Positive pole piece, battery comprising positive pole piece and electric device

Abstract

The invention relates to a positive pole piece, a battery comprising the positive pole piece and an electric device, and belongs to the technical field of batteries. The positive pole piece comprises a positive current collector and a positive active material layer arranged on at least one surface of the positive current collector, the positive active material layer comprises a positive active material, the positive active material comprises lithium manganese iron phosphate and a ternary positive material, and the positive pole piece meets the condition that a / b is greater than or equal to 0.09 and less than or equal to 5.1, a is the mass percentage content of the Ni element in the positive electrode active material layer, and the unit is%; b is the longitudinal wettability of the positive pole piece, and the unit is%. The LMFP and the ternary positive electrode material are compounded, and the content of the Ni element in the positive electrode active material layer and the longitudinal wettability of the positive electrode plate are reasonably controlled, so that after the positive electrode plate is applied to the battery, the charging time of the battery in a high-voltage stage can be remarkably shortened, and the battery performance is improved. Meanwhile, the balance of the lithium ion transmission rate and the electron transmission rate of the positive pole piece in the longitudinal direction is realized, and the fast charging performance and the high-temperature cycle performance of the battery are effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a positive electrode sheet, a battery comprising the positive electrode sheet, and an electrical device. Background Art

[0002] Lithium manganese iron phosphate (LMFP) material has a high voltage platform, large theoretical specific capacity, wide sources, and is environmentally friendly. It is considered to be a very promising positive electrode active material for lithium-ion batteries.

[0003] During the charging process of the LMFP battery, it is first charged to the cut-off voltage by constant current charging, and then charged to the cut-off current by constant voltage charging. However, when the battery is charged to a high SOC, the electronic conductivity and ionic conductivity of the LMFP body and surface interface are relatively poor, resulting in the deterioration of the fast charging performance of the battery. At the same time, under high SOC, the LMFP and the electrolyte are continuously charged at high voltage and low current, the positive electrode and the electrolyte continue to react chemically, the effective solvent in the electrolyte is continuously consumed, the battery DCR continues to increase, and the LMFP charge and discharge polarization continues to increase. Before the charge and discharge voltage is cut off, the positive electrode active material has no time to participate in the electrochemical reaction, and the released active lithium continues to decrease, resulting in poor cycle performance.

[0004] Therefore, it is necessary to improve the fast charging performance and high temperature cycle performance of LMFP batteries. Summary of the invention

[0005] The object of the present invention is to overcome the above-mentioned deficiencies of the prior art and provide a positive electrode plate, a battery and an electrical device comprising the positive electrode plate, so as to improve the fast charging performance and high temperature cycle performance of the LMFP battery.

[0006] To achieve the above object, in a first aspect, the present invention provides a positive electrode plate, comprising a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material, wherein the positive electrode active material comprises lithium manganese iron phosphate and a ternary positive electrode material, and wherein the positive electrode plate satisfies:

[0007] 0.09≤a / b≤5.1,

[0008] Wherein, a is the mass percentage of Ni element in the positive electrode active material layer, in %;

[0009] b is the longitudinal wettability of the positive electrode sheet, in %.

[0010] In a second aspect, the present invention provides a battery, comprising the positive electrode plate.

[0011] In a third aspect, the present invention provides an electrical device, comprising the battery.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: by compounding LMFP with a ternary positive electrode material, and adjusting the content of the Ni element in the positive electrode active material layer and the longitudinal wettability of the positive electrode plate to satisfy a specific relationship, the present invention can significantly shorten the charging time of the battery in the high-voltage stage after the positive electrode plate is applied to the battery, and at the same time achieve a balance between the lithium ion transmission rate and the electron transmission rate of the positive electrode plate in the longitudinal direction, effectively improving the fast charging performance and high-temperature cycle performance of the battery. DETAILED DESCRIPTION

[0013] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0014] 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.

[0015] In the present invention, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0016] In the present invention, there is no particular limitation on the specific dispersion and stirring treatment methods.

[0017] The reagents or instruments used in the present invention without indicating the manufacturer are all conventional products that can be obtained through commercial purchase.

[0018] In the present invention, "first time", "second time" and other similar expressions are not used to limit the number of times.

[0019] Positive electrode

[0020] The present invention provides a positive electrode plate, comprising a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material, wherein the positive electrode active material comprises lithium manganese iron phosphate and a ternary positive electrode material, and the positive electrode plate satisfies:

[0021] 0.09≤a / b≤5.1,

[0022] Wherein, a is the mass percentage of Ni element in the positive electrode active material layer, in %;

[0023] b is the longitudinal wettability of the positive electrode sheet, in %.

[0024] LMFP itself has poor electronic and ionic conductivity, while the electronic and ionic conductivity of the ternary cathode material is better. This is because the ternary cathode material is a layered oxide, and its layered structure makes Li + The transmission path is shorter, and the elements Co and Ni it contains are more beneficial to the electronic conductivity of the material. Doping ternary positive electrode materials in LMFP can promote further lithium deintercalation of LMFP under high SOC, reduce the time for lithium deintercalation in the constant voltage section, thereby reducing the proportion of the constant voltage section during the charging process and reducing the high-voltage charging time; at the same time, doping with ternary positive electrode materials will also make up for the electronic conductivity required for the electrochemical reaction of LMFP under high SOC before the potential cutoff, promote LMFP to release more active lithium and improve the cycle performance. In addition, ternary positive electrode materials are mainly large particles with stronger physical structure; LMFP is mainly small particles, and the physical structure of the material is looser. After rolling, the two materials are supplemented by physical structural characteristics, stress is released, and the compaction density is improved, but this also makes it more difficult for the electrolyte to infiltrate the positive electrode sheet, and the resistance to lithium ion transmission increases.

