Rapid charging method of graphite-based lithium battery

Abstract

The invention discloses a rapid charging method of a graphite-based lithium battery, and belongs to the technical field of lithium batteries, and the method comprises the following steps: setting high-rate current I constant charging, charging to a first-stage charging cut-off capacity Q1, then carrying out first shelving for t1 (0 < t1 < = 2min), starting second-stage charging after the first shelving is completed, and starting second-stage charging after the second-stage charging is completed; the method comprises the following steps: charging at a first stage until the cut-off capacity is Qn, charging at a constant current I until the cut-off capacity is Q2, then carrying out second shelving for t2 (0 < t2 < = 2min), after the second shelving is completed, starting third-stage charging, and so on until the nth full charge, charging at a constant current I until the cut-off capacity is Qn, and carrying out nth shelving for tn (0 < tn < = 2min). The method is simple and convenient to operate, metal lithium on the surface of graphite is subjected to self-lithiation behavior through shelving, lithium precipitation under the fast charging condition can be better regulated and controlled, the fast charging capacity of the battery is improved, the cycle life of the battery is prolonged, and the safety of the battery is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium batteries, and in particular relates to a fast charging method for a graphite-based lithium battery. Background Art

[0002] Since the commercialization of lithium-ion batteries, researchers have developed a variety of positive electrode materials such as lithium cobalt oxide, lithium iron phosphate, and ternary nickel cobalt manganese, while the negative electrode is still mainly graphite. With the rapid development of electric devices, the demand for fast-charging secondary battery technology in modern society is becoming more and more urgent. Therefore, the development of high-performance graphite negative electrodes is the key to further improving the fast-charging performance of lithium-ion batteries.

[0003] However, graphite is also widely considered to be the culprit that hinders the fast charging of lithium batteries. Under high rate (>3C) or low temperature (<0℃) charging conditions, high loading graphite anode (>3mAh / cm 2 ) Due to its low electrochemical potential (80-200mVvs.Li+ / Li) and slow lithium insertion kinetics, it is easy to cause metallic lithium to precipitate on the surface, accelerate capacity decay and reduce cycle life. At the same time, as lithium dendrites grow, lithium dendrites may penetrate the diaphragm, causing battery short circuit, thermal runaway and even battery explosion. Therefore, it is of great significance to develop safe and stable graphite fast charging technology.

[0004] In order to solve the above challenges, the traditional fast charging strategy of researchers is to improve the fast lithium storage performance of graphite negative electrode without lithium precipitation, such as interface coating, structural design, electrolyte modification, etc. However, based on the research of stable lithium precipitation and self-lithiation regulation mechanism, new fast lithiation strategy and charging scheme of graphite negative electrode are rarely involved. Summary of the invention

[0005] The purpose of the embodiments of the present invention is to provide a method for fast charging of a graphite-based lithium battery, which has a simple structure and is easy to use, and can better improve the above-mentioned problems.

[0006] The embodiment of the present invention is achieved as follows:

[0007] The embodiment of the present invention provides a fast charging method for a graphite-based lithium battery, wherein a high-rate current I is set to be constantly charged, and the battery is charged to a first-stage charging cutoff capacity Q1, and then the first standby is performed, and the standby time is t1, wherein 0<t1≤2min. After the first standby is completed, the second-stage charging is started, and the battery is charged to a cutoff capacity of Q2 with a constant current I, and then the second standby is performed, and the standby time is t2, wherein 0<t2≤2min. After the second standby is completed, the third-stage charging is started, and so on, until the nth full charge, the battery is charged to a cutoff capacity of Q with a constant current I. n , the nth suspension, the suspension time is t n, where 0<t n ≤2min, where Q1, Q2...Q n To approach Q / n, the capacity is reasonably set and meets: and Wherein, x is an integer, and 1≤x≤n.

[0008] Furthermore, the constant current charging rate is 3C-20C.

[0009] Furthermore, the total charging time is less than 20 minutes.

[0010] Furthermore, the number of charging times n is not less than 2 times.

[0011] Furthermore, the number of charging times is determined as follows: first, the battery is charged at a constant current and constant rate, and the negative electrode potential information of the battery is detected in real time. When the potential is lower than 0V, the charged capacity is Q0, and n is the integer closest to Q / Q0.

