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Figure 51a shows the first cycle of an HE5050/Li 2032 type coin cell cycled at an effective C/20 rate. The teal shading indicates the difference between the first cycle extraction and first cycle insertion of the HE5050 cathode, which is attributed to the first cycle loss. Figure 51b shows the first cycle of an MCMB/Li coin cell cycled at an effective C/20 rate. The yellow shading indicates the difference between the first cycle insertion and first cycle extraction, which is the first cycle loss of the anode, resulting from SEI formation.

Figure 51: (a) First charge and discharge of HE5050/Li coin cell at an effective C/20 rate. (b) First charge and discharge of MCMB/Li coin cell at an effective C/20 rate.

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Figure 52 depicts the lithium tracking details for the 3-electrode pouch cell tested with 3-day near zero volt storage periods. The starting condition of the cell after construction is depicted in Figure 52a. In this condition, the cathode is in a fully lithiated state, while the anode contains no lithium and no SEI has been formed. The areal capacities for both electrodes during the first charge are calculated based on the half-cell data shown

Figure 52: (a) Depiction of the cell after cell construction, white circles represent lithium ions. (b) Depiction of cell condition after the first charge. Red “X” symbols indicate reversible lithium lost to SEI formation. (c) Depiction of cell condition after the first discharge.

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in Figure 51. The cathode areal capacity calculated based on the half-cell data shown in Figure 51a includes the first cycle extraction capacity of HE5050 to 4.6 V vs. Li/Li+_{. The}

anode areal capacity calculated from the first cycle shown in Figure 51b includes both the amount of charge lost to SEI formation and the insertion capacity of the graphite to 5 mV vs. Li/Li+. Thus, the areal capacity of the anode for the first charge is 3.63 mAh/cm2, which is 11% excess compared to the first charge areal capacity of the cathode.

Figure 52b depicts the end condition of the first constant current charge of the HE5050/MCMB cell. The red “X” over several of the white circles representing lithium depict the reversible lithium consumed in SEI formation on the anode. The amount of lithium consumed by SEI formation is calculated by multiplying the loss per electrode area (as measured by the half-cell shown in Figure 51b) by the area of each electrode used in the pouch cell, since all tests were performed with the same anode coating. The white circles without a red “X” over them represent the amount of reversible lithium in the anode at the end of the charge. This value is calculated by the equation shown to the right of the Figure 52b, which subtracts the amount of lithium lost to SEI from the measured charge capacity of the full cell. Figure 52c depicts the cell condition at the end of the first discharge where the white circles in the anode represent the amount of reversible lithium stored in the anode. This amount of lithium is calculated by the equation shown to the right of Figure 52c which subtracts the measured discharge capacity of the full cell from the amount of reversible lithium calculated to be in the anode at the end of the first charge.

Figure 53 depicts the cell charge and discharge after the first cycle. The values shown in the calculation are specific to the second cycle at a 1.2 mA constant current (~C/10), but the method is general to all cycles after the first cycle. The starting condition

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depicted in Figure 53a is after the first discharge, where 1.85 mAh of reversible lithium is calculated to remain in the anode while 11.13 mAh has inserted into the cathode. Figure 53b depicts the cell on the second cycle charge where the measured charge capacity in the cell is 10.73 mAh. The slightly lower charge capacity compared to the amount of lithium that intercalated into the cathode during the first cycle discharge can be attributed to the higher constant current of the second cycle vs. the first, C/10 vs. C/20, respectively (based on the cell’s rated capacity). Some lithium is consumed by SEI formation on the second cycle, albeit it is more than an order of magnitude less than the first cycle and that is

Figure 53: (a) Depiction of HE5050/MCMB cell after the first discharge. This is also representative of the cell condition after all constant current discharges (b) Depiction of HE5050/MCMB cell after the second charge. This is also representative of the cell condition after all constant current charges. (c) Depiction of HE5050/MCMB cell after the second discharge. This is also representative of the cell condition after all constant current discharges.

