Formation method of battery and battery

Abstract

The application relates to the technical field of batteries and discloses a formation method of a battery and the battery. The application controls the voltage and the current of each formation process in a segmented formation mode, reduces the intensity of side reactions under high potential, effectively discharges reaction gas, avoids continuous gas production of residual active substances in a high-temperature aging stage, eliminates swelling and black spot lithium precipitation defects, and improves long-term stability of the battery; the voltage is further increased to 35%-50% of the nominal capacity, which is beneficial to battery exhaust and can control polarization of the battery to prevent capacity loss and super-thickness risk of the battery under high temperature. In addition, the application controls the current rate of the third charging to be less than the current rate of the second charging, the current rate of the second charging is less than or equal to 0.2C, increases the reaction time of the lithium supplement agent, promotes complete reaction of the lithium supplement agent, simultaneously, lithium ions are embedded into the negative electrode more slowly and uniformly in small-current charging, the risk of lithium precipitation is greatly reduced, swelling and black spot lithium precipitation defects are eliminated, and the long-term stability of the lithium ion battery is improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a battery formation method and a lithium-ion battery. Background Technology

[0002] During the initial charging of a battery, the electrolyte undergoes reduction and decomposition on the surface of the negative electrode, such as graphite, forming a solid electrolyte interphase (SEI) film. This permanently and significantly consumes lithium from the positive electrode. Furthermore, side reactions occurring during the initial lithium intercalation process also consume active lithium, causing irreversible capacity loss and impacting the battery's initial cycle efficiency and cycle life. Battery lithium replenishment technology is a crucial means of improving battery cycle life. By pre-lithiating the battery before operation, lithium ions are added to compensate for irreversible lithium loss, thereby increasing the battery's total capacity and cycle life.

[0003] In existing technologies, adding organic lithium-rich nickel oxide (LNO) and lithium-rich iron oxide (LFO) to the positive electrode can improve battery initial efficiency and optimize electrode capacity matching, thereby reducing capacity loss and greatly improving battery cycle performance and energy efficiency. However, during formation, when the reaction potential of the lithium-rich agent (4.05V) is reached, the organic lithium-rich agent decomposes and releases gas. This gas accumulates in the electrode pores, compresses and carries away free electrolyte, forming a "dry zone" without electrolyte. Lithium ions cannot be smoothly inserted into the negative electrode, leading to an increase in the overpotential on the negative electrode surface and the deposition of metallic lithium. At the same time, side reactions occur at the interface between the positive electrode active material and the current collector in the dry zone, generating impurities such as carbon black and metal oxides, forming black spots. Furthermore, when the reaction potential reaches 4.05V, the electrolyte itself also decomposes, further aggravating electrolyte consumption and interface contamination, and exacerbating black spots and lithium deposition. Furthermore, the sealed space of the battery will contain some unreleased gas during the formation stage. During high-temperature aging, the residual lithium replenishing agent will continue to react and generate new gas, which will accumulate in the casing and gradually increase the internal pressure, resulting in battery swelling.

[0004] Therefore, optimizing and improving the lithium replenishment process of batteries, suppressing gas generation during the lithium replenishment reaction, eliminating swelling and black spot lithium deposition defects, and improving the long-term stability of batteries are technical problems that urgently need to be solved in this field. Summary of the Invention

[0005] This invention provides a battery formation method to solve the problems of battery swelling and lithium plating with black spots in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a method for forming a battery, wherein the positive electrode of the battery comprises a positive electrode active material and a lithium replenishing agent, and the method comprises the following steps: After injecting the first electrolyte into the battery, the battery is charged to the charging cutoff voltage of the positive electrode active material. The battery is then charged a second time to the voltage at which the lithium replenishment agent generates gas; The battery is then charged a third time to the voltage plateau of the lithium replenishment agent; The battery is discharged until the discharge cutoff voltage of the positive electrode active material is reached; After the battery is charged to 35%-50% of its nominal capacity for the fourth time, it is then aged once. The step of resting is performed after the first charging, the second charging, the third charging, the discharging, and the fourth charging, respectively. The first charging includes a first charging, a second charging, and a third charging, wherein the current multiplier of the first charging is less than the current multiplier of the second charging and the current multiplier of the third charging. The current ratio of the third charge is less than or equal to the current ratio of the second charge and less than or equal to 0.2C.

[0007] In one optional implementation, the third charge includes four and five charges, wherein the current multiplier of the five charges is less than the current multiplier of the four charges.

[0008] In one alternative implementation, a resting step is further included before the first charging.

[0009] In one alternative implementation, after the first charging, a second resting step is also included.

[0010] In one alternative implementation, after the second charging, there are three resting steps.

[0011] In one alternative implementation, after the three charging cycles, a four-stage resting step is also included.

[0012] In one alternative implementation, after the second charging, there are also five resting steps.

[0013] In one alternative implementation, after the four charging cycles, a six-time resting step is also included.

[0014] In one alternative implementation, after the five charging cycles, a seven-cycle resting step is also included.

[0015] In one alternative implementation, after the discharge, there are also eight resting steps.

[0016] In one alternative implementation, after the fourth charging, a nine-time resting step is also included.

[0017] In one optional embodiment, the pressure of the initial settling period is -85 kPa to -75 kPa, and the time is 1 min to 3 min.

[0018] In one optional embodiment, the pressure of the secondary settling is -85kPa to -75kPa, and the time is 5min to 15min.

[0019] In one optional embodiment, the three settling periods include: settling at a pressure of -85kPa to -75kPa for 25-35 minutes, settling at normal pressure for 5-10 minutes, and settling at a pressure of -35kPa to -25kPa for 2-5 minutes.

[0020] In one optional embodiment, the four settling periods include: settling for 5-15 minutes at a pressure of -85 kPa to -75 kPa, settling for 55-65 minutes at a pressure of -55 kPa to -45 kPa, and settling for 1-3 minutes at a pressure of -25 kPa to -15 kPa.

