A molybdenum-doped double-coated high-voltage nickel-manganese binary positive electrode material and its preparation method

Abstract

The present invention discloses a molybdenum-doped double-coated high-voltage nickel-manganese binary positive electrode material and a preparation method thereof. The material comprises a molybdenum-doped nickel-manganese positive electrode material and a double coating layer coated on the surface of the molybdenum-doped nickel-manganese positive electrode material; the chemical formula of the molybdenum-doped nickel-manganese positive electrode material is Li(Ni x Mn y ) 1‑z Mo z O2, where 0.5≤x<1,0

Description

Technical Field

[0001] The present invention belongs to the field of battery materials, and particularly relates to a molybdenum-doped double-coated high-voltage nickel-manganese binary cathode material and a preparation method thereof. Background Art

[0002] In order to maximize the performance of cathode materials while achieving high energy density and low cost, more and more researchers in the battery industry have begun to focus on layered cathode materials with high nickel (Ni), low cobalt (Co), or no cobalt (Co). However, due to the rarity of current cobalt ores, their lack and uneven distribution in the earth's crust, they are restricted by high costs and ecological unfriendliness problems. Therefore, developing new cathode materials and reducing or even abandoning the use of cobalt in the battery industry is an inevitable trend in the research and development of high specific energy power batteries. Medium and low nickel content cathode materials such as NCM-523 and NCM-622 have occupied a large share in the global production of ternary cathodes due to their high thermal stability, long cycle life, and low manufacturing cost. In this context, it is very attractive to remove Co from medium and low nickel layered cathodes without affecting their performance. However, due to the absence of cobalt elements, the performance of cobalt-free binary cathode materials is poor. In addition, the higher the nickel content of the material, although the energy density is greater, the relative amount of residual alkali on the surface is more, and the cycle performance and thermal stability of the material become worse, making it difficult to meet the requirements of today's market. During the Li + insertion and extraction process, the layered material structure is in an extremely unstable state, and the cobalt-free binary is more likely to undergo irreversible phase transformation, generating a large number of microcracks, resulting in a large number of side reactions when the electrolyte contacts the new surface of the material. Summary of the Invention

[0003] The purpose of the present invention is to overcome the above-mentioned defects existing in the prior art, and provide a molybdenum-doped double-coated high-voltage nickel-manganese binary cathode material and a preparation method thereof. Using this cathode material to assemble a battery, its cycle stability is significantly enhanced, and at the same time, the discharge specific capacity is increased.

[0004] To achieve the above purpose, the present invention provides the following technical solutions:

[0005] The molybdenum-doped double-coated high-voltage nickel-manganese binary cathode material provided by the present invention includes a molybdenum-doped nickel-manganese cathode material and a double coating layer coated on the surface of the molybdenum-doped nickel-manganese cathode material; the chemical formula of the molybdenum-doped nickel-manganese cathode material is Li(Ni x Mn y ) 1-z Mo z O2, where 0.5 ≤ x < 1, 0 < y ≤ 0.5, 0 < z ≤ 0.05, and x + y = 1; the inner layer of the double coating layer is made of Al material, and the outer layer is PPy (polypyrrole).

[0006] It should be noted that the inner layer of the double coating is Al material, where Al material refers to a compound containing aluminum elements, which is formed by the reaction of an aluminum source with residual alkali on the surface of a molybdenum-doped nickel-manganese positive electrode material and oxidation sintering, such as Al2O3 and LiAlO2.

[0007] Preferably, the mass of the Al material in the double coating layer is 0.4%-2% of the mass of the molybdenum-doped nickel-manganese positive electrode material; the mass of the PPy is 0.5%-3% of the mass of the molybdenum-doped nickel-manganese positive electrode material.

[0008] Preferably, the molybdenum-doped double-coated high-voltage nickel-manganese binary positive electrode material can achieve an initial discharge specific capacity of 185-190 mAh / g at a 1C rate under 4.4V high-voltage charge and discharge conditions, and a capacity retention rate of 84-88% after 100 cycles at 1C.

