A method for liquid injection formation of a lithium ion battery

Abstract

The application belongs to the field of lithium ion batteries, and specifically discloses a liquid injection formation method of a lithium ion battery. In the method, a complete solid electrolyte film is formed first, then gelation is performed, and finally, a gel polymer monomer is supplemented to provide conditions for subsequent self-repair, so that the integrity and cycle stability of the solid electrolyte film and the gel electrolyte film can be improved at the same time. In this way, the situation that the solid electrolyte film is difficult to grow in the formation of the gel electrolyte battery and the cycle performance is reduced due to the damage of the gel electrolyte film is improved, and finally, the cycle performance of the lithium ion battery is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of lithium ion batteries, and particularly relates to a liquid injection and formation method of a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries are widely used in our life, and can be seen in all aspects such as 3C products, power batteries, large-scale energy storage and the like. However, the commonly used lithium ion batteries still use liquid electrolyte, and the solvent is generally an organic solvent such as a carbonate or a carboxylate. These solvents are easy to volatilize and leak after the shell of the lithium ion battery is damaged, and are flammable solvents, which can easily cause safety accidents. As a replacement for liquid electrolyte, the all-solid-state electrolyte has the advantages of no liquid electrolyte and high safety. However, the interface contact resistance between the all-solid-state electrolyte and the electrode is large, and the ion transference rate is low, which has been limiting the development of the all-solid-state electrolyte. The semi-solid-state electrolyte has the advantages of high ion transference rate of the liquid electrolyte and no free electrolyte and high safety of the solid-state electrolyte, and therefore has gradually become a research focus.

[0003] At present, the semi-solid-state electrolyte mainly has two technical routes. One is a gel electrolyte separator technology: a gel coating layer is coated on a separator, and after being assembled into a battery, liquid is injected to allow the gel coating layer to absorb and swell the electrolyte, so as to store the electrolyte in the gel layer. The other is an in-situ gelation technology: polymer monomers and initiators are added to the electrolyte, and after the battery is injected with liquid, in-situ polymerization gelation occurs under the condition of initiating the polymerization reaction. In order to improve the ion transference rate of the gel electrolyte, electrolyte salts, fast ion conductors and the like are also added to the electrolyte. Compared with the gel electrolyte separator technology, the in-situ gelation technology has smaller interface contact resistance between the electrolyte and the electrode, and effectively reduces the internal resistance of the gel electrolyte battery.

[0004] However, the in-situ gelation technology of the electrolyte directly injects the monomers and initiators required by the polymer into the battery, and then performs gelation. The liquid electrolyte after gelation is dispersed in each pore or cavity by the porous gel layer. In the first charging process (formation of the battery) of the battery after the battery is injected with liquid and gelation, the lithium salt and the electrolyte have a side reaction, and a solid-state electrolyte interface film (SEI) is generated on the negative electrode side of the lithium battery. The generation of the solid-state electrolyte film consumes part of the electrolyte, and because the liquid electrolyte after gelation is dispersed in each pore or cavity by the porous gel layer, it is difficult to supplement the electrolyte of the subsequent battery, which leads to the difficulty in forming a good solid-state electrolyte film. Moreover, in the subsequent cycle, the gel electrolyte layer will also be damaged due to multiple cycles. Whether the generation of the solid-state electrolyte film is blocked or the gel electrolyte layer is damaged after long cycle, it will ultimately directly lead to the decline of the cycle performance of the battery. Summary of the Invention

[0005] In view of the problems of poor cycle performance of the gel electrolyte lithium ion battery involved in the above-mentioned prior art, the present invention provides a liquid injection formation method for a lithium ion battery.

[0006] To achieve the above objectives, the following technical solutions are specifically included:

[0007] A method for liquid injection formation of a lithium ion battery comprises the following steps:

[0008] (1) Providing a lithium-ion battery to be liquefied;

[0009] (2) injecting the first electrolyte into the lithium-ion battery to be injected and formed for the first time, then evacuating the battery, sealing the battery, and then allowing the battery to stand and undergo formation in sequence;

[0010] The first electrolyte comprises the following components in percentage by weight: 70-90% solvent, 6-20% lithium salt, and 1-10% film-forming additive;

[0011] The battery is charged at a constant current of 0.02-0.05C to a voltage of 2.75-3.6V, and then at a constant current of 0.1C-0.2C to a voltage of 3.6-4.1V.

