Composite cathode active material, method for preparing the same, secondary battery and electronic device

Abstract

A composite cathode active material includes: a first component, having a first formula of LixNiaCobR1 cR 2 dO2, where R1 is Mn or A1, R2 is selected from a group comprising A1, Ti, Zr, Nb, Ba, La, and Ag, 1≤x≤1.1, 0.5≤a≤0.8, 0<b≤0.3, 0<b+c≤0.5, 0≤d≤0.005; and a second component, having a second formula of LiyMneFefR 3 gPO4, where R3 is selected from a group comprising Mg, Ca, Sr, Ti, V, Cr, Co, Cu, Zn, Zr, Y, Mo, Nb, W, La and Sm, 1≤y≤1.1, 0.5≤e<0.9, 0.1≤f<0.5, 0<g<0.01, and g / f < 0.06. A weight ratio of the second component to the first component is greater than 1:1 and smaller than or equal to 10:1.

Description

[0001]P138344-19679-KOH COMPOSITE CATHODE ACTIVE MATERIAL, METHOD FOR PREPARING THE SAME, SECONDARY BATTERY AND ELECTRONIC DEVICE FIELD The present disclosure relates to the technical field of batteries, and more particularly to a composite cathode active material, a method for preparing a composite cathode active material, and a secondary battery and an electronic device. BACKGROUND Batteries have been widely used in various appliances in recent years. Positive electrode (i.e., cathode) for a battery (such as a secondary battery) affects performances of the battery, and thus there is a need to develop the cathode active material in the battery. There are different types of the cathode active materials including, but not limited to, lithium-containing materials. For example, lithium nickel-cobalt-manganese oxide (NCM) or lithium ferromanganese phosphate (LFMP) may be used for the cathode, but the individual materials usually result in limited performances such as the capacity and the cycle performance of the battery. Therefore, there is still a need for providing a cathode active material for improving performances of a battery including such a cathode active material. SUMMARY Embodiments of the present disclosure seek to solve at least one of the problems existing in the related art to at least some extent. According to a first aspect of the present disclosure, a composite cathode active material is provided. The composite cathode active material includes: a first component, having a first formula of LixNiaCobR1cR2dO2, where R1is Mn or Al, R2is selected from a group including Al, Ti, Zr, Nb, Ba, La, and Ag, 1≤x≤1.1, 0.5≤a≤0.8, 0<b≤0.3, 0<b+c≤0.5, 0≤d≤0.005; and a second component, having a second formula of LiyMneFefR3gPO4, where R3is selected from a group including Mg, Ca, Sr, Ti, V, Cr, Co, Cu, Zn, Zr, Y, Mo, Nb, W, La and Sm, 1≤y≤1.1, 0.5≤e<0.9, 0.1≤f<0.5, 0<g<0.01, and g / f < 0.06. A weight ratio of the second component to the first component is greater than 1:1 and smaller than or equal to 10:1. It can be understood that in each of the first formula and the second formula, a sum of positive valences and negative valences is zero. The composite cathode active material of the present disclosure exhibits high electrochemical performances. In some embodiments, R1is Mn, and / or R2is selected from a group including Zr, Nb, Ba, La, and Ag. For example, the first component is LixNiaCobMncZrdO2. The metallic element R2is doped to stabilize the crystal structure of the first component, and the electrochemical performance of the composite cathode active material is improved. In some embodiments, R3is selected from a group including Ti, Co, Y, Mo, Nb, W, La and Sm. For example, Ti is doped in the second component. Without wishing to be bound by any theory, a bond energy of Ti-O is greater than that of Fe-O, introduction of Ti can reduce a grain size of the second component (i.e., the LFMP), shorten the lithium ion transmission path and improve the capacity of the composite cathode active material. In some embodiments, 1≤y≤1.05, 0.6≤e<0.7, 0.3≤f<0.5, and / or 0<g≤0.003. In some embodiments, 1≤x≤1.08, and / or 0≤d≤0.003. In some embodiments, 0.5≤a≤0.7, 0<b≤0.1, and / or 0.3<b+c≤0.4. The electrochemical performance of the composite cathode active material which meets the further condition(s) may be further improved. In some embodiments, the composite cathode active material has a particle size Dv50 ranging from 1 to 5 μm, for example is about 3 μm. After calcination, the composite cathode active material is crushed by an airflow into particles having a size range from 1 to 5 μm, which improves the processability of the composite cathode active material of the present disclosure. In some embodiments, a molar ratio of R2to R3is in a range from 2:1 to 1:10. The doping elements in the first component and the second component may be presented in a preset ratio in molar. With such a molar ratio, the electrochemical performance of the composite cathode active material is improved. In some embodiments, the composite cathode active material further incudes a carbon coating layer. For example, the composite cathode active material has a carbon coating layer of about 1.0 wt% to 3.0 wt% based on the total weight of the composite cathode active material. The carbon coating layer may further improve an electronic conductivity of the composite cathode active material. According to a second aspect of the present disclosure, a method for preparing the composite cathode active material of the first aspect is provided, the method includes: mixing a precursor containing Ni, Co and R1with lithium hydroxide monohydrate to obtain a first mixture; calcinating the first mixture at a temperature ranging from 600 to 900 °C for 8 to 15 h, cooling to a room temperature, and performing an airflow crushing to obtain a second mixture; adding a phosphorus source material, an iron source material, a manganese source material and a carbon source material into water to obtain a first aqueous solution with a solid content of 20 to 40%, performing drying to obtain a third mixture; mixing a lithium source material with the third mixture to obtain a fourth mixture; calcinating the fourth mixture in a nitrogen atmosphere at a first temperature for 4 to 8 h, and adjusting the temperature to a second temperature and calcinating the fourth mixture for 4 to 8 h to obtain a fifth mixture; adding the fifth mixture into a second aqueous solution containing R3, and adding them into a grinding machine for grinding to obtain a first slurry; adding the second mixture and the first slurry into the grinding machine for grinding to obtain a second slurry, and spray-drying the second slurry to obtain powders; and calcinating the powders in a nitrogen atmosphere to obtain the composite cathode active material, wherein the calcinating includes: calcinating at a temperature ranging from 500 to 600°C for 3 to 7 h, calcinating at a temperature ranging from 670 to 770 °C for 2 to 6 h, and keeping the temperature at a range of 550 to 650 °C for 4 to 8 h, and materials are weighted and controlled to allow the composite cathode active material obtained conforms to the first formula and the second formula. With the method of the present disclosure, the composite cathode active material having a high electrochemical performance is prepared. In some embodiments, the first mixture is obtained by mixing an R2containing material with the precursor containing Ni, Co and R1, and lithium hydroxide monohydrate. After the calcination, Zr is doped in the NiCoR1material, so as to stabilize the crystal structure of the first component. In some embodiments, the phosphorus source