Positive electrode material and preparation method thereof, and lithium ion battery

Abstract

The present invention provides a positive electrode material and a preparation method thereof, and a lithium ion battery. The chemical formula of the positive electrode material is LiNi (1‑x) Mo x Me y O2, wherein 0<x<0.3, 0<y<0.3; Me is selected from one or more of Y, Nb, Ce, Ta, Mn or W. Based on this, the positive electrode material has high energy density, better rate performance, better power performance, better low temperature performance, and higher safety performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a positive electrode material and a preparation method thereof, and a lithium ion battery. Background Art

[0002] Lithium-ion batteries are widely used in electric vehicles and consumer electronics due to their high energy density, high output power, long cycle life, and low environmental pollution. In recent years, with the increasing popularity of electric passenger vehicles, owners have noticed that the range of electric vehicles using lithium iron phosphate batteries is significantly reduced in northern winter, by 30-50% compared to standard range. Electric vehicles using ternary lithium batteries also experience this reduction, but only by 20-30% compared to standard range. Consequently, consumers in northern China are increasingly turning to ternary lithium battery electric vehicles, but they still suffer from issues such as slow charging in low temperatures. A lithium battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. The main reason for the reduced charge and discharge efficiency of lithium-ion batteries is the decreased lithium ion transfer rate at low temperatures. In the existing technology, the low-temperature performance of lithium batteries is improved mainly by improving the positive and negative active materials and electrolytes, specifically as follows: First, the positive and negative active materials, reducing the particle size of the positive and negative electrode materials, increasing the interface of lithium ions entering and exiting the positive and negative electrode materials, is conducive to improving the low-temperature performance; second, by reducing the viscosity of the electrolyte at low temperatures, the migration rate of lithium ions in the electrolyte is increased; third, adjusting the components of the electrolyte additives, changing the composition and thickness of the negative electrode SEI film.

[0003] my country has a vast territory, and the climate varies greatly from place to place. There is the extremely cold Northeast China and the hot Hainan. Such a large temperature change will have a significant impact on the electrical performance of lithium-ion batteries. In these special fields, due to the harsh operating environment, batteries are often required to operate at -30°C or even lower. However, when the operating temperature is below -20°C, lithium-ion batteries cannot maintain their performance under normal temperature conditions. Generally, when the temperature drops to -10°C, the discharge capacity and operating voltage of lithium-ion batteries will decrease. Sun Ho Park (first author) and Myung-Hyun Ryou, Yong Min Lee (corresponding author) and others from Daegu Institute of Science and Technology in South Korea analyzed that the impact of ambient temperature changes on the power performance of lithium-ion batteries is greater than the impact on capacity. The study shows that temperature has a great impact on the power performance of lithium-ion batteries.

[0004] LiNi, a ternary material for lithium-ion batteries 1-x-y Co x Mn yO2 is considered to be a cathode material that can replace lithium cobalt oxide and has development potential due to its advantages such as high gram capacity, good safety, low cost, working voltage matching existing electrolytes, and no environmental pollution. Due to the synergistic effect, the performance of ternary materials is better than any single material. Controlling the ratio of Ni, Co, and Mn elements is one of the key factors in optimizing the performance of ternary cathode materials. Too high Ni content will reduce the safety performance of the battery, and too high Co content will increase the cost of the material. However, reducing the content of the two elements will lead to problems such as low material capacity and unstable structure. A large number of studies have shown that the electrochemical properties of ternary cathode materials can be improved by using surface coating, doping, and a combination of the two. However, a single surface coating or doping method cannot significantly improve the cycle performance of ternary cathode materials.

[0005] Usually, in order to better form the layered structure of the ternary positive electrode material, an excess lithium source needs to be added during the synthesis process, and unreacted lithium oxide in the Li2O state is produced after the synthesis. This unreacted lithium oxide will react with water and carbon dioxide in the air to form residual alkali (main components: LiOH, Li2CO3), which remains on the surface of the positive electrode material. However, the greatly increased surface residual alkaline impurities of ternary positive electrode materials, especially high-nickel positive electrode materials, will cause serious gas production problems in lithium-ion batteries during the charge and discharge process, resulting in battery expansion and deformation, shortened cycle shelf life, and safety hazards. The higher the proportion of nickel in the ternary material, the higher the discharge capacity of the material and the higher the residual alkali. As a result, the cycle life becomes shorter during the charge and discharge process, especially the interface stability between the active material and the electrolyte will also deteriorate accordingly, causing side reactions to occur and affecting the cycle stability of the material.

[0006] Developing a method that can effectively reduce the internal resistance of positive electrode materials and improve their power performance is of great significance. Common methods for reducing the internal resistance of ternary materials include: 1. making the material structure loose and reducing the material's tap density; however, when the material's tap density is low, the pole piece compaction is low when it is made into a pole piece, resulting in low battery cell energy density; 2. reducing the material particle size; however, if the material particle size is too small, it is difficult to control the material morphology during material synthesis. At the same time, the synthesis of small-particle materials is prone to produce fine powder, the magnetic material content of the product exceeds the standard, and the product yield decreases; 3. increasing the material's specific surface area. When the material's specific surface area is too large, the material and the electrolyte undergo more side reactions, thus affecting the battery cell performance. Although layered ternary materials have good power and safety performance, in actual applications, it has been found that ternary materials have good power at high SOC. However, in the low SOC range (less than 50% SOC), the power drops sharply due to the increased internal resistance of the ternary material, resulting in large fluctuations in power values ​​across the entire battery SOC range, and the SOC range in which high power can be used becomes smaller. Therefore, there is still a long way to go to improve the power performance of ternary material batteries at low SOC, especially the power performance at low SOC at low temperatures.

[0007] Direct current internal resistance (DCR) is a key electrical property of lithium-ion batteries. This includes both charge DCR and discharge DCR. It is a crucial metric for evaluating lithium-ion battery performance and directly impacts its energy density and cycle life. Reducing the battery's DCR and improving its kinetic performance are effective approaches to achieving high power performance. Both discharge DCR and charge DCR are crucial performance indicators for lithium-ion batteries. Charge DCR reflects the charge polarization and heat generation of the battery cell, while discharge DCR reflects the polarization and heat generation during discharge. The DCR of a lithium-ion battery is a crucial indicator of battery performance. Low temperatures can cause a sharp increase in internal resistance, leading to a decrease in discharge capacity and rate capability. Low temperatures can also lead to lithium deposition, and the resulting lithium dendrites can potentially pierce the separator, impacting safety. Improving the lithium ion solid-phase transport capability of the cathode material can significantly improve the interfacial resistance and DCR performance of the battery. The DCR during the non-cycling process is the short-term DCR of the battery cell. Due to the short time, there is less polarization accumulation and side reaction accumulation. The DCR after cycling reflects the long-term DCR of the battery cell, which is a comprehensive situation of the battery cell's ohmic internal resistance, polarization accumulation, side reaction accumulation, and electrode health status. If there is a sudden change in DCR, it is often accompanied by a deterioration in cycle performance.

