Battery leakage current calculation method, safety evaluation method, and electronic device

Abstract

The application discloses a battery leakage current calculation method, a safety evaluation method and electronic equipment, and belongs to the technical field of battery safety, and is used for calculating the leakage current of a battery. The method comprises the following steps: determining a first radius, the first radius being configured as the radius of a metal dendrite formed in the battery and a positive electrode side contact surface of the battery; inputting the first radius into a pre-constructed operation model to obtain the leakage current of the battery. The application implants metal foreign matters into the positive electrode side of the battery, and through multiple charging and discharging, the metal foreign matters are dissolved and metal dendrites are generated on the negative electrode side of the battery. The related parameters of the metal dendrites are obtained through actual measurement and disassembly of various metal foreign matters. The obtained related parameters are calculated in combination with battery parameters through the establishment of an operation module, so that the size of the leakage current of the battery is obtained, and the safety condition of the battery can be further judged according to the size of the leakage current.

Description

Technical Field

[0001] The embodiments of this application relate to the field of battery safety technology, and in particular to a battery leakage current calculation method, a safety assessment method, and an electronic device. Background Technology

[0002] With the large-scale application of lithium-ion batteries in electric vehicles, energy storage, and other fields, their safety has become a major concern. Internal defects in lithium-ion batteries caused by foreign metal objects are often more insidious, appearing unchanged on the battery's surface and difficult to detect during the manufacturing process. During battery production, metal foreign particles can easily embed themselves within the coatings of the positive and negative electrode active materials or disperse inside the core. If these particles are present on the positive electrode side, a "dissolution-migration-precipitation" process occurs. In this process, the metal ions generated by the dissolution of the foreign metal particles on the positive electrode side migrate across the separator under the drive of potential, depositing on the negative electrode side and precipitating as metal dendrites. Disassembly can reveal black spots on the negative electrode caused by the reduction and precipitation of foreign metal elements. If the size of the foreign metal particles is large enough, the metal dendrites deposited on the negative electrode side may grow through the pores of the separator to the positive electrode side. Once this connects the positive and negative electrodes, it can cause a short circuit, leading to a dangerous situation. Currently, the changes in metal dendrites inside the battery are difficult to measure externally. Summary of the Invention

[0003] The embodiments of this application provide a battery leakage current calculation method, a safety assessment method, and an electronic device to solve the technical problem that it is difficult to measure the changes in metal dendrites inside the battery from the outside in the prior art.

[0004] To address the aforementioned technical problems, embodiments of this application disclose the following technical solutions: Firstly, a method for calculating battery leakage current is provided, the method comprising: Determining a first radius, wherein the first radius is configured as the radius of the contact surface between the metal dendrites formed inside the battery and the positive electrode side of the battery, wherein the step of determining the first radius includes: A first volume of the metal foreign object forming the metal dendrite is determined, and the first volume is compared with a volume threshold to determine the shape of the metal dendrite; wherein, the volume threshold is a second volume of the largest cone formed by the metal foreign objects of different materials inside the battery; The first radius is determined based on the shape of the metal dendrite and the first diffusion coefficient of the metal foreign matter; wherein the first diffusion coefficient is determined based on the second radius of the metal dendrite forming the frustum and the base radius of the largest cone; The first radius is input into a pre-built computational model to obtain the leakage current of the battery. The computational model is constructed by fitting the relationship between the first radius and the leakage current based on a quadratic equation.

[0005] In conjunction with the first aspect, the quadratic equation in one variable includes: ; In the formula, I i The leakage current is caused by a micro-short circuit generated by a single metallic foreign object. r 短路 The short-circuit radius of the metallic foreign object within its equivalent volume. a , b and c All are fitting coefficients; Multiple sets of the first radius and the leakage current are obtained, and the results are obtained by solving the quadratic equation. a , b and c The specific value.

