Energy release device and method for power battery

Abstract

The present disclosure provides an energy release device and method for a power battery. The energy release method for a power battery comprises: acquiring a thermal runaway signal of battery cells in the power battery; and electrically communicating the power battery with a discharge element, so that the power battery is discharged to a maximum safe state of charge that satisfies a mild exothermic reaction under the condition of thermal runaway, or a state of charge below the maximum safe state of charge, wherein satisfying the mild exothermic reaction is that the temperature per unit volume of the battery cells in the power battery under the condition of thermal runaway does not exceed the temperature at which the thermal runaway is triggered. According to the solution provided by the present disclosure, the development of thermal runaway in a power battery pack can be effectively delayed, time is bought for passenger escape and subsequent thermal runaway control processing, meanwhile, the destructive power of thermal runaway is reduced, and the safety management capability of the power battery is improved.

Description

Power battery energy dissipation device and energy dissipation method Technical Field

[0001] This article involves, but is not limited to, the field of active safety of electric vehicles, involves, but is not limited to, emergency response methods after thermal runaway of battery packs, and especially involves, but is not limited to, power battery energy dissipation devices and methods. Background Art

[0002] With the continuous progress and development of automobile industry technology, cars have greatly facilitated people's lives. However, with the gradual increase in the number of cars, the environmental pollution and energy crisis they bring are becoming more and more serious. Based on this, the development of new energy vehicles has become a key breakthrough direction for automobile companies. The development of new energy vehicles has also become the only way for the global automobile industry to transform, upgrade and achieve green development.

[0003] Lithium-ion batteries, with their advantages of long cycle life, high energy density, high voltage, low self-discharge, and no memory effect, have become the primary power source for hybrid and pure electric vehicles. As a core component of a vehicle, power batteries are crucial to vehicle safety. For lithium-ion batteries, thermal runaway is the most serious safety hazard. Thermal runaway occurs primarily when internal heat generation far exceeds the rate of heat dissipation, accumulating significant heat within the battery and potentially causing fire and explosion.

[0004] However, in the power battery systems of new energy vehicles in the related art, the spread of thermal runaway and the severity of battery fires are slowed down as much as possible by installing flame retardant materials and optimizing battery structure, but there is a lack of emergency control measures after the fire occurs. Prevention of power battery thermal runaway before it occurs and handling of thermal runaway after it occurs are both very important for vehicle safety. Most of the research in the related art focuses on the rational use of batteries and detection and early warning before thermal runaway occurs, while there is little research on handling after thermal runaway occurs. After thermal runaway occurs, the vehicle can only stay as far away as possible and wait for fire rescue, and the vehicle itself cannot perform any intervention operations.

[0005] Related technologies only achieve flame retardant effects by optimizing battery materials or by setting flame retardant materials in the battery system, but lack active emergency control of battery systems that have experienced thermal runaway. It is necessary to develop an active power battery system thermal runaway emergency disaster reduction technology.

[0006] Summary of the Invention

[0007] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0008] In response to the problem that related technologies lack emergency treatment and disaster reduction measures after thermal runaway of power battery systems, the present disclosure proposes an emergency treatment method after thermal runaway of power battery packs, including obtaining the maximum temperature of the battery pack during thermal runaway under different SOC conditions, and also obtaining information such as diffusion time and spread range, and obtaining the minimum SOC value that should be reached by discharging energy when thermal runaway occurs under any SOC conditions, so as to avoid fire or explosion of the battery pack after thermal runaway. Based on the thermal runaway warning results obtained by BMS (battery management system) or other methods, when a thermal runaway warning signal of a certain battery pack is obtained, the BMS disconnects the high voltage and controls the external discharge system connected to the module, and uses methods such as external resistor short-circuiting or bypassing supercapacitors to perform high-rate discharge or motor stall discharge to discharge the module, so as to reduce the internal energy of the thermal runaway module.

[0009] In an embodiment of the present disclosure, a method for discharging energy from a power battery is provided, the method comprising:

[0010] Obtaining a thermal runaway signal of a battery cell in the power battery;

[0011] The power battery is electrically connected to a discharge element to discharge the power battery to a maximum safe state of charge that satisfies a mild exothermic reaction in the case of thermal runaway, or a state of charge lower than the maximum safe state of charge, wherein satisfying the mild exothermic reaction means that the temperature per unit volume of the battery cell in the power battery in the case of thermal runaway does not exceed the temperature at which thermal runaway is triggered.

[0012] In some embodiments, the method for obtaining the maximum safe state of charge includes:

[0013] Establish an electrochemical model to describe the internal electrochemical characteristics of the power battery,

[0014] Establish a thermal model to describe the heat generation of the power battery,

[0015] The electrochemical model and the thermal model are coupled by parameter transfer via electrochemical heat generation and battery temperature, wherein the electrochemical heat generation and heat generated by thermal runaway side reactions are used as inputs of the thermal model to calculate the temperature field distribution of the power battery; and the battery temperature in the thermal model is used as input of the electrochemical model to simulate the electrochemical process;

[0016] The maximum safe state of charge of the power battery that satisfies a mild exothermic reaction under thermal runaway conditions is calculated iteratively.

