Forced battery discharge

Abstract

A method for discharging used batteries prior to disassembly and recycling involves recovering residual stored electrical energy by draining the battery to a zero state of charge and reverse biasing the battery to change the potential from the zero state of charge of about 2.7 V to a zero or near-zero energy state. The reverse bias reverses the normal operating polarity to induce reverse current flow, which continues upon the formation of an internal short circuit formed on the cathode current collector, leaving the battery with little to no energy storage for safe agitation and disassembly.

Description

[Background technology]

[0001] background Lithium-ion batteries (LIBs) have found widespread application in recent decades, especially in electric vehicles (EVs) and plug-in / hybrid electric vehicles (PHEVs) that are equipped with or directly powered by LIBs. LIBs are widely used in portable electronic devices, electric vehicles, and grid storage as primary power sources. LIBs offer considerable capabilities in terms of energy storage, or density, and discharge capacity, retaining residual electrical energy even after their useful charge / discharge performance has been deemed to have exceeded its useful lifespan. Summary of the Invention [Problem to be solved by the invention]

[0002] overview A method for discharging used batteries prior to disassembly and recycling involves draining the battery to a zero state of charge and recovering the residual stored electrical energy by reverse biasing the battery to change the potential from the zero state of charge of about 2.7 V to a zero or near-zero energy state. The reverse bias reverses the normal operating polarity, which is believed to create an internal short circuit on the cathode current collector, leaving the battery with little to no energy storage for safe shredding and / or grinding.

[0003] The framework herein is based, in part, on the observation that secondary (rechargeable) batteries typically degrade to the point of being unusable through normal charge-discharge cycles. In the case of electric vehicles (EVs), these vehicles encounter range and speed limitations that are no longer within acceptable limits, necessitating a replacement battery. Unfortunately, used batteries often retain significant energy storage and discharge capabilities even after being deemed "dead" due to their inability to store and deliver charge (electrical energy) according to sufficient performance standards. Recycling processes that disassemble and grind / shred the physical battery enclosure and contents can induce the sudden release of this residual energy, potentially creating sparks, heat, and fire risks. Connecting an electronic load can extract the residual energy, but it can be extremely slow and difficult to assess completion. [Means for solving the problem]

[0004] Thus, the configurations herein substantially overcome the drawbacks of spent shredding and grinding of batteries by applying a reverse bias overdischarge voltage to the battery or cell and calculating the duration and / or amount of energy applied to bring the battery to a zero energy state so that it has no residual voltage or current capacity, thereby mitigating the tendency for rebound voltage to appear after the reverse voltage bias is removed.

[0005] More specifically, forced discharge of Li-ion batteries from a recycle stream is performed to discharge the batteries to a safe level prior to recycling the batteries and recovering the battery charge material. The amount of energy stored in the batteries is calculated from peak current and decay tests. Discharge and reverse bias logic determines the time and discharge rate to reach a zero energy state based on the calculated amount of energy. A reverse voltage is applied to the battery terminals based on the determined time and discharge rate to induce reverse current flow and continues for the determined time to reach the zero energy state.

[0006] BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other features will become apparent from the following description of specific 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. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a context diagram of a forced or reverse bias discharge configuration. [Figure 2] FIG. 2 is a schematic diagram of the forced discharge device and operation as in FIG. 1. [Figure 3] The results of the discharge examples shown in Figs. [Figure 4] The results of the discharge examples shown in Figs. [Figure 5] The results of the discharge examples shown in Figs. DETAILED DESCRIPTION OF THE INVENTION

[0008] Detailed Description Battery discharge methods and apparatus allow batteries, such as Li-ion batteries, at a zero state of charge to reach a zero energy state prior to recycling the charge material within the battery, which often involves physical grinding and / or shredding to form a granular mass of mixed battery particles, commonly referred to as "black mass." The grinding process is not delicate and can be dangerous if residual electrical energy ("charge") remains within the battery. The following example configuration illustrates discharging batteries in a recycle stream by recovering usable electrical energy for grid sourcing. Once usable energy has been extracted, defined by the battery reaching a zero state of charge, it still exhibits a voltage (potential difference), and a forced discharge process is used to bring the battery to a zero energy state.

