WO2021034455A1

WO2021034455A1 - Process to control a corrosion layer

Info

Publication number: WO2021034455A1
Application number: PCT/US2020/043679
Authority: WO
Inventors: Jeremy Meyers; Catherine MCCARRELL; Paul Everill; Steven SWOGGER; Kurt W. Swogger
Original assignee: Molecular Rebar Design, Llc
Priority date: 2019-08-19
Filing date: 2020-07-27
Publication date: 2021-02-25

Abstract

The present disclosure, in various embodiments, describes a process for controlling a Corrosion Layer in a lead-acid battery, comprising at least one anode and at least one cathode, the anode grid and the cathode grid in at least partial contact with respective mixtures of leady oxide paste, which provides enhanced life in corrosion-intensive environments.

Description

PROCESS TO CONTROL A CORROSION LAYER

Cross-reference to Related Applications

[0001] The present application claims priority to U.S. provisional Application No. 62/888,712 filed August 19, 2019 which application is hereby incorporated by reference in its entirety.

Background and Summary of the Invention

[0002] Corrosion is a significant problem for the battery industry, particularly in very hot climates close to the equator. Although lead acid batteries, through their intrinsic reduction/oxidation (redox) chemistries, must corrode to a certain extent throughout life, runaway corrosion of the positive electrode’s (cathode’s) current collector (the “grid”) can lead to premature failure of the battery as the electrode decomposes, losing the contact it has with the active material, rendering it incapable of continuing electrochemical reactions.

[0003] In automobile applications, the corrosion issue has become even more confounded since the early 1990s. Antimony-free grid alloys began to take precedence, such as the now popular Pb/Ca/Sn varieties, because they significantly decreased water consumption and improved the overall performance of the battery while increasing production speed. These grid types, however, also resulted in the Premature Capacity Loss phenomenon which arose in two flavors: PCL1, now known to be caused by material inadequately attached to the grid surface, and PCL2, which is related to bulk material softening, both being caused by metallurgical events in the grid alloy itself (Hollencamp). The restyling of automobiles for improved aerodynamics that was occurring around this time resulted in substantially less air moving through the engine compartment which increased the temperature of the engine compartment and led to unintended consequences for the battery.

[0004] Corrosion can be exacerbated in high temperature situations when the usual corrosion of the grid becomes intensified through simple thermodynamic principles (i.e. more heat energy, more corrosion). When this happens the grid thins, active material and grid pieces can become detached, and sections of the electrode can fall off and cause either shorting or premature capacity loss, both of which will end the battery’s service. The thinning of the grid can also lead to migration of the grid alloys towards the negative electrode (anode) where they can combine to trigger adverse side reactions, such as water loss or gassing. Antimony is one such example of this detrimental migration effect, with what is termed Antimony Poisoning being a well-established issue in certain applications which have not yet moved away from antimony-based grid designs. [0005] The corrosion layer is the outer most layer of the current collector, or grid, which is in direct contact with the active material (lead compounds and acid). It is the glue that holds the active material onto the grid. The layer begins to take shape during the curing stages of battery production where the active material-coated grids are exposed to high heat and humidity for prolonged periods, often 2-4 days, but it is not until the battery’s first charge, or “formation”, that the layer achieves its final form through acid-based corrosion of the grid itself. The production of a corrosion layer is a necessary step in battery formation since without a firm connection between active material and grid, the material will slough off and lead to Premature Capacity Loss as the active compounds detach from the current collector. This corrosion layer is also the first line of defense against further corrosion of the grid since it forms a sheath around the grid, albeit it frequently imperfect. Many factors affect the structure and composition of the corrosion layer and, if well prepared, that structure/composition can help to ensure strong adhesion between the grid and the active material. A thin corrosion layer can make the plates prone to paste shedding or delamination. Grids made with low calcium, high tin, or silver alloys are so resistant to corrosion that it is difficult to get proper attachment (Prengaman). Alterations of the corrosion layer, or the way in which it corrodes would directly manipulate the way that the active material and grid function together and, in the right circumstances, provide enhancements to corrosion resistance.

[0006] Mahato simulated the cyclic corrosion of a positive grid by linearly sweeping both pure Pb and Pb-Sb alloys through the potential range that the positive plate is expected to experience. This cyclically corroded positive grid developed a multiphase corrosion layer with a b-PbOi rich exterior and a tet-PbO + a-PbCh inner layer. Presence of antimony in the alloy reduces the intensity of stress cracking, and this might explain why there is a difference between steady-state corrosion on overcharge and corrosion during cycling. The bulk positive active material also undergoes changes with cycling. In a study of the softening of positive active mass, Lailler noted that the PbCh grain size grows during battery life. XRD spectra shows that the a-PbCh tends to disappear during cycling; the a phase is unstable at low pH, so the formation of b-PbOi is easier during charging. They suggest that the microstructural evolution halts when the b-PbOi crystallites become too large. They lose contact with the positive plate and no longer take part in the electrochemical reactions. Rogatchev and Pavlov state that the composition of the corrosion layer is non-stoichiometric lead oxide, PbO_n, where n varies between 1.4 and 1.95. This implies that the crystal lattice of the oxide contains both Pb²⁺ and Pb⁴⁺ ions. They claim that the introduction of Sb into the alloy promotes oxidation and increases the stoichiometric coefficient of the alloy. Rogatchev also claims claim that the corrosion layer contains both a and b forms of PbC . The ratio of these two forms depends upon the quantity of electricity passed. Calabek performed experiments to characterize the resistance of the corrosion layer on Sb-containing grids (5.06%) and found that the resistance of the corrosion layer changes with both state of charge and acid concentration of the electrolyte. Various authors have also noted the presence of two distinct corrosion layers present adjacent to one another in various alloys.

