High-dispersity medium-high nickel single crystal ternary positive electrode material, preparation method thereof and lithium ion battery

Abstract

The invention relates to a high-dispersity medium-high-nickel single-crystal ternary positive electrode material, a preparation method thereof and a lithium ion battery. The medium-high-nickel single-crystal ternary positive electrode material comprises single-crystal matrix particles, a symbiotic structure middle layer enriched on the interface of the single-crystal matrix particles, and a lithium-fluorine-cobalt compound coating layer coating the surface of the symbiotic structure middle layer. The preparation method comprises the following steps: mixing, sintering, cooling, crushing and sieving a nickel-cobalt-manganese hydroxide precursor, a lithium source and a high-valence dopant to obtain a high-dispersion primary sintering material; and mixing the obtained primary sintered material with a coating agent, sintering, crushing and sieving to obtain the high-dispersity medium-high nickel single crystal ternary positive electrode material. According to the method, excessive fusion of a single crystal matrix particle interface can be prevented, the primary sintering material is easy to crush and dissociate, the influence on subsequent coating treatment is avoided, and meanwhile, the problem of wastewater caused by water washing by a molten salt method and the problems of short cycle life and low capacity at high voltage and high temperature caused by degradation of the particle interface are avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a high-dispersity medium-high nickel single-crystal ternary cathode material, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] With the rapid development of new energy vehicles, portable electronic devices and large-scale energy storage systems, the requirements for energy density and cycle life of lithium ion batteries as core energy carriers are increasing. The selection of lithium ion battery cathode materials can directly affect the performance of the battery. As the top performer of lithium ion battery cathode materials, ternary materials (often abbreviated as NCM) have attracted much attention due to their excellent energy density. When the nickel content in the material reaches or exceeds 0.6, it is classified as a medium-high nickel ternary cathode material. This type of material has become a research hotspot in recent years.

[0003] Medium-high nickel ternary cathode materials mainly obtain higher energy density by increasing the cut-off voltage. In order to maintain the stability of the material under high voltage system, the material needs to be single-crystallized to obtain higher cycle life. Currently, single-crystal ternary cathode materials are mainly prepared by high-temperature solid-phase sintering, and subsequent deagglomeration by air flow crushing. However, the single-crystal ternary materials prepared by traditional high-temperature solid-phase method often have serious agglomeration and excessive fusion of particle interfaces, which leads to incomplete dissociation of single-crystal particles, affecting the subsequent coating effect, and thus leading to the decline of the electrical performance of the material. In addition, the preparation of single-crystal ternary cathode materials can also use molten salt synthesis method. This method mainly uses molten salt to reduce the melting point of the reaction system to prepare high-dispersity ternary cathode materials. However, this method often needs water washing to remove the molten salt impurities on the surface of the particles, which not only increases the production cost, but also often causes lithium to be removed from the structure during water washing, which deteriorates the interface and leads to the decline of the electrical performance of the material. SUMMARY

[0004] The present application aims to provide a high-dispersity medium-high nickel single-crystal ternary cathode material, a preparation method thereof and a lithium ion battery, which aims to solve the problems of short cycle life and low capacity of current medium-high nickel ternary cathode materials under high voltage and high temperature.

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme: in the first aspect, the present application provides a high-dispersity medium-high nickel single-crystal ternary cathode material, which comprises single-crystal matrix particles, a symbiotic structure intermediate layer enriched on the interface of the single-crystal matrix particles, and a lithium fluorocobalt compound coating layer coated on the surface of the symbiotic structure intermediate layer; the chemical formula of the single-crystal matrix particles is LiNi x Co y Mn 1-x-yO2, 0.60≤x≤0.95, 0.05≤y≤0.20, and x+y<1; the chemical formula of the intermediate layer of the symbiotic structure is Li2MO4-Li 4+z Ni 1-z MO6, 0≤z≤0.1, where M is selected from at least one of W, Mo, Mn and Cr.

