A lithium ion battery and a preparation method thereof

Abstract

The application belongs to the technical field of electrochemical energy storage technology, and particularly relates to a lithium ion battery and a preparation method thereof. The lithium ion battery comprises a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte; the positive electrode comprises a positive electrode active material lithium iron phosphate; and the negative electrode comprises a negative electrode active material polyacrylonitrile sulfide. The positive electrode of the application adopts the extremely stable olivine-type LiFePO4, and has good thermal stability and is not easy to release oxygen at overcharge or high temperature; the negative electrode adopts SPAN, and the sulfur element exists in the form of a covalent bond, thereby avoiding the shuttling of soluble polysulfides in traditional lithium-sulfur batteries and the safety risks caused thereby, and the whole battery system does not use a metal lithium negative electrode, thereby fundamentally eliminating the short circuit hidden danger caused by lithium dendrite growth. In addition, through unique matching of the positive and negative electrode materials, a working voltage of about 1.2V is successfully achieved, thereby filling the market gap of high-performance 1.2V rechargeable lithium ion batteries.

Description

Technical Field

[0001] This application belongs to the field of electrochemical energy storage technology, specifically relating to a lithium-ion battery and its preparation method. Background Technology

[0002] With the rapid development of portable electronic devices, electric vehicles, and large-scale energy storage systems, the demand for high-performance rechargeable batteries is increasing. Lithium-ion batteries, with their high energy density, long cycle life, and lack of memory effect, have become the mainstream in the current market. Traditional commercial lithium-ion batteries, such as those using lithium iron phosphate, lithium cobalt oxide, ternary materials (NCM / NCA), or lithium manganese oxide cathodes with graphite anodes, typically operate at voltages in the range of 3.2-3.8V. Among these, lithium iron phosphate (LiFePO4, LFP), as a highly promising cathode material, has attracted much attention due to its stable olivine structure, low cost, environmental friendliness, excellent cycle performance, and high safety.

[0003] On the other hand, there are numerous applications in the market requiring a 1.2V operating voltage, currently dominated by nickel-cadmium (Ni-Cd) and nickel-metal hydride (Ni-MH) batteries. For example, many household appliances, remote controls, toys, and solar-powered garden lights use standard 1.2V AA / AAA batteries. However, Ni-Cd batteries contain highly toxic cadmium, posing a significant environmental hazard and are gradually being phased out. While Ni-MH batteries are relatively environmentally friendly, they suffer from low energy density, high self-discharge rates, and limited cycle life. Although current lithium-ion battery systems can reduce operating voltages above 3V to 1.2V using external voltage converters, these converters are expensive, increasing the overall cost of the battery system. Therefore, developing a novel battery system with superior performance, safety, environmental friendliness, low cost, and a 1.2V operating voltage is of significant practical and commercial value. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a lithium-ion battery and its preparation method, specifically adopting the following technical solution: In a first aspect, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte; The positive electrode includes lithium iron phosphate as the positive electrode active material; The negative electrode includes the negative electrode active material, vulcanized polyacrylonitrile.

[0005] The lithium-ion battery provided by the present invention includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte; wherein, (1) the positive electrode sheet is composed of a positive electrode current collector and a positive electrode material layer coated thereon. The positive electrode current collector is preferably aluminum foil. The positive electrode material layer contains 85-97% by mass of LiFePO4 active material, 1-10% by mass of conductive agent (such as conductive carbon black Super P, acetylene black, or graphene) and 1-8% by mass of binder (such as polyvinylidene fluoride PVDF or sodium carboxymethyl cellulose CMC). In a preferred embodiment, the surface of the LiFePO4 particles is treated with carbon coating to improve their electronic conductivity.

