Cathode material, preparation method thereof, cathode sheet and battery

Abstract

The application provides a positive electrode material and a preparation method thereof, a positive electrode sheet and a battery. The positive electrode material comprises lithium iron manganese phosphate particles and a first shell layer and a second shell layer successively coated on the surface of the lithium iron manganese phosphate particles. The material of the first shell layer comprises nano-sized SiO2 particles, and the material of the second shell layer comprises nano-sized TiO2 particles. By successively coating the SiO2 layer and the TiO2 layer on the surface of the lithium iron manganese phosphate particles, the application can reduce the contact between the lithium iron manganese phosphate particles and the electrolyte, reduce the occurrence of side reactions between the lithium iron manganese phosphate particles and the electrolyte in the electrochemical reaction process, thereby alleviating the cycle life attenuation of the battery, and reducing the dissolution of Mn elements, thereby alleviating the increase in battery impedance caused by the deposition of Mn 2+ on the negative electrode in the cycle process.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a positive electrode material and its preparation method, a positive electrode sheet, and a battery. Background Technology

[0002] Lithium manganese iron phosphate (LMFP) is a new type of phosphate-based lithium-ion battery cathode material obtained by doping manganese with lithium iron phosphate. Like lithium iron phosphate, it has an olivine structure and not only retains the same safety performance as lithium iron phosphate, but also has a higher voltage platform, which gives it higher energy density and better low-temperature performance, thus attracting much attention.

[0003] However, lithium manganese iron phosphate (LMFP) currently suffers from poor conductivity, rate performance, and cycle performance. The following three methods are commonly used to modify LMFP: 1. Improving the conductivity and electrochemical performance of LMFP by coating the surface with conductive carbon materials (such as graphite, amorphous carbon, carbon nanotubes, pyrolytic carbon, etc.); 2. Improving the electrical performance of LMFP by introducing small amounts of dopants such as cobalt, nickel, and vanadium; 3. Nanostructuring LMFP to shorten the migration path of lithium ions within the primary particles, thereby improving the charge-discharge performance. While these three approaches and methods can improve the performance of LMFP, its electrochemical and cycle performance remains unsatisfactory. Summary of the Invention

[0004] The embodiments of the present invention provide a cathode material and its preparation method, a cathode electrode sheet, and a battery, which can improve the technical problems of unsatisfactory electrochemical performance and cycle performance of lithium manganese iron phosphate in related technologies.

[0005] In a first aspect, embodiments of the present invention provide a cathode material comprising lithium manganese iron phosphate particles and a first shell layer and a second shell layer sequentially coating the surface of the lithium manganese iron phosphate particles, wherein the material of the first shell layer comprises nano-sized SiO2 particles and the material of the second shell layer comprises nano-sized TiO2 particles.

[0006] In one embodiment, the average particle size of the SiO2 particles is ≤8 nm; and / or,

[0007] The average particle size of the TiO2 particles is ≤8 nm; and / or,

[0008] The chemical formula of the lithium manganese iron phosphate particles can be LiMn. x Fe (1-x) PO4, where 0.1 ≤ X ≤ 0.9.

[0009] In one embodiment, the mass percentages of the SiO2 particles, the TiO2 particles, and the lithium manganese iron phosphate particles in the cathode material are (0.3%-0.7%):(0.3%-0.7%):(98.6%-99.4%).

[0010] Secondly, embodiments of the present invention provide a method for preparing a positive electrode material, comprising the following steps:

[0011] Nanoscale SiO2 particles, lithium manganese iron phosphate particles, and an alcohol solvent are provided. The SiO2 particles are dispersed in the alcohol solvent, and the lithium manganese iron phosphate particles are added. The mixture is then heated and stirred to obtain first solid particles.

[0012] Nanoscale TiO2 particles are coated onto the surface of the first solid particle to obtain the cathode material.

[0013] In one embodiment, the mass percentages of the SiO2 particles, the TiO2 particles, and the lithium manganese iron phosphate particles in the positive electrode material are (0.3%-0.7%):(0.3%-0.7%):(98.6%-99.4%); and / or,

[0014] The temperature of the first heating is 60℃~90℃, and the heating time is 4h-12h.