[0007] Corrosion failures are typically addressed by alloy changes, ground-up changes to the grid design or method of manufacture or, less frequently, with inorganic salts added directly to the paste like SnSCri or NaTkBCri whose mechanism of action is poorly understood. Alloys can be changed from Pb-Sb to Pb-Sn-Ca or Pb-Ag or more exotic compositions utilizing barium, for example. This is expensive and hard to implement correctly and can negatively affect the chargeability and life of the battery. Preferred grid designs for automotive batteries are typically very thin and produced via certain equipment to give a “punched”, “concasted”, “conrolled”, or “expanded” design, referring to how the gaps in the grid are developed. These are traditionally poorly corrosion resistant with some manufacturers preferring older “book molded” grid designs which have better corrosion resistance at the expense of manufacturability and production speed.

[0008] In certain battery designs with highly optimized negative electrodes, the positive corrosion issue can be intensified through both overworking of positive electrode (higher degree of corrosion) or increased side reactions in the negative electrode which can lead to higher water loss from the battery and, therefore, concentration of the acid which further increases corrosion of the positive electrode (Maleschitz). With the industry’s focus on higher charge acceptance, usually achieved through improvements made to the negative active material, or anode, the problems associated with positive plate corrosion are again taking the center stage in research establishments around the world.

[0009] Our unique process discloses the use of a nanoscale, paste-structuring agents and a specific charging procedure to develop a desired corrosion layer on the positive grid of a lead acid battery which provides enhanced life in corrosion-intensive situations. When our process is followed, the modified corrosion layer appears denser, thinner, and morphologically more robust than corrosion layers formed without our process.

[0010] The present disclosure, in various embodiments, describes a process for controlling a corrosion layer in a lead acid battery, comprising at least one anode and at least one cathode, the anode grid and the cathode grid in at least partial contact with respective mixtures of leady oxide paste, where the process comprising the steps of: a) incorporating a plurality of discrete carbon nanotubes at a concentration from about 0.01 to about 0.10 weight percent in a leady oxide mixture comprising 60-85 % PbO and 15-40% Pb paste, b) charging/forming the resultant lead-acid battery using a net quantity of charge of about 1.5*C2o to about 4*C2o Amp hour at a current rate between about C2o/20h and C2o/3h, where C20 is the amount of charge the battery was designed to maximally discharges over 20 h in units of Amphour, c) thereby forming on at least one anode grid and/or at least one cathode grid, a corrosion layer with an average thickness from about 10 to about 250 microns.

[0011] In one embodiment, the process describes the formation of a corrosion layer formed only on the cathode grid of a lead acid battery.

[0012] In another embodiment, the process describes a plurality of carbon nanotubes which are only in leady oxide paste material contacting the cathode grid prior to formation.

[0013] In another embodiment, the process describes the formation of a corrosion layer formed only on the anode grid.

[0014] In another embodiment, the process describes a plurality of carbon nanotubes which are only in the mixture of 60-85 % PbO and 15-40% Pb paste material contacting the anode grid.

[0015] One embodiment of the process comprises a carbon nanotube concentration from about 0.03 to about 0.10 weight percent with respect to the mixture of 60-85 % PbO and 15-40% Pb.

[0016] A yet further embodiment of the process comprises a method for first charging, or forming the lead-acid battery using a net quantity of charge from 1.5*C2o to 4*C2o Amphours, more optimally between 2.0*C2o and 3.5*C2o Amphours, and more optimally between 2.1*C2o and 3.0*C2o Amp hours (where C20 is the amount of charge the battery was designed to maximally discharge over 20 h in units of Amp hour).

[0017] A yet further embodiment of the method for charging, or forming, the lead- acid battery using a charge rate of between about C2o/20h and about C2o/3h Amps, or more optimally between about C2o/15h and about C2o/3h Amps, or more still optimally between about C2o/10h and about C2o/3h Amps, where C20 is the amount of charge the battery was designed to maximally discharge over 20 h in units of Amp hour.

[0018] In another embodiment of the process, a plurality of discrete carbon nanotubes that have at least 1% total oxidation, but with more than 20% greater oxidation percentage on the outer surface of the carbon nanotube than the inner surface of the innermost wall, can be utilized.

[0019] In another embodiment, the process describes a plurality of discrete carbon nanotubes which are single-walled carbon nanotubes.

[0020] In one embodiment, the process describes a plurality of discrete carbon nanotubes which are multi-walled carbon nanotubes.

[0021] Another embodiment of the process utilizes at least one anode or at least one cathode which does not comprise an alloy selected for the group consisting of Pb-Sb, Pb-Ca/Sn, Pb-Ag, combinations thereof and derivatives thereof.

[0022] In one embodiment, the process describes an improvement for a lead acid battery comprising of at least one cathode grid having a corrosion layer from about 10 to about 250 microns thickness wherein the cathode material comprises a reaction product from the process of Claim 1 comprising >75% PbCh and less than .01 weight of carbon nanotubes.

[0023] In one embodiment, the process describes an improvement for a lead acid battery comprising of at least one cathode grid having a corrosion layer from about 10 to about 250 microns thickness wherein the cathode material comprises a reaction product from the process of Claim 1 comprising >75% PbCh and a non-detectable weight of carbon nanotubes.