[0021] In one optional implementation, the pressure of the fifth settling period, the pressure of the sixth settling period, and the pressure of the seventh settling period are each independently -45 kPa to -35 kPa, and the time is each independently 1 min to 3 min.

[0022] In one optional embodiment, the eight settling periods include: settling for 5-10 minutes at a pressure of -85 kPa to -75 kPa, settling for 5-10 minutes at normal pressure, and settling for 5-10 minutes at a pressure of -45 kPa to -35 kPa.

[0023] In one optional implementation, the nine resting periods are at atmospheric pressure and last for 5-10 minutes.

[0024] In one optional implementation, the current multiplier of the single charge is 0.05C-0.2C.

[0025] In one optional implementation, the current multiplier of the secondary charge is 0.1C-0.3C.

[0026] In one optional implementation, the current multiplier for the three charges is 0.2C-0.5C.

[0027] In one alternative implementation, the current multiplier for the second charge is 0.05C-0.2C.

[0028] In one alternative implementation, the current multiplier for the four charges is 0.05C-0.2C.

[0029] In one alternative implementation, the current multiplier for the five charges is 0.025C-0.1C.

[0030] In one alternative implementation, the discharge current ratio is 0.5C-1C.

[0031] In one alternative implementation, the current multiplier of the fourth charge is 0.05C-0.2C.

[0032] In one optional implementation, the termination voltage of the first charge is 3.0V-3.2V.

[0033] In one optional implementation, the termination voltage of the secondary charge is 3.25V-3.3V.

[0034] In one optional implementation, the charging cutoff voltage is 3.65V-3.75V.

[0035] In one optional implementation, the gas generation voltage is 3.8V-3.85V.

[0036] In one alternative implementation, the voltage platform is 4.0V-4.05V.

[0037] In one optional implementation, the discharge cutoff voltage is 2.4V-2.5V.

[0038] In one optional implementation, the pressure of the first charge, the second charge, and the third charge is each independently -85kPa to -75kPa.

[0039] In one optional implementation, the pressure of the second charge, the fourth charge, the fifth charge, the discharge, and the fourth charge are each independently -45kPa to -35kPa.

[0040] In one optional implementation, the three charging steps further include first charging to 3.4V-3.5V at a current rate of 0.2C-0.5C, and then charging to the charging cutoff voltage at a current rate of 0.5C-1C.

[0041] In one alternative implementation, the battery is allowed to rest four times after being charged to 3.4V-3.5V, and then allowed to rest ten times after being charged to the charging cutoff voltage.

[0042] In one optional embodiment, the pressure when charging to the charging cutoff voltage at 0.5C-1C is -25kPa to -15kPa.

[0043] In one alternative implementation, after the four rest periods, the process further includes six charging cycles and eleven rest periods in sequence.

[0044] In one optional implementation, the fourth charging also includes first charging at 0.05C-0.2C to 3.15V-3.25V, and then charging at 0.1C-0.3C to 35%-50% of the nominal capacity.

[0045] In one alternative implementation, the battery is allowed to stand for twelve cycles after being charged to 3.15V-3.25V, and then allowed to stand for nine cycles after being charged to 35%-50% of the nominal capacity.

[0046] In one optional implementation, the current multiplier for the six charges is 0.1C-0.3C, the termination voltage is 3.65V-3.75V, and the pressure is -25kPa to -15kPa.

[0047] In one optional embodiment, the pressure of the ten static resting cycles is -45 kPa to -35 kPa, and the time is 5 min to 10 min.

[0048] In one optional embodiment, the pressure of the eleven static resting periods is -45 kPa to -35 kPa, and the time is 5 min to 10 min.

[0049] In one optional embodiment, the pressure of the twelve static resting cycles is -45 kPa to -35 kPa, and the time is 5 min to 15 min.

[0050] In one alternative embodiment, the positive electrode active material of the battery includes lithium iron phosphate.

[0051] In one optional embodiment, the lithium supplement includes at least one of lithium iron tetroxide, lithium nickelate, and lithium carbonate.

[0052] In one optional implementation, the temperature of the first charging, the second charging, the third charging, the discharging, and the fourth charging is 40°C-50°C.

[0053] In one optional embodiment, the temperature of the first aging is 40°C-50°C.

[0054] In one alternative implementation, after the first aging, a second electrolyte injection and a second aging step are further included in sequence.

[0055] In one optional embodiment, the temperature of the secondary aging is 40℃-50℃.

[0056] Secondly, the present invention provides a battery obtained by processing the battery formed by the method described in the first invention.

[0057] The technical solution of this invention has the following advantages: 1. The present invention provides a battery formation method, wherein the positive electrode of the battery comprises a positive electrode active material and a lithium replenishing agent, and the formation method comprises the following steps: injecting a first electrolyte into the battery, performing a first charge on the battery to the charging cutoff voltage of the positive electrode active material; performing a second charge on the battery to the gas generation voltage of the lithium replenishing agent; performing a third charge on the battery to the voltage plateau of the lithium replenishing agent; discharging the battery to the discharge cutoff voltage of the positive electrode active material; performing a fourth charge on the battery to 35%-50% of the nominal capacity and then performing an aging process; wherein a settling step is performed after the first charge, second charge, third charge, discharge, and fourth charge respectively; the first charge includes a first charge, a second charge, and a third charge, wherein the current rate of the first charge < the current rate of the second charge < the current rate of the third charge; and the current rate of the third charge ≤ the current rate of the second charge ≤ 0.2C. This invention employs a segmented formation process, controlling the voltage and current of each stage to reduce the intensity of side reactions at high potentials, effectively expelling reaction gases, and preventing residual active materials from continuously generating gas during high-temperature aging. This eliminates defects such as swelling and lithium plating, improving the long-term stability of the battery. Further boosting the voltage to 35%-50% of the nominal capacity facilitates battery venting and controls battery polarization, preventing capacity loss and excessive thickness risks at high temperatures. Additionally, the high-temperature aging process after formation addresses the issue of battery swelling after sealing. Controlling the current rate of the third charge to be ≤ ≤ 0.2C of the second charge increases the reaction time of the lithium replenishing agent, promoting complete reaction. Simultaneously, the slower and more uniform insertion of lithium ions into the negative electrode during low-current charging significantly reduces the risk of lithium plating, eliminating swelling and lithium plating defects, and improving the long-term stability of the lithium-ion battery. Detailed Implementation

