WO2020135512A1 - Positive active material precursor, preparation method therefor, positive active material, lithium ion secondary battery and apparatus - Google Patents

Abstract

A positive active material precursor, a preparation method therefor, a positive active material, a lithium ion secondary battery and an apparatus. The positive active material precursor comprises a secondary particle made by aggregating a plurality of primary particles, the secondary particle comprising an inner region and an outer region that coats an outer side of the inner region, wherein the density of the inner region is less than the density of the outer region, and the density of the outer region gradually increases from the inside to the outside.

Description

Positive electrode active material precursor, preparation method thereof, positive electrode active material, lithium ion secondary battery and device

Cross-reference of related applications

This application claims the priority of the Chinese patent application 201811594917.3 filed on December 25, 2018, entitled "Positive cathode active material precursor, its preparation method and positive electrode active material", the entire content of which is incorporated herein by reference .

Technical field

The present application belongs to the technical field of batteries, and specifically relates to a positive electrode active material precursor, a preparation method thereof, a positive electrode active material, a lithium ion secondary battery, and a device.

Background technique

The positive electrode active material has an important influence on the improvement of the energy density of the lithium ion battery. Among them, the high-nickel ternary cathode active material has a higher energy density, so it is expected to become the next-generation mainstream cathode active material for lithium ion batteries.

The performance of the high nickel ternary cathode active material is largely affected by the performance of the high nickel ternary cathode active material precursor. The cathode active material synthesized by the existing high nickel ternary cathode active material precursor, or it has a higher capacity, but the cycle performance is poor; or its cycle performance is relatively higher, but the capacity is lower; making the cathode active material It is difficult to have good comprehensive electrochemical performance, thereby reducing the comprehensive electrochemical performance of lithium ion batteries.

Summary of the invention

A first aspect of the present application provides a positive electrode active material precursor, which includes secondary particles aggregated from a plurality of primary particles, the secondary particles including an inner region and an outer region coated outside the inner region; wherein, the inner region The density of is smaller than the density of the outer area, and the density of the outer area gradually increases from the inside to the outside.

A second aspect of the present application provides a method for preparing a cathode active material precursor, which includes the following steps:

Provide mixed salt solution, precipitant solution, complexing agent solution and bottom solution, wherein the mixed salt solution contains the metal salt contained in the precursor of the positive electrode active material;

In the first-stage reaction step, the mixed salt solution, precipitant solution and complexing agent solution are added to the bottom liquid, and the first-stage co-precipitation reaction is carried out under the conditions of keeping the pH of the reaction solution and the concentration of the complexing agent unchanged, and more An initial particle formed by the aggregation of primary particles;

In the second-stage reaction step, continue to add the mixed salt solution, precipitant solution and complexing agent solution to the bottom liquid, and control the pH of the reaction solution to decrease linearly and/or the concentration of the complexing agent to increase linearly. Co-precipitation reaction to coat multiple primary particles on the outside of the initial particles to obtain a positive electrode active material precursor;

The positive electrode active material precursor includes an inner region and an outer region coated on the outer peripheral side of the inner region. The density of the inner region is smaller than the density of the outer region, and the density of the outer region gradually increases from the inside to the outside.

A third aspect of the present application provides a positive electrode active material, which is composed of a positive electrode active material precursor of the first aspect of the present application or a positive electrode active material precursor prepared by the preparation method of the second aspect of the present application and lithium.

A fourth aspect of the present application provides a lithium ion secondary battery, which includes a positive electrode tab, and the positive electrode tab includes the positive electrode active material of the third aspect of the present application.

A fifth aspect of the present application provides an apparatus including the lithium ion secondary battery of the fourth aspect of the present application.

The cathode active material precursor of the present application has a density in the inner region smaller than that in the outer region, and the density of the outer region gradually increases from the inside to the outside. The cathode active material adopting it can also inherit this characteristic, that is, the cathode active material The density of the inner part is smaller than the density of the outer part, and the density of the outer part gradually increases from the inside to the outside.

The high density of the positive electrode active material through the external part ensures its own high structural stability, reduces side reactions with the electrolyte, effectively suppresses gas production, and improves the cycle performance of the positive electrode active material. At the same time, the density of the outer part gradually decreases from the outside to the inside, and the inner part has a smaller density. This structural characteristic is beneficial to delithiation and lithium insertion of the positive electrode active material, and ensures that the positive electrode active material has a higher capacity. Moreover, the structural characteristics can also buffer the volume change of the positive electrode active material during charging and discharging, effectively suppress the cracking of the positive electrode active material due to volume expansion during charging and discharging, and thereby further improve the cycle of the positive electrode active material performance. Therefore, the use of the positive electrode active material precursor of the present application can enable the positive electrode active material to simultaneously take into account the higher first charge specific capacity, first discharge specific capacity, first coulombic efficiency, and cycle performance, thereby enabling the lithium ion secondary battery to take into account both High first charge specific capacity, first discharge specific capacity, first coulombic efficiency and cycle performance.

The device of the present application includes the lithium ion secondary battery provided by the present application, and therefore has at least the same advantages as the lithium ion secondary battery.

BRIEF DESCRIPTION

In order to more clearly explain the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, without paying any creative work, other drawings can also be obtained based on the drawings.

FIG. 1 is a schematic cross-sectional view of a positive electrode active material precursor according to an embodiment of the present application.

2 is a scanning electron microscope (SEM) image of a cross section of the positive electrode active material precursor provided in Example 1. FIG.

3a and 3b are SEM images of the outer surface of the cathode active material precursor provided in Example 1. FIG.

4 is an X-ray diffraction (XRD) pattern of the positive electrode active material precursor provided in Examples 1 to 3 and Comparative Examples 1 to 2. FIG.

5a and 5b are SEM images of the outer surface of the positive electrode active material provided in Example 1. FIG.

6 is a schematic diagram of a lithium ion secondary battery provided by an embodiment of the present application.

7 is a schematic diagram of a battery module provided by an embodiment of the present application.

8 is a schematic diagram of a battery pack provided by an embodiment of the present application.

9 is an exploded view of FIG. 8.

10 is a schematic diagram of an apparatus provided by an embodiment of the present application.

detailed description

In order to make the invention, technical solutions and beneficial technical effects of the present application clearer, the present application will be further described in detail in conjunction with the following embodiments. It should be understood that the embodiments described in this specification are only for explaining this application, not for limiting this application.

For simplicity, only a few numerical ranges are explicitly disclosed. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and likewise any upper limit can be combined with any other upper limit to form an unspecified range. In addition, although not explicitly stated, each point or single value between the end points of the range is included in the range. Thus, each point or single numerical value may be combined with any other point or single numerical value as its own lower limit or upper limit or with other lower or upper limits to form an unspecified range.

In the description of this article, it should be noted that, unless otherwise stated, "above" and "below" are inclusive of this number, "multiple" in "one or more" means two or more, "one or "Multiple" in "multiple" means two or more.

The above summary of the present application is not intended to describe each disclosed embodiment or every implementation of the present application. The following description more specifically exemplifies exemplary embodiments. In many places throughout the application, guidance is provided through a series of embodiments, which can be used in various combinations. In each instance, the list is only a representative group and should not be interpreted as an exhaustive list.

A first aspect of the present application provides a positive electrode active material precursor, as shown in FIGS. 1 and 2, the positive electrode active material precursor includes secondary particles formed by aggregating a plurality of primary particles, and the secondary particles include an internal area and a package The outer area covering the outer side of the inner area; wherein, the density of the inner area is smaller than that of the outer area, and the density of the outer area gradually increases from the inside to the outside.

Herein, "inner region" refers to a region extending a first preset distance d ₁ from the center of the secondary particles to the outer surface, and "outer region" refers to a second pre-extension extending from the outer surface of the secondary particles to the center region disposed a distance d _2, wherein the first predetermined distances d ₁ and the second predetermined distance d ₂ equal to the total sum of the radial distance between the center and the outer surface of the secondary particles. The primary particles in the outer area are denser than the primary particles in the inner area, and the tightness of the outer area from the center of the secondary particles to the outer surface gradually increases. Thus, the density of the inner area is smaller than the density of the outer area, and the outer The density of the area gradually increases from the inside to the outside. More preferably, the direction of the outer region from the center of the secondary particles to the outer surface includes more than two layers of primary particles, and in the two adjacent layers, the primary particles in the layer close to the outer surface of the secondary particles are arranged more closely than The primary particles in the layer in the center of the secondary particles are tightly arranged, and the outermost primary particle layer is tightly arranged. The arrangement of the primary particles in the secondary particles can be detected using instruments known in the art, such as a scanning electron microscope (such as Japanese Hitachi S-4800 type).

