WO2023098236A1 - Method for opening formation of lithium ion battery, and lithium ion battery - Google Patents

Abstract

Provided in the present invention are a method for the opening formation of a lithium ion battery, and a lithium ion battery. The method comprises: injecting an electrolyte into a battery cell under a vacuum condition, and performing pre-charging to obtain an activated battery cell, wherein the electrolyte comprises lithium salt and an organic solvent, and the pre-charging process is performed in an opening state; making the activated battery cell stand in the opening state to obtain a battery cell that has been made to stand; performing, in the opening state, formation on the battery cell that has been made to stand, so as to obtain a formed battery cell, wherein during the formation process, a first charging rate, a second charging rate and a third charging rate are sequentially used to charge the battery cell that has been made to stand to 100% of a designed rated capacity, and the first charging rate and the third charging rate are respectively greater than the second charging rate; and sealing the formed battery cell to obtain a lithium ion battery. By means of the method, the amount of gases generated by a reaction between an organic solvent in an electrolyte and an electrode active material can be reduced, and spontaneous discharging of the generated gases is realized, thereby improving the cycling stability of a lithium ion battery.

Description

Lithium-ion battery aperture forming method and lithium-ion battery

This application is based on the Chinese application with CN application number 202111450967.6 and the application date is November 30, 2021, and claims its priority. The disclosure content of this CN application is incorporated into this application as a whole again.

technical field

The invention relates to the technical field of preparation of lithium-ion batteries, in particular to a method for opening formation of lithium-ion batteries and lithium-ion batteries.

Background technique

During the formation process of the lithium-ion battery, the solvent in the electrolyte reacts electrochemically with the positive electrode active material and the negative electrode active material to generate gases (such as ethylene, propylene, and carbon dioxide, etc.). Compared with other types of lithium-ion batteries, the gas production of high-nickel-nickel-cobalt-manganese ternary lithium-ion batteries and lithium-rich manganese-based lithium-ion batteries is worse, and it is even possible to switch the current interrupt device (CID) during the formation process. overturned, resulting in an open circuit. As a key process for activating lithium-ion batteries, the formation process has a great influence on the stability of the solid electrolyte membrane (SEI film) and the improvement of the cycle performance and rate performance of lithium-ion batteries.

In the traditional chemical formation process, the object of the chemical conversion treatment is the sealed battery cell, which will cause the generated gas to be accumulated inside the battery without being discharged from the battery cell, thereby affecting the formation of the SEI film, reducing its stability, and further affecting Cycle performance and rate performance of lithium-ion batteries.

The existing literature (publication number CN111769332A) provides a method for forming a pre-lithium battery and a pre-lithiated lithium-ion battery. The formation method of the pre-lithium battery includes: injecting liquid and vacuum sealing the pre-lithiated battery, and then shelving it; adopting two-stage variable pressure and a small current of 0.01-0.1CA to charge the shelved battery, forming The charging capacity is 28-48% of the designed capacity of the battery, and the cut-off voltage is 3.1-3.6V; after aging and degassing the charged battery, the battery is charged and discharged to complete the capacity division. This method can give full play to the lithium gram capacity after pre-lithiation, and improve the first coulombic efficiency and charge-discharge cycle of the pre-lithiation lithium-ion battery. The gas produced by the reaction with the positive and negative electrodes is sealed inside the battery, and then vacuumized and degassed after being formed and charged. This method still has a poor degassing effect. In addition, it takes a long time (24-72 hours) for liquid injection and formation, which is not conducive to the improvement of production efficiency.

In order to discharge the produced gas, the method of open chemical formation can be adopted. However, during the opening formation process, the moisture in the environment can easily enter the inside of the cell, which will cause problems in the internal system of the cell.

On this basis, research and develop a method of opening formation of lithium-ion batteries, which is of great significance for reducing the amount of gas generated by the reaction between electrolyte and electrode active materials and improving the cycle stability of lithium-ion batteries.

