Preparation method of carbon-coated modified lithium ion battery manganese positive electrode material

Abstract

The invention discloses a preparation method of a carbon-coated modified lithium ion battery manganese positive electrode material, and relates to the technical field of lithium ion battery positive electrode materials. The preparation method comprises the following steps: adding grinding balls and absolute ethyl alcohol into a mixed raw material, and performing ball milling to obtain a primary grinding material; carrying out primary sintering after grinding and vibrating screening, and grinding to obtain a primary sintered material; mixing with a carbon source in proportion, performing secondary ball milling, taking out an abrasive material after ball milling is finished, continuously washing with deionized water, and sieving to obtain uniformly dispersed secondary slurry; adding pure water according to a certain solid content of the slurry, continuously stirring the slurry, performing spray drying at the same time, and uniformly grinding the powder in the collecting tank after spray drying to obtain a spray-dried material; carrying out secondary sintering on the spray-dried material, and grinding and sieving the obtained sintered powder to prepare a carbon-coated lithium ferric manganese phosphate product; the method is simple in steps and easy to implement, and the prepared positive electrode material has a stable and controlled carbon coating effect.

Description

Technical Field

[0001] The present invention relates to the technical field of cathode materials for lithium-ion batteries, and specifically to a preparation method of a carbon-coated modified manganese-based cathode material for lithium-ion batteries. Background Art

[0002] The cathode material is a key component of a lithium-ion battery, and its performance and price will have a greater impact on the lithium-ion battery. The reasonable selection of the cathode material can significantly improve the capacity performance, cycle stability and rate performance of the lithium-ion battery, and can promote the improvement of its energy density and power density, thereby having a profound impact on a wider range of application fields of the lithium-ion battery. Currently, the commercially available lithium battery cathode materials include lithium cobaltate, lithium manganate, lithium nickelate, lithium iron phosphate and ternary materials, etc. Lithium iron manganese phosphate cathode material belongs to the olivine structure, having a relatively high diffusion coefficient of lithium iron phosphate material and a high working voltage of lithium manganese phosphate material.

[0003] Currently, the preparation methods of lithium-ion battery cathode materials mainly include solid-phase method, hydrothermal method, co-precipitation method, etc. Among them, the solid-phase method has the advantages of simple and convenient operation and low equipment cost, and is widely used in industrial applications in the field of material production. The solid-phase ball milling method is a commonly used synthesis method and can be used to prepare precursors of various materials. During the ball milling process, the powder raw materials are mixed and reacted in the ball milling tank through the action of mechanical force to obtain the required precursor powder. The solid-phase method has also been widely used in the preparation of lithium-ion battery cathode materials, specifically including the preparation of raw material precursors (mainly including processes such as ball milling and sintering) and the main processes such as high-temperature sintering.

[0004] The solid-phase method has relatively prominent advantages in terms of economy and large-scale production, but there are also problems such as unstable ball milling process, resulting in uneven particles of the cathode material precursor and poor physical properties such as morphology, which leads to a low tap density of the cathode material and ultimately has a certain impact on the electrochemical performance of the lithium-ion battery cathode material. Currently, the main modification means for preparing cathode materials by the solid-phase method include surface coating, ion doping and nanosizing, etc.

[0005] The invention patent with the publication number CN115744860B and the name of "A carbon-coated lithium iron manganese phosphate material, its preparation method and battery" discloses that by adding a first carbon source to a mixed iron source, manganese source, phosphorus source and solvent, drying and then sintering, carbon-coated manganese ferrous pyrophosphate is obtained, and then a lithium source, a second carbon source and a solvent are added, dried and then sintered to obtain a carbon-coated lithium iron manganese phosphate material. The carbon content recorded in its claims is 1.2 - 1.5 wt%, and the carbon content recorded in the specification is 1.2 - 5 wt%. However, when multiple parallel preparations are carried out under the same conditions according to its method, the measured values of the carbon content in the obtained products fluctuate greatly and are difficult to control at a stable level. Therefore, there is an urgent need for a preparation method of a carbon-coated modified manganese-based cathode material for lithium-ion batteries to solve this problem. Summary of the Invention

[0006] The purpose of the present invention is to provide a preparation method of a carbon-coated modified manganese-based cathode material for lithium-ion batteries to solve the problem of unstable carbon content in the preparation of a carbon-coated lithium iron manganese phosphate cathode material.

