CN115084529A - Surface modification method of lithium iron phosphate positive electrode material - Google Patents
Surface modification method of lithium iron phosphate positive electrode material Download PDFInfo
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- CN115084529A CN115084529A CN202210980665.8A CN202210980665A CN115084529A CN 115084529 A CN115084529 A CN 115084529A CN 202210980665 A CN202210980665 A CN 202210980665A CN 115084529 A CN115084529 A CN 115084529A
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- iron phosphate
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- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 title claims abstract description 55
- 238000002715 modification method Methods 0.000 title claims abstract description 17
- 239000007774 positive electrode material Substances 0.000 title claims abstract description 16
- 239000000463 material Substances 0.000 claims abstract description 39
- WQZGKKKJIJFFOK-GASJEMHNSA-N Glucose Natural products OC[C@H]1OC(O)[C@H](O)[C@@H](O)[C@@H]1O WQZGKKKJIJFFOK-GASJEMHNSA-N 0.000 claims abstract description 18
- 239000010405 anode material Substances 0.000 claims abstract description 18
- 239000008103 glucose Substances 0.000 claims abstract description 18
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims abstract description 14
- 238000000034 method Methods 0.000 claims abstract description 9
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 4
- 238000005303 weighing Methods 0.000 claims abstract description 4
- 239000000243 solution Substances 0.000 claims description 51
- 238000002425 crystallisation Methods 0.000 claims description 48
- 230000008025 crystallization Effects 0.000 claims description 48
- 230000015572 biosynthetic process Effects 0.000 claims description 40
- 238000003786 synthesis reaction Methods 0.000 claims description 40
- 238000010438 heat treatment Methods 0.000 claims description 35
- 239000007788 liquid Substances 0.000 claims description 29
- 239000013078 crystal Substances 0.000 claims description 24
- 239000012153 distilled water Substances 0.000 claims description 23
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 23
- 238000003756 stirring Methods 0.000 claims description 22
- 238000002347 injection Methods 0.000 claims description 19
- 239000007924 injection Substances 0.000 claims description 19
- CIWBSHSKHKDKBQ-JLAZNSOCSA-N Ascorbic acid Chemical compound OC[C@H](O)[C@H]1OC(=O)C(O)=C1O CIWBSHSKHKDKBQ-JLAZNSOCSA-N 0.000 claims description 14
- 238000001035 drying Methods 0.000 claims description 11
- 238000009423 ventilation Methods 0.000 claims description 11
- 235000017166 Bambusa arundinacea Nutrition 0.000 claims description 9
- 235000017491 Bambusa tulda Nutrition 0.000 claims description 9
- 241001330002 Bambuseae Species 0.000 claims description 9
- 235000015334 Phyllostachys viridis Nutrition 0.000 claims description 9
- 239000011425 bamboo Substances 0.000 claims description 9
- 238000005498 polishing Methods 0.000 claims description 9
- 238000012545 processing Methods 0.000 claims description 8
- 230000002194 synthesizing effect Effects 0.000 claims description 8
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 7
- 239000004372 Polyvinyl alcohol Substances 0.000 claims description 7
- 229960005070 ascorbic acid Drugs 0.000 claims description 7
- 235000010323 ascorbic acid Nutrition 0.000 claims description 7
- 239000011668 ascorbic acid Substances 0.000 claims description 7
- 229920002451 polyvinyl alcohol Polymers 0.000 claims description 7
- 239000000654 additive Substances 0.000 claims description 6
- 150000004676 glycans Chemical class 0.000 claims description 6
- 238000002156 mixing Methods 0.000 claims description 6
- 229920001282 polysaccharide Polymers 0.000 claims description 6
- 239000005017 polysaccharide Substances 0.000 claims description 6
- 238000004321 preservation Methods 0.000 claims description 6
- 239000000126 substance Substances 0.000 claims description 6
- 239000003381 stabilizer Substances 0.000 claims description 5
- 230000000630 rising effect Effects 0.000 claims description 4
- 229920002472 Starch Polymers 0.000 claims description 3
- 230000006978 adaptation Effects 0.000 claims description 3
- 238000001514 detection method Methods 0.000 claims description 3
- 238000011049 filling Methods 0.000 claims description 3
- 239000000203 mixture Substances 0.000 claims description 3
- 229910052757 nitrogen Inorganic materials 0.000 claims description 3
- 239000008107 starch Substances 0.000 claims description 3
- 235000019698 starch Nutrition 0.000 claims description 3
- 230000000996 additive effect Effects 0.000 claims description 2
- 229910052710 silicon Inorganic materials 0.000 claims 1
- 239000010703 silicon Substances 0.000 claims 1
- 125000003003 spiro group Chemical group 0.000 claims 1
- 229910010707 LiFePO 4 Inorganic materials 0.000 abstract description 31
- 239000002245 particle Substances 0.000 abstract description 18
- 238000012986 modification Methods 0.000 abstract description 14
- 230000004048 modification Effects 0.000 abstract description 14
- 229910010710 LiFePO Inorganic materials 0.000 abstract description 12
- 229910052799 carbon Inorganic materials 0.000 abstract description 10
- 239000011248 coating agent Substances 0.000 abstract description 10
- 238000000576 coating method Methods 0.000 abstract description 10
- 238000001027 hydrothermal synthesis Methods 0.000 abstract description 10
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 abstract description 7
- -1 carbon ions Chemical class 0.000 abstract description 5
- 150000002500 ions Chemical class 0.000 abstract description 3
- 239000000047 product Substances 0.000 description 8
- 239000002994 raw material Substances 0.000 description 7
- 239000002243 precursor Substances 0.000 description 5
- 150000001768 cations Chemical class 0.000 description 4
- 239000002184 metal Substances 0.000 description 4
- 229910052751 metal Inorganic materials 0.000 description 4
- 238000004891 communication Methods 0.000 description 3
- 210000002858 crystal cell Anatomy 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 238000001914 filtration Methods 0.000 description 3
- 238000003780 insertion Methods 0.000 description 3
- 230000037431 insertion Effects 0.000 description 3
- 238000002360 preparation method Methods 0.000 description 3
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 2
- 238000000498 ball milling Methods 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 230000003028 elevating effect Effects 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 229910001416 lithium ion Inorganic materials 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 239000002210 silicon-based material Substances 0.000 description 2
