Method for determining heating current of electrochemical device, electrochemical device and electrical equipment

Abstract

The embodiments of the present application provide a method for determining the heating current of an electrochemical device, an electrochemical device, and electrical equipment, including obtaining a plurality of temperatures within a temperature rise range, an impedance-current frequency change relationship of the electrochemical device at a first temperature, and determining the pulse current frequency based on the change relationship; for any target temperature, determining the lithium deposition rate of the electrochemical device at that temperature and the negative electrode lithium deposition potential, obtaining a plurality of currents at different rates at that temperature, and then obtaining a plurality of negative electrode minimum potentials and negative electrode impedances, and then determining the lithium deposition potential difference and correction current at that temperature, using the plurality of correction currents at that temperature to correct the corresponding currents to obtain a plurality of first currents, and determining the maximum value of the plurality of first currents as the heating current. The embodiments of the present application can improve the heating rate of the electrochemical device in different temperature rise ranges, and can also improve the lithium deposition phenomenon of the electrochemical device during self-heating.

Description

Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to a method for determining a heating current of an electrochemical device, an electrochemical device, and electrical equipment. Background Art

[0002] Lithium-ion batteries offer numerous advantages, including high specific energy density, long cycle life, high nominal voltage, low self-discharge rate, compact size, and light weight. They are widely used in various fields, including electric bicycles and electric vehicles. However, lithium-ion batteries are sensitive to ambient temperature. At low temperatures, their discharge capacity and discharge power performance decrease. This necessitates heating lithium-ion batteries to facilitate their use in low-temperature environments. Summary of the Invention

[0003] The present invention aims to provide a method for determining the heating current of an electrochemical device, an electrochemical device, and electrical equipment. These methods can determine the heating current within the temperature rise interval of each target temperature for use in heating the electrochemical device, thereby increasing the heating rate of the electrochemical device within different temperature rise intervals. The specific technical solutions are as follows:

[0004] The first aspect of the present application provides a method for determining the heating current of an electrochemical device, comprising obtaining multiple temperatures within a temperature rise range to obtain each target temperature, and obtaining an impedance-current frequency change relationship of the electrochemical device at a first temperature, and determining a pulse current frequency based on the impedance-current frequency change relationship; for any target temperature, determining the lithium deposition rate and the negative electrode lithium deposition potential of the electrochemical device at the target temperature; obtaining multiple currents of different rates at the target temperature; for any target temperature, obtaining multiple negative electrode minimum potentials and multiple negative electrode impedances at the target temperature based on the target temperature, the pulse current frequency, and the multiple currents of different rates at the target temperature, and determining a lithium deposition potential difference and a correction current at the target temperature based on the negative electrode minimum potential, the negative electrode impedance, and the negative electrode lithium deposition potential; for any target temperature, using the multiple correction currents at the target temperature to correct the corresponding current to obtain multiple first currents, and determining the maximum value of the multiple first currents as the heating current. The first temperature is the lowest temperature among the target temperatures or the initial temperature, and the initial temperature is the initial temperature of the environment or the initial temperature of the electrochemical device, wherein, for the same target temperature, the rate of any current at the target temperature is greater than or equal to the lithium deposition rate of the electrochemical device at the target temperature, wherein the lithium deposition potential difference is the difference between the lowest potential of the negative electrode and the lithium deposition potential of the negative electrode.

[0005] The beneficial effects of the embodiments of the present application are as follows: when the temperature of the electrochemical device is in the temperature rise range of the target temperature, the electrochemical device uses a heating current for pulse charging and heating, which can increase the heating rate of the electrochemical device in different temperature rise ranges and improve the lithium deposition phenomenon of the electrochemical device during self-heating.

[0006] In one embodiment of the present application, the determination of the lithium deposition potential difference and the correction current at the target temperature based on the negative electrode minimum potential, the negative electrode impedance and the negative electrode lithium deposition potential includes, for any of the target temperatures, determining the lithium deposition potential difference corresponding to each of the negative electrode minimum potentials according to the difference between each of the multiple negative electrode minimum potentials at the target temperature and the negative electrode lithium deposition potential; obtaining multiple correction currents at the target temperature according to the ratio of each of the lithium deposition potential differences to the negative electrode impedance, so that when the temperature of the electrochemical device is in the temperature rise range of the target temperature, the electrochemical device uses the heating current for pulse charging and heating, which can increase the heating rate of the electrochemical device in different temperature rise ranges, and can also improve the lithium deposition phenomenon of the electrochemical device during self-heating.

[0007] In one embodiment of the present application, determining the lithium deposition rate and the negative electrode lithium deposition potential of the electrochemical device at any target temperature includes, for any target temperature, at the target temperature, performing multiple charge and discharge tests on the electrochemical device with currents of different rates, and obtaining multiple negative electrode potentials of the electrochemical device during the charge and discharge tests to determine the negative electrode lithium deposition potential and the lithium deposition rate at which lithium deposition occurs in the electrochemical device at the target temperature, which is beneficial to reducing the risk of lithium deposition when the electrochemical device is self-heated in different temperature rise ranges.

[0008] In one embodiment of the present application, for any target temperature, based on the target temperature, the pulse current frequency, and the multiple currents of different rates at the target temperature, obtaining multiple negative electrode minimum potentials and multiple negative electrode impedances at the target temperature includes obtaining multiple currents of different rates at each target temperature, and for any target temperature, the multiple currents of different rates at the target temperature and the pulse current frequency form multiple test groups; performing a pulse charge and discharge heating test on the electrochemical device according to the pulse current frequency and the current of each test group to obtain the negative electrode minimum potential, negative electrode potential drop, and pulse current of each test group at the target temperature; obtaining the negative electrode impedance of each test group at the target temperature according to the negative electrode potential drop and pulse current of each test group. The embodiment of the present application provides a basis for the subsequent determination of the correction current by determining the negative electrode minimum potential, negative electrode potential drop, and negative electrode impedance of the electrochemical device.

