Silicon-carbon negative electrode lithium ion battery, multi-stage relaxation formation process and formation equipment thereof

Abstract

The present disclosure provides a silicon-carbon negative lithium ion battery, a multi-stage relaxation formation process and a formation equipment thereof. The multi-stage relaxation formation process comprises the following steps: obtaining an uncharged battery pack; performing constant current charging on the battery pack; performing static relaxation treatment on the battery pack; performing vibration treatment on the battery pack to release the internal stress of the battery pack, the vibration frequency is 10-100 Hz, the vibration acceleration is 0-1.5 g, and the time is 20-40 min; performing vibration discharge treatment on the battery pack, and synchronously performing auxiliary vibration in the discharge process, the frequency of the auxiliary vibration is 5-20 Hz. Through the physical and electrochemical synergistic regulation mechanism, compared with the traditional electrochemical process, the battery pack of the present application can actively release the stress of the pole piece in the formation stage, significantly improve the interface stability of the battery pack, and further improve the cycle durability and electrical performance of the battery pack.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of lithium ion battery manufacturing, in particular to a silicon-carbon negative electrode lithium ion battery, a multi-stage relaxation formation process and a formation equipment thereof. BACKGROUND

[0002] With the continuous growth of demand for high-energy-density batteries in the new energy industry, silicon materials have become a research hotspot in the field of lithium ion batteries due to their theoretical specific capacity (about 4200 mAh / g), which is much higher than that of traditional graphite negative electrodes (372 mAh / g). However, the volume expansion effect of silicon materials during lithium intercalation is as high as 300%, which leads to a series of problems such as electrode structure pulverization, repeated rupture and regeneration of the solid electrolyte interface film (SEI), and loss of contact between active materials and current collectors, which seriously restricts its commercial application.

[0003] In the battery manufacturing process, the formation process is a key step to activate the battery performance, which directly determines the stability of the SEI film and the stress distribution inside the electrode. Although the traditional constant current charging and discharging mode (such as charging to the cut-off voltage at 0.1C and then standing still) is simple to operate, it has significant defects: first, the rapid intercalation of lithium ions causes the silicon particles to expand dramatically, resulting in significant differences in SEI film thickness, forming an ion transport barrier and exacerbating side reactions; second, there is a lack of stress release mechanism during the formation process, and the residual stress continues to accumulate in the cycle, leading to electrode crack propagation and interface peeling; third, static standing still cannot achieve uniform redistribution of lithium ions, resulting in insufficient wetting of the electrode / electrolyte interface. Although existing technologies attempt to improve the first efficiency through means such as step charging and pre-lithiation, these methods are still limited to the optimization of electrochemical parameters and do not address the physical nature of stress management, and the battery expansion rate and cycle life have not been fundamentally improved. The root cause is that the traditional process separates the electrochemical activation and mechanical stress regulation, ignoring the strong coupling characteristics of dynamic deformation and interface reconstruction of the silicon-carbon system during lithiation. In addition, the post-formation treatment (such as high-temperature aging) commonly used in the industry can partially alleviate stress, but it is time-consuming, energy-consuming, and may accelerate the decomposition of electrolyte. Therefore, developing a new process that simultaneously achieves uniform SEI film growth and active stress release during the formation stage is key to breaking through the industrialization bottleneck of silicon-carbon batteries. SUMMARY

[0004] The purpose of the present disclosure is to overcome the deficiencies in the prior art and provide a silicon-carbon negative electrode lithium ion battery, a multi-stage relaxation formation process and a formation equipment thereof that simultaneously achieve uniform SEI film growth and active stress release during the formation stage.

[0005] The purpose of the present disclosure is achieved by the following technical solutions:

[0006] A multi-stage relaxation formation process, comprising the following steps:

[0007] obtaining a battery pack which is not charged;

[0008] carrying out constant current charging on the battery pack at a current rate of 0.01C-0.05C, so that the voltage of the battery pack is 3.7V-3.9V;

[0009] carrying out static relaxation treatment on the battery pack, wherein the temperature is 20℃-30℃, and the time is 1h-3h;

[0010] carrying out vibration treatment on the battery pack to release the internal stress of the battery pack, wherein the vibration frequency is 10Hz-100Hz, the vibration acceleration is 0g-1.5g, and the time is 20min-40min;

[0011] carrying out vibration discharge treatment on the battery pack at a discharge current rate of 0.03C-0.1C, so that the voltage of the battery pack is discharged to 2.75V-3.0V, and simultaneously carrying out auxiliary vibration during the discharge process, wherein the frequency of the auxiliary vibration is 5Hz-20Hz.

[0012] In one of the embodiments, the vibration treatment on the battery pack specifically includes the following steps:

[0013] carrying out high-frequency vibration treatment on the battery pack, wherein the vibration frequency is 50Hz-80Hz, the acceleration is 1g-1.5g, and the time is 7min-15min;

[0014] carrying out medium-frequency vibration treatment on the battery pack, wherein the vibration frequency is 30Hz-50Hz, the acceleration is 0.5g-1g, and the time is 7min-15min;

[0015] carrying out low-frequency vibration treatment on the battery pack, wherein the vibration frequency is 10Hz-30Hz, the acceleration is 0g-0.5g, and the time is 7min-15min.

