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

Abstract

The application discloses a high-safety soft package lithium ion battery and a preparation method thereof. The battery comprises a cell main body bag, and a gas bag is arranged at the side of the cell main body bag. Microcapsules are arranged in the gas bag, and the microcapsules contain a flame retardant. The connection part of the gas bag and the cell main body bag is a double-sealed edge area A. The gas bag further comprises a middle area B and an outer sealed edge area C. The sealing strength of the double-sealed edge is lower than that of the side sealed edge and the top sealed edge. When thermal runaway occurs, the gas generated in the cell main body bag breaks through the connection part of the gas bag and the cell main body bag first, so that the gas bag and the cell main body bag are connected. In the application, the microcapsules of the high-molecular polymer are separated from the cell main body. When the battery has an out-of-control reaction and a combustion reaction, the generated gas breaks through the double-sealed edge area A with low sealing strength first and enters the middle area B. The microcapsules contain a gas-liquid phase change material, which expands and releases the internal flame retardant into the soft package cell to achieve flame retardation.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a high-safety soft-pack lithium-ion battery and its preparation method. Background Technology

[0002] Lithium-ion batteries have significant advantages such as high operating voltage, high energy density, low self-discharge rate, and no memory effect. However, while achieving high energy density, their safety issues have also attracted widespread attention. While increasing energy density, it is necessary to improve safety protection to prevent lithium batteries from catching fire and exploding due to thermal runaway.

[0003] The safety of pouch lithium-ion cells is typically improved through two aspects. First, material modification involves adding high-boiling-point, high-flash-point, and non-flammable solvents or additives to improve electrolyte stability. However, since the electrolyte directly participates in the battery's chemical reactions, the addition of flame-retardant solvents and additives directly affects the cell's capacity, internal resistance, and cycle performance. Furthermore, the selection of additives needs to minimize the impact of the SEI film and prevent redox reactions at high potentials, making additive selection challenging and significantly increasing electrolyte costs. Second, structural design utilizes thicker foils and separators to enhance mechanical strength and thermal shrinkage, preventing deformation and contact between the positive and negative electrodes during thermal runaway. However, this increases the cell's thickness, compromising its high energy density.

[0004] The present invention addresses the aforementioned technical problems. Summary of the Invention

[0005] Based on the above-mentioned shortcomings of the existing technology, the present invention provides a high-safety soft-pack lithium-ion battery and its preparation method. The present invention can reduce the safety problems of thermal runaway of the battery cell without increasing the cost of electrolyte, increasing the thickness of the cell, or affecting the chemical system of the cell.

[0006] The technical solution of this invention is as follows:

[0007] This invention relates to a high-safety soft-pack lithium-ion battery, comprising a main cell bag, an airbag on the side of the main cell bag, and microcapsules containing flame retardants inside the airbag. In the event of thermal runaway, the gas generated inside the main cell bag preferentially breaks through the connection between the airbag and the main cell bag, thereby connecting the airbag and the main cell bag.

[0008] Preferably, after the battery cell body is packaged, it forms a side seal, a top seal, and a second seal. The connection between the airbag and the battery cell body is located at the second seal, and the packaging strength of the second seal is lower than that of the side seal and the top seal.

[0009] Preferably, the connection between the airbag and the main cell bag is referred to as the second sealing area A. The airbag also includes a middle area B and an outer sealing area C. The microcapsule is disposed inside the middle area B. One end of the second sealing area A is connected to the main cell bag, and the other end of the second sealing area A is bent upward to form the middle area B. The top of the middle area B is bent towards the side closer to the main cell bag to form the outer sealing area C.

[0010] Preferably, the end of the outer sealing edge region C is folded downwards.

[0011] Preferably, the encapsulation strength of the second sealing region A is lower than that of the outer sealing region C. More preferably, the encapsulation strength of the second sealing region A is 70% of that of the outer sealing region C.

[0012] Preferably, in the deployed state of the airbag, the width of the second sealing area A is 1.5-2.5mm, the width of the middle area B is 3.5-4.5mm, and the width of the outer sealing area C is 4-5mm.

