Formation method of lithium ion battery

Abstract

The invention discloses a formation method of a lithium ion battery. The formation method comprises the following steps: (1) carrying out constant-current charging with a 0.04C-0.2C current; (2) carrying out the constant-current charging with a 0.2C-1.0C current; (3) placing; (4) carrying out the constant-current discharging to a cut-off voltage with a 0.2C-0.6C discharging current; (5) placing; (6) carrying out the constant-current charging with a 0.5C-1.0C current; (7) carrying out the constant-current charging to the cut-off voltage with a 0.04C-0.2C current, and then converting into constant-voltage charging; and (8) maintaining a micro-vacuum state with the pressure being -0.03MPa-0.01MPa all the time in the lithium ion battery during the whole formation stage. The formation method disclosed by the invention has the advantages that in formation, gas generated in the battery can be exhausted in time, so that the lower capacity of the battery caused by bubbles adhered onto the surface of a negative pole piece is avoided; the phenomenon of overflowing of the electrolyte with the gas in the formation is avoided, so that the condition that the inventory of the electrolyte meets the process requirement is guaranteed; the discharging step is added after the charging step, so that the circulating performance and the rate capability of the prepared battery are respectively improved to a certain extent.

Description

technical field [0001] The invention relates to the production field of lithium ion batteries, in particular to a formation method of lithium ion batteries. Background technique [0002] With the depletion of traditional energy sources and the intensification of environmental pollution, green and environmentally friendly lithium-ion batteries have been greatly favored by people, and they have been widely promoted and applied in 3C, transportation, energy storage, aerospace and other fields, especially in The demand for high energy density lithium-ion batteries is the most urgent. The capacity performance of lithium-ion batteries is not only related to the electrochemical energy storage properties of the material itself, but also the process control in the formation stage plays a very important role in the performance of its capacity, and it also affects its later cycle performance and rate performance. have a non-negligible impact. [0003] The formation of lithium-ion bat...

AI Technical Summary

Problems solved by technology

[0004] First of all, the lithium ions deintercalated from the positive electrode active material through the electrolyte and through the separator cannot be intercalated into the negative electrode graphite due to the hindrance of the gas, which will react with the free lithium ion produced by the electrochemical reduction reaction of the electrolyte solvent. The base undergoes various complex chain reactions to generate organic lithium salts. When the bubbles disappear, this part of lithium salts will deposit on the surface of the negative electrode to form white spots, which are electrochemically inert, that is, when the battery is discharged, the lithium in the white spots The ions will not move back into the positive electrode active material, and the discharge capacity of the battery will decrease at this time. In addition, the white spots deposited on the surface of the negative electrode have poor lithium conductivity, which makes the battery rate and cycle performance poor.

[0005] Secondly, the lithium ions that should be embedded in the graphite of the negative electrode to undergo electrochemical reactions are hindered by the gas, causing the negative electrode to undergo concentration polarization, and the potential of the negative electrode drops rapidly. The electrochemical reduction reaction produces metallic lithium, and the accumulation of metallic lithium produces lithium dendrites, which pose a safety hazard of piercing the separator; at the same time, the SEI film formed on the surface of the negative electrode is not uniform and dense.

[0006] Finally, with the deepening of the formation depth, the potential of the negative electrode is getting lower and lower, and a large amount of LiC with high reduction activity is generated at the same time. 6 , LiC 6 It will chemically react with the gas generated during the formation process and be partially consumed, resulting in a loss of battery capacity

[0007] In addition, the gas generated during the formation process takes away a large amount of electrolyte, and the overflowing electrolyte will corrode the battery shell and the formation cabinet, affecting the appearance of the battery and shortening the service life of the formation cabinet

The most important thing is that the overflow of the electrolyte makes the actual amount of liquid remaining in the battery less than the process value, and the performance of the battery will be adversely affected

[0008] Chinese patent application number CN103094621A discloses a lithium-ion battery formation method, such as: control the internal pressure of the battery at 0.15MPa-2.0MPa, and use a current of 0.03C-0.1C to charge it into 30%-40% of the battery design capacity , and then control the internal pressure of the battery at -0.01~-0.1MPa, charge with a current of 0.1C~0.5C, and the charged power is 20%-30% of the design capacity, adopt positive pressure formation at the initial stage of formation, and negative pressure at the later stage of formation The formation method activates the battery, but this method of positive pressure at the initial stage of formation will cause a large amount of gas to be filled between the pole pieces and the pole pieces, and between the pole pieces and the diaphragm inside the battery, which cannot keep them the tightest state, expanding the diffusion distance of lithium ions, increasing its concentration polarization and forming a large number of electrochemically inert white spots on the surface of the negative electrode due to the barrier effect of the gas, which affects the electrochemical performance of the later battery

Chinese patent application number CN101908647A discloses a lithium-ion battery formation method in which normal pressure formation is performed according to 10% of the design capacity of the battery, and then negative pressure formation is carried out according to 60% of the design capacity. This method still cannot effectively reduce the surface of the negative electrode. The white spot at the place, because when the charging capacity is 2% ~ 3% SOC, the battery voltage has reached 2.5V, at this time the EC in the electrolyte begins to reduce and decompose on the surface of the carbon negative electrode, when the charging capacity is about 5% SOC , the voltage reaches 3.0V. At this time, DMC and DEC begin to decompose at the negative electrode. The electrochemical reduction reaction of the organic solvent produces a large amount of gas. The untimely discharge of the gas not only hinders the lithium ions from being well embedded in the graphite, but also causes Polarization, the risk of lithium precipitation, and the formation of white spots waste the limited lithium ions in the battery, which has an adverse effect on the electrical performance of the battery

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