Battery pack capacity equalization method and apparatus

Abstract

The application discloses a battery pack capacity equalization method and device. The battery pack capacity equalization method comprises the following steps: providing a battery pack, wherein the battery pack comprises n battery monomers; providing a plurality of voltage values U i The same and the frequency P x The different preset alternating voltages are respectively applied to the battery monomers, and the test currents I m of the battery monomers under the action of the preset alternating voltages are collected within a preset collection time T i and a preset time interval ΔT; the impedance characteristic values Z i of the battery monomers under the preset alternating voltages are obtained according to the voltage values U i of the preset alternating voltages, the test currents I x and a preset function; and whether to perform capacity equalization processing is judged according to the impedance characteristic values Z x of all the battery monomers under different preset alternating voltages. The capacity equalization method can more sensitively sense the inconsistency of the health states of the battery monomers of the battery pack, thereby more accurately regulating and controlling the residual capacity of the battery monomers of the battery pack.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a battery pack capacity balancing method and apparatus. Background Technology

[0002] Power batteries, such as lithium-ion batteries, have advantages such as high power density, long cycle life, and good environmental performance, and are increasingly being used in many fields.

[0003] Due to unavoidable factors such as process fluctuations and batch differences in incoming materials, individual battery cells exhibit varying performance characteristics, including differences in capacity, internal resistance, and settling voltage. Battery packs typically consist of multiple individual cells. When these cells are connected in series or parallel to meet high voltage and high capacity requirements, these differences are amplified during the battery pack's cyclic charging and discharging process. The health status and remaining capacity of each cell gradually differ, leading to a significant reduction in their lifespan. Therefore, proactive balancing strategies are needed to improve the consistency of the individual cells within the battery pack, thereby enhancing their operational stability and lifespan. Summary of the Invention

[0004] This application provides a battery pack capacity balancing method and apparatus, which can solve the problem of difficulty in effectively balancing individual battery cells.

[0005] In a first aspect, this application provides a battery pack capacity balancing method, including:

[0006] A battery pack is provided, the battery pack comprising n individual battery cells, where n is an integer greater than or equal to 2;

[0007] Multiple preset AC voltages are provided, wherein the voltage value U of the preset AC voltage is... i Same and frequency P x Unlike other methods, the preset AC voltage is applied to each individual battery cell, and the sampling time is T. m At a preset time interval ΔT, the test current I corresponding to the battery cell under the preset AC voltage is collected. i ;

[0008] According to the preset AC voltage value U i The test current I corresponding to the preset AC voltage i Using a preset function, the impedance characteristic value Z of the battery cell under the preset AC voltage is obtained. x For the battery cell, the preset AC voltage and the impedance characteristic value Z x One-to-one correspondence;

[0009] Based on the impedance characteristic value Z of all the battery cells under different preset AC voltages x Determine whether to perform capacity balancing.

[0010] In some exemplary embodiments, the number of preset AC voltages applied to the battery cell is x, where x is an integer greater than or equal to 4;

[0011] The frequency P of the preset AC voltage x Satisfies: 0.01 Hz ≤ P x ≤1000Hz;

[0012] The voltage value U of the preset AC voltage i Satisfy: -30mV≤U i ≤30mV.

[0013] In some exemplary embodiments, the number of preset AC voltages x is 4, and the frequency P of the 4 preset AC voltages is... x They are P1, P2, P3, and P4, respectively, where P1 is the high-frequency electron transport frequency, P2 is the mid-to-high-frequency ion transport frequency, P3 is the mid-frequency ion-electron reaction frequency, and P4 is the low-frequency ion-solid diffusion frequency.

[0014] P1 satisfies: 100Hz < P1 ≤ 1000Hz;

[0015] P2 satisfies: 1 Hz < P2 ≤ 100 Hz;

[0016] P3 satisfies: 0.1 Hz < P3 ≤ 1 Hz;

[0017] P4 satisfies: 0.01hz≤P4≤0.1hz.

[0018] In some exemplary embodiments, multiple test currents I corresponding to the battery cell under the preset AC voltage are obtained. i This includes: acquiring the test current I once at a preset time interval ΔT. i ΔT satisfies: 0.2s≤ΔT≤3s;

[0019] The preset collection duration T m Satisfy: 30s≤T m ≤120s.

[0020] In some exemplary embodiments, based on the voltage value U of the preset AC voltage i The multiple test currents I corresponding to the preset AC voltage i The impedance characteristic value Z is obtained by the preset function shown in equation (1). x :

[0021]

[0022] The preset function shown in equation (1) is a Fourier function.

[0023] In some exemplary embodiments, determining whether to perform capacity balancing includes:

[0024] Obtain the impedance characteristic value Z of all the battery cells under the same preset AC voltage. x average impedance value

[0025] Obtain the impedance characteristic value Z of the battery cell under the preset AC voltage. x The average impedance value of the preset AC voltage Impedance deviation ΔZ x ;

[0026] The impedance deviation ΔZ x With preset impedance threshold Z m When comparing, the impedance deviation ΔZ x Greater than or equal to Z m When the impedance deviation ΔZ is reached, capacity balancing is performed. x Less than Z m If the impedance threshold Z is not set, no capacity equalization will be performed. m Satisfy: 3% ≤ Z m ≤6%.

