Forced discharge of battery

Abstract

A method for discharging an end-of-life battery prior to disassembly and reuse includes recovering residual stored electrical energy by consuming the battery to a zero state of charge, and reverse biasing the battery to change a potential from a zero state of charge of about 2.7 V to a zero or near-zero energy state. The reverse bias inverts the normal use polarity to cause a reverse current and continues based on the formation of an internal short circuit formed on the cathode current collector to make the battery have little or no energy storage for safe agitation and disassembly.

Description

BACKGROUND OF THE INVENTION

[0001] In recent decades, lithium-ion batteries (LIBs) have been widely used, especially in electric vehicles (EVs) and plug-in / hybrid electric vehicles (PHEVs) that are already equipped with LIBs or directly powered by LIBs. LIBs have been widely used as the main power source in portable electronic devices, electric vehicles, and grid energy storage. LIBs offer strong capabilities in terms of energy storage or density and discharge capacity, and can continue to retain residual electrical energy even after being considered to have exceeded the effective service life of charge / discharge performance. SUMMARY OF THE INVENTION

[0002] A method for discharging end-of-life batteries before disassembly and reuse includes recovering residual stored electrical energy by discharging the battery to a zero state of charge, and reverse biasing the battery to change the electrical potential from a zero state of charge of about 2.7 V to a zero or near-zero energy state. Reverse biasing reverses the normal use polarity, which is believed to create an internal short circuit on the cathode current collector, thereby leaving the battery with little or no energy storage for safe shredding and / or grinding.

[0003] The configurations herein are based in part on the observation that secondary (rechargeable) batteries typically degrade to an unusable extent through normal charge and discharge cycles. In the case of electric vehicles (EVs), these vehicles experience range and speed limitations that are no longer within acceptable parameters and require battery replacement. Unfortunately, even after end-of-life batteries are considered "depleted" because they cannot store and deliver charge (electrical energy) according to sufficient performance criteria, these end-of-life batteries typically still retain a significant amount of energy storage and discharge capacity. The process of disassembling and shredding / grinding the physical battery containment and contents can trigger a sudden release of this residual energy, resulting in a risk of sparks, heat, and fire. Connecting an electronic load can draw the residual energy, but extremely slowly and may be difficult to assess as complete.

[0004] Accordingly, the configurations herein mitigate the tendency for a bounce voltage to occur after removal of the reverse voltage bias by applying a reverse-biased over-discharge voltage to the battery or battery cells and calculating the duration and / or amount of energy to be applied to bring the battery to a zero energy state with no residual voltage or current capacity, thereby substantially overcoming the disadvantages of end-of-life shredding and grinding of the battery.

[0005] More specifically, before reusing a battery and recycling battery charge materials, the lithium-ion battery in the reuse stream is forcibly discharged to discharge the battery to a safe level. The amount of energy stored in the battery is calculated based on peak current and decay tests. The discharge and reverse bias logic determines the time and discharge rate for reaching a zero energy state based on the calculated amount of energy. A reverse voltage is applied to the terminals of the battery based on the determined time and discharge rate to cause a reverse current, and the application of the reverse voltage continues for the determined time to reach a zero energy state. Brief Description of the Drawings

[0006] Based on the following description of specific embodiments disclosed herein and shown in the drawings, the above and other features will be apparent, in which like reference numerals refer to like parts in different views. These drawings are not necessarily to scale, but rather are focused on showing the principles of the present invention.

[0007] Figure 1 is a context diagram of a forced or reverse bias discharge configuration;

[0008] Figure 2 is as Figure 1 shown in a schematic diagram of the apparatus and operation for forced discharge; and

[0009] Figures 3 to 5 shows the results of an example discharge as Figures 1 to 2 in. Detailed Description

[0010] A battery discharge method and apparatus bring a battery (such as a lithium-ion battery) in a zero charge state to a zero energy state before reusing the charge materials in the battery. Reuse typically involves physical grinding and / or pulverization to form an agglomerate of mixed battery particles, commonly referred to as a "black mass". This grinding process is not delicate and can be dangerous if there is still residual electrical energy ("charge") in the battery. The following example configuration shows discharging the battery in the reuse stream by recovering available electrical energy for grid supply. Once the available energy has been extracted, which is defined by the battery reaching a zero charge state, the battery still exhibits a voltage (potential difference), and a forced discharge process is used to bring the battery to a zero energy state.