[0009] The present invention also provides a method for preparing the molybdenum-doped double-coated high-voltage nickel-manganese binary positive electrode material, comprising the following steps:

[0010] (1) Using nickel salt and manganese salt as raw materials, spherical hydroxide precursor Ni x Mn y (OH)2;

[0011] (2) Ni prepared in step (1) x Mn y (OH)2 is mixed with the molybdenum source and the lithium source to obtain a mixture;

[0012] (3) Sintering the mixture obtained in step (2) in an oxygen atmosphere and cooling naturally to obtain a molybdenum-doped nickel-manganese positive electrode material Li (Ni x Mn y ) 1-z Mo z O2;

[0013] (4) Li(Ni) obtained in step (3) x Mn y ) 1-z Mo z O2 is mixed with aluminum source and then sintered in oxygen atmosphere to obtain Li(Ni x Mn y ) 1-z Mo z O2@Al materials;

[0014] (5) Li(Ni) obtained in step (4) x Mn y ) 1-z Mo z The surface of O2@Al material is coated with PPy to obtain molybdenum-doped double-coated high-voltage nickel-manganese binary positive electrode material Li(Nix Mn y ) 1-z Mo z O2@Al-PPy.

[0015] Preferably, in step (1), the nickel salt is selected from one or more of nickel sulfate, nickel nitrate, nickel carbonate, and nickel halide.

[0016] Preferably, in step (1), the manganese salt is selected from one or more of manganese sulfate, manganese nitrate, manganese acetate, and manganese halides.

[0017] Preferably, in step (2), the lithium source is selected from one or more of lithium hydroxide, lithium carbonate, lithium acetate and lithium nitrate.

[0018] Preferably, in step (2), the molybdenum source is selected from one or more of molybdenum oxide, ammonium molybdate, and sodium molybdate.

[0019] Preferably, in step (3), the sintering process conditions are: calcining at 400-600°C for 3-8 hours, and calcining at 750-850°C for 8-16 hours.

[0020] Preferably, in step (4), the aluminum source is selected from one or more of aluminum oxide, aluminum hydroxide, lithium metaaluminate, sodium metaaluminate, and aluminum halides.

[0021] Preferably, in step (4), the sintering process conditions are: calcination at 400-700° C. for 6-10 hours.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The molybdenum-doped double-coated high-voltage nickel-manganese binary positive electrode material of the present invention has a much higher capacity at a high-voltage cut-off voltage of 4.4V than at a cut-off voltage of 4.3V. Under the condition of 4.4V high-voltage charge and discharge, at a rate of 1C, the first discharge specific capacity can reach 185-190mAh / g, and after 100 cycles at 1C, the capacity retention rate can reach 84-88%.

[0024] (2) The present invention adds Mo to the nickel-manganese binary positive electrode material to construct a strong covalent Mo-O bond, which stabilizes the crystal structure while inhibiting the release of lattice oxygen during the cycle and reduces the structural phase change. 6+ The radius is slightly larger than Ni 3+ The addition of molybdenum can increase the c-axis of the material, which is more conducive to the +The high-valence element Mo increases the number of free electrons, thereby improving electronic conductivity. The material is then double-coated with aluminum and PPy to suppress side reactions with the electrolyte, enhancing material stability and improving both ionic and electronic conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 SEM image of O2@Al-PPy.

[0026] Figure 2 The positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 Cycling performance diagram of O2@Al-PPy at 1C rate.

[0027] Figure 3 The positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 The first charge and discharge curve of O2@Al-PPy.

[0028] Figure 4 This is an SEM image of the positive electrode material obtained in Comparative Example 2 of the present invention.

[0029] Figure 5 This is an SEM image of the positive electrode material obtained in Comparative Example 3 of the present invention.

[0030] Figure 6 This is an SEM image of the positive electrode material obtained in Comparative Example 4 of the present invention. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described in detail below with reference to specific embodiments.

[0032] Example 1

[0033] (1) First, prepare a 2 mol / L metal ion solution with a nickel-manganese molar ratio of 3:1. Dissolve NiSO4·6H2O and MnSO4·H2O in distilled water. Add the 2 mol / L metal ion solution, 2 mol / L ammonia solution, and 4 mol / L sodium hydroxide solution into the reactor at controlled flow rates. Maintain the pH value of the reactor at 11 and perform a coprecipitation reaction. 50When the particles grew to 6.5 μm, the reaction was stopped, filtered, washed with distilled water, and dried to obtain Ni 0.75 Mn 0.25 (OH)2 precursor.

