Positive electrode material, preparation method thereof and battery

Abstract

The invention relates to the field of lithium ion batteries, and discloses a positive electrode material, a preparation method thereof and a battery, the general formula of the positive electrode material is Li (1 + x) TM (1-x) O2, TM comprises a transition metal element and an element A, the transition metal element comprises Ni, Mn and Co, the element A is selected from cations of any one of Ti, V, Cr, Y, Zr, Nb, Mo, Ta and W, the valence of A is greater than or equal to 3 + valence, the molar ratio of Ni to Mn to Co to A in TM is y: z: t: 1-y-z-t, x is more than 0 and less than 1, z is more than or equal to 0.475 and less than 0.75, t is more than or equal to 0 and less than or equal to 0.1, and x is more than or equal to 1. 0.2375 < = y + t < 0.5, and 0.95 < = y + z + t < 1. The positive electrode material disclosed by the invention is good in crystallinity, excellent in rate capability, high in cycling stability and simple in preparation method, and has industrial production potential.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, specifically to a cathode material, its preparation method, and a battery. Background Technology

[0002] Lithium-ion batteries are widely used in modern society in portable electronic devices, electric vehicles, and energy storage systems. As one of the core components of lithium-ion batteries, the cathode material not only determines the battery's capacity, power density, and energy density, but also directly affects its cycle stability, safety, and cost. Lithium-rich cathode materials, especially lithium-rich manganese-based oxides, have attracted much attention due to their high specific energy and low cost, but they still face some challenges in practical applications. Lithium-rich materials experience significant capacity and voltage decay after multiple charge-discharge cycles, mainly due to structural transformations and oxygen loss during the charge-discharge process, leading to the loss of active material and a decline in electrochemical performance. Furthermore, the high capacity achieved by lithium-rich materials results in poor rate performance, primarily because the diffusion kinetics of lithium ions under high current are limited.

[0003] Currently, the common method to solve the above problems is to perform surface modification. Through surface coating or coating technology, a protective layer can be constructed to isolate the material from direct contact with the electrolyte, reduce side reactions, and improve the cycle stability and safety of the material. However, most of these methods come at the cost of capacity, and the modification methods are relatively complex and difficult to achieve industrial production.

[0004] Improving the rate performance and cycle stability of lithium-rich cathode materials while maintaining their high capacity is a key focus and challenge in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of poor rate performance and cycle stability, and low first-cycle coulombic efficiency of existing cathode materials, and to provide a cathode material, its preparation method, and a battery. The cathode material provided by this invention has good crystallinity, excellent rate performance, strong cycle stability, and a simple preparation method, and has the potential for industrial production.

[0006] To achieve the above objectives, a first aspect of the present invention provides a cathode material, wherein the general formula of the cathode material is:

[0007] Li (1+x) TM (1-x) O2,

[0008] TM includes transition metal elements and element A. The transition metal elements include Ni, Mn, and Co. The element A is selected from any one of Ti, V, Cr, Y, Zr, Nb, Mo, Ta, and W, and the oxidation state of A is ≥3. +The molar ratio of Ni, Mn, Co, and A in TM is y:z:t:1-yzt, 0<x<1, 0.475≤z<0.75, 0≤t≤0.1, 0.2375≤y+t<0.5, and 0.95≤y+z+t<1.

[0009] Doping cathode materials with alumina (A) can suppress the formation of irreversible phase transitions, thereby effectively increasing the cycle stability of the battery. On one hand, A can replace Ni, Mn, and Co to form stronger AO bonds, resisting the stress generated during lithium-ion insertion and extraction, reducing structural damage and microcrack formation, and helping to maintain the layered structure of the material. On the other hand, stronger AO bonds stabilize lattice oxygen, preventing irreversible oxygen loss due to excessive anion oxidation and avoiding structural instability caused by lattice oxygen framework collapse. The introduction of A improves the structural stability of the material, regulates the reversibility of redox reactions between cations and anions, and thus increases the energy density of the cathode material.

[0010] Furthermore, nickel ions provide a higher redox potential, so cathode materials with high nickel content can store more energy per unit mass and volume, increasing the material's energy density. However, stability and safety may decrease, so the amount of nickel needs to be controlled within a reasonable range. Manganese plays an important role in improving the structural stability of the material. Its presence helps maintain the structural integrity of the cathode material during multiple charge-discharge cycles, thereby extending battery life. Cobalt stabilizes the layered structure of the cathode material, contributing to improved cycle stability and thermal stability, and also enhancing the battery's power performance.

[0011] A second aspect of the present invention provides a method for preparing a positive electrode material, wherein the preparation method includes the following steps:

[0012] (1) Prepare a first metal salt solution, the first metal salt solution including salts of transition metal elements, the transition metal elements including nickel, manganese and cobalt, mix the first metal salt solution, a first precipitant containing carbonate and an ammonia solution, and carry out a first step co-precipitation reaction to obtain the initial product.

[0013] (2) Prepare a second metal salt solution, the second metal salt solution comprising a salt of a transition metal element and a salt of element A, wherein the transition metal element comprises nickel, manganese and cobalt, and element A is selected from any one of the cations of Ti, V, Cr, Y, Zr, Nb, Mo, Ta and W, and the oxidation state of A is greater than or equal to 3. + price;

[0014] The second metal salt solution, the second precipitant containing hydroxide ions, and the ammonia solution are simultaneously added to the primary product to carry out the second co-precipitation reaction, followed by aging to obtain the precursor.

[0015] (3) The lithium source and the precursor are calcined to obtain the cathode material.

[0016] In the first coprecipitation step, a first precipitant containing carbonate ions is added to obtain a carbonate precursor. The carbonate precursor formed inside decomposes during the calcination step to produce carbon dioxide gas, thus resulting in a hollow structure of the material. In the second coprecipitation step, a second precipitant containing hydroxide ions is added to form a more dense shell structure. Ammonia solution is used to adjust the pH so that the coprecipitation reaction proceeds at a suitable pH. In addition, ammonia acts as a complexing agent, forming complexes with metal ions in the first and second metal salt solutions, reducing the effective concentration of metal ions, thereby reducing the nucleation rate and improving the crystal morphology.

