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

Abstract

The positive electrode active material and its manufacturing method, a positive electrode sheet, a secondary battery, and an electric device are provided. The positive electrode active material is a carbon complex polyanion compound having the general formula Na 4-x R 3-y M z (PO4)2P2O7 / C, 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; and 0≦x≦0.5, 0≦y≦0.5, 0≦z

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application cites Chinese Patent Application No. 202310128853.2, filed on February 16, 2023, entitled "Positive electrode active material and manufacturing method thereof, positive electrode sheet, secondary battery and electrical device," the entire contents of which are incorporated herein by reference.

[0002] The present application relates to the technical field of secondary batteries, and in particular to a positive electrode active material and a manufacturing method thereof, a positive electrode sheet, a secondary battery, and an electric device. [Background technology]

[0003] Sodium batteries have great potential for application in large-scale energy storage due to their abundant reserves, low cost, and wide operating temperature range.

[0004] The performance of the positive electrode active material plays a key role in the performance of the battery, but currently the performance of the positive electrode active material itself cannot meet the application needs of the new generation of electrochemical systems. Summary of the Invention

[0005] The present application has been made in view of the above-mentioned problems, and aims to provide a positive electrode active material having a low residual alkali content, which contributes to improving the processability of the positive electrode active material and optimizing the coulombic efficiency and cycle performance of the battery.

[0006] A first aspect of the present application is a carbon-complex polyanionic compound having the general formula:

[0007] [ka] In the formula, R contains 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 contains 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, to provide a positive electrode active material.

[0008] The positive electrode active material can provide Na vacancies or R metal vacancies, and R contains 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 the one hand, due to the presence of Na vacancies or R metal vacancies, the strain of the chemical bonds between other elements in the positive electrode active material changes, the diffusion channel of Na ions expands, the movement of Na ions is effectively promoted, the formation of residual alkali in the positive electrode active material is suppressed or reduced, and the sheet resistance of the positive electrode sheet decreases. On the other hand, the optimized Na ion diffusion channel can also improve the conductivity of the positive electrode active material. In addition, doping with a metal containing 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 affects the change in the structure of the positive electrode active material, increases the intercrystalline layer distance, accelerates the movement of Na ions, further improves the cycle performance of the battery, and can improve the performance of the battery.

[0009] In any embodiment, 0 < x ≦ 0.5, and optionally 0.01 ≦ x ≦ 0.2.

[0010] <000008The Na vacancies provided by the positive electrode active material can effectively promote the movement of Na ions and suppress or reduce the formation of residual alkali in the positive electrode active material. On the one hand, due to the presence of Na vacancies, the valence state of other metals in the positive electrode active material is increased, the antioxidant ability of the positive electrode active material is enhanced, thereby suppressing or reducing the reaction between the positive electrode active material and water, reducing the amount of residual alkali in the positive electrode active material, and reducing the sheet resistance of the positive electrode sheet. On the other hand, the optimized Na ion migration path can improve the kinetic performance of the positive electrode active material, improve the Coulomb efficiency and cycle performance of the battery, and improve the electrical performance of the battery. Further controlling to 0.01≦x≦0.2 contributes to further reducing the amount of residual alkali in the positive electrode active material and the sheet resistance of the positive electrode sheet.

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

[0012] The positive electrode active material provides R metal vacancies, and 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. On the one hand, by distorting the chemical bonds between other elements in the positive electrode active material, the diffusion channel of Na ions is widened, the transport rate of Na ions during charge and discharge is increased, the conductivity of the positive electrode active material is increased, and the Coulomb efficiency and cycle performance of the battery can be improved. On the other hand, the R metal vacancies can also increase the conductivity of the positive electrode active material and improve the cycle performance of the battery by changing the electron cloud distribution of elements such as P and O.

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

[0014] The positive electrode active material provides Na vacancies, and 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. The doped metal occupies the R metal vacancies, which affects the structure of the positive electrode active material, increases the interlayer distance, accelerates the migration of Na ions, and further increases the conductivity of the positive electrode active material, thereby improving the cycle performance of the battery.

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

[0016] All of the above metal materials can achieve a low residual alkali content in the positive electrode active material, a low sheet resistance in the positive electrode sheet, and excellent coulomb efficiency and cycle performance in the battery.

[0017] In any embodiment, the median diameter D v 50 is 1.0μm≦D v 50≦10 μm, and optionally 1.5 μm to 5.0 μm.

[0018] By controlling the particle size of the positive electrode active material within an appropriate range, it is possible to avoid or reduce the difficulty of coating due to the subsequent physical gelation of the slurry caused by a particle size that is too small. It is also possible to avoid or reduce the effect of a particle size that is too large, resulting in a decrease in compaction degree and an impact on the dynamic performance of the positive electrode active material during charge and discharge, thereby achieving both processability and dynamic performance. The median diameter D of the positive electrode active material v Further controlling the particle size to 1.5 μm to 5.0 μm contributes to further improvement of the coulomb efficiency and cycle performance of the battery.

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

[0020] A cathode active material with an appropriate amount of residual alkali of NaHCO₃ can suppress the manufacturing cost of the manufacturing process, and can also avoid or reduce the subsequent chemical gelation of the slurry due to an excessive amount of residual alkali, making coating difficult. It is possible to consider the manufacturing cost, processability, and performance of the cathode active material simultaneously, contribute to the reduction of the sheet resistance of the cathode sheet, and endow the battery with excellent electrical performance and future application potential. By further controlling the amount of residual alkali of NaHCO₃ in the cathode active material to 0.05% - 0.5%, it contributes to the further reduction of the sheet resistance of the cathode sheet and the improvement of the Coulomb efficiency and cycle performance of the battery.

[0021] The second aspect of the present application is a method for manufacturing a cathode active material, comprising: dissolving a raw material containing a sodium source, an R source, a phosphorus source, and a carbon source in deionized water, and uniformly mixing to obtain a mixed slurry, and optionally, the step that the raw material further contains an M source; after drying the mixed slurry, firing it to manufacture the cathode active material, wherein the cathode active material is a carbon composite polyanion compound and has the following general formula:

[0022]

Chemical formula

[0023] The manufacturing method of the positive electrode active material is simple and low in manufacturing cost. The manufactured positive electrode active material has Na vacancies or R metal vacancies, where 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. This contributes to reducing the residual alkali content of the positive electrode active material and the sheet resistance of the positive electrode sheet, and improving the coulombic efficiency and cycle efficiency of the battery.

[0024] In any embodiment, 0 <y-z≦0.3である。

[0025] The positive electrode active material provides R metal vacancies, where 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. These vacancies distort the chemical bonds between other elements in the positive electrode active material, widening the diffusion channels for sodium ions and increasing the transport rate of sodium ions during charging and discharging. They also enhance the electrical conductivity of the positive electrode active material, improving the battery's Coulombic efficiency and cycling performance. The R metal vacancies also alter the electron cloud distribution of elements such as phosphorus and oxygen, improving the electrical conductivity of the positive electrode active material and improving the battery's Coulombic efficiency and cycling performance.

[0026] In any embodiment, the step of drying and then calcining the mixed slurry comprises: drying the mixed slurry to obtain a precursor powder; and calcining the precursor powder at a calcination temperature of 400° C. to 650° C. for a calcination time of 5 hours to 15 hours to produce the positive electrode active material.

[0027] By controlling the baking temperature and baking time appropriately, the positive electrode active material has Na vacancies or R metal vacancies, which contributes to reducing the amount of residual alkali in the positive electrode active material and the sheet resistance of the positive electrode sheet, as well as improving the coulomb efficiency and cycle efficiency of the battery.

[0028] In any embodiment, the firing temperature is between 500°C and 600°C.

[0029] Controlling the firing temperature to 500°C to 600°C contributes to further reducing the amount of residual alkali in the positive electrode active material and the sheet resistance of the positive electrode sheet.

