High-safety lithium battery and preparation method thereof

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a high-safety lithium battery and a preparation method thereof. The lithium battery comprises a positive plate, a negative plate, a diaphragm, a high-flame-retardant electrolyte and a ceramic fiber membrane, the high-flame-retardant electrolyte comprises the following raw materials: an organic solvent, a lithium salt, a functional additive and a polymer. Through the formula design of the flame-retardant electrolyte obtained by matching triethyl phosphate, hexachlorocyclotriphosphazene and tri (trimethylsilane) borate ternary additives with the brominated polymer, and in combination with the integrated innovation of the ceramic fiber membrane, the thermal safety boundary is greatly improved while the cycle performance of the battery is basically maintained, and the service life of the battery is prolonged. And the potential safety hazard of the high-energy-density lithium battery is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a high-safety lithium battery and a preparation method thereof. BACKGROUND

[0002] With the explosive growth of demand for high energy density energy storage in new energy vehicles, smart grids and portable electronic devices, the safety of lithium ion batteries as the core power source has become a key bottleneck restricting the development of the industry. Traditional lithium batteries generally use liquid electrolytes based on carbonate systems. Although this system has excellent ion conduction ability and electrode compatibility, the inherent low flash point and high volatility of organic solvents make it extremely easy to cause combustion accidents under conditions of thermal abuse, mechanical abuse or electrical abuse. Especially under the background of the continuous improvement of energy density driven by advanced materials systems such as high-nickel ternary and silicon-carbon anodes, the propagation speed of internal thermal runaway of the battery is accelerated, further amplifying the flammability risk of the electrolyte.

[0003] The current industry mainly approaches from three technical paths to improve the safety of the battery, but all have significant limitations:

[0004] 1. Flame retardant additive modification: by introducing flame-retardant elements such as phosphorus and halogen into the electrolyte, the flammability of the solvent can be reduced to some extent. However, single-component additives such as phosphates or fluorinated compounds often cause serious side effects - phosphate esters hinder lithium ion migration due to high viscosity, significantly degrading the rate performance; halogen compounds are prone to electrochemical decomposition during cycling, destroying the stability of the solid electrolyte interface film (SEI) and accelerating capacity decay. More importantly, such additives are difficult to form an effective condensed phase barrier layer at high temperatures, which cannot block the thermal runaway chain reaction.

[0005] 2. Development of gel polymer electrolytes: gel systems based on polyvinylidene fluoride copolymer (PVDF-HFP), polyacrylonitrile (PAN) and the like, by physically absorbing liquid electrolyte to form a semi-solid structure, theoretically combining the safety of solid-state batteries with the high ionic conductivity of liquid batteries. However, in practical applications, the polymer network is prone to swelling and cracking under high liquid absorption conditions during long-term charging and discharging, leading to electrolyte leakage; at the same time, organic solvent molecules still have the ability to move freely in the polymer backbone, and the possibility of combustion cannot be fundamentally eliminated.

[0006] 3. Modification of the function of the separator: inorganic ceramic particles such as aluminum oxide and silicon dioxide are used to coat the surface of the polyolefin separator, which can improve its thermal stability and delay heat diffusion. However, the interfacial adhesion between the ceramic layer and the polymer matrix is weak, and it is easy to peel off under electrode winding or cyclic stress, and the detached particles not only block the pores of the separator, causing ion transport to be hindered, but also may pierce the separator, causing internal short circuit of the detached electrode powder. SUMMARY

[0007] In view of the deficiencies of the prior art, the present application provides a high-safety lithium battery with excellent flame-retardant performance, excellent thermal runaway inhibition capability and excellent battery cycle performance.

[0008] To achieve the above-mentioned purpose, the present application discloses the following technical solutions:

[0009] In a first aspect, the present application provides a high-safety lithium battery, which comprises a positive electrode sheet, a negative electrode sheet, a separator, a high-flame-retardant electrolyte and a ceramic fiber membrane.

[0010] The high-flame-retardant electrolyte comprises the following raw materials: an organic solvent, a lithium salt, a functional additive and a polymer.

[0011] The preparation method of the high-flame-retardant electrolyte comprises the following steps:

[0012] (1) first dissolve the lithium salt in the organic solvent, then add the functional additive to obtain an electrolyte;

[0013] (2) add the polymer to the electrolyte and mix uniformly to obtain the high-flame-retardant electrolyte.

[0014] Preferably, the high-flame-retardant electrolyte comprises the following raw materials: 6-11% lithium salt, 3-5% functional additive, 18-20% polymer and organic solvent.

