Lithium ion battery

Abstract

The invention discloses a lithium ion battery and belongs to the technical field of batteries, a positive pole piece is arranged in the lithium ion battery, lithium iron manganese phosphate particles and nickel cobalt lithium manganate particles are introduced into a positive pole material at the same time, and the valence state of the manganese element in the positive pole material is subjected to proportional regulation and control; and meanwhile, a relation is established with a proportional relation of an enclosed area of the two particles, so that not only can the fast charging performance of the product in a high SOC state be effectively improved, but also excellent cycle performance can be realized in a high-temperature environment.

Description

Technical Field

[0001] This application relates to the technical field of batteries, and particularly to a lithium-ion battery. Background Art

[0002] On the premise of ensuring safety and applicability, the fast charging ability of lithium-ion batteries has always been a key technical index that people continuously improve. In existing products, lithium iron manganese phosphate system battery products have high safety, low production costs, high energy density, and good low-temperature performance. However, due to the low ion / electron deintercalation efficiency of the lithium iron manganese phosphate cathode material, especially under high SOC conditions, the fast charging performance of such products is far from that of other system battery products. Summary of the Invention

[0003] The purpose of this application is to overcome the deficiencies of the prior art and provide a positive electrode sheet. By simultaneously introducing lithium iron manganese phosphate particles and lithium nickel cobalt manganese oxide particles into the cathode material, the valence state ratio of manganese elements in the cathode material is regulated, and at the same time, a connection is established with the enclosed area ratio relationship of the two particles, which can not only effectively improve the fast charging performance of the product under high SOC conditions, but also achieve excellent cycle performance in a high-temperature environment.

[0004] To achieve the above purpose, in the first aspect of this application, this application provides a positive electrode sheet, and the positive electrode sheet includes a cathode material layer, and the cathode material layer includes lithium iron manganese phosphate particles and lithium nickel cobalt manganese oxide particles; The positive electrode sheet satisfies: 0.5 ≤ 10000b / a ≤ 2.5; The aCPS.eV is the sum of the characteristic peak areas of divalent manganese elements and trivalent manganese elements at a depth of 10 nm of XPS etching on the side of the cathode material layer away from the current collector when the positive electrode sheet is subjected to XPS testing; The b = S2 / S1, where S2 nm 2 is the total enclosed area of the lithium nickel cobalt manganese oxide particles in the positive electrode sheet at a magnification of 30K, and S1 nm 2 is the total enclosed area of the lithium iron manganese phosphate particles in the positive electrode sheet at a magnification of 30K.

[0005] The beneficial effects of this application are as follows: This application provides a positive electrode sheet. By simultaneously introducing lithium iron manganese phosphate particles and lithium nickel cobalt manganese oxide particles into the cathode material, the valence state ratio of the total manganese elements in the cathode material is regulated, and at the same time, a connection is established with the enclosed area ratio relationship of the two particles, which can not only effectively improve the fast charging performance of the product under high SOC conditions, but also achieve excellent cycle performance in a high-temperature environment. Description of the Drawings

[0006] Figure 1XPS test result diagram of the positive electrode plate described in Embodiment 1 of the present application.

[0007] Figure 2 Schematic scanning electron microscope diagram of lithium nickel cobalt manganese oxide particles and lithium iron manganese phosphate particles in the positive electrode plate described in Embodiment 1 of the present application at a magnification of 30K. Detailed implementation mode

[0008] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. Apparently, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the protection scope of the present application.

[0009] In the present application, among the technical features described in an open-ended manner, a closed technical solution composed of the listed features is included, and an open technical solution including the listed features is also included.

[0010] In the present application, regarding numerical ranges, unless otherwise specified, the above numerical ranges are considered continuous and include the minimum and maximum values of the range, as well as each value between such minimum and maximum values. Further, when the range refers to an integer, each integer between the minimum and maximum values of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0011] The present application will be further elaborated below with specific embodiments: A positive electrode plate, the positive electrode plate includes a positive electrode material layer, and the positive electrode material layer includes lithium iron manganese phosphate particles and lithium nickel cobalt manganese oxide particles; The positive electrode plate satisfies: 0.5 ≤ 10000b / a ≤ 2.5; The aCPS.eV is the sum of the characteristic peak areas of divalent manganese element and trivalent manganese element at an XPS etching depth of 10 nm on the side of the positive electrode material layer away from the current collector when the positive electrode plate is subjected to XPS (X-ray Photoelectron Spectroscopy) test; The b = S2 / S1, where S2 nm 2 is the total enclosed area of lithium nickel cobalt manganese oxide particles in the positive electrode plate at a magnification of 30K, and S1 nm 2 is the total enclosed area of lithium iron manganese phosphate particles in the positive electrode plate at a magnification of 30K.