[0025] The longitudinal wettability (b) of the positive electrode plate refers to the degree of electrolyte infiltration into the positive electrode plate in the direction perpendicular to the positive current collector (i.e., along the thickness direction of the positive current collector), which is calculated based on the mass change of the positive electrode plate before and after the electrolyte infiltration. During fast charging, high current density requires efficient transmission of electrolyte ions in a short time. Insufficient longitudinal wettability will lead to an increase in the electrolyte concentration gradient deep inside the plate, limiting ion transmission. When the plate thickness is large, and in high-rate fast charging design, the requirements for longitudinal wettability are more stringent, which directly affects the utilization rate of deep active substances. It is necessary to ensure that the electrolyte is evenly distributed throughout the thickness of the plate to avoid the formation of a "dead zone" for ion transmission. The impact of insufficient overall wettability is mostly uneven reaction in the surface area, while insufficient longitudinal wettability is the direct "failure" or reduced reaction rate of active substances in the deep area. The degradation problem in the deep area is more hidden and difficult to detect in time through ordinary detection methods. Long-term accumulated degradation will lead to irreversible performance degradation of the battery. The improvement of the longitudinal wettability of the positive electrode sheet, that is, the improvement of the longitudinal wetting effect of the positive electrode sheet, helps to improve the lithium ion transmission rate in the longitudinal direction of the positive electrode sheet and enhance the fast charging performance of the battery. However, if the longitudinal wettability of the positive electrode sheet is too high, it means that the structure of the positive electrode active material layer is too loose in the longitudinal direction, which will lead to poor electronic contact and poor conductivity of the positive electrode active material in the longitudinal direction, and the electrolyte is more likely to react with the positive electrode active material during the cycle, resulting in increased impedance. The longitudinal wettability of the positive electrode sheet should not be too low, otherwise the longitudinal wetting effect of the positive electrode sheet is poor, the lithium ion transmission rate is poor, and the wettability of the electrolyte between the particles of the positive electrode active material layer is insufficient, resulting in rapid decay of the battery cycle performance.

[0026] The value of the longitudinal wettability (b) of the positive electrode sheet can be adjusted by adjusting the type of ternary positive electrode material and / or LMFP (such as selecting single crystal or polycrystalline for ternary positive electrode material, and selecting single crystal or polycrystalline for LMFP), the content of the conductive agent, or adjusting the pressure during the rolling process. Among them, the single crystal of the ternary positive electrode material is the primary particle of the ternary positive electrode material; the polycrystalline of the ternary positive electrode material refers to the secondary particle of the ternary positive electrode material, which is composed of multiple primary particles; the LMFP single crystal refers to non-agglomerated primary particles, or secondary particles with a low degree of agglomeration (aggregation of two or three primary particles); LMFP polycrystalline refers to LMFP agglomerates, and agglomerates refer to secondary particles that are aggregated by more than three (i.e., more than four) primary particles and present an agglomerated state.

[0027] The present invention does not limit the detection method of the longitudinal wettability (b) of the positive electrode sheet. Those skilled in the art can detect the longitudinal wettability (b) of the positive electrode sheet according to conventional technical means. Exemplarily, the longitudinal wettability (b) of the positive electrode sheet can be detected by the following method:

[0028] Take the positive electrode after emptying, soak it in dimethyl carbonate for 2h, dry it at 80℃, cut it into a size of 1.5*1.5cm after drying, weigh the mass of the electrode M0 (unit g), and then hot-press it together with a polymer film containing a circular hole with a radius r=0.5cm. After hot-pressing, the surface of the positive electrode is covered with a polymer film, and the circular hole is located at the center of the polymer film. It is placed flat on a horizontal table, and the pre-prepared electrolyte (the solvent is EC and EMC, the mass ratio of the two is EC:EMC=3:7, containing 1mol / L lithium salt, and the lithium salt is lithium hexafluorophosphate) is dripped into the circular hole of the polymer film on the surface of the electrode at a dripping speed of 0.5mL / min. The amount of electrolyte dripped is 2mL. After the electrolyte diffuses for 2min, the mass of the electrode at this time M1 (unit g) is measured, and the longitudinal wettability (b) of the positive electrode is calculated according to the following formula:

[0029] b = (M1 - M0) / M0 x 100%.

[0030] The material of the polymer film can be any polymer film material that is impermeable to the electrolyte and does not react with the electrolyte at room temperature or high temperature, such as a PET-based-EVA hot melt adhesive composite film.

[0031] The mass percentage of Ni in the positive electrode active material layer (a) will affect the fast charging performance, cycle performance and safety performance of the battery. When the mass percentage of Ni in the positive electrode active material layer is too high, the proportion of the ternary positive electrode material is too high, the probability of its high reaction activity with the electrolyte increases, the battery DCR increases too fast, and the cycle performance, fast charging performance and safety performance will all decrease; when it is too low, the proportion of the ternary positive electrode material in the positive electrode active material is too low, and the ionic conductivity and electronic conductivity of the positive electrode active material cannot be effectively improved, resulting in poor cycle performance and fast charging performance of the battery.

[0032] The mass percentage of the Ni element in the positive electrode active material layer (a) can be adjusted by adjusting the ratio of LMFP to the ternary positive electrode material, the molar ratio of the nickel element in the structural formula of the ternary positive electrode material, etc.

[0033] The present invention does not limit the detection method of the mass percentage content (a) of the Ni element in the positive electrode active material layer. Those skilled in the art can detect the content of the Ni element in the positive electrode active material layer according to conventional technical means. Exemplarily, the mass percentage content (a) of the Ni element in the positive electrode active material layer can be detected by the following method:

[0034] Disassemble the empty lithium-ion battery to obtain the positive electrode sheet, soak the positive electrode sheet in DMC (dimethyl carbonate) at room temperature (25° C., the same below) for 60 minutes to remove the residual electrolyte and by-products on the surface of the electrode sheet, take it out, and dry it at room temperature with a humidity of ≤15%; scrape off the positive electrode active material layer on the surface of the current collector, calcine it at 400° C. for 3 hours to remove the binder, etc., and then tap the electrode sheet to obtain the positive electrode active material powder;

[0035] Accurately weigh 0.5g of positive electrode active material powder, disperse it in 20mL of water, then add 10mL of nitric acid (HNO3 mass percentage is 65% to 68%), disperse and heat until the positive electrode active material powder is completely dissolved, and dilute to 100mL with water to obtain the test solution; conduct ICP test on the test solution, and prepare the standard solution before the test, and dilute the standard solution with a Ni element concentration of 1000mg / L (the standard solution can be prepared by dissolving metallic nickel in nitric acid) with deionized water to different concentrations (generally 0, 1mg / 100mL, 2mg / 100mL, 3mg / 100mL), test and calculate the relationship between the Ni element concentration and the peak area of ​​the standard product, and the linear correlation coefficient of the relationship must be above 0.999 to be used as a normal standard product, and then calculate the Ni element content a in the positive electrode active material layer according to the relationship and the corresponding peak area of ​​the sample to be tested. The working conditions of the ICP instrument were set as follows: gas flow rate 0.5 L / min, power 1150 W, element test Ni was selected, and wavelength was 231.604 nm.

