Method and system for discharging used lithium-ion batteries

Abstract

A method for discharging a used lithium-ion (Li-ion) battery may include bringing the external electrodes of the used Li-ion battery into contact with a discharge solution. The discharge solution comprises an aqueous solution of a salt having the same anion and a redox pair as cations. The redox pair comprises a first cation of the metal having a first oxidation state and a second cation of the same metal having a second oxidation state different from the first oxidation state.

Description

Cross-reference of related applications

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 450,560, filed on 7 March 2023, which is incorporated herein by reference in its entirety for all purposes. [Technical Field]

[0002] This disclosure generally relates to the field of recycling used lithium-ion batteries, and more specifically, to systems and methods for discharging used lithium-ion batteries. [Background technology]

[0003] As electric devices such as automobiles and power tools become more common, the number of used lithium-ion batteries is projected to increase rapidly. Given the finite amount of metals and other natural resources used as raw materials for lithium-ion batteries, an economically viable method for recycling used batteries is needed to keep the cost of raw materials (and consequently, batteries) affordable.

[0004] Any discarded battery typically has some residual voltage. Depending on the battery size and residual voltage, suddenly discharging the battery during the recycling process can generate a large current, potentially generating a considerable amount of heat, or even sparks. Lithium-based batteries, due to their design and chemistry, typically tend to have higher residual voltages and higher residual charges. Furthermore, lithium-based batteries contain flammable materials that can burn as a result of heat and / or sparks, thereby creating harmful conditions during the recycling process when discarded batteries are crushed and / or disassembled.

[0005] As a result, lithium-ion batteries are regularly pre-treated before recycling to reduce their residual voltage to an acceptable level. Pre-treatment typically involves chemically discharging the battery using an aqueous salt solution. In most cases, sodium chloride (NaCl) salt solutions are considered an efficient mode of cell discharge. However, the corrosive nature of NaCl salt solutions can damage cells, leading to leakage and loss of valuable cell components. Furthermore, by-products of such discharge processes (e.g., chlorine gas) are toxic to the environment and human health.

[0006] As alternatives to NaCl, salts such as ferrous sulfate and manganese sulfate have also been tested and reported to have shown some success in the discharge process. Nevertheless, these discharge fluids lack efficient kinetics for cell discharge, and the discharge process generally takes several hours, or sometimes longer than a day. Secondly, despite the slow discharge reaction rate, the final cell potential is relatively high, leaving some safety concerns.

[0007] As a result, current technologies for discharging used batteries are not safe or time-efficient. Therefore, there is a need for a cost-effective, low-energy, sustainable, safe, and rapid technology for discharging used batteries. [Overview of the Initiative]

[0008] Embodiments disclosed herein arise from the understanding that using an aqueous solution containing a suitably selected salt of the same metal in different oxidation states, having a reversible redox process at a suitable potential, as a discharge fluid can avoid the generation of toxic gases without reducing the discharge rate. This application discloses a system and method for discharging a used battery, such as a used lithium-ion battery, using an aqueous solution of a salt containing a redox pair and the same anion. When the battery is discharged through the aqueous solution, metal ions from the solution undergo reversible reduction and oxidation reactions at both electrodes. By suitably selecting a cationic redox pair together with a counter anion, the generation of toxic gases can be avoided.

[0009] The discharge solution in the embodiments of this disclosure is selected so that the metal cations can undergo a reversible redox process at the battery's external electrodes, and thus their effective solution concentration can be maintained without altering the battery's external electrodes. Secondly, the anions in the discharge salt solution also have considerable redox activity along with an efficient reaction rate, so the redox reaction rates at both external electrodes are similar. Therefore, corrosion of the battery's external electrodes can also be avoided. Furthermore, by selecting redox pairs with suitable reduction potentials, the battery can be discharged to a sufficiently low voltage with respect to the individual electrode potentials of the battery. Therefore, the possibility of spark discharge when disassembling the battery is further reduced.

[0010] Advantageously, the embodiments disclosed herein enable the discharge of spent Li-ion batteries to a safe potential using efficient reaction rates without generating harmful or toxic gases. Furthermore, as will become apparent, the systems and methods disclosed herein avoid potential corrosion of battery components during the discharge process, thereby improving the recycling yield when the battery components are recycled.

[0011] Therefore, in at least one embodiment, a method for discharging a spent Li-ion battery may include bringing the external electrodes of the spent Li-ion battery into contact with a discharge solution. The discharge solution is an aqueous solution containing a salt having the same anion and a redox pair as cations. The redox pair comprises a first cation of the metal having a first oxidation state and a second cation of the same metal having a second oxidation state different from the first oxidation state.

[0012] According to at least one embodiment, a system for discharging a spent lithium-ion battery may include a container having a discharge solution. The discharge solution includes an aqueous solution of a salt having the same anion and a redox pair as cations. The redox pair includes a first cation of the metal having a first oxidation state and a second cation of the same metal having a second oxidation state different from the first oxidation state. The system further includes a voltage sensor configured to measure the voltage across the external electrodes of a spent lithium-ion battery and a controller operably connected to the voltage sensor. The controller is configured to initiate contact between the external electrodes of the spent lithium-ion battery and the discharge solution, and to release the contact between the external electrodes and the discharge solution when the voltage measured by the voltage sensor across the external electrodes of the spent lithium-ion battery is below a threshold voltage.

[0013] Additional features and advantages of the subject technology are described below, some of which are evident from the description or can be learned through practice of the subject technology. The advantages of the subject technology will be realized and achieved through the written description and its embodiments, as well as the structures specifically indicated in the accompanying drawings.

[0014] It should be understood that both the above-mentioned overview and the following “Modes for Carrying Out the Invention” are illustrative and descriptive, and are intended to provide further explanation of the subject art. [Brief explanation of the drawing]

[0015] Various features of illustrative embodiments of this disclosure are described below with reference to the drawings. The illustrated embodiments are intended to illustrate, but not to limit, this disclosure. The drawings include the following figures.

