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

Abstract

The invention provides a positive active material and a preparation method thereof, a positive plate, a battery, a battery pack and electric equipment. The positive electrode active material comprises QxTzMyO2, and Q comprises one or more of Na, K and Li elements; t comprises one or more elements of Ni, Mn, Fe and Ti; m comprises one or more of metal elements of which the valence state is greater than or equal to + 4; wherein x is greater than 0; z > 0; 0.01 < = y < = 0.1; z + y = 1. And the positive electrode active material has relatively high energy density and relatively good ion diffusion performance, so that the rate of the battery is increased and the cycle life of the battery is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a positive electrode active material and a preparation method thereof, a positive electrode sheet, a battery, a battery pack, and an electrical device. Background Art

[0002] Currently, secondary batteries are widely used in portable electronic products, electric vehicles, and large-scale energy storage systems because they can be used repeatedly and have high energy density and cycle life.

[0003] Among the many cathode active materials for secondary batteries, layered oxides are favored due to their high energy density. Layered oxide cathode active materials have two structures: P2 and O3. In O3-type layered oxide cathode active materials, oxygen atoms form an octahedral coordination environment, with active metal ions (such as sodium, potassium, and lithium) located between the oxygen atomic layers. The P2-type structure also uses oxygen as a framework, with active metal ions (such as sodium, potassium, and lithium) located in a prismatic coordination environment. Therefore, O3-type layered oxide cathode active materials have a high energy density and are suitable for large-scale energy storage applications. However, in this type of material, the diffusion energy barrier of active metal ions is high and the diffusion path is complex, so the battery rate performance prepared with this material is poor; secondly, the phase change of O3-type layered oxide positive electrode active materials is more complex during the cycle process. The internal stress generated by the phase change will cause microcracks inside the positive electrode active material and further diffuse to the outside of the positive electrode active material, exacerbating the side reaction between the electrolyte and the positive electrode active material, thereby affecting the cycle performance of the battery.

[0004] Therefore, there is an urgent need for a positive electrode active material that has high energy density, stability and ion diffusion performance to improve the battery rate and cycle life. Summary of the Invention

[0005] The present invention provides a positive electrode active material, which has high energy density, stability and good ion diffusion performance, and can improve the rate and cycle life of the battery.

[0006] The present invention provides a method for preparing a positive electrode active material, which can prepare a positive electrode active material with high energy density and good ion diffusion performance, thereby facilitating the improvement of the rate and cycle life of a battery.

[0007] The present invention provides a positive electrode sheet, comprising the positive electrode active material or the positive electrode active material prepared by the method for preparing the positive electrode active material. The positive electrode sheet has high ion diffusion performance and stability.

[0008] The present invention provides a battery comprising the positive electrode sheet. The battery has higher rate performance and longer cycle life.

[0009] The present invention provides a battery pack comprising the above-mentioned battery, and the battery pack can operate stably for a long time.

[0010] The present invention provides an electrical device comprising the above-mentioned battery or battery pack, which has high operating reliability.

[0011] One aspect of the present invention provides a positive electrode active material, including Q x T z M y O2, Q includes one or more elements selected from the group consisting of Na, K, and Li; T includes one or more elements selected from the group consisting of Ni, Mn, Fe, and Ti; and M includes one or more metal elements having a valence greater than or equal to +4.

[0012] Among them, x>0; z>0; 0.01≤y≤0.1; z+y=1.

[0013] In one embodiment of the present invention, the Na ion diffusion coefficient of the positive electrode active material is ≥1*10 -9 cm 2 / s;

[0014] Or, the K ion diffusion coefficient of the positive electrode active material is ≥1*10 -10 cm 2 / s;

[0015] Or, the Li ion diffusion coefficient of the positive electrode active material is ≥1*10 -8 cm 2 / s.

[0016] In one embodiment of the present invention, the Na ion diffusion coefficient of the positive electrode active material is 1*10 -9 ~4*10 -9 cm 2 / s;

[0017] Or, the K ion diffusion coefficient of the positive electrode active material is 1*10 -10 ~1*10 -9 cm 2 / s;

[0018] Or, the Li ion diffusion coefficient of the positive electrode active material is 1*10 -8 ~1*10 -7 cm 2 / s.

[0019] In one embodiment of the present invention, the M element is selected from one or more elements of Zr, Nb, Mo, Ru and W.

[0020] According to one embodiment of the present invention,

[0021] 0.9≤x≤1;

[0022] and / or, 0.9≤z≤0.99.

[0023] In one embodiment of the present invention, a coating layer is provided on a portion of the surface of the positive electrode active material, and the coating layer includes at least one of NaAlPO 4 , Na 2 SiO 3 , NaCaPO 4 , and Al 2 O 3 .

[0024] In one embodiment of the present invention, the T element includes a plurality of elements, and the molar number of each T element in the positive electrode active material is the same.

[0025] In one embodiment of the present invention, the T element includes Ni, Mn, and Fe.

