Fast-charging lithium-ion battery, and preparation method therefor and application thereof

Abstract

The present disclosure relates to the technical field of lithium-ion batteries, and provides a fast-charging lithium-ion battery, and a preparation method therefor and an application thereof. Specifically, a positive electrode of the lithium-ion battery comprises lithium iron phosphate and a positive electrode additive; the positive electrode additive comprises at least one of lithium ferrite, lithium oxalate, and lithium squarate; an electrolyte of the lithium-ion battery comprises a solvent, a lithium salt, and electrolyte additives; the solvent includes a low-viscosity solvent with a viscosity of ≤0.5 cps; and the electrolyte additives include a carbonate-based additive, a sulfur-containing additive, and a lithium salt additive. The lithium-ion battery of the present disclosure can effectively improve the fast-charging performance and low-temperature performance of lithium iron phosphate batteries, without causing degradation in the cycle performance and high-temperature performance of batteries. That is, the lithium-ion battery takes into account various electrical properties and has a good application prospect.

Description

A fast-charging lithium-ion battery, its preparation method and application

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 2024109941659, filed on July 24, 2024, entitled "A Fast-Charging Lithium-ion Battery and Its Preparation Method and Application", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of lithium-ion battery technology, and more specifically, to a fast-charging lithium-ion battery, its preparation method, and its application. Background Technology

[0004] Lithium-ion rechargeable batteries boast advantages such as high energy density, long cycle life, and environmental friendliness. In recent years, with the increasing competition in the new energy vehicle market (e.g., continuously rising demands for driving range, fast charging, low cost, and safety performance), developing lithium-ion power batteries that balance energy density and fast charging performance has become a powerful way to meet market demands and enhance corporate competitiveness and survival. Lithium iron phosphate batteries, due to their good thermal stability and safety performance, moderate energy density, and relatively low cost, have gradually gained a dominant position in the new energy vehicle battery market.

[0005] However, due to its poor kinetic properties, lithium iron phosphate (LFP) materials exhibit relatively poor low-temperature and fast-charging performance. Furthermore, the iron leaching problem at the positive electrode of LFP materials can damage the SEI (Sediment Interphase) at the negative electrode. To ensure its cycle and high-temperature performance, the electrolyte typically contains a larger amount of negative electrode film-forming additives such as vinylene carbonate (usually more than twice that of ternary lithium batteries). This results in a higher negative electrode interface impedance for LFP cells, exacerbating their disadvantages in fast charging and low-temperature performance.

[0006] Traditional methods for improving fast-charging performance require increasing the amount of low-resistance additives or reducing the total amount of negative electrode film-forming additives, but this sacrifices the cell's cycle life and high-temperature performance. Improving the fast-charging performance of lithium iron phosphate batteries while balancing cell cycle life and high-temperature performance can be achieved by optimizing the conductive electron network of the electrode sheets, optimizing the porosity of the positive and negative electrode sheets, and improving the ionic conductivity of the electrolyte. Currently, the ionic conductivity of traditional carbonate solvent systems has reached a bottleneck. Low-viscosity carboxylic esters (such as ethyl acetate, methyl propionate, methyl acetate, etc.) and nitrile solvents (such as acetonitrile, fluoroacetonitrile, propionitrile, etc.) can significantly improve the ionic conductivity of the electrolyte and reduce the ohmic impedance of the cell; however, these low-viscosity solvents generally have worse compatibility with the negative electrode than carbonates, requiring more negative electrode film-forming additives for protection, leading to a further increase in the negative electrode interface impedance of the cell.

[0007] In view of this, this disclosure is made to provide a solution that can effectively improve the cycle performance and fast charging performance of lithium iron phosphate cells.

[0008] Application content

[0009] The primary objective of this disclosure is to provide a fast-charging lithium-ion battery that addresses the technical deficiency of the inability to simultaneously achieve fast-charging performance and high / low temperature performance. By defining the electrolyte, electrolyte additives, positive electrode lithium replenishment additives, and their dosage ratios, a specific combination of a positive electrode sheet and a high lithium-ion conductivity electrolyte is achieved. This combination can simultaneously and significantly reduce the ohmic impedance of the battery liquid phase and the interface impedance of the negative electrode, thereby significantly improving the fast-charging and low-temperature performance of lithium iron phosphate cells without causing a decrease in cell cycle performance and high-temperature performance.