[0015] Preferably, the organic solvent is at least one of ethylene carbonate, dimethyl carbonate and diethyl carbonate.

[0016] Preferably, the lithium salt is at least one of lithium hexafluorophosphate and lithium bis(trifluoromethanesulfonyl)imide.

[0017] Preferably, the polymer is poly(vinylidene fluoride)-hexafluoropropylene copolymer and poly(3-bromostyrene) in a mass ratio of (2-3):1.

[0018] Preferably, the functional additive is composed of triethyl phosphate, hexachlorocyclotriphosphazene and tris(trimethylsilyl)borate in a mass ratio of 1:(1-2):(0.5-1).

[0019] Preferably, the ceramic fiber membrane is a silicon oxide ceramic fiber membrane.

[0020] Further preferably, the silicon oxide ceramic fiber membrane is prepared by an electrospinning process; wherein the thickness of the silicon oxide ceramic fiber membrane is 50-100 microns and the porosity is 40%-60%.

[0021] Preferably, the separator is a polypropylene (PP) separator.

[0022] In a second aspect, the application provides a preparation method of the high-safety lithium battery, comprising the following steps:

[0023] The positive electrode sheet, the separator, the ceramic fiber membrane, the separator and the negative electrode sheet are sequentially stacked, and the stacked bare battery cell is wound in the same direction to obtain a bare battery cell, and then the high-flame-retardant electrolyte is injected after packaging, and then the high-safety lithium battery is obtained through the processes of packaging, storage, formation, aging, secondary packaging, capacity grading and detection.

[0024] Preferably, the positive electrode sheet, the separator, the ceramic fiber membrane, the separator and the negative electrode sheet are sequentially stacked, and the stacked bare battery cell is wound in the same direction to obtain a bare battery cell, and then the high-flame-retardant electrolyte is injected after packaging, and then the high-safety lithium battery is obtained through the processes of packaging, storage, formation, aging, secondary packaging, capacity grading and detection.

[0025] Preferably, the bare battery cell is packaged with an aluminum plastic film and then the high-flame-retardant electrolyte is injected.

[0026] The application has the following beneficial effects:

[0027] The application uses the flame-retardant electrolyte formula design obtained by combining the ternary additive of triethyl phosphate, hexachlorocyclotriphosphazene and tris(trimethylsilyl) borate with the brominated polymer, and integrates the ceramic fiber membrane, thereby substantially maintaining the cycle performance of the battery while greatly improving the thermal safety boundary, and solving the safety hidden danger of the high-energy-density lithium battery. DETAILED DESCRIPTION

[0028] Those skilled in the art can improve the process parameters as appropriate based on the content herein. In particular, it should be pointed out that all similar replacements and changes are obvious to those skilled in the art, and they are considered to be included in the application.

[0029] The products and methods of the application have been described by preferred embodiments, and relevant personnel can obviously make changes or appropriate changes and combinations to the products and methods described herein without departing from the content, spirit and scope of the application, to realize and apply the technical solutions of the application.

[0030] Preparation of high-flame-retardant electrolyte

[0031] Step 1. The raw materials are accurately weighed according to the mass fraction in Table 1.

[0032] Step 2. Dissolve the lithium salt in the organic solvent first, and then add the functional additive to obtain the electrolyte.

[0033] Step 3. Add the polymer to the electrolyte and mix uniformly to obtain the high-flame-retardant electrolyte.

[0034] wherein,

[0035] The organic solvent is at least one of ethylene carbonate, dimethyl carbonate and diethyl carbonate.

[0036] The lithium salt is at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide;

[0037] The polymer is poly(vinylidene fluoride)-hexafluoropropylene copolymer and poly(3-bromostyrene) in a mass ratio of (2-3):1;

[0038] The functional additive is composed of triethyl phosphate, hexachlorocyclotriphosphazene and tris(trimethylsilyl)borate in a mass ratio of 1:(1-2):(0.5-1).

[0039] Table 1 mass percentage of raw materials of high flame-retardant electrolyte

[0040]

[0041]

[0042] Microporous ceramic fiber membrane

[0043] The material is selected from silicon oxide (SiO2), and a silicon oxide ceramic fiber membrane with a thickness of 50-100 μm and a porosity of 40-60% is prepared by an electrostatic spinning process, which has electrolyte wettability and insulation, and the silicon oxide ceramic fiber can be commercially available, and the silicon oxide ceramic fiber membrane used in the examples and comparative examples of the present application has a thickness of 66.5±1 μm and a porosity of 54±1%.

