Preparation method of coated modified lithium manganate positive electrode material

Abstract

The application discloses a preparation method of coated modified lithium manganate positive electrode material and belongs to the technical field of positive electrode materials. The coated modified lithium manganate positive electrode material prepared by the method can form a protective layer through coating of nano single-crystal lithium-rich manganese-based positive electrode material, so as to prevent dissolution of manganese ions. The coating layer can stabilize the lithium manganate crystal structure, reduce the activity of manganese ions and reduce the reaction between the manganese ions and electrolyte, thereby inhibiting the dissolution of manganese, improving the cycle stability and capacity retention rate of the battery. The coated modified lithium manganate positive electrode material prepared by the method has high initial coulomb efficiency and discharge specific capacity and has good cycle performance, especially high-temperature cycle performance and high-temperature storage performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of positive electrode materials, and particularly relates to a preparation method of a coated modified lithium manganate positive electrode material. BACKGROUND

[0002] With the rapid development of electric vehicles and renewable energy, lithium-ion batteries have received widespread attention as a high-efficiency, lightweight, and environmentally friendly energy storage device. It has high energy density, long cycle life, and fast charging and discharging advantages, and has become the preferred technology for current energy storage and mobile power. With the rapid development of renewable energy and the popularity of electric transportation, there is an increasing demand for higher performance, safer and more reliable lithium-ion batteries. As one of the core components of lithium-ion batteries, the positive electrode material is crucial to the performance of the battery. The positive electrode material needs to have high specific capacity, excellent cycle stability and good safety performance. Lithium manganate has many advantages such as simple preparation process, low raw material cost and good safety performance, and has become a commercialized lithium-ion battery positive electrode material.

[0003] However, lithium manganate also has the following problems: (1) Jahn-Teller effect during the cycle process, leading to Mn 2+ ion dissolution; (2) corrosion of the material surface primary particles caused by direct contact with the electrolyte; (3) corrosion of the material internal primary particles caused by the electrolyte entering from the material surface pores; these problems make the cycle performance of lithium manganate poor. The specific capacity of the commercialized lithium manganate is low, usually 100-115 mAh / g, which is difficult to meet the demand of high energy density batteries. In the prior art, the modification methods of lithium manganate mainly include: doping metal ions to stabilize the crystal structure of lithium manganate material; surface coating can avoid direct contact of the material with the electrolyte and reduce the corrosion of the electrolyte on the material; controlling the morphology of lithium manganate can reduce the specific surface area of the material, thereby reducing the interface area of manganese dissolution.

[0004] The existing solid phase coating method mostly uses nano inorganic oxide as a coating agent, and the thickness of the coating is directly related to the particle size of the nano oxide. The difficulty of dispersing inorganic oxide leads to the discontinuity of the coating layer and the over-thickness of the coating layer. Moreover, the nano inorganic oxide usually has no electrochemical activity, which reduces the specific discharge capacity of the material and affects the electrochemical performance of the material. The existing liquid phase coating method mostly uses an aqueous solution containing metal salt as a coating agent. Water can also dissolve lithium ions on the surface of lithium manganate, leading to deterioration of the material performance. At the same time, under the action of capillary phenomenon, the solution will infiltrate into the material through the pores on the surface of the material, causing the inorganic oxide to deposit and crystallize in the interior of the material particles, leading to an increase in the stress in the material and deterioration of the cycle performance of the material. Therefore, the current lithium manganate positive electrode material has low first coulomb efficiency, low specific discharge capacity, and poor cycle performance, especially poor high-temperature cycle performance and high-temperature storage performance.

[0005] In recent years, nano-structure regulation of lithium manganate positive electrode materials through nano-material technology has been widely studied. Nano-structure has a large specific surface area, a short ion transmission path, and excellent electrochemical performance, which helps to overcome the limitations of traditional lithium manganate materials and improve the capacity, cycle stability, and rapid charge-discharge performance of the battery. For example, CN202111649067 provides a preparation method of silver nanoparticle-coated lithium manganate positive electrode material. The silver nanoparticle coating layer not only has excellent electronic conductivity and a low lithium ion diffusion barrier, but also does not react with trace hydrofluoric acid in the electrolyte, thereby enhancing the electrochemical performance of the lithium manganate positive electrode material. However, silver is a noble metal, which increases the cost and is not conducive to industrialization. CN202211743016 provides multi-element carbon-coated lithium manganate and a preparation method thereof. The multi-element carbon-coated lithium manganate has high conductivity, rate performance, cycle performance, and safety performance. However, the double-layer coating of the carbon nanotube layer and the hard carbon layer is too costly, and the synthesis conditions are harsh, which is not conducive to industrialization. SUMMARY

