Method and system for acoustically assisting battery operation

Abstract

Operating a battery with auxiliary non-electrical input energy has been demonstrated to effectively extend the service life of the battery. Non-destructive on-the-fly reconfiguration of the pore pressure distribution across the cross-section of a porous electrode immersed in a fluid electrolyte extends the cycle life of the battery cell. A secondary sonic energy input by a distributed transducer embedded in the battery case guides bulk longitudinal waves through the electrolyte, causing a beneficial reconfiguration of the pore pressure distribution. The reconfigured pore pressure distribution promotes the penetration of electroactive ions into the porous electrode matrix, thereby suppressing the accumulation of discharge by-products that cause capacity fading. Finally, the secondary sonic energy input assists in charge balancing of all battery cells by estimating the health of each cell. Balanced charging can maintain the overall health of the battery, thereby extending the service life.

Description

[Technical Field]

[0001] The inventions disclosed herein relate to the operation of secondary batteries (i.e., discharging, charging, recharging, or a continuous combination thereof), and specifically to extending the cycle life of batteries by mitigating, minimizing, or preventing the formation of discharge by-products that cause a decrease in the battery's charge storage capability over time (i.e., capacity fade). [Background technology]

[0002] A battery is a form of electrochemical storage that relies on the quasi-reversible operation of chemical change processes between materials, retaining charge in one form and transferring that charge as an electric current to another. The chemical storage processes are half-cell reactions that result in the production or demand of electrons. The equations describing these electrochemical processes implicitly assume that the reactor is well mixed. However, batteries are typically designed with poor mixing, prioritizing portability and mechanical stability at the expense of mixing. Poor mixing within a battery cell exacerbates the quasi-reversibility of the process through the formation of discharge by-products that accumulate over time at rates that depend on the design and operating conditions. The discharge by-products eventually passivate the electrodes, reducing the battery's ability to adequately retain charge and resulting in an end-of-cycle life.

[0003] Long-lasting, 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). As countries around the world transition away from fossil fuel-based power generation technologies, known for their greenhouse gas emissions that negatively impact the global climate, renewable energy sources are becoming an increasingly important component of the energy mix. Renewable power generation facilities typically produce variable, undispatched electrical output. Variable renewable generation is specifically seen in solar power output fluctuations due to cloud movement and wind power output fluctuations due to wind speed fluctuations. Curtailment of excess renewable generation occurs when renewable energy is abundant and demand is low, resulting in missed opportunities to integrate clean energy into the energy mix. Grid constraints also prevent excess renewable generation from being transported to other sites, leading to curtailment. Utility-scale battery energy storage systems (BESS) are one of the most effective solutions for reducing renewable energy curtailment. Combining specific renewable energy generation sources with BESSs smooths out intermittent power output at the grid connection point, thereby facilitating the integration of renewable energy. Excess power is stored and used during peak demand periods when it is needed most.

[0004] In contrast to other energy storage technologies, such as hydrogen or flywheels, batteries can rapidly absorb, retain, and release electricity. However, electrochemical degradation shortens battery cycle life, regardless of battery chemistry. One type of degradation is sulfation in lead-acid batteries. Sulfation occurs when batteries are insufficiently charged, as occurs in renewable energy applications such as solar and wind power, where energy supplies are intermittent. Sulfation also occurs when batteries are left for excessively long periods between charges (even as short as 24 hours in hot climates). A discharge by-product known as lead sulfate (PbSO4) forms when a battery supplies current to a load or during natural discharge. This material accumulates for partial reconversion during recharge. This partial reconversion occurs because of poor mixing of electroactive species, leading to diffusion-limited transport. When PbSO4 accumulates, the electrodes become essentially passivated, reducing their ability to store charge and shortening battery life. Over time, this capacity decreases and the battery becomes less useful for energy storage.

[0005] Thus, while mixing is crucial to battery chemistry, most commercial batteries are not designed with components or features for mixing. Instead, batteries are designed to be portable and durable, which means there is little room for incorporating mixing functionality. For example, batteries using solid electrolytes must be as thin as the diffusion layer. In the case of liquid electrolytes, mixing is induced by intentionally boiling the electrolyte during overcharging, which also causes thermal runaway and long-term damage to the battery. Some batteries replace liquid electrolytes with gel electrolytes. Gel electrolytes are more durable but make mixing by thermal or mechanical action more difficult. A non-destructive method for inducing mixing in batteries is exposure to sound or acoustic waves. Sound waves can generate reconfigured pressure distributions, especially on porous battery components, which can facilitate mass transfer through the electrodes. However, sound waves can also induce gas bubbles, especially in liquid electrolytes, through a mechanism known as atomization or nebulization. This effect can also cause misting of the electrolyte in addition to the gas bubbles that occur when the battery is overcharged. In the specific example of sulfuric acid, the mist of this acid can be harmful to the lungs and may even be carcinogenic if inhaled, so any means of acoustic excitation must consider the trade-off between mist generation and mixing.

[0006] Several prior patents have applied acoustic waves to improve battery performance in some way. U.S. Pat. No. 8,487,627 discloses a method utilizing acoustic transducers that emit elastic waves to assist interfacial processes in promoting, rather than preventing, the deposition of reaction by-products. Embodiments for retrofitting existing battery installations involving contact with the battery case or electrolyte are also disclosed. Similar inventions disclosed in U.S. Pat. No. 5,932,991 and WO 1998 / 034317 involve acoustic excitation in the form of an ultrasonicator with a separate fluid container surrounding the entire battery, resulting in a rather bulky means for enhancing battery charging performance. However, neither invention focuses on inductive mixing within the battery or battery cell.

[0007] Some later patents also disclose the use of vibrational energy from acoustic waves to prevent or delay the formation of discharge by-products. For example, Patent Document 4 (U.S. Patent No. 7,592,094 (or Patent Document 5 (EP 1,639,672))) and Patent Document 6 (U.S. Patent Application Publication No. 2020 / 0020990) disclose methods of vibrating the solid electrodes of cell elements by embedding or stacking piezoelectric transducers. The mechanical vibration of this transducer results in agitation of surrounding less rigid components (e.g., liquid or solid electrolyte), which can cause discharge by-products to separate from the electrode surface or, with certain excitation, prevent them from forming at all on the electrode surface. However, an additional protective layer coating this embedded piezoelectric material can reduce the electrode's porosity for ion migration, allowing for deeper interaction between the electrolyte and the electrode. Furthermore, because piezoelectric materials are necessarily brittle, strain from collisions with rigid materials during vibration can cause mechanical failure or thermal cracking of the piezoelectric material. Additionally, the high acceleration caused by vibration of this layer can induce nebulization and transfer heat to the electrolyte with continued operation, all of which can have a negative impact on long-term battery capacity and cycle life as discharge by-products build up, a challenge both solutions seek to address.

