A polycrystalline ultra-high nickel ternary cathode material, its preparation method and use

Abstract

This application relates to the field of new energy technologies and discloses a polycrystalline ultra-high nickel ternary cathode material, which includes a core layer doped with metal element A and metal element B, and a shell layer containing cobalt element and boron element at the same time; wherein metal element A is selected from at least one of aluminum element and magnesium element, and metal element B is selected from at least one of zirconium element, yttrium element, titanium element, tungsten element, and strontium element. In this application, the structural stability of the cathode material crystal is improved by metal element A, the shallow structure strength of the cathode material is improved by metal element B, a coating layer is formed on the surface of the cathode material by cobalt, and the soluble lithium in the cathode material is further consumed by boron and cobalt. In summary, the lithium-nickel mixing of the cathode material is restricted and the adverse effects of soluble lithium on the cathode material are inhibited from four dimensions. In addition, this application also discloses a method for preparing the above polycrystalline ultra-high nickel ternary cathode material and its uses.

Description

Technical Field

[0001] This application relates to the field of new energy technologies, and particularly to a polycrystalline ultra-high nickel ternary cathode material, its preparation method, and uses. Background Art

[0002] Ultra-high nickel ternary cathode materials generally refer to ternary cathode materials with a relatively high nickel content. Under current technical conditions, the high-nickel ternary technology route has become the preferred choice for developing high-capacity batteries. As the nickel content increases, the energy density of ternary batteries also increases significantly. At the same time, the high-nickel ternary cathode material increases the proportion of relatively inexpensive nickel, which also has certain advantages in terms of cost.

[0003] However, ultra-high nickel ternary cathode materials also pose some challenges and problems. A high nickel content can lead to lithium-nickel mixing, resulting in lithium precipitation and poor cycling performance. Traditional polycrystalline NCM particles are composed of submicron primary grains with random orientations, which can cause enrichment of Li + diffusion paths, uneven Li concentration inside the particles, and thus cause stress / strain concentration and eventual internal cracks along the grain boundaries. At the same time, the Ni, Co, and Mn ratios in ultra-high nickel ternary cathode materials tend towards Ni, resulting in a relatively small amount of Mn element acting as a support, making its structure more unstable.

[0004] Based on this, due to the enrichment of Li + diffusion paths, the ultra-high nickel material surface has more soluble lithium. If not consumed or removed, after the material is made into a battery, the soluble lithium on the surface will undergo a series of side reactions with the electrolyte, resulting in battery swelling and increasing the occurrence of serious safety problems. In the industry, the water washing process of the high-nickel 8 series is generally used to reduce the soluble lithium on the material surface. However, the structure of the ultra-high nickel material itself is unstable. During the water washing process, H + ionized by water will + exchange positions with Li in the material, resulting in the precipitation of structural lithium and the collapse of the material structure.

[0005] In response to this, Existing Technology 1: Chinese Patent Application No. 202410944242.X discloses a ternary cathode material and its preparation method, including the following steps: mixing a lithium salt, a ternary precursor (Ni x Co y Mn z (OH2), and a metal compound containing element A to obtain a mixture; then subjecting the mixture obtained in step 1 to a first sintering to obtain a first sintered material; then crushing the first sintered material obtained in step 2 to obtain a powder; finally, mixing the powder obtained in step 3 with a metal compound containing element B and performing a second sintering to obtain the ternary cathode material; by improving the doping and coating processes, the residual lithium content on the surface of the cathode material is reduced;

[0006] Further observing the specification of this solution, it can be seen that the doping element used is element A, specifically one or more of Zr, B, W, Ti, and Y, and element A at least includes Zr;

[0007] The coating element used is element B, specifically one or more of Co, Ti, W, and Al, and element B at least includes Co;

[0008] Among them, in paragraph 11 of the specification of this solution, the functions of the doping element A and the coating element B are described in relatively more detail. Specifically, "the doping metal element A can form a protective layer structure mainly composed of A-O bonds on the ternary cathode material, effectively inhibiting oxygen evolution and transition metal dissolution, and maintaining a relatively smooth Li + migration channel; the coating of the metal element B can effectively reduce the residual lithium in the material. The B element reacts with the free Li on the surface of the ternary cathode material, which can not only reduce the residual lithium, but also generate compounds of B, effectively improving the electrochemical performance such as the rate and capacity of the material."

[0009] It can be seen that the actual purpose of the doping element A in this solution is closer to protecting the surface of the cathode material and preventing the dissolution of nickel, cobalt, and manganese;

[0010] The coating of the metal element B is designed for the residual lithium on the material surface.

