Positive electrode active material, method for preparing the same, positive electrode sheet, secondary battery, and electric device

Abstract

The application provides a positive electrode active material, a preparation method thereof, a positive electrode sheet, a secondary battery and an electric device. The positive electrode active material is a carbon-complexed polyanion compound, and the positive electrode active material has the following general formula: Na 4‑x R 3‑y M z (PO4)2P2O7 / C, wherein R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W and Pb, M includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, Si, W and Pb, 0<=x<=0.5, 0<=y<=0.5 and 0<=z

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a positive electrode active material, a preparation method thereof, a positive electrode sheet, a secondary battery and an electric device. BACKGROUND

[0002] Sodium batteries have great application potential in large-scale energy storage due to their abundant reserves, low prices and wide working temperature.

[0003] The performance of the positive electrode active material plays a key role in the performance of the battery. At present, the performance of the positive electrode active material itself cannot meet the application needs of the new generation of electrochemical systems. SUMMARY

[0004] The present application is made in view of the above-mentioned problems, and aims to provide a positive electrode active material having a low residual alkali content, which is beneficial to improve the processing performance of the positive electrode active material and optimize the coulomb efficiency and cycle performance of the battery.

[0005] In a first aspect, the present application provides a positive electrode active material, which is a carbon-complexed polyanion compound, and has the following general formula:

[0006] Na 4-x R 3-y M z (PO4)2P2O7 / C

[0007] wherein R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W and Pb, M includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, Si, W and Pb, 0≤x≤0.5, 0≤y≤0.5, 0≤z<x+y, and x and y are not 0 at the same time.

[0008] The positive active material can provide Na vacancies or R metal vacancies, R including at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W and Pb. In one aspect, the presence of the Na vacancies or the R metal vacancies changes the chemical bond distortion between other elements in the positive active material, widens the diffusion channel of Na ions, effectively promotes the migration of Na ions, and inhibits or reduces the formation of residual alkali in the positive active material, thereby reducing the electrode resistance of the positive electrode plate. In another aspect, the optimized Na ion diffusion channel can also improve the electrical conductivity of the positive active material. In addition, the metal doping including at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W and Pb can affect the change of the structure of the positive active material, expand the interplanar spacing, accelerate the migration of Na ions, further improve the cycle performance of the battery, and improve the performance of the battery.

[0009] In any embodiment, 0 < x ≤ 0.5, which can be 0.01 ≤ x ≤ 0.2.

[0010] The Na vacancies provided by the positive active material can effectively promote the migration of Na ions and inhibit or reduce the formation of residual alkali in the positive active material. In one aspect, the presence of the Na vacancies can increase the valence of other metals in the positive active material, enhance the oxidation resistance of the positive active material, thereby inhibiting or reducing the reaction of the positive active material with water, reducing the amount of residual alkali in the positive active material, and reducing the electrode resistance of the positive electrode plate. In another aspect, the optimized Na ion migration path can improve the kinetic performance of the positive active material, improve the coulombic efficiency and cycle performance of the battery, and improve the electrical performance of the battery. Further controlling 0.01 ≤ x ≤ 0.2 is conducive to further reducing the amount of residual alkali in the positive active material and the electrode resistance of the positive electrode plate.

[0011] In any embodiment, 0 < y-z ≤ 0.3.

[0012] The positive active material provides R metal vacancies, R including at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W and Pb. In one aspect, the R metal vacancies can distort the chemical bond between other elements in the positive active material, thereby widening the diffusion channel of Na ions, improving the transmission speed of Na ions during charging and discharging, improving the electrical conductivity of the positive active material, and thereby improving the coulombic efficiency and cycle performance of the battery. In another aspect, the R metal vacancies can also change the electron cloud distribution of elements such as P and O, thereby improving the electrical conductivity of the positive active material and improving the cycle performance of the battery.

[0013] In any embodiment, 0 < x ≤ 0.5 and 0 < z ≤ y ≤ 0.5.

[0014] On the basis of providing Na vacancies, the positive electrode active material is further doped with at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, Si, W and Pb, and the doped metal occupies R metal vacancies, which can affect the change of the structure of the positive electrode active material, expand the interplanar spacing, accelerate the migration of Na ions, and further improve the electrical conductivity of the positive electrode active material, thereby improving the cycle performance of the battery.

[0015] In any embodiment, R includes one or more of Fe, Co, Ni and Mn; and M includes one or more of Mg, Al, Sc, Ti, V, Cr, Mn, Si and Co.

[0016] The above metal materials can all achieve a positive electrode active material with a lower residual alkali content, a positive electrode plate with a lower plate resistance, and a battery with excellent coulomb efficiency and cycle performance.

[0017] In any embodiment, the median particle size D v 50 is 1.0 µm ≤ D v 50 ≤ 10 µm, and can be 1.5 µm ~ 5.0 µm.

[0018] Controlling the particle size of the positive electrode active material in a suitable range can avoid or reduce the phenomenon of physical gelation of the subsequent slurry due to too small particle size, increasing the difficulty of coating. It can also avoid or reduce the influence of dynamics performance of the positive electrode active material in the charge and discharge process due to too large particle size, reducing the compaction density, and can balance the processability and dynamics performance. Further controlling the median particle size D v 50 of the positive electrode active material to be 1.5 µm ~ 5.0 µm is beneficial to further improve the coulomb efficiency and cycle performance of the battery.

[0019] In any embodiment, the NaHCO3 residual alkali content of the positive electrode active material is 0.05% ~ 2.5%, and can be 0.05% ~ 0.5%, based on the total mass of the positive electrode active material.

[0020] The positive electrode active material with a proper NaHCO3 residual alkali amount can control the production cost of the production process, can avoid or reduce the chemical gel of the subsequent slurry caused by excessive residual alkali amount, and can increase the coating difficulty. The production cost, processing performance and performance of the positive electrode active material can be considered, which is beneficial to reduce the electrode sheet resistance of the positive electrode active material, so that the battery has excellent electrical performance and application prospect. Further controlling the NaHCO3 residual alkali amount of the positive electrode active material to be 0.05% to 0.5% is beneficial to further reduce the electrode sheet resistance of the positive electrode active material, and improve the coulomb efficiency and cycle performance of the battery.

[0021] The second aspect of the present application provides a preparation method of a positive electrode active material, comprising the following steps:

[0022] The raw materials including a sodium source, an R source, a phosphorus source and a carbon source are dissolved in deionized water and uniformly mixed to obtain a mixed slurry. Optionally, the raw materials further include an M source;

[0023] The mixed slurry is dried and calcined to prepare the positive electrode active material. The positive electrode active material is a carbon-complexed polyanion compound, and the positive electrode active material has the following general formula:

[0024] Na 4-x R 3-y M z (PO4)2P2O7 / C

[0025] wherein R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W and Pb, M includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, Si, W and Pb, 0≤x≤0.5, 0≤y≤0.5, 0≤z<x+y, and x and y are not 0 at the same time.

[0026] The preparation method of the positive electrode active material is simple and has low manufacturing cost. The prepared positive electrode active material has Na vacancies or R metal vacancies, R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W and Pb, which is beneficial to reduce the residual alkali amount of the positive electrode active material and the electrode sheet resistance of the positive electrode active material, and improve the coulomb efficiency and cycle efficiency of the battery.

[0027] In any embodiment, 0<y-z≤0.3.

[0028] The positive electrode active material provides R metal vacancies, R including at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W and Pb, which can, on the one hand, distort the chemical bonds between other elements in the positive electrode active material, thereby widening the diffusion channel of Na ions, improving the transmission speed of Na ions in the charging and discharging process, and improving the electrical conductivity of the positive electrode active material, thereby improving the coulomb efficiency and cycle performance of the battery. On the other hand, the R metal vacancies can also change the electron cloud distribution of elements such as P and O, thereby improving the electrical conductivity of the positive electrode active material, thereby improving the coulomb efficiency and cycle performance of the battery.

[0029] In any embodiment, the calcining after drying the mixed slurry comprises the following steps:

[0030] drying the mixed slurry to obtain a precursor powder;

[0031] calcining the precursor powder at a calcining temperature of 400 ℃ to 650 ℃ for a calcining time of 5 h to 15 h to prepare the positive electrode active material.

[0032] Controlling the appropriate calcining temperature and calcining time enables the positive electrode active material to have Na vacancies or R metal vacancies, which is beneficial to reducing the residual alkali content of the positive electrode active material and the electrode sheet resistance of the positive electrode sheet, and improving the coulomb efficiency and cycle efficiency of the battery.

