Positive electrode active material and preparation method, electrode sheet, energy storage device, and electric device

Abstract

Provided are a positive electrode active material and a preparation method, an electrode sheet, an energy storage device, and an electric device. The positive electrode active material comprises LiMnaFe1-a-b-cM1bM2cPO4, wherein 0＜a≤0.8, 0＜b≤0.1, 0＜c≤0.1, M1 comprises titanium element, and M2 comprises aluminum element. The positive electrode active material is granular; and the doping amount of titanium element in the central region of a positive electrode active material particle is greater than that in the surface layer of the positive electrode active material particle, and the doping amount of aluminum element in the central region of a positive electrode active material particle is less than that in the surface layer of the positive electrode active material particle. The positive electrode active material has both relatively high structural thermal stability and relatively low impedance, and is beneficial to considering both the safety performance and electrochemical performance of a battery.

Description

Positive electrode active material and preparation method, pole piece, energy storage device and power device Technical Field

[0001] The present application belongs to the field of batteries, and specifically relates to positive electrode active materials and preparation methods, pole pieces, energy storage devices and power-consuming devices. Background Art

[0002] Commonly used cathode active materials for batteries include nickel-cobalt-manganese ternary materials, lithium iron phosphate, and lithium iron manganese phosphate. Lithium iron phosphate has an olivine-type crystal structure. Compared with nickel-cobalt-manganese ternary materials, lithium iron phosphate has better structural stability, which translates to better safety, but also has lower energy density. Lithium iron manganese phosphate shares a similar crystal structure with lithium iron phosphate, offering not only greater structural stability but also a higher energy density than lithium iron phosphate, showing promising development prospects.

[0003] Summary of the Invention

[0004] This application is mainly based on the following questions and findings:

[0005] Although lithium manganese iron phosphate has a relatively stable crystal structure and a high energy density, it has the following shortcomings: 1) The electrical conductivity and ion diffusion coefficient of lithium manganese iron phosphate are low, which affects the speed of battery charging and discharging and increases the heat generated by the battery; 2) When the material undergoes the Jan-Taylor effect, the crystal structure is distorted, which easily leads to manganese dissolution, which not only deteriorates the structural stability of the material, but also affects the cycle performance of the battery; 3) When the battery experiences thermal runaway, the lithium manganese iron phosphate material is easily decomposed by heat and reacts with the electrolyte to release heat, which will further accelerate the thermal runaway process of the battery and easily cause the battery to burn or even explode. At present, the main method to improve the structural thermal stability of the material is to perform multi-element blending or coating treatment on lithium manganese iron phosphate, but the degree of improvement is limited. In order to pursue high battery safety, it is necessary to further explore ways to improve lithium manganese iron phosphate.

[0006] This application aims to address, at least to some extent, one of the technical problems in the related art. To this end, one objective of this application is to provide a positive electrode active material and preparation method, a pole piece, an energy storage device, and an electrical device. This positive electrode active material combines high structural thermal stability with low impedance, which helps balance the safety and electrochemical performance of the battery.

[0007] In a first aspect of the present application, the present application provides a positive electrode active material. According to an embodiment of the present application, the positive electrode active material includes:

[0008] LiMn a Fe 1-a-b-c M1 b M2 c PO4,

[0009] Among them, 0 < a ≤ 0.8, 0 < b ≤ 0.1, 0 < c ≤ 0.1, M1 includes titanium element, M2 includes aluminum element, the positive electrode active material is granular, the doping amount of the titanium element in the central region of the positive electrode active material particles is greater than that in the surface layer of the positive electrode active material particles, and the doping amount of the aluminum element in the central region of the positive electrode active material particles is less than that in the surface layer of the positive electrode active material particles.

[0010] The positive electrode active material according to the above embodiments of the present application has at least the following beneficial effects: 1) Doping titanium element in lithium iron phosphate manganese, and controlling the doping amount of the titanium element in the central region of the positive electrode active material particles to be greater than that in the surface layer of the positive electrode active material particles is beneficial to improving the conductivity and ion diffusion coefficient in the central region of the positive electrode active material, reducing the material impedance, improving the conductivity of the battery, and can also improve the structural stability of the positive electrode active material to a certain extent, reducing the side reaction with the electrolyte and its heat generation value; 2) Doping aluminum element in lithium iron phosphate manganese, and controlling the doping amount of the aluminum element in the central region of the positive electrode active material particles to be less than that in the surface layer of the positive electrode active material particles is beneficial to inhibiting the Jahn-Teller effect, reducing the risk of lattice distortion of the material, reducing the side reaction with the electrolyte and its heat generation value, improving the structural stability of the positive electrode active material, and improving the cycle performance; 3) Doping titanium element and aluminum element simultaneously, and controlling the distribution of the above elements can improve the thermal stability of the material, reduce the heat generation value of the reaction between the material and the electrolyte when the battery cell gets out of control, fundamentally reduce the generation and accumulation of heat, and improve the safety performance of the battery. In summary, the positive electrode active material has both high structural thermal stability and low impedance, which is beneficial to balancing the safety performance and electrochemical performance of the battery.

[0011] In the second aspect of the present application, the present application proposes a method for preparing the above positive electrode active material. According to the embodiments of the present application, the method includes: mixing a phosphorus source, a manganese source, an iron source, a lithium source, a titanium source, an aluminum source with a solvent to obtain multiple groups of salt solutions, the multiple groups of salt solutions include the first salt solution, ……, the nth salt solution, in the first salt solution, ……, the nth salt solution, the concentration of titanium ions decreases in sequence, and the concentration of aluminum ions increases in sequence, n is a positive integer not less than 2; adding the first salt solution, ……, the nth salt solution into a precipitating agent and a complexing agent in a segmented and stepwise manner for coprecipitation reaction to obtain a precursor; performing calcination treatment on the precursor to obtain the positive electrode active material. This method not only has a simple process, but also can prepare a positive electrode active material with both high structural thermal stability and low impedance, which is beneficial to balancing the safety performance and electrochemical performance of the battery.

[0012] In the third aspect of the present application, the present application proposes a positive electrode plate. According to an embodiment of the present application, the positive electrode plate includes the above-mentioned positive electrode active material, or the positive electrode active material prepared by the above-mentioned method. The positive electrode plate has all the characteristics and effects of the above-mentioned positive electrode active material, or the above-mentioned method for preparing the positive electrode active material, which will not be repeated here. In general, the positive electrode plate has both high structural thermal stability and low impedance, which is conducive to balancing the safety performance and electrochemical performance of the battery.

[0013] In the fourth aspect of the present application, the present application proposes an energy storage device. According to an embodiment of the present application, the energy storage device includes the above-mentioned positive electrode sheet, or the above-mentioned positive electrode active material, or the positive electrode active material prepared by the above-mentioned method. The energy storage device has all the features and effects of the above-mentioned positive electrode sheet, or the above-mentioned positive electrode active material, or the above-mentioned method for preparing the positive electrode active material, which will not be repeated here. In general, the energy storage device has both good safety performance and electrochemical performance, and has high market satisfaction.

