Battery cell discharge system and battery cell discharge method

Abstract

To provide a battery cell discharge system and a battery cell discharge method.SOLUTION: Forced discharge of Li-ion batteries for recycling extracts residual electrical energy from battery cells to avoid sudden and unexpected release of residual energy during recycling. A battery cell containment device applies a physical restraint to one or more battery cells, and engages positive and negative terminals of the cells for electrical communication. A cooling medium flows through a containment part for thermal transfer of 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 forces current through the anode to make the battery into a zero-energy state. The reverse voltage continues until internal short circuits resulting from degradation of current collectors in the battery render it benign.SELECTED DRAWING: Figure 3

Description

Background Art

[0001] Background 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 an electric motor is required to accelerate rapidly. Li-ion batteries include a current collector, typically a planar sheet of copper or aluminum, an electroactive material applied or deposited thereon, a conductive powder, and a binder. The electroactive material includes an anode electroactive material (typically graphite or carbon) and a cathode electroactive material (including metals such as lithium, nickel, manganese, cobalt, aluminum, iron, and phosphorus in a predetermined ratio), which defines the so-called "battery chemistry" of the Li-ion cell. In the recycling of Li-ion batteries, a large amount of electroactive material metals are recovered, which would otherwise typically need to be supplied from sources managed as a result of mining and refining.

Prior Art Documents

Patent Documents

[0002]

Patent Document 1

Summary of the Invention

Means for Solving the Problems

[0003] Summary The forced discharge of Li-ion batteries, such as battery cells and packs for EVs (electric vehicles), is carried out prior to the physical disassembly and agitation of the cells, in view of the recycling of battery materials including carbon and graphite, which are metals of the charge materials, and current collectors such as aluminum and copper. The forced discharge extracts residual electrical energy from the battery cells and prevents the sudden and unexpected release of the residual energy during recycling. The storage device applies physical restraint to one or more battery cells and connects the positive and negative terminals of the battery electrically by joining them. The storage device forms a rigid housing that clamps from above and below, physically compressing the battery cells to mitigate the generation of gaseous products due to forced discharge, but this can cause pressure to accumulate within the battery cells. The cooling medium flows through the storage device for the heat transfer of the extra heat generated during discharge. Depending on the residual charge remaining in the battery cells, the extra electrical energy is discharged through the positive and negative terminals to a fully discharged state. By applying a reverse voltage to effectively force a current through the anode and thereby reverse the polarity, the battery is brought to a zero-energy state. The reverse polarity causes a short circuit due to the degradation of the current collector of the battery and makes the battery safe. The suppression port in the storage device can release a fire suppressant in the event of a thermal runaway or fire during forced discharge.

[0004] More specifically, Li-ion batteries for EVs are often present in battery packs installed in the chassis of the vehicle. Each battery pack includes a number of interconnected battery cells, each having a structured arrangement consisting of a cathode material and an anode material connected to the positive and negative terminals. In the configuration of the present specification, the battery recycling of Li-ion cells includes physically disassembling the battery pack to obtain the individual battery cells therein for recycling, which usually involves crushing, shredding, and pulverizing, creating a granular mass (i.e., a black mass) of the contents of the battery cells.

[0005] Unfortunately, the conventional approach to battery cell recycling has the drawback that the battery pack in the recycling stream has an unknown state of charge depending on the vehicle provided, the number of years, and the end use. Physical crushing and shredding of the battery pack and / or cells can induce a sudden release of residual electrical energy, which can cause an explosion or fire. Accordingly, the configuration herein provides a forced discharge cell storage device that substantially overcomes the drawbacks of battery disassembly by rapidly moving residual electrical energy from the battery cells while controlling, suppressing excessive gas or exothermic reactions, making the battery cells safe or inert, and performing fire suppression through a drain port in the event of an accidental over-discharge.

