Abstract: Lithium ion batteries of coin-cell form factor (2032) are subjected to thermal aging at 60 °C
and 70 °C for a period of up to 8 weeks after being charged to 4.2 V at ambient temperatures.
The cells thermodynamic properties, including open-circuit potential (OCP), discharge
capacity (QD), entropy (ΔS) and enthalpy (ΔH), are measured each week. Post-mortem
analysis of aged anodes and cathodes is carried out by X-ray diffractometry (XRD) and
Raman Scattering spectrometry (RS) in an attempt to correlate thermodynamic data to
changes in the crystal structure characteristics. We show that degradation of the electrode
materials’ crystal structure accounts for most of the observed changes in the cells’
thermodynamics with well-defined and distinct contributions from anode and cathode.
Abstract: Lithium ion batteries (LiB) have been cycled under galvanostatic regime (~C/2-rate) between 2.75V and 4.2V for up to 1000 cycles. After each finished 100 cycles, cells undergo an additional charge and discharge cycle at C/6 rate followed by a thermodynamics measurements test. This enables discharge capacity, capacity loss, average discharge potential, open-circuit potential (OCP), entropy (ΔS) and enthalpy (ΔH) data to be assessed.
It is found that with increasing cycle number, entropy and enthalpy profiles show more important changes than those observed in the discharge and the OCP curves at particular SOC and OCP values. Differences are attributed to 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 ageing compared to the free energy ΔG alone. Thermodynamics findings are supported by post-mortem X-ray diffractometry (XRD) and Raman Scattering (RS) analyses on electrode materials. The results show important LCO crystal structure degradation, whereas the graphite anode remains almost unaffected, if not improved by heavy cycling.
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.
Abstract: We have investigated the evolution of the thermodynamics behavior 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 4.2 V and 4.9 V 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).
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.
Abstract: We have studied the first lithiation/delithiation cycle of the Li-ion battery electrode material
LixNi0.25TiOPO4 applying X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray
scattering (RIXS). A set of ten identical LixNi0.25TiOPO4 battery electrodes have been cycled and
left in different states of charge in the range of x = 0.5 . . . 2.5, before disassembly in an Ar filled
glove box. We find that Ni-, Ti-, and O-ions are affected simultaneously, rather than sequentially,
upon lithiation of the material. In particular, Ni is reduced from Ni2+ to Ni0 but only partially
re-oxidized to Ni1+, again, by delithiation. Overall, there is considerable ‘‘crosstalk’’ between the
different atomic species and non-linearity in the response of the electronic structure during the
lithiation/delithiation process. Fortuitously, the background variation in Ni L-XAS shows to
contain valuable information about solid–electrolyte interface (SEI) creation, showing that the
SEI is a function of the degree of lithiation.
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 â—¦C for a short time
(1 h). Structural, electrochemical and magnetic properties of this material were investigated. Rietveld
analysis of the XRD pattern shows this compound as having the -NaFeO2 type structure (S.G. R-3m;
a = 2.8399(2) ´˚A; c = 14.165(1) ´˚A) 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 LixNi0.2Mn0.2Co0.6O2 phases reveals that the rhombohedral
symmetry was maintained during Li-extraction, confirmed by the monotonous variation of the
potential–composition curve of the Li//LixNi0.2Mn0.2Co0.6O2 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 0.2–2 C. 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.
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 (∼1m) 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 200 mAh/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.
Abstract: Li-ion batteries (LiB) in coin-cell form factor (2032) rated capacity of ~ 44 mAh were subjected to high temperature (HT), high voltage (HV) and long cycle (LC) ageing tests. For HT tests, cells were stored at initial charged state of 4.2V in an oven at 60°C±1°C and 70°C±1°C for a period of time up to 8 weeks. For HV tests, cells were charged between 4.2V and 4.9V cut of voltages at ambient temperature and for LC tests, cells were cycled between 4.2-2.75V at a C/2 rate at ambient temperature for up to 1000 cycles. Thermodynamics proprieties of aged cells including open-circuit potential (OCP), entropy (ΔS) and enthalpy (ΔH) were measured using electrochemical thermodynamics measurement system (ETMS) [1].
