WO2021184376A1

WO2021184376A1 - Method for improving battery cycle performance and electronic device

Info

Publication number: WO2021184376A1
Application number: PCT/CN2020/080489
Authority: WO
Inventors: 刘奥; 高潮; 方占召
Original assignee: 宁德新能源科技有限公司
Priority date: 2020-03-20
Filing date: 2020-03-20
Publication date: 2021-09-23
Also published as: CN113632290A; CN113632290B

Abstract

The present application provides a method for improving battery cycle performance, applied to a battery. The battery comprises a positive electrode membrane; the positive electrode membrane comprises a positive active material capable of inserting and extracting lithium ions; the positive active material comprises lithium cobaltate primary particles and lithium cobaltate secondary particles composed of the lithium cobaltate primary particles; the average particle size of the lithium cobaltate primary particles is 0.1-5 μm, and the average particle size of the lithium cobaltate secondary particles is 10-25 μm. The method comprises: in a first stage, charging the battery with a first-stage current to a first-stage voltage; and in a second stage, charging the battery with a second-stage current to a second-stage voltage, the second-stage voltage being greater than the first-stage voltage, and the second-stage current being less than the first-stage current. The present application further provides an electronic device. According to the method, the low-temperature discharge performance in the battery cycle process can be remarkably improved.

Description

Method and electronic device for improving battery cycle performance

Technical field

This application relates to the field of battery technology, and in particular to a method and electronic device for improving battery cycle performance.

Background technique

The current charging method is usually a constant current and constant voltage charging method, that is, the battery is first charged to the charging limit voltage with a constant current, and then constant voltage charging is performed at the charging limit voltage. The constant current and constant voltage charging method is used because of the polarization of the battery during the charging process. The greater the current, the more obvious the polarization. When the constant current is charged to the charging limit voltage, since there is a phenomenon that the polarized cell is not fully charged, it is necessary to continue constant voltage charging. During the constant voltage charging process, the voltage of the battery remains constant, and the current is gradually reduced to a very small cut-off current, thus completing the full charge. When using constant current and constant voltage charging to charge the battery, the cathode potential is the highest at the end of the constant voltage charging process, and the maintenance time is very long, so it damages the battery cathode material and affects the thermal stability, and worsens the battery during the cycle. The low-temperature discharge performance.

Summary of the invention

In view of this, it is necessary to provide a method and electronic device for improving battery cycle performance, which can significantly improve the low-temperature discharge performance of the battery after cycling.

An embodiment of the present application provides a method for improving the cycle performance of a battery, which is applied to a battery, the battery includes a positive electrode film, the positive electrode film includes a positive electrode active material capable of inserting and extracting lithium ions, and the positive electrode The active material includes lithium cobalt oxide primary particles and lithium cobalt oxide secondary particles composed of the lithium cobalt oxide primary particles, the average particle size of the lithium cobalt oxide primary particles is 0.1 μm-5 μm, and the lithium cobalt oxide secondary particles The average particle size of the particles is 10μm-25μm, and the method includes: in the first stage, charging the battery to the first stage voltage with the first stage current; in the second stage, charging the battery with the second stage current Charge to the second stage voltage, the second stage voltage is greater than the first stage voltage, and the second stage current is less than the first stage current.

According to some embodiments of the present application, the chemical formulas of the lithium cobalt oxide primary particles and the lithium cobalt oxide secondary particles are Li _a Co _1-b M _b O _2-b , wherein M is selected from Na, Mg, Al At least one of, Ti, Zr, Y, Ha, Ni, Mn, V, Cr, La and Ce, 0.99≤a≤1.01, 0<b≤0.05.

According to some embodiments of the present application, the surfaces of the lithium cobalt oxide primary particles and the lithium cobalt oxide secondary particles are both provided with a coating layer, and the chemical formula of the coating layer is LiNO _d , wherein N is selected from Al, At least one of Ti, Cr and Y, 2<d≤3.

According to some embodiments of the present application, the weight ratio of the lithium cobalt oxide primary particles and the lithium cobalt oxide secondary particles is 5:95-50:50.

According to some embodiments of the present application, the second stage adopts a first charging method or a second charging method to charge the battery to the second stage voltage; the first charging method includes sequential K charging sub-stages, K is an integer greater than or equal to 2, the K charging sub-stages are respectively defined as the i-th charging sub-stage, i = 1, 2, ..., K; in the i-th charging sub-stage, the i-th current, One of the i-th voltage and the i-th power is used to charge the battery; in the i+1-th charging sub-phase, one of the i+1-th current, the i+1-th voltage, and the i+1-th power is used Charging the battery; wherein the charging current in the i+1th charging substage is less than or equal to the charging current in the ith charging substage, or the i+1th voltage is greater than or equal to The i-th voltage or the i+1-th power is less than or equal to the i-th power; and the second charging method includes D charging sub-stages in sequence, where D is an integer greater than or equal to 2, so The D charging sub-stages are respectively defined as the j-th charging sub-stage, j = 1, 2, ..., D, and each of the j-th charging sub-stages includes the j-th pre-charging sub-stage and the j-th post-charging sub-stage; In one of the j-th pre-charge sub-phase and the j-th post-charge sub-phase, the battery is not charged or is charged or discharged with the j-th pre-charger current for Tj1; The other one of the pre-charge sub-phase and the j-th post-charge sub-phase charges the battery with the j-th post-charger current for a period of Tj2; wherein the absolute value of the j-th pre-charger current is less than The absolute value of the current of the j-th post-charger.

According to some embodiments of the present application, the average value of the charging current of the jth charging substage is less than the charging current of the first phase, and the average value of the charging current of the j+1th charging substage is less than or equal to the jth charging current. The charging current of the electronic phase.

According to some embodiments of the present application, the first stage adopts a third charging method to charge the battery to the first stage voltage, and the third charging method adopts the first charging method or the second charging method.

According to some embodiments of the present application, when the third charging method adopts the first charging method, the number of charging sub-stages K between the two is the same; or when the third charging method adopts the second charging method In the charging mode, the number of charging sub-stages D between the two is the same.

According to some embodiments of the present application, the first stage voltage is equal to the charge limit voltage of the battery, and the second stage voltage is less than the oxidative decomposition voltage of the electrolyte in the battery.

According to some embodiments of the present application, the second stage voltage is less than or equal to the first stage voltage plus 500 millivolts.

According to some embodiments of the present application, the method further includes: in the third stage, performing constant voltage charging on the battery with the second stage voltage.

An embodiment of the present application also provides an electronic device, including a battery and a battery management module. The battery includes a positive electrode film, the positive electrode film includes a positive electrode active material capable of inserting and extracting lithium ions, and the positive electrode active material Including lithium cobalt oxide primary particles and lithium cobalt oxide secondary particles composed of the lithium cobalt oxide primary particles, the average particle size of the lithium cobalt oxide primary particles is 0.1 μm-5 μm, and the lithium cobalt oxide secondary particles The average particle size is 10 μm-25 μm, and the battery management module is used to perform any of the methods described above.