[0006] In view of the problems of low first coulomb efficiency, low specific discharge capacity, poor cycle performance, especially poor high-temperature cycle performance and high-temperature storage performance of the existing lithium manganate positive electrode material, the present application provides an coated modified lithium manganate positive electrode material with high first coulomb efficiency and specific discharge capacity, and good cycle performance, especially high-temperature cycle performance and high-temperature storage performance, comprising the following steps:

[0007] 1) mechanically mixing manganese source and lithium source in a certain proportion, and calcining the uniformly mixed material under an atmosphere, and then crushing and grading the calcined material to obtain lithium manganate positive electrode material;

[0008] 2) The nickel salt, cobalt salt, manganese salt, lithium salt is mechanically mixed according to a certain mixing ratio, water or ethanol is added according to a certain solid content, the obtained material is put into a beater to beat, the obtained slurry is input into a sand mill to sand mill, and the slurry after sand milling is dried and granulated by a spray dryer to obtain a nano single-crystal lithium-rich manganese-based positive electrode material precursor;

[0009] 3) The nano single-crystal lithium-rich manganese-based positive electrode material precursor is once calcined under an atmosphere condition, and the calcined material is crushed and graded to obtain a nano single-crystal lithium-rich manganese-based positive electrode material.

[0010] 4) The lithium manganate positive electrode material is mechanically mixed with the nano single-crystal lithium-rich manganese-based positive electrode material to obtain a lithium manganate positive electrode material coated and modified by the nano single-crystal lithium-rich manganese-based positive electrode material.

[0011] Preferably, in step 1), the manganese source is one or more of MnCO3, MnO2, Mn2O3, Mn3O4, Mn(OH)2, and MnSO4, the lithium source is one or more of LiNO3, LiNO2, LiCl, LiOH, LiBr, LiI, Li2S, LiF, Li2CO3, Li2SO4, Li2SO3, LiClO4, LiMnO4, Li2O2, LiO2, and Li2S2O3, and the lithium-manganese molar ratio of the lithium source and the manganese source is 0.45-0.65:1.

[0012] Preferably, in step 1), the calcination temperature is 600-1000℃, and the calcination time is 8-20h.

[0013] Preferably, in step 1), the lithium manganate positive electrode material is spinel lithium manganate.

[0014] Preferably, in step 2), the nickel salt is one or more of Ni(CH3COO)2, NiC2O4, NiCO3, NiO, Ni2O3, Ni(OH)2, and NiSO4, the cobalt salt is one or more of Co(CH3COO)2, CoC2O4, CoCO3, CoO, Co3O4, Co2O3, Co(OH)2, and CoSO4, the manganese salt is one or more of Mn(CH3COO)2, MnC2O4, MnCO3, MnO2, Mn2O3, Mn3O4, Mn(OH)2, and MnSO4, and the lithium salt is one or more of LiNO3, LiNO2, LiCl, LiOH, LiBr, LiI, Li2S, LiF, Li2CO3, Li2SO4, Li2SO3, LiClO4, LiMnO4, Li2O2, LiO2, and Li2S2O3.

[0015] Preferably, the ratio of the molar mass of lithium in the lithium salt in step 2) to the sum of the molar masses of the three metal elements of nickel, cobalt and manganese is 1.05-1.45:1.

[0016] Preferably, the solid content in step 2) is 10-50%.

[0017] Preferably, the temperature of the calcination in step 3) is 800-1100℃, and the time is 8-20h.

[0018] Preferably, the structure formula of the nanometer single-crystal lithium-rich manganese-based positive electrode material in step 3) is xLi2MnO3·(1-x)LiNi y Co z Mn w O2, wherein 0

[0019] Preferably, the mass ratio of the lithium manganate positive electrode material to the nanometer single-crystal lithium-rich manganese-based positive electrode material in step 4) is 17 / 3-19:1.

[0020] Compared with the prior art, the present application has the following advantages:

[0021] 1. The coated modified lithium manganate positive electrode material prepared by the method of the present application can improve the electrode activity of the lithium manganate positive electrode material, provide a larger specific surface area and a shorter ion diffusion path, increase the lithium ion intercalation / deintercalation rate, and thus improve the capacity.

[0022] 2. The method of the present application can improve the chemical stability of the lithium manganate positive electrode material, reduce the reaction of the electrolyte with the lithium manganate, delay the structural damage of the positive electrode material, and thus prolong the cycle life of the material.

[0023] 3. The nanometer single-crystal structure of the coated modified lithium manganate positive electrode material prepared by the method of the present application can provide more active sites to accelerate the diffusion speed of lithium ions inside the positive electrode material. At the same time, the nanometer single-crystal structure has a lower resistance and a shorter ion path, which is conducive to the rapid transmission of lithium ions and improves the discharge performance of the battery.

