A positive electrode active material, a method for preparing the same, and an application thereof

Abstract

This application discloses a positive electrode active material, its preparation method, and its application. The positive electrode active material is characterized by comprising a core and a shell, wherein the core comprises a phosphate with the chemical formula αNa. 4‑a Fe 3‑b‑c Mn b M c (PO4)2P2O7·βNa 2‑ d Fe 1‑b / 3‑c / 3 Mn b / 3 M c / 3 P₂O₇, 0 ≤ a ≤ 1.5, 0

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a positive electrode active material, its preparation method, and its application. Background Technology

[0002] The demand for large-scale electrical energy storage is increasing in today's society, and sodium-ion batteries have attracted much attention due to their abundant sodium resources and low cost. Among these, the cathode material, as a key component of the battery, has a significant impact on electrochemical performance. Currently, the challenge lies in simultaneously meeting the requirements of high energy density and cycle stability. In the field of sodium-ion batteries, researchers have explored many cathode materials, including polyanionic compounds, transition metal oxides, and Prussian blue analogs. Among them, mixed iron-based phosphate materials (NFPP) with a NASICON structure possess an extremely stable molecular structure and a 3D framework with strong covalent bonds, exhibiting minimal volume change during charge and discharge and theoretically excellent cycle stability. However, NFPP materials also suffer from poor intrinsic electronic conductivity, poor rate performance, low compaction density, and phase purity issues.

[0003] The related technology discloses a method for preparing sodium iron pyrophosphate cathode, which involves adding a composite uncarbonized organic carbon source to a sodium iron pyrophosphate precursor to form a composite conductive carbon, and then dispersing it by ball milling to obtain the sodium iron pyrophosphate cathode. However, this method may result in free carbon, which affects its electrochemical performance and compaction density.

[0004] Therefore, there is an urgent need for a phosphate material that is free of free carbon, has good electrochemical performance, and high compaction density. Summary of the Invention

[0005] In view of this, one object of this application is to provide a positive electrode active material, which uses a nitrogen- and carbon-containing material as a coating material to coat the chemical formula αNa. 4-a Fe 3-b-c Mn b M c (PO4)2P2O7·βNa 2-d Fe 1-b / 3-c / 3 Mn b / 3 M c / 3 Phosphate of P2O7, with its high nitrogen doping, increases the disorder of carbon materials, increases active sites, and improves the electrical conductivity and compaction density of the materials.

[0006] Another objective of this application is to provide a method for preparing a positive electrode active material.

[0007] Another objective of this application is to provide a positive electrode sheet.

[0008] Another object of this application is to provide a secondary battery.

[0009] Another object of the present application is to provide an electrical device.

[0010] To achieve the above object, a first aspect of the present application provides a positive electrode active material, comprising:

[0011] A core, the core comprising a phosphate, the chemical formula of the phosphate being αNa 4-a Fe 3-b-c Mn b M c (PO4)2P2O7·βNa 2-d Fe 1-b / 3-c / 3 Mn b / 3 M c / 3 P2O7, wherein 0≤a≤1.5, 0<b≤2, 0≤c≤2, 0<3-b-c<3, 0≤d≤2, 0<1-b / 3-c / 3<1, 95wt%≤α≤100wt%, 0wt%≤β<5wt%, and M comprises at least one of Mg, Al, Ca, Ti, Ni, Co, Cu, Zn, Zr elements;

[0012] A shell, the shell covering at least a part of the surface of the core; the shell comprises C2N3.

[0013] The positive electrode active material of the present application uses a nitrogen- and carbon-containing material as a coating material to coat a phosphate with the chemical formula αNa 4-a Fe 3-b-c Mn b M c (PO4)2P2O7·βNa 2-d Fe 1-b / 3-c / 3 Mn b / 3 M c / 3 P2O7, wherein the higher nitrogen doping increases the disorder degree of the carbon material, increases the active sites, and improves the conductivity and tap density of the material.

[0014] In some embodiments, 0≤a≤1, and / or, 0<b≤1, and / or, 0≤c≤1, and / or, 0≤d≤1.5, and / or, 96wt%≤α≤100wt%, and / or, 0wt%≤β≤4wt%.

[0015] In some embodiments, the M comprises at least one of Mg, Ti, Co, Cu, Zn elements. [[ID=​​​​​​

[0018] In some embodiments, the X-ray diffraction pattern of the positive electrode active material shows that the (411) interplanar spacing is 3.30- .

[0019] In some embodiments, the median particle size of the primary particles of the positive electrode active material is 0.2-3 μm.

[0020] In some embodiments, the compaction density of the positive electrode active material under 3 tons of pressure is 2.0-2.35 g / cm³. 3 .

[0021] The second aspect of this application discloses a method for preparing a positive electrode active material, comprising:

[0022] An iron source, a phosphorus source, and an oxidant are reacted in a first solvent to obtain a first precursor material.

[0023] The first precursor material is dispersed in a second solvent, and the pH is adjusted to acidic, followed by aging to obtain the second precursor material;

[0024] The second precursor material, manganese source, M source, and carbon-nitrogen source are subjected to a second reaction in a third solvent to obtain a third precursor material; the M element in the M source includes at least one of Mg, Al, Ca, Ti, Ni, Co, Cu, Zn, and Zr.

[0025] The third precursor material, sodium source, and carbon source are subjected to a third reaction in a fourth solvent, followed by drying and sintering to obtain the positive electrode active material.

[0026] The cathode active material described in this application employs a unique in-situ nitrogen-containing carbon source (Mn / M-MET, i.e., metal triazole salt) to induce crystal growth, forming an extremely thin and uniform carbon-nitrogen layer (i.e., shell) on the primary particle surface of the mixed iron-based phosphate cathode active material. This significantly improves the material's compaction density while ensuring its conductivity. Furthermore, the introduction of Mn and M elements, synergistically altering the specific (411) crystal plane spacing through nitrogen doping, increases the Na+ content of the cathode active material. + The diffusion rate and kinetic properties, as well as the rate performance, have been significantly improved. In summary, this application addresses the shortcomings of poor rate performance and low compaction density in mixed iron-based phosphate cathode materials.

[0027] In some embodiments, the carbon and nitrogen source includes at least one of 1,2,3-triazole, 1,2,4-triazole, and chloromethyltriazole.

[0028] In some embodiments, the third solvent includes water, C1-5 alcohols, ammonia, and N,N-dimethylformamide.

[0029] In some embodiments, the iron source, the manganese source, and the M source are all soluble salts.

[0030] In some embodiments, the molar ratio of manganese in the manganese source to M in the M source is (1:100)-(100:1).

[0031] In some embodiments, the amount of the carbon and nitrogen source is mg mol, and the total amount of the manganese source and the M source is n mol, wherein m and n satisfy: 1.0 ≤ m / n ≤ 4.5.

[0032] In some embodiments, the second reaction is carried out under stirring conditions, and the reaction temperature is room temperature.

[0033] In some embodiments, the third precursor material is a material coated with a metal triazole salt (Mn / M-MET), wherein the metal is manganese and the M element.

[0034] In some embodiments, the soluble salt includes at least one of sulfate, nitrate, chloride, acetate, and oxalate.

[0035] In some embodiments, the volume ratio of water, C1-5 alcohols, ammonia, and N,N-dimethylformamide in the third solvent is 1:(1-10):1:1.

[0036] In some embodiments, the step of performing a second reaction in a third solvent with the second precursor material, manganese source, M source, and carbon and nitrogen sources to obtain the third precursor material includes:

[0037] Water, the manganese source, the M source, the C1-5 alcohol, ammonia, and N,N-dimethylformamide are added sequentially to the second precursor material, and then the carbon and nitrogen source is added dropwise to carry out the second reaction to obtain the third precursor material.

[0038] In some embodiments, the phosphorus source includes at least one of ammonium phosphate, ammonium dihydrogen phosphate, monoammonium phosphate, sodium dihydrogen phosphate, and sodium pyrophosphate.

[0039] In some embodiments, the molar ratio of iron in the iron source to phosphorus in the phosphorus source is (1-3):4.

[0040] In some embodiments, the molar ratio of iron in the iron source to manganese in the manganese source is (0.001-3):(0.001-2).

[0041] In some embodiments, the oxidant includes at least one of hydrogen peroxide and ozone.

[0042] In some embodiments, the molar ratio of iron in the iron source to hydrogen peroxide in the hydrogen peroxide solution is 1:(0.5-0.8).

[0043] In some embodiments, the first solvent, the second solvent, and the fourth solvent all comprise water.

[0044] In some embodiments, the first reaction is a coprecipitation reaction.

[0045] In some embodiments, the first reaction is carried out under stirring conditions, and the reaction temperature is room temperature.

[0046] In some embodiments, during the process of obtaining the second precursor material, the pH is adjusted to acidic by adding phosphoric acid and / or ammonia.

[0047] In some embodiments, the pH is adjusted to 1-6 during the process of obtaining the second precursor material.

[0048] In some embodiments, the aging temperature is 20-50°C, and the aging time is 1-16 hours.

[0049] In some embodiments, the carbon source includes at least one of polyethylene glycol, glucose, and sucrose.

[0050] In some embodiments, the molar amount of C in the carbon source is h mol, the molar amount of sodium source is imol, and the molar amount of Fe in the third precursor material is j mol, wherein h, i, and j satisfy:

[0051] h:i:j=[(3-bc) / 2]:(4-a):(3-bc),

[0052] Where, 0 ≤ a ≤ 1.5, 0 <b≤2,0≤c≤2,0<3-b-c<3。

[0053] In some embodiments, the third reaction is carried out under stirring conditions, and the reaction temperature of the third reaction is room temperature.

[0054] In some embodiments, the drying and / or sintering are carried out in an inert gas atmosphere.

[0055] In some embodiments, the drying temperature is 100-140°C.

[0056] In some embodiments, the sintering includes a first sintering and a second sintering performed sequentially, wherein the temperature of the first sintering is lower than the temperature of the second sintering.

