Battery discharging method

Abstract

The invention provides a battery discharging method which comprises the steps that a bias direct current and an alternating current are superposed at the same time to discharge a battery, the current value of the bias direct current is IC, the current peak value of the alternating current is Ia, the frequency of the alternating current is fC, the total discharging current IB of the battery is equal to Ic + Iasin (2pifct), and t is the discharging time. According to the battery discharging method provided by the invention, the polarization voltage in the battery discharging process can be reduced, so that the battery discharging capacity is improved, and the discharging requirements in different scenes are met.

Description

Technical Field

[0001] The present application relates to the technical field of battery discharge, and in particular to a battery discharge method. Background Art

[0002] Lithium-ion batteries play a vital role in modern electronic devices and electric vehicles due to their excellent energy density and cycle stability. With the continuous advancement of science and technology and the increasing requirements for energy efficiency, the traditional DC discharge mode has been unable to meet the growing high-performance needs. Although the DC discharge mode is simple, its efficiency is relatively low. Especially under high power demand, it will cause the internal temperature of the battery to rise, affecting the battery performance and life. During the discharge process, due to the limitation of the electrochemical reaction rate, there will be a difference between the actual working voltage of the battery and the theoretical equilibrium voltage, that is, the polarization voltage, and this polarization will cause the internal resistance of the battery to increase, so that the actual amount of electricity that can be discharged is often lower than the theoretical capacity, resulting in low discharge capacity. Among them, low temperature and high rate discharge are the main factors that cause polarization. At low temperatures, the viscosity of the electrolyte inside the battery increases, resulting in a decrease in the diffusion coefficient of lithium ions, which significantly slows down the transmission rate in the electrolyte and electrode materials, and cannot quickly reach the electrode surface to participate in the reaction, causing the lithium ion concentration gradient at the electrode interface to increase, causing concentration polarization. At the same time, low temperature will also increase the charge transfer impedance, further increasing the battery polarization. In addition, the electrochemical reaction activity of electrode materials decreases at low temperatures, resulting in a decrease in exchange current density, a slowdown in the rate of electrode interface reaction, and a significant increase in electrochemical polarization.

[0003] The rate of electrode reaction is fast under high-rate discharge, and the reaction rate of lithium ions on the electrode surface is much lower than the electron transmission speed, which leads to an increase in the reaction overpotential. The electrochemical reaction at the two poles of the battery cannot be completed quickly, resulting in an increase in the electrochemical polarization voltage. At the same time, the current through the electrolyte, electrode materials, and internal impedances such as contact resistance will also increase under high-rate discharge. The greater the current, the greater the ohmic voltage drop will be, which will eventually increase the ohmic polarization and further increase the polarization voltage. In addition, during high-rate discharge, the diffusion rate of lithium ions in the electrolyte cannot keep up with the current demand, which will also cause the concentration gradient of lithium ions in the electrolyte to increase, thereby causing an electrochemical potential difference and generating concentration polarization. In summary, the increase in the overall polarization voltage of the battery will not only lead to a decrease in the discharge capacity of the battery, but may also cause problems such as battery heating and capacity attenuation. In severe cases, it may also lead to a decrease in battery safety. Therefore, reducing battery polarization is of great significance.

[0004] Based on this, it is necessary to provide a more effective and reliable technical solution to reduce the polarization voltage during battery discharge, increase the current rate during battery discharge, and thus improve the battery discharge capacity. Summary of the invention

[0005] The present application provides a battery discharge method, which can reduce the polarization voltage during battery discharge and increase the current rate during battery discharge, thereby improving the battery discharge capacity and meeting the discharge requirements in different scenarios.

[0006] The present application provides a battery discharging method, comprising: discharging the battery by superimposing an alternating current with a biased direct current, wherein the current value of the biased direct current is I c , the peak current of the alternating current is I a , the frequency of the alternating current is f c , the total current of the battery discharge

[0007] I B = c + a sin(2f c t), t is the discharge time.

[0008] In some embodiments of the present application, the I c Less than or equal to the maximum discharge current of the battery.

[0009] In some embodiments of the present application, the I c The discharge rate is 1C to 1.5C.

