A method for low-temperature charging of lithium-ion batteries

Abstract

This invention relates to a low-temperature charging method for lithium-ion batteries. The method includes acquiring constant-capacity data of the battery measured at room temperature, where n1, n2, and n3 represent the charging capacities corresponding to 25–35% SOC, 45–55% SOC, and 75–85% SOC, respectively, and aV, bV, and cV represent the corresponding voltages; preparing for charging at low temperature; charging to aV at a first-rate constant current, recording the capacity m1; determining whether the condition n1 / m1 ≥ 65% is met; if not, maintaining a constant voltage to 0.08–0.12C; if the condition is met, charging to bV at a second-rate constant current, recording the capacity m2; determining whether n2 / m2 ≥ 65% is met; if not, maintaining a constant voltage to 0.03–0.07C; if the condition is met, charging to cV at a rate of 0.33C, recording the capacity m3; determining whether n3 / m3 ≥ 65% is met; if not, maintaining a constant voltage to 0.08–0.12C; if the condition is met, charging at a third-rate constant current. This invention can improve charging capacity and charging efficiency, and improve or prevent lithium plating.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a method for low-temperature charging of lithium-ion batteries. Background Technology

[0002] With the promotion and popularization of electric vehicles, a typical problem faced by power lithium-ion batteries is the sharp reduction in driving range in winter. Lithium batteries experience capacity decay and lithium plating in low-temperature environments, making them impossible to charge at low temperatures. Companies are using low currents to charge the batteries at low temperatures, but this results in very long charging times.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for low-temperature charging of lithium-ion batteries.

[0005] In a first aspect, the present invention provides a low-temperature charging method for lithium-ion batteries, comprising the following steps: acquiring constant-capacity data of the battery measured at room temperature, where n1, n2, and n3 are the charging capacities corresponding to 25-35% SOC, 45-55% SOC, and 75-85% SOC, respectively, and aV, bV, and cV are the corresponding voltages; preparing for charging at low temperature; charging to aV at a constant current of a first rate, recording the capacity m1, and determining whether the condition n1 / m1≥65% is met. If the condition is not met, the voltage is kept constant to 0.08–0.12C. If the condition is met, the battery is charged at a second-rate constant current to bV, and the capacity m2 is recorded. The condition n2 / m2 ≥ 65% is then checked. If not, the voltage is kept constant to 0.03–0.07C. If the condition is met, the battery is charged at a rate of 0.33C to cV, and the capacity m3 is recorded. The condition n3 / m3 ≥ 65% is then checked. If not, the voltage is kept constant to 0.08–0.12C. If the condition is met, the battery is charged at a third-rate constant current. This invention proposes a low-temperature charging method for lithium-ion batteries that can improve charging capacity and avoid lithium plating by changing the charging method.

[0006] According to the present invention, the first rate is 0.8–1.2C; the second rate is 0.4–0.6C; and the third rate is 0.4–0.6C. The present invention, by employing the charging method described above and optimizing the constant current charging rate, effectively improves charging capacity and avoids lithium plating through a specific rate-coordinated charging mode from the first rate to the third rate.

[0007] The preferred method of this invention can significantly improve the low-temperature charging effect of lithium-ion batteries, further increase the charging capacity, and prevent lithium plating.

[0008] Preferably, the low-temperature charging method for lithium-ion batteries includes the following steps:

[0009] 1) Obtain the constant capacity data of the battery measured at room temperature. n1, n2, and n3 are the charging capacities corresponding to 25-35% SOC, 45-55% SOC, and 75-85% SOC, respectively. aV, bV, and cV are the voltages corresponding to the charging capacities corresponding to 25-35% SOC, 45-55% SOC, and 75-85% SOC, respectively.

[0010] 2) Discharge the battery and prepare it for charging under low temperature conditions;

[0011] 3) Charge the battery to aV at a constant current rate of 0.8 to 1.2C, record the capacity m1, and check if the condition m1 / n1≥65% is met. If not, charge the battery to 0.1C at a constant voltage. If the condition is met, continue to the next step.

