Lithium battery internal short circuit simulation device, lithium battery internal short circuit test device, lithium battery internal short circuit diagnosis method

Abstract

The invention provides a lithium battery internal short circuit simulation device, a lithium battery internal short circuit test device, a lithium battery internal short circuit test method and a lithium battery internal short circuit diagnosis method, and the lithium battery internal short circuit test device comprises the lithium battery internal short circuit simulation device which comprises a lithium battery; the charging and discharging tester is connected with the set positions of the positive plate and the negative plate through conductive leads, so that the lithium battery is internally short-circuited to generate internal short-circuit current; the impedance testing device is connected with the lithium battery, and the impedance testing device is configured to perform impedance testing on the lithium battery; and the upper computer is connected with the impedance test device and the lithium battery internal short circuit simulation device, and the upper computer receives the impedance test data of the impedance test device and processes the impedance test data into an impedance spectrum and a phase change diagram.

Description

Technical Field

[0001] The present application relates to the field of lithium-ion battery internal short circuit triggering and detection, and in particular to a lithium battery internal short circuit simulation device, a testing device and method, and a lithium battery internal short circuit diagnosis method. Background Art

[0002] With the depletion of fossil energy and the emergence of environmental problems, electric vehicles are developing rapidly around the world. Among them, lithium-ion power batteries, as one of the core components of current new energy vehicles, have received widespread attention for their safety, and frequent safety accidents have become an important reason affecting their promotion. The main causes of safety accidents are overcharge and overdischarge of batteries, external short circuits and internal short circuits. Among them, the first two problems have been well controlled by installing reliable detection circuits, external sensors and protection devices, while the internal short circuit is difficult to install sensors inside the battery, and there is a lag in the internal temperature transmission to the battery surface, which makes it impossible for conventional detection methods to perform rapid detection. At the same time, the existing battery thermal management system can control conventional heat generation well, but it often cannot play a role in the concentrated and large-scale heat generation of internal short circuits, which leads to major safety problems such as smoke, fire and explosion, posing a huge threat to the safety of users' lives and property. At present, it is urgent to study the mechanism characteristics and detection methods of internal short circuits, and then take reasonable and effective safety measures to improve the safety of power batteries and promote the development of electric vehicles.

[0003] Therefore, it is necessary to provide more effective and reliable technical solutions. Summary of the invention

[0004] The present application provides a lithium battery internal short circuit simulation device, a testing device and method, and a lithium battery internal short circuit diagnosis method, which can simply determine whether a lithium battery has an internal short circuit.

[0005] The present application provides a lithium battery testing device, comprising: a lithium battery; an external device, connected to a set position of the lithium battery via a conductive lead, the external device comprising any one or more of a voltmeter, an ammeter, a power supply resistor, an impedance testing device and a charge and discharge tester.

[0006] In some embodiments of the present application, the set position includes: any one or more of the center or edge of the positive electrode sheet of the lithium battery, the center or edge of the negative electrode sheet of the lithium battery, the positive electrode ear of the lithium battery, and the negative electrode ear of the lithium battery.

[0007] The present application provides a lithium battery internal short circuit simulation device, comprising: a lithium battery; a charge and discharge tester, wherein a set position of a positive electrode sheet of the lithium battery and a corresponding position of a negative electrode sheet of the lithium battery are connected by a conductive lead to cause an internal short circuit in the lithium battery.

[0008] The present application provides a lithium battery internal short-circuit testing device, comprising: a lithium battery internal short-circuit simulation device, comprising: a lithium battery; a charge and discharge tester, connecting a set position of a positive electrode sheet of the lithium battery and a corresponding position of a negative electrode sheet of the lithium battery through a conductive lead so that an internal short-circuit current is generated in the lithium battery; an impedance testing device, connected to the lithium battery, the impedance testing device being configured to perform an impedance test on the lithium battery; a host computer, connected to the impedance testing device and the lithium battery internal short-circuit simulation device, the host computer receiving impedance test data of the impedance testing device and processing it into an impedance spectrum and / or a phase change diagram.

[0009] In some embodiments of the present application, the heat generation of the conductive lead is the same as the heat generation of the lithium battery.

[0010] In some embodiments of the present application, the thickness of the conductive lead is less than 0.05 mm.

[0011] In some embodiments of the present application, the host computer also records the internal short-circuit current and combines different internal short-circuit currents with corresponding impedance spectra and / or phase change diagrams to process them into corresponding impedance spectra and / or phase change diagrams under different internal short-circuit currents.

[0012] The present application provides a lithium battery internal short circuit test method, comprising: providing a lithium battery internal short circuit test device as described above; connecting the charge and discharge tester to the conductive lead to cause an internal short circuit in the lithium battery; performing an impedance test on the lithium battery through the impedance test device; receiving impedance test data of the impedance test device through the host computer and processing it into an impedance spectrum and / or a phase change diagram.

[0013] In some embodiments of the present application, the impedance test includes: discharging the lithium battery that is not connected to the charge and discharge tester at room temperature to a set SOC and then standing for 2 hours, and then performing an impedance test on the lithium battery; connecting the charge and discharge tester to the conductive lead so that the lithium battery is short-circuited and the internal short-circuit current is a first current, and then performing an impedance test on the lithium battery; controlling the charge and discharge tester so that the first current becomes a second current, and then performing an impedance test on the lithium battery.

[0014] The present application provides a method for diagnosing an internal short circuit in a lithium battery, comprising: providing a lithium battery, performing an impedance test on the lithium battery and obtaining an impedance spectrum and / or a phase change diagram of the lithium battery; and determining whether an internal short circuit occurs in the lithium battery based on the impedance spectrum and / or the phase change diagram.

