CN111554991A - A kind of negative pressure formation method and battery - Google Patents

Abstract

The invention discloses a negative pressure formation method and a battery. The method comprises the following steps: vacuumizing, charging and standing the semi-finished product battery cell to obtain a formed battery cell; the vacuumizing and the charging are carried out in multiple steps, the vacuum degree is gradually reduced in each step, and the charging current is gradually increased. The method provided by the invention can shorten the formation time, reduce the liquid loss amount in the formation process, improve the consistency and stability of the SEI film, improve the cycle performance of the battery, meet the requirements of high specific energy, quick charge, long service life and the like of the power battery for the new energy automobile, and is particularly suitable for the formation of the lithium ion battery.

Description

A kind of negative pressure formation method and battery

technical field

The invention belongs to the technical field of energy storage, and relates to a chemical formation method and a battery, in particular to a negative pressure chemical formation method and a battery.

Background technique

Benefiting from the country's encouraging policies for new energy vehicles and the expansion of the production and sales scale of new energy vehicles, the power battery market has maintained continuous growth. It is the goal pursued by the power battery manufacturing industry to meet the high specific energy, fast charging, long life and other requirements of power batteries for new energy vehicles, so that electric vehicles can reach the operating conditions close to fuel vehicles. In the production process of power battery, chemical formation is undoubtedly a key step. The formation of lithium-ion batteries is for the electrochemical reaction between the electrode material and the electrolyte at the solid-liquid interface during the first charge and discharge process to form a solid electrolyte interface film (SEI film) covering the surface of the electrode material. Formation has an important influence on the first effect, discharge capacity, rate performance, cycle performance and self-discharge performance of lithium-ion batteries.

At present, the main chemical forming processes are as follows:

1. According to whether the injection port is open or closed, it can be divided into open formation and closed formation:

(1) Opening formation: During the formation process, the liquid injection port of the battery cell is in an open state at atmospheric pressure, and the gas generated by the formation can be directly discharged from the liquid injection port, which ensures the consistency of the interface from a certain aspect. The equipment is relatively simple and the cost is relatively high. Low, but the generated gas will pollute the workshop environment, the amount of liquid loss is large, the standing time is long, and the relative humidity of the environment is high.

(2) closed-mouth formation: use the formation nozzle to block the liquid injection port. During the formation process, the cell liquid injection nozzle is in a sealed state, and a certain vacuum value is pumped to the cell from the formation nozzle, so that the formation gas can be discharged in time. The closed-mouth formation requires low environmental humidity, but the air extraction process is more complicated, and the liquid loss will also occur during the formation process, and there is a risk of plastic deformation of the cell casing.

2. According to the temperature of formation, it is divided into high temperature formation and low temperature formation:

(1) High temperature formation: During the formation process, the cells are in a high temperature (greater than 40°C) environment. Generally, the higher the formation temperature, the lower the viscosity of the electrolyte, the higher the conductivity of the electrolyte, and the faster the ion diffusion rate of the electrode material, so the smaller the polarization, the better the formation effect. High temperature formation can speed up the electrochemical reaction speed and the growth rate of SEI film, and improve the consistency of SEI film. However, when the temperature is too high, the structure of the formed SEI film will be destroyed, the formed SEI film will be loose and unstable, and its composition will be changed. into effect.

(2) Low temperature formation: During the formation process, the cell is in a normal temperature (less than 30°C) environment. The chemical formation at low temperature is mainly based on solvent reduction, the reduction rate of lithium salts is slow, and the formation rate of SEI film is slow, so the deposition of solvent products is more orderly and dense, and the formed SEI film is dense and stable, but the low temperature chemical formation has ionic conductivity. The rate is not good, and the formation time is generally long.