[0016] In one of the embodiments, the vibration energy density of the vibration treatment on the battery pack is 0.8J / cm 2 -1.5J / cm 2 ; and / or,

[0017] the vibration energy density of the auxiliary vibration on the battery pack is 0.8J / cm 2 -1.5J / cm 2 .

[0018] In one of the embodiments, the vibration discharge treatment on the battery pack is carried out, wherein the acceleration of the auxiliary vibration linearly changes with the depth of discharge (DOD) and satisfies the following relationship:

[0019]

[0020] wherein A Max is 1.5g, and DOD is depth of discharge percentage.

[0021] In one of the embodiments, the battery pack is charged with constant current, specifically comprising the following steps:

[0022] The battery pack is charged with first-stage constant current, wherein the charging current rate is 0.01C-0.03C, so as to charge the voltage of the battery pack to 3.5V-3.6V.

[0023] The battery pack is charged with second-stage constant current, wherein the charging current rate is 0.03C-0.05C, so as to charge the voltage of the battery pack to 3.7V-3.9V.

[0024] In one of the embodiments, the vibration waveform for the vibration treatment of the battery pack is pulse modulation wave.

[0025] In one of the embodiments, the battery pack is subjected to vibration treatment, wherein the vibration direction is perpendicular to the surface of the pole piece of the battery pack.

[0026] A formation device of multi-stage relaxation formation process, comprising:

[0027] a box body;

[0028] a charging and discharging mechanism, mounted on the box body, for charging and discharging the battery pack;

[0029] a multi-dimensional vibration mechanism, mounted on the box body, having a receiving cavity for accommodating the battery pack, and an acting end of the multi-dimensional vibration mechanism abutting against the battery pack so as to vibrate the battery pack;

[0030] a stress detection mechanism, mounted on the box body, having a detection end abutting against the pole piece of the battery pack so as to detect the stress of the pole piece of the battery pack.

[0031] In one of the embodiments, the multi-dimensional vibration mechanism comprises an air-floating vibration isolation base, an angle adjusting assembly and a vibration assembly, the air-floating vibration isolation base is mounted on the box body, the receiving cavity is formed in the air-floating vibration isolation base, the angle adjusting assembly is mounted on the box body, a power output end of the angle adjusting assembly is connected with the vibration assembly, and an acting end of the vibration assembly abuts against the battery pack.

[0032] A silicon-carbon negative electrode lithium ion battery is prepared by using the formation device of multi-stage relaxation formation process according to any one of the above embodiments.

[0033] Compared with the prior art, the present disclosure has at least the following advantages:

[0034] The multi-stage relaxation formation process described above uses a silicon-carbon composite negative electrode and a lithium cobalt oxide positive electrode to manufacture a battery pack. The battery pack is charged at an ultra-low rate of 0.01-0.05C for the first cycle to form a uniform SEI film base for the battery pack. Then the battery is placed in an environment of 20-30°C for 1-3 hours to promote redistribution of lithium ions in the battery pack. After standing, the battery pack is subjected to directional vibration with a frequency of 10-100Hz and an acceleration of 0-1.5g to generate vibration in the battery pack. The mechanical energy assists in releasing the internal stress of the battery pack. Finally, an auxiliary vibration of 5-20Hz is applied simultaneously during the discharge of the battery pack to discharge the battery pack to 2.75-3.0V, while optimizing the electrode and electrolyte interface stability. Through this physical and electrochemical synergistic regulation mechanism, compared with the traditional electrochemical process of standing aging, the battery pack of the present application can actively release the stress of the electrode sheet during the formation stage, significantly improving the interface stability of the battery pack, and thus improving the cycle durability and electrical performance of the battery pack. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present disclosure, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0036] Figure 1 A process flow chart of the multi-stage relaxation formation process in an embodiment;

[0037] Figure 2 A structure schematic diagram of the formation equipment of the multi-stage relaxation formation process in an embodiment. DETAILED DESCRIPTION

[0038] In order to facilitate the understanding of the present disclosure, the present disclosure will be described more fully below with reference to the related drawings. The preferred embodiments of the present disclosure are shown in the drawings. However, the present disclosure can be implemented in many different forms, and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present disclosure more thorough and comprehensive.

[0039] It should be noted that when an element is referred to as being "on" another element, it can be directly on the other element or intervening elements can also be present. When an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements can also be present. The terms "vertical", "horizontal", "left", "right", and the like as used herein are used for illustration only and are not intended to limit the embodiments of the present disclosure to the orientations described.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used in the description of the disclosure herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0041] The present disclosure provides a multi-stage relaxation formation process, comprising the following steps: obtaining an uncharged battery pack; charging the battery pack at a constant current with a current rate of 0.01C-0.05C, so that the voltage of the battery pack is 3.7V-3.9V; performing a static relaxation treatment on the battery pack, wherein the temperature is 20℃-30℃ and the time is 1h-3h; performing a vibration treatment on the battery pack to release the internal stress of the battery pack, with a vibration frequency of 10Hz-100Hz, a vibration acceleration of 0g-1.5g, and a time of 20min-40min; performing a vibration discharge treatment on the battery pack with a discharge current rate of 0.03C-0.1C, so that the voltage of the battery pack is discharged to 2.75V-3.0V, and simultaneously performing an auxiliary vibration during the discharge process, with a frequency of 5Hz-20Hz.

