Positive electrode material, preparation method thereof and lithium ion battery

Abstract

A cathode material, a preparation method thereof, and a lithium-ion battery, comprising: uniformly mixing a matrix of the cathode material with a first carbon source, a solvent, and a dispersant to obtain a mixed slurry, and spray-drying the mixed slurry to obtain a precursor of the cathode material; placing the precursor in a reactor, introducing a protective gas and a second carbon source, calcining the precursor once and then cooling to obtain the cathode material. The preparation method of the cathode material provided by this application obtains the cathode material by controlling the primary calcination process, greatly saving the preparation cost of the cathode material; and introducing the second carbon source during calcination can make the carbon film coated on the outer surface of the cathode material more uniform, and the rate performance of the lithium-ion battery prepared by using this cathode material is greatly improved.

Description

Technical Field

[0001] This application relates to the technical field of lithium-ion battery electrode materials, and particularly to a cathode material, a preparation method thereof, and a lithium-ion battery. Background Art

[0002] The development of new energy vehicles has driven the rapid expansion of the battery industry. In particular, the lithium-ion battery industry has continued to develop rapidly, with fierce market competition and an obvious trend of rapid price reduction of lithium-ion batteries. Reducing production costs and improving product performance to increase market competitiveness is of great significance for the long-term development of enterprises.

[0003] As one of the cores of lithium-ion batteries, the cathode material directly affects its performance, cost, lifespan, and safety. In most current preparation methods of cathode materials, in order to enable the outer surface of the cathode material to have a uniform and stable carbon film, multiple sinterings are required. However, the method of multiple sinterings not only greatly increases the preparation cost of the cathode material, but also increases the probability of agglomeration and caking of the cathode material, increasing the difficulty of grinding and crushing the cathode material. Therefore, how to reduce the preparation cost of the cathode material while ensuring uniform coating of the carbon film on the outer surface of the cathode material has become a key issue. Summary of the Invention

[0004] The purpose of this application is to provide a cathode material, a preparation method thereof, and a lithium-ion battery. The preparation method greatly simplifies the production process of the cathode material, and the prepared cathode material has excellent performance.

[0005] To achieve the purpose of this application, the following technical solutions are provided in this application:

[0006] In the first aspect, a preparation method of a cathode material includes: uniformly mixing a matrix of the cathode material with a first carbon source, a solvent, and a dispersant to obtain a mixed slurry, spray-drying the mixed slurry to obtain a precursor of the cathode material; placing the precursor in a reactor, introducing a protective gas and a second carbon source, and after calcining the precursor once and cooling, obtaining the cathode material.

[0007] The cathode material obtained by calcining the precursor once in this application has smaller grain particle size, simplifies the preparation process, reduces the process difficulty, and thus reduces the preparation cost of the cathode material. And a second carbon source is introduced during calcination so that the precursor can be formed into the cathode material through one calcination, avoiding the step of multiple calcinations to ensure the uniformity of the coated carbon film. The carbon film on the outer surface of the obtained cathode material has better uniformity and better electrochemical performance.

[0008] In one embodiment, through the spray drying, the particle size of the precursor is not greater than 2 μm. Through spray drying, the matrix of the cathode material can be uniformly mixed with the first carbon source, and the obtained precursor has a uniform particle structure. Moreover, by controlling the particle size of the precursor, the thickness of the carbon film of the prepared cathode material can be maintained within a suitable range, and the cathode material can have good electrochemical performance.

[0009] In one embodiment, the spraying speed of the spray drying is 10 mL / min - 30 mL / min, and the nozzle diameter of the spray drying is 0.05 mm - 1 mm. The spraying speed is the volume of the mixed slurry passing through at the drying temperature per unit time. At this spraying speed, the volume of the dried mixed slurry per unit time can be maintained within a suitable range, which can ensure that all the mixed slurry can be fully dried at the drying temperature to remove the dispersion liquid. And by controlling the spraying speed within this range, the possibility of phase separation during drying can be reduced, thereby improving the adhesion strength of the first carbon source on the matrix. By controlling the nozzle diameter within a suitable range, it is beneficial to control the particle size of the precursor within a reasonable range and avoid the precursor particle size being too large or too small.

[0010] In one embodiment, the reactor includes any one of a rotary kiln, a rotary furnace, a rotary sintering furnace or a rotary tube furnace, and the precursor rotates in the reactor. By using the reactor and driving the precursor to rotate by the reactor, the precursor can crystallize and react in a rotating state, the precursor is heated more uniformly, the crystallization temperature can be reduced, and the crystallization is more complete. At the same time, all surfaces of the precursor can also be in contact with the second carbon source. Compared with the existing calcination method, the drawback of insufficient calcination is avoided, and the carbon film coating is more uniform.

[0011] In one embodiment, the precursor spirally moves around a central axis within the reactor. The central axis forms an angle with both the horizontal direction and the vertical direction. The second carbon source is introduced from a position higher than the precursor. The reactor can be the rotary kiln mentioned in the above embodiment. The inner cavity of the rotary kiln is cylindrical, and the central axis is a straight line or a curve parallel to the extending direction of the inner cavity. The rotation mode of the reactor can be continuous rotation in the counterclockwise or clockwise direction, or it can be a reciprocating rocking rotation. When the reactor forms an angle with the horizontal direction, after the precursor enters the reactor from a higher point, the reactor can rotate continuously in the clockwise direction, and thus the precursor should rotate and move spirally to the discharge port. Therefore, the reactor can drive the precursor to move spirally. In the rolling state of the precursor, the precursor is heated more evenly, the temperature of the crystallization reaction can be reduced, the crystallization of the cathode material is more complete, and the obtained cathode material can have orientation. At the same time, compared with the method without spiral movement, this calcination method can also make the carbon film coated on the surface of the cathode material more uniform.

