Technical Field

The invention disclosed herein relates to rechargeable battery operation (i.e. discharging, charging, recharging, or a sequential combination thereof) and specifically to the lengthening of the battery cycle life through the mitigation, minimization or prevention of the formation of discharge byproducts that degrade the battery’s capacity to store electrical charge (i.e., capacity fade) over time.

Background Art

A battery is a form of electrochemical storage that works on the quasi-reversibility of the chemical change processes among certain materials, holding an electrical charge in one form and mobilizing those charges as electric current into another form. The chemical storage processes are the half-cell reactions that produce or require electrons to happen. The equations that represent such electrochemical processes are written with the implicit assumption of a well-mixed reactor. However, batteries are typically designed with low mixing capabilities because of the countervailing preferences in favor of portability and mechanical stability. The poor mixing inside the battery cell magnifies the quasi=reversibility of the process through the formation of discharge byproducts that accumulate in time at a rate depending on the design and operation conditions. The discharge byproducts eventually passivate the electrodes, diminishing the battery’s capacity to hold enough electric charge, ending its cycle life.

Long-lasting and safe batteries are essential and cost-effective for energy storage applications, especially for the deployment of renewable energy (RE) solutions, e.g., off-grid RE, microgrids, and grid integration. RE sources are becoming a rising component of the energy mix as countries worldwide are migrating away from fossil- fuel-based power generation technology known for greenhouse gas emissions that adversely affect the Earth’s climate. RE-generating facilities typically put out a fluctuating, non-dispatchable electrical output. Specifically, variable RE generation is seen in the power fluctuations in solar PV generation due to cloud movements and wind power generation due to wind velocity variability. Excess RE generation curtailment, which happens during high RE intensities, but low demand, results in a missed opportunity to assimilating clean energy into the energy mix. Also, grid constraints hinder the transportation of excess RE generation to other sites, resulting in curtailment. Utility-scale battery energy storage systems (BESS) are among the most effective solutions to cut down RE curtailment. Coupling a specific variable RE generation source with BESS would smoothen the power output’s intermittence at the point of grid interconnection, thus facilitating better integration of renewables. Excess electricity can then be stored and utilized at peak demand when most needed.

In contrast to other energy-storage technologies, such as hydrogen, flywheels, and the like, batteries can quickly absorb, hold, and reinject electricity. However, electrochemical degradation shortens the cycle life of batteries, regardless of battery chemistry. One form of degradation is sulfation in lead-acid batteries. Sulfation happens when the battery gets insufficient charge, such as in RE applications, wherein the energy sources like sunlight and wind are intermittent. It could also occur when the battery sits excessively long between charges, as short as 24 hours in hot climates. The discharge byproduct, known as lead sulfate (PbS0 ₄ ) forms during the discharge phase when the battery supplies electric current to a load or spontaneously. This material accumulates due to its partial reconversion during recharging. This partial reconversion is due to the poor mixing of electroactive species leading to diffusion- limited migration. Battery life is cut short when the PbSC>4 accumulates to the extent that substantially passivates the electrodes and reducing their capacity to store electrical charge. Over time, this capacity fades so that the battery will become less useful for energy storage.

Mixing is thus important to the battery chemistry, but most commercial batteries are not designed with a mixer component or feature. Rather, batteries are designed to be portable and durable, implying lesser room to incorporate the mixing functionality, e.g., batteries with solid-state electrolytes, which must be as thin as the diffusion layer. In the case of liquid electrolytes, the mixing is induced by deliberately boiling the electrolyte by over-charging, which also causes thermal runaway and long-term damage to the battery. In some batteries, the liquid electrolyte is replaced by a gel- type electrolyte, which is more durable but to which mixing by thermal action or mechanical motion is even less feasible. A potential non-invasive method to induce mixing in the battery is by exposure to sound or acoustic waves. Sound waves will potentially generate a reconfigured pressure distribution especially to the porous components of the battery that might enhance mass transfer through the electrodes. However, sound waves may also potentially generate bubbles, especially to a liquid electrolyte, through a mechanism known as atomization or nebulization. This effect can lead to the misting of the electrolyte in addition to those generated from over charging the battery. In the specific example of sulfuric acid, the acid mist could be harmful to the lungs and even carcinogenic if inhaled. Therefore, any means of acoustic excitation must consider the tradeoff between misting and mixing.

Several previous patents have applied acoustic waves to cause some form of performance enhancement on batteries. The US Patent 8487627B2 disclosed a method of utilizing acoustic transducers to emit elastic waves that assist interfacial processes in enhancing, rather than preventing, the deposition of the byproducts of the reaction. Further disclosure is an embodiment for retrofitting an existing battery installation involving contact with the battery case or electrolyte. A similar invention disclosed in US Patent 5932991 A/WO 1998034317A1 related to acoustic excitation in the form of an ultrasonic bath that involved a separate fluid container that encloses the entire battery, rendering this invention as a rather bulky means to enhance that battery’s charging performance. Both inventions, however, did not focus on induced mixing inside the battery or battery cell.

