Modified high-nickel positive electrode material and preparation method thereof

Abstract

The invention belongs to the field of lithium battery positive electrode materials, and discloses a modified high-nickel positive electrode material, which is characterized in that a matrix contains a metal doping element with a solubility product constant less than 10-30, a grain boundary coating layer exists on the grain boundary surface of the matrix, and primary particles are radially extended and arranged towards the periphery by taking the sphere center of secondary particles as the center. The modified high-nickel positive electrode material has a stable intergranular structure and a special primary particle arrangement mode, and is combined with a grain boundary coating layer, so that the generation of side reaction of an electrode-electrolyte interface is effectively inhibited, the grain boundary stability is enhanced, and the formation of an inert rock salt phase is reduced; and the metal doping element increases the cell parameter, increases the oxygen vacancy, and effectively improves the electronic conductivity of the material. According to the preparation method, the surface layer of the material is prevented from being too dense in a gradient feeding mode in the precursor synthesis process, and a special primary particle arrangement mode is still kept after heat treatment. The lithium ion diffusivity is enhanced, the stress accumulation of the material in the lithium de-intercalation process is relieved, and the generation of cracks is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery positive electrode materials, and particularly relates to a high-nickel positive electrode material with a stable intercrystalline structure and a special primary particle arrangement mode and a preparation method thereof. Background Art

[0002] With the rapid development of new energy hybrid electric vehicles (HEVs) and pure electric vehicles (EVs), the development of lithium-ion batteries with high energy density, long cycle life, and strong rate capability is imperative. Among the components of lithium-ion batteries, the cathode material is the primary factor restricting their development. Nickel-based transition metal oxides have attracted widespread attention due to their high energy density, excellent cycle stability, and cost-effectiveness. To achieve even higher energy density, the trend has been towards high-nickel and ultra-high-nickel cathode materials. While increasing nickel content increases the specific capacity of these high-nickel and ultra-high-nickel cathode materials, they face more severe electrochemical performance degradation and safety issues. The high reactivity associated with excessive nickel content can lead to severe phase transitions and interfacial side reactions during cycling. The accumulation of internal stress can form microcracks within the particles, exacerbating the deterioration of structural stability and ultimately leading to particle breakage, compromising the cycling stability of the cathode material.

[0003] Currently, the interface stability of high-nickel positive electrode materials is mainly enhanced by element doping and surface coating. Although these two methods can solve the interface side reactions between the positive electrode surface and the electrolyte to a certain extent and improve the cycle stability, they are prone to cause additional capacity loss and cannot solve the problem of particle breakage caused by the accumulation of grain boundary stress.

[0004] In the element doping modification of high-nickel positive electrode materials for lithium-ion batteries, elements such as Zr, W, Ti, and Ce are generally selected as dopants to improve the crystal structure stability of high-nickel positive electrode materials for lithium-ion batteries. During the doping modification process of lithium-ion battery positive electrode materials, it is necessary to ensure the uniformity of the doping phase, at least the same spherical ring layer must be uniform. Otherwise, the material will form weak points in places where the doping phase is less, and during the charging and discharging process, the crystal structure will collapse, seriously affecting the overall performance of the lithium-ion battery. In addition, during the heat treatment process, the primary particles of the positive electrode material will fuse and grow. The coarse primary particles will cause stress accumulation during the material cycle, causing cracks in the positive electrode material, which in turn leads to particle breakage, seriously deteriorating the battery's cycle performance. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology and provide a modified high-nickel positive electrode material with a stable intercrystalline structure and a special primary particle arrangement achieved by doping elements by co-precipitation and a preparation method thereof.

[0006] In order to solve the above technical problems, the technical solution proposed by the present invention is: A modified high nickel cathode material, the chemical formula of the high nickel cathode material matrix is ​​LiNi x M 1-x O2, wherein 0.9≤x<1, M is a metal doping element; an oxide containing a metal doping element and lithium exists on the grain boundary surface of the high nickel positive electrode material matrix as a grain boundary coating layer (formed by the metal doping element precipitated beyond the lattice solubility limit); the metal doping element has a solubility product constant of less than 10 in the nickel hydroxide precursor coprecipitation system -30 The primary particles in the modified high-nickel positive electrode material are arranged radially extending around the center of the secondary particle.

[0007] The modified high nickel cathode material is further characterized in that the metal doping element is at least one of Zr (zirconium), Ce (cerium), Sn (tin), Cr (chromium) and Ti (titanium). The solubility product constant of these metal doping elements is less than 10 -30 , which increases the unit cell parameters of the material, increases the oxygen vacancy concentration, and effectively improves the electronic conductivity of the material; it also refines the primary particles of the precursor, and the positive electrode material can still maintain this feature after heat treatment. The presence of the doped element grain boundary coating layer can also inhibit the grain fusion and growth, and maintain the refinement of the primary particles. These two factors enable the primary particles of the modified high-nickel positive electrode material to remain arranged radially around the center of the secondary particle after heat treatment.

[0008] Furthermore, the doping concentration of the metal doping element in the modified high-nickel positive electrode material is 0.01~1.00mol% (for example, 0.01mol%, 0.02mol%, 0.03mol%, 0.04mol%, 0.05mol%, 0.06mol%, 0.07mol%, 0.08mol%, 0.09mol%, 0.10mol%, 0.20mol%, 0.30mol%, 0.40mol%, 0.50mol%, 0.60mol%, 0.70mol%, 0.80mol%, 0.90mol%, 1.00mol%).

