CN107910543A - A kind of high-capacity lithium ion cell tertiary cathode modified material and preparation method thereof - Google Patents

Abstract

The invention relates to a high-capacity lithium-ion battery ternary positive electrode modified material and a preparation method thereof, comprising a positive electrode material, the outer layer of the positive electrode material is wrapped with a layer of coating material, and the mass ratio of the coating material to the positive electrode material is 1-6wt%. , the general chemical formula of the cathode material is Li(Ni _0.7 Co _0.1 Mn _0.2 ) _1‑x M _x O _2‑y N _y , where M is Mo, Fe, Ti, Mg, Al or Cr; N is F, Cl or Br, 0<x≤0.10, 0<y≤0.10, and the coating material is TiO ₂ , A1 ₂ O ₃ or FePO ₄ . During preparation, the raw materials are first obtained by sol-gel method to obtain a gel, and after heating and drying, After two times of burning and grinding, the positive electrode material was obtained, and then the positive electrode material and the coating material were suspended in deionized water, stirred at a constant temperature, then left to stand, filtered, washed, dried, and calcined to obtain a 721-type ternary positive electrode modified lithium-ion battery. sexual material. The preparation method of the present invention is simple, the steps are easy to operate, the prepared ternary cathode modified particle size distribution is uniform, the crystallinity is high, the rate performance and cycle performance of the material are improved, and the capacity is obviously improved.

Description

A kind of high-capacity lithium-ion battery ternary cathode modified material and preparation method thereof

technical field

The invention relates to a high-capacity lithium-ion battery ternary cathode modified material and a preparation method thereof, belonging to the technical field of lithium-ion battery cathode materials.

Background technique

In the components of lithium-ion batteries, the cathode material occupies a dominant factor in terms of price and performance. As far as the current level of development is concerned, the development of cathode materials is much slower than that of anode materials and electrolytes. Further improvement in the performance and safety of lithium-ion batteries requires continuous improvement in the cycle, rate performance, and thermal stability of cathode materials. . The ternary cathode material is a eutectic system of LiCoO ₂ /LiNiO ₂ /LiMn ₂ O ₄ , which combines the characteristics of LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ materials.

The higher content of Ni helps the material to obtain higher discharge capacity. At the same time, increasing the content of Mn, which contributes the most to the safety and stability of the material, can make the material cyclability and safety better, and is more suitable for practical applications. Therefore, LiNi _0.8 Co _0.1 Mn _0.1 O ₂ is a ternary cathode with more research value. Material.

As far as the requirements of commercial applications are concerned, what LiNi _0.7 Co _0.1 Mn _0.2 O ₂ cathode materials need to improve is the tap density, capacity density, cycle capacity, and high-rate charge-discharge capacity. In view of the shortcomings of the current LiNi _0.7 Co _0.1 Mn _0.2 O ₂ ternary cathode materials, researchers have mainly carried out partial doping or surface coating modification on the materials, and the doping modification is mainly by partially doping the cathode materials. Other metal ions with a radius similar to the host transition metal ion, or partially doped with anions such as F, Cl or Br, to achieve a more stable material structure and better cycle performance; coating this modification method on the surface of the positive electrode material Attaching a layer of chemically stable substances effectively avoids direct contact between the material and the electrolyte, and inhibits the interaction between them in this way to ensure the integrity and stability of the structure of the material during the cycle. In addition, the coating modification can also appropriately increase the electrical conductivity and tap density of the positive electrode material, so that the rate performance of the coated positive electrode material is better and it is conducive to industrial processing. This patent combines the two modification methods to perform synergistic modification of the LiNi _0.7 Co _0.1 Mn _0.2 O ₂ positive electrode material by doping or coating.

Contents of the invention

The object of the present invention is to solve the above problems, and provide a 721-type ternary positive electrode modified material and a preparation method thereof. The prepared positive electrode material has better particle rate performance and cycle performance.

The present invention adopts the following technical scheme: a high-capacity lithium-ion battery ternary positive electrode modified material, including a doped modified positive electrode material, the outer layer of the doped modified positive electrode material is wrapped with a layer of coating material, so The quality of the coating material is 1-6wt% of the doped modified positive electrode material, and the chemical formula of the doped modified positive electrode material is Li(Ni _0.7 Co. ₀₁ Mn _0.2 ) _1-x M _x O _2-y N _y , wherein, M is Mo, Fe, Ti,

Mg, Al or Cr; N is F, Cl or Br, 0<x≤0.10, 0<y≤0.10, and the coating material is TiO ₂ , Al ₂ O ₃ or FePO ₄ .