[0012] (3) injecting the formed lithium-ion battery with a second electrolyte for a second time, followed by evacuation, sealing, and then performing a gelation reaction;

[0013] The second electrolyte comprises the following components in percentage by weight: 69-92.9% solvent, 0-20% lithium salt, 1-10% gel polymer monomer, and 0.1-1% initiator;

[0014] (4) injecting the third electrolyte into the lithium-ion battery after the gelation reaction for the third time, then evacuating the battery, sealing the battery, and allowing the battery to stand;

[0015] The third electrolyte comprises the following components in percentage by weight: 79-99% solvent, 0-20% lithium salt, 1-10% polymer monomer, and 0-1% initiator;

[0016] In steps (2)-(4), taking the total mass percentage of the first electrolyte, the second electrolyte and the third electrolyte as 100%, the mass percentage of the first electrolyte is 70-90%, the mass percentage of the second electrolyte is 5-25%, and the mass percentage of the third electrolyte is 5-25%.

[0017] In the liquid injection and formation method of the present application, first, the first electrolyte containing lithium salt and film-forming additive is used to perform the first liquid injection and formation, the electrolyte is sufficient, which is conducive to the interaction of lithium ions and film-forming additive, and a solid-state electrolyte film (SEI) beneficial to improve the cycle performance of lithium ion battery is generated; then the second electrolyte containing gel polymer monomer and initiator is used to perform the second liquid injection and gelation, and the electrolyte is still sufficient, which is conducive to the interaction of gel polymer monomer and initiator, and a gel electrolyte layer beneficial to improve the cycle performance of lithium ion battery is generated; finally, the third electrolyte containing gel polymer monomer is used to perform the third liquid injection and standing, and the gel polymer monomer in the third electrolyte provides material conditions for subsequent self-repair, which is conducive to the stability of the gel electrolyte layer in the subsequent long cycle process of the battery and is conducive to improving the cycle performance of the lithium ion battery.

[0018] In the method of the present application, the complete solid-state electrolyte film is formed by formation first, then gelation, and finally, the gel polymer monomer is supplemented to provide conditions for subsequent self-repair, so that a good solid-state electrolyte film is formed in the formation, and the gelation monomer is also retained as a repair material for the subsequent gel electrolyte, achieving the purpose of improving the integrity and cycle stability of the solid-state electrolyte film and the gel electrolyte film at the same time, thereby improving the situation that the solid-state electrolyte film is difficult to grow in the formation of the gel electrolyte battery and the cycle performance is reduced due to the damage of the gel electrolyte layer, and finally realizing the improvement of the cycle performance of the lithium ion battery.

[0019] Preferably, in step (2), the temperature of the standing is room temperature, and the time of the standing is 24-72h.

[0020] Preferably, in step (2), the temperature of the gelation reaction is 30-80℃, and the time of the gelation reaction is 0.5-12h.

[0021] Under the above gelation conditions, the gel polymer monomer can be polymerized in situ by thermal initiation to achieve in-situ polymerization gelation, and a more stable gel electrolyte layer can be obtained.

[0022] Preferably, in step (4), the temperature of the standing is 30-45℃, and the time of the standing is 12-72h.

[0023] Preferably, in steps (2)-(4), the solvents in the first electrolyte, the second electrolyte, and the third electrolyte are each selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, gamma-butyrolactone, methyl formate, ethyl formate, methyl acetate, ethyl acetate, ethyl propionate, methyl butyrate, and ethyl butyrate.

[0024] Preferably, in steps (2)-(4), the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium trifluoromethylsulfonate, lithium bis-trifluoromethylsulfonimide, lithium bisfluorosulfonimide, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate.

[0025] Preferably, in step (2), the film-forming additive comprises at least one of vinylene carbonate, lithium bis(oxalato)borate, lithium tetrafluoroborate, lithium difluorophosphate, lithium difluoro(oxalato)borate.