[0012] Preferably, the angle between the central axis and the horizontal direction is 5°-10°. It can be understood that one end of the rotary kiln is lifted from the horizontal direction, the feeding port of the precursor can be higher than the discharging port of the cathode material, and the precursor can move downward under the action of gravity in the inner cavity. And because the reactor also drives the precursor to rotate, the precursor can move spirally around the central axis to the discharging port. By designing the angle between the central axis of the reactor and the horizontal direction to be between 5°-10°, the precursor can move forward under the action of gravity in the reactor, and the moving speed of the precursor in the reactor can be controlled within a reasonable range, so that the precursor can be fully calcined at the above temperature. At the same time, it is also possible to avoid using a pushing device and instead use the self-weight of the precursor to complete the movement of the material, saving the preparation cost.

[0013] In one embodiment, the calcination temperature is 300-600 °C and the calcination time is 10-14 h.

[0014] In one embodiment, the second carbon source includes one or more of ethanol, paraffin, propane, n-butane, and n-pentane. The second carbon source can be an aerosol containing a liquid, that is, the liquid is formed into tiny liquid droplets and dispersed in a gas medium. The gas medium can be the protective gas provided in the above embodiment. After the above second carbon source is sprayed above the material, the second carbon source can be deposited on the material under the drive of the air flow. Since the particle size of the second carbon source is smaller after carbonization, it can fully fill the gaps in the formed carbon film, thereby filling the carbon film on the outer surface of the cathode material to ensure the uniformity of the carbon film.

[0015] In one embodiment, the weight of the second carbon source introduced is 0.36 - 0.5 kg, and the introduction rate of the second carbon source is 0.37 - 0.73 g / min.

[0016] In one embodiment, after calcining the precursor at a high temperature, it further includes grinding the positive electrode material with a jet mill.

[0017] In a second aspect, the present application further provides a positive electrode material, and the positive electrode material for a lithium-ion battery is prepared by the preparation method of the positive electrode material according to any one of the first aspect.

[0018] In a third aspect, the present application further provides a lithium-ion battery, and the lithium-ion battery includes the positive electrode material described in the second aspect. Description of the Drawings

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0020] Figure 1 is a process flow chart of the preparation of the positive electrode material in one embodiment;

[0021] Figure 2 is a SEM characterization diagram of the positive electrode material prepared in Example 1 of the present application;

[0022] Figure 3 is a rate performance test diagram of the lithium-ion battery prepared in Application Example 1 of the present application. Detailed Embodiments

[0023] The following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts belong to the scope of protection of the present application.

[0024] It should be noted that when a component is referred to as being "fixed to" another component, it can be directly on the other component or there can also be an intermediate component. When a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be an intermediate component at the same time.

[0025] Unless otherwise defined, all technical and scientific terms used in this application shall have the same meanings as commonly understood by those of ordinary skill in the technical field to which this application pertains. The terms used in the description of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" used in this application includes any and all combinations of one or more of the related listed items.

[0026] The following will describe in detail some embodiments of this application with reference to the accompanying drawings. Without conflict, the following embodiments and the features in the embodiments may be combined with each other.

[0027] An object of this application is to provide a method for preparing a cathode material. By controlling the primary calcination process, this method can obtain the cathode material, and by introducing a second carbon source during calcination, the uniformity of the carbon film coated on the outer surface of the cathode material can be improved, and the rate performance of the lithium-ion battery prepared using this cathode material can be significantly enhanced.

[0028] Please refer to Figure 1 , Figure 1 which is a process flow chart of the cathode material preparation provided by this application, including the following steps:

[0029] Step S01: Uniformly mix the matrix of the cathode material with a first carbon source, a solvent, and a dispersant to obtain a mixed slurry, and perform spray drying on the mixed slurry to obtain a precursor of the cathode material;

[0030] Step S02: Place the precursor in a reactor, introduce a protective gas and a second carbon source, calcine the precursor once and then cool it to obtain the cathode material.

[0031] Specifically, the preparation method provided by this application can be used to prepare cathode materials of transition metal oxides and phosphates, including but not limited to LiCoO 2 , LiNiO 2 , LiNi 1-x-y MnxCo y O 2 , LiMn 2 O 4 , LiFePO 4 , LiMnPO 4 or LiMn x Fe 1-x PO 4 etc. Preferably, this preparation method can be used to prepare the LiMn x Fe 1-x PO 4 cathode material.

[0032] In step S01, the matrix can be a compound containing the elements in the desired cathode material to be prepared. For example, when the cathode material to be prepared is LiMn x Fe 1-x PO 4 , the matrix used can be a lithium source, an iron source, a phosphorus source, and a manganese source. Among them, the lithium source can include Li 2 CO 3 , LiH 2 PO 4 , LiOH·H 2 O, CH 3 COOLi, LiNO 3 or a mixture of one or more of them; the iron source can include Fe(NO 3 ) 3 , Fe 2 O 3 , FeSO 4 ·7H 2 O or a mixture of one or more of them; the phosphorus source can include (NH 4 ) 3 PO 4 , NH 4 H 2 PO 4 , LiH 2 PO 4 , H 3 PO 4 or a mixture of one or more of them; the manganese source can include MnO 2 , Mn(NO 3 ) 2 , MnSO 4 , Mn 3 (PO 4 ) 2 ·3H 2 O or a mixture of one or more of them. It can be understood that the above compounds are only partial examples of the compounds that can be used to prepare the LiMn x Fe 1-x PO 4 cathode material. In other embodiments, other compounds can also be used to prepare this cathode material, or other cathode materials among the above, and specific limitations are not made.

