Doped lithium tungstate and preparation method and application thereof

Abstract

The invention provides doped lithium tungstate as well as a preparation method and application thereof. The preparation method of the doped lithium tungstate comprises the following steps: mixing a tungsten source and a lithium source in water, adding a doping agent to obtain slurry, grinding the slurry in an ice-water bath, carrying out spray drying on the slurry to obtain powder, sintering the powder, and crushing to obtain the doped lithium tungstate LixWyMzO4. According to the technical scheme, low-energy-consumption preparation of lithium tungstate is realized, and the product has uniform nanoscale particle size distribution and controllable doped element content. According to the method, the problems of particle aggregation, high energy consumption and uneven doping in the traditional process are effectively solved, the obtained material can be used as an efficient modifier of a ternary positive electrode, and by improving the uniformity of a coating layer and the conductivity of bulk phase ions, the initial DCR of a battery is improved, and the first efficiency and the charge-discharge capacity of the battery are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a doped lithium tungstate as well as a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of new energy vehicles and portable electronic devices, the performance requirements of lithium ion batteries as core energy storage devices are increasingly improved. The positive electrode material is one of the key factors determining the energy density, cycle life and safety of lithium ion batteries. The ternary material (such as lithium nickel cobalt manganese oxide, LiNi x Co y Mn (1-x-y) O2) has become a research hotspot due to its high specific capacity and energy density, especially the ternary material can significantly improve the energy density of the battery. However, with the increase of nickel content, the structural stability of the material decreases, and problems such as lattice oxygen precipitation, phase transition and electrolyte corrosion occur during the cycle process, resulting in battery capacity attenuation and safety hazards. Therefore, how to improve the cycle stability and safety of the ternary positive electrode through material modification has become the focus of current research.

[0003] Lithium tungstate (Li2WO4) is a metal lithium salt with fast ionic conductivity, widely used in the coating and doping modification of positive electrode materials. Its unique cubic structure and nanoscale particle characteristics can effectively inhibit the corrosion of electrolyte on the positive electrode material, reduce the release of lattice oxygen, and provide a stable channel for lithium ion transmission, thereby significantly improving the cycle performance of the battery. However, the traditional preparation method of lithium tungstate has obvious limitations. The high-temperature solid-phase method requires harsh reaction conditions (such as high-temperature sintering for a long time), has high energy consumption and is prone to particle agglomeration, and the particle size distribution of the product is uneven; although the liquid-phase method can achieve synthesis at a lower temperature, the process is complex, organic solvents are used, and the product purity and morphology controllability are poor. For example, CN117098730A proposes a room-temperature solid-phase method for preparing lithium tungstate, which introduces easily decomposable ammonium salt to absorb reaction heat, solving the energy consumption problem of the high-temperature solid-phase method, but the particle size of the product is still concentrated in the micron level (2-10 μm), which is difficult to meet the demand of high uniformity coating. While CN118745003A uses a sol-gel method to prepare nanoscale lithium tungstate (100-150 nm), which can achieve high purity and uniform particle size, but relies on polyvinyl alcohol as a gelling agent, and the process conditions are strict (such as calcination temperature, heating rate, etc.), and the subsequent drying and calcination steps take a long time, making industrial production difficult. In addition, the existing technology still has the following problems in the application of lithium tungstate in ternary positive electrode materials: first, the mixing uniformity of lithium tungstate and the base material in the traditional coating process is insufficient, leading to uneven distribution of the coating layer and ineffective inhibition of electrolyte corrosion; second, the conductivity of ternary materials is poor, and simple surface coating cannot solve the problem of low lithium ion diffusion rate in the bulk phase, which easily causes polarization during charging and discharging, affecting the rate performance and cycle life. For example, CN117098730A realizes lithium tungstate coating through ball milling and sintering, but the optimization window of coating amount (500-2000 ppm) and sintering temperature (550-700℃) is narrow, and excessive coating may hinder lithium ion migration, while improper temperature control may easily cause damage to the base material structure. Therefore, it is urgent to develop a simple process for synthesizing lithium tungstate with controllable particle size and morphology, and further optimize the coating strategy in ternary positive electrode materials to synergistically improve the conductivity, cycle stability and safety of the materials.

[0004] In summary, the existing technology has complex doping synthesis process of lithium tungstate, poor controllability of product particle size and morphology, and the cycle stability and safety defects of ternary positive electrode materials caused by insufficient conductivity and electrolyte contact corrosion have not been fundamentally solved. This has become a key technical bottleneck restricting the development of high-energy-density lithium-ion batteries. SUMMARY

[0005] The present application aims to at least solve one of the above technical problems in the prior art. To this end, the present application provides a preparation method of doped lithium tungstate, effectively solving the problems of particle agglomeration, high energy consumption and uneven doping in traditional processes. The obtained material can be used as an efficient modifier of ternary positive electrodes, improving the uniformity of the coating layer and the ion conductivity in the bulk phase, and improving the cycle stability and rate performance of the battery.

[0006] The present application also provides a doped lithium tungstate.

[0007] The present application also provides a coated ternary positive electrode material.

[0008] The first aspect of the present application provides a preparation method of doped lithium tungstate, comprising the following steps:

[0009] S1: mixing a tungsten source and a lithium source in water, adding a dopant to obtain a slurry;

[0010] S2: grinding the slurry Li x W y M z O4 under an ice water bath;

[0011] S3: spray drying the slurry of step S2 to obtain a powder;

[0012] S4: sintering the powder and then crushing to obtain the doped lithium tungstate, which has a composition of Li x W y M z O4, wherein x is 1.9-2.1, 0≤z≤0.05, y+z=1, and M includes at least one of Nb, Ta and Mo.