material includes at least one selected from ferric phosphate and lithium dihydrogen phosphate. In some embodiments, the iron source material includes at least one selected from ferric phosphate and ferric nitrate. In some embodiments, the manganese source material includes at least one selected from manganese carbonate and manganese sulfate. In this way, proportions of elements P, Fe, Mn and a proportion of Li element are controlled separately, resulting in precise element amount control. In some embodiments, the carbon source material includes sucrose and polyethylene glycol (PEG). In some embodiments, the third mixture includes the carbon source material of 1 to 5 wt% based on a total weight of the third mixture. In some embodiments, before drying, the first aqueous solution is stirred and subjected to grinding to make particles in the first aqueous solution have a particle size Dv50 of 300 nm to 500 nm. In some embodiments, the first aqueous solution is dried by spray drying with a nebulizer, wherein the nebulizer has an inlet temperature of 250 to 350 °C, an outlet temperature of 50 to 150 °C and an atomization frequency of 40 to 80 Hz. In some embodiments, the third mixture spray-dried has a particle size Dv50 of 10 to 50 μm. In this way, impurities and moisture may be removed, the particle size Dv50 is reduced and uniformity is improved. In some embodiments, the fourth mixture is added to a third aqueous solution containing sodium dodecylbenzene sulfonate, which is used as a surfactant and a dispersant. They are stirred at a speed of 50 to 200 rad / min for 1 to 10 min, and dried, so as to improve the uniformity of the components. In some embodiments, the first temperature is ranged from 330 to 430 °C at which the carbon source material is decomposed and / or the second temperature is ranged from 480 to 580 °C, at which a lithium ferromanganese phosphate crystal is formed. In some embodiments, the second slurry is obtained by adding a carbon source material with the second mixture and the first slurry. In some embodiments, the carbon source material includes sucrose and polyethylene glycol, and / or the carbon source material has an amount of 1 to 10 wt% based on a total weight of the second mixture and the fifth mixture. In this way, the carbon source material is formed as the carbon coating layer. The carbon coating layer may not only prevent an interface reaction between an electrolyte and the composite cathode active material of the present disclosure, but also improve the electronic conductivity of the composite cathode active material. In some embodiments, after calcination, the composite cathode active material is crushed by an airflow into particles having a size range from 1 to 5 μm, which facilitates the application of the present material on a substrate of the positive electrode, improving the processability of the composite cathode active material of the present disclosure. According to a third aspect of the present disclosure, a secondary battery including a positive electrode including the composite cathode active material of the first aspect is provided. Due to the composite cathode active material, the secondary battery of the present disclosure has a high capacity and a long service life. According to a fourth aspect of the present disclosure, an electronic device including the secondary battery of the third aspect is provided. The electronic device of the present disclosure is powered by the secondary battery and may be working stably. It is to be understood that both the foregoing general description and the following detailed description are illustrative and explanatory only and shall not be construed to limit the present disclosure. DETAILED DESCRIPTION Reference will now be made in detail to embodiments. The implementations set forth in the following description of the embodiments do not represent all implementations consistent with the present disclosure. Terms used herein in embodiments of the present disclosure are only for the purpose of describing specific embodiments, but should not be construed to limit the present disclosure. As used in the embodiments of the present disclosure and the appended claims, “a / an”, and “the” in singular forms are intended to include plural forms, unless clearly indicated in the context otherwise. It should also be understood that, the term “and / or” used herein represents and contains any or all possible combinations of one or more associated listed items. When term “about” is used, this term may mean that there can be a variance in value of up to ±10%, of up to 5%, of up to 2%, of up to 1%, of up to 0.5%, of up to 0.1%, or up to 0.01%. Term “range” disclosed in the present disclosure is defined in the form of a lower limit and an upper limit, a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The range defined in this way can be inclusive or exclusive, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is understood that ranges of 60-110 and 80-120 are also obtained. In addition, if the listed minimum values are 1 and 2, and if the listed maximum values are 3, 4 and 5, the ranges of 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5 may be obtained. In the present disclosure, unless otherwise specified, the numerical range “a-b” means the abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range “0-5” means that all the real numbers between “0-5” have been listed, and “0-5” is only the abbreviated representation of these numerical combinations. In addition, when a parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. Composite cathode active material The present disclosure provides in embodiments a cathode active material and its preparation method. Compared with the individual cathode active materials such as NCM and LFMP materials, electrochemical performances of a battery including a positive electrode including the cathode active material of the present disclosure are improved. In the present disclosure, a composite cathode active material including a first component and a second component is provided. The first component has a first formula of LixNiaCobR1cR2dO2, where R1is Mn or Al, R2is selected from a group including Al, Ti, Zr, Nb, Ba, La, and Ag, 1≤x≤1.1, 0.5≤a≤0.8, 0<b≤0.3, 0<b+c≤0.5, 0≤d≤0.005. The second component has a second formula of LiyMneFefR3gPO4, where R3is selected from a group including Mg, Ca, Sr, Ti, V, Cr, Co, Cu, Zn, Zr, Y, Mo, Nb, W, La and Sm, 1≤y≤1.1, 0.5≤e<0.9, 0.1≤f<0.5, 0<g<0.01, and g / f < 0.06. A weight ratio of the second component to the first component is greater than 1:1 and smaller than or equal to 10:1. It can be understood that in each of the first formula and the second formula, a sum of positive valences and negative valences is zero. In the present disclosure, R3is doped in the second component. Because a bond energy of R3- O is greater than that of Fe-O, introduction of R3can reduce a grain size of the second component (i.e., the LFMP component), shorten the lithium ion transmission path and improve the capacity of the composite cathode active material. It has been found that that the amount of R3should not be too high, i.e., g<0.01. Without wishing to be bound by any theory, when the amount of R3is high, some R3ions may form oxides on the surface of the composite cathode active material instead of being inserted into a crystal lattice of the LFMP component. The weight ratio of the second