Method for preparing composite cathode active material, composite cathode active material, secondary battery and electronic device

Abstract

A method for preparing a composite cathode active material includes: providing a carbon material having: a specific surface area of > 350 m2 / g, a cumulative pore volume of > 0.34 cm3 / g, and an ID / IG ratio of < 0.80, where the ID / IG ratio represents an intensity ratio of D band to G band in Raman spectroscopy; mixing the carbon material with a precursor source material for preparing a cathode active material having a formula of LiMPO4 to obtain a mixture, where an amount of the carbon material is in a range of 0.5 to 4 wt% based on a total weight of 1 mol of the cathode active material; adding the mixture into water to form a slurry; grinding the slurry, and spray drying the slurry to obtain a precursor material; and calcinating the precursor material to obtain the composite cathode active material.

Description

[0001] P139805-19679-KT

[0002] METHOD FOR PREPARING COMPOSITE CATHODE ACTIVE MATERIAL, COMPOSITE CATHODE ACTIVE MATERIAL, SECONDARY BATTERY AND ELECTRONIC DEVICE

[0003] FIELD

[0004] The present disclosure relates to the technical field of batteries, and more particularly to a method for preparing a composite cathode active material, a composite cathode active material, a secondary battery and an electronic device.

[0005] BACKGROUND

[0006] Olivine cathode active materials (such as LiFePO4 referred as LFP) are widely used in secondary batteries for electric vehicles and energy storage. However, when the secondary battery is applied at a low temperature (for example, -20 °C), the capacity performance of the secondary battery is degraded, which limits its application in the low-temperature environment.

[0007] Therefore, there is a need to develop a method for preparing a cathode active material which is able to provide a cathode active material with improved electrochemical performances.

[0008] SUMMARY

[0009] Embodiments of the present disclosure seek to solve at least one of the problems existing in the related art to at least some extent. Objects of the present disclosure are to provide a method for preparing a composite cathode active material, in which a carbon material is applied to improve the electrochemical performances of the olivine cathode active materials and provide a composite cathode active material with improved electrochemical performances such as an electric capacity, and a discharge capacity retention rate at the low temperature.

[0010] The finding of the present disclosure is to provide a method for preparing a composite cathode active material, a composite cathode active material, a secondary battery and an electronic device.

[0011] According to a first aspect of the present disclosure, a method for preparing a composite cathode active material includes: providing a carbon material having: a specific surface area of > 350 m2 / g, a cumulative pore volume of > 0.34 cm3 / g, and an ID / IG ratio of < 0.80, where the ID / IG ratio represents an intensity ratio of D band to G band in Raman spectroscopy; mixing the carbon material with a precursor source material to obtain a mixture, where the precursor source material is used for preparing a cathode active material having a formula of LiMPCU, where M represents Fe, or Fe and Mn, where an amount of the carbon material is in a range of 0.5 to 4 wt% based on a total weight of 1 mol of the cathode active material; adding the mixture into water to form a slurry; grinding the slurry, and spray drying the slurry to obtain a precursor material; and calcinating the precursor material in an atmosphere of a mixture gas including nitrogen and a reducing gas to obtain the composite cathode active material.

[0012] In the present disclosure, the inventors have found that the specific carbon material having a good balance between the porosity and the graphitization degree can be applied in the composite cathode active material for improving the electrochemical performances such as an electric capacity, and a discharge capacity retention rate at the low temperature of the composite cathode active material.

[0013] In some embodiments, the cathode active material has a formula of LiMnaFebP04, where a + b = 1, and 0.5 < a < 0.9.

[0014] In some embodiments, the carbon material has the specific surface area of > 400 m2 / g, the cumulative pore volume of > 0.50 cm3 / g, and / or the ID / IG ratio of < 0.50.

[0015] In some embodiments, an amount of the carbon material is in a range of 1.0 to 3.0 wt% based on a total weight of 1 mol of the cathode active material.

[0016] In some embodiments, the slurry has a solid content ranging from 20 to 60 wt%.

[0017] In some embodiments, the reducing gas includes hydrogen and / or CO, and / or a flow volume of the reducing gas ranges from 5 to 10% of the flow volume of the mixture gas.

[0018] In some embodiments, calcinating the precursor material includes: calcinating the precursor material at a temperature of 600 to 900 °C for 2 to 24 h, where the temperature is increased at a rate of 1 to 10 °C / min.

[0019] In some embodiments, the carbon material is prepared by: adding pyrrole and an oxidant into a hydrochloric acid solution to form a pyrrole solution and an oxidant solution, respectively; dissolving manganese chloride tetrahydrate in the pyrrole solution, wherein a molar ratio of Mn to pyrrole is in a range of 2:3 to 3:2; adding the oxidant solution into the pyrrole solution under stirring to form a gel mixture, and performing aging on the gel mixture at a room temperature for at least 12 h; freeze drying the gel mixture to obtain a polypyrrole hydrogel composite material; calcinating the polypyrrole hydrogel composite material at a temperature ranging from 900 to 1200 °C for 2 to 6 h in a nitrogen atmosphere to obtain solid powders; immersing the solid powders in an acid solution for removing Mn, filtering, washing and drying the solid powders to obtain the carbon material.