[0013] The present application relates to a technical solution in the preparation method of doped lithium tungstate, which has at least the following beneficial effects:

[0014] In the prior art, lithium ion battery positive electrode materials have higher requirements for material structure stability and safety. The traditional preparation method of lithium tungstate has problems such as high energy consumption of high-temperature sintering, serious particle agglomeration and uneven particle size distribution. Although the liquid phase method reduces the reaction temperature, the process is complex and the product morphology is difficult to control. In the existing coating technology, the uneven mixing of lithium tungstate and the substrate leads to discontinuous distribution of the coating layer, which cannot effectively inhibit the corrosion of the electrolyte on the positive electrode material, and the problem of low lithium ion diffusion rate has not been solved.

[0015] To solve the above problems, the inventors found that the high-temperature environment in the traditional process is the key factor leading to particle agglomeration and high energy consumption, and the uneven distribution of doping elements directly affects the electrical conductivity and structural stability of the material. By analyzing the physical and chemical changes at different stages of preparation, it is proposed to construct a uniform slurry under low temperature conditions, combined with mechanical dispersion and instantaneous drying to inhibit grain growth. It is further found that the water-based reaction system can avoid the influence of organic solvent residues on the performance of the material, and by accurately controlling the lithium-tungsten ratio and the doping amount, the intrinsic properties of the material are optimized at the atomic level.

[0016] Therefore, the present application proposes a preparation method of doped lithium tungstate, comprising the following steps: mixing a tungsten source and a lithium source in water, adding a dopant to obtain a slurry; sanding the slurry in an ice water bath environment; spray drying the sanded slurry to obtain a powder; sintering and crushing the powder to obtain the final product Li x W y M z O4, wherein x is 1.9 to 2.1, z is 0 to 0.05, the sum of y and z is 1, and M is selected from at least one of niobium, tantalum, and molybdenum.

[0017] The slurry refers to a homogeneous mixture formed by water solution blending. Specifically, tungstic acid and lithium hydroxide can be used as raw materials, and metal ions are fully complexed by adjusting the pH value. The molar ratio of lithium to tungsten is controlled at 1.9 to 2.1 to 1 to ensure the accuracy of the stoichiometric ratio.

[0018] The tungstic acid includes at least one of yellow tungstic acid (WO3·H2O), white tungstic acid, and metatungstic acid. The dopant is selected from at least one of ammonium niobate, potassium tantalate, or sodium molybdate, and the doping amount is not more than 5% of the total metal molar amount, which is used to form defect sites in the crystal structure to improve ion mobility. Ice water bath sanding refers to mechanical grinding in a 0-10℃ environment. Specifically, a zirconia ball mill jar can be used in combination with a circulating cooling system to reduce agglomeration by relieving the reaction unevenness caused by intense heat release during mixing through low temperature. Spray drying is achieved by atomizing the slurry into small droplets and then rapidly dehydrating. The sintering process is carried out in an air atmosphere, and the temperature is controlled within the range of 120-150℃ to avoid abnormal grain growth caused by high temperature.

[0019] Specifically, in the slurry preparation stage, water as a reaction medium makes metal ions fully dispersed, and the accurate lithium-tungsten ratio ensures the uniformity of the chemical composition of the slurry. The introduction of doping elements changes the lattice parameters through ion replacement, while maintaining the stability of the main structure and enhancing the continuity of the lithium ion transmission channel. Mechanical grinding in an ice water bath environment reduces the surface energy of the particles, allowing nanoscale particles to remain dispersed. In the sintering stage, the directional growth of the grains is promoted by controlling the thermodynamic conditions, and the final crushing process eliminates residual stress and optimizes the particle size distribution.

[0020] Compared with the prior art, the traditional high-temperature solid-phase method needs to be sintered at 600 DEG C or above for a long time, resulting in serious particle agglomeration and uneven distribution of doped elements. The present application reduces energy consumption to less than 30% of the traditional process by combining water-based reaction with low-temperature sintering, while avoiding organic solvent pollution. Compared with the sol-gel method which relies on complex coordination reaction and strict calcination conditions, the present method improves the uniformity of product particle size by more than 50% through the synergistic effect of physical grinding and spray drying. Compared with the micron-sized particles in CN117098730A, the nanoscale particles obtained by the present application can form a more dense coating layer, effectively blocking electrolyte corrosion.

[0021] Through the above technical solutions, the present application realizes low-energy consumption preparation of lithium tungstate, and the product has uniform nanoscale particle size distribution and controllable doped element content. The method effectively solves the problems of particle agglomeration, high energy consumption, uneven doping and low production capacity in the traditional process, and the obtained material can be used as an efficient modifier for ternary positive electrodes, which improves the uniformity of the coating layer and the bulk ion conductivity, and improves the cycle stability and rate performance of the battery.

[0022] According to some embodiments of the present application, the doped lithium tungstate Li x W y M z In the doped lithium tungstate Li

[0023] According to some embodiments of the present application, x = 1.9, 2.0 or 2.1.

[0024] According to some embodiments of the present application, x = 2.0.

[0025] According to some embodiments of the present application, the dopant includes at least one of a Nb source, a Ta source, and a Mo source.

[0026] The niobium source refers to a compound capable of providing niobium elements, and the niobium ions released after hydrolysis can form a uniform coprecipitation slurry with the tungsten source. The tantalum source refers to a compound capable of providing tantalum elements, and the introduction of tantalum ions can enhance the lattice stability and optimize the electron transport path. The molybdenum source refers to a compound capable of providing molybdenum elements, which can be realized by using ammonium molybdate or molybdenum trioxide, and the doping of molybdenum ions helps to adjust the oxygen vacancy concentration and inhibit the lattice oxygen precipitation.

[0027] Specifically, the selection of the niobium source, the tantalum source and the molybdenum source is based on the adaptability of the ion radius thereof to the tungsten ion in the lithium tungstate crystal lattice. For example, the ion radius of the niobium ion and the tantalum ion is similar to that of the tungsten ion, so that the crystal lattice doping can be realized without significantly changing the crystal structure, and the lattice distortion caused by the difference in ion size is avoided. The introduction of the molybdenum ion reduces the loss of active oxygen in the charging and discharging process. In the liquid phase reaction, the hydrolysis characteristics of these dopants are matched with the tungsten source, ensuring the uniform distribution of each element during the slurry formation process, thereby avoiding the generation of a second phase or local component segregation.