[0014] In a fifth aspect, this application proposes an electrical device. According to an embodiment of this application, this electrical device includes the aforementioned energy storage device. This electrical device possesses all the features and effects of the aforementioned energy storage device, which will not be further described here. Overall, this electrical device has high safety performance and a low risk of thermal runaway.

[0015] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become obvious from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0017] FIG1 is a schematic structural diagram of a positive electrode active material according to one embodiment of the present application;

[0018] FIG2 is a flow chart of a method for preparing a positive electrode active material according to one embodiment of the present application;

[0019] FIG3 is a scanning electron microscope image of a positive electrode active material according to Example 1 of the present application, wherein FIG3 (a) is a schematic diagram of the surface morphology of a particle of the positive electrode active material; wherein FIG3 (b) is a schematic diagram of a cross-section of a particle of the positive electrode active material;

[0020] FIG4 is a particle size distribution curve of the positive electrode active material according to Example 1 of the present application;

[0021] FIG5 is a DSC curve of the reaction between the positive electrode sheet and the electrolyte of the battery according to Example 1 of the present application. DETAILED DESCRIPTION

[0022] Embodiments of the present application will be described in detail below. The embodiments described below are exemplary and are intended to explain the present application, and should not be construed as a limitation to the present application. In the description of the present application, it should be understood that the terms "first" and "second" are only used for descriptive purposes, and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise specifically and clearly defined.

[0023] In the first aspect of the present application, the present application proposes a positive electrode active material. According to an embodiment of the present application, the positive electrode active material includes:

[0024] LiMn a Fe 1-a-b-c M1 b M2 c PO4,

[0025] where 0 < a ≤ 0.8, 0 < b ≤ 0.1, 0 < c ≤ 0.1, M1 includes titanium element, M2 includes aluminum element, the positive electrode active material is granular, the doping amount of titanium element in the central region of the positive electrode active material particles is greater than that in the surface layer of the positive electrode active material particles, and the doping amount of aluminum element in the central region of the positive electrode active material particles is less than that in the surface layer of the positive electrode active material particles.

[0026] According to an embodiment of the present application, doping titanium element into lithium iron manganese phosphate is beneficial to improving the conductivity and ion diffusion coefficient in the central region of the positive electrode active material, reducing the material impedance, enhancing the battery conductivity, and can also improve the structural stability of the positive electrode active material to a certain extent, reducing the side reactions with the electrolyte and their heat generation values; doping aluminum element into lithium iron manganese phosphate is beneficial to suppressing the Jahn-Teller effect, reducing the risk of lattice distortion of the material, reducing the side reactions with the electrolyte and their heat generation values, improving the structural stability of the positive electrode active material, and improving the cycle performance; the applicant found that the impedance of the central region of the lithium iron manganese phosphate particle is larger than that of the particle surface layer, and the particle surface layer is more likely to generate lattice distortion and be eroded by the electrolyte than the central region of the particle. However, if the doping amount in the positive electrode active material is too much, it is easy to generate impurity phases or crystal defects. In this application, by doping titanium element and aluminum element into lithium iron manganese phosphate at the same time, and controlling the doping amount of titanium element in the central region of the positive electrode active material particles to be greater than that in the surface layer of the positive electrode active material particles, and the doping amount of aluminum element in the central region of the positive electrode active material particles to be less than that in the surface layer of the positive electrode active material particles, on the basis of reducing the total doping amount of titanium and aluminum, the thermal stability of the material can be improved, the heat generation value of the reaction between the material and the electrolyte when the battery core gets out of control can be reduced, and the generation and accumulation of heat can be fundamentally reduced, so that the positive electrode active material can have good structural stability, low impedance and good thermal stability, which is beneficial to balancing the safety performance and electrochemical performance of the battery.

[0027] According to an embodiment of the present application, the positive electrode active material can be all LiMn a Fe 1-a-b-c M1 b M2 c PO4, or can be partially LiMn a Fe 1-a-b-c M1 b M2 c PO4, where 0 < a ≤ 0.8, 0 < b ≤ 0.1, 0 < c ≤ 0.1. Among them, the value of a will affect the ratio of manganese to iron. When the value of a increases, the doping ratio of manganese in the positive electrode active material increases, which can increase the voltage platform. However, if the value of a is too large, the doping ratio of manganese is too high, and it is easy to occur the Jahn-Teller effect, resulting in lattice distortion of the positive electrode active material and affecting the capacity retention rate and cycle performance of the battery. The values of b and c respectively limit the doping amounts of the doping elements M1 and M2. If the doping amounts of M1 and M2 are too high, it is easy to generate impurity phases or crystal defects, affecting the stability of the crystal structure of the material. By controlling a, b, and c within the given ranges in this application, it is possible to avoid defects in the positive electrode active material as much as possible, which is beneficial to avoiding the precipitation of excessive transition metals in the form of单质 or the formation of impurity phases inside the lattice, making the positive electrode active material have better structural stability and electrochemical performance.

[0028] According to some embodiments of the present application, LiMn a Fe 1-a-b-c M1 b M2 c PO4 can be a single material that satisfies the general formula, or a composite material made by mixing multiple materials that satisfy the general formula. a Fe 1-a-b-c M1 b M2 c PO4 can include but is not limited to LiMn a Fe 1-a-b-c Ti b Al c By controlling M1 to titanium and M2 to aluminum, it is not only beneficial to improve the structural thermal stability and conductivity of the positive electrode active material, but also beneficial to reduce defects or impurities in the active material, thereby improving the cycle stability and service life of the battery.

[0029] According to some embodiments of the present application, the value range of a can be: 0.2≤a≤0.6. For example, the value of a can be 0.2, 0.3, 0.4, 0.5 or 0.6, etc. If the value of a is too small, the content of Mn element in the positive electrode active material is relatively small, which affects the voltage platform of the material and thus affects the energy density of the battery; if the value of a is too large, on the one hand, it is easy for the positive electrode active material to undergo the Jan-Taylor effect to produce lattice distortion and lead to manganese dissolution, affecting the structural stability and electrical properties of the material. On the other hand, it will also affect the doping amount of M1 and M2, limiting the role of titanium and aluminum elements. The present application helps to better balance the structural stability and electrochemical properties of the positive electrode active material by controlling the value of a to be within the given range.

[0030] According to some embodiments of the present application, the doping amount of titanium element can be gradually reduced and the doping amount of aluminum element can be gradually increased in the direction from the inside to the outside of the positive electrode active material particles. The applicant has found that the risk of lattice distortion or electrolyte corrosion of the positive electrode active material particles increases in the direction from the inside to the outside, and the impedance of the positive electrode active material particles increases in the direction from the outside to the inside. By controlling the above-mentioned doping distribution of titanium element and aluminum element, the present application is beneficial to reducing crystal defects and impurities while improving its internal resistance and structural stability based on the structural characteristics of the positive electrode active material, and is more conducive to taking into account the safety performance, conductivity and cycle stability of the positive electrode active material. It should be noted that in the present application, there is no particular limitation on the reduction range of the doping amount of titanium element and the increase range of the doping amount of aluminum element in the direction from the inside to the outside of the positive electrode active material. Those skilled in the art can flexibly choose according to actual conditions. For example, in the direction from the inside to the outside of the positive electrode active material, the doping amount of titanium element can be uniformly reduced, or gradually reduced, or irregularly reduced, and the doping amount of aluminum element can be uniformly increased, or gradually increased, or irregularly increased, etc. Optionally, in the direction from the inside to the outside of the positive electrode active material, the doping amount of the titanium element can be uniformly reduced, and the doping amount of the aluminum element can be uniformly increased, which is more conducive to realizing process-based mass production and improving processing stability.