[0044] Preparation of positive electrode sheet

[0045] Lithium iron phosphate positive electrode active material, acetylene black and polyvinylidene fluoride are fully stirred and mixed in an appropriate amount of N-methylpyrrolidone in a mass ratio of 97:2:1 to obtain a positive electrode active material slurry; the positive electrode active material slurry is coated on the surface of the positive electrode current collector aluminum foil, and after drying, cold pressing and die cutting, a positive electrode sheet is obtained.

[0046] Preparation of negative electrode sheet

[0047] Artificial graphite, acetylene black, butadiene styrene rubber and sodium carboxymethyl cellulose are fully stirred in an appropriate amount of deionized water in a mass ratio of 95:1:3:1 to form a uniform negative electrode active material slurry; the negative electrode active material slurry is coated on the surface of the negative electrode current collector copper foil, and after drying, cold pressing and die cutting, a negative electrode active material layer is formed on the surface of the copper foil to obtain a negative electrode sheet.

[0048] Preparation of Example 1

[0049] The positive electrode sheet, the separator, the microporous ceramic fiber membrane, the separator, and the negative electrode sheet are sequentially stacked, the alignment error between layers is less than or equal to 0.1 mm on the premise of ensuring OVERHANG, the bare battery is obtained after being wound in the same direction after being stacked, and the battery after being injected with the high-flame-retardant electrolyte ① is packaged, stored, formed, aged, secondarily packaged, distributed, and detected to obtain a high-safety lithium battery; wherein the separator is a polypropylene (PP) separator.

[0050] Preparation of Example 2

[0051] The positive electrode sheet, the separator, the microporous ceramic fiber membrane, the separator, and the negative electrode sheet are sequentially stacked, the alignment error between layers is less than or equal to 0.1 mm on the premise of ensuring OVERHANG, the bare battery is obtained after being wound in the same direction after being stacked, and the battery after being injected with the high-flame-retardant electrolyte ① is packaged, stored, formed, aged, secondarily packaged, distributed, and detected to obtain a high-safety lithium battery; wherein the separator is a polypropylene (PP) separator.

[0052] Preparation of Example 3

[0053] The positive electrode sheet, the separator, the microporous ceramic fiber membrane, the separator, and the negative electrode sheet are sequentially stacked, the alignment error between layers is less than or equal to 0.1 mm on the premise of ensuring OVERHANG, the bare battery is obtained after being wound in the same direction after being stacked, and the battery after being injected with the high-flame-retardant electrolyte ① is packaged, stored, formed, aged, secondarily packaged, distributed, and detected to obtain a high-safety lithium battery; wherein the separator is a polypropylene (PP) separator.

[0054] Preparation of the electrolyte in the comparative example

[0055] Step 1. The raw materials are accurately weighed according to the mass fraction in Table 2;

[0056] Step 2. First, the lithium salt is dissolved in the organic solvent, and then the functional additive is added to obtain the electrolyte;

[0057] Step 3. The polymer is added to the electrolyte and mixed uniformly to obtain the high-flame-retardant electrolyte.

[0058] Table 2 Mass percentage of raw materials of the comparative electrolyte

[0059]

[0060]

[0061] Note: " / " in the table means no addition, and the comparative electrolyte in the table is based on the formula of the high-flame-retardant electrolyte ②, and the necessity of the components is verified by controlling the variables.

[0062] Preparation of Comparative Example 1

[0063] The positive electrode sheet, the separator, the microporous ceramic fiber membrane, the separator, and the negative electrode sheet were sequentially stacked, the alignment error between layers was less than or equal to 0.1 mm on the premise of ensuring OVERHANG on both sides of each layer, and the bare battery was obtained after winding in the same direction after stacking. The battery after injecting the comparative electrolyte 1 was packaged, placed, formed, aged, secondarily packaged, and detected to obtain the lithium battery of Comparative Example 1; wherein the separator was a polypropylene (PP) separator.

[0064] Preparation of Comparative Example 2

[0065] The positive electrode sheet, the separator, the microporous ceramic fiber membrane, the separator, and the negative electrode sheet were sequentially stacked, the alignment error between layers was less than or equal to 0.1 mm on the premise of ensuring OVERHANG on both sides of each layer, and the bare battery was obtained after winding in the same direction after stacking. The battery after injecting the comparative electrolyte 2 was packaged, placed, formed, aged, secondarily packaged, and detected to obtain the lithium battery of Comparative Example 2; wherein the separator was a polypropylene (PP) separator.

