CN116247316A - Battery cell discharging method, battery pack and electric equipment - Google Patents
Battery cell discharging method, battery pack and electric equipment Download PDFInfo
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/44—Methods for charging or discharging
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/44—Methods for charging or discharging
- H01M10/448—End of discharge regulating measures
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
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- Chemical Kinetics & Catalysis (AREA)
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- General Chemical & Material Sciences (AREA)
- Secondary Cells (AREA)
Abstract
The application discloses a battery cell discharging method, a battery pack and electric equipment. The battery cell discharging method comprises the steps that the battery cell discharges at a first discharging multiplying power, one of the following two steps is executed in response to the direct current impedance of the battery cell being larger than or equal to a first resistance threshold value, or in response to the voltage of the battery cell being smaller than or equal to a first voltage threshold value, or in response to the state of charge of the battery cell being smaller than or equal to a first state of charge threshold value: (i) The battery cell discharges at a discharge rate less than or equal to a second discharge rate, wherein the second discharge rate is less than the first discharge rate. (ii) The battery core stops discharging at the first discharging multiplying power and supplies power to a battery management system electrically connected with the battery core, so that the charge state of the battery core is reduced by the first charge state. By the mode, the risk of sharp reduction of the power of the battery cell caused by the increase of the voltage drop of the battery cell can be reduced.
Description
Technical Field
The application relates to the technical field of batteries, in particular to a battery core discharging method, a battery pack and electric equipment.
Background
The lithium iron manganese phosphate (LFMP) system is a new lithium battery system currently in the industry and has a higher energy density than the traditional lithium iron phosphate system, so the lithium iron manganese phosphate (LFMP) system is also a new system which is recently paid close attention.
Wherein the lithium iron manganese phosphate system has a higher mean voltage than the lithium iron phosphate system. The main reason is that there are two phase-change reactions in the lithium iron manganese phosphate system. The two phase transformation reactions are Mn respectively 2+ /Mn 3+ Phase transition reaction with Fe 2+ /Fe 3+ Phase change reaction of (a).
Disclosure of Invention
The application aims to provide a battery cell discharging method, a battery pack and electric equipment, which can reduce the risk of sharp reduction of power of a battery cell caused by increase of voltage drop of the battery cell.
To achieve the above object, in a first aspect, the present application provides a method for discharging a battery cell, including: the battery cell discharges at a first discharge rate, and one of the following two steps is performed in response to the direct current impedance of the battery cell being greater than or equal to a first resistance threshold, or in response to the voltage of the battery cell being less than or equal to a first voltage threshold, or in response to the state of charge of the battery cell being less than or equal to a first state of charge threshold: (i) The battery core discharges at a discharge rate less than or equal to a second discharge rate, wherein the second discharge rate is less than the first discharge rate; (ii) The battery core stops discharging at the first discharging multiplying power and supplies power to a battery management system electrically connected with the battery core, so that the charge state of the battery core is reduced by the first charge state.
By the mode, when the voltage drop of the battery cell increases due to the fact that the direct current impedance of the battery cell increases, the voltage drop of the battery cell can be reduced, and the risk of sharp power reduction of the battery cell is reduced.
In an alternative, step (i) further comprises: the battery cell discharges at a first discharge rate in response to the direct current impedance of the battery cell being less than or equal to a first resistance threshold, or in response to the voltage of the battery cell being less than or equal to a second voltage threshold, or in response to the state of charge of the battery cell being less than or equal to a second state of charge threshold. Wherein the second voltage threshold is less than the first voltage threshold and the second state of charge threshold is less than the first state of charge threshold.
In an alternative manner, the discharging method further comprises: and stopping discharging the battery cell in response to the voltage of the battery cell being less than or equal to the third voltage threshold. Wherein the third voltage threshold is less than the second voltage threshold.
In an alternative, step (ii) further comprises: responsive to the voltage of the battery cell being greater than a fourth voltage threshold, discharging the battery cell at a first discharge rate; or, in response to the voltage of the cell being less than or equal to the fourth voltage threshold, stopping discharging of the cell.
In an alternative, the cathode material of the cellThe material comprises lithium iron manganese phosphate, and the discharge method further comprises the following steps: determining a first resistance threshold based on a first metering ratio of manganese ions in the lithium iron manganese phosphate, wherein the first metering ratio is a ratio between the number of manganese ions in the lithium iron manganese phosphate and the sum of the number of manganese ions and the number of iron ions; and/or determining a first voltage threshold and a first state of charge threshold based on a first phase change reaction and a second phase change reaction, wherein the first phase change reaction is Fe in the battery cell 2+ Conversion to Fe 3+ The second phase change reaction becomes Mn in the cell 2+ Conversion to Mn 3+ Phase change reaction of (a).
In an alternative manner, determining the first resistance threshold based on a first metering ratio of manganese ions in the lithium iron manganese phosphate includes: the first resistance threshold is determined based on the first metering ratio, the preset metering ratio, and the first preset resistance threshold. The preset metering ratio is the ratio of the number of manganese ions in the preset lithium iron manganese phosphate to the sum of the number of manganese ions and the number of iron ions, and the first preset resistance threshold is a preset first resistance threshold.
In an alternative manner, determining the first resistance threshold based on the first metering ratio, the preset metering ratio, and the first preset resistance threshold includes: the first resistance threshold is: dcr1=k1+ (Y-K2) k3. Wherein, DCR1 is the first resistance threshold, K1 is the first preset resistance threshold, Y is the first metering ratio, K2 is the preset metering ratio, and K3 is the preset coefficient.
