Ternary positive electrode material, preparation method thereof and lithium ion battery

Abstract

The invention provides a ternary positive electrode material, a preparation method thereof and a lithium ion battery. The ternary positive electrode material has a core-shell structure, the core is the ternary positive electrode material, and the shell comprises three coating layers, namely a LiCoO2 layer, a lithium supplementing mixed layer and a protective mixed layer from inside to outside in sequence. And the lithium supplementing mixed layer is composed of LiCoO2 and (LiCo *) 2O. A layer of positive electrode lithium supplement agent is constructed on the surface of the positive electrode material in situ, the self-lithium-supplement positive electrode material is synthesized, and the problem of uneven dispersion of the positive electrode lithium supplement agent is solved. And the residual alkali content of the lithium self-supplementing positive electrode material is reduced through surface coating, so that the problem that the viscosity of the slurry is increased is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion positive electrode material preparation, and specifically relates to a ternary positive electrode material and a preparation method thereof, a lithium ion battery, and more specifically relates to a method for preparing a self-replenishing lithium positive electrode material, a positive electrode material and a lithium ion battery. Background Art

[0002] Lithium-ion batteries, due to their high energy density, safety, and environmental friendliness, have been widely used in electric vehicles, power tools, and energy storage power stations. However, during the initial charge of a lithium-ion battery, the formation of the SEI film on the negative electrode consumes lithium from the positive electrode active material, reducing the initial coulombic efficiency of charge and discharge, which in turn affects the capacity and energy density of the lithium-ion battery. Furthermore, during the cycling of a lithium-ion battery, the SEI film on the negative electrode is constantly destroyed and formed, consuming a large amount of lithium from the positive electrode active material, resulting in a decrease in capacity and deteriorating the battery's cycling performance.

[0003] In order to solve the problem of negative electrode lithium consumption reducing the reversible capacity and energy density of the battery, improve the cycle performance and extend the service life of the battery, pre-lithiation is considered to be an effective technology. Among them, positive electrode lithium replenishment has the greatest industrial application prospects due to its high safety and no need to change the existing battery production process. However, the positive electrode lithium replenisher often has a high residual alkali content. When added during the positive electrode slurry process, the local residual alkali content is too high, causing the slurry viscosity to increase and even gelation. The increase in slurry viscosity, in turn, causes uneven dispersion of the positive electrode lithium replenisher, resulting in local lithium precipitation during the later charge and discharge process, posing a safety hazard. The increase in viscosity and lithium precipitation caused by the introduction of the positive electrode lithium replenisher are problems that need to be solved urgently in positive electrode lithium replenishment technology. Summary of the Invention

[0004] In view of the deficiencies in the prior art, the present invention aims to provide a self-replenishing lithium-type ternary cathode material and a preparation method thereof.

[0005] The self-replenishing lithium-type ternary cathode material provided by the present invention has a core-shell structure, wherein the core is the ternary cathode material, and the shell comprises three coating layers, which are, from the inside to the outside, a LiCoO2 layer, a lithium-replenishing mixed layer, and a protective mixed layer;

[0006] The present invention solves the problem of uneven dispersion of the positive electrode lithium replenisher by in-situ constructing a layer of positive electrode lithium replenisher on the surface of the positive electrode material to synthesize a self-replenishing lithium positive electrode material. The residual alkali content of the self-replenishing lithium positive electrode material is then reduced through surface coating, thereby solving the problem of increased slurry viscosity.

[0007] The molecular formula of the ternary positive electrode material is LiNi x A y M 1-x-yO2, wherein A and M are each independently selected from Co, Mn, B, Al, Zr, W, Ta, Nb, Ti, Fe, Y, Ga, Cu, Zn, Ge, Mo, V and Cr, and A and M are different, x ≥ 0.50, 0 ≤ y ≤ 0.20, and x + y ≤ 1.0;

[0008] The lithium-replenishing mixed layer is composed of LiCoO2 and (LiCo*)2O; wherein (LiCo*)2O represents a phase different from Li2O and LiCoO2 generated by the reaction of Li2O and LiCoO2, which can release a large amount of Li+ and has the function of lithium replenishment.

[0009] The protective mixed layer is composed of PVDF and aluminum oxide.

[0010] The self-replenishing lithium ternary cathode material is prepared by a method comprising the following steps:

[0011] 1) Mixing the ternary precursor with a lithium source and sintering in dry air or oxygen atmosphere to obtain a high residual alkali ternary material;

[0012] 2) mixing the high residual alkali ternary material with a cobalt source and sintering in a dry air or oxygen atmosphere to obtain a ternary material intermediate 1;

[0013] 3) sintering the ternary material intermediate 1 in a vacuum environment, and then introducing oxygen to sinter the ternary material intermediate 2;

[0014] 4) ball milling the ternary material intermediate 2 in a high-energy ball mill in an inert atmosphere to obtain the ternary material intermediate 3;

[0015] 5) The ternary material intermediate 3 is mixed with PVDF and alumina, and sintered in a protective atmosphere to obtain a self-replenishing lithium-type ternary positive electrode material.