[0010] In some embodiments of the present application, the I c 10% to 100% of the maximum discharge current of the battery.

[0011] In some embodiments of the present application, the I a The absolute value of I is less than or equal to c .

[0012] In some embodiments of the present application, the I a For the I c 10% to 100%.

[0013] In some embodiments of the present application, the f c 50Hz to 1MHz.

[0014] In some embodiments of the present application, different f c .

[0015] In some embodiments of the present application, when the discharge environment temperature is lower than 0 degrees Celsius, f c The discharge is performed at a frequency of 40KHz to 100KHz.

[0016] In some embodiments of the present application, when the discharge environment temperature is lower than 0 degrees Celsius, f cThe discharge is performed at a frequency at which the imaginary part of the battery's AC impedance is 0 at this temperature.

[0017] In some embodiments of the present application, when the discharge environment temperature is normal temperature and I B When the discharge rate is greater than 1.5C, use f c The discharge frequency is 50Hz to 100KHz.

[0018] In some embodiments of the present application, when the discharge environment temperature is normal temperature and I B When the discharge rate is greater than 1.5C, use f c The discharge is performed at a frequency at which the imaginary part of the battery's AC impedance is 0 at this temperature.

[0019] In some embodiments of the present application, when the discharge environment temperature is lower than 0 degrees Celsius and at I B When the discharge rate is greater than 1.5C, use f c The discharge frequency is 1KHz to 100KHz.

[0020] In some embodiments of the present application, when the discharge environment temperature is lower than 0 degrees Celsius and at I B When the discharge rate is greater than 1.5C, use f c The discharge is performed at a frequency at which the imaginary part of the battery's AC impedance is 0 at this temperature.

[0021] The present application provides a battery discharge method, which can reduce the polarization voltage during battery discharge and increase the current rate during battery discharge, thereby improving the battery discharge capacity and meeting the discharge requirements in different scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 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.

[0023] in:

[0024] Figure 1 A flowchart of a battery discharging method according to some embodiments of the present application;

[0025] Figure 2 This is a diagram of battery voltage variation in test 1 of this application;

[0026] Figure 3 This is a battery temperature variation diagram for test 1 in this application;

[0027] Figure 4 This is the battery voltage variation diagram of test 2 in this application;

[0028] Figure 5 This is a battery temperature variation diagram for test 2 in this application;

[0029] Figure 6 For Nightsquito. DETAILED DESCRIPTION

[0030] 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.

[0031] The technical solution of the present invention is described in detail below in conjunction with the embodiments and drawings.

[0032] In the field of battery depolarization research, researchers start from the internal component structure of the battery and develop new electrode materials, electrolytes or additives to reduce polarization during charging and discharging. In addition, in response to the increase in polarization caused by low temperature, researchers heat the battery to increase the battery temperature, thereby increasing the ion diffusion rate and reducing the concentration polarization and ohmic polarization of the battery. Recent studies have found that by performing small-amplitude pulse discharges on the battery, this discharge method can make the electrolyte salt concentration and the electrode particle lithium concentration more evenly distributed inside the battery during the discharge phase, thereby reducing the concentration gradient in the electrolyte and achieving a certain degree of depolarization effect. However, this method only targets specific battery types and short-term performance in room temperature environments, and does not consider the long-term performance and aging of the battery in other different environments. It has safety risks and is not practical.

[0033] In order to reduce the polarization voltage during battery discharge, meet the discharge requirements in different scenarios, increase the current rate during battery discharge, and improve the battery discharge capacity, the applicant proposed a high-frequency AC discharge method, which enables the battery to discharge with an alternating current of a DC bias superimposed with a small-amplitude AC (frequency of 50Hz to 100KHz). On the one hand, this method can reduce the polarization effect of the battery during discharge, especially at low temperature or high rate discharge, improve low-temperature discharge performance, and reduce energy loss. On the other hand, it can reduce the side reactions such as electrolyte decomposition when the battery is discharged in harsh environments during the discharge depolarization process, and the electrochemical reaction inside the battery is more uniform, which helps to extend the service life of the battery, and ultimately improve the discharge capacity of the battery and the tolerance of the battery in harsh environments, and achieve efficient battery discharge.