3. According to the current size of the formation, it is divided into large current formation and small current formation:

(1) High current formation: use a large current (greater than 0.3C) for formation. High-current formation can speed up the electrochemical reaction and the growth rate of the SEI film, and accordingly it is easier to generate inorganic lithium salt components, but the formed SEI film molecules are more prone to disorderly accumulation, the structure is looser, the corresponding thickness is larger, and the irreversible reaction is more difficult. The resulting SEI film has poor consistency and is unstable.

(2) Small current formation: use a small current (less than 0.1C) for formation. In the case of low-current formation, it is easier to generate organic lithium salt components. The SEI film formed by chemical formation is denser and has fewer irreversible reactions, but the time required for formation is generally longer.

In the prior art, CN108172919A discloses a ternary lithium ion battery formation process, a ternary lithium ion battery and a preparation method thereof. In the ternary lithium-ion battery formation process, the ternary lithium-ion battery is charged in a step-by-step charging mode within the range of 0.01-0.1C charging current, so as to complete the formation treatment of the ternary lithium-ion battery.

CN109950636A discloses a high-nickel ternary lithium-ion battery formation process. The scheme includes the following steps in sequence: (1) vacuum injection of the baked battery cells; (2) pre-sealing; (3) high temperature standing; (4) one-time formation at room temperature; (5) vacuum evacuation; ( 6) Secondary normal temperature formation; (7) High temperature aging; (8) Cooling down; (9) Final sealing.

However, the above two existing solutions both need to further improve the battery performance after formation and reduce the formation time. Therefore, it is necessary to continue to improve and optimize the chemical formation process.

SUMMARY OF THE INVENTION

In view of the deficiencies in the prior art, the purpose of the present invention is to provide a negative pressure chemical formation method and a battery. The negative pressure formation method provided by the invention can shorten the formation time, reduce the liquid loss in the formation process, improve the consistency and stability of the SEI film, improve the cycle performance of the battery, and meet the high specific energy and rapidity of the power battery for new energy vehicles. Charging, long life and other requirements, especially suitable for the formation of lithium-ion batteries.

For this purpose, the present invention adopts the following technical solutions:

In a first aspect, the present invention provides a method for forming negative pressure, the method comprising the following steps:

The semi-finished cell is vacuumed, charged and left to stand to obtain a formed cell; the vacuuming and charging are carried out in multiple steps, the degree of vacuum gradually decreases and the charging current gradually increases between steps.

In the negative pressure formation method provided by the present invention, a small current is used for formation first, and then a stepwise formation process with a large current is gradually adopted. .

In the negative pressure formation method provided by the present invention, high vacuum is used first and then low vacuum is used, the gas production rate is fast in the initial stage of formation, and the produced gas can be discharged in time by using high vacuum, so as to avoid the thickness of the battery caused by the inability to extract the gas produced in time. Ultra-thickness and black spots; low-vacuum evacuation at the end of formation can effectively reduce the liquid loss of formation and avoid waste of electrolyte.

In the negative pressure formation method provided by the present invention, the semi-finished cell refers to a cell that has been assembled and injected, but has not been formed.

In the present invention, the evacuation and charging can be performed in a multi-step gradient.

The following are the preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical purposes and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

As a preferred technical solution of the present invention, in the multiple steps, each step includes vacuuming and charging, and each subsequent step has a lower vacuum degree and a larger charging current than the previous step.

In this way, it can be ensured that the magnitude of the negative pressure and the charging current show step-like changes. The battery using the step-by-step formation process improves the charge and discharge efficiency, reduces the internal resistance, and has better cycle performance.

Preferably, in the multiple steps, the vacuum degree of evacuation in the subsequent step is gradually decreased compared with that in the previous step, and the charging current is gradually increased compared with that in the previous step.

That is, in a high temperature environment, the semi-finished battery cells are first formed by low current and high vacuum, and then gradually high current and low vacuum are used to obtain the formed batteries. The vacuuming and charging are carried out in a multi-step gradient, which is the invention The program with relatively good effect.