[0057] In some embodiments, the temperature of the first sintering is 250-450°C.

[0058] In some embodiments, the first sintering time is 4-7 hours.

[0059] In some embodiments, the heating rate of the first sintering is 0.5-5.5 °C / min.

[0060] In some embodiments, the temperature of the second sintering is 500-650°C.

[0061] In some embodiments, the second sintering time is 6-12 hours.

[0062] In some embodiments, the heating rate of the second sintering is 0.5-3.5 °C / min.

[0063] In some embodiments, the inert gas flow rate during the sintering process is 2-8 L / min.

[0064] In some embodiments, the preparation method of the positive electrode active material further includes a cooling step after sintering, wherein the cooling rate is 100-150°C / h.

[0065] A third aspect of this application discloses a positive electrode sheet, comprising the positive electrode active material described in this application or the positive electrode active material prepared by the method described in this application.

[0066] The fourth aspect of this application provides a secondary battery, including a positive electrode, a negative electrode, and a separator, wherein the positive electrode is the positive electrode described in this application.

[0067] The fifth aspect of this application discloses an electrical device comprising the secondary battery described in this application.

[0068] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0069] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings.

[0070] in:

[0071] Figure 1 This is a flowchart illustrating a method for preparing a positive electrode active material, as shown in an exemplary embodiment of this application.

[0072] Figure 2 Here is a morphology image of the positive electrode active material prepared in Example 1, wherein:

[0073] A is a transmission electron microscope (TEM) image of the outer shell, where the area marked with a thickness of 3 nm is the outer shell;

[0074] B is a scanning electron microscope (SEM) image of the outer shell.

[0075] Figure 3 Here is a morphology image of the positive electrode active material prepared in Comparative Example 1, where:

[0076] C is a transmission electron microscope (TEM) image of the outer shell, where the area marked with a thickness of 8 nm is the outer shell;

[0077] D is a scanning electron microscope (SEM) image of the outer shell. Detailed Implementation

[0078] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0079] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints 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 expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0080] Unless otherwise specified, all raw materials and equipment involved in this application are self-made through commercial means or known methods; and all methods involved are conventional methods unless otherwise specified.

[0081] In this application, room temperature refers to 20 - 30°C.

[0082] <Cathode active material>

[0083] The cathode active material of the embodiment of this application includes a core and a shell. The core includes phosphate, and the chemical formula of the phosphate is αNa 4-a Fe 3-b-c Mn b M c (PO4)2P2O7·βNa 2-d Fe 1-b / 3-c / 3 Mn b / 3 M c / 3 P2O7, where 0 ≤ a ≤ 1.5, 0 < b ≤ 2, 0 ≤ c ≤ 2, 0 < 3 - b - c < 3, 0 ≤ d ≤ 2, 0 < 1 - b / 3 - c / 3 < 1, 95wt% ≤ α ≤ 100wt%, 0wt% ≤ β < 5wt%, and M includes at least one of elements such as Mg, Al, Ca, Ti, Ni, Co, Cu, Zn, Zr, etc. The shell covers at least part of the surface of the core; the shell includes C2N3.

[0084] The cathode active material of the embodiment of this application uses a nitrogen - and - carbon - containing material as a coating material to coat the phosphate with the chemical formula αNa 4-a Fe 3-b-c Mn b M c (PO4)2P2O7·βNa 2-d Fe 1-b / 3-c / 3 Mn b / 3 M c / 3 P2O7. The higher nitrogen doping improves the disorder degree of the carbon material, increases the active sites, and improves the conductivity and tap density of the material.

[0085] It should be noted that in the embodiment of this application, Na 4-a Fe 3-b-c Mn b M c (PO4)2P2O7 and Na 2-d Fe 1-b / 3-c / 3Mn b / 3 M c / 3 P2O7 belong to two different - phase compounds. Among them, Na 4-a Fe 3-b-c Mn b M c (PO4)2P2O7 combines the structural characteristics of phosphate and pyrophosphate, has a NASICON structure, and is the NFPP phase; while Na 2-d Fe 1-b / 3-c / 3 Mn b / 3M c / 3 P2O7 has a stable triclinic crystal structure, composed of MO6 octahedra and PO4 tetrahedra, forming the NFPO phase. The α and β phases can be understood as Na+ in the phosphate. 4-a Fe 3-b-c Mn b M c (PO4)2P2O7 and Na 2-d Fe 1-b / 3-c / 3 Mn b / 3 M c / 3 The mass ratio of P2O7 can also be understood as the ratio of Na in phosphate. 4-a Fe 3-b-c Mn b M c (PO4)2P2O7 and Na 2-d Fe 1-b / 3-c / 3 Mn b / 3 M c / 3 The mass content of P2O7 in the positive electrode active material.

[0086] In the embodiments of this application, when β is not 0, the phosphate also contains Na. 4-a Fe 3-b-c Mn b M c (PO4)2P2O7 and Na 2-d Fe 1-b / 3-c / 3 Mn b / 3 M c / 3 P2O7, compared to those containing only Na 4-a Fe 3-b-c Mn b M c (PO4)2P2O7 or Na 2-d Fe 1-b / 3-c / 3 Mn b / 3 M c / In the case of 3P2O7, higher capacity utilization and compaction density can be achieved.

[0087] For example, the value of 'a' may include, but is not limited to, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, or 1.4.

[0088] As an alternative example, 0 ≤ a ≤ 1.

[0089] For example, the value of b can include, but is not limited to, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, or 1.9.

[0090] As an optional example, 0 <b≤1。

[0091] For example, the value of c can include, but is not limited to, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, or 1.9.

[0092] As an alternative example, 0 ≤ c ≤ 1.

[0093] For example, the values ​​of 3-bc include, but are not limited to, 0.1, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, or 2.9.

[0094] For example, the values ​​of 1-b / 3-c / 3 include, but are not limited to, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9.

[0095] For example, the values ​​of d include, but are not limited to, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, or 1.9.

[0096] As an alternative example, 0 ≤ d ≤ 1.5.

[0097] For example, the value of α may include, but is not limited to, 96.5wt%, 97wt%, 97.5wt%, 98wt%, 98.5wt%, 99wt%, or 99.5wt%.

[0098] As an optional example, 96wt% ≤ α ≤ 100wt%.

[0099] For example, the values ​​of β include, but are not limited to, 0, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, or 4.5 wt%. It should be noted that when the value of β is 0, it means that the phosphate does not contain Na. 2-d Fe 1-b / 3-c / 3 Mn b / 3 M c / 3 P2O7.

[0100] As an optional example, 0wt% ≤ β ≤ 4wt%.

[0101] As an optional example, M includes at least one of the elements Mg, Ti, Co, Cu, and Zn.

[0102] In some embodiments, the mass content of C2N3 in the positive electrode active material is γ, where 0 < γ ≤ 3 wt%.

[0103] In the embodiments of this application, if the mass content of C2N3 in the positive electrode active material is within the above-mentioned range, then the compaction density of the positive electrode active material can reach 2.10-2.35 g / cm³. 3 The 0.2C discharge capacity is 110-120 mAh / g; above 3%, the compaction density is <2.1 g / cm³. 3 Furthermore, its 0.2C discharge capacity is slightly lower than 110mAh / g.

[0104] For example, the value of γ may include, but is not limited to, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, or 3wt%.

[0105] As an alternative example, 0 < γ ≤ 2wt%.

[0106] As an alternative example, the core is the phosphate and the shell is C2N3.

[0107] At this point, the chemical formula of the positive electrode active material in this application embodiment is:

[0108] αNa 4-a Fe 3-b-c Mn b M c (PO4)2P2O7·βNa 2-d Fe 1-b / 3-c / 3 Mn b / 3 M c / 3 P2O7@γ(C2N3),

[0109] Where 0 < γ ≤ 3wt%, other parameters are defined as described above in the chemical formula of phosphate; @ indicates coating.

[0110] Furthermore, the above α, β, and γ satisfy the following relationship: and α + β + γ = 1.

[0111] That is, α is Na in phosphate 4-a Fe 3-b-c Mn b M c The mass content of (PO4)2P2O7 in the positive electrode active material, β is the Na 2-d Fe 1-b / 3-c / 3 Mn b / 3 M c / 3 The mass content of P2O7 in the positive electrode active material, γ is the mass content of C2N3 in the positive electrode active material, and their total mass content is 100wt%.

[0112] In some embodiments, the thickness of the outer shell is 2-7 nm, including but not limited to 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, or 6.5 nm. In the embodiments of this application, if the thickness of the outer shell is within the above range, the compaction density of the positive electrode active material can reach 2.0-2.35 g / cm³. 3 The 0.2C discharge capacity is 110-120 mAh / g; for nm smaller than 2nm, the 0.2C discharge capacity is <110 mAh / g; for nm larger than 7nm, the compaction density is <2.1 g / cm³. 3 Furthermore, its 0.2C discharge capacity is slightly lower than 110mAh / g.

[0113] As an alternative example, the thickness of the shell is 2-6 nm.

[0114] In some embodiments, the X-ray diffraction pattern of the positive electrode active material shows that the interplanar spacing of (411) is... Including but not limited to or wait.

[0115] As an alternative example, the interplanar spacing of (411) is

[0116] In some embodiments, the median particle size (D50) of the primary particles of the positive electrode active material is 0.2-3 μm, including but not limited to 0.5 μm, 1 μm, 1.5 μm, 2 μm or 2.5 μm.

[0117] As an optional example, the median particle size (D50) of the primary particles of the positive electrode active material is 0.3-2.5 μm.

[0118] In some embodiments, the compaction density of the positive electrode active material under 3 tons of pressure is 2.0 g / cm³. 3 The above includes, but is not limited to, 2.05 g / cm³. 3 2.1g / cm 3 2.15g / cm 3 2.20g / cm 3 2.25g / cm 3 Or 2.30 g / cm 3 Or 2.35g / cm 3 wait.