The density of the inner region of the cathode active material precursor of the present application is smaller than that of the outer region, and the density of the outer region gradually increases from the inside to the outside. The cathode active material synthesized by the same can also inherit this characteristic. The density of the inner part is smaller than the density of the outer part, and the density of the outer part gradually increases from the inside to the outside. Among them, the inner part of the positive electrode active material corresponds to the inner region of the positive electrode active material precursor, and the outer part of the positive electrode active material corresponds to the outer region of the positive electrode active material precursor.

The high density of the positive electrode active material through the external part ensures its own high structural stability, reduces side reactions with the electrolyte, effectively suppresses gas production, and improves the cycle performance of the positive electrode active material. At the same time, the density of the outer part gradually decreases from the outside to the inside, and the inner part has a smaller density. This structural characteristic is beneficial to delithiation and lithium insertion of the positive electrode active material, and ensures that the positive electrode active material has a higher capacity. Moreover, the structural characteristics can also buffer the volume change of the positive electrode active material during charging and discharging, effectively suppress the cracking of the positive electrode active material due to volume expansion during charging and discharging, and thereby further improve the cycle of the positive electrode active material performance. Therefore, the use of the positive electrode active material precursor of the present application can enable the positive electrode active material to simultaneously take into account the higher first charge specific capacity, first discharge specific capacity, first coulombic efficiency, and cycle performance, thereby enabling the lithium ion secondary battery to take into account both High first charge specific capacity, first discharge specific capacity, first coulombic efficiency and cycle performance.

In addition, compared with the positive electrode active material that is dense from the inside to the outside, because the positive electrode active material of the present application, the density of the outer part gradually decreases from the outside to the inside, and the inner part has a smaller density, shortening The migration path of lithium ions in the cathode active material is improved, which is beneficial to improve the kinetic performance and rate performance of the cathode active material, and then improve the kinetic performance and rate performance of the lithium ion secondary battery.

In some embodiments, a plurality of primary particles in the inner region of the positive electrode active material precursor are irregularly arranged to form a loose porous structure. The cathode active material synthesized by the cathode active material precursor having such an internal structure provides an environment conducive to the development of the capacity of the internal active material.

Multiple primary particles in the outer area are arranged in the radial direction of the secondary particles, and the density and order of the arrangement gradually increase from the inside to the outside. The cathode active material synthesized by the cathode active material precursor with this external structure has a more stable structure, which can not only prevent particles from cracking due to uneven structure during charging and discharging, but also effectively reduce the Side reactions can improve the performance stability of the positive electrode active material during the cycle. The cathode active material synthesized by the cathode active material precursor with this external structure is also more conducive to the deintercalation of lithium ions.

In some embodiments, the length and thickness of the primary particles in the outer region are greater than the length and thickness of the primary particles in the inner region, that is, the length of the primary particles in the outer region is greater than the length of the primary particles in the inner region, the outer region The thickness of the primary particles in is larger than the thickness of the primary particles in the inner region; and, in the outer region, the length and thickness of the primary particles from the inside to the outside are gradually increased. The cathode active material synthesized by the cathode active material precursor with this external structure is beneficial to delithiation and lithium insertion of the cathode active material, ensuring that the cathode active material has a higher capacity, and at the same time can improve the charging and charging of the cathode active material. Structural stability during discharge to prevent cracking and other problems.

In some embodiments, preferably, in the inner region, the thickness of the primary particles is 5 nm to 20 nm, the length of the primary particles is 50 nm to 100 nm, and the volume ratio of the primary particles in the inner region is 40% to 70%. The “volume ratio of primary particles in the inner region” refers to the percentage of the total volume of the primary particles in the inner region to the total volume of the inner region. This can provide a better internal environment for the capacity of the positive electrode active material, thereby further increasing the gram capacity of the positive electrode active material.

Preferably, in the outer region, the thickness of the primary particles is 10 nm to 200 nm, the length of the primary particles is 70 nm to 1400 nm, and the volume ratio of the primary particles in the outer region is 60% to 95%. "The volume ratio of primary particles in the outer region" refers to the percentage of the total volume of the primary particles in the outer region to the total volume of the outer region. In this way, the obtained positive electrode active material has a higher gram capacity, and further improves its cycle stability, so that the secondary battery has higher capacity performance and cycle performance.

Exemplary test methods for the thickness, length, and volume ratio of primary particles in the inner and outer regions of the secondary particles are as follows: First, cross-sections of the secondary particles are obtained by, for example, the fracturing method, the quenching method, or the ion polishing method. For a specific example of the split method, the material powder is placed between two glass slides, squeezed, and the particles crushed from the center of the secondary particles are selected for testing; then the internal area is tested by a field emission scanning electron microscope (such as ZEISS Sigma 300) 1. The morphology of the external area, obtain the SEM image, the test can refer to the standard JY/T010-1996; through the SEM image and length scale, measure the thickness and length of the primary particles in the internal area of the secondary particles and the external area. The volume ratio is the ratio of the projected area of the primary particles in the cross-sectional SEM image to the total projected area of the area. In some embodiments, the inner area is an area where primary particles are fine and sparse; the outer area is an area where the accumulation of primary particles begins to become dense to the outer surface of the secondary particles.

In some embodiments, as shown in FIG. 3, the thickness of the primary particles in the outer surface layer of the secondary particles is 20 nm to 200 nm, the length is 80 nm to 1400 nm, and the volume of the primary particles in the outer surface of the secondary particles is 90% ~95%. "Secondary particle outer surface layer" refers to the area distinguished by the outermost primary particles of the secondary particles, and is an area extending a third preset distance d ₃ from the outer surface of the secondary particles to the center, the third preset The distance d ₃ corresponds to the length of the primary particles in the outermost layer. The outer surface layer of the secondary particles makes the obtained positive electrode active material have higher structural stability, and the side reaction with the electrolyte is further reduced, thereby further improving the cycle performance.

The thickness, length and volume ratio of the primary particles in the outer surface layer of the secondary particles can be tested with reference to the test methods for the thickness, length and volume ratio of the primary particles in the inner and outer regions of the secondary particles.

In some embodiments, optionally, the morphology of the positive electrode active material precursor includes one or more of a sphere and a spheroid.

In some embodiments, the inner region is a sphere or a spheroid, and the radius is 0.1 μm to 3 μm. The radius of the inner area is equal to the first preset distance d ₁ . By making the radius of the inner region within the above range, it is advantageous for the positive electrode active material to have a high specific capacity.

The outer area is a spherical shell or a spherical shell, and the thickness is 1 μm to 9 μm. The thickness of the outer area is equal to the second preset distance d ₂ . By making the thickness of the outer region within the above range, it is advantageous to make the positive electrode active material have high structural stability and performance stability, thereby improving cycle performance.

In some embodiments, preferably, the ratio of the radius of the inner region to the radius of the secondary particles is 1%-75%. By making the ratio of the radius of the inner region to the radius of the secondary particles within the above range, the positive electrode active material has a higher specific capacity and cycle performance.

You can obtain the SEM image of the cross section of the particle broken from the center of the secondary particle according to the method described above; then measure the distance from the center of the internal area of the secondary particle to the edge of the internal area through the SEM image and the length scale, which is the internal area Radius; the distance from the edge of the inner area of the secondary particles to the outer surface of the secondary particles is the thickness of the outer area; the distance from the center of the inner area of the secondary particles to the outer surface of the secondary particles is the radius of the secondary particles. Among them, the center of the inner area is the geometric center of the projection of the inner area, and the edge of the inner area is the boundary where the particle accumulation begins to become dense. More precisely, you can test the values at different positions on the cross section (such as more than 3, and then 8 to 12), and take the average value.

In some embodiments, optionally, the morphology of the primary particles in the inner region of the positive electrode active material precursor is one or more of needles and flakes, and the morphology of the primary particles in the outer region is needles One or more of shape, spindle shape and lath shape.

In this context, the length of a particle or particle refers to the maximum size of the particle or particle, and the direction of extension of the maximum size is defined as the longitudinal direction. When the particle or particle is in the form of a sheet or lath, the thickness of the particle or particle refers to Is the largest dimension between two larger planes extending along its longitudinal direction; when the particle or particle is needle-shaped or spindle-shaped, the thickness of the particle or particle refers to the largest dimension in the direction perpendicular to its longitudinal direction. The morphology of the primary particles can be determined using instruments and methods known in the art, such as a scanning electron microscope (such as Hitachi S-4800 in Japan).

In some embodiments, the average particle diameter D _v 50 of the positive electrode active material precursor is preferably 3 μm to 20 μm, more preferably 5 μm to 18 μm, and particularly preferably 8 μm to 16 μm. D _v of the positive electrode active material precursor resulting D _v 50 is adapted so that the positive electrode active material 50 within an appropriate range, thereby enabling the positive electrode active material having high capacity and high g of lithium ions and electron transport properties, while The side reaction of the electrolyte on the surface of the positive electrode active material is reduced, so that the lithium ion secondary battery adopting it has higher capacity performance, kinetic performance and cycle performance.

