Positive electrode sheet, battery and electrical equipment

Abstract

The present invention provides a positive electrode sheet, a battery, and an electrical device. The positive electrode sheet includes a positive electrode active material, wherein the positive electrode active material includes lithium manganese iron phosphate particles; the molar ratio of manganese element to iron element in the positive electrode active material is a; the acidity growth rate of the positive electrode sheet is h; k=b / L, wherein L is the depth of the positive electrode sheet etched by XPS, which is 10 nm; k is the peak intensity ratio of the B1s peak at the binding energy position of 188-192 eV in the XPS etching analysis of the positive electrode sheet; b is the peak intensity of the B1s peak at the binding energy position of 188-192 eV in the XPS diagram; a, k, and h satisfy the following relationship: a×h / k=8×10 ‑4 By controlling the manganese to iron ratio, acidity growth rate, and peak intensity ratio at a certain etching depth, the positive electrode forms a stable CEI film containing B on the surface of the positive electrode, preventing the dissolution of manganese ions, reducing active lithium consumption, and improving the cycle.

Description

[0001] This application is a divisional application of the invention with the application date of October 18, 2024, the invention name of which is “A positive electrode sheet, battery and electrical equipment” and the application number is 202411456396.0. Technical Field

[0002] The present invention belongs to the technical field of batteries, and in particular relates to a positive electrode sheet, a battery and an electrical device. Background Art

[0003] As the technology industry strengthens its development, the importance of lithium-ion battery storage capacity has gradually been recognized; however, the problem of transition metal dissolution occurs frequently in almost all layered transition metal oxide positive electrodes.

[0004] For the LMFP system, the dissolution of Mn ions affects the stability of the positive electrode material itself, and at the same time, the deposition at the negative electrode leads to the loss of active lithium. The damage of the negative electrode SEI film gradually intensifies, which is an important reason for the life degradation.

[0005] Therefore, how to improve the cycle performance of batteries and increase their lifespan is an urgent problem that needs to be solved. Summary of the Invention

[0006] In view of this, the object of the present invention is to provide a positive electrode sheet, a battery and an electrical device. The positive electrode sheet forms a stable positive electrode solid electrolyte interface film (CEI film) containing boron (B) on the surface of the positive electrode sheet by controlling the manganese-iron ratio, the acidity growth rate and the peak intensity ratio when etching to a certain depth, thereby preventing the dissolution of manganese ions, reducing the consumption of active lithium and improving the cycle.

[0007] The present invention provides a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material, the positive electrode active material comprising lithium manganese iron phosphate particles;

[0008] The molar ratio of manganese to iron in the positive electrode active material is a; the acidity growth rate of the positive electrode sheet is h, unit: %;

[0009] k=b / L, where L is the depth of the positive electrode sheet etched by XPS, which is 10 nm. At 10 nm, k is the peak intensity ratio of the B1s peak at the binding energy of 188~192 eV in the XPS graph when the positive electrode sheet is etched by XPS, and the unit is counts / s / nm. b is the peak intensity of the B1s peak at the binding energy of 188~192 eV in the XPS graph when the positive electrode sheet is etched by XPS, and the unit is counts / s.

[0010] The a, k and h satisfy the following relationship:

[0011] a×h / k=8×10 -4 ~10.

[0012] By controlling the manganese-iron ratio, acidity growth rate and peak intensity ratio when etching to a certain depth, the positive electrode sheet forms a stable CEI film containing B on the surface of the positive electrode sheet, preventing the dissolution of manganese ions, reducing active lithium consumption and improving the cycle.

[0013] In a specific embodiment of the present invention, a×h / k=0.02~3.

[0014] In a specific embodiment of the present invention, 0.1≤a≤9.

[0015] In a specific embodiment of the present invention, 0.4≤a≤2.5.

[0016] In a specific embodiment of the present invention, 5≤k≤400.

[0017] In a specific embodiment of the present invention, 9≤k≤108.

[0018] In a specific embodiment of the present invention, the acidity growth rate h is 3-18%.

[0019] In a specific embodiment of the present invention, the acidity growth rate h is 4-16%.

[0020] In a specific embodiment of the present invention, the lithium manganese iron phosphate particles include primary particles, and the particle size of the primary particles ranges from 50 to 170 nm.

[0021] Preferably, the XPS etching depth is 10 nm, and the peak intensity of the B1s peak is F1; the XPS etching depth is 35 nm, and the peak intensity of the B1s peak is F2;

[0022] The difference between F1 and F2 is greater than 0 and less than or equal to 2000.

[0023] The present invention provides a battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte;

[0024] The positive electrode sheet is the positive electrode sheet described in the above technical solution.

[0025] In a specific embodiment of the present invention, a boron-containing compound is provided in the electrolyte and / or the positive electrode sheet.

[0026] In a specific embodiment of the present invention, the electrolyte includes a boron-containing compound, and the boron-containing compound is selected from one or more of lithium bis(oxalatoborate), tris(trimethylsilyl)borate, lithium difluorooxalatoborate, lithium tetrafluoroborate, tributyl borate and trimethyl borate.

[0027] The present invention provides an electrical device comprising the battery described in the above technical solution.

[0028] The present invention uses the battery to prepare an electrical device. The battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device, thereby expanding the application range of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the XPS spectrum of the positive electrode sheet prepared in Example 12 of the present invention at an etching depth of 10 nm. DETAILED DESCRIPTION

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0031] In the present invention, 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.

[0032] In the present invention, 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. Furthermore, 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.

[0033] In the present invention, there is no particular limitation on the specific dispersion and stirring treatment methods.

[0034] The reagents and instruments used in the present invention without indicating the manufacturer are all conventional products that can be purchased from the market.

[0035] The present invention provides a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material, the positive electrode active material comprising lithium manganese iron phosphate particles;

[0036] The molar ratio of manganese to iron in the positive electrode active material is a; the acidity growth rate of the positive electrode sheet is h, unit: %;

[0037] k=b / L, where k is the peak intensity ratio of the B1s peak at the binding energy of 188-192 eV in the XPS graph when the positive electrode sheet is subjected to XPS etching analysis, and the unit is counts / s / nm; L is the depth of the XPS etching of the positive electrode sheet, which is 10 nm; b is the peak intensity of the B1s peak at the binding energy of 188-192 eV in the XPS graph when the positive electrode sheet is subjected to XPS etching analysis, and the unit is counts / s;

[0038] The a, k and h satisfy the following relationship:

[0039] a×h / k=8×10 -4 ~10.

[0040] By controlling the manganese-iron ratio, acidity growth rate and peak intensity ratio when etching to a certain depth, the positive electrode sheet forms a stable CEI film containing boron (B) on the surface of the positive electrode sheet, preventing the dissolution of manganese ions, reducing active lithium consumption and improving the cycle.

[0041] In the present invention, a is the molar ratio of manganese element to iron element;

[0042] In the present invention, the value of a is preferably 0.1≤a≤9. If the Mn content is too high, the transition metal will be seriously dissolved, which will deteriorate the cycle; if it is lower than the above preferred value, the specific capacity will be deteriorated. Specifically, the value of a can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4 .4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1, 7.2, 7.3, 7.4, 7.57.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9 or 9.0.

[0043] More preferably, 0.4≤a≤2.5. Within this range, the cycle performance of the battery is better.

[0044] In a specific embodiment of the present invention, the value of a is 0.1, 2.8, 0.5, 2.3, 1.5, 0.4, 2.5, 1.5, 2, 0.4, 0.2, 9, 0.08, or 10.

[0045] In the present invention, k is the peak intensity ratio of boron during XPS etching. Its value reflects the boron content in the surface layer of the positive electrode sheet and can be used to reflect the presence of a certain amount of boron in the solid electrolyte membrane (CEI membrane) formed on the surface of the positive electrode active material. K is the peak intensity ratio of the B1s peak at a binding energy of 188-192 eV in the XPS plot when performing XPS etching analysis on the positive electrode sheet, reflecting the boron content in the surface layer of the positive electrode sheet. The unit is counts / s / nm. k = b / L, where b is the peak intensity of the B1s peak at a binding energy of 188-192 eV in the XPS plot when performing XPS etching analysis on the positive electrode sheet. For example, the peak intensity indirectly reflects the boron content; a higher peak intensity indicates a higher boron content at that depth. L is the depth of the positive electrode sheet during XPS etching, in nm. The role of element B in the surface layer: element B lacks electrons and can combine with anions or anionic groups to form polyanionic groups. The molecular orbital energy level is high and it is easily oxidized. It directly participates in the formation of CEI in the form of anionic groups, thereby protecting the positive electrode and reducing the risk of manganese dissolution in the positive electrode active material.

[0046] In the present invention, the value of k is preferably 5≤k≤400. When it is within the above preferred range, it can protect the positive electrode and avoid transition metal dissolution; at the same time, it can avoid impedance increase and cycle performance degradation. The value of K can be 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200, 205, 210 , 215, 220, 225, 230, 235, 240, 245, 250, 255, 260, 265, 270, 275, 280, 285, 290, 295, 300, 305, 310, 315, 320, 325, 330, 335, 340, 345, 350, 355, 360, 365, 370, 375, 380, 385, 390, 395, or 400.