Some later patents disclosed the use of vibrational energy from acoustic waves to prevent or slow down the formation of discharge byproducts. For instance, US Patent 7592094B2 (also European Patent 1639672B1) and US Patent Application 20200020990A1 disclosed methods of vibrating the solid electrode of the cell element either by embedding or stacking a piezoelectric transducer. The transducer’s mechanical vibrations would consequently agitate the surrounding, less rigid components (e.g., liquid or solid-state electrolyte), which may cause discharge byproducts to disentangle from or not form at all on (due to constant excitation) the electrode surface. However, an added layer of protection coated on the embedded piezoelectric material may reduce the electrodes’ porosity to ion transfer for more in- depth interaction between electrolyte and electrode. Further, the piezoelectric material is necessarily brittle so that the strain from colliding with a rigid material during vibrations could cause mechanical breakage or thermal cracking thereof. The high accelerations caused by this layer’s vibration could also induce nebulization and transfer heat to the electrolyte with continued operation. All these effects could be detrimental to the long-term battery capacity and cycle life as the buildup of discharge byproducts, which both solutions attempted to address. A group from the University of California in San Diego took a different approach to induce mixing using acoustic waves by taking advantage of the electrolyte’s fluid nature. Several patents and patent applications from this group (US 20190237818A1, WO201 8049178A1, W02021026043A1) disclosed surface acoustic wave (SAW) devices to induce mixing of the liquid electrolyte. The technology is highly sustainable for miniature battery cells due to the pronounced acoustic streaming at the length scales in 10 ^-2 meter or less. However, beyond 10 ^-2 meter, the SAW frequency must decrease or, equivalently, the wavelength must increase. Since SAW devices must be thicker and up to a thousand times longer than a wavelength, frequencies below 5 MHz or 5000 kHz would render them impractical. Several useful battery applicatins, especially for cost-effective RE storage (e.g., with deep-cycle lead acid batteries), are larger, at length scales not practically accessible by SAW devices. Also, at the high frequencies produced by SAW devices, the surface accelerations mobilizing the fluid can be as high as 10 ¹⁰ m s ^-2 (Huang et al., 2020), not only driving the acoustic streaming but also the nebulization of any fluid droplet, as some published studies showed. Inertial effects due to huge acceleration contribute to interfacial destabilization that breaks up droplets into smaller droplets. SAW devices generate very small and even ionized droplets at high frequencies, even at low driving power (Kooij et al., 2019). Small mist droplets are ejected at speeds high enough to enable escape or leakage out of the battery cell, as published studies suggested (Qi et al., 2008). This leakage may deplete the electrolyte even without heat input that drives evaporation. The ejected electrolyte mist could pose a threat to health, e.g., the acid mist is known to be carcinogenic and can trigger long-term respiratory complications.

A patent US 1115889B2 was granted to an invention for the acoustic manipulation of batteries. This invention pertained to the procedure for the input of electrical energy that effectively injects a stirring effect to the electrolyte. The consequent stirring, as taught by the disclosure, supposedly melts out and dissolves any trace of solid deposits (i.e., dendrites) forming on the interface between solid parts of lithium anode batteries. The stirring effect taught by this disclosure also presupposes the presence of solid electrochemical byproducts (e.g., dendrites), which the said intervention is targeting to disintegrate. The acoustic energy input must also be accompanied by engineered manipulations of the electrical input requires complex controls that may be sensitive to the slightest deviations from precision. It is important to note that such batteries rely on a cylindrical rather than flat geometry to enhance their energy density. It should also be noted that the effects of the generally nonlinear acoustic interaction with the inside structure and material of a battery cell is strongly determined by geometry. Thus, the effects seen for a cylindrical cell cannot be taken to generalize to other types of battery geometries, such as those that use flat plates. Specifically, the lead-acid battery cell design, which was first introduced by Camille Alphonse Faure, is based on flat electrode plates.

Summary of Inventions This present disclosure draws attention to the general form of recharging a battery using at least two forms of energy input. On the one hand, and conventionally, the battery is recharged through the input of electrical energy, either through the constant supply of electric current, voltage, or a dynamic supply of both, depending on the charging algorithm or procedure. The unconventional, and rather unexplored, recharging strategy is by the use of multiple forms of deliberate energy input. Although a manner of secondary energy input in the form of heat is generated by the exothermic electrochemical reactions taking place during the recharging process, causing mechanical agitations of boiling due to the rupture of gas-laden bubbles, this manner of input is unintentional rather than deliberate. This heat energy may rather be argued as a byproduct of the electrical energy input. The method and implements thereof disclosed herein prescribes to this concept of multi-morphic (i.e., “many form”) energy injection for battery recharging. Specifically, a form of energy input is considered in this disclosure.

This secondary form of deliberate energy input herein disclosed is sound or acoustic energy. The sound energy is transmitted as a pressure wave of a frequency between 36 and 3600 kHz. This frequency range is in the ultrasonic regime and could be generated by devices known as ultrasonic transducers, which are industrially available in many variations and for numerous purposes. Among those common purposes to which such devices are applied include fluid atomization, nebulization, cleaning, and electroplating. None of those purposes include the application of such ultrasound- producing devices for assisting the operation of a battery, such as in the storage (extraction) of electrical energy to (from) the battery or its modular components known as cells.

This disclosure also draws attention to the mechanisms that facilitate the mass transfer of active ions resulting in the dynamic optimization of charge capacity. Indeed, the interaction of the sound waves with the battery cell structure and materials generates the bulk longitudinal waves or BLW. The effect of the BLW manifests in the pressure variations that pervade the interior of the battery cell, not only across the fluid portion but also even within the solid material and the interfaces between them. In particular, the pressure variations can take the form of a reconfigured pore-pressure distribution over the cross-section of the porous materials in the battery cell. The pressure variations can be visualized, at least through computational multiphysics simulations, as a distribution pattern of high and low pressure. This pattern is akin to an atmospheric pressure map typically shown by weather forecast reports. The low pressure areas correspond to regions of high relative velocity. When a low pressure spot occurs on a part of the interface between the solid materials (e.g., electrodes and separators), ions can cross the spot with high mobility. This effect on mobility can be interpreted as a facilitation of the mass transfer between the porous solid materials making up the battery electrodes and separator, which is a requirement for the recovery of active material on recharge.

