CN114361441A - A kind of preparation method of in-situ coating single crystal high nickel ternary positive electrode material - Google Patents

Abstract

The invention belongs to the technical field of lithium ion battery anode materials, and particularly relates to a preparation method of a single crystal high-nickel ternary anode material which is sintered at a low temperature and coated in situ. Mixing Ni_0.8Co_0.1Mn_0.1(OH)₂Mixing the raw materials with a lithium source in a certain proportion, simultaneously mixing a molybdenum-containing fluxing agent and a vanadium-containing fluxing agent, calcining the mixture in a microwave sintering furnace at a certain temperature, and preparing the monocrystal LiNi with in-situ coating layer molybdenum lithium vanadate_0.8Co_0.1Mn_0.1O₂A material. The surface of the electrolyte is coated with the molybdenum lithium vanadate, so that the electrolyte and the single crystal LiNi can be prevented from being coated with the molybdenum lithium vanadate_0.8Co_0.1Mn_0.1O₂Direct contact of the particle surfaces, thereby reducing unwanted side reactions, preventing the growth of CEI films and enhancing single crystal LiNi_0.8Co_0.1Mn_0.1O₂And (5) structural stability of the material. And the molybdenum lithium vanadate is a fast ion conductor, so that the lithium ion deintercalation capability can be enhanced, and the multiplying power performance of the material is further improved.

Description

A kind of preparation method of in-situ coating single crystal high nickel ternary positive electrode material

technical field

The invention belongs to the technical field of positive electrode materials for lithium ion batteries, and in particular relates to a method for preparing a single crystal high nickel ternary positive electrode material which is sintered at a low temperature and coated in-situ.

Background technique

In the context of the continuous warming of the field of new energy vehicles, lithium-ion batteries are also gradually developing under the impetus of the market. As far as the industrial level is concerned, the performance data of ternary cathode materials are relatively excellent. However, with the continuous improvement of consumer market demand and the continuous development of new energy fields, the performance of ternary cathode materials needs to be further improved to meet higher energy density requirements.

Traditional high-nickel ternary cathode materials are usually spherical secondary particles aggregated by nanoscale primary particles. Due to the low mechanical strength of the particles and the large surface area of the primary particles, there are problems such as low mechanical strength, poor high pressure resistance, and low compaction density. It reacts with CO ₂ to generate residual lithium, which affects the electrochemical performance of the cathode material. The ternary cathode material in the form of single crystal can avoid these problems and effectively improve the cycle performance, so it is very promising to be used in the power battery system as the mainstream cathode material in the market. However, it is not easy to synthesize single-crystal cathode materials, especially nickel-rich ternary cathode materials. So far, single-crystal ternary cathode materials are generally prepared by two-stage high-temperature sintering, that is, the first-stage high-temperature sintering is used to prepare single-crystal cathode materials, and the second-stage medium-temperature sintering is used for surface modification. However, high-temperature sintering is likely to cause lithium loss, formation of NiO rock-salt phase, and Li/Ni mixing, which reduces the electrochemical performance of cathode materials. At present, the flux growth method is another synthesis method of single crystal ternary cathode materials. The addition of flux can effectively reduce the sintering temperature of single crystal ternary material, reduce the mixing of Li/Ni, and improve the electrochemical performance. At present, the conventional fluxes are mainly KCl, NaCl, LiNO ₃ , etc., but the single-crystal high-nickel ternary cathode materials prepared with such fluxes need to be washed with water and coated twice to improve the surface of the cathode material. Air Sensitivity.

In order to solve this technical problem, this scheme provides a new method for preparing single-crystal high-nickel ternary cathode materials with surface in-situ modification by one-step sintering. We have used vanadium- and molybdenum-containing compounds as fluxes. On the one hand, the melting point is lower and the boiling point is higher due to the strong fluxing effect of the two. On the other hand, in the process of preparing single crystal ternary cathode material, the flux can react with lithium salt to form a lithium molybdenum vanadate coating layer in situ, thereby improving the electrochemical performance and structural stability of the material.

