Battery

Abstract

The invention provides a battery which comprises a positive plate, the positive plate comprises a positive electrode material layer, the positive electrode material layer comprises a positive electrode material, the positive electrode material comprises a positive electrode active material and a lithium supplementing material, the positive electrode active material comprises lithium iron phosphate, the lithium supplementing material comprises Li2CnOn + 2, and n is at least one of an integer greater than or equal to 1 or Li2O; the battery charging curve comprises a high-voltage platform, the voltage corresponding to the high-voltage platform is 3.9-4.7 V, and the slope of the high-voltage platform is a; the average particle size Dv50 of the positive electrode material is b [mu] m; a and b meet the relational expression shown in the formula I: 0.016 < = a * b < = 1.6. The battery provided by the invention has both fast charging performance and cycle life.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and specifically relates to a battery. Background Technology

[0002] During the first charge and discharge cycle, the positive electrode material in a lithium-ion battery irreversibly consumes active lithium due to the formation of a solid electrolyte interphase (SEI) film, leading to a decrease in the battery's cycle life. To compensate for this loss, lithium replenishment materials are typically introduced into the battery system to provide an additional source of active lithium.

[0003] Lithium oxalate (Li₂C₂O₄) has attracted attention as a potential lithium supplement material due to its high theoretical capacity and relatively low decomposition temperature. However, the following problems still exist in the practical application of Li₂C₂O₄:

[0004] Lithium oxalate has a high delithiation plateau (>4.4V vs. Li). + High voltage (Li) exacerbates internal polarization in the battery, leading to a continuous increase in internal resistance. This increases battery polarization, reducing lithium replenishment efficiency. Furthermore, voltage exceeding the electrolyte's tolerance limit triggers electrolyte oxidation and decomposition, causing aluminum foil corrosion. Ultimately, these issues reduce the battery's fast-charging performance and cycle life.

[0005] Therefore, providing a battery that balances fast charging performance and cycle life has become a problem that needs to be solved. Summary of the Invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a battery that has high fast charging performance and cycle life.

[0007] This invention provides a battery comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode material layer, the positive electrode material layer comprising a positive electrode material, the positive electrode material comprising a positive electrode active material and a lithium supplementation material, the positive electrode active material comprising lithium iron phosphate, and the lithium supplementation material comprising Li₂C. n O n+2 , where n is an integer greater than or equal to 1, or at least one of Li2O; the battery charging curve includes a high voltage plateau, the voltage corresponding to the high voltage plateau is 3.9~4.7V, and the slope of the high voltage plateau is a; the average particle size Dv50 of the positive electrode material is bμm; a and b satisfy the relationship shown in Equation I: 0.016≤a×b≤1.6 Equation I.

[0008] Compared with existing technologies, the battery provided by this invention can balance fast charging performance and cycle life. Attached Figure Description

[0009] Figure 1The charging curve of the battery shows that 3.9-4.7V corresponds to the high voltage plateau of the lithium replenisher. Detailed Implementation

[0010] This invention provides a battery comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode material layer, the positive electrode material layer comprising a positive electrode material, the positive electrode material comprising a positive electrode active material and a lithium supplementation material, the positive electrode active material being selected from lithium iron phosphate, and the lithium supplementation material comprising Li₂C. n O n+2 , where n is an integer greater than or equal to 1, or at least one of Li2O;

[0011] The battery charging curve includes a high-voltage plateau, the voltage of which is 3.9~4.7V, and the slope of the high-voltage plateau is a;

[0012] The average particle size Dv50 of the cathode material is bμm;

[0013] a and b satisfy the relationship shown in equation I:

[0014] 0.016≤a×b≤1.6 Formula I.

[0015] In this invention, when a and b satisfy the relationship shown in Equation I, the battery exhibits high fast-charging performance and cycle life. Controlling the slope of the high-voltage plateau can prevent the lithium delithiation reaction of the positive electrode material from becoming too vigorous, reducing heat accumulation caused by excessively fast reaction rates, further reducing polarization, and improving fast-charging performance. It can also ensure the stability and integrity of the SEI film formed on the negative electrode, thereby reducing side reactions between the electrolyte and the negative electrode interface and improving the battery's cycle life. When a is too large, lithium oxalate polarization intensifies, making lithium-ion insertion / extraction difficult and reducing fast-charging performance. Fast-charging performance can be improved by adjusting the average particle size Dv50 of the positive electrode material. Controlling the average particle size Dv50 of the positive electrode material can shorten the lithium-ion transport path, improving the battery's fast-charging performance, and also reduce the contact area with the electrolyte, thereby reducing side reactions and improving the battery's cycle life.

[0016] Therefore, by controlling the relationship between a and b to satisfy 0.016≤a×b≤1.6, the present invention enables the battery to have high fast charging performance and cycle life.

[0017] In this invention, the calculated value of a×b can be 0.016, 0.02, 0.04, 0.05, 0.06, 0.08, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, or any value between 0.016 and 1.6.

[0018] In some preferred embodiments of the present invention, 0.1 ≤ a × b ≤ 0.8. Wherein, the calculated value of a × b can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or any value between 0.1 and 0.8.

