Ternary positive electrode material, preparation method thereof and electrochemical device

Abstract

The application discloses a ternary positive electrode material, a preparation method thereof and an electrochemical device. The ternary positive electrode material is a polycrystal or a single-crystal-like layered structure, and has a chemical general formula of LiNi x Co y Mn 1‑x‑ y M a N b O2, wherein 0.3<=x<=1, 0<=y<=0.35, 0.001<=a<=0.03, and 0.001<=b<=0.05; and a Warburg impedance coefficient of the ternary positive electrode material is sigma, and sigma<=0.8 Omega.s ‑1 / 2 The ternary positive electrode material has a low initial impedance, small anisotropy difference of ion diffusion in a bulk phase and an interface, low initial impedance and diffusion resistance, and can reduce storage and cycle polarization of the whole material in a high-temperature storage environment, thereby significantly reducing the increase of the bulk phase and interface impedance of the ternary positive electrode material after high-temperature storage, improving the retention rate and recovery rate of the overall capacity, and achieving the electrochemical device which has good cycle stability and rate capability and can significantly improve the high-temperature storage performance of the electrochemical device.

Description

Technical Field

[0001] This application relates to the field of electrochemistry, and in particular to a ternary cathode material and its preparation method, as well as an electrochemical device. Background Technology

[0002] In recent years, ternary cathode materials have been widely used and developed in new energy pure electric passenger vehicles and energy storage batteries due to their comprehensive advantages such as high energy density, excellent rate performance, long cycle life, low environmental pollution, and no memory effect. However, ternary cathode materials still have significant disadvantages in storage performance under high temperature and high humidity environments.

[0003] To address this issue, related technologies focus on solutions such as material modification, process optimization, and structural design. However, the specific issues affecting storage performance are not detailed or clearly defined, and there is a lack of corresponding technical research and methods for improving high-temperature storage performance through material impedance modulation. Summary of the Invention

[0004] In view of this, this application focuses on the problem of storage performance deterioration caused by the increase of material impedance (ohmic polarization), and improves the high-temperature storage performance of the material by controlling the impedance of the ternary cathode material, and provides a ternary cathode material, its preparation method and electrochemical device.

[0005] It should be noted that the invention description in this application uses lithium-ion batteries as an example of electrochemical devices to explain this application, but the electrochemical devices in this application are not limited to lithium-ion batteries.

[0006] The first aspect of this application provides a ternary cathode material, which has a polycrystalline or near-single-crystalline layered structure and its general chemical formula is LiNi. x Co y Mn 1-x-y M a N b O2, where 0.3≤x≤1, 0≤y≤0.35, 0.001≤a≤0.03, 0.001≤b≤0.05; the Warburg impedance coefficient of the ternary cathode material is σ, σ≤0.8Ω·s -1 / 2 .

[0007] Based on the first aspect, in some possible implementations, element M includes magnesium and / or aluminum.

[0008] Based on the first aspect, in some possible implementations, the N element includes at least one selected from zirconium, aluminum, titanium, yttrium, silicon, strontium, niobium, magnesium, tungsten, zinc, phosphorus, fluorine, molybdenum, cerium, and tantalum.

[0009] The second aspect of this application provides a method for preparing a ternary cathode material, comprising: co-precipitating a nickel source, a cobalt source, a manganese source, an alkaline precipitant, and a salt solution containing element M to obtain a nickel-cobalt-manganese compound precursor; mixing the nickel-cobalt-manganese compound precursor, a lithium source, and a dopant to obtain a mixture; sintering the mixture once to obtain a first-sintered material; and sintering the first-sintered material a second time to obtain the ternary cathode material.

[0010] Based on the second aspect, in some possible embodiments, the salt solution containing element M is selected from at least one of aluminum sulfate, aluminum nitrate, aluminum hydroxide, magnesium sulfate, magnesium nitrate, and magnesium carbonate; the dopant is selected from at least one of zirconium oxide, aluminum oxide, titanium oxide, yttrium oxide, silicon oxide, strontium oxide, niobium oxide, magnesium oxide, tungsten oxide, zinc oxide, lithium phosphate, lithium fluoride, molybdenum oxide, cerium oxide, and tantalum oxide.

[0011] Based on the second aspect, in some possible implementations, the molar ratio of lithium ions in the lithium source to the total amount of metal ions in the nickel-cobalt-manganese compound precursor is (0.95-1.2):1.

[0012] Based on the second aspect, in some possible implementations, the mass content of the dopant is 0.1% to 2% based on the total mass of the nickel-cobalt-manganese compound precursor.

[0013] Based on the second aspect, in some possible implementations, the temperature of a single sintering is 650°C to 850°C, and the time of a single sintering is 2 hours to 10 hours.

[0014] Based on the second aspect, in some possible implementations, the secondary sintering temperature is 800°C to 1100°C, and the secondary sintering time is 10h to 18h.

[0015] Based on the second aspect, in some possible implementations, the ratio of the total molar amount of nickel ions in the nickel source, cobalt ions in the cobalt source, and manganese ions in the manganese source to the molar amount of hydroxide ions in the alkaline precipitant is 1:(1.6-2.5).

[0016] Based on the second aspect, in some possible implementations, the mass content of element M is 0.1% to 1.5% based on the total mass of the nickel-cobalt-manganese compound precursor.

