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Supporting Information for:

A Stable Lead (II) Oxide-Carbon Composite Anode

Candidate for Secondary Lithium Batteries

Jason A. Weeks,† Max J. Zuiker,† Hrishikesh S. Srinivasan,†‡ Ho-Hyun Sun,‡ James N. Burrow,‡

Peter Beccar,† Adam Heller,‡ and C. Buddie Mullins*, †, ‡,┴

† Department of Chemistry, The University of Texas at Austin, Austin, Texas 78712-1224, United

States.

‡ John J. McKetta Department of Chemical Engineering, The University of Texas at Austin, Austin,

Texas 78712-1589, United States.

┴ Texas Materials Institute, The University of Texas at Austin, Austin, Texas 78712-1591, United

States.

*Corresponding Author- Email: mullins@che.utexas.edu.

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Table of Contents

S-10: Figure S1- Thermal degradation profiles of the lead citrate and sucrose

S-10: Figure S2- Thermal gravimetric analysis of PbO-C in air.

S-11: Figure S3- Raman shift spectrum

S-12: Figure S4- X-ray photoelectron spectroscopy

S-13: Figure S5- Variable rate galvanostatic cycling of PbO-C vs Li

S-13: Figure S6- Nitrogen isotherms at 77K

S-14: Figure S7- 4-point probe electrical conductivity measurements of PbO-C

S-14: Table S1- Quantified electrical conductivity properties

S-15: Figure S8- Post-mortem scanning electron micrographs

S-16: Figure S9- Pore size distribution and cumulative pore volume plots

S-16: Figure S10- Multi-point BET analysis with fits for surface area

S-17: Figure S11- X-ray diffraction patterns of the PbO-burned

S-17: Figure S12- Scanning electron micrograph of the PbO-burned material

S-18: Figure S13- X-ray diffraction pattern of PbO-C formed at 600 °C

S-18: Figure S14- Scanning electron micrograph of PbO-C formed at 600 °C

S-19: Figure S15- Cross-sectional SEM imaging of PbO-C formed at 600 °C

S-20: Figure S16- Cross-sectional SEM imaging of the PbO-C composite

S-21: Figure S17- Galvanostatic cycling (C/2) of lead citrate 550 °C

S-21: Figure S18- Galvanostatic cycling (C/2) of lead citrate (1:1.5) 550 °C

S-22: Figure S19- Galvanostatic cycling (C/2) of lead citrate: sucrose (1:4.5) 550 °C

S-22: Figure S20- Electrochemical impedance spectroscopy- Nyquist Plot

S-23: Figure S21- Electrochemical impedance spectroscopy- Bode Plots

S-24: Figure S22- Galvanostatic cycling of the NCM 622 cathode vs Li

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Materials. All chemicals were used without further purification or preparation, unless noted

otherwise. The following chemicals were used in the synthesis of the lead oxide-carbon (PbO-C)

composite; sucrose (C12H22O11, 99.0%) purchased from Alfa Aesar and lead citrate

[(C6H5O7)2Pb3 · 3H2O, ] purchased from Sigma-Aldrich. The following lists the chemicals used

for the fabrication of the PbO-C electrodes. Super P, purchased from MTI corporation, was used

as a conductive additive and polyvinylidene fluoride (PVDF) [(C2H2F2)n], purchased from Sigma-

Aldrich was used as a binder. N-Methyl-2-pyrrolidone (NMP). The materials listed below were

employed to construct the PbO-C half-cells for electrochemical analysis. Fluoroethlyene carbonate

(FEC, +99%) was acquired from Solvay, and diethyl carbonate (DEC; 99%) and lithium

hexafluorophosphate (LiPF6; 99.99%) were purchased from Sigma-Aldrich. 100 µm thick Li foil

was procured from Alfa Aesar. Celgard 2400 microporous monolayer membranes (polypropylene,

25 μm) were generously gifted from Celgard.

