CN115763719A - Titanium lanthanum lithium phosphate coated magnesium-doped lithium cobaltate cathode material and preparation method thereof - Google Patents
Titanium lanthanum lithium phosphate coated magnesium-doped lithium cobaltate cathode material and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a titanium lanthanum lithium phosphate coated magnesium-doped lithium cobaltate cathode material and a preparation method thereof. According to the lithium lanthanum titanium phosphate coated magnesium-doped lithium cobaltate cathode material, firstly, the magnesium doping can regulate and control the defects and distribution of the interior of lithium cobaltate particles, and further, the structural phase change of the lithium cobaltate material, which causes the material electrochemical performance to be attenuated in the high-voltage charging and discharging process, is inhibited, secondly, lanthanum lithium titanium phosphate with higher structure and electrochemical stability is coated on the surface, a uniform interface layer with excellent ionic and electronic conductivity is constructed, and finally, the lithium cobaltate material is modified doubly, so that the problem of surface stability of the lithium cobaltate material in the high-voltage charging process is effectively solved.
Description
Technical Field
The invention belongs to the technical field of battery materials, and particularly relates to a titanium lanthanum lithium phosphate coated magnesium-doped lithium cobaltate cathode material and a preparation method thereof.
Background
The lithium cobaltate material has poor thermal stability and potential safety hazard during overcharge, and in addition, the lithium cobaltate material is converted from a hexagonal crystal system into a monoclinic crystal system by the working voltage exceeding 4.2V; deep delithiation of Co at high voltage 3+ Is oxidized into Co 4+ ，Co 4+ Easily generate side reaction with electrolyte to cause LiCoO 2 The electrochemical performance of the material is reduced, and the LiCoO is limited by the problems 2 Further applications of (1).
In order to solve the problems, at present, doping or surface coating is mainly adopted to carry out modification research on a lithium cobaltate positive electrode material, single doping or coating cannot completely meet the requirement of high-capacity high-specific-energy long-cycle application of the positive electrode material, and particularly in the charge-discharge long-cycle process under the high-voltage condition, the capacity retention rate and the structural stability are seriously attenuated due to structural deterioration caused by a series of phase changes. The phase change of lithium cobaltate in the lithium deintercalation process can cause the unit cells to generate larger anisotropic expansion and contraction along the directions of a shaft and a shaft, non-uniform stress is generated in crystal nuclei, the structural stability is deteriorated, and the performance of the lithium cobaltate anode material is deteriorated.
In addition, as the charging voltage is increased, the problems of bulk phase, surface and interface instability of the LCO material are significantly aggravated, which will greatly destroy the electrochemical performance and increase the safety risk. Therefore, in order to ensure that lithium cobaltate can ensure stable and long circulation under a high voltage condition, a method which is simple in modification method, beneficial to large-scale popularization and capable of synthesizing a lithium cobaltate cathode material with good stability and excellent electrochemical performance is urgently needed to be developed.
Disclosure of Invention
The technical problem to be solved by the invention is to overcome the defects and shortcomings mentioned in the background technology and provide a titanium lanthanum lithium phosphate coated magnesium doped lithium cobaltate cathode material and a preparation method thereof.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
the lithium lanthanum phosphate coated magnesium-doped lithium cobaltate cathode material takes lithium cobaltate particles as a matrix, lithium lanthanum phosphate is uniformly coated on the surfaces of the lithium cobaltate particles, and magnesium is doped in the lithium cobaltate particles.
The lithium lanthanum titanium phosphate is an NASICON type fast ion conductor, belongs to an olivine structure, and has a firm polyanion framework and high ionic conductivity. The titanium lanthanum lithium phosphate material synthesized by the phosphate structure is uniformly coated on the surface layer of the lithium cobaltate, and the thickness of the coating layer is nano-scale, so that the capacity of the lithium cobaltate anode material is not influenced, and the uniform coating can be ensured.
Strong Mg-O bond and Mg in Li layer 2+ The Mg doping can stabilize the lattice structure to a great extent; the titanium lanthanum lithium phosphate of the fast ion conductor coats the surface interface of the protective material and improves the ionic conductivity. Meanwhile, magnesium doping occupies lithium sites, lithium ions after raw materials are replaced are recycled on the surface layer, in other words, a NASICON type fast ion conductor three-dimensional conductive coating layer is constructed on the particle surface by utilizing residual lithium on the surface, and fast conduction of the lithium ions is promoted.
Preferably, the chemical formula of the lithium lanthanum titanium phosphate coated magnesium doped lithium cobaltate cathode material is Mg-LiCoO 2 @Li 1+ x La x Ti 2-x (PO 4 ) 3 Wherein x is more than 0.2 and less than 0.5, the coating amount of the titanium lanthanum lithium phosphate is less than 2.0wt% of the magnesium-doped lithium cobaltate particles, and the magnesium doping content is less than 1.0mol% of the cobalt content in the cathode material.
