CN116395759A - Grain boundary braiding precursor, positive electrode material and preparation method - Google Patents

Grain boundary braiding precursor, positive electrode material and preparation method Download PDF

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CN116395759A
CN116395759A CN202310399198.4A CN202310399198A CN116395759A CN 116395759 A CN116395759 A CN 116395759A CN 202310399198 A CN202310399198 A CN 202310399198A CN 116395759 A CN116395759 A CN 116395759A
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precursor
solution
nano
reaction
grain boundary
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余欣瑞
刘喜军
朱端旭
张�诚
寇亮
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Jinghe Xincheng Shaanxi Coal Technology Research Institute New Energy Materials Co ltd
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Jinghe Xincheng Shaanxi Coal Technology Research Institute New Energy Materials Co ltd
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Abstract

The invention discloses a crystal boundary braiding precursor, which comprises a sandwich structure formed by a precursor inner core, a nano oxide braiding layer and a precursor shell. The invention also discloses a preparation method of the precursor, and the positive electrode material prepared by adopting the precursor.

Description

Grain boundary braiding precursor, positive electrode material and preparation method
Technical Field
The invention belongs to the technical field of lithium ion battery materials, relates to a crystal boundary braiding precursor, and further relates to a preparation method of the precursor.
Background
The positive electrode material is a core component of the lithium battery, and has direct influence on many core performance indexes of the lithium battery, including capacity, service life, multiplying power, safety and the like. The deintercalatable lithium ions in a typical lithium battery are derived from the positive electrode active material. The current ternary positive electrode material has three development directions, namely single crystallization, high voltage and high nickel. The doping and surface modification are effective methods for improving the comprehensive performance of the cathode material no matter the common cathode material is or the cathode material is developed to single crystal, high voltage and high nickel. And the doping and modifying method is one of the core competitiveness of the cathode material enterprises. Doping elements include Al, mg, cr, etc., and enhancement mechanisms include stabilization of the main structure, increase of the lithium ion interlayer spacing, segregation at grain boundaries, etc. Common coating agents include Al 2 O 3 、V 2 O 5 、ZnO、ZrO 2 、TiO 2 MgO, etc.
The ternary precursor is a key raw material for realizing the performance of the ternary positive electrode material, and the coating of the ternary positive electrode material can be realized by coating the ternary precursor. The prior art method for preparing the precursor coating layer is to generate a new coating layer on the surface of the precursor secondary particles by coprecipitation of coating elements, and the size and arrangement inequality of the newly generated primary particles can influence Li + The surface coating layer also affects the conductivity of the material, and at the same time, during long-term cycling of the battery, the particle surface cracks and may extend to the core, side reactions with the electrolyte cause irreversible phase changes at the surface and at the crack interface, resulting in material capacity loss and structural degradation.
The nano titanium dioxide has very high chemical stability, thermal stability and super-hydrophilicity, the surface of the ternary precursor is provided with a large number of active sites, the specific surface energy is high, the deposition is easy to adhere and grow, and further, a uniform coating layer is formed on the surface of the ternary precursor, so that a proper amount of nano titanium dioxide can be coated in the preparation process of the ternary precursor, so that the inter-particle stress and the micro-strain of the structure and volume caused in the circulation process are reduced, the circulation stability of the lithium battery material in the charge and discharge process is improved, the electrochemical performance of the battery material is improved, and the service life of the lithium battery is prolonged.
Disclosure of Invention
The invention aims to provide a crystal boundary braiding precursor, which weaves nano oxides on the crystal boundary of the precursor, improves the interface stability of a positive electrode material and improves the electrochemical performance of the material.
The second object of the invention is to provide a method for preparing a crystal boundary braiding precursor.
A third object of the present invention is to provide a method for manufacturing a positive electrode material using a grain boundary woven precursor.
The first technical scheme adopted by the invention is that the precursor is woven by grain boundary, and the precursor comprises a sandwich structure formed by a precursor inner core, a nano oxide woven layer and a precursor shell.