[0028] Compared with the prior art, the present application enables the elements to be uniformly distributed in the crystal lattice through effective single-element doping, enhances the electronic conductivity of the material, and at the same time, inhibits the lattice oxygen precipitation in the cycle process through the stable oxygen vacancy structure, thereby improving the electrochemical stability of the lithium tungstate material in the lithium ion battery.

[0029] The doping element W is an element on the diagonal of the periodic table, has similar physicochemical properties, and has a similar ion size, and is more suitable for doping into the W crystal lattice. In addition, the doping element should not be too much, otherwise it will become another crystal phase, and less will not show the effect. After element doping, the crystal lattice defects can be inhibited, the material stability can be enhanced, and the material conductivity can be improved. Specifically: Nb 5+ / Ta 5+ The ion radius of W 6+ By expanding the crystal lattice, the ion transmission channel is widened, the ion transmission rate is enhanced, and the volume expansion stress is relieved. The high-valence metal ion incorporated can inhibit the breaking of the W-O bond through electrostatic repulsion, reduce the generation of oxygen vacancies during the cycle, and improve the cycle stability.

[0030] According to some embodiments of the present application, 0.01≤z≤0.04.

[0031] According to some embodiments of the present application, 0.02≤z≤0.03.

[0032] Among them, regarding the doping element M, at least one of the niobium source, the tantalum source or the molybdenum source can be used as a dopant to achieve it. The proportion range is adjusted by controlling the feeding ratio of the dopant and the tungsten source, to ensure the uniform distribution of the doping element in the crystal lattice. The lower limit of z 0.01 can ensure sufficient doping concentration to form a stable solid solution structure, and the upper limit 0.04 can prevent excessive doping from causing element enrichment at the grain boundary.

[0033] Specifically, the introduction of the doping element M optimizes the lithium ion migration channel by partially replacing the tungsten atoms in the lithium tungstate lattice while maintaining the crystal phase structure. When z is less than 0.01, the doping concentration is insufficient to effectively regulate lattice defects, and the conductivity cannot be significantly improved; when z exceeds 0.04, excessive doping elements will gather at the grain boundaries, hindering lithium ion transmission and causing particle agglomeration. By limiting z to between 0.01 and 0.04, effective regulation of lattice defect density is achieved, and the problem of structural instability caused by excessive doping is avoided.

[0034] Compared with the prior art, the doping amount in the traditional doping process usually adopts a wide range or is not explicitly defined, for example, the z value in some technologies may reach more than 0.05, resulting in an increase in the bulk resistivity of the material or structural collapse during the cycle process. The present application determines the optimal range of z through experimental verification, maximally maintaining the structural integrity of the material while ensuring the doping effect.

[0035] Through the above technical solution, the present application solves the problem of insufficient conductivity or decreased structural stability caused by inaccurate control of the doping amount, so that the prepared lithium tungstate material has both high lithium ion diffusion rate and stable crystal framework, providing a coating agent with suitable surface activity for subsequent coating modification of the positive electrode material.

[0036] According to some embodiments of the present application, in step S2, the pH of the slurry during the sanding process is controlled to be between 9.0 and 9.3.

[0037] According to some embodiments of the present application, in step S2, the pH of the slurry during the sanding process is controlled to be between 9.1 and 9.2.

[0038] The pH of the slurry refers to the negative logarithm of the hydrogen ion concentration in the slurry, and this pH range can inhibit metal ion hydrolysis and maintain the charge balance on the particle surface. The ice water bath environment refers to placing the sanding container in a low temperature environment of 0 to 5℃, and the temperature can be maintained using an ice water mixture. This condition can reduce the reactivity during the sanding process and avoid local overheating, thereby preventing pH fluctuations.

[0039] Specifically, in a weak alkaline environment, the metal ions in the slurry form stable complexes with hydroxyl groups, reducing the concentration of free metal ions and thereby inhibiting the hydrolysis side reaction. The particle surface forms a double-layer structure due to the adsorption of hydroxyl groups, which reduces the van der Waals force through electrostatic repulsion, preventing particle agglomeration during mechanical grinding. At the same time, when the pH value is close to the isoelectric point, the viscosity of the slurry tends to be stable, which is beneficial to the subsequent spray drying to form uniform droplets. For example, when the pH is less than 9.0, tungstate ions are prone to combine with hydrogen ions to form precipitates; when the pH is greater than 9.3, lithium ions may form lithium hydroxide colloid, both of which will destroy the dispersibility of the slurry.

[0040] Compared with the prior art, the traditional sanding process does not control the slurry pH, leading to uneven distribution of particle surface charge and easy irreversible agglomeration under mechanical force. The present application forms a stable hydration layer on the particle surface by precisely regulating the weak alkaline environment, and maintains the dynamic balance of the dispersion system under low-temperature grinding conditions.

[0041] Through the above technical scheme, the present application effectively reduces the agglomeration of nanoparticles during sanding, improves the uniformity of the slurry dispersion, ensures the powder particle size distribution after spray drying, and ultimately obtains a doped lithium tungstate material with continuous ion channels and complete crystal structure.

[0042] According to some embodiments of the present application, the sanding time in step S2 is 10-20 min.

[0043] The sanding time refers to the length of time that the material stays in the sanding equipment during mechanical grinding. It can be achieved by using a planetary ball mill or a sand mill, and the number of cycles of the material in the sanding chamber is controlled by adjusting the equipment operating parameters. This time range is set as a key parameter for balancing the slurry dispersion efficiency and the change of particle surface energy, which ensures that the solid particles are fully deagglomerated and avoids secondary aggregation caused by excessive friction leading to an increase in active sites on the particle surface.

