A lithium-rich ternary positive electrode material particle with core-shell structure and a preparation method and application thereof

Abstract

The application discloses a kind of lithium-rich ternary positive electrode material particles of core-shell structure and its preparation method and application.The inner core of lithium-rich ternary positive electrode material particles of core-shell structure of the present application is sodium surface doped lithium nickel cobalt manganese oxide particles, and the shell is phosphate coating layer, and the chemical formula of sodium surface doped lithium nickel cobalt manganese oxide particles is Li 1.2‑x Na x Ni 0.2 Co 0.08 Mn 0.52 O2, wherein, 0

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a lithium-rich ternary cathode material particle with core-shell structure and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries have the advantages of light weight, long service life, environmental friendliness, etc., and have been widely used in the field of electric vehicles and new energy vehicles in recent years. However, the current commercial large-scale application of lithium ion battery cathode materials LiCoO2, LiFePO4, high-nickel ternary LiNi x Co y Mn z O2(x+y+z=1, NCM) etc. have the problems of low capacity, high cost, poor safety, etc., which have failed to meet the growing demand of practical application.

[0003] Lithium-rich ternary cathode materials have the advantages of high capacity, high energy density, low cost, etc., and are expected to replace existing lithium ion battery cathode materials, and have received widespread attention from all walks of life. However, the lithium-rich ternary cathode material currently still has the problems of poor cycle stability of the lithium ion battery made therefrom, serious voltage attenuation, etc., which are urgent to be solved, and it is still difficult to realize large-scale commercial application.

[0004] Therefore, it is of great significance to develop a lithium-rich ternary cathode material with excellent cycle stability and excellent voltage stability of the lithium ion battery made therefrom. SUMMARY

[0005] The purpose of the present application is to provide a lithium-rich ternary cathode material particle with core-shell structure and a preparation method and application thereof.

[0006] The technical scheme adopted by the present application is:

[0007] A lithium-rich ternary cathode material particle with core-shell structure, the inner core is a sodium surface doped lithium nickel cobalt manganese oxide particle, and the shell layer is a phosphate coating layer; the chemical formula of the sodium surface doped lithium nickel cobalt manganese oxide particle is Li 1.2- x Na x Ni 0.2 Co 0.08 Mn 0.52 O2, wherein 0

[0008] Preferably, the phosphate coating layer comprises at least one of lithium phosphate and sodium lithium phosphate.

[0009] Preferably, the particle size of the lithium-rich ternary cathode material particle with core-shell structure is 300 nm to 800 nm.

[0010] Preferably, the shell layer has a thickness of 1-3 nm.

[0011] A preparation method of the lithium-rich ternary positive electrode material particle with the core-shell structure as described above comprises the following steps:

[0012] 1) Dissolving a nickel source, a cobalt source and a manganese source in water, adding a precipitant for reaction, and then separating a solid product to obtain a precursor;

[0013] 2) Mixing the precursor and a lithium source for grinding, and then pre-burning and sintering to obtain lithium nickel cobalt manganese oxide particles;

[0014] 3) Mixing the lithium nickel cobalt manganese oxide particles and a sodium phosphate for grinding, and then calcining in a protective atmosphere to obtain a lithium-rich ternary positive electrode material particle with a core-shell structure.

[0015]

[0016] Preferably, the nickel source in step 1) is at least one of nickel acetate, nickel oxalate and nickel nitrate.

[0017] Preferably, the cobalt source in step 1) is at least one of cobalt acetate, cobalt oxalate and cobalt nitrate.

[0018] Preferably, the manganese source in step 1) is at least one of manganese acetate, manganese oxalate and manganese nitrate.

[0019] Preferably, the precipitant in step 1) is at least one of sodium carbonate and sodium oxalate.

[0020] Preferably, the molar ratio of the nickel source, the cobalt source and the manganese source in step 1) is 1:0.4:2.6.

[0021] Preferably, the reaction in step 1) is carried out at 45-55℃, and the reaction time is 14-18h.