[0016] [Figure 1A] The discharge of a used battery according to at least some embodiments of this disclosure is schematically shown. [Figure 1B] The discharge of a used battery according to at least some embodiments of this disclosure is schematically shown. [Figure 2] This disclosure describes a system for discharging used batteries according to at least some embodiments of this disclosure. [Modes for carrying out the invention]

[0017] In the detailed explanation below, numerous specific details are provided to give a complete understanding of the subject's technology. It should be understood that the subject's technology can be practiced without some of these specific details. In other cases, well-known structures and techniques are not shown in detail, so as not to obscure the subject's technology.

[0018] Furthermore, while this description provides specific details of various embodiments, it should be understood that the description is illustrative only and should not be interpreted as limiting in any sense. Additionally, while certain embodiments of this disclosure may be disclosed or shown in the context of recycling lithium-ion batteries, such embodiments are intended to be usable with all types of batteries using modifications within the scope of this disclosure and claims. Moreover, various applications and modifications of such embodiments that may be conceivable to those skilled in the art are also encompassed within the general concepts described herein.

[0019] Lithium-ion (Li-ion) battery cells have a voltage range of approximately 3.6V to 4.2V, depending on the specific chemistry of the battery. For most applications, when the cell voltage falls below 3.4V, the battery cell is generally considered "dead," and most manufacturers build a circuit cutoff to prevent the voltage from falling below approximately 3.0V. Therefore, even at the end of their lifespan, discarded used Li-ion batteries may have a voltage range of approximately 2.5V to 3.0V. In other words, discarded used Li-ion batteries may retain a substantial amount of charge, depending on the battery chemistry, size, and conditions immediately before the battery was discarded.

[0020] In the process of recycling lithium-ion batteries, the first step is generally to crush or dismantle the battery using, for example, a metal crusher. However, if the battery retains a significant amount of charge, it may spontaneously discharge during the crushing process, potentially causing sparks or significant heating of the crusher components.

[0021] To mitigate such risks, battery cells are discharged before being shredded for subsequent recycling processes. The most obvious way to discharge a battery cell is to short-circuit its external electrodes. However, if a large number of battery cells need to be discharged, the resulting high current can generate high heat, which could potentially ignite the materials within the battery cell. High current and high heat can also damage and corrode the battery materials, reducing the recycling yield.

[0022] An alternative method for discharging a battery is to connect external electrodes to a conductive solution, allowing the battery to discharge through the solution. The most commonly used conductive solution is an aqueous solution of table salt or sodium chloride (NaCl), which has high solubility and can maintain a high current density that results in effective battery discharge.

[0023] However, in NaCl-based discharge solutions, high current densities lead to water electrolysis through the reduction of hydrogen gas generation at the negative electrode and oxygen generation at the positive electrode. If chloride ions are present at the positive terminal, they compete with oxygen generation, and their reaction rate becomes faster than oxygen generation. This process causes metal dissolution at the negative terminal, which damages the cell and also generates solids in the discharge solution (e.g., iron hydroxide or copper hydroxide and oxides, depending on the chemistry of the battery and its external electrodes). Furthermore, the deposition on the cell terminals creates a barrier that prevents further cell discharge. As a result, a large residual potential remains in the battery, so the safety issue of cell shattering is not fully mitigated. Moreover, the generated hydrogen is highly flammable and therefore may have other related safety issues.

[0024] The inventors recognize that the reaction rate loading caused by NaCl, particularly in the presence of chloride ions, can be avoided by the presence of suitable electroactive species with a faster reaction rate. As a result, metal dissolution at the negative terminal can be avoided, thereby helping to achieve faster, safer, and cleaner cell discharge.

[0025] According to one aspect of the present disclosure, a method for discharging a spent lithium-ion battery includes bringing the external electrodes of the spent lithium-ion battery into contact with a discharge solution. The discharge solution includes an aqueous solution of a salt having the same anion and a redox pair as cations. The redox pair includes a first cation of the metal having a first oxidation state and a second cation of the same metal having a second oxidation state different from the first oxidation state.

[0026] As used herein, the term “redox pair” refers to a pair of cations of the same metal having different oxidation states. In other words, a redox pair refers to cations of the same metal but with different positive charges. The cations of a redox pair can be converted from one cation to another via oxidation or reduction reactions when a suitable potential is applied. An example of a redox pair is Fe. 2+ / Fe3+ , Fe 2+ / Fe, Fe 3+ / Fe, Cu + / Cu 2+ , Cu + / Cu, Cu 2+ / Cu, Mn 2+ / Mn 3+ , Mn 2+ / Mn 4+ , Mn 2+ / Mn 7+ , Mn 2+ / Mn 5+ , Mn 2+ / Mn, V 2+ / V, V 2+ / V 3+ , V 2+ / V 4+ , V 2+ / V 5+ , Sn 2+ / Sn 4+ , Cr 3+ / Cr 6+ , Cr 2+ / Cr 3+ , Co 2+ / Co 3+ , Ni 2+ / Ni 3+ , Sn 2+ / Sn 4+ , and Pb 2+ / Pb 4+ are exemplified, but not limited thereto.

[0027] One factor in selecting a suitable redox pair for use in a discharge solution is the reduction potential of the redox pair that determines the minimum voltage at which a Li-ion battery can be discharged when contacted with the discharge solution.

[0028] One skilled in the art will understand that, along with the reversible nature of the redox process, it is desirable to have a cation with a high reduction potential compared to the battery negative electrode and a low reduction potential compared to the battery positive electrode. Therefore, during battery discharge, one of the cations can be reduced at the battery negative electrode, and the other cations or cations generated in situ can be oxidized at the battery positive electrode.