[0033] In this embodiment, the first carbon source may include one or a mixture of glucose, sucrose, PVDF, carbon black, PEG, paraffin, graphite, graphene, etc. The solvent may be water, ethanol, methanol, etc. The matrix material of the positive electrode material and the first carbon source are added to the solvent, and the matrix material and the first carbon source can be fully mixed evenly by manual stirring or mechanical stirring to obtain a mixed slurry. The mixed slurry may be a clear solution or a slightly turbid liquid. Preferably, the mixed slurry is a clear solution. Then, the above-mentioned mixed slurry can be spray-dried to obtain a precursor for preparing the positive electrode material.

[0034] The purpose of this step is to fully mix all the raw materials of the matrix, the first carbon source, the dispersant and the solvent evenly into a solution to ensure the best performance of the positive electrode material prepared in the subsequent steps. In one embodiment, the dispersion used may be water, preferably deionized water or ultrapure water. Compared with ethanol or methanol-based dispersions, water has a lower cost, is easier to obtain, and has higher safety. It can be understood that both the above-mentioned matrix and carbon source can be powder materials. Compared with the direct mixing method of solids, dispersing them in the dispersion can enable the matrix and carbon source to be in full contact and mixing, and the mixing effect is better.

[0035] The purpose of spray-drying the mixed slurry is, on the one hand, to remove the solvent to obtain solid powder; on the other hand, it can also control the particle size of the obtained precursor, which helps all the precursors to be converted into the target crystal structure during calcination.

[0036] In step S02, the reactor used may be a high-temperature furnace, and the temperature provided by the reactor can reach above 1000 °C, so that the dried precursor can be reacted by high-temperature calcination to obtain the required positive electrode material. Further, a protective gas can be introduced into the reactor, and the protective gas can be nitrogen, argon, etc. The function of the protective gas is to create an oxygen-free environment to avoid the oxidation of the precursor at high temperature.

[0037] In this embodiment, the second carbon source may be an aerosol, which can be understood as dispersing a liquid or solid carbon source in a gas medium. The density of the liquid or solid particles may be slightly different or very different from the density of the gas medium. The purpose of using the second carbon source in this application is to supplement the first carbon source in step S01. In the preparation of existing positive electrode materials, there are often phenomena such as uneven carbon film wrapping or cracks on the carbon film. By introducing the second carbon source during the calcination process in this application, the small characteristics of the second carbon source can be used to fill and smooth the cracks or unevenness on the carbon film during the calcination process, so that the carbon film wrapped on the surface of the obtained positive electrode material is more uniform.

[0038] In this embodiment, after calcining the precursor, the discharge temperature of the reactor can be controlled at 60 °C or below, thereby avoiding oxidation of the material due to contact with oxygen at too high a temperature.

[0039] The cathode material obtained by calcining the precursor once in this application has smaller grain particle sizes, simplifies the preparation process, reduces the process difficulty, and thus reduces the preparation cost of the cathode material. And a second carbon source is introduced during calcination so that the precursor can be formed into the cathode material by one-time calcination molding, avoiding the steps of multiple calcinations to ensure the uniformity of the coated carbon film. The carbon film on the outer surface of the obtained cathode material has better uniformity and better electrochemical performance.

[0040] In one embodiment, in step S01, the mixed slurry can be spray-dried by a spray dryer to obtain a precursor with a particle size not greater than 2 μm. Specifically, during the calcination process of the precursor, the carbon source can be coated on the surface of the matrix material at high temperature to form a carbon film. The purpose of controlling the particle size of the granulated precursor below 2 μm is to fully convert the precursor into the target crystal during the subsequent roasting process. The matrix material and the organic carbon source will dissolve in the solvent, while the inorganic carbon source will cause the solution to become slightly turbid. The inorganic carbon source particles cannot be too large, on the one hand, it will block the nozzle, and on the other hand, it will affect the coating effect. Compared with ordinary drying, spray drying has the function of granulation, which can reduce the size of the finished product particles to a certain extent and the morphology is relatively regular; compared with the direct dry mixing of solid matrix materials, the obtained cathode material has better purity, stability, smaller particles, and better electrical properties.

[0041] In one embodiment, the temperature of the spray drying is 100 °C - 130 °C, the spraying speed is 10 mL / min - 30 mL / min, and the nozzle diameter of the spray drying is 0.05 mm - 1 mm. The boiling point of the dispersion liquid provided in the above embodiment is below 100 °C. Therefore, in order to fully remove the dispersion liquid in the mixed slurry to obtain the precursor, the temperature of the drying spray dryer can be set above 100 °C and not higher than 130 °C. When the drying temperature is lower than the lower limit of this range, the drying temperature is insufficient, which will cause insufficient removal of the dispersion liquid, and a large number of droplets will appear in the drying chamber, failing to achieve the purpose of drying. When the drying temperature is higher than the upper limit of this range, it may cause the mixed slurry to be overheated and oxidized.