The present disclosure further draws attention to an embodiment of the acoustically assisted battery operation at the cell element level. This embodiment illustrates the attachment of the sound sources to the enclosure of the battery cell module for the smallest commercially available size of the battery. The overall design can be expanded for bigger battery sizes. The attachment of the sound sources are akin, in principle, to bulkhead fittings. Results from the computational simulation and laboratory experiments of this embodiment corroborate with one another, supporting the research hypothesis that the input of sound energy to supplement the electrical energy input optimizes the charge capacity of the battery cell. The corroboration of the said results imply that the empirical evidence agrees with the perceived theory of the interaction between acoustic energy and the battery’s internal structure and materials. While this agreement was confirmed through the embodiment disclosed, it is an anticipated that this corroboration will likewise be applicable for other battery sizes.

Lastly, this disclosure draws attention to a method of non-invasive estimation of the battery state of health (SoH) using the same form of secondary energy input, i.e., sound. This method requires that the sound is used both as an emitted and received signal across the internal structure of the battery during its operation. The emitted acoustic signal serves as the reference signal, whereas the received acoustic signal serves as the diagnosis. This diagnosis is supplied as input to a computational software that has been programmed to perform an automated pattern classification. The result of the pattern classification is a decision to classify the diagnosis as one corresponding to a cell state above a threshold SoH and one below the said threshold. This decision is then supplied as input to a programmed control circuit that switches the level of electrical input to charge any particular battery cell.

The invention can be implemented as a temporary or permanent add-on attachment to the battery casing. The piezoceramic elements can be embedded to the case using methods known to those skilled in the art of plumbing, such as bulkhead fittings. The embedding ensures an efficient energy transfer as the piezoceramic element directly radiates acoustic waves to the electrolyte rather than through a solid material.

Through a superposition of elementary fluid flows, the distributed transducer configuration creates an intricate mixing pattern that maximizes the bulk coverage of mass transfer. The waveforms, phase differences, and frequency differences among the transducers and the acoustic interaction with the micropores of the porous components would make the mixing flow dynamic instead of steady, giving rise to turbulence and vortices while simultaneously reconfiguring pore-pressure distributions of the porous components.

The acoustic transducers are activated on recharge and a possibly non-zero duration after that, e.g., while idling or discharging. The acoustically forced convection will mobilize the electroactive species at the electrode-separator and electrolyte- electrolyte interfaces. During discharging, Pb ²⁺ ions are generated from an electron- transfer step followed by the precipitation of PbSC>4 - the discharge byproduct. On recharge, the Pb ²⁺ ions are generated by a dissolution of PbS0 ₄ followed by the precipitation of PbC>2 or Pb by an electron-transfer step. Mobility may assist the dissolution of solvated Pb ²⁺ ions produced while recharging. It may also cause cracking, destabilization, and eventually flaking off of discharge byproduct deposits on the electrode surface, if already present. The activation of the transducer may be automated using a microcontroller. If placed at the bottom, the transducer generates upward fluid momentum that may oppose the gradients tending toward electrolyte stratification, for which electrolyte concentration increases toward the bottom due to gravity. Stratification, or the presence of a vertical concentration gradient, is also known to promote the accumulation of discharge byproducts. It seems to be caused by the non-uniformity in the vertical distribution of current. A transducer may be placed such that its vibrating face is about parallel to the normal vector of the face of the separator/electrode. A gap between the transducer surface and the cell element can be adjusted. This gap will optimize the flow patterns resulting from the nonlinear interaction between the sound wave and he interior setup (i.e., material, geometry, interfacial microstructure, etc.) of the cell.

Frequencies are high but not beyond a cutoff frequency that generates median droplet sizes in the order of 10 ^-6 meter or less. Very small droplets of this size will easily be ejected through any opening dissipating to the air rather than falling back to the bulk and recombine. Bigger droplets will tend to have a higher rate of droplet recombination to the bulk and recombine. Bigger droplets will tend to have a higher rate of droplet recombination to the bulk electrolyte by means of gravity. The narrow droplet size distribution centered at around 10 ^-6 meter is achievable with piezoceramic disks. Other piezoceramic geometries could shift the center but maintain the narrow width of the distribution. The mixing flow would be generated directly by the bulk longitudinal waves (BLWs) originating from the plurality of vibrating piezoceramic elements. BLWs cause Faraday waves to the surface of the fluid supported by a vibrating solid. Although porous materials, such as the electrodes and separators, contribute flow resistance, the pores may induce turbulence to the flow patterns, which is rather advantageous. The intricate flow pattern resulting from the forced convection driven by the BLWs would mix the electrolyte. The mixing flow would circulate the electroactive species, allowing those to sweep out hotspots of electrochemical interaction. The route to capacity fade of battery cells includes hindrances to the completion of idealized half-cell reaction equations. For example, on battery recharge, if the dissolution-precipitation process does not fully reverse the precipitation during the discharging operations, then the discharge byproducts would accumulate gradually along with the depletion of electroactive materials. The mixing flows resulting from BLWs may assist the discharge byproduct’s dissolution into forms that are readily convertible to active material during the recharge phase.

The manufacturing of piezoceramic elements may utilize the same core material, e.g., Pb, as those found in the battery’s components. The integration of the piezoceramic material production will be economically feasible for the battery manufacturer. Other lead-free piezoceramic materials, e.g., potassium-sodium niobate (KNN) with nickel inner electrodes (Kawada et al., 2009), will be suitable for nickel-based batteries. Known lithium substitution methods in KNN, while remaining to be manufacturable by conventional sintering techniques (Wang et al., 2011 ), may be appropriate for lithium- based batteries. The effect of acoustic wave injection to the basic electrochemical cell, i.e., the fundamental unit of the battery, is simulated computationally and confirmed experimentally. The multi-physics simulation expresses the best mathematical representation of the hypothetical mechanism of the interaction between sound and the battery cell structure and material during a recharge and/or discharge. The laboratory experiments validate the results implied by the computational simulations. The agreement between experiment and simulation results indicate that the theoretical principles underlying the interaction between sound waves and the internal battery cell structure and materials are adequately captured.