[0009] In one embodiment of the present application, the current is corrected using the multiple correction currents at the target temperature to obtain multiple first currents, including when the correction current is positive, adding the current to the absolute value of the current correction current to obtain the first current at the target temperature; or, when the correction current is negative, subtracting the current from the absolute value of the current correction current to obtain the first current at the target temperature. The electrochemical device can use the heating current for pulse charging and heating, thereby increasing the heating rate of the electrochemical device in different temperature rise ranges, and improving the lithium plating phenomenon of the electrochemical device during self-heating.

[0010] In one embodiment of the present application, after obtaining multiple negative electrode potentials of the electrochemical device during the charge and discharge test to determine the negative electrode lithium deposition potential and the lithium deposition rate at which lithium deposition occurs in the electrochemical device at the target temperature, the method further includes obtaining a first function prediction relationship between the negative electrode lithium deposition potential and the temperature based on the negative electrode lithium deposition potential and the lithium deposition rate determined at different target temperatures; using the first function prediction relationship, the negative electrode lithium deposition potential corresponding to any temperature within the temperature rise range is obtained, thereby improving the determination rate of the negative electrode lithium deposition potential, which is conducive to improving the determination rate of the heating current of the electrochemical device.

[0011] In one embodiment of the present application, before obtaining multiple temperatures within the temperature rise range and obtaining each target temperature, the method further includes using the multiple temperatures to divide the temperature rise range into multiple temperature rise intervals, wherein the multiple temperature rise intervals are divided at equal intervals, or the multiple temperature rise intervals are divided at unequal intervals. By dividing the temperature rise intervals, when the temperature of the electrochemical device is in the temperature rise interval where the target temperature is located, the electrochemical device uses a heating current to perform pulse charging and heating, which can increase the heating rate of the electrochemical device in different temperature rise intervals and improve the lithium precipitation phenomenon of the electrochemical device during self-heating.

[0012] In one embodiment of the present application, the temperature rise interval [T0, T N ] includes at least a first temperature rise interval and a second temperature rise interval, wherein the range of the first temperature rise interval is [T0, T1), and the range of the second temperature rise interval is [T1, T N ], T0<T1<T N When the temperature of the electrochemical device is in the temperature rise range of the target temperature, the electrochemical device uses a heating current for pulse charging and heating, which can increase the heating rate of the electrochemical device in different temperature rise ranges and improve the lithium deposition phenomenon of the electrochemical device during self-heating.

[0013] A second aspect of the present application provides an electrochemical device heating method, wherein the electrochemical device heating current determination method provided in the first aspect is applied to determine the heating current of the electrochemical device, and then the electrochemical device is heated with the heating current.

[0014] The third aspect of the present application provides an electrochemical device, which includes a processor and a machine-readable storage medium, wherein the machine-readable storage medium stores machine-executable instructions that can be executed by the processor, and when the processor executes the machine-executable instructions, the method steps described in the first aspect above are implemented.

[0015] The fourth aspect of the present application provides an electrical device, comprising the electrochemical device provided in the third aspect.

[0016] The embodiment of the present application provides a method for determining the heating current of an electrochemical device, an electrochemical device, and an electrical device, by obtaining multiple temperatures within a temperature rise range to obtain each target temperature, and then determining the pulse current frequency based on the impedance-current frequency change relationship at the first temperature obtained, and then determining the lithium deposition rate and the negative electrode lithium deposition potential of the electrochemical device at each target temperature; after obtaining multiple currents of different rates at each target temperature, based on each target temperature, the pulse current frequency, and the multiple currents at each target temperature, obtain multiple negative electrode minimum potentials and multiple negative electrode impedances at each target temperature, and based on the negative electrode minimum potential, the negative electrode impedance, and the negative electrode lithium deposition potential, determine the lithium deposition potential difference and the correction current at each target temperature, and then for any target temperature, use the multiple correction currents at the target temperature to correct the corresponding current to obtain multiple first currents, and determine the maximum value of the multiple first currents as the heating current. When the temperature of the electrochemical device is in the temperature rise interval where the target temperature is located, the electrochemical device uses the heating current for pulse charging and heating, which can increase the heating rate of the electrochemical device in different temperature rise intervals and improve the lithium deposition phenomenon of the electrochemical device during self-heating. Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application.

[0018] Figure 1 This is a flow chart of a method for determining a heating current of an electrochemical device according to one embodiment of the present application;

[0019] Figure 2 This is a graph showing impedance-current frequency variation according to an embodiment of the present application;

[0020] Figure 3 Schematic diagram of the functional relationship between the negative electrode lithium deposition potential and temperature according to one embodiment of the present application;

[0021] Figure 4 A schematic diagram of a negative electrode potential change curve during a pulse charge-discharge heating test in one embodiment of the present application;

[0022] Figure 5 A schematic structural diagram of an electrochemical device according to an embodiment of the present application. DETAILED DESCRIPTION

[0023] The following will be combined with the accompanying drawings in the embodiments of this application to clearly and in detail describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field based on this application are within the scope of protection of this application.

[0024] It should be noted that in the content of this application, lithium-ion batteries are used as an example of electrochemical devices to explain this application, but the electrochemical devices of this application are not limited to lithium-ion batteries, but can also be secondary batteries such as sodium-ion batteries and solid-state batteries.

[0025] In the process of realizing the present application, the inventors of the present application discovered that the available capacity and discharge efficiency of lithium-ion batteries in low-temperature environments are affected by the ambient temperature. Generally speaking, low temperatures will affect the available capacity and charge and discharge efficiency of lithium-ion batteries, making charging more difficult and prone to lithium deposition, affecting the life of lithium-ion batteries, and lithium deposition can easily cause safety hazards. In addition, as the temperature of the lithium-ion battery rises, the pulse charging current that prevents lithium deposition from occurring in the lithium-ion battery also increases accordingly. In the current low-temperature pulse current self-heating method for lithium-ion batteries, the pulse charging current is a constant value throughout the heating process, resulting in a low temperature rise rate for the lithium-ion battery.