The preparation method of lithium ion battery 721 type ternary cathode modified material comprises the following steps:

(1) Dissolve water-soluble lithium source, nickel source, manganese source, cobalt source, M salt, N salt and citric acid in water and mix thoroughly, then adjust the pH value to 7-8 with ammonia water;

(2) stirring and heating the solution obtained in step (1) at 60-100° C. to obtain a gel;

(3) drying the gel obtained in step (2) at 80-150° C. for 8-15 hours to obtain a dry gel;

(4) pre-calcine the dry gel at 300-600°C for 4-8 hours, cool naturally to room temperature and grind to obtain the precursor;

(5) The precursor obtained in step (4) is baked at 700-1000° C. for 10-20 hours, and then ground after cooling to obtain a doped modified positive electrode material;

(6) The quality of the coating material is 1-6wt% of the doped modified positive electrode material to weigh the coating material, and the coating material is TiO ₂ , Al ₂ O ₃ or FePO ₄ ;

(7) Disperse the prepared doped modified cathode material and coating material in water or ethanol to completely dissolve the doped modified cathode material and coating material, stir vigorously at 40-80°C, and Adjust the pH at 9-10 until the solvent is completely volatilized. After stirring, let it stand for 1-2 hours and filter it with quantitative filter paper, wash it with deionized water for 1-2 times, then dry it at 80-85°C for 12-20 hours, and finally The final product is obtained by calcining at 400-500°C for 5-10 hours.

Further, the lithium source, nickel source, manganese source, cobalt source, M salt, and N salt are (1-y):(0.7-x) according to the molar ratio of lithium, nickel, manganese, cobalt, M, and N: (0.2-x):(0.1-x):x:y added, where 0<x≤0.10, 0<y≤0.10.

Further, the molar ratio of the total molar weight of nickel salt, cobalt salt and manganese salt to citric acid is 1:1˜1:2.

Further, the lithium source is one or more of LiNO ₃ , CH ₃ COOLi, and LiOH.

Further, the nickel source is one or more of Ni(NO ₃ ) ₂ , Ni(CH ₃ COO) ₂ , and NiSO ₄ .

Further, the manganese source is one or more of Mn(NO ₃ ) ₂ , Mn(CH ₃ COO) ₂ , and MnSO ₄ .

Further, the cobalt source is one or more of Co(NO ₃ ) ₂ , Co(CH ₃ COO) ₂ , CoSO ₄

Further, the M salt is one of Mg(NO ₃ ) ₂ , C ₁₆ H ₃₆ O ₄ Ti, Al(NO ₃ ) ₃ or Cr(NO ₃ ) ₃ .

Further, the N salt is one of LiCl, LiF, and LiBr.

The preparation method of the present invention is simple, and the steps are easy to operate. The prepared positive electrode material has uniform particle size distribution, high crystallinity, smooth surface, and good particle dispersion. The existence of the material inhibits the occurrence of side reactions on the surface of the material and the electrolyte interface, reduces the impedance during the cycle, increases the diffusion rate of Li ⁺ , makes it easier to extract and insert Li ⁺ on the surface of the material, and improves the efficiency of doping and coating. The comprehensive effect of the properties has improved the rate performance and cycle performance of the material, and the raw materials required for doping and coating modification are cheap, which further reduces the cost required for the production of positive electrode materials and is conducive to promoting the commercialization process.

Description of drawings

Fig. 1 is the X-ray diffraction diagram of the positive electrode materials prepared in Comparative Example and Examples 2, 3 and 5.

Fig. 2 is a scanning electron micrograph of the positive electrode materials prepared in Comparative Example and Examples 2, 3, and 5.

Fig. 3 is the positive electrode material prepared in Comparative Example and Examples 2, 3, and 5, the first charge and discharge curves at room temperature at a current of 0.2C, and the discharge voltage range is 2.5-4.6V.

Fig. 4 is a cycle graph of positive electrode materials prepared in Comparative Example and Examples 2, 3, and 5 at room temperature at a current of 0.2C, and the charge and discharge voltage range is 2.5-4.6V.

Fig. 5 is the cycle graphs of positive electrode materials prepared in Comparative Example and Examples 2, 3, and 5 at different rates at room temperature, and the charge and discharge voltage range is 2.5-4.6V.