[0006] (2) Negative electrode sheet: Composed of a negative electrode current collector and a negative electrode material layer coated thereon. The negative electrode current collector is preferably copper foil. The negative electrode material layer contains 75-90% by mass of SPAN active material, 5-15% by mass of conductive agent and 5-10% by mass of binder. SPAN is prepared by heat treatment reaction of polyacrylonitrile (PAN) powder and elemental sulfur in an inert atmosphere (such as argon or nitrogen) at a temperature range of 250-600℃. The preferred reaction temperature is 300-500℃, the mass ratio of sulfur to PAN is (3-8):1, and the reaction time is 2-12 hours. In the obtained SPAN, sulfur element exists stably in the carbon skeleton in the form of covalent bonds, and its mass content is preferably 35-50 wt%.

[0007] (3) Electrolyte: An organic solvent system containing 1.0-1.5 M lithium salt is used. The lithium salt can be selected from LiPF6, LiBF4, LiTFSI, LiFSI, etc. The organic solvent is a mixture of chain carbonates (such as DMC, DEC, EMC) and cyclic carbonates (such as EC, PC), for example EC / DMC / DEC (1:1:1, v / v / v). To improve interfacial stability and cycle performance, 1-5% of film-forming additives, such as vinylene carbonate (VC) or fluoroethylene carbonate (FEC), can be added to the electrolyte.

[0008] (4) Membrane: Commercially available polyethylene (PE), polypropylene (PP) or PE / PP composite microporous membranes are used, with a thickness of 10-30 micrometers, and have good chemical stability and mechanical strength.

[0009] As a further preferred embodiment, the operating voltage of the lithium-ion battery during the charging and discharging process is 1.0V-1.4V.

[0010] This invention uses lithium iron phosphate (LiFePO4) as the positive electrode active material. LiFePO4 has an efficiency of approximately 3.4 V vs. Li / Li. +The stable discharge platform serves as the positive electrode potential reference for this invention. Secondly, sulfurized polyacrylonitrile (SPAN) is innovatively used as the negative electrode active material. In-depth research revealed that SPAN material exhibits approximately 2.2 V vs. Li / Li during the lithiation / delithiation process. + The electrochemical platform is described. When it is used as the negative electrode and matched with the LiFePO4 positive electrode, the theoretical operating voltage of the battery is the difference between the positive and negative electrode potentials, i.e., Vcell = Vcathode – Vanode ≈ 3.4 V - 2.2 V = 1.2 V. This discovery is key to achieving the target voltage of this invention.

[0011] As a further preferred embodiment, the non-aqueous electrolyte includes lithium salt, organic solvent and additives; The lithium salt is at least one of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), or lithium bis(fluorosulfonyl)imide (LiFSI); The organic solvent is a mixture of at least two of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0012] This invention uses a standard non-aqueous electrolyte containing lithium salt, organic solvent and necessary additives to ensure efficient and stable transport of lithium ions between the positive and negative electrodes.

[0013] As a further preferred embodiment, the diaphragm is a polyolefin microporous membrane or a polyolefin microporous membrane coated with ceramic particles, with a thickness of 10 μm-30 μm.

[0014] This invention employs a porous polyolefin membrane to physically isolate the positive and negative electrodes, preventing internal short circuits while allowing lithium ions to pass freely.

[0015] Secondly, the present invention provides a method for preparing the above-mentioned lithium-ion battery, comprising the following steps: Lithium iron phosphate, a positive electrode active material, a conductive agent, and a binder are mixed in a solvent to prepare a positive electrode slurry. The positive electrode slurry is then uniformly coated onto an aluminum foil current collector, and the positive electrode sheet is obtained after drying and rolling. A negative electrode slurry is prepared by mixing the negative electrode active material, vulcanized polyacrylonitrile, conductive agent and binder in a solvent. The negative electrode slurry is then uniformly coated onto a copper foil current collector, and the negative electrode sheet is obtained after drying and rolling. The positive electrode, separator, and negative electrode are stacked sequentially and placed in a battery casing. After injecting a non-aqueous electrolyte, the battery is encapsulated to obtain the lithium-ion battery.