SUMMARY OF THE INVENTION

The invention provides a preparation method of a single crystal LiNi _0.8 Co _0.1 Mn _0.1 O ₂ positive electrode material coated in-situ with lithium molybdenum vanadate. The precursor Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ of the commercial single crystal LiNi _0.8 Co _0.1 Mn _0.1 O ₂ material is mixed with a lithium source in a certain proportion, and the lithium source is: lithium oxalate, lithium nitrate, lithium carbonate or hydroxide lithium. At the same time, molybdenum-containing and vanadium-containing fluxes are mixed, and calcined in a microwave sintering furnace at a certain temperature to prepare a single-crystal LiNi _0.8 Co _0.1 Mn _0.1 O ₂ material with an in-situ cladding layer of lithium molybdenum vanadate. The direct contact between the electrolyte and the surface of the single crystal LiNi _0.8 Co _0.1 Mn _0.1 O ₂ particles can be prevented by surface coating with lithium molybdenum vanadate, thereby reducing unnecessary side reactions, preventing the growth of the CEI film and improving the single crystal LiNi _0.8 Co _0.1 Structural stability of Mn _0.1 O ₂ materials. Moreover, lithium molybdenum vanadate is a fast ion conductor, which can enhance the ability of lithium ion deintercalation and further improve the rate performance of the material.

The technical effect of the present invention is achieved through the following technical solutions:

A single crystal LiNi _0.8 Co _0.1 Mn _0.1 O ₂ positive electrode material coated in-situ with lithium molybdenum vanadate, the material is prepared by the following method, and the method steps include:

(1) Mix the nickel-cobalt-manganese hydroxide Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ and the lithium salt in a molar ratio of 1:1.06 to 1:1.2, and grind them sufficiently to obtain a mixed powder a;

(2) Mix the mixed powder b formed by the molybdenum-containing flux and the vanadium-containing flux with the mixed powder a and grind them uniformly to obtain the mixed powder c; wherein, the mass fraction of the mixed powder b in the mixed powder c is 2% ~10%;

(3) Under the oxygen atmosphere, the mixed powder c was raised to 120-180°C at a heating rate of 2-10°C/min for 2-3 hours, and was raised to 400-500°C at a heating rate of 2-10°C/min. ℃ and hold for 4-6 hours, then rise to 800-900℃ at a heating rate of 1-2 ℃/min and hold for 12-18 hours, and cool with the furnace to obtain solid block materials;

(4) After crushing and grinding the solid block material, mix it with deionized water at a mass ratio of 1:10, ultrasonically disperse it for 5 minutes, then quickly suction filter it and place it in a blast drying oven at 120°C for 2 hours, and collect the dried solid , to obtain a single-crystal LiNi _0.8 Co _0.1 Mn _0.1 O ₂ positive electrode material coated with lithium molybdenum vanadate in situ.

Preferably, the molar ratio of the nickel-cobalt-manganese hydroxide and the lithium salt in step (1) is 1:1.08-1.15.

Preferably, the lithium salt in step (1) is one of lithium hydroxide, lithium carbonate, lithium nitrate and lithium oxalate, preferably lithium oxalate.

Preferably, the molar ratio of the metal ion vanadium and the metal ion molybdenum in the vanadium-containing flux and the molybdenum-containing flux in the mixed powder b in step (2) is 1:1.

Preferably, the vanadium-containing fluxing agent in step (2) is vanadium trioxide (V ₂ O ₃ ), vanadium pentoxide (V ₂ O ₅ ) or ammonium metavanadate (NH ₄ VO ₃ ); the molybdenum-containing flux The flux is molybdenum oxide (MoO ₃ ) or ammonium molybdate ((NH ₄ ) ₂ MoO ₄ ).

Preferably, in step (2), other fluxes may be added to the mixed powder b, and the other fluxes are potassium fluoride (KF), calcium chloride (CaCl ₂ ), lithium chloride (LiCl), lead oxide One of (PbO), boron oxide (B ₂ O ₃ ), and sodium chloride (NaCl).

Preferably, the mass fraction of the other fluxes is 10% to 50% of the mixed powder b.

