A lithium ion battery pre-charging method

Abstract

The present invention discloses a pre-charging method for a lithium-ion battery, wherein the positive active material of the lithium-ion battery is a nickel-cobalt-aluminum material, and the method comprises a staged charging step and a constant voltage charging step in sequence; wherein the staged charging step comprises a first charging step and a second charging step in sequence, the current of the first charging step is less than the current of the second charging step, and the pre-charging amount of the first charging step is 20%-40% of the total power of the lithium-ion battery. The present invention enables the battery cell to achieve electrical performance equivalent to or even better than that of the battery cell using the traditional small current and long time pre-charging process, while shortening the pre-charging time and improving production efficiency.

Description

[Technical field]

[0001] The invention relates to a lithium ion battery pre-charging method. [Background technology]

[0002] At present, lithium-ion batteries are increasingly widely used, and the demand for batteries is increasing. For battery manufacturers, on the one hand, they need to improve production efficiency to meet market needs, and on the other hand, they need to improve and perfect the process to improve product quality and production efficiency. With the mechanization of production in the lithium battery industry, the pre-charging process has become an important link that restricts production speed and product quality.

[0003] For lithium-ion batteries, during pre-charging, i.e., the first charging, a thin passivation layer covering the graphite surface is inevitably formed at the interface between the graphite negative electrode and the electrolyte due to electrochemical reactions. This thin layer is the solid electrolyte interface (SEI) film. When lithium-ion batteries are pre-charged, while the SEI film is generated on the negative electrode surface, a side reaction will occur to produce gas products. If the gas is not completely generated during the pre-charging process, it will continue to be released during the later electrical cycle of the battery cell, seriously affecting the electrical performance and safety performance of the battery cell. Therefore, the pre-charging step of lithium-ion batteries is an important stage in the manufacture of battery cells, which is related to the performance of the battery cell in many aspects, such as capacity, rate, cycle life, and safety.

[0004] At present, the pre-charging process usually uses a small current for more than ten hours to obtain an ideal SEI film and maintain stable battery performance. However, the long pre-charging step leads to low production efficiency.

[0005] Nickel-cobalt-aluminum material is a positive electrode material with a very high specific capacity. Its specific capacity exceeds that of lithium cobalt oxide and nickel-cobalt-manganese ternary materials. It is the preferred positive electrode material for high energy density battery products. Nickel-cobalt-aluminum material has high activity. In order to improve its stability during battery use, people generally use matching electrolytes, and also need to form a stable SEI film. The electrochemical reaction rate of this material is slow at room temperature, resulting in poor high current charge and discharge performance of this material. Most of the research on this material uses low rate charge and discharge. The low rate performance will seriously affect the application of this system material. Therefore, the pre-charge still uses the traditional lithium cobalt oxide pre-charge method, that is, charging for a long time with a small current, which has become an important link restricting the production efficiency and product performance of this material system. [Summary of the invention]

[0006] In order to overcome the deficiencies of the prior art, the present invention provides a pre-charging method for a lithium-ion battery whose positive electrode active material is a nickel-cobalt-aluminum material, which can greatly improve production efficiency while improving battery cell performance.

[0007] A pre-charging method for a lithium-ion battery, wherein the positive electrode active material of the lithium-ion battery is a nickel-cobalt-aluminum material, and sequentially comprises a staged charging step and a constant voltage charging step;

[0008] The staged charging steps include 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 20%-40% of the total power of the lithium-ion battery.

[0009] In one embodiment,

[0010] The pre-charge amount in the first charging step is 20%-30% of the total charge amount of the lithium-ion battery.

[0011] In one embodiment,

[0012] The charging current of the first charging step is less than 0.2C, and the charging time is 1-3h.

[0013] In one embodiment,

[0014] The charging current of the first charging step is 0.1C-0.2C, and the charging time is 1.5h-3h.

[0015] In one embodiment,

[0016] The charging time is 1.3h-1.5h.

[0017] In one embodiment,

[0018] The charging current of the second charging step is 0.2C-0.33C.

[0019] In one embodiment,

[0020] The charging current of the second charging step is 0.3C.

[0021] In one embodiment,

[0022] The negative electrode of the lithium ion battery is a graphite negative electrode.

[0023] In one embodiment,

[0024] In the nickel-cobalt-aluminum material, Ni:Co:Al=0.8:0.15:0.05.

[0025] In one embodiment,

[0026] The charging current of the first charging step is 0.1C and the charging time is 2h.

[0027] The beneficial effects of the present invention are:

[0028] The precharging method of the present invention is used to precharge lithium-ion batteries using nickel-cobalt-aluminum as positive electrode active materials, so that the battery cells can achieve electrical performance equivalent to or even better than that of battery cells using traditional small current and long time precharging processes, while shortening the precharging time and improving production efficiency; at the same time, the implementation of the precharging method of the present invention provides a solid foundation for the wider application of nickel-cobalt-aluminum materials.

Brief Description of the Drawings

[0029] Figure 1 This is a charging curve diagram of the lithium-ion battery pre-charging method of an embodiment using a current of 0.1C, with the horizontal axis being time and the vertical axis being voltage value. [Specific implementation method]

[0030] The preferred embodiments of the invention are described in further detail below.

[0031] like Figure 1 As shown, a lithium-ion battery pre-charging method according to 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 pre-charging method sequentially comprises a staged charging step and a constant voltage charging step, that is, the staged charging step is before the constant voltage charging step;

[0032] The staged charging steps include 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 20%-40% of the total power of the lithium-ion battery.