[0017] During the aging stage, primary particles agglomerate to form larger secondary particles, which helps to increase the density and conductivity of the cathode material. In addition, the aging process can promote the orderly arrangement of grains, increase the crystallinity of the material, and thus improve electrochemical performance.

[0018] A third aspect of the present invention provides a battery comprising the positive electrode material described in the first aspect of the present invention or the positive electrode material prepared by the preparation method described in the second aspect of the present invention.

[0019] The beneficial effects of the present invention through the above technical solution are as follows:

[0020] The cathode material prepared in this invention incorporates transition metal elements and is doped with element A. Doping the cathode material with element A can suppress the formation of irreversible phase transitions, thereby effectively increasing the cycle stability of the battery. On one hand, element A can replace Ni, Mn, and Co to form stronger AO bonds, resisting the stress generated during lithium-ion insertion and extraction, reducing structural damage and microcrack formation, and helping to maintain the layered structure of the material. On the other hand, stronger AO bonds stabilize lattice oxygen, preventing irreversible oxygen loss due to excessive anion oxidation and avoiding structural instability caused by lattice oxygen framework collapse. The introduction of element A improves the structural stability of the material, regulates the reversibility of redox reactions between cations and anions, and thus increases the energy density of the cathode material.

[0021] The cathode material prepared by this invention exhibits high first-cycle coulombic efficiency, with an activation capacity of 270 mAh·g at a first-cycle 0.1C rate. -1 The coulombic efficiency is above 80%; the cycle stability is good, with an initial capacity of 210 mAh·g at 1C rate. -1 The capacity retention rate after 100 cycles is above 90%; the rate performance is good, with a capacity of 170 mAh·g at a high rate of 5C. -1The above describes the positive electrode material's excellent crystallinity, which is reflected in its X-ray diffraction pattern, showing sharp diffraction peaks.

[0022] The cathode material preparation method provided by this invention is simple to operate. It can simultaneously achieve the design of hollow structure and gradient molar fraction of transition metal element and element A by using co-precipitation method combined with two-step calcination, and has industrialization prospects. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the internal structure of the cathode material;

[0024] Figure 2 These are the X-ray diffraction (XRD) patterns of the cathode materials prepared in Examples 1, 2, and 7;

[0025] Figure 3 These are scanning electron microscope (SEM) images and energy dispersive spectroscopy (EDS) surface scans of the cathode material prepared in Example 1;

[0026] Figure 4 This is a scanning electron microscope (SEM) image of the cross-section of the cathode material prepared in Example 2;

[0027] Figure 5 These are scanning electron microscope (SEM) images and cross-sectional energy dispersive spectroscopy (EDS) line scans of the cathode material prepared in Example 7. Detailed Implementation

[0028] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0029] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature marked "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more. Primary particles refer to tiny solid particles directly formed through chemical synthesis and are the basic unit constituting the cathode material.

[0030] The first aspect of this invention provides a cathode material, wherein the general formula of the cathode material is:

[0031] Li (1+x) TM (1-x) O2,

[0032] TM includes transition metal elements and element A. The transition metal elements include Ni, Mn, and Co. The element A is selected from any one of Ti, V, Cr, Y, Zr, Nb, Mo, Ta, and W, and the oxidation state of A is ≥3. + The molar ratio of Ni, Mn, Co, and A in TM is y:z:t:1-yzt, 0<x<1, 0.475≤z<0.75, 0≤t≤0.1, 0.2375≤y+t<0.5, and 0.95≤y+z+t<1.

[0033] Nickel ions provide a high redox potential, so cathode materials with high nickel content can store more energy per unit mass and volume, increasing the material's energy density, but stability and safety may be reduced. Manganese plays an important role in improving the structural stability of the material; its presence helps maintain the structural integrity of the cathode material during multiple charge-discharge cycles, thereby extending battery life. Cobalt stabilizes the layered structure of the cathode material, helping to improve its cycle stability and thermal stability, and also contributing to improved battery power performance. Therefore, by adjusting the ratio of nickel, manganese, and cobalt in the cathode material, the performance indicators such as energy density, cycle stability, safety, and cost can be optimized.

[0034] Doping cathode materials with alumina (A) can suppress the formation of irreversible phase transitions, thereby effectively increasing the cycle stability of the battery. On one hand, A can replace Ni, Mn, and Co to form stronger AO bonds, resisting the stress generated during lithium-ion insertion and extraction, reducing structural damage and microcrack formation, and helping to maintain the layered structure of the material. On the other hand, stronger AO bonds stabilize lattice oxygen, preventing irreversible oxygen loss due to excessive anion oxidation and avoiding structural instability caused by lattice oxygen framework collapse. The introduction of A improves the structural stability of the material, regulates the reversibility of redox reactions between cations and anions, and thus increases the energy density of the cathode material.

[0035] In some embodiments, preferably, the positive electrode material is a hollow sphere, and based on the total molar amount of the TM elements, the total molar fraction of nickel and cobalt in the positive electrode material tends to increase from the inner surface to the outer surface of the sphere; based on the total molar amount of the TM elements, the molar fraction of manganese in the positive electrode material tends to decrease from the inner surface to the outer surface of the sphere; and based on the total molar amount of the TM elements, the molar fraction of alumina in the positive electrode material tends to increase from the inner surface to the outer surface of the sphere.

[0036] Hollow structure design has demonstrated significant advantages in lithium-ion battery technology. First, the hollow structure can effectively buffer the volume changes in materials caused by lithium-ion insertion and extraction, reducing structural damage and thus improving cycle stability. Second, the hollow structure can shorten the diffusion path of lithium ions within the material, accelerating ion transport and improving the battery's rate performance. Finally, the hollow structure can enhance electrolyte wettability, ensuring good contact between the electrolyte and the cathode material during battery charging and discharging, which is beneficial for efficient electrochemical reactions.

