CN113213447B - Preparation method of high-rate lithium iron phosphate positive electrode material - Google Patents
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Abstract
The invention discloses a preparation method of a high-rate lithium iron phosphate positive electrode material, which specifically comprises the following steps: s1, preparing nano lithium iron phosphate primary particles by a hydrothermal method; s2, dispersing nano lithium iron phosphate primary particles, titanium nitride nanowires and a carbon source in a solvent to prepare a suspension, and granulating to obtain lithium iron phosphate/titanium nitride nanowire composite secondary particles; and S3, calcining the lithium iron phosphate/titanium nitride nanowire composite secondary particles in an inert atmosphere to obtain the high-rate lithium iron phosphate anode material. The titanium nitride nanowire with high electrical conductivity and thermal conductivity is fully contacted with the lithium iron phosphate primary particles, so that secondary particles with a through three-dimensional electrical conduction/thermal conduction network inside are obtained, the rapid transfer of electrons inside the material is promoted, the high-rate discharge performance of the battery is improved, meanwhile, the heat dissipation inside the battery in the high-current discharge process is accelerated, and the electrochemical performance attenuation and the safety risk caused by overhigh temperature are relieved.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and relates to a preparation method of a high-rate lithium iron phosphate positive electrode material.
Background
Along with the discharge of the application markets of hybrid power, intelligent power stations, national defense, military and the like, higher requirements, in particular to the multiplying power discharge capacity, are put forward for the lithium ion battery. Lithium ion batteries used as power supplies for starting and stopping automobiles are generally required to achieve discharge rates of 20-30C, and even required to achieve discharge capacities of more than 50C in the military field. This is an urgent need for optimization and innovation of the internal critical materials of the battery and the system design.
The lithium iron phosphate material has the advantages of safety, cost, cycle life and the like, is a good choice for power batteries and energy storage batteries, but has the defects of low intrinsic conductivity and small ion diffusion coefficient, and meanwhile, the temperature rise of the battery is faster under the condition of large discharge multiplying power, and the requirements on the internal resistance and heat conduction of the battery are higher. In order to solve the problems, the conventional optimization mode of the lithium iron phosphate anode material is to carry out nanocrystallization and/or carbon coating, and good effects are obtained. However, with the continuous expansion of the current application field, the lithium iron phosphate material still needs to be continuously improved and lifted, and the development of the high-rate lithium iron phosphate material is imperative.
Disclosure of Invention
In order to solve the problems in the prior art, the invention aims to provide a preparation method of a high-rate lithium iron phosphate positive electrode material, which can effectively improve the electric conductivity/heat conductivity of the lithium iron phosphate and improve the high-rate discharge performance of the material.
In order to achieve the above purpose, the present invention provides the following technical solutions: the preparation method of the high-rate lithium iron phosphate positive electrode material specifically comprises the following steps:
s1, preparing nano lithium iron phosphate primary particles by a hydrothermal method;
s2, dispersing nano lithium iron phosphate primary particles, titanium nitride nanowires and a carbon source in a solvent, stirring to prepare a suspension, and granulating to obtain lithium iron phosphate/titanium nitride nanowire composite secondary particles;
and S3, calcining the lithium iron phosphate/titanium nitride nanowire composite secondary particles in an inert atmosphere to obtain the high-rate lithium iron phosphate anode material.
In the step S1, the temperature of the hydrothermal reaction is 150-180 ℃ and the reaction time is 8-12 h.
In the step S1, phosphoric acid, ferrous sulfate and lithium hydroxide are used as a phosphorus source, an iron source and a lithium source, polyvinylpyrrolidone serving as a dispersing agent and ascorbic acid serving as a reducing agent are added, the mixture is uniformly mixed, a hydrothermal reaction is carried out to obtain a lithium iron phosphate precipitate, and the lithium iron phosphate precipitate is centrifuged, washed and dried to obtain nano lithium iron phosphate primary particles.
Further, the mole ratio of phosphoric acid, ferrous sulfate and lithium hydroxide is 1: (0.95-1.05): (2.95-3.05).
Further, in step S2, the titanium nitride nanowire is prepared from a lithium hydroxide solution and titanium nitride nanoparticles through an alkaline thermal reaction.