[0006] More specifically, the configuration herein provides a battery cell storage device for high-speed and efficient discharge, comprising an upper plate disposed on a bottom plate for compressing at least one battery cell therebetween, and a coolant system having an inlet, an outlet, and coolant channels configured to circulate coolant through the upper plate, the bottom plate, or both. Accordingly, the rise in heat and pressure (gas expansion) is mitigated, and the fire suppression system is configured to supply a fire suppressant to the compressed battery cells in the event that a non-conforming cell results in an adverse outcome during discharge. Externally accessible electrical probes are arranged to make electrical contact with the terminals of the compressed battery cells for applying and controlling the discharge voltage.

[0007] Brief Description of the Drawings The foregoing and other features will become apparent from the following description of particular embodiments disclosed herein, as illustrated in the accompanying drawings in which like reference numerals refer to the same parts throughout different figures. The drawings are not necessarily to scale, and instead emphasis is placed upon illustrating the principles of the invention.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0009] Detailed Description A method of discharging a battery cell to a safe level for recycling using a storage device for protection in the case of discharge and when the battery cell undergoes an unexpected harmful reaction is shown below.

[0010] Figure 1 is a context diagram of a recycling environment 100 suitable for use in the configuration of this specification. Referring to Figure 1, in the flow of recycling Li-ion batteries, an end-of-life battery pack 105 is obtained from a vehicle 102. Typically, a battery pack having a physical case shaped to be mounted on the underside of the vehicle 102 according to the manufacturer's specifications includes a plurality of interconnected battery cells 110-1...110-N (collectively 110), and in many cases, is arranged in modules to optimize the layout and dimensions of the entire battery pack 105. Typically, to release the materials for recycling, the battery pack 105 and the cells 110 therein are physically shredded, chopped, and pulverized, and a granular product 120 of battery components, sometimes called a black mass, is released. These components provide valuable battery materials for recycling and often include nickel, manganese, cobalt, aluminum, lithium, and graphite, although any suitable battery chemistry can be employed. To be efficient, the formation of the black mass is a mechanically intensive process using a shredder 112, pulverization, and / or other physical agitation that causes random contact between the materials within the battery pack. Due to the high energy density of Li-ion batteries, such contact can cause a sudden release of any excess residual electrical energy remaining in the battery cells 110. In conventional processes, the sudden release of heat, gas, and flame can be somewhat unpredictable.

[0011] Once released, the extraction of the granular product (black mass) 120, which includes cathode material, anode material, current collector, and casing material, forms a leaching solution 122 containing the desired charge material metal at an adjustable ratio as disclosed in incorporated by reference (Patent Document 1) and its continuing applications. The leaching solution 122 is fed for newly recycled battery cells through a coprecipitation reaction 124 to recover the recycled cathode material precursor 126 (pCAM, i.e., precursor cathode active material). Typically, the precursor is in the form of a hydroxide of the above metals based on the battery chemistries of the individual cells and packs that can vary in the recycling stream.

[0012] To reduce the risk of residual electrical energy being suddenly or uncontrolled released, it may be beneficial to fully discharge the battery cell before disassembling. The forced discharge method shown below applies a reverse potential power source to the battery cell to bring the battery cell to a safe state and return the extra residual electrical energy 130 to the grid 134.

[0013] While not wishing to be bound by any particular theory, it is believed that over-discharging a cell with a state of charge less than 0% causes dissolution of the copper current collector, causes an internal short circuit between the cathode and anode of the cell, and dissipates the residual cell energy as heat. The over-discharge process can be accelerated by using the forced discharge approach discussed herein, in which a reverse potential power source is attached to the cell and can accelerate the plating of copper that is thought to be involved in the formation of the internal short circuit.

[0014] By a predetermined calculation, the amount of energy delivered by the reverse potential power source can be estimated. During delivery, the voltage and current of the cell are monitored and, if necessary, this process is repeated until the voltage and current reach zero and / or until the cell reaches an energy-zero state.