[0031] According to some embodiments of the present application, the doping amount of titanium element can be gradually decreased and the doping amount of aluminum element can be gradually increased in the direction from the inside to the outside of the positive electrode active material particles. In this way, not only can the crystal defects and impurities be reduced under the premise of improving its internal resistance and structural stability, and the safety performance, conductivity and cycle stability of the positive electrode active material can be better balanced, but it is also conducive to reducing the difficulty of processing. By controlling the raw material ratio of the crystal growth of each layer, the above-mentioned distribution of the doped metal in the positive electrode active material is achieved. It should be noted that the present application does not specifically limit the number of gradients of decreasing titanium element doping amount and increasing aluminum element doping amount in the positive electrode active material particles. Those skilled in the art can flexibly choose according to actual conditions. According to some specific examples of the present application, in the direction from the inside to the outside of the positive electrode active material particles, the doping amount of titanium element can be 2, 3, 4, 5 or 6 gradients, and the doping amount of aluminum element can be 2, 3, 4, 5 or 6 gradients. Thus, the processing difficulty and the structural stability of the positive electrode active material can be balanced. In addition, it should be noted that the change in the doping amount of the titanium element in multiple gradients can be either an arithmetic progression or an irregular change, as long as it can meet the requirement of a gradient decrease from the inside to the outside of the positive electrode active material particles. The same is true for the change in the doping amount of the aluminum element in multiple gradients.

[0032] According to some embodiments of the present application, in conjunction with FIG1 , the positive electrode active material particles may include a first region 10 and a second region 20 in the direction from the inside to the outside. The distance from the first region 10 to the center of the positive electrode active material is D1, the distance from the second region 20 to the center of the positive electrode active material is D2, the particle size of the positive electrode active material particles is R, and D1 and D2 may satisfy the following relationship: D1 ≤ 2 / 5R, in the first region 10, 0.05 ≤ b ≤ 0.1, 0 ≤ c ≤ 0.05; D2 ≥ 2 / 5R, in the second region 20, 0 ≤ b ≤ 0.05, 0.05 ≤ c ≤ 0.1. FIG1 shows the distance from the outer edge of the first region 10 to the center of the positive electrode active material, and the distance from the outer edge of the second region 20 to the center of the positive electrode active material. By adopting the above-mentioned distribution method, on the one hand, the impedance and structural stability of the positive electrode active material can be improved, and on the other hand, the doping amount of titanium element in the first region can be controlled to be higher than the doping amount in the second region, and the doping amount of aluminum element in the second region can be controlled to be higher than the doping amount in the first region, so as to avoid limiting the content of other doping elements inside the crystal due to excessive doping amount of aluminum element in the first region or excessive doping amount of titanium element in the second region, which may lead to various risks such as a decrease in the voltage platform of the positive electrode active material, an increase in impedance or a deterioration in the crystal structure stability, and is more conducive to taking into account both the safety performance and electrochemical performance of the battery.

[0033] According to some embodiments of the present application, in the first region 10, the value of c can satisfy the following: 0.01≤c≤0.05. The applicant has discovered that the first region also has the risk of lattice distortion caused by the Jan-Taylor effect and the possibility of being corroded by the electrolyte. By doping aluminum elements in each region of the positive electrode active material, and at the same time, the doping amount of aluminum elements in the first region is lower than the doping amount in the second region, the risk of lattice distortion caused by the Jan-Taylor effect in different regions of the active material can be more specifically suppressed. At the same time, the side reactions between the active material and the electrolyte and their heat generation value can be further reduced, which is more conducive to improving the structural stability of the positive electrode active material.

[0034] According to some embodiments of the present application, in the second region 20, the value of b can satisfy the following: 0.01≤b≤0.05. The applicant has discovered that doping the second region with titanium can also appropriately reduce the impedance of the active material surface layer. By doping each region of the positive electrode active material with titanium, and at the same time increasing the doping amount of titanium in the first region compared to the second region, the conductivity of the active material in different regions can be improved more specifically, thereby enhancing the uniformity of the overall conductivity and lithium ion diffusion coefficient of the active material, and more conducive to balancing the electrochemical performance and crystal structure stability of the positive electrode active material.

[0035] According to some embodiments of the present application, the Dv50 of the positive electrode active material can be 1 to 3 μm, the Dv90 can be 7 to 9 μm, and the Dv10 can be 0.2 to 0.8 μm. If the particle size of the positive electrode active material is too large, the specific surface area of ​​the material is small, which can easily affect the bonding strength between the positive electrode active material and the matrix in the battery. When the positive electrode active material is separated from the matrix and is free in the electrolyte, once it comes into contact with the negative electrode material, it can easily cause a local battery short circuit and create a safety hazard. If the particle size of the positive electrode active material is too small, it can easily agglomerate or cause surface defects, which increases the resistance and affects the electrochemical performance of the battery. The present application controls the particle size distribution of the positive electrode active material within the given range, which is conducive to further balancing the safety performance and electrical performance of the positive electrode active material.

[0036] In the embodiments of the present application, when a numerical range a to b is involved, unless otherwise specified, it means that the numerical value can be any numerical value between a and b, including the endpoint numerical value a and the endpoint numerical value b.

[0037] According to some embodiments of the present application, the positive electrode active material may further include a carbon coating layer, which is coated on the surface of the positive electrode active material. By providing the carbon coating layer, on the one hand, the carbon layer can be in contact with the doped and modified lithium manganese iron phosphate particles, which is conducive to forming a good conductive network, further improving the conductivity of the positive electrode active material, and improving the battery's electrical properties such as capacity retention and rate performance. On the other hand, it can also inhibit the corrosion of the electrolyte on the positive electrode active material, which is conducive to improving the structural stability of the positive electrode active material and improving the battery's cycle performance and safety performance. It should be noted that there is no special restriction on the thickness of the carbon coating layer in this application, and those skilled in the art can flexibly choose according to actual conditions. For example, the thickness of the carbon coating layer can be 2nm to 6nm, etc.