- 230000000087 stabilizing effect Effects 0.000 description 2
- 239000013589 supplement Substances 0.000 description 2
- 238000001308 synthesis method Methods 0.000 description 2
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 description 1
- 230000004075 alteration Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 229910001873 dinitrogen Inorganic materials 0.000 description 1
- 239000000428 dust Substances 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 238000005086 pumping Methods 0.000 description 1
- 230000035484 reaction time Effects 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 239000004094 surface-active agent Substances 0.000 description 1
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/021—Physical characteristics, e.g. porosity, surface area
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/028—Positive electrodes
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention discloses a surface modification method of a lithium iron phosphate positive electrode material, and relates to the technical field of lithium iron phosphate batteries. The method comprises the following steps: step one, weighing LiOH & H according to the molar ratio of Li to Fe to P of 3:1.5:0.5 2 O、FeSO 4 ·7H 2 O and H 3 PO 4 . The invention uses a hydrothermal method to control LiFePO 4 The particle size of the product is LiFePO and the product is used in LiFePO 4 The outside is provided with carbon coating and LiFePO 4 The surface of the lithium iron phosphate anode material is modified by reducing the particle size, and the solution C is wrapped by adding glucose in the hydrothermal process of the lithium iron phosphate anode material, so that carbon ions in the glucose can be better mixed with LiFePO 4 The inner ions combine to form LiFePO 4 And (4) wrapping the material to finish the surface modification of the lithium iron phosphate anode material.
Description
Technical Field
The invention relates to the technical field of lithium iron phosphate batteries, in particular to a surface modification method of a lithium iron phosphate positive electrode material.
Background
To solve the problem of LiFePO 4 The very low lithium ion diffusion rate and the electronic conductivity, LiFePO 4 The modification studies of (a) mainly focus on two aspects: firstly, the LiFePO is effectively improved 4 The electron conductivity, including intrinsic conductivity and surface conductivity, of (a) is generally achieved by coating a conductive layer or doping; second, increase Li + This can be achieved by reducing the particle size, wherein the treatment by coating the conductive layer is significantly different from the doping.
The Chinese patent with the patent application number of 'CN 102544505B' discloses a surface modification method of a lithium iron phosphate anode material, which is characterized in that high-valence cations are doped into LiFePO 4 In the material, thereby increasing LiFePO 4 Intrinsic conductivity of the material, but this solution of surface modification introduces more or less carbon or other impurities while doping the metal cations, and therefore it is not clear that LiFePO 4 Is associated with doping with metal cation cations, and is additionally due to the synthesis of LiFePO 4 In the process, the particles are easy to grow freely or agglomerate, the particle size can be controlled only by adopting a low-temperature synthesis method, so that the LiFePO is controlled by using a hydrothermal method 4 The particle size of the product is as large as LiFePO, and the product is adopted in LiFePO 4 The outer is provided with a carbon coating and LiFePO 4 The surface of the lithium iron phosphate positive electrode material is modified in a manner of reducing the particle size.
Disclosure of Invention
The invention aims to provide a surface modification method of a lithium iron phosphate positive electrode material, so as to solve the problems in the background technology.
In order to achieve the purpose, the invention provides the following technical scheme: the surface modification method of the lithium iron phosphate anode material comprises the following steps:
step one, weighing LiOH & H according to the molar ratio of Li to Fe to P of 3:1.5:0.5 2 O 、FeSO 4 ·7H 2 O and H 3 PO 4 ；
Step two, firstly FeSO 4 ·7H 2 O crystal pouring treatment deviceIn the inner synthesis mechanism 1, and simultaneously adding distilled water into the synthesis mechanism 1 until FeSO is obtained 4 ·7H 2 Dissolving O in distilled water, and adding an additive into the treatment device;
step three, dripping H into the synthesis mechanism 1 3 PO 4 A solution such that the solution inside the synthesis mechanism 1 is formed as a solution a;
step four, preparing another cup of distilled water, and adding LiOH & H 2 Dissolving the O crystal in distilled water to prepare solution B, pouring the solution B into the synthesis mechanism 1, and mixing to prepare solution C;
fifthly, taking a trace amount of solution C in the synthesis mechanism for pH value detection, and adjusting the pH value of the solution C to be about 7-10 by repeatedly adding distilled water;
sixthly, starting a heating function arranged in the synthesis mechanism 1, and heating the solution C for a certain time;
seventhly, during heating treatment, adding a modified material into the synthesis mechanism 1, and starting the stirring function of the synthesis mechanism 1;
step eight, after the heating treatment is finished, standing for a period of time until the temperature of the solution C is close to the normal temperature;
step nine, a liquid pump arranged outside the processing device is utilized to convey the solution C from the synthesis mechanism to a crystallization mechanism in the processing device;
step ten, starting a temperature rising function in the crystallization mechanism 4, and drying the solution C until the solution C forms a lithium iron phosphate crystal;
step eleven, taking out the lithium iron phosphate crystal, and putting the lithium iron phosphate crystal and the dried quantitative wrapping material glucose into a planetary ball mill together for polishing treatment;
and step twelve, placing the mixture after polishing treatment in a tubular muffle furnace, filling nitrogen into the tubular muffle furnace, performing heat preservation treatment, and quantifying for a certain time to obtain the lithium iron phosphate wrapping material.