[0033] In any embodiment, the calcining temperature is 500 ℃ to 600 ℃.

[0034] Controlling the calcining temperature to be 500 ℃ to 600 ℃ is beneficial to further reducing the residual alkali content of the positive electrode active material and the electrode sheet resistance of the positive electrode sheet.

[0035] In any embodiment, the calcining time is 8 h to 13 h.

[0036] Controlling the calcining time to be 8 h to 13 h is beneficial to reducing the residual alkali content of the positive electrode active material and the electrode sheet resistance of the positive electrode sheet.

[0037] In any embodiment, the R source includes one or more of a magnesium source, an aluminum source, a scandium source, a titanium source, a vanadium source, a chromium source, a manganese source, an iron source, a cobalt source, a nickel source, a copper source, a zinc source, a zirconium source, a niobium source, a molybdenum source, a tin source, a hafnium source, a tantalum source, a tungsten source and a lead source.

[0038] In any embodiment, the M source includes one or more of a magnesium source, an aluminum source, a scandium source, a titanium source, a vanadium source, a chromium source, a manganese source, an iron source, a cobalt source, a nickel source, a copper source, a zinc source, a zirconium source, a niobium source, a molybdenum source, a tin source, a hafnium source, a tantalum source, a silicon source, a tungsten source and a lead source.

[0039] In any embodiment, the iron source comprises one or more of ferrous oxalate, ferric nitrate, ferrous sulfate, ferrous chloride, ferric oxalate, ferric acetate, iron oxide, ferrous oxide, and metallic iron.

[0040] The third aspect of the present application provides a positive electrode tab, comprising a positive electrode film layer, wherein the positive electrode film layer comprises a binder, at least one of a one-dimensional conductive material and a zero-dimensional conductive material, and the positive electrode active material of the first aspect or the positive electrode active material prepared by the preparation method of the second aspect.

[0041] In any embodiment, the mass content of the binder is 1.5% to 3%, or optionally 2.0% to 2.5%, based on the total mass of the positive electrode film layer.

[0042] Controlling the mass content of the binder within a suitable range can provide sufficient adhesion without causing excessive tab resistance, which is conducive to improving the coulomb efficiency and cycle performance of the battery.

[0043] In any embodiment, the one-dimensional conductive material comprises one or more of single-walled carbon nanotubes and multi-walled carbon nanotubes, and / or

[0044] The mass content of the one-dimensional conductive material is 0.2% to 1%, or optionally 0.5% to 0.9%, based on the total mass of the positive electrode film layer.

[0045] Controlling the mass content of the one-dimensional conductive material within a suitable range is conducive to improving the coulomb efficiency and cycle performance of the battery. Further controlling the mass content of the one-dimensional conductive material to be 0.5% to 0.9% is conducive to further improving the cycle performance.

[0046] In any embodiment, the zero-dimensional conductive material comprises one or more of Super P, Ketjenblack, and acetylene black, and / or

[0047] The mass content of the zero-dimensional conductive material is 1% to 3%, or optionally 2% to 2.8%, based on the total mass of the positive electrode film layer.

[0048] Controlling the mass content of the zero-dimensional conductive material within a suitable range is conducive to improving the coulomb efficiency and cycle performance of the battery. Further controlling the mass content of the zero-dimensional conductive material to be 2% to 2.8% is conducive to further improving the cycle performance.

[0049] The fourth aspect of the present application provides a secondary battery, comprising the positive electrode tab of the third aspect.

[0050] In any embodiment, the secondary battery is a negative electrode-free sodium secondary battery.

[0051] In any embodiment, the secondary battery further comprises a negative electrode tab, the negative electrode tab comprising a negative electrode current collector and a primer layer disposed on at least one surface of the negative electrode current collector, the primer layer comprising one or more of carbon nanotubes, graphite, graphene, silver composite carbon nanoparticles, tin composite carbon nanoparticles.

[0052] The primer layer described above not only has excellent electrical conductivity, but also facilitates uniform deposition of metal ions on the surface of the current collector, improving the coulombic efficiency and cycle performance of the battery.

[0053] In any embodiment, the primer layer has an area density of 5 g / m 2 ~50 g / m 2 .

[0054] The primer layer having an area density of 5 g / m 2 ~50 g / m 2 facilitates uniform distribution of nucleation sites, promotes uniform deposition of metal, and does not affect the transmission behavior of electrons.

[0055] In any embodiment, the primer layer has a thickness of 2 μm~100 μm.

[0056] Controlling the thickness of the primer layer to be 2 μm~100 μm can provide sufficient nucleation sites to facilitate uniform deposition of metal ions and inhibit dendrites.

[0057] A fifth aspect of the present application provides a power consuming device comprising the secondary battery of the fourth aspect of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0058] Figure 1 is a schematic diagram of a secondary battery cell according to an embodiment of the present application;

[0059] Figure 2 is a schematic diagram of a battery module according to an embodiment of the present application; Figure 1

[0060] Figure 3 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0061] Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0062] Figure 5 is a schematic diagram of a battery pack according to an embodiment of the present application; Figure 4

[0063] Figure 6 is a schematic diagram of a power consuming device using the secondary battery as a power source according to an embodiment of the present application.​​

[0064] BRIEF DESCRIPTION OF DRAWINGS

[0065] 1: battery pack; 2: upper case; 3: lower case; 4: battery module; 5: secondary battery cell; 51: case; 52: electrode assembly; 53: cover plate. DETAILED DESCRIPTION

[0066] Hereinafter, embodiments of the positive electrode active material and the method of manufacturing the same, the positive electrode sheet, the secondary battery, and the electric device according to the present application are specifically disclosed while appropriately referring to the accompanying drawings. However, there are cases where unnecessary detailed explanations are omitted. For example, there are cases where detailed explanations of matters well-known, repeated explanations of substantially identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following explanations are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0067] The "ranges" disclosed in the present application are defined in the form of lower and upper limits, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., 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 particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. In addition, if a minimum range value of 1 and 2 is listed, and if a maximum range value of 3, 4, and 5 is listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise stated, a numerical range "a-b" represents a shorthand manner of describing each and every numerical value that is within the range, wherein "a" and "b" are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein, and "0-5" is merely a shorthand manner of describing those numerical combinations. In addition, when it is stated that a parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and the like.

[0068] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0069] If not specifically stated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0070] If not specified otherwise, all steps of the present application can be carried out in sequence or randomly, preferably in sequence. For example, the method comprising steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method can further comprise step (c) means that step (c) can be added to the method in any sequence, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0071] If not specified otherwise, the terms "comprising" and "including" as used in the present application are open-ended and also include closed-ended. For example, the terms "comprising" and "including" can mean that other components not listed can also be included, or only the listed components can be included.

[0072] If not specified otherwise, in the present application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0073] Generally, during the production process of sodium battery cathode materials, residual sodium in the cathode material is easily caused due to preparation process, raw material ratio, etc. In addition, sodium in the bulk phase of the cathode material is also easy to be released, which leads to the generation of residual alkali such as sodium carbonate, sodium hydroxide and sodium bicarbonate in the cathode material, resulting in swelling, poor thermal stability of the cathode material. Not only does it cause low electronic conductivity, low discharge capacity and poor cycle performance of the battery, but also affects the safety of the battery. Therefore, it is necessary to develop a cathode material with low residual alkali content and excellent electrical performance to meet the application needs of the new generation of electrochemical systems.

[0074] [Positive electrode active material]

[0075] Based on this, the present application provides a positive electrode active material, which is a carbon-complexed polyanion compound, and the positive electrode active material has the following general formula:

[0076] Na 4-x R 3-y M z (PO4)2P2O7 / C

[0077] wherein R comprises at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W and Pb, M comprises at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, Si, W and Pb, 0≤x≤0.5, 0≤y≤0.5, 0≤z<x+y, and x and y are not simultaneously 0.

[0078] In some embodiments, x can be selected from 0.001, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or a value in a range between any two of the above values, and y can be selected from 0.001, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or a value in a range between any two of the above values.

[0079] In some embodiments, R comprises Fe, and M comprises Mn. In some embodiments, R comprises Al, and M comprises Mn. In some embodiments, R comprises V, and M comprises Ni. In some embodiments, R comprises Fe, and M comprises Mn, Co and Ni. In some embodiments, R comprises Mn, and M comprises Si.