[0011] Conventional methods of battery discharge are to attempt to consume electrical energy from the battery by applying an external load and / or a simple short circuit (low resistance connection) between the terminals. However, this method is extremely time-consuming and does not always result in a zero energy state. Additionally, once the load or short circuit is removed, the battery has a tendency to "bounce" or recover to a zero charge state of approximately 2.7 volts, which poses a risk of continuous sparking and heat.

[0012] In contrast, in the present disclosure, applying a reverse bias voltage overcomes these problems. It is believed that applying a reverse voltage to the battery terminals causes an internal short circuit (a low-resistance or no-resistance connection) to form by decomposing the copper current collector to which the anode material typically adheres. These internal short circuits result in the battery having no stored energy or residual voltage and thus not causing a spark or sudden release when crushed or shredded for reuse. Calculating the amount (magnitude) 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 methods do not evaluate or calculate the extent or duration of the reverse bias current / voltage, nor do they describe the formation of internal short circuits caused by the decomposition or degradation of the current collector. Further, conventional methods only short-circuit or direct the residual load to a resistive element for heat dissipation and do not disclose receiving the residual electrical energy for storage or redistribution back to the grid.

[0013] Figure 1 is a context diagram of a forced or reverse bias discharge configuration.

[0014] Reference Figure 1 , the battery 10 has two electrical connectors 22-1 and 22-2 connected to the battery electrodes, which are internal charge-carrying members for the battery energy. In normal discharge, when the battery powers a load (such as a vehicle motor), electrons flow in the direction 30’. Specifically, electrical energy in the form of electrons flows from one terminal or pole of the battery, powers the load, and returns to the battery through the other terminal having the opposite polarity. Lithium ions inside the battery complete the cycle as they cross the separator inside the battery.

[0015] In the configuration herein, a reverse voltage source (such as DC power source 20) causes a current 30, thereby driving additional current through the battery, causing the voltage to drop to the extent of voltage reversal. The reverse voltage source is applied by connecting the higher potential of the power source 20 to the lower potential terminal of the battery 10 and connecting the lower potential of the power source to the higher potential battery terminal. The battery terminals are typically labeled positive (+) and negative (-), where the positive is at the higher potential or voltage. Current flows 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 the electron flow and current flow. Regardless of how the polarities are labeled, the reverse voltage causes current to flow through the battery, thereby reversing the battery voltage.

[0016] Lithium-ion batteries typically cycle between 100% and 0% state of charge. However, the open-circuit voltage of the battery when at 0% state of charge (zero state of charge) is still ~2.7 volts, and when the battery is shredded during a reuse operation, it has enough energy to create a spark and fire risk.

[0017] Over-discharging the battery to a state of charge below 0% causes decomposition of the copper current collector, which creates an internal short circuit within the battery and dissipates the remaining battery energy as heat. It is believed that this process can be facilitated by 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 for the short-circuit testing of batteries to ensure that the batteries can safely handle a short circuit.

[0018] Figure 2 is as Figure 1 shown in the schematic diagram of the device at different operating stages for forced discharge. Referring Figure 2 , a schematic diagram showing the transition from the zero state of charge 101-1 to the zero energy state 101-2 of the figure is shown. The method for discharging a battery in a reuse stream includes engaging the terminals 110(-) and 110(+) (collectively 110) of a battery 150 having a non-zero state of charge to receive the electrical energy stored in the battery. Terminal 110(+) is the cathode terminal associated with the emission of current that defines the higher potential (voltage) for vehicle power transfer in use, while terminal 110(-) is the anode side that defines the lower potential.