[0019] In this invention, the battery charging curve includes a high-voltage plateau, the voltage of which is 3.9~4.7V, and the slope of the high-voltage plateau is a.

[0020] This invention controls the value of α within the range of 0.06 to 1. Within this range, it avoids excessively vigorous delithiation reactions in the positive electrode material, reduces heat accumulation caused by excessively fast reaction rates, further reduces polarization, and improves fast-charging performance. It also ensures the stability and integrity of the SEI film formed on the negative electrode, thereby reducing side reactions between the electrolyte and the negative electrode interface and improving the battery's cycle life.

[0021] In this invention, the value of 'a' is controlled to be in the range of 0.06 to 1, and can be any value between 0.06, 0.08, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or 0.06 to 1. Preferably, the value of 'a' is controlled to be in the range of 0.1 to 0.8.

[0022] The present invention does not limit the testing method for 'a'. Those skilled in the art can determine the value of 'a' using conventional technical means. An exemplary testing method for 'a' includes the following steps:

[0023] The prepared battery is charged, and the delithiation plateau, i.e., the high-voltage plateau, of the lithium replenishment material is obtained based on the charging curve data. Then, the slope of the high-voltage plateau is calculated. The voltage of the high-voltage plateau is 3.9~4.7V.

[0024] The test conditions for the charging curve include:

[0025] 1) Discharge the battery at a constant current rate of 0.33C to 2.5V;

[0026] 2) Let stand for 5 minutes;

[0027] 3) Charge at a constant current rate of 0.05C to 4.7V;

[0028] 4) Let stand for 5 minutes;

[0029] 5) Discharge at a constant current rate of 0.3C for 60 minutes to end the test.

[0030] The high-voltage plateau (3.9~4.7V) was obtained from the charging curve data, and then the slope of the high-voltage plateau was calculated. (See [link to relevant documentation]). Figure 1 , Figure 1The charging curves of batteries obtained in some specific embodiments of the present invention are shown. The range of 3.9-4.7V corresponds to the high voltage plateau of the lithium replenishment agent.

[0031] Specifically, for the data points in the selected high-voltage platform region, linear regression was performed using the least squares method to fit the equation:

[0032] V = a × Q + c (Equation II)

[0033] In Equation II, V represents voltage;

[0034] Q represents capacity;

[0035] 'a' represents the slope, specifically the slope of the high-voltage plateau.

[0036] c is the intercept.

[0037] The method for testing capacity is not limited in this invention. Those skilled in the art can determine capacity using conventional techniques. For example, the capacity testing method includes the following steps:

[0038] Charge the battery at 0.33C to 3.65V, then charge it at a constant voltage to the cutoff current of 0.05C; let it stand for 30 minutes, then discharge it at 0.33C to 2.5V; repeat the above operation 3 times, and use the discharge capacity of the third cycle as the battery capacity Q.

[0039] The battery provided by this invention includes a positive electrode sheet, which comprises a positive electrode active material and a lithium supplementation material, wherein the lithium supplementation material comprises Li2C. n O n+2 , where n is an integer greater than or equal to 1, or at least one of Li2O.

[0040] In this invention, the lithium replenishment material includes at least one of Li2C2O4, Li2C3O5, Li2C4O6, Li2CO3, and Li2O.

[0041] In some specific embodiments of the present invention, the lithium replenishing material is selected from Li₂C₂O₄. When the lithium replenishing material is selected from Li₂C₂O₄, the value of 'a' ranges from 0.1 to 0.8. The mass ratio of the lithium replenishing material to the positive electrode active material is 1:19 to 1:199, and can be any value between 1:19, 1:20, 1:40, 1:50, 1:60, 1:80, 1:100, 1:120, 1:140, 1:150, 1:160, 1:180, 1:199, or 1:19 to 1:199. In the present invention, it is necessary to control the mass ratio of the positive electrode active material to the lithium replenishing material. A larger mass ratio leads to uneven dispersion of the lithium replenishing material, thereby reducing the reaction efficiency and resulting in a poorer lithium replenishment effect, leading to a larger value of 'a'.

[0042] In this invention, the lithium replenishment material further includes a catalyst selected from one or more of Co3O4 (cobalt oxide), Fe2O3 (iron oxide), NiO (nickel oxide), MnO2 (manganese dioxide), CuO (copper oxide), TiO2 (titanium dioxide), ZnO (zinc oxide), V2O5 (vanadium pentoxide), Mo2C, and CeO2 (cerium dioxide). The mass content of the catalyst in the cathode material layer ranges from 0.1% to 0.5%, and can be any value between 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or 0.1% to 0.5%. In this invention, the catalyst can provide active sites, reduce the activation energy of lithium oxalate, promote oxalate decomposition, thereby promoting electron transfer and reducing the slope of the delithiation plateau. The catalyst content can affect the lithium replenishment effect, and thus affect the slope of the high-voltage plateau. In this invention, the catalyst can provide active sites, reduce the activation energy of lithium oxalate, promote oxalate decomposition, thereby promoting electron transfer and reducing the slope of the high-voltage plateau.