If the coating amount is too small, the influence on the material is small, and a layer of uniform coating cannot be completely formed on the surface of the particles. If the coating amount is too large, the coating formed on the surface of the material is too thick, which affects the contact between the positive electrode material and the electrolyte.
Under the same technical concept, the invention also provides a preparation method of the titanium lanthanum lithium phosphate coated magnesium doped lithium cobaltate cathode material, which comprises the following steps:
(1) Uniformly mixing a cobalt source and a lithium source, and sintering to prepare a lithium cobaltate precursor material;
(2) Mixing the lithium cobaltate precursor material obtained in the step (1) with a magnesium source, and performing secondary sintering to obtain magnesium-doped lithium cobaltate particles;
(3) And (3) dissolving a lithium source, a lanthanum source, a titanium source and a phosphorus source to prepare lanthanum lithium titanium phosphate, adding the magnesium-doped lithium cobaltate cathode material obtained in the step (2), stirring, heating, evaporating to dryness, grinding and sintering to obtain the lanthanum lithium titanium phosphate-coated magnesium-doped lithium cobaltate cathode material.
The method is adopted to synthesize the anode material, firstly, magnesium doping can regulate and control defects and distribution inside lithium cobaltate particles, further, structural phase change of the lithium cobaltate material, which causes material electrochemical performance attenuation in a high-voltage charging and discharging process, secondly, titanium lanthanum lithium phosphate with higher structure and electrochemical stability is coated on the surface, a uniform interface layer with excellent ionic and electronic conducting characteristics is constructed, and finally, the lithium cobaltate material is modified doubly, so that the problem of surface stability of the lithium cobaltate material in the high-voltage charging process is effectively solved.
Preferably, the step (1) comprises the steps of: uniformly mixing a cobalt source and a lithium source, and sintering for the first time, wherein the molar ratio of cobalt in the cobalt source to lithium in the lithium source is 1 (1.02-1.10); the cobalt source is one or more of cobalt oxide, cobalt carbonate and cobalt acetate, and the lithium source is lithium hydroxide and/or lithium carbonate.
Lithium is volatilized during calcination, so lithium in the lithium source is more excessive than cobalt in the cobalt source and is controlled to a proper range after sintering. If the excessive lithium source is too small, the excessive lithium source is not enough to compensate the volatilization amount of lithium in the sintering process, and if the excessive lithium source is too large, the excessive lithium source is easy to remain in the product, so that residual lithium is further formed to influence the performance.
Preferably, the cobalt source and the lithium source are mixed by ball milling for 3-8h; the primary calcination is low-temperature calcination, the temperature is raised to 550-650 ℃ at the speed of 1-10 ℃/min, the sintering is carried out for 4-6h, and the sintering atmosphere is air or oxygen.
The primary sintering mainly occurs a process of decomposition and mutual reaction of the cobalt source and the lithium source, if the sintering temperature is too low or the time is too short, the cobalt source and the lithium source are not completely decomposed, if the temperature is too high or the time is too long, side reactions other than the decomposition and reaction of the cobalt source and the lithium source occur, and the temperature is too high and the time is too long, which increases the energy consumption.
Preferably, in the step (2), the molar amount of magnesium in the magnesium source is less than 1% of the molar amount of cobalt in the lithium cobaltate precursor, and the magnesium source is one or more of magnesium oxide, magnesium carbonate and magnesium hydroxide.
If the doped magnesium is too little, the influence on the stable structure of the lithium cobaltate is insufficient, and the defect of regulation and control cannot be realized, and if the doped magnesium is too much, the capacity of the doped material is reduced.
Preferably, in the step (2), the lithium cobaltate precursor material and the magnesium source are mixed by ball milling or grinding, the temperature of the secondary calcination is raised to 800-1000 ℃ at a rate of 1-10 ℃/min, more preferably 850-950 ℃, and the sintering is carried out for 8-12h, wherein the sintering atmosphere is air or oxygen.
Introducing a magnesium source into a precursor formed after the primary sintering of the lithium cobaltate in the secondary sintering process to ensure that magnesium enters a bulk phase under a high-temperature condition; in the secondary sintering process, the growth of lithium cobaltate particles after magnesium is doped into a bulk phase is mainly generated, and the internal defects and distribution of the particles are regulated and controlled. If the sintering temperature is too low or the sintering time is too short, the lithium cobaltate particles are not completely grown, meanwhile, the magnesium doping effect is not ideal, if the sintering temperature is too high or the sintering time is too long, side reactions can occur, the chemical formula deviation caused by serious volatilization of reaction substances is caused, and if the sintering temperature is too high and the sintering time is too long, the energy consumption is increased.