[0080] The positive active material can provide Na vacancies or R metal vacancies, R comprising at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W and Pb. On one hand, the presence of Na vacancies or R metal vacancies changes the chemical bond distortion between other elements in the positive active material, widens the diffusion channel of Na ions, effectively promotes the migration of Na ions, and inhibits or reduces the formation of residual alkali in the positive active material, and reduces the sheet resistance of the positive electrode sheet. On the other hand, the optimized Na ion diffusion channel can also improve the electrical conductivity of the positive active material. In addition, metal doping comprising at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, Si, W and Pb can affect the change of the structure of the positive active material, expand the interplanar spacing, accelerate the migration of Na ions, further improve the coulomb efficiency and cycle performance of the battery, and improve the performance of the battery.

[0081] In some embodiments, 0

[0082] In some embodiments, x can be selected from 0.001, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or a value in a range defined by any two of the above.

[0083] In some embodiments, wherein 0 < x < 0.5, 0 < y < 0.5, 0 < z < x + y.

[0084] In some embodiments, wherein 0 < x < 0.3, 0 < y < 0.5, 0 < z < x + y.

[0085] In some embodiments, wherein 0.01 < x < 0.2, 0 < y < 0.3, 0 < z < x + y.

[0086] In some embodiments, wherein 0.01 < x < 0.2, 0 < y < 0.5, 0 < z < x + y.

[0087] In some embodiments, wherein 0.2 < x < 0.5, 0.2 < y < 0.5, 0 < z < x + y.

[0088] The Na vacancies provided by the positive electrode active material can effectively promote the migration of Na ions and inhibit or reduce the formation of residual alkali of the positive electrode active material. On the one hand, the presence of Na vacancies can increase the valence of other metals in the positive electrode active material, enhance the oxidation resistance of the positive electrode active material, and thus inhibit or reduce the reaction of the positive electrode active material with water, reduce the amount of residual alkali of the positive electrode active material, and reduce the tab resistance of the positive electrode tab. On the other hand, the optimized Na ion migration path can improve the kinetic performance of the positive electrode active material, improve the coulombic efficiency and cycle performance of the battery, and improve the electrical performance of the battery. Further controlling 0.01 < x < 0.2 is conducive to further reducing the amount of residual alkali of the positive electrode active material and the tab resistance of the positive electrode tab.

[0089] In some embodiments, wherein 0 < y - z < 0.3.

[0090] In some embodiments, y can be selected from 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.3, or a value in a range defined by any two of the above, z can be selected from 0, 0.02, 0.05, 0.07, 0.1, 0.12, 0.15, 0.17, 0.2, or a value in a range defined by any two of the above, and z < y.

[0091] In some embodiments, wherein 0 < x < 0.5, 0 < y - z < 0.3.

[0092] In some embodiments, wherein 0 < x < 0.2, 0 < y - z < 0.3.

[0093] The positive electrode active material provides R metal vacancies, R including at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W and Pb, which, on one hand, can distort the chemical bonds between other elements in the positive electrode active material, thereby widening the diffusion channel of Na ions, improving the transmission speed of Na ions in the charging and discharging process, and improving the electrical conductivity of the positive electrode active material, thereby improving the coulomb efficiency and cycle performance of the battery thereof. On the other hand, the R metal vacancies can also change the electron cloud distribution of elements such as P and O, thereby improving the electrical conductivity of the positive electrode active material, thereby improving the coulomb efficiency and cycle performance of the battery thereof.

[0094] In some embodiments, 0 < x ≤ 0.5 and 0 < z ≤ y ≤ 0.5.

[0095] In some embodiments, x can be selected as 0.001, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or a value in the range constituted by any two of the above, y can be selected as 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or a value in the range constituted by any two of the above, z can be selected as 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or a value in the range constituted by any two of the above, and z < y.

[0096] In some embodiments, 0 < x ≤ 0.5, 0 < z, and z = y.

[0097] In some embodiments, 0 < x ≤ 0.5 and 0 < z < y.

[0098] On the basis of providing Na vacancies, the positive electrode active material further dopes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, Si, W and Pb in the positive electrode active material, and the doping metal occupies the R metal vacancies, which can affect the change of the structure of the positive electrode active material, enlarge the interplanar spacing, accelerate the migration of Na ions, and further improve the electrical conductivity of the positive electrode active material, thereby improving the coulomb efficiency and cycle performance of the battery thereof.

[0099] In some embodiments, R includes one or more of Fe, Co, Ni and Mn; and M includes one or more of Mg, Al, Sc, Ti, V, Cr, Mn and Co.

[0100] In some embodiments, R includes Fe and M includes Mn. In some embodiments, R includes Fe and M includes Ni. In some embodiments, R includes Fe and M includes both Mn and Ni. In some embodiments, R includes V and M includes Si. In some embodiments, R includes Mn and M includes Si.

[0101] All of the above-mentioned metal materials can achieve a low residual alkali content in the positive electrode active material, a low electrode resistance in the positive electrode sheet, and excellent coulombic efficiency and cycle performance in the battery.

[0102] In some embodiments, the median particle size D of the positive electrode active material v 50 is 1.0 µm≤D v 50 ≤10 µm, can be selected from 1.5 µm to 5.0 µm.

[0103] In some embodiments, the median particle size D of the positive electrode active material v 50 can be selected as 1.0 µm, 1.5 µm, 2.0 µm, 2.5 µm, 3.0 µm, 3.5 µm, 4.0 µm, 4.5 µm, 5.0 µm, 5.5 µm, 6.0 µm, 6.5 µm, 7.0 µm, 7.5 µm, 8.0 µm, 8.5 µm, 9.0 µm, 9.5 µm, 10 µm, or a value within the range formed by any two of the above points.

[0104] Median particle size D of positive electrode active material v 50. Testing can be performed using any method known in the art. As an example, referring to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method, weigh 0.1 g to 0.13 g of the positive electrode active material sample to be tested into a 50 mL beaker, add 5 g of anhydrous ethanol, place a stir bar of approximately 2.5 mm in the beaker, and seal with plastic wrap. After sonicating the sample for 5 min, transfer it to a magnetic stirrer and stir at 500 rpm for at least 20 min. Two samples are taken from each batch for testing. Testing is performed using a Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK.

[0105] Controlling the particle size of the positive electrode active material within a suitable range can avoid or reduce the phenomenon of physical gelation of the slurry caused by excessively small particle size, which increases the difficulty of coating. It can also avoid or reduce the impact on the kinetic performance of the positive electrode active material during charge and discharge due to excessively large particle size, thus balancing processability and kinetic performance. Further control of the median particle size D of the positive electrode active material is also crucial. v50 is 1.5 µm~5.0 µm, which is conducive to further improving the coulomb efficiency and cycle performance of the battery.

[0106] In some embodiments, the NaHCO3 residual base content of the positive electrode active material is 0.05%~2.5%, and can be optionally 0.05%~0.5%, based on the total mass of the positive electrode active material.

[0107] In some embodiments, the NaHCO3 residual base content of the positive electrode active material can be 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, or a value in a range formed by any two of the above, based on the total mass of the positive electrode active material.

[0108] The NaHCO3 residual base content of the positive electrode active material can be tested by any means known in the art. As an example, acid-base titration is used to test the residual base content, hydrochloric acid standard solution is used to titrate sodium bicarbonate and sodium ions in the positive electrode material, a pH electrode is used as an indicator electrode, and the end point is determined by a sudden change in potential. According to the titration end point, the titration volume of the titration standard solution is determined. The mass of NaHCO3 obtained by calculation is divided by the mass of the positive electrode active material to obtain the mass content as the NaHCO3 residual base content of the positive electrode active material.

[0109] In some embodiments, the residual base of the positive electrode active material also includes NaOH, Na2CO3, and other alkaline substances. The content of other alkaline substances has the same trend as the NaHCO3 residual base content, i.e., the NaHCO3 residual base content of the positive electrode active material can be used to characterize the content of alkaline substances. Therefore, the NaHCO3 residual base content can be used to characterize the ability of the positive electrode active material to produce residual base.

[0110] The positive electrode active material with a suitable NaHCO3 residual base content can control the production cost of the production process, and can also avoid or reduce the excessive residual base content leading to subsequent slurry chemical gel, increase the difficulty of coating, and can balance the production cost, processing performance, and performance of the positive electrode active material, which is conducive to reducing the electrode resistance of the positive electrode sheet, and improving the coulomb efficiency and cycle performance of the battery. Further controlling the NaHCO3 residual base content of the positive electrode active material to be 0.05%~0.5% is conducive to further reducing the electrode resistance of the positive electrode sheet and improving the coulomb efficiency and cycle performance of the battery.