[0006] In conjunction with the first aspect, the steps of obtaining multiple sets of the first radius and the leakage current include: The material of the metal dendrites was obtained by disassembling the battery; The resistance value is determined based on the material of the metal dendrites; Determine the positive and negative solid-phase potentials on both sides of the metal dendrite; The solid-phase potential difference is obtained by subtracting the negative solid-phase potential from the positive solid-phase potential; the leakage current is obtained by dividing the solid-phase potential difference by the resistance value. The calculation steps for the positive electrode solid-state potential and the negative electrode solid-state potential include: According to Ohm's law formula for solid phases: ; In the formula, i s Represents solid-state current. σ Indicates the solid-state conductivity. φ s Represents solid-state potential. ▽ This represents the gradient operator; The solid-phase current is obtained from Ohm's law formula for the liquid phase: ; In the formula, i e Represents liquid phase current. σ eff Indicates the effective conductivity of the liquid phase. φ e Represents the liquid phase potential.R Represents the gas constant. T Represents absolute temperature. F Denotes Faraday's constant. t + 0 Represents the migration coefficient. c Indicates ion concentration; in, .

[0007] In conjunction with the first aspect, the step of determining that the shape of the metallic foreign object is a frustum includes: Determine the first volume of the metallic foreign object at the positive terminal of the battery; The first volume is compared with a volume threshold. If the first volume is greater than the volume threshold, then the metal dendrite is a frustum. Wherein, if the first volume is less than or equal to the volume threshold, the metal dendrite is a cone.

[0008] In conjunction with the first aspect, the step of determining the first radius of the frustum based on the first diffusion coefficient of the metallic foreign object includes: The radius of the base of the largest cone is determined based on the second volume and the film height of the battery, using the following formula: ; In the formula, V 锥 Indicates the second volume. π Represents pi (π). r 锥 Indicates the radius of the base. h 锥 This indicates the height of the cone; the film height is equal to the cone height. The first radius is determined based on the first volume, the film height, the bottom radius, and the second diffusion coefficient. The calculation formula includes: According to the formula for the volume of a frustum, we can obtain: ; The first radius and the second radius satisfy the following relationship: ; The volume formula for a frustum can be further simplified to: ; Furthermore, we can obtain: ; In the formula, h 台 This indicates the height of the frustum, which is equal to the height of the film layer. r 上底This represents the first radius of the frustum. r 下底 This represents the second radius of the frustum. V 台 This represents the volume of the frustum, which is equal to the first volume. r 临界 Represents the base radius, N represents the first diffusion coefficient, and h 膜 This indicates the thickness of the battery's film layer.

[0009] In conjunction with the first aspect, the steps for determining the first diffusion coefficient and the second diffusion coefficient include: The metal foreign objects of different sizes and materials were implanted into the positive electrode side of multiple batteries and assembled to obtain test batteries; The test batteries were charged and discharged multiple times to fully dissolve the metallic foreign matter. The test battery was disassembled, and the metal dendrites in the form of cones and frustums were obtained on the negative electrode side of the test battery. The base radius of the largest cone and the first and second radii of the frustum were measured to obtain the total radius of the cone. The radius of a sphere of equal volume is calculated based on the volume of the metallic foreign object. The ratio of the difference between the second radius and the bottom radius to the first radius is the first diffusion coefficient; The ratio of the sphere's radius to the base radius is the second diffusion coefficient.

[0010] Secondly, a battery safety assessment method is provided, the method comprising: Obtain the leakage current as described in any one of the first aspects using the battery leakage current calculation method; The leakage current is evaluated based on the current threshold to obtain the evaluation result of the battery; The current threshold ranges from 30 to 50 μA.

[0011] Thirdly, an electronic device is provided, including a memory and a processor; the memory is used to store a computer program; the processor is used to implement, when executing the computer program, the battery leakage current calculation method as described in any one of the first aspects, or the battery safety assessment method as described in the second aspect.