The average particle size D _v 50 can be determined with reference to the standard GB/T 19077.1-2016 using a laser particle size analyzer (such as Malvern Master Size 3000). Among them, the physical definition of D _v 50 is the corresponding particle size when the cumulative volume distribution percentage of the material reaches 50%.

In some embodiments, the tap density of the positive electrode active material precursor is preferably 1.6 g/cm ³ to 2.3 g/cm ³ . The tap density of the positive electrode active material precursor is suitable for the positive electrode active material to obtain a higher tap density, thereby enabling the positive electrode tab to obtain a higher compact density, which can further improve the capacity performance of the lithium ion secondary battery .

The tap density can be tested using methods known in the art. For example, you can refer to the standard GB/T 5162-2006 and use a powder tap density tester (such as Dandong Baxter BT-301) for testing.

In some embodiments, optionally, the chemical formula of the positive electrode active material precursor is Ni _x Co _y M _1-xy (OH) ₂ , where 0.6<x<1, 0<y<1, 0.6<x+ y<1, M is Mn or Al. The high-nickel ternary cathode active material synthesized by the high-nickel ternary cathode active material precursor has a higher gram capacity, and a battery using the same can obtain a higher energy density.

In some embodiments, as shown in FIG. 4, the ratio of the intensity of the 001 crystal plane diffraction peak to the 101 crystal plane diffraction peak of the positive electrode active material precursor Ni _x Co _y M _1-xy (OH) ₂ is 0.9-1.4, It is preferably 1.0 to 1.2. The X-ray powder diffractometer (X'pert PRO) can be used to obtain the X-ray diffraction spectrum according to the general rule of X-ray diffraction analysis method JIS K0131-1996, and then the positive electrode active material can be obtained according to E=I(001)/I(101) The ratio E between the intensity of the 001 crystal plane diffraction peak and the 101 crystal plane diffraction peak of the precursor, where I(001) is the intensity of the 001 crystal plane diffraction peak and I(101) is the intensity of the 101 crystal plane diffraction peak. Among them, the 2θ angle corresponding to the 001 crystal plane is 17.8°-22.8°; the 2θ angle corresponding to the 101 crystal plane is 36.8°-42.0°.

The diffraction peak intensity ratio of the nickel-cobalt-manganese ternary positive electrode active material precursor is consistent with the standard diffraction peak intensity ratio of perfectly crystallized β-Ni(OH) ₂ , indicating that it has better preferred orientation and higher crystallinity. The positive electrode active material synthesized by using the positive electrode active material precursor with higher crystallinity in the outer layer has a more stable structure, which is conducive to improving the capacity development and cycle performance of the positive electrode active material.

Next, a method for preparing a positive electrode active material precursor provided by examples of the present application will be described. According to this preparation method, any one of the foregoing cathode active material precursors can be prepared.

The preparation methods of different positive electrode active material precursors are similar. The following uses a positive electrode active material precursor of the chemical formula Ni _x Co _y M _1-xy (OH) ₂ as an example for description. A method for preparing a positive electrode active material precursor provided by an embodiment of the present application includes the following steps:

S10. Provide a mixed salt solution, a precipitant solution, a complexing agent solution, and a bottom liquid. The mixed salt solution contains nickel salt, cobalt salt, and M salt, and the M salt is a manganese salt or an aluminum salt.

S20, the first-stage reaction step, adding the mixed salt solution, the precipitant solution and the complexing agent solution to the bottom liquid, and performing the first-stage co-precipitation reaction under the condition that the pH of the reaction solution and the concentration of the complexing agent remain unchanged. Multiple primary particles formed by primary particle aggregation are obtained.

S30, the second-stage reaction step, continue to add the mixed salt solution, the precipitant solution and the complexing agent solution to the bottom liquid, and control the pH of the reaction solution to decrease linearly and/or the concentration of the complexing agent to increase linearly. The secondary co-precipitation reaction allows multiple primary particles to be coated on the outside of the initial particles to obtain a positive electrode active material precursor.

In some embodiments, step S10 may include adding nickel salts, cobalt salts, and M salts to the solvent according to the stoichiometric ratio, and dispersing them uniformly to obtain a mixed salt solution.

The nickel salt may include one or more of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate, and preferably includes nickel sulfate. The cobalt salt may include one or more of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate, and preferably includes cobalt sulfate. The manganese salt may include one or more of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate, and preferably includes manganese sulfate. The aluminum salt may include one or more of aluminum sulfate, aluminum nitrate, aluminum chloride, aluminum oxalate, and aluminum acetate, and preferably includes aluminum sulfate. The solvent may include one or more of deionized water, methanol, ethanol, acetone, isopropanol, and n-hexanol, preferably deionized water.

In some embodiments, preferably, the concentration of the mixed salt solution is 0.1 mol/L to 2.5 mol/L, and more preferably 1.5 mol/L to 2.0 mol/L.

Step S10 may include adding a precipitant to the solvent and dispersing it uniformly to obtain a precipitant solution. Wherein, the precipitating agent may include one or more of LiOH, NaOH and KOH, and preferably includes NaOH. The solvent may include one or more of deionized water, methanol, ethanol, acetone, isopropanol, and n-hexanol, preferably deionized water.

In some embodiments, preferably, the concentration of the precipitant solution is 0.1 mol/L to 10.0 mol/L, more preferably 3 mol/L to 5 mol/L.

Step S10 may include adding a complexing agent to the solvent and dispersing it uniformly to obtain a complexing agent solution. Wherein, the complexing agent may include one or more of ammonia water, ammonium sulfate, ammonium nitrate, ammonium chloride, ammonium citrate, and disodium edetate (EDTA), preferably ammonia water. The solvent may include one or more of deionized water, methanol, ethanol, acetone, isopropanol, and n-hexanol, preferably deionized water.

In some embodiments, preferably, the concentration of the complexing agent solution is 3 mol/L to 14 mol/L, more preferably 5 mol/L to 10 mol/L.

Step S10 may include adding a complexing agent to the solvent and dispersing it uniformly to obtain a bottom solution with a certain pH value. Wherein, the complexing agent may include one or more of ammonia water, ammonium sulfate, ammonium nitrate, ammonium chloride, ammonium citrate, and disodium edetate (EDTA), preferably ammonia water. The solvent may include one or more of deionized water, methanol, ethanol, acetone, isopropanol, and n-hexanol, preferably deionized water. Preferably, the concentration of the complexing agent is 0.02 mol/L to 0.8 mol/L.

A base can be used to adjust the pH of the bottom liquid, wherein the base can be selected from one or more of LiOH, NaOH and KOH. The pH of the base solution is preferably 10.8 to 12.2.

In some embodiments, both the first-stage co-precipitation reaction and the second-stage co-precipitation reaction are performed under an inert gas (such as nitrogen, argon, helium, etc.) protective atmosphere and continuous stirring. The stirring speed may be 100 rpm to 800 rpm. The reaction temperature may be 30°C to 80°C. "Rpm" means revolution per minute, which represents the number of revolutions per minute of the stirring device.

During the reaction, the role of the precipitant is to provide hydroxides, which react with the metal ions in the mixed salt solution to form primary crystal grains (that is, the above-mentioned primary particles). Under a certain feed rate of mixed salt solution, by adjusting the feed rate of the precipitant to control the pH of the reaction solution, different numbers of primary grains can be formed, so as to realize the control of primary grain size, thickness, etc. The role of the complexing agent is to provide ammonium ions and complex with metal ions in the mixed salt solution. Controlling the concentration of the complexing agent in the reaction solution by adjusting the feed rate of the complexing agent can affect the growth rate of the primary crystal grains, the density and order of the primary crystal grain stack, etc. At the same time, there is an interaction between the precipitation agent and the complexing agent. By adjusting the pH of the reaction solution and/or the concentration of the complexing agent, the effect of affecting the number of primary crystals formed, the growth rate, the density of stacking and the degree of order can be achieved. Obtain the expected particle structure.

In the first-stage co-precipitation reaction in step S20, that is, at the initial stage of the reaction, the reaction process conditions are controlled to make it unfavorable for primary grain growth, and the first-stage co-precipitation reaction is carried out by keeping the reaction process conditions unchanged to obtain multiple primary The initial particles formed by the aggregation of the particles, that is, the inner region portion where the positive electrode active material precursor is obtained. After that, the second-stage co-precipitation reaction in step S30 is continued, and the generated primary crystal grains are coated on the outer side of the initial particles, wherein the thickness, length, stacking density, and density of the primary crystal grains are adjusted by slowly adjusting one or more process conditions. The order is gradually increased to form a cathode active material precursor having the structural characteristics described above.

