Positive electrode composite material, preparation method thereof and electrochemical device

Abstract

The invention relates to the technical field of batteries, particularly provides a positive electrode composite material, a preparation method thereof and an electrochemical device, and aims to solve the problem that the cycle performance and the safety performance of a lithium ion battery are reduced due to cracks generated among primary particles caused by non-uniform stress distribution of a positive electrode composite material in the prior art. In order to achieve the purpose, the positive electrode composite material comprises a positive electrode active material and a protective layer coating the surface of the positive electrode active material, the protective layer comprises a conductive polymer, the positive electrode active material is provided with secondary particles, and the positive electrode active material comprises a nickel-containing transition metal oxide, the molar percentage of the nickel element in the nickel-containing transition metal oxide is more than 60%. According to the present invention, with the existence of the secondary particles and the protection layer, the local stress of the positive electrode active material can be converted into the circular stress, the internal stress can be absorbed through the protection layer, and the corrosion of the electrolyte can be resisted so as to effectively improve the cycle performance and the safety performance of the lithium ion battery containing the positive electrode composite material.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and specifically provides a positive electrode composite material, a preparation method thereof, and an electrochemical device. Background Art

[0002] Due to the advantages of high energy density, long service life, and good performance in high and low temperature environments, the application scope of lithium-ion batteries is constantly expanding. Especially, their applications in energy storage systems and new energy vehicles are becoming more and more extensive. People are also investing more and more research efforts in improving the performance of lithium-ion batteries. It is expected that within the next ten years or more, lithium-ion batteries will still dominate the battery market with their relatively high energy density and long cycle life. As a key component in lithium-ion batteries, the positive electrode material not only determines the energy density of the battery but also accounts for a relatively large proportion of the battery manufacturing cost. Therefore, more and more research has been carried out on positive electrode materials. In view of the pursuit of high-endurance batteries by end-users, high-nickel positive electrode materials with high specific capacity have gradually come into view.

[0003] Common high-nickel positive electrode materials are usually obtained by sintering a hydroxide precursor and a lithium salt after blending. The hydroxide precursor is usually prepared by the co-precipitation method. The precursor obtained in this way is generally composed of randomly close-packed primary particles. The high-nickel positive electrode material obtained after subsequent sintering also has similar characteristics, and the primary particles inside it are in a randomly close-packed state. This leads to uneven stress generated by the contraction and expansion of the unit cell during the charge and discharge process, thereby causing local strain. The accumulation of local strain will cause cracks to appear at the grain boundaries between primary particles, increasing the side reactions of the electrolyte at the interface of the high-nickel positive electrode material, leading to interface deterioration, and ultimately resulting in a decline in the cycle performance and safety performance of lithium-ion batteries.

[0004] Correspondingly, a new technical solution is needed in this field to solve the above problems. Summary of the Invention

[0005] The present invention aims to solve the above technical problems, that is, to solve the problem that the cycle performance and safety performance of lithium-ion batteries decline due to uneven stress distribution in the positive electrode composite material in the prior art, resulting in cracks between primary particles.

[0006] In a first aspect, the present invention provides a positive electrode composite material, which includes a positive electrode active material and a protective layer coated on the surface of the positive electrode active material. The protective layer includes a conductive polymer. The positive electrode active material has secondary particles. The positive electrode active material includes a nickel-containing transition metal oxide, and in the nickel-containing transition metal oxide, the molar percentage of nickel element is more than 60%.

[0007] In the optional technical solution of the above positive electrode composite material, the secondary particles include spherical particles formed by the oriented arrangement of radial primary particles.

[0008] In the case of adopting the above technical solution, during the charge and discharge processes, since the positive electrode active material has secondary particles, which are spherical particles formed by the oriented arrangement of radial primary particles, through these secondary particles, the local stress generated during the contraction and expansion of the unit cell can be transformed into circular stress, enabling the positive electrode active material to expand and contract uniformly along the radial direction of the sphere. In this way, cracks can be avoided at the grain boundaries between the primary particles, reducing the generation of internal cracks. At the same time, since the surface of the positive electrode active material is coated with a protective layer, that is, the surface of the secondary particles is coated with a protective layer, this protective layer can resist the erosion of substances in the electrolyte (such as hydrofluoric acid, etc.), ensuring the stability of the positive electrode active material. Moreover, the conductive polymer constituting the protective layer can undergo corresponding deformation when the positive electrode active material expands and contracts, absorbing part of the internal stress generated by the positive electrode active material. In this way, even if the lithium-ion battery is charged and discharged repeatedly, cracks will not occur between the secondary particles. Thus, through the presence of the secondary particles and the protective layer, the stability and cycling performance of the positive electrode composite material can be effectively improved, enabling the lithium-ion battery with this positive electrode composite material to have good cycling performance and high safety performance.

[0009] In the optional technical solution of the above positive electrode composite material, the ratio of the length of the radial primary particles to the maximum width of the radial primary particles is greater than 2.5.

[0010] In the optional technical solution of the above positive electrode composite material, the conductive polymer is any one of poly(3,4-ethylenedioxythiophene), a mixture of polyethylene glycol and polyaniline, and aluminum polyethylene glycolate.

[0011] The protective layer formed on the surface of the positive electrode active material by using the above conductive polymers has a certain deformation ability. When the positive electrode active material expands and contracts, the protective layer can undergo corresponding deformation to absorb the internal stress of the positive electrode active material. Through this protective layer, the erosion of the electrolyte can be resisted to ensure the stability of the positive electrode active material, and this protective layer does not hinder the conduction of lithium ions. Thus, while ensuring the battery performance of the lithium-ion battery, the cycling performance and safety performance of the lithium-ion battery can be improved.

[0012] In the optional technical solution of the above positive electrode composite material, the mass percentage of the protective layer to the positive electrode active material is 0.6% - 1.2%.

[0013] In the optional technical solution of the above-mentioned positive electrode composite material, the positive electrode active material further includes a doping element M, and the M is one or more of Mn, Al, W, and B. In the nickel-containing transition metal oxide, the molar percentage of the M element is 0% to 20%.

[0014] Second, the present invention also provides a preparation method for preparing the positive electrode composite material described in any one of the foregoing solutions, including the following steps:

[0015] Step 1: Obtain a positive electrode active material having secondary particles;

[0016] Step 2: Form a protective layer on the surface of the positive electrode active material to obtain the positive electrode composite material, and the protective layer includes a conductive polymer.

[0017] In the optional technical solution of the above preparation method, Step 2 includes forming the protective layer on the surface of the positive electrode active material by using a chemical vapor deposition method for a conductive polymer monomer under a first condition.

[0018] In the optional technical solution of the above preparation method, the reaction pressure of the first reaction condition is 30 Pa to 50 Pa; and / or

[0019] The reaction temperature of the first reaction condition is 85 °C to 150 °C; and / or

[0020] The reaction time of the first reaction condition is 20 min to 80 min.

[0021] In the optional technical solution of the above preparation method, Step 2 includes forming the protective layer on the surface of the positive electrode active material by using a liquid phase method for the conductive polymer under a second condition.

[0022] In the optional technical solution of the above preparation method, the second temperature of the second reaction condition is 110 °C to 130 °C; and / or

[0023] The second time of the second reaction condition is 10 h to 14 h.

[0024] In the optional technical solution of the above preparation method, Step 1 further includes:

[0025] In an inert atmosphere, through a coprecipitation method, reacting at a first pH value for a first time, and then reacting at a second pH value for a second time, and then preparing the positive electrode active material having secondary particles through sintering, water washing, drying, and demagnetization, wherein the first pH value is greater than the second pH value, and the first time is less than or equal to the second time.

[0026] Among them, the raw materials in the coprecipitation process include a nickel source and a cobalt source, or the raw materials in the coprecipitation process include a nickel source, a cobalt source, and a metal oxide containing a doping element M, where M is one or more of Mn, Al, W, and B.

[0027] In an alternative technical solution of the above preparation method, the first time is 3 h to 8 h; and / or

[0028] the second time is 27 h to 82 h; and / or

[0029] the sum of the first time and the second time is 35 h to 85 h.

[0030] It should be noted that this preparation method has all the technical effects of the foregoing cathode composite material, which will not be elaborated here.

[0031] In a third aspect, the present invention also provides an electrochemical device, and the electrochemical device includes the cathode composite material according to any one of the foregoing solutions.

[0032] It should be noted that this electrochemical device has all the technical effects of the foregoing cathode composite material, which will not be elaborated here. Solution 1. A cathode composite material, characterized in that the cathode composite material includes a cathode active material and a protective layer coated on the surface of the cathode active material, the protective layer includes a conductive polymer, the cathode active material has secondary particles, the cathode active material includes a nickel-containing transition metal oxide, and in the nickel-containing transition metal oxide, the molar percentage of nickel element is more than 60%. Solution 2. The cathode composite material according to Solution 1, characterized in that the secondary particles include spherical particles formed by the directional arrangement of radial primary particles. Solution 3. The cathode composite material according to Solution 2, characterized in that the ratio of the length of the radial primary particle to the maximum width of the radial primary particle is greater than 2.5. Solution 4. The cathode composite material according to Solution 1, characterized in that the conductive polymer is any one of poly(3,4-ethylenedioxythiophene), a mixture of polyethylene glycol and polyaniline, and aluminum polyethylene glycolate. Solution 5. The cathode composite material according to any one of Solutions 1 to 4, characterized in that the mass percentage of the protective layer to the cathode active material is 0.6% to 1.2%. Solution 6. The cathode composite material according to Solution 1, characterized in that the cathode active material further includes a doping element M, where M is one or more of Mn, Al, W, and B, and in the nickel-containing transition metal oxide, the molar percentage of M element is 0% to 20%. Solution 7. A preparation method for preparing the cathode composite material described in any one of Solutions 1 to 5 above, characterized by comprising the following steps: Step 1: Obtain a cathode active material having secondary particles; Step 2: Form a protective layer on the surface of the cathode active material to obtain the cathode composite material, and the protective layer includes a conductive polymer. Solution 8. The preparation method according to Solution 7, characterized in that Step 2 includes forming the protective layer on the surface of the cathode active material by using a chemical vapor deposition method for a conductive polymer monomer under a first reaction condition. Solution 9. The preparation method according to Solution 8, characterized in that the reaction pressure of the first reaction condition is 30 Pa to 50 Pa; and / or the reaction temperature of the first reaction condition is 85 °C to 150 °C; and / or the reaction time of the first reaction condition is 20 min to 80 min. Solution 10. The preparation method according to Solution 7, characterized in that Step 2 includes forming the protective layer on the surface of the cathode active material by using a liquid phase method for a conductive polymer under a second reaction condition. Solution 11. The preparation method according to Solution 10, characterized in that the reaction temperature of the second reaction condition is 110 °C to 130 °C; and / or the reaction time of the second reaction condition is 10 h to 14 h. Solution 12. The preparation method according to Solution 7, characterized in that Step 1 further includes: Under an inert atmosphere, react for a first time at a first pH value by a coprecipitation method, and then react for a second time at a second pH value, and then prepare the cathode active material having secondary particles through sintering, washing with water, drying, and demagnetization. Among them, the first pH value is greater than the second pH value, and the first time is less than or equal to the second time. Among them, the raw materials in the coprecipitation process include a nickel source and a cobalt source, or the raw materials in the coprecipitation process include a nickel source, a cobalt source, and a metal oxide containing a doping element M, and the M is one or more of Mn, Al, W, and B. Solution 13. The preparation method according to Solution 12, characterized in that the first time is 3 h to 8 h; and / or the second time is 27 h to 82 h; and / or the sum of the first time and the second time is 35 h to 85 h. Solution 14. An electrochemical device, characterized in that the electrochemical device comprises a positive electrode composite material as described in Solutions 1 to 6 above. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The preferred embodiments of the present invention will be described below with reference to the drawings, in which:

[0034] Figure 1 is a scanning electron microscope image of the positive electrode composite material of an embodiment of the present invention. DETAILED DESCRIPTION

[0035] The preferred embodiments of the present invention will be described below with reference to the drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principle of the present invention and are not intended to limit the protection scope of the present invention.