[0015] FIG. 2 is a graph 200 of battery cell characteristics during discharge. Referring to FIGS. 1-2, the battery cell characteristics of voltage 210, current 220, and temperature 230 of the battery cell 110 during discharge are shown along the time axis 202 (horizontal). Conventional approaches to cell discharge require an excessive time of about 3 hours. For example, in a conventional approach, the battery cell is immersed in an aqueous conductive salt solution to offset the temperature and discharge the charge, which is a time-consuming process and is prone to failure if the battery cell ruptures and contaminates the electrolyte with the saline solution.

[0016] Lithium-ion battery cells typically cycle between 100% and 0% state of charge. Individual battery cells have an open-circuit voltage of about 2.7 volts at 0% state of charge and have sufficient energy that, if the cell is shredded during recycling operations, can cause a spark and pose a fire hazard. The configuration herein reduces the stored energy in the battery cell below 0% state of charge and further reduces it to a safe zero-energy state described later.

[0017] In Figure 2, for an exemplary discharge, as indicated by arrow 203, the battery module is discharged from 26.8 V to 0 V and the individual cells within the module are discharged from 3.5 V to 0 V over 9 minutes and 21 seconds. Looking at voltage 210 simultaneously, when discharge current 220 remains constant, the voltage decreases and approaches zero after about 6 minutes. In this example, the battery was discharged at about 250 amperes and the voltage dropped to zero 22 minutes and 41 seconds after arrow 204 when temperature 230 rose to 55.8 °C. However, after 2 minutes, the voltage has returned to 5 V as indicated by arrow 207. Of note is vertical line 206 where the voltage reaches zero and the current levels off at 10 A. In the configuration herein, a forced discharge current of reverse polarity is connected and applied at this threshold because the low voltage and moderate current mitigate a sudden surge in electrical energy. Additionally, a shorting wire can be installed to ensure the end of the discharge process at 24 minutes and 26 seconds (arrow 205), preventing the rebound voltage from presenting a potentially unstable battery state.

[0018] During this initial discharge period 250, the excess energy may be directed to an inverter to return it to the grid 134. In section 252, forced discharge occurs, reverse biasing the battery cell, which is thought to induce destruction of the cathode current collector by the formation of dendrites that cause a short circuit of the copper current collector in section 254 to bring the battery cell to a safe state with the rebound voltage mitigated.

[0019] Figure 3 is a schematic side view of a cell storage device 300 used with the forced discharge process described herein. Referring to FIGS. 1-3, discharging the individual pouch cells 110 to a zero energy state involves clamping one or more cells 110 between an upper plate 310-1 and a bottom plate 310-2 (collectively plates 310, and collectively storage fixture 302), and performing forced discharge with a power supply 312 of reverse polarity following discharge by an electronic load until a zero energy state is reached, which can be done quickly and efficiently, such as at a discharge current of 12C for about 5 minutes. One or both of the plates 310 are equipped with a coolant system and a fire suppression system. The clamps or hinges are configured to compress the battery cells between the upper and bottom plates. For example, clamps 305-1 and 305-2 secure an array of cells surrounded by the storage fixture 302 and prevent the spread of cell fires by discharging a fire suppressant into the storage fixture to extinguish any fires. Each cell is electrically connected to a control system for discharge and can be inspected by a spring-loaded electrical probe or terminal 315-1...315-2 for short circuit or open defects by the control system prior to discharge, so that defective cells can be removed from the process and isolated using another process. The individual electrical contacts allow the control system to connect the cell array in parallel or series configuration.

[0020] By clamping and cooling the pouch cells, the state when installed in an EV module is reproduced, preventing a single unconstrained pouch cell from overheating, swelling, and rupturing and releasing harmful electrolytes and VOCs (volatile organic compounds). Using this device, the battery cells can be discharged quickly and safely. For example, the cells can be discharged at a rate of 12C in 5 minutes, which is considerably faster than the conventional 2C peak discharge rate specified by the cell OEM. Additionally, the disclosed system provides containment in the rare event of a cell fire.