[0030] In any embodiment, the baking time is 8 hours to 13 hours.

[0031] Controlling the baking time to 8 to 13 hours contributes to reducing the amount of residual alkali in the positive electrode active material and the sheet resistance of the positive electrode sheet.

[0032] In any embodiment, the source of R comprises 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.

[0033] In any embodiment, the M source comprises 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.

[0034] 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.

[0035] A third aspect of the present application provides a positive electrode sheet including a positive electrode film layer, the positive electrode film layer including 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 a positive electrode active material produced by the production method of the second aspect.

[0036] In any embodiment, the mass content of the binder is 1.5% to 3%, and optionally 2.0% to 2.5%, based on the total mass of the positive electrode membrane layer.

[0037] By controlling the binder mass content within an appropriate range, sufficient binding strength can be obtained without causing excessive sheet resistance, contributing to improved coulomb efficiency and cycle performance of the battery. Further controlling the binder mass content to 2.0% to 2.5% contributes to reducing the sheet resistance of the positive electrode sheet.

[0038] In any embodiment, the one-dimensional conductive material comprises one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, and / or The mass content of the one-dimensional conductive material is 0.2% to 1% based on the total mass of the positive electrode film layer, and optionally 0.5% to 0.9%.

[0039] Controlling the mass content of the one-dimensional conductive material within an appropriate range contributes to improving the battery's coulombic efficiency and cycle performance. Further controlling the mass content of the one-dimensional conductive material to 0.5% to 0.9% contributes to further improving cycle performance.

[0040] In any embodiment, the zero dimensional conductive material comprises one or more of Super P, Ketjen Black, Acetylene Black; and / or The mass content of the zero-dimensional conductive material is 1% to 3%, and optionally 2% to 2.8%, based on the total mass of the positive electrode film layer.

[0041] Controlling the mass content of the zero-dimensional conductive material within an appropriate range contributes to improving the battery's coulombic efficiency and cycle performance. Further controlling the mass content of the zero-dimensional conductive material to 2% to 2.8% contributes to further improving cycle performance.

[0042] A fourth aspect of the present application provides a secondary battery including the positive electrode sheet of the third aspect.

[0043] In any embodiment, the secondary battery is a negative electrode-free sodium secondary battery.

[0044] In any embodiment, the secondary battery further includes a negative electrode sheet, the negative electrode sheet including a negative electrode current collector and a primer layer provided on at least one surface of the negative electrode current collector, the primer layer including one or more of carbon nanotubes, graphite, graphene, silver composite carbon nanoparticles, and tin composite carbon nanoparticles.

[0045] The primer layer not only has excellent electrical conductivity, but also contributes to uniform deposition of metal ions on the surface of the current collector and to improving the coulombic efficiency and cycle performance of the battery.

[0046] In any embodiment, the areal density of the primer layer is 5 g / m 2 ~50g / m 2 is.

[0047] Surface density is 5g / m 2 ~50g / m 2 The primer layer contributes to a uniform distribution of nucleation sites, promotes uniform deposition of the metal, and does not affect the electron transport behavior.

[0048] In any embodiment, the thickness of the primer layer is from 2 μm to 100 μm.

[0049] By controlling the thickness of the primer layer to 2 μm to 100 μm, sufficient nucleation sites can be provided, contributing to uniform deposition of metal ions and suppressing dendrites.

[0050] A fifth aspect of the present application provides an electrical device including the secondary battery of the fourth aspect of the present application. [Brief explanation of the drawings]

[0051] [Figure 1] 1 is a schematic diagram of a secondary battery cell according to an embodiment of the present application; [Figure 2] FIG. 2 is an exploded view of the secondary battery cell shown in FIG. 1 according to the embodiment of the present application. [Figure 3] 1 is a schematic diagram of a battery module according to an embodiment of the present application; [Figure 4] 1 is a schematic diagram of a battery pack according to an embodiment of the present application; [Figure 5] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present application. [Figure 6] 1 is a schematic diagram of an electrical device powered by a secondary battery according to an embodiment of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0052] Hereinafter, with appropriate reference to the drawings, specific embodiments of the present application will be described in detail, with particular reference to the drawings. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and redundant descriptions of structures that are actually the same may be omitted. This is to prevent the following description from becoming unnecessarily long and to facilitate understanding by those skilled in the art. Furthermore, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

[0053] The "ranges" disclosed in this application are defined by lower and upper limits, and a given range is defined by selecting one lower limit and one upper limit, with the selected lower and upper limits defining the boundaries of that particular range. Such defined ranges may or may not include endpoints and may be arbitrarily combined, i.e., any lower limit and any upper limit may be combined to form a single range. For example, if ranges of 60 to 120 and 80 to 110 are recited for a particular parameter, it is understood that the ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if 1 and 2 are recited as minimum range values ​​and 3, 4, and 5 as maximum range values, the ranges of 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5 are all contemplated. In this application, unless otherwise specified, a numerical range of "a to b" represents a shorthand notation for any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0 to 5" means that all real numbers between "0 and 5" have already been enumerated herein, and "0 to 5" is merely a shorthand notation for combinations of these numbers. Note that when a parameter is described as an integer ≧2, this is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0054] Unless otherwise specified, all embodiments and optional embodiments in this application can be combined with each other to form new technical solutions.

[0055] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0056] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method including steps (a) and (b) means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, in the above, when it is stated that the method may further include step (c), it means that step (c) can be added to the method in any order; for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), or may be otherwise.

[0057] Unless otherwise specified, in this application, expressions such as "comprise" and "comprises" may be open-ended or closed-ended. For example, expressions such as "comprise" and "comprises" may indicate that the invention may further include or include other components not listed, or may include or include only the listed components.

[0058] Unless otherwise specified, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any one of the following conditions is met: A is true (or exists) but B is false (or does not exist); A is false (or does not exist) but B is true (or exists); or A and B are both true (or exist).

[0059] Generally, in the manufacturing process of sodium battery cathode materials, due to reasons such as the manufacturing process and raw material ratio, sodium impurities tend to remain in the cathode material. Also, since sodium in the bulk phase of the cathode material is easily desorbed, residual alkalis such as sodium carbonate, sodium hydroxide, and sodium hydrogen carbonate are likely to be generated from the cathode material. As a result, the cathode material swells with gas and its thermal stability decreases, leading to problems such as low electronic conductivity of the battery, low discharge capacity, and low cycle performance. Moreover, it also affects the safety of the battery. Therefore, in order to meet the application needs of the new generation of electrochemical systems, it is necessary to develop a cathode material with a low residual alkali content and excellent electrical performance.

[0060] [Cathode active material] In view of this, the present application provides a carbon composite polyanion compound having the following general formula:

[0061] [Chemical formula] In the formula, R contains 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 contains 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 ≦ ”.5, 0 ≦ z < x + y, and x and y are not simultaneously 0. The present application provides a cathode active material.

[0062] In some embodiments, x is selectively 0.001, 0.1, 0.15, 0.2, 0.25, 0.3, ”0.35, 0.4, 0.45, 0.5, or a value within the range consisting of any two of the above values; y is selectively 0.001, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or a value within the range consisting of any two of the above values.

[0063] In some embodiments, R contains Fe and M contains Mn. In some embodiments, R contains Al and M contains Mn. In some embodiments, R contains V and M contains Ni. In some embodiments, R contains Fe and M contains Mn, Co, and Ni. In some embodiments, R contains Mn and M contains Si.

