A lithium battery safety protection method and lithium battery device

Abstract

The present application discloses a lithium battery safety protection method and a lithium battery device. The lithium battery device includes a battery pack, a battery management system, and a self-discharge circuit. The lithium battery safety protection method includes obtaining real-time parameter data of the battery pack; determining whether the real-time parameter data meets preset conditions; if the real-time parameter data does not meet the preset conditions, obtaining the failure state of the battery pack based on the real-time parameter data; obtaining a target load value of the self-discharge circuit based on the failure state of the battery pack and preset target parameter data; adjusting the initial load value of the self-discharge circuit based on the target load value; and controlling the self-discharge circuit to open based on the failure state of the battery pack, so that the battery pack can achieve rapid discharge through the self-discharge circuit. The lithium battery safety protection method and lithium battery device provided in the present application are intended to prevent thermal runaway and heat spread in lithium batteries.

Description

[0001] This application is a divisional application of the invention patent application with the application date of July 18, 2024, the Chinese application number 202410963243.9, and the invention name “Lithium Battery Safety Protection Method and Lithium Battery Device”. Technical Field

[0002] The present application relates to the field of battery technology, and in particular to a lithium battery safety protection method and a lithium battery device. Background Art

[0003] With the rapid development of the new energy vehicle and battery energy storage industries, lithium-ion batteries, with their advantages such as high integration rate and large capacity, are widely used. However, in a lithium-ion battery system, once a battery cell triggers thermal runaway due to electrical, mechanical, or thermal abuse, it will rapidly release a large amount of heat due to a violent chain redox reaction. This energy may trigger thermal runaway of surrounding batteries, triggering heat propagation and seriously threatening the safety of the battery system and users.

[0004] In the prior art, thermal runaway and heat spread are prevented by external cooling or isolating abnormal batteries, but the effect is poor.

[0005] Therefore, how to prevent thermal runaway and heat spread in lithium batteries is an urgent problem that needs to be solved. Summary of the Invention

[0006] The present application provides a lithium battery safety protection method and a lithium battery device, which aim to prevent thermal runaway and heat spread in lithium batteries.

[0007] On the one hand, an embodiment of the present application provides a lithium battery safety protection method, which is applied to a lithium battery device, wherein the lithium battery includes a battery pack, a battery management system, and a self-discharge circuit. The lithium battery safety protection method includes: obtaining real-time parameter data of the battery pack; judging whether the real-time parameter data meets preset conditions; if the real-time parameter data does not meet the preset conditions, obtaining the failure state of the battery pack according to the real-time parameter data; obtaining the target load value of the self-discharge circuit according to the failure state of the battery pack and preset target parameter data; adjusting the initial load value of the self-discharge circuit according to the target load value; and controlling the self-discharge circuit to turn on according to the failure state of the battery pack, so that the battery pack can be quickly discharged through the self-discharge circuit.

[0008] Optionally, in some embodiments of the present application, the battery pack includes multiple battery cells, and the real-time parameter data includes sub-real-time parameter data corresponding to each of the battery cells; the step of obtaining the real-time parameter data of the battery pack includes: obtaining the sub-real-time parameter data of each of the battery cells, and the type and quantity of parameter values ​​included in the real-time parameter data are the same as the type and quantity of sub-parameter values ​​included in the sub-real-time parameter data; the step of judging whether the real-time parameter data meets the preset conditions includes: the battery management system judging whether each of the sub-parameter values ​​is less than or equal to the corresponding preset threshold value.

[0009] Optionally, in some embodiments of the present application, the sub-real-time parameter data includes at least part of the voltage across the battery cell, the current flowing through the battery cell, the temperature of the battery cell, the pressure of the battery cell, and the gas concentration.

[0010] Optionally, in some embodiments of the present application, if the real-time parameter data does not meet the preset condition, the step of obtaining the failure status of the battery pack based on the real-time parameter data includes: if at least one sub-parameter value in any of the sub-real-time parameter data is greater than the corresponding preset threshold, the sub-parameter value greater than the corresponding preset threshold is determined to be an abnormal sub-parameter value, and the battery cell corresponding to the abnormal sub-parameter value is determined to be a failed battery cell; and the location and failure type of the failed battery cell are obtained based on the abnormal sub-parameter value.

[0011] Optionally, in some embodiments of the present application, the self-discharge circuit includes at least one resistor, and the step of obtaining the target load value of the self-discharge circuit based on the failure state of the battery pack and preset target parameter data includes: the battery management system calculates the target resistance value corresponding to the resistor based on the number of failed battery cells, the abnormal sub-parameter value corresponding to each of the failed battery cells, and the target sub-parameter value corresponding to the abnormal sub-parameter value in the target real-time parameter data.