[0024] 4. The coated modified lithium manganate positive electrode material prepared by the method of the present application, the coating of the nanometer single-crystal lithium-rich manganese-based positive electrode material can form a protective layer to prevent the dissolution of manganese ions. This coating layer can stabilize the crystal structure of lithium manganate, reduce the activity of manganese ions, and reduce their reaction with the electrolyte, thereby inhibiting the dissolution of manganese and improving the cycle stability and capacity retention rate of the battery.

[0025] 5. The method of the present application can effectively reduce the interface impedance and electronic transmission impedance of the material, and improve the high-temperature cycle performance and rate performance of the battery.

[0026] 6、The method of the present application has simple preparation process, wide application range and can be produced in large scale. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The first charge-discharge curve diagram of LMO-S, LMO-1, LMO-2 and LMO-3 prepared by the comparative examples and the examples of the present application;

[0028] Figure 2 The first charge-discharge curve diagram of LMO-P, LMO-4, LMO-5 and LMO-6 prepared by the comparative examples and the examples of the present application;

[0029] Figure 3 The scanning electron microscope diagram of LMO-S, LMO-3, LMO-P, LMO-6 and LRM prepared by the comparative examples and the examples of the present application;

[0030] Figure 4 The X-ray diffraction diagram of LRM, LMO-S and LMO-3 prepared by the comparative examples and the examples of the present application;

[0031] Figure 5 The rate performance curve diagram of LMO-S, LMO-1, LMO-2 and LMO-3 prepared by the comparative examples and the examples of the present application;

[0032] Figure 6 The Nyquist diagram of LMO-S, LMO-1, LMO-2 and LMO-3 prepared by the comparative examples and the examples of the present application;

[0033] Figure 7 The high temperature cycle diagram of LMO-S, LMO-1, LMO-2 and LMO-3 prepared by the comparative examples and the examples of the present application;

[0034] Figure 8 The process flow diagram of the method of the present application. DETAILED DESCRIPTION

[0035] The present application will be further described in detail below in combination with specific examples. Example 1

[0036] A preparation method of a coated modified single crystal lithium manganate positive electrode material, comprising the following steps:

[0037] S1. Preparation of single-crystal lithium manganese oxide cathode material: Li2CO3 and single-crystal granular Mn3O4 were weighed according to a lithium-manganese molar ratio of 0.55, and mixed in a high-speed mixer at 700 r / min for 50 min. The mixed raw materials were then placed in a box furnace for high-temperature calcination at 750℃ for 15 h to form single-crystal lithium manganese oxide crystals. The single-crystal lithium manganese oxide crystals obtained after calcination were crushed and sieved to obtain the single-crystal lithium manganese oxide cathode material LiMn2O4 that meets the requirements.

[0038] S2. Preparation of lithium-rich manganese-based nanocrystalline cathode materials: according to Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 (structural formula 0.5Li2MnO3·0.5LiNi) 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (where x=0.5, y=z=w=1 / 3) The corresponding molar ratios of lithium carbonate, nickel carbonate, cobalt carbonate and manganese carbonate were mixed evenly and then added to a certain amount of pure water with a solid content of 30% to form a suspension. The suspension was then milled in a sand mill. The particle size of the slurry obtained after milling was measured by a particle size analyzer and found to be less than 300nm. The slurry was then spray-dried to obtain the desired lithium-rich manganese-based cathode material precursor. The precursor was then calcined in a furnace at 960℃ for 10h. After pulverization and sieving, nano-monocrystalline lithium-rich manganese-based cathode material was obtained.

[0039] S3. The monocrystalline lithium manganese oxide material obtained in step S1 and the nano-monocrystalline lithium-rich manganese-based cathode material obtained in step S2 are premixed in a container at a mass ratio of 19:1. The premixed material is then mixed using a high-speed mixer at 700 r / min for 30 min to obtain LMO-1 monocrystalline lithium manganese oxide cathode material coated with 5% nano-monocrystalline lithium-rich manganese-based cathode material. Example 2

[0040] A method for preparing a coated and modified single-crystal lithium manganese oxide cathode material includes the following steps:

[0041] S1. Preparation of monocrystalline lithium manganese oxide cathode material: Li₂CO₃ and monocrystalline granular Mn₃O₄ were weighed according to a lithium-manganese molar ratio of 0.55 and placed in a high-speed mixer at 700 r / min for 50 min. The mixed raw materials were then placed in a box furnace for high-temperature calcination at 750℃ for 15 h to form monocrystalline lithium manganese oxide crystals. The obtained monocrystalline lithium manganese oxide crystals were then crushed and sieved to obtain the required monocrystalline lithium manganese oxide cathode material LiMn₂O₄.

