Positive electrode active material, preparation method thereof, positive electrode plate, battery and electric equipment

Abstract

Relates to a positive active material and a preparation method thereof, a positive pole piece, a battery and electric equipment, the positive active material comprises Na4-aAbFe3-cBd (PO4) 2-eDf (P2O7), A comprises at least one of Li or K, B comprises a metal element, D comprises at least one of halogen anions, silicate ions, sulfate ions or borate ions,-0.12 < = a < = 0.12, b > = 0, 0 < = c < = 0.3, d > = 0, f > 0, and 0 < e < = 0.1.

Description

Positive electrode active material and preparation method, positive electrode sheet, battery and electrical equipment Technical Field

[0001] The present application relates to the field of batteries, and in particular to positive electrode active materials and preparation methods, as well as positive electrode sheets, batteries, and electrical equipment. Background Art

[0002] Batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power stations, but are also widely used in electric vehicles such as electric bicycles, electric motorcycles, and electric vehicles, as well as in military equipment and aerospace. Sodium-ion batteries are a type of battery. The Na4Fe3(PO4)2P2O7 cathode active material in sodium-ion batteries is abundant in resources, environmentally friendly, and easy to mass-produce, making it a popular cathode active material for sodium-ion batteries. However, this material has poor intrinsic conductivity, which affects its specific capacity and reduces the battery's energy density and rate performance.

[0003] Summary of the Invention

[0004] In view of the technical problems existing in the background technology, the present application provides a positive electrode active material, which can increase the gram capacity of the positive electrode active material and improve the energy density and rate performance of the battery.

[0005] The first aspect of the present application provides a positive electrode active material, comprising Na 4-a A b Fe 3-c B d (PO4) 2-e D f (P2O7), wherein A includes at least one of Li or K, B includes a metal element, D includes at least one of a halogen anion, a silicate ion, a sulfate ion or a borate ion, -0.12≤a≤0.12, b≥0, 0≤c≤0.3, d≥0, f>0, 0<e≤0.1.

[0006] The positive electrode active material proposed in this application, when only anion D is doped in the positive electrode active material, the anion can replace part of the phosphate ions, thereby regulating the local chemical bonds and electron distribution of the positive electrode active material, thereby improving the intrinsic conductivity of the positive electrode active material, increasing the specific capacity of the positive electrode active material, and improving the energy density and rate performance of the battery. When the positive electrode active material is simultaneously doped with anion D and at least one of cations A and B, the anion and cation synergistically can improve the purity of the positive electrode active material, improve the stability of the positive electrode active material structure, improve the ionic conductivity and electronic conductivity of the positive electrode active material, improve the phase purity, increase the specific capacity of the positive electrode active material, and improve the energy density and rate performance of the battery.

[0007] According to some embodiments of the present application, 1≤f / e≤3. This improves the intrinsic conductivity of the positive electrode active material, increases the gram capacity of the material, and improves the energy density and rate performance of the battery.

[0008] According to some embodiments of the present application, 0<f≤0.3, thereby increasing the intrinsic conductivity of the positive electrode active material and increasing the gram capacity of the positive electrode active material.

[0009] According to some embodiments of the present application, 0<f≤0.15, thereby increasing the intrinsic conductivity of the positive electrode active material and increasing the gram capacity of the positive electrode active material.

[0010] According to some embodiments of the present application, 0<e≤0.05, thereby increasing the intrinsic conductivity of the positive electrode active material and increasing the gram capacity of the positive electrode active material.

[0011] According to some embodiments of the present application, 3.88≤4-a+b≤4.12, thereby improving the stability of the positive electrode active material.

[0012] According to some embodiments of the present application, 2.7≤3-c+d≤3. This can improve the phase purity of the positive electrode active material, thereby increasing the material's gram capacity and improving the energy density of the battery.

[0013] According to some embodiments of the present application, B includes at least one of Al, Mg, Ca, Ni, Co, Mn, Cu, Zn, Cr, V, Ti, Sr, Y, Mo, Nb, or W.

[0014] According to some embodiments of the present application, D includes at least one of the halogen anions, the silicate ions, or the borate ions.

[0015] According to some embodiments of the present application, the halogen anion includes F - or Cl - .

[0016] Therefore, by doping the positive electrode active material with the above-mentioned types of anions and cations, the ionic conductivity and electronic conductivity of the positive electrode active material are improved, the purity of the positive electrode active material is improved, the gram capacity of the material is increased, and the energy density and rate performance of the battery are improved.

[0017] According to some embodiments of the present application, D includes any two of the halogen anions, silicate ions, sulfate ions, or borate ions, and 1≤f / e≤3. This improves the intrinsic conductivity of the positive electrode active material, increases the material's specific capacity, and improves the energy density and rate performance of the battery.

[0018] According to some embodiments of the present application, 0≤b≤0.1.

[0019] According to some embodiments of the present application, 0.05≤c≤0.2.

[0020] According to some embodiments of the present application, 0≤d≤0.3, c≥d.

[0021] Therefore, by making the values ​​of b, c and d within the above ranges, the ionic conductivity and electronic conductivity of the positive electrode active material are improved, the purity of the positive electrode active material is improved, the gram capacity of the material is increased, and the energy density and rate performance of the battery are improved.

[0022] According to some embodiments of the present application, the positive electrode active material further comprises carbon, thereby improving the phase purity and conductivity of the positive electrode active material and enhancing the energy density and rate performance of the battery.

[0023] According to some embodiments of the present application, the carbon accounts for 0.5% to 4% of the total mass of the positive electrode active material, thereby improving the phase purity and conductivity of the positive electrode active material and enhancing the energy density and rate performance of the battery.

[0024] According to some embodiments of the present application, the carbon accounts for 1% to 3% of the total mass of the positive electrode active material, thereby improving the phase purity and conductivity of the positive electrode active material and enhancing the energy density and rate performance of the battery.

[0025] According to some embodiments of the present application, the volume average particle size D of the positive electrode active material is v 50 is 0.7μm-7μm.

[0026] According to some embodiments of the present application, the volume average particle size D of the positive electrode active material is v 50 is 1.2μm-4μm.