[0033] The use of a small current in the first charging step has a positive effect on the formation of the SEI film, which is beneficial to improving the performance of the battery cell. However, long-term charging with a small current will cause the impedance of the formed SEI film to increase, thereby affecting the rate discharge performance of the finished battery cell (that is, the discharge capacity performance under different currents). The long time also affects the production efficiency. According to previous studies, the SEI film can be completely formed when the charging amount in the first charging step is 20%-30%. In the second charging step, a large current is introduced. The charging method of large current can improve efficiency, but it is easy to damage the SEI film or cause lithium precipitation, affecting the performance of the battery cell. At the same time, the stability and error of the pre-charging cabinet using large current are large, so a suitable charging current and charging time should be selected. The current in the second charging step of this embodiment is selected between 0.2C-0.33C, and the battery cell voltage is charged until it reaches the voltage of constant voltage charging, for example 4.2V.

[0034] For the same batch of battery cells, the above-mentioned lithium-ion battery precharging method was adopted, and according to the charging current, time and pre-charge amount, Examples 1 to 9 were respectively obtained, as shown in Table 1, wherein the battery cells used in Examples 1 to 9 and Comparative Examples 1 and 2 are 18650-2.6Ah battery cells produced from the same batch, and the positive electrode active material is nickel-cobalt-aluminum. The battery cells from the same batch have consistent positive and negative electrode dressing amounts and electrode densities, adopt the same electrolyte injection and injection amount, and maintain the same experimental conditions such as injection, sealing, cleaning, and aging.

[0035] The specific process of the lithium-ion battery pre-charging method of an embodiment can be as follows: the aged battery cell is charged in a pre-charging cabinet at 0.1C for 3 hours, 0.2C to 4.2V, and then 4.2V constant voltage charging is stopped until the current drops to 26mA. After the battery cell 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 are investigated, and the results are shown in Table 3.

[0036] The internal resistance and rate performance of the battery cell are investigated because small internal resistance and good rate performance indicate good interface performance and good performance of SEI film formation. There are many factors affecting the internal resistance and rate performance of the battery cell. Since the battery cells we selected are produced from the same batch and different pre-charging methods are tested, the interference caused by other processes other than the pre-charging method can be eliminated as much as possible. If the pre-charging method is unreasonable, resulting in unstable SEI film or local lithium deposition on the electrode, the interface internal resistance will be relatively high, the internal resistance will be relatively large, and the rate performance will be relatively poor. Therefore, in the embodiments of the present invention, the internal resistance and rate performance can be used as indicators that indirectly reflect the charging effect.

[0037] The reason for examining the normal temperature cycle and 45℃ cycle is that during the battery cell cycle, the SEI membrane will experience the process of lithium ions passing through it for a long time. If the SEI membrane is unstable, the passage of lithium ions will be hindered, and the charge and discharge capacity will be reduced, which is reflected in the cycle performance decline; the temperature of 45℃ is more severe for the stability of the SEI membrane. Therefore, the normal temperature cycle and 45℃ cycle can be used as key indicators to reflect the charging effect.

[0038] Similarly, other embodiments and comparative examples 1 and 2 use the same steps, except that the time and current used in the pre-charging method are different.

[0039] The pre-charging methods of all embodiments and comparative examples are shown in Table 1, and their technical effect data are shown in Table 3.

[0040] Table 1. Pre-charging methods of various embodiments and comparative examples

[0041]

[0042] Table 2. Capacity division system

[0043] Steps Working Mode Current mA Voltage mV End current mA End voltage mV End time min 1 Constant current charging 520 4200 120 2 Constant voltage charging 520 4200 26 4200 120 3 Shelf 5 4 Constant current discharge 520 2500 2500 360

[0044] The capacity of the battery cell is tested in this process, which is called capacity division.

[0045] Table 3. Technical effects of various embodiments and comparative examples

[0046]

[0047] In Table 3, 3C discharge capacity / 0.2C discharge capacity indicates the rate discharge performance of the battery cell.

[0048] The data of Examples 1-9 and Comparative Examples 1-2 show that by using the pre-charging method of the present invention, the battery cell can achieve electrochemical performance equivalent to or even better than that of the battery cell of the traditional pre-charging process, and at the same time can greatly shorten the pre-charging time and improve production efficiency. The data of Examples 1-9 and Comparative Example 2 show the necessity of the first small current charging. If the first small current pre-charging is not performed, the battery cell capacity, internal resistance, rate performance and cycle performance will be worse.

[0049] 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: charging at 0.2C for 1.5h, then charging at 0.3C to 4.2V, and then charging at a constant voltage of 4.2V until the current drops to 0.01C.

[0050] In one embodiment, the lithium-ion battery to which the pre-charging method is applicable has a nickel-cobalt-aluminum preferred element ratio in the positive electrode active material that satisfies 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 the wider application of nickel-cobalt-aluminum materials.

[0051] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as belonging to the patent protection scope of the present invention determined by the submitted claims.

Claims

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, characterized in that: It includes a staged charging step and a constant voltage charging step in sequence; The staged charging step includes a first charging step and a second charging step in sequence, the current of the first charging step is less than the current of the second charging step, and the pre-charge amount of the first charging step is 20%-30% of the total power of the lithium-ion battery, the charging current is 0.15-0.2C, and the charging time is 1.5-2h, so that the SEI film is completely formed; The charging current of the second charging step is 0.3-0.33C, and the battery cell voltage is charged until it reaches the constant voltage charging voltage; In the nickel-cobalt-aluminum material, the element ratio of Ni:Co:Al is 0.8:0.15:0.

05.

2. The lithium-ion battery pre-charging method according to claim 1, wherein: The negative electrode of the lithium ion battery is a graphite negative electrode.

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