[0015] In some embodiments of the present application, judging whether the lithium battery has an internal short circuit according to the impedance spectrum and / or the phase change diagram includes: when the low-frequency impedance slope in the impedance spectrum is smaller than the low-frequency impedance slope in the impedance spectrum when the lithium battery has no internal short circuit and / or when the absolute value of the low-frequency phase in the phase change diagram is smaller than the absolute value of the low-frequency phase in the phase change diagram when the lithium battery has no internal short circuit, the lithium battery has an internal short circuit.

[0016] In some embodiments of the present application, the greater the difference between the low-frequency impedance slope in the impedance spectrum and the low-frequency impedance slope in the impedance spectrum when the lithium battery does not have an internal short circuit and / or the greater the difference between the absolute value of the low-frequency phase in the phase change diagram and the absolute value of the low-frequency phase in the phase change diagram when the lithium battery does not have an internal short circuit, the greater the internal short-circuit current of the lithium battery.

[0017] The lithium battery testing device described in the present application realizes local point-to-point charging and discharging inside the lithium battery through external equipment and conductive leads, truly restores local overcharging and over-discharging, internal electrode inconsistency, etc. inside the lithium battery, and can be used to study their impact on the life and performance of the lithium battery.

[0018] The lithium battery internal short circuit simulation device described in the present application generates a controllable internal short circuit current locally inside the lithium battery through a charge and discharge tester and a conductive lead, simulating the internal short circuit caused by direct contact between the positive and negative electrodes inside the lithium battery due to damage to the diaphragm.

[0019] The lithium battery internal short circuit testing device and method described in the present application can test and obtain the impedance spectrum and / or phase change diagram of the lithium battery when an internal short circuit occurs through a lithium battery internal short circuit simulation device.

[0020] The lithium battery internal short circuit diagnosis method described in the present application can determine whether the lithium battery has an internal short circuit through the impedance spectrum and / or phase change diagram of the lithium battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The following figures describe in detail the exemplary embodiments disclosed in this application. The same reference numerals represent similar structures in several views of the drawings. Those skilled in the art will understand that these embodiments are non-limiting, exemplary embodiments, and the drawings are only for the purpose of illustration and description, and are not intended to limit the scope of this application. Other embodiments may also accomplish the inventive intent in this application. It should be understood that the drawings are not drawn to scale.

[0022] in:

[0023] Figure 1 This is a schematic diagram of the structure of the lithium battery testing device described in an embodiment of the present application;

[0024] Figure 2 and Figure 3 This is a schematic diagram of the structure of the lithium battery internal short circuit simulation device described in an embodiment of the present application;

[0025] Figure 4 This is a schematic diagram of the structure of the lithium battery internal short circuit test device described in an embodiment of the present application;

[0026] Figure 5 This is a flow chart of the lithium battery internal short circuit testing method described in an embodiment of the present application;

[0027] Figure 6 This is a flow chart of impedance testing in the lithium battery internal short circuit testing method described in an embodiment of the present application;

[0028] Figure 7 The impedance spectrum at room temperature and 50% SOC in the lithium battery internal short circuit test method described in the embodiment of the present application;

[0029] Figure 8 A graph showing the change of the low-frequency slope in the impedance spectrum at different SOCs at room temperature in the lithium battery internal short-circuit test method described in the embodiment of the present application;

[0030] Fig. 9 This is a phase change diagram at room temperature and 50% SOC in the lithium battery internal short circuit test method described in the embodiment of the present application;

[0031] Fig.10 This is a low-frequency phase change diagram at room temperature and 50% SOC in the lithium battery internal short circuit test method described in the embodiment of the present application;

[0032] Fig.11 This is a low-frequency phase change diagram under different SOCs at room temperature in the lithium battery internal short-circuit testing method described in an embodiment of the present application. DETAILED DESCRIPTION

[0033] The following description provides specific application scenarios and requirements of the present application, with the purpose of enabling those skilled in the art to make and use the content in the present application. It will be apparent to those skilled in the art that various local modifications to the disclosed embodiments are apparent, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present application. Therefore, the present application is not limited to the embodiments shown, but to the widest scope consistent with the claims.

[0034] The technical solution of the present invention is described in detail below in conjunction with the embodiments and drawings.

[0035] Battery short circuit refers to an abnormal path in which the positive and negative electrodes of a battery are connected to each other with very low resistance. Battery internal short circuit can be divided into four forms: the first is an internal short circuit caused by a fault in the diaphragm alone; the second is an internal short circuit caused by a fault in both the diaphragm and the positive electrode active material; the third is an internal short circuit caused by a fault in both the diaphragm and the negative electrode active material; the fourth is an internal short circuit caused by a fault in both the diaphragm and the positive and negative electrode active materials (at this time, the positive and negative electrode current collectors have already been internally short-circuited).

[0036] In addition to the violent external short circuit and internal short circuit, there is also a milder form of short circuit failure, namely micro short circuit. Micro internal short circuit of battery generally refers to the self-circuit inside the battery caused by diaphragm defects inside the battery, local drying of the electrode, micro-thorns on the surface of the electrode material, etc., which will continuously consume the battery power.

[0037] In order to reveal the formation mechanism of internal short circuit, domestic and foreign scholars have conducted a lot of research on experimental methods for simulating internal short circuit, among which the experimental methods mainly include mechanical abuse test, built-in material method and induced dendrite growth method. Internal short circuit replacement methods have problems in repeatability and authenticity to varying degrees, resulting in no recognized unified method yet.