In some embodiments, preferably, the above adjustment of one or more process conditions may be to control the pH of the reaction solution to decrease linearly, to control the concentration of the complexing agent of the reaction solution to increase linearly, or to control the reaction The pH of the solution decreased linearly and the concentration of the complexing agent increased linearly. Among them, the effect of adjusting the pH of the reaction solution and the concentration of the complexing agent at the same time is the best.

As an example, in step S20, the bottom liquid is added to the control crystallization reactor (the bottom liquid can also be directly prepared in the crystallization reactor), and the amount of the bottom liquid is preferably 1/5 to 4/ of the volume of the control crystallization reactor 5. More preferably 1/3 to 2/3. Under the protective atmosphere of inert gas (such as nitrogen, argon, helium, etc.), heat the controlled crystallization reaction kettle to 30 ℃ ~ 80 ℃, and stir at a speed of 100rpm ~ 800rpm, the mixed salt solution, precipitant solution and The complexing agent solution is added to the controlled crystallization reaction kettle at a certain flow rate, wherein the pH of the reaction solution is controlled to 10.8 to 11.8 at a certain mixed salt solution flow rate, and the concentration of the complexing agent is 0.02mol/L to 0.8mol/L , The reaction is carried out for a period of time until the particle size of the internal region of the cathode active material precursor is reached. After that, in step S30, maintaining other process conditions unchanged, the concentration of the complexing agent in the reaction solution is controlled to increase linearly at a rate of 0.005 mol/L/h to 0.02 mol/L/h, preferably 0.005 mol/L The rate from /h to 0.01mol/L/h increases linearly, and the reaction is continued for a period of time until the target particle size of the cathode active material precursor is reached and the reaction is stopped to obtain a cathode active material precursor.

As another example, in step S20, the bottom liquid is added to the controlled crystallization reactor (the bottom liquid can also be directly prepared in the crystallization reactor), and the amount of the bottom liquid is preferably 1/5 to 4 of the volume of the controlled crystallization reactor /5, more preferably 1/3 to 2/3. Under the protective atmosphere of inert gas (such as nitrogen, argon, helium, etc.), heat the controlled crystallization reaction kettle to 30 ℃ ~ 80 ℃, and stir at a speed of 100rpm ~ 800rpm, the mixed salt solution, precipitant solution and The complexing agent solution is added to the controlled crystallization reactor at a certain flow rate, wherein the pH of the reaction solution is controlled to be 11.7 to 12.2 at a certain mixed salt solution flow rate, and the concentration of the complexing agent is 0.2mol/L to 0.8mol/L , The reaction is carried out for a period of time until the particle size of the internal region of the cathode active material precursor is reached. After that, in step S30, maintaining other process conditions unchanged, the pH of the reaction solution is controlled to decrease linearly at a rate of 0.01h ^-1 to 0.05h ^-1 , preferably at a rate of 0.01h ^-1 to 0.03h ^-1 Linear decrease, continue the reaction for a period of time until the target particle size of the cathode active material precursor is reached, and then stop the reaction to obtain the cathode active material precursor.

As another example, in step S20, the bottom liquid is added to the control crystallization reaction kettle (the bottom liquid can also be directly prepared in the crystallization reaction kettle), and the amount of the bottom solution is preferably 1/5 to 4 of the volume of the control crystallization reaction kettle /5, more preferably 1/3 to 2/3. Under the protective atmosphere of inert gas (such as nitrogen, argon, helium, etc.), heat the controlled crystallization reaction kettle to 30 ℃ ~ 80 ℃, and stir at a speed of 100rpm ~ 800rpm, the mixed salt solution, precipitant solution and The complexing agent solution is added to the controlled crystallization reaction kettle in parallel flow at a certain flow rate, in which the pH of the reaction solution is controlled at a certain mixed salt solution flow rate of 10.8 to 12.2, and the concentration of the complexing agent is 0.02mol/L to 0.5mol/L , The reaction is carried out for a period of time until the particle size of the internal region of the cathode active material precursor is reached. After that, in step S30, the other process conditions are kept unchanged, and the pH of the reaction solution is linearly decreased at a rate of 0.01h ^-1 to 0.05h ^-1 and the concentration of the complexing agent is 0.005mol/L/h to 0.02mol/ The rate of L/h increases linearly, and the reaction is continued for a period of time until the target particle size of the cathode active material precursor is reached and the reaction is stopped to obtain a cathode active material precursor. Among them, preferably, the pH of the reaction solution decreases linearly at a rate of 0.01h ^-1 to 0.03h ^-1 . Preferably, the concentration of the complexing agent in the reaction solution increases linearly at a rate of 0.005 mol/L/h to 0.01 mol/L/h.

In some embodiments, after step S30, step S40 may also be included: the cathode active material precursor obtained in step S30 is aged for 0.5 h to 4 h, and washed and dried to obtain a final cathode active material precursor product . In step S40, aging, washing, and drying can all be performed by methods and equipment known in the art, and the application is not specifically limited.

Next, an embodiment of the present application further provides a positive electrode active material. The positive electrode active material is composed of any one or more positive electrode active material precursors of this application and lithium.

As an example, any one or more cathode active material precursors of this application are mixed with a lithium salt and subjected to sintering treatment to obtain a cathode active material.

The cathode active material precursor and the lithium salt can be mixed using a ball mill mixer or a high-speed mixer. Add the mixed materials to the atmosphere sintering furnace for sintering. Optionally, the sintering atmosphere is an air atmosphere or an oxygen atmosphere. The sintering temperature may be 700°C to 950°C, such as 750°C to 900°C. The sintering time can be 5h to 25h, such as 10h to 20h.

Lithium salts may include lithium oxide (Li ₂ O), lithium phosphate (Li ₃ PO ₄ ), lithium dihydrogen phosphate (LiH ₂ PO ₄ ), lithium acetate (CH ₃ COOLi), lithium hydroxide (LiOH), lithium carbonate ( One or more of Li ₂ CO ₃ ) and lithium nitrate (LiNO ₃ ), but not limited thereto.

The positive electrode active material inherits the structural characteristics of the positive electrode active material precursor, which is a secondary particle aggregated from a plurality of primary particles. The positive electrode active material includes an inner portion and an outer portion coated on the outside of the inner portion, wherein the inner portion The density of is smaller than the density of the outer part, and the density of the outer part gradually increases from the inside to the outside.

In some embodiments, the plurality of primary particles in the inner part of the positive electrode active material are irregularly arranged to form a loose porous structure; the plurality of primary particles in the outer part are arranged in the radial direction of the secondary particles, and the density and the density The degree of order increases gradually from inside to outside.

In some embodiments, the length and thickness of the primary particles in the outer portion are greater than the length and thickness of the primary particles in the inner portion, that is, the length of the primary particles in the outer portion is greater than the length of the primary particles in the inner portion, The thickness of the primary particles is larger than the thickness of the primary particles in the inner part; and, in the outer part, the length and thickness of the primary particles from the inside to the outside are gradually increased.

In some embodiments, in the inner portion, the thickness of the primary particles is 10 nm to 30 nm, the length of the primary particles is 60 nm to 120 nm, and the volume ratio of the primary particles in the inner portion is 50% to 80%.

Further, in the outer portion, the thickness of the primary particles is 20 nm to 300 nm, the length of the primary particles is 80 nm to 1500 nm, and the volume ratio of the primary particles in the outer portion is 70% to 95%.

Furthermore, the thickness of the primary particles in the outer surface layer of the positive electrode active material is 50 nm to 400 nm, the length is 100 nm to 1500 nm, and the volume ratio of the primary particles in the outer surface layer of the secondary particles is 90% to 95%. The "positive surface layer of the positive electrode active material" corresponds to the "secondary particle external layer" described above.

In some embodiments, the morphology of the positive electrode active material includes one or more of a sphere and a spheroid.

In some embodiments, the inner portion is a sphere or a spheroid, and the radius is 0.1 μm to 3 μm. Further, the outer part is a spherical shell or a spherical shell, and the thickness is 1 μm to 9 μm.

In some embodiments, in the positive electrode active material, the ratio of the radius of the inner part to the radius of the secondary particles is 1% to 75%.

In some embodiments, the average particle diameter D _v 50 of the positive electrode active material is preferably 3 μm to 25 μm, more preferably 5 μm to 20 μm, and particularly preferably 10 μm to 18 μm.

In some embodiments, the tap density of the positive electrode active material may be 1.8 g/cm ³ to 2.7 g/cm ³ , preferably 2 g/cm ³ to 2.5 g/cm ³ .