Preferably, the preparation of lithium lanthanum titanium phosphate in the step (3) specifically comprises the following steps: adding a phosphorus source into an organic solvent, dissolving a lithium source and a lanthanum source into the organic solvent, and finally adding a titanium source, wherein the preparation process is carried out in an anhydrous environment; the lithium source is one or more of lithium nitrate, lithium acetate and lithium hydroxide; the lanthanum source is one or more of lanthanum nitrate, lanthanum chloride and lanthanum oxide; the titanium source is tetrabutyl titanate, and the phosphorus source is phosphoric acid; the solvent is organic solvent such as absolute ethyl alcohol and ethylene glycol.
The phosphorus source adopts phosphoric acid solution, firstly, the phosphorus source is easy to disperse, secondly, the lithium source and the lanthanum source are solid particles, and finally, the titanium source which is easy to hydrolyze is added, so that the smooth preparation of the lithium lanthanum titanium phosphate is ensured.
Preferably, after the magnesium-doped lithium cobaltate particles are added in the step (3), the solid-to-liquid ratio is adjusted to be 1 (10-50); if the solid content is too high or too low, the coating layer formed later will be affected.
Stirring at normal temperature at the rotating speed of 300-500r/min for 6-8h; the synthesis of reactants is controlled under the condition of normal temperature, and a homogeneous coating substance is formed in the solution. Too low temperature or too short time is not favorable for synthesizing coating material, and too high temperature or too long time can volatilize solvent, and the coating generation and coating process are incomplete.
The temperature rise is that the temperature rises to 70-80 ℃ during stirring after stirring at normal temperature is finished; the evaporation is to heat and stir until the solvent is volatilized; after the reaction is complete and the coating is primarily finished, the solution needs to be evaporated to dryness and the coating substance is uniformly coated on the surface layer of the particles, the evaporation temperature of the solution is moderate, the evaporation to dryness at too low temperature needs to be carried out for too long time, side reactions can occur, the evaporation to dryness at too high temperature is too fast, and the coating is not uniform.
The grinding is to grind the product after evaporation to dryness again. After being dried by distillation, the product may be agglomerated and the particles are further dispersed uniformly by grinding treatment.
Preferably, the sintering is carried out at the speed of 1-10 ℃/min until the temperature is raised to 500-700 ℃, the sintering is carried out for 5-10h, and the sintering atmosphere is air or oxygen. The sintering process mainly comprises the steps of uniformly dispersing the titanium lanthanum lithium phosphate coating layer and reinforcing the coating layer, if the temperature is too low or the time is too short, the coating layer cannot be effectively dispersed and reinforced, and if the temperature is too high or the time is too long, the coating layer can be decomposed and the material structure can be damaged.
Compared with the prior art, the invention has the beneficial effects that:
(1) According to the lithium lanthanum titanium phosphate coated magnesium-doped lithium cobaltate cathode material obtained by the invention, firstly, the magnesium doping can regulate and control the defects and the distribution in lithium cobaltate particles, so that the structural phase change of the lithium cobaltate material, which causes the material electrochemical performance attenuation in the high-voltage charging and discharging process, is inhibited, secondly, lanthanum lithium titanium phosphate with higher structure and electrochemical stability is coated on the surface, a uniform interface layer with excellent ion and electron conduction characteristics is constructed, finally, the magnesium doping can occupy the lithium position, lithium ions after the raw material is replaced are repeatedly utilized on the surface layer, in other words, the NASICON type fast ion conductor three-dimensional conductive coating layer is constructed on the particle surface by utilizing the residual lithium on the surface, and the rapid conduction of the lithium ions is promoted; by combining the double-modified lithium cobaltate material, the problem of surface stability of the lithium cobaltate material in the high-voltage charging process is effectively solved.
(2) The synthesis method of the collection material of the invention is characterized in that magnesium doping and titanium lanthanum lithium phosphate coating are used for synergistically modifying lithium cobaltate; doping is to form a precursor after the lithium cobaltate is subjected to primary sintering at a low temperature, a magnesium source is introduced in the secondary sintering process to enable magnesium to enter a bulk phase under a high-temperature condition, lithium cobaltate particles grow after the magnesium is doped into the bulk phase, and internal defects and distribution of the particles are regulated and controlled; the coating is to uniformly disperse the magnesium-doped lithium cobaltate anode material in an organic solution, then introduce a lithium source, a lanthanum source, a titanium source and a phosphorus source, grow a layer of titanium lanthanum lithium phosphate coating on the surface of the material, finally obtain the magnesium-doped lithium cobaltate anode material coated with the titanium lanthanum lithium phosphate through low-temperature treatment, and finally obtain the uniform dispersion and firmness of the titanium lanthanum lithium phosphate coating, thereby improving the stability of lithium cobaltate particles.
Drawings
In order to more clearly illustrate the embodiments or technical solutions of the present invention, the drawings used in the embodiments or technical solutions in the prior art are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.
Fig. 1 is an XRD chart of the lithium lanthanum titanium phosphate coated magnesium doped lithium cobaltate positive electrode material in example 1 of the present invention.