[0027] According to some embodiments of the present application, the BET specific surface area of ​​the positive electrode active material is 4 m 2 / g-12m 2 / g.

[0028] According to some embodiments of the present application, the BET specific surface area of ​​the positive electrode active material is 5.5 m 2 / g-10m 2 / g.

[0029] Therefore, by making the volume average particle size and BET specific surface area of ​​the positive electrode active material within the above range, the contact area between the positive electrode active material particles can be increased, the conductive electron capacity of the positive electrode sheet can be improved, and at the same time, the transmission path of sodium ions can be shortened, thereby improving the rate performance of the material.

[0030] A second aspect of the present application provides a method for preparing a positive electrode active material, comprising: mixing a sodium source, an iron source, a phosphorus source, and a D source to obtain a precursor material; and sintering the precursor material to obtain the positive electrode active material. The prepared positive electrode active material has a high specific capacity, thereby improving the energy density and rate performance of a battery containing the positive electrode active material.

[0031] According to some embodiments of the present application, the method further includes: adding source A and / or source B to the precursor material. Thus, the synergistic effect of anions and cations can improve the purity of the positive electrode active material, improve the structural stability of the positive electrode active material, improve the ionic conductivity and electronic conductivity of the positive electrode active material, increase the specific capacity of the positive electrode active material, and improve the energy density and rate performance of the battery.

[0032] According to some embodiments of the present application, the method further includes: adding a first carbon source to the precursor material, thereby improving the phase purity and conductivity of the positive electrode active material and enhancing the energy density and rate performance of the battery.

[0033] According to some embodiments of the present application, the method further includes: mixing the positive electrode active material with a second carbon source and sintering the mixture to form a carbon coating layer on the surface of the positive electrode active material. This can improve the conductivity of the positive electrode active material and enhance the energy density and rate performance of the battery.

[0034] According to some embodiments of the present application, the sintering includes a first sintering and a second sintering, the temperature of the first sintering is 200° C.-400° C., and the holding time is 3 h-5 h.

[0035] According to some embodiments of the present application, the sintering includes a first sintering and a second sintering, the temperature of the second sintering is 450° C.-650° C., and the holding time is 8 h-15 h.

[0036] Therefore, by setting the temperature and holding time of the first sintering and the second sintering within the above ranges, the materials can react sufficiently with each other, thereby improving the phase purity and crystallinity of the positive electrode active material.

[0037] In a third aspect, the present application provides a positive electrode plate comprising the positive electrode active material provided in the first aspect of the present application or the positive electrode active material prepared by the method provided in the second aspect of the present application, thereby improving the energy density and rate performance of a battery containing the positive electrode plate.

[0038] The fourth aspect of the present application provides a battery comprising the positive electrode sheet provided in the third aspect of the present application, thereby having excellent energy density and rate performance.

[0039] The fifth aspect of the present application provides an electrical device, comprising the battery provided in the fourth aspect of the present application, thereby increasing the service life of the electrical device.

[0040] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become obvious from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0042] FIG1 is a schematic structural diagram of a battery according to an embodiment of the present application;

[0043] FIG2 is a schematic structural diagram of a battery module according to an embodiment of the present application;

[0044] FIG3 is a schematic structural diagram of a battery pack according to an embodiment of the present application;

[0045] FIG4 is an exploded view of FIG3 ;

[0046] FIG5 is a schematic diagram of an embodiment of an electric device using a battery as a power source.

[0047] Explanation of reference numerals: 1: secondary battery; 2: battery module; 3: battery pack; 4: upper case; 5: lower case. DETAILED DESCRIPTION

[0048] The following embodiments of the technical solution of the present application are described in detail. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only used as examples and are not intended to limit the scope of protection of the present application.

[0049] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0050] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0051] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0052] 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.

[0053] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may 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), etc.

[0054] With the technological advancements and increasing demand for electric vehicles and rechargeable mobile devices, battery research, as a representative of the new energy sector, has also seen rapid growth. Sodium-ion batteries offer significant price advantages over traditional lithium-ion batteries and hold broad application prospects in large-scale energy storage systems.

[0055] The iron-based polyanionic phosphate cathode material Na4Fe3(PO4)2P2O7 has become a popular cathode active material for sodium-ion batteries due to its abundant resources, environmental friendliness, ease of large-scale production, open sodium ion diffusion channels, and good thermal and cycling stability. However, the material's poor intrinsic conductivity limits its specific capacity, reducing the battery's energy density and rate capability.

[0056] The positive electrode active material proposed in this application can be doped with anions or anions and cations at the same time. When only anions are doped in the material, the anions can replace some phosphate ions, thereby adjusting the local chemical bonds and electron distribution of the positive electrode active material, improving the intrinsic conductivity of the positive electrode active material, increasing the gram capacity of the positive electrode active material, and improving the energy density and rate performance of the battery. When anions and cations are doped in the positive electrode active material at the same time, the synergistic effect of anions and cations can improve the purity of the positive electrode active material, improve the stability of the positive electrode active material structure, improve the ionic conductivity and electronic conductivity of the positive electrode active material, increase the gram capacity of the positive electrode active material, and improve the energy density and rate performance of the battery.

[0057] The positive electrode active material disclosed in the embodiments of the present application is suitable for sodium ion batteries, and the battery disclosed in the embodiments of the present application can be used in electrical equipment that uses the battery as a power source or various energy storage systems that use the battery as an energy storage element. Electrical equipment may include but is not limited to mobile phones, tablets, laptops, electric toys, power tools, battery cars, electric cars, ships, spacecraft, etc. Among them, electric toys may include fixed or mobile electric toys, for example, game consoles, electric car toys, electric ship toys and electric airplane toys, etc., and spacecraft may include airplanes, rockets, space shuttles and spacecraft, etc.

[0058] The first aspect of the present application provides a positive electrode active material, wherein the positive electrode active material comprises Na 4-a A b Fe 3-c B d (PO4) 2-e D f (P2O7), wherein A includes at least one of Li or K, B includes a metal element, D includes at least one of a halogen anion, a silicate ion, a sulfate ion or a borate ion, -0.12≤a≤0.12, b≥0, 0≤c≤0.3, d≥0, f>0, 0<e≤0.1.