The first technical scheme of the invention is characterized in that:
the molecular formula of the precursor is: m (OH) 2 Wherein M is selected from Ni, co, mn, al, fe, cu and OH - One or more of the elements that produce hydroxide precipitates.
The particle size of the precursor is 3-20 mu m; the specific surface area of the precursor is 10-14 m 2 /g; the tap density of the precursor is 1.9-2.2 g/cm 3 ；
The particle size of the precursor kernel is 1.2-10.0 mu m; the thickness of the nano oxide woven layer is 0.6-5.0 mu m.
The second technical scheme adopted by the invention is that the preparation method of the grain boundary braiding precursor comprises the following steps:
step 1, according to precursor M (OH) 2 Preparing mixed salt solution A with the molar ratio of 2.0-8.0 mol/L, sodium hydroxide solution B with the molar ratio of 5.0-10.0 mol/L and ammonia water solution C with the molar ratio of 3.0-13.0 mol/L;
step 2, adding pure water, sodium hydroxide solution B and ammonia water C solution into a reaction kettle to prepare reaction base solution, and introducing nitrogen;
step 3, keeping nitrogen gas to be introduced, and adding the prepared mixed salt solution A, the sodium hydroxide solution B and the ammonia water solution C into the bottom solution of the reaction kettle in parallel to carry out coprecipitation reaction, and controlling the reaction temperature and the reaction pH to form a precursor inner core in the reaction kettle;
step 4, stopping adding the solution A, the solution B and the solution C into the reaction kettle when the core particle size of the precursor reaches a target value, switching nitrogen into air, carrying nano oxides into the kettle by the air at a fixed flow rate, thinning primary particles under the micro oxidation of the air, enabling pores to become more, forming a crystal boundary nano oxide woven layer, stopping adding the nano oxides when the nano oxide woven layer reaches a set thickness, and switching the nano oxide into the nitrogen;
step 5, continuously feeding and reacting the solution A, the solution B and the solution C to form a precursor shell, wrapping the nano oxide woven layer in the middle of the particles, stopping the reaction and feeding after the particle size of the precursor reaches the target particle size, and continuously stirring and ageing for 3-4 hours;
and 6, carrying out solid-liquid separation, washing and drying on the aged material in the step 5, and screening and demagnetizing to obtain the precursor with nano oxide grain boundary weaving.
The second technical scheme of the invention is characterized in that:
in the step 1, the mixed salt solution A is at least one of sulfate, acetate, nitrate and chloride.
In the step 4, the air flow rate for carrying the nano oxide is 100-300 mL/min; the nano oxide is super-hydrophilic nano titanium dioxide.
The reaction conditions in the precursor preparation process are as follows: the reaction is carried out at 55-65 ℃ with stirring speed of 450-600 + -5 rpm, pH value of 10.50-12.00 and ammonia concentration of 0.15-0.45 mol/L until the particle diameter D50 of the precursor reaches the target value.
The third technical scheme adopted by the invention is that the precursor and lithium salt are mixed and sintered.
The third technical scheme of the invention is characterized in that:
the mol ratio of the precursor and the lithium source is 0.95-1.10, and sintering is carried out for 10-30 h at 650-800 ℃, wherein the sintering atmosphere is oxygen atmosphere.
The beneficial effects of the invention are as follows:
1. according to the preparation method, through micro-oxidation of the precursor kernel, the specific surface area is increased, and meanwhile, the nano titanium dioxide is woven at the kernel grain boundary to ensure the high tap density of the precursor.
2. The grain boundary braiding precursor prepared by the method is characterized by protecting the nano titanium dioxide braiding layer, so that the internal structure cracking of the high-nickel positive electrode material main body under long circulation is relieved, electrolyte erosion is avoided, the occurrence of irreversible phase change is reduced, and the dissolution of manganese in the active material under high voltage is inhibited. In addition, the uniform nano titanium dioxide braided layer also reduces the internal impedance of the electrode and improves Li + And (5) diffusion.
3. The nano titanium dioxide grain boundary braided precursor prepared by the method has uniform grain size distribution, good uniformity of primary particles, regular arrangement, high interfacial stability of the positive electrode material obtained after lithium mixing and calcination, and improved cycling stability.