[0011] Prior Art 2: Chinese Patent Application No. 202410595326.7 discloses a cathode material, its preparation method and application. The cathode material includes a cathode matrix and a coating layer on the surface of the cathode matrix; the chemical general formula of the cathode matrix is Li z Ni 1-q-y-a Co q Mn y A a B b O2, where 0.95 < z < 1.3, 0 < q ≤ 0.2, 0 < y ≤ 0.2, 0 < a ≤ 0.1, 0 < b ≤ 0.1, element A is selected from at least one of Zr, Sr, Al, Sb, W, Y, and Ti, and B is selected from tetrahedral polyanions (FO4) n- and its derivative groups (F m O 3m+1 ), n- F is selected from at least one of P, Si, S, As, Mo, and W; the coating layer contains element R, and element R is selected from at least one of Al, Ti, W, Co, and B;

[0012] However, further observation of this solution reveals that during the coating process in this solution, either the cathode material matrix is first washed, or the mixture of the cathode material and element R needs to be calcined and then washed with water. It can be seen that this solution requires water washing treatment in both cases;

[0013] Moreover, this solution records the functions of its dopants and coating agents in paragraph 36 of the specification: "By doping polyanionic group B in the cathode matrix, the TM-O bonds of the layered oxide can be effectively stabilized, enhancing the structural stability and thermal stability of the high-nickel ternary material, thereby improving the high-temperature performance of the material. Additionally, it can effectively expand the distance between the lithium layer and the transition metal layer, promote the migration of lithium ions, reduce the volume shrinkage of the unit cell during cycling, thereby reducing the lattice strain and inhibiting the formation of microcracks. Doping element A in the cathode matrix is beneficial to ensuring the conductivity and high capacity of the cathode material. Further coating the surface of the cathode matrix with a coating layer containing elements Al, Ti, W, Co, and B can further improve the capacity of the cathode material and inhibit the side reactions between the cathode material and the electrolyte."

[0014] The problems to be solved by this solution are: how to provide a polycrystalline ultra-high-nickel ternary cathode material with a low soluble lithium content and without the need to remove soluble lithium by water washing. Summary of the Invention

[0015] The purpose of this application is to provide a polycrystalline ultra-high-nickel ternary cathode material with a low soluble lithium content and without the need to remove soluble lithium by water washing, as well as a preparation method for this cathode material. This method can effectively stabilize the structure of the polycrystalline ternary cathode material in the high-voltage working platform, reduce the surface residual alkali during the production process, and enable the coating elements to be uniformly coated on the surface.

[0016] Unless otherwise specified in this application: nM represents nanomoles per liter, μM represents micromoles per liter, mM represents millimoles per liter, and M represents moles per liter;

[0017] To achieve the above purpose, this application discloses a polycrystalline ultra-high-nickel ternary cathode material, which includes a core layer doped with metal element A and metal element B simultaneously, and a shell layer containing cobalt element and boron element simultaneously;

[0018] The metal element A is selected from at least one of aluminum element and magnesium element;

[0019] The metal element B is selected from at least one of zirconium element, yttrium element, titanium element, tungsten element, and strontium element.

[0020] Among them, due to the small radius of metal element A, it is easy to enter the bulk phase and is an inert metal, and it will not change its valence due to the gain or loss of electrons during the redox reaction. Therefore, metal element A is similar to manganese and provides a more stable supporting role than manganese;

[0021] The metal element B plays a role in promoting fusion and stabilizing the bulk phase during sintering, increasing the thickness of the grain boundary, and stabilizing the oxygen potential without precipitation under long-cycle working conditions; moreover, the metal element B can stabilize the crystal lattice;

[0022] Under the combined action of the metal element A and the metal element B, the crystal of the ultra-high nickel cathode material is more stable, thereby reducing the soluble lithium content on the surface of the material;

[0023] Meanwhile, a shell layer containing cobalt element and boron element is coated on the surface of the ultra-high nickel cathode material. On the one hand, the use of cobalt element can form a protective layer to reduce the direct contact between the cathode material and the electrolyte. On the other hand, cobalt and boron further react with the soluble lithium on the surface of the ultra-high nickel ternary material to consume the soluble lithium on the surface of the ternary material, further inhibiting the residual lithium on the surface of the cathode material.

[0024] Preferably, the matrix of the polycrystalline ultra-high nickel ternary cathode material is LiNi x Co y Mn z O2, where x + y + z = 1 and 0.8 ≤ x ≤ 0.95, y > 0, z > 0.

[0025] Preferably, the matrix of the polycrystalline ultra-high nickel ternary cathode material is LiNi x Co y Mn z O2, where x + y + z = 1 and 0.88 ≤ x ≤ 0.95, y > 0, z > 0.

[0026] As the nickel content is further increased, the lithium-nickel mixing will become more serious, resulting in further precipitation of soluble lithium. However, due to the strong inhibitory ability of the metal element A, the metal element B, and the shell layer containing cobalt element and boron element on soluble lithium, therefore, when dealing with ternary cathode materials with higher nickel content, the advantages of this application will be further manifested.

[0027] Preferably, the grain size of the core layer doped with the metal element A and the metal element B is 300 - 350 nm;

[0028] The mass of the metal element A is 1000 - 5000 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material;

[0029] The mass of the metal element B is 1000 - 3000 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material;

[0030] The mass of the cobalt element is 3000 - 30000 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material;

[0031] The mass of the boron element is 300 - 2000 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material.

[0032] Furthermore, through further optimization of the doping amounts of metal element A and metal element B, and the coating amounts of cobalt element and boron element in the shell layer in this application, the overall ability of metal element A, metal element B, cobalt element, and boron element to inhibit soluble lithium is further improved. On the one hand, by optimizing the doping amounts of metal element A and metal element B, when the ternary cathode material has a more stable crystal structure, the amount of its soluble lithium is more suitable for the formation of the coating layer containing cobalt element and boron element. And due to the optimization of the addition amounts of cobalt element and boron element, the thickness of the coating layer is directly changed, making it have both good protection ability and electrochemical performance.