[0038] In the second aspect of the present application, a method for preparing the above-mentioned positive electrode active material is proposed. According to an embodiment of the present application, the method includes: mixing a phosphorus source, a manganese source, an iron source, a lithium source, a titanium source, and an aluminum source with a solvent to obtain multiple groups of salt solutions, the multiple groups of salt solutions including a first salt solution, ..., and an nth salt solution, wherein the concentration of titanium ions in the first salt solution, ..., and the nth salt solution decreases successively and the concentration of aluminum ions increases successively, and n is a positive integer not less than 2; adding the first salt solution, ..., and the nth salt solution step by step to a precipitant and a complexing agent for a co-precipitation reaction to obtain a precursor; calcining the precursor to obtain a positive electrode active material. This method is not only simple in process, but also can produce a positive electrode active material with both high structural thermal stability and low impedance, which is beneficial for balancing the safety performance and electrochemical performance of the battery.

[0039] The method for preparing the positive electrode active material in the above embodiment of the present application is described in detail below with reference to FIG. 2 .

[0040] S1: Mix the phosphorus source, manganese source, iron source, lithium source, titanium source, aluminum source and solvent to obtain multiple salt solutions

[0041] According to the embodiments of the present application, a phosphorus source, a manganese source, an iron source, a lithium source, a titanium source, and an aluminum source are mixed with a solvent to obtain multiple groups of salt solutions containing phosphorus, manganese, iron, lithium, titanium, and aluminum at the same time. The multiple groups of salt solutions should include a first salt solution, ..., and an nth salt solution, wherein in the first salt solution, ..., and the nth salt solution, the concentration of titanium ions decreases successively, and the concentration of aluminum ions increases successively, and n is a positive integer not less than 2. It is understandable that the concentration of titanium ions can be controlled to decrease successively and the concentration of aluminum ions increases successively in the first salt solution, ..., and the nth salt solution by controlling the distribution ratio of each group in the multiple groups of salt solutions. It should be noted that there is no special restriction on the concentrations of phosphorus, manganese, iron, and lithium in the salt solution in this application. It is sufficient to meet the aforementioned restrictions on the elements in the positive electrode active material. Those skilled in the art can flexibly select according to actual conditions.

[0042] According to some embodiments of the present application, there is no particular restriction on the specific types of phosphorus source, manganese source, iron source, lithium source, titanium source, aluminum source and solvent in the present application. Those skilled in the art can flexibly select according to actual conditions. For example, the phosphorus source can include phosphoric acid and / or ammonium dihydrogen phosphate; the manganese source can include manganese dioxide and / or manganese sulfate; the iron source can include at least one of ferrous oxalate, ferric sulfate, and ferric chloride; the lithium source can include lithium carbonate and / or lithium hydroxide; the titanium source can include titanium dioxide; the aluminum source can include aluminum hydroxide and / or aluminum carbonate; the solvent can include water and / or an organic solvent. In addition, a pH regulator can be mixed with the phosphorus source, manganese source, iron source, lithium source, titanium source, aluminum source and solvent. By adding the pH regulator, the dispersion and dissolution of the phosphorus source, manganese source, iron source, lithium source, titanium source and aluminum source in the solvent can be promoted. There is no particular restriction on the type of pH regulator in the present application. For example, the pH regulator can be selected from acetic acid, propionic acid, oxalic acid, etc., which is more conducive to promoting the full dissolution of each component.

[0043] According to some embodiments of the present application, in the first salt solution, the titanium ion concentration may be 3 mol / L to 5 mol / L, and the aluminum ion concentration may be 0.5 mol / L to 1 mol / L. For example, the titanium ion concentration in the first salt solution may be 3.5 mol / L, 4 mol / L, 4.5 mol / L, 4.8 mol / L, etc., and the aluminum ion concentration may be 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, etc.; in the nth salt solution, the titanium ion concentration may be 0.5 mol / L to 3 mol / L, and the aluminum ion concentration may be 1 mol / L to 5 mol / L. For example, the titanium ion concentration in the nth salt solution may be 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, etc., and the aluminum ion concentration may be 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, etc. Thus, the reaction efficiency of the subsequent coprecipitation reaction can be improved, provided that the concentration of titanium ions decreases and the concentration of aluminum ions increases in the first, ..., and nth salt solutions. It should be noted that the magnitude of the decrease in the titanium ion concentration and the increase in the aluminum ion concentration from the first to the nth salt solutions can be the same or different.

[0044] S2: The first salt solution, ..., and the nth salt solution are added step by step to the precipitant and the complexing agent for co-precipitation reaction to obtain the precursor.

[0045] According to an embodiment of the present application, the first salt solution, ..., and the nth salt solution are sequentially added to a precipitant and a complexing agent in a staged manner to perform a coprecipitation reaction, so as to precipitate the titanium content from high to low and the aluminum content from low to high, thereby achieving a titanium content in the center region of the precursor greater than that in the surface layer of the precursor, and an aluminum content in the center region of the precursor less than that in the surface layer of the precursor. It should be noted that after the coprecipitation reaction is completed, solid-liquid separation, washing, and drying processes may also be included to remove the solvent and unreacted impurity ions.

[0046] According to some embodiments of the present application, during the coprecipitation reaction, the pH value of the reaction system can be controlled to be 8-10, the reaction temperature can be 150°C-200°C, and the reaction time can be 5h-10h. For example, the pH value of the reaction system can be 8.5, 9, 9.5, etc., the reaction temperature can be 160°C, 170°C, 180°C, 190°C, etc., and the reaction time can be 6h, 7h, 8h, 9h, etc. By controlling the reaction conditions within the given range, it is beneficial to control the crystal purity, grain size and morphology in the coprecipitation reaction. It should be noted that if the pH value of the reaction system is too high, it is easy to cause the aluminum hydroxide precipitate to dissolve again, affecting the relative content of aluminum in the precursor. It is understandable that the reaction time can be adjusted according to the number of groups of salt solutions configured. For example, when the value of n is 2, the first salt solution can be reacted with the precipitant and the complexing agent for 2 to 4 hours, and then the second salt solution is added to the reaction system and reacted for 2 to 4 hours to obtain a precursor; when the value of n is 5, the first salt solution can be reacted with the precipitant and the complexing agent for 2 to 3 hours, and then the second salt solution, the third salt solution, the fourth salt solution, and the fifth salt solution are added to the reaction system every 1 to 2 hours, and after the fifth salt solution is added, the reaction is continued for another 1 to 2 hours to obtain a precursor; and so on.

[0047] According to some embodiments of the present application, there is no particular restriction on the specific types of precipitants and complexing agents in the present application, and those skilled in the art can flexibly select according to actual conditions. For example, the precipitant can be a strong alkali solution, specifically a sodium hydroxide solution and / or a potassium hydroxide solution, etc., and the complexing agent can be an ammonia solution. Further, according to some specific examples of the present application, the concentration of the strong alkali solution can be 0.5mol / L~1mol / L, specifically 0.6mol / L, 0.7mol / L, 0.8mol / L, 0.9mol / L, etc., and the concentration of the ammonia solution can be 0.5mol / L~1.5mol / L, specifically 0.8mol / L, 1mol / L, 1.2mol / L, 1.4mol / L, etc. By controlling the concentrations of the precipitant and complexing agent to be within the given range, it is beneficial to obtain a precursor with a narrow particle size distribution and a uniform distribution of the contents of each component in different regions. It should be noted that when a strong base (such as lithium hydroxide, etc.) is included in the metal salt solution, the amount of the precipitant can be reduced as long as the pH value of the reaction system is 8~10.