4. According to the preparation method, nano titanium dioxide grain boundary braiding is carried out in the preparation process of the precursor, an additional reaction vessel is not added, pretreatment of raw materials is not needed, the preparation process is simplified, the production cost is reduced, the prepared material is excellent in performance, and the results show that the nano titanium dioxide braiding layer strategy provides a huge opportunity for exciting an advanced high-energy density positive electrode of a lithium ion battery and being applied to a large-scale power supply.
Drawings
FIG. 1 is a schematic diagram of the structure of a grain boundary woven precursor of the present invention;
FIGS. 2 (a) and (b) are SEM images of the nano titania braided layer and the finally obtained precursor material in the preparation process of example 1 of the preparation method of the grain boundary braided precursor of the present invention;
FIGS. 3 (a) and (b) are SEM images of the nano titania woven layer and the finally obtained precursor material in the preparation process of comparative example 1;
FIGS. 4 (a) and (b) are SEM images of the precursor material prepared in comparative example 2;
FIG. 5 is a graph (3.0 to 4.3V,0.1C,100 cycles) of cycle data of the positive electrode materials prepared in example 1, comparative example 1 and comparative example 2.
Detailed Description
The invention will be described in detail below with reference to the drawings and the detailed description.
The grain boundary woven precursor disclosed by the invention has a three-layer structure as shown in figure 1, and comprises a sandwich structure formed by a precursor inner core, a nano oxide woven layer and a precursor shell.
The molecular formula of the precursor is: m (OH) 2 Wherein M is selected from Ni, co, mn, al, fe, cu and OH - One or more of the elements that produce hydroxide precipitates.
The particle size of the precursor is 3-20 mu m.
The kernel grain size of the precursor is 1.2-10.0 mu m.
The thickness of the nano oxide braiding layer is 0.6-5.0 mu m.
The specific surface area of the precursor is 10.00-14.00 m 2 /g。
The tap density of the precursor is 1.90-2.20 g/cm 3 。
The preparation method of the grain boundary braiding precursor comprises the following steps:
step 1, according to precursor M (OH) 2 Preparing mixed salt solution A with the molar ratio of 2.0-8.0 mol/L, sodium hydroxide solution B with the molar ratio of 5.0-10.0 mol/L and ammonia water solution C with the molar ratio of 3.0-13.0 mol/L;
the mixed salt solution A is one or more than two of sulfate, acetate, nitrate and chloride.
Step 2, adding pure water, sodium hydroxide solution B and ammonia water C solution into a reaction kettle to prepare reaction base solution, and introducing nitrogen;
step 3, keeping nitrogen gas to be introduced, and adding the prepared mixed salt solution A, the sodium hydroxide solution B and the ammonia water solution C into the bottom solution of the reaction kettle in parallel to carry out coprecipitation reaction, and controlling the reaction temperature and the reaction pH to form a precursor inner core in the reaction kettle;
step 4, when the core particle size of the precursor reaches a target value, stopping adding the solution A, the solution B and the solution C, switching nitrogen into air, carrying nano oxides into a kettle by the air at a fixed flow rate, thinning primary particles under the micro oxidation of the air, increasing pores to form a crystal boundary nano oxide braiding layer, stopping adding the nano oxides when the braiding layer reaches a certain thickness, and switching the nano oxides into nitrogen;
in the step 4, the air flow rate for carrying the nano oxide is 100-300 mL/min; the nano oxide is super-hydrophilic nano titanium dioxide.
Step 5, continuously feeding and reacting the solution A, the solution B and the solution C to form a precursor shell, wrapping the nano oxide woven layer in the middle of the particles, stopping the reaction and feeding after the particle size of the precursor reaches the target particle size, and continuously stirring and ageing for 3-4 hours;
the precursor with the nano oxide braiding layer has the following core radius, braiding layer thickness and shell thickness ratio: 2:1:2 (small particle size precursor) or 2:2:1 (conventional particle size precursor) or 2:1:1 (large particle size precursor).
