Battery cell discharge system and battery cell discharge method

Abstract

Forced discharge of the Li-ion battery for reuse can extract residual energy in the battery cell, thereby avoiding sudden unexpected release of residual energy during reuse. The cell enclosure apparatus applies a physical constraint to one or more cells and joins positive and negative terminals on the cells for electrical communication. A cooling medium flows through the enclosure for heat transfer of excess heat generated during the discharge. According to the residual electric quantity in the battery unit, redundant electric energy is discharged to a zero charge state through the positive terminal and the negative terminal. The reverse voltage forces the current to pass through the anode, so that the battery is in a zero-energy state. The reverse voltage is continued until the battery becomes benign due to internal shorting caused by degradation of the current collector in the battery.

Description

Background Art

[0001] Lithium-ion (Li-ion) batteries are the preferred chemistry for secondary (rechargeable) batteries in high-discharge applications where the motor needs to accelerate quickly, such as electric vehicles (EVs) and power tools. Li-ion batteries include charge materials, conductive powders, and binders applied or deposited on a current collector (usually a planar copper or aluminum sheet). The charge materials include an anode charge material (usually graphite or carbon) and a cathode charge material (including a predetermined proportion of metals such as lithium, nickel, manganese, cobalt, aluminum, iron, and phosphorus), thereby defining the so-called "battery chemistry" of a Li-ion battery cell. The reuse of Li-ion batteries recovers a large amount of charge material metals that would otherwise typically need to be collected from controlled sources through mining and refining. Summary of the invention

[0002] Forced discharge of Li-ion batteries, such as EV (electric vehicle) battery cells and battery packs, is performed prior to physical disassembly and stirring of the battery cells in order to reuse battery materials, including charge materials metals, carbon and graphite, and current collectors (such as aluminum and copper). Forced discharge can extract residual electrical energy in the battery cells, thereby avoiding sudden and accidental release of residual energy during reuse. The enclosure applies physical constraints to one or more battery cells and joins the positive and negative terminals on the battery for electrical communication. The enclosure forms a rigid housing that clamps the top and bottom and physically compresses the battery cells to reduce any gaseous products generated by forced discharge, which may cause pressure accumulation in the battery cells. A cooling medium flows through the enclosure to transfer heat to any excess heat generated during discharge. Depending on the residual charge remaining in the battery cell, the excess electrical energy is discharged to a zero charge state through the positive and negative terminals. A reverse voltage is applied to effectively force current through the anode, thereby forcing a polarity reversal to bring the battery to a zero energy state. Reversing polarity will cause a short circuit due to degradation of the current collectors in the cell, rendering the cell benign. If thermal runaway or fire occurs during forced discharge, a fire extinguishing port in the closure device allows injection of an extinguishing agent.

[0003] In more detail, the Li-ion batteries of an EV are located in a battery pack, which is typically mounted to the vehicle chassis. Each battery pack includes a plurality of interconnected battery cells, each of which includes a structured arrangement of cathode material and anode material leading to a positive terminal and a negative terminal. For the configuration herein, battery recycling of Li-ion battery cells involves physically disassembling the battery pack to obtain individual battery cells therein for recycling, which typically involves crushing, shredding, and grinding to produce a granular mass (i.e., a black mass) of the battery cell contents.

[0004] Unfortunately, conventional methods of recycling battery cells suffer from a drawback in that the state of charge of the battery pack in the recycling stream is unknown and depends on the donor vehicle, its age, and the last use. Physically crushing and shredding the battery pack and / or battery cells may cause a sudden release of residual energy, resulting in an explosion or fire. Therefore, the configuration of the present invention substantially overcomes the shortcomings of battery disassembly by providing a battery cell enclosure for forced discharge to quickly transfer residual energy from the battery cell in a controlled manner, suppress excess gas or exothermic reactions, render the battery cell benign or inert, and implement fire suppression via a water injection port in the unlikely event of excess discharge.