Here we carried out a comparative study of thermodynamics properties of cells having experienced a same capacity loss under different ageing modes. We found entropy and enthalpy profiles of equi-capacity loss cells (5% to 25%) varied with the ageing mode, a phenomenon attributed to an ageing memory effect in lithium ion batteries. In fact we found the mechanism of capacity loss, such anode and cathode crystal structure degradation, which were investigated by ex-situ XRD and Raman analyses, and electrolyte decomposition strongly depend on the cells ageing mode. Our thermodynamics method makes it possible distinguish anode and cathode contribution to the cell’ thermodynamics. Capacity losses relate to both anode and cathode degradation, which extends depend on the ageing mode. Accordingly batteries having experienced the same capacity loss should bear a different thermodynamics signature.
Abstract: Electrochemical Thermodynamics Measurement (ETM) is an effective new method to monitor phase transitions and chemical reactions in electrode materials. The entropy (ΔS) and enthalpy (ΔH) profiles vs. the state of charge (SOC) and open-circuit potential (OCP) are achieved by measuring the temperature dependence of the OCP at fixed SOC [1].
The purpose of this study is to investigate the size effect of LCO cathode materials on the electrochemical performances and on the thermodynamics properties.
Nanostructured LCO samples in 8-30nm range were synthesized by hydrothermal reaction using CoOOH and LiOH in aqueous solution as precursors[2]. Crystal structure and morphology of the synthesized powders were characterized by X-ray diffractometry, Raman scattering spectrometry and FESEM. Results show that the reaction temperature and the concentration of the LiOH solution greatly influence the particle size, shape, morphology and degree of crystalinity of nano-LCO.
Thermodynamics measurements showed large differences in ΔS and ΔH profiles between nano-size and micro-size (commercial) materials. This should result from additional disorder in nano-LCO than in micro owing to cation mixing between the oxygen layers. Such differences which appear clearly in the ΔS and ΔH profiles are hardly observable by XRD and Raman spectroscopy. This poses ETM is a complementary (and non-destructive) analytical method to XRD and Raman to accurately investigate electrode materials for lithium ion application.
Abstract: Electrochemical Thermodynamic Measurement (ETMS) is one of the most promising methods for characterizing aging effects of batteries because it provides big amount of information about the thermodynamics behavior of batteries during ageing.
The advantage of ETMS technology is the big changes in the entropy and the enthalpy profiles during again.
In this work, we tested commercial Li-ion full cells to determine their entropy and enthalpy changes by measuring their equilibrated OCV as function of temperature and state of charge (SOC) during thermal ageing at two different temperature (60°C and 70°C), high voltage and cycling ageing.
Comparison of the results revealed that the again causes a decrease of the capacity and also affect the thermodynamic stability of the batteries, by growing SEI surface film in anode side and the conversion of hexagonal phase to spinel inactive phase in the cathode side.
The obtained results can be also used for determination of state of health (SOH) of the batteries.
The results will be discussed in detail during the presentation.
Abstract: We have investigated the evolution of thermodynamics behaviour of lithium ion batteries
(LIB) coin cells in the process of accelerated ageing at high temperatures and after
overcharge at the ambient temperatures. Gibbs free energy, entropy and enthalpy were
measured at different battery states of charge (SOC) using an automatic Electrochemical
Thermodynamics Measurement System (ETMS BA-1000) developed by us shown in Figure
1. Figure 2 shows a typical OCV and entropy profile of a cell before ageing. Onsets of
entropy changes marked with A and C letters correspond to phase transitions occurring in the
anode (staging in graphite) and in the cathode (hexagonal and monoclinic phases in LCO),
respectively. These transitions occur at well defined lithium compositions in the anode and
the cathode. We have used them as markers to determine the battery SOC in the course of
ageing.
Figure 3 and 4 show the evolution of the entropy and differential entropy during cells ageing
at high voltage (overcharge). These results will be discussed in relation with the cells state of
health (SOH) and state of safety (SOS).
Abstract: Pursuing our decade-long research effort on thermodynamics studies of lithiumion cells, we have followed changes in the entropy and enthalpy profiles of full coin cells in the process of thermal ageing, long cycle ageing and highvoltage (over-)charging. We also developed a new differential thermodynamics method that enables a highly accurate assessment of the cells’ state of health(SOH) and state of safety (SOS). We developed the equipment for thermodynamics measurements of battery cells (BA-1000, KVI PTE LTD, Singapore). BA-1000machine automatically scans the cell at different states of charge and collect the rmodynamics data by applying a small, yet highly accurate, temperature change to the cells, which affects its open-circuit voltage (OCV). We willpresent entropy and OCV profiles of a lithium ion battery based on graphiteanode and LiCoO2 cathode. Data refers to onsets of crystal structurechanges in the anode and the cathode, respectively. We’ve used these onsets as“markers†to follow changes in the battery SOH and SOS. The differential entropy profiles during high voltage (HV) ageing, as well as anode and cathode peaks evolution will also be discussed. In this presentation, we will discuss how thermodynamics data converts into SOH and SOS assessment.