[0012] In the technical solution of this application, the positive electrode plate uses lithium iron manganese phosphate particles and lithium nickel cobalt manganese oxide particles as the positive electrode material. The lithium nickel cobalt manganese oxide particles serve as an ionic conductor. Due to the interlayer structure characteristics of lithium nickel cobalt manganese oxide, the migration resistance of lithium ions is small and the ionic conductivity is high. In addition, after being compounded with lithium iron manganese phosphate particles, the lithium nickel cobalt manganese oxide particles will coat on their surface, which can further effectively improve the ionic conductivity on the surface of the overall positive electrode material, thereby improving the fast charging performance of the battery. However, due to the inevitable presence of residual alkali on the surface of the lithium nickel cobalt manganese oxide particles during the preparation process, when the positive electrode material contacts the electrolyte, especially in a heating environment, the probability of side reactions increases, which in turn reduces the cycle performance of the positive electrode plate when applied to a lithium-ion battery, especially the cycle performance in a high-temperature environment. At the same time, in this composite system, manganese elements include divalent manganese elements, trivalent manganese elements, and tetravalent manganese elements, and there are conversions among the three valence states. Therefore, in the solution of this application, the relationship range of the characteristic peak areas of divalent manganese and trivalent manganese (the characteristic peak area is not equivalent to the content ratio of manganese) and the ratio of the enclosed areas of the two positive electrode active material particles in the positive electrode material layer of the positive electrode plate at an etching depth of 10 nm is further regulated within a specific range. By controlling the relationship between these two parameters, while improving the ionic conduction efficiency on the surface of the lithium iron manganese phosphate particles, when the positive electrode material contacts the electrolyte, compared with the lithium nickel cobalt manganese oxide particles, the manganese ions on the surface of the lithium iron manganese phosphate particles will quickly oxidize and decompose lithium salts, solvents, etc. in the electrolyte to form by-products, and overall, the reaction activity with the electrolyte is better, thereby inhibiting the excessive side reactions of the lithium nickel cobalt manganese oxide particles with the electrolyte due to the surface residual alkali. Finally, when the lithium-ion battery corresponding to the positive electrode plate is applied, while achieving excellent fast charging performance, the cycle performance, especially the cycle performance in a high-temperature environment, can still be maintained at a high level.

[0013] At the same time, compared with conventional fast charging, at high state of charge (SOC), secondary batteries usually need to be charged with a small current to avoid the problems of increased dissolution of manganese ions in lithium iron manganese phosphate, lattice change of the material, and serious battery polarization caused by charging with a large current at high SOC. Usually, the charging time at high SOC is relatively long. The solution of this application effectively improves the conductivity of the lithium iron manganese phosphate material, inhibits the probability of manganese ion dissolution in the positive electrode material, and improves the fast charging performance of the secondary battery under high SOC conditions by simultaneously introducing lithium iron manganese phosphate particles and lithium nickel cobalt manganese oxide particles into the positive electrode material, regulating the valence state ratio of manganese elements in the positive electrode material, and establishing a connection with the ratio relationship of the enclosed areas of the two particles.

[0014] In some embodiments, the value of 10000b / a is one of the range values of 0.5, 0.8, 0.9, 0.92, 0.96, 1, 1.1, 1.15, 1.2, 1.3, 1.4, 1.48, 1.5, 1.6, 1.8, 2, 2.1, 2.2, 2.3, 2.4, 2.5 or any range value between any two of them.

[0015] In the positive electrode sheet of the present application, if the enclosed area ratio of lithium nickel cobalt manganese oxide particles to lithium iron manganese phosphate particles is too large, after the positive electrode sheet is infiltrated with the electrolyte, the probability of side reactions between the lithium nickel cobalt manganese oxide particles and the electrolyte due to residual alkali on the surface is relatively large. If the ratio is too small, the improvement amplitude of the ionic conduction on the surface of the lithium iron manganese phosphate particles by these particles cannot reach the expectation; on the other hand, if the characteristic peak areas of divalent and trivalent manganese in the positive electrode sheet are too large or too small, the lithium-ion battery cannot take into account both fast charging performance and cycle performance. Therefore, when constructing the relationship formula between the two, they need to be maintained within a specific range to achieve the improvement of the overall electrochemical performance.

[0016] Further preferably, the value of 10000b / a is 0.5 to 2.1.

[0017] Further preferably, the value of 10000b / a is 0.92 to 1.48.

[0018] When the proportional relationship between the characteristic peak area of divalent and trivalent manganese elements in the positive electrode sheet of the present application and the enclosed area ratio of the two positive electrode material particles in the electrode sheet is within the above preferred range, the overall ion / electron transport efficiency of the lithium-ion battery is higher, better fast charging performance can be achieved, and at the same time, the stability is good, and the cycle life is longer under high-temperature environment.

[0019] In some embodiments, a = 12800 to 58600 CPS.eV.

[0020] Specifically, the value of a is one of or the range value of any two of 12800 CPS.eV, 15000 CPS.eV, 18000 CPS.eV, 20000 CPS.eV, 23500 CPS.eV, 24500 CPS.eV, 25000 CPS.eV, 26000 CPS.eV, 27000 CPS.eV, 28000 CPS.eV, 29000 CPS.eV, 30000 CPS.eV, 31000 CPS.eV, 32000 CPS.eV, 32500 CPS.eV, 33000 CPS.eV, 34000 CPS.eV, 35000 CPS.eV, 35500 CPS.eV, 36000 CPS.eV, 37000 CPS.eV, 38000 CPS.eV, 39000 CPS.eV, 39500 CPS.eV, 40000 CPS.eV, 40500 CPS.eV, 41000 CPS.eV, 42000 CPS.eV, 43000 CPS.eV, 44000 CPS.eV, 45000 CPS.eV, 46000 CPS.eV, 48000 CPS.eV, 50000 CPS.eV, 52000 CPS.eV, 55000 CPS.eV, 58000 CPS.eV, 58600 CPS.eV.