[0009] Furthermore, the chemical formula of the oxide containing the metal doping element and lithium is determined by the valence state of the metal doping element. When the valence state of the metal doping element is +3, the chemical formula of the oxide containing the metal doping element and lithium is LiMO2 (such as Cr); when the valence state of the metal doping element is +4, the chemical formula of the oxide containing the metal doping element and lithium is Li2MO3 (such as Zr, Ce, Sn, Ti); in the oxide containing the metal doping element and lithium, the molar ratio of the metal doping element to lithium is 0.0001~0.01:1.00~1.10.

[0010] Furthermore, when the nickel hydroxide precursor is synthesized, the feed flow rate of the nickel-metal doping element salt solution gradually increases as the particle size of the precursor increases.

[0011] As a general inventive concept, the present invention also provides a method for preparing a modified high-nickel cathode material, comprising the following steps: (1) A nickel hydroxide precursor containing metal doping elements is prepared by a coprecipitation method. During the preparation process, the feed flow rate of the metal salt solution is controlled to gradually increase as the particle size of the precursor increases; (2) The nickel hydroxide precursor containing the metal doping element obtained in step (1) is mixed with lithium hydroxide and heat-treated in an oxygen-containing atmosphere to obtain the modified high-nickel positive electrode material.

[0012] This modified high-nickel cathode material uses a gradient feed method (the feed rate of the nickel-metal doping element salt solution gradually increases as the precursor particle size increases) to synthesize a precursor with the secondary particle center as the center and radially extending outward. The grain boundary coating formed by the metal element precipitated beyond the lattice solubility limit maintains the radial extension of the primary particles of the cathode material. The particle size of the primary particles of this modified high-nickel cathode material is smaller than that of the unmodified material. Since the sphere volume V= π r 3, as the precursor grows, the increase in unit particle size corresponds to an increase in more volume, that is, more solute is consumed. Therefore, if the same feed rate is used for the precursor during the synthesis process, the growth of the particle size will become slower and slower, and the precursor will show a characteristic from loose to dense from the inside to the outside, and the positive electrode material after heat treatment will also retain this characteristic. The overly dense structure of the surface will hinder the transmission of the electrolyte and the migration of lithium ions, deteriorating the electrochemical performance. In addition, in traditional solid-phase doping, the doping elements diffuse from the bulk phase to the crystal lattice. Limited by the diffusion capacity, the doping elements of traditional solid-phase doping cannot be evenly distributed inside the bulk phase, and the doping elements are mainly concentrated at the grain boundaries. The content inside the crystal lattice is not high. The coating formed by the doping elements with too high a content at the grain boundaries will also deteriorate the electronic conductivity and mechanical properties of the material, causing a decrease in the lithium ion diffusion capacity of the material and cracking. The feeding method of the present invention can avoid the overly dense structure on the surface of the material from deteriorating the electrochemical performance, forming primary particles that are arranged radially with the center of the secondary particle as the center. In addition, the doping method of the present invention has uniformly distributed the doping elements in the crystal lattice of the material before heat treatment, which effectively solves the problem of uneven element distribution. At the same time, when the doping element has reached the limit of its solubility in the material crystal lattice, the doping element that exceeds the lattice solubility will precipitate and be enriched at the grain boundary to form a coating layer, which effectively inhibits the occurrence of side reactions at the electrode-electrolyte interface, enhances the stability of the grain boundary, and reduces the formation of the inert rock salt phase; metal doping elements with low solubility product constants (solubility product constants less than 10 -30 ) increases the unit cell parameters of the material, increases the oxygen vacancy concentration, and effectively improves the electronic conductivity of the material; doping with metal elements with low solubility product constants during the precursor synthesis process will refine the primary particles of the precursor, and the positive electrode material can still maintain this feature after heat treatment, and the presence of the grain boundary coating layer of the doped element can also inhibit the fusion and growth of the grains, maintaining the refinement of the primary particles. These two factors enable the primary particles of the modified high-nickel positive electrode material to remain arranged radially extending from the center of the secondary particle sphere to the surrounding area after heat treatment. The primary particles in this arrangement not only enhance the lithium ion diffusion capacity, but also alleviate the stress accumulation of the material during the lithium insertion and extraction process, reduce the generation of cracks, and thus reduce the generation of side reactions. Therefore, the modified high-nickel positive electrode material of the present invention has stable intercrystalline structural characteristics, and the electrochemical cycle stability, rate performance and safety are improved.

[0013] The above preparation method further comprises the following steps: dissolving the salt containing the metal doping element into a nickel salt solution to obtain a nickel-metal doping element salt solution; mixing the nickel-metal doping element salt solution, a liquid alkali solution and ammonia water to react, wherein the feed flow rate of the nickel-metal doping element salt solution gradually increases with the increase of the precursor particle size, controlling the pH of the reaction system to be 9.5-11.5 (for example, 9.5, 10.0, 10.5, 11.0, 11.5), and the particle size of the reaction product D 50 When the particle size reaches 7-18 μm, the precipitated reaction product is washed and centrifuged to obtain a nickel hydroxide precursor containing metal doping elements.