Synthesis of the PbO-C Composite. Using a mortar and pestle lead citrate and sucrose was

mechanically homogenized in a 3:1 (lead citrate: sucrose) molecular ratio. The mixture was then

collected and transferred into a ceramic crucible, which was then tightly capped with aluminum

foil and placed in a horizontal tube furnace (MTI, OTF-1200X) under argon atmosphere. Pyrolysis

of the constituents was induced through the following heat schedule: A heat ramp of 10 °C per

minute from 30 °C to 550 °C, followed by a two-hour hold at 550 °C. After the hold, the tube is

cooled naturally to room temperature. During the synthesis, a flow rate of 100 cc/min of argon was

employed to prevent the build-up of gaseous pyrolysis by-products and to maintain an inert

atmosphere. The subsequent product was collected, weighed, and mechanically homogenized

using a mortar and pestle.

Optimization of PbO-C Composition. Long-term cycling of lead citrate 550 °C (Figure S17)

shows the material’s poor electrochemical performance, going below 80 % capacity retention

within the first ten cycles. This is likely because there is not sufficient carbon to buffer the large

volumetric expansion induced by lithiation of PbO.

To analyze the role that supplemental carbon plays in the electrochemical performance of the

composite material, a composite was synthesize through the pyrolysis of lead citrate: sucrose (1.5:

1) at 550 °C. Long-term performance testing of this composite (Figure S18) shows increased

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electrochemical stability compared to lead citrate 550 °C, demonstrating 80 % capacity retention

after 55 cycles and an initial specific capacity of 405 mAh g-1. However, it has drastically less

capacity retention compared to our PbO-C composite material. Furthermore, the lead citrate:

sucrose (1.5: 1) material demonstrates near linear capacity fade. We hypothesize that this is

because the secondary particle is slowly being deteriorated by the large volumetric expansion of

the lead oxide particles.

A composite was formed using lead citrate: sucrose in a 4.5: 1 molar ratio, in order to probe the

potential to increase further the capacity retention of the material using additional carbon. Long-

term performance testing at a C/2 rate (Figure S19) demonstrates that the lead citrate: sucrose

(4.5:1) composite has a capacity retention comparable to the PbO-C composite, however its

specific capacity is greatly reduced. Therefore, we believe that the composite formed using lead

citrate: sucrose (3: 1) demonstrates optimal electrochemical properties, balancing high reversible

capacity with stable electrochemical cycling.

Fabrication of PbO-C Composite Electrodes. Slurry mixtures of the PbO-C composite were

formed by the dispersal of active material, PVDF, and Super P in NMP in an 80 %, 10 %, 10%

weight ratio, respectively. Slurry mixtures were cast on copper foil using a doctor blade (MTI,

AFA-I). The resulting cast slurry was placed in an oven at 120 °C under ambient atmosphere for

three hours. After three hours had elapsed, the oven was placed under vacuum and the film was

dried overnight. Circular electrodes with a 7/16” diameter were cut from the resulting slurry.

Before the resulting materials were used for electrochemical analysis, the electrodes were

calendared to make sure the material was compactly cast upon the current collector. Heights of the

slurry electrodes were measured using high precision electronic calipers and the calendared copper

foil as a reference. Heights of the electrodes used for electrochemical analysis ranged from 13-18

μm, with an average electrode height of 15 μm.

Electrochemical Analysis of the PbO-C Composite. Four-point probe measurements of the

pristine PbO-C material thickly coated on a glass substrate were conducted with a manual four-

point resistivity probe (Lucas S302; Lucas Laboratories). Sheet resistivity was determined by

measuring the potential at various applied currents of +/- (0.1 mA, 0.5 mA, 1 mA, 5 mA, and 10

mA). Results of these measurements are displayed in Figure S7. The sheet resistivity was then

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calculated via a modified version of Ohm’s law, derived from Smits et al. (Equation 1). Where Rs

is the sheet resistivity and 4.53 is used as a constant to represent films that are much thicker than

the separation between probes.1 The resulting sheet resistivity was used to calculate the inherent

resistivity and conductivity of the PbO-C, which are displayed in Table S1. Cycling performance

and cyclic voltammetry (CV) tests were conducted using a multichannel battery test system (BT

2043, Arbin). We assembled the anode materials in a half-cell configuration using 2032 stainless

steel coin cells. Celgard 2400 membranes (25 μm, Celgard) were used as cell separators. The

electrolyte was composed of 1 M lithium hexfluorophosphate (LiPF6) in fluoroethylene carbonate

(FEC)/diethyl carbonate (DEC) (1:1 by volume) solution. Excess electrolyte was used (>5 drops)

to flood the cell and to provide sufficient wetting.