In some embodiments, optionally, the positive electrode active material includes one or more of a compound of the chemical formula Li _z Ni _x Co _y M _1-xy O ₂ and its doping modified compound, where 0.95≤z ≤1.05, 0.6<x<1, 0<y<1, 0.6<x+y<1, M is Mn or Al.

Optionally, the doping modification compound may be doped with one or more of other transition metals, non-transition metals and non-metals. For example, when M is Mn, one or more doping elements of Fe, Cr, Ti, Zn, V, Al, Zr, Ce, Mg, F, N, and B may be included in the doping modification compound. When M is Al, one or more of Fe, Mn, Cr, Ti, Zn, V, Zr, Ce, Mg, F, N, and B may be included in the doping modification compound. The performance of the positive electrode active material is further improved by doping to improve the capacity performance and cycle performance.

The positive electrode active material can be tested with reference to the test method of the positive electrode active material precursor.

Lithium ion secondary battery

An embodiment of the present application further provides a lithium ion secondary battery, which includes a positive electrode tab, and the positive electrode tab includes any one or more positive electrode active materials of the present application.

The lithium ion secondary battery of the present application uses the positive electrode active material of the present application, so it simultaneously takes into account higher specific capacity for first charge, specific capacity for first discharge, first coulombic efficiency and cycle performance.

In some embodiments, the positive electrode tab includes a positive electrode current collector and a positive electrode active material layer disposed on at least one of two opposite surfaces of the positive electrode current collector, and the positive electrode active material layer includes any one or more positive electrode activities of the present application substance. As an example, a positive electrode slurry may be coated on at least one of two surfaces opposite to the positive electrode current collector. The positive electrode slurry contains a positive electrode active material; after drying and cold pressing, a positive electrode tab is obtained.

In some embodiments, the positive active material layer may further include a conductive agent. This application does not specifically limit the type of conductive agent in the positive electrode active material layer, and can be selected according to actual needs. As an example, the conductive agent may include one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the positive active material layer may further include a binder. This application does not specifically limit the type of binder, and can be selected according to actual needs. As an example, the binder may include styrene-butadiene rubber (SBR), water-based acrylic resin, sodium carboxymethyl cellulose (CMC-Na), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyethylene Butyral (PVB), ethylene-vinyl acetate copolymer (EVA), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, four One or more of vinyl fluoride-hexafluoropropylene copolymer, fluorine-containing acrylic resin and polyvinyl alcohol (PVA).

In some embodiments, the positive electrode current collector may use a metal foil or porous metal plate, for example, a foil or porous plate using metal such as aluminum, copper, nickel, titanium, or silver, or an alloy thereof, such as aluminum foil.

The lithium ion secondary battery also includes a negative pole piece. In some embodiments, the negative electrode tab may include a negative electrode current collector and a negative electrode active material layer disposed on at least one of two opposite surfaces of the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material. As an example, a negative electrode slurry may be coated on at least one of two surfaces opposite to the negative electrode current collector. The negative electrode slurry includes a negative electrode active material, and after drying and cold pressing, a negative electrode sheet is obtained.

This application does not specifically limit the types of negative electrode active materials, and can be selected according to actual needs. As an example, the negative electrode active material may include natural graphite, artificial graphite, mesophase microcarbon balls (MCMB), hard carbon, soft carbon, nanocarbon, carbon fiber, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li -One or more of Sn-O alloy, Sn, SnO, SnO ₂ , spinel-structured lithium titanate Li ₄ Ti ₅ O ₁₂ , Li-Al alloy, and metallic lithium.

In some embodiments, the negative active material layer may further include a conductive agent. This application does not specifically limit the type of the conductive agent in the negative electrode active material layer, and can be selected according to actual needs. As an example, the conductive agent may include one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the negative active material layer may further include a binder. This application does not specifically limit the type of binder in the negative electrode active material layer, and can be selected according to actual needs. As an example, the binder may include one of styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), water-based acrylic resin, or Multiple.

In some embodiments, the negative active material layer optionally further includes a thickener, such as sodium carboxymethyl cellulose (CMC-Na).

In some embodiments, the negative electrode current collector may use a metal foil or a porous metal plate or the like, for example, a foil or porous plate using a metal such as copper, nickel, titanium or iron, or an alloy thereof, such as copper foil.

In other embodiments, the negative pole piece may also use a lithium metal piece.

The lithium ion secondary battery also includes an electrolyte. The electrolyte may be a solid electrolyte, such as a polymer electrolyte, an inorganic solid electrolyte, etc., but it is not limited thereto. Electrolyte can also use electrolyte. The electrolyte includes a solvent and a lithium salt dissolved in the solvent. There are no specific restrictions on the type of solvent and lithium salt, and you can choose according to your needs.

In some embodiments, the solvent in the electrolyte may be an organic solvent. The organic solvent may include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC ), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl formate (MF), ethyl formate (Eft), methyl acetate (MA), ethyl acetate (EA), propyl acetate ( PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB) and propyl butyrate (BP) One or more of them are preferably two or more.

In some embodiments, the lithium salt in the electrolyte may include LiPF ₆ (lithium hexafluorophosphate), LiBF ₄ (lithium tetrafluoroborate), LiClO ₄ (lithium perchlorate), LiAsF ₆ (lithium hexafluoroarsenate), LiFSI ( Lithium difluorosulfonimide), LiTFSI (lithium bistrifluoromethanesulfonimide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiBOB (lithium difluorooxalate borate), LiPO _{One or more of 2} F ₂ (lithium difluorophosphate), LiDFOP (lithium difluorooxalate phosphate) and LiTFOP (lithium tetrafluorooxalate phosphate), such as LiPF ₆ (lithium hexafluorophosphate), LiBF ₄ (lithium tetrafluoroborate) ), one or more of LiBOB (lithium bisoxalate borate), LiDFOB (lithium difluorooxalate borate), LiTFSI (lithium bistrifluoromethanesulfonimide), and LiFSI (lithium bisfluorosulfonimide).

In some embodiments, the electrolyte may optionally contain additives. As an example, additives may include vinylene carbonate (VC), ethylene ethylene carbonate (VEC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethyl ethylene carbonate Ester (TFPC), succinonitrile (SN), adiponitrile (ADN), glutaronitrile (GLN), hexanetrinitrile (HTN), 1,3-propane sultone (1,3-PS), Ethylene sulfate (DTD), methyl methanedisulfonate (MMDS), 1-propene-1,3-sultone (PST), 4-methylethylene sulfate (PCS), 4- Ethylene ethylene sulfate (PES), 4-propyl ethylene sulfate (PEGLST), propylene sulfate (TS), 1,4-butane sultone (1,4-BS), ethylene sulfite Ester (DTO), dimethyl sulfite (DMS), diethyl sulfite (DES), sulfonate cyclic quaternary ammonium salt, tris(trimethylsilane) phosphate (TMSP) and tris (tris One or more of methylsilane) borate (TMSB), but is not limited thereto.

When the electrolyte uses an electrolyte, the lithium ion secondary battery further includes a separator, which acts as a separator between the positive pole piece and the negative pole piece. There is no particular limitation on the separator in this application, and any known porous separator with chemical and mechanical stability can be used. For example, the separator may be selected from single-layer or multi-layer films including one or more of glass fiber, non-woven fabric, polyethylene (PE), polypropylene (PP), and polyvinylidene fluoride (PVDF).

In some embodiments, the lithium ion secondary battery may include an outer package for encapsulating the positive electrode tab, the negative electrode tab, and the electrolyte. As an example, the positive electrode sheet, the negative electrode sheet, and the separator may be laminated or wound to form an electrode assembly of a laminated structure or an electrode assembly of a wound structure (also called a battery cell), and the electrode assembly is packaged in an outer package; The electrolyte can be an electrolyte, which is infiltrated in the electrode assembly. The number of electrode assemblies in the battery can be one or several, which can be adjusted according to requirements.

In some embodiments, the outer package may be a soft bag, such as a bag-type soft bag. The material of the soft bag may be plastic, such as one or more of polypropylene PP, polybutylene terephthalate PBT, polybutylene succinate PBS, etc. The outer packaging of the battery can also be a hard shell, such as an aluminum shell.

The present application has no particular limitation on the shape of the lithium ion secondary battery, and it may be cylindrical, square, or any other shape. As shown in FIG. 6, a lithium ion secondary battery 5 having a square structure as an example.

In some embodiments, the lithium ion secondary battery may be assembled into a battery module, and the number of lithium ion secondary batteries contained in the battery module may be multiple, and the specific number may be adjusted according to the application and capacity of the battery module.

FIG. 7 is a battery module 4 as an example. Referring to FIG. 8, in the battery module 4, a plurality of lithium ion secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, it can also be arranged in any other way. Further, the plurality of lithium ion secondary batteries 5 can be fixed by fasteners.