[0034] Figure 1 This is a flow chart of a battery discharging method according to some embodiments of the present application.

[0035] refer to Figure 1 As shown, the battery discharging method described in some embodiments of the present application includes:

[0036] Step S1: discharging the battery with a biased direct current and an alternating current at the same time.

[0037] In some embodiments of the present application, the current value of the bias DC current is I c (A), the peak current of the alternating current is I a (A), the frequency of the alternating current is f c (Hz), the total current I of the battery discharge B =I c +I a sin(2πf c t), t is the discharge time (s).

[0038] In some embodiments of the present application, the I c Less than or equal to the maximum discharge current of the battery. The maximum discharge current of the battery refers to the maximum current value that the battery can discharge safely. This parameter is usually provided by the battery manufacturer to ensure rapid discharge without damaging the battery life or performance. Exceeding this current may cause battery overheating and internal chemical reactions to become unstable, thus affecting the safety and life of the battery. The maximum discharge current of ordinary lithium-ion batteries is generally 1C to 3C, and the maximum discharge current of high-power lithium-ion batteries is generally 5C to 8C.

[0039] In some embodiments of the present application, the I c The discharge rate is 1C to 1.5C.

[0040] In some embodiments of the present application, the I c The maximum discharge current of the battery is 10% to 100%, for example, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90%. The larger the DC bias current applied to the battery in the discharge strategy of the embodiment of the present application, the more obvious the effect of the discharge strategy in reducing battery polarization is compared with the DC discharge of the same magnitude.

[0041] In some embodiments of the present application, different I c .

[0042] In some embodiments of the present application, the I a The absolute value of I is less than or equal to c.

[0043] In some embodiments of the present application, the I a For the I c 10% to 100%, for example, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90%. In the discharge strategy of the embodiment of the present application, the DC bias current superimposed with a small amplitude AC current can achieve the purpose of reducing battery polarization, and compared with the related methods with a larger AC amplitude, this strategy can reduce the current intensity in the rectifier, reduce the power loss and heat loss in the transmission circuit, and improve the discharge efficiency.

[0044] In some embodiments of the present application, the f c 50Hz to 1MHz.

[0045] In some embodiments of the present application, different f c .

[0046] In some embodiments of the present application, when the discharge environment temperature is lower than 0 degrees Celsius, f c The discharge frequency is 40KHz to 100KHz, for example, 50KHz. According to the experimental test of the applicant, when discharging at low temperature, the discharge polarization voltage can be significantly reduced in the above AC frequency range, and the battery discharge power and total discharge capacity can be increased. For specific experimental results, please refer to the subsequent embodiment part.

[0047] In some embodiments of the present application, when the discharge environment temperature is lower than 0 degrees Celsius, f c The discharge is carried out at a frequency at which the imaginary part of the battery AC impedance is 0 at this temperature. Figure 6 As shown in the figure, the Nyquist plot is a graphical representation method for representing the data of the electrochemical impedance spectroscopy (EIS). It is a complex plane graph, with the horizontal axis representing the real part of the impedance and the vertical axis representing the imaginary part of the impedance. In the electrochemical impedance spectroscopy (EIS) graph, the impedance is measured by measuring the response of the battery or electrode under AC signals of different frequencies. The impedance value at each frequency point corresponds to the electrochemical response at that frequency, so the Nyquist plot can intuitively display the impedance characteristics of the material or battery at different frequencies. Using f c is the frequency f at which the imaginary part of the battery AC impedance is 0 at this temperature c0 Discharge is performed. Where f c0 The corresponding impedance value is Figure 6 shown.

[0048] In some embodiments of the present application, when the discharge environment temperature is normal temperature and I B When the discharge rate is greater than 1.5C, use f cThe discharge frequency is 50Hz to 100KHz.

[0049] In some embodiments of the present application, when the discharge environment temperature is normal temperature and I B When the discharge rate is greater than 1.5C, use f c The discharge is performed at a frequency at which the imaginary part of the battery's AC impedance is 0 at this temperature.