[0008] During the initial charge of a lithium-ion battery, lithium ions are continuously released from the positive electrode. However, during discharge, not all of the lithium ions are reinserted, resulting in lithium ion loss and irreversible capacity loss. Therefore, the initial efficiency of the material is related to its structure, material kinetics, and side reactions at high potentials. At high cutoff voltages and high charge / discharge rates, electrolyte corrosion and transition metal dissolution can occur on the surface of the positive electrode material, causing structural collapse of the positive electrode surface material and deteriorating the battery's cycling performance. Therefore, high voltages are crucial for the structural integrity and surface properties of ternary materials.

[0009] In summary, existing cathode materials for lithium-ion power batteries have problems such as low energy density, poor rate performance, poor power performance, poor low-temperature performance, or poor safety performance. Therefore, it is necessary to provide a cathode material for lithium-ion power batteries that has high energy density, excellent rate performance, high power, excellent low-temperature performance, good safety performance, and can be used at high voltages. Summary of the Invention

[0010] The main purpose of the present invention is to provide a positive electrode material and a preparation method thereof, and a lithium-ion battery, so as to solve the problems of the positive electrode materials in the prior art, such as low energy density, poor rate performance, poor power performance, poor low temperature performance, or poor safety performance.

[0011] In order to achieve the above object, according to one aspect of the present invention, a positive electrode material is provided. The chemical formula of the positive electrode material is LiNi (1-x-y) Mo x Me y O2, wherein 0<x<0.3, 0<y<0.3; Me is selected from one or more of Y, Nb, Ce, Ta, Mn or W.

[0012] Furthermore, the positive electrode material is doped with F; preferably, the doping amount of F is 100 to 500 ppm.

[0013] Furthermore, the positive electrode material is a single crystal material, and the shape of the positive electrode material is spherical particles; preferably, the D50 particle size of the positive electrode material is 2 to 5 μm; more preferably, it is 2.5 to 3.5 μm.

[0014] To achieve the above object, according to one aspect of the present invention, a method for preparing the aforementioned positive electrode material is provided, the preparation method comprising: mixing a Li source, a Ni source, a Mo source and a Me source in a stoichiometric ratio and then sintering to obtain a positive electrode material.

[0015] Furthermore, the preparation method includes the following steps: step S1, adding Li source, Ni source, Mo source and Me source to an aqueous solution of a stabilizer in a stoichiometric ratio for aging to form a glue A; step S2, adding a carbon source to the glue A and then aging and freeze-drying in sequence to obtain an intermediate C; step S3, sintering the intermediate C to obtain a positive electrode material; wherein the sintering includes a first sintering and a second sintering performed in sequence, and the temperature of the first sintering is less than the thermal decomposition temperature of the carbon source and less than the temperature of the second sintering, and the first sintering is carried out in a first atmosphere containing a fluorine source gas.

[0016] Furthermore, in step S2, the carbon source includes an alkali-soluble resin and a polymer fiber material; preferably, the alkali-soluble resin and the polymer fiber material are first mixed and added to a volatile solvent to form a glue solution B, and then the glue solution B is added to the glue solution A to perform aging and freeze-drying in sequence; preferably, the volatile solvent is selected from one or more of C1-C3 alcohols, C1-C3 ketones or C1-C3 ethers; further preferably, the surface tension of the glue solution B is 15-35 mN / m, the viscosity is 3.0-10.0 mPa·s, and the conductivity is 0.3-1 mS / cm; Preferably, the weight ratio of glue A and glue B is 1:(0.1~0.5); further preferably, the treatment temperature during the aging process is 20~40℃, and the treatment time is 4~40h; further preferably, the freeze-drying process includes a first freeze-drying treatment and a second freeze-drying treatment performed sequentially; more preferably, the temperature of the first freeze-drying treatment is -20~0℃, and the time is 0.5~2h; the temperature of the second freeze-drying treatment is -100~0℃, and the time is 1~3h; further preferably, the cooling rate of the material during the freeze-drying process is controlled at 1~5℃ / min.

[0017] Furthermore, in step S3, after the second sintering, the second sintered material is subjected to a third sintering step; preferably, the sintering temperature of the first sintering is 200-400°C, and the sintering time is 2-5h; further preferably, the fluorine source gas is selected from one or more of carbon tetrafluoride, perfluorobutadiene, nitrogen trifluoride, hexafluoroethane, perfluoropropane or trifluoromethane; further preferably, the first atmosphere includes 30-60wt% of fluorine source gas, 0.05-0.01wt% of water and the remainder of oxygen and ozone; preferably, the second sintering is carried out in an oxygen-rich second atmosphere; and the sintering temperature of the second sintering is 800-1000°C, and the sintering time is 12-40h; preferably, the third sintering is carried out in an oxygen-rich third atmosphere; and the sintering temperature of the third sintering is 300-800°C, and the sintering time is 2-6h; further preferably, the mass concentration of oxygen in the second atmosphere and the third atmosphere is independently greater than 50%.

[0018] Furthermore, the Li source is selected from one or more of lithium hydroxide, lithium carbonate, lithium acetate, lithium nitrate or lithium chloride; preferably, the Ni source is selected from one or more of nickel oxide, nickel hydroxide, nickel nitrate, nickel sulfate or nickel carbonate; preferably, the Mo source is selected from one or more of nano-molybdenum oxide, nano-sodium molybdate, nano-ammonium molybdate or nano-molybdic acid; preferably, the Me source is selected from a soluble compound containing one or more elements of Y, Nb, Ce, Ta, Mn or W; preferably, the stabilizer is selected from one or more of citric acid, lactic acid, glycolic acid, fruit acid or tartaric acid; preferably, the alkali-soluble resin contains an unsaturated group; more preferably, the alkali-soluble resin is selected from one or more of polyester resin, acrylic resin, polyurethane resin or styrene-acrylic resin; preferably, the average length of the polymer fiber material is 5 to 50 μm; more preferably, the polymer fiber material is selected from one or more of chitosan fiber, filamentous cellulose, polyvinyl alcohol fiber, and lactic acid-glycolic acid copolymer fiber.

[0019] In order to achieve the above object, according to one aspect of the present invention, a lithium-ion battery is provided. The lithium-ion battery includes the aforementioned positive electrode material, or the positive electrode material prepared by the aforementioned preparation method.