[0024] In other embodiments, the process forms a corrosion layer which is monophasic, consisting of only one clearly-defined, visible, and uniform region of acid and/or oxygen ingress.

[0025] In another embodiment, the process produces a plate which is at least 10% more resistant to mechanical stresses, such as vibrating or crushing.

[0026] Another embodiment of the process produces a battery which is at least 10% more resistant to corrosion on the cathode grid as defined by standard life cycling techniques.

[0027] Another embodiment of the process produces a plate with at least 20% improved grid-mass adhesion in the pre-charged/formed state.

[0028] In another embodiment of the process, the process produces a plate with at least 20% improved grid-mass adhesion in the post-charged/formed state.

[0029] Another embodiment of the process comprises a method to reduce metal released from the cathode grid. [0030] In some embodiments, the mixture of 60-85 % PbO and 15-40% Pb paste is substituted for a mixture containing 10-50% red lead (Pb304), 10-70% PbO, and 15-40% Pb.

[0031] In some embodiments, the process is applied to monopolar battery design.

[0032] In other embodiments, the process is applied to bipolar battery designs.

[0033] In a final embodiment, the process is applied to a lead-acid battery in which at least one of the anodes comprises a capacitive carbon coating.

Brief Description of the Figures

[0034] Figure 1A shows the positive plate failure mode results.

[0035] Figure IB shows a control corrosion layer and a experimental corrosion layer.

[0036] Figure 2A shows a comparison of pore area.

[0037] Figure 2B shows a comparison of pore size.

[0038] Figure 3A shows a view of batteries built with control positives.

[0039] Figure 3B shows a view of batteries built with positive electrodes which included discrete carbon nanotubes.

[0040] Figure 3C shows an evaluation of the plates post-cycling.

[0041] Figure 4A shows an Energy-Dispersive X-Ray (EDX) Spectroscopy reading.

[0042] Figure 4B shows an Energy -Dispersive X-Ray (EDX) Spectroscopy reading.

[0043] Figure 4C shows an Energy -Dispersive X-Ray (EDX) Spectroscopy reading.

[0044] Figure 4D shows an Energy-Dispersive X-Ray (EDX) Spectroscopy reading. Detailed Description

[0045] The nanotubes that may be useful herein and their methods of preparation are described in, for example, U.S. Patent No. 10,414,656 which is incorporated herein by reference. Useful nanotubes and their methods of preparation are also described in U.S. Patent No. 9,636,649 which is incorporated herein by reference.

[0046] General Process to Produce Discrete Carbon Nanotubes Having Targeted Oxidation

[0047] A mixture of 0.5% to 5% carbon nanotubes, preferably 3%, by weight is prepared with CNano grade Flotube 9000 carbon nanotubes and 65% nitric acid. While stirring, the acid and carbon nanotube mixture is heated to 70 to 90 degrees C. for 2 to 4 hours. The formed oxidized carbon nanotubes are then isolated from the acid mixture. Several methods can be used to isolate the oxidized carbon nanotubes, including but not limited to centrifugation, filtration, mechanical expression, decanting and other solid-liquid separation techniques. The residual acid is then removed by washing the oxidized carbon nanotubes with an aqueous medium such as water, preferably deionized water, to a pH of 3 to 4. The carbon nanotubes are then suspended in water at a concentration of 0.5% to 4%, preferably 1.5% by weight. The solution is subjected to intensely disruptive forces generated by shear (turbulent) and/or cavitation with process equipment capable of producing energy densities of 106 to 108 Joules/m.sup.3. Equipment that meet this specification includes but is not limited to ultrasonicators, cavitators, mechanical homogenizers, pressure homogenizers and microfluidizers (Table 1). One such homogenizer is shown in U.S. Pat. No. 756,953, the disclosure of which is incorporated herein by reference. After shear processing, the oxidized carbon nanotubes are discrete and individualized carbon nanotubes. Typically, based on a given starting amount of entangled as-received and as-made carbon nanotubes, a plurality of discrete oxidized carbon nanotubes results from this process, preferably at least about 60%, more preferably at least about 75%, most preferably at least about 95% and as high as 100%, with the minority of the tubes, usually the vast minority of the tubes remaining entangled, or not fully individualized.

