A lithium-ion battery constant-rate heating method

Abstract

The application discloses a lithium ion battery constant-rate heating method, comprising the following features: firstly, EIS characterization is carried out on a battery to be heated to obtain a zero-crossing point frequency and impedance of the battery under a current environment; secondly, the obtained frequency and impedance are used to select an alternating current heating frequency and current, and initial heating is carried out on the battery; finally, a PID control algorithm is used to control the heating rate, so that the temperature rising rate of the battery is kept constant. The battery heating method can accurately control the heating rate and heating time by means of the simple and safe selection scheme of the frequency of the initial current of the alternating current heating, and simultaneously introduces the PID algorithm. Compared with the traditional heating method, the method has the advantages of high heating speed, high safety, simple operability, and controllable heating time.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery heating, in particular to a constant-rate heating method for lithium ion batteries. BACKGROUND

[0002] Lithium ion batteries (LIBs) are considered as the best candidate for electric vehicles due to their high voltage, high energy density, long lifetime and environmental friendliness. However, the significantly increased impedance at low temperature greatly reduces the pulse power and the range of electric vehicles. More seriously, during the low-temperature charging process, lithium deposition is easily formed through unnecessary side reactions, which seriously affects the battery life and even leads to safety hazards such as thermal runaway. Therefore, the key to improving battery performance is how to properly manage the battery temperature. Generally speaking, in cold weather, the lithium ion battery needs to be preheated before charging or discharging until the battery reaches a suitable working temperature.

[0003] At present, the traditional PTC heating film heating and heat pump heating have high cost, low efficiency, long time consumption and uneven heating of the battery during the heating process. The alternating current heating mainly applies a certain frequency and amplitude of alternating current to the positive and negative electrodes to achieve heating. The advantage of this method is that it uses the battery's own impedance to generate heat, which is efficient and uniform in heating. However, in the current reported cases of alternating current heating, the purpose is to improve the heating rate, and there are few methods to control the temperature rise rate and accurately estimate the heating time. SUMMARY

[0004] Therefore, the main purpose of the present application is to provide a constant-rate heating method for lithium ion batteries.

[0005] To achieve the above purpose, the technical scheme of the present application is as follows:

[0006] The present application provides a constant-rate heating method for lithium ion batteries, comprising the following steps:

[0007] S1: EIS characterization is performed on the battery to be heated to obtain the zero-crossing frequency and impedance of the battery under the current environment;

[0008] S2: According to the obtained frequency and impedance, the alternating current heating frequency and current are selected, and the battery is initially heated;

[0009] S3: The heating rate is controlled by a PID control algorithm to keep the battery temperature rise rate constant.

[0010] Preferably, according to step S1, the battery EIS test temperature is -30℃-5℃, the excitation current is 0.05C-0.1C, the frequency range is 0.1Hz-10kHz, and the battery zero-crossing frequency f0 and alternating current impedance R are measured.

[0011] Preferably, according to step S2, in the alternating current heating, the selection standard of the alternating current frequency point f is: greater than or equal to the zero-crossing frequency point f0, that is:

[0012] f=f0+A

[0013] Wherein, A is a constant, and the value is: 0≤A≤800.

[0014] Preferably, according to step S2, the calculation formula of the initial current i is:

[0015]

[0016] Wherein, v is the temperature rise rate, the temperature rise rate v is a set target value, R is the impedance, the impedance R is the EIS test value, c is the specific heat capacity, and m is the battery mass.

[0017] Preferably, according to step S3, in the heating process, the alternating current is continuously adjusted and increased through the PID control algorithm, and the balanced heating rate is maintained.

[0018] Preferably, in the PID control algorithm, the deviation value between the target temperature rise rate and the sampling temperature rise rate is set to carry out PID algorithm regulation and control, and the current is compensated. The compensated current acts on the battery through the ripple generator for heating.

[0019] Preferably, the deviation value calculates the PID output gain, and the calculation formula is as follows:

[0020]

[0021] Wherein, K p is a proportional control coefficient, K i is an integral control coefficient, K d is a differential control coefficient, E is a temperature rise deviation value, that is, a difference value between the set temperature rise rate and the current temperature rise rate; P out0 is a constant.