[0005] In further detail, the configuration of the present invention provides a battery cell enclosure device for fast and efficient discharge, the battery cell enclosure device including a top plate and a coolant system, the top plate is positioned above the bottom plate so that at least one battery cell is compressed between the top plate and the bottom plate, the coolant system includes an inlet, an outlet and a coolant channel, and is configured to circulate the coolant through the top plate, the bottom plate or both. Thus, the increase in heat and pressure (gas expansion) is mitigated, and the fire extinguishing system is configured to supply fire extinguishing agent to the compressed battery cell in the unlikely event that a non-conforming battery cell encounters adverse discharge consequences. An externally accessible electrical probe is positioned to provide electrical contact with the terminals of the compressed battery cell to apply and control the discharge voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The above and other features will be apparent from the following description of specific embodiments disclosed herein, as illustrated in the accompanying drawings, in which like reference numerals refer to the same parts throughout the different views. The drawings are not necessarily drawn to scale, emphasis instead being placed upon illustrating the principles of the invention.

[0007] Figure 1 is a context diagram of a reuse environment suitable for use with the configuration in this article;

[0008] Figure 2 is a graph of battery cell characteristics during discharge;

[0009] Figure 3 is a side view of a battery cell enclosure device for forced discharge;

[0010] Figure 4 yes Figure 3 a perspective view of the configuration of the closure device; and

[0011] Figure 5 is used Figure 3 and Figure 4 Flowchart of the forced discharge operation of a closed device. DETAILED DESCRIPTION

[0012] A method for discharging a battery cell to a safe level for reuse is described below, using a closed device for discharging and protecting the battery cell from unexpected situations where the battery cell may react undesirably.

[0013] Figure 1 is a context diagram of a reuse environment 100 suitable for use with the configurations herein. Figure 1 , in a Li-ion battery recycling stream, an end-of-life battery pack 105 is obtained from a vehicle 102. The battery pack - typically having a physical housing shaped to be attached to the bottom surface of the vehicle 102 according to manufacturer specifications - includes a plurality of interconnected battery cells 110-1...110-N (generally referred to as 110), which are typically arranged in a module form to optimize the placement and size of the entire battery pack 105. Typically, in order to release materials for recycling, the battery pack 105 and the battery cells 110 therein are physically ground, shredded and crushed to release a granular classification 120 of battery components, sometimes referred to as black agglomerates. These components provide valuable battery materials for recycling, typically including nickel, manganese, cobalt, aluminum, lithium and graphite, but any suitable battery chemistry can be used. To improve efficiency, the formation of black agglomerates is a mechanically intensive process that uses a shredder 112, grinding and / or other physical agitation to cause random contact between materials in the battery pack. Due to the high energy density of Li-ion batteries, such contact may result in a sudden release of any excess residual electrical energy remaining in the battery cell 110. In conventional processes, the sudden release of heat, gas, and flame may be somewhat unpredictable.

[0014] Once released, extraction of the particulate assortment (black mass) 120 including cathode material, anode material, current collector and casing material forms a leach solution 122 containing the desired charge material metals in proportions that can be adjusted as desired, as disclosed in U.S. Pat. No. 9,834,827 and its continuation applications, which are incorporated by reference. The leach solution 122 undergoes a coprecipitation reaction 124 to recover a cathode material precursor 126 (pCAM or precursor cathode active material) for reuse, which is then used in a new reused battery cell. Typically, the precursors are hydroxide forms of the metals discussed above based on the battery chemistry of individual battery cells and batteries, which can change in the reuse stream.

[0015] It is beneficial to fully discharge the battery cells before disassembly to reduce the risk of sudden or uncontrolled release of residual energy. The forced discharge method described below applies a reverse potential power supply to the battery cells so that these battery cells are in a benign state and returns excess residual energy 130 to the grid 134.

[0016] Without wishing to be bound by any particular theory, it is believed that overdischarging a battery cell below a 0% state of charge causes the copper current collector to decompose, thereby creating an internal short circuit in the cathode and anode of the battery cell and dissipating the remaining battery cell energy in the form of heat. The overdischarge process can be accelerated by using the forced discharge method discussed herein, in which a reverse potential power source is attached to the battery cell, which can accelerate the copper plating believed to be involved in creating the internal short circuit.