[0012] Furthermore, the graphite negative electrode potential information is detected in real time. When the negative electrode potential recovery fails to reach 0.05V after being left alone, the number of charging times should be increased.

[0013] The beneficial effects of the present invention are:

[0014] The fast charging method of a graphite-based lithium battery provided in an embodiment of the present invention is simple and convenient to operate. It relies on the self-lithiation of graphite during the shelving process after stable lithium precipitation to improve the lithiation degree of graphite and reduce the amount of lithium loss. When a small amount of metallic lithium is deposited on the surface of graphite, it will spontaneously re-embed between graphite layers under the action of electrochemical driving force. Therefore, when a large current is charged to the negative electrode potential below 0V, lithium precipitation will occur on the surface. At this time, shelving allows the metallic lithium on the surface of the graphite to undergo self-lithiation, which can better regulate the lithium precipitation under fast charging conditions and improve the fast charging capability, cycle life and safety of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 The time-voltage diagram of the charging process of Example 1 and Comparative Example 1;

[0017] Figure 2 The time-voltage diagram of the charging process of Example 2 and Comparative Example 2;

[0018] Figure 3The charge capacity voltage diagrams of Example 2 and Comparative Example 2;

[0019] Figure 4 The time-voltage diagram of the charging process of Example 3 and Comparative Example 3;

[0020] Figure 5 The charging cycle capacity retention diagram of Example 3 and Comparative Example 3. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0022] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed but is merely representative of selected embodiments of the present invention.

[0023] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0024] The embodiment of the present invention provides a method for fast charging of a graphite-based lithium battery, and the specific process is as follows:

[0025] Set a high rate current I to charge constantly, charge to the first stage charging cut-off capacity Q1, then perform the first hold, the hold time is t1, where 0<t1≤2min, after the first hold is completed, start the second stage charging, charge to the cut-off capacity Q2 with a constant current I, then perform the second hold, the hold time is t2, where 0<t2≤2min, after the second hold is completed, start the third stage charging, and so on, until the nth full charge, charge to the cut-off capacity Q with a constant current I n , the nth suspension, the suspension time is t n , where 0<t n ≤2min, where Q1, Q2...Q n To be an integer close to Q / n, reasonably set each cutoff capacity and satisfy: and Wherein, x is an integer, and 1≤x≤n.

[0026] The constant current charging rate is generally set to 3C-20C, which is determined according to actual conditions.

[0027] The number of charging times is determined as follows: first, the battery is charged with a constant current and constant rate, and the negative electrode potential information of the battery is detected in real time. When the potential is lower than 0V and the charged capacity is Q0, n can be determined as the integer closest to Q / Q0. The number of charging times n is not less than 2 times.

[0028] It should be noted that the graphite negative electrode potential information should be detected in real time. When the negative electrode potential fails to recover to 0.05V after being left alone, the number of charging times should be increased. First increase it by 1 time. If it does not meet the conditions, increase it by 1 time, and so on, to ensure that the relevant parameters meet the requirements.

[0029] The total charging time using this method is less than 20 minutes.

[0030] Example 1

[0031] The theoretical capacity Q of the graphite pole piece is equal to the mass of the negative electrode active material and the theoretical specific capacity deposition of graphite. After calculation, Q = 0.558mAh, and the number of indirect charges is set to 5 times. Set the cut-off capacity of each stage to 1 / 5 of the theoretical capacity of the graphite pole piece, that is, 0.112mAh, to ensure that the graphite pole piece is completely embedded with lithium after 5 intermittent charges. Set the current rate to 10C for charging, stop at the cut-off capacity, and then leave it for 1 minute;

[0032] Then charge at 10C until the cut-off capacity is reached, and then leave for 1 minute. Repeat this cycle for 5 charges and 5 rests in total. Then perform the following tests:

[0033] (1) Voltage recovery phenomenon: After the charging process is completed, the self-lithiation behavior of graphite can be judged by the time-voltage curve (reference Figure 1 shown).

[0034] (2) Battery specific capacity test: The battery is discharged with a constant current of 1C and the cut-off voltage is 1.5V to complete the test. The specific capacity of the battery at 1.5V is recorded.

[0035] (3) Battery cycle performance test: The battery was discharged with a constant current of 1C and the cut-off voltage was 1.5V to complete the test. The above charge and discharge process was cycled 500 times.