The embodiment of the present application adjusts the weight ratio of lithium cobalt oxide primary particles and lithium cobalt oxide secondary particles in the positive electrode active material of the battery, and increases the charge limit voltage of the battery (that is, increases from the first stage voltage to the second stage voltage). ), etc., which can significantly reduce polarization and reduce the temperature rise of the battery cell. It can also shorten the time that the cathode of the battery is under high voltage, reduce the occurrence of side reactions, and further improve the cycle performance of the battery, and can significantly Improve low-temperature discharge performance during battery cycling.

Description of the drawings

Fig. 1 is a schematic diagram of an electronic device according to an embodiment of the present application.

Fig. 2 is a flowchart of a method for improving battery cycle performance according to an embodiment of the present application.

FIG. 3 is a first specific embodiment of the method for improving the cycle performance of the battery shown in FIG. 2.

FIG. 4 is a schematic diagram of the current and voltage changes with time during the charging process of the battery according to the first embodiment of the present application.

FIG. 5 is a schematic diagram of the current and voltage changes with time during the charging process of the battery according to the second embodiment of the present application.

Fig. 6 is a schematic diagram of the power and voltage changes with time in the first stage and the current and voltage changes with time in the second stage according to an embodiment of the present application.

FIG. 7 is a schematic diagram of the current and voltage changes with time during the charging process of the battery according to the third embodiment of the present application.

FIG. 8 is a schematic diagram of the current and voltage changes with time during the charging process of the battery according to the fourth embodiment of the present application.

FIG. 9 is a second specific embodiment of the method for improving the cycle performance of the battery shown in FIG. 2.

FIG. 10 is a third specific embodiment of the method for improving the cycle performance of the battery shown in FIG. 2.

FIG. 11 is a fourth specific embodiment of the method for improving the cycle performance of the battery shown in FIG. 2.

Symbol description of main components

Electronic device 1

Battery 10

Control unit 11

Battery management module 12

Detailed ways

The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of them.

Based on the implementation in this application, all other implementations obtained by a person of ordinary skill in the art without creative work are within the protection scope of this application.

Please refer to FIG. 1. FIG. 1 is a schematic diagram of an electronic device according to an embodiment of the application. The electronic device 1 includes a battery 10, a control unit 11 and a battery management module 12. The battery 10, the control unit 11 and the battery management module 12 may be connected via a bus or directly. The battery 10 includes at least one battery cell, and the battery 10 can be repeatedly charged in a rechargeable manner. In this embodiment, the battery 10 is mainly composed of a positive electrode film, a negative electrode film, a separator, an electrolyte, and a packaging bag. The control unit 11 may control the battery management module 12 to execute the method for improving battery cycle performance. The control unit 11 can be a microcontroller (Microcontroller, MCU), a processor (Processor), or an application-specific integrated circuit (ASIC), etc., and can control the battery management module 12 to execute The method for improving the cycle performance of the battery.

It should be noted that FIG. 1 is only an example of the electronic device 1. In other embodiments, the electronic device 1 may also include more or fewer elements, or have different element configurations. The electronic device 1 may be an electric motorcycle, an electric bicycle, an electric car, a mobile phone, a tablet computer, a digital assistant, a personal computer, or any other suitable rechargeable equipment.

Although not shown, the electronic device 1 may also include other components such as a wireless fidelity (Wireless Fidelity, WiFi) unit, a Bluetooth unit, a speaker, etc., which will not be repeated here.

Please refer to FIG. 2, which is a flowchart of a method for improving battery cycle performance according to an embodiment of the present application. The method for improving the cycle performance of a battery applied to a battery includes the following steps:

Step S21: In the first stage, the battery is charged to the first stage voltage with the first stage current.

Step S22: In the second stage, the battery is charged to the second stage voltage with the second stage current, the second stage voltage is greater than the first stage voltage, and the second stage current is smaller than the first stage voltage Current. Wherein, the positive electrode membrane of the battery includes a positive electrode active material capable of inserting and extracting lithium ions, and the positive electrode active material includes lithium cobalt oxide primary particles and lithium cobalt oxide secondary particles. In one embodiment, the average particle size of the lithium cobalt oxide primary particles is 0.1 μm-5 μm (small particles), and the average particle size of the lithium cobalt oxide secondary particles is 10 μm-25 μm (large particles). In another embodiment, the average particle size of the lithium cobalt oxide primary particles is 1 μm to 3 μm; the average particle size of the lithium cobalt oxide secondary particles is 15 μm to 20 μm. In one embodiment, the weight ratio of lithium cobalt oxide primary particles and lithium cobalt oxide secondary particles is 5:95 to 50:50. In another embodiment, the weight ratio is 15:85 to 35:65.

In one embodiment, the chemical formula of the lithium cobalt oxide primary particles and the lithium cobalt oxide secondary particles is Li _a Co _1-b M _b O _2-b , wherein M is selected from Na, Mg, Al, Ti At least one of, Zr, Y, Ha, Ni, Mn, V, Cr, La and Ce, 0.99≤a≤1.01, 0<b≤0.05.

In one embodiment, both the lithium cobalt oxide primary particles and the lithium cobalt oxide secondary particles are provided with a coating layer, and the chemical formula of the coating layer is LiNO _d , wherein N is selected from Al, Ti, At least one of Cr and Y, 2<d≤3.

Please refer to FIG. 3. FIG. 3 is a first specific embodiment of the method for improving the cycle performance of the battery shown in FIG. 2.

Step S31: In the first stage, the battery is charged to the first stage voltage with the first stage current.

In this embodiment, the current in the first stage is a constant current, that is, a constant charging current is used when charging is started in the prior art. Alternatively, the current in the first stage may also be a current of varying magnitude. For example, in the first stage, the battery is charged with a constant voltage, and the charging current corresponding to the constant voltage (that is, the first The size of the phase current) will vary, as long as the battery can be charged to the first phase voltage through the first phase current. The first stage voltage is equal to the charging limit voltage of the battery (which can be understood as a well-known charging limit voltage).

Step S32: In the second stage, the battery is charged to the second stage voltage with the second stage current, the second stage voltage is greater than the first stage voltage, and the second stage current is smaller than the first stage voltage Current; the second stage adopts the first charging method or the second charging method to charge the battery to the second stage voltage. Wherein, the battery includes a positive electrode film, the positive electrode film includes a positive electrode active material capable of inserting and extracting lithium ions, and the positive electrode active material includes lithium cobalt oxide primary particles and cobalt composed of the lithium cobalt oxide primary particles. Lithium oxide secondary particles, the average particle size of the lithium cobalt oxide primary particles is 0.1 μm-5 μm, and the average particle size of the lithium cobalt oxide secondary particles is 10 μm-25 μm.

In some embodiments, the average particle size of the lithium cobalt oxide primary particles is 1 μm-3 μm; the average particle size of the lithium cobalt oxide secondary particles is 15 μm-20 μm. The positive active material includes lithium cobalt oxide primary particles and lithium cobalt oxide secondary particles. In one embodiment, the weight ratio of lithium cobalt oxide primary particles and lithium cobalt oxide secondary particles is 5:95 to 50:50. In another embodiment, the weight ratio is 15:85 to 35:65.