[0008] A group at the University of California, San Diego, took a different approach by exploiting the fluid nature of electrolytes and using acoustic waves to induce mixing. Several patents and patent applications by this group (US Patent Application Publication No. 2019 / 0237818, WO 2018 / 049178, WO 2021 / 026043) disclose surface acoustic wave (SAW) devices to induce mixing of liquid electrolytes. This technique has been used for over 10 years. -2 Significant acoustic streaming occurs on length scales of less than a meter, making it highly sustainable for small battery cells. -2Beyond a meter, either the SAW frequency necessarily drops or the wavelength necessarily increases. Frequencies below 5 MHz or 5000 kMz are impractical because SAW devices must be thicker and 1000 times longer than the wavelength. Some useful battery applications, especially cost-effective renewable energy storage (such as deep-cycle lead-acid batteries), are larger, length scales that do not make SAW devices practical. Also, at the high frequencies generated by SAW devices, the surface accelerations required to move fluids are on the order of 10 10 ms -2 The acceleration can be as high as 100 kJ / s (Huang et al., 2020), which, as several published studies have shown, can promote not only acoustic streaming but also the nebulization of any fluid droplets. The inertial effects of very large accelerations contribute to destabilizing the interface, which causes droplets to break up into smaller droplets. SAW devices generate very small, even ionized droplets at high frequencies, even at low driving powers (Kooij et al., 2010). As suggested by published research (Qi et al., 2008), small mist droplets can be ejected with sufficient velocity to cause leakage and leakage from battery cells. This leakage can deplete the electrolyte even without heat input to promote evaporation. The ejected electrolyte mist can pose a health threat. For example, this acidic mist is known to be carcinogenic and may cause long-term respiratory complications.

[0009] Patent document 10 (U.S. Pat. No. 1,115,889) was issued for an invention related to acoustic manipulation of batteries. This invention relates to a method for inputting electrical energy that effectively imparts an agitation effect to the electrolyte. The agitation taught in this disclosure is believed to dissolve and dissolve even small amounts of solid deposits (i.e., dendrites) that form at the interfaces between solid components of a lithium anode battery. The agitation effect taught in this disclosure presupposes the presence of solid electrochemical by-products (e.g., dendrites), and the intervention targets and dissolves these by-products. Furthermore, the input of acoustic energy necessarily involves engineering the electrical input, requiring complex control that is sensitive to even small deviations from the correct value. It is important to note that these batteries rely on a cylindrical, rather than planar, geometry to enhance energy density. It should also be noted that the generally nonlinear acoustic interaction with the internal structure and materials of the battery cell significantly affects the geometry. Therefore, the effects observed in cylindrical batteries cannot be generalized to other battery geometries, such as flat-plate batteries. Specifically, the lead-acid battery cell design, first introduced by Camille-Alfonse Faure, is based on flat electrode plates. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] U.S. Patent No. 8,487,627 [Patent Document 2] U.S. Patent No. 5,932,991 [Patent Document 3] International Publication No. 1998 / 034317 [Patent Document 4] U.S. Patent No. 7,592,094 [Patent Document 5] European Patent No. 1639672 [Patent Document 6] U.S. Patent and Trademark Publication No. 2020 / 0020990 [License 7] U.S. Patent and Trademark Office Publication No. 2019 / 0237818 [License 8] International Publication No. 2018 / 049178 [License 9] International Publication No. 2021 / 026043 [License 10] U.S. Patent No. 1115889 [Non-licensed literature]

[0011] [Non-licensed Document 1] Huang, A., Liu, H., Manor, O., Liu, P., & Friend, J. (2020). Enabling Rapid Charging Lithium Metal Batteries via Surface Acoustic Wave‐Driven Electrolyte Flow. Advanced Materials, 32(14), 1907516. [Non-licensed Document 2] Kooij, S., Astefanei, A., Corthals, GL, & Bonn, D. (2019). Size distributions of droplets produced by ultrasonic nebulizers. Scientific reports, 9(1), 1-8. [Non-licensed Document 3] Qi, A., Yeo, LY, & Friend, JR (2008). Interfacial destabilization and atomization driven by surface acoustic waves. Physics of Fluids, 20(7), 074103. [Non-licensed Document 4] Kawada, S., Kimura, M., Higuchi, Y., & Takagi, H. (2009). (K, Na) NbO3-based multilayer piezoelectric ceramics with nickel inner electrodes. Applied physics express, 2(11), 111401. [Non-Patent Document 5] Wang, K., Li, J. F., & Zhou, J. J. (2011). High normalized strain obtained in Li-modified (K, Na) NbO3 lead-free piezoceramics. Applied physics express, 4(6), 061501. [Non-Patent Document 6] Pohlman, R., Heisler, K., & Cichos, M. (1974). Powdering aluminium and aluminium alloys by ultrasound. Ultrasonics, 12(1), 11-15. [Non-Patent Document 7] Gaete-Garreton, L., Briceno-Gutierrez, D., Vargas-Hernandez, Y., & Zanelli, C. I. (2018). Ultrasonic atomization of distilled water. The Journal of the Acoustical Society of America, 144(1), 222-227. [Non-Patent Document 8] Gandhi, K. S. (2020). Modeling of Sulfation in a Flooded Lead-Acid Battery and Prediction of its Cycle Life. Journal of the Electrochemical Society, 167(1), 013538. [Summary of the Invention] [Problem to be solved by the invention]

[0012] This disclosure focuses on a general form of charging a battery using at least two forms of energy input. Traditionally, batteries are recharged by electrical energy input, either a constant supply of current, a constant supply of voltage, or a dynamic supply of both, depending on the charging algorithm or procedure. Less conventional, even exploratory, charging strategies use multiple forms of deliberate energy input. While exothermic electrochemical reactions occurring during charging generate secondary energy input in the form of heat, causing mechanical boiling agitation due to the collapse of gas-laden bubbles, this aspect of energy input is unintentional rather than deliberate. This thermal energy is sometimes discussed as a by-product of the electrical energy input. The methods and embodiments thereof disclosed herein address this concept: multi-variant (i.e., "multi-form") energy input for battery charging. Specifically, this disclosure considers one form of energy input. [Means for solving the problem]

[0013] The secondary form of intentional energy input disclosed herein is sound or acoustic energy. Sound energy is transmitted as pressure waves with frequencies between 36 and 3600 kHz. This frequency range is in the ultrasonic range and can be generated by devices known as ultrasonic transducers. Such devices are available industrially in many variations and for many purposes. Common uses for such devices include fluid atomization, nebulization, cleaning, electroplating, etc. None of these purposes include the application of such ultrasonic generators to assist in the operation of electrical devices, such as the storage (extraction) of electrical energy in or from modular components of batteries known as batteries or cells.