As a preferred technical solution of the present invention, the temperature of the chemical formation is above 40°C, such as 40°C, 50°C, 60°C, 70°C, 80°C or 90°C, etc. Above 40°C is high temperature formation, which can speed up the electrochemical reaction and the growth rate of SEI film, and reduce the time required for formation.

Preferably, the formation temperature is 40-90°C.

Preferably, the semi-finished batteries include any one or a combination of at least two of semi-finished lithium iron phosphate batteries, semi-finished nickel-cobalt-manganese ternary batteries, or semi-finished nickel-cobalt-aluminum ternary batteries.

Preferably, the semi-finished battery cells are square battery cells.

Preferably, in the method for forming under negative pressure, the vacuum degree of evacuation is -10 to -100KPa, such as -10KPa, -20KPa, -50KPa, -75KPa or -100KPa, etc.

Preferably, in the negative pressure formation method, the charging current is 0.03-0.55C, such as 0.03C, 0.05C, 0.08C, 0.1C, 0.2C, 0.3C, 0.4C, 0.5C or 0.55C, etc.

As a preferred technical solution of the present invention, the multiple steps are 3 to 5 steps, preferably 4 steps. The advantage of adjusting the vacuum degree and charging current in 4 steps is that: if the number of steps is too small, the required vacuum degree cannot be adjusted well, which may cause a large amount of liquid loss; Efficiency is low.

Preferably, in the multiple steps, each step is a constant vacuum operation, and the vacuum degree is adjusted between the steps.

Preferably, in the multiple steps, the charging in the last step is constant-current and constant-voltage charging, and the charging in other steps is constant-current charging.

As the preferred technical solution of the present invention, the negative pressure formation method includes:

(1) Under the formation temperature above 40°C, the semi-finished cell is evacuated to the first vacuum degree, and under the constant first vacuum degree, the first current is charged to the first voltage with a constant current;

(2) stand and reduce the vacuum degree to the second vacuum degree, and charge to the second voltage with a second current constant current under the constant second vacuum degree;

(3) stand and reduce the vacuum degree to the third vacuum degree, and under the constant third vacuum degree, charge to the third voltage with the third current constant current;

(4) Stand still and reduce the vacuum degree to the fourth vacuum degree, under the constant fourth vacuum degree, use the fourth current and constant current to charge to the fourth voltage, and then change to use the fourth voltage and constant voltage to charge When the current reaches the cut-off current, stop charging, and get the formed cell;

Wherein, the current magnitudes of the first current, the second current, the third current and the fourth current increase sequentially.

The above-mentioned preferred technical solution is a step-type negative pressure formation method. In a high temperature environment, first use a small current and high vacuum formation, and gradually adopt a large current and low vacuum formation, and the formation is carried out in multiple steps, which can shorten the formation time of lithium ion batteries. , reduce the liquid loss during the formation process, improve the consistency and stability of the SEI film, improve the battery cycle performance, and meet the needs of high specific energy, fast charging, and long life of power batteries for new energy vehicles.

As a preferred technical solution of the present invention, the first vacuum degree in step (1) is -80 to -100KPa, such as -80KPa, -85KPa, -90KPa, -95KPa or -100KPa, etc.

Preferably, the first current in step (1) is 0.03-0.07C, for example, 0.03C, 0.04C, 0.05C, 0.06C, or 0.07C.

Preferably, the first voltage in step (1) is 2.8-3.2V, for example, 2.8V, 2.9V, 3.0V, 3.1V, or 3.2V.

Preferably, step (1) further includes: before evacuating the semi-finished cell, let it stand for 1-30 minutes, such as 1 minute, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes or 30 minutes, etc.

As a preferred technical solution of the present invention, the second vacuum degree in step (2) is -60 to -80KPa, such as -60KPa, -65KPa, -70KPa, -75KPa or -80KPa, etc.

Preferably, the second current in step (2) is 0.05-0.3C, such as 0.05C, 0.08C, 0.1C, 0.15C, 0.2C, 0.25C or 0.3C, etc.