[0036] It should be noted that in the description of the present invention, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0037] Such as Figure 1As shown, the positive electrode composite material of the present invention includes a positive electrode active material and a protective layer, the protective layer is coated on the surface of the positive electrode active material, the protective layer includes a conductive polymer, and the positive electrode active material has secondary particles, which are spherical particles composed of radial primary particles arranged in a directional manner, that is, the protective layer is coated on the outer surface of the spherical secondary particles. The positive electrode active material includes a nickel-containing transition metal oxide, in which the molar percentage of nickel element is more than 60%. In other words, the positive electrode active material of the present invention is actually a high-nickel material, which has the characteristics of high specific capacity and low cost, and the positive electrode composite material prepared therefrom can also have the advantages of higher energy density and working voltage. During the charging and discharging process of the lithium-ion battery, due to the presence of secondary particles, the local stress generated when the unit cell shrinks and expands can be converted into circular stress, so that the positive electrode active material can expand and shrink uniformly along the radial direction of the sphere, so that cracks can be avoided at the grain boundaries between the primary particles. Furthermore, due to the presence of the protective layer, it can resist the erosion of substances in the electrolyte (such as hydrofluoric acid, etc.), and the protective layer can also deform accordingly with the expansion and contraction of the positive electrode active material, so as to absorb the internal stress of the positive electrode active material, so that the stability of the positive electrode active material can be better ensured by external resistance and internal absorption. Moreover, compared with primary particles, it is easier to form a protective layer on its surface, and only the protective layer needs to be coated on the outer surface of the spherical secondary particles to obtain a better internal stress absorption capacity and the ability to resist electrolyte erosion, which means that adding less conductive polymer can obtain a better effect without affecting the conduction of lithium ions. In this way, by setting the positive electrode active material with secondary particles and the protective layer, the stability and cycle performance of the positive electrode composite material can be effectively improved, so that the lithium ion battery with the positive electrode composite material can have good cycle performance and high safety performance.

[0038] It should be noted that the primary particles are single crystal particles (such as Figure 1 The secondary particles are polycrystalline particles (such as Figure 1 spherical particles shown in ). In this embodiment, "primary particles" refer to crystals within a scale range of several μm, without grain boundaries, and the crystallographic orientation of the crystals is basically consistent everywhere inside; "secondary particles" refer to a collection of primary particles of many oriented grains, and the interior of the secondary particles is based on a lattice-like periodic structure, but is isotropic. Obviously, the secondary particles may not be spherical particles, but other particles such as ellipsoidal shapes.

[0039] In a possible implementation, the ratio of the length of the radial primary particles to their maximum width is greater than 2.5. When observing from the outside to the inside of the secondary particles, the width of the radial primary particles gradually decreases, meaning that their widest position is at their ends. The primary particles with an aspect ratio greater than 2.5 are more conducive to the oriented arrangement to form stable spherical secondary particles, and such secondary particle structures are more stable.

[0040] It should be noted that the length of the primary particles is their dimension along the radial direction, and the width of the primary particles is their dimension in the direction perpendicular to the radial direction.

[0041] In a possible implementation, the conductive polymer is any one of poly(3,4-ethylenedioxythiophene), a mixture of polyethylene glycol and polyaniline, and aluminum polyethylene glycol. The protective layer formed by using these conductive polymers has a certain deformation ability. During the charge and discharge processes, when the positive electrode active material expands and contracts due to internal stress and deforms, the protective layer can deform accordingly to absorb the internal stress. Moreover, through this protective layer, the erosion of the electrolyte can be resisted, and at the same time, the conduction of lithium ions will not be hindered. Through such a setting method, while ensuring the battery performance of the lithium-ion battery, the cycle performance and safety performance of the lithium-ion battery can be improved.

[0042] It should be noted that the conductive polymer can also be other possible polymers such as a mixture of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid. On the premise of not deviating from the basic principle of this application, those skilled in the art can flexibly select the specific type of conductive polymer according to the specific application scenario, as long as the protective layer formed by it can resist the erosion of the electrolyte and does not hinder the conduction of lithium ions.

[0043] In a possible implementation, the mass percentage of the protective layer to the positive electrode active material is 0.6% - 1.2%. For example, the mass percentage of the protective layer to the positive electrode active material is 0.6%, 0.8%, 1.0%, 1.2%, etc. The protective layer within this range can fully absorb the internal stress of the positive electrode active material, better resist the erosion of the electrolyte to the positive electrode active material, does not hinder the conduction of lithium ions, and while ensuring good battery performance of the lithium-ion battery, can effectively improve the cycle performance and safety performance of the lithium-ion battery. Of course, the mass percentage of the protective layer to the positive electrode active material can also be other possible values such as 0.5%, 1.5%, 2.0%, etc.

[0044] In a possible implementation, the positive electrode active material further includes a doping element M, which can be one or more of Mn, Al, W, and B. For example, M is Mn, or Al, or W, or B, or Al + W, or W + B, etc. That is to say, in addition to the three conventional elements of Li, Ni, and Co, the positive electrode active material of the present invention also contains doping elements such as Mn, Al, W, and B. By adding the doping element M, it is possible to promote the primary particles formed in the positive electrode active material to maintain a radial morphology, ensure the stability of the spherical secondary particles, and thus be able to better transform the local strain during the contraction and expansion of the positive electrode active material during the charge and discharge processes into circular strain, uniformly contract and expand along the radial direction of the spherical secondary particles, and better avoid the generation of cracks inside the positive electrode active material, improving the stability of the positive electrode active material.

[0045] It should be noted that M can also be other possible elements such as Mg, Ca, Zr, Mo, Nb, Ta, etc. Without departing from the basic principle of the present application, those skilled in the art can flexibly select the specific type of the doping element M according to the specific application scenario, as long as the addition of the element M can promote the formation of more secondary particles in the positive electrode active material.

[0046] In a possible implementation, the present invention also provides a method for preparing the aforementioned positive electrode composite material, including the following steps:

[0047] Step 1: Obtain a positive electrode active material having secondary particles.

[0048] In Step 1, the positive electrode active material is usually prepared by co-precipitation and sintering. Specifically, first, in an inert atmosphere, through the co-precipitation method, reaction is carried out at a first pH value for a first time, and then at a second pH value for a second time. After sintering, washing, drying, and demagnetization, a positive electrode active material having secondary particles is prepared. Among them, the first pH value is greater than the second pH value, and the first time is less than or equal to the second time. That is to say, during the process of preparing the precursor by co-precipitation reaction, the pH value in the early stage of the reaction is higher than that in the later stage of the reaction. Under this condition, in the early stage of the co-precipitation reaction, the pH value is relatively high, the growth rate of the precursor crystal is slow, and it is mainly nucleation-based. In the later stage of the co-precipitation reaction, the pH value decreases, the growth rate of the precursor crystal accelerates, the whiskers of the generated precursor crystal are finer, and basically no new nuclei will be generated, and they extend along the nuclei formed in the early stage to form radial primary particles.

[0049] Among them, the range of the first time is 3 to 8 hours. For example, the first time is 3 hours, 5 hours, 6.5 hours, 8 hours, etc. The range of the second time is 27 hours to 82 hours. For example, the second time is 27 hours, 39 hours, 45 hours, 56 hours, 67 hours, 75 hours, 82 hours, etc. The range of the sum of the first time and the second time is 35 hours to 85 hours. For example, the sum of the first time and the second time is 35 hours, 47 hours, 58 hours, 65 hours, 72 hours, 85 hours, etc.

[0050] The positive electrode active material includes a nickel-containing transition metal oxide and a doping element M. For example, the nickel-containing transition metal oxide is composed of a nickel source and a cobalt source. During the coprecipitation process, a precipitating agent and a complexing agent are usually added. Through the precipitating agent and the complexing agent, nickel and cobalt in the nickel source and the cobalt source can be precipitated to form precursor crystals. Among them, the precipitating agent can be one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium oxalate, and the complexing agent can be one or more of ammonia water, sodium nitrilotriacetate, ethylenediaminetetraacetate, and diethylenetriaminepentaacetate. Preferably, the precipitating agent is a sodium hydroxide solution and the complexing agent is ammonia water.

[0051] The positive electrode active material further includes a doping element M, and the doping element M is one or more of Mn, Al, W, and B, etc. Since the doping difficulty will be different when the doping element M is different. During the actual operation process, the specific doping timing can be flexibly selected according to the physical and chemical properties of each doping element and the doping difficulty. The following combines two different doping timings to specifically illustrate the possible implementation methods for obtaining the positive electrode active material with secondary particles.

[0052] In a possible implementation, in an inert atmosphere, a nickel source, a cobalt source, and a compound containing a doping element M are mixed in proportion. After mixing, they are put into a reaction kettle, and a sodium hydroxide solution and ammonia water are added into the reaction kettle to carry out a coprecipitation reaction. In the early stage of the coprecipitation reaction, for example, within the first period of time such as 4 h, 5 h, 6 h, 8 h, etc. from the start of the coprecipitation reaction, the pH value of the mixed solution is adjusted to a relatively high first pH value, such as 12.1, 12.2, etc., by adjusting the dosage of ammonia water, so that the nickel source, the cobalt source, and the compound containing the doping element M carry out the coprecipitation reaction at a relatively high pH value. During this process, a large number of crystal nuclei of the precursor crystals are formed. In the later stage of the coprecipitation reaction, for example, after a period of time such as 4 h, 5 h, 6 h, etc. from the start of the coprecipitation reaction, the pH value of the mixed solution is adjusted to a relatively low second pH value, such as 11.8, 12.0, etc., by adjusting the dosage of ammonia water, so that the nickel source, the cobalt source, and the compound containing the doping element M carry out the coprecipitation reaction at a relatively low pH value. During this process, the growth rate of the precursor crystals becomes faster and the whiskers become longer, and they extend orderly on the surface of the crystal nuclei to form radial crystals, that is, radial primary particles. A large number of radial primary particles are arranged directionally to form spherical secondary particles. Then, it is aged in an aging kettle. After aging, through processes such as water washing, drying, and demagnetization, it is mixed with a lithium source and sintered in a tube furnace at 400 °C to 750 °C. After sintering, through processes such as water washing, drying, and demagnetization again, a positive electrode active material with secondary particles is obtained.