[0059] The positive electrode active material proposed in this application, when the positive electrode active material contains anion D, D can replace part of the phosphate ion, because the ionic radius of D is different from the ionic radius of the phosphate ion, doping D can adjust the local chemical bond length and electron distribution of the positive electrode active material, adjust the structural band gap of the material, thereby improving the intrinsic conductivity of the positive electrode active material, increasing the gram capacity of the positive electrode active material, and improving the energy density and rate performance of the battery. On this basis, when the positive electrode active material is further doped with cation A at the Na position, when A is a K ion, since the ionic radius of the K ion is greater than the ionic radius of the Na ion, the above-mentioned content of K ions doped at the Na position will cause the lattice structure to be slightly deformed, expand the Na ion transmission channel, facilitate the rapid deintercalation of Na ions, reduce the Na ion migration barrier, thereby increasing the ionic conductivity and improving the battery rate performance. When A is a lithium ion, the doping of lithium ions can suppress the generation of heterogeneous phases such as sodium iron pyrophosphate and sodium iron phosphate, promote the generation of polyanion phosphate products, thereby improving the phase purity of the positive electrode material, improving the gram capacity of the material, and improving the energy density of the battery. When the metal element B is doped at the Fe site at the above content, it can also inhibit the formation of impurities such as sodium iron pyrophosphate and sodium iron phosphate, promote the formation of polyanion phosphate products, thereby improving the physical purity of the positive electrode material, increasing the specific capacity of the material, and improving the energy density of the battery. In addition, doping the metal element B at the Fe site will also improve the ionic conductivity and electronic conductivity of the material, reduce the electron transfer impedance in the battery, reduce the battery polarization, and improve the reversibility of sodium ion insertion and extraction, thereby improving the rate performance of the battery. The coordinated doping of anions and cations can improve the purity of the positive electrode active material, improve the structural stability of the positive electrode active material, improve the ionic conductivity and electronic conductivity of the positive electrode active material, improve the phase purity, increase the specific capacity of the positive electrode active material, and improve the energy density and rate performance of the battery. When the positive electrode active material is simultaneously doped with element A at the Na site, element B at the Fe site, and element D at the anion site, the three synergistically construct a high-entropy structure compatible with anions and cations, improving the sodium storage performance of the material, increasing the specific capacity of the positive electrode active material, and improving the energy density and rate performance of the battery.

[0060] In the present application, a high entropy structure refers to a structure with a high entropy value formed by simultaneously doping multiple elements in a material.

[0061] It should be noted that the ratio of each element in the positive electrode active material in this application refers to the ratio of each element in the positive electrode active material before the positive electrode active material is made into a positive electrode sheet and assembled into a battery for formation. Those skilled in the art will understand that in the positive electrode sheet, battery or electrical equipment, due to the formation and circulation processes, some elements will be consumed. Even if the corresponding element ratio of the positive electrode active material is measured to be outside the above range, it should fall within the scope of this application. For example, batteries appearing on the market usually undergo cycle aging after assembly. Therefore, in the positive electrode active material, the a may be a>0.12, and / or the c may be c>0.3, and / or the atomic ratio of the P element and the O element may be a non-integer ratio.

[0062] According to some embodiments of the present application, the compound Na 4-a A b Fe 3-c B d (PO4) 2-e D f In (P2O7), a may be -0.12≤a≤0.12, for example, -0.12, -0.1, -0.08, -0.06, -0.04, -0.02, 0, 0.02, 0.04, 0.06, 0.08, 0.1 or 0.12, or may be within a range consisting of any of the above values. Thus, the positive electrode active material includes this content of sodium ions, so that the battery has a higher capacity.

[0063] According to some embodiments of the present application, the compound Na 4-a A b Fe 3-c B d (PO4) 2-e D f (P2O7) In b, b≥0 can be taken, For example, it can be 0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18, 0.2, 0.25, 0.3, 0.35 or 0.4, etc., or it can be a range composed of any of the above numerical values. Thus, by doping the A ions of this content at the Na site of the positive electrode active material, since the A ion radius is larger than the Na ion, the A ions of this content are doped at the Na site, which causes the lattice structure to be slightly deformed, thereby expanding the Na ion transport channel, which is conducive to the rapid deintercalation of Na ions. At the same time, after the A ions of this content are doped at the Na site, the Na ion migration barrier can be reduced, thereby increasing the ionic conductivity and improving the battery rate performance.

[0064] According to some embodiments of the present application, the compound Na 4-a A b Fe3-c B d (PO4) 2-e D f In (P2O7), a and b satisfy 3.88≤4-a+b≤4.12, and can be, for example, 3.88, 3.9, 3.92, 3.94, 3.96, 3.98, 4, 4.02, 4.04, 4.06, 4.08, 4.1, or 4.12, or any range thereof. This reduces distortion of the positive electrode material and improves its stability.

[0065] According to some embodiments of the present application, the compound Na 4-a A b Fe 3-c B d (PO4) 2-e D f In (P2O7), c can be 0≤c≤0.3, for example, 0, 0.05, 0.1, 0.15, 0.2, 0.25, or 0.3, or a range consisting of any of the above values. Thus, including this content of Fe in the positive electrode active material can improve the thermal stability of the positive electrode active material. According to some specific embodiments of the present application, 0.05≤c≤0.2.

[0066] According to some embodiments of the present application, the compound Na 4-a A b Fe 3-c B d (PO4) 2-e D f In (P2O7), d can take d≥0, for example, it can be 0, 0.05, 0.1, 0.15, 0.2, 0.25 or 0.3, etc., or it can be a range composed of any of the above numerical values. Thus, by doping the Fe site in the above-mentioned positive active material with the metal element B of this content, the formation of impurities such as sodium iron pyrophosphate and sodium iron phosphate can be suppressed, and the formation of polyanion phosphate products can be promoted, thereby improving the physical purity of the positive active material, improving the gram capacity of the material, and improving the energy density of the battery. In addition, the metal element B doped at the Fe site of this content can also improve the ionic conductivity and electronic conductivity of the material, reduce the electron transfer impedance in the battery, reduce the battery polarization, improve the reversibility of sodium ion insertion and extraction, and thus improve the rate performance of the battery. According to some specific embodiments of the present application, 0≤d≤0.3.

