Patent Application
20240072256
This invention relates to lead-acid batteries. More particularly, this invention relates to lead-acid batteries comprising an electrode with crystalline lead sulfate of well-defined crystal size and habit in the initial discharged state of the electrode, as well as methods of making the crystalline lead sulfate.
Lead-acid battery manufacturing has two major problems that can be linked to the starting materials for electrode manufacture, and their processing steps.
First, the starting material for lead-acid battery manufacturing is leady oxide (a mixture of metallic lead and lead monoxide) sourced from Pb recovery from spent batteries. This leady oxide is converted into basic lead sulfate materials (xPbO·PbSO4, such as tetrabasic lead sulfate, often described as 4PbO·PbSO4) by reacting with sulfuric acid in the preparation of the paste that makes up current lead battery electrodes. This step, called electrode curing, requires control of both heating and moisture. Curing is highly energy-intensive and may take up to 2 days for completion. This also introduces unwanted variability in battery manufacturing, because of the difficulty in controlling the exact curing conditions.
Second, production of the Pb and PbO2 active materials requires a final formation process, which is the most energy-intensive step during battery manufacturing (6-8 times the energy actually stored in a battery). To date, there have been no attempts to solve these problems by using a well-defined starting material that can be converted to Pb and PbO2 efficiently using less energy and time and improving reliability.
The materials and methods described herein address these ongoing problems in lead-acid battery manufacture.
Described herein is a well-defined PbSO4 material with controlled crystal size and shape for use as an initial electrode active material in discharged lead-acid batteries. A method of preparing the size- and shape-controlled PbSO4 is also described. This material comprises nano- to micro-sized PbSO4 crystals that demonstrate an ability to control the rate of the active electrode formation step with essentially 100% conversion efficiency. In the electrodes and batteries described herein, the starting battery material remains in a Pb(2+) state, which leads to potentially simpler, less energy-intensive battery recycling strategies. Because the starting battery material is already sulfated, the typical curing process is eliminated altogether. The electrodes and batteries described herein also do not require any other chemical reactions to occur during electrolyte fill or prior to the formation step. Finally, controlling the size and shape of the lead sulfate crystals enables control of the efficiency and rate at which the material charges in the battery. This reduces the energy required for electrode formation (i.e., reduction of Pb(2+) to Pb(0)) to a level that is equal to the amount of energy stored in the battery, creating a far more time and energy-efficient formation step.
An electrode for a lead-acid battery, as described herein, comprises, in its initial, discharged state, crystalline PbSO4 having a selected average particle size, as determined by dynamic light scattering and particle imaging using a transmission electron microscope, of about 10 nm to about 2 μm (e.g., about 20 nm to about 2 μm; or about 50 nm to about 1.5 μm), with a particle size distribution in which at least about 90% of the crystals have a particle size within about 20% of the average. The crystals also have a well-defined crystal habit comprising rectangular slabs and/or diamond-shaped crystals.
In some preferred embodiments, the crystalline lead sulfate is combined with particulate carbon, such as carbon black, graphite, free-standing graphene, graphene oxide, reduced graphene oxide, single-walled and multi-walled carbon nanotubes, and the like. The crystalline lead sulfate and carbon, when present, are applied as a paste to a pasted plate grid-type, or tubular-type metallic frame to form the initial electrode structure. Typically, the pasted plate and tubular electrode frames are constructed from a hardened lead alloy (e.g., Pb alloyed with Sb, Ca, Se, and/or Sn). The active material paste fills voids in the grid or tubular structure, while the conductive frame provides a path for current flow throughout the plate. The active electrode is then formed in situ in an assembled battery after filling the battery with sulfuric acid electrolyte. Active electrode formation is accomplished by charging the initial electrode to convert a selected portion of the Pb(2+) to Pb(0) or in its entirety. Typically this can be achieved by passing a current equivalent to the amount of electricity contained in the electrodes over a predetermined amount of time, from 30 minutes to 10 hours, then afterwards holding the cell voltage at a maximum voltage value, for example but not limited to, 2.5V until the current decreases to a steady state value.