[0014] This disclosure also focuses on mechanisms that facilitate the mass transfer of active ions, resulting in dynamic optimization of charge capacity. Indeed, the interaction of acoustic waves with the structure and materials of a battery cell generates bulk longitudinal waves (BLWs). The effects of BLWs manifest as pressure fluctuations that permeate the interior of the battery cell, not only in fluid regions but also within solid materials and at interfaces between them. In particular, the pressure fluctuations can take the form of a reconstructed pore pressure distribution across the cross section of the porous material within the battery cell. Pressure fluctuations can be visualized, at least through computational multiphysics simulations, as a distribution pattern of high and low pressures. This pattern resembles the barometric pressure distribution typically seen in weather forecasts. Regions of low pressure correspond to regions of high relative velocity. When low-pressure spots occur at some interfaces of solid materials (e.g., electrodes and separators), ions can cross those spots with high mobility. This effect on transport can be interpreted as enhanced mass transfer between the porous solid materials that make up the battery electrodes and separators, a necessary condition for the recovery of active materials during recharge.

[0015] This disclosure also focuses on an embodiment of acoustically assisted battery operation at the cell element level. This embodiment describes a method for attaching an acoustic source to a cell module housing for the smallest commercially available batteries. The overall design is scalable to larger battery sizes. The acoustic source attachment is similar in principle to a bulkhead fitting. Results from computational simulations and laboratory experiments of this embodiment corroborate each other and support the research hypothesis that acoustic energy input supplementing electrical energy input optimizes the charge capacity of battery cells. This support implies that empirical evidence is consistent with recognized theories of the interaction between acoustic energy and the internal structure and materials of batteries. While this agreement has been confirmed through the disclosed embodiment, it is expected that this support will apply to other battery sizes as well.

[0016] Finally, this disclosure focuses on a method for nondestructively estimating a battery's state of health (SoH) using the same type of secondary energy input: sound. This method requires the use of sound as both an emitted and received signal traversing the internal structure of an operating battery. The emitted acoustic signal serves as a reference signal, and the received acoustic signal serves as a diagnostic. The results of this diagnostic are provided as input to computational software programmed to perform automatic pattern classification. The result of this pattern classification is a decision categorizing the diagnostic as one corresponding to a cell condition above a threshold SoH or one corresponding to a cell condition below the threshold. This decision is provided as input to a programmed control circuit that switches the electrical input level for charging every battery cell.

[0017] The present invention can be implemented as a temporary or permanent add-on attachment to the battery casing. The piezoceramic element can be embedded into the casing using methods known to those skilled in the plumbing art, such as bulkhead fittings. Embedding ensures efficient energy transfer, as the piezoceramic element radiates acoustic waves directly into the electrolyte, rather than through a solid material.

[0018] Through the superposition of fundamental fluid flows, the distributed transducer configuration creates complex mixing patterns that maximize bulk coverage for mass transfer. The waveforms, phase and frequency differences between the transducers, and acoustic interactions with the micropores of the porous component, make the mixing flow dynamic rather than stationary, creating turbulence and vortices while simultaneously reconfiguring the pore pressure distribution in the porous component.

[0019] The acoustic transducer is activated during recharge and possibly for a non-zero period after charge, such as during idling or discharge. Acoustically forced convection results in the movement of electroactive species at the electrode-separator interface and the electrolyte-electrolyte interface. During discharge, Pb 2+ Ions are produced from the electron transfer step, followed by the deposition of PbSO4, a discharge by-product.2+ The ions are generated by dissolution of PbSO4 followed by precipitation of PbO2 or Pb by an electron transfer step. The transfer occurs via the solvated Pb formed during charging. 2+ This may aid in the dissolution of ions. It may also cause cracking, destabilization, and eventual spalling of discharge by-products if they are already deposited on the electrode surface. Transducer activation can be automated using a microcontroller. When placed at the bottom, the transducer generates an upward fluid momentum that can counteract the gradient of electrolyte stratification, whereby gravity increases electrolyte concentration toward the bottom. It is also known that stratification, i.e., the presence of a vertical concentration gradient, promotes the accumulation of discharge by-products. This may be due to the non-uniform vertical distribution of current. The transducer can be positioned so that its vibration plane is approximately parallel to the normal vector of the separator / electrode plane. The gap between the transducer surface and the cell element can be adjusted. This gap controls the interaction between the sound waves and the internal cell settings (i.e., materials, geometry, etc.). Optimize flow patterns resulting from nonlinear interactions between the fluid and the fluid (fluid, fluid flow, interface microstructure, etc.).

[0020] Although the frequency is high, 10 -6 A cutoff frequency that produces droplets with a median diameter on the order of meters or less is not exceeded. Very small droplets of this size will be more easily ejected from the aperture and dispersed into the air rather than returning to the bulk and recombining. Larger droplets will have a higher recombination rate with the bulk and will tend to recombine. Larger droplets will tend to have a higher recombination rate with the bulk electrolyte due to gravity. Approximately 10 -6 Narrow droplet size distributions centered on a meter can be achieved with piezo-ceramic disks. Other piezo-ceramic shapes can be off-centered while still maintaining a narrow distribution.

