Lithium battery formation method

Abstract

The invention provides a lithium battery formation method, which comprises the following steps that a lithium battery needing to be formed is circularly charged and discharged for multiple times, and at least one of charging and discharging adopts alternating current. According to the lithium battery formation method provided by the invention, the stability and conductivity of an SEI film can be remarkably improved, the charge-discharge performance of a lithium battery is improved, and the service life of the battery is prolonged.

Description

Technical Field

[0001] The present application relates to the technical field of lithium batteries, and in particular to a lithium battery formation method. Background Art

[0002] Lithium batteries have attracted widespread attention due to their high energy density and excellent performance, and have been increasingly widely used in electric vehicles and stationary energy storage systems. However, these application scenarios place strict requirements on the cycle life and overall performance of the battery. In lithium-ion batteries, the formation of the solid electrolyte membrane (SEI) is a key performance factor. It is formed by the decomposition of the electrolyte on the surface of the negative electrode during the first charge and discharge process of the battery, that is, the formation stage. A stable SEI film can protect the negative electrode from further decomposition of the electrolyte and prevent the shedding of graphite materials. Therefore, the formation process is an indispensable and important step in the manufacture of lithium-ion batteries.

[0003] Based on this, how to improve the formation process to improve the performance of lithium batteries is a problem that the industry has been studying. Summary of the invention

[0004] The present application provides a lithium battery formation method, which can significantly improve the stability and conductivity of the SEI film, improve the charge and discharge performance of the lithium battery and extend the service life of the battery.

[0005] The present application provides a lithium battery formation method, comprising: performing multiple cycles of charging and discharging on a lithium battery to be formed, wherein at least one of the charging and discharging uses alternating current.

[0006] In some embodiments of the present application, the charging uses direct current and the discharging uses alternating current.

[0007] In some embodiments of the present application, the charging uses alternating current, and the discharging uses direct current.

[0008] In some embodiments of the present application, the charging uses alternating current, and the discharging uses alternating current.

[0009] In some embodiments of the present application, the frequency f of the alternating current is c 500Hz to 1MHz.

[0010] In some embodiments of the present application, the amplitude of the alternating current is a It is 0.05C-2C.

[0011] In some embodiments of the present application, the number of charge and discharge cycles is 1-50 times.

[0012] In some embodiments of the present application, in each cycle, the charging is stopped when the voltage of the lithium battery reaches a charging cut-off voltage.

[0013] In some embodiments of the present application, in each cycle, the discharging is stopped when the voltage of the lithium battery reaches a discharge cut-off voltage.

[0014] In some embodiments of the present application, when at least one of the charging and discharging uses alternating current, direct current is also superimposed.

[0015] The present application provides a lithium battery formation method, which can significantly improve the stability and conductivity of the SEI film, improve the charge and discharge performance of the lithium battery and extend the service life of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The following figures describe in detail the exemplary embodiments disclosed in this application. The same reference numerals represent similar structures in several views of the drawings. Those skilled in the art will understand that these embodiments are non-limiting, exemplary embodiments, and the drawings are only for the purpose of illustration and description, and are not intended to limit the scope of this application. Other embodiments may also accomplish the inventive intent in this application. It should be understood that the drawings are not drawn to scale.

[0017] in:

[0018] Figure 1 A flow chart of the formation method described in some embodiments of the present application;

[0019] Figure 2 The electrochemical impedance spectroscopy Nyquist plots of the lithium batteries in Example 1 and Comparative Example 1;

[0020] Figure 3 The XPS analysis results of the lithium batteries in Comparative Example 1 and Example 1 are shown. DETAILED DESCRIPTION

[0021] The following description provides specific application scenarios and requirements of the present application, with the purpose of enabling those skilled in the art to make and use the content in the present application. It will be apparent to those skilled in the art that various local modifications to the disclosed embodiments are apparent, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present application. Therefore, the present application is not limited to the embodiments shown, but to the widest scope consistent with the claims.

[0022] The technical solution of the present invention is described in detail below in conjunction with the embodiments and drawings.

[0023] Studies have shown that the increase of inorganic components in the SEI membrane, such as oxides, carbonates, and lithium salt precipitates, can significantly improve the stability of the SEI membrane, because they can fill the pores of the SEI membrane, increase the density of the membrane, and provide channels for ion transmission. Among the inorganic components, lithium carbonate (Li2CO3) and lithium fluoride (LiF) have a greater tendency to be generated thermodynamically, so they enable the generated SEI membrane to exist more stably, reducing the dissolution and destruction of the SEI membrane during the electrochemical cycle. In addition, the increase of inorganic components also helps to improve the conductivity of the SEI membrane. This is because inorganic components such as LiF and Li2CO3 can not only provide a fast transmission channel for lithium ions, but also reduce the further decomposition of the electrolyte, thereby maintaining the stability of the internal environment of the battery.