[0029] In some embodiments, the salt anion in the discharge solution can be selected from the group consisting of sulfates, phosphates, nitrates, oxides, chlorides, acetates, oxalates, carbonates, and hydroxides. However, those skilled in the art will understand that one of the factors in selecting anion is the reaction rate of the anion at the external electrode. As discussed herein, if the reaction rate of the anion at the terminal is slower than that of water electrolysis, metal dissolution occurs at the terminal, thereby corroding the battery terminal and potentially leading to the generation of toxic gases. Therefore, preferred anions are those that have a faster redox reaction rate at the battery terminal. The same applies to the cation redox reaction rate, i.e., the process that occurs at the battery negative terminal. Consequently, in some embodiments, preferred anions are selected from the group consisting of sulfates, nitrates, phosphates, acetates, oxalates, carbonates, oxides, and hydroxides.

[0030] A further implication of the faster redox reaction rate of cations / anions is that, by competing with water electrolysis, dramatic changes in the pH of the discharge solution can be avoided. Therefore, another factor to consider is the electrochemical stability of cations in aqueous solutions, especially at acidic pH.

[0031] Those skilled in the art will further understand that, in order to obtain a discharge solution, both the salt and redox pair cations of the selected anion must be soluble in water. This requirement further reduces the selection of anions available for the discharge solution. Therefore, in some embodiments, the anion is selected from the group consisting of sulfates, nitrates, acetates, carbonates, and oxalates, but other anions are intended within the scope of this disclosure.

[0032] For example, in some embodiments, the discharge solution is Fe 2+ and Fe 3+ , or Cu 2+ and Cu +It may contain sulfates, acetates, or oxalates of Fe. In some embodiments, the discharge solution is Fe 2+ and Fe 3+ It may contain sulfates.

[0033] In some embodiments, the concentration of one or both salts in the discharge solution (before contact with the used battery) may be in the range of about 0.01 M to about 5 M. For example, in some embodiments, the salt with a high oxidation state cation may have a concentration in the range of about 0.01 M to about 0.5 M, and the salt with a low oxidation state cation may have a concentration in the range of 0.05 M to about 1 M.

[0034] In some embodiments, salts with high oxidation state cations may have concentrations in the range of about 0.05 M to about 0.5 M. In some embodiments, salts with high oxidation state cations may have concentrations in the range of about 0.1 M to about 0.5 M. In some embodiments, salts with high oxidation state cations may have concentrations in the range of about 0.15 M to about 0.5 M. In some embodiments, salts with high oxidation state cations may have concentrations in the range of about 0.2 M to about 0.5 M. In some embodiments, salts with high oxidation state cations may have concentrations in the range of about 0.25 M to about 0.5 M. In some embodiments, salts with high oxidation state cations may have concentrations in the range of about 0.3 M to about 0.5 M. In some embodiments, salts with high oxidation state cations may have concentrations in the range of about 0.4 M to about 0.5 M. In some embodiments, salts with high oxidation state cations may have concentrations in the range of about 0.2 M to about 0.5 M. In some embodiments, the salt having a high oxidation state cation may have a concentration in the range of about 0.2 M to about 0.45 M. In some embodiments, the salt having a high oxidation state cation may have a concentration in the range of about 0.2 M to about 0.4 M. In some embodiments, the salt having a high oxidation state cation may have a concentration in the range of about 0.2 M to about 0.3 M.

[0035] In some embodiments, salts with low oxidation state cations may have concentrations in the range of about 0.01 M to about 0.5 M. In some embodiments, salts with low oxidation state cations may have concentrations in the range of about 0.01 M to about 0.3 M. In some embodiments, salts with low oxidation state cations may have concentrations in the range of about 0.1 M to about 0.4 M. In some embodiments, salts with low oxidation state cations may have concentrations in the range of about 0.1 M to about 0.15 M. In some embodiments, salts with low oxidation state cations may have concentrations in the range of about 0.1 M to about 0.3 M.

[0036] Those skilled in the art will understand that the various concentration ranges described herein are limited by the solubility of the corresponding salts in the corresponding solutions and under the corresponding conditions.

[0037] Naturally, the maximum concentration of each salt depends on its solubility. Therefore, in some embodiments, one or both salts may be present in the discharge solution at saturation concentrations. Similarly, in some embodiments, one or both salts may be present in the discharge solution at relatively low concentrations.

[0038] For example, in some embodiments, salts with low oxidation states of cations are present at saturation concentrations, while salts with high oxidation states are present at very low concentrations. When a used battery comes into contact with a discharge solution, the used battery oxidizes the low oxidation states of cations to high oxidation states, thereby increasing the concentration of high oxidation states of cations. In such cases, a high concentration of low oxidation states of cations may be useful in preventing or delaying the discharge reaction rate.

[0039] Figures 1A and 1B schematically illustrate different types of contact between the external electrodes of a used Li-ion battery and the discharge solution according to several embodiments of the present disclosure.

[0040] For example, as depicted in Figure 1A, in some embodiments, bringing the external electrodes 102 and 104 of a used Li-ion battery 100 into contact with the discharge solution 130 involves bringing the external electrodes 102 and 104 into contact with the first ends 106A / 106B of an electrical conductor 106 and bringing the second end 108 of the electrical conductor 106 into contact with the discharge solution 130 contained in a container 120. In some embodiments, a switch (not shown) may be included in one of the conductors 106 to control the contact between the external electrodes 102 / 104 and the discharge solution 130. In such cases, the switch may be turned on or off to enable or disable the discharge of the battery. For example, the switch may be turned off when the voltage between the external electrodes drops below a certain threshold voltage.

[0041] Figure 1B illustrates an alternative type of contact between the external electrodes of a used Li-ion battery and a discharge solution. In the example depicted in Figure 1B, the used Li-ion battery 100 is immersed in a container 120 containing a discharge solution 130 such that the external electrodes 102 / 104 of the battery 100 are in direct contact with the discharge solution 130. In such an embodiment, the battery 100 may be removed from the discharge solution 130 when the discharge process is complete, for example, when the voltage between the external electrodes drops below a certain threshold voltage. Immersion or removal of the battery 100 may be performed, for example, by a robotic arm (not shown).