All half-cell galvanostatic cycling was conducted with a potential window of 5 mV- 3.0 V, chosen

to establish stability at high voltages and to replicate standard anode half-cell performance testing

practices found in the literature. Three conditioning C/20 cycles were performed upon

electrochemical cells to form a consistent SEI prior to commencing galvanostatic charge/discharge

tests. All the data presented in our electrochemical plots are the averages of two identical cells to

ensure reproducibility of our results. Active mass loading of the PbO-C electrodes were kept within

a range of 1.8 – 2.6 mg cm-2. Rate capability testing was conducted using the following

charge/discharge parameters: C/10 for 3 cycles, C/4 for 3 cycles, C/2 for 5 cycles, 1C for 5 cycles,

2C for 5 cycles, and finally the system was recovered at C/4 to examine the capacity retention. For

long-term cycling performance tests, all cells underwent three C/20 formation cycles followed

immediately by long-term cycling at the detailed cycling rate/current density.

Full-cell galvanostatic cycling was performed using a NCM 622 commercial counter-electrode

with an N:P ratio of 1.2:1. In order to determine this cathode compatibility with our electrolyte

solution, initial half-cell testing of this cathode material in 1 M LiPF6 FEC:DEC was conducted

and can be found in Figure S22. The results of this long-term galvanostatic cycling show the

material to be a reversible cathode material, displaying a reversible gravimetric capacity of 181

mAh g-1 over 100 cycles at a current density of C/2 (100 mA g-1). Full-cell performance testing

was conducted using a voltage window of 1.5 V to 4.2 V in 1 M LiPF6 FEC:DEC. Three

conditioning cycles (at C/20, C/10, and C/5; respectively) were conducted on the cell post-

𝑅𝑆 = 4.53*V/I (S1)

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assembly to assure homogenous SEI formation and reduce parasitic effects of initial cycling.

Galvanostatic cycling of the PbO-C composite versus NCM 622 provided a specific volumetric

capacity of 513 mAh cm-3 (Figure 5a) and a gravimetric capacity of 317 mAh g-1 (Figure 5b) with

93.6 % capacity retention over 100 cycles of C/2 rate lithiation/delithiation. Furthermore, the

material demonstrates very reversible electrochemical processes with an average 99.66 %

coulombic efficiency over 100 cycles.

Volumetric capacity of the material was calculated based on the dimensions of the slurry cast

material, exclusively. As previously stated, circular electrodes were cut with a 7/16” diameter

while the heights of the electrodes were determined using electronic calipers and an uncast region

of the calendared copper foil as reference. Due to the lack of knowledge about the precise vol %

the PbO-C composite within the slurry electrodes, volumetric capacity was calculated based on

the overall volume of the electrode, including the Super-P and PVDF additives.

Electrochemical impedance spectroscopy (EIS) was conducted using the PbO-C composite anode

in the half-cell configuration after 1, 10, 50, and 100 cycles; respectively. EIS was conducted using

a 0.1-100000 Hz window and an amplitude of 0.005 V. Nyquist (Figure S20) and bode (Figure

S21) plots were generated using the results of this analysis. EIS measurements of the PbO-C

composite suggest that most of the internal resistance is generated within the first few cycles due

to the formation of the initial SEI, however there is a steady slow increase in the resistance profile

of the system. Simulations of the EIS, suggest this continual increase in resistance is primarily due

to the SEI resistance. This conclusion is in line with the results of our previous post-mortem

analysis (Figure S8), which shows new SEI forming throughout the long-term performance

testing. We attribute this new SEI to be derived from the large volumetric expansion of the lead

oxide particles, which could cause the exposure of new surfaces or loosely adhered SEI to fracture

off.

Cross-Sectional Analysis of PbO-C Composite. We generated cross-sections of the PbO-C

composite using a conductive silver epoxy. A conductive epoxy was chosen to prevent charging

during scanning electron microscopy/energy dispersive spectroscopy (SEM/EDX). The following

steps were taken to generate cross-sections of the material embedded in epoxy: Equal amounts of

epoxy and curing solution were added together and then mixed. Then, the PbO-C composite

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material was added to the mixture and thoroughly mixed together. The resulting mixture was cured

for 24-hours. After, the epoxy was microtomed into cross-sections using a microtome blade. EDX

analysis was then used to identify PbO-C composite particles within the epoxy matrix, while SEM

was utilized to image the resulting cross-sections of the material.