[0021] In some embodiments, when the positive electrode plate is subjected to XPS testing and the XPS etching depth is 10 nm on the side of the positive electrode material layer away from the current collector, the characteristic peak area of divalent manganese element is 10056 - 25191 CPS.eV, and / or the characteristic peak area of trivalent manganese element is 13500 - 32871 CPS.eV.

[0022] The characteristic peak area sizes of the divalent manganese element and the trivalent manganese element are different from the contents of divalent and trivalent manganese in the shallow surface layer at 10 nm in the positive electrode plate, and are also different from the total manganese content in the shallow layer of the electrode plate. When preferably within the above ranges, divalent manganese and trivalent manganese are more likely to contact and react with the electrolyte.

[0023] More preferably, a = 28000 - 40000 CPS.eV.

[0024] The sum of the characteristic peak areas of divalent manganese and trivalent manganese in the positive electrode plate during XPS testing is related to the manganese element content of the overall material, and the priority levels of the reactions with lithium nickel cobalt manganese oxide particles and lithium iron manganese phosphate particles when the electrolyte contacts the positive electrode material. Furthermore, it affects the fast charging performance and cycle life of the product. When the sum of the characteristic peak areas is preferably within the above range, the lithium iron manganese phosphate particles in the positive electrode material react with the electrolyte preferentially, and the side effect of residual alkali on the surface of the lithium nickel cobalt manganese oxide particles in the positive electrode material can be better inhibited, while ensuring higher cycle stability.

[0025] In some embodiments, when the positive electrode plate is subjected to XPS testing and the XPS etching depth is 10 nm on the side of the positive electrode material layer away from the current collector, the ratio of the characteristic peak areas of divalent manganese element and trivalent manganese element is 1:(1.3 - 3.26).

[0026] The ratio of the characteristic peak areas of trivalent manganese element and divalent manganese element reflects the proportion relationship between the two types of particles in the positive electrode active material. Similar to the sum of the two characteristic peak areas, when the area ratio is within the above range, the trivalent manganese in the positive electrode material has higher activity and reacts fully with the electrolyte, thereby inhibiting the side reaction that occurs after the electrolyte contacts the residual alkali on the surface of the lithium nickel cobalt manganese oxide particles. Moreover, the lithium nickel cobalt manganese oxide particles have a higher degree of improving the ionic conductivity of lithium iron manganese phosphate, and the stability of the overall material is better.

[0027] In the technical solution of the present application, the test method for the characteristic peaks of divalent manganese and trivalent manganese is not limited. The specific test method of the present application can be as follows: If the positive electrode plate is not in the lithium-ion battery, it is directly tested; if the positive electrode plate is in the lithium-ion battery, the lithium-ion battery is disassembled in the empty state, and the obtained positive electrode plate is immersed in dimethyl carbonate at room temperature for 60 min, taken out, dried, and then fixed in the test mold with conductive tape. An XPS etching analyzer of model NEXSA GA is used for testing. After the test is completed, the test result value of the areas of the characteristic peaks of divalent manganese and trivalent manganese can be obtained by area integration according to the test data of the corresponding coordinates from the XPS spectrum of the test sample. Among them, the test conditions of XPS are: using a 120W monochromatic Al Kα X-ray source; the energy resolution is less than or equal to 0.48 eV; the test beam spot is 400 μm, and the test pass energy range is automatically supplemented by the instrument to be 632 - 660 eV according to the element to be measured; the etching treatment conditions are: using Ar ions for etching, by adjusting the etching rate or etching time, etc., the etching surface is one side of the positive electrode material layer, and the etching depth is controlled to be 10 nm. After the test is completed, the test result value of the areas of the characteristic peaks of divalent manganese and trivalent manganese can be read from the XPS spectrum of the test sample.

[0028] In some embodiments, when the positive electrode sheet is subjected to XPS testing and the XPS etching depth is 10 nm on the side of the positive electrode material layer away from the current collector, the peak positions of the characteristic peaks of divalent manganese element and trivalent manganese element range from 636 to 646 eV and from 650 to 660 eV.

[0029] In some embodiments, b = 2 to 7.

[0030] Specifically, b is one of 2, 2.1, 2.3, 2.5, 2.6, 2.8, 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2, 4.5, 4.6, 4.8, 5, 5.2, 5.5, 5.8, 6, 6.2, 6.4, 7 or any range value between any two of them.

[0031] Further preferably, b = 2.1 to 6.4.

[0032] Further preferably, b = 3.1 to 4.9.

[0033] The ratio of the enclosed area of two kinds of positive electrode active material particles is related to the volume ratio and surface smoothness of the two materials, which will affect the ionic conductivity on the surface of lithium iron phosphate manganese particles in the positive electrode material and the overall stability of the positive electrode material. When the ratio is preferably within the above range, the degree of improvement of the ionic conductivity of lithium iron phosphate manganese by nickel cobalt manganese oxide particles is higher, and the stability of the overall material is better, and the cycle stability of the lithium ion battery is more excellent.

