Patent Description:
With the increasing requirements for the cruising range of electric vehicles, ternary positive electrode materials with a higher Ni content (such as NCM811) have become the focus of research, and this ternary positive electrode material with a Ni content greater than <NUM> is generally referred to as "high-nickel ternary positive electrode material". This material has a relatively high content of Ni, and high energy density, so it can meet short-term market demand to a certain extent, and alleviate the range anxiety of electric vehicles; furthermore, since the content of cobalt is relatively low, it has a better cost advantage. During the production of ternary positive electrode materials, it is inevitable to produce some by-products, for example, <NUM>-<NUM>% of micropowder is produced during crushing production by means of mechanical grinding. During industrialized mass production, an output of <NUM>-<NUM>% of micropowder is considerable. Moreover, the specifications of the micropowder itself are much smaller than those of normal materials, the collection speed during production is slow, and the packaging is untimely, resulting in a particularly high content of residual alkalies in the product, particularly a particularly high content of Li<NUM>CO<NUM>. The high content of Li<NUM>CO<NUM> can cause the water content to exceed standards, leading to gas production during battery cycles, which affects the safety performance, and if the battery is scrapped directly, greater economic damage and environmental pollution will be caused. In order to response to the call of cost reduction, efficiency improvement, energy conservation and emission reduction in China, and promote clean production, develop circular economy and accelerate energy-saving technological transformation, it is imperative to develop recycling processes for by-products. However, each batch of micropowder has different physical and chemical properties, in particular, the residual alkali content and the button battery capacity, due to different processes or process treatments. Therefore, it is necessary to develop a recycling process suitable for most micropowders.

With the continuous development of the new energy source industry, the requirements for power batteries are getting higher and higher, and consequently, the requirements for the nickel content in ternary materials increases. However, the resulting problems concerning the stability of a positive electrode material, the matching of an electrolyte solution, battery failures caused by high current charging-induced temperature rise, etc. are also attracting more and more attention. Therefore, single crystal materials come into being, which not only enhance the stability of the positive electrode materials, but can also raise the voltage of the entire system to a new level, and proposes a solution to the demand for higher energy density.

<CIT> discloses a method for preparing a powderous positive electrode material comprising single crystal monolithic particles comprising Ni and Co and having a general formula Li<NUM>+a ((Ni<NUM>(Ni<NUM>/<NUM>Mn<NUM>/<NUM>)yCox)<NUM>-kAk)<NUM>-aO<NUM>, the method comprising the steps of - providing a mixture comprising a Ni- and Co- bearing precursor and a Li bearing precursor, - subjecting the mixture to a multiple step sintering process whereby in the final sintering step a sintered lithiated intermediate material is obtained comprising agglomerated primary particles having a primary particle size distribution with a D50 between <NUM> and <NUM>, - subjecting the lithiated intermediate material to a wet ball milling step whereby the agglomerated primary particles are deagglomerated and a slurry comprising deagglomerated primary particles is obtained, - separating the deagglomerated primary particles from the slurry, and - heat treating the deagglomerated primary particles at a temperature between <NUM> and at least <NUM> below the temperature in the final sintering step of the multiple step sintering process, whereby single crystal monolithic particles comprising Ni and Co are obtained.

<CIT> discloses a positive electrode material with a high compacted density and an electrochemical energy storage device. The positive electrode material comprises a lithium nickel transition metal oxide A and a lithium nickel transition metal oxide B. The lithium nickel transition metal oxide A is used for secondary particles, the lithium nickel transition metal oxide B is a single crystal structure or a single crystal-like structure, and the chemical formula thereof is shown in Formula II: Lia<NUM>(Nib<NUM>Coc<NUM>Mnd2)x2M'<NUM>-x2O<NUM>-e2X'e2 (II). The positive electrode material comprises the lithium nickel transition metal oxide A in large particles and the lithium nickel transition metal oxide B in small particles to improve the energy density of a battery.

<CIT> discloses a lithium nickel cobalt manganate positive electrode material for a single crystal lithium-ion battery. The positive electrode material has a general formula LiNixCoyMnzO<NUM> and has the characteristics of large particle size, good dispersibility, moderate specific surface area, high compaction density, high voltage, and good high-temperature cycle performance, etc..