[0038] When the internal short circuit enters the final stage, the battery has significant electrothermal characteristics, which is manifested as the terminal voltage drops rapidly to 0V and the temperature rises rapidly. Its electrical and thermal characteristics are obvious and can be easily identified and diagnosed by the BMS system. However, the battery is likely to be in a state of thermal runaway. At this time, the diagnosis often cannot meet the current national standard safety requirements for power batteries for electric vehicles. Therefore, it is necessary to identify and diagnose in the early stage of the internal short circuit of the battery.

[0039] The internal short circuit detection method relies on reliable internal short circuit triggering test data. A good internal short circuit replacement test should meet the following requirements: (1) It can simulate the electrical and thermal characteristics of the internal short circuit battery at the same time; (2) It can control the short circuit current, form and trigger time of the internal short circuit; (3) The battery damage is similar to the actual situation; (4) The repeatability is good. However, the current internal short circuit replacement test cannot meet the above requirements, and the subsequent internal short circuit detection cannot be carried out.

[0040] Based on this, the present application provides a technical solution, which realizes a point-to-point triggering method of a real internal short circuit of a lithium-ion battery by partial discharge inside the lithium battery. This method can realize an internal short circuit triggering experiment with good controllability and strong repeatability, and can realize early internal micro short circuit triggering. In addition, the in-situ detection method of the AC impedance spectrum is used to diagnose and detect the early internal micro short circuit and the mid-to-late internal short circuit of the battery, and the impedance spectrum and phase change diagram are used to determine whether the battery is short-circuited.

[0041] In layman's terms, the internal short circuit of lithium-ion batteries means that the diaphragm is damaged, resulting in direct contact between the positive and negative electrodes, which in turn generates leakage current, causing the lithium-ion battery voltage and SOC to drop and the temperature to rise. The internal short circuit of the battery can be divided into three stages: the initial short circuit, the middle short circuit and the final short circuit. Among them, the development process in the initial short circuit is self-limiting, the voltage drops slowly, the leakage current is extremely small, and there is no obvious heat generation; in the middle short circuit stage, the development process is affected by the heat dissipation conditions, the voltage drops rapidly, and the heat generation is obvious; at the final stage of the short circuit, when thermal runaway occurs, the development process cannot be blocked, the voltage is small, and heat is generated rapidly. At this time, it is meaningless to detect the internal short circuit.

[0042] Electrochemical impedance spectroscopy (EIS) is an impedance spectrum obtained by applying a small-amplitude sinusoidal potential (or current) perturbation signal to the electrochemical system and measuring the corresponding current (or potential) response generated by the system. This spectrum reflects the relationship between the impedance of the electrochemical system and the frequency, and provides rich information on the interface structure and kinetics. When an internal short circuit occurs in the battery, there is self-discharge inside the battery. This self-discharge leakage current can be compared to the discharge state of the battery. When the battery is discharged, lithium atoms are ionized from the positive electrode surface in the graphite crystal into lithium ions and electrons, and lithium atoms are synthesized at the negative electrode. Compared with the idle state, the internal electrochemical reaction of the battery in the discharged state is more active, and the resistance to ion transport is smaller, so its influence will be reflected in the electrochemical impedance spectrum.

[0043] Figure 1 This is a schematic diagram of the structure of the lithium battery testing device described in an embodiment of the present application.

[0044] refer to Figure 1 As shown, a lithium battery testing device described in an embodiment of the present application includes: a lithium battery. The lithium battery includes: a negative electrode sheet 01, a positive electrode sheet 02, a negative electrode ear 03, a positive electrode ear 04 and a separator 05, and the lithium battery also includes other necessary components such as an electrolyte (omitted here for the purpose of simplicity).

[0045] The embodiment of the present application describes a lithium battery testing device, which is used to perform various tests on lithium batteries. Therefore, the lithium battery included in the lithium battery testing device described in the embodiment of the present application can be any lithium battery model, specification or type that needs to be tested. The detailed structure and manufacturing process of the lithium battery are not described here.

[0046] Continue to refer Figure 1 As shown, a lithium battery testing device described in an embodiment of the present application also includes: an external device 07, which is connected to a set position of the lithium battery via a conductive lead 06, and the external device 07 includes any one or more of a voltmeter, an ammeter, a power supply, a resistor, an impedance testing device, and a charge and discharge tester.

[0047] In some embodiments of the present application, the set position includes: any one or more of the center or edge of the positive electrode sheet 02 of the lithium battery, the center or edge of the negative electrode sheet 01 of the lithium battery, the positive electrode ear 04 of the lithium battery, and the negative electrode ear 03 of the lithium battery.

[0048] In some embodiments of the present application, the conductive lead 06 may be connected to the lithium battery after the lithium battery is prepared and then electrically connected to the positive electrode sheet 02 and the negative electrode sheet 01. In other embodiments of the present application, the conductive lead 06 may also be added during the preparation of the lithium battery, for example: when preparing the lithium battery, one end of the conductive lead 06 is placed at a set position on both sides of the diaphragm 05 during the process of stacking or winding the positive and negative electrode sheets; and then subsequent steps such as liquid injection and packaging are performed to prepare the lithium battery described in the present application. Among them, unlike conventional lithium batteries, the lithium battery of the present application has the conductive lead 06 extending from the inside.

[0049] In some embodiments of the present application, the size and shape of the conductive lead 06 can be controlled to control the area of ​​contact between the conductive lead 06 and the positive electrode sheet 02 and the negative electrode sheet 01. For example, the end of the conductive lead 06 that contacts the positive electrode sheet 02 and the negative electrode sheet 01 is set to a flat square or circle, and the contact area can be controlled by controlling the area of ​​the square or circle.