[0016] As a further preferred embodiment, the mass percentage of the positive electrode active material lithium iron phosphate, conductive agent and binder in the positive electrode sheet is 85-97:1-10:1-8; The mass percentage of the negative electrode active material, vulcanized polyacrylonitrile conductive agent, and binder in the negative electrode sheet is 75-90: 5-15: 5-10.

[0017] As a further preferred embodiment, the negative electrode active material, vulcanized polyacrylonitrile, is prepared by heat treatment reaction of polyacrylonitrile and elemental sulfur at a temperature of 250℃-600℃ under an inert atmosphere.

[0018] As a further preferred embodiment, the mass ratio of polyacrylonitrile to elemental sulfur is 1:3-8.

[0019] As a further preferred embodiment, the sulfur content in the vulcanized polyacrylonitrile is 35wt%-50wt% of its total mass.

[0020] As a further preferred embodiment, the temperature of the heat treatment reaction is 300℃-500℃, and the time of the heat treatment reaction is 2h-12h.

[0021] The beneficial effects of this invention are as follows: (1) This invention achieves a working voltage of approximately 1.2V through unique matching of positive and negative electrode materials, which is perfectly compatible with and can replace existing Ni-Cd and Ni-MH batteries on the market, filling the market gap for high-performance 1.2V rechargeable lithium-ion batteries.

[0022] (2) The positive electrode of this invention adopts olivine-type LiFePO4 with an extremely stable structure, which has good thermal stability and is not easy to release oxygen under overcharge or high temperature. The negative electrode adopts SPAN, in which sulfur exists in the form of covalent bonds, avoiding the shuttle of soluble polysulfides in traditional lithium-sulfur batteries and the safety risks caused therefrom. The entire battery system does not use metallic lithium negative electrode, fundamentally eliminating the short circuit hazard caused by lithium dendrite growth.

[0023] (3) The LiFePO4 cathode used in this invention has excellent cycle stability; in addition, the charging and discharging process of the SPAN anode does not involve drastic volume changes, and its stable polymer skeleton ensures the integrity of the structure in multiple cycles. The combination of the two enables the battery system of this invention to achieve thousands of deep charge and discharge cycles, far exceeding Ni-MH batteries, and has an ultra-long cycle life.

[0024] (4) Compared with Ni-MH batteries (energy density of about 60-120 Wh / kg), the lithium-ion battery provided by the present invention is expected to achieve an energy density of 150-180 Wh / kg (with higher energy density) based on its higher specific capacity and operating voltage, and provide a longer driving time under the same volume or weight.

[0025] (5) The positive electrode material LiFePO4 used in this invention does not contain precious metals such as cobalt, and the main raw materials iron and phosphorus are abundant and inexpensive; the raw materials polyacrylonitrile and sulfur of the negative electrode SPAN are also inexpensive mass-market chemical products; the entire battery system does not contain toxic or harmful elements, is environmentally friendly, and conforms to the development trend of green energy. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 The diagram shows the charge and discharge voltage of a coin cell with a positive electrode active material to negative electrode active material capacity ratio of 1:0.3 and a cutoff voltage of 0.6-2.5V in Example 1. Figure 2 The diagram shows the charge and discharge voltage of a coin cell with a positive electrode active material to negative electrode active material capacity ratio of 1:0.5 and a cutoff voltage of 0.6-2.5V in Example 2. Figure 3 The diagram shows the charge and discharge voltage of a coin cell with a positive electrode active material to negative electrode active material capacity ratio of 1:1 and a cutoff voltage of 0.6-2.5V in Example 3. Figure 4 The diagram shows the charge and discharge voltage of a coin cell with a positive electrode active material to negative electrode active material capacity ratio of 1:1.2 and a cutoff voltage of 0.6-2.5V in Example 4. Figure 5 The diagram shows the charge and discharge voltage of a coin cell with a positive electrode active material to negative electrode active material capacity ratio of 1:1 and a cutoff voltage of 0.9-2.5V in Example 5. Figure 6 The figure shown is a cycle capacity curve of a coin cell with a positive electrode active material to negative electrode active material capacity ratio of 1:1 and a cutoff voltage of 0.9-2.5V in Example 5. Detailed Implementation