[0026] In view of this, the present invention provides a method for determining the heating current of an electrochemical device, such as Figure 1 As shown, the method includes the following steps:

[0027] S101: Acquire multiple temperatures within a temperature rise range to obtain target temperatures, obtain an impedance-current frequency variation relationship of an electrochemical device at a first temperature, and determine a pulse current frequency based on the impedance-current frequency variation relationship.

[0028] The execution subject of the embodiment of the present application can be an electrochemical device, or it can be an electrical device containing an electrochemical device, such as a two-wheeled vehicle, an electric car, a drone, a mobile phone, a tablet computer or a laptop computer, etc., or it can be an external charger or test equipment. For example, when the execution subject is an electrochemical device, the BMS (Battery Management System) in the electrochemical device can obtain multiple temperatures within the temperature rise range, thereby using the above multiple temperatures as each target temperature. The BMS of the embodiment of the present application can be integrated in the electrochemical device.

[0029] In the embodiment of the present application, the first temperature may be the lowest temperature or the initial temperature among the target temperatures. The temperature rise range may refer to the temperature range included in the electrochemical device rising from temperature To to temperature Te, wherein To may be the initial temperature and Te may be the highest temperature within the temperature rise range. The initial temperature To may refer to the initial temperature of the environment or the initial temperature of the electrochemical device, wherein the initial temperature of the environment may refer to the temperature of the environment in which the electrochemical device or the electrical equipment containing the electrochemical device is located before heating; the initial temperature of the electrochemical device may refer to the temperature of the electrochemical device itself before heating. Te is also the highest temperature among the above-mentioned multiple target temperatures.

[0030] In one example, the storage medium of the electrochemical device pre-stores a temperature rise range and a plurality of temperatures within the temperature rise range, so that each target temperature can be obtained. For example, the storage medium of the electrochemical device pre-stores a temperature rise range [-20°C, 10°C] and a plurality of temperatures within the temperature rise range: -20°C, -10°C, 0°C, 10°C, then -20°C, -10°C, 0°C, 10°C can be used as the target temperatures. Of course, the multiple temperatures within the temperature rise range are not limited to the above examples. For example, within the temperature rise range [-20°C, 10°C], temperatures such as -15°C, -5°C, and 5°C can also be included. It can be seen that the above multiple target temperatures can be obtained by dividing the temperature rise range at equal intervals, or by dividing the temperature rise range at unequal intervals.

[0031] In another example, the maximum temperature rise of the electrochemical device is pre-stored in the storage medium of the electrochemical device. The electrochemical device can detect and obtain the initial temperature, and then determine the temperature rise range based on the initial temperature and the maximum temperature rise temperature, and then divide the temperature rise range into equal intervals or unequal intervals to obtain multiple target temperatures.

[0032] In another example, the storage medium of the electrochemical device pre-stores a temperature rise range and multiple temperatures within the temperature rise range. The electrochemical device can also detect and obtain an initial temperature, and the electrochemical device can use the obtained initial temperature as the first temperature.

[0033] In one example, the storage medium of the electrochemical device pre-stores the impedance-current frequency variation relationship of the electrochemical device at the first temperature, and the electrochemical device can read the impedance-current frequency variation relationship to determine the pulse current frequency.

[0034] The impedance-current frequency variation relationship can be obtained based on an electrochemical impedance spectroscopy (EIS) test. Specifically, an EIS test can be performed on the electrochemical device at a first temperature. The EIS test applies a small-amplitude alternating current potential wave with different frequencies to the electrochemical device and measures how the ratio of the alternating current potential to the current signal changes with the frequency of the sine wave, thereby analyzing the electrode process dynamics of the electrochemical device and obtaining the impedance-current frequency variation relationship for each model of electrochemical device at the first temperature.

[0035] The obtained impedance-current frequency change relationship can be stored in a storage medium of an electrochemical device, an electrical device, an external charger or a test device, and can be expressed in the form of a curve or a table, which is not particularly limited in the embodiment of the present application. Figure 2 The changes in impedance and current frequency are shown in the impedance-current frequency curve. The horizontal axis of this curve represents the current frequency in Hz, and the vertical axis represents the impedance in mohm, reflecting the relationship between the impedance and current frequency of the electrochemical device. In the present embodiment, a current frequency in the range of 0.1 Hz to 4 Hz can be selected as the pulse current frequency. At this pulse current frequency, the electrochemical device has a larger impedance, is more likely to generate heat during EIS testing, and has a shorter response time for the hardware control circuit.

[0036] S102: for any target temperature, determining the lithium deposition rate and the negative electrode lithium deposition potential of the electrochemical device at the target temperature;

[0037] In the embodiment of the present application, the lithium deposition rate refers to the charging rate corresponding to the occurrence of lithium deposition in the electrochemical device, which may be related to temperature, and the negative electrode lithium deposition potential refers to the lowest negative electrode potential corresponding to the occurrence of lithium deposition when the electrochemical device is charged at the lithium deposition rate. In one example, the temperature rise range is [-20°C, 10°C], and the multiple target temperatures are -20°C, -10°C, 0°C, and 10°C. For the target temperature of -20°C, the electrochemical device can be charged and discharged at rates of 0.1C (rate), 0.5C, 1C, 1.5C, 2C, 2.5C, 3C, 3.5C, and 4C at -20°C, while monitoring the negative electrode potential of the electrochemical device. If lithium deposition occurs at multiple charging rates at the same target temperature, the smallest of these charging rates is the lithium deposition rate, and the lowest negative electrode potential monitored corresponding to the lithium deposition rate is the negative electrode lithium deposition potential, recorded as Va Similarly, the above charge and discharge test can be performed on the electrochemical device at -10°C, 0°C or 10°C, and the lithium deposition rate and negative electrode lithium deposition potential of the electrochemical device at the corresponding target temperature can be obtained.

