阅读说明：本技术 一种电压控制型的多步注液化成方法 (Voltage control type multi-step liquid injection formation method ) 是由 王鹏 于 2020-11-25 设计创作，主要内容包括：本发明公开了一种电压控制型的多步注液化成方法,包括以下步骤,制备软包电芯,软包电芯的正极材料采用磷酸铁锂、镍钴锰三元材料中的一种,负极材料采用人造石墨；将含有碳酸丙烯酯的电解液A注入至软包电芯内,并进行低电压化成；将含有负极成膜添加剂的电解液B注入低电压化成后的软包电芯,并进行二次化成；将含由正极成膜添加剂的电解液C注入至二次化成后的软包电芯,并进行满电压化成、分容,完成注液化成步骤；其中,低电压化成的截止电压低于二次化成的截止电压、且二次化成的化成电压低于满电压化成的截止电压。本发明所述的注液化成方法实现在正负极材料表面得到一层稳定性优良的SEI膜,从而提高锂离子电池的循环性能。(The invention discloses a voltage control type multi-step liquid injection formation method, which comprises the following steps of preparing a soft package battery cell, wherein a positive electrode material of the soft package battery cell adopts one of ternary materials of lithium iron phosphate and nickel cobalt manganese, and a negative electrode material adopts artificial graphite; injecting an electrolyte A containing propylene carbonate into the soft package electric core, and carrying out low-voltage formation; injecting electrolyte B containing a negative film-forming additive into the soft-packaged battery cell after low-voltage formation, and carrying out secondary formation; injecting electrolyte C containing the positive electrode film-forming additive into the soft package battery cell after secondary formation, and performing full voltage formation and capacity grading to complete the liquid injection formation step; wherein the cut-off voltage for the low-voltage formation is lower than the cut-off voltage for the secondary formation, and the formation voltage for the secondary formation is lower than the cut-off voltage for the full-voltage formation. The liquid injection formation method provided by the invention realizes that a layer of SEI film with excellent stability is obtained on the surface of the anode material and the cathode material, thereby improving the cycle performance of the lithium ion battery.)

1. A voltage control type multi-step liquid injection formation method is characterized by comprising the following steps,

preparing a soft-package battery cell, wherein the positive electrode material of the soft-package battery cell is one of lithium iron phosphate and nickel cobalt manganese ternary materials, and the negative electrode material is artificial graphite;

injecting an electrolyte A containing propylene carbonate into the soft package electric core, and carrying out low-voltage formation;

injecting electrolyte B containing a negative film-forming additive into the soft-packaged battery cell after low-voltage formation, and carrying out secondary formation;

injecting electrolyte C containing the positive electrode film-forming additive into the soft package battery cell after secondary formation, and performing full voltage formation and capacity grading to complete the liquid injection formation step;

wherein the cut-off voltage for the low-voltage formation is lower than the cut-off voltage for the secondary formation, and the formation voltage for the secondary formation is lower than the cut-off voltage for the full-voltage formation.

2. The voltage-controlled multi-stage injection molding method according to claim 1, wherein the mass ratio of the electrolyte a containing propylene carbonate, the electrolyte B containing a negative electrode film-forming additive, and the electrolyte C containing a positive electrode film-forming additive is 6:2: 2.

3. The voltage-controlled multi-stage injection molding method according to claim 1 or 2, wherein the propylene carbonate in the electrolyte a accounts for 1 to 10% of the total mass of the electrolyte a.

4. The voltage control type multi-step liquid injection and formation method according to claim 1 or 2, wherein the negative electrode film forming additive is one or a combination of vinylene carbonate, fluoroethylene carbonate, butylene carbonate and 1, 3-propane sultone, and the negative electrode film forming additive accounts for 0.5-5% of the total mass of the electrolyte B.

5. The voltage control type multi-step electrolyte injection formation method is characterized in that the positive electrode film forming additive is one or a combination of more of lithium bis (fluorosulfonyl) imide, lithium bis (trifluoromethyl sulfonyl) imide, lithium difluoro oxalato borate and tris (trimethylsilyl) borate, and accounts for 0.5-5% of the total mass of the electrolyte C.

6. The multi-step injection formation method of voltage control type according to claim 1 or 2, wherein the electrolyte a, the electrolyte B and the electrolyte C further contain a solvent and a lithium salt, wherein the solvent is one or a combination of several of Ethylene Carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC), γ -Butyrolactone (BL), Methyl Formate (MF), Methyl Acetate (MA) and Ethyl Propionate (EP); the lithium salt is lithium hexafluorophosphate.

