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The thermal performance of lithium-ion battery cells is critical for ensuring their safe and reliable operation across various applications. In this study, we employed an isothermal calorimetry method to investigate the heat generation of commercial 18650 lithium-ion battery fresh cells during charge and discharge at different current rates, ranging from 0.05C to 0.5C, and across various temperatures: 20 °C, 30 °C, 40 °C, and 50 °C. Our findings revealed a direct correlation between heat generation and current rates, indicating that higher current rates lead to increased heat generation within the cells. Conversely, we observed that heat generation remained relatively stable as the temperature rose, suggesting that temperature changes within this range may not significantly impact the heat generation of fresh cells during typical operations. Furthermore, our study explored irreversible heat generation, which depends on the applied current and overpotential, using the galvanostatic intermittent titration technique at 0.05C–0.5C and 30 °C. Additionally, electrochemical impedance spectroscopy was performed on the same cells during charge and discharge at 20 °C, 30 °C, and 40 °C to analyze cell impedance. Our results indicated a consistent dependence of impedance on the state of charge and depth of discharge, with a significant increase in impedance observed at the end of the discharge process. • Comprehensive analysis of heat generation in commercial 18650 Li-ion battery cells. • Comparison of heat generation at different operating temperatures. • Higher C-rates significantly increase heat generation and affect cell performance. • Irreversible heat is influenced by overpotential and internal resistance. • Differentiation between Joule heating and entropy changes across the state of charge. [ABSTRACT FROM AUTHOR]

Lithium ion batteries in the coin-cell form factor (2032) initially charged to 4.2 V at ambient temperature are stored at 60 °C and 70 °C for up to 8 weeks. The cells discharge capacity (Q d) and thermodynamic properties, including open-circuit potential (OCP), entropy (ΔS) and enthalpy (ΔH) are measured after each completed ageing week. Post-mortem analysis of aged anodes and cathodes is investigated by X-ray diffractometry (XRD) and Raman Scattering spectrometry (RS) in an attempt to correlate thermodynamic data to changes in the crystal structure characteristics. It is found that degradation of the electrode materials' crystal structure accounts for most of the observed changes in the cells' thermodynamics with well quantified and distinct contributions from anode and cathode. [ABSTRACT FROM AUTHOR]

Abstract: Lithium ion batteries (LiB) are cycled under a galvanostatic regime (∼C/2-rate) between 2.75 V and 4.2 V for up to 1000 cycles. After each completed 100 cycles, the discharge capacity, capacity loss, average discharge potential were determined under the same C/2 rate. Then cells undergo an additional charge and discharge cycle at C/6 rate followed by a thermodynamics measurements test. This enables open-circuit potential (OCP), entropy (ΔS) and enthalpy (ΔH) data to be assessed. It is found that with increasing cycle number, the entropy and enthalpy profiles show more significant changes than those observed in the discharge and the OCP curves especially at particular SOC and OCP values. These differences are attributed to the higher sensitivity of entropy and enthalpy state functions to changes in the crystal structure of the graphite anode and the lithiated cobalt oxide (LCO) induced by cycle aging compared to the free energy ΔG (OCP) alone. The thermodynamics data are supported by post-mortem X-ray diffractometry (XRD) and Raman scattering (RS) analyses on the electrode materials. The results show important LCO crystal structure degradation, whereas, surprisingly, the graphite anode remains almost unaffected by heavy cycling, if not improved. [Copyright &y& Elsevier]

Abstract: We have investigated the evolution of the thermodynamics behaviour and of the crystal structure of electrodes materials of lithium-ion batteries based on graphite anode and lithium cobalt oxide (LCO) cathode after applying high voltage charging between 4.2V and 4.9V cut-off voltages (COV). We found the entropy and enthalpy profiles vary dramatically with the applied COV. These changes correlate well with the anode and the cathode crystal structure degradation as evidenced by post-mortem X-ray diffractometry and Raman scattering spectrometry. Our finding is thermodynamics measurements can be used as a new and non-destructive investigation tool to characterize the degradation level of electrode materials and consequently assess the cell's state of health (SOH). [Copyright &y& Elsevier]