Contents of the invention

The main purpose of the present invention is to provide a method for lithium-ion battery opening formation and lithium-ion battery, to solve the problem of the gas volume produced by the reaction of electrolyte and electrode active material in the formation step in the production process of lithium-ion battery in the prior art. Large, and the problem that the spontaneous discharge of gas cannot be realized.

In order to achieve the above object, the present invention provides a method for opening formation of a lithium-ion battery on the one hand. The method for forming an opening of a lithium-ion battery includes: injecting an electrolyte solution into the battery cell under vacuum conditions, and obtaining an activated battery cell after pre-charging. Core; the electrolyte includes lithium salt and organic solvent, and the pre-charging process is carried out in the open state; the activated battery cell is shelved in the open state to obtain the shelved battery cell; the shelved battery cell is placed in the open state Carry out chemical formation to obtain the battery cell after formation; in the process of formation, the first charging rate, the second charging rate and the third charging rate are used in sequence to charge the shelved battery cell to 100% of the designed rated capacity, and the first charging rate and the third charging rate are respectively greater than the second charging rate; sealing the formed cell to obtain a lithium-ion battery.

Further, when the battery cell is a nickel-cobalt-manganese ternary lithium-ion battery with a nickel content higher than 83% and/or a manganese-based lithium-ion battery with a lithium content higher than 75%, the forming process includes: using the first charging rate to The cells after shelving are charged in the first stage to the first cut-off voltage, the first charge rate is 0.3-0.5C, and the first cut-off voltage is 3.6-3.8V; Stage charging to the second cut-off voltage, the second charge rate is 0.05-0.2C, and the second cut-off voltage is 4.0-4.2V; the third charge rate is used to carry out the third stage charge to the third cut-off voltage of the batteries after shelving, The third charge rate is 0.33-1C, and the third cut-off voltage is 4.2-4.6V.

Further, during the pre-charging process, the shelving process and the formation process, the dew point of the environment is independently selected from -65 to -55°C

Further, the vacuum degree of the vacuum condition is 500-100 Pa, and the vacuum treatment time is 24-32 minutes.

Further, the pre-charging process includes: using the fourth charging rate to charge the battery cell to the fourth cut-off voltage to complete the activation of the battery cell; preferably, when the battery cell is a nickel-cobalt-manganese ternary lithium ion with a nickel content higher than 83% When the battery and/or the manganese-based lithium-ion battery with lithium content higher than 75%, the fourth charging rate is 0.05-0.2C, and the fourth cut-off voltage is 0.3-0.5V.

Further, the time of the pre-charging process is 5-60 minutes.

Further, the shelving time is 4-8 hours.

Further, the sealing process includes: discharging the formed battery cell to 3.0-3.6V, and then performing the sealing operation to obtain the sealed battery cell; after the sealing operation is completed, fully charge the sealed battery cell to the lithium-ion battery The designed capacity is obtained after aging treatment; preferably, the temperature of aging treatment is 40-50° C., and the time is 4-6 days.

Further, the lithium-ion battery is a cylindrical lithium-ion battery, and the shell of the lithium-ion battery is made of steel shell material.

In order to achieve the above object, another aspect of the present invention also provides a lithium ion battery, which is subjected to formation treatment by using the above-mentioned open formation method of the lithium ion battery provided in this application.

Applying the technical scheme of the present invention, compared with the traditional Li-ion battery formation method, the processes of precharging, shelving and formation in the above method are all carried out in the open state, which is conducive to timely dissolving the electrolyte in the battery cell. The gas (such as ethylene, propylene, and carbon dioxide, etc.) produced by the electrochemical reaction between the organic solvent and the positive electrode active material and the negative electrode active material can realize the spontaneous discharge of the gas, which is beneficial to improve the stability of the solid electrolyte membrane (SEI membrane), thereby Improve the cycle stability of lithium-ion batteries. At the same time, the chemical conversion treatment of the battery cell in the open state can greatly reduce the possibility of the current interrupt device (CID) being overcharged under the condition of overcharging (battery failure), thereby improving the safety performance of the lithium-ion battery.