[0010] The second objective of this disclosure is to provide a method for preparing the fast-charging lithium-ion battery, which is simple and easy to implement and can meet the needs of mass production.

[0011] A third objective of this disclosure is to provide an electrical appliance.

[0012] In order to achieve the above-mentioned objectives of this disclosure, the following technical solution is adopted:

[0013] A fast-charging lithium-ion battery, wherein the positive electrode of the lithium-ion battery comprises lithium iron phosphate and a positive electrode additive; the positive electrode additive comprises at least one of lithium iron phosphate, lithium oxalate and lithium squartz oxide;

[0014] The electrolyte of the lithium-ion battery includes a solvent, a lithium salt, and electrolyte additives; the solvent includes a low-viscosity solvent with a viscosity ≤0.5 cps; the electrolyte additives include carbonate additives, sulfur-containing additives, and lithium salt additives.

[0015] The method for preparing the fast-charging lithium-ion battery includes the following steps:

[0016] The raw material components of the lithium-ion battery positive electrode are thoroughly mixed to prepare a positive electrode slurry; the slurry is then coated onto an aluminum foil current collector using a double-layer coating method and dried to obtain a positive electrode sheet.

[0017] The raw material components of lithium-ion battery electrolyte are thoroughly mixed to obtain the electrolyte;

[0018] A fast-charging lithium-ion battery is prepared by assembling a positive electrode, a negative electrode, a separator, and an electrolyte.

[0019] An electrical device comprising the aforementioned lithium-ion battery. Detailed Implementation

[0020] The technical solutions of this disclosure will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of this disclosure, not all embodiments, and are only used to illustrate this disclosure, and should not be regarded as limiting the scope of this disclosure. Based on the embodiments in this disclosure, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this disclosure. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially. In addition, the terms "a", "b", "1", "2", etc. are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0021] The first aspect of this disclosure is to provide a fast-charging lithium-ion battery, which belongs to the category of secondary batteries.

[0022] The positive electrode of the lithium-ion battery includes lithium iron phosphate and a positive electrode additive; the positive electrode additive includes at least one of lithium iron phosphate, lithium oxalate, and lithium squaric acid; the electrolyte of the lithium-ion battery includes a solvent, a lithium salt, and an electrolyte additive; the solvent includes a low-viscosity solvent with a viscosity ≤0.5 cps; the electrolyte additive includes carbonate additives, sulfur-containing additives, and lithium salt additives.

[0023] Furthermore, the positive electrode additive is lithium ferrite.

[0024] Furthermore, with the mass ratio of the positive electrode additive to the positive electrode slurry being W1, where 0.3% ≤ W1 ≤ 1%, in some embodiments, the value of W1 includes, but is not limited to, any one or any two of the following: 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, and 1%. It should be noted that the preparation of the "positive electrode slurry" is a necessary step in the conventional electrode preparation process in this field; it is a slurry obtained by mixing the positive electrode active material, positive electrode additive, and other components (such as conductive agents, binders, etc.) with a solvent.

[0025] Furthermore, with the mass ratio of the low-viscosity solvent to the electrolyte being W2, 20% ≤ W2 ≤ 60%, in some embodiments, the value of W2 includes, but is not limited to, any one or any two of 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, and 60%.

[0026] Furthermore, with the mass ratio of the carbonate additive to the electrolyte being W3, 4% ≤ W3 ≤ 6%, in some embodiments, the value of W3 includes, but is not limited to, any one or any two of 4%, 4.2%, 4.5%, 4.8%, 5%, 5.2%, 5.5%, 5.8%, and 6%.

[0027] Furthermore, with the mass ratio of the sulfur-containing additive to the electrolyte being W4, 0.3% ≤ W4 ≤ 2%, in some embodiments, the value of W4 includes, but is not limited to, any one or any two of the following: 0.3%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.5%, 1.6%, 1.8%, and 2%.

[0028] Furthermore, with the mass ratio of lithium salt additive to electrolyte being W5, 0.3% ≤ W5 ≤ 1%, in some embodiments, the value of W5 includes, but is not limited to, any one or any two of the following: 0.3%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.5%, 1.6%, 1.8%, and 2%.