[0064] The positive electrode active material can provide Na vacancies or R metal vacancies, and R contains 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, due to the presence of Na vacancies or R metal vacancies, the strain of the chemical bonds between other elements in the positive electrode active material changes, the diffusion channel of Na ions expands, the movement of Na ions is effectively promoted, the formation of residual alkali in the positive electrode active material is suppressed or reduced, and the sheet resistance of the positive electrode sheet decreases. On the other hand, the optimized Na ion diffusion channel can also improve the conductivity of the positive electrode active material. Also, by doping with a metal containing 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, it affects the structural change of the positive electrode active material, increases the intercrystalline layer distance, accelerates the movement of Na ions, further improves the cycle performance of the battery, and can improve the performance of the battery.

[0065] In some embodiments, 0 < x ≤ 0.5, and optionally 0.01 ≤ x ≤ 0.2. <​​​​​​​​​In some embodiments, 0 <x≦0.3、0≦y≦0.5、0≦z<x+yである。

[0069] In some embodiments, 0.01≦x≦0.2, 0≦y≦0.3, 0≦z <x+yである。

[0070] In some embodiments, 0.01≦x≦0.2, 0≦y≦0.5, 0≦z <x+yである。

[0071] In some embodiments, 0.2≦x≦0.5, 0.2≦y≦0.5, and 0≦z <x+yである。

[0072] The Na vacancies provided by the positive electrode active material effectively promote the migration of Na ions, suppressing or reducing the formation of residual alkali in the positive electrode active material. On the one hand, the presence of Na vacancies increases the valence state of other metals in the positive electrode active material, enhancing the antioxidant capacity of the positive electrode active material, thereby suppressing or reducing the reaction between the positive electrode active material and water, reducing the amount of residual alkali in the positive electrode active material, and reducing the sheet resistance of the positive electrode sheet. On the other hand, the optimized Na ion migration path improves the kinetic performance of the positive electrode active material, improving the coulombic efficiency and cycling performance of the battery, and improving the electrical performance of the battery. Furthermore, controlling x so that 0.01≦x≦0.2 contributes to further reducing the amount of residual alkali in the positive electrode active material and the sheet resistance of the positive electrode sheet.

[0073] In some embodiments, 0 <y-z≦0.3である。

[0074] In some embodiments, y is optionally 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5 or a value within a range consisting of any two of the above values, and z is optionally 0, 0.02, 0.05, 0.07, 0.1, 0.12, 0.15, 0.17, 0.2, or a value within a range consisting of any two of the above values, and z <yである。

[0075] In some embodiments, 0 < x ≤ 0.5 and 0 < y - z ≤ 0.3.

[0076] In some embodiments, 0 ≤ x ≤ 0.2 and 0 < y - z ≤ 0.3.

[0077] The positive electrode active material provides R metal vacancies, where 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. On one hand, by distorting the chemical bonds between other elements in the positive electrode active material, it can widen the diffusion channels of Na ions, increase the transport rate of Na ions during charge and discharge, increase the conductivity of the positive electrode active material, and improve the Coulomb efficiency and cycle performance of the battery. On the other hand, the R metal vacancies can also increase the conductivity of the positive electrode active material and improve the Coulomb efficiency and cycle performance of the battery by changing the electron cloud distribution of elements such as P and O.

[0078] In some embodiments, 0 < x ≤ 0.5 and 0 < z ≤ y ≤ 0.5.

[0079] In some embodiments, x is optionally 0.001, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or a value within the range consisting of any two of the above values; y is optionally 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or a value within the range consisting of any two of the above values; z is optionally 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or a value within the range consisting of any two of the above values, and z < y.

[0080] In some embodiments, 0 < x ≤ 0.5, 0 < z, and z = y.

[0081] In some embodiments, 0 < x ≤ 0.5 and 0 < z < y.

[0082] The positive electrode active material provides Na vacancies, and 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. The doped metal occupies the R metal vacancies, which affects the structure of the positive electrode active material, increases the crystal interlayer distance, accelerates the migration of Na ions, and further increases the conductivity of the positive electrode active material, thereby improving the coulombic efficiency and cycle performance of the battery.

[0083] In some embodiments, R comprises one or more of Fe, Co, Ni, Mn, and M comprises one or more of Mg, Al, Sc, Ti, V, Cr, Mn, Si, Co.

[0084] In some embodiments, R comprises Fe and M comprises Mn. In some embodiments, R comprises Fe and M comprises Ni. In some embodiments, R comprises Fe and M comprises Mn and Ni. In some embodiments, R comprises V and M comprises Si. In some embodiments, R comprises Mn and M comprises Si.

[0085] All of the above metal materials can achieve a low residual alkali content in the positive electrode active material, a low sheet resistance in the positive electrode sheet, and excellent coulomb efficiency and cycle performance in the battery.

[0086] In some embodiments, the median diameter D of the positive electrode active material v 50 is 1.0 μm≦D v 50≦10 μm, and optionally 1.5 μm to 5.0 μm.

[0087] In some embodiments, the median diameter D of the positive electrode active material v50 is optionally 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 a range consisting of any two of the above values.

[0088] Median diameter D of the positive electrode active material v The particle size distribution (50) can be measured by any method known in the art. For example, GB / T 19077-2016, Laser Diffraction Method for Particle Size Distribution, was used. 0.1 g to 0.13 g of a test positive electrode active material sample was weighed into a 50 mL beaker, 5 g of anhydrous ethanol was added, and a stirring bar of approximately 2.5 mm was placed inside. The beaker was then sealed with plastic wrap. The sample was ultrasonically treated for 5 minutes, then transferred to a magnetic stirrer and stirred at 500 rpm for at least 20 minutes. Two samples were extracted from each batch and measured. Measurements were performed using a Mastersizer 2000E laser particle size analyzer from Malvern Instruments, UK.

[0089] By controlling the particle size of the positive electrode active material within an appropriate range, it is possible to avoid or reduce the phenomenon that occurs when the particle size is too small, resulting in physical gelation of the slurry, making coating difficult. It is also possible to avoid or reduce the effect of a particle size that is too large, resulting in a decrease in compaction degree and an impact on the dynamic performance of the positive electrode active material during charge and discharge, thereby achieving both processability and dynamic performance. The median diameter D of the positive electrode active material v Further controlling the particle size to 1.5 μm to 5.0 μm contributes to further improvement of the coulomb efficiency and cycle performance of the battery.

[0090] In some embodiments, the residual alkali content of NaHCO3 in the positive electrode active material is 0.05% to 2.5%, and optionally 0.05% to 0.5%, based on the total weight of the positive electrode active material.

[0091] In some embodiments, the residual alkalinity of NaHCO in the active cathode material is, based on the total weight of the active cathode material, optionally 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 range consisting of any two of the foregoing.

[0092] The residual alkalinity of NaHCO3 in the positive electrode active material can be measured by any method known in the art. For example, the residual alkalinity was measured using acid-base titration. The sodium bicarbonate and sodium ions in the positive electrode material were titrated with a standard hydrochloric acid solution. A pH electrode was used as the indicator electrode, and the endpoint was determined by the potential jump. The titration volume of the standard titration solution was determined based on the endpoint. The calculated mass of NaHCO3 was divided by the mass of the positive electrode active material to obtain the residual alkalinity of NaHCO3 in the positive electrode active material.

[0093] In some embodiments, the residual alkalinity of the positive electrode active material further includes other alkaline substances, such as NaOH or Na2CO3. The content of the other alkaline substances varies in the same manner as the residual alkalinity of NaHCO3. That is, the residual alkalinity of NaHCO3 in the positive electrode active material can indicate the amount of alkaline substances contained. Therefore, the residual alkalinity of NaHCO3 can indicate the ability of the positive electrode active material to generate residual alkalinity.

[0094] A cathode active material with an appropriate amount of residual alkali of NaHCO₃ can suppress the manufacturing cost of the manufacturing process, and can also avoid or reduce the subsequent chemical gelation of the slurry due to an excessive amount of residual alkali, making coating difficult, and can achieve a balance among the manufacturing cost, processing performance, and performance of the cathode active material, contribute to the reduction of the sheet resistance of the cathode sheet, and endow the battery with excellent electrical performance and application prospects. By further controlling the amount of residual alkali of NaHCO₃ in the cathode active material to 0.05% - 0.5%, it contributes to the further reduction of the sheet resistance of the cathode sheet, the improvement of the Coulomb efficiency and cycle performance of the battery.