Typically, the crystalline PbSO4 is mixed with a particulate carbon material and binder to form a paste, which is then loaded onto a pasted plate grid or tubular electrode frame, followed by drying to form the initial electrode in a fully discharged state. Other optional components of the paste include, but not limited to, solid expander additives such as lignosulfonate powder and the like, baryte group inorganic crystals (e.g., BaSO4, CaSO4, SrSO4, and mixtures thereof), polymer fibers, and glass fibers.
A method of preparing size-and shape-defined crystalline lead sulfate comprises gradually mixing equimolar amounts of Pb(2+)-containing and SO4(2−)-containing precursor solutions into an acidic crystal-growth control solution comprising a crystal-growth modifier (CGM; e.g., a linear or branched polyimine, for example, poly(ethyleneimine) (PEI) and the like) and acetic acid at a pH in the range of about 1 to about 5, at a defined rate of addition in the range of about 0.01 micromoles to 1000 millimoles of Pb(2+) and SO4(2−) per minute. Preferably, the crystal-growth modifier is present in the control solution at a concentration in the range of about 0.01 to 50 g/L, and the volume of control solution is about 0.1 to about 10 times the total volume of Pb(2+) and SO4(2−) being added. The crystals can also be allowed to grow for a selected period of time in the range of about 0.01 to about 5000 minutes, before the crystals are isolated and washed with water to remove the crystal-growth modifier and soluble salt contaminants. The Pb(2+)-containing precursor solution and the SO4(2−)-containing precursor solution typically have concentrations in the range of about 0.001 to about 1M.
The crystal habit can be affected by the ratio of Pb to CGM. For Example, when the CGM is PEI, predominately tabular crystals are formed when the ratio of Pb to PEI is about 6 mmol Pb2+ per gram PEI or less, while predominately diamond-shaped crystals are formed when the ratio of Pb to PEI is about 11 mmol Pb2+ per gram PEI or more Between about 6 to 11 mmol Pb2+ per gram PEI is a transition between the crystal habits.
In an electrochemical cell, the counter electrode typically is a lead flat plate electrode, and the electrodes are immersed in an electrolyte comprising about 1 to about 5 M aqueous sulfuric acid, with a porous membrane between the PbSO4 and counter electrodes. In some other embodiments, the counter electrode can comprise PbO2, or a mixture of Pb and PbO2. In some other embodiments, the cell can comprise two of the electrodes comprising the crystalline PbSO4 described herein, polarized to form Pb and PbO2 in situ.
The following non-limiting embodiments are provided below to illustrate certain aspects and features of the electrochemical cells and batteries described herein.
Embodiment 1 is an electrode for a lead-acid battery comprising, in an initial, discharged state, a paste of tabular and/or diamond-shaped PbSO4 crystals in a conductive metal grid framework; wherein the crystals have a selected average crystal size, as determined by dynamic light scattering and particle imaging using a transmission electron microscope, of about 10 nm to about 2 μm, with a particle size distribution in which at least about 90% of the crystals have a particle size within about 20% of the average diameter.
Embodiment 2 is the electrode of embodiment 1, wherein the paste further comprises a particulate carbon material.
Embodiment 3 is the electrode of embodiment 2, wherein the particulate carbon material comprises at least one material selected from the group consisting of carbon black, graphite, free-standing graphene, graphene oxide, reduced graphene oxide, single-walled carbon nanotubes, and multi-walled carbon nanotubes.
Embodiment 4 is the electrode of any one of embodiments 1 to 3, wherein the paste further comprises solid expander additives, baryte group inorganic crystals (e.g., BaSO4, CaSO4, SrSO4, and mixtures thereof), polymeric fibers, and glass fibers.
Embodiment 5 is the electrode of any one of embodiments 1 to 4, wherein the PbSO4 crystals have an average particle size in the range of about 140 nm to about 160 nm.
Embodiment 6 is the electrode of any one of embodiments 1 to 4, wherein the PbSO4 crystals have an average particle size in the range of about 180 nm to about 220 nm.
Embodiment 7 is the electrode of any one of embodiments 1 to 4, wherein the PbSO4 crystals have an average particle size in the range of about 250 nm to about 290 nm.