[0016] Furthermore, in step 1), the molecular formula of the ternary precursor is Ni x A y M 1-x-y (OH)2, wherein A and M are each independently selected from Co, Mn, B, Al, Zr, W, Ta, Nb, Ti, Fe, Y, Ga, Cu, Zn, Ge, Mo, V and Cr, and A and M are different, x ≥ 0.50, 0 ≤ y ≤ 0.20, and x + y ≤ 1.0;

[0017] Furthermore, in step 1), the lithium source is one or more of lithium hydroxide, lithium carbonate, lithium oxide and lithium peroxide;

[0018] Furthermore, in step 1), the mass ratio of the element Li in the lithium source to the element TM (Ni+A+M) in the precursor is 1.02 to 1.15;

[0019] Furthermore, in step 1), the sintering temperature is 700-1000° C., and the holding time is 8-20 hours;

[0020] Furthermore, in step 1), the molecular formula of the high residual alkali ternary material obtained is LiNi x A y M 1-x-y O2, the free Li content in the ternary material is 0.25wt% to 1.05wt% (calculation formula: Free Li = mLiOH / 23.94*6.94+mLi2CO3 / 73.89*2*6.94, where mLiOH and mLLi2CO3 are the masses of LiOH and Li2CO3 in the residual alkali, 23.94 is the relative molecular mass of LiOH, 73.89 is the relative molecular mass of Li2CO3, and 6.94 is the relative atomic mass of Li);

[0021] The above method further includes, after step 1), performing air flow milling on the obtained high residual alkali ternary material to control the particle size Dmin≥0.7μm, D10≥1.2μm, D50=3.0~3.6μm, D90≤9μm, and Dmax≤14μm;

[0022] Furthermore, in step 2), the cobalt source is one or more of cobalt hydroxide, cobalt oxyhydroxide, cobalt oxide, cobalt trioxide, cobalt trioxide, and cobalt carbonate;

[0023] The cobalt source is added in accordance with the cobalt element, and the amount of the cobalt element added accounts for 0.20-1.00% of the total mass of the high residual alkali ternary material, and the D50 of the cobalt source is controlled to be ≤200nm and Dmax ≤500nm;

[0024] Furthermore, in step 2), the relationship between the residual alkali Free Li in the high residual alkali ternary material and the cobalt source Co is δ=(mLi / 6.94-mCo / 58.93) / 2(mCo / 58.93), δ=3.0-5.0; mLi represents the mass of Free Li, and mCo represents the mass of Co in the cobalt source;

[0025] Furthermore, in step 2), the sintering temperature is 500-800° C., and the holding time is 2-10 hours;

[0026] Furthermore, in step 3), the vacuum environment pressure value is controlled to be -0.040 to -0.090 MPa, the sintering temperature is 600 to 800° C., the vacuum environment sintering time is 3 to 20 hours, the oxygen sintering temperature is 600 to 800° C., and the oxygen sintering time is 0.5 to 5 hours;

[0027] Furthermore, in step 4), the ball-to-material ratio of high-energy ball milling is 1:0.1-5, and the ball milling time is 3-24 hours;

[0028] Furthermore, in step 5), the PVDF coating amount is 0.05-0.2% of the mass of the ternary material 3, the alumina coating amount is 0.05-0.3% of the mass of the ternary material intermediate 3, the protective atmosphere is one or more of nitrogen, helium, neon, argon, and xenon, the sintering temperature is 180-210°C, and the sintering time is 2-8h.

[0029] The application of the above-mentioned self-replenishing lithium type ternary cathode material in lithium-ion batteries also falls within the protection scope of the present invention.

[0030] In the application, the self-replenishing lithium ternary cathode material is used as a cathode active material for a lithium-ion battery or is used to prepare a cathode material for a lithium-ion battery.

[0031] The present invention also provides a lithium-ion battery, wherein the positive electrode material of the lithium-ion battery contains the self-replenishing lithium ternary positive electrode material.

[0032] The present invention has the following beneficial effects:

[0033] 1. By controlling the Li / TM ratio and sintering temperature, a ternary material with a high residual alkali content is obtained. Under high-temperature oxidation conditions, the residual alkali reacts with the cobalt source to form a layer of LiCoO2 on the surface of the ternary material. By controlling the amount of cobalt source added, some residual alkali remains unreacted and remains as residual alkali. Using vacuum and low-temperature sintering, the LiOH and Li2CO3 in the residual alkali decompose into Li2O. High-energy ball milling partially implants the transition metal element Co in the coating layer of LiCoO2 into Li2O, forming (LiCo*)2O. Finally, low-temperature calcination in a protective atmosphere coats the surface of the ternary material with PVDF and nano-Al2O3.