[0014] Furthermore, the nickel salt includes at least one of nickel nitrate, nickel chloride and nickel sulfate; the nickel molar concentration in the nickel salt solution is 1 to 3 mol / L (for example, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L); the salt of the metal doping element includes at least one of nitrate, chloride and sulfate; the molar concentration of the metal doping element in the nickel-metal doping element salt solution is 0.00015 to 0.030 mol / L (for example, 0.00015 mol / L, 0.00045 mol / L, 0.00075 mol / L , 0.001mol / L, 0.002mol / L, 0.004mol / L, 0.008mol / L, 0.012mol / L, 0.016mol / L, 0.020mol / L, 0.024mol / L, 0.028mol / L, 0.030mol / L), the doping content of the metal element is controlled by adjusting the concentration of the metal ions in the salt solution; the liquid alkali solution is a sodium hydroxide solution, wherein the concentration of sodium hydroxide is 1.5~4mol / L (for example, 1.5mol / L, 2.5mol / L, 3.5mol / L, 4mol / L).

[0015] Furthermore, the reaction is carried out under stirring conditions, the reaction temperature is controlled at 50~70°C (for example, 50°C, 55°C, 60°C, 65°C, 70°C), and the feed flow rate of the nickel-metal doping element salt solution is 0.3~10L / h (for example, 0.3~4L / h, 0.3~5 L / h, 0.3~6 L / h, 0.3~7L / h, 0.3~8 L / h, 0.3~9 L / h, 0.3~10 L / h); the washing comprises the following steps: first, centrifugal washing is performed using a dilute alkali solution with a liquid alkali concentration of 1%~5% (for example, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%), followed by washing with pure water. During the washing process, the temperature of the solution is 50~70°C (for example, 50°C, 55°C, 60°C, 65°C, 70°C).

[0016] Furthermore, the nickel hydroxide precursor containing the metal doping element is mixed with lithium hydroxide according to lithium ratios of 1.00, 1.02, 1.04, 1.06, 1.08, and 1.10.

[0017] Furthermore, the heat treatment includes two stages of heat treatment, and the specific process conditions are as follows: the first stage heat treatment temperature is 300-500°C (for example, 300°C, 350°C, 400°C, 450°C, 500°C), and the holding time is 2-6h (for example, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h); the second stage heat treatment temperature is 600-800°C (for example, 600°C, 650°C, 700°C, 750°C). , 800℃), time is 12~15h (for example, 12h, 12.5h, 13h, 13.5h, 14h, 14.5h, 15h); heating rate is 3~20℃ / min (for example, 3℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, 12℃ / min, 14℃ / min, 16℃ / min, 18℃ / min, 20℃ / min); the oxygen-containing atmosphere is oxygen or air.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. The modified high-nickel cathode material of the present invention has a stable intercrystalline structure and a special primary particle arrangement. The metal elements precipitated beyond the lattice solubility limit are used to form a grain boundary coating layer, which effectively inhibits the occurrence of side reactions at the electrode-electrolyte interface, enhances grain boundary stability, and reduces the formation of inert rock salt phases. In addition, the metal doping elements increase the unit cell parameters and increase oxygen vacancies, effectively improving the electronic conductivity of the material.

[0019] 2. The gradient feeding method of the present invention in the precursor synthesis process can avoid the surface layer of the material from being too dense, and after heat treatment, a positive electrode material is formed in which primary particles are arranged radially around the center of the secondary particle. Since the metal elements with low solubility product constants can form more nucleation sites during the co-precipitation process, more nucleation sites result in a slower growth rate. The newly generated grains do not have time to grow longitudinally on the needle-shaped primary particles, and then form new needle-shaped primary particles together with other grains; in addition, the metal doping elements form heterogeneous grains different from the nickel hydroxide grains in the co-precipitation system, which hinders the growth of the newly generated nickel hydroxide grains on the original matrix; combining the above two reasons, the metal elements with low solubility product constants can refine the primary particles of the precursor in the co-precipitation system, and the characteristics of primary particle refinement are still retained in the positive electrode material after heat treatment. In addition, during the heat treatment process, the presence of the grain boundary coating layer can hinder the fusion of grains and refine the primary particles of the positive electrode material. For these reasons, the fusion and growth of primary particles during heat treatment is suppressed, and the primary particles introduced by the gradient feed method are retained, extending radially from the center of the secondary particle sphere. This primary particle arrangement not only enhances lithium-ion diffusion but also alleviates stress accumulation during lithium insertion and extraction, reducing the occurrence of cracks.