[0042] The above-mentioned multi-stage relaxation formation process is used to produce a battery pack with a silicon-carbon composite negative electrode and a lithium cobalt oxide positive electrode. The battery pack is charged at a first cycle with a super-low rate of 0.01-0.05C to form a uniform SEI film base. Then the battery is placed in an environment of 20℃-30℃ for 1-3 hours to promote the redistribution of lithium ions in the battery pack. After that, a directional vibration with a frequency of 10Hz-100Hz and an acceleration of 0g-1.5g is applied to the battery pack to generate vibration and release the internal stress of the battery pack through mechanical energy assistance. Finally, an auxiliary vibration with a frequency of 5Hz-20Hz is applied simultaneously during the discharge process of the battery pack to discharge the battery pack to 2.75V-3.0V, while optimizing the stability of the electrode and electrolyte interface. Through this physical and electrochemical synergistic regulation mechanism, compared with the traditional static aging electrochemical process, the battery pack of the present application can actively release the stress of the electrode sheet during the formation stage, significantly improving the interface stability of the battery pack, and further improving the cycle durability and electrical performance of the battery pack.

[0043] To better understand the technical solutions and beneficial effects of this disclosure, the following detailed description is provided in conjunction with specific embodiments:

[0044] like Figure 1 and Figure 2 As shown, a multi-stage relaxation formation process according to one embodiment includes the following steps:

[0045] S100: Obtain the uncharged battery pack. In this embodiment, a silicon-carbon composite material with a silicon content of 10wt% is used to make the battery negative electrode, and lithium cobalt oxide is used as the positive electrode. After the battery positive and negative electrodes are installed in the casing, electrolyte is injected to form a battery pack. Because the battery anode uses silicon-carbon composite material, the theoretical specific capacity of silicon is 4200 mAh / g, which is much higher than that of graphite anode material widely used in current commercial lithium batteries (capacity is about 360 mAh / g, close to its theoretical specific capacity of 372 mAh / g). Therefore, the performance of batteries using silicon-carbon composite material as the anode is better than that of batteries using graphite anode. However, due to the volume expansion effect of up to 300% of silicon material during lithium intercalation, the electrode structure is pulverized and the solid electrolyte interphase (SEI) film is repeatedly broken and regenerated. That is, local stress concentration leads to significant differences in SEI film thickness. Traditional formation process lacks stress release mechanism during static aging, and residual stress continues to accumulate during cycling, causing electrode crack propagation and interface peeling. Therefore, it is necessary to adopt electrochemical and physical synergistic mechanisms to release stress during battery cycling, so that the SEI film formed by the battery is more uniform and stable.

[0046] S200: The battery pack is charged with a constant current at a rate of 0.01C-0.05C to achieve a battery pack voltage of 3.7V-3.9V. In this embodiment, a constant current charging rate of 0.01C-0.05C is used to charge the battery pack, i.e., a relatively low charging rate is employed. This allows the battery to form a uniform SEI film substrate during cycling and ensures that the battery pack voltage is 3.7V-3.9V.

[0047] S300: The battery pack is subjected to a static relaxation treatment at a temperature of 20℃-30℃ for 1-3 hours. In this embodiment, the battery pack after constant current charging is subjected to a static relaxation treatment, also known as static aging. Under the conditions of 20℃-30℃ and 1-3 hours, the active materials in the positive and negative electrodes can accelerate the occurrence of some side effects, such as gas generation and electrolyte decomposition, thereby rapidly stabilizing the electrochemical performance of the lithium battery. At the same time, it helps the SEI structure to recombine and form a loose and porous film, thereby improving battery performance.

[0048] S400: The battery pack is subjected to vibration treatment to release the internal stress of the battery pack, the vibration frequency is 10-100 Hz, the vibration acceleration is 0-1.5 g, and the time is 20-40 min. It can be understood that after the battery pack is subjected to static relaxation treatment, although the internal stress of the battery pole piece can be relieved to a certain extent, due to the dramatic expansion of silicon particles caused by lithium ion insertion, local stress concentration leads to significant differences in SEI film thickness, and pure standing aging cannot completely eliminate the stress of the pole piece, and the residual stress will continue to accumulate in the cycle, thereby causing electrode crack propagation and interface peeling. Therefore, in the present embodiment, the battery pack after static relaxation is subjected to vibration treatment, the vibration frequency is 10-100 Hz, the vibration acceleration is 0-1.5 g (the vibration acceleration is the physical quantity of the speed change during the vibration process) to vibrate the surface of the battery pole piece of the battery pack. In this way, through the physical way, the residual stress between the pole pieces will be released during the vibration process, so that the residual stress of the pole piece is eliminated through the synergistic regulation mechanism of electrochemistry and physics, thereby making the SEI film thickness uniform and the electrolyte interface stable, thereby improving the performance of the battery.