[0048] S3: Calcination treatment of the precursor to obtain the positive electrode active material

[0049] According to the embodiments of the present application, the precursor is calcined to obtain a titanium and aluminum doped lithium manganese iron phosphate positive electrode active material. According to some specific examples of the present application, the calcination treatment can be carried out under nitrogen and / or inert gas, the calcination treatment temperature can be 650°C to 750°C, and the calcination time can be 5h to 8h. By controlling the calcination treatment conditions within the given range, it is easier to control the grain size of the positive electrode active material, improve the crystallinity and structural stability of the crystal, and facilitate the acquisition of spherical or quasi-spherical positive electrode active materials, thereby improving the safety and electrochemical performance of the battery.

[0050] According to some embodiments of the present application, during the calcination process, the precursor can be mixed with a carbon source to form a carbon coating layer on the surface of the positive electrode active material. The purpose and effect of forming the carbon coating layer have been described in the previous section and will not be repeated here. It should be noted that there is no particular limitation on the type of carbon source in this application, and those skilled in the art can flexibly select it according to actual conditions. For example, the carbon source can include at least one of glucose, citric acid, and ascorbic acid.

[0051] According to some embodiments of the present application, the mass ratio of the positive electrode active material to the carbon source can be (90-95): (5-10), for example, the mass ratio of the positive electrode active material to the carbon source can be 90 / 5, 92 / 5, 95 / 5, 90 / 8, 90 / 10, 95 / 10, etc., thereby not only facilitating the uniform coating of the doped and modified lithium manganese iron phosphate by the carbon layer, but also enabling the control of the relative content of the active material, which is beneficial for taking into account both the conductivity and energy density of the positive electrode active material after carbon coating.

[0052] In the third aspect of the present application, the present application proposes a positive electrode plate. According to an embodiment of the present application, the positive electrode plate includes the above-mentioned positive electrode active material, or the positive electrode active material prepared by the above-mentioned method. The positive electrode plate has all the characteristics and effects of the above-mentioned positive electrode active material, or the above-mentioned method for preparing the positive electrode active material, which will not be repeated here. In general, the positive electrode plate has both high structural thermal stability and low impedance, which is beneficial to taking into account the safety performance and electrochemical performance of the battery. It should be noted that the positive electrode plate may include a positive electrode current collector and a positive electrode active material layer provided on at least one side of the positive electrode current collector. The positive electrode active material layer may include the above-mentioned positive electrode active material, a binder and a conductive agent. In the present application, there is no special restriction on the specific types of the binder and the conductive agent. For example, the conductive agent may include conductive carbon black, etc., and the binder may include polyvinylidene fluoride, etc.

[0053] In the fourth aspect of the present application, the present application proposes an energy storage device. According to an embodiment of the present application, the energy storage device includes the above-mentioned positive electrode sheet, or the above-mentioned positive electrode active material, or the positive electrode active material prepared by the above-mentioned method. The energy storage device has all the features and effects of the above-mentioned positive electrode sheet, or the above-mentioned positive electrode active material, or the above-mentioned method for preparing the positive electrode active material, which will not be repeated here. In general, the energy storage device has both good safety performance and electrochemical performance, and has high market satisfaction. It should be noted that there is no particular restriction on the specific type of energy storage device in the present application, and those skilled in the art can flexibly select according to actual conditions. For example, the energy storage device may include a battery, and the battery may include a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. The positive electrode sheet may be the above-mentioned positive electrode sheet, wherein the present application does not particularly limit the specific composition of the negative electrode sheet, the separator and the electrolyte, for example, conventional selections in the art can be adopted. For example, the negative electrode sheet may include a negative electrode collector and a negative electrode active material layer provided on at least one side of the negative electrode collector, the negative electrode active material layer may include a negative electrode active material, a binder and a conductive agent, the negative electrode active material may include artificial graphite, etc., the conductive agent may include conductive carbon black, etc., the binder may include styrene-butadiene rubber, sodium carboxymethyl cellulose, etc.; the separator may include at least one of polypropylene (PP), polyethylene (PE), and ceramic separator; the electrolyte may include an electrolyte salt and an organic solvent, wherein the specific types and compositions of the electrolyte salt and the organic solvent are not particularly limited, and those skilled in the art can select according to actual needs. In addition, there is no particular limitation on the specific type of battery in this application, and those skilled in the art can flexibly select according to actual circumstances. For example, the battery can be a square battery or a cylindrical battery. For another example, the battery can be a liquid battery or a semi-solid battery.

[0054] In the fifth aspect of the present application, the present application proposes an electrical device. According to an embodiment of the present application, the electrical device includes the above-mentioned energy storage device. The electrical device has all the characteristics and effects of the above-mentioned energy storage device, which will not be repeated here. In general, the electrical device has high safety performance and a low risk of thermal runaway. It should be noted that there is no special restriction on the specific type of electrical device in this application, and those skilled in the art can flexibly choose according to actual conditions. For example, the electrical device may include but is not limited to electronic equipment, vehicles, aircraft, household appliances, etc.

[0055] The embodiments of the present application are described in detail below. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this area or according to the product specifications. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0056] Example 1

[0057] (1) According to LiMn 0.2 Fe 0.74 Ti 0.05 Al 0.01 The first metal salt solution is prepared by weighing ferrous oxalate, manganese dioxide, phosphoric acid, lithium carbonate, titanium dioxide, aluminum hydroxide and acetic acid in the required stoichiometric ratio in PO4. The molar concentration of titanium ions in the first metal salt solution is 3 mol / L and the molar concentration of aluminum ions is 0.5 mol / L.

[0058] According to LiMn 0.2 Fe 0.74 Ti 0.04 Al 0.02 The second metal salt solution is prepared by weighing ferrous oxalate, phosphoric acid, lithium carbonate, titanium dioxide, aluminum hydroxide and acetic acid in the required stoichiometric ratio in PO4. The molar concentration of titanium ions in the second metal salt solution is 2.5 mol / L and the molar concentration of aluminum ions is 1.5 mol / L.

[0059] According to LiMn 0.2 Fe 0.74 Ti 0.03 Al 0.03 The third metal salt solution is prepared by weighing ferrous oxalate, phosphoric acid, lithium carbonate, titanium dioxide, aluminum hydroxide and acetic acid in the required stoichiometric ratio in PO4. The molar concentration of titanium ions in the third metal salt solution is 2 mol / L and the molar concentration of aluminum ions is 2 mol / L.

[0060] According to LiMn 0.2 Fe 0.74 Ti 0.04 Al 0.02 The fourth metal salt solution is prepared by weighing ferrous oxalate, phosphoric acid, lithium carbonate, titanium dioxide, aluminum hydroxide and acetic acid in the required stoichiometric ratio in PO4. The molar concentration of titanium ions in the fourth metal salt solution is 1.5 mol / L and the molar concentration of aluminum ions is 2.5 mol / L.