[0043] In this invention, the conductive agent is a raw material for preparing the positive electrode material layer in the positive electrode sheet. Increasing the content of the conductive agent leads to a denser conductive network, accelerating the transfer of electrons from the active material to the current collector, thereby improving the efficiency of the lithium replenishment reaction. A smaller α value results in a higher efficiency. In this invention, the conductive agent accounts for 0.1% to 0.5% of the mass of lithium iron phosphate, and can be any value between 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or 0.1% to 0.5%.

[0044] In this invention, the value of a can be controlled to satisfy 0.06~1 by adding the amount of lithium-supplementing material, catalyst and conductive agent.

[0045] In this invention, the value of b in Equation I can also affect the fast charging performance and cycle life of the battery.

[0046] The average particle size Dv50 of the cathode material is b μm. In this invention, if the b value is too large, the lithium ion transport path is prolonged, and the fast charging performance of the battery decreases; if the b value is too small, the specific surface area of ​​the material increases, the side reactions with the electrolyte increase, and the cycle life of the battery decreases.

[0047] The present invention controls the range of b μm to be 0.2~2μm, which can be 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.85μm, 0.9μm, 0.95μm, 1.0μm, 1.05μm, 1.10μm, 1.15μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2μm, or any value between 0.2~2μm. Preferably, the value of b is controlled within the range of 0.88~0.98μm, and can be 0.8μm, 0.85μm, 0.9μm, 0.95μm, 1.0μm, 1.05μm, 1.10μm, 1.15μm, 1.2μm, or any value between 0.8 and 1.2μm.

[0048] Therefore, by controlling the b value to a range of 0.8~1.15μm, the present invention controls the average particle size Dv50 of the cathode material, which can shorten the lithium ion transport path, improve the fast charging performance of the battery, reduce the contact area with the electrolyte, thereby reducing side reactions and improving the cycle life of the battery.

[0049] The present invention does not limit the testing method for b. Those skilled in the art can determine the value of b using conventional technical means. An exemplary testing method for b includes the following steps:

[0050] 1) Pretreatment: Discharge the battery to 2.5V at 0.33C, remove the empty battery, disassemble the positive electrode sheet, soak the positive electrode sheet in dimethyl carbonate (DMC) solution for 4 hours, and dry it; scrape the positive electrode material layer powder from the surface of the positive electrode sheet to obtain the positive electrode material powder.

[0051] 2) The particle size Dv50 of the cathode material powder can be measured using a laser particle size distribution measuring instrument (Mastersizer 3000). The particle size distribution is measured by the particle size distribution laser diffraction method (specific steps refer to GB / T19077-2016). The particle size corresponding to the cumulative particle size distribution percentage reaching 50% is Dv50.

[0052] In this invention, the particle size of the cathode material can be controlled by adjusting the solid content of the spray-drying slurry used to prepare the cathode active material and by adjusting the feed rate. Specifically, the lower the solid content of the spray slurry and the slower the feed rate, the smaller the particle size of the cathode material.

[0053] The present invention does not impose any special restrictions on the preparation method of the positive electrode active material; any preparation method of the positive electrode active material known to those skilled in the art is acceptable.

[0054] In this invention, the lithium iron phosphate cathode material can be prepared according to the following method:

[0055] (1) Add iron phosphate and lithium source in a certain proportion to ensure n(Li):n(Fe) = 1.03~1.05, and add carbon source and doping element raw materials to prepare a slurry with a certain solid content;

[0056] (2) The slurry is ground and then dried to obtain spherical lithium iron phosphate precursor;

[0057] (3) The lithium iron phosphate precursor is sintered and pulverized to obtain lithium iron phosphate cathode material.

[0058] The lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium acetate. The carbon source includes at least one of sucrose, glucose, and polyethylene glycol. The doping element includes at least one of Ti, V, Mg, Al, Mn, Zn, and Mo. Doping can stabilize the crystal structure of the material, reduce side reactions at the cathode interface and electrolyte, and improve the cycle life of the battery. It can also prevent distortion of the crystal structure, which would disrupt the diffusion channels of lithium ions, increase the resistance to lithium ion migration, and improve the fast-charging performance of the battery.

[0059] The slurry has a solid content ranging from 25% to 45%, and can be any value between 25%, 30%, 35%, 40%, 45%, or 25% to 45%.

[0060] The grinding process is preferably carried out by coarse and fine grinding in a sand mill to control the particle size of the material between 350 and 440 nm.

[0061] The drying process involves using a spray drying device to form spherical lithium iron phosphate.

[0062] The sintering and pulverizing process involves placing the lithium iron phosphate precursor into a box furnace for high-temperature sintering, followed by pulverizing to synthesize lithium iron phosphate material. The sintering temperature is 700~800℃, and can be any value between 700℃, 720℃, 740℃, 750℃, 760℃, 780℃, 800℃, or 700~800℃.

[0063] In this invention, the lithium iron phosphate battery has a coating layer on its surface. This coating layer is a carbon coating layer with a thickness of 2-10 nm, which can be 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, or any value between 2 and 10 nm. If the carbon coating layer is too thick, the diffusion path of lithium ions is prolonged, resulting in a decrease in the battery's fast-charging performance. If the carbon coating layer is too thin, the side reactions between the electrolyte and the lithium iron phosphate increase, leading to a decrease in the battery's cycle life.