[0020] In some embodiments, the oxidant includes ammonium persulfate and / or ferric chloride.

[0021] In some embodiments, a molar ratio of pyrrole to the oxidant ranges from 10: 1 to 1 : 1.

[0022] In some embodiments, the hydrochloric acid solution has a concentration of 0.1-12 mol / L.

[0023] In some embodiments, immersing the solid powders in an acid solution at 40 to 100 °C for at least 2 hours, and the acid solution has a concentration of 0.1 to 2 mol / L.

[0024] In some embodiments, drying is carried out under vacuum at the temperature of 30-80 °C. In some embodiments, the precursor source material includes a lithium source, an iron source, a phosphorus source and an optional manganese source, wherein a molar ratio of Li : (Fe+Mn) : P is (1-1.05) : 1 : (0.96-1).

[0025] In some embodiments, the lithium source includes at least one selected from lithium carbonate, lithium hydroxide, lithium acetate and lithium dihydrogen phosphate.

[0026] In some embodiments, the manganese source includes at least one selected from manganese acetate, manganese nitrate, ammonium manganous sulfate, manganese carbonate and manganese oxalate.

[0027] In some embodiments, the iron source includes at least one selected from iron phosphate, ferrous oxalate, iron nitrate, ferric oxide and ferric chloride.

[0028] In some embodiments, the phosphorus source includes at least one selected from phosphoric acid, lithium dihydrogen phosphate, monoammonium phosphate and ammonium dihydrogen phosphate.

[0029] According to a second aspect of the present disclosure, a composite cathode active material prepared by the method as described in the first aspect is provided. In the present disclosure, the composite cathode active material exhibit improved electrochemical performances such as an electric capacity, and a discharge capacity retention rate at the low temperature.

[0030] In some embodiments, the composite cathode active material has a particle size Dv50 ranging from 0.5 to 2.0 pm.

[0031] In some embodiments, the composite cathode active material has a compaction density measured at 3 tons of greater than 2.20 g / cm3.

[0032] In some embodiments, the composite cathode active material has a resistivity less than 300 (1 cm measured at 25 °C.

[0033] According to a third aspect of the present disclosure, a secondary battery including a positive electrode including the composite cathode active material of the second aspect is provided. Due to the composite cathode active material, the secondary battery of the present disclosure has a high capacity and a high stability at the low temperature.

[0034] According to a fourth aspect of the present disclosure, an electronic device including the secondary battery of the fifth aspect is provided. The electronic device of the present disclosure is powered by the secondary battery and may be working stably.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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%.

[0039] 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.

[0040] Olivine cathode active materials are widely used in secondary batteries for electric vehicles and energy storage. However, when the secondary battery is applied at a low temperature, the capacity performance of the battery is degraded, which limits its application in the low-temperature environment. For example, for the LFP secondary battery, the discharge capacity retention rate thereof at -20 °C is less than 50%. Such a degradation may be caused by the low conductivity and low lithium ion diffusion coefficient of the LFP secondary battery.

[0041] In the existing technologies, carbon materials such as graphene, carbon nanotubes and nitrogen-doped carbon materials are used to improve the performance of the LFP. However, in the related studies, attentions are usually drawn to a single factor of carbon materials, which impacts the performance of the cathode active material. Inventors of the present disclosure have found that a balance of the graphitization degree and the porosity of the carbon material can effectively improve the electrochemical performance of the olivine cathode active materials (such as LiFePC or LiMmFei-xPCU).

[0042] In the present disclosure, the graphitization degree of the carbon material is indicated by an ID / IG ratio in the Raman spectroscopy, and the specific surface area and the porosity of the material are indicated by the BET analysis.

[0043] The ID / IG ratio, also known as the D band to G band intensity ratio, is a crucial parameter obtained from the Raman spectroscopy that provides information about the structural disorder and defects in carbon-based materials. The D band is located at a peak of about 1350 cm'1and the G band is located at a peak of about 1590 cm'1. It is known that the smaller the ID / IG ratio is, the higher the graphitization degree is.

[0044] Carbon material

[0045] The present disclosure provides in embodiments a carbon material and its preparation method.

[0046] In the present disclosure, the carbon material is provided, having a specific surface area of > 350 m2 / g, a cumulative pore volume of > 0.34 cm3 / g, and an ID / IG ratio of < 0.80, where the ID / IG ratio represents an intensity ratio of D band to G band in Raman spectroscopy.

[0047] The carbon material has high porosity and graphitization degree can be used in the olivine cathode active materials to produce a positive electrode and thus a second battery which has improved electrochemical performances at the low temperature.

[0048] In some embodiments, the carbon material has the ID / IG ratio of < 0.70, 0.60, or 0.50. In some embodiments, the carbon material has the specific surface area of > 360 m2 / g, 370 m2 / g, 380 m2 / g, 390 m2 / g, 400 m2 / g, 410 m2 / g, 420 m2 / g, 430 m2 / g, 440 m2 / g, 450 m2 / g, 460 m2 / g, 470 m2 / g, or 480 m2 / g. In some embodiments, the carbon material has the cumulative pore volume of > 0.35 cm3 / g, 0.40 cm3 / g, 0.45 cm3 / g, 0.50 cm3 / g, or 0.55 cm3 / g.