[0019] Reviewing the structure of the battery 101-1 for reuse, the cathode 152 contains an adhesive, metal, and conductive particles adhered to the current collector 162, which is typically aluminum. The metal can include nickel, manganese, cobalt, aluminum, and other metals that bind with lithium in the mixture, which defines the battery chemistry and adheres to the current collector 162 along with the adhesive and conductive particles (typically carbon). During discharge, current exits from the cathode terminal 110(+), and then powers a load before continuing to flow to the anode terminal 110(-), which includes an anode 154 typically containing carbon or graphite on the anode current collector 164, which is typically copper. Lithium ions pass through the separator 156 between the cathode 152 and the anode 154, thus completing the circuit.

[0020] The discharge load 112 discharges the residual voltage / current to a storage or grid interface 114 and detects when the potential difference between the terminals is essentially zero. This indicates a low-resistance connection for drawing the residual electrical energy and continues until a state of zero state of charge of approximately 2.5 - 2.7 volts is reached.

[0021] Once the zero state of charge is achieved, with reference to battery 101-2, a reverse bias 120 (such as a DC power supply) is engaged to apply a voltage across terminals 110(+) and 110(-) to over-discharge the battery to below 0 volts. This effectively forces current or electrons to flow through the battery, thereby reducing the residual voltage below 2.7 volts down to 0 volts.

[0022] It is important to recognize the difference between zero voltage and zero energy. Zero voltage refers to the time of zero electric potential between terminals 110, even if the charge material retains residual energy. Once only load / drain 112 is removed, the voltage rebounds to approximately 2.5 - 2.7V within a short interval. Zero energy refers to a state where, for example, by creating an internal short circuit or electrical path, there is no residual energy rebound back to 2.5 - 2.7V. Reverse voltage is a reverse potential power source defined by the reversal of the voltage polarity of the battery during normal charging; in other words, when charging a vehicle, it is a negative voltage relative to the polarity during use.

[0023] The reverse bias logic 122 that monitors the reverse bias current completes the application of the reverse voltage based on the determination of an internal short circuit in the battery. The short circuit detector tracks the degradation of the current collector 164 by closing (shorting) the battery terminals 110 and measuring the peak current and decay rate to calculate the amount of reverse bias energy that will be delivered by the reverse bias circuit 120 to neutralize the over-discharged battery 101-2. The short circuit detector determines the amount of energy value to be delivered by the reverse voltage source to achieve zero voltage and zero current capacity in the battery. The amount or value of the energy is based on switching between an open load and a closed load on the battery 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 neutralize the battery from further releasing harmful or unexpected electrical energy.

[0024] The determination of the residual charge involves briefly connecting the battery terminals ("shorting") and measuring the peak current and decay rate. The decay rate is used to calculate the total time required to discharge the battery (or its module) to the zero energy state. The energy required for reverse discharge is predicted by measuring the initial decay rate and identifying when the decay rate slows down and asymptotes to 0. Trapezoidal integration is used to calculate the current-time (I-T), and the total discharge time is equal to the area under the curve / the discharge current used:

[0025] ∫I dt / discharge current = time

[0026] Accordingly, the amount of energy is calculated based on the area defined by the graph of the measured peak current and the asymptotic decay of the current estimated based on the decay rate. In an example configuration, an internal short circuit is based on the decomposition of the copper current collector 164 in contact with the anode material 154 in the battery 101. The reverse bias 120 effectively forces current to flow through the battery 150', causing an internal short circuit due to the decomposition of the copper current collector, where the reverse is with respect to the normal charging current during normal battery charging.

[0027] Generally, batteries that are degraded into the reuse stream for discharge contain available, recyclable charge in the form of electrical energy, and thus the discharge load receives electrical energy from a battery with a non-zero state of charge. The recovered energy can be obtained from the battery current transferred to the power grid for storage or transmission.