The simulation results are presented for a cell element unit subjected to a control condition without sound input and for the experimental condition with sound input. The control case serves as the reference to test whether or not any apparent deviation indicated by the results from the experimental case are statistically significant. The simulations incorporate the same charge-discharge sequence executed by a real potentiostat. The relevant physics are identified and coupled with one another as a systematic representation of the sound-matter interaction occurring inside the battery cell. The results indicate that the injected sound waves effectively slow down the factors of degradation, especially at the innermost portion of the cell element unit where the degradation rate seems the highest. Arresting the degradation factors by sound directly lengthens the cycle life of the cell element, as the results suggest. Various frequencies of the sound offer different levels of this effect, which implies that there may be other parameter combinations (beyond those examined in the study from which the present disclosure is based) that could maximize the cycle life. Detailed visualization of the pressure and velocity patterns lend support to the hypothesized mechanism that allows sound to facilitate the mass transfer of active ions. This facilitated mass transfer seems to influence the distribution of the active ions, which effectively maximize the capacity of the electrodes within the cell element to store electric charge. This capacity maximization induced by sound input is apparently significant relative to the control scenario without sound input.

The results of confirmatory experiments are also presented in this disclosure. The BOO laboratory experiments were conducted in a controlled environment with an average temperature of 25 deg C and relative humidity of 50%. For every trial, a control and experimental case were run simultaneously to eliminate temporal effects and ensuring consistency in the ambient conditions, such as temperature and humidity, that could affect the results. The charge-discharge cycles were administered by an automated 305 battery potentiostat (Biologic VSP-3e system) through its Charge Efficiency Determination (CED) test protocol. This test protocol drained the cells all the way to 100% depth of discharge, which is equivalent to performing a torture test of accelerated degradation. The ultrasonic transducers operated only when the battery was charging. An experiment terminated at the second cycle in which the charge 310 capacity failed to exceed 70%. The experimental results indeed confirmed what the simulations predicted. The sound input assisted the battery cell to achieve longer cycling by as much as 200% on average.

The use of sound to improve the cycle life of the battery is not only for the passive intervention of battery operation, but also for active intervention. Sound can be used 315 as a signal to detect any developments of the internal structure of the battery, such as the formation of sulfate deposits along its lifetime. Also disclosed herein is a method and apparatus of implementing active intervention that influences the charging process of the entire battery. This intervention implies a novel procedure of charging in parallel rather than in series, which is the conventional way. In parallel charging, 320 each cell element of the battery may receive a different amount of current than the other cell elements charging at the same time. This setup is motivated by the observation that the cells in the battery do not perform in synchrony all the time. Some cells discharge earlier than others, which eventually determines the entire battery’s state of charge. If charging is done in series, the same current is made to pass through all the cells until those cells that were least drained become full again. Overcharging these already full cells is evident in the heat generated that can cause the boiling of the electrolyte. However, the most drained cells, which were the very reason that the battery was recharged, may not have been necessarily filled with charge. Thus, when the battery is put into discharging operation again, the imbalance in the state of charge of the cells only worsens the entire state of the battery. Estimating the SoH at the cell level can be challenging and must be non-invasive to avoid influencing the condition of the electrodes or electrolyte. With sound, this non-invasive method of SoH estimation was made possible by utilizing ultrasonic transducer arrays that consist of a sound emitter and receivers that detect the transmitted, reflected and diffracted sound across the interior of the battery cell.

The patterns of the received sound contain information of the internal structure of the battery cell that can be used to deduce SoH. Thus, by classifying those patterns to belong to either a “good” (SoH above 80%) and “bad” (SoH below 80%) cell, the SoH information can be extracted. The assumption that the pattern contains relevant information of the battery SoH is motivated by the fact that sulfates are solid and typically originate at the interfaces between the electrode and separators. The solid sulfates accumulating at these interfaces can induce delays to the propagating sound waves, which then changes the cross-correlations between the emitted and the received sound. The extraction of the information embedded in the patterns of the received sound is then used to control the amount of current dispensed to a cell element when the battery is charging. This “customized” current input would enable the battery to reach a state of balance among its component cells after recharging. This balance should lengthen the lifespan of the battery because overcharging (which causes heating and boiling) and undercharging (which accelerates sulfation) can be mitigated, minimized or prevented.

Brief Description of Drawings

FIGURE 1. Multiview of the battery cell with emphasis on the part excluding the top lid (displayed in the axonometric view), showing sound wave sources embedded in the battery case, the cell element consisting of a plurality of electrodes (both positive and negative), and interelectrode spacing with or without separators.

FIGURE 2. Lateral view of the battery cell showing the gap between each sound wave source and the nearest edge of the cell element, which is immersed in the electrolyte.

FIGURE 3. Lateral view of the battery cell with emphasis on the flow field lines depicting the mixing of the electrolyte due to the sound waves generated by the sound wave sources that induce momentum on the electrolyte.

FIGURE 4. The conceptual diagram of the connectivity of the battery cell and the charging system supplying power to the battery terminals and the embedded sound wave source FIGURE 5. Mass transfer of electroactive species as a result of the acoustic mixing generated by a distributed transducer configuration.