[0064] In this invention, the positive electrode sheet includes a positive current collector and a positive electrode material layer composited on the surface of the positive current collector;

[0065] The cathode material layer includes the aforementioned positive electrode active material, lithium iron phosphate, and a lithium replenishment material. The doping amount of the lithium iron phosphate in the cathode material layer is 2000~5000 ppm, which can be 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 5000 ppm, or any value between 2000~5000 ppm. When the doping amount is too high, it will cause lattice distortion in the cathode material. This distortion will hinder the diffusion of lithium ions in the lattice, increase internal resistance, and thus reduce the fast-charging performance of the battery. When the doping amount is too low, the crystal structure of the material cannot be stabilized, easily leading to particle cracking and structural collapse, resulting in increased side reactions between the cathode material and the electrolyte, and a decrease in the cycle life of the battery.

[0066] The positive electrode current collector comprises an aluminum foil substrate and a carbon layer composited on the surface of the aluminum foil substrate. The carbon layer not only improves the conductivity of lithium iron phosphate and enhances the battery's fast-charging performance, but also acts as a physical barrier, inhibiting electrolyte corrosion of the aluminum foil under high voltage and improving the battery's cycle life. In some specific embodiments of the present invention, the thickness of the carbon layer is 1~4 μm, and can be 1 μm, 2 μm, 3 μm, 4 μm, or any value between 1 and 4 μm.

[0067] In this invention, the positive electrode material layer further includes a binder, a conductive agent, and a dispersant.

[0068] The binder improves the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Therefore, the binder suitable for use in the embodiments is a fluorinated polyolefin binder, which may include, but is not limited to, polyvinylidene fluoride (PVDF), PVDF copolymers, or their modified derivatives (e.g., modified with carboxylic acid, acrylic acid, acrylonitrile, etc.).

[0069] In this invention, a conductive agent is used to provide conductivity in the electrode. The conductive agent used in this invention can be any conductive agent without particular limitation, as long as it has suitable electronic conductivity and does not cause adverse chemical changes in the battery. Preferably, the conductive agent includes one or more of carbon black, graphite, carbon nanotubes, and graphene; the carbon black includes acetylene black (AB), Super P (conductive carbon black), and Ketjenblack; the graphite includes natural graphite and artificial graphite; the carbon nanotubes include single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs); and the graphene includes graphene oxide (GO), reduced graphene oxide (rGO), and graphene nanosheets (GNPs).

[0070] The dispersant is used to improve the uniformity and stability of the slurry, ensuring that the positive electrode active material, conductive agent, and binder are uniformly dispersed in the solvent, avoiding agglomeration or sedimentation, thereby improving the electrochemical performance of the electrode. In this invention, the dispersant is selected from one or more of polyacrylic acid (PAA) and acrylates.

[0071] In this invention, the positive electrode active material lithium iron phosphate and the lithium replenishing material constitute the main material. The mass ratio of the main material, conductive agent, binder and dispersant is 94.5~98.5:0.5~1.5:1.3~2.2:0.05~2. The lithium replenishing material accounts for 0.5%~5% of the mass of the lithium iron phosphate, and can be any value between 0.5%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or 0.5%~5%.

[0072] This invention does not impose any particular limitation on the preparation method of the positive electrode sheet; any preparation method known to those skilled in the art is acceptable. The preparation can be carried out according to the following method:

[0073] The positive electrode active material, lithium supplement material, binder, conductive agent and dispersant are mixed evenly according to the mass ratio, solvent is added, and the mixture is stirred under vacuum until the system is homogeneous to obtain a positive electrode slurry with a certain solid content; the positive electrode slurry is coated on the surface of the positive electrode current collector and then rolled and cut to obtain a positive electrode sheet.

[0074] The present invention does not have any particular limitation on the type of solvent, which can be N-methylpyrrolidone (NMP).

[0075] The solid content of the positive electrode slurry is 50%-70%, and can be any value between 50%, 55%, 60%, 65%, 70%, or 50%~70%.

[0076] The final positive electrode sheet has an areal density ranging from 360 to 480 g / m². 2, the range of the compaction density is 2.5 - 2.7 g / cm 3 .

[0077] In the present invention, the compaction density of the positive electrode sheet is controlled to be 2.5 - 2.7 g / cm 3 , and it can be 2.5 g / cm 3 , 2.55 g / cm 3 , 2.6 g / cm 3 , 2.65 g / cm 3 , 2.7 g / cm 3 , or any value between 2.5 - 2.7 g / cm 3 . Among them, when the compaction density is too large, the porosity of the electrode sheet will be significantly reduced, which hinders the infiltration of the electrolyte, resulting in the hindrance of lithium ion transmission, the increase of the local current density, and instead exacerbates the polarization, and the slope of the high voltage platform increases. When the compaction density is too small, the contact area between the electrode sheet and the electrolyte increases, and the probability of side reactions (such as electrolyte decomposition and SEI film thickening) increases. Side reactions will consume active lithium, resulting in a decrease in the delithiation capacity. Insufficient delithiation capacity will force the voltage of the plateau period to drop in advance, and the slope of the high voltage platform decreases.