[0042] S2. Preparation of lithium-rich manganese-based nanocrystalline cathode materials: according to Li 1.2Ni 0.13 Co 0.13 Mn 0.54 O2 (structural formula 0.5Li2MnO3·0.5LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, wherein x=0.5, y=z=w=1 / 3) The molar ratio of the corresponding lithium carbonate, nickel carbonate, cobalt carbonate, and manganese carbonate is mixed uniformly, and then a certain amount of pure water is added to prepare a suspension with a solid content of 30%. The suspension is then ground by a sand mill. The particle size of the obtained slurry after sand grinding is less than 300 nm measured by a particle size detector. The obtained slurry is then sprayed and granulated by a spray dryer to obtain the desired lithium-rich manganese-based positive electrode material precursor. The precursor is then calcined at 960℃ in a box furnace for 10h, and then crushed and sieved to obtain a nanocrystalline lithium-rich manganese-based positive electrode material.

[0043] S3, the single crystal lithium manganate material obtained in step S1 is premixed with the nanocrystalline lithium-rich manganese-based positive electrode material obtained in step S2 in a container at a mass ratio of 9:1. The obtained premixed material is mixed by a high-speed mixer at 700r / min for 30min to obtain a single crystal lithium manganate positive electrode material LMO-2 coated with 10% nanocrystalline lithium-rich manganese-based positive electrode material. Example 3

[0044] A method for preparing a coated modified single crystal lithium manganate positive electrode material, comprising the following steps:

[0045] S1, preparation of single crystal lithium manganate positive electrode material: Li2CO3 and single crystal granular Mn3O4 are weighed according to a lithium-manganese molar ratio of 0.55, and then put into a high-speed mixer and mixed at 700r / min for 50min. The mixed raw materials are put into a box furnace for high-temperature calcination at 750℃, and the calcination time is 15h to form single crystal lithium manganate crystals. The single crystal lithium manganate crystals obtained after calcination are crushed and sieved to obtain the required single crystal lithium manganate positive electrode material LiMn2O4.

[0046] S2, preparation of nanocrystalline lithium-rich manganese-based positive electrode material: Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 (structural formula 0.5Li2MnO3·0.5LiNi 1 / 3 Co 1 / 3 Mn 1 / 3O2 (where x=0.5, y=z=w=1 / 3) The corresponding molar ratios of lithium carbonate, nickel carbonate, cobalt carbonate and manganese carbonate were mixed evenly and then added to a certain amount of pure water with a solid content of 30% to form a suspension. The suspension was then milled in a sand mill. The particle size of the slurry obtained after milling was measured by a particle size analyzer and found to be less than 300nm. The slurry was then spray-dried to obtain the desired lithium-rich manganese-based cathode material precursor. The precursor was then calcined in a furnace at 960℃ for 10h. After pulverization and sieving, nano-monocrystalline lithium-rich manganese-based cathode material was obtained.

[0047] S3. The monocrystalline lithium manganese oxide material obtained in step S1 and the nano-monocrystalline lithium-rich manganese-based cathode material obtained in step S2 are premixed in a container at a mass ratio of 5.67:1. The resulting premixed material is mixed using a high-speed mixer at 700 r / min for 30 min to obtain monocrystalline lithium manganese oxide cathode material LMO-3 coated with 15% nano-monocrystalline lithium-rich manganese-based cathode material. Example 4

[0048] A method for preparing a coated and modified polycrystalline lithium manganese oxide cathode material includes the following steps:

[0049] S1. Preparation of polycrystalline lithium manganese oxide cathode material: Li2CO3 and polycrystalline spherical granular Mn3O4 were weighed according to a lithium-manganese molar ratio of 0.55 and placed in a high-speed mixer at 700 r / min for 50 min. The mixed raw materials were then placed in a box furnace for high-temperature calcination at 710℃ for 15 h to form polycrystalline lithium manganese oxide crystals. The polycrystalline lithium manganese oxide crystals obtained after calcination were crushed and sieved to obtain the polycrystalline lithium manganese oxide cathode material LiMn2O4 that meets the requirements.

[0050] S2. Preparation of lithium-rich manganese-based nanocrystalline cathode materials: according to Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 (structural formula 0.5Li2MnO3·0.5LiNi) 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (where x=0.5, y=z=w=1 / 3) The corresponding molar ratios of lithium carbonate, nickel carbonate, cobalt carbonate and manganese carbonate were mixed evenly and then added to a certain amount of pure water with a solid content of 30% to form a suspension. The suspension was then milled in a sand mill. The particle size of the slurry obtained after milling was measured by a particle size analyzer and found to be less than 300nm. The slurry was then spray-dried to obtain the desired lithium-rich manganese-based cathode material precursor. The precursor was then calcined in a furnace at 960℃ for 10h. After pulverization and sieving, nano-monocrystalline lithium-rich manganese-based cathode material was obtained.