[0033] Preferably, the metal element A is provided by an oxide containing the metal element A;

[0034] The metal element B is provided by an oxide containing the metal element B;

[0035] The cobalt element is provided by cobalt oxyhydroxide and / or cobaltous oxide;

[0036] The boron element is provided by boron nitride and / or boric acid and / or boron oxide.

[0037] Preferably, the metal element A is aluminum element, and the metal element B is zirconium element.

[0038] Preferably, the cobalt element is provided by cobalt oxyhydroxide;

[0039] The boron element is provided by boron nitride.

[0040] Furthermore, during the experiment process of this application, through repeated experiments on various cobalt sources and boron sources, it is found that cobalt oxyhydroxide and boron nitride show the most excellent improvement effect.

[0041] In addition, this application also discloses a method for preparing the above polycrystalline ultra-high nickel ternary cathode material, doping metal element A and metal element B into the matrix of the polycrystalline ultra-high nickel ternary cathode material as the core layer;

[0042] Coating cobalt element and boron element on the surface of the core layer simultaneously to obtain the polycrystalline ultra-high nickel ternary cathode material.

[0043] Preferably, it includes the following steps:

[0044] Step 1: Mix the nickel-cobalt-manganese precursor, the oxide containing metal element A, the oxide containing metal element B, and the lithium source together to obtain a first mixed material. Then, place the first mixed material in an oxygen-rich environment and heat it at a heating rate of 1 - 2 °C / min to 520 - 580 °C, and keep it warm for 1.5 - 2.5 h;

[0045] Then, heat it at a heating rate of 0.5 - 1 °C / min to 700 - 750 °C, keep it warm for 10 - 14 h, and then naturally cool it to room temperature, take it out, crush it, and screen it to obtain a first-fired material;

[0046] Step 2: Mix the first-fired material obtained in Step 1 with cobalt oxyhydroxide and / or cobaltous oxide, boron nitride and / or boric acid and / or boron oxide together to obtain a second mixed material. Then, place the second mixed material in an oxygen-rich environment and heat it at a heating rate of 1.2 - 1.8 °C / min to 550 - 700 °C, keep it warm for 8 - 10 h, and then naturally cool it to room temperature, take it out, crush it, and screen it to obtain a polycrystalline ultra-high nickel ternary cathode material.

[0047] In addition, this application also discloses a battery, which includes the above polycrystalline ultra-high nickel ternary cathode material.

[0048] Compared with the prior art, the present invention has the following advantages:

[0049] 1. There is no water washing process in the production process, no heavy metal-containing wastewater is generated, which is environmentally friendly. At the same time, because the ultra-high nickel polycrystalline material does not undergo the water washing process, most of the Li in the crystal lattice can stably exist in the Li site, greatly improving the stability of the material, and then improving the cycle performance of the material; + Most of them can stably exist in the Li site, greatly improving the stability of the material, and then improving the cycle performance of the material;

[0050] 2. Through the simultaneous doping of metal element A and metal element B, on the one hand, the stable grain boundaries in the lattice of metal element B are utilized, and on the other hand, metal element A plays a supporting role in the lattice like the Mn element, jointly stabilizing the structure of the ultra-high nickel crystal, and then restricting the soluble lithium on the surface of the cathode material;

[0051] 3. Through the shell layer containing cobalt element and boron element coated on the surface of the cathode material, reacting with the soluble lithium on the surface of the cathode material, consuming most of the soluble lithium, and at the same time, a thin layer of lithium cobaltate coating layer can be formed on the surface to form a core-shell structure, so that the ultra-high nickel ternary material does not directly contact the electrolyte, slowing down the erosion of the electrolyte on the main material, improving the cycle stability, and at the same time, boron element reacts with the soluble lithium on the surface to generate a Li-B-O fast ion conductor, improving the ionic conductivity, and then improving the capacity. Description of the Drawings

[0052] Figure 1Cyclic capacity test charts of the cathode materials prepared in Example 1, Example 6, and Example 7;

[0053] Figure 2 Cyclic capacity test charts of the cathode materials prepared in Comparative Example 7, Comparative Example 8, and Comparative Example 9;

[0054] Figure 3 Scanning electron microscope image of the second mixed material in Example 1;

[0055] Figure 4 Electron microscope image of the polycrystalline ultra-high nickel ternary cathode material prepared in Example 1. Detailed implementation mode

[0056] In the description of the present invention, it should be noted that for those not specified in the examples, the operations are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0057] Example 1

[0058] Step 1: Mix nickel cobalt manganese precursor (Ni 0.88 Co 0.6 Mn 0.6 O2), alumina, zirconia, and lithium carbonate together to obtain a first mixed material, where the molar ratio of lithium element in lithium carbonate to the total molar amount of nickel, cobalt, and manganese in the nickel cobalt manganese precursor is 1.03:1. Subsequently, place the first mixed material in an oxygen-rich environment and heat it at a heating rate of 1.5 °C / min to 560 °C, and keep it for 2 h;

[0059] Then heat it at a heating rate of 0.8 °C / min to 720 °C, keep it at a constant temperature for 12 h, and then naturally cool it to room temperature, take it out, crush it, and screen it to obtain a first-fired material;

