Battery cyclic charging and discharging method, battery module, battery pack and power supply device

Abstract

The invention relates to a battery cyclic charging and discharging method, a battery module, a battery pack and a power supply device.The battery cyclic charging and discharging method comprises the steps that a battery is charged, and the charging process at least comprises a first charging stage and a second charging stage which are conducted in sequence, the first charging rate of the first charging stage is greater than the second charging rate of the second charging stage; the battery is discharged, the discharging process at least comprises a first discharging stage and a second discharging stage which are conducted in sequence, and the first discharging rate of the first discharging stage is larger than the second discharging rate of the second discharging stage. Therefore, the capacity retention ratio and the cycle performance of the battery can be improved.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a battery cyclic charging and discharging method, a battery module, a battery pack and a power supply device. Background Art

[0002] With the application of high-nickel materials for the positive electrode and silicon-carbon composite materials for the negative electrode, the energy density of lithium-ion batteries (LIB) has reached more than 300Wh / kg, which is close to the maximum energy density that lithium-ion batteries can achieve (about 350Wh / kg). Therefore, it is difficult to further increase the energy density of lithium-ion batteries.

[0003] If the battery is to achieve an energy density of more than 400Wh / kg, a new material system needs to be developed. Alkali metals generally have a higher theoretical capacity. For example, lithium metal has a higher theoretical capacity (about 3860mAh / g), and lithium metal has a lower electrode potential (-3.04V vs. standard hydrogen electrode) and a lower density (about 0.534g / cm 3 ), is a good choice for high energy density battery negative electrode materials.

[0004] The deposition behavior of lithium ions in lithium metal batteries (LMBs) is different from the insertion and extraction behavior of lithium ions in LIBs. During the charging of LMBs, lithium ions obtain electrons from the external circuit, are converted into lithium metal and deposited on the negative electrode in the form of particles. In the existing lithium metal battery cycle system, lithium metal is prone to uneven deposition on the negative electrode, generating lithium dendrites and "dead lithium", which affects the battery's cycle performance and can cause battery short circuits and thermal runaway in severe cases. Summary of the invention

[0005] In view of this, embodiments of the present application provide a battery cyclic charging and discharging method, a battery module, a battery pack, and a power supply device to solve at least one problem existing in the background technology.

[0006] In a first aspect, an embodiment of the present application provides a battery cyclic charging and discharging method, the method comprising:

[0007] Charging the battery, the charging process at least comprising a first charging stage and a second charging stage performed in sequence, a first charging rate in the first charging stage being greater than a second charging rate in the second charging stage;

[0008] The battery is discharged, and the discharge process at least includes a first discharge stage and a second discharge stage performed in sequence, and a first discharge rate in the first discharge stage is greater than a second discharge rate in the second discharge stage.

[0009] In conjunction with the first aspect of the present application, in an optional implementation manner, the first charging rate is 10C to 50C; and / or,

[0010] The duration of the first charging stage is 3s to 30s.

[0011] In conjunction with the first aspect of the present application, in an optional implementation manner, the second charging rate is 0.05C to 1C; and / or,

[0012] The voltage upper limit of the second charging stage is 3.6V to 4.5V.

[0013] In conjunction with the first aspect of the present application, in an optional implementation manner, the first discharge rate is 5C to 10C; and / or,

[0014] The duration of the first discharge stage is 10s to 120s.

[0015] In combination with the first aspect of the present application, in an optional implementation manner, the second discharge rate is 0.05C to 1C; and / or,

[0016] The voltage lower limit of the second discharge stage is 2.5V to 3.0V.

[0017] In conjunction with the first aspect of the present application, in an optional implementation manner, the ambient temperature during the charging process and / or the discharging process is 20° C. to 30° C.; and / or,

[0018] During the charging process and / or the discharging process, pressure is applied to the battery, and the pressure is 0.1 MPa to 1 MPa.

[0019] In combination with the first aspect of the present application, in an optional embodiment, the battery includes a lithium metal battery.

[0020] In a second aspect, an embodiment of the present application provides a battery module, comprising a battery body and a battery management unit connected to the battery body, wherein the battery management unit charges and discharges the battery body using the battery cycle charge and discharge method as described in any one of the first aspects.

[0021] In a third aspect, an embodiment of the present application provides a battery pack comprising the battery module as described in the second aspect.

[0022] In a fourth aspect, an embodiment of the present application provides a power supply device, comprising a battery module as described in the second aspect or a battery pack as described in the third aspect.