component to the first component is greater than 1:1 and smaller than or equal to 10:1, such as 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 and 10:1. The second component of the composite cathode active material is used as the main component, that is, the first component may be considered to be provided to modify the second component to achieve better battery performances compared to the second component only. During electrode homogenization, the LFMP material is easy to absorb water, which affects its coating performance. After adding the first component according to the above ratios, the cathode active material has a better processability. A problem of uneven mixing of the NCM and the LFMP is solved, and the composite cathode active material is coated on a positive electrode plate uniformly, and thus the battery performance can be improved. When the weight ratio of the second component to the first component is greater than 10:1, the amount of the first component is low, and it is not enough for realizing the modification described above. Compared with the NCM, the composite cathode active material of the present disclosure is safer for application. Compared with the LFMP, the composite cathode active material of the present disclosure exhibits a higher capacity and a better processability. For the present composite cathode active material, a good balance of the electrochemical performance and processability is achieved. In some embodiments, R1is Mn, and / or R2is selected from a group including Zr, Nb, Ba, La, and Ag. For example, the first component is LixNiaCobMncZrdO2. The metallic element such as Zr is doped to stabilize the crystal structure of the first component, and the electrochemical performance of the composite cathode active material is improved. In some embodiments, R3is selected from a group including Ti, Co, Y, Mo, Nb, W, La and Sm. For example, Ti is doped in the second component. Because a bond energy of Ti-O is greater than that of Fe-O, introduction of Ti can reduce a grain size of the second component (i.e., the LFMP), shorten the lithium ion transmission path and improve the capacity of the composite cathode active material. In some embodiments, in the first formula and the second formula, indicators presented amounts of the elements meet any one of conditions of 1≤x≤1.08, 0≤d≤0.003, 0.5≤a≤0.7, 0<b≤0.1, 0.3<b+c≤0.4, 1≤y≤1.05, 0.6≤e<0.7, 0.3≤f<0.5, 0<g≤0.003 or any combinations thereof. It can be known that a range of an indicator includes an upper limit and a lower limit and points therebetween. For example, x is 1, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07 or 1.08. The composite cathode active material of the present disclosure may achieve the good balance of the electrochemical performance and processability. In some embodiments, the composite cathode active material has a particle size Dv50 ranging from 1 to 5 μm, for example is about 3 μm. After calcination, the composite cathode active material is crushed by an airflow into particles having a size range from 1 to 5 μm, which facilitates the application of the present material on a substrate of the positive electrode, improving the processability of the composite cathode active material of the present disclosure. In some embodiments, a molar ratio of R2to R3is in a range from 2:1 to 1:10, for example, is 2:1, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 and 1: 10. The doping elements in the first component and the second component may be presented in a preset ratio in molar. With such a molar ratio, the electrochemical performance of the composite cathode active material is improved. In some embodiments, the composite cathode active material further incudes a carbon coating layer. For example, the composite cathode active material has a carbon coating layer of about 1.0 wt% to 3.0 wt% based on the total weight of the composite cathode active material. The carbon coating layer may further improve an electronic conductivity of the composite cathode active material. Preparation method The composite cathode active material of the present disclosure is prepared by the following steps: Step 1, mixing a precursor containing Ni, Co and R1with lithium hydroxide monohydrate to obtain a first mixture; Step 2, calcinating the first mixture at a temperature ranging from 600 to 900 °C for 8 to 15 h, cooling to a room temperature, and performing an airflow crushing to obtain a second mixture; Step 3, adding a phosphorus source material, an iron source material, a manganese source material and a carbon source material into water to obtain a first aqueous solution with a solid content of 20 to 40%, performing drying to obtain a third mixture; Step 4, mixing a lithium source material with the third mixture to obtain a fourth mixture; Step 5, calcinating the fourth mixture in a nitrogen atmosphere at a first temperature for 4 to 8 h, and adjusting the temperature to a second temperature and calcinating the fourth mixture for 4 to 8 h to obtain a fifth mixture; Step 6, adding the fifth mixture into a second aqueous solution containing R3, and adding them into a grinding machine for grinding to obtain a first slurry; Step 7, adding the second mixture and the first slurry into the grinding machine for grinding to obtain a second slurry, and spray-drying the second slurry to obtain powders; and Step 8, calcinating the powders in a nitrogen atmosphere to obtain the composite cathode active material, wherein the calcinating includes: calcinating at a temperature ranging from 500 to 600°C for 3 to 7 h, calcinating at a temperature ranging from 670 to 770 °C for 2 to 6 h, and keeping the temperature at a range of 550 to 650 °C for 4 to 8 h, and materials are weighted and controlled to allow the composite cathode active material obtained conforms to the first formula and the second formula. It should be note that the above steps may be performed in sequence or not. That is, the steps may be performed in the sequence as the numbering of the steps, or in any other suitable sequence. For example, Steps 1 and 2 are performed before Steps 3 to 6, at the same time as Steps 3 to 6, or after Steps 3 to 6. With the method of the present disclosure, the composite cathode active material having a high electrochemical performance is obtained. Details of the composite cathode active material may refer to the above embodiments which will not be elaborated here. Compared with the NCM, the obtained composite cathode active material of the present disclosure is safer. Compared with the LFMP, the composite cathode active material of the present disclosure exhibits a higher capacity and a better processability. For the present composite cathode active material, a good balance of the electrochemical performance and processability is achieved. Moreover, during electrode homogenization, the LFMP is easy to absorb water, which affects its coating performance. With the method of the present disclosure, the cathode active material has a better processability, a problem of uneven mixing of the NCM and the LFMP is solved, and the composite cathode active material is coated on a positive electrode plate uniformly. In some embodiments, in Step 1, an R2containing material is added with the precursor containing Ni, Co and R1, and lithium hydroxide monohydrate to obtain the first mixture. After the calcinating in Step 2, Zr is doped in the NiCoR1material, so as to stabilize