Embodiment 8 is the electrode of any one of embodiments 1 to 4, wherein the PbSO4 crystals have an average particle size in the range of about 1 μm to about 1.4 μm.
Embodiment 9 is the electrode of any one of embodiments 1 to 8, wherein the metal grid framework is composed of a hardened lead alloy.
Embodiment 10 is a lead-acid electrochemical cell comprising the electrode of any one of embodiments 1 to 9 and a counter electrode with a proton-conductive separator therebetween, wherein the electrode, counter electrode, and separator are immersed in an electrolyte comprising aqueous sulfuric acid.
Embodiment 11 is the electrochemical cell of embodiment 10, wherein the counter electrode comprises at least one material selected from the group consisting of metallic lead, PbO2, and crystalline PbSO4.
Embodiment 12 is the electrochemical cell of embodiment 10 or 11, wherein the sulfuric acid has a concentration in the range of about 1 to about 5 M.
Embodiment 13 is the electrochemical cell of any one of embodiments 10 to 12, wherein the cell has been electrochemically cycled within a voltage window of about −1.35 V to −0.85 V versus Hg/Hg2SO4 reference electrode to convert at least a portion of the PbSO4 to Pb(0) and achieve a state of charge in the range of about 50 to about 100%, thereby forming an active, charged electrode.
Embodiment 14 is a lead-acid battery comprising two or more of the electrochemical cells of any one of embodiments 1 to 13 electrically connected in series, in parallel, or in both series and parallel.
Embodiment 15 is a method of preparing PbSO4 crystals with a tabular and/or diamond crystal shape and a selected average crystal size; the method comprising:
Embodiment 16 is the method of embodiment 15, wherein the crystal-growth modifier is present in the control solution at a concentration in the range of 0.01 to 50 g/L, and the volume of the crystal-growth control solution is about 0.1 to about 10 times the total volume of Pb(2+) and SO4(2−) being added.
Embodiment 17 is the method of embodiment 15, wherein the Pb(2+)-containing precursor solution and the SO4(2−) containing precursor solution have concentrations in the range of about 0.001 to about 1M.
Embodiment 18 is the method of any one of embodiments 15 to 17, wherein the crystals are allowed to grow for a selected period of time in the range of about 0.1 to about 5000 minutes, before the crystals are isolated and washed with water to remove the crystal-growth modifier and soluble salt contaminants.
Embodiment 19 is crystalline PbSO4 comprising tabular and/or diamond-shaped crystals having an average crystal size, as determined by dynamic light scattering and particle imaging using a transmission electron microscope, of about 10 nm to about 2 μm, with a particle size distribution in which at least about 90% of the crystals have a particle size within about 20% of the average diameter.
Embodiment 20 is the crystalline PbSO4 of embodiment 18, wherein the crystals have an average diameter selected from the group consisting of (a) about 140 nm to about 160 nm; (b) about 180 nm to about 220 nm; (c) about 250 nm to about 290 nm; and (d) about 1 μm to about 1.4 μm.
The crystalline PbSO4 materials described herein provide significant advantages when used to form active electrode materials for use in lead-acid cells and batteries. In particular, the crystalline PbSO4 materials provide advantages such as, e.g., the starting battery material remains in a Pb(2+) state, which leads to potentially simpler, less energy-intensive battery recycling strategies; the typical electrode curing process is eliminated; the electrodes and batteries do not require any other chemical reactions to occur during electrolyte fill or prior to the formation step; and controlling the size and shape of the lead sulfate crystals enables control of the efficiency and rate at which the material charges in the battery. This reduces the energy required for electrode formation to a level that is equal to the amount of energy stored in the battery, creating a far more time and energy-efficient formation step.
As described herein, PbSO4 crystals with a well-defined crystal size distribution are prepared by a controlled precipitation method using slow injection of soluble Pb2+ and SO42− precursors. The method utilizes a crystal-growth modifier (CGM), such as polyethylenimine (PEI), to control the nucleation and growth of PbSO4 in an aqueous solution acidified with acetic acid. Without the CGM, PbSO4 precipitates immediately in an uncontrolled manner, leading to micron-sized particles that are non-uniform in shape. The CGM serves to slow the kinetics of nucleation and growth so that PbSO4 particles with narrow size distribution can be synthesized.