[0021] The mixed flow is generated directly by bulk longitudinal waves (BLW) generated by multiple vibrating piezo-ceramic elements. BLW induces Faraday waves on the surface of a fluid supported by a vibrating solid. While porous materials such as electrodes and separators contribute to flow resistance, the pores can induce turbulence in the flow pattern, which can be advantageous. The complex flow pattern resulting from forced convection driven by BLW will mix the electrolyte. The mixed flow can circulate electroactive species and clear hot spots of electrochemical interactions. The path to capacity degradation in battery cells involves factors that prevent the establishment of ideal half-cell reaction equations. For example, during battery recharge, if the dissolution-precipitation process does not completely reverse precipitation during discharge operation, discharge byproducts will gradually accumulate as the electroactive materials are depleted. The mixed flow resulting from BLW can help dissolve discharge byproducts into forms that can be easily converted into active materials during the recharge phase.

[0022] The fabrication of piezo-ceramic elements may utilize the same core materials, such as Pb, found in battery components. Integrating the fabrication of piezo-ceramic materials may be economically feasible for battery manufacturers. Other lead-free piezo-ceramic materials, such as potassium-sodium niobate (KNN) with nickel inner electrodes (Kawada et al., 2009), are suitable for nickel-based batteries. While still manufacturable by conventional sintering techniques (Wang et al., 2011), the known lithium substitution method for KNN may be suitable for lithium-based batteries.

[0023] The effect of injecting acoustic waves into a basic electrochemical cell, the building block of a battery, was computationally simulated and experimentally confirmed. The multiphysics simulation provides the best mathematical representation of the hypothetical mechanisms of sound interaction with the battery cell structure and materials during recharge and / or discharge. Laboratory experiments validate the results suggested by the computational simulation. The agreement between experimental and simulation results demonstrates that the theoretical principles underlying the interaction of sound waves with the structures and materials inside the battery cell are adequately captured.

[0024] Simulation results are presented for cell element units under control conditions without sound input and for experimental conditions with sound input. The control case serves as a baseline for verifying whether the apparent deviations in the experimental results are statistically significant. The simulation incorporates the same charge / discharge sequence as would be performed in an actual potentiostat. Relevant physical phenomena are identified and combined to systematically represent the sound-material interactions occurring within a battery cell. Results show that the injected sound waves effectively slow down the generation of degradation factors, particularly in the innermost cell element units where degradation rates are likely to be highest. The results suggest that acoustic suppression of degradation factors directly extends the cycle life of the cell elements. The magnitude of this effect varies with different sound frequencies, suggesting the existence of other parameter combinations (other than those considered in the study underlying this disclosure) that may maximize cycle life. Detailed visualization of pressure and velocity patterns supports the hypothesized mechanism of sound enhancing mass transfer of active ions. This facilitated mass transfer appears to influence the distribution of active ions, effectively maximizing the charge storage capacity of the electrodes within the cell element. This capacity maximization induced by sound input is clearly significant compared to the control scenario without sound input.

[0025] The results of the confirmation experiment are also presented in this disclosure. Laboratory experiments were conducted in a controlled environment with an average temperature of 25°C and a relative humidity of 50%. To eliminate time effects and ensure consistent environmental conditions, such as temperature and humidity, which could affect the results, all tests were run simultaneously with the control and experimental cases. Charge-discharge cycles were performed using an automated battery potentiostat (Biologic VSP-3e system) using a charge efficiency determination (CED) test protocol. This test protocol discharged the cells to a depth of 100%, equivalent to conducting an accelerated aging endurance test. The ultrasonic transducer operated only when the battery was being charged. The experiment was terminated after the second cycle, when the charge capacity failed to exceed 70%. The experimental results were indeed as predicted by the simulation. With the assistance of sound input, the battery cells were able to achieve approximately 200% longer cycles on average.

[0026] The use of sound to improve battery cycle life is effective not only for passive intervention in battery operation but also for active intervention. Sound can be used as a signal to detect any changes in the battery's internal structure, such as the formation of sulfate deposits, over the battery's lifespan. Also disclosed are methods and apparatus for active intervention that affect the overall battery charging process. This intervention involves a novel procedure called parallel charging, rather than the traditional method of series charging. In parallel charging, each cell element of a battery can receive a different amount of current than other cell elements that are simultaneously charging. This use is motivated by the observation that battery cells do not always operate in sync. Some cells discharge faster than others, which ultimately determines the overall battery state of charge. When charging is performed in series, the same current flows through all cells until the least discharged cell is fully charged again. Overcharging of an already full cell is evident by the generation of heat that can boil the electrolyte. However, the presence of the most discharged cell, the very reason for recharging the battery, may not always be fully charged. Therefore, when the battery resumes discharging operation, any imbalance in the cell's state of charge will only worsen the overall battery health. Estimating the SoH at the cell level can be challenging and must be non-destructive to avoid affecting the condition of the electrodes or electrolyte. This non-destructive acoustic SoH estimation method is made possible by utilizing an ultrasonic transducer array consisting of a sound emitter and receiver that detects transmitted, reflected, and diffracted sound throughout the battery cell.

[0027] The received sound patterns contain information about the internal structure of the battery cell and can be used to infer the State of Health (SoH). Therefore, SoH information can be extracted by classifying these patterns as belonging to either "good" (above 80% SoH) or "bad" (below 80% SoH) cells. The assumption that the patterns contain information related to the battery's SoH is motivated by the fact that sulfates are solid and typically occur at the interfaces between electrodes and separators. Solid sulfates that accumulate at these interfaces cause delays in the propagating sound waves, altering the cross-correlation between the emitted and received sounds. The information embedded in the received sound patterns is then used to control the amount of current applied to the cell elements during battery charging. This "customized" current input allows the battery to achieve a balanced state between its component cells after charging. This balance should extend the battery's lifespan by mitigating, minimizing, or preventing overcharging (which causes heat generation and boiling) and undercharging (which accelerates sulfation). [Brief explanation of the drawings]

