CN106876813A - A kind of lithium ion battery precharging method - Google Patents

Abstract

The invention discloses a kind of method for pre-charging lithium ion batteries, the positive active material of the lithium ion battery is nickel cobalt aluminum, successively including stage charge step and constant-voltage charge step；Wherein, the stage charge step includes the first charge step and the second charge step successively, the electric current of first charge step less than the second charge step electric current, and first charge step preliminary filling electricity be the lithium ion battery total electricity 20%-40%.The present invention can make battery core reach even more excellent electric property suitable with the battery core using traditional low current long-time preliminary filling technique, while shortening pre-charging time, improve production efficiency.

Description

A kind of lithium ion battery precharging method

【Technical field】

The invention relates to a lithium ion battery precharging method.

【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. . With the mechanization of production in the lithium battery industry, the pre-charging process has become an important link that currently restricts production speed and product quality.

For lithium-ion batteries, when pre-charging is the first charge, due to electrochemical reactions, a passivation layer covering the graphite surface will inevitably be formed on the phase interface between the graphite negative electrode and the electrolyte, and this thin layer is the solid electrolyte. Interface (solid electrolyte interface) or SEI film. When precharging the lithium-ion battery, while the SEI film is formed on the surface of the negative electrode, a side reaction will occur to produce gas products. If the gas is not completely generated during the precharging process, it will continue to be released during the later electric cycle of the battery, which is serious. Affect the electrical performance and safety performance of the battery. Therefore, the pre-charging step of lithium-ion batteries is an important stage in the manufacture of batteries, which is related to the performance of the batteries in many aspects such as capacity, rate, cycle life, and safety.

The pre-charging process at this stage usually uses a small current for charging for up to ten hours, in order to obtain an ideal SEI film and maintain the stability of battery performance. But the long priming step leads to low production efficiency.

Nickel-cobalt-aluminum material is a positive electrode material with a high specific capacity. Its specific capacity exceeds that of lithium cobaltate and nickel-cobalt-manganese ternary materials. It is the preferred positive electrode material for high energy density battery products. Nickel-cobalt-aluminum materials have high activity. In order to improve their stability during battery use, people generally use matching electrolytes, and also need to form a stable SEI film. The electrochemical reaction rate of the material is slow at room temperature, resulting in poor high-current charge and discharge performance of the material. Most studies on this material use low-rate charge-discharge, and the low rate will seriously affect the application of this system material. , so pre-charging still adopts the traditional lithium cobalt oxide pre-charging method, that is, charging with a small current for a long time, which has become an important link that currently restricts the production efficiency and product performance of this material system.

【Content of invention】

In order to overcome the deficiencies of the prior art, the present invention provides a method for precharging a lithium-ion battery whose positive electrode active material is nickel-cobalt-aluminum, which can greatly improve production efficiency on the premise of improving battery performance.

A lithium-ion battery pre-charging method, wherein the positive electrode active material of the lithium-ion battery is a nickel-cobalt-aluminum material, which sequentially includes a staged charging step and a constant voltage charging step;

Wherein, the staged charging step includes a first charging step and a second charging step in sequence, the current of the first charging step is smaller than the current of the second charging step, and the pre-charging amount of the first charging step is the 20%-40% of the total charge of the lithium-ion battery.

In one embodiment,

The pre-charged amount in the first charging step is 20%-30% of the total electric quantity of the lithium-ion battery.

In one embodiment,

The charging current in the first charging step is less than 0.2C, and the charging time is 1-3h.

In one embodiment,

The charging current in the first charging step is 0.1C-0.2C, and the charging time is 1.5h-3h.

In one embodiment,

The charging time is 1.3h-1.5h.

In one embodiment,

The charging current in the second charging step is 0.2C-0.33C.

In one embodiment,

The charging current for the second charging step is 0.3C.

In one embodiment,

The negative pole of the lithium ion battery is a graphite negative pole.

In one embodiment,

In the nickel-cobalt-aluminum material, Ni:Co:Al=0.8:0.15:0.05.

In one embodiment,

The charging current in the first charging step is 0.1C, and the charging time is 2h.