[0042] In some embodiments, the threshold voltage is in the range of about 10mV to about 1.5V. Those skilled in the art will understand that the threshold voltage can be selected to have a specific value, but the final potential of a discharged battery is determined by the redox potential of the redox pair. For example, Fe 3+ From Fe 2+The reduction potential for conversion to is approximately 0.77V. The threshold potential can be selected to be greater than 0.77V, for example, approximately 0.80V, 0.85V, 0.90V, 0.95V, 1.0V, 1.05V, 1.10V, 1.15V, 1.20V, 1.25V, 1.30V, 1.35V, 1.40V, 1.45V, 1.50V, or any other suitable potential between any two of these values. In some embodiments, the threshold potential can be within a suitable range near any two of these values.

[0043] While we do not wish to be constrained by theory, it is possible to obtain a threshold potential lower than the redox pair reduction potential by suitably manipulating various parameters associated with the discharge process, for example, by suitably stirring the discharge solution to replenish cations or anions in the discharge solution, or by replenishing the redox pair with one or more other ionic species. Therefore, in some embodiments, the threshold potential may be, for example, about 50 mV, about 100 mV, about 150 mV, about 200 mV, about 250 mV, about 300 mV, about 350 mV, about 400 mV, about 450 mV, about 500 mV, about 550 mV, about 600 mV, about 650 mV, about 700 mV, about 750 mV, about 800 mV, about 850 mV, about 900 mV, about 950 mV, about 1 V, or any value between any two of these values, or within a preferred range near any two of these values.

[0044] In some embodiments, it may be more efficient to determine a threshold voltage that can be achieved quickly while maintaining safety during the subsequent recycling process. Therefore, a suitable threshold potential may be selected, for example, based on the risk of sparks or high currents during the process of disassembling the battery for the subsequent recycling process. As a result, a suitable threshold voltage may be set based on specific steps performed when recycling a discharged battery.

[0045] While we do not wish to be bound by theory, the process of discharging a battery and the resulting current flow through the discharge solution can raise the temperature of the discharge solution, which can affect the efficiency of the discharge, the reaction at the battery terminals, and / or the minimum voltage achievable during discharge. Therefore, in some embodiments, it may be useful to actively maintain the temperature of the discharge solution while the battery is discharging through it. Consequently, in some embodiments, the container holding the discharge solution may be cooled using a cooling mechanism, such as a water-based heat exchanger, to maintain the discharge solution at a specific temperature, e.g., 25°C.

[0046] While we do not wish to be constrained by theory, the reaction rate efficiency at battery terminals can be increased by actively removing any materials generated at the battery terminals (e.g., generated gases such as oxygen, and / or deposited materials such as salts of the external electrode material and / or other metals in the battery). Therefore, in some embodiments, the discharge solution may be stirred to maintain the flow of the discharge solution around the battery terminals. In some embodiments, stirring can be achieved by continuously stirring the discharge solution, for example, using a stirrer in a container holding the discharge solution. Any suitable stirrer, such as a magnetic stirrer, may be used to stir the discharge solution. In some embodiments, stirring can be achieved, for example, using ultrasonic vibrations applied to the wall of a container holding the discharge solution. Any suitable ultrasonic generator, such as a piezoelectric generator, may be used to apply ultrasonic vibrations to the discharge solution. In some embodiments, stirring can be achieved, for example, using a rocker with a seesaw mechanism for oscillating the container at a suitable vibration frequency.

[0047] Figure 2 schematically illustrates a system for discharging a used Li-ion battery according to several embodiments of the present disclosure.

[0048] In some embodiments, the system 200 includes a container 220 containing a discharge solution 230, a controller 250, and terminals 242 and 244.

[0049] The container 220 can be any suitable container capable of holding the discharge solution being used without corroding it and without its components leaching into the discharge solution when an electric current is applied to it. In some embodiments, the container may be made of ceramic material or glass. In some embodiments, the container may be made of a polymer material that is inert to the discharge solution under different pH and temperature conditions.

[0050] The discharge solution 230 may be an aqueous solution containing a salt of the same anion and a redox pair as cations. The redox pair comprises a first cation of the metal having a first oxidation state and a second cation of the same metal having a second oxidation state different from the first oxidation state. The cations of the redox pair can be converted from one cation to another via oxidation or reduction reactions when a suitable potential is applied. An example of a redox pair is Fe. 2+ / Fe 3+ Fe 2+ / Fe, Fe 3+ / Fe, Cu + / Cu 2+ Cu + / Cu, Cu 2+ / Cu, Mn 2+ / Mn 3+ Mn 2+ / Mn 4+ Mn 2+ / Mn 7+ Mn 2+ / Mn 5+ Mn 2+ / Mn, V 2+ / V, V 2+ / V 3+ , V 2+ / V 4+ , V 2+ / V 5 +, Sn 2+ / Sn 4+ , Cr 3+ / Cr 6+ , Cr 2+ / Cr 3+ Co 2+ / Co 3+ Ni 2+ / Ni 3+ 、Sn 2+ / Sn 4+ 、and Pb 2+ / Pb 4+ are exemplified, but not limited thereto.

[0051] In some embodiments, the anion is selected from the group consisting of sulfate, nitrate, acetate, carbonate, and oxalate, although other anions are contemplated within the scope of the present disclosure.

[0052] For example, in some embodiments, the discharge solution may include sulfates, acetates, or oxalates of Fe 2+ and Fe 3+ , or Cu 2+ and Cu + . In some embodiments, the discharge solution may include sulfates of Fe 2+ and Fe 3+ .

[0053] In some embodiments, the concentration of one or both salts in the discharge solution (before contacting the used battery) can be in the range of about 0.01 M to about 5 M. For example, in some embodiments, salts having a high oxidation number cation can have a concentration in the range of about 0.01 M to about 0.5 M, and salts having a low oxidation number cation can have a concentration in the range of about 0.05 M to about 5 M.