[0034] 2. The residual alkali reacts with the cobalt source to form a layer of LiCoO2 on the surface of the ternary material. This coating layer is beneficial to improving the rate / power performance of the ternary material. In addition, the vacuum environment is conducive to promoting the decomposition of the residual alkali LiOH and Li2CO3 into Li2O under low temperature conditions. After vacuum, "oxygen" is added and sintered, which can effectively prevent the oxygen escape in the ternary material from causing lattice oxygen defects to deteriorate the structural stability of the material. High-energy ball milling partially implants the transition metal element Co in the LiCoO2 coating into Li2O to form defective Li2O, reducing the decomposition potential of Li2O and promoting Li +It is easier to escape from the Li2O lattice, significantly improving the charge capacity of Li2O. Nano-Al2O3 coating helps reduce the contact area between the ternary material and the electrolyte under working conditions, reduces the occurrence of side reactions between the ternary material and the electrolyte, and improves the interfacial stability of the ternary material. PVDF is introduced at the same time as the introduction of nano-Al2O3 coating. PVDF melts upon low-temperature heating and is evenly coated on the ternary material, which helps reduce the contact between the self-replenishing lithium positive electrode material and air during storage and prevents Li2O from being reacted. In addition, the introduction of a protective atmosphere during this process can prevent PVDF from being oxidized and decomposed, thereby preventing the coating effect from being achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 LiNi in Example 1 of the present invention 0.88 Co 0.07 Mn 0.05 SEM image of O2@LiCoO2 ternary material (prepared in step 2);

[0036] Figure 2 LiNi in Example 1 of the present invention 0.88 Co 0.07 Mn 0.05 TEM image of the ternary material O2@LiCoO2@Li2O (prepared in step 3);

[0037] Figure 3 This is a SEM image of the finished self-lithium-replenishing cathode material in Example 1 of the present invention;

[0038] Figure 4 This is a TEM image of the finished self-lithium-replenishing cathode material in Example 1 of the present invention;

[0039] Figure 5 LiNi in Comparative Example 1 0.88 Co 0.07 Mn 0.05 SEM image of O2 ternary material;

[0040] Figure 6 The self-replenishing lithium type positive electrode material in Example 1 and the LiNi in Comparative Example 1 0.88 Co 0.07 Mn 0.05 XRD patterns of O2 ternary materials;

[0041] Figure 7 The self-replenishing lithium type positive electrode material in Example 1 and the LiNi in Comparative Example 1 0.88 Co 0.07 Mn 0.05 Comparison of XRD main peaks of O2 ternary materials;

[0042] Figure 8TEM image of the self-lithium-replenishing cathode material in Comparative Example 6;

[0043] Figure 9 This is a comparison of the XRD patterns of the Li2O and LiCoO2 mixture before and after ball milling in Comparative Example 20. DETAILED DESCRIPTION

[0044] The present invention will be further described in detail below in conjunction with specific embodiments. The examples provided are only for illustrating the present invention and are not intended to limit the scope of the present invention. The examples provided below can serve as a guide for further improvements by those skilled in the art and are not intended to limit the present invention in any way.

[0045] Unless otherwise specified, the experimental methods in the following examples are conventional methods and were performed according to the techniques or conditions described in the literature in the field or according to the product instructions. The materials and reagents used in the following examples, unless otherwise specified, were all commercially available.

[0046] The first aspect of the present invention discloses a self-lithium-replenishing ternary positive electrode material, which has a core-shell structure. The core is the ternary positive electrode material, and the shell comprises three coating layers, which are, from the inside to the outside, a LiCoO2 layer, a lithium-replenishing mixed layer, and a protective mixed layer.

[0047] The second aspect of the present invention discloses a method for preparing the self-replenishing lithium ternary cathode material, which specifically comprises the following steps:

[0048] S1: Mixing the ternary precursor with a lithium source and sintering in dry air or oxygen atmosphere to obtain a high residual alkali ternary material;

[0049] S2: The high residual alkali ternary material is mixed with a cobalt source and sintered in dry air or oxygen atmosphere to obtain intermediate 1;

[0050] S3: Intermediate 1 is first sintered in a vacuum environment, and then oxygen is introduced to sinter it to obtain intermediate 2;

[0051] S4: intermediate 2 is ball-milled in a high-energy ball mill to obtain intermediate 3;

[0052] S5: Intermediate 3 is mixed with PVDF and alumina, and sintered in a protective atmosphere to obtain a self-lithium-replenishing ternary positive electrode material.

[0053] The present invention first obtains a ternary material with a high residual alkali content by controlling the lithium content (i.e., the Li / TM ratio) and the sintering temperature. Then, a cobalt source coating is performed and the amount of cobalt source added is controlled, so that part of the residual alkali reacts with the cobalt source to form a LiCoO2 coating layer on the surface of the ternary material. This coating layer is beneficial for improving the rate / power performance of the ternary material. The unreacted residual alkali is decomposed and converted into Li2O by low-temperature sintering in a vacuum environment. To prevent the escape of lattice oxygen from the ternary material during this conversion process, which leads to the generation of oxygen vacancies, oxygen is introduced at the end of the vacuum decomposition to replenish "oxygen". High-energy ball milling is then used to implant the transition metal element Co in the LiCoO2 into the Li2O lattice, which is beneficial for improving the lithium ion conductivity and electronic conductivity of Li2O and significantly increasing the charge capacity of Li2O. Finally, nano-Al2O3 coating helps to reduce the contact area between the ternary material and the electrolyte, reduce the occurrence of side reactions with the electrolyte, and improve the interfacial stability of the ternary material. PVDF melts when heated at low temperature in a protective atmosphere and is evenly coated on the ternary material, which helps reduce the contact of the self-replenishing lithium positive electrode material with air during storage and prevents the ternary material and the surface Li2O layer from reacting with H2O and CO2 in the air and becoming ineffective.