[0026] According to an embodiment of the present invention, the particle size of the positive electrode active material is 3-5 μm.

[0027] Another aspect of the present invention provides a method for preparing a positive electrode active material, which is used for the positive electrode active material as described above, comprising the following steps:

[0028] co-precipitating a metal salt solution including a T source and a portion of an M source to obtain a positive electrode active material precursor;

[0029] The positive electrode active material precursor is sintered with raw materials including a Q source, an O source, and a remaining M source to obtain the positive electrode active material.

[0030] In one embodiment of the present invention, the molar ratio of the part of the M source to the remaining M source is 0.1-2:1.

[0031] In one embodiment of the present invention, the sintering process includes a primary sintering process and a secondary sintering process;

[0032] The heating rate of the primary sintering treatment is 1-10°C / min, the treatment temperature is 100-600°C, and the treatment time is 1-20h;

[0033] The heating rate of the secondary sintering treatment is 1-10° C. / min, the treatment temperature is 600-1100° C., and the treatment time is 1-20 hours.

[0034] In one embodiment of the present invention, the sintering process further includes ball milling the raw materials including the Q source, the O source, and part of the M source, and the positive electrode active material precursor;

[0035] The ball milling process has a rotation speed of 50 to 1000 rpm and a processing time of 0.1 to 5 hours.

[0036] Another aspect of the present invention provides a positive electrode sheet, comprising the positive electrode active material as described above or the positive electrode active material prepared by the method for preparing the positive electrode active material as described above.

[0037] Another aspect of the present invention provides a battery comprising the positive electrode sheet as described above.

[0038] Yet another aspect of the present invention provides a battery pack comprising the battery as described above.

[0039] The present invention also provides an electrical device, comprising the battery or the battery pack as described above.

[0040] An embodiment of the present invention provides a positive electrode active material. By doping an O3-type layered oxide positive electrode active material with an element having higher stability, the ion diffusion performance and stability of the positive electrode active material can be improved while having a higher energy density, thereby facilitating improvement of the rate performance and cycle life of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0042] Figure 1 X-ray diffraction pattern of the positive electrode active material provided in Example 1 of the present invention;

[0043] Figure 2 This is a scanning electron microscope image of the positive electrode active material provided in Example 1 of the present invention.

[0044] The above drawings illustrate specific embodiments of the present invention, which will be described in more detail below. These drawings and the accompanying description are not intended to limit the scope of the present invention in any way, but rather to illustrate the concept of the present invention to those skilled in the art by reference to specific embodiments. DETAILED DESCRIPTION

[0045] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0046] In the preparation of secondary batteries, layered oxide cathode active materials have attracted much attention due to their high energy density. O3-type layered oxide cathode active materials have more sites for active metal ion embedding, resulting in higher energy density. However, batteries prepared with these materials suffer from poor rate and cycle performance, limiting their use in secondary batteries.

[0047] After long-term research, the inventors found that the reason why the rate performance of batteries prepared using O3-type layered oxide positive electrode active materials is poor is that the diffusion mode of the active metal ions in this type of material is the TSH mechanism, that is, the active metal ions in the O3-type layered oxide positive electrode active material jump and diffuse between two different crystal sites (usually octahedral sites and tetrahedral sites). In this process, the active metal ions need to jump from an octahedral site to a tetrahedral site, and then jump back to another octahedral site or continue to migrate. Therefore, the diffusion path is relatively complicated, and since it involves jumping between different sites, the active metal ions need to overcome a higher energy barrier, which leads to the low ion diffusion rate of the O3-type layered oxide positive electrode active material.

[0048] In addition, the O3-type layered oxide positive electrode active material has poor lattice stability during battery operation, and is prone to microcracks inside and on the surface of the material, affecting the cycle life of the battery.

[0049] If the diffusion mode of active metal ions can be made simpler and the lattice structure more stable while maintaining the high energy density of O3-type layered oxide positive electrode active materials, the application of O3-type layered oxide positive electrode active materials in batteries will be greatly improved, which can further enhance the rate performance and cycle life of the battery.

[0050] Based on this, the embodiment of the present invention provides a positive electrode active material, including Q x T z M y O2, Q includes one or more elements selected from the group consisting of Na, K, and Li; T includes one or more elements selected from the group consisting of Ni, Mn, Fe, and Ti; and M includes one or more metal elements having a valence greater than or equal to +4; wherein, x>0; z>0; 0.01≤y≤0.1; and z+y=1.

[0051] It should be clarified that the above-mentioned positive electrode active material complies with the principle of electrical neutrality. The above-mentioned positive electrode active material is an O3-type layered oxide positive electrode active material. That is, in the positive electrode active material of the present invention, the oxygen atoms form an octahedral coordination environment, and the active metal ion Q is located between the oxygen atom layers. Therefore, the active metal ion Q in the embodiment of the present invention has a large number of embedding sites in the positive electrode active material, and thus the positive electrode active material has a high energy density.

