High-safety lithium ion soft package battery and preparation method thereof

Abstract

The invention discloses a high-safety lithium ion soft package battery and a preparation method thereof, and belongs to the technical field of new energy batteries. The high-safety lithium ion soft package battery comprises a current collector base material and an electrode slurry layer, a safe priming coat is arranged between the current collector base material and the electrode slurry layer, and the safe priming coat contains flame-retardant microcapsules and a conductive agent; the flame-retardant microcapsule comprises a core layer and a shell layer, the core layer is an organic flame retardant and / or an inorganic flame retardant, and the shell layer is a heat-sensitive polymer. The needling passing rate can be increased, the problems caused by thermal runaway are reduced, and the safety performance of the lithium ion battery is improved.

Description

Technical Field

[0001] The present invention relates to a high - safety lithium - ion soft - pack battery and a preparation method thereof, belonging to the technical field of new - energy batteries. Background Art

[0002] Lithium - ion batteries are an indispensable part of new - energy vehicles and 3C products such as mobile phones and computers. With the development of society and the improvement of people's living standards, lithium - ion batteries are developing towards high energy density and high power density. Therefore, when applied, extremely high requirements are placed on the safety performance of lithium - ion batteries. However, lithium - ion batteries have poor thermal stability. When the battery undergoes thermal runaway, it is easy to cause a fire, thus threatening people's lives and property safety.

[0003] The prior art solves the problem caused by battery thermal runaway by adding flame retardants to the electrolyte and controlling the fire through the flame - retardant effect of the flame retardants. However, this method will affect the cycle stability performance of the battery. Summary of the Invention

[0004] Aiming at the above - mentioned deficiencies of the prior art, the present invention provides a high - safety lithium - ion soft - pack battery and a preparation method thereof, which can improve the puncture passing rate, reduce the problems caused by thermal runaway, and enhance the safety performance of lithium - ion batteries.

[0005] The first aspect of the present invention relates to a high - safety lithium - ion soft - pack battery, comprising: a current - collector substrate and an electrode paste layer;

[0006] A safety primer layer is provided between the current - collector substrate and the electrode paste layer, and the safety primer layer contains flame - retardant microcapsules and a conductive agent;

[0007] The flame - retardant microcapsules include a core layer and a shell layer. Among them, the core layer is an organic flame retardant and / or an inorganic flame retardant, and the shell layer is a thermosensitive polymer.

[0008] For some specific embodiments, the weight ratio of the flame - retardant microcapsules to the conductive agent is (3 - 7):(9 - 15).

[0009] For some specific embodiments, the organic flame retardant includes at least one of bromine - based, nitrogen - phosphorus - based, and nitrogen - containing compounds, the inorganic flame retardant includes at least one of magnesium hydroxide, antimony trioxide, aluminum hydroxide, and silicon - based compounds, and the thermosensitive polymer includes at least one of urea - formaldehyde resin, polyacrylamide, and polyurethane.

[0010] For some specific embodiments, the current - collector substrate is copper foil or aluminum foil.

[0011] The second aspect of the present invention relates to a preparation method of a high - safety lithium - ion soft - pack battery, comprising:

[0012] Steps for preparing flame-retardant microcapsules: The in-situ polymerization method is used to prepare flame-retardant microcapsules with an organic flame retardant and / or an inorganic flame retardant as the core layer and a heat-sensitive polymer as the shell layer;

[0013] Steps for preparing the bottom coating slurry: By weight, 9-15 parts of a conductive agent, 3-7 parts of flame-retardant microcapsules, 0.2-1 part of a dispersant, and 0.2-1 part of a binder are dispersed in 76-87.6 parts of deionized water. The above materials total 100 parts by weight, and are mixed evenly to obtain the bottom coating slurry;

[0014] Steps for preparing the electrode sheet: The bottom coating slurry and the electrode slurry are sequentially coated on the current collector substrate to obtain a positive electrode sheet and a negative electrode sheet respectively;

[0015] Steps for battery assembly: The positive electrode sheet, the separator, and the negative electrode sheet are assembled into a battery using the stacking process, an electrolyte is injected, and the soft-pack battery is obtained by encapsulation.