[0049] It is found by the inventors that a high graphitization degree of the carbon material leads to a high electronic conductivity, which is beneficial to improve the electrochemical performance of the cathode active material. However, the high graphitization degree will also limit the conduction of lithium ions, especially under the conditions of low temperature and high rate charge and discharge. It is difficult for lithium ions to quickly go through the highly graphitized carbon material. The inventors of the present disclosure found that the carbon materials with high porosity and graphitization degree are beneficial to the rapid de-intercalation of the lithium ions, which not only improves the electronic conductivity of the cathode active material, but also improves the diffusion rate of the lithium ions in the cathode active material, so that the cathode active material exhibits excellent electrochemical performances under the conditions of low temperature and high rate charge and discharge. On this basis, the present disclosure provides a use of the carbon material having a specific surface area of > 350 m2 / g, a cumulative pore volume of > 0.34 cm3 / g, and an ID / IG ratio of < 0.80, where the ID / IG ratio represents an intensity ratio of D band to G band in Raman spectroscopy in a cathode active material having a formula of LiMPO4, where M represents Fe, or Fe and Mn, for improving the electrochemical performances such as an electric capacity, and a discharge capacity retention rate at the low temperature of a final composite cathode active material compared to a cathode active material without applying such a carbon material.

[0050] The present disclosure provides in embodiments a method for preparing a carbon material, which is able to obtain the carbon material described above.

[0051] The method includes: adding pyrrole and oxidant into a hydrochloric acid solution to form a pyrrole solution and an oxidant solution, respectively; dissolving manganese chloride tetrahydrate in the pyrrole solution, where a molar ratio of Mn to pyrrole is in a range of 2:3 to 3:2; adding the oxidant solution into the pyrrole solution under stirring to form a gel mixture, and performing aging on the gel mixture at a room temperature (e.g., 25 °C) for at least 12 h; freeze drying the gel mixture to obtain a polypyrrole hydrogel composite material; calcinating the polypyrrole hydrogel composite material at a temperature ranging from 900 to 1200 °C for 2 to 6 h in a nitrogen atmosphere to obtain solid powders; immersing the solid powders in an acid solution for removing Mn, filtering, washing and drying the solid powders to obtain the carbon material.

[0052] With the method provided in the present disclosure, the carbon material having the high porosity and graphitization degree is prepared. The manganese chloride tetrahydrate serves as a catalyst for preparing the polypyrrole hydrogel composite material. The polypyrrole hydrogel composite material is carbonized at a high temperature ranging from 900 to 1200 °C. After that, manganese is dissolved in the acid solution, leaving a large number of microporous structures. With the Mn-based catalysis and the high calcinating temperature, the high graphitization degree and porosity are achieved.

[0053] In the present disclosure, if the polypyrrole hydrogel composite material is calcinated below 900 °C, the graphitization degree of the carbon material will be low (that is, the ID / IG ratio increases) and if the polypyrrole hydrogel composite material is calcinated above 1200 °C, the graphitization degree is basically the same, but the specific surface area of the carbon material will be decreased. That is, the overhigh temperature may damage the pore structure in the carbon material. Moreover, the overhigh temperature will cause a large energy consumption and reduce the service life of the carbonization furnace.

[0054] In the present disclosure, a specific catalyst, i.e., Mn-based catalyst is used. Other elements- based catalysts such as Fe, Co, Ni-based catalysts cannot make the carbon material achieve the high graphitization degree. In the present disclosure, the molar ratio of Mn to pyrrole is in a range of 2:3 to 3:2, for example, the molar ratio of Mn to pyrrole is 2:3, 1 : 1 or 3 :2. When the molar ratio of Mn to pyrrole is 1 : 1, the graphitization degree and the porosity reach a perfect balance for improving the electrochemical performance of the cathode active materials. When the amount of Mn is too much (for example, when the malar ratio is 7:3), Mn-based catalyst material may be agglomerated and form macropores after being dissolved by the acid added, and the specific surface area and the cumulative pore volume of the carbon material decrease.

[0055] In some embodiments, the oxidant includes ammonium persulfate and / or ferric chloride.

[0056] In some embodiments, a molar ratio of pyrrole to ammonium persulfate ranges from 10: 1 to 1 : 1.

[0057] In some embodiments, the hydrochloric acid solution has a concentration of 0.1-12 mol / L.

[0058] In some embodiments, the solid powders are immersed in an acid solution at 40 to 100 °C for at least 2 hours, and the acid solution has a concentration of 0.1 to 2 mol / L. For example, the acid solution is a sulfuric acid solution.

[0059] In some embodiments, drying is carried out under vacuum at a temperature of 30-80 °C.