[0027] In some exemplary embodiments, when the impedance deviation ΔZ x Greater than or equal to Z m During capacity balancing, the process includes:

[0028] For the battery cell, the impedance characteristic value Z corresponding to the battery cell under all the preset AC voltages is... x The impedance summation value Z of the battery cell is obtained by summing the impedances. x n;

[0029] The sum of the impedances of all the aforementioned battery cells, Z. x n is compared, and at least one of the impedance sum values ​​Z is compared. x The battery cells with larger n are charged to perform capacity balancing.

[0030] In some exemplary embodiments, capacity balancing includes:

[0031] Using the impedance summation value Z x The smaller of the individual cells contributes to the sum of the impedance Z. xThe battery cells with larger n are discharged to perform capacity balancing.

[0032] In some exemplary embodiments, applying multiple preset AC voltages to the battery cell includes:

[0033] Multiple preset AC voltages are applied to the battery cells using an active voltage excitation source, wherein the active voltage excitation source includes at least one battery cell in the battery pack and at least one charger for charging the battery pack.

[0034] Secondly, this application provides a battery pack capacity balancing device, comprising:

[0035] An active voltage excitation source is used to apply multiple preset AC voltages to the battery cells, wherein the voltage value U of all the preset AC voltages is... i Same and frequency P x different;

[0036] The detection module, during the preset data acquisition time T m At a preset time interval ΔT, multiple test currents I corresponding to the battery cell under the preset AC voltage are collected. i ;and

[0037] The control module, based on the preset AC voltage value U i The multiple test currents I corresponding to the preset AC voltage i Using a preset function, the impedance characteristic value Z of the battery cell under the preset AC voltage is obtained. x For the battery cell, the preset AC voltage and the impedance characteristic value Z x One-to-one correspondence; based on the impedance characteristic value Z of all the battery cells under different preset AC voltages. x Determine whether to perform capacity balancing.

[0038] The battery pack capacity balancing method and apparatus based on the embodiments of this application have at least the following beneficial effects:

[0039] By collecting multiple test currents I corresponding to AC voltages of different frequencies applied to individual battery cells. i According to the preset AC voltage value U i Multiple test currents I i And a preset function to obtain the impedance characteristic value Z related to the impedance of the battery cell. x According to the impedance characteristic value Z xThe method of this application determines the health status of individual battery cells in the battery pack, thereby triggering capacity equalization processing. The capacity equalization method of this application determines the remaining capacity of individual battery cells by comparing the impedance characteristics of individual battery cells at different frequencies. It can more sensitively detect the problem of impedance inconsistency among individual battery cells in the battery pack, thereby enabling more accurate control of the remaining capacity of individual battery cells in the battery pack, rather than performing capacity equalization processing solely based on parameters such as voltage, capacity, and impedance. Attached Figure Description

[0040] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings.

[0041] Figure 1 A graph showing the impedance deviation values ​​of four battery cells before capacity equalization in Embodiment 1 of this application;

[0042] Figure 2 This is a graph showing the impedance deviation values ​​of the four battery cells after capacity equalization in Embodiment 1 of this application. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0044] The inventors discovered that voltage equalization methods that measure the voltage of different battery cells and discharge from high-voltage cells to low-voltage cells do not consider the impact of cell material degradation and changes in cell open-circuit voltage (OCV, representing the equilibrium potential of a cell when it is not charging or discharging) on ​​battery equalization during use. Furthermore, triggering equalization with high and low voltages easily leads to large equalization errors, making it difficult to effectively equalize battery cells. Therefore, this application provides a battery pack capacity equalization method.

[0045] This application provides a battery pack capacity balancing method, which includes:

[0046] Step S110: Provide a battery pack, which includes n battery cells, where n is an integer greater than or equal to 2. The n battery cells are connected in series or in parallel.

[0047] Step S120: Provide multiple preset AC voltages, the voltage value U of the preset AC voltages. i Same and frequency P xUnlike other methods, a preset AC voltage is applied to each battery cell, and the data is collected for a preset duration T. m At a preset time interval ΔT, the test current I corresponding to the battery cell under a preset AC voltage is collected. i Among them, the test current I corresponding to a single battery cell under the same preset AC voltage is... i The quantity can be multiple, for example, the test current I. i The number is greater than or equal to 5.

[0048] Step S130: According to the preset AC voltage value U i The test current I corresponding to the preset AC voltage i Using a preset function, obtain the impedance characteristic value Z of a single battery cell under a corresponding preset AC voltage. x .

[0049] For a single battery cell, the preset AC voltage and impedance characteristic value Z are... x One-to-one correspondence, that is, when a preset AC voltage is applied to a battery cell, multiple test currents I corresponding to the battery cell under the preset AC voltage are collected. i According to the preset AC voltage value U i Multiple test currents I i Using a preset function, obtain an impedance characteristic value Z of the battery cell under the preset AC voltage. x Each battery cell has its corresponding impedance characteristic value Z under the corresponding preset AC voltage. x .

