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Figure 3. Evolution of the end-of-charge and discharge potentials of both electrodes during cycling at 5°C between 2.7 V and 4.2 V. Measurements obtained wi reference electrode inserted in 16 Ah Li-ion cell #4. In the literature, some authors reported that metallic lithium de- posited on the surface of the graphite electrode can diffuse into the active material during the relaxation time by chemical reaction to form graphite intercalation compounds resulting in a capacity Ono one 1e hand, the end-of-charge potential (CV phase) of the nega- tive electrode decreases from 62.57 mV vs. Lit/Li (1 cycle) to 7.784 mV vs. Lit/Li (50% cycle) as a decrease of about 55 mV as shown

Figure 3 Evolution of the end-of-charge and discharge potentials of both electrodes during cycling at 5°C between 2.7 V and 4.2 V. Measurements obtained wi reference electrode inserted in 16 Ah Li-ion cell #4. In the literature, some authors reported that metallic lithium de- posited on the surface of the graphite electrode can diffuse into the active material during the relaxation time by chemical reaction to form graphite intercalation compounds resulting in a capacity Ono one 1e hand, the end-of-charge potential (CV phase) of the nega- tive electrode decreases from 62.57 mV vs. Lit/Li (1 cycle) to 7.784 mV vs. Lit/Li (50% cycle) as a decrease of about 55 mV as shown

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used. A voltage range of 2.74.2 V is allowed. Graphite is the negative electrode and NMC oxide is the positive electrode while the separator is constituted by microporous polyethylene film and the electrolyte is based on carbonates. and Fourier Transform Infrared Spectroscopy (FTIR) measurements it was possible to identify the constituents of the outer and inner SEI.** Further investigations of graphite electrodes can be achieved with Glow Discharge Optical Emission Spectroscopy (GD-OES). N. Ghanbari et al. used this technique to determine significant differences between anodes with Li deposition and with SEI.“4 Table I. Protocol of cycling at 5°C according to the following voltage limits strategies. The capacity of each Li-ion cell is measured at the beginning of life (BOL) and at the end of life (EOL) at a rate of 1C at 25°C.
used. A voltage range of 2.74.2 V is allowed. Graphite is the negative electrode and NMC oxide is the positive electrode while the separator is constituted by microporous polyethylene film and the electrolyte is based on carbonates. and Fourier Transform Infrared Spectroscopy (FTIR) measurements it was possible to identify the constituents of the outer and inner SEI.** Further investigations of graphite electrodes can be achieved with Glow Discharge Optical Emission Spectroscopy (GD-OES). N. Ghanbari et al. used this technique to determine significant differences between anodes with Li deposition and with SEI.“4 Table I. Protocol of cycling at 5°C according to the following voltage limits strategies. The capacity of each Li-ion cell is measured at the beginning of life (BOL) and at the end of life (EOL) at a rate of 1C at 25°C.
Figure 1. Procedure of the insertion of metal lithium as reference electrode into a 16 Ah commercial Li-ion cell. (1): Illustration of the fresh 16 Ah commercial high power Li-ion pouch cell. (2): A lithium metal electrode of a surface of 16 mm? and a thickness of 50 \.m is inserted into the cell. Ni is used as the current collector. (3): Once the reference electrode is introduced into the battery, external incisions are done for isolation. The second reference electrode serves as a backup. (4): The cell is placed in a mold before being resined. (5): The instrumented cell is then completely resined for safety reasons. (6): 16 Ah commercial Li-ion pouch cell instrumented with reference electrodes.
Figure 1. Procedure of the insertion of metal lithium as reference electrode into a 16 Ah commercial Li-ion cell. (1): Illustration of the fresh 16 Ah commercial high power Li-ion pouch cell. (2): A lithium metal electrode of a surface of 16 mm? and a thickness of 50 \.m is inserted into the cell. Ni is used as the current collector. (3): Once the reference electrode is introduced into the battery, external incisions are done for isolation. The second reference electrode serves as a backup. (4): The cell is placed in a mold before being resined. (5): The instrumented cell is then completely resined for safety reasons. (6): 16 Ah commercial Li-ion pouch cell instrumented with reference electrodes.
ible II. Post-mortem electrochemical measurements (performed at 25°C) of single components with coin half cells. The nominal capacity of each raphite/Li metal coin half-cell is 3.3 mAh with Vinin = 0.02 V and Vinax = 1.5 V while the nominal capacity of each NMC/Li metal coin half-cell 2.88 mAh with Vinin = 2.6 V and Vmax = 4.1 V. The capacity shown in this Table is measured at 0.1 C.
ible II. Post-mortem electrochemical measurements (performed at 25°C) of single components with coin half cells. The nominal capacity of each raphite/Li metal coin half-cell is 3.3 mAh with Vinin = 0.02 V and Vinax = 1.5 V while the nominal capacity of each NMC/Li metal coin half-cell 2.88 mAh with Vinin = 2.6 V and Vmax = 4.1 V. The capacity shown in this Table is measured at 0.1 C.