[0022] Preferably, the lithium source in step 2) is at least one of lithium carbonate, lithium hydroxide and lithium acetate.

[0023] Preferably, the molar ratio of the precursor and the lithium source in step 2) is 1:1.23-1.29.

[0024] Preferably, the specific operation of the pre-burning in step 2) is to increase the temperature to 400-500℃ at a temperature increasing rate of 4-6℃ / min, and then keep the temperature for 4-6h.

[0025] Preferably, the specific operation of the sintering in step 2) is to increase the temperature to 850-950℃ at a temperature increasing rate of 4-6℃ / min, and then keep the temperature for 12-18h.

[0026] ​Preferably, the sodium phosphate in step 3) is at least one of sodium dihydrogen phosphate, sodium phosphate, disodium hydrogen phosphate.

[0027] Preferably, the sodium phosphate in step 3) is used in an amount of 0.5% to 5% of the mass of the lithium nickel cobalt manganese oxide particles.

[0028] Preferably, the protective atmosphere in step 3) is a nitrogen atmosphere.

[0029] Preferably, the specific operation of calcining in step 3) is to raise the temperature to 400-600°C at a temperature raising rate of 1-3°C / min, and then maintain the temperature for 3-5h.

[0030] A lithium ion battery cathode comprising the lithium-rich ternary cathode material particle with core-shell structure described above.

[0031] A preparation method of a lithium ion battery cathode as described above comprises the following steps: dispersing the lithium-rich ternary cathode material particle with core-shell structure, acetylene black and polyvinylidene fluoride (PVDF) in N-methyl pyrrolidone (NMP) to form a slurry, coating the slurry on an aluminum foil and drying to form a film, thereby obtaining the lithium ion battery cathode.

[0032] Preferably, the mass ratio of the lithium-rich ternary cathode material particle with core-shell structure, acetylene black and polyvinylidene fluoride is 8:1:1.

[0033] A lithium ion battery comprising the lithium-rich ternary cathode material particle with core-shell structure described above.

[0034] The lithium ion battery prepared by using the lithium-rich ternary cathode material particle with core-shell structure as the cathode material has excellent cycle stability and voltage stability, and is suitable for large-scale industrial application.

[0035] Specifically:

[0036] 1) The present application realizes surface doping of sodium ions by lithium-sodium exchange. The incorporation of sodium ions acts as structural support for the material, expands the interlayer spacing, improves the structural stability and diffusion capacity of lithium ions, and inhibits phase change (phase change of the positive electrode material during the cycle process, i.e. structural change, which starts from the surface layer of the material and spreads to the inside. Designing surface layer doping can better consolidate the surface layer structure of the material, thereby inhibiting the phase change of the bulk structure, which is better than traditional bulk doping). In combination with the phosphate coating layer formed at the same time as the sodium surface doping, the material can effectively avoid direct contact with the electrolyte, effectively reducing the occurrence of side reactions, and the appropriate thickness is beneficial to the transmission of lithium ions, which has the effect of improving the cycle stability, voltage stability and rate performance of the material. In addition, the process is simplified, and the final core-shell structure of the lithium-rich ternary positive electrode material particle assembly CR2016 type button cell has excellent cycle stability and voltage stability, with a specific capacity greater than 160 mAh / g at a large current density of 5C and a charge-discharge voltage interval of 2.0V-4.8V. After 500 cycles, the specific capacity is still greater than 120 mAh / g, the capacity retention rate is more than 70%, and the battery has a long service life.

[0037] 2) The present application realizes coating and ion exchange through simple surface treatment, and prepares sodium surface-doped phosphate-coated lithium nickel cobalt manganese oxide particles. In the process of realizing phosphate coating, sodium doping is also realized, and the doping amount and coating amount can be adjusted by controlling the addition amount and type of sodium phosphate.