[0029] Furthermore, the weight ratio of each component in the lithium-ion battery satisfies the following relationship: 0.12≤(W3+W4+W5) / W2≤0.23, which means that the ratio of the total amount of electrolyte additives to the amount of low-viscosity solvent is strictly limited. Since the low-viscosity solvent introduced in this disclosure has the potential to undergo side reactions with the negative electrode interface, that is, it has a certain degree of instability compared to conventional electrolyte solvents, it is necessary to ensure the amount of electrolyte additives used to enhance the interface stability of the cell. However, correspondingly, there is also a certain upper limit to the amount of electrolyte additives used to prevent an increase in battery impedance and to offset the improvement of fast charging capability by the low-viscosity solvent.

[0030] Furthermore, the weight ratio of each component in the lithium-ion battery satisfies the following relationship: 2≤W3 / (W4+W5)≤6; that is, the ratio of organic additives to inorganic additives in the electrolyte additives is specifically limited. When the ratio of the two is within an appropriate range, the thermal stability and mechanical toughness of the cell SEI can be effectively balanced, further balancing the high-temperature storage performance and cycle performance of the battery.

[0031] Furthermore, the weight ratio of each component in the lithium-ion battery satisfies the following relationship: 0.08≤W1 / W3≤0.16, that is, the ratio of the positive electrode additive to the carbonate additive is specifically defined; wherein, the carbonate additive is a key additive in lithium iron phosphate batteries, and the internal resistance of the battery is positively correlated with its amount added, while the positive electrode additive can reduce the battery impedance. Therefore, as the amount of the positive electrode additive increases, the amount of the carbonate additive can be increased simultaneously without causing an increase in the cell impedance, thus ensuring good cycle performance and high-temperature performance while maintaining low cell impedance.

[0032] Furthermore, the positive electrode of the lithium-ion battery includes lithium iron phosphate, a positive electrode additive, a conductive agent, and a binder; wherein, lithium iron phosphate can be understood as the positive electrode active component. In some embodiments, the lithium-ion battery also includes other positive electrode active components, but this disclosure is based on an improvement of the lithium iron phosphate battery, therefore the positive electrode active material is only lithium iron phosphate or lithium iron phosphate is the main active component; further still, the conductive agent includes at least one of carbon nanotubes, acetylene black, Ketjen black, or carbon fiber, and the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylonitrile, or polyacrylic acid.

[0033] Furthermore, in the positive electrode of the lithium-ion battery, the mass ratio of the lithium iron phosphate, the positive electrode additive, the conductive agent, and the binder is (95-97):(0.3-1.0):(0.5-2):(1.5-2.5).

[0034] Furthermore, the positive electrode of the lithium-ion battery includes a current collector and a positive electrode coating layer coated on both sides of the current collector. The double coating can effectively improve the distribution of pores in the positive electrode sheet. It is understood that the lithium iron phosphate and the positive electrode additive (including the conductive agent and the binder) are both components in the positive electrode coating layer. The positive electrode additive exists only in the positive electrode coating layer on one side. Furthermore, the positive electrode additive exists only on the side of the positive electrode sheet close to the electrode surface and away from the current collector.

[0035] Furthermore, the electrolyte has an ionic conductivity of ≥13 mS / cm at room temperature, exhibiting high ionic conductivity.

[0036] Furthermore, the low-viscosity solvent includes at least one of carboxylic acid esters, acetonitrile, fluoroacetonitrile, and propionitrile, wherein the carboxylic acid ester includes at least one of ethyl acetate, methyl acetate, and methyl propionate; the overall viscosity range of the solvent is within a suitable range through the above-mentioned low-viscosity solvent components.

[0037] Furthermore, the mass ratio of the sum of the masses of the acetonitrile, the fluoroacetonitrile, or the propionitrile to the mass of the electrolyte is W6, where W6 < 20%. This can be understood as meaning that there should be an upper limit to the amount of low-viscosity nitrile solvent used, in order to avoid negative impacts on the high-temperature performance of the battery when the amount of nitrile solvent is too high.

[0038] Furthermore, the low-viscosity solvent is selected from ethyl acetate, or a two-component combination of ethyl acetate and acetonitrile.