In the step S2, the concentration of the lithium hydroxide solution is 8-10M, the mass ratio of the titanium nitride nano particles to the lithium hydroxide is 1 (1-20), the alkaline thermal reaction temperature is 120-180 ℃, and the reaction time is 8-24 h.
Further, in step S2, the mass ratio of the nano lithium iron phosphate primary particles, the titanium nitride nanowires and the carbon source is 1: (0.05-0.1): (0.03-0.1).
In step S2, spray granulation is adopted, the spray inlet temperature is 150-200 ℃, and the spray outlet temperature is 75-100 ℃.
Further, in step S2, the solvent is one or more of water, ethanol, and isopropanol; the carbon source is one or more of starch, glucose, phenolic resin and asphalt.
In step S3, the calcination temperature is 650-800 ℃ and the calcination time is 8-15 h.
Compared with the prior art, the invention has at least the following beneficial effects:
the invention provides a preparation method of a high-rate lithium iron phosphate positive electrode material, which comprises the steps of firstly synthesizing superfine nanoscale lithium iron phosphate primary particles with uniform particle size distribution by a hydrothermal method, and then introducing titanium nitride nanowires into the process of preparing composite secondary particles by a granulating process, wherein the composite secondary particles formed by the nano lithium iron phosphate primary particles and the titanium nitride nanowires have higher pore structures, and are favorable for infiltration of electrolyte to the positive electrode material so as to be favorable for ion transmission. Meanwhile, the titanium nitride nanowire with high electrical conductivity and thermal conductivity is fully contacted with the lithium iron phosphate primary particles, so that a through three-dimensional electrical conduction/thermal conduction network is formed inside the lithium iron phosphate/titanium nitride nanowire composite secondary particles, the rapid transfer of electrons inside the material is promoted, the internal and surface resistance of the material is reduced, and the high-rate discharge performance of the battery is improved. And meanwhile, the heat dissipation inside the battery in the heavy current discharging process is quickened, the temperature rise of the battery is favorably controlled, and the electrochemical performance attenuation and the safety risk caused by overhigh temperature are relieved. The preparation method has the advantages of simple process, stability, controllability, wide raw material sources and easy large-scale industrialized production.
The mass ratio of the invention is 1: the nano lithium iron phosphate primary particles (0.05-0.1) and the titanium nitride nanowire are mixed to prepare the high-rate lithium iron phosphate positive electrode material, under the condition of the mass ratio, the titanium nitride nanowire can be ensured to be dispersed in the nano lithium iron phosphate primary particles, and meanwhile, the capacity of the positive electrode material can not be reduced too much under the condition of improving the rate performance.
The invention adopts spray granulation, the spray granulation carries out fluidization treatment on the materials to be dried through mechanical action, the materials are dispersed into very fine particles like fog, and most of water is removed at the moment of contact with hot air, so that solid matters in the materials are dried to form spherical particles with regular shapes. By adopting spray granulation, re-agglomeration and sedimentation separation of nano lithium iron phosphate primary particles, titanium nitride nanowires and carbon sources are avoided, and the original uniformity of the suspension is maintained. And meanwhile, the spray granulation can uniformly atomize suspension, the drying speed is high, the surface area of the suspension after atomization is greatly increased, and the obtained product is spherical particles, uniform in particle size distribution and good in fluidity.
Drawings
FIG. 1 is a graph showing the discharge curve and the temperature rise curve at different rates for example 1;
fig. 2 is a discharge curve and a temperature rise curve at different magnifications of comparative example 1.
Detailed Description
The invention will be described in further detail with reference to the accompanying drawings and specific examples. It should be noted that the examples described below are only for explaining the present invention and are not intended to limit the present invention.