[0015] In one embodiment, coating the surface of the first solid particle with nano-sized TiO2 particles includes:

[0016] Tetrabutyl titanate and anhydrous ethanol are provided. The tetrabutyl titanate is dispersed in the anhydrous ethanol and then mixed with the first solid particles to obtain a suspension.

[0017] Water is added to the suspension, and the mixture is then heated and stirred.

[0018] In one embodiment, the temperature of the second heating is 50°C-70°C, and the heating time is 4h-8h.

[0019] In one embodiment, providing water, adding it to the suspension, includes:

[0020] An aqueous solution of ethanol is provided and added to the suspension.

[0021] In one embodiment, the volume ratio of ethanol to water in the aqueous solution of ethanol is (1-3):1.

[0022] In one embodiment, the method further includes: coating the surface of the first solid particles with nano-sized TiO2 particles and then sintering them to obtain a positive electrode material.

[0023] In one embodiment, the sintering temperature is 400℃-600℃, and the sintering time is 3h-6h.

[0024] Thirdly, embodiments of the present invention provide a positive electrode sheet comprising the aforementioned positive electrode material.

[0025] Fourthly, embodiments of the present invention provide a battery including the above-described positive electrode.

[0026] The beneficial effects of the embodiments of the present invention are as follows:

[0027] In embodiments of the present invention, by sequentially coating the surface of lithium manganese iron phosphate particles with SiO2 and TiO2 layers, the contact between the lithium manganese iron phosphate particles and the electrolyte can be reduced, thereby reducing the occurrence of side reactions between the lithium manganese iron phosphate particles and the electrolyte during the electrochemical reaction, thus alleviating the degradation of battery cycle life. Simultaneously, it reduces the dissolution of Mn elements, thereby mitigating Mn degradation during cycling. 2+ The deposition on the negative electrode leads to an increase in battery impedance; TiO2 is an electrochemically inactive material that does not participate in electrochemical reactions. During the Li ion insertion / extraction process, the TiO2 lattice can act as a conductor for electrons and ions, allowing Li ions to pass freely through the TiO2 lattice, thereby improving the rate performance of the battery; SiO2 is an electrochemically inactive material with a thin and uniform coating effect and high mechanical properties, and it can remain stable after multiple charge and discharge cycles. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Furthermore, it should be understood that the specific embodiments described herein are only for illustration and explanation of the present invention and are not intended to limit the present invention. In the present invention, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of the device in actual use or operation; while "inner" and "outer" refer to the outline of the device.

[0029] The technical solution of this application is as follows:

[0030] In a first aspect, embodiments of this application provide a cathode material comprising lithium manganese iron phosphate particles and a first shell layer and a second shell layer sequentially coating the surface of the lithium manganese iron phosphate particles. The material of the first shell layer comprises nano-sized SiO2 particles, and the material of the second shell layer comprises nano-sized TiO2 particles.

[0031] In this application, by sequentially coating the surface of lithium manganese iron phosphate particles with SiO2 and TiO2 layers, the contact between the lithium manganese iron phosphate particles and the electrolyte can be reduced, thereby reducing the occurrence of side reactions between the lithium manganese iron phosphate particles and the electrolyte during the electrochemical reaction, thus mitigating the degradation of battery cycle life. Simultaneously, it reduces the dissolution of Mn elements, thereby alleviating Mn degradation during cycling. 2+ The deposition on the negative electrode leads to an increase in battery impedance; TiO2 is an electrochemically inactive material that does not participate in electrochemical reactions. During the Li ion insertion / extraction process, the TiO2 lattice can act as a conductor for electrons and ions, allowing Li ions to pass freely through the TiO2 lattice, thereby improving the rate performance of the battery; SiO2 is an electrochemically inactive material with a thin and uniform coating effect and high mechanical properties, and it can remain stable after multiple charge and discharge cycles.

[0032] In some embodiments, the average particle size of the SiO2 particles is ≤8nm, for example, it can be 8nm, 7nm, 6.5nm, 6nm, 5.5nm, 5nm, 4.5nm, 4nm, 3.5nm, etc. Within this range, a good coating effect can be achieved on lithium manganese iron phosphate particles, reducing the occurrence of vacancies.

[0033] In some embodiments, the average particle size of the TiO2 particles is ≤8nm, for example, it can be 8nm, 7nm, 6.5nm, 6nm, 5.5nm, 5nm, 4.5nm, 4nm, 3.5nm, etc. Within this range, a good coating effect can be achieved on lithium manganese iron phosphate particles, reducing the occurrence of vacancies.

