A lithium-ion battery

Abstract

The present invention discloses a lithium-ion battery, belonging to the field of battery technology. The lithium-ion battery is provided with a positive electrode plate. By simultaneously introducing lithium iron manganese phosphate particles and lithium nickel cobalt manganese oxide particles into the positive electrode material, the valence state of the manganese element in the positive electrode material is proportionally regulated, and a connection is established with the proportional relationship of the enclosed areas of the two particles. This can not only effectively improve the fast charging performance of the product under high SOC conditions, but also achieve excellent cycle performance in high-temperature environments.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a lithium-ion battery. Background Art

[0002] While ensuring safety and applicability, the fast-charging capability of lithium-ion batteries has been a key technical indicator that continues to be improved. Among existing products, lithium iron manganese phosphate (LiMnFePO4)-based batteries offer high safety, low production costs, high energy density, and excellent low-temperature performance. However, due to the low ion / electron intercalation and deintercalation efficiency of the LiMnFePO4 cathode material, especially at high SOC conditions, the fast-charging performance of these products lags far behind that of other battery systems. Summary of the Invention

[0003] The purpose of this application is to overcome the shortcomings of the existing technology and provide a positive electrode plate. By introducing lithium iron manganese phosphate particles and lithium nickel cobalt manganese oxide particles into the positive electrode material at the same time, the valence state of the manganese element in the positive electrode material is proportionally regulated, and at the same time, a connection is established with the proportional relationship of the enclosed area of ​​the two particles. This can not only effectively improve the fast charging performance of the product under high SOC conditions, but also achieve excellent cycle performance in high temperature environments.

[0004] To achieve the above-mentioned object, in a first aspect of the present application, the present application provides a positive electrode plate, wherein the positive electrode plate comprises a positive electrode material layer, wherein the positive electrode material layer comprises lithium manganese iron phosphate particles and lithium nickel cobalt manganese oxide particles;

[0005] The positive electrode sheet meets the following requirements: 0.5≤10000b / a≤2.5;

[0006] The aCPS.eV is the sum of the characteristic peak areas of divalent manganese and trivalent manganese when the positive electrode 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;

[0007] b=S2 / S1, S2nm 2 is the total enclosed area of ​​lithium nickel cobalt manganese oxide particles in the positive electrode at 30K magnification, S1nm 2 It is the total enclosed area of ​​the lithium manganese iron phosphate particles in the positive electrode sheet at a magnification of 30K.

[0008] The beneficial effects of this application are:

[0009] The present application provides a positive electrode plate, which introduces lithium iron manganese phosphate particles and lithium nickel cobalt manganese oxide particles into the positive electrode material at the same time, proportionally controls the valence state of the total manganese element in the positive electrode material, and establishes a connection with the proportional relationship of the enclosed area of ​​the two particles. This can not only effectively improve the fast charging performance of the product under high SOC conditions, but also achieve excellent cycle performance in high temperature environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is the XPS test result diagram of the positive electrode sheet described in Example 1 of the present application.

[0011] Figure 2 This is a schematic scanning electron microscope diagram of lithium nickel cobalt manganese oxide particles and lithium manganese iron phosphate particles in the positive electrode sheet described in Example 1 of the present application at a magnification of 30K. DETAILED DESCRIPTION

[0012] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0013] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0014] In this application, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0015] The present application is further described below with specific examples:

[0016] A positive electrode plate, comprising a positive electrode material layer, wherein the positive electrode material layer comprises lithium manganese iron phosphate particles and lithium nickel cobalt manganese oxide particles;

[0017] The positive electrode sheet meets the following requirements: 0.5≤10000b / a≤2.5;

[0018] The aCPS.eV is the sum of the characteristic peak areas of divalent manganese and trivalent manganese when the positive electrode is subjected to XPS (X-ray Photoelectron Spectroscopy) testing and at an XPS etching depth of 10 nm on the side of the positive electrode material layer away from the current collector;

[0019] b=S2 / S1, S2nm 2is the total enclosed area of ​​lithium nickel cobalt manganese oxide particles in the positive electrode at 30K magnification, S1nm 2 It is the total enclosed area of ​​the lithium manganese iron phosphate particles in the positive electrode sheet at a magnification of 30K.