[0037] By adjusting the proportion of transition metal elements in different regions of the material through gradient design, the cycling stability and first-cycle coulombic efficiency of the material can be effectively improved. In this application, by reducing Mn and increasing Ni and Co on the outer surface of the material, a more stable surface layer can be formed, reducing the occurrence of side reactions, reducing the dissolution of Mn, and also regulating the stress distribution inside the material, reducing local stress concentration, thereby reducing the formation and propagation of cracks and lowering the risk of structural degradation. Furthermore, the higher Ni and Co concentration on the outer surface helps to form more efficient lithium-ion transport channels, reducing the diffusion resistance of lithium ions in the cathode material, thereby reducing irreversible capacity loss during the first charge and discharge process.

[0038] A higher A content on the surface of the cathode material helps stabilize the lattice oxygen on the material surface and avoid damage to the material surface structure. However, A is not electrochemically active and cannot provide capacity. Therefore, by adjusting the proportion of A in different regions of the material through gradient design, the molar fraction of A decreases from the outer surface to the inner surface, thereby reducing its impact on capacity.

[0039] In some embodiments, preferably, the particle size of the positive electrode material is D, where D is 5-15 μm, and the pore size of the hollow structure inside the positive electrode material is d, where d:D is 1-2:10.

[0040] A schematic diagram of the cathode material is shown below. Figure 1 As shown, the particle size D of the cathode material is its outer diameter, and the pore size d of the internal hollow structure is the diameter of its internal pores. Smaller particle sizes in spherical cathode materials mean a larger specific surface area, which increases the number of electrochemical active sites, facilitating rapid lithium-ion insertion and extraction, thereby improving the battery's rate performance and capacity. Simultaneously, smaller particle sizes shorten the diffusion distance of lithium ions within the material, accelerating their migration rate and increasing the battery's charge and discharge rates. Furthermore, smaller particle sizes result in less stress caused by volume changes during charge and discharge, helping to maintain the material's structural integrity, reducing crack formation, and thus improving cycle stability. Larger particle sizes, on the other hand, help increase the material's compaction density, thereby increasing the battery's volumetric energy density.

[0041] The ratio of the pore size of the hollow structure to the particle size of the cathode material actually reflects the proportion of hollow structures in the cathode material. A larger hollow structure ratio provides more space to mitigate volume changes during charge and discharge, reducing internal stress and improving cycle stability. Simultaneously, larger pore sizes allow for shorter ion transport distances, accelerating lithium-ion diffusion and improving the battery's rate performance. Reducing the proportion of hollow structures enhances the overall structural strength of the material, reducing breakage and wear during cycling and extending battery life.

[0042] The value of d:D can be any value between any two numbers in the range of 1:10, 1.1:10, 1.2:10, 1.3:10, 1.4:10, and 1.5:10.

[0043] A second aspect of the present invention provides a method for preparing a positive electrode material, wherein the preparation method includes the following steps:

[0044] (1) Prepare a first metal salt solution, the first metal salt solution including salts of transition metal elements, the transition metal elements including nickel, manganese and cobalt, mix the first metal salt solution, a first precipitant containing carbonate and an ammonia solution, and carry out a first step co-precipitation reaction to obtain the initial product.

[0045] (2) Prepare a second metal salt solution, the second metal salt solution comprising a salt of a transition metal element and a salt of element A, wherein the transition metal element comprises nickel, manganese and cobalt, and element A is selected from any one of the cations of Ti, V, Cr, Y, Zr, Nb, Mo, Ta and W, and the oxidation state of A is greater than or equal to 3. + price;

[0046] The second metal salt solution, the second precipitant containing hydroxide ions, and the ammonia solution are simultaneously added to the primary product to carry out the second co-precipitation reaction, followed by aging to obtain the precursor.

[0047] (3) The lithium source and the precursor are calcined to obtain the cathode material.

[0048] In the first coprecipitation step, a first precipitant containing carbonate ions is added to obtain a carbonate precursor. The carbonate precursor formed inside decomposes during the calcination step to produce carbon dioxide gas, thus resulting in a hollow structure of the material. In the second coprecipitation step, a second precipitant containing hydroxide ions is added to form a more dense shell structure. Ammonia solution is used to adjust the pH so that the coprecipitation reaction proceeds at a suitable pH. In addition, ammonia acts as a complexing agent, forming complexes with metal ions in the first and second metal salt solutions, reducing the effective concentration of metal ions, thereby reducing the nucleation rate and improving the crystal morphology.

[0049] In some embodiments, preferably, the total concentration of nickel, manganese and cobalt in the first metal salt solution is 1-4 mol / L, and the molar ratio of nickel, manganese and cobalt is Y1:Z1:T1, wherein 15≤Y1<50, 50<Z1≤75, and 0≤T1≤10.

[0050] In some embodiments, preferably, the total concentration of nickel, manganese, cobalt and alumina in the second metal salt solution is 1-4 mol / L, and the molar ratio of nickel, manganese, cobalt and alumina is Y2:Z2:T2:P, wherein 15<Y2<50, 45≤Z2<75, 0≤T2≤10, and 0<P≤10.

[0051] The concentration of the metal salt solution directly affects the rate of the coprecipitation reaction, thus influencing the particle size. Higher concentrations result in a faster reaction rate and larger particles. Excessively high concentrations can lead to overly vigorous localized reactions, causing uneven distribution of chemical components; conversely, excessively low concentrations reduce the precipitation efficiency of metal ions, resulting in low raw material utilization.

[0052] The total concentration of nickel, manganese, and cobalt in the first metal salt solution can be any value between any two of the following: 1 mol / L, 2 mol / L, 3 mol / L, and 4 mol / L. The total concentration of nickel, manganese, cobalt, and aluminum in the second metal salt solution can also be any value between any two of the following: 1 mol / L, 2 mol / L, 3 mol / L, and 4 mol / L.

[0053] The molar ratio of nickel, manganese, cobalt, and alumina in a metal salt solution affects the distribution of metal elements on the surface and inside the cathode material, thereby affecting the performance of the cathode material.