[0038] S103: Acquire a plurality of currents at different rates at the target temperature;

[0039] After obtaining each target temperature, the embodiment of the present application can obtain a plurality of currents of different rates at the target temperature for any target temperature. For the same target temperature, the rate of any current at the target temperature is greater than or equal to the lithium plating rate of the electrochemical device at the target temperature. It is understandable that when the capacity of the electrochemical device is constant, its current is proportional to the rate, for example, its charging current is proportional to the charging rate. The above-mentioned multiple currents of different rates can be generated according to certain interval values, for example, 3A (ampere), 6A, 9A, 12A, and the interval value is 3. Of course, the interval value can also be 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4 or any point value in between.

[0040] S104: For any target temperature, based on the target temperature, the pulse current frequency and the currents of multiple different rates at the target temperature, obtain multiple negative electrode minimum potentials and multiple negative electrode impedances at the target temperature, and based on the negative electrode minimum potential, the negative electrode impedance and the negative electrode lithium deposition potential, determine the lithium deposition potential difference and the correction current at the target temperature.

[0041] After obtaining the currents of multiple different rates at the target temperature, for any target temperature, the embodiment of the present application can perform pulse charge and discharge heating tests on the electrochemical device at the target temperature using the determined pulse current frequency and the currents of multiple different rates, thereby obtaining multiple negative electrode minimum potentials and multiple negative electrode impedances at the target temperature. Among them, the negative electrode minimum potential and the negative electrode impedance have a one-to-one correspondence. The negative electrode minimum potential of the embodiment of the present application can characterize the negative electrode potential under the test conditions for comparison with the negative electrode lithium plating potential. The negative electrode impedance can characterize the negative electrode impedance size under the test conditions for calculating the correction current.

[0042] After obtaining multiple negative electrode minimum potentials and multiple negative electrode impedances, the lithium deposition potential difference and the correction current at the target temperature can be calculated based on the negative electrode minimum potential, the negative electrode impedance and the negative electrode lithium deposition potential. Wherein, the lithium deposition potential difference is the difference between the negative electrode minimum potential and the negative electrode lithium deposition potential. In the embodiment of the present application, multiple negative electrode minimum potentials and multiple negative electrode impedances can be obtained at a target temperature. Since the negative electrode minimum potential and the negative electrode impedance have a one-to-one correspondence, multiple lithium deposition potential differences can be obtained, and then multiple correction currents at the target temperature are obtained based on the multiple lithium deposition potential differences. Similarly, for other target temperatures, multiple correction currents corresponding to each target temperature can also be obtained, and the embodiments of the present application will not be repeated here.

[0043] S105 , for any target temperature, using a plurality of correction currents at the target temperature to correct the corresponding current to obtain a plurality of first currents, and determining a maximum value among the plurality of first currents as the heating current.

[0044] In an embodiment of the present application, for any target temperature, since multiple correction currents are calculated based on currents of multiple different magnifications, there is a corresponding relationship between each correction current and the current of each magnification. Based on this, after obtaining multiple correction currents at any target temperature, each correction current can be used to correct the corresponding current, thereby obtaining multiple first currents, and then the maximum value of the multiple first currents is determined as the heating current, which can be the heating current corresponding to the temperature rise interval of the target temperature. In an embodiment of the present application, after determining the heating current, the electrochemical device can use the heating current for pulse charging and heating, which can increase the heating rate of the electrochemical device in different temperature rise intervals, and can also improve the lithium precipitation phenomenon of the electrochemical device during self-heating.

[0045] In an embodiment of the present application, the temperature rise range may include multiple temperature rise intervals, each of which is based on multiple target temperatures. For example, if the temperature rise range is [-20°C, 10°C] and the target temperatures are -20°C, -10°C, 0°C, and 10°C, respectively, then the temperature rise range [-20°C, 10°C] may include the following temperature rise intervals: [-20°C, -10°C), [-10°C, 0°C), and [0°C, 10°C].

[0046] When the temperature of the electrochemical device is in the corresponding temperature rise interval, since the temperature rise interval contains at least one target temperature and a heating current is determined at the target temperature, the electrochemical device can use the determined heating current for pulse charging and heating. In one example, when the electrochemical device monitors a temperature of -15°C, the current temperature of -15°C is in the temperature rise interval of [-20°C, -10°C), the electrochemical device can use the heating current determined at the target temperature of -20°C for pulse charging and heating; as the temperature of the electrochemical device rises, when the temperature is monitored to be -5°C, the current temperature of -5°C is in the temperature rise interval of [-10°C, 0°C), the electrochemical device can use the heating current determined at -10°C for pulse charging and heating; as the temperature of the electrochemical device further rises, when the temperature is monitored to be 5°C, the current temperature of 5°C is in the temperature rise interval of [0°C, 10°C], the electrochemical device can use the heating current determined at 0°C for pulse charging and heating until the temperature of the electrochemical device reaches the highest temperature of the temperature rise range of 10°C, that is, the heating process of the electrochemical device is completed. If a temperature rise interval contains at least two target temperatures, the heating current determined by the minimum target temperature is used as the current for pulse charging and heating. The embodiment of the present application has no special restrictions on the pulse current frequency, as long as the purpose of the present application can be achieved. For example, it can be any value between 0.1Hz and 4Hz, such as 0.1Hz, 0.5, 1Hz, 1.5Hz, 2Hz, 3Hz or 4Hz. In the embodiment of the present application, the electrochemical device can monitor the temperature in real time through a temperature sensor. The temperature sensor can be arranged on the surface of the electrochemical device or inside the electrochemical device. It can monitor the ambient temperature or the temperature of the electrochemical device itself. The embodiment of the present application has no special restrictions.