In an alternative, the first preset resistance threshold is 25mΩ when the preset metering ratio is 0.7.
In an alternative manner, determining the first voltage threshold and the first state of charge threshold based on the first phase change reaction and the second phase change reaction includes: and determining a first voltage threshold based on a voltage interval between the first voltage and the second voltage, wherein the first voltage is a corresponding cell voltage when the first phase change reaction occurs, and the second voltage is a corresponding cell voltage when the second phase change reaction occurs. And/or determining a first state of charge threshold based on a state of charge interval between a second state of charge and a third state of charge, wherein the second state of charge is a state of charge corresponding to when the first phase change reaction occurs, and the third state of charge is a state of charge corresponding to when the second phase change reaction occurs.
In a second aspect, the present application provides a battery pack. The battery pack comprises a battery module and a battery management system, and the battery module is electrically connected with the battery management system. The battery module comprises at least one electric core. The battery management system includes at least one processor and a memory communicatively coupled to the at least one processor. Wherein the memory stores instructions executable by the at least one processor to cause the battery pack to perform the discharging method of the first aspect.
In a third aspect, the present application provides a powered device comprising a load and a battery pack of the third aspect. The battery pack is used for supplying power to the load.
The beneficial effects of this application are: the discharging method of the battery cell realizes that when the battery cell discharges at the first discharging multiplying power, the operation of reducing the voltage drop of the battery cell is executed as long as the direct current impedance of the battery cell, the voltage of the battery cell or the charge state of the battery cell meets certain conditions. The operation of reducing the voltage drop of the battery cell includes controlling the battery cell to discharge at a discharge rate less than or equal to the second discharge rate, or controlling the battery cell to stop discharging at the first discharge rate and controlling the battery cell to supply power to a battery management system electrically connected with the battery cell, so that the charge state of the battery cell is reduced by the first charge state. In addition, when the voltage drop of the battery cell increases due to the increase of the direct current impedance of the battery cell, the voltage drop of the battery cell can be reduced, so that the risk of sharp power reduction of the battery cell is reduced.
Drawings
One or more embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements, and in which the figures of the drawings are not to be taken in a limiting sense, unless otherwise indicated.
Fig. 1 is a schematic structural view of a battery pack according to an embodiment of the present disclosure;
FIG. 2 is a flow chart of a discharging method of a battery cell according to an embodiment of the present disclosure;
FIG. 3 is a schematic diagram of DC impedance of a battery cell during discharging according to an embodiment of the present disclosure;
FIG. 4 is a schematic diagram of method steps performed after step 21 shown in FIG. 2, according to one embodiment of the present application;
FIG. 5 is a flowchart of a method for discharging a battery cell according to an embodiment of the present disclosure;
FIG. 6 is a flow chart of a method for discharging a battery cell when the battery cell uses lithium iron manganese phosphate as a cathode material according to an embodiment of the present application;
FIG. 7 is a schematic diagram of an implementation of step 61 shown in FIG. 6 provided in an example of the present application;
FIG. 8 is a schematic diagram of an implementation of step 71 shown in FIG. 7 provided in an example of the present application;
FIG. 9 is a schematic diagram of an open circuit voltage of a battery cell in a full SOC according to an embodiment of the present disclosure;
FIG. 10 is a schematic diagram of an implementation of step 62 shown in FIG. 6 provided in an example of the present application;
fig. 11 is a schematic structural diagram of an electric device according to an embodiment of the present application.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions of the embodiments of the present application will be described in detail below with reference to the accompanying drawings in the embodiments of the present application. The following examples are illustrative and not limiting, are intended to provide a basic understanding of the present application, and are not intended to identify key or critical elements of the application or to delineate the scope of the protection.
It will be understood that when an element is referred to as being "connected" to another element, it can be directly connected to the other element or one or more intervening elements may be present therebetween.
In addition, technical features which are described below and which are involved in the various embodiments of the present application may be combined with each other without constituting a conflict.
Referring to fig. 1, fig. 1 is a schematic structural diagram of a battery pack 1000 according to an embodiment of the present disclosure. The battery pack 1000 includes the battery management system 100 and the battery module 200. The elements can be connected through a bus or directly.
The battery module 200 is used to store and provide electrical energy. The battery module 200 includes at least one cell 202 (only one shown). When the battery module 200 includes more than two battery cells 202, each battery cell 202 may be connected in series, connected in parallel, or in a hybrid form of series and parallel connection. In some embodiments, the battery module 200 is a rechargeable battery. For example, the battery module 200 may be a lead-acid battery, a nickel-cadmium battery, a nickel-hydrogen battery, a lithium ion battery, a lithium polymer battery, a lithium iron phosphate battery, or the like. The battery module 200 may be repeatedly charged in a recyclable manner.
In some embodiments, the cell 202 has a lithium iron manganese phosphate (LFMP) material as the cathode host material. The cell 202 includes a positive electrode sheet, a negative electrode sheet, an isolating film, and an electrolyte.