[0054] Furthermore, the ternary precursor in step S1 adopts the molecular formula Ni x A y M 1-x-y (OH)2, wherein A and M are each independently selected from Co, Mn, B, Al, Zr, W, Ta, Nb, Ti, Fe, Y, Ga, Cu, Zn, Ge, Mo, V and Cr, and A and M are different, x ≥ 0.50, 0 ≤ y ≤ 0.20, x + y ≤ 1.0;

[0055] The lithium source is one or more of lithium hydroxide, lithium carbonate, lithium oxide or lithium peroxide;

[0056] Furthermore, in step S1, the ratio of the element Li in the lithium source to the element TM=Ni+A+M in the precursor is 1.02-1.15; the sintering temperature of the lithium source and precursor mixture is 700-1000° C., and the holding time is 8-20 hours;

[0057] Furthermore, the molecular formula of the high residual alkali ternary material obtained in step S1 is LiNi x A y M 1-x-y O2, the free Li content in the ternary material is 0.25%wt~1.05%wt;

[0058] Furthermore, in step S2, the cobalt source is one or more of cobalt hydroxide, cobalt oxyhydroxide, cobalt oxide, cobalt trioxide, cobalt tetroxide, and cobalt carbonate. The cobalt source is added as the cobalt element, and the amount of cobalt added accounts for 0.20-1.00% of the total mass of the high residual alkali ternary material. The particle size D50 is controlled to be ≤200 nm and Dmax is ≤500 nm.

[0059] Furthermore, in step S2, the relationship between the residual alkali Free Li in the high residual alkali ternary material and the Co element in the cobalt source is δ=(mLi / 6.94-mCo / 58.93) / 2(mCo / 58.93), δ=3.00-5.00;

[0060] Furthermore, in step S2, the sintering temperature is 500-800°C, and the holding time is 2-10 hours;

[0061] Furthermore, in step S3, the vacuum environment pressure value is controlled to be -0.040 to -0.090 MPa, the sintering temperature is 600 to 800° C., the vacuum environment sintering time is 3 to 20 hours, the oxygen sintering temperature is 600 to 800° C., and the oxygen sintering time is 0.5 to 5 hours;

[0062] Furthermore, in step S4, the ball-to-material ratio of high-energy ball milling is 1:0.1-5, and the ball milling time is 3-24 hours;

[0063] Furthermore, in step S5, the PVDF coating amount is 0.05-0.2% of the mass of the ternary material intermediate 3, the alumina coating amount is 0.05-0.3% of the mass of the ternary material intermediate 3, the protective atmosphere is one or more of nitrogen, helium, neon, argon, and xenon, the sintering temperature is 180-210°C, and the sintering time is 2-8h.

[0064] The invention also discloses the application of the self-replenishing lithium type ternary positive electrode material prepared according to the method in lithium ion batteries.

[0065] The present invention also discloses a lithium ion battery, wherein the positive electrode material of the lithium ion battery contains the self-replenishing lithium ternary positive electrode material.

[0066] Example 1

[0067] 1) Take 1kg Ni 0.88 Co 0.07 Mn 0.05 The (OH)2 precursor (the total mass of Ni+Co+Mn elements accounts for 61.57% of the precursor) was mixed with 0.488kg LiOH·H2O, Li / TM=1.10, placed in a box furnace, introduced oxygen, and heated from room temperature to 800℃ at a heating rate of 2℃ / min, and kept warm for 13h. After the holding time was over, it was naturally cooled to room temperature to obtain LiNi0.88 Co 0.07 Mn 0.05 Then, the ternary material is subjected to air flow powder crushing to control Dmin≥0.7μm, D10≥1.2μm, D50=3.0~3.6μm, D90≤9μm, and Dmax≤14μm.

[0068] 2) The above LiNi was measured by acid-base titration 0.88 Co 0.07 Mn 0.05 The content of LiOH in the O2 ternary material is 1.89%, the content of Li2CO3 is 1.77%, and the content of Free Li is 0.88%. Then, 500g of the ternary material and the particle size D 50 The mixture is mixed with 100nm Co2O3, wherein the addition amount of Co2O3 is 5.81g, δ = (mLi / 6.94-mCo / 58.93) / 2(mCo / 58.93) = 4.03. The mixture is placed in a box furnace, oxygen is introduced, and it is heated from room temperature to 700℃ at a heating rate of 2℃ / min, and kept warm for 7h. After the holding time is over, it is naturally cooled to room temperature to obtain LiNi 0.88 Co 0.07 Mn 0.05 O2@LiCoO2 ternary material.

[0069] 3) The obtained LiNi 0.88 Co 0.07 Mn 0.05 The O2@LiCoO2 ternary material was placed in a box furnace, vacuumed to -0.050 MPa, and heated from room temperature to 600°C at a heating rate of 5°C / min, and kept warm for 5 hours. Oxygen was then introduced, kept warm for 1 hour, and then naturally cooled to room temperature to obtain LiNi 0.88 Co 0.07 Mn 0.05 O2@LiCoO2@Li2O ternary material.

[0070] 4) LiNi 0.88 Co 0.07 Mn 0.05 The O2@LiCoO2@Li2O ternary material and zirconia balls with a particle size of 5 mm were loaded into a ball mill at a mass ratio of 3:1. Nitrogen was introduced into the ball mill to replace the air. Then, a high-energy ball mill was used for ball milling for 5 h to obtain LiNi 0.88 Co 0.07 Mn 0.05 O2@LiCoO2@(LiCo*)2O ternary material.