[0054] Nickel ions provide a high redox potential, so cathode materials with high nickel content can store more energy per unit mass and volume, increasing the material's energy density, but stability and safety may be reduced. Manganese contributes less to energy density, but plays an important role in improving the structural stability of the material. The presence of manganese helps maintain the structural integrity of the cathode material during multiple charge-discharge cycles, thereby extending battery life. Cobalt stabilizes the layered structure of the cathode material, helping to improve its cycle stability and thermal stability, and also contributing to improved battery power performance; however, cobalt is expensive, and its usage needs to be controlled to reduce costs. Therefore, by adjusting the ratio of nickel, manganese, and cobalt in the cathode material, the performance indicators such as energy density, cycle stability, safety, and cost can be optimized.

[0055] Doping cathode materials with alumina (A) can suppress the formation of irreversible phase transitions, thereby effectively increasing the cycle stability of the battery. On one hand, A can replace Ni, Mn, and Co to form stronger AO bonds, resisting the stress generated during lithium-ion insertion and extraction, reducing structural damage and microcrack formation, and helping to maintain the layered structure of the material. On the other hand, stronger AO bonds stabilize lattice oxygen, preventing irreversible oxygen loss due to excessive anion oxidation and avoiding structural instability caused by lattice oxygen framework collapse. The introduction of A improves the structural stability of the material, regulates the reversibility of redox reactions between cations and anions, and thus increases the energy density of the cathode material.

[0056] In some embodiments, preferably, the nickel element is derived from one or more of nickel nitrate, nickel sulfate, nickel chloride, and nickel acetate; the manganese element is derived from one or more of manganese nitrate, manganese sulfate, manganese chloride, and manganese acetate; and the cobalt element is derived from one or more of cobalt nitrate, cobalt sulfate, cobalt chloride, and cobalt acetate.

[0057] In some embodiments, preferably, the cation of element A is selected from Ti. 4+ V 5+ Cr 6+ Y 3+ Zr 4+ 、Nb 5+ Mo 6+ Ta 5+ W 6+ Any one of them.

[0058] In some embodiments, preferably, the concentration of the first precipitant is 1-4 mol / L, and the first precipitant is preferably one or more of Na2CO3, NaHCO3, K2CO3, and KHCO3.

[0059] In some embodiments, preferably, the concentration of the second precipitant is 2-8 mol / L, and the second precipitant is preferably one or more of NaOH and KOH.

[0060] The higher the concentration of the precipitant, the greater the reaction rate of the coprecipitation reaction, and the larger the particle size formed. Excessively high concentrations can lead to overly vigorous local reactions, resulting in uneven distribution of chemical components; excessively low concentrations will reduce the precipitation efficiency of metal ions, leading to low raw material utilization. The concentration of the first precipitant can be any value between any two numbers from 1 mol / L, 2 mol / L, 3 mol / L, and 4 mol / L. The concentration of the second precipitant can be any value between any two numbers from 2 mol / L, 4 mol / L, 6 mol / L, and 8 mol / L.

[0061] In some embodiments, preferably, the reaction temperature of both the first and second coprecipitation reactions is 40-60°C, and the pH is 8-12. Higher reaction temperatures result in a faster coprecipitation rate, but also increase the solubility of the substance, which is unfavorable for the reaction to move towards precipitation. Within a specific pH range, the precipitant can effectively promote the formation of precipitates from metal ions in the solution. The reaction temperatures of the first and second coprecipitation reactions can be any value between any two of 40°C, 45°C, 50°C, 55°C, and 60°C, and the pH can be any value between any two of 8, 9, 10, 11, and 12.

[0062] In some embodiments, the aging time is preferably 4-12 hours. Aging refers to the process of placing the newly formed precipitate under certain conditions for a period of time to allow it to further grow and crystallize. During the aging stage, primary particles agglomerate to form larger secondary particles, which helps to increase the density and conductivity of the cathode material. In addition, the aging process can promote the orderly arrangement of grains, increase the crystallinity of the material, and thus improve electrochemical performance. If the aging time is too short, sufficient crystallization may not be achieved; if the aging time is too long, the particles may become too large, affecting the specific surface area and electrochemical performance of the material. The aging time can be any value between any two of 4 hours, 6 hours, 8 hours, 10 hours, and 12 hours.

[0063] In some embodiments, preferably, the molar ratio of TM element in the precursor to lithium element in the lithium source is 1:1-1.05. The ratio of TM element to lithium element affects the lithium content in the cathode material. Theoretically, the higher the lithium content, the higher the energy density of the cathode material. However, when the lithium content is too high, excess lithium will remain on the material surface, reacting with carbon dioxide to form a Li₂CO insulating film, increasing the interfacial impedance of the electrochemical reaction, hindering the diffusion of lithium ions, and thus reducing the rate performance and energy density of the battery. The molar ratio of TM element in the precursor to lithium element in the lithium source can be any value between any two numbers from 1:1, 1:1.01, 1:1.02, 1:1.03, 1:1.04, and 1:1.05.

[0064] In some embodiments, preferably, the lithium source is selected from one or more of lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, and lithium fluoride.

[0065] In some embodiments, preferably, the calcination includes a first calcination and a second calcination.

[0066] In some embodiments, preferably, the temperature of the first calcination is 400-600℃, the time is 4-6h, and the heating rate of the first calcination is preferably 1-6℃ / min.

[0067] In some embodiments, preferably, the second calcination temperature is 800-1000℃, the time is 10-16h, and the heating rate of the second calcination is preferably 2-10℃ / min.

[0068] The first calcination is typically carried out at a lower temperature to remove residual raw materials from the first and second coprecipitation reactions, promote uniform mixing of the various components in the precursor, and initiate the formation of the desired crystal structure. The second calcination is conducted at a higher temperature to form a more stable and crystallinity-rich crystal structure, which is crucial for the performance of the cathode material. During the first and second calcinations, carbonates decompose to form metal oxides, releasing carbon dioxide and creating a hollow structure. Hydroxides decompose into metal oxides and water. Lithium ions react with these metal oxides, embedding themselves into the metal oxide lattice to form a layered structure.