Preferably, the second voltage in step (2) is 3.0-3.7V, such as 3.0V, 3.1V, 3.2V, 3.3V, 3.4V, 3.5V, 3.6V or 3.7V, etc.

Preferably, the standing time in step (2) is 1 to 30 minutes, such as 1 minute, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes.

As a preferred technical solution of the present invention, the third degree of vacuum in step (3) is -40 to -60KPa, such as -40KPa, -45KPa, -50KPa, -55KPa or -60KPa, etc.

Preferably, the third current in step (3) is 0.2-0.5C, such as 0.25C, 0.30C, 0.35C, 0.40C or 0.50C, and the like.

Preferably, the third voltage in step (3) is 3.5-4.0V, such as 3.5V, 3.6V, 3.7V, 3.8V, 3.9V, or 4.0V.

Preferably, the standing time in step (3) is 1 to 30 minutes, such as 1 minute, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes.

As a preferred technical solution of the present invention, the fourth degree of vacuum in step (4) is -10 to -40KPa, such as -10KPa, -20KPa, -30KPa or -40KPa, etc.

Preferably, the fourth current in step (4) is 0.3-1.0C, such as 0.35C, 0.45C, 0.50C, 0.6C, 0.7C, 0.8C or 1.0C, etc.

Preferably, the fourth voltage in step (4) is 3.7-4.3V, for example, 3.7V, 3.9V, 4.0V, 4.2V, or 4.3V.

Preferably, the cut-off current in step (4) is 0.04-0.06C, for example, 0.04C, 0.045C, 0.05C, 0.055C, or 0.06C.

Preferably, the standing time in step (4) is 1 to 30 minutes, such as 1 minute, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes.

Preferably, step (4) further comprises: standing for 1-30 minutes after stopping charging, such as 1 minute, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes or 30 minutes, etc.

As a further preferred technical solution of the negative pressure formation method of the present invention, the method comprises the following steps:

(1) Under the formation temperature of 40～90℃, let the semi-finished battery cell stand for 1～30min, vacuumize the semi-finished product battery until the vacuum degree is -80～-100KPa, keep the vacuum degree constant, use 0.03～ 0.07C current constant current charging to 2.8~3.2V;

(2) Stand for 1～30min and reduce the vacuum degree to -60～-80KPa, keep the vacuum degree constant, and charge to 3.0～3.7V with a constant current of 0.05～0.3C;

(3) Let stand for 1～30min and reduce the vacuum degree to -40～-60KPa, keep the vacuum degree constant, and charge to 3.5～4.0V with a constant current of 0.20～0.50C;

(4) Let stand for 1～30min and reduce the vacuum degree to -10～-40KPa, keep the vacuum degree constant, charge to 3.7～4.3V with a constant current of 0.30～1.0C, then use this voltage instead Constant voltage charging until the current reaches the cut-off current of 0.04-0.06C, stop charging, and let it stand for 1-30 minutes to obtain the formed cell.

In a second aspect, the present invention provides a battery, which is subjected to negative pressure formation using the method described in the first aspect.

Compared with the prior art, the present invention has the following beneficial effects:

The negative pressure formation method provided by the invention adopts high temperature formation, which can speed up the speed of electrochemical reaction and the growth rate of SEI film, and reduce the time required for formation. First use small current for formation, and gradually adopt high current stepwise formation process. Small current makes the formed SEI film molecules dense and stable. High current can speed up the formation speed of SEI film and reduce formation time. The battery using the stepwise formation process is charged and discharged. The efficiency is improved, the internal resistance is reduced, and it has better cycle performance. First use high vacuum and then use low vacuum staged pumping method, the gas production rate is fast at the beginning of formation, and high vacuum can be used to discharge the produced gas in time to avoid the battery thickness and black spots caused by the failure of gas production to be pumped out in time. Phenomenon; low vacuum pumping is used at the end of the formation, which can effectively reduce the liquid loss of the formation and avoid the waste of electrolyte. The negative pressure formation method provided by the present invention can be gradient negative pressure formation. The liquid loss rate of the negative pressure formation method provided by the invention can be as low as 0.11%, and the capacity retention rate of 200 cycles can reach 98.89%.