[0052] The inventors have found that the reasons for the ion diffusion rate and stability of the positive electrode active material of the embodiment of the present invention are: First, in the above-mentioned positive electrode active material, the embodiment of the present invention uses the above-mentioned M element to replace part of the T element and control Q x T z M y The content of Q, T, and M elements in O2, based on the principle of charge conservation, a large number of active metal ions Q in the positive electrode active material lattice will be attracted to the transition element T to form a Q ion-enriched region. The increase in the distribution density of active metal ions Q around the T element reduces the energy barrier when the Q ions jump, allowing the Q ions to diffuse through a simple ODH mechanism, thereby improving the battery's rate performance. In detail, the ODH mechanism, also known as the one-dimensional jump diffusion mechanism, is a jumping diffusion behavior of ions in a one-dimensional channel. It has the characteristics of low energy barriers, high diffusion rate, and anisotropy. It is an important mechanism for optimizing battery rate performance and cycle life. At the same time, the metal element M with a valence greater than or equal to +4 has a lower redox activity than the transition metal element T. During battery operation, the M element does not participate in the electrochemical redox reaction. Therefore, after doping the positive electrode active material with the M element, the lattice structure of the positive electrode active material can be stabilized, the stress generated by the positive electrode active material during the cycle can be resisted, and cracks can be avoided inside the positive electrode active material. Therefore, the stability of the positive electrode active material during the battery cycle can be maintained, and side reactions with the electrolyte can be avoided, thereby helping to improve the cycle life of the battery. The chemical element composition of the above-mentioned positive electrode active material can be tested by commonly used means and instruments, such as X-ray diffraction, transmission electron microscopy, inductively coupled plasma technology (ICP), etc.

[0053] In some embodiments, at least 90% of the Q elements are Na elements, that is, the main active metal ions are Na ions, and the Na ion diffusion coefficient of the positive electrode active material of the present invention is ≥1*10 -9 cm 2 / s. At this time, the resistance of Na active metal ions is further reduced when diffusing in ODH, thereby better improving the rate performance of the battery. Specifically, the Na ion diffusion coefficient of the positive electrode active material can be made to meet the above requirements by further controlling the ratio of Na element, T element, M element, and O oxygen element in the positive electrode active material. Furthermore, the Na ion diffusion coefficient of the positive electrode active material is 1*10 -9 ~4*10 -9 cm 2 / s.

[0054] In some embodiments, at least 90% of the Q elements are K elements, that is, the main active metal ions are K ions, and the K ion diffusion coefficient of the positive electrode active material of the present invention is ≥1*10 -10 cm 2 / s. At this time, the resistance of K active metal ions when diffusing in ODH is further reduced, thereby better improving the rate performance of the battery. Specifically, the K ion diffusion coefficient of the positive electrode active material can be made to meet the above requirements by further controlling the ratio of K element, T element, M element, and O oxygen element in the positive electrode active material. Furthermore, the K ion diffusion coefficient of the positive electrode active material is 1*10 -10 ~1*10 -9 cm 2 / s.

[0055] In some embodiments, at least 90% of the Q elements are Li elements, that is, the main active metal ions are Li ions, and the Li ion diffusion coefficient of the positive electrode active material of the present invention is ≥1*10 -8 cm 2 / s. At this time, the resistance of K active metal ions when diffusing in ODH is further reduced, thereby better improving the rate performance of the battery. Specifically, the Li ion diffusion coefficient of the positive electrode active material can be made to meet the above requirements by controlling the ratio of Li element, T element, M element, and O oxygen element in the positive electrode active material. Furthermore, the Li ion diffusion coefficient of the positive electrode active material is 1*10 -8 ~1*10 -7 cm 2 / s.

[0056] When the ion diffusion coefficient of the positive electrode active material meets the above range, the resistance of the active metal ions Q in the positive electrode active material to diffuse by the ODH mechanism is further reduced, which further increases the ion diffusion rate of the positive electrode active material, thereby better improving the rate performance of the battery.

[0057] The ion diffusion coefficient of the positive electrode active material can be measured by conventional test methods and instruments in the art. In some embodiments, the ion diffusion coefficient of the positive electrode active material can be measured by constant current intermittent titration technique (GITT). The specific test method is: assemble the positive electrode active material into a battery so that the battery is in the voltage range of 2.0-4.0V vs. Na + / Na (if Q element is Na element), pulse current is 0.05-0.1C, pulse time is 10-30min, constant current charge / discharge pulse is performed (that is, first use constant current 0.05-0.1C to charge the battery until the voltage reaches 4.0V, and then use pulse current 0.05-0.1C to discharge the battery. Record the voltage change curve over time, and the voltage difference after the pulse charge and discharge is recorded as ΔE s , and the SOC curve is also drawn). After each pulse time, the battery is allowed to relax (the voltage difference after relaxation is recorded as ΔE t ), that is, interrupt the current flow to the battery and let it rest until the voltage curve is stable. The rest time is 1 to 2 hours. Then repeat the above steps until the battery voltage reaches the set range (lithium-ion battery: 2 to 4.3V, sodium-ion battery: 2 to 4V, potassium-ion battery: 2 to 3V). The calculation method of the ion diffusion coefficient (D) is:

[0058]

[0059] Where, i: current density; V m :Material molar volume (30-40cm 3 / mol); Z: ionic charge number (lithium, sodium, and potassium are 1); F: Faraday constant (96485 C / mol); S: effective electrode contact area (1.5-2 cm 2 ); ΔE s : voltage change caused by pulse; ΔE t : voltage change at the end of relaxation; τ: relaxation time; t: pulse time.