[0071] 5) Take the LiNi obtained above 0.88 Co0.07 Mn 0.05 500g of O2@LiCoO2@(LiCo*)2O ternary material was added with 2g of nano-alumina and 1.5g of PVDF and mixed at high speed. The mixture was then placed in a box furnace, nitrogen was introduced, and the temperature was increased from room temperature to 200℃ at a rate of 2℃ / min. The temperature was kept at this temperature for 2h. After the temperature was kept at this temperature, the mixture was naturally cooled to room temperature to obtain LiNi 0.88 Co 0.07 Mn 0.05 O2@LiCoO2@(LiCo*)2O@Al2O3&PVDF self-replenishing lithium positive electrode material.

[0072] Comparative Example 1

[0073] The difference from Example 1 is that: Ni 0.88 Co 0.07 Mn 0.05 The (OH)2 precursor and LiOH·H2O mixture is only subjected to high-temperature sintering and airflow milling without other treatments.

[0074] Comparative Example 2

[0075] The difference from Example 1 is that the nano-Co2O3 coated LiNi 0.88 Co 0.07 Mn 0.05 O2 step.

[0076] Comparative Example 3

[0077] The difference from Example 1 is that: LiNi 0.88 Co 0.07 Mn 0.05 After the O2 ternary material is coated with nano-Co2O3, vacuum sintering is not performed.

[0078] Comparative Example 4

[0079] The difference from Example 1 is that: LiNi 0.88 Co 0.07 Mn 0.05 Oxygen sintering is not performed at the back end of vacuum sintering of O2 ternary materials.

[0080] Comparative Example 5

[0081] The difference from Example 1 is that: LiNi 0.88 Co 0.07 Mn 0.05 The O2 ternary material is not subjected to high-energy ball milling treatment after vacuum sintering.

[0082] Comparative Example 6

[0083] The difference from Example 1 is that: LiNi 0.88 Co0.07 Mn 0.05 The O2 ternary material is not coated with nano-alumina after high-energy ball milling.

[0084] Comparative Example 7

[0085] The difference from Example 1 is that: LiNi 0.88 Co 0.07 Mn 0.05 The O2 ternary material is not coated with PVDF after high-energy ball milling.

[0086] Example 2

[0087] The difference from Example 1 is that the amount of LiOH·H2O added is reduced from 0.488 kg to 0.470 kg, and the Li / TM ratio is 1.06.

[0088] Comparative Example 8

[0089] The difference from Example 1 is that the amount of LiOH·H2O added is increased from 0.488 kg to 0.532 kg, and the Li / TM ratio is 1.20.

[0090] Comparative Example 9

[0091] The difference from Example 1 is that the amount of LiOH·H2O added is reduced from 0.488 kg to 0.443 kg, and the Li / TM ratio is 1.00.

[0092] Example 3

[0093] The difference from Example 1 is that the addition amount of nano-Co2O3 is reduced from 5.81g to 5.26g, and δ is controlled to be (mLi / 6.94-mCo / 58.93) / 2(mCo / 58.93)=4.50.

[0094] Comparative Example 10

[0095] The difference from Example 1 is that the addition amount of nano-Co2O3 is reduced from 5.81g to 4.62g, and δ is controlled to be (mLi / 6.94-mCo / 58.93) / 2(mCo / 58.93)=5.19.

[0096] Comparative Example 11

[0097] The difference from Example 1 is that the addition amount of nano-Co2O3 is increased from 5.81g to 8.78g, and δ is controlled to be (mLi / 6.94-mCo / 58.93) / 2(mCo / 58.93)=2.50.

[0098] Example 4

[0099] The difference from Example 1 is that: 0.88 Co 0.07 Mn 0.05 The vacuum degree of sintering O2@LiCoO2 material was adjusted from -0.050MPa to -0.080MPa.

[0100] Comparative Example 12

[0101] The difference from Example 1 is that: reducing LiNi 0.88 Co 0.07 Mn 0.05 The vacuum degree of sintering O2@LiCoO2 material was adjusted from -0.050MPa to -0.002MPa.

[0102] Example 5

[0103] The difference from Example 1 is that the ratio of the ternary material to the zirconium balls is increased from 3:1 to 5:1.

[0104] Comparative Example 13

[0105] The difference from Example 1 is that the ratio of the ternary material to the zirconium balls is increased from 3:1 to 10:1.

[0106] Example 6

[0107] The difference from Example 1 is that the coating amount of PVDF is increased from 1.5 g to 2.5 g.

[0108] Comparative Example 14

[0109] The difference from Example 1 is that the coating amount of PVDF is increased from 1.5 g to 4.0 g.

[0110] Comparative Example 15

[0111] The difference from Example 1 is that the coating amount of PVDF is reduced from 1.5 g to 0.1 g.

[0112] Example 7

[0113] The difference from Example 1 is that the coating amount of nano-Al2O3 is increased from 2.0g to 3.0g.

[0114] Comparative Example 16

[0115] The difference from Example 1 is that the coating amount of nano-Al2O3 is increased from 2.0g to 5.0g.