[0017] In some embodiments, the heat generated by the power battery includes ohmic heat, polarization heat, reversible entropy change heat, and heat generated by thermal runaway side reactions;

[0018] The heat generated by the thermal runaway side reactions includes heat generated by decomposition of the battery separator, heat generated by the reaction of the negative electrode active material with the electrolyte, heat generated by the reaction of the positive electrode active material with the electrolyte, and heat generated by the oxidative decomposition reaction of the electrolyte.

[0019] In some embodiments, the power battery discharge time is a preset time.

[0020] The preset time is: according to the wire electrically connecting the power battery and the discharge element and the maximum current that the discharge element can carry, the shortest time for the power battery to discharge to the maximum safe state of charge based on the maximum current is obtained.

[0021] In some embodiments, the thermal runaway includes any one or more of thermal runaway caused by overheating, thermal runaway caused by overcharging, thermal runaway caused by overdischarging, or thermal runaway caused by external force.

[0022] In some embodiments, the energy dissipation method further includes: cooling the discharge element during the discharge process of the power battery.

[0023] In some embodiments, the energy dissipation method further includes: performing maximum power cooling on battery cells that have not been affected by the thermal runaway during the discharge process of the power battery.

[0024] In another aspect, the present disclosure provides a power battery energy dissipation device, the power battery energy dissipation device comprising:

[0025] A sensor module is used to send a signal to indicate whether any cell or module in the power battery is experiencing thermal runaway;

[0026] a discharge module comprising a switch and a discharge element connected in series between the positive and negative electrodes of the power battery;

[0027] The thermal runaway management module is configured to control the switch to close so as to discharge the power battery through the discharge element after receiving a thermal runaway signal from the sensor module.

[0028] On the other hand, the present disclosure provides an electric vehicle comprising the above-mentioned power battery energy dissipation device.

[0029] In some embodiments, the connection wires of the power battery energy dissipation device are arranged in an independent wiring harness.

[0030] On the other hand, the present disclosure provides a power battery energy dissipation management device, which includes a memory, a processor, and a processor-executable program stored in the memory and executable on the processor. When the processor-executable program is executed by the processor, the above-mentioned power battery energy dissipation method is implemented.

[0031] On the other hand, the present disclosure provides a computer-readable storage medium having a computer-executable program stored thereon. When the computer-executable program is executed by a processor, the above-mentioned power battery energy discharge method is implemented.

[0032] The beneficial effects of the present disclosure include:

[0033] The energy dissipation device and method provided by this disclosure can effectively delay the development of thermal runaway within a power battery pack, buying time for occupant escape and subsequent thermal runaway control, while also reducing the destructive power of thermal runaway and improving the safety management capabilities of power batteries. This disclosure overcomes the shortcomings of traditional passive emergency management after thermal runaway, which relies on flame retardant materials to slow the spread of thermal runaway. By enabling proactive system emergency response after thermal runaway occurs, the system reduces the degree of thermal runaway damage, indirectly improving the safety of the power battery system and addressing the high risk and rapid spread of thermal runaway in power batteries.

[0034] The present disclosure can perform energy dissipation processing after identifying thermal runaway of the battery pack, thereby delaying the development of thermal runaway in the battery pack, delaying the occurrence of open flames or even suppressing the occurrence of open flames, and buying time for occupants to escape and subsequent thermal runaway control processing.

[0035] The thermal runaway warning method provided by the present disclosure for the power battery management system can realize rapid energy discharge of the power battery pack before severe thermal runaway occurs, reduce the available energy of the power battery pack, thereby reducing the destructive power of thermal runaway and improving the safety management capability of the power battery.

[0036] Other features and advantages of the present disclosure will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present disclosure. Other advantages of the present disclosure can be invented and achieved through the solutions described in the description. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings are used to provide an understanding of the technical solution of the present disclosure and constitute a part of the specification. Together with the embodiments of the present disclosure, they are used to explain the technical solution of the present disclosure and do not constitute a limitation to the technical solution of the present disclosure.

[0038] Figure 1 shows a battery pack at 30% SOC, exhibiting smoke but no fire or explosion (i.e., a mild exothermic reaction). The battery pack was fully charged, allowed to rest, and then discharged at a 1C constant current at actual capacity, reaching approximately 30% SOC after 0.7 hours. The open flame in Figure 1 was used to trigger battery pack failure, with the outer flame temperature exceeding 500°C.

[0039] FIG2 is a schematic diagram of a power battery energy dissipation device provided by the present disclosure. DETAILED DESCRIPTION

[0040] To make the purpose, technical solutions and advantages of the present disclosure more clear, the embodiments of the present disclosure are described in detail below. It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present disclosure can be combined with each other in any manner.

[0041] In an exemplary embodiment of the present disclosure, a method for discharging energy from a power battery is provided, the method comprising:

[0042] Obtaining a thermal runaway signal of a battery cell in the power battery;

[0043] The power battery is electrically connected to a discharge element to discharge the power battery to a maximum safe state of charge (SOC) or a lower SOC that satisfies a mild exothermic reaction in the event of thermal runaway. It is understood that, to avoid fire or explosion after a battery cell in the power battery experiences thermal runaway, the power battery may be electrically connected to a discharge element to discharge the power battery to a maximum safe SOC or a SOC lower than the maximum safe SOC.