[0050] Step S140: Based on the impedance characteristic value Z of each battery cell under different preset AC voltages... x The system determines whether to perform capacity balancing. If the result is no, there is no need to perform capacity balancing on the n individual cells of the battery pack. If the result is yes, a capacity balancing strategy is adopted to perform capacity balancing on the n individual cells of the battery pack, adjusting the capacity of the individual cells in the battery pack and improving the consistency of the capacity of the n individual cells.

[0051] The inventors discovered that under AC voltages of different frequencies, the electrolyte, positive electrode material, and negative electrode material inside a battery cell undergo different electrochemical reactions, resulting in varying impedance values ​​within the battery cell. The battery pack capacity balancing method in this application collects multiple test currents I corresponding to the battery cells under AC voltages of different frequencies. i According to the preset AC voltage value U i Multiple test currents I i And a preset function to obtain the impedance characteristic value Z related to the impedance of the battery cell. xAccording to the impedance characteristic value Z x The method assesses the health status of individual battery cells in the battery pack, thereby triggering capacity equalization. This capacity equalization method compares the impedance characteristics of individual battery cells at different frequencies to determine their remaining capacity. This allows for more sensitive detection of impedance inconsistencies among battery cells within the battery pack, enabling more accurate control of the remaining capacity of individual cells, rather than relying solely on parameters such as voltage, capacity, and impedance for capacity equalization.

[0052] In step S120, a preset AC voltage can be selected and applied to one of the battery cells, and the sampling time T is set. m At a preset time interval ΔT, multiple test currents I of the battery cells are collected under the preset AC voltage. i Then, another preset AC voltage is selected and applied to the same battery for the same preset acquisition time T. m At a preset time interval ΔT, multiple test currents I of the battery cells are collected under the preset AC voltage. i Using the same test method, the same battery cell was subjected to all preset AC voltages, and the test current I corresponding to the battery cell under the preset AC voltage was obtained. i Using the same method, a preset AC voltage is applied to each of the other battery cells, causing each of the n battery cells in the battery pack to traverse all preset AC voltages, and the corresponding test current I of each of the n battery cells under the preset AC voltage is obtained. i .

[0053] When a preset AC voltage is applied to a single battery cell, the preset AC voltage can be applied to each of the n battery cells one by one, and the test current I corresponding to the preset AC voltage applied to one of the battery cells can be obtained one by one. i Alternatively, one preset AC voltage can be applied simultaneously to all battery cells, and the corresponding test current I for each battery cell can be obtained. i When one of the preset AC voltages is applied to all the battery cells, the test current I is obtained. i Then, another preset AC voltage is selected and applied simultaneously to all battery cells, and the corresponding test current I of each battery cell is obtained. i .

[0054] Optionally, applying multiple preset AC voltages to a single battery cell includes: applying multiple preset AC voltages to a single battery cell using an active voltage excitation source, wherein the active voltage excitation source includes at least one of a single battery cell in a battery pack and at least one of a charger for charging the battery pack.

[0055] When the active voltage excitation source is a charger that charges the battery pack, the charger can apply a preset AC voltage to each individual cell of the battery pack. For example, the charger can apply a voltage value U to all the individual cells of the battery pack simultaneously. i Same, frequency P x One of the preset AC voltages is applied, and then, in the same way, one of the preset AC voltages is applied to all the battery cells in the same time period each time, until all the battery cells in the battery pack have experienced all the preset AC voltages.

[0056] When the active voltage excitation source is a single cell in the battery pack, one of the cells in the battery pack can discharge to one or more other cells to apply a preset AC voltage to the other cells until all the cells in the battery pack have experienced all the preset AC voltages.

[0057] The embodiments of this application do not limit the type of battery cell. Conventional battery cells in the art are all applicable to the battery pack capacity balancing method of this application. For example, the battery cells in the embodiments of this application can be battery cells of lithium cobalt oxide system, lithium iron phosphate system, or ternary material system.

[0058] During the charging and discharging process of a battery cell, electrochemical reactions such as ion transfer, electron transfer, material reaction, and material diffusion occur within the cell's electrolyte, positive electrode material, and negative electrode material. By applying a preset AC voltage to the battery cell, maximizing the electrochemical reactions that occur during the charge-discharge cycle, the obtained impedance characteristic values ​​can be used more accurately to assess the battery cell's health status. Specifically, at different frequencies P... x Under the influence of a preset AC voltage, the electrochemical reactions occurring within the battery cells differ. In this embodiment, the number of preset AC voltages applied to the battery cells is x, i.e., x different frequencies of P are selected. x The same voltage value U i The preset AC voltage is applied to the battery cell. Here, x is an integer greater than or equal to 4; for example, x can be 4, 5, or 6, etc.