[0009] Conventional approaches to battery discharge attempt to drain electrical energy from the battery by applying an external load and / or a simple short circuit (a low-resistance connection) across the terminals. However, this approach is extremely time-consuming and does not always result in a zero-energy state. Furthermore, batteries tend to "rebound," i.e., revert to a zero-charge state of approximately 2.7 volts, once the load or short circuit is removed, posing a continuing risk of sparks and heat.

[0010] In comparison, the present disclosure overcomes these problems by applying a reverse bias voltage. It is believed that application of a reverse voltage to the battery terminals causes the formation of internal short circuits (low-resistance or no-resistance connections) due to the dissolution of the copper current collectors to which the anode material is typically attached. These internal short circuits result in batteries with no stored energy or residual voltage, and therefore do not cause sparks or sudden releases when crushed or shredded for recycling. Calculating the amount of over-discharge energy delivered by the reverse bias allows for precise and efficient timing and delivery of the over-discharge energy needed to bring the battery to a zero-energy storage state. Conventional approaches do not evaluate or calculate the extent or duration of the reverse bias current / voltage, nor do they account for the formation of internal short circuits due to the melting or degradation of the current collectors. Furthermore, conventional approaches simply short-circuit or direct the residual load to a resistive element for heat dissipation, but do not disclose receiving the residual electrical energy back to the power grid for storage or redistribution.

[0011] FIG. 1 is a context diagram of a forced or reverse bias discharge configuration.

[0012] Referring to Figure 1, battery 10 has two electrical connections 22-1 and 22-2 to the battery electrodes, which are the internal charge carriers for the battery's energy. During normal discharge, when the battery supplies power to a load such as a vehicle motor, electrons flow in direction 30'. Specifically, electrical energy in the form of electrons flows from one terminal, or pole, of the battery, powering the load, and returns to the battery through the other terminal of opposite polarity. Lithium ions within the battery complete a cycle as they pass through a separator within the battery.

[0013] In the configurations herein, a reverse voltage source, such as DC power supply 20, induces current flow 30, thereby driving additional current into the battery and reducing the voltage to such an extent that the voltage is reversed. The reverse voltage source is applied by connecting the high potential of power supply 20 to the low potential terminal of battery 10 and the low potential of the power supply to the high potential battery terminal. Battery terminals are often labeled positive (+) and negative (-), with positive being at a higher potential or voltage. Current flow is from the positive, high potential terminal to the negative, low potential terminal. Somewhat paradoxically, electrons have a negative charge. Thus, typical nomenclature often labels the negative terminal as the terminal from which negatively charged electrons flow and the positive terminal as the terminal to which electrons flow and from which current flows. Regardless of the polarity label, reverse voltage induces current flow in the battery, thereby reversing the battery voltage.

[0014] Lithium-ion batteries are typically cycled between 100% and 0% state of charge. However, at 0% state of charge (zero state of charge), the batteries still have an open circuit voltage of approximately 2.7 volts, which contains enough energy to create a spark and fire risk when the batteries are shredded during recycling operations.

[0015] Deep discharge of a battery below 0% state of charge can cause the copper current collector to dissolve, creating an internal short circuit within the battery and dissipating remaining battery energy as heat. It is believed that this process can be accelerated using the forced discharge method described herein, in which a reverse potential power source is attached to the battery to accelerate the copper plating involved in creating the internal short circuit. Forced discharge is used in short circuit testing of batteries to ensure that the battery can safely handle a short circuit.

[0016] Figure 2 is a schematic diagram of an apparatus such as that of Figure 1 at various stages of operation for forced discharge. Referring to Figure 2, a schematic diagram of the transition from the zero state of charge 101-1 to the zero energy state 101-2 of the diagram is shown. A method for discharging a battery in a recycle stream includes engaging terminals 110(-) and 110(+) (generally 110) of a battery 150 having a non-zero state of charge to receive electrical energy stored in the battery. Terminal 110(+) is the cathode terminal associated with the discharge current flow that defines the higher potential (voltage) of the vehicle electrical delivery during use, while terminal 110(-) is the anode side that defines the lower potential.