[0028] Figure 3 is a graph of the battery energy level during an example discharge process. Refer to Figures 1 to 3 , the incoming battery from the reuse stream has an unknown state of charge, but even near the end of the "service life", the battery may be in a state above zero state of charge. Therefore, the remaining electrical energy can be drawn for grid power or otherwise recovered. Figure 3 Shows the concurrent timing progression of voltage (line 320) and current (line 310) over time during a forced discharge process.

[0029] The application of the reverse voltage can occur at any time, preferably at or just before achieving a zero state of charge. The process can start by receiving electrical energy from a battery with a non-zero state of charge that serves as an anti-polarity power source. Heat generation is mitigated by diverting excess electrical energy to the power grid or storage resources until the battery is depleted to a zero state of charge. The reverse voltage starts at interval 302. When the calculated reverse voltage is applied, the current (negative value with respect to the normal discharge load) quickly reaches a steady state, here -240 amperes. The voltage at the battery terminals quickly drops to 0 within interval 304. At zero voltage, an internal short circuit may start, putting the battery in a benign state. Conventional methods attach or weld conductors between opposite terminals to "short circuit" the battery and ensure a benign state. The reverse voltage achieves this benign state more efficiently. In interval 306, the reverse bias continues while the voltage remains near 0 and the required current draw decreases. Iterative reverse voltage can be employed as an improvement.

[0030] Figure 4 Shows the results of an example discharge as in Figures 1 to 3 , and the timing for accelerating the discharge while managing the heat generated. In Figure 4In it, line 410 shows the current (amperes) flowing into the battery while line 420 shows the corresponding voltage, both the current and the corresponding voltage being relative to the horizontal time axis 430. As Figure 3 shown, interval 302 marks the application of a reverse bias voltage and the corresponding increase in current and decrease in voltage to 0. Interval 304 shows a constant current while the battery voltage continues to tend towards 0. Interval 306 represents a constant voltage while the battery current is consumed, rendering the battery harmless, similar to an external short circuit used in conventional methods. Iterative steps can occur, as shown by the voltage increase at 310, where the battery maintains a non-zero energy state even after the calculated discharge time. Successive iterations can occur to ensure that the residual voltage reaches a safe level and is preferably completely eliminated.

[0031] In Figure 5 another view of the process and device is shown. 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 supply 520. The load and the power supply are separated by a switch 515 which alternately connects and disconnects the battery from the power supply.

[0032] As shown, when switch 520 is in position 1, a circuit is completed between the load and the battery. In this position, the load discharges the battery to a lower energy state, preferably a zero state of charge. This is described in Figure 5 where the voltage 550 gradually decays over time to approximately 2.5 - 2.7 volts (denoted as time "b"). Additionally, the current 560 generated by the battery also significantly decreases but is not eliminated. Thus, as discussed above, the battery has not been depleted of energy (i.e., is not yet in a zero energy state).

[0033] At this stage, in a conventional process, a shorting wire is typically applied across the battery terminals in order to dissipate the remaining energy in the battery. However, this process takes a rather long time and it may be difficult to know when the zero energy state has actually been reached, which poses a risk of voltage bounce and essentially re - energizing the battery. Instead, as Figure 5 shown, a forced discharge method is used.

[0034] Specifically, when the zero state of charge is reached, switch 515 moves to position 2, thereby connecting battery 501 and load 511 to power supply 520. Figure 5The corresponding changes in current and voltage caused by this forced discharge process are shown. Thus, when the switch is repositioned at time "b", the voltage rises sharply to time "c", while the current from the power supply increases significantly (appearing as a significant decrease on the negative current scale). This voltage is maintained until the battery 501 reaches a negative voltage value, which does not change at time "e" (i.e., until the polarity of the battery is reversed). This value can be, for example, -5V. The forced discharge is continued until the voltage starts to increase, indicating that the battery can no longer hold the charge. Then, for example, the power supply 520 is turned off at time "f", with a voltage of -2V, and then the load 511 is turned off. If desired, a shorting wire can also be applied to the battery terminals at this time.

[0035] Although the systems and methods defined herein have been specifically shown and described with reference to their embodiments, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of the invention covered by the appended claims.