Description of drawings

FIG. 1 is a schematic flowchart of the negative pressure chemical formation method provided in Embodiment 1 of the present invention.

Detailed ways

In order to better illustrate the present invention and facilitate understanding of the technical solutions of the present invention, the present invention is further described in detail below. However, the following embodiments are only simple examples of the present invention, and do not represent or limit the protection scope of the present invention, and the protection scope of the present invention is subject to the claims.

The following are typical but non-limiting examples of the present invention:

Example 1

The present embodiment carries out negative pressure formation according to the following method:

(1) Under the formation temperature of 45°C, let the semi-finished battery cell stand for 15 minutes, vacuumize the semi-finished product battery cell to a vacuum degree of -90KPa, keep the vacuum degree constant, and charge it to 3V with a constant current of 0.05C. ;

(2) Stand for 15min and reduce the vacuum degree to -70KPa, keep the vacuum degree constant, and charge to 3.4V with a constant current of 0.1C;

(3) let stand for 15min and reduce the vacuum degree to a vacuum degree of -50KPa, keep the vacuum degree constant, and use a constant current of 0.3C to charge to 3.8V;

(4) Let stand for 15min and reduce the vacuum degree to -25KPa, keep the vacuum degree constant, charge it to 4V with a constant current of 0.5C, and then change it to charge with a constant voltage of 4V until the current reaches the cut-off current of 0.05C, Stop charging and let it stand for 15 minutes to obtain the formed cells.

The semi-finished cell is a square ternary nickel-cobalt lithium manganate 622 semi-finished cell, and the positive electrode coating is composed of nickel-cobalt lithium manganate with a mass ratio of wt%/wt%=98:1:1, a conductive agent CNT and a bonding agent. The negative electrode coating is composed of graphite, conductive agent CNT, glue and binder SBR with a mass ratio of wt%/wt%=96:1.5:1.0:1.5, the diaphragm is Celgard2400 diaphragm, and the electrolyte is 1mol/L of LiPF ₆ /EC+DMC+EMC (v/v=1:1:1) electrolyte.

A schematic flowchart of the negative pressure chemical formation method provided in this embodiment is shown in FIG. 1 .

The test results of this embodiment are shown in Table 1.

Example 2

The present embodiment carries out negative pressure formation according to the following method:

(1) Under the formation temperature of 90°C, let the semi-finished battery cell stand for 1min, vacuumize the semi-finished product battery cell to a vacuum degree of -80KPa, keep the vacuum degree constant, and charge it with a constant current of 0.03C to 2.8 V;

(2) let stand for 1min and reduce the vacuum degree to a vacuum degree of -60KPa, keep the vacuum degree constant, and charge it to 3.0V with a constant current of 0.1C;

(3) let stand for 1min and reduce the vacuum degree to -40KPa, keep the vacuum degree constant, and charge it to 3.5V with a constant current of 0.2C;

(4) Let stand for 1min and reduce the vacuum degree to -10KPa, keep the vacuum degree constant, charge to 3.7V with a constant current of 0.3C, and then change to charge with a constant voltage of this voltage until the current reaches the cut-off current of 0.04 C, stop charging, let stand for 1min, and get the battery cell after formation.

The semi-finished cell in step (1) of this embodiment is exactly the same as the semi-finished cell in Embodiment 1.

The test results of this embodiment are shown in Table 1.