[0119] As an optional example, the compaction density of the positive electrode active material under 3 tons of pressure is 2.0-2.35 g / cm³. 3 Further options include 2.1-2.35 g / cm³. 3 .

[0120] <Preparation Methods of Positive Electrode Active Materials>

[0121] The preparation method of the positive electrode active material in this application aims to: use Mn / M-MET (metal triazole salt) in-situ nitrogen-containing carbon source (i.e., carbon-nitrogen source) to coat the material. On the one hand, Mn / M and nitrogen in Mn / M-MET are synergistically introduced into the material to obtain a specific (411) crystal plane spacing, improve the phase purity of NFPP in the material, and increase the diffusion rate of Na+, thereby improving its rate performance. On the other hand, due to the unique nitrogen-containing five-membered ring-metal coordination structure of Mn / M-MET, it can form a uniform and extremely thin nitrogen-containing carbon layer on the material surface, which improves the conductivity of the carbon layer while ensuring extremely high compaction density. This invention can solve the problems of low compaction density and poor rate performance in the prior art.

[0122] The method for preparing the positive electrode active material in this application embodiment can be used to prepare the positive electrode active material in this application embodiment.

[0123] Figure 1 This is a flowchart illustrating a method for preparing a positive electrode active material, as shown in an exemplary embodiment of this application.

[0124] like Figure 1 As shown, the preparation method of this positive electrode active material includes the following steps:

[0125] S101. An iron source, a phosphorus source, and an oxidant are reacted in a first solvent to obtain a first precursor material.

[0126] In some embodiments, the iron source is a soluble salt.

[0127] For example, the iron source is selected from at least one of iron sulfate, nitrate, chloride, acetate, oxalate, etc.

[0128] In some embodiments, the phosphorus source includes, but is not limited to, at least one of ammonium phosphate, ammonium dihydrogen phosphate, monoammonium phosphate, sodium dihydrogen phosphate, and sodium pyrophosphate.

[0129] In some embodiments, the molar ratio of iron in the iron source to phosphorus in the phosphorus source is (1-3):4, including but not limited to 1:4, 1.1:4, 1.5:4, 1.75:4, 2:4, 2.25:4, 2.5:4, 2.75:4, 2.9:4 or 3:4, etc.

[0130] In some embodiments, the oxidant includes, but is not limited to, at least one of hydrogen peroxide, ozone, etc.

[0131] As an alternative example, the oxidant is hydrogen peroxide.

[0132] For example, the molar concentration of hydrogen peroxide is 0.1-1 mol / L, including but not limited to 0.25 mol / L, 0.5 mol / L or 0.75 mol / L.

[0133] Optionally, hydrogen peroxide can be added to the reaction system of the first reaction via a peristaltic pump.

[0134] In some embodiments, the molar ratio of iron in the iron source to hydrogen peroxide in the hydrogen peroxide solution is 1:(0.5-0.8), including but not limited to 1:0.5, 1:0.6, 1:0.7 or 1:0.8.

[0135] In some embodiments, the first solvent includes, but is not limited to, water, and may be selected as deionized water, etc.

[0136] In some embodiments, the first reaction is a coprecipitation reaction.

[0137] In some embodiments, the first reaction is carried out under stirring conditions.

[0138] In some embodiments, the reaction temperature of the first reaction is room temperature.

[0139] In some implementations, the time for the first reaction is 2-8 hours, including but not limited to 2.5 hours, 3 hours, 4 hours, 5 hours, 6 hours or 7 hours.

[0140] In some embodiments, the preparation method of the positive electrode active material further includes steps of filtration and washing after the first reaction.

[0141] S102. The first precursor material is dispersed in the second solvent and the pH is adjusted to acidic, followed by aging to obtain the second precursor material.

[0142] In some embodiments, the second solvent includes, but is not limited to, at least one of water, and may be deionized water.

[0143] In some embodiments, during the process of obtaining the second precursor material, the pH is adjusted to acidic by adding phosphoric acid and / or ammonia.

[0144] In some embodiments, during the process of obtaining the second precursor material, the pH is adjusted to 1-6, including but not limited to 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or 5.5.

[0145] As an alternative, the pH is adjusted to 2-4 during the process of obtaining the second precursor material.

[0146] In some embodiments, the aging temperature is 20-50°C, including but not limited to 25°C, 30°C, 35°C, 40°C, or 45°C.

[0147] In some embodiments, the aging time is 1-16 hours, including but not limited to 2.5 hours, 5 hours, 7.5 hours, 10 hours, 12.5 hours or 15 hours.

[0148] In some embodiments, the preparation method of the positive electrode active material further includes steps of filtration and washing after aging.

[0149] S103. The second precursor material, manganese source, M source and carbon-nitrogen source are subjected to a second reaction in a third solvent to obtain a third precursor material; the M element in the M source includes, but is not limited to, at least one of Mg, Al, Ca, Ti, Ni, Co, Cu, Zn, Zr.

[0150] In some embodiments, the carbon and nitrogen source includes, but is not limited to, at least one of 1,2,3-triazole, 1,2,4-triazole, and chloromethyltriazole.

[0151] As an alternative example, the carbon and nitrogen source is 1,2,3-triazole.

[0152] In some embodiments, both the manganese source and the M source are soluble salts.

[0153] In some embodiments, the soluble salt includes, but is not limited to, at least one of sulfates, nitrates, chlorides, acetates, and oxalates. For example, the manganese source includes, but is not limited to, at least one of manganese sulfate, nitrates, manganese chloride, manganese acetate, and manganese oxalate, and the M source includes, but is not limited to, at least one of manganese sulfate, nitrates, manganese chloride, manganese acetate, and oxalates of Mg, Al, Ca, Ti, Ni, Co, Cu, Zn, and Zr.

[0154] In some embodiments, the molar ratio of manganese in the manganese source to M in the M source is (1:100)-(100:1), including but not limited to 1:90, 1:75, 1:50, 1:25, 1:1, 25:1, 50:1, 75:1 or 90:1, etc.

[0155] In some embodiments, the amount of the carbon and nitrogen source is mg mol, and the total amount of the manganese source and the M source is n mol, wherein m and n satisfy: 1.0 ≤ m / n ≤ 4.5.

[0156] For example, the values ​​of m / n mentioned above include, but are not limited to, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5 or 4.0, and can be selected as 2.

[0157] In some embodiments, the molar ratio of iron in the iron source to manganese in the manganese source is (0.001-3):(0.001-2), including but not limited to 0.01:0.001, 0.01:1, 0.01:2, 0.5:1, 0.5:0.001, 0.5:2, 1.5:0.001, 1.5:0.1, 1.5:1, 1.5:2, or 3:1.

[0158] In some embodiments, the second reaction is carried out under stirring conditions.

[0159] In some embodiments, the reaction temperature of the second reaction is room temperature.

[0160] In some embodiments, the second reaction time is 1-16 hours, including but not limited to 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours or 14 hours.

[0161] In some embodiments, the third solvent includes, but is not limited to, water, C1-5 alcohols, ammonia, and N,N-dimethylformamide (DMF).

[0162] For example, alcohols include, but are not limited to, at least one of ethanol, methanol, ethylene glycol, etc.

[0163] For example, the concentration of ammonia water is 0.05-0.2 mol / L, including but not limited to 0.05 mol / L, 0.1 mol / L, 0.15 mol / L or 0.2 mol / L.

[0164] In some embodiments, the volume ratio of water, C1-5 alcohols, ammonia and N,N-dimethylformamide in the third solvent is 1:(1-10):1:1, including but not limited to 1:2:1:1, 1:4:1:1, 1:6:1:1 or 1:8:1:1, etc.

[0165] It should be noted that in the embodiments of this application, the third solvent must simultaneously contain water, C1-5 alcohols, ammonia, and N,N-dimethylformamide. This is to facilitate the synthesis of Mn / M-MET, enabling it to form a uniform and thin coating layer on the precursor surface. If any one of these is missing, a nitrogen-containing Mn / M- coating layer cannot be formed on the precursor surface, resulting in a significant reduction in capacity. For example, if the third solvent lacks C1-5 alcohols such as methanol, ethanol, or ethylene glycol, the amount of Mn / M-MET generated will be reduced, thus affecting the electrochemical performance and compaction density of the cathode material. If the third solvent lacks ammonia, it cannot provide the alkaline environment necessary for the synthesis of Mn / M-MET, leading to a decrease in capacity. If the third solvent lacks N,N-dimethylformamide, Mn / M-MET cannot be synthesized, resulting in a cathode material with low capacity and compaction density.

[0166] In some embodiments, the step of performing a second reaction in a third solvent with the second precursor material, manganese source, M source, and carbon and nitrogen sources to obtain the third precursor material includes:

[0167] Water, the manganese source, the M source, the C1-5 alcohol, ammonia, and N,N-dimethylformamide are added sequentially to the second precursor material, and then the carbon and nitrogen source is added dropwise to carry out the second reaction to obtain the third precursor material.

[0168] In some embodiments, the third precursor material is a material coated with a metal triazole salt (Mn / M-MET), wherein the metal is manganese and the M element.

[0169] In some embodiments, the method for preparing the positive electrode active material includes a filtration step after the second reaction.

[0170] S104. The third precursor material, sodium source, and carbon source are subjected to a third reaction in a fourth solvent, followed by drying and sintering to obtain the positive electrode active material.

[0171] In some embodiments, the carbon source includes, but is not limited to, at least one of polyethylene glycol (PEG), glucose, sucrose, etc.

[0172] In some embodiments, the molar amount of C in the carbon source is h mol, the molar amount of sodium source is imol, and the molar amount of Fe in the third precursor material is j mol, wherein h, i, and j satisfy:

[0173] h:i:j=[(3-bc) / 2]:(4-a):(3-bc),

[0174] Where, 0 ≤ a ≤ 1.5, 0 <b≤2,0≤c≤2,0<3-b-c<3。

[0175] For example, the value of 'a' may include, but is not limited to, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, or 1.4.

