Battery discharge method

Abstract

The present invention relates to a battery discharging method including a first discharging step of discharging the battery by connecting a battery and a power converter and applying a voltage thereto, and a second discharging step of discharging the battery by applying a voltage reverse to that of the first discharging step after the first discharging step. According to the present invention, it is possible to recover and recycle the electric energy of the battery, as well as to ensure an electrically safe state in a subsequent dismantling process by putting the battery in a fully discharged state in which normal operation is not possible.

Description

Technical Field

[0001] The present invention relates to a battery discharge method.

Background Art

[0002] The process of recovering expensive metals used in batteries such as small lithium-ion batteries used in mobile and home appliances mainly uses a method of wet smelting after going through processes of crushing, pulverizing, firing, and separation after discharge. However, in some cases, the discharge process is omitted, and a process of separating after dry melting is commercialized and used. The most common discharge method in the wet process is to immerse it in a chemical aqueous solution manufactured for the purpose of complete discharge of the secondary battery and allow natural discharge.

[0003] On the other hand, secondary batteries for automobiles are manufactured to use a relatively very high voltage (currently at the 800V level) compared to the voltage of a single battery of 4V by connecting a large number of secondary batteries in series and parallel for the efficiency of automobile driving, and are structurally robustly assembled for safety.

[0004] When such an automotive secondary battery assembly is immersed in a chemical aqueous solution for natural discharge treatment, the difficulty of the process of disassembling unnecessary parts to increase the recovery rate of the target metal increases. Therefore, after discharging the energy of the secondary battery to the 0 level using an electrical load, it is mainly disassembled manually and immersed in a chemical aqueous solution for natural discharge.

[0005] At this time, after performing normal energy discharge to the "0" level, after a certain period of time, the output voltage of a normal battery recovers from 0V to the 2.5V level, and an automotive battery at the 800V level comes to maintain a voltage of about 500V level, which may pose a threat to safety, and manual operation still remains a difficulty.

Summary of the Invention

Problems to be Solved by the Invention

[0006] This invention was devised in consideration of the above-mentioned circumstances, and aims to provide a battery discharge method that not only recovers and recycles the electrical energy of a battery, but also puts the battery into a completely discharged state where it cannot operate normally, thereby ensuring an electrically safe state in subsequent dismantling processes. [Means for solving the problem]

[0007] According to one aspect of the present invention, a battery discharge method is provided, which includes a first discharge step of connecting a battery and a power converter and applying a voltage to discharge the battery, and a second discharge step of applying the reverse voltage of the first discharge step after the first discharge step to discharge the battery.

[0008] The first discharge stage described above can be performed until the battery's SOC (state of charge) becomes 0.

[0009] The process may include a step where, after the battery's State of Charge (SOC) reaches 0, the battery is discharged until its terminal voltage reaches 0V.

[0010] A short circuit in the battery can occur during the discharge phase, when the battery terminal voltage reaches 0V.

[0011] In the first discharge stage described above, the applied voltage can be 2.5 to 4V, and the current can be 0.3C or more.

[0012] In the first discharge stage described above, the battery temperature can be 60°C or lower.

[0013] In the first discharge stage described above, the power converter can operate in energy regeneration mode.

[0014] In the second discharge stage described above, the applied voltage can be 0 to 3V, and the current can be 0.05 to 1C.

[0015] The above second discharge stage can be performed multiple times.

[0016] The above second discharge stage can be terminated when the short-circuit resistance is 30 to 60 mΩ.

[0017] In the second discharge stage described above, the power converter can independently distribute energy to multiple batteries being discharged. [Effects of the Invention]

[0018] According to the present invention, not only is it possible to recover and recycle the electrical energy of the battery, but it is also possible to put the battery into a completely discharged state where it cannot operate normally, thereby ensuring an electrically safe state in subsequent dismantling processes. [Brief explanation of the drawing]

[0019] [Figure 1] This graph shows the voltage change when a lithium-ion battery is discharged, left idle, and then discharged again. [Figure 2] This shows a battery discharge device according to one embodiment of the present invention. [Figure 3] This is an example of discharging a battery using a DC-DC converter configured with a Buck-Boost power converter according to one embodiment of the present invention. [Modes for carrying out the invention]

[0020] Preferred embodiments of the present invention will be described below with reference to various examples. However, embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below.

[0021] The present invention relates to a battery discharge method.