Material Characterization. X-ray diffraction patterns were obtained with a Rigaku Miniflex 600

diffractometer utilizing Cu Kα radiation (λ = 1.5418 Å). Diffraction patterns were analyzed from

5 -80° in a continuous scan mode (2° min−1) with a step width of 2θ = 0.025°.

Raman spectroscopy is commonly employed to analyze graphitic carbon and determine the degree

of graphitization within a carbonaceous species. This was done by examining the peak shape and

intensity of the D and G bands of carbon, commonly found in the region of 1000 cm-1- 1750cm-

1.2,3 The ratio of the intensity of the D band to that of the G band (ID/IG ratio) provides an

approximation for the graphitization for a material. Thus, this analysis was used to determine the

degree of graphitization for the carbon support in the PbO-C composite. A Witec Micro-Raman

spectrometer, employing a 40-watt blue laser, characterized the Raman shift of the composite

material. The spectrometer utilized a Nikon E Plan objective and camera to focus on the fine

powder sample. We used an excitation wavelength of 488 nm and a spectral center of 2498 cm-1

to acquire the Raman shift. The entire Raman spectrum was explored, but the only noticeable peaks

were found in the D and G bands of the carbon species. Figure S3 depicts the D and G bands of

the PbO-C Raman shift spectra. Spectra were acquired using a 2 sec integration time, and 30

accumulations were compiled to generate an accurate representation of the Raman shift. The Witec

Suite software was employed to produce and extrapolate the spectrum. Literature values and a

Voigt computation (convolution of Gaussian and Lorentzian functions), employed through the

origin 2018b software, was used to deconvoluted the spectra into its inherent peaks. Comparing

the D and G peaks yielded an ID/IG ratio of 0.81, signifying that the framework consists of a

relatively disordered graphitic carbon.

XPS spectra were obtained through a monochromated 120 W Al-Kα1 X-ray source (hν = 1486.5

eV), hybrid optics (employing a magnetic and electrostatic lens simultaneously) and a multi-

channel plate coupled to a hemispherical photoelectron kinetic analyzer. The spectrometer was

calibrated by using the Ag 3d5/2 (368.3 eV) peak. Pressure of the analysis chamber was maintained

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at 1 × 10−9 Torr throughout the analysis. The photoelectron’s take-off angle was normalized to the

surface of the sample and 45° with respect to the X-ray beam. All spectra were recorded using one

sweep and an aperture slot of 300 × 700 µm2. Survey spectra were collected employing a pass

energy of 80 eV and 1 eV per step. Elemental regions were collected with a pass energy of 20 eV

and 0.1 eV per step with a total acquisition time ranging from 5 to 10 minutes. To prevent any shift

in spectra caused by charging of the sample, all spectra were corrected based on the peak of typical

adventitious carbon, at 284.8 eV.4,5 The CasaXPS software was employed to analyze and calibrate

the resulting spectra. When analyzing and deconvoluting the XPS spectra of PbO-C, a baseline

was generated using a Shirley motif. Various literature references were used to determine the peak

location of the functional groups and families of molecules found within the composite.6 The

deconvoluted spectra of the composite is displayed in Figure S4.

Thermal Gravimetric Analysis. Initial thermal decomposition testing of the lead citrate and

sucrose precursors was conducted to gain a better understanding of the materials’ pyrolysis

reactions. Thermographs of the precursors were generated under N2 atmosphere using a 10 °C/min

heat ramp from 30 °C to 750 °C. The resulting thermographs can be found in Figure S8. To obtain

the composition of the PbO-C composite, a quantification of the carbon was conducted. It is widely

known that pyrolysis formed, carbonaceous species will burn in air at high temperatures (≥400

°C). This technique was employed to remove the carbon from the PbO-C composite during a TGA

to determine the wt % of the carbon coating. Parameters for this thermograph are as follows: An

initial heat ramp from 30 °C to 100 °C and a thirty-minute hold at 100 °C (employed to remove

any adsorbed water), followed by a heat ramp from 100 °C to 800 °C. The resulting thermograph

is shown in Figure S2. TGA of the PbO-C composite suggests that approximately 28 % of the

composite consists of carbon.