the crystal structure of the first component, and the electrochemical performance of the composite cathode active material is improved. In some embodiments, the phosphorus source material includes at least one selected from ferric phosphate and lithium dihydrogen phosphate. In some embodiments, the iron source material includes at least one selected from ferric phosphate and ferric nitrate. In some embodiments, the manganese source material includes at least one selected from manganese carbonate and manganese sulfate. In Step 3, P, Fe, Mn source materials are provided and amounts of P, Fe, Mn are controlled, for example, an amount ratio P: (Fe+Mn) is controlled to be 1 : (0.95 to 1). After this, the lithium source material is added into the third mixture as described in Step 4. In this way, proportions of elements P, Fe, Mn and a proportion of Li element are controlled separately, resulting in precise element amount control. It should be understood that a source material may provide one or more elements. For example, ferric phosphate as both the Fe and P sources, manganese carbonate as the Mn source, and lithium dihydrogen phosphate as the P source are mixed in Step 3. The amounts / molar numbers of elements Fe, Mn and P are controlled. The P source here also provides Li, but it is not enough, so lithium carbonate is added in Step 4. In some embodiments, the carbon source material includes at least one selected from sucrose and polyethylene glycol (PEG). In some embodiments, the third mixture includes the carbon source material of 1 to 5 wt% based on a total weight of the third mixture. For example, PEG is added in Step 3, and it is not only a carbon source material, but also a dispersant, which makes the components better dispersed. In some embodiments, before drying, the first aqueous solution is stirred and subjected to grinding to make particles in the first aqueous solution have a particle size Dv50 of 300 nm to 500 nm. In some embodiments, the first aqueous solution is dried by spray drying with a nebulizer, wherein the nebulizer has an inlet temperature of 250 to 350 °C, an outlet temperature of 50 to 150 °C and an atomization frequency of 40 to 80 Hz. In some embodiments, the third mixture spray-dried has a particle size Dv50 of 10 to 50 μm. In this way, impurities and moisture may be removed, the particle size Dv50 is reduced and uniformity is improved. In some embodiments, the fourth mixture is added to a third aqueous solution containing sodium dodecylbenzene sulfonate, which is used as a surfactant and a dispersant. They are stirred at a speed of 50 to 200 rad / min for 1 to 10 min, and dried, so as to improve the uniformity. In some embodiments, in Step 5, the first temperature is ranged from 330 to 430 °C at which the carbon source material is decomposed and / or the second temperature is ranged from 480 to 580 °C, at which a lithium ferromanganese phosphate crystal is formed. As described above, in Step 6, R3is introduced. For example, the second aqueous solution containing titanium dioxide is added. In some embodiments, after the grinding in Step 6, particles in the first slurry have a particle size Dv50 of 350 to 550 nm. The first component is further mixed in Step 7. Then all the components are calcinated in Step 8. With the specific calcinating process in Step 8, R3, for example, Ti, can be doped into the second component. Without wishing to be bound by any theory, a bond energy of Ti-O is greater than that of Fe-O, introduction of Ti can reduce a grain size of the second component (i.e., the LFMP), shorten the lithium ion transmission path and improve the capacity of the composite cathode active material. In some embodiments, in Step 7, the second slurry is obtained by adding a carbon source material with the second mixture and the first slurry. In some embodiments, the carbon source material includes sucrose and polyethylene glycol, and / or the carbon source material has an amount of 1 to 10 wt% based on a total weight of the second mixture and the fifth mixture. In this way, the carbon source material is formed as the carbon coating layer. The carbon coating layer may not only prevent an interface reaction between an electrolyte and the composite cathode active material of the present disclosure, but also improve the electronic conductivity of the composite cathode active material. In some embodiments, after calcination, the composite cathode active material is crushed by an airflow into particles having a size range from 1 to 5 μm, which facilitates the application of the present material on a substrate of the positive electrode, improving the processability of the composite cathode active material of the present disclosure. Positive electrode plate The composite cathode active material may be used to preparing a positive electrode plate. The positive electrode plate includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, and the positive electrode film layer includes the cathode active material, i.e., the composite material of the present disclosure. As an example, the positive electrode current collector has two surfaces that are opposite in its thickness direction, and the positive electrode film layer is arranged on either or both of the two opposite surfaces of the positive electrode current collector. The positive electrode film layer includes the present material that is capable of absorbing and releasing lithium. In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, an aluminum foil is used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. The composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy) on the polymer material (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE)). The positive electrode film layer optionally includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride- hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, or any combination thereof. In some embodiments, the positive electrode film layer includes the binder of 0.1 to 3.5%, optionally 0.5 to 2.5% by weight. In some embodiments, the positive electrode film layer optionally includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Cochin black, carbon dots, carbon nanotubes, graphene, carbon nanofibers or any combination thereof. In some embodiments, the positive electrode film layer includes the conductive agent of 0.05% to 5%, optionally 0.5% to 3% by weight. In some embodiments, the positive electrode plate can be prepared by dispersing the above- mentioned components for preparing the positive electrode plate, such as the cathode active material, the conductive agent, the binder and any other components, in a solvent (such as N- methylpyrrolidone) to form a positive paste. The positive paste is coated on the positive electrode current collector, and after drying and cold pressing, the positive electrode plate is obtained. Secondary battery A secondary battery may include the positive electrode plate of the present disclosure described above, a negative electrode plate, a separator and an electrolyte. The secondary battery may be a battery module or a battery pack, which may be applied in electronic devices, such as mobile terminals and vehicles. Due to the composite cathode active material, the secondary battery of the present disclosure has a high capacity and a long service life. The electronic device of the present disclosure is powered by the secondary battery and may be working