[0024] In summary, the increase of inorganic components in the SEI film is of great significance for improving the charge and discharge performance of lithium batteries and extending battery life. By optimizing the formation method and increasing the content of inorganic components in the SEI film, the stability and conductivity of the SEI film can be effectively enhanced, thereby improving the overall performance and reliability of the battery. However, during the formation process, the charge and discharge current, charge and discharge time, charge and discharge cut-off voltage, and ambient temperature of the formation will have a significant impact on the formation of the battery SEI film and the battery capacity impedance. How to systematically optimize the formation process to form the best SEI film and ultimately improve battery performance has become a major problem.

[0025] In order to improve the battery formation effect, relevant scholars start from optimizing the battery formation charge and discharge method by adjusting the formation charge and discharge current, formation charge and discharge time, formation charge and discharge cut-off voltage, formation aging time and temperature and other parameters. Although these methods can improve the cycle performance of the battery to a certain extent, there are still few in-depth studies and analyses of the battery mechanism. In addition, the formation process takes a long time, and batteries under some formation methods cannot meet high performance requirements. At the same time, the synergy between these technical parameters is highly complex, resulting in high equipment manufacturing costs and environmental control costs, and limited improvement effects.

[0026] On the other hand, from the perspective of battery manufacturing technology, by changing the ratio of battery positive and negative electrode materials, diaphragms, electrolytes and other materials, although the battery performance can be improved to a certain extent, this method will lead to increased production costs and is not universal. At the same time, some scholars have effectively improved the battery formation performance by improving the contact between the electrolyte and the electrode from the perspective of electrolyte wettability. However, this method cannot accurately determine the specific wetting effect of the battery, and has high requirements for the experimental environment. There is a risk of uneven wetting leading to a serious reduction in battery life.

[0027] In order to meet the formation requirements of different batteries and improve the formation effect of batteries under different environments, thereby achieving a balance between efficient battery charging and discharging and battery life, the present application provides a lithium battery formation method.

[0028] Figure 1 This is a flow chart of the formation method described in some embodiments of the present application.

[0029] refer to Figure 1 As shown, the present application provides a lithium battery formation method, comprising: step S1: charging and discharging the lithium battery to be formed for multiple cycles, at least one of the charging and discharging using alternating current. Among them, the lithium battery to be formed refers to a lithium battery that has not been charged and discharged for the first time after liquid injection during the lithium battery manufacturing process. The formation process is a conventional step in the lithium battery manufacturing process, and the present application will not repeat the detailed background of the formation process here.

[0030] The current formation process uses direct current to charge and discharge lithium batteries. In the technical solution of the present application, alternating current is used to charge and discharge lithium batteries during formation, which can significantly increase the content of inorganic components in the SEI film. The increase in inorganic components in the SEI film can significantly improve the stability and conductivity of the SEI film, which has a significant positive impact on improving the charge and discharge performance of the battery and extending the service life of the battery.

[0031] In some embodiments of the present application, the charging adopts direct current, and the discharging adopts alternating current. In some embodiments of the present application, the charging adopts alternating current, and the discharging adopts direct current. In some embodiments of the present application, the charging adopts alternating current, and the discharging adopts alternating current. The formation method of the present application can adopt alternating current during any charging or discharging, specifically, it is selected to adopt alternating current during charging or adopting alternating current during discharging, or adopting alternating current during both charging and discharging according to needs.

[0032] In some embodiments of the present application, when at least one of the charging and discharging uses alternating current, direct current is also superimposed.

[0033] In some embodiments of the present application, the frequency f of the alternating current is c It is 500Hz to 1MHz, for example, 1KHz, 2KHz, 3KHz, 5KHz, 8KHz, 10KHz, 20KHz, 50KHz, etc.

[0034] In some embodiments of the present application, the amplitude of the alternating current is a Specifically, the amplitude of the alternating current is 0.05C-2C. a You can choose according to the type and characteristics of the lithium battery to adapt to different battery systems.

[0035] In some embodiments of the present application, the number of cycles of charging and discharging is 1-2 times. In conventional formation methods, the optimal formation effect can be achieved by cyclic charging at least 3 times, while in the technical solution of the present application, the optimal formation effect can be achieved by only about 1-2 times, which can effectively reduce the number of charging and discharging cycles and improve the formation efficiency.

[0036] In some embodiments of the present application, in each cycle, the charging stops when the voltage of the lithium battery reaches the charging cut-off voltage. In some embodiments of the present application, in each cycle, the discharging stops when the voltage of the lithium battery reaches the discharging cut-off voltage.

