High nickel ternary cathode material for lithium-ion batteries and its preparation method and application

Abstract

The present invention discloses a high-nickel ternary cathode material for lithium-ion batteries, its preparation method, and its application. First, a precursor with an elemental concentration gradient structure prepared by a coprecipitation method is mixed with lithium hydroxide. The concentration gradient sample is then rapidly heated using Joule heat from the powdered sample as a heat source. Through short-term control and ultra-fast heating and cooling rates, the interdiffusion of transition metal elements is suppressed, preserving the elemental concentration gradient structure to the greatest extent possible. The high-nickel ternary cathode material's structural design—a high-nickel core and a low-nickel shell—can reduce electrolyte corrosion and side reactions on the material matrix, further improving the cycle life and safety performance of the high-nickel ternary cathode material.

Description

Technical Field

[0001] This application relates to the field of new energy, in particular to a lithium-ion battery high-nickel ternary positive electrode material for lithium-ion power batteries and its preparation method and application Background Art

[0002] With the continuous development of new energy vehicles, the market has increasingly higher requirements for the energy density, cycle life, and safety of lithium-ion batteries. In recent years, nickel-cobalt-manganese / aluminum ternary cathode materials have achieved a certain degree of development and application due to their relatively low cost, high specific capacity / energy, and low toxicity. As a result, high-nickel ternary cathode materials have been used commercially on a large scale. As the nickel content in the ternary material increases, the specific capacity gradually increases, but at the same time, various performance properties such as the material's cycle stability significantly decrease. How to ensure that high-nickel cathode materials have both high capacity and excellent cycle stability has always been a research focus in the industry.

[0003] One of the main reasons for the poor stability of high nickel ternary cathode materials is that when the battery is in the charging state, the highly reactive Ni 4+ It is easy to produce side reactions with the electrolyte solution, causing structural damage to the material and releasing large amounts of oxygen and heat, thereby reducing the thermal stability and safety performance of the battery. Secondly, the mutual migration of transition metal ions and lithium ions during the charge / discharge process and the corrosion of the electrolyte solution cause the surface of the primary particles to become rough, destroying the initial layered structure and surface damage, and ultimately transforming into a completely disordered and inactive NiO rock salt phase.

[0004] The full concentration gradient structure design of the material can minimize the nickel content on the surface and reduce the Ni 4+The high reactivity reduces the corrosion of the material matrix by the electrolyte and the occurrence of side reactions. In the full concentration gradient material, the nickel content in the core of the secondary particles is high within the entire particle range, providing a higher capacity. It shows a gradual downward trend from the core to the particle surface, and the concentration of the elements is a gradual process, so the material has good compatibility and a more stable surface, resulting in better cycle performance. Concentration gradient materials are very likely to be used on a large scale in the future. China Guolian Automotive Power Battery Research Institute Co., Ltd. (application publication number CN111092221A) discloses a method for preparing a high-nickel ternary material with a transition metal element concentration gradient and the prepared material. Through a multi-stage roasting method, a long time in the low-temperature stage is combined with a short time in the high-temperature stage, thereby suppressing the abnormal growth of primary particles and the mutual diffusion of transition metals in the current gradient precursor during the post-lithium roasting process. The resulting performance is improved to a certain extent. South Korea's ECOPRO BM (application publication number CN107112516A) has disclosed a method for preparing a positive electrode active material for lithium secondary batteries that exhibits a concentration gradient. This method utilizes a barrier layer to maintain the concentration gradient during subsequent heat treatment, resulting in a positive electrode active material with a concentration gradient. Both methods utilize a precursor preparation process and control the calcination process to suppress the interdiffusion of transition metal elements.