[0048] Another illustrative process for producing discrete carbon nanotubes follows: A mixture of 0.5% to 5% carbon nanotubes, preferably 3%, by weight is prepared with CNano Flotube 9000 grade carbon nanotubes and an acid mixture that consists of 3 parts by weight of sulfuric acid (97% sulfuric acid and 3% water) and 1 part by weight of nitric acid (65-70 percent nitric acid). The mixture is held at room temperature while stirring for 3-4 hours. The formed oxidized carbon nanotubes are then isolated from the acid mixture. Several methods can be used to isolate the oxidized carbon nanotubes, including but not limited to centrifugation, filtration, mechanical expression, decanting and other solid-liquid separation techniques. The acid is then removed by washing the oxidized carbon nanotubes with an aqueous medium, such as water, preferably deionized water, to a pH of 3 to 4. The oxidized carbon nanotubes are then suspended in water at a concentration of 0.5% to 4%, preferably 1.5% by weight. The solution is subjected to intensely disruptive forces generated by shear (turbulent) and/or cavitation with process equipment capable of producing energy densities of 106 to 108 Joules/m.sup.3. Equipment that meet this specification includes but is not limited to ultrasonicators, cavitators mechanical homogenizers, pressure homogenizers and microfluidizers (Table 1). After shear and/or cavitation processing, the oxidized carbon nanotubes become oxidized, discrete carbon nanotubes. Typically, based on a given starting amount of entangled as-received and as-made carbon nanotubes, a plurality of discrete oxidized carbon nanotubes results from this process, preferably at least about 60%, more preferably at least about 75%, most preferably at least about 95% and as high as 100%, with the minority of the tubes, usually the vast minority of the tubes remaining entangled, or not fully individualized. [0049] Embodiments of nanotubes with targeted oxidation may include: 1. A composition comprising a plurality of discrete carbon nanotubes, wherein the discrete carbon nanotubes comprise an interior and exterior surface, each surface comprising an interior surface oxidized species content and an exterior surface oxidized species content, wherein the interior surface oxidized species content differs from the exterior surface oxidized species content by at least 20%, and as high as 100%. 2. The composition of embodiment 1 wherein the interior surface oxidized species content is less than the exterior surface oxidized species content. 3. The composition of embodiment 1 wherein the interior surface oxidized species content is up to 3 weight percent relative to carbon nanotube weight, preferably from about 0.01 to about 3 weight percent relative to carbon nanotube weight, more preferably from about 0.01 to about 2, most preferably from about 0.01 to about 1. 4. The composition of embodiment 1 wherein the exterior surface oxidized species content is from about 1 to about 6 weight percent relative to carbon nanotube weight, preferably from about 1 to about 4, more preferably from about 1 to about 2. 5. The composition of embodiment 1 wherein the interior and exterior surface oxidized species content totals from about 1 to about 9 weight percent relative to carbon nanotube weight. 6. A composition comprising a plurality of discrete carbon nanotubes, wherein the discrete carbon nanotubes comprise an interior and exterior surface, each surface comprising an interior surface and an exterior surface oxidized species content, wherein the interior surface oxidized species content comprises from about 0.01 to less than about 1 percent relative to carbon nanotube weight and the exterior surface oxidized species content comprises more than about 1 to about 3 percent relative to carbon nanotube weight. 7. The composition of embodiment 6 wherein the discrete carbon nanotubes comprise a plurality of open ended tubes. 8. The composition of embodiment 6 wherein the plurality of discrete carbon nanotubes comprise a plurality of open ended tubes. 9. The composition of embodiment 1 wherein the discrete carbon nanotubes comprise a plurality of open ended tubes.

Example 1: Construction of a Lead-Acid Battery Implementing the Disclosed Process

[0050] A lead-acid battery is constructed over a series of steps, two of which are modified in the present disclosure. Specifically, the mixing process (1) is modified to include a plurality of discrete carbon nanotubes and the formation process (5) is modified to elicit construction of the intended corrosion layer on at least one anode or at least one cathode of a lead-acid battery. This corrosion layer is in at least partial contact with lead oxide paste and the lead or lead-alloy grid.

[0051] Paste Mixing. Lead- Acid Battery construction begins with the mixing of active materials which typically comprise Leady Oxide (defined as a mixture of 60-85 % PbO and 15-40% Pb formed through the incomplete aid oxidation of pure Pb ingots by either heated ball-milling or a Barton Pot furnace), reinforcing fibers, water, acid, and, in the case of the negative active mass, a quotient of Expander (a mixture of lignin sulfonate, barium sulfate, and carbon). Additional additives are in existence, but this list details the most basic lead-acid battery paste mixture. The dry ingredients are added to a planetary or double-planetary mixer, for example, mixed for a short period, combined with water, mixed again, and introduced to a quantity of acid over an extended period to control temperature increases as the chemical reactions take place. A plurality of discrete carbon nanotubes is introduced into the leady oxide paste as a fluid suspension of no less than 0.3 percent solids towards an in-paste concentration of about 0.01 to about 0.10 weight percent with respect to the mass of leady oxide in the paste alongside the water. Some manufacturers change the order of addition to adapt to their equipment or climate, but the discrete carbon nanotubes are always added alongside the water addition and always before the acid addition. Final paste density, moisture analysis, and/or Humboldt penetration are typically used as quality controls to determine adequate paste consistency. The addition of discrete carbon nanotubes to the paste does not change the density appreciably but will change the rheology of the mixture which impacts, in some cases, the feel of the mixture and enhances its workability.

[0052] Gridding/Plate Production. Once the paste mixture has successfully reached its Quality Control benchmarks, the material is applied to to a lead or lead-alloy grid either manually or mechanically to produce a paste-coated grid. These grids adopt various designs depending on application and system of manufacture. Grids can be produced from molten lead alloy through various means comprising “book molding”, “con-casting”, “con-rolling”, “punching”, and “expanding; details of which are commonly understood by those familiar with the art (Pavlov, Garche). The process disclosed is applicable to the list comprising these grid designs. After the paste material is applied to the grid, it is often passed through a flash drying oven which dries the outer layer of the plate and makes it easier to handle in subsequent steps. The flash drying oven is usually held at temperatures over 75 °C but residence time is less than a few minutes.