[0006] Through extensive experiments, the inventors discovered that in medium-to-high nickel systems, high-valence doping element M is difficult to completely dope into the bulk phase. It can only form a symbiotic intermediate layer (equivalent to a shallow doping and coating structure). The symbiotic intermediate layer enriched at the interface of single-crystal matrix particles can not only prevent excessive fusion at the single-crystal matrix particle interface, but also effectively suppress harmful phase transitions in ternary cathode materials during charge and discharge, reduce lattice shrinkage and microcrack formation, and enhance the mechanical stability and electrochemical activity of ternary cathode materials, thereby improving the cycle life and capacity of ternary cathode materials under high temperature and high voltage.

[0007] Preferably, the particle size distribution span of the single-crystal matrix particles [(D90-D10) / D50] < 1.0. The single-crystal matrix particles are uniform in size and highly dispersed, which is beneficial for constructing a more complete coating layer, has high mechanical strength, and facilitates more uniform Li+ insertion / extraction during high-voltage charge and discharge processes, thus extending the cycle life of the single-crystal ternary cathode material.

[0008] Preferably, the thickness of the intermediate layer of the symbiotic structure is 1~10nm.

[0009] Preferably, the thickness of the lithium fluorine cobalt compound coating layer is 1~100 nm.

[0010] Secondly, this invention proposes a method for preparing the highly dispersed, high-nickel single-crystal ternary cathode material, comprising the following steps: mixing a nickel-cobalt-manganese hydroxide precursor, a lithium source, and a high-valence dopant; after mixing, transferring the mixture into an alumina crucible, placing it in a muffle furnace, heating it to 500-800°C at a heating rate of 3°C / min, holding it at that temperature for 3-5 hours, heating it to 900-1100°C at a heating rate of 3°C / min, holding it at that temperature for 1-3 hours, and then cooling it down at a rate of 3°C / min. The material is cooled to 650-850℃ and held at that temperature for 6-8 hours, then allowed to cool naturally to room temperature. It is then removed, crushed, and sieved to obtain highly dispersed primary sintered material. This primary sintered material is mixed with a coating agent. After mixing, the mixture is transferred to a corundum sagger and placed in a muffle furnace. The temperature is increased to 450-850℃ at a rate of 2℃ / min and held for 6-12 hours. The material is then removed, crushed, and sieved to obtain secondary sintered material, i.e., highly dispersed medium-high nickel single-crystal ternary cathode material.

[0011] The application adopts high-temperature solid-phase sintering method to prepare high-dispersity middle-high nickel single-crystal ternary positive electrode material, in the preparation process, lithium source and high-valence dopant react to obtain Li2MO4, lithium source, high-valence dopant and the surface Ni of nickel-cobalt-manganese hydroxide precursor react to obtain Li 4+x Ni 1-x MO6, both of which are enriched in the single-crystal matrix particle interface in symbiotic structure, prevent excessive fusion of the particle interface, ensure easy crushing and dissociation of the primary sintered material, avoid affecting the subsequent coating treatment, and at the same time avoid the problems of wastewater caused by water washing in the molten salt method and the problem of electric performance decline caused by particle interface degradation.

[0012] Preferably, the ratio of the total metal (Me) molar number of nickel, cobalt and manganese in the nickel-cobalt-manganese hydroxide precursor to the molar number of Li element is 1.000:1.000~1.090, i.e. Li / Me=1.000~1.090.

[0013] Preferably, the addition amount of the high-valence dopant is 500~8000ppm, and the high-valence dopant is at least one selected from WO2, WO3, H2WO4, Li2WO4, Na2WO4, CaWO4, (NH4)6W7O 26 *6H2O, MoO3, H2MoO4, Na2MoO4, (NH4)6Mo7O 26 *6H2O, K2MnO4, Na2MnO4, Li2MnO4, BaMnO4, Na2CrO4, K2CrO4, SrCrO4, BaCrO4, (NH4)2Cr2O7, CrO3. When the addition amount of the high-valence dopant is too small, its effect of improving excessive fusion of the particle interface is poor, and when the addition amount of the high-valence dopant is too large, its effect of improving excessive fusion of the particle interface is too strong, so that the particle size is too small, which will cause particle interface degradation in the cycle process, and further cause electric performance decline.

[0014] Preferably, the lithium source is one of Li2CO3, LiOH or a mixture of the two. More preferably, the lithium source is LiOH, which is a strong base and is more likely to react with H2WO4, and at the same time, due to the lower melting point of LiOH, M elements can be carried to penetrate the particle interface in the reaction process, so that the intermediate layer of the symbiotic structure can be more evenly distributed in the single-crystal matrix particle interface.