[0111] The present application also provides a preparation method of the positive electrode active material, comprising the following steps:

[0112] The raw materials including a sodium source, an R source, a phosphorus source, and a carbon source are dissolved in deionized water, mixed uniformly to obtain a mixed slurry, and optionally, the raw materials further include an M source;

[0113] The mixed slurry is dried and calcined to prepare a positive electrode active material, the positive electrode active material is a carbon-complexed polyanion compound, and the positive electrode active material has the following general formula:

[0114] Na 4-x R 3-y M z (PO4)2P2O7 / C

[0115] wherein R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W, and Pb, M includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, Si, W, and Pb, 0≤x≤0.5, 0≤y≤0.5, 0≤z<x+y, and x and y are not simultaneously 0.

[0116] In some embodiments, x can be selected as 0.001, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or a value in a range constituted by any two of the above, and y can be selected as 0.001, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or a value in a range constituted by any two of the above.

[0117] The preparation method of the positive electrode active material is simple, and the production cost is low. The prepared positive electrode active material has Na vacancies or R metal vacancies, R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W, and Pb, which is beneficial to reduce the residual alkali content of the positive electrode active material and the electrode sheet resistance of the positive electrode sheet, and improve the coulomb efficiency and cycle efficiency of the battery.

[0118] In some embodiments, 0<y-z≤0.3.

[0119] In some embodiments, y can be selected as 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.3, or a value in a range constituted by any two of the above, z can be selected as 0, 0.02, 0.05, 0.07, 0.1, 0.12, 0.15, 0.17, 0.2, or a value in a range constituted by any two of the above, and z<y.

[0120] The positive electrode active material provides R metal vacancies, R including at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W and Pb, which on the one hand can distort the chemical bonds between other elements in the positive electrode active material, thereby widening the diffusion channel of Na ions, improving the transmission speed of Na ions in the charging and discharging process, and improving the electrical conductivity of the positive electrode active material, thereby improving the coulomb efficiency and cycle performance of the battery. On the other hand, the R metal vacancies can also change the electron cloud distribution of elements such as P and O, thereby improving the electrical conductivity of the positive electrode active material, thereby improving the coulomb efficiency and cycle performance of the battery.

[0121] In some embodiments, calcining the dried mixed slurry comprises the following steps:

[0122] drying the mixed slurry to obtain a precursor powder;

[0123] calcining the precursor powder at a calcining temperature of 400-650°C for a calcining time of 5-15 h to prepare the positive electrode active material.

[0124] In some embodiments, the calcining temperature can be selected from 400°C, 420°C, 450°C, 480°C, 500°C, 530°C, 550°C, 570°C, 600°C, 650°C, or a value in a range defined by any two of the above.

[0125] In some embodiments, the calcining time can be selected from 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, or a value in a range defined by any two of the above.

[0126] Controlling the appropriate calcining temperature and calcining time can make the positive electrode active material have Na vacancies or R metal vacancies, which is beneficial to reducing the residual alkali content of the positive electrode active material and the electrode sheet resistance of the positive electrode sheet, and improving the coulomb efficiency and cycle efficiency of the battery.

[0127] In some embodiments, the calcining temperature is 500-600°C.

[0128] In some embodiments, the calcining temperature can be selected from 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C, 600°C, or a value in a range defined by any two of the above.

[0129] The calcination temperature is controlled to be 500-600 ℃, which is beneficial to further reduce the residual alkali content of the positive electrode active material and the electrode sheet resistance of the positive electrode sheet.

[0130] In some embodiments, the calcination time is 8-13 h.

[0131] In some embodiments, the calcination time can be selected to be 8 h, 9 h, 9.5 h, 10 h, 10.5 h, 11 h, 12 h, 12.5 h, 13 h, or a value in the range formed by any two of the above.

[0132] The calcination time is controlled to be 8-13 h, which is beneficial to reduce the residual alkali content of the positive electrode active material and the electrode sheet resistance of the positive electrode sheet.

[0133] In some embodiments, the R source includes one or more of a magnesium source, an aluminum source, a scandium source, a titanium source, a vanadium source, a chromium source, a manganese source, an iron source, a cobalt source, a nickel source, a copper source, a zinc source, a zirconium source, a niobium source, a molybdenum source, a tin source, a hafnium source, a tantalum source, a tungsten source, and a lead source.

[0134] In some embodiments, the M source includes one or more of a magnesium source, an aluminum source, a scandium source, a titanium source, a vanadium source, a chromium source, a manganese source, an iron source, a cobalt source, a nickel source, a copper source, a zinc source, a zirconium source, a niobium source, a molybdenum source, a tin source, a hafnium source, a tantalum source, a silicon source, a tungsten source, and a lead source.

[0135] In some embodiments, the iron source includes one or more of ferrous oxalate, ferric nitrate, ferrous sulfate, ferrous chloride, ferric oxalate, ferric acetate, iron oxide, ferrous oxide, and metallic iron.

[0136] [Positive electrode sheet]

[0137] The application also provides a positive electrode sheet, which includes a positive electrode film layer, the positive electrode film layer containing a binder, at least one of a one-dimensional conductive material and a zero-dimensional conductive material, and the positive electrode active material of some embodiments or the positive electrode active material prepared by the preparation method of some embodiments.

[0138] In some embodiments, the positive electrode film layer includes a one-dimensional conductive material. In some embodiments, the positive electrode film layer includes a zero-dimensional conductive material.

[0139] In some embodiments, the positive electrode film layer contains both a one-dimensional conductive material and a zero-dimensional conductive material. The addition of both forms of conductive materials is beneficial to further increase the conductivity of the positive electrode sheet.

[0140] In some embodiments, the mass content of the binder is 1.5%-3%, which can be selected to be 2.0%-2.5%, based on the total mass of the positive electrode film layer.

[0141] In some embodiments, the mass content of the binder can be selected to be 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, or a value within a range defined by any two of the foregoing, based on the total mass of the positive electrode film layer.

[0142] Controlling the mass content of the binder within a suitable range is conducive to improving the coulombic efficiency and cycle performance of the battery. Further controlling the mass content of the binder to be 2.0% to 2.5% is conducive to reducing the electrode sheet resistance of the positive electrode sheet.

[0143] In some embodiments, the one-dimensional conductive material includes one or more of single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0144] In some embodiments, the one-dimensional conductive material includes one or more of single-walled carbon nanotubes and multi-walled carbon nanotubes, and the mass content of the one-dimensional conductive material is 0.2% to 1%, which can be selected to be 0.5% to 0.9%, based on the total mass of the positive electrode film layer.

[0145] In some embodiments, the one-dimensional conductive material includes single-walled carbon nanotubes. In some embodiments, the one-dimensional conductive material includes multi-walled carbon nanotubes. In some embodiments, the one-dimensional conductive material includes single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0146] In some embodiments, the mass content of the one-dimensional conductive material can be selected to be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or a value within a range defined by any two of the foregoing, based on the total mass of the positive electrode film layer.

[0147] Controlling the mass content of the one-dimensional conductive material within a suitable range is conducive to improving the coulombic efficiency and cycle performance of the battery. Further controlling the mass content of the one-dimensional conductive material to be 0.5% to 0.9% is conducive to further improving the cycle performance.

[0148] In some embodiments, the zero-dimensional conductive material includes one or more of Super P, Ketjen black, and acetylene black.

[0149] In some embodiments, the zero-dimensional conductive material includes one or more of Super P, Ketjen black, and acetylene black, and the mass content of the zero-dimensional conductive material is 1% to 3%, which can be selected to be 2% to 2.8%, based on the total mass of the positive electrode film layer.

[0150] In some embodiments, the zero-dimensional conductive material includes Super P. In some embodiments, the zero-dimensional conductive material includes Ketjen black. In some embodiments, the zero-dimensional conductive material includes Super P and Ketjen black.

[0151] In some embodiments, the mass content of the zero-dimensional conductive material can be selected to be 1%, 1.2%, 1.5%, 1.7%, 2%, 2.2%, 2.5%, 2.7%, 3%, or a value in a range constituted by any two of the above, based on the total mass of the positive electrode film layer.

[0152] Controlling the mass content of the zero-dimensional conductive material in a suitable range is beneficial to improve the coulombic efficiency and cycle performance of the battery. Further controlling the mass content of the zero-dimensional conductive material to be 2% to 2.8% is beneficial to further improve the cycle performance.

[0153] The positive electrode tab also includes a positive electrode current collector.