[0026] Preferably, in step (3), the gel polymer monomer comprises at least one of ethylene glycol diacrylate, methyl methacrylate, trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, acrylic acid, methacrylic acid, triethylene glycol divinyl ether.

[0027] Preferably, in step (4), the initiator comprises one of dibenzoyl peroxide, azobisisobutyronitrile, dimethyl azobisisobutyrate, dibenzoyl peroxide, lauryl peroxide, diisopropyl peroxydicarbonate, dicyclohexyl peroxydicarbonate.

[0028] Compared with the prior art, the present application has the following beneficial effects: in the method of the present application, the complete solid-state electrolyte film is first formed by chemical formation, then gelled, and finally supplemented with gel polymer monomers to provide conditions for subsequent self-repair, so that a good solid-state electrolyte film is formed during chemical formation, and at the same time, gel monomers are retained as repair materials for subsequent gel electrolyte, achieving the purpose of improving the integrity and cycle stability of the solid-state electrolyte film and the gel electrolyte film, thereby improving the situation that the solid-state electrolyte film is difficult to grow during the chemical formation of the gel electrolyte battery, and the cycle performance is reduced due to damage to the gel electrolyte layer, and ultimately improving the cycle performance of the lithium ion battery. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 Effect diagram of the influence of different liquid injection chemical formation methods in examples 1-3 and comparative examples 1-2 on the cycle performance of lithium ion batteries. DETAILED DESCRIPTION

[0030] In order to better illustrate the purpose, technical scheme and advantages of the present application, the present application will be further described below through specific examples. Unless otherwise specified, the test methods used in the examples and / or comparative examples are conventional methods; and the materials, reagents, etc. used are commercially available unless otherwise specified.

[0031] Example 1

[0032] A liquid injection chemical formation method for a lithium ion battery, comprising the following steps:

[0033] (1) Prepare the blank soft package battery cell to be injected (lithium ion battery soft package to be injected);

[0034] (2) The electrolyte is injected in three times as follows. After the third injection, the total weight of the electrolyte is 100%. First, the first electrolyte is used to inject the blank soft package battery cell to be injected. Then, the air is extracted and the opening is sealed. The liquid volume of the first electrolyte is 70% of the total weight of the electrolyte. The first electrolyte is composed of the following components with mass percentage: ethylene carbonate 90%, lithium hexafluorophosphate 6%, and vinylene carbonate 4%;

[0035] (3) After 72 hours of standing at room temperature, the battery is formed. The formation process is as follows: 0.02C constant current charging to 3.6V, with a time limit of 120 minutes; then 0.1C constant current charging to 3.9V, with a time limit of 120 minutes;

[0036] (4) The second electrolyte is injected from the gas bag packaging side of the formed battery cell using a syringe. The air is extracted and the opening is sealed. The liquid volume of the second electrolyte is 25% of the total weight of the electrolyte. The second electrolyte is composed of the following components with mass percentage: ethylene carbonate 80%, lithium hexafluorophosphate 10%, ethylene glycol dipropenoate 9%, and dibenzoyl peroxide 1%;

[0037] (5) The battery cell after the second injection is placed in an oven at 80°C. The in-situ polymerization gelation reaction is initiated by the temperature. The reaction time is 6 hours;

[0038] (6) Finally, the third electrolyte is injected from the second packaging side of the gelated battery cell using a syringe. The air is extracted and the opening is sealed. Then, the battery is placed in an oven at 55°C for 12 hours. The liquid volume of the third electrolyte is 5% of the total weight of the electrolyte. The third electrolyte is composed of the following components with mass percentage: ethylene carbonate 80%, lithium hexafluorophosphate 15%, ethylene glycol dipropenoate 4%, and dibenzoyl peroxide 1%.