[0020] 3. In the modified high-nickel positive electrode material synthesized by the process of the present invention, the metal doping elements are uniformly distributed in the precursor, and under the electron microscope, they appear to be a homogeneous co-precipitation state with no obvious second phase. While ensuring the strength of the prepared doped lithium-ion battery positive electrode material precursor, the doping elements are uniformly distributed in the precursor, effectively making up for the defects of the existing technology and having good practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 This is an SEM image of the nickel hydroxide precursor prepared in Example 2; Figure 2 The SEM images of the lithium nickelate positive electrode materials prepared in Examples 1 to 4 are shown, wherein (a) and (c) are SEM images of the lithium nickelate positive electrode material prepared in Example 2, and (b), (d), and (e) are SEM images of the lithium nickelate positive electrode materials prepared in Examples 1, 3, and 4, respectively; Figure 3The XRD pattern and XRD Rietveld refinement pattern of the lithium nickelate positive electrode material prepared in Example 2, wherein (a) is the XRD pattern and (b) is the XRD Rietveld refinement pattern; Figure 4 The cross-sectional element distribution diagram and HRTEM diagram of the lithium nickelate positive electrode material prepared in Example 2, wherein (a) is the HAADF diagram of Example 2 and its corresponding EDS mapping results of (b) Ni, (c) O, and (d) Zr elements, (e) is the HRTEM diagram of Example 2, and (fk) are the HRTEM diagrams of positions A (f) and B (i) enlarged in the yellow box area in Figure (e), as well as the FFT results of the four areas of position A (g, h) and position B (j, k); Figure 5 This is a graph showing the lithium ion transfer rate of the lithium nickelate positive electrode material prepared in Example 2; Figure 6 This is the paramagnetic resonance spectrum of the lithium nickelate positive electrode material prepared in Example 2; Figure 7 This is a graph showing the cycling performance of the lithium nickelate positive electrode material prepared in Example 2 at a current density of 1C; Figure 8 This is an SEM image of the nickel hydroxide precursor prepared in Comparative Example 1; Figure 9 The SEM images of the lithium nickelate positive electrode material prepared in Comparative Example 1, wherein (a) is a surface SEM image of the positive electrode material, and (b) is a cross-sectional SEM image of the positive electrode material; Figure 10 The XRD pattern and XRD Rietveld refinement pattern of the lithium nickelate positive electrode material prepared in Comparative Example 1, wherein (a) is the XRD pattern and (b) is the XRD Rietveld refinement pattern; Figure 11 HRTEM image of the lithium nickelate positive electrode material prepared in Comparative Example 1; Figure 12 This is a graph showing the lithium ion transfer rate of the lithium nickelate positive electrode material prepared in Comparative Example 1; Figure 13 This is the paramagnetic resonance spectrum of the lithium nickelate positive electrode material prepared in Comparative Example 1; Figure 14 This is a graph showing the cycling performance of the lithium nickelate positive electrode material prepared in Comparative Example 1 at a current density of 1C; Figure 15 This is an SEM image of the nickel hydroxide precursor prepared in Example 6; Figure 16 This is an SEM image of the nickel hydroxide precursor prepared in Comparative Example 2; Figure 17Cross-sectional SEM images of the lithium nickelate positive electrode materials prepared in Comparative Example 2 and Examples 5 to 8, wherein (a) is an SEM image of the lithium nickelate positive electrode material prepared in Comparative Example 2, and (b), (c), (d), and (e) are SEM images of the lithium nickelate positive electrode materials prepared in Examples 5, 6, 7, and 8, respectively; Figure 18 This is an SEM image of the nickel hydroxide precursor prepared in Example 10; Figure 19 This is an SEM image of the nickel hydroxide precursor prepared in Comparative Example 3; Figure 20 Cross-sectional SEM images of the lithium nickelate positive electrode materials prepared in Comparative Example 3 and Examples 9 to 12, wherein (a) is an SEM image of the lithium nickelate positive electrode material prepared in Comparative Example 3, and (b), (c), (d), and (e) are SEM images of the lithium nickelate positive electrode materials prepared in Examples 9, 10, 11, and 12, respectively; Figure 21 This is an SEM image of the nickel hydroxide precursor prepared in Comparative Example 4; Figure 22 This is a cross-sectional SEM image of the lithium nickelate positive electrode material prepared in Comparative Example 4; Figure 23 This is a cross-sectional SEM image of the lithium nickelate positive electrode material prepared in Comparative Example 5. DETAILED DESCRIPTION

[0023] To facilitate understanding of the present invention, the present invention will be described in more comprehensive and detailed form below in conjunction with the accompanying drawings and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0024] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0025] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0026] K sp represents the solubility product constant.

[0027] Example 1: A modified high nickel cathode material (K of Ni(OH)2) of the present invention sp =5.48×10 -16 , K of Zr(OH)4 sp =1×10 -50 ), the preparation method of which comprises the following steps: (1) Nickel sulfate crystals were dissolved in industrial pure water, and after filtering, a nickel salt solution with a nickel ion concentration of 2 mol / L was prepared; industrial liquid caustic soda with a mass concentration of 32% was diluted in industrial pure water, and after filtering, a liquid caustic soda solution with a sodium hydroxide concentration of 4 mol / L was prepared; (2) A certain amount of zirconium sulfate tetrahydrate was dissolved in a nickel salt solution to prepare a nickel-zirconium composite salt solution, wherein the molar concentration of zirconium in the solution was 0.002 mol / L and the zirconium doping concentration was 0.1 mol; (3) Nickel-zirconium composite salt solution, liquid alkali solution and ammonia water are added to the reactor in a quantitative parallel flow method through a metering pump. The feed flow rate of the salt solution increases gradually with the increase of particle size and is 0.3-5L / h. Under stirring conditions, the pH is controlled at 11, the reaction temperature is controlled at 65℃, and the reaction D is added. 50 When the particle size reaches 10 μm, after precipitation, it is first washed with a dilute alkali solution with a liquid alkali concentration of 2.5%, and then washed with pure water. During the washing process, the temperature of the solution is 60°C. After centrifugation, nickel hydroxide uniformly doped with zirconium is obtained; (4) Nickel hydroxide uniformly doped with zirconium was mixed with lithium hydroxide at a lithium ratio of 1.03 and heat-treated in an oxygen atmosphere using a two-stage heat treatment process. The first stage of heat treatment was heated to 500°C at a heating rate of 5°C / min and kept warm for 5 hours, and then heated to 640°C at a heating rate of 3°C / min and kept warm for 15 hours. A lithium nickelate positive electrode material LiNi with a stable intercrystalline structure and a special primary particle arrangement was obtained. 0.999 Zr 0.001 O2, on the grain boundary surface of the high nickel positive electrode material matrix, there is a grain boundary coating layer Li2ZrO3 formed by metal doping elements precipitated beyond the lattice solubility limit.