Furthermore, the content of the distilled water in the second step and the fourth step is 200ml to 400ml, the total volume of the synthesis mechanism 1 in the second step is 1.25L to 1.75L, and the total volume of the crystallization mechanism 4 in the ninth step is 2.5L to 3.5L.
Furthermore, the additives in the second step are ascorbic acid and polyvinyl alcohol, wherein the content ratio of the ascorbic acid to the polyvinyl alcohol to the distilled water in the second step is 0.25:0.35: 2.4.
Furthermore, the heating time of the sixth step is 140-220 ℃, the heating time is 1-6 h, the modified material in the seventh step is polysaccharide substance, wherein the polysaccharide substance is one of starch and glucose, the drying temperature of the tenth step is 60-85 ℃, and the drying time is 10-15 h.
Furthermore, the amount of the glucose in the eleventh step is 200 g-450 g, the polishing time in the eleventh step is 3 h-5 h, the temperature of the muffle furnace in the twelfth step is 600 ℃ -830 ℃, and the heat preservation time is 3 h-5 h.
Furthermore, the processing device in the second step includes a synthesizing mechanism 1, a liquid pump 2 and a crystallizing mechanism 4, the synthesizing mechanism 1 and the crystallizing mechanism 4 are communicated with each other through the liquid pump 2, the synthesizing mechanism includes a material injecting kit, a connecting kit and a bearing kit which are sequentially screwed, the crystallizing mechanism includes a storage component, a dial-sending component is fixedly connected to a midpoint inside the storage component, a temperature rising component is covered on a top end of the storage component, a liquid discharge pipe and a communicating pipe are respectively installed at a liquid suction end and a liquid discharge end of the liquid pump, one end of the liquid discharge pipe is fixed to a bottom end outside the connecting kit, and one end of the communicating pipe is fixed to one end outside the storage component.
Furthermore, the connection kit comprises a connection pipe, one end of the exterior of the connection pipe is fixedly connected with a liquid injection pipe communicated with the interior of the connection pipe, a heating assembly is installed inside the connection pipe, the heating assembly comprises a charging control panel, the inner wall of the charging control panel is fixed with the outer wall of the connection pipe, the inner wall of the connection pipe is fixedly connected with a power supply base, a heating resistor is installed inside the power supply base, the output end of the charging control panel is fixedly connected with a power supply wire bundle, and one end of the power supply wire bundle penetrates through the connection pipe and is fixed with the input end of the power supply base;
the material injection kit comprises an upper connecting cover, the bottom end of the upper connecting cover is in threaded connection with one end of the connecting pipe, the top of the upper connecting cover is fixedly connected with a material injection pipe, a pressure pipe and a pressure type thermometer, and the material injection pipe, the pressure pipe and the pressure type thermometer are all communicated with the inside of the upper connecting cover;
the bearing external member includes the bearing seat, and the internally mounted of bearing seat has the rotation motor, and a screw thread section of thick bamboo is installed on the top of bearing seat, the assembly breach has been seted up to the inside of a screw thread section of thick bamboo, and rotatable stirring subassembly is installed at the assembly breach to a screw thread section of thick bamboo, the stirring subassembly pass through the connecting piece with the output end of rotating the motor is fixed mutually.
Further, the stirring subassembly includes the rotation post, the bottom of rotation post outer wall with the inner wall looks sliding connection of screw thread section of thick bamboo in assembly breach department rotates the top fixedly connected with stirring piece of post, and the stirring piece is provided with a plurality ofly, and the even setting of equal angle is in the top of rotation post, the locating hole has been seted up to the central point position of rotation capital portion, the output fixedly connected with screw sleeve of rotation motor, screw sleeve pass through the locating hole with the rotation post becomes interference fit relation, the connecting piece is set screw, set screw with screw sleeve looks adaptation.
Furthermore, the storage assembly comprises a crystallization box, wherein the periphery of the bottom of the crystallization box is fixedly connected with bottom feet respectively, a containing drawer is fixedly connected among the four bottom feet, one end inside the crystallization box is provided with a communicating notch, an electronic check valve is arranged inside the communicating notch, a through pipeline is arranged between the crystallization box and the containing drawer and is arranged at the position of the communicating notch, and one end of the through pipeline penetrates through the top end of the containing drawer and is communicated with the inside of the containing drawer;
dial and send subassembly including spacing, spacing is fixed the inside middle-end of crystal box, spacing top one end fixedly connected with input motor, the output fixedly connected with screw shaft of input motor, the end of screw shaft with the other end at spacing top rotates the connection, the both sides difference fixedly connected with of spacing top one end place the arch, place the arch and place fixedly connected with stabilizer bar between the spacing top other end, sliding connection has the articulated arm between two stabilizer bars, the inside of articulated arm with the outside looks threaded connection of screw shaft, the bottom of articulated arm is pegged graft and is had the grafting arm, and the outside sliding connection of grafting arm has the stirring board.
Further, the intensification subassembly is including placing the board, places the plate cover and puts the top of crystallization box, the one end fixedly connected with of placing the board top supplies with power, places the other end at board top and has seted up multichannel ventilation breach, place the board at the ventilation breach, the output of supplying with power is fixed to be linked there is intensification resistance, the bottom fixedly connected with couple of placing the board, the couple is silicon material, and the couple is provided with a plurality ofly, wherein is provided with two couples between every two ventilation breachs, intensification resistance is installed through the couple place the bottom of board.