[0028] [Figure 1] Shows a multi-view of a battery cell (shown in axonometric projection) with the top cover removed, highlighting the acoustic source integrated into the battery case, the cell elements consisting of multiple electrodes (both positive and negative), and the spacing between the electrodes with and without a separator. [Figure 2] FIG. 1 shows a side view of a battery cell illustrating the gap between each acoustic wave source and the nearest edge of the battery element immersed in the electrolyte. [Figure 3] 1 shows a side view of a battery cell with highlighted flow field lines illustrating electrolyte mixing due to acoustic waves generated from an acoustic source that imparts momentum to the electrolyte. [Figure 4] 1 shows a conceptual diagram of a battery cell and its connection to the battery terminals and a charging system that provides power to the built-in acoustic source. [Figure 5] 1 illustrates mass transfer of electroactive species due to acoustic mixing generated by a distributed transducer configuration. [Figure 6] A detailed diagram of the cell element unit inside the housing incorporating ultrasound is shown in the top row, a three-dimensional diagram of the cell element in the control experiment where no sound is emitted is shown in the bottom left, and a three-dimensional diagram of the cell element in the experiment where sound is emitted is shown in the bottom right. [Figure 7] The basic geometry of the multiphysics model of a battery cell element unit is shown in see-through view in the upper left for the experimental model and the upper right for the control model. The cell element unit consists of alternating stacks of positive electrodes, separators, and negative electrodes until the positive and negative electrodes are on the outer surfaces of each side. The experimental setup includes embedded transducers (disk-shaped objects) attached to the sides and bottom of the cell housing. [Figure 8] FIG. 1 shows a block diagram of a computational multiphysics model illustrating the different types of physics that virtually represent the underlying mechanisms of sound interacting with the internal structure and materials of a battery cell. [Figure 9] Charge-discharge cycling protocols performed by an automated potentiostat (left) and simulated using computational multiphysics software (right). [Figure 10] Comparison of simulated concentrations of battery active material throughout the cell element after 10 charge-discharge cycles, using different frequencies at the same driving voltage (18 Vpp) with a control experiment (no sound). [Figure 11] Shown (top to bottom) are simulated changes in the concentration of the battery active material along the axis perpendicular to the plane of the stacked cell plates from the first to fourth cycles. [Figure 12] Simulations of the concentration evolution of the battery active material along the axis perpendicular to the plane of the stacked cell plates are shown for the 8th (top) and 10th (bottom) cycles. [Figure 13]The graph above shows a simulation of the change in electrode state of health (SoH) over multiple cycles, overlaid with results for various conditions (control (no sound) and sound at different frequencies). The graph below shows the change in SoH for different electrodes across the cell element unit for each condition. [Figure 14] Scan simulations of pressure (top) and mass transfer rate (bottom) on different electrode plates of a cell element unit at an acoustic frequency of 110 kHz driven by 18 V peak-to-peak voltage. [Figure 15] Scan simulations of pressure (top set of panels) and mass transfer rate (bottom set of panels) on different electrode plates of a cell element unit at an acoustic frequency of 1700 kHz driven by a peak-to-peak voltage of 18 V. [Figure 16] Scan simulations of pressure (top set of panels) and mass transfer rate (bottom set of panels) on different electrode plates of a cell element unit at an acoustic frequency of 2400 kHz driven by a peak-to-peak voltage of 18 V. [Figure 17] Figure 17a shows a typical course of a laboratory experiment for a control experimental setup (no sound). The corresponding charge-discharge cycling performance is shown in the bottom panel, plotting the evolution of the voltage curve and charge-discharge capacity line over multiple cycles. Figure 17b shows a typical course of a laboratory experiment for a hypothetical setup incorporating ultrasound. The corresponding charge-discharge cycling performance is shown in the bottom panel, plotting the evolution of the voltage curve and charge-discharge capacity line over multiple cycles. [Figure 18] The cycle performance is summarized from a number of experiments comparing different conditions, including a control experiment without sound and experiments using sound at different frequencies and driving voltages (peak-to-peak). [Figure 19] FIG. 1 illustrates a three-dimensional view of an embodiment of a cell-level parallel charger with SoH estimation using non-destructive acoustic diagnostics. [Figure 20]1 shows a schematic diagram of cell-level parallel charging of a battery using information from acoustic diagnostics. DETAILED DESCRIPTION OF THE INVENTION

[0029] The battery case 101 is the least innovative part of the battery because it does not actively participate in the battery's electrochemistry. This disclosure focuses on using acoustic waves to induce mixing of the battery cell's electroactive species in a non-destructive manner, with the hope of maximizing the yield and rate of essential electrochemical reactions analyzed under the assumption of a well-mixed battery cell. Solving the mixing problem through reconstructing the pore pressure distribution is the core subject of this disclosure. Acoustic wave sources, e.g., in the form of piezoceramic transducers, can be located on the bottom 103, non-bottom / sides 102, 104 of the battery case 101. The non-bottom transducers may also include the top portion of the cell, as long as the lid covering the battery cell compartment is free of obstructions (e.g., terminals, vents). The cell elements 105 found inside the case 101 may, in some variations, be arranged in a stacked configuration consisting of electrodes 107 and inter-electrode spaces 106, which may or may not include an electrically insulating but porous separator material. The stack of electrodes 107 may, in some variations, consist of alternating positive and negative electrodes. Each electrode is a plate of metallic material, with or without a non-metallic active material coating, which may or may not be porous. The entire cell element is fixed in place within the cell compartment 101 to achieve mechanical stability or durability in anticipation of movement of the platform on which the battery is mounted. The acoustic wave sources may be piezoceramic transducers 102, 103, and 104, which may be placed in strategic locations relative to the cell element 105. The number of transducers depicted in the figure is not intended to be limiting in any way, but merely as a means of illustrating the concept.

[0030] The attachment of the transducer to the battery case must be hermetically sealed to prevent leakage of the electrolyte 201 and other active materials from the battery interior, while still allowing the transducer to directly interact with the battery interior, such as the electrolyte 201. The attachment may be made using standard connections such as bulk fittings. The connections may be integrated as part of the design, or may be supplied during manufacture of the battery case 101. In some variations, the attachment may be retrofitted to existing battery cases that do not have access points for mounting the transducer inside the cells.

[0031] Direct interaction between the acoustic wave source and the cell interior increases the efficiency of energy and momentum transfer, so mixing 301 occurs with minimal input power and / or minimal losses due to thermal and / or viscous heating. Leak-tight connections isolate the interior from the exterior. External electrical wiring 405, 406, and 407 may be present to connect the acoustic transducers 102, 103, and 104 to a power source for transducer operation. The acoustic transducers may be powered by a battery management module 404, which is connected to an external energy source 409 via a supply line 408. This energy source 409 may be a solar power system, a wind turbine system, an alternator, or other means of generating electricity. The microcontroller 404 branches the supply lines 403, 405, 406, and 407 to different portions of the battery cell. Supply line 403 conducts charge to battery terminals 401 and 402 during charging / recharging. Charging and acoustic transducer activation operations are managed by battery management module 404, which may include an on-board computer that generates variations in the procedures for driving the transducers and providing charge to the battery. This management module 404 may receive feedback through supply lines 403, 405, 406, and 407 and estimate conditions related to battery degradation for monitoring and control purposes. This management module 404 attempts to minimize cases of overcharging and undercharging the battery or overdriving and underdriving the acoustic transducers. Thus, acoustic transducers 102, 103, and 104 may be capable of detecting changes related to battery degradation through sound waves, which can convey information related to the interaction of sound with dynamic changes occurring within the battery cells (e.g., formation of deposition by-products, temperature increase, or fine mist formation).