[0017] Based on the second aspect, in some possible implementations, during the co-precipitation reaction, a salt solution containing element M is added dropwise at a dropping rate of 1 L / h to 2 L / h, wherein element M in the nickel-cobalt-manganese compound precursor exhibits a gradient distribution and satisfies the relationship: C M ≥C0+k(r-r0); where the nickel-cobalt-manganese compound precursor is spherical, C Mdenoted as M, where r is the concentration of element M at a distance r from the core of the nickel-cobalt-manganese compound precursor; C0 is the concentration of element M at a distance r0 from the core of the nickel-cobalt-manganese compound precursor, ranging from 0.1 mol% to 2 mol%; k ​​is a concentration constant of 0.001 mol%·µm. -1 Up to 0.1 mol%·µm -1 r is the radius of the nickel-cobalt-manganese compound precursor and is 0µm < r ≤ 12µm; r0 is 0.5µm to 12µm. For ease of understanding, it is hereby added that: the above "r0" is the distance from the core of the nickel-cobalt-manganese compound precursor at the initial position of the M element doping.

[0018] The third aspect of this application provides an electrochemical device, which includes a positive electrode sheet, the positive electrode sheet including a positive electrode material, the positive electrode material being the ternary positive electrode material provided in the first aspect of this application or the ternary positive electrode material prepared by the preparation method provided in the second aspect of this application.

[0019] A fourth aspect of this application provides an electronic device that includes the electrochemical device provided in the third aspect of this application.

[0020] The polycrystalline or near-monocrystalline layered ternary cathode material provided in this application has a Warburg impedance coefficient σ that meets a specific range. This results in small anisotropy differences in bulk and interfacial ion diffusion, low initial impedance and diffusion resistance, and can reduce the overall storage and cycling polarization of the material in high-temperature storage environments. This significantly reduces the growth of bulk and interfacial impedance of the ternary cathode material after high-temperature storage, and improves the overall capacity retention and recovery rate. In this way, the electrochemical device can maintain good cycling stability and rate performance while significantly improving the high-temperature storage performance of the electrochemical device. Detailed Implementation

[0021] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0022] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of electrochemical devices to explain this application, but the electrochemical devices of this application are not limited to lithium-ion batteries.

[0023] The first aspect of this application provides a ternary cathode material, which has a polycrystalline or near-single-crystalline layered structure and its general chemical formula is LiNi. x Co y Mn 1-x-y M a N bO2, where 0.3≤x≤1, 0≤y≤0.35, 0.001≤a≤0.03, 0.001≤b≤0.05; the Warburg impedance coefficient of the ternary cathode material is σ, σ≤0.8Ω·s -1 / 2 More preferably, σ≤0.3Ω·s -1 / 2 For example, the Warburg impedance coefficient of ternary cathode materials can be 0.2 Ω·s. -1 / 2 0.25Ω·s -1 / 2 0.3Ω·s -1 / 2 0.35Ω·s -1 / 2 0.4Ω·s -1 / 2 0.45Ω·s -1 / 2 0.5Ω·s -1 / 2 0.55Ω·s -1 / 2 0.6Ω·s -1 / 2 0.65Ω·s -1 / 2 0.7Ω·s -1 / 2 0.75Ω·s -1 / 2 0.8Ω·s -1 / 2 Or it can be a range consisting of any two of these values. The polycrystalline or near-monocrystalline layered ternary cathode material provided in this application has a Warburg impedance coefficient that meets the above-mentioned range. This results in small anisotropy differences in bulk and interfacial ion diffusion, low initial impedance and diffusion resistance, and can reduce the overall storage and cycling polarization of the material in high-temperature storage environments. This significantly reduces the growth of bulk and interfacial impedance of the ternary cathode material after high-temperature storage, and improves the overall capacity retention and recovery rate. In this way, the electrochemical device can maintain good cycle stability and rate performance while significantly improving the high-temperature storage performance of the electrochemical device.

[0024] In the above, x represents the molar content of nickel in the ternary cathode material, y represents the molar content of cobalt in the ternary cathode material, a represents the molar mass of dopant element M in the ternary cathode material, and b represents the molar mass of element N in the ternary cathode material. 0.3 ≤ x ≤ 1, for example, x can be 0.3, 0.35, 0.45, 0.65, 0.9, 1, or any range of two values. 0 ≤ y ≤ 0.35, for example, y can be 0, 0.05, 0.15, 0.25, 0.30, 0.35, or any range of two values. 0.001 ≤ a ≤ 0.03, for example, a can be 0.001, 0.005, 0.01, 0.015, 0.025, 0.03, or any range of two values. 0.001≤b≤0.05, for example, b can be 0.001, 0.005, 0.01, 0.015, 0.025, 0.03, 0.045, 0.04, 0.045, 0.05 or a range of any two of these values.

[0025] In one embodiment of this application, the aforementioned low-valence state (≤+3) element M includes magnesium and / or aluminum. The element N includes at least one selected from zirconium, aluminum, titanium, yttrium, silicon, strontium, niobium, magnesium, tungsten, zinc, phosphorus, fluorine, molybdenum, cerium, and tantalum. More preferably, the element N includes at least one selected from zirconium, aluminum, titanium, phosphorus, yttrium, and silicon. Doping the ternary cathode material with the aforementioned elements M and N improves the overall structural stability of the material, reduces impedance growth during storage or cycling, and thus enhances the high-temperature cycling and storage performance of the electrochemical device.

[0026] A second aspect of this application provides a method for preparing the above-mentioned ternary cathode material, comprising: Step S1: Add nickel source, cobalt source, manganese source and alkaline precipitant to the reactor for coprecipitation reaction. During the coprecipitation reaction, add salt solution containing element M stepwise at a dropping rate of 1L / h to 2L / h to obtain nickel cobalt manganese compound precursor.