[0042] In this embodiment, the spraying rate is the volume that the mixed slurry passes through at the drying temperature per unit time. At this spraying rate, the volume of the mixed slurry is maintained within a suitable range, which can ensure that all the mixed slurry can be fully dried at the drying temperature to remove the dispersion liquid. And by controlling the spraying rate within this range, the possibility of phase separation during drying can be reduced, thereby improving the adhesion strength of the first carbon source on the substrate. When the spraying rate is lower than the lower limit of this range, too little mixed slurry is dried per unit time, and fewer precursors are obtained, resulting in a reduction in preparation efficiency; when the spraying rate is higher than the upper limit of this range, too much mixed slurry is dried per unit time, which may lead to insufficient drying, and a small amount of dispersion liquid will be contained in the precursor.

[0043] Of course, in other embodiments, the temperature and spraying rate of spray drying can also be adjusted according to actual needs. For example, when the dispersion liquid used is methanol or a dispersion liquid with too low a boiling point, the temperature of spray drying can be lower than 100 °C, such as 95 °C, 90 °C or 85 °C. The spraying rate can be higher than 30 mL / min, such as 33 mL / min, 37 mL / min or 45 mL / min. Because the boiling point of the dispersion liquid is relatively low and the evaporation rate of the dispersion liquid is relatively fast, appropriately reducing the drying temperature or spraying rate is beneficial to reducing the energy consumption cost and increasing the yield.

[0044] The nozzle diameter of spray drying should be the nozzle diameter of the spray dryer used. By restricting the nozzle diameter, the particle size of the obtained precursor can be controlled. When the nozzle diameter is higher than the upper limit of this range, the particle size of the obtained precursor is relatively large, which will cause the thickness of the formed carbon film to be relatively large, that is, the overall particle size of the prepared cathode material will also be slightly larger, affecting the electrochemical performance of the finished product. Preferably, the nozzle diameter can be 0.5 mm.

[0045] In one embodiment, after spray drying, a sieving process can also be used to further screen the precursor particles. The mesh number of the sieve used can be 5000 mesh or more, and is used to screen out precursor particles with a particle size of less than 2 μm.

[0046] In one embodiment, the reactor includes any one of a rotary kiln, a rotary furnace, a rotary sintering furnace or a rotary tube furnace, and the precursor rotates inside the reactor. Specifically, the reactor should be a tubular structure that can rotate internally. The precursor can be placed into one end of the reactor, and the rotation inside the reactor drives the precursor to rotate inside the tube. High temperature can be generated inside the reactor for calcining the precursor to obtain the cathode material. Among the above types of reactors, the precursor can rotate and move forward inside the rotary kiln or rotary furnace, rotating and moving from one end of the rotary kiln to the relatively farthest end. That is, the moving speed and the moving distance are the calcination time. For example, after the precursor is placed into the reactor, the reactor can be sealed, a protective gas can be introduced, and the self-rotation speed of the reactor can be set to 0.3 - 1.5 r / min to control the rotation of the precursor in the reactor so that each side of the precursor can contact the introduced second carbon source. Then, a pushing device or the self-gravity of the precursor is used to drive the precursor to move to the farthest end. After determining the moving speed and the moving distance, the obtained cathode material can be taken out from the other end.

[0047] Meanwhile, in this embodiment, the reactor can be set to a constant temperature mode or a stepped temperature increase mode. In the constant temperature mode, the temperature inside the reactor is always maintained at a constant setting, which can be 300 °C, 400 °C or 500 °C. The calcination temperature that the precursor experiences during the movement and rotation is balanced. Of course, in the stepped temperature increase mode, the temperature inside the reactor can be set to increase step by step starting from the feeding direction, with temperature segments of 300 °C, 400 °C and 500 °C respectively. The calcination temperature that the precursor experiences during the movement and rotation increases gradually. The stepped temperature increase method can remove the volatile components in the precursor through low-temperature pre-calcination and improve the final electrochemical performance of the cathode material.

[0048] In one embodiment, the precursor can also only rotate in the reactor without moving in a certain direction. For example, after the precursor is placed into the reactor, the reactor can be sealed, a protective gas can be introduced, and the self-rotation speed of the reactor can be set to 0.3 - 1.5 r / min to control the rotation of the precursor in the reactor so that each side of the precursor can contact the introduced second carbon source. And after the calcination is completed, the reactor can be opened and the obtained cathode material can be taken out.

[0049] Meanwhile, in this embodiment, the reactor can be in a constant-temperature mode or a heating-up mode. In the constant-temperature mode, the temperature inside the reactor is always maintained at a constant set value, which can be 300 °C, 400 °C or 500 °C. The calcination temperature that the precursor receives during rotation is balanced. Of course, in the heating-up mode, the reactor can be set to heat up from room temperature after the precursor is put in, and the heating rate can be 5 °C / min, 20 °C / min or 50 °C / min until it reaches 500 °C or other temperature, and then calcine at a constant temperature. The heating method can remove impurities in the precursor through low-temperature pre-calcination and improve the purity of the cathode material.

[0050] By using the reactor and driving the precursor to rotate with the reactor, the precursor can crystallize and react in a rotating state. The precursor is heated more evenly, the crystallization temperature can be reduced, and the crystallization is more complete. At the same time, all surfaces of the precursor can be in contact with the second carbon source. Compared with the existing calcination method, the disadvantage of insufficient calcination is avoided, and the carbon film coating is more uniform.