[0054] Terminals 242 and 244 can be immersed in the discharge solution 230. Terminals 242 and 244 can be, in some embodiments, the external electrodes of the battery. In some embodiments, terminals 242 and 244 can be conductors connected to the external electrodes of the battery to be discharged.

[0055] In addition, a contact controller 246 is provided to the system 200. The contact controller 246 controls the contact between the external electrodes of the battery and the discharge solution. Therefore, in embodiments where terminals 242 and 244 are conductors connected to the external electrodes of the battery, the contact controller 246 may be a switch that can close or open the circuit between the external electrodes of the battery and terminals 242 / 244. On the other hand, in embodiments where terminals 242 / 244 themselves are the external electrodes of the battery, the contact controller 246 may be an immersion controller (e.g., a robotic arm or similar) that can immerse the battery in the discharge solution 230 or remove it from the discharge solution 230.

[0056] The system further includes a controller 250 configured to control various subsystems associated with the system 200. For example, the controller 250 may include a temperature controller 252 configured to maintain the temperature of the discharge solution 230, a battery discharge controller 254 configured to start or stop the battery discharge process, and a stirring controller 256 configured to control the stirring level of the discharge solution.

[0057] The temperature controller 252 may be a PID controller coupled to any suitable controller, for example, a temperature regulator 262 configured to maintain the temperature of the discharge solution. The temperature regulator 262 may be a suitable heat exchanger, for example, a water jacket around the container 220. In some embodiments, the temperature controller 252 may be coupled to a water pump that draws water through the water jacket around the container 220 and a temperature sensor (not shown) configured to sense the temperature of the discharge solution. Thus, the temperature controller 252 may increase or decrease the circulation of water around the container 220 in response to the temperature of the discharge solution as sensed by the temperature sensor.

[0058] The battery discharge controller 254 may be coupled to a voltage sensor 248 included in the discharge circuit and may be configured to control a contact controller 246 to initiate or deactivate contact between the battery's external electrodes and the discharge solution 230. For example, in embodiments where the contact controller 246 is a switch as discussed herein, the battery discharge controller 254 may turn the switch on (therefore closing the discharge circuit) or off (therefore opening the discharge circuit) based on the voltage across the battery's external electrodes as sensed by the voltage sensor 248. Therefore, when the voltage across the battery's external electrodes drops below a certain threshold, the battery discharge controller 254 may turn the switch off, thereby stopping the discharge process.

[0059] Similarly, in embodiments where the contact controller 246 is a robotic arm capable of immersing or removing the battery from the discharge solution 230, the battery discharge controller 254 may cause the robotic arm to remove the battery from the discharge solution 230, thereby stopping the discharge process, when the voltage across the external electrodes of the battery drops below a certain threshold.

[0060] As discussed elsewhere in this specification, a suitable threshold voltage may be determined based on the redox potential of the redox pairs in the discharge fluid and the risk tolerance of the process used during subsequent battery recycling.

[0061] While we do not wish to be bound by theory, when the voltage across the battery terminals decreases, the discharge rate may decrease, for example, due to the reaction rates of various species generated during the discharge process. By stirring the discharge solution, the reaction rates of various ionic species can be suitably altered (for example, by increasing the mobility of the ionic species), thereby increasing and / or maintaining the discharge rate.

[0062] The stirring controller 256 may be coupled to means 264 for stirring the discharge solution 230, such as a stirrer, ultrasonic generator, or rocker. The stirring controller 256 may be further coupled to a voltage sensor 248 and configured to determine the battery discharge rate based on the voltage sensed by the voltage sensor 248.

[0063] For example, in an embodiment where the means 264 for stirring the discharge solution 230 is an ultrasonic generator, the stirring controller 256 may increase or decrease the amplitude and / or frequency of the ultrasonic vibrations to maintain, decrease, and / or increase the battery discharge rate when the discharge circuit is closed.

[0064] Similarly, in embodiments where the means 264 for stirring the discharge solution 230 is a stirrer, for example, a magnetic stirrer, the stirring controller 256 may increase or decrease the rotational speed of the stirrer based on the battery discharge rate.

[0065] Similarly, in embodiments where the means 264 for stirring the discharge solution 230 is a rocker, the stirring controller 256 may change the amplitude and / or frequency of the oscillating of the container to maintain, decrease, and / or increase the rate at which the battery is discharged when the discharge circuit is closed.

[0066] Those skilled in the art will understand that batteries and / or battery cells are available in many form factors and have connector tabs made from various materials depending on the specific use case. Consequently, in some embodiments, the discharge solution may contain additional salts, acids, or bases for the specific type of battery to protect the tab material from corrosion due to reactions with cations or anions in the discharge solution. For example, in some embodiments, the discharge solution may additionally contain an organic acid, such as citric acid, at a suitable concentration.

[0067] Therefore, by suitably selecting a threshold voltage for stopping the discharge process, and by suitably controlling the temperature and agitation of the discharge solution during the battery discharge process, the efficiency of the discharge process can be further increased without compromising the safety of the discharge process or subsequent discharge processes.

[0068] Therefore, this disclosure provides a system and method for safely and efficiently discharging used lithium-ion batteries without generating harmful byproducts. Advantageously, by suitably selecting redox pairs in the discharge solution, byproducts of the discharge process can be reused in the discharge solution without consuming additional energy, thereby making the process cost-effective. [Examples]

[0069] Experiments were conducted to determine the filling rate (i.e., the number of batteries used at one time in a bath of a given size) and the amount of discharge solution required to immerse a given number of cells was determined. A given number of cells were placed in a glass container of a suitable size (e.g., a 1-liter beaker), and the discharge solution was added to the container until all cells were completely immersed in the discharge solution. Using a 1-liter beaker, approximately 230 ml of liquid was required to immerse 14 cells. For cylindrical batteries, which are typically found in electric vehicles, the optimal filling rate was found to be cell:solution = 1:16 (volume ratio). For mobile batteries, this ratio was 1:17. The discharge solution can be stirred either by a magnetic stirrer or by an electric pump, depending on the size of the container used. During these tests, it was also observed that, at the bulk level, collective phenomena accelerate the reaction rate of the discharge process, and therefore batteries with different form factors can also be repeatedly discharged.