The preparation method of the high-rate lithium iron phosphate positive electrode material comprises the following steps:
step 1: the molar ratio was set to 1: (0.95-1.05): (2.95-3.05) taking phosphoric acid, ferrous sulfate and lithium hydroxide as a phosphorus source, an iron source and a lithium source, adding a dispersing agent polyvinylpyrrolidone and a reducing agent ascorbic acid, uniformly mixing, transferring to a reaction kettle, carrying out hydrothermal reaction for 8-12 h at 150-180 ℃ to obtain lithium iron phosphate precipitation liquid, centrifuging, washing and drying to obtain nano lithium iron phosphate primary particles;
step 2: uniformly mixing titanium nitride nano particles and lithium hydroxide according to the mass ratio of 1 (1-20) by taking a lithium hydroxide solution with the concentration of 8-10M as a reaction medium, transferring the mixture into a reaction kettle, performing alkaline thermal reaction for 8-24 hours at 120-180 ℃ to obtain a precipitation solution, and performing acid washing, water washing, centrifugation and drying to obtain the titanium nitride nano wire;
step 3: the nano lithium iron phosphate primary particles prepared in the step 1, the titanium nitride nanowires prepared in the step 2 and a carbon source are mixed according to the mass ratio of 1: (0.05-0.1): (0.03-0.1) dispersing the materials in a solvent, stirring uniformly to prepare a suspension, spraying and granulating the suspension, wherein the spraying inlet temperature is 150-200 ℃, the spraying outlet temperature is 75-100 ℃, and calcining the suspension for 8-15 hours at 650-800 ℃ in an inert atmosphere after granulating, so that a carbon source is firmly coated on the surface of the lithium iron phosphate/titanium nitride nanowire composite secondary particles, and the high-rate lithium iron phosphate anode material is prepared.
Preferably, the solvent is one or more of water, ethanol, and isopropanol.
Preferably, the carbon source is one or more of starch, glucose, phenolic resin and asphalt.
Example 1
The preparation method of the high-rate lithium iron phosphate positive electrode material comprises the following steps:
step 1: taking phosphoric acid, ferrous sulfate and lithium hydroxide as a phosphorus source, an iron source and a lithium source, wherein the molar ratio is 1:0.95:2.95. adding a dispersing agent polyvinylpyrrolidone and a reducing agent ascorbic acid, uniformly mixing, transferring to a reaction kettle, carrying out hydrothermal reaction at 150 ℃ for 8 hours to obtain a lithium iron phosphate precipitate, centrifuging, washing and drying to obtain nano lithium iron phosphate primary particles;
step 2: adding titanium nitride nano particles into an 8M lithium hydroxide solution serving as a reaction medium according to the mass ratio of the titanium nitride nano particles to the lithium hydroxide of 1:1, uniformly mixing, transferring to a reaction kettle, carrying out alkaline thermal reaction at 120 ℃ for 8 hours to obtain a precipitation solution, and carrying out acid washing, water washing, centrifugation and drying to obtain titanium nitride nano wires;
step 3: the method comprises the steps of mixing nano lithium iron phosphate primary particles, titanium nitride nanowires and starch according to a mass ratio of 1:0.05: dispersing 0.03 in water, stirring uniformly to prepare a suspension, spraying and granulating the suspension, wherein the spraying inlet temperature is 150 ℃, and the spraying outlet temperature is 75 ℃, so as to obtain the lithium iron phosphate/titanium nitride nanowire composite secondary particles.
Step 4: and (3) calcining the lithium iron phosphate/titanium nitride nanowire composite secondary particles prepared in the step (3) for 8 hours at 650 ℃ in an inert atmosphere to prepare the final high-rate lithium iron phosphate positive electrode material.
Example 2
The preparation method of the high-rate lithium iron phosphate positive electrode material comprises the following steps:
step 1: taking phosphoric acid, ferrous sulfate and lithium hydroxide as a phosphorus source, an iron source and a lithium source, wherein the molar ratio is 1:1:3. adding a dispersing agent polyvinylpyrrolidone and a reducing agent ascorbic acid, uniformly mixing, transferring to a reaction kettle, carrying out hydrothermal reaction at 170 ℃ for 10 hours to obtain a lithium iron phosphate precipitate, centrifuging, washing and drying to obtain nano lithium iron phosphate primary particles;
step 2: adding titanium nitride nano particles into a 9M lithium hydroxide solution serving as a reaction medium according to the mass ratio of the titanium nitride nano particles to the lithium hydroxide of 1:5, uniformly mixing, transferring to a reaction kettle, carrying out alkaline thermal reaction at 150 ℃ for 20 hours to obtain a precipitate, and carrying out acid washing, water washing, centrifugation and drying to obtain titanium nitride nano wires;
step 3: the method comprises the steps of mixing nano lithium iron phosphate primary particles, titanium nitride nanowires and phenolic resin according to a mass ratio of 1:0.1: dispersing 0.05 in ethanol, stirring uniformly to obtain suspension, spraying and granulating the suspension, wherein the spraying inlet temperature is 180 ℃, and the spraying outlet temperature is 80 ℃, so as to obtain the lithium iron phosphate/titanium nitride nanowire composite secondary particles.