[0038] 3) The raw materials of the core-shell structure of the lithium-rich ternary positive electrode material particles of the present application are widely available and inexpensive, and the preparation operation is simple, which is suitable for large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The XRD pattern of the core-shell structure of the lithium-rich ternary positive electrode material particles of Example 2 and the lithium nickel cobalt manganese oxide particles of Comparative Example 1.

[0040] Figure 2 The XRD pattern of the core-shell structure of the lithium-rich ternary positive electrode material particles of Example 2 and the lithium nickel cobalt manganese oxide particles of Comparative Example 1. Figure 1 The XRD pattern of the core-shell structure of the lithium-rich ternary positive electrode material particles of Example 2 and the lithium nickel cobalt manganese oxide particles of Comparative Example 1.

[0041] Figure 3 The XRD pattern of the core-shell structure of the lithium-rich ternary positive electrode material particles of Example 2 and the lithium nickel cobalt manganese oxide particles of Comparative Example 1. Figure 1 The XRD pattern of the core-shell structure of the lithium-rich ternary positive electrode material particles of Example 2 and the lithium nickel cobalt manganese oxide particles of Comparative Example 1.

[0042] Figure 4 The SEM and TEM patterns of the core-shell structure of the lithium-rich ternary positive electrode material particles of Example 2 and the lithium nickel cobalt manganese oxide particles of Comparative Example 1.

[0043] Figure 5The results of the cycle performance test of the lithium ion batteries of Example 2 and Comparative Example 1 are shown in the following graph.

[0044] Figure 6 The median voltage-cycle number relationship curve of the lithium ion batteries of Example 2 and Comparative Example 1 during the cycle test is shown in the following graph. DETAILED DESCRIPTION

[0045] The application will be further explained and described with reference to the following specific examples.

[0046] Example 1:

[0047] A lithium-rich ternary positive electrode material particle with core-shell structure, and a preparation method thereof, are provided.

[0048] 1) 4.9768 g (0.02 mol) of nickel acetate, 1.9926 g (0.008 mol) of cobalt acetate, and 12.7447 g (0.052 mol) of manganese acetate were added into 100 mL of deionized water, and stirred until the solids were completely dissolved. Then, 10.1750 g (0.096 mol) of sodium carbonate was dissolved in 100 mL of deionized water, and slowly poured into the above solution. After the addition was completed, the mixture was stirred at 50°C for 15 h, and then filtered. The obtained solid was washed with water, and dried to obtain a precursor;

[0049] 2) 3.7212 g (0.04 mol) of the precursor and 1.8621 g (0.0252 mol) of lithium carbonate were mixed and ground, and then placed in a muffle furnace. The temperature was raised to 450°C at a rate of 5°C / min in air, and maintained for 5 h. Then, the temperature was raised to 900°C at a rate of 5°C / min, and maintained for 15 h. The temperature was then naturally cooled to room temperature to obtain lithium nickel cobalt manganese oxide particles;

[0050] 3) 1.00 g of the lithium nickel cobalt manganese oxide particles and 0.01 g of sodium dihydrogen phosphate were mixed and ground, and then placed in a tube furnace. The temperature was raised to 450°C at a rate of 2°C / min in a nitrogen atmosphere, and maintained for 5 h. The temperature was then naturally cooled to room temperature to obtain lithium-rich ternary positive electrode material particles with core-shell structure (particle size: 300 nm-800 nm, core: sodium-doped lithium nickel cobalt manganese oxide particles, shell: phosphate, shell thickness: 1 nm-3 nm).

[0051] A lithium ion battery positive electrode, and a preparation method thereof, are provided.

[0052] 0.16 g of the lithium-rich ternary positive electrode material particles with core-shell structure, 0.02 g of acetylene black, and 0.02 g of polyvinylidene fluoride (PVDF) were added into 1 mL of N-methyl pyrrolidone (NMP), and stirred for 1 h to form a slurry. The slurry was then coated on an aluminum foil, and vacuum dried to form a film, thereby obtaining a lithium ion battery positive electrode.