[0012] One of the above technical solutions has the following advantages or beneficial effects: Compared with existing technologies, this application provides a battery leakage current calculation method. The method includes: determining a first radius, configured as the radius of the contact surface between a metal dendrite formed inside the battery and the positive electrode side; and inputting the first radius into a pre-built computational model to obtain the battery leakage current. This application calculates the battery leakage current by inputting the first radius of the metal dendrite into the computational module, thereby obtaining the battery leakage status and further determining the battery's safety based on the leakage current magnitude. Attached Figure Description

[0013] The technical solution and other beneficial effects of this application will become apparent from the following detailed description of specific embodiments in conjunction with the accompanying drawings.

[0014] Figure 1 A flowchart illustrating the leakage current calculation method provided in this application embodiment; Figure 2 A schematic flowchart illustrating the method for calculating the first radius provided in an embodiment of this application; Figure 3 A schematic diagram illustrating the accumulation process of metal dendrites inside a battery as provided in an embodiment of this application; Figure 4 These are schematic diagrams of metal dendrites in different metallic foreign objects provided in the embodiments of this application; Figure 5 A schematic diagram of the metal dendrites of the largest cone provided in an embodiment of this application; Figure 6 This is a schematic diagram of the metal dendrites of a frustum provided in an embodiment of this application; Figure 7 This is a schematic diagram of a two-dimensional geometric model of a battery provided in an embodiment of this application.

[0015] Figure label: 100-Metal dendrites, 200-Metal foreign matter, 300-Positive current collector, 400-Positive electrode material, 500-Separator, 600-Negative electrode material, 700-Negative electrode current collector. Detailed Implementation

[0016] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0017] Those skilled in the art have noted that with the large-scale application of lithium-ion batteries in electric vehicles, energy storage, and other fields, the safety of lithium-ion batteries has also attracted attention. Compared to lithium-ion battery failures caused by external conditions such as mechanical abuse, electrical abuse, and thermal abuse, internal defects in lithium-ion batteries caused by metal foreign objects are more insidious. When internal defects occur, the battery's appearance remains unchanged, and metal foreign objects are difficult to detect during the manufacturing process. The particle size of metal foreign objects is generally very small (usually less than 200 μm) and easily embeds into the coating of the positive and negative electrode active materials or disperses inside the core. Conventional X-ray, industrial CT, and Hi-Pot tests are difficult to effectively detect these small and inconspicuous defects. In the early stages of a lithium-ion battery's lifespan, it is also difficult to detect the impact of foreign objects on the battery through capacity or voltage monitoring. However, as lithium-ion batteries are used, the impact of metal foreign object particles on the battery evolves. With the increase of internal expansion forces and the aging of the separator, metal foreign objects may puncture the separator, leading to a short circuit.

[0018] Metal foreign objects not only cause physical damage, but also dissolve and precipitate inside lithium-ion batteries. If a metal foreign object is present on the positive electrode side, a "dissolution-migration-precipitation" process occurs. In this process, metal ions generated from the dissolution of metal particles on the positive electrode side migrate across the separator under the drive of potential, depositing on the negative electrode side and precipitating as metal dendrites. By disassembling the negative electrode, black spots caused by the reduction and precipitation of foreign metal elements can be observed. If the size of the metal foreign object particles is large enough, the metal dendrites deposited on the negative electrode side may grow to the positive electrode side through the pores of the separator. Once the positive and negative electrodes are connected, a short circuit will occur.

[0019] In order to assess the changes of metallic foreign objects inside the battery and the critical size that may lead to a short circuit, this application establishes an idealized mathematical model and calculates the potential impact of metallic foreign object defects based on the changes of metallic foreign objects.

[0020] The specific implementation methods of this application are illustrated below through examples: like Figures 1 to 7 As shown in the figure, this application provides a method for calculating battery leakage current, including: S1: Determine the battery parameter information; Battery parameter information includes electrochemical model parameters and basic battery parameters, including electrode conductivity, electrode thickness, foreign object size, foreign object material, and cell SOC state during short circuit.