Wherein, the first charging method includes K charging sub-phases in sequence, K is an integer greater than or equal to 2, and the K charging sub-phases are respectively defined as the i-th charging sub-phase, i=1, 2,... , K; in the i-th charging sub-phase, charge the battery with one of the i-th current, the i-th voltage, and the i-th power; in the i+1-th charging sub-phase, use the i+th One of a current, an i+1th voltage, and an i+1th power charges the battery. In an embodiment, the charging current in the (i+1)th charging sub-phase is less than or equal to the charging current in the i-th charging sub-phase. In another embodiment, the (i+1)th voltage is greater than or equal to the (i)th voltage. In another embodiment, the (i+1)th power is less than or equal to the (i)th power.

The second charging method includes D charging sub-phases in sequence, D is an integer greater than or equal to 2, and the D charging sub-phases are respectively defined as the j-th charging sub-phase, j = 1, 2, ..., D , And each of the j-th charging sub-stage includes a j-th pre-charge sub-stage and a j-th post-charge sub-stage; in one of the j-th pre-charge sub-stage and the j-th post-charge sub-stage, The battery is not charged or is charged or discharged with the j-th pre-charge sub-current for Tj1; in the other of the j-th pre-charge sub-stage and the j-th post-charge sub-stage, the battery is The j-th post-charger current is charged for a duration of Tj2; wherein the absolute value of the j-th pre-charger current is smaller than the absolute value of the j-th post-charger current.

In this embodiment, the average value of the charging current of the j+1th charging substage is less than or equal to the charging current of the jth charging substage, and when the third charging method adopts the second charging method, The average value of the charging current in the jth charging substage is smaller than the charging current in the first charging mode or the second charging mode.

It should be noted that the first stage voltage is equal to the charging limit voltage of the battery.

Since the charging current in the first charging sub-phase of the second phase is smaller than the current in the first phase, and the charging current in the i+1th charging sub-phase is less than or equal to the charging current in the i-th charging sub-phase , So that the anode potential of the battery is not lower than the anode lithium evolution potential. Lithium evolution potential can be obtained by testing in the following way. For the battery in this embodiment, another three-electrode battery with the same specifications is produced. Compared with the battery in this embodiment, the three-electrode battery has one more electrode, that is, it contains three electrodes, which are anodes. , Cathode and reference electrode. The material of the reference electrode is lithium, and the three-electrode battery is used for testing to obtain the lithium evolution potential of the anode of the battery of this embodiment.

The specific test method for the lithium evolution potential of the anode is as follows: make a plurality of three-electrode batteries, and charge and discharge the three-electrode battery with charging currents of different magnifications (for example, 1C, 2C, 3C), and cycle multiple times ( For example, 10 times), and detect the potential difference between the anode and the reference electrode during the charge and discharge process. Then, the three-electrode battery was fully charged and disassembled, and the anodes of the three-electrode batteries charged with different rates were observed whether lithium evolution occurred (that is, whether lithium metal was deposited on the surface of the anode). To determine the maximum rate corresponding to the three-electrode battery without lithium evolution, the minimum potential difference between the anode and the reference electrode during the charge and discharge process at the rate is used as the anode lithium evolution potential. In addition, it should be noted that the charging current of lithium batteries is generally referred to by the rate C, which is the value corresponding to the capacity of the lithium battery. Lithium battery capacity is generally expressed in Ah and mAh. For example, when the battery capacity is 1200mAh, the corresponding 1C is 1200mA, and 0.2C is equal to 240mA.

For another example, charge and discharge multiple three-electrode batteries with charging currents of 1C, 2C, and 3C, respectively, and cycle 10 times. Through dismantling the three-electrode battery, it is found that the anode does not undergo lithium evolution when using 1C and 2C charging and discharging, and the anode occurs when using 3C charging and discharging. Then, the minimum value of the potential difference between the anode and the reference electrode at the 2C rate is the anode lithium evolution potential. In addition, the lithium evolution potential of the cathode can also be tested in a similar manner, which will not be repeated here. The anode potential and the cathode potential of the battery can be further understood through the above anode lithium evolution potential test process as follows: the anode potential is the potential difference between the anode and the reference electrode, that is, the anode versus lithium potential, and the cathode potential is the cathode and the reference electrode. The potential difference than the electrode, that is, the potential of the cathode to lithium.

The second stage voltage is less than the oxidative decomposition voltage of the electrolyte in the battery. The oxidative decomposition voltage of the electrolyte in the battery can be understood as follows: when the potential of the battery exceeds a certain potential threshold, the solvent molecules, additive molecules, and even impurity molecules in the electrolyte will irreversibly reduce at the interface between the electrode and the electrolyte. Or oxidative decomposition reaction, this phenomenon is called electrolyte decomposition. The potential threshold is the reduction decomposition voltage and the oxidation decomposition voltage of the electrolyte in the battery. In this embodiment, the second stage voltage is also less than or equal to the first stage voltage plus 500 millivolts.

During the Kth charging substage or the Dth charging substage of the second stage, the battery is charged to the second stage voltage. At this time, the cut-off condition for charging the battery may be A cut-off voltage, a cut-off current, or a cut-off capacity. More specifically, in the K-th charging sub-phase or the D-th charging sub-phase, when the charging current of the battery is equal to the cut-off current, the reached charging voltage (that is, the voltage difference between the positive electrode and the negative electrode) is equal to that of the battery. When the cut-off voltage or the electric capacity of the battery is equal to the cut-off capacity, the battery is stopped charging, that is, the charging is cut off. For the batteries of different specifications, the cut-off current, the cut-off voltage, and the cut-off capacity can be obtained by using the aforementioned three-electrode battery test method and observing that the cathode of the three-electrode battery does not undergo excessive delithiation. In order to ensure that the electric capacity of the battery is equivalent to that of the conventional charging method in the prior art, and to ensure that the cathode of the battery does not undergo excessive delithiation.

In addition, it should be supplemented that: in this embodiment, the first stage current, the first stage voltage, the i-th current of the i-th charging substage of the first stage, the One of the i-th voltage, and the i-th power, one of the i-th current, the i-th voltage, and the i-th power in the i-th charging substage of the second stage The value of the second stage voltage and the cut-off condition may be stored in the battery management module in advance.

Referring to FIG. 4, the first charging method is used to charge the battery in the first stage, and the first charging method includes K charging sub-stages in sequence, and the K charging sub-stages are respectively defined as the i-th charger In the stage, i=1, 2,..., K; in the i-th charging sub-stage, the battery is charged with the i-th current. In the second stage, the first charging method is used to charge the battery, and the first charging method includes K charging sub-phases in sequence, and the K charging sub-phases are respectively defined as the i-th charging sub-phase, i=1, 2.... K; charge the battery with the i-th current in the i-th charging sub-phase, and charge the battery with the i-th voltage in the i+1-th charging sub-phase, and so on alternately Cycle charging.