[0017] The predetermined calculation can estimate the amount of energy to be delivered by the reverse potential power supply. During delivery, the voltage and current of the battery cell are monitored, and the process is repeated as needed until zero voltage and current are achieved, and / or until a zero energy state of the battery cell is reached.

[0018] Figure 2 is a graph 200 of battery cell characteristics during discharge. Figure 1 to Figure 2 , the cell characteristics of the discharged cell 110, namely, voltage 210, current 220, and temperature 230 are shown along the time axis 202 (horizontally). Conventional methods of discharging a cell require more than about 3 hours. For example, conventional methods involve immersing the cell in a conductive salt water solution to counteract the temperature and discharge the charge, which is a slow process and prone to failure if the cell ruptures and contaminates the salt water with electrolyte.

[0019] Lithium-ion battery cells are typically cycled between 100% and 0% state of charge. At 0% state of charge, the open circuit voltage of an individual battery cell is still ~2.7 volts, and the energy of the battery cell is sufficient to create a spark and flame risk when shredded during a recycling operation. The configuration herein allows the energy stored in the battery cell to drop below 0% state of charge to a benign zero energy state discussed further below.

[0020] exist Figure 2In the example, as shown by arrow 203, the example discharge discharges the battery module from 26.8V to 0V and the individual battery cells in the module from 3.5V to 0V over a duration of 9 minutes and 21 seconds. Observe the voltage 210 at the same time, when the discharge current 220 is kept constant, the voltage drops until the voltage approaches zero after about 6 minutes. In this example, the battery is discharged at about 250amps, and when the temperature 230 rises to 55.8°C, the voltage drops to zero after 22 minutes and 41 seconds (arrow 204). However, 2 minutes later, the voltage rebounds to 5V, as shown by arrow 207. It is worth noting that the vertical line 206, at this time, the voltage is 0 and the current stabilizes at 10A. The configuration of this article connects and applies a reverse polarity forced discharge current at this threshold, because the low voltage and moderate current will mitigate the sudden surge of electrical energy. In addition, a short line can also be installed to ensure that the discharge process ends after 24 minutes and 26 seconds (arrow 205), thereby preventing the rebound voltage from presenting a potentially volatile battery state.

[0021] During this initial discharge period 250, excess energy may be directed to the inverter for distribution back to the grid 134. At interval 252, a forced discharge occurs to reverse bias the cell, which is believed to cause cathode current collector breakdown by forming a dendrite-induced copper current collector short, rendering the cell benign, wherein at interval 254 the bounce voltage is mitigated.

[0022] Figure 3 is a schematic side view of a battery cell enclosure 300 for use in conjunction with the forced discharge process described herein. Figures 1 to 3, individual soft-pack battery cells 110 can be discharged to a zero energy state quickly and efficiently (e.g., within about 5 minutes and at a discharge current of 12C) by clamping one or more battery cells 110 between a top plate 310-1 and a bottom plate 310-2 (generally referred to as plates 310 and collectively referred to as closed fixtures 302) and discharging with an electronic load, followed by forced discharge to a zero energy state with a reverse polarity power supply 312. One or both of the plates 310 are provided with a coolant system and a fire extinguishing system. The clamps or hinges are configured to compress the battery cells between the top plate and the bottom plate. For example, clamps 305-1 and 305-2 secure the battery cell array enclosed in the closed fixture 302 to prevent the battery cell fire from spreading by allowing the closed fixture to inject a fire extinguishing agent to extinguish any flame. Electrical contact is made to the battery cells by spring loaded electrical probes or terminals 315-1 ... 315-2, which allows each battery cell to be electrically connected to the control system for discharge and also allows it to be checked by the control system for short circuit or open circuit defects before discharge so that the defective battery cells can be removed from the process and de-energized using an alternative process. The separate electrical contacts allow the control system to connect the battery cell array in a parallel or series configuration.