[0051] In one embodiment, the precursor moves spirally around a central axis inside the reactor. The central axis has an angle with both the horizontal direction and the vertical direction. The second carbon source is introduced from a position higher than the precursor. Specifically, the reactor can be the rotary kiln mentioned in the above embodiment. The inner cavity of the rotary kiln is cylindrical, and the central axis is a straight line or a curve parallel to the extension direction of the inner cavity. The angle between the central axis and the horizontal direction can be 5° - 10°. It can be understood that one end of the rotary kiln is lifted from the horizontal direction, the feed port of the precursor can be higher than the discharge port of the cathode material, and the precursor can move downward under the action of gravity in the inner cavity. And because the reactor also drives the precursor to rotate, the precursor can move spirally around the central axis to the discharge port. The design method of this step can avoid using a pushing device, but use the self-weight of the precursor to complete the movement of the material, saving the preparation cost. At the same time, after the material moves automatically, other process equipment, such as a crushing device or a screening device, can be set at the discharge port to directly crush or screen the obtained cathode material. In this way, the cost of manual material transportation is reduced, and the degree of automation is improved. By driving the precursor to move spirally with the reactor, in the rolling state of the precursor, the precursor is heated more evenly, the temperature of the crystallization reaction can be reduced, the crystallization of the cathode material is more complete, and the obtained cathode material can have orientation; at the same time, compared with the method without spiral movement, this calcination method can also make the carbon film coated on the surface of the cathode material more uniform.

[0052] Moreover, by setting the angle between the central axis and the horizontal direction, the moving speed of the precursor in the reactor can also be controlled. It can be understood that the larger the angle, the faster the moving speed of the precursor, and the smaller the angle, the slower the moving speed of the precursor. When the length of the reactor used is fixed, the angle can be adjusted within a suitable range so that the time for the precursor to pass through the reactor is within the required calcination time. This overcomes the drawback of the fixed specifications of the existing reactors.

[0053] In one embodiment, the rotation mode of the reactor can be continuous counterclockwise or clockwise rotation, or it can be reciprocating swinging rotation. Specifically, when there is an angle between the reactor and the horizontal direction, after the precursor enters the reactor from a higher point, the reactor can rotate continuously clockwise, and thus the precursor should move in a spiral rotation to the discharge port. Of course, the reactor can also be in a swinging rotation, and the precursor can move to the discharge port by intermittent clockwise or counterclockwise rotation.

[0054] In one embodiment, the second carbon source is introduced from a position higher than the precursor. That is, the injection port of the second carbon source can be located at the top of the inner cavity, and compared with the horizontal plane, the second carbon source is sprayed downward from a position higher than the precursor. During the rotation of the precursor, the second carbon source can evenly fall on the precursor. Compared with the way of introducing from the side in parallel or from the bottom, the second carbon source introduced in this way can be more uniform.

[0055] In one embodiment, the calcination temperature is 300 - 600 °C, and the calcination time is 10 - 14 h. Specifically, high-temperature calcination is the key to the crystal growth of the material, and the precursor needs to absorb a certain amount of energy before it can be completely crystallized. Compared with the existing preparation method of the cathode material, in this application, the second carbon source is added in one calcination, and the second carbon source can be used to fill the carbon film on the outer surface of the cathode material due to its small size and good dispersibility, so the process steps of filling the carbon film through secondary or multiple calcination are avoided. It can be understood that the higher the calcination temperature, the higher the energy absorbed by the precursor, and the better the effect of the second carbon source covering and forming a film. When the calcination temperature is lower than the lower limit of this range, the calcination temperature is insufficient, the crystallization effect of the cathode material is poor, and the electrochemical performance of the prepared lithium-ion battery is reduced. When the calcination temperature is higher than the upper limit of this range, the primary particle size of the prepared product is too large and the aggregation is serious, affecting the electrical performance of the product.

[0056] In one embodiment, the second carbon source includes one or more of ethanol, paraffin, propane, n-butane, and n-pentane. Specifically, the second carbon source may be an aerosol containing a liquid, that is, the liquid is formed into tiny liquid droplets and dispersed in a gas medium. The gas medium may be the protective gas provided in the above embodiment. After the second carbon source is sprayed above the material, the second carbon source can be deposited on the material under the drive of the air flow. Since the particle size of the second carbon source is smaller after carbonization, it can be fully filled into the gaps of the formed carbon film, thereby filling the carbon film on the outer surface of the cathode material and ensuring the uniformity of the carbon film.

[0057] Of course, in other embodiments, the second carbon source may also be an aerosol containing a solid, that is, solid fine particles are dispersed in a gas medium. The second carbon source may include carbon black, graphite, carbon nanotubes, fullerenes, graphene, etc. It can be understood that the above solid carbon materials are light in weight and small in size, and are extremely easy to be dispersed in a gas medium to form an aerosol. And the size of the solid carbon materials in the aerosol should be smaller than the size of the solid carbon source, so as to be able to fill the carbon film. When using such an aerosol as the second carbon source, it can be added at various positions in the reactor, and this type of second carbon source does not need to consider volatility and has a higher safety factor.

[0058] In one embodiment, the weight of the second carbon source introduced is 0.36 - 0.5 kg, and the introduction speed of the second carbon source is 0.37 - 0.73 g / min. The role of the second carbon source is to supplement the first carbon source, so the second carbon source should be controlled within a suitable range to avoid being too much or too little. The weight of the second carbon source should be the actual weight of the liquid or solid contained in the aerosol. When the weight of the second carbon source meets this range, the thickness of the carbon source coated on the outer surface of the cathode material is appropriate, and the lithium-ion battery prepared using this cathode material has higher electrical performance. When the weight of the second carbon source is lower than the lower limit of this range, the filling of the carbon film by the second carbon source is insufficient, the thickness of the carbon film is small and the uniformity is poor, and the electrical performance of the lithium-ion battery prepared using this cathode material is reduced; when the weight of the second carbon source is higher than the upper limit of this range, the filling of the carbon film by the second carbon source is excessive, the thickness of the carbon film is thick, which hinders the diffusion of lithium ions during charging and discharging, and the electrical performance is reduced.