[0060] During the battery charging and discharging process, the ion diffusion coefficient increases first and then decreases with the increase of SOC value. During this process, the peak value of the ion diffusion coefficient is greater than or equal to 1*10 -9 cm 2 / s (if it is a sodium ion battery), it means that the active metal ions in the positive electrode active material diffuse by the ODH mechanism. During the entire charge and discharge process, it is greater than or equal to 1*10 -9 cm 2 / s (if it is a sodium ion battery), the more processes there are, the faster the active metal ions in the positive electrode active material can diffuse and the smaller the internal resistance during the diffusion process.

[0061] Specifically, the above-mentioned battery can be prepared by the following method: the positive electrode active material is mixed with the conductive agent (SuperP) and the binder (PVDF) in a mass ratio of 8:1:1, coated on aluminum foil, and punched into positive electrode sheets after drying; then sodium metal is used as the negative electrode, glass fiber is used as the separator, and 1-1.5M NaPF6 / EC / DEC is used as the electrolyte (wherein the volume ratio of EC and DEC is 3:7, and the molar concentration of NaPF6 in the mixture of EC and DEC is 1-1.5M), 2032 button batteries are assembled, and the test is started after standing for 12-24 hours.

[0062] In some embodiments, the M element is selected from one or more elements of Zr, Nb, Mo, Ru, and W. These elements have lower redox activity and can further stabilize the lattice structure of the positive electrode active material, thereby better improving the stability of the positive electrode active material and further increasing the cycle life of the battery.

[0063] In some embodiments, 0.9≤x≤1, so that the positive electrode active material has a higher energy density, which is beneficial to further improve the energy density of the battery.

[0064] In a specific embodiment, when 0.9≤z≤0.99, the electrochemical activity of the positive electrode active material is better, which is beneficial to further improve the ion diffusion rate of the positive electrode active material and better improve the rate performance of the battery.

[0065] To improve the ion diffusion rate and stability of the positive electrode active material, some embodiments of the present invention include a coating layer disposed on a portion of the surface of the positive electrode active material. The coating layer comprises at least one of NaAlPO4, Na2SiO3, NaCaPO4, and Al2O3. Specifically, when Al2O3 is used as the coating layer, a small amount of the Q active metal ions in the positive electrode active material will enter the Al2O3 coating layer, further improving the ion diffusion rate of the positive electrode active material.

[0066] The present invention can use conventional methods and instruments in the art to prepare the coating layer.

[0067] In a specific embodiment, the Al2O3 coating layer can be prepared by the following method: after mixing the positive electrode active material with Al2O3 (1wt%), drying it at 120°C for 6h and placing it in a ball mill, ball milling it at a speed of 200rpm for 40min, heating it to 500°C in an air atmosphere at a heating rate of 5°C / min and keeping it warm for 2h, then heating it to 900°C at a heating rate of 3°C / min and keeping it warm for 3h, and passing it through an 800-mesh sieve to obtain a positive electrode active material with a coating layer.

[0068] In some embodiments, the T element comprises multiple elements, and the molar number of each T element in the positive electrode active material is the same. When the positive electrode active material meets the above conditions, its ion diffusion rate and stability can be further improved, resulting in a battery with better rate performance and cycle life.

[0069] In some embodiments, the T element includes Ni, Mn, and Fe. When the T element includes the above three elements, the molar numbers of the three elements can be the same. The positive electrode active materials in these embodiments have both higher ion diffusion rate and stability, thereby further improving the rate performance and cycle life of the battery.

[0070] To further improve the ion diffusion performance of the positive electrode active material, the present invention controls the particle size of the positive electrode active material to be 3-5 μm. For example, the particle size of the positive electrode active material is 3 μm, 4 μm, 5 μm, or any combination thereof.

[0071] An embodiment of the present invention further provides a method for preparing a positive electrode active material, which is used to prepare the positive electrode active material, comprising the following steps:

[0072] co-precipitating a metal salt solution including a T source and a portion of an M source to obtain a positive electrode active material precursor;

[0073] The positive electrode active material precursor is sintered with raw materials including a Q source, an O source, and a remaining M source to obtain a positive electrode active material.