7. The voltage-controlled multi-step liquid injection formation method according to claim 1, wherein the cut-off voltage of the low-voltage formation is not more than 2.8V.

8. The voltage-controlled multi-step liquid injection formation method according to claim 1, wherein the cut-off voltage of the secondary formation is not more than 3.2V.

9. The voltage-controlled multi-step liquid injection formation method according to claim 1, wherein the cut-off voltage of the full voltage formation is 3.0 to 4.2V.

Technical Field

The invention relates to the technical field of battery manufacturing, in particular to a voltage control type multi-step liquid injection formation method.

Background

Compared with the traditional secondary battery, the lithium ion battery has the advantages of high working voltage, large energy density, long cycle life, environmental friendliness and the like, so that the lithium ion battery is widely applied to various industries. With the widespread acceptance of lithium ion batteries by users, people are also in urgent need to develop lithium battery systems with excellent safety performance and longer service life. On one hand, researchers continuously update and improve the battery materials, and on the other hand, reasonable optimization of the preparation process of the battery is also an important way for prolonging the cycle life of the battery.

The electrolyte is the blood of the lithium ion battery, is a carrier and a medium for transmitting lithium ions between the anode and the cathode, and simultaneously, the components of the electrolyte can form a stable SEI (solid electrolyte interphase) substance film on the cathode material, so that the continuous decomposition of the electrolyte on the surface of the cathode can be effectively inhibited, and the long-time charge-discharge cycle of the lithium ion battery is ensured. Experimental studies by Chen Hou et al of shanghai transportation university show that the SEI film has a double-layer mixed structure, and the failure of the SEI film is mainly related to dissolution of inorganic components of an inner layer caused by destruction of organic components on the surface of the SEI film. Therefore, how to form an SEI film with good stability is an important way for improving the cycle performance of the lithium ion battery from the perspective of an electrolyte.

Disclosure of Invention

In order to solve the technical problem, the invention provides a voltage control type multi-step injection formation method.

In order to solve the technical problems, the invention adopts the following technical scheme:

a voltage control type multi-step liquid injection formation method comprises the following steps,

preparing a soft-package battery cell, wherein the positive electrode material of the soft-package battery cell is one of lithium iron phosphate and nickel cobalt manganese ternary materials, and the negative electrode material is artificial graphite;

injecting an electrolyte A containing propylene carbonate into the soft package electric core, and carrying out low-voltage formation;

injecting electrolyte B containing a negative film-forming additive into the soft-packaged battery cell after low-voltage formation, and carrying out secondary formation;

injecting electrolyte C containing the positive electrode film-forming additive into the soft package battery cell after secondary formation, and performing full voltage formation and capacity grading to complete the liquid injection formation step;

wherein the cut-off voltage for the low-voltage formation is lower than the cut-off voltage for the secondary formation, and the formation voltage for the secondary formation is lower than the cut-off voltage for the full-voltage formation.

Furthermore, the mass ratio of the electrolyte A containing propylene carbonate, the electrolyte B containing a negative electrode film forming additive and the electrolyte C containing a positive electrode film forming additive is 6:2: 2.

Furthermore, the propylene carbonate in the electrolyte A accounts for 1-10% of the total mass of the electrolyte A.

Further, the negative electrode film forming additive is one or a combination of several of vinylene carbonate, fluoroethylene carbonate, butylene carbonate and 1, 3-propane sultone, and accounts for 0.5-5% of the total mass of the electrolyte B.

Further, the positive electrode film forming additive is one or a combination of more of bis (fluorosulfonyl) imide lithium, bis (trifluoromethanesulfonyl) imide lithium, lithium difluoro-oxalato-borate and tris (trimethylsilyl) borate, and accounts for 0.5-5% of the total mass of the electrolyte C.

Further, the electrolyte A, the electrolyte B and the electrolyte C also contain a solvent and a lithium salt, wherein the solvent is one or a combination of several of Ethylene Carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC), gamma-Butyrolactone (BL), Methyl Formate (MF), Methyl Acetate (MA) and Ethyl Propionate (EP); the lithium salt is lithium hexafluorophosphate.

Further, the cut-off voltage of the low voltage formation is not more than 2.8V.

Further, the cut-off voltage of the secondary formation is not more than 3.2V.

Further, the cut-off voltage of the full-voltage formation is 3.0-4.2V.