[0028] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0029] Example 1 A lithium-ion button battery, the preparation method of which includes the following steps: (1) Lithium iron phosphate, super-p conductive agent and polyvinylidene fluoride binder are mixed with 3.5g N-methyl-2-pyrrolidone in a mass ratio of 8:1:1 (total amount is 1g) to form a uniform slurry. The slurry is then uniformly coated onto aluminum foil using a coating method with a scraper of different heights. The slurry is then vacuum dried at 120℃ for 12h. After drying, the slurry is punched into a circular electrode sheet.

[0030] (2) Weigh 2g of sublimed sulfur and 1g of PAN, add 10g of anhydrous ethanol as a dispersant, transfer to a ball mill jar, and mix at 500 rpm for 6 hours. Then, place the ball-milled slurry in an 80℃ forced-air drying oven and remove it after the ethanol is completely dried. Place the dried powder in an agate mortar and grind it thoroughly. Weigh 2.5g of the powder and place it in a crucible, cover the crucible, and place it in a tube furnace under an argon atmosphere. Heat at 120℃, 200℃, and 350℃ for 3 hours at a heating rate of 3℃ / min to obtain vulcanized polyacrylonitrile.

[0031] (3) Mix SPAN, super-p conductive agent and LA-133 binder in a mass ratio of 8:1:1 (total amount is 1g), add 3g water and 1g alcohol to form a uniform slurry, and coat it evenly on copper foil using a coating method with a scraper of different heights. Dry it under vacuum at 120℃ for 12h. After drying, punch it into a circular electrode sheet.

[0032] (4) Using the lithium iron phosphate electrode prepared in step (1) as the positive electrode and the sulfurized polyacrylonitrile electrode prepared in step (3) as the negative electrode, select an electrode with a capacity ratio of 1:0.3 between the positive electrode active material and the negative electrode active material according to C=m×C0×n (m is the mass of the active material on the electrode; C0 is the theoretical specific capacity of the active material; n is the surface density coefficient), and use EC / DMC (volume ratio of 1:1) as the electrolyte and PP separator, assemble them into a button cell in a glove box.

[0033] Electrical performance testing: The obtained button cell battery was charged to 2.5V at 0.1C at 25±2℃, and then discharged to 0.6V at 0.1C. The results show that when the capacity ratio of the positive electrode active material to the negative electrode active material is 1:0.3, the initial discharge capacity at a 0.1C current density is 45 mAhg. -1After 100 cycles, the reversible discharge capacity is 37.79 mAhg. -1 .

[0034] Example 2 A lithium-ion button battery, the preparation method of which includes the following steps: (1) Lithium iron phosphate, super-p conductive agent and polyvinylidene fluoride binder are mixed with 3.5g N-methyl-2-pyrrolidone in a mass ratio of 8:1:1 (total amount is 1g) to form a uniform slurry. The slurry is then uniformly coated onto aluminum foil using a coating method with a scraper of different heights. The slurry is then vacuum dried at 120℃ for 12h. After drying, the slurry is punched into a circular electrode sheet.

[0035] (2) Weigh 2g of sublimed sulfur and 1g of PAN, add 10g of anhydrous ethanol as a dispersant, transfer to a ball mill jar, and mix at 500 rpm for 6 hours. Then, place the ball-milled slurry in an 80℃ forced-air drying oven and remove it after the ethanol is completely dried. Place the dried powder in an agate mortar and grind it thoroughly. Weigh 2.5g of the powder and place it in a crucible, cover the crucible, and place it in a tube furnace under an argon atmosphere. Heat at 120℃, 200℃, and 350℃ for 3 hours at a heating rate of 3℃ / min to obtain vulcanized polyacrylonitrile.