[0034] (2) Ni was added at a ratio of (Ni+Mn):Mo=0.99:0.01 0.75 Mn 0.25 The (OH)2 precursor was dispersed in ammonium molybdate (water solution, then stirred vigorously at 80 ° C until the solvent was completely evaporated, and dried in an oven at 120 ° C to obtain (Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 (OH)2 precursor.

[0035] (3) LiOH·H2O and (Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 The (OH)2 precursor material is prepared with a metal ion ratio of Li:(Ni+Mn+Mo)=1.04:1, and appropriate amounts of LiOH·H2O and (Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 (OH)2, mixed in a high-efficiency mixer for 0.5h to make the materials uniformly mixed, and then sintered in two stages under an oxygen atmosphere, calcined at 500℃ for 4-6 hours and 800℃ for 12 hours, and naturally cooled to 100℃ to take out the sample to obtain the positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 O2.

[0036] (4) For the positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 O2 was used to detect the residual alkali. The content of Li2CO3 on the surface of the material was 0.103% and the content of LiOH was 0.283%. According to calculations, the surface of the material needs to be quantitatively coated with 1.134% Al(OH)3 to make the residual alkali on the surface of the material completely react with aluminum to form LiAlO2. It is worth noting that LiAlO2 is unstable and will decompose into Al2O3, eventually achieving Al2O3 / LiAlO2 coating. 0.75 Mn 0.25 ) 0.99 Mo 0.01O2 was fully mixed in anhydrous ethanol, ball milled at 100 revolutions per minute for 1 hour in a ball mill, and then dried. The obtained powder mixture was calcined at 600 ° C for 8 hours to obtain the positive electrode material Li (Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 O2@Al.

[0037] (5) In terms of molar ratio, 25 mg of pyrrole monomer and sodium p-toluenesulfonate were mixed at a ratio of 3:1 (mol / mol) under constant stirring, and an appropriate amount of anhydrous ethanol was added. 5 g of positive electrode material Li (Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 O2@Al was dissolved in the mixture and stirred continuously, and then the mixture was ultrasonically treated for 30 minutes. Then, under continuous stirring, FeCl3 anhydrous ethanol solution (100mg FeCl3 dissolved in 10ml anhydrous ethanol) was added dropwise to initiate polymerization. The reaction was stirred continuously in an ice bath for 6 hours, filtered, washed with anhydrous ethanol, and dried in a vacuum oven at 60℃ for 12 hours to obtain the positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 O2@Al-PPy.

[0038] Figure 1 The positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 SEM image of O2@Al-PPy.

[0039] Figure 2 The positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 Cycling performance diagram of O2@Al-PPy at 1C rate; Figure 3 The positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 The first charge and discharge curve of O2@Al-PPy. The positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01O2@Al-PPy was assembled into a battery: at a voltage of 2.8-4.4V and a rate of 1C, the initial discharge capacity reached 187.9mAh / g. After 100 cycles at 1C, the capacity was 162.3mAh / g, and the capacity retention rate reached 86.38%.

[0040] Example 2

[0041] (1) Preparation of Ni 0.75 Mn 0.25 (OH)2 precursor: same as in Example 1(1);

[0042] (2) Preparation (Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 (OH)2 precursor: same as in Example 1(2);

[0043] (3) Preparation of positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 O2: same as Example 1 (3);

[0044] (4) Preparation of positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 O2@Al: same as Example 1 (4);

[0045] (5) In terms of molar ratio, 50 mg of pyrrole monomer and sodium p-toluenesulfonate were mixed at a ratio of 3:1 (mol / mol) under constant stirring, and an appropriate amount of anhydrous ethanol was added. 5 g of positive electrode material Li (Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 O2@Al was dissolved in the mixture and stirred continuously, and then the mixture was ultrasonically treated for 30 minutes. Then, under continuous stirring, FeCl3 anhydrous ethanol solution (100mg FeCl3 dissolved in 10ml anhydrous ethanol) was added dropwise to initiate polymerization. The reaction was stirred continuously in an ice bath for 6 hours, filtered, washed with anhydrous ethanol, and dried in a vacuum oven at 60℃ for 12 hours to obtain the positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 O2@Al-PPy.