[0069] The temperature for the first calcination can be any value between any two numbers from 400℃, 450℃, 500℃, 550℃, and 600℃; the time can be any value between any two numbers from 4h, 4.5h, 5h, 5.5h, and 6h; and the heating rate can be any value between any two numbers from 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, and 6℃ / min. The temperature for the second calcination can be any value between any two numbers from 800℃, 850℃, 900℃, 950℃, and 1000℃; the time can be any value between any two numbers from 10h, 11h, 12h, 13h, 14h, 15h, and 16h; and the heating rate can be any value between any two numbers from 2℃ / min, 4℃ / min, 6℃ / min, 8℃ / min, and 10℃ / min.

[0070] In some embodiments, preferably, the first coprecipitation reaction and the second coprecipitation reaction are carried out under inert gas protection.

[0071] A third aspect of the present invention provides a battery comprising the positive electrode material described in the first aspect of the present invention or the positive electrode material prepared by the preparation method described in the second aspect of the present invention.

[0072] The present invention will be described in detail below through examples. Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0073] The X-ray diffraction pattern of the cathode material was obtained by X-ray diffractometer (Bruker D8 Advance), the scanning electron microscope (SEM) pattern was obtained by scanning electron microscope (FEIQUANTA 250), the energy dispersive spectroscopy surface scan pattern and energy dispersive spectroscopy line scan pattern were obtained by scanning electron microscope (FEI QUANTA 250), and the electrochemical performance was obtained by charge-discharge testing of the assembled battery using a LAND CT 2001A tester from Wuhan Landian Electronics Co., Ltd.

[0074] Example 1

[0075] Prepare a 2 mol / L first metal salt solution, wherein the molar ratio of Ni in nickel sulfate and Mn in manganese sulfate is 25:75. Prepare a 2 mol / L second metal salt solution, wherein the molar ratio of Ni in nickel sulfate, Mn in manganese sulfate and W in ammonium metatungstate is 48:48:4.

[0076] 0.5 L of the first metal salt solution was pumped into a continuously stirred reactor at a feed rate of 150 mL / h. At the same time, 2 mol / L sodium carbonate solution and 1.5 mol / L ammonia solution were pumped into the reactor at a feed rate of 150 mL / h. The reaction temperature was maintained at 55 °C, pH at 8, and the rotation speed at 1000 rpm. The reaction was protected under a nitrogen atmosphere.

[0077] After the first metal salt solution was pumped in, 0.5 L of the second metal salt solution was pumped into the continuously stirred reactor at a feed rate of 150 mL / h. At the same time, 4 mol / L sodium hydroxide solution and 1.8 mol / L ammonia solution were pumped into the reactor at a feed rate of 150 mL / h. The reaction temperature was maintained at 55 °C, pH at 10.5, and the rotation speed at 1000 rpm. The reaction was protected under a nitrogen atmosphere. After the second metal salt solution was pumped in, the mixture was aged for 6 h, then filtered, washed with water, and dried in an oven at 80 °C for 12 h to obtain the precursor.

[0078] A precursor and lithium hydroxide were mixed, wherein the molar ratio of TM element in the precursor to lithium element in the lithium source was 1:1.05, and a two-step calcination was performed in air. First, the temperature was increased to 450℃ at a heating rate of 5℃ / min and held for 5 h; then, the temperature was increased to 850℃ at a heating rate of 5℃ / min and held for 13 h. Finally, the mixture was cooled to room temperature to obtain the cathode material Li. 1.2 (Ni 0.365 Mn 0.615 W 0.02 ) 0.8 O2.

[0079] The SEM image and energy-dispersive X-ray spectroscopy (EDS) surface scan of the cathode material prepared in Example 1 are shown below. Figure 3 As shown, the first image in the first row is a SEM image, the second image in the first row is an EDS surface scan of Ni, the first image in the second row is an EDS surface scan of Mn, and the second image in the second row is an EDS surface scan of W.

[0080] The cathode materials of Examples 1-13 have similar scanning electron microscope (SEM) images, with the SEM image of Example 1 being representative. As can be seen from the image, the cathode material has a spherical structure with a particle size D of about 6.5 μm. The primary particles are clearly visible, with a size of about 300 nm, and the pore size d of the hollow structure is 1 μm.

[0081] EDS surface scans of W element show that W element was successfully doped into the cathode material and is uniformly distributed.

[0082] Example 2

[0083] The method was followed according to Example 1, except that: in the second metal salt solution, the molar ratio of Ni in nickel sulfate, Mn in manganese sulfate, and W in ammonium metatungstate was 32:64:4; the first calcination temperature was 500℃; the second calcination temperature was 900℃; the holding time was 12 h; and the heating rate was 2℃ / min, thus preparing the positive electrode material Li. 1.2 (Ni 0.285 Mn 0.695 W 0.02 ) 0.8 O2.

[0084] Cross-sectional scanning electron microscope image of the cathode material as shown below Figure 4 As shown, the cathode material is spherical with a particle size of about 6.5 μm and has a hollow structure with a pore size of about 1 μm.

[0085] Example 3

[0086] The method of Example 1 was followed, with the only difference being that the molar ratio of Ni in nickel sulfate and Mn in manganese sulfate in the first metal salt solution was 35:65, thus preparing the positive electrode material Li. 1.2 (Ni 0.415 Mn 0.565 W 0.02 ) 0.8 O2.

[0087] Example 4

[0088] The method was followed according to Example 1, except that: in the first metal salt solution, the molar ratio of Ni in nickel sulfate, Mn in manganese sulfate, and Co in cobalt sulfate was 21:75:4; and in the second metal salt solution, the molar ratio of Ni in nickel sulfate, Mn in manganese sulfate, Co in cobalt sulfate, and W in ammonium metatungstate was 44:48:4:4, resulting in the positive electrode material Li. 1.2 (Ni 0.325 Mn 0.615 Co 0.04 W 0.02 ) 0.8 O2.