[0047] In an optional embodiment, the step of determining the lithium deposition potential difference and the correction current at the target temperature based on the negative electrode minimum potential, the negative electrode impedance, and the negative electrode lithium deposition potential may include:

[0048] Step a: for any target temperature, determining the lithium deposition potential difference corresponding to each negative electrode minimum potential based on the difference between each of the multiple negative electrode minimum potentials at the target temperature and the negative electrode lithium deposition potential;

[0049] In the embodiment of the present application, after obtaining multiple negative electrode minimum potentials and negative electrode lithium deposition potentials at any target temperature, the difference between each of the multiple negative electrode minimum potentials and the negative electrode lithium deposition potential can be calculated to obtain the lithium deposition potential difference corresponding to each negative electrode minimum potential, which is recorded as ΔV, ΔV=Va min -Va, where Va min Represents the lowest potential of the negative electrode, and Va represents the lithium deposition potential of the negative electrode.

[0050] Step b: obtaining a plurality of correction currents at the target temperature according to the ratio of each lithium deposition potential difference to the negative electrode impedance.

[0051] In the embodiment of the present application, after obtaining the lithium deposition potential difference corresponding to the lowest potential of each negative electrode, the ratio of each lithium deposition potential difference to the negative electrode impedance can be calculated to obtain multiple correction currents at the target temperature, recorded as ΔI, ΔI = ΔV / Ra, where Ra represents the negative electrode impedance. Similarly, for each target temperature, the lithium deposition potential difference and correction current at each target temperature can be obtained according to the above steps a and b.

[0052] The embodiment of the present application can obtain multiple correction currents at each target temperature, and the correction current can be used to obtain the heating current. Therefore, when the temperature of the electrochemical device is in the temperature rise range of the target temperature, the electrochemical device uses the heating current to perform pulse charging and heating, which can increase the heating rate of the electrochemical device in different temperature rise ranges and improve the lithium deposition phenomenon of the electrochemical device during self-heating.

[0053] In an optional implementation, step S102 specifically includes:

[0054] For any target temperature, at that target temperature, the electrochemical device is subjected to multiple charge and discharge tests using currents at different rates, and multiple negative electrode potentials of the electrochemical device are obtained during the charge and discharge tests to determine the negative electrode lithium deposition potential and lithium deposition rate at which lithium deposition occurs in the electrochemical device at that target temperature. Since the temperature rise range can be obtained based on multiple target temperatures, determining the negative electrode lithium deposition potential and lithium deposition rate at which lithium deposition occurs in the electrochemical device at each target temperature is beneficial to reducing the risk of lithium deposition when the electrochemical device is self-heated in different temperature rise ranges.

[0055] In an embodiment of the present application, for any target temperature, multiple charge and discharge tests can be performed on the electrochemical device at the target temperature using currents of different rates. For example, each target temperature is -20°C, -10°C, 0°C, and 10°C. For the target temperature of -20°C, the electrochemical device can be charged and discharged at -20°C at charge rates of 0.1C (rate), 0.5C, 1C, 1.5C, 2C, 2.5C, 3C, 3.5C, and 4C, respectively, with 10 charge and discharge cycles for each rate. During the test, the negative electrode potential of the electrochemical device can be monitored in real time and recorded to obtain multiple negative electrode potentials of the electrochemical device during the charge and discharge test.

[0056] After multiple charge and discharge tests are performed on the electrochemical device at the same target temperature using currents of different rates, some of the electrochemical devices will undergo lithium deposition. Based on this, the negative electrode potential corresponding to the occurrence of lithium deposition in the electrochemical device where lithium deposition occurs can be determined as the negative electrode lithium deposition potential, and the corresponding charge rate can be determined as the lithium deposition rate. Similarly, for other target temperatures, multiple charge and discharge tests can be performed on the electrochemical device at the target temperature using currents of different rates to determine the corresponding negative electrode lithium deposition potential and lithium deposition rate, which will not be described in detail in the embodiments of this application.

[0057] In one embodiment, the method for determining the heating current of an electrochemical device according to an embodiment of the present application further includes:

[0058] Step I: Based on the negative electrode lithium deposition potential and lithium deposition rate determined at different target temperatures, a first function prediction relationship between the negative electrode lithium deposition potential and the temperature is obtained;

[0059] The inventors of the present application have found that after charging and discharging the electrochemical device at different ambient temperatures, the test results of the negative electrode lithium deposition potential and lithium deposition rate are shown in Table 1:

[0060] Table 1:

[0061] Ambient temperature T(℃) -20 -10 0 10 <![CDATA[Negative electrode lithium plating potential V a (V)]]> 0.08 0.01 -0.03 -0.1 Lithium deposition rate 0.5C 1C 2C 3.5C

[0062] In the embodiment of the present application, since the test is carried out at different ambient temperatures, the above-mentioned ambient temperatures can be used as target temperatures. Figure 3 As shown in Table 1, based on the test results, the embodiment of the present application can establish a coordinate system with temperature as the horizontal coordinate and the negative electrode lithium deposition potential as the vertical coordinate, mark the test results on the coordinate system, and fit the first function prediction relationship, which is expressed as: V a (T) = -0.0059T-0.037, the first function prediction relationship can express the negative electrode lithium deposition potential V a The relationship between the target temperature T and the target temperature T can be the ambient temperature or the temperature of the electrochemical device.

[0063] Step II: Using the first function prediction relationship, obtain the negative electrode lithium deposition potential corresponding to any temperature within the temperature rise range.

[0064] In the embodiment of the present application, since the first function prediction relationship can represent the negative electrode lithium deposition potential V a The relationship between V and temperature T can be used to predict the negative electrode lithium deposition potential at any temperature within the temperature rise range. For example, if you want to get the negative electrode lithium deposition potential corresponding to -15°C, you can substitute -15 into the first function prediction formula to get V a =-0.0059×(-15)-0.037≈0.05(V).

