Low-temperature type ternary cathode material, preparation method thereof and lithium ion battery

Abstract

The present invention discloses a low-temperature type ternary cathode material, a preparation method thereof and a lithium-ion battery. The main steps of the preparation method of the low-temperature type ternary cathode material are as follows: providing a first mixed slurry containing kaolin and a first coupling agent; adding a ternary cathode precursor to the first mixed slurry, mixing and then drying to obtain a pre-sintered precursor; after mixing the pre-sintered precursor with a lithium source solution to obtain a second mixed slurry, coating to form a precursor wet film; sintering the precursor wet film, and depositing isocyanate, a second coupling agent and a diol on the surface of the material to obtain the low-temperature type ternary cathode material. Through this preparation method, a polymer / metakaolin coating layer can be formed on the surface of the ternary cathode material. The coating layer has good chemical stability, can improve the conductivity of the ternary cathode material and reduce the DC impedance at low temperature and low state of charge. At the same time, it can effectively reduce the residual alkali in the sintering process and improve the cycle stability of the lithium-ion battery at high rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a low-temperature ternary cathode material, a preparation method of the low-temperature ternary cathode material, and a lithium-ion battery containing the low-temperature ternary cathode material. Background Art

[0002] Ternary cathode materials are widely used as the main cathode materials for power lithium-ion batteries. Among them, the three elements play their respective roles. Nickel (Ni) is mainly used to increase the material capacity, cobalt (Co) is mainly used to stabilize the layered structure, and manganese (Mn) or aluminum (Al) is mainly used to reduce the material cost and improve safety. Compared with other types of cathode materials, ternary cathode materials have the advantages of high energy density, large discharge capacity, good cycle performance, and relatively stable structure.

[0003] However, there are still some common problems in the practical application of ternary cathode materials: (1) At low temperature and low state of charge, the internal DC impedance of the battery increases significantly, which limits the application range; (2) The strong interfacial reaction between the material and the electrolyte will form gas, thus triggering safety problems; (3) During the repeated cycle charge and discharge process of the material, the expansion of the crystal will cause structural changes, thus affecting its rate performance.

[0004] Therefore, aiming at the technical problems existing in the above ternary cathode materials, it is necessary to be solved urgently to broaden the application of ternary cathode materials. Summary of the Invention

[0005] In view of this, the present invention is necessary to provide a preparation method of a low-temperature ternary cathode material. Through this preparation method, a polymer / metakaolin coating layer can be formed on the surface of the ternary cathode material. The coating layer has good chemical stability, can improve the conductivity of the ternary cathode material and reduce the DC impedance at low temperature and low state of charge. At the same time, it can effectively reduce the residual alkali in the sintering process and improve the cycle stability of the lithium-ion battery at high rates.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The first aspect of the present invention provides a preparation method of a low-temperature ternary cathode material, comprising the following steps:

[0008] Provide a first mixed slurry, wherein the first mixed slurry contains kaolin and a first coupling agent;

[0009] Slowly add a ternary cathode precursor to the first mixed slurry, fully mix and then dry to obtain a pre-sintered precursor;

[0010] After fully mixing the pre-sintered precursor with a lithium source solution to obtain a second mixed slurry, coat to form a wet precursor film;

[0011] Sinter the precursor wet film, and at the same time deposit isocyanate, a second coupling agent and a diol on the surface of the material to obtain a low-temperature ternary cathode material.

[0012] In the present invention, first, a first coupling agent is used to cause a combined action between kaolin and a ternary precursor. During the subsequent calcination, kaolin can effectively form a coating structure with the generated ternary material, that is, a layer-shell structure of kaolin-ternary material; further, during the sintering process, isocyanate, a second coupling agent and a diol are vapor-deposited on the layer-shell structure of kaolin-ternary material, and finally a multi-component composite structure of polymer / metakaolin-ternary cathode material is formed.

[0013] The ternary cathode material prepared by the present invention has excellent low-temperature performance, which is mainly due to:

[0014] (1) A metakaolin coating layer forming a aluminosilicate network structure is formed by kaolin, providing channels and paths for the migration of lithium ions, which is beneficial to the migration of lithium ions at low temperatures.