[0037] Below, in order to more clearly illustrate the technical effect of the application, the application is provided with different embodiments and comparative examples. Specifically, provide some lithium batteries of the same specification that adopt the same process to make, then adopt conventional formation process and the formation process of the application to form these lithium batteries respectively, then test the lithium battery after formation to obtain its charge capacity retention rate and cycle performance etc. Wherein, the comparative example is a conventional formation method. And the embodiment is for adopting the formation method of the application, wherein, the parameters such as current frequency and cycle number are different in different embodiments. The relevant parameters and test data etc. in the described comparative example and the embodiment are recorded in the following table 1.

[0038]

[0039] With reference to Table 1, it can be found that the technical solution of the embodiment of the present application can increase the performance of the lithium battery after formation.

[0040] The Nyquist plot of electrochemical impedance spectroscopy (EIS) is often used as a scientific and effective method to compare battery performance. The Nyquist plot can intuitively display the electrochemical process inside the battery mainly through the combination of the real part (Z') and the negative imaginary part (-Z") of the impedance. The diameter of the semicircle in the high-frequency zone mainly reflects the ohmic resistance and charge transfer resistance of the battery, among which the formation of the SEI (solid electrolyte interface) film has a significant effect on the ohmic resistance. The SEI film is formed on the surface of the negative electrode of the battery and is the product of the reaction between the electrolyte and the electrode. In the Nyquist plot of EIS, the resistance of the SEI film is usually manifested as a semicircle in the high-frequency zone, and its diameter reflects the resistance value of the SEI film. As the battery is used and aged, the SEI film may thicken or change, resulting in an increase in its resistance. Therefore, by observing the changes in the diameter of the semicircle in the high-frequency zone in the Nyquist plot, the changes in the SEI film can be inferred, and a smaller semicircle diameter usually indicates that the SEI film is relatively stable and thin, while a larger diameter may mean that the SEI film is thickened or has other He is unfavorable to change. And in the electrochemical impedance spectroscopy (EIS) of lithium-ion batteries, the second semicircle is mainly related to the charge transfer process, and the change of the SEI film will indirectly affect this process, mainly because the stability of the SEI film has an important influence on the electrochemical reaction environment on the electrode surface. When the SEI film is unstable or uneven, it will cause the chemical environment on the electrode surface to change, thereby affecting the size of the charge transfer resistance (Rct). For example, the unevenness of the SEI film may cause the electrochemical active area on the electrode surface to change, thereby affecting the transmission efficiency of electrons and ions in the charge transfer process. In addition, the instability of the SEI film may lead to an increase in side reactions between the electrolyte and the electrode, and these side reactions will increase the charge transfer resistance. Therefore, although the second semicircle mainly reflects the charge transfer process, the change of the SEI film will indirectly affect the size of the charge transfer resistance by changing the electrochemical reaction environment on the electrode surface.

[0041] Figure 2 The Nyquist plots of electrochemical impedance spectroscopy of the lithium batteries in Example 1 and Comparative Example 1 are shown.

[0042] refer to Figure 2As shown, by comparing the Nyquist plots of the electrochemical impedance spectroscopy (EIS) of Comparative Example 1 and Example 1, it can be found that the radii of the two semicircles in the high-frequency region of Example 1 are smaller than those of Comparative Example 1. This phenomenon shows that Example 1 has advantages in ohmic resistance and charge transfer resistance. The first semicircle in the high-frequency region mainly reflects the resistance (Rsei) of the SEI film, and the smaller radius means that the SEI film is more stable and uniform. A stable SEI film can effectively reduce the impedance of lithium ions passing through the film layer, thereby reducing the overall impedance of the battery. In addition, the second semicircle is related to the charge transfer resistance (Rct), and the smaller radius indicates that the kinetics of the electrode reaction is faster. This may be due to the stability of the SEI film, which improves the electrochemical reaction environment on the electrode surface and reduces the side reactions between the electrolyte and the electrode. Therefore, the superiority of Example 1 is not only reflected in the lower impedance value, but also reflects its improvement in SEI film stability and electrochemical reaction efficiency.

[0043] X-ray photoelectron spectroscopy (XPS) is a commonly used surface analysis technique that can qualitatively and quantitatively analyze the elemental composition and chemical state of materials. In the study of lithium-ion batteries, XPS is widely used to analyze the composition of SEI films. XPS can detect the main components in the SEI film, and the fluorine (F) content is a key indicator for evaluating the quality of the SEI film. The fluorine in the SEI film mainly exists in the form of LiF. LiF is a stable inorganic compound with good ionic conductivity and electronic insulation. It can effectively prevent further reactions between the electrolyte and the electrode, thereby reducing the decomposition of the electrolyte and the irreversible loss of lithium, and improving the cycle stability and life of the battery.

