A method for fast charging lithium-ion batteries

Abstract

The present invention discloses a method for fast charging of lithium-ion batteries. During the charging process of the lithium-ion battery, the lithium-ion battery is charged in stages to an upper limit voltage using a constant current charging method, and then charged to a final current using a constant current constant voltage charging method to complete the charging. In the constant current charging stage, the constant current charging rate of the latter stage is lower than the constant current charging rate of the previous stage, and the voltage reached by the constant current charging in the latter stage is higher than the voltage reached by the constant current charging in the previous stage, thereby improving the service life of the battery in a staged manner. In particular, the current rate and the voltage reached, as well as the final current, used in each stage of the battery charging are quickly determined in combination with a non-destructive lithium plating detection method, thereby greatly shortening the battery charging time while ensuring that lithium plating does not occur in the battery.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology and relates to a method for fast charging of lithium-ion batteries. Background Art

[0002] Lithium-ion batteries possess advantages such as high voltage, high specific energy, and long charge-discharge life, making them widely used in electronic products, portable small appliances, energy storage systems, and many other fields. Following the issuance of the new national standard for two-wheeled vehicles, the trend towards lithium-ion batteries has become even more pronounced, and higher demands are being placed on future lithium-ion batteries.

[0003] (1) Longer lifespan (battery lifespan exceeds 10 years);

[0004] (2) High energy;

[0005] (3) Excellent low-temperature cycling performance and capacity recovery capability;

[0006] (4) Impeccable security performance.

[0007] Among these, fast charging of batteries can save users a lot of time, so a certain level of fast charging performance must be met in the process of improving battery energy.

[0008] For lithium-ion batteries, during the charging process, the negative electrode potential and the lithium metal potential are basically close, which easily causes lithium dendrites to precipitate, also known as lithium plating. The precipitation of lithium dendrites causes battery aging and changes in negative electrode reaction kinetics, which not only reduce battery performance and shorten cycle life, but also limit the battery's fast charging capacity and may cause catastrophic consequences such as combustion and explosion. Fast charging is more likely to cause lithium plating in batteries.

[0009] For the reasons mentioned above, there is an urgent need to further study the charging methods of lithium-ion batteries, and to research a safe and reliable method for fast charging of lithium-ion secondary batteries. Summary of the Invention

[0010] To overcome the aforementioned problems, the inventors have conducted in-depth research on lithium-ion battery charging methods, developing a method for fast charging lithium-ion batteries. During the lithium-ion battery charging process, the battery is charged in stages using a constant current charging method to the upper limit voltage, followed by a constant current-constant voltage charging method to the final current, completing the charging process. In the constant current charging stage, the rate of change in each subsequent stage is lower than that of the previous stage, while the voltage reached in each stage is higher than that reached in the previous stage. This staged approach improves the battery's lifespan. In particular, by combining a non-destructive lithium plating detection method to quickly determine the current rate, voltage, and final current at each stage of battery charging, the charging time is significantly shortened while preventing lithium plating, thus completing this invention.

[0011] Specifically, the purpose of this invention is to provide a method for fast charging of a lithium-ion battery, the method comprising: charging the lithium-ion battery in stages using a constant current charging method to the upper limit voltage, and then charging it in a constant current and constant voltage charging method to the final current, thereby completing the charging process.

[0012] The aforementioned stages are divided into 1 to 7 segments.

[0013] In this process, the rate of constant current charging in the later stage is smaller than that in the earlier stage, and the voltage reached in the later stage is larger than that reached in the earlier stage.

[0014] In this process, the rate of constant current charging in the later stage is lower than that in the previous stage by x1C, where x1 ranges from 0.1 to 1, preferably from 0.4 to 0.6. In each stage of constant current charging, the voltage value is not greater than the threshold voltage under the corresponding constant current charging conditions to prevent lithium plating.

[0015] The rate of the first stage of constant current charging is between 1 and 10C, preferably between 1 and 6C.

[0016] The upper limit voltage is the threshold voltage at which lithium plating does not occur when charging with the current of the last constant current charging stage.

[0017] The final current is the threshold cutoff current at which lithium plating does not occur when charging with the current and voltage of the final stage.

[0018] The threshold cutoff current and the threshold voltage during the constant current charging stage are obtained through a non-destructive lithium plating detection method.

[0019] The method for obtaining the threshold voltage using a non-destructive lithium plating detection method includes the following steps:

[0020] Step 1: Charge multiple lithium-ion batteries at different rates with constant current to different set voltages;

[0021] Step 2: Let the battery that has finished charging in Step 1 rest for a few minutes, and then discharge it at the same constant current rate until the discharge termination voltage is reached.

[0022] Step 3, Determining the threshold voltage.