[0154] The positive electrode current collector can adopt a conductive carbon sheet, a metal foil, a carbon-coated metal foil, a porous metal plate, or a composite current collector. The conductive carbon material of the conductive carbon sheet can be selected from one or more of Super P, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite, graphene, and carbon nanofibers. The metal material of the metal foil, the carbon-coated metal foil, and the porous metal plate is independently selected from at least one of copper, aluminum, nickel, and stainless steel. The composite current collector can be a composite current collector formed by combining a metal foil and a polymer-based film.

[0155] In some embodiments, the positive electrode tab can be prepared by dispersing the above-mentioned components for preparing the positive electrode tab, such as the positive electrode active material, the conductive material, the binder, and any other components, in a solvent (such as N-methyl pyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode tab can be obtained.

[0156] [Negative electrode tab]

[0157] The negative electrode tab can only include a negative electrode current collector without containing a negative electrode active material. The negative electrode tab can also pre-deposit a metal phase on the negative electrode current collector.

[0158] In some embodiments, the negative current collector can employ a metal foil or a composite current collector. For example, as a metal foil, an aluminum foil or a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base layer (such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0159] In some embodiments, the negative electrode tab includes a negative current collector and a primer layer disposed on at least one surface of the negative current collector, the primer layer including one or more of carbon nanotubes, graphite, graphene, silver composite carbon nanoparticles, and tin composite carbon nanoparticles.

[0160] The primer layer described above not only has excellent electrical conductivity, but also facilitates uniform deposition of metal ions on the surface of the current collector, thereby improving the coulombic efficiency and cycle performance of the battery.

[0161] In some embodiments, the areal density of the primer layer is 5 g / m 2 ~50 g / m 2 .

[0162] In some embodiments, the areal density of the primer layer can be selected as 5 g / m 2 , 10 g / m 2 , 15 g / m 2 , 20 g / m 2 , 25 g / m 2 , 30 g / m 2 , 35 g / m 2 , 40 g / m 2 , 45 g / m 2 , 50 g / m 2 , or a value in a range defined by any two of the above.

[0163] The primer layer with an areal density of 5 g / m 2 ~50 g / m 2 facilitates uniform distribution of nucleation sites and promotes uniform deposition of metal, while not affecting the transmission behavior of electrons.

[0164] In some embodiments, the thickness of the primer layer is 2 μm~100 μm.

[0165] In some embodiments, the thickness of the primer layer can be selected from 2 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, or a range defined by any two of the above values.

[0166] Controlling the thickness of the primer layer to be 2 μm to 100 μm can provide sufficient nucleation sites to facilitate uniform deposition of metal ions and inhibit dendrites.

[0167] [Separator]

[0168] In some embodiments, the secondary battery further comprises a separator. The type of the separator is not particularly limited in the present application, and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0169] In some embodiments, the material of the separator can be selected from at least one of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fiber. The separator can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited.

[0170] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be used to make an electrode assembly by a winding process or a stacking process.

[0171] In some embodiments, the secondary battery can comprise an outer package. The outer package can be used to package the above-mentioned electrode assembly and electrolyte.

[0172] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate, etc. can be listed.

[0173] [Secondary battery]

[0174] The secondary battery can comprise various forms, including, by way of example, but not limited to, a battery cell, a battery module, and a battery pack.

[0175] The battery cell comprises the positive electrode sheet in some embodiments, which comprises the positive active material in some embodiments or the positive active material prepared by the preparation method in some embodiments.

[0176] The shape of the battery cell is not particularly limited, and can be cylindrical, square, or any other shape. For example, Figure 1 is a square structure as an example of a secondary battery cell 5, Figure 2 is an exploded view of the secondary battery cell 5.

[0177] In some embodiments, the secondary battery cell further includes a negative electrode tab, a separator, and an electrolyte.

[0178] In some embodiments, the secondary battery cell is a negative electrode-free sodium secondary battery.

[0179] In a negative electrode-free sodium secondary battery, no negative active material is pre-deposited, and only a negative current collector is included. During the first charge, sodium ions receive electrons on the cathode side to deposit metal sodium on the surface of the current collector to form a sodium metal phase. During discharge, the metal sodium can be converted into sodium ions to return to the positive electrode, realizing cyclic charging and discharging. Compared to other sodium secondary batteries, the negative electrode-free sodium secondary battery can achieve higher energy density because it is not limited by the negative electrode material. Moreover, while maintaining high electrochemical performance of the battery, the production cycle of the battery can be shortened, the manufacturing cost of the battery can be reduced, and the production efficiency can be greatly improved.

[0180] In some embodiments, the CB value of the negative electrode-free sodium secondary battery is less than or equal to 0.1.

[0181] The CB value is the capacity per unit area of the negative electrode tab divided by the capacity per unit area of the positive electrode tab in a secondary battery. Since the negative electrode-free battery does not include negative active material, the capacity per unit area of the negative electrode tab is small, and the CB value of the secondary battery is less than or equal to 0.1.

[0182] In some embodiments, with reference to Figure 2 The outer package can include a housing 51 and a cover plate 53. The housing 51 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be provided on the opening to close the receiving cavity. The positive electrode tab, the negative electrode tab, and the separator can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The number of electrode assemblies 52 contained in the secondary battery cell 5 can be one or more, and a person skilled in the art can select according to the specific actual needs.

[0183] [Battery module]

[0184] In some embodiments, the battery cells can be assembled into a battery module, and the number of battery cells contained in the battery module can be one or more, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery module.

[0185] Figure 3is a battery module 4 as an example. Refer to Figure 3 In the battery module 4, the plurality of secondary battery cells 5 can be arranged in series along the length direction of the battery module 4. Of course, the arrangement can be in any other manner. Further, the plurality of secondary battery cells 5 can be fixed by fasteners.

[0186] Optionally, the battery module 4 can further include a housing having an accommodation space, and the plurality of secondary battery cells 5 are accommodated in the accommodation space.

[0187] [Battery pack]

[0188] In some embodiments, the above-described battery module can be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0189] Figure 4 and Figure 5 is a battery pack 1 as an example. Refer to Figure 4 and Figure 5 In the battery pack 1, a battery box and a plurality of battery modules 4 arranged in the battery box can be included. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be arranged on the lower box body 3 to form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0190] [Power consuming device]

[0191] In one embodiment of the present application, a power consuming device is provided, which includes at least one of the secondary battery of any embodiment, the battery module of any embodiment, or the battery pack of any embodiment.

[0192] The power consuming device includes at least one of the secondary battery, the battery module, or the battery pack provided by the present application. The secondary battery, the battery module, or the battery pack can be used as a power source of the power consuming device, or can be used as an energy storage unit of the power consuming device. The power consuming device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0193] As the power consuming device, the secondary battery, the battery module, or the battery pack can be selected according to the use requirement thereof.

[0194] Figure 6The electric device is, for example, an electric vehicle. The electric device is, for example, a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the demand for high power and high energy density of the secondary battery for the electric device, a battery pack or a battery module can be used.

[0195] The device is, for example, a mobile phone, a tablet computer, a notebook computer, or the like. The device is generally required to be thin and light, and a secondary battery can be used as a power source.

[0196] Embodiments

[0197] Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are for the purpose of explanation of the present application and should not be understood as a limitation of the present application. In the embodiments, unless a specific technique or condition is specified, the technique or condition described in the literature in the art or according to the product manual is used. Unless the manufacturer of the reagent or instrument is specified, it is a conventional product that can be obtained on the market.

[0198] I. Preparation method

[0199] Embodiment 1

[0200] 1) Preparation of positive electrode active material

[0201] Sodium pyrophosphate, ferrous oxalate, and ammonium dihydrogen phosphate were dissolved in deionized water at a molar ratio of 1:2.8:2, and continuously stirred at room temperature for 30 min to obtain a mixed slurry. The mixed slurry was sand-milled to an average particle size of 0.2 μm, and then mixed with a glucose aqueous solution for 30 min to obtain a final slurry. The slurry was spray-dried at an inlet temperature of 220°C and an outlet temperature of 109°C to obtain a powdery precursor. Finally, the precursor was heated to 320°C at a heating rate of 2°C, and held for 4 h, and then heated to 550°C at a heating rate of 2°C, and held for 10 h, under a N2 atmosphere. The sintered product was crushed and sieved to obtain a Na4Fe 2.8 (PO4)2P2O7 / C positive electrode active material. The carbon content was 2% based on the total mass of the positive electrode active material, the median particle size D50 of the positive electrode active material was 3.0 μm, and the residual alkali content of the positive electrode active material was 0.52%. v

[0202] 2) Preparation of positive electrode sheet

[0203] 2.5 wt% of polyvinylidene fluoride binder was sufficiently dissolved in N ​In methylpyrrolidone (NMP), 2.0 wt% Super P, 1.0 wt% single-walled carbon nanotubes, and 94.5 wt% of the above-mentioned positive electrode active material are added and mixed evenly to obtain a positive electrode slurry. The slurry is uniformly coated on the surface of the current collector aluminum foil and then transferred to a vacuum drying oven for complete drying. The dried electrode sheet is then rolled and punched to obtain the positive electrode sheet. The compaction density of the positive electrode film layer is 1.9 g / cm³. 3 The electrode resistance is 0.6 Ω·cm.

