Over-Lithiated Layered Oxides with PEDOT:PSS Conducting Polymer in Lithium-Ion Batteries

Abstract

Over-lithiated layered oxide (OLO) materials were coated with a PEDOT:PSS conducting polymer via a simple wet-coating method. The prepared samples were observed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The electrochemical properties of the samples were determined by galvanostatic testing and electrochemical impedance spectroscopy (EIS). PEDOT:PSS coated cathode materials showed better rate capability and cyclability between 2.0 V and 4.6 V. X-ray photoelectron spectroscopy (XPS) data imply that the improved electrochemical performance of coated OLO is due to the suppression of the formation and growth of the solid electrolyte interface. 1-7 Among the many candidates, over-lithiated layered oxide (OLO), reported by the Thackeray group in 2005, exhibits a higher capacity (>200 mAh/g) and can reduce the use of expensive cobalt. Therefore, OLO is receiving attention as a cathode material for lithium-ion batteries (LIBs). 8,9 However, OLO experiences an inevitable oxygen loss and, subsequently, an irreversible capacity during the initial charge and discharge process. Additionally, the layered structure of OLO transforms into the spinel phase on cycling. The Li 2 MnO 3 phase in OLO materials exhibits a relatively low electronic conductivity owing to the insulating characteristics of the Li 2 MnO 3 component. 8,9 Referring to the reports by the Thackeray group, OLO material properties such as particle size, morphology control, compositional control by cationic substitution, and surface modification of parent OLO materials have been investigated to improve electrochemical properties. [10][11][12][13][14][15][16] Among the various researches published, investigations of surface modification mostly aim to decrease the initial irreversible capacity at initial cycles and suppress the side reaction between the cathode and electrolyte. Most materials for surface modification can be categorized into three groups: inorganic oxides, carbonbased materials, and polymer-based materials. The inorganic materials, which include AlF 3 , AlPO 4 , CoPO 4 , TiO 2 , V 2 O 5 , Al 2 O 3 , MnO 2 , ZnO, ZrO, MgO, Sm 2 O 3 , Li-Mn-PO 4 , and Li-Ni-PO 4 , are known to decrease the irreversible capacity and improve the electrochemical performances of OLO materials owing to the enforcement of stability on the surface in the high-voltage region. 17-31The carbon materials, including graphene-based materials, are employed to improve the electronic conductivity of OLO cathode materials.19,32-34 Also, surface modification by conducting polymers, such as polypyrrole, has been recently reported to provide improved electronic conductivity as well as a thin protective layer on OLO cathode materials. 35 Among various conducting polymers, thin film Poly(3,4-ethylenedioxythiophene) Polystyrene sulfonate (PEDOT: PSS) is known to exhibit superior electronic conductivity.36 Also, * Electrochemical Society Active Member. z E-mail: wonchangchoi@kist.r...

1D Building Blocks‐Intermingled Heteronanomats as a Platform Architecture For High‐Performance Ultrahigh‐Capacity Lithium‐Ion Battery Cathodes

“…At charge/ discharge current density of 0.1/0.1 C, the areal capacity of the 450 µm (= 8 sheets) HM OLO cathode was 13.0 mAh cm cathode −2 , which is a remarkably high value that corresponds to stripping/ plating of a lithium metal layer with a thickness of 65 µm. [ 52 ] Notably, Figure 3 c also presents that the areal capacity of the 450 µm HM OLO cathode is approximately 6 times higher than those of the previously reported results, [ 33,46,53,54 ] underscoring the electrochemical superiority of the heteronanomat architecture. The cycling performance of the multistacked HM OLO cathodes was examined at charge/discharge current density of 0.5/0.…”

“…c) Charge/discharge capacities per cathode area (mAh cm cathode −2 ) of multistacked HM OLO cathodes, wherein discharge capacities of the previously reported OLO cathodes were marked by star symbols (pink, [ 31 ] blue, [ 45 ] green, [ 53 ] black. [ 54 ] The cycling performance of the 8 sheets-stacked HM LNMO cathode was examined using a half cell (HM LMNO cathode/ Li metal anode), where the cell was cycled at charge/discharge current density of 0.2/0.2 C under voltage range of 3.50-4.95 V. Even at such harsh operating condition (i.e., ultrathick (= 420 µm) cathode and high charging voltage (= 4.95 V)), the HM LNMO cathode showed good cycling performance (capacity retention after 30 cycles = 78.5%, Figure 4 f), although its capacity retention was slightly lower than that of thinner HM LNMO cathodes. Future works will be devoted to further improving the capacity retention with cycling.…”

An in-situ gas chromatography investigation into the suppression of oxygen gas evolution by coated amorphous cobalt-phosphate nanoparticles on oxide electrode

“…It is highly likely that the slightly high capacity retention capability of the surface modified OLO originates from the reduction of electrolyte decomposition due to the protective coating layer of a -CoPO 4 on the surface of OLO particles. The phenomenon of voltage decay and degradation of electrodes in fact are very typical electrochemical trends for high manganese based lithium rich materials due to their structural transformation to spinel like structure, thereby lowering energy density during extended cycling2232. The ex-situ STEM EDAX (see Supplementary Fig.…”

“…They also reported that wetting the fabricated cathode with vanadium precursor solution to facilitate the impregnation of VO x into the layered structure also results in enhanced electrode stability19. Furthermore, several studies reported that surface modification of OLO nanocomposite cathodes with various materials such as self-catalyzed Polyaniline (PANI)20, lithium conductive Li 2 TiF 6 21, and Poly (3, 4-ehtylenedioxythiophene) Polystyrene sulfonate (PEDOT: PSS) led to the improvement of electrode performance and stability22.…”

Performance Improvements of Cobalt Oxide Cathodes for Rechargeable Lithium Batteries

“…Because conductive polymers can interact synergistically with inorganic compounds, the electrode lifetime, rate capability, thermal stability, etc. are greatly improved [113]. Mantione et al [114] PEDOT:PSS ((poly(3,4-ethylenedioxythiophene) polystyrene sulfonate)) has a promising rate capability and cyclability between 2.0 V and 4.6 V. Kim et al [115,116] found that polymer-coated LiCoO 2 delivered a significant improvement in electrochemical performance and thermal stability of lithiumion batteries compared with bare LiCoO 2 and that coated with Al 2 O 3 (Fig.…”