[0020] In the technical solution of the present application, the positive electrode plate uses lithium manganese iron phosphate particles and lithium nickel cobalt manganate particles as the positive electrode material, and the lithium nickel cobalt manganate particles serve as ion conductors. Due to the interlayer structure characteristics of lithium nickel cobalt manganate, the movement resistance of lithium ions is small and the ion conductivity is high. In addition, after compounding with lithium manganese iron phosphate particles, the lithium nickel cobalt manganate particles will be coated on its surface, which can further effectively improve the ion conductivity of the overall positive electrode material surface, 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 manganate particles during the preparation process, the probability of side reactions occurring when the positive electrode material contacts the electrolyte, especially in a heated environment, increases, thereby reducing the cycle performance of the positive electrode plate when applied to lithium ion batteries, especially the cycle performance in a high temperature environment; at the same time, in this composite system, the manganese element includes divalent manganese, trivalent manganese and tetravalent manganese, and the three valence states undergo transformation. For this reason In the present application, the characteristic peak areas of divalent manganese and trivalent manganese (the characteristic peak areas are not equivalent to the proportion of manganese content) in the positive electrode material layer in the positive electrode plate at an etching depth of 10 nm and the ratio of the enclosed areas of the two positive electrode active material particles are further regulated within a specific range. By controlling these two parameters to establish a relationship, the surface ion conduction efficiency of the lithium manganese iron phosphate particles can be improved. When the positive electrode material contacts the electrolyte, the manganese ions on the surface of the lithium manganese iron phosphate particles will be rapidly oxidized and decomposed into lithium salts, solvents, etc. in the electrolyte to form by-products, compared with the lithium nickel cobalt manganese oxide particles. Overall, the reaction activity with the electrolyte is better, thereby inhibiting the lithium nickel cobalt manganese oxide particles from undergoing excessive side reactions with the electrolyte due to residual alkali on the surface. Ultimately, the lithium-ion battery used in the corresponding application of the positive electrode plate can achieve excellent fast charging performance while maintaining a high level of cycle performance, especially the cycle performance in a high temperature environment.

[0021] At the same time, compared with conventional fast charging, at high SOC, secondary batteries usually need to be charged with a small current to avoid the problem of increased dissolution of manganese ions in lithium iron manganese phosphate, changes in the material lattice, and severe battery polarization caused by charging with a large current at high SOC. Usually, the charging time at high SOC is longer. The present application scheme introduces lithium iron manganese phosphate particles and lithium nickel cobalt manganese oxide particles into the positive electrode material at the same time, proportionally regulates the valence state of the manganese element in the positive electrode material, and establishes a connection with the proportional relationship of the enclosed area of ​​the two particles. This can effectively improve the conductive properties of the lithium iron manganese phosphate material, inhibit and reduce the probability of manganese ion dissolution in the positive electrode material, and improve the fast charging performance of the secondary battery under high SOC conditions.

[0022] In some embodiments, the 10000b / a=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 two of the range values.

[0023] In the positive electrode plate of the present application, if the ratio of the enclosed area of ​​the lithium nickel cobalt manganese oxide particles to the lithium iron manganese phosphate particles is too large, then after the positive electrode plate is immersed in the electrolyte, the lithium nickel cobalt manganese oxide particles are more likely to undergo side reactions with the electrolyte due to the residual alkali on the surface. If the ratio is too small, the improvement in the ion conduction of the particles on the surface of the lithium iron manganese phosphate particles will not reach the expected level. On the other hand, if the characteristic peak area of ​​divalent and trivalent manganese in the positive electrode plate is 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 between the two, they need to be maintained within a specific range to achieve an improvement in the overall electrochemical performance.

[0024] Further preferably, the 10000b / a=0.5~2.1.

[0025] Further preferably, the 10000b / a=0.92~1.48.

[0026] When the ratio of the characteristic peak area of ​​the divalent and trivalent manganese elements of the positive electrode plate of the present application to the enclosed area ratio of the two positive electrode material particles in the plate is within the above-mentioned preferred range, the overall ion / electron transmission efficiency of the lithium-ion battery is higher, and better fast charging performance can be achieved. At the same time, the stability is better and the cycle life is longer in a high temperature environment.

[0027] In some embodiments, a=12800~58600 CPS.eV.

[0028] Specifically, the a=12800CPS.eV, 15000CPS.eV, 18000CPS.eV, 20000CPS.eV, 23500CPS.eV, 24500CPS.eV, 25000CPS.eV, 26000CPS.eV, 27000CPS.eV, 280 360 00CPS.eV, 37000CPS.eV, 38000CPS.eV, 39000CPS.eV, 39500CPS.eV, 40000CPS.eV, 40500CPS.eV, 41000CPS.eV, 42000CPS.eV, 43000CPS.eV, 44000CPS.eV, 45000CPS.eV, 46000CPS.eV, 48000CPS.eV, 50000CPS.eV, 52000CPS.eV, 55000CPS.eV, 58000CPS.eV, 58600CPS.eV, or a range value of one or any two of the above.