[0016] For some specific embodiments, the coating thickness of the bottom coating slurry on the current collector substrate is 1-3 μm.

[0017] For some specific embodiments, the conductive agent is at least one of acetylene black, carbon black, carbon nanotubes, and graphene; the dispersant is at least one of polydimethylsiloxane and PVP; the binder is a polyacrylic acid binder.

[0018] For some specific embodiments, the electrode slurry is divided into a positive electrode slurry and a negative electrode slurry;

[0019] The positive electrode slurry contains a ternary lithium battery positive electrode material, a conductive agent, a binder, and a solvent; the conductive agent is at least one of carbon nanotubes, acetylene black, and graphene, the binder is PVDF and / or PTFE, and the solvent is NMP;

[0020] The negative electrode slurry contains a negative electrode active material, a conductive agent, and a binder; the negative electrode active material is at least one of graphite, silicon oxide, silicon carbon, and hard carbon, the conductive agent is carbon nanotubes and / or acetylene black, and the binder is at least one of SBR, PAA, and CMC.

[0021] Compared with the prior art, the present invention has the following technical effects:

[0022] For a pouch cell, the present invention provides a safety bottom coating containing flame retardant microcapsules and a conductive agent on a current collector substrate. In the case of damaging the battery during a nail penetration test and during thermal runaway, the flame retardant microcapsules can rupture to release a flame retardant, improving the safety performance of the lithium-ion battery. The above design does not require large-scale modification of the internal structure of the battery, which not only reduces production costs but also avoids the risk of reducing the electrochemical performance of the battery and does not have an adverse impact on the cycle stability performance of the battery. Detailed implementation manners

[0023] The present invention will be described in detail below in conjunction with specific implementation manners. Experimental methods without specific conditions noted in the examples are carried out according to conventional methods and conditions.

[0024] Example 1

[0025] The process of preparing a high-safety lithium-ion pouch cell in this example is as follows.

[0026] S1, Dissolve urea and formaldehyde with a molar mass ratio of 1:1.5 in water, add an appropriate amount of NaOH solution until the pH of the mixed solution reaches 8-9, then heat to 70 °C, keep warm for 60 min, add 60 ml of water and cool to room temperature to obtain a first mixed solution;

[0027] Add 2.5 g of aluminum diethylphosphinate (ADP) to the first mixed solution, stir for 10 min to mix evenly to obtain a second mixed solution; then add 200 μL each of dodecylphenol polyoxyethylene ether (OP-10) and fatty alcohol polyoxyethylene ether (JFC emulsifier), heat to 50 °C, and keep warm for 10 min;

[0028] Add 10 mL of 0.05 g / mL NH4Cl solution, continue to heat and keep warm at 50 °C for 1 h, then dropwise add citric acid to adjust the solution pH = 2-4, then raise the heating temperature to 70 °C, keep warm for 2 h, and finally cool at room temperature for 24 h;

[0029] Filter the above solution by suction, then wash it three times with deionized water and then three times with ethanol to obtain a white solid product, heat and dry it for 24 h to obtain flame retardant microcapsules ADP@UF, where UF is urea-formaldehyde resin;

[0030] S2, By weight, disperse 10 parts of a conductive agent, 3 parts of flame retardant microcapsules, 0.5 part of a dispersant, and 0.5 part of a binder in 86 parts of deionized water, stir and mix evenly to obtain a bottom coating slurry;

[0031] S3, Coat the above bottom coating slurry on both sides of the current collector aluminum foil and copper foil respectively, and the single-sided coating thickness is 1 μm;

[0032] S4. Coat the ternary cathode slurry on the aluminum foil current collector with the undercoat slurry, and coat the negative graphite slurry on the copper foil current collector with the undercoat slurry. Then assemble the cathode, separator, and anode in a stacked manner to form a soft-pack battery.