Detailed ways

The present invention will be further described below in conjunction with specific embodiments.

Comparative example: preparation of unmodified LiNi _0.7 Co _0.1 Mn _0.2 O ₂ cathode material.

Weigh analytically pure CH ₃ COOLi, Ni(CH ₃ COO) ₂ , Co(CH ₃ COO) ₂ , Mn(CH ₃ COO) ₂ according to the stoichiometric ratio (1.05:0.7:0.1:0.2) with deionized water Fully dissolve, add citric acid solution, the amount of citric acid solution added is equal to the sum of the molar weight of transition metal ions, after mixing evenly, adjust the pH value of the solution to 7.5 with concentrated ammonia water, heat and stir in a water bath at 80°C, so that various ions are fully complexed and evaporate the water to form a dark purple gel; dry the gel at 120°C for 10 hours, then place it at 500°C for 6 hours, grind it after cooling, and then bake it at 850°C for 20 hours to obtain LiNi _0.8 Co _0.1 Mn _0.1 O ₂ cathode material.

Embodiment 1: A kind of preparation method of high-capacity lithium-ion battery ternary cathode modified material, comprises the following steps:

(1) Weigh analytically pure CH ₃ COOLi·2H ₂ O, Ni(CH ₃ COO) ₂ ·4H ₂ O, Co(CH ₃ COO ) ₂ 4H ₂ O, Mn(CH ₃ COO) 4H ₂ O, Mg(NO ₃ ) ₂ 6H ₂ O, LiF were completely dissolved in deionized water respectively, and then added citric acid solution, the amount of citric acid solution Equal to the sum of the molar weights of transition metal ions, adjust the pH value to 7 with concentrated ammonia water after mixing;

(2) heating the mixed solution obtained in step (1) in a water bath at 60° C. to evaporate water, and stirring continuously to obtain a gel;

(3) drying the gel body in a blast drying oven, the drying temperature is 80°C, and the drying time is 8 hours to obtain a dry gel body;

(4) Pre-calcining the dried gel, the pre-calcination temperature is 300°C, and the pre-calcination time is 8 hours to obtain the precursor; the precursor is naturally cooled to room temperature and ground, and the ground precursor is heated at 700°C Carry out calcination, the calcination time is 10 hours, after calcination, naturally cool to room temperature, and then grind again to obtain the doped modified positive electrode material Li(Ni _0.7 Co _0.1 Mn _0.2 ) _0.97 Mg _0.03 O _1.97 F _0.03 .

(5) Disperse the above prepared doped modified positive electrode material and the coating material TiO with a mass fraction ratio of 1.0wt% in _an ethanol solvent, stir vigorously at 40°C, and adjust the pH at 9 until the solvent is completely volatilized After the stirring, the mixture was left to stand for 1 hour and filtered with quantitative filter paper, washed once with deionized water, dried at 80°C for 20 hours, and finally calcined at 400°C for 10h to obtain _the Li( Ni _0.7 Co _0.1 Mn _0.2 ) _0.97 Mg _0.03 O _1.97 F _0.03 .

Embodiment 2: a kind of preparation method of high-capacity lithium-ion battery ternary cathode modified material, comprises the following steps:

(1) Weigh analytically pure LiNO ₃ , Ni(NO ₃ ) ₂ ·6H ₂ O, Co(NO ₃ ) ₂ ·6H ₂ O, Mn(NO ₃ ) ₂ ·4H ₂ O, C ₁₆ H ₃₆ O ₄ Ti, and LiCl were completely dissolved in deionized water, respectively, and then added with citric acid solution. The amount of citric acid solution added was equal to the sum of the molar amounts of transition metal ions. After mixing evenly, adjust the pH value to 7.5 with concentrated ammonia water;

(2) heating the mixed solution obtained in step (1) in a water bath at 80° C. to evaporate water, and stirring continuously to obtain a gel;

(3) drying the gel body in a blast drying oven, the drying temperature is 100° C., and the drying time is 10 hours to obtain a dry gel body;

(4) Pre-calcining the dried gel, the pre-calcination temperature is 400°C, and the pre-calcination time is 5 hours to obtain the precursor; the precursor is naturally cooled to room temperature and ground, and the ground precursor is heated at 850°C Carry out calcination, the calcination time is 15 hours, after calcination, cool naturally to room temperature and then grind again to obtain the doped modified positive electrode material Li(Ni _0.7 Co _0.1 Mn _0.2 ) _0.95 Ti _0.05 O _1.95 Cl _0.05 .