Preferably, in step (3), the mixed powder c is raised to 160°C at a heating rate of 5°C/min in an oxygen atmosphere for 2 hours, then raised to 450°C at a heating rate of 5°C/min and kept for 5 hours, and then The temperature was raised to 880°C at a heating rate of 1°C/min and kept for 16h, followed by cooling in the furnace to obtain a solid block material.

A lithium ion battery, the positive electrode material of the battery adopts the single crystal NCM ternary material in-situ coated with lithium molybdenum vanadate according to the present invention.

Beneficial effects:

In the method of the present invention, firstly, the single crystal LiNi _0.8 Co _0.1 Mn _0.1 O ₂ positive electrode material precursor is mixed with the lithium salt, and the molybdenum-containing flux and the vanadium-containing flux are added at the same time, and then the mixed powder is heat-treated and then crushed , water washing, in which the molybdenum-containing flux and vanadium-containing flux can not only promote the independent growth of primary particles in the early stage of calcination, but also control the particle size.

At the same time, in the later stage of high temperature calcination, the molybdenum-containing flux, vanadium-containing flux and lithium salt react to generate lithium molybdenum vanadate, which is coated on the surface of the single-crystal LiNi _0.8 Co _0.1 Mn _0.1 O ₂ positive electrode material, and finally an in-situ coating is obtained. A micron-scale single crystal LiNi _0.8 Co _0.1 Mn _0.1 O ₂ positive electrode material with better single crystal morphology covered with lithium molybdenum vanadate.

In the material prepared by the method of the present invention, the lithium molybdenum vanadate coating layer can inhibit the direct contact between the electrolyte and the single crystal LiNi _0.8 Co _0.1 Mn _0.1 O ₂ positive electrode material, thereby reducing the side reactions at the interface and maintaining the stability of the material structure. At the same time, lithium molybdenum vanadate, as a fast ion conductor, can promote lithium ion deintercalation and improve the electrochemical performance of single crystal LiNi _0.8 Co _0.1 Mn _0.1 O ₂ cathode material.

In the method of the present invention, the simultaneous addition of other fluxes in the powder mixing stage can further promote the growth of primary particles of the single crystal LiNi _0.8 Co _0.1 Mn _0.1 O ₂ positive electrode material and reduce the calcination temperature.

In the method of the present invention, a better single-crystal LiNi _0.8 Co _0.1 Mn _0.1 O ₂ positive electrode material can be obtained by pre-firing treatment in the high-temperature calcination stage.

Description of drawings

FIG. 1 is a cycle performance comparison diagram of the single-crystal LiNi _0.8 Co _0.1 Mn _0.1 O ₂ cathode materials prepared in Example 1 and Comparative Example 1. FIG.

FIG. 2 is a comparison diagram of the rate performance of the single-crystal LiNi _0.8 Co _0.1 Mn _0.1 O ₂ cathode materials prepared in Example 1 and Comparative Example 1. FIG.

Fig. 3 SEM image of the LiNi _0.8 Co _0.1 Mn _0.1 O ₂ cathode material coated with lithium molybdenum vanadate in Example 1

Fig. 4 TEM image of the LiNi _0.8 Co _0.1 Mn _0.1 O ₂ cathode material coated with lithium molybdenum vanadate in Example 1

Detailed ways

Comparative Example 1:

(1) grinding Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ and lithium oxalate according to a molar ratio of 1:1.08 to obtain mixed powder a;

(2) Mix the mixed powder a and mix it with NaCl as the mixed powder b and grind it uniformly. The obtained powder is marked as mixed powder c, and the mass ratio of the mixed powder b in the mixed powder c is controlled at 4%; the NaCl in the mixed powder b The quality score is 100%;

(3) Then put the mixed powder c in a microwave sintering furnace, raise the temperature to 160°C at a heating rate of 5°C/min for 2 hours, and then raise it to 450°C at a heating rate of 5°C/min and keep it for 5 hours. , and then raised to 880°C at a heating rate of 1°C/min and kept for 16h, followed by cooling in the furnace to obtain a solid block material;

(4) After crushing and grinding the solid block material, mix it with deionized water at a mass ratio of 1:10, ultrasonically disperse it for 5 minutes, and then place it in a blast drying oven at 120° C. for 2 hours after rapid suction filtration. After the solid is collected and dried, a single crystal LiNi _0.8 Co _0.1 Mn _0.1 O ₂ positive electrode material is obtained.