[0053] In another possible implementation, first, in an inert atmosphere, a nickel source and a cobalt source are mixed in proportion and then put into a reaction kettle. A sodium hydroxide solution and ammonia water are added to the reaction kettle to carry out a coprecipitation reaction. In the early stage of the coprecipitation reaction, for example, within the first period of time such as 4 h, 5 h, 6 h, 8 h, etc. after the start of the coprecipitation reaction, the pH value of the mixed solution is adjusted to a relatively high first pH value, such as 12.1, 12.2, etc., by adjusting the dosage of ammonia water, so that the nickel source and the cobalt source carry out the coprecipitation reaction at a relatively high pH value. During this process, a large number of crystal nuclei of the precursor crystals are formed. In the later stage of the coprecipitation reaction, for example, after 4 h, 5 h, 6 h, etc. of the start of the coprecipitation reaction, the pH value of the mixed solution is adjusted to a relatively low second pH value, such as 11.8, 12.0, etc., by adjusting the dosage of ammonia water, so that the nickel source and the cobalt source carry out the coprecipitation reaction at a relatively low pH value. During this process, the growth rate of the precursor crystals becomes faster and the whiskers become longer, and they extend orderly on the surface of the crystal nuclei to form radially arranged crystals, that is, radially arranged primary particles. A large number of radially arranged primary particles are arranged directionally to form spherical secondary particles. Then it is aged in an aging kettle. After aging, through water washing, drying, and demagnetization processes, it is mixed with a lithium source and a compound containing a doping element M, and sintered in a tubular furnace at 400 °C to 750 °C. After sintering, through water washing, drying, and demagnetization processes again, a positive electrode active material with secondary particles is obtained.

[0054] During the process of preparing the positive electrode active material by the above two preparation methods, by controlling the pH values in the early and later stages of the coprecipitation reaction, making the pH value in the early stage of the reaction greater than that in the later stage of the reaction, and controlling the growth rate of the crystal nuclei of the precursor crystals, so that radially arranged primary particles can be formed during the coprecipitation reaction, and then directionally arranged to form spherical secondary particles. At the same time, a doping element M is also added, and through different doping methods, the doping element M can be evenly distributed in the positive electrode active material. During sintering, the doping element M can reduce the surface energy of the layered material (003) in the positive electrode active material, and can promote more (003) planes to be exposed during the crystal growth process, so that the primary particles of the layered material are formed into a radially arranged structure, and the side surface of this radially arranged structure is mainly the (003) plane. In this way, multiple primary particles of the layered structure can maintain the radially arranged structure to form stable spherical secondary particles, and a positive electrode active material with secondary particles is obtained.

[0055] It should be noted that in the above two preparation methods, during the coprecipitation reaction and sintering, those skilled in the art can flexibly determine the concentrations of various raw materials (cobalt source, nickel source, lithium source, compound containing doping element M, precipitant, complexing agent, etc.) according to specific requirements, as long as the positive electrode active material with secondary particles can be prepared. During sintering, the initial temperature in the tubular reaction furnace can be 400°C to 550°C. After holding for 1 h to 3 h, it is heated to 700°C to 800°C and then held for 8 h to 15 h, and the heating rate is 1°C / min to 5°C / min. Of course, the sintering temperature, time, and heating rate can also be other values, and the present invention does not make specific limitations, as long as the positive electrode active material with secondary particles can be obtained after sintering.

[0056] It should be noted that the positive electrode active material may not contain doping elements, and spherical secondary particles formed by the oriented arrangement of radial primary particles can also be obtained by controlling the pH value in the early and late stages of the reaction.

[0057] It should be noted that the above nickel source can be selected from one or more of nickel sulfate, nickel nitrate, and nickel chloride, the cobalt source can be selected from one or more of cobalt sulfate, cobalt nitrate, and cobalt chloride, and the lithium source can be selected from one or more of lithium carbonate, lithium nitrate, and lithium hydroxide. Without departing from the basic principle of the present application, those skilled in the art can flexibly select the specific types of nickel source, cobalt source, precipitant, complexing agent, and lithium source according to specific application scenarios, as long as the positive electrode active material with secondary particles can be prepared based on these raw materials.

[0058] Step 2: Form a protective layer on the surface of the positive electrode active material to obtain a positive electrode composite material, and the protective layer includes a conductive polymer.

[0059] In Step 2, since the conductive polymer monomers are different, due to the physical and chemical properties of each conductive polymer, the specific methods and reaction conditions for forming the protective layer on the surface of the positive electrode active material are also different.

[0060] In a possible implementation manner, the conductive polymer monomer can be formed into a protective layer on the surface of the positive electrode active material by chemical vapor deposition under the first conditions. The reaction pressure of the first reaction conditions is an absolute pressure of 30 Pa to 50 Pa, the reaction temperature is 85°C to 150°C, and the reaction time is 20 min to 80 min.

[0061] Taking the conductive polymer as poly(3,4-ethylenedioxythiophene) as an example, in this case, the positive electrode active material obtained in the above Step 1 is placed in a rotary oxidative chemical vapor deposition apparatus, and the polymer monomer 3,4-ethylenedioxythiophene vapor is passed at a flow rate of 2 cm 3 / min, and vanadium oxychloride vapor is passed at a flow rate of 0.25 cm 3The flow rate of / min is introduced into the generation device, and the generation device rotates at a speed of 140 rpm. Under the first reaction conditions, for example, the reaction pressure is an absolute pressure of 40 Pa, the reaction temperature is 90 °C, and the reaction time is 70 min, a 25-nm-thick poly(3,4-ethylenedioxythiophene) can grow on the surface of the positive electrode active material, thus forming a protective layer composed of poly(3,4-ethylenedioxythiophene) on the surface of the positive electrode active material.

[0062] It should be noted that when the conductive polymer is poly(3,4-ethylenedioxythiophene), the rotation speed of the rotary oxidative chemical vapor deposition generation device can be any value in the range of 140 rpm - 160 rpm, and the flow rate of the polymer monomer 3,4-ethylenedioxythiophene vapor entering the generation device can be 1.5 cm 3 / min - 3.5 cm 3 / min, and the flow rate of vanadyl trichloride vapor entering the generation device can be 0.2 cm 3 / min - 0.3 cm 3 / min. The reaction pressure of the first reaction conditions can also be any value in the range of absolute pressure 30 Pa - 50 Pa, the reaction temperature can also be any value in the range of 85 °C to 105 °C, and the reaction time can also be any value in the range of 60 - 80 min. Of course, the rotation speed of the generation device, the flow rate of the polymer monomer, the reaction pressure, the reaction temperature, and the reaction time can also be other possible values. Without departing from the basic principle of this application, those skilled in the art can flexibly determine the rotation speed of the generation device, the flow rates of the polymer monomer 3,4-ethylenedioxythiophene vapor and vanadyl trichloride vapor, and the specific values of the first reaction conditions according to the specific application scenario, as long as a protective layer composed of poly(3,4-ethylenedioxythiophene) can be formed on the surface of the positive electrode active material under the first reaction conditions by chemical vapor deposition.

[0063] Taking poly(aluminum glycolate) as the conductive polymer as an example, in this case, the positive electrode active material prepared in the above step 1 is placed in the deposition reaction chamber and the positive electrode active material is in a fluidized state, and the reaction conditions in the reaction chamber are adjusted to the first reaction conditions, for example, the reaction pressure is an absolute pressure of 40 Pa and the reaction temperature is 135 °C. The ethylene glycol is preheated to 95 °C to obtain ethylene glycol vapor, and ethylene glycol vapor is sent into the reaction chamber for 0.03 s, and then purged with argon for 15 s. Using argon as the carrier gas, trimethylaluminum at room temperature is sent into the reaction chamber for 0.03 s, and after purging with argon for 15 s, ethylene glycol vapor - argon purging - trimethylaluminum feeding - argon purging is carried out again. After performing this 68 times, that is, after the reaction for about 33 min, a protective layer about 15 nm thick composed of poly(aluminum glycolate) can grow on the surface of the positive electrode active material, thus forming a protective layer composed of poly(aluminum glycolate) on the surface of the positive electrode active material.

[0064] It should be noted that the reaction pressure of the first reaction condition can also be any value between 30 Pa and 50 Pa in absolute pressure, and the reaction temperature can also be any value between 120 °C and 150 °C. Obviously, the specific number of repetitions of ethylene glycol vapor - argon purge - trimethylaluminum - argon purge can also be more times such as 70 times, 72 times, etc., or less times such as 65 times, 63 times, etc. Of course, the reaction pressure, reaction temperature, and the number of repetitions of ethylene glycol vapor - argon purge - trimethylaluminum - argon purge can also be other possible values. Without departing from the basic principle of this application, those skilled in the art can flexibly select according to the specific application scenario, as long as a protective layer composed of aluminum polyethylene glycol can be formed on the surface of the positive electrode active material under the first reaction condition by chemical vapor deposition.

[0065] It should be noted that other conductive polymers can also form a protective layer on the surface of the positive electrode active material under the first reaction condition by chemical vapor deposition. Obviously, the equipment for chemical vapor deposition treatment can also be other types of chemical vapor deposition devices. Those skilled in the art can flexibly select the specific type of conductive polymer and the specific type of chemical vapor deposition treatment equipment, as long as a protective layer can be formed on the surface of the positive electrode active material by chemical vapor deposition.

[0066] In a possible implementation manner, a conductive polymer can also be used to form a protective layer on the surface of the positive electrode active material under the second reaction condition by a liquid phase method. The reaction temperature of the second reaction condition is 110 °C to 130 °C, and the reaction time is 10 h to 14 h.

[0067] Taking the mixture of polyethylene glycol and polyaniline as the conductive polymer as an example, in this case, polyethylene glycol (with a molecular weight of 1500), polyaniline, and the positive electrode active material prepared in step 1 above are put into N - methylpyrrolidone according to a mass ratio of 1.5:1.5:10, stirred at a stirring rate of 200 rpm at 50 °C for 1 h to 2 h. After mixing evenly, the mixed solution is filtered and dried at 120 °C for 12 h, and a protective layer about 35 nm thick composed of a mixture of polyethylene glycol and polyaniline can be formed on the surface of the positive electrode active material, thus forming a protective layer composed of a mixture of polyethylene glycol and polyaniline on the surface of the positive electrode active material.