[0036] The mass percentage of Ni element in the positive electrode active material layer and the longitudinal wettability of the positive electrode plate affect the fast charging performance and high temperature cycle performance of the battery to varying degrees, and have a certain mutual influence. It is difficult to achieve a battery with good fast charging performance and high temperature cycle performance by controlling a single variable. The present invention significantly shortens the charging time of the battery containing the positive electrode plate in the high voltage stage by compounding LMFP with a ternary positive electrode material and adjusting the mass percentage of Ni element in the positive electrode active material layer and the longitudinal wettability of the positive electrode plate to meet the above-mentioned specific relationship, while achieving a balance between the lithium ion transmission rate and the electron transmission rate of the positive electrode plate in the longitudinal direction, effectively improving the fast charging performance and high temperature cycle performance of the battery.

[0037] Exemplarily, the value of a / b can be selected as 0.09, 0.1, 0.3, 0.5, 0.8, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.1 or an interval range formed by any two of the above values.

[0038] In one preferred embodiment, the positive electrode sheet satisfies: 0.17≤a / b≤2.4. The value of a / b is controlled within the range of 0.17 to 2.4 to improve the fast charging performance and high temperature cycle performance of the battery.

[0039] In some embodiments, the mass percentage content (a) of the Ni element in the positive electrode active material layer ranges from 0.9% to 47%, such as 0.9%, 1.5%, 2%, 5%, 10%, 20%, 30%, 40%, 43%, 47% or an interval formed by any two of the above values.

[0040] In one preferred embodiment, the mass percentage content (a) of the Ni element in the positive electrode active material layer is in the range of 2% to 42%.

[0041] When the mass percentage content (a) of the Ni element in the positive electrode active material layer is in the range of 0.9% to 47%, especially in the range of 2% to 42%, while having good safety performance, fast charging performance and high-temperature cycle performance are better.

[0042] In some embodiments, the longitudinal wettability (b) of the positive electrode sheet is in the range of 5% to 40%. For example, b is 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, or an interval formed by any two of the above values.

[0043] In one preferred embodiment, the longitudinal wettability (b) of the positive electrode sheet ranges from 10% to 35%.

[0044] When the longitudinal wettability (b) of the positive electrode plate is in the range of 5% to 40%, especially in the range of 10% to 35%, the structural density of the positive electrode active material layer is appropriate, not only the positive electrode active material has good electronic contact in the longitudinal direction and good conductivity, but also during the cycle process, the electrolyte has fewer side reactions with the positive electrode active material and the impedance is low. At the same time, the longitudinal wettability of the positive electrode plate is better, the lithium ion transfer rate in the longitudinal direction of the positive electrode plate is higher, and the battery cycle performance is better, thereby improving the battery's fast charging performance and high temperature cycle performance.

[0045] In some embodiments, in the positive electrode active material, the mass percentage of the ternary positive electrode material is 3% to 93%, and the mass percentage of the lithium manganese iron phosphate is 7% to 97%. For example, the mass percentage of the ternary positive electrode material in the positive electrode active material is 3%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 93% or the interval formed by any two of the above values; the mass percentage of the lithium manganese iron phosphate in the positive electrode active material is 7%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 97% or the interval formed by any two of the above values.

[0046] When the mass percentage of the ternary positive electrode material and the mass percentage of the lithium manganese iron phosphate in the positive electrode active material are within the above range, the electronic and ionic conductivity of the positive electrode active material are relatively good, so that the time for lithium deintercalation in the constant voltage section under high SOC is short, the proportion of the constant voltage section during charging is small, and the LMFP can be well promoted to release active lithium under high SOC. At the same time, the compaction density of the positive electrode plate is appropriate, the electrolyte has good infiltration of the positive electrode plate, and the lithium ion transmission resistance is small, which is conducive to improving the fast charging performance and high temperature cycle performance of the battery.

[0047] In some embodiments, the molar content of manganese in the lithium manganese iron phosphate is 0.5-0.99, for example, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, 0.99 or an interval formed by any two of the above values, based on the total molar number of metal elements other than lithium. When the molar content of manganese in the lithium manganese iron phosphate is 0.6-0.8, based on the total molar number of metal elements other than lithium, it is beneficial for the battery to have high energy density, fast charging performance and cycle performance.

[0048] In some embodiments, the chemical formula of the lithium iron manganese phosphate is LiMn d Fe e Q f nPO4, where 0 < d < 1, 0 < e < 1, 0 ≤ f < 1, Q refers to a doping element, n refers to the valence of the doping element, and it satisfies: 2(d + e)+n·f = 2. Among them, d can be selected as 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, 0.99 or the range formed by any two of the above values; e can be selected as 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5 or the range formed by any two of the above values. The lithium iron manganese phosphate can either contain no doping element or contain a doping element. The present invention has no limitation on the type of Q element. For example, Q includes but is not limited to at least one of V, W, Ti, and Mg. In one of the embodiments, part or all of the surface of the lithium iron manganese phosphate is coated with a carbon layer.

[0049] In the present invention, there is no limitation on the preparation method of the lithium iron manganese phosphate. Those skilled in the art can prepare the lithium iron manganese phosphate according to conventional technical means. Exemplarily, the preparation method of the lithium iron manganese phosphate includes the following steps:

[0050] Mix a manganese source, an iron source, a phosphorus source, a lithium source, and a first carbon source, and obtain a lithium iron manganese phosphate precursor through first grinding, first spray drying, and first sintering;

[0051] Mix the obtained lithium iron manganese phosphate precursor and a second carbon source, and obtain lithium iron manganese phosphate through second grinding, second spray drying, second sintering, and iron removal by sieving.