Claims

1. A method for discharging a lithium-ion battery in a reuse stream of lithium-ion batteries before shredding or grinding and recovering battery charge materials from the battery, the method comprising: Calculating a magnitude of energy stored in the battery having a zero state of charge; Determining a time and a discharge rate for bringing the battery to a zero energy state based on the calculated magnitude of energy; Applying an external power source to generate a reverse voltage across the terminals of the battery based on the determined time and discharge rate for causing a reverse current; And Continuing the reverse voltage for the determined time to reach the zero energy state.

2. The method according to claim 1, wherein, Applying the reverse voltage includes connecting the higher potential of the voltage source to the lower potential battery terminal and connecting the lower potential of the voltage source to the higher potential battery terminal.

3. The method according to claim 1, wherein Calculating the magnitude of energy stored in the battery includes: Measuring a peak current and a decay rate between the terminals of the battery; and Calculating the magnitude of energy based on an area defined by a graph of the measured peak current and an asymptotic decay of the current estimated based on the decay rate.

4. The method according to claim 1, wherein Calculating the determined time and reverse voltage further includes: Connecting a sensing device across the terminals of the battery for a duration of a test interval; Measuring a peak current and a decay rate of the current received by the sensing device during the test interval; and Calculating a decay function based on the peak current and an estimated decay over a time period beyond the test interval.

5. The method according to claim 1, wherein, Internal short circuits are caused by decomposition of a copper current collector in contact with a cathode material in the battery.

6. The method of claim 5, further comprising causing copper plating by the reverse voltage to define a conduction path between the battery terminals.

7. The method of claim 1, further comprising: Receiving electrical energy from a battery having a non-zero state of charge; Applying the reverse voltage to the battery when a zero state of charge is reached; And Continuing to apply the reverse voltage to achieve a zero energy state.

8. An apparatus for discharging a lithium-ion battery to a safe level before disassembling and recovering battery charge materials, the apparatus comprising: A pair of connectors connected to the battery, each connector connected to a respective opposite electrode; A power source for supplying a voltage; And Reverse bias logic configured to apply a reverse bias voltage from the power source to the pair of connectors to cause a zero energy state in the battery.

9. The apparatus of claim 8, further comprising a grid connector responsive to the reverse bias logic for receiving energy from a residual charge defined by energy transferred when the battery is depleted to a zero state of charge.

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

11. The device according to claim 8, wherein, The reverse bias logic is operable to: Detect a peak voltage from the pair of connectors; Detect a decay rate indicative of a decrease in voltage over time; And Calculate a time and a discharge rate for bringing the battery to a zero energy state.

12. The device according to claim 8, wherein, The reverse bias logic is operable to: forcing a reverse current to flow through the battery to cause an internal short circuit due to decomposition of the copper current collector; and terminating the reverse current when the battery reaches a zero energy state.

13. The device according to claim 11, wherein, The reverse bias logic is configured to direct the voltage source to apply the reverse bias voltage for the calculated time and discharge rate and cause an internal short circuit in the battery due to decomposition of the copper current collector in contact with the cathode material in the battery.

14. The device according to claim 1, wherein The reverse bias voltage is a reverse potential power source defined by inversion of the voltage polarity of the battery during normal use.

15. A method for discharging a battery in a lithium-ion battery reuse stream, the method comprising: connecting terminals on a battery having a non-zero state of charge to receive electrical energy stored in the battery; detecting when the potential difference between the terminals is substantially zero; calculating the amount of energy to be applied to the terminals via a reverse voltage to neutralize residual energy storage and discharge capacity in the battery; and completing the application of the reverse voltage based on determining an internal short circuit in the battery.

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

17. The method of claim 15, further comprising forcing a reverse current to flow through the battery to cause an internal short circuit due to decomposition of the copper current collector.

18. The method according to claim 17, wherein, The internal short circuits are based on decomposition of the copper current collector in contact with the cathode material in the battery.

19. The method of claim 15, further comprising determining the amount of energy transferred by the reverse voltage to achieve a zero energy state in the battery.

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

Images