[0068] It should be noted that the mixing temperature can be any value between 40°C and 60°C, the stirring rate can also be any value between 180 rpm and 220 rpm, and the mixing time can also be any value between 1 h and 3 h. The reaction temperature of the second reaction condition can also be any value between 110°C and 130°C, and the reaction time can also be any value between 10 h and 14 h. Of course, the mixing temperature, stirring rate, reaction temperature, and reaction time can also be other possible values. Without departing from the basic principle of the present application, those skilled in the art can flexibly select according to the specific application scenario, as long as a protective layer composed of a mixture of polyethylene glycol and polyaniline can be formed on the surface of the positive electrode active material under this condition by the liquid phase method.

[0069] Obviously, other types of conductive polymers can also form a protective layer on the surface of the positive electrode active material under the second reaction condition by the liquid phase method.

[0070] It should be noted that the conductive polymer can obviously also form a protective layer on the surface of the positive electrode active material by other methods, such as the ordinary solid phase method, etc. The ordinary solid phase method is to mix the conductive polymer monomer and the positive electrode active material evenly and then calcine. Those skilled in the art can flexibly select the specific formation method according to the specific application scenario, as long as a protective layer with a certain deformation ability and capable of resisting the erosion of the electrolyte can be formed on the surface of the positive electrode active material.

[0071] The positive electrode composite material of the present application and its preparation method will be further elaborated below in combination with specific examples and comparative examples.

[0072] It should be noted that the drugs used in the following examples and comparative examples are all commercially available products. In order to avoid introducing other impurities into the positive electrode composite material, the raw materials used in the following examples and comparative examples, such as nickel sulfate, cobalt sulfate, manganese sulfate, sodium hydroxide, ammonia water, boron oxide, lithium hydroxide, aluminum hydroxide, tungsten sulfide, 3,4-ethylenedioxythiophene, vanadium oxychloride, polyethylene glycol, polyaniline, N-methylpyrrolidone, ethylene glycol, trimethylaluminum, are all battery-grade drugs, and the content of pure reagents in the drugs is greater than or equal to 99%.

[0073] Example 1

[0074] Preparation of the precursor (Ni 0.8 Co 0.1 Mn 0.1 )(OH)2:

[0075] The precursor material is prepared by the co-precipitation method. Prepare a mixed nickel-cobalt-manganese sulfate solution, a precipitant solution, and a complexing agent solution: Accurately weigh soluble nickel sulfate, cobalt sulfate, and manganese sulfate according to the molar ratio of nickel:cobalt:manganese of 80:10:10, add deionized water, and remove oxygen by passing nitrogen to obtain a 2 mol / L mixed nickel-cobalt-manganese salt solution; Add sodium hydroxide powder to deionized water to prepare a 5 mol / L sodium hydroxide precipitant solution; Dilute ammonia water to 9 mol / L to obtain a complexing agent solution;

[0076] Introduce 80% by volume of deionized water into the reaction kettle, start stirring, introduce the inert gas nitrogen, and successively flow the complexing agent solution and the precipitant solution into the reaction kettle under the environment of sufficient nitrogen aeration. In the early stage of the reaction, the pH value is controlled at 12.1 - 12.2, and the ammonia water concentration is controlled between 2.5 g / L and 2.6 g / L. During this process, the crystal nucleus growth rate of the precursor crystal is slow, and this process lasts for about 5 h. In the later stage of the reaction, the pH value is controlled at 11.8 - 12.0, and the ammonia water concentration is controlled between 2.2 g / L and 2.3 g / L. During this process, the crystal nucleus growth rate of the precursor crystal is fast, and this process lasts for about 60 h. After the particle D50 reaches 7.2 μm, make it overflow and leave the reaction kettle and pump it into the aging kettle for aging for 2 h, and then obtain the positive electrode precursor material (Ni 0.8 Co 0.1 Mn 0.1 )(OH)2 after washing, drying, and demagnetization processes.

[0077] Preparation of the first-fired positive electrode material NCM:

[0078] Fully mix the above-prepared positive electrode precursor material (Ni 0.8 Co 0.1 Mn 0.1 )(OH)2 with lithium hydroxide, where the molar ratio of the metal salt in the precursor to the amount of lithium is 1:1.03; After mixing evenly, load the mixture into a crucible, place it in a tubular furnace, heat it to 480 °C in an oxygen atmosphere, keep it warm for 2 h, and then raise the temperature to 700 °C and maintain it for 12 h. The heating rate is 2 °C / min in both cases. Then obtain the first-fired positive electrode material NCM after washing, drying, and demagnetization processes.

[0079] Preparation of the positive electrode composite material NCM:

[0080] Place the above-prepared first-fired positive electrode material NCM into a rotary oxidative chemical vapor deposition device, preheat the polymer monomer 3,4-ethylenedioxythiophene (EDOT) to 110 °C to form monomer vapor, and feed the monomer vapor and the oxidant vanadyl trichloride (VOCl3) vapor at 2 cm 3 / min and 0.25 cm 3Flow in at a rate of / min into the reaction device, set the rotation speed to 140 - 160 rpm, react at an absolute pressure of 40 Pa and 90 °C for 70 min, and grow a 25-nm-thick poly(3,4-ethylenedioxythiophene) (PEDOT) on the surface of the first-fired cathode material. The mass ratio of the corresponding coating is 0.9% wt to obtain the cathode composite material NCM prepared in this example.

[0082] Example 2

[0083] Precursor (Ni 0.89 Co 0.1 B 0.01 )(OH)2 preparation:

[0084] Prepare the precursor material by the co-precipitation method. Prepare a mixed solution of metal sulfates and boron oxide, a precipitant solution, and a complexing agent solution: Accurately weigh soluble nickel sulfate, cobalt sulfate, and boron oxide according to the molar ratio of nickel: cobalt: boron elements of 89:10:1, add deionized water, and remove oxygen by passing nitrogen to obtain a mixed solution. The concentration of metal ions in the mixed solution is 2 mol / L; Add sodium hydroxide powder to deionized water to prepare a 4 mol / L sodium hydroxide precipitant solution; Dilute ammonia water to 2.4 mol / L to obtain a complexing agent solution;

[0085] Introduce 80% volume of deionized water into the reaction kettle, start stirring, introduce the inert gas nitrogen, and successively flow the complexing agent solution and the precipitant solution into the reaction kettle under the environment of sufficient nitrogen aeration. In the early stage of the reaction, control the pH value at 12.1 - 12.2 and the ammonia concentration at 2.5 g / L - 2.6 g / L. During this process, the crystal nucleus growth rate of the precursor crystal is slow, and this process lasts about 5 h. In the later stage of the reaction, control the pH value at 11.8 - 12.0 and the ammonia concentration at 2.2 g / L - 2.3 g / L. During this process, the crystal nucleus growth rate of the precursor crystal is fast, and this process lasts about 55 h. After the particle D50 reaches 7.2 μm, make it overflow and leave the reaction kettle and pump it into the aging kettle for aging for 2 h, and then obtain the cathode precursor material (Ni 0.89 Co 0.1 B 0.01 )(OH)2 after washing with water, drying, and demagnetization processes.

[0086] Preparation of the first-fired cathode material NCB:

[0087] The cathode precursor material (Ni 0.89 Co 0.1 B 0.01)(OH)2 was fully mixed with lithium hydroxide, and the molar ratio of the transition metal to lithium in the precursor was 1:1.01; after mixing evenly, the mixture was loaded into a crucible and placed in a tube furnace. It was heated to 500 °C in a pure oxygen atmosphere and held for 1.5 h, and then heated to 730 °C and maintained for 10 h. The heating rate was 3 °C / min in both cases. After washing, drying, and demagnetization processes, the first-fired cathode material NCB was obtained.

[0088] Preparation of the cathode composite material NCB:

[0089] The first-fired cathode material NCB prepared above was placed into a rotary oxidative chemical vapor deposition apparatus. The polymer monomer 3,4-ethylenedioxythiophene (EDOT) was preheated to 110 °C to form monomer vapor. The monomer vapor and the oxidant vanadyl trichloride (VOCl3) vapor were respectively introduced into the reaction apparatus at a flow rate of 2 cm 3 / min and 0.25 cm 3 / min. The rotation speed was set at 140 - 160 rpm, and the reaction was carried out at an absolute pressure of 40 Pa and 90 °C for 70 min. A 25-nm-thick poly(3,4-ethylenedioxythiophene) (PEDOT) was grown on the surface of the first-fired cathode material to obtain the cathode composite material NCB prepared in this example. The mass ratio of the coating material to the cathode active material was 0.9%.

[0091] Example 3

[0092] Preparation of the precursor (Ni 0.89 Co 0.1 B 0.01 )(OH)2:

[0093] The precursor material was prepared by a co-precipitation method. Prepare a mixed solution of metal sulfates and boron oxide, a precipitant solution, and a complexing agent solution: Weigh soluble nickel sulfate, cobalt sulfate, and boron oxide accurately according to the molar ratio of nickel: cobalt: boron elements of 89:10:1, add deionized water, and remove oxygen by passing nitrogen to obtain a mixed solution. The concentration of metal ions in the mixed solution was 2 mol / L; sodium hydroxide powder was added to deionized water to prepare a 4-mol / L sodium hydroxide precipitant solution; ammonia water was diluted to 2.4 mol / L to obtain a complexing agent solution;

[0094] 80% by volume of deionized water is introduced into the reaction kettle, and stirring is started. Inert gas nitrogen is introduced. Under the environment of sufficient nitrogen aeration, the complexing agent solution and the precipitating agent solution are successively flowed into the reaction kettle. In the early stage of the reaction, the pH value is controlled at 12.1 - 12.2, and the ammonia concentration is controlled between 2.5 g / L and 2.6 g / L. In this process, the crystal nucleus growth rate of the precursor crystal is slow, and this process lasts for about 5 h. In the later stage of the reaction, the pH value is controlled at 11.8 - 12.0, and the ammonia concentration is controlled between 2.2 g / L and 2.3 g / L. In this process, the crystal nucleus growth rate of the precursor crystal is relatively fast, and this process lasts for about 55 h. After the particle D50 reaches 7.2 μm, it overflows from the reaction kettle and is pumped into the aging kettle for aging for 2 h, and then through water washing, drying, and demagnetization processes to obtain the cathode precursor material (Ni 0.89 Co 0.1 B 0.01 )(OH)2.

[0095] Preparation of the first-fired cathode material NCB:

[0096] The above-prepared cathode precursor material (Ni 0.89 Co 0.1 B 0.01 )(OH)2 is fully mixed with lithium hydroxide, and the molar ratio of the transition metal in the precursor to the molar amount of lithium is 1:1.01; after mixing evenly, the mixture is loaded into the crucible and placed in a tubular furnace. Under a pure oxygen atmosphere, it is heated to 500 °C and held for 1.5 h, and then raised to 730 °C and maintained for 10 h. The heating rate is 3 °C / min in both cases. After water washing, drying, and demagnetization processes, the first-fired cathode material NCB is obtained.