And 6, carrying out solid-liquid separation, washing and drying on the aged material in the step 5, and screening and demagnetizing to obtain the precursor with nano oxide grain boundary weaving.
In the process of forming a precursor according to steps 1 to 6, the reaction conditions are: the reaction is carried out at 55-65 ℃ with stirring speed of 450-600 + -5 rpm, pH value of 10.50-12.00 and ammonia concentration of 0.15-0.45 mol/L until the particle diameter D50 of the precursor reaches the target value.
The invention also provides a positive electrode material which is prepared by mixing and sintering the precursor material and lithium salt.
The sintering process comprises the following steps: the molar ratio of the precursor to the lithium source is 0.95-1.10, and the precursor is sintered for 10-30 hours at 650-800 ℃, wherein the sintering atmosphere is oxygen atmosphere.
Aiming at the problems that the surface of the current positive electrode material is coated, particles are cracked under long circulation, side reactions are generated between crystal faces and electrolyte, and the battery circulation performance is poor due to irreversible phase transformation, the invention provides an improved scheme from a precursor end, namely a crystal boundary braiding precursor, nano oxides are braided on the crystal boundary of a nickel cobalt manganese precursor, the interface stability of the positive electrode material is improved, and the circulation performance is improved.
Example 1
Respectively weighing NiSO with certain mass according to the molar ratio of Ni to Co to Mn=0.9 to 0.05 4 、CoSO 4 、MnSO 4 Dissolving in deionized water to prepare 100L of mixed salt solution with the concentration of 8mol/L, 5mol/L of sodium hydroxide solution and 7mol/L of ammonia water solution.
Adding deionized water into a reaction kettle provided with a circulating water bath heating system, an ammonia-alkali salt flow automatic control system and a pH automatic control system to submerge a pH meter probe, adding an aqueous ammonia solution into the reaction kettle until the ammonia concentration of a base solution is 0.20mol/L, adding a sodium hydroxide solution into the reaction kettle until the pH value of the base solution is=10.85, introducing nitrogen at a flow rate of 2.0+/-0.5L/h to protect for 3 hours, introducing nitrogen in the whole process of precursor kernel and shell formation, and keeping the reaction temperature at 60+/-1 ℃ and the rotating speed of a stirrer at 500+/-5 rpm.
And (3) adding the mixed salt solution, the sodium hydroxide solution and the ammonia water solution into the reaction kettle in parallel by using a peristaltic pump to start a precursor nuclear generation process, wherein the flow rate of the mixed salt solution is fixed to be 30+/-2 mL/min, the flow rate of the sodium hydroxide solution is determined in real time according to an automatic control system, and the flow rate of the ammonia water solution is added into the reaction kettle according to the required amount of different stages.
The method comprises the steps of stopping adding a mixed salt solution, a sodium hydroxide solution and an ammonia solution when the particle size of the precursor inner core is 4.0+/-0.5 mu m, switching nitrogen into air, adjusting the air flow rate to be 200mL/min, carrying nano titanium dioxide into a kettle by air, micro-oxidizing newly arranged primary particles on the surface of the precursor inner core, thinning the primary particles, increasing the specific surface area, adsorbing the nano titanium dioxide carried into the kettle by air on the surface of the primary particles until the precursor particles are 8.0+/-0.5 mu m, switching nitrogen, and continuously and parallelly adding the mixed salt solution, the sodium hydroxide solution and the ammonia solution into the reaction kettle for reaction.
When the particle size of the materials in the reaction kettle is detected to reach 10.0+/-0.5 mu m, stopping reaction feeding, and continuing stirring and ageing for 3-4 hours.
Centrifuging and aging the slurry, washing the solid with sodium hydroxide solution, washing with pure water at 65-75 ℃, drying the material, sieving and demagnetizing to obtain a precursor material, and sealing and preserving.