[0012] Optionally, in some embodiments of the present application, the target load value R of the self-discharge circuit is calculated by the following formula:

[0013]

[0014] Among them, t set The self-discharge duration of the battery cell, the maximum set value of which is less than or equal to the total time required for the temperature of the battery cell to exceed the abnormal value and trigger thermal runaway; The battery cell at t setThe average voltage of the battery cell recorded in real time during the discharge process from the fully charged state to the end of the discharge time; Q c is the battery capacity of the battery cell, r bat is the ohmic internal resistance of the battery cell.

[0015] Optionally, in some embodiments of the present application, a plurality of the battery cells are arranged in sequence in a direction away from the battery management system, and the self-discharge circuit further includes a plurality of control switches, which are arranged corresponding to the battery cells and between the battery cells and the resistors. The step of controlling the self-discharge circuit to open according to the failure state of the battery pack so that the battery pack can achieve rapid discharge through the self-discharge circuit includes: the battery management system adjusting the initial resistance values ​​corresponding to at least part of the resistors to the corresponding target resistance values; the battery management system controlling the control switches connected to the failed battery cells to close according to the failure type of the failed battery cells, so that the failed battery cells are connected to the self-discharge circuit and achieve rapid discharge through the self-discharge circuit; or, the battery management system controlling the control switches connected to at least one of the battery cells located around the failed battery cells to close according to the failure type of the failed battery cells, so that at least one of the battery cells is connected to the self-discharge circuit and achieves rapid discharge through the self-discharge circuit.

[0016] Optionally, in some embodiments of the present application, the lithium battery safety protection method further includes: if the real-time parameter data meets the preset condition, the battery management system controls the self-discharge circuit to be in a closed state.

[0017] Optionally, in some embodiments of the present application, the battery management system controls the self-discharge circuit to turn on according to the failure state of the battery pack, and obtains the load feedback signal of the self-discharge circuit in real time; the battery management system estimates the real-time state of the battery pack according to the load feedback signal; the battery management system adjusts the real-time load value of the self-discharge circuit according to the real-time state of the battery pack until the self-discharge of the battery pack ends.

[0018] On the other hand, the present application provides a lithium battery device, including a battery pack, a battery management system and a self-discharge circuit; the battery pack is used to supply power; the battery management system is used to obtain real-time parameter data of the battery pack, and determine whether the real-time parameter data meets preset conditions. If the real-time parameter data does not meet the preset conditions, the failure state of the battery pack is obtained according to the real-time parameter data. The battery management system is also used to obtain a target load value of the self-discharge circuit according to the failure state of the battery pack and preset target parameter data, and adjust the initial load value of the self-discharge circuit according to the target load value, and to control the self-discharge circuit to turn on according to the failure state of the battery pack; the self-discharge circuit is used to quickly discharge the battery pack.

[0019] In the lithium battery safety protection method and lithium battery device provided in the present application, the real-time parameter data of the battery pack is obtained through the battery management system; it is determined whether the real-time parameter data meets the preset conditions; if the real-time parameter data does not meet the preset conditions, the failure state of the battery pack is obtained according to the real-time parameter data; the target load value of the self-discharge circuit is obtained according to the failure state of the battery pack and the preset target parameter data; the initial load value of the self-discharge circuit is adjusted according to the target load value; and the self-discharge circuit is controlled to be turned on according to the failure state of the battery pack, so that the battery pack can achieve rapid discharge through the self-discharge circuit. That is, the real-time parameter data of the battery pack is obtained through the battery management system, and when the real-time parameter data of the battery pack does not meet the preset conditions, the self-discharge circuit is turned on, so that the battery pack can achieve rapid discharge through the self-discharge circuit, thereby transferring the internal energy of the battery pack before thermal runaway occurs in the battery pack, so as to reduce the chemical reaction rate of the battery pack and the total energy released, thereby preventing thermal runaway and heat spread in the lithium battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic diagram of a lithium battery provided by this application;

[0021] Figure 2 This is a flow chart of the lithium battery safety protection method provided by this application;

[0022] Figure 3 yes Figure 2 Flowchart of sub-steps of step S30;

[0023] Figure 4 yes Figure 2 Flowchart of sub-steps of step S60;

[0024] Figure 5 This is a schematic diagram of parameters of lithium batteries that do not adopt lithium battery safety protection methods;

[0025] Figure 6 This is a schematic diagram of lithium battery parameters after adopting the lithium battery safety protection method provided in this application. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. The described technical solutions are only used to explain and illustrate the ideas of the present application and should not be regarded as limiting the scope of protection of the present application.

[0027] The various embodiments provided in this application are similar, and features in different embodiments may be combined with each other.

[0028] like Figure 1 As shown, an embodiment of the present application provides a lithium battery device 100 , including a battery pack 10 , a battery management system 20 , and a self-discharge circuit 30 .

[0029] In the embodiment of the present application, a battery pack 10 is used to supply power. Specifically, the battery pack 10 includes a plurality of battery cells 101. It should be noted that the battery pack 10 may also include any one or more of a battery cell, a battery module, a battery pack, and a battery cluster.