[0097] Preparation of the cathode composite material NCB:

[0098] The above-prepared first-fired cathode material NCB is placed into a rotary oxidative chemical vapor deposition device. The polymer monomer 3,4-ethylenedioxythiophene (EDOT) is preheated to 110 °C to form monomer vapor. The monomer vapor and the oxidant vanadyl trichloride (VOCl3) vapor are respectively introduced into the reaction device at a flow rate of 2 cm 3 / min and 0.25 cm 3 / min. The rotation speed is set to 140 - 160 rpm. The reaction is carried out at an absolute pressure of 40 Pa and 90 °C for 120 min. A 35-nm-thick poly(3,4-ethylenedioxythiophene) (PEDOT) is grown on the surface of the first-fired cathode material to obtain the cathode composite material NCB prepared in this example. The mass ratio of the coating substance to the cathode active material is 1.2%.

[0100] Example 4

[0101] Precursor (Ni 0.89 Co 0.1 B 0.01 Preparation of )(OH)2:

[0102] The precursor material is prepared by a coprecipitation method. A mixed solution of metal sulfate and boron oxide, a precipitant solution and a complexing agent solution are prepared: soluble nickel sulfate, cobalt sulfate and boron oxide are accurately weighed according to the molar ratio of nickel:cobalt:boron element of 89:10:1, deionized water is added and nitrogen is passed through to remove oxygen to obtain a mixed solution, and the concentration of metal ions in the mixed solution is 2 mol / L; sodium hydroxide powder is added to deionized water to prepare a 4 mol / L sodium hydroxide precipitant solution; ammonia water is diluted to 2.4 mol / L to obtain a complexing agent solution;

[0103] 80% volume of deionized water is introduced into the reactor, and stirring is started, and inert gas nitrogen is introduced. In an environment with sufficient nitrogen aeration, the complexing agent solution and the precipitant solution are successively flowed into the reactor. In the early stage of the reaction, the pH value is controlled at 12.1-12.2, and the ammonia concentration is controlled between 2.5g / L and 2.6g / L. During this process, the nucleus growth rate of the precursor crystal is slow, and this process lasts about 5h. In the later stage of the reaction, the pH value is controlled at 11.8-12.0, and the ammonia concentration is controlled between 2.2g / L and 2.3g / L. During this process, the nucleus growth rate of the precursor crystal is relatively fast, and this process lasts about 55h. After the D50 of the particles reaches 7.2μm, the particles are allowed to overflow from the reactor and are driven into the aging kettle for aging for 2h. After washing, drying, and demagnetization, the positive electrode precursor material (Ni 0.89 Co 0.1 B 0.01 )(OH)2.

[0104] Preparation of sintered positive electrode material NCB:

[0105] The positive electrode precursor material (Ni 0.89 Co 0.1 B 0.01 )(OH)2 is fully mixed with lithium hydroxide, wherein the ratio of the amount of transition metal in the precursor to the amount of lithium is 1:1.01; after being evenly mixed, the mixture is loaded into a sagger, placed in a tubular furnace, heated to 500°C in a pure oxygen atmosphere, kept warm for 1.5 hours, and then heated to 730°C and maintained for 10 hours, wherein the heating rate is 3°C / min, and then after washing, drying, and demagnetization processes, a sintered positive electrode material NCB is obtained.

[0106] Preparation of positive electrode composite material NCB:

[0107] Place the prepared first-fired cathode material NCB into a rotary oxidative chemical vapor deposition apparatus. Preheat the polymer monomer 3,4-ethylenedioxythiophene (EDOT) to 110 °C to form monomer vapor. Feed the monomer vapor and the oxidant vanadyl trichloride (VOCl3) vapor into the reaction apparatus at flow rates of 2 cm 3 / min and 0.25 cm 3 / min respectively. Set the rotation speed to 140 - 160 rpm. React for 180 min at an absolute pressure of 40 Pa and 90 °C. A 40-nm-thick poly(3,4-ethylenedioxythiophene) (PEDOT) grows on the surface of the first-fired cathode material to obtain the cathode composite material NCB prepared in this example. The mass ratio of the coating substance to the cathode active material is 1.5%.

[0109] Example 5

[0110] Preparation of the precursor (Ni 0.89 Co 0.1 B 0.01 )(OH)2:

[0111] Prepare the precursor material by the co-precipitation method. Prepare a mixed solution of metal sulfates and boron oxide, a precipitant solution, and a complexing agent solution: Accurately weigh soluble nickel sulfate, cobalt sulfate, and boron oxide according to the molar ratio of nickel: cobalt: boron elements of 89:10:1. Add deionized water and pass nitrogen to remove oxygen to obtain a mixed solution. The concentration of metal ions in the mixed solution is 2 mol / L. Add sodium hydroxide powder to deionized water to prepare a 4 mol / L sodium hydroxide precipitant solution. Dilute ammonia water to 2.4 mol / L to obtain a complexing agent solution;

[0112] Inject 80% by volume of deionized water into the reaction kettle, start stirring, and introduce the inert gas nitrogen. Under the environment of sufficient nitrogen aeration, flow the complexing agent solution and the precipitant solution into the reaction kettle successively. In the early stage of the reaction, control the pH value at 12.1 - 12.2 and the ammonia concentration at 2.5 g / L - 2.6 g / L. During this process, the crystal nucleus growth rate of the precursor crystal is slow, and this process lasts for about 5 h. In the later stage of the reaction, control the pH value at 11.8 - 12.0 and the ammonia concentration at 2.2 g / L - 2.3 g / L. During this process, the crystal nucleus growth rate of the precursor crystal is relatively fast, and this process lasts for about 55 h. After the particle D50 reaches 7.2 μm, let it overflow and leave the reaction kettle and pump it into the aging kettle for aging for 2 h. Then, after washing, drying, and demagnetization processes, obtain the cathode precursor material (Ni 0.89 Co 0.1 B 0.01 )(OH)2.

[0113] Preparation of the first-fired cathode material NCB:

[0114] Mix the above-prepared cathode precursor material (Ni 0.89 Co 0.1 B 0.01 )(OH)₂ thoroughly with lithium hydroxide, where the molar ratio of the transition metal in the precursor to the lithium is 1:1.01; after mixing evenly, load the mixture into a crucible, place it in a tube furnace, heat it to 500 °C in a pure oxygen atmosphere, hold for 1.5 h, then raise the temperature to 730 °C and maintain for 10 h, with a heating rate of 3 °C / min in both cases. After washing with water, drying, and demagnetization processes, the first-fired cathode material NCB is obtained.

[0115] Preparation of the cathode composite material NCB:

[0116] Place the above-prepared first-fired cathode material NCB into a rotary oxidative chemical vapor deposition apparatus. Preheat the polymer monomer 3,4-ethylenedioxythiophene (EDOT) to 110 °C to form monomer vapor, and introduce the monomer vapor and the oxidant vanadyl trichloride (VOCl₃) vapor into the reaction apparatus at flow rates of 2 cm 3 / min and 0.25 cm 3 / min respectively. Set the rotation speed to 140 - 160 rpm, and react at an absolute pressure of 40 Pa and 90 °C for 40 min. A 10-nm-thick poly(3,4-ethylenedioxythiophene) (PEDOT) grows on the surface of the first-fired cathode material to obtain the cathode composite material NCB prepared in this example, and the mass ratio of the coating material to the cathode active material is 0.5%.

[0118] Example 6

[0119] Preparation of the precursor (Ni 0.89 Co 0.1 B 0.01 )(OH)₂:

[0120] Prepare the precursor material by the co-precipitation method. Prepare a mixed solution of metal sulfates and boron oxide, a precipitant solution, and a complexing agent solution: Accurately weigh soluble nickel sulfate, cobalt sulfate, and boron oxide according to the molar ratio of nickel: cobalt: boron elements of 89:10:1, add deionized water, and remove oxygen by passing nitrogen to obtain a mixed solution. The concentration of metal ions in the mixed solution is 2 mol / L; add sodium hydroxide powder to deionized water to prepare a 4 mol / L sodium hydroxide precipitant solution; dilute ammonia water to 2.4 mol / L to obtain a complexing agent solution;

[0121] 80% by volume of deionized water is introduced into the reaction kettle, and stirring is started. Inert gas nitrogen is introduced, and under the environment of sufficient nitrogen aeration, the complexing agent solution and the precipitant solution are successively flowed into the reaction kettle. In the early stage of the reaction, the pH value is controlled at 12.1 - 12.2, and the ammonia concentration is controlled between 2.5 g / L and 2.6 g / L. In this process, the crystal nucleus growth rate of the precursor crystal is slow, and this process lasts for about 5 h. In the later stage of the reaction, the pH value is controlled at 11.8 - 12.0, and the ammonia concentration is controlled between 2.2 g / L and 2.3 g / L. In this process, the crystal nucleus growth rate of the precursor crystal is relatively fast, and this process lasts for about 55 h. After the particle D50 reaches 7.2 μm, it overflows from the reaction kettle and is sent to the aging kettle for aging for 2 h, and then after washing, drying, and demagnetization processes, the positive electrode precursor material (Ni 0.89 Co 0.1 B 0.01 )(OH)2 is obtained.

[0122] Preparation of the first - fired positive electrode material NCB:

[0123] The positive electrode precursor material (Ni 0.89 Co 0.1 B 0.01 )(OH)2 prepared above is fully mixed with lithium hydroxide, and the molar ratio of the transition metal in the precursor to the molar amount of lithium is 1:1.01; after mixing evenly, the mixture is loaded into a crucible and placed in a tube furnace. It is heated to 500 °C in a pure oxygen atmosphere and held for 1.5 h, and then heated to 730 °C and maintained for 10 h. The heating rate is 3 °C / min in both cases. After washing, drying, and demagnetization processes, the first - fired positive electrode material NCB is obtained.

[0124] Preparation of the positive electrode composite material NCB:

[0125] 5 g of the first - fired positive electrode material NCB prepared above is physically dry - mixed with 0.3 g of the polymer monomer 3,4 - ethylenedioxythiophene (EDOT) and the oxidant vanadyl trichloride (VOCl3) mixture in a grinding jar to obtain the positive electrode composite material NCB coated by the solid - phase method, and the mass ratio of the coating material to the positive electrode active material is 1.2%.