[0089] Example 5

[0090] The method was followed according to Example 1, except that: in the first metal salt solution, the molar ratio of Ni in nickel sulfate, Mn in manganese sulfate, and Co in cobalt sulfate was 15:75:10; and in the second metal salt solution, the molar ratio of Ni in nickel sulfate, Mn in manganese sulfate, Co in cobalt sulfate, and W in ammonium metatungstate was 38:48:10:4, resulting in the positive electrode material Li. 1.2 (Ni 0.265 Mn 0.615 Co 0.1 W 0.02 ) 0.8 O2.

[0091] Example 6

[0092] The procedure was carried out according to Example 1, with the only difference being that the molar ratio of Ni in nickel sulfate, Mn in manganese sulfate, and W in ammonium metatungstate in the second metal salt solution was 45:45:10, resulting in the positive electrode material Li. 1.2 (Ni 0.35 Mn 0.6 W 0.05 ) 0.8 O2.

[0093] Example 7

[0094] The procedure was carried out according to Example 2, with the only difference being that tetrabutyl titanate was used instead of ammonium metatungstate, so that the molar ratio of Ni in nickel sulfate, Mn in manganese sulfate, and Ti in tetrabutyl titanate in the second metal salt solution was 32:64:4, thus obtaining the positive electrode material Li. 1.2 (Ni 0.285 Mn 0.695 Ti 0.02 ) 0.8 O2.

[0095] The obtained SEM images and cross-sectional EDS line scan images of the cathode material are as follows: Figure 5As shown, the scanning direction of the cross-sectional EDS line scan is as indicated by the arrow in the SEM image, specifically scanning from one side of the cathode material along its diameter to the other side. The particle size D of the cathode material is 10 μm, and the pore size d of the hollow structure is 2 μm. The Ni, Mn, and Ti elements in the cathode material exhibit a gradient distribution. From the outer surface to the inner surface of the cathode material, the proportion of Mn to the total molar amount of TM elements increases, while the proportion of Ni and Ti to the total molar amount of TM elements decreases. Conversely, from the inner surface to the outer surface, the proportion of Mn to the total molar amount of TM elements decreases, while the proportion of Ni and Ti to the total molar amount of TM elements increases. The molar amounts of transition metal elements and A elements at the hollow structure are 0; the elemental distribution at the hollow structure is omitted in the attached figure. The cathode materials prepared in Examples 1-6 and 8-13 show similar gradient trends in the content of transition metal elements and A elements.

[0096] Example 8

[0097] The procedure was carried out according to Example 2, with the only difference being that yttrium nitrate was used instead of ammonium metatungstate, so that the molar ratio of Ni in nickel sulfate, Mn in manganese sulfate, and Y in yttrium nitrate in the second metal salt solution was 32:64:4, thus obtaining the positive electrode material Li. 1.2 (Ni 0.285 Mn 0.695 Y 0.02 ) 0.8 O2.

[0098] Example 9

[0099] Prepare a 1 mol / L first metal salt solution, wherein the molar ratio of Ni in nickel sulfate to Mn in manganese sulfate is 25:75. Prepare a 1 mol / L second metal salt solution, wherein the molar ratio of Ni in nickel sulfate, Mn in manganese sulfate, and W in ammonium metatungstate is 48:48:4.

[0100] 0.5 L of the first metal salt solution was pumped into a continuously stirred reactor at a feed rate of 150 mL / h. At the same time, 1 mol / L sodium bicarbonate solution and 1.5 mol / L ammonia solution were pumped into the reactor at a feed rate of 150 mL / h. The reaction temperature was maintained at 40 °C, pH at 8, and the rotation speed at 1000 rpm. The reaction was protected under a nitrogen atmosphere.

[0101] After the first metal salt solution was pumped in, 0.5 L of the second metal salt solution was pumped into the continuously stirred reactor at a feed rate of 150 mL / h. At the same time, 2 mol / L sodium hydroxide solution and 1.8 mol / L ammonia solution were pumped into the reactor at a feed rate of 150 mL / h. The reaction temperature was maintained at 40 °C, pH at 10.5, and the rotation speed at 1000 rpm. The reaction was protected under a nitrogen atmosphere. After the second metal salt solution was pumped in, the mixture was aged for 4 h, then filtered, washed with water, and dried in an oven at 80 °C for 12 h to obtain the precursor.

[0102] A precursor and lithium hydroxide were mixed, wherein the molar ratio of TM element in the precursor to lithium element in the lithium source was 1:1, and a two-step calcination was performed in air. First, the temperature was increased to 400℃ at a heating rate of 1℃ / min and held for 4 h; then, the temperature was increased to 800℃ at a heating rate of 10℃ / min and held for 10 h. Finally, the mixture was cooled to room temperature to obtain the cathode material Li. 1.2 (Ni 0.365 Mn 0.615 W 0.02 ) 0.8 O2.

[0103] Example 10

[0104] Prepare a 4 mol / L first metal salt solution, wherein the molar ratio of Ni in nickel sulfate and Mn in manganese sulfate is 25:75. Prepare a 4 mol / L second metal salt solution, wherein the molar ratio of Ni in nickel sulfate, Mn in manganese sulfate and W in ammonium metatungstate is 48:48:4.

[0105] 0.5 L of the first metal salt solution was pumped into a continuously stirred reactor at a feed rate of 150 mL / h. At the same time, 4 mol / L sodium carbonate solution and 1.5 mol / L ammonia solution were pumped into the reactor at a feed rate of 150 mL / h. The reaction temperature was maintained at 60 °C, pH at 8, and the rotation speed at 1000 rpm. The reaction was protected under a nitrogen atmosphere.

[0106] After the first metal salt solution was pumped in, 0.5 L of the second metal salt solution was pumped into the continuously stirred reactor at a feed rate of 150 mL / h. At the same time, 8 mol / L sodium hydroxide solution and 2 mol / L ammonia solution were pumped into the reactor at a feed rate of 150 mL / h. The reaction temperature was maintained at 60 °C, pH at 12, and the rotation speed at 1000 rpm. The reaction was protected under a nitrogen atmosphere. After the second metal salt solution was pumped in, the mixture was aged for 12 h, then filtered, washed with water, and dried in an oven at 80 °C for 12 h to obtain the precursor.