[0036] (3) Mix SPAN, super-p conductive agent and LA-133 binder in a mass ratio of 8:1:1 (total amount is 1g), add 3g water and 1g alcohol to form a uniform slurry, and coat it evenly on copper foil using a coating method with a scraper of different heights. Dry it in vacuum at 120℃ for 12h. After drying, punch it into a circular electrode sheet.

[0037] (4) Using the lithium iron phosphate electrode prepared in step (1) as the positive electrode and the sulfurized polyacrylonitrile electrode prepared in step (3) as the negative electrode, select an electrode with a positive electrode active material to negative electrode active material capacity ratio of 1:0.5 according to C=m×C0×n (m is the mass of active material on the electrode; C0 is the theoretical specific capacity of the active material; n is the areal density coefficient), and use EC / DMC (volume ratio of 1:1) as electrolyte and PP separator, assemble them into a button cell in a glove box.

[0038] Electrical performance testing: The obtained coin cells were charged to 2.5V at 0.1C at 25±2℃, and then discharged to 0.6V at 0.1C. The results show that when the capacity ratio of the positive electrode active material to the negative electrode active material is 1:0.5, the initial discharge capacity at a current density of 0.1C is 83.35 mAh g⁻¹. -1 After 100 cycles, the reversible discharge capacity is 72.73 mAh g. -1 .

[0039] Example 3 A lithium-ion button battery, the preparation method of which includes the following steps: (1) Lithium iron phosphate, super-p conductive agent and polyvinylidene fluoride binder are mixed with 3.5g N-methyl-2-pyrrolidone in a mass ratio of 8:1:1 (total amount is 1g) to form a uniform slurry. The slurry is then uniformly coated onto aluminum foil using a coating method with a scraper of different heights. The slurry is then vacuum dried at 120℃ for 12h. After drying, the slurry is punched into a circular electrode sheet.

[0040] (2) Weigh 2g of sublimed sulfur and 1g of PAN, add 10g of anhydrous ethanol as a dispersant, transfer to a ball mill jar, and mix at 500 rpm for 6 hours. Then, place the ball-milled slurry in an 80℃ forced-air drying oven and remove it after the ethanol is completely dried. Place the dried powder in an agate mortar and grind it thoroughly. Weigh 2.5g of the powder and place it in a crucible, cover the crucible, and place it in a tube furnace under an argon atmosphere. Heat at 120℃, 200℃, and 350℃ for 3 hours at a heating rate of 3℃ / min to obtain vulcanized polyacrylonitrile.

[0041] (3) Mix SPAN, super-p conductive agent and LA-133 binder in a mass ratio of 8:1:1 (total amount is 1g), add 3g water and 1g alcohol to form a uniform slurry, and use a coating method to uniformly coat it on copper foil with a scraper of different heights. Dry it in vacuum at 120℃ for 12h. After drying, punch it into a circular electrode sheet.

[0042] (4) Using the lithium iron phosphate electrode prepared in step (1) as the positive electrode and the sulfurized polyacrylonitrile electrode prepared in step (3) as the negative electrode, select an electrode with a positive electrode active material to negative electrode active material capacity ratio of 1:1 according to C=m×C0×n (m is the mass of active material on the electrode; C0 is the theoretical specific capacity of the active material; n is the areal density coefficient), and use EC / DMC (volume ratio of 1:1) as electrolyte and PP separator, assemble them into a button cell in a glove box.

[0043] Electrical performance testing: The obtained coin cells were charged to 2.5V at 0.1C at 25±2℃, and then discharged to 0.6V at 0.1C. The results show that when the capacity ratio of the positive electrode active material to the negative electrode active material is 1:1, the initial discharge capacity at a current density of 0.1C is 124.64 mAh g⁻¹. -1 After 100 cycles, the reversible discharge capacity is 101.81 mAhg. -1 .