[0050] In some embodiments of the present application, the heat generation of the conductive lead 06 is the same as that of the lithium battery, simulating a real internal short circuit heat generation state. The conductive lead 06 should also have good conductivity so that electrons can be quickly transmitted through the conductive lead 06.

[0051] In some embodiments of the present application, the thickness of the conductive lead 06 is less than 0.05 mm, so as to prevent the lithium battery from being squeezed and short-circuited due to vacuum sealing.

[0052] The positive and negative electrodes of lithium batteries generally include an electrode current collector and an electrode active material. In some embodiments of the present application, the negative electrode 01 includes a copper current collector and a graphite negative electrode material; the positive electrode 02 includes an aluminum current collector and a positive electrode material NCM811.

[0053] In some other embodiments of the present application, at least one of the positive electrode sheet 02 and the negative electrode sheet 01 may not be coated with an electrode active material and only include an electrode current collector.

[0054] In some embodiments of the present application, the setting position where the conductive lead 06 is connected to the lithium battery can be set according to the test requirements. For example, the setting position can be any suitable position such as the center area or edge area of ​​the positive electrode sheet 02 and the negative electrode sheet 01.

[0055] The lithium battery testing device described in the present application realizes local point-to-point charging and discharging inside the lithium battery through external equipment and conductive leads. By connecting different types of external equipment (power supplies or charge and discharge testers, etc.), it can truly restore local overcharging and over-discharging, internal electrode inconsistency, etc. inside the lithium battery, and can be used to study their impact on the life and performance of the lithium battery.

[0056] Figure 2 and Figure 3 This is a schematic diagram of the structure of the lithium battery internal short circuit simulation device described in the embodiment of the present application. Figure 3 for Figure 2 Cross-sectional view of .

[0057] refer to Figure 2 and Figure 3 As shown, a lithium battery internal short circuit simulation device described in the present application includes: a lithium battery. The lithium battery includes: a negative electrode sheet 11, a positive electrode sheet 12, a negative electrode ear 13, a positive electrode ear 14 and a separator 15, and the lithium battery also includes other necessary components such as an electrolyte (omitted here for the purpose of simplicity).

[0058] Continue to refer Figure 2 and Figure 3 As shown, the lithium battery internal short circuit simulation device described in the present application also includes: a charge and discharge tester 17, which connects the set position of the positive electrode sheet 12 of the lithium battery and the corresponding position of the negative electrode sheet 11 of the lithium battery through a conductive lead 16 to cause an internal short circuit in the lithium battery. The corresponding position of the negative electrode sheet 11 of the lithium battery refers to the position on the negative electrode sheet 11 corresponding to the set position of the positive electrode sheet 12. For example, when the set position of the positive electrode sheet 12 is the center area, the corresponding position of the negative electrode sheet 11 is also the center area.

[0059] It should be noted that the short-circuit simulation device for a lithium battery described in this application is actually a specific application of the aforementioned lithium battery test device when the external device is a charge-discharge tester. Therefore, except for the use of a charge-discharge tester as an external device, the other parts of the short-circuit simulation device for a lithium battery described in this application can be the same. Therefore, the description of other parts of the short-circuit simulation device for a lithium battery described in this application can refer to the corresponding description of the aforementioned lithium battery test device.

[0060] The lithium battery internal short circuit simulation device described in the present application generates a controllable internal short circuit current in a very small area of ​​the local surface of the positive and negative electrodes inside the lithium battery through a charge and discharge tester and a conductive lead, simulating the internal short circuit caused by direct contact between the positive and negative electrodes inside the lithium battery due to damage to the diaphragm. The lithium battery internal short circuit simulation device described in the present application can simulate four types of lithium battery internal short circuits: positive-negative electrode short circuit, positive-negative electrode collector short circuit, negative-positive electrode collector short circuit, and positive electrode collector-negative electrode collector short circuit. The lithium battery internal short circuit simulation device described in the present application can change the size of the internal short circuit current by controlling the charge and discharge tester, thereby simulating the entire cycle from the initial to the final stage of the development of the battery internal short circuit. The lithium battery internal short circuit simulation device described in the present application can realize the study of multiple short circuits in the same layer or multiple short circuits in different layers by changing the set position of the conductive lead connection.

[0061] Figure 4 This is a schematic diagram of the structure of the lithium battery internal short circuit testing device described in an embodiment of the present application.

[0062] refer to Figure 4 As shown, a lithium battery internal short-circuit test device described in the present application includes: a lithium battery internal short-circuit simulation device, including: a lithium battery 3; a charge and discharge tester 28, which connects the set positions of the positive and negative plates of the lithium battery 3 through conductive leads (including a positive conductive lead 26 and a negative conductive lead 27) so that the lithium battery 3 is short-circuited to generate an internal short-circuit current; an impedance testing device 22, connected to the lithium battery 3, and the impedance testing device 22 is configured to perform an impedance test on the lithium battery 3; a host computer 21, connected to the impedance testing device 22 and the lithium battery internal short-circuit simulation device, and the host computer 21 receives the impedance test data of the impedance testing device 22 and processes it into an impedance spectrum and / or a phase change diagram.

[0063] In some embodiments of the present application, the impedance testing device 22 may be an electrochemical workstation.

[0064] It should be noted that the lithium battery internal short circuit simulation device included in the lithium battery internal short circuit test device described in the present application can be the lithium battery internal short circuit simulation device described above. Therefore, the detailed description of the lithium battery internal short circuit simulation device here can refer to the above.

[0065] refer to Figure 4 As shown, the lithium battery 23 includes a positive electrode tab 24 and a negative electrode tab 25. The impedance testing device 22 is electrically connected to the lithium battery 23 via the positive electrode tab 24 and the negative electrode tab 25.