[0039] Furthermore, the solvent also includes cyclic carbonates; wherein the cyclic carbonates include, for example, ethylene carbonate, propylene carbonate, etc.; even further, the mass ratio of the cyclic carbonates to the electrolyte is 8% to 12%, and appropriately reducing the amount of the cyclic carbonates is beneficial to improving the fast charging and low-temperature performance of the battery cell.

[0040] In one embodiment, the solvent further includes chain esters; wherein the chain esters include, for example, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propyl propionate, methyl butyrate, ethyl butyrate, butyl butyrate, etc.

[0041] Furthermore, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium bistrifluoromethylsulfonylimide, lithium perchlorate, or lithium tetrafluoroborate.

[0042] Furthermore, the mass ratio of the lithium salt to the electrolyte is 12% to 20%.

[0043] Further, the carbonate additive includes at least one of vinylene carbonate, fluoroethylene carbonate, or EBC; wherein the structural formula of the EBC is:

[0044] Further, the sulfur-containing additive includes at least one of vinyl sulfate, propylene sulfate, 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, methylene disulfonate, vinyl disulfate, spirovinyl sulfate, or dimethyl sulfite.

[0045] Furthermore, the lithium salt additive includes at least one of lithium difluorophosphate, lithium bis(oxalate)borate, lithium bis(oxalate)phosphate, lithium difluoro(oxalate)borate, or lithium fluorosulfonate.

[0046] Furthermore, this disclosure does not impose any restrictions on the negative electrode and separator of the fast-charging lithium-ion battery; those skilled in the art can use any commercially available product or a product obtained in-house; under the premise of realizing the function of a secondary battery, any negative electrode or separator can be used as an implementation of this disclosure.

[0047] Furthermore, when the positive electrode additive contains lithium ferrite, the first full charge cutoff voltage of the fast-charging lithium-ion battery is ≥4.2V; when the positive electrode additive contains lithium squartz oxide, the first full charge cutoff voltage of the fast-charging lithium-ion battery is ≥4.3V; when the positive electrode additive contains lithium oxalate, the first full charge cutoff voltage of the fast-charging lithium-ion battery is ≥4.8V.

[0048] A second aspect of this disclosure is to provide a method for preparing the fast-charging lithium-ion battery described above.

[0049] The preparation method includes the following steps: thoroughly mixing the raw material components of the lithium-ion battery positive electrode to prepare a positive electrode slurry; coating it onto an aluminum foil current collector using a double-layer coating method, and drying it to obtain a positive electrode sheet; thoroughly mixing the raw material components of the lithium-ion battery electrolyte to obtain an electrolyte; and assembling the positive electrode sheet, negative electrode sheet, separator, and electrolyte to obtain a fast-charging lithium-ion battery.

[0050] The solvent composition and amount of the positive electrode slurry, the specific coating operation, the drying temperature or time, and the assembly of battery functional components involved in this disclosure can all adopt conventional features or parameter ranges in the art, and this disclosure does not impose additional limitations on the above features.

[0051] Furthermore, the fast-charging lithium-ion battery is obtained by sequentially assembling, packaging, injecting electrolyte, forming, and finally sealing the positive electrode, negative electrode, separator, and electrolyte; wherein the forming is carried out at a high temperature of 40°C to 50°C.

[0052] A third aspect of this disclosure is to provide an electrical appliance.

[0053] The electrical equipment described herein shall include the lithium-ion battery as described in the first aspect; those skilled in the art will understand that the electrical equipment includes, but is not limited to, electric vehicles, home appliances, mobile communication devices, office appliances, industrial equipment, etc., and any device that includes the fast-charging lithium-ion battery described herein can be considered a feasible implementation of this disclosure.

[0054] Compared with the prior art, the beneficial effects of this disclosure are as follows:

[0055] (1) This disclosure designs and uses a positive electrode sheet with a specific composition; wherein, a positive electrode additive is added to the positive electrode sheet, which can release oxygen (such as lithium ferrite) or carbon dioxide (such as lithium oxalate or lithium squarnet) during the cell formation process, so that the negative electrode is in a slightly oxidizing atmosphere during the first formation process of the cell, which is conducive to the formation of a low-resistance SEI film with slightly inorganic components on the surface of the negative electrode, which can significantly reduce the interface impedance of the negative electrode; this means that even if more negative electrode film-forming additives are added to the high ionic conductivity electrolyte (to ensure cycle and high temperature performance), the interface impedance of the cell negative electrode will not increase significantly.