[0022] FIG. 1 is a graph showing the voltage change when discharging is performed again after leaving a lithium-ion battery standing after discharging. Referring to FIG. 1, generally, after discharging a battery such as a lithium-ion battery until the state of charge (SOC) value is 0 or less (2.5 V to 3 V) down to 0 V and leaving it standing for several minutes to several tens of minutes, it is possible to confirm the phenomenon that the terminal voltage recovers. At this time, when discharging again, it can be confirmed that a considerable amount of initial discharge current is generated. From this, it can be understood that there is a considerable amount of lithium (Li) that has not been discharged to the negative electrode through normal discharging. The inventors of the present invention intensively studied to solve the problem caused by the presence of lithium remaining in the negative electrode, and found that if a reverse voltage, that is, a voltage opposite to the previous discharging, is applied from the time when the voltage of the battery appears as 0 V during discharging, it becomes possible to move the remaining lithium in the negative electrode to the positive electrode faster. When this state is maintained for a certain period of time, it was discovered that it develops into an internal short circuit and the terminal voltage of the battery cannot be recovered, and thus the present invention was completed.

[0023] According to one aspect of the present invention, there is provided a battery discharging method including a first discharging stage in which a battery and a power converter are connected to apply a voltage to discharge the battery, and a second discharging stage in which, after the first discharging stage, a reverse voltage of the first discharging stage is applied to discharge the battery.

[0024] The first discharging stage is preferably performed until the state of charge (SOC) of the battery becomes 0. In the discharging section of the first discharging stage, it is preferable to set the maximum value within the range of the rated current and the allowable temperature according to the battery standard for the discharging speed to ensure a fast discharging speed. Thereby, in the first discharging stage, the applied voltage can be 2.5 to 4 V, the current can be .3C or more, and the temperature of the battery is preferably 60° C or less.

[0025] As described above, after the state of charge (SOC) of the battery reaches 0, it can include a step of discharging the battery until the terminal voltage of the battery becomes 0V. Specifically, when the value obtained by dividing the terminal voltage of the battery by the internal impedance of the power converter, that is, the magnitude of the short-circuit current, reaches the lower limit of the operating current of the power semiconductor used in the power converter, it is preferable to switch from the energy recovery operation mode to the short-circuit operation mode or reverse voltage to approach 0V. The reason is that since the effective operating range of the power converter is designed in the 3V region based on a single cell, the operation around 0V is not only inefficient but also acts as a factor to slow down the discharge speed. Although not particularly limited, the short-circuit operation mode can be adjusted so that the sum of the short-circuit operation time and the reverse voltage operation time is minimized according to the type of battery, and it is preferably performed within a time of 1 minute or less.

[0026] Also, in the first discharge stage, it is preferable for the power converter to operate in the energy regeneration mode. Through this, it is possible to recover and recycle the energy remaining in the battery.

[0027] After the above first discharge stage, a second discharge stage can be performed in which the reverse voltage of the first discharge stage is applied to discharge the battery.

[0028] At this time, the voltage applied in the second discharge stage is preferably 0 to 3V, and the current is preferably 0.05 to 1C, and it is preferably operated in response to the change in the internal resistance. More specifically, if the current is quickly increased to the 1C level through the application of the reverse voltage and the terminal voltage of the battery is increased to the 2 to 3V level in the negative direction and then the current is maintained, the terminal voltage will show a form of decreasing again. After passing through the inflection point representing the maximum voltage, it is preferable to decrease the reverse voltage and maintain the current level at 0.

[0029] The above second discharge stage can be performed multiple times. After the current becomes 0 due to operation with reverse voltage application, the battery voltage gradually approaches 0V, but the voltage fluctuation can be stabilized by repeatedly performing secondary reverse voltage operation in a manner similar to primary reverse voltage operation.

[0030] The above second discharge stage can be performed until the short-circuit resistance is 30 to 60 mΩ. More specifically, the maximum negative voltage that appears when the above second discharge stage is performed tends to decrease gradually. This is because the internal short circuit progresses and the short-circuit resistance decreases. Therefore, the decision to terminate the reverse voltage operation can be made when the short-circuit resistance obtained by dividing the maximum negative voltage that appears during repeated operation of the second discharge stage by the reverse current is 30 to 60 mΩ.

[0031] The operating time in the second discharge stage is finely adjusted through experimentation to minimize the sum of the short-circuit operation duration and the reverse voltage operation time, depending on the type of secondary battery, and it is usually possible to repeat operation for less than one minute.