[0015] Preferably, the coating agent comprises nanometer fluoride, low-melting lithium compound and nanometer cobalt compound; the nanometer fluoride is selected from one or two of LiF, NaF, CaF2, MgF2, and AlF3, and the coating amount is 500-5000 ppm; the low-melting lithium compound is selected from one of LiOH, LiNO3, LiCl, LiBr, and LiI, and the coating amount is 500-10000 ppm; the nanometer cobalt compound is selected from one of CoOOH, Co(OH)2, CoCO3, CoC2O4, and Co(CH3COO)2*4H2O, and the coating amount is 1000-50000 ppm. Among them, the nanometer fluoride plays a passivation role to protect the material from HF corrosion; the low-melting lithium compound melts the coating agent, making the coating layer more uniform, and at the same time repairing the surface defects caused by crushing; the nanometer cobalt compound makes the surface rich in cobalt, which can improve the conductivity of the material, improve the capacity of the material, and reduce the influence of the fluoride passivation layer on the capacity reduction of the material.

[0016] In a third aspect, the present application provides a lithium ion battery comprising the high-dispersity medium-high-nickel single-crystal ternary positive electrode material.

[0017] The present application has the beneficial effects that: the present application adopts a high-temperature solid-phase sintering method to prepare a high-dispersity medium-high-nickel single-crystal ternary positive electrode material, in the preparation process, the high-valence dopant reacts with the lithium source to obtain Li2MO4, and the high-valence dopant and the lithium source, and the surface Ni of the nickel-cobalt-manganese hydroxide precursor react to obtain Li 4+x Ni 1-x MO6, which are enriched in the single-crystal matrix particle interface in a symbiotic structure, prevent excessive fusion of the particle interface, ensure easy crushing and dissociation of the primary sintered material, and avoid affecting the subsequent coating treatment; and the intermediate layer of the symbiotic structure enriched in the single-crystal matrix particle interface can effectively inhibit harmful phase changes of the ternary positive electrode material during charging and discharging, reduce lattice shrinkage and micro-crack formation, and enhance the mechanical stability and electrochemical activity of the ternary positive electrode material, thereby improving the cycle life and capacity of the ternary positive electrode material at high temperature and high voltage. In addition, the present application also performs coating treatment on the primary sintered material to form a uniform and complete lithium-fluoride-cobalt compound coating layer, which can improve the conductivity of the material and also improve the capacity of the material. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a scanning electron microscope image of the product (not crushed) obtained after the primary sintered material in Comparative Example 5 is mixed with the coating agent and sintered; Figure 2 is a scanning electron microscope image of the product (not crushed) obtained after the primary sintered material in Example 11 is mixed with the coating agent and sintered; Figure 3 is a scanning electron microscope image of the single-crystal ternary positive electrode material (crushed) in Comparative Example 5; Figure 4 Scanning electron microscope image of the single-crystal ternary cathode material (crushed) of Example 11. DETAILED DESCRIPTION

[0019] The application will be described in further detail below with reference to the specific embodiments and drawings attached hereto, but the embodiments of the application are not limited thereto.

[0020] Example 1 A preparation method of a high-dispersion medium-high-nickel single-crystal ternary cathode material, comprising the following steps: mixing a nickel-cobalt-manganese hydroxide precursor Ni 0.69 Co 0.07 Mn 0.24 (OH)2, a lithium source LiOH, and a high-valence dopant H2WO4 in a ratio of Li / Me = 1.050, mixing uniformly, then transferring the mixed material into a corundum box, placing it in a muffle furnace, and raising the temperature to 500°C at a temperature raising speed of 3°C / min, keeping the temperature constant for 3h, raising the temperature to 1000°C at a temperature raising speed of 3°C / min, keeping the temperature constant for 1h, lowering the temperature to 800°C at a temperature lowering speed of 3°C / min, keeping the temperature constant for 9h, and naturally cooling to room temperature, then taking it out for crushing and sieving to obtain a high-dispersion primary sintered material; mixing the obtained primary sintered material with a coating agent LiF (coating amount: 1000ppm), a coating agent LiOH (coating amount: 1000ppm), and a coating agent CoOOH (coating amount: 5000ppm), after the mixing is completed, transferring the mixed material into a corundum box, placing it in a muffle furnace, raising the temperature to 680°C at a temperature raising speed of 2°C / min, keeping the temperature constant for 9h, naturally cooling to room temperature, taking it out and crushing and sieving to obtain a high-dispersion medium-high-nickel single-crystal ternary cathode material.