[0056] (2) This disclosure uses a positive electrode slurry containing positive electrode additives to leave pores in the positive electrode sheet after formation, thereby improving the tortuosity of the positive electrode sheet, enhancing the dynamic performance of the positive electrode sheet, and improving the overall fast charging and low temperature performance of the battery cell.

[0057] (3) This disclosure uses a high ionic conductivity electrolyte prepared with a low viscosity solvent, which can significantly reduce the ohmic impedance of the cell and eliminate the concentration polarization between the surface of the negative electrode and the surface of the internal active material during high-rate charging, thereby increasing the lithium plating current threshold of the negative electrode.

[0058] Example 1

[0059] This embodiment provides a secondary lithium-ion battery, which consists of a positive electrode, a negative electrode, a separator, an electrolyte, and a casing. Its manufacturing process is as follows.

[0060] (1) Positive electrode manufacturing: Lithium iron phosphate, lithium ferrite, conductive carbon black, carbon nanotubes, and polyvinylidene fluoride are prepared and mixed in a certain mass ratio. During the mixing process, N-methylpyrrolidone is used to prepare a positive electrode slurry with a solid content of 60%. A double-layer coating process is adopted, with each layer accounting for 50 wt.%. Among them, lithium iron phosphate, lithium ferrite, conductive carbon black, carbon nanotubes, and polyvinylidene fluoride are mixed in a mass ratio of 96.5:0:1:0.5:2 in the upper layer, and lithium iron phosphate, lithium ferrite, conductive carbon black, carbon nanotubes, and polyvinylidene fluoride are mixed in a mass ratio of 95.5:1:1:0.5:2 in the lower layer. Then, the slurries of the upper and lower layers are coated on aluminum foil current collectors respectively, dried at 60°C, and then rolled and die-cut to form the required positive electrode sheet.

[0061] (2) Anode manufacturing: Graphite, conductive carbon black, sodium carboxymethyl cellulose and styrene-butadiene rubber are prepared in a mass ratio of 96:1:1:2 and mixed with deionized water as solvent to form a slurry with a solid content of 51%. The slurry is then coated on copper foil current collector, dried at 60°C and then rolled and die-cut to form the required anode sheet.

[0062] (3) Electrolyte preparation: The electrolyte is prepared by mixing the following components in the indicated mass ratios: lithium hexafluorophosphate 12wt%, lithium difluorosulfonyl imide 3wt%, ethylene carbonate 25wt%, methyl ethyl carbonate 10wt%, ethyl acetate 43wt%, vinylene carbonate 4wt%, fluorocarbonate 2wt%, ethylene sulfate 0.5wt%, lithium difluorophosphate 0.3wt%, and tris(trimethylsilyl)phosphate 0.2wt%.

[0063] (4) Dry cell manufacturing: The positive and negative electrode sheets obtained above are stacked with ceramic-coated PP separators of corresponding size and thickness of 12 micrometers using a stacking machine to obtain a core with a capacity of 4Ah; after welding the tabs, they are packaged with aluminum-plastic film, baked at 85℃ for 24h, then liquid injection is performed, and after standing, formation is carried out.

[0064] The formation process was carried out in a 45℃ chamber, and the steps were as follows: 1) Charge the battery with a current of 0.2A for 2 hours, with a cutoff voltage of 3.65V; 2) Then charge the battery with a constant current and constant voltage of 0.8A to 4.2V, with a cutoff current of 0.2A; 3) Let the battery cell stand in the 45℃ chamber for 24 hours to age, remove it, vent it, and repackage it; 4) Charge the battery cell with a constant current and constant voltage of 1.33A to 3.65V, with a cutoff current of 0.2A; 5) Discharge the battery cell with a constant current of 1.33A, with a cutoff voltage of 2.0V; 6) Continue to charge and discharge the battery cell with a current of 1.33A in the range of 2.0V to 3.65V for 2 weeks.

[0065] After formation is completed, final sealing is performed to obtain the lithium-ion secondary battery of this embodiment.