[0023] Compared with the prior art, the embodiments of the present application have the following beneficial effects:

[0024] The battery cyclic charge and discharge method, battery module, battery pack and power supply device provided in the embodiments of the present application, the battery cyclic charge and discharge method comprises: charging the battery, the charging process at least comprises a first charging stage and a second charging stage which are performed sequentially, and a first charging rate of the first charging stage is greater than a second charging rate of the second charging stage; discharging the battery, the discharging process at least comprises a first discharging stage and a second discharging stage which are performed sequentially, and a first discharging rate of the first discharging stage is greater than a second discharging rate of the second discharging stage. In the embodiments of the present application, the deposition behavior of active ions (such as lithium ions) can be changed by controlling the battery cycle charge and discharge method. On the one hand, during the charging process, charging at a high charge rate first will form dense and uniform nucleation points on the surface of the negative electrode, and then charging at a low charge rate can promote the uniform deposition of highly dense block metals (such as lithium metal) on the surface of the negative electrode, which can block the electrolyte from entering the negative electrode and reduce the thickness of the SEI (Solid Electrolyte Interface) film, thereby reducing the internal resistance of the battery and reducing the battery polarization, thereby improving the battery cycle performance; on the other hand, during the discharge process, the battery is first discharged at a high discharge rate and then discharged at a low discharge rate. In this way, the inactive metals generated during the battery cycle, such as "dead lithium", can lose electrons and return to the positive electrode in the form of ions, and be converted into active ions that can be reused, thereby improving the battery capacity retention rate and further improving the battery cycle performance.

[0025] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0027] Figure 1 A schematic diagram of a battery cycle charge and discharge method provided in an embodiment of the present application;

[0028] Figure 2 This is an electron microscope image of the lithium metal negative electrode after the lithium metal battery is cycled in Example 1;

[0029] Figure 3 This is an electron microscope image of the lithium metal negative electrode after the lithium metal battery is cycled in Comparative Example 1;

[0030] Figure 4 This is an electron microscope image of the lithium metal negative electrode after the lithium metal battery is cycled in Comparative Example 2;

[0031] Figure 5This is an electron microscope image of the lithium metal negative electrode after the lithium metal battery in Comparative Example 3 is cycled. DETAILED DESCRIPTION

[0032] In order to make the technical scheme and beneficial effects of the present invention more obvious and easy to understand, the following is described in detail by combining the accompanying drawings and listing specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. The experimental methods in the following examples without specifying specific conditions are usually based on conventional experimental conditions. The reagents and raw materials used in the present invention are commercially available unless otherwise specified.

[0033] In the following description, a large number of specific details are given to provide a more thorough understanding of the present application. However, it is obvious to those skilled in the art that the present application can be implemented without one or more of these details. In other examples, in order to avoid confusion with the present application, some technical features known in the art are not described; that is, all features of the actual embodiments are not described here, and well-known functions and steps are not described in detail.

[0034] The purpose of the terms used herein is only to describe specific embodiments and is not intended to be limiting of the present application. When used herein, the singular forms "a", "an" and "said / the" are also intended to include plural forms, unless the context clearly indicates otherwise. The terms "consisting of" and / or "comprising", when used in this specification, determine the presence of the features, integers, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups. When used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0035] In order to thoroughly understand the present application, detailed steps and detailed structures will be presented in the following description to illustrate the technical solution of the present application. The preferred embodiments of the present application are described in detail below, but in addition to these detailed descriptions, the present application may also have other implementation methods.

[0036] Unless otherwise defined, technical and scientific terms used in this application have the same meanings as those in the technical field to which this application belongs.

[0037] If no specific techniques or conditions are specified in the following examples, the conventional techniques or conditions described in the literature in the art, or the conditions recommended by the product instructions and the manufacturer are generally used. The numerical ranges in the following examples all include the endpoint values.

[0038] During the charge and discharge process of lithium metal batteries, the non-uniformity of the passivation layer on the surface of the negative electrode lithium metal can easily lead to non-uniform deposition of lithium on the negative electrode. Moreover, during the high current charge and discharge process, the current density is non-uniform, and the non-uniform deposition of lithium is more serious. The non-uniform deposition of lithium will lead to the growth of lithium dendrites on the surface of lithium metal, aggravating the occurrence of side reactions between lithium metal and electrolyte. In severe cases, lithium dendrites will pierce the diaphragm, causing a short circuit, thereby affecting the cycle performance and safety of the battery. In addition, the growth of lithium dendrites may lead to the formation of "dead lithium", which can no longer participate in the charge and discharge process of the battery, resulting in a shortened battery cycle life. At present, the methods for inhibiting the growth of negative electrode lithium dendrites include the preparation of three-dimensional skeletons, interface modification engineering, and optimization of electrolyte components. Although these methods can alleviate the problem of negative electrode lithium dendrite growth to a certain extent, they each have certain limiting factors. For example, the addition of a three-dimensional skeleton will significantly reduce the energy density of the negative electrode material; interface modification is difficult to take into account flexibility, mechanical strength, ionic conductivity and lithium affinity, and the preparation process of the interface modification layer is complicated and it is difficult to ensure uniformity; the electrolyte additives in the improved electrolyte formula are continuously consumed during the cycle, and the amount used is small, the effect is limited, and it is difficult to play a long-term role.