The beneficial effects of the present invention are:

Using the precharging method of the present invention to precharge the lithium-ion battery with nickel-cobalt-aluminum as the positive electrode active material can make the battery achieve equivalent or even better electrical performance than the battery using the traditional low-current long-time precharging process, At the same time, the pre-charging time is shortened, and the production efficiency is improved; meanwhile, the implementation of the pre-charging method of the present invention provides a solid foundation for wider application of nickel-cobalt-aluminum materials.

【Description of drawings】

Fig. 1 is a lithium-ion battery precharging method of an embodiment using a charging curve with a current of 0.1C, the abscissa is time, and the ordinate is voltage.

【detailed description】

The preferred embodiments of the invention will be further described in detail below.

As shown in Figure 1, a lithium-ion battery pre-charging method of an embodiment, wherein, the positive electrode active material of the lithium-ion battery is a nickel-cobalt-aluminum material, the negative electrode of the lithium-ion battery is a graphite negative electrode, and the lithium-ion battery is pre-charged. The charging method sequentially includes a staged charging step and a constant voltage charging step, that is, the staged charging step is before the constant voltage charging step;

Wherein, the staged charging step includes a first charging step and a second charging step in sequence, the current of the first charging step is smaller than the current of the second charging step, and the pre-charging amount of the first charging step is the 20%-40% of the total charge of the lithium-ion battery.

The use of a small current in the first charging step has a positive effect on the formation of the SEI film and is beneficial to improve the performance of the battery cell. However, long-term low-current charging will lead to an increase in the resistance of the formed SEI film, thereby affecting the rate discharge performance of the finished battery cell. (that is, the discharge capacity performance under different currents), longer time also affects production efficiency. According to previous studies, the SEI film can be completely formed when the charging capacity is 20%-30% in the first charging step. A large current is introduced in the second charging step. The high current charging method can improve the efficiency, but it is easy to damage the SEI film or cause lithium precipitation, which affects the performance of the battery cell. At the same time, the stability and error of the pre-charging cabinet using a large current are relatively large, so Should choose the appropriate charging current and charging time. The current in the second charging step of this embodiment is selected between 0.2C-0.33C, and the battery is charged until the cell voltage reaches the voltage of constant voltage charging, such as 4.2V.

For the same batch of batteries, using the above lithium ion battery pre-charging method, according to the difference in charging current, time and pre-charging amount, Examples 1 to 9 were respectively obtained, as shown in Table 1, wherein, Examples 1 to 9 , and the batteries used in Comparative Examples 1 and 2 are all 18650-2.6Ah batteries produced in the same batch, and the positive electrode active material is nickel-cobalt-aluminum. For electrode density, use the same electrolyte injection and injection volume, and maintain the same experimental conditions such as injection, sealing, cleaning, and aging.

The specific process of the lithium-ion battery pre-charging method in an embodiment can be as follows: charge the pre-charging cabinet on the aged battery cell at 0.1C for 3 hours, charge at 0.2C to 4.2V, and then charge at a constant voltage of 4.2V until the current drops. stop at 26mA. After the battery core is aged for 3 days, the capacity is divided, and the capacity division system is carried out according to the parameters shown in Table 2. The capacity, internal resistance, rate, normal temperature cycle and 45°C cycle performance were investigated, and the results are shown in Table 3.

Among them, the internal resistance and rate performance of the battery are investigated because the small internal resistance and good rate performance indicate good interface performance and good SEI film formation performance. There are many factors affecting the internal resistance of the battery cell and the rate performance. Since the battery cells we choose are produced in the same batch for different pre-charging method experiments, we can try to eliminate the interference caused by other processes other than the pre-charging method. . If the pre-charging method is unreasonable, resulting in unstable SEI film or partial lithium precipitation on the pole piece, the internal resistance of the interface will be relatively high at this time, the internal resistance will be relatively large, and the rate performance will be relatively poor. Therefore, the implementation of the present invention In the example, the internal resistance and rate performance can be used as indicators to reflect the charging effect from the side.