Abstract: We used the ETMS [1] technology to follow changes in the thermodynamics behavior of full lithium ion cells during thermal ageing and high voltage ageing.
For thermal ageing cells were stored in an oven at 60C and 70C at their initial full charged state (4.2V). Cells were removed each week, left to cool to the ambient temperature and were then tested by ETMS. For the high voltage ageing, cells were over-charged by 100mV increments of the end of charge voltages between 4.2V and 4.9V at ambient temperature then cells were tested by ETMS.
Fig. 1 and 2 show the entropy profiles obtained in cells aged at 60C and 70C for up to 7 weeks, respectively. Changes can be observed particularly in the 60-90% and 0-10% SOC areas. The changes are the signature of anode and cathode materials degradation during ageing. In fact we can assign each peak and minima in the entropy profile to phase transitions occurring in the anode and the cathode, respectively.
Fig. 3 shows the entropy profile evolution before and after overcharging between 4.2 (standard) up to 4.9V. Dramatic changes take place in the entropy profiles in the SOC area as above but also in the 10-40% area.
Changes in the entropy profiles arise from changes in lithium ion and electron configurations in anode and cathode as they degrade upon ageing. Here the cathode and the anode consist of LiCoO2 and graphite, respectively as evidenced for ex-situ XRD analysis. LiCoO2 undergoes phase transformations during both delithiation (charge) and ageing. Irreversible changes such as the conversion of hexagonal to spinel phases in LiCoO2 [2] and the possible solvent co-intercalation at the graphite-electrolyte interface (SEI) both account not only for capacity loses but also affect the overall thermodynamics behavior of the lithium cell. We will introduce our newly developed differential thermodynamics technique that allows better magnifying changes in the entropy and the enthalpy state functions with application to accurate state of health (SOH) assessment.
These results will be further discussed in detail during the presentation.
Abstract: Electrochemical Thermodynamic Measurement (ETMS) is one of the most promising methods for characterizing aging effects of batteries because it provides big amount of information about the thermodynamics behavior of batteries during ageing.
The advantage of ETMS technology is the big changes in the entropy and the enthalpy profiles during again.
In this work, we tested commercial Li-ion full cells to determine their entropy and enthalpy changes by measuring their equilibrated OCV as function of temperature and state of charge (SOC) during thermal ageing at two different temperature (60°C and 70°C), high voltage and cycling ageing.
Comparison of the results revealed that the again causes a decrease of the capacity and also affect the thermodynamic stability of the batteries, by growing SEI surface film in anode side and the conversion of hexagonal phase to spinel inactive phase in the cathode side.
The obtained results can be also used for determination of state of health (SOH) of the batteries.
The results will be discussed in detail during the presentation.
Abstract: This thesis is devoted to finding new negative electrode materials for Li-ion batteries and more particularly to oxyaphosphates compounds. These materials exhibit a higher volumetric densities than those used of carbon compounds.
Li0,5Ni0,25TiOPO4 and Ni0,5TiOPO4 oxyphosphates were prepared by coprecipitation method, coated by a carbon layer and then characterized by X-ray diffraction, Raman spectroscopy, TGA, SEM and TEM microscopies.
The galvanostatic tests of these oxyphosphates showed a better reversibility of the electrochemical process and a good cycling stability after the first discharge, either for long-term cycling at constant rate or for power cycling.
Detailed analysis of electrochemical process during the first cycle discharge/charge consist in a reduction of Ti4+ ions into Ti3+ and Ni2+ ions into Ni0 via Ni+ during discharge and their partial reoxidation during charge.
The observed irreversibility during the first discharge has been studied by X-ray absorption spectroscopy (XAS), resonant inelastic X-ray scattering (RIXS) and in situ synchrotron. This irreversibility is related to the formation of a solid electrolyte interface (SEI) on the surface of oxyphosphates particles and to the amorphization of the parent phase accompanied by the formation of a new nanostructural and/or amorphous phase during the first discharge.