[0029] In some embodiments, when the positive electrode sheet is subjected to XPS testing and at an XPS etching depth of 10 nm on a side of the positive electrode material layer away from the current collector, the characteristic peak area of ​​the divalent manganese element is 10056~25191CPS.eV, and / or the characteristic peak area of ​​the trivalent manganese element is 13500~32871CPS.eV.

[0030] The characteristic peak area of ​​the divalent manganese element and the trivalent manganese element is different from the content of divalent and trivalent manganese in the shallow layer of the positive electrode at 10nm, and the total manganese content in the shallow layer of the electrode. When preferably within the above range, divalent manganese and trivalent manganese are more likely to contact and react with the electrolyte.

[0031] Further preferably, a=28000~40000 CPS.eV.

[0032] The sum of the characteristic peak areas of divalent manganese and trivalent manganese in the XPS test of the positive electrode is related to the manganese content of the overall material, as well as the priority of the reaction between the electrolyte and the lithium nickel cobalt manganese oxide particles and lithium manganese iron phosphate particles when the electrolyte contacts the positive electrode material, thereby affecting 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 manganese iron phosphate particles in the positive electrode material react preferentially with the electrolyte, and the side effects of residual alkali on the surface of the lithium nickel cobalt manganese oxide particles in the positive electrode material can be better suppressed, while ensuring higher cycle stability.

[0033] In some embodiments, when the positive electrode sheet is subjected to XPS testing and the XPS etching depth of 10 nm on the side of the positive electrode material layer away from the current collector is 1: (1.3~3.26), the ratio of the characteristic peak areas of the divalent manganese element to the trivalent manganese element is 1.

[0034] The ratio of the characteristic peak areas of trivalent manganese and divalent manganese reflects the proportion of the two particles in the positive electrode active material, which is 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 is more active and fully reacts with the electrolyte, thereby inhibiting the side reaction after the electrolyte contacts the residual alkali on the surface of the lithium nickel cobalt manganese oxide particles. In addition, the ionic conductivity of the lithium nickel cobalt manganese oxide particles for lithium manganese iron phosphate is further improved, and the overall material stability is better.

[0035] In the technical solution of the present application, there is no limitation on the test method for the characteristic peaks of divalent manganese and trivalent manganese. The solution of the present application can be specifically tested by the following test method: if the positive electrode plate is not in a lithium-ion battery, the test is performed directly; if the positive electrode plate is in a lithium-ion battery, the lithium-ion battery is disassembled in an empty state, and the obtained positive electrode plate is placed in dimethyl carbonate and soaked for 60 minutes at room temperature, taken out, dried, and then fixed in a test mold with conductive tape. The test is performed using a NEXSA GA model XPS etching analyzer. After the test is completed, the area integration of the characteristic peaks of divalent manganese and trivalent manganese can be performed from the XPS spectrum of the test sample according to the test data of the corresponding coordinates to obtain the test result value of the area of ​​​​the characteristic peaks of divalent manganese and trivalent manganese. Among them, the XPS test conditions are: using a 120W monochromatized Al Kα X-ray source; the energy resolution is less than or equal to 0.48 eV; the test beam spot is 400μm, and the instrument automatically supplements the test energy range between 632~660eV according to the element to be tested; the etching treatment conditions are: using Ar ions for etching, by adjusting the etching rate or etching time, etc., the etching surface is the positive electrode material layer, and the etching depth is controlled to be 10nm. After the test is completed, the test result values ​​of the characteristic peak areas of divalent manganese and trivalent manganese can be read from the XPS spectrum of the test sample.

[0036] In some embodiments, when the positive electrode sheet is subjected to XPS testing and the XPS etching depth of 10 nm on the side of the positive electrode material layer away from the current collector is 10 nm, the peak positions of the characteristic peaks of divalent manganese and trivalent manganese are in the range of 636-646 eV and 650-660 eV.

[0037] In some embodiments, b=2~7.

[0038] Specifically, b=one or any two of the range values ​​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.

[0039] Further preferably, b=2.1~6.4.

[0040] More preferably, b=3.1~4.9.

[0041] The ratio of the enclosed areas of the two positive electrode active material particles is related to the volume share and surface smoothness of the two materials, which will affect the ionic conductivity of the surface of the lithium manganese iron phosphate 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 ionic conductivity of the lithium nickel cobalt manganese oxide particles for lithium manganese iron phosphate is further improved, and the overall material stability is better, and the lithium-ion battery cycle stability is better.

