Patent Application
20240421367
Lithium-ion (Li-ion) batteries are a preferred chemistry for secondary (rechargeable) batteries in high discharge applications such as electric vehicles (EVs) and power tools where electric motors are called upon for rapid acceleration. Li-ion batteries include a charge material, conductive powder, and binder applied to or deposited on a current collector, typically a planar sheet of copper or aluminum. The charge material includes anode charge material, typically graphite or carbon, and cathode charge material, which includes a predetermined ratio of metals such as lithium, nickel, manganese, cobalt, aluminum, iron and phosphorous, defining a so-called “battery chemistry” of the Li-ion cells. Recycling of the Li-ion batteries recovers large amounts of charge material metals that would otherwise need to be sourced from controlled sources, typically as a result of mining and refining.
Forced discharge of Li-ion batteries such as EV (electric vehicle) battery cells and packs precedes physical dismantling and agitation of the cells in anticipation for recycling of battery materials, including charge material metals, carbon and graphite, and current collectors such as aluminum and copper. Forced discharge extracts residual electrical energy from the battery cells to avoid sudden and unexpected release of residual energy during recycling. A containment device applies a physical restraint to one or more battery cells and engages positive and negative terminals on the battery for electrical communication. The containment device forms a rigid enclosure with a clamping top and bottom and physically compresses the battery cells to mitigate any gaseous product formation from the forced discharge, which might result in a buildup of pressure in the battery cell. A cooling medium flows through the containment device for thermal transfer of any excess heat generated during the discharge. Depending on the residual charge remaining in the battery cells, excess electrical energy is discharged through the positive and negative terminals to a state of zero charge. A reverse voltage is applied to effectively force current through the anode and thus forcing the polarity to reverse, bringing the battery to a zero-energy state. The reverse polarity incurs short circuits resulting from degradation of current collectors in the battery, rendering it benign. A suppression port in the containment device allows flooding with a fire suppressant in the event of a thermal runaway or fire during the forced discharge.
In more detail, Li-ion batteries for EVs reside in a battery pack, often mounted to the vehicle undercarriage. Each battery pack includes a number of interconnected battery cells, each including a structured arrangement of cathode and anode materials leading to positive and negative terminals. For configurations herein battery recycling of Li-ion cells involves physically dismantling the battery packs to obtain the individual battery cells therein for recycling, which usually involves crushing, shredding and grinding to generate a granular mass (i.e., a black mass) of the battery cell contents.
Unfortunately, conventional approaches to battery cell recycling suffer from the shortcoming that the battery packs in the recycling stream have an unknown state of charge, depending on the donor vehicle, age, and last usage. Physical crushing and shredding of battery packs and/or cells can trigger a sudden release of residual electrical energy, leading to an explosion or fire. Accordingly, configurations herein substantially overcome the shortcoming of battery dismantling by providing a forced discharge cell containment device to quickly transfer residual electrical energy from a battery cell in a controlled manner, suppress excess gaseous or exothermic reactions, render the battery cell benign or inert, and invoke fire suppression via a flooding port in the unlikely event of excessive discharge.
In further detail, configurations herein provide a battery cell containment device for fast, efficient discharge including a top plate positioned above a bottom plate to compress at least one battery cell therebetween, and a coolant system comprising an inlet, an outlet, and a coolant channel and configured to circulate a coolant through the top plate, the bottom plate, or both. Thermal and pressure increases (gaseous expansion) are therefore moderated, and a fire suppression system is configured to supply a fire suppressant to the compressed battery cell in the unlikely event of a nonconforming cell encountering an adverse result to discharging. Electrical probes accessible from the exterior are positioned to provide electrical contact to terminals of the compressed battery cell for applying and controlling discharge voltage.
The foregoing and other features will be apparent from the following description of particular embodiments disclosed herein, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
Depicted below is a method for discharging a battery cell to safe levels for recycling using a containment device for discharge and protection in the unexpected event of an adverse response by the battery cell.
Once liberated, extraction of the granular assortment (black mass) 120, including cathode materials, anode materials, current collectors and casing materials, forms a leach solution 122 containing desirable charge material metals in a ratio that can be adjusted as needed, as disclosed in U.S. Pat. No. 9,834,827 and continuations thereof, incorporated by reference. The leach solution 122 undergoes a coprecipitation reaction 124 for recovering recycled cathode material precursor 126 (pCAM, or precursor Cathode Active Material), which is then sourced for new, recycled battery cells. Typically, the precursor is a hydroxide form of the metals discussed above, based on the battery chemistry of the individual cells and pack, which can vary in the recycling stream.
It would be beneficial to fully discharge the battery cells prior to dismantling to mitigate the risk of a sudden or uncontrolled release of residual electrical energy. A forced discharge method as depicted below applies a reverse potential power supply to battery cells, rendering them in a benign state, and returns excess residual electrical energy 130 to the grid 134.
Without wishing to be bound by any particular theory, it is believed that overdischarging of the cell below 0% state of charge causes dissolution of the copper current collector, creating internal short circuits in the cell cathode and anode and dissipating the remaining cell energy as heat. The overdischarge process can be accelerated by using the forced discharge approach discussed herein in which a reverse potential power supply is attached to the cell that may accelerate the copper plating believed to be involved in creating the internal short circuits.
A predetermined calculation can estimate the amount of energy to be delivered by the reverse potential power supply. During delivery, the cell voltage and current is monitored, and the process is repeated if needed, until zero voltage and current has been achieved, and/or until a zero-energy state of the battery cell is reached.