[0023] The method for obtaining the threshold cutoff current using a non-destructive lithium plating detection method includes the following steps:

[0024] Step 1': Charge multiple lithium-ion batteries with constant current and constant voltage until the set cutoff current is reached;

[0025] Step 2': After charging is complete in Step 1', let the battery rest for a few minutes, and then discharge it at the same constant current rate until the discharge termination voltage is reached.

[0026] Step 3': Determining the threshold cutoff current.

[0027] The beneficial effects of this invention include:

[0028] (1) The method for fast charging of lithium-ion batteries provided by the present invention achieves maximum charging speed, saves charging time, and extends service life while protecting battery safety.

[0029] (2) The lithium-ion battery fast charging method provided by the present invention gradually reaches the upper limit voltage of the battery in a phased manner, and the battery charging process does not reduce the energy and capacity of the battery.

[0030] (3) The lithium-ion battery fast charging method provided by the present invention combines a non-destructive lithium plating detection method to quickly determine the current ratio and voltage used in each stage of battery charging, as well as the final current reached during charging. Under the premise of ensuring that lithium plating does not occur in the battery, the battery charging time is effectively shortened.

[0031] (4) The method for fast charging of lithium-ion batteries provided by the present invention is simple, easy to operate, and highly practical, and has excellent development prospects. DETAILED DESCRIPTION

[0032] The present invention will be further described in detail below with reference to embodiments. Through these descriptions, the features and advantages of the present invention will become clearer and more apparent.

[0033] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments.

[0034] In recent years, with the development of 3C digital energy storage devices, the application of lithium-ion batteries has become more and more widespread, and their market share has also increased. After the promulgation of the new national standard for two-wheeled vehicles, the trend of lithium-ion batteries has become more obvious, and the development of new energy vehicles has entered a golden age. High energy and low cost are the consistent pursuits of future lithium-ion battery development.

[0035] Simple lithium-ion battery charging methods mainly include constant current charging and constant voltage charging. These two methods are inefficient and cannot meet the growing demands of the modern electric vehicle industry. To accelerate charging speed, improve charging efficiency, or maximize battery life, the industry has tried various lithium-ion battery charging methods, including improvements to charging waveforms, battery model coupling, and AC charging. While these methods have significantly shortened lithium-ion battery charging time, they have also accelerated battery aging and increased the risk of lithium plating on the negative electrode.

[0036] Currently, the commonly used method for detecting lithium plating involves disassembling the battery, extracting the negative electrode, and analyzing for the presence of lithium plating. This method provides a direct assessment of lithium plating but is destructive. Non-destructive lithium plating detection is a novel approach that primarily relies on the battery's electrochemical characteristic parameters. It allows for the assessment of potential lithium plating within the cell without damaging the battery's appearance. Therefore, a fast-charging method for batteries can be proposed by combining non-destructive lithium plating detection techniques.

[0037] Based on this, the present invention provides a method for fast charging of lithium-ion batteries, the method comprising: charging the lithium-ion battery in stages using constant current charging to the upper limit voltage, and then charging it to the final current using constant current and constant voltage charging to complete the charging.

[0038] The stages are divided into 1 to 7 segments, preferably 3 to 5 segments.

[0039] According to the present invention, the rate of constant current charging in the later stage is lower than that in the earlier stage, and the voltage value of constant current charging in the later stage is higher than that in the earlier stage. By charging to the upper limit voltage of the battery in a staged manner, or by slowing down the rate at which the battery reaches the upper limit voltage, the battery life can be effectively improved, and the battery energy and capacity will not be reduced during the charging process.

[0040] In this invention, the rate of constant current charging in the later stage is lower than the rate of constant current charging in the previous stage by x1C, where x1 ranges from 0.1 to 1, preferably from 0.4 to 0.6, for example 0.5.

[0041] According to the present invention, as the charging reaction proceeds, the constant current charging rate decreases, reducing the anodic polarization of the battery. Of course, the constant current charging rate difference can be chosen to be less than 0.1C, which would result in too many charging stages. While this would further shorten the charging time, it would also significantly increase the workload of obtaining lithium plating voltages at different rates. Alternatively, the constant current charging rate difference can be chosen to be greater than C. Although this would reduce the workload of obtaining lithium plating voltages at different rates, it would result in too few charging stages and a longer charging time. Choosing a constant current charging rate difference within the range of 0.1 to 1C can balance the workload of obtaining lithium plating voltages at different rates with the number of stages, shortening the battery charging time and achieving fast battery charging.

[0042] In this invention, constant current charging is performed in each stage until the voltage value is not greater than the threshold voltage under the corresponding constant current charging conditions to prevent lithium plating. In order to shorten the battery charging time, preferably, constant current charging is performed in each stage until the voltage value is equal to the threshold voltage under the corresponding constant current charging conditions to prevent lithium plating.