[0095] This application is a method for manufacturing a cathode active material, comprising: dissolving a raw material containing a sodium source, an R source, a phosphorus source, and a carbon source in deionized water, and uniformly mixing to obtain a mixed slurry, and optionally, the raw material further contains an M source; after drying the mixed slurry, firing it to produce a cathode active material, wherein the cathode active material is a carbon composite polyanion compound and has the following general formula:

[0096]

Chemical formula

[0097] In some embodiments, x is optionally 0.001, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or a value within a range consisting of any two of the foregoing values; and y is optionally 0.001, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or a value within a range consisting of any two of the foregoing values.

[0098] The manufacturing method of the positive electrode active material is simple and low in manufacturing cost. The manufactured positive electrode active material has Na vacancies or R metal vacancies, where 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 contributes to reducing the residual alkali content of the positive electrode active material and the sheet resistance of the positive electrode sheet, and improving the coulombic efficiency and cycle efficiency of the battery.

[0099] In some embodiments, 0 <y-z≦0.3である。

[0100] In some embodiments, y is optionally 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5 or a value within a range consisting of any two of the above values, and z is optionally 0, 0.02, 0.05, 0.07, 0.1, 0.12, 0.15, 0.17, 0.2, or a value within a range consisting of any two of the above values, and z <yである。

[0101] The positive electrode active material provides R metal vacancies, where 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. These vacancies distort the chemical bonds between other elements in the positive electrode active material, widening the diffusion channels for sodium ions and increasing the transport rate of sodium ions during charging and discharging. They also enhance the electrical conductivity of the positive electrode active material, improving the battery's Coulombic efficiency and cycling performance. The R metal vacancies also alter the electron cloud distribution of elements such as phosphorus and oxygen, improving the electrical conductivity of the positive electrode active material and improving the battery's Coulombic efficiency and cycling performance.

[0102] In some embodiments, the step of drying the mixed slurry and then calcining the mixture comprises: drying the mixed slurry to obtain a precursor powder; and calcining the precursor powder at a calcination temperature of 400° C. to 650° C. for a calcination time of 5 hours to 15 hours to produce a positive electrode active material.

[0103] In some embodiments, the firing temperature is optionally 400°C, 420°C, 450°C, 480°C, 500°C, 530°C, 550°C, 570°C, 600°C, 650°C, or a value within a range consisting of any two of the foregoing values.

[0104] In some embodiments, the baking time is optionally 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, or a value within a range consisting of any two of the above values.

[0105] By controlling the baking temperature and baking time appropriately, the positive electrode active material has Na vacancies or R metal vacancies, which contributes to reducing the amount of residual alkali in the positive electrode active material and the sheet resistance of the positive electrode sheet, as well as improving the coulomb efficiency and cycle efficiency of the battery.

[0106] In some embodiments, the firing temperature is between 500°C and 600°C.

[0107] In some embodiments, the firing temperature is optionally 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 within a range consisting of any two of the foregoing values.

[0108] Controlling the firing temperature to 500°C to 600°C contributes to further reducing the amount of residual alkali in the positive electrode active material and the sheet resistance of the positive electrode sheet.

[0109] In some embodiments, the baking time is 8 hours to 13 hours.

[0110] In some embodiments, the baking time is optionally 8 hours, 9 hours, 9.5 hours, 10 hours, 10.5 hours, 11 hours, 12 hours, 12.5 hours, 13 hours, or a value within a range consisting of any two of the above values.

[0111] Controlling the baking time to 8 to 13 hours contributes to reducing the amount of residual alkali in the positive electrode active material and the sheet resistance of the positive electrode sheet.

[0112] In some embodiments, the source of R comprises 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.

[0113] In some embodiments, the M source comprises 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.

[0114] In some embodiments, 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.

[0115] [Positive electrode sheet] The present application further provides a positive electrode sheet including a positive electrode film layer, the positive electrode film layer including 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 a positive electrode active material produced by the production method of some embodiments.

[0116] In some embodiments, the positive electrode film layer comprises a one-dimensional conductive material. In some embodiments, the positive electrode film layer comprises a zero-dimensional conductive material.

[0117] In some embodiments, the positive electrode film layer includes both one-dimensional and zero-dimensional conductive materials. The simultaneous addition of two forms of conductive material contributes to further improving the conductivity of the positive electrode sheet.

[0118] In some embodiments, the mass content of the binder is 1.5% to 3%, and optionally 2.0% to 2.5%, based on the total mass of the positive electrode membrane layer.

[0119] In some embodiments, the mass content of the binder is optionally 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 consisting of any two of the foregoing values, based on the total mass of the positive electrode membrane layer.

[0120] By controlling the binder mass content within an appropriate range, sufficient binding strength can be obtained without causing excessive sheet resistance, contributing to improved coulomb efficiency and cycle performance of the battery. Further controlling the binder mass content to 2.0% to 2.5% contributes to reducing the sheet resistance of the positive electrode sheet.

[0121] In some embodiments, the one-dimensional conductive material comprises one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes.

[0122] In some embodiments, the one-dimensional conductive material comprises 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%, and optionally 0.5% to 0.9%, based on the total mass of the positive electrode film layer.

[0123] In some embodiments, the one-dimensional conductive material comprises single-walled carbon nanotubes. In some embodiments, the one-dimensional conductive material comprises multi-walled carbon nanotubes. In some embodiments, the one-dimensional conductive material comprises single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0124] In some embodiments, the mass content of the one-dimensional conductive material is optionally 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or a value within a range consisting of any two of the above values, based on the total mass of the positive electrode film layer.

[0125] Controlling the mass content of the one-dimensional conductive material within an appropriate range contributes to improving the battery's coulombic efficiency and cycle performance. Further controlling the mass content of the one-dimensional conductive material to 0.5% to 0.9% contributes to further improving cycle performance.

[0126] In some embodiments, the zero dimensional conductive material comprises one or more of Super P, Ketjen Black, and Acetylene Black.

[0127] In some embodiments, the zero-dimensional conductive material comprises 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%, and optionally 2% to 2.8%, based on the total mass of the positive electrode membrane layer.

[0128] In some embodiments, the zero dimensional conductive material comprises Super P. In some embodiments, the zero dimensional conductive material comprises Ketjen Black. In some embodiments, the zero dimensional conductive material comprises Super P and Ketjen Black.

[0129] In some embodiments, the mass content of the zero-dimensional conductive material is optionally 1%, 1.2%, 1.5%, 1.7%, 2%, 2.2%, 2.5%, 2.7%, 3%, or a value within a range consisting of any two of the above values, based on the total mass of the positive electrode film layer.

[0130] Controlling the mass content of the zero-dimensional conductive material within an appropriate range contributes to improving the battery's coulombic efficiency and cycle performance. Further controlling the mass content of the zero-dimensional conductive material to 2% to 2.8% contributes to further improving cycle performance.

[0131] The positive electrode sheet further includes a positive electrode current collector.

[0132] The positive electrode current collector may be 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 may be one or more of Super P, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite, graphene, and carbon nanofibers. The metal foil, carbon-coated metal foil, and porous metal plate may each independently be at least one selected from copper, aluminum, nickel, and stainless steel. The composite current collector may be a composite current collector formed by combining a metal foil with a polymer substrate film.

[0133] In some embodiments, the positive electrode sheet may be manufactured by the following method: The components for manufacturing the positive electrode sheet, such as the positive electrode active material, conductive material, binder, and any other components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, which is then applied to a positive electrode current collector, and the positive electrode sheet is obtained after steps such as baking and cold pressing.