[0028] Example 2: The only difference from Example 1 is that in step (2), the concentration of zirconium in the composite salt solution is 0.008 mol / L, the zirconium doping concentration is 0.40 mol%, and the obtained positive electrode material is LiNi 0.996 Zr 0.004 O2, and the grain boundary coating is Li2ZrO3.

[0029] Example 3: The only difference from Example 1 is that in step (2), the concentration of zirconium in the composite salt solution is 0.014 mol / L, the zirconium doping concentration is 0.70 mol%, and the obtained positive electrode material is LiNi 0.993 Zr 0.007 O2, and the grain boundary coating is Li2ZrO3.

[0030] Example 4: The only difference from Example 1 is that in step (2), the concentration of zirconium in the composite salt solution is 0.020 mol / L, the zirconium doping concentration is 1.00 mol%, and the obtained positive electrode material is LiNi 0.99 Zr 0.01 O2, and the grain boundary coating is Li2ZrO3.

[0031] The effects of different zirconium doping amounts on the electrochemical properties of lithium nickel oxide positive electrode materials are detailed in Table 1.

[0032] Comparative Example 1: The difference from Example 2 is that zirconium sulfate tetrahydrate is not added, 2 mol / L nickel sulfate solution is passed into the reactor, and the same treatment is performed, and the positive electrode material obtained is LiNiO2.

[0033] The positive electrode materials obtained in Examples 1, 2, 3, 4, and Comparative Example 1 were assembled into button-type half-cells, which were activated for three cycles at 0.1C (1C=200 mAg) in the voltage range of 2.8-4.3 V, and then cycled for 100 cycles at a current density of 1C. The rate performance test was also performed at a current density of 5C.

[0034] The obtained materials were characterized, and the SEM images of the precursors of Example 2 and Comparative Example 1 are shown as follows: Figure 1 and Figure 8 As shown, the SEM images of the positive electrode materials are Figure 2 (a), (c) and Figure 9 As shown in (ab), the XRD patterns and Rietveld refinement patterns of the materials are Figure 3 、 Figure 10 As shown, the HRTEM images of the materials are Figure 4 、 Figure 11 As shown in the figure, the lithium ion transfer rate is as follows Figure 5 、 Figure 12 As shown, the EPR oxygen vacancy test results are as follows Figure 6 、 Figure 13 As shown in the figure, after calculation, the concentration of oxygen vacancies in Example 2 is 2.372×10 -7 mol / L, while the oxygen vacancy concentration of Comparative Example 1 is 1.837×10 -7 mol / L, the cycle performance diagram is as follows Figure 7 、 Figure 14 shown.

[0035] Depend on Figure 9 It can be seen that the primary particles of the lithium nickelate positive electrode material of Comparative Example 1 are arranged in a radial pattern with the secondary particle center as the center, but the primary particles are extremely coarsened. This arrangement will gradually disappear as the heat treatment temperature increases. Figure 1 and Figure 8It can be seen that the zirconium doping in Example 2 makes the primary particles of the precursor finer. Figure 2 (c) and Figure 9 (b) It can be seen that in the positive electrode material after heat treatment, the characteristics of primary particle refinement in Example 2 are still retained. Zirconium doping hinders the fusion and growth of primary particles inside the positive electrode material during the heat treatment process, so that the primary particles still extend radially around the center of the secondary particle. Figure 3 and Figure 10 It can be seen that the zirconium element in the bulk phase of the material and the presence of the grain boundary coating layer in Example 2 have no significant effect on the physical phase of the main lithium nickelate positive electrode material, but cause the unit cell parameters a and c to increase. Figure 4 and Figure 11 It can be seen that the lithium nickelate in Comparative Example 1 has a layered structure from the surface to the interior; while the lithium nickelate in Example 2 is divided into two regions from the surface to the interior, among which Region I is the Li2ZrO3 grain boundary coating layer formed by the zirconium precipitated in the crystal structure, and Region II is the layered structure of the lithium nickelate material. The presence of the Li2ZrO3 grain boundary coating layer can effectively reduce the occurrence of electrode-electrolyte side reactions and inhibit the transformation of the layered lithium nickelate positive electrode material to the rock salt phase during the cycle. Figure 5 and Figure 12 It can be seen that the lithium nickelate in Example 2 has a faster lithium ion transmission rate. Figure 6 and Figure 13 The oxygen vacancy concentration of the lithium nickelate material in Example 2 is significantly increased. Analysis shows that this is mainly because zirconium doping in the bulk phase increases oxygen vacancies, improves electronic conductivity, and provides more capacity for the material. The unit cell parameters a and c increase, which reduces the barrier to lithium ion transmission and also improves the lithium ion transmission rate. Figure 7 and Figure 14 It can be seen that the cycle performance of lithium nickelate in Example 1 is greatly improved.