[0050] In some embodiments of the present application, when the discharge environment temperature is lower than 0 degrees Celsius and at I B When the discharge rate is greater than 1.5C, use f c The discharge frequency is 1KHz to 100KHz. According to the experimental test of the applicant, when discharging at a low temperature and a large rate, the discharge polarization voltage can be significantly reduced in the above AC frequency range, and the battery discharge power and total discharge capacity can be increased. For specific experimental results, please refer to the subsequent embodiment section.

[0051] In some embodiments of the present application, when the discharge environment temperature is lower than 0 degrees Celsius and at I B When the discharge rate is greater than 1.5C, use f c The discharge is performed at a frequency at which the imaginary part of the battery's AC impedance is 0 at this temperature.

[0052] The technical solution of the present application also includes: discharging with the above-mentioned discharge strategy until the battery voltage reaches the cut-off voltage of the battery.

[0053] In some embodiments of the present application, selecting a frequency of 50 KHz or above can achieve rapid heating of the battery; selecting a frequency at which the imaginary part of the battery AC impedance is 0 can significantly reduce polarization during discharge.

[0054] The technical solution of the present application can provide higher discharge power in the same time, significantly improve the discharge efficiency of the battery, and by controlling the current input, can effectively reduce the negative impact on the battery SEI film while increasing the discharge speed, avoiding excessive thickening of the SEI layer, thereby maintaining the long-term stability and cycle life of the battery.

[0055] The technical solution of the present application can further increase the temperature rise rate of the battery at low temperatures, allowing the battery to return to normal operating temperature in a shorter time, thereby improving battery performance.

[0056] The technical solution of the present application can effectively reduce the amount of lithium deposition in the battery within a certain range of cycle numbers and increase the service life of the battery by controlling the current amplitude.

[0057] In summary, the above is the basic concept of the technical solution of the present application. First of all, the present application discharges the battery with a biased DC current superimposed on an AC current at the same time, which can reduce the discharge polarization voltage of the battery and increase the battery discharge power and total discharge capacity. Furthermore, by selecting appropriate DC current and AC current sizes, the discharge effect can be further optimized. Furthermore, the technical solution of the present application can also adjust the frequency of the AC current in a targeted manner according to different discharge conditions (such as different discharge temperatures and discharge rates, etc.) to further optimize the discharge effect under different discharge conditions.

[0058] Below, in order to more clearly illustrate the technical effects of the present application, the present application provides different embodiments and comparative examples. Among them, the comparative example is a conventional AC and DC discharge method. And the embodiment is a discharge method using the present application, wherein parameters such as current magnitude or current frequency are different in different embodiments.

[0059] Comparative Example 1

[0060] The battery is discharged using direct current, wherein the current value of the direct current is 2A.

[0061] Comparative Example 2

[0062] The battery is discharged using direct current, wherein the current value of the direct current is 3A.

[0063] Example 1 to Example 5

[0064] At the same time, the battery is discharged by superimposing the biased DC current on the AC current. The DC current value, AC current peak value and AC frequency in different embodiments are different. For detailed data, see Table 1.

[0065] Then, the test battery is discharged using the discharge methods in the above comparative examples and embodiments, and the relevant parameters during the discharge process (discharge time (s), battery voltage (V), average discharge current (A), peak-to-peak discharge current (A), and discharge frequency (Hz)) are recorded. It should be noted that the present application sets up several test batteries, and each comparative example and embodiment uses a brand new, separate test battery with exactly the same specifications (i.e., a new battery of the same specifications is selected each time the discharge is performed to avoid the impact of the battery being overcharged on subsequent tests).

[0066] Test 1

[0067] The discharge method in Comparative Example 1, Comparative Example 2, Example 1, and Example 2 was used to perform a discharge test on the test battery and the battery voltage change during the discharge process was recorded (by Figure 2 ), discharge capacity (shown in Table 1), battery temperature change (shown in Figure 3The test battery is a lithium iron phosphate battery with a battery capacity of 2000mAh. The lowest frequency of the battery impedance at -10℃ is 2KHz, and the discharge cut-off voltage is 2.5V. The discharge environment temperature is -10℃.