[0030] In an embodiment of the present application, the battery management system 20 is used to determine whether the real-time parameter data meets the preset conditions. If the real-time parameter data does not meet the preset conditions, the failure status of the battery pack 10 is obtained based on the real-time parameter data.

[0031] In an embodiment of the present application, the battery management system 20 is also used to obtain a target load value of the self-discharge circuit 30 based on the failure state of the battery pack 10 and preset target parameter data, and to adjust the initial load value of the self-discharge circuit 30 according to the target load value, and to control the self-discharge circuit 30 to turn on according to the failure state of the battery pack 10.

[0032] In the embodiment of the present application, the self-discharge circuit 30 is used to quickly discharge the battery pack 10 .

[0033] In the embodiment of the present application, the battery pack 10 includes a plurality of battery cells 101, and the real-time parameter data includes sub-real-time parameter data corresponding to each battery cell 101. The real-time parameter data of the battery pack 10 includes sub-real-time parameter data for each battery cell 101, and the types and quantities of parameter values ​​included in the real-time parameter data are the same as the types and quantities of sub-parameter values ​​included in the sub-real-time parameter data.

[0034] In the embodiment of the present application, the battery management system 20 is configured to determine whether each sub-parameter value is less than or equal to a corresponding preset threshold.

[0035] In an embodiment of the present application, the sub-real-time parameter data includes at least part of the voltage across the battery cell 101 , the current flowing through the battery cell 101 , the temperature of the battery cell 101 , the pressure of the battery cell 101 , and the gas concentration.

[0036] In an embodiment of the present application, if at least one sub-parameter value in any sub-real-time parameter data is greater than a corresponding preset threshold, the sub-parameter value greater than the corresponding preset threshold is determined to be an abnormal sub-parameter value, and the battery cell 101 corresponding to the abnormal sub-parameter value is determined to be a failed battery cell 101. The location and failure type of the failed battery cell 101 are obtained based on the abnormal sub-parameter value.

[0037] In an embodiment of the present application, the self-discharge circuit 30 includes at least one resistor R1, and the battery management system 20 calculates the target resistance value corresponding to the resistor based on the number of failed battery cells 101, the abnormal sub-parameter value corresponding to each failed battery cell 101, and the target sub-parameter value corresponding to the abnormal sub-parameter value in the target real-time parameter data.

[0038] In an embodiment of the present application, a plurality of battery cells 101 are arranged sequentially in a direction away from the battery management system 20. The self-discharge circuit 30 further includes a plurality of control switches 301. The control switches 301 are provided corresponding to the battery cells 101 and are provided between the battery cells 101 and the resistor R1. The control switches 301 include a first control switch 301a and a second control switch 301b. The number of the first control switches 301a is equal to the number of the battery cells 101 and the number of the second control switches 301b.

[0039] Specifically, the positive electrode of each battery cell 101 is electrically connected to one end of a first control switch 301a, and the other end of each first control switch 301a is electrically connected to a first connection terminal Q on the circuit of the self-discharge circuit 30. The negative electrode of the battery cell 101 is electrically connected to one end of a second control switch 301b, and the other end of each second control switch 301b is electrically connected to a second connection terminal S on the circuit of the self-discharge circuit 30.

[0040] In the embodiment of the present application, the control switch 301 can at least withstand the discharge current of a single cell with a discharge rate of 6C and ensure that the temperature rise rate does not exceed 12°C / min. The single cell with a discharge rate of 6C can reduce the SOC from 100% to 0% within 10 minutes.

[0041] In the embodiment of the present application, the battery management system 20 is further configured to obtain in real time the voltage across the resistor in the self-discharge circuit 30 , the current flowing through the resistor, the temperature of the resistor, and the like.

[0042] In an embodiment of the present application, the self-discharge circuit 30 includes 6 to 10 resistors R1. The plurality of resistors R1 include at least one resistor R1 with adjustable resistance. If only one resistor R1 is included, the resistance of the resistor R1 is adjustable. Specifically, the number of resistors R1 included in the self-discharge circuit 30 may be 6, 7, 8, 9, or 10. Preferably, the self-discharge circuit 30 includes 8 resistors R1. The first ends of four resistors R1 are electrically connected to the first connection terminal Q, the second ends of four resistors R1 are electrically connected to the first ends of the other four resistors R1, and the second ends of the other four resistors R1 are electrically connected to the second connection terminal S.

[0043] In an embodiment of the present application, the battery management system 20 adjusts the initial resistance values ​​corresponding to at least part of the resistors R1 to the corresponding target resistance values, or adjusts the number of resistors R1 in the self-discharge circuit 30 so that the total resistance of the self-discharge circuit 30 is the target load value.