[0059] In this embodiment, the feeding rate of the second carbon source can also affect the carbon film coated on the cathode material. When the feeding rate of the second carbon source meets this range, the feeding rate of the second carbon source and the rotation speed of the reactor are within a suitable proportional range, and the ratio of each side of the precursor that can contact the second carbon source during rotation is balanced. Therefore, the uniformity of the carbon film can be increased. When the feeding rate of the second carbon source is lower than the lower limit of this range, the feeding mass of the second carbon source is insufficient during the calcination time, resulting in a thinner carbon film or poor uniformity. When the feeding rate of the second carbon source is higher than the upper limit of this range, the mass of the second carbon source fed per unit time is too high, easily causing the carbon source to deposit on some surfaces of the cathode material, that is, the uniformity of the carbon film is poor and the thickness is too thick.

[0060] In other embodiments, when using an aerosol containing solids as the second carbon source, the weight of the second carbon source fed should be based on the weight of the solids in the aerosol. And compared with the liquid of the same volume, the solid has a greater density and weight. Therefore, the feeding rate of this type of second carbon source can be lower or higher.

[0061] In one embodiment, the method for preparing the cathode material provided by the present application may further include:

[0062] Step S03, pulverize the cathode material by a jet mill. Specifically, the cathode material can be pulverized by a jet mill through a jet mill. The jet mill can compress gas and use the pressure difference generated by the compressed gas to eject the cathode material. The compressed air flow can carry the cathode material to move at a high speed, so that strong collisions, frictions and shears can occur between the cathode materials to achieve the purpose of pulverization. The purpose of using this step is to decompose the cathode material agglomerates obtained after calcination, which is convenient for subsequent battery preparation and processing, and has a certain positive effect on the electrochemical performance.

[0063] In addition, the present application also provides a cathode material, which is prepared by the method for preparing the cathode material in any of the above embodiments. The cathode material can be in the form of nanoparticles, and its outer surface can be coated with a carbon film.

[0064] On the other hand, the present application also provides a lithium-ion battery and a method for preparing a lithium-ion battery, including the following steps:

[0065] Step S101, provide the cathode material, conductive agent, and binder prepared in the above embodiments, and uniformly mix them in a solvent to obtain a cathode slurry.

[0066] Step S102, coat the cathode slurry on an aluminum foil, and obtain a cathode sheet after drying and embossing.

[0067] Step S103, assemble the cathode sheet, anode sheet, separator, and electrolyte to obtain a lithium-ion battery.

[0068] The technical solution of the present invention will be described in detail below through specific embodiments.

[0069] Example 1

[0070] This example provides a method for preparing a cathode material, specifically granular LiMn 0.05 Fe 0.95 PO 4 , including the following steps:

[0071] (1) Take 3.60 kg of LiNO 3 , 11.98 kg of Fe(NO 3 ) 3 , 6.00 kg of NH 4 H 2 PO 4 , 0.47 kg of Mn(NO 3 ) 2 , 1.10 kg of sucrose, and 13.23 kg of water, mix them evenly to obtain a mixed slurry in a clear solution state. Place the mixed slurry in a spray dryer for spray drying to obtain a precursor, and the particle size is 1.4 μm;

[0072] (2) The precursor is fed into the rotary kiln from the feeding port. The atmosphere in the kiln is nitrogen. 0.44 kg of n-pentane is sprayed downward from the upper part of the drum. The precursor rolls forward under the drive of the drum in the rotary kiln, stays in the constant temperature heating zone at 450 °C for 13 h, and is uniformly coated with a carbon film, and then enters the cooling zone and is cooled to below 60 °C;

[0073] (3) The obtained cathode material is pulverized by a jet mill and then obtained by filtration and screening to obtain the active component of LiMn 0.05 Fe 0.95 PO 4 .

[0074] Figure 2 is the SEM characterization diagram of the cathode material (LiMn 0.05 Fe 0.95 PO 4 ) prepared in Example 1. It can be seen from the figure that the obtained cathode material is nano-granular with oriented growth, and the longest size of the crystal grains is about 150 nm.

[0075] In this example, the inlet air temperature of the spray dryer used is 130 °C, the nozzle size is 0.5 mm, and the spraying speed is 20 ml / min.

[0076] In this example, the thickness of the carbon film coated on the obtained cathode material is about 2 nm, and specific details can be seen in Table 1.

[0077] Example 2

[0078] This example provides a method for preparing a cathode material, specifically granular LiMn 0.8 Fe 0.2 PO 4 , which includes the following steps:

[0079] (1) Take 3.60 kg of LiNO 3 , 2.52 kg of Fe(NO 3 ) 3 , 6.00 kg of NH 4 H 2 PO 4 , 7.47 kg of Mn(NO 3 ) 2 , 1.10 kg of sucrose, and 13.23 kg of water, mix them evenly to obtain a mixed slurry in a clear solution state. Place the mixed slurry in a spray dryer for spray drying to obtain a precursor, and the particle size is 1.4 μm;

[0080] (2) The precursor is fed into the rotary kiln from the feeding port. The atmosphere in the kiln is nitrogen. 0.44 kg of n-pentane is sprayed downward from the upper part of the drum. The precursor rolls forward under the drive of the drum in the rotary kiln, stays in the constant temperature heating zone at 450 °C for 13 h, and is evenly coated with a carbon film, and then enters the cooling zone and is cooled to below 60 °C;

[0081] (3) The obtained cathode material is pulverized by a jet mill and then obtained as the active component of LiMn 0.8 Fe 0.2 PO 4 through filtration and screening.