[0043] In this invention, the rate of the first stage of constant current charging can be set arbitrarily, ranging from 1 to 10C, preferably from 1 to 6C, such as 3C.

[0044] In order to achieve fast charging, the constant current charging rate in the first stage can be chosen to be large enough. Correspondingly, the threshold voltage at which lithium plating does not occur during constant current charging at the selected rate will become smaller. However, an excessively large constant current charging rate will not only increase the workload of testing lithium plating voltage at different rates, but may also lead to battery damage.

[0045] According to the present invention, the upper limit voltage is the threshold voltage at which lithium plating does not occur when charging with the current of the last constant current charging stage.

[0046] Furthermore, the current and voltage used in the constant current and constant voltage charging stage are the same as those used in the last constant current charging stage; the final current is the threshold cutoff current at which lithium plating does not occur when charging with the current and voltage of the last stage.

[0047] The threshold cutoff current and the threshold voltage during the constant current charging stage are obtained through a non-destructive lithium plating detection method.

[0048] In this invention, the method steps for obtaining the threshold voltage using a non-destructive lithium plating detection method include:

[0049] Step 1: Charge multiple lithium-ion batteries at different constant current rates to different set voltages.

[0050] According to a preferred embodiment, in step 1, multiple lithium-ion batteries are charged to different set voltages at the same constant current rate, and then the constant current charging rate is changed to charge the multiple lithium-ion batteries to different set voltages at the changed same constant current rate.

[0051] The constant current charging rate can be set arbitrarily, ranging from 0.1 to 10C, preferably from 0.5 to 5C, and more preferably from 1 to 3C.

[0052] Furthermore, to quickly select the optimal charging rate and threshold voltage that achieve the best results, such as the shortest battery charging time and the highest efficiency, it is preferable to set the constant current charging rate, denoted as x1C, in an incremental manner with the same difference. The value of x1 ranges from 0.1 to 1, preferably from 0.4 to 0.6, for example, 0.5. When the selected rate difference is 0.5C, the constant current charging rates for different batches of batteries can be set to 1C, 1.5C, 2C, 2.5C, and 3C, respectively.

[0053] In step 1, the set voltage is 4.2–4.7V, preferably 4.43–4.53V. To obtain better results, it is preferable to set the voltage in increments of the same difference, such as 0.01–0.02V. For example, if the voltage is set to 4.43–4.53V in increments of 0.01V, the voltages set for different batteries at the same rate are 4.43V, 4.44V, 4.45V, 4.46V, 4.47V, 4.48V, 4.49V, 4.5V, 4.51V, 4.52V, and 4.53V, respectively.

[0054] Among them, when the voltage is set to 4.43 to 4.53V, it is particularly suitable for any commercially available lithium cobalt oxide battery.

[0055] Step 2: Let the battery that has finished charging in Step 1 rest for a few minutes, and then discharge it at the same constant current rate until the discharge termination voltage is reached.

[0056] The termination voltage can be set to 2.5V to 3V, preferably 3V.

[0057] In step 2, the resting time is 10 to 100 minutes, preferably 20 to 40 minutes, for example 30 minutes.

[0058] One method is to charge the battery and then leave it for a period of time, which can reduce or even eliminate battery polarization. However, leaving it for too long is unnecessary.

[0059] In step 2, the constant current discharge rate is 0.05 to 1C, preferably 0.1 to 0.5C, for example 0.2C.

[0060] Among them, the smaller the constant current discharge rate, the more thoroughly the battery capacity is released, which can effectively avoid battery polarization caused by discharge. However, the corresponding time will be extended. The above-mentioned constant current discharge rate is more suitable.

[0061] Step 3, Determining the threshold voltage.

[0062] According to the present invention, step 3 includes the following steps:

[0063] Step 3-1: Obtain the battery charging energy, charging capacity, discharging energy, and discharging capacity;

[0064] Step 3-2: Calculate the coulombic efficiency and the charge / discharge plateau voltage difference;

[0065] Step 3-3: Determine the voltage at which lithium plating begins in the battery, and then determine the threshold voltage.

[0066] In step 3-1, the above-mentioned charging energy, charging capacity, discharging energy, and discharging capacity data are acquired at the electrochemical workstation.