[0044] In the embodiment of the present application, the target load value R of the self-discharge circuit 30 is calculated by the following formula:

[0045]

[0046] Among them, t set The self-discharge duration of the battery cell 101, whose maximum setting value is less than or equal to the total time required for the temperature of the battery cell 101 to exceed the abnormal value and trigger thermal runaway; The battery cell 101 is set The average voltage of the battery cell 101 recorded in real time during the discharge from the fully charged state to the cut-off voltage within the time period; Q c is the power of the battery cell 101, r bat is the ohmic internal resistance of the battery cell 101. Specifically, t set The maximum setting value can refer to the battery temperature exceeding the abnormal value T under the heating method described in GB-38031-2020 or newer versions of the safety requirements for power batteries for electric vehicles. ab The total time required to trigger thermal runaway must be less than or equal to this total time. Under the heating method described in GB-38031-2020 or later versions of Safety requirements for power batteries for electric vehicles, the battery temperature abnormality value Tab should not be less than 50°C.

[0047] In an embodiment of the present application, the battery management system 20 controls the control switch 301 connected to the failed battery cell 101 to close according to the failure type of the failed battery cell 101, so that the failed battery cell 101 is connected to the self-discharge circuit 30 and achieves rapid discharge through the self-discharge circuit 30.

[0048] Specifically, if the battery management system 20 determines that the failed battery cell 101 is in a non-intervention state, after t set After a certain time, thermal runaway will be triggered, and if the failure mode of the failed battery cell 101 is thermal failure or internal micro-short circuit failure, the failed battery cell 101 will be connected to the self-discharge circuit 30 to achieve rapid discharge through the self-discharge circuit 30.

[0049] As another embodiment, the battery management system 20 controls the control switch 301 connected to at least one battery cell 101 located around the failed battery cell 101 to close according to the failure type of the failed battery cell 101, so that at least one battery cell 101 is connected to the self-discharge circuit 30 and achieves rapid discharge through the self-discharge circuit 30.

[0050] Specifically, if the battery management system 20 determines that the failed battery cell 101 is in a non-intervention state, after t set If thermal runaway is triggered after a certain period of time and the failed battery cell 101 fails due to other reasons (such as extrusion, puncture, overcharging, etc.), the battery cells 101 located around the failed battery cell 101 are connected to the self-discharge circuit 30 to achieve rapid discharge through the self-discharge circuit 30.

[0051] In the embodiment of the present application, if the real-time parameter data meets the preset conditions, the battery management system 20 controls the self-discharge circuit 30 to be in the off state. Specifically, if the battery management system 20 determines that the failed battery cell 101 is in the non-intervention state, after t set If thermal runaway is not triggered after a certain time, the self-discharge protection will not be activated.

[0052] In the lithium battery device 100 provided in the present application, real-time parameter data of the battery pack 10 is obtained through the battery management system 20 to determine whether the real-time parameter data meets preset conditions. If the real-time parameter data does not meet the preset conditions, the failure state of the battery pack 10 is obtained based on the real-time parameter data. A target load value of the self-discharge circuit 30 is obtained based on the failure state of the battery pack 10 and preset target parameter data. The initial load value of the self-discharge circuit 30 is adjusted based on the target load value. The self-discharge circuit 30 is controlled to be turned on based on the failure state of the battery pack 10, so that the battery pack 10 can achieve rapid discharge through the self-discharge circuit 30. That is, the real-time parameter data of the battery pack 10 is obtained through the battery management system 20. When the real-time parameter data of the battery pack 10 does not meet the preset conditions, the self-discharge circuit 30 is turned on, so that the battery pack 10 can achieve rapid discharge through the self-discharge circuit 30, thereby transferring the internal energy of the battery pack 10 before thermal runaway occurs in the battery pack 10, thereby reducing the chemical reaction rate and the total energy released in the battery pack 10, and thus preventing thermal runaway and heat spread in the lithium battery device 100.

[0053] like Figure 2 As shown, the embodiment of the present application provides a lithium battery safety control method, which is applied to Figure 1 The lithium battery device 100 shown includes a battery pack 10, a battery management system 20, and a self-discharge circuit 30. The lithium battery safety control method includes:

[0054] S10. Acquire real-time parameter data of the battery pack.

[0055] In an embodiment of the present application, the battery pack includes a plurality of battery cells, and the real-time parameter data includes sub-real-time parameter data corresponding to each battery cell.

[0056] In the embodiment of the present application, sub-real-time parameter data is obtained for each battery cell. The types and number of parameter values ​​included in the real-time parameter data are the same as the types and number of sub-parameter values ​​included in the sub-real-time parameter data. By obtaining the sub-real-time parameter data for each battery cell in real time, the safety status of each battery pack can be accurately monitored.