[0066] Example 2

[0067] It is basically the same as Example 1, except that:

[0068] (3) Electrolyte preparation: The electrolyte is prepared by mixing the following components in the indicated mass ratios: lithium hexafluorophosphate 12wt%, lithium bis(fluorosulfonyl)imide 3wt%, ethylene carbonate 20wt%, methyl ethyl carbonate 8wt%, ethyl acetate 40wt%, acetonitrile 10wt%, vinylene carbonate 4wt%, fluoroethylene carbonate 2wt%, ethylene sulfate 0.6wt%, and lithium bis(oxalato)borate 0.4%.

[0069] Example 3

[0070] It is basically the same as Example 1, except that:

[0071] (1) Positive electrode manufacturing: Lithium iron phosphate, lithium ferrite, conductive carbon black, carbon nanotubes and polyvinylidene fluoride are mixed in a mass ratio of 95.5:1:1:0.5:2. During the mixing process, N-methylpyrrolidone is used to prepare a positive electrode slurry with a solid content of 60%. The slurry is then coated on an aluminum foil current collector to make a double-sided coated electrode sheet. After drying at 60°C, it is rolled and die-cut to form the required positive electrode sheet.

[0072] (3) Electrolyte preparation: The electrolyte is prepared by mixing the following components in the indicated mass ratios: lithium hexafluorophosphate 12wt%, lithium difluorosulfonyl imide 3wt%, ethylene carbonate 20wt%, methyl ethyl carbonate 8wt%, ethyl acetate 40wt%, acetonitrile 10wt%, vinylene carbonate 4wt%, fluoroethylene carbonate 2wt%, ethylene sulfate 0.8wt%, lithium difluorophosphate 0.3wt%, and tris(trimethylsilyl)phosphate 0.2wt%.

[0073] Example 4

[0074] It is basically the same as Example 1, except that:

[0075] (1) Positive electrode manufacturing: Replace lithium iron ferrite entirely with lithium squartz oxide;

[0076] (4) The formation process is carried out in a 45°C oven, and the steps are as follows: 1) Charge the battery with a current of 0.2A for 2 hours, and cut off the voltage of 3.65V; 2) Then charge the battery with a constant current and constant voltage of 0.8A to 4.3V, and cut off the current of 0.2A; 3) Let the cell stand in the 45°C oven for 24 hours to age, remove it, vent it, and repackage it; 4) Charge the cell with a constant current and constant voltage of 1.33A to 3.65V, and cut off the current of 0.2A; 5) Discharge the cell with a constant current of 1.33A, and cut off the voltage of 2.0V; 6) Continue to charge and discharge the cell with a current of 1.33A in the range of 2.0V to 3.65V for 2 weeks.

[0077] Example 5

[0078] It is basically the same as Example 1, except that:

[0079] (3) Electrolyte preparation: The electrolyte is prepared by mixing the following components in the indicated mass ratios: lithium hexafluorophosphate 12wt%, lithium difluorosulfonyl imide 3wt%, ethylene carbonate 25wt%, methyl ethyl carbonate 10wt%, methyl propionate 43wt%, vinylene carbonate 4wt%, fluorocarbonate 2wt%, ethylene sulfate 0.7wt%, lithium difluorophosphate 0.2wt%, and tris(trimethylsilyl)phosphate 0.1wt%.

[0080] Example 6

[0081] It is basically the same as Example 1, except that:

[0082] (3) Electrolyte preparation: The electrolyte is prepared by mixing the following components in the indicated mass ratios: lithium hexafluorophosphate 12wt%, lithium difluorosulfonyl imide 3wt%, ethylene carbonate 25wt%, methyl ethyl carbonate 10wt%, methyl acetate 43wt%, vinylene carbonate 4wt%, fluorocarbonate 2wt%, ethylene sulfate 0.6wt%, and lithium difluorooxalate borate 0.4wt%.

[0083] Example 7

[0084] It is basically the same as Example 1, except that:

[0085] (3) Electrolyte preparation: The electrolyte is prepared by mixing the following components in the indicated mass ratios: lithium hexafluorophosphate 12wt%, lithium difluorosulfonyl imide 3wt%, ethylene carbonate 25wt%, methyl ethyl carbonate 32wt%, acetonitrile 20wt%, vinylene carbonate 4wt%, fluorocarbonate 2wt%, ethylene sulfate 1wt%, propanesulfonate lactone 0.5wt%, and lithium difluorophosphate bis(oxalate) 0.5wt%.