[0021] Example 2 Different from Example 1, in this embodiment, the addition amount of the high-valence dopant H2WO4 is 3000ppm, and Li / Me = 1.020.

[0022] The rest is the same as Example 1, which will not be repeated here.

[0023] Example 3 Different from Example 1, in this embodiment, the addition amount of the high-valence dopant H2WO4 is 3000ppm, and Li / Me = 1.080.

[0024] The rest is the same as Example 1, which will not be repeated here.

[0025] Example 4 Different from Example 1, in this embodiment, the addition amount of the high-valence dopant H2WO4 is 8000ppm, and Li / Me = 1.020.

[0026] The rest is the same as example 1, which will not be repeated here.

[0027] Example 5 Different from example 1: in this example, the addition amount of high valence state dopant H2WO4 is 8000 ppm, Li / Me = 1.080.

[0028] The rest is the same as example 1, which will not be repeated here.

[0029] Example 6 Different from example 1: in this example, the lithium source is Li2CO3.

[0030] The rest is the same as example 1, which will not be repeated here.

[0031] Example 7 Different from example 1: in this example, the lithium source is Li2CO3, and the high valence state dopant is MoO3.

[0032] The rest is the same as example 1, which will not be repeated here.

[0033] Example 8 Different from example 1: in this example, the lithium source is Li2CO3, and the high valence state dopant is WO3.

[0034] The rest is the same as example 1, which will not be repeated here.

[0035] Example 9 Different from example 1: in this example, the high valence state dopant is Li2WO4.

[0036] The rest is the same as example 1, which will not be repeated here.

[0037] Example 10 Different from example 1: in this example, the high valence state dopant is a mixture of H2WO4 and MoO3, with a mass ratio of 1:1.

[0038] The rest is the same as example 1, which will not be repeated here.

[0039] Example 11 Different from example 1: in this example, the coating agent LiF is replaced by a mixture of LiF and MgF2 with a mass ratio of 1:1.

[0040] The rest is the same as example 1, which will not be repeated here.

[0041] Example 12 Different from example 1: in this example, the coating agent LiOH is replaced by LiNO3.

[0042] The rest is the same as Example 1, which will not be repeated here.

[0043] Comparative Example 1 A preparation method of a medium-high nickel single-crystal ternary positive electrode material, comprising the following steps: mixing nickel-cobalt-manganese hydroxide precursor Ni 0.69 Co 0.07 Mn 0.24 (OH)2, lithium source LiOH, and mixing according to Li / Me=1.050 ratio, after uniform mixing, the mixed material is transferred into a corundum box, placed in a muffle furnace, the temperature is raised to 500℃ at a rate of 3℃ / min, and kept constant for 3h, the temperature is raised to 1000℃ at a rate of 3℃ / min, and kept constant for 1h, the temperature is lowered to 800℃ at a rate of 3℃ / min, and kept constant for 9h, and then cooled to room temperature, and then taken out for crushing and sieving, to obtain a medium-high nickel single-crystal ternary positive electrode material.

[0044] Comparative Example 2 A preparation method of a medium-high nickel single-crystal ternary positive electrode material, comprising the following steps: mixing nickel-cobalt-manganese hydroxide precursor Ni 0.69 Co 0.07 Mn 0.24 (OH)2, lithium source LiOH, and mixing according to Li / Me=1.050 ratio, after uniform mixing, the mixed material is transferred into a corundum box, placed in a muffle furnace, the temperature is raised to 500℃ at a rate of 3℃ / min, and kept constant for 3h, the temperature is raised to 1000℃ at a rate of 3℃ / min, and kept constant for 1h, the temperature is lowered to 800℃ at a rate of 3℃ / min, and kept constant for 9h, and then cooled to room temperature, and then taken out for crushing and sieving, to obtain a medium-high nickel single-crystal ternary positive electrode material.