stably. The negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector. The negative electrode film layer includes an anode active material. As an example, the negative electrode current collector has two surfaces along a thickness direction thereof and facing in opposite directions, and the negative electrode film layer is provided on either or both of the two surfaces. In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector may be formed by forming a metallic material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a substrate of a high molecular material such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc. In some embodiments, the anode active material may be an anode active material known in the art. As an example, the anode active material may include at least one selected from artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials and lithium titanate. The silicon-based material may be at least one selected from elemental silicon, silicon-oxygen compounds, silicon-carbon complexes, silicon-nitrogen complexes, and silicon alloys. The tin-based material may be at least one selected from elemental tin, tin oxide compounds, and tin alloys. The present disclosure is not limited to these materials, and other materials that may be used as an anode active material for a battery may be used. These anode active materials may be used separately or in combination (for example two or more kinds of materials are used). In some embodiments, the negative electrode film layer optionally includes a binder. The binder may be at least one selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS). In some embodiments, the negative electrode film layer optionally includes a conductive agent. The conductive agent may be at least one selected from superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the negative electrode film layer optionally includes other adjuvants, such as thickeners (e.g. sodium carboxymethylcellulose (CMC-Na)). In some embodiments, the negative electrode plate may be prepared by: dispersing the above- mentioned components for preparing the negative electrode plate, such as the anode active material, the conductive agent, the binder and any other components in a solvent (such as deionized water) to form a negative electrode slurry; coating the negative electrode slurry on the negative electrode current collector, and obtaining the negative electrode plate after drying, cold pressing and other processes. The electrolyte serves to conduct ions between the positive electrode plate and the negative electrode plate. The kind of the electrolyte is not particularly limited in the present disclosure, and may be selected according to requirements. For example, the electrolyte may be liquid, gel, or solid. In some embodiments, the electrolyte is an electrolyte solution. The electrolyte includes an electrolyte salt and a solvent. In some embodiments, the electrolyte salt may include at least one selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonimide, lithium bis-trifluoromethane sulfonimide, lithium triflate, lithium difluorophosphate, lithium difluorooxalato borate, lithium dioxalato borate, lithium difluorooxalato phosphate, and lithium tetrafluorooxalato phosphate. In some embodiments, the solvent may include at least one selected from ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone. In some embodiments, the electrolyte optionally includes an additive. For example, the additive may include a negative electrode film-forming additive, a positive electrode film-forming additive, and may further include an additive capable of improving properties of the battery, such as an additive for improving overcharge properties of the battery, and an additive for improving high-temperature or low-temperature properties of the battery. In some embodiments, the separator is further included in the secondary battery. The type of the separator is not particularly limited in the present disclosure, and any known separator having a porous structure and good chemical and mechanical stability may be used. In some embodiments, the material of the separator may be at least one selected from glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, which is not limited in the present disclosure. In a case where the separator is a multilayer composite film, the materials of individual layers may be the same or different. In some embodiments, the electrolyte is a lithium ion solid electrolyte. In some embodiments, the positive electrode plate, the negative electrode plate, and the separator may be prepared into an electrode assembly by a winding process or a lamination process. In some embodiments, the secondary battery includes an outer package. The outer package is used to package the electrodes and the electrolyte. In some embodiments, the outer package of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell and the like. Alternatively, the outer package of the secondary battery may be a soft package, such as a soft bag. The soft bag may be made of a polymer material such as plastics, polypropylene, polybutylene terephthalate and polybutylene succinate. The shape of the secondary battery may be cylindrical, square or any other shape, which is not limited in the present disclosure. Experimental Section The following Examples are included to demonstrate certain aspects and embodiments of the present disclosure. It should be appreciated by those of skill in the art, however, that the following description is illustrative only and should not be taken in any way as a restriction of the present disclosure. Test methods Carbon content of the composite cathode active material is measured by a carbon-sulfur analyzer. Element of the composite cathode active material is measured by an inductively coupled plasma (ICP) spectrometer. Particle size of a material is measured by a laser particle size analyzer (Malvern Master Size 2000) according to GB / T19077-2016 / ISO 13320:2009. The particle size measured in the present disclosure is a median particle size by volume Dv50. Electrochemical performance Coin cell is prepared as follows. (1) According to a weight ratio of 90:5:5, the cathode active material, SURPER P conductive carbon black and polytetrafluoroethylene powders are mixed, and further added with toluene. The obtained mixture is dried and applied to obtain a positive electrode plate with a thickness of 150 μm. (2) An aluminum foil with a thickness of 20 μm is used as a positive electrode current collector, porous polypropylene with a thickness of 25 μm is used as a separator, a lithium foil with a thickness of 500 μm is used as a negative electrode, and an electrolyte is 1 mol / L LiPF6 / EC+DEC (that is, a solute of the electrolyte is LiPF6, and a solvent is a mixed solvent of ethylene carbonate and diethyl carbonate with a mass ratio of 1:1). Components for the battery are assembled in a glovebox with an argon atmosphere to obtain the battery. During electrochemical test, the coin cell is charged to 4.3 V at 25 °C with a load current of 75mA per 1g cathode active material, and then discharged to 2.0 V with a load current of 75mA per 1g cathode active material, and an initial discharge capacity (i.e., 1C capacity shown in the following tables) is obtained. Battery charge-discharge cycle is performed for 50 times (1C charge and discharge, a voltage range of 2.0 to 4.3 V). A cycle performance is presented