[0039] Based on this, the present application embodiment provides a battery cycle charging and discharging method, please refer to Figure 1 , the battery cycle charge and discharge method includes:

[0040] Step S1: charging the battery, wherein the charging process at least includes a first charging stage and a second charging stage performed in sequence, wherein a first charging rate in the first charging stage is greater than a second charging rate in the second charging stage;

[0041] Step S2: discharging the battery, wherein the discharging process at least includes a first discharging stage and a second discharging stage performed in sequence, wherein a first discharging rate in the first discharging stage is greater than a second discharging rate in the second discharging stage.

[0042] In the embodiments of the present application, the deposition behavior of active ions (such as lithium ions) can be changed by controlling the battery cycle charge and discharge method. On the one hand, during the charging process, charging at a large charging rate, that is, charging with a large current, will form dense and uniform nucleation points on the surface of the negative electrode, and then charging at a small charging rate, that is, charging with a small current, can promote the uniform deposition of highly dense block metals (such as lithium metal) on the surface of the negative electrode, which can block the electrolyte from entering the negative electrode and reduce the thickness of the SEI film. Therefore, the internal resistance of the battery can be reduced, the battery polarization can be reduced, and thus the battery cycle performance can be improved; on the other hand, during the discharge process, the battery is first discharged at a large discharge rate, that is, discharged with a large current, and then discharged at a small discharge rate, that is, discharged with a small current. In this way, the inactive metals generated during the battery cycle, such as "dead lithium", can lose electrons and return to the positive electrode in the form of ions, and be converted into active ions that can be reused, thereby improving the capacity retention rate of the battery and further improving the battery cycle performance.

[0043] It should be understood that, although the steps in the above flowchart are shown in sequence as indicated by the arrows, these steps are not necessarily performed in the order indicated by the arrows. Moreover, at least a portion of the steps in the above flowchart may include multiple steps or multiple stages, and these steps or stages are not necessarily performed at the same time or performed in sequence.

[0044] In some embodiments, the first charging rate in step S1 may be 10C to 50C, for example, 10C, 20C, 30C, 40C, 50C or any value between any two of the above ranges. Considering that the capacity density of a general positive electrode sheet is about 2 mAh / cm 2 ~5mAh / cm 2 By controlling the first charging rate in the first charging stage within the above range, it can promote the formation of more dense and uniform nucleation points on the negative electrode surface during the cycle while ensuring the battery charging and discharging speed and reducing the battery polarization, thereby better promoting the uniform deposition of metal on the negative electrode surface.

[0045] It should be noted that the first charging rate can also be converted into a charging current density. The first charging current density in the first charging stage can be 40 mA / cm 2 ~200mA / cm 2 , for example, it can be 40mA / cm 2 、80mA / cm 2 , 120mA / cm 2 , 160mA / cm 2 , 200mA / cm 2 Or any value between any two of the above numerical ranges.

[0046] It can be understood that when the time of the first charging stage is too short, it is not conducive to the formation of relatively dense and uniform nucleation points on the surface of the negative electrode; when the time of the first charging stage is too long, it may cause the nucleation points to be too large and unevenly grown, thereby affecting the subsequent uniform deposition of metals on the surface of the negative electrode. Therefore, in some specific embodiments, the time of the first charging stage can be 3s to 30s, for example, it can be 3s, 5s, 10s, 15s, 20s, 25s, 30s or any value between any two of the above numerical ranges. In this way, by charging with a large current for a relatively short time, which can also be called instantaneous large current charging, more dense and uniform nucleation points can be formed on the surface of the negative electrode, which can better improve the uniformity of subsequent metal deposition on the surface of the negative electrode, thereby further improving the cycle life and cycle performance of the battery.

[0047] In some embodiments, the second charge rate may be 0.05C to 1C, for example, 0.05C, 0.15C, 0.25C, 0.35C, 0.45C, 0.55C, 0.65C, 0.75C, 0.85C, 0.95C, 1C or any value between any two of the above ranges. This can promote the deposition of more uniform and dense bulk metal on the negative electrode, better block the electrolyte from entering the negative electrode, further reduce the battery internal resistance and battery polarization, and thus better improve the battery cycle performance.

[0048] It should be noted that the second charging rate can also be converted into a charging current density. The second charging current density in the second charging stage can be 0.2 mA / cm 2 ~4mA / cm 2 , for example, it can be 0.2 mA / cm 2 , 1mA / cm 2 , 2mA / cm 2 , 3mA / cm 2 , 4mA / cm 2 Or any value between any two of the above numerical ranges.

[0049] It should also be noted that during the battery cycle, the second charging stage is the stage in which the active metal is stably deposited at the negative electrode, and is the charging stage that makes the main contribution to the battery's charging capacity. Therefore, the time of the second charging stage is usually significantly increased relative to the first charging stage, for example, usually more than 1 hour, which varies depending on the different battery types.