[0044] Example 4 A lithium-ion button battery, the preparation method of which includes the following steps: (1) Lithium iron phosphate, super-p conductive agent and polyvinylidene fluoride binder are mixed with 3.5g N-methyl-2-pyrrolidone in a mass ratio of 8:1:1 (total amount is 1g) to form a uniform slurry. The slurry is then uniformly coated onto aluminum foil using a coating method with a scraper of different heights. The slurry is then vacuum dried at 120℃ for 12h. After drying, the slurry is punched into a circular electrode sheet.

[0045] (2) Weigh 2g of sublimed sulfur and 1g of PAN, add 10g of anhydrous ethanol as a dispersant, transfer to a ball mill jar, and mix at 500 rpm for 6 hours. Then, place the ball-milled slurry in an 80℃ forced-air drying oven and remove it after the ethanol is completely dried. Place the dried powder in an agate mortar and grind it thoroughly. Weigh 2.5g of the powder and place it in a crucible, cover the crucible, and place it in a tube furnace under an argon atmosphere. Heat at 120℃, 200℃, and 350℃ for 3 hours at a heating rate of 3℃ / min to obtain vulcanized polyacrylonitrile.

[0046] (3) Mix SPAN, super-p conductive agent and LA-133 binder in a mass ratio of 8:1:1 (total amount is 1g), add 3g water and 1g alcohol to form a uniform slurry, and coat it evenly on copper foil using a coating method with a scraper of different heights. Dry it in vacuum at 120℃ for 12h. After drying, punch it into a circular electrode sheet.

[0047] (4) Using the lithium iron phosphate electrode prepared in step (1) as the positive electrode and the sulfurized polyacrylonitrile electrode prepared in step (3) as the negative electrode, select an electrode with a capacity ratio of 1:1.2 between the positive electrode active material and the negative electrode active material according to C=m×C0×n (m is the mass of the active material on the electrode; C0 is the theoretical specific capacity of the active material; n is the areal density coefficient), and use EC / DMC (volume ratio of 1:1) as the electrolyte and PP separator, assemble them into a button cell in a glove box.

[0048] Electrical performance testing: The obtained coin cells were charged to 2.5V at 0.1C at 25±2℃, and then discharged to 0.6V at 0.1C. The results show that when the capacity ratio of the positive electrode active material to the negative electrode active material is 1:1.2, the initial discharge capacity at a current density of 0.1C is 77.96 mAh g⁻¹. -1 After 100 cycles, the reversible discharge capacity is 60.03 mAhg. -1 .

[0049] Example 5 A lithium-ion button battery, the preparation method of which includes the following steps: (1) Lithium iron phosphate, super-p conductive agent and polyvinylidene fluoride binder are mixed with 3.5g N-methyl-2-pyrrolidone in a mass ratio of 8:1:1 (total amount is 1g) to form a uniform slurry. The slurry is then uniformly coated onto aluminum foil using a coating method with a scraper of different heights. The slurry is then vacuum dried at 120℃ for 12h. After drying, the slurry is punched into a circular electrode sheet.

[0050] (2) Weigh 2g of sublimed sulfur and 1g of PAN, add 10g of anhydrous ethanol as a dispersant, transfer to a ball mill jar, and mix at 500 rpm for 6 hours. Then, place the ball-milled slurry in an 80℃ forced-air drying oven and remove it after the ethanol is completely dried. Place the dried powder in an agate mortar and grind it thoroughly. Weigh 2.5g of the powder and place it in a crucible, cover the crucible, and place it in a tube furnace under an argon atmosphere. Heat at 120℃, 200℃, and 350℃ for 3 hours at a heating rate of 3℃ / min to obtain vulcanized polyacrylonitrile.

[0051] (3) Mix SPAN, super-p conductive agent and LA-133 binder in a mass ratio of 8:1:1 (total amount is 1g), add 3g water and 1g alcohol to form a uniform slurry, and coat it evenly on copper foil using a coating method with a scraper of different heights. Dry it in vacuum at 120℃ for 12h. After drying, punch it into a circular electrode sheet.

