Battery charging method

Abstract

The invention provides a battery charging method. The battery charging method comprises the following steps: converting direct current or alternating current of a charging power supply into bias direct current superposed alternating current; and meanwhile, the converted bias direct current and alternating current are applied to charge the battery. According to the battery charging method provided by the invention, the polarization voltage in the battery charging process can be reduced, so that the battery charging capacity is improved, and the charging requirements in different scenes are met.

Description

Technical Field

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

[0002] Lithium batteries have attracted widespread attention due to their high energy density and excellent performance. During the charging 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. This polarization will increase the internal resistance of the battery, so that the actual amount of electricity that can be charged is often lower than the theoretical capacity, resulting in a low charging capacity. Among them, low temperature (generally refers to the charging temperature below 0 degrees Celsius) and high rate charging (generally refers to the charging rate greater than 1.5C) 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, which will further increase the polarization of the battery. In addition, the electrochemical reaction activity of the electrode material at low temperatures decreases, resulting in a decrease in the exchange current density, a slow rate of electrode interface reaction, and a significant increase in electrochemical polarization. In addition, the rate at which lithium ions are embedded in the negative electrode material slows down at low temperatures, causing some lithium ions to precipitate on the negative electrode surface to form metallic lithium, which not only reduces the coulombic efficiency of the battery, but also reacts with the electrolyte to generate byproducts (such as lithium dendrites and unstable solid electrolyte interface membranes (SE I membranes)), thereby increasing the interface impedance, further exacerbating electrochemical polarization and concentration polarization, and causing the polarization voltage to rise further, ultimately leading to a decrease in the battery's charging capacity. At the same time, the precipitated lithium will continue to accumulate, resulting in the formation of lithium dendrites that may pierce the diaphragm, causing an internal short circuit, which can cause battery failure or safety accidents in severe cases.

[0003] The rate of electrode reaction is fast under high-rate charging, 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 charging. 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, when charging at a high rate, 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 battery charging capacity, 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 charging, increase the current rate during battery charging, and thus improve the battery charging capacity. Summary of the invention

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

[0006] The present application provides a battery charging method, comprising: simultaneously applying a bias direct current and superimposing an alternating current to charge the battery, wherein the current value of the bias 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 I for charging the battery B =I c +I a sin(2πf c t), t is the charging time.

[0007] In some embodiments of the present application, the I c Less than or equal to the maximum charging current of the battery.

[0008] In some embodiments of the present application, the I c The charging rate is 1C to 1.5C.

[0009] In some embodiments of the present application, the I c 10% to 100% of the battery's maximum charging current.

[0010] In some embodiments of the present application, the I a The absolute value of which is less than or equal to the I c .

[0011] In some embodiments of the present application, the I a For the I c 10% to 100%.

[0012] In some embodiments of the present application, the f c 50Hz to 1MHz.

[0013] In some embodiments of the present application, different f c .

[0014] In some embodiments of the present application, when the charging environment temperature is lower than 0 degrees Celsius, f cCharges at frequencies from 40KHz to 100KHz.

[0015] In some embodiments of the present application, when the charging environment temperature is lower than 0 degrees Celsius, f c The battery is charged at a frequency at which the imaginary part of the AC impedance is zero at this temperature.

[0016] In some embodiments of the present application, when the charging environment temperature is normal temperature and I B When the charging rate is greater than 1.5C, use f c Charging is done at frequencies from 50Hz to 100KHz.

[0017] In some embodiments of the present application, when the charging environment temperature is normal temperature and I B When the charging rate is greater than 1.5C, use f c The battery is charged at a frequency at which the imaginary part of the AC impedance is zero at this temperature.

[0018] In some embodiments of the present application, when the charging environment temperature is below 0 degrees Celsius and at I B When the charging rate is greater than 1.5C, use f c Charges at frequencies from 1KHz to 100KHz.

[0019] In some embodiments of the present application, when the charging environment temperature is below 0 degrees Celsius and at I B When the charging rate is greater than 1.5C, use f c The battery is charged at a frequency at which the imaginary part of the AC impedance is zero at this temperature.

[0020] The present application provides a battery charging method, which can reduce the polarization voltage during battery charging and increase the current rate during battery charging, thereby improving the battery charging capacity and meeting charging requirements in different scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0022] in:

[0023] Figure 1 A flowchart of a battery charging method according to some embodiments of the present application;

[0024] Figure 2This is a diagram of battery voltage variation in test 1 of this application;

[0025] Figure 3 This is a battery temperature variation diagram for test 1 in this application;

[0026] Figure 4 This is the battery temperature variation diagram of test three in this application;

[0027] Figure 5 This is the battery voltage variation diagram of test three in this application;

[0028] Figure 6 This is the battery voltage variation diagram of test 2 in this application;

[0029] Figure 7 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 charging on the battery, this charging method can make the electrolyte salt concentration and the electrode particle lithium concentration more evenly distributed inside the battery during the charging stage, 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 charging, meet the charging requirements in different scenarios, increase the current rate during battery charging, and improve the battery charging capacity, we proposed a high-frequency AC charging method, which charges the battery by applying a DC bias superimposed with a small-amplitude AC current (frequency of 50Hz to 1MHz). On the one hand, this method can reduce the polarization effect of the battery during charging, especially at low temperatures or high-rate charging. On the other hand, it can reduce side reactions such as electrolyte decomposition when the battery is charged in harsh environments during the charging depolarization process, ultimately improving the battery's charging capacity and the battery's tolerance in harsh environments, and achieving efficient battery charging.