[0058] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0059] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0060] In a first aspect, the present invention provides a method for forming a battery, wherein the positive electrode of the battery comprises a positive electrode active material and a lithium replenishing agent, and the method comprises the following steps: After injecting the first electrolyte into the battery, the battery is charged to the charging cutoff voltage of the positive electrode active material. The battery is then charged a second time to the voltage at which the lithium replenishment agent generates gas; The battery is then charged a third time to the voltage plateau of the lithium replenishment agent; The battery is discharged until the discharge cutoff voltage of the positive electrode active material is reached; After the battery is charged to 35%-50% of its nominal capacity for the fourth time, it is then aged once. Among them, a settling step is performed after the first charging, the second charging, the third charging, the discharging, and the fourth charging, respectively; The first charging includes a first charging, a second charging, and a third charging, wherein the current multiplier of the first charging is less than the current multiplier of the second charging and the current multiplier of the third charging. The current ratio of the third charge is less than or equal to the current ratio of the second charge and less than or equal to 0.2C.

[0061] In one optional implementation, the third charge includes four and five charges, wherein the current multiplier of the five charges is less than the current multiplier of the four charges.

[0062] In one alternative implementation, a resting step is further included before the first charging.

[0063] In one alternative implementation, after the first charging, a second resting step is also included.

[0064] In one alternative implementation, after the second charging, there are three resting steps.

[0065] In one alternative implementation, after the three charging cycles, a four-stage resting step is also included.

[0066] In one alternative implementation, after the second charging, there are also five resting steps.

[0067] In one alternative implementation, after the four charging cycles, a six-time resting step is also included.

[0068] In one alternative implementation, after the five charging cycles, a seven-cycle resting step is also included.

[0069] In one alternative implementation, after the discharge, there are also eight resting steps.

[0070] In one alternative implementation, after the fourth charging, a nine-time resting step is also included.

[0071] In one optional embodiment, the pressure of the initial settling period is -85 kPa to -75 kPa, and the time is 1 min to 3 min.

[0072] In one optional embodiment, the pressure of the secondary settling is -85kPa to -75kPa, and the time is 5min to 15min.

[0073] In one optional embodiment, the three settling periods include: settling at a pressure of -85kPa to -75kPa for 25-35 minutes, settling at normal pressure for 5-10 minutes, and settling at a pressure of -35kPa to -25kPa for 2-5 minutes.

[0074] In this invention, the three static periods are adjusted by adjusting the static pressure to prevent the battery electrodes from sticking too tightly due to continuous suction under high vacuum negative pressure, and the electrolyte from floating on the top of the battery, making it difficult for gas to escape. Adjusting the negative pressure to normal pressure allows the electrolyte to fall back down, and the electrodes will also temporarily not stick too tightly due to the vacuum being broken to normal pressure, which facilitates venting and solves the venting problem caused by black spots in the non-lithium replenishment stage.

[0075] In one optional embodiment, the four settling periods include: settling for 5-15 minutes at a pressure of -85 kPa to -75 kPa, settling for 55-65 minutes at a pressure of -55 kPa to -45 kPa, and settling for 1-3 minutes at a pressure of -25 kPa to -15 kPa.

[0076] In this invention, the negative pressure gradually decreases during the four periods of static storage because the gas has been completely exhausted, and the negative pressure is slowly reduced to reach the pressure required for the four charging cycles.

[0077] In one optional implementation, the pressure of the fifth settling period, the pressure of the sixth settling period, and the pressure of the seventh settling period are each independently -45 kPa to -35 kPa, and the time is each independently 1 min to 3 min.

[0078] In one optional embodiment, the eight settling periods include: settling for 5-10 minutes at a pressure of -85 kPa to -75 kPa, settling for 5-10 minutes at normal pressure, and settling for 5-10 minutes at a pressure of -45 kPa to -35 kPa.

[0079] In one optional implementation, the nine resting periods are at atmospheric pressure and last for 5-10 minutes.

[0080] In one optional implementation, the current multiplier of the single charge is 0.05C-0.2C.

[0081] In one optional implementation, the current multiplier of the secondary charge is 0.1C-0.3C.

[0082] In one optional implementation, the current multiplier for the three charges is 0.2C-0.5C.

[0083] In one alternative implementation, the current multiplier for the second charge is 0.05C-0.2C.

[0084] In one alternative implementation, the current multiplier for the four charges is 0.05C-0.2C.

[0085] In one alternative implementation, the current multiplier for the five charges is 0.025C-0.1C.

[0086] In one alternative implementation, the discharge current ratio is 0.5C-1C.

[0087] In one alternative implementation, the current multiplier of the fourth charge is 0.05C-0.2C.

[0088] In one optional implementation, the termination voltage of the first charge is 3.0V-3.2V.

[0089] In one optional implementation, the termination voltage of the secondary charge is 3.25V-3.3V.

[0090] In one optional implementation, the charging cutoff voltage is 3.65V-3.75V.

[0091] In one optional implementation, the gas generation voltage is 3.8V-3.85V.

[0092] In one alternative implementation, the voltage platform is 4.0V-4.05V.

[0093] In one optional implementation, the discharge cutoff voltage is 2.4V-2.5V.

[0094] In one optional implementation, the pressure of the first charge, the second charge, and the third charge is each independently -85kPa to -75kPa.

[0095] In one optional implementation, the voltages of the second charge, the fourth charge, the fifth charge, the discharge, and the fourth charge are each independently -45kPa to -35kPa.