Step 4: and (3) calcining the lithium iron phosphate/titanium nitride nanowire composite secondary particles prepared in the step (3) for 10 hours at 700 ℃ in an inert atmosphere to prepare the final high-rate lithium iron phosphate positive electrode material.
Example 3
The preparation method of the high-rate lithium iron phosphate positive electrode material comprises the following steps:
step 1: taking phosphoric acid, ferrous sulfate and lithium hydroxide as a phosphorus source, an iron source and a lithium source, wherein the molar ratio is 1:1.05:3.05. adding a dispersing agent polyvinylpyrrolidone and a reducing agent ascorbic acid, uniformly mixing, transferring to a reaction kettle, carrying out hydrothermal reaction at 180 ℃ for 12 hours to obtain a lithium iron phosphate precipitate, centrifuging, washing and drying to obtain nano lithium iron phosphate primary particles;
step 2: adding titanium nitride nano particles into a 10M lithium hydroxide solution serving as a reaction medium according to the mass ratio of the titanium nitride nano particles to the lithium hydroxide of 1:20, uniformly mixing, transferring to a reaction kettle, performing alkali thermal reaction at 180 ℃ for 24 hours to obtain a precipitate, and performing acid washing, water washing, centrifugation and drying to obtain titanium nitride nano wires;
step 3: the method comprises the steps of mixing nano lithium iron phosphate primary particles, titanium nitride nanowires and asphalt according to a mass ratio of 1:0.1:0.1 is dispersed in isopropanol, and is stirred uniformly to prepare suspension, the suspension is sprayed and granulated, the spraying inlet temperature is 200 ℃, the spraying outlet temperature is 100 ℃, and the lithium iron phosphate/titanium nitride nanowire composite secondary particles are obtained.
Step 4: and calcining the lithium iron phosphate/titanium nitride nanowire composite secondary particles for 15 hours at 800 ℃ in an inert atmosphere to obtain the final high-rate lithium iron phosphate positive electrode material.
Example 4
The preparation method of the high-rate lithium iron phosphate positive electrode material comprises the following steps:
step 1: taking phosphoric acid, ferrous sulfate and lithium hydroxide as a phosphorus source, an iron source and a lithium source, wherein the molar ratio is 1:1:3. adding a dispersing agent polyvinylpyrrolidone and a reducing agent ascorbic acid, uniformly mixing, transferring to a reaction kettle, carrying out hydrothermal reaction at 160 ℃ for 10 hours to obtain a lithium iron phosphate precipitate, centrifuging, washing and drying to obtain nano lithium iron phosphate primary particles;
step 2: adding titanium nitride nano particles into a 9M lithium hydroxide solution serving as a reaction medium according to the mass ratio of the titanium nitride nano particles to the lithium hydroxide of 1:10, uniformly mixing, transferring to a reaction kettle, performing alkaline thermal reaction at 130 ℃ for 22 hours to obtain a precipitation solution, and performing acid washing, water washing, centrifugation and drying to obtain titanium nitride nano wires;
step 3: the method comprises the steps of mixing nano lithium iron phosphate primary particles, titanium nitride nanowires and a carbon source (a mixture of phenolic resin and glucose) according to a mass ratio of 1:0.5:0.1 is dispersed in a mixed solution of ethanol and water, the mixture is stirred uniformly to prepare a suspension, the suspension is sprayed and granulated, the spraying inlet temperature is 160 ℃, and the spraying outlet temperature is 90 ℃, so that the lithium iron phosphate/titanium nitride nanowire composite secondary particles are obtained.
Step 4: and (3) calcining the lithium iron phosphate/titanium nitride nanowire composite secondary particles prepared in the step (3) for 12 hours at 750 ℃ in an inert atmosphere to prepare the final high-rate lithium iron phosphate positive electrode material.