In the first stage, from time 0 to t1, the battery is charged to voltage U1 with a constant current I1; from time t1 to t2, the battery is charged to voltage U2 with a constant current I2; from time t(i-2) to During t(i-1), charge with constant current I(i-1) to voltage U(i-1); during time ti-1 to ti, charge with constant current Ii to voltage Ui; at time t(K -1) Between tK, charge with constant current Icl to voltage Ucl. Between time t2 and t(i-2), and between time ti and t(K-1), similar charging is performed, but it is omitted in the figure and not shown.

In the second stage, from time t1' to t2', the battery is charged with a constant current I1' to the voltage U1'; from time t2' to t3', the battery is charged with a constant voltage U1', the corresponding charging current for this period of time Decrease from I1' to current I2'; from time t3' to t4', charge the battery with a constant current I2' to voltage U2'; from time t4' to t5', charge the battery with a constant voltage U2'; Between time t(i-1)' and ti', charge the battery with a constant current Ii' to the voltage Ui'; between time ti' and t(i+1)', charge the battery with a constant voltage Ui', this period The charging current corresponding to time drops from I1' to the current I(i+1)'; between time t(K-2)' and t(K-1)', the charging current is charged to the voltage Um with a constant current Im; at time t (K-1) From'to tK', charge the battery with a constant voltage Um, and the corresponding charging current during this period of time drops from Im to current Im'. From time t5' to t(i-1)', and from time t(i+1)' to t(K-1)', similar charging is performed, but it is omitted and not shown in the figure.

It should be noted that the tK and t1' are the same time. In each of the K charging sub-stages of the first stage, the battery is charged with a constant charging current, and I1≧I2≧…≧Icl, U1≦U2≦…≦Ucl; Each of the K charging sub-phases of the two stages charges the battery alternately with a constant charging current and a constant voltage, Icl≧I1'≧I2'≧…≧Im', Ucl≦U1' ≦U2'≦…≦Um.

Referring to FIG. 5, the first charging method is used to charge the battery in the first stage, and the first charging method includes sequential K charging sub-stages, and the K charging sub-stages are respectively defined as the i-th charging sub-stage, i=1, 2,..., K; in the i-th charging substage, the battery is charged with the i-th voltage. In the second stage, the first charging method is used to charge the battery, and the first charging method includes K charging sub-phases in sequence, and the K charging sub-phases are respectively defined as the i-th charging sub-phase, i=1, 2.... K; charge the battery with the i-th current in the i-th charging sub-phase, and charge the battery with the i-th voltage in the i+1-th charging sub-phase, and so on alternately Cycle charging.

In the first stage, between time 0 and t1, the battery is charged with a constant voltage U1 until the current is I1; between time t1 and t2, the battery is charged with a constant voltage U2 until the current is I2; at time t(i-1 From) to ti, charge with a constant voltage Ui until the current is Ii; from time t(K-1) to tK, charge with a constant voltage Ucl until the current is Icl. Similar charging is performed between time t2 and t(i-1) and between time ti and t(K-1), but is omitted in the figure and not shown.

In the second stage, from time t1' to t2', the battery is charged with a constant current I1' to the voltage U1'; from time t2' to t3', the battery is charged with a constant voltage U1', the corresponding charging current for this period of time Decrease from I1' to current I2'; from time t3' to t4', charge the battery with a constant current I2' to voltage U2'; from time t4' to t5', charge the battery with a constant voltage U2'; Between time t(i-1)' and ti', charge the battery with a constant current Ii' to the voltage Ui'; between time ti' and t(i+1)', charge the battery with a constant voltage Ui', this period The charging current corresponding to time drops from Ii' to the current I(i+1)'; between time t(K-2)' and t(K-1)', the charging current is charged to the voltage Um with a constant current Im; at time t (K-1) From'to tK', charge the battery with a constant voltage Um, and the corresponding charging current during this period of time drops from Im to current Im'. From time t5' to t(i-1)', and from time t(i+1)' to t(K-2)', similar charging is performed, but it is omitted in the figure and not shown.

It should be noted that the tK and t1' are the same time. In each of the K charging sub-phases of the first stage, the battery is charged with a constant charging voltage, and U1≦U2≦...≦Ucl, I1≧I2≧…≧Icl. In each of the K charging sub-stages of the second stage, the battery is charged alternately with a constant charging current and a constant charging voltage, and Ucl≦U1'≦U2'≦...≦Um, Icl≧I1'≧I2'≧…≧Im'.

Referring to FIG. 6, the first charging method is used to charge the battery in the first stage, and the first charging method includes K charging sub-stages in sequence, and the K charging sub-stages are respectively defined as the i-th charger. In the stage, i=1, 2,..., K; in the i-th charging sub-stage, the battery is charged with the i-th power. In the second stage, the first charging method is used to charge the battery, and the first charging method includes K charging sub-phases in sequence, and the K charging sub-phases are respectively defined as the i-th charging sub-phase, i=1, 2.... K; charge the battery with the i-th current in the i-th charging sub-phase, and charge the battery with the i-th voltage in the i+1-th charging sub-phase, and so on alternately Cycle charging.

In the first stage, between time 0 and t1, the battery is charged with constant power P1 until the voltage is U1; between time t1 and t2, the battery is charged with constant power P2 to voltage U2; at time t(i-2) To t(i-1), charge to voltage U(i-1) with constant power P(i-1); from time t(i-1) to ti, charge to voltage Ui with constant power Pi; Between time t(K-1) and tK, the battery is charged to the voltage Ucl with a constant power Pcl. Between time t2 and t(i-2), and between time ti and t(K-1), similar charging is performed, but it is omitted in the figure and not shown.

In the second stage, from time t1' to t2', the battery is charged with a constant current I1' to the voltage U1'; from time t2' to t3', the battery is charged with a constant voltage U1', the corresponding charging current for this period of time Decrease from I1' to current I2'; from time t3' to t4', charge the battery with a constant current I2' to voltage U2'; from time t4' to t5', charge the battery with a constant voltage U2'; Between time t(i-1)' and ti', charge the battery with a constant current Ii' to the voltage Ui'; between time ti' and t(i+1)', charge the battery with a constant voltage Ui', this period The charging current corresponding to time drops from I1' to the current I(i+1)'; between time t(K-2)' and t(K-1)', the charging current is charged to the voltage Um with a constant current Im; at time t (K-1) From'to tK', charge the battery with a constant voltage Um, and the corresponding charging current during this period of time drops from Im to current Im'. From time t5' to t(i-1)', and from time t(i+1)' to t(K-2)', similar charging is performed, but it is omitted in the figure and not shown.

It should be noted that in each of the K charging sub-stages of the first stage, the battery is charged with a constant power, and P1≧P2≧…≧Pcl, U1≦U2≦…≦ Ucl. In each of the K charging sub-stages of the second stage, the battery is charged alternately with a constant charging current and a constant charging voltage, and Ucl≦U1'≦U2'≦...≦Um, Icl≧I1'≧I2'≧…≧Im'.