[0013] Preferably, the microcapsule comprises a capsule wall and a capsule core, the microcapsule having a particle size of 500 nm-50 μm, and the capsule wall having a thickness of 10-50 nm. The flame-retardant polymer microcapsules are separated from the battery cell body and do not participate in the reaction during normal battery cell operation. The polymer material is not subject to electrolyte corrosion or high-potential oxidation, and does not increase ionic or electronic conductivity.

[0014] Preferably, the material used to make the capsule wall is one or more of polymethyl methacrylate, polyethylene glycol, and polyurethane;

[0015] The core contains a flame retardant and a phase change material. The flame retardant is one or more of the following: halogenated flame retardants (chlorinated paraffin, chlorinated alicyclic hydrocarbons, tetrachlorophthalic anhydride, decabromodiphenyl ether, decabromodiphenyl ethane tetrabromobisphenol A), phosphorus-based flame retardants (red phosphorus, polyammonium polyphosphate, phosphatidyl phosphate, triphenyl phosphate, trimethyl phosphate, melamine phosphate, phosphate esters), and organosilicon flame retardants (polysiloxane, siloxane resin, polysiloxane-polycarbonate copolymer). The phase change material is DMC (dimethyl carbonate). This invention locks the DMC solution within microcapsules. The polymer microcapsules, being solid substances, ensure a certain mechanical strength and provide partial sustained-release of the DMC, thereby raising the lower limit of the thermal runaway temperature.

[0016] Preferably, the core is a DMC (boiling point 90.2°C) solution containing flame retardant.

[0017] Preferably, the mass of the microcapsule is 1-5 wt% of the total weight of the battery cell.

[0018] This invention also relates to a method for preparing the aforementioned high-safety pouch lithium-ion battery. This invention pertains to a pouch cell, utilizing commonly used pouch aluminum-plastic film, eliminating the need for laser welding, and employing conventional packaging. The method includes the following steps:

[0019] (1) The aluminum-plastic film is punched to form a punching groove, leaving the punched shell in the middle area B.

[0020] (2) Place the bare cell into the cell body, perform normal welding, encapsulation, liquid injection, formation, and assemble the cell. After the cell body is encapsulated, it forms the side sealing edge, top sealing edge and second sealing edge area A.

[0021] (3) After the second sealing, add the microcapsules to the middle area B;

[0022] (4) Encapsulate the outer edge area C.

[0023] Preferably, after step (4), the battery is folded and tape is applied.

[0024] The beneficial effects of this invention are:

[0025] (1) In this invention, the polymer microcapsules are separated from the main body of the battery cell. During thermal runaway, a large amount of heat and gas are generated in the main body of the battery cell due to the decomposition of the electrolyte and SEI film. The internal pressure of the battery cell increases. After thermal runaway, the large amount of gas and heat generated in the main body of the battery cell preferentially breaks through the second sealing edge region A with low encapsulation strength. The gas and the transferred heat enter the middle region B. The microcapsules contain gas-liquid phase change materials, which expand when heated and release the internal flame retardant, which enters the soft-pack battery cell to achieve flame retardancy.

[0026] (2) In this invention, DMC solution is locked in microcapsules. The polymer microcapsules are solid substances, which ensure a certain mechanical strength and play a partial role in the slow release of DMC, thereby increasing the lower limit of the temperature of thermal runaway. The gas-liquid phase change material DMC solution rapidly vaporizes when it is above its boiling point, changing from liquid to gas, increasing the pressure in the region. In addition, DMC can also be used as a solvent for dispersing flame retardants.

[0027] (3) Compared with the prior art, the present invention reduces the safety problem of thermal runaway of the battery cell by improving the structure of the battery cell without changing the material system or introducing new substances during the entire battery operation process, and does not affect the electrochemical performance of the battery cell. The method of the present invention is simple to operate and low in cost. Attached Figure Description

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0029] Figure 1 This is a schematic diagram of a soft-pack lithium-ion battery when the airbag is in the deployed state.

[0030] Figure 2 This is a cross-sectional view of a soft-pack lithium-ion battery after folding.

[0031] Figure 3 This is a schematic diagram illustrating the working principle during thermal runaway;

[0032] Figure 4 This is a schematic diagram of the aluminum-plastic film after the deep drawing process;

[0033] Figure 5 This is a picture of the battery cell of the present invention after overcharging.