[0067] According to some embodiments of the present application, the compound Na 4-a A b Fe 3-c B d (PO4) 2-e D fIn (P2O7), c and d satisfy c≥d, 2.7≤3-c+d≤3, and can be, for example, 2.7, 2.75, 2.8, 2.85, 2.9, 2.95, or 3, or can be within a range consisting of any of the above values. Thus, the structural stability of the positive electrode active material can be improved.

[0068] According to some embodiments of the present application, the compound Na 4-a A b Fe 3-c B d (PO4) 2-e D f In (P2O7), f and e satisfy 1≤f / e≤3, and can be, for example, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, or 3, or can be within a range consisting of any of the above values. Thus, the intrinsic conductivity of the positive electrode active material is improved, the specific capacity of the material is increased, and the energy density and rate performance of the battery are improved.

[0069] According to some embodiments of the present application, the compound Na 4-a A b Fe 3-c B d (PO4) 2-e D f In (P2O7), f can be 0 < f ≤ 0.3, for example, 0.05, 0.1, 0.15, 0.2, 0.25, or 0.3, or any range thereof. This improves the intrinsic conductivity of the positive electrode active material and increases the specific capacity of the positive electrode active material. According to some specific embodiments of the present application, 0 < f ≤ 0.15.

[0070] According to some embodiments of the present application, the compound Na 4-a A b Fe 3-c B d (PO4) 2-e D f In (P2O7), e can be 0<e≤0.1, for example, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1, or a range consisting of any of the above values. Thus, the intrinsic conductivity of the positive electrode active material is improved, and the gram capacity of the positive electrode active material is increased. According to some specific embodiments of the present application, 0<e≤0.05.

[0071] According to some embodiments of the present application, the compound Na 4-a A b Fe 3-c B d (PO4)2-e D f B in (P2O7) includes at least one of Al, Mg, Ca, Ni, Co, Mn, Cu, Zn, Cr, V, Ti, Sr, Y, Mo, Nb or W. Therefore, the metal element B in this composition can not only reduce the impurity phase in the positive electrode active material, but also improve the conductivity of the positive electrode active material, thereby improving the energy density and rate performance of the battery.

[0072] According to some embodiments of the present application, the compound Na 4-a A b Fe 3-c B d (PO4) 2-e D f In (P2O7), D includes at least one of a halogen anion, the silicate ion, or the borate ion. Thus, the above anions can replace part of the phosphate ions. Since the ionic radius of D is different from that of the phosphate ion, doping D can adjust the local chemical bond length and electron distribution of the positive electrode active material, adjust the structural band gap of the material, thereby improving the intrinsic conductivity of the positive electrode active material, increasing the gram capacity of the positive electrode active material, and improving the energy density and rate performance of the battery. According to some specific embodiments of the present application, the halogen anion includes F - or Cl - .

[0073] According to some embodiments of the present application, the compound Na 4-a A b Fe 3-c B d (PO4) 2-e D f When D in (P2O7) includes any two of the halogen anion, the silicate ion, the sulfate ion, or the borate ion, 1≤f / e≤3, for example, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, or 3, or a range consisting of any of the above values. Thus, the intrinsic conductivity of the positive electrode active material is improved, the gram capacity of the material is increased, and the energy density and rate performance of the battery are improved.

[0074] According to some embodiments of the present application, the positive electrode active material may further include carbon, for example, carbon may be mixed inside the positive electrode active material and / or coated on at least part of the surface of the positive electrode active material particles. Specifically, the carbon mixed inside the positive electrode active material can improve the phase purity of the material, reduce the content of impurities in the material, increase the gram capacity of the material, and also improve the conductivity of the positive electrode active material. The carbon coated on the surface of the positive electrode active material, that is, forming a carbon coating layer on the surface of the positive electrode active material particles, can not only improve the conductivity of the material, but also reduce the contact area between the positive electrode active material and the electrolyte in the battery, reduce the side reactions of the positive electrode active material, and facilitate the use of the material capacity.

[0075] According to some embodiments of the present application, based on the total mass of the positive electrode active material, the mass proportion of the carbon is 0.5%-4%, for example, it can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5% or 4%, or it can be a range composed of any of the above values. Specifically, if the carbon is mixed in the interior of the positive electrode active material, the carbon content here is the carbon content mixed in the interior of the positive electrode active material; if the carbon is coated on the surface of the positive electrode active material, the carbon content here is the carbon content formed on the surface of the positive electrode active material; if the carbon is both mixed in the interior of the positive electrode active material and coated on the surface of the positive electrode active material, the carbon content here is the sum of the carbon content mixed in the interior of the positive electrode active material and the carbon content coated on the surface of the positive electrode active material. In this application, the carbon content within the above ratio range can improve the conductivity and gram capacity of the positive electrode active material. According to some specific embodiments of the present application, based on the total mass of the positive electrode active material, the mass proportion of the carbon is 1%-3%.

[0076] According to some embodiments of the present application, the volume average particle size D of the positive electrode active material is v 50 can be 0.7μm-7μm, for example, it can be 0.7μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm or 7μm, etc., or it can be a range composed of any of the above numerical values. Thus, by making the volume average particle size of the positive electrode active material within the above range, the contact area between the positive electrode active material particles and other particles on the positive electrode sheet can be increased, the conductivity of the positive electrode sheet can be increased, the transmission path of sodium ions can be shortened, and the rate performance of the positive electrode active material can be improved. By making the volume average particle size of the positive electrode active material within the above range, the specific surface area of ​​the positive electrode active material is reduced, the amount of electrolyte added to the battery is reduced, the side reaction between the positive electrode active material and the electrolyte is reduced, the energy density of the battery is increased, and the probability of deterioration of battery performance is reduced. According to some specific embodiments of the present application, the volume average particle size D of the positive electrode active material is v50 can be 1.2μm-4μm.