[0032] Acoustic interaction is based on the generation of bulk longitudinal waves (BLWs) in the electrolyte through the porous structure within the battery cell. The acoustic transducer vibrates at a frequency F, generating pressure fluctuations in the fluid that force convection. The porosity of the cell elements creates a resistance to flow, but this resistance is overcome by forced convection induced through momentum resulting from acceleration near the transducer surface. This acceleration induces density changes that propagate through the bulk at a rapid pace. Due to the bulk resistance, the density wave propagates an effective distance that depends on the viscosity, surface tension, and density of the bulk fluid, as well as the F of the transducer. The propagation of the acoustic waves can facilitate mass transfer of solvated ions or electroactive species dissolved in the bulk electrolyte through a mixing process 301 through the inter-electrode gap 106. This resulting mass transfer 501 can pass through the pores of the cell elements 105, evenly distributing ionic species throughout the container. In effect, the BLW imparts momentum to the fluid electrolyte, making the cell operate like a well-mixed reactor, as implied by the half-cell reaction equations used to describe the battery's underlying electrochemical mechanisms. The actual enhancement of mass transfer of electroactive species501 due to acoustically induced mixing influenced by porous acoustics within the cell is a dynamic means by which the yield of the half-cell reactions can be maximized throughout the cycle life of the battery.

[0033] The momentum of the enhanced flow caused by the direct interaction between the acoustic wave source and the cell interior, particularly the fluid electrolyte, is also the fundamental basis for converting such electrolytes into aerosol droplets that have the ability to leave the cell and evaporate. Atomization or nebulization occurs due to capillary waves (or Faraday waves) formed at the fluid surface supported by a solid platform vibrating at a frequency F. The Faraday wavelength can be estimated from the following equation, where σ is the surface tension of the electrolyte and ρ is its density:

[0034]

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[0035] High values ​​of F result in significant acceleration, and the vibration amplitude is long enough to separate the droplets from the bulk. The median diameter of these droplets is a factor of the Faraday wavelength. Therefore, higher frequencies are expected to produce smaller droplets. Indeed, fine droplets, collectively manifesting as mist, form at ultrasonic frequencies. Treating mist formation as a result of interfacial instability (Qi et al., 2008), atomization can be predicted by finding a threshold condition. In fact, the atomization threshold is a mathematical relationship first presented by Pohlman and Stamm (cited in Pohlman et al., 1974). This mathematical relationship relates the transducer vibration amplitude A and the onset of atomization to the viscosity η of the electrolyte fluid, its surface tension and density, and the Faraday wavelength λ.

[0036]

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[0037] The minimum amplitude of transducer vibration decreases as the excitation frequency, F, increases. Consequently, higher ultrasonic frequencies require smaller vibration amplitudes to begin generating mist from the bulk fluid. While mist generation is beneficial for medical nebulizers (e.g., as a means to more effectively deliver certain therapeutic agents via aerosol inhalation), it is undesirable for batteries. Electrolyte mist, especially acidic ones, is known to be carcinogenic. In fact, battery factories are required to purify acidic mist as a health precaution for workers, as inhaling the mist can cause lung ulcers and ultimately lead to fatal effects.

[0038] The distributed transducer configuration optimizes the trade-off between mist generation and mixing. Individual transducers do not need to be driven with large power inputs. For example, any transducer in this configuration can be driven with less than 10 mW / cm². 2The cell can be driven with a power input of less than 100 kJ / s. Such low power limits the extent of pressure fluctuations caused by the acceleration of the vibrating transducer. However, the distributed configuration compensates for this limiting effect by ensuring a wide range of mixing effects, i.e., mass transfer (501). The strategic positioning of the transducers relies on the three-dimensional structure of the cell and the overall stacking configuration of the cell elements. The inter-electrode spacing, if narrow enough, acts as a bridge for ion transfer between the electrodes, thus doubling as a porous acoustic channel (in the presence of a separator) to induce turbulence in the mixing pattern. The resulting complex mixing pattern effectively injects sufficient randomness into the forced convection, increasing the likelihood that electroactive species will sweep through potential sites of chemical interaction at any given time. This increased probability of chemical interaction allows for the stagnation of the battery's fundamental mechanism: the formation of discharge byproducts that no longer participate in the electrochemical reaction. With acoustically assisted mixing, the so-called dissolution and precipitation mechanism continues to operate, even under conditions that would otherwise accelerate battery capacity loss (e.g., deep-cycle charging in renewable energy storage applications).

[0039] The production of piezo ceramic transducers can be co-located within battery factories, potentially utilizing the same raw materials. This co-location could potentially reduce the overall manufacturing cost of batteries with acoustic assist charging, with the benefits of extended cycle life outweighing the additional costs. This advantage would make batteries more suitable for renewable energy storage without extensive modifications or the use of novel chemistries that are less understood than existing chemistries used in mature battery technologies. A cycle life increase of at least 25% would be sufficient to improve the economics of renewable energy storage, thereby increasing the use of cleaner energy forms and facilitating society's weaning from fossil fuels as a primary energy source. Emissions from fossil fuels are widely believed to be the cause of impending global climate change, which could have devastating consequences for civilization. Therefore, the deployment of cost-effective battery technology with long cycle life and acoustic assist charging would facilitate the widespread adoption of renewable energy sources worldwide. Such widespread adoption could one day help avoid the long-term damage of maintaining the dominance of fossil fuels in the global energy mix. Increasing battery demand will not only motivate existing battery manufacturers to scale up production, but may also further expand the supplier base with add-on technologies that do not require significant changes to the electrochemistry of existing battery technology. This motivation is further strengthened by the prospect of reducing the additional cost of equipping the battery case with an acoustic source, as described in this disclosure.