[0059] The frequency P of the preset AC voltage x Satisfies: 0.01 Hz ≤ P x ≤1000Hz, for example, P x The frequencies can be 0.01 Hz, 0.05 Hz, 0.1 Hz, 0.5 Hz, 1 Hz, 10 Hz, 50 Hz, 100 Hz, 500 Hz, 1000 Hz, etc. The selected preset AC voltage frequency P... x Within the aforementioned frequency range, effective impedance characteristic values ​​can be obtained to trigger capacity equalization processing.

[0060] Preset AC voltage value U i Satisfy: -30mV≤U i ≤30mV, for example, U i The voltage values ​​can be -30mV, -15mV, -10mV, -5mV, 5mV, 10mV, 15mV, 30mV, etc. The selected preset AC voltage value U... i Within the above range, it can be related to frequency P. x By sensing the impedance differences of individual battery cells in the battery pack, the remaining capacity of each battery cell can be estimated for capacity balancing.

[0061] Optionally, the number of preset AC voltages x is 4, and the frequency P of the 4 preset AC voltages is... x The frequencies are P1, P2, P3, and P4, respectively, with P1 > P2 > P3 > P4. Here, P1 is the high-frequency electron transport frequency, P2 is the mid-to-high-frequency ion transport frequency, P3 is the mid-frequency ion-electron reaction frequency, and P4 is the low-frequency ion-solid diffusion frequency. The battery cell operates at these four frequencies P... x These correspond to four electrochemical processes: high-frequency electron transport, mid-to-high-frequency ion transport, mid-frequency ion-electron reaction, and low-frequency ion-solid diffusion. By combining the AC impedance data of these four electrochemical processes, the impedance differences of individual battery cells can be more sensitively detected. Furthermore, by comparing different frequencies P... x By analyzing the impedance characteristics of individual battery cells, we can determine their remaining capacity. This approach takes into full account the inconsistencies in impedance among different battery cells, enabling a more accurate prediction of their remaining capacity.

[0062] Among them, P1 satisfies: 100hz < P1 ≤ 1000hz, P2 satisfies: 1hz < P2 ≤ 100hz, P3 satisfies: 0.1hz < P3 ≤ 1hz, and P4 satisfies: 0.01hz ≤ P4 ≤ 0.1hz.

[0063] Obtain multiple test currents I corresponding to a single battery cell under a preset AC voltage. i Includes: acquiring a test current I once at a preset time interval ΔT. i Among them, the test current I corresponding to each battery cell under the preset AC voltage is collected each time. i The quantity can be m, based on the preset AC voltage value U. i m test currents I i And a preset function, to obtain the corresponding impedance characteristic value Z x m is an integer, and m satisfies: 5 ≤ m ≤ 100.

[0064] Furthermore, ΔT satisfies: 0.2s ≤ ΔT ≤ 3s. For example, ΔT can be: 0.2s, 0.5s, 0.8s, 1.0s, 1.5s, 2.0s, 3.0s, etc. The preset acquisition duration T... m Satisfy: 30s≤T m ≤120s, for example, T m It can be: 30s, 60s, 80s, 100s, 120s, etc.

[0065] In this embodiment of the application, the voltage value U of the preset AC voltage is used. i Multiple test currents I corresponding to preset AC voltages i The impedance characteristic value Z is obtained by the preset function shown in equation (1). x :

[0066]

[0067] Among them, the preset function shown in equation (1) is the Fourier function.

[0068] Based on the impedance characteristic value Z of each battery cell under different preset AC voltages x Determining whether to perform capacity balancing includes:

[0069] Step S210: Obtain the impedance characteristic value Z of all battery cells under the same preset AC voltage. x average impedance value )

[0070] Step S220: Obtain the impedance characteristic value Z of a single battery cell under a preset AC voltage. x The average impedance value of the preset AC voltage Impedance deviation ΔZ x .in,

[0071] Step S230: Adjust the impedance deviation ΔZ x With preset impedance threshold Z m Perform a comparison. When the impedance deviation ΔZ x Less than Z m When the battery cells in the battery pack have nearly identical capacities, no capacity balancing is performed, and the impedance deviation ΔZ is significant. x The smaller the value, the better the capacity consistency of the individual cells within the battery pack. When the impedance deviation ΔZ... x Greater than or equal to Z m When this happens, capacity balancing is performed. Furthermore, when the impedance deviation ΔZ of any single cell within the battery pack... x Greater than or equal to the preset impedance threshold Z mIf so, then capacity balancing will be performed.

[0072] Among them, the preset impedance threshold Z m Satisfy: 3% ≤ Z m ≤6%, for example, Z m It can be 3%, 4%, 4.5%, 5%, 6%, etc.

[0073] When the impedance deviation ΔZ x Greater than or equal to Z m During capacity balancing, the process includes:

[0074] Step S310: For each battery cell, calculate the impedance characteristic value Z corresponding to the battery cell under all preset AC voltages. x The impedance summation value Z of the battery cell is obtained by summing the impedances. x n.