[0034] In some embodiments, TiO2 particles are obtained by the hydrolysis reaction of tetrabutyl titanate, and the average particle size of the TiO2 particles obtained by the hydrolysis reaction of tetrabutyl titanate is ≤8nm.

[0035] In some embodiments, the mass percentage of SiO2 particles, TiO2 particles, and lithium manganese iron phosphate particles in the cathode material is (0.3%-0.7%):(0.3%-0.7%):(98.6%-99.4%), for example, 0.7%:0.7%:98.6%, 0.6%:0.6%:98.8%, 0.5%:0.7%:98.8%, or 0.7%:0.5%. The following concentrations are possible: 98.8%, 0.5%:0.5%:99%, 0.3%:0.7%:99%, 0.7%:0.3%:99%, 0.4%:0.6%:99%, 0.6%:0.4%:99%, 0.4%:0.4%:99.2%, 0.5%:0.3%:99.2%, 0.3%:0.5%:99.2%, 0.3%:0.3%:99.4%, etc. Within this range, lithium manganese iron phosphate particles can be better coated by SiO2 and TiO2 particles, thus forming a coating layer. Simultaneously, the thickness of the coating layer can be moderate, allowing for effective lithium ion insertion / extraction.

[0036] As an example, the chemical formula of lithium manganese iron phosphate used in this application can be LiMn. x Fe (1-x) PO4, where 0.1 ≤ X ≤ 0.9.

[0037] Secondly, embodiments of this application provide a method for preparing a positive electrode material, comprising the following steps:

[0038] S1. Provide nano-sized SiO2 particles, lithium manganese iron phosphate particles and an alcohol solvent. Disperse the SiO2 particles in the alcohol solvent, add the lithium manganese iron phosphate particles, perform a first heating and stirring to obtain a first solid particle.

[0039] S2. Coat the surface of the first solid particle with nano-sized TiO2 particles to obtain the cathode material.

[0040] In step S1,

[0041] In some embodiments, dispersing the SiO2 particles in the alcohol solvent includes:

[0042] The SiO2 particles were added to the alcohol solvent, stirred, and then subjected to ultrasonic treatment.

[0043] In this application, since nano-sized SiO2 particles are prone to agglomeration, the nano-sized SiO2 can be effectively dispersed by dispersing it in an alcohol solvent and then subjecting it to ultrasonic treatment, thereby making its coating on lithium manganese iron phosphate particles more uniform and improving the coating effect.

[0044] In some embodiments, the stirring time is 5 min-15 min, for example, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, etc., and the ultrasonic treatment time is 20 min-40 min, for example, 20 min, 22 min, 24 min, 26 min, 28 min, 30 min, 32 min, 34 min, 36 min, 38 min, 40 min, etc.

[0045] In some embodiments, the mass percentage of SiO2 particles, TiO2 particles, and lithium manganese iron phosphate particles in the cathode material is (0.3%-0.7%):(0.3%-0.7%):(98.6%-99.4%), for example, 0.7%:0.7%:98.6%, 0.6%:0.6%:98.8%, 0.5%:0.7%:98.8%, or 0.7%:0.5%. The following concentrations are possible: 98.8%, 0.5%:0.5%:99%, 0.3%:0.7%:99%, 0.7%:0.3%:99%, 0.4%:0.6%:99%, 0.6%:0.4%:99%, 0.4%:0.4%:99.2%, 0.5%:0.3%:99.2%, 0.3%:0.5%:99.2%, 0.3%:0.3%:99.4%, etc. Within this range, lithium manganese iron phosphate particles can be better coated by SiO2 and TiO2 particles, thus forming a coating layer. Simultaneously, the thickness of the coating layer can be moderate, allowing for effective lithium ion insertion / extraction.

[0046] As an example, the alcohol solvent includes isopropanol, methanol, ethanol, propanol, butanol, benzyl alcohol, and ethylene glycol. This improves the dispersion of nano-SiO2 particles, while the easy evaporation of the alcohol solvent facilitates handling and thus enhances the coating effect.