[0078] The battery provided by the present invention further includes a negative electrode sheet. The negative electrode sheet of the present invention includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The negative electrode material layer includes a negative electrode material, and the negative electrode material includes a negative electrode active material, and may also include a conductive agent and / or a binder.

[0079] Among them, the particle size Dv50 of the negative electrode material is 5 - 15 μm, and it can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or any value between 5 - 15 μm. Among them, when the particle size of the negative electrode active substance is within the above range, it can shorten the lithium ion diffusion path, improve the fast charging performance of the battery, and reduce the side reactions between the negative electrode active material and the electrolyte.

[0080] For the negative electrode active material, the present invention does not specifically limit the type of the negative electrode active material, and it can be selected according to actual needs. As an example, the negative electrode active material is selected from at least one of graphite and silicon-based materials, and can be natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO m (0 < m < 2, such as m = 1) or more of them.

[0081] This invention does not impose specific limitations on the types of conductive agents and binders in the negative electrode active material layer, and they can be selected according to actual needs. As an example, the conductive agent is one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; the binder is one or more of styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl butyral, waterborne acrylic resin, and carboxymethyl cellulose. The negative electrode active material layer may also optionally include a thickener, such as carboxymethyl cellulose.

[0082] The present invention does not impose any particular limitation on the negative electrode current collector, as long as it has high conductivity and will not cause adverse chemical changes in the battery. The negative electrode current collector is selected from metal foil or composite current collector.

[0083] Specifically, the metal foil can be copper or a copper alloy;

[0084] Specifically, the composite current collector includes an intermediate high-molecular layer and metal layers disposed on both sides of the polymer layer. The polymer layer comprises polymer materials, including at least one of polyamide (PA), polyterephthalate, polyimide (PI), polyethylene (PE), polypropylene (PP), polystyrene (PPE), polyvinyl chloride (PVC), aramid, acrylonitrile-butadiene-styrene copolymer (ABS), polybutylene terephthalate (PET), poly(p-phenylene terephthalamide) (PPTA), polypropylene (PPE), polyoxymethylene (POM), epoxy resin, phenolic resin, polytetrafluoroethylene (PTEE), polyvinylidene fluoride (PVDF), silicone rubber, polycarbonate (PC), polyvinyl alcohol (PVA), polyethylene glycol (PEG), cellulose, starch, protein, their derivatives, their crosslinks, and their copolymers. The metal layers are selected from at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys.

[0085] This invention does not impose any particular limitation on the preparation method of the negative electrode sheet; any preparation method known to those skilled in the art is acceptable. The preparation can be carried out according to the following method:

[0086] The negative electrode active material, binder, conductive agent and dispersant are mixed evenly according to the mass ratio, solvent is added, and the mixture is stirred under vacuum until the system is homogeneous to obtain a negative electrode slurry with a certain solid content; the negative electrode slurry is coated on the surface of the negative electrode current collector and then rolled and cut to obtain a negative electrode sheet.

[0087] The mass ratio of the negative electrode active material, binder, dispersant and conductive agent is 90%-98%: 1-3%: 0.5%-5%: 0.5%-2%.

[0088] The areal density of the obtained negative electrode sheet is 170~220 g / m³. 2 The compacted density is 1.2~1.8 g / cm³. 3 .

[0089] The battery provided by this invention also includes an electrolyte. The electrolyte of this invention can be any electrolyte suitable for electrochemical energy storage devices in the art.

[0090] In this invention, the viscosity of the electrolyte is in the range of 2~5 mPa·s, and can be 2 mPa·s, 3 mPa·s, 4 mPa·s, 5 mPa·s, or any value between 2 and 5 mPa·s. When the viscosity of the electrolyte is too high, lithium-ion transport is hindered, and the fast-charging performance of the battery decreases. When the viscosity of the electrolyte is too low, the side reactions at the interface between the electrolyte and the positive and negative electrodes increase, and the cycle life of the battery decreases.

[0091] In this invention, the electrolyte comprises an electrolyte, a solvent, and additives. The electrolyte typically includes a lithium salt.

[0092] Specifically, the lithium salt includes at least one selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). The concentration of the electrolyte in the electrolyte solution can be 0.5~5 mol / L.

[0093] The solvent is selected from at least one of ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dimethyl carbonate (DMC). The solvent accounts for 80% to 90% of the electrolyte by mass, and can be any value between 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, or 80% to 90%. This invention uses the above-mentioned solvent to promote lithium-ion transport and improve the fast-charging performance of the battery.

[0094] The additive is at least one selected from vinylene carbonate and fluoroethylene carbonate. The additive content in the electrolyte ranges from 0.1% to 5%, and can be any value between 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or 0.1% to 5%. The additive can promote the formation of the SEI film on the negative electrode, improve interface stability, reduce charge transfer impedance, enhance the fast-charging performance of the battery, and prevent physical contact between the electrolyte and the negative electrode interface, reducing side reactions and improving the cycle life of the battery.

[0095] The electrochemical device may further include a separator located between the positive and negative electrode plates to separate them and prevent short circuits. The separator can be any material suitable for separators in electrochemical energy storage devices. Specifically, the separator includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers.