Suitable crystal-growth modifiers include, for example, linear or branched cationic polymers such as polyimines (e.g., poly(ethyleneimine) (PEI), poly(propyleneimine), poly(ethyleneimine-co-propyleneimine), and the like), polymers comprising charged quaternary amino groups (e.g., poly(diallyldimethylammonium chloride), PDDAC); linear or branched non-polymeric amines (e.g., ethylamine, propylamine, hexadecylamine, tert-butylamine, ethylenediamine, propylenediamine, tris(aminomethyl)methane, and the like), and water soluble polymers such as polyethyene glycol, polyacrylamide, polyacrylic acid, polyvinylalcohol, polyvinylpyrrolidone, carboxymethylcellulose, and the like.
The sizes of the PbSO4 crystals were controlled by varying either the injection time of the Pb2+ and SO42− precursors, or the growth time, defined as the length of time in the reactor after precursor injection is ceased. Due to the comparatively high solubility of PbSO4 in the reaction solution, the particles continue to grow by Ostwald ripening if left in the reactor indefinitely. Once washed and dispersed in pure water, the PbSO4 crystals exhibit excellent stability in their size and shape. As examples, lead sulfate of four particle sizes (156 nm, 200 nm, 270 nm, and 1.2 μm) were synthesized and studied electrochemically. The 200 nm particles were made at the faster injection rate compared to the other sizes, creating more or less a mixture of the two crystal habits (diamond-shaped and rectangular slabs), whereas the other crystals exhibited predominantly one major crystal habit. The samples were characterized with X-ray diffraction and Raman spectroscopy to confirm that they were pure PbSO4 phase and that the reaction chemicals had been sufficiently washed away. Finally, the particles were mixed with VULCAN XC-72 carbon black in a mass ratio of 80:20 or 90:10 PbSO4:C for electrochemical evaluation. The carbon provides conductivity for enhancing the electrochemical reactions of the PbSO4 crystals.
Electrochemical studies of these particles were performed by dropcasting the PbSO4/carbon composite onto glassy carbon electrodes. PbSO4 particle cycling was studied as a function of potential window and scan rate to establish the approximate potentials and rates at which these particles were electrochemically active. During charging, lead(II) ion from the PbSO4 is reduced to Pb(0). In the discharge phase of cycling, Pb(0) is oxidized back to Pb(2+). All experiments were performed in 5 M H2SO4 under Ar purging with a Hg/Hg2SO4 reference electrode, and all potentials are given relative to the Hg/Hg2SO4 reference potential. The PbSO4 particles demonstrated a clearly defined onset potential for charging at approximately −1.12 V. As the negative potential limit was expanded from −1.25 to −1.35 V, additional charging of the PbSO4 occurred. The potential window was standardized to be −0.85 to −1.35 V, where the positive limit was chosen to ensure full discharge and the negative limit to avoid catalyzing hydrogen evolution.
A single cyclic voltammogram (CV) of these particles at scan rates ranging from 5 to 0.1 mV/s provided understanding of the charging kinetics of pure 200 nm PbSO4 crystals.
Single cyclic voltammograms on polished Plante Pb disks also indicate that after forming a PbSO4 film on discharge, the charging scan has a well-defined peak around −1.07 V. When charging PbSO4 particles for the first time, a charging peak is not observed, even at slow scan rates such as 0.1 mV/s. However, if cycled a second time at a scan rate of 0.5 mV/s or slower, the charging peak begins to develop, and the peak grows in size on the third cycle. Because of the scan rate dependence of the formation of the charging peak, the peak's presence appears linked to the charge and discharge capacities of the first cycle. In other words, the peak only appears if the electrode exists at a certain state-of-charge (SoC) before the start of the second cycle. Because the charging peak barely develops on the second cycle at 0.5 mV/s, the charge and discharge capacities from the first cycle at 0.5 mV/s were used to determine that the minimum SoC for 200 nm particles to develop a charging peak is about 13% with an 80:20 mass ratio of PbSO4:C. Therefore, this charging peak is indicative of a sufficient Pb/PbSO4 interface that accepts charge through deposition of Pb2+ onto Pb at a lower overpotential than the pure PbSO4 electrode. This finding aligns well with the standard use of lead-acid batteries at high or partial SoC and their failure during deep discharge due to sulfation.
