WO2010081422A1

WO2010081422A1 - Pre-charging method for lithium-ion battery

Info

Publication number: WO2010081422A1
Application number: PCT/CN2010/070202
Authority: WO
Inventors: 滕鑫; 何伟; 何名; 饶汝宇
Original assignee: 深圳市比克电池有限公司
Priority date: 2009-01-15
Filing date: 2010-01-15
Publication date: 2010-07-22

Abstract

A pre-charging method for lithium-ion battery which includes at least two charging steps, charging current of the first charging step is higher than that of the second step, and the total pre-charging electric quantity of the two charging steps is 10%-45% of total charge capacity.

Description

Lithium ion battery pre-filling method

The present invention relates to the field of lithium ion battery technology, and in particular to a method for precharging a lithium ion battery.

Background technique

At present, the application of lithium-ion batteries is becoming more and more widespread, and the demand for batteries is increasing. For battery manufacturers, on the one hand, it is necessary to improve production efficiency to meet market needs, on the other hand, it is required to improve and improve processes, while improving product quality. Improve the efficiency of production books. With the mechanization of production in the lithium battery industry, the pre-filling process has become a key link that restricts production rates and product quality.

For a lithium-ion battery, when the pre-charge is the first charge, due to the electrochemical reaction, a passivation thin layer covering the surface of the carbon electrode is inevitably formed at the interface between the carbon negative electrode and the electrolyte, and the thin layer is solid. The electrolyte interface (sol id e lectrolyte interface) or SEI month Mo. The process of charging a lithium-ion battery for the first time is also called chemical conversion. In the battery formation process, a SEI film is formed on the surface of the negative electrode, and a side reaction generates a gas product. The generated gas needs to be discharged out of the battery in time. Otherwise, the gas will accumulate inside the battery and cause the battery to expand. The outer casing will be drummed, deformed, and even cause the battery to explode. However, if the gas is incomplete during the formation process, it will continue to be released during the electrical cycle of the battery, which will seriously affect the electrical performance and safety performance of the battery. Therefore, the formation step of the lithium ion secondary rechargeable battery is an important stage in the manufacture of the battery, and is related to the quality of the battery, the cycle life, and the safety performance.

At this stage, the formation process is usually carried out with a small current for several tens of hours of charging, in order to obtain an ideal SEI film to maintain stable battery performance. However, long-term chemical conversion steps result in inefficient production.

Summary of the invention

SUMMARY OF THE INVENTION An object of the present invention is to provide a lithium ion battery prefilling method which can improve the performance of a battery core and greatly shorten the charging time and improve the production efficiency in view of the deficiencies of the prior art.

The invention discloses a method for pre-charging a lithium ion battery, wherein the pre-charging method of the lithium ion battery is a stage charging, the stage charging comprises at least two charging steps, and the charging current of the second charging step is greater than the first a charging current of a charging step, and the first charging step and the second charging The total pre-charge amount of the electrical step is 10% to 45% of the total amount of the lithium ion battery. In a specific embodiment of the present invention, the positive active material of the lithium ion battery is lithium cobaltate, and the total precharge amount of the first charging step and the second charging step is the total amount of the lithium ion battery. 10% to 35%, preferably 10% to 30%. The charging current of the first charging step is preferably less than 0.1 C, and the charging time is 5 to 30 min. The charging current of the first charging step is further preferably 0.05 C to 0.1 C, and the charging time is 5 to 15 min. The charging current of the second charging step is preferably 0.3C - 0.6C, and the charging time is 10 ~ 60min. More preferably, the charging current of the first charging step is 0.05 C, the charging time is 10 min, the charging current of the second charging step is 0.5 C, and the charging time is 12 min. Preferably, the electrolyte injection amount before the staged charging is 80% to 85%, and the refilling liquid is 10% to 15% after the stage charging.

In another specific embodiment of the present invention, the positive active material of the lithium ion battery is a mixed material of lithium cobaltate and lithium nickel cobalt manganese oxide, and the total pre-charging of the first charging step and the second charging step The amount is 15% to 35%, preferably 15% to 30%, of the total amount of the lithium ion battery. Preferably, among the positive electrode active materials of the lithium ion battery, lithium cobaltate accounts for 60% to 80%, lithium nickel cobalt manganese oxide accounts for 20% to 40%, and more preferably, lithium cobalt oxide accounts for 80%, lithium nickel cobalt manganese oxide. 20%, said weight percentage. Preferably, the charging current in the first charging step is less than 0.1 C, and the charging time is 5 to 30 min. Further preferably, the charging current in the first charging step is 0.05 C to 0.1 C, and the charging time is 5 to 15 min. Or preferably, the charging current of the second charging step is 0.3C-0.6C, and the charging time is 10~60min. Further preferably, the charging current of the first charging step is 0.05 C, the charging time is 1 Omin, the charging current of the second charging step is 0.4 C, and the charging time is 22 min. Preferably, the electrolyte injection amount before the staged charging is 80% to 85%, and the electrolyte is injected 15% to 10% after the stage charging.