[0020] First, the Mo element has a high valence state and combines well with oxygen, which can form a more stable Mo-O bond, and Mo and Ni can also form a eutectic, which not only effectively improves the structural stability of the product during low-temperature use, but also further reduces the occurrence of mixed rows, effectively improving the cycle stability of the product. Secondly, one or more high-valence Me elements Y, Nb, Ce, Ta or W are doped. First, this can form partial lithium vacancies and electron vacancies inside the material, and can also form strong Me-O bonds, which can not only inhibit the dissolution of transition metals, but also the presence of lithium vacancies can promote the transmission of lithium ions. Second, the introduction of doping ions with strong Me-O bonds can also inhibit Ni in the Li layer. 2+ The irreversible oxidation of ions and the irreversible phase transition caused by vacancy rearrangement under high delithiation conditions enable the positive electrode material to have excellent cycling stability at high voltages. While increasing the operating voltage, the energy density of the positive electrode material is significantly improved, which in turn makes the above-mentioned positive electrode material have better performance stability when used in high-voltage environments. Thirdly, the large ionic radius of Y, Nb, Ce, Ta, and W can increase the interlayer spacing, provide a smoother channel for lithium ion conduction, effectively reduce impedance, and thus further improve the conductivity of lithium ions, thereby significantly improving the low-temperature performance of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0022] Figure 1 The SEM test image of the positive electrode material in Example 1 of the present invention is shown;

[0023] Figure 2 The XRD test patterns of the positive electrode materials in Example 1 and Comparative Example 1 of the present invention are shown;

[0024] Figure 3 Shows the median voltage test graph of the positive electrode materials in Example 1 of the present invention and Comparative Example 1;

[0025] Figure 4 The constant current injection ratio test diagram of the positive electrode materials in Example 1 of the present invention and Comparative Example 1 is shown. DETAILED DESCRIPTION

[0026] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0027] As described in the background of the present invention, the positive electrode materials in the prior art have problems such as low energy density, poor rate performance, poor power performance, poor low temperature performance, or poor safety performance. In order to solve this problem, the present invention provides a positive electrode material, the chemical formula of which is LiNi (1-x) Mo x Me y O2, wherein 0<x<0.3, 0<y<0.3; Me is selected from one or more of Y, Nb, Ce, Ta, Mn or W.

[0028] First, the Mo element has a high valence state and combines well with oxygen, which can form a more stable Mo-O bond, and Mo and Ni can also form a eutectic, which not only effectively improves the structural stability of the product during low-temperature use, but also further reduces the occurrence of mixed rows, effectively improving the cycle stability of the product. Secondly, one or more high-valence Me elements Y, Nb, Ce, Ta or W are doped. First, this can form partial lithium vacancies and electron vacancies inside the material, and can also form strong Me-O bonds, which can not only inhibit the dissolution of transition metals, but also the presence of lithium vacancies can promote the transmission of lithium ions. Second, the introduction of doping ions with strong Me-O bonds can also inhibit Ni in the Li layer. 2+The irreversible oxidation of ions and the irreversible phase transition caused by vacancy rearrangement under high delithiation conditions enable the positive electrode material to have excellent cycling stability at high voltages. While increasing the operating voltage, the energy density of the positive electrode material is significantly improved, which in turn makes the above-mentioned positive electrode material have better performance stability when used in high-voltage environments. Thirdly, the large ionic radius of Y, Nb, Ce, Ta, and W can increase the interlayer spacing, provide a smoother channel for lithium ion conduction, effectively reduce impedance, and thus further improve the conductivity of lithium ions, thereby significantly improving the low-temperature performance of the material.

[0029] In a preferred embodiment, the positive electrode material is further doped with F; preferably, the F doping amount is 100-500 ppm. Fluorine doping of the ternary positive electrode material can further improve the stability of the crystal structure of the ternary positive electrode material and broaden the diffusion channels of lithium ions, which is beneficial to improving the diffusion kinetics of lithium ions and improving the rate performance and cycle performance of the material. In order to further balance the above-mentioned excellent performance of the product, the F doping amount in the positive electrode material is preferably 200-400 ppm, for example, 200 ppm, 250 ppm, 300 ppm, 350 ppm or 400 ppm.

[0030] In a preferred embodiment, the positive electrode material is a single crystal material and is shaped like spherical particles. Such a positive electrode material is more conducive to forming a dense and stable SEI film during subsequent applications, reducing side reactions and ensuring lithium ion diffusion, thereby improving the battery's cycling stability. Furthermore, the spherical particles also provide the positive electrode material with good fluidity, which is conducive to improving material compaction. Preferably, the particle size of the positive electrode material is 2 to 5 μm; more preferably, it is 2.5 to 3.5 μm.

[0031] The present invention also provides a method for preparing the aforementioned positive electrode material, the preparation method comprising: mixing a Li source, a Ni source, a Mo source and a Me source according to a stoichiometric ratio and then sintering to obtain the positive electrode material.

[0032] Based on the reasons mentioned above, the positive electrode material thus prepared in this application has the following beneficial effects: First, the Mo element has a high valence state and is well combined with oxygen, which can form a more stable Mo-O bond, and Mo and Ni can form a eutectic body, which not only effectively improves the structural stability of the product during use at low temperatures, but also further reduces the occurrence of mixed rows, effectively improving the cycle stability of the product. Secondly, by doping one or more of the high-valence Me elements Y, Nb, Ce, Ta or W, on the one hand, partial lithium vacancies and electron vacancies can be formed inside the material to form strong Me-O bonds, inhibiting the dissolution of transition metals, and the presence of lithium vacancies will also promote the transmission of lithium ions. Secondly, the introduction of doping ions with strong Me-O bonds plays a role in inhibiting the Ni in the Li layer. 2+Irreversible oxidation and vacancy rearrangement under high delithiation trigger irreversible phase transitions. This enables the cathode material to have excellent cycling stability at high voltages, significantly improving the energy density of the cathode material while increasing the operating voltage. Thirdly, the large ionic radii of Y, Nb, Ce, Ta, and W can increase the interlayer spacing, providing a smoother channel for lithium ion conduction, effectively reducing impedance, thereby further improving lithium ion conductivity and significantly enhancing the low-temperature performance of the material.

[0033] In a preferred embodiment, the preparation method includes the following steps: step S1, adding Li source, Ni source, Mo source and Me source to an aqueous solution of a stabilizer in a stoichiometric ratio for aging to form a glue A; step S2, adding a carbon source to the glue A and then aging and freeze-drying it in sequence to obtain a precursor C; step S3, sintering the precursor C to obtain a positive electrode material; wherein the sintering includes a first sintering and a second sintering performed in sequence, and the temperature of the first sintering is less than the thermal decomposition temperature of the carbon source and less than the temperature of the second sintering, and the first sintering is carried out in a first atmosphere containing a fluorine source gas.

[0034] First, the present invention first adds Li, Ni, Mo, and Me sources in a stoichiometric ratio to an aqueous stabilizer solution and ages them to form a glue solution A. This produces a uniformly doped cathode material with similar crystal structure stability and deformation resistance at all locations, resulting in a uniform stress distribution within the material. Furthermore, during subsequent cyclic applications, the cathode material is less likely to crack due to uneven stress, and the exposed fresh surface, which causes side reactions, effectively avoids the drawback of a significant decrease in battery capacity and cycle performance.