[0047] More preferably, 9≤k≤108; the value of k can be 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54 , 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, or 105.

[0048] In specific embodiments of the present invention, the value of k is 400, 5, 108, 12, 45, 95, 9, 380, 43, 90, 7, 125, 100, or 20.

[0049] In the present invention, h represents the acidity growth rate (unit: %). The acidity growth rate is the growth rate of hydrogen ion content generated when the positive electrode sheet is immersed in a mixed solution containing lithium perchlorate. Due to side reactions between the positive electrode active material and the electrolyte, electrons are gained or lost. EC borrows electrons from the LMFP during charge and discharge, and EC undergoes ring-opening dehydrogenation. Keeping the acidity growth rate within a certain range can protect the positive electrode sheet, reduce excessive side reactions between the positive electrode sheet and the electrolyte, and ensure kinetic performance. Excessive acidity growth rates increase side reactions between the lithium manganese iron phosphate and the electrolyte, deteriorating the cycle life. Excessively low acidity growth rates increase solid-phase diffusion of lithium ions, deteriorating kinetic performance. Therefore, the acidity growth rate h is preferably 3-18%, more preferably 4-16%. The acidity growth rate is dependent on various factors, such as the primary particle diameter, the thickness of the carbon layer of the positive electrode active material, and the amount of conductive agent in the positive electrode sheet.

[0050] In the present invention, the specific value of h can be 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, and 18%.

[0051] In specific embodiments of the present invention, the acidity growth rate h is specifically 3.2, 17.5, 4.5, 15.5, 7, 4.2, 16, 15, 16.2, 5, 3, 18, 2, or 19.

[0052] The present invention does not limit the test of acidity growth rate, and those skilled in the art can perform the test by conventional means; for example, the test can be performed by the following method:

[0053] 3 pieces of 7×7cm 2 The fully charged positive electrode was immersed in a mixed solution of EC, EMC and lithium perchlorate (the total mixed volume was 20 ml, the mass ratio of EC to EMC was 3:7, and the amount of lithium perchlorate added was 1 mol / L). It was stored at 60 °C for 2 days and the H + The H content in the solution was measured at 1 ppm. The solution was stored at 60°C for 3 days. + Amount m2 ppm; get H + Growth rate, that is, acidity growth rate h, h is (m2-m1) / m1.

[0054] The a, k and h in the present invention satisfy the following relationship: a×h / k=8×10 -4 ~10; in the above relationship, when the upper limit is exceeded, the manganese content is high, and the acidity growth rate is relatively large, if the B content is too low, a dense and stable CEI film cannot be formed at the positive electrode, resulting in more manganese dissolution, large active lithium consumption, and deterioration of the cycle performance; the above relationship exceeds the lower limit, and the boron (B) element content is too high, resulting in increased interface resistance (Rct), SEI film carbon source (Rsei) and diffusion resistance (Ws) during the cycle, resulting in poor cycle performance.

[0055] Specifically, a×h / k=0.0008, 0.0009, 0.001, 0.0015, 0.0020, 0.0025, 0.0030, 0.0035, 0.0040, 0.0045, 0.0050, 0.0060, 0.0070, 0.0080, 0.0090, 0.0095, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0 .14, 0.1436, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2.0, 2.5, 3.0, 3.5, 4, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0.

[0056] In the present invention, the preferred range of a×h / k is 0.02-3; within this range, the cycle performance of the battery is more excellent.

[0057] In specific embodiments of the present invention, a×h / k=0.0008, 9.800, 0.0208, 2.9708, 0.2333, 0.0177, 4.4444, 0.0592, 0.7200, 0.0222, 0.0857, 1.2960, 0.0016, or 9.5000.

[0058] The active material in the positive electrode sheet provided by the present invention includes lithium iron manganese phosphate particles; the lithium iron manganese phosphate particles include primary particles, and the average particle size of the primary particles ranges from 50 to 170 nm, or may be 70 to 160 nm. Specifically, the average particle size of the primary particles is 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, 105 nm, 110 nm, 115 nm, 120 nm, 125 nm, 130 nm, 135 nm, 140 nm, 145 nm, 150 nm, 155 nm, 160 nm, 165 nm, or 170 nm. The present invention does not regulate the method for adjusting the primary particle size. The primary particle size can be changed by regulating the sintering process or the grinding process. In a specific embodiment of the present invention, the particle size of the primary particles is 162 nm, 76 nm, 151 nm, 95 nm, 130 nm, 155 nm, 93 nm, 92 nm, 41 nm, 202 nm, 132 nm, 200 nm or 136 nm.

[0059] The positive electrode sheet provided by the present invention uses the XPS method to characterize the intensity of the boron (B) element at a certain etching depth. In a preferred embodiment of the present invention, the peak intensity (F1) of the XPS at 10nm and the peak intensity (F2) at 35nm are greater than 0 and less than or equal to 2000. In the present invention, the B element is mainly in the CEI film layer on the surface of the positive electrode sheet. The B element mainly participates in the formation of the CEI film layer on the positive electrode surface. The presence of the B element on the surface contributes to the stability and density of the CEI film layer. If the B element is in the active material layer, direct contact between the electrode and the electrolyte causes corrosion of the positive electrode active material by the electrolyte, thereby reducing the cycle stability of the battery. By limiting the peak intensity to greater than 0 and less than or equal to 2000, the B element on the surface stabilizes the CEI layer and avoids the problem of excessive surface B. In the present invention, the difference between F1 and F2 is specifically 45, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300, 1350, 1400, 1450, 1500, 1550, 1600, 1650, 1700, 1750, 1800, 1850, 1900, 1950 or 2000.

[0060] In a specific embodiment of the present invention, the difference between F1 and F2 is 3950, 45, 600, 100, 420, 880, 75, 3550, 400, 750, 50, 980, 890 or 160.

[0061] The present invention adjusts the boron content in the positive electrode sheet to form a uniform CEI film on the positive electrode surface, inhibiting the dissolution of manganese ions, reducing the consumption of active lithium, and improving the cycle performance of the battery. In the present invention, the boron element is provided in the electrolyte and / or a boron-containing compound is provided in the positive electrode sheet.

[0062] The boron element is introduced by adding a boron-containing compound to the electrolyte, wherein the boron-containing compound is selected from one or more of lithium bis(oxalatoborate) (LiBOB), tris(trimethylsilyl)borate (TMSB), lithium difluorooxalatoborate (LIODFB), lithium tetrafluoroborate, tributyl borate and trimethyl borate;

[0063] The boron element is used to set a coating layer on the surface of the positive electrode active material; or a doping substance M is added during the slurrying process; the doping substance M is selected from one or more of boric acid, organic borane, borohydride and metal boride; the boron-containing compound in the coating layer is selected from metal boride and / or borate LiMBO3.

[0064] The positive electrode sheet described in the above technical solution of the present invention includes a positive electrode active material; the positive electrode active material includes lithium manganese iron phosphate particles (LMFP);

[0065] In the present invention, the preparation method of the positive electrode active material is not limited. Those skilled in the art can prepare the positive electrode active material according to conventional technical means. Exemplarily, the preparation method of the positive electrode active material includes the following steps:

[0066] The lithium source, manganese source, iron source and phosphorus source required for synthesizing the lithium manganese iron phosphate material are weighed in proportion and added with deionized water, and ground to obtain a lithium manganese iron phosphate precursor slurry;

[0067] Adding the coated carbon source and the lithium manganese iron phosphate precursor slurry, mixing them evenly, grinding, adjusting the solid content, and spray drying to obtain a dry powder;

[0068] The dried powder is sintered under a protective atmosphere and cooled to obtain the positive electrode active material.

[0069] The above cooling method obtains agglomerated lithium manganese iron phosphate with relatively large particle size; the agglomerated lithium manganese iron phosphate is composed of multiple primary particles.

[0070] In some other embodiments, the synthesized positive electrode active material can also be crushed and graded to obtain small particles of lithium manganese iron phosphate, where the small particles of lithium manganese iron phosphate refer to a single particle, or there may be two or three particles connected together and not broken apart.

[0071] The primary particle size in Table 1 below of the present invention refers to: the primary particle size in the agglomerate; or the small particle size.

[0072] In the present invention, the lithium source is selected from at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxalate, lithium dihydrogen phosphate, lithium citrate, and lithium acetate. The manganese source is selected from at least one of manganese carbonate, manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate. The iron source is selected from at least one of ferrous oxalate, ferric hydroxide, ferrous hydroxide, ferric phosphate, ferrous phosphate, ferrous acetate, ferrous acetate, ferrous carbonate, ferrous carbonate, ferrous oxide, ferrous oxide, and ferric oxalate. The phosphorus source is selected from at least one of diammonium hydrogen phosphate, lithium dihydrogen phosphate, ammonium phosphate, and lithium phosphate. In the present invention, ferromanganese phosphate is preferably used as the manganese source, iron source, and phosphorus source; and ferric phosphate is preferably used as the iron source and phosphorus source.