[0007] To achieve the above purpose, the present invention provides the following technical solutions: A preparation method of a carbon-coated modified manganese-based cathode material for lithium-ion batteries, including the following specific steps:

[0008] S1 Mix a lithium iron manganese phosphate precursor or the phosphorus source, iron source, and manganese source required for preparing the lithium iron manganese phosphate precursor with a lithium source to obtain a mixed raw material, and add grinding balls and anhydrous ethanol according to a certain ball-to-material ratio, large and small ball ratio, and solid-to-liquid ratio.

[0009] S2 Ball-mill the mixed material for a certain period of time. During the ball-milling period, pause the operation at a certain interval, perform exhaust treatment and supplement anhydrous ethanol for ball-milling. After the ball-milling is completed, take out the mixture in the ball-mill tank and dry it to obtain a primary abrasive.

[0010] S3 Grind and sieve the primary abrasive, then place it in a high-temperature tube furnace for primary sintering. After the sintering is completed, pour the obtained sintered powder into a mortar for grinding to obtain a primary sintered material.

[0011] S4 Mix the primary sintered material with a carbon source in proportion, and add grinding balls and anhydrous ethanol for secondary ball-milling according to the same ball-to-material ratio, large and small ball ratio, and solid-to-liquid ratio as in step S1. During the ball-milling period, pause the operation at a certain interval, perform exhaust treatment and supplement anhydrous ethanol for ball-milling. After the ball-milling is completed, take out the abrasive, continuously rinse it with deionized water and sieve it to obtain a uniformly dispersed secondary slurry.

[0012] S5 Uniformly mix the secondary slurry, homogenize it and continuously stir, and add pure water according to a certain slurry solid content. Then continuously stir the slurry while performing spray drying. After the spray drying is completed, grind the powder in the collection tank evenly to obtain a spray-dried material.

[0013] S6 places the spray-dried material in a high-temperature tubular furnace for secondary sintering. After sintering is completed, the obtained sintered powder is ground and sieved to obtain the carbon-coated lithium iron manganese phosphate product.

[0014] Preferably, in the above step S1, the mixed raw materials are for obtaining the cathode material active substance LiFe x Mn 1-x PO4, where the range of X is from 0.1 to 0.9; the lithium source is one or more of lithium carbonate, lithium acetate, lithium dihydrogen phosphate, and lithium oxalate; the manganese source is one or more of manganese tetroxide, manganese oxide, manganese sesquioxide, manganese acetate, and manganese oxalate; the phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, lithium dihydrogen phosphate, and phosphoric acid; the iron source is one or more of iron phosphate, iron tetroxide, iron sesquioxide, ferrous acetate, and ferrous oxalate.

[0015] Preferably, in the above step S1, the mass ratio of the grinding balls to the abrasive is (0.5 - 6):1, the diameter range of the grinding balls is 0.2 - 4 mm, the ratio of large and small balls refers to the grinding balls having two diameters, where the ratio of the larger one to the other, the difference in diameter between the two grinding balls is not less than 1 mm, and the ratio of large and small balls is 1:(2 - 3); the solid-liquid ratio after adding anhydrous ethanol is 1:4 - 4:1.

[0016] Preferably, in the above steps S2 and S4, the ball milling time is 8 - 12 h respectively, and the operating speed is 500 - 550 revolutions per minute respectively; the pause intervals for the two ball milling operations are as follows: within the first 1 h of ball milling operation, it pauses at the 30th minute and 60th minute respectively, and then pauses once every 1 h. Each time it pauses, loosen the fixed clamping seat and discharge the gas in the ball milling tank.

[0017] Preferably, in the above step S3, the temperature of the first sintering is 300 - 350 °C, and the whole sintering process is carried out under a protective gas atmosphere.

[0018] Preferably, in the above step S4, the mass of the added carbon source is 5 - 35% of the mass of the first sintered material, and the carbon source is carbon nanotubes or graphene.

[0019] Preferably, in the above step S5, the solid content of the slurry is 5 - 30%, the continuous stirring rate is 200 - 550 r / min, the rotation speed of the peristaltic pump used for spray drying is 5 - 20 rpm, the inlet air temperature of the spray dryer is 220 - 280 °C, and the outlet air temperature is 110 - 130 °C.