[0057] In an embodiment of the present application, the sub-real-time parameter data includes at least a portion of the voltage across the battery cell, the current flowing through the battery cell, the temperature of the battery cell, the pressure of the battery cell, and the gas concentration. For example, both the real-time parameter data and the sub-real-time parameter data include the voltage across the battery cell, the current flowing through the battery cell, and the temperature of the battery cell. Specifically, the parameter value and the sub-parameter value can each be any one of the voltage across the battery cell, the current flowing through the battery cell, the temperature of the battery cell, the pressure of the battery cell, and the gas concentration.

[0058] S20: Determine whether the real-time parameter data meets the preset conditions.

[0059] In an embodiment of the present application, the battery management system determines whether each sub-parameter value is less than or equal to a corresponding preset threshold value. For example, the battery management system determines whether the temperature of each battery cell is less than or equal to 50°C.

[0060] S30: If the real-time parameter data does not meet the preset conditions, obtain the failure status of the battery pack according to the real-time parameter data.

[0061] In an embodiment of the present application, the failure state of the battery pack includes at least mechanical abuse failure, electrical abuse failure, and thermal abuse failure.

[0062] like Figure 3 As shown, step S30 specifically includes the following sub-steps:

[0063] S301: If at least one sub-parameter value in any sub-real-time parameter data is greater than a corresponding preset threshold, the sub-parameter value greater than the corresponding preset threshold is determined to be an abnormal sub-parameter value, and the battery cell corresponding to the abnormal sub-parameter value is determined to be a failed battery cell.

[0064] S302: Obtain the location and failure type of the failed battery cell according to the abnormal sub-parameter value.

[0065] In this application, if the battery pack failure state is determined to be thermal abuse failure, the self-discharge protection process is activated. For example, if the battery temperature is detected to be greater than the preset threshold temperature of 50°C and there are no other parameters indicating that the battery is in a state of mechanical or electrical abuse, it can be considered that the battery is in a thermal abuse failure state and the self-discharge protection process should be activated.

[0066] In this application example, before the self-discharge protection is activated, the temperature rise rate of the battery during the self-discharge process is estimated according to the following formula:

[0067]

[0068] Among them, formula 1 contains multiple variables, Q c is the battery capacity; r bat is the ohmic internal resistance of the battery cell; t set The estimated time required to discharge all the battery power through the self-discharge protection system (this value is the initial setting value, a feasible setting is 10 minutes); c p is the specific heat capacity of the battery cell; E is the mass energy density of the battery cell (its value is a known quantity, for example, a 2.5Ah, 45g 18650 ternary battery NMC622 has a mass energy density of 202.8Whkg -1 ).

[0069] ΔH SEI,d and ΔH SEI,r The total energy released by the SEI decomposition and regeneration reaction of a fully charged lithium-ion battery cell during thermal runaway (its value can be measured by differential scanning calorimetry and is a known quantity). Taking a 2.5Ah 18650 ternary battery NMC622 as an example, ΔH SEI,d =2362.5J, ΔH SEI,r =7796.3J), SOC represents the current state of charge of the battery (this value can be obtained through the power estimation system of the BMS), m bat is the mass of the battery cell, k SEI,d and k SEI,r are the reaction rates of the SEI decomposition and regeneration reactions during the thermal runaway process of lithium-ion battery cells, and their values ​​are calculated by formula 2 and formula 3 respectively; cSEI,d0 is the initial dimensionless concentration of the SEI decomposition reaction, which can be taken as but not limited to 0.15. SEI,r0 is the initial dimensionless concentration of the SEI regeneration reaction, which can be but is not limited to 1.

[0070]

[0071] In Formula 2 and Formula 3, A SEI,d With A SEI,r Represent the SEI decomposition and regeneration reaction frequency constants, Ea SEI,d With Ea SEI,r Represents the activation energy of SEI decomposition and regeneration reaction (the value can be obtained by differential scanning calorimetry. For example, Ea SEI,d =9.64×106 J mol -1 ,Ea SEI,r =1.3508×10 5 J mol -1 , A SEI,d =5.32×1010s -1 , A SEI,r =2.5×10 13 s -1 ), R′ is the gas constant, which is approximately 8.314 J mol -1 K -1 .f(c SEI,d ·SOC) and f(c SEI,r SOC) in the form of a linear function or exponential function (for example, f(c SEI,d ·SOC)=c SEI,d ·SOC,f(c SEI,r ·SOC)=c SEI,r ·SOC), z and z0 are the dimensionless SEI thickness and dimensionless SEI initial thickness, respectively (for example, z is calculated by formula (6), z0 = 0.033), and T is the temperature of the failed battery cell. If this temperature cannot be obtained (because in actual operation, thermocouples are not necessarily arranged on the battery), the highest temperature of all battery cell temperature signals collected by the BMS can also be used for calculation.

