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A technology of lithium-ion batteries and formation methods, which is applied in the field of formation of lithium-ion batteries, can solve the problems of battery capacity loss, safety hazards of piercing the diaphragm, and reduction of discharge capacity, etc., and achieve the effect of improving cycle and rate performance
Inactive Publication Date: 2014-09-10
HEFEI GUOXUAN HIGH TECH POWER ENERGY
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[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 p
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Embodiment 1
[0026] Take the formation of 12.5Ah lithium iron phosphate lithium ion battery as an example. Specifically include the following steps:
[0027] (1) Control the internal pressure of the battery case at -0.02MPa, and charge it with a constant current of 0.04C (500mA) for 150min (charge 10% of the nominal capacity);
[0028] (2) Charge it with a constant current of 0.2C (2500mA) for 240min (charge 80% of the nominal capacity), so that the battery is initialized to a total capacity of 90% SOC;
[0029] (3) Stand still for 4 minutes;
[0030] (4) Discharge it with a constant current of 0.2C (2500mA) to 2.0V;
[0031] (5) Stand still for 4 minutes;
[0032] (6) Charge it with a constant current of 0.5C (6250mA) for 108min (charging 90% of the nominal capacity);
[0033] (7) Then charge with a current of 0.04C (500mA) to 3.65V, then switch to constant voltage charging, and stop when the current drops to 0.02C (250mA).
Embodiment 2
[0035] Take the formation of 20Ah lithium iron phosphate lithium ion battery as an example. Specifically include the following steps:
[0036] (1) Control the internal pressure of the battery case at -0.03MPa, and charge it with a constant current of 0.2C (4000mA) for 30 minutes (charged with 10% of the nominal capacity);
[0037] (2) Charge it with a constant current of 1.0C (20000mA) for 42 minutes (charge 70% of the nominal capacity), so that the battery is initialized to a total capacity of 80% SOC;
[0038] (3) Stand still for 5 minutes;
[0039] (4) Discharge it with a constant current of 0.6C (12000mA) to 2.0V;
[0040] (5) Stand still for 5 minutes;
[0041] (6) Charge it with a constant current of 1.0C (20000mA) for 48 minutes (charging 80% of the nominal capacity);
[0042] (7) Then charge with a current of 0.2C (4000mA) to 3.65V, then switch to constant voltage charging, and stop when the current drops to 0.02C (400mA).
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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...
Claims
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