[0073] In the preparation of lithium manganese iron phosphate particles, the present invention can also dope other elements as needed, such as vanadium, tungsten, titanium, magnesium, etc.; to provide the above elements, the vanadium source used is selected from vanadium pentoxide, etc., the tungsten source is selected from ammonium metatungstate, etc., the titanium source is selected from titanium oxide, etc., and the magnesium source is selected from magnesium carbonate, etc. The content of other doped elements in the present invention is based on the total molar ratio of manganese and iron, and is preferably 1000~5000ppm. The structural formula of the lithium manganese iron phosphate particles described in the present invention is: LiMn x Fe y M z n PO4, wherein x is greater than 0 and less than 1; y is greater than 0 and less than 1; z is greater than or equal to 0 and less than 1; n refers to the valence of the doping element; 2(x+y)+n×z=2.

[0074] The carbon source content in the present invention is based on the total amount of solid matter in the lithium manganese iron phosphate precursor slurry, preferably 5-35%, and the carbon source content is specifically 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, or 35%.

[0075] In specific embodiments of the present invention, the carbon source content is 30%, 12%, 25%, 17%, 20%, 28%, 15%, 16%, 5%, 20%, 28%, 12%, 35%, or 10%.

[0076] The present invention mixes a lithium source, a manganese source, an iron source, and a phosphorus source to produce a manganese iron lithium slurry, which is then mixed with a coating carbon source. The coating carbon source is selected from at least one of glucose, polyethylene glycol, acetylene black, glycine, starch, acetylene black, sucrose, phenolic resin, and ascorbic acid. The solvent used in the present invention is water and / or ethanol. The grinding method in the present invention can be ball milling.

[0077] The present invention sintered the precursor using a gradient sintering method; the gradient sintering method includes:

[0078] The temperature was raised to 150-630°C at a heating rate of 4-6°C / min and pre-fired for 280-330 min. The temperature was then raised to 300-950°C at a heating rate of 9-11°C / min and calcined for 700-750 min.

[0079] The present invention preferably adopts a natural cooling method to obtain lithium manganese iron phosphate particles.

[0080] The positive electrode active material in the present invention preferably also includes lithium iron phosphate (LFP), with the specific structural formula being LiFePO4, i.e., a composite of lithium iron manganese phosphate particles and lithium iron phosphate. The mass ratio of the lithium iron manganese phosphate particles to the lithium iron phosphate is 0.14 to 56. In specific embodiments of the present application, the mass ratio of the LFP to LFP is 0.14, 56.0, 0.81, 13.14, 4, 0.61, 20, 4, 8, 0.61, 0.29, 0.11, or 22.2.

[0081] The positive electrode sheet provided by the present invention includes not only a positive electrode active material, but also a conductive agent and a binder. The mass ratio of the positive electrode active material, the conductive agent, and the binder is 96: (0.1-3): (3.9-1).

[0082] The conductive agent included in the positive electrode sheet provided by the present invention is not particularly limited in type, as long as it has suitable electronic conductivity and does not cause adverse chemical changes in the battery. Specifically, the conductive agent can be at least one of carbon nanotubes, carbon black, and graphene.

[0083] The binder included in the positive electrode sheet provided by the present invention is used to improve the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. In the present invention, the binder can be a conventional choice in the battery field. Specifically, the binder can be at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylate, polyolefin, sodium carboxymethyl cellulose (CMC), and sodium alginate.

[0084] The positive electrode sheet provided by the present invention also includes a positive electrode current collector. This is not particularly limited, as long as it is conductive and does not cause adverse chemical changes in the battery. Examples of materials that can be used include stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, and silver.

[0085] In the present invention, the positive electrode sheet can be prepared according to conventional methods in the art. For example, the positive electrode active material, conductive agent, and binder are dispersed in a solvent such as NMP (N-methylpyrrolidone) to form a uniform positive electrode slurry. The positive electrode slurry is then coated on the positive electrode current collector. After drying and roller pressing, the positive electrode sheet is obtained.

[0086] The present invention also provides a battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte;

[0087] The positive electrode sheet is the positive electrode sheet described in any one of the above technical solutions.

[0088] The battery provided by the present invention has excellent cycle performance by adopting the above-mentioned positive electrode sheet.

[0089] The present invention can introduce boron into the prepared battery by providing a boron-containing compound in the electrolyte and / or the positive electrode sheet. The boron-containing compound in the electrolyte of the present invention is selected from one or more of lithium bis(oxalatoborate) (LiBOB), tris(trimethylsilyl)borate (TMSB), lithium difluorooxalatoborate (LIODFB), lithium tetrafluoroborate, tributyl borate, and trimethyl borate.

[0090] In the present invention, boron is introduced into the positive electrode sheet by providing a coating layer on the surface of the positive electrode active material; or a dopant M can be added during the slurry mixing process. The boron-containing compound in the coating layer is selected from metal borides and / or borates LiMBO3; and the dopant M is selected from one or more of boric acid, organoboranes, borohydrides, and metal borides.

[0091] The negative electrode sheet in the present invention includes a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0092] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0093] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector; for example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer substrate (such as polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0094] The present invention provides an electrical device comprising the battery described in the above technical solution.

[0095] The battery can be used as a power source or energy storage unit for the power-consuming devices. These power-consuming devices may include, but are not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, and energy storage systems.

[0096] In order to further illustrate the present invention, a positive electrode sheet, a battery and an electrical device provided by the present invention are described in detail below in conjunction with embodiments, but they should not be understood as limiting the scope of protection of the present invention.

[0097] Example 1

[0098] (1) Lithium iron manganese phosphate (LiMn 0.75 Fe 0.25 PO4) positive electrode material: LiMn 0.75 Fe 0.25 The molar ratio of each element Li, Mn, Fe, and P in the PO4 chemical formula is as follows: lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate are weighed respectively, deionized water is added, mixed, and ball milled to obtain a lithium iron manganese phosphate precursor slurry, and then 30% glucose with a mass fraction is weighed and mixed evenly with the lithium iron manganese phosphate precursor slurry, ball milled for 20 hours, and then the solid content is adjusted and spray dried to obtain a dry powder; the dry powder is then placed in a tube furnace and calcined at a heating rate of 5°C / min to 600°C for pre-calcination for 300 minutes, and then heated to 800°C at a heating rate of 10°C / min, calcined for 720 minutes, and naturally cooled to obtain a solid powder; the solid powder is then crushed, and after crushing for 8 hours, it is screened to obtain the target material LiMn 0.75 Fe 0.25 PO4 positive electrode material.

[0099] (2) Preparation of positive electrode sheet: The lithium manganese iron phosphate (LiMn 0.75 Fe 0.25 PO4) and lithium iron phosphate (LiFePO4) positive electrode materials are mixed evenly according to the Mn / Fe molar ratio of 1:10 as the main material, and the compounding ratio of LMFP and LFP is 0.14. The main material, conductive agent SP, and binder polyvinylidene fluoride (PVDF) are mixed evenly in NMP according to the mass ratio of 96:3:1. Then, the mixed positive electrode slurry is mixed with the surface density of 400g / m 2 The positive electrode sheet is evenly coated on aluminum foil and dried in a vacuum oven at 100°C to obtain the positive electrode sheet, which is then slit; then rolled and cut to obtain the positive electrode sheet.

[0100] (3) The electrolyte used was ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 3:7 wt% as the solvent system, 1.15M LiPF6 as the lithium salt, and lithium bis(oxalato)borate (LiBOB) containing 3300ppm of B element additives, 1% vinylene carbonate (VC), and 1% methylene disulfonate (MMDS) as the film-forming additives.

[0101] (4) Preparation of negative electrode sheet

[0102] The negative electrode active material (artificial graphite), conductive agent (SP), and binder (carboxymethyl cellulose, CMC) are mixed in a mass ratio of 96.4:1:2.6 and dispersed in deionized water to obtain a negative electrode slurry. The negative electrode slurry is evenly coated on the negative electrode collector (copper foil). The negative electrode collector coated with the negative electrode slurry is transferred to a vacuum environment in an oven and dried at 100°C. The negative electrode sheet is then rolled, cut, and baked.

[0103] (5) Preparation of diaphragm

[0104] Use polyethylene (PE) diaphragm.

[0105] (6) Battery preparation

[0106] The positive electrode sheet, separator and negative electrode sheet prepared above are wound to obtain a bare cell without liquid injection; the bare cell is placed in an outer packaging foil, and the prepared electrolyte is injected into the dried bare cell. After vacuum packaging, standing, forming, shaping, sorting and other processes, a lithium-ion battery is obtained.

[0107] Example 2

[0108] (1) Lithium iron manganese phosphate (LiMn 0.75 Fe 0.25 PO4) positive electrode material: LiMn 0.75 Fe 0.25 The molar ratio of each element Li, Mn, Fe, and P in the PO4 chemical formula is as follows: lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate are weighed respectively, deionized water is added, mixed, and ball milled to obtain a lithium iron manganese phosphate precursor slurry, and then 12% by mass of glucose is weighed and mixed evenly with the lithium iron manganese phosphate precursor slurry, ball milled for 20 hours, and then the solid content is adjusted and spray dried to obtain a dry powder; the dry powder is then placed in a tube furnace and calcined at a heating rate of 5°C / min to 200°C for pre-calcination for 300min, and then heated to 400°C at a heating rate of 10°C / min, calcined for 720min, and naturally cooled to obtain LiMn 0.75 Fe 0.25 PO4 material.