[0072] In the embodiments of the present application, in order to simplify calculations and reduce the difficulty of system implementation, in the process of obtaining the target load value of the self-discharge circuit based on the failure status of the battery pack and the preset target parameter data, some heat generation terms can be ignored by using simplified or approximate means. For example, Formula 1 can be simplified to Formula 4 for calculation:

[0073]

[0074] After obtaining the predicted battery temperature rise rate, the self-discharge load value can be set or adjusted using Formula 5 and Formula 6.

[0075] S40, according to the failure state of the battery pack and the preset target parameter data, the target load value of the self-discharge circuit is obtained. The load value setting is calculated by formula 5:

[0076]

[0077] Among them, t set The self-discharge duration of the battery cell, the maximum set value of which is less than or equal to the total time required for the temperature of the battery cell to exceed the abnormal value and trigger thermal runaway; The battery cell at t set The average voltage of the battery cell recorded in real time during the discharge from the fully charged state to the cut-off voltage within a certain time period; Q c is the battery capacity, r bat is the ohmic internal resistance of the battery cell.

[0078] Specifically, t set The maximum setting value can refer to the battery temperature exceeding the abnormal value T under the heating method described in GB-38031-2020 or newer versions of the safety requirements for power batteries for electric vehicles. ab The total time required to trigger thermal runaway, but must be less than or equal to this total time. Under the heating method described in GB-38031-2020 or newer versions of Safety requirements for power batteries for electric vehicles, the battery temperature abnormal value T ab The temperature should not be less than 50°C. In an embodiment of the present application, the self-discharge circuit includes multiple resistors. The battery management system calculates target resistance values ​​corresponding to at least some of the resistors based on the number of failed battery cells, the abnormal sub-parameter value corresponding to each failed battery cell, and the target sub-parameter value corresponding to the abnormal sub-parameter value in the target real-time parameter data.

[0079] In an embodiment of the present application, a battery management system (BMS) determines whether to adjust the initial load value of the self-discharge circuit according to Formula 6:

[0080]

[0081] The thermal runaway characteristic temperature T2 is the thermal runaway trigger temperature of the battery during the Heat-Wait-Seek test of an accelerating rate calorimeter (ARC). If Equation 6 holds true, the initial load value of the self-discharge circuit remains unchanged.

[0082] In the embodiment of the present application, if formula 6 does not hold, the discharge time t is increased. set Until formula 6 is established (increase t setWill significantly reduce the battery heating rate This reduces the value to the left of the less-than sign in formula six).

[0083] Use t at this time set Set the target load value R of the self-discharge circuit according to Formula 5:

[0084] In the embodiment of the present application, when the power of the self-discharging battery cell is greater than the SOC TRS When the self-discharge circuit is turned on, adjust the initial load value of the self-discharge circuit to ensure that the self-discharge rate of the battery cell is not less than K, where K∈[0C,6C] is defined as the minimum discharge rate of a single battery that does not trigger thermal runaway when performing a self-discharge test in the heating mode described in GB-38031-2020 or later versions of Safety requirements for power batteries for electric vehicles. TRS ∈[50%,100%], which is defined as the maximum battery capacity of a single battery that does not trigger thermal runaway under the heating method described in GB-38031-2020 or newer versions of Safety requirements for power batteries for electric vehicles.

[0085] In the embodiment of the present application, when the power of the self-discharging battery cell is less than or equal to SOC TRS When the temperature is lower than the thermal runaway characteristic temperature T1, the initial load value of the self-discharge circuit is adjusted to ensure that the self-discharge rate of the battery cell is between 0 and K, where K∈[0C,6C]. If the temperature is greater than or equal to the thermal runaway characteristic temperature T1, the self-discharge circuit is disconnected. The thermal runaway characteristic temperature T1 is the thermal runaway instability temperature of the battery in the Heat-Wait-Seek test of the Accelerating Rate Calorimeter (ARC). TRS ∈[50%,100%], which is defined as the maximum battery capacity of a single battery that does not trigger thermal runaway under the heating method described in GB-38031-2020 or newer versions of Safety requirements for power batteries for electric vehicles.

[0086] S50: Adjust the initial load value of the self-discharge circuit according to the target load value.

[0087] In an embodiment of the present application, the battery management system calculates the target resistance values ​​corresponding to at least some of the resistors based on the number of failed battery cells, the abnormal sub-parameter value corresponding to each failed battery cell, and the target sub-parameter value corresponding to the abnormal sub-parameter value in the target real-time parameter data, so as to adjust the initial load value of the self-discharge circuit to the target load value.

[0088] S60: Control the self-discharge circuit to start according to the failure state of the battery pack, so that the battery pack can be quickly discharged through the self-discharge circuit.

[0089] In an embodiment of the present application, multiple battery cells are arranged in sequence in a direction away from the battery management system. The self-discharge circuit further includes multiple control switches, which are arranged corresponding to the battery cells and between the battery cells and the resistors.