[0096] In this invention, the formation process is mainly divided into two stages: a normal formation stage and a lithium replenishment reaction stage. The normal formation stage involves the initial charging of the lithium battery to activate the active materials and to the battery's full charge voltage. Taking a lithium iron phosphate battery as an example, its charging cutoff voltage is 3.65V-3.75V. Specifically, the battery is first charged at a current rate of 0.05C-0.2C to 3.0V-3.2V, activating the active materials and forming a solid electrolyte interphase (SEI) film. Because a significant amount of gas is generated during this stage, charging at a lower current rate of 0.05C-0.2C allows for slow lithium intercalation to form a stable SEI film. Then, the battery is charged at a current rate of 0.1C-0.3C to 3.25V-3.3V. Since the SEI film has initially stabilized after the first charge and the gas generation rate has significantly decreased, the current rate can be increased for charging. Then charge at 0.2C-0.5C to 3.65V-3.75V. This stage is to charge to the full charge voltage of the lithium iron phosphate battery, while being lower than the reaction voltage of the lithium replenishment agent. The fast charging saves process time and prepares for the lithium replenishment charge and discharge process.

[0097] In this invention, the lithium replenishment reaction stage involves charging to 3.7V-4.05V. This stage primarily involves charging to the lithium replenishment reaction voltage, prompting the lithium replenishment reaction to insert lithium into the negative electrode. Simultaneously, this stage generates a large amount of gas, which is the main reason for the black spots and lithium deposition at the interface of the lithium-replenished battery. This invention first charges to 3.8V-3.85V at a current rate of 0.05C-0.2C and allows it to stand. Then, it charges to 4.0V-4.05V at an even lower current rate of 0.05C-0.2C, forcing the lithium replenishment reaction to release lithium ions for insertion into the negative electrode. The main reason for using a 0.05C-0.2C current rate is that the lower the current, the smaller the electrochemical polarization of the battery, and the greater the capacity charged. At this point, the lithium replenishment reaction time is longer, making it easier for the battery to expel the large amount of gas released during the lithium replenishment reaction, preventing a sudden surge of gas that cannot be contained in time. The process involves first draining the battery to remove black spots; then charging it again at a lower current rate of 0.025C-0.1C to 4.0V-4.05V, allowing the unreacted lithium replenishing agent to continue reacting, thus ensuring a complete reaction and preventing battery swelling due to gas production from the decomposition of unreacted active materials; then venting it to the standard lithium iron phosphate voltage of 2.4V-2.5V at a current rate of 0.5C-1C, followed by charging to the nominal capacity SOC (35%-50%), preventing high SOC from causing capacity loss due to high-temperature aging and facilitating subsequent capacity testing.

[0098] In one optional embodiment, the three charging steps further include first charging to 3.4V-3.5V at a current rate of 0.2C-0.5C, and then charging to the charging cutoff voltage at a rate of 0.5C-1C.

[0099] It should be noted that the cell is first charged at a current density of 0.2C-0.5C to 3.4V-3.5V. At this point, the gas production of the SEI film in the cell is basically finished, but there is still a small amount of gas. The SEI film is basically stable, and the current rate can be increased to fast charge the cell to increase the lithium intercalation rate. Then, the cell is charged at 0.5C-1C to 3.65V-3.75V. This stage is to charge the cell to the full charge voltage of the lithium iron phosphate battery, while keeping it below the reaction voltage of the lithium replenishment agent. Fast charging saves process time and prepares the cell for the lithium replenishment charge-discharge process.

[0100] In one alternative implementation, the battery is allowed to rest four times after being charged to 3.4V-3.5V, and then allowed to rest ten times after being charged to the charging cutoff voltage.

[0101] In one optional embodiment, the pressure when charging to the charging cutoff voltage at 0.5C-1C is -25kPa to -15kPa.

[0102] In one alternative implementation, after the four rest periods, the process further includes six charging cycles and eleven rest periods in sequence.

[0103] In one alternative implementation, the battery is highly polarized during the first charge. The current is reduced and the battery is recharged to the standard full charge voltage of lithium iron phosphate to ensure that the battery is fully charged in the non-lithiation stage so that the battery can quickly reach the lithium replenishment reaction voltage in the lithium replenishment stage.

[0104] In one optional implementation, the fourth charging also includes first charging at 0.05C-0.2C to 3.15V-3.25V, and then charging at 0.1C-0.3C to 35%-50% of the nominal capacity.

[0105] In one alternative implementation, the battery is allowed to stand for twelve cycles after being charged to 3.15V-3.25V, and then allowed to stand for nine cycles after being charged to 35%-50% of the nominal capacity.

[0106] In one optional implementation, the current multiplier for the six charges is 0.1C-0.3C, the termination voltage is 3.65V-3.75V, and the pressure is -25kPa to -15kPa.

[0107] In one optional embodiment, the pressure of the ten static resting cycles is -45 kPa to -35 kPa, and the time is 5 min to 10 min.

[0108] In one optional embodiment, the pressure of the eleven static resting periods is -45 kPa to -35 kPa, and the time is 5 min to 10 min.

[0109] In one optional embodiment, the pressure of the twelve static resting cycles is -45 kPa to -35 kPa, and the time is 5 min to 15 min.

[0110] In one alternative embodiment, the positive electrode active material of the lithium-ion battery includes lithium iron phosphate.

[0111] In one optional embodiment, the lithium supplement includes at least one of lithium iron tetroxide, lithium nickelate, and lithium carbonate.

[0112] It should be noted that the reaction potential of lithium iron tetroxide (LFO) is divided into 3.5V-3.8V and 3.9V-4.1V. When the voltage is greater than 3.8V, the gas production rate will increase sharply. Therefore, the current rate is reduced during the fourth charge to avoid excessive current causing the lithium supplement to react rapidly, resulting in the formation of black spots after the battery is formed due to insufficient gas discharge. During the fifth charge, the battery is also charged to 4.0V-4.05V. This is because when the voltage is greater than 4.05V, the gas production rate will increase sharply again, which may lead to the risk of black spots due to insufficient gas discharge. Therefore, the voltage of the seventh charge is controlled at 4.05V. At the same time, controlling the current rate of the fifth charge to be lower than that of the fourth charge can ensure that the lithium supplement that has not fully reacted during the sixth charge can fully react.