[0042] In the technical solution of the present application, the test method of S1 or S2 is not limited. The present application can be specifically tested by the following test method: if the positive electrode sheet is not in a lithium-ion battery, the test is performed directly; if the positive electrode sheet is in a lithium-ion battery, the lithium-ion battery is disassembled in an empty state, and the obtained positive electrode sheet is placed in dimethyl carbonate and soaked for 60 minutes at room temperature, taken out, and dried. A layer of conductive glue is first applied to the sample holder, and the positive electrode sheet is glued to the sample holder, and then a conductive film is coated. The tools and sample stage are wiped with anhydrous ethanol, and a certain amount of the sample to be tested is placed on the sample stage; then, it is observed under a scanning electron microscope (SEM), and 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 area of ​​LMFP particles and NCM particles in the image.

[0043] In some embodiments, the average diameter of the lithium iron manganese phosphate particles is D μm, and D / b=1.29-4.28.

[0044] Specifically, the D / b is in the range of one or any two 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, and 4.28.

[0045] More preferably, D / b=1.31~3.84.

[0046] In some specific embodiments, D=5~16 μm.

[0047] More preferably, D=6~12 μm.

[0048] In some embodiments, the testing method for D can be specifically as follows: disassembling the lithium-ion battery to obtain the positive electrode sheet, then scraping the positive electrode active material layer on the positive electrode sheet to obtain powder, evenly sprinkling the powder on the conductive glue, and directly placing it in a scanning electron microscope, selecting a SEM photo with a magnification of 30K and a clear image, and measuring the particle size distribution of the lithium iron manganese phosphate using particle size measurement software (Nano Measurer) (measuring 400 particles) to obtain the average diameter D of the lithium iron manganese phosphate particles.

[0049] In some embodiments, the mass ratio of the lithium nickel cobalt manganese oxide particles to the lithium manganese iron phosphate particles is (5:95) to (50:50).

[0050] 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.

[0051] In some embodiments, the lithium manganese iron phosphate 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; and x+y=1.

[0052] Furthermore, the lithium manganese iron phosphate particles further include a carbon layer disposed on the surface of the particles.

[0053] More preferably, the LiMn x Fe y In PO4, x≥0.65 and in the positive electrode sheet, b=2.5~5.

[0054] When the proportion of manganese element content in the lithium manganese iron phosphate particles and the proportion of the enclosed area of ​​the two particles in the positive electrode sheet are preferably within the above range, on the one hand, based on the effect of the lithium nickel cobalt manganese oxide particles, the ionic conductivity of the lithium manganese iron phosphate particles is significantly improved, and the ion / electron deintercalation efficiency is improved. On the other hand, the degree of side reactions caused by residual alkali on the surface of the lithium nickel cobalt manganese oxide particles is lower, and the overall stability is better.

[0055] Furthermore, the LiNi a Co b Mn c In O2, a=0.6~0.8.

[0056] When the proportion of nickel elements in lithium nickel cobalt manganese oxide particles is increased to the above range, the crystal structure of the particles can be effectively improved, thereby improving the ionic conductivity of the material. At the same time, the residual alkali content on the surface of the particles will not increase due to the excessive proportion of nickel elements, thereby achieving good cycle stability.

[0057] In some embodiments, the lithium nickel cobalt manganese oxide particles further include a doping element M, wherein M includes at least one of Zr, Al, Sr, W, Y, Nb, Sb, and Mg.

[0058] Further preferably, the content of the doping element M in the lithium nickel cobalt manganese oxide particles is 500-3000 ppm.

[0059] By introducing certain doping elements into the lithium nickel cobalt manganese oxide particles, the transmission channels of lithium ions in the particles can be further improved while ensuring the expected performance of the positive electrode plate described in this application, thereby improving the ionic conductivity of the overall positive electrode active material.

[0060] In some embodiments, the lithium manganese iron phosphate particles may be commercially available products or may be obtained by a homemade method. Specifically, the lithium manganese iron phosphate particles may be prepared by the following method:

[0061] A lithium source and a phosphorus source are mixed in a solvent, an iron source, a manganese source, and a carbon source are added to the obtained mixture, mixed evenly, spray-dried, and the obtained powder particles are calcined to obtain the lithium manganese iron phosphate particles;

[0062] In some embodiments, the solvent comprises water.