Compared with the prior art, the invention has the beneficial effects that:
the surface modification method of the lithium iron phosphate anode material adopts a hydrothermal method to control LiFePO 4 The particle size of the product is as large as LiFePO, and the product is adopted in LiFePO 4 The outside is provided with carbon coating and LiFePO 4 The surface of the lithium iron phosphate anode material is modified by reducing the particle size, and the solution C is wrapped by adding glucose in the hydrothermal process of the lithium iron phosphate anode material, so that carbon ions in the glucose can better react with LiFePO 4 The inner ions are combined by filtering and drying to form LiFePO 4 Ball milling, mixing and heat treating the precursor and glucose prepared additionally to finally form LiFePO 4 And (4) wrapping the material to finish the surface modification of the lithium iron phosphate anode material.
According to the surface modification method of the lithium iron phosphate anode material, the pH value of the solution C is detected, and is adjusted by adding distilled water, so that the final synthesis of LiFePO is realized 4 The particle size of the wrapping material is controlled, and the modification of the surface of the lithium iron phosphate anode material is indirectly finished.
Drawings
Fig. 1 is a flow chart illustrating modification of a lithium iron phosphate positive electrode material according to the present invention;
FIG. 2 is an isometric view of a treatment device of the present invention;
FIG. 3 is an exploded view of the internal structure of the synthesizing mechanism of the present invention;
FIG. 4 is an isometric view of a connection kit in the synthesis mechanism of the invention;
FIG. 5 is an isometric view of the heating assembly of the present invention installed in a connection kit;
FIG. 6 is an isometric view of a fill kit in the synthesis mechanism of the invention;
FIG. 7 is an isometric view of a load bearing sleeve within the resultant mechanism of the present invention;
FIG. 8 is an assembly view of the mixing assembly and input motor within the load bearing kit of the present invention;
FIG. 9 is an exploded view of the internal structure of the crystallization mechanism of the present invention with the feet removed;
FIG. 10 is an isometric view of a storage assembly within a crystallization mechanism according to the present invention;
FIG. 11 is an isometric view of a dial assembly in a crystallization mechanism of the present invention;
FIG. 12 is an isometric view of a temperature elevating assembly within a crystallization mechanism according to the invention;
FIG. 13 is a schematic bottom view of a temperature elevating assembly in a crystallization mechanism according to the present invention.
In the figure: 1. a synthesizing mechanism; 11. a connecting kit; 111. a connecting pipe; 112. a liquid injection pipe; 113. carrying a frame; 114. a liquid discharge pipe; 12. a material injection kit; 121. an upper connecting cover; 122. a pressure type thermometer; 123. a material injection pipe; 124. a pressure pipe; 13. a load bearing kit; 131. a load bearing seat; 132. a plug pin; 133. a threaded barrel; 134. a positioning tube; 135. rotating the motor; 2. a liquid pump; 3. a containing drawer; 4. a crystallization mechanism; 41. storing the components; 411. a crystallization box; 412. a communication gap; 413. an electronic check valve; 414. defining a frame; 415. a communicating pipe; 42. a dial-up assembly; 421. a limiting frame; 422. a threaded shaft; 423. a stabilizer bar; 424. an articulated arm; 425. placing the bulge; 426. inputting a motor; 427. a poking plate; 428. a plugging arm; 43. a temperature raising component; 431. supplying power; 432. placing the plate; 433. positioning a projection; 434. a stressed handle; 435. a vent gap; 436. hooking; 437. a sloping plate; 438. heating a resistor; 5. a heating assembly; 51. a charging control panel; 52. a power supply harness; 53. a power supply base; 54. a heating resistor; 6. a stirring assembly; 61. rotating the column; 62. stirring blocks; 63. a set screw; 64. positioning holes; 65. a threaded sleeve.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that in the description of the present invention, the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, which are only for convenience of description and simplification of description, and do not indicate or imply that the referred device or element must have a specific orientation, be configured in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention.
Further, it will be appreciated that the dimensions of the various elements shown in the figures are not drawn to scale, for ease of description, and that the thickness or width of some layers may be exaggerated relative to other layers, for example.
It should be noted that like reference numerals and letters refer to like items in the following figures, and thus, once an item is defined or illustrated in one figure, it will not need to be further discussed or illustrated in detail in the description of the following figure.
To solve the problem of LiFePO 4 The LiFePO has two defects of extremely low lithium ion diffusion rate and electronic conductivity 4 The modification studies of (a) mainly focus on two aspects: firstly, the LiFePO is effectively improved 4 Including intrinsic and surface conductivity, typically by coating with a conductive layer orDoping; second, increase Li + This can be achieved by reducing the particle size, wherein the treatment by coating the conductive layer is significantly different from the doping.
At the present stage, a surface modification method of a lithium iron phosphate anode material is provided, and the method is characterized in that high-valence cations are doped into LiFePO 4 In the material, thereby increasing LiFePO 4 Intrinsic conductivity of the material, but this solution of surface modification introduces more or less carbon or other impurities while doping the metal cations, and therefore it is not clear that LiFePO 4 Is associated with doping with metal cation cations, and is additionally due to the synthesis of LiFePO 4 In the process, the particles are easy to grow freely or agglomerate, the particle size can be controlled only by adopting a low-temperature synthesis method, so that the LiFePO is controlled by using a hydrothermal method 4 The particle size of the product is as large as LiFePO, and the product is adopted in LiFePO 4 The outside is provided with carbon coating and LiFePO 4 The method for modifying the surface of the lithium iron phosphate positive electrode material by reducing the particle size, as shown in fig. 1, comprises the following steps:
step one, weighing LiOH & H according to the molar ratio of Li to Fe to P of 3:1.5:0.5 2 O 、FeSO 4 ·7H 2 O and H 3 PO 4 ；
Step two, firstly FeSO 4 ·7H 2 Pouring O crystal into the synthesis mechanism 1 in the treatment device, and simultaneously adding distilled water into the synthesis mechanism 1 until FeSO 4 ·7H 2 After dissolving O in distilled water, adding additives into the treatment device, wherein in the second step, the additives are ascorbic acid and polyvinyl alcohol, wherein the ratio of the content of the ascorbic acid to the content of the polyvinyl alcohol to the content of the distilled water in the second step is 0.25:0.35:2.4, and as can be known from the research on preparation of lithium iron phosphate by hydrothermal method and modification thereof published in 2013 by Changsha university of science and technology, ascorbic acid is used for preventing FeSO 4 ·7H 2 And oxidizing ferrous iron in the O solution, wherein the polyvinyl alcohol is used as a surfactant.