[0044] Specifically, when the sanding time is less than 10 minutes, the ion dispersion of the tungsten source and the lithium source has not been completed, and there may be micron-sized agglomerates in the slurry that have not been fully broken down, resulting in uneven distribution of internal components of the powder particles formed by subsequent spray drying; when the time exceeds 20 minutes, the surface lattice defects of the nanoparticles increase under the continuous action of mechanical force, the slurry viscosity rises, and the van der Waals force between particles increases, which easily forms hard agglomeration in the ice water bath low-temperature environment. By limiting the time in this range, the slurry achieves sufficient shear force for nanodispersion, while the generation rate of active groups such as hydroxyl groups on the particle surface and the adsorption rate of solvent molecules reach a dynamic balance, thereby maintaining the stable dispersion state of the slurry system.

[0045] Compared with the prior art, the sanding time in the traditional process is usually set based on experience. The present application quantifies the correlation between the sanding time and the particle dispersion degree, and establishes a process control standard with strong repeatability.

[0046] Through the above technical scheme, the present application realizes uniform distribution of active ingredients in the slurry and effective control of particle size, provides a basis for subsequent spray drying to form a powder with high sphericity and good flowability, and at the same time avoids the impurity segregation phenomenon at the grain boundaries of sintered bodies caused by particle agglomeration, ultimately obtaining a doped lithium tungstate product with regular morphology and stable crystal structure.

[0047] According to some embodiments of the present application, in step S3, the spray drying is performed by a centrifugal spray dryer, the inlet temperature is 180-220℃, the outlet temperature is 90-130℃, and the atomizer frequency is 200-400Hz.

[0048] The centrifugal spray dryer refers to an equipment that realizes slurry breaking by using a high-speed rotating atomizing disc, and can be specifically realized by using a centrifugal atomizer with a variable frequency speed regulation function. The rotating speed of the atomizing disc is adjusted to match the characteristics of the slurry, so that uniform and small droplets are generated.

[0049] The inlet temperature refers to the hot air temperature at the inlet of the atomizing chamber, and can be specifically realized by using a segmented heater in linkage control with a temperature sensor, so as to ensure that a dry shell is quickly formed on the surface of the droplet, and prevent the internal moisture from being evaporated violently to cause particle rupture.

[0050] The outlet temperature refers to the airflow temperature at the end of the atomizing chamber, and can be specifically realized by adjusting the balance relationship between the air inlet amount and the air exhaust rate, so as to avoid surface melting or crystal structure damage of the powder due to overheating.

[0051] The atomizer frequency refers to the working frequency of the motor driving the atomizing disc to rotate, and can be specifically realized by adjusting the rotating speed of the motor by using a frequency converter, so as to reduce the droplet size by increasing the rotating speed, or increase the droplet size by reducing the rotating speed, thereby accurately controlling the powder particle size distribution.

[0052] Specifically, the slurry is atomized into micron-level droplets under the action of centrifugal force. The outlet temperature is maintained above the minimum threshold required for complete drying of the droplets, so as to avoid particle adhesion caused by residual moisture. The atomizing frequency is dynamically adapted to the viscosity of the slurry. When the solid content of the slurry increases, the atomizing energy is compensated by increasing the frequency, so as to ensure that the droplet size is stable in the nanometer range. The thermal gradient formed during the drying process promotes stress relaxation in the interior of the particles, and finally a powder with a smooth surface and no hard agglomeration is obtained.

[0053] Compared with the prior art, the traditional spray drying process uses fixed atomizing pressure and constant temperature field, which is prone to produce a problem of excessively wide particle size distribution, and the long residence time in the high temperature section causes particle sintering. By combining centrifugal atomization and dynamic parameter adjustment, the present application avoids the use of organic dispersants, realizes an improvement of about 40% in the concentration degree of particle size distribution, and shortens the drying time to 1 / 3 of the traditional process.

[0054] Through the above technical solutions, the present application effectively suppresses the agglomeration phenomenon of nanoparticles during the drying process, and obtains a powder with a regular spherical morphology and a narrow particle size distribution, which provides a high specific surface area and excellent dispersibility of the dopant for subsequent positive electrode material coating, thereby improving the ion conduction efficiency and structural stability of the positive electrode interface of the lithium ion battery.

[0055] Spray drying technology is more uniform in the consistency of particle morphology control, shorter drying time, suitable for large-scale production. Ball milling method may cause local overheating, mechanical grinding is not detailed enough for the control of the morphology, and is not suitable for large-scale production. Gel method sintering temperature is high, sintering time is long, although the particle is smaller, but it is not easy to form uniform particles in morphology.

[0056] According to some embodiments of the present application, in step S4, sintering is carried out in air atmosphere, the sintering temperature is 120-150℃, and the sintering time is 5-9h.

[0057] Wherein, the air atmosphere refers to sintering in normal pressure atmospheric environment, without additional introduction of inert gas or vacuum environment, which can be realized by using open hearth equipment, and the oxidation environment is maintained by natural air flow. This condition helps to stabilize the material lattice structure and avoid the complex equipment configuration required by inert gas protection.

[0058] Wherein, the sintering temperature refers to the peak temperature reached by the material during heat treatment, which can be realized by using gradient temperature rising program, for example, the temperature is raised to the target interval at a rate of 2-5℃ per minute. This temperature range is significantly lower than the temperature required by conventional solid phase method, which can inhibit the excessive sintering and agglomeration between particles.

[0059] Wherein, the sintering time refers to the duration of the material being heated at the target temperature range, which can be realized by setting the holding time through the temperature controller. This time range ensures that the crystal is fully formed while avoiding abnormal grain growth, maintaining the uniformity of product particle size.