[0074] It should be noted that in the above-mentioned method for preparing the positive electrode active material, the molar ratio of each metal salt in the metal salt solution including the T source and part of the M source in the coprecipitation process and the molar ratio of the raw materials including the Q source, the O source and the remaining M source in the sintering process can be adjusted to synthesize the positive electrode active material including the Q source. x T z M y O2 positive electrode active material to obtain the target compound. For example, when the Q element of the target product is Na, the T element includes Ni, Fe, and Mn, and the M element includes Nb, the Q source can be a Na source, the T source can be a Ni source, Fe, or Mn source, and the M source can be a Nb source. Furthermore, when the ratio of Ni, Fe, and Mn in the target product is 1:1:1, the Ni source, Fe source, and Mn source can be added in a molar ratio of 1:1:1 in the above preparation method.

[0075] In the embodiment of the present invention, an inert gas (such as argon) is introduced into the co-precipitation process to avoid the influence of air on the co-precipitation process.

[0076] The embodiment of the present invention does not impose any particular limitation on the treatment time and treatment temperature of the co-precipitation treatment. For example, the treatment time of the co-precipitation treatment may be 12 to 36 hours, and the treatment temperature may be 60°C.

[0077] In the above-mentioned coprecipitation treatment, a precipitant may also be added to improve the efficiency of the coprecipitation treatment. The present invention does not impose any particular restrictions on the type of precipitant, as long as the coprecipitation treatment can be performed. At least one of sodium hydroxide and ammonia water can be used as a precipitant. The present invention does not impose any particular restrictions on the concentration and dosage of the precipitant, and it can be selected according to actual conditions. In specific implementation, the metal salt solution including the T source and the M source can be simultaneously pumped into the reactor with a 10 mol / L sodium hydroxide solution and a 5 mol / L ammonia water for precipitation treatment. During this process, the pH value in the coprecipitation treatment system can be controlled to be maintained at 10.5±0.2. The embodiment of the present invention can also control the flow rate of the metal salt solution and the solution including the precipitant to make the coprecipitation treatment more efficient. In specific implementation, the flow rate of the precipitant ammonia water can be controlled to be 0.03 L / h, the flow rate of the precipitant sodium hydroxide solution can be controlled to be 0.1 to 5 L / h, the flow rate of the metal salt solution including the T source can be 5 L / h, and the flow rate of the metal salt solution including part of the M source can be controlled to be 10 L / h. In addition, the efficiency of the coprecipitation process can be improved by stirring. For example, the stirring rate can be 700 rpm.

[0078] The present invention does not specifically limit the type of metal salt, and can be selected based on actual conditions. For example, the M metal salt includes one or more metal salts selected from sulfates, nitrates, and ammonium salts containing the element M, and the T metal salt includes one or more metal salts selected from sulfates, nitrates, and ammonium salts containing the element T. These metal salts have the advantage of low residual content and minimal impact on battery performance.

[0079] The metal salt solution including the T source and the M source is subjected to a coprecipitation treatment to obtain a positive electrode active material precursor. At this time, the positive electrode active material precursor exists in the solution in the form of a metal hydroxide.

[0080] In order to enable the active metal element Q element in the embodiment of the present invention to diffuse by the ODH mechanism, the embodiment of the present invention divides the M source into two parts. First, part of the M source is added in the co-precipitation treatment to ensure that part of the M element is present in the positive electrode active material precursor in the form of metal hydroxide, laying the foundation for the subsequent final acquisition of the positive electrode active material that diffuses by the ODH mechanism.

[0081] Based on the consideration of the dispersion performance of the solution, in the co-precipitation process, the embodiment of the present invention mainly adopts M metal salt with good solubility as part of the M source.

[0082] In some embodiments, after the coprecipitation treatment, the solution comprising the positive electrode active material precursor is further aged and allowed to stand. The aging and standing may be performed at room temperature for 5 to 24 hours.

[0083] After the aging and standing, the slurry is filtered, and then the filtered solid is washed with deionized water. After washing, it is placed in an oven for drying to obtain a positive electrode active material precursor.

[0084] Next, the positive electrode active material precursor is sintered with raw materials including a Q source, an O source, and an M source to obtain a positive electrode active material.

[0085] In the present embodiment, the raw materials for the Q source, the O source, and the M source are not particularly limited and can be selected according to actual needs. The raw materials for the Q source can be one or more of oxides, oxalates, sulfates, and carbonates containing the Q element, and the raw materials for the M source can be one or more of oxides, oxalates, sulfates, and carbonates containing the M element. In specific implementations, the carbonate containing the Q element and the oxide containing the M element can be mixed and then sintered.

[0086] In the subsequent sintering process, the embodiment of the present invention uses the raw materials including the remaining M source for processing again. At this time, part of the M source added in the co-precipitation process and the remaining M source added in the sintering process are simultaneously doped into the crystal during the sintering process, replacing the T element located at some special sites. The crystal construction is completed during the sintering process to obtain a positive electrode active material that diffuses in an ODH manner.