[0012] 4) Charge the battery to bV at a constant current rate of 0.4 to 0.6C, record the capacity m2, and check if the condition m2 / n2 ≥ 65% is met. If not, charge the battery to 0.05C at a constant voltage. If the condition is met, continue to the next step.

[0013] 5) Charge the battery to cV at a constant current rate of 0.3 to 0.35C, record the capacity m3, and check if the condition m3 / n3 ≥ 65% is met. If not, charge the battery to 0.01C at a constant voltage. If the condition is met, continue to the next step.

[0014] 6) Charge at a constant current and constant voltage rate of 0.4 to 0.6C to 3.55 to 3.6V, with a cutoff current of 0.04 to 0.06C.

[0015] Further optimization, in step 1), the battery is charged and discharged at 0.5C for 3 weeks at room temperature, and 30% SOC of the average charging capacity over 3 weeks is taken as n1Ah, 50% SOC as n2Ah, and 80% SOC as n3Ah, and the average voltage aV, bV, and cV corresponding to the charging capacity over 3 weeks are taken.

[0016] Further optimization involves discharging the battery at room temperature in step 2) with a constant current discharge of 0.5C to 2.0V; then placing it in low-temperature conditions and letting it stand for at least 10 hours to observe whether the temperature reaches the target low-temperature value.

[0017] Further optimization, in step 3), a constant current of 1C is used to charge the battery to aV. During the charging process, the capacity of aV is recorded as m1. If the capacity of m1 meets the condition that m1 / n1≥70%, the battery is charged to 0.1C under constant voltage. If the condition is met, the next step is performed.

[0018] Further optimization, in step 4), a constant current of 0.5C is used to charge the battery to bV. During the charging process, the capacity of bV is recorded as m2. If the capacity of m2 meets the condition that m2 / n2≥70%, the battery is charged to 0.05C under constant voltage. If the condition is met, the next step is performed.

[0019] Further optimization, in step 5), a constant current of 0.33C is used to charge the battery to cV. During the charging process, the capacity of cV is recorded as m3. If the capacity of m3 meets the condition that m3 / n3≥70%, the battery is charged to 0.05C under constant voltage. If the condition is met, the next step is performed.

[0020] Further optimization, in step 6), the voltage is constant-current and constant-voltage charged at a rate of 0.5C to 3.6V, and the cutoff current is 0.05C.

[0021] In this invention, by optimizing the charging process and parameter range under low temperature conditions, the charging capacity of the battery cell under low temperature conditions can be further improved, lithium plating is eliminated, charging efficiency is improved, and the performance of the battery cell can be significantly improved under low temperature conditions.

[0022] Preferably, the temperature for low-temperature charging of the battery is -10 to -40°C.

[0023] Secondly, the present invention provides a system for low-temperature charging of lithium-ion batteries, wherein the system employs the aforementioned low-temperature charging method for lithium-ion batteries.

[0024] The beneficial effects of the present invention are at least as follows: The low-temperature charging method for lithium-ion batteries proposed in this invention improves charging capacity and charging efficiency by changing the charging process, and improves or avoids lithium plating. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0026] It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0027] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0028] Unless otherwise specified, all methods used in the examples were conventional or performed according to techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents and instruments used without specified manufacturers were all conventional products that could be purchased from legitimate channels.

[0029] In some specific embodiments provided by this invention, the following steps are included:

[0030] S1. The battery is charged and discharged at 0.5C for 3 weeks at room temperature, with capacities of C1, C2, and C3; the corresponding voltages are V1, V2, and V3, respectively. The average charging capacity of the 3 weeks, C0 = (C1 + C2 + C3) / 3, is taken as n1Ah at 30%, n2Ah at 50%, and n3Ah at 80%. The average voltage of the charging capacity (30%, 50%, and 80%) over the 3 weeks, V0 = (V1 + V2 + V3) / 3, is taken as aV, bV, and cV, respectively.

[0031] S2, discharge the battery at room temperature using a constant current of 0.5C to discharge it to 2.0V. Place it in a low-temperature oven and let it stand in the oven for at least 10 hours, observing whether the temperature reaches the target low temperature value.

[0032] S3, use a constant current of 1C to charge the battery to aV. During the charging process, record the capacity of aV as m1. If this capacity satisfies m1 / n1≥70%, proceed to step S4. If not, charge the battery to 0.1C using a constant voltage.