[0046] The positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01O2@Al-PPy was assembled into a battery: at a voltage of 2.8-4.4V and a rate of 1C, the initial discharge capacity reached 186.3mAh / g. After 100 cycles at 1C, the capacity was 160.2mAh / g, and the capacity retention rate reached 85.99%.

[0047] Example 3

[0048] (1) Preparation of Ni 0.75 Mn 0.25 (OH)2 precursor: same as in Example 1(1);

[0049] (2) Preparation (Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 (OH)2 precursor: same as in Example 1(2);

[0050] (3) Preparation of positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 O2: same as Example 1 (3);

[0051] (4) Preparation of positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 O2@Al: same as Example 1 (4);

[0052] (5) In terms of molar ratio, 100 mg of pyrrole monomer and sodium p-toluenesulfonate were mixed at a ratio of 3:1 (mol / mol) under constant stirring, and an appropriate amount of anhydrous ethanol was added. 5 g of positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 O2@Al was dissolved in the mixture and stirred continuously, and then the mixture was ultrasonically treated for 30 minutes. Then, under continuous stirring, FeCl3 anhydrous ethanol solution (100mg FeCl3 dissolved in 10ml anhydrous ethanol) was added dropwise to initiate polymerization. The reaction was stirred continuously in an ice bath for 6 hours, filtered, washed with anhydrous ethanol, and dried in a vacuum oven at 60℃ for 12 hours to obtain the positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 O2@Al-PPy.

[0053] The positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01O2@Al-PPy was assembled into a battery: at a voltage of 2.8-4.4V and a rate of 1C, the initial discharge capacity reached 185.0mAh / g. After 100 cycles at 1C, the capacity was 158.5mAh / g, and the capacity retention rate reached 85.68%.

[0054] Example 4

[0055] (1) Preparation of Ni 0.75 Mn 0.25 (OH)2 precursor: same as in Example 1(1);

[0056] (2) Preparation (Ni 0.75 Mn 0.25 ) 0.995 Mo 0.005 (OH)2 precursor: Ni is mixed with Mn in a ratio of (Ni+Mn):Mo=0.995:0.005. 0.75 Mn 0.25 The (OH)2 precursor was dispersed in ammonium molybdate (water solution, then stirred vigorously at 80 ° C until the solvent was completely evaporated, and dried in an oven at 120 ° C to obtain (Ni 0.75 Mn 0.25 ) 0.995 Mo 0.005 (OH)2 precursor;

[0057] (3) LiOH·H2O and (Ni 0.75 Mn 0.25 ) 0.995 Mo 0.005 The (OH)2 precursor material is prepared with a metal ion ratio of Li:(Ni+Mn+Mo)=1.04:1, and appropriate amounts of LiOH·H2O and (Ni 0.75 Mn 0.25 ) 0.995 Mo 0.005 (OH)2, mixed in a high-efficiency mixer for 0.5h to make the materials uniformly mixed, and then sintered in two stages under an oxygen atmosphere, calcined at 500℃ for 4-6 hours and 800℃ for 12 hours, and naturally cooled to 100℃ to take out the sample to obtain the positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.995 Mo 0.005 O2;

[0058] (4) For the positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.995 Mo 0.005O2 was used to detect the residual alkali. The content of Li2CO3 on the surface of the material was 0.131% and the content of LiOH was 0.396%. According to calculations, 1.563% Al(OH)3 should be quantitatively coated on the surface of the material to make the residual alkali on the surface of the material completely react with aluminum to form LiAlO2. It is worth noting that LiAlO2 is unstable and will decompose into Al2O3, eventually achieving Al2O3 / LiAlO2 coating. 0.75 Mn 0.25 ) 0.995 Mo 0.005 O2 was fully mixed in anhydrous ethanol, ball milled at 100 revolutions per minute for 1 hour in a ball mill, and then dried. The obtained powder mixture was calcined at 600 ° C for 8 hours to obtain the positive electrode material Li (Ni 0.75 Mn 0.25 ) 0.995 Mo 0.005 O2@Al;