[0051] S3, the polycrystalline lithium manganate material obtained in step S1 is premixed with the nanometer single crystal lithium-rich manganese-based positive electrode material obtained in step S2 in a container according to a mass ratio of 19:1. The obtained premixed material is mixed by a high-speed mixer at 700 r / min for 30 min, and a polycrystalline lithium manganate positive electrode material coated with 5% nanometer single crystal lithium-rich manganese-based positive electrode material LMO-4 is obtained. Example 5

[0052] A preparation method of a coated modified polycrystalline lithium manganate positive electrode material, comprising the following steps:

[0053] S1, preparation of a polycrystalline lithium manganate positive electrode material: Li2CO3 and polycrystalline spherical particle-shaped Mn3O4 are weighed according to a lithium-manganese molar ratio of 0.55, put into a high-speed mixer, mixed at 700 r / min for 50 min, and then put into a box furnace for high-temperature calcination at 710℃, with a calcination time of 15 h, to form polycrystalline lithium manganate crystals. The polycrystalline lithium manganate crystals obtained after calcination are crushed and sieved to obtain the required polycrystalline lithium manganate positive electrode material LiMn2O4.

[0054] S2, preparation of a nanometer single crystal lithium-rich manganese-based positive electrode material: Li2CO3, NiCO3, CoCO3 and MnCO3 are mixed uniformly according to a molar ratio of 0.5:0.5:0.5:0.5, and then added into a certain amount of pure water to prepare a suspension liquid with a solid content of 30%. The suspension liquid is then ground by a sand mill, and the particle size of the obtained slurry after sand grinding is measured by a particle size detector to be less than 300 nm. The obtained slurry is then sprayed and granulated by a spray dryer to obtain the required lithium-rich manganese-based positive electrode material precursor. The precursor is then calcined in a box furnace at 960℃ for 10 h, and then crushed and sieved to obtain the nanometer single crystal lithium-rich manganese-based positive electrode material. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 (structure formula is 0.5Li2MnO3·0.5LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, wherein x=0.5, y=z=w=1 / 3) are mixed uniformly, and then added into a certain amount of pure water to prepare a suspension liquid with a solid content of 30%. The suspension liquid is then ground by a sand mill, and the particle size of the obtained slurry after sand grinding is measured by a particle size detector to be less than 300 nm. The obtained slurry is then sprayed and granulated by a spray dryer to obtain the required lithium-rich manganese-based positive electrode material precursor. The precursor is then calcined in a box furnace at 960℃ for 10 h, and then crushed and sieved to obtain the nanometer single crystal lithium-rich manganese-based positive electrode material.

[0055] S3, the polycrystalline lithium manganate material obtained in step S1 is premixed with the nanometer single crystal lithium-rich manganese-based positive electrode material obtained in step S2 in a container according to a mass ratio of 19:1. The obtained premixed material is mixed by a high-speed mixer at 700 r / min for 30 min, and a polycrystalline lithium manganate positive electrode material coated with 5% nanometer single crystal lithium-rich manganese-based positive electrode material LMO-4 is obtained. Example 6

[0056] A preparation method of a coated modified polycrystalline lithium manganate positive electrode material, comprising the following steps:

[0057] S1, Preparation of polycrystalline lithium manganate positive electrode material: Li2CO3 and polycrystalline spherical particle-shaped Mn3O4 are weighed according to a lithium-manganese molar ratio of 0.55, put into a high-speed mixer to mix for 50 min at 700 r / min, and the mixed raw materials are put into a box furnace to be calcined at 710°C for 15 h to form polycrystalline lithium manganate crystals. The polycrystalline lithium manganate crystals obtained after calcination are crushed and sieved to obtain the required polycrystalline lithium manganate positive electrode material LiMn2O4.