In this example, the positive electrode sheet was prepared as follows: lithium iron manganese phosphate (LFMP), conductive carbon black (Super P) and polyvinylidene fluoride (PVDF) are mixed according to the weight ratio of 97.5:1.0:1.5, N-methyl pyrrolidone (NMP) is added as a solvent, and the mixture is prepared into slurry with the solid content of 0.75, and the slurry is uniformly stirred. Uniformly coating the slurry on aluminum foil with the thickness of 12 mu m, wherein the weight of positive electrode active substance on the pole piece is 180g/m 2 . Drying at 90 ℃ to finish the single-sided coating of the positive electrode plate, and then finishing the coating of the other side by the same method. After the coating was completed, the positive electrode active material layer of the pole piece was cold-pressed to 4.1g/cm 3 And then auxiliary processes such as tab welding, gummed paper and the like are carried out to complete the whole preparation process of the double-sided coated positive plate.
The preparation process of the negative electrode plate comprises the following steps: mixing negative electrode active material Graphite (Graphite), conductive carbon black (Super P) and Styrene Butadiene Rubber (SBR) according to the weight ratio of 96:1.5:2.5, and adding deionized water (H) 2 O) was used as a solvent, and the slurry was prepared to have a solid content of 0.7, and stirred uniformly. The slurry was uniformly coated on a copper foil of 8 μm, the electrodeThe weight of the negative electrode active material on the sheet was 95g/m 2 . Drying at 110 ℃ to finish the single-sided coating of the negative electrode plate of the electrode plate, and then finishing the coating of the other side by the same method. After the coating was completed, the negative electrode active material layer of the pole piece was cold-pressed to 1.7g/cm 3 Is a compact density of (a). And then auxiliary processes such as tab welding and gummed paper pasting are carried out, so that all preparation processes of the double-sided coated negative electrode plate are completed.
The preparation process of the electrolyte is as follows: in a dry argon atmosphere, the organic solvents Ethylene Carbonate (EC), ethylmethyl carbonate (EMC) and diethyl carbonate (DEC) were first mixed in mass ratio EC: EMC: dec=30:50:20, and then lithium salt lithium hexafluorophosphate (LiPF) was added to the organic solvent 6 ) Dissolving and mixing uniformly to obtain the electrolyte with the lithium salt concentration of 1.15M.
The preparation process of the cell 202 is as follows: polyethylene (PE) with thickness of 15 μm is selected as a base film of the isolating film and is coated with a ceramic coating (2 μm) and a polymer coating (2.5 mg/1540.25 mm) 2 ) And fixing the prepared positive pole piece and isolating film on a structure formed by the negative pole piece, and stacking and winding the positive pole piece and the isolating film into a bare cell according to the sequence. After top sealing and side sealing, the battery cell is injected with liquid, and the battery cell after the injection is formed (for example, the battery cell is charged to 3.3V by 0.02C constant current and then charged to 3.6V by 0.1C constant current), so that the active substance of the battery cell is activated, and finally the battery cell 202 is obtained.
It should be noted that the foregoing illustrates only one preparation process of the battery cell 202, and in other embodiments, the preparation may be performed in other manners, which is not limited herein.
The battery management system (Battery Management System, BMS) 100 is used for detecting, managing, and/or protecting the battery module 200, etc. In some embodiments, the BMS100 is configured to obtain a dc impedance, a voltage, and a State of Charge (SOC) of the battery 202. SOC is the ratio of the remaining capacity to the battery capacity and is commonly expressed as a percentage. The SOC ranges from 0 to 100%, and indicates that the battery is completely discharged when soc=0 and that the battery is completely charged when soc=100%.
In some embodiments, the BMS100 applies a dc signal to the battery cell 202, and obtains the voltage of the battery cell 202, and calculates the dc resistance of the battery cell 202 according to the physical formula resistance=voltage/current.
In other embodiments, the BMS100 obtains the SOC of the cell 202 by ampere-hour integration (also known as current integration or coulomb counting). Specifically, the SOC at the initial time of discharging the battery cell 202 is obtained (denoted as SOC 1), the SOC (denoted as SOC 2) of the change in the discharging time is calculated by calculating the integral of the discharging current and the corresponding time in a certain time, and the current SOC of the battery cell 202 is calculated based on the difference between the SOC1 and the SOC 2.
It should be noted that the foregoing embodiments only illustrate one way for the BMS100 to obtain the dc resistance and the SOC of the battery cell 202, and in other embodiments, other ways may be adopted, which are not limited herein.
The battery management system 100 comprises at least one processor 104 and a memory 102 in communication with the at least one processor 104, wherein the memory 102 may be built in the battery management system 100, or may be external to the battery management system 100, or the memory 102 may be a remotely located memory, and the battery management system 100 is connected through a network.
The memory 102 is used as a non-volatile computer-readable storage medium for storing non-volatile software programs, non-volatile computer-executable programs, and modules. The memory 102 may include a storage program area that may store an operating system, at least one application program required for functions, and a storage data area; the storage data area may store data created according to the use of the terminal, etc. In addition, memory 102 may include high-speed random access memory, and may also include non-volatile memory, such as at least one magnetic disk storage device, flash memory device, or other non-volatile solid-state storage device. In some embodiments, memory 102 may optionally include memory located remotely from processor 104, which may be connected to the terminal via a network. Examples of such networks include, but are not limited to, the internet, intranets, local area networks, mobile communication networks, and combinations thereof.
The processor 104 performs various functions of the terminal and processes the data by running or executing software programs and/or modules stored in the memory 102 and invoking the data stored in the memory 102, thereby performing overall monitoring of the terminal, for example, implementing the discharging method of the cells in any of the embodiments of the present application.