[0059] (5) In terms of molar ratio, 25 mg of pyrrole monomer and sodium p-toluenesulfonate were mixed at a ratio of 3:1 (mol / mol) under constant stirring, and an appropriate amount of anhydrous ethanol was added. 5 g of positive electrode material Li (Ni 0.75 Mn 0.25 ) 0.995 Mo 0.005 O2@Al was dissolved in the mixture and stirred continuously, and then the mixture was ultrasonically treated for 30 minutes. Then, under continuous stirring, FeCl3 anhydrous ethanol solution (100mg FeCl3 dissolved in 10ml anhydrous ethanol) was added dropwise to initiate polymerization. The reaction was stirred continuously in an ice bath for 6 hours, filtered, washed with anhydrous ethanol, and dried in a vacuum oven at 60℃ for 12 hours to obtain the positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.995 Mo 0.005 O2@Al-PPy.

[0060] The positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.995 Mo 0.005 O2@Al-PPy was assembled into a battery: at a voltage of 2.8-4.4V and a rate of 1C, the initial discharge capacity reached 188.2mAh / g. After 100 cycles at 1C, the capacity was 160.5mAh / g, and the capacity retention rate reached 85.28%.

[0061] Example 5

[0062] (1) Preparation of Ni 0.75 Mn 0.25(OH)2 precursor: same as in Example 1(1);

[0063] (2) Ni was added at a ratio of (Ni+Mn):Mo=0.98:0.02 0.75 Mn 0.25 The (OH)2 precursor was dispersed in ammonium molybdate (water solution, then stirred vigorously at 80 ° C until the solvent was completely evaporated, and dried in an oven at 120 ° C to obtain (Ni 0.75 Mn 0.25 ) 0.98 Mo 0.02 (OH)2 precursor;

[0064] (3) LiOH·H2O and (Ni 0.75 Mn 0.25 ) 0.98 Mo 0.02 The (OH)2 precursor material is prepared with a metal ion ratio of Li:(Ni+Mn+Mo)=1.04:1, and appropriate amounts of LiOH·H2O and (Ni 0.75 Mn 0.25 ) 0.98 Mo 0.02 (OH)2, mixed in a high-efficiency mixer for 0.5h to make the materials uniformly mixed, and then sintered in two stages under an oxygen atmosphere, calcined at 500℃ for 4-6 hours and 800℃ for 12 hours, and naturally cooled to 100℃ to take out the sample to obtain the positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.98 Mo 0.02 O2.

[0065] (4) For the positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.98 Mo 0.02 O2 was used to detect the residual alkali. The content of Li2CO3 on the surface of the material was 0.247% and the content of LiOH was 0.145%. According to calculations, 0.992% Al(OH)3 should be quantitatively coated on the surface of the material to make the residual alkali on the surface of the material completely react with aluminum to form LiAlO2. It is worth noting that LiAlO2 is unstable and will decompose into Al2O3, eventually achieving Al2O3 / LiAlO2 coating. 0.75 Mn 0.25 ) 0.98 Mo 0.02 O2 was fully mixed in anhydrous ethanol, ball milled at 100 revolutions per minute for 1 hour in a ball mill, and then dried. The obtained powder mixture was calcined at 600 ° C for 8 hours to obtain the positive electrode material Li (Ni 0.75 Mn0.25 ) 0.98 Mo 0.02 O2@Al.

[0066] (5) In terms of molar ratio, 25 mg of pyrrole monomer and sodium p-toluenesulfonate were mixed at a ratio of 3:1 (mol / mol) under constant stirring, and an appropriate amount of anhydrous ethanol was added. 5 g of positive electrode material Li (Ni 0.75 Mn 0.25 ) 0.98 Mo 0.02 O2@Al was dissolved in the mixture and stirred continuously, and then the mixture was ultrasonically treated for 30 minutes. Then, under continuous stirring, FeCl3 anhydrous ethanol solution (100mg FeCl3 dissolved in 10ml anhydrous ethanol) was added dropwise to initiate polymerization. The reaction was stirred continuously in an ice bath for 6 hours, filtered, washed with anhydrous ethanol, and dried in a vacuum oven at 60℃ for 12 hours to obtain the positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.98 Mo 0.02 O2@Al-PPy.

[0067] The positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.98 Mo 0.02 O2@Al-PPy was assembled into a battery: at a voltage of 2.8-4.4V and a rate of 1C, the initial discharge capacity reached 187.0mAh / g. After 100 cycles at 1C, the capacity was 160.6mAh / g, and the capacity retention rate reached 85.88%.