[0066] In some embodiments of the present application, the host computer 21 also records the internal short-circuit current and combines different internal short-circuit currents with corresponding impedance spectra and / or phase change diagrams to process them into corresponding impedance spectra and / or phase change diagrams under different internal short-circuit currents.

[0067] The lithium battery internal short-circuit testing device described in the present application can artificially control the triggering of the lithium battery internal short-circuit through a lithium battery internal short-circuit simulation device, and then test and obtain the impedance spectrum and / or phase change diagram of the lithium battery when an internal short circuit occurs through an impedance testing device and a host computer, thereby realizing a controllable study of the lithium battery internal short-circuit situation.

[0068] Figure 5 This is a flow chart of the lithium battery internal short circuit testing method described in an embodiment of the present application.

[0069] refer to Figure 5 As shown, the present application provides a lithium battery internal short circuit testing method, comprising:

[0070] Step S01: providing a lithium battery internal short circuit testing device as described in the above embodiment of the present application;

[0071] Step S02: connecting the charge and discharge tester to the conductive lead to cause a short circuit in the lithium battery;

[0072] Step S03: performing an impedance test on the lithium battery by using the impedance testing device;

[0073] Step S04: receiving the impedance test data of the impedance test device through the host computer and processing it into an impedance spectrum and / or a phase change diagram.

[0074] It should be noted that the embodiments of the present application do not limit the order of the steps. For example, step S03 may actually include multiple impedance tests, and the order of the multiple impedance tests may be before step S02 or after step S02. For another example, the lithium battery internal short circuit test device provided in step S01 may be a test device that only includes the main structure but is not electrically connected. The corresponding structures are connected separately in subsequent steps.

[0075] Figure 6 This is a flow chart of the impedance test in the lithium battery internal short circuit test method described in the embodiment of the present application.

[0076] refer to Figure 6 As shown, in some embodiments of the present application, the impedance test described in step S03 includes:

[0077] Step S11: discharging the lithium battery that is not connected to the charge and discharge tester to a set SOC at room temperature and then standing for 2 hours, and then performing an impedance test on the lithium battery;

[0078] Step S12: After the charge and discharge tester is connected to the conductive lead so that the lithium battery is short-circuited and the internal short-circuit current is a first current, an impedance test is performed on the lithium battery;

[0079] Step S13: controlling the charge and discharge tester to change the first current into a second current, and then performing an impedance test on the lithium battery.

[0080] In some embodiments of the present application, a frequency range of 10 KHz to 0.01 Hz is selected in the impedance test, and a disturbance current of 50 mA.

[0081] The lithium battery internal short circuit testing method described in the embodiment of the present application is described below with a relatively complete specific implementation method.

[0082] Step S01, providing a lithium battery internal short circuit test device. Mainly to make a lithium battery with an internal short circuit trigger structure. That is, in the normal process of preparing a lithium battery, the conductive lead is added. Other structures such as a host computer, an impedance test device and a charge and discharge tester can all be ready-made devices.

[0083] Step S11, the lithium battery produced in step S01 that is not connected to the charge and discharge tester (i.e., no internal short circuit occurs) is subjected to 0.2C cycle (activation) discharge at room temperature (generally 25 degrees Celsius) to the set SOC and then left to stand for 2 hours, and then the impedance test is performed on the lithium battery through an impedance test device. The set SOC is, for example, 50% SOC. This step is to connect the impedance test device to perform impedance testing on the lithium battery when the lithium battery is in a steady state, and the impedance data obtained is ISC0mA (50SOC), which is the comparative reference data when the lithium battery does not have an internal short circuit.

[0084] Step S02 and step S12, after the charge and discharge tester is connected to the conductive lead so that the lithium battery is short-circuited and the internal short-circuit current is the first current, the impedance test of the lithium battery is continuously performed during the internal short-circuit process. The first current is, for example, 6mA, the capacity of the lithium battery is 700mAh, and the discharge of 6mA is relatively within the range of a small internal short circuit. The impedance data obtained is ISC6mA (50SOC), which is the impedance data when the lithium battery has a small internal short circuit of 6mA.

[0085] Step S13, after the lithium battery is fully placed to ensure that the battery state is stable, the charge and discharge tester is controlled to change the first current into a second current, and then the lithium battery is subjected to an impedance test. The second current is, for example, 10 mA. The impedance data obtained is ISC 10 mA (50 SOC), which is the impedance data when a small internal short circuit of 10 mA occurs in the battery.

[0086] Step S04: receiving all the impedance test data of the impedance test device through the host computer and processing them into an impedance spectrum and / or a phase change diagram.

[0087] Figure 7 This is the impedance spectrum at room temperature and 50% SOC in the lithium battery internal short circuit testing method described in the embodiment of the present application.

[0088] The horizontal coordinate Z' of the electrochemical impedance spectrum is the real part of the impedance, and the vertical coordinate -Z" is the imaginary part of the impedance. The meanings of the other parts are as follows: The first part I is the ultra-high frequency part (above 10kHz), the part where the impedance curve intersects with the horizontal axis: Ohmic impedance R b ; The second part II is the high frequency part (frequency range 10K-630.957Hz), semicircle: lithium ions pass through the solid electrolyte impedance R sei ; The third part III is the intermediate frequency part (frequency 630.957-1.58489Hz), semicircle: charge transfer impedance, also known as electrode polarization impedance R ct ; The fourth part IV is the low frequency part (frequency is less than 1.58489Hz), 45° straight line: lithium ion diffusion impedance, also known as concentration polarization impedance W. In actual battery testing, due to R sei Smaller, so the second part II and the third part III overlap to form a semicircle.