[0021] FIG. 4 is a perspective view of a specific configuration of the cell storage device of FIG. 3. Referring to FIGS. 1-4, the battery cell storage fixture 302 is disposed above the bottom plate 310-2 and includes an upper plate 310-1 that compresses at least one battery cell 110 therebetween (three examples 110-1, 110-2, and 110-3 are shown). The storage device further includes a coolant system having an inlet 330, an outlet 332, and coolant channels 334 configured to circulate coolant within the upper plate 310-1, the bottom plate 310-2, or both. For example, the coolant channels may provide a serpentine path for circulating coolant within the bottom plate. Similarly, the fire suppression system is typically configured to supply a fire suppressant to the compressed battery cells through an inlet 340 for providing fluid access to the cells stored within the storage fixture 302. Both the coolant and the fire suppressant may be water, although the coolant preferably flows through the upper and / or bottom plates similar to a heat exchanger or radiator, while the fire suppressant inlet 340 directs the flow of the suppressant into the interior of the fixture to immerse the battery cells. The electrical probe 315 is disposed to make electrical contact with the terminals of the compressed battery cells.

[0022] The storage device may further include one or more side plates 311-1...311-4 (collectively 311) that contact the upper plate 310-1 and / or the bottom plate 310-2 to form a cavity 313 that contains the compressed battery cell 110. Thus, the storage fixture 302 of the cell storage device encloses the battery cell 110 to mitigate unstable reactions by the battery cell 110. The side plates 311 can be adjustable / movable to directly contact the compressed battery cell so as to maintain a secure enclosure. Additionally, the upper plate 310-1 and / or the bottom plate 310-2 may further include a fixed or adjustable cell cavity surface configured to contact and compress the battery cell. For example, the adjustable surface 317 may be a floating plate attached to the upper plate by a plurality of springs 319 or other elastic mechanisms to conform the cavity 313 to the battery cell. The bottom plate 310-2 can also define a cell cavity configured to store the compressed battery cell.

[0023] From within the storage fixture 302 of the cell storage device 300, contact pads or contacts aligned with the terminals in the battery cell 110 extend through the plate 310 for electrical communication with the discharge connection. In this exemplary configuration, the electrical probe 315 is disposed within the cell cavity 313 of the bottom plate and extends through the bottom plate 310-2 so as not to interfere with the coolant line 334, or the spring-type attachment or clamp used to compress and secure the plates 310 together. The electrical probe 315 can include a spring-type electrical contact pin to bias the probe for forming a good connection with the battery cell 110 since a significant number of amperes can be expected. As described above, electrical communication with the battery cell 110 within the storage fixture 302 of the cell storage device 300 enables discharging, monitoring, and forced discharging of the middle cells, as shown in FIG. 2.

[0024] Turning again to fire and heat management capabilities, a typical coolant for circulating through a coolant channel 334, such as a tube or container, is water, which can be connected to an inlet 330 and an outlet 332 via any suitable pumping device. The coolant channel 334 can flow through the plate 310 in any suitable manner, such as a series of parallel straight paths or an "S" channel that snakes back and forth. The plate is preferably composed of a material that can withstand compressive forces while allowing sufficient heat transfer from the cell to the coolant. For example, plates and sides composed of aluminum aid in heat transfer and non-flammability, although copper would also provide excellent thermal properties. While the coolant flows through the plate 310 (and optionally the side 311), the fire suppression system directly supplies a fire suppressant into the cavity 313 through the upper plate, the bottom plate, or both to suppress a fire or runaway reaction in the compressed battery cell 110. That is, the cell storage device disclosed herein provides fluid communication through the upper and side internal channels 334 for heat transfer and direct fluid communication to the cavity 313 for fire suppression using an inert gas / liquid such as water, foam, nitrogen, or other suitable fire suppression fluid, defining a fully compressed or clamped housing around the discharge battery cell 110.