[0067] In step 3-2, the coulombic efficiency and the charge / discharge plateau voltage difference are obtained according to formulas 1 and 2, respectively:

[0068] Coulomb efficiency (%) = Discharge capacity (mA·h) / Charge capacity (mA·h) × 100% Formula 1

[0069] Platform voltage difference (V) = Charging energy (W·h) / Charging capacity (mA·h) - Discharging energy (W·h) / Discharging capacity (mA·h) Formula 2

[0070] In step 3-3, when the coulombic efficiency of the lithium-ion battery decreases with the increase of the charging rate or the charging cut-off voltage, and the plateau voltage difference increases with the increase of the charging rate or the charging cut-off voltage, it indicates that the lithium-ion battery under test has undergone lithium plating. Preferably, it is determined whether lithium plating occurs in the battery cell at a certain set voltage according to formula 3 and / or formula 4, thereby determining the voltage at which lithium plating begins in the battery cell, which is recorded as the lithium plating voltage.

[0071] {Y coulomb efficiency - (Y+1) coulomb efficiency} / {(Y-1) coulomb efficiency - Y coulomb efficiency} > N Formula 3

[0072] {(Y+1) platform voltage difference) - Y platform voltage difference} / {Y platform voltage difference - (Y-1) platform voltage difference} > N Formula 4

[0073] In formulas 3 and 4:

[0074] Y-coulomb efficiency — Coulomb efficiency under Y voltage;

[0075] (Y+1) Coulomb efficiency – the Coulomb efficiency at a voltage greater than the Y voltage that is adjacent to the increasing voltage difference of Y.

[0076] (Y-1) Coulomb efficiency – the Coulomb efficiency at a voltage smaller than the Y voltage that is adjacent to the increasing voltage difference of Y.

[0077] Y-platform voltage difference — the platform voltage difference under Y voltage;

[0078] (Y+1) Plateau Voltage Difference – The plateau voltage difference adjacent to the increasing Y voltage difference value, and the voltage difference under a voltage greater than the Y voltage.

[0079] (Y-1) Plateau Voltage Difference – The plateau voltage difference at a voltage smaller than the Y voltage, adjacent to the increasing Y voltage difference value;

[0080] N – a parameter for determining lithium plating.

[0081] Where N > 1, it can be determined that lithium plating will occur at the (Y+1) voltage, i.e., the lithium plating voltage. Preferably, N ≥ 2, more preferably, N is between 3 and 6, for example, N is 5.

[0082] As the value of N increases, it becomes easier to determine the lithium plating voltage. However, if the value of N is too large, lithium plating may have already occurred before this voltage, resulting in an inaccurate determination of the lithium plating voltage.

[0083] In this invention, in order to avoid lithium plating during charging, the charging threshold voltage is lower than the lithium plating voltage. Preferably, a voltage value that is 0.01 to 0.02V lower than the lithium plating voltage is recorded as the threshold voltage.

[0084] In this invention, the method steps for obtaining the threshold cutoff current using a non-destructive lithium plating detection method include:

[0085] Step 1': Charge multiple lithium-ion batteries with constant current and constant voltage until the set cutoff current is reached.

[0086] The constant current and constant voltage charging process involves first charging the battery at a constant current rate to a threshold voltage, and then charging it at this voltage to a set cutoff current.

[0087] According to a preferred embodiment, multiple lithium-ion batteries are first charged at the same constant current rate to a threshold voltage, and then charged at the threshold voltage to a set cutoff current; then the constant current charging rate is changed, and the multiple lithium-ion batteries are charged at the same constant current rate after the change to the aforementioned threshold voltage, and then charged at the threshold voltage to a set cutoff current.

[0088] The constant current charging rate is 0.5–3C, preferably 1–3C. To achieve better results, it is preferable to set the constant current charging rate in an incremental manner with the same difference; more preferably, it should be consistent with the constant current charging rate selected when obtaining the threshold voltage using a non-destructive lithium plating detection method. For example, when the selected rate difference is 0.5C, the constant current charging rate for different batteries can be set to 1C, 1.5C, 2C, 2.5C, and 3C, respectively.

[0089] In step 1', as the name suggests, the cutoff current is set to a manually predetermined cutoff current, which is 0.01 to 2C, preferably 0.1 to 1C.

[0090] Setting the cutoff current too high will cause charging to end earlier, resulting in a loss of charging capacity. To achieve better results, it is preferable to set the cutoff current in increments of the same value, such as 0.05 to 0.1C. For example, by setting the cutoff current in increments of 0.1C to 1C, the cutoff currents for different batteries at the same charging rate would be 1C, 0.9C, 0.8C, 0.7C, 0.6C, 0.5C, 0.4C, 0.3C, 0.2C, and 0.1C, respectively.

[0091] Step 2': Let the battery that has finished charging in Step 1' rest for a few minutes, and then discharge it at the same constant current rate until the discharge termination voltage.

[0092] The termination voltage can be set to 2.5V to 3V, preferably 3V.

[0093] In step 2', the resting time is 10 to 100 minutes, preferably 20 to 40 minutes, for example 30 minutes.

