Debasish Mohanty

Investigating phase transformation in the Li1.2Co0.1Mn0.55Ni0.15O2 lithium-ion battery cathode during high-voltage hold (4.5 V) via magnetic, X-ray diffraction and electron microscopy studies

This study is the first that provides evidence of phase transformation in a Li-rich Li1.2Co0.1Mn0.55Ni0.15O2 cathode material for lithium-ion batteries (LIBs) during constant voltage charging. Diffraction and magnetic measurement techniques were successfully implemented to investigate the structural transformation in this cathode material during holding a half-cell at 4.5 V in a charged state. The results from X-ray diffraction showed a decrease in c-lattice parameters during high-voltage hold. Magnetic data revealed an increase in average effective magnetic moments of transition metal (TM) ions at constant voltage corresponding to a change in electronic states of TM ions. Analysis showed the reduction of Ni4+ to Ni2+, which was attributed to charge compensation due to oxygen loss. The appearance of the strong {100} forbidden reflection in the single-crystal selected area electron diffraction (SAED) data was attributed to migration of transition metal ions to the octahedral vacancy sites in the lithium layer during high-voltage hold, which was in agreement with the magnetization results. After prolonged hold at 4.5 V, high-resolution transmission electron microscopy (TEM) images along with SAED results showed the presence of spinel phases in the particles, indicating a layered to spinel like phase transformation at constant voltage in agreement with the magnetic data. The results obtained from these magnetic and diffraction studies furnish the fundamental understanding of the structural transformation pathways in Li-rich cathodes at constant voltage and will be instrumental for modifying the parent structure to achieve greater stability.

Correlating cation ordering and voltage fade in a lithium–manganese-rich lithium-ion battery cathode oxide: a joint magnetic susceptibility and TEM study

Structure-electrochemical property correlation is presented for lithium-manganese-rich layered-layered nickel manganese cobalt oxide (LMR-NMC) having composition Li1.2Co0.1Mn0.55Ni0.15O2 (TODA HE5050) in order to examine the possible reasons for voltage fade during short-to-mid-term electrochemical cycling. The Li1.2Co0.1Mn0.55Ni0.15O2 based cathodes were cycled at two different upper cutoff voltages (UCV), 4.2 V and 4.8 V, for 1, 10, and 125 cycles; voltage fade was observed after 10 and 125 cycles only when the UCV was 4.8 V. Magnetic susceptibility and selected-area electron diffraction data showed the presence of cation ordering in the pristine material, which remained after 125 cycles when the UCV was 4.2 V. When cycled at 4.8 V, the magnetic susceptibility results showed the suppression of cation ordering after one cycle; the cation ordering diminished upon further cycling and was not observed after 125 cycles. Selected-area electron diffraction data from oxides oriented towards the [0001] zone axis revealed a decrease in the intensity of cation-ordering reflections after one cycle and an introduction of spinel-type reflections after 10 cycles at 4.8 V; after 125 cycles, only the spinel-type reflections and the fundamental O3 layered oxide reflections were observed. A significant decrease in the effective magnetic moment of the compound after one cycle at 4.8 V indicated the presence of lithium and/or oxygen vacancies; analysis showed a reduction of Mn(4+) (high spin/low spin) in the pristine oxide to Mn(3+) (low spin) after one cycle. The effective magnetic moment was higher after 10 and 125 cycles at 4.8 V, suggesting the presence of Mn(3+) in a high spin state, which is believed to originate from distorted spinel (Li2Mn2O4) and/or spinel (LiMn2O4) compounds. The increase in effective magnetic moments was not observed when the oxide was cycled at 4.2 V, indicating the stability of the structure under these conditions. This study shows that structural rearrangements in the LMR-NMC oxide happen only at higher potentials (4.8 V, for example) and provides evidence of a direct correlation between cation ordering and voltage fade.