[0096] The air permeability of the diaphragm is 100~500s / 100mL, and can be any value between 100 s / 100mL, 150 s / 100mL, 200 s / 100mL, 250 s / 100mL, 300 s / 100mL, 350 s / 100mL, 400 s / 100mL, 450 s / 100mL, 500 s / 100mL, or 100~500s / 100mL.

[0097] The present invention also provides an electronic device comprising the battery described above. The electrochemical device serves as the power source for the electronic device.

[0098] The electronic device refers to any device that can utilize electrical energy and convert it into mechanical energy, thermal energy, light energy, or one or more other energy forms, such as electric motors, electric heaters, and electric light sources. Specifically, it can include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, and energy storage systems. Mobile devices can include mobile phones, laptops, drones, robot vacuum cleaners, e-cigarettes, etc.; electric vehicles can include pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.

[0099] To further understand the present invention, the battery provided by the present invention will be described below with reference to embodiments. The scope of protection of the present invention is not limited by the following embodiments.

[0100] Example 1

[0101] 1. Preparation of Lithium Iron Phosphate as the Positive Electrode Active Material

[0102] (1) Add iron phosphate and lithium source in a certain proportion to ensure n(Li):n(Fe) = 1.05, and add carbon source and titanium oxide to prepare a slurry with a solid content of 37%; wherein, the lithium source is lithium carbonate; the carbon source includes sucrose and polyethylene glycol PEG1500, the mass ratio of the two is 2:1, and the content of the carbon source accounts for 5% of the total mass of the iron phosphate and lithium source. The doping element is titanium, and the mass fraction of Ti in the cathode material layer is 3000ppm.

[0103] (2) The slurry is ground and then dried to obtain spherical lithium iron phosphate precursor; the grinding is coarse and fine grinding by a sand mill to control the particle size of the material between 350 and 440 nm; the drying is carried out by spray drying equipment to form spherical lithium iron phosphate precursor; the feed rate during spray drying is 12 mL / min.

[0104] (3) The lithium iron phosphate precursor is sintered and pulverized to obtain lithium iron phosphate cathode material. The sintering and pulverizing are performed by placing the lithium iron phosphate precursor into a box furnace for high-temperature sintering and then pulverizing to synthesize lithium iron phosphate material; the sintering temperature is 800℃.

[0105] 2. Preparation of the positive electrode:

[0106] The main material is a mixture of lithium supplement material and positive electrode active material lithium iron phosphate at a mass ratio of 1:74. The lithium supplement material includes Li2C2O4 and catalyst Co3O4 (cobalt oxide), wherein the catalyst accounts for 0.40% of the mass percentage of the positive electrode material layer.

[0107] The main material, binder PVDF, conductive agent CNT, conductive agent SP, and dispersant polyacrylic acid (PAA) were mixed evenly in a mass ratio of 96.8%:2%:0.5%:0.5%:0.2% and dispersed in NMP to obtain a positive electrode slurry. This positive electrode slurry was coated onto aluminum foil to obtain a double-sided coated positive electrode sheet. The sheet was then rolled and cut to obtain the positive electrode sheet. A 2μm thick carbon layer was laminated onto the surface of the aluminum foil.

[0108] The areal density of the positive electrode is 387 g / m³. 2 Compacted density: 2.55 g / cm³ 3 .

[0109] 3. Negative electrode preparation:

[0110] Graphite, conductive agent SP, dispersant styrene-butadiene rubber latex (SBR), and binder CMC were mixed evenly in a mass ratio of 96.4%:0.6%:1.8%:1.2% and dispersed in deionized water to obtain a negative electrode slurry. This negative electrode slurry was then coated onto copper foil to obtain a double-sided coated electrode sheet. After rolling and cutting, the negative electrode sheet was obtained with an areal density of 180 g / m³. 2 Compacted density: 1.6 g / cm³ 3 The particle size Dv50 of the negative electrode material in the negative electrode sheet is 13.4 μm.

[0111] 4. Preparation of electrolyte:

[0112] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, thoroughly dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L. The organic solvent contained 1% fluoroethylene carbonate (FEC) and 2% vinylene carbonate (VC).

[0113] 5. Preparation of the diaphragm:

[0114] The base membrane of the diaphragm is a 9μm thick PE membrane with an alumina coating on one side and a thickness of 3μm. The outer layers on both sides of the diaphragm are also coated with 2μm thick PVDF coatings.

[0115] 6. Assembly and formation:

[0116] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a lithium-ion battery is obtained.

[0117] Examples 2-17 and Comparative Examples 1-4

[0118] Examples 2-17 and Comparative Examples 1-4 each provide a lithium-ion battery, and the preparation method is similar to that of Example 1. The differences are shown in Tables 1-2.

[0119] The testing methods for various parameters of the batteries prepared in each embodiment and comparative example are as follows:

[0120] (1) Quantitative testing of catalyst in cathode material layer:

[0121] ① Pretreatment: The battery is discharged to 2.5V at 0.33C. The lithium-ion battery in the empty state is disassembled to obtain the positive electrode sheet. The positive electrode sheet is soaked in DMC (dimethyl carbonate) at room temperature for 60 minutes, taken out and dried at room temperature with humidity ≤15%. The positive electrode material layer on the surface of the current collector is scraped off and calcined at 400℃ for 3 hours. After washing and drying, the positive electrode material layer powder is obtained.