Example 3

The present embodiment carries out negative pressure formation according to the following method:

(1) Under the formation temperature of 40°C, let the semi-finished battery cell stand for 30 minutes, vacuumize the semi-finished product battery cell to a vacuum degree of -100KPa, keep the vacuum degree constant, and charge it with a constant current of 0.07C to 3.2 V;

(2) stand for 30min and reduce the vacuum degree to a vacuum degree of -80KPa, keep the vacuum degree constant, and charge it to 3.7V with a constant current of 0.3C;

(3) stand for 30min and reduce the vacuum degree to a vacuum degree of -60KPa, keep the vacuum degree constant, and charge it to 4.0V with a constant current of 0.5C;

(4) Let stand for 30min and reduce the vacuum degree to -40KPa, keep the vacuum degree constant, charge to 4.3V with a constant current of 1.0C, and then change to charge with a constant voltage of this voltage until the current reaches the cut-off current of 0.06 C, stop charging, let stand for 30 minutes, and obtain the battery cell after formation.

The semi-finished cell in step (1) of this embodiment is exactly the same as the semi-finished cell in Embodiment 1.

The test results of this embodiment are shown in Table 1.

Example 4

The present embodiment carries out negative pressure formation according to the following method:

(1) Under the formation temperature of 45°C, let the semi-finished battery cell stand for 15 minutes, vacuumize the semi-finished product battery cell to a vacuum degree of -90KPa, keep the vacuum degree constant, and charge it with a constant current of 0.05C to 3.2 V;

(2) Let stand for 15min and reduce the vacuum degree to -60KPa, keep the vacuum degree constant, and charge it to 3.8V with a constant current of 0.3C;

(3) Let stand for 15min and reduce the vacuum degree to -25KPa, keep the vacuum degree constant, charge it to 4V with a constant current of 0.5C, and then change it to charge with a constant voltage of 4V until the current reaches the cut-off current of 0.05C, Stop charging and let it stand for 15 minutes to obtain the formed cells.

The semi-finished cell is a square lithium iron phosphate semi-finished cell, and the positive electrode coating is composed of lithium iron phosphate with a mass ratio of wt%/wt%=97.5:1.5:1, conductive agent CNT and binder PVDF, and the negative electrode coating is It is composed of graphite with mass ratio wt%/wt%=96:2.0:1.0:1.0, conductive agent CNT, glue and binder SBR, the diaphragm is Celgard2400 diaphragm, and the electrolyte is 1mol/L LiPF ₆ /EC+DMC +EMC (v/v=1:1:1) electrolyte.

The test results of this embodiment are shown in Table 1.

Example 5

The present embodiment carries out negative pressure formation according to the following method:

(1) Under the formation temperature of 45°C, let the semi-finished battery cell stand for 15 minutes, vacuumize the semi-finished product battery cell to a vacuum degree of -90KPa, keep the vacuum degree constant, and charge it to 3V with a constant current of 0.05C. ;

(2) stand for 15min and reduce the vacuum degree to -75KPa, keep the vacuum degree constant, and charge to 3.2V with a constant current of 0.1C;

(3) stand for 15min and reduce the vacuum degree to a vacuum degree of -65KPa, keep the vacuum degree constant, and charge to 3.5V with a constant current of 0.2C;

(4) let stand for 15min and reduce the vacuum degree to a vacuum degree of -50KPa, keep the vacuum degree constant, and use a constant current of 0.3C to charge to 3.8V;

(5) Let stand for 15min and reduce the vacuum degree to -25KPa, keep the vacuum degree constant, charge it to 4V with a constant current of 0.5C, and then change it to charge with a constant voltage of 4V until the current reaches the cut-off current of 0.05C, Stop charging and let it stand for 15 minutes to obtain the formed cells.

The semi-finished cell is a square ternary nickel-cobalt lithium aluminate 111 semi-finished cell, and its positive electrode coating is composed of nickel-cobalt lithium aluminate with a mass ratio of wt%/wt%=97:1.5:1.5, a conductive agent CNT and a bonding agent. The negative electrode coating is composed of graphite, conductive agent CNT, glue and binder SBR with a mass ratio of wt%/wt%=96:1.0:1.5:1.5, the diaphragm is Celgard2400 diaphragm, and the electrolyte is 1mol/L of LiPF _6/ EC+DMC+EMC (v/v=1:1:1) electrolyte.