[0036] Table 1 Electrochemical properties of the positive electrode materials prepared in Examples 1 to 4 and Comparative Example 1

[0037] As can be seen from Table 1, compared with Comparative Example 1, the rate performance and cycle performance of Example 2 are significantly improved, and the discharge capacity is further improved. Combined with the above analysis, the reason for this phenomenon may be that on the one hand, zirconium doping increases the concentration of oxygen vacancies in the material, increases the unit cell parameters of the a and c axes, refines the primary particles, reduces the lithium ion transmission barrier, and improves the electronic conductivity of the material, thereby increasing the discharge capacity and improving the rate performance. On the other hand, the lithium zirconate coating formed on the grain boundary surface stabilizes the layered structure and reduces the occurrence of electrode-electrolyte interface side reactions. In addition, the primary particles arranged radially extending around the secondary particle center relieve the stress accumulation of the material during the lithium insertion and extraction process, reduce the cracks generated by the material during the charge and discharge process, thereby reducing the occurrence of electrode-electrolyte interface side reactions and improving cycle stability.

[0038] Example 5: A modified high nickel cathode material (K of Ni(OH)2) of the present invention sp =5.48×10 -16 , K of Ce(OH)4 sp =2×10 -48 ), the preparation method of which comprises the following steps: (1) Dissolve nickel sulfate crystals with industrial pure water, and filter to obtain a nickel salt solution with a nickel ion concentration of 1.5 mol / L; dilute industrial liquid caustic soda with a mass concentration of 32% with industrial pure water, and filter to obtain a liquid caustic soda solution with a sodium hydroxide concentration of 3 mol / L; (2) A certain amount of cerium sulfate tetrahydrate was dissolved in a nickel salt solution to prepare a nickel-cerium composite salt solution, wherein the molar concentration of cerium in the solution was 0.0015 mol / L and the cerium doping concentration was 0.1 mol; (3) nickel-cerium composite salt solution, liquid alkali solution and ammonia water are quantitatively added to the reactor by a metering pump in parallel flow method, and the feed flow rate of the salt solution increases gradually with the increase of particle size, and is 0.3-7 L / h. Under stirring conditions, the pH is controlled at 11.5, and the reaction temperature is controlled at 60°C. When the particle size reaches 8 μm, after precipitation, it is first washed with a dilute alkali solution with an alkali concentration of 3.5%, and then washed with pure water. During the washing process, the temperature of the solution is 55°C. After centrifugation, nickel hydroxide doped with uniform cerium is obtained; (4) Nickel hydroxide uniformly doped with cerium was mixed with lithium hydroxide in a lithium ratio of 1.03 and heat-treated in an oxygen atmosphere. The heat treatment process adopted a two-stage sintering process. The first stage of heat treatment was heated to 400°C at a heating rate of 10°C / min and kept warm for 6 hours. Then, it was heated to 600°C at a heating rate of 5°C / min and kept warm for 13 hours. The lithium nickelate positive electrode material LiNi with a stable intergranular structure and a special primary particle arrangement was obtained. 0.999 Ce 0.001O2, the cerium doping concentration is 0.1mol%, and there is a grain boundary coating layer Li2CeO3 formed by metal doping elements precipitated beyond the lattice solubility limit on the grain boundary surface of the high nickel positive electrode material matrix.

[0039] Example 6: The only difference from Example 5 is that in step (2), the concentration of cerium in the salt solution is 0.006 mol / L, the cerium doping concentration is 0.4 mol%, and the obtained positive electrode material is LiNi 0.996 Ce 0.004 O2, and the grain boundary coating is Li2CeO3.

[0040] Depend on Figure 15 It can be seen that the Ce-doped precursor is a secondary sphere, and the primary particles of the precursor are fine needles with a width of about 100 nm.

[0041] Example 7: The only difference from Example 5 is that in step (2), the concentration of cerium in the salt solution is 0.0105 mol / L, the cerium doping concentration is 0.7 mol%, and the obtained positive electrode material is LiNi 0.993 Ce 0.007 O2, and the grain boundary coating is Li2CeO3.

[0042] Example 8: The only difference from Example 5 is that in step (2), the concentration of cerium in the salt solution is 0.015 mol / L, the cerium doping concentration is 1.0 mol%, and the obtained positive electrode material is LiNi 0.99 Ce 0.01 O2, and the grain boundary coating is Li2CeO3.

[0043] The effects of different cerium doping amounts on the electrochemical properties of lithium nickel oxide positive electrode materials are detailed in Table 2.

[0044] Comparative Example 2: The difference from Example 6 is that no cerium sulfate tetrahydrate is added, and a 1.5 mol / L nickel sulfate solution is introduced into the reactor and the same treatment is performed, and the obtained positive electrode material is LiNiO2.

[0045] The positive electrode materials obtained in Examples 5 to 8 and Comparative Example 2 were assembled into button-type half-cells. After activation for three cycles at 0.1C (1C = 200 mAg) in the voltage range of 2.8-4.3 V, they were cycled for 100 cycles at a current density of 1C, and the rate performance was tested at a current density of 5C.

[0046] Table 2 Electrochemical properties of the positive electrode materials prepared in Examples 5 to 8 and Comparative Example 2

[0047] like Figure 16 It can be seen that the primary particles of the undoped Ce precursor are thin rod-shaped, and the primary particles are relatively coarse with a width of about 200 nm. Depend on Figure 17 It can be seen that the primary particles of the positive electrode materials prepared in Examples 5 to 8 and Comparative Example 2 are arranged radially extending around the center of the secondary particle. The primary particles of the positive electrode material are more significantly refined with the increase of Ce doping content, and the radial extension feature is more obvious.