[0036] Example 2

[0037] The theoretical capacity Q of the graphite pole piece is equal to the mass of the negative electrode active material and the theoretical specific capacity deposition of graphite. After calculation, Q = 0.558mAh, and the number of indirect charging is set to 5. Set the cut-off capacity of each stage to 1 / 5 of the theoretical capacity of the graphite pole piece, that is, 0.112mAh, to ensure that the graphite pole piece is completely lithium-intercalated after 5 intermittent charges. Set the current rate to 8C for charging, stop at the cut-off capacity, and then leave it for 1 minute;

[0038] Then charge at 8C until the cut-off capacity is reached, and then leave for 1 minute. Repeat this cycle for 5 charges and 5 rests in total. Then perform the following tests:

[0039] (1) Voltage recovery phenomenon: After the charging process is completed, the self-lithiation behavior of graphite can be judged by the time-voltage curve. (Ref. Figure 2 (shown)

[0040] (2) Battery specific capacity test: The battery is discharged with a constant current of 1C and the cut-off voltage is 1.5V to complete the test. The specific capacity of the battery at 1.5V is recorded.

[0041] (3) Battery cycle performance test: The battery was discharged with a constant current of 1C and the cut-off voltage was 1.5V to complete the test. The above charge and discharge process was cycled 500 times.

[0042] Example 3

[0043] The theoretical capacity Q of the graphite pole piece is equal to the mass of the negative electrode active material and the theoretical specific capacity deposition of graphite. After calculation, Q = 0.550mAh, and the number of indirect charging is set to 5. Set the cut-off capacity of each stage to 1 / 5 of the theoretical capacity of the graphite pole piece, that is, 0.110mAh, to ensure that the graphite pole piece is completely lithium-intercalated after 5 intermittent charges. Set the current rate to 12C for charging, stop at the cut-off capacity, and then leave it for 1 minute;

[0044] Then charge at 12C until the cut-off capacity is reached, and then leave for 1 minute. Repeat this cycle for 5 charges and 5 rests in total. Then perform the following tests:

[0045] (1) Voltage recovery phenomenon: After the charging process is completed, the self-lithiation behavior of graphite can be judged by the time-voltage curve. (Ref. Figure 4 (shown)

[0046] (2) Battery specific capacity test: The battery is discharged with a constant current of 1C and the cut-off voltage is 1.5V to complete the test. The specific capacity of the battery at 1.5V is recorded.

[0047] (3) Battery cycle performance test: The battery was discharged with a constant current of 1C and the cut-off voltage was 1.5V to complete the test. The above charge and discharge process was cycled 500 times.

[0048] Comparative Example 1

[0049] This comparative example is a one-time charge, and the charging process is not suspended. Specifically, the theoretical capacity Q of the graphite pole piece is equal to the mass of the active material of the graphite pole piece and the theoretical specific capacity of graphite deposition. After calculation, Q = 0.558mAh, set the current rate to 6C for charging, 0.01V cutoff, discharge the battery with a constant current of 1C, and complete the test with a cutoff voltage of 1.5V, and record the specific capacity of the battery at a voltage of 1.5V. Cycle the above charge and discharge process 500 times.

[0050] Comparative Example 2

[0051] This comparative example is a one-time charge, and the charging process is not suspended. The theoretical capacity Q of the graphite pole piece is equal to the mass of the active material of the graphite pole piece and the theoretical specific capacity of graphite deposition. After calculation, Q = 0.558mAh, set the current rate to 6C for charging, and place it for 5 minutes after each charge and discharge. The cut-off voltage is 0.01V, and the battery is discharged with a constant current of 1C. The cut-off voltage is 1.5V to complete the test, and the specific capacity of the battery at 1.5V is recorded. The above charge and discharge process is cycled 500 times.

[0052] Comparative Example 3

[0053] This comparative example is a one-time charge, and the charging process is not suspended. The theoretical capacity Q of the graphite pole piece is equal to the mass of the active material of the graphite pole piece and the theoretical specific capacity of graphite deposition. After calculation, Q = 0.558mAh, set the current rate to 5C for charging, charge to the theoretical capacity of 0.558mAh, then put it aside for 1min, and then discharge the battery with a constant current of 1C, and the cut-off voltage is 1.5V to complete the test, and record the specific capacity of the battery at 1.5V. Cycle the above charge and discharge process 500 times.