[0065] The embodiment of the present application can use the first function prediction relationship to obtain the negative electrode lithium deposition potential at any temperature within the temperature rise range, without the need for additional charge and discharge tests to determine the negative electrode lithium deposition potential at a certain temperature, thereby improving the determination rate of the negative electrode lithium deposition potential, which is beneficial to improving the determination rate of the heating current of the electrochemical device.

[0066] In one embodiment, for any target temperature, the step of obtaining multiple negative electrode minimum potentials and multiple negative electrode impedances at the target temperature based on the target temperature, the pulse current frequency, and multiple currents at the target temperature includes:

[0067] Step A: obtaining a plurality of currents at different magnifications at each target temperature, and for any target temperature, forming a plurality of test groups of currents at different magnifications and pulse current frequencies at the target temperature;

[0068] For example, when the ambient temperature is -20°C and the current is 4 with different magnifications and the pulse current frequency is 1, 4 test groups can be formed. Table 2 records the parameters of the pulse charge-discharge heating test at an ambient temperature of -20°C:

[0069] Table 2

[0070]

[0071]

[0072] In the embodiment of the present application, since the test is carried out at different ambient temperatures, the above ambient temperatures can be used as target temperatures. Among them, the pulse current frequency is 1Hz, and the currents of different rates are 3A (corresponding to 0.5C), 6A (corresponding to 1C), 9A (corresponding to 1.5C), and 12A (corresponding to 2C), with a total of 4 test groups. Table 2 also records the temperature rise (°C), temperature rise rate (°C / min), and negative electrode minimum potential of the electrochemical device in each test group. Negative electrode maximum potential Maximum potential drop at negative electrode ΔV a (V), negative electrode impedance R a During the pulse charge-discharge heating test, the above parameters of the electrochemical device can be detected by a temperature sensor or a voltage sensor.

[0073] Figure 4 Schematic diagram of the negative electrode potential change curve during the pulse charge and discharge heating test of the test group with a target temperature of -20°C, a current of 0.5C, and a pulse current frequency of 1Hz. Figure 4 In the equation, the horizontal axis is time, in seconds (s); the vertical axis is the negative electrode potential, in volts (V). Figure 4It can be seen that the highest potential of the negative electrode 0.97V, the lowest potential of the negative electrode is 0.2V.

[0074] Step B: performing a pulse charge-discharge heating test on the electrochemical device according to the pulse current frequency and current of each test group to obtain the lowest negative electrode potential, negative electrode potential drop, and pulse current of each test group at the target temperature;

[0075] The lowest potential of the negative electrode of each test group obtained in this application embodiment is recorded as Va min And the lowest potential of the negative electrode is recorded as Va max The negative electrode potential drop of each test group obtained during the pulse charge and discharge heating test is recorded as ΔVa, and the negative electrode potential drop ΔVa is the highest potential Va of the negative electrode. max and the lowest potential of the negative electrode Va min The pulse current is recorded as I, which is the current of different magnifications.

[0076] Step C: Obtain the cathode impedance of each test group at the target temperature based on the cathode potential drop and pulse current of each test group.

[0077] In the embodiment of the present application, for each group in each test group at the same target temperature, the ratio between the negative electrode potential drop and the pulse current of the test group can be calculated to obtain the negative electrode impedance of each test group at the target temperature. For example, based on the ratio between the negative electrode potential drop ΔVa of a single test group and the corresponding current I, the negative electrode impedance Ra of the test group can be obtained, that is, Ra=ΔVa / I. The embodiment of the present application provides a basis for the subsequent determination of the correction current by determining the lowest negative electrode potential, negative electrode potential drop and negative electrode impedance of the electrochemical device.

[0078] In one embodiment, the step of correcting the corresponding currents using the multiple correction currents at the target temperature to obtain the multiple first currents includes:

[0079] When the correction current is positive, the current is added to the absolute value of the current correction current to obtain the first current at the target temperature; or when the correction current is negative, the current is subtracted from the absolute value of the current correction current to obtain the first current at the target temperature.

[0080] In the embodiment of the present application, for any target temperature, multiple first currents at the target temperature can be obtained, thereby determining the heating current from the multiple first currents. When the temperature of the electrochemical device is within the temperature rise interval of the target temperature, the electrochemical device can use the heating current for pulse charging and heating, thereby increasing the heating rate of the electrochemical device in different temperature rise intervals and improving the lithium deposition phenomenon of the electrochemical device during self-heating.

[0081] For example, the temperature rise interval of the target temperature of -20°C is [-20°C, -10°C). Based on the test results shown in Tables 1 and 2, the heating current of the target temperature of -20°C is determined. The heating current is the heating current corresponding to the temperature rise interval [-20°C, -10°C). The results are shown in Table 3.

[0082] Table 3:

[0083]

[0084] In Table 3, the calculation method of the lithium deposition potential difference ΔV corresponding to the current of different rates is: The calculation method of the correction current ΔI is ΔI=ΔV / R a The calculation process of the first current is as follows: for a current with a magnification of 0.5C (3A), the corresponding first current value is 3+|0.47|=3.47 (A), which is approximately 3.5A; for a current with a magnification of 1C (6A), the corresponding first current value is 6+|0.38|=6.38 (A), which is approximately 6.4A; for a current with a magnification of 1.5C (9A), the corresponding first current value is 9+|0.17|=9.17 (A), which is approximately 9.2A; for a current with a magnification of 2C (12A), the corresponding first current value is 12-|-2.26|=9.74 (A), which is approximately 9.7A. It can be seen that among the four first currents, the largest is 9.7A, so 9.7A can be determined as the heating current.

[0085] Similarly, for other target temperatures, the heating current corresponding to the target temperature (or the temperature rise range within which the target temperature falls) can be determined using the above method. The specific process is not repeated here. The heating currents for the three temperature rise ranges of [-20°C, -10°C), [-10°C, 0°C), and [0°C, 10°C] are shown in Table 4.