[0066] Preparation of Comparative Example 3

[0067] The positive electrode sheet, the separator, the microporous ceramic fiber membrane, the separator, and the negative electrode sheet were sequentially stacked, the alignment error between layers was less than or equal to 0.1 mm on the premise of ensuring OVERHANG on both sides of each layer, and the bare battery was obtained after winding in the same direction after stacking. The battery after injecting the comparative electrolyte 3 was packaged, placed, formed, aged, secondarily packaged, and detected to obtain the lithium battery of Comparative Example 3; wherein the separator was a polypropylene (PP) separator.

[0068] Preparation of Comparative Example 4

[0069] The positive electrode sheet, the separator, the microporous ceramic fiber membrane, the separator, and the negative electrode sheet were sequentially stacked, the alignment error between layers was less than or equal to 0.1 mm on the premise of ensuring OVERHANG on both sides of each layer, and the bare battery was obtained after winding in the same direction after stacking. The battery after injecting the comparative electrolyte 4 was packaged, placed, formed, aged, secondarily packaged, and detected to obtain the lithium battery of Comparative Example 4; wherein the separator was a polypropylene (PP) separator.

[0070] Preparation of Comparative Example 5

[0071] The positive electrode sheet, the separator, and the negative electrode sheet are sequentially stacked, and each layer is aligned with an error of ≤0.1 mm under the premise of ensuring OVERHANG, and the stacked bare battery is wound in the same direction to obtain a bare battery, and the bare battery is packaged with an aluminum plastic film, and the battery after injection of high-flame-retardant electrolyte ② is subjected to packaging, storage, formation, aging, secondary packaging, capacity grading, and detection processes to obtain the lithium battery of Comparative Example 5; wherein the separator is a polypropylene (PP) separator.

[0072] Performance test

[0073] 1. Normal temperature cycle performance test

[0074] At 25°C, the lithium batteries of Examples 1-3 and Comparative Examples 1-5 are charged at 0.2C constant current and constant voltage to 3.65V, with a cutoff current of 0.02C, and then discharged at 0.2C constant current to 2.0V, and the cycle is repeated, and the capacity retention rate at the 500th cycle is calculated after 500 cycles of charge and discharge, and the calculation formula is as follows:

[0075] N(%) = N 500 / N1x 100%

[0076] In the formula: N1 is the discharge capacity at the first cycle;

[0077] N 2500 is the discharge capacity at the 500th cycle;

[0078] N is the capacity retention rate at the 500th cycle, %.

[0079] Table 3: Normal temperature cycle performance test results

[0080] Group 500 cycle capacity retention rate / % Example 1 94.17 Example 2 95.44 Example 3 95.29 Comparative Example 1 96.41 Comparative Example 2 93.68 Comparative Example 3 95.04 Comparative Example 4 94.62 Comparative Example 5 92.10

[0081] 2. Electrolyte self-extinguishing time test

[0082] The self-extinguishing time refers to the time required for a unit mass of experimental sample to be ignited and naturally extinguished, and is an index widely used to measure the combustion ability of combustible materials. A 0.2g high-flame-retardant electrolyte ①-③ and a comparative electrolyte ①-④ are respectively absorbed by a 5mm diameter non-combustible glass fiber ball, which is ignited and the burning time of the glass fiber ball is recorded, and the burning time of a unit mass of electrolyte sample is calculated, and each group is repeated three times, and the average value is taken.

[0083] The calculation formula is as follows:

[0084] S = T / M

[0085] In the formula: T is the time experienced by the experimental sample from being ignited to being naturally extinguished, in seconds;

[0086] M is the mass of the experimental sample, in grams.

[0087] Table 4 electrolyte burning time

[0088]

[0089]

[0090] 3. Battery heat radiation test

[0091] The lithium batteries obtained from Examples 1-3 and Comparative Examples 1-5 were subjected to 450℃ heat radiation, and the state of the batteries and the change in battery voltage at each time period under continuous high-temperature radiation were observed, and the observation time lasted for 200s, and the results are shown in Table 5.