Studies have shown that with the increase in the number of cycles of a polycrystalline ternary positive electrode material, duce to the different crystal plane orientations and glide planes of primary particles in secondary spheres, and the anisotropy of the expansion and contraction of the lattice between crystal grains, in the cycle later period of the polycrystalline ternary positive electrode material, secondary particle breakage may occur and microcracks may occur among the primary particles, which will increase the contact area between the material and the electrolyte solution, intensify the side reaction with the electrolyte solution, and cause serious capacity attenuation. However, single crystal materials can avoid this situation and maintain the integrity of the structure during repeated cycles, thereby improving the cycle stability. Single crystal materials improve the cycle stability due to the combination of their lower specific surface area and excellent structural stability, and can still maintain the original morphology of particles after a long cycle.

At present, by means of coating and sintering, the surface properties of the ternary material can be improved, the surface transfer resistance thereof can be reduced, the ion conductivity thereof can be improved, the water absorption performance thereof can also be reduced, and the side reaction between the material and the electrolyte solution is reduced. Therefore, there is an urgent need to develop a ternary single crystal positive electrode material with few side reactions and a small resistivity and a preparation method therefor.

The features of method according to embodiments of the present disclosure are set out in the appended set of claims.

The objective of the present disclosure is to provide a ternary single crystal positive electrode material and a preparation method therefor. In this method, a ternary polycrystalline micropowder is used as the raw material, which improves the utilization of the material and increases product benefits. The prepared ternary single crystal positive electrode material has advantages of not only reducing the diffusion length of lithium ions, providing channels for the rapid transport of lithium ions, but also improving the capacity retention rate of the material under a high charge cut-off voltage. In addition, by means of coating and sintering, the surface properties of the ternary material can be improved, the surface transfer resistance thereof can be reduced, the ion conductivity thereof can be improved, the water absorption performance thereof can also be reduced, and the side reaction between the material and an electrolyte solution can be reduced.

In order to achieve the above-mentioned objective, the present disclosure uses the following technical solution:
A method for preparing a ternary single crystal positive electrode material is provided, which comprises the following steps:.

A single crystal nickel cobalt manganese ternary positive electrode material LiNixCoyMnzO<NUM> has advantages of not only reducing the diffusion length of lithium ions, providing channels for the rapid transport of lithium ions, but also improving the capacity retention rate of the material under a high charge cut-off voltage, and effectively improving the cycle, inflation, capacity recovery and other problems of the material at high temperatures, thereby effectively improving the electrochemical properties of the material. The single crystal nickel cobalt manganese ternary positive electrode material has a high mechanical strength, a larger compaction density, which makes the material not fragile during electrode compaction, and also a smaller specific surface area, which can greatly reduce the contact area between the material and the electrolyte solution, thereby effectively inhibiting the occurrence of side reactions during cycles, enhancing the structural stability of the material, and significantly improving the cycle life of a battery. Therefore, the preparation of a ternary polycrystalline micropowder into a ternary single crystal positive electrode material by means of a new process can not only recycle the by-product, increase the utilization of the material, and increase product benefits, but can also improve the cycle performance, safety performance, and electrochemical performance of the product to produce a single crystal product with a higher energy density. By using a jet pulverization device to open the polycrystalline material to form small single crystal particles, the electrochemical performance of the material is improved; secondly, by means of a process of washing with water, centrifugal drying to wash away excess residual alkali, the processing performance and safety performance of the material can be improved; and finally by means of coating and sintering, the surface properties of the ternary material can be improved, the surface transfer resistance thereof can be reduced, the ion conductivity thereof can be improved, the water absorption performance thereof can also be reduced, and the side reaction between the material and an electrolyte solution is reduced.

Preferably, in step (<NUM>), the size of the ternary polycrystalline powder is <NUM>-<NUM>.

Preferably, in step (<NUM>), an equipment used for the mixing is one of a coulter mixer, a screw mixer, a non-gravity mixer, a V-type mixer, a double spiral cone mixer, a three-dimensional mixer, a powder mixer, a high-speed mixer, or a ball mill. By means of mixing, the residual LiOH, Li<NUM>CO<NUM> and doped additives in the micropowder become more uniform; moreover, the uniformity of the particle size of the micropowder is relatively poor, and the mixing can make the sintering raw material uniform, which is beneficial for the primary particles of the micropowder to grow into full, round and uniform-size small particles during high temperature sintering.