[0116] Comparative Example 17

[0117] The difference from Example 1 is that the coating amount of nano-Al2O3 is reduced from 2.0g to 0.5g.

[0118] Comparative Example 18

[0119] The difference from Example 1 is that the sintering temperature of PVDF and nano-Al2O3 coating is lowered from 200°C to 150°C.

[0120] Comparative Example 19

[0121] The difference from Example 1 is that the sintering temperature of PVDF and nano-Al2O3 coating is increased from 200°C to 300°C.

[0122] Comparative Example 20

[0123] Take 1kg Ni 0.88 Co 0.07 Mn 0.05 The (OH)2 precursor was mixed with 0.452kg LiOH·H2O, Li / TM=1.02, placed in a box furnace, introduced oxygen, and heated from room temperature to 800℃ at a heating rate of 2℃ / min, and kept warm for 13h. After the holding time was over, it was naturally cooled to room temperature to obtain LiNi 0.88 Co 0.07 Mn 0.05 Then, the ternary material is subjected to air flow powder crushing, and Dmin≥0.7um, D10≥1.2um, D50=3.0~3.6um, D90≤9um, and Dmax≤14um are controlled.

[0124] 100 g of Li2O and 24.5 g of LiCoO2 were placed in a ball mill, and then 41.5 g of zirconia balls with a particle size of 5 mm were added at a ball-to-material ratio of 1:3. Nitrogen was introduced and ball milled for 5 h to obtain the lithium supplement (LiCo*)2O.

[0125] LiNi 0.88 Co 0.07 Mn 0.05 The O2 ternary material and the lithium supplement (LiCo*)2O were mixed in a ratio of 100 / 1 to prepare button batteries and full batteries.

[0126] Test Case

[0127] 1. From Figure 1 and Figure 5 It can be seen that LiNi in Example 1 0.88 Co 0.07 Mn 0.05 The particle morphology of O2 ternary material is basically unchanged after being coated with Co2O3; LiNi 0.88 Co0.07 Mn 0.05 After the O2 ternary material is treated in vacuum, oxygen and high temperature, a small amount of amorphous clusters will appear on the particle surface, such as Figure 2 shown; from Figure 3 and Figure 4 It can be seen that a large number of nanoparticles exist on the surface of the finished self-replenishing lithium cathode material in Example 1, and are evenly coated on the surface of the cathode material; by comparing the XRD patterns of the finished products of Example 1 and Comparative Example 1, as shown in FIG. Figure 6 and Figure 7 It was found that the self-replenishing lithium-type cathode material in Example 1 and the ternary material in the comparative example both maintained a good layered structure. Since the self-replenishing lithium-type cathode material in Example 1 was modified by Co2O3 coating, its corresponding XRD main peak position shifted to the right compared with that in the comparative example 1; Figure 8 This is a TEM image of the finished self-replenishing lithium-type positive electrode material in Comparative Example 6, showing that an ultra-thin coating layer of less than 10 nm exists on the surface of the positive electrode material; Figure 9 The XRD patterns of the mixed material of Li2O and LiCoO2 before and after ball milling in Comparative Example 20 are compared. It is found that characteristic peaks other than Li2O and LiCoO2 exist in the material after ball milling.

[0128] 2. The ternary materials in Examples 1-7 and Comparative Examples 1-20, the conductive agent SP, and the binder PVDF were respectively prepared in a mass ratio of 97.5:1:1.5 using NMP as a solvent to prepare a pole piece, which was coated on a carbon-coated aluminum foil, dried at 100°C for 5h, and compacted on a roller press to obtain a positive electrode sheet.

[0129] 3. Lithium metal sheets were used as negative electrodes, 1M LiPF6 solution was used as electrolyte, and Cellgard 2300 was used as separator. The above positive electrodes were assembled into button cells. The cells were charged and discharged at a rate of 0.2C within a cut-off voltage range of 2.8 to 4.35V. The results are shown in Table 1.

[0130] The ternary materials in Examples 1-7 and Comparative Examples 1-20, the conductive agent CNTs, and the binder PVDF were mixed in a mass ratio of 98:1:1 using NMP as solvent, and the solid content was controlled to 70%. The slurry was then coated on the current collector aluminum foil, and the single surface density was controlled to 215g / m 2 The compaction density of the pole piece after roller pressing is 3.60g / cm 3 A 3Ah soft-pack battery was assembled with a NP ratio of 1.13, matched to a silicon-carbon anode, using a 1M LiPF6 solution as the electrolyte and Cellgard 2300 as the separator. The electrochemical performance of the product is shown in Table 2.

[0131] Table 1

[0132]

[0133]

[0134] Table 2

[0135]

[0136] It can be seen from the description in Tables 1 and 2 that the residual alkali content in Example 1 is significantly reduced compared with Comparative Examples 1 and 2. This is because after Co2O3 coating, part of the residual alkali on the surface of the ternary material reacts with Co2O3 to generate LiCoO2, and then undergoes vacuum high-temperature sintering, most of the residual alkali is converted into Li2O, and during high-energy ball milling, part of the LiCoO2 on the surface of the ternary material is combined with Li2O to transform into a (LiCo*)2O phase, leaving only a small amount of residual alkali. Since the residual alkali has poor electron and ion conductivity, reducing the residual alkali content is beneficial to the electrochemical performance. Therefore, Example 1 has a higher discharge gram capacity than Comparative Examples 1 and 2. In addition, since Example 1 generates the (LiCo*)2O phase, which has the function of replenishing lithium at the positive electrode, the charging gram capacity of Example 1 is significantly improved compared with Comparative Examples 1 and 2, and the cycle performance is significantly improved.