[0068] Example 6

[0069] (1) Preparation of Ni 0.75 Mn 0.25 (OH)2 precursor: same as in Example 1(1);

[0070] (2) Ni was added at a ratio of (Ni+Mn):Mo=0.97:0.03 0.75 Mn 0.25 The (OH)2 precursor was dispersed in ammonium molybdate (water solution, then stirred vigorously at 80 ° C until the solvent was completely evaporated, and dried in an oven at 120 ° C to obtain (Ni 0.75 Mn 0.25 ) 0.97 Mo 0.03 (OH)2 precursor.

[0071] (3) LiOH·H2O and (Ni 0.75 Mn 0.25 ) 0.97Mo 0.03 The (OH)2 precursor material is prepared with a metal ion ratio of Li:(Ni+Mn+Mo)=1.04:1, and appropriate amounts of LiOH·H2O and (Ni 0.75 Mn 0.25 ) 0.97 Mo 0.03 (OH)2, mixed in a high-efficiency mixer for 0.5h to make the materials uniformly mixed, and then sintered in two stages under an oxygen atmosphere, calcined at 500℃ for 4-6 hours and 800℃ for 12 hours, and naturally cooled to 100℃ to take out the sample to obtain the positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.97 Mo 0.03 O2.

[0072] (4) For the positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.97 Mo 0.03 O2 was used to detect the residual alkali. The content of Li2CO3 on the surface of the material was 0.158% and the content of LiOH was 0.199%. According to calculations, 0.980% Al(OH)3 should be quantitatively coated on the surface of the material to make the residual alkali on the surface of the material completely react with aluminum to form LiAlO2. It is worth noting that LiAlO2 is unstable and will decompose into Al2O3, eventually achieving Al2O3 / LiAlO2 coating. 0.75 Mn 0.25 ) 0.97 Mo 0.03 O2 was fully mixed in anhydrous ethanol, ball milled at 100 revolutions per minute for 1 hour in a ball mill, and then dried. The obtained powder mixture was calcined at 600 ° C for 8 hours to obtain the positive electrode material Li (Ni 0.75 Mn 0.25 ) 0.97 Mo 0.03 O2@Al.

[0073] (5) In terms of molar ratio, 25 mg of pyrrole monomer and sodium p-toluenesulfonate were mixed at a ratio of 3:1 (mol / mol) under constant stirring, and an appropriate amount of anhydrous ethanol was added. 5 g of positive electrode material Li (Ni 0.75 Mn 0.25 ) 0.97 Mo 0.03O2@Al was dissolved in the mixture and stirred continuously, and then the mixture was ultrasonically treated for 30 minutes. Then, under continuous stirring, FeCl3 anhydrous ethanol solution (100mg FeCl3 dissolved in 10ml anhydrous ethanol) was added dropwise to initiate polymerization. The reaction was stirred continuously in an ice bath for 6 hours, filtered, washed with anhydrous ethanol, and dried in a vacuum oven at 60℃ for 12 hours to obtain the positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.97 Mo 0.03 O2@Al-PPy.

[0074] The positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.97 Mo 0.03 O2@Al-PPy was assembled into a battery: at a voltage of 2.8-4.4V and a rate of 1C, the initial discharge capacity reached 185.2mAh / g. After 100 cycles at 1C, the capacity was 157.4mAh / g, and the capacity retention rate reached 84.99%.

[0075] Comparative Example 1

[0076] (1) First, prepare a 2 mol / L metal ion solution with a nickel-manganese molar ratio of 3:1. Dissolve NiSO4·6H2O and MnSO4·H2O in distilled water. Add the 2 mol / L metal ion solution, 2 mol / L ammonia solution, and 4 mol / L sodium hydroxide solution into the reactor at controlled flow rates. Maintain the pH value of the reactor at 11 and perform a coprecipitation reaction. 50 When the particles grew to 6.5 μm, the reaction was stopped, filtered, washed with distilled water, and dried to obtain Ni 0.75 Mn 0.25 (OH)2 precursor.