[0134] [Negative electrode sheet] The negative electrode sheet may include only a negative electrode current collector without including a negative electrode active material. The negative electrode sheet may also include a negative electrode current collector on which a metal phase has been pre-deposited.

[0135] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil or copper foil may be used as the metal foil. The composite current collector may include a polymeric substrate layer and a metal layer formed on at least one surface of the polymeric substrate. The composite current collector may be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy) on a polymeric substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0136] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a primer layer provided on at least one surface of the negative electrode current collector, the primer layer including one or more of carbon nanotubes, graphite, graphene, silver composite carbon nanoparticles, and tin composite carbon nanoparticles.

[0137] The primer layer not only has excellent electrical conductivity, but also contributes to uniform deposition of metal ions on the surface of the current collector and to improving the coulombic efficiency and cycle performance of the battery.

[0138] In some embodiments, the areal density of the primer layer is 5 g / m 2 ~50g / m 2 is.

[0139] In some embodiments, the areal density of the primer layer is optionally 5 g / m 2 , 10g / m 2 , 15g / m 2 , 20g / m 2 , 25g / m 2 , 30g / m 2 , 35g / m 2, 40g / m 2 , 45g / m 2 , 50g / m 2 or a value within a range consisting of any two of the above values.

[0140] Surface density is 5g / m 2 ~50g / m 2 The primer layer contributes to a uniform distribution of nucleation sites, promotes uniform deposition of the metal, and does not affect the electron transport behavior.

[0141] In some embodiments, the thickness of the primer layer is between 2 μm and 100 μm.

[0142] In some embodiments, the thickness of the primer layer is optionally 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 value within a range consisting of any two of the foregoing values.

[0143] By controlling the thickness of the primer layer to 2 μm to 100 μm, sufficient nucleation sites can be provided, contributing to uniform deposition of metal ions and suppressing dendrites.

[0144] [Separator] In some embodiments, the secondary battery further includes a separator. The present application does not particularly limit the type of separator, and any known porous separator having good chemical stability and mechanical stability may be selected.

[0145] In some embodiments, the separator may be made of at least one material selected from the group consisting of polyethylene, polypropylene, polyvinylidene fluoride, aramid fiber, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fiber. The separator is not particularly limited and may be a single-layer film or a multilayer composite film. When the separator is a multilayer composite film, the materials of the layers are not particularly limited and may be the same or different.

[0146] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be fabricated into an electrode assembly by a winding process or a lamination process.

[0147] In some embodiments, the secondary battery may include an exterior body that can be used to encapsulate the electrode assembly and electrolyte.

[0148] In some embodiments, the exterior of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The exterior of the secondary battery may be a soft pack, such as a bag-shaped soft pack. The soft pack may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0149] [Secondary battery] Secondary batteries may include various forms, examples of which include, but are not limited to, battery cells, battery modules, and battery packs.

[0150] The battery cell includes a positive electrode sheet according to some examples, and the positive electrode sheet includes a positive electrode active material according to some embodiments or a positive electrode active material produced by the manufacturing method according to some embodiments.

[0151] The present application does not particularly limit the shape of the battery cell, and it may be cylindrical, rectangular, or any other shape. For example, Figure 1 shows an example of a rectangular battery cell 5, and Figure 2 is an exploded view of the battery cell 5.

[0152] In some embodiments, the secondary battery cell further comprises a negative electrode sheet, a separator, and an electrolyte.

[0153] In some embodiments, the secondary battery cell is a negative electrode-free sodium secondary battery.

[0154] Anode-free sodium secondary batteries do not have a pre-deposited anode active material and only contain anode current collectors. During the initial charge, sodium ions gain electrons at the cathode and deposit as metallic sodium on the current collector surface, forming a sodium metal phase. During discharge, the metallic sodium converts back to sodium ions and returns to the cathode, enabling cyclic charge-discharge. Compared to other sodium secondary batteries, anode-free sodium secondary batteries are not limited by the anode material, allowing for higher energy density. Furthermore, while maintaining high electrochemical performance, they can shorten the battery production cycle, reduce battery manufacturing costs, and significantly improve production efficiency.

[0155] In some embodiments, the CB value of the negative electrode-free sodium secondary battery is 0.1 or less.

[0156] The CB value is the capacity per unit area of ​​the negative electrode sheet in a secondary battery divided by the capacity per unit area of ​​the positive electrode sheet. Because negative-electrode-free batteries do not contain negative electrode active material, the capacity per unit area of ​​the negative electrode sheet is small, and the CB value of the secondary battery is 0.1 or less.

[0157] In some embodiments, referring to FIG. 2 , the exterior body may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, and a receiving cavity is formed between the bottom plate and the side plates. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 is provided to cover the opening and seal the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is sealed within the receiving cavity. The secondary battery 5 may include one or more electrode assemblies 52, and this can be selected by those skilled in the art according to actual needs.

[0158] [Battery module] In some embodiments, the battery cells may be assembled into a battery module, and the number of battery cells included in the battery module may be one or more, the specific number of which can be selected by one skilled in the art based on the application and capacity of the battery module.

[0159] Fig. 3 shows an example of a battery module 4. Referring to Fig. 3, in the battery module 4, the plurality of battery cells 5 may be arranged in order along the length of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the plurality of battery cells 5 may be fixed using fasteners.

[0160] Optionally, the battery module 4 may include a housing having an accommodating space, and the plurality of battery cells 5 are accommodated in the accommodating space.

[0161] [Battery pack] In some embodiments, the battery modules may be assembled into a battery pack, and the battery pack may include one or more battery modules, the specific number of which can be selected by a person skilled in the art based on the application and capacity of the battery pack.

[0162] 4 and 5 show an example of a battery pack 1. Referring to FIGS. 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 provided in the battery box. The battery box includes an upper box 2 and a lower box 3, and the upper box 2 is provided to cover the lower box 3 and form an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in any manner within the battery box.

[0163] [Electrical Equipment] In one embodiment of the present application, there is provided an electric device including at least one of the secondary battery according to any of the embodiments, the battery module according to any of the embodiments, or the battery pack according to any of the embodiments.

[0164] The electric device includes at least one of the secondary batteries, battery modules, or battery packs provided in the present application. The secondary batteries, battery modules, or battery packs may be used as a power source for the electric device or as an energy storage unit for the electric device. The electric device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), trains, ships, satellites, energy storage systems, etc.

[0165] The electric device can be selected from a secondary battery, a battery module, or a battery pack depending on the requirements of use.

[0166] 6 shows an example of an electric device, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the demand for high power and high energy density of secondary batteries in the electric device, a battery pack or a battery module may be adopted.

[0167] Other examples of the device may be a mobile phone, a tablet computer, a laptop computer, etc. Such devices are usually required to be lightweight and thin, and may employ a secondary battery as a power source.

[0168] Example Examples of the present application are described below. The examples described below are illustrative and are intended only to interpret the present application, and should not be understood as limiting the present application. In the examples, specific techniques or conditions are not specified, and are carried out in accordance with the techniques or conditions or product specifications described in literature in the field. Reagents or instruments used without specifying the manufacturer are all ordinary products that are commercially available.

[0169] 1. Manufacturing method Example 1 1) Manufacturing of positive electrode active material Sodium pyrophosphate, ferrous oxalate, and ammonium dihydrogen phosphate were dissolved in deionized water in a molar ratio of 1:2.8:2 and stirred at room temperature for 30 minutes to obtain a mixed slurry. The mixed slurry was sanded to an average particle size of 0.2 μm, and then an aqueous glucose solution was added and mixed and ground for 30 minutes 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 powder precursor. Finally, the mixture was heated to 320°C at a rate of 2°C in a N2 atmosphere and held at that temperature for 4 hours, then heated to 550°C at a rate of 2°C and held at that temperature for 10 hours. The sintered product was crushed, sieved, and purified to obtain Na4Fe 2.8 A (PO4)2P2O7 / C positive electrode active material was obtained. Here, the carbon content was 2% based on the total mass of the positive electrode active material, and the median diameter D v 50 was 3.0 μm, and the amount of residual alkali in the positive electrode active material was 0.52%.