Table III. Composition of different electrolytes based on elements detected from the fresh electrolyte with GC-MS: ethyl methyl carbonate (EMC); ethylene carbonate (EC); biphenyl (BP); 1,3 propane sultone (PS); vinylene carbonate (VC), fluoroethylene carbonate (FEC). C-rate is repeated 5 times except the first C-rate at 0.1C which is repeated only 3 times.
Table III. Composition of different electrolytes based on elements detected from the fresh electrolyte with GC-MS: ethyl methyl carbonate (EMC); ethylene carbonate (EC); biphenyl (BP); 1,3 propane sultone (PS); vinylene carbonate (VC), fluoroethylene carbonate (FEC). C-rate is repeated 5 times except the first C-rate at 0.1C which is repeated only 3 times.
Figure 2. Evolution of the capacity during the cycling test performed at 5°C. Fast loss of capacity is observed for all the Li-ion cells for which cycling tests are performed between 2.7 V and 4.2 V.
Figure 2. Evolution of the capacity during the cycling test performed at 5°C. Fast loss of capacity is observed for all the Li-ion cells for which cycling tests are performed between 2.7 V and 4.2 V.
Figure 4. Visual inspections at discharged state of both negative and positive electrodes and separators of 16 Ah C/NMC commercial Li-ion pouch cells after cycling at 5°C and at a rate of 1 C.
Figure 4. Visual inspections at discharged state of both negative and positive electrodes and separators of 16 Ah C/NMC commercial Li-ion pouch cells after cycling at 5°C and at a rate of 1 C.
Figure 5. SEM analysis performed on a sample of graphite electrode recov: ered from the fresh commercial cell and on a sample graphite electrode from the cell #3, after cycling between 2.7 V and 4.2 V. Table IV presents the percentage of each element detected with Energy-dispersive X-ray spectroscopy (EDS) that confirms that there is no contamination by elements originating from the positive elec- trode. Lithium element could not be detected. However, due to its low atomic mass and its low energy of characteristic radiation, lithium element is not detectable with EDS.
Figure 5. SEM analysis performed on a sample of graphite electrode recov: ered from the fresh commercial cell and on a sample graphite electrode from the cell #3, after cycling between 2.7 V and 4.2 V. Table IV presents the percentage of each element detected with Energy-dispersive X-ray spectroscopy (EDS) that confirms that there is no contamination by elements originating from the positive elec- trode. Lithium element could not be detected. However, due to its low atomic mass and its low energy of characteristic radiation, lithium element is not detectable with EDS.
Table IV. Percentage of each element detected with SEM/EDS on samples of graphite electrodes respectively recovered from a fresh cell and from the cell #3. There is no contamination by elements of the positive electrode. State of health of each electrode.—Electrochemical measure- ments of single components with coin half cells.—As it seems difficult to extract more lithium ions from the graphite electrode to intercalate to the positive electrode, we aim to study de/re-intercalation mecha- nisms. Harvested cells are useful to test if it is still possible to delithiate or to relithiate aged electrodes. NMC/Li metal and Graphite/Li metal coin half cells based on electrodes respectively recovered from a fresh Li-ion cell and from the cell #3 are assembled.
Table IV. Percentage of each element detected with SEM/EDS on samples of graphite electrodes respectively recovered from a fresh cell and from the cell #3. There is no contamination by elements of the positive electrode. State of health of each electrode.—Electrochemical measure- ments of single components with coin half cells.—As it seems difficult to extract more lithium ions from the graphite electrode to intercalate to the positive electrode, we aim to study de/re-intercalation mecha- nisms. Harvested cells are useful to test if it is still possible to delithiate or to relithiate aged electrodes. NMC/Li metal and Graphite/Li metal coin half cells based on electrodes respectively recovered from a fresh Li-ion cell and from the cell #3 are assembled.