by a ratio of the fiftieth discharge capacity to the initial discharge capacity. It should be noted that the present disclosure only describes some test method and conditions. Materials, measurements and processes that are known in the art are not described herein. Examples Inventive Example 1 (IE1) A precursor of Ni0.68Co0.07Mn0.25(OH)2, LiOH·H2O, and ZrO2were weighted and mixed to obtain a first mixture. The first mixture was calcinated at 780°C for 10 h, and cooled to a room temperature. After an airflow crushing, a second mixture, i.e., Zr-doped NCM material was obtained. Ferric phosphate, manganese carbonate and lithium dihydrogen phosphate were added into an aqueous solution containing sucrose and PEG in a weight ratio of 1 : 1.4, and mixed. The solution has a solid content of 30%. The solution was stirred at a room temperature for 30 min, and added into a grinding machine to obtain a particle size Dv50 of 400 nm, followed by introducing to a nebulizer for spray drying to obtain a third mixture. The nebulizer has an inlet temperature of 300 °C, an outlet temperature of 100 °C and an atomization frequency of 60 Hz. The third mixture spray-dried has a particle size Dv50 of 30 μm. Lithium carbonate was mixed with the third mixture, and added into an aqueous solution containing 0.5% sodium dodecylbenzene sulfonate. They were stirred at a speed of 100 rad / min for 5 min, dried at 200 °C and sieved with a 200 mesh screen to obtain a fourth mixture. The fourth mixture was calcinated in a nitrogen atmosphere at 380 °C for 6 h. The temperature was adjusted to 500 °C and the fourth mixture was calcinated for 6 h to obtain a fifth mixture. 100 g of the fifth mixture was added into an aqueous solution containing metatitanic acid, and the solution was added into a grinding machine with 0.3 mm zirconium bead and 0.3 mm screen. A size Dv50 of particles after grinding is 450nm±50nm, and thus a first slurry was obtained. 25 g of the second mixture and the obtained first slurry were added into the grinding machine as well as 4.14 g sucrose and 5.78 g PEG. After grinding, a second slurry was obtained with a particle size Dv50 of 5 microns. The second slurry was spray-dried to obtain powders. The powders were calcinated in a nitrogen atmosphere at 550 °C for 5h, further calcinated at an increased temperature of 720 °C for 4 h, and kept for 6 h at a decreased temperature of 600 °C to obtain a composite cathode active material. The composite cathode active material was further crushed by an airflow. The composite cathode active material obtained in Example 1 includes a first component, i.e., a Zr-doped NCM component, a second component, i.e., a Ti-doped LFMP component, and a carbon component as a coating layer. In the first component, an amount ratio of Li : Ni : Co : Mn : Zr is 1.02 : 0.68 : 0.07 : 0.25 : 0.002, and in the second component, an amount ratio of Li : Mn : Fe : Ti is 1.02 : 0.6 : 0.4 : 0.003. The composite cathode active material has a particle size Dv50 of 3 μm, a carbon content of 1.3 wt%, and a weight ratio of the second component to the first component is about 4:1. Inventive Example 2 (IE2) Composite cathode active material for IE2 was prepared in the same way as IE1 expect that an aqueous solution containing metatitanic acid in a different amount was used, resulting in an amount ratio of Li : Mn : Fe : Ti being 1.02 : 0.6 : 0.4 : 0.002 in the second component. Inventive Example 3 (IE3) Composite cathode active material for IE3 was prepared in the same way as IE1 expect that ZrO2was not added. Inventive Example 4 (IE4) Composite cathode active material for IE4 was prepared in the same way as IE1 expect that ZrO2was added in a different amount, resulting in an amount ratio of Li : Ni : Co : Mn : Zr being 1.02 : 0.68 : 0.07 : 0.25 : 0.01 in the first component. Inventive Example 5 (IE5) Composite cathode active material for IE5 was prepared in the same way as IE1 expect that TiO2was added instead of ZrO2, resulting in a Ti-doped NCM component as a first component. In the first component, an amount ratio of Li : Ni : Co : Mn : Ti is 1.02 : 0.68 : 0.07 : 0.25 : 0.002. Inventive Example 6 (IE6) Composite cathode active material for IE6 was prepared in the same way as IE1 expect that Al2O3was added instead of ZrO2, resulting in an Al-doped NCM component as a first component. In the first component, an amount ratio of Li : Ni : Co : Mn : Al is 1.02 : 0.68 : 0.07 : 0.25 : 0.002. Inventive Example 7 (IE7) Composite cathode active material for IE7 was prepared in the same way as IE1 expect that magnesium hydrate was used instead of metatitanic acid, resulting in an Mg-doped LFMP component as a second component. In the second component, an amount ratio of Li : Mn : Fe : Mg is 1.02 : 0.6 : 0.4 : 0.003. Inventive Example 8 (IE8) Composite cathode active material for IE8 was prepared in the same way as IE1 expect that tin oxide was used instead of metatitanic acid, resulting in a Sn-doped LFMP component as a second component. In the second component, an amount ratio of Li : Mn : Fe : Sn is 1.02 : 0.6 : 0.4 : 0.003. Inventive Example 9 (IE9) Composite cathode active material for IE9 was prepared in the same way as IE1 expect that ammonium metavanadate was used instead of metatitanic acid, resulting in a V-doped LFMP component as a second component. In the second component, an amount ratio of Li : Mn : Fe : V is 1.02 : 0.6 : 0.4 : 0.003. Inventive Example 10 (IE10) Composite cathode active material for IE10 was prepared in the same way as IE1 expect that 20 g of the second mixture was added, resulting in a weight ratio of the second component to the first component of about 5:1 in the composite cathode active material of IE10. Inventive Example 11 (IE11) Composite cathode active material for IE11 was prepared in the same way as IE1 expect that 10 g of the second mixture was added, resulting in a weight ratio of the second component to the first component of about 10:1 in the composite cathode active material of IE11. Comparative Example 1 (CE1) A precursor of Ni0.68Co0.07Mn0.25(OH)2, LiOH·H2O, and ZrO2were weighted and mixed to obtain a first mixture. The first mixture was calcinated at 780°C for 10 h, and cooled to a room temperature. After an airflow crushing, a second mixture, i.e., Zr-doped NCM material was obtained, where an amount ratio Li : Ni : Co : Mn : Zr is 1.02 : 0.68 : 0.07 : 0.25 : 0.002. Comparative Example 2 (CE2) Ferric phosphate, manganese carbonate and lithium dihydrogen phosphate were added into water to obtain a solution. The solution has a solid content of 30%. The solution was stirred at a room temperature for 30 min, and added into a grinding machine to obtain a particle size Dv50 of 400 nm, followed by introducing to a nebulizer for spray drying to obtain a first mixture. The nebulizer has an inlet temperature of 300 °C, an outlet temperature of 100 °C and an atomization frequency of 60 Hz. The third mixture spray-dried has a particle size Dv50 of 30 μm. Lithium carbonate was mixed with the first mixture, and added into an aqueous solution containing 0.5% sodium dodecylbenzene sulfonate. They were stirred at a speed of 100 rad / min for 5 min, dried at 200 °C and sieved with a 200 mesh screen to obtain a second mixture. The second mixture was calcinated in a nitrogen atmosphere at 380 °C for 6 h. The temperature was adjusted to 500 °C and the second mixture was calcinated for 6 h to obtain a third mixture. The