FIGURE 6. Detailed view of the cell element unit inside an enclosure with embedded ultrasonics (top row). 3D view of the cell element unit for the control with no sound (left, bottom row) and experiment with sound (right, bottom row) FIGURE 7. Basic geometry of the multi-physics model of the cell element unit of the battery, showing the experimental (top, left) and control (top, right) see-through views. The cell element unit is an alternating stack of positive, separator, and negative electrodes until each side presents the outer face of a positive and negative electrode. The experimental setup includes embedded transducers (disc-shaped objects attached to the lateral and bottom faces of the cell enclosure.

FIGURE 8. Block diagram of the computational multi-physics model showing the different kinds of physics hypothetically governing the underlying mechanism of the interaction between sound and the battery cell internal structure and material.

FIGURE 9. Charge-discharge cycling protocol as implemented by an automated potentiostat (left) and simulated using a computational multi-physics software (right).

FIGURE 10. Comparison of simulated concentration of the active battery material across the entire cell element after 10 charge-discharge cycles: control (no sound), and various frequencies at the same driving voltage, 18 Vpp.

FIGURE 11. Simulated progression of the concentration of the active battery material along an axis normal to face of the stacked cell plates from Cycle 1 through 4 (Top to bottom).

FIGURE 12. Simulated progression of the concentration of the active battery material along an axis normal to the face of the stacked cell plates in Cycle 8 (top) and 10 (bottom). FIGURE 13. Simulated progression of the state of health (SoH) of the electrodes through several cycles superimposing the result at different conditions: control (no sound), and with sound at different frequencies (top). The SoH progression of different electrodes across a cell element unit for each condition (bottom).

FIGURE 14. Simulated scans of the pressure (top panel set) and mass transfer velocity (bottom panel set) on the different electrode plates of the cell element unit at a sound frequency of 110 kHz driven by a peak-to-peak voltage of 18 V.

FIGURE 15. Simulated scans of the pressure (top panel set) and mass transfer velocity (bottom panel set) on the different electrode plates of the cell element unit at a sound frequency of 1700 kHz driven by a peak-to-peak voltage of 18 V. FIGURE 16. Simulated scans of the pressure (top panel set) and mass transfer velocity (bottom panel set) on the different electrode plates of the cell element unit at a sound frequency of 2400 kHz driven by a peak-to-peak voltage of 18 V.

FIGURE 17a. Typical course of the laboratory experiments for the control setup, with no sound. The corresponding charge-discharge cycling performance are shown at the bottom row, plotting the voltage curves and the charge/discharge capacity lines progressing through the cycles.

FIGURE 17b. Typical course of the laboratory experiments for the hypothetical setup with embedded ultrasonics. The corresponding charge-discharge cycling performance are shown at the bottom row, plotting the voltage curves and the charge/discharge capacity lines progressing through the cycles.

FIGURE 18. Consolidated cycling performance for numerous experiments compared among different conditions, including the control with no sound, and experimental with sound at different frequencies and driving voltages (peak-to-peak). FIGURE 19. 3D view of an embodiment of a cell-level parallel charger with SoH estimation using non-invasive acoustic diagnostics.

FIGURE 20. Schematic view of the cell-level parallel charging of a battery using information from the acoustic diagnostics.

Description of Embodiments

The battery case 101 is the least innovated part of the battery because of its non active participation in the battery’s electrochemistry. The present disclosure points to the use of sound waves to induce, in a non-destructive way, the mixing of the electroactive species of the battery cell in the hopes of maximizing the yield and rate of essential electrochemical reactions that are analyzed under the assumption of a well-mixed battery cell. A solution to the mixing problem through the reconfiguring of the pore pressure distribution forms the core subject matter of this disclosure. Sound wave sources, e.g., in the form of piezoceramic transducers, which can be placed at the bottom 103 and non-bottom portions/faces 102, 104 of the battery case 101. The non-bottom transducers may include the top portion of the cell, as long as there are no hindrances (e.g., terminals, vents) place on lid covering the battery cell compartment. A cell element 105 found inside the case 101 may, in some variations, be arranged in a stacking configuration consisting of electrodes 107 and interelectrode spacing 106, which may or may not include an electrically insulating but porous separator material. The stacking of the electrodes 107 may, in some variations, consist of the alternative placing of positive and negative electrodes. Each electrode is, in some variations, a plate consisting of metallic material with or without non-metallic active material coating and may or may not be porous. The entire cell element is fixed in position inside the cell compartment 101 to achieve mechanical stability or durability in anticipation of the motion of platforms on which the batteries are applied. The sound wave sources may be piezoceramic transducers 102, 103, 104 and placed at strategic positions relative to the cell element 105. The number of transducers portrayed in the diagrams does not, in any way, be interpreted as a limitation, but only as a means for illustration of the concept.

The attachment of a transducer to the battery case must be sealed to prevent the leakage of electrolyte 201 and other active materials from inside the cell while allowing the transducer to directly interact with the interior of the cell, such as with the electrolyte 201. The attachment may be fabricated using standard fittings, such as bulkhead fittings. The fittings may be integrated as part of the design so that the manufacture of the battery case 101 includes provisions for the fitting. In some variations, the attachment may be retrofitted to an existing battery cases that do not provide the access point for the transducer to the interior of the cell.

