The intensities of the X-ray powder diffraction of cobalt aluminum oxides (spinel type) heat-treated at 1400°C and 1300°C under various partial pressures of oxygen (PO2) were measured. The optimum ...value of the fraction of tetrahedral sites occupied by aluminum (x), the fraction of tetrahedral sites occupied by vacancy (y), the fraction of octahedral sites occupied by vacancy (z), and the oxygen parameter (u) were determined as ones gave the best linearity in the relation between in (Iobs(hκl)/Icalc(hκl)) and sin2θhκl/λ2. The results are listed in Table 2. The values of x and u did not vary significantly with the condition of heat-treatment. It was concluded that 20-30% of tetrahedral sites were occupied by aluminum and the rest was occupied by cobalt in cobalt aluminum oxides, i.e. the cation distribution was intermediate between normal and inverse. In the photoacoustic spectra, the peaks of Co3+ ions in octahedral sites were observed for the samples heat-treated at high PO2 (Yogyo-Kyokai-Shi, 91, 131-36 (1983)). It was supposed that Co3+ ions were formed by the oxidation of Co2+ ions at high PO2, and that the defective spinel was formed by the change of the ratio of bivalent cations (Co2+ ions) to trivalent cations (Al3+ ions and Co3+ ions). The amount of Co3+ ions formed at high PO2 was estimated to be too small to affect the cation distribution in cobalt aluminum oxides.
The effect of the atmosphere of heat-treatment on the valence and the coordination state of the cobalt ions were investigated. Cobalt carbonate and α-alumina were mixed in the equimolar ratio, and ...the mixture was heat-treated at 1400°C or 1300°C under various partial pressure of oxygen (Po2) from 2.1×10-1 atm to 1.7×10-7 atm for the heat-treatment at 1400°C, and from 2.1×10-1 atm to 1.1×10-8 atm at 1300°C. The lattice constants and the photoacoustic spectra (PAS) of the samples were measured. The lattice constants were scarcely changed with temperature and oxygen partial pressure of the heat-treatment (Table 1). In the PAS of the samples heat-treated in low Po2 region, only the peak corresponding to the 4A2(F)→4T1(P) transition of Co2+ ions in the tetrahedral sites was observed. On the samples heat-treated in high Po2 region, however, additional peaks were observed, correspoding to the 4T1g(F)→4T1g(P) transition of Co2+ ions in the octahedral sites and also to the 1A1g(D)→1T2g(D) and 1A1g(D)→1T1g(D) transitions of Co3+ ions in the octahedral sites (Figs. 1 and 2, and Tables 2, 3 and 4). Then the following conclusions were deduced. In low Po2 region, the cobalt ions in the samples were all bivalent and occupied the tetrahedral sites (normal spinel). In high Po2 region, the following four reactions were supposed to take place at the same time. (1) The Co3+ ions were formed by the oxidation of the Co2+ ions. (2) By the reaction (1), the quantity of the Co2+ ions was decreased. Then the quantity of Al2O3 exceeded the stoichiometric quantity of CoO, and the defective spinel was formed. (3) The Co3+ ions substituted for the Al3+ ions in the defective spinel. (4) A part of the Co2+ ions occupied the octahedral sites. The lattice constants were favored to decrease by the formation of the defective spinel (reaction (2)), but favored to increase by the substitution of the Co3+ ions for the Al3+ ions (reaction (3)). As the result of the competition of the above two reactions, the lattice constants were scarcely changed.
•Surfaces coating with CoAl2O4 for LNMO improve its thermal stability distinctly.•The dissolution of transition metal of LNMO in electrolyte is alleviated, which keep the structure of electrode ...integrity.•The electrochemical performance of LNMO at high temperature is improved obviously after CoAl2O4 coating.
Aluminum cobalt oxide-coated LiNi0.5Mn1.5O4 (LNMO) cathode materials are synthesized via a wet-coating method. The surface coating of the LNMO with cobalt aluminum oxide (CoAl2O4) does not alter its spinel structure, but greatly affects its thermostability. The complete, thin cobalt aluminum oxide coating layer strongly adheres to the host material and possesses a great thermal stability and electrochemical resistance, and it is not damaged in acid or alkali environments. The CoAl2O4 coating layer in this work successfully inhibits the dissolution of transition metal ions and maintain the stability of the LNMO structure. This CoAl2O4 coating layer also hold back the HF scavenger of the spinel structure in the electrolyte, which leads to enhanced electrochemical properties, especially at high temperatures. Furthermore, the coated LNMO exhibits an obviously improved thermostability compared with bare LNMO.