[0047] In some embodiments, the temperature of the first heating is 60℃ to 90℃, for example, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, etc., and the heating time is 4h to 12h, for example, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, etc. Within this range, the solvent can be fully evaporated, and the nano-SiO2 particles can be effectively coated on the surface of the lithium manganese iron phosphate particles. If the temperature is too low, the solvent cannot be fully evaporated; if the temperature is too high, the solvent evaporates quickly, the surface tension of the solvent decreases, and it will lead to agglomeration between SiO2 particles.

[0048] In step S2,

[0049] In some embodiments, coating the surface of the first solid particle with nanoscale TiO2 particles includes:

[0050] Tetrabutyl titanate and anhydrous ethanol are provided. The tetrabutyl titanate is dispersed in the anhydrous ethanol and then mixed with the first solid particles to obtain a suspension.

[0051] Water is added to the suspension, and the mixture is then heated and stirred.

[0052] In this embodiment, tetrabutyl titanate hydrolysis generates TiO2. By adding the first solid particles to the tetrabutyl titanate hydrolysis process, the generated TiO2 can coat the first solid particles, improving the coating effect. Tetrabutyl titanate can coordinate with anhydrous ethanol to form a complex, thereby stabilizing the structure of the tetrabutyl titanate molecule and slowing down the hydrolysis reaction. Simultaneously, anhydrous ethanol can fully dissolve the tetrabutyl titanate, ensuring uniform dispersion.

[0053] In some embodiments, dispersing the tetrabutyl titanate in anhydrous ethanol includes:

[0054] The tetrabutyl titanate was mixed with anhydrous ethanol and then subjected to ultrasonic treatment.

[0055] In some embodiments, the ultrasonic treatment time is 20-40 minutes, for example, 20 minutes, 22 minutes, 24 minutes, 26 minutes, 28 minutes, 30 minutes, 32 minutes, 34 minutes, 36 minutes, 68 minutes, 40 minutes, etc. Within this range, tetrabutyl titanate can be fully dispersed in anhydrous ethanol, which can alleviate its aggregation phenomenon.

[0056] In some embodiments, the second heating temperature is 50℃-70℃, for example, 50℃, 52℃, 54℃, 56℃, 58℃, 60℃, 62℃, 64℃, 66℃, 68℃, 70℃, etc. The second heating time is 4h-8h, for example, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 8h, etc. Within this range, ethanol can be fully evaporated, and the generated nano-TiO2 particles can effectively coat the surface of the lithium manganese iron phosphate particles coated with SiO2 particles. If the temperature is too low, the ethanol solvent cannot be fully evaporated; if the temperature is too high, the solvent evaporates quickly, the surface tension of the solvent decreases, and it will lead to agglomeration between TiO2 particles.

[0057] In some embodiments, providing water to the suspension includes:

[0058] An aqueous solution of ethanol is provided and added to the suspension.

[0059] In this application, the use of an aqueous solution of ethanol can dilute the concentration of water, thereby slowing down the hydrolysis rate of tetrabutyl titanate. At the same time, the ethanol solvent is easy to evaporate, making it convenient to operate.

[0060] In some embodiments, the volume ratio of ethanol to water in the aqueous ethanol solution is (1-3):1, for example, 1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1, 2:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1, or 3:1. Within this range, by controlling the volume ratio of ethanol to water, the hydrolysis rate of tetrabutyl titanate can be controlled, thereby resulting in a more uniform distribution of TiO2 particles generated from the hydrolysis of tetrabutyl titanate on the surface of lithium manganese iron phosphate particles coated with SiO2 particles.

[0061] In some embodiments, the method further includes: coating the surface of the first solid particles with nano-sized TiO2 particles and then sintering them to obtain a positive electrode material.

[0062] In some embodiments, the method further includes: after a second heating and stirring, sintering is performed to obtain a positive electrode material.

[0063] In some embodiments, the sintering temperature is 400℃-600℃, for example, 400℃, 420℃, 440℃, 460℃, 480℃, 500℃, 520℃, 540℃, 560℃, 580℃, etc. The sintering time is 3h-6h, for example, 3h, 3.5h, 4h, 4.5h, 5.5h, 6h, etc. Within this range, the lithium manganese iron phosphate particles can be melted and regenerated, thereby bonding more firmly with SiO2 and TiO2 particles, and thus reducing defects on the surface of the lithium manganese iron phosphate particles.