[0060] Specifically, by limiting the sintering environment to air atmosphere, the complexity of the equipment is simplified, and the oxygen in the air is used to participate in the lattice construction, promoting the integrity of the lithium tungstate crystal structure. The sintering temperature is selected in the low temperature range of 120-150℃, which can effectively block the surface melting and mutual adhesion of particles at high temperature, thereby inhibiting the agglomeration phenomenon. At this temperature, the sintering time is set to 5 to 9 hours, and lithium ions and tungstate ions realize ordered arrangement through solid phase diffusion, forming a stable structure, which not only ensures the ion migration to complete the lattice reconstruction, but also avoids the problem of grain boundary coarsening caused by long time heat treatment. The synergistic control of temperature and time limits the grain size to the nanometer to submicron level, providing high specific surface area and fast ion conduction channel for the material.

[0061] Compared with the prior art, the traditional solid phase method usually needs high-temperature sintering above 500 DEG C and needs to be prevented from oxidation under inert gas protection, resulting in high energy consumption and complex equipment. Although the sol-gel method can synthesize materials at a lower temperature, the calcination process still needs a temperature above 300 DEG C and depends on the precise heating rate control. The present application is sintered in a low-temperature air atmosphere, avoids the damage of high temperature to the substrate structure, stabilizes the crystal growth in the oxidation environment, and realizes the double advantages of process simplification and energy consumption reduction.

[0062] Through the above technical solutions, the present application solves the problems of particle agglomeration and substrate damage caused by high-temperature sintering, reduces the production energy consumption, and obtains doped lithium tungstate with high crystallinity and uniform particle size distribution. The ion conduction performance of the material is effectively guaranteed, which provides an ideal physical property basis for the material as a positive electrode coating material, thereby improving the cycle stability and safety of lithium ion batteries.

[0063] The second aspect of the present application provides a doped lithium tungstate with a chemical formula of Li x W y M z O4,

[0064] Wherein, x is 1.9-2.1, 0≤z≤0.05, y+z=1, and M includes at least one of Nb, Ta and Mo.

[0065] According to some embodiments of the present application, the doped lithium tungstate of the present application is prepared by the preparation method of the first aspect of the present application.

[0066] The preparation method of the doped lithium tungstate of the present application includes mixing a tungsten source and a lithium source in water and adding a dopant to form a slurry, performing sanding treatment on the slurry under ice water bath conditions by controlling the pH value of the slurry, preparing a powder by using a centrifugal spray dryer, and finally performing low-temperature sintering and crushing treatment in an air atmosphere.

[0067] Wherein, the ice water bath sanding refers to mechanical grinding of the slurry in an ice water mixture, and specifically, a circulating cooling system can be used to maintain an environmental temperature of 0-5 DEG C to achieve this, which can inhibit the grain growth caused by reaction heat release and maintain the uniformity of particle size. The pH value is controlled between 9.0-9.3, and this alkaline environment is conducive to the stable dispersion of metal ions and avoids local agglomeration. The inlet temperature of the spray drying is set to 180-220 DEG C, and specifically, a segmented heating system can be used to achieve this, and this temperature range can ensure rapid dewatering of the slurry. The air atmosphere sintering temperature is limited to 120-150 DEG C, and specifically, a box-type resistance furnace can be used in combination with an air flow meter to achieve this, and the low-temperature condition can avoid lattice distortion of lithium tungstate and maintain the integrity of the crystal phase structure.

[0068] Specifically, the slurry is subjected to short-time sanding in an ice-water bath environment, and a stable colloidal system is formed by synergistic control of temperature and pH value, so that metal ions are uniformly dispersed. In the spray drying process, the slurry is broken into micron-sized droplets by high-frequency vibration of the atomizer, and the solvent is rapidly evaporated at a specific inlet temperature to form a powder with concentrated particle size distribution. In the low-temperature sintering stage, oxygen elements in the air atmosphere fill the lattice vacancies and inhibit the segregation of doped elements, and finally, the nanoscale product is obtained by mechanical crushing. Through precise matching of process parameters, the process solves the problems of coarse particles and uneven morphology in the traditional method.

[0069] Compared with the prior art, the existing solid phase method needs to be sintered at a high temperature of 500 DEG C or above, which causes abnormal grain growth. The present application adopts low-temperature treatment at 120-150 DEG C, which maintains the stability of the crystal structure while avoiding agglomeration caused by grain boundary migration. Compared with the sol-gel method which relies on organic gelatinizing agents and complex calcination procedures, the present application directly obtains high-purity powder through aqueous phase mixing and spray drying, simplifying the process flow. The obtained nanoparticles can realize dense coating on the surface of the ternary material, effectively blocking the erosion of the electrolyte.

[0070] Through the above technical solutions, the doped lithium tungstate of the present application forms a continuous and thickness-controllable coating layer on the surface of the ternary positive electrode material, significantly reduces the occurrence rate of interface side reactions, and at the same time, the nanoscale particle size provides a fast transmission channel for lithium ion diffusion, alleviates the polarization phenomenon in the charging and discharging process, thereby prolonging the cycle life of the battery and improving the safety.

[0071] According to some embodiments of the present application, the D50 of the doped lithium tungstate is 0.2-0.5 μm, and the specific surface area is 5-9 cm 2 / g.

[0072] D50 refers to the particle size value corresponding to 50% of the particle volume distribution, which can be realized by adjusting the spray drying parameters and sintering conditions, for example, controlling the combination of the atomizer frequency and the sintering temperature, so that the particles obtain a narrower particle size distribution during the formation process. This parameter directly affects the uniformity of the coating of the particles on the surface of the positive electrode material, and a too large particle size will cause particle agglomeration and prevent the formation of a continuous coating layer. The specific surface area refers to the total surface area per unit mass of particles, which can be realized by adjusting the sanding time and the pH value of the slurry, for example, extending the sanding time can increase the roughness of the particle surface, thereby increasing the specific surface area. This parameter is directly related to the number of active sites on the particle surface, and a too high specific surface area will intensify the electrolyte decomposition reaction.