[0063] 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, and lithium acetate;

[0064] The phosphorus source includes at least one of ammonium dihydrogen phosphate and ammonium phosphate;

[0065] The iron source includes at least one of ferrous oxalate, ferric hydroxide, ferrous hydroxide, ferric phosphate, ferrous phosphate, ferric acetate, ferrous acetate, ferric carbonate, ferrous carbonate, ferrous oxide, ferrous oxide, and ferric oxalate;

[0066] The manganese source includes at least one of manganese oxide, manganese carbonate, manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate.

[0067] In some embodiments, the mixing can be achieved by ball milling, and the ball milling time is 1.5 h to 2.5 h, and the rotation speed is 400 to 500 r / min.

[0068] In some embodiments, the pressure during spray drying is 0.4-0.7 MPa, the air inlet temperature is 200-290° C., and the air outlet temperature is 80-120° C.

[0069] In some embodiments, the calcination includes a first-stage calcination and a second-stage calcination, wherein the first-stage calcination is performed at a temperature of 400-500° C. for 1-3 hours; and the second-stage calcination is performed at a temperature of 700-800° C. for 9-11 hours.

[0070] In some embodiments, the lithium nickel cobalt manganese oxide particles may be commercially available products or may be obtained by a homemade method. Specifically, the lithium nickel cobalt manganese oxide particles may be obtained by the following preparation method:

[0071] A nickel source, a cobalt source and a manganese source are mixed in a solvent, a precipitant is added for precipitation reaction, and the mixture is allowed to stand. After filtering, washing and drying, the obtained mixed precursor is mixed with a lithium source and ball milled, and calcined to obtain the nickel-chromium-manganese oxide lithium particles.

[0072] In some embodiments, the nickel source includes at least one of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate;

[0073] In some embodiments, the cobalt source used includes at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate;

[0074] In some embodiments, the manganese source includes at least one of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate;

[0075] 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;

[0076] In some embodiments, the precipitant comprises at least one of sodium hydroxide, sodium carbonate, and oxalic acid.

[0077] In some embodiments, the precipitation reaction time is 0.5 to 1.5 hours.

[0078] In some embodiments, the heating rate during calcination is 3-8° C. / min, the calcination temperature is 700-900° C., and the calcination time is 10-15 h.

[0079] In some embodiments, the positive electrode material layer further includes a carbon material.

[0080] Carbon materials, especially graphite and graphene with high conductivity and high adsorption efficiency, can take into account both improving the overall conductivity of the positive electrode material and inhibiting the dissolution of transition metal elements. Those skilled in the art can add a certain content and configuration of carbon materials to the positive electrode material layer to compound the lithium deintercalation active material according to actual conditions. As long as it does not affect the regulation of key parameters in the positive electrode sheet described in the technical solution of this application, it is acceptable.

[0081] In some embodiments, the positive electrode material layer in the positive electrode sheet includes a positive electrode material, a binder, and a conductive agent. The positive electrode material includes lithium nickel cobalt manganese oxide particles and lithium manganese iron phosphate particles. The mass percentage of the positive electrode material in the positive electrode material layer is 92~99%.

[0082] In some embodiments, the binder is used to improve the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode 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 a fluorinated polyolefin binder, which includes but is not limited to polyvinylidene fluoride (PVDF), vinylidene fluoride copolymers, or modified derivatives thereof (e.g., modified with carboxylic acid, acrylic acid, acrylonitrile, etc.).

[0083] Specifically, the binder is selected from polytetrafluoroethylene or polyvinylidene fluoride.

[0084] In some embodiments, the mass percentage of the binder in the positive electrode material layer is 1% to 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 an interval formed by any two of the above values.

[0085] In some embodiments, the conductive agent is used to provide electrical conductivity. Any conductive agent can be used without particular limitation, as long as it has suitable electronic conductivity and does not significantly cause adverse chemical changes in the battery. Exemplary conductive agents in the positive electrode active material layer include, but are not limited to, at least one of carbon nanotubes, carbon black, graphite, carbon fibers, activated carbon, mesoporous carbon, and fullerenes, wherein carbon fibers include carbon nanofibers, and carbon black includes SP (Super P, the same below), acetylene black, and Ketjen black.

[0086] In some embodiments, the mass percentage of the conductive agent in the positive electrode material layer is 1.0% to 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 an interval formed by any two of the above values.

[0087] In some embodiments, in the positive electrode sheet, the average diameter of the secondary particles of the lithium nickel cobalt manganese oxide particles is 2-5 μm.

[0088] In some embodiments, in the positive electrode sheet, the average diameter of the primary particles of lithium nickel cobalt manganese oxide is 1.8-2.1 μm.