[0027] In one embodiment of this application, the nickel-cobalt-manganese compound precursor can be nickel-cobalt-manganese oxide or nickel-cobalt-manganese hydroxide, and can be synthesized using conventional methods in the prior art, such as solid-phase method, co-precipitation method, sol-gel method, hydrothermal method, etc. In this application, the nickel-manganese compound precursor is preferably prepared by co-precipitation method, specifically including: adding a precipitant to a mixed solution of metal ions containing nickel source, cobalt source and manganese source, reacting under stirring, and the resulting precipitate product is the nickel-manganese compound precursor. Based on conventional co-precipitation processes, this application achieves stepwise addition of the M-element salt solution in a continuous reactor by controlling the feed flow rate through a program. The initial addition is at a rate of 0.1 mol% to 0.5 mol% of the M-element salt solution's molar concentration. Subsequently, for every 1 µm increase in the nickel-manganese compound precursor particle size, the M-element salt solution's molar concentration is increased by 0.01 mol% to 0.05 mol%, with a dropping rate of 1 L / h to 2 L / h. This ensures that the M-element in the prepared nickel-cobalt-manganese compound precursor exhibits a gradient distribution satisfying the relationship: C M ≥C0+k(r-r0); where the nickel-cobalt-manganese compound precursor is spherical, C M denoted as M, where r is the concentration of element M at a distance r from the core of the nickel-cobalt-manganese compound precursor; C0 is the concentration of element M at a distance r0 from the core of the nickel-cobalt-manganese compound precursor, ranging from 0.1 mol% to 2 mol%; k ​​is a concentration constant of 0.001 mol%·µm. -1 Up to 0.1 mol%·µm -1 r is the radius of the nickel-cobalt-manganese compound precursor and is 0µm < r ≤ 12µm; r0 is 0.5µm to 12µm.

[0028] In one embodiment of this application, the specific parameters of the co-precipitation process are set as follows: the stirring speed is 20Hz to 38Hz, for example, the stirring speed can be 20Hz, 22Hz, 24Hz, 26Hz, 28Hz, 30Hz, 32Hz, 34Hz, 36Hz, 38Hz, or any range of two of these values. The reaction temperature is 40℃ to 70℃, for example, the reaction temperature can be 40℃, 42℃, 44℃, 46℃, 48℃, 50℃, 52℃, 54℃, 56℃, 58℃, 60℃, 62℃, 64℃, 66℃, 68℃, 60℃, 62℃, 64℃, 66℃, 68℃, 70℃, or any range of two of these values. The pH of the solution is controlled to be between 9 and 11 by adjusting the amount of alkaline precipitant (e.g., sodium hydroxide, at a concentration of 2 mol / L to 8 mol / L). For example, the pH of the solution can be 9, 9.2, 9.5, 9.7, 10, 10.2, 10.5, 10.7, 11, or any combination of two of these values. An inert gas (e.g., nitrogen) is introduced to ensure that the oxygen content in the reactor is less than or equal to 110 ppm. For example, the oxygen content can be 110 ppm, 100 ppm, 80 ppm, 60 ppm, 50 ppm, 30 ppm, or any combination of two of these values. A complexing agent (e.g., ammonia, at a concentration of 1 mol / L to 4 mol / L) is added to match the release of gradient ions.

[0029] In one embodiment of this application, the salt solution containing element M is selected from at least one of aluminum sulfate, aluminum nitrate, aluminum hydroxide, magnesium sulfate, magnesium nitrate, and magnesium carbonate; based on the total mass of the nickel-cobalt-manganese compound precursor, the mass content of element M is 0.1% to 1.5%, preferably 0.1% to 1.5%. For example, the mass content of the salt solution containing element M can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, or a range consisting of any two of these values.

[0030] This application introduces a salt solution containing element M within the aforementioned range of types and mass content in step S1. The introduced gradient doping element M causes the lattice parameter a (interlayer metal-metal spacing) of the material to decrease from the inside to the outside, while the c-axis (interlayer spacing) increases. Therefore, it shortens the horizontal diffusion distance of lithium ions in the core region of the material and widens the vertical diffusion channel in the outer shell region. This effectively reduces the lithium ion diffusion barrier in the bulk phase and interface of the material, making the diffusion anisotropy and anisotropic strain of the material interface and bulk phase smaller. In other words, it significantly improves the diffusion kinetics of lithium ions inside the material, reduces the polarization, charge transfer resistance (Rct), and interface impedance growth after high-temperature storage of the ternary cathode material, and reduces lattice shrinkage, lattice stress concentration, and microcrack generation during the charging and discharging process. This helps to reduce the internal resistance and polarization of the material, reduce the growth of storage impedance and cycling impedance, and make its structure more stable. In this way, the electrochemical device can maintain good cycling stability and rate performance while significantly improving the high-temperature storage performance of the electrochemical device.

[0031] In one embodiment of this application, the ratio of the total molar amount of nickel ions in the nickel source, cobalt ions in the cobalt source, and manganese ions in the manganese source to the molar amount of hydroxide ions in the alkaline precipitant is 1:(1.6-2.5). Taking 1 mol of the total content of nickel ions in the nickel source, cobalt ions in the cobalt source, and manganese ions in the manganese source as 1 mol, the molar amount of hydroxide ions in the alkaline precipitant is 1.6 mol to 2.5 mol. For example, the molar amount of hydroxide ions can be 1.6 mol, 1.7 mol, 1.8 mol, 1.9 mol, 2 mol, 2.1 mol, 2.2 mol, 2.3 mol, 2.4 mol, 2.5 mol, or a range consisting of any two of these values.

[0032] In one embodiment of this application, the specific type of nickel source added in step S1 is not particularly limited here. For example, it may be selected from at least one of nickel hydroxide, nickel sulfate, nickel carbonate, nickel acetate, nickel nitrate and nickel chloride.

[0033] In one embodiment of this application, the specific type of cobalt source added in step S1 is not particularly limited here. For example, it may be selected from at least one of cobalt hydroxide, cobalt sulfate, cobalt carbonate and cobalt chloride.

[0034] In one embodiment of this application, the specific type of manganese source added in step S1 is not particularly limited here. For example, it may be selected from at least one of manganese hydroxide, manganese sulfate, manganese carbonate, manganese acetate, manganese nitrate, and manganese chloride.