[0094] In step 2', the constant current discharge rate is 0.06 to 0.6C, preferably 0.1 to 0.4C, for example 0.2C.

[0095] Step 3': Determining the threshold cutoff current.

[0096] According to the present invention, step 3' includes the following steps:

[0097] Step 3'-1: Obtain the battery charging energy, charging capacity, discharging energy, and discharging capacity;

[0098] Step 3'-2: Calculate the coulombic efficiency and the voltage difference between the charge and discharge plateaus;

[0099] Step 3'-3: Determine the cutoff current at which lithium plating begins in the battery cell, and then determine the threshold cutoff current.

[0100] In step 3'-2, the coulombic efficiency and the charge / discharge plateau voltage difference are obtained according to formulas 1 and 2, respectively.

[0101] Coulomb efficiency (%) = Discharge capacity (mA·h) / Charge capacity (mA·h) × 100% Formula 1

[0102] Platform voltage difference (V) = Charging energy (W·h) / Charging capacity (mA·h) - Discharging energy (W·h) / Discharging capacity (mA·h) Formula 2

[0103] In step 3'-3, when the coulombic efficiency of the lithium-ion battery decreases as the cutoff current decreases and the plateau voltage difference increases as the cutoff current decreases, it indicates that lithium plating has occurred in the lithium-ion battery. Preferably, it is determined whether lithium plating occurs in the battery cell at a certain cutoff current according to formula 5 and / or formula 6, thereby determining the cutoff current at which lithium plating begins to occur in the battery, which is denoted as the lithium plating cutoff current.

[0104] {W coulomb efficiency - (W+1) coulomb efficiency} / {(W-1) coulomb efficiency - W coulomb efficiency} > N Formula 5

[0105] {(W+1) platform voltage difference) - W platform voltage difference} / {W platform voltage difference - (W-1) platform voltage difference} > N Formula 6

[0106] In formulas 5 and 6:

[0107] W Coulomb efficiency — Coulomb efficiency at the set cutoff current;

[0108] (W+1) Coulomb efficiency — the Coulomb efficiency at a set cutoff current that is larger than the set cutoff current and adjacent to the increasing difference between the set cutoff current and the set cutoff current of W.

[0109] (W-1) Coulomb efficiency — the Coulomb efficiency at a set cutoff current smaller than the set cutoff current, which is adjacent to the increasing difference between the set cutoff current and the set cutoff current W.

[0110] W platform voltage difference — the platform voltage difference with W set cutoff current;

[0111] (W+1) Platform voltage difference - The platform voltage difference under a cutoff current larger than the W set cutoff current, which is adjacent to the increasing W set cutoff current difference value.

[0112] (W-1) Platform voltage difference - The platform voltage difference under a set cutoff current that is smaller than the set cutoff current and adjacent to the increasing difference value of W set cutoff current;

[0113] N – a parameter for determining lithium plating.

[0114] Where N > 1, it can be determined that lithium plating will occur at the (W-1) cutoff current, i.e., the lithium plating cutoff current. Preferably, N ≥ 2, more preferably, N is between 3 and 6, for example, N is 5. As the set value of N increases, it is relatively easier to determine the lithium plating cutoff current. However, if the set N is too large, lithium plating may have already occurred before this current, and the determined lithium plating cutoff current will be inaccurate.

[0115] In this invention, in order to avoid lithium plating during charging, the threshold cutoff current of charging is greater than the lithium plating cutoff current. Preferably, a current value that is 0.08 to 0.12C greater than the lithium plating cutoff current, such as 0.1C, is denoted as the threshold cutoff current.

[0116] According to the present invention, during the charging process of the lithium-ion battery, the ambient temperature is maintained at -40 to 60°C. To avoid the influence of high or low temperatures on battery polarization, the ambient temperature is maintained at 15 to 35°C, for example, 25°C.

[0117] In this invention, during the battery charging process, a method for determining fast battery charging is developed that breaks through the traditional constant current, constant voltage, and / or constant current and constant voltage charging methods and combines non-destructive lithium plating detection methods. This achieves the goal of maximizing charging speed and saving charging time while protecting the battery.

[0118] Example

[0119] The present invention is further described below through specific examples; however, these examples are merely exemplary and do not constitute any limitation on the scope of protection of the present invention.

[0120] Example 1

[0121] The lithium-ion battery used in this embodiment is a 3600mAh-406080 soft-pack battery, and the operating temperature is 25℃.

[0122] (1) Charge 13 lithium-ion batteries at a constant current rate of 1C to 4.43V, 4.44V, 4.45V, 4.46V, 4.47V, 4.48V, 4.49V, 4.5V, 4.51V, 4.52V, 4.53V, 4.54V and 4.55V respectively;

[0123] (2) Charge 13 lithium-ion batteries in a manner similar to step (1), except that the constant current charging rate is 1.5C.