[0044] The state of charge can be represented by SOC (State Of Charge, the remaining capacity of the battery). At the maximum safe state of charge, the temperature per unit volume of the battery cell in the power battery does not exceed the temperature at which thermal runaway is triggered.

[0045] The discharge element may include a device for rapidly consuming energy, such as one or more of an ohmic resistor, an equivalent resistor, a power semiconductor device, a supercapacitor, and an onboard motor.

[0046] Illustratively, the temperature per unit volume of any battery cell in the power battery that satisfies the exothermic reaction mild thermal runaway condition does not exceed the temperature at which thermal runaway is triggered; the temperature may be 100° C. to 300° C.

[0047] Exemplarily, the exothermic reaction is mild in that there is no fire or explosion.

[0048] Exemplarily, the method for obtaining the maximum safe state of charge includes:

[0049] Establishing an electrochemical model to describe the internal electrochemical characteristics of the power battery, establishing a thermal model to describe the heat generation of the power battery, and transferring and coupling parameters between the two models through electrochemical heat generation and battery temperature;

[0050] The electrochemical heat generation and the heat generated by the thermal runaway side reaction are used as inputs of the thermal model to calculate the temperature field distribution of the power battery; the battery temperature T in the thermal model is used as input of the electrochemical model to simulate the electrochemical process;

[0051] The maximum safe state of charge of the power battery that satisfies a mild exothermic reaction under thermal runaway conditions is predicted through iteration.

[0052] Exemplarily, the heat generated by the power battery includes ohmic heat, polarization heat, reversible entropy change heat and heat generated by thermal runaway side reactions;

[0053] The heat generated by the thermal runaway side reaction includes heat generated by the decomposition of the battery separator, heat generated by the reaction of the negative electrode active material with the electrolyte, heat generated by the reaction of the positive electrode active material with the electrolyte, and heat generated by the oxidative decomposition reaction of the electrolyte.

[0054] Exemplarily, the discharge time of the power battery is a preset time, and the preset time is: based on the wire electrically connecting the power battery and the discharge element and the maximum current that the discharge element can carry, the shortest time for the power battery to discharge to the maximum safe state of charge based on the maximum current is obtained.

[0055] Exemplarily, the thermal runaway includes any one or more of thermal runaway caused by overheating, thermal runaway caused by overcharging, thermal runaway caused by overdischarging, or thermal runaway caused by external force.

[0056] Exemplarily, the discharge current is a maximum discharge current that does not promote thermal runaway of the power battery or a current at a maximum discharge power that does not promote thermal runaway of the power battery.

[0057] Exemplarily, the energy dissipation method further includes cooling the discharge element during the discharge process.

[0058] Exemplarily, the power battery energy dissipation method further includes:

[0059] Conduct thermal runaway experiments or simulation modeling and energy dissipation target analysis on power batteries. This can be done by conducting multi-level power battery thermal runaway experiments to analyze the thermal runaway triggering behavior and propagation paths of power battery cells, modules, systems, and vehicle levels. Comprehensively measure the emergency management time of power batteries under different triggering conditions (the time from the onset of thermal runaway to the occurrence of large-scale heat diffusion, open flames, and other phenomena). Design thermal runaway experiments for power batteries under different SOC and voltage conditions, analyze the SOC and voltage points corresponding to thermal runaway modules with low destructiveness, and analyze the SOC critical point at which the battery pack does not catch fire or explode after thermal runaway as the energy dissipation target. Alternatively, use a model to predict the thermal diffusion phenomenon of the battery system when a single cell is forced to undergo thermal runaway, and analyze information such as the system's maximum temperature, thermal diffusion rate, and thermal diffusion range.

[0060] Analyze the active energy dissipation capability of power batteries. Calculate the energy and discharge rate of power batteries during rapid energy dissipation under thermal runaway conditions, analyze the energy dissipation boundaries of power batteries, and guide the design of energy dissipation systems.

[0061] Design the active emergency system hardware and control system. The hardware can be implemented using high-current, high-temperature-resistant wires and appropriately powered discharge components (including energy-discharging resistors, supercapacitors, and onboard motors), connected to battery modules or single cells. A controller (including high-current relays and electronic control components) is also provided to control system activation and deactivation.

[0062] Exemplarily, the energy dissipation method further includes cooling the discharge element during the discharge process. To prevent the discharge element from overheating during discharge, the discharge element is connected to a thermal management system, which cools the discharge element during the discharge process.

[0063] Exemplarily, the energy dissipation method further includes performing maximum power cooling on power batteries that have not been affected by thermal runaway (eg, battery cells that have not been affected by thermal runaway) during the discharge process.

[0064] In another aspect, an embodiment of the present disclosure provides a power battery energy dissipation device, the power battery energy dissipation device comprising:

[0065] A sensing module, such as a sensor, is used to send a signal as to whether any cell or module in the power battery is experiencing thermal runaway;

[0066] a discharge module comprising a switch and a discharge element connected in series between the positive and negative electrodes of the power battery;

[0067] The thermal runaway management module is configured to control the switch to close so as to discharge the power battery through the discharge element after receiving a thermal runaway signal from the sensor module.