[0109] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn 0.75 Fe 0.25 PO4) and lithium iron phosphate (LiFePO4) positive electrode materials are mixed evenly according to the Mn / Fe molar ratio of 2.8 as the main material, and the compounding ratio of LMFP and LFP is 56.0. The main material, conductive agent SP, and binder are mixed evenly in NMP according to the mass ratio of 96:0.2:3.8. Finally, trimethyl borate containing 45ppm of B element is added and the slurry is stirred. Subsequently, the mixed positive electrode slurry is mixed according to the surface density of 400g / m 2The positive electrode sheet is evenly coated on aluminum foil and dried in a vacuum oven at 100°C to obtain the positive electrode sheet, which is then slit; then rolled and cut to obtain the positive electrode sheet.

[0110] (3) The electrolyte used was EC:EMC=3:7 wt% as solvent system, 1.15M LiPF6 as lithium salt, and 1% VC and 1% MMDS as film-forming additives.

[0111] (4) Preparation of negative electrode sheet: same as in Example 1.

[0112] (5) Preparation of diaphragm: same as in Example 1.

[0113] (6) Preparation of battery: same as in Example 1.

[0114] Example 3

[0115] (1) Lithium iron manganese phosphate (LiMn 0.75 Fe 0.25 PO4) positive electrode material: LiMn 0.75 Fe 0.25 The molar ratios of Li, Mn, Fe, and P in the PO4 chemical formula are as follows: lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate are weighed respectively, deionized water is added, mixed, and ball milled to obtain a lithium iron manganese phosphate precursor slurry. Then, 25% glucose is weighed and mixed evenly with the lithium iron manganese phosphate precursor slurry, ball milled for 20 hours, and then the solid content is adjusted and spray dried to obtain a dry powder. The dry powder is then mixed evenly with boric acid (B content 900ppm) and placed in a tube furnace for calcination. The temperature is raised at a rate of 5°C / min to 400°C for pre-calcination for 300 minutes, and then the temperature is raised to 750°C at a rate of 10°C / min, calcined for 720 minutes, and naturally cooled to obtain a solid powder. The solid powder is then crushed for 6 hours to obtain LiMn 0.75 Fe 0.25 PO4 material.

[0116] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn 0.75 Fe 0.25 PO4) and lithium iron phosphate (LiFePO4) positive electrode materials are mixed evenly according to the Mn / Fe molar ratio of 0.5 as the main material, and the compounding ratio of LMFP and LFP is 0.81. The main material, conductive agent SP, and binder are mixed evenly in NMP according to the mass ratio of 96:2.5:1.5. Then, the mixed positive electrode slurry is mixed at a surface density of 400g / m 2 The positive electrode sheet is evenly coated on aluminum foil and dried in a vacuum oven at 100°C to obtain the positive electrode sheet, which is then slit; then rolled and cut to obtain the positive electrode sheet.

[0117] (3) The electrolyte is the same as that in Example 2.

[0118] (4) Preparation of negative electrode sheet: same as in Example 1.

[0119] (5) Preparation of diaphragm: same as in Example 1.

[0120] (6) Preparation of battery: same as in Example 1.

[0121] Example 4

[0122] (1) Lithium iron manganese phosphate (LiMn 0.75 Fe 0.25 PO4) positive electrode material: LiMn 0.75 Fe 0.25 The molar ratio of each element Li, Mn, Fe, and P in the PO4 chemical formula is respectively weighed. Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate are weighed, deionized water is added, mixed, and ball milled to obtain a lithium iron manganese phosphate precursor slurry. Then, 17% glucose is weighed and mixed evenly with the lithium iron manganese phosphate precursor slurry, ball milled for 15 hours, and then the solid content is adjusted and spray dried to obtain a dry powder. The dry powder is then placed in a tube furnace and calcined at a heating rate of 5°C / min to 300°C for pre-calcination for 300 min, then heated to 500°C at a heating rate of 10°C / min, calcined for 720 minutes, and naturally cooled to obtain LiMn 0.75 Fe 0.25 PO4 material.

[0123] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn 0.75 Fe0 .25 PO4) and lithium iron phosphate (LiFePO4) positive electrode materials are mixed evenly according to the Mn / Fe molar ratio of 2.3 as the main material, and the compounding ratio of LMFP and LFP is 13.14. The main material, conductive agent SP, and binder are mixed evenly in NMP according to the mass ratio of 96:0.8:3.2. Then, the mixed positive electrode slurry is mixed at a surface density of 400g / m 2 The positive electrode sheet is evenly coated on aluminum foil and dried in a vacuum oven at 100°C to obtain the positive electrode sheet, which is then slit; then rolled and cut to obtain the positive electrode sheet.

[0124] (3) The electrolyte is different from that in Example 1: LiBOB, an additive containing 130 ppm of element B, is used.

[0125] (4) Preparation of negative electrode sheet: same as in Example 1.

[0126] (5) Preparation of diaphragm: same as in Example 1.

[0127] (6) Preparation of battery: same as in Example 1.

[0128] Example 5

[0129] (1) Lithium iron manganese phosphate (LiMn 0.75 Fe 0.25 PO4) positive electrode material: LiMn 0.75 Fe 0.25 The molar ratio of each element Li, Mn, Fe, and P in the PO4 chemical formula is respectively weighed. Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate are weighed, deionized water is added, mixed, and ball milled to obtain a lithium iron manganese phosphate precursor slurry. Then, 20% glucose is weighed and mixed evenly with the lithium iron manganese phosphate precursor slurry, ball milled for 20 hours, and then the solid content is adjusted and spray dried to obtain a dry powder. The dry powder is then placed in a tube furnace and calcined at a heating rate of 5°C / min to 400°C for pre-calcination for 300 minutes, and then heated to 600°C at a heating rate of 10°C / min, calcined for 720 minutes, and naturally cooled to obtain a solid powder. The solid powder is crushed and after 12 hours, LiMn 0.75 Fe 0.25 PO4 material.

[0130] (2) Preparation of positive electrode sheet:

[0131] Lithium manganese iron phosphate (LiMn 0.75 Fe 0.25 PO4) and lithium iron phosphate (LiFePO4) positive electrode materials are mixed evenly according to the Mn / Fe molar ratio of 1.5 as the main material, and the compounding ratio of LMFP and LFP is 4. The main material, conductive agent SP, and binder are mixed evenly in NMP according to the mass ratio of 96:1:3. Then, the mixed positive electrode slurry is mixed at a surface density of 400g / m 2 The positive electrode sheet is evenly coated on aluminum foil and dried in a vacuum oven at 100°C to obtain the positive electrode sheet, which is then slit; then rolled and cut to obtain the positive electrode sheet.

[0132] (3) Preparation of negative electrode sheet: same as in Example 1.

[0133] (4) Preparation of electrolyte: Compared with Example 1, a LIODFB additive containing 380 ppm of B element was selected.

[0134] (5) Preparation of isolation membrane: PP is used as the isolation membrane.

[0135] (6) Preparation of battery: same as in Example 1.

[0136] Example 6

[0137] (1) Lithium iron manganese phosphate (LiMn 0.75 Fe 0.25PO4) positive electrode material: LiMn 0.75 Fe 0.25 The molar ratio of each element of Li, Mn, Fe, and P in the PO4 chemical formula is respectively weighed. Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate are weighed, deionized water is added, mixed, and ball milled to obtain a lithium iron manganese phosphate precursor slurry. Then, 28% glucose is weighed and mixed evenly with the lithium iron manganese phosphate precursor slurry, ball milled for 20 hours, and then the solid content is adjusted and spray dried to obtain a dry powder. The dry powder is then placed in a tube furnace and calcined at a heating rate of 5°C / min to 400°C for pre-calcination for 300 minutes, and then heated to 800°C at a heating rate of 10°C / min, calcined for 720 minutes, and naturally cooled to obtain a solid powder. The solid powder is then crushed for 6 hours to obtain LiMn 0.75 Fe 0.25 PO4 material.

[0138] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn 0.75 Fe 0.25 PO4) and lithium iron phosphate (LiFePO4) positive electrode materials are mixed evenly according to the Mn / Fe molar ratio of 0.4 as the main material, and the compounding ratio of LMFP and LFP is 0.61. The main material, conductive agent SP, and binder are mixed evenly in NMP according to the mass ratio of 96:3:1. Then, the mixed positive electrode slurry is mixed at a surface density of 400g / m 2 The positive electrode sheet is evenly coated on aluminum foil and dried in a vacuum oven at 100°C to obtain the positive electrode sheet, which is then slit; then rolled and cut to obtain the positive electrode sheet.

[0139] (3) Compared with the embodiment, the electrolyte used is an additive LIODFB containing 805 ppm of boron.

[0140] (4) Preparation of negative electrode sheet: same as in Example 1.

[0141] (5) Preparation of diaphragm: same as in Example 1.

[0142] (6) Preparation of battery: same as in Example 1.