[0020] Preferably, in the above step S6, the temperature of the second sintering is 650 - 750 °C, and the whole sintering process is carried out under a protective gas atmosphere.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] The preparation method of the carbon-coated modified lithium-ion battery manganese-based cathode material has simple and easy-to-implement steps. Through comprehensive control of raw materials, two ball milling processes, two sintering processes, spray drying, etc., and adjustment of the addition timing of the carbon source, the carbon-coated effect of the cathode material prepared under the same conditions is stable and controllable. This carbon-coated modification method of the cathode material is conducive to controlling the quality of the final product derived therefrom within a stable range, which is beneficial to the further stable development of lithium-ion battery technology. Detailed implementation mode

[0023] In order to make the coating effects of the carbon-coated lithium iron manganese phosphate products prepared under the same conditions and in different batches consistent, through a large amount of theoretical research and experimental verification, the present invention proposes the following preparation method:

[0024] S1 Mix the lithium iron manganese phosphate precursor or the phosphorus source, iron source, and manganese source required for preparing the lithium iron manganese phosphate precursor with the lithium source to obtain a mixed raw material, and add grinding balls and anhydrous ethanol according to a certain ball-to-material ratio, large-to-small ball ratio, and solid-to-liquid ratio.

[0025] The above mixed raw material is for obtaining the cathode material active substance LiFe x Mn 1-x PO4, where the range of X can further be selected from 0.1 to 0.9;

[0026] For reference, the lithium source is one or more of lithium carbonate, lithium acetate, lithium dihydrogen phosphate, lithium oxalate, etc.; the manganese source is one or more of manganese tetroxide, manganese oxide, manganese sesquioxide, manganese acetate, manganese oxalate, etc.; the phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, lithium dihydrogen phosphate, phosphoric acid, etc.; the iron source is one or more of iron phosphate, iron tetroxide, iron sesquioxide, ferrous acetate, ferrous oxalate, etc.

[0027] In a preferred implementation mode, the mass ratio of the grinding balls to the abrasive is (0.5 - 6):1, the diameter range of the grinding balls is 0.2 - 4 mm, the large-to-small ball ratio refers to that the grinding balls adopt two diameters, and the ratio of the larger diameter one to the other one, the difference between the two grinding ball diameters is not less than 1 mm, and the large-to-small ball ratio is 1:(2 - 3); the solid-to-liquid ratio after adding anhydrous ethanol is 1:4 - 4:1.

[0028] S2 Ball mill the mixed material for a certain time. During the ball milling, pause the operation at certain intervals for exhaust treatment and supplement anhydrous ethanol for ball milling. After the ball milling is completed, take out the mixture in the ball mill tank and dry it to obtain the primary abrasive.

[0029] In a preferred implementation mode, the ball milling time is 8 - 12 h, and the operating rotation speed is 500 - 550 revolutions per minute;

[0030] For reference, during the intermittent pauses of ball milling, in the first hour of ball milling operation, pauses can be made at the 30th minute and 60th minute respectively, and then once every hour. Each time a pause occurs, loosen the fixed clamping seat to exhaust the gas in the ball milling tank.

[0031] S3 The primary abrasive is placed in a high-temperature tubular furnace for primary sintering after grinding and sieving by vibration. After sintering is completed, the obtained sintered powder is poured into a mortar for grinding to obtain the primary sintered material.

[0032] Optionally, the temperature of the primary sintering is 300 - 350 °C, and the entire sintering process is carried out under a protective gas atmosphere.

[0033] S4 After mixing the primary sintered material and the carbon source in proportion, add grinding balls and anhydrous ethanol according to the same ball-to-material ratio, large-to-small ball ratio, and solid-to-liquid ratio as in step S1 for secondary ball milling. During ball milling, the operation is paused at certain intervals for exhaust treatment and to supplement anhydrous ethanol for ball milling. After ball milling is completed, take out the abrasive, continuously rinse it with deionized water and sieve it to obtain a uniformly dispersed secondary slurry.

[0034] In a preferred embodiment, the mass of the added carbon source is 5 - 35% of the mass of the primary sintered material, and the carbon source is carbon nanotubes or graphene.

[0035] In addition, the conditions for secondary ball milling can be the same as those for primary ball milling. Specifically, the ball milling time is 8 - 12 h, and the operating rotation speed is 500 - 550 revolutions per minute. During the intermittent pauses of ball milling, in the first hour of ball milling operation, pauses can be made at the 30th minute and 60th minute respectively, and then once every hour. Each time a pause occurs, loosen the fixed clamping seat to exhaust the gas in the ball milling tank.

[0036] S5 The secondary slurry is uniformly mixed, homogenized and then continuously stirred. Pure water is added according to a certain solid content of the slurry, and then the slurry is continuously stirred while spray drying is carried out. After spray drying is completed, the powder in the collection tank is ground evenly to obtain the spray-dried material.

[0037] In a preferred embodiment, the solid content of the slurry is controlled at 5 - 30%, the continuous stirring rate is 200 - 550 r / min, the rotation speed of the peristaltic pump used for spray drying is 5 - 20 rpm, the inlet air temperature of the spray dryer is 220 - 280 °C, and the outlet air temperature is 110 - 130 °C.