The test results of this embodiment are shown in Table 1.

Comparative Example 1

This comparative example is the same as Example 1 except that the constant vacuum degree of -80KPa is used in each step, and the method of reducing the vacuum degree in a stepwise manner is not adopted.

The test results of this comparative example are shown in Table 1.

Comparative Example 2

In this comparative example, except that the constant current charging operation in each step uses a constant charging current of 0.3C instead of the step-by-step method of increasing the constant current charging current, the other operations and the types of semi-finished cells processed are the same as those of the embodiment. 1 is the same.

The test results of this comparative example are shown in Table 1.

testing method

The formation time was measured using a timer.

Using the electronic weighing method, by measuring the difference between the weight of the cell before the formation and the weight of the cell after the formation, the liquid loss rate of the electrolyte (that is, the percentage of the electrolyte lost to the mass of the injected electrolyte) is tested.

By dismantling the formed cell, the state of the formed pole piece is confirmed, and the standard for judging the normality of the pole piece is: there is no obvious black spot on the surface of the pole piece, and the color of the formed interface is uniform.

Using charging and discharging equipment, charge at 1C constant current at 25℃±2℃, switch to constant current charging when the battery voltage reaches 4.2V, stop charging when the current drops to 0.05C current, and let it stand for 1h after charging. Discharge at 1C current at 25°C±2°C, stop discharging when the battery voltage reaches 2.8V, and test the electrochemical performance of the battery after 200 cycles.

The test results are shown in the table below:

Table 1

Combining the above embodiments and comparative examples, it can be seen that the negative pressure formation method provided by the embodiment adopts high temperature formation, first uses small current formation, and gradually adopts high current stepped formation process and first uses high vacuum and then uses low vacuum segmental pumping mode, It can shorten the formation time, reduce the liquid loss during the formation process, improve the consistency and stability of the SEI film, improve the battery cycle performance, and meet the high specific energy, fast charging, long life and other needs of power batteries for new energy vehicles.

Comparative Example 1 did not use the staged pumping method of first using high vacuum and then using low vacuum, and directly used constant vacuum -80Kpa for formation, resulting in a large liquid loss rate after formation.

Comparative Example 2 did not use a low current formation and then gradually adopted a high current step formation process, and directly used a 0.3C constant current formation, which required a short formation time, but the SEI film formed by formation was unstable, resulting in poor cycle performance.

The applicant declares that the present invention illustrates the detailed method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed method, that is, it does not mean that the present invention must rely on the above-mentioned detailed method to be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent replacement of each raw material of the product of the present invention, the addition of auxiliary components, the selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims (10)

