阅读说明：本技术 一种锂二次电池的变压注液化成工艺 (Variable-pressure liquid injection formation process of lithium secondary battery ) 是由 李锐 于 2019-10-12 设计创作，主要内容包括：本发明提供了一种锂二次电池的变压注液化成工艺,通过在化成工艺中,多次抽真空,然后缓压,并多次注入电解液,从而增加电解液对电极的渗透能力,使电池形成更稳定的SEI膜,提高电池的循环性能；本发明提供的变压注液化成工艺所形成的SEI膜更加均匀、致密,在提高寿命的同时,还能够提高电池的安全性能。(The invention provides a variable-pressure liquid injection formation process of a lithium secondary battery, which comprises the steps of vacuumizing for multiple times, then decompressing, and injecting electrolyte for multiple times in the formation process, so that the permeability of the electrolyte to an electrode is improved, a more stable SEI film is formed by the battery, and the cycle performance of the battery is improved; the SEI film formed by the variable-pressure liquid injection formation process provided by the invention is more uniform and compact, and the safety performance of the battery can be improved while the service life is prolonged.)

1. A transformation liquid injection formation method of a lithium secondary battery comprises the following steps:

1) vacuumizing the battery to ensure that gauge pressure is-0.7, and simultaneously injecting a first electrolyte, wherein the first electrolyte comprises a first film forming additive;

2) the pressure of the battery is relieved, so that the pressure in the battery shell is recovered to 0.6 atmospheric pressure;

3) opening the battery to form a working procedure;

4) vacuumizing the battery to ensure that gauge pressure is-0.7, simultaneously injecting a second electrolyte, wherein the second electrolyte comprises a second film forming additive, and sealing after liquid injection;

5) and finishing the rest formation process.

2. The method of claim 1, wherein the first film forming additive is selected from the group consisting of vinylene carbonate, vinyl sulfite, and propylene sulfite.

3. The method of claim 1, wherein the second film-forming additive is selected from the group consisting of dimethyl sulfite, diethyl sulfite, and fluoroethylene carbonate (FEC).

4. The method of claim 1, wherein the first electrolyte solution includes 8-16 wt% of the first film forming additive.

5. The method of claim 1, wherein the second electrolyte solution includes 2-6 wt% of a second film-forming additive.

6. The method of claim 1, wherein the first and second electrolytes each independently comprise an organic solvent selected from the group consisting of EC, PC, DEC, DMC and EMC.

7. The method of claim 1, wherein the first electrolyte and the second electrolyte are injected in a volume ratio of 2:6 to 8: 2.

Technical Field

The invention relates to the technical field of batteries, in particular to a variable-pressure liquid injection formation process of a lithium secondary battery.

Background

Since the first lithium secondary battery developed by SONY corporation in 1992, lithium secondary batteries gradually replaced the markets of lead-acid batteries and nickel-metal hydride batteries, and became a new generation of energy storage elements. With the rapid development of lithium secondary battery technology, lithium secondary batteries are also beginning to be widely used as power and energy storage power sources, and the application fields include electric vehicles, electric components, uninterruptible power systems and the like, while the service life and safety of lithium secondary batteries are bottlenecks that hinder further development of lithium secondary batteries, and the research on the aspect is one of the key points of the current research.

Disclosure of Invention

The invention provides a variable-pressure liquid injection formation process of a lithium secondary battery, which is characterized in that in the formation process, multiple times of vacuumizing, pressure relief and multiple times of injection of electrolyte are carried out, so that the permeability of the electrolyte to an electrode is increased, a more stable SEI (solid electrolyte interphase) film is formed by the battery, and the cycle performance of the battery is improved; the SEI film formed by the variable-pressure liquid injection formation process provided by the invention is more uniform and compact, and the safety performance of the battery can be improved while the service life is prolonged.

The specific scheme is as follows:

a variable-pressure liquid injection formation process of a lithium secondary battery comprises the following steps:

1) vacuumizing the battery to ensure that gauge pressure is-0.7, and simultaneously injecting a first electrolyte, wherein the first electrolyte comprises a first film forming additive;

2) the pressure of the battery is relieved, so that the pressure in the battery shell is recovered to 0.6 atmospheric pressure;

3) opening the battery to form a working procedure;

4) vacuumizing the battery to ensure that gauge pressure is-0.7, simultaneously injecting a second electrolyte, wherein the second electrolyte comprises a second film forming additive, and sealing after liquid injection;

5) and finishing the rest formation process.