[0113] In one optional implementation, the temperature of the first charging, the second charging, the third charging, the discharging, and the fourth charging is 40°C-50°C.

[0114] In one optional embodiment, the temperature of the first aging is 40°C-50°C.

[0115] In one alternative implementation, after the first aging, a second electrolyte injection and a second aging step are further included in sequence.

[0116] It should be noted that, in this invention, the raw material composition of the first electrolyte, by mass percentage, includes: ethyl methyl carbonate (EMC) 5wt%-25wt%, dimethyl carbonate (DMC) 35wt%-55wt%, ethylene carbonate (EC) 10wt%-18wt%, lithium salt 5wt%-12wt%, lithium bis(fluorosulfonyl)imide (LiFSI) 2wt%-7wt%, vinylene carbonate (VC) 1wt%-3wt%, and ethylene fluorophosphate (FEC) 0.3wt%-1.5wt%.

[0117] It should be noted that, in this invention, the raw material composition of the second electrolyte, by mass percentage, includes: ethyl methyl carbonate (EMC) 25wt%-50wt%, dimethyl carbonate (DMC) 10wt%-25wt%, ethylene carbonate (EC) 20wt%-40wt%, lithium salt 15wt%-20wt%, and vinylene carbonate (VC) 5wt%-15wt%.

[0118] Furthermore, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6) and lithium tetrafluoroborate (LiBF4).

[0119] In this invention, the first aging process can completely react the active materials in the incompletely reacted lithium replenishment agent. During this process, gas will also be generated, which can be discharged before the second liquid injection and sealing to prevent the battery from swelling.

[0120] In one optional embodiment, the temperature of the secondary aging is 40℃-50℃.

[0121] Compared to ordinary non-replenished lithium iron phosphate (LFP) batteries, this battery has the advantage of a longer cycle life. Cycling requires supportive electrolyte properties, and vinylene phosphate (VC) is a relatively good additive for forming the SEI film. High VC content significantly improves the cell's cycle life. However, a high VC content in the first electrolyte injection can lead to higher film impedance. Therefore, in the first electrolyte injection, the total electrolyte volume is 80wt%-95wt%, with a lower VC content; in the second electrolyte injection, the total electrolyte volume is 5wt%-20wt%, with a higher VC content. Simultaneously, to reduce gas generation and ensure a good cell interface, the content of the electrolyte solvent EC (ethylene phosphate) is reduced. However, EC alone easily generates gas; therefore, fluoroethylene phosphate (FEC) is added to block the gas generation from the side reaction between the electrolyte and the negative electrode.

[0122] Secondly, the present invention provides a lithium-ion battery, which is obtained by processing the battery according to the formation method described in the first aspect.

[0123] Example 1 This embodiment provides a battery formation method, including the following steps: (1) The lithium iron phosphate battery with positive electrode lithium replenishment was injected once (EMC 22wt%, DMC 45wt%, EC 15wt%, LiPF6 10wt%, LiFSI 5wt%, VC 2wt%, FEC 1wt%), the amount of liquid injected once was 90wt% of the total amount of liquid injected, and then aged at 45℃ for 48h, and then stood at -80kPa for 1min; (2) Charge to 3.2V at a current rate of 0.05C under -80kPa, and then let stand at -80kPa for 10min; (3) Charge to 3.3V at a current rate of 0.1C under -80kPa, and then let stand for 30min, 7min and 3min respectively under -80kPa, normal pressure and -30kPa; (4) Charge to 3.45V at a current rate of 0.2C under -80kPa, and then let stand for 10min, 60min and 2min respectively under -80kPa, -50kPa and -20kPa; (5) Charge to 3.65V at a current rate of 0.5C under -20kPa, and then let stand for 7 minutes under -40kPa; (6) Charge to 3.8V at a current rate of 0.05C under -40kPa, and then let stand at -40kPa for 2 minutes; (7) Charge to 4.05V at a current rate of 0.05C under -40kPa, and then let stand at -40kPa for 2 minutes; (8) Charge to 4.05V at a current rate of 0.025C under -40kPa, and then let stand at -40kPa for 2 minutes; (9) Discharge to 2.5V at a current rate of 0.5C under -40kPa, and then let stand for 7min, 7min and 7min respectively under -80kPa, normal pressure and -40kPa; (10) Charge to 3.2V at a current rate of 0.05C under -40kPa, and then let stand at -40kPa for 10min; (11) Charge to 3.3V at a current rate of 0.1C under -40kPa, and then let stand for 7 minutes under normal pressure; (12) The battery is aged at 45°C for 48 hours, and then a second liquid injection is performed (EMC 40wt%, DMC 10wt%, EC 30wt%, LiPF6 15wt%, VC 5wt%). The amount of the second liquid injection is 10wt% of the total liquid injection amount, and then aged at 45°C for 48 hours.