[0060] Among them, the mass of aluminum in alumina is added at 3000 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material;

[0061] The mass of zirconium in zirconia is added at 2000 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material;

[0062] Step 2: Mix the first-fired material prepared in Step 1 with cobalt oxyhydroxide and boron nitride to obtain a second mixed material;

[0063] Among them, the mass of cobalt element in cobalt oxyhydroxide is added at 15000 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material;

[0064] The mass of boron element in boron nitride is added at 1000 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material;

[0065] Subsequently, the second mixed material is placed in an oxygen-rich environment and heated at a heating rate of 1.6 °C / min to 620 °C, held at a constant temperature for 9 h, and then naturally cooled to room temperature, taken out, crushed, and sieved to obtain a polycrystalline ultra-high nickel ternary cathode material.

[0066] Example 2

[0067] Step 1: Mix nickel cobalt manganese precursor (Ni 0.88 Co 0.6 Mn 0.6 O2), alumina, zirconia, and lithium carbonate together to obtain a first mixed material. The molar ratio of the lithium element in lithium carbonate to the total molar amount of nickel, cobalt, and manganese in the nickel cobalt manganese precursor is 1.03:1. Subsequently, the first mixed material is placed in an oxygen-rich environment and heated at a heating rate of 2 °C / min to 580 °C and held at a constant temperature for 1.5 h;

[0068] Then, it is heated at a heating rate of 1 °C / min to 750 °C, held at a constant temperature for 10 h, and then naturally cooled to room temperature, taken out, crushed, and sieved to obtain a first-fired material;

[0069] Among them, the mass of aluminum in alumina is added at 5000 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material;

[0070] The mass of zirconium in zirconia is added at 3000 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material;

[0071] Step 2: Mix the first-fired material obtained in Step 1 with cobalt oxyhydroxide and boron nitride to obtain a second mixed material;

[0072] Among them, the mass of cobalt element in cobalt oxyhydroxide is 30000 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material;

[0073] The mass of boron element in boron nitride is 2000 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material;

[0074] Subsequently, the second mixed material is placed in an oxygen-rich environment and heated at a heating rate of 1.8 °C / min to 700 °C, held at a constant temperature for 8 h, and then naturally cooled to room temperature, taken out, crushed, and sieved to obtain a polycrystalline ultra-high nickel ternary cathode material.

[0075] Example 3

[0076] Step 1: Mix nickel cobalt manganese precursor (Ni 0.88 Co 0.6 Mn 0.6O2), alumina, zirconia, and lithium carbonate are mixed together to obtain a first mixed material, where the molar ratio of the lithium element in lithium carbonate to the total molar amount of nickel, cobalt, and manganese in the nickel-cobalt-manganese precursor is 1.03:1. Subsequently, the first mixed material is placed in an oxygen-rich environment and heated at a rate of 1 °C / min to 520 °C and held for 2.5 h;

[0077] Then, it is heated at a rate of 0.5 °C / min to 700 °C and held at a constant temperature for 14 h. Subsequently, it is naturally cooled to room temperature, taken out, crushed, and sieved to obtain a first-fired material;

[0078] Among them, the mass of aluminum in alumina is added at 1000 ppm based on the total mass of the polycrystalline ultra-high nickel ternary cathode material;

[0079] The mass of zirconium in zirconia is added at 1000 ppm based on the total mass of the polycrystalline ultra-high nickel ternary cathode material;

[0080] Step 2: The first-fired material obtained in Step 1 is mixed with cobalt oxyhydroxide and boron nitride to obtain a second mixed material;

[0081] Among them, the mass of cobalt element in cobalt oxyhydroxide is added at 3000 ppm based on the total mass of the polycrystalline ultra-high nickel ternary cathode material;

[0082] The mass of boron element in boron nitride is added at 300 ppm based on the total mass of the polycrystalline ultra-high nickel ternary cathode material;

[0083] Subsequently, the second mixed material is placed in an oxygen-rich environment and heated at a rate of 1.2 °C / min to 550 °C and held at a constant temperature for 10 h. Subsequently, it is naturally cooled to room temperature, taken out, crushed, and sieved to obtain a polycrystalline ultra-high nickel ternary cathode material.

[0084] Example 4

[0085] It is basically the same as Example 1, except that magnesium oxide is used to replace alumina, and the mass of magnesium in magnesium oxide is added at 3000 ppm based on the total mass of the polycrystalline ultra-high nickel ternary cathode material.

[0086] Example 5

[0087] It is basically the same as Example 1, except that yttrium oxide is used to replace zirconia, and the mass of yttrium in yttrium oxide is added at 2000 ppm based on the total mass of the polycrystalline ultra-high nickel ternary cathode material.

[0088] Example 6

[0089] It is basically the same as Example 1, except that the nickel-cobalt-manganese precursor is Ni 0.8 Co 0.1 Mn 0.1 O2.

[0090] Example 7

[0091] Basically the same as Example 1, except that the nickel-cobalt-manganese precursor is Ni 0.95 Co 0.02 Mn 0.03 O2.

[0092] Example 8

[0093] Basically the same as Example 1, except that cobalt oxide is used instead of cobalt oxyhydroxide, and the mass of cobalt element in the cobalt oxide is 15000 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material.