[0077] In this application, D v 50 refers to the particle size corresponding to when the cumulative volume distribution percentage reaches 50%, for example, with reference to the standard GB / T 19077-2016, and is measured using a laser particle size analyzer (such as Malvern Master Size 3000).

[0078] According to some embodiments of the present application, the BET specific surface area of ​​the positive electrode active material is 4 m 2 / g-12m 2 / g, for example, it can be 4m 2 / g, 4.5m 2 / g、5m 2 / g, 5.5m 2 / g、6m 2 / g, 6.5m 2 / g、7m 2 / g, 7.5m 2 / g、8m 2 / g、8.5m 2 / g、9m 2 / g, 9.5m 2 / g、10m 2 / g, 10.5m 2 / g、11m 2 / g, 11.5m 2 / g or 12m 2 / g, etc., or can be a range composed of any of the above numerical values. Thus, by making the specific surface area of ​​the positive electrode active material within the above range, the contact area between the positive electrode active material particles and other particles on the positive electrode sheet can be increased, the conductivity of the positive electrode sheet can be increased, the transmission path of sodium ions can be shortened, and the rate performance of the positive electrode active material can be improved. By making the specific surface area of ​​the positive electrode active material within the above range, the amount of electrolyte added to the battery is reduced, the side reaction between the positive electrode active material and the electrolyte is reduced, the energy density of the battery is increased, and the probability of deterioration of battery performance is reduced. According to some specific embodiments of the present application, the BET specific surface area of ​​the positive electrode active material can be 5.5m 2 / g-10m 2 / g.

[0079] In this application, the BET specific surface area of ​​the positive electrode active material can be tested by referring to the following method: using the American Microelectronics multi-station fully automatic specific surface area and pore analyzer GeminiVII2390, take about 7g of the positive electrode active material and put it into a 9cc long tube with a bulb, degas at 200℃ for 2h, and then put it into the host for testing to obtain the BET (specific surface area) data of the positive electrode active material.

[0080] The second aspect of the present application provides a method for preparing the positive electrode active material provided in the first aspect of the present application, comprising:

[0081] S100: Mixing the sodium source, iron source, phosphorus source and D source to obtain a precursor material

[0082] According to some embodiments of the present application, a sodium source, an iron source, a phosphorus source, and a D source are mixed and added to water, stirred and ground to obtain a mixed slurry, and then the slurry is dried to obtain a precursor material.

[0083] According to some embodiments of the present application, the method further comprises: adding source A and / or source B to the precursor material. According to some specific embodiments of the present application, a sodium source, a source A, an iron source, a phosphorus source and a source D are mixed and added to water, stirred and ground to obtain a mixed slurry, and then the above slurry is dried to obtain a precursor material. According to some specific embodiments of the present application, a sodium source, a source A, an iron source, a source B, a phosphorus source and a source D are mixed and added to water, stirred and ground to obtain a mixed slurry, and then the above slurry is dried to obtain a precursor material. According to some specific embodiments of the present application, a sodium source, a source A, an iron source, a source B, a phosphorus source and a source D are mixed and added to water, stirred and ground to obtain a mixed slurry, and then the above slurry is dried to obtain a precursor material.

[0084] It should be noted that the sodium source, A source, iron source, B source, phosphorus source and D source are conventional materials in the art, and those skilled in the art can select them according to actual conditions. For example, the sodium source includes at least one of sodium pyrophosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium carbonate, sodium acetate and sodium oxalate; the A source includes at least one of potassium pyrophosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, potassium phosphate, potassium metaphosphate, potassium citrate, potassium carbonate, potassium bicarbonate, potassium oxalate, potassium acetate, lithium hydroxide, lithium carbonate, lithium formate, lithium acetate and lithium oxalate. At least one; the iron source includes at least one of ferric nitrate, ferric chloride, ferric oxide, ferric phosphate and ferrous oxalate; the B source includes at least one of the chloride, oxide, acetate and nitrate of element B; the phosphorus source includes at least one of sodium pyrophosphate, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, ferric phosphate, phosphoric acid and pyrophosphoric acid; the D source includes at least one of ammonium fluoride, sodium fluoride, ammonium chloride, sodium chloride, ammonium bromide, sodium metasilicate, sodium silicate, tetraethyl silicate, sodium fluorosilicate, boric acid, sodium sulfate and sodium bisulfate.

[0085] According to some embodiments of the present application, if carbon is required to be mixed within the positive electrode active material, the sodium source, source A, iron source, source B, phosphorus source, source D, and a first carbon source are mixed. It should be noted that the first carbon source includes at least one of sucrose, tannic acid, polyethylene glycol, polyvinyl pyrrolidone, glucose, ascorbic acid, conductive carbon black, carbon nanotubes, graphene, and citric acid.

[0086] S200: Sintering the precursor material to obtain a positive electrode active material

[0087] According to some embodiments of the present application, the precursor material obtained above is placed in a tube furnace for sintering.

[0088] According to some embodiments of the present application, multi-step sintering may be adopted, for example, a two-step sintering is adopted, where the precursor material is first sintered and then subjected to a second sintering.

[0089] According to some embodiments of the present application, the temperature of the first sintering can be 200°C-400°C, for example, 200°C, 250°C, 300°C, 350°C or 400°C, or a range consisting of any of the above values. The holding time of the first sintering can be 3h, 3.5h, 4h, 4.5h or 5h, etc., or a range consisting of any of the above values. In this way, the materials react fully, improving the phase purity and crystallinity of the positive electrode active material.

[0090] According to some embodiments of the present application, the temperature of the second sintering may be 450°C-650°C, for example, 450°C, 500°C, 550°C, 600°C or 650°C, or a range consisting of any of the above values. The holding time of the second sintering may be 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h, 12h, 12.5h, 13h, 13.5h, 14h, 14.5h or 15h, etc., or a range consisting of any of the above values. Thus, the materials are fully reacted to improve the phase purity and crystallinity of the positive electrode active material.