[0061] According to LiMn 0.2 Fe 0.74 Ti 0.05 Al 0.01 The fifth metal salt solution is prepared by weighing ferrous oxalate, phosphoric acid, lithium carbonate, titanium dioxide, aluminum hydroxide and acetic acid in the required stoichiometric ratio in PO4. The molar concentration of titanium ions in the fifth metal salt solution is 1 mol / L and the molar concentration of aluminum ions is 3 mol / L.

[0062] (2) adding the first metal salt solution, sodium hydroxide solution (concentration of 0.5 mol / L) and ammonia solution (concentration of 1 mol / L) obtained in step (1) into a reactor, controlling the pH value of the reaction system to 9, the reaction temperature to 160° C., stirring and reacting for 2 h, and subsequently adding the second metal salt solution, the third metal salt solution, the fourth metal salt solution, and the fifth metal salt solution into the reaction system step by step every 1 h. After the fifth metal salt solution is added, stirring and reacting for 1 h, the reaction system is subjected to solid-liquid separation, washing, and drying treatment to obtain a precursor;

[0063] (3) The precursor obtained in step (2) was weighed and mixed with glucose in a mass ratio of 94:6, and calcined at 700°C for 6 hours in a nitrogen atmosphere. After the calcination, the product was crushed to obtain a positive electrode active material with a Dv50 of 1.2 μm. The composition of the surface layer of the positive electrode active material particles was LiMn except for the carbon coating layer. 0.2 Fe 0.74 Ti 0.01 Al 0.05 PO4.

[0064] Example 2

[0065] The difference from Example 1 is that in step (1), according to LiMn 0.2 Fe 0.73 Ti 0.06 Al 0.01 The first metal salt solution is prepared by weighing ferrous oxalate, manganese dioxide, phosphoric acid, lithium carbonate, titanium dioxide, aluminum hydroxide and acetic acid in the required stoichiometric ratio in PO4.

[0066] Example 3

[0067] The difference from Example 1 is that in step (1), according to LiMn 0.2 Fe 0.72 Ti 0.07 Al 0.01 The first metal salt solution is prepared by weighing ferrous oxalate, manganese dioxide, phosphoric acid, lithium carbonate, titanium dioxide, aluminum hydroxide and acetic acid in the required stoichiometric ratio in PO4.

[0068] Example 4

[0069] The difference from Example 1 is that in step (1), according to LiMn 0.2 Fe 0.71 Ti 0.08 Al 0.01 The first metal salt solution is prepared by weighing ferrous oxalate, manganese dioxide, phosphoric acid, lithium carbonate, titanium dioxide, aluminum hydroxide and acetic acid in the required stoichiometric ratio in PO4.

[0070] Example 5

[0071] The difference from Example 1 is that in step (1), according to LiMn 0.2 Fe 0.70 Ti 0.09 Al 0.01 The first metal salt solution is prepared by weighing ferrous oxalate, manganese dioxide, phosphoric acid, lithium carbonate, titanium dioxide, aluminum hydroxide and acetic acid in the required stoichiometric ratio in PO4.

[0072] Example 6

[0073] The difference from Example 1 is that in step (1), according to LiMn 0.2 Fe 0.69 Ti 0.1 Al 0.01 The first metal salt solution is prepared by weighing ferrous oxalate, manganese dioxide, phosphoric acid, lithium carbonate, titanium dioxide, aluminum hydroxide and acetic acid in the required stoichiometric ratio in PO4.

[0074] Example 7

[0075] The difference from Example 1 is that in step (1), the molar concentration of each ion in the second to fifth metal salt solutions is regulated, and the obtained positive electrode active material is detected by Auger electron spectroscopy. Except for the carbon coating layer, the composition of the surface layer of the positive electrode active material particles is approximately LiMn 0.2 Fe 0.73 Ti 0.01 Al 0.06 PO4.

[0076] Example 8

[0077] The difference from Example 1 is that in step (1), the molar concentration of each ion in the second to fifth metal salt solutions is regulated, and the obtained positive electrode active material is detected by Auger electron spectroscopy. Except for the carbon coating layer, the composition of the surface layer of the positive electrode active material particles is approximately LiMn 0.2 Fe 0.72 Ti 0.01 Al 0.07 PO4.

[0078] Example 9

[0079] The difference from Example 1 is that in step (1), the molar concentration of each ion in the second to fifth metal salt solutions is regulated, and the obtained positive electrode active material is detected by Auger electron spectroscopy. Except for the carbon coating layer, the composition of the surface layer of the positive electrode active material particles is approximately LiMn 0.2 Fe 0.71 Ti 0.01 Al 0.08 PO4.

[0080] Example 10

[0081] The difference from Example 1 is that in step (1), the molar concentration of each ion in the second to fifth metal salt solutions is regulated, and the obtained positive electrode active material is detected by Auger electron spectroscopy. Except for the carbon coating layer, the composition of the surface layer of the positive electrode active material particles is approximately LiMn 0.2 Fe 0.70 Ti 0.01 Al 0.09 PO4.

[0082] Example 11

[0083] The difference from Example 1 is that in step (1), the molar concentration of each ion in the second to fifth metal salt solutions is regulated, and the obtained positive electrode active material is detected by Auger electron spectroscopy. Except for the carbon coating layer, the composition of the surface layer of the positive electrode active material particles is approximately LiMn 0.2 Fe 0.69 Ti 0.01 Al 0.1 PO4.

[0084] Example 12

[0085] The difference from Example 1 is that in step (1), according to LiMn 0.4 Fe 0.53 Ti 0.05 Al 0.01 The first metal salt solution is prepared by weighing ferrous oxalate, manganese dioxide, phosphoric acid, lithium carbonate, titanium dioxide, aluminum hydroxide and acetic acid in the required stoichiometric ratio in PO4.

[0086] Example 13

[0087] The difference from Example 1 is that in step (1), according to LiMn 0.6 Fe 0.33 Ti 0.05 Al 0.01 The first metal salt solution is prepared by weighing ferrous oxalate, manganese dioxide, phosphoric acid, lithium carbonate, titanium dioxide, aluminum hydroxide and acetic acid in the required stoichiometric ratio in PO4.

[0088] Example 14

[0089] The difference from Example 1 is that in step (1), according to LiMn 0.8 Fe 0.13 Ti 0.05 Al 0.01 The first metal salt solution is prepared by weighing ferrous oxalate, manganese dioxide, phosphoric acid, lithium carbonate, titanium dioxide, aluminum hydroxide and acetic acid in the required stoichiometric ratio in PO4.

[0090] Comparative Example 1

[0091] The difference from Example 1 is:

[0092] In step (1), according to LiMn 0.2 Fe 0.8 Prepare a metal salt solution by weighing ferrous oxalate, manganese dioxide, phosphoric acid, lithium carbonate and acetic acid in the required stoichiometric ratio in PO4;

[0093] In step (2), the metal salt solution obtained in step (1) is subjected to a coprecipitation reaction with a precipitant and a complexing agent to obtain a precursor.