[0022] Compared with the prior art, the beneficial effects of the present application are:

[0023] The battery heating method can accurately control the heating rate and heating time by introducing the PID algorithm through the simple and safe alternating current heating initial current frequency selection scheme. Compared with the traditional heating method, the heating speed is fast, the safety is high, the operability is simple, and the heating time is controllable. BRIEF DESCRIPTION OF DRAWINGS

[0024] The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the application. In the drawings:

[0025] Figure 1 A flowchart of a lithium ion battery constant-rate heating method according to an embodiment of the application is shown in the figure;

[0026] Figure 2 A flowchart of a PID control strategy according to an embodiment of the application is shown in the figure;

[0027] Figure 3 An AC heating temperature rise rate comparison curve according to an embodiment of the application is shown in the figure. DETAILED DESCRIPTION

[0028] In order to make the objects, technical solutions and advantages of the application clearer, the application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the application and do not limit the application.

[0029] The same or similar reference numerals in the drawings of the embodiments correspond to the same or similar components; in the description of the application, it should be understood that the terms "upper", "lower", "left", "right", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings, and are only used to facilitate the description of the application and simplify the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the terms describing the positional relationship in the drawings are used only for illustrative purposes, and cannot be understood as limiting the patent, for those skilled in the art, the specific meanings of the above terms can be understood according to the specific circumstances.

[0030] It should be noted that in this document, the terms "comprise", "contain" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, article or device. Without more limitations, the element defined by the statement "comprises a" does not exclude the presence of another identical element in the process, article or device comprising the element.

[0031] An embodiment of the application provides a lithium ion battery constant-rate heating method, as shown in the figure, comprising the following steps: Figures 1-3

[0032] S1: EIS characterization is performed on the battery to be heated to obtain the zero-crossing frequency and impedance of the battery under the current environment; ​

[0033] S2: Selecting the AC heating frequency and current according to the obtained frequency and impedance, and initially heating the battery;

[0034] S3: Controlling the heating rate by a PID control algorithm to keep the battery temperature rising rate constant.

[0035] According to step S1, the battery EIS test temperature is -30℃-5℃, the excitation current is 0.05C-0.1C, the frequency range is 0.1Hz-10kHz, and the battery zero crossing frequency f0 and AC impedance R are measured.

[0036] According to step S2, the selection standard of the AC frequency point f in the AC heating is that it is greater than or equal to the zero crossing frequency point f0, that is:

[0037] f = f0 + A

[0038] Wherein, A is a constant, and the value is: 0≤A≤800.

[0039] According to step S2, the calculation formula of the initial current i is:

[0040]

[0041] Wherein, v is the temperature rising rate, the temperature rising rate v is the set target value, R is the impedance, the impedance R is the EIS test value, c is the specific heat capacity, and m is the battery mass.

[0042] According to step S3, during the heating process, the AC current is continuously adjusted and increased by the PID control algorithm to maintain a balanced heating rate.

[0043] In the PID control algorithm, the deviation value between the target temperature rising rate and the sampling temperature rising rate is set to control the PID algorithm, the current is compensated, and the compensated current is applied to the battery by the ripple generator for heating.

[0044] The deviation value calculates the PID output gain, and the calculation formula is as follows:

[0045]

[0046] Wherein, K p is the proportional control coefficient, K i is the integral control coefficient, K d is the differential control coefficient, E is the temperature rising deviation value, that is, the difference between the set temperature rising rate and the current temperature rising rate; P out0 is a constant.

[0047] Example 1

[0048] The battery is heated from -25℃ to 0℃ at a constant rate, and the heating steps are as followsFigure 1 The specific implementation steps are as follows:

[0049] S1: According to the EIS test of the battery at -25°C with 0.05C excitation current and 0.1Hz-10kHz frequency range, the electrochemical impedance spectrum is obtained;

[0050] S2: According to the test results, the zero-crossing point (the point where the imaginary part of the EIS impedance spectrum is zero) frequency f0 and the impedance R are calculated; preferably, the AC heating AC frequency point f = f0+500;

[0051] Preferably, the initial current i is obtained according to the following formula:

[0052]

[0053] Wherein, the temperature rise rate v is a set target value, the impedance R is an EIS test value, the specific heat capacity c and the battery mass m are provided by the battery manufacturer according to different specifications of the battery.