[0087] During the sintering process, considering the impurity problem, the embodiment of the present invention uses one or more of the oxides, oxalates, sulfates, and carbonates of the M element as the residual M source. The above substances have less residual impurities after the sintering process.

[0088] In some embodiments, the positive electrode active material is screened after the sintering process to remove components with larger particle sizes in the positive electrode active material, thereby further optimizing the ion diffusion performance of the positive electrode active material in the battery.

[0089] The embodiment of the present invention can prepare a positive electrode active material with good stability and ion diffusion rate through the above-mentioned preparation method, which is beneficial to improving the cycle life and rate performance of the battery.

[0090] In order to make the M element diffuse more evenly in the crystals of the positive electrode active material, the embodiment of the present invention further controls the molar ratio of the M source in the coprecipitation process to the M source in the sintering process to be (0.1-2):1. When the molar ratio of the M source in the coprecipitation process to the M source in the sintering process meets the above requirements, the M element is more evenly distributed in the lattice of the prepared positive electrode active material, which further improves the ion diffusion rate and stability of the positive electrode active material, thereby further improving the battery rate performance and cycle life.

[0091] Based on the consideration of the uniformity of element distribution in the lattice of the positive electrode active material, the sintering treatment of the embodiment of the present invention includes a primary sintering treatment and a secondary sintering treatment; the heating rate of the primary sintering treatment is 1 to 10°C / min, the treatment temperature is 100 to 600°C, and the treatment time is 1 to 20 hours; the heating rate of the secondary sintering treatment is 1 to 10°C / min, the treatment temperature is 600 to 1100°C, and the treatment time is 1 to 20 hours.

[0092] In addition, in some embodiments, prior to the sintering process, the raw materials including the Q source, O source, and M source, and the cathode active material precursor are subjected to ball milling; the ball milling speed is 50 to 1000 rpm, and the processing time is 0.1 to 5 hours. The ball milling process used in the embodiments of the present invention can not only increase the uniformity of the dispersion of the above-mentioned elements in the cathode active material lattice, but also reduce the particle size of the cathode active material, so that the cathode active material has a higher ion diffusion rate, which is conducive to further improving the rate performance of the battery.

[0093] An embodiment of the present invention further provides a positive electrode sheet, comprising the above-mentioned positive electrode active material or the positive electrode active material prepared by the above-mentioned method for preparing the positive electrode active material. The positive electrode sheet has the corresponding advantages of the above-mentioned positive electrode active material, which will not be described in detail here.

[0094] The embodiment of the present invention further provides a battery comprising the above-mentioned positive electrode active material. The battery provided by the present invention has corresponding advantages to the above-mentioned positive electrode active material, which will not be described in detail here.

[0095] In the embodiments of the present invention, unless otherwise specified, the processes of coating, drying, rolling and the like involved are all conventional operations in the art, and the equipment used may be conventional equipment in the art, without particular limitation.

[0096] The battery of the embodiment of the present invention can be a lithium-ion battery (such as a lithium-ion power battery), a potassium-ion battery, a sodium-ion battery or other new energy storage batteries. Specifically, when the Q element is only Na, the battery is a sodium-ion battery; when the Q element is only K, the battery is a potassium-ion battery; when the Q element is only Li, the battery is a lithium-ion battery. In addition, the Q element can also be a variety of elements among Na, K, and Li. For example, the Li element can be used to dope the positive active material precursor of the sodium-ion battery to obtain the positive active material of the embodiment of the present invention.

[0097] Generally speaking, a battery includes an electrolyte, a cell, and a casing that encapsulates the cell. The electrolyte is injected into the cell within the casing, and the cell includes a positive electrode sheet, a negative electrode sheet, and a separator located between the positive and negative electrodes. The cell can be a laminated cell, where the positive electrode sheet, separator, and negative electrode sheet are stacked in an alternating pattern. Alternatively, the cell can be a wound cell, where the positive electrode sheet, separator, and negative electrode sheet are stacked and then wound.

[0098] Specifically, the positive electrode sheet includes a positive electrode collector and a positive electrode active layer located on at least one side surface of the positive electrode collector. Specifically, the positive electrode active layer can be provided on one side surface in the thickness direction of the positive electrode collector, or the positive electrode active layer can be provided on the surfaces of the opposite sides in the thickness direction of the positive electrode collector.

[0099] The positive electrode active layer may include the positive electrode active material, the conductive agent and the binder provided in the embodiment of the present invention. In the positive electrode active layer, the mass percentage of the positive electrode active material may be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99% or a range consisting of any two thereof, the mass fraction of the conductive agent may be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15% or a range consisting of any two thereof, and the mass fraction of the binder may be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15% or a range consisting of any two thereof.

[0100] In an embodiment of the present invention, the conductive agent in the positive electrode active layer can be a conventional conductive material in the art. For example, the conductive agent in the positive electrode active layer can include one or more of conductive carbon black, conductive graphite, carbon nanotubes (CNTs), carbon fibers, graphene, acetylene black, and Ketjen black.