[0050] It is understood that the upper voltage limit of the second charging stage can be adjusted according to the type of positive electrode material of the battery, so as to better balance the safety of the battery and improve the cycle performance of the battery. In some specific embodiments, the upper voltage limit of the second charging stage can be 3.6V to 4.5V, for example, 3.6V, 3.8V, 4.0V, 4.2V, 4.5V or any value between any two of the above ranges.

[0051] Specifically, when the positive electrode material of the battery includes lithium iron phosphate, the upper voltage limit of the second charging stage can be, for example, 3.35V; when the positive electrode material of the battery includes a ternary positive electrode material, the upper voltage limit of the second charging stage can be, for example, 4.2V to 4.5V; when the positive electrode material of the battery includes lithium cobalt oxide, the upper voltage limit of the second charging stage can be, for example, 4.5V; when the positive electrode material of the battery includes lithium manganate, the upper voltage limit of the second charging stage can be, for example, 4.3V. It can be seen that the battery cycle charge and discharge method in the embodiment of the present application has a wide range of applicability and is applicable to batteries composed of a variety of common positive electrode materials.

[0052] In some embodiments, the first discharge rate may be 5C to 10C, for example, 5C, 6C, 7C, 8C, 9C, 10C or any value between any two of the above value ranges.

[0053] It should be noted that the first discharge rate can also be converted into a discharge current density. The first discharge current density in the first discharge stage can be 20 mA / cm 2 ~40mA / cm 2 , for example, it can be 20mA / cm 2 , 25mA / cm 2 、30mA / cm 2 、35mA / cm 2 , 40mA / cm 2 Or any value between any two of the above numerical ranges.

[0054] Furthermore, the duration of the first discharge stage may be 10 s to 120 s, for example, 10 s, 30 s, 50 s, 70 s, 90 s, 110 s, 120 s or any value between any two of the above value ranges.

[0055] In some embodiments, the second discharge rate can be 0.05C to 1C, for example, 0.05C, 0.15C, 0.25C, 0.35C, 0.45C, 0.55C, 0.65C, 0.75C, 0.85C, 0.95C, 1C or any value between any two of the above value ranges.

[0056] It should be noted that the second discharge rate can also be converted into a discharge current density. The second discharge current density in the second discharge stage can be 0.2 mA / cm 2 ~4mA / cm 2 , for example, it can be 0.2 mA / cm 2 , 1mA / cm 2 , 2mA / cm 2 , 3mA / cm 2 , 4mA / cm 2 Or any value between any two of the above numerical ranges.

[0057] By controlling the discharge rates of the first discharge stage and the second discharge stage and the time of the first discharge stage within the above range, the inactive metals generated during the battery cycle can be better promoted to be converted into active ions that can be reused, such as converting "dead lithium" more quickly and thoroughly into active lithium that can be reused, thereby further improving the battery's capacity retention rate, and better reducing the polarization of the battery, further improving the battery's cycle performance.

[0058] It is understood that the lower voltage limit of the second discharge stage can be adjusted according to the type of positive electrode material of the battery, so as to better balance the safety of the battery and improve the cycle performance of the battery. In some specific embodiments, the lower voltage limit of the second discharge stage can be 2.5V to 3.0V, for example, 2.5V, 2.6V, 2.7V, 2.8V, 2.9V, 3.0V or any value between any two of the above ranges.

[0059] Specifically, when the positive electrode material of the battery includes lithium iron phosphate, the lower voltage limit of the second discharge stage can be, for example, 2.5V; when the positive electrode material of the battery includes a ternary positive electrode material, the lower voltage limit of the second discharge stage can be, for example, 2.5V to 3.0V; when the positive electrode material of the battery includes lithium cobalt oxide, the lower voltage limit of the second discharge stage can be, for example, 3.0V; when the positive electrode material of the battery includes lithium manganate, the lower voltage limit of the second discharge stage can be, for example, 3.0V. It can be seen that the battery cycle charge and discharge method in the embodiment of the present application has a wide applicability and is applicable to batteries composed of a variety of common positive electrode materials.

[0060] In a specific embodiment, a cycle in the battery cyclic charge and discharge method of the present application may include: charging the battery at a first charge rate, then charging the battery at a second charge rate to an upper voltage limit, leaving it for 10 minutes to 30 minutes, then discharging the battery at a first discharge rate, then discharging the battery at a second discharge rate to a lower voltage limit, and leaving it for 10 minutes to 30 minutes.

[0061] In some embodiments, the ambient temperature during the charging process and / or the discharging process may be 20° C. to 30° C.

[0062] The temperature of at least one of the charging process and the discharging process is within the above range. The battery cycle charge and discharge method of the present application can promote more uniform deposition of active ions on the negative electrode surface, thereby further improving the capacity retention rate and cycle performance of the battery.