[0060] Composite cathode active material

[0061] The present disclosure provides in embodiments a method for preparing a composite cathode active material. The method includes: providing a carbon material having: a specific surface area of > 350 m2 / g, a cumulative pore volume of > 0.34 cm3 / g, and an ID / IG ratio of < 0.80, where the ID / IG ratio represents an intensity ratio of D band to G band in Raman spectroscopy; mixing the carbon material with a precursor source material to obtain a mixture, where the precursor source material is used for preparing a cathode active material having a formula of LiMPCU, where M represents Fe, or Fe and Mn, where an amount of the carbon material is in a range of 0.5 to 4 wt% based on a total weight of 1 mol of the cathode active material; adding the mixture into water to form a slurry; grinding the slurry, and spray drying the slurry to obtain a precursor material; and calcinating the precursor material in an atmosphere of a mixture gas including nitrogen and a reducing gas to obtain the composite cathode active material.

[0062] In the present disclosure, the inventors have found that the specific carbon material having a good balance between the porosity and the graphitization degree can be applied in the composite cathode active material for improving the electrochemical performances such as an electric capacity, and a discharge capacity retention rate at the low temperature of the composite cathode active material.

[0063] In the present disclosure, the amount of the carbon material is in the range of 0.5 to 4 wt% based on a total weight of 1 mol of the cathode active material. In some embodiments, the amount of the carbon material is in a range of 1.0 wt% to 3.0 wt%, such as 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2.0 wt%, 2.1 wt%, 2.2 wt%, 2.3 wt%,

[0064] 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.7 wt%, 2.8 wt%, or 2.9 wt%. When the amount of the carbon material is too low, the resistivity of the composite cathode active material is high and the capacity of the composite cathode active material is low. Appropriate addition amount of the carbon material leads to low resistivity and high capacity for the composite cathode active material. When the amount of the carbon material is too high, the resistivity will be low but the capacity will also be low, this is because the carbon material itself has no electrochemical activity, and thus excess carbon material will negatively affect the capacity of the composite cathode active material.

[0065] In some embodiments, the cathode active component has a formula of LiMnaFebPO4, where a + b = 1, and 0.5 < a < 0.9. For example, the cathode active component is LiMno.9Feo.1PO4, LiMno.sFeo.2PO4, LiMno.7Feo.3PO4, LiMno.6Feo.4PO4, or LiMno.5Feo.5PO4.

[0066] In some embodiments, the carbon material has the specific surface area of > 400 m2 / g, the cumulative pore volume of > 0.50 cm3 / g, and / or the ID / IG ratio of < 0.50.

[0067] In some embodiments, the slurry has a solid content ranging from 20 to 60 wt%.

[0068] In some embodiments, the reducing gas includes hydrogen and / or CO, and / or a flow volume of the reducing gas ranges from 5 to 10% of the flow volume of the mixture gas.

[0069] In some embodiments, calcinating the precursor material includes: calcinating the precursor material at a temperature of 600 to 900 °C for 2 to 24 h, where the temperature is increased at a rate of 1 to 10 °C / min.

[0070] In some embodiments, the carbon material is prepared by: adding pyrrole and an oxidant into a hydrochloric acid solution to form a pyrrole solution and an oxidant solution, respectively; dissolving manganese chloride tetrahydrate in the pyrrole solution, wherein a molar ratio of Mn to pyrrole is in a range of 2:3 to 3:2; adding the oxidant solution into the pyrrole solution under stirring to form a gel mixture, and performing aging on the gel mixture at a room temperature for at least 12 h; freeze drying the gel mixture to obtain a polypyrrole hydrogel composite material; calcinating the polypyrrole hydrogel composite material at a temperature ranging from 900 to 1200 °C for 2 to 6 h in a nitrogen atmosphere to obtain solid powders; immersing the solid powders in an acid solution for removing Mn, filtering, washing and drying the solid powders to obtain the carbon material.

[0071] Details of preparation of the carbon material may refer to the relevant description of the carbon material described above, which are not elaborated here.

[0072] In some embodiments, the precursor source material includes a lithium source, an iron source, a phosphorus source and an optional manganese source, wherein a molar ratio of Li : (Fe+Mn) : P is (1-1.05) : 1 : (0.96-1).

[0073] In some embodiments, the lithium source includes at least one selected from lithium carbonate, lithium hydroxide, lithium acetate and lithium dihydrogen phosphate.

[0074] In some embodiments, the manganese source includes at least one selected from manganese acetate, manganese nitrate, ammonium manganous sulfate, manganese carbonate and manganese oxalate.

[0075] In some embodiments, the iron source includes at least one selected from iron phosphate, ferrous oxalate, iron nitrate, ferric oxide and ferric chloride.

[0076] In some embodiments, the phosphorus source includes at least one selected from phosphoric acid, lithium dihydrogen phosphate, monoammonium phosphate and ammonium dihydrogen phosphate.

[0077] In the present disclosure, the composite cathode active material prepared by the method is provided. As described above, the carbon material having a good balance between the porosity and the graphitization degree is applied in the preparation process of the composite cathode active material to improve the electrochemical performances, such as capacity and the discharge capacity retention rate at -20 °C of the final composite cathode active material.

[0078] In some embodiments, the composite cathode active material has a particle size Dv50 ranging from 0.5 to 2.0 pm, which improves the processability of the composite cathode active material of the present disclosure.

[0079] In some embodiments, the composite cathode active material has a compaction density measured at 3 tons of greater than 2.20 g / cm3.

[0080] In some embodiments, the composite cathode active material has a resistivity less than 300 cm.