[0075] Step S320: Sum the impedances of all individual battery cells to obtain the value Z. x n is compared, and at least one of the impedance sums Z is used. x Larger battery cells are charged to perform capacity balancing. The sum of impedances, Z, is also considered. x The larger n is, the greater the impedance change of the battery cell, the smaller the remaining capacity of the battery cell, and the more the battery cell needs to be charged to increase its remaining capacity.

[0076] In step S320, the summation value Z of at least one of the impedances is... x During the charging process of a battery cell with a large n, the methods in steps S110 to S140 and steps S210 to S230 can be used to obtain the impedance deviation ΔZ of the battery cell under a preset AC voltage. x and the impedance deviation ΔZ x With equalization impedance threshold Z n When comparing, the impedance deviation ΔZ x Less than the equalization impedance threshold Z n Then, charging of individual battery cells in the battery pack can be stopped when the impedance deviation ΔZ x Greater than or equal to the equalization impedance threshold Z n Then continue charging the individual battery cells in the battery pack until the impedance deviation of all battery cells is ΔZ. x All are less than the equal impedance threshold Z n Then stop charging the individual battery cells in the battery pack.

[0077] Among them, Z n ≤Z m Furthermore, Z n Satisfy: 1% ≤ Z n ≤5%, for example, Zn It can be 1%, 2%, 3%, 4%, 5%, etc.

[0078] In step S320, the capacity equalization process includes: using the impedance summation value Z x n is a relatively small sum of the impedance of a single cell in the battery. x Capacity balancing is achieved by discharging larger battery cells (n) from one group of cells within the battery pack to another. In other embodiments, an external power source can also be used to discharge the battery cells within the battery pack for capacity balancing.

[0079] This application also provides a battery pack capacity balancing device, including an active voltage excitation source, a detection module, and a control module.

[0080] An active voltage excitation source is used to apply multiple preset AC voltages to individual battery cells, and the voltage values ​​U of all preset AC voltages are... i Same and frequency P x different.

[0081] The detection module collects data for a preset duration T. m At a preset time interval ΔT, multiple test currents I corresponding to the battery cells under a preset AC voltage are collected. i The detection module can be a circuit board for the battery pack, electrically connected to each individual battery cell to obtain the test current I passing through the cell. i Alternatively, the detection module can be an external circuit, which is electrically connected to the battery cell via wires to obtain the test current I passing through the battery cell. i .

[0082] The control module determines the voltage value U based on the preset AC voltage. i Multiple test currents I corresponding to preset AC voltages i Using a preset function, obtain the impedance characteristic value Z of a single battery cell under a corresponding preset AC voltage. x For a single battery cell, the preset AC voltage and impedance characteristic value Z x One-to-one correspondence; based on the impedance characteristic value Z of each battery cell under different preset AC voltages. x Determine whether to perform capacity balancing.

[0083] The battery pack capacity balancing device in this application embodiment collects multiple test currents I corresponding to individual battery cells under AC voltage at different frequencies through a detection module. i The control module determines the AC voltage value U based on the preset voltage value. i Multiple test currents I i And a preset function to obtain the impedance characteristic value Z related to the impedance of the battery cell.x The control module is based on the impedance characteristic value Z x By assessing the remaining capacity of individual battery cells in the battery pack and triggering capacity balancing, it can more sensitively detect changes in the health status of individual battery cells, rather than relying solely on parameters such as voltage, capacity, and impedance for capacity balancing. This allows for a more accurate determination of which battery cells require capacity balancing.

[0084] The capacity balancing method of this application is described below with reference to specific embodiments. The embodiments use lithium-ion batteries as the battery cells for description, and the specific test methods are as follows:

[0085] Example 1

[0086] I. Preparation methods of lithium-ion batteries

[0087] (1) Preparation of negative electrode sheet

[0088] Graphite, conductive carbon (Super-P), styrene-butadiene rubber, and sodium carboxymethyl cellulose (CMC) were mixed in deionized water at a mass ratio of approximately 95:2:2:1 and stirred until homogeneous to obtain a negative electrode slurry. The slurry was coated onto a copper foil with a thickness of approximately 12 μm, dried, cold-pressed, and then cut and welded with tabs to obtain the negative electrode sheet.

[0089] (2) Preparation of positive electrode sheet

[0090] Lithium cobalt oxide (LiCoO2), conductive carbon (Super-P), and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of approximately 95:2:3 in the solvent N-methylpyrrolidone and stirred until homogeneous to obtain a positive electrode slurry. The slurry was coated onto an aluminum foil with a thickness of approximately 12 μm, dried, cold-pressed, and then cut and welded with tabs to obtain the positive electrode sheet.

[0091] (3) Preparation of electrolyte

[0092] Lithium salt (LiPF6) was dissolved in a mixed solvent of EC / PC / DEC (mass ratio 1:1:1) to prepare a 1 mol / L LiPF6 electrolyte.

[0093] (4) Preparation of the separating membrane

[0094] PE porous polymer film is used as the separator.