(5) Disperse the prepared doped and modified positive electrode material and the coating material A1 ₂ O ₃ with a mass fraction ratio of 2.0 wt% in an appropriate amount of solvent, stir vigorously at 60°C, and adjust the pH to about 9, until the solvent evaporates completely. After stirring, let stand for 2 hours and filter with quantitative filter paper, wash twice with deionized water, dry at 85°C for 12 hours, and finally calcined at 450°C for 8 hours to obtain the final product surface coated with 2.0wt% A1 ₂ O ₃ Li (Ni _0.7 Co _0.1 Mn _0.2 ) _0.95 Ti _0.05 O _1.95 Cl _0.05 .

Embodiment 3: A kind of preparation method of lithium-ion battery 811 type ternary cathode modified material, comprises the following steps:

(1) Weigh analytically pure LiOH·H ₂ O, NiSO ₄ ·6H ₂ O, CoSO ₄ ·7H ₂ O, MnSO ₄ ·H ₂ according to the stoichiometric ratio (0.95:0.701:0.10:0.20:0.1:0.1) Dissolve O, Al(NO ₃ ) ₃ , and LiBr completely in deionized water, add citric acid solution in an amount equal to the sum of the molar amounts of transition metal ions, mix well and adjust the pH value to about 8 with concentrated ammonia water;

(2) heating the mixed solution obtained in step (1) in a water bath at 90° C. to evaporate water, and stirring continuously to obtain a gel;

(3) drying the gel body in a blast drying oven, the drying temperature is 120° C., and the drying time is 12 hours to obtain a dry gel body;

(4) Pre-calcining the dried gel, the pre-calcination temperature is 500°C, and the pre-calcination time is 6 hours to obtain the precursor; the precursor is naturally cooled to room temperature and ground, and the ground precursor is ground at 900°C Carry out calcination, the calcination time is 18 hours, after calcination, naturally cool to room temperature and then grind again to obtain the doped modified positive electrode material Li(Ni _0.7 Co _0.1 Mn _0.2 ) _0.9 Al _0.1 O _1.9 Br _0.1 .

(5) Disperse the doped modified positive electrode material prepared above and the coating material FePO ₄ with a mass fraction ratio of 3.0wt% in an appropriate amount of solvent, stir vigorously at 80°C, and adjust the pH at about 9 until the solvent completely volatile. After stirring, let stand for 1.5 hours and filter with quantitative filter paper, wash twice with deionized water, dry at 80°C for 15 hours, and finally calcinate at 500°C for 5h to obtain the final product surface coated with 3.0wt% FePO ₄ Li(Ni _0.7 Co _0.1 Mn _0.2 ) _0.9 Al _0.1 O _1.9 Br _0.1 .

Embodiment 4: a kind of preparation method of high-capacity lithium-ion battery ternary cathode modified material, comprises the following steps:

(1) Weigh analytically pure LiNO ₃ , Ni(NO ₃ ) ₂ ·6H ₂ O, Co(NO ₃ ) ₂ ·6H ₂ O, Mn(NO ₃ ) ₂ 4H ₂ O, Cr(NO ₃ ) ₃ 4H ₂ O and LiF were completely dissolved in deionized water respectively, then added to citric acid solution in an amount equal to the sum of the molar amounts of transition metal ions, mixed After uniformity, adjust the pH value to about 7.0 with concentrated ammonia water;

(2) heating the mixed solution obtained in step (1) in a water bath at 100° C. to evaporate water, and stirring continuously to obtain a gel;

(3) drying the gel body in a blast drying oven, the drying temperature is 150° C., and the drying time is 15 hours to obtain a dry gel body;

(4) Pre-calcining the dried gel, the pre-calcination temperature is 600°C, and the pre-calcination time is 4 hours to obtain the precursor; the precursor is naturally cooled to room temperature and ground, and the ground precursor is heated at 1000°C Carry out calcination, the calcination time is 20 hours, after calcination, naturally cool to room temperature and then grind again to obtain the doped modified positive electrode material Li(Ni _0.7 Co _0.1 Mn _0.2 ) _0.95 Cr _0.05 O _1.95 F _0.05 .