In still another specific embodiment of the present invention, the positive active material of the lithium ion battery is a mixed material of lithium cobaltate and lithium nickel cobaltate, and the total precharge amount of the first charging step and the second charging step It is 25%~45% of the total amount of the lithium ion battery, preferably 25%~40%. Preferably, in the positive electrode active material of the lithium ion battery, the lithium nickel cobaltate has a molecular formula of LiNi _x Co _1-x 0 ₂ and x=0.75 to 0.85. Among the positive electrode active materials of the lithium ion battery, lithium cobaltate accounts for 75% to 85%, lithium nickel cobaltate accounts for 15% to 25%, more preferably, lithium cobaltate accounts for 80%, and lithium nickel cobaltate accounts for 20%. The percentage is by weight. Preferably, the charging current of the first charging step is less than 0.1 C, and the charging time is 5 to 30 min. Further preferably, the charging current of the first charging step is 0.05 C~0.1 C, and the charging time is 5-15 min. Or preferably, the second charging The charging current of the step is 0.3C ~ 0.6C, and the charging time is 25 ~ 80min. Most preferably, the charging current of the first charging step is 0.05 C, the charging time is 10 min, the charging current of the second charging step is 0.4 C, and the charging time is 38 min. Preferably, the electrolyte injection amount before the staged charging is 80% to 85%, and the electrolyte is injected 15% to 10% after the stage charging.

The pre-charging of the lithium ion battery by the pre-charging method of the present invention enables the battery core to achieve comparable or even better electrical performance than the battery core of the conventional small current long-time pre-charging process, and greatly shortens the pre-charging. Time, at the same time, can shorten the aging time of the battery core and greatly improve production efficiency. Save on production costs.

DRAWINGS

Fig. 1 is a charging graph showing a current of 0.1 C for a lithium ion battery in which a positive electrode active material is lithium cobaltate.

2 is a lithium ion battery in which a positive electrode active material is a mixture of lithium cobaltate and lithium nickel cobalt manganate in a weight ratio of 8:2, and a charging current of 0.1 C is used, and the abscissa is time (min), vertical. The coordinates are voltage values.

3 is a lithium ion battery in which a positive electrode active material is lithium cobaltate (LiCo0 ₂ ) and lithium nickel cobaltate (LiNi _x Co _1-x 0 ₂ , x=0.75 to 0.85) in a weight ratio of 8:2, and the like. Using a charging curve with a current of 0.1 C, the abscissa is time (min) and the ordinate is voltage value (V).

detailed description

At present, the application of lithium-ion batteries is becoming more and more extensive, and the demand for batteries is increasing. For battery manufacturers, on the one hand, it is necessary to improve production efficiency to meet market needs, on the other hand, it is required to improve and improve processes, and improve production while improving product quality. effectiveness. With the mechanization of production in the lithium battery industry, the pre-filling process has become a key link that restricts the production rate and product quality. The present invention provides a pre-charging method for a lithium ion battery, which can greatly improve the performance of the battery core. Improve production efficiency.

The invention accelerates the progress of the side reaction in the formation process of the SEI film by introducing a pre-charging step of a large current, so that the pre-charging can be achieved in a shorter time. The invention firstly determines the relationship between the pre-charging amount and the pre-charging pressure through experiments, and then determines the appropriate amount of pre-charging by the voltage at the time of film formation, and finally through a series of embodiments, through the introduction of the large current pre-charging step, The side reaction of the film formation is completed in a short time, and a product with improved overall performance is obtained. Reduce the aging time of the battery. The purpose of aging is to fully infiltrate the electrolyte into the pole piece, thus ensuring avoidance of polarization and electrolyte loss during pre-charging, and ensuring residual electrolysis of the sealed cell. The amount of electrolyte in the liquid, etc., because the conventional process uses a one-time 100% injection, and the pre-filling time is long, so the aging time is relatively long, usually takes more than ten hours; after adjustment to the new pre-filling process of the present invention The injection is divided into two parts. The first injection is 80% ~ 85%. After pre-filling, the refilling liquid is 10% ~ 15%. Although the second step current is relatively large, but the time is short, it will be aged on this basis. The time is also shortened and can be shortened to 1 ~ 2h.

1. The positive active material is lithium cobaltate

First, a charging profile in which the positive active material is a lithium cobaltate precharge flow of 0.1 C is examined, as shown in FIG.

According to the 0.1C charging time-voltage value graph, the charge is between 10% (60min), 20% (120min) and 30% (180min) (corresponding to 3.74V, 3.82V and 3.84V). Finished battery performance. Since the film formation voltage of the SEI film is 3.60 V, the main reaction of forming the SEI film on the surface of the negative electrode may differ depending on the formation voltage during the precharge process, but when the charge voltage reaches the film formation voltage of 3.60 V, the SEI The film begins to form and gradually changes its structure and properties as the reaction progresses during subsequent charging. That is to say, as can be seen from Fig. 1, when the charge amount is 10%, since the voltage exceeds 3.60 V by 3.74 V, the SEI film is sufficiently formed. Therefore, the present invention uses different precharge currents and time combinations to obtain different reverse voltage values of precharge amounts between about 10% and 30%, and inspects the capacity (capacity), internal resistance, size, and Its cycle performance meets the requirements.