[0015] (2) The organic coating layer and organic solvents in the electrolyte such as EC, DMC, etc. are all carbonate substances, and there is a characteristic of similar solubility. At low temperatures, they can maintain good contact with this type of lipid solvent. At the same time, the rough surface of the material can bring high interfacial energy, and the non-crystallization characteristic of the lipid solvent can still be ensured at the contact part of the interface. The lipid solvent ensures high activity, so that lithium ions can be better dissolved in the liquid phase, ensuring the movement of lithium ions at low temperatures.

[0016] Therefore, the ternary cathode material prepared by the preparation method in the present invention has excellent low-temperature performance.

[0017] In a further aspect, the ternary cathode precursor described herein is selected according to the finally prepared ternary cathode material, and there is no particular limitation. In some specific embodiments of the present invention, the ternary cathode material is lithium nickel cobalt manganate, so the composition of the ternary cathode precursor is Ni x Co y Mn 1-x-y (OH)2, where 0.7 ≤ x < 1 and 0 < y ≤ 0.3.

[0018] In a further aspect, the first mixed slurry is formed by mixing kaolin, a first coupling agent and a solvent. In the first mixed slurry, the mass fraction of kaolin is 2% - 5%; the solvent is selected according to the properties of kaolin and the first coupling agent, and specific examples that can be mentioned are one or more mixtures of acetone, ethanol, and isopropanol.

[0019] In a further aspect, the properties of the finally formed ternary cathode material can be adjusted by the coating condition of the coating layer. Therefore, the coating condition of the coating layer can be adjusted by adjusting the ratio of kaolin to the ternary cathode precursor, and then the properties of the ternary cathode material can be adjusted. In some preferred embodiments of the present invention, the mass ratio of the kaolin, the first coupling agent, and the ternary cathode precursor is 1:(0.2 - 0.8):(120 - 160).

[0020] In a further aspect, the first coupling agent described herein is a coupling agent containing an inorganic-philic group, so that kaolin and the ternary cathode precursor can be combined and sintered to form a metakaolin coating layer with a uniform thickness and a natural mineral aluminosilicate network structure. Specific examples of the first coupling agent that can be mentioned include one or a mixture of two of tetraisopropyl titanate and diisopropylaluminum distearate.

[0021] In a further aspect, in the step of obtaining the pre-sintered precursor, the first mixed slurry and the ternary cathode precursor can both adopt a conventional mechanical mixing process, as long as the mixing is uniform. In some specific embodiments of the present invention, the process of sufficient mixing is: magnetic stirring at 60 - 80 °C and 1000 - 1200 r / min for 1 - 2 h.

[0022] In a further aspect, in the step of obtaining the pre-sintered precursor, the drying is carried out by flash evaporation. This is because a fluffy powder can be formed during the drying process, which is convenient for subsequent further sintering and can simplify the process flow. In some specific embodiments of the present invention, the specific process of flash evaporation is: flash drying at 120 - 140 °C for 4 - 8 s.

[0023] In a further aspect, the concentration of the specific lithium source solution can be selected according to the composition of the final material, and the mass concentration of the lithium source solution is 20% - 30%.

[0024] In a further aspect, the lithium source adopted herein can be a raw material conventionally used in the field for preparing ternary cathode materials. Specific examples that can be mentioned include, but are not limited to, one or a mixture of two or more of lithium hydroxide, lithium hexafluorophosphate, and lithium perchlorate.

[0025] In a further aspect, the precursor wet film is formed by spin-coating the second mixed slurry on a substrate. There is no special limitation on the substrate here, and any high-temperature resistant material similar to the ternary crucible can be used. Specific examples that can be mentioned include corundum, ceramics, etc., and will not be specifically elaborated here.

[0026] In some specific embodiments of the present invention, the spin-coating step is: dropping the second mixed slurry on the substrate, and the substrate is centrifuged at a rate of 10000 - 15000 r / min for 25 - 30 s to complete one spin-coating, and the spin-coating is repeated 3 - 5 times to obtain the precursor wet film.

[0027] In a further embodiment, the thickness of the precursor wet film is between 4 and 8 μm.