Abstract: The complex structural transformations of Li0.5Ni0.25TiOPO4 during electrochemical lithiation have been examined by in situ X-ray diffraction. During the first lithiation two structural changes take place: first a transition to a second monoclinic phase (a =9.085(4), b =8.414(5), c =6.886(5), β =99.85(4)) and secondly a transition to a third phase with limited long-range order. The third phase is held together by a network of corner sharing Ti–O octahedra and phosphate ions with disordered Ni–Li channels. During delithiation the third phase is partially transformed back to a slightly disordered original phase, Li0.5Ni0.25TiOPO4 without formation of the second intermediate phase. These phase transitions correspond well to the different voltage plateaus that this material shows during electrochemical cycling. [Copyright &y& Elsevier]

Abstract: Ni0.5TiOPO4 oxyphosphate exhibits good electrochemical properties as an anode material in lithium ion batteries but suffers from its low conductivity. We present here the electrochemical performances of the synthesized Ni0.5TiOPO4/carbon composite by using sucrose as the carbon source. X-ray diffraction study confirms that this phosphate crystallizes in the monoclinic system (S.G. P21/c). The use of the Ni0.5TiOPO4/C composite in lithium batteries shows enhanced electrochemical performances compared with the uncoated material. Capacities up to 200mAhg−1 could be reached during cycling of this electrode. Furthermore, an acceptable rate capability was obtained with very low capacity fading even at 0.5C rate. Nevertheless, a considerable irreversible capacity was evidenced during the first discharge. In situ synchrotron X-ray radiation was utilized to study the structural change during the first discharge in order to evidence the origin of this irreversible capacity. Lithium insertion during the first discharge induces an amorphization of the crystal structure of the parent material accompanied by an irreversible formation of a new phase. [Copyright &y& Elsevier]

Abstract: Li0.5Ni0.25TiOPO4/C composite was synthesized by the co-precipitation method using polyethylene glycol as carbon source. X-ray diffraction study showed that the as-prepared material crystallizes in the monoclinic system (S.G. P21/c). This 3D structure exhibits an open framework favourable to intercalation reactions. The morphology and the microstructure characterisation was performed by scanning electron microscopy (SEM). Small particles (∼1μm) coated by carbon were observed. Raman study confirms the presence of carbon graphite in the Li0.5Ni0.25TiOPO4/C composite. Cyclic voltammetry (CV) and charge–discharge galvanostatic cycling were used to characterize its electrochemical properties. The Li0.5Ni0.25TiOPO4/C composite exhibits excellent electrochemical performances with good capacity retention for 50 cycles. Approximately 200mAh/g could be reached at C, C/2, C/5 and C/20 rates in the 0.5–3V potential range. These results clearly evidenced the positive effect of the carbon coating on the electrochemical properties of the studied phosphate. [Copyright &y& Elsevier]

Abstract: Layered LiNi0.2Mn0.2Co0.6O2 phase, belonging to a solid solution between LiNi1/2Mn1/2O2 and LiCoO2 most commercialized cathodes, was prepared via the combustion method at 900°C for a short time (1h). Structural, electrochemical and magnetic properties of this material were investigated. Rietveld analysis of the XRD pattern shows this compound as having the α-NaFeO2 type structure (S.G. R-3m; a =2.8399(2)Ǻ; c =14.165(1)Ǻ) with almost none of the well-known Li/Ni cation disorder. SQUID measurements clearly indicate that the studied compound consists of Ni2+, Co3+ and Mn4+ ions in the crystal structure. X-ray analysis of the chemically delithiated Li x Ni0.2Mn0.2Co0.6O2 phases reveals that the rhombohedral symmetry was maintained during Li-extraction, confirmed by the monotonous variation of the potential–composition curve of the Li//Li x Ni0.2Mn0.2Co0.6O2 cell. LiNi0.2Mn0.2Co0.6O2 cathode has a discharge capacity of ∼160mAhg−1 in the voltage range 2.7–4.3V corresponding to the extraction/insertion of 0.6 lithium ion with very low polarization. It exhibits a stable capacity on cycling and good rate capability in the rate range 0.2–2C. The almost 2D structure of this cathode material, its good electrochemical performances and its relatively low cost comparing to LiCoO2, make this material very promising for applications. [Copyright &y& Elsevier]