[0035] In one embodiment of this application, an alkaline precipitant is added in step S1 to provide OH. -A nickel-cobalt-manganese compound precursor is obtained by co-precipitation reaction with cobalt ions from a cobalt source, manganese ions from a manganese source, and nickel ions from a nickel source. The specific type of precursor is not particularly limited herein, but may be selected from at least one of ammonia, ammonium bicarbonate, ammonium carbonate, sodium carbonate, and sodium hydroxide.

[0036] Step S2 involves mixing the nickel-cobalt-manganese compound precursor, lithium source, and dopant to obtain a mixture.

[0037] In one embodiment of this application, the dopant is selected from at least one of zirconium oxide, aluminum oxide, titanium oxide, yttrium oxide, silicon oxide, strontium oxide, niobium oxide, magnesium oxide, tungsten oxide, zinc oxide, lithium phosphate, lithium fluoride, molybdenum oxide, cerium oxide, and tantalum oxide. More preferably, the additive N is selected from at least one of zirconium oxide, aluminum oxide, titanium oxide, lithium phosphate, yttrium oxide, and silicon oxide. Based on the total mass of the nickel-cobalt-manganese compound precursor, the mass content of the dopant is 0.1% to 2%, preferably 0.3% to 2%. For example, the mass content of the dopant can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, or a range consisting of any two of these values.

[0038] By adding dopants of the above-mentioned types and mass content ranges in step S2, this application can improve the structural and interfacial stability of ternary cathode materials as well as the diffusion kinetics performance inside the materials. At the same time, it reduces phase transition, oxygen release, dissolution of transition metals (Ni / Co / Mn) and formation of rock salt phase under high temperature environment, further reducing the internal resistance and polarization of the materials, which is beneficial to improving the high temperature storage performance and high temperature cycling stability of electrochemical devices.

[0039] In one embodiment of this application, the specific type of lithium source added in step S2 is not particularly limited here. For example, it can be selected from at least one of lithium carbonate, lithium nitrate, lithium hydroxide, lithium acetate, lithium acetate, and lithium oxalate. The molar ratio of lithium ions in the lithium source to the total amount of metal ions in the nickel-cobalt-manganese compound precursor is (0.95-1.2):1. Taking 1 mol of total metal ion content in the nickel-cobalt-manganese compound precursor as a unit, the molar amount of lithium ions in the lithium source is 0.95 mol to 1.2 mol. For example, the molar amount of lithium ions in the lithium source can be 0.95 mol, 0.97 mol, 0.99 mol, 1 mol, 1.02 mol, 1.04 mol, 1.06 mol, 1.08 mol, 1.1 mol, 1.12 mol, 1.14 mol, 1.16 mol, 1.18 mol, 1.2 mol, or a range consisting of any two of these values. The researchers in this application discovered that when the aforementioned molar ratio is too small, for example, below the lower limit of this application, it leads to an excessive number of Li vacancies in the lattice of the prepared ternary cathode material, making the layered structure of the ternary cathode material prone to collapse. When the aforementioned molar ratio is too large, for example, above the upper limit of this application, it easily forms a LiO2-like impurity phase, destroying the layered structure, increasing the diffusion resistance of the material, increasing the free lithium on the material surface, and thus reducing the structural stability of the material during cycling and the storage performance of the material. Therefore, this application achieves this by controlling the molar ratio of lithium ions in the lithium source to the total amount of metal ions in the nickel-cobalt-manganese compound precursor to meet the above-mentioned range, enabling the ternary cathode material to have excellent capacity, rate capability, and cycling isoelectric properties, while also exhibiting low impedance and excellent storage performance.

[0040] In one embodiment of this application, the purpose of the mixing process in step S2 is to uniformly mix the nickel-cobalt-manganese compound precursor, lithium source, and dopant. Specifically, this application employs ball milling and / or high-speed mixing, more preferably high-speed mixing, which is more conducive to improving mixing efficiency and uniformity.

[0041] Specifically, the rotational speed of the ball milling mixing process is from 100 rpm to 500 rpm. For example, the rotational speed can be 100 rpm, 120 rpm, 140 rpm, 160 rpm, 180 rpm, 200 rpm, 220 rpm, 240 rpm, 260 rpm, 280 rpm, 300 rpm, 320 rpm, 340 rpm, 360 rpm, 380 rpm, 400 rpm, 420 rpm, 440 rpm, 460 rpm, 480 rpm, 500 rpm, or any range of two such values. The ball milling mixing process time is from 1 hour to 6 hours. For example, the time can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or any range of two such values.

[0042] Specifically, the high-speed mixing process mentioned above includes at least a first mixing stage and a second mixing stage performed sequentially, and the rotation speed of the first mixing stage is lower than that of the second mixing stage. This has the advantages of high mixing efficiency and good mixing uniformity. The reason is that segmented mixing is conducive to improving the dispersibility of additives and their binding force on the precursor, thereby improving the mixing uniformity. At the same time, compared with ball milling, it greatly shortens the mixing time and improves the mixing efficiency.

[0043] The rotational speed of the first mixing stage is between 100 rpm and 300 rpm. For example, the rotational speed can be 100 rpm, 120 rpm, 140 rpm, 160 rpm, 180 rpm, 200 rpm, 220 rpm, 240 rpm, 260 rpm, 280 rpm, 300 rpm, or any range of two such values. The duration of the first mixing stage is between 3 min and 10 min. For example, the duration can be 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, or any range of two such values. The rotational speed of the second mixing stage is from 500 rpm to 900 rpm. For example, the rotational speed can be 500 rpm, 520 rpm, 540 rpm, 560 rpm, 580 rpm, 600 rpm, 620 rpm, 640 rpm, 660 rpm, 680 rpm, 700 rpm, 720 rpm, 740 rpm, 760 rpm, 780 rpm, 800 rpm, 820 rpm, 840 rpm, 860 rpm, 880 rpm, 900 rpm, or a range of any two of these values. The duration of the second mixing stage is from 15 min to 35 min. For example, the duration can be 15 min, 17 min, 19 min, 20 min, 22 min, 24 min, 26 min, 28 min, 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, or a range of any two of these values.