[0033] The ternary cathode slurry is a mixed slurry of ternary cathode, conductive agent, and binder with a weight ratio of 96.5:2:1.5.

[0034] The negative electrode slurry is a mixed slurry of graphite, conductive agent, and binder with a weight ratio of 96:1.5:2.5.

[0035] The separator is a ceramic-coated PE separator.

[0036] Example 2

[0037] Assemble the cathode electrode sheet coated with a 1-μm thick safety undercoat slurry on both sides and the negative electrode sheet without the undercoat slurry into a battery according to the normal process of assembling a soft-pack battery.

[0038] Example 3

[0039] Compared with Example 2, the only difference in this example is that the single-sided coating thickness is 2 μm for both.

[0040] Example 4

[0041] Compared with Example 2, the only difference in this example is that the weight fraction of the flame-retardant microcapsules is increased to 7 parts, and the weight fraction of deionized water is correspondingly reduced by 4 parts.

[0042] Example 5

[0043] Compared with Example 2, the only difference in this example is that the weight fraction of the conductive agent is increased to 15 parts, and the weight fraction of deionized water is correspondingly reduced by 5 parts.

[0044] Example 6

[0045] Compared with Example 2, the only difference in this example is that the undercoat slurry is not coated on the positive current collector substrate, while the undercoat slurry is coated on the negative current collector substrate.

[0046] Comparative Example 1

[0047] Compared with Example 1, the difference in this comparative example is that the undercoat slurry is not prepared, and the electrode slurry is directly coated on the current collector substrate.

[0048] Comparative Example 2

[0049] Compared with Example 1, the difference in this comparative example is that there is no flame-retardant microcapsule ADP@UF in the undercoat slurry, and the weight fraction of deionized water is correspondingly increased by 3 parts.

[0050] Comparative Example 3

[0051] Compared with Comparative Example 2, the difference in this comparative example is that the graphite anode slurry is coated after the primer slurry is coated.

[0052] The batteries prepared in the above examples and comparative examples were subjected to a needle-punch safety performance test, and the obtained data are shown in Table 1.

[0053] Table 1 Needle-punch safety performance test result table Group 100% SOC 80% SOC 50% SOC 30% SOC Example 1 5 / 5 5 / 5 5 / 5 5 / 5 Example 2 3 / 5 5 / 5 5 / 5 5 / 5 Example 3 4 / 5 5 / 5 5 / 5 5 / 5 Example 4 4 / 5 4 / 5 5 / 5 5 / 5 Example 5 3 / 5 4 / 5 5 / 5 5 / 5 Example 6 3 / 5 5 / 5 5 / 5 5 / 5 Comparative Example 1 1 / 5 3 / 5 4 / 5 5 / 5 Comparative Example 2 0 / 5 2 / 5 4 / 5 5 / 5 Comparative Example 3 0 / 5 2 / 5 4 / 5 5 / 5

[0054] It can be seen from the data in the table that the flame-retardant microcapsule safety primer slurry greatly improves the needle-punch safety performance of the battery cell. When the flame-retardant microcapsule primer slurry is coated on both the copper foil and aluminum foil current collectors at the same time, the probability that the battery cell passes the needle-punch at 100% SOC can reach 100%. In the case of only double-sided coating of the positive electrode sheet, the probability of passing the needle-punch at 80% SOC is at least 80%. Compared with the battery cell without coating the flame-retardant microcapsule safety primer slurry at all, the safety performance is greatly improved.

[0055] It should be emphasized that the above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A high-safety lithium-ion soft-pack battery, characterized in that, Comprising: a current collector substrate and an electrode paste layer; a safety primer layer is provided between the current collector substrate and the electrode paste layer, and the safety primer layer contains flame retardant microcapsules and a conductive agent; the flame retardant microcapsules include a core layer and a shell layer, wherein the core layer is an organic flame retardant and / or an inorganic flame retardant, and the shell layer is a heat-sensitive polymer.

2. The high-safety lithium-ion soft-pack battery according to claim 1, wherein The weight ratio of the flame retardant microcapsules to the conductive agent is (3 - 7):(9 - 15).