[0053] A lithium ion battery (CR2016 type button cell), the preparation method comprising the following steps:

[0054] The above lithium ion battery positive electrode is used as the positive electrode, lithium metal is used as the counter electrode, and a LiPF6 solution is used as the electrolyte (the solvent is composed of ethylene carbonate, diethyl carbonate and dimethyl carbonate in a volume ratio of 1:1:1), and a CR2016 type button cell is assembled in an argon-filled glove box.

[0055] Example 2:

[0056] A lithium ion battery (CR2016 type button cell), the preparation method comprising the following steps:

[0057] 1) 4.9768 g (0.02 mol) of nickel acetate, 1.9926 g (0.008 mol) of cobalt acetate and 12.7447 g (0.052 mol) of manganese acetate are added to 100 mL of deionized water, stirred until the solids are completely dissolved, and then 10.1750 g (0.096 mol) of sodium carbonate is dissolved in 100 mL of deionized water and slowly poured in, and after pouring, 50℃ stirring for 15 h, suction filtration, and the obtained solid is washed with water and dried to obtain a precursor;

[0058] 2) 3.7212 g (0.04 mol) of the precursor and 1.8621 g (0.0252 mol) of lithium carbonate are mixed and ground, and then placed in a muffle furnace, first heated to 450℃ at a heating rate of 5℃ / min in an air atmosphere, and then heated to 900℃ at a heating rate of 5℃ / min, and kept for 15 h, and then naturally cooled to room temperature to obtain lithium nickel cobalt manganese oxide particles;

[0059] 3) 1.00 g of lithium nickel cobalt manganese oxide particles and 0.03 g of sodium dihydrogen phosphate are mixed and ground, and then placed in a tube furnace and heated to 450℃ at a heating rate of 2℃ / min in a nitrogen atmosphere, and kept for 5 h, and then naturally cooled to room temperature to obtain lithium-rich ternary positive electrode material particles with a core-shell structure (particle size of 300 nm to 800 nm, the core is sodium-doped lithium nickel cobalt manganese oxide particles, the shell is phosphate, and the shell thickness is 1 nm to 3 nm).

[0060] A lithium ion battery positive electrode is prepared according to Example 1.

[0061] A lithium ion battery (CR2016 type button cell) is prepared according to Example 1.

[0062] Example 3:

[0063] A lithium ion battery (CR2016 type button cell), the preparation method comprising the following steps:

[0064] 1) 4.9768 g (0.02 mol) of nickel acetate, 1.9926 g (0.008 mol) of cobalt acetate and 12.7447 g (0.052 mol) of manganese acetate were added into 100 mL of deionized water, stirred until the solids were completely dissolved, then 10.1750 g (0.096 mol) of sodium carbonate was dissolved in 100 mL of deionized water and slowly poured in, after adding, stirred at 50°C for 15 h, suction filtered, the obtained solid was washed with water, and then dried to obtain a precursor;

[0065] 2) 3.7212 g (0.04 mol) of the precursor and 1.8621 g (0.0252 mol) of lithium carbonate were mixed and ground, then placed in a muffle furnace, first heated to 450°C at a heating rate of 5°C / min, kept for 5 h, then heated to 900°C at a heating rate of 5°C / min, kept for 15 h, and naturally cooled to room temperature to obtain lithium nickel cobalt manganese oxide particles;

[0066] 3) 1.00 g of the lithium nickel cobalt manganese oxide particles and 0.05 g of sodium dihydrogen phosphate were mixed and ground, then placed in a tube furnace, heated to 450°C at a heating rate of 2°C / min under nitrogen atmosphere, kept for 5 h, and naturally cooled to room temperature to obtain core-shell structure lithium-rich ternary positive electrode material particles (particle size of 300 nm to 800 nm, the core is sodium surface-doped lithium nickel cobalt manganese oxide particles, the shell is phosphate, and the thickness of the shell is 1 nm to 3 nm).

[0067] A lithium ion battery positive electrode was prepared according to the method of Example 1.

[0068] A lithium ion battery (CR2016 type button cell) was prepared according to the method of Example 1.