Step three, dripping H into the synthesis mechanism 1 3 PO 4 A solution such that the solution inside the synthesizer, 1, is formed as a solution a;
step four, preparing another cup of distilled water, and adding LiOH & H 2 Dissolving the O crystal into the distilled water to prepare a solution B, pouring the solution B into the synthesis mechanism 1, and mixing to prepare a solution C, wherein the content of the distilled water in the second step and the fourth step is 200-400 ml, the total volume of the synthesis mechanism 1 in the second step is 1.25-1.75L, and the total volume of the crystallization mechanism 4 in the ninth step is 2.5-3.5L.
And step five, taking a trace amount of solution C in the synthesis mechanism 1 for pH value detection, and adjusting the pH value of the solution C to be about 7-10 by repeatedly adding distilled water.
It should be noted that, according to the numerical values in the article "research on preparation of lithium iron phosphate by hydrothermal method and modification", it can be known that the crystal grain size increases with the increase of the reaction time when determining the reaction temperature, but the crystal cell volume decreases because the crystal cell volume decreases and the crystal cell volume decreases when adjusting the pH of the solution C by adding distilled water 4 The particle size of the wrapping material is controlled, and the modification of the surface of the lithium iron phosphate anode material is indirectly finished.
Sixthly, starting a heating function arranged in the synthesis mechanism 1, and heating the solution C for a certain time;
and step seven, adding a modified material into the synthesis mechanism 1 during heating treatment, and starting the stirring function of the synthesis mechanism 1, wherein the heating time of the step six is 140-220 ℃, the heating time is 1-6 h, the modified material in the step seven is a polysaccharide substance, the polysaccharide substance is one of starch and glucose, the drying temperature of the step ten is 60-85 ℃, and the drying time is 10-15 h.
Step eight, after the heating treatment is finished, standing for a period of time until the temperature of the solution C is close to the normal temperature;
step nine, a liquid pump 2 arranged outside the treatment device is utilized to convey the solution C from the synthesis mechanism 1 to a crystallization mechanism 4 in the treatment device;
step ten, starting a temperature rising function of the crystallization mechanism 4, and drying the solution C until the solution C forms a lithium iron phosphate crystal;
step eleven, taking out the lithium iron phosphate crystal, and putting the lithium iron phosphate crystal and the dried quantitative wrapping material glucose into a planetary ball mill together for polishing treatment;
and step twelve, placing the mixture after polishing treatment in a tubular muffle furnace, filling nitrogen into the tubular muffle furnace, performing heat preservation treatment, and quantifying time to obtain the lithium iron phosphate wrapping material, wherein the amount of glucose in the step eleven is 200 g-450 g, the polishing treatment time in the step eleven is 3 h-5 h, the temperature of the muffle furnace in the step twelve is 600 ℃ -830 ℃, and the heat preservation time is 3 h-5 h.
It should be added that the results obtained in the present application were confirmed to be feasible by the study on the hydrothermal preparation of lithium iron phosphate and modification, the present application controlling LiFePO by using the hydrothermal method 4 The particle size of the product is as large as LiFePO, and the product is adopted in LiFePO 4 The outside is provided with carbon coating and LiFePO 4 The surface of the lithium iron phosphate anode material is modified by reducing the particle size, and the solution C is wrapped by adding glucose in the hydrothermal process of the lithium iron phosphate anode material, so that carbon ions in the glucose can better react with LiFePO 4 The inner ions are combined by filtering and drying to form LiFePO 4 Ball-milling, mixing and heat-treating the precursor and glucose prepared additionally to finally form LiFePO 4 And (4) wrapping the material to finish the surface modification of the lithium iron phosphate anode material.
It should be added that the processing device in the second step in the present application comprises a synthesis mechanism 1, a liquid pump 2 and a crystallization mechanism 4, wherein the synthesis mechanism 1 and the crystallization mechanism 4 are communicated through the liquid pump 2.
Referring to fig. 3, it can be seen that the synthesizing mechanism 1 includes a material injection kit 12, a connection kit 11 and a bearing kit 13 which are screwed in sequence, the crystallization mechanism 4 includes a storage component 41, a dial-up component 42 is fixedly connected to a midpoint inside the storage component 41, a temperature raising component 43 is covered on a top end of the storage component 41, a liquid discharge pipe 114 and a communication pipe 415 are respectively installed at a liquid suction end and a liquid discharge end of the liquid suction pump 2, wherein one end of the liquid discharge pipe 114 is fixed to a bottom end outside the connection kit 11, one end of the communication pipe 415 is fixed to one end outside the storage component 41, and it is necessary to supplement that a filter screen is installed inside the liquid discharge pipe 114 in the present application, wherein the filter screen plays a role of filtering crystals formed.
Wherein, referring to fig. 4, the connection kit 11 includes a connection tube 111, a carrying frame 113 which is convenient for dismounting the connection tube 111 and the bearing kit 13 under stress is installed outside the connection tube 111, an injection tube 112 is fixedly connected to an outer end of the connection tube 111 and is communicated with the inside of the connection tube, a heating assembly 5 is installed inside the connection tube 111, referring to fig. 5, the heating assembly 5 includes a live control panel 51, an inner wall of the live control panel 51 and an outer wall of the connection tube 111 are fixed, an inner wall of the connection tube 111 is fixedly connected with a power supply base 53, a heating resistor 54 is installed inside the power supply base 53, an output end of the live control panel 51 is fixedly connected with a power supply harness 52, and one end of the power supply harness 52 penetrates through the connection tube 111 and an input end of the power supply base 53 to be fixed.