[0034] In the technical solution of the present application, the test method of S1 or S2 is not limited. Specifically, the present application can be tested by the following test method: if the positive electrode sheet is not in the lithium ion battery, it is directly tested; if the positive electrode sheet is in the lithium ion battery, the lithium ion battery is disassembled in an empty state, and the obtained positive electrode sheet is immersed in dimethyl carbonate at room temperature for 60 min, taken out, dried, a layer of conductive adhesive is first pasted on the sample holder, the positive electrode sheet is adhered to the sample holder, and then a layer of conductive film is plated. The tools and the sample stage are wiped with absolute ethanol, and a certain amount of the sample to be tested is placed on the sample stage; subsequently, it is observed under a scanning electron microscope (SEM). At a magnification of 30K, the SEM image is analyzed using Image Pro-Plus software, the size is calibrated, the area range is set, and the software is allowed to calculate the areas of LMFP particles and NCM particles in the figure.

[0035] In some embodiments, the average diameter of the lithium iron phosphate manganese particles is D μm, and D / b = 1.29 to 4.28.

[0036] Specifically, D / b is one of 1.29, 1.31, 1.35, 1.4, 1.5, 1.55, 1.7, 1.8, 2.0, 2.2, 2.5, 2.8, 3.0, 3.2, 3.5, 3.8, 3.84, 4, 4.2, 4.28 or the range value of any two of them.

[0037] Further preferably, D / b = 1.31 to 3.84.

[0038] In some specific embodiments, D = 5 to 16 μm.

[0039] Further preferably, D = 6 to 12 μm.

[0040] In some embodiments, the test method of D can be specifically: disassemble the lithium-ion battery to obtain the positive electrode plate, then scrape the positive electrode active material layer on the positive electrode plate into powder, evenly sprinkle it on the conductive adhesive, directly put it into the scanning electron microscope, select the SEM photo with a magnification of 30K and clear image, and measure the particle size distribution of lithium iron phosphate manganese (measure 400) through the particle size measurement software (Nano Measurer) to obtain the average diameter D of the lithium iron phosphate manganese particles.

[0041] In some embodiments, the mass ratio of the lithium nickel cobalt manganese oxide particles to the lithium iron phosphate manganese particles is (5:95) to (50:50).

[0042] In some embodiments, the lithium nickel cobalt manganese oxide particles include LiNi a Co b Mn c O2, where a is greater than 0 and less than 1; b is greater than 0 and less than 1; c is greater than 0 and less than 1; a + b + c = 1.

[0043] In some embodiments, the lithium iron phosphate manganese particles include LiMn x Fe y PO4, where x is greater than 0 and less than 1; y is greater than 0 and less than 1; x + y = 1.

[0044] Further, the lithium iron phosphate manganese particles further include a carbon layer provided on the particle surface.

[0045] Further preferably, in LiMn x Fe y PO4, x ≥ 0.65 and b = 2.5 to 5 in the positive electrode plate.

[0046] When the content ratio of manganese element in the lithium iron manganese phosphate particles and the enclosed area ratio of the two types of particles in the positive electrode sheet are within the above ranges, on the one hand, due to the effect of the lithium nickel cobalt manganese oxide particles, the ionic conductivity of the lithium iron manganese phosphate particles is significantly improved, enhancing the ion / electron insertion and extraction efficiency. On the other hand, the side reaction degree caused by the residual alkali on the surface of the lithium nickel cobalt manganese oxide particles is lower, and the comprehensive stability is better.

[0047] Further, in the LiNi a Co b Mn c O2, a = 0.6 - 0.8.

[0048] When the nickel ratio in the lithium nickel cobalt manganese oxide particles is increased to the above range, the crystal structure of the particles can be effectively improved, thereby enhancing the ionic conductivity of the material. At the same time, the content of residual alkali on the particle surface will not increase due to the too high nickel ratio, thus achieving good cycle stability.

[0049] In some embodiments, the lithium nickel cobalt manganese oxide particles further include a doping element M, and the M includes at least one of Zr, Al, Sr, W, Y, Nb, Sb, Mg.

[0050] Further preferably, the content of the doping element M in the lithium nickel cobalt manganese oxide particles is 500 - 3000 ppm.

[0051] By introducing a certain doping element into the lithium nickel cobalt manganese oxide particles, on the premise of ensuring the expected performance of the positive electrode sheet described in this application, the lithium ion transmission channels in the particles can be further improved, thereby enhancing the ionic conductivity of the overall positive electrode active material.

[0052] In some embodiments, the lithium iron manganese phosphate particles can be commercially available products or obtained by a self-made method. Specifically, the lithium iron manganese phosphate particles can be prepared by the following method: Mix a lithium source and a phosphorus source in a solvent, add the obtained mixture to an iron source, a manganese source, and a carbon source and mix evenly, then perform spray drying. The obtained powder particles are calcined to obtain the lithium iron manganese phosphate particles; In some embodiments, the solvent includes water.

[0053] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxalate, lithium dihydrogen phosphate, lithium citrate, lithium acetate; The phosphorus source includes at least one of ammonium dihydrogen phosphate, ammonium phosphate; The iron source includes at least one of ferrous oxalate, iron hydroxide, ferrous hydroxide, iron phosphate, ferrous phosphate, iron acetate, ferrous acetate, iron carbonate, ferrous carbonate, iron(III) oxide, iron(II,III) oxide, iron oxalate; The manganese source includes at least one of manganese oxide, manganese carbonate, manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate.