[0124] (3) Charge the 13 lithium-ion batteries in a manner similar to step (1), except that the constant current charging rate is 2C.

[0125] (4) Charge the 13 lithium-ion batteries in a manner similar to step (1), except that the constant current charging rate is 2.5C.

[0126] (5) Charge the 13 lithium-ion batteries in a manner similar to step (1), except that the constant current charging rate is 3C.

[0127] After the charging process, the lithium-ion batteries were left to rest for 30 minutes and then discharged at a constant current rate of 0.2C to 3V. The charging energy, charging capacity, discharging energy, and discharging capacity of the 55 lithium-ion batteries were obtained using an electrochemical workstation. The coulombic efficiency and the charge / discharge plateau voltage difference were calculated using Formulas 1 and 2, respectively.

[0128] Coulomb efficiency (%) = Discharge capacity (mA·h) / Charge capacity (mA·h) × 100% Formula 1

[0129] Platform voltage difference (V) = Charging energy (W·h) / Charging capacity (mA·h) - Discharging energy (W·h) / Discharging capacity (mA·h) Formula 2

[0130] Then, based on Formulas 3 and 4, determine whether lithium plating occurs at a certain set voltage, thereby determining the voltage at which lithium plating begins in the battery.

[0131] {Y coulomb efficiency - (Y+1) coulomb efficiency} / {(Y-1) coulomb efficiency - Y coulomb efficiency} > N Formula 3

[0132] {(Y+1) platform voltage difference) - Y platform voltage difference} / {Y platform voltage difference - (Y-1) platform voltage difference} > N Formula 4

[0133] In formulas 3 and 4, N is 5.

[0134] The coulombic efficiency results of the above 65 lithium-ion batteries are shown in Table 1.

[0135] Table 1:

[0136]

[0137]

[0138] The results of the plateau voltage difference for the above 65 lithium-ion batteries are shown in Table 2.

[0139] Table 2:

[0140]

[0141] Combining Tables 1 and 2, we can see that lithium plating occurs when charging at a 1C rate to 4.54V, so the lithium plating voltage is 4.54V. Therefore, the threshold voltage is determined to be 4.53V. Similarly, we can determine that the threshold voltage is 4.5V for 1.5C charging, 4.48V for 2C charging, 4.45V for 2.5C charging, and 4.43V for 3C charging.

[0142] Next, proceed with the following steps:

[0143] (6) Charge 10 lithium-ion batteries at a constant current of 1C to 4.53V, and then charge them at 4.53V to cutoff currents of 1C, 0.9C, 0.8C, 0.7C, 0.6C, 0.5C, 0.4C, 0.3C, 0.2C and 0.1C respectively.

[0144] (7) Charge 10 lithium-ion batteries at a constant current of 1.5C to 4.5V, and then charge them at 4.5V to cutoff currents of 1C, 0.9C, 0.8C, 0.7C, 0.6C, 0.5C, 0.4C, 0.3C, 0.2C and 0.1C respectively.

[0145] (8) Charge 10 lithium-ion batteries at a constant current of 2C to 4.48V, and then charge them at 4.48V to cutoff currents of 1C, 0.9C, 0.8C, 0.7C, 0.6C, 0.5C, 0.4C, 0.3C, 0.2C and 0.1C respectively.

[0146] (9) Charge 10 lithium-ion batteries at a constant current of 2.5C to 4.45V, and then charge them at 4.45V to cutoff currents of 1C, 0.9C, 0.8C, 0.7C, 0.6C, 0.5C, 0.4C, 0.3C, 0.2C and 0.1C respectively.

[0147] (10) Charge 10 lithium-ion batteries at a constant current of 3C to 4.43V, and then charge them at 4.43V to cutoff currents of 1C, 0.9C, 0.8C, 0.7C, 0.6C, 0.5C, 0.4C, 0.3C, 0.2C and 0.1C respectively.

[0148] After the lithium-ion batteries were charged in steps (6) to (9) above, they were left to stand for 30 minutes and then discharged at a constant current of 0.2C to 3V. The charging energy, charging capacity, discharging energy and discharging capacity of the above 50 lithium-ion batteries were obtained on the electrochemical workstation. The coulombic efficiency and the voltage difference between the charging and discharging plateaus were calculated according to formulas 1 and 2 respectively. Then, according to formulas 5 and 6, it was determined whether lithium plating occurred at a certain cutoff current, thereby determining the cutoff current at which lithium plating began in the battery cell.