[0052] Exemplarily, in the process of preparing the lithium iron manganese phosphate precursor, the manganese source used includes but is not limited to at least one of manganese tetraoxide, manganese nitrate, manganese carbonate, manganese oxalate, manganese sulfate, manganese chloride, and manganese acetate;

[0053] and / or, the iron source used includes but is not limited to at least one of iron phosphate, ferrous phosphate, iron hydroxide, ferrous hydroxide, iron carbonate, ferrous carbonate, iron acetate, ferrous acetate, ferric oxide, ferroferric oxide, ferrous oxalate, and iron oxalate;

[0054] and / or, the phosphorus source used includes but is not limited to at least one of lithium dihydrogen phosphate, lithium phosphate, diammonium hydrogen phosphate, and ammonium phosphate;

[0055] and / or, the lithium source used includes but is not limited to at least one of lithium dihydrogen phosphate, lithium phosphate, lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxalate, lithium citrate, and lithium acetate;

[0056] And / or, the first carbon source used includes but is not limited to at least one of glucose (GLC), sucrose, polyethylene glycol (PEG), and polyvinyl alcohol. In addition, when preparing LMFP, a certain amount of doping element source (if any) can be mixed with the manganese source, iron source, phosphorus source and lithium source as needed, such as a vanadium source (such as vanadium pentoxide), a tungsten source (such as ammonium metatungstate), a titanium source (such as titanium oxide), a magnesium source (such as magnesium carbonate), etc., to obtain a LMFP containing a certain amount of doping elements.

[0057] In some embodiments, in the process of preparing the lithium manganese iron phosphate precursor, the amount of the manganese source, iron source, phosphorus source and lithium source used can be selected to meet the following conditions: Li element molar amount: the sum of the molar amounts of the Mn element and the Fe element: P element molar amount = (1-1.04): 1: (1-1.02) (such as 1: 1: 1, 1: 1: 1.02, 1.04: 1: 1 or the interval formed by any two of the above values), the Mn element molar amount is more than 50% of the sum of the molar amounts of the Mn element and the Fe element, such as 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or the interval formed by any two of the above values. In one preferred embodiment, the Mn element molar amount is 65% to 80% of the sum of the molar amounts of the Mn element and the Fe element.

[0058] In some embodiments, the residual carbon content in the lithium manganese iron phosphate precursor is 0.1wt.% to 0.5wt.%, such as 0.1wt.%, 0.2wt.%, 0.3wt.%, 0.4wt.%, 0.5wt.%, or an interval formed by any two of the above values. In some embodiments, a dispersant can also be added during the first grinding process, wherein the dispersant can be selected from at least one of water and ethanol.

[0059] In some embodiments, the first grinding can be performed by ball milling, wherein the ball milling beads can be made of zirconium oxide, etc. In one embodiment, the first grinding satisfies: the ball milling time is 0 to 48 hours, and the number of ball milling times is 1 to 6 times.

[0060] In one embodiment, the pressure of the first spray drying can be selected to be 0.1-1.2 MPa, such as 0.1 MPa, 0.3 MPa, 0.5 MPa, 0.8 MPa, 1 MPa, 1.2 MPa, or an interval formed by any two of the above values.

[0061] In one embodiment, the sintering atmosphere of the first sintering is an inert atmosphere, such as a nitrogen atmosphere.

[0062] In one embodiment, the temperature of the first sintering can be selected to be 300-680°C, for example, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 680°C or an interval formed by any two of the above values.

[0063] In one embodiment, the time for the first sintering can be selected to be 2 to 18 hours, for example, 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours or an interval formed by any two of the above values.

[0064] Exemplarily, the second carbon source includes, but is not limited to, at least one of glucose (GLC), sucrose, polyethylene glycol (PEG), and polyvinyl alcohol.

[0065] In some embodiments, the residual carbon content in the lithium manganese iron phosphate can be selected to be 1.4wt.% to 2.6wt.%, for example, 1.4wt.%, 1.8wt.%, 2.0wt.%, 2.2wt.%, 2.4wt.%, 2.6wt.% or an interval formed by any two of the above values.

[0066] In some embodiments, the second grinding can be performed by ball milling, wherein the ball milling beads can be made of zirconium oxide, etc. In one embodiment, the second grinding satisfies: the ball milling time is 0 to 48 hours, and the number of ball milling times is 1 to 6 times.

[0067] In one embodiment, the pressure of the second spray drying can be selected to be 0.1-1.5 MPa, such as 0.1 MPa, 0.3 MPa, 0.5 MPa, 0.8 MPa, 1 MPa, 1.2 MPa, 1.5 MPa or an interval formed by any two of the above values.

[0068] In one embodiment, the sintering atmosphere of the second sintering is an inert atmosphere, such as a nitrogen atmosphere.

[0069] In one embodiment, the temperature of the second sintering can be selected to be 400-800°C, for example, 400°C, 450°C, 500°C, 550°C, 600°C, 620°C, 640°C, 660°C, 680°C, 700°C, 720°C, 750°C, 800°C or an interval formed by any two of the above values.

[0070] In one embodiment, the second sintering time can be selected to be 3 to 18 hours, such as 3 hours, 5 hours, 7 hours, 10 hours, 12 hours, 15 hours, 18 hours or an interval formed by any two of the above values.

[0071] In the process of preparing lithium iron manganese phosphate, the carbon source can be added in two steps as described above, or the carbon source can be added only in the process of preparing lithium iron manganese phosphate using the lithium iron manganese phosphate precursor, and no carbon source is added in the process of preparing the lithium iron manganese phosphate precursor.

[0072] In order to obtain lithium iron manganese phosphate single crystals, a centrifugal spray device can be selected for the second spray drying, and a gas crushing process needs to be added after the second calcination. The type of spray equipment used in the first spray drying is not limited, such as centrifugal spray equipment or two-fluid spray equipment. In order to obtain lithium iron manganese phosphate polycrystals, a two-fluid spray device can be selected for the second spray drying. The type of spray equipment used in the first spray drying is not limited, such as centrifugal spray equipment or two-fluid spray equipment.

[0073] In some embodiments, in the ternary positive electrode material, the molar content of nickel is in the range of 0.1-0.92 based on the total moles of metal elements other than lithium. For example, in the ternary positive electrode material, the molar content of nickel is in the range of 0.1-0.92 based on the total moles of metal elements other than lithium, such as 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.63, 0.65, 0.67, 0.70, 0.73, 0.75, 0.77, 0.80, 0.83, 0.85, 0.87, 0.90, 0.92 or the interval formed by any two of the above values. When the molar content of nickel in the ternary positive electrode material is above 0.6 based on the total moles of metal elements other than lithium, the ternary positive electrode material is a high-nickel material, which is beneficial for the battery to obtain a higher energy density.