[0170] 2) Manufacturing of positive electrode sheets 2.5 wt% polyvinylidene fluoride binder was completely dissolved in N-methylpyrrolidone (NMP), and 2.0 wt% Super P, 1.0 wt% single-walled carbon nanotubes, and 94.5 wt% of the above positive electrode active material were added and stirred uniformly to obtain a positive electrode slurry. The slurry was evenly applied to the surface of an aluminum foil current collector and then transferred to a vacuum drying oven for complete drying. The dried sheet was roll-pressed and punched to obtain a positive electrode sheet. Here, the compaction density of the positive electrode film layer was 1.9 g / cm. 3 The sheet resistance was 0.6 Ω·cm.

[0171] 3) Manufacturing of negative electrode sheets 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 then applied to the surface of a negative electrode current collector copper foil, which was then transferred to a vacuum drying oven to completely dry it. The sheet was then punched out to obtain a negative electrode sheet with a free-standing structure. The thickness of the undercoat layer was 20 μm, and the surface density was 25 g / m. 2 It was.

[0172] 4) Electrolyte In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), sodium hexafluorophosphate NaPF6, a sodium salt, was dissolved in ethylene glycol dimethyl ether (DME), an organic solvent, and the solution was stirred uniformly to obtain an electrolyte solution with a sodium salt concentration of 1.5 mol / L.

[0173] 5) Separator A polypropylene film was used as a separator.

[0174] 6) Battery manufacturing The positive electrode sheet, separator, and negative electrode sheet were stacked in order with the separator between the positive and negative electrode sheets to separate them, then wound to obtain a bare cell. A tab was welded to the bare cell, which was then placed in an aluminum case and baked at 80°C to remove water. The case was then immediately filled with electrolyte and sealed to obtain an uncharged battery. The uncharged battery was then left to stand, and then passed through processes such as hot pressing, cold pressing, chemical formation, molding, and capacity measurement to obtain the negative electrode-free sodium secondary battery product of Example 1.

[0175] Examples 2 to 6 The batteries of Examples 2 to 6 were manufactured using the same method as the battery of Example 1, except that the y value of Fe or the x value of Na in the positive electrode active material was adjusted. Specific parameters are as shown in Table 1.

[0176] Example 7 1) Manufacturing of positive electrode active material Sodium pyrophosphate, ferrous oxalate, ammonium dihydrogen phosphate, and manganese oxide were dissolved in deionized water in a molar ratio of 0.98:2.8:2:0.1 and stirred at room temperature for 30 minutes to obtain a mixed slurry. The mixed slurry was sanded to an average particle size of 0.2 μm, and then an aqueous glucose solution was added and mixed and ground for 30 minutes 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 powder precursor. Finally, the mixture was heated to 320°C at a rate of 2°C in a N2 atmosphere and held at that temperature for 4 hours, then heated to 550°C at a rate of 2°C and held at that temperature for 10 hours. The sintered product was crushed, sieved, and purified by NaCl. 3.95 Fe 2.8 Mn 0.1 A (PO4)2P2O7 / C positive electrode active material was obtained. Here, the carbon content was 2% based on the total mass of the positive electrode active material, and the median diameter D v 50 was 3.0 μm, and the amount of residual alkali in the positive electrode active material was 0.2%.

[0177] 2) Manufacturing of positive electrode sheets 2.5 wt% polyvinylidene fluoride binder was completely dissolved in N-methylpyrrolidone (NMP), 2.0 wt% Super P, 1.0 wt% single-walled carbon nanotubes, and 94.5 wt% of the above positive electrode active material were added and stirred uniformly to obtain a positive electrode slurry. The slurry was uniformly applied to the surface of a current collector aluminum foil and then transferred to a vacuum drying oven for complete drying. The dried sheet was roll-pressed and punched to obtain a positive electrode sheet. Here, the compaction density of the positive electrode film layer was 1.9 g / cm. 3 The sheet resistance was 0.3 Ω·cm.

[0178] 3) Manufacturing of negative electrode sheets Single-walled carbon nanotubes and sodium carboxymethyl cellulose (CMC) were added to deionized water in a mass ratio of 1:0.4 and stirred until a uniform slurry was formed. The slurry was then applied to the surface of a negative electrode current collector copper foil, which was then transferred to a vacuum drying oven for complete drying and then punched out to obtain a negative electrode sheet with a negative electrode-free structure. Here, the thickness of the primer layer was 20 μm and the areal density was 25 g / m. 2 It was.

[0179] 4) Electrolyte In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), sodium hexafluorophosphate NaPF6, a sodium salt, was dissolved in ethylene glycol dimethyl ether (DME), an organic solvent, and the solution was stirred uniformly to obtain an electrolyte solution with a sodium salt concentration of 1.5 mol / L.

[0180] 5) Separator A polypropylene film was used as a separator.

[0181] 6) Battery manufacturing The positive electrode sheet, separator, and negative electrode sheet were stacked in order with the separator between the positive and negative electrode sheets to separate them, then wound to obtain a bare cell. A tab was welded to the bare cell, which was then placed in an aluminum case and baked at 80°C to remove water. The case was then immediately filled with electrolyte and sealed to obtain an uncharged battery. The uncharged battery was then left to stand, and then subjected to processes such as hot pressing, cold pressing, chemical formation, molding, and capacity testing to obtain the negative electrode-free sodium secondary battery product of Example 7.

[0182] Examples 8 to 10 The batteries of Examples 8 to 10 were manufactured using the same method as the battery of Example 1, except that the x value of Na, the y value of Fe, or the z value of Mn in the positive electrode active material was adjusted, and the specific parameters are as shown in Table 1.

[0183] Example 11 The battery of Example 11 was manufactured in the same manner as the battery of Example 1, except that Fe in the positive electrode active material of Example 8 was changed to Mn. Specific parameters are as shown in Table 1.

[0184] Example 12 The battery of Example 12 was manufactured using the same method as that of Example 8, except that Fe in the positive electrode active material of Example 8 was adjusted to Mn, and Mn in the positive electrode active material of Example 8 was adjusted to Co, and the specific parameters are as shown in Table 1.

[0185] Comparative Example 1 The battery of Comparative Example 1 was manufactured in the same manner as the battery of Example 1, except that the manufacturing method of the positive electrode active material was adjusted. The specific manufacturing method is as follows.

[0186] 1) Manufacturing of positive electrode active material Sodium pyrophosphate, ferrous oxalate, and ammonium dihydrogen phosphate were dissolved in deionized water in a molar ratio of 1:3:2 and stirred continuously at room temperature for 30 minutes to obtain a mixed slurry. The mixed slurry was sanded to an average particle size of 0.2 μm, and then an aqueous glucose solution was added and mixed and milled for 10 minutes 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 powder precursor. Finally, the mixture was heated to 320°C at a 2°C rate in a N2 atmosphere and held at that temperature for 4 hours, then heated to 550°C at a 2°C rate and held at that temperature for 10 hours. The sintered product was crushed, sieved, and purified to obtain Na4Fe3(PO4)2P2O. 7 / C A positive electrode active material was obtained. Here, the carbon content was 2% based on the total mass of the positive electrode active material, and the median diameter D v 50 was 3.0 μm, and the amount of residual alkali in the positive electrode active material was 0.6%.