Preferably, the mixing in step (<NUM>) lasts for <NUM>-<NUM>.

Preferably, in step (<NUM>), a temperature of the primary sintering is <NUM>-<NUM>, and the primary sintering lasts for <NUM>-<NUM>.

Preferably, in step (<NUM>), a rate for raising the temperature is <NUM>-<NUM>/min; and a rate for lowering the temperature is <NUM>-<NUM>/min.

Preferably, in step (<NUM>), an atmosphere in which the primary sintering is carried out is one of air or oxygen.

Preferably, in step (<NUM>), a gas introduction rate during the primary sintering is <NUM>-<NUM><NUM>/h.

Preferably, in step (<NUM>), an equipment used for the crushing process is a fluidized bed jet mill; and the fluidized bed jet mill comprises an induced draft fan, a grinding chamber, a classification wheel, and a cyclone separator.

More preferably, a classification frequency of the jet pulverization is <NUM>-<NUM>, an induced air pressure is -<NUM> KPa to <NUM> KPa, a gas pressure is <NUM>-<NUM> KPa, and a grinding base material is <NUM>-<NUM>.

Preferably, in step (<NUM>), a mass ratio of the water to the single crystal material (water-to-material ratio) during the washing process is (<NUM>-<NUM>): <NUM>.

Preferably, in step (<NUM>), a rotation speed of the centrifugation is <NUM>-<NUM>; and the centrifugation lasts for <NUM>-<NUM>.

Preferably, in step (<NUM>), the drying is conducted at a temperature of <NUM>-<NUM>; and the drying lasts for <NUM>-<NUM>.

Preferably, in step (<NUM>), a temperature of the secondary sintering is <NUM>-<NUM>, and the secondary sintering lasts for <NUM>-<NUM>.

Preferably, in step (<NUM>), an atmosphere in which the secondary sintering is carried out is one of air or oxygen.

Preferably, in step (<NUM>), a gas introduction rate during the secondary sintering is <NUM>-<NUM><NUM>/h.

Preferably, in step (<NUM>), a volume concentration of the oxygen atmosphere is <NUM>-<NUM>%.

Preferably, in step (<NUM>), a rate for raising the temperature is <NUM>-<NUM>/min; a rate for lowering the temperature is <NUM>-<NUM>/min.

In order to have an in-depth understanding of the present disclosure, preferred experimental schemes of the present disclosure are described in conjunction with examples to further illustrate the characteristics and advantages of the present disclosure. Any alterations or changes that do not deviate from the gist of the present disclosure can be understood by a person skilled in the art. The scope of protection of the present disclosure is determined by the scope of the claims.

If no specific conditions are indicated in the examples of the present disclosure, conventional conditions or the conditions suggested by the manufacturer shall be followed. The raw materials, reagents etc., which are used without indicating the manufacturers, are all conventional products that are commercially available.

A ternary single crystal positive electrode material was provided, the chemical formula of which was LiNi<NUM>Co<NUM>Mn<NUM>O<NUM>@B.

A method for preparing a ternary single crystal positive electrode material was provided, which comprised the following steps:.

The ternary single crystal positive electrode material prepared in Example <NUM>, the conductive agent SP, and the binder PVDF were mixed at a ratio of <NUM> : <NUM> : <NUM> (with a total mass of <NUM>), and then added to <NUM> of an NMP organic solvent solution to obtain a mixed solution; the mixed solution was stirred to obtain a slurry; the slurry was evenly smeared on an <NUM> aluminum foil with a thickness of <NUM>, and dried in a vacuum drying oven at <NUM> for <NUM>; the dried pole piece was then compacted on a 30T roller press and finally cut into a round positive electrode piece with a diameter of <NUM>, wherein the mass of the active substance in the round piece was about <NUM>; the cut positive electrode piece, an electrolyte solution and a separator were assembled into a button battery; and the button battery was left to stand and then tested for the electrochemical performance, wherein the first discharge specific capacity tested at a current of <NUM> C was <NUM> mAh/g, the first charge-discharge efficiency was <NUM>%, under the current condition of <NUM> C, the 50th cycle specific capacity was maintained at <NUM> mAh/g, and the 50th cycle capacity retention rate was <NUM>%.