[0107] A precursor and lithium hydroxide were mixed, wherein the molar ratio of TM element in the precursor to lithium element in the lithium source was 1:1.03, and a two-step calcination was performed in air. First, the temperature was increased to 600℃ at a heating rate of 6℃ / min and held for 6 h; then, the temperature was increased to 1000℃ at a heating rate of 5℃ / min and held for 16 h. Finally, the mixture was cooled to room temperature to obtain the cathode material Li. 1.2 (Ni 0.365 Mn 0.615 W 0.02 ) 0.8 O2.

[0108] Example 11

[0109] The procedure was followed according to Example 1, except that the molar ratio of TM element in the precursor to lithium element in the lithium source was 1:1.2, resulting in the cathode material Li. 1.2 (Ni 0.365 Mn 0.615 W 0.02 ) 0.8 O2.

[0110] Example 12

[0111] The procedure was carried out according to Example 1, except that: in the first metal salt solution, the molar ratio of Ni in nickel sulfate to Mn in manganese sulfate was 45:55; and in the second metal salt solution, the molar ratio of Ni in nickel sulfate, Mn in manganese sulfate, and W in ammonium metatungstate was 48:48:4, resulting in the positive electrode material Li. 1.2 (Ni 0.465 Mn 0.515 W 0.02 ) 0.8 O2.

[0112] Example 13

[0113] The procedure was carried out according to Example 1, except that: in the first metal salt solution, the molar ratio of Ni in nickel sulfate, Mn in manganese sulfate, and Co in cobalt sulfate was 15:75:10; and in the second metal salt solution, the molar ratio of Ni in nickel sulfate, Mn in manganese sulfate, Co in cobalt sulfate, and W in ammonium metatungstate was 20:66:10:4, resulting in the positive electrode material Li. 1.2 (Ni 0.175 Mn 0.705 Co 0.1 W 0.02 ) 0.8 O2.

[0114] Comparative Example 1

[0115] The procedure was carried out according to Example 1, with the only difference being that ammonium metatungstate was not added to the second metal salt solution, and the molar ratio of Ni in nickel sulfate to Mn in manganese sulfate was 50:50, resulting in the positive electrode material Li. 1.2 (Ni 0.375 Mn 0.625 ) 0.8 O2.

[0116] Comparative Example 2

[0117] The method of Example 1 was followed, with the only difference being that cobalt was used instead of nickel to eliminate nickel from the cathode material. Specifically, the molar ratio of Co in cobalt sulfate and Mn in manganese sulfate in the first metal salt solution was 25:75, and the molar ratio of Co in cobalt sulfate, Mn in manganese sulfate, and W in ammonium metatungstate in the second metal salt solution was 48:48:4, resulting in the cathode material Li. 1.2 (Co 0.365 Mn 0.615 W 0.02 ) 0.8 O2.

[0118] Comparative Example 3

[0119] The procedure was carried out according to Example 1, with the only difference being that the molar ratio of Ni in nickel sulfate and Mn in manganese sulfate in the first metal salt solution was 15:85, and the molar ratio of Ni in nickel sulfate, Mn in manganese sulfate, and W in ammonium metatungstate in the second metal salt solution was 16:80:4, resulting in the positive electrode material Li. 1.2 (Ni 0.155 Mn 0.825 W 0.02 ) 0.8 O2.

[0120] Comparative Example 4

[0121] The procedure was carried out according to Example 1, with the only difference being that the molar ratio of Ni in nickel sulfate, Mn in manganese sulfate, and W in ammonium metatungstate in the second metal salt solution was 40:40:20, resulting in the positive electrode material Li. 1.2 (Ni 0.325 Mn 0.575 W 0.1 ) 0.8 O2.

[0122] The cathode materials of Examples 1-13 have similar X-ray diffraction patterns, represented by the X-ray diffraction patterns of Examples 1, 2, and 7, such as... Figure 2As shown, the sharp diffraction peaks indicate that the cathode material has good crystallinity. The weak diffraction peaks between 2θ and 25° belong to the Li2MnO3 phase of the C2 / m space group, indicating the formation of a lithium-rich phase structure. In addition, the obvious splitting between the (108) peak and the (110) peak indicates that the material has a good layered structure.

[0123] Test Example 1

[0124] The positive electrode materials prepared in Examples 1-13 and Comparative Examples 1-4 were added to N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1 with acetylene black and polyvinylidene fluoride (PVDF). The mixture was ground and homogenized, coated onto aluminum foil, and vacuum dried to form a circular electrode. Dimethyl carbonate, diethyl carbonate, and ethyl carbonate were mixed in a volume ratio of 1:1:1 to prepare a mixed solvent. LiPF6 was dissolved in this mixed solvent to prepare a 1 mol / L electrolyte. In an argon glove box, lithium foil, porous polypropylene film Celgard 2400, and the aforementioned circular electrode were assembled together, and the electrolyte was added to obtain a CR2025 coin cell. The assembled battery was subjected to charge-discharge tests, with a charge-discharge cutoff voltage of 2-4.8V (1C = 250 mA·g). -1 ).

[0125] The test results are shown in Table 1.

[0126] Table 1 Electrochemical performance test results of cathode materials

[0127]

[0128] As shown in Table 1, the cathode material prepared by this invention exhibits excellent electrochemical performance. Compared to Example 1, Examples 2-3 altered the molar ratio of Ni and Mn elements in the metal salt solution. In Example 2, the molar fraction of Ni on the outer surface of the cathode material increased, while the molar fraction of Mn decreased, resulting in improved cycle performance and increased capacity. In Example 3, the molar fraction of Ni on the inner surface of the cathode material increased, while the molar fraction of Mn decreased, leading to improved rate performance. This indicates that the gradient distribution of transition metal elements within the cathode material has a certain influence on its electrochemical performance. Compared to Example 1, Example 6 altered the content of element A in the cathode material, resulting in excellent cycle performance, indicating that a higher element A content leads to more stable cycle performance. Compared to Example 2, Examples 7-8 altered the type of element A. The chemical bond strength between element A and oxygen increased from WO < Ti-O < YO, correspondingly increasing capacity retention. This indicates that a stronger chemical bond between the doped element A and oxygen results in greater cycle stability of the cathode material. Compared to Y, the relatively weaker bond strength of Ti and W provides less inhibition of lattice oxygen oxidation, resulting in higher specific capacity.