[0028] In a further scheme, the sintering and deposition steps are carried out in a tubular furnace, and the specific steps are: placing isocyanate, a second coupling agent and a diol in a first temperature zone, and placing the precursor wet film in a second temperature zone; introducing oxygen, repeatedly pumping and exhausting the gas 3-5 times, and cleaning the tubular furnace; heating the second temperature zone to 650-840°C at 2-4°C / min, sintering at a constant temperature for 12-20h, and then cooling to 200-250°C at the same rate, and keeping warm for 2-4h; when there is 5-15min of insulation time remaining in the second temperature zone, raising the temperature of the first temperature zone to 260-300°C until the insulation time ends, and naturally cooling to room temperature.

[0029] Among them, the second coupling agent described in this article is a coupling agent containing a group that is affinity for an organophilic matrix, through which chemical vapor deposition is carried out, the polymer and kaolin are efficiently compounded to achieve effective coating modification of the ternary positive electrode material.

[0030] In a further embodiment, the oxygen introduction rate is 2-8 mL / min.

[0031] In a further solution, the specific raw material ratio can be adjusted according to the coating needs, thereby adjusting the performance of the final ternary positive electrode material. In some specific embodiments of the present invention, the mass ratio of the second coupling agent, isocyanate, diol and precursor wet film is 1: (13.7-20): (19.8-32): (150-200).

[0032] In a further embodiment, the isocyanate is toluene diisocyanate, hexamethylene diisocyanate or a mixture of the two;

[0033] And / or, the diol is one or a mixture of diethylene glycol and 1,4-butanediol;

[0034] And / or, the second coupling agent is one of vinyltriethoxysilane and tetra-n-propyl zirconate, or a mixture of both.

[0035] The second aspect of the present invention provides a low-temperature ternary positive electrode material, which is prepared by the preparation method described in the first aspect of the present invention.

[0036] The third aspect of the present invention provides a lithium ion battery, which contains the low temperature ternary positive electrode material described in the second aspect of the present invention. It is understandable that other components of the lithium ion battery, such as the negative electrode, the separator, the electrolyte, etc., and the specific assembly process can all adopt conventional methods in the art, which will not be elaborated here.

[0037] The "low-temperature type ternary cathode material" and "lithium-ion battery" in the present invention have the same effects or advantages, which will not be elaborated specifically here.

[0038] Advantages of the present invention:

[0039] In the present invention, kaolin is combined with a ternary cathode precursor through a coupling agent containing an inorganic-philic group, and sintered to form a uniformly thick metakaolin coating layer with a natural mineral aluminosilicate network structure. Then, chemical vapor deposition is carried out through a coupling agent containing an organic matrix-philic group, and the polymer is efficiently compounded with metakaolin, achieving effective coating modification of the cathode material.

[0040] Compared with the conventional chemical vapor deposition step, the present invention provides a deposition scheme during the material sintering process to achieve effective coating on the material surface. Without affecting the material performance, resources are maximally saved and the material manufacturing cost is reduced.

[0041] The polymer / metakaolin composite coating layer prepared by the present invention has good chemical stability, can improve the conductivity of the ternary cathode material at low temperature and low state of charge, reduce the DC impedance of the battery, and at the same time can effectively reduce the residual alkali during the sintering process and improve the cycle stability of the battery at high rate. Description of the drawings

[0042] Figure 1 Microscopic morphology of the ternary cathode material prepared in Comparative Example 1;

[0043] Figure 2 Microscopic morphology of the low-temperature type ternary cathode material prepared in Example 1;

[0044] Figure 3 Discharge curves of the lithium-ion batteries prepared from the ternary cathode materials prepared in Comparative Example 1 and Example 1 at a current of 0.2C. Detailed implementation manners

[0045] The embodiments of the present invention will be described in detail below. The following described embodiments are exemplary and are only used to explain the present invention, and should not be construed as a limitation to the present invention.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the description of the present invention in this specification are only for the purpose of describing specific implementation manners and are not intended to limit the present invention. Additionally, unless otherwise specified, the methods without specific recorded conditions or steps are all conventional methods, and the reagents and materials used can be obtained from commercial channels.