[0081] Positive electrode plate

[0082] The composite cathode active material may be used to preparing a positive electrode plate.

[0083] 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.

[0084] 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.

[0085] 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)).

[0086] 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 fluoridehexafluoropropyl ene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, or any combination thereof.

[0087] 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.

[0088] 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 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.

[0089] Secondary battery

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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).

[0095] 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).

[0096] 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.

[0097] In some embodiments, the negative electrode film layer optionally includes other adjuvants, such as thickeners (e.g. sodium carboxymethylcellulose (CMC -Na)).

[0098] 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.

[0099] 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.

[0100] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte includes an electrolyte salt and a solvent.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] In some embodiments, the secondary battery includes an outer package. The outer package is used to package the electrodes and the electrolyte.

[0108] 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.

[0109] The shape of the secondary battery may be cylindrical, square or any other shape, which is not limited in the present disclosure.

[0110] Experimental Section

[0111] 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.

[0112] Test methods

[0113] Carbon content of the composite cathode active material is measured by a carbon-sulfur analyzer HF-2000B.

[0114] Element of the composite cathode active material is measured by an inductively coupled plasma (ICP) spectrometer.

[0115] Resistivity of the composite cathode active material is measured by a volume resistivity tester according to GB / T 30835-2014 at 25 °C.

[0116] Graphitization degree of the carbon material is indicated by an ID / IG ratio in the Raman spectroscopy, and the ID / IG ratio is tested and calculated according to a general principle of Raman spectroscopy SN / T 5566-2023.

[0117] Specific surface area and cumulative pore volume of the carbon material are measured by a static specific surface area tester according to GB / T 19587-2004.

[0118] Particle size of a material is measured by a laser particle size analyzer (Malvern Master Size 2000) according to GB / T 19077-2016 / ISO 13320:2009. The particle size measured in the present disclosure is a median particle size by volume Dv50.

[0119] Compaction density is measured by a compaction density instrument at a testing pressure of 3 tons according to GB / T 30835-2014.

[0120] Electrochemical performance

[0121] Coin cell is prepared as follows.

[0122] (1) According to a weight ratio of 80:10: 10, the cathode active material, carbon black and polyvinylidene fluoride are mixed, and further added into N-methyl-pyrrolidone. The obtained mixture is applied to an aluminum foil, and further dried and cut into a coin having a diameter of 12 mm as a positive electrode plate.

[0123] (2) A lithium foil is used as a negative electrode and a polypropylene microporous membrane is used as a separator, and an electrolyte is 1 mol / L LiPFe / EC+DMC (that is, a solute of the electrolyte is LiPFe, and a solvent is a mixed solvent of ethylene carbonate and dimethyl carbonate with a mass ratio of 1 : 1). Components for the battery are assembled in a glovebox with an argon atmosphere to obtain the coin cell CR2025.

[0124] During electrochemical test, charging and discharging of the coin cell are tested and recorded by BTS-5V / 5mA battery testing system, and the test voltage is from 4.3 to 2.5 V.

[0125] Charge / discharge capacity: in an incubator at 25 °C, the coin cell is charged to 4.3V at a constant current and a rate of 0.1C and then be charged at a constant voltage of 4.3 V until the cut- off current is 0.05C, and the coin cell is discharged to 2.5V at a rate of 0.1C, 1C, 5C and IOC to obtain the charge / discharge capacities.

[0126] Cycle performance: in an incubator at -20 °C, the coin cell is charged to 4.3V at a constant current and a rate of 1C and then be charged at a constant voltage of 4.3 V until the cut-off current is 0.05C, and the coin cell is discharged to 2.5V at a rate of 1C to obtain an initial capacity (Cl). The coin cell is tested in cycles and a 200thcycle discharge capacity (C200) is recorded.

[0127] Capacity retention rate is = C200 / C 1*100%

[0128] 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.

[0129] Examples

[0130] Inventive Exampl e 1-1 (IE 1 - 1 )

[0131] 50g (0.74mol) of pyrrole and 85g (0.37mol) of ammonium persulfate were added in 400mL of 2M hydrochloric acid solution to form a pyrrole solution and an ammonium persulfate solution, respectively.

[0132] 197.84g (0.74 mol) of manganese chloride tetrahydrate was dissolved in the pyrrole solution, and the ammonium persulfate solution is slowly dropped into the pyrrole solution under stirring to form a gel mixture, which was aged for 24 h at a room temperature.

[0133] Freeze drying was performed on the gel mixture to obtain a polypyrrole hydrogel composite material.

[0134] The polypyrrole hydrogel composite material was calcinated at 1000 °C for 5 h in a nitrogen atmosphere to obtain solid powders.

[0135] The solid powders was immersed in a 0.5M sulfuric acid solution at 60 °C, followed by filtering, washing and drying to obtain the carbon material.

[0136] Inventive Example 1-2 (IE 1-2)

[0137] 50g (0.74mol) of pyrrole and 33.7g (0.148mol) of ammonium persulfate were added in 300mL of IM hydrochloric acid solution to form a pyrrole solution and an ammonium persulfate solution, respectively.