[0129] The cathode material prepared in Comparative Example 1 was not doped with element A, the cathode material prepared in Comparative Example 2 did not contain element Ni, the molar ratio of element Ni to element Mn in the first metal salt solution used in Comparative Example 3 exceeded the specified range, and the cathode material prepared in Comparative Example 4 contained a high content of element A. Compared with Comparative Examples 1-4, the examples showed better rate performance and cycle stability, indicating that the presence of element Ni and element A, as well as the content of element Li, element A, and the molar ratio of transition metals have an important influence on the electrochemical performance of cathode materials.

[0130] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A positive electrode material, characterized in that, The general formula for the cathode material is: Li (1+x) TM (1-x) O2, TM includes transition metal elements and element A. The transition metal elements include Ni, Mn, and Co. The element A is selected from any one of the cations Ti, V, Cr, Y, Zr, Nb, Mo, Ta, and W, and the oxidation state of A is ≥3. + The molar ratio of Ni, Mn, Co, and A in TM is y:z:t:1-yzt, 0 < x < 1, 0.475 ≤ z < 0.75, 0 ≤ t ≤ 0.1, 0.2375 ≤ y + t < 0.5, and 0.95 ≤ y + z + t < 1.

2. The cathode material according to claim 1, wherein, The cathode material is a hollow sphere. Based on the total molar amount of the TM elements, the total molar fraction of nickel and cobalt elements in the cathode material increases from the inner surface of the sphere to its outer surface. Based on the total molar amount of the TM element, the molar fraction of manganese in the cathode material decreases from the inner surface of the spherical shape towards its outer surface. Based on the total molar amount of the TM element, the molar fraction of element A in the cathode material tends to increase from the inner surface of the spherical shape towards its outer surface.

3. The cathode material according to claim 1 or 2, wherein, The particle size of the positive electrode material is D, which is 5-15 μm, and the pore size of the hollow structure inside the positive electrode material is d, where d:D is 1-2:

10.

4. A method for preparing a positive electrode material, wherein, The preparation method includes the following steps: (1) Prepare a first metal salt solution, the first metal salt solution including salts of transition metal elements, the transition metal elements including nickel, manganese and cobalt, mix the first metal salt solution, a first precipitant containing carbonate and an ammonia solution, and carry out a first step co-precipitation reaction to obtain the initial product. (2) Prepare a second metal salt solution, the second metal salt solution comprising a salt of a transition metal element and a salt of element A, wherein the transition metal element comprises nickel, manganese and cobalt, and element A is selected from any one of the cations of Ti, V, Cr, Y, Zr, Nb, Mo, Ta and W, and the oxidation state of A is greater than or equal to 3. + price; The second metal salt solution, the second precipitant containing hydroxide ions, and the ammonia solution are simultaneously added to the primary product to carry out the second co-precipitation reaction, followed by aging to obtain the precursor. (3) The lithium source and the precursor are calcined to obtain the cathode material.

5. The preparation method according to claim 4, wherein, The total concentration of nickel, manganese and cobalt in the first metal salt solution is 1-4 mol / L, and the molar ratio of nickel, manganese and cobalt is Y1:Z1:T1, wherein 15≤Y1<50, 50<Z1≤75, and 0≤T1≤10. And / or, the total concentration of nickel, manganese, cobalt and alumina in the second metal salt solution is 1-4 mol / L, and the molar ratio of nickel, manganese, cobalt and alumina is Y2:Z2:T2:P, wherein 15<Y2<50, 45≤Z2<75, 0≤T2≤10, and 0<P≤10.

6. The preparation method according to claim 4 or 5, wherein, The nickel element is derived from one or more of nickel nitrate, nickel sulfate, nickel chloride, and nickel acetate; The manganese element is derived from one or more of manganese nitrate, manganese sulfate, manganese chloride, and manganese acetate; The cobalt element is derived from one or more of cobalt nitrate, cobalt sulfate, cobalt chloride, and cobalt acetate; And / or, the cation of element A is selected from Ti. 4+ V 5+ Cr 6+ Y 3+ Zr 4+ 、Nb 5+ Mo 6+ Ta 5+ W 6+ Any one of them; And / or, the concentration of the first precipitant is 1-4 mol / L, and the first precipitant is preferably one or more of Na2CO3, NaHCO3, K2CO3, and KHCO3; And / or, the concentration of the second precipitant is 2-8 mol / L, and the second precipitant is preferably one or more of NaOH and KOH.

7. The preparation method according to any one of claims 3-6, wherein, The reaction temperature for both the first and second coprecipitation reactions is 40-60℃, and the pH is 8-12. And / or, the aging time is 4-12 hours; And / or, the molar ratio of TM element in the precursor to lithium element in the lithium source is 1:1-1.05; And / or, the lithium source is selected from one or more of lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, and lithium fluoride; And / or, the calcination includes a first calcination and a second calcination.

8. The preparation method according to claim 7, wherein, The temperature of the first calcination is 400-600℃, the time is 4-6h, and the heating rate of the first calcination is preferably 1-6℃ / min; And / or, the second calcination temperature is 800-1000℃, the time is 10-16h, and the heating rate of the second calcination is preferably 2-10℃ / min.

9. The preparation method according to any one of claims 3-8, wherein, The first and second coprecipitation reactions were carried out under inert gas protection.

10. A battery comprising the positive electrode material according to any one of claims 1-3 or the positive electrode material prepared by the preparation method according to any one of claims 4-9.

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