[0127] Example 7

[0128] Preparation of the precursor (Ni 0.9 Co 0.1 )(OH)2:

[0129] This embodiment adopts a coprecipitation method to prepare the precursor material. Prepare a mixed solution of metal sulfate, a precipitant solution and a complexing agent solution: accurately weigh soluble nickel sulfate and cobalt sulfate according to a molar ratio of nickel:cobalt element of 90:10, add deionized water and pass nitrogen to remove oxygen to obtain a mixed solution, the concentration of metal ions in the mixed solution is 2 mol / L; add sodium hydroxide powder to deionized water to prepare a 4 mol / L sodium hydroxide precipitant solution; dilute ammonia water to 2.4 mol / L to obtain a complexing agent solution;

[0130] 80% volume of deionized water is introduced into the reactor, and stirring is started, and inert gas nitrogen is introduced. In an environment with sufficient nitrogen aeration, the complexing agent solution and the precipitant solution are successively flowed into the reactor. In the early stage of the reaction, the pH value is controlled at 12.1-12.2. During this process, the nucleus growth rate of the precursor crystal is slow, and the ammonia concentration is controlled between 2.5g / L and 2.6g / L. This process lasts about 5h. In the later stage of the reaction, the pH value is controlled at 11.8-12.0, and the ammonia concentration is controlled between 2.2g / L and 23g / L. During this process, the nucleus growth rate of the precursor crystal is faster, and this process lasts about 30h. After the D50 of the particles reaches 7.2μm, it overflows from the reactor and is poured into the aging kettle for aging for 2h. After washing, drying, and demagnetization, the positive electrode precursor material (Ni 0.9 Co 0.1 )(OH)2.

[0131] Preparation of the first sintered cathode material W-NCA:

[0132] The positive electrode precursor material (Ni 0.9 Co 0.1 )(OH)2 is fully mixed with lithium hydroxide, aluminum hydroxide and tungsten sulfide, and the molar ratio of each element is controlled to be Li:(Ni+Co+Al+W):Al:W=1.01:1:0.015:0.005; after being evenly mixed, the mixture is put into a sagger, placed in a tubular furnace, heated to 500℃ in a pure oxygen atmosphere, kept warm for 1.5h, and then heated to 730℃ and kept for 10h, wherein the heating rate is 4℃ / min, and then after washing, drying and demagnetization processes, a sintered positive electrode material 0.5mol%W-doped Li[Ni 0.885 Co 0.1 Al 0.015 ]O2(W-NCA).

[0133] Preparation of positive electrode composite material W-NCA:

[0134] The obtained first-fired cathode material W-NCA is placed into an atomic layer / molecular layer (ALD / MLD) deposition reaction chamber, equipped with a fluidization device to keep the first-fired cathode material W-NCA in a fluidized state for self-limiting molecular layer deposition reaction. The ethylene glycol (EG) precursor is preheated to 95 °C to obtain EG vapor, the trimethylaluminum (TMA) precursor is kept at room temperature, and argon is used as the carrier gas. One deposition reaction cycle is: EG precursor pulse for 0.03 s - argon purge for 15 s - TMA precursor pulse for 0.03 s - argon purge for 15 s, to undergo a self-limiting reaction to generate aluminum polyethylene glycolate. The absolute pressure in the reaction chamber is maintained at 40 Pa and the temperature is maintained at 135 °C. A total of 68 deposition reaction cycles are carried out in the reaction chamber to grow an aluminum polyethylene glycolate film about 15 nm thick on the surface of the first-fired cathode material, obtaining the cathode composite material W-NCA prepared in this example, and the mass ratio of the coating substance to the cathode active material is 0.6%.

[0136] Example 8

[0137] Preparation of the precursor (Ni 0.9 Co 0.1 )(OH)2:

[0138] In this example, a co-precipitation method is used to prepare the precursor material. Prepare a mixed solution of metal sulfates, a precipitant solution, and a complexing agent solution: Weigh soluble nickel sulfate and cobalt sulfate accurately according to the molar ratio of nickel to cobalt elements of 90:10, add deionized water, and remove oxygen by passing nitrogen to obtain a mixed solution. The concentration of metal ions in the mixed solution is 2 mol / L; Add sodium hydroxide powder to deionized water to prepare a 4 mol / L sodium hydroxide precipitant solution; Dilute ammonia water to 2.4 mol / L to obtain a complexing agent solution;

[0139] Introduce 80% by volume of deionized water into the reaction kettle, start stirring, introduce the inert gas nitrogen, and successively flow the complexing agent solution and the precipitant solution into the reaction kettle under the environment of sufficient nitrogen aeration. In the early stage of the reaction, the pH value is controlled at 12.1 - 12.2, and the ammonia water concentration is controlled between 2.5 g / L and 2.6 g / L. During this process, the crystal nucleus growth rate of the precursor crystal is slow, and this process lasts for about 5 h. In the later stage of the reaction, the pH value is controlled at 11.8 - 12.0, and the ammonia water concentration is controlled between 2.2 g / L and 2.3 g / L. During this process, the crystal nucleus growth rate of the precursor crystal is relatively fast, and this process lasts for about 30 h. After the particle D50 reaches 7.2 μm, it overflows from the reaction kettle and is pumped into an aging kettle for aging for 2 h, and then obtained the cathode precursor material (Ni 0.9 Co 0.1 )(OH)2 after washing with water, drying, and demagnetization processes.

[0140] Preparation of the first sintered cathode material W-NCA:

[0141] The positive electrode precursor material (Ni 0.9 Co 0.1 )(OH)2 is fully mixed with lithium hydroxide, aluminum hydroxide and tungsten sulfide, and the molar ratio of each element is controlled to be Li:(Ni+Co+Al+W):Al:W=1.01:1:0.015:0.005; after being evenly mixed, the mixture is put into a sagger, placed in a tubular furnace, heated to 500℃ in a pure oxygen atmosphere, kept warm for 1.5h, and then heated to 730℃ and kept for 10h, wherein the heating rate is 4℃ / min, and then after washing, drying and demagnetization processes, a sintered positive electrode material 0.5mol%W-doped Li[Ni 0.885 Co 0.1 Al 0.015 ]O2(W-NCA).

[0142] Preparation of positive electrode composite material W-NCA:

[0143] The above-prepared W-NCA cathode material is placed in an atomic layer / molecular layer (ALD / MLD) deposition reaction chamber, and a fluidizing device is provided to make the W-NCA cathode material in a fluidized state to perform a self-limiting molecular layer deposition reaction. The ethylene glycol (EG) precursor is preheated to 95°C to obtain EG vapor, the trimethylaluminum (TMA) precursor is kept at room temperature, and argon is used as a carrier gas. A deposition reaction cycle is: EG precursor pulse 0.03s-argon purge 15s-TMA precursor pulse 0.03s-argon purge 15s, so that a self-limiting reaction occurs to generate polyethylene glycol aluminum, the absolute pressure of the reaction chamber is maintained at 40Pa and the temperature is maintained at 135°C, and a total of 99 deposition reaction cycles are performed in the reaction chamber to grow a polyethylene glycol aluminum film of about 20nm thick on the surface of the sintered cathode material, and obtain the cathode composite material W-NCA prepared in this embodiment, and the coating material occupies 0.9% of the mass ratio of the cathode active material.

[0145] Example 9

[0146] Precursor (Ni 0.9 Co 0.1 Preparation of )(OH)2:

[0147] This embodiment adopts a coprecipitation method to prepare the precursor material. Prepare a mixed solution of metal sulfate, a precipitant solution and a complexing agent solution: accurately weigh soluble nickel sulfate and cobalt sulfate according to a molar ratio of nickel:cobalt element of 90:10, add deionized water and pass nitrogen to remove oxygen to obtain a mixed solution, the concentration of metal ions in the mixed solution is 2 mol / L; add sodium hydroxide powder to deionized water to prepare a 4 mol / L sodium hydroxide precipitant solution; dilute ammonia water to 2.4 mol / L to obtain a complexing agent solution;

[0148] 80% volume of deionized water is introduced into the reactor, and stirring is started, and inert gas nitrogen is introduced. In an environment with sufficient nitrogen aeration, the complexing agent solution and the precipitant solution are successively flowed into the reactor. In the early stage of the reaction, the pH value is controlled at 12.1-12.2, and the ammonia concentration is controlled between 2.5g / L and 2.6g / L. During this process, the nucleus growth rate of the precursor crystal is slow, and this process lasts about 5h. In the later stage of the reaction, the pH value is controlled at 11.8-12.0, and the ammonia concentration is controlled between 2.2g / L and 2.3g / L. During this process, the nucleus growth rate of the precursor crystal is relatively fast, and this process lasts about 30h. After the D50 of the particles reaches 7.2μm, the overflow is allowed to leave the reactor and is poured into the aging kettle for aging for 2h, and then the positive electrode precursor material (Ni 0.9 Co 0.1 )(OH)2.

[0149] Preparation of the first sintered cathode material W-NCA:

[0150] The positive electrode precursor material (Ni 0.9 Co 0.1 )(OH)2 is fully mixed with lithium hydroxide, aluminum hydroxide and tungsten sulfide, and the molar ratio of each element is controlled to be Li:(Ni+Co+Al+W):Al:W=1.01:1:0.015:0.005; after being evenly mixed, the mixture is put into a sagger, placed in a tubular furnace, heated to 500℃ in a pure oxygen atmosphere, kept warm for 1.5h, and then heated to 730℃ and kept for 10h, wherein the heating rate is 4℃ / min, and then after washing, drying and demagnetization processes, a sintered positive electrode material 0.5mol%W-doped Li[Ni 0.885 Co 0.1 Al 0.015 ]O2(W-NCA).

[0151] Preparation of positive electrode composite material W-NCA:

[0152] The as-prepared first-fired cathode material W-NCA was placed into an atomic layer / molecular layer (ALD / MLD) deposition reaction chamber, equipped with a fluidization device to keep the first-fired cathode material W-NCA in a fluidized state for self-limiting molecular layer deposition reaction. The ethylene glycol (EG) precursor was preheated to 95 °C to obtain EG vapor, the trimethylaluminum (TMA) precursor was kept at room temperature, and argon was used as the carrier gas. One deposition reaction cycle was: EG precursor pulse for 0.03 s - argon purge for 15 s - TMA precursor pulse for 0.03 s - argon purge for 15 s, to undergo a self-limiting reaction to generate aluminum polyethylene glycolate. The absolute pressure in the reaction chamber was maintained at 40 Pa and the temperature was maintained at 135 °C. A total of 150 deposition reaction cycles were carried out in the reaction chamber to grow an aluminum polyethylene glycolate film about 20 nm thick on the surface of the first-fired cathode material, obtaining the cathode composite material W-NCA prepared in this example. The mass ratio of the coating substance to the cathode active material was 1.4%.