[0025] FIG. 5 is a flowchart 500 of a forced discharge operation using the storage device of FIGS. 3 and 4. Referring to FIGS. 1-5, a method of discharging a battery cell via a reverse bias over-discharge voltage involves, in step 502, securing the cell 110 between the upper and lower plates of the device, such as within the cavity 313, thereby enclosing or encapsulating it within the storage fixture 302 of the device. The storage fixture 302 encloses and secures the battery cell 110 while maintaining electrical communication with the battery cell from an external probe or contact. The terminals on the cell are aligned with the probe contacts within the storage device such that, as depicted in step 504, the probe 315 extends through the plate 310 for external connection. The discharge connection is made at the distal / external end of the probe external to the storage fixture of the device, as shown in step 506. In other words, the electrical connection outside the storage device passes through the plate and extends to contact the battery cell.

[0026] The residual charge is discharged to the grid 134 or the like to discharge excess electrical energy, as disclosed in step 508. This includes connecting to an inverter, as depicted in step 510, to convert the discharged DC current to AC in phase with the grid. During grid discharge, the voltage and current of the residual energy are monitored until they reach a zero charge state, as shown in step 512. A check is made in step 514 to determine whether the zero charge state has been achieved. Even at the zero charge state, there is still a significant, and in some cases dangerous, amount of electrical energy remaining in the cell. During use, a Li-ion battery is not fully discharged and is charged and discharged between 100% and 0% state of charge. Battery and vehicle manufacturers have discretion regarding cell parameters, but a typical battery cell is approximately 4.5V at 100% state of charge and shows approximately 2.5 - 2.7V at 0% state of charge. At this point, the Li-ion battery should be charged to extend its life and maximize the number of charge cycles over the life of the battery cell.

[0027] Simultaneously with the discharge, the temperature monitoring system measures the temperature of the compressed cell 110 and adjusts the flow of the coolant through the inlet 330 accordingly, as depicted in step 516. At step 518, a check for runaway temperature is made, and fire suppression is carried out by filling the cavity 313 with an inert suppression fluid through the fire suppression port 340, as shown in step 520.

[0028] When the zero charge state is achieved, based on the predetermined voltage and current characteristics of the probe 315, the discharge connection is switched to the reverse bias over-discharge power supply as disclosed in step 522. As a result, with a polarity opposite to that of a normal charging cycle, the higher voltage is applied to the negative terminal of the battery, and the lower voltage is applied to the positive terminal of the battery. The forced discharge starts from the zero charge state. The reverse-polarity power supply 312 continues until the zero energy state of the battery cell is achieved based on the confirmation in step 524. The reverse bias voltage / current continues as depicted in step 526 until the cell becomes safe against internal short circuit of the current collector.

[0029] The systems and methods defined herein have been shown and described with particular reference to their embodiments, but it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as encompassed by the appended claims.

Explanation of Signs

[0030] 100 Recycling environment 102 Vehicle 105 Battery pack 110 Battery cell 112 Shredder 120 Granular product 122 Leaching solution 124 Coprecipitation reaction 126 Cathode material precursor 130 Residual electrical energy 134 Grid 200 Graph 202 Time axis 203 Arrow 204 Arrow 205 Arrow 206 Vertical line 207 Arrow 210 Voltage 220 Current 230 Temperature 250 Initial discharge period 300 Cell storage device 302 Storage fixture 305-1 Clamp 305-2 Clamp 310-1 Upper Plate 310-2 Bottom Plate 311 Side Plate 312 Reverse Polarity Power Supply 313 Cavity 315 Electrical Probe 315-1 Terminal 315-2 Terminal 317 Surface 319 Spring 330 Inlet 332 Outlet 334 Coolant Channel 340 Inlet 500 Flowchart

Claims

1. A battery cell storage device, comprising: an upper plate disposed above a bottom plate and compressing at least one battery cell therebetween; a coolant system having an inlet, an outlet, and coolant channels, and configured to circulate coolant through the upper plate, the bottom plate, or both; a fire suppression system configured to supply a fire suppressant to the compressed battery cell; and an electrical probe disposed to make electrical contact with a terminal of the compressed battery cell. The battery cell storage device as described above.