Fig. 2 is an SEM image of the lithium lanthanum titanium phosphate coated magnesium doped lithium cobaltate cathode material in example 1 of the present invention.
Fig. 3 is a charge-discharge cycle curve and a charge-discharge coulomb curve chart of a battery assembled by the lithium lanthanum titanium phosphate coated magnesium-doped lithium cobaltate cathode material and the preparation method thereof in example 1 of the invention.
Fig. 4 is a charge-discharge cycle curve and a charge-discharge coulomb curve chart of a battery assembled by the lithium lanthanum titanium phosphate coated magnesium-doped lithium cobaltate cathode material and the preparation method thereof in example 2 of the invention.
Fig. 5 is a charge-discharge cycle curve and a charge-discharge coulomb curve chart of a battery assembled by the lanthanum lithium titanium phosphate coated magnesium doped lithium cobaltate cathode material and the preparation method thereof in example 3 of the invention.
Fig. 6 is an SEM image of the lithium cobaltate positive electrode material of comparative example 1 of the present invention.
Fig. 7 is an SEM image of comparative example 2 magnesium-doped lithium cobaltate of the present invention.
Fig. 8 is an SEM image of comparative example 3 magnesium-doped lithium cobaltate of the present invention.
Detailed Description
In order to facilitate understanding of the invention, the invention will be described more fully and in detail with reference to the accompanying drawings and preferred embodiments, but the scope of the invention is not limited to the specific embodiments below.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention.
Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.
Example 1:
a lithium lanthanum lithium titanate coated magnesium doped lithium cobaltate cathode material takes lithium cobaltate particles as a matrix, the lithium lanthanum lithium titanate is uniformly coated on the surfaces of the lithium cobaltate particles, and magnesium is doped in the lithium cobaltate particles.
Has a chemical formula of Mg-LiCoO 2 @Li 1.3 La 0.3 Ti 1.7 (PO 4 ) 3 The coating amount of lanthanum lithium titanium phosphate is 0.6wt% of the magnesium-doped lithium cobaltate particles, and the magnesium doping content is 1mol% of the cobalt content in the cathode material.
The preparation method comprises the following steps:
(1) 0.79271g (0.01073 mol) Li is weighed 2 CO 3 And 1.6402g (0.0068 mol) Co 3 O 4 And placing the mixture in a ball milling tank, and mixing and grinding the mixture for 5 hours. And in an oxygen atmosphere, heating to 600 ℃ at the speed of 5 ℃/min, keeping for 5h, cooling to room temperature, and thus obtaining the lithium cobaltate precursor material.
(2) Weighing 0.008236g (0.204 mmol) MgO, adding the MgO into 2g (0.020435 mol) of the lithium cobaltate precursor material obtained in the step (2), grinding for 0.5h, and raising the temperature to 900 ℃ at the first stage of heating rate for secondary sintering for 10h to obtain the magnesium-doped lithium cobaltate cathode material.
(3) 0.0048mL (0.0917 mmol) of H 3 PO 4 Dissolved in 30mL of absolute ethanol and then 0.00274g (0.03974 mmol) of LiNO was added 3 And 0.003971g (0.00917 mmol) La (NO) 3 ) 3 ·6H 2 O, finally weighing 0.017686mL (0.051969 mmol) C 16 H 36 O 4 And (3) Ti. And (3) after uniformly mixing, adding 2g (0.020435 mmol) of the magnesium-doped lithium cobaltate cathode material obtained in the step (2), stirring for 6h at normal temperature, heating to 80 ℃ until the mixture is evaporated to dryness, taking out, grinding for 0.5h, heating to 600 ℃ at the speed of 5 ℃/min in an oxygen atmosphere, keeping for 6h, cooling to room temperature, and thus obtaining the titanium lanthanum lithium phosphate coated magnesium-doped lithium cobaltate cathode material.
As shown in fig. 1, the lithium lanthanum titanium phosphate coated magnesium doped lithium cobaltate cathode material and PDF card LiCoO in this embodiment 2 The characteristic peaks of (PDF # 75-0532) are coincident without the formation of a hetero-phase.
As shown in fig. 2, the SEM image of the lithium lanthanum titanate phosphate coated magnesium doped lithium cobaltate cathode material of the present embodiment has a layer of obvious coating on the surface layer.
Assembling the battery: 0.08g of the lithium lanthanum titanium phosphate-coated magnesium-doped lithium cobalt oxide positive electrode material obtained in the embodiment is weighed, 0.01g of acetylene black serving as a conductive agent and 0.01g of PVDF polyvinylidene fluoride serving as a binder are added, and N-methylpyrrolidone is used as a solventMixing and grinding the agents to form a positive electrode material; coating the obtained anode material on the surface of an aluminum foil to prepare a pole piece; in a closed glove box filled with argon, the electrode plate is taken as a positive electrode, a metal lithium plate is taken as a negative electrode, a microporous polypropylene film is taken as a diaphragm, and 1mol/LLIPF 6 EC: DMC: DEC (volume ratio 1.