[0143] Example 7:

[0144] (1) Lithium iron manganese phosphate (LiMn 0.75 Fe 0.25 PO4) positive electrode material: LiMn 0.75 Fe 0.25The molar ratio of each element Li, Mn, Fe, and P in the PO4 chemical formula is as follows: lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate are weighed respectively, deionized water is added, mixed, and ball milled to obtain a lithium iron manganese phosphate precursor slurry. Then, 15% glucose is weighed and mixed evenly with the lithium iron manganese phosphate precursor slurry, ball milled for 22 hours, and then the solid content is adjusted and spray dried to obtain a dry powder. The dry powder is then placed in a tube furnace and calcined at a heating rate of 5°C / min to 250°C for pre-calcination for 300 min, then heated to 450°C at a heating rate of 10°C / min, calcined for 720 minutes, and cooled naturally to obtain LiMn 0.75 Fe 0.25 PO4 material.

[0145] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn 0.75 Fe 0.25 PO4) and lithium iron phosphate (LiFePO4) positive electrode materials are mixed evenly according to the Mn / Fe molar ratio of 2.5 as the main material, and the compounding ratio of LMFP and LFP is 20. The main material, conductive agent SP, and binder are mixed evenly in NMP according to the mass ratio of 96:0.3:3.7. Then, the mixed positive electrode slurry is mixed at a surface density of 400g / m 2 The positive electrode sheet is evenly coated on aluminum foil and dried in a vacuum oven at 100°C to obtain the positive electrode sheet, which is then slit; then rolled and cut to obtain the positive electrode sheet.

[0146] (3) Compared with Example 1, the electrolyte used was trimethyl borate as an additive containing 80 ppm of B element.

[0147] (4) Preparation of negative electrode sheet: same as in Example 1.

[0148] (5) Preparation of diaphragm: same as in Example 1.

[0149] (6) Preparation of battery: same as in Example 1.

[0150] Example 8:

[0151] (1) Lithium iron manganese phosphate (LiMn 0.75 Fe 0.25 PO4) positive electrode material: LiMn 0.75 Fe 0.25The molar ratio of each element Li, Mn, Fe, and P in the PO4 chemical formula is respectively weighed. Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate are weighed, deionized water is added, mixed, and ball milled to obtain a lithium iron manganese phosphate precursor slurry. Then, 20% glucose is weighed and mixed evenly with the lithium iron manganese phosphate precursor slurry, ball milled for 20 hours, and then the solid content is adjusted and spray dried to obtain a dry powder. The dry powder is then placed in a tube furnace and calcined at a heating rate of 5°C / min to 400°C for pre-calcination for 300 minutes, then heated to 480°C at a heating rate of 10°C / min, calcined for 720 minutes, and naturally cooled to obtain LiMn 0.75 Fe 0.25 PO4 material.

[0152] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn 0.75 Fe 0.25 PO4) and lithium iron phosphate (LiFePO4) positive electrode materials are mixed evenly according to the Mn / Fe molar ratio of 1.5 as the main material, and the compounding ratio of LMFP and LFP is 4. The main material, conductive agent SP, and binder are mixed evenly in NMP according to the mass ratio of 96:1:3. Then, the mixed positive electrode slurry is mixed at a surface density of 400g / m 2 The positive electrode sheet is evenly coated on aluminum foil and dried in a vacuum oven at 100°C to obtain the positive electrode sheet, which is then slit; then rolled and cut to obtain the positive electrode sheet.

[0153] (3) Preparation of negative electrode sheet: same as in Example 1.

[0154] (4) Compared with Example 1, the electrolyte used was a tributyl borate additive containing 3210 ppm of B element.

[0155] (5) Preparation of diaphragm: same as in Example 1.

[0156] (6) Preparation of battery: same as in Example 1.

[0157] Example 9:

[0158] 1) Preparation of LMFP cathode material: According to LiMn 0.75 Fe 0.25The molar ratio of each element Li, Mn, Fe, and P in the PO4 chemical formula is respectively weighed. Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate are weighed, deionized water is added, mixed, and ball milled to obtain a lithium iron manganese phosphate precursor slurry. Then, 20% glucose is weighed and mixed evenly with the lithium iron manganese phosphate precursor slurry, ball milled for 30 hours, and then the solid content is adjusted and spray dried to obtain a dry powder. The dry powder is then placed in a tube furnace and calcined at a heating rate of 5°C / min to 150°C for pre-calcination for 300min, then heated to 300°C at a heating rate of 10°C / min, calcined for 720min, and cooled naturally to obtain LiMn 0.75 Fe 0.25 PO4 material.

[0159] 2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn 0.75 Fe 0.25 PO4) and lithium iron phosphate (LiFePO4) positive electrode materials are mixed evenly according to the Mn / Fe molar ratio of 2 as the main material, and the compounding ratio of LMFP and LFP is 8. The main material, conductive agent SP, and binder are mixed evenly in NMP according to the mass ratio of 96:1.5:2.5. Then, the mixed positive electrode slurry is mixed at a surface density of 400g / m 2 The positive electrode sheet is evenly coated on aluminum foil and dried in a vacuum oven at 100°C to obtain the positive electrode sheet, which is then slit; then rolled and cut to obtain the positive electrode sheet.

[0160] 3) Preparation of negative electrode sheet: same as in Example 1.

[0161] 4) Compared with Example 1, the electrolyte used was a trimethyl borate additive containing 350 ppm of B element.

[0162] Example 10:

[0163] (1) Lithium iron manganese phosphate (LiMn 0.75 Fe 0.25 PO4) positive electrode material: LiMn 0.75 Fe 0.25 The molar ratio of each element Li, Mn, Fe, and P in the PO4 chemical formula is as follows: lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate are weighed respectively, deionized water is added, mixed, and ball milled to obtain a lithium iron manganese phosphate precursor slurry. Then, 20% glucose is weighed and mixed evenly with the lithium iron manganese phosphate precursor slurry, ball milled for 20 hours, and then the solid content is adjusted and spray dried to obtain a dry powder. The dry powder is then placed in a tube furnace and calcined at a heating rate of 5°C / min to 650°C for pre-calcination for 300 minutes, and then heated to 900°C at a heating rate of 10°C / min, calcined for 720 minutes, and naturally cooled to obtain a solid powder. The solid powder is then crushed for 9 hours to obtain LiMn0.75 Fe 0.25 PO4 materials

[0164] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn 0.75 Fe 0.25 PO4) and lithium iron phosphate (LiFePO4) positive electrode materials are mixed evenly according to the Mn / Fe molar ratio of 0.4 as the main material, and the compounding ratio of LMFP and LFP is 0.61. The main material, conductive agent SP, and binder are mixed evenly in NMP according to the mass ratio of 96:1.5:2.5. Then, the mixed positive electrode slurry is mixed at a surface density of 400g / m 2 The positive electrode sheet is evenly coated on aluminum foil and dried in a vacuum oven at 100°C to obtain the positive electrode sheet, which is then slit; then rolled and cut to obtain the positive electrode sheet.

[0165] (3) Preparation of negative electrode sheet: same as in Example 1.

[0166] (4) Compared with Example 1, the electrolyte used was a trimethyl borate additive containing 760 ppm of B element.

[0167] (5) Preparation of diaphragm: same as in Example 1.

[0168] (6) Preparation of battery: same as in Example 1.

[0169] Example 11:

[0170] (1) Lithium iron manganese phosphate (LiMn 0.75 Fe 0.25 PO4) positive electrode material: LiMn 0.75 Fe 0.25 The molar ratio of each element Li, Mn, Fe, and P in the PO4 chemical formula is respectively weighed. Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate are weighed, deionized water is added, mixed, and ball milled to obtain a lithium iron manganese phosphate precursor slurry. Then, 28% glucose is weighed and mixed evenly with the lithium iron manganese phosphate precursor slurry, ball milled for 20 hours, and then the solid content is adjusted and spray dried to obtain a dry powder. The dry powder is then placed in a tube furnace and calcined at a heating rate of 5°C / min to 400°C for pre-calcination for 300 minutes, then heated to 600°C at a heating rate of 10°C / min, calcined for 720 minutes, and naturally cooled to obtain a solid powder, which is crushed for 10 hours to obtain LiMn 0.75 Fe 0.25 PO4 material.

[0171] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn 0.75 Fe 0.25PO4) and lithium iron phosphate (LiFePO4) positive electrode materials are mixed evenly according to the Mn / Fe molar ratio of 0.2 as the main material, and the compounding ratio of LMFP and LFP is 0.29. The main material, conductive agent SP, and binder are mixed evenly in NMP according to the mass ratio of 96:3:1. Then, the mixed positive electrode slurry is mixed at a surface density of 400g / m 2 The positive electrode sheet is evenly coated on aluminum foil and dried in a vacuum oven at 100°C to obtain the positive electrode sheet, which is then slit; then rolled and cut to obtain the positive electrode sheet.

[0172] (3) Preparation of negative electrode sheet: same as in Example 1.

[0173] (4) Compared with Example 1, the electrolyte used was a TMSB additive containing 70 ppm of B element.

[0174] (5) Preparation of diaphragm: same as in Example 1.

[0175] (6) Preparation of battery: same as in Example 1.