[0021] S2: Determine the first radius, which is configured as the radius of the contact surface between the metal dendrites formed inside the battery and the positive electrode side of the battery.

[0022] like Figure 2 As shown, the specific steps include: S201: The shape of the metal dendrite is determined to be a frustum; In this embodiment, a first volume of the metal foreign object at the positive terminal of the battery is determined; the first volume is compared with a volume threshold; if the first volume is greater than the volume threshold, the metal dendrite is a frustum; if the first volume is less than or equal to the volume threshold, the metal dendrite is a cone. The calculation step of the volume threshold includes: obtaining the largest cone formed inside the battery by metal foreign objects of different materials; the second volume of the largest cone is the volume threshold.

[0023] like Figure 3As shown, the dissolution and deposition of metallic foreign objects inside a battery requires a process. Generally, metallic foreign objects are dispersed in the form of particles on the positive electrode side of the battery. With continuous charging and discharging and battery aging, the metallic foreign objects dissolve and form metal dendrites on the negative electrode. The metal dendrites first diffuse towards the positive electrode in a cone shape and accumulate until the tip of the cone pierces the separator and connects to the positive electrode. If the battery can continue to charge and discharge at this point, the metal dendrites will diffuse laterally to the surrounding areas of the battery, thus forming a frustum. Therefore, the formation of metal dendrites requires two processes. The first process is the formation of a cone (such as...). Figure 3 and Figure 5 The second process is the formation of a frustum (such as...). Figure 6 In other words, a frustum can only form after the largest cone has formed inside the battery. Therefore, the volume of the largest cone can be used as a volume threshold to determine whether a metallic foreign object can form a frustum. If the volume of the metallic foreign object is greater than the volume threshold, it means that the formed metal dendrite must be a frustum, and a planar short circuit occurs at the positive and negative electrodes of the battery. If the volume of the metallic foreign object is equal to the volume threshold, it means that the formed metal dendrite is more likely to be the largest cone, and a point short circuit occurs at the positive and negative electrodes of the battery. If the volume of the metallic foreign object is less than the volume threshold, it means that the volume of the formed metal dendrite is smaller than the largest cone, and the metal dendrite is not connected to the positive and negative electrodes and will not affect the safety of the battery.

[0024] It should be noted that the amount of metallic foreign matter mixed inside the battery is not always sufficient to form a truncated cone, and the material of the metallic foreign matter varies, resulting in different shapes of the cone formed by different metallic foreign matter (e.g., Figure 4 (As shown). This requires experimental investigation to establish the specific relationship between different metallic foreign bodies and metallic dendrites.

[0025] Furthermore, in this embodiment, experimental batteries are manufactured by implanting metal particles with a diameter of 10-200 micrometers into the positive electrode side of a lithium battery, following normal production procedures. Simultaneously, a batch of normal batteries is manufactured as a control group. The experimental batteries are activated by cycling through 0.33C constant current / constant voltage charging and 0.33C constant current discharging for 5 cycles, and then left at room temperature for 7 days at full charge to observe the voltage drop. The self-discharge level caused by the metal particles is evaluated by comparing the experimental batteries with the control group batteries. The smallest metal particle size in the experimental battery with a significantly higher voltage drop than that in the control group batteries is defined as the critical size of that metal particle.

[0026] S202: Determine the first radius of the frustum based on the first diffusion coefficient of the metallic foreign object.

[0027] The specific steps include: In this embodiment, the volume of the largest cone that can be formed inside the battery can first be obtained based on the type of metallic foreign object. Then, the radius of the base of the cone can be obtained based on the height of the battery's film layer. The formula for calculating the volume of the cone is as follows: ; In the formula, V 锥 Indicates the second volume. π Represents pi (π). r 锥 Indicates the radius of the base. h 锥 This indicates the height of the cone; the film height is equal to the cone height.