The direct interaction between the sound wave source and the cell interior will enhance the efficiency of the energy and momentum transfer so that mixing 301 will take place with minimal input power and/or losses due to thermal and/or viscous heating. The leak-proof fitting will isolate the interior from the exterior part, where electrical wiring 405, 406, 407 may be present to connect the sound transducers 102, 103, 104 to a power supply for their operation. The sound transducers may be driven by a battery management module 404, which is connected via a supply line 408 to an external energy source 409. The energy source 409 may be a solar PV system, wind turbine system, alternator, or any other means for generating electricity. The microcontroller 404 diverges into supply lines 403, 405, 406, 407 to the different parts of the battery cell. The supply line 403 directs electrical charge to the battery terminals 401 and 402 during charging/recharging. The operation of the charging and activation of the sound transducers is managed by the battery management module 404, which may include an on-board computer to cause variations to the procedure through which the transducers are driven and battery charge is dispensed. The management module 404 may receive feedback through the supply lines 403, 405, 406, 407 to estimate a state relating to the battery health for monitoring and control purposes. This management module 404 will ensure to minimize the instances of over-charging and under-charging the battery, or over-driving and under-driving the sound transducers. The acoustic transducers 102, 103, 104 may therefore consist of the ability to sense changes related to the battery health through the sound waves that may carry the information related to the interaction of sound to the dynamic changes taking place within the battery cell, e.g., formation of deposit byproducts, temperature increase, or fine mist formation. The acoustic interaction is based on the generation of bulk longitudinal waves (BLW) to the electrolyte and through the porous structures in the battery cell. The acoustic transducer vibrates at a frequency and produces pressure variations in the fluid that forces convection. The porosity of the cell element contributes resistance to flow, which the forced convection overcomes through the momentum arising from the acceleration near the transducer surface. The acceleration causes a high rate of density changes that propagate through the bulk. Due to the bulk resistance, the density waves propagate up to an effective length that depends on the viscosity, surface tension, and density of the bulk fluid and F of the transducer. The acoustic wave propagation could drive the mass transfer of solvated ions or the electroactive species dissolved in the bulk electrolyte through a mixing process 301 that can take place through the interelectrode spacing 106. The resulting mass transfer 501 could pass through the pores of the cell element 105, enabling an equalized distribution of the said ionic species throughout the container. Indeed, the BLW imparts momentum to the fluid electrolyte, which attunes the operation of the cell to well-mixed reactor as implied by the half-cell reaction equations used to represent the underlying electrochemical mechanism of the battery. The actual enhancement of the mass transfer 501 of electroactive species due to the acoustically induced mixing mediated by poroacoustics in the cell provides a dynamic means by which the yield of the half cell reactions could be maximized throughout the cycle life of the battery. The invigorated flow momentum caused by the direct interaction of sound wave sources and the interior of the cell, especially a fluid electrolyte, is also the underlying reason behind the conversion of such electrolyte into aerosol droplets capable of escaping and be evaporated away from the cell. Atomization or nebulization takes place because of capillary (or Faraday) waves that form on the fluid surface that is supported by a solid platform that vibrates at a frequency F. The Faraday wavelength can be estimated from the following expression in which ais the surface tension of the electrolyte and p is its density.

Due to the substantial accelerations caused by high value of F, the amplitude of the vibrations is sufficiently long to cause droplets to detach from the bulk. The median diameter of such droplets is a factor of the Faraday wavelength. Thus, higher frequencies are expected to generate smaller droplets. Indeed, microscopic droplets, which collectively appear as mists, are formed at ultrasonic frequencies. By treating the mist formation as a consequence of interfacial instability (Qi et al., 2008), then atomization can be predicted by finding a threshold condition. Indeed, the atomization threshold is a mathematical relation first expressed by Pohlman and Stamm (cited in Pohlman et al., 1974). It relates the amplitude A of the transducer vibration and the onset of atomization to the viscosity h of the electrolyte fluid and its surface tension and density, and the Faraday wavelength l.

The minimum amplitude of the transducer vibration decreases with increasing excitation frequency F. Consequently, higher ultrasonic frequencies require smaller vibration amplitudes to start generating mists from the bulk fluid. Although misting is beneficial for medical nebulizers (e.g., as a means to more effectively deliver certain therapeutics through aerosol inhalation), for batteries it is rather not preferable. Electrolyte mists, especially the acidic variety, are known to be carcinogenic. Indeed, battery factories are required to clean up acid mists as a health precaution for workers who are exposed to the inhalation of the mists that could eventually ulcerate their lungs to fatal levels. The distributed transducer configuration optimizes the tradeoff between misting and mixing. No individual transducer must be driven with substantial power input. For example, any single transducer in the configuration can be driven with a power input of less than 10 mW/cm ² . This low power would limit the extent to which the pressure variations caused by the acceleration of the vibrating transducer. The distributed configuration, however, compensates for this limited influence by ensuring that the scope of the mixing effect, i.e., mass transfer 501 , is extensive. The strategic positioning of the transducers relies on the three-dimensional structure of the cell and the generic stacking setup of the cell element. The interelectrode spacing, which are sufficiently narrow, to act as bridge for ionic transfer between electrodes, doubly serves as a poroacoustic channel (in the presence of a separator) that causes turbulent flows in the mixing pattern. Consequently, the complex mixing pattern would effectively inject an ample intensity of randomness to the forced convection, which increases the chances that the electroactive species will sweep out any available site of chemical interaction at any given time. This enhanced probability of chemical interactions would defer the stagnation of the battery’s underlying mechanism, i.e., the formation of discharge byproducts that do not anymore participate in the electrochemical reactions. The so-called dissolution-precipitation mechanism would keep on operating in the presence of acoustically assisted mixing despite subjecting the battery to conditions that would otherwise hasten its capacity fade, e.g., deep cycle charging in RE storage applications.