[0090] In an embodiment of the present application, the battery management system adjusts the initial resistance values ​​corresponding to at least some resistors to corresponding target resistance values. The battery management system controls the closure of a control switch connected to the failed battery cell based on the failure type of the failed battery cell, thereby connecting the failed battery cell to a self-discharge circuit and achieving rapid discharge through the self-discharge circuit.

[0091] As another embodiment, the battery management system controls the closure of a control switch connected to at least one battery cell located around the failed battery cell according to the failure type of the failed battery cell, so that the at least one battery cell is connected to the self-discharge circuit and achieves rapid discharge through the self-discharge circuit.

[0092] like Figure 4 As shown, step S60 includes the following sub-steps:

[0093] S601: The battery management system controls the self-discharge circuit to start according to the failure state of the battery pack, and obtains a load feedback signal of the self-discharge circuit in real time.

[0094] In an embodiment of the present application, the load feedback signal includes at least one of a load current, a load voltage, and a load temperature of the self-discharge circuit.

[0095] S602: The battery management system estimates the real-time status of the battery pack according to the load feedback signal.

[0096] S603: The battery management system adjusts the real-time load value of the self-discharge circuit according to the real-time status of the battery pack until the self-discharge of the battery pack ends.

[0097] In an embodiment of the present application, the real-time status of the battery pack includes the current charge SOC of the battery cell, the rate of solid electrolyte interface (SEI) decomposition reaction, the dimensionless concentration of SEI decomposition reaction, the SEI regeneration reaction rate, the dimensionless concentration of SEI regeneration reaction, and the temperature rise rate of the battery cell.

[0098] In an embodiment of the present application, the lithium battery safety protection method further includes: if the real-time parameter data meets the preset conditions, the battery management system controls the self-discharge circuit to be in a closed state.

[0099] like Figure 5 and Figure 6As shown in the figure, a battery pack with a size of 148mm×91mm×26.5mm, a capacity of 50Ah, and a model of NMC532 square battery is used to conduct a thermal runaway test of the battery pack in contact with a heating block with a power of 600W and the same size as the battery pack. heater is the heater temperature, T h is the temperature of the hot surface, that is, the temperature of the contact surface between the battery pack and the heater, T c is the temperature of the cold surface, that is, the temperature of the battery side away from the heater and parallel to the heating surface, and U is the voltage across the battery pack.

[0100] Specifically, Figure 5 The data are for temperature and voltage experiments conducted without any discharge measures. The battery pack voltage remained unchanged throughout the experiment. After approximately 580 seconds of heating, the pack experienced thermal runaway, causing damage and a rapid drop in voltage to zero. The hot and cold surface temperatures increased dramatically. Fluctuations in the temperature curve during the measurement are attributed to fluctuations in the jet fire and battery deformation.

[0101] Specifically, Figure 6 After adopting the lithium battery safety protection method provided in the embodiment of the present application, the voltage of the battery pack smoothly dropped to below 2.7V (almost all the electricity was discharged) during the heating time of the battery pack of about 580s, so the battery energy was very low and no thermal runaway was triggered.

[0102] For example, when it is detected that the hot surface temperature of the battery pack exceeds 50°C, the resistance of the resistor on the self-discharge circuit is adjusted to 12 milliohms. At this time, the battery cell connected to the self-discharge circuit begins to discharge at a discharge rate of 6C. The heater still maintains a heating power of 600W to start heating. Before the temperature of the battery pack reaches the critical thermal runaway temperature, the voltage has dropped below 2.7V, but the thermal runaway is not triggered and is successfully suppressed. It should be noted that the parameters in this embodiment, such as: 50°C, 12mΩ discharge, 6C discharge rate, is only a specific embodiment protected by this patent. Those skilled in the art can set specific parameters according to actual needs.

[0103] Experimental verification shows that the lithium battery safety protection method provided in the embodiments of the present application can promptly detect battery cells with thermal runaway risks, discharge failed battery cells or battery cells located around the failed battery cells according to a reasonable strategy before thermal runaway is triggered, quickly transfer the energy of battery cells at any position in the battery pack to the self-discharge circuit, and dissipate the energy through thermal management design, thereby preventing thermal runaway and heat spread of lithium batteries to a great extent.

[0104] In the lithium battery safety protection method provided in the present application, the real-time parameter data of the battery pack is obtained through the battery management system to determine whether the real-time parameter data meets the preset conditions. If the real-time parameter data does not meet the preset conditions, the failure state of the battery pack is obtained based on the real-time parameter data. The target load value of the self-discharge circuit is obtained based on the failure state of the battery pack and the preset target parameter data. The initial load value of the self-discharge circuit is adjusted according to the target load value. The self-discharge circuit is controlled to be turned on according to the failure state of the battery pack so that the battery pack can be quickly discharged through the self-discharge circuit. That is, the real-time parameter data of the battery pack is obtained through the battery management system, and the self-discharge circuit is turned on when the real-time parameter data of the battery pack does not meet the preset conditions so that the battery pack can be quickly discharged through the self-discharge circuit, thereby transferring the internal energy of the battery pack before thermal runaway occurs in the battery pack, so as to reduce the chemical reaction rate of the battery pack and the total energy released, thereby preventing thermal runaway and heat spread in the lithium battery.