According to the scanning electron microscope results of the final product, it can be seen that the final product is a single crystal particle with a smooth surface and no impurities.

According to the electrochemical test results of the final product, the assembled battery was found to have a capacity retention rate of 70.8% after 200 cycles of cycling at a rate of 1C (1C=200mAh·g ^-1 ) within the cut-off voltage range of 2.8-4.3V. , and then the rate performance test at 0.1C-5C was carried out, and the discharge capacity at 5C reached 95.2mAh·g ^-1 . This indicates that the material has poor cycle stability and rate performance.

Example 1

(1) grinding Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ and lithium oxalate according to a molar ratio of 1:1.08 to obtain mixed powder a;

(2) Weigh mixed powder b of vanadium oxide and molybdenum oxide and mix with mixed powder a, grind and mix evenly to obtain mixed powder c, wherein the mass fraction of mixed powder b in mixed powder c is 4%; Vanadium oxide and molybdenum oxide are mixed according to the molar ratio of metal ion vanadium and metal ion molybdenum 1:1;

(3) The mixed powder c was then placed in a microwave sintering furnace, raised to 160°C at a heating rate of 5°C/min for 2 hours, and then raised to 450°C at a heating rate of 5°C/min, and kept for 5 hours , and then raised to 880°C at a heating rate of 1°C/min and kept for 16h, followed by cooling in the furnace to obtain solid bulk materials;

(4) After crushing and grinding the solid block material, mix it with deionized water at a mass ratio of 1:10, ultrasonically disperse it for 5 minutes, and then place it in a blast drying oven at 120° C. for 2 hours after rapid suction filtration. After the solid is collected and dried, a single crystal LiNi _0.8 Co _0.1 Mn _0.1 O ₂ positive electrode material in-situ coated with lithium molybdenum vanadate is obtained;

According to the scanning electron microscope results of the prepared material, Fig. 3, it can be seen that the morphology is micron-scale single crystal particles. As shown in Fig. 4, it can be found that there are coatings on the surface of the single crystal particles.

According to the electrochemical test results of the final product, the assembled battery was found to have a capacity retention rate of 85.15% after 200 cycles of cycling at a rate of 1 C within the cut-off voltage range of 2.8-4.3 V. Subsequently, the rate performance test of 0.1C-5C was carried out, and the discharge capacity at 5C reached 132.2mAh·g ^-1 . It shows that the cycling stability and rate performance of the material after in-situ coating of lithium molybdenum vanadate are improved.

Example 2

(1) grinding Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ and lithium oxalate according to a molar ratio of 1:1.08 to obtain mixed powder a;

(2) Weigh mixed powder b of vanadium oxide and molybdenum oxide and mix with mixed powder a, grind and mix evenly to obtain mixed powder c, wherein the mass fraction of mixed powder b in mixed powder c is 6%; Vanadium oxide and molybdenum oxide are mixed according to the molar ratio of metal ion vanadium and metal ion molybdenum 1:1;

(3) Then put the mixed powder c in a microwave sintering furnace, raise the temperature to 160°C at a heating rate of 5°C/min for 2 hours, and then raise it to 450°C at a heating rate of 5°C/min and keep it for 5 hours. , and then raised to 880°C at a heating rate of 1°C/min and kept for 16h, followed by cooling in the furnace to obtain a solid block material;

(4) After crushing and grinding the solid block material, mix it with deionized water at a mass ratio of 1:10, ultrasonically disperse it for 5 minutes, and then place it in a blast drying oven at 120° C. for 2 hours after rapid suction filtration. After the solid is collected and dried, a single crystal LiNi _0.8 Co _0.1 Mn _0.1 O ₂ positive electrode material in-situ coated with lithium molybdenum vanadate is obtained;

According to the scanning electron microscope results of the prepared materials, which are similar to those in Figure 3, it can be seen that the morphology is micron-sized single crystal particles. Similar to Figure 4, it can be found that there is a coating on the surface of the single crystal particles.