The invention adopts a stage charging method, which comprises a first charging step and a second charging step. In the first step, a small current has a positive effect on the formation of the SEI film, which is beneficial to increase the cell capacity, but a long time of small current charging may cause an increase in the impedance of the formed SEI film, thereby affecting the rate discharge performance of the finished cell. The long time process also affects the production efficiency. Therefore, the first step of small current (within 0.1C) is short (within 30min). For the stage precharge method, the impact on the performance of the battery core is almost negligible. . According to the charging curve of Fig. 1, when the voltage is charged for 5 minutes at 0.1 C, the voltage is 3.22 V, and before this time, the change (rise) of the voltage value is fast and unstable, thereby, for the first step, the small current charging time The lower limit value is preferably 5 minutes when charged at 0.1 C, and preferably 10 minutes when charged at 0.05 C. The second step introduces a large current, and the charging method of the large current can accelerate the progress of the side reaction and improve the formation efficiency, but it is easy to damage the formation of the SEI film and cause deterioration of the performance of the battery core, and at the same time, the high current stability and error are pre-filled. Larger, so you should choose the right charging current and charging time. In the pre-charging method of the present invention, the large current is selected between 0.3C and 0.6C, and the charging time is adjusted according to the magnitude of the current, usually within 10 to 60 minutes. For the stage pre-filling process of the present invention, since the first step current is small and charging The short distance, therefore, the amount of electricity achieved in the first step can be neglected, and the amount of electricity to be reached after the second step of high current precharge should be about 10% ~ 30% of the total electricity.

The details are described in further detail below by way of specific examples. The above-mentioned parts and the batteries used in the following Examples 1-18 are all 053450Al-900mAh batteries produced in the same batch, the positive active material is lithium cobaltate, and the electrolytes of Examples 1-18 have consistent positive and negative dressings. The amount of the electrode, the density of the electrode, the same electrolyte injection, the amount of liquid injection, and the same conditions for pre-filling and sealing, cleaning, etc.

Example 1

The specific process steps are as follows: The first sample is injected into the sample cell, the amount of liquid injection is 85% of the process requirement, and the cell is aged for 1 ~ 2 hours, then pre-filled and refused to be 0.05C, lOmin; 0.3C, 20min precharge The method pre-charges, then refuses to measure the voltage, and re-fills the liquid 15%, then squeezes the battery and completes the sealing. The above steps are all carried out under the same temperature and humidity environment, the temperature is ≤26°C; the humidity is ≤2 %. In the room temperature environment, the sealed cell is cleaned and measured, and after 6 days of aging, the cell is tested and divided. The capacity system is based on the parameters shown in Table 2. The capacity, internal resistance, 3.92V size and cycle performance test were examined. The results are shown in Table 3.

Among them, the purpose of the test voltage is to investigate whether there is abnormality in the precharge process, such as the setting of current magnitude and charging time, the stability of the reject current in the charging process, etc., compared with the 0.1C charging curve, the voltage value under the same charging power. It should be the same, with an error of ±0.01V, excluding the interference factors for the performance of the finished battery.

The pre-charging process is a process in which the SEI film and its side reactions occur. If the pre-charging amount is insufficient or the pre-charging does not achieve the desired effect, for example, if the gas is not completely discharged, the cleaned cell will have a drum shell phenomenon. Therefore, measuring the size after cleaning can reflect the pre-filling effect to some extent. Under the same pre-filling conditions, the pre-filling effect is relatively good when the cleaning size is small.

The internal resistance of the cell is investigated because the small internal resistance indicates good interface performance and the SEI film has good performance. There are many factors affecting the internal resistance of the battery, such as the welding of the positive and negative ear solder joints, different materials, material ratio, pre-filling method. Since the batteries we selected are those of the same batch of batteries that are subjected to different pre-filling methods, the interference from the rest of the pre-filling process can be eliminated as much as possible. That is to say, using the same material, the same electrode density, and thickness, the normal core of the tab is welded to perform the pre-filling method experiment. If the pre-filling method is unreasonable, the pole piece has a local overcharge, lithium deposition, etc., and the internal resistance is relatively high at this time. Therefore, the resistor in the embodiment of the present invention can be used as an indicator of the side reaction charging effect.

And charging the battery to 3.92V, and then examining its dimensional change is the battery industry battery A customary indicator of the performance of finished products.

Similarly, the other examples and the comparative example 1 use the same steps except that the time and current used in the pre-filling method are different. In the present invention, the injection is divided into two parts, the first injection is 80% - 85%, and after the pre-filling, the refilling liquid is 10% ~ 15%. Comparative Example 2 is a conventional process, except that the one-time 100% injection, the prefilling method is shown in Table 1 and the aging time is 12 to 16 hours, and the other steps are the same as the above embodiment.

The prefilling methods of all the examples and comparative examples are shown in Table 1, and the technical effect data are shown in Table 3.