Brunauer–Emmett–Teller (BET) Analysis. The textural properties of the PbO-C sample were

characterized by nitrogen sorption isotherms at 77 K using an Anton Paar Autosorb iQ pore size

analyzer. Ultra-high purity nitrogen and helium were obtained from Airgas, Inc. An empty 9mm

bulb sample cell was weighed and filled with approximately 250 mg of PbO-C. The sample cell

was then heated to 200 °C under vacuum for 12 hours to degas any previously adsorbed species.

After vacuum degassing, the powder-filled sample cell was backfilled with nitrogen and weighed

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again to calculate the degassed mass of PbO-C inside the cell. A filler rod was inserted into the

sample cells, and the void volume of the sample cells were measured with helium. A bath of

liquid nitrogen was employed to maintain a temperature of 77 K during the adsorption analysis.

A nitrogen sorption isotherm was obtained by a volumetric dosing method in the relative

pressure range of 0.005 to 0.99 (absolute pressure range of 3.8 mmHg to 752.5 mmHg). The

resulting isotherm was analyzed quantitatively with both (1) Brunauer-Emmett-Teller (BET)

theory and (2) quenched-solid density functional theory (QSDFT). The BET surface area was

calculated by fitting the linear segment of the initial portion of the adsorption branch of the

nitrogen isotherm. ASiQwinTM software was applied to fit kernels derived from QSDFT,

representing slit and cylindrical pore geometry, to the adsorption isotherm to quantify the pore

size distribution of the PbO-C product. The total pore volume was quantified with the uptake at

a relative pressure of 0.99 (absolute pressure of 752 mmHg).

BET analysis suggests a surface area around 132 m2/g, and QSDFT analysis elucidates

this hierarchical pore size distribution with a cumulative pore volume of around 0.07 cc/g as

displayed in Figure S9. Based on these analyses, we conclude that the lead oxide-carbon

composite has a moderate surface area derived primarily by microporosity.

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Supplementary Figures:

Figure S2. Thermal gravimetric analysis of PbO-C in air. An ambient atmosphere was employed to

decompose the carbon framework.

Figure S1. (a-b) Thermal degradation profiles of the lead citrate and sucrose precursors, respectively,

in a nitrogen environment.

a) b)

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Figure S3. Raman Spectrum of the PbO-C composite, focused on the D and G graphite region. A

ratio of the deconvoluted D and G bands is denoted in bold.

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Figure S4. The resulting XPS analysis of the PbO-C composite material. (a) Survey scan of PbO-C

composite employing a spectral window of 0 – 1200 eV. Relavant peaks of the survey have been

labeled in the cooresponding colors and bolded. (b-d) High-resolution peak scans of C 1s, O 1s, and

Pb 4f; respectively.

a)

d)

b)

c)

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Figure S5. Variable rate galvanostatic cycling of PbO-C vs Li.

Figure S6. Nitrogen isotherms at 77K of the PbO-C composite. Quantification and analysis

of the textural properties of the composite were conducted through QSDFT.

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Figure S7. Results of a 4-point probe test conducted on a PbO-C thick film at various applied

currents.

Table S1. Electrical Properties of the PbO-C material determined using 4-point probe analysis.

Numerical values were determined using a 95% confidence interval.

RS (Ω/□) ρ (Ω/m) σ (S/m)

137.3 ± 1.6 0.03300 ± 0.0040 30.32 ± 0.35

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Figure S8. (a-d) Post-mortem scanning electron micrographs of the PbO-C composite after 1,

50, 100, and 400 cycles; respectively.

1 μm 1 μm

1 μm 2 μm

1st 50th

100th 400th

a)

d) c)

b)

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Figure S9. Pore size distribution and cumulative pore volume derived by fitting kernels

derived from QSDFT to the equilibrium branch of the nitrogen isotherm surfaces assuming

slit-shaped pores. Most of the porosity in this range comes from narrow micropores < 1 nm.

Figure S10. Multi-point BET plot used for quantification of surface area with optimized

point selection.

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Figure S12. SEM micrograph of the PbO-burned product drop-casted onto a silicon wafer. Scale bars

were applied to various particles in order to permit an easy assessment of size. This result shows the

maintenance of particle size even after burning of the carbon framework.