During the formation process, the above-mentioned three stages are used in sequence to charge the shelved batteries, and a specific charging rate is used for charging. Among them, in the first stage, charging the shelved cells faster can shorten the formation time while increasing the power of the cells; in the second stage, charging the shelved cells slower can inhibit electrolysis. The reduction and decomposition reaction of the organic solvent in the liquid, thereby reducing the gas production, reducing the gas production from the source, and at the same time reducing the calorific value of the battery; in the third stage, the SEI film has been basically formed, and the SEI film inhibits the reduction of the organic solvent Decomposition reaction, less gas production in this stage, can achieve faster charging. In addition, the above method can shorten the time required for electrolyte injection, aging and chemical conversion treatment, thereby improving the production efficiency of lithium-ion batteries.

Description of drawings

The accompanying drawings constituting a part of the present application are used to provide a further understanding of the present invention, and the schematic embodiments and descriptions of the present invention are used to explain the present invention, and do not constitute an improper limitation of the present invention. In the attached picture:

FIG. 1 shows the cycle stability test curves of the lithium-ion batteries in Example 1 and Comparative Example 1 of the present application.

Detailed ways

It should be noted that, in the case of no conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below in conjunction with examples.

As described in the background art, the existing opening formation method of lithium-ion batteries has the problem that a large amount of gas is generated by the reaction between the electrolyte and the electrode active material during the formation step, and the gas cannot be discharged spontaneously. In order to solve the above-mentioned technical problems, the application provides a method for opening formation of lithium-ion batteries. The method for opening formation of lithium-ion batteries includes: injecting electrolyte solution into the battery cells under vacuum conditions, and obtaining activated batteries after pre-charging ; The electrolyte includes lithium salt and organic solvent, and the pre-charging process is carried out in the open state; the activated cell is placed on hold in the open state to obtain the cell after shelving; the cell after the cell is placed in the open state Formation, to obtain the batteries after formation; in the process of formation, the first charging rate, the second charging rate and the third charging rate are used to charge the shelved batteries to 100% of the designed rated capacity, the first charging rate and the third charging rate The third charging rate is respectively higher than the second charging rate; sealing the formed battery cell to obtain a lithium ion battery.

Compared with the traditional lithium-ion battery formation method, the above method achieves the effect of gas production and self-exhaust rate improvement through two aspects of treatment:

First, the above-mentioned precharging, shelving and formation processes are all carried out in an open state, which is conducive to timely electrochemically reacting the organic solvent in the electrolyte in the battery cell with the positive active material and the negative active material. Gas (such as ethylene, propylene, and carbon dioxide, etc.), realizes the spontaneous discharge of gas, which is conducive to improving the stability of the solid electrolyte membrane (SEI membrane), thereby improving the cycle stability of the lithium-ion battery. At the same time, the chemical conversion treatment of the battery cell in the open state can greatly reduce the possibility of the current interrupt device (CID) being overcharged under the condition of overcharging (battery failure), thereby improving the safety performance of the lithium-ion battery.

Second, during the formation process, the above-mentioned three stages are used in sequence to charge the shelved battery cells, and a specific charging rate is used for charging. Among them, in the first stage, charging the shelved cells faster can shorten the formation time while increasing the power of the cells; in the second stage, charging the shelved cells slower can inhibit electrolysis. The reduction and decomposition reaction of the organic solvent in the liquid, thereby reducing the gas production, reducing the gas production from the source, and at the same time reducing the calorific value of the battery; in the third stage, the SEI film has been basically formed, and the SEI film inhibits the reduction of the organic solvent Decomposition reaction, less gas production in this stage, can achieve faster charging. In addition, the above method can shorten the time required for electrolyte injection, aging and chemical conversion treatment, thereby improving the production efficiency of lithium-ion batteries.