The battery module 4 also optionally includes a case having an accommodation space in which a plurality of lithium ion secondary batteries 5 are accommodated.

In some embodiments, the above battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

8 and 9 are a battery pack 1 as an example. 8 and 9, the battery pack 1 may include a battery box and a plurality of battery modules 4 provided in the battery box. The battery case includes an upper case 2 and a lower case 3. The upper case 2 can be covered on the lower case 3 and forms an enclosed space for accommodating the battery module 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

Device

An embodiment of the present application provides a device including any one or more lithium ion secondary batteries of the present application. The lithium ion secondary battery may be used as a power source of the device, or as an energy storage unit of the device. The device may be, but not limited to, mobile equipment (such as mobile phones, notebook computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf balls) Vehicles, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc. The device can select different electrochemical devices, such as batteries, battery modules, or battery packs, according to its usage requirements.

Fig. 10 is a device as an example. The device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the needs of the device for high power and high energy density of batteries, battery packs or battery modules can be used.

As another example, the device may be a mobile phone, a tablet computer, a notebook computer, or the like. The device is usually required to be light and thin, and a lithium ion secondary battery can be used as a power source.

Examples

The following examples describe the disclosure of the present application more specifically, and these examples are only for illustrative purposes, because it is obvious to those skilled in the art that various modifications and changes can be made within the scope of the present disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods, and can be directly It is used without further processing, and the instruments used in the examples are commercially available.

Example 1

Preparation of cathode active material precursor

Nickel sulfate, cobalt sulfate, and manganese sulfate are used as a mixed salt solution with a concentration of 1.5mol/L according to the molar ratio of Ni:Co:Mn=8:1:1, and with NaOH as a precipitant solution with a concentration of 5mol/L. Ammonia water with a concentration of 8 mol/L is used as the complexing agent solution.

In a 20L controlled crystallization reactor, add 10L of deionized water, add a certain amount of concentrated ammonia to make the ammonia concentration 0.45mol/L ~ 0.55mol/L, and add a certain amount of NaOH solution to make the pH 11.70 ~ 11.75, to obtain a bottom solution.

Under a N ₂ protective atmosphere, the bottom solution was heated to 55° C. and maintained. At a stirring speed of 600 rpm, the mixed salt solution, precipitant solution, and complexing agent solution were added to the bottom solution in parallel, where the flow rate of the mixed salt solution was 14.5ml/min, the pH of the reaction solution is controlled to 11.70～11.75, the ammonia concentration is 0.45mol/L～0.55mol/L, the reaction is carried out for a period of time, and then the other process conditions are maintained, and the pH of the reaction solution is controlled to 0.02h The rate of ^-1 decreases linearly until the initial positive electrode active material precursor with D _v 50 = 11 μm is obtained, the reaction is stopped, the initial positive electrode active material precursor is aged for 1.5 h, and washed and dried to obtain the positive electrode active material Precursor.

Preparation of positive active material

Mix the obtained cathode active material precursor product with LiOH·H ₂ O at a molar ratio of 1:1.05, and then sinter it in a box furnace at 750°C for 20h under a pure oxygen atmosphere. It can be obtained by crushing and sieving. Positive active material.

Preparation of positive pole pieces

Disperse the obtained positive electrode active material, conductive carbon black and binder PVDF in the solvent N-methylpyrrolidone (NMP) in a weight ratio of 90:5:5 and mix them uniformly to obtain a positive electrode slurry; uniform the positive electrode slurry It is coated on the aluminum foil of the positive electrode collector, and after drying and cold pressing, the positive electrode sheet is obtained.

Preparation of negative pole pieces

Adopt metal lithium sheet.

Preparation of electrolyte

After mixing EC, DEC, and DMC in a volume ratio of 1:1:1, a solvent is obtained, and then the lithium salt LiPF _{6 is} dissolved in the above solvent to obtain an electrolyte, wherein the concentration of LiPF ₆ is 1 mol/L.

Preparation of button cell

The positive pole piece, the polyethylene porous separator and the negative pole piece are stacked in this order, and the electrolyte is injected to assemble a button battery.

Example 2

Different from Example 1, in the preparation of the cathode active material precursor:

Nickel sulfate, cobalt sulfate, and manganese sulfate are used as a mixed salt solution with a concentration of 2.0 mol/L according to the molar ratio of Ni:Co:Mn=8:1:1, and a precipitant solution with a concentration of 3 mol/L using NaOH. Ammonia water with a concentration of 14 mol/L is used as the complexing agent solution.

Add 15L of deionized water to a 20L controlled crystallization reactor, add a certain amount of concentrated ammonia to make the ammonia concentration be 0.15mol/L ~ 0.25mol/L, and add a certain amount of NaOH solution to make the pH 11.15 ~ 11.25, get the bottom solution.

Under the protective atmosphere of N ₂ , the bottom liquid was heated to 55° C. and maintained. At a stirring speed of 800 rpm, the mixed salt solution, precipitant solution, and complexing agent solution were added to the bottom liquid in parallel. The flow rate of the mixed salt solution was 13.0ml/min, control the pH of the reaction solution to be 11.15～11.25, the ammonia concentration is 0.15mol/L～0.25mol/L, carry out the reaction for a period of time, then keep other process conditions unchanged, and control the ammonia concentration of the reaction solution to 0.01 The rate of mol/L/h increases linearly until the initial positive electrode active material precursor with D _v 50=11 μm is obtained, the reaction is stopped, the initial positive electrode active material precursor is aged for 3 hours, and washed and dried to obtain the positive electrode Active substance precursor.

Example 3

Different from Example 1, in the preparation of the cathode active material precursor:

Nickel sulfate, cobalt sulfate and manganese sulfate are used as a mixed salt solution with a concentration of 2.0mol/L according to the molar ratio of Ni:Co:Mn=8:1:1, and a precipitant solution with a concentration of 5mol/L using NaOH. Ammonia water with a concentration of 10 mol/L is used as the complexing agent solution.

Add 5L of deionized water to a 20L controlled crystallization reaction kettle, add a certain amount of concentrated ammonia to make the ammonia concentration be 0.15mol/L～0.25mol/L, and add a certain amount of NaOH solution to make the pH 12.05～12.15 to get the bottom solution.

Under the protective atmosphere of N ₂ , the bottom liquid was heated to 65° C. and maintained. At a stirring speed of 800 rpm, the mixed salt solution, precipitant solution, and complexing agent solution were added to the bottom liquid in parallel. The flow rate of the mixed salt solution was 13.0ml/min, control the pH of the reaction solution to be 12.05～12.15, the ammonia concentration is 0.15mol/L～0.25mol/L, carry out the reaction for a period of time, then keep other process conditions unchanged, and control the ammonia concentration of the reaction solution to 0.01 The rate of mol/L/h increased linearly and the pH decreased linearly at a rate of 0.03h ^-1 until the synthesis of the initial cathode active material precursor with D _v 50 = 11 μm, the reaction was stopped, and the initial cathode active material precursor After aging for 4 hours, and after washing and drying, the final cathode active material precursor product is obtained.

Example 4

Different from Example 1, in the preparation of the cathode active material precursor:

Nickel sulfate, cobalt sulfate and manganese sulfate are used as a mixed salt solution with a concentration of 2.0mol/L according to the molar ratio of Ni:Co:Mn=90:5:5, and a precipitant solution with a concentration of 5mol/L using NaOH. Ammonia water with a concentration of 10 mol/L is used as the complexing agent solution.

Add 5L of deionized water to a 20L controlled crystallization reaction kettle, add a certain amount of concentrated ammonia to make the ammonia concentration be 0.15mol/L～0.25mol/L, and add a certain amount of NaOH solution to make the pH 12.05～12.15 to get the bottom solution.

Under the protective atmosphere of N ₂ , the bottom liquid was heated to 65° C. and maintained. At a stirring speed of 800 rpm, the mixed salt solution, precipitant solution, and complexing agent solution were added to the bottom liquid in parallel. The flow rate of the mixed salt solution was 13.5 ml/min, control the pH of the reaction solution to 12.05～12.15, the ammonia concentration is 0.15mol/L～0.25mol/L, carry out the reaction for a period of time, then keep other process conditions unchanged, and control the ammonia concentration of the reaction solution to 0.01 The rate of mol/L/h increased linearly and the pH decreased linearly at a rate of 0.03h ^-1 until the synthesis of the initial cathode active material precursor with D _v 50 = 11 μm, the reaction was stopped, and the initial cathode active material precursor After aging for 4 hours, and after washing and drying, the final cathode active material precursor product is obtained.