The particle size distribution data obtained by taking a dry qualified sample are as follows: dmin=5.42 μm, d10=7.5 μm, d50=10.22 μm, d90=13.62 μm, dmax=17.52 μm, and particle size distribution span=0.60. Tap density td=1.93 g/cm 3 Specific surface area bet=11.15 m 2 /g。
The preparation of the positive electrode material comprises the steps of uniformly mixing lithium hydroxide monohydrate and the obtained precursor in a high-speed mixer according to a molar ratio of 0.95:1, sintering for 10 hours at 800 ℃ in an oxygen atmosphere, naturally cooling to room temperature, grinding, pulverizing and sieving to obtain the positive electrode material, namely NCM-TY955.
And uniformly mixing the obtained positive electrode material with acetylene black and PVDF, coating the mixture on an aluminum foil to prepare a positive electrode plate, assembling the positive electrode plate, a lithium metal plate, a diaphragm and electrolyte in a vacuum glove box to form a button cell, and carrying out cycle and multiplying power performance test on the button cell.
Fig. 2 (a) and (b) are SEM images of the nano titania braid (fig. 2 (a)) and the finally obtained precursor material (fig. 2 (b)) in the preparation process of example 1, respectively. From the figure, the nano titanium dioxide weaving layer is uniformly distributed on the precursor primary particle sheet, and the primary particles on the surface of the prepared final precursor material are in a sheet shape and are closely distributed.
Example 2
Respectively weighing NiSO with certain mass according to the molar ratio of Ni to Co to Mn=0.6 to 0.1 to 0.3 4 、CoSO 4 、MnSO 4 Dissolving in deionized water to prepare 100L of nickel-cobalt-manganese mixed salt solution with the concentration of 4mol/L, 10mol/L of sodium hydroxide solution and 13mol/L of ammonia water.
Adding deionized water into a reaction kettle provided with a circulating water bath heating system, an ammonia-alkali salt flow automatic control system and a pH automatic control system to submerge a pH meter probe, adding an aqueous ammonia solution into the reaction kettle until the ammonia concentration of a base solution is 0.15mol/L, adding a sodium hydroxide solution into the reaction kettle until the pH value of the base solution is=12.00, introducing nitrogen at a flow rate of 2.0+/-0.5L/h to protect for 3 hours, introducing nitrogen in the whole process of precursor kernel and shell formation, and keeping the reaction temperature at 55+/-1 ℃ and the rotating speed of a stirrer at 600+/-5 rpm.
And (3) adding the mixed salt solution, the sodium hydroxide solution and the ammonia water solution into the reaction kettle in parallel by using a peristaltic pump to start a precursor nuclear generation process, wherein the flow rate of the mixed salt solution is fixed to be 30+/-2 mL/min, the flow rate of the sodium hydroxide solution is determined in real time according to an automatic control system, and the flow rate of the ammonia water solution is added into the reaction kettle according to the required amount of different stages.
The method comprises the steps of stopping adding a mixed salt solution, a sodium hydroxide solution and an ammonia solution when the particle size of the precursor inner core is 1.2+/-0.2 mu m, switching nitrogen into air, adjusting the air flow rate to be 100mL/min, carrying nano titanium dioxide into a kettle by air, micro-oxidizing newly arranged primary particles on the surface of the precursor inner core, thinning the primary particles, increasing the specific surface area, adsorbing the nano titanium dioxide carried into the kettle by air on the surface of the primary particles until the precursor particles are 1.8+/-0.2 mu m, switching nitrogen, and continuously and parallelly adding the mixed salt solution, the sodium hydroxide solution and the ammonia solution into the reaction kettle for reaction.
When the particle size of the materials in the reaction kettle is detected to reach D50 of 3.0+/-0.5 mu m, stopping reaction feeding, and continuing stirring and ageing for 3-4 hours.
Centrifuging and aging the slurry, washing the solid with sodium hydroxide solution, washing with pure water at 65-75 ℃, drying the material, sieving and demagnetizing to obtain a precursor material, and sealing and preserving.