[0074] In some embodiments, the chemical formula of the ternary cathode material is LiNi x Co y Mn (1-x-y) O2, where

[0075] x is 0.1 to 0.92, such as 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.63, 0.65, 0.67, 0.70, 0.73, 0.75, 0.77, 0.80, 0.83, 0.85, 0.87, 0.90, 0.92 or an interval formed by any two of the above values;

[0076] y is 0.05-0.35, such as 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.220, 0.240, 0.260, 0.280, 0.3, 0.32, 0.35 or an interval formed by any two of the above values.

[0077] When the molar content of manganese in the lithium manganese iron phosphate is ≥0.75 (such as 0.75, 0.77, 0.80, 0.83, 0.85, 0.87, 0.90, 0.92 or an interval formed by any two of the above values), based on the total molar number of metal elements other than lithium, the b is ≥10% (such as 10%, 15%, 20%, 25%, 30%, 35%, 40% or an interval formed by any two of the above values) to better balance the kinetic properties of the ternary positive electrode material itself and the wetting effect of the electrolyte on the positive electrode plate, so as to improve the fast charging performance and cycle performance of the battery.

[0078] When the molar content of manganese in the lithium manganese iron phosphate is ≥0.75 (such as 0.75, 0.77, 0.80, 0.83, 0.85, 0.87, 0.90, 0.92 or an interval formed by any two of the above values), based on the total molar number of metal elements other than lithium, the ternary positive electrode material is preferably polycrystalline to improve the wetting effect of the electrolyte on the positive electrode plate and enhance the fast charging performance and cycle performance.

[0079] The ternary positive electrode material may contain no doping element or may contain a doping element M. The present invention has no limitation on the type of the doping element M, for example, at least one of niobium, titanium, tantalum, tin, and lanthanide metal elements may be selected.

[0080] In the present invention, the preparation method of the ternary positive electrode material is not limited, and those skilled in the art can prepare the ternary positive electrode material according to conventional technical means. Exemplarily, the preparation method of the ternary positive electrode material includes the following steps:

[0081] The ternary cathode material precursor and the lithium source are mixed and sintered to obtain the ternary cathode material.

[0082] The ternary cathode material precursor contains Ni, Co and Mn in a target stoichiometric ratio. The ternary cathode material precursor is one or more of oxides, hydroxides and carbonates of Ni, Co and Mn. For example, the ternary cathode material precursor is hydroxide of Ni, Co and Mn.

[0083] The ternary cathode material precursor can be obtained by methods known in the art, such as coprecipitation, gelation or solid phase method. As an example, the preparation method of the ternary cathode material precursor includes the following steps:

[0084] Dispersing a Ni source, a Co source and a Mn source in a solvent to obtain a mixed solution;

[0085] The mixed solution, strong alkali solution and complexing agent solution are pumped into a stirred reactor at the same time, the pH value of the reaction solution is controlled to be 10-13, the temperature in the reactor is 25°C-90°C, and inert gas protection is passed during the reaction; after the reaction is completed, after aging, filtration, washing and vacuum drying, a hydroxide containing Ni, Co and Mn is obtained, that is, a ternary positive electrode material precursor is obtained.

[0086] In the process of preparing the ternary cathode material precursor, the Ni source used includes but is not limited to at least one of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate;

[0087] And / or, the Co source used includes but is not limited to at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate;

[0088] And / or, the Mn source used includes but is not limited to at least one of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate;

[0089] And / or, the alkali of the strong alkaline solution used includes at least one of sodium hydroxide and potassium hydroxide;

[0090] And / or, the complexing agent in the complexing agent solution used includes aqueous ammonia.

[0091] In the process of preparing the ternary positive electrode material precursor, the amounts of the Ni source, Co source and Mn source used can be selected to satisfy: Ni element molar amount: Co element molar amount: Mn element molar amount = (92-10): (5-35): (3-80). By adjusting the proportion of the Ni element molar amount in the Ni source to the total molar amount of the Ni element, Co element and Mn element in the Ni source, Co source and Mn source, the molar proportion of the nickel element in the ternary positive electrode material structure can be adjusted.

[0092] In the process of preparing the ternary positive electrode material, the Li source used includes but is not limited to at least one of lithium oxide (Li2O), lithium phosphate (Li3PO4), lithium dihydrogen phosphate (LiH2PO4), lithium acetate (CH3COOLi), lithium hydroxide (LiOH), lithium carbonate (Li2CO3), and lithium nitrate (LiNO3).

[0093] In the process of preparing the ternary positive electrode material, the amounts of the ternary positive electrode material precursor and the lithium source satisfy: molar amount of Li element: sum of molar amounts of Ni, Co and Mn elements = (0.99-1.09): (0.99-1.02).

[0094] The sintering atmosphere for mixed sintering can be an oxygen-containing atmosphere, such as an air atmosphere or an oxygen atmosphere, using a ball mill mixer or a high-speed mixer; in the process of preparing a ternary positive electrode material using a ternary positive electrode material precursor, the ternary positive electrode material precursor and the lithium source can be mixed using a ball mill mixer or a high-speed mixer; the sintering atmosphere is an oxygen-containing atmosphere, such as an air atmosphere or an oxygen atmosphere. In order to obtain a single crystal of a ternary positive electrode material, the sintering temperature is 850-1100°C, and a gas crushing process needs to be added after the sintering is completed. In order to obtain a polycrystalline ternary positive electrode material, the sintering temperature is 700-850°C.

[0095] In addition, when preparing the ternary positive electrode material, a certain amount of doping element source (if any) can be dispersed in a solvent together with the Ni source, Co source and Mn source as needed to prepare a ternary positive electrode material precursor, such as a niobium source, a titanium source, a tantalum source, a tin source, a lanthanide metal element source, etc., to obtain a ternary positive electrode material containing a certain amount of doping elements.

[0096] In addition, the ternary cathode material precursor may be subjected to a coating process, specifically, a coating material is coated on the surface of the cathode active material by dry coating (high temperature solid phase method), and the surface of the cathode active material is partially or completely coated with a coating layer formed by the coating material. The coating layer contains at least one element selected from the following (hereinafter referred to as "coating element"): aluminum (Al), titanium (Ti), tungsten (W), boron (B), phosphorus (P), cobalt (Co), yttrium (Y) or silicon (Si).

[0097] In some embodiments, the mass percentage of the positive electrode active material in the positive electrode active material layer is 94% to 97.5%, such as 94%, 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5% or an interval formed by any two of the above values.

[0098] The positive electrode active material layer further includes a conductive agent and a binder in addition to the positive electrode active material described above.