[0089] Another object of the present application is to provide a lithium-ion battery comprising the positive electrode sheet described in the present application.

[0090] In some embodiments, the lithium-ion battery further includes a negative electrode plate and an electrolyte.

[0091] In some embodiments, the electrolyte includes an additive, a solvent, and a lithium salt.

[0092] In some embodiments, the solvent includes at least one of a carbonate solvent, a carboxylate solvent, an ether solvent, a sulfone solvent, a nitrile solvent, and a phosphate solvent.

[0093] Illustratively, the carbonate solvent includes but is 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 solvent includes but is not limited to at least one of ethyl acetate, methyl formate, and 1,4-butyrolactone; the ether solvent includes at least one of dimethyltetrahydrofuran, tetrahydrofuran, and 1,2-dimethoxyethane; the sulfone solvent includes at least one of methyl sulfone and dimethyl sulfoxide; the nitrile solvent includes at least one of propionitrile, butyronitrile, 1-(2-cyanoethyl)pyrrole, and 1,3,6-hexanetrinitrile; and the phosphate solvent includes at least one of trimethyl triphosphate and triethyl phosphate.

[0094] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium trifluoromethanesulfonate, lithium bisfluoromethanesulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, and the like.

[0095] In some embodiments, the additive includes, but is not limited to, vinylene carbonate.

[0096] In some embodiments, the negative electrode plate 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, mesophase carbon microbeads, hard carbon, soft carbon, elemental silicon, silicon oxide, silicon-carbon composite material, and lithium titanate.

[0097] The negative electrode material layer may further include a conductive agent and / or a binder.

[0098] The conductive agent in the negative electrode active material layer is used to provide electrical conductivity. Any conductive agent can be used without particular limitation, as long as it has suitable electronic conductivity and does not significantly cause adverse chemical changes in the battery. Exemplary conductive agents include, but are not limited to, at least one of carbon nanotubes, carbon black, graphite, carbon fibers, activated carbon, mesoporous carbon, and fullerenes. Examples of carbon fibers include carbon nanofibers; and examples of carbon black include SP, acetylene black, and Ketjen black.

[0099] In some embodiments, the mass percentage of the conductive agent in the negative electrode material layer is 0.4% to 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 an interval formed by any two of the above values.

[0100] The binder in the negative electrode active layer is used to improve the adhesion between the 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 suitable binding properties and does not significantly cause adverse chemical changes in the battery. Exemplary binders include, but are not limited to, at least one of carboxymethyl cellulose (CMC), styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl butyral, and a water-based acrylic resin.

[0101] In some embodiments, the mass percentage of the binder in the negative electrode material layer is 1.0% to 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 an interval formed by any two of the above values.

[0102] In some embodiments, the negative electrode material layer in the negative electrode sheet includes a negative electrode material, a binder, and a conductive agent, and the mass percentage of the negative electrode material in the negative electrode material layer is 70-99%.

[0103] The present invention is further described below with reference to specific examples, which are not to be construed as limiting the scope of the present invention.

[0104] Example 1

[0105] A positive electrode sheet and a lithium-ion battery prepared therefrom, the preparation method comprising the following steps:

[0106] (1.1) Preparation of lithium iron manganese phosphate particles: lithium carbonate and aqueous phosphoric acid solution were mixed and reacted according to the stoichiometric ratio, followed by the addition of manganese carbonate and ferrous oxalate, and the mixture was ball-milled, wherein the molar ratio of manganese atoms to iron atoms was 68:32. The resulting slurry was further sand-milled to a suitable particle size and then atomized using a spray dryer. The resulting particles were calcined in a tubular furnace in a first stage, then heated and calcined in a second stage to obtain lithium iron manganese phosphate particles;

[0107] (1.2) Preparation of lithium nickel cobalt manganese oxide particles: nickel sulfate solution, cobalt sulfate solution, and manganese sulfate solution were mixed in a stoichiometric ratio, followed by the addition of sodium hydroxide as a precipitant. The pH was adjusted to 11 and the temperature was kept at 55°C for 1 h. After filtration, washing, and drying, the resulting precursor was mixed with lithium carbonate and ball-milled at a molar ratio of lithium atoms to the total atoms of nickel, cobalt, and manganese in the precursor of 1.05:1. The mixture was then calcined at 850°C for 12 h under a nitrogen atmosphere to obtain lithium nickel cobalt manganese oxide particles.