[0048] Example 9: A modified high nickel cathode material (K of Ni(OH)2) of the present invention sp =5.48×10 -16 , K of Ti(OH)4 sp =1×10 -35 ), the preparation method of which comprises the following steps: (1) Dissolve nickel sulfate crystals with industrial pure water, and filter to obtain a nickel salt solution with a nickel ion concentration of 3 mol / L; dilute industrial liquid caustic soda with a mass concentration of 32% with industrial pure water, and filter to obtain a liquid caustic soda solution with a sodium hydroxide concentration of 2.5 mol / L; (2) A certain amount of titanium sulfate was dissolved in a nickel salt solution to prepare a nickel-titanium composite salt solution, wherein the molar concentration of titanium in the solution was 0.003 mol / L and the titanium doping concentration was 0.1 mol; (3) nickel-titanium composite salt solution, liquid alkali solution and ammonia water are quantitatively added to the reactor by a metering pump in parallel flow, and the feed flow rate of the salt solution increases with the increase of particle size, and the pH is controlled at 10.5 and the reaction temperature is controlled at 55°C under stirring conditions. When the particle size reaches 14 μm, after precipitation, it is first washed with a dilute alkali solution with an alkali concentration of 5.0%, and then washed with pure water. During the washing process, the temperature of the solution is 70°C. After centrifugation, nickel hydroxide doped with uniform titanium is obtained; (4) Nickel hydroxide uniformly doped with titanium was mixed with lithium hydroxide at a lithium ratio of 1.03 and heat treated in an oxygen atmosphere. The heat treatment process adopted a two-stage sintering process. The first stage of heat treatment was heated to 300°C at a heating rate of 15°C / min and kept warm for 4.5 hours. Then, it was heated to 700°C at a heating rate of 8°C / min and kept warm for 12 hours. LiNi nickelate positive electrode material with a stable intergranular structure and a special primary particle arrangement was obtained. 0.999 Ti 0.001 O2, the titanium doping concentration is 0.1mol%, and there is a grain boundary coating layer Li2TiO3 formed by metal doping elements precipitated beyond the lattice solubility limit on the grain boundary surface of the high nickel positive electrode material matrix.

[0049] Example 10: The only difference from Example 9 is that in step (2), the concentration of titanium in the salt solution is 0.012 mol / L, the titanium doping concentration is 0.4 mol%, and the obtained positive electrode material is LiNi 0.996 Ti 0.004 O2, and the grain boundary coating is Li2TiO3.

[0050] Depend on Figure 18 It can be seen that the Ti-doped precursor is a secondary sphere, and the primary particles of the precursor are fine needles with a width of about 80 nm.

[0051] Example 11: The only difference from Example 9 is that in step (2), the concentration of titanium in the salt solution is 0.021 mol / L, the titanium doping concentration is 0.7 mol%, and the obtained positive electrode material is LiNi 0.993 Ti 0.007 O2, and the grain boundary coating is Li2TiO3.

[0052] Example 12: The only difference from Example 9 is that in step (2), the concentration of titanium in the salt solution is 0.030 mol / L, the titanium doping concentration is 1.0 mol%, and the obtained positive electrode material is LiNi 0.99 Ti 0.01 O2, and the grain boundary coating is Li2TiO3.

[0053] The effects of different titanium doping amounts on the electrochemical properties of lithium nickel oxide positive electrode materials are detailed in Table 3.

[0054] Comparative Example 3: The difference from Example 10 is that titanium sulfate is not added, 3 mol / L nickel sulfate solution is passed into the reactor, and the same treatment is performed, and the positive electrode material obtained is LiNiO2.

[0055] Depend on Figure 19 It can be seen that the primary particles of the undoped Ti precursor are rod-shaped, relatively coarse, and have a width of about 350 nm.

[0056] Depend on Figure 20 It can be seen that the primary particles of the positive electrode materials prepared in Examples 9-12 and Comparative Example 3 are arranged radially extending around the center of the secondary particle. The primary particles of the positive electrode material are more significantly refined with the increase of Ti doping content, and the radial extension feature is more obvious.

[0057] Comparative Example 4: The difference from Example 10 is that magnesium sulfate is added to the 3 mol / L nickel sulfate solution without adding titanium sulfate (K sp =5.48×10-16 , K of Mg(OH)4 sp =5.61×10 -12 ), the concentration of magnesium in the salt solution is 0.012 mol / L, the magnesium doping concentration is 0.4 mol%, and the obtained positive electrode material is LiNi 0.996 Mg 0.004 O2.

[0058] Depend on Figures 21 and 22 It can be seen that due to the K of Mg hydroxide sp The primary particles of the precursor are relatively large and close to those of Ni. Therefore, Mg doping does not refine the primary particles of the precursor. The primary particles of the precursor of Comparative Example 3 are close to those of Comparative Example 4. After the precursor of Comparative Example 4 is sintered into a positive electrode material, the primary particles of the positive electrode material are arranged radially with the center of the secondary particle as the center. However, the primary particles are relatively coarse, close to those of the positive electrode material of Comparative Example 3.

[0059] Comparative Example 5: The difference from Example 10 is that titanium sulfate is not added, 3 mol / L nickel sulfate solution is passed into the reactor, the reaction salt solution feed flow rate is constant at 2 L / h, the reaction salt flow rate does not change with particle size, and other processes are treated in the same way. The resulting positive electrode material is LiNiO2.