[0054] In some embodiments, the mixing can be achieved by ball milling. The ball milling time is 1.5 h to 2.5 h, and the rotation speed is 400 to 500 r / min.

[0055] In some embodiments, the pressure during spray drying is 0.4 to 0.7 Mpa, the inlet air temperature is 200 to 290 °C, and the outlet air temperature is 80 to 120 °C.

[0056] In some embodiments, the calcination includes first-stage calcination and second-stage calcination. The temperature of the first-stage calcination is 400 to 500 °C, and the time is 1 to 3 h; the temperature of the second-stage calcination is 700 to 800 °C, and the time is 9 to 11 h.

[0057] In some embodiments, the nickel cobalt manganese lithium oxide particles can be commercially available products or obtained by a self-made method. Specifically, the nickel cobalt manganese lithium oxide particles can be obtained by the following preparation method: Mix a nickel source, a cobalt source, and a manganese source in a solvent, add a precipitating agent for precipitation reaction, let it stand, and after filtration, washing, and drying, mix the obtained mixed precursor with a lithium source for ball milling and calcination to obtain the nickel cobalt manganese lithium oxide particles.

[0058] In some embodiments, the nickel source includes at least one of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate; In some embodiments, the cobalt source used includes at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate; In some embodiments, the manganese source includes at least one of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate; In some embodiments, the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxalate, lithium dihydrogen phosphate, lithium citrate, and lithium acetate; In some embodiments, the precipitating agent includes at least one of sodium hydroxide, sodium carbonate, and oxalic acid.

[0059] In some embodiments, the time for the precipitation reaction is 0.5 to 1.5 h.

[0060] In some embodiments, the heating rate during calcination is 3 to 8 °C / min, the calcination temperature is 700 to 900 °C, and the time is 10 to 15 h.

[0061] In some embodiments, the positive electrode material layer further includes a carbon material.

[0062] Carbon materials, especially graphite, graphene, etc. with high conductivity and high adsorption efficiency, can both improve the overall conductivity of the cathode material and inhibit the dissolution of transition metal elements. Those skilled in the art can, according to the actual situation, add a certain content and configuration of carbon materials to the cathode material layer to compound with the lithium deintercalation active material, as long as it does not affect the regulation of the key parameters in the cathode plate described in the technical solution of this application, it is acceptable.

[0063] In some embodiments, the cathode material layer in the cathode plate includes a cathode material, a binder, and a conductive agent. The cathode material includes lithium nickel cobalt manganese oxide particles and lithium iron manganese phosphate particles, and the mass percentage of the cathode material in the cathode material layer is 92% - 99%.

[0064] In some embodiments, the binder is used to improve the adhesion between the cathode active material particles and the adhesion between the cathode active material and the cathode current collector. Any binder can be used without particular limitation, as long as it has suitable binding properties and does not significantly cause adverse chemical changes in the battery. For example, the binder includes fluorinated polyolefin binders, and fluorinated polyolefin binders include, but are not limited to, polyvinylidene fluoride (PVDF), vinylidene fluoride copolymers, or their modified (e.g., carboxylic acid, acrylic acid, acrylonitrile, etc.) derivatives.

[0065] Specifically, the binder is selected from polytetrafluoroethylene or polyvinylidene fluoride.

[0066] In some of these embodiments, the mass percentage of the binder in the cathode material layer is 1% - 4.0%, such as 1%, 1.2%, 1.5%, 1.8%, 2.0%, 2.2%, 2.5%, 2.7%, 3.0%, 3.2%, 3.5%, 3.8%, 4.0%, or the range formed by any two of the above values.

[0067] In some embodiments, the conductive agent is used to provide conductivity. Any conductive agent can be used without particular limitation, as long as it has suitable electron conductivity and does not significantly cause adverse chemical changes in the battery. Exemplarily, the conductive agent in the cathode active material layer includes, but is not limited to, at least one of carbon nanotubes, carbon black, graphite, carbon fiber, activated carbon, mesoporous carbon, fullerenes, etc. Among them, carbon fiber such as carbon nanofiber, etc.; carbon black such as SP (Super P, the same below), acetylene black, Ketjen black, etc.

[0068] In some of these embodiments, the mass percentage of the conductive agent in the cathode material layer is 1.0% - 2.0%, such as 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, or the range formed by any two of the above values.

[0069] In some embodiments, in the positive electrode sheet, the average diameter of the secondary particles of lithium nickel cobalt manganate is 2 to 5 μm.

[0070] In some embodiments, in the positive electrode sheet, the average diameter of the primary particles of lithium nickel cobalt manganate is 1.8 to 2.1 μm.

[0071] Another object of the present application is also to provide a lithium ion battery, including the positive electrode sheet of the present application.

[0072] In some embodiments, the lithium ion battery further includes a negative electrode sheet and an electrolyte.

[0073] In some embodiments, the electrolyte includes additives, a solvent, and a lithium salt.

[0074] In some embodiments, the solvent includes at least one of carbonate solvents, carboxylate solvents, ether solvents, sulfone solvents, nitrile solvents, and phosphate solvents.