[0070] Table 1 provides a summary of the discharge reaction rates of batteries of different form factors using different discharge solutions, and whether the discharge solutions are reusable for a given form factor. [Table 1]

[0071] Further considerations In some embodiments, any of the provisions herein may be dependent on any one of the independent provisions or any one of the dependent provisions. In one embodiment, any of the provisions (e.g., dependent or independent provisions) may be combined with any one or more other provisions (e.g., dependent or independent provisions). In one embodiment, a claim may include some or all of the words (e.g., steps, actions, means, or components) enumerated within a provision, sentence, phrase, or paragraph. In one embodiment, a claim may include some or all of the words enumerated within one or more provisions, sentences, phrases, or paragraphs. In one embodiment, some of the words in each provision, sentence, phrase, or paragraph may be deleted. In one embodiment, additional words or elements may be added within a provision, sentence, phrase, or paragraph. In one embodiment, the subject art may be implemented without utilizing some of the components, elements, functions, or actions described herein. In one embodiment, the subject art may be implemented using additional components, elements, functions, or actions.

[0072] The subject matter technology is illustrated, for example, in various embodiments as described below. These various embodiments of the subject matter technology are, for convenience, described as numbered clauses (1, 2, 3, etc.). These are provided as examples and are not intended to limit the subject matter technology. Note that any of the dependent clauses may be combined in any combination and placed in their respective independent clauses, for example, Clause 1 or Clause 5. Other clauses may also be presented in a similar manner.

[0073] Clause 1. A method of discharging a used lithium-ion (Li-ion) battery, the method comprising contacting an external electrode of the used Li-ion battery with a discharge solution. The discharge solution comprises an aqueous solution of a salt having the same anion and a redox pair as the cation. The redox pair comprises a first cation of a metal having a first oxidation state and a second cation of the same metal having a second oxidation state different from the first oxidation state.

[0074] Clause 2. The method of clause 1, wherein the redox pair is selected from the group consisting of Fe 2+ / Fe 3+ 、Cu + / Cu 2+ 、Mn 2+ / Mn 3+ 、Sn 2+ / Sn 4+ 、Cr 3+ / Cr 6+ 、Co 2+ / Co 3+ 、Ni 2+ / Ni 3+ 、Sn 2+ / Sn 4+ 、and Pb 2+ / Pb 4+ selected from the group consisting of.

[0075] Clause 3. The method of clause 1 or 2, wherein the anion is selected from the group consisting of sulfate, phosphate, nitrate, oxide, chloride, acetate, oxalate, carbonate, and hydroxide.

[0076] Clause 4. The method of any one of clauses 1 to 3, wherein the solution comprises a salt having the first cation at a saturated concentration and / or a salt having the second cation at a saturated concentration.

[0077] Clause 5. The method of any one of clauses 1 to 4, wherein the solution comprises a salt having the first cation at a concentration within the range of about 0.1 M to about 0.3 M and a salt having the second cation at a concentration within the range of about 0.1 M to about 0.15 M.

[0078] Clause 6. Any method of Clauses 1 to 5, wherein bringing the external electrode into contact with the discharge solution includes immersing the external electrode in a container filled with the discharge solution.

[0079] Clause 7. Any one of the methods of Clauses 1 to 6, wherein bringing an external electrode into contact with the discharge solution includes bringing the external electrode into contact with a first end of an electrical conductor and bringing the second end of an electrical conductor into contact with the discharge solution.

[0080] Clause 8. Any one of the methods of Clauses 1 to 7, further comprising maintaining the temperature of the discharge solution while the external electrode is in contact with the discharge solution.

[0081] Clause 9. Any one of the methods of Clauses 1 to 8, further comprising applying ultrasonic vibration to the discharge solution while the external electrode is in contact with the discharge solution.

[0082] Clause 10. Any one of the methods of Clauses 1 to 9, further comprising measuring the potential across both ends of the external electrode while the external electrode is in contact with the discharge solution.

[0083] Clause 11. Any one of the methods of Clauses 1 to 10, further comprising maintaining contact between the external electrode and the discharge solution until the potential across both ends of the external electrode drops below a threshold voltage.

[0084] Clause 12. The method of Clause 11, wherein the threshold voltage is within the range of approximately 50mV to approximately 1.5V.

[0085] Clause 13. Any method of Clauses 1 to 12 wherein the discharge solution comprises ferrous sulfate and ferric sulfate, ferrous nitrate and ferric nitrate, ferrous chloride and ferric chloride, ferrous acetate and ferric acetate, or ferrous oxalate and ferric oxalate.

[0086] Clause 14. A system for discharging a spent lithium-ion battery, the system comprising: a container containing a discharge solution comprising an aqueous solution of a salt having the same anion and a redox pair as a cation; a voltage sensor configured to measure the voltage across the external electrodes of a spent lithium-ion battery; and a controller operably connected to the voltage sensor. The controller is configured to initiate contact between the external electrodes of the spent lithium-ion battery and the discharge solution, and to release the contact between the external electrodes and the discharge solution when the voltage measured by the voltage sensor across the external electrodes of the spent lithium-ion battery is below a threshold voltage. The redox pair comprises a first cation of a metal having a first oxidation state and a second cation of the same metal having a second oxidation state different from the first oxidation state.

[0087] Clause 15. The system of Clause 14, wherein the anion is selected from the group consisting of sulfates, phosphates, nitrates, oxides, chlorides, acetates, oxalates, carbonates, and hydroxides.