According to the electrochemical test results of the final product, the assembled battery was found to have a capacity retention rate of 83.27% after 200 cycles of cycling at a rate of 1 C within the cut-off voltage range of 2.8-4.3 V. Subsequently, the rate performance test of 0.1C-5C was carried out, and the discharge capacity at 5C reached 127.2mAh·g ^-1 . It shows that the cycling stability and rate performance of the material after in-situ coating of lithium molybdenum vanadate are improved.

Example 3

(1) grinding Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ and lithium oxalate according to a molar ratio of 1:1.08 to obtain mixed powder a;

(2) Weigh mixed powder b of vanadium oxide and molybdenum oxide and mix with mixed powder a, grind and mix uniformly to obtain mixed powder c, wherein the mass fraction of mixed powder b in mixed powder c is 8%; Vanadium oxide and molybdenum oxide are mixed according to the molar ratio of metal ion vanadium and metal ion molybdenum 1:1;

(3) The mixed powder c was then placed in a microwave sintering furnace, raised to 160°C at a heating rate of 5°C/min for 2 hours, and then raised to 450°C at a heating rate of 5°C/min, and kept for 5 hours , and then raised to 880°C at a heating rate of 1°C/min and kept for 16h, followed by cooling in the furnace to obtain solid bulk materials;

(4) After crushing and grinding the solid block material, mix it with deionized water at a mass ratio of 1:10, ultrasonically disperse it for 5 minutes, and then place it in a 120°C blast drying oven for 2 hours after rapid suction filtration. After the solid is collected and dried, a single crystal LiNi _0.8 Co _0.1 Mn _0.1 O ₂ positive electrode material coated in-situ with lithium molybdenum vanadate is obtained;

According to the scanning electron microscope results of the prepared materials, which are similar to those in Figure 3, it can be seen that the morphology is micron-scale single crystal particles. Similar to Figure 4, it can be found that there are coatings on the surface of the single crystal particles.

According to the electrochemical test results of the final product, the assembled battery was found to have a capacity retention rate of 81.77% after 200 cycles of cycling at a rate of 1 C within the cut-off voltage range of 2.8-4.3 V. Subsequently, the rate performance test of 0.1C-5C was carried out, and the discharge capacity at 5C reached 125.2mAh·g ^-1 . It shows that the cycling stability and rate performance of the material after in-situ coating of lithium molybdenum vanadate are improved.

Example 4

(1) grinding Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ and lithium oxalate according to a molar ratio of 1:1.08 to obtain mixed powder a;

(2) Weigh mixed powder b of vanadium oxide, molybdenum oxide and lead oxide and mix with mixed powder a, grind and mix evenly to obtain mixed powder c, wherein the mass fraction of mixed powder b in mixed powder c is 8%; Vanadium oxide and molybdenum oxide in powder b are mixed according to the metal ion molar ratio of 1:1, and the mass fraction of lead oxide accounts for 40% of the mixed powder b;

(3) Then put the mixed powder c in a microwave sintering furnace, raise the temperature to 160°C at a heating rate of 5°C/min for 2 hours, and then raise it to 450°C at a heating rate of 5°C/min and keep it for 5 hours. , and then raised to 880°C at a heating rate of 1°C/min and kept for 16h, followed by cooling in the furnace to obtain a solid block material;

(4) After crushing and grinding the solid block material, mix it with deionized water at a mass ratio of 1:10, ultrasonically disperse it for 5 minutes, and then place it in a blast drying oven at 120° C. for 2 hours after rapid suction filtration. After the solid is collected and dried, a single crystal LiNi _0.8 Co _0.1 Mn _0.1 O ₂ positive electrode material in-situ coated with lithium molybdenum vanadate is obtained;

According to the scanning electron microscope results of the prepared materials, which are similar to those in Figure 3, it can be seen that the morphology is micron-scale single crystal particles. Similar to Figure 4, it can be found that there are coatings on the surface of the single crystal particles.

According to the electrochemical test results of the final product, the assembled battery was found to have a capacity retention rate of 82.54% after 200 cycles of cycling at a rate of 1 C within the cut-off voltage range of 2.8-4.3 V. Subsequently, the rate performance test of 0.1C-5C was carried out, and the discharge capacity at 5C reached 122.1mAh·g ^-1 . It shows that the cycle stability and rate performance of the prepared single crystal ternary cathode material are improved.