[0092] Table 5 test results

[0093]

[0094]

[0095] Result analysis

[0096] According to the results in Table 4, the burning time of the high-flame-retardant electrolytes 1-3 is much lower than that of the comparative electrolytes 1-4, which proves that the flame-retardant system composed of poly(3-bromostyrene), triethyl phosphate, hexachlorocyclotriphosphazene and tris(trimethylsilyl) borate provided by the present application can effectively improve the flame retardancy of the electrolyte. The comparative electrolytes 1-4 respectively lack four components, resulting in a 2-3 times longer burning time, indicating that the four components are indispensable and have a synergistic effect of improving the flame-retardant efficiency.

[0097] According to the results in Table 5, the heat runaway suppression ability of Examples 1-3 is excellent, compared with the comparative examples, the initial bulging time is significantly prolonged, the short circuit phenomenon is significantly prolonged, and the burning duration is significantly shortened; compared with Comparative Example 5, Example 2 lacks a silicon oxide ceramic fiber membrane, resulting in a shortened time of bulging and short circuit phenomenon, which proves that the ceramic fiber membrane plays a role of isolating the positive current collector and the negative current collector in the battery, reducing the short circuit phenomenon, at the same time, the ceramic fiber membrane delays heat diffusion, and delays the heat runaway phenomenon by physically isolating heat conduction.

[0098] According to the electrochemical performance results in Table 3, the capacity retention rate of Examples 1-3 is 94.17-95.44%, which is close to that of Comparative Example 1 (96.41%), indicating that the introduction of the bromine-containing polymer does not significantly sacrifice the cycle life; the bromine element of poly(3-bromostyrene) may slightly affect the SEI film, and the capacity retention rate is slightly higher when Comparative Example 1 is not added, but its flame-retardant contribution is much greater than the negative effect.

[0099] In summary, the application solves the safety hidden trouble of high energy density lithium battery by integrating the innovative design of flame-retardant electrolyte formula (phosphoric acid triethyl ester, hexachlorocyclotriphosphazene and tris(trimethylsilyl) borate ternary additive + brominated polymer) and ceramic fiber membrane, while substantially maintaining the battery cycle performance, greatly improving the thermal safety boundary.

[0100] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A high safety lithium battery, characterized in that, The lithium battery comprises a positive electrode sheet, a negative electrode sheet, a diaphragm, a high flame-retardant electrolyte and a ceramic fiber membrane. The high flame-retardant electrolyte comprises the following raw materials: an organic solvent, a lithium salt, a functional additive and a polymer. The preparation method of the high flame-retardant electrolyte comprises the following steps: (1) first, the lithium salt is dissolved in the organic solvent, and then the functional additive is added to obtain an electrolyte; (2) the polymer is added to the electrolyte and uniformly mixed to obtain the high flame-retardant electrolyte.

2. The lithium battery of claim 1, wherein, The organic solvent is at least one of ethylene carbonate, dimethyl carbonate and diethyl carbonate.

3. The lithium battery of claim 1, wherein, The lithium salt is at least one of lithium hexafluorophosphate and lithium bis-trifluoromethanesulfonimide.

4. The lithium battery of claim 1, wherein, The polymer is polyvinylidene fluoride-hexafluoropropylene copolymer and poly(3-bromostyrene) with a mass ratio of (2-3):

1.

5. The lithium battery of claim 1, wherein, The functional additive is composed of triethyl phosphate, hexachlorocyclotriphosphazene and tris(trimethylsilyl)borate with a mass ratio of 1:(1-2):(0.5-1).

6. The lithium battery of claim 1, wherein, The ceramic fiber membrane is a silicon oxide ceramic fiber membrane.

7. The lithium battery of claim 6, wherein, The silicon oxide ceramic fiber membrane is prepared by an electrostatic spinning process; wherein the thickness of the silicon oxide ceramic fiber membrane is 50-100 microns, and the porosity is 40-60%.

8. The lithium battery of claim 1, wherein, The diaphragm is a polypropylene (PP) diaphragm.

9. The method of producing a high safety lithium battery according to any one of claims 1 to 8, characterized in that, The method comprises the following steps: The positive electrode sheet, the diaphragm, the ceramic fiber membrane, the diaphragm and the negative electrode sheet are sequentially stacked, and then wound in the same direction to obtain a bare battery cell; the high flame-retardant electrolyte is injected after packaging; and then the high safety lithium battery is obtained through the processes of packaging, storage, formation, aging, secondary packaging, capacity distribution and detection.

10. The lithium battery of claim 9, wherein, After the positive electrode sheet, the diaphragm, the ceramic fiber membrane, the diaphragm and the negative electrode sheet are sequentially stacked, the alignment error between layers is less than or equal to 0.1 mm on the premise of ensuring OVERHANG.

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