The reason for investigating normal temperature cycle and 45°C cycle is that during the cycle of the battery cell, the SEI film will experience the process of passing lithium ions through it for a long time. If the SEI film is unstable, the passage of lithium ions will be hindered, and the charge and discharge capacity will decrease, which is reflected in In terms of cycle, the cycle performance is reduced; the temperature of 45°C is more severe for the stability of the SEI film. Therefore, normal temperature cycle and 45°C cycle can be used as key indicators to reflect the charging effect.

Similarly, other embodiments and comparative examples 1 and 2 use the same steps, but the time and current used in the pre-charging method are different.

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

Table 1. The prefilling method of each embodiment and comparative example

Table 2. Capacity classification system

Work step Operating mode Current mA Voltage mV End current mA End voltage mV end timemin 1 Constant current charging 520 4200 120 2 Constant voltage charging 520 4200 26 4200 120 3 on hold 5 4 Constant current discharge 520 2500 2500 360

The capacity of the battery cell is tested in this process, which is called the rated capacity.

Table 3. each embodiment and comparative example technical effect

In Table 3, 3C discharge capacity/0.2C discharge capacity indicates the rate discharge performance of the cell.

The data of Examples 1-9 and Comparative Examples 1-2 show that by selecting the pre-charging method of the present invention, the battery cell can achieve equivalent or even better electrochemical performance than the battery cell of the traditional pre-charging process, and at the same time it can greatly improve the battery life. Shorten pre-charging time and improve production efficiency. However, the data of Examples 1-9 and Comparative Example 2 show the necessity of charging with the first low current. If the first step of low current precharging is not performed, the battery capacity, internal resistance, rate performance and cycle performance must all be worse.

The present invention can shorten the pre-charging time of the battery cell by introducing staged pre-charging. In one embodiment, the lithium-ion battery pre-charging method is: charge at 0.2C for 1.5h, then charge at 0.3C to 4.2V, and then charge at 4.2V V is charged at a constant voltage until the current drops to 0.01C.

In one embodiment, for the lithium-ion battery to which the precharging method is applied, the nickel-cobalt-aluminum in the positive electrode active material preferably has an element ratio satisfying Ni:Co:Al=0.8:0.15:0.05. The implementation of the pre-charging method of the present invention lays a solid foundation for wider application of nickel-cobalt-aluminum materials.

The above content is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it cannot be assumed that the specific implementation of the present invention is limited to these descriptions. For those of ordinary skill in the technical field of the present invention, without departing from the concept of the present invention, they can also make some simple deduction or replacement, which should be regarded as belonging to the patent of the present invention determined by the submitted claims. protected range.

Claims (10)

1. A method for precharging a lithium-ion battery, wherein the positive electrode active material of the lithium-ion battery is a nickel-cobalt-aluminum material, which is characterized in that it includes successively a staged charging step and a constant voltage charging step; Wherein, the staged charging step includes a first charging step and a second charging step in sequence, the current of the first charging step is smaller than the current of the second charging step, and the pre-charging amount of the first charging step is the 20%-40% of the total charge of the lithium-ion battery. 2. The lithium-ion battery precharging method according to claim 1, wherein the pre-charging amount in the first charging step is 20%-30% of the total electric quantity of the lithium-ion battery. 3. The lithium-ion battery precharging method according to claim 1, wherein the charging current in the first charging step is less than 0.2C, and the charging time is 1-3h. 4. The lithium ion battery precharging method according to claim 3, wherein the charging current in the first charging step is 0.1C-0.2C, and the charging time is 1.5h-3h. 5. The lithium ion battery precharging method according to claim 3, wherein the charging time is 1.3h-1.5h. 6. The lithium ion battery precharging method according to claim 1, characterized in that, the charging current in the second charging step is 0.2C-0.33C. 7. The lithium ion battery precharging method as claimed in claim 6, wherein the charging current in the second charging step is 0.3C. 8. The lithium-ion battery precharging method according to claim 1, wherein the negative electrode of the lithium-ion battery is a graphite negative electrode. 9. The method for precharging a lithium-ion battery according to claim 1, wherein, in the nickel-cobalt-aluminum material, Ni:Co:Al=0.8:0.15:0.05. 10. The lithium ion battery precharging method according to claim 1, wherein the charging current in the first charging step is 0.1C, and the charging time is 2h.