[0094] Example 9

[0095] Basically the same as Example 1, except that boric acid is used instead of boron nitride, and the mass of boron element in the boric acid is 1000 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material.

[0096] Example 10

[0097] Basically the same as Example 1, except that the mass of aluminum in aluminum oxide is added at 4000 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material;

[0098] The mass of zirconium in zirconia is added at 1000 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material.

[0099] Example 11

[0100] Basically the same as Example 1, except that the mass of aluminum in aluminum oxide is added at 1000 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material;

[0101] The mass of zirconium in zirconia is added at 4000 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material.

[0102] Example 12

[0103] Basically the same as Example 1, except that the mass of cobalt element in cobalt oxyhydroxide is added at 15700 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material;

[0104] The mass of boron element in boron nitride is added at 300 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material.

[0105] Example 13

[0106] Basically the same as Example 1, except that the mass of cobalt element in cobalt oxyhydroxide is added at 14000 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material;

[0107] The mass of boron element in boron nitride is added at 2000 ppm based on the total mass of the polycrystalline ultra-high nickel ternary cathode material.

[0108] Example 14

[0109] It is basically the same as Example 1, except that the mass of aluminum in alumina is added at 5000 ppm based on the total mass of the polycrystalline ultra-high nickel ternary cathode material;

[0110] The mass of zirconium in zirconia is added at 3000 ppm based on the total mass of the polycrystalline ultra-high nickel ternary cathode material.

[0111] Example 15

[0112] It is basically the same as Example 1, except that the mass of cobalt element in cobalt oxyhydroxide is added at 30000 ppm based on the total mass of the polycrystalline ultra-high nickel ternary cathode material;

[0113] The mass of boron element in boron nitride is added at 2000 ppm based on the total mass of the polycrystalline ultra-high nickel ternary cathode material.

[0114] Comparative Example 1

[0115] Step 1: Mix the nickel-cobalt-manganese precursor (Ni 0.88 Co 0.6 Mn 0.6 O2), alumina, zirconia, and lithium carbonate together to obtain a first mixed material, where the molar ratio of the molar amount of lithium element in lithium carbonate to the total molar amount of nickel, cobalt, and manganese in the nickel-cobalt-manganese precursor is 1.03:1. Subsequently, heat the first mixed material in an oxygen-rich environment at a heating rate of 1.5 °C / min to 560 °C and hold for 2 h;

[0116] Then, heat it at a heating rate of 0.8 °C / min to 720 °C, keep it at a constant temperature for 12 h, and then naturally cool it to room temperature, take it out, crush it, and screen it to obtain a first-fired material;

[0117] Among them, the mass of aluminum in alumina is added at 3000 ppm based on the total mass of the polycrystalline ultra-high nickel ternary cathode material;

[0118] The mass of zirconium in zirconia is added at 2000 ppm based on the total mass of the polycrystalline ultra-high nickel ternary cathode material;

[0119] Subsequently, heat the first-fired material in an oxygen-rich environment at a heating rate of 1.6 °C / min to 620 °C, keep it at a constant temperature for 9 h, and then naturally cool it to room temperature, take it out, crush it, and screen it to obtain the ultra-high nickel ternary cathode material.

[0120] Comparative Example 2

[0121] Step 1: Mix the nickel-cobalt-manganese precursor (Ni 0.88 Co0.6 Mn 0.6 Mix lithium carbonate together with (Ni

[0122] Co

[0123] Mn)O2 to obtain a first mixed material, where the molar ratio of lithium element in lithium carbonate to the total molar amount of Ni, Co, and Mn in the Ni-Co-Mn precursor is 1.03:1. Subsequently, place the first mixed material in an oxygen-rich environment and heat it at a heating rate of 1.5 °C / min to 560 °C, and keep it warm for 2 h;

[0124] Then heat it at a heating rate of 0.8 °C / min to 720 °C, keep it at a constant temperature for 12 h, then naturally cool it to room temperature, take it out, crush it, and screen it to obtain a first-fired material;

[0125] Step 2: Mix the first-fired material obtained in Step 1 together with cobalt oxyhydroxide and boron nitride to obtain a second mixed material;

[0126] Among them, the mass of cobalt element in cobalt oxyhydroxide is 15000 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material;

[0127] The mass of boron element in boron nitride is 1000 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material;

[0128] Subsequently, place the second mixed material in an oxygen-rich environment and heat it at a heating rate of 1.6 °C / min to 620 °C, keep it at a constant temperature for 9 h, then naturally cool it to room temperature, take it out, crush it, and screen it to obtain the polycrystalline ultra-high nickel ternary cathode material.

[0129] Comparative Example 3

[0130] It is basically the same as Example 1, except that niobium oxide is used to replace alumina.

[0131] Comparative Example 4

[0132] It is basically the same as Example 1, except that boron oxide is used to replace zirconia.

[0133] Comparative Example 5

[0134] It is basically the same as Example 1, except that alumina is used to replace cobalt oxyhydroxide.