The number of processors 104 may be one or more, one processor 104 being illustrated in fig. 1. The processor 104 and the memory 102 may be connected by a bus or other means. The processor 104 may include a Central Processing Unit (CPU), a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a controller, a Field Programmable Gate Array (FPGA) device, or the like. The processor 104 may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.
Referring to fig. 2, fig. 2 is a flowchart of a discharging method of a battery cell according to an embodiment of the present application. As shown in fig. 2, the discharging method of the battery cell includes the following steps:
step 21: the battery cell discharges at a first discharge rate, and the battery cell discharges at a discharge rate less than or equal to a second discharge rate in response to a direct current impedance of the battery cell being greater than or equal to a first resistance threshold, or in response to a voltage of the battery cell being less than or equal to a first voltage threshold, or in response to a state of charge of the battery cell being less than or equal to a first state of charge threshold.
The second discharge rate and the first discharge rate are both discharge rates during the discharge of the battery cells. The second discharge rate is smaller than the first discharge rate.
In some embodiments, the first discharge rate is the discharge rate of the cell during normal use. For example, the first discharge rate was set to 1.5C for a battery cell using lithium manganese iron phosphate as a cathode material. The discharge rate of 1.5C means that 1.5 hours are required for the electric quantity of the battery cell to be full to zero at the discharge rate.
Referring to fig. 3 together, fig. 3 is a schematic diagram illustrating the dc impedance of the battery cell during discharging. Wherein, the abscissa is SOC, and the ordinate is DCR. DCR is the dc impedance of the cell. Curve L1 is a schematic diagram of the dc impedance of the cell. As shown in fig. 3, during the discharge of the battery cell, the dc impedance of the battery cell tends to increase and decrease. In the process of increasing the direct current impedance of the battery cell, the voltage drop on the battery cell is determined by the product of the discharge current of the battery cell and the direct current impedance of the battery cell, and the voltage drop on the battery cell is increased, so that the power of the battery cell is reduced sharply.
In the related art, in order to reduce the risk of sharp reduction of power, schemes of optimizing the material level (such as material nanocrystallization) or improving the conductivity of the electrolyte are generally adopted. These schemes reduce the voltage drop across the cell by reducing the dc impedance of the cell. However, these solutions require an increase in development effort and costs on the one hand and, on the other hand, lead to a deterioration in the stability of the system.
In the embodiment of the application, when the direct current impedance of the battery cell is increased to be larger than or equal to the first resistance threshold value, the battery cell discharges at a discharge rate smaller than the second discharge rate. And the discharge current of the battery cell and the discharge multiplying power of the battery cell show positive correlation. The larger the discharge multiplying power is, the larger the discharge current of the battery cell is, and the larger the voltage drop on the battery cell is; conversely, the smaller the discharge rate, the smaller the discharge current of the cell and the smaller the voltage drop across the cell. Therefore, the battery cell is discharged at a discharge rate smaller than the second discharge rate, the discharge rate of the battery cell is correspondingly reduced, and the voltage drop of the battery cell can be reduced. And further the risk of sharp power reduction of the battery cell can be reduced. The first resistance threshold may be set according to an actual application, which is not specifically limited in the embodiment of the present application.
In addition, the voltage is gradually reduced during the discharge of the battery cells. The discharge rate of the cells can also be controlled based on the voltage of the cells. Specifically, when the battery cell discharges, if the voltage of the battery cell is reduced to be less than or equal to the first voltage threshold, the battery cell is controlled to discharge at a discharge rate smaller than the second discharge rate so as to reduce the voltage drop of the battery cell. Thereby reducing the risk of sharp power reduction of the battery cell. The first voltage threshold may be set according to an actual application, which is not specifically limited in the embodiment of the present application.
Similarly, during the discharge of the cell, the SOC is gradually reduced. The discharge rate of the battery cells can also be controlled based on the SOC of the battery cells. Specifically, when the battery cell discharges, if the SOC of the battery cell is reduced to be less than or equal to the first state of charge threshold, the battery cell is controlled to discharge at a discharge rate less than the second discharge rate, so as to reduce the voltage drop of the battery cell. Thereby reducing the risk of sharp power reduction of the battery cell. The first state of charge threshold may be set according to an actual application, which is not specifically limited in the embodiment of the present application.
To sum up, in this embodiment, when determining that a larger voltage drop may occur in the battery cell based on the dc impedance, voltage or SOC of the battery cell, the discharge rate of the battery cell is reduced, so that the risk of sharp power drop of the battery cell may be reduced. The required cost investment is lower, the risk of system stability deterioration is also reduced, and the method has stronger practicability.
In one embodiment, as shown in fig. 4, after performing step 21, the discharging method of the battery cell further includes the following steps:
step 41: the battery cell discharges at a first discharge rate in response to the direct current impedance of the battery cell being less than a first resistance threshold, or in response to the voltage of the battery cell being less than or equal to a second voltage threshold, or in response to the state of charge of the battery cell being less than or equal to a second state of charge threshold.