[0033] S4. Use a constant current of 0.5C to charge the battery to bV. Record the capacity of bV as m2 during the charging process. If this capacity satisfies m2 / n2≥70%, proceed to step S5. If not, charge the battery to 0.05C using a constant voltage.

[0034] S5, use a constant current of 0.33C to charge to cV. During the charging process, record the capacity of cV as m3. If this capacity satisfies m3 / n3≥70%, proceed to step S6. If not, charge the battery to 0.05C using a constant voltage.

[0035] S6, 0.5C rate constant current constant voltage charging to 3.6V cutoff current is 0.05C.

[0036] In the following examples, a 15Ah lithium iron phosphate cell (the positive electrode material is lithium iron phosphate, the negative electrode material is artificial graphite, the positive and negative electrode conductive adhesives are acetylene black, the positive electrode binder is PVDF, and the negative electrode binders are CMC and SBR) was used as the experimental object, and the experiment was conducted at -20℃.

[0037] Example 1

[0038] The low-temperature charging method for lithium-ion batteries provided in this embodiment includes the following steps:

[0039] Step 1: Discharge the battery at room temperature using a constant current of 7.5A until the cutoff voltage reaches 2V. Then charge it using a constant current and constant voltage of 7.5A, with a cutoff voltage of 3.6V and a cutoff current of 0.75A. Cycle for 3 cycles. Record the voltage values ​​corresponding to 30% SOC, 50% SOC, and 80% SOC after three cycles. The resulting 30%, 50%, and 80% SOC values ​​are then used to calculate the corresponding voltage values. The %SOC charging capacity and corresponding voltage are calculated using average values ​​C0 = (C1 + C2 + C3) and V0 = (V1 + V2 + V3). The average voltage for 30% SOC is 4.675 Ah, for 50% SOC it is 7.792 Ah, and for 80% SOC it is 12.466 Ah. The average voltage for the charging capacity over 3 weeks is calculated as V0 = (V1 + V2 + V3) / 3, which are 3.344V, 3.357V, and 3.395V, respectively.

[0040] Step 2: Discharge the battery at room temperature using a constant current of 7.5A to discharge it to 2.0V. Place it in a low-temperature oven set to -20℃, attach a temperature sensing wire to the surface of the battery cell, and let it stand in the low-temperature oven for at least 10 hours. Observe whether the surface temperature of the battery cell reaches the target low temperature value of -20℃.

[0041] Step 3: Use a constant current of 15A (1C) to charge to 3.344V. During the charging process, record the capacity at 3.344V as 2.310Ah. If this capacity meets the requirement of 2.310 / 4.675 = 49%, and cannot meet the requirement of m1 / n1 ≥ 70%, continue charging at 3.344V constant voltage. The cutoff current is 0.47A (0.1C).

[0042] Step 4: Use a constant current of 7.5A (0.5C) to charge to 3.357V. During the charging process, record the capacity at 3.357V as 5.58Ah. Check if this capacity satisfies 5.58 / 7.792 = 71%. If the condition is met, m2 / n2 ≥ 70%, continue to step S5.

[0043] Step 5: Use a constant current of 4.5A (0.33C) to charge to 3.395V. During the charging process, record the capacity at 3.395V as 9.04. Check if this capacity satisfies 9.04 / 12.466 = 73% and satisfies m3 / n3 ≥ 70%. Continue to step S6.

[0044] Step 6: Charge at a constant current and constant voltage rate of 0.5C until the cutoff current is 0.05C at 3.6V.

[0045] Comparative Example 1

[0046] The same battery cell as in Example 1 was selected as the experimental subject. After being placed in a low-temperature -20°C oven, it was charged to 3.6V using the conventional 7.5A constant current and constant voltage method, with a cutoff current of 0.75A.