[0045] Comparative Example 3 A preparation method of a medium-high nickel single-crystal ternary positive electrode material, comprising the following steps: mixing nickel-cobalt-manganese hydroxide precursor Ni 0.69 Co 0.07 Mn 0.24Ni0.5Co0.2Mn0.3(OH)2, lithium source LiOH, mixed in a ratio of Li / Me = 1.050, after uniform mixing, the mixed material was transferred into a corundum box, placed in a muffle furnace, and heated to 500°C at a heating rate of 3°C / min, kept at 500°C for 3h, heated to 1000°C at a heating rate of 3°C / min, kept at 1000°C for 1h, cooled to 800°C at a cooling rate of 3°C / min, kept at 800°C for 9h, naturally cooled to room temperature, then taken out for crushing and sieving to obtain a primary sintered material; the obtained primary sintered material was mixed with a coating agent MgF2 (coating amount 1000ppm), after mixing was completed, the mixed material was transferred into a corundum box, placed in a muffle furnace, heated to 680°C at a heating rate of 2°C / min, kept at 680°C for 9h, naturally cooled to room temperature, taken out and crushed and sieved to obtain a MgF2-coated middle-high nickel single-crystal ternary positive electrode material.

[0046] Comparative Example 4 A preparation method of a middle-high nickel single-crystal ternary positive electrode material, comprising the following steps: mixing a nickel-cobalt-manganese hydroxide precursor Ni 0.69 Co 0.07 Mn 0.24 Ni0.5Co0.2Mn0.3(OH)2, lithium source LiOH, mixed in a ratio of Li / Me = 1.050, after uniform mixing, the mixed material was transferred into a corundum box, placed in a muffle furnace, and heated to 500°C at a heating rate of 3°C / min, kept at 500°C for 3h, heated to 1000°C at a heating rate of 3°C / min, kept at 1000°C for 1h, cooled to 800°C at a cooling rate of 3°C / min, kept at 800°C for 9h, naturally cooled to room temperature, then taken out for crushing and sieving to obtain a primary sintered material.

[0047] The obtained primary sintered material was mixed with a coating agent MgF2 (coating amount 1000ppm) and a coating agent LiOH (coating amount 1000ppm), after mixing was completed, the mixed material was transferred into a corundum box, placed in a muffle furnace, heated to 680°C at a heating rate of 2°C / min, kept at 680°C for 9h, naturally cooled to room temperature, taken out and crushed and sieved to obtain a MgF2 and LiOH-coated middle-high nickel single-crystal ternary positive electrode material.

[0048] Comparative Example 5 A preparation method of a middle-high nickel single-crystal ternary positive electrode material, comprising the following steps: mixing a nickel-cobalt-manganese hydroxide precursor Ni 0.69 Co 0.07 Mn 0.24OH, Li source LiOH, mixed in proportion of Li / Me = 1.050, after uniform mixing, the mixed material was transferred into a corundum box, placed in a muffle furnace, the temperature was raised to 500℃ at a rate of 3℃ / min, kept constant for 3h, the temperature was raised to 1000℃ at a rate of 3℃ / min, kept constant for 1h, the temperature was lowered to 800℃ at a rate of 3℃ / min, kept constant for 9h, and then cooled to room temperature, followed by crushing, sieving, to obtain a primary sintered material; the obtained primary sintered material was mixed with coating agent MgF2 (coating amount 1000ppm), coating agent LiOH (coating amount 1000ppm) and coating agent CoOOH (coating amount 5000ppm), after mixing, the mixed material was transferred into a corundum box, placed in a muffle furnace, the temperature was raised to 680℃ at a rate of 2℃ / min, kept constant for 9h, and then cooled to room temperature, taken out and crushed, sieved, to obtain Mg, F and Co coated middle-high nickel single crystal ternary positive electrode material.

[0049] Comparative Example 6 Different from Example 1: in this comparative example, high-valence state dopant H2WO4 was replaced by dopant MgO.

[0050] The rest is the same as Example 1, which will not be repeated here.

[0051] Comparative Example 7 Different from Example 1: in this comparative example, high-valence state dopant H2WO4 was replaced by dopant Al2O3.

[0052] The rest is the same as Example 1, which will not be repeated here.