As shown in fig. 3, in the battery assembled by the lanthanum lithium titanium phosphate coated magnesium-doped lithium cobaltate cathode material and the preparation method thereof obtained in this embodiment, the first discharge specific capacity is 192.6mAh/g, the charge specific capacity is 200.4mAh/g, and the first charge-discharge coulombic efficiency is 96.15% under the conditions that the charge-discharge voltage is 2.7-4.5v and the current density is 0.1c (1c =200ma/g). Under the current density of 1C, the initial discharge specific capacity is 191.6mAh/g, the charge specific capacity is 195.2mAh/g, the initial charge-discharge coulombic efficiency is 98.2%, after the current density of 1C is cycled for 100 circles, the discharge specific capacity can still reach 181.8mAh/g, and the capacity retention rate is 94.89%. The method for coating the magnesium-doped lithium cobaltate cathode material with lanthanum lithium titanium phosphate in the embodiment is favorable for the transportation of lithium ions in the charging and discharging processes, and has stable discharging specific capacity, charging and discharging performance, coulombic efficiency and good cycle performance.
Example 2:
a lithium lanthanum lithium phosphate coated magnesium-doped lithium cobaltate cathode material is a lithium lanthanum lithium phosphate coated magnesium-doped lithium cobaltate cathode material, lithium cobaltate particles are used as a matrix, lithium lanthanum phosphate is uniformly coated on the surfaces of the lithium cobaltate particles, and magnesium is doped in the lithium cobaltate particles.
Has a chemical formula of Mg-LiCoO 2 @Li 1.3 La 0.3 Ti 1.7 (PO 4 ) 3 The coating amount of the lanthanum lithium titanium phosphate is 0.9wt% of the magnesium-doped lithium cobaltate particles, and the magnesium doping content is 1mol% of the cobalt content in the cathode material.
The preparation method comprises the following steps:
(1) 0.79271g (0.01073 mol) Li is weighed 2 CO 3 With 1.6402g (0.0068 mol) Co 3 O 4 And putting the mixture into a ball milling tank, and mixing and grinding for 5 hours. Heating to 600 deg.C at a rate of 5 deg.C/min in oxygen atmosphere for 5h, cooling to room temperatureAnd obtaining the lithium cobaltate precursor material.
(2) Weighing 0.008236g (0.204 mmol) MgO, adding the MgO into 2g (0.020435 mol) of the lithium cobaltate precursor material obtained in the step (2), grinding for 0.5h, and raising the temperature to 900 ℃ at the first stage of heating rate for secondary sintering for 10h to obtain the magnesium-doped lithium cobaltate cathode material.
(3) 0.0072mL (0.13756 mmol) of H 3 PO 4 Dissolved in 35mL of absolute ethanol, and 0.00411g (0.059612 mmol) of LiNO was added 3 And 0.0059567g (0.013757 mmol) La (NO) 3 ) 3 ·6H 2 O, finally weighing 0.026529mL (0.077954 mmol) C 16 H 36 O 4 And (3) Ti. And (3) after uniformly mixing, adding 2g (0.020435 mmol) of the magnesium-doped lithium cobaltate cathode material obtained in the step (2), stirring for 6h at normal temperature, heating to 80 ℃ until the mixture is evaporated to dryness, taking out, grinding for 0.5h, heating to 600 ℃ at the speed of 5 ℃/min in an oxygen atmosphere, keeping for 6h, cooling to room temperature, and thus obtaining the titanium lanthanum lithium phosphate coated magnesium-doped lithium cobaltate cathode material.
Through detection, the lithium lanthanum titanium phosphate coated magnesium-doped lithium cobaltate cathode material and the PDF card LiCoO in the embodiment 2 The characteristic peaks of (PDF # 75-0532) are coincident without the formation of a hetero-phase.
Through detection, in the SEM image of the lithium lanthanum titanium phosphate coated magnesium-doped lithium cobaltate cathode material of the present embodiment, a layer of obvious coating is formed on the surface layer.
Assembling the battery: the same as in example 1.
As shown in fig. 4, in the battery assembled by the lanthanum lithium titanium phosphate coated magnesium-doped lithium cobaltate cathode material and the preparation method thereof obtained in this embodiment, the first discharge specific capacity is 195.5mAh/g, the charge specific capacity is 204.6mAh/g, and the first charge-discharge coulombic efficiency is 95.57% under the charge-discharge voltage of 2.7-4.5v and the current density of 0.1c (1c =200ma/g). Under the current density of 1C, the first discharge specific capacity is 184.2mAh/g, the charge specific capacity is 195.5mAh/g, the first charge-discharge coulombic efficiency is 97.96%, after the current density of 1C is cycled for 100 circles, the discharge specific capacity can still reach 175.3mAh/g, and the capacity retention rate is 95.17%. The method for coating the magnesium-doped lithium cobaltate cathode material with lanthanum lithium titanium phosphate in the embodiment is favorable for the transportation of lithium ions in the charging and discharging processes, and has stable discharging specific capacity, charging and discharging performance, coulombic efficiency and good cycle performance.