[0044] Step S3: In an oxygen-containing atmosphere (e.g., using air, pure oxygen, or a mixture of oxygen and inert gases such as argon), the mixture is sintered once to obtain a sintered material.

[0045] In one embodiment of this application, the sintering temperature is 650°C to 850°C, the sintering time is 2 hours to 10 hours, and the heating rate is less than or equal to 5°C / min. For example, the sintering temperature can be 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, 720°C, 740°C, 760°C, 780°C, 800°C, 810°C, 820°C, 830°C, 840°C, 850°C, or a range of any two of these values. For example, the sintering time can be 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, or a range of any two of these values. For example, the sintering rate can be 1°C / min, 2°C / min, 2.5°C / min, 3°C / min, 4°C / min, 5°C / min, or a range of any two of these values. This application controls the temperature and time of the first sintering to meet the above-mentioned range. Its main purpose is to pre-treat the mixture of lithium source and nickel cobalt manganese compound precursor. Through slow reaction, impurity removal and structural pre-forming, crystal defects are avoided during the material sintering process, structural stress is reduced, and the foundation is laid for the formation of a complete and stable ternary cathode material layered structure in the subsequent second sintering, thereby ensuring the comprehensive improvement of the performance of the ternary cathode material.

[0046] Step S4: In an oxygen-containing atmosphere (e.g., using air, pure oxygen, or a mixture of oxygen and inert gases such as argon), the material that was sintered once is sintered a second time to obtain the ternary cathode material.

[0047] In one embodiment of this application, the secondary sintering temperature is 800℃ to 1100℃, the secondary sintering time is 10h to 18h, and the heating rate of the secondary sintering is less than or equal to 10℃ / min. For example, the secondary sintering temperature can be 800℃, 810℃, 820℃, 830℃, 840℃, 850℃, 860℃, 880℃, 900℃, 920℃, 940℃, 960℃, 980℃, 1000℃, 1020℃, 1040℃, 1060℃, 1080℃, 1100℃, or a range of any two of these values. For example, the secondary sintering time can be 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, or a range of any two of these values. For example, the heating rate of the secondary sintering can be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, or any two of these values. This application controls the temperature and time of the secondary sintering to meet the above range, mainly to achieve the following objectives: (1) to further improve and stabilize the layered structure of the ternary cathode material, and reduce the diffusion impedance of the bulk phase; (2) to promote optimized grain boundary fusion and reduce grain boundary impedance; (3) to suppress insulating impurities and reduce interfacial impedance; (4) to enhance the stability of the crystal structure and reduce chemical reactivity; (5) to suppress the dissolution of transition metal ions such as nickel, cobalt, and manganese; and (6) to regulate the particle density and surface morphology of the material and reduce side reactions during storage. In summary, the purpose is to comprehensively improve the capacity, cycle life, rate capability, impedance, and storage performance of the ternary cathode material.

[0048] In summary, the preparation method of the ternary cathode material provided in this application adopts a combination of wet gradient doping and dry doping processes. Due to the design of wet gradient doping of nickel-cobalt-manganese compound precursors, the diffusion energy barrier of Li⁺ in the bulk phase and interface is reduced, which reduces the diffusion anisotropy, strain and impedance of the interface and bulk phase. At the same time, the combination of dry doping further reduces the charge transfer resistance (Rct) of the ternary cathode material and the increase of interface impedance after high-temperature storage, as well as the oxygen release reaction, phase transition and transition metal dissolution under high-temperature environment. Ultimately, the ternary cathode material has excellent high-temperature storage, cycle performance and rate performance.

[0049] In addition, the above preparation method has the advantages of simple process, few steps, high product purity, low production cost, excellent electrochemical and storage properties of the prepared material, and suitability for large-scale production, and has good promotion and application value.

[0050] A third aspect of this application provides an electrochemical device comprising a positive electrode, the positive electrode comprising a positive electrode material, wherein the positive electrode material is either the ternary positive electrode material provided in the first aspect of this application or a ternary positive electrode material prepared by the preparation method provided in the second aspect of this application. The electrochemical device of this application exhibits excellent high-temperature cycling stability and rate performance, as well as superior high-temperature storage performance.

[0051] A fourth aspect of this application provides an electronic device that includes the electrochemical device provided in the third aspect of this application. Because the electrochemical device of this application possesses excellent high-temperature cycling stability and rate performance, as well as superior high-temperature storage performance, the electronic device incorporating this electrochemical device has a long service life and good versatility in high-temperature environments.

[0052] Example The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0053] Test methods and equipment Preparation of coin cell full cells: Ternary cathode material, conductive agent SuperP, and binder PVDF were mixed in a mass ratio of 90:4:6. The slurry viscosity was controlled to 8000 mPa·s in a degassing machine. Then, the slurry was uniformly coated onto aluminum foil using an automatic coating machine to form the original electrode sheet. The electrode sheet was then dried in a vacuum oven at 130℃ for 20 minutes to obtain the test sheet. Several small electrode sheets were cut from different positions of the test sheet using a 14mm diameter die. Small electrode sheets with regular morphology and smooth surfaces and edges were selected. Weigh the electrode sheets using a balance, place them in a 120℃ vacuum drying oven and dry them for 4 hours to obtain the positive electrode sheet, which is then stored for later use. In an inert gas glove box with water and oxygen content of less than or equal to 0.0005%, coin cells are assembled according to the CR2023 battery specifications. The negative electrode is a lithium sheet, the separator is a polypropylene membrane, the high-voltage electrolyte solvent is a 1:1 volume ratio mixture of ethylene carbonate and diethyl carbonate, and the conductive salt is 1M lithium hexafluorophosphate. After assembly, the cells are encapsulated at 800Pa for 5 seconds to obtain a coin cell.