Different types of cells require different cut-off voltages during the formation process to match the rated capacity of the Li-ion battery. In a preferred embodiment, when the battery cell is a nickel-cobalt-manganese ternary lithium-ion battery with a nickel content higher than 83% and/or a manganese-based lithium-ion battery with a lithium content higher than 75%, the formation process includes: Use the first charging rate to charge the batteries after shelving in the first stage to the first cut-off voltage, the first charging rate is 0.3-0.5C, and the first cut-off voltage is 3.6-3.8V; Carry out the second-stage charge to the second cut-off voltage of the battery cell, the second charge rate is 0.05-0.2C, and the second cut-off voltage is 4.0-4.2V; use the third charge rate to carry out the third-stage charge for the battery cell after shelving Up to the third cut-off voltage, the third charging rate is 0.33-1C, and the third cut-off voltage is 4.2-4.6V.

During the formation process, the first charging rate and the first cut-off voltage in the first stage include but are not limited to the above-mentioned range, and limiting them within the above-mentioned range is beneficial to further increase the power of the battery cell while shortening the formation time; in the second stage, the first The second charging rate and the second cut-off voltage include but are not limited to the above-mentioned range, and limiting it within the above-mentioned range is beneficial to further inhibit the reduction and decomposition reaction of the organic solvent, further reduce the gas production and the calorific value of the battery cell; in the third stage, the third The charging rate and the third cut-off voltage include but are not limited to the above-mentioned ranges, and limiting them within the above-mentioned ranges is beneficial to further speed up the completion of the forming step.

In an optional embodiment, the electrolyte solution includes a lithium salt and an organic solvent. Lithium salts include but not limited to lithium hexafluorophosphate and/or lithium dioxalate borate; organic solvents include but not limited to one or more of the group consisting of ethylene carbonate, propylene carbonate and polycarbonate; positive electrode active materials include but Not limited to nickel-cobalt-manganese ternary lithium-ion batteries with a nickel content higher than 83% and/or manganese-based lithium-ion batteries with a lithium content higher than 75%; negative electrode active materials include but are not limited to artificial graphite, natural graphite, and graphite and pre- One or more of the group consisting of pre-lithiated materials obtained by compounding lithiated silicon and oxygen.

Excessive moisture will cause the lithium-ion battery to swell, and in severe cases, it will lead to battery failure. At the same time, side reactions will occur inside the battery, causing interface damage, resulting in increased polarization during the formation process, making charging in a shorter time point, resulting in a decrease in charging capacity. In a preferred embodiment, during the pre-charging process, the shelving process and the formation process, the dew point of the environment respectively independently includes but not limited to -65--55°C. The dew point of the environment in the above process includes but is not limited to the above range. Limiting it within the above range is beneficial to inhibit the electrode material from absorbing moisture in the environment, reduce the possibility of lithium-ion battery inflation, and reduce the amount of gas produced.

Since the chemical formation process is carried out in an open state, the wettability of the electrode sheet will be affected. In a preferred embodiment, the vacuum degree of the vacuum condition is 500-100 Pa, and the vacuum treatment time is 24-32 minutes. The vacuum degree and vacuum treatment time of the vacuum condition include but are not limited to the above-mentioned range, and it is beneficial to improve the wettability of the electrolyte on the surface of the electrode sheet and the diaphragm, and provide favorable conditions for the subsequent steps.

In a preferred implementation manner, the pre-charging process includes: charging the battery cell to a fourth cut-off voltage at a fourth charging rate to complete activation of the battery cell. The pre-charging process can adjust the potential of the positive and negative electrodes to ensure that a potential difference can be formed between the positive and negative electrodes, so that the ions in the electrolyte begin to enrich in an orderly manner, preparing for the subsequent formation.

In order to form a potential difference suitable for a specific type of battery between the positive electrode and the negative electrode, and then make the ion distribution in the electrolyte more orderly, thereby better activating the battery core, preferably, when the battery core is nickel content higher than 83% For nickel-cobalt-manganese ternary lithium-ion batteries and/or manganese-based lithium-ion batteries with a lithium content higher than 75%, the fourth charge rate is 0.05-0.2C, and the fourth cut-off voltage is 0.3-0.5V.

In order to form a potential difference suitable for a specific type of battery between the positive electrode and the negative electrode, and then make the ion distribution in the electrolyte more orderly, thereby better activating the battery cell, in a preferred embodiment, the time of the pre-charging process 5 to 60 minutes.