[0069] Example 4:

[0070] A core-shell structure lithium-rich ternary positive electrode material particle, and a preparation method thereof, includes the following steps:

[0071] 1) 4.9768 g (0.02 mol) of nickel acetate, 1.9926 g (0.008 mol) of cobalt acetate and 12.7447 g (0.052 mol) of manganese acetate were added into 100 mL of deionized water, stirred until the solids were completely dissolved, then 10.1750 g (0.096 mol) of sodium carbonate was dissolved in 100 mL of deionized water and slowly poured in, after adding, stirred at 50°C for 15 h, suction filtered, the obtained solid was washed with water, and then dried to obtain a precursor;

[0072] 2) 3.7212 g (0.04 mol) of the precursor and 1.8974 g (0.0257 mol) of lithium carbonate were mixed and ground, and then placed in a muffle furnace, and heated to 450°C at a rate of 5°C / min in an air atmosphere, and then heated to 900°C at a rate of 5°C / min, and kept for 15 h, and then naturally cooled to room temperature to obtain lithium nickel cobalt manganese oxide particles;

[0073] 3) 1.00 g of the lithium nickel cobalt manganese oxide particles and 0.01 g of sodium dihydrogen phosphate were mixed and ground, and then placed in a tube furnace, and heated to 450°C at a rate of 2°C / min in a nitrogen atmosphere, and kept for 5 h, and then naturally cooled to room temperature to obtain core-shell structure lithium-rich ternary positive electrode material particles (particle size: 300-800 nm, core: sodium surface-doped lithium nickel cobalt manganese oxide particles, shell: phosphate, shell thickness: 1-3 nm).

[0074] A lithium ion battery positive electrode was prepared according to the method of Example 1.

[0075] A lithium ion battery (CR2016 type button cell) was prepared according to the method of Example 1.

[0076] Example 5:

[0077] A core-shell structure lithium-rich ternary positive electrode material particle was prepared by the following method:

[0078] 1) 4.9768 g (0.02 mol) of nickel acetate, 1.9926 g (0.008 mol) of cobalt acetate and 12.7447 g (0.052 mol) of manganese acetate were added to 100 mL of deionized water, and stirred until the solids were completely dissolved, and then 10.1750 g (0.096 mol) of sodium carbonate was dissolved in 100 mL of deionized water and slowly poured in, and after addition, stirred at 50°C for 15 h, and then suction filtered, and the obtained solid was washed with water and then dried to obtain a precursor;

[0079] 2) 3.7212 g (0.04 mol) of the precursor and 1.8974 g (0.0257 mol) of lithium carbonate were mixed and ground, and then placed in a muffle furnace, and heated to 450°C at a rate of 5°C / min in an air atmosphere, and then heated to 900°C at a rate of 5°C / min, and kept for 15 h, and then naturally cooled to room temperature to obtain lithium nickel cobalt manganese oxide particles;

[0080] 3) 1.00 g of the lithium nickel cobalt manganese oxide particles and 0.03 g of sodium dihydrogen phosphate are mixed and ground, and then placed in a tube furnace and heated to 600°C at a heating rate of 2°C / min under a nitrogen atmosphere, and kept at 600°C for 5 h, and then naturally cooled to room temperature to obtain lithium-rich ternary positive electrode material particles with a core-shell structure (particle size of 300-800 nm, the core is sodium surface-doped lithium nickel cobalt manganese oxide particles, the shell is phosphate, and the thickness of the shell is 1-3 nm).

[0081] A lithium ion battery positive electrode is prepared according to Example 1.

[0082] A lithium ion battery (CR2016 type button cell) is prepared according to Example 1.