[0049] S500: The battery pack is subjected to vibration discharge treatment, the discharge current rate is 0.03C-0.1C, so that the voltage of the battery pack is discharged to 2.75-3.0V, and auxiliary vibration is performed during the discharge process. The frequency of the auxiliary vibration is 5-20 Hz. In the present embodiment, the battery pack is discharged at a current rate of 0.03C-0.1C, and at the same time, the battery pack is vibrated at a frequency of 5-20 Hz during the discharge process of the battery pack. In order to make the stress generated during the discharge process of the battery pack released with vibration, further ensure that the SEI film thickness is uniform and the electrolyte interface is stable during the discharge process of the battery, thereby making the battery performance better.

[0050] The multi-stage relaxation formation process described above uses a silicon-carbon composite negative electrode and a lithium cobalt oxide positive electrode to make a battery pack. The battery pack is charged at 0.01-0.05C super low rate for the first cycle to form a uniform SEI film base for the battery pack. Then the battery is placed in an environment of 20-30°C for 1-3 hours to promote redistribution of lithium ions in the battery pack. After standing, the battery pack is subjected to directional vibration with a frequency of 10-100 Hz and an acceleration of 0-1.5 g to generate vibration in the battery pack. The mechanical energy assists in releasing the internal stress of the battery pack. Finally, an auxiliary vibration of 5-20 Hz is applied simultaneously during the discharge of the battery pack to discharge the battery pack to 2.75-3.0 V, while optimizing the stability of the electrode and electrolyte interface. Through this physical and electrochemical synergistic regulation mechanism, compared with the traditional electrochemical process of static aging, the battery pack of the present application can actively release the stress of the electrode plate during the formation stage, significantly improve the interface stability of the battery pack, and further improve the cycle durability and electrical performance of the battery pack.

[0051] In one embodiment, the battery pack is subjected to vibration treatment, specifically including the following steps:

[0052] The battery pack is subjected to high-frequency vibration treatment, wherein the vibration frequency is 50-80 Hz, the acceleration is 1-1.5 g, and the time is 7-15 min.

[0053] The battery pack is subjected to medium-frequency vibration treatment, wherein the vibration frequency is 30-50 Hz, the acceleration is 0.5-1 g, and the time is 7-15 min.

[0054] The battery pack is subjected to low-frequency vibration treatment, wherein the vibration frequency is 10-30 Hz, the acceleration is 0-0.5 g, and the time is 7-15 min.

[0055] In the present embodiment, the battery pack is divided into three stages during the vibration treatment process. The first stage is a high-frequency vibration treatment stage, with a vibration frequency of 50-80 Hz, an acceleration of 1-1.5 g, and a time of 7-15 min. The high-frequency vibration generates shear force, destroys the van der Waals force between silicon particles, suppresses crack propagation, and breaks through the yield strength of about 1.2 GPa of the silicon particle surface oxide layer to produce dislocation slip and form a lithium ion rapid diffusion channel. The elastic vibration of the silicon particle surface oxide layer is excited, and the pre-stored stress is released by resonance effect. The second stage is a medium-frequency vibration treatment stage, with a vibration frequency of 30-50 Hz, an acceleration of 0.5-1 g, and a time of 7-15 min. The frequency is lowered to release the internal stress gradient of the battery, avoid mechanical damage to the newly grown solid electrolyte interface, and promote lithium ions to be directionally embedded along the 111 crystal plane of silicon through the piezoelectric effect. The third stage is a low-frequency vibration treatment stage, with a vibration frequency of 10-30 Hz, an acceleration of 0 g-0.5 g, and a time of 7-15 min. Low-frequency vibration can penetrate thick structures and easily form large stress waves inside the structure, forcing the mechanical closure of micro-cracks caused by lithium extraction, thereby reducing the interface contact resistance. By vibrating the battery pack through the three vibration stages, the residual stress inside the battery electrode is released, the SEI film thickness of the battery is uniform, the electrolyte interface is stable, and the cycle durability and electrical performance of the battery pack are improved.

[0056] In one embodiment, the vibration energy density of the vibration treatment of the battery pack is 0.8-1.5 J / cm 2 -1.5 J / cm 2 In the present embodiment, the vibration energy density of the vibration treatment of the battery pack is controlled to be 0.8-1.5 J / cm 2 -1.5 J / cm 2 interval to avoid problems such as electrode dislocation or separator damage caused by excessive vibration energy of the battery pack, and to avoid the problem of not being able to resonate due to too low vibration energy of the battery pack.

[0057] In one embodiment, the vibration energy density of the auxiliary vibration of the battery pack is 0.8-1.5 J / cm 2 -1.5 J / cm 2 In the present embodiment, auxiliary vibration is performed simultaneously when discharging the battery pack, and the energy of the auxiliary vibration is controlled to be in the range of 0.8-1.5 J / cm 2 -1.5 J / cm 2 interval to avoid problems such as electrode dislocation or separator damage caused by excessive vibration energy of the battery pack, and to avoid the problem of not being able to resonate due to too low vibration energy of the battery pack.