[0077] (2) LiOH·H2O and Ni 0.75 Mn 0.25 The (OH)2 precursor material is prepared with a metal ion ratio of Li:(Ni+Mn)=1.04:1, and appropriate amounts of LiOH·H2O and Ni 0.75 Mn 0.25 (OH)2, mixed in a high-efficiency mixer for 0.5h to make the materials uniformly mixed, and then sintered in two stages under an oxygen atmosphere, calcined at 500℃ for 4-6 hours and 800℃ for 12 hours, and naturally cooled to 100℃ to take out the sample to obtain the positive electrode material LiNi 0.75 Mn 0.25 O2.

[0078] The positive electrode material LiNi obtained by this comparative example0.75 Mn 0.25 O2 is assembled into a battery: at a voltage of 2.8-4.4V and a rate of 1C, the initial discharge capacity reaches 175.6mAh / g. After 100 cycles at 1C, the capacity is 128.6mAh / g, and the capacity retention rate reaches 73.2%.

[0079] Comparative Example 2

[0080] (1) Preparation of Ni 0.75 Mn 0.25 (OH)2 precursor: same as (1) in Example 1.

[0081] (2) Preparation (Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 (OH)2 precursor: same as (2) in Example 1.

[0082] (3) Preparation of positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 O2: Same as (3) in Example 1.

[0083] The positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 The SEM image of O2 is as follows Figure 4 As shown. The positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 O2 is assembled into a battery: at a voltage of 2.8-4.4V and a rate of 1C, the initial discharge capacity reaches 176.0mAh / g. After 100 cycles at 1C, the capacity is 149.4mAh / g, and the capacity retention rate reaches 84.9%.

[0084] Comparative Example 3

[0085] (1) Preparation of Ni 0.75 Mn 0.25 (OH)2 precursor: same as (1) in Example 1;

[0086] (2) Preparation (Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 (OH)2 precursor: same as (2) in Example 1;

[0087] (3) Preparation of positive electrode material Li(Ni 0.75 Mn 0.25) 0.99 Mo 0.01 O2: same as (3) in Example 1;

[0088] (4) Preparation of positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 O2@Al: Same as (4) in Example 1.

[0089] The positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 The SEM image of O2@Al is shown in Figure 5 As shown. The positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 O2@Al is assembled into a battery: at a voltage of 2.8-4.4V and a rate of 1C, the initial discharge capacity reaches 184.1mAh / g. After 100 cycles at 1C, the capacity is 159.0mAh / g, and the capacity retention rate reaches 86.4%.

[0090] Comparative Example 4

[0091] (1) Preparation of Ni 0.75 Mn 0.25 (OH)2 precursor: same as (1) in Example 1;

[0092] (2) Preparation (Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 (OH)2 precursor: same as (2) in Example 1;

[0093] (3) Preparation of positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 O2: same as (3) in Example 1;

[0094] (4) Preparation of positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 O2@PPy: In terms of molar ratio,

[0095] 25mg of pyrrole monomer and sodium p-toluenesulfonate were mixed in a ratio of 3:1 (mol / mol) under constant stirring, and an appropriate amount of anhydrous ethanol was added. 5g of positive electrode material Li(Ni 0.75 Mn 0.25 )0.99 Mo 0.01 O2 was dissolved in it and stirred continuously, and then the mixture was ultrasonically treated for 30 minutes. Then, under continuous stirring, FeCl3 anhydrous ethanol solution (100 mg dissolved in 10 ml anhydrous ethanol) was dropped to initiate polymerization. The reaction was stirred continuously in an ice bath for 6 hours, filtered, washed with anhydrous ethanol, and dried in a vacuum oven at 60°C for 12 hours to obtain the positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 O2@PPy.

[0096] The positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 The SEM image of O2@PPy is shown in Figure 6 As shown. The positive electrode material Li(Ni 0.75 Mn 0.25 ) 0.99 Mo 0.01 O2@PPy was assembled into a battery: at a voltage of 2.8-4.4V and a rate of 1C, the initial discharge capacity reached 182.9mAh / g. After 100 cycles at 1C, the capacity was 157.2mAh / g, and the capacity retention rate reached 86.0%.

