Abstract
Recently, rapid fluctuations in cobalt prices have created a worsening supply chain constraint that has become a serious cause of concern amidst global battery manufacturers. To address this challenge, here we report a new class of cobalt-free, nickel-rich layered cathode material termed the NFA class with general formula LiNixFeyAlzO2 (x + y + z = 1). Using co-precipitation reaction in a continuous stirred tank reactor, we synthesized NFA(OH)2 precursors with the constituent Ni, Fe and Al elements successfully incorporated. The obtained LiNFAO2 cathode was characterized using X-Ray diffraction, Mössbauer spectroscopy and scanning electron microscopy. Electrochemical behavior was assessed using cyclic voltammetry, galvanostatic charge/discharge, electrochemical impedance spectroscopy and galvanostatic intermittent titration technique at various states of lithiation/delithiation. Electrochemical performance evaluations revealed that our cobalt-free material delivers high capacity of 190 mAh/g at 0.1C. Rate and cycling performance evaluations also indicated good rate capability and cycling stability with 88% capacity retention after 100 cycles at C/3. Using NFA cathodes, we also fabricated a 0.5Ah (C/3) cobalt-free Li-ion battery which demonstrated reasonable cycling stability with ~72% capacity retained after 200 cycles. Overall, our work demonstrates the immense potential of the cobalt-free NFA class cathodes as viable candidates towards development of next generation cost effective lithium ion batteries.
Original language | English |
---|---|
Article number | 228389 |
Journal | Journal of Power Sources |
Volume | 471 |
DOIs | |
State | Published - Sep 30 2020 |
Funding
This research at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE) under contract DE-AC05-00OR22725 , was sponsored by the Energy Efficiency and Renewable Energy (EERE) , Vehicle Technologies Office (VTO) . X-Ray diffraction and electron microscopy was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. We also acknowledge Dr. Jagjit Nanda, Dr. Ethan Self, Devendrasinh Darbar, Dr. David Wood, Kelsey Grady, Andrew Todd and all the members of the Roll-to-Roll Manufacturing Group, in the Energy and Transportation Sciences division at Oak Ridge National Laboratory for the useful discussions and feedback. Further assessment of electrochemical behavior was performed using galvanostatic intermittent titration technique. The GITT measurement profiles exhibited a sloping behavior as observed in the case of normal charged-discharge profiles (see supporting information, fig. S6 (A) and (B)). Sample EIS spectra recorded on the NFA half-cell at different states of delithiation is also shown in supporting information, fig. S7 (A). The cell was held at the open-circuit voltage (OCV) for 3 h with a voltage decay rate of 2 mV/h at the end of the rest interval. Under the OCV conditions, the material's voltage lies between the oxidation and reduction states where the small bias potentials applied during the EIS measurements could induce slight lithiation and delithiation. The measured Nyquist plots of NFA consist of the following features: (i) a high frequency intercept due to the ionic resistance of the electrolyte along with a minor contribution of the solid electrolyte interphase (SEI), (ii) a first semi-circle, at the medium-high frequencies due to the electronic conductivity of the material along with the charge transfer resistance at the lithium/electrolyte interface, (iii) a second semi-circle, at the medium-low frequencies, due to the charge transfer reaction at the NFA/electrolyte interface, since the associated capacitance value is higher (10?5F) than that of the first semicircle (10?9F) and (iv) a Warburg response at the lower frequency part of obtained spectra. Similar impedance spectra were measured during the other states of the charge as well as the discharge process. The different resistance processes in the NFA electrochemical cell were extracted by fitting the obtained spectra using an equivalent circuit (see supporting information, fig. S7 (B)). The determined values for the various resistance processes as a function of the cell voltage are shown in Fig. 4 (A) and 4 (B). The various resistance processes associated with the cell are also shown in a schematic in Fig. 4 (C). It can be observed that the resistances of anode-electrolyte interface (R2) gradually decreases with the degree of delithiation up to around 3.7V and thereafter it is almost constant even with further delithiation. On the other hand, resistance process associated with the cathode-electrolyte interface (R3) initially decreases with charging up to 3.9V and thereafter, gradually increases with further delithiation. It can be noted that, the interfacial charge transfer at the cathode-electrolyte interface is induced by the change of electronic conductivity and ionic diffusivity of the active particles of the NFA cathode. Initially valence state of nickel in NFA is +3 and upon oxidation gradually converts to Ni4+ with the partial delithiation. The concentration of the mixed valent state of Ni3+/Ni4+ increases upon further delithiation and forms an electronically conducting percolation network. Upon further delithiation, the concentration of Ni3+ decreases and Ni4+ increases and a gradual break down of the percolation network occurs. Therefore, the cathode-electrolyte interfacial resistance, R3 exhibits this trend. It should also be noted that R2 should not change with state of charge (SOC) assuming that it is only associated with the charge transfer reaction at the lithium/electrolyte interface. However, the electronic conductivity of active material changes with SOC and therefore it also impacts the charge transfer resistance at lithium/electrolyte interface. It can also be observed from Fig. 4A and B that there is a slight increase of R2 with SOC. This can be attributed to the sharp increase in electronic conductivity increase in layered materials at the beginning phase of delithiation as reported elsewhere [ 35?37] resulting in a decrease in R2 initially. Also, our recent report shows that the charge transfer kinetics at electrode-electrolyte interfacial reaction can be further enhanced with the increase of electronic conductivity of active material [35,36]. It can also be observed that R3 is higher for the higher lithium concentrations. Indeed, the electronic conductivity of the material is relatively low in the fully lithiated phase. The obtained EIS results likely imply that the interfacial charge transfer resistance is a rate limiting factor particularly at high lithium concentration intervals.This research at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE) under contract DE-AC05-00OR22725, was sponsored by the Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office (VTO). X-Ray diffraction and electron microscopy was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. We also acknowledge Dr. Jagjit Nanda, Dr. Ethan Self, Devendrasinh Darbar, Dr. David Wood, Kelsey Grady, Andrew Todd and all the members of the Roll-to-Roll Manufacturing Group, in the Energy and Transportation Sciences division at Oak Ridge National Laboratory for the useful discussions and feedback. This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ).
Keywords
- Cobalt-free
- Electric vehicles
- Electrochemistry
- Layered cathodes
- Li-ion batteries
- NFA