[0094] Comparative Example 2

[0095] The difference from Comparative Example 1 is that, according to LiMn 0.4 Fe 0.6 PO4 to prepare metal salt solution.

[0096] Comparative Example 3

[0097] The difference from Comparative Example 1 is that, according to LiMn 0.6 Fe 0.4 PO4 to prepare metal salt solution.

[0098] Comparative Example 4

[0099] The difference from Comparative Example 1 is that, according to LiMn 0.8 Fe 0.2 PO4 to prepare metal salt solution.

[0100] Comparative Example 5

[0101] The difference from Example 1 is that

[0102] In step (1), according to LiMn 0.2 Fe 0.74 Ti 0.05 Al 0.01 Prepare a metal salt solution by weighing ferrous oxalate, manganese dioxide, phosphoric acid, lithium carbonate, titanium dioxide, aluminum hydroxide and acetic acid in the required stoichiometric ratio in PO4;

[0103] In step (2), the metal salt solution obtained in step (1) is subjected to a coprecipitation reaction with a precipitant and a complexing agent to obtain a precursor.

[0104] Comparative Example 6

[0105] The difference from Example 1 is that

[0106] In step (1), according to LiMn 0.2 Fe 0.74Ti 0.01 Al 0.05 Prepare a metal salt solution by weighing ferrous oxalate, manganese dioxide, phosphoric acid, lithium carbonate, titanium dioxide, aluminum hydroxide and acetic acid in the required stoichiometric ratio in PO4;

[0107] In step (2), the metal salt solution obtained in step (1) is subjected to a coprecipitation reaction with a precipitant and a complexing agent to obtain a precursor.

[0108] Comparative Example 7

[0109] The difference from Example 1 is:

[0110] In step (1), according to LiMn 0.2 Fe 0.75 Ti 0.05 Prepare a metal salt solution by weighing ferrous oxalate, manganese dioxide, phosphoric acid, lithium carbonate, titanium dioxide and acetic acid in the required stoichiometric ratio in PO4;

[0111] In step (2), the metal salt solution obtained in step (1) is subjected to a coprecipitation reaction with a precipitant and a complexing agent to obtain a precursor.

[0112] Comparative Example 8

[0113] The difference from Example 1 is:

[0114] In step (1), according to LiMn 0.2 Fe 0.75 Al 0.05 Prepare a metal salt solution by weighing ferrous oxalate, manganese dioxide, phosphoric acid, lithium carbonate, aluminum hydroxide and acetic acid in the required stoichiometric ratio in PO4;

[0115] In step (2), the metal salt solution obtained in step (1) is subjected to a coprecipitation reaction with a precipitant and a complexing agent to obtain a precursor.

[0116] The differences between the positive electrode active materials prepared in Examples 1 to 14 and Comparative Examples 1 to 8 are shown in Table 1.

[0117] Battery assembly and testing:

[0118] The battery shells prepared in Examples 1 to 14 and Comparative Examples 1 to 8 were assembled to form batteries. The specific process is as follows:

[0119] <Positive electrode>

[0120] (1) Weigh the corresponding amount of positive electrode active material, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 95:2:3 in a stirring tank, then add an appropriate amount of N-methylpyrrolidone (NMP) and stir for 5 hours to obtain a uniform slurry with appropriate viscosity;

[0121] (2) The slurry is evenly coated on the aluminum foil by extrusion coating to form a single-sided coating layer, and then fully dried in an oven to obtain a positive electrode sheet. The surface density of the positive electrode sheet coating is 230g / m 2 .

[0122] <Negative electrode>

[0123] (1) Weigh the corresponding amount of artificial graphite, conductive carbon black, and sodium carboxymethyl cellulose in a mass ratio of 95:2.5:2.5 in a stirring tank, add appropriate amount of deionized water and stir for 6 hours to obtain a uniform slurry with appropriate viscosity;

[0124] (2) The slurry was coated on a copper foil with a thickness of 10 μm to form a single-side coating layer, and then placed in a vacuum oven and dried at 150°C for 16 hours to obtain a negative electrode sheet. The surface density of the negative electrode sheet coating was 180 g / m 2 .

[0125] <Battery Assembly>

[0126] (1) The positive and negative electrode sheets were placed in a press and pressed, and then a punch was used to cut out 15 mm diameter positive electrode discs and 18 mm diameter negative electrode discs respectively;

[0127] (2) The positive and negative electrode discs are placed in a glove box filled with argon protective atmosphere for battery assembly, 1 mol / L lithium hexafluorophosphate is dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate with a molar ratio of 1:1 to obtain an electrolyte; the positive electrode disc, the negative electrode disc, the polyethylene diaphragm and other components are assembled together, and then the electrolyte is injected to obtain a lithium-ion battery.

[0128] <Performance Test>

[0129] (1) Morphology Characterization of Positive Electrode Active Materials: The morphology and structure of the positive electrode active materials obtained in Examples 1 to 14 and Comparative Examples 1 to 8 were characterized using a scanning electron microscope. Taking Example 1 as an example, the particle morphology of the positive electrode active materials obtained is shown in FIG3

[0130] (2) Particle size test of positive electrode active material: A laser diffraction particle size distribution measuring instrument (Malvern Mastersizer 3000) was used to measure the particle size distribution according to the particle size distribution laser diffraction method GB / T 19077-2016 to obtain Dv50. Taking Example 1 as an example, the particle size distribution curve of the positive electrode active material obtained is shown in FIG4 ;

[0131] (3) Battery thermal stability test: (I) At 25°C, the lithium batteries prepared in the above examples and comparative examples were charged to 4.5V (fully charged state) at a rate of 0.05C. The lithium batteries were then disassembled in a glove box, the positive electrode sheets were removed, and the positive electrode sheets were placed in a DMC solution (dimethyl carbonate) for cleaning and drying. (II) 1 mg of powder was scraped from the positive electrode sheet in the glove box and placed in a disposable high-pressure crucible. 5 μL of electrolyte was then weighed and dripped into the crucible using a pipette. The crucible was then strictly sealed for standby use. (III) A DSC test (differential scanning calorimetry) was performed in a synchronous thermal analyzer (MicroCal PEAQ) under the conditions of 25-450°C, N2 atmosphere, flow rate of 30 mL / min, and heating rate of 5°C / min to obtain a DSC test curve. The calorific value of the positive electrode active material in the electrolyte can be obtained by the peak area of ​​the DSC curve. Taking Example 1 as an example, the DSC curve is shown in Figure 5.

[0132] The heat generation values ​​of the positive electrode active materials of the batteries prepared in Examples 1 to 14 and Comparative Examples 1 to 8 in the electrolyte are shown in Table 1.

[0133] Lithium battery impedance test: The lithium battery was tested using an AC impedance tester. The test results are shown in Table 1.

[0134] Rate Discharge Capacity Test: At 25°C, the lithium batteries prepared in each Example and Comparative Example were charged at a 0.5C rate to 4.3V, then discharged at a 0.5C rate to 2.5V. This was recorded as the 0.5C discharge capacity. They were then charged at a 1C rate to 4.3V, then discharged at a 1C rate to 2.5V. This was recorded as the 1C discharge capacity. The specific test results are shown in Table 1.