[0038] S6 The spray-dried material is placed in a high-temperature tubular furnace for secondary sintering. After sintering is completed, the obtained sintered powder is ground and sieved to obtain the carbon-coated lithium iron manganese phosphate product.

[0039] In a preferred embodiment, the temperature of the secondary sintering is 650 - 750 °C, and the entire sintering process is carried out under a protective gas atmosphere.

[0040] The content of the present invention is further illustrated by several embodiments. Obviously, the following embodiments are not all embodiments of the present invention and should not be used as an absolute limitation of the protection scope of the present invention.

[0041] Example 1

[0042] (1) Weigh 13.56 g of lithium carbonate and 45 g of manganese iron phosphate precursor in sequence and pour them into a 250 ml ball milling jar. At the same time, add grinding balls and absolute ethanol in proportion. The addition mechanism of grinding balls and absolute ethanol in the ball milling jar is as follows: the mass ratio of grinding balls to abrasive is 4:1, the mass ratio of large balls (2 mm) to small balls (1 mm) is 2:3, and the ratio of absolute ethanol to abrasive is 2:3.

[0043] (2) Conduct ball milling at a speed of 500 r / min for a cumulative of 10 h. In the first hour of ball milling operation, pause at the 30th minute and 60th minute respectively, loosen the fixed clamping seat, and discharge the gas in the ball milling jar; then pause every 1 h, discharge the gas in the ball milling jar each time, and inject 5 ml of absolute ethanol. After 10 h of ball milling, take out the mixture in the ball milling jar and dry it to obtain the primary abrasive.

[0044] (3) After the primary abrasive powder is ground and sieved by vibration, it is loaded into a firing boat and placed in a high-temperature tube furnace for primary sintering. The sintering mechanism is as follows: start at room temperature → heat up at a rate of 1 °C / min in a nitrogen atmosphere (flow rate 300) to 300 °C, hold for 5 h → cool naturally to room temperature. After sintering is completed, pour the obtained sintered powder into a mortar and grind it to obtain the primary sintered material.

[0045] (4) Mix the primary sintered material with graphene at 10% of the total grinding mass, add grinding balls and absolute ethanol according to the same ball-to-material ratio, large-to-small ball ratio, and solid-to-liquid ratio as the primary ball milling, and then conduct ball milling at a speed of 500 r / min for a cumulative of 10 h. In the first hour of ball milling operation, pause at the 30th minute and 60th minute respectively, loosen the fixed clamping seat, and discharge the gas in the ball milling jar; then pause every 1 h, discharge the gas in the ball milling jar each time, and inject 10 ml of absolute ethanol. After 10 h of ball milling, take out the abrasive, continuously rinse it with deionized water and sieve it to obtain a uniformly dispersed secondary slurry.

[0046] (5) Mix the secondary slurry evenly, homogenize it and continue stirring, and add pure water according to 10% of the solid content of the slurry. Subsequently, continuously stir the slurry at a stirring rate of 600 r / min, and at the same time conduct the spray drying process. The parameter settings of the spray drying process are as follows: peristaltic pump speed 5 rpm, inlet air temperature of the spray dryer 280 °C, outlet air temperature 130 °C. After the spray drying process is completed, grind the powder in the collection tank evenly to obtain the spray-dried material.

[0047] (6) After the spray-dried material is ground and mixed evenly, it is placed in a high-temperature tube furnace for secondary sintering. The sintering mechanism is as follows: starting from room temperature → heating to 650 °C at a rate of 1 °C / min under a nitrogen atmosphere (flow rate 300), holding for 10 h → natural cooling to room temperature. After sintering is completed, the obtained sintered powder is ground and sieved.

[0048] Using the same conditions as above for 5 preparations, 5 batches of carbon-coated modified lithium-ion battery cathode materials are obtained, and the carbon contents in the materials are measured to be 4.43%, 4.39%, 4.43%, 4.45%, and 4.40% respectively.

[0049] Example 2

[0050] (1) Weigh 8.88 g of lithium carbonate, 12.84 g of manganese tetroxide, 13.94 g of ammonium dihydrogen phosphate, and 12.06 g of iron phosphate in sequence, and at the same time add grinding balls and absolute ethanol in proportion. The addition mechanism of grinding balls and absolute ethanol in the ball mill tank is as follows: the mass ratio of grinding balls to abrasive is 4:1, the mass ratio of large balls (2 mm) to small balls (1 mm) is 2:3, and the ratio of absolute ethanol to abrasive is 2:3.