Putting the activated cell aside can allow the electrolyte to further infiltrate inside the activated cell. In a preferred embodiment, the resting time is 4-8 hours. The storage time includes but is not limited to the above range, which is beneficial to improve the wettability while reducing the entry of moisture in the environment in the open state, thereby reducing the possibility of lithium precipitation in the subsequent formation process.

In a preferred embodiment, the sealing process includes: discharging the formed battery cell to 3.0-3.6V, and then performing the sealing operation to obtain the sealed battery cell; after the sealing operation is completed, the sealed battery cell Fully charge to the design capacity of the lithium-ion battery, and obtain a lithium-ion battery after aging treatment. Discharging the formed cells to a specific voltage is conducive to the subsequent sealing operation, in order to prevent ignition during sealing. Aging treatment is beneficial to improve the structural stability of the SEI film, which in turn is beneficial to improve the cycle performance of lithium-ion batteries. In order to further improve the structural stability of the SEI film and further improve the cycle performance of the lithium-ion battery, preferably, the temperature of the aging treatment is 40-50° C. and the time is 4-6 days.

In a preferred embodiment, the sealing operation includes: sticking a sealing material on the battery cap. The sealing material includes but not limited to one or more of the group consisting of Teflon, polytetrafluoroethylene and polyethylene terephthalate (PET) insulating surface mat.

In a preferred embodiment, the lithium-ion battery is a cylindrical lithium-ion battery, and the shell of the lithium-ion battery is made of steel shell material. The above-mentioned opening formation method for lithium-ion batteries is particularly suitable for cylindrical lithium-ion batteries, which usually have a metal shell.

The second aspect of the present application also provides a lithium-ion battery, which is subjected to formation treatment by using the above-mentioned opening formation method of the lithium-ion battery provided in the present application.

The amount of gas accumulated inside the lithium ion battery is extremely small, and it has excellent cycle stability.

The present application will be described in further detail below in conjunction with specific examples, and these examples should not be construed as limiting the scope of protection claimed in the present application.

Example 1

A method for opening formation of a lithium-ion battery, comprising:

Under the condition of vacuum degree of -0.9MPa, the electrolyte solution was injected into the cylindrical high-nickel Ni88/SiO system of model 21700, and the electrolyte solution included EC and DMC (Zhuhai Saiwei, TH2R020/TH2R025). The injection time is 24 minutes, and the vacuum treatment time is 24 minutes.

After the liquid injection is completed, without sealing, the cell is charged to the fourth cut-off voltage of 0.3V at the fourth charge rate of 0.05C (current is 250mA) in the open state to obtain the activated cell. Wherein, during the pre-charging process, the dew point of the environment is -60° C., and the time of the pre-charging process is 8 minutes.

In the open state, and under the condition that the dew point of the environment is -60°C, the activated battery is left in a static state for 6 hours. After shelving, it was observed that the infiltration was good and there was no suction line.

Place the shelved cells on the charging and discharging cabinet, and prepare to start the formation process. During the formation process, the dew point of the environment is -60°C. Use the first charge rate to carry out the first stage charging to the first cut-off voltage of the batteries after shelving. The first charge rate is 0.33C (the current is 1650mA), and the first cut-off voltage is 3.6V; Charge rate Carry out second-stage charging to the second cut-off voltage of the batteries after shelving, the second charge rate is 0.1C (current is 500mA), and the second cut-off voltage is 4.0V; The cells after shelving are charged in the third stage to the third cut-off voltage, the third charge rate is 0.33C (the current is 100mA), and the third cut-off voltage is 4.2V.

After the formation process is over, set discharge step 1C to discharge to a voltage of 3.0V (current is 5000mA). After the discharge is completed, seal the formed cell.

After coating and inkjet printing, it is first charged at a rate of 0.5C (current is 2500mA), then charged at a rate of 0.02C (cut-off current of 100mA) to 4.2V, and transferred to a high-temperature aging box for aging at 45°C for 4 days , to obtain a lithium-ion battery.