[0058] In one embodiment, the battery pack is subjected to a vibration discharge process, wherein the acceleration of the auxiliary vibration linearly changes with the depth of discharge (DOD) and satisfies the following relationship:

[0059]

[0060] wherein A Max is 1.5g and DOD is the depth of discharge percentage.

[0061] In this embodiment, the acceleration of the auxiliary vibration is a physical quantity that reflects the speed change during the vibration process, and reflects the dynamic load strength applied to the battery pack by the vibration. The acceleration of the auxiliary vibration is linearly related to the depth of discharge of the battery pack, A Max is the maximum value of the auxiliary vibration, i.e. 1.5g, and the depth of discharge of the battery pack is the percentage of the capacity released by the battery during discharge to the nominal total capacity. As the depth of discharge percentage DOG of the battery pack increases, the acceleration of the auxiliary vibration decreases. That is, in the initial state, the acceleration of the auxiliary vibration is the maximum value when the battery pack is initially discharged, so that the electrode of the battery pack synchronously resonates, thereby making the electrode of the battery pack release stress better.

[0062] In one embodiment, the battery pack is subjected to constant current charging, specifically including the following steps:

[0063] The battery pack is subjected to first-stage constant current charging, wherein the charging current ratio is 0.01C-0.03C, so that the voltage of the battery pack is charged to 3.5V-3.6V.

[0064] The battery pack is subjected to second-stage constant current charging, wherein the charging current ratio is 0.03C-0.05C, so that the voltage of the battery pack is charged to 3.7V-3.9V.

[0065] In this embodiment, the constant current charging of the battery pack is divided into two stages: the current ratio of the first-stage constant current charging is 0.01C-0.03C, which activates the battery by low current ratio to avoid large current impact, and at this time the voltage of the battery pack is charged to 3.5V-3.6V; then, the battery pack is subjected to second-stage constant current charging, and the current ratio is 0.03C-0.05C, which is greater than the current ratio of the first-stage constant current charging, so that the battery pack quickly replenishes the electric quantity, and the voltage of the battery pack is charged to 3.7V-3.9V. In this way, through the two-stage constant current charging, the rapidity, safety and service life of the battery charging are improved.

[0066] In one embodiment, the vibration waveform of the vibration process for the battery pack is a pulse modulation wave. It can be understood that the pulse modulation wave adjusts the frequency, acceleration and the like of the vibration by changing the parameters of the pulse signal, so that the adjustment of the vibration of the battery pack is more accurate.

[0067] In one embodiment, the battery pack is subjected to vibration treatment, wherein the vibration direction is perpendicular to the surface of the electrode plate of the battery pack. It can be understood that when the battery pack is subjected to vibration treatment, the vibration direction is perpendicular to the surface of the electrode plate of the battery pack, so that the vibration effect of the electrode plate is better and is more prone to resonance with the vibration end to release the residual stress of the electrode plate.

[0068] It can be understood that the volume expansion and contraction caused by the charging and discharging process of the battery anode with different silicon contents are also different, that is, the stress generated by the charging and discharging of the battery with different silicon contents is also inconsistent. If the frequency of vibration is too high during the discharging process of the battery, the active material on the electrode plate of the battery will fall off. If the frequency of vibration is too low, the stress inside the battery cannot be completely released, resulting in uneven thickness of the generated SEI film and low battery performance. Therefore, in order to adapt to the battery anode with different silicon contents and make the battery stress release effect better, in one embodiment, the battery pack is subjected to vibration discharge treatment, further comprising the following steps:

[0069] Obtaining the real-time stress of the electrode plate of the battery pack;

[0070] Matching the real-time stress of the electrode plate with the preset stress;

[0071] When the real-time stress of the electrode plate is greater than or equal to the preset stress, increasing the vibration frequency and synchronously reducing the temperature of the electrode plate.

[0072] In this embodiment, during the discharging process of the battery pack, the stress of the electrode plate of the battery pack is detected in real time by the optical fiber sensor, and the real-time stress of the electrode plate is matched with the preset stress. For example, the preset stress is 100 kPa-120 kPa, and within the preset stress range, the battery is subjected to vibration treatment by the preset vibration frequency and temperature. For example, the vibration frequency is 50 Hz-70 Hz, and the temperature of the electrode plate is 30℃-40℃. When the detected real-time stress of the electrode plate is greater than or equal to the preset stress, it indicates that the stress in the battery pack is large at this time. If the battery pack is vibrated at a vibration frequency of 50 Hz-70 Hz, there is a problem that the stress in the battery pack cannot be completely released. Therefore, at this time, the vibration frequency is increased, that is, the vibration frequency of the electrode plate in the battery pack is increased to excite the elastic vibration of the oxide layer on the surface of the silicon particles, release the pre-stored stress by resonance effect, and better release the stress in the battery pack. At the same time, the temperature of the electrode plate needs to be reduced at this time, because when the vibration frequency is increased, there is a risk of active material falling off the electrode plate. By reducing the temperature of the electrode plate, the electrochemical activity of the active material is reduced, and the embedding and extraction of lithium ions in the active material becomes more difficult, so as to ensure that the active material will not fall off when it is vibrated at a high frequency.