[0138] 197.84g (0.74 mol) of manganese chloride tetrahydrate was dissolved in the pyrrole solution, and the ammonium persulfate solution is slowly dropped into the pyrrole solution under stirring to form a gel mixture, which was aged for 12 h at a room temperature.

[0139] Freeze drying was performed on the gel mixture to obtain a polypyrrole hydrogel composite material.

[0140] The polypyrrole hydrogel composite material was calcinated at 1000 °C for 3 h in a nitrogen atmosphere to obtain solid powders.

[0141] The solid powders was immersed in a IM sulfuric acid solution at 40 °C, followed by filtering, washing and drying to obtain the carbon material.

[0142] Inventive Example 1-3 (IE1-3)

[0143] A carbon material was prepared in the same way as IE1 - 1 except that the polypyrrole hydrogel composite material was calcinated at 1100 °C.

[0144] Inventive Example 1-4 (IE 1-4)

[0145] A carbon material was prepared in the same way as IE1 - 1 except that the polypyrrole hydrogel composite material was calcinated at 1200 °C.

[0146] Inventive Example 1-5 (IE1-5)

[0147] A carbon material was prepared in the same way as IE1 - 1 except that the polypyrrole hydrogel composite material was calcinated at 900 °C.

[0148] Inventive Example 1-6 (IE 1-6)

[0149] A carbon material was prepared in the same way as IE1-1 except that 1.11 mol of manganese chloride tetrahydrate was dissolved in the pyrrole solution.

[0150] Inventive Example 1-7 (IE1-7)

[0151] A carbon material was prepared in the same way as IE1-1 except that 0.493 mol of manganese chloride tetrahydrate was dissolved in the pyrrole solution.

[0152] Comparative Example 1-1 (CE1-1)

[0153] A carbon material was prepared in the same way as IE1-1 except that 0.74 mol of ferric chloride was dissolved in the pyrrole solution instead of the manganese chloride tetrahydrate.

[0154] Comparative Example 1-2 (CE1-2)

[0155] A carbon material was prepared in the same way as IE1-1 except that 0.74 mol of cobalt chloride was dissolved in the pyrrole solution instead of the manganese chloride tetrahydrate.

[0156] Comparative Example 1-3 (CE1-3)

[0157] A carbon material was prepared in the same way as IE1-1 except that 0.74 mol of nickel chloride was dissolved in the pyrrole solution instead of the manganese chloride tetrahydrate.

[0158] Comparative Example 1-4 (CE1-4)

[0159] A carbon material was prepared in the same way as IE1 - 1 except that the polypyrrole hydrogel composite material was calcinated at 800 °C.

[0160] Comparative Example 1-5 (CE1-5)

[0161] A carbon material was prepared in the same way as IE1 - 1 except that the polypyrrole hydrogel composite material was calcinated at 700 °C.

[0162] Comparative Example 1-6 (CE1-6)

[0163] A carbon material was prepared in the same way as IE1 - 1 except that the polypyrrole hydrogel composite material was calcinated at 600 °C.

[0164] Comparative Example 1-7 (CE1-7) A carbon material was prepared in the same way as IE1 - 1 except that the polypyrrole hydrogel composite material was calcinated at 500 °C.

[0165] Comparative Example 1-8 (CE1-8)

[0166] A carbon material was prepared in the same way as IE1 - 1 except that the polypyrrole hydrogel composite material was calcinated at 1300 °C.

[0167] Comparative Example 1-9 (CE1-9)

[0168] A carbon material was prepared in the same way as IE1-1 except that 0.317 mol of manganese chloride tetrahydrate was dissolved in the pyrrole solution.

[0169] Comparative Example 1-10 (CE1-10)

[0170] A carbon material was prepared in the same way as IE1 - 1 except that 0.185 mol of manganese chloride tetrahydrate was dissolved in the pyrrole solution.

[0171] Comparative Example 1-11 (CE1-11)

[0172] A carbon material was prepared in the same way as IE1-1 except that 0.082 mol of manganese chloride tetrahydrate was dissolved in the pyrrole solution.

[0173] Comparative Example 1-12 (CE1-12)

[0174] A carbon material was prepared in the same way as IE1-1 except that no manganese chloride tetrahydrate was added.

[0175] Comparative Example 1-13 (CE1-13)

[0176] A carbon material was prepared in the same way as IE1-1 except that 1.727 mol of manganese chloride tetrahydrate was dissolved in the pyrrole solution.

[0177] Performances of the carbon materials of the inventive examples and comparative examples are tested and recorded in tables as follows.

[0178] Table 1

[0179] From Table 1, it can be seen that the carbon materials of IE1-1 and IE1-2 have a lower ID / IG value, indicating a higher graphitization degree, compared with the carbon materials of CEs. For IE1-1 and IE1-2, manganese chloride is used as a catalyst for preparing the polypyrrole hydrogel composite material. Compared with other catalysts based on Fe, Co or Ni, the Mn-based catalyst greatly improves the graphitization degree of the carbon material. Table 2

[0180] It can be known from Table 2 that with decrease of the temperature at which the polypyrrole hydrogel composite material is calcinated when preparing the carbon material, the graphitization degree of the carbon material decreases (that is, the ratio ID / IG increases) and the cumulative pore volume decreases. Compared with other temperatures, the carbon material prepared at 1000°C has the highest graphitization degree and porosity. After the temperature continues to increase from 1000°C, the graphitization degree and cumulative pore volume do not continue to increase and the specific surface area decreases. Without wishing to be bound by any theory, overhigh temperature may damage some pore structures in the carbon material and lead to the decrease of the specific surface area and the cumulative pore volume of the carbon materials. In addition, when the temperature increases, there will be disadvantages of increasing energy consumption and reducing the service life of the carbonization furnace.