[0149] {W coulomb efficiency - (W+1) coulomb efficiency} / {(W-1) coulomb efficiency - W coulomb efficiency} > N Formula 5

[0150] {(W+1) platform voltage difference) - W platform voltage difference} / {W platform voltage difference - (W-1) platform voltage difference} > N Formula 6

[0151] In formulas 5 and 6, N is 5.

[0152] The coulombic efficiency results of the above 50 lithium-ion batteries are shown in Table 3.

[0153] Table 3:

[0154]

[0155] The results of the plateau voltage difference of the above 50 lithium-ion batteries are shown in Table 4.

[0156] Table 4:

[0157]

[0158]

[0159] Combining Tables 3 and 4, it can be seen that lithium plating occurs when charging to 0.2C at a 1C rate and 4.53V. Therefore, the lithium plating cutoff current is 0.2C, and the threshold cutoff current is determined to be 0.3C. Similarly, it can be determined that the threshold cutoff current is 0.6C at 1.5C and 4.5V, 0.8C at 2C and 4.48V, 1C at 2.5C and 4.45V, and 1C at 3C and 4.43V.

[0160] By combining Tables 1 and 2, we can obtain the lithium plating situation of lithium-ion batteries under different cutoff voltages, and the results are shown in Table 5.

[0161] Table 5:

[0162]

[0163] By combining Tables 3 and 4, we can obtain the lithium deposition situation of lithium-ion batteries under different cutoff currents, and the results are shown in Table 6.

[0164] Table 6:

[0165]

[0166] In summary, the fast charging method for the lithium-ion battery is determined as follows: constant current charging at a 3C rate to 4.43V, then constant current charging at a 2.5C rate to 4.45V, constant current charging at a 2C rate to 4.48V, constant current charging at a 1.5C rate to 4.5V, constant current and constant voltage charging at a 1C rate to 4.53V, with a cutoff current of 0.3C.

[0167] Example 2

[0168] Five 3600mAh-406080 pouch batteries were charged in a 25℃ constant temperature chamber using the charging method determined in Example 1, and then discharged at 0.2C to 3V. This process was repeated 800 times.

[0169] Example 3

[0170] Five 3600mAh-406080 pouch batteries were charged to 4.43V at a constant current rate of 3C, to 4.48V at a constant current rate of 2C, and to 4.53V at a constant current rate of 1C in a 25℃ constant temperature chamber. The cutoff current was 0.3C, and then the batteries were discharged to 3V at 0.2C. This process was repeated 800 times.

[0171] Comparative Example

[0172] Comparative Example 1

[0173] Five 3600mAh-406080 pouch batteries were charged to 4.53V at a constant current of 3C in a 25℃ constant temperature chamber, with a cutoff current of 0.3C, and then discharged to 3V at 0.2C. This process was repeated 800 times.

[0174] Comparative Example 2

[0175] Five 3600mAh-406080 pouch batteries were charged to 4.53V at a constant current of 1C in a 25℃ constant temperature chamber, with a cutoff current of 0.3C, and then discharged to 3V at 0.2C. This process was repeated 800 times.

[0176] Experimental Example

[0177] Experimental Example 1

[0178] The capacity retention rate of the batteries in Examples 2-3 and Comparative Examples 1-2 after 800 cycles was calculated, and the average capacity retention rate of each example battery was recorded in Table 1.

[0179] Wherein, capacity retention rate (%) = discharge capacity (mAh) for the corresponding number of cycles / discharge capacity (mAh) for the third cycle x 100%

[0180]

[0181] The above results show that there are no significant differences in discharge capacity, initial coulombic efficiency, and charge / discharge plateau voltage difference between Examples 1-2 and Comparative Example 2. This is because the charging methods of Examples 1-2 and Comparative Example 2 do not involve lithium plating. However, the charging time of Comparative Example 2 is significantly longer than that of Examples 1 and 2. The charging time of Example 2 is slightly longer than that of Example 1. This is because Example 2 has fewer charging steps than Example 1. However, too many charging steps would make battery charging more troublesome. Therefore, multi-stage charging is generally set to 3 to 5 steps.

[0182] After 800 cycles at room temperature, there was no significant difference in capacity retention between Example 1 and Example 2. Comparative Example 2 was slightly better than Examples 1 and 2. This is because Comparative Example 2 has a smaller charging current and less battery polarization, resulting in slightly better cycle performance. The discharge capacity of Comparative Example 1 was significantly lower than that of Examples 1-2 and Comparative Example 2. This is because Comparative Example 1 was directly charged to the cutoff voltage at a high rate of 3C, which resulted in severe lithium plating, consuming the lithium source and causing irreversible capacity loss. At the same time, the capacity retention of Comparative Example 1 during room temperature cycling was significantly lower than that of Examples 1-2 and Comparative Example 2.