[0073] In another embodiment, when the real-time stress of the pole piece is less than the preset stress, the vibration frequency is reduced, and the temperature of the pole piece is simultaneously increased.

[0074] In this embodiment, when the detected real-time stress of the pole piece is less than the preset stress, it indicates that the stress in the battery pack at this time is small, and the vibration frequency corresponding to the preset stress is large, so the vibration frequency needs to be reduced, that is, the vibration frequency in the battery pack is reduced, so that the stress in the battery pack can be released while ensuring that the active material does not fall off during the vibration process. Further, while reducing the vibration frequency, the temperature of the pole piece is increased, so that the electrochemical activity of the active material is increased, the embedding and extraction of lithium ions are accelerated, and the discharging process is accelerated, thereby improving the production efficiency.

[0075] In another embodiment, when the real-time stress of the pole piece is equal to the preset stress, it indicates that the real-time stress formed by the pole piece is equal to the preset stress, and then the battery pack is vibrated at the vibration frequency and temperature matched with the preset stress to release the stress of the pole piece, that is, there is no need to adjust the parameters of the vibration frequency and temperature.

[0076] Further, during the charging and discharging process of the battery, when the battery pack is continuously vibrated in one direction, the battery separator may be displaced, which leads to a decrease in the performance and safety of the battery, and even a risk of short circuit caused by the contact between the positive and negative pole pieces. Therefore, in order to solve the above problems, in one of the embodiments, the battery pack is vibrated, specifically including the following steps:

[0077] vibrating the battery pack in a first direction for 10-20 minutes;

[0078] vibrating the battery pack in a second direction for 10-20 minutes, wherein the first direction is opposite to the second direction.

[0079] In this embodiment, when the battery pack is vibrated, in the first half of the time, that is, 10-20 minutes, the battery pack is vibrated in the first direction, and the first direction is the direction in which the vibration source abuts against the battery pack and generates vibration, for example, the first direction is vertically downward, and in the second half of the time, that is, 10-20 minutes, the battery pack is vibrated in the second direction, and the second direction is vertically upward, that is, the first direction is opposite to the second direction. In this way, through the mutual compensation of the first direction vibration and the second direction vibration, the problem of separator displacement caused by long-time vibration in one direction is avoided, and at the same time, through the mutual compensation of the first direction vibration and the second direction vibration, the amplitude of the vibration of the battery pack is more uniform, which is more likely to resonate with the stress of the pole piece, so that the stress of the pole piece is better released.

[0080] AsFigure 2 As shown, the application also provides a formation device 10 of a multi-stage relaxation formation process, comprising:

[0081] a box body 100;

[0082] a charging and discharging mechanism 200, which is installed on the box body 100, and is used for charging and discharging the battery pack;

[0083] a multi-dimensional vibration mechanism 300, which is installed on the box body 100, and is provided with a receiving cavity for accommodating the battery pack, and an acting end of the multi-dimensional vibration mechanism 300 abuts against the battery pack to vibrate the battery pack;

[0084] a stress detection mechanism (not shown in the figure), which is installed on the box body 100, and a detection end of the stress detection mechanism abuts against the pole piece of the battery pack to detect the stress of the pole piece of the battery pack.

[0085] In the embodiment, the charging and discharging mechanism 200 is a precision charging and discharging module, which has a 0.01-1C continuously adjustable current output capability, a voltage control precision of ±5mV, the multi-dimensional vibration mechanism 300 is an integrated piezoelectric ceramic driver and electromagnetic vibrator, which has a frequency coverage of 5-150Hz and an acceleration range of 0.1-3.0g, and the stress detection mechanism is an embedded optical fiber sensor, which is used to detect the stress of the pole piece in real time. The use process of the above formation device is as follows: the battery is placed in the box body 100, specifically in the receiving cavity, first, the battery is charged by the charging and discharging mechanism 200, then the temperature is adjusted to 20-30℃ by the heat control system of the box body 100 to perform the static relaxation stage, then the battery is vibrated by the multi-dimensional vibration mechanism 300 to release the stress of the pole piece of the battery, at the same time, the stress of the pole piece of the battery is detected by the stress detection mechanism, finally, the battery pack is discharged by the charging and discharging mechanism 200, and at the same time, the battery pack is assisted by the multi-dimensional vibration mechanism 300 during the discharging process.

[0086] In one of the embodiments, the multi-dimensional vibration mechanism comprises an air-floating vibration isolation base, an angle adjustment assembly and a vibration assembly, the air-floating vibration isolation base is installed on the box, the accommodating cavity is opened on the air-floating vibration isolation base, the angle adjustment assembly is installed on the box, the power output end of the angle adjustment assembly is connected with the vibration assembly, and the action end of the vibration assembly is in abutment with the battery pack. In this embodiment, the air-floating vibration isolation base is installed on the box, the accommodating cavity is opened on the air-floating vibration isolation base, and the accommodating cavity is used for accommodating the battery pack. The angle adjustment assembly comprises a plurality of motors, so that the angle adjustment assembly can adjust three free angle directions, so as to ensure that the vibration direction of the vibration assembly and the surface normal of the pole piece are ≤5°, and then the pole piece vibration effect is better. Further, the vibration assembly is an electromagnetic vibrator.