[0124] Example 2 This embodiment provides a battery formation method, including the following steps: (1) The lithium iron phosphate battery with lithium replenishment of positive electrode is injected once (EMC 22wt%, DMC 45wt%, EC 15wt%, LiPF6 10wt%, LiFSI 5wt%, VC 2wt%, FEC 1wt%), the amount of liquid injected once is 80wt% of the total amount of liquid injected, then aged at 40℃ for 32h, and then stood at -80kPa for 3min; (2) Charge to 3.2V at a current rate of 0.1C under -80kPa, and then let stand at -80kPa for 5 minutes; (3) Charge to 3.3V at a current rate of 0.2C under -80kPa, and then let stand for 25min, 5min and 2min respectively under -80kPa, normal pressure and -30kPa; (4) Charge to 3.45V at a current rate of 0.3C under -80kPa, and then let stand for 5min, 55min and 1min under -80kPa, -50kPa and -20kPa respectively; (5) Charge to 3.75V at a current rate of 0.8C under -20kPa, and then let stand for 5 minutes under -40kPa; (6) Charge to 3.8V at a current rate of 0.1C under -40kPa, and then let stand at -40kPa for 1min; (7) Charge to 4.05V at a current rate of 0.1C under -40kPa, and then let stand at -40kPa for 1min; (8) Charge to 4.05V at a current rate of 0.05C under -40kPa, and then let stand at -40kPa for 1min; (9) Discharge to 2.5V at a current rate of 1C under -40kPa, and then let stand for 5min, 5min and 5min respectively under -80kPa, normal pressure and -40kPa; (10) Charge to 3.2V at a current rate of 0.15C under -40kPa, and then let stand at -40kPa for 5min; (11) Charge to 3.3V at a current rate of 0.25C under -40kPa, and then let stand for 5 minutes under normal pressure; (12) The battery was aged at 50°C for 36 hours and then injected with electrolyte (EMC 40wt%, DMC 10wt%, EC 30wt%, LiPF6 15wt%, VC 5wt%). The amount of electrolyte injected was 20wt% of the total amount of electrolyte injected. The battery was then aged at 50°C for 36 hours.

[0125] Example 3 This embodiment provides a battery formation method, including the following steps: (1) The lithium iron phosphate battery with positive electrode lithium replenishment was injected once (EMC 22wt%, DMC 45wt%, EC 15wt%, LiPF6 10wt%, LiFSI 5wt%, VC 2wt%, FEC 1wt%), the total injection volume was 85wt%, and then aged at 50℃ for 42h, and then stood at -80kPa for 2min; (2) Charge to 3.2V at a current rate of 0.15C under -80kPa, and then let stand at -80kPa for 15min; (3) Charge to 3.3V at a current rate of 0.25C under -80kPa, and then let stand for 35min, 10min and 5min respectively under -80kPa, normal pressure and -30kPa; (4) Charge to 3.45V at a current rate of 0.5C under -80kPa, and then let stand for 15min, 65min and 3min respectively under -80kPa, -50kPa and -20kPa; (5) Charge to 3.7V at a current rate of 1C at -20kPa, and then let stand at -40kPa for 10min; (6) Charge to 3.8V at a current rate of 0.2C under -40kPa, and then let stand at -40kPa for 3min; (7) Charge to 4.05V at a current rate of 0.2C under -40kPa, and then let stand at -40kPa for 3 minutes; (8) Charge to 4.05V at a current rate of 0.1C under -40kPa, and then let stand at -40kPa for 3 minutes; (9) Discharge to 2.5V at a current rate of 0.8C under -40kPa, and then let stand for 10min, 10min and 10min respectively under -80kPa, normal pressure and -40kPa; (10) Charge to 3.2V at a current rate of 0.2C under -40kPa, and then let stand at -40kPa for 15min; (11) Charge to 3.3V at a current rate of 0.3C under -40kPa, and then let stand for 10min under normal pressure; (12) The battery was aged at 40°C for 42 hours and then injected with a second solution (EMC 40wt%, DMC 10wt%, EC 30wt%, LiPF6 15wt%, VC 5wt%). The amount of the second solution was 15wt% of the total solution. The battery was then aged at 40°C for 42 hours.

[0126] Example 4 This embodiment provides a battery formation method, including the following steps: (1) The lithium iron phosphate battery with positive electrode lithium replenishment was injected once (EMC 5wt%, DMC 55wt%, EC 18wt%, LiPF6 12wt%, LiFSI 7wt%, VC 1.5wt%, FEC 1.5wt%), the amount of liquid injected once was 90wt% of the total amount of liquid injected, and then aged at 45℃ for 48h, and then stood at -85kPa for 2min; (2) Charge to 3V at a current rate of 0.075C under -75kPa, and then let stand at -75kPa for 12min; (3) Charge to 3.25V at a current rate of 0.15C under -75kPa, and then let stand for 28min, 6min and 4min respectively under -85kPa, normal pressure and -25kPa; (4) Charge to 3.7V at a current rate of 0.2C at -80kPa, and then let stand for 8min, 62min and 1min at -85kPa, -55kPa and -15kPa respectively; (5) Charge to 3.85V at a current rate of 0.15C under -45kPa, and then let stand for 3min under -35kPa; (6) Charge to 4V at a current rate of 0.075C under -45kPa, and then let stand for 1min under -35kPa; (7) Charge to 4V at a current rate of 0.05C at -45kPa, and then let stand at -35kPa for 3min; (8) Discharge to 2.4V at a current rate of 0.6C under -45kPa, and then let stand for 6min, 8min and 8min respectively under -75kPa, normal pressure and -35kPa; (9) Charge to 3.35V (50% of nominal capacity) at a current rate of 0.1C under -40kPa, and then let stand for 8 minutes under normal pressure; (10) The battery is aged at 45°C for 48 hours, and then a second liquid injection is performed (EMC 45wt%, DMC 10wt%, EC 20wt%, LiPF6 15wt%, VC 10wt%). The amount of the second liquid injection is 10wt% of the total liquid injection amount, and then aged at 45°C for 48 hours.