[0086] Comparative Example 1

[0087] It is basically the same as Example 1, except that:

[0088] (1) Positive electrode manufacturing: Lithium iron phosphate, conductive carbon black, carbon nanotubes and polyvinylidene fluoride are mixed in a mass ratio of 96.5:1:0.5:2. During the mixing process, N-methylpyrrolidone is used to prepare a positive electrode slurry with a solid content of 60%. The slurry is then coated on an aluminum foil current collector, dried at 60°C, and then rolled and die-cut into the required positive electrode sheet.

[0089] (3) Electrolyte preparation: The electrolyte is prepared by mixing the following components in the indicated mass ratios: lithium hexafluorophosphate 10wt%, lithium difluorosulfonyl imide 3wt%, ethylene carbonate 25wt%, methyl ethyl carbonate 25wt%, dimethyl carbonate 32wt%, vinylene carbonate 3wt%, fluorocarbonate 1wt%, ethylene sulfate 0.7wt%, lithium difluorophosphate 0.2%, and tris(trimethylsilyl)phosphate 0.1wt%.

[0090] Comparative Example 2

[0091] It is basically the same as Example 1, except that:

[0092] (3) Electrolyte preparation: The electrolyte is prepared by mixing the following components in the indicated mass ratios: lithium hexafluorophosphate 12wt%, lithium difluorosulfonyl imide 3wt%, ethylene carbonate 20wt%, methyl ethyl carbonate 8wt%, ethyl acetate 40wt%, acetonitrile 10wt%, vinylene carbonate 4wt%, fluoroethylene carbonate 2wt%, ethylene sulfate 0.7wt%, lithium difluorophosphate 0.2%, and tris(trimethylsilyl)phosphate 0.1wt%.

[0093] Comparative Example 3

[0094] It is basically the same as Example 1, except that:

[0095] (3) Electrolyte preparation: The electrolyte is prepared by mixing the following components in the indicated mass ratios: lithium hexafluorophosphate 12wt%, lithium difluorosulfonyl imide 3wt%, ethylene carbonate 25wt%, methyl ethyl carbonate 10wt%, ethyl acetate 45wt%, vinylene carbonate 3wt%, fluorocarbonate 1wt%, ethylene sulfate 0.7wt%, lithium difluorophosphate 0.2%, and tris(trimethylsilyl)phosphate 0.1wt%.

[0096] Table 1 below provides the characteristic relationship between the above embodiments and comparative examples of this disclosure.

[0097] Table 1

[0098] Test case

[0099] To facilitate comparison of the performance differences between the embodiments and the comparative examples, the following four aspects of testing were conducted, and the test results for each embodiment and comparative example are provided in Table 2 below.

[0100] (I) Three-electrode charging capability test: Use the negative electrode constant voltage charging step to monitor the current change during the charging process; use an electrochemical workstation to monitor the voltage change of the negative electrode relative to the reference electrode and control the current magnitude to keep the potential difference between the negative electrode and the reference electrode at 5mV until the charging process is completed. The battery's limit charging time can be calculated by the magnitude of the current during the charging process.

[0101] (II) DC internal resistance test at 25℃ / -20℃: The charging DC internal resistance and discharging DC internal resistance at 50% SOC are tested respectively.

[0102] (III) 25℃ / 45℃ Cycling Test: The capacity retention rate was tested after 500 cycles at 25℃ and 45℃ respectively.

[0103] (iv) 60℃ high temperature storage test: The capacity recovery rate and gas production of the battery were tested after 30 days under high temperature conditions.

[0104] Table 2

[0105] Although this disclosure has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of this disclosure and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of this disclosure; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this disclosure; therefore, this means that all such substitutions and modifications that fall within the scope of this disclosure are included in the appended claims. Industrial applicability

[0106] The fast-charging lithium-ion battery disclosed herein can solve the technical defect that traditional fast-charging performance and high and low temperature performance cannot be simultaneously achieved. By designing and adopting a positive electrode sheet with a specific composition, and designing the electrolyte, electrolyte additives, positive electrode lithium replenishment additives and their dosage ratios, the lithium-ion battery achieves good performance in fast charging, high temperature performance and low temperature performance, effectively expanding the application of lithium-ion batteries in various extreme scenarios.