[0035] Secondly, the present invention adds a carbon source to the glue A and then ages and freeze-dries it in sequence to obtain an intermediate C. The carbon source can be coated on the outer surface of the intermediate during the subsequent first sintering process at a lower temperature to control the intermediate to form a relatively rounded single-crystal quasi-spherical particle morphology. Moreover, this part of the carbon source can be volatilized and removed in the subsequent second sintering at a higher temperature, and will not have any negative impact on the product itself. Based on this, the present invention can obtain single-crystal quasi-spherical positive electrode material particles with better morphology, and the particle size distribution is uniform and the morphology is regular. The particle size D50 is mainly distributed in the range of 2 to 5 μm, thereby improving the discharge capacity of the lithium battery. In this way, it is more conducive to the formation of a dense and stable SEI film in the subsequent application process, with tighter bonding, reduced side reactions, satisfactory lithium ion diffusion, and improved battery cycle stability. Moreover, the particles present a quasi-spherical morphology, which makes them have good fluidity, is conducive to improving the compaction of the material, and can also effectively slow down the serious intercrystalline cracks caused by the expansion and contraction of the lattice during charging and discharging. In particular, this can further reduce the internal stress of the material, prevent overcharging and over-discharging in local areas of the material, and improve the fluidity and tap density of the material.

[0036] Third, the first sintering is carried out in a first atmosphere containing a fluorine source gas. Fluorine-containing gas is corrosive and can etch the material, making the chemical reaction deeper. With the formation of the ternary material crystal nucleus, the fluorine element can be doped into the ternary material bulk. Fluorine doping of the ternary positive electrode material can improve the stability of the crystal structure of the ternary positive electrode material and broaden the diffusion channel of lithium ions, which is beneficial to improving the diffusion kinetics of lithium ions and improving the rate performance and cycle performance of the material. At the same time, fluorine-containing gas is corrosive and can also form an uneven morphology on the surface of the particles. In this way, when the battery cell is subsequently slurried, it will bond more closely with the conductive agent.

[0037] Fourthly, the cathode material prepared in this manner has low residual alkali on its surface, which helps improve the stability and safety of lithium-ion batteries. Furthermore, the cathode material also has excellent electrical conductivity, which can improve the power performance of the cathode material, resulting in excellent rate performance and low-temperature capacity retention.

[0038] Fifth, the positive electrode material prepared by the present invention has a high specific capacity, a high coulombic efficiency of the first charge and discharge, and excellent low-temperature performance. At various rates, the discharge capacity of the positive electrode material at a low temperature of -20°C can reach more than 80% of its discharge capacity at room temperature.

[0039] Sixth, the preparation method of the present invention is simple in process and is applicable to existing production equipment.

[0040] In a preferred embodiment, in step S1, in order to make the Li source, Ni source, Mo source and Me source more evenly dispersed in the aqueous solution of the stabilizer, the Li source, Ni source, Mo source and Me source are added to the aqueous solution of the stabilizer in a stoichiometric ratio and stirred and mixed, with a stirring speed of 50 to 250 rpm / min and a stirring time of 3 to 24 hours. In order to form a more suitable viscosity of the glue A, the aging time is preferably 12 to 36 hours and the temperature is 30 to 50°C. More preferably, the stabilizer is selected from one or more of citric acid, lactic acid, glycolic acid, fruit acid or tartaric acid. The stabilizer can not only stabilize the viscosity of the glue, but also make the ions evenly dispersed in the glue.

[0041] In a preferred embodiment, in step S2, the carbon source includes an alkali-soluble resin and a polymer fiber material; preferably, the alkali-soluble resin and the polymer fiber material are first mixed to form a glue B, and then the glue A and the glue B are mixed to be aged and freeze-dried in sequence. First, this can obtain a positive electrode material with more uniform doping. Second, this can also obtain single-crystal spherical positive electrode material particles with better morphology, and the particle size distribution is more uniform and the morphology is more regular, which can further improve the discharge capacity of the lithium battery. Third, in the subsequent application process, it is more conducive to the formation of a dense and stable SEI film, reducing the occurrence of side reactions, meeting the diffusion of lithium ions, and improving the battery cycle stability. Fourth, the material has better fluidity and tap density, which can effectively slow down the serious intergranular cracks caused by the expansion and contraction of the lattice during charging and discharging. Fifth, this can further reduce the internal stress of the material and prevent overcharge and overdischarge in local areas of the material.

[0042] More preferably, the alkali-soluble resin contains an unsaturated group; more preferably, the alkali-soluble resin is selected from one or more of polyester resin, acrylic resin, polyurethane resin, or styrene-acrylic resin. The average length of the polymer fiber material is 5 to 50 μm; more preferably, the polymer fiber material is selected from one or more of chitosan fiber, filamentous cellulose, polyvinyl alcohol fiber, and lactic acid-glycolic acid copolymer fiber.

[0043] To further balance the material's aforementioned excellent properties, the preferred surface tension of glue B is 15-35 mN / m, the viscosity is 3.0-10.0 mPa·s, and the conductivity is 0.3-1 μS / cm. This allows the present invention to produce a more uniformly doped positive electrode material, with similar crystal structure stability and deformation resistance across the material, resulting in a more uniform stress distribution within the material. More preferably, glue B comprises, by weight, 1-3 parts alkali-soluble resin and 0.5-1 part polymer fiber material.

[0044] The preferred weight ratio of glue A to glue B is 1:(0.1-0.5). This not only effectively avoids the drawback of a significant decrease in battery capacity and cycle performance, but more importantly, it also effectively controls the precursor to have a good single crystal particle morphology. Preferably, the treatment temperature during the aging process is 30-50°C, and the treatment time is 12-36 hours.

[0045] To further improve subsequent sintering efficiency, the freeze-drying process preferably includes a first freeze-drying treatment and a second freeze-drying treatment, performed sequentially. More preferably, the first freeze-drying treatment is performed at a temperature of 0 to -20°C for 0.5 to 2 hours, while the second freeze-drying treatment is performed at a temperature of 0 to -100°C for 1 to 3 hours. Furthermore, the cooling rate of the material during the freeze-drying process is preferably controlled at 1 to 5°C / min. This results in a higher porosity in the freeze-dried sample, which facilitates contact with the sintering atmosphere.

[0046] In order to further improve the F doping effect. In a preferred embodiment, the sintering temperature of the first sintering is 200-400°C, and the sintering time is 2-5 hours; more preferably, the fluorine source gas is selected from one or more of carbon tetrafluoride, perfluorobutadiene, nitrogen trifluoride, hexafluoroethane, perfluoropropane or trifluoromethane; and even more preferably, the first atmosphere comprises 30-60 wt% of the fluorine source gas, 0.05-0.01 wt% of water, and the remainder of oxygen and ozone.

[0047] In order to further reduce the residual alkali on the surface of the material, thereby improving the stability and safety of the lithium-ion battery. Preferably, the second sintering is carried out in an oxygen-rich second atmosphere; and the sintering temperature of the second sintering is 800-1000°C, and the sintering time is 12-40h. More preferably, after the second sintering, the sintering also performs a third sintering step on the second sintered material. The third sintering is carried out in an oxygen-rich third atmosphere; and the sintering temperature of the third sintering is 300-800°C, and the sintering time is 2-6h. Further preferably, in the second atmosphere and the third atmosphere, the concentration of oxygen is independently greater than 50% (the remaining components may be nitrogen).

[0048] It is additionally supplemented that, after the above sintering, in a preferred embodiment, the present invention further performs crushing and sieving on the sintered material in sequence to obtain a positive electrode material with a suitable particle size.