Example 5

Different from Example 1, in the preparation of the cathode active material precursor:

Nickel sulfate, cobalt sulfate and aluminum sulfate are used as a mixed salt solution with a concentration of 1.5mol/L according to the molar ratio of Ni:Co:Al=8:1:1, and a precipitant solution with a concentration of 5mol/L using NaOH. Ammonia water with a concentration of 8 mol/L is used as the complexing agent solution.

In a 20L controlled crystallization reactor, add 10L of deionized water, add a certain amount of concentrated ammonia to make the ammonia concentration 0.45mol/L ~ 0.55mol/L, and add a certain amount of NaOH solution to make the pH 11.65 ~ 11.75, to obtain a bottom solution.

Under a N ₂ protective atmosphere, the bottom solution was heated to 55° C. and maintained. At a stirring speed of 600 rpm, the mixed salt solution, precipitant solution, and complexing agent solution were added to the bottom solution in parallel, where the flow rate of the mixed salt solution was 14.0ml/min, the pH of the reaction solution is controlled to 11.65～11.75, the ammonia concentration is 0.15mol/L～0.25mol/L, the reaction is carried out for a period of time, then the other process conditions are maintained unchanged, and the ammonia concentration of the reaction solution is controlled to 0.01 The rate of mol/L/h increased linearly and the pH decreased linearly at a rate of 0.02h ^-1 until the synthesis of the initial positive electrode active material precursor with D _v 50 = 11 μm, the reaction was stopped, and the initial positive electrode active material precursor After aging for 3 hours, and after washing and drying, the final cathode active material precursor product is obtained.

Comparative Example 1

Different from Example 1, in the preparation of the cathode active material precursor:

Nickel sulfate, cobalt sulfate, and manganese sulfate are used as a mixed salt solution with a concentration of 1.5mol/L according to the molar ratio of Ni:Co:Mn=8:1:1, and with NaOH as a precipitant solution with a concentration of 5mol/L. Ammonia water with a concentration of 8 mol/L is used as the complexing agent solution.

Add 10L of deionized water to a 20L controlled crystallization reaction kettle, add a certain amount of concentrated ammonia water to make the ammonia concentration 0.45mol/L～0.55mol/L, and add a certain amount of NaOH solution to make the pH 11.65～11.75 to get the bottom solution.

Under a N ₂ protective atmosphere, the bottom solution was heated to 55° C. and maintained. At a stirring speed of 600 rpm, the mixed salt solution, precipitant solution, and complexing agent solution were added to the bottom solution in parallel, where the flow rate of the mixed salt solution was 14.5ml/min, control the pH of the reaction solution to 11.65～11.75, the ammonia concentration is 0.45mol/L～0.55mol/L, carry out the reaction, until the synthesis of the initial cathode active material precursor D _v 50 = 11μm, stop the reaction, The initial positive electrode active material precursor is aged for 1.5 hours, and washed and dried to obtain the final positive electrode active material precursor product, in which the morphology of the primary particles is needle-shaped.

Comparative Example 2

Different from Example 1, in the preparation of the cathode active material precursor:

Nickel sulfate, cobalt sulfate, and manganese sulfate are used as a mixed salt solution with a concentration of 1.5mol/L according to the molar ratio of Ni:Co:Mn=8:1:1, and with NaOH as a precipitant solution with a concentration of 5mol/L. Ammonia water with a concentration of 8 mol/L is used as the complexing agent solution.

Add 10L of deionized water to a 20L controlled crystallization reactor, add a certain amount of concentrated ammonia to make the ammonia concentration 0.45mol/L ~ 0.55mol/L, and add a certain amount of NaOH solution to make the pH 11.15 ~ 11.25, get the bottom solution.

Under a N ₂ protective atmosphere, the bottom solution was heated to 55° C. and maintained. At a stirring speed of 600 rpm, the mixed salt solution, precipitant solution, and complexing agent solution were added to the bottom solution in parallel, where the flow rate of the mixed salt solution was 14.5ml/min, control the pH of the reaction solution to be 11.15 to 11.25, and the ammonia concentration to be 0.45mol/L to 0.55mol/L, and carry out the reaction until the synthesis of the initial positive electrode active material precursor with D _v 50=11μm, and stop the reaction. The initial positive electrode active material precursor is aged for 1.5 hours, and washed and dried to obtain the final positive electrode active material precursor product, in which the morphology of the primary particles is lath.

Test section

(1) Characterization test of cathode active material precursor and cathode active material

SEM test was performed on the positive electrode active material precursor and positive electrode active material using Japanese Hitachi S-4800 scanning electron microscope.

The XRD test of the positive electrode active material precursor was carried out using the Panalytical X'Pert PRO X-ray diffractometer of Phlips, the Netherlands, where CuK _α rays were used as the radiation source and the ray wavelength

The scanning 2θ angle range is 15°～70°, and the scanning rate is 4°/min.

(2) Capacity of coin cell and first Coulomb efficiency test

At 25°C, charge the battery at a constant current of 0.1C to 4.25V, and then charge it at a constant voltage until the current is less than or equal to 0.05mA, and then leave it for 2 minutes. The charging capacity this time is recorded as the specific capacity C ₀ for the first charge; then 0.1 C constant current discharge to 2.8V, the discharge capacity this time is recorded as the first discharge specific capacity D ₀ , which is the initial gram capacity of the battery.

The first coulombic efficiency (%) of the button cell = D ₀ /C ₀ ×100%.

(3) Cycle performance test of button cell

At 25°C, charge the battery at a constant current of 0.5C to 4.25V, then charge it at a constant voltage until the current is less than or equal to 0.05mA, then leave it for 2 minutes, and then discharge at a constant current of 0.5C to 2.8V, which is a charge and discharge cycle The discharge capacity this time is recorded as the discharge specific capacity D ₁ of the battery in the first cycle. The battery was subjected to 50 cycles of charge and discharge tests according to the above method, and the discharge specific capacity D _{50 at the 50th} cycle was recorded.

Cyclic battery capacity retention rate (%) = D ₅₀ /D ₁ ×100%.

The test results of Examples 1 to 5 and Comparative Examples 1 to 2 are shown in Table 1.

Table 1

Comparative Examples 1 to 2 The positive electrode active material precursor prepared by the traditional method does not have the special structure of this application, and the lithium ion secondary battery prepared by using the positive electrode active material synthesized therefrom cannot simultaneously consider the first charge-discharge specific capacity and the first coulomb Efficiency and cycle capacity retention rate. The positive electrode active material synthesized from the positive electrode active material precursor formed by needle-shaped primary grains in Comparative Example 1 has a higher specific charge-discharge specific capacity, but the first Coulomb efficiency is lower, especially the cycle capacity retention rate is significantly lower于实施例1至3。 In Examples 1 to 3. Comparative Example 2 The positive electrode active material synthesized from the positive electrode active material precursor formed by medium-thick lath-shaped primary grains has a higher first-time Coulomb efficiency and cycle capacity retention rate, but the first charge-discharge specific capacity is significantly lower Examples 1 to 3. The cathode active materials synthesized by using the cathode active material precursor with a special structure in Examples 1 to 3 not only have a higher specific charge-discharge capacity for the first time, but also have a higher first coulombic efficiency and cycle Capacity retention rate.

It can be seen from Example 1 that by using the scheme of fixing the concentration of the complexing agent of the reaction solution and adjusting the pH to increase linearly, the cathode active material synthesized by the prepared cathode active material precursor can simultaneously take into account the higher first charge and discharge grams Specific capacity and excellent first-time Coulomb efficiency and cycle capacity retention rate.

It can be seen from Example 2 that the solution of fixing the pH of the reaction solution and adjusting the concentration of the complexing agent to decrease linearly, the cathode active material synthesized by the prepared cathode active material precursor can also take into account the higher first charge and discharge grams Specific capacity and excellent first-time Coulomb efficiency and cycle capacity retention rate.

It can be seen from Example 3 that the positive electrode active material synthesized by the prepared positive electrode active material precursor while adjusting the pH of the reaction solution to increase linearly and the concentration of the complexing agent to decrease linearly at the same time can also take into account the higher initial charge and discharge grams. Specific capacity and excellent first-time Coulomb efficiency and cycle capacity retention rate, and has the best comprehensive effect.

It can be seen from Examples 1 to 5 that the high-nickel ternary positive electrode active materials synthesized based on the Ni80 and Ni90 high-nickel ternary positive electrode active material precursors of the special structure of the present application all have higher specific charge-discharge specific capacity and Excellent first-time Coulomb efficiency and cycle capacity retention rate.