[0127] Example 5 This embodiment provides a battery formation method, including the following steps: (1) The lithium iron phosphate battery with positive electrode lithium replenishment was injected once (EMC 25wt%, DMC 46wt%, EC 15wt%, LiPF 67wt%, LiFSI 4wt%, VC 1.5wt%, FEC 1.5wt%), the injection volume was 90wt% of the total injection volume, then aged at 45℃ for 48h, and then stood at -75kPa for 1min; (2) Charge to 3.1V at a current rate of 0.2C under -85kPa, and then let stand at -85kPa for 8 minutes; (3) Charge to 3.3V at a current rate of 0.3C under -85kPa, and then let stand for 32min, 9min and 5min respectively under -75kPa, normal pressure and -35kPa; (4) Charge to 3.75V at a current rate of 0.4C at -80kPa, and then let stand for 12min, 58min and 3min at -75kPa, -45kPa and -25kPa respectively; (5) Charge to 3.75V at a current rate of 0.2C under -20kPa, and then let stand for 5 minutes under -40kPa; (6) Charge to 3.85V at a current rate of 0.2C under -35kPa, and then let stand for 1 minute under -45kPa; (7) Charge to 4.0V at a current rate of 0.15C at -35kPa, and then let stand at -45kPa for 3min; (8) Charge to 4.0V at a current rate of 0.05C at -35kPa, and then let stand at -45kPa for 1min; (9) Discharge to 2.45V at a current rate of 0.9C under -35kPa, and then let stand for 9min, 9min and 6min respectively under -85kPa, normal pressure and -45kPa; (10) Charge to 3.3V (35% of nominal capacity) at a current rate of 0.2C under -45kPa, and then let stand for 6 minutes under normal pressure; (11) The battery is aged at 45°C for 48 hours, and then a second liquid injection is performed (EMC 25wt%, DMC 15wt%, EC 30wt%, LiPF6 20wt%, VC 10wt%). The amount of the second liquid injection is 10wt% of the total liquid injection amount, and then aged at 45°C for 48 hours.

[0128] Comparative Example 1 This embodiment provides a battery formation method, which is basically the same as the steps in Embodiment 1, except that step (12) does not involve high-temperature aging for secondary electrolyte injection.

[0129] Comparative Example 2 This comparative example provides a battery formation method, which is basically the same as the steps in Example 1, except that the current ratio in step (6) is 0.8C.

[0130] Comparative Example 3 This comparative example provides a battery formation method, which is basically the same as the steps in Example 1, except that steps (8) to (10) are omitted.

[0131] Comparative Example 4 This comparative example provides a battery formation method, which is basically the same as the steps in Example 1, except that the termination voltage of steps (6), (7) and (8) is 3.7V.

[0132] Comparative Example 5 This comparative example provides a battery formation method, which is basically the same as the steps in Example 1, except that the termination voltage of steps (7) and (8) is 4.1V.

[0133] Comparative Example 6 This comparative example provides a battery formation method, which is basically the same as the steps in Example 1, except that the current ratio in step (3) is 0.2C.

[0134] Comparative Example 7 This comparative example provides a battery formation method, which is basically the same as the steps in Example 1, except that the standing step in step (6) is removed.

[0135] Comparative Example 8 This comparative example provides a battery formation method, which is basically the same as the steps in Example 1, except that the standing step in step (8) is removed.

[0136] Experimental Example The electrical performance of the batteries treated by the formation methods of Examples 1-5 and Comparative Examples 1-8 were tested, and the results are shown in Table 1; specifically: The battery after secondary electrolyte injection was disassembled to observe whether there were black spots of lithium plating at the negative electrode interface; swelling was to check whether there was a change in thickness when the cell was removed from the production line; the cell was cycled 1000 times at 25°C and 0.5P rate, and its energy efficiency and capacity were tested; among them, the capacity was the discharge capacity of the second cycle, and the energy efficiency was the ratio of the discharge energy to the charging energy of the second cycle and the capacity retention rate after 1000 cycles. Table 1. Battery performance test results for each embodiment and comparative example.

[0137] As can be seen from Table 1, compared with Comparative Examples 1-6, the batteries prepared by the formation method of this invention do not exhibit lithium plating, black spots, swelling, etc., and have higher energy efficiency, capacity, and capacity retention. In Comparative Example 1, because step (12) did not undergo high-temperature aging before secondary liquid injection, the residual lithium replenishing agent active material in the cell will decompose and generate gas under high-temperature aging after the second injection and sealing, at which point the cell will swell; in Comparative Example 2, due to high-current rate charging during the lithium replenishing agent reaction stage, the side reaction gas could not be discharged in time, resulting in black spots and lithium plating at the battery interface; in Comparative Example 3, steps (8)-(10) were omitted, and the SOC was close to 100%, so there was a risk of battery swelling under high-temperature aging; at the same time, some of the remaining active materials... The material continues to react and produce gas during secondary aging, causing the battery to swell. In Comparative Example 4, the termination voltage for steps (6), (7), and (8) is 3.7V. The positive electrode lithium replenishment agent hardly reacts, and lithium ions are not extracted to the negative electrode. Furthermore, during subsequent high-temperature aging, the lithium replenishment agent will undergo side reactions and produce gas, causing the battery to swell and the electrode to wrinkle, which greatly affects battery performance and safety, resulting in low battery capacity and energy efficiency. In Comparative Example 5, the termination voltage for steps (7) and (8) is 4.1V. At this time, the formation voltage during the lithium replenishment stage is relatively low. Under high voltage and high oxygen concentration conditions, battery side reactions will increase, and there will be risks of black spots and lithium plating due to insufficient venting. In Comparative Example 6, step (3) is charged directly using the same current rate as step (4). The excessive and constant current cannot allow the SEI film to transition from dense to uniform in a reasonable way. This will cause the dense SEI film initially formed in step (1) to decompose and recombine. The resulting SEI film is thick and porous, with a loose and unstable structure, which may affect the battery's cycle performance. In Comparative Example 7, since the battery was not allowed to stand after the first stage of the lithium replenishment reaction and was directly charged, the battery will rapidly increase to the cutoff voltage of the next charging step due to the electrochemical polarization voltage. This is not conducive to the complete reaction of the lithium replenishment agent and may cause black spots and swelling due to poor venting. In Comparative Example 8, the battery was not allowed to stand when it was charged to the highest voltage (4V-4.05V). During charging, the lithium ions were extracted from the positive electrode faster than they were inserted into the negative electrode. The lithium ions that were not inserted in time would precipitate metallic lithium dendrites on the surface of the negative electrode. Standing allows the lithium ions to diffuse and insert fully, reducing the risk of lithium plating.