The Cover Feature shows lithium nickel cobalt aluminum oxide/reduced graphene oxide composites, which can be potentially used as cathodes in high energy density Li‐ion batteries for electric ...vehicles. These cathodes exhibit excellent electrochemical performances, owing to the unique microstructures. More information can be found in the Article by R. Chen et al on page 3176 in Issue 21, 2018 (DOI: 10.1002/celc.201800878).
Aluminum cobalt oxide-coated LiNi sub(0.5)Mn sub(1.5)O sub(4) (LNMO) cathode materials are synthesized via a wet-coating method. The surface coating of the LNMO with cobalt aluminum oxide (CoAl ...sub(2)O sub(4)) does not alter its spinel structure, but greatly affects its thermostability. The complete, thin cobalt aluminum oxide coating layer strongly adheres to the host material and possesses a great thermal stability and electrochemical resistance, and it is not damaged in acid or alkali environments. The CoAl sub(2)O sub(4) coating layer in this work successfully inhibits the dissolution of transition metal ions and maintain the stability of the LNMO structure. This CoAl sub(2)O sub(4) coating layer also hold back the HF scavenger of the spinel structure in the electrolyte, which leads to enhanced electrochemical properties, especially at high temperatures. Furthermore, the coated LNMO exhibits an obviously improved thermostability compared with bare LNMO.
An Equivalent Circuit Model (ECM) of a lithium ion (Li-ion) battery is an empirical, linear dynamic model and the bandwidth of the input current signal and level of non-linearity in the voltage ...response are important for the model’s validity. An ECM is, however, generally parametrised with a pulse current signal, which is low in signal bandwidth (Part 1) and any non-linear dependence of the voltage on the current due to transport limitations is ignored. This paper presents a general modelling methodology which utilises the higher bandwidth and number of signal levels of a pulse-multisine signal to estimate the battery dynamics and non-linear characteristics without the need of a 3D look-up table for the model parameters. In the proposed methodology a non-parametric estimate of the battery dynamics and non-linear characteristics are first obtained which assists in the model order selection, and to assess the level of non-linearity. The new model structure, termed as the Non-linear ECM (NL-ECM), gives a lower Root Mean Square (RMS) and peak error when compared to an ECM estimated using a pulse data set.
•Presents a novel lithium ion model, NL-ECM, for use in Battery Management Systems.•Includes a 2nd order linear model, non-linear sigmoid function and hysteresis OCV.•Model developed with pulse-multisine signals.•The model is SoC, temperature and current dependent without a 3D look-up table.•Model accuracy is improved compared to an ECM estimated with a pulse.
Ni‐rich materials are promising Li‐ion battery cathodes due to their high capacity but still suffer from electrolyte corrosions and inferior thermal stability, limiting the lithium storage ...capability. To improve both, lithium storage performances and thermal stability, LiNi0.815Co0.15Al0.035O2 (LNCAO)/reduced graphene oxide (RGO) composites are synthesized by chemical lithiation of commercial Ni0.815Co0.15Al0.035(OH)2 precursors with LiOH ⋅ H2O, followed by simply wet coating with RGO. The effects of such RGO modifications on lithium storage performances and thermal stability of the achieved LNCAO/RGO are investigated. Compared to LNCAO, the unique LNCAO/RGO (with ∼2.5 wt.% RGO) electrodes exhibit considerably improved cycling stability and high‐rate capability (a reversible capacity of 135 mAh g−1 at 10 C), with a capacity decay rate of 0.07 % per cycle at 1 C, half of that of pristine LNCAO (0.14 %/cycle). As evidenced by differential scanning calorimetry, thermal stability is also significantly enhanced since the heat generation decreases from 912 to 586 J g−1 for pristine LNCAO and LNCAO/RGO, respectively. This could be ascribed to the unique structures and the encapsulated RGO coating layers, effectively protecting LNCAO against electrolyte corrosions and decreasing the level of Li+/Ni2+ disordering. This study helps us further understand the critical roles of RGO layers in electrochemical performances and thermal stability of Ni‐rich‐based cathodes for lithium/sodium storage.