2. The battery cell storage device according to claim 1, further comprising one or more side plates in contact with the upper plate or the bottom plate, forming a cavity containing the compressed battery cell.

3. The battery cell storage device according to claim 1, wherein the upper plate includes a cell cavity configured to store the compressed battery cell.

4. The battery cell storage device according to claim 1, wherein the upper plate includes a floating plate attached to the upper plate by a plurality of springs.

5. The battery cell storage device according to claim 1, wherein the bottom plate includes a cell cavity configured to store the compressed battery cell.

6. The battery cell storage device according to claim 5, wherein the electrical probe is disposed within the cell cavity of the bottom plate.

7. The battery cell storage device according to claim 1, wherein the electrical probe is a spring-type electrical contact pin.

8. The battery cell storage device according to claim 1, wherein the upper plate and the bottom plate include cell cavities configured to store the compressed battery cell.

9. The battery cell storage device according to claim 1, wherein the coolant system circulates the coolant in the bottom plate from the inlet through the coolant channels to the outlet.

10. The battery cell storage device according to claim 1, wherein the coolant is water.

11. The battery cell storage device according to claim 1, wherein the fire suppression system supplies the fire suppressant to the compressed battery cell through the upper plate, the bottom plate, or both.

12. The battery cell storage device according to claim 11, wherein the fire suppression system supplies the fire suppressant through the bottom plate.

13. The battery cell storage device according to claim 5, wherein the fire suppression system supplies the fire suppressant to the cell cavity of the bottom plate.

14. The battery cell storage device according to claim 1, wherein the fire suppressant is liquid nitrogen or water.

15. The battery cell storage device according to claim 1, further comprising a clamp or hinge configured to compress the battery cell between the upper plate and the bottom plate.

16. The battery cell storage device according to claim 1, further comprising a temperature monitoring system for measuring the temperature of the compressed cell.

17. A battery cell discharge system including a battery cell storage device and a reverse bias over-discharge device, wherein the battery cell storage device An upper plate disposed above the bottom plate and configured to compress at least one battery cell therebetween; A coolant system having an inlet, an outlet, and coolant channels and configured to circulate coolant through the upper plate, the bottom plate, or both; A fire suppression system configured to supply a fire suppressant to the compressed battery cell; And an electrical probe disposed to make electrical contact with the terminals of the compressed battery cell A battery cell discharge system comprising.

18. A method of discharging a battery cell, comprising: Placing at least one battery cell In a battery cell storage device comprising an upper plate disposed above a bottom plate and configured to compress at least one battery cell therebetween; A coolant system having an inlet, an outlet, and coolant channels and configured to circulate coolant through the upper plate, the bottom plate, or both; A fire suppression system configured to supply a fire suppressant to the compressed battery cell; And an electrical probe disposed to make electrical contact with the terminals of the compressed battery cell Compressing the battery cell between the upper plate and the bottom plate; Applying a reverse bias over-discharge voltage to the terminals to discharge the battery cell to a zero energy state A method comprising.

19. Coupling the electrical probe to direct current from the compressed battery cell to a power distribution grid; Flowing the current through an inverter that generates an AC (alternating current) signal before flowing the current through the power distribution grid The method according to claim 18, further comprising.

20. Determining when the compressed battery cell reaches a zero charge state based on measured values of current and voltage; ​ When the zero charge state is reached, applying the reverse bias over-discharge voltage to the compressed battery cell to achieve a zero energy state due to internal degradation of the current collector within the compressed battery cell The method according to claim 18, further comprising.

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