Specifically, as shown in fig. 3, in the process of discharging the battery cell, when the dc impedance of the battery cell reaches the maximum value, the dc impedance of the battery cell instead shows a decreasing trend, that is, the voltage drop of the battery cell also decreases. Then, after step 21 is performed, if it is detected that the dc impedance of the battery cell is less than the first resistance threshold, or the voltage of the battery cell is less than or equal to the second voltage threshold, or the state of charge of the battery cell is less than or equal to the second state of charge threshold, it is determined that the voltage drop of the battery cell has been reduced, and the discharge rate of the battery cell can be increased again (in this embodiment, the discharge rate of the battery cell is restored to the first discharge rate), so as to meet the electricity consumption requirement of the user.
In this embodiment, the discharge rate of the recovery cell is exemplified as the first discharge rate. In other embodiments, the discharge rate of the battery cell may be adjusted to other discharge rates, which is not particularly limited in the embodiments of the present application.
Secondly, in this embodiment, in the process of decreasing the dc impedance of the battery cell, the voltage and SOC of the battery cell also decrease, so the second voltage threshold needs to be set smaller than the first voltage threshold, and the first state of charge threshold needs to be set smaller than the second state of charge threshold, so as to improve the effectiveness of the scheme. The second voltage threshold and the second state of charge threshold may be set according to actual application conditions, which is not particularly limited in the embodiments of the present application.
In another embodiment, the discharging method of the battery cell further includes the following steps: and controlling the battery cell to stop discharging in response to the voltage of the battery cell being less than or equal to the third voltage threshold.
Wherein the third voltage threshold is less than the second voltage threshold. The third voltage threshold may be set according to practical application, which is not particularly limited in the embodiment of the present application. In some embodiments, the third voltage threshold may be set to a lower limit voltage of the battery cell, where the lower limit voltage is a cut-off voltage when the battery cell discharges, and if the battery cell discharges to a voltage below the lower limit voltage, the capacity of the battery cell may be severely reduced or even damaged. Through setting the third voltage threshold as the lower limit voltage of the battery cell, the risk of overdischarge of the battery cell can be reduced, and the service life of the battery cell is prolonged.
Referring to fig. 5, fig. 5 is a flowchart of a discharging method of a battery cell according to another embodiment of the present application. As shown in fig. 5, the discharging method of the battery cell includes the following steps:
step 51: the battery cell discharges at a first discharge rate, and in response to the direct current impedance of the battery cell being greater than or equal to a first resistance threshold, or in response to the voltage of the battery cell being less than or equal to a first voltage threshold, or in response to the state of charge of the battery cell being less than or equal to a first state of charge threshold, the battery cell stops discharging at the first discharge rate and supplies power to a battery management system electrically connected to the battery cell, such that the state of charge of the battery cell is reduced by the first state of charge.
Specifically, as can be seen from the above embodiments, in the discharging process of the battery cell, if it is detected that the dc impedance of the battery cell is greater than or equal to the first resistance threshold, or the voltage of the battery cell is less than or equal to the first voltage threshold, or the state of charge of the battery cell is less than or equal to the first state of charge threshold, it is determined that the voltage drop of the battery cell has increased to a level that can cause a sharp decrease in the power of the battery cell. At this time, in the present embodiment, the battery cell is first controlled to stop discharging at the first discharge rate. And then, the electric quantity of the battery cell is consumed through the BMS, and the state of charge of the battery cell is reduced by the first state of charge. The direct current impedance of the battery cell can be reduced, and the voltage drop of the battery cell during discharging can be reduced. The first state of charge is a preset state of charge, which may be set according to an actual application condition, which is not specifically limited in the embodiment of the present application. For example, in some embodiments, the first state of charge is set to 5%, and the SOC of the battery cell is 50% when the battery cell is controlled to stop discharging at the first discharge rate, the battery cell is consumed by the BMS to reduce the SOC of the battery cell from 50% to 45%.
Taking the dc impedance of the cell shown in fig. 3 as an example. Also, in this embodiment, the first resistance threshold is set to 30mΩ, and the first state of charge is set to 5% as an example. And taking the condition that the direct current impedance of the triggered battery cell is greater than or equal to the first resistance threshold value as an example. And when the direct current impedance of the battery cell is detected to be larger than 30mΩ, the battery cell is controlled to stop discharging, and the SOC of the battery cell is close to 45%. The battery cell charge is consumed by the BMS until the SOC of the battery cell is 40%. At this time, the dc impedance of the cell is smaller than the first resistance threshold, thereby reducing the voltage drop of the cell at the time of discharging and reducing the risk of causing sharp reduction of the power of the cell.
In another embodiment, after performing step 51, the discharging method of the battery cell further includes the following steps: responsive to the voltage of the battery cell being greater than a fourth voltage threshold, discharging the battery cell at a first discharge rate; or, in response to the voltage of the cell being less than or equal to the fourth voltage threshold, stopping discharging of the cell.
Specifically, the fourth voltage threshold may be set according to the actual application, which is not specifically limited in the embodiment of the present application.
In some embodiments, the fourth voltage threshold may be set to a lower voltage of the battery cell. After step 51 is performed, the SOC of the battery cell decreases by the first state of charge, and if the voltage of the battery cell is greater than the fourth voltage threshold, it is determined that the battery cell may continue to discharge. And then the battery cell can continue to discharge at the first discharge rate so as to meet the electricity consumption requirement of a user.
Otherwise, if the voltage of the battery cell is smaller than or equal to the fourth voltage threshold, it is determined that the battery cell cannot continue to discharge. And then the cell stops discharging. In this embodiment, by setting the fourth voltage threshold to the lower limit voltage of the battery cell, the risk of overdischarge of the battery cell can be reduced, thereby prolonging the service life of the battery cell.