[0068] Test 2

[0069] The discharge method in Comparative Example 2, Example 3, Example 4, and Example 5 was used to perform a discharge test on the test battery and the battery voltage change during the discharge process was recorded (by Figure 4 ), discharge capacity (shown in Table 1), battery temperature change (shown in Figure 5 The test battery is a ternary lithium battery with a battery capacity of 2000mAh and a discharge cut-off voltage of 3V. The discharge environment temperature is -20℃.

[0070] Table 1 below shows the test results of different comparative examples and embodiments.

[0071]

[0072] Referring to Table 1, whether in Test 1 or Test 2, the solution of this embodiment can achieve the effect of improving the discharge capacity compared with the conventional DC discharge, and the increase in the AC frequency can further improve the battery discharge capacity.

[0073] refer to Figure 2 As shown, Figure 2 The horizontal axis is time (seconds). Compared with conventional DC discharge, the solution of the present application can reduce the polarization voltage of the battery.

[0074] refer to Figure 3 As shown, Figure 3 The vertical axis is temperature (degrees Celsius). In test 1, the solution of the present application does not cause a significant temperature rise.

[0075] refer to Figure 4 and Figure 5 As shown, compared with DC discharge, it is found that the discharge strategy of the present application can effectively reduce polarization, but it does not necessarily increase the battery temperature, which means that the discharge strategy of the present application mainly reduces battery polarization and thus increases the battery discharge capacity, and the effect of reducing polarization is not caused by temperature increase.

[0076] The present application provides a battery discharge method, which can reduce the polarization voltage during battery discharge, and further increase the current rate during battery discharge, thereby improving the battery discharge capacity and meeting the discharge requirements in different scenarios.

[0077] 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.

[0078] 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.

[0079] It should also be understood that the "low temperature" and "high rate" used in this embodiment refer to the low temperature and discharge rate understood by ordinary technicians in the field of lithium battery discharge.

[0080] It should also be understood that the terms “comprises,” “comprising,” “including,” or “comprising,” when used in this application document, indicate the presence of the recorded features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or combinations thereof.

Claims

1. A battery discharging method, characterized in that: include: At the same time, the battery is discharged by superimposing a bias DC current on an AC current, and the current value of the bias DC current is I c , the peak current of the alternating current is I a , the frequency of the alternating current is f c , the total current of the battery discharge I B =I c +I a sin(2πf c t), t is the discharge time.

2. The battery discharging method according to claim 1, characterized in that: I c Less than or equal to the maximum discharge current of the battery.

3. The battery discharging method according to claim 2, characterized in that: I c 10% to 100% of the maximum discharge current of the battery.

4. The battery discharging method according to claim 1, characterized in that: I a The absolute value of which is less than or equal to the I c .

5. The battery discharging method according to claim 4, characterized in that: I a For the I c 10% to 100%.

6. The battery discharging method according to claim 1, characterized in that: The f c 50Hz to 100kHz.

7. The battery discharging method according to claim 6, characterized in that: According to different discharge conditions, different f c .

8. The battery discharging method according to claim 7, characterized in that: When the discharge ambient temperature is below 0 degrees Celsius, use f c The discharge frequency is 50Hz to 100KHz.

9. The battery discharging method according to claim 7, characterized in that: When the discharge ambient temperature is below 0 degrees Celsius, use f c The discharge is performed at a frequency at which the imaginary part of the battery's AC impedance is 0 at this temperature.

10. The battery discharging method according to claim 7, characterized in that: When the discharge environment temperature is normal temperature and I B When the discharge rate is greater than 1.5C, use f c The discharge frequency is 50Hz to 100KHz.

11. The battery discharging method according to claim 7, characterized in that: When the discharge environment temperature is normal temperature and I B When the discharge rate is greater than 1.5C, use f c The discharge is performed at a frequency at which the imaginary part of the battery's AC impedance is 0 at this temperature.

12. The battery discharging method according to claim 7, characterized in that: When the discharge environment temperature is below 0 degrees Celsius and I B When the discharge rate is greater than 1.5C, use f c The discharge frequency is 50Hz to 100KHz.

13. The battery discharging method according to claim 7, characterized in that: When the discharge environment temperature is below 0 degrees Celsius and I B When the discharge rate is greater than 1.5C, use f c The discharge is performed at a frequency at which the imaginary part of the battery's AC impedance is 0 at this temperature.

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