[0137] Compared with Comparative Example 3, Example 1 has a significantly lower residual alkali content, a significantly increased charge capacity, and improved cycle performance. This is mainly because the vacuum sintering treatment converts the residual alkali into Li2O. The generated Li2O reacts with LiCoO2 on the surface of the ternary material to form a lithium-supplemented phase (LiCo*)2O.

[0138] Compared with Comparative Example 4, Example 1 has significantly better discharge capacity and cycle performance than the latter. This is mainly because oxygen vacancies are generated inside the ternary material during vacuum sintering. The generation of oxygen vacancies makes the structure of the ternary material unstable, resulting in reduced discharge capacity and worsened cycle stability.

[0139] Compared with comparative example 5, the residual alkali content in Example 1 is significantly reduced, and the charge-discharge capacity and cycle performance are significantly improved. This is because ball milling can promote the combination and transformation of LiCoO2 and Li2O on the surface of the ternary material to form (LiCo*)2O phase, while without ball milling operation, LiCoO2 and Li2O exist independently, and Li2O releases Li + The potential is relatively high, so the purpose of replenishing lithium at the positive electrode cannot be achieved.

[0140] Compared with Comparative Example 6, Example 1 has improved charge and discharge capacity and cycle performance. This is because the aluminum oxide coating can reduce the contact between the electrolyte and the surface of the positive electrode material, thereby reducing the occurrence of side reactions.

[0141] The stability of Example 1 is significantly improved compared with Comparative Example 7 because PVDF coating is conducive to forming a thinner coating layer on the surface of the ternary material. This coating layer can hinder the reaction of the ternary material with H2O and CO2 in the environment, thereby improving stability.

[0142] Compared with Comparative Examples 8-9, Examples 1-2 have higher discharge capacity and room temperature cycle performance, and no lithium plating occurs. This is mainly because too much (LiCo*)2O phase is generated, resulting in a significant reduction in the ternary material in the self-replenishing lithium positive electrode material, causing a significant decrease in the material discharge capacity. Excessive lithium-replenishing phase will also cause lithium plating in the full-electric system, deteriorating the cycle performance. Too little lithium-replenishing phase will result in poor lithium-replenishing effect of the positive electrode material, which will also lead to poor cycle performance.

[0143] In Examples 1 and 3 and Comparative Examples 10-11, excessive increase or decrease of δ leads to a decrease in the amount of (LiCo*)2O phase generated, resulting in deterioration of the cycle performance of the self-replenishing lithium positive electrode material and lower capacity utilization.

[0144] Compared with Comparative Example 12, Examples 1 and 4 have increased residual alkali content, decreased discharge capacity, and deteriorated cycle performance. This is mainly because the reduced vacuum degree results in the inability of residual alkali to be converted into Li2O and the inability to generate the lithium-replenishing phase (LiCo*)2O.

[0145] In Examples 1 and 5 and Comparative Example 13, reducing the ball-to-material ratio will result in more Li2O being unable to react with LiCoO2 to form the lithium-supplementing phase (LiCo*)2O, causing part of the Li2O to be converted back into residual alkali, significantly increasing the residual alkali content, and reducing the discharge capacity and cycle number.

[0146] Compared with Comparative Examples 14-15, Examples 1 and 6 increase the PVDF coating amount too much, increase the thickness of the PVDF coating layer, and reduce the ability of the positive electrode material to conduct electrons and ions, so the capacity is reduced. Excessive reduction of the PVDF coating amount reduces the PVDF coating coverage, resulting in more surface exposure and poor stability. After exposure to a dew point of -20°C for 24 hours, the slurry exhibits gelation.

[0147] Compared with Comparative Examples 16-17, Examples 1 and 7 increase the alumina coating amount too much, making the alumina coating layer thicker, worsening the rate performance, and affecting the capacity performance. However, if the alumina coating amount is reduced too much, more surface of the positive electrode material will be in contact with the electrolyte during the electrochemical reaction, which will increase side reactions, reduce capacity performance, and worsen cycle performance.

[0148] Compared with Comparative Examples 18-19, in Example 1, if the PVDF and alumina coating temperature is increased too much, the originally uniform coating layer of PVDF will be locally unevenly agglomerated, resulting in exposure of the surface of the positive electrode material. If the modification temperature is lowered too much, the melting temperature of PVDF will not be reached, resulting in the inability to form a uniform coating layer, resulting in exposure of the surface of the positive electrode material. Both situations will lead to deterioration of material stability.

[0149] Example 1 and Comparative Example 20: The latter significantly improves cycling performance by adding the lithium-supplementing phase (LiCo*)2O. However, due to the lack of PVDF coating, its stability is poor, with the slurry showing signs of gelling after 24 hours of exposure. Furthermore, due to the lack of alumina coating, its capacity and cycling performance are significantly worse than those of Example 1.