In some embodiments, the cathode material of the cell comprises lithium manganese iron phosphate. In this case, embodiments of the present application also provide a way to determine the first resistance threshold, the first voltage threshold, and the first state of charge threshold. Specifically, as shown in fig. 6, the discharging method of the battery cell further includes the following steps:
step 61: a first resistance threshold is determined based on a first metering ratio of manganese ions in the lithium iron manganese phosphate.
Wherein the first metering ratio is the ratio between the amount of manganese ions in the lithium iron manganese phosphate and the sum of the amounts of manganese ions and iron ions.
LFMP material is used as LiMn 0.7 Fe 0.3 PO 4 As an example. The metering ratio corresponding to the number of Mn ions is 0.7 and the metering ratio corresponding to the number of Fe ions is 0.3, so the ratio between the number of Mn ions and the sum of the number of Mn ions and Fe ions is 0.7/(0.3+0.7) =0.7, i.e., the first metering ratio is 0.7.
In another embodiment, as shown in fig. 7, the process of determining the first resistance threshold in step 61 based on the first metering ratio of manganese ions in lithium iron manganese phosphate includes the steps of:
step 71: the first resistance threshold is determined based on the first metering ratio, the preset metering ratio, and the first preset resistance threshold.
The preset metering ratio is a ratio between the number of manganese ions in the preset lithium iron manganese phosphate and the sum of the number of manganese ions and the number of iron ions, and the first preset resistance threshold is a preset first resistance threshold.
LFMP material is used as LiMn 0.7 Fe 0.3 PO 4 The parameters are used as references for setting the parameters in other LFMP materials. In this embodiment, the preset metering ratio is 0.7/(0.7+0.3) =0.7. At the same time, for LiMn 0.7 Fe 0.3 PO 4 The cell as cathode material is tested or otherwise empirically determined to determine the first resistance threshold that is desired to be set for the cell. The first resistance threshold value may be a preset first resistance threshold value, that is, a first preset resistance threshold value. In some embodiments, for LiMn 0.7 Fe 0.3 PO 4 As the battery cell of the cathode material, the corresponding first resistance threshold is set to 25mΩ, i.e. the first preset resistance threshold is set to 25mΩ.
In practical application, when the LFMP material is selected to be LiMn-removed 0.7 Fe 0.3 PO 4 When other materials are used, the first preset resistance threshold value can be correspondingly modified based on the difference between the first metering ratio and the preset metering ratio of the actual LFMP material so as to obtain the actual first resistance threshold value.
In some embodiments, as shown in fig. 8, one way of correspondingly modifying the first preset resistance threshold to obtain an actual first resistance threshold is illustrated in fig. 8, based on the difference between the actual first and preset metering ratios of LFMP material. Specifically, the process of determining the first resistance threshold in step 71 based on the first metering ratio, the preset metering ratio and the first preset resistance threshold includes the following steps:
step 81: the first resistance threshold is: dcr1=k1+ (Y-K2) k3.
Wherein, DCR1 is the first resistance threshold, K1 is the first preset resistance threshold, Y is the first metering ratio, K2 is the preset metering ratio, and K3 is the preset coefficient. In some embodiments, K3 may be set to 30.
In this embodiment, K3 times the difference between the first metering ratio and the preset metering ratio is taken as the difference to be adjusted. The difference is the difference between the first resistance threshold value correspondingly set when the LFMP material is used as the cell of the cathode material and the first resistance threshold value correspondingly set when the LFMP material actually used is used as the cell of the cathode material.
The LFMP material based on standard is LiMn 0.7 Fe 0.3 PO 4 An example is described. The preset metering ratio K2 is 0.7. And by LiMn 0.7 Fe 0.3 PO 4 The first resistance threshold value set correspondingly when the material is used as the battery core of the cathode material is 25mΩ, namely a first preset resistance threshold value k1=25mΩ. And K3 is set to 30. The first resistance threshold value set correspondingly when the LFMP material actually used is used as the cell of the cathode material is: 25- (Y1-0.7) x 30.
For example, in one embodiment, the LFMP material actually used is LiMn 0.6 Fe 0.4 PO 4 The first measurement ratio Y1 is 0.6/(0.6+0.4) =0.6, and at this time, the first resistance threshold value set correspondingly when the LFMP material actually used is used as the cell of the cathode material is: 25+ (0.6-0.7) 30=22mΩ. For the battery cell, when the battery cell discharges at the first discharge rate, if the direct current impedance of the battery cell is greater than or equal to 22mΩ, the battery cell is controlled to discharge at the discharge rate which is less than or equal to the second discharge rate, or the battery cell is controlled to stop discharging at the first discharge rate, and the electric quantity of the battery cell is consumed through the BMS. Furthermore, the voltage drop of the battery cell can be reduced, and the risk of sharp power reduction of the battery cell is reduced.
Step 62: a first voltage threshold and a first state of charge threshold are determined based on the first phase change reaction and the second phase change reaction.
Wherein the first phase change reaction is Fe in the battery cell 2+ Conversion to Fe 3+ The second phase change reaction becomes Mn in the cell 2+ Conversion to Mn 3+ Phase change reaction of (a).