[0034] The markings in the diagram are: 1. Battery cell body bag; 2. Airbag bag; 3. Side seal; 4. Top seal; A. Second seal area A; B. Middle area B; C. Outer seal area C. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0036] like Figure 1 and Figure 2 As shown, a high-safety soft-pack lithium-ion battery includes a main cell pouch 1, an airbag 2 on the side of the main cell pouch 1, and microcapsules inside the airbag 2, the mass of which is 1-5 wt% of the total weight of the cell. After the main cell pouch 1 is sealed, it forms a side seal 3, a top seal 4, and a second seal. The connection between the airbag 2 and the main cell pouch 1 is located at the second seal.

[0037] The connection between the airbag 2 and the main cell bag 1 is designated as the second sealing area A. The airbag 2 also includes a middle area B and an outer sealing area C. The microcapsule is located inside the middle area B. The sealing strength of the second sealing area A is lower than that of the outer sealing area C. More preferably, the sealing strength of the second sealing area A is 70% of that of the outer sealing area C. Both the second sealing area A and the outer sealing area C are heat-sealed with aluminum-plastic film, and different heat-sealing temperatures and times are selected. The sealing strength of the second sealing area A is required to be lower than that of the other side sealing areas 3 and top sealing areas 4 to ensure that in the event of thermal runaway, the generated gas preferentially breaks through the aluminum-plastic film of the second sealing area A and enters the airbag containing the polymer microcapsule. The capsule shell is ruptured by the impact of hydrofluoric acid and high temperature, releasing the internal flame retardant, which comes into contact with the electrolyte and diffuses into the cell to rapidly participate in the flame retardant reaction.

[0038] One end of the second sealing area A is connected to the main body of the battery cell, the other end of the second sealing area A is bent upward to form the middle area B, the top of the middle area B is bent towards the side closer to the main body of the battery cell, forming the outer sealing area C, and the end of the outer sealing area C is folded downward. Preferably, in the unfolded state of the airbag 2, the width of the second sealing area A is 1.5-2.5mm, the width of the middle area B is 3.5-4.5mm, and the width of the outer sealing area C is 4-5mm.

[0039] The microcapsules consist of a capsule wall and a core. The microcapsule size is 500 nm-50 μm, and the capsule wall thickness is 10-50 nm. The capsule wall is made of one or more of polymethyl methacrylate, polyethylene glycol, and polyurethane. The core is a DMC (boiling point 90.2℃) solution containing a flame retardant, wherein the flame retardant is one or more of halogenated flame retardants (chlorinated paraffin, chlorinated alicyclic hydrocarbons, tetrachlorophthalic anhydride, decabromodiphenyl ether, decabromodiphenyl ethane tetrabromobisphenol A), phosphorus-based flame retardants (red phosphorus, polyammonium polyphosphate, phosphatidyl phosphate, triphenyl phosphate, trimethyl phosphate, melamine phosphate, phosphate ester), or organosilicon flame retardants (polysiloxane, siloxane resin, polysiloxane-polycarbonate copolymer). This invention locks the DMC solution within the microcapsules. The polymer microcapsules are solid substances, ensuring a certain mechanical strength and providing partial sustained-release of DMC, thereby raising the lower limit of the thermal runaway temperature.

[0040] like Figure 3 As shown, this invention separates the polymer microcapsules from the main body of the battery cell. When the soft-pack lithium-ion battery undergoes a runaway reaction or a combustion reaction, the generated gas preferentially breaks through the low-strength second-side sealing region A and enters the middle region B containing the polymer microcapsules. The microcapsules contain a gas-liquid phase change material, which expands when heated (above 90°C) and releases the internal flame retardant, which enters the interior of the soft-pack battery cell to achieve flame retardancy.

[0041] A method for preparing a high-safety soft-pack lithium-ion battery specifically includes the following steps:

[0042] (1) The aluminum-plastic film is subjected to a deep punching process to form a deep punching groove, wherein the depth of a single groove a1 is 4mm, leaving a punched shell in area B. The width of the punched shell in area B is 4mm, and the depth of the punched shell a2 is 3mm. (Details are as follows...) Figure 4 As shown;

[0043] (2) The wound bare cell (including positive and negative electrode plates and separator) is placed into the cell body bag, and then normally welded, packaged, injected with liquid, and formed to form a cell. After the cell body bag is packaged, it forms side sealing edge, top sealing edge and second sealing edge area A.