[0068] Exemplarily, the discharge module includes a controlled switch, a wire, and a discharge element. When the controlled switch is closed, the discharge current of the power battery is discharged through the wire and the discharge element.

[0069] Exemplarily, the discharge element includes any one or more of an energy dissipation resistor, a supercapacitor, and a vehicle-mounted motor; and the controlled switch includes a relay capable of withstanding large currents.

[0070] Exemplarily, the power battery energy discharging device further includes a cooling module for cooling the discharging module. The cooling module may include a water pump and / or a radiator fan, etc.

[0071] Exemplarily, the wire is a high-current-resistant wire, and the method for determining the high current that the wire and the relay can carry includes: calculating the resistance of the discharge element based on the preset energy discharge time of the power battery and the capacity of the power battery, and determining the high current that the wire and the relay can carry based on the maximum voltage of the power battery and the resistance of the discharge element.

[0072] On the other hand, an electric vehicle is provided in an embodiment of the present disclosure, and the electric vehicle includes the above-mentioned power battery energy discharge device.

[0073] Exemplarily, the connection wires of the power battery energy dissipation device are arranged in an independent wiring harness.

[0074] For example, the connection wires of the power battery energy dissipation device are independently provided and are arranged in different wiring harnesses from the drive circuits and conventional signal transmission circuits of the electric vehicle. The connection wires can be signal connection wires, high current carrying wires, and other connection wires.

[0075] Exemplarily, the discharge module is further configured to be temperature-controlled by a vehicle thermal management system to avoid excessive temperature.

[0076] Exemplarily, the signal control module is a battery management system BMS of the electric vehicle.

[0077] For example, the power battery may be the entire power battery pack of the electric vehicle, may be a module in the entire power pack, or may be a single cell or a combination of multiple cells.

[0078] Illustratively, the present disclosure provides the following Example 1:

[0079] The power battery described in this embodiment is a lithium-ion battery suitable for automotive powertrain applications. It consists of several modules connected in series and parallel, with no specific requirements for the battery structure or design. The battery pack is configured with 12 modules in series, using a ternary lithium-ion battery system with a rated voltage of 44.4V, a maximum voltage of 49.8V, and a total module capacity of 50Ah.

[0080] Set the energy release time to 20 to 30 minutes.

[0081] The target for energy dissipation after thermal runaway is to ensure neither fire nor explosion (i.e., a mild exothermic reaction). Simulation modeling demonstrates that the maximum safe state of charge (SOC) for this mild exothermic reaction is a maximum temperature of no more than 200°C (i.e., the maximum cell temperature for a mild exothermic reaction during thermal runaway is 200°C). Iterative simulations concluded that at 30% SOC, the system exhibits only smoke but no fire after thermal runaway, and the power battery's own heat generation does not exceed 200°C. Therefore, 30% SOC was set as the target for energy dissipation, and an emergency management system was designed based on the energy content and duration of the battery modules being discharged.

[0082] In this embodiment, the power battery can be set to discharge at a rate of 3C, that is, it can be fully discharged in 20 minutes, with an average discharge current of 150 A. That is, the wires connecting the discharge module and the discharge module to the power battery must be able to carry at least about 150 A of current.

[0083] In this embodiment, the power battery can also be set to discharge to below SOC 30% within 30 minutes, that is, 0.7Q / 0.5h=1.4C, that is, a 1.4C rate discharge is performed. The wires connecting the discharge module and the discharge module and the power battery must be able to carry at least about 70A of current (50A×1.4C).

[0084] In this embodiment, as shown in Figure 2, a BMS can be used to control the on / off switching of the module and the discharge module. The BMS controls the battery pack and its internal modules through manual switches. When necessary, it connects the module and the discharge module via high-temperature-resistant wires for rapid discharge. It can also cool the discharge module through components such as a thermal management system.

[0085] In this embodiment, when a BMS, cloud, or other thermal runaway identification system identifies that thermal runaway has occurred in a module in the battery pack, or that a shock that may cause thermal runaway has occurred, the BMS controls the module to be electrically connected to the discharge module.

[0086] In this embodiment, the controlled switch electrically connected between the thermal runaway module controlled by the BMS and the discharge module can use but is not limited to high-current relays and other devices. The controlled switch is strictly prohibited from being turned on in non-thermal runaway situations, and cannot be disconnected due to failure of the BMS control after being turned on in the event of thermal runaway. The wires connecting the power battery between the thermal runaway module and the discharge module need to carry a large current, for example, a large current of about 150A, and the time for carrying the large current can be at least the set energy dissipation time, and can have good high-temperature resistance. The wires carrying large currents and the signal lines for controlling the controlled switches can be set separately to avoid interference with the conventional wiring harness of the electric vehicle.

[0087] In this embodiment, energy-consuming components such as ohmic resistors and power semiconductor devices can be used to quickly consume energy. In order to prevent the discharge module from overheating, the vehicle's thermal management system can be used to dissipate heat from the discharge module.