[0095] (5) Preparation of lithium-ion batteries

[0096] The obtained positive electrode, negative electrode, and separator are wound sequentially and placed in an outer packaging foil, leaving an injection port. Electrolyte is injected through the injection port, the battery is sealed, and then processed through formation and capacity testing to obtain a lithium-ion battery. Four lithium-ion batteries were prepared using the above method.

[0097] II. Capacity Balancing Methods

[0098] Step S410: Provide a battery pack, which includes four lithium-ion batteries prepared using the above method, connected in series. For ease of description, the four batteries will be referred to as battery 1, battery 2, battery 3, and battery 4. The four individual batteries are discharged at a low rate (0.1C) to obtain their capacities. The capacity C of battery 1 is... 11 =2215mAh, the capacity C of a size 2 battery 12 =2120mAh, the capacity C of a size 3 battery 13 =2092mAh, the capacity C of a size 4 battery 14 =2001mah.

[0099] Step S420: Apply voltage value U to the four lithium-ion batteries of the battery pack using a charger. i A preset AC voltage of 10mV and frequency P1 of 1000Hz is used. For ease of description, this preset AC voltage will be referred to as the first preset AC voltage. The preset acquisition time T is... m With a preset time interval ΔT of 1 second and a time interval of 50 seconds, 50 test currents I corresponding to each battery cell under the first preset AC voltage are collected. i .

[0100] Step S430: According to the voltage value U of the first preset AC voltage i 50 test currents I under the first preset AC voltage i Using the preset function shown in equation (1), the impedance characteristic value Z1 of the battery cell under the first preset AC voltage is obtained.

[0101]

[0102] Step S430: Apply voltage value U to the four lithium-ion batteries of the battery pack using a charger. i A preset AC voltage of 10mV and frequency P2 of 100Hz is used. For ease of description, this preset AC voltage will be referred to as the second preset AC voltage. The impedance characteristic value Z2 of the battery cell under the second preset AC voltage is obtained by using the same method as in steps S410 and S420.

[0103] Step S440: Apply voltage value U to the four lithium-ion batteries of the battery pack using a charger. iA preset AC voltage of 10mV and frequency P3 of 1Hz is used. For ease of description, this preset AC voltage will be referred to as the third preset AC voltage. The impedance characteristic value Z3 of the battery cell under the third preset AC voltage is obtained by using the same method as in steps S410 and S420.

[0104] Step S450: Apply voltage value U to the four lithium-ion batteries of the battery pack using a charger. i A preset AC voltage of 10mV and frequency P4 of 0.1Hz is used. For ease of description, this preset AC voltage will be referred to as the fourth preset AC voltage. The impedance characteristic value Z4 of the battery cell under the fourth preset AC voltage is obtained by using the same method as in steps S410 and S420.

[0105] The impedance characteristic value Z1 and the sum of impedance values ​​Z of the four lithium-ion batteries x n and average impedance value As shown in Table 1.

[0106] Table 1

[0107]

[0108] Impedance deviation ΔZ of 4 lithium-ion batteries x As shown in Table 2.

[0109] Table 2

[0110] <![CDATA[Impedance deviation △Z1]]> <![CDATA[Impedance deviation △Z2]]> <![CDATA[Impedance deviation △Z3]]> <![CDATA[Impedance deviation △Z4]]> No. 1 battery 1.21％ 3.03％ 5.96％ 3.15％ No. 2 battery 0.40％ 4.67％ 5.04％ 5.50％ No. 3 battery 1.21％ 1.82％ 3.67％ 0.07％ No. 4 battery 2.02％ 3.83％ 14.68％ 8.58％

[0111] Step S450: Adjust the impedance deviation ΔZ x With preset impedance threshold Z m Perform a comparison, preset impedance threshold Z m The impedance deviation is 5%. According to the results in Table 2, the impedance deviations ΔZ3 and ΔZ4 of battery 1, and ΔZ3 and ΔZ4 of battery 4 are all greater than 5%. Therefore, there is an impedance deviation ΔZ among the four lithium-ion batteries. x Greater than the preset impedance threshold Z m In this case, capacity balancing is required. Specifically, the impedance deviations ΔZ3 and ΔZ4 of battery #4 are both significantly greater than the preset impedance threshold Z. m (5%), the impedance of battery No. 4 changes greatly and the remaining capacity is small. It is preliminarily determined that at least battery No. 4 needs to be charged.

[0112] Step S460: Sum the impedance characteristic values ​​Z1 to Z4 of battery No. 1 to obtain the impedance sum value Z. x 1 is 71.6; the impedance characteristic values ​​Z1 to Z4 of battery 2 are summed to obtain the impedance sum value Z. x2 is 72.1; the impedance characteristic values ​​Z1 to Z4 of battery 3 are summed to obtain the impedance sum value Z. x 3 is 73.8; the impedance characteristic values ​​Z1 to Z4 of battery 4 are summed to obtain the impedance sum value Z. x 2 is 80.2, therefore, Z x 1 < Z x 2 < Z x 3 < Z x 4. Using the method of discharging battery 1 to battery 4 and battery 2 to battery 3, the impedance deviation ΔZ of the four lithium-ion batteries is obtained simultaneously. x When the impedance deviation ΔZ of the four lithium-ion batteries x All are less than the equal impedance threshold Z n At this time, discharge from battery 1 to battery 4 and from battery 2 to battery 3 is stopped to complete the equalization process. The equalization impedance threshold Z is... n It is 3%.