[0047] Example 2

[0048] The low-temperature charging method for lithium-ion batteries provided in this embodiment includes the following steps:

[0049] Step 1: Discharge the battery at room temperature using a constant current of 7.5A until the cutoff voltage reaches 2V. Then charge it using a constant current and constant voltage of 7.5A, with a cutoff voltage of 3.6V and a cutoff current of 0.75A. Cycle for 3 cycles. Record the voltage values ​​corresponding to 30% SOC, 50% SOC, and 80% SOC after three cycles. The resulting 30%, 50%, and 80% SOC values ​​are then used to calculate the corresponding voltage values. The %SOC charging capacity and corresponding voltage are calculated using average values ​​C0 = (C1 + C2 + C3) and V0 = (V1 + V2 + V3). The average voltage for 30% SOC is 4.675 Ah, for 50% SOC it is 7.792 Ah, and for 80% SOC it is 12.466 Ah. The average voltage for the charging capacity over 3 weeks is calculated as V0 = (V1 + V2 + V3) / 3, which are 3.344V, 3.357V, and 3.395V, respectively.

[0050] Step 2: Discharge the battery at room temperature using a constant current of 7.5A to discharge it to 2.0V. Place it in a low-temperature oven set to -20℃, attach a temperature sensing wire to the surface of the battery cell, and let it stand in the low-temperature oven for at least 10 hours. Observe whether the surface temperature of the battery cell reaches the target low temperature value of -20℃.

[0051] Step 3: Use a constant current of 15A (1C) to charge to 3.344V. During the charging process, record the capacity at 3.344V as 2.310Ah. If this capacity meets the requirement of 2.310 / 4.675 = 49%, and cannot meet the requirement of m1 / n1 ≥ 70%, continue charging at 3.344V constant voltage. The cutoff current is 0.47A (0.1C).

[0052] Step 4: Use a constant current of 15A (0.5C) to charge to 3.357V. During the charging process, record the capacity at 3.357V as 5.58Ah. Check if this capacity meets the condition 4.4 / 7.792 = 71%. If the condition is not met, m2 / n2 ≥ 70%. Continue charging at 3.357V constant voltage, with a cutoff current of 0.78A (0.1C).

[0053] Step 5: Use a constant current of 7.5A (0.33C) to charge to 3.395V. During the charging process, record the capacity at 3.395V as 9.04. Check if this capacity meets the condition 8.04 / 12.466 = 64%. If the condition is not met, m3 / n3 ≥ 70%. Continue charging at 3.357V constant voltage with a cutoff current of 1.25A (0.1C).

[0054] Step 6: Charge at a constant current and constant voltage rate of 0.5C until the cutoff current is 0.05C at 3.6V.

[0055] Comparative Example 2

[0056] The same battery cell as in Example 1 was selected as the experimental subject. After being placed in a low-temperature -20°C oven, it was charged to 3.6V using the conventional 15A constant current and constant voltage method, with a cutoff current of 0.75A.

[0057] Table 1. Comparison of low-temperature charging results of batteries obtained in Examples 1-2 and Comparative Examples 1-2

[0058] Constant volume capacity at normal temperature Low temperature charging capacity Lithium plating Example 1 15.547Ah 11.660Ah none Comparative Example 1 15.542Ah 9.325Ah have Example 2 15.549Ah 11.038Ah none Comparative Example 2 15.541Ah 4.662Ah have

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for low-temperature charging of a lithium-ion battery, characterized in that, include: Obtain the constant-capacity data of the battery measured at room temperature. n1, n2, and n3 represent the charging capacities corresponding to 25~35% SOC, 45~55% SOC, and 75~85% SOC, respectively, and aV, bV, and cV represent the corresponding voltages. Prepare for charging at low temperature. Charge to aV at a constant current rate of the first factor and record the capacity m1. Determine if the condition m1 / n1 ≥ 65% is met. If not, maintain a constant voltage to 0.08~0.12C and continue charging at a constant current rate of the second factor to bV, recording the capacity m2. If the condition is met... The device is charged to bV at a constant current rate of the second multiplier, and the capacity m2 is recorded. It is then determined whether the condition m2 / n2≥65% is met. If not, the device is charged to a constant voltage of 0.03~0.07C and then charged to cV at a constant current rate of 0.33C. The capacity m3 is recorded. If the condition is met, the device is charged to cV at a constant current rate of 0.33C and the capacity m3 is recorded. It is then determined whether the condition m3 / n3≥65% is met. If not, the device is charged to a constant voltage of 0.08~0.12C and then charged to a constant current rate of the third multiplier. If the condition is met, the device is charged to a constant current rate of the third multiplier.