[0154] Example 10

[0155] Precursor (Ni 0.89 Co 0.1 B 0.01 )(OH)2 Preparation:

[0156] The precursor material was prepared by a co-precipitation method. Prepare a mixed solution of metal sulfates and boron oxide, a precipitant solution, and a complexing agent solution: Weigh soluble nickel sulfate, cobalt sulfate, and boron oxide accurately according to the molar ratio of nickel: cobalt: boron elements of 89:10:1, add deionized water, and remove oxygen by passing nitrogen to obtain a mixed solution. The concentration of metal ions in the mixed solution was 2 mol / L; Add sodium hydroxide powder to deionized water to prepare a 4 mol / L sodium hydroxide precipitant solution; Dilute ammonia water to 2.4 mol / L to obtain a complexing agent solution;

[0157] 80% by volume of deionized water was introduced into the reaction kettle, and stirring was started. Inert gas nitrogen was introduced. Under the environment of sufficient nitrogen aeration, the complexing agent solution and the precipitant solution were successively introduced into the reaction kettle. In the early stage of the reaction, the pH value was controlled at 12.1 - 12.2, and the ammonia water concentration was controlled between 2.5 g / L - 2.6 g / L. During this process, the crystal nucleus growth rate of the precursor crystal was slow, and this process lasted about 5 h. In the later stage of the reaction, the pH value was controlled at 11.8 - 12.0, and the ammonia water concentration was controlled between 2.2 g / L - 2.3 g / L. During this process, the crystal nucleus growth rate of the precursor crystal was relatively fast, and this process lasted about 55 h. After the particle D50 reached 7.2 μm, it overflowed from the reaction kettle and was pumped into the aging kettle for aging for 2 h, and then obtained the cathode precursor material (Ni 0.89 Co 0.1 B0.01 )(OH)2.

[0158] Preparation of sintered positive electrode material NCB:

[0159] The positive electrode precursor material (Ni 0.89 Co 0.1 B 0.01 )(OH)2 is fully mixed with lithium hydroxide, wherein the ratio of the amount of transition metal in the precursor to the amount of lithium is 1:1.01; after being evenly mixed, the mixture is loaded into a sagger, placed in a tubular furnace, heated to 500°C in a pure oxygen atmosphere, kept warm for 1.5 hours, and then heated to 730°C and maintained for 10 hours, wherein the heating rate is 3°C / min, and then after washing, drying, and demagnetization processes, a sintered positive electrode material NCB is obtained.

[0160] Preparation of positive electrode composite material NCB:

[0161] The above-prepared one-fired positive electrode material NCB is placed in an atomic layer / molecular layer (ALD / MLD) deposition reaction chamber, and a fluidizing device is equipped to make the one-fired positive electrode material W-NCA in a fluidized state to perform a self-limiting molecular layer deposition reaction. The ethylene glycol (EG) precursor is preheated to 95°C to obtain EG vapor, the trimethylaluminum (TMA) precursor is kept at room temperature, and argon is used as a carrier gas. One deposition reaction cycle is: EG precursor pulse 0.03s-argon purge 15s-TMA precursor pulse 0.03s-argon purge 15s, so that a self-limiting reaction occurs to generate polyethylene glycol aluminum, the absolute pressure of the reaction chamber is maintained at 40Pa and the temperature is maintained at 135°C, and a total of 68 deposition reaction cycles are performed in the reaction chamber to grow a polyethylene glycol aluminum film of about 15nm thick on the surface of the one-fired positive electrode material, and obtain the positive electrode composite material NCB prepared in this embodiment, and the coating material occupies 0.6% of the mass ratio of the positive electrode active material.

[0163] Embodiment 11

[0164] Precursor (Ni 0.89 Co 0.1 B 0.01 Preparation of )(OH)2:

[0165] The precursor material is prepared by a coprecipitation method. A mixed solution of metal sulfate and boron oxide, a precipitant solution and a complexing agent solution are prepared: soluble nickel sulfate, cobalt sulfate and boron oxide are accurately weighed according to the molar ratio of nickel:cobalt:boron element of 89:10:1, deionized water is added and nitrogen is passed through to remove oxygen to obtain a mixed solution, and the concentration of metal ions in the mixed solution is 2 mol / L; sodium hydroxide powder is added to deionized water to prepare a 4 mol / L sodium hydroxide precipitant solution; ammonia water is diluted to 2.4 mol / L to obtain a complexing agent solution;

[0166] 80% volume of deionized water is introduced into the reactor, and stirring is started, and inert gas nitrogen is introduced. In an environment with sufficient nitrogen aeration, the complexing agent solution and the precipitant solution are successively flowed into the reactor. In the early stage of the reaction, the pH value is controlled at 12.1-12.2, and the ammonia concentration is controlled between 2.5g / L and 2.6g / L. During this process, the nucleus growth rate of the precursor crystal is slow, and this process lasts about 5h. In the later stage of the reaction, the pH value is controlled at 11.8-12.0, and the ammonia concentration is controlled between 2.2g / L and 2.3g / L. During this process, the nucleus growth rate of the precursor crystal is relatively fast, and this process lasts about 55h. After the D50 of the particles reaches 7.2μm, the particles are allowed to overflow from the reactor and are driven into the aging kettle for aging for 2h. After washing, drying, and demagnetization, the positive electrode precursor material (Ni 0.89 Co 0.1 B 0.01 )(OH)2.

[0167] Preparation of sintered positive electrode material NCB:

[0168] The positive electrode precursor material (Ni 0.89 Co 0.1 B 0.01 )(OH)2 is fully mixed with lithium hydroxide, wherein the ratio of the amount of transition metal in the precursor to the amount of lithium is 1:1.01; after being evenly mixed, the mixture is loaded into a sagger, placed in a tubular furnace, heated to 500°C in a pure oxygen atmosphere, kept warm for 1.5 hours, and then heated to 730°C and maintained for 10 hours, wherein the heating rate is 3°C / min, and then after washing, drying, and demagnetization processes, a sintered positive electrode material NCB is obtained.

[0169] Preparation of positive electrode composite material NCB:

[0170] Polyethylene glycol PEG (with a molecular weight of 1500), polyaniline PANI, and the above-prepared first-fired material NCB were added to N-methylpyrrolidone in a mass ratio of 1.5:1.5:10, and mixed at 50 °C at a stirring rate of 200 rpm for 1 h to 2 h. The mixed solution was filtered and dried at 120 °C for 12 h to form an amorphous and uniform mixture protective film of PEG and PANI with a thickness of about 35 nm on the surface of the first-fired cathode material. The mass ratio of the coating material to the cathode active material was 1.2%, and the cathode composite material NCB prepared in this example was obtained.

[0172] Example 12

[0173] Precursor (Ni 0.8 Co 0.1 Mn 0.1 )(OH)2 Preparation:

[0174] The precursor material was prepared by a co-precipitation method. A mixed nickel-cobalt-manganese sulfate solution, a precipitant solution, and a complexing agent solution were prepared: Soluble nickel sulfate, cobalt sulfate, and manganese sulfate were accurately weighed according to the molar ratio of nickel: cobalt: manganese of 80:10:10, and deionized water was added and nitrogen was passed through to remove oxygen to obtain a 2 mol / L mixed nickel-cobalt-manganese salt solution; Sodium hydroxide powder was added to deionized water to prepare a 5 mol / L sodium hydroxide precipitant solution; Ammonia water was diluted to 2.4 mol / L to obtain a complexing agent solution;

[0175] 80% by volume of deionized water was introduced into the reaction kettle, and stirring was started. Inert gas nitrogen was introduced. Under the environment of sufficient nitrogen aeration, the complexing agent solution and the precipitant solution were successively introduced into the reaction kettle. In the early stage of the reaction, the pH value was controlled at 12.1 - 12.2, and the ammonia water concentration was controlled between 2.5 g / L and 2.6 g / L. During this process, the crystal nucleus growth rate of the precursor crystal was slow, and this process lasted for about 5 h. In the later stage of the reaction, the pH value was controlled at 11.8 - 12.0, and the ammonia water concentration was controlled between 2.2 g / L and 2.3 g / L. During this process, the crystal nucleus growth rate of the precursor crystal was fast, and this process lasted for about 55 h. After the particle D50 reached 7.2 μm, it was overflowed from the reaction kettle and pumped into the aging kettle for aging for 2 h, and then obtained the cathode precursor material (Ni 0.8 Co 0.1 Mn 0.1 )(OH)2 after washing, drying, and demagnetization processes.

[0176] Preparation of the first-fired cathode material NCM:

[0177] The above-prepared cathode precursor material (Ni 0.8 Co 0.1 Mn 0.1)(OH)2 is fully mixed with lithium hydroxide, where the molar ratio of the metal salt in the precursor to the molar amount of lithium is 1:1.03; after mixing evenly, the mixture is loaded into a crucible and placed in a tubular furnace. It is heated to 480 °C in an oxygen atmosphere, held for 2 h, and then heated to 700 °C and maintained for 12 h. The heating rate is 2 °C / min in both cases. After washing, drying, and demagnetization processes, the first-fired cathode material NCM is obtained.

[0178] Preparation of the cathode composite material NCM:

[0179] Polyethylene glycol PEG (with a molecular weight of 1500), polyaniline PANI, and the above-prepared first-fired material NCM are added to N-methylpyrrolidone according to a mass ratio of 1.5:1.5:10, and mixed at a stirring rate of 200 rpm at 50 °C for 1 h to 2 h. The mixed solution is filtered and dried at 120 °C for 12 h to form an amorphous and uniform mixture protective film of PEG and PANI with a thickness of about 35 nm on the surface of the first-fired cathode material. The mass ratio of the coating substance to the cathode active material is 1.2%, and the cathode composite material NCM prepared in this example is obtained.

[0181] Comparative Example 1

[0182] Preparation of the precursor (Ni 0.9 Co 0.1 )(OH)2:

[0183] The precursor material is prepared by a co-precipitation method. Prepare a mixed solution of metal sulfates, a precipitant solution, and a complexing agent solution: Weigh soluble nickel sulfate and cobalt sulfate accurately according to the molar ratio of nickel to cobalt elements of 90:10, add deionized water, and remove oxygen by passing nitrogen to obtain a mixed solution. The concentration of metal ions in the mixed solution is 2 mol / L; Add sodium hydroxide powder to deionized water to prepare a 4 mol / L sodium hydroxide precipitant solution; Dilute ammonia water to 2.4 mol / L to obtain a complexing agent solution;

[0184] 80% by volume of deionized water is introduced into the reaction kettle, and stirring is started. Inert gas nitrogen is introduced. Under the environment of sufficient nitrogen aeration, the complexing agent solution and the precipitant solution are successively flowed into the reaction kettle. During the reaction process, the pH value is controlled at 12 ± 0.2, the ammonia water concentration is controlled between 2.2 g / L and 2.6 g / L, and the reaction duration is controlled at 35 h. After the reaction is completed, the generated precipitate overflows from the reaction kettle and is pumped into the aging kettle for aging for 2 h. After washing, drying, and demagnetization processes, the cathode precursor material (Ni 0.9 Co 0.1 )(OH)2 is obtained.

[0185] The above-prepared cathode precursor material (Ni0.9 Co 0.1 )(OH)2 is fully mixed with lithium hydroxide, where the molar ratio of the transition metal to lithium in the precursor is 1:1.01; after mixing evenly, the mixture is loaded into a crucible and placed in a tube furnace. It is heated to 500 °C in a pure oxygen atmosphere, held for 1.5 h, and then heated to 730 °C and maintained for 10 h. The heating rate is 3 °C / min in both cases. After washing, drying, and demagnetization processes, the un-doped and un-coated cathode material NC is obtained.