Example 5
The preparation method of the high-rate lithium iron phosphate positive electrode material comprises the following steps:
step 1: taking phosphoric acid, ferrous sulfate and lithium hydroxide as a phosphorus source, an iron source and a lithium source, wherein the molar ratio is 1:1.05:3.05. adding a dispersing agent polyvinylpyrrolidone and a reducing agent ascorbic acid, uniformly mixing, transferring to a reaction kettle, carrying out hydrothermal reaction at 180 ℃ for 12 hours to obtain a lithium iron phosphate precipitate, centrifuging, washing and drying to obtain nano lithium iron phosphate primary particles;
step 2: adding titanium nitride nano particles into a 10M lithium hydroxide solution serving as a reaction medium according to the mass ratio of the titanium nitride nano particles to the lithium hydroxide of 1:15, uniformly mixing, transferring to a reaction kettle, performing alkaline thermal reaction at 130 ℃ for 15 hours to obtain a precipitate, and performing acid washing, water washing, centrifugation and drying to obtain titanium nitride nano wires;
step 3: the method comprises the steps of mixing nano lithium iron phosphate primary particles, titanium nitride nanowires and a carbon source (mixture of asphalt, starch and glucose) according to a mass ratio of 1:0.07: dispersing 0.05 in a mixture of isopropyl alcohol and water, stirring uniformly to prepare a suspension, spraying and granulating the suspension, wherein the spraying inlet temperature is 200 ℃, and the spraying outlet temperature is 100 ℃, so as to obtain the lithium iron phosphate/titanium nitride nanowire composite secondary particles.
Step 4: and calcining the lithium iron phosphate/titanium nitride nanowire composite secondary particles for 15 hours at 650 ℃ in an inert atmosphere to obtain the final high-rate lithium iron phosphate positive electrode material.
Example 6
The preparation method of the high-rate lithium iron phosphate positive electrode material comprises the following steps:
step 1: taking phosphoric acid, ferrous sulfate and lithium hydroxide as a phosphorus source, an iron source and a lithium source, wherein the molar ratio is 1:0.95:2.95. adding a dispersing agent polyvinylpyrrolidone and a reducing agent ascorbic acid, uniformly mixing, transferring to a reaction kettle, carrying out hydrothermal reaction at 165 ℃ for 10 hours to obtain a lithium iron phosphate precipitate, centrifuging, washing and drying to obtain nano lithium iron phosphate primary particles;
step 2: adding titanium nitride nano particles into an 8M lithium hydroxide solution serving as a reaction medium according to the mass ratio of the titanium nitride nano particles to the lithium hydroxide of 1:5, uniformly mixing, transferring the mixture into a reaction kettle, performing alkaline thermal reaction at 170 ℃ for 20 hours to obtain a precipitation solution, and performing acid washing, water washing, centrifugation and drying to obtain titanium nitride nano wires;
step 3: the method comprises the steps of mixing nano lithium iron phosphate primary particles, titanium nitride nanowires and a carbon source (a mixture of starch, phenolic resin and glucose) according to a mass ratio of 1:0.1:0.07 is dispersed in a mixed solution of water, ethanol and isopropanol, the mixed solution is stirred uniformly to prepare a suspension, the suspension is sprayed and granulated, the spraying inlet temperature is 200 ℃, and the outlet temperature is 100 ℃, so that the lithium iron phosphate/titanium nitride nanowire composite secondary particles are obtained.
Step 4: and (3) calcining the lithium iron phosphate/titanium nitride nanowire composite secondary particles prepared in the step (3) for 8 hours at 650 ℃ in an inert atmosphere to prepare the final high-rate lithium iron phosphate positive electrode material.
Comparative example 1
Mixing ferric phosphate, lithium carbonate and starch uniformly according to a molar ratio of 1:3:0.5, adding ethanol, ball milling for 1h, introducing nitrogen, pre-treating for 5h at 200 ℃, and sintering for 12h at 650 ℃ to obtain the lithium iron phosphate material.
Performance testing
Taking a 5Ah laminated soft package battery as an example, the lithium iron phosphate material prepared in the example 1 and the comparative example 1 is used as a positive electrode, graphite is used as a negative electrode, the negative electrode excess coefficient is 1.08, and the positive electrode slurry (mass ratio): lithium iron phosphate: super P: carbon nanotubes: pvdf=95: 2:1:2, negative electrode slurry (mass ratio): graphite: super P: CMC: sbr=94: 2:1.5:2.5, the performance results obtained are shown in Table 1, FIG. 1 and FIG. 2.