[0044] (3) After the second sealing, the microcapsules are added to the intermediate region B at 3.5 wt% of the total weight of the cell;

[0045] (4) Encapsulate region C at a temperature of 180°C for 3 seconds.

[0046] (5) Fold the battery edges and apply tape.

[0047] In existing technologies, battery cells can catch fire after overcharging, while the soft-pack lithium-ion batteries manufactured using the process described in this application, such as Figure 5 As shown, when the battery cell is overcharged, it generates significant gas but does not ignite. Compared with existing technologies, this invention reduces the safety issues of thermal runaway in the battery cell by improving its structure without changing the material system or introducing new substances during the entire battery operation process, and without affecting the electrochemical performance of the battery cell. The method of this invention is simple to operate and low in cost.

[0048] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A high-safety soft-pack lithium-ion battery, characterized in that, The device includes a main cell bag, with an airbag on the side of the main cell bag. The airbag contains microcapsules containing flame retardants. In the event of thermal runaway, the gas generated in the main cell bag will preferentially break through the connection between the airbag and the main cell bag, thus connecting the airbag and the main cell bag. The microcapsule includes a capsule wall and a capsule core, and the capsule wall is made of one or more of polymethyl methacrylate, polyethylene glycol, and polyurethane. The core contains a flame retardant and a phase change material. The flame retardant is one or more of the following: chlorinated paraffin, chlorinated alicyclic hydrocarbon, tetrachlorophthalic anhydride, decabromodiphenyl ether, decabromodiphenyl ethane tetrabromobisphenol A, red phosphorus, polyammonium polyphosphate, phosphatidyl phosphate, triphenyl phosphate, trimethyl phosphate, melamine phosphate, phosphate ester, polysiloxane, siloxane resin, and polysiloxane-polycarbonate copolymer. The phase change material is DMC.

2. The high-safety soft-pack lithium-ion battery according to claim 1, characterized in that, After the main body of the battery cell is packaged, it forms a side seal, a top seal, and a second seal. The connection between the airbag and the main body of the battery cell is located at the second seal. The packaging strength of the second seal is lower than that of the side seal and the top seal.

3. A high-safety soft-pack lithium-ion battery according to claim 2, characterized in that, The connection between the airbag and the main cell bag is referred to as the second sealing area A. The airbag also includes a middle area B and an outer sealing area C. The microcapsule is disposed inside the middle area B. One end of the second sealing area A is connected to the main cell bag, and the other end of the second sealing area A is bent upward to form the middle area B. The top of the middle area B is bent towards the side closer to the main cell bag to form the outer sealing area C.

4. A high-safety soft-pack lithium-ion battery according to claim 3, characterized in that, The end of the outer edge sealing area C is folded downwards.

5. A high-safety soft-pack lithium-ion battery according to claim 3, characterized in that, The encapsulation strength of the second sealing region A is lower than that of the outer sealing region C.

6. A high-safety soft-pack lithium-ion battery according to claim 1, characterized in that, The microcapsules have a particle size of 500nm-50μm and a capsule wall thickness of 10-50nm.

7. A high-safety soft-pack lithium-ion battery according to claim 1, characterized in that, The mass of the microcapsule is 1-5 wt% of the total weight of the battery cell.

8. A method for preparing a high-safety soft-pack lithium-ion battery according to any one of claims 1-7, characterized in that, Specifically, the following steps are included: (1) The aluminum-plastic film is punched to form a punching groove, leaving the punched shell in the middle area B. (2) Place the bare cell into the cell body bag, perform normal welding, encapsulation, liquid injection, formation, and assemble the cell. After the cell body bag is sealed, it forms the side sealing edge, top sealing edge and second sealing edge area A. (3) After the second sealing, add the microcapsules to the middle area B; (4) Encapsulate the outer edge area C.

9. The method for preparing a high-safety soft-pack lithium-ion battery according to claim 8, characterized in that, After step (4), fold the battery edges and apply tape.

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