[0017] Reviewing the structure of battery 101-1 for recycling purposes, cathode 152 contains metal, conductive particles, and a binder attached to current collector 162, usually aluminum. The metals, which can include nickel, manganese, cobalt, and aluminum, combine with lithium in a mixture that defines the battery's chemistry, and are attached to current collector 162 along with binder and conductive particles (usually carbon). During discharge, current flow is released from cathode terminal 110(+) and then continues to anode terminal 110(-) after powering a load. Anode terminal 110(-) includes anode 154, usually containing carbon or graphite, on anode current collector 164, often copper. Li ions pass through separator 156 between cathode 152 and anode 154, completing the electrical circuit.

[0018] Discharge load 112 drains the residual voltage / current into storage or grid interface 114 and detects when the potential difference between its terminals becomes substantially zero. This represents a low resistance connection for drawing residual electrical energy, and continues until a zero state of charge condition is reached at approximately 2.5 to 2.7 volts.

[0019] Referring to battery 101-2, once the zero state of charge is achieved, a reverse bias 120 (such as a DC power supply) is involved to apply a voltage to terminals 110(+) and 110(-) to deep discharge the battery below 0 volts. This effectively forces current or electron flow through the battery, driving the residual voltage of less than 2.7 V towards 0.

[0020] It is important to recognize the difference between zero voltage and zero energy. Zero voltage refers to a time when the potential across the terminals 110 is zero, even though the charged material retains residual energy. If the load / drain 112 is simply removed, the voltage rebounds to approximately 2.5-2.7 V for a short period of time. Zero energy refers to a state where there is no residual energy to rebound back to 2.5-2.7 V, such as through the formation of an internal short circuit or electrical pathway. Reverse voltage is a reverse potential source defined by the reversal of the battery's voltage polarity during normal charging, in other words, a negative voltage relative to the polarity in use when charging a vehicle.

[0021] The reverse bias logic 122, which monitors the flow of reverse bias electricity, completes the application of reverse voltage based on the determination of an internal short circuit in the battery. The short circuit detector closes (shortens) the battery terminals 110, tracks the degradation of the current collectors 164 by measuring the peak current and decay rate, and calculates the amount of reverse bias energy the reverse bias circuit 120 should deliver to disable the over-discharged battery 101-2. The short circuit detector determines the amount of energy for the reverse voltage source to deliver to achieve zero voltage and zero current capacity of the battery. The amount or quantity of energy is based on switching the battery between open and closed loads and measuring the peak current and decay rate. Any suitable combination of voltage and current delivery over time can be employed to determine the optimal amount of over-discharge energy to disable the battery from further harmful or unexpected release of electrical energy.

[0022] Determining the residual charge involves briefly connecting ("short-circuiting") the battery terminals and measuring the peak current and decay rate. The decay rate is used to calculate the total time required to drain the battery (or its modules) to a zero-energy state. Predicting the energy required for reverse discharge is done by measuring the initial decay rate and noting that the decay rate slows and asymptotically approaches zero. Trapezoidal integration is used to calculate current-time (IT), where the total discharge time is equal to the area under the curve divided by the discharge current used. ∫Idt / Discharge current = Time

[0023] The calculation of the amount of energy is therefore based on the area bounded by the graph of the measured peak current and an estimated asymptotic decay of the current based on the decay rate. In the constructed example, the internal short circuit is based on the dissolution of the copper current collector 164 in contact with the anode material 154 in the battery 101. The reverse bias 120 effectively forces current flow through the battery 150', inducing an internal short circuit from the dissolution of the copper current collector, where the reverse is relative to the normal charging current flow during normal battery charging.

[0024] Generally, batteries transferred to the recycle stream for discharge contain useful recoverable charge in the form of electrical energy, and thus a discharging load receives electrical energy from batteries having a non-zero state of charge. The recovered energy is available from the battery current transferred to the electrical grid for storage or transmission.

[0025] Figure 3 is a graph of battery energy levels during an example discharge process. Referring to Figures 1-3, batteries coming in from the recycle stream have an unknown state of charge, but even as they approach the end of their "useful life," they are likely to be above zero state of charge. As such, any remaining electrical energy can be extracted for grid supply or otherwise recovered. Figure 3 shows the simultaneous timing progression of voltage (line 320) and current flow (line 310) over time during a forced discharge process.