Referring to FIG. 7, in the first stage, the first charging method is used to charge the battery, and the first charging method includes K charging sub-stages in sequence, and the K charging sub-stages are respectively defined as the i-th charger. Stage, i=1, 2,..., K; in the i-th charging sub-stage, the battery is charged with the i-th current; in the i+1-th charging sub-stage, the i-th voltage is used to The battery is charged, and the battery is charged alternately in this way. In the second stage, the first charging method is used to charge the battery, and the first charging method includes K charging sub-phases in sequence, and the K charging sub-phases are respectively defined as the i-th charging sub-phase, i=1, 2.... K; charge the battery with the i-th current in the i-th charging sub-phase, and charge the battery with the i-th voltage in the i+1-th charging sub-phase, and so on alternately Cycle charging.

In the first stage, between time 0 and t1, the battery is charged with a constant current I1 to the voltage U1; between time t1 and t2, the battery is charged with a constant voltage U1, and the corresponding charging current during this period is reduced from I1 To the current I2; from time t2 to t3, the battery is charged with a constant current I2 to the voltage U2; from time t3 to t4, the battery is charged with a constant voltage U2, the corresponding charging current for this period of time drops from I2 to the current I3; From time t(i-2) to t(i-1), charge the battery with a constant current Ii to the voltage Ui; from time t(i-1) to ti, charge the battery with a constant voltage Ui; at time t(K From -2) to t(K-1), charge the battery with a constant current Icl to the voltage Ucl; from time t(K-1) to tK, charge the battery with a constant voltage Ucl, the corresponding charging current for this period of time is determined by Icl Decrease to current I1'. Between time t4 and t(i-2), and between time ti and t(K-2), similar charging is performed, but it is omitted in the figure and not shown.

In the second stage, from time t1' to t2', the battery is charged with a constant current I1' to the voltage U1'; from time t2' to t3', the battery is charged with a constant voltage U1', the corresponding charging current for this period of time Decrease from I1' to current I2'; from time t3' to t4', charge the battery with a constant current I2' to voltage U2'; from time t4' to t5', charge the battery with a constant voltage U2'; Between time t(i-1)' and ti', charge the battery with a constant current Ii' to the voltage Ui'; between time ti' and t(i+1)', charge the battery with a constant voltage Ui', this period The charging current corresponding to time drops from I1' to the current I(i+1)'; between time t(K-2)' and t(K-1)', the charging current is charged to the voltage Um with a constant current Im; at time t (K-1) From'to tK', charge the battery with a constant voltage Um, and the corresponding charging current during this period of time drops from Im to current Im'. Between time t5' and t(i-1)' and between time t(i+1)' and t(K-2)', similar charging is performed, but it is omitted in the figure and not shown.

It should be noted that, in each of the K charging sub-stages of the first stage, a constant charging current and a constant charging voltage alternately charge the battery, and I1≧I2≧…≧Icl, U1≦ U2≦…≦Ucl. In each of the K charging sub-phases of the second stage, the battery is also charged alternately with a constant charging current and a constant charging voltage, and I1'≧I2'≧…≧Im', U1'≦U2'≦...≦Um, and Icl≧I1', Ucl≦U1'.

When the second charging method is used to charge the battery, the first stage includes sequential D charging substages, D is a positive integer, and the D charging substages are defined as the jth charging substage, j=1 , 2,..., D, each of the j-th charging sub-stages includes a j-th pre-charging sub-stage and a j-th post-charging sub-stage. The second stage also includes sequential D charging sub-stages, D is a positive integer, and the D charging sub-stages are defined as the j-th charging sub-stages, j = 1, 2, ..., D, each The j-th charging sub-stage includes a j-th pre-charging sub-stage and a j-th post-charging sub-stage. It should be noted that the number D of charging sub-stages in the first stage and D in the second stage may be the same or different.

In one of the j-th pre-charge sub-stage and the j-th post-charge sub-stage, the battery is not charged or is charged or discharged with a j-th pre-charger current for Tj1. In the other of the j-th pre-charging sub-stage and the j-th post-charging sub-stage, the battery is charged with a j-th post-charge sub-current for a duration of Tj2. The absolute value of the j-th front charger current is smaller than the absolute value of the j-th rear charger current.

That is to say, in each of the jth charging substages, the battery is charged by pulse charging or pulse charging and discharging, and the average value of the charging current of the j+1 charging substage is less than or It is equal to the charging current of the j-th charging sub-stage, for example, (the first front charger current*T11+the first rear charger current*T12)/(T11+T12) is greater than or equal to (the second front charger current*T21+ The second rear charger current*T22)/(T21+T22), (the second front charger current*T21+the second rear charger current*T22)/(T21+T22) is greater than or equal to (the third front charger current *T31+3rd post-charger current*T32)/(T31+T32) and so on. The sum of the duration of each Tj1 and the duration of Tj2 is the charging period or the charging and discharging period of the pulse charging or the pulse charging and discharging in the jth charging sub-phase.

In addition, it should be specifically supplemented that: in this embodiment, in the j-th pre-charger sub-phase, the j-th pre-charger current is used to charge or discharge for Tj1 time, and the j-th post-charger In the stage, charging is performed with the j-th post-charger current for a duration of Tj2. In other embodiments, it is also possible to perform charging with the j-th post-charger current for Tj2 in the j-th pre-charging sub-stage, and use the j-th post-charge sub-stage to charge The charge or discharge current of the front charger is Tj1. In other embodiments, it may be that the charging sub-phase before the jth charge is not charged or is left to stand (that is, the charging current is 0 at this time) for Tj1, and the charging sub-phase after the jth charge After the jth sub-current is charged or discharged for Tj2 duration.

Referring to FIG. 8, between time t1 and t1000, that is, in each charging sub-stage from the first charging sub-stage to the 1000th charging sub-stage of the first stage, the current I2 is first applied to The battery is charged, and then the battery is charged with a current I3. Between time tx and t1000, similar charging is performed, but it is omitted and not shown in the figure.

From time t1000 to t2000, that is, in each sub-charging stage from the 1001th charging sub-stage to the 2000th charging sub-stage of the first stage, the battery is first charged with a current I10011, and then Let the battery stand still (that is, neither charge nor discharge). Between time ty and t2000, similar charging is performed, but it is omitted and not shown in the figure. Between time t2000 and tD, that is, in each charging sub-stage from the 2001th charging sub-stage to the D-th charging sub-stage of the first stage, the battery is first charged with the current I20011, and then The battery is discharged with the current I20012 until the voltage of the battery is equal to the voltage Ucl (that is, the cut-off voltage). Between time t2002 and t(D-1), similar charging is performed, but it is omitted and not shown in the figure.

That is, in the D charging sub-phases of the first phase, the battery is charged in three different pulse charging or pulse charging and discharging methods. In addition, it should be supplemented that the pulse charging or pulse charging and discharging charging cycle or charging and discharging cycle of each of the D charging sub-phases is the same, that is, t1=(t1001-t1000)=(t2001-t2000), and in the other In the embodiment, the charging period or the charging and discharging period of different pulse charging or pulse charging and discharging may also be different.