[0058] S2, Preparation of nano-single-crystal lithium-rich manganese-based positive electrode material: Li2CO3, NiCO3, CoCO3 and MnCO3 are mixed uniformly according to the molar ratio of 0.5Li2MnO3·0.5LiNi0.5Co0.5MnO2, and then a certain amount of pure water is added to prepare a suspension with a solid content of 30%. The suspension is then ground by a sand mill, and the particle size of the slurry obtained after sand grinding is measured by a particle size detector to be less than 300 nm. The slurry is then sprayed and granulated by a spray dryer to obtain the required lithium-rich manganese-based positive electrode material precursor. The precursor is then calcined at 960°C in a box furnace for 10 h, and then crushed and sieved to obtain the nano-single-crystal lithium-rich manganese-based positive electrode material. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 (structure formula is 0.5Li2MnO3·0.5LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, wherein x=0.5, y=z=w=1 / 3) are mixed uniformly, and then a certain amount of pure water is added to prepare a suspension with a solid content of 30%. The suspension is then ground by a sand mill, and the particle size of the slurry obtained after sand grinding is measured by a particle size detector to be less than 300 nm. The slurry is then sprayed and granulated by a spray dryer to obtain the required lithium-rich manganese-based positive electrode material precursor. The precursor is then calcined at 960°C in a box furnace for 10 h, and then crushed and sieved to obtain the nano-single-crystal lithium-rich manganese-based positive electrode material.

[0059] S3, The polycrystalline lithium manganate material obtained in step S1 is pre-mixed with the nano-single-crystal lithium-rich manganese-based positive electrode material obtained in step S2 in a container according to a mass ratio of 5.67:1. The obtained pre-mixed material is mixed by a high-speed mixer at 700 r / min for 30 min to obtain a polycrystalline lithium manganate positive electrode material LMO-6 coated with 15% nano-single-crystal lithium-rich manganese-based positive electrode material. Comparative Example 1

[0060] The preparation method of the uncoated modified single-crystal lithium manganate positive electrode material comprises the following steps:

[0061] S1, Preparation of single-crystal lithium manganate positive electrode material: Li2CO3 and single-crystal particle-shaped Mn3O4 are weighed according to a lithium-manganese molar ratio of 11:20, put into a high-speed mixer to mix for 50 min at 700 r / min, and the mixed raw materials are put into a box furnace to be calcined at 750°C for 15 h to form single-crystal lithium manganate crystals. The single-crystal lithium manganate crystals obtained after calcination are crushed and sieved to obtain the required single-crystal lithium manganate positive electrode material LMO-S. Comparative Example 2

[0062] A preparation method of a non-coated modified polycrystalline lithium manganate positive electrode material, comprising the following steps:

[0063] S1, preparation of the polycrystalline lithium manganate positive electrode material: Li2CO3 and polycrystalline spherical particle-shaped Mn3O4 are weighed according to a lithium-manganese molar ratio of 0.55, and are put into a high-speed mixer for mixing at 700 r / min for 50 min. The mixed raw materials are put into a box furnace for high-temperature calcination at 710 ℃, and the calcination time is 15 h to form polycrystalline lithium manganate crystals. The polycrystalline lithium manganate crystals obtained after calcination are crushed and sieved to obtain the required polycrystalline lithium manganate positive electrode material LMO-P. Comparative Example 3

[0064] A preparation method of a nano-single-crystal lithium-rich manganese-based positive electrode material, comprising the following steps:

[0065] S1, preparation of the nano-single-crystal lithium-rich manganese-based positive electrode material: Li2CO3, NiCO3, CoCO3 and MnCO3 are mixed uniformly according to a molar ratio of 0.5:0.5:0.5:0.5, and then a certain amount of pure water is added to the mixture to prepare a suspension, which is then ground by a sand mill. The D50 of the particle size of the slurry obtained after sand grinding is less than 300 nm. The slurry is then sprayed and granulated by a spray dryer to obtain a lithium-rich manganese-based positive electrode material precursor. The precursor is calcined at 960 ℃ in a box furnace for 10 h, and then crushed and sieved to obtain the nano-single-crystal lithium-rich manganese-based positive electrode material LRM. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 (the structural formula is 0.5Li2MnO3·0.5LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, wherein x=0.5, y=z=w=1 / 3) are mixed uniformly, and then a certain amount of pure water is added to the mixture to prepare a suspension, which is then ground by a sand mill. The D50 of the particle size of the slurry obtained after sand grinding is less than 300 nm. The slurry is then sprayed and granulated by a spray dryer to obtain a lithium-rich manganese-based positive electrode material precursor. The precursor is calcined at 960 ℃ in a box furnace for 10 h, and then crushed and sieved to obtain the nano-single-crystal lithium-rich manganese-based positive electrode material LRM.