[0176] Example 12:

[0177] (1) Lithium iron manganese phosphate (LiMn 0.9 Fe 0.1 PO4) positive electrode material: LiMn 0.9 Fe 0.1 The molar ratio of each element Li, Mn, Fe, and P in the PO4 chemical formula is as follows: lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate are weighed respectively, deionized water is added, mixed, and ball milled to obtain a lithium iron manganese phosphate precursor slurry, and then 12% by mass of glucose is weighed and mixed evenly with the lithium iron manganese phosphate precursor slurry, and ball milled for 20 hours. After that, the solid content is adjusted and spray dried to obtain a dry powder; the dry powder is then placed in a tube furnace and calcined at a heating rate of 5°C / min to 400°C for pre-calcination for 300 min, and then heated to 600°C at a heating rate of 10°C / min, calcined for 720 min, and naturally cooled to obtain a solid powder. After 14 hours of crushing and screening, the primary particle size shown in Table 1 is obtained;

[0178] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn 0.9 Fe 0.1 PO4) and conductive agent SP and binder were mixed in NMP at a mass ratio of 96:1:3. Then, the mixed positive electrode slurry was prepared at a surface density of 400 g / m 2 The positive electrode sheet is evenly coated on aluminum foil and dried in a vacuum oven at 100°C to obtain the positive electrode sheet, which is then slit; then rolled and cut to obtain the positive electrode sheet.

[0179] (3) Preparation of negative electrode sheet: same as in Example 1.

[0180] (4) Compared with Example 1, the electrolyte used was a TMSB additive containing 980 ppm of B element.

[0181] (5) Preparation of diaphragm: same as in Example 1.

[0182] (6) Preparation of battery: same as in Example 1.

[0183] Figure 1 This is the XPS spectrum of the positive electrode sheet prepared in Example 12 of the present invention at an etching depth of 10 nm; Figure 1 It can be seen that the peak appearing in the XPS spectrum represents the peak of element B, among which the peak value represents the peak intensity of element B of the positive electrode sheet at the etching position of 10 nm, which is about 1250 counts / s.

[0184] Example 13:

[0185] (1) Lithium iron manganese phosphate (LiMn 0.75 Fe 0.25 PO4) positive electrode material: LiMn 0.75 Fe 0.25 The molar ratio of each element Li, Mn, Fe, and P in the PO4 chemical formula is as follows: lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate are weighed respectively, deionized water is added, mixed, and ball milled to obtain a lithium iron manganese phosphate precursor slurry. Then, 35% glucose is weighed and mixed evenly with the lithium iron manganese phosphate precursor slurry, ball milled for 20 hours, and then the solid content is adjusted and spray dried to obtain a dry powder. The dry powder is then placed in a tube furnace and calcined at a heating rate of 5°C / min to 650°C for pre-calcination for 300 minutes, then heated to 900°C at a heating rate of 10°C / min, calcined for 720 minutes, and cooled naturally to obtain LiMn 0.75 Fe 0.25 PO4 material. Then LiMn 0.75 Fe 0.25 The PO4 material was crushed and ground, and after 8 h of crushing and screening, the primary particle size was obtained as shown in Table 1;

[0186] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn 0.75 Fe 0.25 PO4) and lithium iron phosphate (LiFePO4) positive electrode materials are mixed evenly according to the Mn / Fe molar ratio of 0.08 as the main material, and the compounding ratio of LMFP and LFP is 0.11. The main material, conductive agent SP, and binder are mixed evenly in NMP according to the mass ratio of 96:3:1. Then, the mixed positive electrode slurry is mixed at a surface density of 400g / m 2The positive electrode sheet is evenly coated on aluminum foil and dried in a vacuum oven at 100°C to obtain the positive electrode sheet, which is then slit; then rolled and cut to obtain the positive electrode sheet.

[0187] (3) Preparation of negative electrode sheet: same as in Example 1.

[0188] (4) Compared with Example 1, the electrolyte used was a LiBOB additive containing 850 ppm of B element.

[0189] (5) Preparation of diaphragm: same as in Example 1.

[0190] (6) Preparation of battery: same as in Example 1.

[0191] Example 14:

[0192] (1) Lithium iron manganese phosphate (LiMn 0.95 Fe 0.05 PO4) positive electrode material: LiMn 0.95 Fe 0.05 The molar ratio of each element Li, Mn, Fe, and P in the PO4 chemical formula is respectively weighed. Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate are weighed, deionized water is added, mixed, and ball milled to obtain a lithium iron manganese phosphate precursor slurry. Then, 10% glucose is weighed and mixed evenly with the lithium iron manganese phosphate precursor slurry, ball milled for 25 hours, and then the solid content is adjusted and spray dried to obtain a dry powder. The dry powder is then placed in a tube furnace and calcined at a heating rate of 5°C / min to 200°C for pre-calcination for 300 minutes, then heated to 450°C at a heating rate of 10°C / min, calcined for 720 minutes, and cooled naturally to obtain LiMn 0.95 Fe 0.05 PO4 material.

[0193] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn 0.95 Fe 0.05 PO4) and lithium iron phosphate (LiFePO4) positive electrode materials are mixed evenly according to the Mn / Fe molar ratio of 10 as the main material, and the compounding ratio of LMFP and LFP is 22.2. The main material, conductive agent SP, and binder are mixed evenly in NMP according to the mass ratio of 96:0.1:3.9. Then, the mixed positive electrode slurry is mixed at a surface density of 400g / m 2 The positive electrode sheet is evenly coated on aluminum foil and dried in a vacuum oven at 100°C to obtain the positive electrode sheet, which is then slit; then rolled and cut to obtain the positive electrode sheet.

[0194] (3) Preparation of negative electrode sheet: same as in Example 1.

[0195] (4) Compared with Example 1, the electrolyte used was a LiBOB additive containing 190 ppm of B element.

[0196] (5) Preparation of diaphragm: same as in Example 1.

[0197] (6) Preparation of battery: same as in Example 1.

[0198] Comparative Example 1

[0199] (1) Lithium iron manganese phosphate (LiMn 0.9 Fe 0.1 PO4) positive electrode material: LiMn 0.9 Fe 0.1 The molar ratio of each element of Li, Mn, Fe, and P in the PO4 chemical formula is respectively weighed. Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate are weighed, deionized water is added, mixed, and ball milled to obtain lithium iron manganese phosphate precursor slurry. Then, 10% glucose is weighed and mixed evenly with the lithium iron manganese phosphate precursor slurry, ball milled for 20 hours, and then the solid content is adjusted and spray dried to obtain dry powder. The dry powder is then placed in a tube furnace and calcined at a heating rate of 5°C / min to 100°C for pre-calcination for 300min, then heated to 300°C at a heating rate of 10°C / min, calcined for 720min, and cooled naturally to obtain LiMn 0.9 Fe 0.01 PO4 material.

[0200] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn 0.9 Fe 0.1 PO4) The positive electrode material, conductive agent SP and binder are mixed evenly in NMP at a mass ratio of 96:1:3. Then, the mixed positive electrode slurry is mixed at a surface density of 400g / m 2 Evenly coat the aluminum foil, dry it in a vacuum oven at 100°C to obtain the positive electrode sheet, and then cut it into strips; then roll and cut it to obtain the positive electrode sheet;

[0201] (3) Preparation of negative electrode sheet: same as in Example 1;

[0202] (4) Compared with Example 1, the electrolyte solution selected LiBF4 containing 90 ppm of B element, 1% VC, and 1% MMDS as film-forming additives.

[0203] (5) Preparation of diaphragm: same as in Example 1.

[0204] (6) Preparation of battery: same as in Example 1.

[0205] Comparative Example 2:

[0206] (1) Lithium iron manganese phosphate (LiMn 0.75 Fe 0.25 PO4) positive electrode material: LiMn0.75 Fe 0.25 The molar ratios of Li, Mn, Fe, and P in the PO4 chemical formula are as follows: lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate are weighed respectively, deionized water is added, mixed, and ball-milled to obtain a lithium iron manganese phosphate precursor slurry. Then, 40% glucose by mass is weighed and mixed evenly with the lithium iron manganese phosphate precursor slurry, ball-milled for 20 hours, and then the solid content is adjusted and spray-dried to obtain a dry powder. The dry powder is then placed in a tube furnace and calcined at a heating rate of 5°C / min to 600°C for pre-calcination for 300 minutes, then heated to 1000°C at a heating rate of 10°C / min, calcined for 720 minutes, and cooled naturally to obtain a solid powder; the solid powder is then crushed, crushed for 3.5 hours, and screened to obtain the primary particle size shown in Table 1;

[0207] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn 0.75 Fe 0.25 PO4) and lithium iron phosphate (LiFePO4) positive electrode materials are mixed evenly according to the Mn / Fe molar ratio of 0.1 as the main material, and the compounding ratio of LMFP and LFP is 0.14. The main material, conductive agent SP, and binder are mixed evenly in NMP according to the mass ratio of 96:2.5:1.5. Then, the mixed positive electrode slurry is mixed at a surface density of 400g / m 2 The positive electrode sheet is evenly coated on aluminum foil and dried in a vacuum oven at 100°C to obtain the positive electrode sheet, which is then slit; then rolled and cut to obtain the positive electrode sheet.