Claims

1. A molybdenum-doped double-coated high-voltage nickel-manganese binary positive electrode material, characterized in that: It includes a molybdenum-doped nickel manganese cathode material and a double coating layer coated on the surface of the molybdenum-doped nickel manganese cathode material; the chemical formula of the molybdenum-doped nickel manganese cathode material is Li(Ni x Mn y ) 1-z Mo z O2, where 0.5 ≤ x < 1, 0 < y ≤ 0.5, 0 < z ≤ 0.05, and x + y = 1; the inner layer of the double coating layer is made of Al material, and the outer layer is PPy; The molybdenum-doped double-coated high-voltage nickel-manganese binary positive electrode material is prepared by a preparation method comprising the following steps: (1) Using nickel salt and manganese salt as raw materials, synthesize spherical hydroxide precursor Ni x Mn y (OH)2; (2) Ni prepared in step (1) x Mn y (OH)2 is mixed with the molybdenum source and the lithium source to obtain a mixture; (3) The mixture obtained in step (2) is sintered in an oxygen atmosphere and cooled naturally to obtain a molybdenum-doped nickel-manganese positive electrode material Li(Ni x Mn y ) 1-z Mo z O2; (4) Li(Ni x Mn y ) 1-z Mo z O2 is mixed with aluminum source and then sintered in oxygen atmosphere to obtain Li(Ni x Mn y ) 1-z Mo z O2@Al materials; (5) Li(Ni x Mn y ) 1-z Mo z The surface of O2@Al material is coated with PPy to obtain molybdenum-doped double-coated high-voltage nickel-manganese binary positive electrode material Li(Ni x Mn y ) 1-z Mo z O2@Al-PPy; Wherein, the amount of the aluminum source in step (4) is such that the Li(Ni x Mn y ) 1-z Mo z The amount of residual alkali on the surface of O2 is completely reacted to form an Al material coating layer.

2. The molybdenum-doped double-coated high-voltage nickel-manganese binary positive electrode material according to claim 1, characterized in that: In the double coating layer, the mass of the Al material is 0.4-2% of the mass of the molybdenum-doped nickel-manganese positive electrode material, and the mass of the PPy layer is 0.5-3% of the mass of the molybdenum-doped nickel-manganese positive electrode material.

3. A method for preparing the molybdenum-doped double-coated high-voltage nickel-manganese binary positive electrode material according to claim 1 or 2, comprising the following steps: (1) Using nickel salt and manganese salt as raw materials, synthesize spherical hydroxide precursor Ni x Mn y (OH)2; (2) Ni prepared in step (1) x Mn y (OH)2 is mixed with the molybdenum source and the lithium source to obtain a mixture; (3) The mixture obtained in step (2) is sintered in an oxygen atmosphere and cooled naturally to obtain a molybdenum-doped nickel-manganese positive electrode material Li(Ni x Mn y ) 1-z Mo z O2; (4) Li(Ni x Mn y ) 1-z Mo z O2 is mixed with aluminum source and then sintered in oxygen atmosphere to obtain Li(Ni x Mn y ) 1-z Mo z O2@Al materials; (5) Li(Ni x Mn y ) 1-z Mo z The surface of O2@Al material is coated with PPy to obtain molybdenum-doped double-coated high-voltage nickel-manganese binary positive electrode material Li(Ni x Mn y ) 1-z Mo z O2@Al-PPy.

4. The preparation method according to claim 3, characterized in that In step (1), the nickel salt is selected from one or more of nickel sulfate, nickel nitrate, nickel carbonate, and nickel halides; the manganese salt is selected from one or more of manganese sulfate, manganese nitrate, manganese acetate, and manganese halides.

5. The preparation method according to claim 3, characterized in that In step (2), the lithium source is selected from one or more of lithium hydroxide, lithium carbonate, lithium acetate and lithium nitrate; the molybdenum source is selected from one or more of molybdenum oxide, ammonium molybdate and sodium molybdate.

6. The preparation method according to claim 3, characterized in that In step (3), the sintering process conditions are: calcining at 400-600°C for 3-8 hours, and calcining at 750-850°C for 8-16 hours.

7. The preparation method according to claim 3, characterized in that In step (4), the aluminum source is selected from one or more of aluminum oxide, aluminum hydroxide, lithium metaaluminate, sodium metaaluminate, and aluminum halides.

8. The preparation method according to claim 3, characterized in that In step (4), the sintering process conditions are: calcination at 400-700°C for 6-10 hours.

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