(5) Disperse the doped modified positive electrode material prepared above and the coating material _FePO with a mass fraction ratio of 5.5wt% in an appropriate amount of solvent, stir vigorously at 80°C, and adjust the pH at 9 until the solvent is completely Volatile. After stirring, let it stand for 1 hour and filter it with quantitative filter paper, wash it twice with deionized water, dry it at 80° C. for 12 hours, and finally calcinate it at 450° C. for ₅ hours to obtain the Li(Ni _0.7 Co _0.1 Mn _0.2 ) _0.95 Cr _0.05 O _1.95 F _0.05 .

Embodiment 5: A kind of preparation method of high-capacity lithium-ion battery ternary cathode modified material, comprises the following steps:

(1) Weigh analytically pure LiOH·H ₂ O, NiSO ₄ ·6H ₂ O, CoSO ₄ ·7H ₂ O, MnSO ₄ ·H ₂ according to the stoichiometric ratio (1.00:0.698:0.103:0.205:0.05:0.05) O, C ₁₆ H ₃₆ O ₄ Ti, and LiF were completely dissolved in deionized water respectively, and citric acid solution was added in an amount equal to the sum of molar amounts of transition metal ions. After mixing evenly, adjust the pH value to 7.5 with concentrated ammonia water;

(2) heating the mixed solution obtained in step (1) in a water bath at 90° C. to evaporate water, and stirring continuously to obtain a gel;

(3) drying the gel body in a blast drying oven, the drying temperature is 120° C., and the drying time is 12 hours to obtain a dry gel body;

(4) Pre-calcining the dried gel, the pre-calcination temperature is 500°C, and the pre-calcination time is 6 hours to obtain the precursor; the precursor is naturally cooled to room temperature and ground, and the ground precursor is ground at 850°C Carry out calcination, the calcination time is 20 hours, after calcination, naturally cool to room temperature and then grind again to obtain the doped modified positive electrode material Li(Ni _0.7 Co _0.1 Mn _0.2 ) _0.95 Ti _0.05 O _1.95 F _0.05 .

(5) Disperse the prepared doped modified positive electrode material and the coating material _TiO2 with a mass fraction ratio of 2.0wt% in an ethanol solvent, stir vigorously at 80 ° C, and adjust the pH at 9 until the solvent is completely volatilized After stirring, leave it to stand for 2 hours and filter it with quantitative filter paper, wash it twice with deionized water, then dry it at 82°C for 15 hours, and finally calcined at 480°C for 6h to obtain the final product surface coated with 2.0wt% TiO ₂ Li ( Ni _0.7 Co _0.1 Mn _0.2 ) _0.95 Ti _0.05 O _1.95 F _0.05 .

Embodiment 6: a kind of preparation method of high-capacity lithium-ion battery ternary cathode modified material, comprises the following steps:

(1) Weigh analytically pure CH ₃ COOLi·2H ₂ O, Ni(CH ₃ COO) ₂ ·4H ₂ O, Co(CH ₃ COO ) ₂ 4H ₂ O, Mn(CH ₃ COO) 4H ₂ O, Al(NO ₃ ) ₂ 9H ₂ O, LiCl were completely dissolved in deionized water respectively, then added citric acid solution, the amount of citric acid solution Equal to the sum of the molar weights of transition metal ions, adjust the pH value to 7 with concentrated ammonia water after mixing;

(2) heating the mixed solution obtained in step (1) in a water bath at 80° C. to evaporate water, and stirring continuously to obtain a gel;

(3) drying the gel body in a blast drying oven, the drying temperature is 100° C., and the drying time is 15 hours to obtain a dry gel body;

(4) Pre-calcining the dried gel, the pre-calcination temperature is 600°C, and the pre-calcination time is 6 hours to obtain the precursor; the precursor is naturally cooled to room temperature and ground, and the ground precursor is ground at 850°C Calcination was carried out for 20 hours. After calcination, it was naturally cooled to room temperature and then ground again to obtain a doped modified positive electrode material Li(Ni _0.7 Co _0.1 Mn _0.2 ) _0.97 Al _0.03 O _1.95 Cl _0.05 .

(5) Disperse the above-mentioned doped modified positive electrode material and the coating material _TiO with a mass fraction ratio of 5.5wt% in water, stir vigorously at 80 ° C, and adjust the pH to 9 until the solvent is completely volatilized, Stand still for 2 hours after stirring, filter with quantitative filter paper, wash with deionized water for 2 times, dry at 85°C for 18 hours, then calcinate at 450°C for 5h to obtain the final product surface coated with 5.5wt% TiO ₂ Li(Ni _0.7 Co _0.1 Mn _0.2 ) _0.97 Al _0.03 O _1.95 Cl _0.05 .