[0082] In this example, the inlet air temperature of the spray dryer used is 130 °C, the nozzle size is 0.5 mm, and the spraying speed is 20 ml / min.

[0083] In this example, the thickness of the carbon film coated on the obtained cathode material is about 2 nm, and specific details can be seen in Table 1.

[0084] Example 3

[0085] This example provides a method for preparing a cathode material, specifically granular LiMn 0.8 Fe 0.2 PO 4 . The difference between the preparation method and that of Example 2 is only that step (1) is replaced with: the nozzle size is 0.3 mm, and the particle size of the obtained precursor is 1.1 μm.

[0086] In this example, the thickness of the carbon film coated on the obtained cathode material is about 2 nm, and specific details can be seen in Table 1.

[0087] Example 4

[0088] This example provides a preparation method of a cathode material, specifically granular LiMn 0.8 Fe 0.2 PO 4 , the difference between the preparation method and that of Example 2 is only that step (1) is replaced with: the nozzle size is 0.6 mm, and the particle size of the obtained precursor is 1.6 μm.

[0089] In this example, the thickness of the carbon film coated on the obtained cathode material is about 2.1 nm, and specific values can be seen in Table 1.

[0090] Example 5

[0091] This example provides a preparation method of a cathode material, specifically granular LiMn 0.05 Fe 0.95 PO 4 , the difference between the preparation method and that of Example 2 is only that step (2) is replaced with: the precursor rolls forward driven by the roller in the rotary kiln and stays in the constant temperature heating zone at 500 °C for 11 h.

[0092] In this example, the thickness of the carbon film coated on the obtained cathode material is about 2 μm, and specific values can be seen in Table 1.

[0093] The present invention also provides a comparative example.

[0094] Comparative Example 1

[0095] This example provides a preparation method of a cathode material, specifically granular LiMn 0.05 Fe 0.95 PO 4 , the difference between the preparation method and that of Example 1 is only that step (1) is replaced with: taking 3.60 kg of LiNO 3 , 11.98 kg of Fe(NO 3 ) 3 , 6.00 kg of NH 4 H 2 PO 4 , 0.47 kg of Mn(NO 3 ) 2 , 1.10 kg of sucrose, and 13.23 kg of water are mixed evenly. The inlet air temperature of the spray dryer used is 130 °C, the nozzle size is 1.5 mm, and the spraying speed is 20 ml / min, obtaining precursor particle size of 5 μm.

[0096] In this embodiment, the thickness of the carbon film coated on the positive electrode material is about 2.4 nm, which is thicker than that in Embodiment 1. Specifically, please refer to Table 1.

[0097] Comparative Example 2

[0098] This embodiment provides a method for preparing a positive electrode material, specifically granular LiMn 0.05 Fe 0.95 PO 4 , and the difference between the preparation method and that of Embodiment 1 is only that step (2) is replaced with: the precursor is fed into the rotary kiln from the feeding port, the inside of the kiln is an inert atmosphere, 0.05 kg of n-pentane is sprayed downward from the upper part of the drum, the precursor rolls forward under the drive of the drum in the furnace, stays in the constant temperature heating zone at 450 °C for 13 h, and is evenly coated with a carbon film and then enters the cooling zone.

[0099] In this embodiment, the thickness of the carbon film coated on the positive electrode material is between 1.7 nm and 2.0 nm, which is thinner than that in Embodiment 1, and the thickness uniformity of the carbon film is poor, and the difference in the carbon film thickness measured at different positions is relatively large. Specifically, please refer to Table 1.

[0100] Comparative Example 3

[0101] This embodiment provides a method for preparing a positive electrode material, specifically granular LiMn 0.05 Fe 0.95 PO 4 , and the difference between the preparation method and that of Embodiment 1 is only that step (2) is replaced with: the precursor is fed into the rotary kiln from the feeding port, the inside of the kiln is an inert atmosphere, 0.7 kg of n-pentane is sprayed downward from the upper part of the drum, the precursor rolls forward under the drive of the drum in the furnace, stays in the constant temperature heating zone at 450 °C for 13 h, and is evenly coated with a carbon film and then enters the cooling zone.

[0102] In this embodiment, the thickness of the carbon film coated on the positive electrode material is about 2.2 nm, which is thicker than that in Embodiment 1. Specifically, please refer to Table 1.

[0103] Table 1

[0104]

[0105] Table 1 shows the detection of the carbon film thickness of the positive electrode material prepared in the above embodiments of the present application. Positions 1, 2, and 3 are the carbon film thicknesses at different positions of the positive electrode material under this embodiment. It can be seen from Embodiments 1-2 that when using this method to prepare positive electrode materials with different components, under the condition that various parameters remain unchanged, the carbon film thicknesses of the obtained positive electrode materials are close. Therefore, it shows that this method can be applied to positive electrode materials with various components.

[0106] From Examples 2-4, Example 1 and Comparative Example 1, it can be seen that precursors with different particle sizes can be obtained by controlling the nozzle diameter. The particle sizes of the granulated precursors in Examples 2-4 are relatively close. Finally, after high-temperature calcination and pulverization, the carbon film thickness of the primary particle size of the active component of the obtained cathode material has a relatively small difference; while the particle sizes of the granulated precursors in Example 1 and Comparative Example 1 are quite different, and the carbon film thickness of the primary particle size of the obtained cathode material has a large difference. In both comparison groups, there is a trend that as the particle size of the granulated precursor increases, the carbon layer of the primary crystal grains in the finished product becomes thicker.