[0099] The conductive agent in the positive electrode active material layer is used to provide conductivity, and 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. Exemplarily, the conductive agent in the positive electrode active material layer includes, but is not limited to, at least one of carbon nanotubes, carbon black, graphite, carbon fiber, activated carbon, mesoporous carbon, and fullerenes, wherein the carbon fiber is, for example, carbon nanofiber, etc.; carbon black is, for example, SP (Super P, the same below), acetylene black, Ketjen black, etc.

[0100] In some embodiments, the mass percentage of the conductive agent in the positive electrode active 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.

[0101] The binder in the positive electrode active material layer 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 binder properties and does not significantly cause adverse chemical changes in the battery. Exemplarily, the binder in the positive electrode active material layer includes but is not limited to fluorinated polyolefin binders, and the fluorinated polyolefin binders include but are not limited to polyvinylidene fluoride (PVDF), vinylidene fluoride copolymers or their modified (e.g., carboxylic acid, acrylic acid, acrylonitrile, etc.) derivatives, etc.

[0102] In some embodiments, the mass percentage of the binder in the positive electrode active 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.

[0103] The present invention has no particular limitation on the positive electrode current collector as long as it has conductivity and does not cause adverse chemical changes in the battery, and can use, for example: aluminum, nickel, titanium, stainless steel, fired carbon; or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc.

[0104] The positive electrode sheet of the present invention can be prepared according to conventional methods in the art. For example, the positive electrode active material, the conductive agent and the binder are dispersed in a solvent to obtain a positive electrode slurry, and then the positive electrode slurry is coated on at least one side of the positive electrode current collector, and after drying, rolling, cutting and other processes, a positive electrode sheet is obtained. The solvent includes but is not limited to at least one of N-methylpyrrolidone (NMP) and deionized water.

[0105] Battery

[0106] The present invention also provides a battery, comprising the positive electrode sheet, the negative electrode sheet and the electrolyte.

[0107] The negative electrode sheet of the present invention comprises a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, and the negative active material layer contains a negative active material.

[0108] The present invention places no particular limitation on the negative active material. Exemplarily, the negative active material includes, but is not limited to, natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, SiO f (0 < f < 2, such as f = 1), silicon carbide, Li4Ti5O 12 and at least one of the following.

[0109] In some embodiments, the mass percentage content of the negative active material in the negative active material layer is 94% - 97.5%. For example, the content of the positive active material in the negative active material layer is 94%, 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5% or the range formed by any two of the above values.

[0110] The negative active material layer may further contain a conductive agent and / or a binder.

[0111] The conductive agent in the negative active material layer is used to provide conductivity, and any conductive agent can be used without particular limitation as long as it has suitable electron conductivity and does not significantly cause adverse chemical changes in the battery. Exemplarily, the conductive agent in the negative active material layer includes, but is not limited to, at least one of carbon nanotubes, carbon black, graphite, carbon fiber, activated carbon, mesoporous carbon, fullerenes, etc., wherein the carbon fiber is, for example, carbon nanofiber, etc.; the carbon black is, for example, SP, acetylene black, Ketjen black, etc.

[0112] In some embodiments, the mass percentage content of the conductive agent in the negative active material layer is 0.4% - 2%, such as 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2% or the range formed by any two of the above values.

[0113] The binder in the negative electrode active material 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 binder properties and does not significantly cause adverse chemical changes in the battery. Exemplarily, the binder in the negative electrode active material layer includes but is not limited to at least one of carboxymethyl cellulose (CMC), styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl butyral, and aqueous acrylic resin.

[0114] In some embodiments, the mass percentage of the binder in the negative electrode active 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.

[0115] The present invention has no particular limitation on the negative electrode current collector as long as it has conductivity and does not cause adverse chemical changes in the battery, and can use, for example: copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel surface-treated with at least one of carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy.

[0116] The electrolyte of the present invention can be selected from various electrolytes suitable for batteries in the art. The electrolyte includes an electrolyte and a solvent, and the electrolyte generally includes a lithium salt.

[0117] Exemplarily, the lithium salt includes, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP), and lithium tetrafluorooxalatophosphate (LiTFOP). The concentration of the electrolyte in the electrolyte can be selected to be 0.5 to 5 mol / L.

[0118] Exemplarily, the solvent includes, but is not limited to, at least one of ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), propylene carbonate (PC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), cyclopentane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE). The mass percentage of the solvent in the electrolyte can be selected to be 70% to 98%.

[0119] In addition, the electrolyte may further include additives. Exemplarily, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery high temperature performance, additives that improve battery overcharge performance, and additives that improve battery low temperature performance.

[0120] The battery may further include a diaphragm, which is located between the positive electrode sheet and the negative electrode sheet and is used to separate the positive electrode sheet and the negative electrode sheet to prevent the positive electrode sheet and the negative electrode sheet from short-circuiting. The diaphragm may be any isolation film material suitable for batteries in the art. Exemplarily, the diaphragm includes but is not limited to at least one of polypropylene and polyethylene.

[0121] Electrical devices

[0122] The present invention further provides an electric device, comprising the battery. The battery serves as a power supply for the electric device.

[0123] The electrical device refers to any device that can utilize electrical energy and convert it into mechanical energy, thermal energy, light energy or other energy forms, such as electric motors, electric heat engines, electric light sources, etc. Specifically, it may include but is not limited to mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Mobile devices may be mobile phones, laptops, drones, sweeping robots, electronic cigarettes, etc.; electric vehicles may be pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.

[0124] The present invention is further described below with specific examples. It should be noted that the sintering is carried out in an air atmosphere unless otherwise specified.

[0125] Example 1

[0126] This embodiment provides a lithium ion battery, and the specific preparation method is as follows:

[0127] (1) Preparation of positive electrode sheet

[0128] (1.1) Preparation of LMFP materials

[0129] According to LiMn f Fe 1-f PO4 (f value see Table 1) The molar ratio of each element Li, Mn, Fe, P in the chemical formula is added to a ball mill. Mn3O4, FePO4 and LiH2PO4 are added, and then glucose and polyethylene glycol are added. Then, water is used as a dispersant, and the raw materials are ground at a speed of 2000rpm for 12h, and the grinding is repeated three times. Then, the first spray drying is carried out at a pressure of 1MPa, and then sintered at 400℃ for 8h to obtain a lithium manganese iron phosphate precursor, wherein the ratio of glucose sucrose to polyvinyl alcohol is 1:3 (mass ratio), and the total amount of glucose sucrose and polyvinyl alcohol is 15wt.% of the total amount of Mn3O4, FePO4 and LiH2PO4.