[0052] (4) Using the lithium iron phosphate electrode prepared in step (1) as the positive electrode and the sulfurized polyacrylonitrile electrode prepared in step (3) as the negative electrode, select an electrode with a positive electrode active material to negative electrode active material capacity ratio of 1:1 according to C=m×C0×n (m is the mass of active material on the electrode; C0 is the theoretical specific capacity of the active material; n is the surface density coefficient), and use EC / DMC (volume ratio of 1:1) as electrolyte and PP separator, assemble them into a button cell in a glove box.

[0053] Electrical performance testing: The obtained coin cells were charged to 2.5V at 0.1C at 25±2℃, and then discharged to 0.9V at 0.1C. The results show that when the capacity ratio of the positive electrode active material to the negative electrode active material is 1:1, the initial discharge capacity at a current density of 0.1C is 116.1 mAhg. -1 After 100 cycles, the reversible discharge capacity is 108.67 mAhg. -1 After 250 cycles, the reversible discharge capacity is 105.50 mAhg. -1 Excellent cycle performance.

[0054] The embodiments of this application have been described above with reference to the accompanying drawings. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the core ideas of this application. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte; The positive electrode includes lithium iron phosphate as the positive electrode active material; The negative electrode includes the negative electrode active material, sulfurized polyacrylonitrile; the operating voltage of the lithium-ion battery during charging and discharging is 1.0V-1.4V.

2. The lithium-ion battery according to claim 1, characterized in that, The non-aqueous electrolyte includes lithium salts, organic solvents, and additives; The lithium salt is at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, or lithium bis(fluorosulfonyl)imide; The organic solvent is a mixture of at least two of ethylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

3. The lithium-ion battery according to claim 1, characterized in that, The diaphragm is a polyolefin microporous membrane or a polyolefin microporous membrane coated with ceramic particles, with a thickness of 10 μm-30 μm.

4. The method for preparing a lithium-ion battery according to any one of claims 1-3, characterized in that, Includes the following steps: Lithium iron phosphate, a positive electrode active material, a conductive agent, and a binder are mixed in a solvent to prepare a positive electrode slurry. The positive electrode slurry is then uniformly coated onto an aluminum foil current collector, and the positive electrode sheet is obtained after drying and rolling. A negative electrode slurry is prepared by mixing the negative electrode active material, vulcanized polyacrylonitrile, conductive agent and binder in a solvent. The negative electrode slurry is then uniformly coated onto a copper foil current collector, and the negative electrode sheet is obtained after drying and rolling. The positive electrode, separator, and negative electrode are stacked sequentially and placed in a battery casing. After injecting a non-aqueous electrolyte, the battery is encapsulated to obtain the lithium-ion battery.

5. The preparation method according to claim 4, characterized in that, The mass percentage of the positive electrode active material lithium iron phosphate, conductive agent and binder in the positive electrode sheet is 85-97:1-10:1-8; The mass percentage of the negative electrode active material, vulcanized polyacrylonitrile conductive agent, and binder in the negative electrode sheet is 75-90: 5-15: 5-10.

6. The preparation method according to claim 4, characterized in that, The negative electrode active material, vulcanized polyacrylonitrile, is prepared by heat treatment reaction of polyacrylonitrile and elemental sulfur at a temperature of 250℃-600℃ under an inert atmosphere.

7. The preparation method according to claim 6, characterized in that, The mass ratio of polyacrylonitrile to elemental sulfur is 1:3-8.

8. The preparation method according to claim 7, characterized in that, The sulfur content in vulcanized polyacrylonitrile is 35 wt%-50 wt% of its total mass.

9. The preparation method according to claim 6, characterized in that, The temperature of the heat treatment reaction is 300℃-500℃, and the time of the heat treatment reaction is 2h-12h.

Images