In the second stage, from time t1' to t2', the battery is charged with a constant current I1' to the voltage U1'; from time t2' to t3', the battery is charged with a constant voltage U1', the corresponding charging current for this period of time Decrease from I1' to current I2'; from time t3' to t4', charge the battery with a constant current I2' to the voltage U2'; from time t4' to t5', charge the battery with a constant voltage U2'; Between time ti' and t(i+1)', charge with constant current Ii' to voltage Ui'; between time t(i+1)' and t(i+2)', use constant voltage Ui' to When charging the battery, the charging current corresponding to this period of time drops from I1' to the current I(i+1)'; during the time t(D-2)' to t(D-1)', the constant current Im is charged to the voltage Um; between time t(D-1)' and tD', the battery is charged with a constant voltage Um, and the corresponding charging current during this period of time drops from Im to current Im'. From time t5' to ti', and from time t(i+2)' to t(D-2)', similar charging is performed, but it is omitted and not shown in the figure.

In summary, the method for improving battery cycle performance provided by this application adjusts the weight ratio of lithium cobalt oxide primary particles and lithium cobalt oxide secondary particles in the positive electrode active material of the battery, and increases the charge limit voltage of the battery (that is, from The combination of increasing the voltage in the first stage to the voltage in the second stage, etc., can significantly reduce the polarization and reduce the temperature rise of the battery cell. It can also shorten the time that the battery’s cathode is under high voltage and reduce the occurrence of side reactions. It can further improve the cycle performance of the battery, and can significantly improve the low-temperature discharge performance of the battery during the cycle.

In order to make the invention objectives, technical solutions and technical effects of the present application clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the examples given in this specification are only for explaining the application, not for limiting the application, and the application is not limited to the examples given in the specification.

The battery system used in the comparative examples and examples described below uses lithium cobalt oxide as the cathode, graphite as the anode, plus a diaphragm, electrolyte and packaging shell, through mixing, coating, assembling, forming and aging, etc. Craft made. Among them, the cathode is composed of 96.7% LiCoO ₂ (as the cathode active material) plus 1.7% polyvinylidene fluoride (PVDF, as the binder) and 1.6% conductive carbon black (SUPER-P, as the conductive agent). The anode is composed of 98. % Artificial graphite (as the anode active material) plus 1.0% styrene butadiene rubber (SBR, as a binder) plus 1.0% sodium carboxymethyl cellulose (CMC, as a thickener), the diaphragm is PP/PE/PP Composite membrane.

The comparative example and the embodiment used different new charging methods to charge the battery, and used lithium cobalt oxide positive active materials with different weight ratios to test the capacity retention rate, temperature rise, impedance growth rate and after cycling of the battery after cycling charge and discharge. Low-temperature discharge performance, specific schemes and performance summary are shown in Table 1.

Table 1 Capacity retention rate, temperature rise, impedance growth rate and low temperature discharge performance after cycling in each comparative example and Examples 1-20 after cycling charge and discharge

Among them, the existing charging methods in Comparative Example 1 and Comparative Example 3 are the constant current and constant voltage charging methods in the prior art. The specific process of the existing charging method is:

The ambient temperature is 45°C:

Step 1: Charge the battery to 4.4V with 0.7C constant current;

Step 2: Charge the battery to 0.05C with a constant voltage of 4.4V;

Step 3: Let the battery stand for 5 minutes;

Step 4: Discharge the battery to 3.0V at a constant current of 0.5C;

Step 5: Let the battery stand for 5 minutes;

Step 6: Cycle the above steps 1 to 5 500 times.

In this embodiment, C is a value corresponding to the capacity of the lithium ion battery. Lithium-ion battery capacity is generally expressed in Ah and mAh. For example, when the battery capacity is 1200mAh, the corresponding 1C is 1200mA, and 0.2C is equal to 240mA.

Comparative Example 2 and Examples 1-16 adopt the new charging method 1 in this application, and the specific process is as follows:

The ambient temperature is 45℃;

Step 1: Charge the battery to 4.4V with 0.7C constant current;

Step 2: Charge the battery to 4.45V with a constant current of 0.5C;

Step 3: Charge the battery to 4.54V with 0.4C constant current;

Step 4: Let the battery stand for 5 minutes;

Step 5: Discharge the battery to 3.0V at a constant current of 0.5C;

Step 6: Let the battery stand for 5 minutes;

Step 7: Cycle the above steps 1 to 6 for 500 times.

Embodiment 17 adopts the new charging method 2 in this application, and the specific process is as follows:

The ambient temperature is 45℃;

Step 1: Charge the battery to 4.4V with 0.7C constant current;

Step 2: Charge the battery to 0.4C with a constant voltage of 4.35V;

Step 3: Charge the battery to 0.13C with a constant voltage of 4.45V;

Step 4: Let the battery stand for 5 minutes;

Step 5: Discharge the battery to 3.0V at a constant current of 0.5C;

Step 6: Let the battery stand for 5 minutes;

Step 7: Cycle the above steps 1 to 6 for 500 times.

Embodiment 18 adopts the new charging method 3 in this application, and the specific process is as follows: the ambient temperature is 45°C;

Step 1: Charge the battery to 4.4V with 0.7C (2.1A) constant current;

Step 2: Charge the battery to 4.45V with a constant power of 7W;

Step 3: Charge the battery to 4.55V with a constant power of 5.5W;

Step 4: Let the battery stand for 5 minutes;

Step 5: Discharge the battery to 3.0V at a constant current of 0.5C;

Step 6: Let the battery stand for 5 minutes;

Step 7: Cycle the above steps 1 to 6 for 500 times.

Embodiment 19 adopts the new charging method 4 in this application, and the specific process is as follows:

The ambient temperature is 45℃;

Step 1: Charge the battery to 4.4V with 0.7C constant current;

Step 2: Charge the battery to 0.5C with a constant voltage of 4.4V;

Step 3: Charge the battery to 4.45V at a constant current of 0.5C;

Step 4: Charge the battery to 0.3C with a constant voltage of 4.45V;

Step 5: Let the battery stand for 5 minutes;

Step 6: Discharge the battery to 3.0V at a constant current of 0.5C;

Step 7: Let the battery stand for 5 minutes;

Step 8: Circulate 500 times from step 1 to step 7 above.

Embodiment 20 adopts the new charging method 5 in this application, and the specific charging process is as follows:

The ambient temperature is 45℃;

Step 1: Charge the battery to 4.4V with 0.7C constant current;

Step 2: Leave the battery for 2.9 seconds;

Step 3: Charge the battery with a constant current of 0.7C for 7.1 seconds, and judge whether the battery voltage is greater than or equal to 4.45V. When the battery voltage is greater than or equal to 4.45V, skip to step five;

Step 4: Cycle Step 2 to Step 3 100000 times;

Step 5: Discharge the battery for 1 second at a constant current of 0.05C;

Step 6: Charge the battery with a constant current of 0.41C for 9 seconds, and judge whether the battery voltage is greater than or equal to 4.54V. When the battery voltage is greater than or equal to 4.54V, skip to step 8;

Step 7: Let the battery stand for 5 minutes;

Step 8: Discharge the battery to 3.0V at a constant current of 0.5C;

Step 9: Let the battery stand for 5 minutes;

Step 10: Cycle the above steps 1 to 9 500 times.

In addition, it should be noted that the calculation method of the capacity retention rate after 500 cycles of charge and discharge at 45°C in Table 1 is: when the ambient temperature is 45°C, the batteries of the comparative example and the examples use the corresponding charging process cycle For 500 cycles, the discharge capacity after 500 cycles of the battery is divided by the discharge capacity at the first cycle.