[0005] However, the industrialization of concentration gradient materials still faces many challenges, the most important of which is maintaining the element concentration gradient. During the long calcination process in a traditional furnace, ion diffusion inevitably homogenizes, causing the element concentration gradient to decrease. The resulting cathode material cannot strictly meet the continuous element concentration gradient distribution trend, resulting in poor performance. Summary of the Invention

[0006] The present invention addresses the problem of poor stability of positive electrode materials in the prior art. By rationally configuring the precursor composition and introducing thermal shock measures, the problem of disappearance of element concentration gradient caused by homogenization of ion diffusion during the calcination of the synthesized concentration gradient precursor is overcome. A high-nickel ternary positive electrode material with a continuous element concentration gradient distribution trend is obtained, showing the advantages of high capacity and high cycle stability.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A method for preparing a high nickel ternary cathode material for lithium ion batteries, comprising: preparing a precursor Ni x Co y M 1-x-y (OH)2 and lithium hydroxide are mixed, and the mixed powder is subjected to thermal shock treatment using Joule heat to obtain a high-performance high-nickel ternary positive electrode material with element gradient distribution; Ni x Coy M 1-x-y In (OH)2, 0.7≤x<1.0, 0.01≤y<0.1; M is Mn, Al, W, Nb, Mo, Ta or Zr; the concentration of nickel decreases gradually from the core to the particle surface; lithium hydroxide and Ni x Co y M 1-x-y The total molar ratio of metal ions in (OH)2 is 1.0-1.2:1; the thermal shock treatment is carried out in a pure oxygen atmosphere, with a heating and cooling rate of 373 K / s-773 K / s, a target temperature of 700℃-900℃, and a holding time of 120s-360s.

[0009] The precursor Ni with element concentration gradient structure of the present invention x Co y M 1-x-y (OH)2 is prepared in one step by a co-precipitation method, including but not limited to the preparation methods of the precursors disclosed in the aforementioned CN111092221A and CN107112516A.

[0010] In certain embodiments of the present invention, the mixed powder is spread on a heated substrate, and the heated substrate is electrified in an air atmosphere to achieve thermal shock treatment on the powder.

[0011] In certain embodiments of the present invention, the heating substrate used is carbon cloth, graphite paper, or metal foil.

[0012] The present invention also relates to a positive electrode material prepared by the above method, wherein the positive electrode material is a high nickel ternary positive electrode material having an α-NaFeO2 layered material and belongs to R The secondary particles of the positive electrode material are spherical, with an average particle size of 6-13 μm and a tap density of 1.8-2.7 g / cm 3 .

[0013] The present invention also relates to the application of the above-mentioned positive electrode material in lithium-ion power batteries.

[0014] The positive electrode material formed by sintering of the present invention has a significant internal concentration gradient trend, high tap density, high capacity, and stable cycle performance, can well meet the requirements of power batteries for high energy density, and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The high nickel ternary precursor Ni with a concentration gradient structure prepared in Example 1 0.8 Co 0.15 Al 0.05 Radial distribution of Ni, Co, and Al element contents in the cross section of (OH)2 secondary particles.

[0016] Figure 2 The high nickel ternary positive electrode material Ni with a concentration gradient structure prepared in Example 1 0.8 Co 0.15 Al 0.05 Radial distribution of Ni, Co, and Al element contents in the cross section of O2 secondary particles.

[0017] Figure 3 The high nickel ternary positive electrode material Ni prepared in Example 1 0.8 Co 0.15 Al 0.05 XRD pattern of O2.

[0018] Figure 4 The high nickel ternary precursor Ni prepared in Example 1 0.8 Co 0.15 Al 0.05 (OH)2 and positive electrode material Ni 0.8 Co 0.15 Al 0.05 Electron microscopic image of O2.

[0019] Figure 5 The high nickel ternary positive electrode material Ni with a concentration gradient structure prepared in Example 1 0.8 Co 0.15 Al 0.05 O2 first charge and discharge curve and cycle performance curve.

[0020] Figure 6 The high nickel ternary precursor Ni with a concentration gradient structure prepared in Example 2 0.8 Co 0.15 Al 0.05 Radial distribution of Ni, Co, and Al element contents in the cross section of (OH)2 secondary particles.