[0023] Clamping and cooling the pouch cells replicates the conditions when installed in an EV module and prevents individual unconstrained pouch cells from overheating, swelling, and bursting, thereby releasing hazardous electrolytes and VOCs (volatile organic compounds). Using the apparatus of the present invention, the cells can be discharged quickly and safely. For example, the cells can be discharged at a 12C rate in 5 minutes, which is substantially faster than the traditional 2C peak discharge rate specified by the cell OEM, while in addition, the disclosed system provides containment in the rare event of a cell fire.

[0024] Figure 4 yes Figure 3 A perspective view of a specific configuration of a battery cell enclosure device. Figures 1 to 4, the battery cell enclosed fixture 302 includes a top plate 310-1, which is positioned above the bottom plate 310-2 so that at least one battery cell 110 (three, i.e., 110-1, 110-2, and 110-3, are shown as an example) is compressed between the top plate and the bottom plate. The closed device further includes a coolant system, which includes an inlet 330, an outlet 332, and a coolant channel 334, and is configured to circulate the coolant in the top plate 310-1, the bottom plate 310-2, or both. For example, the coolant channel can provide a serpentine path for circulating the coolant in the bottom plate. Similarly, the fire extinguishing system is configured to supply a fire extinguishing agent to the compressed battery cells, typically via an inlet 340 for fluid to enter the (multiple) battery cells contained in the enclosed fixture 302. Both the coolant and the extinguishing agent may be water, but the coolant preferably flows through the top and / or bottom plates (similar to a heat exchanger or radiator), while the extinguishing agent inlet 340 directs the extinguishing agent flow into the interior of the fixture to immerse the battery cells. The electrical probe 315 is positioned to provide electrical contact with the terminals of the compressed battery cells.

[0025] The enclosed device may further include one or more side plates 311-1 ... 311-4 (generally referred to as 311) in contact with the top plate 310-1 and / or the bottom plate 310-2 to form a cavity 313 for accommodating the compressed battery cell 110. Therefore, the enclosed fixture 302 encapsulates the battery cell 110 to mitigate any volatile reaction of the battery cell 110. The side plate 311 may be adjustable / removable to provide direct contact with the compressed battery cell to maintain a tight package. In addition, the top plate 310-1 and / or the bottom plate 310-2 may also include a fixed or adjustable battery cell cavity surface that is configured to contact and compress the battery cell. For example, the adjustable surface 317 may be a floating plate that is attached to the top plate by a plurality of spring members 319 or other elastic mechanisms to conform the cavity 313 to the battery cell. The bottom plate 310-2 may also define a battery cell cavity configured to accommodate a compressed battery cell.

[0026] From within the enclosure fixture 302 of the battery cell enclosure 300, contact pads or contact points aligned with the terminals on the battery cells 110 extend through the plate 310 for electrical communication with the discharge connector. In an example configuration, an electrical probe 315 is positioned within the battery cell cavity 313 of the base plate and extends through the base plate 310-2 in a manner that does not interfere with any coolant lines 334 or spring-loaded attachments or clamps used to compress and secure the plates 310 together. The electrical probe 315 may include a spring-loaded electrical contact pin for biasing the probe to form a good connection with the battery cell 110 as high amperages are expected. As described above, electrical communication with the battery cell 110 in the enclosure fixture 302 of the battery cell enclosure 300 allows for the following: Figure 2 The battery cells therein are discharged, monitored and forcefully discharged as shown.