[0187] Comparative Example 2

[0188] Preparation of the precursor (Ni 0.9 Co 0.1 )(OH)2:

[0189] The precursor material is prepared by the co-precipitation method. Prepare a mixed solution of metal sulfates, a precipitant solution, and a complexing agent solution: Weigh soluble nickel sulfate and cobalt sulfate accurately according to the molar ratio of nickel: cobalt elements of 90:10, add deionized water, and remove oxygen by passing nitrogen to obtain a mixed solution. The concentration of metal ions in the mixed solution is 2 mol / L; Add sodium hydroxide powder to deionized water to prepare a 4 mol / L sodium hydroxide precipitant solution; Dilute ammonia water to 2.4 mol / L to obtain a complexing agent solution;

[0190] 80% by volume of deionized water is introduced into the reaction kettle, and stirring is started. Inert gas nitrogen is introduced. Under the environment of sufficient nitrogen aeration, the complexing agent solution and the precipitant solution are successively introduced into the reaction kettle. In the early stage of the reaction, the pH value is controlled at 12.1 - 12.2, and the ammonia water concentration is controlled between 2.5 g / L - 2.6 g / L. During this process, the crystal nucleus growth rate of the precursor crystal is slow, and this process lasts for about 5 h. In the later stage of the reaction, the pH value is controlled at 11.8 - 12.0, and the ammonia water concentration is controlled between 2.2 g / L - 2.3 g / L. During this process, the crystal nucleus growth rate of the precursor crystal is relatively fast, and this process lasts for about 30 h. After the particle D50 reaches 7.2 μm, it overflows from the reaction kettle and is pumped into the aging kettle for aging for 2 h. After washing, drying, and demagnetization processes, the cathode precursor material (Ni 0.9 Co 0.1 )(OH)2 is obtained.

[0191] The above-prepared cathode precursor material (Ni 0.9 Co 0.1(OH)2 was fully mixed with lithium hydroxide, where the molar ratio of transition metal to lithium in the precursor was 1:1.01; after uniform mixing, the mixture was loaded into a crucible and placed in a tubular furnace. It was heated to 500 °C in a pure oxygen atmosphere and held for 1.5 h, then further heated to 730 °C and maintained for 10 h, with a heating rate of 3 °C / min in both cases. After washing, drying, and demagnetization processes, the un-doped and un-coated cathode material NC was obtained.

[0193] Comparative Example 3

[0194] Precursor (Ni 0.89 Co 0.1 B 0.01 )(OH)2 preparation:

[0195] The precursor material was prepared by a co-precipitation method. A mixed solution of metal sulfates and boron oxide, a precipitant solution, and a complexing agent solution were prepared: soluble nickel sulfate, cobalt sulfate, and boron oxide were accurately weighed according to the molar ratio of nickel: cobalt: boron elements of 89:10:1, and deionized water was added. After purging oxygen with nitrogen, a mixed solution was obtained, and the concentration of metal ions in the mixed solution was 2 mol / L; sodium hydroxide powder was added to deionized water to prepare a 4 mol / L sodium hydroxide precipitant solution; ammonia water was diluted to 2.4 mol / L to obtain a complexing agent solution;

[0196] 80% by volume of deionized water was introduced into the reaction kettle, and stirring was started. Inert gas nitrogen was introduced. Under the environment of sufficient nitrogen aeration, the complexing agent solution and the precipitant solution were successively introduced into the reaction kettle. In the early stage of the reaction, the pH value was controlled at 12.1 - 12.2, and the ammonia water concentration was controlled between 2.5 g / L - 2.6 g / L. During this process, the crystal nucleus growth rate of the precursor crystal was slow, and this process lasted for about 5 h. In the later stage of the reaction, the pH value was controlled at 11.8 - 12.0, and the ammonia water concentration was controlled between 2.2 g / L - 2.3 g / L. During this process, the crystal nucleus growth rate of the precursor crystal was relatively fast, and this process lasted for about 55 h. After the particle D50 reached 7.2 μm, it overflowed from the reaction kettle and was pumped into the aging kettle for aging for 2 h. After washing, drying, and demagnetization processes, the cathode precursor material (Ni 0.89 Co 0.1 B 0.01 )(OH)2 was obtained.

[0197] Preparation of the first-fired cathode material NCB:

[0198] The above-prepared cathode precursor material (Ni 0.89 Co 0.1 B 0.01)(OH)2 is fully mixed with lithium hydroxide, wherein the ratio of the amount of transition metal in the precursor to the amount of lithium is 1:1.01; after being evenly mixed, the mixture is loaded into a sagger, placed in a tubular furnace, heated to 500°C in a pure oxygen atmosphere, kept warm for 1.5 hours, and then heated to 730°C and maintained for 10 hours, wherein the heating rate is 3°C / min, and then after water washing, drying, and demagnetization processes, a doped, uncoated, sintered positive electrode material NCB is obtained.

[0200] The positive electrode composite material, carbon black conductive agent (SP) and binder polyvinylidene fluoride (PVDF) prepared in the above Examples 1 to 12 and Comparative Examples 1 to 3 are mixed in a weight ratio of 98:1:1, and then 120% of the weight of the mixture is added as a solvent. N-methylpyrrolidone (NMP) is added as a solvent, and after sufficient mixing, a positive electrode slurry is prepared. The slurry is coated on an aluminum foil, and then rolled and cut to obtain a positive electrode sheet; the positive electrode sheet, PE separator, and negative electrode sheet (lithium sheet) are assembled into a battery in a stacking order from bottom to top and an electrolyte (1mol / L LiPF6 / EC:DEC:DMC (volume ratio 1:1:1)) is injected. EC is an ethylene carbonate solution, DEC is a diethyl carbonate solution, and DMC is a dimethyl carbonate solution. Package on a packaging machine to obtain a CR2025 button battery.

[0201] The button cell prepared above was tested for cycle capacity retention and 1C rate performance. The test results are shown in Table 1 below.

[0202] 1. Test method for cycle capacity retention rate

[0203] The assembled CR2025 button cell was placed in the Blue Electric electrochemical test system for button verification. The test was performed at a current of 1C (1C = 220mA / g), and the voltage test window was 2.5-4.3V. The button cell was first charged to 4.3V at a constant current of 1C, and then discharged to 2.5V at 1C to complete one cycle. The above procedure was repeated for 200 cycles to obtain the capacity cycle retention rate.

[0204] 2. Test method for 1C rate performance

[0205] The assembled button cell was tested for rate performance at different currents of 0.1C, 0.2C, 0.5C, and 1.0C (1C = 220 mA / g), and the test was cycled for 5 cycles at each current density. The specific capacity at 1.0C was the rate performance of 1.0C. Table 1

[0206] It can be seen from the test results of Examples 2 to 5 that the optimal mass percentage of the protective layer to the positive electrode active material is 0.6%-1.2%. Too high or too low will affect the cycle performance and safety performance of the lithium-ion battery. It can be seen from the test results of Comparative Examples 1 to 3 that by making the pH value in the early stage of the coprecipitation process higher than that in the later stage and adding the doping element B, the cycle performance and safety performance of the lithium-ion battery can be improved. This also shows that by adjusting the pH value and adding doping elements, the positive electrode active material can be promoted to form spherical secondary particles composed of radially arranged primary particles.

[0207] As can be seen from Table 1, the protective layers formed on the surface of the positive electrode active material by different doping elements M and different conductive polymers in different ways can effectively improve the cycle performance and safety performance of the lithium-ion battery.

[0208] It can also be seen from Table 1 that the cycle capacity retention rate and 1C rate performance of the battery prepared from the positive electrode composite material doped with element M and having a protective layer are significantly better than those of the battery prepared from the positive electrode composite material without adjusting the pH value of the coprecipitation process, without doping, and without setting a protective layer, and are better than those of the battery prepared from the positive electrode composite material that has adjusted the pH value of the coprecipitation process but without doping and without setting a protective layer, and are also better than those of the battery prepared from the positive electrode composite material that has adjusted the pH value of the coprecipitation process and doped but without setting a protective layer. This also shows that the present invention can effectively improve the cycle performance and safety performance of the lithium-ion battery by making the pH value in the early stage of coprecipitation higher than that in the later stage, doping element N in the positive electrode active material, and forming a protective layer on the surface of the positive electrode active material.

[0209] Although the various steps are described in the above order in the above embodiments, those skilled in the art can understand that in order to achieve the effects of this embodiment, different steps do not have to be executed in such an order. They can be executed simultaneously (in parallel) or in a reversed order, and these simple changes are all within the protection scope of this application.

[0210] So far, the technical solution of the present invention has been described in combination with the preferred embodiments shown in the drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the protection scope of the present invention.

Claims

1. A positive electrode composite material, characterized in that, The positive electrode composite material includes a positive electrode active material and a protective layer coated on the surface of the positive electrode active material. The protective layer includes a conductive polymer. The positive electrode active material has secondary particles. The positive electrode active material includes a nickel-containing transition metal oxide. In the nickel-containing transition metal oxide, the molar percentage of nickel element is more than 60%.

2. The positive electrode composite material according to claim 1, characterized in that, The secondary particles include spherical particles formed by the directional arrangement of radial primary particles.

3. The positive electrode composite material according to claim 2, characterized in that, The ratio of the length of the radial primary particle to the maximum width of the radial primary particle is greater than 2.

5.

4. The positive electrode composite material according to claim 1, characterized in that, The conductive polymer is any one of a mixture of poly(3,4-ethylenedioxythiophene), polyethylene glycol and polyaniline, and aluminum polyethylene glycol.

5. The positive electrode composite material according to any one of claims 1 to 4, characterized in that, The mass percentage of the protective layer to the positive electrode active material is 0.6% to 1.2%.

6. The positive electrode composite material according to claim 1, characterized in that, The positive electrode active material further includes a doping element M, and M is one or more of Mn, Al, W, and B. In the nickel-containing transition metal oxide, the molar percentage of M element is 0% to 20%.

7. A preparation method for preparing the positive electrode composite material according to any one of claims 1 to 6, characterized in that, It includes the following steps: Step 1: Obtain a positive electrode active material having secondary particles; Step 2: Form a protective layer on the surface of the positive electrode active material to obtain the positive electrode composite material. The protective layer includes a conductive polymer.

8. The preparation method according to claim 7, characterized in that, Step 2 includes forming the protective layer on the surface of the positive electrode active material by using a chemical vapor deposition method for a conductive polymer monomer under a first reaction condition.

9. The preparation method according to claim 8, characterized in that, The reaction pressure of the first reaction condition is 30 Pa to 50 Pa; and / or The reaction temperature of the first reaction condition is 85 °C to 150 °C; and / or The reaction time of the first reaction condition is 20 min to 80 min.

10. The preparation method according to claim 7, characterized in that, Step 2 includes forming the protective layer on the surface of the positive electrode active material by using a liquid phase method for a conductive polymer under a second reaction condition.

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