[0181] Table 3

[0182] It can be known from Table 3 that when the Mn-based catalyst is not used, the carbon material (CE1-12) has a high ID / IG value indicating a low graphitization degree, and low specific surface area and cumulative pore volume. With decrease of the manganese content, the graphitization degree and porosity of the carbon material decrease. When the molar ratio exceeds 1 : 1, the graphitization degree does not increase. In fact, when the amount of Mn is too much (for example, when the malar ratio is 7:3), particles of the Mn-based catalyst may be agglomerated and leave macropores after being dissolved by the acid added, resulting in decrease in the specific surface area and the cumulative pore volume.

[0183] Inventive Example 2-1 (IE2-1)

[0184] Li2CO3 and FePCU were weighted in a molar ratio of 0.525: 1, and the carbon material of IE1- 1 was added to obtain a mixture. An amount of the carbon material added was 1 wt% based on a total weight of 1 mol LiFePCU.

[0185] The mixture and water were added into a tank to form a slurry and stirred for 30 min. A weight ratio of the mixture to water was 1 : 1.2. The slurry was grinded until a particle size Dv50=0.5±0.05pm. After that, the slurry was spray-dried to obtain a precursor material. The precursor material was calcinated in a furnace in an atmosphere of a mixture gas including nitrogen and hydrogen. A flow volume of hydrogen was 10% based on the total flow volume of the mixture gas. The calcination is performed at 770°C with a heating rate of 5 °C / min and the temperature was kept for 12h to obtain a composite cathode active material.

[0186] Inventive Example 2-2 (IE2-2)

[0187] A composite cathode active material was prepared in the same way as IE2-1 except that Li2CO3, MnCCE, FePCU and H3PO4 were weighted, where a molar ratio of Li : Mn : Fe : P was 1.05 : 0.6 : 0.4 : 1, and an amount of the carbon material added was 1 wt% based on a total weight of 1 mol LiMno.6Feo.4PO4.

[0188] Inventive Example 2-3 (IE2-3)

[0189] A composite cathode active material was prepared in the same way as IE2-1 except that an amount of the carbon material added was 0.5 wt% based on a total weight of 1 mol LiFePO4.

[0190] Inventive Example 2-4 (IE2-4)

[0191] A composite cathode active material was prepared in the same way as IE2-1 except that an amount of the carbon material added was 1.5 wt% based on a total weight of 1 mol LiFePO4.

[0192] Inventive Example 2-5 (IE2-5)

[0193] A composite cathode active material was prepared in the same way as IE2-1 except that an amount of the carbon material added was 2.0 wt% based on a total weight of 1 mol LiFePCU.

[0194] Inventive Example 2-6 (IE2-6)

[0195] A composite cathode active material was prepared in the same way as IE2-1 except that an amount of the carbon material added was 3.0 wt% based on a total weight of 1 mol LiFePCU. Inventive Example 2-7 (IE2-7)

[0196] A composite cathode active material was prepared in the same way as IE2-1 except that an amount of the carbon material added was 4.0 wt% based on a total weight of 1 mol LiFePCE.

[0197] Comparative Example 2-1 (CE2-1)

[0198] A composite cathode active material was prepared in the same way as IE2-1 except that the carbon material of CE1-12 was used.

[0199] Comparative Example 2-2 (CE2-2)

[0200] A composite cathode active material was prepared in the same way as IE2-1 except that the carbon material of CE1-7 was used.

[0201] Comparative Example 2-3 (CE2-3)

[0202] A composite cathode active material was prepared in the same way as IE2-1 except that the carbon material of CE1-3 was used.

[0203] Comparative Example 2-4 (CE2-4)

[0204] A composite cathode active material was prepared in the same way as IE2-1 except that no carbon material was used.

[0205] Comparative Example 2-5 (CE2-5)

[0206] A composite cathode active material was prepared in the same way as IE2-1 except that an amount of the carbon material added was 5.0 wt% based on a total weight of 1 mol LiFePCE.

[0207] Performances of the composite cathode active materials of the inventive examples and comparative examples are tested and recorded in tables as follows.

[0208] Table 4

[0209] Table 4 shows that the carbon material with the high graphitization degree and porosity can effectively improve the electrochemical performance of the composite cathode active materials of IE2-1 and IE2-2. They exhibit excellent electrochemical performances under the conditions of low temperature and high rate discharge. Table 5

[0210] It can be known from Table 5 when the amount of the carbon material is too low, the resistivity of the composite cathode active material is high and the capacity of the composite cathode active material is low. When the amount of the carbon material is too high, the resistivity is low but the capacity is also low because the carbon material itself has no electrochemical activity. It can be seen that compared with CE2-4, the composite cathode active material of CE2-5 has a low resistivity due to the large amount of the carbon material added, but the capacity and the discharge capacity retention rate at -20°C are still not satisfactory.