[0063] In some embodiments, pressure may be applied to the battery during the charging process and / or the discharging process, and the pressure is 0.1 MPa to 1 MPa.

[0064] The pressure of at least one of the charging process and the discharging process is within the above range. The battery cycle charge and discharge method in the present application can promote more uniform deposition of active ions on the negative electrode surface, thereby further improving the capacity retention rate and cycle performance of the battery.

[0065] The battery cycle charge and discharge method in the present application is applicable to various types of batteries, such as alkali metal batteries, more specifically, lithium metal batteries, sodium metal batteries or magnesium metal batteries.

[0066] In some specific embodiments, the battery comprises a lithium metal battery.

[0067] When the battery cyclic charge and discharge method in the present application is applied to a lithium metal battery, it can promote the formation of more dense and uniform lithium nucleation points on the surface of the negative electrode lithium metal, thereby promoting a more uniform deposition of lithium metal on the negative electrode surface, thereby better improving the cycle life and cycle performance of the battery.

[0068] Illustratively, the negative electrode material of a lithium metal battery may include lithium metal and / or lithium alloy; the positive electrode material of a lithium metal battery may include at least one of lithium iron phosphate, a ternary positive electrode material, lithium cobalt oxide, and lithium manganese oxide; the electrolyte of a lithium metal battery may be a solid electrolyte or a liquid electrolyte, and the type of electrolyte can be flexibly adjusted by those skilled in the art according to the type of battery, and this application does not impose any specific restrictions.

[0069] An embodiment of the present application also provides a battery module, which includes a battery body and a battery management unit connected to the battery body, and the battery management unit uses the battery cycle charging and discharging method described in any of the above embodiments to charge and discharge the battery body.

[0070] It can be understood that the beneficial effects of the battery cycle charge and discharge method described in any of the above embodiments are applicable to the battery module in the embodiment of the present application. The battery body is charged and discharged by the battery cycle charge and discharge method described in any of the above embodiments. By first charging with a large current and then charging with a small current during the charging process, the internal resistance of the battery can be reduced, the battery polarization can be reduced, and the battery cycle performance can be improved; by first discharging with a large current and then discharging with a small current during the discharging process, the battery capacity retention rate can be improved, and the battery cycle performance can be further improved.

[0071] An embodiment of the present application also provides a battery pack, which includes the battery module described in the above embodiment.

[0072] It can be understood that the beneficial effects of the battery modules described in the above embodiments are all applicable to the battery pack in the embodiments of the present application.

[0073] It should be noted that the battery pack usually also includes necessary components such as a casing and a bus. The function of these components is to ensure the normal operation of various functions of the battery pack. Since these components and the connection design between these components and the battery module are well known to those skilled in the art, they will not be described in detail here.

[0074] An embodiment of the present application further provides a power supply device, which includes the battery module described in the above embodiment or the battery pack described in the above embodiment.

[0075] It can be understood that the beneficial effects of the battery module and the battery pack described in the above embodiments are all applicable to the power supply device in the embodiments of the present application.

[0076] The power supply device in the embodiments of the present application can be applied to electronic devices such as electronic devices, electric vehicles or power storage systems. Among them, the electronic device includes, for example, various computers, mobile phones, display screens and other devices that use the power supply device as a driving power source. Electric vehicles include, for example, electric cars, electric tricycles, electric bicycles, etc. that use the power supply device as a driving power source. The power storage system includes, for example, a power storage system that uses the power supply device as a power storage source. In these electronic devices, the power supply device can be electrically connected to the electrical components to provide electrical energy to the electrical components.

[0077] The technical solution of the present application is further described below in conjunction with a plurality of embodiments and comparative examples. The batteries involved in the embodiments and comparative examples include lithium metal batteries, sodium metal batteries and lithium ion batteries, wherein the preparation methods of lithium metal batteries, sodium metal batteries and lithium ion batteries are as follows.

[0078] The preparation method of lithium metal battery is as follows: 50μm copper lithium strip is cut into sheets of 3.4cm*4.4cm in size by using a cutting machine as a negative electrode sheet. First, the positive electrode active material NCM613, conductive carbon black (Super P) and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 96:2:2, dispersed in N-methylpyrrolidone (NMP) solvent, and stirred evenly to obtain a positive electrode active material layer slurry; next, the positive electrode active material layer slurry is evenly coated on aluminum foil, and dried at 80°C for 12h to form a positive electrode active material layer; then the sheet is pressed and cut into sheets of 3cm*4cm in size as a positive electrode sheet. The separator is cut into sheets of 4cm*5cm in size. After the positive and negative electrode sheets are welded to the pole ears by an ultrasonic welding machine, the positive electrode sheet, the separator, and the negative electrode sheet are placed in an aluminum-plastic film in turn, and an electrolyte is added at a rate of 4 g / Ah, wherein the electrolyte is a solution of 1 M LiTFSI in a mixed solvent of ethylene glycol dimethyl ether (DME) and 1,1,2,2-tetrafluoroethyl-2,2,3,3,-tetrafluoropropyl ether (TTE) in a volume ratio of 1:1. After vacuum sealing, a lithium metal battery is obtained.