[0053] Comparative Example 8 Different from Example 1: in this comparative example, the sintering process of the primary sintered material was changed from: raising the temperature to 500℃ at a rate of 3℃ / min, keeping constant for 3h, raising the temperature to 1000℃ at a rate of 3℃ / min, keeping constant for 1h, lowering the temperature to 750-850℃ at a rate of 3℃ / min, keeping constant for 8h, to: raising the temperature to 500℃ at a rate of 3℃ / min, raising the temperature to 950℃ at a rate of 3℃ / min, keeping constant for 10h.

[0054] The rest is the same as Example 1, which will not be repeated here.

[0055] Comparative Example 9 Different from Example 1: in this comparative example, nickel cobalt manganese hydroxide precursor Ni 0.69 Co 0.07 Mn 0.24 (OH)2 was replaced by Ni 0.33 Co 0.33 Mn 0.33 (OH)2.

[0056] The rest is the same as Example 1, which will not be repeated here.

[0057] 1. Particle size test Take 0.5 g of ternary positive electrode material prepared in Examples 1-12 and Comparative Examples 1-9 respectively, put it in a beaker, add deionized water and sodium hexametaphosphate dispersant, stir uniformly, then ultrasonic for 2 min, then use the Malvern particle size analyzer for test, wherein D50 represents the corresponding particle size of the cumulative distribution of 50% in the system, PSD represents the particle size distribution, the smaller the value, the more uniform the particle size, and the better the particle dissociation.

[0058] 2. Electrical performance test Grind the ternary positive electrode material prepared in Examples 1-12 and Comparative Examples 1-9 with conductive carbon black and binder PVDF in a mass ratio of 92:5:3 (total mass 15g) respectively, then add 12 mL of NMP to grind into slurry, then uniformly coat the slurry on aluminum foil to make electrode sheet, and place the electrode sheet in a 120°C drying oven for 12h, roll, and cut into the size of the positive electrode sheet of the required button cell for standby.

[0059] Use lithium metal sheet as the counter electrode, use ternary positive electrode material commonly used electrolyte and double-sided coated ceramic coated separator, assemble into CR2016 button cell in an argon-filled glove box.

[0060] Test the electrical performance of the button cell, use 0.1C rate for capacity test, test temperature: 25°C, charge and discharge range: 3.0-4.5V; use 1C rate for high temperature cycle performance test, test temperature: 45°C, charge and discharge range: 3.0-4.5V.

[0061] The above performance test results are shown in Table 1.

[0062]

[0063] As can be seen from Table 1, the high-nickel single-crystal ternary positive electrode material prepared by the preparation method of the present application has a small particle size distribution value, that is, the high-nickel single-crystal ternary positive electrode material of the present application has uniform particle size, good particle dissociation degree and high dispersibility. Moreover, the lithium ion battery prepared by using the high-dispersibility high-nickel single-crystal ternary positive electrode material of Examples 1-12 of the present application has relatively high discharge capacity and cycle retention rate. As can be seen from the comparison of the examples, when at least one of the lithium source, the high-valence dopant and the content thereof is different, the high-nickel ternary positive electrode material prepared thereby also has different performance. Specifically, as can be seen from the comparison of Example 1 and Example 6, when the lithium source is LiCO3, the particle size distribution value is obviously increased, that is, the particle size is not as uniform as that of Example 1. This is because, in Example 1, LiOH is used as the lithium source, and the melting point of LiOH is low. Moreover, as a strong base, the reaction degree of LiOH with H2WO4 is the highest. Since the melting point of LiOH is low, the reaction process can carry M elements to penetrate the particle interface, so that the intermediate layer of the symbiotic structure can be more uniformly distributed in the single-crystal matrix particle interface. In addition, as can be seen from the comparison of Example 1 and Examples 2-5, when the addition amount of the high-valence dopant is too small, the improvement is not obvious, and when the addition amount of the high-valence dopant is too large, the anti-fusion effect is too strong, the generated high-nickel single-crystal ternary positive electrode material has too small particle size, and the particle interface will be deteriorated during the cycle process, thereby causing the electrical performance to decrease.