[0075] Exemplarily, the carbonate solvents include, but are not limited to, at least one of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC); the carboxylate solvents include, but are not limited to, at least one of ethyl acetate, methyl formate, and 1,4-butyrolactone; the ether solvents include at least one of dimethyltetrahydrofuran, tetrahydrofuran, and 1,2-dimethoxyethane; the sulfone solvents include at least one of methyl sulfone and dimethyl sulfoxide; the nitrile solvents include at least one of propionitrile, butyronitrile, 1-(2-cyanoethyl)pyrrole, and 1,3,6-hexanetricarbonitrile; and the phosphate solvents include at least one of trimethyl phosphate and triethyl phosphate.

[0076] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium trifluoromethanesulfonate, lithium bis(fluoromethanesulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorodioxalate phosphate, and lithium tetrafluorodioxalate phosphate.

[0077] In some embodiments, the additives include, but are not limited to, vinylene carbonate.

[0078] In some embodiments, the negative electrode sheet includes a negative electrode material layer, the negative electrode material layer includes a negative electrode material, and the negative electrode material includes at least one of natural graphite, artificial graphite, mesocarbon microbeads, hard carbon, soft carbon, elemental silicon, silicon monoxide, silicon-carbon composite materials, and lithium titanate.

[0079] The negative electrode material layer may further contain a conductive agent and / or a binder.

[0080] The conductive agent in the negative electrode active material layer is used to provide conductivity. Any conductive agent can be used without particular limitation as long as it has appropriate electron conductivity and does not significantly cause adverse chemical changes in the battery. Exemplarily, the conductive agent includes but is not limited to at least one of carbon nanotubes, carbon black, graphite, carbon fiber, activated carbon, mesoporous carbon, fullerenes, etc., where carbon fiber such as carbon nanofiber, etc.; carbon black such as SP, acetylene black, Ketjen black, etc.

[0081] In some of these embodiments, the mass percentage content of the conductive agent in the negative electrode material layer is 0.4% - 2%, such as 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%, 1.7%, 1.8%, 1.9%, 2% or the range formed by any two of the above values.

[0082] The binder in the negative electrode active layer is used to improve the adhesion between negative electrode active material particles and the adhesion between the negative electrode active material and the negative electrode current collector. Any binder can be used without particular limitation as long as it has appropriate binder properties and does not significantly cause adverse chemical changes in the battery. Exemplarily, the binder includes but is not limited to at least one of carboxymethyl cellulose (CMC), styrene - butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl butyral, aqueous acrylic resin.

[0083] In some of these embodiments, the mass percentage content of the binder in the negative electrode material layer is 1.0% - 4.5%, such as 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.2%, 2.5%, 2.7%, 3.0%, 3.2%, 3.5%, 3.8%, 4.0%, 4.2%, 4.5% or the range formed by any two of the above values.

[0084] In some embodiments, the negative electrode material layer in the negative electrode plate includes a negative electrode material, a binder, and a conductive agent. The mass percentage content of the negative electrode material in the negative electrode material layer is 70 - 99%.

[0085] The present invention will be further elaborated with specific examples below, and these examples should not be construed as limiting the scope claimed by the present invention: Example 1 A positive electrode plate and a lithium - ion battery prepared therefrom, the preparation method comprising the following steps: Preparation of lithium iron manganese phosphate particles: Lithium carbonate and phosphoric acid aqueous solution were mixed and reacted according to the stoichiometric ratio, and then manganese carbonate and iron oxalate were added and ball-milled. The molar ratio of manganese atoms to iron atoms was 68:32. The obtained slurry was further sand-milled to an appropriate particle size and then atomized by a spray drying device. The obtained particles were calcined in a tube furnace in the first stage, and then the temperature was raised and calcined in the second stage to obtain lithium iron manganese phosphate particles; Preparation of lithium nickel cobalt manganese oxide particles: Nickel sulfate solution, cobalt sulfate solution, and manganese sulfate solution were mixed according to the stoichiometric ratio, and then a precipitant sodium hydroxide was added to adjust the pH within 11 and react at a temperature within 55 °C for 1 h. After filtration, washing, and drying, the obtained precursor and lithium carbonate were ball-milled according to the molar ratio of lithium atoms to the total atoms of nickel, cobalt, and manganese in the precursor of 1.05:1, and calcined at 850 °C for 12 h in a nitrogen atmosphere to obtain lithium nickel cobalt manganese oxide particles; Preparation of the positive electrode sheet: Lithium iron manganese phosphate particles and lithium nickel cobalt manganese oxide particles were mixed as the positive electrode material according to a certain mass ratio. Then, the positive electrode material, conductive agent SP, and binder polyvinylidene fluoride were dispersed in N-methylpyrrolidone according to the mass ratio of 96:1.5:2.5, and a slurry was prepared by vacuum stirring. Subsequently, it was coated on the current collector aluminum foil, and the coating surface density was set to 380 g / cm 2 , and after drying, cold pressing, and slitting, it was roll-pressed at a compaction density of 2.4 g / cm 3 to obtain the positive electrode sheet; Preparation of the negative electrode sheet: The negative electrode material artificial graphite, conductive agent SP, thickening agent sodium carboxymethyl cellulose, and binder styrene-butadiene rubber were dispersed in water according to the mass ratio of 96.5:1:1:1.5, and a slurry was prepared by vacuum stirring. Subsequently, it was coated on the current collector copper foil, and the coating surface density was set to 172 g / cm 2 , and after drying, cold pressing, and slitting, it was roll-pressed at a compaction density of 1.66 g / cm 3 to obtain the negative electrode sheet; Preparation of the electrolyte: EC, EMC, and DEC were compounded as solvents according to the mass ratio of 1:1:1. Then, based on the total mass of the electrolyte, lithium hexafluorophosphate was added to prepare an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L; (4) The positive electrode sheet, commercially available PP separator, and negative electrode sheet were stacked and assembled into an electric core in sequence. The electric core was placed in an outer packaging shell, dried, and then the electrolyte was injected. After vacuum packaging, standing, formation, and constant volume, the lithium-ion secondary battery was obtained.