[0040] A lead-acid battery cell element unit consists of a stack 602 of electrodes and separators held together by a bracket 601. In a typical cell element configuration, the bracket 601 connects all negative electrodes to one terminal lug and all positive electrodes to the other. This configuration is standard for all cell element units, regardless of size. A three-dimensional diagram illustrates the relationship between the cell element unit 602 and the housing. The control cell shows terminal lugs 603, which serve the additional function of securing the cell element to the lid of the housing 606. The experimental cell includes at least one ultrasonic transducer 604 attached by a connecting member 605 to the face of the housing 607 facing the space between the electrodes of the cell element unit 602. Each connecting member 605 contains a mechanical element that increases the mechanical efficiency of the transducer's vibration and reduces heat generation during sound generation. The connecting members also incorporate a sealant to prevent any form of battery fluid from leaking through them. This sealing ensures that only the vibrating side of the transducer 604 is exposed to the interior of the battery cell.

[0041] The cell element geometries of the control and experimental configurations 701 are similar, except for the presence of transducer 703 in the latter. Here, the location of transducer 703 is visualized relative to cell element unit 702. The electrodes of this cell element are labeled "SU(n)," where n increases from "1" on one side to "n" on the other side. A typical embodiment of this structure is shown for n = 6. In this design, the innermost electrodes are labeled SU3 and SU4. These electrodes are located far enough inside the bulk of the cell element unit that they are least exposed to the electrolyte. Each SU is actually a "sandwich unit" representing an electrochemical cell consisting of a positive electrode, separator, and negative electrode immersed in a fluid electrolyte. For n = 6, there are six such sandwich units stacked one on top of the other (702). This cell element geometry originates from Camille-Alfons Faure, whose flat-plate design has become the successful standard adopted in today's automotive batteries. The flat plate design is also the most economical for mass production.

[0042] The performance of the cell element unit can be predicted from appropriate computational simulations incorporating multiphysics-related aspects of the cell's operation. The transducer multiphysics module 801 incorporates the electrical circuitry for driving the sinusoidal vibrations. The conversion of electricity to vibrations is handled by the electrostatics and solid mechanics module, while pressure acoustics deals with the transfer of vibrational energy to the fluid as a pressure wave. The electrolyte multiphysics module 802 deals with the fluid dynamics resulting from the influence of pressure waves and the heat transfer due to the dissipation of thermal energy generated by the electrochemical reaction from the electrodes to the electrolyte. The electrolyte multiphysics module 802 is coupled to the electrochemistry module 803, which deals with the electrochemical reaction that generates by-products that flow through the electrolyte via mass transfer. The multiphysics computational simulation is driven by the Coulombic Efficiency Determination (CED) protocol of the actual potentiostat at rate 901. The CED protocol is a charge / discharge sequence 902 that operates the cell element units over time until a termination condition 903 is met (ie, the condition that the charge capacity cannot exceed 70% for two consecutive cycles).

[0043] The active material concentration is an important indicator of what happens to the electrode composition after each charge / discharge cycle. The color bar in Figure 10 shows the surface concentration of the active material after 10 cycles. Note that at the start of the simulation, the active material concentration is uniform throughout the cell element. After 10 cycles in control experiment 1001, the interior of the cell element unit (composed of SU3 and SU4) is brighter than the other SUs. This brightness indicates that the SU3 and SU4 active materials did not recover to their initial levels in the control experiment. In an example experiment using a varying acoustic frequency and a driving voltage of 18 Vpp, the interior relative concentrations were less affected than in the control experiment, suggesting that acoustic waves are involved in this effect. Further investigation revealed that the interior relative concentrations were least affected at 110 kHz (1002) compared to 1700 kHz (1003) and 2400 kHz (1004), suggesting that 110 kHz (1002) may generate an acoustic wave pattern that is appropriate for this cell element geometry. The sharp deviation in relative performance within the cell element is most evident from the concentration profile graphs 1101, 1102, 1103, 1201, and 1202. From the first cycle (1101) to the tenth cycle (1202), the active material concentrations within the cell element, namely SU3 and SU4, show the largest deviation in the control experiment. Further optimization of the frequency, driving voltage, phase difference, and ultrasonic transducer position can suppress the deviation in both the internal and overall cell element degradation. (Note that in this accelerated degradation test, the active material concentration reached 24 mol / m by the tenth cycle (1202).) 3 to 22 mol / m 3 (The figure has fallen to 100 million yen.)

[0044] The state of health (SoH) 1301 is the most direct measure of battery life over a series of charge-discharge cycles, and further comparisons demonstrate the positive effect of the BLW introduced into the internal structure of the battery cell. Without acoustic waves, SU3 and SU4 in the control experiment 1302 reached the 70% threshold by the 10th cycle, sooner than all other SUs. Such early threshold violations imply that the entire cell element is deemed "dead" after 10 cycles of this accelerated aging test. On the other hand, the use of acoustic waves appears to prolong this downward trend toward the 70% threshold, extending it by at least 100% over the number of cycles. At a frequency of 110 kHz (1303), this increase in cycle life is more than 200% compared to the control experiment, confirming the findings of experiments 1002 and 1202. SoH traces 1302, 1303, 1304, and 1305 confirm the depletion changes in the active material.

[0045] Simulation results can visualize quantities that are difficult to measure experimentally, and these visualizations provide further insight into the performance improvements offered by 110 kHz acoustic waves. The pore pressure 1401 and mass transfer rate distribution 1402 for each SU of the cell element are shown. The pore pressure 1401 and rate distribution 1402 can illustrate the redistribution of active material due to pressure fluctuations caused by BLW propagation inside the battery cell. Dark areas in the pore pressure distribution indicate low-pressure spots, while bright areas in the rate distribution indicate high momentum of active ions. 110 kHz appears to provide the most uniform redistribution across the SUs of the cell element. Uniform redistribution means the electrode has the largest surface area, which also indicates maximized charge capacity. For 1700 kHz, the corresponding pore pressure 1501 and mass transfer rate 1502 distributions are fairly uniform, with greater contrast between high and low levels. On the other hand, for 2400 kHz, the corresponding pore pressure 1601 and mass transfer rate 1602 distributions are obviously non-uniform across the cross section of the porous interface, which may be unfavorable for the long-term sustainability of active material recovery upon recharging.