The production of piezoceramic transducers could be co-located within the battery factory because of the possibility of utilizing the same raw materials. This co-location may reduce the total cost of fabrication of the battery with the capability for acoustically assisted charging such that the additional cost is outweighed by the benefit in terms of longer cycle life. This benefit will likewise make batteries more suitable for RE storage without extensive modifications nor the use of any novel chemistry that is less understood than the existing one operating within mature battery technology. The increase in cycle life by at least 25% will already be sufficient to increase the economic viability of storing RE, thereby increasing the utilization of cleaner forms of energy and easing society’s disentanglement from fossil fuels as the primary energy source. The emissions from fossil fuels have been widely believed to be the cause of an impending drastic change in the Earth’s climate, which could lead to devastating consequences for civilization. Therefore, by rolling out cost-effective battery technologies with longer cycle lives due to acoustically assisted charging capability, the adoption of RE sources will become wider across the world. This wider adoption could one day avert the possible long-term damage of maintaining the dominance of fossil fuels in the global energy mix. The additional demand for batteries will not only encourage the existing battery manufacturers to scale up production, but also potentially expand the supplier base further through an add-on technology without a substantial modification to the electrochemistry of the existing battery technology. This motivation is further enhanced by the prospect of dampening the additional cost of equipping the battery case with acoustic sources, as the present disclosure describes.

The cell element unit of a lead-acid battery consist of a stack 602 of electrodes and separators bounded together by a bracket 601. A typical cell element structure for which the brackets 601 connect all negative electrodes to one terminal lug and the positive electrodes to the other terminal lug. This structure is standard among all cell element units regardless of size. The relationship between the cell element unit 602 and the enclosure is illustrated in three dimensional views. The control cell shows the terminal lugs 603 serving another role of securing the cell element to the lid of the enclosure 606. The experimental cell now includes at least one ultrasonic transducer 604 attached by a fitting 605 to a face of the enclosure 607 that is facing the interelectrode spacings of the cell element unit 602. Inside each fitting 605 is a mechanical element that enhances the mechanical efficiency of the transducer’s vibrations, keeping it from heating up when producing sound. This fitting also incorporates sealants to prevent any form of battery fluid from leaking out through them. Through this hermetic sealing, only the vibrating side of the transducer 604 is exposed to the interior of the battery cell.

The geometry of the cell element for both control and experimental setups 701 are shown are similar except for the presence of transducers 703 in the latter. Here the position of the transducers 703 are visualized in relation to the cell element unit 702. The electrodes of this cell element are labeled with “SU(n)” where n progresses from “1” on one side to “n” on the opposite side. A typical embodiment of this structure implements n=6 as shown. With this design, the most internal of the electrodes are labeled SU3 and SU4. These are the electrodes least exposed to the electrolyte because they are well within the bulk of the cell element unit. Each SU is actually a “sandwich unit” representing the electrochemical cell consisting of a positive electrode, separator, and negative electrode immersed in a fluid electrolyte. For n=6, six of such sandwich units are stacked sequentially 702. This geometry of the cell element originated from Camille Alphonse Faure, whose flat-plate design became the successful standard implemented in today’s car batteries. The flat-plate design is also the most economical to manufacture in mass production.

The performance of the cell element unit can be anticipated from proper computational simulations that incorporate multiple physics governing relevant aspects of the cell’s operation. The transducer multiphysics 801 incorporate the electrical circuit used to drive the sinusoidal vibration. The conversion from electricity to vibration is handled by the electrostatics and solid mechanics module, while the pressure acoustics considers the transmission of the vibration energy to the fluid as pressure waves. The electrolyte multiphysics 802 considers the fluid dynamics arising from the effect of the pressure waves and the heat transfer due to the dissipation of thermal energy generated by the electrochemical reactions from the electrodes to the electrolyte. The electrolyte multiphysics 802 is coupled with the electrochemistry group 803. The electrochemistry group 803 accounts for the electrochemical reactions that produce byproducts that flow through the electrolyte via mass transfer. The multiphysics computational simulations are driven at a rate 901 by the Coloumbic Efficiency Determination (CED) protocol that of the real potentiostat,. The CED protocol is the sequence of charging and discharging 902 to which the cell element unit is subjected across time until a termination condition 903 is met (i.e., charge capacity failing to exceed 70% for two consecutive cycles).

The concentration of the active material is an important indicator of what happens to the electrode composition after every cycle of charge and discharge. The color bar in Figure 10 indicates the surface concentration of this active material after ten cycles elapsed. Note that at the beginning of the simulation, the concentration of active material is uniform over the entire cell element. After 10 cycles of the control 1001, the interior of the cell element unit (consisting of SU3 and SU4) is brighter than the rest of the SUs. This brightness indicates that the active material in SU3 and SU4 did not recover its initial levels for the control. In the experimental cases with different sound frequencies and 18 Vpp driving voltage, the relative concentration of the interiors are less affected than the control, suggesting that sound waves have to do with such effect. Examining further, the relative concentration at the interior was least affected at 110 kHz (1002) than at 1700 kHz (1003) and 2400 kHz (1004), suggesting the 110 kHz (1002) could be generating acoustic wave patterns that are suitable for this geometry of the cell element. The runaway deviation of relative performance at the interiors is most apparent from the profile graphs 1101, 1102, 1103, 1201, and 1202 of the concentration. From cycle 1 (1101) through 10 (1202), the concentration of active material at the interior, SU 3 and SU 4, deviated the most in the control. Further optimization of frequency, driving voltage, phase difference, and positioning of the ultrasonic transducers can be made to arrest the deviation of the interior’s degradation and the degradation of the entire cell element (note the drop from 24 mol/m ³ to 22 mol/m ³ by cycle 10, 1202 in this accelerated degradation test). The state of health SoH 1301 is the most direct measure of the battery’s life across a series of charge-discharge cycles, and further comparisons demonstrate the positive effect of the BLWs injected to the internal battery cell structure. In the absence of sound waves, the control 1302 SU3 and SU4 reached the 70% threshold by cycle 10, even before all the other SUs. This early threshold excursion means that the entire cell element would be deemed “dead” after cycle 10 of this accelerated degradation test. On the other hand, sound waves appear to extends this downtrend to the 70% threshold by at least 100% more cycles. For the frequency of 110 kHz (1303), this gain in cycle life is more than 200% over the control, which supports the implication of 1002 and 1202. The SoH trajectories 1302, 1303, 1304, 1305 corroborate with the depletion dynamics of the active material.