The particle size distribution data obtained by taking a dry qualified sample are as follows: dmin=1.08 μm, d10=2.48 μm, d50=3.37 μm, d90=4.54 μm, dmax=6.65 μm, and particle size distribution span=0.61. Tap density td=2.20 g/cm 3 Specific surface area bet=12.03 m 2 /g。
The preparation of the positive electrode material comprises the steps of uniformly mixing the lithium hydroxide monohydrate and the obtained precursor in a high-speed mixer according to a molar ratio of 1.05:1, sintering for 12 hours at 750 ℃ in an oxygen atmosphere, naturally cooling to room temperature, grinding, pulverizing and sieving to obtain the positive electrode material, namely NCM-TY613.
And uniformly mixing the obtained positive electrode material with acetylene black and PVDF, coating the mixture on an aluminum foil to prepare a positive electrode plate, assembling the positive electrode plate, a lithium metal plate, a diaphragm and electrolyte in a vacuum glove box to form a button cell, and carrying out cycle and multiplying power performance test on the button cell.
Example 3
Respectively weighing NiSO with certain mass according to the molar ratio of Ni to Co to Mn=0.6 to 0.2 4 、CoSO 4 、MnSO 4 Dissolving in deionized water to prepare 100L of mixed salt solution with the concentration of 2mol/L, 8mol/L of sodium hydroxide solution and 3mol/L of ammonia water solution.
Adding deionized water into a reaction kettle provided with a circulating water bath heating system, an ammonia-alkali salt flow automatic control system and a pH automatic control system to submerge a pH meter probe, adding an aqueous ammonia solution into the reaction kettle until the ammonia concentration of a base solution is 0.45mol/L, adding a sodium hydroxide solution into the reaction kettle until the pH value of the base solution is=10.50, introducing nitrogen at a flow rate of 2.0+/-0.5L/h to protect for 3 hours, introducing nitrogen in the whole process of precursor kernel and shell formation, and keeping the reaction temperature at 65+/-1 ℃ and the rotating speed of a stirrer at 450+/-5 rpm.
And (3) adding the mixed salt solution, the sodium hydroxide solution and the ammonia water into the reaction kettle in parallel by using a peristaltic pump to start a precursor nuclear generation process, wherein the flow rate of the mixed salt solution is fixed to be 30+/-2 mL/min, the flow rate of the sodium hydroxide solution is determined in real time according to an automatic control system, and the flow rate of the ammonia water solution is added into the reaction kettle according to the required amount of different stages.
The method comprises the steps of stopping adding a mixed salt solution, a sodium hydroxide solution and an ammonia solution when the particle size of the precursor inner core is 10.0+/-0.5 mu m, switching nitrogen into air, adjusting the air flow rate to 300mL/min, carrying nano titanium dioxide into a kettle by air, micro-oxidizing newly arranged primary particles on the surface of the precursor inner core, thinning the primary particles, increasing the specific surface area, adsorbing the nano titanium dioxide carried into the kettle by air on the surface of the primary particles until the precursor particles are 15+/-0.5 mu m, switching nitrogen, and continuously adding the mixed salt solution, the sodium hydroxide solution and the ammonia solution into the kettle in parallel flow for reaction.
When the particle size of the materials in the reaction kettle is detected to reach 20+/-0.5 mu m, stopping reaction feeding, and continuing stirring and ageing for 3-4 hours.
Centrifuging and aging the slurry, washing the solid with sodium hydroxide solution, washing with pure water at 65-75 ℃, drying the material, sieving and demagnetizing to obtain a precursor material, and sealing and preserving.
The particle size distribution data obtained by taking a dry qualified sample are as follows: dmin=9.64 μm, d10=13.82 μm, d50=20.19 μm, d90=24.52 μm, dmax= 29.33 μm, and particle size distribution span=0.53. Tap density td=1.90 g/cm 3 Specific surface area bet=14.06 m 2 /g。
The preparation of the positive electrode material comprises the steps of uniformly mixing the lithium hydroxide monohydrate and the obtained precursor in a molar ratio of 1.10:1 in a high-speed mixer, sintering for 30 hours at 650 ℃ in an oxygen atmosphere, naturally cooling to room temperature, grinding, pulverizing and sieving to obtain the positive electrode material, namely NCM-TY622.