[0047] Example 1

[0048] In this embodiment, a preparation method of a low-temperature ternary cathode material is disclosed, and the specific steps are as follows:

[0049] (1) Weigh 5 g of kaolin and 1 g of tetra-isopropyl titanate, add them to 244 g of acetone, and then slowly add 600 g of the ternary cathode precursor Ni 0.7 Co 0.2 Mn 0.1 (OH)2, magnetically stir at 60 °C and 1200 r / min for 2 h, and then flash dry at 120 °C for 4 s to obtain a pre-calcined precursor;

[0050] (2) Weigh 2.4 g of lithium hydroxide and add it to 9.6 g of acetone. Then add 4.99 g of the pre-calcined precursor prepared in step (1) to it. After high-speed mixing at 800 r / min for 30 min, place it on a substrate. The centrifuge spins at a rate of 10000 r / min for 25 s to complete one spin coating, and repeat the spin coating 3 times to obtain a precursor wet film with a thickness of 8 μm;

[0051] (3) Place 20 g of toluene diisocyanate, 1 g of vinyltriethoxysilane, and 32 g of diethylene glycol in the first temperature zone of a tube furnace, and place 200 g of the precursor wet film prepared in step (2) in the second temperature zone; Pass in oxygen, repeatedly evacuate and fill with gas 3 times to wash the tube furnace. Heat the second temperature zone to 840 °C at a rate of 2 °C / min, keep it at a constant temperature for 12 h, and then cool it to 200 °C at the same rate and keep it at a constant temperature for 2 h; When there are 30 min left in the constant temperature time in the second temperature zone, raise the temperature of the first temperature zone to 300 °C until the constant temperature time ends, and naturally cool to room temperature to obtain the low-temperature ternary cathode material.

[0052] Example 2

[0053] In this embodiment, a preparation method of a low-temperature ternary cathode material is disclosed, and the specific steps are as follows:

[0054] (1) Weigh 5 g of kaolin and 4 g of aluminum diisostearoyl oxyisopropyl aluminate, add them to 171 g of ethanol, and then slowly add 800 g of the ternary cathode precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2, magnetically stir at 60 °C and 1000 r / min for 2 h, and then flash dry at 140 °C for 4 s to obtain a pre-calcined precursor;

[0055] (2) Weigh 2.4 g of lithium hexafluorophosphate and add it to 5.6 g of ethanol. Then add 5.4 g of the pre-calcined precursor prepared in step (1) to it. After high-speed mixing at 1000 r / min for 30 min, place it on a substrate. The centrifuge spins at a rate of 10000 r / min for 25 s to complete one spin coating, and repeat the spin coating 3 times to obtain a precursor wet film with a thickness of 6 μm;

[0056] (3) Place 13.7 g of toluene diisocyanate, 1 g of vinyltriethoxysilane, and 24.6 g of diethylene glycol in the first temperature zone of a tube furnace, and place the 150 g of precursor wet film prepared in step (2) in the second temperature zone; introduce oxygen, repeatedly evacuate and fill with gas 3 times to wash the tube furnace, heat the second temperature zone to 830 °C at a rate of 4 °C / min, hold for sintering for 15 h, then cool to 220 °C at the same rate, and keep warm for 4 h; when 10 min remains in the constant temperature time of the second temperature zone, raise the temperature of the first temperature zone to 280 °C until the constant temperature time ends, and then cool naturally to room temperature to obtain a low-temperature type ternary cathode material.

[0057] Example 3

[0058] In this example, a preparation method of a low-temperature type ternary cathode material is disclosed, and the specific steps are as follows:

[0059] (1) Weigh 5 g of kaolin and 3 g of diisopropylaluminum stearate, add them to 152 g of ethanol, and then slowly add 700 g of the ternary cathode precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2, stir magnetically at 80 °C and 1100 r / min for 1 h, and then flash dry at 140 °C for 8 s to obtain a pre-calcined precursor;

[0060] (2) Weigh 2.4 g of lithium hydroxide and add it to 7.2 g of isopropanol, then add 5.3 g of the pre-calcined precursor prepared in step (1) thereto, mix at high speed at 800 r / min for 50 min, then place it on a substrate, centrifuge at a rate of 12000 r / min for 30 s to complete one spin coating, and repeat spin coating 5 times to obtain a precursor wet film with a thickness of 4 μm;