Lithium-ion cells usually cycle between 100% and 0% state of charge. An individual battery cell still has an open circuit voltage of ˜2.7 volts when at 0% state of charge and enough energy to create sparks and a fire risk when the cell is shredded during recycling operations. The configurations herein bring the stored energy in the battery cell below the 0% state of charge, down to a benign zero-energy state, discussed further below.
In
During this initial discharge period 250, excess energy may be directed to an inverter for distribution back out to grid 134. At interval 252, forced discharge occurs to reverse-bias the battery cell which is believed to induce breakdown of the cathode current collector by formation of dendrite-caused shorting of the copper current collector to render the cell benign, where rebound voltage is mitigated, at interval 254.
Clamping and cooling the pouch cell duplicates the conditions when installed in an EV module and prevents a single unconstrained pouch cell from overheating, ballooning, and bursting, which releases hazardous electrolyte and VOCs (Volatile Organic Compounds). With the present device, battery cells can be discharged rapidly and safely. For example, a cell can be discharged in 5 minutes at a rate of 12 C, which is substantially faster than a conventional 2 C peak discharge rate specified by cell OEMs, while additionally the disclosed system provides containment in the rare event of a cell fire.
The containment device may further include one or more side plates 311-1 . . . 311-4 (311 generally) in contact with the top plate 310-1 and/or the bottom plate 310-2 for forming a cavity 313 containing the compressed battery cells 110. The containment fixture 302 therefore encapsulates the battery cells 110 for mitigating any volatile response by the battery cells 110. The side plates 311 can be adjustable/movable to provide direct contact with the compressed battery cell for maintaining a tight encapsulation. In addition, the top plate 310-1 and/or the bottom plate 310-2 may also include a fixed or adjustable cell cavity surface configured to contact and compress the battery cell. For example, an adjustable surface 317 may be a floating plate attached to the top plate by a plurality of springs 319 or other resilient mechanism to conform the cavity 313 to the battery cells. The bottom plate 310-2 may also define a cell cavity configured to contain the compressed battery cell.
From within the containment fixture 302 of cell containment device 300, contact pads or points aligned with the terminals on the battery cells 110 extend through the plate 310 for electrical communication with discharge connections. In the example configuration, the electrical probes 315 are positioned within the cell cavity 313 of the bottom plate and extend through the bottom plate 310-2, in a noninterfering manner with any coolant lines 334 or spring-loaded attachments or clamps used to compress and secure the plates 310 together. The electrical probes 315 may include spring loaded electrical contact pins for biasing the probes to form a good connection with the battery cells 110, as substantial amperage can be expected. As indicated above, electrical communication with the battery cells 110 in the containment fixture 302 of cell containment device 300 allows discharge, monitoring, and forced discharge of the cells therein as shown in
Turning again to the fire and thermal management capabilities, a typical coolant for circulation through the coolant channel 334 such as tubes or vessels is water, which can connect to inlets and outlets 330, 332 via any suitable pumping apparatus. The coolant channel 334 may run in any suitable manner through the plates 310, such as a series of parallel linear runs or a serpentine “S” channel alternating side to side. The plates are preferably constructed of materials capable of withstanding the compressive forces while also providing sufficient heat transfer from the cells to the coolant. For example, aluminum construction of the plates and sides aids thermal transfer and non-combustability; copper would also provide excellent thermal properties. While the coolant flow runs through the plates 310 (and optionally through the sides 311), the fire suppression system supplies the fire suppressant through the top plate, the bottom plate, or both directly into the cavity 313 for drowning any fire or runaway reaction of the compressed battery cells 110. In sum, the cell containment device disclosed herein defines a complete compressed or clamped enclosure around the discharging battery cells 110 with fluid communication through internal channels 334 in the top and sides for thermal transfer, and fluid communication directly into the cavity 313 for fire suppression, using water, foam, inert gas/liquid such as nitrogen, or other suitable fire suppression fluid.
Residual charge is released, such as to grid 134, to drain off an excess of electrical energy, as disclosed at step 508. This involves connecting an inverter to invert the discharged DC current to AC phased with the grid, depicted at step 510. During grid discharge, residual energy voltage and current are monitored until a zero charge state is achieved, as shown at step 512. A check is performed, at step 514, to determine if a zero-charge state has been achieved. The zero-charge state still retains appreciable, and possibly dangerous, electrical energy in the cells. In use, Li-ion batteries are not fully discharged, but rather charged and discharged between a 100% and 0% state of charge. While battery and vehicle manufacturers have discretion around cell parameters, a typical battery cell has around 4.5V at 100% state of charge, and a 0% state of charge exhibits about 2.5-2.7V. It is at this point that Li-ion batteries should be recharged to encourage cell longevity and maximize a number of charge cycles over the battery cell service life.
Concurrently with discharge, a temperature monitoring system measures the temperature of the compressed cells 110, as depicted at step 516, and adjusts coolant flow though inlet 330 accordingly. A check is performed, at step 518, for runaway temperatures, and fire suppression may be invoked by flooding cavity 313 with inert suppression fluids via fire suppression port 340, as depicted at step 520.
Upon attaining the zero-charge state, based on predetermined voltage and current characteristics at probes 315, the discharge connections are switched to the reverse bias overdischarge voltage source, as disclosed at step 522. This applies a higher voltage to the negative battery terminal and a lower voltage to the positive terminal, in reverse polarity to what a normal charge cycle would perform. The forced discharge commences at zero-charge state. The reverse polarity power supply 312 continues until a zero-energy state of the battery cells is achieved, based on the check at step 524. The reverse bias voltage/current continues until cell rendered benign from internal short circuits at the current collector, as depicted at step 526.
While the system and methods defined herein have been particularly shown and described with references to embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.