[0088] Clause 16. Redox pairs are Fe 2+ / Fe 3+ Cu + / Cu 2+ Mn 2+ / Mn 3+ Sn 2+ / Sn 4+ , Cr 3+ / Cr 6+ Co 2+ / Co 3+ Ni 2+ / Ni 3+ Sn 2+ / Sn 4+ , and Pb 2+ / Pb 4+ A system of clauses 14 or 15, selected from the group consisting of the following.

[0089] Clause 17. Any one of the systems in Clauses 14-16, wherein the discharge solution contains aqueous solutions of ferrous sulfate and ferric sulfate.

[0090] Clause 18. Any one of the systems in Clauses 14-17, where the threshold voltage is within the range of approximately 0.1V to approximately 1.5V.

[0091] Clause 19. Any one of the systems in Clauses 14-18, initiating contact between the external electrodes of a used lithium-ion battery and the discharge solution includes immersing the used lithium-ion battery in a container so that the external electrodes of the used lithium-ion battery come into contact with the discharge solution, and releasing contact between the external electrodes of a used lithium-ion battery includes removing the used lithium-ion battery from the container so that the external electrodes do not come into contact with the discharge solution.

[0092] Clause 20. Any one of the systems of Clauses 14-19, further comprising an ultrasonic generator configured to generate ultrasonic vibrations and apply the ultrasonic vibrations to a discharge solution, and a controller further configured to control the ultrasonic generator.

[0093] Clause 21. Any one of the systems of Clauses 14-20, further comprising a temperature regulator operably coupled to the container and configured to maintain the temperature of the discharge solution while the external electrodes are in contact with the discharge solution.

[0094] Clause 22. A discharge solution comprising an aqueous solution of a salt having the same anion and a redox pair as a cation. The redox pair comprises a first cation of a metal having a first oxidation state and a second cation of the same metal having a second oxidation state different from the first oxidation state. The discharge solution is configured to reduce the potential across the battery without generating gaseous byproducts when electrical contact is made between the discharge solution and the external terminals of the battery.

[0095] Clause 23. Redox pair, Fe 2+ / Fe 3+ Cu + / Cu 2+ Mn 2+ / Mn 3+ Sn 2+ / Sn 4+ , Cr 3+ / Cr6+ Co 2+ / Co 3+ Ni 2+ / Ni 3+ Sn 2+ / Sn 4+ , and Pb 2+ / Pb 4+ A discharge solution according to clause 22, selected from the group consisting of the following.

[0096] Clause 24. A discharge solution according to Clause 22 or 23, wherein the anion is selected from the group consisting of sulfates, phosphates, nitrates, oxides, chlorides, acetates, oxalates, carbonates, and hydroxides.

[0097] Clause 25. A discharge solution according to any one of Clauses 22-24, wherein the discharge solution comprises a salt having a first cation at a saturated concentration and / or a salt having a second cation at a saturated concentration.

[0098] Clause 26. A discharge solution according to any one of Clauses 22 to 25, comprising a salt having a first cation at a concentration in the range of approximately 0.1 M to approximately 0.3 M and a salt having a second cation at a concentration in the range of approximately 0.1 M to approximately 0.15 M.

[0099] Clause 27. A discharge solution according to any one of Clauses 22-26, wherein the discharge solution contains ferrous sulfate and ferric sulfate, ferrous nitrate and ferric nitrate, ferrous chloride and ferric chloride, ferrous acetate and ferric acetate, or ferrous oxalate and ferric oxalate.

[0100] Clause 28. A discharge solution according to any one of Clauses 22-27, further comprising an organic acid.

[0101] The foregoing description is provided to enable those skilled in the art to implement the various configurations described herein. While the subject art has been described in particular with reference to various drawings and configurations, it should be understood that these are for illustrative purposes only and should not be construed as limiting the scope of the subject art.

[0102] Many other methods may exist for implementing the subject art. Various functions and elements described herein may be divided in ways different from those shown, without departing from the scope of the subject art. Various modifications to these configurations will be readily apparent to those skilled in the art, and the general principles defined herein may also apply to other configurations. Therefore, many changes and modifications to the subject art may be made by those skilled in the art without departing from the scope of the subject art.

[0103] The specific order or hierarchy of steps in the disclosed process is to be understood as an illustrative example of an exemplary approach. It is understood that the specific order or hierarchy of steps in the process may be rearranged based on design preferences. Some of the steps may be performed simultaneously. The attached method claims present elements of various steps in a sample order and are not intended to be limited to the specific order or hierarchy presented.

[0104] Where used herein, the term “approximately” preceding a quantity indicates variation from that quantity. Variation may be caused by manufacturing tolerances or based on differences in measurement techniques. In some cases, variation can be up to 10% from the listed value. Those skilled in the art will understand that variation in a particular quantity can be context-dependent, and therefore, for example, dimensional variation at the microscale or nanoscale may differ from variation at the metric scale.

[0105] Where used herein, the phrase “at least one of” preceding a set of items uses the terms “and” or “or” to distinguish any of the items, and qualifies the list as a whole rather than each item in the list (i.e., each item). The phrase “at least one of” does not require a selection of at least one of each of the listed items; rather, the phrase allows for meanings that include at least one of any one of the items, and / or at least one of any combination of the items, and / or at least one of each of the items. For example, the phrases “at least one of A, B, and C” or “at least one of A, B, or C” refer to A only, B only, or C only, any combination of A, B, and C, and / or at least one of each of A, B, and C, respectively.

[0106] Terms such as “top,” “bottom,” “front,” and “rear” as used in this disclosure should be understood to refer to any reference frame, not a typical gravity-referenced frame. Therefore, the top, bottom, front, and rear may extend upward, downward, obliquely, or horizontally within the gravity-referenced frame.

[0107] Furthermore, to the extent that terms such as “include” and “have” are used in the specification or claims, such terms are intended to be inclusive in the same manner as the term “comprise” is interpreted as “comprise” when it is used as a transitional term in a claim.