Modification of Ni-Rich FCG NMC and NCA Cathodes by Atomic Layer Deposition: Preventing Surface Phase Transitions for High-Voltage Lithium-Ion Batteries

The energy density of current lithium-ion batteries (LIBs) based on layered LiMO2 cathodes (M = Ni, Mn, Co: NMC; M = Ni, Co, Al: NCA) needs to be improved significantly in order to compete with internal combustion engines and allow for widespread implementation of electric vehicles (EVs). In this report, we show that atomic layer deposition (ALD) of titania (TiO2) and alumina (Al2O3) on Ni-rich FCG NMC and NCA active material particles could substantially improve LIB performance and allow for increased upper cutoff voltage (UCV) during charging, which delivers significantly increased specific energy utilization. Our results show that Al2O3 coating improved the NMC cycling performance by 40% and the NCA cycling performance by 34% at 1 C/−1 C with respectively 4.35 V and 4.4 V UCV in 2 Ah pouch cells. High resolution TEM/SAED structural characterization revealed that Al2O3 coatings prevented surface-initiated layered-to-spinel phase transitions in coated materials which were prevalent in uncoated materials. EIS confirmed that Al2O3-coated materials had significantly lower increase in the charge transfer component of impedance during cycling. The ability to mitigate degradation mechanisms for Ni-rich NMC and NCA illustrated in this report provides insight into a method to enable the performance of high-voltage LIBs.

Structural transformation in a Li1.2Co0.1Mn0.55Ni0.15O2 lithium-ion battery cathode during high-voltage hold

A decrease in the c-lattice parameter was observed in Li1.2Co0.1Mn0.55Ni0.15O2 during constant voltage holding at 4.5 V by in situ X-ray diffraction. Comparison of magnetic susceptibility data before and after high-voltage hold reveals the change in average oxidation states of transition metal ions during high-voltage holding process. Transmission electron microscopy studies show the spinel reflections with fundamental trigonal spots from the particles after high-voltage hold indicating substantial structural modification. The structural transformation was believed to occur due to the oxygen release and/or the migration of transition metal cations to lithium layer during constant voltage holding.

Synthesis and piezoelectric response of cubic and spherical LiNbO3 nanocrystals

Methods have been developed for the shape-selective synthesis of ferroelectric LiNbO3 nanoparticles. Decomposition of the single-source precursor, LiNb(O-Et)6, in the absence of surfactants, can reproducibly lead to either cube- or sphere-like nanoparticles. X-Ray diffraction shows that the LiNbO3 nanoparticles are rhombohedral (R3c). Sample properties were examined by piezoresponse force microscopy (PFM) and Raman where both sets of nanoparticles exhibit ferroelectricity. The longitudinal piezoelectric coefficients, d33, varied with shape where the largest value was exhibited in the nanocubes (17 pm V−1 for the cubes versus 12 pm V−1 for spheres).

Degradation mechanisms of lithium-rich nickel manganese cobalt oxide cathode thin films

This paper reports a method to prepare Li-rich NMC (Li1.2Mn0.55Ni0.15Co0.1O2) thin film cathodes for Li-ion batteries using RF magnetron sputtering and post-annealing in O2. Thin film cathodes with high reversible capacities (260 mA h g−1) and potential profiles similar to those of the powder material have been obtained. Structural and electrochemical studies show that the grown materials consist of a layered structure with trigonal symmetry in which Li/TM ordering is partially achieved. Using XPS we determine that the surface is comprised of Mn4+, Co3+ and Ni2+ cations inside an O2− framework. The loss mechanisms of these electrodes have been studied after 184 cycles. The data after cycling shows the absence of Li/TM ordering, confirming that Li2MnO3 activation is irreversible, while electron diffraction data indicates extensive structural modifications upon cycling. In addition, we identified that the surface chemistry is dominated by inorganic species (LiF, Lix′POy′Fz′, LixPFy), along with small amounts of organic species with C–O and O–CO groups such as PEO, LiOR and RCO2Li. Moreover, XPS results indicate that Ni and Co migrate into the bulk while the reduction of Mn4+ into Mn3+ is clearly evidenced, as expected from the activation of Li2MnO3 domains and discharging to 2.5 V.