[0049] The present invention has no particular limitation on the above-mentioned Li source, Ni source, Mo source and Me source. In a preferred embodiment, the Li source is selected from one or more of lithium hydroxide, lithium carbonate, lithium acetate, lithium nitrate or lithium chloride. Preferably, the Ni source is selected from one or more of nickel oxide, nickel hydroxide, nickel nitrate, nickel sulfate or nickel carbonate. Preferably, the Mo source is selected from one or more of nano-molybdenum oxide, sodium molybdate, ammonium molybdate or molybdic acid. Preferably, the Me source is selected from a soluble compound containing one or more elements of Y, Nb, Ce, Ta, Mn or W. Based on this, the raw material source is wider and the synergistic effect is better.

[0050] In a preferred embodiment, the average particle size of the positive electrode material obtained by scanning electron microscopy is recorded as X, the median particle size of the positive electrode material obtained by laser particle size analyzer is recorded as D50, and the value of X / D50 is 0.4 to 1:1.

[0051] The average particle size D50 of the positive electrode active material is well known in the art and is also called the median particle size. It represents the particle size corresponding to 50% of the volume distribution of the positive electrode active material particles. The average particle size D50 of the positive electrode active material can be measured using instruments and methods well known in the art. For example, it can be conveniently measured using a laser particle size analyzer, such as the Mastersizer 2000 laser particle size analyzer available from Malvern Instruments Ltd. in the United Kingdom.

[0052] The average particle size X of the present invention can be obtained by the following method: first, a scanning electron microscope (SEM) image of the sample is used for testing, and then the SEM measurement software is used to analyze the particle, such as Nano Measurer, to measure the particle diameter Feret diameter (the distance between the two parallel lines of the particle projection outline measured along a certain direction). In order to more accurately reflect the average particle size X of the SEM morphology of the single crystal material, a 10K magnification SEM image is selected, and each particle is measured in different directions more than 10 times, and the average value is obtained as the diameter of the particle. Furthermore, the average value of the diameters of more than 100 particles is selected as the average particle size X of the sample.

[0053] The present invention also provides a lithium-ion battery comprising the aforementioned positive electrode material, or the positive electrode material prepared by the aforementioned preparation method. Based on the aforementioned reasons, the lithium-ion battery of the present invention has high energy density, excellent rate performance, good power performance, excellent low-temperature performance, and good safety performance.

[0054] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0055] Example 1

[0056] S1), providing a Li source (lithium hydroxide monohydrate), a Ni source (nickel sulfate), a Mo source (sodium molybdate), a Mn source (manganese sulfate), and a Nb source (NaNbO3 sodium niobate), according to the stoichiometric ratio of Li: (Ni:Mo:Mn:Nb molar ratio of 70:8:10:12) = 1.05:1, adding them to a stabilizer citric acid solution, stirring magnetically for 2 hours to mix evenly, and aging at room temperature and pressure for 24 hours to form a glue A;

[0057] S2) Alkali-soluble resin acrylic resin and polymer fiber material (average length: 10 μm) are mixed in a mass ratio of 2:1 to obtain glue B, the surface tension of the glue is between 18 mN / m, the viscosity is 4.0 mPa·s, and the conductivity is 0.35 mS / cm.

[0058] S3) Mix glue solution A and glue solution B evenly, with the mass ratio of glue solution A to glue solution B being 1:0.2. Age the mixture at a constant temperature of 30°C at normal pressure for 10 hours. Prefreeze the mixture at -18°C for 0.5 hours. Place the prefrozen mixture in a freeze dryer and freeze-dry it at -30°C for 1 hour. The material cooling rate can reach 2°C / min. After freeze drying, grind the mixture into powder C.

[0059] S4), the powder C is sintered, crushed and sieved multiple times to obtain the positive electrode material LiNi 0.7 Mo 0.08 Mn 0.1 Nb 0.12 O2. During the sintering process, the first sintering is carried out at a low temperature in a fluorine source carbon tetrafluoride gas, which contains 30wt% fluorine gas, the rest of the gas is O2, and the moisture content is 0.05wt%. The first sintering temperature is 400°C and the processing time is 5 hours. The second high-temperature sintering is carried out in an oxygen-rich atmosphere, the oxygen-rich atmosphere is a gas with an oxygen concentration of 90%, and the rest is nitrogen. The sintering temperature is 800°C and the processing time is 15 hours. For the third sintering, the oxygen-rich atmosphere is a gas with an oxygen concentration of 50%, and the rest is nitrogen. The sintering temperature is 300°C and the processing time is 5 hours.

[0060] The value of X / D50 is 0.7. Using F- (fluoride ion) rapid qualitative test paper, the F content of this example is 300 ppm.

[0061] Example 2

[0062] The only difference from Example 1 is:

[0063] S1) Replace the Nb source (NaNbO3 sodium niobate) with a W source (sodium tungstate) and add it to the stabilizer citric acid solution according to the stoichiometric ratio of Li: (Ni:Mo:Mn:W molar ratio of 70:5:15:10) = 1.09:1.

[0064] S2) The surface tension of glue B is 20 mN / m.

[0065] S3) The mass ratio of glue solution A to glue solution B is 1:0.5; pre-freeze at -20°C for 0.5 hour.

[0066] S4), the second sintering temperature is 890°C; the third sintering temperature is 350°C.

[0067] The positive electrode material obtained is LiNi 0.7 Mo 0.05 Mn 0.15 W 0.10 O2.

[0068] The value of X / D50 is 0.72. Using F- (fluoride ion) rapid qualitative test paper, the F content of this example is 300 ppm.

[0069] Example 3

[0070] The only difference from Example 2 is that:

[0071] S1) providing a Li source (lithium hydroxide monohydrate), a Ni source (nickel sulfate), a Mo source (sodium molybdate), a Mn source (manganese sulfate), and a W source (sodium tungstate) in a stoichiometric ratio of Li: (Ni:Mo:Mn:W molar ratio of 70:5:20:5) = 1.09:1, and adding them to a stabilizer citric acid solution.

[0072] The positive electrode material obtained is LiNi 0.7 Mo 0.05 Mn 0.2 W 0.05 O2.

[0073] The value of X / D50 is 0.62.

[0074] Example 4

[0075] The only difference from Example 2 is that:

[0076] S1), providing a Li source (lithium hydroxide monohydrate), a Ni source (nickel sulfate), a Mo source (sodium molybdate), a Mn source (manganese sulfate), and a W source (sodium tungstate), according to the stoichiometric ratio of Li: (Ni: Mo: Mn: W molar ratio of 60: 10: 20: 10) = 1.04: 1, adding them to a stabilizer citric acid solution, stirring magnetically for 6 hours to mix evenly, and aging at room temperature and pressure for 36 hours to form a sol A;

[0077] S4) The second high-temperature sintering is carried out in an oxygen-rich atmosphere, wherein the oxygen-rich atmosphere is a gas with an oxygen concentration of 80% and the remaining component is nitrogen. The sintering temperature is 800° C. and the processing time is 15 hours.

[0078] The positive electrode material obtained is LiNi 0.6 Mo 0.1 Mn 0.2 W 0.1 O2.