[0027] Turning again to flame and thermal management capabilities, a typical coolant that is circulated through coolant channels 334, such as pipes or containers, is water, which can be connected to the inlet and outlet ports 330, 332 via any suitable pumping device. The coolant channels 334 can pass through the plate 310 in any suitable manner, such as a series of parallel linear channels or serpentine "S" channels alternating on both sides. Preferably, the plate is constructed of a material that can withstand the compression force while providing sufficient heat transfer from the battery cells to the coolant. For example, aluminum construction of the plate and sides helps with heat transfer and non-flammability; copper will also provide excellent thermal performance. As the coolant flows through the plate 310 (and optionally through the sides 311), the fire extinguishing system supplies fire extinguishing agent directly into the cavity 313 through the top plate, the bottom plate, or both to drown out any flames or runaway reactions of the compressed battery cells 110. In summary, the battery cell enclosure disclosed herein defines a complete compressed or clamped enclosure around the discharge battery cell 110, is fluidically connected through internal channels 334 on its top and sides for heat transfer, and is fluidly connected directly to the cavity 313 for fire extinguishing using water, foam, inert gas / liquid such as nitrogen, or other suitable fire extinguishing fluids.

[0028] Figure 5 is used Figure 3 and Figure 4 500 is a flow chart of a forced discharge operation of a closed device. Figures 1 to 5, a method for discharging a battery cell via a reverse bias over-discharge voltage includes, at step 502, securing a battery cell 110 between a top plate and a bottom plate of a device (e.g., within a cavity 313) so that it is enclosed or enclosed within a closed fixture 302 of the device. The closed fixture 302 encloses and secures the battery cell 110 while maintaining electrical communication between an external probe or contact and the battery cell. The terminals on the battery cell are aligned with the probe contacts in the closed device so that the probe 315 extends through the plate 310 for external connection, as depicted at step 504. A discharge connection is made to the distal / external end of the probe outside the closed fixture of the device, as shown at step 506. In other words, the electrical connection external to the closed device passes through the plate and extends until it contacts the battery cell.

[0029] The residual charge is discharged to, for example, the grid 134 to drain the excess electrical energy, as disclosed at step 508. This involves connecting an inverter to invert the discharged DC current into an AC current in phase with the grid, depicted at step 510. During grid discharge, the voltage and current of the residual energy are monitored until a zero state of charge is achieved, as shown at step 512. A check is performed at step 514 to determine whether a zero state of charge has been achieved. A zero state of charge still retains considerable and potentially dangerous electrical energy in the battery cell. When in use, the Li-ion battery is not fully discharged, but rather charged and discharged between 100% and 0% states of charge. Although battery and vehicle manufacturers can determine the battery cell parameters at their discretion, a typical battery cell has a voltage of about 4.5V at 100% state of charge and a voltage of about 2.5V to 2.7V at 0% state of charge. At this point, the Li-ion battery should be recharged to extend the battery cell life and maximize the number of charging cycles within the battery cell life.

[0030] While discharging, the temperature monitoring system measures the temperature of the compressed battery cells 110 (as depicted at step 516) and accordingly adjusts the coolant flow through the inlet 330. At step 518, a runaway temperature is checked and fire extinguishing can be implemented by injecting an inert fire extinguishing fluid into the cavity 313 via the fire extinguishing port 340, as depicted at step 520.

[0031] After reaching a zero state of charge, the discharge connection is switched to a reverse bias over-discharge voltage source based on predetermined voltage and current characteristics at the probe 315, as disclosed at step 522. A higher voltage is applied to the negative battery terminal and a lower voltage is applied to the positive terminal, with polarity opposite to that exhibited by a normal charge cycle. The forced discharge begins from a zero state of charge. Based on the check at step 524, the reverse polarity power supply 312 continues until a zero energy state of the battery cell is achieved. The reverse bias voltage / current continues until the battery cell becomes benign due to an internal short circuit occurring at the current collector, as depicted at step 526.

[0032] While the systems and methods defined herein have been particularly shown and described with reference to embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the scope of the invention as encompassed by the appended claims.

Claims

1. A battery cell sealing device, comprising: a top plate positioned above the bottom plate so that at least one battery cell is compressed between the top plate and the bottom plate, a coolant system comprising an inlet, an outlet, and coolant passages and configured to circulate a coolant through the top plate, the bottom plate, or both, a fire extinguishing system configured to supply a fire extinguishing agent to the compacted battery cell, and Electrical probes are positioned to provide electrical contact with the terminals of the compacted battery cell.