[0130] The obtained LMFP precursor was mixed with glucose and polyethylene glycol, and water was used as a dispersant. The raw material was ground at a rotation speed of 4000 rpm for 18 hours, and the grinding was repeated three times. Then, a second spray drying was performed at a pressure of 1 MPa. The spray drying equipment used is shown in Table 1. Then, it was sintered for 10 hours, and the sintering temperature was shown in Table 1. After iron was removed by sieving, LMFP was obtained, in which sucrose: polyvinyl alcohol = 1:2 (mass ratio), and the total amount of glucose sucrose and polyvinyl alcohol was 20wt.% of the total amount of Mn3O4, FePO4 and LiH2PO4.

[0131] (1.2) Preparation of ternary cathode materials

[0132] According to LiNi x Co y Mn (1-x-y) The molar ratio of each element Ni, Co, and Mn in the chemical formula of O2 is respectively weighed nickel sulfate, cobalt sulfate, and manganese sulfate (the values ​​of x and y are shown in Table 1), dispersed in water to obtain a mixed solution;

[0133] The obtained mixed solution was transported to a reactor, and oxygen was introduced as a protective gas, an aqueous NaOH solution was added as a precipitant, and aqueous ammonia was added as a complexing agent. The aqueous ammonia concentration and the amount of the solution were adjusted to control the pH of the solution (i.e., the precursor reaction pH, see Table 1 for details). The temperature in the reactor was 50° C., and the reaction was carried out for 5 hours. The product was filtered and dried to obtain a ternary cathode material precursor.

[0134] The obtained ternary cathode material precursor and LiOH were mixed and sintered for 8 hours. The sintering temperature was shown in Table 1 to obtain a primary sintered material, wherein the amounts of the ternary cathode material precursor and LiOH satisfied: molar amount of Li element: sum of molar amounts of Ni, Co and Mn elements = 1.05:1.

[0135] (1.3) Preparation of positive electrode sheet

[0136] The above-mentioned lithium manganese iron phosphate and ternary positive electrode material are mixed in the ratio in Table 1 as positive electrode active material, and the positive electrode active material is mixed with binder PVDF, conductive agent SP and conductive agent carbon nanotube in a mass ratio of 97:1:1.7:0.3, dispersed in NMP to obtain positive electrode slurry, and the positive electrode slurry is coated on both sides of aluminum foil, and then rolled and cut to obtain positive electrode sheets.

[0137] (2) Preparation of negative electrode sheet

[0138] The negative electrode active material artificial graphite is mixed with the conductive agent SP and the binder CMC in a mass ratio of 96.4:1:2.6, dispersed in deionized water to obtain a negative electrode slurry, and the negative electrode slurry is coated on both sides of the copper foil, and then dried, rolled and cut to obtain a negative electrode sheet.

[0139] (3) Preparation of electrolyte

[0140] Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain a mixed organic solvent, and then dry lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a LiPF6 concentration of 1 mol / L.

[0141] (4) Preparation of isolation membrane

[0142] Polyethylene (PE) diaphragm is used.

[0143] (5) Assembly and formation

[0144] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive and negative electrode sheets to play an isolating role, and then wound to obtain a bare cell; the bare cell is placed in an outer packaging shell, and after drying, the electrolyte is injected, and after vacuum packaging, standing, forming, shaping and other processes, a lithium-ion battery is obtained.

[0145] These embodiments and comparative examples all provide a lithium ion battery, and the preparation method is similar to that of embodiment 1, except that:

[0146] (a) In step (1.1), the value of f, the equipment used for the second spray drying, and whether gas crushing is performed after sintering are shown in Table 1 (if gas crushing is not specified, it means that gas crushing is not performed);

[0147] (b) In step (1.2), the values ​​of x and y and the sintering temperature are shown in Table 1;

[0148] (c) In step (1.3), the ratio of lithium iron manganese phosphate to the ternary positive electrode material is adjusted, and the weight ratio of SP in the total weight of the positive electrode active material, PVDF, SP and carbon nanotubes is adjusted, and the weight ratio of the positive electrode active material in the total weight of the positive electrode active material, PVDF, SP and carbon nanotubes is adjusted accordingly. The specific weight ratio of the ternary positive electrode material in the positive electrode active material and the weight ratio of SP in the positive electrode active material layer are shown in Table 1.

[0149] Table 1

[0150]

[0151]

[0152] The following method was used to detect the content a of Ni in the positive electrode active material layer and the longitudinal wettability b of the positive electrode sheet in each embodiment and comparative example. The test results are shown in Table 2:

[0153] Content of Ni element in the positive electrode active material layer a: disassemble the lithium-ion battery to obtain the positive electrode plate, soak the positive electrode plate in DMC (dimethyl carbonate) at room temperature for 60 minutes, take it out, and dry it at room temperature with humidity ≤15%; scrape the positive electrode active material layer on the surface of the current collector, calcine at 400°C for 3 hours to remove the binder, and then tap the plate to obtain the positive electrode active material powder; accurately weigh 0.5g of the positive electrode active material powder, disperse it in 20mL of water, and then add 10mL of nitric acid (HNO3 content is about 37wt.%), heat it after dispersion until the positive electrode active material powder is completely dissolved, and dilute it to 100mL with water to obtain a solution to be tested; perform ICP test on the solution to be tested, and test Before the test, a standard solution must be prepared. The standard solution with a Ni concentration of 1000 mg / L is diluted with deionized water to different concentrations (0, 1 mg / 100 mL, 2 mg / 100 mL, and 3 mg / 100 mL, respectively). The relationship between the Ni concentration and the peak area of ​​the standard product is tested and calculated. The linear correlation coefficient of the relationship is above 0.999 and can be used as a normal standard product. Then, the Ni content in the positive electrode active material layer is calculated based on the relationship and the corresponding peak area of ​​the sample to be tested. The working conditions of the ICP instrument are set as follows: gas flow rate 0.5 L / min, power 1150 W, element test Ni is selected, and the wavelength is 231.604 nm;

[0154] Longitudinal wettability b of the positive electrode sheet: Take the empty positive electrode sheet, soak it in dimethyl carbonate for 2h, dry it at 80℃, cut it into a size of 1.5*1.5cm after drying, weigh the mass M0 (unit g) of the electrode sheet, and then hot-press it together with a polymer film (PET-based-EVA hot melt adhesive composite film) containing a circular hole with a radius r=0.5cm. The surface of the positive electrode sheet is covered with a polymer film, and the above circular hole is located at the center of the polymer film. It is placed flat on a horizontal table, and the pre-prepared electrolyte (the solvent is EC and EMC, the mass ratio of the two is EC:EMC=3:7, containing 1mol / L lithium salt, and the lithium salt is lithium hexafluorophosphate) is dripped into the circular hole of the polymer film on the surface of the electrode sheet at a dripping speed of 0.5mL / min. The amount of electrolyte dripped is 2mL. After the electrolyte diffuses for 2min, the mass M1 (unit g) of the electrode sheet is measured at this time. The longitudinal wettability (b) of the positive electrode sheet is calculated according to the following formula:

[0155] b = (M1 - M0) / M0 x 100%.