As can be seen from fig. 6, the material injection kit 12 includes an upper connection cover 121, a bottom end of the upper connection cover 121 is screwed to one end of the connection pipe 111, a material injection pipe 123, a pressure pipe 124 and a pressure type thermometer 122 are fixedly connected to a top of the upper connection cover 121, and the material injection pipe 123, the pressure pipe 124 and the pressure type thermometer 122 are all communicated with an interior of the upper connection cover 121; as can be seen from fig. 7, in the present application, the bearing kit 13 includes a bearing seat 131, a rotating motor 135 is installed inside the bearing seat 131, a threaded cylinder 133 is installed on a top end of the bearing seat 131, an assembly gap is opened inside the threaded cylinder 133, a rotatable stirring assembly 6 is installed at the assembly gap by the threaded cylinder 133, the stirring assembly 6 is fixed to an output end of the rotating motor 135 through a connecting member, it is to be supplemented that an insertion pin 132 is fixed to a bottom of the threaded cylinder 133 in the present application, a positioning tube 134 is fixedly connected to an inner wall of the bearing seat 131, wherein the insertion pin 132 is adapted to the positioning tube 134, and when the insertion pin 132 is inserted into the positioning tube 134, the bearing seat 131 completes installation and limitation of the threaded cylinder 133.
Wherein refer to fig. 8 and know, stirring subassembly 6 is including rotating post 61, the bottom of rotating post 61 outer wall and the inner wall looks sliding connection of a screw thread section of thick bamboo 133 in assembly breach department, the top fixedly connected with stirring piece 62 of rotating post 61, stirring piece 62 is provided with a plurality ofly, and the even top that sets up at rotating post 61 of equal angle, locating hole 64 has been seted up to the central point position at rotating post 61 top, the output fixedly connected with threaded sleeve 65 of rotating motor 135, threaded sleeve 65 passes through locating hole 64 and rotates post 61 and form the interference fit relation, the connecting piece is set screw 63, set screw 63 and threaded sleeve 65 looks adaptation.
In practical use, all reaction raw materials are poured into the threaded cylinder 133 through the pouring material injection pipe 123, and it should be noted that, referring to fig. 6, the three material injection pipes 123 are provided in the present application, and the three outsides are all provided with control valves, so that the raw materials are added while the purity of the raw materials is guaranteed through the arrangement of the three material injection pipes 123.
As can be seen from fig. 9, in the present application, the storage assembly 41 includes a crystallization box 411, wherein four bottom feet are fixedly connected to the periphery of the bottom of the crystallization box 411, a containing drawer 3 is fixedly connected between the four bottom feet, a communicating notch 412 is formed at one end inside the crystallization box 411, an electronic check valve 413 is installed inside the communicating notch 412, a through pipe is installed between the crystallization box 411 and the containing drawer 3, the through pipe is disposed at the position of the communicating notch 412, and one end of the through pipe penetrates through the top end of the containing drawer 3 and is communicated with the inside of the containing drawer 3, it should be noted that the raw material falling into the containing drawer 3 at last is the raw material of the lithium iron phosphate precursor shown in fig. 1, the raw material of the lithium iron phosphate precursor is taken out and is treated with the prepared glucose crystal in a ball mill, and after treatment, the mixed crystal is placed together in a heating environment filled with nitrogen gas, finally forming the lithium iron phosphate coating material.
Referring to fig. 11, the dial-up assembly 42 includes a position-limiting frame 421, the position-limiting frame 421 is fixed at the middle end of the interior of the crystal box 411, one end of the top of the position-limiting frame 421 is fixedly connected with an input motor 426, the output end of the input motor 426 is fixedly connected with a threaded shaft 422, the end of the threaded shaft 422 is rotatably connected with the other end of the top of the position-limiting frame 421, two sides of one end of the top of the position-limiting frame 421 are respectively fixedly connected with a placing protrusion 425, a stabilizing rod 423 is fixedly connected between the placing protrusion 425 and the other end of the top of the position-limiting frame 421, a hinge arm 424 is slidably connected between the two stabilizing rods 423, the interior of the hinge arm 424 is in threaded connection with the exterior of the threaded shaft 422, a plug arm 428 is plugged into the bottom of the hinge arm 424, and a dial plate 427 is slidably connected to the exterior of the plug arm 428, wherein when the dial-up assembly 42 is actually used, the input motor 426 drives the threaded shaft 422 to rotate, so that when the threaded shaft 422 rotates, the articulated arm 424 is slowly driven to move, so that the splicing arm 428 spliced at the bottom of the articulated arm 424 drives the poking plate 427 to discharge lithium iron phosphate precursor raw materials forming a crystal state into the drawer 3 along a through pipeline, and what needs to be supplemented is that as the total volume of the crystallization mechanism 4 is 2.5L-3.5L and the total volume of the synthesis mechanism 1 is 1.25L-1.75L, when the liquid pumping pump 2 discharges the solution C into the crystallization box 411, the solution C does not completely fill the crystallization box 411, the factor that a filter screen is arranged in the liquid discharge pipe 114 is considered, and the height of the solution in the crystallization box 411 is generally lower than the height of the limiting frame 421.