Compared with the prior art, the invention has the beneficial technical effects that:

the liquid injection of the soft package battery cell is realized by combining the three steps of liquid injection steps with a voltage control method; firstly, injecting a low-concentration propylene carbonate electrolyte to perform low-voltage formation, and slightly stripping the surface of the negative electrode of the artificial graphite by using the propylene carbonate to form an SEI (solid electrolyte interphase) film containing a small amount of graphene and lithium carbonate; secondly, injecting electrolyte containing a negative electrode film forming additive for secondary formation to form a stable SEI film on the negative electrode; and finally, injecting enough anode film-forming additive to ensure that the anode is formed with a film, thereby realizing that a layer of SEI film with excellent stability is obtained on the surfaces of the anode and cathode materials, and further improving the cycle performance of the lithium ion battery.

Detailed Description

The present invention is further illustrated by the following specific examples, which are, however, not intended to limit the scope of the invention.

The voltage control type multi-step liquid injection formation method is specifically explained as follows:

the invention relates to a voltage control type multi-step injection formation method, which comprises the following steps,

(1) coating, rolling, slitting and baking a positive electrode material and a negative electrode material to prepare a soft package battery cell, wherein the positive electrode material adopts one of ternary materials of lithium iron phosphate and nickel cobalt manganese, and the negative electrode material adopts artificial graphite;

(2) preparing an electrolyte A, an electrolyte B and an electrolyte C by proportioning a main solvent, a secondary solvent and an additive in proportion, wherein the main solvent is one or a combination of more of Ethylene Carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC), gamma-Butyrolactone (BL), Methyl Formate (MF), Methyl Acetate (MA) and Ethyl Propionate (EP), the secondary solvent is a lithium salt, and the lithium salt is preferably lithium hexafluorophosphate;

the electrolyte A comprises an additive, a solvent and a solvent, wherein the additive in the electrolyte A is propylene carbonate, and the propylene carbonate accounts for 1-10% of the total mass of the electrolyte A;

the electrolyte B comprises an electrolyte B, an additive, a negative electrode film-forming additive and a negative electrode film-forming additive, wherein the additive in the electrolyte B is the negative electrode film-forming additive, the negative electrode film-forming additive is one or a combination of more of vinylene carbonate, fluoroethylene carbonate, butylene carbonate and 1, 3-propane sultone, and the negative electrode film-forming additive accounts for 0.5-5% of the total mass of the electrolyte B;

the additive in the electrolyte C is a positive electrode film forming additive, the positive electrode film forming additive is one or a combination of more of bis (fluorosulfonyl) imide lithium, bis (trifluoromethyl sulfonyl) imide lithium, difluoro oxalic acid lithium borate and tris (trimethylsilyl) borate, and the positive electrode film forming additive accounts for 0.5-5% of the total mass of the electrolyte C;

(3) preparing an electrolyte A containing propylene carbonate, an electrolyte B containing a negative electrode film-forming additive and an electrolyte C containing a positive electrode film-forming additive according to the following mass ratio: the mass ratio of the electrolyte A to the electrolyte B to the electrolyte C is 6:2: 2;

(4) injecting the electrolyte A into a soft package battery cell under the condition that the dew point is controlled to be less than or equal to-40 ℃, sealing, standing for 12 hours at normal temperature, carrying out low-voltage formation, keeping the cut-off voltage of the formation to be less than or equal to 2.8V, and continuing to stand for 12 hours at normal temperature after the formation is finished;

(5) injecting the electrolyte B into the soft-packaged battery cell after low-voltage formation, sealing and standing for secondary formation, wherein the cut-off voltage of the formation is not more than 3.2V, and standing for 12h at normal temperature;

(6) injecting the electrolyte C into the soft package battery cell after standing in the step (4), carrying out full voltage formation and capacity grading, wherein the formation cut-off voltage is 3.0-4.2V, and thus completing the liquid injection formation step;

in the above steps (4) to (6), the off-voltage of the low-voltage formation is lower than the off-voltage of the secondary formation, and the off-voltage of the secondary formation is lower than the formation voltage of the full-voltage cut-off.

Example 1

1) Preparing a 2.4Ah soft package battery cell to be injected with liquid by the processes of slurry mixing, coating, rolling, slitting, winding, packaging, baking and the like, wherein the positive electrode material is lithium iron phosphate, and the negative electrode material is artificial graphite;

2) preparing electrolyte A from a main solvent, a secondary solvent and an additive according to the following weight part ratio: 85 parts of ethyl methyl carbonate, 13 parts of lithium hexafluorophosphate and 2 parts of propylene carbonate; electrolyte B: 30 parts of ethylene carbonate, 55 parts of ethyl methyl carbonate, 13 parts of lithium hexafluorophosphate and 2 parts of vinylene carbonate; electrolyte C: 20 parts of ethylene carbonate, 65 parts of ethyl methyl carbonate, 13 parts of lithium hexafluorophosphate and 2 parts of lithium bis (fluorosulfonyl) imide;