[0087] The application also provides a silicon-carbon negative electrode lithium ion battery prepared by using the formation equipment of the multi-stage relaxation formation process in any one of the above embodiments.

[0088] Some specific embodiments are listed below. If the temperature is mentioned, it means Celsius. It should be noted that the following examples do not exhaust all possible cases, and the materials used in the following examples can be obtained from commercial channels unless otherwise specified.

[0089] Example 1

[0090] Battery assembly: a silicon-carbon composite negative electrode with a silicon content of 10wt% is used, and a positive electrode is LiCoO2, and a soft package battery with a nominal capacity of 3Ah is prepared. O O2.

[0091] First circle charging: 0.02C constant current charging to 3.8V, ambient temperature 25±1℃;

[0092] Static relaxation: 25℃ constant temperature box for 2 hours, voltage fluctuation <2mV during the period;

[0093] Vibration treatment: vibration frequency 50Hz, acceleration 1.2g, vibration time 30 minutes;

[0094] Discharge activation: 0.05C discharge to 2.75V, and 10Hz auxiliary vibration is applied synchronously.

[0095] Example 2

[0096] Battery assembly: a silicon-carbon composite negative electrode with a silicon content of 10wt% is used, and a positive electrode is LiCoO2, and a soft package battery with a nominal capacity of 3Ah is prepared. O O2.

[0097] First circle charging: 0.02C constant current charging to 3.8V, ambient temperature 25±1℃;

[0098] Resting relaxation: 2 hours in 25℃ constant temperature box, voltage fluctuation <2mV during the period;

[0099] Vibration treatment: vibration frequency 80Hz, acceleration 1.8g, vibration duration 30 minutes;

[0100] Discharge activation: 0.05C discharge to 2.75V, with 15Hz auxiliary vibration.

[0101] Example 3

[0102] Battery assembly: using silicon-carbon composite negative electrode with 10wt% silicon content, positive electrode LiC O O2, to make soft package battery with nominal capacity of 3Ah.

[0103] First circle charging: 0.02C constant current charging to 3.8V, ambient temperature 25±1℃;

[0104] Resting relaxation: 2 hours in 25℃ constant temperature box, voltage fluctuation <2mV during the period;

[0105] Vibration treatment: vibration frequency 30Hz, acceleration 0.8g, vibration duration 30 minutes;

[0106] Discharge activation: 0.05C discharge to 2.75V, with 5Hz auxiliary vibration.

[0107] Comparative Example 1

[0108] Battery assembly: using silicon-carbon composite negative electrode with 10wt% silicon content, positive electrode LiC O O2, to make soft package battery with nominal capacity of 3Ah.

[0109] First circle charging: 0.1C constant current charging to 3.8V, ambient temperature 25±1℃;

[0110] Resting relaxation: 12 hours in 25℃ constant temperature box, voltage fluctuation <2mV during the period;

[0111] Discharge activation: 0.1C discharge to 2.75V, without vibration treatment.

[0112] Comparative Example 2

[0113] Battery assembly: using silicon-carbon composite negative electrode with 10wt% silicon content, positive electrode LiC O O2, to make soft package battery with nominal capacity of 3Ah.

[0114] First circle charging: 0.02C constant current charging to 3.8V, ambient temperature 25±1℃;

[0115] Resting relaxation: 2 hours in 25℃ constant temperature box, voltage fluctuation <2mV during the period;

[0116] Vibration treatment: vibration frequency 150 Hz, acceleration 3.0 g, vibration duration 30 minutes;

[0117] Discharge activation: 0.05C discharge to 2.75 V, with synchronous application of 10 Hz auxiliary vibration.

[0118] The test results are shown as follows:

[0119]

[0120] It can be understood that Example 1, Example 2 and Example 3 all adopt vibration treatment after static relaxation, Comparative Example 1 adopts traditional static relaxation treatment, Example 1 adopts medium frequency vibration, Example 2 adopts high frequency vibration, and Example 3 adopts low frequency vibration. From the above experimental data, it can be concluded that the electrode residual stress of Example 1, Example 2 and Example 3 is smaller than that of Comparative Example 1, and the SEI film thickness relative standard deviation, the first coulomb efficiency and the capacity retention rate after 500 cycles and other parameters are better than those of Comparative Example 1. Although the electrode residual stress of Comparative Example 2 is small, the SEI film thickness relative standard deviation, the first coulomb efficiency and the capacity retention rate after 500 cycles and other parameters are poor. Therefore, from the above data, it can be known that the medium frequency vibration is preferably adopted, which can relieve the electrode stress and also make the battery performance higher.