[0064] Thirdly, embodiments of this application provide a positive electrode sheet, including the aforementioned positive electrode material.

[0065] Fourthly, embodiments of this application provide a battery including the aforementioned positive electrode.

[0066] Example 1

[0067] A method for preparing a positive electrode material includes the following steps:

[0068] (1) Add SiO2 particles with a particle size D50 of 6 nm to isopropanol and stir for 10 min, then sonicate for 30 min, and then add LiMn to SiO2 particles at a mass ratio of 0.5:99. 0.5 Fe 0.5 PO4 particles were then stirred at 75°C for 8 hours to obtain the first solid particles.

[0069] (2) Tetrabutyl titanate (C 16H 36 SiO2 particles were dissolved in anhydrous ethanol and sonicated for 30 min. The dissolved SiO2 particles were then added to the first solid particles (wherein, the mass ratio of the equivalent amount of SiO2 particles to TiO2 in tetrabutyl titanate in the first solid particles was 0.5:0.5, that is, the mass ratio of SiO2 particles to tetrabutyl titanate was 0.5:2.13). The mixture was then mixed to obtain a suspension. An aqueous solution of ethanol (the volume ratio of ethanol to water was 2:1) was added to the suspension, and the mixture was stirred at 60 °C for 6 h to obtain the second solid particles.

[0070] (3) The second solid powder was added to a muffle furnace and sintered at 500°C for 4 hours in an air atmosphere to obtain the positive electrode material.

[0071] Example 2

[0072] This embodiment is basically the same as Embodiment 1, except that the SiO2 particles, the calculated amount of TiO2 in tetrabutyl titanate, and the LiMn content are different. 0.5 Fe 0.5 The mass ratio of PO4 is 0.3:0.5:99.2.

[0073] Example 3

[0074] This embodiment is basically the same as Embodiment 1, except that the SiO2 particles, the calculated amount of TiO2 in tetrabutyl titanate, and the LiMn content are different. 0.5 Fe 0.5 The mass ratio of PO4 is 0.7:0.5:98.8.

[0075] Example 4

[0076] This embodiment is basically the same as Embodiment 1, except that the SiO2 particles, the calculated amount of TiO2 in tetrabutyl titanate, and the LiMn content are different. 0.5 Fe 0.5 The mass ratio of PO4 is 0.5:0.3:99.2.

[0077] Example 5

[0078] This embodiment is basically the same as Embodiment 1, except that the SiO2 particles, the calculated amount of TiO2 in tetrabutyl titanate, and the LiMn content are different. 0.5 Fe 0.5 The mass ratio of PO4 is 0.5:0.7:98.8.

[0079] Example 6

[0080] This embodiment is basically the same as Embodiment 1, except that the SiO2 particles, the calculated amount of TiO2 in tetrabutyl titanate, and the LiMn content are different. 0.5 Fe0.5 The mass ratio of PO4 is 1.2:0.5:98.3.

[0081] Example 7

[0082] This embodiment is basically the same as Example 1, except that the calculated amount of SiO2 particles, TiO2 in tetrabutyl titanate, and LiMn in this embodiment are different. 0.5 Fe 0.5 The mass ratio of PO4 is 0.5:1.2:98.3.

[0083] Example 8

[0084] This embodiment is basically the same as embodiment 1, except that the sintering temperature in step (3) of this embodiment is 400℃.

[0085] Example 9

[0086] This embodiment is basically the same as embodiment 1, except that the sintering temperature in step (3) of this embodiment is 600℃.

[0087] Comparative Example 1

[0088] (1) SiO2 particles (particle size D50 is 6nm) and tetrabutyl titanate (C 16 H 36 O4Ti) was added to anhydrous ethanol at a mass ratio of SiO2 particles to TiO2 in tetrabutyl titanate of 0.5:0.5. After stirring for 10 min, the mixture was sonicated for 30 min, and then LiMn was added. 05 Fe 05 PO4 (SiO2 particles and LiMn) 0.5 Fe 0.5 The mass ratio of PO4 particles was 0.5:99, and then an aqueous solution of ethanol (volume ratio of ethanol to water was 2:1) was added. The mixture was then stirred at 75°C for 8 hours to obtain the first solid particles.