[0135] Comparative Example 6

[0136] Step 1: Use a nickel-cobalt-manganese precursor (Ni 0.88 Co 0.6 Mn 0.6O2), and lithium carbonate are mixed together to obtain a first mixed material. The molar ratio of the lithium element in lithium carbonate to the total molar amount of nickel, cobalt, and manganese in the nickel-cobalt-manganese precursor is 1.03:1. Subsequently, the first mixed material is placed in an oxygen-rich environment and heated at a rate of 1.5 °C / min to 560 °C, and held for 2 h;

[0137] Then, it is heated at a rate of 0.8 °C / min to 720 °C and held at a constant temperature for 12 h. Subsequently, it is naturally cooled to room temperature, taken out, crushed, and sieved to obtain a first-fired material;

[0138] Step 2: The first-fired material prepared in Step 1 is placed in an oxygen-rich environment and heated at a rate of 1.6 °C / min to 620 °C, and held at a constant temperature for 9 h. Subsequently, it is naturally cooled to room temperature, taken out, crushed, and sieved to obtain a high-nickel ternary cathode material.

[0139] Comparative Example 8

[0140] It is basically the same as Comparative Example 7, except that the nickel-cobalt-manganese precursor (Ni 0.8 Co 0.1 Mn 0.1 O2) is used to replace the nickel-cobalt-manganese precursor (Ni 0.88 Co 0.6 Mn 0.6 O2).

[0141] Comparative Example 9

[0142] It is basically the same as Comparative Example 7, except that the nickel-cobalt-manganese precursor (Ni 0.95 Co 0.02 Mn 0.03 O2) is used to replace the nickel-cobalt-manganese precursor (Ni 0.88 Co 0.6 Mn 0.6 O2).

[0143] Performance test:

[0144] Electrochemical analysis of the button cells is carried out on the polycrystalline ternary cathode materials obtained in Examples 1-15 and Comparative Examples 1-9. The main comparison is the discharge capacity at 0.1C and the 100-cycle retention rate of 1C charge and discharge.

[0145] The lithium battery cycle life detection method is: the capacity retention rate after 100 cycles of 1C for the coin cell. The test standard is: voltage 3.0V - 4.3V, charge and discharge rate 1C, temperature 25 °C, nominal specific capacity 200 mAh / g.

[0146] The detection method for the rate performance of lithium batteries is as follows: the initial cycle capacity of coin cells at different rates, the test criteria are: 3.0 - 4.3V, the temperature is 25°C, the charge and discharge rates are: 0.1C, 0.5C, 1C, and the nominal specific capacity is 200 mAh / g.

[0147] The detection method for free lithium on the material surface is as follows: calculate according to the acid-base titration method for the determination of lithium carbonate content in the first part of Chemical analysis methods for lithium carbonate, lithium hydroxide monohydrate and lithium chloride - Part 1: Determination of lithium carbonate content in GB / T 11064.1 - 2013.

[0148] Detect the surface soluble lithium, pH, and cycle life of lithium batteries for the examples and comparative examples. The specific conditions are the above methods, and the results are shown in Table 1:

[0149] Table 1

[0150]

[0151] Result analysis:

[0152] 1. It can be seen from Examples 1 - 3 that when the production parameters, mass ratio between doping elements, and mass ratio between coating elements in the preparation process of Examples 1 - 3 are slightly changed, although there is a certain fluctuating trend among Examples 1 - 3 in terms of lithium ion content, charge and discharge rate, and cycle retention rate, the overall amplitude is not obvious.

[0153] 2. Further observing Examples 1, 4 - 5, it can be seen that when the types of metal element A and metal element B are changed, the lithium ion content in Examples 4 and 5 is relatively increased compared with Example 1. The reason is that the improvement of the stabilizing ability of magnesium on the crystal structure compared with aluminum is not obvious, which further leads to the aggravation of lithium dissolution phenomenon in Example 4 and the increase of lithium ion content. At the same time, with the increase of lithium ion content, the rate performance and cycle performance both show a downward trend to varying degrees;

[0154] On the other hand, after using yttrium oxide to replace zirconium oxide in Example 5, due to the relatively poor stabilizing ability of yttrium on the material bulk phase compared with zirconium, the lithium ion content in Example 5 is increased, and the rate performance and cycle performance show a certain downward trend.

[0155] 3. Observing Examples 1 and 8 - 9, it can be seen that when using cobaltous oxide to replace cobalt hydroxide oxide, the lithium ion content in Example 8 is increased, and the rate performance and cycle performance show a certain downward trend. The reason is that the reaction activity of cobaltous oxide with the soluble lithium on the surface of the cathode material may be relatively low, which further leads to too little consumption of soluble lithium, resulting in the increase of lithium ion content in the cathode material, and then the decrease of the rate performance and cycle performance of the material;

[0156] Meanwhile, when boric acid was used to replace boron nitride in Example 9, although the amount of boron element was the same, in the molecular structure of boron nitride, nitrogen and boron were connected by a covalent bond of nitrogen-boron triple bond, with a higher bond energy, and boron nitride was more stable, requiring a higher temperature to break the bond and form active free radicals for reaction. Therefore, it could still combine with soluble lithium on the material surface at a high temperature of 620 °C to generate Li-Co-B-O fast ion conductor.