Example 3:
a lithium lanthanum lithium titanate coated magnesium doped lithium cobaltate cathode material is characterized in that lithium cobaltate particles are used as a matrix, lithium lanthanum titanate is uniformly coated on the surfaces of the lithium cobaltate particles, and magnesium is doped in the lithium cobaltate particles.
Has a chemical formula of Mg-LiCoO 2 @Li 1.2 La 0.2 Ti 1.8 (PO 4 ) 3 The coating amount of lanthanum lithium titanium phosphate is 0.3wt% of the magnesium-doped lithium cobaltate particles, and the magnesium doping content is 1.2mol% of the cobalt content in the cathode material.
The preparation method comprises the following steps:
(1) 0.40013g (0.0054 mol) Li are weighed 2 CO 3 And 0.8201g (0.0034 mol) Co 3 O 4 And putting the mixture into a ball milling tank, and mixing and grinding for 5 hours. And in an oxygen atmosphere, heating to 600 ℃ at the speed of 5 ℃/min, keeping for 5h, cooling to room temperature, and thus obtaining the lithium cobaltate precursor material.
(2) Weighing 0.00494g (0.12 mmol) MgO, adding the MgO into 1g (0.01022 mol) of the lithium cobaltate precursor material obtained in the step (2), grinding for 0.5h, and raising the temperature to 900 ℃ at the first stage of heating rate for secondary sintering for 10h to obtain the magnesium-doped lithium cobaltate cathode material.
(3) 0.0024mL (0.046049 mmol) of H 3 PO 4 Dissolved in 25mL of absolute ethanol, and then 0.00127g (0.018419 mmol) of LiNO was added 3 And 0.001329g (0.000307 mmol) La (NO) 3 ) 3 ·6H 2 O, finally weighing 0.009403mL (0.047049 mmol) C 16 H 36 O 4 And (3) Ti. And (3) uniformly mixing, adding 1g (0.01022 mol) of the magnesium-doped lithium cobaltate cathode material obtained in the step (2), stirring at normal temperature for 6h, heating to 80 ℃ until the mixture is evaporated to dryness, taking out, grinding for 0.5h, heating to 600 ℃ at the speed of 5 ℃/min in an oxygen atmosphere, keeping for 6h, cooling to room temperature, and thus obtaining the titanium lanthanum lithium phosphate coated magnesium-doped lithium cobaltate cathode material.
Through detection, the lithium lanthanum titanium phosphate coated magnesium-doped lithium cobaltate cathode material and the PDF card LiCoO in the embodiment 2 The characteristic peaks of (PDF # 75-0532) are coincident without the formation of a hetero-phase.
Through detection, in the SEM image of the lithium lanthanum titanium phosphate coated magnesium-doped lithium cobaltate cathode material of the present embodiment, a layer of obvious coating is formed on the surface layer.
Assembling the battery: the same as in example 1.
As shown in fig. 5, in the battery assembled by the lanthanum lithium titanium phosphate coated magnesium-doped lithium cobaltate cathode material and the preparation method thereof obtained in this embodiment, the first discharge specific capacity is 188.5mAh/g, the charge specific capacity is 197.4mAh/g, and the first charge-discharge coulombic efficiency is 95.49% under the charge-discharge voltage of 2.7-4.5v and the current density of 0.1c (1c = 200ma/g). Under the current density of 1C, the initial discharge specific capacity is 182.2mAh/g, the charge specific capacity is 185.5mAh/g, the initial charge-discharge coulombic efficiency is 98.24%, after the current density of 1C is cycled for 100 circles, the discharge specific capacity can still reach 173mAh/g, and the capacity retention rate is 94.95%. The method for coating the magnesium-doped lithium cobaltate positive electrode material with lanthanum lithium titanium phosphate in the embodiment is favorable for transportation of lithium ions in the charging and discharging processes, and has stable discharging specific capacity, charging and discharging performance, coulombic efficiency and good cycle performance.
Comparative example 1:
a preparation method of a lithium cobaltate positive electrode material comprises the following steps:
(1) 0.79271g (0.01073 mol) Li is weighed 2 CO 3 With 1.6402g (0.0068 mol) Co 3 O 4 And putting the mixture into a ball milling tank, and mixing and grinding for 5 hours.