[0150] The present invention has been described in detail above. For those skilled in the art, without departing from the purpose and scope of the present invention, and without the need to carry out unnecessary experimental conditions, the present invention can be implemented in a wide range under equivalent parameters, concentrations and conditions. Although the present invention provides specific embodiments, it should be understood that further improvements can be made to the present invention. In short, according to the principles of the present invention, this application is intended to include any changes, uses or improvements to the present invention, including changes that depart from the disclosed scope in this application and are made using conventional techniques known in the art.

Claims

1. A ternary cathode material having a core-shell structure, wherein the core is the ternary cathode material and the shell comprises three coating layers, namely, a LiCoO2 layer, a lithium supplementation mixed layer, and a protective mixed layer, from the inside to the outside; in, The lithium-supplemented mixed layer is composed of LiCoO2 and (LiCo*)2O; wherein (LiCo*)2O represents a phase different from Li2O and LiCoO2 generated by the reaction of Li2O and LiCoO2; The protective mixed layer is composed of PVDF and aluminum oxide.

2. The ternary cathode material according to claim 1, characterized in that The molecular formula of the ternary positive electrode material is LiNi x A y M 1-x-y O2, wherein A and M are each independently selected from any one of Co, Mn, B, Al, Zr, W, Ta, Nb, Ti, Fe, Y, Ga, Cu, Zn, Ge, Mo, V and Cr, and A and M are different, x≥0.50, 0≤y≤0.20, x+y≤1.

0.

3. A method for preparing the ternary cathode material according to claim 1 or 2, comprising the following steps: 1) Mixing the ternary precursor with a lithium source and sintering in dry air or oxygen atmosphere to obtain a high residual alkali ternary material; 2) mixing the high residual alkali ternary material with a cobalt source and sintering in a dry air or oxygen atmosphere to obtain a ternary material intermediate 1; 3) sintering the ternary material intermediate 1 in a vacuum environment, and then introducing oxygen to sinter the ternary material intermediate 2; 4) ball milling the ternary material intermediate 2 in a high-energy ball mill in an inert atmosphere to obtain the ternary material intermediate 3; 5) The ternary material intermediate 3 is mixed with PVDF and alumina, and sintered in a protective atmosphere to obtain a self-replenishing lithium-type ternary positive electrode material.

4. The method according to claim 3, characterized in that In step 1), the molecular formula of the ternary precursor is Ni x A y M 1-x-y (OH)2, wherein A and M are each independently selected from Co, Mn, B, Al, Zr, W, Ta, Nb, Ti, Fe, Y, Ga, Cu, Zn, Ge, Mo, V and Cr, and A and M are different, x ≥ 0.50, 0 ≤ y ≤ 0.20, and x + y ≤ 1.0; The lithium source is one or more of lithium hydroxide, lithium carbonate, lithium oxide and lithium peroxide; The mass ratio of the element Li in the lithium source to the element TM (Ni+A+M) in the precursor is 1.02 to 1.15; The sintering temperature is 700-1000°C and the holding time is 8-20h; The molecular formula of the high residual alkali ternary material obtained is LiNi x A y M 1-x-y O2, the Free Li content in the ternary material is 0.25wt%~1.05wt%, and the calculation formula is: Free Li=mLiOH / 23.94*6.94+mLi2CO3 / 73.89*2*6.

94.

5. The method according to claim 3, characterized in that In step 2), the cobalt source is one or more of cobalt hydroxide, cobalt oxyhydroxide, cobalt oxide, cobalt trioxide, cobalt trioxide, and cobalt carbonate; The cobalt source is added in accordance with the cobalt element, and the amount of the cobalt element added accounts for 0.20-1.00% of the total mass of the high residual alkali ternary material, and the D50 of the cobalt source is controlled to be ≤200nm and Dmax ≤500nm; The relationship between the residual alkali Free Li and the cobalt source Co in the high residual alkali ternary material is δ = (mLi / 6.94-mCo / 58.93) / 2(mCo / 58.93), δ = 3.0-5.0; mLi represents the mass of Free Li, and mCo represents the mass of Co in the cobalt source; The sintering temperature is 500-800° C., and the heat preservation time is 2-10 hours.

6. The method according to claim 3, characterized in that In step 3), the vacuum environment pressure value is controlled to be -0.040 to -0.090 MPa, the sintering temperature is 600 to 800° C., the vacuum environment sintering time is 3 to 20 hours, the oxygen sintering temperature is 600 to 800° C., and the oxygen sintering time is 0.5 to 5 hours.

7. The method according to claim 3, characterized in that In step 4), the ball-to-material ratio of high-energy ball milling is 1:0.1-5, and the ball milling time is 3-24 hours.

8. The method according to claim 3, characterized in that In step 5), the PVDF coating amount is 0.05-0.2% of the mass of the ternary material 3, the alumina coating amount is 0.05-0.3% of the mass of the ternary material intermediate 3, the protective atmosphere is one or more of nitrogen, helium, neon, argon, and xenon, the sintering temperature is 180-210°C, and the sintering time is 2-8h.

9. The ternary cathode material according to claim 1 or 2 is used as a cathode active material for a lithium ion battery or is used for preparing a cathode material for a lithium ion battery.

10. A lithium-ion battery, wherein the positive electrode material of the lithium-ion battery contains the ternary positive electrode material according to claim 1 or 2.

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