[0073] Specifically, when the D50 is in the submicron range, the particles are more easily dispersed on the surface of the ternary material during the coating process, forming a coating layer with uniform thickness. When the specific surface area is 5-9 cm 2When the particle size is less than or equal to 1.5 μm and the specific surface area is greater than or equal to 1.5 m2 / g, the particle surface has sufficient lithium ion transmission channels while avoiding excessive specific surface area to cause the electrolyte to excessively contact the active material. Through the synergistic control of D50 and the specific surface area, the coating layer can effectively prevent the corrosion of the electrolyte on the positive electrode matrix and maintain the rapid diffusion of lithium ions in the coating layer, thereby solving the problem of ion transmission obstruction caused by the excessively large particle size of the traditional coating layer.

[0074] In some embodiments, the slurry is atomized into micron-sized droplets by a centrifugal spray dryer, and the inlet temperature is controlled in the range of 180-220 DEG C. Subsequently, sintering is performed at 120-150 DEG C to form a stable lattice structure in the interior of the particles while maintaining a sub-micron particle size. During the sanding process, the pH value of the slurry is stabilized at 9.0-9.3, and the surface charge state of the particles is controlled by the concentration of hydroxyl ions to inhibit excessive growth of the particles.

[0075] Compared with the prior art, the D50 of the lithium tungstate particles prepared by the traditional method is usually large, and the specific surface area is low, resulting in obvious gaps in the coating layer, and the electrolyte is easily penetrated to the surface of the positive electrode material. The present application optimizes the particle size and specific surface area to form a dense and continuous physical barrier in the coating layer while retaining sufficient lithium ion transmission channels. In the prior art, micron-sized particles are used, and the coating amount needs to be increased to compensate for the coating defects, but this will hinder the migration of lithium ions. The present application can achieve better coating effect while reducing the coating amount.

[0076] Through the above technical solutions, the present application can improve the uniformity of the lithium tungstate coating layer on the surface of the ternary positive electrode material, effectively inhibit the side reaction between the electrolyte and the positive electrode active material. At the same time, the optimized specific surface area parameter ensures that the coating layer can block the electrolyte while maintaining a rapid diffusion channel for lithium ions, thereby relieving the polarization phenomenon during charging and discharging, prolonging the cycle life of the battery and improving the safety.

[0077] The third aspect of the present application provides a coated ternary positive electrode material, and the preparation raw material comprises the doped lithium tungstate of the second aspect of the present application.

[0078] Compared with the prior art, the traditional lithium tungstate preparation method has the problems of serious particle agglomeration and wide particle size distribution, resulting in poor uniformity of the coating layer and inability to effectively block the electrolyte erosion. The existing coating process mostly uses physical mixing method, and the distribution of doped elements is uneven, which is difficult to improve the intrinsic conductivity of the material. The present application realizes the atomic dispersion of the doped elements by combining the aqueous synthesis system with the low-temperature sintering process, and forms a stable solid solution structure. Compared with the high-temperature solid phase method, the low-temperature treatment avoids the lattice distortion of the material, ensuring the interface compatibility between the coating layer and the substrate. Compared with the sol-gel method, the spray drying process simplifies the production process and does not need to use organic gelling agents, which is more suitable for industrial production.

[0079] By the technical scheme, the application can improve the stability of the interface between the positive electrode material and the electrolyte, reduce the dissolution of the active material and the lattice oxygen precipitation in the cycle process. The high ion conductivity of the doped lithium tungstate reduces the electrode polarization phenomenon, and improves the rate performance of the battery. The uniform and dense coating layer effectively blocks the corrosion of the electrolyte on the ternary material, and inhibits the phase change reaction in the charging and discharging process, thereby prolonging the cycle life of the battery and improving the safety performance.

[0080] According to some embodiments of the application, the doped lithium tungstate of the second aspect of the application can be mixed with the Al and Ti containing additives uniformly, and then sintered at 400-450℃ for about 18-20h to obtain the coated ternary positive electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0081] Figure 1 is a micro-morphology diagram of the doped lithium tungstate prepared in Example 1.

[0082] Figure 2 is a micro-morphology diagram of the ternary material finished product using the doped lithium tungstate prepared in Example 1.

[0083] Figure 3 is an XRD diagram of the doped lithium tungstate prepared in Example 1.

[0084] Figure 4 is a micro-morphology diagram of the doped lithium tungstate prepared in Comparative Example 1.

[0085] Figure 5 is a micro-morphology diagram of the doped lithium tungstate prepared in Comparative Example 2. DETAILED DESCRIPTION

[0086] The concept and the technical effects of the application will be described in detail below with the embodiments, so as to fully understand the purpose, features and effects of the application. Obviously, the described embodiments are only some of the embodiments of the application, but not all the embodiments. Based on the embodiments of the application, other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the application.

[0087] In the description of the application, the description of the terms "one embodiment", "some embodiments", "illustrative embodiment", "example", "specific example" or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the application. In the specification, the illustrative description of the above terms does not necessarily mean the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0088] Unless otherwise specified, "room temperature" in the present application means 25°C ± 5°C.

[0089] Unless otherwise specified, "about" in the present application means that the allowable error is within ± 2%.

[0090] Unless otherwise specified in the examples, the routine conditions or the conditions recommended by the manufacturer are used. Unless otherwise specified, the reagents or instruments used are conventional products that can be obtained by commercial purchase.

[0091] Example 1

[0092] A doped lithium tungstate was prepared, and the specific process was as follows:

[0093] Yellow tungstic acid, lithium hydroxide, and 0.01 mol of Nb2O5·3H2O were slowly added together to pure water in a molar ratio of 1:2:0.01, to obtain a slurry. The weight ratio of pure water to yellow tungstic acid was 1:5.

[0094] The slurry was ground in an ice water bath (temperature 3°C) for about 10 min. The grinding speed was 600 rpm.