[0089] refer to Figure 7 As shown in the first part of the UHF region, the ohmic resistance related to the transport of lithium ions and electrons through the electrolyte, porous diaphragm, wire, active material particles, etc., appears as a point on the EIS spectrum. This process can be represented by a resistor R s Indicates that Figure 7 As shown, in an internally short-circuited battery, the ohmic resistance remains almost unchanged.

[0090] Continue to refer Figure 7 As shown in the figure, in the second part II and the third part III of the medium and high frequency region, there is a semicircle related to the diffusion migration of lithium ions through the insulating layer on the surface of the active material particles and the charge transfer process. This process can be represented by an R SEI / C SEI Parallel circuit and one R ct / C dl Parallel circuits are represented in series. SEI It is the resistance of lithium ion diffusion and migration through the SEI film, R ct is the charge transfer resistance, or electrochemical reaction resistance, C dlis the double-layer capacitor. The charge transfer resistance is related to the rate of the electrochemical reaction. For fast reactions, the charge transfer resistance is usually small; for slow reactions, the charge transfer resistance is usually large. Therefore, when there is a large internal short-circuit current inside the battery, the electrode current quickly fills the double-layer capacitor, thereby converting all the current into Faraday current. The ion transport is active and the reaction rate is fast, so the charge transfer impedance will show a decreasing trend. However, when a micro-short circuit occurs, the electrode current charges the double-layer capacitor, the Faraday current is small, and the lithium ion concentration has not reached the electrochemical window inflection point concentration of the battery electrode. Therefore, its charge transfer resistance will show an increasing trend, but because the current is very small, the increase is not obvious, such as Figure 7 As shown, the micro-short circuit impedance and the normal impedance almost overlap in the high frequency.

[0091] Continue to refer Figure 7 As shown in the fourth part of the low-frequency region, there is a slant line related to the solid diffusion process of lithium ions inside the active material particles, also known as concentration polarization impedance. This process can be described by a Warburg impedance Z W Indicates that this process takes a long time to test. The detected charge transfer resistance increases and the concentration polarization causes the real part of the low-frequency impedance of the tiny internal short-circuit battery to increase, thus causing the low-frequency slope to decrease. Figure 7 As shown in the figure, as the micro short-circuit current increases, the low-frequency impedance shows a clockwise rotation trend, that is, the slope becomes smaller. Figure 7 In the fourth part IV, the impedance data slope without internal short circuit is greater than the impedance data slope of 6mA internal short circuit current is greater than the impedance slope of 10mA internal short circuit current.

[0092] Figure 8 This is a graph showing the change in low-frequency slope in the impedance spectrum at different SOCs at room temperature in the lithium battery internal short-circuit testing method described in an embodiment of the present application.

[0093] In order to explore whether there is a general rule for impedance detection of internal short circuit under different SOC, a micro-internal short circuit impedance test was performed on lithium-ion batteries under full SOC at room temperature 25°C. The impedance signal was obtained from the host computer and analyzed in the software. The detection range was from 90% SOC to 30% SOC. The low-frequency slope with the largest difference was analyzed. The slope of the battery in the non-short circuit state was used as the reference 0, and the difference in the low-frequency slope of the micro-short circuit battery impedance was compared. Figure 8 As shown in the figure, the impedance low-frequency slope change trend is consistent at 90% SOC-30% SOC, and the difference between the micro-short-circuited battery and the normal battery is larger, and as the short-circuit current increases, the difference value increases accordingly. In addition, the impedance difference at high SOC is smaller than that at low SOC, because the diffusion impedance is larger at low charge state, and when there is a short-circuit current, the low-frequency impedance changes even more.

[0094] Fig. 9 This is a phase change diagram at room temperature and 50% SOC in the lithium battery internal short circuit testing method described in the embodiment of the present application.

[0095] The impedance measured by the impedance test device includes Nyquist diagram and Bode diagram. The Nyquist diagram is what we call the impedance spectrum with the vertical axis as the imaginary part and the horizontal axis as the real part. The Bode diagram includes the amplitude-frequency diagram (amplitude-frequency diagram) and the phase-frequency diagram (phase-frequency diagram). When a small internal short circuit occurs, its charge transfer resistance, that is, the charge transfer impedance, will increase, resulting in an increase in the real part of the low-frequency impedance. The increase in the real part will change the phase value of the measured frequency point, so we can diagnose the short-circuited battery through the phase. Fig. 9 As shown in the figure, at room temperature, the influence of the tiny internal short-circuit current of the battery with a charge state of 50% on the impedance phase is not significant because the overall micro short-circuit current is small.

[0096] Fig.10 This is a low-frequency phase change diagram at room temperature and 50% SOC in the lithium battery internal short-circuit test method described in an embodiment of the present application.

[0097] However, the change of low-frequency phase cannot be ignored. Fig.10 As shown, it can be found that at low frequencies, especially at 0.01 Hz, the influence of the short-circuit current on the potential changes regularly. As the short-circuit current increases, the absolute value of the phase decreases.

[0098] Fig.11 This is a low-frequency phase change diagram under different SOCs at room temperature in the lithium battery internal short-circuit testing method described in an embodiment of the present application.

[0099] In order to explore whether there is a general rule for phase detection of internal short circuits at different SOCs, a phase analysis of lithium-ion batteries with micro-internal short circuits was performed at room temperature 25°C. The phase values ​​at 0.01Hz were compared from 90% SOC to 30% SOC. The phase of the battery in the non-short circuit state was used as the reference 0 to compare the low-frequency phase difference of the micro-short circuit battery. Fig.11 As shown, the phase change trend is consistent at 90% SOC-30% SOC, the difference between the micro-short-circuit battery and the normal battery is larger, and as the short-circuit current increases, the difference value increases accordingly.