It can be seen from Figure 1 that, compared with the chemical conversion under sealing conditions, the lithium-ion battery prepared in Example 1 still maintains a capacity retention rate of more than 90% after 500 cycles, which is 94.5%, while the lithium-ion battery prepared in Comparative Example 1 The capacity retention rate of lithium-ion batteries is less than 90%. This shows that adopting the method in Example 1 of the present application can smoothly discharge the gas generated during the formation of the shelved battery cell, thereby improving the cycle performance of the lithium-ion battery.

Example 2

The difference from Embodiment 1 is: the first charging rate is 0.5C; the second charging rate is 0.05C; the third charging rate is 0.33C.

The cycle performance test results are shown in Table 1.

Example 3

The difference from Embodiment 1 is that: the first charging rate is 0.3C; the second charging rate is 0.2C; and the third charging rate is 1C.

The cycle performance test results are shown in Table 1.

Example 4

The difference from Embodiment 1 is that the first charge rate is 0.2C.

The cycle performance test results are shown in Table 1.

Example 5

The difference from Embodiment 1 is that the second charging rate is 0.25C.

The cycle performance test results are shown in Table 1.

Example 6

The difference from Embodiment 1 is that the third charge rate is 0.25C.

The cycle performance test results are shown in Table 1.

Example 7

The difference from Example 1 is that the dew point of the environment is -65°C.

The cycle performance test results are shown in Table 1.

Example 8

The difference from Example 1 is that the dew point of the environment is -55°C.

The cycle performance test results are shown in Table 1.

Example 9

The difference from Example 1 is that the dew point of the environment is -45°C.

The cycle performance test results are shown in Table 1.

Example 10

The difference from Embodiment 1 is that the fourth charge rate is 0.2C, and the fourth cut-off voltage is 0.5V.

The cycle performance test results are shown in Table 1.

Example 11

The difference from Embodiment 1 is that the fourth charging rate is 0.25C, and the fourth cut-off voltage is 0.6V.

The cycle performance test results are shown in Table 1.

Example 12

The difference from Example 1 is that: in the open state, the activated battery was left in a static state for 4 hours. After shelving, it was observed that the infiltration was good and there was no suction line.

The cycle performance test results are shown in Table 1.

Example 13

The difference from Example 1 is that: in the open state, the activated battery was left in a static state for 8 hours. After shelving, it was observed that the infiltration was good and there was no suction line.

The cycle performance test results are shown in Table 1.

Example 14

The difference from Example 1 is that: in the open state, the activated battery was left in a static state for 12 hours. After the storage was completed, it was observed that the battery absorbs liquid well, but after the formation, it was disassembled and found that its edges were oxidized and turned black.

The cycle performance test results are shown in Table 1.

Example 15

The difference from Example 1 is that the positive electrode active material in the battery cell is a lithium-rich manganese-based positive electrode material (BASF).

During the pre-charging process, the fourth cut-off voltage is 0.3V;

During the formation process, the first cut-off voltage is 3.8V; the second cut-off voltage is 4.2V; and the third cut-off voltage is 4.6V.

The cycle performance test results are shown in Table 1.

Comparative example 1

The difference from Example 1 is that the processes of precharging, shelving and formation are all carried out in the sealed state of the battery cell.

The cycle performance test results are shown in Table 1.

Comparative example 2

The difference from Embodiment 1 is that the first charging rate, the second charging rate and the third charging rate are all 0.6C.

The cycle performance test results are shown in Table 1.

The lithium-ion batteries prepared in all the examples and comparative examples in this application were tested for cycle performance. The test conditions were as follows: 0.5C (2500mA) charge and 1C (5000mA) discharge at room temperature at 25°C. The test results are shown in Table 1.