[0108] The term “exemplary” is used herein to mean “serving as an example, case, or illustration.” Any embodiment described herein as “exemplary” should not necessarily be construed as being preferable or advantageous to other embodiments.

[0109] References to elements in the singular form are intended to mean "one or more" and not "one and only" unless specifically stated otherwise. Masculine pronouns (e.g., his) include feminine and neuter pronouns (e.g., her and its), and vice versa. The term "several" refers to one or more. Underlined and / or italicized headings and subheadings are used for convenience only and do not limit the subject art and are not referenced in connection with the interpretation of the description of the subject art. All structural and functional equivalents to elements of the various constructs described throughout this disclosure, which are known to those skilled in the art or which will become known thereafter, are expressly incorporated herein by reference and are intended to be included in the subject art. Furthermore, nothing disclosed herein is intended to be publicly dedicated, whether such disclosure is expressly enumerated in the above specification or not.

Claims

1. A method for discharging a used lithium-ion (Li-ion) battery, wherein the method is This includes bringing the external electrodes of the used Li-ion battery into contact with a discharge solution. The discharge solution comprises an aqueous solution of a salt having the same anion and a redox pair as a cation. A method wherein the redox pair comprises a first cation of a metal having a first oxidation state and a second cation of the same metal having a second oxidation state different from the first oxidation state.

2. wherein the redox pair is Fe ２＋ / Fe ３＋ 、Cu ＋ / Cu ２＋ 、Mn ２＋ / Mn ３＋ 、Sn ２＋ / Sn ４＋ 、Cr ３＋ / Cr ６＋ 、Co ２＋ / Co ３＋ 、Ni ２＋ / Ni ３＋ 、Sn ２＋ / Sn ４＋ 、and Pb ２＋／ Pb ４＋ The method according to claim 1, selected from the group consisting of.

3. The method according to claim 1, wherein the anion is selected from the group consisting of sulfates, phosphates, nitrates, oxides, chlorides, acetates, oxalates, carbonates, and hydroxides.

4. The method according to claim 1, wherein the solution comprises a salt having the first cation at a saturated concentration and / or a salt having the second cation at a saturated concentration.

5. The method according to claim 1, wherein the solution comprises a salt having the first cation at a concentration in the range of about 0.1 M to about 0.3 M, and a salt having the second cation at a concentration in the range of about 0.1 M to about 0.15 M.

6. The method according to claim 1, wherein bringing the external electrode into contact with the discharge solution includes immersing the external electrode in a container filled with the discharge solution.

7. The method according to claim 1, wherein bringing the external electrode into contact with the discharge solution includes bringing the external electrode into contact with a first end of an electrical conductor and bringing the second end of the electrical conductor into contact with the discharge solution.

8. The method according to claim 1, further comprising maintaining the temperature of the discharge solution while the external electrode is in contact with the discharge solution.

9. The method according to claim 1, further comprising applying ultrasonic vibrations to the discharge solution while the external electrode is in contact with the discharge solution.

10. The method according to claim 1, further comprising measuring the potential at both ends of the external electrode while the external electrode is in contact with the discharge solution.

11. The method according to claim 10, further comprising maintaining contact between the external electrode and the discharge solution until the potential across the external electrode falls below a threshold voltage.

12. The method according to claim 11, wherein the threshold voltage is in the range of approximately 50 mV to approximately 1.5 V.

13. The method according to claim 1, wherein the discharge solution comprises ferrous sulfate and ferric sulfate, ferrous nitrate and ferric nitrate, ferrous chloride and ferric chloride, ferrous acetate and ferric acetate, or ferrous oxalate and ferric oxalate.

14. A system for discharging a used Li-ion battery, wherein the system is A container containing a discharge solution containing an aqueous solution of a salt having the same anion and a redox pair as a cation, A voltage sensor configured to measure the voltage across the external electrodes of the used Li-ion battery, A controller operably connected to the voltage sensor, Contact is initiated between the external electrode of the used Li-ion battery and the discharge solution, and A controller configured to release the contact between the external electrode and the discharge solution when the voltage measured by the voltage sensors at both ends of the external electrode of the used Li-ion battery is below a threshold voltage, A system in which the redox pair comprises a first cation of a metal having a first oxidation state and a second cation of the same metal having a second oxidation state different from the first oxidation state.

15. The system according to claim 14, wherein the anion is selected from the group consisting of sulfates, phosphates, nitrates, oxides, chlorides, acetates, oxalates, carbonates, and hydroxides.

16. The aforementioned redox pair, Fe ２＋ / Fe ３＋ ,Cd ＋ / Cu ２＋ Mn ２＋／ Mn ３＋ Sn ２＋ / Sn ４＋ , Cr ３＋ / Cr ６＋、 Co ２＋ / Co ３＋ Ni ２＋ / Ni ３＋ Sn ２＋ / Sn ４＋ , and Pb ２＋ / Pb ４＋ The system according to claim 14, selected from the group consisting of the following.

17. The system according to claim 14, wherein the discharge solution comprises aqueous solutions of ferrous sulfate and ferric sulfate.

18. The system according to claim 14, wherein the threshold voltage is in the range of approximately 0.1V to approximately 1.5V.

19. The system according to claim 14, wherein initiating contact between the external electrodes of the used Li-ion battery and the discharge solution includes immersing the used Li-ion battery in the container so that the external electrodes of the used Li-ion battery are in contact with the discharge solution, and releasing the contact between the external electrodes of the used Li-ion battery includes removing the used Li-ion battery from the container so that the external electrodes are not in contact with the discharge solution.

20. The system according to claim 14, further comprising an ultrasonic generator configured to generate ultrasonic vibrations and apply the ultrasonic vibrations to the discharge solution, wherein the controller is further configured to control the ultrasonic generator.

21. The system according to claim 14, further comprising a temperature controller operably coupled to the container and configured to maintain the temperature of the discharge solution while the external electrodes are in contact with the discharge solution.

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