[0122] ② Accurately weigh 0.2g of positive electrode material powder, disperse it in 15ml of aqua regia, digest it at 160℃ for 1h to obtain the test solution, and perform ICP test on the test solution; before the test, a standard solution must be prepared. The linear correlation coefficient of the standard concentration must be above 0.999 before it can be used as a normal standard. The 1000 mg / L standard solution was diluted with deionized water to different concentrations (generally 0, 1 mg / 100 mL, 2 mg / 100 mL, and 3 mg / 100 mL). The element detection wavelength was selected, and the experimental conditions were set: based on the sample characteristics and the element to be detected, appropriate ICP instrument operating conditions were set: gas flow rate 0.5 L / min, power 1150 W, and the element detection wavelength selected, depending on the element being tested (e.g., Co wavelength 238.89 nm, Mo wavelength 202.03 nm, Ti wavelength 334.94 nm). The self-service analysis function of the ICP testing software can read the element content in the sample. Dividing this by the mass percentage of the element in the corresponding compound molecule yields the mass percentage of the corresponding catalyst compound.

[0123] (2) The specific test method for electrolyte viscosity is as follows:

[0124] 1) Electrolyte Collection: The secondary battery under test is discharged using a battery charge / discharge device. Discharge conditions: current 0.3C, cutoff 2.5V. The battery is disassembled and the electrolyte collected in a glove box (H2O≤0.1ppm, O2≤0.1ppm). There are three methods for collecting the electrolyte: After removing the battery cover, ① if there is free electrolyte, collect it into a 5mL sample tube using a pipette and seal it with sealing tape to prevent leakage. ② if there is no free electrolyte, a hydraulic press (Beijing Heng'ao Technology Co., Ltd.'s FY-30 hydraulic press) can be used to continuously pressurize until free electrolyte appears. Collect the electrolyte into a sample tube and seal it. ③ Add an appropriate amount of dichloromethane extractant to the battery and record the dichloromethane content. After adding dichloromethane, put the battery into an aluminum-plastic bag and seal it with a heat sealer. Transfer it to an ultrasonic oscillator and oscillate for 12 hours to allow the electrolyte in the electrode to mix thoroughly with the dichloromethane. Then, use a pipette to draw the mixture of dichloromethane and electrolyte into a 5mL sample tube and seal the sample tube with sealing glue.

[0125] 2) Remove the electrolyte and test it using a Cambridge viscometer. The Cambridge viscometer is designed based on electromagnetic oscillation viscosity detection technology and uses a magnetically levitated probe for viscosity measurement. Specifically, place the electrolyte in a beaker and control the sample temperature at 25°C for testing. Read the value after the display value stabilizes.

[0126] The lithium-ion batteries prepared in the above embodiments and comparative examples were subjected to performance tests, and the specific items and methods are as follows:

[0127] (1) Test method for fast charging time:

[0128] During the assembly of the secondary battery, a copper wire is added to the negative electrode side. After assembling the secondary battery, it is left to stand for 24 hours, then charged at a constant current of 0.33C to 3.65V, and then charged at a constant voltage of 0.05C. After that, it is discharged at 0.33C to 2.5V. After three cycles, it is charged at 0.33C to 10% SOC, and then charged at 3C, 2.8C, 2.4C, 2.2C, 1.8C, and 1.6C to 20%, 40%, 50%, 60%, 70%, and 80% SOC, respectively. After the test, the charging time t from 10% to 80% SOC is calculated.

[0129] (2) Cycle life test method:

[0130] The lithium-ion batteries prepared in the examples and comparative examples were subjected to cycle tests at 25°C according to the following procedure:

[0131] 1) Charge at a constant current of 0.33C to 3.65V, then charge at a constant voltage to 0.05C to stop charging;

[0132] 2) Discharge at a constant current of 0.33C to 2.5V;

[0133] 3) Repeat the above steps for a total of 3 charge-discharge cycles to obtain the third discharge capacity Q1, which is taken as the fixed capacity.

[0134] 4) Then charge the battery at a constant voltage of 0.33C until it reaches 3.65V. Charge the battery at a constant voltage until the cutoff current is reached. Then discharge the battery at a constant voltage of 0.33C until it reaches 2.5V. This is one cycle. Repeat this cycle 200 times. Record the battery discharge capacity Q2 on the 200th cycle. Calculate the capacity retention rate = Q2 / Q1×100%.

[0135] The test results are shown in Table 2.

[0136] Table 1

[0137]

[0138] Table 2

[0139]

[0140] As shown in Tables 1 and 2, the lithium-ion batteries prepared in Examples 1 to 17 of this invention all have a 200cls cycle capacity retention rate of ≥96.10% and a fast charging time of ≤19.9min. This indicates that the lithium-ion batteries of this invention have high fast charging performance and good cycle life.