Table 1 shows the capacity retention and temperature rise at different rates for example 1 and comparative example 1
Table 1 shows the capacity retention and the temperature rise at different rates for example 1 and comparative example 1. Fig. 1 is a discharge curve and a temperature rise curve of example 1 at different rates, and fig. 2 is a discharge curve and a temperature rise curve of comparative example 1 at different rates, and as can be seen from table 1, fig. 1 and fig. 2, the capacity retention rate of comparative example 1 is only 89.6% and the temperature rise is 49.7 ℃ under the 20C high current discharge condition. Example 1 under 20C discharge conditions, capacity retention was able to reach 97.1% with a temperature rise of only 23.9 ℃. The capacity retention rate of example 1 was increased by 7.5% and the temperature rise was reduced by 25.8 ℃ compared to comparative example 1. The lithium iron phosphate cathode material preparation method adopted in example 1 is shown to have obvious effects on capacity retention and temperature rise improvement of the battery under high-rate discharge.
The embodiments described above are preferred modes of the present invention. It should be noted that appropriate changes and modifications to the above-described embodiments may be made by those skilled in the art in light of the foregoing disclosure and teachings of the invention without departing from the principles of the invention. Such variations and modifications are intended to be included within the scope of the present invention.
Claims (7)
1. The preparation method of the high-rate lithium iron phosphate positive electrode material is characterized by comprising the following steps of:
s1, preparing nano lithium iron phosphate primary particles by a hydrothermal method;
s2, dispersing nano lithium iron phosphate primary particles, titanium nitride nanowires and a carbon source in a solvent to prepare a suspension, and granulating to obtain lithium iron phosphate/titanium nitride nanowire composite secondary particles;
s3, calcining the lithium iron phosphate/titanium nitride nanowire composite secondary particles in an inert atmosphere to obtain a high-rate lithium iron phosphate positive electrode material;
in the step S2, spray granulation is adopted for granulation, the spray inlet temperature is 150-200 ℃, and the outlet temperature is 75-100 ℃;
in the step S2, the mass ratio of the nano lithium iron phosphate primary particles to the titanium nitride nanowires to the carbon source is 1: (0.05-0.1): (0.03-0.1);
in the step S3, the calcination temperature is 650-800 ℃ and the calcination time is 8-15 h.
2. The preparation method of the high-rate lithium iron phosphate positive electrode material according to claim 1, wherein in the step S1, the temperature of the hydrothermal reaction is 150-180 ℃, and the reaction time is 8-12 h.
3. The preparation method of the high-rate lithium iron phosphate positive electrode material according to claim 1, wherein in the step S1, phosphoric acid, ferrous sulfate and lithium hydroxide are used as a phosphorus source, an iron source and a lithium source, polyvinylpyrrolidone serving as a dispersing agent and ascorbic acid serving as a reducing agent are added, the mixture is uniformly mixed, a hydrothermal reaction is carried out to obtain a lithium iron phosphate precipitate, and the lithium iron phosphate precipitate is centrifuged, washed and dried to obtain nano lithium iron phosphate primary particles.
4. The method for preparing a high-rate lithium iron phosphate positive electrode material according to claim 3, wherein the molar ratio of phosphoric acid to ferrous sulfate to lithium hydroxide is 1: (0.95-1.05): (2.95-3.05).
5. The method for preparing a high-rate lithium iron phosphate positive electrode material according to claim 1, wherein in the step S2, the titanium nitride nanowires are prepared from a lithium hydroxide solution and titanium nitride nanoparticles by an alkaline thermal reaction.
6. The preparation method of the high-rate lithium iron phosphate positive electrode material according to claim 5, wherein in the step S2, the concentration of a lithium hydroxide solution is 8-10M, the mass ratio of titanium nitride nano particles to lithium hydroxide is 1 (1-20), the alkaline thermal reaction temperature is 120-180 ℃, and the reaction time is 8-24 hours.
7. The method for preparing a high-rate lithium iron phosphate positive electrode material according to claim 1, wherein in the step S2, the solvent is one or more of water, ethanol and isopropanol; the carbon source is one or more of starch, glucose, phenolic resin and asphalt.
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