[0187] 2) Manufacturing of positive electrode sheets 2.5 wt% polyvinylidene fluoride binder was completely dissolved in N-methylpyrrolidone (NMP), 2.0 wt% Super P, 1.0 wt% single-walled carbon nanotubes, and 94.5 wt% of the above positive electrode active material were added and stirred uniformly to obtain a positive electrode slurry. The slurry was uniformly applied to the surface of a current collector aluminum foil and then transferred to a vacuum drying oven for complete drying. The dried sheet was roll-pressed and punched to obtain a positive electrode sheet. Here, the compaction density of the positive electrode film layer was 1.9 g / cm. 3 The sheet resistance was 0.7 Ω·cm.

[0188] 3) Manufacturing of negative electrode sheets Single-walled carbon nanotubes and sodium carboxymethyl cellulose (CMC) were added to deionized water in a mass ratio of 1:0.4 and stirred until a uniform slurry was formed. The slurry was then applied to the surface of a negative electrode current collector copper foil, which was then transferred to a vacuum drying oven for complete drying and then punched out to obtain a negative electrode sheet with a negative electrode-free structure. Here, the thickness of the primer layer was 20 μm and the areal density was 25 g / m. 2 It was.

[0189] 4) Electrolyte In an argon atmosphere glove box (H2O<0.1 ppm, O2<0.1 ppm), sodium hexafluorophosphate NaPF6, a sodium salt, was dissolved in ethylene glycol dimethyl ether (DME), an organic solvent, and the solution was stirred uniformly to obtain an electrolyte solution with a sodium salt concentration of 1.5 mol / L.

[0190] 5) Separator A polypropylene film was used as a separator.

[0191] 6) Battery manufacturing The positive electrode sheet, separator, and negative electrode sheet were stacked in order with the separator between the positive and negative electrode sheets to separate them, then wound to obtain a bare cell. A tab was welded to the bare cell, which was then placed in an aluminum case and baked at 80°C to remove water. The case was then immediately filled with electrolyte and sealed to obtain an uncharged battery. The uncharged battery was then left to stand, and then went through processes such as hot pressing, cold pressing, chemical formation, molding, and capacity testing to obtain the negative electrode-free sodium secondary battery product of Comparative Example 1.

[0192] Comparative Example 2 The battery of Comparative Example 2 was manufactured using the same method as the battery of Comparative Example 1, except that carbon was not included in the positive electrode active material. Specific parameters are as shown in Table 1.

[0193] Comparative Examples 3 and 4 Comparative Examples 3 and 4 were manufactured in the same manner as Comparative Example 1 except that different contents of Mn element were introduced into the positive electrode active material and the content of Fe element was adjusted. The specific parameters were as shown in Table 1.

[0194] Comparative Example 5 Comparative Example 5 was manufactured in the same manner as Comparative Example 1 except that the Fe element in the positive electrode active material was replaced with the Mn element. Specific parameters are as shown in Table 1.

[0195] 2. Performance measurement 1. Measurement of positive electrode active material 1) Measurement of median diameter Dv50 Referring to GB / T 19077-2016, particle size distribution laser diffraction method, 0.1g to 0.13g of test positive electrode active material sample was weighed into a 50mL beaker, 5g of anhydrous ethanol was added, and a 2.5mm stir bar was inserted and sealed with plastic wrap. The sample was sonicated for 5 minutes, then transferred to a magnetic stirrer and stirred at 500 rpm for at least 20 minutes. Two samples were extracted from each batch and measured. Measurements were performed using a Malvern Mastersizer 2000E laser particle size analyzer.

[0196] 2) Measurement of residual alkali content Measurement principle (acid-base titration method) NaHCO3 and Na in the positive electrode active material + The titration was performed with a hydrochloric acid standard solution, using a pH electrode as the indicator electrode. The endpoint was determined by the jump in potential. Reference can be made to GB / T 9725-2007. Specifically, for the measurement of NaHCO3, a Metrohm 905 Titrando potentiometric titrator was used. The positive electrode active material was dissolved in deionized water, and the aqueous solution of the positive electrode active material was titrated with the titration standard. 0.1 mL of the titration standard was added dropwise, and the potential or pH value was recorded. The titration was stopped when the potential or pH value no longer changed significantly. The volume of the added titration standard and the measured potential or pH value were recorded, and the titration endpoint was determined by the graphical method or the second-order differential method, and the titration volume of the titration standard was determined. The calculated mass of NaHCO3 was divided by the mass of the positive electrode active material, and the mass content was determined as the residual alkalinity of NaHCO3 in the positive electrode active material.

[0197] 2. Measurement of the performance of the positive electrode sheet 1) Compaction According to the embodiment of the present application, the compaction density PD of the positive electrode film layer is calculated by the mass per unit area (g / cm 2 ) and the thickness (cm) of the positive electrode film layer on one side (number of samples > 14). Specifically, the compaction density of the positive electrode sheet PD = mass per unit area of ​​the positive electrode film layer on one side (g / cm 2 ) / thickness of the positive electrode film layer (cm).

[0198] 2) Sheet resistance The baked positive electrode film layers on the left, middle, and right sides of the positive electrode sheet were cut into small circular sheets with a diameter of 3 mm. The IEST sheet resistance meter was turned on, the probe was placed in the appropriate position, the "start" button was pressed, and the reading was read once it stabilized. Two points were measured for each small circular sheet, and the average of the six measurements was finally calculated as the sheet resistance of the sheet.

[0199] 3. Battery performance measurement 1) Measurement of initial discharge capacity The initial discharge capacity was measured as follows: At 25°C, the fabricated battery was charged to 3.75 V at a constant current of 1 C, then charged at a constant voltage of 3.75 V until the current decreased to 0.05 C, and then discharged to 1.5 V at a constant current of 1 C to obtain the initial discharge capacity (Cd1).

[0200] 2) Measurement of initial coulombic efficiency The initial coulombic efficiency was measured as follows: At 25°C, the fabricated battery was charged to 3.75 V at a constant current of 1 / 5 C, and then charged at a constant voltage of 3.75 V until the current decreased to 0.05 C to obtain the initial charge capacity (Cc1). The battery was then discharged to 1.5 V at a constant current of 1 / 5 C to obtain the initial discharge capacity (Cd1). The battery coulombic efficiency was calculated using the following formula: initial coulombic efficiency of battery = initial discharge capacity (Cd1) / initial charge capacity (Cc1). The measurement procedures for the comparative example and other examples were the same as above.

[0201] 3) Measurement of battery cycle capacity retention rate The battery capacity retention rate was measured as follows: At 25°C, the fabricated battery was charged to 3.75 V at a constant current of 1 C, then charged at a constant voltage of 3.75 V until the current decreased to 0.05 C, and then discharged to 1.5 V at a constant current of 1 C. The resulting capacity was designated as the initial capacity (C0). The same battery was repeated, and the discharge capacity (Cn) after n cycles was recorded. The battery capacity retention rate after each cycle, Pn = Cn / C0 × 100%, was calculated. A graph of battery capacity retention rate versus cycle number was obtained, with 100 values ​​(P1, P2, ... 100) plotted on the vertical axis and the corresponding cycle number on the horizontal axis. In this measurement process, n = 1 for the first cycle, n = 2 for the second cycle, ... 100 for the 100th cycle. The battery capacity retention rate data in Table 2 for the Examples or Comparative Examples was measured after 100 cycles under the above measurement conditions, i.e., the value P100. The measurement process for the comparative example and other examples was the same as above.

[0202] 3. Analysis of the test results of each example and comparative example According to the above method, the batteries of the examples and comparative examples were manufactured, and the performance parameters were measured. The results are shown in Tables 1 and 2 below.

[0203] [Table 1-1] [Table 1-2]

[0204] [Table 2]

[0205] As can be seen from the above results, all of Examples 1 to 12 include a positive electrode active material, and the positive electrode active material is a carbon composite polyanion compound, and the positive electrode active material has the following general formula:

[0206] [ka] In the formula, R contains 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 contains 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.