[0053] Curing and Drying. The paste-applied, flash-dried grids (aka “the plate”) are then loaded into a second, specialized oven which is designed to nurture the growth of specific crystal types inside the plate; a process known as curing. By storing these grids in high- humidity ovens, water can move in and out of the plate as crystal morphologies take shape on the soon-to-be-active materials and corrosion processes continue on the residual, free lead (Pb°) in the material, and the grid itself. During this stage, the environment is held at >70% humidity and <75 °C. Curing conditions vary by manufacturer and application, but the process disclosed requires only a successful cure measured by analysis of the finished plate components comprising free Pb° content <7.5% and tribasic-lead sulfate (3PbO PbSCri ^O, or “3BS”) or tetrabasic-lead sulfate (4PbO PbSCri, or “4BS”) or combinations thereof >20%, more optimally <5% Pb° and >30% 3BS or 4BS or combinations there of, and more optimally <2% Pb°, and >35% 3BS or 4BS or combinations thereof. Following the curing process, which lasts anywhere from 12-200 h in some cases, a drying step is employed to drive off any remaining water from the plates. In this step, humidity is held <15% and temperature is held >75 °C. Here, process quality control targets comprise a plate moisture level <2%.

[0054] Construction. After the plate drying process is complete and quality control metrics comprising Pb° %, 3BS or 4BS or a mixture thereof, and final plate moisture % are met, the battery system can be assembled. Some number of negative plates (anodes) are bound together with molten cast-on strapping while the same happens to the positive plates (cathodes). In a typical cell, the positive active material weight, not including the grid itself, is present in an excess versus the negative plate material due to intrinsic inefficiencies in the lead-acid battery, usually with 5-20% excess PAM. Rubber, polymer, or advanced glass-mat separators encase either the positive or negative plates to protect against shorting while leaving enough pore structure in their material of construction to allow transfer of acid between plates. Between 1 and 6 cells, comprising strapped negatives, strapped positives, and seperator covering either negative or positive plates, are placed together in a battery case and joined in series to produce the required voltage in the end battery (1 cell ~ 2.1 V, 2 cells ~4.2 V... 6 cells -12.6 V). Cells are welded together through or over the casing to produce the required voltage. A lid is placed on the battery which includes acid-fill holes. The battery is filled with sulfuric acid of density 1.05-1.30 specific gravity through those holes and then sealed with vent plugs, screw caps, or catalyst caps which protect the user from acid leads or, in the case of the later, decrease the amount of water consumption exhibited by the battery. Optionally, various additives could be added to the acid including NaS04 or MgS04, gelation agents, or polymers. Two posts, protruding from the battery at the ends of the series circuit, will be the physical attachment point for the battery rectifier (charger) and the end use application (ex. car electrical system)

[0055] Formation. A specifically modified formation is critical for the process disclosed. Formation is the term used to describe the battery’s first charge which acts to bring the battery materials from their inactive cured/dried state into their active forms, specifically by reducing Pb0/3BS/4BS/lBS/PbS04/PbC03 minerals to Pb° on the anode/negative plate and oxidizing Pb0/3BS/4BS/lBS/PbS04/PbC03 minerals to PbC on the cathode/positive plate. There are many protocols which have been utilized in the field including constant current charging, pulsed charging when current is intermittently delivered to the battery, constant temperature charging when current is defined by the input required to keep a battery at a certain temperature, and other more unique profiles. For our disclosed process, the battery’s formation must be modified so that the desired corrosion layer may form. Specifically, we disclose an aspect of the invention wherein the battery is charged using a net quantity of charge of about 1.5*C2O to about 4*C2o Amphour, where C20 is the amount of charge the battery was designed to maximally discharge over 20 h in units of Amp hour. This prevents over forming which negatively affects the discrete carbon nanotube-developed positive plate structure through a series of undesired processes comprising intense gas bubble development within the plate, excess heat generation in the battery, higher water loss leading to increased acid concentrations, and a litany of other events. More optimally, the battery is charged using a net quantity of charge of about 2.0*C2o and 3.5*C2o Ah, and still more optimally between about 2.1*C2o and 3.0*C2O Ah. The rate at which the current is delivered is also important since the battery, in its early charging, handles high currents poorly and this can lead to paste shedding, undesired crystal morphologies in the plate and, from a more fiscal point of view, inefficient use of the rectifier energy which increases overall cost of manufacture. In our process, we disclose an aspect of the invention which describes a current rate between about C2o/20h and about C2o/3h, where C20 is the amount of charge the battery was designed to maximally discharge over 20 h in units of Amp hour.

[0056] A final type of first charging is known as Tank Formation where NAM and PAM plates are formed outside of the case in a large, acid filled vat prior to strapping, tabbing, posting, and cell assembly. The tank formation tactic is particularly popular with Valve- Regulated Lead-Acid batteries and very large-format flooded batteries where water loss incurred during the formation process is not replaceable and therefor held within very tight specifications or plate thickness or weight lead to decreased formation efficiencies that are mitigated by out-of-case formation, respectively. In this example, the formulae disclosed prior for charge input and charge rate break down since there is no intended C20 available for a tank of battery plates. In this case, we disclose an aspect of the invention wherein the battery plates are charged using a net quantity of charge in units of Amp hour equal to about 200*(IPRAM * X) to about 950*(mpAM * X), more optimally about 250*(IPRAM *X) to about 500*(IPRAM * X), and still more optimally about 260*(IPRAM * X) to about 350*(IPRAM * X), where IΏRAM is the total mass of positive active material in kilograms to be formed in the bath including only the active material weight and excluding grid weight of all plates in the bath, and X is the solids percentage of mpAM which corrects the formula for any moisture still contained in the plate. X can be calculated using moisture analyzing devices such as a Torball ATS60, or by simply measuring the weight of the plate before and after extensive drying; either method will return a solids percentage. In the formation tank, PAM and NAM plates should be balanced such that the active material weight, not including the weight of the grids themselves, is within the ratio of P/N of about 1.05 to 1.30, more optimally 1.07 to 1.25, as is understood to those familiar with the art. The Tank Formation process should occur over a period of 15-25 h for most applications.