3) injecting the electrolyte A into a soft package battery cell under the condition that the dew point is controlled to be less than or equal to minus 40 ℃, sealing, standing for 12 hours at normal temperature, then carrying out low-voltage formation, wherein the formation cut-off voltage is 2.8V, and standing for 12 hours at normal temperature after the formation is finished;

4) injecting the electrolyte B into the formed battery cell, sealing and standing the battery cell, performing secondary formation, wherein the formation cut-off voltage is 3.2V, and continuously standing the battery cell at normal temperature for 12 hours;

5) and injecting the electrolyte C into the formed battery cell, sealing and standing, and then completely forming and grading to obtain a to-be-circulated battery cell with a formation cut-off voltage of 4.0V.

Example 2

1) Preparing a 2.4Ah soft package battery cell to be injected with liquid by the processes of slurry mixing, coating, rolling, slitting, winding, packaging, baking and the like, wherein the positive electrode material is lithium iron phosphate, and the negative electrode material is artificial graphite;

2) preparing electrolyte A from a main solvent, a secondary solvent and an additive according to the following weight part ratio: 80 parts of ethyl methyl carbonate, 13 parts of lithium hexafluorophosphate and 7 parts of propylene carbonate; electrolyte B: 30 parts of ethylene carbonate, 55 parts of ethyl methyl carbonate, 13 parts of lithium hexafluorophosphate and 2 parts of vinylene carbonate; electrolyte C: 20 parts of ethylene carbonate, 65 parts of ethyl methyl carbonate, 13 parts of lithium hexafluorophosphate and 2 parts of lithium bis (fluorosulfonyl) imide;

3) injecting the electrolyte A into a soft package battery cell under the condition that the dew point is controlled to be less than or equal to minus 40 ℃, sealing, standing for 12 hours at normal temperature, then carrying out low-voltage formation, wherein the formation cut-off voltage is 2.8V, and standing for 12 hours at normal temperature after the formation is finished;

4) injecting the electrolyte B into the formed battery cell, sealing and standing the battery cell, performing secondary formation, wherein the formation cut-off voltage is 3.2V, and continuously standing the battery cell at normal temperature for 12 hours;

5) and injecting the electrolyte C into the formed battery cell, sealing and standing, and then completely forming and grading to obtain a to-be-circulated battery cell with a formation cut-off voltage of 4.0V.

Example 3

1) Preparing a 2.4Ah soft package battery cell to be injected with liquid by the processes of slurry mixing, coating, rolling, slitting, winding, packaging, baking and the like, wherein the positive electrode material is lithium iron phosphate, and the negative electrode material is artificial graphite;

2) preparing electrolyte A from a main solvent, a secondary solvent and an additive according to the following weight part ratio: 82 parts of ethyl methyl carbonate, 13 parts of lithium hexafluorophosphate and 5 parts of propylene carbonate; electrolyte B: 30 parts of ethylene carbonate, 55 parts of ethyl methyl carbonate, 13 parts of lithium hexafluorophosphate and 2 parts of vinylene carbonate; electrolyte C: 20 parts of ethylene carbonate, 65 parts of ethyl methyl carbonate, 13 parts of lithium hexafluorophosphate and 2 parts of lithium bis (fluorosulfonyl) imide;

3) injecting the electrolyte A into a battery cell to be injected under the condition that the dew point is controlled to be less than or equal to-40 ℃, sealing, standing for 12 hours at normal temperature, then carrying out low-voltage formation, wherein the formation cut-off voltage is 2.8V, and standing for 12 hours at normal temperature after the formation is finished;

4) injecting the electrolyte B into the formed battery cell, sealing and standing the battery cell, performing secondary formation, wherein the formation cut-off voltage is 3.2V, and continuously standing the battery cell at normal temperature for 12 hours;

5) and injecting the electrolyte C into the formed battery cell, sealing and standing, and then completely forming and grading to obtain a to-be-circulated battery cell with a formation cut-off voltage of 4.0V.