[0083] Comparative Example 1:

[0084] A lithium nickel cobalt manganese oxide particle is prepared by the following steps:

[0085] 1) 4.9768 g (0.02 mol) of nickel acetate, 1.9926 g (0.008 mol) of cobalt acetate, and 12.7447 g (0.052 mol) of manganese acetate are added to 100 mL of deionized water, and stirred until the solids are completely dissolved, then 10.1750 g (0.096 mol) of sodium carbonate is dissolved in 100 mL of deionized water and slowly poured in, and after pouring is complete, the mixture is stirred at 50°C for 15 h, and then suction filtered, and the obtained solid is washed with water and dried to obtain a precursor;

[0086] 2) 3.7212 g (0.04 mol) of the precursor and 1.8621 g (0.0252 mol) of lithium carbonate are mixed and ground, and then placed in a muffle furnace and heated to 450°C at a heating rate of 5°C / min under an air atmosphere, and kept at 450°C for 5 h, and then heated to 900°C at a heating rate of 5°C / min, and kept at 900°C for 15 h, and then naturally cooled to room temperature to obtain lithium nickel cobalt manganese oxide particles.

[0087] A lithium ion battery positive electrode is prepared by the following steps:

[0088] 0.16 g of the above lithium nickel cobalt manganese oxide particles, 0.02 g of acetylene black, and 0.02 g of polyvinylidene fluoride (PVDF) are added to 1 mL of N-methyl pyrrolidone (NMP), and then stirred for 1 h to form a slurry, and then coated on an aluminum foil and vacuum dried to form a film, to obtain a lithium ion battery positive electrode.

[0089] A lithium ion battery (CR2016 type button cell) is prepared by the following steps:

[0090] The above lithium ion battery cathode was used as the positive electrode, lithium metal was used as the counter electrode, and a LiPF6 solution was used as the electrolyte (the solvent was composed of ethylene carbonate, diethyl carbonate, and dimethyl carbonate in a volume ratio of 1:1:1) to assemble a CR2016 type button cell in an argon-filled glove box.

[0091] Comparative Example 2:

[0092] A lithium nickel cobalt manganese oxide particle, a preparation method thereof includes the following steps:

[0093] 1) 4.9768 g (0.02 mol) of nickel acetate, 1.9926 g (0.008 mol) of cobalt acetate, and 12.7447 g (0.052 mol) of manganese acetate were added to 100 mL of deionized water, stirred until the solids were completely dissolved, 10.1750 g (0.096 mol) of sodium carbonate was dissolved in 100 mL of deionized water and slowly poured in, and after pouring, 50°C stirring was performed for 15 h, suction filtration was performed, the obtained solid was washed with water, and then dried to obtain a precursor;

[0094] 2) 3.7212 g (0.04 mol) of the precursor and 1.8974 g (0.0257 mol) of lithium carbonate were mixed and ground, and then placed in a muffle furnace, and first heated to 450°C at a heating rate of 5°C / min, and then heated to 900°C at a heating rate of 5°C / min, and then naturally cooled to room temperature to obtain a lithium nickel cobalt manganese oxide particle.

[0095] A lithium ion battery cathode, a preparation method thereof includes the following steps:

[0096] 0.16 g of the above lithium nickel cobalt manganese oxide particle, 0.02 g of acetylene black, and 0.02 g of polyvinylidene fluoride (PVDF) were added to 1 mL of N-methyl pyrrolidone (NMP), stirred for 1 h to prepare a slurry, and then coated on an aluminum foil and vacuum dried to form a film to obtain a lithium ion battery cathode.

[0097] A lithium ion battery (CR2016 type button cell), a preparation method thereof includes the following steps:

[0098] The above lithium ion battery cathode was used as the positive electrode, lithium metal was used as the counter electrode, and a LiPF6 solution was used as the electrolyte (the solvent was composed of ethylene carbonate, diethyl carbonate, and dimethyl carbonate in a volume ratio of 1:1:1) to assemble a CR2016 type button cell in an argon-filled glove box.

[0099] Performance test:

[0100] 1) X-ray diffraction (XRD) patterns of the core-shell structured lithium-rich ternary cathode material particles of Example 2 and the lithium nickel cobalt manganese oxide particles of Comparative Example 1 are shown below. Figure 1 As shown, a magnified view of a portion of the XRD pattern is as follows: Figure 2 (2θ = 18.0°~19.5°) and Figure 3 As shown in (2θ=43.5°~45.5°).