LFMP material is used as LiMn 0.7 Fe 0.3 PO 4 As an example. Referring to FIG. 9, the LiMn is shown in FIG. 9 0.7 Fe 0.3 PO 4 System as cathode materialSchematic of open circuit voltage (Open circuit voltage, OCV) at State of Charge (SOC). Wherein, full SOC refers to SOC from 0-100%. OCV refers to the potential difference between the poles of a cell when the cell is not discharging.
As shown in fig. 9, the abscissa is SOC and the ordinate is OCV. Curve L2 is LiMn 0.7 Fe 0.3 PO 4 OCV curve of battery cell of system as cathode material under full SOC. At an SOC of about 30%, a first phase change reaction occurs, specifically corresponding to Fe 2+ Conversion to Fe by phase transition reaction 3+ . At a SOC of about 50%, a second phase change reaction, specifically Mn, occurs 2+ Conversion to Mn by phase transition reaction 3+ . At the same time, as can be obtained in connection with FIG. 3, when the SOC is at [30%,50%]This interval also enables the maximum value of the dc impedance of the cell to be obtained. In summary, it can be determined that the SOC interval corresponding to the first phase change reaction and the second phase change reaction matches the SOC interval corresponding to the maximum value of the dc resistance of the battery cell to a higher degree. Based on this, the first state of charge threshold may be determined by the first phase change reaction and the second phase change reaction described above. Next, as shown in fig. 9, the first phase change reaction and the second phase change reaction can also correspond to the voltage interval of the battery cell. Therefore, the first voltage threshold can also be determined based on the first phase change reaction and the second phase change reaction.
In some embodiments, as shown in fig. 10, the process of determining the first voltage threshold and the first state of charge threshold based on the first phase change reaction and the second phase change reaction in step 62 includes the steps of:
step 101: a first voltage threshold is determined based on a voltage interval between the first voltage and the second voltage.
The first voltage is a corresponding cell voltage when the first phase change reaction occurs, and the second voltage is a corresponding cell voltage when the second phase change reaction occurs.
LFMP material is used as LiMn 0.7 Fe 0.3 PO 4 As an example. As shown in fig. 9, when the OCV is about 3.4V, the first phase change reaction occurs, that is, the corresponding cell voltage is about 3.4V when the first phase change reaction occurs, and the first voltage is 3.4V. At an OCV of about 3.9VA second phase change reaction occurs, i.e. the corresponding cell voltage is about 3.9V when the second phase change reaction occurs, the second voltage being 3.9V.
When the OCV is in the [3.4V,3.9V ] interval, the SOC is about in the [30%,50% ] interval. As shown in fig. 3, the dc impedance of the cell can reach a maximum value when the SOC is in the [30%,50% ] range. In summary, when the OCV is in the [3.4v,3.9v ] range, the dc impedance of the battery cell can reach the maximum value, and the operation of reducing the voltage drop of the battery cell can be performed. Wherein, reducing the voltage drop of the battery cell includes step 21 shown in fig. 2 and step 51 shown in fig. 5.
In some embodiments, any of the voltages [3.4V,3.9V ] may be used as the first voltage threshold, such as 3.9V. The purpose of reducing the risk of sharp power reduction of the battery cell by reducing the voltage drop of the battery cell can be achieved.
Step 102: the first state of charge threshold is determined based on a state of charge interval between the second state of charge and the third state of charge.
The second charge state is the charge state corresponding to the first phase change reaction, and the third charge state is the charge state corresponding to the second phase change reaction.
Likewise, LFMP material is LiMn 0.7 Fe 0.3 PO 4 As an example. As shown in fig. 9, the first phase change reaction occurs at an SOC of about 30%, i.e., the corresponding SOC at which the first phase change reaction occurs is about 30%, and the second state of charge is 30%. When the SOC is about 50%, the second phase change reaction occurs, that is, the corresponding SOC when the second phase change reaction occurs is about 50%, and the third state of charge is 50%.
As shown in fig. 3, in the SOC range of 30%,50%, the dc resistance of the battery cell can be maximized, and the voltage drop of the battery cell can be reduced. Then, in some embodiments, the SOC in [30%,50% ] may be taken as the first state of charge threshold, such as 50% as the first state of charge threshold. The purpose of reducing the risk of sharp power reduction of the battery cell by reducing the voltage drop of the battery cell can be achieved.
The following is the actual LFMP materialLiMn 0.8 Fe 0.2 PO 4 An example is described.
As can be seen from the above examples, the LiMn is aimed at 0.7 Fe 0.3 PO 4 As the cell of the cathode material, the preset metering ratio K2 is 0.7, and the corresponding first resistance threshold is 25mΩ. K3 is set to 30. The first resistance threshold value set correspondingly when the LFMP material actually used is used as the cell of the cathode material is: 25+ (0.8-0.7) 30=28mΩ.
Next, as can be seen from the above embodiments, the first voltage threshold may be set to 3.9V, and the first state of charge threshold may be set to 50%.
In conclusion, for LiMn 0.8 Fe 0.2 PO 4 As for the cell of the cathode material, when the dc impedance of the cell is equal to or 28mΩ, or the voltage of the cell is less than or equal to 3.9V, or the state of charge of the cell is less than or equal to 50%, the operation of reducing the voltage drop of the cell is performed, so that the risk of sharp reduction of the power of the cell can be reduced.
The embodiment of the application also provides electric equipment, as shown in fig. 9, the electric equipment 1 comprises a battery pack 1000 and a load 2000. The load 2000 may be an electrical device in the electrical consumer 1.
