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Title: Structural Transformations in High-Capacity Li 2 Cu 0.5 Ni 0.5 O 2 Cathodes

Abstract

Cathode materials that can cycle > 1 Li+ per transition metal are of substantial interest to increase the overall energy density of lithium-ion batteries. Li2Cu0.5Ni0.5O2 has a very high theoretical capacity of ~ 500 mAh/g assuming both Li+ are cycled reversibly. The Cu2+/3+ and Ni2+/3+/4+ redox couples are also at high voltage, which could further boost the energy density of this system. Despite such promise, Li2Cu0.5Ni0.5O2 undergoes irreversible phase changes during charge (delithiation) that result in large first-cycle irreversible loss and poor long-term cycling stability. Oxygen is evolved before the Cu2+/3+ or Ni3+/4+ transitions are accessed. In this contribution, XRD, TEM, and TXM-XANES are used to follow the chemical and structural changes that occur in Li2Cu0.5Ni0.5O2 during electrochemical cycling. Li2Cu0.5Ni0.5O2 is a solid solution of orthorhombic Li2CuO2 and Li2NiO2, but the structural changes more closely mimic the Li2NiO2 endmember. Li2Cu0.5Ni0.5O2 loses long-range order during charge, but TEM analysis provides clear evidence for particle exfoliation and the transformation from orthorhombic to a partially layered structure. Linear combination fitting and principal component analysis of TXM-XANES are used to map the different phases that emerge during cycling ex situ and in situ. Significant changes in the XANES at the Cu and Ni K-edgesmore » correlate with the onset of oxygen evolution.« less

Authors:
ORCiD logo; ORCiD logo; ; ; ; ORCiD logo
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office (EE-3V)
OSTI Identifier:
1356495
Report Number(s):
PNNL-SA-123197
Journal ID: ISSN 0897-4756; 49321; KP1704020
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Chemistry of Materials; Journal Volume: 29; Journal Issue: 7
Country of Publication:
United States
Language:
English
Subject:
Environmental Molecular Sciences Laboratory