[0088] Illustratively, the present disclosure provides the following Example 2:

[0089] The method for obtaining the maximum safe state of charge may include performing thermal runaway simulation on the power battery and performing iterative simulation calculations using an electrochemical-thermal-side reaction coupling model.

[0090] The electrochemical-thermal-side reaction coupling model used to simulate thermal runaway consists of two parts: a one-dimensional electrochemical model and a three-dimensional thermal model. The two parts transfer and couple parameters through the electrochemical heat generation Qh and the battery temperature T in the thermal model. The electrochemical model is established based on the Newman electrochemical model, and the obtained electrochemical heat generation Qh is coupled to the three-dimensional thermal model. The electrochemical heat generation Qh and the heat generated by the thermal runaway side reaction are jointly input as heat sources to calculate the temperature field distribution of the power battery. The temperature T in the three-dimensional thermal model is coupled to the electrochemical model as an input condition for simulating the electrochemical process.

[0091] The input parameters are substituted into the solid-phase lithium ion diffusion equation, the liquid-phase lithium ion material conservation equation, the solid-phase charge conservation equation, the liquid-phase charge conservation equation, the electrode reaction kinetics equation, the SEI film decomposition exothermic reaction equation, the reaction equation between the negative electrode active material and the electrolyte, the reaction equation between the positive electrode active material and the electrolyte, and the oxidation decomposition reaction equation of the electrolyte for calculation. Parameters such as the battery potential, electrochemical heat generation, side reaction heat generation, and battery temperature are obtained in turn to determine the degree of battery thermal runaway, and then the maximum safe SOC value that satisfies the mild exothermic reaction when the power battery experiences thermal runaway is obtained, such as that shown in Figure 1.

[0092] Obtain the following parameters of the power battery:

[0093] Solid phase lithium ion concentration C s , solid-phase lithium ion diffusion coefficient D s , the radial distance r inside the spherical particle, the reaction time t;

[0094] Volume fraction of electrolyte ε e , liquid lithium ion concentration C e , reaction time t, effective diffusion coefficient D of lithium ions in liquid phase eff , the migration number of lithium ions t + , x is the length direction of the pole piece;

[0095] Solid phase potential

[0096] Solid phase conductivity σ, solid phase volume fraction of positive and negative electrode active materials ε s ;

[0097] Average activity coefficient f of electrolyte, liquid phase potential

[0098] Liquid phase lithium ion conductivity κ;

[0099] Total active area of ​​battery electrode S e , anode transfer coefficient α a , cathode transfer coefficient α c ;

[0100] Maximum solid phase lithium insertion concentration C s max , the surface lithium insertion concentration C of solid spherical particles se ;

[0101] The equilibrium potential U of the positive electrode or negative electrode i ;

[0102] Solid phase effective diffusion coefficient

[0103] The dimensionless number C of the metastable state content in the SEI film sei ; Forward factor A of the reaction sei Activation energy E of the reaction a,sei ; Reaction order m sei ; Reaction rate R sei ; Carbon content W c ; Unit heat generation of the reaction H sei ;

[0104] The proportion of lithium in the negative electrode material that can react with the electrolyte C ne ; Forward factor A of the reaction ne Activation energy E of the reaction a,ne ; Reaction order m ne ; Reaction rate R ne ; Unit heat generation of the reaction H ne ;

[0105] The conversion rate of the positive electrode material reaction α; the forward factor of the reaction A pe ; Activation energy E of the reaction a,pe ;m pe,p1 and m pe,p2 is the reaction order; the reaction rate R pe ; The content of positive electrode active material W p ; Unit heat generation of the reaction H pe ;

[0106] Electrolyte content C e ; Forward factor A of the reaction e Activation energy E of the reaction a,e ; Reaction order m e ; Reaction rate R e ; The content of electrolyte W e ; Unit heat generation of the reaction H e ;

[0107] Battery density ρ; battery specific heat capacity C p ;Battery thermal conductivity λ;Battery heat generation power per unit volume

[0108] The convection heat transfer coefficient h of the battery to the environment; the emissivity ε of the battery surface, which is set according to the material of the battery shell; the temperature T0 of the battery surface, the ambient temperature T ∞ ;

[0109] The parameters are substituted into the corresponding formulas and coupled iteratively obtained in turn to obtain parameters such as battery potential, electrochemical heat generation, side reaction heat generation, battery temperature, etc., to determine the degree of battery thermal runaway, and then simulate and calculate to obtain the maximum safe state of charge.

[0110] ①Electrochemical model:

[0111] This disclosure uses a P2D (pseudo-two-dimensions) model based on porous electrode theory to describe the electrochemical characteristics inside lithium-ion batteries. The equations involved in the model are as follows:

[0112] (a) Material conservation equation:

[0113] (1) Solid-phase lithium ion diffusion equation:

[0114] Fick's diffusion law is used to describe the diffusion process of lithium ions inside active particles, without considering the possible volume changes of spherical particles:

[0115] In formula (1): C s is the solid phase lithium ion concentration, in mol / m 3 ;D s is the solid phase lithium ion diffusion coefficient, unit is m 2 ·s -1 ; r is the radial distance inside the spherical particle, in meters; t is the time, in seconds;

[0116] The left side of the equation is the change of solid phase lithium ion concentration with time.