1. a negative pressure formation method, it is characterized in that, described method comprises the following steps: carry out vacuuming, charging and standstill to semi-finished product cell, obtain the cell after formation; Described vacuuming and charging are carried out in multiple steps , the vacuum degree gradually decreases and the charging current gradually increases between each step. 2. The method for forming under negative pressure according to claim 1, wherein in the multiple steps, each step includes vacuuming and charging, and each subsequent step is lower than the vacuum degree of the previous step And the charging current is large. 3. The negative pressure chemical forming method according to claim 1 or 2, wherein the temperature of the chemical forming is above 40°C; Preferably, the formation temperature is 40-90°C; Preferably, the semi-finished batteries include any one or a combination of at least two of semi-finished lithium iron phosphate batteries, semi-finished nickel-cobalt-manganese ternary batteries or semi-finished nickel-cobalt-aluminum ternary batteries; Preferably, the semi-finished battery cells are square battery cells; Preferably, in the method for forming under negative pressure, the vacuum degree of evacuation is -10～-100KPa; Preferably, in the negative pressure formation method, the charging current is 0.03-0.55C. 4. The negative pressure chemical forming method according to any one of claims 1-3, wherein the multiple steps are 3 to 5 steps, preferably 4 steps; Preferably, in the multiple steps, each step is a constant vacuum degree operation, and the vacuum degree is adjusted between the steps; Preferably, in the multiple steps, the charging in the last step is constant-current and constant-voltage charging, and the charging in other steps is constant-current charging. 5. The negative pressure chemical forming method according to claim 4, wherein the negative pressure chemical forming method comprises: (1) Under the formation temperature above 40°C, the semi-finished cell is evacuated to the first vacuum degree, and under the constant first vacuum degree, the first current is charged to the first voltage with a constant current; (2) stand and reduce the vacuum degree to the second vacuum degree, and charge to the second voltage with a second current constant current under the constant second vacuum degree; (3) stand and reduce the vacuum degree to the third vacuum degree, and under the constant third vacuum degree, charge to the third voltage with the third current constant current; (4) Stand still and reduce the vacuum degree to the fourth vacuum degree, under the constant fourth vacuum degree, use the fourth current and constant current to charge to the fourth voltage, and then change to use the fourth voltage and constant voltage to charge When the current reaches the cut-off current, stop charging, and get the formed cell; Wherein, the current magnitudes of the first current, the second current, the third current and the fourth current increase sequentially. 6. The negative pressure chemical forming method according to claim 5, wherein the first vacuum degree of step (1) is -80～-100KPa; Preferably, the first current in step (1) is 0.03-0.07C; Preferably, the first voltage in step (1) is 2.8-3.2V; Preferably, step (1) further includes: before vacuuming the semi-finished battery cell, let it stand for 1-30 minutes. 7. The negative pressure chemical forming method according to claim 5 or 6, wherein the second vacuum degree of step (2) is -60～-80KPa; Preferably, the second current in step (2) is 0.05-0.3C; Preferably, the second voltage in step (2) is 3.0-3.7V; Preferably, the standing time in step (2) is 1-30 min. 8. The negative pressure chemical forming method according to any one of claims 5-7, wherein the third vacuum degree of step (3) is -40～-60KPa; Preferably, the third current in step (3) is 0.2-0.5C; Preferably, the third voltage in step (3) is 3.5-4.0V; Preferably, the standing time of step (3) is 1-30 min; Preferably, the fourth degree of vacuum in step (4) is -10 to -40KPa; Preferably, the fourth current in step (4) is 0.3-1.0C; Preferably, the fourth voltage in step (4) is 3.7-4.3V; Preferably, the cut-off current in step (4) is 0.04-0.06C; Preferably, the standing time of step (4) is 1-30 min; Preferably, step (4) further comprises: standing for 1-30 minutes after stopping charging. 9. The method for forming negative pressure according to any one of claims 1-8, wherein the method comprises the following steps: (1) Under the formation temperature of 40～90℃, let the semi-finished battery cell stand for 1～30min, vacuumize the semi-finished product battery until the vacuum degree is -80～-100KPa, keep the vacuum degree constant, use 0.03～ 0.07C current constant current charging to 2.8~3.2V; (2) Stand for 1～30min and reduce the vacuum degree to -60～-80KPa, keep the vacuum degree constant, and charge to 3.0～3.7V with a constant current of 0.05～0.3C; (3) Stand for 1～30min and reduce the vacuum degree to -40～-60KPa, keep the vacuum degree constant, and charge to 3.5～4.0V with a constant current of 0.2～0.5C; (4) Stand for 1～30min and reduce the vacuum degree to -10～-40KPa, keep the vacuum degree constant, charge to 3.7～4.3V with a constant current of 0.3～1.0C, and then use this voltage instead Constant voltage charging until the current reaches the cut-off current of 0.04-0.06C, stop charging, and let it stand for 1-30 minutes to obtain the formed cell. 10. A battery, characterized in that, the battery is subjected to negative pressure formation using the method according to any one of claims 1-9.

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