[0066] First discharge performance: the positive electrode material provided by the examples is used as the positive electrode material of a lithium ion battery, and metal lithium is used as the negative electrode material to assemble a button cell, and the first discharge capacity and coulombic efficiency of the button cell are tested. The results are shown in Table 1:

[0067] Table 1

[0068]

[0069] The first charge-discharge curves of the single-crystal lithium manganate positive electrode material LMO-S provided by Comparative Example 1 and the single-crystal lithium manganate positive electrode material LMO-1, LMO-2 and LMO-3 coated with the nano-single-crystal lithium-rich manganese-based positive electrode material provided by Examples 1, 2 and 3 are shown in Figure 1It can be seen that the first discharge gram capacity of the nanometer single-crystal lithium-rich manganese-based positive electrode material coated polycrystalline lithium manganate positive electrode material is better than that of the single polycrystalline lithium manganate positive electrode material, and the capacity increases regularly with the increase of the mixed mass.

[0070] The first charge-discharge curves of the polycrystalline lithium manganate positive electrode material LMO-P provided by Comparative Example 2 and the nanometer single-crystal lithium-rich manganese-based positive electrode material coated polycrystalline lithium manganate positive electrode materials LMO-4, LMO-5, LMO-6 provided by Examples 4, 5, 6 are shown in Figure 2 It can be seen that the first discharge gram capacity of the nanometer single-crystal lithium-rich manganese-based positive electrode material coated polycrystalline lithium manganate positive electrode material is better than that of the single polycrystalline lithium manganate positive electrode material, and the capacity increases regularly with the increase of the mixed mass.

[0071] Micro-morphology test: the single-crystal lithium manganate positive electrode material LMO-S provided by Comparative Example 1, the polycrystalline lithium manganate positive electrode material LMO-P provided by Comparative Example 2, the nanometer single-crystal lithium-rich manganese-based positive electrode material LRM provided by Comparative Example 3, the nanometer single-crystal lithium-rich manganese-based positive electrode material coated single-crystal lithium manganate positive electrode material LMO-3 provided by Example 3 and the nanometer single-crystal lithium-rich manganese-based positive electrode material coated polycrystalline lithium manganate positive electrode material LMO-6 provided by Example 6 were respectively tested by scanning electron microscope, as shown in Figure 3 It can be found from Figure 3 that the nanometer single-crystal lithium-rich manganese-based positive electrode material fills in the gap of the single-crystal and polycrystalline lithium manganate positive electrode material particles and coats the surface of the single-crystal and polycrystalline lithium manganate positive electrode particles.

[0072] Crystallinity test: the single-crystal lithium manganate positive electrode material LMO-S provided by Comparative Example 1, the nanometer single-crystal lithium-rich manganese-based positive electrode material LRM provided by Comparative Example 3 and the nanometer single-crystal lithium-rich manganese-based positive electrode material coated single-crystal lithium manganate positive electrode material LMO-3 provided by Example 3 were respectively characterized by X-ray diffraction, as shown in Figure 4 It can be found from Figure 4 the XRD data that the nanometer single-crystal lithium-rich manganese-based positive electrode material coated single-crystal lithium manganate positive electrode material appears Li2MnO3 characteristic peak, and has good crystallinity without impurity peaks.

[0073] Rate test: the single-crystal lithium manganate positive electrode material LMO-S provided by Comparative Example 1 and the nanometer single-crystal lithium-rich manganese-based positive electrode material coated single-crystal lithium manganate positive electrode materials LMO-1, LMO-2, LMO-3 provided by Examples 1, 2, 3 were respectively tested by rate, and the rate curves are shown in Figure 5 It can be found from Figure 5 that the rate performance of the nanometer single-crystal lithium-rich manganese-based positive electrode material coated single-crystal lithium manganate positive electrode material is better than that of the single single-crystal lithium manganate positive electrode material.

[0074] Electrochemical impedance spectroscopy (EIS) tests were performed on the monocrystalline lithium manganese oxide cathode material LMO-S provided in Comparative Example 1 and the monocrystalline lithium manganese oxide cathode materials LMO-1, LMO-2, and LMO-3 coated with nanocrystalline lithium-rich manganese-based cathode materials provided in Examples 1, 2, and 3, respectively. The Nyquist curves are shown in the figures. Figure 6 ,from Figure 6 It can be seen that the charge transfer resistance of the single-crystal lithium manganese oxide cathode material coated with nano-single-crystal lithium-rich manganese-based cathode material is better than that of the single-crystal lithium manganese oxide cathode material. The coating with nano-single-crystal lithium-rich manganese-based cathode material is beneficial to reducing the resistance of electron transfer inside the electrode in the single-crystal lithium manganese oxide cathode material.

[0075] Cyclic performance testing: The monocrystalline lithium manganese oxide cathode material LMO-S provided in Comparative Example 1 and the monocrystalline lithium manganese oxide cathode materials LMO-1, LMO-2, and LMO-3 coated with nanocrystalline lithium-rich manganese-based cathode materials provided in Examples 1, 2, and 3 were subjected to high-temperature cycling (45°C) performance testing at 4.3V. Figure 7 As shown, from Figure 7 It can be seen that single-crystal lithium manganese oxide cathode materials coated with nano-single-crystal lithium-rich manganese-based cathode materials have superior high-temperature cycling performance.