The positive electrode material prepared in Example <NUM>, the conductive agent SP, and the binder PVDF were mixed at a ratio of <NUM> : <NUM> : <NUM> (with a total mass of <NUM>), and then added to <NUM> of an NMP organic solvent solution to obtain a mixed solution; the mixed solution was stirred to obtain a slurry; the slurry was evenly smeared on an <NUM> aluminum foil with a thickness of <NUM>, and dried in a vacuum drying oven at <NUM> for <NUM>; the dried pole piece was then compacted on a 30T roller press and finally cut into a round positive electrode piece with a diameter of <NUM>, wherein the mass of the active substance in the round piece was about <NUM>; the cut positive electrode piece, an electrolyte solution and a separator were assembled into a button battery, and the button battery was left to stand and then tested for the electrochemical performance, wherein the first discharge specific capacity tested at a current of <NUM> C was <NUM> mAh/g, and the first charge-discharge efficiency was <NUM>%, and under the current condition of <NUM> C, the 50th cycle specific capacity was maintained at <NUM> mAh/g, and the 50th cycle capacity retention rate was <NUM>%.

The steps of Comparative Example <NUM> were almost the same as those of Example <NUM>, except that step (<NUM>) of Comparative Example <NUM> was changed to the following step (<NUM>).

The steps of Comparative Example <NUM> were almost the same as those of Example <NUM>, except that the conditions of step (<NUM>) in Comparative Example <NUM> were changed to the following step (<NUM>).

(<NUM>) The micropowder single crystal material was washed with water and centrifugally dried, wherein the mass ratio of pure water to the micropowder single crystal material was <NUM>:<NUM> and the water washing time was <NUM>; the material, which has been washed with water, was then vacuum dried at <NUM> to obtain a material with a lower residual alkali content; and the material was further subjected to coating sintering to obtain a ternary single crystal positive electrode material. The morphology of the obtained ternary single crystal positive electrode material was shown in <FIG>.

(<NUM>) The material, which has been washed with water, was dry coated with Al(OH)<NUM> as an additive (with an Al content of <NUM> ppm); under an air pressure of <NUM> MPa, the material was subjected to coating sintering; the temperature was raised to <NUM> at a temperature rise rate of <NUM>/min, continued to rise to <NUM> at a temperature rise rate of <NUM>/min, and maintained for <NUM>; and the material was then naturally cooled to room temperature to obtain a ternary single crystal positive electrode material.

<FIG> is an SEM image of a recovered ternary polycrystalline micropowder raw material. It can be seen from the figure that there is a lot of residual lithium on the surface of the polycrystalline micropowder, the micropowder particles are smaller than normal materials, with nonuniform shapes, sizes and distribution, indicating the necessity of premixing and re-sintering. <FIG> is an XRD pattern of the ternary single crystal positive electrode material prepared in Example <NUM>, wherein the (<NUM>)/(<NUM>) and (<NUM>)/(<NUM>) crystal plane peaks are clearly separated, indicating that the ternary single crystal positive electrode material has a higher degree of crystallinity and a good layered structure; and the (<NUM>)/(<NUM>) crystal plane peak intensity ratio in the XRD is greater than <NUM>, indicating that the ternary single crystal positive electrode material maintains a better crystal structure and low cation mixing, which is beneficial to improve the ion utilization. <FIG> is an SEM image of the ternary single crystal positive electrode material prepared in Example <NUM>, which has been sintered in oxygen. It can be seen from the <FIG> that the surface of the ternary single crystal positive electrode material is smooth, and most of the particles are between <NUM> and <NUM> in size. <FIG> is an SEM image of the ternary single crystal positive electrode material prepared in Example <NUM>, which has been sintered in the air, it can be seen that the material has a relative smooth surface, a relative uniform particle size, and less agglomerations. <FIG> is a ternary single crystal positive electrode material obtained by means of primary sintering with a short temperature maintaining time, it can be seen that the primary particles are relatively small and have more agglomerations, so that the capacity cannot be exploited. <FIG> is a ternary single crystal material prepared with a relatively low water washing strength, wherein the water washing strength is low, some weak agglomerations are not opened, and the surface of the material is relatively uniform and smooth. <FIG> is a ternary positive electrode material obtained by means of coating sintering with a different coating additive (Al(OH)<NUM>), wherein the surface of the material is relatively smooth and the coating effect is good.