The above is only the specific implementation of this application, but the scope of protection of this application is not limited to this, any person skilled in the art can easily think of various equivalents within the technical scope disclosed in this application Modifications or replacements, these modifications or replacements should be covered within the scope of protection of this application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims (25)

1. A positive electrode active material precursor, including secondary particles aggregated from a plurality of primary particles, the secondary particles including an inner region and an outer region coated outside the inner region;

   Wherein, the density of the inner area is smaller than the density of the outer area, and the density of the outer area gradually increases from the inside to the outside.
2. The cathode active material precursor according to claim 1, wherein a plurality of the primary particles in the inner region are irregularly arranged to form a loose porous structure;

   A plurality of the primary particles in the outer region are arranged along the radial direction of the secondary particles, and the arrangement density and the degree of order are gradually increased from the inside to the outside.
3. The cathode active material precursor according to claim 1 or 2, wherein the length and thickness of the primary particles in the outer region are greater than the length and thickness of the primary particles in the inner region;

   In the outer region, the length and thickness of the primary particles from the inside to the outside gradually increase.
4. The cathode active material precursor according to claim 3, wherein the thickness of the primary particles in the inner region is 5 nm to 20 nm, the length of the primary particles is 50 nm to 100 nm, and the primary particles are in the The volume ratio in the internal area is 40% to 70%;

   The thickness of the primary particles in the outer region is 10 nm to 200 nm, the length of the primary particles is 70 nm to 1400 nm, and the volume ratio of the primary particles in the outer region is 60% to 95%.
5. The cathode active material precursor according to claim 4, wherein the thickness of the primary particles in the outer surface layer of the secondary particles is 20 nm to 200 nm, the length of the primary particles is 80 nm to 1400 nm, and the primary particles are The volume ratio of the outer surface layer of the secondary particles is 90%-95%.
6. The cathode active material precursor according to any one of claims 1 to 5, wherein the inner region is a sphere or a spheroid, and the radius is 0.1 μm to 3 μm;

   The outer area is a spherical shell or a spherical shell, and the thickness is 1 μm to 9 μm.
7. The cathode active material precursor according to any one of claims 1 to 6, wherein the morphology of the primary particles in the inner region is one or more of needle-like and sheet-like, and the outer The morphology of the primary particles in the area is one or more of needle shape, spindle shape and lath shape.
8. The cathode active material precursor according to any one of claims 1 to 7, wherein the average particle size D _v 50 of the cathode active material precursor is 3 μm to 20 μm; and/or,

   The tap density of the positive electrode active material precursor is 1.6 g/cm ³ to 2.3 g/cm ³ .
9. The positive electrode active material precursor according to any one of claims 1 to 8, wherein the chemical formula of the positive electrode active material precursor is Ni _x Co _y M _1-xy (OH) ₂ , where 0.6<x< 1, 0<y<1, 0.6<x+y<1, M is Mn or Al.
10. The positive electrode active material precursor according to claim 9, wherein the ratio of the intensity of the 001 crystal plane diffraction peak to the 101 crystal plane diffraction peak of the positive electrode active material precursor is 0.9 to 1.4, preferably 1.0 to 1.2.
11. A method for preparing a cathode active material precursor, which includes the following steps:

    Providing a mixed salt solution, a precipitant solution, a complexing agent solution and a bottom liquid, wherein the mixed salt solution contains a metal salt contained in the positive electrode active material precursor;

    In the first-stage reaction step, the mixed salt solution, the precipitant solution and the complexing agent solution are added to the base solution, while maintaining the pH of the reaction solution and the concentration of the complexing agent unchanged, proceeding First-level co-precipitation reaction to obtain multiple primary particles formed by primary particle aggregation;

    In the second reaction step, continue to add the mixed salt solution, the precipitant solution and the complexing agent solution to the base solution, and control the pH of the reaction solution to decrease linearly and/or the concentration of the complexing agent to appear Increase linearly, perform a second-stage co-precipitation reaction, and coat multiple primary particles on the outside of the initial particles to obtain the positive electrode active material precursor;

    Wherein, the positive electrode active material precursor includes an inner region and an outer region coated on the outer peripheral side of the inner region, the density of the inner region is smaller than the density of the outer region, and the density of the outer region is from inner to The outside gradually increases.
12. The method according to claim 11, wherein in the first-stage reaction step, the pH of the reaction solution is 10.8-11.8, and the concentration of the complexing agent is 0.02mol/L-0.8mol/L;

    In the second-stage reaction step, the concentration of the complexing agent in the reaction solution increases linearly at a rate of 0.005 mol/L/h to 0.02 mol/L/h, preferably 0.005 mol/L/h to 0.01 The rate of mol/L/h increased linearly.
13. The method according to claim 11, wherein in the first-stage reaction step, the pH of the reaction solution is 10.8 to 12.2, and the concentration of the complexing agent is 0.02mol/L to 0.5mol/L;

    In the second-stage reaction step, the pH of the reaction solution decreases linearly at a rate of 0.01h ^-1 to 0.05h ^-1 and the concentration of the complexing agent ranges from 0.005mol/L/h to 0.02mol/L/ The rate of h increases linearly, preferably, the pH decreases linearly at a rate of 0.01h ^-1 to 0.03h ^-1 and the concentration of the complexing agent at a rate of 0.005mol/L/h to 0.01mol/L/h Increased linearly.
14. The method according to claim 11, wherein in the first-stage reaction step, the pH of the reaction solution is 11.7 to 12.2, and the concentration of the complexing agent is 0.2 mol/L to 0.8 mol/L;

    In the second-stage reaction step, the pH of the reaction solution decreases linearly at a rate of 0.01h ^-1 to 0.05h ^-1 , preferably linearly at a rate of 0.01h ^-1 to 0.03h ^-1 .
15. A positive electrode active material includes secondary particles formed by aggregating a plurality of primary particles, the secondary particles including an inner portion and an outer portion coated outside the inner portion;

    Wherein, the density of the inner portion is smaller than the density of the outer portion, and the density of the outer portion gradually increases from the inside to the outside.
16. The positive electrode active material according to claim 15, wherein a plurality of the primary particles in the inner portion are irregularly arranged to form a loose porous structure;

    A plurality of the primary particles in the outer portion are arranged along the radial direction of the secondary particles, and the arrangement density and orderness gradually increase from the inside to the outside.
17. The positive electrode active material according to claim 15 or 16, wherein the length and thickness of the primary particles in the outer portion are greater than the length and thickness of the primary particles in the inner portion;

    In the outer portion, the length and thickness of the primary particles from inside to outside gradually increase.
18. The positive electrode active material according to claim 17, wherein the thickness of the primary particles in the inner portion is 10 nm to 30 nm, the length of the primary particles is 60 nm to 120 nm, and the primary particles are in the inner portion The volume ratio in is 50%～80%;

    The thickness of the primary particles in the outer portion is 20 nm to 300 nm, the length of the primary particles is 80 nm to 1500 nm, and the volume ratio of the primary particles in the outer portion is 70% to 95%.
19. The positive electrode active material according to claim 18, wherein the thickness of the primary particles in the outer surface layer of the secondary particles is 50 nm to 400 nm, the length of the primary particles is 100 nm to 1500 nm, and the primary particles are in the The volume ratio of the outer surface layer of the secondary particles is 90% to 95%.
20. The positive electrode active material according to any one of claims 15 to 19, wherein the inner portion is a sphere or a spheroid, and the radius is 0.1 μm to 3 μm;

    The outer part is a spherical shell or a spherical shell and has a thickness of 1 μm to 9 μm.
21. The positive electrode active material according to any one of claims 15 to 20, wherein the morphology of the positive electrode active material includes one or more of a sphere and a spheroid, and the radius of the inner portion and the secondary The ratio of the radius of the particles is 1% to 75%.
22. The positive electrode active material according to any one of claims 15 to 21, wherein the average particle diameter D _v 50 of the positive electrode active material is 3 μm to 25 μm; and/or,

    The tap density of the positive electrode active material is 1.8 g/cm ³ to 2.7 g/cm ³ .
23. The positive electrode active material according to any one of claims 15 to 22, wherein the positive electrode active material includes one of a compound having a chemical formula of Li _z Ni _x Co _y M _1-xy O ₂ and a doping modified compound thereof One or more species, where 0.95≤z≤1.05, 0.6<x<1, 0<y<1, 0.6<x+y<1, M is Mn or Al;

    Preferably, when M is Mn, the doping modification compound contains one or more dopings of Fe, Cr, Ti, Zn, V, Al, Zr, Ce, Mg, F, N and B Element; when M is Al, the doping modification compound contains one or more doping elements of Fe, Mn, Cr, Ti, Zn, V, Zr, Ce, Mg, F, N and B .
24. A lithium ion secondary battery includes a positive pole piece, and the positive pole piece includes the positive electrode active material according to any one of claims 15 to 23.
25. An apparatus comprising the lithium ion secondary battery of claim 24.

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