[0057] Discrete Carbon Nanotube Presence. During formation, the oxidative environment generated on the positive plate/cathode destroys the discrete carbon nanotubes and they will no longer be detectable in significant amounts after the process. In the disclosed process, the discrete carbon nanotubes are considered a sacrificial agent responsible for the structural rearrangement and reinforcement of the active material in the cured/dried state which, when combined with a specific formation procedure, act to generate the desired corrosion layer.

Example 2: Process-Induced Corrosion Layer Improvements Provide Enhanced Cyclability at 50 °C

[0058] Preparation of Material: Positive paste mixtures were prepared by mixing 680 kg of leady oxide with -0.2% standard polypropylene fiber for a period of 2 mins followed by a volume of battery-grade water. Discrete carbon nanotubes were added to the mixture by substituting a part of the standard, control quantity of battery -grade water with a volume of discrete carbon nanotube suspension such that the final concentration of the discrete carbon nanotubes relative to the weight of leady oxide was 0.1%. These components were mixed for an additional 2 mins and then 1.4 spgr acid was slowly added to the paste over the course of 5 mins. After the mixing period was complete, density was confirmed to be -4 g/mL. Pb-Sb Grids were pasted with material using standard equipment and then cured in a high humidity oven for 32-48h at 45-50 °C prior to a 24h drying step at 90 °C and low humidity.

[0059] Building of Cells/Batteries: 12 V llOAh batteries were produced using manufactured negative plates and the experimental positive plate variety described above using an 8 positive / 8 negative configuration of electrodes. Batteries were filled with sulfuric acid per MFR recommendation and formed also per MFR recommendation which were within the charge and current ranges stipulated by this disclosure.

[0060] Electrical Testing of Batteries: After initial capacity testing per SAE J537 requirements, batteries were placed on the SAE J2185 cyclic testing program which places the batteries under CHR/DCH defined by the protocol to mimic a heavy-duty truck workload at 50 °C until such a time as their measured high-rate discharge performance (part of a weekly health check) dropped below the parameter set by the specification.

[0061] Results and Corrosion Layer Observations: Baheries containing discrete carbon nanotubes in the positive electrode increased longevity 20% over a design lacking these discrete carbon nanotubes in the positive plate.

[0062] Upon failure mode analysis, CON baheries were found to have ceased operation because of undercharge conditions in the negative and softening of the positive electrodes. Builds with an improved negative plate design showed healthier (more properly charged) negative plates but the failure mode had switched to the positive plate which contained soft positive material and the beginnings of grid corrosion. In the build with the discrete carbon nanotube-attenuated corrosion layer, we find that the positive plate failure mode (softening, corrosion) induced by the new negative design had been further delayed, with baheries persisting another 2 weeks of testing (Figure 1A). When a positive plate from the battery containing the disclosed corrosion layer was removed from the failed battery and dropped from a height of 1 m, the grid was left intact and only 30% of the active material had softened to the point of falling out of the grid. When the same test was conducted on a control positive plate which did not employ the disclosed corrosion layer the grid shahered and 90% of the active material had softened to the point of falling out of the grid.

[0063] Plates from failed baheries were washed in alternating water and acetone, dried overnight under vacuum, and sections of the grid were excised and mounted in clear epoxy. When the epoxy was solid, a cut was made into the epoxy/grid to reveal a cross-section of the grid. This section was then further cut with a microtome. Spuher-coating with platinum improved the resolution of the samples and was applied to all.

[0064] Upon evaluation of the corrosion layer, we find the discrete carbon nanotube- attenuated corrosion layer was in place, showing a thinner, more uniform corrosion layer in the experimental build, but a thick, biphasic corrosion layer in the control build (See Figure IB). We ahribute the biphasic nature of the Control grid to represent the beginnings of further corrosion into the interior of the grid instigated by the oxygen produced at the positive electrode during charge through an imperfect protective sheath (i.e. the corrosion layer itself).

Example 3: Process-Induced Material Changes and a Templating Effect

[0065] Preparation of Material: 1000 g of leady oxide (20% Free Pb) was mixed with 2 g of Kanecaron fiber and mixed for 1 min. 69.5 mL of battery-grade water and 33.3 mL of a discrete carbon nanotube suspension were added such that the final concentration of the nanomaterial attenuator was 0.1% with respect to the weight of the leady oxide and the material was mixed again for 1 min. Over the course of 5 mins, 113 g of 1.4 spgr acid was added to the mixture to start the reactions. After the mixing procedure, the density of the resultant paste was 4.25+/-0.05 g/mL, by pycnometer (density cup). 20 g of the paste was then manually smeared into Pb-Sn-Ca grids of motorbike sizing (~5x8 cm). These completed grids were cured and dried in a temperature and humidity-controlled oven for 48h, until free Pb in the plates had decreased to <6% and moisture <1.5% .

[0066] Building of Cells: Small-scale 2V cells were build using a 3 positive/2 negative design where all plates were produced manually using the procedures common to those familiar in the art. Positive plates are secured together by a custom-casted strap and tab which uses molten Pb poured into a specifically-designed, 3D-printed, negative-space mold. Cells are filled with about 75 mL of 1.25 spgr for lh prior to formation.