Given that the SoC was determined to be important to the cycling behavior of the PbSO4 crystals, we established a cycling protocol that enables control over SoC under potentiostatic conditions within the first cycle.
Finally, a discharge scan from −1.35 V to −0.85 V was performed, followed by a second charge scan back to −1.35 V.
The control over the SoC provides further insight into the PbSO4 reduction at the charging peak (approximately −1.07 V) versus PbSO4 reduction at higher overpotential (below −1.12 V). At a condition of 25% SoC, the electrode is relatively starved of Pb surface during discharge, resulting in a smaller discharge capacity than at 50% or 75% SoC. Interestingly, the discharge capacity is relatively equal after charging to either 50% or 75% SoC, but the discharge current is higher in the 75% SoC electrode. The equivalence in discharge capacity is indicative of the Peukert effect, which limits the discharge capacity because the discharge rate (scan rate) is the same. The 75% SoC demonstrates a slightly higher discharge capacity due to the larger Pb surface area generated during charge, while it demonstrates significantly higher discharge current due to the decreased resistance within the electrode layer from increased formation of metallic Pb.
During the second charge scan, the charging capacity and current at −1.07 V increases with increasing first cycle SoC. The higher SoC exhibits a larger Pb/PbSO4 interface, accelerating charge kinetics in the low overpotential region. At higher overpotential, the current plateaus in all cases. The plateau current is equivalent for the 25% and 50% SoC due to significant amounts of remaining bulk PbSO4 that are kinetically limited by the dissolution rate, while the 75% SoC has a smaller plateau current, because it has less bulk PbSO4 remaining. Ultimately, all three electrodes attain similar charging capacity in the second charge, although by different mechanisms of charging at the Pb/PbSO4 interface versus bulk PbSO4.
The comprehensive understanding of the kinetics and mechanisms of charging well-defined PbSO4 particles establishes the background knowledge needed to study the impact of PbSO4 particle size on lead-acid electrochemistry.
On discharge, the current and capacity were highest for the 156 nm particles due to the higher surface area for Pb discharge and the less resistive electrode with higher Pb content. As discussed previously, the Peukert effect limits the discharge capacity. In the previous example (
Finally, the second charge for each particle size provides interesting insight into the charging mechanisms. The SoC levels at the beginning of the second charge scan are 23%, 18%, and 31% for 156 nm, 270 nm, and 1.2 μm particles, respectively. The 1.2 μm particles maintain such a high SoC because their discharge performance was so poor. This causes the charging peak on the second charge scan to be much larger for the 1.2 μm particles. The 150 nm particles have the next largest charging peak due to their next highest SoC, followed by the 270 nm particles with the smallest charging peak due to their smallest SoC. The 1.2 μm particles have a large Pb/PbSO4 interface for charging at low overpotential, but at higher overpotential, they still demonstrate less charging of bulk PbSO4. As expected, the 156 nm particles exhibit the best charging of bulk PbSO4 at high overpotential and the highest charging capacity overall on the second charge.
To quantify the overall impact of the particle size on the charging performance of the PbSO4 material, a Kinetic Charge Acceptance (KCA) parameter was defined as shown in Equation 2:
The KCA demonstrates the overall impact of the particle size on the rate and capacity of charging. The KCA parameter demonstrates that the 156 nm PbSO4 particles improve charging performance by a factor of over two and over 10 times compared to the 270 nm and 1.2 μm particles.