[0121] Compared with the prior art, the present disclosure has at least the following advantages:

[0122] The above multi-stage relaxation formation process is used to produce a battery pack with a silicon-carbon composite negative electrode and a lithium cobalt oxide positive electrode. The battery pack is charged at a super low rate of 0.01-0.05C for the first cycle to form a uniform SEI film base. Then the battery is placed in an environment of 20-30°C for 1-3 hours to promote redistribution of lithium ions in the battery pack. After static relaxation, the battery pack is subjected to directional vibration with a frequency of 10-100 Hz and an acceleration of 0-1.5 g to generate vibration and release internal stress in the battery pack through mechanical energy. Finally, 5-20 Hz auxiliary vibration is applied synchronously during the discharge of the battery pack to discharge the battery pack to 2.75-3.0 V, while optimizing the electrode and electrolyte interface stability. Through this physical and electrochemical synergistic regulation mechanism, compared with the traditional static aging electrochemical process, the battery pack of the present application can actively release the stress of the electrode sheet during the formation stage, significantly improve the interface stability of the battery pack, and further improve the cycle durability and electrical performance of the battery pack.

[0123] The above-described embodiments are merely illustrative of several embodiments of the present disclosure, which are described in a more specific and detailed manner, but should not be construed as limiting the scope of the patent. It should be noted that for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present disclosure, and these are all within the scope of the present disclosure. Therefore, the scope of protection of the patent of the present disclosure should be subject to the appended claims.

Claims

1. A multi-stage relaxation formation process characterized by, The method comprises the following steps: obtaining an uncharged battery pack; carrying out constant current charging on the battery pack at a charging current rate of 0.01C-0.05C, so that the voltage of the battery pack is 3.7V-3.9V; carrying out static relaxation treatment on the battery pack, wherein the temperature is 20°C-30°C, and the time is 1h-3h; carrying out vibration treatment on the battery pack to release the internal stress of the battery pack, wherein the vibration frequency is 10 Hz-100Hz, the vibration acceleration is 0g-1.5g, and the time is 20min-40min, and the vibration treatment specifically comprises the following steps: carrying out high-frequency vibration treatment on the battery pack, wherein the vibration frequency is 50Hz-80Hz, the acceleration is 1g-1.5g, and the time is 7min-15min; carrying out medium-frequency vibration treatment on the battery pack, wherein the vibration frequency is 30Hz-50Hz, the acceleration is 0.5g-1g, and the time is 7min-15min; carrying out low-frequency vibration treatment on the battery pack, wherein the vibration frequency is 10Hz-30Hz, the acceleration is 0g-0.5g, and the time is 7min-15min; vibration discharge treatment is performed on the battery pack at a discharge current rate of 0.03C-0.1C to discharge the voltage of the battery pack to 2.75V-3.0V, and auxiliary vibration is performed synchronously during the discharge process, the frequency of the auxiliary vibration being 5 Hz-20 Hz; the vibration energy density of the vibration treatment performed on the battery pack being 0.8 J / cm 2 -1.5 J / cm 2 The vibration energy density of the auxiliary vibration performed on the battery pack is 0.8 J / cm 2 -1.5 J / cm 2 .

2. The multi-stage relaxation formation process of claim 1, wherein, carrying out vibration discharge treatment on the battery pack, wherein the acceleration of the auxiliary vibration linearly changes with the depth of discharge (DOD) and satisfies the following relationship: wherein A Max is 1.5 g, and DOD is depth of discharge in percent.

3. The multi-stage relaxation formation process of claim 1, wherein, carrying out constant current charging on the battery pack, specifically comprising the following steps: carrying out first-stage constant current charging on the battery pack, wherein the charging current rate is 0.01C-0.03C, so that the voltage of the battery pack is charged to 3.5V-3.6V; carrying out second-stage constant current charging on the battery pack, wherein the charging current rate is 0.03C-0.05C, so that the voltage of the battery pack is charged to 3.7V-3.9V.

4. The multi-stage relaxation formation process of claim 1, wherein, The vibration waveform of the vibration treatment on the battery pack is a pulse modulation wave.

5. The multi-stage relaxation formation process of claim 1, wherein, The vibration treatment on the battery pack is carried out in a vibration direction perpendicular to the surface of the pole piece of the battery pack.

6. A formation apparatus of a multi-stage relaxation formation process, characterized by, The formation equipment for the multi-stage relaxation formation process comprises: a box body; a charging and discharging mechanism mounted on the box body, used for charging and discharging the battery pack; a multi-dimensional vibration mechanism mounted on the box body, provided with a containing cavity for containing the battery pack, and having an acting end abutting against the battery pack to vibrate the battery pack; a stress detection mechanism mounted on the box body, having a detection end abutting against the pole piece of the battery pack to detect the stress of the pole piece of the battery pack.

7. The formation apparatus of a multi-stage relaxation formation process according to claim 6, characterized by, The multi-dimensional vibration mechanism comprises an air-floating vibration isolation base, an angle adjusting assembly and a vibration assembly, the air-floating vibration isolation base is installed on the box, the accommodating cavity is arranged on the air-floating vibration isolation base, the angle adjusting assembly is installed on the box, the power output end of the angle adjusting assembly is connected with the vibration assembly, and the action end of the vibration assembly is abutted with the battery pack.

8. A silicon-carbon negative lithium-ion battery, characterized in that, The formation equipment of the multi-stage relaxation formation process of claim 6 is used for preparation.

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