[0176] For example, the value of b can include, but is not limited to, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, or 1.9.

[0177] For example, the value of c can include, but is not limited to, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, or 1.9.

[0178] For example, the values ​​of 3-bc include, but are not limited to, 0.1, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, or 2.9.

[0179] For example, the above h:i:j includes, but is not limited to, 1.4:4:2.8, 1:4:2, 1:3:2, 1:2.5:1, 0.5:4:1 or 0.5:3:1, etc.

[0180] In some embodiments, the sodium source includes, but is not limited to, at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium acetate, or sodium chlorate, and sodium carbonate may be selected.

[0181] In some embodiments, the fourth solvent includes at least one of water, ethanol, etc., and may be deionized water.

[0182] In some embodiments, the third reaction is carried out under stirring conditions.

[0183] In some embodiments, the reaction temperature of the third reaction is room temperature.

[0184] In some implementations, the third reaction time is 2-8 hours, including but not limited to 3 hours, 4 hours, 5 hours, 6 hours, or 7 hours.

[0185] In some embodiments, the drying and / or sintering are carried out in an inert gas atmosphere.

[0186] For example, inert gases include, but are not limited to, at least one of nitrogen, argon, helium, etc.

[0187] In some embodiments, the drying temperature is 100-140°C, including but not limited to 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, or 135°C.

[0188] For example, the drying method includes, but is not limited to, at least one of baking, spray drying, vacuum drying, etc., and spray drying may be selected.

[0189] As an alternative example, when the drying method is spray drying, the inlet air temperature of the spray dryer is 100-140℃ and the exhaust air temperature is 70-100℃.

[0190] In some embodiments, the sintering includes a first sintering and a second sintering performed sequentially, wherein the temperature of the first sintering is lower than the temperature of the second sintering. The purpose of this arrangement is that the low-temperature sintering (i.e., the first sintering) initially carbonizes Mn / M-MET while promoting the uniform dispersion of Mn / M elements within the material; the high-temperature sintering (i.e., the second sintering) promotes the formation of NFPP and NFPO phases in the material, resulting in a high-capacity, high-compact mixed phosphate material.

[0191] In some embodiments, the temperature of the first sintering is 250-450°C, including but not limited to 275°C, 300°C, 325°C, 350°C, 375°C, 400°C or 425°C.

[0192] In some embodiments, the first sintering time is 4-7 hours, including but not limited to 4.5 hours, 5 hours, 5.5 hours, 6 hours or 6.5 hours.

[0193] In some embodiments, the heating rate of the first sintering is 0.5-5.5℃ / min, including but not limited to 1℃ / min, 2.2℃ / min, 2.5℃ / min, 2.7℃ / min, 3℃ / min, 4℃ / min, 5℃ / min or 5.5℃ / min, etc.

[0194] In some embodiments, the second sintering temperature is 500-650°C, including but not limited to 525°C, 550°C, 575°C, 600°C, 625°C, or 640°C.

[0195] In some embodiments, the second sintering time is 6-12 hours, including but not limited to 7 hours, 8 hours, 9 hours, 10 hours or 11 hours.

[0196] In some embodiments, the heating rate of the second sintering is 0.5-3.5℃ / min, including but not limited to 0.7℃ / min, 1℃ / min, 1.3℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min, 3℃ / min or 3.5℃ / min, etc., and can be selected as 1℃ / min.

[0197] In some embodiments, during the sintering process, the flow rate of the inert gas is 2-8 L / min, including but not limited to 3 L / min, 4 L / min, 5 L / min, 6 L / min or 7 L / min.

[0198] In some embodiments, the preparation method of the positive electrode active material further includes a cooling step after sintering, wherein the cooling rate is 100-150℃ / h, including but not limited to 110℃ / h, 120℃ / h, 130℃ / h or 140℃ / h.

[0199] As an optional example, a method for preparing a positive electrode active material includes the following steps:

[0200] 1) Soluble iron salt, phosphate salt and deionized water are added to the reaction vessel and stirred to prepare a reaction solution. Hydrogen peroxide is then added to the solution using a peristaltic pump and stirred to obtain a slurry. The slurry is then filtered and washed to obtain the first precursor material.

[0201] 2) The first precursor material is put into the reactor, deionized water is added and stirred to disperse it. Phosphoric acid and ammonia are added dropwise to adjust the pH. After a period of aging, the second precursor material is obtained after filtration and washing.

[0202] 3) Place the second precursor material into a reaction vessel, add deionized water, and then add a certain amount of soluble manganese salt, soluble M salt, ethanol, ammonia, and N,N-dimethylformamide solution (DMF) to the water in sequence. Finally, add 1,2,3-triazole dropwise, stir and filter at room temperature to obtain the third precursor material coated with Mn / M-MET.

[0203] 4) A mixed solution was prepared by mixing the third precursor material, sodium salt, PEG and water. After stirring, the solution was added to a spray drying device and spray dried in an inert atmosphere to obtain the fourth precursor material.

[0204] 5) The fourth precursor material is subjected to high-temperature sintering heat treatment to obtain mixed iron-based phosphate material (i.e., positive electrode active material).

[0205] The positive electrode active material of this application embodiment uses Mn / M-MET (metal triazole salt) in-situ nitrogen-containing carbon source (i.e. carbon-nitrogen source) coating material. The higher nitrogen doping increases the disorder of carbon material, increases active sites, and improves the conductivity of the material. Due to its unique MET molecular framework, it forms a uniform and extremely thin carbon layer on the material surface. While ensuring its conductivity, it can also form a uniform and extremely thin carbon layer on the material surface, resulting in an NFPP material with extremely high compaction density.

[0206] <Positive Electrode>

[0207] The positive electrode sheet of this application embodiment includes the positive active material of this application embodiment or the positive active material prepared by the preparation method of the positive active material of this application embodiment.

[0208] In some embodiments, the positive electrode sheet includes a positive electrode material, which includes the positive electrode active material of the embodiments of this application.

[0209] In some embodiments, the cathode material also includes other cathode active materials, such as polyanionic compounds, Prussian blue analogs, etc.

[0210] As an example, polyanionic compounds can be those containing sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The valence state. Polyanionic compounds can also have sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl, or Br. Polyanionic compounds can also have sodium ions, tetrahedral (YO4) valence states. n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) m+The valence state; the halogen can be at least one of F, Cl, and Br. Examples of polyanionic compounds include NaFePO4, Na3V2(PO4)3, NaM'PO4F (M' is one or more of V, Fe, Mn, and Ni), and Na3(VO4)2(PO4)3. y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0211] As an example, Prussian blue compounds can be those containing sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Prussian blue compounds include, for example, Na. a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0212] In some embodiments, the positive electrode material further includes a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0213] In some embodiments, the positive electrode binder accounts for 0.1-3.5% of the total weight of the positive electrode material, optionally 0.5-2.5%.

[0214] In some embodiments, the positive electrode material further includes a positive electrode conductive agent. As an example, the positive electrode conductive agent may include, but is not limited to, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0215] In some embodiments, the positive electrode conductive agent accounts for 0.05-5% of the total weight of the positive electrode material, optionally 0.5-3%.

[0216] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, wherein the material of the positive electrode film layer is the aforementioned positive electrode material.

[0217] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0218] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0219] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, positive conductive agent, positive binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0220] Secondary batteries

[0221] The secondary battery of this application embodiment includes a positive electrode, a separator, and a negative electrode, wherein the positive electrode is the positive electrode of this application embodiment.

[0222] In some embodiments, the aforementioned secondary battery is a sodium-ion battery.

[0223] In some embodiments, the negative electrode sheet typically includes a negative current collector and a negative electrode material layer disposed on the negative current collector, wherein the material of the negative electrode material layer includes a negative electrode active material.

[0224] In some embodiments, the negative electrode may only include a negative current collector, i.e., it may not contain a negative electrode material. The negative electrode may also include a pre-deposited metallic phase on the negative current collector. The negative current collector can be made of conventional metal foil, carbon-coated metal foil, or porous metal plate, etc. As an example, the negative current collector can be made of copper foil or aluminum foil.

[0225] In the embodiments of this application, the specific type of negative electrode active material is not limited. Any active material known in the art that can be used as a negative electrode in sodium-ion batteries can be used, and those skilled in the art can select according to actual needs. As an example, the negative electrode active material may include, but is not limited to, one or more of sodium metal, carbon materials, alloy materials, transition metal oxides and / or sulfides, phosphorus-based materials, and titanate materials. Specifically, carbon materials may include one or more of hard carbon, soft carbon, amorphous carbon, and nanostructured carbon materials; alloy materials may include alloys formed from one or more of Si, Ge, Sn, Pb, and Sb; the general formula for transition metal oxides and sulfides is MxNy, where M includes one or more of Fe, Co, Ni, Mn, Sn, Mo, Sb, and V, and N includes O or S; phosphorus-based materials may include one or more of red phosphorus, white phosphorus, and black phosphorus; titanate materials may include Na2Ti3O7 and Na2Ti6O7. 13 Na4Ti5O 12 Li4Ti5O 12 One or more of NaTi2(PO4)3. These materials are all commercially available.

[0226] In some embodiments, the material of the negative electrode active material layer may optionally include a negative electrode binder and a negative electrode conductive agent. The negative electrode conductive agent is used to improve the conductivity of the negative electrode active material, and the negative electrode binder is used to firmly bond the negative electrode active material and the negative electrode conductive agent to the negative electrode current collector. In the embodiments of this application, the types of negative electrode conductive agents and negative electrode binders are not specifically limited, and can be selected according to actual needs.

[0227] As an example, the negative electrode conductive agent may include, but is not limited to, one or more of the following: superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0228] As an example, the negative electrode binder may include, but is not limited to, one or more of styrene-butadiene rubber (SBR), styrene-butadiene rubber (SBCs), water-based acrylic resin, and carboxymethyl cellulose (CMC).