Referring to fig. 12 and 13, it can be seen that the temperature raising assembly 43 comprises a placing plate 432, the placing plate 432 is placed on the top end of the crystallization box 411, and it is added that, in this application, two ends of the top of the inner wall of the crystallization box 411 are respectively fixedly connected with a limiting frame 414, two ends of the bottom of the placing plate 432 are respectively fixedly connected with a positioning protrusion 433, wherein the positioning protrusion 433 is matched with the limiting frame 414, and there is an interference fit relationship between the positioning protrusion 433 and the limiting frame 414, therefore, the placing plate 432 is placed on the top end of the crystallization box 411 through the positioning protrusion 433 and the limiting frame 414, it is added that, in order to ensure that the placing plate 432 can be separated from the crystallization box 411, a force-bearing handle 434 is also fixedly installed on the top of the placing plate 432, and it should be noted that, at the other end of the top of the placing plate 432, a plurality of ventilation gaps 435 are opened, at the placing plate 432 is in the ventilation gaps 435, it should be added that the placing plate 432 is fixedly connected with a sloping plate 437 on the inner wall of the ventilation gap 435, wherein the sloping plate 437 plays a role of preventing dust from entering the interior of the crystallization box 411 to a certain extent.
It should be noted that, in the present application, one end of the top of the placing plate 432 is fixedly connected with the power supply 431, wherein the output end of the power supply 431 is fixedly connected with the temperature-raising resistor 438, the bottom of the placing plate 432 is fixedly connected with the hook 436, the hook 436 is made of silicon material, and the hook 436 is provided with a plurality of hooks, wherein two hooks 436 are provided between every two ventilation gaps 435, the temperature-raising resistor 438 is installed at the bottom end of the placing plate 432 through the hooks 436, it is necessary to supplement that, in the present application, in order to improve the temperature-raising efficiency, a blower can be provided at the crystallization box 411, an exhaust pipe cover is installed at the output end of the blower, and one end of the exhaust pipe cover is installed on the placing plate 432, so that the heat generated by the temperature-raising resistor 438 can further enter the interior of the crystallization box 411, when the solution in the crystallization box 411 needs to be cooled, the connection between the power supply 431 and the temperature-raising resistor 438 is manually disconnected, and the blower is replaced by an air cooler to cool the inside of the crystal box 411, wherein it should be noted that when one end of the exhaust duct cover is installed on the placing plate 432, one or more ventilation gaps 435 are required to be reserved for exhausting air.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (10)
1. The surface modification method of the lithium iron phosphate anode material is characterized by comprising the following steps of: the method comprises the following steps:
step one, weighing LiOH & H according to the molar ratio of Li to Fe to P of 3:1.5:0.5 2 O 、FeSO 4 ·7H 2 O and H 3 PO 4 ；
Step two, firstly FeSO 4 ·7H 2 The O crystal is poured into a synthesizing mechanism (1) in the processing device and simultaneously enters the synthesizing mechanism (1)Adding distilled water to FeSO 4 ·7H 2 Dissolving O in distilled water, and adding an additive into the treatment device;
step three, dripping H into the synthesis mechanism (1) 3 PO 4 A solution such that the solution inside the synthesis mechanism (1) is formed as a solution A;
step four, preparing another cup of distilled water, and adding LiOH & H 2 Dissolving the O crystal in distilled water to prepare solution B, pouring the solution B into the synthesis mechanism (1), and mixing to prepare solution C;
fifthly, taking a trace amount of solution C in the synthesis mechanism (1) for pH value detection, and adjusting the pH value of the solution C to about 7-10 by repeatedly adding distilled water;
sixthly, starting a heating function arranged in the synthesis mechanism (1) and heating the solution C for a certain time;
seventhly, adding a modified material into the synthesis mechanism (1) during heating treatment, and starting the stirring function of the synthesis mechanism (1);
step eight, after the heating treatment is finished, standing for a period of time until the temperature of the solution C is close to the normal temperature;
step nine, a liquid pump (2) arranged outside the processing device is utilized to convey the solution C from the synthesis mechanism to a crystallization mechanism (4) in the processing device;
step ten, starting a temperature rising function in the crystallization mechanism (4), and drying the solution C until the solution C forms a lithium iron phosphate crystal;
step eleven, taking out the lithium iron phosphate crystal, and putting the lithium iron phosphate crystal and the dried quantitative wrapping material glucose into a planetary ball mill together for polishing treatment;
and step twelve, placing the mixture after polishing treatment in a tubular muffle furnace, filling nitrogen into the tubular muffle furnace, performing heat preservation treatment, and quantifying for a certain time to obtain the lithium iron phosphate wrapping material.
2. The surface modification method for a lithium iron phosphate positive electrode material according to claim 1, characterized in that: the content of distilled water in the second step and the fourth step is 200 ml-400 ml, the total volume of the synthesis mechanism (1) in the second step is 1.25L-1.75L, and the total volume of the crystallization mechanism (4) in the ninth step is 2.5L-3.5L.
3. The method for modifying the surface of a lithium iron phosphate positive electrode material according to claim 2, characterized in that: and the additives in the second step are ascorbic acid and polyvinyl alcohol, wherein the content ratio of the ascorbic acid to the polyvinyl alcohol to the distilled water in the second step is 0.25:0.35: 2.4.
4. The method for modifying the surface of a lithium iron phosphate positive electrode material according to claim 1, characterized in that: the heating time of the sixth step is 140-220 ℃, the heating time is 1-6 h, the modified material in the seventh step is polysaccharide substance, wherein the polysaccharide substance is one of starch and glucose, the drying temperature of the tenth step is 60-85 ℃, and the drying time is 10-15 h.
5. The surface modification method for a lithium iron phosphate positive electrode material according to claim 1, characterized in that: the amount of the glucose in the eleventh step is 200 g-450 g, the polishing time in the eleventh step is 3 h-5 h, the temperature of the muffle furnace in the twelfth step is 600-830 ℃, and the heat preservation time is 3 h-5 h.