[0095] A centrifugal spray dryer was used, with an inlet temperature of 200°C, an outlet temperature set at 105°C, and an atomizer frequency of 300 Hz.

[0096] The powder was collected and sintered in an air atmosphere at 140°C for about 7 h to obtain a sintered powder.

[0097] The powder was airflow crushed to control the D50 at 0.35 μm, to obtain a cubic finished doped lithium tungstate.

[0098] Further, the lithium tungstate material was used as a coating agent, and was mixed with Al2O3, TiO2 additives (according to the weight ratio, NCM (ternary positive electrode material): lithium tungstate: Al2O3: TiO2 = 1000:3:2:2) together with the ternary material Ni 0.6 Co 0.2 Mn 0.2 O2 was mixed uniformly and sintered at 420°C for 15 h to obtain a finished product, and the electrochemical performance was tested.

[0099] Example 2

[0100] A doped lithium tungstate was prepared, and the specific process was as follows:

[0101] Yellow tungstic acid, lithium hydroxide, and 0.005 mol of Nb2O5·3H2O were slowly added together to pure water in a molar ratio of 1:1.9:0.005, to obtain a slurry. The weight ratio of pure water to yellow tungstic acid was 1:5.

[0102] The slurry was ground for about 10 min under ice water bath (temperature 5℃). The grinding speed was 650ppm.

[0103] The inlet temperature was 180℃, the outlet temperature was set at 90℃, and the frequency of the atomizer was 300Hz.

[0104] The powder was collected and sintered in air atmosphere at 120℃ for about 9h to obtain the sintered powder.

[0105] The powder was air-jet milled to control the D50 at 0.32μm to obtain the cubic finished product of doped lithium tungstate.

[0106] Further, the lithium tungstate material was used as a coating agent and mixed with Al2O3, TiO2 additives (according to the weight ratio, NCM (ternary positive electrode material): lithium tungstate: Al2O3: TiO2=1000:3:2:2) together with the ternary material Ni 0.6 Co 0.2 Mn 0.2 After uniform mixing, the mixture was sintered at 420℃ for 15h to obtain the finished product, and the electrochemical performance was tested.

[0107] Example 3

[0108] A doped lithium tungstate was prepared, and the specific process was as follows:

[0109] Yellow tungsten acid and lithium hydroxide were added slowly into pure water according to a molar ratio of 1:2.1 and 0.02mol of Nb2O5·3H2O to obtain a slurry. The weight ratio of pure water to yellow tungsten acid was 1:5.

[0110] The slurry was ground for about 10 min under ice water bath (temperature 1℃). The grinding speed was 700ppm.

[0111] The inlet temperature was 220℃, the outlet temperature was set at 130℃, and the frequency of the atomizer was 300Hz.

[0112] The powder was collected and sintered in air atmosphere at 150℃ for about 5h to obtain the sintered powder.

[0113] The powder was air-jet milled to control the D50 at 0.36μm to obtain the cubic finished product of doped lithium tungstate.

[0114] Further, the lithium tungstate material was used as a coating agent and mixed with Al2O3, TiO2 additives (according to the weight ratio, NCM (ternary positive electrode material): lithium tungstate: Al2O3: TiO2=1000:3:2:2) together with the ternary material Ni 0.6 Co 0.2 Mn 0.2After mixing evenly, burn at 420℃ for 15h to get the finished product, and test the electrochemical performance.

[0115] Example 4

[0116] On the basis of Example 1, replace 0.01 mol of Nb2O5·3H2O with 0.02 mol of ammonium molybdate (NH4)2MoO4, and the rest is the same as Example 1.

[0117] Comparative Example 1 (without adding Nb2O5·3H2O)

[0118] A doped lithium tungstate was prepared, and the specific process was as follows:

[0119] Yellow tungstate and lithium hydroxide were slowly added to pure water in a molar ratio of 1:2 to obtain a slurry. The weight ratio of pure water to yellow tungstate was 1:5.

[0120] Grind the slurry in an ice water bath (temperature 5℃) for about 10 min. The grinding speed was 600ppm.

[0121] Use a centrifugal spray dryer, the inlet temperature is 200℃, the outlet temperature is set to 105℃, and the atomizer frequency is 300Hz.

[0122] Collect the powder, sinter in air atmosphere at 140℃ for about 7h to obtain the sintered powder.

[0123] Airflow crush the powder, control D50 at 0.32μm, to get cubic finished doped lithium tungstate.

[0124] Further, the lithium tungstate material is used as a coating agent, and is mixed with Al2O3, TiO2 additives (according to the weight ratio, NCM (ternary positive electrode material): lithium tungstate: Al2O3: TiO2 = 1000:3:2:2) together with the ternary material Ni 0.6 Co 0.2 Mn 0.2 After mixing evenly, burn at 420℃ for 15h to get the finished product, and test the electrochemical performance.

[0125] Comparative Example 2 (without ice water bath)

[0126] A doped lithium tungstate was prepared, and the specific process was as follows:

[0127] Yellow tungstate, lithium hydroxide and 0.02 mol of Nb2O5·3H2O were slowly added to pure water in a molar ratio of 1:2 to obtain a slurry. The weight ratio of pure water to yellow tungstate was 1:5.

[0128] Grind the slurry at room temperature for about 10 min. The grinding speed was 700ppm.

[0129] The centrifugal spray dryer was used, the inlet temperature was 200℃, the outlet temperature was set at 105℃, and the atomizer frequency was 300Hz.

[0130] The powder was collected and sintered at 140℃ for about 7h in air atmosphere to obtain the sintered powder.

[0131] The powder was airflow pulverized to control the D50 at 0.40μm to obtain the cubic finished product of doped lithium tungstate.