[0076] The test results show that the present invention uses nano-single-crystal lithium-rich manganese-based cathode material to coat lithium manganese oxide cathode material, which can effectively improve the first-cycle discharge capacity and rate performance, effectively reduce charge transfer resistance, and has good cycle performance. It also has low energy consumption, low cost, simple preparation process, and strong applicability, and can be widely used in large-scale industrial production.

[0077] The above description is merely an embodiment of the present invention. It should be noted that, for those skilled in the art, various changes, modifications, substitutions and variations can be made to these embodiments without departing from the technical principles of the present invention. These changes, modifications, substitutions and variations should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a coated and modified lithium manganese oxide cathode material, characterized in that, Includes the following steps: 1) The manganese source and lithium source are mechanically mixed in proportion, and the uniformly mixed material is calcined under atmospheric conditions. The calcined material is crushed and graded to obtain lithium manganese oxide cathode material. 2) Mix nickel salt, cobalt salt, manganese salt and lithium salt in a certain mixing ratio, add one of water and ethanol according to a certain solid content, put the resulting material into a pulping machine to pulp, input the resulting slurry into a sand mill for sand milling, and dry and granulate the sand milled slurry using a spray dryer to obtain a nano-single crystal lithium-rich manganese-based cathode material precursor. 3) The precursor of the nano-single crystal lithium-rich manganese-based cathode material is calcined once under atmospheric conditions. The sintered material is crushed and graded to obtain the nano-single crystal lithium-rich manganese-based cathode material. 4) The lithium manganese oxide cathode material is mechanically mixed with the nano-single crystal lithium-rich manganese-based cathode material to obtain the lithium manganese oxide cathode material coated and modified with the nano-single crystal lithium-rich manganese-based cathode material. In step 2), the ratio of the molar mass of lithium in the lithium salt to the sum of the molar masses of the three metal elements nickel, cobalt, and manganese is 1.05-1.45:

1. The solid content mentioned in step 2) is 10-50%; The roasting temperature in step 3) is 800-1100℃, and the time is 8-20h; The structural formula of the nano-single-crystal lithium-rich manganese-based cathode material mentioned in step 3) is xLi2MnO3·(1-x)LiNi y Co z Mn w O2, where 0<x<1, y+z+w=1, 0<y<1.0, 0<z<1.0, 0<w<1.0; The mass ratio of the lithium manganese oxide cathode material to the nano-monocrystalline lithium-rich manganese-based cathode material in step 4) is 17 / 3-19:

1.

2. The method for preparing a coated and modified lithium manganese oxide cathode material according to claim 1, characterized in that, The manganese source mentioned in step 1) is one or more of MnCO3, MnO2, Mn2O3, Mn3O4, Mn(OH)2, and MnSO4, and the lithium source is one or more of LiNO3, LiNO2, LiCl, LiOH, LiBr, LiI, Li2S, LiF, Li2CO3, Li2SO4, Li2SO3, LiClO4, LiMnO4, Li2O2, LiO2, and Li2S2O3. The lithium-manganese molar ratio of the lithium source to the manganese source is 0.45-0.65:

1.

3. The method for preparing a coated and modified lithium manganese oxide cathode material according to claim 1, characterized in that, The roasting temperature in step 1) is 600-1000℃, and the roasting time is 8-20h.

4. The method for preparing a coated and modified lithium manganese oxide cathode material according to claim 1, characterized in that, The lithium manganese oxide cathode material mentioned in step 1) is spinel lithium manganese oxide.

5. The method for preparing a coated and modified lithium manganese oxide cathode material according to claim 1, characterized in that, In step 2), the nickel salt is one or more of Ni(CH3COO)2, NiC2O4, NiCO3, NiO, Ni2O3, Ni(OH)2, and NiSO4; the cobalt salt is one or more of Co(CH3COO)2, CoC2O4, CoCO3, CoO, Co3O4, Co2O3, Co(OH)2, and CoSO4; the manganese salt is one or more of Mn(CH3COO)2, MnC2O4, MnCO3, MnO2, Mn2O3, Mn3O4, Mn(OH)2, and MnSO4; and the lithium salt is one or more of LiNO3, LiNO2, LiCl, LiOH, LiBr, LiI, Li2S, LiF, Li2CO3, Li2SO4, Li2SO3, LiClO4, LiMnO4, Li2O2, LiO2, and Li2S2O3.

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