Figure 6. Electrochemical characterizations at 25°C with Graphite/Li metal and NMC/Li metal coin half-cells. No loss of capacity of insertion is observed with the NMC material recovered from the aged Li-ion cell. Lithium de/re-intercalation mechanisms are hindered with the aged graphite electrode. As presented in Figure 6 and in Table II, the first discharged and charged capacities are respectively 0 mAh and 2.411 mAh for NMC/Li metal coin half-cell based on fresh electrode (D). This result confirms On one hand, the first charged and discharged capacities are respec- tively 0 mAh and 2.602 mAh for the Graphite/Li metal coin half-cell based on fresh electrode (A). It is a confirmation that the fresh graphite was ful y delithiated. It is not possible at all to more delithiate. On the other hand, the first charged and discharged capacities are respec- tively 0. half-cel .153 mAh and 1.3602 mAh for the Graphite/Li metal coin based on aged electrode (B). They are respectively 0.202 mAh and 1.4752 mAh for the other one (C). In fact, even by applying alow c electrod Moreov: harge C-rate, it appears very difficult to delithiate this aged e, which nevertheless remains lithiated as described above. er, by applying a low discharge C-rate thereafter, it is diffi- cult to insert more lithium into the graphite, which is certainly fully lithiated anisms . It should be noted that lithium de/re-intercalation mech- into aged graphite particles are not totally obstructed since a part of Li, about 0.9 mAh, is recovered at a low rate (0.1 C) as seen in Figure 6 with Graphite/Li metal half coin cells based on har- vested graphite materials. Indeed, this capacity of about 0.9 mAh measured at 0.1 C represent about 1/3 of the capacity of the fresh graphite at the same C-rate which is about 2.8 mAh. It appears here clearly that only the negative electrode is involved in the loss of capacity.
Figure 6. Electrochemical characterizations at 25°C with Graphite/Li metal and NMC/Li metal coin half-cells. No loss of capacity of insertion is observed with the NMC material recovered from the aged Li-ion cell. Lithium de/re-intercalation mechanisms are hindered with the aged graphite electrode. As presented in Figure 6 and in Table II, the first discharged and charged capacities are respectively 0 mAh and 2.411 mAh for NMC/Li metal coin half-cell based on fresh electrode (D). This result confirms On one hand, the first charged and discharged capacities are respec- tively 0 mAh and 2.602 mAh for the Graphite/Li metal coin half-cell based on fresh electrode (A). It is a confirmation that the fresh graphite was ful y delithiated. It is not possible at all to more delithiate. On the other hand, the first charged and discharged capacities are respec- tively 0. half-cel .153 mAh and 1.3602 mAh for the Graphite/Li metal coin based on aged electrode (B). They are respectively 0.202 mAh and 1.4752 mAh for the other one (C). In fact, even by applying alow c electrod Moreov: harge C-rate, it appears very difficult to delithiate this aged e, which nevertheless remains lithiated as described above. er, by applying a low discharge C-rate thereafter, it is diffi- cult to insert more lithium into the graphite, which is certainly fully lithiated anisms . It should be noted that lithium de/re-intercalation mech- into aged graphite particles are not totally obstructed since a part of Li, about 0.9 mAh, is recovered at a low rate (0.1 C) as seen in Figure 6 with Graphite/Li metal half coin cells based on har- vested graphite materials. Indeed, this capacity of about 0.9 mAh measured at 0.1 C represent about 1/3 of the capacity of the fresh graphite at the same C-rate which is about 2.8 mAh. It appears here clearly that only the negative electrode is involved in the loss of capacity.