[0054] (1) Warburg impedance coefficient test of ternary cathode material The Warburg impedance coefficient of the ternary cathode material can be derived by performing electrochemical impedance spectroscopy (EIS) on the aforementioned coin cell. The specific steps are as follows: 1) In the experimental preparation stage, a three-electrode system (working electrode, reference electrode, and counter electrode) is constructed. Next, an electrolyte containing diffusing species is prepared. Finally, an electrochemical workstation (such as CHI or Autolab) is used for testing, ensuring proper instrument grounding to avoid interference. 2) EIS test parameter settings: Select "Electrochemical Impedance Spectroscopy (EIS)" as the test mode, set the test at open circuit potential (OCP), and set the frequency range to 10⁵ ~ 10⁻² Hz (the lower limit of the low frequency is sufficiently low to ensure a 45° straight line segment). Apply a small sinusoidal potential perturbation of 5~10 mV to avoid disrupting the electrode surface balance and to meet the linear approximation condition. Finally, set the number of data points: use a "logarithmic distribution" for frequency scanning, setting 10~15 points per order of magnitude to ensure sufficient data points in the low-frequency band. 3) Data processing: Export the EIS data obtained from the test. Calculate ω for each data point according to the formula ω=2πf. Then, on the Nyquist plot (Z''-Z' plot), find the low-frequency region with a slope of ≈45°, filter the corresponding data points, and calculate the σ value for each filtered point according to σ=Z'·(ω)1 / 2. Take the average value as the final Warburg coefficient.

[0055] (2) Charge and discharge performance test Under normal temperature battery laboratory conditions, the coin cell was charged at a constant current of 0.1C to a voltage of 4.3V, then charged at a constant voltage of 4.3V to a current of 0.02C, left to stand for 5 minutes, and the charging capacity was recorded. The coin cell was then discharged at a constant current of 0.1C to a voltage of 3.0V, and the discharge capacity was recorded. The initial discharge capacity at 0.1C was calculated.

[0056] (3) Ratio performance test Under normal temperature battery laboratory conditions, the coin cell was charged at a constant current of 3C to a voltage of 4.3V, then charged at a constant voltage of 4.3V to a current of 0.05C, left to stand for 5 minutes, and the charging capacity was recorded. The coin cell was then discharged at a constant current of 3C to a voltage of 3.0V, and the discharge capacity was recorded. The discharge capacity at 3C was calculated, and the ratio of the discharge capacity at 3C to the initial discharge capacity at 0.1C was calculated.

[0057] (4) Cyclic performance test Under normal and high temperature battery laboratory conditions, coin cells were charged and discharged at a constant current of 0.5C within a voltage range of 3.0~4.3V for 100 cycles at normal temperature and 50 cycles at high temperature, and the capacity retention rate of the cells before and after the cycles was calculated.

[0058] (5) Storage performance test A coin cell testing system was used to perform DCR tests on batteries stored at 60℃ for 30 days at 50% SOC. The storage performance, including impedance, of the prepared ternary cathode material was characterized by its capacity retention, capacity recovery, and DCR growth before and after different storage days. The specific testing methods are as follows: 1) Battery capacity test: Place the coin cell in a 25℃ temperature chamber, let the battery stand for 2 minutes, then discharge the battery to the cutoff voltage with a 1C current, let it stand for 2 minutes, and then charge the battery with a 1C current at constant current and constant voltage until it is fully charged. Repeat the above steps and use the capacity of the second discharge as the actual capacity of the battery. 2) Adjust to target SOC: Let the fully charged battery rest for 1 hour, then discharge the battery to 50% SOC using a 1C current. After the discharge is complete, let it rest for 30 minutes and record the voltage V0 at this time as the OCV (open circuit voltage) of 50% SOC. 3) Apply pulse current and measure voltage: Discharge ts (e.g., 10s) using discharge current I1 (e.g., 5C), and record the voltage V1 at ts. 4) Calculate the discharge DC internal resistance: Calculate the discharge DC internal resistance at 50% SOC according to the formula DCR=(V0-V1) / I1.

[0059] (6) Measurement of r The nickel-cobalt-manganese compound precursor was dispersed in anhydrous ethanol for particle size distribution measurement. The particle size analysis instrument was a MasterSizer3000, and the particle size Dv50 of the cathode material was obtained. Dv50 represents the cumulative value under the particle size volume distribution, indicating that particles smaller than this particle size account for 50% of the total sample volume. r is half of the particle size Dv50.

[0060] (7) Element content test in cathode material Elemental content was determined using inductively coupled plasma emission spectrometry (ICP).

[0061] Example 1 Step S1: Weigh 87.95g of nickel sulfate, 93.70g of cobalt sulfate, and 56.34g of manganese sulfate in a nickel-cobalt-manganese molar ratio of 1:1:1 and dissolve them in deionized water to obtain a metal ion solution. Dissolve 91.9g of sodium hydroxide as a precipitant, dissolve 1.68g of aluminum sulfate in deionized water as a gradient dopant, and use 112.8ml of ammonia water with a molar concentration of 13.3mol / L as a complexing agent. React at 50℃, pH 10.5, stirring speed 30Hz, and an oxygen content of 80ppm. Under certain conditions, a co-precipitation reaction was carried out to obtain a suspension. The suspension was then filtered, washed, and dried to obtain a nickel-cobalt-manganese compound precursor (containing gradient-doped aluminum). The gradient doping was achieved by stepwise dropwise addition of aluminum sulfate solution, which met the gradient design requirements. Initially, the aluminum sulfate solution was added at a rate of 0.3 mol%, and thereafter, for every 1 µm increase in precursor particle size, the aluminum sulfate solution was added at a rate of 0.05 mol%, with the addition rate increasing from 1 L / h to 2 L / h.