[0157] 4. It can be seen from Example 1, Example 10, and Example 11 that when the total amount of dopants remained unchanged and the mass ratio between aluminum and zirconium changed, the lithium ion content in Example 10 and Example 11 increased relative to Example 1. The reason is that aluminum element mainly enters the crystal phase through its smaller radius and plays a role in supporting the crystal structure, while zirconium mainly enhances the stability of the surface structure on the surface or in the shallow layer of the crystal;

[0158] The two cooperate with each other to improve the structural strength of the crystal, thereby inhibiting the mixing of lithium and nickel and the generation of soluble lithium. Therefore, even if the total doping amount remains unchanged, too low stability inside or on the surface of the crystal will lead to an increase in lithium-nickel mixing relative to Example 1, and then an increase in the lithium ion content relative to Example 1, resulting in poor rate performance and cycling performance;

[0159] Similarly, it can be seen from Example 12 and Example 13 that when the total amount of the coating agent remains unchanged, changing the mass ratio between cobalt and boron will also lead to an increase in the lithium ion content. The reason is that cobalt element plays a role in forming a protective layer in the shell layer. On the other hand, it also needs to jointly generate Li-Co-B-O fast ion conductor with boron and lithium;

[0160] When the thickness of the protective layer is too high and too much cobalt is consumed, the generation amount of Li-Co-B-O fast ion conductor will decrease, and then soluble lithium cannot be consumed more;

[0161] When the addition amount of cobalt is too small, the protective layer becomes too sparse to play an adequate protective role, resulting in a decrease in the overall rate performance and cycling performance.

[0162] 5. It can be seen from Example 1, Example 14, and Example 15 that when the mass ratio gap between the dopant and the coating agent is further increased, since the four elements of aluminum, zirconium, cobalt, and boron all inhibit soluble lithium from 4 dimensions respectively. When the amount of the dopant is too much, although the stability of the crystal lattice does increase and the amount of soluble lithium on the surface decreases, too low amount of soluble lithium on the surface will lead to the generation of Li-Co-B-O fast ion conductor because the material cannot provide enough lithium for Li-Co-B-O fast ion conductor. As a result, in the actual use process, the protection ability of the cathode material shell to the core decreases, leading to an increase in the lithium ion content and a decrease in the rate performance and cycling performance at the same time;

[0163] Meanwhile, when the coating agent is excessive, the shell formed by cobalt is too thick, which will cause the peeling off of the protective layer. After increasing the boron content, since the mass of soluble lithium does not change much relatively, therefore, it is also impossible to generate a more advantageous Li-Co-B-O fast ion conductor. And with the peeling off of cobalt, the quality of the Li-Co-B-O fast ion conductor will further decline, which will lead to a decrease in the protection ability of the cathode material shell to the core body, resulting in an increase in the lithium ion content, and at the same time, the rate performance and cycle performance will decline.

[0164] 6. It can be seen from Comparative Examples 1-2 that when only doping or coating the cathode material, the lithium ion content of the material will be further increased. The reason is that only doping is equivalent to completely abandoning the protection ability of the shell to the core and the effect of consuming soluble lithium through coating;

[0165] Although only coating can consume soluble lithium, the crystal structure is too fragile, the amount of soluble lithium is too large, and increasing the coating agent may cause the peeling off of the coating layer. Therefore, only coating treatment is still difficult to inhibit the soluble lithium content on the surface of the material;

[0166] Meanwhile, it can be seen from Comparative Examples 1-2 and Comparative Example 7 that although Comparative Examples 1-2 have a certain degree of improvement in inhibiting the lithium ion content compared with Comparative Example 7, the lithium ion content of Comparative Example 1 is reduced by 384 compared with Comparative Example 7, and the lithium ion content of Comparative Example 2 is reduced by 412 compared with Comparative Example 7. However, looking at the gap between Example 1 and Comparative Example 7, the lithium ion content of Example 1 is reduced by 1488 compared with Comparative Example 7. It can be seen that the inhibition ability of Example 1 for the lithium ion content exceeds the simple superposition of Comparative Example 1 and Comparative Example 2. At the same time, the improvement of Example 1 in rate performance and cycle performance compared with Comparative Example 7 also exceeds the improvement of Comparative Example 1 and Comparative Example 2 compared with Comparative Example 7. It can be seen that when doping and coating are carried out simultaneously, a synergistic effect is generated between the two, further inhibiting the soluble lithium content of the cathode material.

[0167] 7. It can be seen from Example 1 and Comparative Examples 3-6 that after replacing any doping element and coating element in the present application with other commonly used doping elements and coating elements, the lithium ion content of Comparative Examples 3-6 is increased compared with Example 1, and the rate performance and cycle performance are both decreased;

[0168] The reason is that, on the one hand, the niobium used in Comparative Example 3 has a relatively large ionic radius and cannot provide a support ability similar to that of aluminum. After using boron to replace zirconium for doping, boron will react with lithium hydroxide to form Li-B-O oxides at a relatively high first firing temperature. Since the bond energy after Li-B combination is higher than that of Li-Me (Me is Ni, Co, Mn), according to the reaction kinetics principle, reactants tend to proceed towards products with lower energy, which in turn leads to an increase in the surface lithium ion content and a deficiency in lattice lithium.

[0169] When using aluminum and zirconium to replace cobalt for coating, both aluminum and zirconium are inert metal oxides with high melting points and low chemical activities, and they cannot react with the soluble lithium on the surface during the second firing stage, thus leading to an increase in the surface lithium ion content; however, they can coat the material to a certain extent, weaken the erosion of the electrolyte on the material, and improve the cycle performance to a certain extent. However, because they are inert metals and cannot gain or lose electrons, they cannot provide capacity during the charge and discharge process of the battery, reducing the content of active substances and having a certain impact on the capacity.