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calculated by the equation on the right side of Figure 53b. Figure 53c depicts the cell after the second cycle discharge, which is similar to Figure 52c, shows that some reversible lithium remains in the anode after the discharge. The lower discharge capacity compared to the charge capacity on the second cycle can be attributed to some loss (~4%) from the HE5050 on the second cycle. By the third cycle, no loss is observed from the HE5050.

The calculations used to determine the amount of reversible lithium in the anode after the discharge step of each cycle are collated by equations S1 and S2, where 𝜉_𝑖 is the amount of excess reversible lithium stored in the anode after discharge on cycle 𝑖, 𝐶 is the charge capacity of the cell, 𝐷 is the discharge capacity of the cell, and 𝜁 is the loss of reversible lithium due to SEI formation on the anode. The measured charge and discharge capacities of the full cell, the loss due to SEI formation calculated based on half-cell measurements, and the resulting values of reversible lithium stored in the anode after cell discharge are shown in Table 1. After five conditioning cycles, the stabilization of the anode is evident by the significant decrease in SEI loss while maintaining near constant reversible lithium excess of ~2.1 mAh after each discharge.

(S1) (S2) 𝜉𝑖 = 𝐶 − 𝜁 − 𝐷 + 𝜉𝑖−1 𝑤ℎ𝑒𝑛 𝑖 > 1

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Table 1: Summary of lithium tracking results for the first 5 cycles of the cell of Figures 1, 2, and 3. Column 1.) Cycle Index. Column 2.) Expected loss based on calculating the loss per area from half- cell data and multiplying that by the area of the anode in the full pouch cell. Column 3.) Charge capacity of HE5050/MCMB cell. Column 4.) Discharge capacity of HE5050/MCMB cell. Column 5.) Amount of Excess reversible lithium stored in anode of HE5050/MCNM cell as calculated by Equation S1 for Cycle 1 and Equation S2 for Cycle 2-5. Column 6.) Charge and discharge rate for each cycle.

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Figure 54: 1.2 mA constant current (CC) discharge curves of HE5050/MCMB cell prior to and after 1, 2, 3, 4, and 5 seventy two hour, near zero volt storage periods.

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Figure 55: (a) Overlay of reference electrode measurements for the constant current discharge and fixed load, near zero volt storage period of HE5050/MCMB cell tested with 3-day near zero volt storage periods. (b) Overlay of reference electrode measurements for the constant current discharge and fixed load, near zero volt storage period of HE5050/MCMB cell tested with 7-day near zero volt storage periods.

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Figure 57: Discharge capacity (including capacity from the 1.2 mA constant current discharge step to 2.0 V cell voltage and the 7-day fixed load step) plotted with the charge capacity of the cell charge on subsequent cycle after near zero volt storage period.

Figure 56: 1.2 mA constant current (CC) discharge curves of HE5050/MCMB cell prior to and after 1, 2, 3, 4, and 5 seventy two hour, near zero volt storage periods.

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Figure 58: Voltage plotted as a function of time for prototype HE5050/MCMB pouch cell discharged and then stored at open circuit for 3 days.

Figure 59: Reference electrode data of HE5050/MCMB cell first discharged at constant current (leftmost unshaded region). Then a fixed resistive load is applied for 72 hours (gray shaded region), then the cell is left at open circuit (rightmost unshaded region)

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Figure 61: Overlay of reference electrode measurements for the constant current discharge cell tested with 3-day near zero volt storage periods at 40°C after cycle 7 and 8.

Figure 60: 0.09 mA constant current (CC) discharge curves of HE5050/MCMB cell prior to and after 1 and 2 3-day, near zero volt storage periods at 40°C.

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Figure 62: Overlay of reference electrode measurements for the constant current discharge and fixed load, near zero volt storage period of HE5050/MCMB cell tested with 3-day near zero volt storage periods at 40°C.

Figure 63: (At 40°C) Discharge capacity (including capacity from the 0.09 mA constant current discharge step to 2.0 V cell voltage and the 3-day fixed load step) plotted with the charge capacity of the cell charge on subsequent cycle after near zero volt storage period.

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