[0061] (3) Place 16 g of hexamethylene diisocyanate, 1 g of tetra-n-propyl zirconate, and 20 g of 1,4-butanediol in the first temperature zone of a tube furnace, and place the 180 g of precursor wet film prepared in step (2) in the second temperature zone; introduce oxygen, repeatedly evacuate and fill with gas 5 times to wash the tube furnace, heat the second temperature zone to 780 °C at a rate of 2 °C / min, hold for sintering for 15 h, then cool to 250 °C at the same rate, and keep warm for 2 h; when 20 min remains in the constant temperature time of the second temperature zone, raise the temperature of the first temperature zone to 270 °C until the constant temperature time ends, and then cool naturally to room temperature to obtain a low-temperature type ternary cathode material.

[0062] Example 4

[0063] In this example, a preparation method of a low-temperature type ternary cathode material is disclosed, and the specific steps are as follows:

[0064] (1) Weigh 5 g of kaolin and 2 g of isopropylaluminum dioleate, add them to 226 g of isopropanol, and then slowly add 910 g of the ternary cathode precursor Ni 0.9 Co 0.05 Mn 0.05 (OH)2. Stir magnetically at 60 °C and 1000 r / min for 2 h, and then flash dry at 120 °C for 8 s to obtain the pre-calcined precursor;

[0065] (2) Weigh 2.4 g of lithium perchlorate, add it to 5.6 g of isopropanol, and then add 5.04 g of the pre-calcined precursor prepared in step (1). After high-speed mixing at 100 r / min for 50 min, place it on the substrate. Centrifuge at a rate of 12000 r / min for 25 s to complete one spin coating, and repeat the spin coating 3 times to obtain a precursor wet film with a thickness of 6 μm;

[0066] (3) Place 13.7 g of toluene diisocyanate, 1 g of vinyltriethoxysilane, and 24.6 g of diethylene glycol in the first temperature zone of the tube furnace, and place the 150 g of precursor wet film prepared in step (2) in the second temperature zone; Pass in oxygen, repeatedly evacuate and fill with gas 3 times to clean the tube furnace. Heat the second temperature zone to 780 °C at a rate of 4 °C / min, keep it at a constant temperature for 15 h, and then cool it to 220 °C at the same rate and keep it at a constant temperature for 4 h; When there are 10 min left in the constant temperature time in the second temperature zone, raise the temperature of the first temperature zone to 280 °C until the constant temperature time ends, and then cool it naturally to room temperature to obtain the low-temperature type ternary cathode material.

[0067] Example 5

[0068] In this example, a preparation method of a low-temperature type ternary cathode material is disclosed, and the specific steps are as follows:

[0069] (1) Weigh 5 g of kaolin and 2 g of tetraisopropyl titanate, add them to 226 g of isopropanol, and then slowly add 910 g of the ternary cathode precursor Ni 0.9 Co 0.05 Mn 0.05 (OH)2. Stir magnetically at 60 °C and 1200 r / min for 1 h, and then flash dry at 140 °C for 5 s to obtain the pre-calcined precursor;

[0070] (2) Weigh 2.4 g of lithium hexafluorophosphate, add it to 7.2 g of isopropanol, and then add 5.3 g of the pre-calcined precursor prepared in step (1). After high-speed mixing at 800 r / min for 50 min, place it on the substrate. Centrifuge at a rate of 12000 r / min for 30 s to complete one spin coating, and repeat the spin coating 5 times to obtain a precursor wet film with a thickness of 4 μm;

[0071] (3) Place 16 g of hexamethylene diisocyanate, 1 g of tetra-n-propyl zirconate, and 20 g of 1,4-butanediol in the first temperature zone of a tube furnace, and place the 180 g of the precursor wet film prepared in step (2) in the second temperature zone; introduce oxygen, evacuate and refill the gas 5 times repeatedly to clean the tube furnace, heat the second temperature zone to 780 °C at a rate of 2 °C / min, keep it at a constant temperature for 15 h, then cool it to 250 °C at the same rate, and keep it at a constant temperature for 2 h; when there are 20 min left in the constant temperature time in the second temperature zone, raise the temperature of the first temperature zone to 270 °C until the constant temperature time ends, and then cool it naturally to room temperature to obtain a low-temperature ternary cathode material.