Table 1

the	Capacity retention after 500 cycles (%)
Example 1	94.5
Example 2	93.2
Example 3	93.5
Example 4	90.0
Example 5	90.8
Example 6	90.7
Example 7	94.2
Example 8	94.4
Example 9	90.1
Example 10	93.5
Example 11	91.7
Example 12	94.6
Example 13	94.3
Example 14	89.5
Example 15	93.8
Comparative example 1	87.6
Comparative example 2	86.2

From the above description, it can be seen that the above-mentioned embodiments of the present invention have achieved the following technical effects:

The processes of precharging, shelving and formation in Comparative Example 1 were all carried out in the sealed state of the battery cell, while in Example 1 it was carried out in the open state of the battery cell. According to the test results in Table 1, the capacity retention rate of Example 1 after 500 cycles is 94.5%, while that of Comparative Example 1 is only 87.6%. Example 15 uses different positive electrode active materials and different cell systems from Example 1, but the processes of precharging, storage and formation are all carried out in the open state of the cells. By comparing Examples 1, 15 and Comparative Example 1, it can be seen that compared with the traditional lithium-ion battery formation method (formation in a sealed state), the processes of pre-charging, shelving and formation in the above-mentioned method provided by the application are all in an open state This is beneficial to timely discharge the gas generated by the electrochemical reaction between the organic solvent in the electrolyte in the battery cell and the positive electrode active material and negative electrode active material, so as to realize the spontaneous discharge of the gas produced, which in turn is beneficial to improve the stability of the SEI film. performance, thereby improving the cycle stability of lithium-ion batteries.

The formation process in Comparative Example 2 is always charged at the same rate, while Examples 1 and 15 are charged in three stages in sequence. According to the test results in Table 1, the capacity retention rate of Example 1 after 500 cycles is 94.5%, while that of Comparative Example 1 is only 86.2%. By comparing Examples 1, 15 and Comparative Example 2, it can be seen that during the formation process, the above three stages are sequentially used to charge the battery cells after shelving, and a specific charging rate is used for charging. Among them, in the first stage, charging the shelved cells faster can shorten the formation time while increasing the power of the cells; in the second stage, charging the shelved cells slower can inhibit electrolysis. The reduction and decomposition reaction of the organic solvent in the liquid, thereby reducing the gas production, and reducing the gas production from the source; in the third stage, the SEI film has basically formed, and the SEI film inhibits the reduction and decomposition reaction of the organic solvent. The gas production in this stage is relatively low. Less, faster charging can be achieved.

In Example 4, the first charging rate takes a value outside the preferred range of the present application, while Examples 1 to 3 all take values within the preferred range of the present application. Comparing Examples 1, 2, 3 and 4, it can be seen that in the process of formation, the first charging rate and the first cut-off voltage in the first stage include but are not limited to the preferred range of this application, and it is beneficial to limit it within the preferred range of this application. Further increase the power of the battery while shortening the formation time. In embodiment 5, the second charging rate takes a value outside the preferred range of the present application, and compares

Examples 1, 2, 3 and 5 show that the second charging rate and the second cut-off voltage in the second stage include but are not limited to the preferred range of this application, and limiting them to the preferred range of this application is beneficial to further inhibit the reduction of organic solvents Decomposition reaction further reduces gas production. In Example 6, the third charging rate takes a value outside the preferred range of the present application. Comparing Examples 1, 2, 3 and 6, it can be seen that the third charging rate and the third cut-off voltage in the third stage include but are not limited to the preferred range of the present application. Limiting it within the preferred range of the present application is conducive to further accelerating the completion of the chemical conversion step.

Comparing Examples 1, 7 to 9, it can be seen that the dew point of the environment in the above-mentioned process includes but is not limited to the preferred range of the present application, and limiting it to the preferred range of the present application is beneficial to inhibit the absorption of moisture in the environment by the electrode material and reduce the lithium-ion battery. Possibility of bloating, reduces gas production.

Comparing Examples 1, 10 and 11, it can be seen that the fourth charging rate and the fourth cut-off voltage include but are not limited to the preferred range of the present application, and limiting them within the preferred range of the present application is conducive to forming a suitable model between the positive electrode and the negative electrode. The potential difference of the 21700 cylindrical high-nickel Ni88/SiO battery makes the ion distribution in the electrolyte more orderly.

Comparing Examples 1, 12 to 14, it can be seen that the time of shelving includes but is not limited to the preferred range of the present application, and limiting it within the preferred range of the present application is conducive to improving the wettability while reducing the entry of moisture in the environment when the opening is in the state, and then Reduce the possibility of lithium precipitation in the subsequent chemical formation process.