A lithium nickel cobalt aluminium oxide/reduced graphene oxide (LNCAO/RGO) composite is synthesized by chemical lithiation of commercial NCA, followed by coating with RGO. The effects on electrochemical performances and thermal stability are investigated. RGO shells provide protection against electrolyte corrosions and diminish Li+/Ni2+ disordering, resulting in remarkable long‐term cycling stability, rate capability and thermal stability.
Accurate battery modelling requires precise measurements of key battery characteristics, including their surface temperature during fast charging and discharging states. Battery surface temperature ...measurements are also used to mitigate thermal events such as thermal runaway, which can cause fires. Established literature has shown that there are significant variations in temperature measurements of the surface of lithium-ion cells between various thermocouple sensors, including common K and T-Type thermocouples. In this paper, these variations in temperature measurements are investigated for the first time in the context of battery characterisation. The surface temperatures of two lithium-ion cells, a 21700-model Lithium Nickel Cobalt Aluminium Oxide (NCA) cylindrical cell and a Lithium Titanate Oxide (LTO) pouch cell, are measured during high current cycling using a variety of different thermocouples and an infrared camera to study the variations and response times in the temperature measurements recorded. The impact of electromagnetic fields emitted by the lithium-ion cells on the temperature measurements is also investigated. Results reported indicate a trend in the size of the temperature sensor with the response time of the cell surface temperature measurements. The recommendations of temperature sensors based on these findings allow for improved response time and accuracy of cell surface temperature measurements.
•Measurement of sensor response time of Li-ion cell surface temperature.•Comparison of thermocouples and IR camera for Li-ion thermal testing.•Determine the effects of magnetic field on thermocouple temperature measurement.
Lithium-Ion batteries used for electric vehicle applications are subject to large currents and various operation conditions, making battery pack design and life extension a challenging problem. With ...increase in complexity, modeling and simulation can lead to insights that ensure optimal performance and life extension. In this manuscript, an electrochemical-thermal (ECT) coupled model for a 6 series × 5 parallel pack is developed for Li ion cells with NCA/C electrodes and validated against experimental data. Contribution of the cathode to overall degradation at various operating conditions is assessed. Pack asymmetry is analyzed from a design and an operational perspective. Design based asymmetry leads to a new approach of obtaining the individual cell responses of the pack from an average ECT output. Operational asymmetry is demonstrated in terms of effects of thermal gradients on cycle life, and an efficient model predictive control technique is developed. Concept of reconfigurable battery pack is studied using detailed simulations that can be used for effective monitoring and extension of battery pack life.
•Development of a physics based series parallel pack model.•Contributions of cathode degradation towards capacity fade.•Design and operation based asymmetry analysis.•Predictive control algorithm for temperature management.•Life extension using reconfigurable battery pack.
A reduced order model (ROM) is proposed for accurate prediction of electrochemical and thermal response of lithium ion cells. The order reduction is carried on the coupled partial differential ...equations (PDE) of the electrochemical thermal model by consistent volume averaging of local heat generation and spatial temperature variation. The model is validated with experimental data for temperatures ranging from 253 K–333 K. It is seen that modification of ROM to account for low electronic conductivity results in accurate voltage estimation of cells with lithium nickel cobalt aluminium oxide (LNCO) cathodes. A detailed parametric sensitivity to operating conditions is provided. The utility of ROM for on-board state estimation is demonstrated by applying to realistic drive cycle protocols such as the Hybrid Pulse Power Characterization (HPPC) and the Urban Dynamometer Driving Schedule (UDDS) data. The electrochemical structure of ROM enables identification of controlling processes, and analysis of HPPC results reveal that Ohmic drop of cathode is controlling at high rates and the electrolyte potential during rest phase. Based on accurate voltage prediction, computational speed and physical insights, it can be concluded that the proposed ROM is an adequate state estimation and a cell design tool.
•Reduced order model for coupled electrochemical thermal response•Thermal balance with local heat generation used for model order reduction.•Model validated with experimental data at low, high and room temperatures.•Model validation with HPPC and UDDS data.
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