[0101] Depend on Figures 1 to 3 It can be seen that after modification, the (003) and (104) peaks of lithium nickel cobalt manganese oxide particles shift to a lower angle, indicating that the interlayer spacing of the material has increased. + It was successfully incorporated into the crystal structure of the material.

[0102] 2) Scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the core-shell structured lithium-rich ternary cathode material particles of Example 2 and the lithium nickel cobalt manganese oxide particles of Comparative Example 1 are shown below. Figure 4 (a and c are SEM and TEM images of lithium nickel cobalt manganese oxide particles in Comparative Example 1, respectively; b and d are SEM and TEM images of core-shell structured lithium-rich ternary cathode material particles in Example 2, respectively.)

[0103] Depend on Figure 4 It can be seen that: the lithium nickel cobalt manganese oxide particles of Comparative Example 1 are irregular polyhedral in shape, with a particle size of 300nm to 800nm, and a smooth surface without any coating layer; the core-shell structure lithium-rich ternary cathode material particles (after modification) of Example 2 have no significant change in shape compared with the lithium nickel cobalt manganese oxide particles of Comparative Example 1, but there is a thin coating layer (about 1nm thick) on the surface. Based on the analysis of the element types of the modifier, it can be seen that the coating layer is phosphate.

[0104] Furthermore, the microstructure of the lithium-rich ternary cathode material particles with core-shell structure in Examples 1 and 3-5 was tested and found to be similar to that of the lithium-rich ternary cathode material particles with core-shell structure in Example 1.

[0105] 3) The lithium-ion batteries from Examples 1-5 and Comparative Examples 1-2 were left at room temperature for 12 hours, and then subjected to a 500-cycle test under the conditions of room temperature, voltage test range of 2.0V-4.8V, and current density of 1000mA / g. The cycle performance test results of the lithium-ion batteries were obtained (see the figure for the cycle performance test results of the lithium-ion batteries from Example 2 and Comparative Example 1). Figure 5 As shown below:

[0106] a) The initial capacity of the lithium-ion batteries in Examples 1-5 was 170.18 mAh·g. -1 169.62mAh·g -1 138.45mAh·g -1153.18mAh·g -1 and 172.53mAh·g -1 After 500 laps, the capacity retention rates were 57.19%, 73.60%, 61.65%, 64.99%, and 60.22%, respectively.

[0107] b) The initial capacity of the lithium-ion batteries in Comparative Examples 1 and 2 was 155.84 mAh·g. -1 and 125.59mAh·g -1 The capacity retention rates were 45.28% and 56.85%, respectively.

[0108] Therefore, increasing the amount of sodium dihydrogen phosphate will increase the molar number of sodium ions. The principle of doping is lithium-sodium exchange. After the exchange, more sodium ions enter the material surface and make the material have a thicker coating layer. However, adding more lithium source during the preparation of lithium nickel cobalt manganese oxide particles will lead to lithium excess, which will accumulate on the material surface. Similar to the excess sodium source in modification, lithium ion migration is hindered and the specific capacity of the material decreases. However, due to the thicker outer coating layer, the material surface is less damaged and the capacity retention rate is slightly improved.

[0109] Depend on Figure 5 It can be seen that the cycle stability of lithium-ion batteries assembled from core-shell structured lithium-rich ternary cathode material particles after appropriate sodium surface doping and phosphate coating is significantly improved, and the battery exhibits a cycle stability of 169.62 mAh·g. -1 Its high specific capacity means that after 500 cycles, the capacity still reaches 124.84 mAh·g. -1 In contrast, the lithium-ion battery assembled from nickel-cobalt-manganese lithium oxide particles in Comparative Example 1 had a capacity of only 70.56 mAh·g. -1 This indicates that the introduction of an appropriate amount of sodium ions and the synergistic effect of the outer coating layer enable the material to exhibit superior performance.