[0021] Figure 7 The high nickel ternary positive electrode material Ni with a concentration gradient structure prepared in Example 2 0.8 Co 0.15 Al 0.05 Radial distribution of Ni, Co, and Al element contents in the cross section of O2 secondary particles.

[0022] Figure 8 The high nickel ternary positive electrode material Ni prepared in Example 2 0.8 Co 0.15 Al 0.05 XRD pattern of O2.

[0023] Figure 9 The high nickel ternary precursor Ni prepared in Example 2 0.8 Co 0.15 Al0.05 (OH)2 and positive electrode material Ni 0.8 Co 0.15 Al 0.05 Electron microscopic image of O2.

[0024] Figure 10 The high nickel ternary positive electrode material Ni with a concentration gradient structure prepared in Example 2 0.8 Co 0.15 Al 0.05 O2 first charge and discharge curve and cycle performance curve.

[0025] Figure 11 The high nickel ternary positive electrode material Ni with a concentration gradient structure prepared in Example 3 0.8 Co 0.15 Al 0.05 Radial distribution of Ni, Co, and Al element contents in the cross section of O2 secondary particles.

[0026] Figure 12 The high nickel ternary positive electrode material Ni with a concentration gradient structure prepared in Comparative Example 1 0.8 Co 0.15 Al 0.05 Radial distribution of Ni, Co, and Al element contents in the cross section of O2 secondary particles.

[0027] Figure 13 The high nickel ternary positive electrode material Ni prepared in comparative example 1 0.8 Co 0.15 Al 0.05 O2 first charge and discharge curve and cycle performance curve.

[0028] Figure 14 This is the radial distribution of the element content of the high-nickel ternary positive electrode material prepared in Example 2.

[0029] Figure 15 These are the first charge and discharge curves and cycle performance curves of Comparative Example 2. DETAILED DESCRIPTION

[0030] The present invention optimizes the parameters of the rapid Joule heating process after mixing a high-nickel ternary precursor with a concentration gradient structure with lithium hydroxide. This achieves the goal of suppressing the uniform diffusion of transition metal ions during the long-term roasting process of the concentration gradient precursor, and circumvents the problem of the disappearance of element concentration gradients caused by traditional furnace roasting. The concentration gradient distribution of elements in the high-nickel ternary cathode material is preserved to the greatest extent, inheriting the concentration gradient distribution of the high-nickel ternary precursor. This realizes the preparation of a high-nickel ternary cathode material with high capacity and high cycle stability.

[0031] The following will provide a clear and complete description of the technical solutions and advantages of the present invention in conjunction with the embodiments of the present invention. The described embodiments are only some of the embodiments of the present invention, not all of them. All other embodiments obtained by persons of ordinary skill in the art without inventive effort are within the scope of protection of the present invention.

[0032] Unless otherwise specified, the raw materials used in the present invention are conventional commercial products; the methods used in the present invention are conventional methods in the art unless otherwise specified.

[0033] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "an", "the" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0034] In the following examples, a high nickel ternary precursor Ni with a concentration gradient structure is used. 0.8 Co 0.15 Al 0.05 (OH)2 is used as a sample to illustrate the present invention so that those skilled in the art can fully understand the embodiments and technical effects of the present invention. It should be understood by those skilled in the art that other high nickel ternary precursors Ni with a concentration gradient structure obtained by coprecipitation method x Co y M 1-x-y (OH)2 (0.7≤x<1.0, 0.01≤y<0.1; M is Mn, Al, W, Nb, Mo, Ta or Zr) is also applicable to the present invention. 0.8 Co 0.15 Al 0.05 (OH)2 is only for the purpose of describing specific embodiments and is not intended to limit the present application.