And uniformly mixing the obtained positive electrode material with acetylene black and PVDF, coating the mixture on an aluminum foil to prepare a positive electrode plate, assembling the positive electrode plate, a lithium metal plate, a diaphragm and electrolyte in a vacuum glove box to form a button cell, and carrying out cycle and multiplying power performance test on the button cell.
Comparative example 1
A seed boundary braiding precursor which differs from example 1 in that: and taking the gas of the nano titanium dioxide brought into the reaction kettle as nitrogen, and preparing the precursor. The particle size distribution data obtained by taking a dry qualified sample are as follows: dmin=6.29 μm, d10=8.48 μm, d50=11.18 μm, d90=14.87 μm, dmax=17.52 μm, and particle size distribution span=0.57. Tap density td=2.05 g/cm 3 Specific surface area bet=10.87 m 2 /g。
The preparation of the positive electrode material comprises the steps of uniformly mixing lithium hydroxide monohydrate and the obtained precursor in a high-speed mixer according to a molar ratio of 0.95:1, sintering for 10 hours at 800 ℃ in an oxygen atmosphere, naturally cooling to room temperature, grinding, pulverizing and sieving to obtain the positive electrode material, namely NCM-TY955.
And uniformly mixing the obtained positive electrode material with acetylene black and PVDF, coating the mixture on an aluminum foil to prepare a positive electrode plate, assembling the positive electrode plate, a lithium metal plate, a diaphragm and electrolyte in a vacuum glove box to form a button cell, and carrying out cycle and multiplying power performance test on the button cell.
Fig. 3 (a) and (b) are SEM images of the nano titania braid (fig. 3 (a)) and the finally obtained precursor material (fig. 3 (b)) during the preparation of comparative example 1, respectively. From the figure, the nano titanium dioxide weaving layer is uniformly distributed on the precursor primary particle sheet, and the prepared primary particles on the surface of the final precursor material are thick plate-shaped and are closely distributed.
Comparative example 2
A seed boundary braiding precursor which differs from example 1 in that: and (3) preparing a pure precursor without a nano titanium dioxide weaving layer. The particle size distribution data obtained by taking a dry qualified sample are as follows: dmin=6.85 μm, d10=8.71 μm, d50=11.38 μm, d90=15.11 μm, dmax=17.52 μm, particle size distribution span=0.56. Tap density td=1.98 g/cm 3 Specific surface area bet=11.57 m 2 /g。
The preparation of the positive electrode material comprises the steps of uniformly mixing lithium hydroxide monohydrate and the obtained precursor in a high-speed mixer according to a molar ratio of 0.95:1, sintering for 10 hours at 800 ℃ in an oxygen atmosphere, naturally cooling to room temperature, grinding, pulverizing and sieving to obtain the positive electrode material, namely NCM.
And uniformly mixing the obtained positive electrode material with acetylene black and PVDF, coating the mixture on an aluminum foil to prepare a positive electrode plate, assembling the positive electrode plate, a lithium metal plate, a diaphragm and electrolyte in a vacuum glove box to form a button cell, and carrying out cycle and multiplying power performance test on the button cell.
Fig. 4 (a) and (b) are SEM images of fig. 4 (a) and the final precursor material (fig. 4 (b)) of the non-nano titania woven layer in the preparation process of comparative example 2, respectively.
As can be seen from the figure, the precursor material prepared is spherical particles with uniform size, and the primary particles are flaky and are closely distributed.
To verify the progress of the examples of the present application, the button cells obtained in example 1, comparative example 1 and comparative example 2 were subjected to cycle performance test, and the results are shown in table 1, and a graph of the 100-cycle discharge capacity of the button cell versus the cycle number is shown in fig. 5.
TABLE 1 electrochemical performance parameters of button cell
Figure BDA0004178777810000121
As can be seen from table 1, compared with the precursor materials coated by nitrogen and the uncoated precursor materials, the capacity retention rate of the assembled button cell is higher after the precursor prepared by the technical scheme provided by the invention is baked into the positive electrode material. As can be seen from fig. 5, after the precursor prepared by the technical scheme provided by the invention is baked into the positive electrode material, the cycle stability and the cycle durability of the assembled button cell are more advantageous.