[0028] Based on the first volume, film height, bottom radius, and second diffusion coefficient, the first radius is determined using the following formulas: First, the volume of the metallic foreign object is equivalent to that of a sphere of the same volume. The formula for calculating the volume of a sphere is: ; because V 球 = V 锥 Assuming r 球 = Mr 锥 Then we can obtain the formula: ; In the formula, M This represents the second diffusion coefficient. Wherein, the second diffusion coefficient... M This represents the lateral diffusion coefficient, which is the radius of the base of the cone-shaped metal dendrite formed by the lateral free diffusion of metal ions relative to the radius of the sphere formed by the metal foreign object. The growth and evolution of metal dendrites vary slightly among different metal particles, such as... Figure 4 As shown, the second diffusion coefficient M There are also some differences. Through the previous experimental design, metal foreign objects of different sizes and materials were implanted into the experimental batteries. By observing and comparing the self-discharge differences between the batteries containing metal foreign objects and the control group of normal batteries, the minimum self-discharge value that a metal foreign object of a certain radius can cause can be obtained. Furthermore, the second diffusion coefficient corresponding to different metals at the corresponding separator thickness can be calculated. M According to the second diffusion coefficient M By combining the above formulas, we can obtain the theoretical critical size at which metal particles cause micro-short circuits for different diaphragm thicknesses. r 临界 .

[0029] Furthermore, as previously stated, if the metal foreign matter forms a metal dendrite with the largest cone shape inside the battery and remains connected to the positive and negative electrodes, and continues to dissolve, the metal dendrite stops growing longitudinally due to the constraints of the positive and negative electrode plates, and lateral growth becomes dominant. The growth model changes from a cone shape to a frustum shape, and the corresponding short-circuit point changes from a point shape to a surface shape. Moreover, the short-circuit area continuously expands with the dissolution of metal particles and the growth of metal dendrites.

[0030] Therefore, the volume of the final frustum formed can be determined by the volume of the metallic foreign object. According to the formula for the volume of a frustum, we can obtain: ; The first radius and the second radius satisfy the following relationship: ; The volume formula for a frustum can be further simplified to: ; Furthermore, we can obtain: ; In the formula, h 台 This indicates the height of the frustum, which is equal to the height of the film layer. r 上底 The radius of the upper base of the frustum, i.e. the first radius referred to in this application, is the short-circuit radius corresponding to the short-circuit area where the metal dendrite contacts the positive electrode side of the battery. r 下底 This refers to the radius of the lower base of the frustum, which is the second radius as referred to in this application. V 台 This represents the volume of the frustum, which is equal to the first volume. r 临界 The base radius is represented by N, the first diffusion coefficient is represented by h. 膜 This indicates the thickness of the battery's film layer.

[0031] It should be noted that the actual short-circuit radius needs to take into account the membrane porosity. n The effect of membrane porosity n As a correction factor, the final short-circuit radius can be obtained as: ; r 短路 This is the calibrated equivalent short-circuit radius, which represents the actual short-circuit size.

[0032] In this embodiment of the application, the steps for determining the first diffusion coefficient and the second diffusion coefficient include: Metal foreign objects of different volumes and materials were implanted into the positive electrode side of multiple batteries to assemble test batteries. Multiple test batteries were charged and discharged repeatedly to fully dissolve the metal foreign objects. The test batteries were disassembled, and conical and frustum-shaped metal dendrites were obtained from the negative electrode side. The base radius of the largest cone and the upper and lower base radii of the frustum were measured. The radius of a sphere of equal volume was calculated based on the volume of the metal foreign objects. The ratio of the difference between the lower base radius and the base radius to the upper base radius is the first diffusion coefficient; the ratio of the sphere radius to the base radius is the second diffusion coefficient.

[0033] S2: Input the parameter information and the first radius into the pre-built computational model to obtain the battery leakage current.