[0035] Example 1

[0036] Step 1: Prepare the mixture by mixing lithium hydroxide with the concentration gradient precursor Ni 0.8 Co 0.15 Al 0.05 (OH)2 were mixed in a total molar ratio of 1.03:1 and placed in a ball mill and stirred evenly to obtain a mixed material;

[0037] Ni 0.8 Co 0.15 Al 0.05 The core component of (OH)2 is designed to be Ni 0.95 Al 0.05 (OH)2, the surface component is designed to be Ni 0.55 Co0.4 ACol 0.05 (OH)2, by adjusting the feed rate of various salt solutions using the co-precipitation method, the nickel element concentration gradient from the core to the surface of the high-nickel precursor secondary particles shows a gradually decreasing trend, the cobalt element concentration gradient shows a gradually increasing trend, and the aluminum element concentration gradient trend remains unchanged. Figure 1 The radial distribution of Ni, Co, and Al element contents in the cross section of high-nickel ternary precursor particles with a concentration gradient structure prepared by the co-precipitation method is demonstrated.

[0038] Step 2: The mixture obtained above was calcined by a rapid Joule heating process. The sample was heated at an ultra-fast heating rate of 673 K / s in an oxygen atmosphere, kept at 800 ° C for 210 s, and cooled naturally at a cooling rate of 673 K / s to obtain a high nickel ternary material LiNi 0.8 Co 0.15 Al 0.05 O2.

[0039] The concentration gradient distribution of elements in the prepared high nickel ternary cathode material is retained to the greatest extent, inheriting the concentration gradient distribution of the high nickel ternary precursor, such as Figure 2 , and has a typical α-NaFeO2 layered material, belonging to R m space group (such as Figure 3 ), the secondary particles of the positive electrode material are spherical or quasi-spherical (such as Figure 4 ), with an average particle size of 12 μm and a tap density of 2.3 g / cm 3 The electrochemical performance of button half-cells was tested by constant current and constant voltage charging and constant current discharge with a cut-off voltage of 2.8-4.3 V. The first discharge capacity at 0.1C was 200 mAh / g, and the capacity retention rate after 100 cycles at 1C was 90.4%. Figure 5 .

[0040] Example 2

[0041] Step 1: Prepare the mixture by mixing lithium hydroxide with the concentration gradient precursor Ni 0.8 Co 0.15 Al 0.05 (OH)2 were mixed in a total molar ratio of 1:1 and placed in a ball mill and stirred evenly to obtain a mixed material;

[0042] Ni 0.8 Co 0.15 Al 0.05 The core component of (OH)2 is designed to be Ni 0.85 Co 0.15 (OH)2, the surface component is designed to be Ni 0.75 Co 0.15 ACol0.1 (OH)2, by adjusting the feed rate of various salt solutions using the co-precipitation method, the nickel element concentration gradient from the core to the surface of the high-nickel precursor secondary particles shows a gradually decreasing trend, the aluminum element concentration gradient shows a gradually increasing trend, and the cobalt element concentration gradient trend remains unchanged. Figure 6 The radial distribution of Ni, Co, and Al element contents in the cross section of high-nickel ternary precursor particles with a concentration gradient structure prepared by the co-precipitation method is demonstrated.

[0043] Step 2: The mixture obtained above was calcined by a rapid Joule heating process. The sample was heated at an ultra-fast heating rate of 673 K / s in an oxygen atmosphere, kept at 700 ° C for 360 s, and cooled naturally at a cooling rate of 373 K / s to obtain a high nickel ternary material LiNi 0.8 Co 0.15 Al 0.05 O2.

[0044] The concentration gradient distribution of elements in the prepared high nickel ternary cathode material is retained to the greatest extent, inheriting the concentration gradient distribution of the high nickel ternary precursor, such as Figure 7 , and has a typical α-NaFeO2 layered material, belonging to R m space group (such as Figure 8 ), the secondary particles of the positive electrode material are spherical or quasi-spherical (such as Figure 9 ), with an average particle size of 11 μm and a tap density of 2.35 g / cm 3 The electrochemical performance of button half-cells was tested by constant current and constant voltage charging and constant current discharge with a cut-off voltage of 2.8-4.3 V. The first discharge capacity at 0.1C was 200 mAh / g, and the capacity retention rate after 100 cycles at 1C was 93%. Figure 10 .