[0100] According to the above tests, we can find that when an internal short circuit occurs in a lithium battery, the low-frequency slope and absolute value of the low-frequency phase of its electrochemical impedance spectrum will be lower than the baseline value when no internal short circuit occurs, and the greater the internal short circuit current, the greater the difference.

[0101] The lithium battery internal short circuit test device and method described in the present application can test and obtain the impedance spectrum and / or phase change diagram of the lithium battery when an internal short circuit occurs through a lithium battery internal short circuit simulation device. When a short circuit occurs inside a lithium-ion battery, its impedance low-frequency slope decreases, and as the short-circuit current increases, the downward trend becomes more obvious; its low-frequency phase absolute value will decrease, and as the short-circuit current increases, its value decreases more obviously.

[0102] An embodiment of the present application also provides a method for diagnosing an internal short circuit in a lithium battery, comprising: providing a lithium battery, performing an impedance test on the lithium battery and obtaining an impedance spectrum and / or a phase change diagram of the lithium battery; and determining whether an internal short circuit occurs in the lithium battery based on the impedance spectrum and / or the phase change diagram.

[0103] In some embodiments of the present application, judging whether the lithium battery has an internal short circuit according to the impedance spectrum and / or the phase change diagram includes: when the low-frequency impedance slope in the impedance spectrum is smaller than the low-frequency impedance slope in the impedance spectrum when the lithium battery has no internal short circuit and / or when the absolute value of the low-frequency phase in the phase change diagram is smaller than the absolute value of the low-frequency phase in the phase change diagram when the lithium battery has no internal short circuit, the lithium battery has an internal short circuit.

[0104] In some embodiments of the present application, the greater the difference between the low-frequency impedance slope in the impedance spectrum and the low-frequency impedance slope in the impedance spectrum when the lithium battery does not have an internal short circuit and / or the greater the difference between the absolute value of the low-frequency phase in the phase change diagram and the absolute value of the low-frequency phase in the phase change diagram when the lithium battery does not have an internal short circuit, the greater the internal short-circuit current of the lithium battery.

[0105] The principle of the above-mentioned diagnosis method is based on the relevant test results of the lithium battery internal short circuit test method mentioned above, which can effectively and simply diagnose whether the lithium battery has an internal short circuit.

[0106] The lithium battery internal short circuit diagnosis method described in the present application can determine whether the lithium battery has an internal short circuit through the impedance spectrum and / or phase change diagram of the lithium battery.

[0107] In summary, the present application adopts a point-to-point internal short-circuit simulation device and method that is more in line with the actual internal short-circuit scenario. The simulation device and method can control the size of the short-circuit current and have high repeatability, which is of great help to the subsequent study of the impact of different short-circuit currents on the pole pieces and the study of the internal short-circuit mechanism. The simulation device and method are used to make an internal short-circuit battery, and the electrochemical impedance spectroscopy is used to diagnose the tiny internal short circuit. When the low-frequency slope and the absolute value of the low-frequency phase of the battery impedance spectrum are lower than the reference value, it can be judged that a short circuit will occur inside the battery. The short circuit diagnosis can be realized as early as possible to improve the safety of battery use.

[0108] Compared with the prior art, the technical solution of this application includes but is not limited to the following advantages:

[0109] The lithium battery internal short-circuit simulation device of the present application can realize a real internal short-circuit scenario, and has good repeatability and strong controllability, and can trigger an internal short circuit with tiny different currents.

[0110] The lithium battery internal short circuit diagnosis method of the present application uses impedance as an in-situ, non-destructive detection method, which can perform internal short circuit diagnosis on lithium-ion batteries at any time, and adopts a phase method to diagnose internal short circuits. The present application only requires one frequency point, namely 0.01Hz phase, for identification, which is rapid and accurate.

[0111] In the lithium battery internal short circuit diagnosis method of the present application, the larger the short circuit current, the greater the phase difference. The specific magnitude of the short circuit current can be determined through the phase change difference, which is more conducive to the management of the battery system.

[0112] The technical solution of the present application can be applied to the internal short circuit detection of various lithium battery models and realize the online internal short circuit detection of lithium batteries. With the development of AC impedance spectroscopy, the impedance method can be further applied to the battery management system to provide more reliable and effective internal short circuit detection information for battery fault diagnosis.

[0113] The lithium battery internal short circuit simulation device and method of the present application are applicable to all types of lithium battery internal short circuit triggering. It is relatively simple to make in a soft pack, and the method is universal. To make an internal short circuit battery, place conductive leads on both sides of the battery separator to simulate the most common point-to-point positive and negative short circuit phenomenon in the internal short circuit, and inject liquid into the soft pack battery with internal short circuit triggering, encapsulate it, and let it stand to allow the electrolyte to fully infiltrate to make a controllable internal short circuit battery.

[0114] The lithium battery internal short circuit diagnosis method of the present application can be used in combination with the above-mentioned lithium battery internal short circuit simulation device and test device, or can be used alone, and is also universal.

[0115] The lithium battery internal short circuit diagnosis method of the present application can be used at the full SOC of the battery, and its regular changes are consistent. Under different charge states, the low-frequency impedance slope of the internal short-circuited battery is reduced compared to the normal battery, and the absolute value of the low-frequency phase is reduced, and as the short-circuit current increases, the difference also increases accordingly.

[0116] In summary, after reading the contents of this application, those skilled in the art will appreciate that the aforementioned application contents may be presented only in an exemplary manner and may not be restrictive. Although not explicitly stated herein, those skilled in the art will appreciate that this application is intended to encompass various reasonable changes, improvements and modifications to the embodiments. These changes, improvements and modifications are within the spirit and scope of the exemplary embodiments of this application.