The low-temperature discharge performance of the battery in Table 1 describes the low-temperature discharge capacity retention rate of the battery. The low-temperature discharge capacity retention rate was measured by the following method: before the cycle test, the battery was discharged at a capacity of 0.2C to 3.0V under an environment of 25°C (comparative example and example) as the reference capacity; after the discharge was completed, the comparative example was used The charging process corresponding to the embodiment has 500 cycles of charging and discharging. After 500 cycles, the battery is transferred to an environment of -10°C and discharged at 0.2C to 3.0V. The discharge capacity at this step is divided by the reference capacity to obtain the low-temperature discharge capacity retention rate. For details, please refer to the following test methods:

The ambient temperature is 25℃;

Step 1: Charge the battery to 4.4V with 0.2C constant current;

Step 2: Charge the battery to 0.05C with a constant voltage of 4.4V;

Step 3: Discharge the battery to 3.0V at a constant current of 0.2C; (calculate the discharge capacity of this step, and use this step as the benchmark);

Step 4: Let the battery stand for 5 minutes;

Step 5: Use the test procedure of the comparative example and the embodiment to complete 500 cycles and remove the battery cell, transfer to -10°C and let it stand for 10 minutes, and then install the cell into the battery;

Step 6: Charge the battery to 4.4V with 0.2C constant current;

Step 7: Charge the battery to 0.05C with a constant voltage of 4.4V;

Step 8: Discharge the battery to 3.0V with a constant current of 0.2C; (calculate the discharge capacity of this step, and divide the discharge capacity of this step by the discharge capacity calculated in step 3 is the low-temperature discharge capacity retention rate);

Step 9: Let the battery stand for 5 minutes;

The calculation method of the impedance growth rate after 500 cycles of charge-discharge cycles at 45°C in Table 1 is: before the cycle test, the Autolab electrochemical workstation is used, and the battery impedance test is carried out with a 10mV disturbance voltage in the range of 1MHz-0.1MHz to obtain the cycle test. After charging and discharging the battery for 500 cycles using the charging method in Comparative Example 1-3 and Example 1-20, the impedance of the battery after the 500-cycle cycle test was tested using the same test method, and then passed the following The formula calculates the impedance growth rate.

Impedance growth rate=impedance before cycle test/impedance after 500 cycles test -1.

It can be seen from Table 1 above that by comparing Comparative Example 2 (using the new charging method 1) and Comparative Example 1 (using the existing charging method), it can be seen that the constant current charging method of the present application can improve the capacity retention rate after the battery cell is cycled. , But there is no significant improvement in the thermal stability of the cell after cycling. This is mainly because the constant current charging method of the present application can significantly shorten the full charging time and reduce the damage of the cathode during the cycle. However, due to the higher temperature rise of the battery cell due to the increase of the charging speed, the generation of by-products is intensified, and the low-temperature discharge performance of the battery after the cycle is not significantly improved.

By comparing Comparative Example 3 (using the existing charging method) with Comparative Example 1 (using the existing charging method), it can be seen that increasing the content of primary lithium cobalt oxide particles (small particles of lithium cobalt oxide) has a significant effect on battery cell cycle. Certain improvement, no obvious improvement in low-temperature discharge performance after cycling. This is mainly due to the fact that increasing the content of lithium cobalt oxide primary particles can reduce polarization and temperature rise, but with the constant current and constant voltage charging method of the prior art, the cathode of the battery has a longer time under high voltage, and the cathode material has been reduced. Causes a certain degree of damage, so there is no significant improvement in the low-temperature discharge performance of the battery after cycling.

It can be seen from Examples 1-20 and Comparative Example 2 and Comparative Example 3 that by adjusting the weight ratio of lithium cobalt oxide primary particles and lithium cobalt oxide secondary particles in the positive electrode active material of the battery and using the charging method of the application (such as New charging method 1, new charging method 2, new charging method 3, etc.), can significantly reduce the battery impedance growth rate and the temperature rise of the battery cell, improve the battery cycle capacity retention rate and low-temperature discharge performance after cycling. Especially after 500 cycles of charge and discharge at 45°C, the low-temperature discharge performance of the battery is improved by about 20%. This is mainly because the charging method of the present application can significantly shorten the time that the cathode is under high voltage, and by increasing the content of lithium cobalt oxide primary particles, the temperature rise caused by excessive charging speed can be reduced. Therefore, the damage to the cathode of the battery can be significantly reduced during the entire cycle, and the side reactions can be reduced at the same time, so that the low-temperature discharge performance of the battery after the cycle can be significantly improved.

Therefore, this application adjusts the weight ratio of the lithium cobalt oxide primary particles and the lithium cobalt oxide secondary particles in the positive electrode active material of the battery, and increases the charge limit voltage of the battery (as in Example 1, the charging of Comparative Examples 1 and 3) The combination of limiting the voltage from 4.4V to 4.45V, etc.) can significantly reduce polarization and reduce the temperature rise of the battery cell. It can also shorten the time that the battery’s cathode is under high voltage and reduce the occurrence of side reactions. Improve the cycle performance of the battery, and can significantly improve the low-temperature discharge performance of the battery during the cycle.

Please refer to FIG. 9. FIG. 9 is a second specific embodiment of the method for improving battery cycle performance shown in FIG. 2. The second specific embodiment is similar to the first specific embodiment, and the second specific embodiment also includes step S91 and step S92. The difference lies in step S91, which is specifically as follows:

Step S91: In the first stage, the battery is charged to the first stage voltage with the first stage current. In the first stage, a third charging method is used to charge the battery to the first stage voltage, and the third charging method is the first charging method or the second charging method.

In this embodiment, the first charging method and the second charging method are the same as the first charging method and the second charging method in the first specific embodiment, and will not be repeated here.

When the third charging method adopts the first charging method, the number of charging sub-stages K between the two may be the same, that is, the charging sub-stages included in the first charging method adopted in the first stage The number may be the same as the number of charging sub-stages included in the first charging method adopted in the second stage; or when the third charging method adopts the second charging method, the charging between the two The number D of electronic stages may be the same, that is, the number of charging sub-stages included in the second charging method adopted in the first stage and the charging sub-stages included in the second charging method adopted in the second stage The number can be the same.

When the third charging method adopts the first charging method, the number of charging sub-stages K between the two may be different, that is, the charging sub-stages included in the first charging method adopted in the first stage The number may be different from the number of charging sub-stages included in the first charging method used in the second stage; or when the third charging method uses the second charging method, the charge between the two The number D of electronic stages may be different, that is, the number of charging sub-stages included in the second charging method adopted in the first stage and the number of charging sub-stages included in the second charging method adopted in the second stage The number can be different.

Please refer to FIG. 10. FIG. 10 is a third specific embodiment of the method for improving the cycle performance of the battery shown in FIG. 2. The third specific embodiment is similar to the first specific embodiment, and the third specific embodiment also includes step S101 and step S102. The difference lies in step S101 and step S102, which are specifically as follows:

Step S101: In the first stage, the battery is charged to the first stage voltage with the first stage current. In the first stage, a third charging method is used to charge the battery to the first stage voltage, and the third charging method is the first charging method or the second charging method.