[0117] (2) Liquid phase lithium ion material conservation equation

[0118] Lithium ions escape from solid spherical particles and enter the liquid phase, where they diffuse and migrate in the electrolyte. The concentrated solution theory is used to describe this process:

[0119] In formula (2): ε e is the volume fraction of the electrolyte, in %; C e is the concentration of lithium ions in the liquid phase, in mol / m 3 ;D eff is the effective diffusion coefficient of lithium ions in the liquid phase, in m 2 ·s -1 ;t +represents the migration number of lithium ions, dimensionless; F is the Faraday constant, unit is C / mol; x is the length direction of the electrode, unit is m; j is the local current density, calculated according to formula (3), unit is A / m 3 .

[0120] (b) Charge conservation equation:

[0121] (1) Solid phase charge conservation equation

[0122] The solid phase charge distribution in the positive and negative active materials conforms to Ohm's law:

[0123] In formula (3): σ eff is the solid phase effective conductivity, calculated according to formula (4), and the unit is S·m -1 ; x is the length direction of the pole piece, unit is m; is the solid phase potential, in V.

[0124] The solid phase effective conductivity σ in formula (3) eff , calculated according to formula (4):

[0125] In formula (4): σ is the solid phase conductivity, the unit is S·m -1 ; ε s is the solid phase volume fraction of the positive and negative electrode active materials; Brug is the Bruggman coefficient.

[0126] (2) Liquid phase charge conservation equation

[0127] In formula (5), x is the length direction of the electrode, in m; f is the average activity coefficient of the electrolyte; is the liquid phase potential, unit is V; R is the ideal gas constant, unit is mol -1 ·K -1 ; F is the Faraday constant, unit is C / mol; t + Indicates the migration number of lithium ions; C e is the concentration of lithium ions in the liquid phase, in mol / m 3 ; T is the battery temperature, unit is K; j is the local current density, calculated according to formula (3), unit is A / m 3 κ eff is the effective conductivity of lithium ions in the electrolyte, in S·m -1 , and its correction is shown in formula (5.1):

[0128] In formula (5.1): κ eff is the effective conductivity of lithium ions in the electrolyte, in S·m-1 ; κ is the liquid phase lithium ion conductivity, unit is S·m -1 ; ε e is the volume fraction of the electrolyte, in %.

[0129] (c) Electrode dynamics equation:

[0130] The Butler-Volmer equation is used to describe the electrochemical process at the interface between the solid surface and the liquid electrolyte:

[0131] In formula (6): j is the local current density, in A / m 3 ; Se is the total active area of ​​the battery electrode, in m2; R is the ideal gas constant, in mol -1 ·K -1 ; F is the Faraday constant, unit is C / mol; T is the battery temperature, unit is K; η is the electrode overpotential, calculated according to formula (8), unit is V; α a is the anode transfer coefficient, dimensionless; α c is the cathode transfer coefficient, dimensionless; i0 is the exchange current density calculated according to formula (7), unit is A / m 2 .

[0132] The exchange current density i0 is calculated as follows:

[0133] In formula (7): k is the electrode reaction rate constant, unit is m 2.5 ·mol -0.5 ·s -1 ; F is the Faraday constant, unit is C / mol; α a is the anode transfer coefficient, dimensionless; α c is the cathode transfer coefficient, dimensionless; C e is the concentration of lithium ions in the liquid phase, in mol / m 3 ; C s max is the maximum lithium insertion concentration in the solid phase, in mol; C se is the surface lithium insertion concentration of solid spherical particles, in mol.

[0134] The overpotential characterizes the phenomenon that the electrode potential deviates from the equilibrium potential due to the electrochemical reaction of lithium ions on the surface of solid particles. Its calculation formula is as follows:

[0135] η=φ s -φ e -U i ,i=n,p………………(8)

[0136] Where: is the solid phase potential, unit is V; is the liquid phase potential, in V, U i It is the equilibrium potential of the positive or negative electrode, measured in V.

[0137] Temperature affects the electrochemical processes within the battery. Temperature-related parameters in the model need to be corrected, including the diffusion coefficients and conductivity of the solid and liquid phases. The Arrhenius equation is used for correction:

[0138] Where: Ф represents the temperature-related parameter that needs to be corrected, dimensionless; E act,Ф is the activation energy, in kJ / mol; Ф ref is the value of the relevant parameter at the reference temperature, dimensionless; T ref is the reference temperature in K, T is the battery temperature in K; R is the ideal gas constant in mol -1 ·K -1 .