Figure 7. XRD studies of the cathode Lix(Mno,4Coo.2Nio,4)O2 and anode (Graphite) materials. In situ XRD measurements are performed on a sample of a fresh cathode electrode in order to obtain a calibration curve of lattice parameters in function of lithium rate. Figure 7 illustrates XRD measurements performed on positive electrodes (left figure) and the calibration curve obtained from in situ measurements with a fresh NMC sample (right figure). The left figure presents the contribution of Ka, of the reflections 018, 110 and 113 for the fresh and cycled samples. The Aluminum collector peaks are visible. Lattice parameters obtained from the NMC recovered from the cell #5 are equal to those determined from the fresh cathode while those obtained with the NMC electrode recovered from the cell #3 have significantly evolved. Determination of the state of lithiation of electrodes with XRD measurements.— XRD studies of the cathode material_—Samples of positive elec- trodes respectively recovered from the fresh 16 Ah Li-ion cell, from the cell #3 (dismantled after full cycling at 5°C) and from the cell #5 (dismantled after cycling at 5°C between 3.42 V —4.08 V) are analyzed with XRD measurements. All samples possess a layered structure de- scribed in the R-3m space group for which lattice parameters a and c are calculated. The NMC samples respectively recovered from the fresh cell and the cell #5 present the expected lithiated state while the cathode from the most degraded cell is highly delithiated. We hypothesize that the rate of lithium x = 1 for the fresh material failing to dispose of a sample of pristines commercial cathode material. Note that the value of the a parameter has decreased from 2.862 A (fresh - lithi- ated) to 2.823 A (aged - delithiated) and that of the c parameter has increased from 14.274 A (fresh - lithiated) to 14.524 A (aged - delithiated). This reflects a delithiated state in the structure of the cathode material recovered from the cell #3. The decrease of a and the increase of c with delithiation are in good agreement with the observations of S.-C. Yin et al. using Neutron Diffraction studies on Li,.,Niy3Mnj/3Co 1302 samples.*® J. Choi et al.°? further investigated in the variations of the lattice parameters with lithium content (1-x) in Li,..Niy3Mn1/3Co 1/30, using XRD measurements. They reported that the c parameter increases initially with decreasing lithium content due In situ XRD measurements are performed on a sample of the fresh NMC electrode. This technique is used to obtain lattice parameters of the R-3m rhombohedral phase as a function of the state of charge and the lithium content x in Li,(Mng37C09,22Nio,4,)O2. This calibration curve is useful for the estimation of the lithium rate “x” into the aged NMC electrode based on the values of lattice parameters. In the litera- ture, as reported by I. Buchberger”’ et al., various methods have been used to demonstrate that the lattice parameters are correlated to the lithium content of the NMC electrode (x in Li,..Ni,3Mny/3Co,/302) such as chemical or electrochemical delithiation combined with Induc- tively Coupled Plasma, XRD, Neutron Diffraction, or combinations of these methods. But to quantify the Li-loss, an in situ XRD cali- bration curve is suitable to correlate the transferred electrochemical charge to the Li content of NMC and its lattice parameters. This can be obtained using in situ XRD during charging and discharging of NMC electrode.*’
Figure 7. XRD studies of the cathode Lix(Mno,4Coo.2Nio,4)O2 and anode (Graphite) materials. In situ XRD measurements are performed on a sample of a fresh cathode electrode in order to obtain a calibration curve of lattice parameters in function of lithium rate. Figure 7 illustrates XRD measurements performed on positive electrodes (left figure) and the calibration curve obtained from in situ measurements with a fresh NMC sample (right figure). The left figure presents the contribution of Ka, of the reflections 018, 110 and 113 for the fresh and cycled samples. The Aluminum collector peaks are visible. Lattice parameters obtained from the NMC recovered from the cell #5 are equal to those determined from the fresh cathode while those obtained with the NMC electrode recovered from the cell #3 have significantly evolved. Determination of the state of lithiation of electrodes with XRD measurements.— XRD studies of the cathode material_—Samples of positive elec- trodes respectively recovered from the fresh 16 Ah Li-ion cell, from the cell #3 (dismantled after full cycling at 5°C) and from the cell #5 (dismantled after cycling at 5°C between 3.42 V —4.08 V) are analyzed with XRD measurements. All samples possess a layered structure de- scribed in the R-3m space group for which lattice parameters a and c are calculated. The NMC samples respectively recovered from the fresh cell and the cell #5 present the expected lithiated state while the cathode from the most degraded cell is highly delithiated. We hypothesize that the rate of lithium x = 1 for the fresh material failing to dispose of a sample of pristines commercial cathode material. Note that the value of the a parameter has decreased from 2.862 A (fresh - lithi- ated) to 2.823 A (aged - delithiated) and that of the c parameter has increased from 14.274 A (fresh - lithiated) to 14.524 A (aged - delithiated). This reflects a delithiated state in the structure of the cathode material recovered from the cell #3. The decrease of a and the increase of c with delithiation are in good agreement with the observations of S.-C. Yin et al. using Neutron Diffraction studies on Li,.,Niy3Mnj/3Co 1302 samples.*® J. Choi et al.°? further investigated in the variations of the lattice parameters with lithium content (1-x) in Li,..Niy3Mn1/3Co 1/30, using XRD measurements. They reported that the c parameter increases initially with decreasing lithium content due In situ XRD measurements are performed on a sample of the fresh NMC electrode. This technique is used to obtain lattice parameters of the R-3m rhombohedral phase as a function of the state of charge and the lithium content x in Li,(Mng37C09,22Nio,4,)O2. This calibration curve is useful for the estimation of the lithium rate “x” into the aged NMC electrode based on the values of lattice parameters. In the litera- ture, as reported by I. Buchberger”’ et al., various methods have been used to demonstrate that the lattice parameters are correlated to the lithium content of the NMC electrode (x in Li,..Ni,3Mny/3Co,/302) such as chemical or electrochemical delithiation combined with Induc- tively Coupled Plasma, XRD, Neutron Diffraction, or combinations of these methods. But to quantify the Li-loss, an in situ XRD cali- bration curve is suitable to correlate the transferred electrochemical charge to the Li content of NMC and its lattice parameters. This can be obtained using in situ XRD during charging and discharging of NMC electrode.*’
lycol bis-(methyl carbonate) (EGMC), 2-ethoxycarbonyloxyethyl methyl carbonate and diethyl 2,5-dioxhane dicarboxylate (DEDOHC).
