Surface and Interface Analysis of LiCoO₂ and LiPON Thin Films by Photoemission: Implications for Li-Ion Batteries

Abstract

Thin film technology is applied in different fields of Li-ion battery research and development, such as the fabrication of thin film cells and model electrodes. Data obtained by surface and interface analysis of thin films provides important insights into fundamental processes such as charge compensation mechanism or interface formation. In this overview, we present the analysis of LiCoO

Experimental Studies on Work Functions of Li+ Ions and Electrons in the Battery Electrode Material LiCoO2: A Thermodynamic Cycle Combining Ionic and Electronic Structure

“…Less information is available on the electronic work function of LiCoO 2 . Values reported range from 5.0 to 5.3 eV for pristine LiCoO 2 thin films, and within this investigation we have obtained a value of 5.1 eV. Combining this information on the electronic work functions of the electrode materials, LiCoO 2 and Li, leads to an estimate of the expected cell potential in the range from 1.9 to 3.0 eV.…”

“…This number refers to a lithium‐deficient state of the LiCoO 2 . The measured electronic work function of lithium is 2.6–2.9 eV, that of LiCoO 2 is 5.0–5.3 eV . In a first approximation, the cell voltage expected based on considering the difference of electronic work functions only, is thus (2.4 ± 0.3) eV.…”

“…For the Li//LiCoO 2 model battery discussed above a typical cell voltage (plateau of the charge/discharge curve) is around 3.9 V . This number refers to a lithium‐deficient state of the LiCoO 2 .…”

“…Both electrochemical potentials can be obtained from work function measurements. Electron work functions are routinely measured using standard techniques at room temperature, such as photoelectron spectroscopy or Kelvin probe, and have been determined for a (small) number of Li‐ion insertion materials, such as LiCoO 2 . Ionic work functions can be obtained via thermionic emission, a technique which has been known for 100 years, but which has, to our knowledge, so far not been applied to electrode materials for Lithium ion batteries …”

Photoemission Study on the Interaction Between LiCoO2 Thin Films and Adsorbed Water

“…18,19 According to the literature, Li 2 O incorporated in LiCoO 2 shows an O 1s emission at binding energies below the O 1s main emission of LiCoO 2 , which supports our assignment. 20 With exposure time, mainly component d (water) increases, while for component b and c (hydroxide and oxide) only a small increase is observed. The spectrum after desorption of water resembles the spectrum after exposure to 0.1L.…”