[0141] The data from Examples 1-5 and Examples 8-9, combined with those from Examples 6-7, Examples 10-17, and Comparative Examples 1-4, show that when a and b meet the preferred parameter range defined in this invention, the fast charging performance and cycle performance of the lithium-ion battery are relatively better.

[0142] From Examples 1-5 and Examples 6-7, it can be seen that when the battery satisfies 0.016≤a×b≤1.6, the fast charging performance and cycle performance of the lithium-ion battery are relatively higher.

[0143] The results from Comparative Examples 1-4 show that when the formula exceeds the upper limit, the slope of the high-voltage plateau is too large, the polarization of lithium oxalate intensifies, lithium ion insertion / extraction becomes difficult, the average particle size Dv50 of the cathode material is too large, the lithium ion transport path is too long, and the fast-charging performance of the battery decreases. When the formula exceeds the lower limit, the slope of the high-voltage plateau is too small, the stability and integrity of the SEI film formed on the negative electrode are poor, the side reactions between the electrolyte and the negative electrode interface increase, the average particle size Dv50 of the cathode material is too small, the side reactions between the electrolyte and the positive electrode interface also increase, leading to a decrease in the cycle life of the battery.

[0144] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A battery, characterized in that, The cathode includes a positive electrode sheet, the positive electrode sheet includes a positive electrode material layer, the positive electrode material layer includes a positive electrode material, the positive electrode material includes a positive electrode active material and a lithium supplement material, the positive electrode active material is selected from lithium iron phosphate, and the lithium supplement material includes Li2C. n O n+2 , where n is an integer greater than or equal to 1, or at least one of Li2O; The battery charging curve includes a high-voltage plateau, the voltage of which is 3.9~4.7V, and the slope of the high-voltage plateau is a; The average particle size Dv50 of the cathode material is bμm; a and b satisfy the relationship shown in equation I: 0.016≤a×b≤1.6 Formula I.

2. The battery according to claim 1, characterized in that, 0.1≤a×b≤0.

8.

3. The battery according to claim 1, characterized in that, The value of a ranges from 0.06 to 1, and / or the value of bμm ranges from 0.2 to 2μm.

4. The battery according to claim 1, characterized in that, The value of a ranges from 0.1 to 0.8, and / or the value of bμm ranges from 0.8 to 1.2μm.

5. The battery according to claim 1, characterized in that, The positive electrode sheet includes a positive current collector and a positive electrode material layer composited on the surface of the positive current collector; The positive current collector includes an aluminum foil substrate and a carbon layer composited on the surface of the aluminum foil substrate.

6. The battery according to claim 5, characterized in that, The thickness of the carbon layer is 1~4μm.

7. The battery according to claim 5, characterized in that, In the positive electrode current collector, the mass ratio of carbon layer to aluminum foil is 0.002~0.

005.

8. The battery according to claim 1, characterized in that, The lithium replenishing material includes at least one of Li2C2O4, Li2C3O5, Li2C4O6, Li2CO3, and Li2O.

9. The battery according to claim 1, characterized in that, The lithium replenishing material is selected from Li2C2O4, and the value of a ranges from 0.1 to 0.

8.

10. The battery according to claim 1, characterized in that, The lithium supplement material also includes a catalyst, which is selected from one or more of Co3O4, Fe2O3, NiO, MnO2, CuO, TiO2, ZnO, Mo2C, V2O5 and CeO2.

11. The battery according to claim 10, characterized in that, The mass content of the catalyst in the cathode material layer ranges from 0.1% to 0.5%.

12. The battery according to claim 1, characterized in that, The compaction density of the positive electrode sheet is 2.5~2.7 g / cm³. 3 .

13. The battery according to claim 5, characterized in that, The positive electrode material layer includes doping elements, which are selected from at least one of Ti, V, Mg, Al, Mn, Zn, and Mo.

14. The battery according to claim 13, characterized in that, The doping amount of the doping element in the cathode material layer is 2000~5000ppm.

15. The battery according to claim 1, characterized in that, The lithium iron phosphate has a coating layer on its surface, and the thickness of the coating layer is 2~10nm.

16. The battery according to claim 1, characterized in that, The battery includes a negative electrode sheet, the negative electrode sheet includes a negative electrode material layer, the negative electrode material layer includes a negative electrode material, the negative electrode material includes a negative electrode active material, and the negative electrode active material is selected from at least one of graphite and silicon-based materials.

17. The battery according to claim 16, characterized in that, The particle size Dv50 of the negative electrode material is 5-15 μm.

18. The battery according to claim 1, characterized in that, The battery also includes an electrolyte with a viscosity range of 2 to 5 mPa·s.

19. The battery according to claim 18, characterized in that, The electrolyte includes a solvent selected from at least one of ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dimethyl carbonate (DMC), and the solvent accounts for 80% to 90% of the mass of the electrolyte.

20. The battery according to claim 18, characterized in that, The electrolyte includes an additive, which is at least one of vinylene carbonate and fluoroethylene carbonate, and the additive is present in the electrolyte at a concentration ranging from 0.1% to 5%.

21. The battery according to claim 1, characterized in that, The battery also includes a separator, the air permeability of which is 100~500s / 100mL.

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