Table 1. Prefilling methods of various examples and comparative examples

Table 2. Capacity-sharing system

The lithium battery is here to get the capacity, and know the size of the capacity, that is, the volume. Through the capacity, the level of the battery cell is determined. Table 3. Technical effects of various examples and comparative examples

The data of the respective examples and Comparative Example 2 show that by selecting the pre-filling method of the present invention, the pre-filling time can be greatly reduced, and the production efficiency can be improved. The data of the respective examples and Comparative Example 1 indicate the necessity of the first small current charging. If the first step of the small current precharging is not performed, the effects of the size, capacity, and cycle performance of the finished battery are worse.

The invention can shorten the pre-charging time of the battery core by introducing a large current pre-charging, and further optimize the lithium ion pre-charging method of the positive electrode active material to be lithium cobaltate to be 0.05 C, lOmin; 0.5 C, 12 min. The optimized pre-filling method is a horizontal and vertical comparison of the above embodiments, and the data which best reflects the advantages and disadvantages of the pre-filling method are the positive gram capacity and the cycle performance and the pre-charge time, and then the comprehensive performances such as internal resistance and size are examined. , thus comparing the optimized pre-filling method.

In the above specific embodiment of the present invention, a battery of 900 mAh is selected. For other capacity batteries, it is only necessary to satisfy the positive electrode active material as lithium cobaltate, and the precharge method of the present invention The same is true. However, considering that if the nominal capacity of the lithium-ion battery cell is too large, it is greater than

At 1500 mAh, the charging current of the second step of the corresponding pre-charging method is relatively large, and the current error of the pre-charging is relatively large, or the stability is relatively poor, thereby having a certain influence on the performance of the battery. Therefore, the cell capacity range suitable for the prefilling method of the present invention is preferably less than 1500 mAh, preferably less than 1200 mAh. However, if the error caused by the pre-filling of the large current charging is overcome or the stability is ensured, the capacity of the battery to which the precharging method of the present invention is applied is not limited. 2. The positive active materials are lithium cobalt oxide and lithium nickel cobalt manganese oxide.

The charge activity chart of the positive electrode active material was lithium cobaltate and lithium nickel cobalt manganate mixed in a ratio of 8:2, and the precharge current was 0.1 C, as shown in Fig. 2.

According to the 0.1C charging time-voltage value graph, the charge is 10% respectively.

Finished cell performance between (60min), 20% (120min) and 30% (180min) (voltage values corresponding to 3.61V, 3.72V and 3.81V). Since the film formation voltage of the SEI film is 3.60V, it is precharged.

During the formation process, although the main reaction of forming the SEI film on the surface of the negative electrode may be different depending on the formation voltage, when the charging voltage reaches the film formation voltage of 3.60 V, the SEI film starts to form and is subsequently charged during the subsequent charging process. The progress of the reaction gradually changes its structure and properties. That is to say, as shown in Fig. (2), when the charge amount is 10%, since the voltage exceeds 3.60 V by 3.61 V, the SEI film has begun to form. In order to further verify whether the film formation and its side reactions are fully completed, this patent first charges the cells with 0.1C for 60min, 90min, 120min and 180min respectively, so that the pre-charge amount of the cells is 10%, 15%, 20% and 30%. The properties of the capacity, size, and internal resistance were examined separately. According to the results, when the pre-charge amount was 10%, the exhaust gas due to the film formation side reaction was insufficient, and the battery core had excessive thickness and lithium deposition. Therefore, this patent uses different pre-charge currents and time combinations, so that the pre-charge amount is between 15% - 35%, preferably 15% - 30%, and the voltage capacity (capacity play) is investigated. Internal resistance, size and cycle performance.

The invention adopts a stage charging method, which comprises a first charging step and a second charging step. In the first step, a small current has a positive effect on the formation of the SEI film, which is beneficial to increase the cell capacity, but a long time of small current charging may cause an increase in the impedance of the formed SEI film, thereby affecting the rate discharge performance of the finished cell. The long time process also affects the production efficiency. Therefore, the first step of small current (within 0.1C) is short (within 30min). For the stage precharge method, the impact on the performance of the battery core is almost negligible. . According to the charging curve of (2), when the voltage is charged for 0.1 minutes at 0.1C, the voltage is 2.89V, and before that, the voltage value changes (rises) quickly and is unstable, thus, the first step is small current. The lower limit of the charging time, if charging at 0.1C, it is preferable It is 5 minutes, and if it is charged at 0.05 C, it is preferably 10 minutes. The second step introduces a large current. The charging method of high current can accelerate the side reaction and improve the formation efficiency, but it is easy to damage the formation of the SEI film and cause deterioration of the performance of the cell. At the same time, the pre-filling uses large current stability and error. Larger, so you should choose the right charging current and charging time. In the pre-charging method of the present invention, the large current is selected between 0.3C and 0.6C, and the charging time is adjusted according to the magnitude of the current, usually within 10 to 60 minutes. For the stage pre-filling process of the present invention, since the first step current is small and the charging time is short, the amount of electricity reached in the first step is negligible, and the amount of electricity to be reached after the second step of high current pre-charging is It should be 15% ~ 35% of the total electricity, preferably 15% ~ 30%.