[0113] Table 2 shows the impedance deviation ΔZ of the four batteries after the capacity equalization process in step S460. x .

[0114] Table 3

[0115] <![CDATA[Impedance deviation △Z1]]> <![CDATA[Impedance deviation △Z2]]> <![CDATA[Impedance deviation △Z3]]> <![CDATA[Impedance deviation △Z4]]> No. 1 battery 0.98％ 1.45％ 0.75％ 1.10％ No. 2 battery 1.23％ 0.87％ 1.20％ 2.65％ No. 3 battery 0.80％ 1.70％ 1.70％ 1.65％ No. 4 battery 1.40％ 2.05％ 2.70％ 1.97％

[0116] Figure 1 The impedance deviation ΔZ of the four cells is calculated before the capacity equalization process in step S460. x Distribution curve, Figure 2 After the capacity equalization process in step S460, the impedance deviation ΔZ of the four cells is... x Distribution curve, based on Figure 1 and Figure 2 It can be seen that the impedance deviation ΔZ of the four batteries after capacity equalization is... x The impedance deviation ΔZ of the four cells after capacity equalization is small and the fluctuation is small. x All less than 3%.

[0117] The four battery cells obtained after step S460 are discharged at a low rate (0.1C) to obtain the actual remaining capacity of the equalized battery cells. The remaining capacity C of battery number 1 is... 21 =2112mAh, the remaining capacity C of size 2 battery 22 =2100mAh, the remaining capacity C of a size 3 battery 23 =2097mAh, the remaining capacity C of a size 4 battery 24 =2070mAh. After capacity balancing, the capacity range ΔC of the four battery cells is 42mAh, which is relatively small and the capacity balancing effect is good.

[0118] Comparative Example 1

[0119] Four battery cells prepared using the lithium-ion battery preparation method in Example 1 were selected. Each battery cell has a nominal capacity of 4200 mAh. Capacity balancing was performed by directly comparing the open-circuit voltages of the four battery cells. The capacity balancing steps are as follows:

[0120] Step S510: First, obtain the voltage of the four individual battery cells: the voltage of battery 1' is V1 = 3.91V, the voltage of battery 2' is V2 = 3.93V, the voltage of battery 3' is V3 = 3.95V, and the voltage of battery 4' is V4 = 3.91V.

[0121] Step S520: Sort the voltages of the four battery cells and calculate the average value of the four voltages, Vav = 3.925V. Charge the battery cells with voltages lower than the average value and discharge the battery cells with voltages higher than the average value. Specifically, battery 3' discharges to battery 1' and battery 2' discharges to battery 4'. Stop charging when the voltage of a single cell approaches 3.925V.

[0122] Step S530: Discharge the four battery cells at a low rate (0.1C) to obtain the actual remaining capacity of the battery cells after equalization. The remaining capacity of battery 1' is C1' = 2000mAh, the remaining capacity of battery 2' is C2' = 2050mAh, the remaining capacity of battery 3' is C3' = 2100mAh, and the remaining capacity of battery 4' is C4 = 2070mAh.

[0123] In Comparative Example 1, the capacity balancing process was performed by directly comparing the open-circuit voltage of the four battery cells. After capacity balancing, the capacity range ΔC' of the four battery cells was 100 mAh, which showed significant fluctuations and did not achieve a satisfactory balancing effect. Therefore, when Comparative Example 1 used open-circuit voltage monitoring for capacity balancing, the open-circuit voltage of the battery cells included the polarization voltage of the battery cells. Directly using the open-circuit voltage for capacity balancing did not ensure the consistency of polarization among the multiple battery cells, resulting in poor balancing performance.

[0124] In the description of this application, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another instance, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C.