[0229] The material of the negative electrode active material layer may also include thickeners, such as carboxymethyl cellulose (CMC). However, the embodiments of this application are not limited to this, and other materials that can be used as thickeners for the negative electrode sheet of sodium-ion batteries may also be used in the embodiments of this application.

[0230] As for the aforementioned separator, there are no particular limitations in the embodiments of this application. Any known porous structure separator with electrochemical and mechanical stability can be selected according to actual needs. For example, it can be a single-layer or multi-layer film containing one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0231] In some embodiments, the secondary battery also includes an electrolyte.

[0232] The electrolyte acts as a conductor of ions between the positive and negative electrodes. The electrolyte can include electrolyte salts and solvents.

[0233] As an example, the electrolyte sodium salt includes, but is not limited to, at least one of sodium hexafluorophosphate, sodium difluorooxalate borate, sodium tetrafluoroborate, sodium dioxalate borate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, and sodium bis(trifluoromethanesulfonyl)imide.

[0234] As an example, solvents may include, but are not limited to, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), and methyl butyrate. One or more of the following: ester (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), diethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, tetrahydrofuran, methyltetrahydrofuran, 1,3-dioxopentane, 1,3-dioxane, 1,4-dioxane, tetrahydropyran, methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0235] In some embodiments, the electrolyte also includes additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0236] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0237] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte.

[0238] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0239] It should be noted that, in the embodiments of this application, there are no particular restrictions on the shape of the secondary battery, which can be cylindrical, square or other arbitrary shapes.

[0240] <Electrical Appliances>

[0241] The electrical device in this application includes the secondary battery in this application.

[0242] In some embodiments, the aforementioned electrical appliances include electronic devices, lighting equipment, vehicles, etc.

[0243] The positive electrode sheet, secondary battery, and power device of the present application embodiments all have at least the beneficial effects of the positive electrode active material and the preparation method of the positive electrode active material of the present application embodiments.

[0244] The following non-limiting embodiments further illustrate certain features of the present technology.

[0245] I. Examples and Comparative Examples

[0246] The main sources of raw materials involved in the following examples and comparative examples are shown in Table 1.

[0247] Table 1. Main sources of raw materials involved in the examples and comparative examples.

[0248] raw material source manganese chloride Sinopharm Zinc chloride Sinopharm cobalt chloride Sinopharm Copper chloride Sinopharm Magnesium chloride Sinopharm Ferrous sulfate Sinopharm Sodium dihydrogen phosphate Sinopharm hydrogen peroxide Sinopharm Sodium carbonate Sinopharm ammonia Aladdin 1,2,3-Triazole Aladdin N,N-Dimethylformamide Aladdin ethanol Aladdin

[0249] The room temperature involved in the following examples and comparative examples is 25°C.

[0250] Example 1

[0251] The preparation method of the positive electrode active material in this embodiment includes the following steps:

[0252] (1) Preparation of the first precursor material: A certain amount of ferrous sulfate and sodium dihydrogen phosphate were dissolved in deionized water at a molar ratio of 5:8. After stirring, a reaction solution was prepared, with the molar concentrations of ferrous sulfate and sodium dihydrogen phosphate in the reaction solution being 0.5 mol / L and 0.8 mol / L, respectively. Then, 0.2 mol / L of hydrogen peroxide was added to the above reaction solution using a peristaltic pump, so that the molar ratio of hydrogen peroxide to ferrous sulfate in the total added hydrogen peroxide was H2O2:ferrous sulfate = 1:2. The reaction was continued at room temperature for 4 hours under stirring. After that, the mixture was filtered and washed to obtain the first precursor material.

[0253] (2) Preparation of the second precursor material: The first precursor material obtained in step (1) was put into the first reaction vessel, 200g of deionized water was added, and then 0.08wt% phosphoric acid and 0.06wt% ammonia water were added dropwise (the dropping rate of phosphoric acid and ammonia water was 30ml / min). The amount of addition was adjusted to make the pH of the system 2.6. The system was then aged at 25℃ for 6h. After that, it was filtered and washed to obtain the second precursor material.

[0254] (3) Preparation of the third precursor material: The third precursor material obtained in step (2) and deionized water were added to the second reactor simultaneously, and manganese chloride and zinc chloride were added sequentially. After stirring for 0.5 h, the mixture was dissolved to obtain a mixed solution. The molar ratio of Fe:Mn:Zn in the mixed solution was 25:4:1. Subsequently, ethanol, 20wt% ammonia and N,N-dimethylformamide solution (DMF) were added sequentially to the mixed solution in the second reactor to make the volume ratio of deionized water, ethanol, ammonia and DMF 1:2:1:1, ensuring that the total molar concentration of Mn and Zn in the solution in the second reactor was 0.05mol / L. Then, 1,2,3-triazole was added dropwise at a rate of 15ml / min using a syringe pump until the molar ratio of 1,2,3-triazole:Mn:Zn was 10:4:1. After stirring at room temperature for 4 h, the mixture was filtered to obtain loaded Mn. 0.8 Zn 0.2 -(C2H3N3)2 is the third precursor material.

[0255] (4) Preparation of the fourth precursor material: First, PEG was dissolved in deionized water by stirring for 1 hour. Then, sodium carbonate and the third precursor material obtained in step (3) were added, so that the molar ratio of C in the added PEG: molar ratio of sodium carbonate: molar ratio of Fe in the third precursor material = 25:64:50. After stirring at room temperature for 2 hours, the mixture was dried in a spray dryer to obtain the fourth precursor material. The inlet air temperature of the spray dryer was 120℃, and the exhaust air temperature was 100℃.

[0256] (5) Sintering: The fourth precursor material obtained in step (4) was placed in a box furnace, and N2 was introduced at a gas flow rate of 6 L / min. The temperature was increased to 250°C at a rate of 2°C / min and held for 5 h. Then the temperature was increased to 540°C at a rate of 1°C / min and held for 8 h. Subsequently, the temperature was cooled at a rate of 100°C / h to obtain Na with the chemical formula 98.4 wt%. 3.2 Fe 2.5 Mn 0.4 Zn 0.1 (PO4)2P2O7·0.7wt%Na 1.74 Fe 0.84 Mn 0.13 Zn 0.03 P2O7@0.9wt% (C2N3) positive electrode active material.

[0257] Example 2

[0258] The preparation method of the positive electrode active material in this embodiment includes the following steps:

[0259] (1) Preparation of the first precursor material: A certain amount of ferrous sulfate and sodium dihydrogen phosphate were dissolved in deionized water at a molar ratio of 1:2. After stirring, a reaction solution was prepared, with the molar concentrations of ferrous sulfate and sodium dihydrogen phosphate in the reaction solution being 0.4 mol / L and 0.8 mol / L, respectively. Then, 0.2 mol / L of hydrogen peroxide was added to the above reaction solution using a peristaltic pump, so that the molar ratio of hydrogen peroxide to ferrous sulfate in the total added hydrogen peroxide was H2O2:ferrous sulfate = 1:2. The reaction was continued at room temperature for 2 hours under stirring. After that, the mixture was filtered and washed to obtain the first precursor material.

[0260] (2) Preparation of the second precursor material: The first precursor material obtained in step (1) was put into the first reaction vessel, 300g of deionized water was added, and then 0.08wt% phosphoric acid and 0.07wt% ammonia water were added dropwise (the dropping rate of phosphoric acid and ammonia water was 30ml / min). The amount of addition was adjusted to make the pH of the system 3.0. The system was then aged at 30℃ for 10h. After that, it was filtered and washed to obtain the second precursor material.

[0261] (3) Preparation of the third precursor material: The third precursor material obtained in step (2) and deionized water were added to the second reactor simultaneously, and manganese chloride, cobalt chloride and copper chloride were added in sequence and stirred for 0.5 h to dissolve, resulting in a mixed solution. The molar ratio of Fe:Mn:Co:Cu in the mixed solution was 20:5:2:3. Subsequently, ethanol, 14wt% ammonia and N,N-dimethylformamide solution (DMF) were added to the mixed solution in the second reactor in sequence, so that the volume ratio of deionized water, ethanol, ammonia and DMF was 1:4:1:1, ensuring that the total molar concentration of Mn, Co and Cu in the solution in the second reactor was 0.1mol / L. Then, 1,2,3-triazole was added dropwise at a rate of 15ml / min using a syringe pump until the molar ratio of 1,2,3-triazole:Mn:Co:Cu was 20:5:2:3. After stirring at room temperature for 4 h, the mixture was filtered to obtain loaded Mn. 0.5 Co 0.2 Cu 0.3 -(C2H3N3)2 is the third precursor material.

[0262] (4) Preparation of the fourth precursor material: First, PEG was dissolved in deionized water by stirring for 1 hour. Then, sodium carbonate and the third precursor material obtained in step (3) were added, so that the molar ratio of C in the added PEG: molar ratio of sodium carbonate: molar ratio of Fe in the third precursor material = 5:14:10. After stirring at room temperature for 2 hours, the mixture was dried in a spray dryer to obtain the fourth precursor material. The inlet air temperature of the spray dryer was 100℃, and the outlet air temperature was 90℃.

[0263] (5) Sintering: The fourth precursor material obtained in step (4) was placed in a box furnace, and N2 was introduced at a gas flow rate of 6 L / min. The temperature was increased to 220°C at a rate of 2°C / min and held for 5 h. Then the temperature was increased to 520°C at a rate of 1°C / min and held for 10 h. Subsequently, the temperature was cooled at a rate of 100°C / h to obtain Na with the chemical formula 98.8 wt%. 2.8 Fe 2.0 Mn 0.5 Co 0.2 Cu 0.3 (PO4)2P2O7·0.5wt%Na 1.66 Fe 0.66 Mn 0.17 Co 0.07 Cu 0.1 P2O7@0.7wt% (C2N3) positive electrode active material.