[0101] In an embodiment of the present invention, the binder in the positive electrode active layer may be a conventional binding material in the art. For example, the binder in the positive electrode active layer may include one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, and the like.

[0102] The embodiment of the present invention may adopt a conventional positive electrode current collector in the art, for example, the positive electrode current collector includes aluminum foil.

[0103] In the embodiments of the present invention, the positive electrode sheet can be prepared by conventional methods in the art, such as by a coating method. Specifically, the components used to form the positive electrode active layer, such as the positive electrode active material, conductive agent, and binder, can be dispersed in a solvent, such as N-methylpyrrolidone (NMP), to prepare a positive electrode slurry, which is then coated on the surface of the positive electrode current collector. After drying and roller pressing, the positive electrode sheet is prepared. The coating, drying, and roller pressing steps involved are conventional operations for preparing positive electrode sheets using a coating method and are not particularly limited thereto.

[0104] Specifically, the negative electrode sheet includes a negative electrode collector and a negative electrode active layer located on at least one side surface of the negative electrode collector. Specifically, the negative electrode active layer can be provided on one side surface of the negative electrode collector, or the negative electrode active layer can be provided on both sides of the negative electrode collector in the thickness direction.

[0105] Specifically, the negative electrode active layer may include a negative electrode active material, a conductive agent and a binder, all of which may be conventional materials in the art. For example, the negative electrode active material may include one or more of natural graphite, artificial graphite, petroleum coke, and silicon-carbon materials; the conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNTs), acetylene black, graphene, Ketjen black, and carbon fibers; the binder may include one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0106] The embodiment of the present invention may adopt a conventional negative electrode current collector in the art, for example, the negative electrode current collector includes copper foil.

[0107] In the embodiments of the present invention, the negative electrode sheet can be prepared by conventional methods in the art, such as a coating method. Specifically, the components used to form the negative electrode active layer, such as the negative electrode active material, conductive agent, and binder, can be dispersed in a solvent, such as water, to prepare a negative electrode slurry. The slurry is then coated on the surface of the negative electrode current collector. After drying and roller pressing, the negative electrode sheet is prepared. The coating, drying, and roller pressing steps involved are conventional operations for preparing negative electrode sheets using a coating method and are not particularly limited thereto.

[0108] The electrolyte of the embodiment of the present invention can be a conventional electrolyte in the field. For example, the electrolyte is a non-aqueous electrolyte, which may specifically include an organic solvent, an additive and an electrolyte salt. The organic solvent includes, for example, one or more of ethylene carbonate (EC), diethyl carbonate (DEC) and propylene carbonate (PC), the additive includes, for example, fluoroethylene carbonate (FEC), the additive includes, for example, vinylene carbonate (VC), the electrolyte salt may include a lithium salt, the lithium salt includes, for example, lithium hexafluorophosphate (LiPF6), etc., but is not limited thereto.

[0109] In the embodiments of the present invention, a separator is used to separate the positive and negative electrodes to prevent contact and short circuits between the positive and negative electrodes. Conventional separators in the art can be used in the embodiments of the present invention, without particular limitation. For example, the separator material can be made from one or more of high-density polyethylene, ultra-high-density polyethylene, low-density polyethylene, linear low-density polyethylene, high-density polypropylene, ultra-high-density polypropylene, polyimide, and polyvinylidene fluoride.

[0110] In the embodiment of the present invention, conventional shell materials in the art may be used to encapsulate the battery cell. The shell may include, for example, a soft packaging material such as an aluminum-plastic film, but is not limited thereto.

[0111] In the embodiment of the present invention, components such as positive electrode sheets, separators and negative electrode sheets can be assembled into a battery by conventional methods in the field. For example, the positive electrode sheets, separators and negative electrode sheets can be stacked in an alternating manner to produce a laminated battery cell (or wound into a wound battery cell); the battery cell is then placed in a shell (outer packaging), and after conventional processes such as liquid injection (i.e., injecting electrolyte) and packaging, the battery is produced.

[0112] An embodiment of the present invention further provides a battery pack including the above-mentioned battery. The battery pack has advantages corresponding to the above-mentioned positive electrode active material, which will not be described in detail.

[0113] Generally, a battery pack includes multiple batteries as described above, which are connected as single cells to form a battery pack. These batteries can be electrically connected using conventional methods in the art, such as series connection, parallel connection, or a combination of these connection methods, without particular limitation.

[0114] An embodiment of the present invention further provides an electrical device, comprising the above-mentioned battery or the above-mentioned battery pack. The electrical device has advantages corresponding to the above-mentioned positive electrode active material, which will not be described in detail.

[0115] The electrical equipment in the embodiments of the present invention can be conventional electrical equipment in this field, such as power equipment (such as electric vehicles, electric cars), electronic equipment (such as mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (such as watches, bracelets, VR glasses, etc.), energy storage power stations, etc., without special restrictions.