(2) And (2) heating the uniformly mixed material obtained in the step (1) to 600 ℃ at the speed of 5 ℃/min in an oxygen atmosphere, keeping for 5h, cooling to room temperature, taking out the material, grinding for 30min, heating to 900 ℃ at the first-stage heating speed, and sintering for 10h for the second time to obtain the lithium cobaltate cathode material.
Through detection, the lithium cobaltate cathode material and the PDF card LiCoO of the embodiment 2 The characteristic peaks of (PDF # 75-0532) were consistent without the formation of a hetero-phase.
As shown in fig. 6, SEM image of the lithium cobaltate positive electrode material of the present example.
Assembling the battery: the same as in example 1.
Through detection, the lithium cobaltate positive electrode material obtained in the comparative example and the battery assembled by the preparation method of the lithium cobaltate positive electrode material have the first discharge specific capacity of 192mAh/g, the charge specific capacity of 203.8mAh/g and the first charge-discharge coulombic efficiency of 94.2% under the conditions that the charge-discharge voltage is 2.7-4.5V and the current density is 0.1C (1C=200mA/g). Under the current density of 1C, the first discharge specific capacity is 185.5mAh/g, the charge specific capacity is 190.2mAh/g, after the current density of 1C is cycled for 100 circles, the discharge specific capacity is attenuated to 134mAh/g, and the capacity retention rate is only 72.24%.
Comparative example 2:
a preparation method of a magnesium-doped lithium cobaltate cathode material comprises the following steps:
(1) 0.79271g (0.01073 mol) Li is weighed 2 CO 3 And 1.6402g (0.0068 mol) Co 3 O 4 And putting the mixture into a ball milling tank, and mixing and grinding for 5 hours.
(2) And (2) heating the uniformly mixed material obtained in the step (1) to 600 ℃ at the speed of 5 ℃/min in an oxygen atmosphere, keeping for 5h, cooling to room temperature, and thus obtaining the lithium cobaltate precursor material.
(3) Weighing 0.008236g (0.000204 mol) MgO, adding the MgO into 2g (0.020435 mol) of the lithium cobaltate precursor material obtained in the step (2), grinding for 0.5h, and raising the temperature to 900 ℃ at a first-stage heating rate for secondary sintering for 10h to obtain the magnesium-doped lithium cobaltate cathode material.
Through detection, the lithium cobaltate positive electrode material and PDF card LiCoO of the embodiment 2 The characteristic peaks of (PDF # 75-0532) are coincident without the formation of a hetero-phase.
As shown in fig. 7, SEM image of the magnesium-doped lithium cobaltate cathode material of the present example.
Assembling the battery: the same as in example 1.
Through detection, the initial discharge specific capacity of the battery assembled by the magnesium-doped lithium cobaltate positive electrode material and the preparation method thereof in the comparative example is 190.6mAh/g, the charge specific capacity is 203.1mAh/g, and the initial charge-discharge coulombic efficiency is 93.85% under the charge-discharge voltage of 2.7-4.5V and the current density of 0.1C (1C =200mA/g). Under the current density of 1C, the first discharge specific capacity is 181.6mAh/g, the charge specific capacity is 186.3mAh/g, after the current density of 1C is cycled for 100 circles, the discharge specific capacity is attenuated to 152.3mAh/g, and the capacity retention rate is 83.87%.
Comparative example 3:
a preparation method of a magnesium-doped lithium cobaltate cathode material comprises the following steps:
(1) 0.40013g (0.005415 mol) Li is weighed 2 CO 3 And 0.82011g (0.0034057 mol) Co 3 O 4 And putting the mixture into a ball milling tank, and mixing and grinding for 5 hours.
(2) And (2) heating the uniformly mixed material obtained in the step (1) to 600 ℃ at the speed of 5 ℃/min in an oxygen atmosphere, keeping for 5h, cooling to room temperature, and thus obtaining the lithium cobaltate precursor material.
(3) Weighing 0.00494g (0.00012 mol) MgO, adding the MgO into 1g (0.01022 mol) of the lithium cobaltate precursor material obtained in the step (2), grinding for 0.5h, and raising the temperature to 900 ℃ at the first stage of heating rate for secondary sintering for 10h to obtain the magnesium-doped lithium cobaltate cathode material.
Through detection, the lithium cobaltate positive electrode material and PDF card LiCoO of the embodiment 2 The characteristic peaks of (PDF # 75-0532) were consistent without the formation of a hetero-phase.
As shown in fig. 8, SEM image of the magnesium-doped lithium cobaltate cathode material of the present example.
Assembling the battery: the same as in example 1.
Through detection, the magnesium-doped lithium cobaltate cathode material obtained in the comparative example and the battery assembled by the preparation method thereof have the first discharge specific capacity of 182mAh/g, the charge specific capacity of 193.2mAh/g and the first charge-discharge coulombic efficiency of 94.2% under the charge-discharge voltage of 2.7-4.5V and the current density of 0.1C (1C = 200mA/g). Under the current density of 1C, the initial discharge specific capacity is 181.1mAh/g, the charge specific capacity is 186.4mAh/g, after the current density of 1C is cycled for 100 circles, the discharge specific capacity is attenuated to 146.2mAh/g, and the capacity retention rate is 80.73%.