[0264] Example 3

[0265] The preparation method of the positive electrode active material in this embodiment includes the following steps:

[0266] (1) Preparation of the first precursor material: A certain amount of ferrous sulfate and sodium dihydrogen phosphate were dissolved in deionized water at a molar ratio of 3:5. After stirring, a reaction solution was prepared, with the molar concentrations of ferrous sulfate and sodium dihydrogen phosphate in the reaction solution being 0.48 mol / L and 0.8 mol / L, respectively. Then, 0.2 mol / L of hydrogen peroxide was added to the above reaction solution using a peristaltic pump, so that the molar ratio of hydrogen peroxide to ferrous sulfate in the total added hydrogen peroxide was H2O2:ferrous sulfate = 1:2. The reaction was continued at room temperature for 6 hours under stirring. After that, the mixture was filtered and washed to obtain the first precursor material.

[0267] (2) Preparation of the second precursor material: The first precursor material obtained in step (1) was put into the first reaction vessel, 250g of deionized water was added, and then 0.09wt% phosphoric acid and 0.06wt% ammonia water were added dropwise (the dropping rate of phosphoric acid and ammonia water was 30ml / min). The amount of addition was adjusted to make the pH of the system 2.1. Then, the system was aged at 40℃ for 3h. After that, it was filtered and washed to obtain the second precursor material.

[0268] (3) Preparation of the third precursor material: The third precursor material obtained in step (2) and deionized water were added to the second reactor simultaneously, and manganese chloride, titanium oxysulfate, and magnesium chloride were added sequentially. After stirring for 0.5 h, the mixture was dissolved to obtain a mixed solution. The molar ratio of Fe:Mn:Ti:Mg in the mixed solution was 24:3:1:2. Subsequently, ethanol, 12.5wt% ammonia and N,N-dimethylformamide solution (DMF) were added sequentially to the mixed solution in the second reactor to make the volume ratio of deionized water, ethanol, ammonia and DMF 1:5:1:1, ensuring that the total molar concentration of Mn, Ti and Mg in the solution in the second reactor was 0.06mol / L. Then, 1,2,3-triazole was added dropwise at a rate of 15ml / min using a syringe pump until the molar ratio of 1,2,3-triazole:Mn:Ti:Mg was 12:3:1:2. After stirring at room temperature for 4 h, the mixture was filtered to obtain loaded Mn. 0.5 Ti 0.17 Mg 0.33 -(C2H3N3)2 is the third precursor material.

[0269] (4) Preparation of the fourth precursor material: First, PEG was dissolved in deionized water by stirring for 1 hour. Then, sodium carbonate and the third precursor material obtained in step (3) were added, so that the molar ratio of C in the added PEG: molar ratio of sodium carbonate: molar ratio of Fe in the third precursor material = 3:8:6. After stirring at room temperature for 2 hours, the mixture was dried in a spray dryer to obtain the fourth precursor material. The inlet air temperature of the spray dryer was 130℃ and the exhaust air temperature was 80℃.

[0270] (5) Sintering: The fourth precursor material obtained in step (4) was placed in a box furnace, and N2 was introduced at a gas flow rate of 6 L / min. The temperature was increased to 300℃ at a rate of 2℃ / min and held for 5 h. Then the temperature was increased to 545℃ at a rate of 1℃ / min and held for 8 h. Subsequently, the temperature was cooled at a rate of 100℃ / h to obtain Na with the chemical formula 97.1wt%. 3.2 Fe 2.4 Mn 0.3 Ti 0.1 Mg 0.2 (PO4)2P2O7·0.9wt%Na 1.74 Fe 0.8 Mn 0.1 Ti 0.03 Mg 0.07 P2O7@2.0wt% (C2N3) positive electrode active material.

[0271] Example 4 (Chemical formula without Na) 2-d Fe 1-b / 3-c / 3 Mn b / 3 M c / 3 P2O7, β=0)

[0272] This embodiment is basically the same as embodiment 1, except that:

[0273] In the preparation method of the positive electrode active material in this embodiment, step (5) sintering process is as follows:

[0274] The fourth precursor material obtained in step (4) was placed in a box furnace, and N2 was introduced at a gas flow rate of 6 L / min. The temperature was increased to 250°C at a rate of 2°C / min and held for 5 h. Then, the temperature was increased to 500°C at a rate of 1°C / min and held for 8 h. Subsequently, the temperature was cooled at a rate of 100°C / h to obtain 99.1 wt% Na. 3.2 Fe 2.5 Mn 0.4 Zn 0.1 (PO4)2P2O7@0.9wt% (C2N3) positive electrode active material.

[0275] Example 5 (Chemical formula β is the value near the upper limit of 5 wt%)

[0276] This embodiment is basically the same as embodiment 1, except that:

[0277] In the preparation method of the positive electrode active material in this embodiment, step (5) sintering process is as follows:

[0278] The fourth precursor material obtained in step (4) was placed in a box furnace, and N2 was introduced at a gas flow rate of 6 L / min. The temperature was increased to 250°C at a rate of 2°C / min and held for 5 h. Then, the temperature was increased to 650°C at a rate of 1°C / min and held for 8 h. Subsequently, the temperature was cooled at a rate of 100°C / h to obtain 95wt% Na. 3.2 Fe 2.5 Mn 0.4 Zn 0.1 (PO4)2P2O7·4.1wt%Na 1.74 Fe 0.84 Mn 0.13 Zn 0.03 P2O7@0.9wt% (C2N3) positive electrode active material.

[0279] Example 6 (Chemical formula β is an intermediate value)

[0280] This embodiment is basically the same as embodiment 1, except that:

[0281] In the preparation method of the positive electrode active material in this embodiment, step (5) sintering process is as follows:

[0282] The fourth precursor material obtained in step (4) was placed in a box furnace, and N2 was introduced at a gas flow rate of 6 L / min. The temperature was increased to 250°C at a rate of 2°C / min and held for 5 h. Then, the temperature was increased to 600°C at a rate of 1°C / min and held for 8 h. Subsequently, the temperature was cooled at a rate of 100°C / h to obtain Na with the chemical formula 96.6 wt%. 3.2 Fe 2.5 Mn 0.4 Zn 0.1 (PO4)2P2O7·2.5wt%Na 1.74 Fe 0.84 Mn 0.13 Zn 0.03 P2O7@0.9wt% (C2N3) positive electrode active material.

[0283] Example 7 (γ is the upper limit of the preferred range, 3 wt%)

[0284] This embodiment is basically the same as embodiment 1, except that:

[0285] In the preparation method of the positive electrode active material in this embodiment:

[0286] In step (3), 1,2,3-triazole was added dropwise at a rate of 15 ml / min using a syringe pump until the molar ratio of 1,2,3-triazole:Mn:Zn was 30:4:1. After stirring at room temperature for 4 h, the mixture was filtered to obtain the loaded Mn. 0.8 Zn 0.2-(C2H3N3)6 is the third precursor material.

[0287] In step (5), the final product is Na with the chemical formula 96.31 wt%. 3.2 Fe 2.5 Mn 0.4 Zn 0.1 (PO4)2P2O7·0.69wt%Na 1.74 Fe 0.84 Mn 0.13 Zn 0.03 P2O7@3wt% (C2N3) positive electrode active material.

[0288] Example 8 (γ exceeds the upper limit of the preferred range -4wt%)

[0289] This embodiment is basically the same as embodiment 1, except that:

[0290] In the preparation method of the positive electrode active material in this embodiment:

[0291] In step (3), 1,2,3-triazole was added dropwise at a rate of 15 ml / min using a syringe pump until the molar ratio of 1,2,3-triazole:Mn:Zn was 40:4:1. After stirring at room temperature for 4 h, the mixture was filtered to obtain the loaded Mn. 0.8 Zn 0.2 -(C2H3N3)8 is the third precursor material.

[0292] In step (5), the final product is Na with the chemical formula 95.32 wt%. 3.2 Fe 2.5 Mn 0.4 Zn 0.1 (PO4)2P2O7·0.68wt%Na 1.74 Fe 0.84 Mn 0.13 Zn 0.03 P2O7@4wt% (C2N3) positive electrode active material.

[0293] Example 9 (c = 0, no M element)

[0294] This embodiment is basically the same as embodiment 1, except that:

[0295] In the preparation method of the positive electrode active material in this embodiment:

[0296] In step (3), the third precursor material obtained in step (2) and deionized water are added to the second reactor at the same time, and manganese chloride is added sequentially and stirred for 0.5 h to dissolve, so as to obtain a mixed solution. The molar ratio of Fe:Mn in the mixed solution is 13:2; the molar ratio of 1,2,3-triazole:Mn is 9.3:3.7.

[0297] In step (5), the final product is Na with the chemical formula 98.4 wt%. 3.2 Fe 2.6 Mn 0.4 (PO4)2P2O7·0.7wt%Na 1.74 Fe 0.87 Mn 0.13 P2O7@0.9wt% (C2N3) positive electrode active material.

[0298] Example 10 (lower limit of the preferred range for m / n: 1.0)

[0299] This embodiment is basically the same as embodiment 1, except that:

[0300] In step (3), the molar ratio of Fe:Mn:Zn in the mixed solution is 10:1:1; the molar ratio of 1,2,3-triazole:Mn:Zn is 10:2.5:2.5; thus, loaded Mn is obtained. 0.5 Zn 0.5 -(C2H3N3)2 third precursor material

[0301] In step (5), 98.4 wt% Na was obtained. 3.2 Fe 2.5 Mn 0.25 Zn 0.25 (PO4)2P2O7·0.7wt%Na 1.74 Fe 0.84 Mn 0.08 Zn 0.08 P2O7@0.9wt% (C2N3) positive electrode active material.

[0302] Example 11 (preferred range upper limit of m / n: 4.5)

[0303] This embodiment is basically the same as embodiment 1, except that:

[0304] In step (3), the molar ratio of Fe:Mn:Zn in the mixed solution is 25:4.1:0.9; the molar ratio of 1,2,3-triazole:Mn:Zn is 10:4.1:0.9; thus, loaded Mn is obtained. 0.82 Zn 0.18 -(C2H3N3)2 third precursor material

[0305] In step (5), 98.4 wt% Na was obtained. 3.2 Fe 2.5 Mn 0.41 Zn 0.09 (PO4)2P2O7·0.7wt%Na 1.74 Fe0.84 Mn 0.13 Zn 0.03 P2O7@0.9wt% (C2N3) positive electrode active material.