[0072] Comparative Example 1

[0073] This comparative example discloses a preparation method of a ternary cathode material, and the specific steps are as follows:

[0074] Weigh 2.4 g of lithium hydroxide and 4.83 g of the ternary cathode precursor Ni 0.7 Co 0.2 Mn 0.1 (OH)2, mix them at a high speed of 800 r / min for 30 min and then place them in a tube furnace, introduce oxygen, heat it to 840 °C at a rate of 2 °C / min, keep it at a constant temperature for 12 h, then cool it to 200 °C at the same rate, keep it at a constant temperature for 2 h, and then cool it naturally to room temperature to obtain a ternary cathode material.

[0075] Comparative Example 2

[0076] This comparative example adopts the same implementation method as in Example 1, and the only difference is that: kaolin coating is not carried out. Other processes are the same as in Example 1, and the specific steps are as follows:

[0077] (1) Slowly add 600 g of the ternary cathode precursor Ni 0.7 Co 0.2 Mn 0.1 (OH)2 to 244 g of acetone, stir magnetically at 60 °C and 1200 r / min for 2 h, and then flash dry at 120 °C for 4 s to obtain a pre-calcined precursor;

[0078] (2) Weigh 2.4 g of lithium hydroxide and add it to 9.6 g of acetone, then add 4.99 g of the pre-calcined precursor prepared in step (1) to it, mix them at a high speed of 800 r / min for 30 min and then place them on a substrate, centrifuge at a rate of 10000 r / min for 25 s by a centrifuge to complete one spin coating, and repeat the spin coating 3 times to obtain a precursor wet film with a thickness of 8 μm;

[0079] (3) Place 20 g of toluene diisocyanate, 1 g of vinyltriethoxysilane, and 32 g of diethylene glycol in the first temperature zone of a tubular furnace, and place the 200 g of the precursor wet film prepared in step (2) in the second temperature zone; introduce oxygen, evacuate and refill the gas 3 times repeatedly to clean the tubular furnace. Heat the second temperature zone to 840 °C at a rate of 2 °C / min, sinter at a constant temperature for 12 h, then cool to 200 °C at the same rate, and keep the temperature for 2 h; when the remaining constant temperature time in the second temperature zone is 30 min, raise the temperature of the first temperature zone to 300 °C until the end of the constant temperature time, and then cool naturally to room temperature to obtain the ternary cathode material.

[0080] Comparative Example 3

[0081] This comparative example uses the same implementation method as in Example 1, with the only difference being that no polymer coating is carried out. All other processes are the same as in Example 1, and the specific steps are as follows:

[0082] (1) Weigh 5 g of kaolin and 1 g of tetra-isopropyl titanate, add them to 244 g of acetone, and then slowly add 600 g of the ternary cathode precursor Ni 0.7 Co 0.2 Mn 0.1 (OH)2, magnetically stir at 60 °C and 1200 r / min for 2 h, and then flash dry at 120 °C for 4 s to obtain the pre-sintered precursor;

[0083] (2) Weigh 2.4 g of lithium hydroxide and add it to 9.6 g of acetone, then add 4.99 g of the pre-sintered precursor prepared in step (1) to it. After high-speed mixing at 800 r / min for 30 min, place it on a substrate, and centrifuge at a rate of 10000 r / min for 25 s to complete one spin coating. Repeat the spin coating 3 times to obtain a precursor wet film with a thickness of 8 μm;

[0084] (3) Place the 200 g of the precursor wet film prepared in step (2) in a tubular furnace, introduce oxygen, evacuate and refill the gas 3 times repeatedly to clean the tubular furnace. Heat it to 840 °C at a rate of 2 °C / min, sinter at a constant temperature for 12 h, then cool to 200 °C at the same rate, keep the temperature for 2 h, and then cool naturally to room temperature to obtain the ternary cathode material.