[0026] The application of reverse voltage can occur at any time, preferably just before or upon achieving a zero state of charge. The process can begin by receiving electrical energy from a battery with a non-zero state of charge as a reverse polarity power source. Heat generation is mitigated by directing excess electrical energy to the grid or storage resource until the battery is depleted to a zero state of charge. Reverse voltage begins in section 302. When the calculated reverse voltage is applied, the current (negative for a normal discharge load) quickly reaches a plateau, here -240 amps. The voltage at the battery terminals quickly drops to zero through section 304. Once zero voltage is reached, an internal short circuit begins, rendering the battery harmless. Traditionally, a conductor is attached or welded between the opposing terminals to "short" the battery and ensure a harmless state. Reverse voltage achieves this harmless state more efficiently. In section 306, the reverse bias continues as the voltage remains near zero and the required current draw decreases. Repeated reverse voltage may be employed as an improvement.

[0027] FIG. 4 illustrates the results of a discharge example like those in FIGS. 1-3, along with timing for accelerating discharge while managing generated heat. In FIG. 4, line 410 represents the current (in amperes) flowing into the battery, and line 420 represents the corresponding voltage, both against a horizontal time axis 430. As in FIG. 3, section 302 represents the application of a reverse bias voltage and the corresponding current increase and voltage drop to zero. Section 304 represents a constant current while the battery voltage continues toward zero. Section 306 represents a constant voltage as the battery current is drained, rendering the battery harmless, similar to an external short circuit used in conventional approaches. If the battery continues to have a non-zero energy state after the calculated discharge time, an iterative step, shown as a voltage increase at 310, may be performed. Successive iterations may be performed to ensure the residual voltage is at a safe level, preferably completely disabled.

[0028] Another diagram of this process and apparatus is shown in Figure 5. Battery 501 includes an anode terminal 510(-) and a cathode terminal 510(+). The cathode terminal is electrically connected to a load 511, while the anode terminal is electrically connected to a power source 520. The load and power source are isolated by a switch 515 that alternately connects and disconnects the battery from the power source.

[0029] As shown, when switch 520 is in position 1, a circuit is completed between the load and the battery. In this position, the load drains the battery to a low-energy state, preferably a zero-charge state. This is illustrated in FIG. 5, where the voltage 550 gradually decays over time to approximately 2.5-2.7 volts (annotated as time "b"). In addition, the current 560 generated by the battery is also significantly reduced, but not eliminated. Therefore, as noted above, the battery is not yet devoid of energy (i.e., not yet in a zero-energy state).

[0030] At this stage, conventional processes typically apply a shorting wire across the battery terminals to dissipate any remaining energy in the battery. However, this process can take a significant amount of time, and it can be difficult to know when the zero-energy state has actually been achieved, which poses the risk of voltage rebound, essentially re-energizing the battery. Instead, a forced discharge technique is used, as shown in Figure 5.

[0031] Specifically, when the zero charge state is reached, switch 515 is moved to position 2, thereby connecting battery 501 and load 511 to power source 520. FIG. 5 shows the corresponding changes in current and voltage that result from this forced discharge process. Thus, when the switch is repositioned at time "b," a large increase in current from the power source (shown as a large decrease on the negative amperage scale) results, along with a sudden rise in voltage until time "c." This voltage is maintained until battery 501 reaches a constant negative voltage value (i.e., the battery's polarity reverses) at time "e." This value may be, for example, -5V. The forced discharge continues until the voltage begins to rise, indicating that the battery can no longer hold a charge. Power source 520 is then turned off, such as at time "f," with a voltage of -2V, after which load 511 is turned off. If desired, a shorting wire can also be applied to the battery terminals at this point.

[0032] Although the systems and methods defined herein have been shown and described with particular reference 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 as encompassed by the appended claims.

Claims

1. 1. A method for discharging Li-ion batteries in a Li-ion battery recycle stream prior to shredding or grinding the Li-ion batteries to recover battery charge material therefrom, comprising: calculating the amount of energy stored in the battery, the battery having a zero state of charge; determining a time and discharge rate for the battery to reach a zero energy state based on the calculated amount of energy; applying an external power source to induce a reverse voltage across the battery terminals based on the determined time and discharge rate to induce a reverse current flow; continuing the reverse voltage for the determined time to reach the zero energy state; A method comprising:

2. 2. The method of claim 1, wherein applying the reverse voltage comprises connecting a high potential of the voltage source to a low potential battery terminal and connecting a low potential of the voltage source to a high potential battery terminal.