[0034] In this embodiment of the application, the steps for constructing the computational model include: The computational equations are constructed based on the battery's parameter information and the material properties of the metallic foreign object to obtain the computational model; First, establish such as Figure 7 The two-dimensional geometric model shown contains six regions: positive electrode current collector 300, negative electrode current collector 700, positive electrode material 400, negative electrode material 600, separator 500, and metallic foreign object 200. The model is calculated using axisymmetric boundary conditions with the central axis of metallic foreign object 200 as the side of symmetry. Therefore, only the cross-section of the overall structure needs to be constructed, which can reduce the computational load of the model.

[0035] After establishing the model's geometric structure, finite element analysis was performed on the five regions, assigning them corresponding material properties and governing equations. The governing equations used in the calculations were based on the porous electrode theory framework. The battery's parameter information included the positive electrode current collector, negative electrode current collector, positive electrode material, negative electrode material, and the thicknesses of the positive and negative electrode separators.

[0036] The steps for constructing a computational model based on a geometric model include: The relationship between the first radius and the leakage current is fitted based on a quadratic equation, which includes: ; In the formula, I i The leakage current is caused by a micro-short circuit generated by a single metallic foreign object. r 短路 The short-circuit radius of the metallic foreign object within its equivalent volume. a , b and c All are fitting coefficients; Multiple sets of first radii and leakage currents are obtained, and then solved using a quadratic equation to obtain... a , b and c The specific value.

[0037] Furthermore, in this embodiment of the application, the step of obtaining multiple sets of first radii and leakage currents includes: The process involves: obtaining the material of the metal dendrites by disassembling the battery; determining the resistance value based on the material of the metal dendrites; determining the positive and negative solid-phase potentials on both sides of the metal dendrites; subtracting the negative solid-phase potential from the positive solid-phase potential to obtain the solid-phase potential difference; and dividing the solid-phase potential difference by the resistance value to obtain the leakage current. The calculation steps for the positive and negative solid-phase potentials include: According to Ohm's law formula for solid phases: ; In the formula, i s Represents solid-state current. σ Indicates the solid-state conductivity. φ s Represents solid-state potential. ▽ This represents the gradient operator; The liquid phase current is obtained from Ohm's law formula for liquid phase: ; In the formula, i e Represents liquid phase current. σ eff Indicates the effective conductivity of the liquid phase. φ e Represents the liquid phase potential. R Represents the gas constant. T Represents absolute temperature. F Denotes Faraday's constant. t + 0 Represents the migration coefficient. c Indicates ion concentration; in, ; The liquid phase potential in the above formula φ e With solid potential φ s There is a corresponding relationship between them, through multiple sets of liquid phase potentials. φ e With solid potential φ s The liquid phase potential can be obtained φ e For the characteristic solution and detailed solution process, please refer to the master's thesis: "Research on Electrochemical Behavior and Optimization of Lithium-ion Batteries Based on Mechanism Model", pages 12 to 18, author: Zheng Jili, domestic book classification number: TM911, international book classification number: 621.3.

[0038] In the embodiments of this application, the solid-phase ion diffusion equation is as follows: ; In the formula, C s Indicates the concentration of ions in the solid phase. t Indicates time, D s Represents the solid-phase diffusion coefficient. r Indicates the radius of solid particles; Liquid-phase ion diffusion equation: ; In the formula, e Indicates the liquid volume fraction. C e Indicates the ion concentration in the liquid phase. x Indicates the position coordinates in the thickness direction of the electrode. D e eff Indicates the effective diffusion coefficient of the electrode liquid; Electrochemical reaction equation (BV equation): ; In the formula, i Represents the electrochemical reaction current. i 0 represents the exchange current density. a a Indicates the negative electrode transfer coefficient. a c Indicates the positive electrode transfer coefficient. η It represents overpotential.

[0039] To describe the micro-short circuit caused by multiple metallic foreign objects inside a single battery, the accumulated leakage current is used. I 累积 To assess the severity of micro-short circuits: ; I 累积 The cumulative leakage current caused by micro-short circuits resulting from multiple metallic foreign objects within a single lithium battery can be used to comprehensively assess the severity of metallic foreign object defects. Therefore, when multiple metallic foreign objects are present in a lithium battery, the above formula can be used to... I i Replace with I 累积 Solve the problem.