[0032] Furthermore, it is preferable that the power converter in the second discharge stage independently distributes energy to the multiple batteries being discharged.

[0033] On the other hand, Figure 2 shows a battery discharge device according to one embodiment of the present invention, and according to another aspect of the present invention, a battery discharge device is provided that includes a power converter including an AC-DC power supply and a DC-DC power supply, and a controller.

[0034] The above AC-DC power supply unit controls a shared DC power supply, such as a factory power supply, and can reverse-fetch the electrical energy obtained when a lower-level DC-DC power supply unit performs a battery discharge function back to the shared power supply. The total amount of electrical energy reverse-fetched is defined as the maximum value obtained by summing the total battery discharge energy of each lower-level DC-DC power supply unit, and the capacity of the AC-DC power supply unit can be designed to operate with this total amount.

[0035] As a result, the AC-DC power supply unit can maintain a shared DC voltage so that sufficient energy can be supplied when the DC-DC power supply unit applies a reverse voltage to the secondary battery.

[0036] The above DC-DC power supply device is not particularly limited and may consist of a combination of a unipolar Buck-Boost converter and a mechanical switch capable of reversing the output polarity, or it may consist of a bipolar single-phase PWM converter.

[0037] On the other hand, the controller plays a role in controlling the discharge process of the secondary battery, which includes a first discharge stage in which the battery and power converter are connected and a voltage is applied to discharge the secondary battery, and a second discharge stage in which the voltage opposite to that of the first discharge stage (reverse voltage) is applied after the first discharge stage to discharge the secondary battery. The controller builds a database of discharge control patterns for the power converter according to the electric vehicle model and battery type, which the driver can select and operate on-site or remotely, and the database can be configured to be remotely updateable. [Examples]

[0038] The present invention will be described in more detail below with reference to examples. The following examples are provided to illustrate the present invention in more detail and are not intended to limit the present invention.

[0039] Referring to Figure 3, in the first discharge stage, S / W1 is closed, S / W2 is closed, S / W3 is closed, S / W4 is open, S1 is not operating, and the switching operation of S2 transmits the energy from the secondary battery to the DC power supply capacitor of the AC-DC converter, and the AC-DC converter transmits the energy transmitted from the battery through the DC-DC converter.

[0040] Subsequently, when the battery voltage drops to 0V after being fully discharged and considering the internal impedance of the converter, the S2 On state is maintained and a short-circuit discharge is performed. At this time, S1 does not operate.

[0041] Subsequently, by closing S / W4 and opening S / W3 to switch to reverse voltage operation mode, turning S2 off, and using S1 to perform reverse voltage operation, the battery can be completely discharged.

[0042] Although embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and it will be obvious to those with ordinary skill in the art that various modifications and variations are possible without departing from the technical idea of ​​the present invention as described in the claims.

Claims

1. A first discharge step involves connecting the battery and a power converter, applying voltage to the battery, and discharging the battery. After the first discharge stage, a second discharge stage is performed in which the battery is discharged by applying the reverse voltage of the first discharge stage to the battery, which leads to an internal short circuit in the battery. Includes, In the second discharge stage, the applied voltage is 0 to 3V, and the current is 0.05 to 1C. The second discharge stage ends when the short-circuit resistance is 30 to 60 mΩ. In this battery discharge method, the short-circuit resistance is a value obtained by dividing the maximum negative voltage that appears when the second discharge stage is performed by the reverse current.

2. The battery discharge method according to claim 1, wherein the first discharge step is performed until the state of charge (SOC) of the battery becomes 0.

3. The battery discharge method according to claim 1, further comprising the step of discharging the battery until the terminal voltage of the battery becomes 0V after the State of Charge (SOC) of the battery becomes 0V.

4. The battery discharge method according to claim 1, wherein the first discharge stage is characterized by an applied voltage of 2.5 to 4V and a current of 0.3C or more.

5. The battery discharge method according to claim 1, wherein the temperature of the battery is 60°C or lower during the first discharge stage.

6. The battery discharge method according to claim 1, wherein in the first discharge stage, the power converter operates in energy regeneration mode.

7. The battery discharge method according to claim 1, wherein the second discharge step is performed multiple times.

8. The power converter includes an AC-DC power supply and a DC-DC power supply, The battery discharge method according to claim 1, wherein in the second discharge stage, the power converter independently distributes energy to a plurality of batteries to be discharged.

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