[0051] (2) Perform ball milling at a speed of 500 r / min for a cumulative of 8 h. In the first 1 h of ball milling operation, pause at the 30th min and 60th min respectively, loosen the fixed clamping seat, and discharge the gas in the ball mill tank; then pause every 1 h, discharge the gas in the ball mill tank each time, and inject 5 ml of absolute ethanol. After 10 h of ball milling is completed, take out the mixture in the ball mill tank and dry it to obtain the primary abrasive.

[0052] (3) After the primary abrasive powder is ground and sieved, it is loaded into a firing boat and placed in a high-temperature tube furnace for primary sintering. The sintering mechanism is as follows: starting from room temperature → heating to 300 °C at a rate of 1 °C / min under a nitrogen atmosphere (flow rate 300), holding for 5 h → natural cooling to room temperature. After sintering is completed, pour the obtained sintered powder into a mortar and grind it to obtain the primary sintered material.

[0053] (4) Mix the primary sintered material with graphene at 10% of the total mass, add grinding balls and absolute ethanol according to the same ball-to-material ratio, large-to-small ball ratio, and solid-to-liquid ratio as the primary ball milling, and then perform ball milling at a speed of 500 r / min for a cumulative of 10 h. In the first 1 h of ball milling operation, pause at the 30th min and 60th min respectively, loosen the fixed clamping seat, and discharge the gas in the ball mill tank; then pause every 1 h, discharge the gas in the ball mill tank each time, and inject 5 ml of absolute ethanol. After 10 h of ball milling is completed, take out the abrasive, continuously rinse it with deionized water and sieve it to obtain a uniformly dispersed secondary slurry.

[0054] (5) Mix the secondary slurry evenly, continue stirring after homogenization, and add pure water according to 10% of the solid content of the slurry. Subsequently, stir the slurry continuously at a stirring rate of 550 r / min, and at the same time carry out the spray drying process. The parameters of the spray drying process are set as follows: the peristaltic pump rotation speed is 5 rpm, the inlet air temperature of the spray dryer is 280 °C, and the outlet air temperature is 130 °C. After the spray drying process is completed, grind the powder in the collection tank evenly to obtain the spray-dried material.

[0055] (6) After grinding and mixing the spray-dried material evenly, place it in a high-temperature tube furnace for secondary sintering. The sintering mechanism is as follows: start from room temperature → heat up to 650 °C at a rate of 1 °C / min in a nitrogen atmosphere (flow rate 300), hold for 10 h → cool naturally to room temperature. After sintering is completed, grind and screen the obtained sintered powder.

[0056] Perform 5 preparations under the same above conditions to obtain 5 batches of carbon-coated modified lithium-ion battery cathode materials. The carbon contents in the materials are measured to be 4.54%, 4.58%, 4.49%, 4.53%, and 4.52% respectively.

[0057] Comparative Example 1:

[0058] (1) Weigh 13.56 g of lithium carbonate and 45 g of manganese iron phosphate precursor in sequence and pour them into a 250 ml ball milling jar. At the same time, add grinding balls and absolute ethanol in proportion. The addition mechanism of grinding balls and absolute ethanol in the ball milling jar is as follows: the mass ratio of grinding balls to abrasive is 4:1, the mass ratio of large balls (2 mm) to small balls (1 mm) is 2:3, and the ratio of absolute ethanol to abrasive is 2:3.

[0059] (2) Carry out ball milling at a rotation speed of 500 r / min for a total of 10 h. Before the ball milling runs for 1 h, pause at the 30th min and 60th min respectively, loosen the fixed clamp, and discharge the gas in the ball milling jar; then pause every 1 h, discharge the gas in the ball milling jar each time, and inject 5 ml of absolute ethanol. After 10 h of ball milling is completed, take out the mixture in the ball milling jar and dry it to obtain the primary abrasive.

[0060] (3) After grinding and sieving the primary abrasive powder, load it into a firing boat and place it in a high-temperature tube furnace for primary sintering. The sintering mechanism is as follows: start from room temperature → heat up to 300 °C at a rate of 1 °C / min in a nitrogen atmosphere (flow rate 300), hold for 5 h → cool naturally to room temperature. After sintering is completed, pour the obtained sintered powder into a mortar and grind it to obtain the primary sintered material.

[0061] (4) Add grinding balls and absolute ethanol to the ground primary sintered material at the same ball-to-material ratio, large-to-small ball ratio, and solid-to-liquid ratio as in primary ball milling, and perform ball milling at a rotation speed of 500 r / min for a cumulative 10 h. One hour before the ball milling operation, pause at the 30th minute and 60th minute respectively, loosen the fixed clamping seat, and discharge the gas in the ball milling tank; then pause every 1 h, discharge the gas in the ball milling tank each time, and inject 10 ml of absolute ethanol. After 10 h of ball milling, take out the abrasive, continuously rinse it with deionized water and sieve it to obtain a uniformly dispersed secondary slurry.