third mixture was added into water, and further added into a grinding machine with 0.3 mm zirconium bead and 0.3 mm screen. A size of particles after grinding is 450nm±50nm, and thus a first slurry was obtained. The first slurry was spray-dried to obtain powders. The powders were calcinated in a nitrogen atmosphere at 550 °C for 5 h, further calcinated at an increased temperature of 720 °C for 4 h, and kept for 6 h at a decreased temperature of 600 °C to obtain a composite cathode active material. The composite cathode active material was further crushed by an airflow. The cathode active material obtained in CE2 is an LFMP material which has a particle size Dv50 of 3 μm, and an amount ratio of Li : Mn : Fe is 1.02 : 0.6 : 0.4. Comparative Example 3 (CE3) Composite cathode active material for CE3 was prepared in the same way as IE1 expect that metatitanic acid is not added. Comparative Example 4 (CE4) Composite cathode active material for CE4 was prepared in the same way as IE1 expect that an aqueous solution containing metatitanic acid in a different amount was used, resulting in an amount ratio of Li : Mn : Fe : Ti being 1.02 : 0.6 : 0.4 : 0.01 in the second component. Comparative Example 5 (CE5) Composite cathode active material for CE5 was prepared in the same way as IE1 expect that 5 g of the second mixture was added, resulting in a weight ratio of the second component to the first component of about 20:1 in the composite cathode active material of CE5. Electrochemical performances of IE1 and CE1-3 are shown in Table 1. Table 1 1C capacity cycle performance IE1 155mAh / g 98% CE1 187mAh / g 86% CE2 148mAh / g 90% CE3 152mAh / g 94% From Table 1, it can be seen that compared with the NCM material of CE1, the cycle performance of the composite cathode active material of IE1 is much higher, resulting in a good stability and a long service long of the battery. Compared with the LFMP of CE2, the composite cathode active material of IE1 exhibits higher capacity and cycle performance. In addition, based on the comparison of IE1 and CE3, Ti-doping improves the capacity and the cycle performance. Therefore, compared with the CEs, the present material has a good balance of the capacity and the cycle performance. Electrochemical performances of IE1-2 and CE3-4 are shown in Table 2. Table 2 1C capacity cycle performance IE1 155mAh / g 98% IE2 154mAh / g 98% CE3 152mAh / g 94% CE4 153mAh / g 95% Table 2 shows performances of materials with different Ti amounts. It can be seen that the material of IE1, where an amount ratio of Li : Mn : Fe : Ti is 1.02 : 0.6 : 0.4 : 0.003 in the second component, has greater capacity and cycle performances than the material of IE2 where an amount ratio of Li : Mn : Fe : Ti is 1.02 : 0.6 : 0.4 : 0.002 in the second component. It can be further noted that the material of CE4, where an amount ratio of Li : Mn : Fe : Ti is 1.02 : 0.6 : 0.4 : 0.01 in the second component, has decreased performances compared with the material of IE1 / IE2. Without wishing to be bound by any theory, the decreased performances may be caused by a relatively high Ti amount. When a concentration of Ti ions is high, some Ti ions may form TiO2on the surface of the material (e.g., the LFMP) instead of being inserted into a crystal lattice of the LFMP, and thus the material of CE4 shows decreased performances compared with the examples with a relatively low Ti amount. Electrochemical performances of IE1, and IE3-4 are shown in Table 3. Table 3 1C capacity cycle performance IE1 155mAh / g 98% IE3 153mAh / g 96% IE4 151mAh / g 95% Table 3 shows performances of composite cathode active materials with different Zr amounts. It can be seen that the material of IE1, where an amount ratio of Li : Ni : Co : Mn : Zr is 1.02 : 0.68 : 0.07 : 0.25 : 0.002 in the first component, has greater capacity and cycle performance than the material of IE3 where Zr is not doped, and the material of IE4, where an amount ratio of Li : Ni : Co : Mn : Zr is 1.02 : 0.68 : 0.07 : 0.25 : 0.01 in the first component. That is, the material with a suitable doped amount is better than the material without doping and also better than the material with a high doped amount. Electrochemical performances of IE1, and IE5-6 are shown in Table 4. Table 4 1C capacity cycle performance IE1 155mAh / g 98% IE5 154mAh / g 96% IE6 153mAh / g 95% Table 4 shows performances of composite cathode active materials including the first component doped with different elements, i.e., Zr for IE1, Ti for IE5, and Al for IE6. These examples exhibit good capacity and cycle performance, and it shows that different elements can be selected for the first component of the composite cathode active material of the present disclosure. Electrochemical performances of IE1, and IE7-9 are shown in Table 5. Table 5 1C capacity cycle performance IE1 155mAh / g 98% IE7 154mAh / g 96% IE8 153mAh / g 96% IE9 154mAh / g 95% Table 5 shows performances of composite cathode active materials including the second component doped with different elements, i.e., Ti for IE1, Mg for IE7, Sn for IE8, and V for IE9. These examples exhibit good capacity and cycle performance, and it shows that different elements can be selected for the second component of the composite cathode active material of the present disclosure. Electrochemical performances of IE1, IE10-11, and CE5 are shown in Table 6. Table 6 1C capacity cycle performance IE1 155mAh / g 98% IE10 154mAh / g 96% IE11 151mAh / g 95% CE5 149mAh / g 92% Table 6 shows performances of composite cathode active materials with different weight ratios of the second component to the first component. In the composite cathode active material of the present disclosure, the second component is used as the main component, that is, the first component is considered to be provided to modify the second component. During electrode homogenization, the LFMP material is easy to absorb water, which affects its coating performance. It can be seen from Table 6 that the capacity and the cycle performance of CE5 are relatively low compared with the inventive examples of the present disclosure. It indicates that if the amount of the first component is too low, it is not enough for realizing the modification for the second component. Reference throughout this specification to “an embodiment,” “some embodiments,” “one embodiment”, “another example,” “an example,” “a specific example,” or “some examples,” means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present disclosure. Thus, the appearances of the phrases such as “in some embodiments,” “in one embodiment”, “in an embodiment”, “in another example,” “in an example,” “in a specific example,” or “in some examples,” in various places throughout this specification are not necessarily referring to the same embodiment or example of the present disclosure. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples. Other embodiments of the present disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure disclosed here. This application is intended to cover any variations, uses, or adaptations of the disclosure following the general principles thereof and including such departures from the present disclosure as come within known or customary practice in the art. It is intended that the specification and examples be considered as illustrative only, with a true scope and spirit of the disclosure being indicated by the following claims.