[0062] Step S2: Lithium carbonate, zirconium oxide, lithium phosphate and the nickel-cobalt-manganese compound precursor prepared in step S1 are placed in a high-speed mixer and mixed at 200 rpm for 10 min, and then at 750 rpm for 25 min to obtain a mixture.

[0063] Step S3: The mixture is heated to 800℃ at a heating rate of 2.8℃ / min and sintered for 6 hours to obtain the first sintered material.

[0064] Step S4: The material sintered once is heated to 920°C at a heating rate of 1.5°C / min and subjected to a second sintering treatment for 12 hours to obtain the ternary cathode material of this application.

[0065] In step S2, the molar ratio of lithium ions in lithium carbonate to the total amount of metal ions in the nickel cobalt manganese compound precursor is 1.1:1; based on the total mass of the nickel cobalt manganese compound precursor, the mass content of zirconium oxide is 0.8% and the mass content of lithium phosphate is 0.5%.

[0066] Example 2 Step S1: Weigh 87.95g of nickel sulfate, 93.70g of cobalt sulfate, and 56.34g of manganese sulfate in a nickel-cobalt-manganese molar ratio of 1:1:1 and dissolve them in deionized water to obtain a metal ion solution. Dissolve 91.9g of sodium hydroxide as a precipitant, dissolve 1.3g of magnesium sulfate in deionized water as a gradient dopant, and use 112.8ml of ammonia water with a molar concentration of 13.3mol / L as a complexing agent. Under reaction conditions of 50℃, pH 10.5, stirring speed of 30Hz, and reaction oxygen content of 80ppm, a co-precipitation reaction is carried out to obtain a suspension. The suspension is filtered, washed, and dried to obtain a nickel-cobalt-manganese compound precursor (containing gradient-doped magnesium). The gradient doping is achieved by stepwise dropwise addition of magnesium sulfate solution, which meets the gradient design requirements (see Example 1 for details).

[0067] Step S2: Lithium carbonate, zirconium oxide, aluminum oxide and the nickel-cobalt-manganese compound precursor prepared in step S1 are placed in a high-speed mixer and mixed at 200 rpm for 10 min, and then at 750 rpm for 25 min to obtain a mixture.

[0068] Step S3: The mixture is heated to 800℃ at a heating rate of 2.8℃ / min and sintered for 6 hours to obtain the first sintered material.

[0069] Step S4: The material sintered once is heated to 920°C at a heating rate of 1.5°C / min and subjected to a second sintering treatment for 12 hours to obtain the ternary cathode material of this application.

[0070] In step S2, the molar ratio of lithium ions in lithium carbonate to the total amount of metal ions in the nickel cobalt manganese compound precursor is 1.1:1; based on the total mass of the nickel cobalt manganese compound precursor, the mass content of zirconium oxide is 0.8% and the mass content of aluminum oxide is 0.6%.

[0071] Example 3 Step S1: Weigh 87.95g of nickel sulfate, 93.70g of cobalt sulfate, and 56.34g of manganese sulfate in a nickel-cobalt-manganese molar ratio of 1:1:1 and dissolve them in deionized water to obtain a metal ion solution. Dissolve 91.9g of sodium hydroxide as a precipitant, and dissolve 1.3g of magnesium sulfate and 1.68g of aluminum sulfate in deionized water as gradient dopant. Use 112.8ml of ammonia water with a molar concentration of 13.3mol / L as a complexing agent. Under reaction conditions of 50℃, pH 10.5, stirring speed of 30Hz, and reaction oxygen content of 80ppm, a coprecipitation reaction is carried out to obtain a suspension. The suspension is filtered, washed, and dried to obtain a nickel-cobalt-manganese compound precursor (containing gradient doped magnesium and aluminum). The gradient doping is achieved by stepwise dropwise addition of magnesium sulfate and aluminum sulfate solution, which meets the gradient design requirements (see Example 1 for details).

[0072] Step S2: Lithium carbonate, zirconium oxide, aluminum oxide and the nickel-cobalt-manganese compound precursor prepared in step S1 are placed in a high-speed mixer and mixed at 200 rpm for 10 min, and then at 750 rpm for 25 min to obtain a mixture.

[0073] Step S3: The mixture is heated to 800℃ at a heating rate of 2.8℃ / min and sintered for 6 hours to obtain the first sintered material.

[0074] Step S4: The material sintered once is heated to 920°C at a heating rate of 1.5°C / min and subjected to a second sintering treatment for 12 hours to obtain the ternary cathode material of this application.

[0075] In step S2, the molar ratio of lithium ions in lithium carbonate to the total amount of metal ions in the nickel cobalt manganese compound precursor is 1.1:1; based on the total mass of the nickel cobalt manganese compound precursor, the mass content of zirconium oxide is 0.8% and the mass content of aluminum oxide is 0.1%.

[0076] Example 4 The difference from Example 1 is that lithium phosphate in step S2 is replaced with titanium oxide and silicon oxide, and the mass content of titanium oxide is 0.4% and the mass content of silicon oxide is 0.25% based on the total mass of the nickel cobalt manganese compound precursor.

[0077] Example 5 The difference from Example 1 is that lithium phosphate in step S2 is replaced with magnesium oxide and aluminum oxide, with the magnesium oxide content being 0.5% and the aluminum oxide content being 0.15% based on the total mass of the nickel cobalt manganese compound precursor.

[0078] Example 6 The difference from Example 1 is that lithium phosphate in step S2 is replaced with yttrium oxide, and the mass content of yttrium oxide is 0.4% based on the total mass of the nickel cobalt manganese compound precursor.