[0132] Further, the lithium tungstate material was used as a coating agent, and mixed with Al2O3, TiO2 additives (according to the weight ratio, NCM (ternary positive electrode material) : lithium tungstate : Al2O3 : TiO2 = 1000 : 3 : 2 : 2) together with the ternary material Ni 0.6 Co 0.2 Mn 0.2 After mixing uniformly, the mixture was sintered at 420℃ for 15h to obtain the finished product, and the electrochemical performance was tested.

[0133] Comparative Example 3

[0134] A doped lithium tungstate was prepared, and the difference from Example 1 was that the new spray process of the application was not used, but a traditional spray process was used.

[0135] Comparative Example 4

[0136] This comparative example was a ternary lithium nickel cobalt manganese oxide without coated lithium tungstate.

[0137] Performance test

[0138] The micro-morphology of the doped lithium tungstate prepared in Example 1 is shown in Figure 1 It can be seen from Figure 1 that the particles are uniform cubic morphology, and the size is between 150-400nm.

[0139] The micro-morphology of the ternary material finished product using the doped lithium tungstate prepared in Example 1 is shown in Figure 2 It can be seen from Figure 2 that the additives are uniformly coated on the surface of the ternary positive electrode.

[0140] The X-ray powder diffraction result of the doped lithium tungstate prepared in Example 1 is shown in Figure 3 It can be seen from Figure 3 that the spectrum is consistent with the standard card PDF: 72-0395, indicating that the target sample is obtained.

[0141] The micro-morphology of the doped lithium tungstate prepared in Comparative Example 2 is shown in Figure 5 It can be seen from Figure 5It can be seen that, without ice water bath, the particle size is larger and the agglomeration is larger.

[0142] The samples of the examples and the comparative examples were prepared into button cells, and the button cells were tested at 2.8-4.4V, 0.1C with the ternary material without coated lithium tungstate, and the data are shown in Table 1.

[0143] The button cells were prepared, and the lithium ion battery positive electrode material: conductive agent Super P, binder polyvinylidene fluoride (PVDF) were mixed and stirred uniformly at a mass ratio of 90:5:5, and N-methyl pyrrolidone (NMP) to prepare a positive electrode slurry (solid content about 40%), coated on the current collector aluminum foil, dried at 105℃, and then rolled at room temperature to a surface density of 2.8-3.3g / cm 3 , then punched, cut into round sheets, and prepared into positive electrode sheets. The assembly of the button cells was carried out in a glove box. The button cells were assembled in the order of "negative shell-foam nickel-lithium sheet -8 drops of electrolyte-separator 16μm thick-8 drops of electrolyte-positive electrode sheet-positive shell", wherein the electrolyte is composed of ethylene carbonate (EC), methyl ethyl carbonate (EMC) and dimethyl carbonate (DMC) (EC:EMC:DMC volume ratio = 1:1:1), containing 1.0M LiPF6; the size of the battery shell (positive shell and negative shell) is 24mm. The assembled button cells were placed in the mold groove of a hydraulic sealer (purchased from Shenzhen Kejing Zhida Technology Co., Ltd.), locked, and the pressure was >450kg / cm 2 , then unlocked, and the sealed button cells were taken out.

[0144] Table 1

[0145] Sample No. Initial efficiency (%) Initial charge (mAh / g) Initial discharge (mAh / g) Example 1 89.60 223.0 199.8 Example 2 89.52 223.0 199.6 Example 3 89.63 223.4 200.2 Example 4 89.59 222.8 199.6 Comparative Example 1 89.32 222.5 198.7 Comparative Example 2 88.89 220.9 196.4 Comparative Example 3 89.01 220.4 196.2 Comparative Example 4 88.56 220.4 195.2

[0146] The doped lithium tungstate of the application can better control the particle size of the product by using a new spray drying process. By doping lithium tungstate with elements, the conductivity and cycle stability of the material are improved. As a ternary material coating agent, it isolates the contact with the electrolyte and improves the cycle stability of the positive electrode material.

[0147] The application has been described in detail above in combination with the examples, but the application is not limited to the above examples, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the purpose of the application.

Claims

1. A method for preparing a doped lithium tungstate, characterized in that, The method comprises the following steps: S1: mixing a tungsten source and a lithium source in water, adding a dopant to obtain a slurry; S2: sanding the slurry under an ice water bath; S3: spray drying the slurry of step S2 to obtain a powder; S4: the sintered powder is crushed to obtain the doped lithium tungstate, which has a composition of Li x W y M z O4, wherein x is 1.9-2.1, 0≤z≤0.05, y+z=1, and M includes at least one of Nb, Ta and Mo.

2. The production method according to claim 1, characterized by, The dopant comprises at least one of a Nb source, a Ta source and a Mo source.

3. The preparation method according to claim 1, characterized in that, 0.01≤z≤0.04。 4. The method of claim 1, wherein, In step S2, the pH of the slurry during the sanding process is controlled between 9.0 and 9.

3.

5. The preparation method according to claim 1, characterized in that, In step S2, the sanding time is 10-20 min.

6. The method of claim 1, wherein, In step S3, the spray drying is performed by a centrifugal spray dryer, the inlet temperature is 180-220℃, the outlet temperature is 90-130℃, and the frequency of the atomizer is 200-400Hz.

7. The preparation method according to claim 1, characterized in that, In step S4, the sintering is performed in an air atmosphere, the sintering temperature is 120-150℃, and the sintering time is 5-9h.

8. A doped lithium tungstate characterized in that, Li x W y M z O4, In the formula, x is 1.9-2.1, 0≤z≤0.05, y+z=1, and M comprises at least one of Nb, Ta and Mo.

9. The doped lithium tungstate of claim 8, wherein, The doped lithium tungstate has a D50 of 0.2-0.5 μm, a specific surface area of 5-9 cm2 / g. 2 / g.

10. A coated ternary cathode material, characterized in that, The preparation raw material of the coated ternary positive electrode material comprises the doped lithium tungstate as claimed in any one of claims 8-9.

Images