[0039] Example 2

[0040] A method for injecting and forming a lithium ion battery, comprising the following steps:

[0041] (1) Prepare the blank soft package battery cell to be injected (lithium ion battery soft package to be injected);

[0042] (2) The electrolyte is injected three times as follows. After the three injections, the total weight of the electrolyte in the lithium-ion battery soft pack is calculated as 100%. The first electrolyte is first injected into the blank soft pack battery cell to be injected, and then the battery cell is evacuated and sealed. The amount of the first electrolyte is 85% of the total electrolyte weight, and the first electrolyte is composed of the following components in percentage by weight: 90% ethylene carbonate, 9% lithium hexafluorophosphate, and 1% vinylene carbonate;

[0043] (3) After standing at room temperature for 48 hours, the battery was formed. The formation process was as follows: charging at a constant current of 0.05C to a voltage of 3.5V, with a time limit of 120 minutes; then charging at a constant current of 0.1C to a voltage of 3.9V, with a time limit of 120 minutes;

[0044] (4) Using a syringe, inject the second electrolyte from the air bag packaging side of the formed battery cell for the second time, evacuate the air, and seal the cell. The second electrolyte volume is 10% of the total electrolyte weight. The second electrolyte is composed of the following components by weight: 90% ethylene carbonate, 6% lithium hexafluorophosphate, 3% methyl methacrylate, and 1% dibenzoyl peroxide;

[0045] (5) Place the battery cell after the second injection and degassing packaging in an oven at 75°C to initiate the in-situ polymerization and gelation reaction at this temperature for 12 hours;

[0046] (6) Finally, a syringe is used to inject the third electrolyte into the second packaging side of the battery cell air bag after gelation is completed, evacuate the air, seal the bag, and then place it in a 55°C oven for 12 hours to obtain a lithium-ion battery. The amount of the third electrolyte is 5% of the total electrolyte weight. The third electrolyte is composed of the following components in percentage by weight: 99% ethylene carbonate and 1% methyl methacrylate.

[0047] Example 3

[0048] A method for liquid injection formation of a lithium ion battery comprises the following steps:

[0049] (1) Prepare a blank soft-pack battery cell to be injected with liquid (a lithium-ion battery soft pack to be injected with liquid);

[0050] (2) The electrolyte is injected three times as follows. After the three injections, the total weight of the electrolyte in the lithium-ion battery soft pack is calculated as 100%. The first electrolyte is first injected into the blank soft pack battery cell to be injected, and then the battery cell is evacuated and sealed. The amount of the first electrolyte is 80% of the total electrolyte weight, and the first electrolyte is composed of the following components in percentage by weight: 85% ethylene carbonate, 14% lithium hexafluorophosphate, and 1% vinylene carbonate;

[0051] (3) After standing at room temperature for 48 h, the battery was formed, and the formation process was as follows: 0.04C constant current charging to 3.0V, and the time limit was 120 min; then 0.2C constant current charging to 4.0V, and the time limit was 120 min;

[0052] (4) The second electrolyte was injected into the gas bag package side of the formed cell using a syringe, and then the gas was extracted and sealed. The second electrolyte was 10% of the total electrolyte weight, and was composed of the following components with mass percentages: ethylene carbonate 90%, lithium hexafluorophosphate 0%, methyl methacrylate 9.9%, and dibenzoyl peroxide 0.1%;

[0053] (5) The cell after the second injection, gas extraction and sealing was placed in an 80°C oven to initiate in-situ polymerization and gelation reaction by heat, and the reaction time was 6 h;

[0054] (6) Finally, the third electrolyte was injected into the second package side of the cell after gelation using a syringe, and then the gas was extracted and sealed. The cell was then placed in a 55°C oven for 12 h to obtain a lithium ion battery. The third electrolyte was 10% of the total electrolyte weight, and was composed of the following components with mass percentages: ethylene carbonate 85%, lithium hexafluorophosphate 10%, and methyl methacrylate 5%.