6. The method for modifying the surface of a lithium iron phosphate positive electrode material according to claim 1, characterized in that: the processing device in the second step comprises a synthesis mechanism (1), a liquid pump (2) and a crystallization mechanism (4), wherein the synthesis mechanism (1) is communicated with the crystallization mechanism (4) through the liquid pump (2);
synthetic mechanism (1) is including annotating material external member (12), connection external member (11) and bearing external member (13) of looks spiro union in proper order, crystallization mechanism (4) are including storing subassembly (41), the midpoint department fixedly connected with of storing subassembly (41) inside dials and send subassembly (42), the top of storing subassembly (41) is covered and is heated up subassembly (43), fluid-discharge tube (114) and communicating pipe (415) are installed respectively to the drawing liquid end and the flowing back end of drawing liquid pump (2), wherein the one end of fluid-discharge tube (114) with the outside bottom of connection external member (11) is fixed mutually, wherein the one end of communicating pipe (415) with the one end of storing the outside of subassembly (41) is fixed mutually.
7. The surface modification method for a lithium iron phosphate positive electrode material according to claim 6, characterized in that: the connecting kit (11) comprises a connecting pipe (111), one end of the outside of the connecting pipe (111) is fixedly connected with a liquid injection pipe (112) communicated with the inside of the connecting pipe (111), a heating assembly (5) is installed inside the connecting pipe (111), the heating assembly (5) comprises a charging control panel (51), the inner wall of the charging control panel (51) is fixed with the outer wall of the connecting pipe (111), the inner wall of the connecting pipe (111) is fixedly connected with a power supply seat (53), a heating resistor (54) is installed inside the power supply seat (53), the output end of the charging control panel (51) is fixedly connected with a power supply wire bundle (52), and one end of the power supply wire bundle (52) penetrates through the connecting pipe (111) and is fixed with the input end of the power supply seat (53);
the material injection kit (12) comprises an upper connecting cover (121), the bottom end of the upper connecting cover (121) is in threaded connection with one end of the connecting pipe (111), a material injection pipe (123), a pressure pipe (124) and a pressure type thermometer (122) are fixedly connected to the top of the upper connecting cover (121), and the material injection pipe (123), the pressure pipe (124) and the pressure type thermometer (122) are communicated with the inside of the upper connecting cover (121);
the bearing external member (13) includes bearing seat (131), and the internally mounted of bearing seat (131) has rotation motor (135), and a screw thread section of thick bamboo (133) is installed on the top of bearing seat (131), the assembly breach has been seted up to the inside of a screw thread section of thick bamboo (133), and rotatable stirring subassembly (6) is installed at the assembly breach in a screw thread section of thick bamboo (133), stirring subassembly (6) through the connecting piece with the output end of rotating motor (135) is fixed mutually.
8. The surface modification method for a lithium iron phosphate positive electrode material according to claim 7, characterized in that: stirring subassembly (6) including rotating post (61), rotate the bottom of post (61) outer wall with inner wall looks sliding connection of screw thread section of thick bamboo (133) in assembly breach department rotates top fixedly connected with stirring piece (62) of post (61), and stirring piece (62) are provided with a plurality ofly, and wait the even setting of angle and be in the top of rotating post (61), locating hole (64) have been seted up to the central point position at rotation post (61) top, the output fixedly connected with screw sleeve (65) of rotating motor (135), screw sleeve (65) through locating hole (64) with it forms interference fit relation to rotate post (61), the connecting piece is set screw (63), set screw (63) with screw sleeve (65) looks adaptation.
9. The surface modification method for a lithium iron phosphate positive electrode material according to claim 6, characterized in that: the storage assembly (41) comprises a crystallization box (411), the periphery of the bottom of the crystallization box (411) is fixedly connected with feet respectively, the containing drawer (3) is fixedly connected among the four feet, one end inside the crystallization box (411) is provided with a communicating notch (412), an electronic check valve (413) is installed inside the communicating notch (412), a through pipeline is installed between the crystallization box (411) and the containing drawer (3), the through pipeline is arranged at the position of the communicating notch (412), and one end of the through pipeline penetrates through the top end of the containing drawer (3) and is communicated with the inside of the containing drawer (3);
the poking and sending assembly (42) comprises a limiting frame (421), the limiting frame (421) is fixed at the middle end inside the crystal box (411), one end of the top of the limiting frame (421) is fixedly connected with an input motor (426), the output end of the input motor (426) is fixedly connected with a threaded shaft (422), the tail end of the threaded shaft (422) is rotatably connected with the other end of the top of the limiting frame (421), both sides of spacing (421) top one end fixedly connected with respectively place arch (425), place fixedly connected with stabilizer bar (423) between arch (425) and spacing (421) top other end, sliding connection has articulated arm (424) between two stabilizer bar (423), the inside of articulated arm (424) with the outside looks threaded connection of screw spindle (422), the bottom of articulated arm (424) is pegged graft and is had grafting arm (428), and the outside sliding connection of grafting arm (428) has stirring board (427).
10. The surface modification method for a lithium iron phosphate positive electrode material according to claim 9, characterized in that: the heating assembly (43) comprises a placing plate (432), the placing plate (432) is placed at the top end of the crystallization box (411) in a covering mode, a power supply (431) is fixedly connected to one end of the top of the placing plate (432), a plurality of ventilation notches (435) are formed in the other end of the top of the placing plate (432), the placing plate (432) is arranged in the ventilation notches (435), a heating resistor (438) is fixedly connected to the output end of the power supply (431), a hook (436) is fixedly connected to the bottom of the placing plate (432), the hook (436) is made of silicon, a plurality of hooks (436) are arranged, two hooks (436) are arranged between every two ventilation notches (435), and the heating resistor (438) is installed at the bottom end of the placing plate (432) through the hooks (436).
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