The details are described in further detail below by way of specific examples. The above-mentioned parts and the batteries used in the following Examples 19 to 34 and Comparative Examples 3 and 4 were all 613048AM-1000mAh batteries produced in the same batch, and the positive electrode active materials were lithium cobaltate and lithium nickel cobalt manganate according to 8: The weight ratio of 2 is mixed; the batteries used in Examples 35 to 39 and Comparative Examples 5 and 6 are 613048AM-1000mAh batteries produced in another batch, and the positive active materials are lithium cobalt oxide and nickel cobalt manganese. Lithium acid is mixed in a weight ratio of 6:4. All the cells in the same batch have the same positive and negative dressing amount, electrode density, the same electrolyte injection, the amount of liquid injection, and the same pre-filling and sealing, cleaning and other experimental conditions.

Example 19

The specific process steps are as follows: The first sample is injected into the sample cell, the amount of liquid injection is 85% of the process requirement, and the cell is aged for 1 ~ 2 hours, then pre-filled and refused to press 0.05C, lOmin; 0.3C, 29min pre-charge The method pre-charges, then refuses to measure the voltage, and re-fills the liquid 10%, then squeezes the battery and completes the sealing. The above steps are all carried out under the same temperature and humidity environment, the temperature is ≤26°C; the humidity is ≤2 %. In the room temperature environment, the sealed cell is cleaned and measured, and after 6 days of aging, the cell is tested and divided. The capacity system is based on the parameters shown in Table 5. The capacity, internal resistance, 3.92V size and cycle performance test were examined. The results are shown in Table 6.

Similarly, the other examples and Comparative Examples 3, 5 use the same steps except that the precharge method uses different times and currents.

Comparative Examples 4 and 6 are conventional processes, except for the one-time 100% injection, the prefilling method is shown in Table 4 and the aging time is 12 to 16 hours, and the other steps are the same as the above embodiment.

The prefilling methods of all the examples and comparative examples are shown in Table 4, and the technical effect data thereof is shown in Table 6. Table 4. Prefilling methods for each of the examples and comparative examples

Table 5. Capacity sharing system

The lithium battery is here to get the capacity, and know the size of the capacity, that is, the volume. Through the capacity, the level of the battery cell is determined. Table 6. Technical effects of various examples and comparative examples

The data of Examples 19 to 34 and Comparative Example 4 and Examples 35 to 39 and Comparative Example 6 show that by selecting the prefilling method of the present invention, it is possible to make the cell reach or even more than that of the conventional prefilling process. Excellent electrical performance, while greatly reducing pre-filling time and improving production efficiency. The data of Examples 19 to 34 and Comparative Example 3 and Examples 35 to 39 and Comparative Example 5 indicate the necessity of the first small current charging, and if the first step of the small current precharging is not performed, the finished cell size, The effects of capacity and loop performance are even worse. The invention can shorten the pre-charging time of the electric core by introducing a large current pre-charging, and further optimize the pre-charging method of the lithium ion battery in which the positive active material is a mixture of lithium cobaltate and lithium nickel cobalt manganate.

0.05C, lOmin; 0.4C, 22min. The optimized pre-filling method is a horizontal and vertical comparison of the above embodiments, and the data which best reflects the advantages and disadvantages of the pre-filling method are the positive gram capacity and the cycle performance and the pre-charge time, and then the comprehensive performances such as internal resistance and size are examined. , thus comparing the optimized pre-filling method.

During the pre-charging process of the lithium ion battery, as the proportion of the ternary nickel-cobalt-manganese oxide in the positive electrode active material increases, the time during the production of the pre-charged SEI film by the side reaction gas production and the exhaust process will increase accordingly. The lithium ion battery to which the lithium ion battery pre-filling method is applied has a certain range of requirements for the mixing ratio of lithium cobaltate and lithium nickel cobalt manganese oxide in the positive electrode active material, that is, the weight percentage of lithium cobalt oxide should be For 60% ~ 80%, lithium nickel cobalt manganese oxide should account for 20% ~ 40%.

In the above specific embodiment of the present invention, a battery of 1000 mAh is selected. For other capacity batteries, only the positive active material is required to be a mixture of lithium cobaltate and lithium nickel cobalt manganate, and the mixing ratio ranges from lithium cobaltate. The pre-filling method of the present invention is equally suitable for 60% to 80% and lithium nickel cobalt manganese oxide for 20% to 40%. However, considering that if the nominal capacity of the lithium ion battery cell is too large, greater than 1500 mAh, the current error of the second step is relatively large due to the corresponding precharge method, and the current error is relatively large or stable. Poor sex, which will have a certain impact on the performance of the battery. At the same time, considering the ternary nickel-cobalt-manganese hydride cathode material has not been widely commercialized with respect to lithium cobaltate, and the proportion of its mixing is limited. If the capacity is too large, its side-by-side reaction gas is required to be exhausted. More time-consuming than theoretical, the time will be much longer. Therefore, the cell capacity range suitable for the pre-filling method of the present invention is less than 1500 mAh, preferably less than 1200 mAh.