In some preferred embodiments, the cathode comprises a particulate carbon material. Preferably the particulate carbon material comprises carbon nanoparticles or microparticles. As used herein, the term “nanoparticle” refers to particles in the range of about 1 up to about 900 nanometers (nm) in average size. As used herein, the term “microparticle” refers to particles in the range of greater than 900 nm to about 10 micrometers (μm) in average size. Nonlimiting examples of suitable carbon materials include, e.g., carbon nanotubes (e.g., single-walled carbon nanotubes, multi-walled carbon nanotubes, and the like), carbon nanofibers, graphene, graphene oxide, reduced graphene oxide, carbon black, and graphite. The term nanotube refers to tubular carbon materials with a tubular diameter in the range of about 0.4 to about 100 nm, which can have lengths of 1 nm to 1 micrometer, or more. Single-walled carbon nanotubes typically have a tubular wall that has a thickness of a single carbon atom, while multi-walled nanotubes have tubular walls with several nested layers of carbon. The term nanofiber refers to fibrous carbon materials with a fiber diameter in the range of about 50 to about 200 nm, which typically can have lengths of about 1 to 200 micrometers. Preferably, the particulate carbon material is mixed with the lead sulfate crystals in a past that is coated or packed onto pasted plate grid or a tubular plate electrode framework to form the electrode in its initial discharged state. The mass ratio of lead sulfate to carbon can be from about 99.9:0.1 to about 50:50 (e.g., about 80:20 or 90:10). The lead sulfate/carbon mixture is combined with at least one protic solvent such as water or an alcohol (e.g., methanol, isopropanol, and the like) to form a suspension with a solids concentration in the range of about 1 mg/L to about 100 g/L (based on mass of solids in volume of solvent) constituting the paste. The pasted plate or tubular framework acts as a current collector for the electrode.
The counter electrode for the lead-acid electrochemical cell typically comprises a hardened metallic lead alloy. For example, the counter electrode can be a rod or bar, a sheet, a foil, or a foam of metallic lead or an alloy thereof.
In each electrochemical cell, the electrolyte contacts both electrodes and comprises an aqueous solution of sulfuric acid. Typically, the sulfuric acid is present in the electrolyte solution at a concentration of about 1 to about 5 M. In some embodiments, the sulfuric acid solution is about 5 M.
Each cell also includes a separator membrane between the electrodes. The separator is a proton-permeable or conducting membrane or film that allows hydrogen ions to pass through the membrane or film to balance the electrical charges formed at the electrodes during charging and discharging of the cell, while preventing passage of zinc ions to the cathode. The separator can be any ion-conductive material. Non-limiting examples of such materials include, e.g., a fluorinated ionomer (such as a NAFION sulfonated tetrafluoroethylene based fluoropolymer-copolymer), a sulfonated polyether ether ketone (S-PEEK), a polybenzirnidazole (PBI) membrane doped with a strong mineral acid, an interpenetrating network of polybenzimidazole (PBI) and polyvinylphosphonic acid, a proton-conducting ceramic film (e.g., barium zirconates (BaZrO3) or cerates (BaCeO3) doped with an acceptor ion such as yttrium), and the like.
The electrochemical cell can be embodied in a number of different battery configurations, in which the cells are electrically connected in series, in parallel, or in both series and parallel.
The following non-limiting examples are provided to illustrate certain aspects and features of the methods, electrodes, cells and batteries described herein.
Lead sulfate crystals were formed by the following procedure:
A 0.8 wt % PEI, 20.3 wt % HOAc solution is prepared by weighing 5.36 g 30% w/v PEI into a 250 mL fluorinated ethylene propylene (FEP) bottle; 156.77 g H2O is weighed into the bottle; 41.37 g HOAc is weighed into the bottle in a fume hood, and the resulting mixture was shaken well. The pH of this solution was about 2.46. Sulfate and lead solutions were separately prepared as 0.5 M Na2SO4 and 0.5 M Pb(NO3)2.
To prepare for lead sulfate synthesis, about 0.4 mmol (0.13248 g) of Pb(NO3)2 was weighed into a 100 mL round bottom perfluoroalkoxy alkanes (PFA) flask with a stir bar. About 40 mL of the PEPHOAc solution was added and the resulting mixture is stirred at room temperature to dissolve the Pb(NO3)2.