The powered device 1 may be any suitable device that requires power from the battery pack 1000, such as an unmanned aerial vehicle, an energy storage product, an electric tool, a two-wheeled vehicle, etc.
Embodiments also provide a non-transitory computer readable storage medium storing computer executable instructions that, when executed by a processor, cause the process to perform a method of discharging a cell in any of the embodiments of the present application.
Embodiments of the present application also provide a computer program product comprising a computer program stored on a computer readable storage medium, the computer program comprising program instructions which, when executed by a computer, cause the computer to perform the method of discharging a cell in any of the embodiments of the present application.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present application, and are not limiting thereof; the technical features of the above embodiments or in the different embodiments may also be combined under the idea of the present application, the steps may be implemented in any order, and there are many other variations of the different aspects of the present application as described above, which are not provided in details for the sake of brevity; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.
Claims (11)
1. A method of discharging a cell, comprising:
the battery cell discharges at a first discharge rate, and one of the following two steps is performed in response to the direct current impedance of the battery cell being greater than or equal to a first resistance threshold, or in response to the voltage of the battery cell being less than or equal to a first voltage threshold, or in response to the state of charge of the battery cell being less than or equal to a first state of charge threshold:
(i) The battery cell discharges at a discharge rate less than or equal to a second discharge rate, wherein the second discharge rate is less than the first discharge rate;
(ii) And stopping discharging the battery cell at the first discharge rate, and supplying power to a battery management system electrically connected with the battery cell, so that the charge state of the battery cell is reduced by a first charge state.
2. The discharge method of claim 1, wherein step (i) further comprises:
responsive to the dc impedance of the cell being less than or equal to the first resistance threshold, or responsive to the voltage of the cell being less than or equal to a second voltage threshold, or responsive to the state of charge of the cell being less than or equal to a second state of charge threshold, the cell discharging at the first discharge rate;
wherein the second voltage threshold is less than the first voltage threshold and the second state of charge threshold is less than the first state of charge threshold.
3. The discharge method according to claim 1 or 2, characterized in that the method further comprises:
and stopping discharging the battery cell in response to the voltage of the battery cell being less than or equal to a third voltage threshold, wherein the third voltage threshold is less than the second voltage threshold.
4. The discharge method of claim 1, wherein step (ii) further comprises:
responsive to the voltage of the cell being greater than a fourth voltage threshold, the cell is discharged at a first discharge rate; or alternatively, the first and second heat exchangers may be,
and stopping discharging the battery cell in response to the voltage of the battery cell being less than or equal to the fourth voltage threshold.
5. The discharge method of claim 1, wherein the cathode material of the cell comprises lithium manganese iron phosphate, the method further comprising:
determining the first resistance threshold based on a first metering ratio of manganese ions in the lithium iron manganese phosphate, wherein the first metering ratio is a ratio between the number of manganese ions in the lithium iron manganese phosphate and the sum of the number of manganese ions and the number of iron ions; and/or the number of the groups of groups,
determining the first voltage threshold and the first state of charge threshold based on a first phase change reaction and a second phase change reaction, wherein the first phase change reaction is Fe in the battery cell 2+ Conversion to Fe 3+ The second phase transformation reaction is Mn in the battery cell 2+ Conversion to Mn 3+ Phase change reaction of (a).
6. The discharge method of claim 5, wherein the determining the first resistance threshold based on the first metering ratio of manganese ions in the lithium iron manganese phosphate comprises:
determining a first resistance threshold based on the first metering ratio, a preset metering ratio and a first preset resistance threshold, wherein the preset metering ratio is a ratio between the number of manganese ions in preset lithium iron manganese phosphate and the sum of the number of manganese ions and the number of iron ions, and the first preset resistance threshold is a preset first resistance threshold.
7. The discharge method of claim 6, wherein the determining the first resistance threshold based on the first metering ratio, a preset metering ratio, and a first preset resistance threshold comprises:
the first resistance threshold is: dcr1=k1+ (Y-K2) ×k3, where dcr1 is the first resistance threshold, K1 is the first preset resistance threshold, Y is the first metering ratio, K2 is the preset metering ratio, and K3 is a preset coefficient.
8. The discharge method of claim 6, wherein the first preset resistance threshold is 25mΩ when the preset metering ratio is 0.7.
9. The discharge method of claim 5, wherein the determining the first voltage threshold and the first state of charge threshold based on a first phase change reaction and a second phase change reaction comprises:
determining a first voltage threshold based on a voltage interval between a first voltage and a second voltage, wherein the first voltage is a corresponding cell voltage when the first phase change reaction occurs, and the second voltage is a corresponding cell voltage when the second phase change reaction occurs; and/or the number of the groups of groups,
and determining the first state of charge threshold based on a state of charge interval between a second state of charge and a third state of charge, wherein the second state of charge is a state of charge corresponding to the occurrence of the first phase change reaction, and the third state of charge is a state of charge corresponding to the occurrence of the second phase change reaction.
10. The battery pack is characterized by comprising a battery module and a battery management system, wherein the battery module is electrically connected with the battery management system;
the battery module comprises at least one electric core;
the battery management system includes at least one processor and a memory communicatively coupled to the at least one processor;
wherein the memory stores instructions executable by the at least one processor to cause the battery pack to perform the discharging method of any one of claims 1-9.
11. A powered device comprising a load and the battery pack of claim 10 for powering the load.
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