[0086] Table 4

[0087] Temperature rise range Heating current [-20℃，-10℃) 9.7A [-10℃，0℃) 12.4A [0℃，10℃] 14.8A

[0088] In one embodiment, the method for determining the heating current of an electrochemical device according to an embodiment of the present application further includes:

[0089] The temperature rise range is divided into a plurality of temperature rise intervals using a plurality of temperatures, wherein the plurality of temperature rise intervals are divided at equal intervals, or the plurality of temperature rise intervals are divided at unequal intervals.

[0090] This step can be located after obtaining multiple temperatures within the temperature rise range. In an embodiment of the present application, the temperature rise range can be divided into multiple temperature rise intervals using multiple temperatures. The temperature rise intervals are divided at equal intervals, and the division rules are simple; the temperature rise intervals are divided at unequal intervals, and the division rules are more flexible. By dividing the temperature rise intervals, when the temperature of the electrochemical device is in the temperature rise interval where the target temperature is located, the electrochemical device uses a heating current for pulse charging and heating, which can increase the heating rate of the electrochemical device in different temperature rise intervals, and can also improve the lithium precipitation phenomenon of the electrochemical device during self-heating.

[0091] In one embodiment, the temperature rise interval [T0, T N ] includes at least a first temperature rise interval and a second temperature rise interval, wherein the range of the first temperature rise interval is [T0, T1), and the range of the second temperature rise interval is [T1, T N ], T0<T1<T N .

[0092] It is understandable that when the temperature rise range is constant, as the number of temperature rise intervals increases, the number of heating currents to be determined will also increase, and the precision of pulse charging and heating of the electrochemical device will be improved accordingly, but the amount of calculation required will increase. Based on this, the temperature rise intervals [T0, T N ] includes at least a first temperature rise interval and a second temperature rise interval, wherein the range of the first temperature rise interval is [T0, T1), and the range of the second temperature rise interval is [T1, T N ], T0<T1<T N .

[0093] In one embodiment, the embodiment of the present application includes three temperature rise intervals [-20°C, -10°C), [-10°C, 0°C), and [0°C, 10°C]. When the temperature of the electrochemical device is in the temperature rise interval where the target temperature is located, the electrochemical device uses a heating current for pulse charging and heating, which can increase the heating rate of the electrochemical device in different temperature rise intervals, and can also improve the lithium precipitation phenomenon of the electrochemical device during self-heating.

[0094] The present application also provides an electrochemical device heating method, which applies the electrochemical device heating current determination method provided in any of the above embodiments to determine the heating current of the electrochemical device, and then heats the electrochemical device with the heating current. Specifically, when the temperature of the electrochemical device is in the corresponding temperature rise interval, that is, when the temperature of the electrochemical device is in the temperature rise interval where the target temperature is located, the determined heating current can be used to heat the electrochemical device, which can increase the heating rate of the electrochemical device in different temperature rise intervals and improve the lithium precipitation phenomenon of the electrochemical device during self-heating.

[0095] The present application also provides an electrochemical device, such as Figure 5As shown, the electrochemical device 500 includes a processor 501 and a machine-readable storage medium 502. The processor 501 can be integrated into a BMS (Battery Management System). The machine-readable storage medium 502 stores machine-executable instructions that can be executed by the processor 501. When the processor 501 executes the machine-executable instructions, the method for determining the heating current of the electrochemical device described in any of the above embodiments is implemented.

[0096] The present application also provides an electrical device including the electrochemical device described in the above embodiment. In some examples, the electrical device may include a two-wheeled vehicle, an electric vehicle, a drone, a mobile phone, a tablet computer, or a laptop computer, and may also be an external charger or testing equipment.

[0097] The machine-readable storage medium may include random access memory (RAM) or non-volatile memory, such as at least one disk storage. Alternatively, the memory may be at least one storage device located away from the processor.

[0098] The above-mentioned processor can be a general-purpose processor, including a central processing unit (CPU), a network processor (NP), etc.; it can also be a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, and discrete hardware components.

[0099] Specifically, the effects of the embodiments of the present application will be described below in combination with multiple embodiments and comparative examples.

[0100] Example

[0101] The initial temperature of the lithium-ion battery (model 6052C9) was set to -20°C. The electrochemical device was pulse-charged and heated according to the temperature rise range and heating current shown in Table 4: when the lithium-ion battery temperature was between [-20°C, -10°C), pulse charging and heating were performed with a heating current of 9.7A; when the lithium-ion battery temperature was between [-10°C, 0°C), pulse charging and heating were performed with a heating current of 12.4A; when the lithium-ion battery temperature was between [0°C, 10°C], pulse charging and heating were performed with a heating current of 14.8A. Heating was stopped when the lithium-ion battery temperature reached 10°C. The time it took for the lithium-ion battery to heat up from -20°C to 10°C was calculated. The pulse current frequency was 1Hz for all of the above tests. The test results are shown in Table 5.

[0102] Comparative Example

[0103] The initial temperature of the lithium-ion battery (model 6052C9) was set to -20°C. Pulse charging and heating were performed at a constant current of 9.7A. Heating was stopped when the temperature of the lithium-ion battery reached 10°C. The time it took for the lithium-ion battery to heat from -20°C to 10°C was calculated. The pulse current frequency was 1Hz. The test results are shown in Table 5.

[0104] Table 5

[0105] Heating method Heating rate Heating time Example 3.46℃ / min 8.67min Comparative Example 1.92℃ / min 15.625min

[0106] As can be seen from Table 5, the time for the lithium-ion battery to heat up from the same initial temperature (-20°C) to the target temperature (10°C) in the embodiment of the present application is shortened by 6.955 minutes compared to the comparative example. It can be seen that when the heating current determined by the heating current determination method of the present application is used for heating, the time for the lithium-ion battery to reach the target temperature is greatly shortened. In addition, the heating rate of the embodiment of the present application is increased by 1.54°C / min compared to the comparative example, which shows that the heating rate of the embodiment of the present application is also greatly improved. Therefore, the embodiment of the present application can improve the heating rate of the electrochemical device (such as a lithium-ion battery) in different temperature rise ranges and improve the lithium precipitation phenomenon of the electrochemical device during self-heating.