[0204] 3) Preparation of negative electrode sheet

[0205] Single-walled carbon nanotubes and carboxymethyl cellulose (CMC) were added to deionized water at a mass ratio of 1:0.4 and stirred to form a homogeneous slurry. This slurry was then coated onto the surface of a copper foil current collector for the negative electrode. After complete drying in a vacuum drying oven, the coating was punched to obtain a negative electrode sheet without a negative electrode structure. The thickness of the undercoating layer was 20 μm, and the areal density was 25 g / m³. 2 .

[0206] 4) Electrolyte

[0207] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), sodium hexafluorophosphate (NaPF6) was dissolved in the organic solvent dimethyl ethylene glycol (DME) and stirred until homogeneous to obtain an electrolyte with a sodium salt concentration of 1.5 mol / L.

[0208] 5) Separating membrane

[0209] Polypropylene film is used as the separator.

[0210] 6) Battery manufacturing

[0211] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The resulting bare cell is then wound, tabs are welded onto it, and the cell is placed in an aluminum casing. It is then baked at 80°C to remove moisture, followed by the injection of electrolyte and sealing to obtain a non-charged battery. This non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain the sodium-free secondary battery product of Example 1.

[0212] Examples 2-6

[0213] The batteries in Examples 2-6 are prepared in a similar manner to the battery in Example 1, but the y-value of Fe or the x-value of Na in the positive electrode active material are adjusted. The specific parameters are shown in Table 1.

[0214] Example 7

[0215] 1) Preparation of positive electrode active materials

[0216] Sodium pyrophosphate, ferrous oxalate, ammonium dihydrogen phosphate, manganese oxide were dissolved in deionized water according to a molar ratio of 0.98:2.8:2:0.1, and stirred continuously for 30 min at room temperature to obtain a mixed slurry. The mixed slurry was sand-milled to an average particle size of 0.2 µm, and then mixed with an aqueous glucose solution for 30 min to obtain a final slurry. The above slurry was spray-dried at an inlet temperature of 220 ℃ and an outlet temperature of 109 ℃ to obtain a powdered precursor. Finally, the precursor was heated to 320 ℃ at a heating rate of 2 ℃ and held for 4 h, and then heated to 550 ℃ at a heating rate of 2 ℃ and held for 10 h under a N2 atmosphere. The sintered product was crushed and sieved to obtain Na 3.95 Fe 2.8 Mn 0.1 (PO4)2P2O7 / C positive electrode active material. The carbon content is 2% based on the total mass of the positive electrode active material, the median particle size D v 50 of the positive electrode active material is 3.0 µm, and the residual alkali content of the positive electrode active material is 0.2%.

[0217] 2) Preparation of positive electrode sheet

[0218] 2.5 wt% polyvinylidene fluoride binder was fully dissolved in N methylpyrrolidone (NMP), and then 2.0 wt% Super P, 1.0 wt% single-walled carbon nanotubes, and 94.5 wt% of the above positive electrode active material were stirred and mixed uniformly to obtain a positive electrode slurry. The slurry was uniformly coated on the surface of the current collector aluminum foil, and then transferred to a vacuum drying oven for complete drying. The dried sheet was rolled and punched to obtain a positive electrode sheet. The compaction density of the positive electrode film layer was 1.9 g / cm 3 , and the sheet resistance was 0.3 Ω·cm.

[0219] 3) Preparation of negative electrode sheet

[0220] Single-walled carbon nanotubes and carboxymethyl cellulose (CMC) were added to deionized water in a mass ratio of 1:0.4 and stirred to form a uniform slurry. The slurry was coated on the surface of the negative electrode current collector copper foil, and then transferred to a vacuum drying oven for complete drying, and then punched to obtain a negative electrode sheet without negative electrode structure. The thickness of the primer layer was 20 µm, and the area density was 25 g / m 2 .

[0221] 4) Electrolyte

[0222] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), sodium salt sodium hexafluorophosphate NaPF6 was dissolved in an organic solvent ethylene glycol dimethyl ether (DME) and stirred uniformly to obtain an electrolyte with a sodium salt concentration of 1.5 mol / L.

[0223] 5) separator film

[0224] The polypropylene film is used as the separator film.

[0225] 6) preparation of the battery

[0226] The positive electrode sheet, the separator film, and the negative electrode sheet are stacked in order, with the separator film between the positive electrode sheet and the negative electrode sheet to play a separating role, and then the bare battery cell is obtained by winding. The bare battery cell is welded with the tab, and is loaded into the aluminum shell. The bare battery cell is baked at 80°C to remove water, and then the electrolyte is injected and sealed to obtain the uncharged battery. The uncharged battery is sequentially subjected to the processes of standing, hot and cold pressing, formation, shaping, capacity testing, and the like, to obtain the negative electrode-free sodium secondary battery product of Example 7.

[0227] Examples 8-10

[0228] The battery of Examples 8-10 is prepared in a similar manner to the battery of Example 1, but the x value of Na, the y value of Fe, or the z value of Mn in the positive electrode active material is adjusted, and the specific parameters are shown in Table 1.

[0229] Example 11

[0230] The battery of Example 11 is prepared in a similar manner to the battery of Example 1, but the Fe in the positive electrode active material of Example 8 is adjusted to Mn, and the specific parameters are shown in Table 1.

[0231] Example 12

[0232] The battery of Example 12 is prepared in a similar manner to the battery of Example 8, but the Fe in the positive electrode active material of Example 8 is adjusted to Mn, and the Mn in the positive electrode active material of Example 8 is adjusted to Co, and the specific parameters are shown in Table 1.

[0233] Comparative Example 1

[0234] The battery of Comparative Example 1 is prepared in a similar manner to the battery of Example 1, but the preparation method of the positive electrode active material is adjusted, and the preparation method is as follows:

[0235] 1) preparation of the positive electrode active material

[0236] Sodium pyrophosphate, ferrous oxalate, and ammonium dihydrogen phosphate were dissolved in deionized water at a molar ratio of 1:3:2 and stirred continuously at room temperature for 30 min to obtain a mixed slurry. This mixed slurry was milled to an average particle size of 0.2 µm, and then a glucose aqueous solution was added and milled for 10 min to obtain the final slurry. The slurry was spray-dried at an inlet air temperature of 220 °C and an outlet air temperature of 109 °C to obtain a powdered precursor. Finally, under a N2 atmosphere, the temperature was increased to 320 °C at a heating rate of 2 °C and held for 4 h, then increased to 550 °C at a heating rate of 2 °C and held for 10 h. The sintered product was crushed and sieved to obtain Na4Fe3(PO4)2P2O. 7 / C Positive electrode active material. Based on the total mass of the positive electrode active material, the carbon content is 2%, and the median particle size D of the positive electrode active material is... v The thickness of 50 is 3.0 μm, and the residual alkali content of the positive electrode active material is 0.6%.

[0237] 2) Preparation of positive electrode sheet

[0238] Dissolve 2.5 wt% polyvinylidene fluoride adhesive thoroughly in N In methylpyrrolidone (NMP), 2.0 wt% Super P, 1.0 wt% single-walled carbon nanotubes, and 94.5 wt% of the above-mentioned positive electrode active material are added and mixed evenly to obtain a positive electrode slurry. The slurry is uniformly coated on the surface of the current collector aluminum foil and then transferred to a vacuum drying oven for complete drying. The dried electrode sheet is then rolled and punched to obtain the positive electrode sheet. The compaction density of the positive electrode film layer is 1.9 g / cm³. 3 The electrode resistance is 0.7 Ω·cm.