The equipment for reacting the precursor solutions, including a programable syringe pump with a LUER LOK-type syringe of a selected syringe diameter was set up, and the pump was programed for a selected injection rate (such as 0.1 or 0.4 mL/min or both), injection volume, or injection time (such as 5.5 to 240 min). The syringes were filled with the appropriate volume of 0.5 M Na2SO4 and 0.5 M Pb(NO3)2. Finally, the syringe pump program is initiated to prepare the lead sulfate. After finishing injection of lead and sulfate precursors, the reaction mixture was optionally allowed to stir for a selected period of hold time (such as from about 1 minute to about 2 days).
After synthesis, the PbSO4 crystals were washed as follows: the final reaction volume was split into 50 mL centrifuge tubes with about 22 mL in each tube. Each tube was filled to the 35 mL mark with water, and the resulting mixture was centrifuged at about 8000 rpm for about 5 min. The PbSO4 crystals were then washed an additional 3 times with water and isolated after each wash by centrifuging at about 8000 rpm for about 5 min. The tubes were then refilled with as much water as desired to disperse the final sample. The crystals can be recovered by filtration and drying, if desired.
The washed PbSO4 in water suspension was filtered and dried at about 80° C. in vacuum for about 20 min. From the dried PbSO4, a 30 mg/mL suspension was prepared by adding the appropriate amount of water and sonicating for 15 min. An approximate 1 mg/mL suspension of VXC72 carbon in IPA was prepared by sonicating for about 20-40 min, or until no VXC72 carbon chunks can be observed. An appropriate amount of the 30 mg/mL PbSO4 suspension was pipetted into the VXC72/IPA suspension to obtain a desired wt % of PbSO4 and carbon. The PbSO4 and carbon were sonicated together for about 5 min.
A 3:1 volume ratio of hexane:IPA was added to the centrifuge tube of PbSO4/C/IPA/H2O. The carbon/PbSO4 crashed out of the suspension when the hexane was added. The resulting mixture was centrifuged at about 8000 rpm for about 5 min, and the solvent was poured off carefully. The powders were dried (e.g., at room temperature) and then were ready to prepare inks for electrochemistry evaluation.
5 M H2SO4 was prepared by confirming that the density of the 5 M H2SO4 was between 1.28-1.285 g/mL. The electrochemical cell was rinsed with H2O and filled with about 60 mL of 5 M H2SO4 . The electrolyte was purged with Ar for about 30 min.
Note: all voltages are versus a Hg/Hg2SO4 reference filled with saturated K2SO4.
Each glassy carbon (GC) rotating disk electrode RDE) was polished with 0.05 μm Al2O3 polishing slurry and rinsed under some H2O and then put in IPA. The GC RDE were sonicated 15 min in the IPA, rinsed 3-4 times with H2O, then sonicated 15 min in H2O. When the electrolyte in the cell was sufficiently purged with Ar, GC conditioning was started. The GC RDE was immersed in the electrolyte at −0.7 V.
The conditioning protocol was CV from −0.6 to −1.8 V, at 200 mV/s, for 10 cycles, at 1000 rpm.
After conditioning, the RDE was dipped in a beaker of water and rotated at about 1000 rpm to rinse for a few seconds.
A certain amount of a PbSO4/C sample (about 5-10 mg) was weighed and IPA was added to create an ink with a concentration of 1.85 mg PbSO4/mL. For example, if the PbSO4/C composite was 20 wt % carbon, the ink would be 2.31 mg composite/mL. The ink was sonicated 30 min to disperse the composite well. To prepare the active electrode, an RDE was screwed onto an inverted rotator shaft. The RDE was rotated at about 700 rpm while about 5 μL of the ink was dropcast 4 times, with drying in between each droplet. The ink was re-sonicated for about 10 sec before each droplet.
C. Electrochemical Testing Protocol
The GC electrode with active material was immersed into the electrolyte at −0.85 V. The cycling protocol consisted of:
The cycling protocol can of course be varied in many ways to probe effect of SoC, sweep rate, number of cycles, or stop on discharge instead of charge. After testing, the RDE was dipped in a beaker of water and rotated at about 400 rpm to rinse for a few seconds. The RDE was removed from the shaft and dried in air.
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
The United States Government has rights in this invention pursuant to Contract No. DE-AC02-06CH11357 between the United States Government and UChicago Argonne, LLC representing Argonne National Laboratory.