[0054] in conclusion

[0055] Figure 1 The time-voltage specific capacity diagram of Example 1 and Comparative Example 1. As can be seen from the figure, when charging is performed in the manner of Example 1, the potential rises significantly during each standby process, and the voltage can be stably restored to above 0V after being stood by, which is higher than the lithium deposition potential. When charging is performed in the manner of Comparative Example 1, the potential is maintained above 0V. This indicates that self-lithiation behavior of graphite occurs.

[0056] Figure 2 The time-voltage capacity diagram of Example 2 and Comparative Example 2. As can be seen from the figure, when charging is performed in the manner of Example 2, the potential rises significantly during each standby process, and the voltage can be stably restored to above 0V after being stood by, which is higher than the lithium deposition potential. When charging is performed in the manner of Comparative Example 2, the potential is maintained above 0V. This indicates that self-lithiation behavior of graphite occurs. Figure 3The specific capacity voltage diagrams of Example 2 and Comparative Example 2 show that when charged to 1.5V using the method of Example 2, the specific charge capacity reaches 345mAh / g, which is close to the theoretical specific capacity of graphite, while when charged to 1.5V using the method of Comparative Example 2, the charge ratio is only 262.5mAh / g, and the capacity retention rate is much lower than that of the optimization scheme. This indicates that shelving during fast charging is conducive to the self-lithiation behavior of graphite, which is conducive to the retention of battery capacity.

[0057] Figure 4 The time-voltage specific capacity diagram of Example 3 and Comparative Example 3. As can be seen from the figure, when charging is performed in the manner of Example 3, the potential rises significantly during each standby process, and the voltage can be stably restored to above 0V after being stood aside, which is higher than the lithium deposition potential. When charging is performed in the manner of Comparative Example 3, the potential is maintained above 0V. This indicates that self-lithiation behavior of graphite occurs. Figure 5 The figure is a charge cycle capacity retention diagram of Example 3 and Comparative Example 3. It can be seen from the figure that the charging method of Example 3 is used to charge, and the average charge and discharge efficiency is greater than 99% after 400 cycles, while the charging method of Comparative Example 3 is used to charge, and the charge and discharge efficiency is significantly reduced after 265 cycles. It shows that intermittent charging can significantly improve the battery cycle capacity.

[0058] The charging specific capacity, stable cycle number and charging time of Examples 1-3 and Comparative Examples 1-3 are shown in the following table.

[0059]

[0060] It can be seen that intermittent charging is beneficial to maintaining battery capacity and improving battery cycle capacity.

[0061] The present invention is not limited to the above optional implementation modes. Anyone who derives other implementation modes under the inspiration of the present invention and any technical solutions falling within the scope defined by the claims of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for fast charging of a graphite-based lithium battery, characterized in that: Set a high rate current I to charge constantly, charge to the first stage charging cut-off capacity Q1, then perform the first hold, the hold time is t1, where 0<t1≤2min, after the first hold is completed, start the second stage charging, charge to the cut-off capacity Q2 with a constant current I, then perform the second hold, the hold time is t2, where 0<t2≤2min, after the second hold is completed, start the third stage charging, and so on, until the nth full charge, charge to the cut-off capacity Q with a constant current I n , the nth suspension, the suspension time is t n , where 0<t n ≤2min, where Q1, Q2...Q n To be close to Q / n, the capacity is reasonably set and meets: and Wherein, x is an integer, and 1≤x≤n.

2. The fast charging method of a graphite-based lithium battery according to claim 1, characterized in that: The constant current charging rate is 3C-20C.

3. The fast charging method of a graphite-based lithium battery according to claim 1, characterized in that: The total charging time is less than 20 minutes.

4. The fast charging method of a graphite-based lithium battery according to claim 1, characterized in that: The number of charging times n is not less than 2 times.

5. The fast charging method of a graphite-based lithium battery according to claim 1, characterized in that: The number of charging times is determined as follows: first, the battery is charged at a constant current and constant rate, and the negative electrode potential information of the battery is detected in real time. When the potential is lower than 0V, the charged capacity is Q0, and n is the integer closest to Q / Q0.

6. The fast charging method of a graphite-based lithium battery according to claim 1, characterized in that: Real-time detection of graphite negative electrode potential information, when the negative electrode potential recovery after being shelved does not reach 0.05V, the number of charging times should be increased.

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