[0207] As can be seen from the comparison between Examples 1 to 10 and Comparative Example 1, and between Examples 11 to 12 and Comparative Example 5, compared with the conventional positive electrode active material, the positive electrode active material containing the carbon composite polyanion compound in the examples of the present application provides Na vacancies, Fe vacancies, or Mn vacancies, thereby further reducing the residual alkali amount of the positive electrode active material while maintaining the high discharge capacity and Coulomb efficiency of the positive electrode active material, improving the processability of the positive electrode active material, reducing the sheet resistance of the positive electrode sheet, and improving the cycle performance of the battery.

[0208] As can be seen from Examples 1 to 6, due to the presence of sodium vacancies and / or iron vacancies, the residual alkali amount of the positive electrode active material can be significantly reduced, and the battery will have a high cycle capacity retention rate. By controlling to 0 < x ≦ 0.2 and / or 0 < y - z ≦ 0.3, the contents of sodium vacancies and iron vacancies can be controlled, and the positive electrode active material can simultaneously maintain a high discharge capacity and Coulomb efficiency.

[0209] As can be seen from the comparison between Examples 1 to 6 and Comparative Example 2, compared with the polyanion compound not containing carbon, the positive electrode active material of the examples of the present application is a carbon composite polyanion compound and can provide Na vacancies or Fe vacancies, reducing the residual alkali amount of the positive electrode active material and the sheet resistance of the positive electrode sheet, increasing the tap density of the film layer of the positive electrode sheet, increasing the initial Coulomb efficiency of the battery and the capacity retention rate after 100 cycles, and contributing to improving the battery performance.

[0210] As can be seen from the comparison of Examples 7 and 8 with Comparative Example 3, and Example 10 with Comparative Example 4, compared to conventional Mn-doped iron-based polyanion compounds, the positive electrode active materials of the examples of the present application can provide Na vacancies or Fe vacancies, which contributes to reducing the amount of residual alkali in the positive electrode active material and the sheet resistance of the positive electrode sheet.

[0211] As can be seen from the comparison between Example 12 and Comparative Example 5, compared with conventional manganese-based polyanion compounds, the polyanion compounds in the positive electrode active materials of the Examples of the present application are doped with manganese, and the positive electrode active materials can provide Na vacancies and Mn vacancies, which reduces the residual alkali content of the positive electrode active material and the sheet resistance of the positive electrode sheet, increases the compaction degree of the membrane layer of the positive electrode sheet, and improves the initial coulombic efficiency of the battery and the capacity retention rate after 100 cycles, thereby contributing to improving battery performance.

[0212] As can be seen from a comparison between Example 4 and Example 3, the example of the present application simultaneously provides Na vacancies and Fe vacancies, further reducing the amount of residual alkali in the positive electrode active material and the sheet resistance of the positive electrode sheet, thereby contributing to an improvement in the capacity retention rate after 100 battery cycles.

[0213] As can be seen from a comparison between Example 8 and Example 4, the polyanion compound in the positive electrode active material of the example of the present application is doped with manganese, which contributes to further improvement in the initial discharge capacity and initial coulombic efficiency of the battery.

[0214] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and all embodiments that have substantially the same technical ideas and provide the same functions and effects within the scope of the technical solution of the present application are included in the technical scope of the present application. Furthermore, various modifications that a person skilled in the art may make to the embodiments and other forms formed by combining some of the components of the embodiments are also included in the scope of the present application, as long as they do not deviate from the gist of the present application. [Explanation of symbols]

[0215] 1 battery pack 2 Upper Box 3 Lower Box 4 Battery Module 5 Secondary battery cells 51 cases 52 Electrode assembly 53 Lid plate

Claims

1. It is a carbon complex polyanion compound having the following general formula: 【Chemistry 1】 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.

2. The positive electrode active material according to claim 1 , wherein 0<x≦0.5, and optionally 0.01≦x≦0.

2.

3. 3. The positive electrode active material according to claim 1, wherein 0<y−z≦0.

3.

4. 3. The positive electrode active material according to claim 1, wherein 0<x≦0.5 and 0<z≦y≦0.

5.

5. 5. The positive electrode active material according to claim 1, wherein R comprises one or more of Fe, Co, Ni, and Mn, and M comprises one or more of Mg, Al, Sc, Ti, V, Cr, Mn, Si, and Co.

6. The median diameter D of the positive electrode active material ｖ 50 is 1.0 μm≦D ｖ 6. The positive electrode active material according to claim 1, wherein the thickness is 50≦10 μm, and optionally 1.5 μm to 5.0 μm.

7. The positive electrode active material NaHCO ３ The amount of residual alkali is 0.05% to 2.5% based on the total mass of the positive electrode active material, and optionally 0.05% to 0.5%. The positive electrode active material according to any one of claims 1 to 6.

8. A method for producing a positive electrode active material, A step of dissolving raw materials including a sodium source, an R source, a phosphorus source, and a carbon source in deionized water and uniformly mixing them to obtain a mixed slurry, wherein the raw materials optionally further include an M source; and drying the mixed slurry and then calcining it to produce the positive electrode active material, wherein the positive electrode active material is a carbon complex polyanion compound having the following general formula: 【Chemistry 2】 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; and 0≦x≦0.5, 0≦y≦0.5, 0≦z<x+y, and x and y are not simultaneously 0.

9. The method according to claim 8, wherein 0<y−z≦0.

3.

10. The step of drying and then firing the mixed slurry includes: drying the mixed slurry to obtain a precursor powder; and calcining the precursor powder at a calcination temperature of 400° C. to 650° C. for a calcination time of 5 hours to 15 hours to produce the positive electrode active material.

11. The method according to claim 10, wherein the firing temperature is 500°C to 600°C.

12. The method according to claim 10 or 11, wherein the baking time is 8 hours to 13 hours.

13. 13. The method of claim 8, wherein the R source comprises 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.

14. 14. The method of claim 8, wherein the M source comprises 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.

15. 15. The method of claim 13 or 14, wherein 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.

16. 16. A positive electrode sheet comprising a positive electrode film layer, the positive electrode film layer comprising a binder, at least one of a one-dimensional conductive material and a zero-dimensional conductive material, and the positive electrode active material according to claim 1 or a positive electrode active material manufactured by the manufacturing method according to claim 8.

17. The positive electrode sheet according to claim 16, wherein the mass content of the binder is 1.5% to 3%, and optionally 2.0% to 2.5%, based on the total mass of the positive electrode membrane layer.

18. the one-dimensional conductive material comprises one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, and / or The mass content of the one-dimensional conductive material is 0.2% to 1% based on the total mass of the positive electrode film layer, and optionally 0.5% to 0.9%. The positive electrode sheet according to claim 16 or 17.

19. The zero-dimensional conductive material comprises one or more of Super P, Ketjen Black, Acetylene Black; and / or The mass content of the zero-dimensional conductive material is 1% to 3% based on the total mass of the positive electrode film layer, and optionally 2% to 2.8%. The positive electrode sheet according to any one of claims 16 to 18.

20. A secondary battery comprising the positive electrode sheet according to any one of claims 16 to 19.

21. 21. The secondary battery according to claim 20, wherein the secondary battery is a negative electrode-free sodium secondary battery.

22. 22. The secondary battery according to claim 20 or 21, wherein the secondary battery further includes a negative electrode sheet, the negative electrode sheet including a negative electrode current collector and an undercoat layer provided on at least one surface of the negative electrode current collector, the undercoat layer including one or more of carbon nanotubes, graphite, graphene, silver composite carbon nanoparticles, and tin composite carbon nanoparticles.

23. The surface density of the primer layer is 5 g / m ２ ~50g / m ２ The secondary battery according to claim 22,

24. 24. The secondary battery according to claim 22, wherein the thickness of the undercoat layer is 2 μm to 100 μm.

25. An electrical device comprising a secondary battery according to any one of claims 20 to 24.

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