[0079] The preparation method of sodium metal battery is as follows: 50 μm copper sodium ribbon is cut into sheets of 3.4 cm*4.4 cm in size by using a cutting machine as the negative electrode sheet. 3 V 2 (PO 4 )) 3 , conductive agent Super P and binder PVDF are mixed in a mass ratio of 96:2:2, dispersed in NMP solvent, and stirred evenly to obtain the positive electrode active material layer slurry; next, the positive electrode active material layer slurry is evenly coated on aluminum foil, and dried at 80°C for 12 hours to form a positive electrode active material layer; then pressed into sheets and cut into sheets with a size of 3cm*4cm as positive electrode sheets. The diaphragm is cut into sheets with a size of 4cm*5cm. After the positive and negative electrode sheets are welded to the pole ears by an ultrasonic welding machine, the positive electrode sheet, diaphragm, and negative electrode sheet are placed in the aluminum-plastic film in turn, and the electrolyte is added at 4g / Ah, where the electrolyte is 1M NaPF 6 A sodium metal battery was obtained by vacuum sealing a solution in a mixed solvent of fluoroethylene carbonate (FEC), propylene carbonate (PC) and TTE in a volume ratio of 1:1:1.

[0080] It should be noted that in the following examples and comparative examples, the ambient temperature of the battery during the charging and discharging process is 25°C, and the pressure applied to the battery during the charging and discharging process is 0.1 MPa. The batteries in Examples 1 to 13 and Comparative Examples 1 to 3 are the lithium metal batteries prepared above, and the batteries in Example 14 and Comparative Example 4 are the sodium metal batteries prepared above.

[0081] Example 1

[0082] The battery cyclic charge and discharge method in this embodiment is: charging at a first charge rate constant current of 25C for 10s (first charging stage) on the charging and discharging device, then charging at a second charge rate constant current of 0.2C to 4.3V (second charging stage), leaving for 15min, discharging at a first discharge rate of 8C for 60s (first discharge stage), then discharging at a second discharge rate of 0.5C to 2.8V (second discharge stage), leaving for 15min, this is one cycle, and the cycle is repeated 100 times. The charging capacity at the 1st and 100th cycles is recorded, and the capacity retention rate of the battery after 100 cycles is obtained by dividing the charging capacity at the 100th cycle by the charging capacity at the 1st cycle.

[0083] Example 2

[0084] The battery cyclic charging and discharging method in this embodiment is basically the same as that in embodiment 1, except that:

[0085] The first charging rate in the first charging stage is 10C.

[0086] Example 3

[0087] The battery cyclic charging and discharging method in this embodiment is basically the same as that in embodiment 1, except that:

[0088] The first charging rate in the first charging stage is 50C.

[0089] Example 4

[0090] The battery cyclic charging and discharging method in this embodiment is basically the same as that in embodiment 1, except that:

[0091] The first discharge rate in the first discharge stage is 5C.

[0092] Example 5

[0093] The battery cyclic charge and discharge method in this embodiment is basically the same as that in Embodiment 1, except that: the first discharge rate in the first discharge stage is 10C.

[0094] Example 6

[0095] The battery cyclic charging and discharging method in this embodiment is basically the same as that in Embodiment 1, except that the charging time in the first charging stage is 3s.

[0096] Example 7

[0097] The battery cyclic charging and discharging method in this embodiment is basically the same as that in Embodiment 1, except that the charging time in the first charging stage is 30 seconds.

[0098] Example 8

[0099] The battery cyclic charge and discharge method in this embodiment is basically the same as that in Embodiment 1, except that the discharge time in the first discharge stage is 10s.

[0100] Example 9

[0101] The battery cyclic charge and discharge method in this embodiment is basically the same as that in Embodiment 1, except that the discharge time in the first discharge stage is 120s.

[0102] Example 10

[0103] The battery cyclic charge and discharge method in this embodiment is basically the same as that in Embodiment 1, except that the second charge rate in the second charging stage is 0.05C.

[0104] Embodiment 11

[0105] The battery cyclic charge and discharge method in this embodiment is basically the same as that in Embodiment 1, except that the second charging rate in the second charging stage is 1C.

[0106] Example 12

[0107] The battery cyclic charge and discharge method in this embodiment is basically the same as that in Embodiment 1, except that the second discharge rate in the second discharge stage is 0.05C.

[0108] Embodiment 13

[0109] The battery cyclic charging and discharging method in this embodiment is basically the same as that in embodiment 1, except that:

[0110] The second discharge rate in the second discharge stage is 1C.