[0125] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A battery pack capacity balancing method, characterized in that, include: A battery pack is provided, the battery pack comprising n individual battery cells, where n is an integer greater than or equal to 2; Multiple preset AC voltages are provided, wherein the voltage value U of the preset AC voltage is... i Same and frequency P x Unlike other methods, the preset AC voltage is applied to each individual battery cell, and the sampling time is T. m At a preset time interval ΔT, the test current I corresponding to the battery cell under the preset AC voltage is collected. i ; According to the preset AC voltage value U i The test current I corresponding to the preset AC voltage i Using a preset function, the impedance characteristic value Z of the battery cell under the preset AC voltage is obtained. x ; For the battery cell, the preset AC voltage and the impedance characteristic value Z x One-to-one correspondence; Based on the impedance characteristic value Z of all the battery cells under different preset AC voltages x Determine whether to perform capacity balancing. Determining whether to perform capacity balancing includes: Obtain the impedance characteristic value Z of all the battery cells under the same preset AC voltage. x average impedance value Z x ; Obtain the impedance characteristic value Z of the battery cell under the preset AC voltage. x The average impedance value of the preset AC voltage Z x Impedance deviation ΔZ x ; The impedance deviation ΔZ x With preset impedance threshold Z m When comparing, the impedance deviation ΔZ x Greater than or equal to Z m When the impedance deviation ΔZ is reached, capacity balancing is performed. x Less than Z m If the impedance threshold Z is not set, no capacity equalization will be performed. m Satisfy: 3%≤Z m ≤6%; When the impedance deviation ΔZ x Greater than or equal to Z m During capacity balancing, the process includes: For the battery cell, the impedance characteristic value Z corresponding to the battery cell under all the preset AC voltages is... x The impedance summation value Z of the battery cell is obtained by summing the impedances. x n; The sum of the impedances of all the aforementioned battery cells, Z. x n is compared, and at least one of the impedance sum values ​​Z is compared. x The battery cells with larger n are charged to perform capacity balancing. Capacity balancing includes: Using the impedance summation value Z x The smaller of the individual cells contributes to the impedance sum value Z. x The battery cells with larger n are discharged to perform capacity balancing.

2. The battery pack capacity equalization method according to claim 1, characterized in that, The number of preset AC voltages applied to the battery cell is x, where x is an integer greater than or equal to 4; The frequency P of the preset AC voltage x Satisfies: 0.01 Hz ≤ P x ≤1000Hz; The voltage value U of the preset AC voltage i Satisfy: -30mV≤U i ≤30mV.

3. The battery pack capacity balancing method according to claim 2, characterized in that, The number of preset AC voltages x is 4, and the frequency P of the 4 preset AC voltages is... x They are P1, P2, P3, and P4, respectively. P1 satisfies: 100Hz < P1 ≤ 1000Hz; P2 satisfies: 1 Hz < P2 ≤ 100 Hz; P3 satisfies: 0.1 Hz < P3 ≤ 1 Hz; P4 satisfies: 0.01hz≤P4≤0.1hz.

4. The battery pack capacity balancing method according to claim 1, characterized in that, Obtain multiple test currents I corresponding to the battery cell under the preset AC voltage. i This includes: acquiring the test current I once at a preset time interval ΔT. i ΔT satisfies: 0.2s≤ΔT≤3s; The preset collection duration T m Satisfy: 30s≤T m ≤120s.

5. The battery pack capacity balancing method according to claim 1, characterized in that, According to the preset AC voltage value U i The multiple test currents I corresponding to the preset AC voltage i The impedance characteristic value Z is obtained by the preset function shown in equation (1). x : （1） Among them, the preset function shown in equation (1) is the Fourier function.

6. The battery pack capacity balancing method according to claim 1, characterized in that, Applying multiple preset AC voltages to the battery cell includes: Multiple preset AC voltages are applied to the battery cells using an active voltage excitation source, wherein the active voltage excitation source includes at least one battery cell in the battery pack and at least one charger for charging the battery pack.

7. A battery pack capacity balancing device, characterized in that, include: An active voltage excitation source is used to apply multiple preset AC voltages to a single battery cell, wherein the voltage value U of all the preset AC voltages is... i Same and frequency P x different; The detection module, during the preset data acquisition time T m At a preset time interval ΔT, multiple test currents I corresponding to the battery cell under the preset AC voltage are collected. i ; and The control module, based on the preset AC voltage value U i The multiple test currents I corresponding to the preset AC voltage i Using a preset function, the impedance characteristic value Z of the battery cell under the preset AC voltage is obtained. x For the battery cell, the preset AC voltage and the impedance characteristic value Z x One-to-one correspondence; based on the impedance characteristic value Z of all the battery cells under different preset AC voltages. x Determine whether to perform capacity balancing. Determining whether to perform capacity balancing includes: Obtain the impedance characteristic value Z of all the battery cells under the same preset AC voltage. x average impedance value Z x ; Obtain the impedance characteristic value Z of the battery cell under the preset AC voltage. x The average impedance value of the preset AC voltage Z x Impedance deviation ΔZ x ; The impedance deviation ΔZ x With preset impedance threshold Z m When comparing, the impedance deviation ΔZ x Greater than or equal to Z m When the impedance deviation ΔZ is reached, capacity balancing is performed. x Less than Z m If the impedance threshold Z is not set, no capacity equalization will be performed. m Satisfy: 3%≤Z m ≤6%; When the impedance deviation ΔZ x Greater than or equal to Z m During capacity balancing, the process includes: For the battery cell, the impedance characteristic value Z corresponding to the battery cell under all the preset AC voltages is... x The impedance summation value Z of the battery cell is obtained by summing the impedances. x n; The sum of the impedances of all the aforementioned battery cells, Z. x n is compared, and at least one of the impedance sum values ​​Z is compared. x The battery cells with larger n are charged to perform capacity balancing. Capacity balancing includes: Using the impedance summation value Z x The smaller of the individual cells contributes to the impedance sum value Z. x The battery cells with larger n are discharged to perform capacity balancing.

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