[0045] Example 3

[0046] This embodiment provides a method for preparing a high-nickel ternary positive electrode material. The preparation method is the same as that of Example 1, except that the holding time at 900°C in the rapid Joule heating process described in step 2 is 120s and the natural cooling rate is measured to be 773K / s.

[0047] The concentration gradient distribution of elements in the prepared high nickel ternary cathode material is retained to the greatest extent, such as Figure 11 ,By prolonging the holding time of rapid Joule heating, the concentration gradient distribution trend of the elements does not change, and the concentration gradient distribution trend of the high-nickel ternary precursor is inherited.

[0048] Comparative Example 1

[0049] Step 1: Prepare the mixture by mixing lithium hydroxide with the concentration gradient precursor Ni 0.8 Co 0.15 Al 0.05 (OH)2 was mixed in a total molar ratio of 1.2:1 and placed in a ball mill to stir evenly to obtain a mixed material; the concentration gradient precursor Ni 0.8 Co 0.15 Al 0.05 (OH)2 is the same as in Example 1.

[0050] Step 2: The mixture obtained above was calcined in a traditional tube furnace, heated at a heating rate of 2 ° C / min in an oxygen atmosphere, kept at a high temperature of 800 ° C for 12 hours, and then slowly cooled to obtain the high nickel ternary material LiNi 0.8 Co 0.15 Al 0.05 O2.

[0051] Without any treatment, the concentration gradient trend of Ni and Co elements in the prepared high nickel ternary cathode material particles slowed down significantly and almost disappeared. Figure 12 The electrochemical performance of button half-cells was tested by constant current and constant voltage charging and constant current discharge with a cut-off voltage of 2.8-4.3 V. The first discharge capacity at 0.1C was 193 mAh / g, and the capacity retention rate after 100 cycles at 0.5C was 75%. Figure 13 .

[0052] Figure 12 The paper shows that a mixture of a high nickel ternary precursor and lithium with a concentration gradient structure is calcined for a long time in a traditional tube furnace. During the long high temperature holding process, the concentration gradient of nickel and cobalt elements gradually slows down until it disappears. At the same time, Figure 13 The corresponding electrochemical performance is shown. The disappearance of the concentration gradient does not bring about a change in the initial capacity, but affects the cycle stability of the material. The nickel content on its surface returns to its previous high nickel content. The highly reactive Ni 4+ It also produces side reactions with the electrolyte solution, causing structural damage to the material, thereby reducing the cycle stability. The slowdown or disappearance of the concentration gradient trend is a challenge currently faced in the preparation of high-concentration-gradient nickel ternary materials.

[0053] Comparative Example 2

[0054] Step 1: Prepare the mixture by mixing lithium hydroxide with the concentration gradient precursor Ni 0.8 Co 0.15 Al 0.05 (OH)2 was mixed in a total molar ratio of 1.03:1 and placed in a ball mill to stir evenly to obtain a mixed material; the concentration gradient precursor Ni 0.8 Co0.15 Al 0.05 (OH)2 is the same as in Example 1.

[0055] Step 2: The mixture obtained above is calcined in a traditional tube furnace in multiple stages, and the temperature is increased at a heating rate of 2°C / min in an oxygen atmosphere, 450°C → 650°C → 780°C → 500°C → room temperature, and then slowly cooled to obtain the high nickel ternary positive electrode material LiNi 0.8 Co 0.15 Al 0.05 O2.

[0056] The prepared high nickel ternary cathode material was calcined by a multi-stage calcination method, and the concentration gradient trend of Ni and Co elements in the particles still slowed down significantly, such as Figure 14 The electrochemical performance of button half-cells was tested by constant current and constant voltage charging and constant current discharge with a cut-off voltage of 2.8-4.3 V. The first discharge capacity at 0.1C was 198 mAh / g, and the capacity retention rate after 100 cycles at 1C was 78%. Figure 15 .