2. The battery cell enclosure device of claim 1, further comprising one or more side plates, the one or more side plates being in contact with the top plate or the bottom plate to form a cavity for accommodating the compressed battery cell.

3. The battery cell enclosure device according to claim 2, wherein: The side plates can be adjusted to contact the compressed battery cell.

4. The battery cell enclosure device according to claim 1, wherein: The top plate includes a battery cell cavity configured to receive the compacted battery cell.

5. The battery cell enclosure device according to claim 1, wherein: The top plate includes an adjustable surface that contacts the compressed battery cell.

6. The battery cell enclosure device according to claim 5, wherein: The adjustable surface is a floating plate attached to the top plate by a plurality of spring members.

7. The battery cell enclosure device according to claim 1, wherein: The base plate includes a battery cell cavity configured to receive the compacted battery cell.

8. The battery cell enclosure device according to claim 7, wherein: The electrical probes are positioned within the battery cell cavities of the base plate.

9. The battery cell enclosure device according to claim 1, wherein: These electrical probes are spring loaded electrical contact pins.

10. The battery cell enclosure device according to claim 1, wherein: The top plate and the bottom plate include battery cell cavities configured to receive the compacted battery cells.

11. The battery cell enclosure device according to claim 11, wherein: The coolant system circulates coolant within the base plate through the channel from the inlet to the outlet.

12. The battery cell enclosure device according to claim 1, wherein: The coolant is water.

13. The battery cell enclosure device according to claim 1, wherein: The fire extinguishing system supplies the fire extinguishing agent to the compressed battery cell through the top plate, the bottom plate, or both.

14. The battery cell enclosure device according to claim 13, wherein: The fire extinguishing system supplies the fire extinguishing agent through the base plate.

15. The battery cell enclosure device according to claim 7, wherein: The fire extinguishing system supplies the fire extinguishing agent into the battery cell cavity of the base plate.

16. The battery cell enclosure device according to claim 1, wherein: The extinguishing agent is liquid nitrogen or water.

17. The battery cell enclosure of claim 1, further comprising a clamp or hinge configured to compress the battery cell between the top plate and the bottom plate.

18. The battery cell enclosure of claim 1, further comprising a temperature monitoring system for measuring the temperature of the compressed battery cell.

19. A battery cell discharge system, comprising a battery cell sealing device and a reverse bias over-discharge device, wherein: The battery cell enclosure device comprises a top plate positioned above the bottom plate so that at least one battery cell is compressed between the top plate and the bottom plate, a coolant system comprising an inlet, an outlet, and coolant passages and configured to circulate a coolant through the top plate, the bottom plate, or both, a fire extinguishing system configured to supply a fire extinguishing agent to the compacted battery cell, and Electrical probes are positioned to provide electrical contact with the terminals of the compacted battery cell.

20. A method for discharging a battery cell, the method comprising: At least one battery cell is positioned within a battery cell enclosure, the battery cell enclosure comprising: a top plate positioned above the bottom plate so that at least one battery cell is compressed between the top plate and the bottom plate, a coolant system comprising an inlet, an outlet, and coolant passages and configured to circulate a coolant through the top plate, the bottom plate, or both, a fire extinguishing system configured to supply a fire extinguishing agent to the compacted battery cell; and electrical probes positioned to provide electrical contact with the terminals of the compressed battery cell so that the battery cell is compressed between the top plate and the bottom plate, and A reverse biased over-discharge voltage is applied to the terminals for discharging the battery cell to a zero energy state.

21. The method of claim 20, further comprising: engaging the electrical probes for directing electrical current from the compacted battery cell to a power distribution network; as well as Before passing the current to the power distribution network, the current passes through an inverter for generating an AC (alternating current) signal.

22. The method of claim 20, further comprising: determining when the compacted battery cell reaches a zero state of charge based on the current and voltage readings; as well as When the zero charge state is reached, the reverse bias over-discharge voltage is applied to the compacted battery cell to achieve a zero energy state due to internal degradation of the current collector in the compacted battery cell.

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