[0091] According to some embodiments of the present application, if a positive electrode active material having a carbon coating layer is desired, the positive electrode active material obtained in the above steps is mixed with a second carbon source and then sintered. Specifically, the positive electrode active material and the second carbon source can be directly mixed and then sintered, or the positive electrode active material and the second carbon source can be dissolved in a solvent and mixed into a slurry, which is then dried and sintered. The mixture including the positive electrode active material and the second carbon source is placed in a tubular furnace and nitrogen is passed through as a protective gas. As non-carbon elements in the second carbon source are released, a carbon-containing coating is formed on the surface of the positive electrode active material.

[0092] According to some embodiments of the present application, if a composite material with internal mixed carbon and surface-coated carbon is required, the precursor material including the sodium source, A source, iron source, B source, phosphorus source, D source and the first carbon source is first sintered under a nitrogen atmosphere, and then the obtained positive electrode active material is mixed with the second carbon source and sintered under a nitrogen atmosphere.

[0093] It should be noted that the second carbon source includes at least one of sucrose, tannic acid, polyethylene glycol, polyacrylonitrile, cellulose, polyvinyl pyrrolidone, glucose, ascorbic acid, conductive carbon black, carbon nanotubes, graphene and citric acid. In the above preparation process, the mixing ratio of the sodium source, A source, iron source, phosphorus source, D source, the first carbon source and the second carbon source is based on the composition of the above-mentioned positive electrode active material compound. 4-a A b Fe 3-c B d (PO4) 2-e D f (P2O7) is the standard and will not be repeated here.

[0094] In a third aspect, the present application provides a positive electrode plate comprising the positive electrode active material provided in the first aspect of the present application or the positive electrode active material prepared by the method provided in the second aspect of the present application, thereby improving the energy density and rate performance of a battery containing the positive electrode plate.

[0095] In a sodium ion battery, the positive electrode sheet generally includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material.

[0096] The positive electrode current collector may be a conventional metal foil or a composite current collector (a metal material may be disposed on a polymer substrate to form a composite current collector). As an example, the positive electrode current collector may include one or more of copper foil, aluminum foil, nickel foil, stainless steel foil, stainless steel mesh, and carbon-coated aluminum foil.

[0097] In addition to the aforementioned positive electrode active material, the positive electrode active material layer may also optionally include a conductive agent and a binder. The conductive agent is used to improve the conductivity of the positive electrode active material layer, and the binder is used to firmly bond the positive electrode active material and the conductive agent to the positive electrode current collector. This application does not specifically limit the types of conductive agent and binder, and they can be selected based on actual needs.

[0098] As an example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers; the binder may be one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA) and polyvinyl alcohol (PVA).

[0099] As an example, the binder may include one or more of styrene-butadiene rubber (SBR), styrene-butadiene rubber (SBCs), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and carboxymethyl cellulose (CMC).

[0100] These materials are all commercially available.

[0101] The fourth aspect of the present application provides a battery comprising the positive electrode sheet provided in the third aspect of the present application, thereby having excellent energy density and rate performance.

[0102] A battery is a battery that can be recharged to activate the active materials after discharge and continue to be used.

[0103] It can be understood that the battery proposed in this application can be a sodium ion battery.

[0104] Typically, a battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The separator is placed between the positive and negative electrodes to isolate them. The electrolyte conducts ions between the positive and negative electrodes.

[0105] [Negative electrode]

[0106] In a sodium ion battery, the negative electrode plate generally includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0107] The negative electrode sheet may also include only a negative electrode current collector, i.e., without the negative electrode active material. Alternatively, the negative electrode sheet may include a pre-deposited metal phase on the negative electrode current collector. The negative electrode current collector may be made of materials such as conventional metal foil, carbon-coated metal foil, or porous metal sheet. For example, the negative electrode current collector may be copper foil or aluminum foil.

[0108] There is no limitation on the specific type of the negative electrode active material, and active materials known in the art that can be used for the negative electrode of sodium ion batteries can be used, and those skilled in the art can choose according to actual needs. As an example, the negative electrode active material may include but is not limited to one or more of sodium metal, carbon material, alloy material, transition metal oxide and / or sulfide, phosphorus-based material, and titanate material. Specifically, the carbon material may include one or more of hard carbon, soft carbon, amorphous carbon, and nanostructured carbon material; the alloy material may include an alloy material formed by one or more of Si, Ge, Sn, Pb, and Sb; the general formula of the transition metal oxide and sulfide is M x N y , wherein M includes one or more of Fe, Co, Ni, Mn, Sn, Mo, Sb, and V, and N includes O or S; the phosphorus-based material may include one or more of red phosphorus, white phosphorus, and black phosphorus; the titanate material may include Na2Ti3O7, Na2Ti6O 13 、Na4Ti5O12 、Li4Ti5O 12 , NaTi2(PO4)3. These materials can be obtained through commercial channels.

[0109] The negative electrode active material layer typically also optionally includes a binder and a conductive agent. The conductive agent is used to improve the conductivity of the negative electrode active material layer, and the binder is used to firmly bond the negative electrode active material and the conductive agent to the negative electrode current collector. This application does not specifically limit the types of conductive agent and binder, and they can be selected according to actual needs.

[0110] As an example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0111] As an example, the binder may include one or more of styrene-butadiene rubber (SBR), styrene-butadiene rubber (SBCs), water-based acrylic resin, and carboxymethyl cellulose (CMC).

[0112] The negative electrode active material layer may also optionally include a thickener, such as carboxymethyl cellulose (CMC). However, the present application is not limited thereto, and other materials that can be used as thickeners for sodium ion battery negative electrode sheets may also be used in the present application.

[0113] [Isolation film]

[0114] As the above-mentioned isolation membrane, the present application has no special restrictions, and any well-known porous structure isolation membrane with electrochemical stability and mechanical stability can be selected according to actual needs. For example, it can be a single-layer or multi-layer film containing one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0115] [Electrolyte]

[0116] The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The electrolyte may include an electrolyte salt and a solvent.

[0117] As an example, the electrolyte sodium salt includes at least one of sodium hexafluorophosphate, sodium difluorooxalatoborate, sodium tetrafluoroborate, sodium bisoxalatoborate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, and sodium bis(trifluoromethylsulfonyl)imide.