[0239] 3) Preparation of negative electrode sheet

[0240] Single-walled carbon nanotubes and carboxymethyl cellulose (CMC) were added to deionized water at a mass ratio of 1:0.4 and stirred to form a homogeneous slurry. This slurry was then coated onto the surface of a copper foil current collector for the negative electrode. After complete drying in a vacuum drying oven, the coating was punched to obtain a negative electrode sheet without a negative electrode structure. The thickness of the undercoating layer was 20 μm, and the areal density was 25 g / m³. 2 .

[0241] 4) Electrolyte

[0242] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), sodium hexafluorophosphate (NaPF6) was dissolved in the organic solvent dimethyl ethylene glycol (DME) and stirred until homogeneous to obtain an electrolyte with a sodium salt concentration of 1.5 mol / L.

[0243] 5) Separating membrane

[0244] A polypropylene film is used as the separator film.

[0245] 6) Preparation of the battery

[0246] The positive electrode sheet, the separator film, and the negative electrode sheet are stacked in order, with the separator film between the positive and negative electrode sheets to serve as a separator, and then wound to obtain a bare battery cell. The bare battery cell is welded with tabs, and is then placed in an aluminum shell and baked at 80°C to remove water. Then, the battery cell is injected with electrolyte and sealed to obtain a non-charged battery cell. The non-charged battery cell is then subjected to the processes of standing, hot and cold pressing, formation, shaping, and capacity testing, to obtain the negative electrode-free sodium secondary battery product of Comparative Example 1.

[0247] Comparative Example 2

[0248] The battery of Comparative Example 2 is prepared in a similar manner to the battery of Comparative Example 1, but the positive active material does not contain carbon. The specific parameters are shown in Table 1.

[0249] Comparative Examples 3-4

[0250] The batteries of Comparative Examples 3-4 are prepared in a similar manner to the battery of Comparative Example 1, but the positive active material contains different amounts of Mn element and the content of Fe element is adjusted. The specific parameters are shown in Table 1.

[0251] Comparative Example 5

[0252] The battery of Comparative Example 5 is prepared in a similar manner to the battery of Comparative Example 1, but the Fe element in the positive active material is replaced by the Mn element. The specific parameters are shown in Table 1.

[0253] II. Performance testing

[0254] 1. Positive active material testing

[0255] 1) Median particle size Dv50 testing

[0256] Referring to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method, 0.1 g to 0.13 g of the sample of the positive active material to be tested is weighed in a 50 mL beaker, 5 g of anhydrous ethanol is added, a stirring bar of about 2.5 mm is added, and then the beaker is sealed with plastic wrap. After the sample is ultrasonically treated for 5 min, it is transferred to a magnetic stirrer and stirred at 500 rpm for 20 min or more. Two samples are taken from each batch of product for testing. The testing is performed using a Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK.

[0257] 2) Residual alkali content testing

[0258] Test principle (acid-base titration method):

[0259] The NaHCO3 and Na2CO3 in the positive active material are titrated with a hydrochloric acid standard solution + The end point is determined by the jump of potential change with the pH electrode as the indicating electrode. The standard GB / T 9725-2007 can be referred to. Specifically, taking the test of NaHCO3 as an example, the Swiss Metrohm 905 Titrando potential titrator can be used, the positive active material is dissolved in deionized water, the positive active material aqueous solution is titrated with a standard titration solution, 0.1 ml of the standard titration solution is added each time, the potential or pH value is recorded, and when the potential or pH value changes little, the titration is stopped. The volume of the added standard titration solution and the measured potential or pH value are recorded, and the titration end point is determined by the graphic method or the second derivative method, and the titration volume of the standard solution is determined. The mass of the obtained NaHCO3 is divided by the mass of the positive active material to obtain the mass content as the NaHCO3 residual alkali content of the positive active material.

[0260] 2. Performance test of positive electrode sheet

[0261] 1) Compaction density

[0262] According to the embodiments of the present application, the compaction density PD of the positive electrode film layer is determined by measuring the one-side positive electrode film layer mass per unit area (g / cm 2 ) and the one-side positive electrode film layer thickness (cm) (the number of collected points > 14). Specifically, the compaction density PD of the positive electrode sheet = the one-side positive electrode film layer mass per unit area (g / cm 2 ) / the positive electrode film layer thickness (cm).

[0263] 2) Sheet resistance

[0264] The dried positive electrode film layer is cut at the left, middle and right of the positive electrode sheet into small round pieces with a diameter of 3 mm. The power of the JMT sheet resistance meter is turned on, and the sheet resistance meter is placed at the appropriate position of the "probe". Click the "start" button, and then read the value when the value is stable. Two positions of each small round piece are tested, and the average value of six measurements is calculated as the sheet resistance of the positive electrode sheet.

[0265] 3. Performance test of battery

[0266] 1) First discharge capacity test

[0267] The first discharge capacity test process is as follows: at 25 °C, the prepared battery is charged to 3.75 V at a constant current of 1 C, then charged to 3.75 V at a constant voltage until the current drops to 0.05 C, and then discharged to 1.5 V at a constant current of 1 C to obtain the first cycle discharge capacity (Cd1).

[0268] 2) First coulombic efficiency test

[0269] The first coulombic efficiency test process is as follows: at 25 °C, the prepared battery is charged to 3.75 V at a constant current of 1 / 5 C, then charged at 3.75 V constant voltage until the current drops to 0.05 C, to obtain the first charge capacity (Cc1); then discharged to 1.5 V at a constant current of 1 / 5 C to obtain the first discharge capacity (Cd1), and the battery coulombic efficiency is calculated according to the following formula: battery first coulombic efficiency = first discharge capacity (Cd1) / first charge capacity (Cc1). The test process of the comparative examples and other examples is the same as above.

[0270] 3) Battery cycle capacity retention rate test

[0271] The battery capacity retention rate test process is as follows: at 25 °C, the prepared battery is charged to 3.75 V at a constant current of 1 C, then charged at 3.75 V constant voltage until the current drops to 0.05 C, then discharged to 1.5 V at a constant current of 1 C, and the obtained capacity is recorded as the initial capacity (C0). Repeat the above steps for the same battery as above, and record the discharge capacity of the battery after the nth cycle (Cn) at the same time, then the battery capacity retention rate Pn = Cn / C0 x 100% after each cycle, and take the P1, P2 … 100 point values as the vertical coordinates and the corresponding cycle numbers as the horizontal coordinates to obtain the battery capacity retention rate and cycle number curve. In this test process, the first cycle corresponds to n = 1, the second cycle corresponds to n = 2, … and the 100th cycle corresponds to n = 100, and the battery capacity retention rate data of the examples or comparative examples in Table 2 is the data measured after 100 cycles under the above test conditions, i.e. the value of P100. The test process of the comparative examples and other examples is the same as above.

[0272] III. Analysis of test results of each example and comparative example

[0273] The batteries of each example and comparative example were prepared according to the above method, and each performance parameter was measured, and the results are shown in Table 1 and Table 2 below.

[0274] Table 1

[0275]

[0276] Table 2

[0277]

[0278] According to the above results, examples 1-12 all include a positive electrode active material, the positive electrode active material is a carbon-complexed polyanion compound, and the positive electrode active material has the following general formula:

[0279] Na 4-x R 3-y M z(PO4)2P2O7 / C

[0280] wherein R comprises at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W and Pb, M comprises at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, Si, W and Pb, 0≤x≤0.5, 0≤y≤0.5, 0≤z<x+y, and x, y are not simultaneously 0.

[0281] From the comparison of Examples 1-10 and Comparative Example 1, Examples 11-12 and Comparative Example 5, it can be seen that, compared with the conventional positive electrode active material, the positive electrode active material comprising the carbon-composite polyanion compound in the examples of the present application can further reduce the residual alkali content of the positive electrode active material, improve the processing performance of the positive electrode active material, reduce the electrode resistance of the positive electrode sheet, and improve the cycle performance of the battery by providing Na vacancies, Fe vacancies or Mn vacancies, while maintaining the high discharge capacity and coulombic efficiency of the positive electrode active material.

[0282] From Examples 1-6, it can be seen that the presence of sodium vacancies and / or iron vacancies can significantly reduce the residual alkali content of the positive electrode active material, so that the battery has a high cycle capacity retention rate. Controlling 0

[0283] From the comparison of Examples 1-6 and Comparative Example 2, it can be seen that, compared with the polyanion compound without carbon, the positive electrode active material in the examples of the present application is a carbon-composite polyanion compound and can provide Na vacancies or Fe vacancies, which is beneficial to reduce the residual alkali content of the positive electrode active material and the electrode resistance of the positive electrode sheet thereof, improve the film layer compaction density of the positive electrode sheet thereof, and improve the initial coulombic efficiency and the capacity retention rate after 100 cycles of the battery, thereby improving the performance of the battery.