[0089] (2) The second solid powder was added to a muffle furnace and sintered at 500°C for 4 hours in an air atmosphere to obtain the positive electrode material.

[0090] Comparative Example 2

[0091] This comparative example is basically the same as Example 1, except that step (2) was not performed in this comparative example, and the mass of SiO2 and the amount of TiO2 generated are the same as in Example 1.

[0092] Comparative Example 3

[0093] This comparative example is basically the same as Example 1, except that step (1) is not performed in this comparative example, where LiMn is... 0.5 Fe0.5 PO4 was directly added to anhydrous ethanol containing dissolved tetrabutyl titanate, and the mass of TiO2 generated was the same as that of SiO2 and the amount of TiO2 generated in Example 1.

[0094] Test example:

[0095] The cathode materials obtained by the examples and comparative examples, and the uncoated LiMn, are respectively used. 0.5 Fe 0.5 PO4 is used as the positive electrode active material, graphite is used as the negative electrode active material, and PE membrane is used as the separator. The positive electrode, separator and negative electrode are stacked in sequence and the cell is obtained through the stacking process. The cell is placed in the outer packaging shell, dried, and electrolyte (a solution of 1.2 mol / L LiPF6 dissolved in a 3:7 mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC)) is injected at an electrolyte injection coefficient of 4.4 g / Ah. After vacuum sealing, standing, formation and capacity testing, the lithium-ion battery is obtained.

[0096] The obtained lithium-ion batteries were subjected to HPPC discharge tests: The batteries were charged using a constant current and constant voltage of 4.25V and 1 / 3C, and fully charged with a cutoff current of 0.05C. Then, they were discharged using a constant current of 1 / 3C, with cutoff capacities of 0.3C, 0.5C, and 0.7C, respectively. The HPPC values ​​for 30%, 50%, and 70% SOC were then calculated using the following formula: R = (V2 - V1) / 1C, where V2 is the voltage after 30 seconds of 1C discharge, V1 is the voltage after 30 seconds of 1C discharge, 1C = 1Q, and Q is the nominal capacity of the battery.

[0097] The discharge capacity retention rate of the obtained lithium-ion battery was tested: the battery was charged with constant current and constant voltage at 4.25V and 1 / 3C, and after being fully charged with a cutoff current of 0.05C, it was discharged with constant current at 1C, 2C and 3C, and the cutoff voltage was 2.5V.

[0098] The obtained lithium-ion batteries were subjected to cycle performance tests and Mn element dissolution tests: The batteries were charged at 4.25V and 1C constant current and constant voltage, with a cutoff current of 0.05C for full charge, and then discharged at 1C constant current to 2.5V, undergoing 500 charge-discharge cycles. The negative electrode sheets obtained from the disassembled empty batteries (empty batteries refer to batteries with 0% SOC, meaning zero charge) were soaked in DMC for 5 hours, dried, and then powdered for ICP testing to determine the Mn element dissolution of the negative electrode.

[0099] The test data is shown in Table 1.

[0100] Table 1

[0101]

[0102] As can be seen from Table 1:

[0103] Compared with Examples 1-5, the battery in Example 1 has a higher discharge capacity retention rate and cycle performance, indicating that the amount of SiO2 and the amount of TiO2 generated affect the battery's discharge capacity retention rate and cycle performance.

[0104] Compared to Example 6, the batteries in Examples 1-5 exhibited lower internal resistance, less Mn leaching, and higher discharge capacity retention, demonstrating that the amount of SiO2 used affects battery performance. Compared to Examples 8 and 9, the battery in Example 1 exhibited lower internal resistance, less Mn leaching, higher discharge capacity retention, and better cycle performance, demonstrating that sintering temperature affects battery performance.

[0105] Compared with Comparative Example 1, the battery in the embodiment has lower internal resistance, less Mn element dissolution, higher discharge capacity retention and cycle performance. This is because the positive electrode material of the battery in the embodiment is coated with SiO2 particles and TiO2 particles in sequence on the surface of lithium manganese iron phosphate particles, while the positive electrode material of the battery in Comparative Example 1 is coated with a mixture of SiO2 particles and TiO2 particles on the surface of lithium manganese iron phosphate particles.