The simulation results can visualize quantities that are not easy to measure in experiments, and these visualizations provide further hints to the performance gain induced by sound waves at 110 kHz. The pore pressure 1401 and mass transfer velocity distributions 1402 on each SU of the cell element. The pore pressure 1401 and velocity distributions 1402 can indicate the manner of redistribution of active material exerted by the pressure variations induced by BLW propagation inside the battery cell. The darker portions of the pore pressure distribution imply low pressure spots, while the brighter portions of the velocity distribution imply higher momenta of the active ions. It appears that 110 kHz offers the most uniform redistribution across the SUs of the cell element. A uniform redistribution implies that the surface area of the electrodes are maximized, which also indicate the maximization of charge capacity. For 1700 kHz, corresponding pore-pressure 1501 and mass transfer velocity 1502 distributions are appreciably even with higher contrast between highs and lows. On the other hand, for 2400 kHz, corresponding pore-pressure 1601 and mass transfer velocity 1602 distributions are apparently imbalance over the cross section of the porous interfaces, which may not be preferable for long-term sustainability of the active material recovery on recharge.

The laboratory procedure runs the hypothetical 1702 and control 1712 samples simultaneously while being connected to the same potentiostat system. This simultaneous manner of running the control with the hypothetical sample aims to minimize the influence of temporal effects of environment and electrical fluctuations. The graph of the cycling performance for the hypothetical 1701 and control 1711 is recorded live during the course of the experiment trial. The voltage of the cell element is monitored while the charge capacity is traced during the charging and discharging stages. The capacity trace is as an increasing line that terminates at the time when the mode switches from discharging to charging, or vice versa. The SoH is a percentage quantity that corresponds to the maximum level reached by a capacity trace at a given cycle divided by the maximum level at cycle 1. It is assumed that the cell element, consisting of brand new electrodes, is at its maximum health state at the beginning of the test. This SoH measured in this manner is the most accurate representation of the cell’s health status to accept and store electrical charge. Practically, however, this method of measurement, which requires an expensive equipment like a potentiostat system is not commonly implemented in commercial settings, e.g., vehicle service centers. Thus, there is a need to estimate the SoH using other means that are cost-effective. The presence of transducers 1703 of the hypothetical sample 1702 appears to cause an apparent multivalued voltage course on recharge in the cycling trace 1701. This result is different from the rather smooth traces of voltage on recharge 1711 for the control sample 1712. The multivalued voltage traces on recharge 1701 is an indirect evidence of the facilitated mass transfer arising from the reconfiguring of the pore pressure distribution at the interfaces.

A summary of the comparative cycling performance of the control and various experiment cases would provide validation for the predicted effect of the auxiliary sound energy. The box-and-whisker plot 1801 shows the median performance of the cell element subjected to accelerated degradation for different cases. The control case has a median cycle life of 4 cycles, but could reach as high as 6 cycles. This dispersion can be a result of the factory variations among the cell components, which is expected in mass production. At 110 kHz, the median cycle life is significantly higher than the control and even with respect to the other tested frequencies. Higher driving voltages also appear to enhance the cycle life at this frequency, although this trend is less conclusive for the other tested frequencies. This experimental observation corroborates with the results obtained from the computational simulations, especially with respect to the gains on the cycle life due to the injection of sound to the internal battery structure. For an 18V driving voltage (peak-to-peak), the median cycle life at 110 kHz is more than 100% of the same quantity at control. At 1700 kHz, the cycle life was found over a wider range at 18V driving voltage (peak-to-peak). The performance at 2400 kHz, however, is not far different from the control, corroborating with the imbalance in the reconfigured pore-pressure distribution 1601. The imbalance does not redistribute the recovered active material uniformly, which results in an insignificant gain in cycle life. Sound can also be used in a standalone, or integrated, technology to implement an active balancing of the state of charge of the cells in the recharging stage. An embodiment of such an apparatus consists of an array of diagnostic subsystems 1904, one for each cell compartment 1906. In this illustration, there are six subsystems 1904, one for each of the six cell compartments 1906 of this six-cell battery. Each diagnostic subsystem consists of at least one ultrasound receiver 1905. This diagnostic subsystem would capture the information relating to changes happening inside the cell compartment in relation to the formation of electrochemical byproducts that could impair the long term capacity of the cell. The diagnostic subsystems feed information to a central controller drawing power from the source 1901 via a regulator 1903 that relays the supply of electric current to a cell via a switching voltage regulator 1902. The value of the current relayed to the cell matches the SoH of the given cell. Cells with low SoH may require higher current rates, while those that have high SoH may only require a relatively lower current rate. The high current rates for low SoH cells is meant to make them catch up in charge capacity with neighboring cells that have higher SoH. This variability of the current supplied among the cells imply that the charging must proceed in parallel as implemented by the device 2001. The parallel connection of subsystems 2004 ensures that each cell element only gets the amount of charge it needs to restore its previous SoH. The device 2001 also features a display 2002 and control knob 2003 to accommodate different sizes and models of the battery. This parallel charging strategy is a way of ensuring balance across the entire battery. A balanced battery will tend to last longer because the stresses from overcharging and sulfation are minimized. Indeed, any imbalance of SoH can shorten the battery’s lifespan.

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