Further, the first film-forming additive is selected from vinylene carbonate, ethylene sulfite and propylene sulfite.

Further, the second film-forming additive is selected from dimethyl sulfite, diethyl sulfite, fluoroethylene carbonate (FEC).

Further, the first film-forming additive is selected from vinylene carbonate, ethylene sulfite and propylene sulfite.

Further, the second film-forming additive is selected from dimethyl sulfite, diethyl sulfite, fluoroethylene carbonate (FEC).

Further, the first electrolyte comprises 8-16 wt% of a first film forming additive.

Further, the second electrolyte comprises 2-6 wt% of a second film-forming additive.

Further, the first and second electrolytes each independently comprise an organic solvent selected from the group consisting of EC, PC, DEC, DMC and EMC.

Further, the volume ratio of the injection amount of the first electrolyte to the injection amount of the second electrolyte is 2:6-8: 2.

Further, the formation process of step 3 includes the following steps:

(1) charging the battery to 2.6V by using a current of 0.2-0.6C in a constant current manner;

(2) stopping charging, and standing for 2-6 hours;

(3) charging at a constant voltage of 2.6V until the charging current becomes a trickle or less, wherein the trickle charging current is 0.02 mu A;

(4) stopping charging, and standing for 2-6 hours;

(5) carrying out alternating current charging at the frequency of 35-65Hz and the alternating voltage of 2.8-3.8V for 2-6 hours;

(6) stopping charging, and standing for 3-8 hours;

(7) charging with a current of 0.3-0.5C until the final voltage is 4.0-4.5V;

(8) stopping charging, and standing for 0.6-2.6 hours;

(9) and (4) charging at constant voltage by using the termination voltage of the step (7) until the charging current is below trickle, wherein the trickle charging current is 0.02 mu A;

(10) carrying out alternating current charging at the frequency of 55-65Hz and the alternating voltage of 4.0-4.5V for 3-5 hours;

(11) stopping charging, and standing for 2-6 hours;

(12) charging the battery to a termination voltage of 5V by a constant current of 0.6-0.8C;

(13) stopping charging, and standing for 0.5-1.5 hours;

(14) discharging with 0.2-0.8C discharge current until the battery voltage is 2.5V;

further, the formation step of step 5 includes: repeating the steps (1) to (14) for 2 to 6 times;

charging with 0.5-0.8C charging current until the battery voltage is 5V, and finally charging with 5V constant voltage for 5-6 hours.

The invention has the following beneficial effects:

1. the first electrolyte with the film forming additive is injected while vacuumizing is performed, the permeation of the electrolyte to the electrode is accelerated, then the electrolyte uniformly covers the surface of the electrode along with the increase of pressure through a pressure relieving process, and a compact and uniform SEI film is formed in the electrolyte with the high concentration of the film forming additive.

2. And then, injecting a second electrolyte, and injecting a second film-forming additive with lower concentration but different components, so that the SEI film is formed more perfectly while the average concentration of the film-forming additive is reduced, and the surface of the finally formed SEI film is more uniform and smoother.

3. Through the formation of progressive low-rate constant-current charging and progressive constant-voltage charging, the morphology of the SEI film can be further perfected, and the SEI films which are layered and have different densities are formed, so that the embedding and the separation of lithium ions are controlled, the degradation of an electrode material structure is inhibited, and the service life of the battery is prolonged.

4. The alternating current charging formation process is adopted, and the high-frequency change of the oxidation reduction mode of the electrode material is realized through the change of the direction of current, so that the flexibility of an SEI film on the surface of the electrode material is improved, the electrode material is not easy to damage under the working condition of high-frequency charging use, the structure of the electrode material is stably protected, and the service life of a battery is prolonged.

Detailed Description

The present invention will be described in more detail below with reference to specific examples, but the scope of the present invention is not limited to these examples.

Test example:

a semi-finished lithium secondary battery comprises a positive electrode, a negative electrode and a diaphragm arranged between the positive electrode and the negative electrode, wherein the positive electrode comprises a positive active material, a conductive agent and a binder, and the negative electrode comprises a negative active material and a binder. The diaphragm comprises a polypropylene/polyethylene composite film; the anode active material is lithium iron phosphate, and the cathode active material is artificial graphite; the conductive agent is superconducting carbon black, and the binder is PVDF.

The batteries used in the examples and comparative examples of the present invention were the batteries of the above-described test examples.