[0086] Examples 2 to 42, Comparative Examples 1 to 4 A positive electrode sheet and a lithium-ion battery prepared therefrom, which are only different from those in Example 1 in that the preparation process of the positive electrode sheet is different, The parameters of each positive electrode plate during preparation, the test results and parameters of the products are shown in Tables 1 and 2, and Figure 1 and Figure 2 as shown. The test methods for the parameters of each product are as described above. Among them, a is regulated by the manganese element content in the lithium iron manganese phosphate particles, the manganese element content in the lithium nickel cobalt manganese oxide particles, and their mass compound ratio; b and D are adjusted by the material addition ratio of the lithium iron manganese phosphate particles and the lithium nickel cobalt manganese oxide particles during preparation, the process during the calcination of the lithium iron manganese phosphate particles, the slurry mixing time of the positive electrode paste, and the mixing mass ratio of the two kinds of particles.

[0087] Table 1 Table 2 Effect Example The lithium-ion batteries obtained from each example and comparative example were tested as follows: (1) Cycle capacity retention rate test: (I) The formed lithium-ion secondary batteries obtained from each example and comparative example were charged at a constant current rate of 0.33C, then charged at a constant voltage of 4.25V (cut-off voltage 4.25V), and then discharged at 0.33C (cut-off voltage 2.5V). The constant volume was repeated twice, and the constant volume capacity was recorded. They were charged at a constant current of 0.33C to the upper limit voltage of 4.25V and charged at a constant voltage until the current was less than 0.05C; then discharged at 0.33C to 2.5V. This was taken as one cycle, and the above steps were repeated 200 times. The capacity retention rate was calculated by: capacity retention rate = 100% × discharge capacity at the 200th time / constant volume capacity.

[0088] (2) Fast charging performance test: (I) The formed lithium-ion secondary batteries obtained from each example and comparative example were charged at a constant current rate of 0.33C, then charged at a constant voltage of 4.25V (cut-off voltage 4.25V), and then discharged at 0.33C (cut-off voltage 2.5V). The constant volume was repeated twice; (II) Regarding each lithium-ion secondary battery, with the discharge capacity of the last cycle being 100% SOC, first charge at a rate of 0.33C to 10% SOC; then charge at a reduced rate of 0.2C, starting from 4C (the cut-off voltage is 4.25V, the auxiliary voltage ≤ 0), which are 3.8C, 3.6C, 3.8C, 3.6C, 3.4C, 3.2C, 3C, 2.8C, 2.6C, 2.4C, 2.2C, 2C, 1.8C, 1.6C, 1.4C, 1.2C, 1C, 0.8C, 0.6C, 0.4C, 0.2C, 0.1C, 0.05C respectively, and record the time taken from charging to 10% SOC to 80% SOC.

[0089] The test results are shown in Table 3.

[0090] Table 3 It can be seen from Table 3 that: (1) In the lithium-ion secondary battery described in this application, by using lithium iron manganese phosphate particles and lithium nickel cobalt manganese oxide particles together as the cathode material in the cathode electrode sheet, based on their synergistic effect, while regulating the relationship range of the characteristic peak areas of divalent manganese and trivalent manganese and the ratio of the enclosed areas of the two cathode active material particles at an etching depth of 10 nm in the cathode material layer of the cathode electrode sheet, the constructed relationship 10000b / a within the range of 0.5 - 2.5 can enable the overall material to have a high ion conduction efficiency. And when the cathode material contacts the electrolyte, the surface residual alkali activity of the lithium nickel cobalt manganese oxide particles can be effectively inhibited. Finally, the lithium-ion battery can achieve excellent fast charging performance, with the time taken from charging to 10% SOC to 80% SOC within 25 min, and excellent cycling performance at high temperature. After 200 cycles, the capacity retention rate can reach more than 90%, and the comprehensive performance is excellent.

[0091] (2) At the same time, since the enclosed area of lithium iron phosphate particles and lithium nickel cobalt manganese oxide particles is related to the residual alkali reaction activity on the surface of lithium nickel cobalt manganese oxide particles and the ionic conductivity of the material, the sum of the characteristic peak areas of divalent and trivalent manganese in the material is related to the manganese element of the overall material. When the electrolyte contacts the positive electrode material, it is also related to the priority of the reaction between the electrolyte and lithium nickel cobalt manganese oxide particles and lithium manganese iron phosphate particles, thereby affecting the fast charging performance and cycle life of the product. Therefore, when constructing the relational expression 10000b / a, when further preferably within the range of 0.92 to 1.48, the fast charging time of the lithium ion battery can be further shortened to within 20 min, and the cycle capacity retention rate can be increased to more than 93%; and according to Examples 1 to 32, it can be seen that when the relational expression 10000b / a range of the positive electrode sheet of the present application is optimized, and further the sum of the characteristic peak areas of divalent manganese and trivalent manganese and the enclosed area range of the two kinds of particles are further optimized: a = 28000 to 40000, and / or, b = 3.1 to 4.9, the electrochemical performance of the lithium ion battery can be further improved, the time for charging to 80% SOC can be shortened to within 18 min, and the capacity retention rate at high temperature can reach more than 95%, up to 95.7%.