250 nm

34 nm

Figure S11. X-ray diffraction patterns of the PbO-burned material formed by burning the PbO-C

composite material in air. Literature based diffraction patterns of PbO (PDF #01-072-0093) and Pb

(PDF #00-004-0686) are presented as reference.

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Figure S14. (a) SEM micrograph of the PbO-C formed at 600 °C particle on a silicon wafer. (b) EDX

elemental region mapping of the PbO-C composite. (c-e) EDX elemental mapping of carbon, oxygen,

and lead; respectively.

1 μm

C O Pb C

O Pb

a) b) c)

c)

Figure S13. X-ray diffraction patterns of the PbO-C composite formed at 600 °C. Literature based

diffraction patterns of PbO (PDF #01-072-0093) and Pb (PDF #00-004-0686) are presented as

reference.

e)

b)

d)

a)

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a) b)

c) d)

a) b)

c)

f) e) d)

Figure S15 (a) SEM micrograph of a silver epoxy embedded, microtomed slice of a PbO-C 600 °C

composite particle. (b-c) EDX elemental maps of silver and lead defining the location of the

composite in the silver epoxy. (d-f) Micrographs showing the morphology of the interior of a PbO-C

composite particle at different magnifications.

Pb

10 μm

Ag O Ag

Pb 5 μm

a) b) c)

d) e)

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Figure S16 (a) SEM micrograph of a silver epoxy embedded, microtomed slice of a PbO-C

composite particle. (b-c) EDX elemental maps of silver and lead defining the location of the

composite in the silver epoxy. (d-f) Micrographs showing the morphology of the interior of a PbO-C

composite particle at different magnifications.

5 μm

1 μm 350 nm 200 nm

Pb

Ag

40 nm

40 nm

a) b)

c)

d) e) f)

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Figure S17. Electrochemistry of lead citrate 550 °C composite electrode cycled versus lithium and

using a 1 M LiPF6 in FEC:DEC electrolytic solution. Results demonstrate long-term specific

gravimetric capacity upon cycling at 225 mA g-1 (C/2).

Figure S18. Electrochemistry of lead citrate: sucrose (1.5: 1, mol: mol) 550 °C composite electrode

cycled versus lithium and using a 1 M LiPF6 in FEC:DEC electrolytic solution. Results demonstrate

long-term specific gravimetric capacity upon cycling at 225 mA g-1 (C/2).

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Figure S19. Electrochemistry of lead citrate: sucrose (4.5: 1, mol: mol) 550 °C composite electrode

cycled versus lithium and using a 1 M LiPF6 in FEC:DEC electrolytic solution. Results demonstrate

long-term specific gravimetric capacity upon cycling at 225 mA g-1 (C/2).

Figure S20. Nyquist plot of PbO-C composite resulting from electrochemical impedance

spectroscopy conducted at various cycle counts.

W W W w

w

= Resistor

= Capacitor

= Warburg Element

R

Q

W

Electrolyte Resistance

Lithium(cathode)

SEI C60Hx

(Anode)PbO-C CompositeCounter

Electrode

PbO-C

CompositeSEI

Electrolyte

Resistance

W W W w

w

= Resistor

= Capacitor

= Warburg Element

R

Q

W

Electrolyte Resistance

Lithium(cathode)

SEI C60Hx

(Anode)

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Figure S21. (a-d) Bode plots of PbO-C composite resulting from electrochemical impedance

spectroscopy conducted at 1, 10, 50, and 100 cycles; respectively.

a) b)

c) d)

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REFERENCES

1. F. M. Smits, Bell System Technical Journal, 37, 711–718 (1958).

2. A. C. Ferrari, Solid State Communications, 143, 47–57 (2007).

3. A. C. Ferrari and J. Robertson, Phys. Rev. B, 61, 14095–14107 (2000).

4. P. Swift, Surface and Interface Analysis, 4, 47–51 (1982).

5. T. L. Barr and S. Seal, Journal of Vacuum Science & Technology A, 13, 1239–1246 (1995).

6. H. Hantsche, Advanced Materials, 5, 778–778 (1993).

Figure S22. Electrochemistry of the NCM 622 cathode cycled versus lithium. (a) Resulting long-term

specific gravimetric capacities upon cycling at 100 mA g-1 (C/2). (b) Variable rate galvanostatic cycling

at a 0.2, 0.5, 1, 2, and 5 C rate.

.

a) b)