[0110] 4) The lithium-ion batteries from Example 2 and Comparative Example 1 were left at room temperature for 12 hours, and then subjected to a 500-cycle test under the conditions of room temperature, voltage test range of 2.0V to 4.8V, and current density of 1000mA / g. The median voltage-cycle count curves obtained are shown below. Figure 6 As shown.

[0111] Depend on Figure 6 It can be seen that sodium surface doping and phosphate coating improve the voltage stability of lithium-rich ternary cathode materials.

[0112] The above embodiments are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above embodiments, and any changes, modifications, substitutions, combinations, simplifications, etc. made without departing from the spirit and principles of the present application should be equivalent replacement manners and should be included in the protection scope of the present application.

Claims

1. A core-shell structured lithium-rich ternary cathode material particle, characterized in that, The core is lithium nickel cobalt manganese oxide particles doped with sodium on the surface, and the shell is a phosphate coating layer; the chemical formula of the lithium nickel cobalt manganese oxide particles doped with sodium on the surface is Li 1.2- x Na x Ni 0.2 Co 0.08 Mn 0.52 O2, where 0 < x < 0.05; the phosphate coating layer contains at least one of lithium phosphate and lithium sodium phosphate; the particle size of the core-shell structured lithium-rich ternary cathode material particles is 300 nm to 800 nm; the thickness of the shell layer is 1 nm to 3 nm.

2. A method for preparing lithium-rich ternary cathode material particles with a core-shell structure as described in claim 1, characterized in that, Includes the following steps: 1) Dissolve nickel, cobalt and manganese sources in water, add a precipitant to react, and then separate the solid product to obtain the precursor; 2) The precursor and lithium source are mixed and ground, and then pre-calcined and sintered to obtain lithium nickel cobalt manganese oxide particles. 3) Mix lithium nickel cobalt manganese oxide particles with sodium phosphate, grind them, and then calcine them in a protective atmosphere to obtain core-shell structured lithium-rich ternary cathode material particles.

3. The preparation method according to claim 2, characterized in that: Step 1) The nickel source is at least one of nickel acetate, nickel oxalate, and nickel nitrate; Step 1) The cobalt source is at least one of cobalt acetate, cobalt oxalate, and cobalt nitrate; Step 1) The manganese source is at least one of manganese acetate, manganese oxalate, and manganese nitrate; Step 1) The precipitant is at least one of sodium carbonate and sodium oxalate; Step 2) The lithium source is at least one of lithium carbonate, lithium hydroxide, and lithium acetate; Step 3) The sodium phosphate is at least one of sodium dihydrogen phosphate, sodium phosphate, and disodium hydrogen phosphate.

4. The preparation method according to claim 2 or 3, characterized in that: Step 1) The molar ratio of the nickel source, cobalt source, and manganese source is 1:0.4:2.6; Step 2) The molar ratio of the precursor and lithium source is 1:1.23 to 1.29; Step 3) The amount of sodium phosphate used is 0.5% to 5% of the mass of lithium nickel cobalt manganese oxide particles.

5. The preparation method according to claim 2 or 3, characterized in that: The reaction described in step 1) is carried out at room temperature for 14-18 hours; the specific operation of the pre-calcination in step 2) is as follows: the temperature is increased to 400-500℃ at a heating rate of 4℃ / min-6℃ / min, and then held for 4-6 hours; the specific operation of the sintering in step 2) is as follows: the temperature is increased to 850-950℃ at a heating rate of 4℃ / min-6℃ / min, and then held for 12-18 hours; the specific operation of the calcination in step 3) is as follows: the temperature is increased to 400-600℃ at a heating rate of 1℃ / min-3℃ / min, and then held for 3-5 hours.

6. A lithium-ion battery positive electrode, characterized in that, Lithium-rich ternary cathode material particles containing the core-shell structure described in claim 1.

7. A lithium-ion battery, characterized in that, Lithium-rich ternary cathode material particles containing the core-shell structure described in claim 1.

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