Citation Formats

Ruther, Rose E., Samuthira Pandian, Amaresh, Yan, Pengfei, Weker, Johanna Nelson, Wang, Chongmin, and Nanda, Jagjit. Structural Transformations in High-Capacity Li 2 Cu 0.5 Ni 0.5 O 2 Cathodes. United States: N. p., 2017. Web. doi:10.1021/acs.chemmater.6b05442.
Ruther, Rose E., Samuthira Pandian, Amaresh, Yan, Pengfei, Weker, Johanna Nelson, Wang, Chongmin, & Nanda, Jagjit. Structural Transformations in High-Capacity Li 2 Cu 0.5 Ni 0.5 O 2 Cathodes. United States. doi:10.1021/acs.chemmater.6b05442.
Ruther, Rose E., Samuthira Pandian, Amaresh, Yan, Pengfei, Weker, Johanna Nelson, Wang, Chongmin, and Nanda, Jagjit. Tue . "Structural Transformations in High-Capacity Li 2 Cu 0.5 Ni 0.5 O 2 Cathodes". United States. doi:10.1021/acs.chemmater.6b05442.
@article{osti_1356495,
title = {Structural Transformations in High-Capacity Li 2 Cu 0.5 Ni 0.5 O 2 Cathodes},
author = {Ruther, Rose E. and Samuthira Pandian, Amaresh and Yan, Pengfei and Weker, Johanna Nelson and Wang, Chongmin and Nanda, Jagjit},
abstractNote = {Cathode materials that can cycle > 1 Li+ per transition metal are of substantial interest to increase the overall energy density of lithium-ion batteries. Li2Cu0.5Ni0.5O2 has a very high theoretical capacity of ~ 500 mAh/g assuming both Li+ are cycled reversibly. The Cu2+/3+ and Ni2+/3+/4+ redox couples are also at high voltage, which could further boost the energy density of this system. Despite such promise, Li2Cu0.5Ni0.5O2 undergoes irreversible phase changes during charge (delithiation) that result in large first-cycle irreversible loss and poor long-term cycling stability. Oxygen is evolved before the Cu2+/3+ or Ni3+/4+ transitions are accessed. In this contribution, XRD, TEM, and TXM-XANES are used to follow the chemical and structural changes that occur in Li2Cu0.5Ni0.5O2 during electrochemical cycling. Li2Cu0.5Ni0.5O2 is a solid solution of orthorhombic Li2CuO2 and Li2NiO2, but the structural changes more closely mimic the Li2NiO2 endmember. Li2Cu0.5Ni0.5O2 loses long-range order during charge, but TEM analysis provides clear evidence for particle exfoliation and the transformation from orthorhombic to a partially layered structure. Linear combination fitting and principal component analysis of TXM-XANES are used to map the different phases that emerge during cycling ex situ and in situ. Significant changes in the XANES at the Cu and Ni K-edges correlate with the onset of oxygen evolution.},
doi = {10.1021/acs.chemmater.6b05442},
journal = {Chemistry of Materials},
number = 7,
volume = 29,
place = {United States},
year = {Tue Mar 21 00:00:00 EDT 2017},
month = {Tue Mar 21 00:00:00 EDT 2017}
}
  • Cathode materials that can cycle >1 Li + per transition metal are of substantial interest for increasing the overall energy density of lithium-ion batteries. Li 2Cu 0.5Ni 0.5O 2 has a very high theoretical capacity of ~500 mAh/g assuming both Li+ ions are cycled reversibly. The Cu 2+/3+ and Ni 2+/3+/4+ redox couples are also at high voltage, which could further boost the energy density of this system. Despite such promise, Li 2Cu 0.5Ni 0.5O 2 undergoes irreversible phase changes during charge (delithiation) that result in large first-cycle irreversible loss and poor long-term cycling stability. Oxygen evolves before the Cumore » 2+/3+ or Ni 3+/4+ transitions are accessed. In this contribution, X-ray diffraction, transmission electron microscopy (TEM), and transmission X-ray microscopy combined with X-ray absorption near edge structure (TXM–XANES) are used to follow the chemical and structural changes that occur in Li 2Cu 0.5Ni 0.5O 2 during electrochemical cycling. Li 2Cu 0.5Ni 0.5O 2 is a solid solution of orthorhombic Li2CuO2 and Li2NiO2, but the structural changes more closely mimic the changes that the Li 2NiO 2 endmember undergoes. Li 2Cu 0.5Ni 0.5O 2 loses long-range order during charge, but TEM analysis provides clear evidence of particle exfoliation and the transformation from orthorhombic to a partially layered structure. Linear combination fitting and principal component analysis of TXM–XANES are used to map the different phases that emerge during cycling ex situ and in situ. Lastly, significant changes in the XANES at the Cu and Ni K-edges correlate with the onset of oxygen evolution.« less
  • Orthorhombic Li 2NiO 2, Li 2CuO 2, and solid solutions thereof have been studied as potential cathode materials for lithium-ion batteries due to their high theoretical capacity and relatively low cost. While neither endmember shows good cycling stability, the intermediate composition, Li 2Cu 0.5Ni 0.5O 2, yields reasonably high reversible capacities. A new synthetic approach and detailed characterization of this phase and the parent Li 2CuO 2 are presented. The cycle life of Li 2Cu 0.5Ni 0.5O 2 is shown to depend critically on the voltage window. The formation of Cu 1+ at low voltage and oxygen evolution at highmore » voltage limit the electrochemical reversibility. In situ X-ray absorption spectroscopy (XAS), in situ Raman spectroscopy, and gas evolution measurements are used to follow the chemical and structural changes that occur as a function of cell voltage.« less
  • For this study, cells based on nickel manganese cobalt oxide (NMC)/graphite electrodes, which contained polyvinylidene difluoride (PVDF) binders in the electrodes, were systematically charged to 100, 120, 140, 160, 180, and 250% state of charge (SOC). Characterization of the anodes by inductively-coupled-plasma mass spectrometry (ICP-MS), X-ray photoelectron spectroscopy (XPS), and high-performance liquid chromatography coupled with electrospray ionization mass spectrometry (HPLC-ESI-MS) showed several extent-of-overcharge-dependent trends. The concentrations (by wt) of nickel, manganese, and cobalt in the negative electrode increased with SOC, but the metals remained in the same ratio as that of the positive. Electrolyte reaction products, such as LiF:LiPO 3,more » increased with overcharge, as expected. Three organic products were found by HPLC-ESI-MS. From an analysis of the mass spectra, two of these compounds seem to be organophosphates, which were formed by the reaction of polymerized electrolyte decomposition products and PF 3 or O=PF 3. Their concentration tended to reach a constant ratio. The third was seen at 250% SOC only.« less
  • X-ray diffraction and X-ray absorption spectroscopy experiments were used to study chemical and electrochemical Li insertion and extraction reactions of LiNi{sub 0.5}Mn{sub 0.5}O{sub 2}. These results, along with galvanostatic cycling data, suggest that LiNi{sub 0.5}Mn{sub 0.5}O{sub 2} layered electrodes in lithium batteries operate predominantly off two-electron redox couples, Ni{sup 4+}/Ni{sup 2+}, between approximately 4.5 and 1.25 V and Mn{sup 4+}/Mn{sup 2+} between 1.25 and 1.0 V versus metallic Li, respectively. The retention of a stable layered framework structure and the apparent absence of Jahn-Teller ions Ni{sup 3+} and Mn{sup 3+} in the high- or low-voltage region is believed to bemore » responsible for the excellent structural and electrochemical stability of these electrodes. The LiNi{sub 0.5}Mn{sub 0.5}O{sub 2} layered oxide reversibly reacts chemically or electrochemically with Li to form an air-sensitive, dilithium compound, Li{sub 2}Ni{sub 0.5}Mn{sub 0.5}O{sub 2}, with a hexagonal structure analogous to Li{sub 2}MnO{sub 2}. The cycling behavior of Li/LiNi{sub 0.5}Mn{sub 0.5}O{sub 2} cells over a large voltage window (4.6-1.0 V) and with very slow rates shows that rechargeable capacities >500 mA{center_dot}h/g can be obtained.« less