[0055] Comparative Example 1

[0056] The comparative example used a traditional injection and formation method, which included the following steps:

[0057] (1) A blank soft package cell to be injected (lithium ion battery soft package to be injected) was prepared;

[0058] (2) The injection process of the electrolyte was completed once, and the gas was extracted and sealed. The electrolyte composition and content were the same as the total electrolyte of the lithium ion battery soft package after three injections in Example 1, i.e., the electrolyte included the following components with mass percentages: ethylene carbonate 87%, lithium hexafluorophosphate 7.45%, vinylene carbonate 2.8%, ethylene glycol diacrylate 2.45%, and dibenzoyl peroxide 0.3%;

[0059] (3) The cell after injection, gas extraction and sealing was placed in an 80°C oven to initiate in-situ polymerization and gelation reaction by heat, and the reaction time was 6 h;

[0060] (4) The battery was formed, and the formation process was as follows: 0.02C constant current charging to 3.6V, and the time limit was 120 min; then 0.1C constant current charging to 3.9V, and the time limit was 120 min, to obtain a lithium ion battery.

[0061] Comparative Example 2

[0062] This comparative example was only injected twice, and the specific steps included the following steps:

[0063] (1) Prepare a blank soft-pack battery to be injected (lithium ion battery soft-pack to be injected);

[0064] (2) The electrolyte is injected in two times as follows. After the two injections, the total weight of the electrolyte in the lithium ion battery soft-pack is 100%. First, the first electrolyte is used to inject the blank soft-pack battery to be injected for the first time. Then, the air is extracted and the opening is sealed. The liquid volume of the first electrolyte is 70% of the total weight of the electrolyte, and the first electrolyte is composed of the following mass percentage components: ethylene carbonate 90%, lithium hexafluorophosphate 6%, and vinylene carbonate 4%.

[0065] (3) After 72 hours of standing at room temperature, the battery is formed. The formation process is as follows: 0.02C constant current charging to a voltage of 3.6V, with a time limit of 120 minutes; then 0.1C constant current charging to a voltage of 3.9V, with a time limit of 120 minutes.

[0066] (4) The second electrolyte is injected from the air bag package side of the battery after formation using a syringe for the second time. The air is extracted and the opening is sealed. The liquid volume of the second electrolyte is 30% of the total weight of the electrolyte, and the second electrolyte is composed of the following mass percentage components: ethylene carbonate 80%, lithium hexafluorophosphate 70.83%, ethylene glycol dipropenoate 8.17%, and dibenzoyl peroxide 1%.

[0067] (5) The battery after the second injection of air sealing is placed in an oven at 80°C, and the in-situ polymerization gelation reaction is initiated by the temperature. The reaction time is 6 hours, and the lithium ion battery is obtained.

[0068] Table 1 Composition of each electrolyte

[0069]

[0070]

[0071] The lithium ion batteries prepared in the above examples and comparative examples were subjected to cycle performance tests. The cycle test used 1C constant current charging to 3.65V, followed by constant voltage charging to the cutoff current 0.05C, 1C constant current discharging to the cutoff voltage 2.5V, and standing for 30 minutes during the charging and discharging process. The cycle test results are shown in Table 2 and the accompanying Figure 1

[0072] Table 2

[0073]