[0079] Example 7 The difference from Example 1 is that in step S2, based on the total mass of the nickel-cobalt-manganese compound precursor, the mass content of zirconium oxide is 1.5% and the mass content of lithium phosphate is 1%.

[0080] Example 8 The difference from Example 1 is that in step S2, the molar ratio of lithium ions in lithium carbonate to the total amount of metal ions in the nickel-cobalt-manganese compound precursor is 1.2:1.

[0081] Comparative Example 1 The difference from Example 1 is that aluminum sulfate is not added in step S1.

[0082] Comparative Example 2 The difference from Example 2 is that magnesium sulfate is not added in step S1.

[0083] Comparative Example 3 The difference from Example 3 is that aluminum sulfate and magnesium sulfate are not added in step S1.

[0084] Comparative Example 4 The difference from Example 1 is that zirconium oxide and lithium phosphate are not added in step S2.

[0085] The relevant test results of Examples 1 to 8 and Comparative Examples 1 to 7 are recorded in Tables 1 to 3.

[0086] Table 1 Table 2 Table 3 As can be seen from Tables 1 to 3, compared with Comparative Examples 1 to 4, the Warburg impedance coefficient of the ternary cathode materials in Examples 1 to 8 (satisfying σ≤0.8Ω·s) -1 / 2 The significant reduction in the anisotropy of bulk and interfacial ion diffusion in the ternary cathode material results in low initial impedance and diffusion resistance. This also reduces the overall storage and cycling polarization of the material in high-temperature storage environments, thereby significantly reducing the growth of bulk and interfacial impedance after high-temperature storage and improving the overall capacity retention and recovery rate. This allows the electrochemical device to maintain good cycle stability and rate performance while significantly improving its high-temperature storage performance.

[0087] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. A method for preparing a ternary cathode material, characterized in that, include: A nickel-cobalt-manganese compound precursor was obtained by co-precipitation reaction of nickel source, cobalt source, manganese source, alkaline precipitant and salt solution containing element M. The nickel-cobalt-manganese compound precursor, lithium source, and nitrogen-containing dopant are mixed to obtain a mixture. The mixture is sintered once to obtain a sintered material; The ternary cathode material is obtained by performing a second sintering on the material that was sintered in the first sintering. The ternary cathode material has a polycrystalline or near-monocrystalline layered structure, and its general chemical formula is LiNi. x Co y Mn 1-x-y M a N b O2, where 0.3≤x≤1, 0≤y≤0.35, 0.001≤a≤0.03, 0.001≤b≤0.05; The Warburg impedance coefficient of the ternary cathode material is σ, where σ ≤ 0.8 Ω·s -1 / 2 ; The M element includes magnesium and / or aluminum; The nitrogen element includes at least one of zirconium, aluminum, titanium, yttrium, silicon, strontium, niobium, magnesium, tungsten, zinc, phosphorus, fluorine, molybdenum, cerium, and tantalum. During the co-precipitation reaction, the salt solution containing element M is added dropwise at a rate of 1 L / h to 2 L / h. The element M in the nickel-cobalt-manganese compound precursor exhibits a gradient distribution and satisfies the following relationship: C M ≥C0+k(r-r0); The nickel-cobalt-manganese compound precursor is spherical, C M C0 is the concentration of element M at a distance r from the core of the nickel-cobalt-manganese compound precursor; C0 is the concentration of element M at a distance r0 from the core of the nickel-cobalt-manganese compound precursor, and is between 0.1 mol% and 2 mol%; k ​​is a concentration constant and is 0.001 mol%·µm. -1 Up to 0.1 mol%·µm -1 r is the radius of the nickel-cobalt-manganese compound precursor and is 0µm < r ≤ 12µm; r0 is 0.5µm to 12µm.

2. The method for preparing the ternary cathode material according to claim 1, characterized in that, The salt solution containing element M is selected from at least one of aluminum sulfate, aluminum nitrate, aluminum hydroxide, magnesium sulfate, magnesium nitrate, and magnesium carbonate. The nitrogen-containing dopant is selected from at least one of zirconium oxide, aluminum oxide, titanium oxide, yttrium oxide, silicon oxide, strontium oxide, niobium oxide, magnesium oxide, tungsten oxide, zinc oxide, lithium phosphate, lithium fluoride, molybdenum oxide, cerium oxide, and tantalum oxide.

3. The method for preparing the ternary cathode material according to claim 1, characterized in that, The molar ratio of lithium ions in the lithium source to the total amount of metal ions in the nickel-cobalt-manganese compound precursor is (0.95-1.2):

1.

4. The method for preparing the ternary cathode material according to claim 1, characterized in that, Based on the total mass of the nickel-cobalt-manganese compound precursor, the mass content of the N-containing dopant is 0.1% to 2%.

5. The method for preparing the ternary cathode material according to claim 1, characterized in that, The temperature of the first sintering is 650°C to 850°C, and the time of the first sintering is 2 hours to 10 hours; and / or The secondary sintering temperature is 800℃ to 1100℃, and the secondary sintering time is 10h to 18h.

6. The method for preparing the ternary cathode material according to claim 1, characterized in that, The preparation method satisfies at least one of the following conditions: (1) The ratio of the total molar amount of nickel ions in the nickel source, cobalt ions in the cobalt source, and manganese ions in the manganese source to the molar amount of hydroxide ions in the alkaline precipitant is 1:(1.6-2.5). (2) Based on the total mass of the nickel-cobalt-manganese compound precursor, the mass content of the M element is 0.1% to 1.5%.

7. An electrochemical device, characterized in that, The electrochemical device includes a positive electrode sheet, the positive electrode sheet includes a positive electrode material, and the positive electrode material is a ternary positive electrode material prepared by the preparation method according to any one of claims 1 to 6.

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