[0107] From Example 1 and Comparative Examples 2-3, it can be seen that cathode materials with different carbon film thicknesses can be obtained by controlling the dosage of the second carbon source. Comparative Example 2 is an example where the second carbon source is used in step (2) below the provided range. Comparative Example 3 is an example where the second carbon source is used above the provided range. From the test results, it can be concluded that when the mass of the second carbon source is within the compliant range, the carbon film coated on the obtained cathode material has good uniformity and appropriate thickness. However, when the dosage of the second carbon source is below the range, the carbon film is thinner and the thickness is uneven, and when it is above the range, the carbon film is thicker, resulting in a decline in electrical performance.

[0108] Effect Example

[0109] This example provides a preparation method for a lithium-ion battery, including the following steps:

[0110] 800 g of the cathode materials of Example 1-2 and Comparative Examples 1-3, 100 g of conductive agent acetylene black, and 100 g of binder (polyvinylidene fluoride PVDF) were respectively added to 800 g of N-methylpyrrolidone solvent (NMP solvent), and stirred in a vacuum mixer for 2 h to prepare a cathode slurry.

[0111] The slurry was evenly coated on aluminum foil, then placed in a vacuum drying oven and dried at 120 °C for 12 h, and after rolling, it was punched into circular sheets with a diameter of 14 mm as the cathode sheets.

[0112] The cathode sheets, anode sheets (metal lithium sheets with a diameter of 14.5 mm), separators, and electrolytes (1 mol / L LiPF6 / EC+DMC (volume ratio 1:1)) were assembled into five lithium-ion batteries in a glove box filled with an inert atmosphere.

[0113] Moreover, the rate performance of the above five lithium-ion batteries was tested. The specific test conditions were as follows: under the condition of 25 ± 0.5 °C, the charge and discharge tests were carried out using a lithium-ion battery charge and discharge test system. Charge and discharge conditions: charge termination voltage 4.3 V; discharge termination voltage 2.00 V; charge and discharge current density: 1C, 2C, 3C, 5C, 10C.

[0114] Figure 3It is the rate performance test chart of the lithium-ion battery prepared with the cathode material in Example 1 obtained under this test condition. Among them, the discharge specific capacities at 1C, 2C, 3C, 5C, and 10C are 154.8 mAh / g, 151.3 mAh / g, 148.6 mAh / g, 143.6 mAh / g, and 128.6 mAh / g respectively.

[0115] Table 2 shows the comparison of the discharge specific capacities at 1C of five lithium-ion batteries obtained under this test condition. Among them, Effect Example 1 is the lithium-ion battery prepared with the cathode material in Example 1. Correspondingly, the other Effect Examples or Effect Comparative Examples correspond to the above-mentioned Examples or Comparative Examples.

[0116] Table 2

[0117]

[0118] In the description of the embodiments of the present application, it should be noted that the orientation or positional relationship indicated by terms such as "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or component referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present application.

[0119] The above-disclosed is only a preferred embodiment of the present application. Of course, it cannot be used to limit the scope of rights of the present application. Those of ordinary skill in the art can understand the entire or part of the process of implementing the above embodiments, and the equivalent changes made according to the claims of the present application still fall within the scope covered by the application.

Claims

1. A method for preparing a cathode material, characterized in that, comprising: uniformly mixing a matrix of the cathode material with a first carbon source, a solvent and a dispersant to obtain a mixed slurry, and subjecting the mixed slurry to spray drying to obtain a precursor of the cathode material; placing the precursor in a reactor, introducing a protective gas and a second carbon source, calcining the precursor once and then cooling to obtain the cathode material; the second carbon source is an aerosol, and the aerosol is a carbon source in which liquid beads and / or solid fine particles are dispersed in a gas medium; the feeding rate of the second carbon source is 0.37 g / min - 0.73 g / min; the calcination temperature is 300°C - 600°C.

2. The method for preparing a cathode material according to claim 1, characterized in that, by the spray drying, the particle size of the obtained precursor is not greater than 2 μm.

3. The method for preparing a cathode material according to claim 2, characterized in that, the spraying rate of the spray drying is 10 mL / min - 30 mL / min, and the nozzle diameter of the spray drying is 0.05 mm - 1 mm.

4. The method for preparing a cathode material according to claim 1, characterized in that, the reactor includes any one of a rotary kiln, a rotary furnace, a rotary sintering furnace or a rotary tube furnace, and the precursor rotates in the reactor.

5. The method for preparing a cathode material according to claim 4, characterized in that, the precursor spirally moves around a center line in the reactor, the center line has an angle with both the horizontal direction and the vertical direction, and the second carbon source is introduced from a position higher than the precursor.

6. The method for preparing a cathode material according to claim 1, characterized in that, the calcination time is 10 h - 14 h.

7. The method for preparing a cathode material according to claim 1, characterized in that, the second carbon source includes one or more of ethanol, paraffin, and n-pentane.

8. The method for preparing a cathode material according to claim 1, characterized in that, after calcining the precursor at a high temperature, it further includes pulverizing the cathode material by a jet mill.

9. A cathode material, characterized in that, the cathode material is prepared by the method for preparing a cathode material according to any one of claims 1 - 8.

10. A lithium ion battery, characterized in that, the lithium ion battery includes the cathode material according to claim 9.

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