[0208] (3) Preparation of negative electrode sheet: same as in Example 1;

[0209] (4) Compared with Example 1, the electrolyte used is an additive LiBF4 containing 3260 ppm of B element.

[0210] (5) Preparation of diaphragm: same as in Example 1.

[0211] (6) Preparation of battery: same as in Example 1.

[0212] Comparative Example 3:

[0213] (1) Lithium iron manganese phosphate (LiMn 0.75 Fe 0.25 PO4) positive electrode material: LiMn 0.75 Fe 0.25The molar ratio of each element Li, Mn, Fe, and P in the PO4 chemical formula is respectively weighed. Lithium carbonate, manganese carbonate, ferrous oxalate, and diammonium hydrogen phosphate are weighed, deionized water is added, mixed, and ball milled to obtain a lithium iron manganese phosphate precursor slurry. Then, 40% glucose is weighed and mixed evenly with the lithium iron manganese phosphate precursor slurry, ball milled for 20 hours, and then the solid content is adjusted and spray dried to obtain a dry powder. The dry powder is then placed in a tube furnace and calcined at a heating rate of 5°C / min to 400°C for pre-calcination for 300 minutes, then heated to 600°C at a heating rate of 10°C / min, calcined for 720 minutes, and cooled naturally to obtain LiMn 0.75 Fe 0.25 PO4 material. Then LiMn 0.75 Fe 0.25 The PO4 material was crushed, ground and crushed for 12 hours, and screened to obtain the primary particle size shown in Table 1.

[0214] (2) Preparation of positive electrode: Lithium manganese iron phosphate (LiMn 0.75 Fe 0.25 The main material is a mixture of lithium phosphate (LiPO4) and lithium iron phosphate (LiFePO4) cathode materials at a Mn / Fe molar ratio of 1.5. The LMFP and LFP compounding ratio is 4. The main material, conductive agent SP, and binder are mixed in NMP at a mass ratio of 96:1:3. A portion of the slurry is taken out and 35ppm of LiBF4 is added to form the first slurry. The remaining portion is used as the second slurry.

[0215] The first slurry is evenly coated on the aluminum foil and dried in a vacuum oven at 100°C; the second slurry is coated on the first slurry and dried in a vacuum oven at 100°C, then slit, rolled and cut to obtain the positive electrode sheet.

[0216] (3) Preparation of negative electrode sheet: same as in Example 1;

[0217] (4) Preparation of diaphragm: same as in Example 1.

[0218] (5) Preparation of battery: same as in Example 1.

[0219] Table 1 The values ​​and relationships of a, k, h, etc. in the positive electrode sheets in the examples and comparative examples and the battery performance test results

[0220] / a k a×h / k Acidity growth rate h / % F2-F1 Primary particle size / nm (the size of the primary particles in the agglomerate; or the size of the primary particles directly after the agglomerate is broken) Capacity retention rate after 400 cycles at 25℃ / % 400clsDCR growth rate / % Example 1 0.10 400 0.0008 3.20 3950 162 68.2 56.1 Example 2 2.8 5 9.80000 17.50 45 76 65.3 41.9 Example 3 0.5 108 0.0208 4.50 600 151 91.5 36.0 Example 4 2.3 12 2.9708 15.50 100 95 96.4 27.2 Example 5 1.5 45 0.2333 7.00 420 130 94.1 24.3 Example 6 0.4 95 0.0177 4.20 880 155 94.2 40.1 Example 7 2.5 9 4.4444 16.00 75 83 76.0 33.5 Example 8 1.5 380 0.0592 15.00 3550 92 77.4 50.6 Example 9 2.0 43 0.7200 16.20 400 41 72.9 36.1 Example 10 0.4 90 0.0222 5.00 750 202 79.4 39.7 Example 11 0.2 7 0.0857 3.00 50 132 86.3 38.2 Example 12 9.0 125 1.2960 18.00 980 136 90.4 30.3 Example 13 0.08 100 0.0016 2.00 890 200 75.6 60.3 Example 14 10 20 9.5000 19.00 160 82 60.3 45.2 Comparative Example 1 9 10 16.2000 18.00 30 33 45.3 63.0 Comparative Example 2 0.1 398 0.0005 2.00 3950 251 50.4 68.5 Comparative Example 3 1.5 3 12.5000 25.00 -50 128 47.5 71.5

[0221] Table 2 Raw material dosage and process conditions for preparing positive electrode sheets in Examples and Comparative Examples

[0222] / Manganese-iron ratio in the positive electrode active material LMFP:LFP compound ratio Boron addition amount / ppm Example 1 0.1 0.14 3300 Example 2 2.8 56.0 45 Example 3 0.5 0.81 900 Example 4 2.3 13.14 130 Example 5 1.5 4 380 Example 6 0.4 0.61 805 Example 7 2.5 20 80 Example 8 1.5 4 3210 Example 9 2 8 350 Example 10 0.4 0.61 760 Example 11 0.2 0.29 70 Example 12 9 / (Simple manganese iron lithium) 980 Example 13 0.08 0.11 850 Example 14 10 22.2 190 Comparative Example 1 9 / (Simple manganese iron lithium 90 Comparative Example 2 0.1 0.14 3260 Comparative Example 3 1.5 4 35

[0223] Test: Manganese to Iron Ratio (a) Test Method: ICP

[0224] ① Pretreatment: Disassemble the lithium-ion battery to obtain the positive electrode sheet, soak the positive electrode sheet in DMC (dimethyl carbonate) at room temperature for 60 minutes, take it out, and dry it at room temperature with a humidity of ≤15%; scrape the positive electrode active material layer on the surface of the current collector and calcine it at 400℃ for 3 hours to remove the conductive agent, binder, surface side reaction products, and residual electrolyte. After washing and drying, the positive electrode active material powder is obtained.

[0225] ② Accurately weigh 0.5g of cathode active material powder and disperse it in 20ml of water. Add 10ml of nitric acid, mix thoroughly, and heat. After the cathode active material powder dissolves, dilute to 100ml with water to obtain the test solution. Perform ICP testing on the test solution. Before testing, prepare a standard solution. The standard solution must have a linear correlation coefficient of 0.999 or higher to be used as a standard. Dilute the 1000 mg / L standard solution with deionized water to different concentrations (typically 0, 1 mg / 100ml, 2 mg / 100ml, and 3 mg / 100ml). Select the element detection wavelength and set the experimental conditions: Based on the sample characteristics and the elements to be detected, set the appropriate ICP instrument operating conditions: gas flow rate 0.5L / min, power 1150W, and select the element detection wavelengths of 259.94nm for Fe and 257.61nm for Mn. The Fe and Mn concentrations in the sample can be read using the ICP test software's self-analysis function.

[0226] Peak Intensity Ratio:

[0227] ① Pretreatment: Disassemble the lithium-ion battery to obtain the positive electrode sheet, soak the positive electrode sheet in DMC (dimethyl carbonate) at room temperature for 60 minutes, take it out, and dry it at room temperature with a humidity of ≤15%;

[0228] ② XPS etching peak intensity ratio (k):

[0229] The electrode to be tested is subjected to XPS etching analysis, and the peak intensity b of the B1s peak at the binding energy position of 188-192 eV in the XPS graph is obtained. Specifically, the etching depth L can be selected to be 10 nm.

[0230] Where, k=b / L;

[0231] The sample is secured in an appropriate position, such as on conductive tape on a copper sheet, and then transported to the analysis chamber via a rapid sample loading chamber. A 120W monochromatized Al Kα X-ray source is used, with an energy resolution of 0.48 eV or less. The test beam spot is 400 microns, and the instrument automatically adjusts the test energy range based on the element being measured. Etching conditions: Ar ions are used for etching, and the etch depth is controlled by adjusting the etch rate and time. In this invention, the etch depth is 10 nm (or 35 nm). After the test, the instrument automatically displays the test results, including the peak intensity b. Combined with the etch depth L, b / L, the peak intensity ratio k is calculated.

[0232] Acidity growth rate:

[0233] Disassemble the fully charged battery (discharge the battery at 0.33C to a lower voltage of 2.5V, then charge it at a constant current of 0.33C to an upper voltage of 4.25V, and then charge it at a constant voltage until the current is less than or equal to 0.05C) to obtain the positive electrode sheet in the fully charged state. Soak the electrode sheet in DMC (dimethyl carbonate) for 1 hour, clean it, and dry it at 80℃ for 4 hours to obtain the positive electrode sheet. Cut the positive electrode sheet into 7cm×7cm pieces to be tested;

[0234] At 60°C, immerse the electrode to be tested in 20 ml of a mixed solution consisting of ethylene carbonate, ethyl methyl carbonate, and lithium perchlorate, wherein the volume ratio of ethylene carbonate to ethyl methyl carbonate is 3:7, and the molar concentration of lithium perchlorate in the mixed solution is 1 mol / L.

[0235] When the electrode to be tested is immersed in the mixed solution for 48 hours, the hydrogen ion content in the mixed solution is detected and recorded as h1 ppm; when the electrode to be tested is immersed in the mixed solution for 72 hours, the hydrogen ion content in the mixed solution is detected again and recorded as h2 ppm;

[0236] Calculate the growth rate of hydrogen ion content when the positive electrode is immersed in a mixed solution containing lithium perchlorate: h = (h2-h1) / h1×100%; this is the acidity growth rate.