[0034] Figure 1 This is a flow chart of a battery charging method described in some embodiments of the present application.

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

[0036] Step S1: converting the direct current or alternating current of the charging power source into a bias direct current superimposed on an alternating current.

[0037] In some embodiments of the present application, a current conversion module or a current conversion device may be used to perform the above current conversion.

[0038] Continue to refer Figure 1 As shown, the battery charging method described in some embodiments of the present application also includes:

[0039] Step S2: simultaneously applying the above converted bias DC current and superimposing the AC current to charge the battery.

[0040] 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 for charging the battery B =I c +I a sin(2πf c t), t is the charging time (s).

[0041] In some embodiments of the present application, the I cLess than or equal to the maximum charging current of the battery. The maximum charging current of the battery refers to the maximum current value that the battery can safely accept. This parameter is usually provided by the battery manufacturer to ensure fast charging without compromising 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 charging current of ordinary lithium-ion batteries is generally 1C to 3C, and the maximum charging current of high-power lithium-ion batteries is generally 5C to 8C.

[0042] In some embodiments of the present application, the I c The charging rate is 1C to 1.5C.

[0043] In some embodiments of the present application, the I c The maximum charging current of the battery is 10% to 100%, for example, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90%. The greater the DC bias current applied to the battery in the charging strategy of the embodiment of the present application, the more obvious the effect of the charging strategy in reducing battery polarization is compared with the same DC charging.

[0044] In some embodiments of the present application, different I c .

[0045] In some embodiments of the present application, the I a The absolute value of which is less than or equal to the I c .

[0046] 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 charging 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 charging efficiency.

[0047] In some embodiments of the present application, the f c 50Hz to 1MHz.

[0048] In some embodiments of the present application, different f c .

[0049] In some embodiments of the present application, when the charging environment temperature is lower than 0 degrees Celsius, f cThe frequency of the battery is 40KHz to 100KHz. According to the experimental test of the applicant, when charging at low temperature, the charging polarization voltage can be significantly reduced within the above AC frequency range, and the battery charging power and total charging capacity can be increased. For specific experimental results, please refer to the subsequent embodiment section.

[0050] In some embodiments of the present application, when the charging environment temperature is lower than 0 degrees Celsius, f c The battery is charged at a frequency at which the imaginary part of the AC impedance of the battery is 0 at this temperature. Figure 7 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 For charging. Where f c0 The corresponding impedance value is Figure 7 shown.

[0051] In some embodiments of the present application, when the charging environment temperature is normal temperature and I B When the charging rate is greater than 1.5C, use f c Charging is done at frequencies from 50Hz to 100KHz.

[0052] In some embodiments of the present application, when the charging environment temperature is normal temperature and I B When the charging rate is greater than 1.5C, use f c The battery is charged at a frequency at which the imaginary part of the AC impedance is zero at this temperature.

[0053] In some embodiments of the present application, when the charging environment temperature is below 0 degrees Celsius and at i B When the charging rate is greater than 1.5C, use f c The battery is charged at a frequency of 1KHz to 100KHz. According to the experimental test of the applicant, when charging at a high rate at low temperature, the charging polarization voltage can be significantly reduced within the above AC frequency range, and the battery charging power and total charging capacity can be increased. For specific experimental results, please refer to the subsequent embodiment section.

[0054] In some embodiments of the present application, when the charging environment temperature is below 0 degrees Celsius and at I B When the charging rate is greater than 1.5C, use f cThe battery is charged at a frequency at which the imaginary part of the AC impedance is zero at this temperature.

[0055] The technical solution of the present application also includes: charging with the above-mentioned charging strategy until the battery voltage reaches the cut-off voltage of the battery.

[0056] In summary, the above is the basic concept of the technical solution of the present application. First of all, the present application adopts the method of simultaneously applying a bias DC current and superimposing an AC current to charge the battery, which can reduce the charging polarization voltage of the battery and increase the charging power and total charging capacity of the battery. Furthermore, by selecting appropriate DC current and AC current sizes, the charging 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 charging conditions (such as different charging temperatures and charging rates, etc.) to further optimize the charging effect under different charging conditions.

[0057] Below, in order to more clearly illustrate the technical effects of the present application, the present application sets up different embodiments and comparative examples. Among them, the comparative example is the current conventional AC and DC charging method. And the embodiment is the charging method of the present application, among which the parameters such as current magnitude or current frequency are different in different embodiments.

[0058] Comparative Example 1

[0059] The battery is charged with direct current, wherein the current value of the direct current is 2A.