[0085] Comparative Example 4

[0086] This comparative example uses the same implementation method as in Example 1, with the only difference being that conventional chemical vapor deposition is used for coating. All other processes are the same as in Example 1, and the specific steps are as follows:

[0087] (1) Weigh 5 g of kaolin and 1 g of tetra-isopropyl titanate, add them to 244 g of acetone, and then slowly add 600 g of the ternary cathode precursor Ni 0.7 Co 0.2 Mn 0.1(OH)2 was magnetically stirred at 60 °C and 1200 r / min for 2 h, and then flash-dried at 120 °C for 4 s to obtain a pre-sintered precursor;

[0088] (2) Weigh 2.4 g of lithium hydroxide and add it to 9.6 g of acetone. Then add 4.99 g of the pre-sintered precursor prepared in step (1). After high-speed mixing at 800 r / min for 30 min, place it on a substrate. The centrifuge spins at a rate of 10000 r / min for 25 s to complete one spin coating. Repeat the spin coating 3 times to obtain a wet precursor film with a thickness of 8 μm;

[0089] (3) Place 200 g of the wet precursor film prepared in step (2) in the second temperature zone; introduce oxygen, repeatedly evacuate and fill with gas 3 times to clean the tube furnace. Heat the second temperature zone to 840 °C at a rate of 2 °C / min, keep it at a constant temperature for sintering for 12 h, and then naturally cool to room temperature to obtain a ternary cathode material; outside the tube furnace, heat 20 g of toluene diisocyanate, 1 g of vinyltriethoxysilane, and 32 g of diethylene glycol to 300 °C, introduce oxygen as the carrier gas into the tube furnace, and deposit the volatile organic matter on the above ternary cathode material to obtain a coated and modified ternary cathode material.

[0090] Performance Test

[0091] Mix the ternary cathode materials prepared in the examples and comparative examples with conductive carbon black and polyvinylidene fluoride in a mass ratio of 90:5:5, stir and mix evenly with N-methylpyrrolidone as a dispersant, then evenly coat it on aluminum foil, dry it and cut it into a positive electrode disc with a diameter of 8 mm, and transfer it to a vacuum oven at 120 °C for drying for 24 h. Use the prepared positive electrode disc as the working electrode, a metal lithium sheet as the counter electrode, and an electrolyte of 1 mol / L LiPF6 dissolved in a mixed solution of ethylene carbonate and dimethyl carbonate (wt% = 1:1). Assemble it into a 2032-type button cell in a glove box.

[0092] (1) Low-temperature and low-SOC battery DCR test:

[0093] At a cut-off voltage of 2.8 - 4.35 V, first charge the batteries prepared from the ternary cathode materials in the examples and comparative examples to full charge at a current of 1 C, then discharge at a current of 1 C to 5%, 20%, and 30% of the full charge capacity, then put them into a temperature-changing box and cool down to -20 °C, let them stand for 4 h and then discharge to 0%, and calculate the resistance value.

[0094] (2) First discharge and rate performance test:

[0095] Charge the batteries prepared from the ternary cathode materials in the examples and comparative examples from 2.8 V to 4.35 V at a constant current of 3 C, keep the constant voltage charging at 4.35 V, and then perform cyclic charge and discharge tests at a current of 3 C, and record the discharge capacity retention rate after 50 cycles.

[0096] The specific test results are shown in Table 1.

[0097] Table 1 Test Results of Electrochemical Performance of Lithium-Ion Batteries

[0098]

[0099] It can be seen from the test results in Table 1 that the DC internal resistance (DCR) of the batteries of Examples 1-5 at low temperature and low SOC is significantly lower than that of Comparative Examples 1-4, showing excellent low-temperature performance. In addition, during the charge and discharge test at a current of 3C, after 50 cycles of charge and discharge, the capacity of Examples 1-5 can still be maintained above 90%, indicating that the modified kaolin coating has a significant improvement effect on the charge and discharge performance of the ternary cathode material at high current.

[0100] Furthermore, Figure 1 and Figure 2 Figs. 1 and 2 are the micrographs of the ternary cathode materials of Comparative Example 1 and Example 1 magnified 10,000 times. It can be seen from the figures that the modified kaolin is uniformly coated on the surface of the ternary cathode material, and the cathode particles are evenly distributed.