[0067] Electrical Testing of Cells/Batteries: Cells were formed with 0.55 A (C2o/10h, within the disclosed process limits) for 28h for a total of 15.4 Ah (2.8* C20, within the disclosed process limits) at which point, the acid concentration has risen to 1.275-1.280 spgr.

[0068] Results and Corrosion Layer Observations: Control and discrete carbon nanotube plates are compared by Mercury Intrusion Porosimetry before and after formation. The addition of carbon nanotubes to the paste produces about a 20% increase in pore area prior to formation, but this enhancement is lost following formation. Importantly, the percentage increase in pore area during formation (expected moving from PbO/3BS crystal forms to Pb02) is limited by the attenuator which is one aspect of its templating effect.

[0069] The average pore diameter of the battery plate is decreased by the addition of attenuator by almost a factor of 2 but, during formation, this trend reverses with control having smaller diameter than the plate with attenuator (Figure 2B). Again, we see this as evidence of templating; that the post-formation plate is more like its pre-formation state with attenuator than it would be without.

[0070] This indicates that the structure built in the cured plate can be more directly conveyed to the formed plate structure.

[0071] The data in figure 2 represents an average from multiple builds, for illustrative purposes. Some builds include variations from the preparation noted in Example 3, but all fit within our disclosed process parameters. Example 4: Process-Attenuated Corrosion Layer Is Created During Formation and Endures

[0072] Preparation of Material: Lead- Acid battery pastes were manufactured with a standard SLI mix of leady oxide, water, and 1.4 spgr acid. Solids were mixed first for 3 mins, followed by a 5 min water or water plus attenuator suspension addition, and then the acid was added over the course of 12 mins as the mixture was agitated. Discrete carbon nanotube suspension was added such that the final concentration of solids was 0.1% with respect to leady oxide. This mixture produced a paste with density of 4.2 g/mL. Finished paste was then used to produce full plates using Pb-Ca alloy grids. These plates were cured and dried by standard conditions (high humidity /low heat for 32h, low humidity /high head for 16h).

[0073] Building of Cells/Batteries: Control and discrete carbon nanotube-laden positive plates were paired with control negative plates in a 4+/5- configuration to form a 32 Ah, 12V battery.

[0074] Electrical Testing of Batteries: Cells are formed with 8.2 A (C2o/3.9h, within our disclosed process limits) for 15h for atotal of 123 Ah (3.8*C2o, within our disclosed process limits) at which point, the acid concentration has risen to 1.27-1.28 spgr. A portion of the batteries were tom down immediately following formation to harvest their positive plates and evaluate the corrosion layer. Other batteries progressed into cycles of charge and discharge defined by the JIS D5301 endurance testing (light load, 41 °C).

[0075] Results and Corrosion Layer Observations: Positive electrodes are washed in alternating baths of water and acetone to remove residual acid, then dried overnight under vacuum. When dry, sections of the grid are cut out and mounted in epoxy which is set overnight. When the epoxy was solid, a cut was made into the epoxy/grid to reveal a cross- section of the grid. This section was then further cut with a microtome. Sputter-coating with platinum improved the resolution of the samples and was applied to all.

[0076] When viewed with a JOEL STEM instrument, 2 corrosion layers were obvious in batteries built with control positives, but only one morphology was present in batteries built with positive electrodes which included discrete carbon nanotubes (See Figure 3A and B). In total, the corrosion layer with the attenuator is also thinner.

[0077] Evaluation of the plates post-cycling show that the addition of attenuator to the positive active mass allows a positive plate to remain more intact during cycling (Figure 3C). In this test, undercharge can be a failure mode which requires the use of a charge enhancing additive in the negative electrode. Best results and highest residual capacity are seen with the combination of the two additives, with the carbon nanotubes providing tougher plates which, thanks to the bolstered corrosion layer, retain more of their active material as cycling endures.

Example 5: Process-Developed Corrosion Layer Is Thinner, Monophasic, and Sharply Transitioning

[0078] Preparation of Material: Lead- Acid battery plates were manufactured as in other examples above, on Pb-Ca grids.

[0079] Building of Cells: Cells were built with 7+/8- designs into 70 Ah 12 V batteries and filled with 1.2 spgr acid prior to formation.

[0080] Electrical Testing of Cells/Batteries: Formation included a total of over 4.2*C2O Ah (within our disclosed process limits) administered at charge rates between 0.25- 0.44*C2O (within our disclosed process limits). These are within the required ranges for formation of the nanomaterial-attenuated corrosion layer.

[0081] Results and Corrosion Layer Observations: Grid section are removed from dry, unformed positive battery plates as well as washed, formed positive battery plates. These are mounted in epoxy which is set overnight. When the epoxy was solid, a cut was made into the epoxy/grid to reveal a cross-section of the grid. This section was then further cut with a microtome. Sputter-coating with platinum improved the resolution of the samples and was applied to all.

[0082] Dry/unformed plates show very little corrosion layer, and this is reflected in the Energy-Dispersive X-Ray (EDX) Spectroscopy readings which indicate a near-digital response when the beam moves from grid to active material and then to epoxy highlighted by white circles in Figure 4A and 4C. There is very little apparent corrosion layer in these samples, simply an immediate transition between lead-grid and epoxy or residual active material.