[0057] from Figure 14 The element distribution shows that after the multi-stage calcination method in the literature is used to combine a long low-temperature stage with a short high-temperature stage, the concentration gradient trend of the nickel and cobalt elements in the positive electrode material is still slow due to the mutual diffusion of metal elements caused by long-term calcination. The multi-stage calcination mode still cannot solve the problem of the slowing trend of the continuous concentration gradient distribution of elements. The nickel content on its surface has also returned to the previous high nickel content composition. The highly reactive Ni 4+ It also produces side reactions with the electrolyte solution, causing structural damage to the material, thereby reducing the cycle stability and poor performance.

[0058] The present invention first utilizes a coprecipitation method to prepare a high-nickel ternary precursor with an element concentration gradient structure, and then obtains a high-nickel ternary positive electrode material with a full concentration gradient structure through a rapid Joule heating process, rapid heating, short-term heat preservation, and rapid cooling. By controlling the rapid Joule heating process, the concentration gradient distribution of the elements in the high-nickel ternary positive electrode material is retained to the greatest extent, inheriting the concentration gradient distribution of the high-nickel ternary precursor, suppressing the uniform diffusion of transition metal ions in the concentration gradient precursor during a long calcination process, and avoiding the problem of disappearance of the element concentration gradient caused by traditional furnace calcination. The principle is that the ultra-rapid heating during the rapid Joule heating process causes lithium hydroxide to quickly decompose into Li2O, and lithium ions quickly diffuse from the surface into the bulk phase, accelerating the generation of the lithiation reaction and the structural phase transition of the precursor, forming a good layered structure in a short time at high temperature. Compared with the traditional long-term furnace calcination, the extremely short heat preservation time makes the transition metal ions inside the precursor particles have no time to diffuse, and the ultra-rapid cooling achieves the maintenance of the element concentration gradient. This also enables the preparation of a high-nickel ternary cathode material with high capacity and high cycle stability. The preparation process is simple, and the sintered cathode material has a clear internal concentration gradient, making it suitable for industrial production.

[0059] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make some changes or modifications to equivalent embodiments using the technical contents disclosed above. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a high-nickel ternary positive electrode material for lithium-ion batteries, characterized in that: The method is: Ni with element concentration gradient structure precursor x Co y M 1-x-y (OH)2 and lithium hydroxide are mixed, and the mixed powder is subjected to a thermal shock treatment using Joule heat to obtain a high-performance high-nickel ternary positive electrode material containing an element gradient distribution; Ni x Co y M 1-x-y In (OH)2, 0.7≤x<1.0, 0.01≤y<0.1; M is Mn, Al, W, Nb, Mo, Ta or Zr; the concentration of nickel decreases gradually from the core to the particle surface; Lithium hydroxide and Ni x Co y M 1-x-y The total molar ratio of metal ions in (OH)2 is 1.0-1.2:1; The thermal shock treatment is carried out in a pure oxygen atmosphere with a heating and cooling rate of 373 K / s-773 K / s, a target temperature of 700°C-900°C, and a holding time of 120s-360s.

2. The preparation method according to claim 1, characterized in that The precursor Ni with element concentration gradient structure x Co y M 1-x-y (OH)2 is prepared in one step by coprecipitation.

3. The preparation method according to claim 1, characterized in that The method comprises the following steps: spreading the mixed powder on a heating substrate, and applying electricity to the heating substrate in an oxygen atmosphere to achieve thermal shock treatment on the powder.

4. The preparation method according to claim 3, characterized in that The heating substrates used are carbon cloth, graphite paper, and metal foil.

5. The positive electrode material prepared by the preparation method according to claim 1, characterized in that: The positive electrode material is a high nickel ternary positive electrode material with an α-NaFeO2 layered structure and belongs to R The secondary particles of the positive electrode material are spherical, with an average particle size of 6-13 μm and a tap density of 1.8-2.7 g / cm 3 .

6. Use of the positive electrode material as claimed in claim 5 in a lithium-ion power battery.

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