[0183] Experiment Example 2

[0184] The 65 lithium-ion battery cells after charging in steps (1) to (5) of Example 1 were disassembled, and the lithium deposition at the negative electrode interface of the cells was observed. The overall results are shown in Table 7.

[0185] Table 7:

[0186]

[0187] During the disassembly process, it was found that the method of using the electrochemical parameters described in Example 1 to determine lithium plating achieved an accuracy rate of 93.8%, and the determination of lithium plating was more stringent, effectively preventing lithium plating from occurring in the battery during fast charging.

[0188] Fifty lithium-ion battery cells were disassembled after charging was completed in steps (6) to (9) of Example 1. The lithium deposition at the negative electrode interface of the cells was observed and the overall results are shown in Table 8.

[0189] Table 8:

[0190]

[0191] During the disassembly process, it was found that using the electrochemical parameters described in Example 1 to determine lithium plating achieved an accuracy rate of 94%, and the determination of lithium plating was more stringent, effectively preventing lithium plating from occurring in the battery during fast charging.

[0192] The above experiments further verified the feasibility and reliability of the fast charging method for lithium-ion batteries described in this invention.

[0193] The present invention has been described in detail above with reference to preferred embodiments and exemplary examples. However, it should be noted that these specific embodiments are merely illustrative explanations of the invention and do not constitute any limitation on the scope of protection of the invention. Various improvements, equivalent substitutions, or modifications can be made to the technical content and embodiments of the present invention without departing from the spirit and scope of protection of the invention, and all such modifications fall within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for fast charging a lithium-ion battery, characterized in that, The method includes: charging the lithium-ion battery in stages using constant current charging to the upper limit voltage, and then charging it to the final current using constant current and constant voltage charging to complete the charging; the stages are 1 to 7. The upper limit voltage is the threshold voltage at which lithium plating does not occur when charging with the current of the last constant current charging stage, and the final current is the threshold cutoff current at which lithium plating does not occur when charging with the current and voltage of the last stage. The threshold cutoff current and the threshold voltage during the constant current charging stage are obtained through a non-destructive lithium plating detection method. The steps of obtaining the threshold voltage using the non-destructive lithium plating detection method include: Step 1: Charge multiple lithium-ion batteries to different set voltages at the same constant current rate, then change the constant current charging rate and charge multiple lithium-ion batteries to different set voltages at the changed constant current rate. Step 2: Let the battery that has finished charging in Step 1 rest for 10 to 100 minutes, and then discharge it at the same constant current rate until the discharge termination voltage is 2.5V to 3V. Step 3, Determining the threshold voltage; Step 3 includes the following steps: Step 3-1: Obtain the battery charging energy, charging capacity, discharging energy, and discharging capacity; Step 3-2: Calculate the coulombic efficiency and the charge / discharge plateau voltage difference; Step 3-3: Determine the voltage at which lithium plating begins in the battery, and then determine the threshold voltage; The steps for obtaining the threshold cutoff current using a non-destructive lithium plating detection method include: Step 1': First, charge multiple lithium-ion batteries at the same constant current rate to the threshold voltage, and then charge them to the set cutoff current at the threshold voltage; then change the constant current charging rate, charge multiple lithium-ion batteries at the changed constant current rate to the aforementioned threshold voltage, and then charge them to the set cutoff current at the threshold voltage. Step 2': After charging in Step 1', let the battery rest for 10 to 100 minutes, then discharge it at the same constant current rate until the discharge termination voltage is 2.5V to 3V. Step 3', Determination of the threshold cutoff current; Step 3' includes the following steps: Step 3'-1: Obtain the battery charging energy, charging capacity, discharging energy, and discharging capacity; Step 3'-2: Calculate the coulombic efficiency and the voltage difference between the charge and discharge plateaus; Step 3'-3: Determine the cutoff current at which lithium plating begins in the battery cell, and then determine the threshold cutoff current.

2. The method according to claim 1, characterized in that, The rate of constant current charging in the later stage is smaller than that in the previous stage, and the voltage reached in the later stage is larger than that in the previous stage.

3. The method according to claim 2, characterized in that, The rate of constant current charging in the later stage is lower than that in the previous stage by x1C, where x1 ranges from 0.1 to 1. Each stage of constant current charging is performed until the voltage value is not greater than the threshold voltage under the corresponding constant current charging conditions to prevent lithium plating.

4. The method according to claim 1, characterized in that, The rate of constant current charging in the first stage is between 1 and 10C.

5. The method according to claim 3, characterized in that, The value of x1 ranges from 0.4 to 0.

6.

6. The method according to claim 4, characterized in that, The rate of the first stage of constant current charging is between 1 and 6C.

Images