[0092] (3) According to Examples 1, 8, 22, and 33 to 36, it can be seen that when preparing lithium manganese iron phosphate particles, different calcination conditions will cause changes in particle size. When the ratio of the average diameter D of the lithium manganese iron phosphate particles to b is preferably within the range of 1.31 to 3.84, the cycle stability and fast charging performance of the lithium ion battery are better.

[0093] (4) According to the comparison between Examples 39 to 42 and other examples, it can be seen that when the proportions of divalent manganese element and trivalent manganese element change, the activity of the trivalent manganese element in the material is also different. When the ratio of the characteristic peak areas of divalent manganese element and trivalent manganese element is preferably within 1:(1.3 to 3.26), the reaction between the trivalent manganese element in the material and the electrolyte is more sufficient, the reaction between the electrolyte and the residual alkali on the surface of lithium nickel cobalt manganese oxide can be further inhibited, and finally better ion conduction efficiency and structural stability can be achieved, and the electrochemical performance of the secondary battery is better.

Claims

1. A positive electrode plate, characterized in that, The positive electrode plate includes a positive electrode material layer, and the positive electrode material layer includes lithium iron manganese phosphate particles and lithium nickel cobalt manganese oxide particles; The positive electrode plate satisfies: 0.5 ≤ 10000b / a ≤ 2.5; The aCPS.eV is the sum of the characteristic peak areas of divalent manganese element and trivalent manganese element at an XPS etching depth of 10 nm on the side of the positive electrode material layer away from the current collector when the positive electrode plate is subjected to XPS testing; where b = S2 / S1, S2 is the total enclosed area of the lithium nickel cobalt manganese oxide particles in the positive electrode sheet at a magnification of 30K, and S1 is the total enclosed area of the lithium iron manganese phosphate particles in the positive electrode sheet at a magnification of 30K. 2 is the total enclosed area of the lithium nickel cobalt manganese oxide particles in the positive electrode sheet at a magnification of 30K, and S1 nm 2 is the total enclosed area of the lithium iron manganese phosphate particles in the positive electrode sheet at a magnification of 30K.

2. The positive electrode sheet according to claim 1, characterized in that, The 10000b / a = 0.92 to 1.

48.

3. The positive electrode sheet according to claim 1, characterized in that, The a = 12800 to 58600, and / or, the b = 2 to 7.

4. The positive electrode sheet according to claim 1, wherein, When the positive electrode plate is subjected to XPS testing and at an XPS etching depth of 10 nm on the side of the positive electrode material layer away from the current collector, the ratio of the characteristic peak area of divalent manganese element to that of trivalent manganese element is 1:(1.3 to 3.26).

5. The positive electrode sheet according to claim 3, wherein, When the positive electrode plate is subjected to XPS testing and at an XPS etching depth of 10 nm on the side of the positive electrode material layer away from the current collector, the characteristic peak area of divalent manganese element is 10056 to 25191 CPS.eV, and / or, the characteristic peak area of trivalent manganese element is 13500 to 32871 CPS.eV.

6. The positive electrode sheet according to claim 1, wherein, The average diameter of the lithium iron manganese phosphate particles is D μm, and D / b = 1.31 to 3.

84.

7. The positive electrode sheet according to claim 6, wherein, The D = 6 to 12 μm.

8. The positive electrode sheet according to claim 1, wherein The mass ratio of the lithium nickel cobalt manganese oxide particles to the lithium iron manganese phosphate particles is (5:95) to (50:50).

9. The positive electrode sheet according to claim 1, wherein, The lithium nickel cobalt manganese oxide particles include LiNi a Co b Mn c O2, where 0 < a < 1; 0 < b < 1; 0 < c < 1; a + b + c = 1, and / or, the lithium iron manganese phosphate particles comprise LiMn x Fe y PO4, where 0 < x < 1; 0 < y < 1; x + y = 1.

10. The positive electrode sheet according to claim 9, wherein The LiMn x Fe y PO4, where x ≥ 0.65, and in the positive electrode sheet, b = 2.5 to 5.

11. The positive electrode sheet according to claim 9, characterized in that, The lithium nickel cobalt manganese oxide particles further include a doping element M, and the M includes at least one of Zr, Al, Sr, W, Y, Nb, Sb, and Mg.

12. The positive electrode sheet according to claim 11, characterized in that, The content of the doping element M in the lithium nickel cobalt manganese oxide particles is 500 to 3000 ppm.

13. The positive electrode sheet according to claim 9, characterized in that, The LiNi a Co b Mn c in O2 has a value of a ranging from 0.6 to 0.

8.

14. A lithium-ion battery, characterized in that, Including the positive electrode plate according to any one of claims 1 to 13.

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