Claims (10)
1. The lithium lanthanum titanium phosphate coated magnesium-doped lithium cobaltate cathode material is characterized in that lithium cobaltate particles are used as a matrix of the cathode material, lithium lanthanum titanium phosphate is uniformly coated on the surfaces of the lithium cobaltate particles, and magnesium is doped in the lithium cobaltate particles.
2. Lanthanum lithium titanium phosphate according to claim 1The magnesium-doped lithium cobaltate cathode material is characterized in that the chemical formula of the titanium lanthanum lithium phosphate-coated magnesium-doped lithium cobaltate cathode material is Mg-LiCoO 2 @Li 1+x La x Ti 2-x (PO 4 ) 3 Wherein x is more than 0.2 and less than 0.5, the coating amount of the titanium lanthanum lithium phosphate is less than 2.0wt% of the magnesium-doped lithium cobaltate particles, and the magnesium doping content is less than or equal to 1.2mol% of the cobalt content in the cathode material.
3. A preparation method of a lithium lanthanum phosphate coated magnesium-doped lithium cobaltate cathode material is characterized by comprising the following steps:
(1) Uniformly mixing a cobalt source and a lithium source, and sintering to prepare a lithium cobaltate precursor material;
(2) Mixing the lithium cobaltate precursor material obtained in the step (1) with a magnesium source, and performing secondary sintering to obtain magnesium-doped lithium cobaltate particles;
(3) And (3) dissolving a lithium source, a lanthanum source, a titanium source and a phosphorus source to prepare lanthanum lithium titanium phosphate, adding the magnesium-doped lithium cobaltate cathode material obtained in the step (2), stirring, heating, evaporating to dryness, grinding and sintering to obtain the lanthanum lithium titanium phosphate-coated magnesium-doped lithium cobaltate cathode material.
4. The method of claim 3, wherein the step (1) comprises the steps of: uniformly mixing a cobalt source and a lithium source, and sintering for the first time, wherein the molar ratio of cobalt in the cobalt source to lithium in the lithium source is 1 (1.02-1.10); the cobalt source is one or more of cobalt oxide, cobalt carbonate and cobalt acetate, and the lithium source is lithium hydroxide and/or lithium carbonate.
5. The preparation method according to claim 4, wherein the cobalt source and the lithium source are mixed by ball milling for 3 to 8 hours; the primary calcination is low-temperature calcination, the temperature is raised to 550-650 ℃ at the speed of 1-10 ℃/min, the sintering is carried out for 4-6h, and the sintering atmosphere is air or oxygen.
6. The method according to claim 3, wherein the molar amount of magnesium in the magnesium source in step (2) is less than 1% of the molar amount of cobalt in the lithium cobaltate precursor, and the magnesium source is one or more of magnesium oxide, magnesium carbonate, and magnesium hydroxide.
7. The method according to claim 3, wherein in the step (2), the lithium cobaltate precursor material and the magnesium source are mixed by ball milling or grinding, the secondary calcination is performed at a rate of 1-10 ℃/min to 800-1000 ℃, and the sintering is performed for 8-12h, wherein the sintering atmosphere is air or oxygen.
8. The preparation method according to claim 3, wherein the preparation of lithium lanthanum titanium phosphate in step (3) is specifically: adding a phosphorus source into an organic solvent, dissolving a lithium source and a lanthanum source into the organic solvent, and finally adding a titanium source, wherein the preparation process is carried out in an anhydrous environment; the lithium source is one or more of lithium nitrate, lithium acetate and lithium hydroxide; the lanthanum source is one or more of lanthanum nitrate, lanthanum chloride and lanthanum oxide; the titanium source is tetrabutyl titanate, and the phosphorus source is phosphoric acid; the solvent is organic solvent such as absolute ethyl alcohol and ethylene glycol.
9. The preparation method according to claim 3, wherein after the magnesium-doped lithium cobaltate particles are added in the step (3), the solid-to-liquid ratio is adjusted to 1 (10-50); stirring at normal temperature at the rotating speed of 300-500r/min for 6-8h; the temperature rise is that the temperature rises to 70-80 ℃ during stirring after stirring at normal temperature is finished; the evaporation is to heat and stir until the solvent is volatilized; the grinding is to grind the product after evaporation to dryness again.
10. The method of claim 3, wherein the sintering is carried out at a rate of 1-10 ℃/min up to 500-700 ℃ for 5-10h in an atmosphere of air or oxygen.
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| CN116544418B (en) * | 2023-07-07 | 2023-09-19 | 英德市科恒新能源科技有限公司 | Lithium cobalt oxide positive electrode material, preparation method thereof and battery |
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