[0106] Compared with Comparative Example 2, the battery in the embodiment has lower internal resistance, higher discharge capacity retention rate, and higher cycle performance. This is because the surface of the positive electrode material lithium iron phosphate particles in the embodiment is sequentially coated with SiO2 particles and TiO2 particles, while the surface of the positive electrode material lithium iron phosphate particles in Comparative Example 2 is only coated with SiO2 particles.

[0107] Compared with Comparative Example 3, the battery of the embodiment has higher cycle performance. The reason is that the surface of the positive electrode material lithium manganese iron phosphate particles of the battery of the embodiment is coated with SiO2 particles and TiO2 particles in sequence, while the surface of the positive electrode material lithium manganese iron phosphate particles of the battery of Comparative Example 3 is only coated with TiO2 particles.

[0108] Compared with the use of uncoated LiMn 0.5 Fe 0.5 Compared to batteries made from PO4 powder, the batteries in this embodiment exhibit lower internal resistance, less Mn leaching, higher discharge capacity retention, and better cycle performance. This demonstrates that this method, through the modification of LiMn... 0.5 Fe 0.5 Coating SiO2 and TiO2 with PO4 powder in sequence can improve battery performance.

[0109] The embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A positive electrode material, characterized by, Comprising: Comprising manganese iron phosphate particles and a first shell layer and a second shell layer successively coated on the surface of the manganese iron phosphate particles, the material of the first shell layer comprising nano-sized SiO2 particles, and the material of the second shell layer comprising nano-sized TiO2 particles; The average particle size of the SiO2 particles is ≤8nm; The average particle size of the TiO2 particles is ≤8nm; The chemical formula of the lithium manganese iron phosphate particles is LiMn x Fe (1-x) PO4, wherein 0.1≤X≤0.9; In the positive electrode material, the mass percentage of the SiO2 particles, the TiO2 particles and the manganese iron phosphate particles is (0.3%-0.7%):(0.3%-0.7%):(98.6%-99.4%).

2. A method for producing a positive electrode material, characterized by, Comprising the following steps: Providing nano-sized SiO2 particles, manganese iron phosphate particles and an alcohol solvent, dispersing the SiO2 particles in the alcohol solvent, adding the manganese iron phosphate particles, performing first heating and stirring to obtain first solid particles; Coating nano-sized TiO2 particles on the surface of the first solid particles to obtain the positive electrode material of claim 1.

3. The preparation method of the positive electrode material of claim 2, wherein, In the positive electrode material, the mass percentage of the SiO2 particles, the TiO2 particles and the manganese iron phosphate particles is (0.3%-0.7%):(0.3%-0.7%):(98.6%-99.4%); and / or, The temperature of the first heating is 60-90℃, and the time of the first heating is 4-12h.

4. The method for preparing the cathode material according to claim 2, characterized in that, The coating of nano-sized TiO2 particles on the surface of the first solid particles comprises: Providing tetra-n-butyl titanate and anhydrous ethanol, dispersing the tetra-n-butyl titanate in the anhydrous ethanol, and mixing the dispersed tetra-n-butyl titanate with the first solid particles to obtain a suspension; Providing water, adding the water to the suspension, and performing second heating and stirring.

5. The preparation method of the positive electrode material of claim 4, wherein, The temperature of the second heating is 50-70℃, and the time of the second heating is 4-8h.

6. The method for preparing the cathode material according to claim 4, characterized in that, The providing of water and adding of the water to the suspension comprises: Providing an aqueous solution of ethanol and adding the aqueous solution of ethanol to the suspension.

7. The method of claim 6, wherein the method further comprises a step of calcining the mixture at a temperature of 700-900°C for 5-20 hours. The volume ratio of ethanol to water in the aqueous solution of ethanol is (1-3):

1.

8. The method of producing a cathode material according to any one of claims 2 to 6, characterized in that, Further comprising: After coating nano-sized TiO2 particles on the surface of the first solid particles, performing sintering to obtain a positive electrode material.

9. The preparation method of the positive electrode material of claim 8, wherein, The temperature of the sintering is 400-600℃, and the time of the sintering is 3-6h.

10. A positive electrode sheet characterized by comprising: The positive electrode material comprises the positive electrode material of claim 1 or the positive electrode material prepared by the preparation method of any one of claims 2-9.

11. A battery, characterized by The positive electrode tab comprises the positive electrode tab of claim 10.

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