[0139] ② Thermal model:

[0140] The heat generation of lithium-ion batteries mainly includes four parts:

[0141] In formula (10): It is Ohmic heat, is polarization heat, is the reversible entropy change heat, is the heat power generated by the thermal runaway side reaction:

[0142] In formulas (10.1) to (10.3): is the solid phase potential, unit is V; is the liquid phase potential, in V; x is the length direction of the electrode, in m; C e is the concentration of lithium ions in the liquid phase, in mol / m 3 ; σ eff is the solid phase effective conductivity, unit is S·m -1 ; j is the local current density, in A / m 3 κ eff is the effective conductivity of lithium ions in the electrolyte, in S·m -1 , and its correction is shown in formula (5.1); is the solid phase effective diffusion coefficient, in m 2; T is the battery temperature, unit is K; F is the Faraday constant, unit is C / mol; ΔS is the entropy change of the electrode system after the reduction reaction of the reactant per unit amount of substance at the interface; ΔS=(dU i / dT)nF, n is the number of lithium ion charges, which is 1; U i It is the equilibrium potential of the positive or negative electrode, measured in V.

[0143] ③ Thermal runaway side reaction heat generation model:

[0144] The side reaction heat generation model in the thermal runaway process is established by combining the Arrhenius equation in chemical reaction kinetics. The main side reactions included in the model are: SEI film decomposition heat release reaction; reaction between negative electrode active material and electrolyte; reaction between positive electrode active material and electrolyte and oxidation decomposition reaction of electrolyte. The heat generation rate calculation formula is:

[0145] The exothermic reaction of SEI film decomposition is obtained according to formula (11.1) to formula (11.3):

[0146] In formulas (11.1) to (11.3): C sei A is the dimensionless number of the metastable state content in the SEI film; sei is the forward factor of the reaction, in s -1 ;E a,sei is the activation energy of the reaction, in J / mol; R is the universal gas constant, which is 8.314 J / mol·K; T is the battery temperature, in K; m sei is the reaction order; R sei is the reaction rate, in s -1 ; Wc is the carbon content, unit is kg / m 3 ;H sei is the unit heat production of the reaction, in J / kg -1 .

[0147] The reaction between the negative electrode active material and the electrolyte is obtained according to formula (11.4) to formula (11.6):

[0148] In formulas (11.4) to (11.6): C ne A is the proportion of lithium in the negative electrode material that can react with the electrolyte, which is a dimensionless number; ne is the forward factor of the reaction, s -1 ;E a,neis the activation energy of the reaction in J / mol; R is the universal gas constant, which is 8.314 J / mol·K; T is the cell temperature in K; m ne is the reaction order; R ne is the reaction rate, s -1 ;W c Indicates carbon content, kg / m 3 ;H ne is the unit heat production of the reaction, J / kg -1 .

[0149] The exothermic reaction between the positive electrode active material and the electrolyte is obtained according to formula (11.7) to formula (11.9):

[0150] In formulas (11.7) to (11.9), α is the conversion rate of the positive electrode material reaction, which represents the proportion of the positive electrode material that has undergone exothermic reaction to the total positive electrode material, and is a dimensionless number; A pe is the forward factor of the reaction, s -1 ;E a,pe is the activation energy of the reaction, J / mol; R is the universal gas constant, which is 8.314 J / mol·K; T is the battery temperature, unit is K; m pe,p1 and m pe,p2 is the reaction order; R pe is the reaction rate, s -1 ;W p is the content of positive electrode active material, kg / m 3 ;H pe is the unit heat production of the reaction, J / kg -1 .

[0151] The oxidative decomposition reaction of the electrolyte is obtained according to formula (11.7) to formula (11.9):

[0152] Where: C e is the concentration of lithium ions in the liquid phase, in mol / m 3 ; A e is the forward factor of the reaction, s -1 ;E a,e is the activation energy of the reaction, J / mol; m e is the reaction order; R is the universal gas constant, which is 8.314 J / mol·K; T is the battery temperature, in K; R e is the reaction rate, s -1 , W e is the content of electrolyte, kg / m3 ;H e is the unit heat production of the reaction, J / kg -1 .

[0153] ④Heat transfer model:

[0154] When a power battery experiences thermal runaway and generates heat, it also exchanges heat with the outside world, which is a non-steady-state heat transfer process. The battery thermal effect model is applied to any microelement inside the battery:

[0155] In formula (12): ρ is the battery density, unit is kg / m 3 ; C p is the specific heat capacity of the battery, in J / (kg·K); T is the temperature of the battery, in K; λ is the thermal conductivity of the battery, in W / (m·K); The heat generation power per unit volume of the battery, in W / m 3 .

[0156] The boundary conditions for heat transfer on the battery surface include convection heat transfer and radiation heat transfer. The boundary conditions are:

[0157] Where: h is the convection heat transfer coefficient of the battery to the environment, the unit is W / (m 2 K); σ=5.67×10 -8 W·m -2 ·K -4 is the Stefan-Boltzmann constant; ε is the emissivity of the battery surface, which is set to 0.3 according to the material of the battery shell; T0 is the temperature of the battery surface, T ∞ It is the ambient temperature, for example, set its value to 30℃; is the heat flux density dissipated from the battery surface to the environment.