[0118] As an example, the solvent may include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, tetrahydrofuran, methyltetrahydrofuran, 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, tetrahydropyran, ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0119] In some embodiments, the electrolyte further includes additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives capable of improving certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0120] The embodiment of the present application has no particular limitation on the shape of the sodium ion battery, which can be cylindrical, square or any other shape. FIG1 shows a secondary battery 1 with a square structure as an example.

[0121] In some embodiments, the secondary battery may include an outer packaging for encapsulating the positive electrode sheet, the negative electrode sheet, and the electrolyte.

[0122] In some embodiments, the outer packaging may include a housing and a cover. The housing may include a bottom plate and side plates connected to the bottom plate, with the bottom plate and side plates enclosing a receiving cavity. The housing may have an opening communicating with the receiving cavity, and the cover may be positioned over the opening to seal the receiving cavity.

[0123] The positive electrode sheet, negative electrode sheet, and separator can be wound or laminated to form an electrode assembly. The electrode assembly is encapsulated in the housing. The electrolyte can be an electrolyte solution, which is impregnated into the electrode assembly. The number of electrode assemblies in a sodium-ion battery can be one or more, and can be adjusted according to demand.

[0124] In some embodiments, the outer packaging of the sodium ion battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell.

[0125] The outer packaging of the sodium ion battery can also be a soft bag, such as a bag-type soft bag. The material of the soft bag can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0126] In some embodiments, sodium ion batteries can be assembled into a battery module. The battery module can contain multiple sodium ion batteries, and the specific number can be adjusted according to the application and capacity of the battery module.

[0127] Figure 2 shows an example battery module 2. Referring to Figure 2 , within the battery module 2, multiple secondary batteries 1 may be arranged sequentially along the length of the battery module 2. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 1 may be secured together using fasteners.

[0128] The battery module 2 may further include a housing having a housing space, wherein the housing space accommodates a plurality of secondary batteries 1. In some embodiments, the battery modules may be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0129] Figures 3 and 4 illustrate an example battery pack 3. Referring to Figures 3 and 4 , the battery pack 3 may include a battery box and multiple battery modules 2 disposed within the battery box. The battery box comprises an upper case 4 and a lower case 5. The upper case 4 can be placed over the lower case 5 to form an enclosed space for accommodating the battery modules 2. The multiple battery modules 2 can be arranged in any manner within the battery box.

[0130] The fifth aspect of the present application provides an electrical device, comprising the battery provided in the fourth aspect of the present application, thereby increasing the service life of the electrical device.

[0131] The electrical equipment includes at least one of the sodium ion battery, battery module, and battery pack. The sodium ion battery, battery module, or battery pack can serve as a power source for the electrical equipment or as an energy storage unit for the electrical equipment. The electrical equipment can be, but is not limited to, mobile devices (such as mobile phones and laptops), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, and electric trucks), electric trains, ships, satellites, and energy storage systems.

[0132] The electrical equipment can select sodium ion batteries, battery modules or battery packs according to its usage requirements.

[0133] Figure 5 shows an example of an electric device. This device includes a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of sodium-ion batteries, a battery pack or battery module can be used.

[0134] As another example, electric devices may include mobile phones, tablet computers, and laptop computers. These electric devices are generally required to be lightweight and thin, and may use sodium ion batteries as power sources.

[0135] In order to make the technical problems, technical solutions and beneficial effects solved by the embodiments of the present application clearer, the following will be further described in detail with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0136] Example 1

[0137] 1. Preparation of positive electrode active materials

[0138] Sodium pyrophosphate, ferrous oxalate, ammonium dihydrogen phosphate, glucose and ammonium fluoride were prepared according to the chemical formula Na 4-a A b Fe 3-c B d (PO4) 2-e D f (P2O7) was added to deionized water and ground with a sand mill for 10 hours to obtain a mixed slurry; the mixed slurry was dried by a spray drying device to obtain a dry precursor powder; the precursor was placed in a tubular furnace, nitrogen was passed as a protective gas, and a first calcination was performed, the temperature was raised to 300°C, and the temperature was kept for 4 hours, and then a second calcination was performed, the temperature was raised to 550°C, and the temperature was kept for 12 hours to obtain a positive electrode active material.

[0139] 2. Preparation of positive electrode sheet

[0140] The polyvinylidene fluoride binder is fully dissolved in N-methylpyrrolidone, and a carbon black conductive agent and the above-mentioned positive electrode active material are added to prepare a uniformly dispersed positive electrode slurry (the mass ratio of polyvinylidene fluoride binder, carbon black conductive agent and positive electrode active material is 10:10:80). The positive electrode slurry is evenly coated on the upper and lower surfaces of the aluminum foil, and then transferred to a vacuum drying oven for complete drying. The obtained electrode sheet is rolled and then punched to obtain the positive electrode sheet.

[0141] 3. Preparation of negative electrode sheet

[0142] The carbon nanotube material and the binder sodium carboxymethyl cellulose are added to water in a mass ratio of 4:1.6 and stirred to form a uniform negative electrode slurry. The negative electrode slurry is coated on the upper and lower surfaces of the copper foil, and then transferred to a vacuum drying oven for complete drying, and then punched to obtain the negative electrode sheet.

[0143] 4. Prepare electrolyte

[0144] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), sodium hexafluorophosphate NaPF6 was dissolved in an organic solvent, ethylene glycol dimethyl ether (DME), and stirred evenly to obtain an electrolyte with a sodium salt concentration of 1 mol / L.

[0145] 5. Isolation film

[0146] Polypropylene film is used as the isolation film.

[0147] 6. Preparation of button batteries

[0148] The prepared positive electrode sheet is pressed into a circular electrode sheet, and then a small circular sodium sheet is used as a counter electrode, a Celgard 2400 isolation membrane is used, and an electrolyte is injected to assemble a button battery.

[0149] 7. Preparation of sodium-ion batteries

[0150] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is placed between the positive and negative electrode sheets to play an isolating role, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer package, and the prepared electrolyte is injected into the dried sodium ion battery. After vacuum packaging, standing, formation, and shaping processes, a sodium ion battery is obtained.

[0151] The preparation methods of the batteries in Examples 2 to 27 and Comparative Examples 1 to 3 are the same as those in Example 1, with the differences detailed in Table 1.