[0170] 8. It can be seen from the comparison between Example 1, Example 6, Example 7 and Comparative Examples 7-9 that as the nickel content increases, the ability of this application to inhibit the lithium ion content is further amplified. When applied to a ternary cathode material with a nickel content of 0.95, its ability to inhibit the lithium ion content is maximally presented. However, due to the severe lithium-nickel mixing in the ultra-high nickel material, even though the nickel content has been maximally inhibited, as the cathode material is continuously used, it is still difficult to maintain good cycle performance.

[0171] Further, referring to Figure 1-2 it can be seen that when no doping and coating treatments are performed, the cathode material prepared from the nickel-cobalt-manganese precursor (Ni 0.8 Co 0.1 Mn 0.1 O2) has a better cycle capacity retention ability than the nickel-cobalt-manganese precursors (Ni 0.88 Co 0.6 Mn 0.6 O2), nickel-cobalt-manganese precursors (Ni 0.95 Co 0.02 Mn 0.03 O2);

[0172] However, with the application of doping and coating technologies, the cycle capacity retention ability of the cathode material prepared from the nickel-cobalt-manganese precursor (Ni 0.88 Co 0.6 Mn 0.6 O2) rises to the highest. It can be seen that doping and coating technologies are relatively more suitable for application to cathode materials with higher nickel contents.

[0173] Refer to simultaneously Figure 3-4 It can be seen that before sintering, the surface of the second mixture is smoother because the coating layers of cobalt and boron have not yet formed. Observe Figure 4 It can be seen that Figure 4 certain island-like protrusions appear on the surface because most of the soluble lithium on the surface of the cathode material is combined during the formation of Li-Co-B-O and coated on the outermost layer of the material, thus forming island-like protrusions.

[0174] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A polycrystalline ultra-high nickel ternary cathode material, characterized in that, It includes a core layer co-doped with metal element A and metal element B, and a shell layer containing cobalt element and boron element simultaneously; The metal element A is aluminum element, and the metal element B is zirconium element; The shell layer is obtained by coating cobalt element and boron element on the surface of the core layer simultaneously; The matrix of the polycrystalline ultra-high nickel ternary cathode material is LiNi x Co y Mn z O₂, where x + y + z = 1 and 0.88 ≤ x ≤ 0.95, y > 0, z > 0; The mass of the metal element A is 1000 - 5000 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material; The mass of the metal element B is 1000 - 3000 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material; The mass of cobalt element in the shell layer is 3000 - 30000 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material; The mass of boron element in the shell layer is 300 - 2000 ppm of the total mass of the polycrystalline ultra-high nickel ternary cathode material.

2. The polycrystalline ultra-high nickel ternary cathode material according to claim 1, wherein The grain size of the core layer doped with metal element A and metal element B is 300 - 350 nm.

3. The polycrystalline ultra-high nickel ternary cathode material according to claim 1, characterized in that The metal element A is provided by an oxide containing metal element A; The metal element B is provided by an oxide containing metal element B; The cobalt element is provided by cobalt oxyhydroxide and / or cobaltous oxide; The boron element is provided by boron nitride and / or boric acid and / or boron oxide.

4. The polycrystalline ultra-high nickel ternary cathode material according to claim 3, characterized in that, The cobalt element is provided by cobalt oxyhydroxide; The boron element is provided by boron nitride.

5. A preparation method for preparing the polycrystalline ultra-high nickel ternary cathode material according to any one of claims 1-4, characterized in that, Dope metal element A and metal element B into the matrix of the polycrystalline ultra-high nickel ternary cathode material and use it as the core layer; Coat cobalt element and boron element on the surface of the core layer simultaneously to obtain the polycrystalline ultra-high nickel ternary cathode material.

6. The preparation method of the polycrystalline ultra-high nickel ternary cathode material according to claim 5, characterized in that, It includes the following steps: Step 1: Mix a nickel-cobalt-manganese precursor, an oxide containing metal element A, an oxide containing metal element B, and a lithium source together to obtain a first mixed material. Then place the first mixed material in an oxygen-rich environment and heat it at a heating rate of 1 - 2 °C / min to 520 - 580 °C, and keep it warm for 1.5 - 2.5 h; Then heat it at a heating rate of 0.5 - 1 °C / min to 700 - 750 °C, keep it warm for 10 - 14 h, then naturally cool it to room temperature, take it out, crush it, and screen it to obtain a first-fired material; Step 2: Mix the first-fired material obtained in Step 1 with cobalt oxyhydroxide and / or cobaltous oxide, boron nitride and / or boric acid and / or boron oxide together to obtain a second mixed material. Then place the second mixed material in an oxygen-rich environment and heat it at a heating rate of 1.2 - 1.8 °C / min to 550 - 700 °C, keep it warm for 8 - 10 h, then naturally cool it to room temperature, take it out, crush it, and screen it to obtain the polycrystalline ultra-high nickel ternary cathode material.

7. A battery, characterized in that, It contains the polycrystalline ultra-high nickel ternary cathode material described in any one of claims 1 - 4.

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