Claims

CLAIMS 1. A composite cathode active material, comprising: a first component, having a first formula of LixNiaCobR1cR2dO2, where R1is Mn or Al, R2is selected from a group comprising Al, Ti, Zr, Nb, Ba, La, and Ag, 1≤x≤1.1, 0.5≤a≤0.8, 0<b≤0.3, 0<b+c≤0.5, 0≤d≤0.005; and a second component, having a second formula of LiyMneFefR3gPO4, where R3is selected from a group comprising Mg, Ca, Sr, Ti, V, Cr, Co, Cu, Zn, Zr, Y, Mo, Nb, W, La and Sm, 1≤y≤1.1, 0.5≤e<0.9, 0.1≤f<0.5, 0<g<0.01, and g / f < 0.06; wherein a weight ratio of the second component to the first component is greater than 1:1 and smaller than or equal to 10:

1.

2. The composite cathode active material according to claim 1, wherein R1is Mn, and / or R2is selected from a group consisting of Zr, Nb, Ba, La, and Ag.

3. The composite cathode active material according to claim 1 or 2, wherein R3is selected from a group consisting of Ti, Co, Y, Mo, Nb, W, La and Sm.

4. The composite cathode active material according to any one of claims 1 to 3, wherein 1≤y≤1.05, 0.6≤e<0.7, 0.3≤f<0.5, and / or 0<g≤0.

003.

5. The composite cathode active material according to any one claims 1 to 4, wherein 1≤x≤1.08, and / or 0≤d≤0.

003.

6. The composite cathode active material according to any one claims 1 to 5, wherein 0.5≤a≤0.7, 0<b≤0.1, and / or 0.3<b+c≤0.

4.

7. The composite cathode active material according to any one of claims 1 to 6, wherein the composite cathode active material has a particle size Dv50 ranging from 1 to 5 μm.

8. The composite cathode active material according to any one of claims 1 to 7, wherein a molar ratio of R2to R3is in a range from 2:1 to 1:

10.

9. The composite cathode active material according to any one of claims 1 to 8, further comprising:1.0 wt% to 3.0 wt% based on the total weight of the composite cathode active material of a carbon coating layer.

10. A method for preparing the composite cathode active material according to claim 1, comprising: mixing a precursor containing Ni, Co and R1with lithium hydroxide monohydrate to obtain a first mixture; calcinating the first mixture at a temperature ranging from 600 to 900 °C for 8 to 15 h, cooling to a room temperature, and performing an airflow crushing to obtain a second mixture; adding a phosphorus source material, an iron source material, a manganese source material and a carbon source material into water to obtain a first aqueous solution with a solid content of 20 to 40%, performing drying to obtain a third mixture; mixing a lithium source material with the third mixture to obtain a fourth mixture; calcinating the fourth mixture in a nitrogen atmosphere at a first temperature for 4 to 8 h, and adjusting the temperature to a second temperature and calcinating the fourth mixture for 4 to 8 h to obtain a fifth mixture; adding the fifth mixture into a second aqueous solution containing R3, and adding them into a grinding machine for grinding to obtain a first slurry; adding the second mixture and the first slurry into the grinding machine for grinding to obtain a second slurry, and spray-drying the second slurry to obtain powders; and calcinating the powders in a nitrogen atmosphere to obtain the composite cathode active material, wherein the calcinating comprises: calcinating at a temperature ranging from 500 to 600°C for 3 to 7 h, calcinating at a temperature ranging from 670 to 770 °C for 2 to 6 h, and keeping the temperature at a range of 550 to 650 °C for 4 to 8 h, and materials are weighted and controlled to allow the composite cathode active material obtained conforms to the first formula and the second formula.

11. The method according to claim 10, wherein the first mixture is obtained by mixing an R2containing material with the precursor containing Ni, Co and R1, and lithium hydroxide monohydrate.

12. The method according to claim 10 or 11, wherein the phosphorus source material comprises at least one selected from ferric phosphate and lithium dihydrogen phosphate, and / or the iron source material comprises at least one selected from ferric phosphate and ferric nitrate, and / orthe manganese source material comprises at least one selected from manganese carbonate and manganese sulfate, and / or the carbon source material comprises at least one selected from sucrose and polyethylene glycol.

13. The method according to any one of claims 10 to 12, wherein the third mixture comprises the carbon source material of 1 to 5 wt% based on a total weight of the third mixture.

14. The method according to any one of claims 10 to 13, wherein before drying, the method further comprises: stirring the first aqueous solution and performing grinding to make particles in the first aqueous solution have a particle size Dv50 of 300 nm to 500 nm.

15. The method according to any one of claims 10 to 14, wherein the first aqueous solution is dried by spray drying with a nebulizer, wherein the nebulizer has an inlet temperature of 250 to 350 °C, an outlet temperature of 50 to 150 °C and an atomization frequency of 40 to 80 Hz.

16. The method according to claim 15, wherein the third mixture spray-dried has a particle size Dv50 of 10 to 50 μm.

17. The method according to any one of claims 10 to 16, further comprising: adding the fourth mixture to a third aqueous solution containing sodium dodecylbenzene sulfonate, stirring at a speed of 50 to 200 rad / min for 1 to 10 min, and drying.

18. The method according to any one of claims 10 to 17, wherein the first temperature is ranged from 330 to 430 °C, and / or the second temperature is ranged from 480 to 580 °C.

19. The method according to any one of claims 10 to 18, wherein particles in the first slurry have a particle size Dv50 of 350 to 550 nm.

20. The method according to any one of claims 10 to 19, wherein the second slurry is obtained by adding a carbon source material with the second mixture and the first slurry.

21. The method according to claim 20, wherein the carbon source material comprises sucrose and polyethylene glycol, and / or the carbon source material has an amount of 1 to 10 wt% basedon a total weight of the second mixture and the fifth mixture.

22. The method according to any one of claims 10 to 21, further comprising: crushing the composite cathode active material by an airflow, wherein the composite cathode active material has a particle size Dv50 ranging from 1 to 5 μm.

23. A secondary battery, comprising: a positive electrode comprising the composite cathode active material according to any one of claims 1 to 9.

24. An electronic device, comprising: the secondary battery according to claim 23.