[0108] (1.3) Preparation of positive electrode sheet: Lithium manganese iron phosphate particles and lithium nickel cobalt manganese oxide particles were mixed in a certain mass ratio as the positive electrode material. Then, the positive electrode material, conductive agent SP and binder polyvinylidene fluoride were dispersed in N-methylpyrrolidone in a mass ratio of 96:1.5:2.5. The slurry was prepared by vacuum stirring and then coated on the current collector aluminum foil. The coating surface density was set to 380g / cm 2 After drying, cold pressing and slitting, the 3 The positive electrode sheet is obtained by rolling the positive electrode sheet to a compaction density of

[0109] (2) Preparation of negative electrode sheet: artificial graphite as negative electrode material, conductive agent SP, thickener sodium carboxymethyl cellulose, and binder styrene-butadiene rubber were dispersed in water at a mass ratio of 96.5:1:1:1.5, and the slurry was prepared by vacuum stirring. The slurry was then coated on the current collector copper foil. The coating surface density was set to 172 g / cm 2 After drying, cold pressing and slitting, the 3 Roll-pressing the negative electrode sheet to obtain the compaction density of the negative electrode sheet;

[0110] (3) Preparation of electrolyte: EC, EMC and DEC were mixed in a mass ratio of 1:1:1 as a solvent, and then lithium hexafluorophosphate was added based on the total mass of the electrolyte to prepare an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L;

[0111] (4) The positive electrode sheet, the commercially available PP separator, and the negative electrode sheet are stacked in order to form a battery cell, and the battery cell is placed in an outer packaging shell. After drying, the electrolyte is injected, and after vacuum packaging, standing, forming, and constant capacity, the lithium-ion secondary battery is obtained.

[0112] Examples 2-42, Comparative Examples 1-4

[0113] A positive electrode sheet and a lithium-ion battery prepared therefrom, the difference from Example 1 being that the preparation process of the positive electrode sheet is different.

[0114] The parameters of each positive electrode during preparation and the test results and parameters of the product are shown in Tables 1 and 2 and Figure 1 and Figure 2 As shown, the test methods of various product parameters are as described above, wherein a is regulated by the manganese content of lithium manganese iron phosphate particles, the manganese content in lithium nickel cobalt manganate particles and the mass ratio of the two, and b and D are adjusted by the material addition ratio of lithium manganese iron phosphate particles and lithium nickel cobalt manganate particles during preparation, the process of lithium manganese iron phosphate particles during calcination, the slurry mixing time of the positive electrode slurry, and the mixing mass ratio of the two particles.

[0115] Table 1

[0116]

[0117] Table 2

[0118]

[0119] Effect Examples

[0120] The lithium ion batteries obtained in each embodiment and comparative example were tested as follows:

[0121] (1) Cycle capacity retention test:

[0122] (I) The lithium-ion secondary batteries formed in the Examples and Comparative Examples 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). This cycle was repeated twice to constant capacity, and the constant capacity was recorded. The batteries were then charged at a constant current of 0.33C to an upper limit voltage of 4.25V, and then charged at a constant voltage until the current was less than 0.05C; then discharged at 0.33C to 2.5V. This cycle was repeated 200 times, and the capacity retention rate after the 200th cycle was calculated by: capacity retention rate = 100% × 200th discharge capacity / constant capacity.

[0123] (2) Fast charging performance test:

[0124] (I) The lithium-ion secondary batteries obtained in the Examples and Comparative Examples were charged at a constant current rate of 0.33C, then charged at a constant voltage of 4.25V (cut-off voltage of 4.25V), and then discharged at 0.33C (cut-off voltage of 2.5V), and the charge was repeated twice to constant capacity;

[0125] (II) Each lithium-ion secondary battery was charged at a rate of 0.33C to 10% SOC with a discharge capacity of 100% SOC in the last cycle. Then, the battery was charged at a rate of 0.2C, starting from 4C (cut-off voltage was 4.25V, auxiliary voltage ≤ 0), and then at 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, and 0.05C, respectively. The time taken to charge from 10% SOC to 80% SOC was recorded.

[0126] The test results are shown in Table 3.

[0127] Table 3

[0128]

[0129] According to Table 3, we can see that:

[0130] (1) The lithium-ion secondary battery described in the present application uses lithium manganese iron phosphate particles and lithium nickel cobalt manganese oxide particles as positive electrode materials in the positive electrode sheet. Based on the synergistic effect of the two, the relationship between the characteristic peak areas of divalent manganese and trivalent manganese in the positive electrode material layer at an etching depth of 10 nm and the ratio of the enclosed areas of the two positive electrode active material particles is regulated to be within the range of 0.5 to 2.5. This allows the overall material to have a high ion conduction efficiency, and when the positive electrode material contacts the electrolyte, the surface residual alkali activity of the lithium nickel cobalt manganese oxide particles can be effectively suppressed, ultimately allowing the lithium-ion battery to achieve excellent fast charging performance, with the time taken to charge from 10% SOC to 80% SOC being less than 25 minutes, and excellent cycle performance at high temperatures, with the capacity retention rate reaching more than 90% after 200 cycles, and excellent comprehensive performance.