Example 4

1) Preparing a 2.4Ah soft package battery cell to be injected with liquid by the processes of slurry mixing, coating, rolling, slitting, winding, packaging, baking and the like, wherein the positive electrode material is lithium iron phosphate, and the negative electrode material is artificial graphite;

2) preparing electrolyte A from a main solvent, a secondary solvent and an additive according to the following weight part ratio: 77 parts of ethyl methyl carbonate, 13 parts of lithium hexafluorophosphate and 10 parts of propylene carbonate; electrolyte B: 30 parts of ethylene carbonate, 55 parts of ethyl methyl carbonate, 13 parts of lithium hexafluorophosphate and 2 parts of vinylene carbonate; electrolyte C: 20 parts of ethylene carbonate, 65 parts of ethyl methyl carbonate, 13 parts of lithium hexafluorophosphate and 2 parts of lithium bis (fluorosulfonyl) imide;

3) injecting the electrolyte A into a battery cell to be injected under the condition that the dew point is controlled to be less than or equal to-40 ℃, sealing, standing for 12h at normal temperature, carrying out low-voltage formation, wherein the formation voltage is 2.8V, and standing for 12h at normal temperature after the formation is finished;

4) injecting the electrolyte B into the formed battery cell, sealing and standing the battery cell, performing secondary formation, wherein the formation voltage is 3.2V, and continuously standing the battery cell at normal temperature for 12 hours;

5) and injecting the electrolyte C into the formed battery cell, sealing and standing, and then completely forming and grading to obtain a forming voltage of 4.0V, thereby finally obtaining the battery cell to be circulated.

Comparative example 1

1) Preparing a 2.4Ah soft package battery cell to be injected with liquid by the processes of slurry mixing, coating, rolling, slitting, winding, packaging, baking and the like, wherein the positive electrode material is lithium iron phosphate, and the negative electrode material is artificial graphite;

2) preparing electrolyte from a main solvent, a secondary solvent and an additive according to the following weight part ratio: 85 parts of ethyl methyl carbonate, 13 parts of lithium hexafluorophosphate and 2 parts of propylene carbonate;

3) injecting the electrolyte into the battery cell to be injected under the condition that the dew point is controlled to be less than or equal to-40 ℃, sealing, standing for 12 hours at normal temperature, then performing voltage formation, wherein the formation voltage is 2.8V, and continuing to stand for 12 hours at normal temperature after the formation is finished. And after standing, performing capacity grading to finally obtain the battery cell to be circulated.

Comparative example 2

1) Preparing a 2.4Ah soft package battery cell to be injected with liquid by the processes of slurry mixing, coating, rolling, slitting, winding, packaging, baking and the like, wherein the positive electrode material is lithium iron phosphate, and the negative electrode material is artificial graphite;

2) preparing electrolyte from a main solvent, a secondary solvent and an additive according to the following weight part ratio: 30 parts of ethylene carbonate, 55 parts of ethyl methyl carbonate, 13 parts of lithium hexafluorophosphate and 2 parts of vinylene carbonate;

3) injecting electrolyte into the battery cell to be injected under the condition that the dew point is controlled to be less than or equal to-40 ℃, sealing, standing for 12 hours at normal temperature, then performing voltage formation, wherein the formation voltage is 3.2V, continuing to stand for 12 hours at normal temperature after the formation is finished, and performing capacity separation after the standing is finished to finally obtain the battery cell to be circulated.

Comparative example 3

1) Preparing a 2.4Ah soft package battery cell to be injected with liquid by the processes of slurry mixing, coating, rolling, slitting, winding, packaging, baking and the like, wherein the positive electrode material is lithium iron phosphate, and the negative electrode material is artificial graphite;

2) preparing electrolyte A from a main solvent, a secondary solvent and an additive according to the following weight part ratio: 30 parts of ethylene carbonate, 55 parts of ethyl methyl carbonate, 13 parts of lithium hexafluorophosphate and 2 parts of vinylene carbonate; electrolyte B: 20 parts of ethylene carbonate, 65 parts of methyl ethyl carbonate, 13 parts of lithium hexafluorophosphate and 2 parts of tris (trimethylsilyl) borate;

3) injecting the electrolyte A into a battery cell to be injected under the condition that the dew point is controlled to be less than or equal to-40 ℃, sealing, standing for 12 hours at normal temperature, then carrying out one-time formation, wherein the formation cut-off voltage is 3.2V, and standing for 12 hours at normal temperature after the formation is finished;

4) and injecting the electrolyte B into the formed battery cell, sealing and standing the battery cell, performing secondary formation, wherein the formation cut-off voltage is 4.0V, continuously standing the battery cell at normal temperature for 12h, and then performing capacity grading to finally obtain the battery cell to be circulated.

The cycle performance of the cells of examples 1-4 of the invention and comparative examples 1-3 is shown in the table below.

It can be seen from the table that by controlling the addition amount of propylene carbonate and the formation voltage range, damage to the negative electrode material is avoided, an SEI film containing a small amount of graphene and lithium carbonate is formed, and then by the two subsequent voltage control formation steps, a more stable SEI film can be formed, so that the cycle performance of the battery cell is improved.

Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.