Claims

1. A fast-charging lithium ion battery, characterized by, The positive electrode of the lithium ion battery comprises lithium iron phosphate and a positive electrode additive; the positive electrode additive comprises at least one of lithium ferrite, lithium oxalate and lithium square acid; The electrolyte of the lithium ion battery comprises a solvent, a lithium salt and an electrolyte additive; the solvent comprises a low-viscosity solvent, the viscosity of the low-viscosity solvent is ≤0.5 cps; the electrolyte additive comprises a carbonate additive, a sulfur-containing additive and a lithium salt additive.

2. The fast-charge lithium-ion battery of claim 1, wherein, The fast-charging lithium ion battery comprises at least one of the following features (A) to (E): (A) the mass ratio of the positive electrode additive to the positive electrode slurry is W1, 0.3%≤W1≤1%; (B) the mass ratio of the low-viscosity solvent to the electrolyte is W2, 20%≤W2≤60%; (C) the mass ratio of the carbonate additive to the electrolyte is W3, 4%≤W3≤6%; (D) the mass ratio of the sulfur-containing additive to the electrolyte is W4, 0.3%≤W4≤2%; (E) the mass ratio of the lithium salt additive to the electrolyte is W5, 0.3%≤W5≤1%.

3. The fast-charge lithium-ion battery of claim 2, wherein, The fast-charging lithium ion battery comprises at least one of the following features (a) to (c): (a) 0.12≤(W3+W4+W5) / W2≤0.23; (b) 2≤W3 / (W4+W5)≤6; (c) 0.08≤W1 / W3≤0.

16.

4. The fast-charge lithium-ion battery of claim 1, wherein, The positive electrode of the lithium ion battery comprises lithium iron phosphate, a positive electrode additive, a conductive agent and a binder; The mass ratio of the lithium iron phosphate, the positive electrode additive, the conductive agent and the binder is (95-97):(0.8-1.5):(0.1-1):(1.5-2.5).

5. The fast-charge lithium-ion battery of claim 1, wherein, The low-viscosity solvent comprises at least one of carboxylic acid ester, acetonitrile, fluoroacetonitrile and propionitrile, wherein the carboxylic acid ester comprises at least one of ethyl acetate, methyl acetate and methyl propionate; The solvent further comprises a cyclic carbonate; wherein the cyclic carbonate comprises ethylene carbonate or propylene carbonate, and the mass ratio of the cyclic carbonate to the electrolyte is 8%-12%.

6. The fast-charge lithium-ion battery of claim 1, wherein, The lithium salt comprises at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethylsulfonylimide, lithium perchlorate or lithium tetrafluoroborate; The mass ratio of the lithium salt to the electrolyte is 12%-20%.

7. The fast-charge lithium-ion battery of claim 1, wherein, The fast-charging lithium ion battery comprises at least one of the following features (1) to (3): (1) the carbonate additive comprises at least one of vinylene carbonate, fluoro-vinylene carbonate or EBC; (2) the sulfur-containing additive comprises at least one of vinyl sulfate, propylene sulfate, 1,3-propane sultone, 1,4-butane sultone, methane dimethyl sulfonate, bis-vinyl sulfate, spiro vinyl sulfate or dimethyl sulfite; (3) the lithium salt additive comprises at least one of lithium difluorophosphate, lithium bis-oxalate borate, lithium bis-oxalate phosphate, lithium difluoro-oxalate borate or lithium fluorosulfate.

8. The fast-charge lithium-ion battery of claim 1, wherein, The positive electrode of the lithium ion battery comprises a current collector and a positive electrode coating layer coated on both sides of the current collector; One side of the positive electrode coating layer comprises the positive electrode additive, and the other side of the positive electrode coating layer does not comprise the positive electrode additive.

9. The method for producing a fast-charge type lithium-ion battery according to any one of claims 1 to 8, characterized by, The preparation method comprises the following steps: The raw material components of the lithium ion battery positive electrode are fully mixed to prepare a positive electrode slurry; the positive electrode slurry is coated on an aluminum foil current collector by a double-layer coating method, and a positive electrode sheet is prepared after drying; The raw material components of the lithium ion battery electrolyte are fully mixed to prepare an electrolyte; The positive electrode sheet, the negative electrode sheet, the separator and the electrolyte are assembled to prepare a fast-charging lithium ion battery.

10. An electric device, characterized by The electric device comprises the fast-charging lithium ion battery according to any one of claims 1-8.

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