As can be seen from the X-ray diffraction patterns of Comparative Example and Examples 2, 3, and 5 in Fig. 1, the positive electrode material synthesized in Examples 2, 3, and 5 has a highly ordered two-dimensional hexagonal layered structure, and There are no impurity peaks belonging to doping elements and cladding materials, the main peaks (1003) and (104) of the XRD of each sample are obviously sharp, and the peaks of (101) and (006) are significantly split, which shows that the embodiment 2, The positive electrode materials prepared in 3 and 5 have obvious layered structure and good crystal form, especially the layered structure in Example 5 is the best.

As can be seen from the scanning electron microscope images of the comparative example in Figure 2 and Examples 2, 3, and 5, the comparative example particles are relatively fine and have a uniform particle size distribution, and the surface is smooth and the crystallinity is good. After doping and coating modification In the example of the example, the material particles are enlarged, and the particle agglomeration is more compact. In addition, the more obvious change of the modified material particles is that fine particles are attached to the surface of the material particles, indicating that TiO ₂ , A1 ₂ O ₃ and FePO ₄ coating materials are successfully coated on the surface of material particles.

Mix the positive electrode material powder, acetylene black, and polyvinylidene fluoride (PVDF) synthesized in Examples 1-6 at a mass fraction ratio of 80:12:8, add an appropriate amount of pyrrolidone, grind it into a uniform slurry, and evenly coat it on aluminum foil On, dry at 100°C, gun-cut (diameter 14mm), roll at 3MPa to make pole pieces, vacuum-dry at 80°C for 12 hours before use, assemble a button-type (CR2032) test battery in a glove box filled with argon , the negative electrode is a lithium sheet, the electrolyte is LB315[m(DMC):m(EMC):m(EC)=1:1:1] solution, and the diaphragm is a Celgard2325 porous film. The assembled battery was charged and discharged with LAND-CT2001A. The charging and discharging range is 2.5-4.6V.

Since the Li element in the obtained positive electrode material is volatile during high-temperature calcination, about 5% of Li will be lost, so the actual molar amount of lithium salt is about 5% higher than the theoretical amount.

Table 1 shows the electrochemical performance characterization results of batteries assembled from the positive electrode materials synthesized in Comparative Examples and Examples 2, 3, and 5 at room temperature and at a current density of 0.2C.

The assembled battery of the positive electrode material of comparative example and embodiment 2, 3, 5, the first charge-discharge curve figure under the current of 0.2C when normal temperature is as shown in Figure 3; As can be seen from Figure 3, the present invention implements 2, 3, 5 The charge-discharge curve of the battery assembled with the positive electrode material prepared in 1 is very smooth, and the voltage platform of the charge curve is lower than that of the comparative example, while the discharge curve platform of Example 5 is higher than that of the comparative example. OK, the result is consistent with the XRD test result above. The battery assembled by the positive electrode materials of Comparative Examples and Examples 2, 3, and 5 has a cycle curve at normal temperature as shown in Figure 4; as can be seen from Figure 4, the battery cycle stability of the materials of each Example is higher than that of the Comparative Example High, especially the cycle stability of Example 5 is the best, the battery assembled by the positive electrode material of Comparative Example and Example 2, 3, 5, respectively at 0.2C, 0.5C, 1C, 2.5C, The cycle graph of each cycle of 10 cycles under the condition of 0.2C rate is shown in Figure 5. It can be seen from Figure 5 that the electrochemical performance of the positive electrode material prepared in each embodiment is improved by coating the preparation method of the present invention. Be improved, especially the effect of 2% TiO2 coating is the best.

Table 1 Under the current density of 0.2C, the test results of charge and discharge performance of each embodiment are shown in the following table:

It can be seen from Table 1 that, compared with the positive electrode material without coating material in the comparative example, the coating of the positive electrode material by TiO ₂ , Al ₂ O ₃ or FePO ₄ coating material in Example 1-Example 6 of the present invention, The initial discharge specific capacity of the prepared positive electrode material is improved, and the cycle stability is improved, especially the Li(Ni _0.4 Co _0.2 Mn _0.4 ) _0.95 Ti _0.05 O _1.95 coated with 2.0wt% TiO ₂ prepared in Example 5 F _0.05 has the best effect, the capacity retention rate after 50 cycles is 99.8%, and the first discharge specific capacity is 188.9mAh/g.