[0074] ​It can be seen from the above Examples 1-3 and Comparative Examples 1-2 that, compared with the traditional method of one injection followed by gelation and formation, in the method of the present invention, a first electrolyte containing a lithium salt and a film-forming additive is first used for the first injection and formation. The electrolyte is sufficient, which is conducive to the interaction between lithium ions and the film-forming additive, thereby generating a solid electrolyte membrane (SEI) that is beneficial to improving the cycle performance of the lithium ion battery; then, a second electrolyte containing a gel polymer monomer and an initiator is used for the second injection and gelation. During this process, the electrolyte remains sufficient, which is beneficial to the interaction between the gel polymer monomer and the initiator, thereby generating a gel electrolyte layer that is beneficial to improving the cycle performance of the lithium ion battery; finally, a third electrolyte containing a gel polymer monomer is used for the third injection and allowed to stand. The gel polymer monomer in the third electrolyte provides material conditions for subsequent self-repair, which is beneficial to the stability of the gel electrolyte layer in the subsequent long cycle process of the battery, thereby improving the cycle performance of the lithium ion battery. The present invention first forms a complete solid electrolyte membrane through chemical formation, then performs gelation, and finally supplements gel polymer monomers to provide conditions for subsequent self-repair, so that a good solid electrolyte membrane can be formed during chemical formation while retaining the gelled monomers as a repair material for the subsequent gel electrolyte, thereby achieving the purpose of simultaneously improving the integrity and cycle stability of the solid electrolyte membrane and the gel electrolyte membrane, thereby improving the situation in which the solid electrolyte membrane is difficult to grow during the chemical formation of the gel electrolyte battery and the cycle performance is reduced due to damage to the gel electrolyte layer, and ultimately achieving improved cycle performance of the lithium ion battery.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for liquid injection formation of a lithium ion battery, characterized in that: The steps include: (1) Providing lithium-ion batteries to be liquefied; (2) injecting the first electrolyte into the lithium-ion battery to be injected and formed for the first time, then evacuating the battery, sealing the battery, and then allowing the battery to stand and undergo formation in sequence; The first electrolyte comprises the following components in percentage by weight: 70-90% solvent, 6-20% lithium salt, and 1-10% film-forming additive; The battery is charged at a constant current of 0.02-0.05C to a voltage of 2.75-3.6V, and then at a constant current of 0.1C-0.2C to a voltage of 3.6-4.1V. (3) injecting the formed lithium-ion battery with the second electrolyte for the second time, followed by evacuation, sealing, and gelation reaction; The second electrolyte comprises the following components in percentage by weight: 69-92.9% solvent, 0-20% lithium salt, 1-10% gel polymer monomer, and 0.1-1% initiator; (4) injecting the third electrolyte into the lithium-ion battery after the gelation reaction for the third time, then evacuating the battery, sealing the battery, and allowing the battery to stand; The third electrolyte comprises the following components in percentage by weight: 79-99% solvent, 0-20% lithium salt, 1-10% gel polymer monomer, and 0-1% initiator; In steps (2) to (4), taking the total mass percentage of the first electrolyte, the second electrolyte and the third electrolyte as 100%, the mass percentage of the first electrolyte is 70-90%, the mass percentage of the second electrolyte is 5-25%, and the mass percentage of the third electrolyte is 5-25%.

2. The method for forming a lithium ion battery by liquid injection according to claim 1, wherein: In step (3), the temperature of the gelation reaction is 30-80° C., and the time of the gelation reaction is 0.5-12 h.

3. The method for forming a lithium ion battery by liquid injection according to claim 1, wherein: In step (2), the standing temperature is room temperature, and the standing time is 24-72 hours.

4. The method for forming a lithium ion battery by liquid injection according to claim 1, wherein: In step (4), the standing temperature is 30-45° C., and the standing time is 12-72 h.

5. The method for forming a lithium ion battery by liquid injection according to claim 1, wherein: In steps (2) to (4), the solvent in each of the first electrolyte, the second electrolyte, and the third electrolyte is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, γ-butyrolactone, methyl formate, ethyl formate, methyl acetate, ethyl acetate, ethyl propionate, methyl butyrate, and ethyl butyrate.

6. The method for forming a lithium-ion battery by liquid injection according to claim 1, wherein: In steps (2) to (4), the lithium salt is each selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonylimide), lithium bis(fluorosulfonylimide), lithium difluorooxalatoborate, and lithium bis(oxalatoborate).

7. The method for forming a lithium-ion battery by liquid injection according to claim 1, wherein: In step (2), the film-forming additive includes at least one of vinylene carbonate, lithium dioxalatoborate, lithium tetrafluoroborate, lithium difluorophosphate, and lithium difluorooxalatoborate.

8. The method for forming a lithium ion battery by liquid injection according to claim 1, wherein: In step (3), the gel polymer monomer includes at least one of ethylene glycol diacrylate, methyl methacrylate, trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, acrylic acid, methacrylic acid, and triethylene glycol divinyl ether.

9. The method for forming a lithium ion battery by liquid injection according to claim 1, wherein: In step (4), the initiator includes one of dibenzoyl peroxide, azobisisobutyronitrile, dimethyl azobisisobutyrate, lauroyl peroxide, diisopropyl peroxydicarbonate, and dicyclohexyl peroxydicarbonate.

Images