[0079] The value of X / D50 is 0.42.

[0080] Example 5

[0081] The only difference from Example 1 is that the Nb source (NaNbO3 sodium niobate) is replaced by an equimolar amount of Y source (yttrium acetate).

[0082] The positive electrode material obtained is LiNi 0.7 Mo0.08 Mn 0.1 Y 0.12 O2.

[0083] Example 6

[0084] The only difference from Example 1 is that the Nb source (NaNbO 3 sodium niobate) is replaced by an equimolar amount of Ce source (cerium acetate).

[0085] The positive electrode material obtained is LiNi 0.7 Mo 0.08 Mn 0.1 Ce 0.12 O2.

[0086] Example 7

[0087] The only difference from Example 1 is that the Nb source (NaNbO3 sodium niobate) is replaced by an equal molar amount of Ta source (tantalum acetate).

[0088] The positive electrode material obtained is LiNi 0.7 Mo 0.08 Mn 0.1 Ta 0.12 O2.

[0089] Comparative Example 1

[0090] The only difference from Example 1 is that no Mo source (sodium molybdate) is added in step S1. The stoichiometric ratio of Li: (Ni:Mn:Nb molar ratio is 78:10:12) = 1.05:1.

[0091] Comparative Example 2

[0092] The only difference from Example 1 is that no basic resin is added in step S2.

[0093] Comparative Example 3

[0094] The only difference from Example 1 is that freeze drying is not performed in step S3.

[0095] Comparative Example 4

[0096] The only difference from Example 1 is that the first sintering is not performed in step S4. Using F- (fluoride ion) rapid qualitative test paper, the F content of this example is 0 pm.

[0097] Comparative Example 5

[0098] Compared with Example 1, the first atmosphere of the first sintering in step S4 does not contain fluorine source gas. Using F- (fluoride ion) rapid qualitative test paper, the F content in this example is 0 ppm.

[0099] Comparative Example 6

[0100] The only difference from Example 1 is that no Me source is added in step S1. The stoichiometric ratio of Li: (Ni:Mn:Mo molar ratio is 78:10:12) = 1.05:1.

[0101] Comparative Example 7

[0102] The only difference from Example 1 is that no polymer fiber material is added in step S2.

[0103] Comparative Example 8

[0104] The only difference from Example 1 is that the polymer fiber material and the alkaline resin in step S2 are replaced by asphalt of equal mass.

[0105] Performance characterization:

[0106] (1) Electrochemical performance test:

[0107] Preparation of button cells: The positive electrode active material, conductive carbon black, and binder PVDF prepared in the examples and comparative examples were dispersed in a solvent N-methylpyrrolidone (NMP) at a weight ratio of 90:5:5 and mixed evenly to obtain a positive electrode slurry; the slurry was coated on aluminum foil and then placed in a vacuum oven and dried at 120°C for 12 hours to obtain a surface density of 20 g / cm 2 The pole piece is rolled after drying, and the compaction density is 3.2g / cm 3 , cut the electrode sheet to obtain the positive electrode sheet. Using lithium metal as the negative electrode, EC, DEC, and DMC are mixed in a volume ratio of 1:1:1 to obtain a solvent. The lithium salt LiPF6 is then dissolved in the above solvent to obtain an electrolyte, wherein the concentration of LiPF6 is 1 mol / L. Celgard 2400 (commercially available) is used as a separator. In an argon-filled glove box, the positive electrode sheet, separator, and metal lithium sheet are stacked in sequence and injected with the above electrolyte to assemble into a 2016-type button cell. (The current density is set at 1C = 200mA / g during the constant current charge and discharge cycle performance test)

[0108] Test conditions are as follows: 25°C constant temperature chamber, tested on a blue battery tester; rate and discharge performance tested at 0.2C, 0.33C, and 1C constant current and constant voltage charging; 0.2C, 0.33C, and 1C constant current discharge; constant voltage cutoff condition: 0.05C; test voltage range: 2.8-4.45V. Charge and discharge cycle testing was performed at a 1C rate for 50 cycles, and the cycle capacity retention was calculated.

[0109] DC discharge resistance test (DCR): At a constant temperature of 25°C, the lithium-ion battery is allowed to stand for 30 minutes, then charged to 4.45V at a constant current rate of 1C, then charged to a current of ≤0.05C at a constant voltage of 4.45V and allowed to stand for 5 minutes, and then discharged to 2.8V at a constant current rate of 1C. The obtained discharge capacity is taken as the rated capacity of the lithium-ion battery, i.e. 100% SOC. The lithium-ion battery is then charged at a current of 1C for 20 minutes, the state of charge of the lithium-ion battery is adjusted to 30% SOC, and the lithium-ion battery is discharged at a constant current of 3C for 30 seconds. The voltage before and after discharge is recorded. The DC discharge resistance (DCR) is calculated as follows: DCR = (U0-U1) / I. Wherein, U0 represents the voltage before 30s discharge at a 3C rate, U1 represents the voltage after 30s discharge, and I represents the current at a 3C rate.

[0110] Before and after 50 cycles at 1C, the battery was tested for DCR at 25°C, and the DCR growth rate was calculated. The DCR growth rate formula is as follows: Growth rate (R%) = (DCR2 - DCR1) / DCR1 × 100, where DCR1 represents the DC internal resistance at 25°C before 50 cycles, and DCR2 represents the DC internal resistance after 50 cycles.

[0111] -20℃ low temperature capacity retention rate: In order to measure the low temperature capacity retention rate performance of the lithium ion battery prepared using the present invention, the following operations are performed: first, the battery is placed in a 25℃ constant temperature box for two cycles at 0.2C, and the average discharge capacity of the two cycles is recorded as Q1. Then, the battery is fully charged at 0.2C. Then, the battery is placed in a -20℃ low temperature cabinet and allowed to stand for 2 hours. The discharge capacity Q2 is obtained at a rate of 0.2C. The voltage range is 2.8-4.45V. The low temperature capacity retention rate = (Q2-Q1) / Q1×100%.

[0112] (2) Residual alkali test:

[0113] Residual Alkali Test Method: Weigh the sample according to the table below to the nearest 0.0001g. Place the sample in a 100mL beaker, add 50mL of deionized water, place the magnetic beads in the beaker, and seal it with plastic wrap. Place the beaker on a magnetic stirrer and stir for approximately 10-15 minutes. Remove the beaker and let it sit for 5 minutes. Filter the filtered solution using a glass funnel. The clear solution is the test solution. The parameter settings for the residual alkali test method are shown in Table 1.

[0114] Table 1

[0115]

[0116] Accurately transfer the solution to be tested into a 100mL beaker, place a stirring rotor, control the sample volume to approximately 50mL (make up with water if less than 50mL), place the beaker on the magnetic stirrer of the automatic potentiometric titrator, add phenolphthalein dropwise for 2d, select HCl standard solution according to the table and titrate until it changes from red to colorless. The instrument will record the volume Ep1 (V1) of HCl standard solution consumed at the stoichiometric point and the pH; then add methyl orange dropwise for 2d, continue titrating until it changes from yellow to orange, and the instrument will record the volume Ep2 (V2) of HCl standard solution consumed at the stoichiometric point and the pH.