[0158] In the model, the battery is fully charged and the boundary conditions are adiabatic. This means there is no heat exchange between the battery and the outside world, and all heat generated / absorbed by the battery materials is used to change their own temperature. Both thermal and electrochemical simulations of lithium-ion batteries are performed by varying the lithium ion concentrations in the positive and negative electrode materials and electrolyte. Therefore, the coupled thermal-electrical simulation model for lithium-ion batteries also couples the thermal and electrochemical simulations through lithium ion concentration. Furthermore, according to the principle of conservation of energy, all heat generated in a lithium-ion battery is directly related to changes in battery temperature. Therefore, the energy components of the thermal and electrochemical simulations are coupled together through the battery temperature / energy conservation principle.

[0159] On the other hand, an embodiment of the present disclosure provides a power battery energy dissipation management device, which includes a memory, a processor, and a processor executable program stored on the memory and runnable on the processor. When the processor executable program is executed by the processor, the steps of the power battery energy dissipation method described above are implemented.

[0160] The device includes: at least one processor, at least one communication interface, at least one memory and at least one communication bus; optionally, the communication interface can be an interface of a communication module, such as an interface of a GSM module; the processor may be a processor CPU, or a specific integrated circuit ASIC (Application Specific Integrated Circuit), or one or more integrated circuits configured to implement the embodiments of the present disclosure. The memory may include a high-speed RAM memory, and may also include a non-volatile memory (non-volatile memory), such as at least one disk memory. The memory stores a program, and the processor calls the program stored in the memory to execute some or all of the above-mentioned method embodiments.

[0161] In yet another aspect, the present disclosure provides a computer-readable storage medium having a computer-executable program stored thereon. When the computer-executable program is executed by a processor, the steps of the power battery energy discharge method described above are implemented.

Claims

1. A method for discharging energy of a power battery, characterized in that: The energy release method comprises: Acquire a signal of thermal runaway of a battery cell in the power battery; The power battery is electrically connected to a discharge element, so that the power battery is discharged to a maximum safe state of charge that satisfies a mild exothermic reaction in the case of thermal runaway, or a state of charge lower than the maximum safe state of charge, wherein satisfying the mild exothermic reaction means that the temperature per unit volume of the battery cell in the power battery in the case of thermal runaway does not exceed the temperature at which the thermal runaway is triggered.

2. The energy dissipation method according to claim 1, characterized in that: The method for obtaining the maximum safe state of charge includes: Establish an electrochemical model to describe the internal electrochemical characteristics of the power battery, Establish a thermal model to describe the heat generation of the power battery. The electrochemical model and the thermal model are parameter-transferred and coupled through electrochemical heat generation and battery temperature, wherein the electrochemical heat generation and heat generation due to thermal runaway side reactions are used as inputs of the thermal model to calculate the temperature field distribution of the power battery; and the battery temperature in the thermal model is used as input of the electrochemical model to simulate the electrochemical process; The maximum safe state of charge of the power battery that satisfies a mild exothermic reaction under thermal runaway conditions is calculated iteratively.

3. The energy dissipation method according to claim 2, characterized in that: The heat generated by the power battery includes ohmic heat, polarization heat, reversible entropy change heat and heat generated by thermal runaway side reactions; The heat generated by the thermal runaway side reactions includes heat generated by decomposition of the battery separator, heat generated by the reaction of the negative electrode active material with the electrolyte, heat generated by the reaction of the positive electrode active material with the electrolyte, and heat generated by the oxidation decomposition reaction of the electrolyte.

4. The energy dissipation method according to claim 1, characterized in that: The power battery discharge time is a preset time, The preset time is: according to the wire electrically connecting the power battery and the discharge element and the maximum current that the discharge element can carry, the shortest time for the power battery to discharge to the maximum safe state of charge based on the maximum current is obtained.

5. The energy release method according to any one of claims 1 to 4, characterized in that: The thermal runaway includes any one or more of thermal runaway caused by overheating, thermal runaway caused by overcharging, thermal runaway caused by overdischarging, or thermal runaway caused by external force.

6. The energy dissipation method according to any one of claims 1 to 5, characterized in that: Also includes: The discharge element is cooled during the discharge process of the power battery.

7. The energy dissipation method according to any one of claims 1 to 6, characterized in that: Also includes: The battery cells that have not been affected by the thermal runaway during the discharge process of the power battery are cooled at maximum power.

8. A power battery energy dissipation device, characterized in that: The power battery energy dissipation device comprises: A sensor module is used to send a signal indicating whether any cell or module in the power battery is in thermal runaway; A discharge module, comprising a switch and a discharge element connected in series between the positive and negative electrodes of the power battery; The thermal runaway management module is used to control the switch to close so as to discharge the power battery through the discharge element after receiving the thermal runaway signal sent by the sensor module.

9. An electric vehicle, characterized in that: Including the power battery energy dissipation device as described in claim 8.

10. The electric vehicle according to claim 9, characterized in that: The connection wires of the power battery energy dissipation device are arranged in an independent wiring harness.

11. A power battery energy dissipation management device, characterized in that: The power battery energy dissipation management device includes a memory, a processor, and a processor executable program stored in the memory and executable on the processor. When the processor executable program is executed by the processor, the power battery energy dissipation method according to any one of claims 1 to 7 is implemented.

12. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer-executable program, and when the computer-executable program is executed by a processor, the method for discharging energy of a power battery according to any one of claims 1 to 7 is implemented.

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