[0138] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for forming a battery, characterized in that, The positive electrode of the battery includes a positive electrode active material and a lithium replenishing agent, and the formation method includes the following steps: After injecting the first electrolyte into the battery, the battery is charged to the charging cutoff voltage of the positive electrode active material. The battery is then charged a second time to the voltage at which the lithium replenishment agent generates gas; The battery is then charged a third time to the voltage plateau of the lithium replenishment agent; The battery is discharged until the discharge cutoff voltage of the positive electrode active material is reached; After the battery is charged to 35%-50% of its nominal capacity for the fourth time, it is then aged once. The step of resting is performed after the first charging, the second charging, the third charging, the discharging, and the fourth charging, respectively. The first charging includes a first charging, a second charging, and a third charging, wherein the current multiplier of the first charging is less than the current multiplier of the second charging and the current multiplier of the third charging. The current ratio of the third charge is less than or equal to the current ratio of the second charge and less than or equal to 0.2C.

2. The battery formation method according to claim 1, characterized in that, The third charge includes four and five charges, wherein the current ratio of the five charges is less than the current ratio of the four charges.

3. The battery formation method according to claim 1 or 2, characterized in that, Before the first charging, a resting step is also included; And / or, after the first charging, a second resting step is also included; And / or, after the second charging, the process further includes three resting steps; And / or, after the three charging steps, a four-stage resting step is also included; And / or, after the second charge, there are also five resting steps; And / or, after the four charging cycles, a six-stage resting step is also included; And / or, after the five charging cycles, a seven-cycle resting step is also included; And / or, after the discharge, the process further includes eight settling steps; And / or, after the fourth charge, there are also nine resting steps.

4. The battery formation method according to claim 3, characterized in that, The pressure of the first static settling is -85kPa to -75kPa, and the time is 1min to 3min. And / or, the pressure of the secondary settling is -85kPa to -75kPa, and the time is 5min to 15min; And / or, the three settling periods include: settling at a pressure of -85kPa to -75kPa for 25min to 35min, settling at normal pressure for 5min to 10min, and settling at a pressure of -35kPa to -25kPa for 2min to 5min; And / or, the four settling periods include: settling for 5 min to 15 min at a pressure of -85 kPa to -75 kPa, settling for 55 min to 65 min at a pressure of -55 kPa to -45 kPa, and settling for 1 min to 3 min at a pressure of -25 kPa to -15 kPa. And / or, the pressure of the five settling periods, the pressure of the six settling periods, and the pressure of the seven settling periods are each independently -45kPa to -35kPa, and the time is each independently 1min to 3min; And / or, the eight settling periods include: settling for 5-10 minutes at a pressure of -85 kPa to -75 kPa, settling for 5-10 minutes at normal pressure, and settling for 5-10 minutes at a pressure of -45 kPa to -35 kPa. And / or, the nine resting periods are at atmospheric pressure and the time is 5-10 minutes.

5. The battery formation method according to claim 2, characterized in that, The current rating for a single charge is 0.05C-0.2C; And / or, the current multiplier of the secondary charge is 0.1C-0.3C; And / or, the current multiplier for the three charges is 0.2C-0.5C; And / or, the current multiplier of the second charge is 0.05C-0.2C; And / or, the current multiplier for the four charges is 0.05C-0.2C; And / or, the current multiplier for the five charges is 0.025C-0.1C; And / or, the discharge current ratio is 0.5C-1C; And / or, the current multiplier of the fourth charge is 0.05C-0.2C.

6. The battery formation method according to claim 2 or 5, characterized in that, The termination voltage for the first charge is 3.0V-3.2V; And / or, the termination voltage of the secondary charge is 3.25V-3.3V; And / or, the charging cutoff voltage is 3.65V-3.75V; And / or, the gas generation voltage is 3.8V-3.85V; And / or, the voltage platform is 4.0V-4.05V; And / or, the discharge cutoff voltage is 2.4V-2.5V.

7. The battery formation method according to claim 6, characterized in that, The pressure for each of the first charge, the second charge, and the third charge is independently -85kPa to -75kPa. And / or, the pressure of the second charge, the fourth charge, the fifth charge, the discharge, and the fourth charge is each independently -45kPa to -35kPa.

8. The battery formation method according to claim 2, characterized in that, The three charging steps also include first charging at a current rate of 0.2C-0.5C to 3.4V-3.5V, and then charging at a current rate of 0.5C-1C to the charging cutoff voltage; Optionally, the battery is allowed to rest four times after being charged to 3.4V-3.5V, and then allowed to rest ten times after being charged to the charging cutoff voltage. Optionally, the pressure when charging to the charging cutoff voltage at 0.5C-1C is -25kPa to -15kPa; And / or, after the four resting periods, the process further includes six charging cycles and eleven resting periods in sequence; And / or, the fourth charging also includes first charging at 0.05C-0.2C to 3.15V-3.25V, and then charging at 0.1C-0.3C to 35%-50% of the nominal capacity; Optionally, the battery can be left to stand for twelve cycles after being charged to 3.15V-3.25V, or left to stand for nine cycles after being charged to 35%-50% of the nominal capacity. Optionally, the current multiplier for the six charges is 0.1C-0.3C, the termination voltage is 3.65V-3.75V, and the pressure is -25kPa to -15kPa; Optionally, the pressure for the ten static resting cycles is -45 kPa to -35 kPa, and the time is 5 min to 10 min. Optionally, the pressure of the eleven static resting periods is -45 kPa to -35 kPa, and the time is 5 min to 10 min; Optionally, the pressure for the twelve static resting cycles is -45 kPa to -35 kPa, and the time is 5 min to 15 min.

9. The battery formation method according to claim 1, characterized in that, The positive electrode active material of the battery includes lithium iron phosphate; And / or, the lithium supplement includes at least one of lithium iron tetroxide, lithium nickelate, and lithium carbonate; And / or, the temperature of the first charging, the second charging, the third charging, the discharging, and the fourth charging is 40℃-50℃; And / or, the temperature of the first aging is 40℃-50℃; And / or, after the first aging, the process further includes the sequential injection of a second electrolyte and a second aging step; Optionally, the temperature for the secondary aging is 40℃-50℃.

10. A battery, characterized in that, It is obtained by processing the battery according to any one of claims 1-9.

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