[0101] Figure 3 Fig. 3 shows the first discharge capacity curves of the lithium-ion batteries prepared from the cathode materials of Example 1 and Comparative Example 1 at a current of 0.2C. It can be seen from Figure 3 Fig. 3 that the 0.2C discharge capacity of the lithium-ion battery prepared from the ternary cathode material of Example 1 is 191.4 mAh·g -1 , while the discharge capacity of the lithium-ion battery prepared from the ternary cathode material of Comparative Example 1 is only 182.7 mA·hg -1 ; thus, it can be shown that the battery assembled with the ternary cathode material coated with modified kaolin has excellent first discharge performance.

[0102] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0103] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A preparation method of a low-temperature type ternary cathode material, characterized in that, It includes the following steps: Provide a first mixed slurry, which contains kaolin and a first coupling agent; Slowly add a ternary cathode precursor to the first mixed slurry, mix well and then dry to obtain a pre-calcined precursor; After fully mixing the pre-calcined precursor with a lithium source solution to obtain a second mixed slurry, coat it to form a precursor wet film; Sinter the precursor wet film, and deposit isocyanate, a second coupling agent and a diol on the surface of the material to obtain a low-temperature type ternary cathode material; Among them, the steps of sintering and deposition are carried out in a tubular furnace. The steps are specifically as follows: Place isocyanate, a second coupling agent and a diol in the first temperature zone, and place the precursor wet film in the second temperature zone; Pass in oxygen, repeatedly evacuate and fill the gas 3-5 times to wash the tubular furnace; Heat the second temperature zone to 650-840 °C at a rate of 2-4 °C / min, keep it at a constant temperature and sinter for 12-20 h, then cool it to 200-250 °C at the same rate, and keep it warm for 2-4 h; When the remaining heat preservation time in the second temperature zone is 5-15 min, raise the temperature of the first temperature zone to 260-300 °C until the heat preservation time ends, and then cool it naturally to room temperature; The isocyanate is one or a mixture of two of toluene diisocyanate and hexamethylene diisocyanate; The diol is one or a mixture of two of diethylene glycol and 1,4-butanediol.

2. The preparation method according to claim 1, characterized in that, In the first mixed slurry, the mass fraction of kaolin is 2%-5%.

3. The preparation method according to claim 2, characterized in that, The mass ratio of the kaolin, the first coupling agent and the ternary cathode precursor is 1:(0.2-0.8):(120-160).

4. The preparation method according to claim 3, characterized in that, The first coupling agent is one or a mixture of two of tetra-isopropyl titanate and diisostearoyl oxyisopropyl aluminate.

5. The preparation method according to claim 1, characterized in that, In the step of obtaining the pre-calcined precursor, the process of the full mixing is: magnetic stirring at 60-80 °C and 1000-1200 r / min for 1-2 h.

6. The preparation method according to claim 1, characterized in that, The process of the drying is: flash drying at 120-140 °C for 4-8 s.

7. The preparation method according to claim 1, characterized in that, The mass concentration of the lithium source solution is 20%-30%.

8. The preparation method according to claim 7, characterized in that, The lithium source is one or a mixture of two or more of lithium hydroxide, lithium hexafluorophosphate and lithium perchlorate.

9. The preparation method according to claim 1, wherein, The precursor wet film is formed by spin-coating the second mixed slurry on a substrate.

10. The preparation method according to claim 9, characterized in that, The steps of the spin-coating are: Drop the second mixed slurry on the substrate, and the substrate is centrifuged at a rate of 10000-15000 r / min for 25-30 s to complete one spin-coating, and repeat the spin-coating 3-5 times to obtain a precursor wet film.

11. The preparation method according to claim 10, characterized in that, The thickness of the precursor wet film is between 4-8 μm.

12. The preparation method according to claim 1, characterized in that, The feeding rate of the oxygen is 2-8 mL / min.

13. The preparation method according to claim 1, characterized in that, The mass ratio of the second coupling agent, isocyanate, diol and the precursor wet film is 1:(13.7-20):(19.8-32):(150-200).

14. The preparation method according to claim 1, wherein, The second coupling agent is one or a mixture of two of vinyltriethoxysilane and tetra-n-propyl zirconate.

15. A low-temperature type ternary cathode material, characterized in that, It is prepared by using the preparation method described in any one of claims 1-14.

16. A lithium-ion battery, characterized in that, It contains the low-temperature type ternary cathode material described in claim 15.

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