[0040] This application also provides a battery capacity assessment method, including: acquiring metal foreign objects that may appear inside lithium batteries in the production line; measuring the radius of the corresponding sphere of the metal foreign object based on its volume; calculating the radius of the black spot formed on the negative electrode side using the leakage current calculation method provided above; calculating whether the battery will cause a micro-short circuit and the leakage current corresponding to the micro-short circuit using the black spot radius; and assessing the battery capacity loss by multiplying the leakage current by the time.

[0041] This application also provides a battery safety assessment method, including: performing micro-current discharge (<1mA) at different SOCs, with the discharge time set to 7 days or 30 days, recording the battery voltage and discharge capacity before and after discharge, and calculating the ratio of the voltage difference before and after discharge to the change in battery capacity. k The leakage current is obtained based on the leakage current calculation method provided above. I 累积 The ratio of voltage difference to capacity change obtained from microcurrent discharge of the corresponding battery model. k This allows for the assessment of the cumulative leakage current caused by micro-short circuits resulting from metal particles. I 累积 Caused monomer pressure drop △U This can be used to evaluate and screen lithium batteries that may have metal foreign object defects, and to develop targeted treatment plans. The formula for calculating the ratio is: ; The formula for calculating pressure drop is: ; This application also provides a battery safety assessment method, which includes: obtaining the leakage current of the battery leakage current calculation method provided in any of the above claims; assessing the leakage current based on a current threshold to obtain the battery assessment result; wherein the current threshold ranges from 30 to 50 μA.

[0042] Furthermore, by disassembling and statistically analyzing the lithium batteries containing metallic foreign objects, the number and size of black spots formed by metal particles on the negative electrode surface can be obtained. Based on the black spot size information and the leakage current calculation method mentioned above, the initial size of the contained metallic foreign objects can be deduced. At the same time, the leakage current and capacity loss caused by the micro-short circuit due to the metallic foreign objects can also be calculated.

[0043] This application also provides an electronic device, including a memory and a processor; the memory is used to store a computer program; the processor is used to implement the battery safety assessment method provided in any of the above when the computer program is executed.

[0044] The above provides a detailed description of a battery leakage current calculation method, safety assessment method, and electronic device provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for calculating battery leakage current, characterized in that, The method for calculating the leakage current of a battery includes: Determining a first radius, wherein the first radius is configured as the radius of the contact surface between the metal dendrites formed inside the battery and the positive electrode side of the battery, wherein the step of determining the first radius includes: A first volume of the metal foreign object forming the metal dendrite is determined, and the first volume is compared with a volume threshold to determine whether the shape of the metal dendrite is a frustum or a cone; wherein, the volume threshold is a second volume of the largest cone formed by the metal foreign object of different materials inside the battery; The first radius is determined based on the shape of the metal dendrites and the first diffusion coefficient of the metal foreign object. The first diffusion coefficient is determined based on the second radius of the metal dendrites forming the frustum and the base radius of the largest cone, wherein the lower base radius of the frustum is the second radius, and the ratio of the difference between the second radius and the base radius to the first radius is the first diffusion coefficient. When determining the first radius, the volume of the metal foreign object is equivalent to a sphere of the same volume. r 球 = Mr 锥 The ratio of the sphere's radius to its base radius is the second diffusion coefficient M; The first radius is input into a pre-built computational model to obtain the leakage current of the battery. The computational model is constructed by fitting the relationship between the first radius and the leakage current based on a quadratic equation.

2. The battery leakage current calculation method as described in claim 1, characterized in that, The quadratic equation in one variable includes: ； In the formula, I i The leakage current is caused by a micro-short circuit generated by a single metallic foreign object. r 短路 The short-circuit radius of the metallic foreign object within its equivalent volume. a , b and c All are fitting coefficients; The construction of the computational model includes: Multiple sets of the first radius and the leakage current are obtained, and the results are obtained by solving the quadratic equation. a , b and c The specific value.