[0060] Comparative Example 2

[0061] The battery is charged with direct current, wherein the current value of the direct current is 3A.

[0062] Example 1 to Example 7

[0063] At the same time, a bias DC current is applied to superimpose an AC current to charge the battery. The DC current value, AC current peak value and AC frequency in different embodiments are different. For detailed data, see Table 1.

[0064] Then, the test battery is charged using the charging methods in the above comparative examples and embodiments, and the relevant parameters in the charging process (charging time (s), battery voltage (V), average charging current (A), peak-to-peak charging current (A), charging 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 charging to avoid the impact of overcharging the battery on subsequent tests).

[0065] Test 1

[0066] The charging method in Comparative Example 1, Example 1, Example 2, and Example 3 is used to charge the test battery and record the battery voltage change during the charging process (by Figure 2 ), charging capacity (shown in Table 1), and battery temperature change (shown in Figure 3 The test battery is a ternary lithium battery with a battery capacity of 2900mAh. The frequency of the lowest battery impedance at -10℃ is 2KHz, and the charging cut-off voltage is 4.2V. The charging environment temperature is -10℃, and the charging rate is 1C.

[0067] Test 2

[0068] The charging method in Comparative Example 2, Example 5, Example 6, and Example 7 is used to perform a charging test on the test battery and record the battery voltage change during the charging process (by Figure 6 The test battery is a ternary lithium battery with a battery capacity of 2900mAh and a charging cut-off voltage of 4.2V. The charging environment temperature is -10℃ and the charging rate is 1.5C.

[0069] Test Three

[0070] The charging method in Comparative Example 1 and Example 4 was used to test the test battery and the battery temperature change during the charging process was recorded (by Figure 4 Display) and battery voltage changes (by Figure 5 The test battery is a ternary lithium battery with a battery capacity of 3500mAh and a charging cut-off voltage of 4.2V. The charging environment temperature is -10℃ and the charging rate is 1C.

[0071] Table 1 below shows the test results of different comparative examples and embodiments.

[0072]

[0073] Referring to Table 1, whether in Test 1 or Test 2, the solution of this embodiment can achieve the effect of improving the charging capacity compared with conventional DC charging, and the increase in AC frequency can further improve the battery charging capacity.

[0074] refer to Figure 2 As shown, Figure 2 The horizontal axis is time (seconds). Compared with conventional DC charging, the solution of the present application can reduce the polarization voltage of the battery.

[0075] 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.

[0076] refer to Figure 4 and Figure 5 As shown, compared with DC charging, it is found that the charging strategy of the present application can effectively reduce polarization, but it does not necessarily increase the battery temperature, which means that the charging strategy of the present application mainly reduces battery polarization and thus increases the battery charging capacity, and the effect of reducing polarization is not caused by temperature increase.

[0077] refer to Figure 6 As shown, in the scheme of the present application, the polarization reduction effect is obvious when the AC current amplitude is high at the same AC current frequency (compare Examples 6 and 7), and the polarization reduction effect is obvious when the AC current frequency is large at the same AC current amplitude (compare Examples 5 and 6).

[0078] The present application provides a battery charging method, which can reduce the polarization voltage during the battery charging process, and further increase the current rate during the battery charging, thereby improving the battery charging capacity and meeting the charging requirements in different scenarios.

[0079] 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.

[0080] 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.

[0081] It should also be understood that the "low temperature" and "high rate" used in this embodiment refer to the low temperature and charging rate understood by ordinary technicians in the field of lithium battery charging.

[0082] 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 charging method, characterized in that: include: At the same time, a bias DC current is applied to charge the battery by superimposing 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 I for charging the battery B =I c +I a sin(2πf c t), t is the charging time.

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

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

4. The battery charging method according to claim 1, wherein: I a The absolute value of I is less than or equal to c .

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

6. The battery charging method according to claim 1, wherein: The f c 50Hz to 1MHz.

7. The battery charging method according to claim 6, characterized in that: Use different f according to different charging conditions c .

8. The battery charging method according to claim 7, characterized in that: When the charging environment temperature is below 0 degrees Celsius, use f c Charges at frequencies from 40KHz to 100KHz.

9. The battery charging method according to claim 7, characterized in that: When the charging environment temperature is below 0 degrees Celsius, use f c The battery is charged at a frequency at which the imaginary part of the AC impedance is zero at this temperature.

10. The battery charging method according to claim 7, characterized in that: When the charging environment temperature is normal and I B When the charging rate is greater than 1.5C, use f c Charging is done at frequencies from 50Hz to 100KHz.

11. The battery charging method according to claim 7, wherein: When the charging environment temperature is normal and I B When the charging rate is greater than 1.5C, use f c The battery is charged at a frequency at which the imaginary part of the AC impedance is zero at this temperature.

12. The battery charging method according to claim 7, wherein: When the charging environment temperature is below 0 degrees Celsius and I B When the charging rate is greater than 1.5C, use f c Charges at frequencies from 1KHz to 100KHz.

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

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