[0064] Specifically, as can be seen from the comparison of Example 1 and Comparative Example 1, the high-nickel single-crystal ternary positive electrode material prepared without adding the high-valence dopant and the coating agent has an obviously increased particle size distribution value, and the capacity retention rate is obviously decreased. This is because, in Comparative Example 1, the intermediate layer of the symbiotic structure and the lithium fluorine cobalt compound coating layer are not formed on the surface of the single-crystal matrix particle, thereby causing the single-crystal matrix particle interface to be excessively fused, not easy to be dispersed and dissociated, the particles to be agglomerated, the dispersibility to be poor, and the particle interface to be deteriorated, thereby further causing the electrical performance to decrease.

[0065] Similarly, as can be seen from the comparison of Example 1 and Comparative Examples 2-5, the high-nickel single-crystal ternary positive electrode material prepared without adding the high-valence dopant has an obviously increased particle size distribution value, but different from Comparative Example 1, the surface of the single-crystal matrix particle is coated in Comparative Examples 2-5, so that the capacity retention rate is only slightly decreased. That is, the surface of the single-crystal matrix particle is coated, which can improve the electrical performance of the material.

[0066] As can be seen from the comparison of Example 1 and Comparative Examples 6-7, when the high-valence dopant is not added during preparation, but a conventional metal dopant is added, since the low-valence metal ion has a small radius and tends to be bulk doping, it cannot form an intermediate phase structure at the interface, so it cannot play a role in protecting the particle interface and preventing the single-crystal matrix particle interface from being excessively fused.

[0067] Furthermore, a comparison between Example 1 and Comparative Example 8 shows that the D50 value and cycle capacity retention of Comparative Example 8 are significantly smaller. This is because, in the medium-high nickel system, high-valence dopants are difficult to completely dop into the bulk phase and can only form a symbiotic intermediate layer (equivalent to a shallow doping and coating structure). At this time, the symbiotic intermediate layer at the enrichment interface mainly plays the role of preventing particle fusion and growth. When the sintering reaction temperature is increased, it can promote particle growth. However, Comparative Example 8 uses a conventional sintering process, which does not reach 1000°C and is held at that temperature for 1 hour. Therefore, its particles are smaller, and the side reactions between the particles and the electrolyte increase, resulting in poorer cycle performance.

[0068] As can be seen from the comparison between Example 1 and Comparative Example 9, the performance of the nickel-cobalt-manganese hydroxide precursor deteriorates significantly when the contents of Ni, Co, and Mn are changed. The inventors discovered during the experiment that, with increased Co and Mn contents, the high-valence dopants completely diffuse into the interior of the single-crystal matrix particles, failing to form a symbiotic intermediate layer. This results in an inability to effectively suppress harmful phase transitions in the ternary cathode material during charge and discharge, reduce lattice shrinkage and microcrack formation, and consequently lead to performance degradation.

[0069] In addition, by Figure 1 and Figure 2 A comparison of the two shows that the high-nickel single-crystal ternary cathode material in Example 11 exhibits significant interface separation after doping with high-valence elements, with the "grooves" between particles becoming deeper and more pronounced; similarly, the high-nickel single-crystal ternary cathode material in Example 11 shows... Figure 3 and Figure 4 A comparison of the two materials shows that the high-nickel single-crystal ternary cathode material of Example 11 exhibits higher particle dispersion after doping with high-valence elements, while the high-nickel single-crystal ternary cathode material of Comparative Example 5, without high-valence elements, shows more severe particle adhesion and lower dispersion compared to Example 11. This is because, during the primary sintering material preparation process, the high-valence dopant reacts with the lithium source to form Li₂MO₄, and simultaneously, the high-valence dopant reacts with the lithium source and Ni on the surface of the nickel-cobalt-manganese hydroxide precursor to form Li. 4+x Ni 1-x MO6 and the other two are enriched in a symbiotic structure at the interface of single crystal matrix particles, preventing excessive fusion of the particle interface and ensuring that the material sintered in one step is easy to crush and dissociate.