3. The battery leakage current calculation method as described in claim 1, characterized in that, The steps for obtaining the leakage current include: The material of the metal dendrites was obtained by disassembling the battery; The resistance value is determined based on the material of the metal dendrites; Determine the positive and negative solid-phase potentials on both sides of the metal dendrite; The solid-phase potential difference is obtained by subtracting the negative solid-phase potential from the positive solid-phase potential; the leakage current is obtained by dividing the solid-phase potential difference by the resistance value. The calculation steps for the positive electrode solid-state potential and the negative electrode solid-state potential include: According to Ohm's law formula for solid phases: ； In the formula, i s Represents solid-state current. σ Indicates solid-state conductivity. Represents solid-state potential. ▽ This represents the gradient operator; The liquid phase current is obtained from Ohm's law formula for the liquid phase: ； In the formula, i e Represents liquid phase current. σ eff Indicates the effective conductivity of the liquid phase. Represents the liquid phase potential. R Represents the gas constant. T Represents absolute temperature. F Denotes Faraday's constant. t + 0 Represents the migration coefficient. c Indicates ion concentration; in, .

4. The battery leakage current calculation method as described in claim 1, characterized in that, The step of determining the shape of the metal dendrites includes: If the first volume is greater than the volume threshold, then the metal dendrite is a frustum. Wherein, if the first volume is less than or equal to the volume threshold, the metal dendrite is a cone.

5. The battery leakage current calculation method as described in claim 1, characterized in that, The steps for determining the first radius include: The radius of the base of the largest cone is determined based on the second volume and the film height of the battery, using the following formula: ； In the formula, V 锥 Indicates the second volume. π Represents pi (π). r 锥 Indicates the radius of the base. h 锥 This indicates the height of the cone; the film height is equal to the cone height. The first radius is determined based on the first volume, the film height, the bottom radius, and the second diffusion coefficient. The calculation formula includes: According to the formula for the volume of a frustum, we can obtain: ； The first radius and the second radius satisfy the following relationship: ； The volume formula for a frustum can be further simplified to: ； Furthermore, we can obtain: ； In the formula, h 台 This indicates the height of the frustum, which is equal to the height of the film layer. r 上底 This represents the first radius of the frustum. r 下底 This represents the second radius of the frustum. V 台 This represents the volume of the frustum, which is equal to the first volume. r 临界 The base radius is represented by N, the first diffusion coefficient is represented by h. 膜 This indicates the thickness of the battery's film layer.

6. The battery leakage current calculation method as described in claim 5, characterized in that, The steps for determining the first diffusion coefficient and the second diffusion coefficient include: The metal foreign objects of different sizes and materials were implanted into the positive electrode side of multiple batteries and assembled to obtain test batteries; The test batteries were charged and discharged multiple times to fully dissolve the metallic foreign matter. The test battery was disassembled, and the metal dendrites in the form of cones and frustums were obtained on the negative electrode side of the test battery. The base radius of the largest cone and the first and second radii of the frustum were measured to obtain the total radius of the cone. The radius of a sphere of equal volume is calculated based on the volume of the metallic foreign object. The ratio of the difference between the second radius and the bottom radius to the first radius is the first diffusion coefficient; The ratio of the sphere's radius to the base radius is the second diffusion coefficient.

7. A battery safety assessment method, characterized in that, The method includes: Obtain the leakage current from the battery leakage current calculation method as described in any one of claims 1-6; The leakage current is evaluated based on the current threshold to obtain the evaluation result of the battery; The current threshold ranges from 30 to 50 μA.

8. An electronic device, characterized in that: It includes a memory and a processor; the memory is used to store a computer program; the processor is used to implement, when executing the computer program, the battery leakage current calculation method as described in any one of claims 1-6, or the battery safety assessment method as described in claim 7.

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