Claims (10)

1. A ternary positive electrode modified material for a high-capacity lithium-ion battery and a preparation method thereof, characterized in that: it comprises a doped modified positive electrode material, and the outer layer of the doped modified positive electrode material is wrapped with a layer of coating material, the mass of the coating material is 1-6wt% of the doped modified positive electrode material, and the chemical general formula of the doped modified positive electrode material is Li(Ni _0.4 Co _0.2 Mn _0.4 ) _1-x M _x O _2-y N _y , wherein, M is Mo, Fe, Ti, Mg, Al or Cr; N is F, Cl or Br, 0<x≤0.10, 0<y≤0.10, the cladding material is TiO ₂ , Al ₂ O ₃ or FePO ₄ . 2. the preparation method of high-capacity lithium-ion battery ternary cathode modified material as claimed in claim 1, is characterized in that: comprise the steps: (1) Dissolve water-soluble lithium source, nickel source, manganese source, cobalt source, M salt, N salt and citric acid in deionized water and mix thoroughly, then adjust the pH value to 7-8 with ammonia water; (2) stirring and heating the solution obtained in step (1) at 60-100° C. to obtain a gel; (3) drying the gel obtained in step (2) at 80-150° C. for 8-15 hours to obtain a dry gel; (4) pre-calcine the dry gel at 300-600°C for 4-8 hours, cool naturally to room temperature and grind to obtain the precursor; (5) Put the precursor obtained in step (4) at 700-1000° C. for 10-20 hours, and continue grinding after cooling to obtain a doped modified positive electrode material; (6) The quality of the coating material is 1-6% of the doped modified positive electrode material and the coating material is weighed, and the coating material is TiO ₂ , Al ₂ O ₃ or FePO ₄ ; (7) Disperse the prepared doped modified cathode material and coating material in water or ethanol to completely dissolve the doped modified cathode material and coating material, stir vigorously at 40-80°C, and Adjust the pH to 9-10 until the solvent is completely volatilized. After stirring, let stand for 1-2 hours and filter with quantitative filter paper, wash with deionized water for 1-2 times, then dry at 80-85°C for 12-20 hours, and finally The final product is obtained by calcining at 400-500°C for 5-10 hours. 3. the preparation method of high-capacity lithium-ion battery ternary cathode modified material as claimed in claim 2, is characterized in that: described lithium source, nickel source, manganese source, cobalt source, M salt, N salt according to lithium, The molar ratio of nickel, manganese, cobalt, M, and N is (1-y):(0.7-x):(0.2-x):(0.1-x):x:y, where 0<x≤0.10, 0 <y≤0.10. 4. the preparation method of high-capacity lithium-ion battery ternary cathode modified material as claimed in claim 2 is characterized in that: the total molar weight of described nickel salt, cobalt salt and manganese salt and the mol ratio of citric acid are 1 :1～1:2. 5. The method for preparing a modified material for a ternary positive electrode of a high-capacity lithium-ion battery according to claim 2, wherein the lithium source is one or more of LiNO ₃ , CH ₃ COOLi, and LiOH. 6. The method for preparing a modified material for a ternary positive electrode of a high-capacity lithium-ion battery according to claim 2, wherein the nickel source is Ni(NO ₃ ) ₂ , Ni(CH ₃ COO) ₂ , NiSO ₄ one or more of. 7. The method for preparing a modified material for a ternary positive electrode of a high-capacity lithium-ion battery according to claim 2, wherein the manganese source is Mn(NO ₃ ) ₂ , Mn(CH ₃ COO) ₂ , MnSO ₄ one or more of. 8. The method for preparing a modified material for a ternary positive electrode of a high-capacity lithium-ion battery according to claim 2, wherein the cobalt source is Co(NO ₃ ) ₂ , Co(CH ₃ COO) ₂ , CoSO ₄ one or more of. 9. The preparation method of high-capacity lithium-ion battery ternary cathode modified material as claimed in claim 2, characterized in that: said M salt is Mg(NO ₃ ) ₂ , C ₁₆ H ₃₆ O ₄ Ti, Al( One of NO ₃ ) ₃ or Cr(NO ₃ ) ₃ . 10. The method for preparing a modified material for a ternary positive electrode of a high-capacity lithium-ion battery as claimed in claim 2, wherein the N salt is one of LiCl, LiF, and LiBr.