[0044] Figure 3 The XPS analysis results of the lithium batteries in Comparative Example 1 and Example 1 are shown.

[0045] refer to Figure 3 As shown, by comparing the XPS analysis results of Comparative Example 1 and Example 1, it can be clearly seen that the peak area of ​​the sub-peaks of fluorine (F) and LiF contained therein in Example 1 is significantly larger than that in Comparative Example 1, and the content of fluorine (F) and LiF in Example 1 is higher. This phenomenon shows that the SEI film of Example 1 is rich in more LiF components, and LiF has good ionic conductivity and electronic insulation and can effectively prevent further reaction between the electrolyte and the electrode, thereby reducing the decomposition of the electrolyte and the irreversible loss of lithium, and improving the cycle stability and life of the battery. In addition, the LiF-rich SEI film can promote the uniform deposition of lithium and inhibit the growth of lithium dendrites. Therefore, the higher F and LiF content in Example 1 indicates that its SEI film has better stability and performance, so that Example 1 is superior to Comparative Example 1 in terms of battery performance.

[0046] The technical solution of the present application can make the SEI film formed after chemical formation more uniform and dense in morphology, and can have better ion transmission and electronic insulation; the technical solution of the present application can effectively improve the battery charging capacity retention rate and extend the battery life; the technical solution of the present application can effectively increase the inorganic components in the components of the SEI formation process during chemical formation, making the SEI film more stable and uniform, and improving the cycle performance of the battery; the technical solution of the present application can reduce the polarization of the battery during the cycle charging process and improve the charging capacity.

[0047] The present application provides a lithium battery formation method, which can optimize the lithium battery formation process to ensure that the lithium battery can maintain a low charging polarization voltage during cyclic use, reduce uneven reactions on the electrodes, thereby increasing the battery capacity and capacity retention rate, and ultimately extending the battery life.

[0048] In summary, after reading the contents of this application, those skilled in the art will appreciate that the aforementioned application contents may be presented only in an exemplary manner and may not be restrictive. Although not explicitly stated herein, those skilled in the art will appreciate that this application is intended to encompass various reasonable changes, improvements and modifications to the embodiments. These changes, improvements and modifications are within the spirit and scope of the exemplary embodiments of this application.

[0049] It should be understood that the term "and / or" used in this embodiment includes any or all combinations of one or more of the associated listed items. It should be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to another element, or there can also be intermediate elements.

[0050] It should also be understood that the terms "comprising", "containing", "including" or "comprising", when used in this application document, indicate the presence of the recorded features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or groups thereof.

[0051] It should also be understood that although the terms first, second, third, etc. can be used to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. Therefore, without departing from the teachings of the present application, the first element in some embodiments can be referred to as the second element in other embodiments. The same reference numerals or the same reference signs represent the same elements throughout the specification.

[0052] In addition, the present specification describes exemplary embodiments by reference to idealized exemplary cross-sectional views and / or plan views and / or stereograms. Therefore, differences from the illustrated shapes due to, for example, manufacturing techniques and / or tolerances are foreseeable. Therefore, the exemplary embodiments should not be interpreted as being limited to the shapes of the regions shown herein, but should include deviations in shapes caused by, for example, manufacturing. Therefore, the regions shown in the figures are schematic in nature, and their shapes are not intended to illustrate the actual shapes of the regions of the device nor to limit the scope of the exemplary embodiments.

Claims

1. A lithium battery formation method, characterized in that: include: The lithium battery to be formed is charged and discharged for multiple cycles, at least one of the charging and discharging using alternating current.

2. The chemical formation method according to claim 1, characterized in that The charging adopts direct current, and the discharging adopts alternating current.

3. The chemical formation method according to claim 1, characterized in that: The charging adopts alternating current, and the discharging adopts direct current.

4. The chemical formation method according to claim 1, characterized in that: The charging adopts alternating current, and the discharging adopts alternating current.

5. The chemical formation method according to claim 1, characterized in that: The frequency f of the alternating current c 500Hz to 1MHz.

6. The chemical formation method according to claim 1, characterized in that: The amplitude of the alternating current I a It is 0.05C-2C.

7. The chemical formation method according to claim 1, characterized in that: The number of cycles of charging and discharging is 1 to 50 times.

8. The chemical formation method according to claim 1, characterized in that: In each cycle, the charging is stopped when the voltage of the lithium battery reaches the charging cut-off voltage.

9. The chemical formation method according to claim 1, characterized in that: In each cycle, the discharge is stopped when the voltage of the lithium battery reaches the discharge cut-off voltage.

10. The chemical formation method according to claim 1, characterized in that: When at least one of the charging and discharging uses alternating current, direct current is superimposed.

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