[0211] 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.

[0212] 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

CLAIMS1. A method for preparing a composite cathode active material, comprising: providing a carbon material having: a specific surface area of > 350 m2 / g, a cumulative pore volume of > 0.34 cm3 / g, and an ID / IG ratio of < 0.80, where the ID / IG ratio represents an intensity ratio of D band to G band in Raman spectroscopy; mixing the carbon material with a precursor source material to obtain a mixture, wherein the precursor source material is used for preparing a cathode active material having a formula of LiMPCU, where M represents Fe, or Fe and Mn, wherein an amount of the carbon material is in a range of 0.5 to 4 wt% based on a total weight of 1 mol of the cathode active material; adding the mixture into water to form a slurry; grinding the slurry, and spray drying the slurry to obtain a precursor material; and calcinating the precursor material in an atmosphere of a mixture gas comprising nitrogen and a reducing gas to obtain the composite cathode active material.

2. The method according to claim 1, wherein the cathode active material has a formula of LiMnaFebPO4, where a + b = 1, and 0.5 < a < 0.9.

3. The method according to claim 1 or 2, wherein the carbon material has: the specific surface area of > 400 m2 / g, the cumulative pore volume of > 0.50 cm3 / g, and / or the ID / IG ratio of < 0.50.

4. The method according to any one of claims 1 to 3, wherein an amount of the carbon material is in a range of 1.0 to 3.0 wt% based on a total weight of 1 mol of the cathode active material.

5. The method according to any one of claims 1 to 4, wherein the slurry has a solid content ranging from 20 to 60 wt%.

6. The method according to any one of claim 1 to 5, wherein the reducing gas comprises hydrogen and / or CO, and / or a flow volume of the reducing gas ranges from 5 to 10% of the flow volume of the mixture gas.

7. The method according to any one of claims 1 to 6, wherein calcinating the precursor material comprises: calcinating the precursor material at a temperature of 600 to 900 °C for 2 to 24 h, wherein the temperature is increased at a rate of 1 to 10 °C / min.

8. The method according to any one of claims 1 to 7, wherein the carbon material is prepared by: adding pyrrole and an oxidant into a hydrochloric acid solution to form a pyrrole solution and an oxidant solution, respectively; dissolving manganese chloride tetrahydrate in the pyrrole solution, wherein a molar ratio of Mn to pyrrole is in a range of 2:3 to 3 :2; adding the oxidant solution into the pyrrole solution under stirring to form a gel mixture, and performing aging on the gel mixture at a room temperature for at least 12 h; freeze drying the gel mixture to obtain a polypyrrole hydrogel composite material; calcinating the polypyrrole hydrogel composite material at a temperature ranging from 900 to 1200 °C for 2 to 6 h in a nitrogen atmosphere to obtain solid powders; and immersing the solid powders in an acid solution for removing Mn, filtering, washing and drying the solid powders to obtain the carbon material.

9. The method according to claim 8, wherein the oxidant comprises ammonium persulfate and / or ferric chloride.

10. The method according to claim 8 or 9, wherein a molar ratio of pyrrole to the oxidant ranges from 10: 1 to 1 :1.

11. The method according to any one of claims 8 to 10, wherein the hydrochloric acid solution has a concentration of 0.1-12 mol / L.

12. The method according to any one of claims 8 to 11, wherein immersing the solid powders in an acid solution at 40 to 100 °C for at least 2 hours, and the acid solution has a concentration of 0.1 to 2 mol / L.

13. The method according to any one of claims 8 to 12, wherein drying is carried out under vacuum at the temperature of 30-80 °C.

14. The method according to any one of claims 1 to 13, wherein the precursor source material comprises a lithium source, an iron source, a phosphorus source and an optional manganese source, wherein a molar ratio of Li : (Fe+Mn) : P is (1-1.05) : 1 : (0.96-1).

15. The method according to any one of claims 14, wherein the lithium source comprises at least one selected from lithium carbonate, lithium hydroxide, lithium acetate and lithium dihydrogen phosphate; the manganese source comprises at least one selected from manganese acetate, manganese nitrate, ammonium manganous sulfate, manganese carbonate and manganese oxalate; the iron source comprises at least one selected from iron phosphate, ferrous oxalate, iron nitrate, ferric oxide and ferric chloride; and / or the phosphorus source comprises at least one selected from phosphoric acid, lithium dihydrogen phosphate, monoammonium phosphate and ammonium dihydrogen phosphate.

16. A composite cathode active material prepared by the method according to any one of claims 1 to 15.

17. The composite cathode active material according to claim 16, wherein the composite cathode active material has: a particle size Dv50 ranging from 0.5 to 2.0 pm; a compaction density measured at 3 tons of greater than 2.20 g / cm3; and / or a resistivity less than 300 (1 cm measured at 25 °C.

18. A secondary battery, comprising: a positive electrode comprising the composite cathode active material according to claim 16 or 17.

19. An electronic device, comprising: the secondary battery according to claim 18.

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