[0237] The hydrogen ion content (h1, h2) in the mixed solution is detected by the following method:

[0238] Prepare a 0.05 mol / L triethylamine titrant by mixing triethylamine and ethyl methyl carbonate (EMC). Take the mixed solution used to immerse the positive electrode as the test solution, add 10-30 drops of methyl red as an indicator, and drip the triethylamine titrant into the test solution containing methyl red. Record the amount of triethylamine titrant used when the test solution turns orange. Then calculate the hydrogen ion content according to the formula:

[0239] Hydrogen ion content = M × V × 20010 / m, the unit of hydrogen ion content is ppm;

[0240] Where: M is the concentration of triethylamine titrant, unit is mol / L,

[0241] V is the volume of titrant consumed by triethylamine, in mL.

[0242] m is the mass of the solution to be tested, in g,

[0243] 20010=20.01×10 3 , 20.01 is the molecular weight of HF. The fully charged positive electrode contains the electrolyte component LiPF6. The positive electrode active material reacts with EC and EMC to dehydrogenate and produce HF in the presence of LiPF6. The amount of HF represents hydrogen ions.

[0244] 400 cycles capacity retention test at 25°C:

[0245] At 25° C., the lithium-ion secondary batteries prepared in the examples and comparative examples were subjected to cycle tests according to the following procedure:

[0246] 1) Charge the battery at a constant current of 1C to 4.25V, then charge it at a constant voltage until the current is less than 0.05C. Repeat this process for more than three times and record the battery capacity C1.

[0247] 2) Charge at a constant current of 1C to 4.25V, and charge at a constant voltage until the current is less than 0.05C.

[0248] 3) Let it sit for 5 minutes;

[0249] 4) Discharge at a rate of 1C to 2.5V;

[0250] 5) Let it sit for 5 minutes,

[0251] Perform a cycle test according to steps 2) to 5) until the lithium-ion secondary battery has been cycled 400 times, and record the capacity C2 of the battery after 400 cycles.

[0252] 25℃ cycle capacity retention rate = C2 / C1×100%.

[0253] DCR growth rate:

[0254] The lithium-ion battery was fixed in capacity and charged to 4.25V at a constant current of 0.33C. Then, it was charged at a constant voltage to a cut-off current of 0.05C. The battery was discharged at 0.33C to adjust the load to 50% SOC, left to stand for 2 hours, and then discharged at 1C at 50% SOC. The initial battery internal resistance was obtained to obtain DCR1.

[0255] The lithium-ion battery was placed in a constant temperature box at 25°C, and the lithium-ion battery was discharged at a constant current of 0.33C. Then, the battery was cycled in the constant temperature box at a charge and discharge test rate of 1C / 1C and a cycle voltage range of 2.5-4.25V for a total of 400 cycles.

[0256] After 400 cycles, the battery was discharged at 0.33C to 50% SOC, left to rest for 2 hours, and then discharged at 1C at 50% SOC. The internal resistance of the battery after the cycle was measured to obtain DCR2.

[0257] The battery internal resistance test method is: take the voltage at the last second of static state as V0, the voltage after 18s discharge as V1, the current during discharge as I, DCR=(V0-V1) / I;

[0258] Calculate the DCR growth rate = (DCR2-DCR1) / DCR1×100%.

[0259] It can be seen from the above embodiments that the present invention provides a positive electrode sheet, wherein the positive electrode sheet includes a positive electrode active material, wherein the positive electrode active material includes lithium manganese iron phosphate particles; the molar ratio of manganese element to iron element in the positive electrode active material is a; the acidity growth rate of the positive electrode sheet is h, unit: %; k=b / L, wherein L is the depth of the positive electrode sheet etched by XPS, which is 10nm; k is the peak intensity ratio of the B1s peak at the binding energy of 188~192eV in the XPS graph when the positive electrode sheet is subjected to XPS etching analysis, unit: counts / s / nm; b is the peak intensity of the B1s peak at the binding energy of 188~192eV in the XPS graph when the positive electrode sheet is subjected to XPS etching analysis, unit: counts / s; a, k and h satisfy the following relationship: a×h / k=8×10 -4 By controlling the manganese to iron ratio, acidity growth rate, and peak intensity ratio at a certain etching depth, the positive electrode forms a stable CEI film containing B on the surface of the positive electrode, preventing the dissolution of manganese ions, reducing active lithium consumption, and improving the cycle.

[0260] Experimental results show that the batteries prepared in the present invention maintain a capacity of 60.3-96.4% after 400 cycles at room temperature, with a DCR growth rate of 24.3-56.1% after 400 cycles. In contrast, the batteries prepared in the comparative example maintain a capacity of 45.3-50.4% after 400 cycles at room temperature, with a DCR growth rate of 63-71.5% after 400 cycles. This indicates that by controlling experimental parameters such as a, k, h, a×h / k, and F2-F1, the present invention forms a stable boron-containing positive electrode solid electrolyte interface (CEI) film on the surface of the positive electrode sheet, preventing manganese ion dissolution, reducing active lithium consumption, and improving cycling.

[0261] In Examples 3 to 5 of the present application, the values ​​of a×h / k, a, h, and k are all within the preferred range, and the peak intensity difference F2-F1 is also within the preferred range. The resulting battery has a capacity retention rate of 91.5-96.4% after 400 cycles at room temperature, and a DCR growth rate of 24.3-36.0% after 400 cycles. If any of the above values ​​are not within the preferred range, the battery cycle performance will be slightly poor; for example, in Example 8 of the present application, a×h / k is 0.0592, which is within the preferred range of 0.02-3, but the peak intensity difference F2-F1 is 3550, and the surface peak intensity is large, which is not within the preferred range of 0-2000, resulting in slightly poor battery cycle performance.

[0262] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A positive electrode sheet, characterized in that: The positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes lithium manganese iron phosphate particles; The molar ratio of manganese to iron in the positive electrode active material is a; the acidity growth rate of the positive electrode sheet is h, unit: %; 0.1≤a≤9; the acidity growth rate h is 3-18%; When the XPS etching depth is 10 nm, the peak intensity of the B1s peak is F1; when the XPS etching depth is 35 nm, the peak intensity of the B1s peak is F2; The difference between F1 and F2 is greater than 0 and less than or equal to 2000; The test method of described peak intensity is as follows: ① Pretreatment: disassemble the lithium-ion battery to obtain the positive electrode sheet, soak the positive electrode sheet in dimethyl carbonate at room temperature for 60 minutes, take it out, and dry it at room temperature with a humidity of ≤15%; ② XPS etching: The electrode to be tested is subjected to XPS etching analysis, and the peak intensity of the B1s peak at the binding energy position of 188-192eV in the XPS graph is obtained; The sample was fixed on a conductive tape on a copper sheet and then transported into the analysis chamber through a rapid sample introduction chamber using a 120W monochromatized Al Kα X-ray source; Energy resolution is less than or equal to 0.48 eV; the test beam spot is 400 microns, and the instrument automatically expands the test energy range according to the element being tested. Etching conditions: Ar ions are used for etching, and the etching depth is controlled by adjusting the etching rate or etching time. The etching depth is 10nm or 35nm. After the test, the instrument automatically outputs the test results, which can be used to obtain the peak intensity of the B1s peak at the etching position of 10nm and 35nm. k=b / L, where k is the peak intensity ratio of the B1s peak at the binding energy of 188-192 eV in the XPS graph when the positive electrode sheet is subjected to XPS etching analysis, and the unit is counts / s / nm; L is the depth of the XPS etching of the positive electrode sheet, which is 10 nm; b is the peak intensity of the B1s peak at the binding energy of 188-192 eV in the XPS graph when the positive electrode sheet is subjected to XPS etching analysis, and the unit is counts / s; The a, k and h satisfy the following relationship: a×h / k=0.02~3.

2. The positive electrode sheet according to claim 1, characterized in that 0.4≤a≤2.5。 3. The positive electrode sheet according to claim 1, characterized in that 5≤k≤400。 4. The positive electrode sheet according to claim 3, characterized in that 9≤k≤108。 5. The positive electrode sheet according to claim 1, characterized in that: The acidity growth rate h is 4~16%.

6. The positive electrode sheet according to claim 1, characterized in that The lithium manganese iron phosphate particles include primary particles, and the average particle size of the primary particles ranges from 50 to 170 nm.

7. A battery, characterized in that: Including positive electrode sheet, negative electrode sheet, separator and electrolyte; The positive electrode sheet is the positive electrode sheet according to any one of claims 1 to 6.

8. The battery according to claim 7, characterized in that A boron-containing compound is provided in the electrolyte and / or the positive electrode sheet.

9. The battery according to claim 8, characterized in that The electrolyte includes a boron-containing compound, which is selected from one or more of lithium bis(oxalatoborate), tris(trimethylsilyl)borate, lithium difluorooxalatoborate, lithium tetrafluoroborate, tributyl borate and trimethyl borate.

10. An electrical device, characterized in that: A battery comprising the battery according to any one of claims 7 to 9.

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