[0046] This experimental procedure involves running the virtual sample 1702 and the control sample 1712 simultaneously while connected to the same potentiostat system. The purpose of running the control and virtual samples simultaneously in this manner is to minimize the effects of environmental and electrical fluctuations over time. Graphs of the cycling performance of the virtual sample 1701 and the control sample 1711 are recorded live during the experiment. The voltage of the cell elements is monitored, while the charge capacity is tracked during charging and discharging. This capacity tracking is shown as an increasing line and ends when the mode switches from discharge to charge, or vice versa. The State of Health (SoH) is calculated as a percentage of the maximum level reached by the capacity tracking line in a given cycle divided by the maximum level reached in the first cycle. Cell elements constructed with new electrodes are assumed to be in their best health at the start of the test. The SoH measured in this manner most accurately represents the cell's state of health for accepting and storing charge. However, in practice, this measurement method, which requires expensive equipment such as a potentiostat system, is not commonly performed in commercial settings, such as automotive service centers. Therefore, other cost-effective means of estimating SoH must be used. The transducer 1703 of the hypothetical sample 1702 appears to produce a clearly multi-value voltage curve 1701 during recharge in the cycle trace. This result differs from the fairly smooth voltage trace 1711 during recharge of the control sample 1712. The multi-value voltage trace 1701 during recharge is indirect evidence of enhanced mass transfer resulting from a reorganization of the pore pressure distribution at the interface.

[0047] Comparison of the cycle performance of the control experiment and the various experimental cases confirms the predicted effect of supplemental sound energy. Boxplot 1801 shows the median performance of cell elements subjected to accelerated aging tests for the various experimental cases. In the control experiment, the median cycle life is four cycles, but could reach six cycles. This variation may be the result of factory variations between cell components expected in mass production. At 110 kHz, the median cycle life is significantly greater than the control experiment, and this is also true for the other test frequencies. Higher driving voltages appear to improve cycle life at this frequency, but this trend is less conclusive at other test frequencies. This experimental observation supports the results obtained from computational simulations, particularly regarding the improvement of cycle life due to sound injection into the battery's internal structure. For a driving voltage of 18 V (peak-to-peak), the median cycle life at 110 kHz is more than 100% greater than the control experiment. At 1700 kHz, a wider range of cycle life was observed at a driving voltage of 18 V (peak-to-peak). However, performance at 2400 kHz was not significantly different from the control, confirming the non-uniformity of the reconstructed pore pressure distribution 1601. Such non-uniformity does not uniformly redistribute the recovered active material, resulting in only a small improvement in cycle life.

[0048] Sound can also be used independently or in an integrated manner to actively balance the state of charge of cells during the charging phase. One embodiment of such a device 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 is comprised of at least one ultrasonic receiver 1905. The diagnostic subsystems capture information related to changes occurring within the cell compartments, related to the formation of electrochemical by-products that can impair the long-term capacity of the cells. The diagnostic subsystems provide information to a central controller that draws power from a power source 1901 via a regulator 1903, which relays current supply to the cells via a switching voltage regulator 1902. The value of the current relayed to the cell corresponds to the State of Charge (SoH) of a given cell. Cells with a low SoH may require a higher C-rate, while cells with a high SoH may require a relatively low C-rate. A high C-rate for a cell with a low SoH allows it to catch up with an adjacent cell with a relatively high SoH in terms of charge capacity. This difference in current delivered between cells means that charging, as implemented by device 2001, must proceed in parallel. The parallel connection of subsystem 2004 ensures that each cell element receives only the amount of charge necessary to restore it to its previous SoH. Device 2001 also includes display 2002 and control knob 2003 to accommodate different battery sizes and models. This parallel charging strategy is a way to ensure balance across batteries. Balanced batteries will tend to last longer because stress from overcharging and sulfation is minimized. In fact, uneven SoH reduces battery life.

Claims

1. 1. A method for assisting the operation of a battery by non-destructively reconfiguring the pore pressure distribution of a porous component within at least one battery cell through the input of energy from at least two energy input sources to prevent or delay the formation of sulfate deposits from the start of operation by improving the transmission of electroactive ions through a diffusion layer formed on an electrode surface during discharge, wherein the input of energy from the at least two energy input sources is sonic energy, the sonic energy having a frequency within a range of 90 to 3600 kHz and having a phase difference within a range of 0 to 180 degrees between each energy input source.

2. 1. A system for assisting battery operation by non-destructively reconfiguring pore pressure distribution of porous components within at least one battery cell through the input of at least one other form of energy than electrical energy to prevent or delay the formation of sulfate deposits from the start of operation by improving the transmission of electroactive ions through a diffusion layer formed on an electrode surface during discharge, comprising: the at least one battery cell is housed in an independent compartment having a sealed attachment that not only seals against leakage of the fluid electrolyte out of the compartment but also ensures mechanical efficiency of the piezoelectric vibration of the ultrasonic transducer; A system that assists in the operation of a battery, wherein the sealed attachment may include a threaded structure to reduce heat generation due to energy loss of transducer vibration, a sealant adjacent to the element that prevents leakage of fluid electrolyte of the at least one battery cell, and a mechanical component that increases the efficiency of input of at least one other form of energy different from electrical energy.

3. The system of claim 2 , wherein the input of at least one other form of energy different from electrical energy occurs simultaneously or overlaps in time with the input of electrical energy.

4. 3. The system of claim 2, wherein the at least one other form different from electrical energy is sound energy at a frequency between 90 and 3600 kHz.

5. The system of claim 2 , wherein at least one battery cell is an independent compartment comprising a fluid electrolyte that immerses a porous component of the battery cell.

6. 3. The system of claim 2, wherein the input of at least one other form of energy than electrical energy is achieved by operation of at least one ultrasonic transducer, driven at a sufficiently low power such that the vibration amplitude is below the atomization threshold of the fluid electrolyte material.

7. 7. The system of claim 6, wherein the at least one ultrasonic transducer is made of a composite material including lead, zirconium, titanium, potassium, sodium, and / or niobium, and is formed into a disk shape having piezoelectric properties that allow it to vibrate along a specific axis at a specific fundamental frequency upon input of electrical energy, the composite material being selected to provide an appropriate match with battery chemistry, particularly taking into account manufacturing costs, since at least one component of the transducer is exposed to an electrolyte.

8. 7. The system of claim 6, wherein operation of the at least one ultrasonic transducer refers to a manner in which each of the plurality of transducers vibrates as a sine wave at a single or various frequencies within a range of 90 to 3600 kHz with a phase difference between each transducer within a range of 0 degrees to 180 degrees, with vibrating portions of all transducers exposed to the fluid electrolyte of the battery cell.

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