[0083] When the control sample is formed/charged for the first time (Figure 4B), two corrosion layers are formed; CL1, a 25-50 pm thick direct blending of the grid into the active material, and CL2 a visibly punctate section of the grid which shows the beginnings of corrosion. As the EDX informs, CL2 is clearly visualized as an increased oxygen content, circled in white, and then a slow increase in oxygen as the corrosion layer blends with the PbCh of the active material over 60 pm or so.

[0084] When the plate the discrete carbon nanotubes is formed (Figure 4D), a single corrosion layer is formed which is thin, about 10-20 pm (half the size of the control’s CL1 region) and monophasic, i.e. no CL2 region exists either visibly, or by EDX (white circle indicates only background oxygen readings in the grid, not the step change in oxygen noted in 4B).

Claims

CLAIMS What is claimed is:

1. A process for controlling a corrosion layer in a lead acid battery, comprising at least one anode and at least one cathode, wherein an anode grid and a cathode grid are in at least partial contact with respective mixtures of leady oxide paste, the process comprising the steps of: a. incorporating a plurality of discrete carbon nanotubes at a concentration from about 0.01 to about 0.10 weight percent in a leady oxide mixtures comprising 60-85 % PbO and 15-40% Pb paste to form a lead-acid battery, b. charging the lead-acid battery using a net quantity of charge of about 1.5*C2o to about 4*C2O Amp hour at a current rate between about C2o/20h and C2o/3h, where C20 is the amount of charge the battery maximally discharges over 20 h in units of Amp hour, and wherein a corrosion layer with an average thickness from about 10 to about 250 microns is formed on the anode grid, the cathode grid, or both.

2. The process of Claim 1 whereby the corrosion layer is formed only on the cathode grid.

3. The process of Claim 1 whereby a plurality of carbon nanotubes are only present in the paste material contacting the cathode grid prior to formation.

4. The process of Claim 1 whereby the corrosion layer is formed only on the anode grid.

5. The process of Claim 1 whereby the carbon nanotubes are only in a mixture of 60-85 % PbO and 15-40% Pb paste material contacting the anode grid.

6. The process of Claim 1 whereby the carbon nanotube concentration is from about 0.03 to about 0.10 weight percent with respect to the mixture of 60-85 % PbO and 15-40% Pb.

7. The process of Claim 1 where the lead acid battery is charged using a net quantity of charge from about 1.5*C2o to about 4*C2o Amphours, more optimally between about 2.0*C2O and about 3.5*C2o Amp hours, and more optimally between about 2. C20 and about 3.0*C2O Amp hours, where C20 is the amount of charge the battery was designed to maximally discharge over 20 h in units of Amp hour.

8. The process of Claim 7 where the current is delivered at a rate between about C2o/20h and about C2o/3h Amps, or more optimally between about C2o/15h and about C2o/3h Amps, or still optimally between about C2o/10h and about C2o/3h Amps, where C20 is the amount of charge the battery was designed to maximally discharge over 20 h in units of Amp hour.

9. The process of Claim 1 whereby the plurality of discrete carbon nanotubes has at least 1% oxidation with more than 20% greater percentage oxidation of the outer surface of the carbon nanotube than the inner surface of the innermost wall.

10. The process of Claim 1 whereby the plurality of discrete carbon nanotubes are single wall carbon nanotubes.

11. The process of Claim 1 whereby the plurality of discrete carbon nanotubes are multi wall carbon nanotubes.

12. The process of Claim 1 whereby at least one anode grid or at least one cathode grid does not comprise an alloy selected for the group consisting of Pb-Sb, Pb-Ca/Sn, Pb- Ag, combinations thereof and derivatives thereof.

13. In a lead acid battery, improvement comprising of at least one cathode grid having a corrosion layer from about 10 to about 250 microns thickness wherein the cathode material comprises a reaction product from the process of Claim 1 comprising >75% PbC and wherein has less than .01 weight of carbon nanotubes.

14. In a lead acid battery, the improvement comprising at least one cathode grid having a corrosion layer from about 10 to about 250 microns thickness wherein the cathode material comprises a reaction product from the process of Claim 1 comprising >75% PbCh and wherein the cathode has a non-detectable weight of carbon nanotubes.

15. The process of Claim 1, wherein the corrosion layer formed is monophasic, consisting of only one clearly-defined, visible, and uniform region of acid and/or oxygen ingress.

16. The process of Claim 1, wherein the resultant cathode is at least 10% more resistant to mechanical stresses, such as vibrating or crushing.

17. The process of Claim 1, wherein the resultant cathode is at least 10% more resistant to corrosion on the cathode grid as defined by standard life cycling techniques.

18. The process of Claim 1, wherein the resultant cathode has at least 20% improved grid- mass adhesion in the pre-charged/formed state.

19. The process of Claim 1 , wherein the resultant cathode has at least at least 20% improved grid-mass adhesion in the post-charged/formed state.

20. In a lead acid battery, a method to reduce metal released from the cathode grid by controlling the corrosion layer by the process of Claim 1.

21. The process of Claim 1 wherein the mixture of 60-85 % PbO and 15-40% Pb paste is substituted for a mixture containing 10-50% red lead (PbsCri), 10-70% PbO, and 15- 40% Pb.

22. The process of Claim 1 wherein the process is applied to monopolar battery design.

23. The process of Claim 1 wherein the process is applied to bipolar battery designs.

24. The process of Claim 1 applied to a lead-acid battery in which at least one of the anodes comprises a capacitive carbon coating.