Claims (8)

1. a preparation method of in-situ coating single crystal high nickel ternary positive electrode material, is characterized in that, concrete steps are as follows: (1) Mix the nickel-cobalt-manganese hydroxide Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ and the lithium salt in a molar ratio of 1:1.06 to 1:1.2, and grind to obtain a mixed powder a; (2) Mix the mixed powder b formed by the molybdenum-containing flux and the vanadium-containing flux with the mixed powder a and grind them uniformly to obtain the mixed powder c; wherein, the mass fraction of the mixed powder b in the mixed powder c is 2% ~10%; (3) Under the oxygen atmosphere, the mixed powder c was raised to 120-180°C at a heating rate of 2-10°C/min for 2-3 hours, and was raised to 400-500°C at a heating rate of 2-10°C/min. ℃ and hold for 4-6 hours, then rise to 800-900℃ at a heating rate of 1-2 ℃/min and hold for 12-18 hours, and cool with the furnace to obtain solid block materials; (4) after the solid block material is crushed and ground, mixed with deionized water, placed in a blast drying oven to dry after ultrasonic dispersion and suction filtration, and the dried solid is collected to obtain a single crystal of in-situ coated lithium molybdenum vanadate LiNi _0.8 Co _0.1 Mn _0.1 O ₂ positive electrode material. 2. the preparation method of a kind of in-situ coating single crystal high nickel ternary positive electrode material as claimed in claim 1, is characterized in that, in step (1), the mole of described nickel cobalt manganese hydroxide and lithium salt The ratio is 1:1.08-1.15; the lithium salt is one of lithium hydroxide, lithium carbonate, lithium nitrate and lithium oxalate. 3 . The method for preparing an in-situ coated single-crystal high-nickel ternary positive electrode material according to claim 2 , wherein the lithium salt is lithium oxalate. 4 . 4. the preparation method of a kind of in-situ coating single crystal high nickel ternary positive electrode material as claimed in claim 1, is characterized in that, in step (2), in described mixed powder b, vanadium-containing flux and molybdenum-containing The molar ratio of metal ion vanadium and metal ion molybdenum in the flux is 1:1; the vanadium-containing flux is vanadium trioxide (V ₂ O ₃ ), vanadium pentoxide (V ₂ O ₅ ) or ammonium metavanadate (NH ₄ VO ₃ ); the molybdenum-containing flux is molybdenum oxide (MoO ₃ ) or ammonium molybdate ((NH ₄ ) ₂ MoO ₄ ). 5. A kind of preparation method of in-situ coating single crystal high nickel ternary positive electrode material as claimed in claim 1, it is characterized in that, in step (2), add other fluxing agent in mixed powder b, described other auxiliary The flux is one of potassium fluoride (KF), calcium chloride (CaCl ₂ ), lithium chloride (LiCl), lead oxide (PbO), boron oxide (B ₂ O ₃ ), and sodium chloride (NaCl); The mass fraction of the other fluxes is 10% to 50% of the mixed powder b. 6 . The method for preparing an in-situ coated single-crystal high-nickel ternary positive electrode material according to claim 1 , wherein in step (3), the mixed powder c is heated at 5° C. in an oxygen atmosphere. 7 . The heating rate per min was raised to 160°C for 2 h, then increased to 450°C with a heating rate of 5°C/min and kept for 5 h, then raised to 880°C with a heating rate of 1°C/min and kept for 16 h, and cooled with the furnace to obtain a solid bulk material. 7. the preparation method of a kind of in-situ coating single crystal high nickel ternary positive electrode material as claimed in claim 1, is characterized in that, in step (3), after described solid block material is crushed and ground and deionized The water was mixed at a mass ratio of 1:10, dispersed by ultrasonic for 5 minutes, and then quickly filtered and placed in a blast drying oven at 120 °C for 2 hours. 8 . A lithium ion battery, wherein the positive electrode material of the lithium ion battery adopts the in-situ coated single crystal high nickel ternary positive electrode material prepared by the preparation method according to any one of claims 1 to 7 .

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