[0156] The performance test was performed on the positive electrode sheets or lithium-ion batteries obtained in each embodiment and comparative example. The test results are shown in Table 2. The specific test method is as follows:

[0157] Fast charging test method: The above-mentioned positive electrode plate and metallic lithium are combined into a half-battery, and the electrolyte used is the same as that in Example 1. At 25°C, 0.33C constant current charging is performed to an upper limit voltage of 4.25V, and then constant voltage charging is performed until the current is less than or equal to 0.05C; then 0.33C discharge is performed to 2.5V, and this is regarded as a cycle. After two cycles of charging and discharging, the discharge capacity of the second cycle is used as the capacity of the battery; then a double charge test is performed, with a double charge rate of 1C / 2C / 6C, and a discharge rate, charging cutoff condition, and discharge cutoff condition are the same as above. The constant current ratio under the 2C double charge test is used to evaluate the fast charging performance, 2C constant current ratio = 2C constant current charging capacity / 2C total charging capacity × 100%, the higher the constant current ratio, the better the fast charging performance;

[0158] High temperature cycle performance test: After the battery is formed and fixed to capacity, it is allowed to stand for 2 hours at a high temperature of 45°C, then discharged at 0.33C to 2.5V, allowed to stand for 10 minutes, and then charged at 1C constant current to 4.25V. The charging cutoff current at 4.25V constant voltage is 0.05C. It is allowed to stand for 10 minutes, and then discharged at 1C to 2.5V. The first cycle 1C discharge capacity is used as the initial first cycle discharge capacity, and the ratio of the discharge capacity after 500 cycles of 1C charge and discharge to the initial first cycle discharge capacity is used as the discharge capacity retention rate of the battery at high temperature. The cutoff conditions of the 1C charge and discharge cycle are the same as above, charging to the upper limit voltage of 4.25V, and discharging to 2.5V with a cutoff current less than or equal to 0.05C.

[0159] Table 2

[0160]

[0161] For the batteries prepared in various embodiments of the present invention, the 2C constant current ratio is ≥66%, and the capacity retention rate after 500 cycles at 45°C 1C is ≥66.5%. It can be seen that the battery containing the positive electrode plate of the present invention has excellent fast charging performance and high temperature cycle performance.

[0162] It can be seen from the comparison between Examples 1 to 5 and Examples 6 to 10, and between Examples 11 to 12 and Example 13 that when the mass percentage of the Ni element in the positive electrode active material layer and the longitudinal wettability of the positive electrode sheet meet the preferred range described in the present invention, the fast charging performance and high temperature cycle performance of the battery are relatively better.

[0163] It can be seen from the comparison between Examples 1 to 5 and Examples 11 to 12 that when the positive electrode sheet satisfies 0.31≤a / b≤3.9, the fast charging performance and high temperature cycle performance of the battery are relatively better.

[0164] According to Comparative Examples 1 to 2, even if the mass percentage of the Ni element in the positive electrode active material layer and the longitudinal wettability of the positive electrode sheet are in the appropriate range, when the a / b value exceeds the range of 0.14 to 5.82, the fast charging performance and high temperature cycle performance of the battery are relatively poor.

[0165] From Example 4 and Examples 16 to 17, it can be seen that when the molar content of manganese element in lithium manganese iron phosphate, calculated on the total molar number of metal elements other than lithium, is ≥0.75, b ≥10% will make the fast charging performance and high temperature cycle performance of the battery relatively better.

[0166] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of this article rather than to limit the scope of protection of this article. Although the present application is described in detail with reference to the preferred embodiments, ordinary technicians in this field should understand that the technical solution of this article can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of this article.

Claims

1. A positive electrode sheet, characterized in that: The invention comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material, wherein the positive electrode active material comprises lithium manganese iron phosphate and a ternary positive electrode material, and the positive electrode plate satisfies: 0.09≤a / b≤5.1, Wherein, a is the mass percentage of Ni element in the positive electrode active material layer, in %; b is the longitudinal wettability of the positive electrode sheet, in %.

2. The positive electrode sheet according to claim 1, characterized in that: The positive electrode plate satisfies: 0.17≤a / b≤2.

4.

3. The positive electrode sheet according to claim 1, characterized in that: The range of a is 0.9% to 47%.

4. The positive electrode sheet according to claim 3, characterized in that: The range of a is 2% to 42%.

5. The positive electrode sheet according to claim 1, characterized in that: The range of b is 5% to 40%.

6. The positive electrode sheet according to claim 5, characterized in that: The range of b is 10% to 35%.

7. The positive electrode sheet according to claim 1, characterized in that: In the lithium manganese iron phosphate, the molar content of manganese element is in the range of 0.6-0.8, calculated based on the total molar number of metal elements other than lithium; in the ternary positive electrode material, the molar content of nickel element is in the range of 0.1-0.92, calculated based on the total molar number of metal elements other than lithium.

8. The positive electrode sheet according to claim 7, characterized in that: In the lithium manganese iron phosphate, when the molar content of manganese element is ≥0.75 based on the total molar number of metal elements except lithium, b is ≥10%.

9. The positive electrode sheet according to claim 7 or 8, characterized in that: In the lithium manganese iron phosphate, when the molar content of manganese element is ≥0.75 based on the total molar number of metal elements except lithium, the ternary positive electrode material is polycrystalline.

10. A battery, characterized in that: It comprises the positive electrode sheet as claimed in any one of claims 1 to 9.

11. An electrical device, characterized in that: Comprising the battery as claimed in claim 10.

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