[0135] Cycling Performance Test: At 25°C, the lithium batteries prepared in the Examples and Comparative Examples were charged to 4.3V at a 1C rate and then discharged to 2.5V at a 1C rate. The capacity at the first cycle was taken as the initial capacity, and the capacity at the 200th cycle was divided by the initial capacity to obtain the retention rate. The specific test results are shown in Table 1.

[0136] Table 1 Test results of Examples 1 to 14 and Comparative Examples 1 to 8

[0137] Results and Discussion

[0138] The test results above indicate that the positive electrode active material particles in the above-mentioned embodiments of the present application have a uniform and regular morphology, tending towards spherical shape, and a narrow particle size distribution. Compared to the comparative example, the positive electrode active material in the above-mentioned embodiments of the present application has a lower calorific value in the electrolyte, indicating that it undergoes fewer side reactions with the electrolyte. Furthermore, the positive electrode active material in the above-mentioned embodiments of the present application has a lower impedance, a higher discharge capacity at 0.5C and 1C rates, and a higher capacity retention rate after 200 cycles. This demonstrates that the positive electrode active material in the above-mentioned embodiments of the present application has both good safety and electrochemical performance, and a low risk of thermal runaway during use. Specifically, in combination with Experimental Examples 1 to 6, it is understood that as the amount of titanium doping in the central region of the positive electrode active material increases, the discharge capacity of the battery at 0.5C and 1C rates increases and the capacity retention rate improves, indicating that increasing the amount of titanium doping in the central region of the positive electrode active material is beneficial to reducing the internal resistance of the battery and improving the safety performance of the battery; in combination with Examples 1 and 7 to 11, it is understood that as the amount of aluminum doping in the surface layer of the positive electrode active material increases, the heat generated by the reaction between the positive electrode active material and the electrolyte decreases, indicating that increasing the amount of aluminum doping in the surface layer of the positive electrode active material is beneficial to reducing the side reaction between the positive electrode active material and the electrolyte and its heat generation value, and improving the structural stability of the positive electrode active material; in combination with Examples 12 to 14 and Comparative Examples 1 to 4, it is understood that as the manganese content in the positive electrode active material increases, the heat generated by the reaction between the positive electrode active material and the electrolyte increases, and the trend increases, the discharge capacity of the battery at 0.5C and 1C rates decreases, and the capacity retention rate decreases. This shows that the battery of the above embodiment of the present application, by adopting the above-mentioned positive electrode active material, is conducive to taking into account both the safety performance and electrochemical performance of the battery.

[0139] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0140] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A positive electrode active material, characterized in that: Comprising: <h2 style=";text-align:left;direction:ltr">LiMn<h2 style=";text-align:left;direction:ltr"> a <h2 style=";text-align:left;direction:ltr"> Fe<h2 style=";text-align:left;direction:ltr"> 1-a-b-c <h2 style=";text-align:left;direction:ltr"> M1<h2 style=";text-align:left;direction:ltr"> b <h2 style=";text-align:left;direction:ltr"> M2<h2 style=";text-align:left;direction:ltr"> c <h2 style=";text-align:left;direction:ltr"> PO4, Wherein, 0 < a ≤ 0.8, 0 < b ≤ 0.1, 0 < c ≤ 0.1, M1 comprises titanium element, M2 comprises aluminum element, the positive electrode active material is granular, the doping amount of the titanium element in the central region of the positive electrode active material particles is greater than that in the surface layer of the positive electrode active material particles, and the doping amount of the aluminum element in the central region of the positive electrode active material particles is less than that in the surface layer of the positive electrode active material particles.

2. The positive electrode active material according to claim 1, characterized in that The LiMn a Fe 1-a-b-c M1 b M2 c PO4 includes: LiMn a Fe 1-a-b-c Ti b Al c PO4; and / or, 0.2≤a≤0.

6.

3. The positive electrode active material according to claim 1, characterized in that In the direction from the inside to the outside of the positive electrode active material particles, the doping amount of the titanium element gradually decreases, and the doping amount of the aluminum element gradually increases.

4. The positive electrode active material according to claim 1, characterized in that In the direction from the inside to the outside of the positive electrode active material particles, the doping amount gradient of the titanium element decreases, and the doping amount gradient of the aluminum element increases.

5. The positive electrode active material according to any one of claims 1 to 4, characterized in that The positive electrode active material particles include a first region and a second region in the direction from the inside to the outside. The distance from the first region to the center of the positive electrode active material particles is D1, and the distance from the second region to the center of the positive electrode active material is D2. The particle size of the positive electrode active material particles is R, where: D1 ≤ 2 / 5R, in the first region, 0.05 ≤ b ≤ 0.1, 0 ≤ c ≤ 0.05; D2 ≥ 2 / 5R, in the second region, 0 ≤ b ≤ 0.05, 0.05 ≤ c ≤ 0.

1.

6. The positive electrode active material according to claim 5, characterized in that In the first region, 0.01 ≤ c ≤ 0.05; and / or, in the second region, 0.01 ≤ b ≤ 0.

05.

7. The positive electrode active material according to claim 1 or 6, characterized in that: The particle size distribution of the positive electrode active material satisfies: Dv50 is 1 - 3 μm, Dv90 is 7 - 9 μm, and Dv10 is 0.2 - 0.8 μm.

8. The positive electrode active material according to claim 1 or 6, characterized in that: Also comprising: A carbon coating layer, which coats the surface of the positive electrode active material.

9. A method for preparing the positive electrode active material according to any one of claims 1 to 8, characterized in that: Comprising: Mixing a phosphorus source, a manganese source, an iron source, a lithium source, a titanium source, an aluminum source with a solvent to obtain multiple groups of salt solutions. The multiple groups of salt solutions include the first salt solution, ……, the nth salt solution. In the first salt solution, ……, the nth salt solution, the concentration of titanium ions decreases in sequence, and the concentration of aluminum ions increases in sequence. n is a positive integer not less than 2; Adding the first salt solution, ……, the nth salt solution step by step in segments to a precipitating agent and a complexing agent for coprecipitation reaction to obtain a precursor; Performing a calcination treatment on the precursor to obtain the positive electrode active material.

10. The method according to claim 9, characterized in that In the calcination treatment, the precursor is mixed with a carbon source so as to form a carbon coating layer on the surface of the positive electrode active material.

11. The method according to claim 10, characterized in that The mass ratio of the positive electrode active material to the carbon source is (90 - 95):(5 - 10).

12. A positive electrode sheet, characterized in that: Comprising: The positive electrode active material according to any one of claims 1 - 8, or the positive electrode active material prepared by the method according to any one of claims 9 - 11.

13. An energy storage device, characterized in that: Comprising: The positive electrode plate according to claim 12, or the positive electrode active material according to any one of claims 1 - 8, or the positive electrode active material prepared by the method according to any one of claims 9 - 11.

14. An electrical device, characterized in that: Comprising the energy storage device according to claim 13.

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