[0117] It should be understood that the term "and / or" used in this embodiment includes any or all combinations of one or more of the associated listed items. It should be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to another element, or there can also be intermediate elements.

[0118] It should also be understood that the terms "comprising", "containing", "including" or "comprising", when used in this application document, indicate the presence of the recorded features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or groups thereof.

[0119] It should also be understood that although the terms first, second, third, etc. can be used to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. Therefore, without departing from the teachings of the present application, the first element in some embodiments can be referred to as the second element in other embodiments. The same reference numerals or the same reference signs represent the same elements throughout the specification.

[0120] In addition, the present specification describes exemplary embodiments by reference to idealized exemplary cross-sectional views and / or plan views and / or stereograms. Therefore, differences from the illustrated shapes due to, for example, manufacturing techniques and / or tolerances are foreseeable. Therefore, the exemplary embodiments should not be interpreted as being limited to the shapes of the regions shown herein, but should include deviations in shapes caused by, for example, manufacturing. Therefore, the regions shown in the figures are schematic in nature, and their shapes are not intended to illustrate the actual shapes of the regions of the device nor to limit the scope of the exemplary embodiments.

Claims

1. A lithium battery testing device, characterized in that: include: Lithium batteries; The external device is connected to the set position of the lithium battery through a conductive lead, and the external device includes any one or more of a voltmeter, an ammeter, a power supply, a resistor, an impedance test device and a charge and discharge tester.

2. The lithium battery testing device according to claim 1, characterized in that: The set position includes: any one or more of the center or edge of the positive electrode sheet of the lithium battery, the center or edge of the negative electrode sheet of the lithium battery, the positive electrode ear of the lithium battery, and the negative electrode ear of the lithium battery.

3. A lithium battery internal short circuit simulation device, characterized in that: include: Lithium batteries; The charge and discharge tester connects the set position of the positive electrode sheet of the lithium battery and the corresponding position of the negative electrode sheet of the lithium battery through a conductive lead to cause a short circuit in the lithium battery.

4. A lithium battery internal short circuit test device, characterized in that: include: A lithium battery internal short circuit simulation device comprises: a lithium battery; a charge and discharge tester, wherein a set position of a positive electrode sheet of the lithium battery is connected to a corresponding position of a negative electrode sheet of the lithium battery through a conductive lead so that an internal short circuit of the lithium battery generates an internal short circuit current; An impedance testing device, connected to the lithium battery, and configured to perform an impedance test on the lithium battery; A host computer is connected to the impedance testing device and the lithium battery internal short circuit simulation device, and the host computer receives impedance test data from the impedance testing device and processes it into an impedance spectrum and a phase change diagram.

5. The lithium battery internal short circuit test device according to claim 4, characterized in that: The heat generation of the conductive lead is the same as the heat generation of the lithium battery.

6. The lithium battery internal short circuit test device according to claim 4, characterized in that: The thickness of the conductive lead is less than 0.05 mm.

7. The lithium battery internal short circuit testing device according to claim 4, characterized in that: The host computer also records the internal short-circuit current and combines different internal short-circuit currents with corresponding impedance spectra and phase change diagrams to form corresponding impedance spectra and phase change diagrams under different internal short-circuit currents.

8. A lithium battery internal short circuit testing method, characterized in that: include: Providing a lithium battery internal short circuit testing device as claimed in any one of claims 4 to 7; Connecting the charge and discharge tester to the conductive lead to cause a short circuit in the lithium battery; Performing an impedance test on the lithium battery by using the impedance testing device; The impedance test data of the impedance test device is received by the host computer and processed into an impedance spectrum and a phase change diagram.

9. The lithium battery internal short circuit testing method according to claim 8, characterized in that: The impedance test includes: Discharging the lithium battery that is not connected to the charge and discharge tester to a set SOC at room temperature and then standing for 2 hours, then performing an impedance test on the lithium battery; After connecting the charge and discharge tester to the conductive lead so that the lithium battery is short-circuited internally and the internal short-circuit current is a first current, an impedance test is performed on the lithium battery; After controlling the charge and discharge tester so that the first current changes to a second current, an impedance test is performed on the lithium battery.

10. A method for diagnosing short circuit in a lithium battery, characterized in that: include: Providing a lithium battery, performing an impedance test on the lithium battery and obtaining an impedance spectrum and / or a phase change diagram of the lithium battery; Whether an internal short circuit occurs in the lithium battery is determined according to the impedance spectrum and / or the phase change diagram.

11. The lithium battery internal short circuit diagnosis method according to claim 10, characterized in that: Judging whether an internal short circuit occurs in the lithium battery according to the impedance spectrum and / or the phase change diagram includes: When the low-frequency impedance slope in the impedance spectrum is smaller than the low-frequency impedance slope in the impedance spectrum when the lithium battery does not have an internal short circuit and / or when the low-frequency phase absolute value in the phase change diagram is smaller than the low-frequency phase absolute value in the phase change diagram when the lithium battery does not have an internal short circuit, the lithium battery has an internal short circuit.

12. The lithium battery internal short circuit diagnosis method according to claim 11, characterized in that: The greater the difference between the low-frequency impedance slope in the impedance spectrum and the low-frequency impedance slope in the impedance spectrum when the lithium battery does not have an internal short circuit and / or the greater the difference between the absolute value of the low-frequency phase in the phase change diagram and the absolute value of the low-frequency phase in the phase change diagram when the lithium battery does not have an internal short circuit, the greater the internal short-circuit current of the lithium battery.

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