[0152] Table 1

[0153] Performance Testing

[0154] Button cell performance test: At 25°C and normal pressure, charge the button cell at a constant current rate of 0.1C to a voltage of 3.75V. Then charge it at a constant voltage of 3.75V until the current drops to 0.05C. Record the charge specific capacity at this time, which is the first sodium removal capacity. Then discharge it at a constant current rate of 0.1C to a voltage of 1.5V. Record the discharge specific capacity at this time, which is the first sodium insertion capacity. The gram capacity of the positive electrode active material is the first sodium insertion capacity.

[0155] Sodium ion battery rate performance test: At 25°C, the prepared sodium ion battery was placed in a 25°C constant temperature box and allowed to stand for 30 minutes to allow the battery to reach a constant temperature. The battery that reached a constant temperature was charged to 3.7V at 25°C at a constant current of 0.33C, charged to 0.05C at a constant voltage at 3.7V, allowed to stand for 5 minutes, and then discharged to 1.5V at a constant current of 0.33C, allowed to stand for 5 minutes, and the capacity C1 of 0.33C discharge was obtained; then the battery was charged to 3.7V at a constant current of 0.33C, charged to 0.05C at a constant voltage at 3.7V, allowed to stand for 5 minutes, and then discharged to 1.5V at a constant current of 3C, allowed to stand for 5 minutes, and the capacity C2 of 3C discharge was obtained. The capacity retention rate at the 3C rate is R=C2 / C1×100%.

[0156] The test results of the batteries in Examples 1 to 27 and Comparative Examples 1 to 3 are shown in Table 2.

[0157] Table 2

[0158] Conclusion: The gram capacity of the positive electrode active materials in Examples 1 to 27 is higher than that in Comparative Examples 1 to 3, and the capacity retention rate of the batteries in Examples 1 to 27 is higher than that in Comparative Examples 1 to 3, indicating that the positive electrode active material proposed in this application has a higher gram capacity and can improve the energy density and rate performance of the battery.

[0159] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A positive electrode active material, wherein include: So 4-a A b Feb 3-c B d (PO4) 2-e D f (P2O7) Wherein, A includes at least one of Li or K, B includes a metal element, D includes at least one of a halogen anion, a silicate ion, a sulfate ion or a borate ion, -0.12≤a≤0.12, b≥0, 0≤c≤0.3, d≥0, f>0, 0<e≤0.

1.

2. The positive electrode active material according to claim 1, wherein 1≤f / e≤3.

3. The positive electrode active material according to claim 1 or 2, wherein The values ​​of f and e satisfy at least one of the following conditions: 0<f≤0.3; 0<e≤0.

05.

4. The positive electrode active material according to any one of claims 1 to 3, wherein 0＜f≤0.15。 5. The positive electrode active material according to any one of claims 1 to 4, wherein 3.88≤4-a+b≤4.

12.

6. The positive electrode active material according to any one of claims 1 to 5, wherein 2.7≤3-c+d≤3.

7. The positive electrode active material according to any one of claims 1 to 6, wherein Satisfy at least one of the following conditions: B includes at least one of Al, Mg, Ca, Ni, Co, Mn, Cu, Zn, Cr, V, Ti, Sr, Y, Mo, Nb or W; D includes at least one of the halogen anions, the silicate ions, or the borate ions.

8. The positive electrode active material according to any one of claims 1 to 7, wherein: The halogen anions include F - or Cl - .

9. The positive electrode active material according to any one of claims 1 to 8, wherein D includes any two of the halogen anions, the silicate ions, the sulfate ions or the borate ions, and 1≤f / e≤3.

10. The positive electrode active material according to any one of claims 1 to 9, wherein: The values ​​of b, c and d satisfy at least one of the following conditions: 0≤b≤0.1; 0.05≤c≤0.2; 0≤d≤0.3, c≥d.

11. The positive electrode active material according to any one of claims 1 to 10, wherein: The positive electrode active material also includes carbon.

12. The positive electrode active material according to claim 11, wherein Based on the total mass of the positive electrode active material, the mass proportion of the carbon is 0.5%-4%.

13. The positive electrode active material according to claim 11 or 12, wherein Based on the total mass of the positive electrode active material, the mass proportion of the carbon is 1%-3%.

14. The positive electrode active material according to any one of claims 1 to 13, wherein Satisfy at least one of the following conditions: The volume average particle size D of the positive electrode active material v 50: 0.7μm-7μm; The BET specific surface area of ​​the positive electrode active material is 4 m 2 / g-12m 2 / g.

15. The positive electrode active material according to any one of claims 1 to 14, wherein: Satisfy at least one of the following conditions: The volume average particle size D of the positive electrode active material v 50: 1.2μm-4μm; The BET specific surface area of ​​the positive electrode active material is 5.5 m 2 / g-10m 2 / g.

16. A method for preparing the positive electrode active material according to any one of claims 1 to 15, wherein: include: mixing a sodium source, an iron source, a phosphorus source, and a D source to obtain a precursor material; The precursor material is sintered to obtain a positive electrode active material.

17. The method according to claim 16, wherein: The method further comprises: adding source A and / or source B to the precursor material.

18. The method according to claim 16 or 17, wherein: The method further includes adding a first carbon source to the precursor material.

19. The method according to any one of claims 16 to 18, wherein: The method further includes: mixing the positive electrode active material with a second carbon source and sintering the mixture to form a carbon coating layer on the surface of the positive electrode active material.

20. The method according to any one of claims 16 to 19, wherein: The sintering includes a first sintering and a second sintering, and the first sintering and the second sintering satisfy at least one of the following conditions: The first sintering temperature is 200°C-400°C, and the holding time is 3h-5h; The second sintering temperature is 450° C.-650° C., and the holding time is 8 h-15 h.

21. A positive electrode sheet, wherein: The invention comprises the positive electrode active material according to any one of claims 1 to 15 or the positive electrode active material prepared by the method according to any one of claims 16 to 20.

22. A battery, wherein: Including the positive electrode sheet as described in claim 21.

23. An electrical device, wherein: Comprising the battery of claim 22.

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