[0117] Calculation of analysis results: (1) When 2V1>V2, containing LiOH and Li2CO3, the calculation formula is as follows:

[0118]

[0119]

[0120] (2) When 2V1<V2, it contains Li2CO3 and LiHCO3, and the calculation formula is as follows:

[0121]

[0122]

[0123] (3) When 2V1=V2, only Li2CO3 is contained, and the calculation formula is as follows:

[0124]

[0125] In the above formula: c: concentration of HCl standard solution (mol / L); V1(Ep1): volume of HCl standard solution consumed at the first equivalence point (mL); V2(Ep2): volume of HCl standard solution consumed at the second equivalence point (including the first equivalence point) (mL); V': volume of the test solution (mL); V: volume of the sample (mL); 23.95: molar mass of LiOH (g / mol); 73.89: molar mass of Li2CO3 g / mol; 67.96: molar mass of LiHCO3 g / mol; m: mass of the sample (g).

[0126] Surface residual alkali mainly refers to substances such as LiOH and Li2CO3 on the surface of positive electrode material particles. The main sources are Li that is not burned in during the sintering reaction, or residual lithium produced by the decomposition of the material due to high-temperature sintering. On the other hand, it is also produced by the material being left in the air for too long. The higher the Ni content, the more stringent the sintering conditions, and the more difficult it is to sinter to form a material with a specific lithium metal ratio, resulting in more residual lithium in the sintered product. On the other hand, the higher the Ni content, the easier it is to react with water and CO2 in the air to generate LiOH and Li2CO3, resulting in high surface residual alkali.

[0127] (3) Transition metal dissolution test:

[0128] After 50 cycles at 25°C, the button battery was charged and then fully charged to 4.45V. The battery was disassembled in a glove box, the positive electrode sheet was taken out, 10 button positive electrode discs were scraped off the powder, immersed in 10g of electrolyte, sealed in a glass bottle, and immersed for 60 hours at a constant temperature of 55°C. The upper clear liquid was taken, and finally the metal (Ni\Co\Mn) composition in the test liquid was detected by inductively coupled plasma emission spectrometry (ICP). The positive electrode material of the button battery after 50 cycles can be measured, and then the content of each metal component in its metal dissolution under high temperature storage conditions can be determined, thereby judging the lattice stability performance of the positive electrode material.

[0129] The dissolution of transition metal elements in the positive electrode material causes structural damage to the NCM material. At the same time, the dissolved Mn element will also damage the SEI film of the negative electrode, which is an important reason for the rapid decline in the life of NCM batteries. Researchers such as Marco Evertz proposed the dissolution mechanism of transition metal elements in NCM materials: due to the large volume expansion and large stress caused by the insertion and extraction of lithium in the NCM material lattice structure, cracks will be formed on the active material particles, and the electrolyte PF6 - Under the action of , the metal elements will further undergo solvation, resulting in the dissolution of the transition metal elements. This mechanism of action is more obvious at high cut-off voltage.

[0130] Research has shown that the dissolution of transition metals is primarily due to three factors: 1) lattice defects, such as oxygen vacancies, introduced during the synthesis process; 2) atomic-scale structural distortions, such as lattice expansion and contraction caused by lithium ion insertion and deinsertion, which can lead to material fracture; and 3) the transition from a layered structure to a spinel structure during cycling. These are areas for improvement in the development of the present material to stabilize the material structure and enhance its cycling stability at high voltages.

[0131] from Figure 1It can be seen that the material is a single crystal type spherical particle, and the particle diameter is mainly distributed in the range of 2 to 5 μm. The surface coating of the particles is tightly bound and there are fewer agglomerates. The particles have a uniform particle size distribution and regular morphology, which is more conducive to the formation of a dense and stable SEI film, reducing the occurrence of side reactions, ensuring the diffusion of lithium ions, and improving the cycle stability of the battery. The particles in the SEM image are relatively round. After sintering, the edges and corners of the single crystal particles are removed, so that the particles have good fluidity, which is conducive to improving the compaction of the material. The rounded single crystal morphology can effectively slow down the expansion and contraction of the lattice during charging and discharging, causing the occurrence of serious intercrystalline cracks. The average particle size of the low-temperature lithium-ion positive electrode material particles measured by SEM morphology is X, 2.45 μm, and the median particle size tested by laser particle size analyzer is D50, 3.61 μm. The X / D50 value of the sample obtained in Example 1 is 0.679. At the same time, Figure 1 The circled part indicates that the particle surface has an uneven morphology.

[0132] from Figure 2 The cathode material in Example 1 is an α-NaFeO2-type layered rock salt structure belonging to the R-3m space group. Two main peaks, (003) and (104), appear around 2θ = 18° and 45°, respectively. No other impurity peaks are present. The 006 / 101 and 108 / 110 peaks are clearly separated, indicating that the sample has a well-defined layered structure, good crystallization, and a perfect crystalline form.

[0133] The ternary cathode materials of Examples 2 to 4 were also subjected to SEM characterization and XRD characterization, and the characterization results obtained were similar to those of Example 1.

[0134] When the voltage reaches a certain set value. During the battery charging process, the voltage continues to rise. Constant current charging is generally used first. During this process, charging transitions from constant current to constant voltage. The constant current ratio in a battery refers to the percentage of constant current charging to the total charge capacity. Starting with constant current, and using a relatively high current, improves charging efficiency. At the end of charging, the pseudo-voltage is high due to the polarization internal resistance of the battery. Using constant voltage mode reduces the charging current and allows the battery to be fully charged. The constant current charge ratio reflects the degree of polarization in the battery and the rate performance of the material. A higher constant current charge ratio reduces battery polarization and improves the rate performance of the material. The median voltage is the voltage at half the battery capacity. The median voltage is a very important indicator for battery performance; high and low median voltages reflect the strengths and weaknesses of battery characteristics. A higher median voltage indicates a higher energy capacity and a longer battery life. Figure 3 and Figure 4 The results show that the improved material of the present invention has a good constant current charge ratio and median voltage. The product of the discharge median voltage and the discharge current can represent the power performance of the lithium-ion battery.

[0135] Table 2 shows the residual alkali test results of the embodiments and comparative examples.

[0136] Table 2

[0137]

[0138]

[0139] Table 3 shows the electrochemical performance test results of the embodiments and comparative examples.

[0140] Table 3

[0141]

[0142] The present invention can make the raw materials mixed evenly and react fully, thereby improving production efficiency, making the particle size more consistent, stabilizing the structure, reducing the residual alkali content on the surface of the material, and improving the electrical conductivity of the material, thereby improving the power performance of the positive electrode material and ensuring the rate performance and low-temperature capacity retention rate of the material.

[0143] Table 4 shows the amount of metal ions dissolved in the positive electrode materials in the examples and comparative examples.