In the lithium ion battery to which the pre-filling method of the present invention is applied, the nickel-cobalt-manganese oxide in the positive electrode active material preferably has an element ratio of Ni:Co:Mn = 1/3: 1/3: 1/3 of nickel-cobalt-manganic acid. Lithium, and lithium nickel cobalt manganese oxide used in the specific embodiments of the present invention and all the examples and comparative examples, the molecular formula is LiNi^Co^Mn^C^

The implementation of the pre-filling method of the present invention will surely lay a solid foundation for the wider application of lithium nickel cobalt manganate ternary materials.

3. The positive active materials are lithium cobaltate and lithium nickel cobaltate.

The charge activity of the positive electrode active material was lithium cobaltate (LiCo0 ₂ ) and lithium nickel cobaltate (LiNi _x Co _1-x 0 ₂ , x=0.75-0.85) mixed at a weight ratio of 8:2, and the precharge current was 0.1C. Figure, as shown in Figure 3.

According to the 0.1C charging time-voltage value graph, the charge is 10% respectively. Finished cell performance between (60min), 20% (120min) and 30% (180min) (voltage values corresponding to 3.63V, 3.68V and 3.80V). Since the film formation voltage of the SEI film is 3.60V, it is precharged.

During the formation process, although the main reaction of forming the SEI film on the surface of the negative electrode may be different depending on the formation voltage, when the charging voltage reaches the film formation voltage of 3.60 V, the SEI film starts to form and is subsequently charged during the subsequent charging process. The progress of the reaction gradually changes its structure and properties. That is to say, as shown in Fig. (3), when the charge amount is 10%, since the voltage exceeds 3.60 V by 3.63 V, the SEI film has begun to form. However, since the binary material is mixed in the system and the content of nickel in the binary material is relatively high, in order to further verify whether the film formation and its side reactions are fully completed, the present invention first charges the cells with 0.1 C for 60 min, 90 min, and 120 min, respectively. And 150min, the cell pre-charge amount is 10%, 15%, 20% and 25%, respectively, the capacity, size, internal resistance and other properties are examined. By examining the results, the pre-charge amounts are 10%, 15% and 20%. At the time of the film formation side reaction, the exhaust gas is insufficient, and the battery core has a problem of excessive size and lithium deposition. The invention uses a pre-charging method of a small current and a large current stage, respectively, to investigate the influence of the small current and the large current pre-charging on the material system, and the result is the influence of the small current charging time on the performance of the battery in 30 minutes. It is not a key factor, and the charging current is too large, and the lithium core is more than 0.6C. Therefore, the present invention uses different pre-charge currents and time combinations, so that the pre-charge amount is between 25% and 45%, and the voltage capacity (capacity play), internal resistance, size, and cycle thereof are investigated. performance.

The invention adopts a stage charging method, which comprises a first charging step and a second charging step. In the first step, a small current has a positive effect on the formation of the SEI film, which is beneficial to increase the cell capacity, but a long time of small current charging may cause an increase in the impedance of the formed SEI film, thereby affecting the rate discharge performance of the finished cell. The long time process also affects the production efficiency. Therefore, the first step of small current (within 0.1C) is short (within 30min). For the stage precharge method, the impact on the performance of the battery core is almost negligible. . According to the charging curve of (3), when the voltage is charged for 0.1 minutes at 0.1C, the voltage is 2.89V, and before that, the voltage value changes (rises) quickly and is unstable, thus, the first step is small current. The lower limit of the charging time is preferably 5 minutes when charged at 0.1 C, and preferably 10 minutes when charged at 0.05 C. The second step introduces a large current. The charging method of high current can accelerate the side reaction and improve the formation efficiency, but it is easy to damage the formation of the SEI film and cause deterioration of the performance of the cell. At the same time, the pre-filling uses large current stability and error. Larger, so you should choose the right charging current and charging time. In the pre-charging method of the present invention, the large current is selected between 0.3C and 0.6C, and the charging time is adjusted according to the magnitude of the current, usually within 25 to 80 minutes. For the stage pre-charging process of the present invention, since the first step current is small and the charging time is short, the amount of electricity achieved in the first step is negligible, and the second step is pre-charging the large current. The amount of electricity to be reached afterwards should be 25% to 45% of the total amount of electricity, preferably 25% to 40%, more preferably 25% to 35%.

The details are described in further detail below by way of specific examples. The batteries used in the above sections, Examples 40-53 and Comparative Examples 7-8 were all 043855A-950mAh cells produced in the same batch, and the positive active materials were LiCo0 ₂ and LiNi _x Co _1-x 0 ₂ (x =0.75 - 0.85) Mixed in a ratio of LiCo0 ₂ : LiNi _x Coi _-x 0 ₂ = 8:2. All the cells in the same batch have the same positive and negative dressing amount, electrode density, the same electrolyte injection, the amount of liquid injection, and the same pre-filling and sealing, cleaning and other experimental conditions.