2. The low-temperature charging method for lithium-ion batteries according to claim 1, characterized in that, The first multiplier is 0.8~1.2C; the second multiplier is 0.4~0.6C; and the third multiplier is 0.4~0.6C.

3. The low-temperature charging method for lithium-ion batteries according to claim 2, characterized in that, Includes the following steps: 1) Obtain the constant capacity data of the battery measured at room temperature. n1, n2, and n3 are the charging capacities corresponding to 25~35% SOC, 45~55% SOC, and 75~85% SOC, respectively. aV, bV, and cV are the voltages corresponding to the charging capacities corresponding to 25~35% SOC, 45~55% SOC, and 75~85% SOC, respectively. 2) Discharge the battery and prepare it for charging under low temperature conditions; 3) Charge the battery to aV at a constant current rate of 0.8~1.2C, record the capacity m1, and check if the condition m1 / n1≥65% is met. If not, charge the battery to 0.1C at a constant voltage rate. If the condition is met, continue to the next step. 4) Charge the battery to bV at a constant current rate of 0.4~0.6C, record the capacity m2, and check if the condition m2 / n2≥65% is met. If not, charge the battery to 0.05C at a constant voltage. If the condition is met, continue to the next step. 5) Charge the battery to cV at a constant current rate of 0.33C, record the capacity m3, and check if the condition m3 / n3≥65% is met. If not, charge the battery to 0.01C at a constant voltage. If the condition is met, continue to the next step. 6) Charge at a constant current and constant voltage rate of 0.4~0.6C to 3.55~3.6V, with a cutoff current of 0.04~0.06C.

4. The low-temperature charging method for lithium-ion batteries according to claim 3, characterized in that, In step 1), the battery is charged and discharged at 0.5C for 3 weeks at room temperature. The average SOC of the charging capacity over the 3 weeks is taken as n1Ah, 50% as n2Ah, and 80% as n3Ah. The average voltage aV, bV, and cV corresponding to the charging capacity over the 3 weeks are taken.

5. The low-temperature charging method for lithium-ion batteries according to claim 3, characterized in that, In step 2), the battery is discharged at room temperature with a constant current of 0.5C to 2.0V; then it is placed in a low-temperature condition and left to stand for at least 10 hours to observe whether the temperature reaches the target low-temperature value.

6. The low-temperature charging method for lithium-ion batteries according to any one of claims 2-5, characterized in that, In step 3), a constant current of 1C is used to charge the battery to aV. During the charging process, the capacity of aV is recorded as m1. If the capacity of m1 meets the condition that m1 / n1≥70%, the battery is charged to 0.1C under constant voltage. If the condition is met, the next step is performed.

7. The low-temperature charging method for lithium-ion batteries according to any one of claims 2-5, characterized in that, In step 4), a constant current of 0.5C is used to charge the battery to bV. During the charging process, the capacity of bV is recorded as m2. If the capacity of m2 meets the condition that m2 / n2≥70%, the battery is charged to 0.05C using a constant voltage. If the condition is met, the next step is performed.

8. The low-temperature charging method for lithium-ion batteries according to any one of claims 2-5, characterized in that, In step 5), a constant current of 0.33C is used to charge the battery to cV. During the charging process, the capacity of cV is recorded as m3. If the capacity of m3 meets the condition that m3 / n3≥70%, the battery is charged to 0.05C under constant voltage. If the condition is met, the next step is performed.

9. The low-temperature charging method for lithium-ion batteries according to any one of claims 2-5, characterized in that, In step 6), the battery is charged to 3.6V at a constant current and constant voltage rate of 0.5C, with a cutoff current of 0.05C.

10. The method for low-temperature charging of a lithium-ion battery according to any one of claims 1-5, characterized in that, The battery can be charged at temperatures ranging from -10°C to -40°C.

11. A system for low-temperature charging of lithium-ion batteries, characterized in that, The system employs the low-temperature charging method for lithium-ion batteries as described in any one of claims 1-10.