[0144] Table 4

[0145]

[0146]

[0147] Table 4 shows the amount of metal ion dissolution from a button-type battery after high-temperature storage and charge-discharge cycling, as measured by ICP. The modified cathode material significantly inhibits metal ion dissolution. Comparing this with the electrochemical properties in Table 1, it can be seen that the cathode material obtained using the modification method of the present invention exhibits improved cycling stability and discharge specific capacity, particularly at a high cutoff voltage of 4.45V. The modified cathode material inhibits metal ion dissolution, stabilizes the crystal structure, and inhibits collapse of the highly delithiated crystal structure, thereby improving the cycling stability of the cathode material used in batteries, reducing the rate of capacity decay, and improving the DCR growth rate during cycling.

[0148] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A positive electrode material, characterized in that The chemical formula of the positive electrode material is LiNi (1-x-y) Mo x Me y O2, wherein 0<x<0.3, 0<y<0.3; Me is selected from one or more of Y, Nb, Ce, Ta, Mn or W; The positive electrode material is further doped with F; and the doping amount of F is 100-500 ppm; The preparation method of the positive electrode material comprises the following steps: Step S1, adding a Li source, a Ni source, a Mo source, and a Me source into an aqueous solution of a stabilizer according to a stoichiometric ratio for aging to form a glue solution A; Step S2, adding a carbon source to the glue solution A, and then aging and freeze-drying in sequence to obtain an intermediate C; Step S3, sintering the intermediate C to obtain the positive electrode material; The sintering includes a first sintering and a second sintering performed sequentially, and the temperature of the first sintering is less than the thermal decomposition temperature of the carbon source and less than the temperature of the second sintering, and the first sintering is performed in a first atmosphere containing a fluorine source gas; In the step S2, the carbon source includes an alkali-soluble resin and a polymer fiber material.

2. The positive electrode material according to claim 1, characterized in that The positive electrode material is a single crystal material, and the shape of the positive electrode material is spherical particles.

3. The positive electrode material according to claim 2, characterized in that The D50 particle size of the positive electrode material is 2-5 μm.

4. A method for preparing the positive electrode material according to any one of claims 1 to 3, characterized in that: The preparation method comprises: Step S1, adding the Li source, the Ni source, the Mo source, and the Me source to an aqueous solution of a stabilizer according to a stoichiometric ratio for aging to form a glue solution A; Step S2, adding a carbon source to the glue solution A, and then aging and freeze-drying in sequence to obtain an intermediate C; Step S3, sintering the intermediate C to obtain the positive electrode material; The sintering includes a first sintering and a second sintering performed sequentially, and the temperature of the first sintering is less than the thermal decomposition temperature of the carbon source and less than the temperature of the second sintering, and the first sintering is performed in a first atmosphere containing a fluorine source gas; In the step S2, the carbon source includes an alkali-soluble resin and a polymer fiber material.

5. The preparation method according to claim 4, characterized in that First, the alkali-soluble resin and the polymer fiber material are mixed and added into a volatile solvent to form glue solution B, and then the glue solution B is added into the glue solution A to perform the aging and freeze-drying in sequence.

6. The preparation method according to claim 5, characterized in that The volatile solvent is selected from one or more of C1-C3 alcohols, C1-C3 ketones or C1-C3 ethers.

7. The preparation method according to claim 5, characterized in that The glue B has a surface tension of 15-35 mN / m, a viscosity of 3.0-10.0 mPa•s, and an electrical conductivity of 0.3-1 mS / cm.

8. The preparation method according to claim 5, characterized in that The weight ratio of the glue A to the glue B is 1:(0.1~0.5).

9. The preparation method according to claim 5, characterized in that The treatment temperature during the aging process is 20-40° C., and the treatment time is 4-40 hours.

10. The preparation method according to claim 5, characterized in that The freeze-drying process includes a first freeze-drying process and a second freeze-drying process performed sequentially.

11. The preparation method according to claim 10, characterized in that: The temperature of the first freeze-drying treatment is -20~0°C, and the time is 0.5~2 hours; the temperature of the second freeze-drying treatment is -100~0°C, and the time is 1~3 hours.

12. The preparation method according to claim 10, characterized in that The cooling rate of the material during the freeze-drying process is controlled at 1-5°C / min.

13. The preparation method according to claim 4, characterized in that In the step S3, after the second sintering, the sintering further includes performing a third sintering step on the second sintered material.

14. The preparation method according to claim 4, characterized in that The sintering temperature of the first sintering is 200-400° C., and the sintering time is 2-5 hours.

15. The preparation method according to claim 4, characterized in that The fluorine source gas is selected from one or more of carbon tetrafluoride, perfluorobutadiene, nitrogen trifluoride, hexafluoroethane, perfluoropropane or trifluoromethane.

16. The preparation method according to claim 4, characterized in that The first atmosphere includes 30-60 wt % of the fluorine source gas, 0.05-0.01 wt % of water, and the remainder of oxygen and ozone.

17. The preparation method according to claim 4, characterized in that The second sintering is performed in a second oxygen-rich atmosphere; the sintering temperature of the second sintering is 800-1000° C., and the sintering time is 12-40 hours.

18. The preparation method according to claim 13, characterized in that The third sintering is performed in a third oxygen-rich atmosphere; the sintering temperature of the third sintering is 300-800° C., and the sintering time is 2-6 hours.

19. The preparation method according to claim 17, characterized in that In the second atmosphere, the mass concentration of oxygen is greater than 50%.

20. The preparation method according to claim 18, characterized in that In the third atmosphere, the mass concentration of oxygen is greater than 50%.

21. The preparation method according to any one of claims 4 to 20, characterized in that The Li source is selected from one or more of lithium hydroxide, lithium carbonate, lithium acetate, lithium nitrate or lithium chloride.

22. The preparation method according to any one of claims 4 to 20, characterized in that The Ni source is selected from one or more of nickel oxide, nickel hydroxide, nickel nitrate, nickel sulfate or nickel carbonate.

23. The preparation method according to any one of claims 4 to 20, characterized in that The Mo source is selected from one or more of nano-molybdenum oxide, nano-sodium molybdate, nano-ammonium molybdate or nano-molybdic acid.

24. The preparation method according to any one of claims 4 to 20, characterized in that The Me source is selected from soluble compounds containing one or more elements of Y, Nb, Ce, Ta, Mn or W.

25. The preparation method according to any one of claims 4 to 20, characterized in that The stabilizer is selected from one or more of citric acid, lactic acid, glycolic acid, fruit acid or tartaric acid.

26. The preparation method according to any one of claims 4 to 12, characterized in that The alkali-soluble resin contains an unsaturated group.

27. The preparation method according to claim 26, characterized in that The alkali-soluble resin is selected from one or more of polyester resin, acrylic resin, polyurethane resin or styrene-acrylic resin.

28. The preparation method according to any one of claims 4 to 12, characterized in that The average length of the polymer fiber material is 5-50 μm.

29. The preparation method according to claim 28, characterized in that The polymer fiber material is selected from one or more of chitosan fiber, filamentous cellulose, polyvinyl alcohol fiber, and lactic acid-glycolic acid copolymer fiber.

30. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode material according to any one of claims 1 to 3, or the positive electrode material prepared by the preparation method according to any one of claims 4 to 29.

Images