Example 40

The specific process steps are as follows: The sample cell is firstly injected, the amount of liquid injection is 85% of the process requirement, and the cell is aged for 1 to 2 hours, and then pre-filled to 0.05 C, lOmin; 0.3 C, 50 min precharge The method pre-charges, then refuses to measure the voltage, and re-fills the liquid 10%, then squeezes the battery and completes the sealing. The above steps are all carried out under the same temperature and humidity environment, the temperature is ≤26°C; the humidity is ≤2 %. At room temperature, the sealed cells are cleaned and measured. After 6 days of aging, the cells are tested and divided. The volumetric system is based on the parameters shown in Table 8. The capacity, internal resistance, 3.92V size and cycle performance test were examined. The results are shown in Table 9.

Similarly, the other steps and the same procedure were used for the other examples, except that the time and current used in the pre-filling method were different. Comparative Example 8 is a conventional process, except that the one-time 100% injection, the prefilling method is the same as shown in Table 7 and the aging time is 12 to 16 hours, and the other steps are the same as the above embodiment. The prefilling methods of all the examples and comparative examples are shown in Table 7, and the technical effect data thereof is shown in Table 9.

Table 7. Prefilling methods for each of the examples and comparative examples

Example 50 0.05 C 12 min 0.4 C 38 min 26.3 % Example 51 0.05 C 20 min 0.4 C 38 min 27.0 % Example 52 0.05 C 30 min 0.4 C 38 min 27.8 % Example 53 0.05 C 5 min 0.4 C 38 min 25.8 % Comparative Example 7 0 0 0.4C 38 min 25.3 % Comparative Example 8 0.1C 360min 0 0 60.0 % Table 8. Capacity-sharing system

The lithium battery is here to get the capacity, and know the size of the capacity, that is, the volume. Through the capacity, the level of the battery cell is determined.

Table 9. Technical effects of various examples and comparative examples

The data of Examples 40 to 53 and Comparative Example 8 show that by selecting the prefilling method of the present invention, the precharge time can be greatly reduced, and the production efficiency can be improved. The data of Examples 40 ~ 53 and Comparative Example 7 indicate the necessity of the first small current charging. If the first step of small current precharging is not carried out, the effect of the finished cell size, capacity and cycle performance will be more effective. difference.

The invention can shorten the pre-charging time of the battery core by introducing large current pre-charging, and the further optimized pre-charging method is 0.05C, lOmin; 0.4C, 38min. The optimized pre-filling method is a horizontal and vertical comparison of the above embodiments, and the data which best reflects the advantages and disadvantages of the pre-filling method are the positive gram capacity and the cycle performance and the pre-charge time, and then the comprehensive performances such as internal resistance and size are examined. , thus comparing the optimized pre-filling method.

It was confirmed by further experiments that the lithium ion battery with a positive electrode active material of a mixed material of lithium cobaltate (LiCo0 ₂ ) and lithium nickel cobaltate (LiNi _x Co _1-x 0 ₂ , x=0.75 ~ 0.85 ), when cobalt acid When the weight ratio of lithium to lithium nickel cobaltate satisfies 75% to 85% of lithium cobaltate and 15% to 25% of lithium nickel cobaltate, the precharge amount of the lithium ion battery is achieved by the precharge method of the present invention. 25% ~ 45% of the total amount of electricity, preferably 25% ~ 40%, that is, using the stage charging method, including the first charging step and the second charging step, the charging current of the first charging step is less than 0.1 C, preferably 0.05 ~ 0.1C, charging time is 5 ~ 30min, preferably 5 ~ 15min; charging current of the second charging step is 0.3 ~ 0.6C, charging time is 25 ~ 80 minutes, both can optimize the performance of the battery while improving the pre-charging efficiency The purpose is to meet production requirements.

In the above specific embodiment of the present invention, a 950 mAh battery cell is selected. For other capacity batteries, it is only necessary to satisfy the mixture of the positive electrode active material as lithium cobaltate and lithium nickel cobaltate, and preferably the mixed proportion of lithium cobaltate. 75% to 85%, lithium nickel cobaltate accounts for 15% to 25%, and the prefilling method of the present invention is equally suitable. However, considering that if the nominal capacity of the lithium ion battery cell is too large, greater than 1200 mAh, the current error of the pre-filling is relatively large or stable due to the relatively large charging current of the second step of the corresponding pre-charging method. Poor sex, which will have a certain impact on the performance of the battery; at the same time consider that the binary lithium nickel cobalt oxide cathode material has not been widely commercialized relative to lithium cobalt oxide, and the proportion of nickel in the binary material is higher. (Limited between 0.75 and 0.85), if the capacity is too large, the secondary reaction gas is exhausted in the precharge process, which is more complicated than the theoretical one, and the time is much longer. Therefore, the precharge method of the present invention is suitable for electricity. The core capacity range is preferably ≤ 1200 mAh. The implementation of the pre-filling method of the present invention will surely lay a solid foundation for the wider application of binary materials such as lithium nickel cobaltate.

Claims

Claim

A method for pre-charging a lithium ion battery, characterized in that: the pre-charging method of the lithium ion battery is a stage charging, the stage charging comprises at least two charging steps, and the charging current of the second charging step The charging current is greater than the charging current of the first charging step, and the total pre-charging amount of the first charging step and the second charging step is 10% to 45% of the total amount of the lithium ion battery.