[0070] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A high-dispersibility medium-high nickel single-crystal ternary cathode material, characterized in that, The single crystal matrix particle, the interlayer of paragenetic structure enriched in the interface of the single crystal matrix particle, and the coating layer of lithium fluorocobalt compound coated on the surface of the interlayer of paragenetic structure; the chemical formula of the single crystal matrix particle is LiNi x Co y Mn 1-x-y O2, 0.60≤x≤0.95, 0.05≤y≤0.20, and x+y<1; the chemical formula of the interlayer of paragenetic structure is Li2MO4-Li 4+z Ni 1-z MO6, 0≤z≤0.1, M is selected from at least one of W, Mo, Mn and Cr. 2.The high dispersibility medium-high nickel single-crystal ternary cathode material of claim 1, characterized in that, The particle size distribution span [(D90-D10) / D50] of the single crystal substrate particles is less than 1.

0. 3.The high dispersibility medium-high nickel single-crystal ternary cathode material of claim 1, characterized in that, The thickness of the intermediate layer of the symbiotic structure is 1-10 nm. 4.The high dispersibility medium-high nickel single-crystal ternary cathode material of claim 1, characterized in that, The thickness of the lithium fluoride cobalt compound coating layer is 1-100 nm.

5. A method for preparing the high-dispersible medium-high nickel single-crystal ternary cathode material according to any one of claims 1-4, characterized in that, The method comprises the following steps: mixing a nickel-cobalt-manganese hydroxide precursor, a lithium source and a high-valence dopant, after the mixing is completed, transferring the mixed material into a corundum box, placing it in a muffle furnace, and increasing the temperature to 500-800 DEG C at a temperature increasing rate of 3 DEG C / min, keeping the temperature constant for 3-5 h, increasing the temperature to 900-1100 DEG C at a temperature increasing rate of 3 DEG C / min, keeping the temperature constant for 1-3 h, decreasing the temperature to 650-850 DEG C at a temperature decreasing rate of 3 DEG C / min, keeping the temperature constant for 6-8 h, naturally cooling to room temperature, and then taking it out for crushing and sieving to obtain a high-dispersion primary sintered material; mixing the obtained primary sintered material with a coating agent, after the mixing is completed, transferring the mixed material into a corundum box, placing it in a muffle furnace, and increasing the temperature to 450 DEG C-850 DEG C at a temperature increasing rate of 2 DEG C / min, keeping the temperature constant for 6-12 h, taking it out and crushing and sieving to obtain a secondary sintered material, i.e., a high-dispersion medium-high nickel single crystal ternary positive electrode material.

6. The preparation method of the high dispersion medium-high nickel single crystal ternary positive electrode material according to claim 5, characterized in that, The ratio of the total metal (Me) molar number of nickel, cobalt and manganese in the nickel-cobalt-manganese hydroxide precursor to the molar number of Li element is 1.000:1.000-1.090, i.e., Li / Me=1.000-1.

090.

7. The preparation method of the high dispersion medium-high nickel single crystal ternary cathode material according to claim 5, characterized in that, The high valence dopant is selected from at least one of WO2, WO3, H2WO4, Li2WO4, Na2WO4, CaWO4, (NH4)6W7O 26 *6H2O, MoO3, H2MoO4, Na2MoO4, (NH4)6Mo7O 26 *6H2O, K2MnO4, Na2MnO4, Li2MnO4, BaMnO4, Na2CrO4, K2CrO4, SrCrO4, BaCrO4, (NH4)2Cr2O7, CrO3.

8. The method for preparing the highly dispersed, high-nickel single-crystal ternary cathode material according to claim 5, characterized in that, The lithium source is one of Li2CO3 and LiOH or a mixture of the two.

9. The preparation method of the high dispersion medium-high nickel single crystal ternary cathode material according to claim 5, characterized in that, The coating agent comprises nanometer fluoride, low-melting-point lithium compound and nanometer cobalt compound; the nanometer fluoride is selected from one or two of LiF, NaF, CaF2, MgF2 and AlF3, and the coating amount is 500-5000 ppm; the low-melting-point lithium compound is selected from one of LiOH, LiNO3, LiCl, LiBr and LiI, and the coating amount is 500-10000 ppm; the nanometer cobalt compound is selected from one of CoOOH, Co(OH)2, CoCO3, CoC2O4 and Co(CH3COO)2*4H2O, and the coating amount is 1000-50000 ppm.

10. A lithium-ion battery, characterized by, The high-dispersion medium-high nickel single crystal ternary positive electrode material of any one of claims 1-4.

Images