[0062] (5) Uniformly mix the secondary slurry, continuously stir it after homogenization, and add pure water according to 10% of the solid content of the slurry. Subsequently, continuously stir the slurry at a stirring rate of 600 r / min, and at the same time carry out the spray drying process. The parameters of the spray drying process are set as follows: the rotation speed of the peristaltic pump is 5 rpm, the inlet air temperature of the spray dryer is 280 °C, and the outlet air temperature is 130 °C. After the spray drying process is completed, grind the powder in the collection tank evenly to obtain the spray-dried material.

[0063] (6) After grinding and mixing the spray-dried material evenly, place it in a high-temperature tube furnace for secondary sintering. The sintering mechanism is as follows: start from room temperature → heat up to 650 °C at a rate of 1 °C / min under a nitrogen atmosphere (flow rate 300), hold for 10 h → cool naturally to room temperature. After sintering is completed, grind and sieve the obtained sintered powder.

[0064] Perform 5 preparations under the same above conditions to obtain 5 batches of carbon-coated modified lithium-ion battery cathode materials. The carbon contents in the materials are measured to be 1.11%, 1.13%, 1.11%, 1.10%, and 1.12% respectively.

[0065] Comparative Example 2:

[0066] (1) Weigh 3.7 g of lithium carbonate, 19.25 g of manganese tetroxide, 11.62 g of ammonium dihydrogen phosphate, and 6.03 g of iron phosphate in sequence and pour them into the ball milling tank, and add grinding balls and absolute ethanol according to the ratio. The addition mechanism of the grinding balls and absolute ethanol is as follows: the mass ratio of the grinding balls to the abrasive is 4:1, the mass ratio of the large balls (6 mm) to the small balls (4 mm) is 2:3, and the ratio of absolute ethanol to the abrasive is 1.5:1.

[0067] (2) Ball mill the mixed material at a rotation speed of 500 r / min for a cumulative 6 h. Pause at the 30th minute and 60th minute respectively during the ball milling operation, loosen the fixed clamping seat, discharge the gas in the ball milling tank, and inject 5 ml of absolute ethanol. After 4 h of ball milling, take out the mixture in the ball milling tank, continuously rinse it with deionized water and sieve it to obtain a uniformly dispersed slurry.

[0068] (3) Continuously stir the slurry and add pure water until the solid content reaches 10%. Subsequently, continuously stir the slurry at a stirring rate of 550 r / min while performing spray drying. The parameters of the spray drying process are set as follows: peristaltic pump rotation speed 5 rpm, inlet air temperature of the spray dryer 220 °C, outlet air temperature 130 °C;

[0069] (4) After the spray drying is completed, load the obtained spray-dried powder material into a firing boat and place it in a high-temperature tube furnace for high-temperature sintering. The sintering mechanism is as follows: starting from room temperature → heating at a rate of 5 °C / min in a nitrogen atmosphere (flow rate 300) to 300 °C and holding for 5 h → continuing to heat at a rate of 5 °C / min in a nitrogen atmosphere (flow rate 300) to 650 °C and holding for 10 h → natural cooling to room temperature. After the sintering is completed, pour the obtained sintered powder into a mortar for grinding, and finally obtain the lithium iron manganese phosphate cathode material.

[0070] The above same conditions are used for 5 preparations to obtain 5 batches of carbon-coated modified lithium-ion battery cathode materials. The measured carbon contents in the materials are 1.08%, 1.14%, 1.21%, 1.16%, and 1.11% respectively.

[0071] Comparative Example 3:

[0072] (1) Weigh 3.7 g of lithium carbonate, 19.25 g of manganese tetraoxide, 11.62 g of ammonium dihydrogen phosphate, 6.03 g of iron phosphate, and 4 g of graphene in sequence and pour them into a ball mill jar, and add grinding balls and anhydrous ethanol according to the ratio. The addition mechanism of the grinding balls and anhydrous ethanol is as follows: the mass ratio of the grinding balls to the abrasive is 4:1, the mass ratio of the large balls (6 mm) to the small balls (4 mm) is 2:3, and the ratio of anhydrous ethanol to the abrasive is 1.5:1.