[0111] Embodiment 14

[0112] The battery cyclic charge and discharge method in this embodiment is the same as that in Embodiment 1, and the difference from Embodiment 1 is that the lithium metal battery is replaced by a sodium metal battery.

[0113] Comparative Example 1

[0114] The battery cyclic charge and discharge method in this comparative example is: charge to 4.3V at a constant current rate of 0.2C on the charge and discharge equipment, leave for 15 minutes, discharge to 2.8V at a rate of 0.5C, leave for 15 minutes, this is one cycle, and the cycle is 100 times. The charging capacity at the 1st and 100th cycles is recorded, and the capacity retention rate of the battery after 100 cycles is obtained by dividing the charging capacity at the 100th cycle by the charging capacity at the 1st cycle.

[0115] Comparative Example 2

[0116] The battery cyclic charge and discharge method in this comparative example is: charging at a constant current rate of 25C for 10s on the charging and discharging device, then charging at a constant current rate of 0.2C to 4.3V, leaving it for 15min, discharging at a rate of 0.5C to 2.8V, leaving it for 15min, and this is a cycle, and the cycle is repeated 100 times. The charging capacity at the 1st and 100th cycles is recorded, and the capacity retention rate of the battery after 100 cycles is obtained by dividing the charging capacity at the 100th cycle by the charging capacity at the 1st cycle.

[0117] Comparative Example 3

[0118] The battery cyclic charge and discharge method in this comparative example is: charge to 4.3V at a constant current rate of 0.2C on the charge and discharge equipment, leave for 15 minutes, discharge at a rate of 8C for 60 seconds, and then discharge to 2.8V at a rate of 0.5C, leave for 15 minutes, this is a cycle, and the cycle is repeated 100 times. The charge capacity at the 1st and 100th cycles is recorded, and the capacity retention rate of the battery after 100 cycles is obtained by dividing the charge capacity at the 100th cycle by the charge capacity at the 1st cycle.

[0119] Comparative Example 4

[0120] The battery cycle charge and discharge method in this comparative example is the same as that in comparative example 1, except that the lithium metal battery is replaced by a sodium metal battery.

[0121] The capacity retention rates of the batteries in the above-mentioned embodiments and comparative examples after 100 cycles are shown in Table 1.

[0122] Table 1

[0123] Battery capacity retention after 100 cycles (%) Example 1 94.3 Example 2 93.4 Example 3 93.8 Example 4 93.5 Example 5 93.9 Example 6 93.8 Example 7 94.2 Example 8 93.0 Example 9 93.9 Example 10 94.2 Embodiment 11 94.3 Example 12 94.6 Embodiment 13 92.8 Embodiment 14 90.5 Comparative Example 1 87.2 Comparative Example 2 90.1 Comparative Example 3 89.5 Comparative Example 4 86.2

[0124] It can be seen from the data in Table 1 that the capacity retention rates of the batteries of Examples 1 to 13 after 100 cycles are all higher than the capacity retention rates of the batteries of Comparative Examples 1 to 3 after 100 cycles. The capacity retention rate of the battery of Example 14 after 100 cycles is higher than the capacity retention rate of the battery of Comparative Example 4 after 100 cycles. This shows that the battery cycle charge and discharge method in the present application is applicable to various types of batteries such as lithium metal batteries and sodium metal batteries. The battery cyclic charge and discharge method in the present application, during the charging process, first charges at a high charge rate, which will form dense and uniform nucleation points on the surface of the negative electrode, and then charges at a low charge rate, which can promote the uniform deposition of highly dense block metals (such as lithium metal) on the surface of the negative electrode, which can block the electrolyte from entering the negative electrode and reduce the thickness of the SEI film, thereby reducing the internal resistance of the battery, reducing the battery polarization, and thus improving the battery cycle performance; during the discharging process, first discharge at a high discharge rate, and then discharge at a low discharge rate, so that the inactive metals generated during the battery cycle, such as "dead lithium" or "dead sodium", can lose electrons and return to the positive electrode in the form of ions, and be converted into active ions that can be reused, thereby improving the battery capacity retention rate and further improving the battery cycle performance.

[0125] In Comparative Examples 1 and 4, since the charging process only includes a charging stage with a small charging rate, and the discharging process only includes a discharging stage with a small discharging rate, it is difficult to improve the deposition behavior of the metal on the negative electrode surface, and it is impossible to promote the uniform deposition of the metal on the negative electrode surface, and it is also difficult to convert the inactive metals generated during the battery cycle, such as "dead lithium" or "dead sodium", into active ions that can be reused. Therefore, compared with other embodiments with the same battery type, the cycle life of the batteries in Comparative Examples 1 and 4 is shorter, and the cycle performance cannot be improved.