It should be noted that the terms "first" and "second" in the specification and claims of the present application are used to distinguish similar objects, but not necessarily used to describe a specific order or sequence. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the application described herein are, for example, capable of operation in sequences other than those described herein.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. A method for forming an opening of a lithium-ion battery, characterized in that the method for forming an opening of a lithium-ion battery comprises:

   The electrolyte is injected into the cell under vacuum conditions, and the activated cell is obtained after pre-charging; the electrolyte includes lithium salt and organic solvent, and the pre-charging process is carried out in an open state;

   Shelving the activated battery core in the open state to obtain the battery core after shelving;

   In the open state, the battery cell after being put on hold is formed to obtain the battery cell after formation; in the process of the formation, the first charging rate, the second charging rate and the third charging rate are sequentially used to charge the battery cell after being put on hold. The battery cell is charged to 100% of the designed rated capacity, and the first charging rate and the third charging rate are respectively greater than the second charging rate;

   Sealing the formed cell to obtain the lithium ion battery.
2. The method for opening formation of a lithium-ion battery according to claim 1, wherein when the battery cell is a nickel-cobalt-manganese ternary lithium-ion battery with a nickel content higher than 83% and/or a lithium content higher than 75% During manganese-based lithium ion battery, the process of described formation comprises:

   Using a first charge rate to perform a first-stage charge on the shelved cells to a first cut-off voltage, the first charge rate is 0.3-0.5C, and the first cut-off voltage is 3.6-3.8V;

   Carrying out second-stage charging to the second cut-off voltage of the battery cell after being put aside by using a second charge rate, the second charge rate is 0.05-0.2C, and the second cut-off voltage is 4.0-4.2V;

   The third charging rate is used to charge the battery cell after shelving to a third cut-off voltage in a third stage, the third charging rate is 0.33-1C, and the third cut-off voltage is 4.2-4.6V.
3. According to the method of claim 1 or 2, the open formation of lithium ion battery, it is characterized in that, in the process of described pre-charging, the process of described shelving and the process of described formation, the dew point of environment is independently selected from -65～-55℃.
4. The method for opening formation of a lithium ion battery according to any one of claims 1 to 3, characterized in that the vacuum degree of the vacuum condition is 500-100 Pa, and the vacuum treatment time is 24-32 minutes.
5. The method for opening formation of lithium-ion batteries according to claim 4, wherein the pre-charging process comprises:

   Charging the cell to a fourth cut-off voltage with a fourth charge rate to complete the activation of the cell;

   Preferably, when the battery cell is a nickel-cobalt-manganese ternary lithium-ion battery with a nickel content higher than 83% and/or a manganese-based lithium-ion battery with a lithium content higher than 75%, the fourth charging rate is 0.05- 0.2C, the fourth cut-off voltage is 0.3-0.5V.
6. The method for opening formation of lithium-ion batteries according to claim 5, characterized in that the time of the pre-charging process is 5-60 minutes.
7. The method for opening formation of a lithium ion battery according to claim 5 or 6, characterized in that, the time for the shelving is 4 to 8 hours.
8. The method for forming an opening of a lithium-ion battery according to any one of claims 5 to 7, wherein the sealing process comprises:

   Discharging the formed battery cell to 3.0-3.6V, and then performing the sealing operation to obtain the sealed battery cell;

   After the sealing operation is completed, fully charge the sealed cell to the design capacity of the lithium-ion battery, and obtain the lithium-ion battery after aging treatment;

   Preferably, the temperature of the aging treatment is 40-50° C., and the time is 4-6 days.
9. The method for opening formation of a lithium ion battery according to claim 8, wherein the lithium ion battery is a cylindrical lithium ion battery, and the shell of the lithium ion battery is a steel shell material.
10. A lithium-ion battery, characterized in that, the lithium-ion battery is subjected to chemical conversion using the open-formation method of the lithium-ion battery according to any one of claims 1 to 9.

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