[0131] (2) At the same time, since the encirclement 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 ion 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 level of the reaction between 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 relationship, when 10000b / a is further preferably in the range of 0.92~1.48, the fast charging time of the lithium ion battery can be further shortened to less than 20min. and the cycle capacity retention rate can be improved to more than 93%; and according to Examples 1 to 32, it can be seen that when the relationship formula 10000b / a of the positive electrode sheet of the present application is optimized, the sum of the characteristic peak areas of divalent manganese and trivalent manganese and the area enclosed by the two particles are further optimized in the range of a=28000~40000, and / or b=3.1~4.9, the electrochemical performance of the lithium ion battery can be further improved, and the time for charging to 80% SOC can be shortened to within 18 minutes, and the capacity retention rate at high temperature can reach more than 95%, with a maximum of 95.7%.

[0132] (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 the particle size to change. When the ratio of the average diameter D to b of the lithium manganese iron phosphate particles is preferably in the range of 1.31 to 3.84, the cycle stability and fast charging performance of the lithium ion battery are better.

[0133] (4) According to the comparison between Examples 39 to 42 and other Examples, it can be seen that when the ratio of the divalent manganese element to the trivalent manganese element changes, the activity of the trivalent manganese element in the material also varies. When the ratio of the characteristic peak area of ​​the divalent manganese element to the trivalent manganese element is preferably within 1: (1.3 to 3.26), the reaction of the trivalent manganese element in the material with the electrolyte is more sufficient, which can further inhibit the reaction of the electrolyte with the residual alkali on the surface of the lithium nickel cobalt manganese oxide, and ultimately achieve better ion transfer efficiency and structural stability, 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 manganese iron phosphate particles and lithium nickel cobalt manganese oxide particles; The positive electrode sheet satisfies: 0.5≤10000b / a≤2.5; The above a is the sum of the characteristic peak areas of divalent manganese and trivalent manganese 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 sheet is subjected to XPS testing. The unit of a is CPS.eV. The above b=S2 / S1, S2 is the total enclosed area of ​​lithium nickel cobalt manganese oxide particles in the positive electrode sheet at a magnification of 30K, S1 is the total enclosed area of ​​lithium manganese iron phosphate particles in the positive electrode sheet at a magnification of 30K, and the units of S1 and S2 are nm 2 .

2. The positive electrode sheet according to claim 1, wherein: The 10000b / a=0.92~1.

48.

3. The positive electrode sheet according to claim 1, wherein: When the positive electrode plate is subjected to XPS testing, the sum of the characteristic peak areas of divalent manganese and trivalent manganese at an XPS etching depth of 10 nm on the side of the positive electrode material layer away from the current collector is a=12800~58600 CPS.eV, and / or, b=S2 / S1, b=2~7.

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

5. The positive electrode sheet according to claim 3, wherein: When the positive electrode sheet is subjected to XPS testing, 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 ​​the divalent manganese element is 10056~25191 CPS.eV, and / or the characteristic peak area of ​​the trivalent manganese element is 13500~32871 CPS.eV.

6. The positive electrode sheet according to claim 1, wherein: The average diameter of the lithium manganese iron phosphate particles is D, and D / b=1.31-3.84, where the unit of D is μm.

7. The positive electrode sheet according to claim 6, wherein: The average diameter D of the lithium manganese iron phosphate particles is 6-12 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, the LiNi a Co b Mn c In O2, 0<a<1; 0＜b＜1； 0<c<1;a+b+c=1, and / or, the lithium manganese iron phosphate particles include LiMn x Fe y PO4, the LiMn x Fe y In PO4, 0<x<1; 0<y<1; x+y=1.

10. The positive electrode sheet according to claim 9, wherein: The LiMn x Fe y In PO4, x≥0.65 and in the positive electrode sheet, b=S2 / S1, b=2.5~5.

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

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

13. The positive electrode sheet according to claim 9, wherein: The LiNi a Co b Mn c In O2, a=0.6~0.

8.

14. A lithium ion battery, characterized in that: Comprising the positive electrode sheet according to any one of claims 1 to 13.

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