[0054] During the heating process, as the temperature rises, the internal resistance of the battery gradually decreases, and the heating rate decreases accordingly. In order to maintain a balanced and efficient heating rate, a PID control algorithm is introduced to continuously adjust and increase the AC current.

[0055] Wherein, when the battery is required to be heated from -25°C to 0°C, the target temperature rise rate is set to 5°C / min, and the temperature rise rate is calculated as follows: Figure 3 Under the ordinary control strategy of fixed frequency and fixed current, the heating time is 7.6min; under the PID control, the heating time is 5.2min. Since the temperature sampling is external to the battery and the AC heating temperature is transferred from the inside to the outside, there is about 30s of temperature rise process at the beginning.

[0056] As shown in Figure 2 The PID control algorithm mainly adjusts the current through the PID algorithm by setting the deviation value between the target temperature rise rate and the sampling temperature rise rate, and compensates the current. The compensated current is applied to the battery by the ripple generator for heating. The deviation parameter calculates the output gain of the PID, and the specific calculation method is as follows:

[0057]

[0058] Wherein, K p represents the proportional control coefficient; K i represents the integral control coefficient; K d represents the differential control coefficient; E represents the temperature rise deviation value, i.e. the difference between the set temperature rise rate and the current temperature rise rate; P out0 represents a constant.

[0059] The heating rate selected for the heating process above is not limited to a constant rate for the battery, but can be a linearly increasing and linearly decreasing rate. The above description is specific to the preferred embodiments of the present application, but the present application is not limited to the embodiments described. Those skilled in the art will recognize that various equivalents and substitutions can be made without departing from the spirit of the present application, and such equivalents and substitutions are included within the scope of the claims.

Claims

1. A constant-rate heating method for a lithium-ion battery, characterized in that, Includes the following steps: S1: Perform EIS characterization on the battery to be heated to obtain the zero-crossing frequency f0 and impedance R of the battery under the current environment; S2: Select the AC heating frequency f and current i based on the obtained zero-crossing frequency f0 and impedance R to perform initial heating of the battery; S3: The heating rate is controlled by a PID control algorithm to keep the battery temperature rise rate constant; In step S2, the selection criterion for the AC heating frequency f in the AC heating is: greater than or equal to the zero-crossing frequency f0. f=f0+A Where A is a constant, and its value is: 0≤A≤800; According to step S2, the formula for calculating the initial current i is: → Where v is the temperature rise rate, which is a set target value; R is the impedance, which is an EIS test value; c is the specific heat capacity; and m is the battery mass.

2. The constant-rate heating method for lithium-ion batteries according to claim 1, characterized in that, According to step S1, the battery EIS test temperature is -30℃ to 5℃, the excitation current is 0.05C to 0.1C, the frequency range is 0.1Hz to 10kHz, and the battery zero-crossing frequency f0 and impedance R are measured.

3. The constant-rate heating method for lithium-ion batteries according to claim 1, characterized in that, According to step S3, during the heating process, the AC current is continuously increased through a PID control algorithm to maintain a balanced heating rate.

4. The constant-rate heating method for lithium-ion batteries according to claim 3, characterized in that, In the PID control algorithm, the deviation between the target temperature rise rate and the sampled temperature rise rate is set, and the PID algorithm is used to adjust the current to compensate for the current. The compensated current is then applied to the battery for heating through the ripple generator.

5. The constant-rate heating method for lithium-ion batteries according to claim 4, characterized in that, The deviation value is used to calculate the PID output gain, and the calculation formula is as follows: Among them, K p For proportional control coefficient, K i For integral control coefficients, K d P is the differential control coefficient, E is the temperature rise deviation value, i.e., the difference between the set temperature rise rate and the current temperature rise rate; out0 It is a constant.

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