[0060] Figure 23 It can be seen that the primary particles of the positive electrode material obtained in Comparative Example 5 are coarse and randomly arranged in the secondary particles, and do not show the characteristic of radially extending from the center of the secondary particle to the surrounding area. It can be seen that the gradient feeding method is adopted, that is, as the particle size increases, the flow gradient of the reaction salt solution increases, so as to achieve a comparable density inside and outside the precursor, so that the primary particles of the positive electrode material show a radially extending arrangement with the center of the secondary particle as the center. However, this feature easily disappears during the grain fusion and growth process of high-temperature heat treatment, and by doping the precursor with a metal element with a low solubility product constant by coprecipitation, the primary particles of the precursor can be refined, and after heat treatment, the primary particles of the positive electrode material can maintain the characteristic of radially extending from the center of the secondary particle as the center to the surrounding area; at the same time, the lateral growth of the primary particles of the precursor is suppressed, exposing more active crystal faces, and realizing a high-nickel positive electrode material with excellent lithium ion diffusion kinetics.

[0061] The cathode materials obtained in Examples 9-12 and Comparative Examples 3-5 were assembled into coin-shaped half-cells. After activation for three cycles at 0.1C (1C = 200 mAg) in the voltage range of 2.8-4.3V, they were cycled for 100 cycles at a current density of 1C. Rate performance was also tested at a current density of 5C. See Table 3 for details.

[0062] Table 3 Electrochemical properties of the positive electrode materials prepared in Examples 9-12 and Comparative Examples 3-5

[0063] In summary, the lithium nickelate positive electrode material prepared by the present invention has a stable intercrystalline structure and a special primary particle arrangement, and its cycle stability and rate performance are significantly improved. It is a simple and effective strategy to improve ultra-high nickel materials.

Claims

1. A modified high nickel cathode material, characterized in that: The chemical formula of the high nickel cathode material matrix is ​​LiNi x M 1-x O2, wherein 0.9≤x<1, M is a metal doping element; an oxide containing a metal doping element and lithium exists on the grain boundary surface of the high nickel positive electrode material matrix as a grain boundary coating layer; the metal doping element is a metal doping element having a solubility product constant of less than 10 in the nickel hydroxide precursor coprecipitation system -30 The primary particles in the modified high-nickel positive electrode material are arranged radially extending around the center of the secondary particle.

2. The modified high nickel cathode material according to claim 1, characterized in that The metal doping element is at least one of Zr, Ce, Sn, Cr and Ti.

3. The modified high nickel cathode material according to claim 1, characterized in that The doping concentration of the metal doping element in the modified high-nickel positive electrode material is 0.01-1.00 mol %.

4. The modified high-nickel cathode material according to any one of claims 1 to 3, characterized in that When the valence state of the metal doping element is +3, the chemical formula of the oxide containing the metal doping element and lithium is LiMO2; when the valence state of the metal doping element is +4, the chemical formula of the oxide containing the metal doping element and lithium is Li2MO3; in the oxide containing the metal doping element and lithium, the molar ratio of the metal doping element to lithium is 0.0001~0.01:1.00~1.

10.

5. A method for preparing a modified high-nickel cathode material according to any one of claims 1 to 4, characterized in that: The steps include: (1) A nickel hydroxide precursor containing metal doping elements is prepared by a coprecipitation method. During the preparation process, the feed flow rate of the metal salt solution is controlled to gradually increase as the particle size of the precursor increases; (2) The nickel hydroxide precursor containing the metal doping element obtained in step (1) is mixed with lithium hydroxide and heat-treated in an oxygen-containing atmosphere to obtain the modified high-nickel positive electrode material.

6. The preparation method according to claim 5, characterized in that Step (1) specifically comprises the following steps: dissolving the salt containing the metal doping element into a nickel salt solution to obtain a nickel-metal doping element salt solution; mixing the nickel-metal doping element salt solution, a liquid alkali solution and ammonia water to react, wherein the feed flow rate of the nickel-metal doping element salt solution gradually increases with the increase of the precursor particle size, controlling the pH of the reaction system to be 9.5-11.5, and the particle size of the reaction product D 50 When the particle size reaches 7-18 μm, the precipitated reaction product is washed and centrifuged to obtain a nickel hydroxide precursor containing metal doping elements.

7. The preparation method according to claim 6, characterized in that The nickel salt includes at least one of nickel nitrate, nickel chloride and nickel sulfate; the molar concentration of nickel in the nickel salt solution is 1-3 mol / L; the salt of the metal doping element includes at least one of nitrate, chloride and sulfate; in the nickel-metal doping element salt solution, the molar concentration of the metal doping element is 0.00015-0.030 mol / L; the liquid alkali solution is a sodium hydroxide solution, wherein the concentration of sodium hydroxide is 1.5-4 mol / L.

8. The preparation method according to claim 6, characterized in that The reaction is carried out under stirring conditions, the reaction temperature is controlled at 50-70°C, the feed flow rate of the nickel-metal doping element salt solution is 0.3-10 L / h, and gradually increases with the increase of the precursor particle size; the washing includes the following steps: first using a dilute alkali solution with a liquid alkali mass concentration of 1%-5% for centrifugal washing, and then using pure water for washing. During the washing process, the temperature of the solution is 50-70°C.

9. The preparation method according to claim 5, characterized in that The nickel hydroxide precursor containing the metal doping element is mixed with lithium hydroxide at a lithium ratio of 1.00 to 1.

10.

10. The preparation method according to claim 5, characterized in that The heat treatment includes two stages of heat treatment, and the specific process conditions are as follows: the first stage heat treatment temperature is 300-500°C, and the holding time is 2-6 hours; the second stage heat treatment temperature is 600-800°C, and the holding time is 12-15 hours; the heating rate is 3-20°C / min; the oxygen-containing atmosphere is oxygen or air.

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