The comparison results of the electrochemical and physical performances of the raw material and the ternary positive electrode materials of Example <NUM> and <NUM> and Comparative Example <NUM>-<NUM> are as shown in Table <NUM>:.

Table <NUM> is a comparison of the electrochemical performance and physical performance of the ternary positive electrode materials of Examples <NUM> and <NUM> and Comparative Examples <NUM>-<NUM>. The data of the raw material shows that due to improper storage of the ternary polycrystalline micropowder, the residual lithium is high, the resistivity of the powder is high, and the corresponding button battery capacity is relatively low. For Example <NUM>, under the conditions of a voltage of <NUM> V and a current of <NUM> C, the first discharge specific capacity is <NUM> mAh/g, and the first charge-discharge efficiency is <NUM>%; and after <NUM> cycles, the discharge specific capacity is <NUM> mAh/g, and the capacity retention rate is <NUM>%, which are significantly better than the electrochemical performances of the ternary positive electrode materials of Comparative Examples <NUM>-<NUM>, and the powder resistivity thereof is significantly reduced relative to that of the raw material, and also relatively lower relative to those of the comparative examples. For Example <NUM>, under the conditions of a voltage of <NUM> V and a current of <NUM> C, the first discharge specific capacity is <NUM> mAh/g, and the first charge-discharge efficiency is <NUM>%; and after <NUM> cycles, the discharge specific capacity is <NUM> mAh/g, and the capacity retention rate is <NUM>%, that is, the performance of Example <NUM> is slightly poorer than that of Example <NUM>; however, compared to Comparative Examples <NUM>-<NUM>, the electrochemical performance of Example <NUM> is better and the powder resistivity is lower. For Comparative Example <NUM>, due to the short temperature maintaining time, the particles do not grow up, and have many agglomerations, the corresponding button battery capacity is low, the powder resistivity is high, and the capacity retention rate is low. The water washing strength in Comparative Example <NUM> is weaker than that in Example <NUM>, there are more weak agglomerations, the button battery capacity thereof is relatively lower, and the powder resistivity is slightly higher. In Comparative Example <NUM>, a different coating additive is used, and the obtained single crystal ternary positive electrode material powder has a high resistivity, which affects the electrochemical performance thereof.

Therefore, the preparation of a ternary polycrystalline micropowder into a ternary single crystal positive electrode material by means of the method of the present disclosure can not only recycle the by-product, increase the utilization of the material, and increase product benefits, but can also improve the cycle performance, safety performance, and electrochemical performance of the product to produce a single crystal ternary positive electrode material with a higher energy density.

Claim 1:
A method for preparing a ternary single crystal positive electrode material, comprising the following steps:
(<NUM>) mixing a ternary polycrystalline micropowder, raising a temperature, carrying out a primary sintering, and lowering the temperature to obtain an intermediate;
(<NUM>) subjecting the intermediate to jet pulverization to obtain a single crystal material, washing the single crystal material with water, and centrifugally drying the single crystal material to obtain a material with a residual alkali content of less than <NUM> ppm; and
(<NUM>) adding a coating agent to the material, raising a temperature, carrying out a secondary sintering, and lowering the temperature to obtain the ternary single crystal positive electrode material; wherein the coating agent is at least one of an oxide, hydroxide and salt of a metal, or an oxide and fluoride of a non-metal, or a corresponding acid and salt of the non-metal; the metal is at least one of Al, Ce, Y, Zn, Cr, Nb, Mg, La, Sr, Zr, Sn, Na, Ca, Sb, V, and W; and the non-metal is at least one of B, P, F, C, and S, with aluminum hydroxide being excluded;
wherein in step (<NUM>), the ternary polycrystalline micropowder is an unqualified product produced by means of mechanical grinding of the ternary polycrystalline material during crushing, which is a by-product produced during crushing of the ternary polycrystalline material; and a chemical formula of the ternary polycrystalline micropowder is LiNixCoyMnzO<NUM>, with <NUM> ≤ x ≤ <NUM>, <NUM> ≤ y ≤ <NUM>, <NUM> ≤ z ≤ <NUM>, and x + y + z = <NUM>;
wherein in step (<NUM>), requirements for the particle size of the single crystal material are: a Dv<NUM> of <NUM>-<NUM> and a Dv<NUM> of less than <NUM>.