Claims (9)

1. The precursor is woven to grain boundary, its characterized in that: the nano-oxide composite material comprises a sandwich structure formed by a precursor inner core, a nano-oxide woven layer and a precursor outer shell.
2. The grain boundary woven precursor according to claim 1, wherein: the molecular formula of the precursor is as follows: m (OH) 2 Wherein M is selected from Ni, co, mn, al, fe, cu and OH - One or more of the elements that produce hydroxide precipitates.
3. The grain boundary woven precursor according to claim 2, characterized in that: the particle size of the precursor is 3-20 mu m; the specific surface area of the precursor is 10.00-14.00 m 2 /g; the tap density of the precursor is 1.90-2.20 g/cm 3 ；
The particle size of the precursor kernel is 1.2-10.0 mu m; the thickness of the nano oxide woven layer is 0.6-5.0 mu m.
4. A method of preparing a grain boundary woven precursor according to claim 3, characterized in that: the method specifically comprises the following steps:
step 1, according to precursor M (OH) 2 Preparing mixed salt solution A with the molar ratio of 2.0-8.0 mol/L, sodium hydroxide solution B with the molar ratio of 5.0-10.0 mol/L and ammonia water solution C with the molar ratio of 3.0-13.0 mol/L;
step 2, adding pure water, sodium hydroxide solution B and ammonia water C solution into a reaction kettle to prepare reaction base solution, and introducing nitrogen;
step 3, keeping nitrogen gas to be introduced, and adding the prepared mixed salt solution A, the sodium hydroxide solution B and the ammonia water solution C into the bottom solution of the reaction kettle in parallel to carry out coprecipitation reaction, and controlling the reaction temperature and the reaction pH to form a precursor inner core in the reaction kettle;
step 4, stopping adding the solution A, the solution B and the solution C into the reaction kettle when the core particle size of the precursor reaches a target value, switching nitrogen into air, carrying nano oxides into the kettle by the air at a fixed flow rate, thinning primary particles under the micro oxidation of the air, enabling pores to become more, forming a crystal boundary nano oxide woven layer, stopping adding the nano oxides when the nano oxide woven layer reaches a set thickness, and switching the nano oxide into the nitrogen;
step 5, continuously feeding and reacting the solution A, the solution B and the solution C to form a precursor shell, wrapping the nano oxide woven layer in the middle of the particles, stopping the reaction and feeding after the particle size of the precursor reaches the target particle size, and continuously stirring and ageing for 3-4 hours;
and 6, carrying out solid-liquid separation, washing and drying on the aged material in the step 5, and screening and demagnetizing to obtain the precursor with nano oxide grain boundary weaving.
5. The method for producing a grain boundary woven precursor according to claim 4, wherein: in the step 1, the mixed salt solution a is at least one of sulfate, acetate, nitrate and chloride.
6. The method for producing a grain boundary woven precursor according to claim 5, wherein: in the step 4, the air flow rate for carrying the nano oxide is 100-300 mL/min; the nano oxide is super-hydrophilic nano titanium dioxide.
7. The method for producing a grain boundary woven precursor according to claim 4, wherein: the reaction conditions in the precursor preparation process are as follows: the reaction is carried out at 55-65 ℃ with stirring speed of 450-600 + -5 rpm, pH value of 10.50-12.00 and ammonia concentration of 0.15-0.45 mol/L until the particle diameter D50 of the precursor reaches the target value.
8. A method of producing a positive electrode material according to claim 3, wherein: the precursor is prepared by mixing and sintering with lithium salt.
9. The method of producing a positive electrode material according to claim 8, wherein: the sintering process comprises the following steps: the molar ratio of the precursor to the lithium source is 0.95-1.10, and the precursor is sintered for 10-30 hours at 650-800 ℃, wherein the sintering atmosphere is oxygen atmosphere.
CN202310399198.4A 2023-04-14 2023-04-14 Grain boundary braiding precursor, positive electrode material and preparation method Pending CN116395759A (en)

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