2 . The method of precharging a lithium ion battery according to claim 1 , wherein: the positive active material of the lithium ion battery is lithium cobaltate, and the total pre-step of the first charging step and the second charging step The amount of charge is 10% to 35% of the total amount of the lithium ion battery.

The method for precharging a lithium ion battery according to claim 2, wherein: the total precharge amount of the first charging step and the second charging step is 10% to 30 of the total amount of the lithium ion battery. %.

The method for precharging a lithium ion battery according to claim 2 or 3, wherein: the charging current in the first charging step is less than 0.1 C, and the charging time is 5 to 30 min.

The method for precharging a lithium ion battery according to claim 4, wherein the charging current in the first charging step is 0.05 C - 0.1 C, and the charging time is 5 ~ 15 min.

The method for precharging a lithium ion battery according to claim 2 or 3, wherein the charging current in the second charging step is 0.3 C to 0.6 C, and the charging time is 10 to 60 min.

The method for precharging a lithium ion battery according to claim 4, wherein the charging current in the second charging step is 0.3 C to 0.6 C, and the charging time is 10 to 60 min.

The method for precharging a lithium ion battery according to claim 7, wherein: the charging current in the first charging step is 0.05 C, the charging time is 10 min, and the charging current in the second charging step is 0.5 C. , charging time is 12min.

9. The method of precharging a lithium ion battery according to claim 1, wherein: the positive active material of the lithium ion battery is a mixed material of lithium cobaltate and lithium nickel cobalt manganese oxide, and the first charging step The total pre-charge amount with the second charging step is 15% to 35% of the total amount of the lithium ion battery.

10 . The method of precharging a lithium ion battery according to claim 9 , wherein: the total pre-charging amount of the first charging step and the second charging step is 15% to 30 of the total amount of the lithium ion battery %.

A method for precharging a lithium ion battery according to claim 9 or 10, characterized in that

1 In the positive electrode active material of the lithium ion battery, lithium cobaltate accounts for 60% to 80%, and lithium nickel cobalt manganese oxide accounts for 20% to 40%, which is a weight percentage.

12. The method of precharging a lithium ion battery according to claim 11, wherein: the charging current in the first charging step is less than 0.1 C, and the charging time is 5 to 30 min.

13. The method of precharging a lithium ion battery according to claim 12, wherein: the charging current in the first charging step is 0.05 C to 0.1 C, and the charging time is 5 to 15 min.

14. The method of precharging a lithium ion battery according to claim 11, wherein: the charging current in the second charging step is 0.3 C to 0.6 C, and the charging time is 10 to 60 min.

15. The method of precharging a lithium ion battery according to claim 12, wherein: the charging current in the second charging step is 0.3 C to 0.6 C, and the charging time is 10 to 60 min.

The method for precharging a lithium ion battery according to claim 15, wherein: the charging current of the first charging step is 0.05 C, the charging time is 10 min, and the charging current of the second charging step is 0.4 C. , charging time is 22min.

17. The method of precharging a lithium ion battery according to claim 1, wherein: the positive active material of the lithium ion battery is a mixed material of lithium cobaltate and lithium nickel cobaltate, and the first charging step is The total pre-charge amount of the second charging step is 25% to 45% of the total amount of the lithium ion battery.

18. The method of precharging a lithium ion battery according to claim 17, wherein: the total precharge amount of the first charging step and the second charging step is 25% to 40% of the total amount of the lithium ion battery. %.

The method for precharging a lithium ion battery according to claim 17 or 18, wherein: in the positive electrode active material of the lithium ion battery, the molecular formula of lithium nickel cobaltate is LiNi _x Co _1-x 0 ₂ , x=0.75 ~ 0.85.

The method for precharging a lithium ion battery according to claim 19, wherein: among the positive active materials of the lithium ion battery, lithium cobaltate accounts for 75% to 85%, and lithium nickel cobaltate accounts for 15%. ~ 25%, the percentage is by weight.

The method for precharging a lithium ion battery according to claim 20, wherein: in the positive active material of the lithium ion battery, lithium cobaltate accounts for 80%, and lithium nickel cobaltate accounts for 20%. As a percentage by weight.

22. A lithium ion battery according to any one of claims 17, 18, 20, The precharging method is characterized in that: the charging current of the first charging step is less than 0.1 C, and the charging time is 5 to 30 min.

The method for precharging a lithium ion battery according to any one of claims 17, 18, 20, 21, wherein: the charging current of the second charging step is 0.3 C ~ 0.6 C, charging time It is 25 ~ 80min.

The method for precharging a lithium ion battery according to claim 22, wherein: the charging current in the second charging step is 0.3 C to 0.6 C, and the charging time is 25 to 80 min.

The method for precharging a lithium ion battery according to claim 24, wherein: the charging current of the first charging step is 0.05 C, the charging time is 10 min, and the charging current of the second charging step is 0.4 C. , charging time is 38min.

The method for precharging a lithium ion battery according to any one of claims 2, 9 and 17, wherein: the electrolyte injection amount before the staged charging is 80% to 85%, the stage After charging, inject 15% ~ 10% of electrolyte.

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