Step S102: In the second stage, the battery is charged to the second stage voltage with the second stage current, the second stage voltage is greater than the first stage voltage, and the second stage current is smaller than the first stage voltage Current; the second stage adopts the first charging method or the second charging method to charge the battery to the second stage voltage;

Wherein, the battery includes a positive electrode film, the positive electrode film includes a positive electrode active material capable of inserting and extracting lithium ions, and the positive electrode active material includes lithium cobalt oxide primary particles and cobalt composed of the lithium cobalt oxide primary particles. Lithium oxide secondary particles, the average particle size of the lithium cobalt oxide primary particles is 0.1 μm-5 μm, and the average particle size of the lithium cobalt oxide secondary particles is 10 μm-25 μm.

In this embodiment, the second stage current is a constant current, that is, an existing charging current that uses constant current charging when charging is started. Alternatively, the current in the second stage may also be a current of varying magnitude. For example, in the second stage, the battery is charged with a constant voltage, and the charging current corresponding to the constant voltage (that is, the second The size of the phase current) will vary, as long as the battery can be charged to the second phase voltage through the second phase current.

Please refer to FIG. 11. FIG. 11 is a fourth specific embodiment of the method for improving battery cycle performance shown in FIG. 2. The fourth specific embodiment is similar to the first specific embodiment, and the fourth specific embodiment also includes step S111 and step S112. The difference is that the fourth specific embodiment further includes step S113, which is specifically as follows:

Step S113: In the third stage, charge the battery at a constant voltage with the second stage voltage.

In this embodiment, in the third stage, the battery is charged at a constant voltage with the second stage voltage until the battery is fully charged.

In other embodiments, the second specific embodiment can be improved with reference to the fourth embodiment, and step S113 is added: in the third stage, the battery is charged at a constant voltage with the second stage voltage.

In other embodiments, if the current in the second phase of the second phase in the third specific embodiment is a constant current, the third specific embodiment can be improved with reference to the fourth embodiment, and step S113 is added: In the third stage, the battery is charged at a constant voltage with the second stage voltage.

For those skilled in the art, it is obvious that the present application is not limited to the details of the foregoing exemplary embodiments, and the present application can be implemented in other specific forms without departing from the spirit or basic characteristics of the application. Therefore, no matter from which point of view, the above-mentioned embodiments of this application should be regarded as exemplary and non-limiting. The scope of this application is defined by the appended claims rather than the above description, so it is intended to All changes falling within the meaning and scope of equivalent elements of the claims are included in this application.

Claims

A method for improving the cycle performance of a battery, applied to a battery, the battery includes a positive electrode film, the positive electrode film includes a positive electrode active material capable of inserting and extracting lithium ions, the positive electrode active material includes lithium cobalt oxide primary Particles and lithium cobalt oxide secondary particles composed of the lithium cobalt oxide primary particles, the average particle size of the lithium cobalt oxide primary particles is 0.1 μm-5 μm, and the average particle size of the lithium cobalt oxide secondary particles is 10 μm -25μm, the method includes:

In the first stage, the battery is charged to the first stage voltage with the first stage current;

In the second stage, the battery is charged to a second stage voltage with a second stage current, the second stage voltage is greater than the first stage voltage, and the second stage current is less than the first stage current.
The method of claim 1, wherein the chemical formulas of the lithium cobalt oxide primary particles and the lithium cobalt oxide secondary particles are Li a Co 1-b M b O 2-b , wherein M is selected from At least one of Na, Mg, Al, Ti, Zr, Y, Ha, Ni, Mn, V, Cr, La, and Ce, 0.99≤a≤1.01, 0<b≤0.05.
The method according to claim 1, wherein the surfaces of the lithium cobalt oxide primary particles and the lithium cobalt oxide secondary particles are both provided with a coating layer, and the chemical formula of the coating layer is LiNO d , wherein: N is selected from at least one of Al, Ti, Cr and Y, 2<d≦3.
The method of claim 1, wherein the weight ratio of the lithium cobalt oxide primary particles and the lithium cobalt oxide secondary particles is 5:95-50:50.
The method according to claim 1, wherein the second stage adopts a first charging method or a second charging method to charge the battery to the second stage voltage;

The first charging mode includes K charging sub-phases in sequence, K is an integer greater than or equal to 2, and the K charging sub-phases are defined as the i-th charging sub-phases, i = 1, 2, ..., K In the i-th charging sub-phase, charge the battery with one of the i-th current, the i-th voltage and the i-th power; in the i+1-th charging sub-phase, use the i+1-th current , One of the i+1th voltage and the i+1th power charges the battery; wherein the charging current in the i+1th charging substage is less than or equal to the i+1th charging substage The charging current at, or the (i+1)th voltage is greater than or equal to the i-th voltage, or the (i+1)th power is less than or equal to the i-th power; and

The second charging method includes D charging sub-phases in sequence, D is an integer greater than or equal to 2, and the D charging sub-phases are respectively defined as the j-th charging sub-phase, j = 1, 2, ..., D , And each of the j-th charging sub-stage includes a j-th pre-charge sub-stage and a j-th post-charge sub-stage; in one of the j-th pre-charge sub-stage and the j-th post-charge sub-stage, The battery is not charged or is charged or discharged with the j-th pre-charge sub-current for Tj1; in the other of the j-th pre-charge sub-stage and the j-th post-charge sub-stage, the battery is The j-th post-charger current is charged for a duration of Tj2; wherein the absolute value of the j-th pre-charger current is smaller than the absolute value of the j-th post-charger current.
The method according to claim 5, wherein the average value of the charging current of the jth charging substage is less than the charging current of the first phase, and the average value of the charging current of the j+1th charging substage is less than or equal to The charging current of the jth charging substage.
The method of claim 5, wherein the first stage adopts a third charging method to charge the battery to the first stage voltage, and the third charging method adopts the first charging method or the The second charging method.
The method according to claim 7, wherein when the third charging method adopts the first charging method, the number of charging sub-stages K between the two is the same; or when the third charging method When the second charging method is used, the number of charging sub-stages D between the two is the same.
The method according to claim 1, wherein the first stage voltage is equal to the charge limit voltage of the battery, and the second stage voltage is less than the oxidation decomposition voltage of the electrolyte in the battery.
The method of claim 1, wherein the second stage voltage is less than or equal to the first stage voltage plus 500 millivolts.
An electronic device, comprising a battery and a battery management module, characterized in that the battery includes a positive electrode film, the positive electrode film includes a positive electrode active material capable of inserting and extracting lithium ions, and the positive electrode active material includes lithium cobalt oxide Primary particles and lithium cobalt oxide secondary particles composed of the lithium cobalt oxide primary particles, the average particle size of the lithium cobalt oxide primary particles is 0.1 μm-5 μm, and the average particle size of the lithium cobalt oxide secondary particles is 10 μm-25 μm, the battery management module is used to perform the method according to any one of claims 1 to 10.