lycol bis-(methyl carbonate) (EGMC), 2-ethoxycarbonyloxyethyl methyl carbonate and diethyl 2,5-dioxhane dicarboxylate (DEDOHC).
Figure 9. 7Li NMR analysis: Metallic lithium detection on graphite electrode recovered from the cell #3. Influence of passivation films on graphite electrodes.—Detection of metallic lithium with ’Li NUR.—'Li NMR under fast magic angle spinning appears to be useful for ex situ and post-mortem analyses of battery electrodes. Figure 9 illustrates 7Li NMR measurements performed on graphite electrodes retrieved respectively from the cell result demonstrates that there is no notable influence of the nature of the electrolyte in this aging mechanism. It is therefore the graphite electrode that would be involved.
Figure 9. 7Li NMR analysis: Metallic lithium detection on graphite electrode recovered from the cell #3. Influence of passivation films on graphite electrodes.—Detection of metallic lithium with ’Li NUR.—'Li NMR under fast magic angle spinning appears to be useful for ex situ and post-mortem analyses of battery electrodes. Figure 9 illustrates 7Li NMR measurements performed on graphite electrodes retrieved respectively from the cell result demonstrates that there is no notable influence of the nature of the electrolyte in this aging mechanism. It is therefore the graphite electrode that would be involved.
Figure 10. ToF-SIMS images: Standardization of the rate of each characteristic element in function of the graphite “carbon” rate. No significant changes with standardization is observed with the graphite recovered from the cell #5 (cycling between 3.42 V and 4.08 V). Lithium is trapped, seen enriched in inter-particles cavities of the graphite electrode recovered from cell #3 (cycling between 2.7 V and 4.2 V). In blue circular areas, the Li/C ratio and P/C ratio are more important.
Figure 10. ToF-SIMS images: Standardization of the rate of each characteristic element in function of the graphite “carbon” rate. No significant changes with standardization is observed with the graphite recovered from the cell #5 (cycling between 3.42 V and 4.08 V). Lithium is trapped, seen enriched in inter-particles cavities of the graphite electrode recovered from cell #3 (cycling between 2.7 V and 4.2 V). In blue circular areas, the Li/C ratio and P/C ratio are more important.
Table VII. Percentage of each element detected with XPS on the surface of samples of graphite electrodes respectively recovered from the cell #3 (cycling between 2.70 V and 4.20 V) and from the cell #5 (cycling 3.42 V and 4.08 V).
Table VII. Percentage of each element detected with XPS on the surface of samples of graphite electrodes respectively recovered from the cell #3 (cycling between 2.70 V and 4.20 V) and from the cell #5 (cycling 3.42 V and 4.08 V).
Figure 11. Spectroscopic analysis of graphite electrodes with XPS technique.
Figure 11. Spectroscopic analysis of graphite electrodes with XPS technique.
Figure 13. Representation of the mechanism leading to the hindrance of Li diffusion into graphite electrode, observed during cycling at 5°C between 2.7 V and 4.2 V.
Figure 13. Representation of the mechanism leading to the hindrance of Li diffusion into graphite electrode, observed during cycling at 5°C between 2.7 V and 4.2 V.
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