[0105] The above is a detailed introduction to a lithium battery safety protection method and a lithium battery device input in the embodiments of the present application. The description of the above embodiments is only used to help understand the core idea of ​​the present application, and the above description should not be understood as limiting the scope of protection of the present application.

Claims

1. A lithium battery safety protection method, applied to a lithium battery device, characterized in that: The lithium battery device includes a battery pack, a battery management system, and a self-discharge circuit. The lithium battery safety protection method includes: Acquiring real-time parameter data of the battery pack; Determining whether the real-time parameter data meets a preset condition; If the real-time parameter data does not meet the preset condition, obtaining the failure state of the battery pack according to the real-time parameter data; Obtaining a target load value of the self-discharge circuit according to the failure state of the battery pack and preset target parameter data; adjusting an initial load value of the self-discharge circuit according to the target load value; controlling the self-discharge circuit to start according to the failure state of the battery pack, so that the battery pack can be quickly discharged through the self-discharge circuit; The battery pack includes a plurality of battery cells, the real-time parameter data includes sub-real-time parameter data corresponding to each battery cell, and the step of obtaining the real-time parameter data of the battery pack includes: Acquire the sub-real-time parameter data of each battery cell, where the type and quantity of parameter values ​​included in the real-time parameter data are the same as the type and quantity of sub-parameter values ​​included in the sub-real-time parameter data; The step of determining whether the real-time parameter data meets the preset conditions includes: The battery management system determines whether each sub-parameter value is less than or equal to a corresponding preset threshold; Wherein, if the real-time parameter data does not meet the preset condition, the step of obtaining the failure status of the battery pack according to the real-time parameter data includes: If at least one of the sub-parameter values ​​in any of the sub-real-time parameter data is greater than the corresponding preset threshold, the sub-parameter value greater than the corresponding preset threshold is determined to be an abnormal sub-parameter value, and the battery cell corresponding to the abnormal sub-parameter value is determined to be a failed battery cell; Obtaining the location and failure type of the failed battery cell according to the abnormal sub-parameter value; The self-discharge circuit includes at least one resistor, and the step of obtaining a target load value of the self-discharge circuit according to the failure state of the battery pack and preset target parameter data includes: The battery management system calculates a target resistance value corresponding to the resistor according to the number of the failed battery cells, the abnormal sub-parameter value corresponding to each of the failed battery cells, and the target sub-parameter value corresponding to the abnormal sub-parameter value in the target parameter data; Specifically, the target load value R of the self-discharge circuit is calculated by the following formula: ； in, The self-discharge duration of the battery cell, the maximum set value of which is less than or equal to the total time required for the temperature of the battery cell to exceed the abnormal value and trigger thermal runaway; For battery cells The average voltage of the battery cell recorded in real time during the discharge process from the fully charged state to the end of the discharge; is the power of the battery cell, is the ohmic internal resistance of the battery cell.

2. The lithium battery safety protection method according to claim 1, characterized in that: The sub-real-time parameter data includes at least part of the voltage across the battery cell, the current flowing through the battery cell, the temperature of the battery cell, the pressure of the battery cell, and the gas concentration.

3. The lithium battery safety protection method according to claim 1, characterized in that: The lithium battery safety protection method further includes: If the real-time parameter data meets the preset condition, the battery management system controls the self-discharge circuit to be in a closed state.

4. The lithium battery safety protection method according to claim 1, characterized in that: The step of controlling the self-discharge circuit to start according to the failure state of the battery pack so that the battery pack can be quickly discharged through the self-discharge circuit includes: The battery management system controls the self-discharge circuit to start according to the failure state of the battery pack, and obtains a load feedback signal of the self-discharge circuit in real time; The battery management system estimates the real-time state of the battery pack according to the load feedback signal; The battery management system adjusts the real-time load value of the self-discharge circuit according to the real-time state of the battery pack until the self-discharge of the battery pack is completed.

5. A lithium battery device, used to implement the lithium battery safety protection method according to any one of claims 1 to 4, characterized in that: Including battery pack, battery management system and self-discharge circuit; The battery pack is used for power supply; The battery management system is used to obtain real-time parameter data of the battery pack, determine whether the real-time parameter data meets a preset condition, and if the real-time parameter data does not meet the preset condition, obtain a failure state of the battery pack based on the real-time parameter data. The battery management system is also used to obtain a target load value of the self-discharge circuit based on the failure state of the battery pack and preset target parameter data, adjust an initial load value of the self-discharge circuit based on the target load value, and control the self-discharge circuit to be turned on according to the failure state of the battery pack; The self-discharge circuit is used to quickly discharge the battery pack.

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