[0073] (2) Ball mill the mixed material at a rotation speed of 500 r / min for a cumulative 6 h. Pause the ball milling operation at the 30th minute and 60th minute respectively during the ball milling process, loosen the fixed clamping seat, discharge the gas in the ball mill jar, and inject 5 ml of anhydrous ethanol. After 4 h of ball milling, take out the mixture in the ball mill jar, continuously rinse it with deionized water and sieve it to obtain a uniformly dispersed slurry.

[0074] (3) Continuously stir the slurry and add pure water until the solid content reaches 10%. Subsequently, continuously stir the slurry at a stirring rate of 550 r / min while performing spray drying. The parameters of the spray drying process are set as follows: peristaltic pump rotation speed 5 rpm, inlet air temperature of the spray dryer 220 °C, outlet air temperature 130 °C;

[0075] (4) After spray drying is completed, the obtained spray-dried powder material is loaded into a firing boat and placed in a high-temperature tube furnace for high-temperature sintering. The sintering mechanism is as follows: starting from room temperature → heating at a rate of 5 °C / min to 300 °C in a nitrogen atmosphere (flow rate 300) and holding for 5 h → continuing to heat at a rate of 5 °C / min to 650 °C in a nitrogen atmosphere (flow rate 300) and holding for 10 h → naturally cooling to room temperature. After sintering is completed, the obtained sintered powder is poured into a mortar and ground to finally obtain the lithium iron manganese phosphate cathode material.

[0076] Five batches of carbon-coated modified lithium-ion battery cathode materials were prepared under the same above conditions, and the carbon contents in the materials were measured to be 3.05%, 2.54%, 3.10%, 3.92%, and 2.88% respectively.

[0077] Comparative Example 4:

[0078] Using the method of Example 1 in Patent CN115744860B (hereinafter referred to as the comparative patent), according to the target cathode material active substance LiFe 0.25 Mn 0.75 PO4 ratio raw materials, using iron powder, manganese monoxide, glucose, phosphoric acid, and lithium carbonate as iron source, manganese source, carbon source, phosphorus source, and lithium source. Due to insufficient public data in the comparative patent, the following are relatively similar experimental examples obtained after multiple attempts;

[0079] Mix the raw materials other than the lithium source (to reduce the amount of the first carbon source added in its Example 1, which is 1.5% of the total amount of the iron source, manganese source, and phosphorus source), add water for dispersion and wet ball milling to obtain a pretreatment slurry with a solid content of 35 wt%, perform spray drying on the pretreatment slurry, and sinter in a sintering atmosphere. Since the specific sintering parameters are not disclosed in the comparative patent, the sintering control method in the present invention and the temperature range in the comparative patent are adopted. Starting from room temperature → heating at a rate of 5 °C / min to 300 °C in a nitrogen atmosphere (flow rate 300) and holding for 2 h → continuing to heat at a rate of 5 °C / min to 650 °C in a nitrogen atmosphere (flow rate 300) and holding for 6 h → naturally cooling to room temperature, to obtain carbon-coated manganese iron pyrophosphate with a carbon content of 0.6 wt%.

[0080] Mix the lithium source, the second carbon source, water, and carbon-coated manganese iron pyrophosphate. The second carbon source is 10% of the total mass of the lithium source and carbon-coated manganese iron pyrophosphate. After dispersion and wet ball milling, a precursor slurry with a solid content of 35 wt% is obtained. After spray drying and sintering, a carbon-coated lithium iron manganese phosphate material with a carbon content of 3.98% is prepared for the first time.

[0081] Seven additional batches of carbon-coated lithium iron manganese phosphate materials were prepared under the same above conditions, and the carbon contents in the materials were measured to be 4.61%, 3.74%, 3.91%, 4.22%, 3.80%, 4.04%, and 4.53% in sequence.

[0082] It can be seen from Examples 1 and 2 that the carbon content of the product obtained by the method of the present invention is consistent. Combined with Comparative Example 1, it is proved that the method of the present invention can better implement the carbon coating modification process, which is beneficial to control the quality of the final product within a stable range. In Comparative Examples 2, 3, and 4, it can be seen that the existing carbon coating method has shortcomings. Even if exactly the same experimental parameters and processes are used, it is difficult to control the carbon content of the product within a stable range.

[0083] The above are only preferred embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope defined by the claims.

[0084] The matters not described in detail in the present invention are all known technologies to those skilled in the art.