3. The high-safety lithium-ion soft-pack battery according to claim 1, wherein The organic flame retardant includes at least one of bromine-based, nitrogen-phosphorus-based, and nitrogen-containing compounds, the inorganic flame retardant includes at least one of magnesium hydroxide, antimony trioxide, aluminum hydroxide, and silicon-based, and the heat-sensitive polymer includes at least one of urea-formaldehyde resin, polyacrylamide, and polyurethane.

4. The high-safety lithium-ion soft-pack battery according to claim 1, wherein, The current collector substrate is copper foil or aluminum foil.

5. A method for preparing a high-safety lithium-ion soft-pack battery according to any one of claims 1 to 4, characterized in that, Comprising: Steps for preparing flame retardant microcapsules: preparing flame retardant microcapsules with an organic flame retardant and / or an inorganic flame retardant as the core layer and a heat-sensitive polymer as the shell layer by in-situ polymerization; Steps for preparing the primer paste: dispersing 9 - 15 parts by weight of a conductive agent, 3 - 7 parts by weight of flame retardant microcapsules, 0.2 - 1 part of a dispersant, and 0.2 - 1 part of a binder in 76 - 87.6 parts by weight of deionized water, mixing evenly to obtain the primer paste, and the above materials total 100 parts by weight; Steps for preparing the electrode sheet: coating the primer paste and the electrode paste on the current collector substrate in sequence to obtain a positive electrode sheet and a negative electrode sheet respectively; Steps for assembling the battery: assembling the positive electrode sheet, the separator, and the negative electrode sheet into a battery by a stacking process, injecting an electrolyte, and encapsulating to obtain a soft-pack battery.

6. The preparation method according to claim 5, characterized in that, The flame retardant microcapsules are ADP@UF, and the preparation steps specifically include: S11, dissolving urea and formaldehyde with a molar mass ratio of 1:1.5 in water, adding an appropriate amount of NaOH solution until the pH of the mixed solution reaches 8 - 9, then heating to 70 °C, keeping warm for 60 min, adding 60 ml of water and cooling to room temperature to obtain a first mixed solution; S12, adding 2.5 g of aluminum diethylphosphinate to the first mixed solution, stirring for 10 min and mixing evenly to obtain a second mixed solution; then adding 200 μL each of dodecylphenol polyoxyethylene ether and fatty alcohol polyoxyethylene ether, heating to 50 °C, and keeping warm for 10 min; S13, adding 10 mL of a 0.05 g / mL NH4Cl solution, continuing to heat and keep warm at 50 °C for 1 h, then dropping citric acid to adjust the solution pH = 2 - 4, then raising the heating temperature to 70 °C, keeping warm for 2 h, and finally cooling at room temperature for 24 h; S14, filtering the above solution by suction, then washing three times with deionized water and then three times with ethanol to obtain a white solid product, heating and drying for 24 h to obtain the flame retardant microcapsules ADP@UF.

7. The preparation method according to claim 5, characterized in that, The coating thickness of the primer paste on the current collector substrate is 1 - 3 μm.

8. The preparation method according to claim 5, characterized in that, The conductive agent is at least one of acetylene black, carbon black, carbon nanotubes, and graphene; the dispersant is at least one of polydimethylsiloxane and PVP; the binder is a polyacrylic acid-based binder.

9. The preparation method according to claim 5, characterized in that, The electrode paste is divided into a positive electrode paste and a negative electrode paste; The described positive electrode slurry contains a ternary lithium battery positive electrode material, a conductive agent, a binder, and a solvent; the conductive agent is at least one of carbon nanotubes, acetylene black, and graphene, the binder is PVDF and / or PTFE, and the solvent is NMP; The described negative electrode slurry contains a negative electrode active material, a conductive agent, and a binder; the negative electrode active material is at least one of graphite, silicon oxide, silicon carbide, and hard carbon, the conductive agent is carbon nanotubes and / or acetylene black, and the binder is at least one of SBR, PAA, and CMC.