Cathode materials review

The electrochemical potential of cathode materials defines the positive side of the terminal voltage of a battery. Traditionally, cathode materials are the energy-limiting or voltage-limiting electrode. One of the first electrochemical batteries, the voltaic pile invented by Alessandro Volta in 1800 (Phil. Trans. Roy. Soc. 90, 403-431) had a copper-zinc galvanic element with a terminal voltage of 0.76 V. Since then, the research community has increased capacity and voltage for primary (nonrechargeable) batteries and round-trip efficiency for secondary (rechargeable) batteries. Successful secondary batteries have been the lead-acid with a lead oxide cathode and a terminal voltage of 2.1 V and later the NiCd with a nickel(III) oxide-hydroxide cathode and a 1.2 V terminal voltage. The relatively low voltage of those aqueous systems and the low round-trip efficiency due to activation energies in the conversion reactions limited their use. In 1976, Wittingham (J. Electrochem. Soc., 123, 315) and Besenhard (J. ...

Non-destructive evaluation of slot-die-coated lithium secondary battery electrodes by in-line laser caliper and IR thermography methods

Non-destructive, in-line quality control methods were adopted for evaluating the thickness and homogeneity of wet and dry lithium secondary battery electrodes. Laser caliper and infrared (IR) thermography methods were implemented in a systematic fashion for the first time to evaluate the quality of electrodes during the coating process on a slot-die coater. Laser caliper sensors were mounted, aligned, and subsequently calibrated at the oven inlet of the coating line in order to examine the thicknesses of different cathodes and anodes. The effect of various factors such as substrate vibration, temperature, surface reflectivity and laser positions on the thickness measurement during slot-die coating were evaluated. The setup was used to monitor the wet thickness of the cathode and anode, and the precision of the in-line laser thickness measurement was determined to be less than ±2%. Thickness deviation for cathodes was typically ±2.0–2.3%, and for anodes it was typically ±2.2–2.6%, which confirms excellent precision of the measurement. The homogeneity of the dried electrodes was also evaluated by IR thermography at the oven outlet of the coating line. Temperature profiles from thermography images of dry electrodes were carefully examined to detect any flaws and inhomogeneity present in the electrodes. An increase or decrease in the temperature profiles indicated defects/flaws in the electrodes that could not be observed in optical images. The techniques applied in this work will be helpful for detection of electrode flaws and contamination during large-scale manufacturing and to identify flawed product prior to lithium-ion cell assembly.

Topochemical Synthesis of Alkali-Metal Hydroxide Layers within Double-and Triple-Layered Perovskites

The formation of alkali-metal hydroxide layers within lamellar perovskites has been accomplished by a two-step topochemical reaction strategy. Reductive intercalation of ALaNb2O7 with alkali metal (A = K, Rb) and RbCa2Nb3O10 with Rb leads to A2LaNb2O7 and Rb2Ca2Nb3O10, respectively. Oxidative intercalation with stoichiometric amounts of water vapor, produced by the decomposition of calcium oxalate monohydrate in a sealed ampule, allows the insertion hydroxide species. Compounds of the form (A2OH)LaNb2O7 (A = K, Rb) and (Rb2OH)Ca2Nb3O10 are accessible. X-ray diffraction data indicates a clear layer expansion of almost 3 Å on the insertion of hydroxide relative to that of the parent. Rietveld refinement of neutron diffraction data collected on deuterated samples of (Rb2OD)LaNb2O7 (P4/mmm space group, a = 3.9348(1) Å, c = 14.7950(7) Å) finds that both rubidium and oxygen species reside in cubic sites forming a CsCl-like interlayer structure between niobate perovskite blocks. Hydrogens, attached to the interlayer oxygens, are disordered over a 4-fold site in the x-y plane and have O-H bond distances (0.98 Å) consistent with known hydroxide species. This synthetic approach expands the library of available topochemical reactions, providing a facile method for the construction of alkali-metal hydroxide layers within receptive perovskite hosts.

Magnetic Properties of LixCoO2 and its Thermally Decomposed Phases

Stoichiometric LiCoO2 is nonmagnetic in nature. When lithium ion is removed from the lattice magnetic character is introduced in the lattice due to change of spin states of cobalt ions. These lithium deficient phases are not stable at elevated temperature eventually transform to a mixture of LiCoO2 and Co3O4 under evolution of oxygen. Here we report the magnetic behavior of LixCoO2 (x=1.03, 0.98, 0.76, 0.55) and its thermally decomposed products.