[0306] Example 12 (m / n exceeds the lower limit of the preferred range of this application)

[0307] This embodiment is basically the same as embodiment 1, except that:

[0308] In step (3), the molar ratio of Fe:Mn:Zn in the mixed solution is 25:2.2:2.8; the molar ratio of 1,2,3-triazole:Mn:Zn is 10:2.2:2.8; thus, loaded Mn is obtained. 0.44 Zn 0.56 -(C2H3N3)2 third precursor material

[0309] In step (5), 98.4 wt% Na was obtained. 3.2 Fe 2.5 Mn 0.22 Zn 0.28 (PO4)2P2O7·0.7wt%Na 1.74 Fe 0.84 Mn 0.07 Zn 0.09 P2O7@0.9wt% (C2N3) positive electrode active material.

[0310] Example 13 (m / n exceeds the upper limit of the preferred range of this application)

[0311] This embodiment is basically the same as embodiment 1, except that:

[0312] In step (3), the molar ratio of Fe:Mn:Zn in the mixed solution is 25:4.38:0.62; the molar ratio of 1,2,3-triazole:Mn:Zn is 10:4.38:0.62; thus, loaded Mn is obtained. 0.88 Zn 0.12 -(C2H3N3)2 third precursor material

[0313] In step (5), 98.4 wt% Na was obtained. 3.2 Fe 2.5 Mn 0.44 Zn 0.06 (PO4)2P2O7·0.7wt%Na 1.74 Fe 0.84 Mn 0.14 Zn 0.02 P2O7@0.9wt% (C2N3) positive electrode active material.

[0314] Example 14 (carbon and nitrogen source not 1,2,3-triazole)

[0315] This embodiment is basically the same as embodiment 1, except that:

[0316] In step (3), 1,2,3-triazole is replaced with 1,2,4-triazole to obtain 98.4 wt% Na 3.2 Fe 2.5 Mn 0.4 Zn 0.1 (PO4)2P2O7 0.7wt% Na 1.74 Fe 0.84 Mn 0.13 Zn 0.03 P2O7@0.9wt% (C2N3) positive electrode active material.

[0317] Example 15 (pH is the upper limit of the preferred range, 6)

[0318] This embodiment is basically the same as embodiment 1, except that:

[0319] In step (2), the amount of liquid added is adjusted to make the pH of the system 6. In step (5), 98.4 wt% Na is obtained. 3.2 Fe 2.5 Mn 0.4 Zn 0.1 (PO4)2P2O7·0.7wt%Na 1.74 Fe 0.84 Mn 0.13 Zn 0.03 P2O7@0.9wt% (C2N3) positive electrode active material.

[0320] Comparative Example 1

[0321] The preparation method of the positive electrode active material in this comparative example is as follows:

[0322] (1) Preparation of the first precursor material: A certain amount of ferrous sulfate and sodium dihydrogen phosphate were dissolved in deionized water at a molar ratio of 3:4. After stirring, a reaction solution was prepared, with the molar concentrations of ferrous sulfate and sodium dihydrogen phosphate in the reaction solution being 0.6 mol / L and 0.8 mol / L, respectively. Then, 0.2 mol / L of hydrogen peroxide was added to the above reaction solution using a peristaltic pump, so that the molar ratio of hydrogen peroxide to ferrous sulfate in the total added hydrogen peroxide was H2O2:ferrous sulfate = 1:2. The reaction was continued at room temperature for 4 hours under stirring. After that, the mixture was filtered and washed to obtain the first precursor material.

[0323] (2) Preparation of the second precursor material: The first precursor material obtained in step (1) was put into the first reaction vessel, 200g of deionized water was added, and then 0.08wt% phosphoric acid and 0.06wt% ammonia water were added dropwise (the dropping rate of phosphoric acid and ammonia water was 30ml / min). The amount of addition was adjusted to make the pH of the system 2.6. The system was then aged at 25℃ for 6h. After that, it was filtered and washed to obtain the second precursor material.

[0324] (3) Preparation of the third precursor material: The second precursor material obtained in step (2) and deionized water were added to the second reactor, and PEG was added and stirred for 1 hour to dissolve it. Sodium carbonate was then added so that the molar ratio of C in the added PEG to that of sodium carbonate to that of Fe in the second precursor material was 9:4:3. After stirring at room temperature for 2 hours, the mixture was dried in a spray dryer to obtain the third precursor material. The inlet air temperature of the spray dryer was 120℃ and the exhaust air temperature was 100℃.

[0325] (4) Sintering: The third precursor material obtained in step (3) is placed in a box furnace, N2 is introduced at a gas flow rate of 6 L / min, the temperature is raised to 250℃ at a rate of 2℃ / min and held for 5h; then the temperature is raised to 540℃ at a rate of 1℃ / min and held for 8h; then the temperature is cooled at a rate of 100℃ / h to obtain a positive electrode active material with the chemical formula 94wt%Na4Fe3(PO4)2P2O7·2.9wt%Na2FeP2O7@3.1wt%C.

[0326] Comparative Example 2 (compared to Example 1, step (3) did not involve the addition of 1,2,3-triazole)

[0327] This comparative example is basically the same as Example 1, except that:

[0328] In step (3), remove “Then 1,2,3-triazole is added dropwise at a rate of 15 ml / min using a syringe pump until the molar ratio of 1,2,3-triazole:Mn:Zn is 10:4:1”.

[0329] In step (5), a positive electrode active material with the chemical formula 94wt% Na4Fe3(PO4)2P2O7·2.8wt% Na2FeP2O7@3.2wt% C is obtained.

[0330] Comparative Example 3 (All raw materials reacted together)

[0331] This comparative example is basically the same as Example 1, except that all raw materials are reacted together.

[0332] Specifically, the preparation method of the positive electrode active material is as follows:

[0333] A certain amount of ferrous sulfate and sodium dihydrogen phosphate were dissolved in deionized water at a molar ratio of 5:8. After stirring, a reaction solution was prepared, with the molar concentrations of ferrous sulfate and sodium dihydrogen phosphate in the reaction solution being 0.5 mol / L and 0.8 mol / L, respectively. Then, 0.2 mol / L of hydrogen peroxide was added to the above reaction solution using a peristaltic pump, so that the molar ratio of hydrogen peroxide to ferrous sulfate in the total added hydrogen peroxide was H2O2:ferrous sulfate = 1:2. Subsequently, manganese chloride and zinc chloride were added and stirred for 0.5 h to dissolve, resulting in a mixed solution with a Fe:Mn:Zn molar ratio of 25:4:1. Ethanol, 20wt% ammonia, and N,N-dimethylformamide (DMF) solution were added sequentially to the mixed solution to achieve a volume ratio of deionized water, ethanol, ammonia, and DMF of 1:2:1:1, ensuring that the total molar concentration of Mn and Zn in the solution was 0.05 mol / L. Then, 1,2,3-triazole was added dropwise at a rate of 15 ml / min using a syringe pump until the molar ratio of 1,2,3-triazole:Mn:Zn was 10:4:1. After stirring at room temperature for 4 h, the precursor material was obtained by filtration.

[0334] The precursor material was spray-dried and sintered in the same manner as in Experimental Example 1 to obtain 95.7 wt% Na. 3.2 Fe 2.75 Mn 0.2 Zn 0.05 (PO4)2P2O7·0.68wt%Na 1.74 Fe 0.93 Mn 0.06 Zn 0.01 P2O7@3.6wt%C positive electrode active material.

[0335] II. Material Characterization and Performance Testing

[0336] 1. Morphological test

[0337] The morphology of the positive electrode active materials prepared in each example and comparative example was tested using transmission electron microscopy (TEM) and scanning electron microscopy (SEM), respectively.

[0338] The morphology test results of the positive electrode active materials prepared in Example 1 and Comparative Example 1 are as follows: Figure 2 and Figure 3 As shown.

[0339] from Figure 2 It can be seen that the nitrogen-containing carbon layer in Example 1 is uniform and extremely thin, with a thickness of 3 nm.

[0340] from Figure 3It can be seen that the carbon layer in Comparative Example 1 is thicker and unevenly distributed. The carbon layer (i.e., the coating layer, shell) at the marked location is 8 nm thick, and the thickness at the thicker location is >8 nm.

[0341] 2. XRD test

[0342] The positive electrode active materials prepared in the above examples or comparative examples were tested using a Bruker D8 Advance XRD diffractometer. The XRD patterns were refined using Highscore software combined with the Rietvald method. The specific refinement method was as follows: first, the default settings were used for automatic fitting; then, the material phase cards were imported, and the inserted phases, peak shapes, pattern parameters, and structural parameters were manually refined and analyzed. The positions and intensities of the (411) diffraction peaks were recorded. Afterward, the material underwent ordinary refinement to obtain the (411) interplanar spacing. The results are shown in Table 2. Simultaneously, phase composition fitting analysis was performed based on the refined XRD data to obtain the compositional proportions of the NFPP and NFPO phases, which are reflected in the chemical formula composition.

[0343] 3. Button test

[0344] The positive electrode active material prepared using the above embodiments or comparative examples was mixed with conductive additives carbon black and polyvinylidene fluoride binder at a mass ratio of 75:15:10 to form a slurry. This slurry was then uniformly coated onto two opposite surfaces of an aluminum foil with a thickness of 16 micrometers. After drying in an 80°C vacuum oven for 12 hours, a working electrode with a diameter of 10 mm and an active material loading of 1.7 mg / cm³ was obtained. 2 -2.3mg / cm 2 The working electrode was taken out from the glove box and assembled into a battery. The negative electrode shell, nickel foam, sodium sheet, and separator (3μm thick glass fiber) were assembled in sequence. Then, the electrolyte (a 1mol / L mixture of NaPF6 + diethyl carbonate (DEC) / ethylene carbonate (EC) (DEC and EC volume ratio 1:1)) was added. The working electrode (material side facing the sodium sheet) and positive electrode shell were then placed on top. The assembled battery was placed in a constant temperature chamber at 25℃±0.5℃. The button cell model was CR2032. The battery performance was tested using a Wuhan Landian CT2001A charge / discharge meter. Test conditions: nominal capacity 130mAh / g, test voltage 2.0V-4.0V, first cycle 0.2C charge / discharge, followed by rate testing: 0.2C charging, 0.5C / 1C / 2C discharging. The test results are shown in Table 3.