[0284] From the comparison of Examples 7-8 and Comparative Example 3, and Examples 10 and Comparative Example 4, it can be seen that, compared with the conventional Mn-doped iron-based polyanion compound, the positive electrode active material in the examples of the present application can provide Na vacancies or Fe vacancies, which is beneficial to reduce the residual alkali content of the positive electrode active material and the electrode resistance of the positive electrode sheet thereof.

[0285] From the comparison of Example 12 and Comparative Example 5, it can be seen that, compared with the traditional manganese-based polyanion compound, the polyanion compound in the positive active material in the examples of the present application is doped with manganese, and the positive active material can provide Na vacancies and Mn vacancies, which is beneficial to reduce the residual alkali content of the positive active material and the electrode resistance of the positive electrode sheet thereof, improve the film layer compaction density of the positive electrode sheet thereof, and improve the initial coulombic efficiency of the battery thereof and the capacity retention rate after 100 cycles, thereby improving the performance of the battery.

[0286] From the comparison of Example 4 and Example 3, it can be seen that, in the examples of the present application, Na vacancies and Fe vacancies are provided at the same time, which is beneficial to further reduce the residual alkali content of the positive active material and the electrode resistance of the positive electrode sheet thereof, and improve the capacity retention rate of the battery thereof after 100 cycles.

[0287] From the comparison of Example 8 and Example 4, it can be seen that, in the examples of the present application, the polyanion compound in the positive active material is doped with manganese, which is beneficial to further improve the initial discharge capacity and the initial coulombic efficiency of the battery thereof.

[0288] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments having substantially the same configuration and playing the same role and effect as the technical idea within the scope of the technical solutions of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications that can be thought of by those skilled in the art are applied to the embodiments, and other ways are constructed by combining part of the constituent elements in the embodiments, which are also included in the scope of the present application.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material is a carbon-composite polyanion compound, and the positive electrode active material has the following general formula: Na 4-x R 3-y M z (PO4)2P2O7 / C where R includes at least one of Mg, Al, Sc, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W, and Pb; M includes at least one of Mg, Al, Sc, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, Si, W, and Pb; 0 < x ≤ 0.5, 0 ≤ y ≤ 0.5, 0 ≤ z < x + y.

2. The positive electrode active material according to claim 1, characterized in that, where 0.01≤x≤0.2。 3. The positive electrode active material according to claim 1 or 2, characterized in that, where 0 < y - z ≤ 0.

3.

4. The positive electrode active material according to claim 1 or 2, characterized in that, where 0 < x ≤ 0.5 and 0 < z ≤ y ≤ 0.

5.

5. The positive electrode active material according to any one of claims 1 to 4, characterized in that, R includes one or more of Fe, Co, Ni, and Mn; M includes one or more of Mg, Al, Sc, Ti, Cr, Mn, Si, and Co.

6. The positive electrode active material according to any one of claims 1 to 5, characterized in that, The median particle size D of the positive electrode active material v 50 is 1.0 µm≤D v 50 ≤10 µm.

7. The positive electrode active material according to claim 6, characterized in that, The median particle size D of the positive electrode active material v 50 is 1.5 µm to 5.0 µm.

8. The positive electrode active material according to any one of claims 1 to 7, characterized in that, Based on the total mass of the positive electrode active material, the residual alkali amount of NaHCO₃ in the positive electrode active material is 0.05% - 2.5%.

9. The positive electrode active material according to claim 8, characterized in that, Based on the total mass of the positive electrode active material, the residual alkali amount of NaHCO₃ in the positive electrode active material is 0.05% - 0.5%.

10. A method for preparing a positive electrode active material, characterized in that, including the following steps: Dissolve raw materials including a sodium source, an R source, a phosphorus source, and a carbon source in deionized water, mix them evenly to obtain a mixed slurry, and the raw materials further include an M source; Dry the mixed slurry and then conduct calcination to prepare the positive electrode active material. The positive electrode active material is a carbon-composite polyanion compound, and the positive electrode active material has the following general formula: Na 4-x R 3-y M z (PO4)2P2O7 / C where R includes at least one of Mg, Al, Sc, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W, and Pb; M includes at least one of Mg, Al, Sc, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, Si, W, and Pb; 0 < x ≤ 0.5, 0 ≤ y ≤ 0.5, 0 ≤ z < x + y.

11. The preparation method according to claim 10, characterized in that, 0 < y - z ≤ 0.

3.

12. The preparation method according to claim 10 or 11, characterized in that, The step of drying the mixed slurry and then conducting calcination includes the following steps: Dry the mixed slurry to obtain a precursor powder; Calcine the precursor powder at a calcination temperature of 400 °C - 650 °C for a calcination time of 5 h - 15 h to prepare the positive electrode active material.

13. The preparation method according to claim 12, characterized in that, The calcination temperature is 500 °C - 600 °C.

14. The preparation method according to claim 12 or 13, characterized in that, The calcination time is 8 h - 13 h.

15. The preparation method according to any one of claims 10 to 14, characterized in that, The R source includes one or more of a magnesium source, an aluminum source, a scandium source, a titanium source, a vanadium source, a chromium source, a manganese source, an iron source, a cobalt source, a nickel source, a copper source, a zinc source, a zirconium source, a niobium source, a molybdenum source, a tin source, a hafnium source, a tantalum source, a tungsten source, and a lead source.

16. The preparation method according to any one of claims 10 to 15, characterized in that, The M source includes one or more of a magnesium source, an aluminum source, a scandium source, a titanium source, a vanadium source, a chromium source, a manganese source, an iron source, a cobalt source, a nickel source, a copper source, a zinc source, a zirconium source, a niobium source, a molybdenum source, a tin source, a hafnium source, a tantalum source, a silicon source, a tungsten source, and a lead source.

17. The preparation method according to claim 15 or 16, characterized in that, The iron source includes one or more of ferrous oxalate, ferric nitrate, ferrous sulfate, ferrous chloride, ferric oxalate, ferric acetate, ferric oxide, ferrous oxide, and metallic iron.

18. A positive electrode plate, characterized in that, It includes a positive electrode film layer, which comprises at least one of a binder, a one-dimensional conductive material and a zero-dimensional conductive material, and a positive electrode active material according to any one of claims 1 to 9 or a positive electrode active material prepared by any one of claims 10 to 17.

19. The positive electrode sheet according to claim 18, characterized in that, Based on the total mass of the positive electrode film, the mass content of the binder is 1.5% to 3%.

20. The positive electrode sheet according to claim 19, characterized in that, Based on the total mass of the positive electrode film, the mass content of the binder is 2.0% to 2.5%.

21. The positive electrode sheet according to any one of claims 18 to 20, characterized in that, The one-dimensional conductive material includes one or more of single-walled carbon nanotubes and multi-walled carbon nanotubes, and / or Based on the total mass of the positive electrode film, the mass content of the one-dimensional conductive material is 0.2% to 1%.

22. The positive electrode sheet according to claim 21, characterized in that, Based on the total mass of the positive electrode film, the mass content of the one-dimensional conductive material is 0.5% to 0.9%.

23. The positive electrode sheet according to any one of claims 18 to 22, characterized in that, The zero-dimensional conductive material includes one or more of Super P, Ketjen Black, and acetylene black, and / or Based on the total mass of the positive electrode film, the mass content of the zero-dimensional conductive material is 1% to 3%.

24. The positive electrode sheet according to claim 23, characterized in that, Based on the total mass of the positive electrode film, the mass content of the zero-dimensional conductive material is 2% to 2.8%.

25. A secondary battery, characterized in that, Includes the positive electrode sheet according to any one of claims 18 to 24.

26. The secondary battery according to claim 25, characterized in that, The secondary battery is a sodium-free secondary battery without a negative electrode.

27. The secondary battery according to claim 25 or 26, characterized in that, The secondary battery further includes a negative electrode sheet, which includes a negative current collector and a base coating disposed on at least one surface of the negative current collector. The base coating includes one or more of carbon nanotubes, graphite, graphene, silver composite carbon nanoparticles, and tin composite carbon nanoparticles.

28. The secondary battery according to claim 27, characterized in that, The areal density of the base coating is 5 g / m³. 2 ~50g / m 2 .

29. The secondary battery according to claim 27 or 28, characterized in that, The thickness of the base coating is 2 μm to 100 μm.

30. An electrical device, characterized in that, Includes a secondary battery selected from any one of claims 25 to 29.

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