3. Calculating the amount of energy stored in the battery comprises: measuring the peak current and decay rate between the terminals of the battery; calculating the amount of energy based on an area subtended by a graph of the measured peak current and an estimated asymptotic decay of the current based on the decay rate; The method of claim 1 , comprising:

4. Calculating the determined time and reverse voltage includes: connecting a sensing device across the terminals of said battery for the duration of a test period; measuring the peak current and decay rate of the current received by the sensing device during the test period; calculating a decay function based on the peak current and an estimated decay over time over the test period; The method of claim 1 further comprising:

5. 10. The method of claim 1, wherein the internal short circuit occurs as a result of dissolution of a copper current collector in contact with a cathode material within the battery.

6. 6. The method of claim 5, further comprising inducing copper plating from the reverse voltage to define a conductive path between the battery terminals.

7. receiving electrical energy from a battery having a non-zero state of charge; applying the reverse voltage to the battery once it has reached a zero state of charge; continuing to apply the reverse voltage to achieve a zero energy state; The method of claim 1 further comprising:

8. 1. An apparatus for discharging a Li-ion battery to a safe level prior to disassembly and recovery of the battery's charge material, comprising: a pair of connections to the battery, each connection being connected to a respective counter electrode; a power supply for supplying a voltage; reverse bias logic configured to apply a reverse bias voltage from the power source to the pair of connections to induce a zero energy state in the battery; and An apparatus comprising:

9. 10. The apparatus of claim 8, further comprising a grid connection, the grid connection responsive to the reverse bias logic to receive energy from a residual charge, the residual charge defined by energy delivered as the battery is depleted to a zero charge state.

10. 9. The apparatus of claim 8, further comprising a discharge switch, the discharge switch responsive to the reverse bias logic for switching the pair of connections to the reverse bias voltage when the battery reaches a zero state of charge.

11. The reverse bias logic includes: detecting a peak voltage from said pair of connections; Detects the decay rate, which indicates the voltage drop over time, Calculate the time and discharge rate for the battery to reach a zero energy state 9. The apparatus of claim 8, wherein the apparatus is operable to:

12. The reverse bias logic includes: forcing a reverse current flow through the battery to induce an internal short circuit from dissolution of the copper current collector; Terminating the reverse current flow when the battery reaches a zero energy state.

9. The apparatus of claim 8, wherein the apparatus is operable to:

13. 12. The apparatus of claim 11, wherein the reverse bias logic is configured to direct the power supply to apply the reverse bias voltage for the calculated time and discharge rate, resulting in an internal short circuit in the battery from dissolution of a copper current collector in contact with the cathode material within the battery.

14. 2. The apparatus of claim 1, wherein the reverse bias voltage is a reverse potential power supply defined by a reversal of the voltage polarity of the battery during normal use.

15. 1. A method for discharging batteries in a Li-ion battery recycle stream, comprising: engaging terminals on a battery having a non-zero state of charge to receive electrical energy stored in said battery; detecting when the potential difference between the terminals is substantially zero; calculating an amount of energy to apply via a reverse voltage to the terminals to nullify any remaining energy storage and discharge capacity in the battery; completing the application of the reverse voltage based on the determination of an internal short circuit in the battery; A method comprising:

16. applying a reverse voltage to the terminals to over-discharge the battery below a zero state of charge; continuing said application of said reverse voltage until a zero energy state is reached within said battery; The apparatus of claim 15 further comprising:

17. 16. The method of claim 15, further comprising forcing a reverse current flow through the battery to induce an internal short circuit from dissolution of a copper current collector.

18. 18. The method of claim 17, wherein the internal short circuit is due to dissolution of a copper current collector in contact with the cathode material within the battery.

19. 16. The method of claim 15, further comprising determining an amount of energy for the reverse voltage to deliver to achieve a zero energy state in the battery.

20. 16. The method of claim 15, further comprising determining the amount of energy based on repeatedly opening and closing a circuit with the battery to determine a peak current and a decay rate.

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