[0345] First-cycle discharge efficiency = 0.2C discharge capacity / 0.2C charging capacity

[0346] 2C rate = 0.2C charging condition, 2C discharge capacity / 0.2C first-cycle discharge capacity

[0347] 4. Compacted density test

[0348] The compaction density of the positive electrode active materials prepared in each embodiment or comparative example was tested using a powder compaction density tester. The test pressure was 3T, and the test results are shown in Table 2.

[0349] 5. Primary particle size test

[0350] The particle size Dv50 was determined according to standard GB / T19077-2016 / ISO 13320:2009. SEM analysis of the materials was performed using NanoMeasurer software to obtain the primary particle size D50 data. The primary particle size D50 data of the positive electrode active materials prepared in each embodiment or comparative example are shown in Table 2.

[0351] Table 2 Chemical formulas and structural parameters of positive electrode active materials

[0352]

[0353]

[0354]

[0355] Note: In Table 2, the coating layer refers to the coating layer formed by the material after @ in the chemical formula of each embodiment or comparative example, such as C2N3 or C.

[0356] As can be seen from Table 2, the coating material of the positive electrode active material prepared in each embodiment is C2N3, and its coating layer is uniform and thin, and its compaction density is significantly improved compared with the comparative example.

[0357] Table 3. Electrode charge data for positive electrode active materials

[0358]

[0359]

[0360] As can be seen from Table 3, compared with the comparative example, the positive electrode active material of the embodiment containing the C2N3 coating layer has a higher capacity, and its capacity, first efficiency and rate performance are better. This indicates that the nitrogen-containing carbon layer (C2N3) is conducive to the extraction and insertion of sodium ions, improves the conductivity of the carbon layer, and significantly improves the electrochemical performance of its positive electrode material.

[0361] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0362] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order, or primary and secondary relationship of the indicated technical features.

[0363] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0364] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this document, unless otherwise specified, generally indicates that the preceding and following related objects have an "or" relationship.

[0365] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces), unless otherwise explicitly specified.

Claims

1. A positive electrode active material, characterized in that, Comprising: a core, the core comprising a phosphate, the chemical formula of the phosphate being αNa 4-a Fe 3-b-c Mn b M c (PO4)2P2O7·βNa 2-d Fe 1-b / 3-c / 3 Mn b / 3 M c / 3 P2O7, wherein, 0 ≤ a ≤ 1.5, 0 < b ≤ 2, 0 ≤ c ≤ 2, 0 < 3 - b - c < 3, 0 ≤ d ≤ 2, 0 < 1 - b / 3 - c / 3 < 1, 95wt% ≤ α ≤ 100wt%, 0wt% ≤ β < 5wt%, and M comprises at least one of the elements Mg, Al, Ca, Ti, Ni, Co, Cu, Zn, Zr; A casing that covers at least part of the surface of the core; the casing includes C2N3.

2. The positive electrode active material according to claim 1, characterized in that, 0 ≤ a ≤ 1, and / or, 0 < b ≤ 1, and / or, 0 ≤ c ≤ 1, and / or, 0 ≤ d ≤ 1.5, and / or, 96 wt% ≤ α ≤ 100 wt%, and / or, 0 wt% ≤ β ≤ 4 wt%; and / or, The M includes at least one of the elements Mg, Ti, Co, Cu, and Zn.

3. The positive electrode active material according to claim 1, characterized in that, The mass content of C2N3 in the cathode active material is γ, 0 < γ ≤ 3 wt%, and α + β + γ = 1; and / or, The thickness of the casing is 2 - 7 nm.

4. The positive electrode active material according to any one of claims 1 to 3, characterized in that, In the X-ray diffraction pattern of the positive electrode active material, the interplanar spacing of (411) is... And / or, The median particle size of the primary particles of the cathode active material is 0.2 - 3 μm; and / or, The compaction density of the positive electrode active material under 3 tons of pressure is 2.0-2.35 g / cm³. 3 .

5. A method for preparing a positive electrode active material, characterized in that, Comprising: Performing a first reaction on an iron source, a phosphorus source, and an oxidant in a first solvent to obtain a first precursor material; Dispersing the first precursor material in a second solvent, adjusting the pH to acidic, and then aging to obtain a second precursor material; Performing a second reaction on the second precursor material, a manganese source, an M source, and a carbonitrogen source in a third solvent to obtain a third precursor material; the M element in the M source includes at least one of Mg, Al, Ca, Ti, Ni, Co, Cu, Zn, and Zr; Performing a third reaction on the third precursor material, a sodium source, and a carbon source in a fourth solvent, and then drying and sintering to obtain the cathode active material.

6. The preparation method according to claim 5, characterized in that, The carbonitrogen source includes at least one of 1,2,3 - triazole, 1,2,4 - triazole, and chloromethyltriazole; and / or, The third solvent includes water, C1 - 5 alcohols, ammonia water, and N,N - dimethylformamide; and / or, The iron source, the manganese source, and the M source are all soluble salts; and / or, The molar ratio of the manganese element in the manganese source to the M element in the M source is (1:100) - (100:1); and / or, The amount of substance of the carbonitrogen source is m mol, the total amount of substance of the manganese source and the M source is n mol, and m and n satisfy: 1.0 ≤ m / n ≤ 4.5; and / or, The second reaction is carried out under stirring conditions, and the reaction temperature of the second reaction is room temperature; and / or, The third precursor material is a material coated with a metal triazole salt, where the metal is the manganese element and the M element.

7. The preparation method according to claim 6, characterized in that, The soluble salt includes at least one of sulfates, nitrates, chlorides, acetates, and oxalates; and / or, In the third solvent, the volume ratio of water, C1 - 5 alcohols, ammonia water, and N,N - dimethylformamide is 1:(1 - 10):1:1; and / or, The step of performing a second reaction on the second precursor material, a manganese source, an M source, and a carbonitrogen source in a third solvent to obtain a third precursor material includes: Sequentially adding water, the manganese source, the M source, the C1 - 5 alcohols, ammonia water, and N,N - dimethylformamide to the second precursor material, and then dropping the carbonitrogen source to carry out the second reaction to obtain the third precursor material.

8. The preparation method according to claim 5, characterized in that, The phosphorus source includes at least one of ammonium phosphate, ammonium dihydrogen phosphate, monoammonium phosphate, sodium dihydrogen phosphate, and sodium pyrophosphate; and / or, The molar ratio of iron element in the iron source to phosphorus element in the phosphorus source is (1 - 3):4; and / or, The molar ratio of iron element in the iron source to manganese element in the manganese source is (0.001 - 3):(0.001 - 2); and / or, The oxidant includes at least one of hydrogen peroxide and ozone; and / or, The molar ratio of iron element in the iron source to hydrogen peroxide in the hydrogen peroxide is 1:(0.5 - 0.8); and / or, The first solvent, the second solvent and the fourth solvent all include water; and / or, The first reaction is a co - precipitation reaction; and / or, The first reaction is carried out under stirring, and the reaction temperature of the first reaction is room temperature.

9. The preparation method according to claim 5, characterized in that, During the process of obtaining the second precursor material, the pH is adjusted to acidic by dropping phosphoric acid and / or ammonia water; and / or, During the process of obtaining the second precursor material, the pH is adjusted to 1 - 6; and / or, The temperature of the aging is 20 - 50 °C, and the time of the aging is 1 - 16 h.

10. The preparation method according to claim 5, characterized in that, The carbon source includes at least one of polyethylene glycol, glucose and sucrose; and / or, The molar amount of C element in the carbon source is h mol, the molar amount of the sodium source is i mol, and the molar amount of Fe in the third precursor material is j mol, and the h, the i and the j satisfy: h:i:j = [(3 - b - c) / 2]:(4 - a):(3 - b - c), where 0 ≤ a ≤ 1.5, 0 < b ≤ 2, 0 ≤ c ≤ 2, 0 < 3 - b - c < 3; and / or, The third reaction is carried out under stirring, and the reaction temperature of the third reaction is room temperature; and / or, The drying and / or the sintering are carried out in an inert gas atmosphere; and / or, The temperature of the drying is 100 - 140 °C; and / or, The sintering includes a first sintering and a second sintering carried out in sequence, and the temperature of the first sintering is lower than that of the second sintering.

11. The preparation method according to claim 10, characterized in that, The temperature of the first sintering is 250 - 450 °C; and / or, The time of the first sintering is 4 - 7 h; and / or, The heating rate of the first sintering is 0.5 - 5.5 °C / min; and / or, The temperature of the second sintering is 500 - 650 °C; and / or, The time of the second sintering is 6 - 12 h; and / or, The heating rate of the second sintering is 0.5 - 3.5 °C / min; and / or, During the sintering process, the flow rate of the inert gas is 2 - 8 L / min; and / or, The method for preparing the positive electrode active material further includes a step of cooling after the sintering, and the cooling rate is 100 - 150 °C / h.

12. A positive electrode plate, characterized in that, It includes the positive electrode active material described in any one of claims 1 to 4 or the positive electrode active material prepared by the preparation method described in any one of claims 5 to 11.

13. A secondary battery, comprising a positive electrode, a negative electrode, and a separator, characterized in that, The positive electrode plate is the positive electrode plate described in claim 12.

14. An electrical appliance, characterized in that, It includes the secondary battery described in claim 13.

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