[0107] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0108] Each embodiment in this specification is described in a related manner. Similar portions between embodiments can be referenced to each other. Each embodiment focuses on the differences from other embodiments. The electrochemical device / electrical equipment embodiments are generally similar to the method embodiments, so their description is relatively simple. For relevant portions, refer to the description of the method embodiments.

[0109] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A method for determining a heating current of an electrochemical device, wherein: The method comprises: Acquiring multiple temperatures within a temperature rise range to obtain target temperatures, and obtaining an impedance-current frequency change relationship of the electrochemical device at a first temperature, and determining a pulse current frequency based on the impedance-current frequency change relationship, wherein the first temperature is the lowest temperature or the initial temperature among the target temperatures, and the initial temperature is the initial temperature of the environment or the initial temperature of the electrochemical device; For any target temperature, determining the lithium deposition rate and the negative electrode lithium deposition potential of the electrochemical device at the target temperature; Obtaining a first function prediction relationship between the negative electrode lithium deposition potential and temperature based on the negative electrode lithium deposition potential and the lithium deposition rate determined at different target temperatures; Using the first function prediction relationship, obtain the negative electrode lithium deposition potential corresponding to any temperature within the temperature rise range; Obtaining a plurality of currents at different rates at the target temperature, wherein, for the same target temperature, the rate of any current at the target temperature is greater than or equal to the lithium deposition rate of the electrochemical device at the target temperature; For any target temperature, based on the target temperature, the pulse current frequency, and the currents of the multiple different rates at the target temperature, multiple negative electrode minimum potentials and multiple negative electrode impedances at the target temperature are obtained, and based on the negative electrode minimum potential, the negative electrode impedance, and the negative electrode lithium deposition potential, the lithium deposition potential difference and the correction current at the target temperature are determined, wherein the lithium deposition potential difference is the difference between the negative electrode minimum potential and the negative electrode lithium deposition potential; For any target temperature, the corresponding current is corrected using the multiple correction currents at the target temperature to obtain multiple first currents, and the maximum value of the multiple first currents is determined as the heating current.

2. The method for determining the heating current of an electrochemical device according to claim 1, wherein: The determining of the lithium deposition potential difference and the correction current at the target temperature based on the negative electrode minimum potential, the negative electrode impedance, and the negative electrode lithium deposition potential includes: For any of the target temperatures, determining the lithium deposition potential difference corresponding to each of the negative electrode lowest potentials according to the difference between each of the multiple negative electrode lowest potentials at the target temperature and the negative electrode lithium deposition potential; A plurality of correction currents at the target temperature are obtained according to the ratio of each of the lithium deposition potential differences to the negative electrode impedance.

3. The method for determining the heating current of an electrochemical device according to claim 1, wherein: For any target temperature, determining the lithium deposition rate and the negative electrode lithium deposition potential of the electrochemical device at the target temperature includes: For any target temperature, at the target temperature, the electrochemical device is subjected to multiple charge and discharge tests with currents of different rates, and multiple negative electrode potentials of the electrochemical device are obtained during the charge and discharge tests to determine the negative electrode lithium deposition potential and the lithium deposition rate at which lithium deposition occurs in the electrochemical device at the target temperature.

4. The method for determining the heating current of an electrochemical device according to claim 1, wherein: The step of obtaining, for any target temperature, a plurality of negative electrode minimum potentials and a plurality of negative electrode impedances at the target temperature based on the target temperature, the pulse current frequency, and the plurality of currents of different magnifications at the target temperature comprises: Acquire multiple currents with different magnifications at each target temperature, and for any target temperature, group the multiple currents with different magnifications and pulse current frequencies at the target temperature into multiple test groups; Performing a pulse charge-discharge heating test on the electrochemical device according to the pulse current frequency and the current of each test group to obtain the lowest negative electrode potential, negative electrode potential drop, and pulse current of each test group at the target temperature; The negative electrode impedance of each test group at the target temperature is obtained according to the negative electrode potential drop and the pulse current of each test group.

5. The method for determining the heating current of an electrochemical device according to claim 2, wherein: The correcting the current by using the multiple correction currents at the target temperature to obtain multiple first currents includes: When the correction current is a positive value, the current is added to the absolute value of the current correction current to obtain the first current at the target temperature; or, When the correction current is a negative value, the current is subtracted from the absolute value of the current correction current to obtain the first current at the target temperature.

6. The method for determining the heating current of an electrochemical device according to claim 1, wherein: The method further comprises: The temperature rise range is divided into a plurality of temperature rise intervals using the plurality of temperatures, wherein the plurality of temperature rise intervals are divided at equal intervals, or the plurality of temperature rise intervals are divided at unequal intervals.

7. The method for determining the heating current of an electrochemical device according to claim 6, wherein: The temperature rise range [T0, T N ] includes at least a first temperature rise interval and a second temperature rise interval, wherein the range of the first temperature rise interval is [T0, T1), and the range of the second temperature rise interval is [T1, T N ], T0<T1<T N .

8. A method for heating an electrochemical device, wherein: The method for determining a heating current of an electrochemical device according to any one of claims 1 to 7 is applied to heat the electrochemical device with the heating current.

9. An electrochemical device, wherein: The method comprises a processor and a machine-readable storage medium, wherein the machine-readable storage medium stores machine-executable instructions that can be executed by the processor, and when the processor executes the machine-executable instructions, the method according to any one of claims 1 to 7 is implemented.

10. An electrical equipment comprising the electrochemical device according to claim 9.

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