[0126] In Comparative Example 2, although charging is performed at a high charging rate first and then at a low charging rate during the charging process, since the cycle method of first discharging at a high discharge rate and then discharging at a low discharge rate is not adopted during the discharge process, compared with other embodiments with the same battery type, the cycle life of the battery in Comparative Example 2 is shorter and the cycle performance cannot be improved.

[0127] In Comparative Example 3, although the discharge process is performed at a high discharge rate first and then at a low discharge rate, since the charging process does not adopt a cycle method of charging at a high charge rate first and then at a low charge rate, compared with other embodiments with the same battery type, the cycle life of the battery in Comparative Example 3 is shorter and the cycle performance cannot be improved.

[0128] Figure 2 This is an electron microscope image of the lithium metal negative electrode after the lithium metal battery is cycled in Example 1. Figures 3 to 5 The electron microscope images of the lithium metal negative electrode after the lithium metal battery cycle in Comparative Examples 1 to 3 are respectively. Figure 3 and Figure 5 It can be seen that the lithium metal deposited on the lithium metal negative electrode in Comparative Examples 1 and 3 contains randomly distributed spike-shaped lithium dendrites. Figure 4 It can be seen that the lithium metal deposited on the lithium metal negative electrode in Comparative Example 2 is in the form of uneven blocks and long strips. Figure 2 and Figures 3 to 5 It can be seen from the comparison that the battery cyclic charge and discharge method in the present application can promote the uniform deposition of lithium metal, effectively inhibit the formation of lithium dendrites, so that the lithium metal deposited on the negative electrode presents a highly dense and uniform block, which can block the electrolyte from entering the negative electrode and reduce the thickness of the SEI film. Therefore, it can reduce the internal resistance of the battery and reduce the battery polarization, thereby improving the capacity retention rate and cycle performance of the battery.

[0129] In the present application, the metal deposition behavior on the negative electrode surface is changed through the battery charging and discharging mode. The staged high current charging and discharging is adopted in the charging and discharging process, which can promote the activation of highly dense block metals and inactive metals (such as "dead lithium") uniformly deposited on the negative electrode surface, thereby improving the battery cycle stability. At the same time, it can reduce the dependence of the battery, especially the lithium metal battery, on the optimized special electrolyte, so that the battery can show excellent cycle performance in different types of electrolytes.

[0130] It should be noted that the battery cycle charge and discharge method embodiments, battery module embodiments, battery pack embodiments and power supply device embodiments provided in the present application belong to the same concept; the technical features in the technical solutions recorded in each embodiment can be combined arbitrarily without conflict.

[0131] It should be understood that the above embodiments are exemplary and are not intended to include all possible implementations. Various modifications and changes may be made on the basis of the above embodiments without departing from the scope of the present disclosure. Similarly, the various technical features of the above embodiments may be arbitrarily combined to form other embodiments of the present invention that may not be explicitly described. Therefore, the above embodiments only express several implementations of the present invention and do not limit the scope of protection of the patent of the present invention.

Claims

1. A battery cyclic charging and discharging method, characterized in that: The method comprises: Charging the battery, the charging process at least comprising a first charging stage and a second charging stage performed in sequence, a first charging rate in the first charging stage being greater than a second charging rate in the second charging stage; The battery is discharged, wherein the discharge process at least includes a first discharge stage and a second discharge stage performed in sequence, wherein a first discharge rate in the first discharge stage is greater than a second discharge rate in the second discharge stage.

2. The battery cyclic charge and discharge method according to claim 1, characterized in that: The first charging rate is 10C to 50C; and / or, The duration of the first charging stage is 3s to 30s.

3. The battery cyclic charge and discharge method according to claim 1, characterized in that: The second charging rate is 0.05C to 1C; and / or, The voltage upper limit of the second charging stage is 3.6V to 4.5V.

4. The battery cyclic charge and discharge method according to claim 1, characterized in that: The first discharge rate is 5C to 10C; and / or, The duration of the first discharge stage is 10s to 120s.

5. The battery cyclic charge and discharge method according to claim 1, characterized in that: The second discharge rate is 0.05C to 1C; and / or, The voltage lower limit of the second discharge stage is 2.5V to 3.0V.

6. The battery cyclic charging and discharging method according to claim 1, characterized in that: The ambient temperature during the charging process and / or the discharging process is 20° C. to 30° C.; and / or, During the charging process and / or the discharging process, pressure is applied to the battery, and the pressure is 0.1 MPa to 1 MPa.

7. The battery cyclic charge and discharge method according to any one of claims 1 to 6, characterized in that: The battery comprises a lithium metal battery.

8. A battery module, comprising a battery body and a battery management unit connected to the battery body, characterized in that: The battery management unit charges and discharges the battery body using a battery cycle charge and discharge method as described in any one of claims 1 to 7.

9. A battery pack, characterized in that: Comprising the battery module as claimed in claim 8.

10. A power supply device, characterized in that: Comprising the battery module as claimed in claim 8 or the battery pack as claimed in claim 9.

Images