Claims

1. A preparation method of a carbon-coated modified lithium-ion battery manganese-based cathode material, characterized in that, It includes the following specific steps: S1 Mix the manganese iron phosphate precursor or the phosphorus source, iron source, and manganese source required for preparing the manganese iron phosphate precursor with the lithium source to obtain a mixed raw material, and add grinding balls and absolute ethanol according to a certain ball-to-material ratio, large-to-small ball ratio, and solid-to-liquid ratio; S2 Ball-mill the mixed material for a certain period of time. During the ball-milling process, pause the operation at certain intervals to perform exhaust treatment and supplement the absolute ethanol for ball-milling. After the ball-milling is completed, take out the mixture in the ball-milling tank and dry it to obtain the primary milled material; S3 Grind the primary milled material, screen it through a vibrating sieve, and then place it in a high-temperature tube furnace for primary sintering. After the sintering is completed, pour the obtained sintered powder into a mortar and grind it to obtain the primary sintered material; S4 Mix the primary sintered material with the carbon source in a certain proportion, and add grinding balls and absolute ethanol for secondary ball-milling according to the same ball-to-material ratio, large-to-small ball ratio, and solid-to-liquid ratio as in step S1. During the ball-milling process, pause the operation at certain intervals to perform exhaust treatment and supplement the absolute ethanol for ball-milling. After the ball-milling is completed, take out the milled material, continuously rinse it with deionized water, and screen it to obtain a uniformly dispersed secondary slurry; S5 Uniformly mix the secondary slurry, continuously stir it after homogenization, and add pure water according to a certain solid content of the slurry. Subsequently, continuously stir the slurry while performing spray drying. After the spray drying is completed, grind the powder in the collection tank evenly to obtain the spray-dried material; S6 Place the spray-dried material in a high-temperature tube furnace for secondary sintering. After the sintering is completed, grind and screen the obtained sintered powder to obtain the carbon-coated lithium manganese iron phosphate product.

2. The preparation method of a carbon-coated modified lithium-ion battery manganese-based cathode material according to claim 1, wherein: In the step S1, the mixed raw materials are used to obtain the cathode active material LiFe x Mn 1-x PO4, where the range of X is from 0.1 to 0.9; the lithium source is one or more of lithium carbonate, lithium acetate, lithium dihydrogen phosphate, and lithium oxalate; the manganese source is one or more of manganese tetroxide, manganese oxide, manganese sesquioxide, manganese acetate, and manganese oxalate; the phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, lithium dihydrogen phosphate, and phosphoric acid; and the iron source is one or more of iron phosphate, iron tetroxide, iron sesquioxide, ferrous acetate, and ferrous oxalate.

3. The preparation method of a carbon-coated modified lithium-ion battery manganese-based cathode material according to claim 1, characterized in that: In step S1, the mass ratio of the grinding balls to the milled material is (0.5 - 6):1, the diameter range of the grinding balls is 0.2 - 4 mm, the large-to-small ball ratio refers to using two diameters of grinding balls, and the ratio of the larger diameter one to the other, with the difference in the diameters of the two grinding balls being not less than 1 mm, and the large-to-small ball ratio is 1:(2 - 3); the solid-to-liquid ratio after adding absolute ethanol is 1:4 - 4:

1.

4. The preparation method of a carbon-coated modified lithium-ion battery manganese-based cathode material according to claim 1, characterized in that: In steps S2 and S4, the ball-milling times are 8 - 12 h respectively, and the operating speeds are 500 - 550 revolutions per minute respectively; the pause intervals for the two ball-millings are as follows: within the first 1 h of ball-milling operation, pause at the 30th minute and 60th minute respectively, and then pause every 1 h. Each time when pausing, loosen the fixed clamping seat to discharge the gas in the ball-milling tank.

5. The preparation method of a carbon-coated modified lithium-ion battery manganese-based cathode material according to claim 1, characterized in that: In step S3, the temperature of the primary sintering is 300 - 350 °C, and the entire sintering process is carried out under a protective gas atmosphere.

6. The preparation method of a carbon-coated modified lithium-ion battery manganese-based cathode material according to claim 1, characterized in that: In step S4, the mass of the added carbon source is 5 - 35% of the mass of the primary sintered material, and the carbon source is carbon nanotubes or graphene.

7. The preparation method of a carbon-coated modified lithium-ion battery manganese-based cathode material according to claim 1, characterized in that: In step S5, the solid content of the slurry is 5 - 30%, the continuous stirring rate is 200 - 550 r / min, the rotation speed of the peristaltic pump used for spray drying is 5 - 20 rpm, the inlet air temperature of the spray dryer is 220 - 280 °C, and the outlet air temperature is 110 - 130 °C.

8. The preparation method of a carbon-coated modified lithium-ion battery manganese-based cathode material according to claim 1, characterized in that: In step S6, the temperature of the secondary sintering is 650 - 750 °C, and the entire sintering process is carried out under a protective gas atmosphere.