[0116] The technical solution of the present invention is further described below with reference to specific embodiments.

[0117] Example 1

[0118] The positive electrode active material of this embodiment is prepared by the following steps:

[0119] 1) nickel sulfate, iron sulfate, and manganese sulfate are prepared in a certain molar ratio to form a first metal salt solution (i.e., a metal salt solution including a T source), and a second metal salt solution, NaNbO3 solution (i.e., a metal salt solution including part of the M source). The above two metal salt solutions are simultaneously pumped into the reactor in a certain molar ratio with a 10 mol / L NaOH solution and a 5 mol / L ammonia solution. The flow rate of the Ni, Fe, and Mn metal salt solutions is 5 L / h, the flow rate of the NaNbO3 solution is 10 L / h, and the flow rate of the ammonia solution is 10 L / h. The amount was 0.03 L / h, the flow rate of the NaOH solution was controlled to maintain the pH value of the reaction solution at 10.5 ± 0.2, nitrogen was introduced into the reactor as a protective atmosphere, and the coprecipitation reaction was carried out by heating and stirring. The reaction temperature was 60 ° C and the stirring rate was 700 rpm. After the reaction for 24 hours, the mixture was aged and allowed to stand for 12 hours to obtain a slurry including a positive electrode active material precursor, and then the slurry was filtered, and the filtered solid was washed with deionized water. After washing, it was placed in an oven for drying to obtain a positive electrode active material precursor (N i0.33 Fe 0.33 Mn 0.33 ) 0.99 Nb 0.01 (OH)2.

[0120] 2) The above-mentioned cathode active material precursor and Na2CO3 (i.e., the raw material including the Q source) and Nb2O5 (i.e., the raw material including the remaining M source, and also providing part of the O source) were placed in a ball mill according to a certain molar ratio, and ball milled at a speed of 300 rpm for 1 hour. Then, in an air atmosphere (providing the O source), the mixture was heated to 500°C at a heating rate of 3°C / min and kept warm for 5 hours. Then, the mixture was heated to 900°C at a heating rate of 2°C / min and kept warm for 11 hours. The mixture was passed through a 1000 mesh sieve to obtain the cathode active material Na(Ni 0.33 Fe0.33 Mn 0.33 ) 0.98 Nb 0.02 The remaining process conditions of this embodiment are shown in Table 1.

[0121] The X-ray diffraction (XRD) pattern of the positive electrode active material prepared in this example is as follows: Figure 1 As shown by Figure 1 It can be seen that the modified sample still maintains the crystal structure of O3-type sodium ion positive electrode material.

[0122] The scanning electron microscope (SEM) of the positive electrode active material prepared in this example is as follows: Figure 2 As shown by Figure 2 It can be seen that the material is spherical particles with a particle size of about 4 μm.

[0123] Example 2

[0124] This embodiment is basically the same as embodiment 1, except that the second metal salt solution added in step 1) of this embodiment is a Na2WO4 solution; the raw material of the M source added in step 2) is WO3. The positive electrode active material obtained is Na(Ni 0.33 Fe 0.33 Mn 0.33 ) 0.98 W 0.02 O2.

[0125] Example 3

[0126] This embodiment is basically the same as embodiment 1, except that the second metal salt solution added in step 1) of this embodiment is a Na2ZrO3 solution; the raw material of the M source added in step 2) is ZrO2. The positive electrode active material obtained is Na(Ni 0.33 Fe 0.33 Mn 0.33 ) 0.98 Zr 0.02 O2.

[0127] Example 4

[0128] This embodiment is basically the same as embodiment 1, except that the second metal salt solution added in step 1) of this embodiment is a Na2MoO4 solution; the raw material of the M source added in step 2) is MoO3. The positive electrode active material obtained is Na(Ni 0.33 Fe 0.33 Mn 0.33 ) 0.98 Mo 0.02 O2.

[0129] Example 5

[0130] This embodiment is basically the same as embodiment 1, except that the second metal salt solution added in step 1) of this embodiment is a Na2RuO4 solution; the raw material of the M source added in step 2) is RuO2. The positive electrode active material obtained is Na(Ni 0.33 Fe 0.33 Mn 0.33 ) 0.98 Ru 0.02 O2.

[0131] Example 6

[0132] This embodiment is basically the same as embodiment 1, except that the molar ratio of the first metal salt to the second metal salt added in step 1) of this embodiment is different from that in embodiment 1; the molar ratio of the positive electrode active material precursor to Na2CO3 and Nb2O5 is different from that in embodiment 1. 0.33 Fe 0.33 Mn 0.33 ) 0.99 Nb 0.01 O2.

[0133] Example 7

[0134] This embodiment is basically the same as embodiment 1, except that the molar ratio of the second metal salt to the first metal salt added in step 1) of this embodiment is different from that in embodiment 1; the molar ratio of the positive electrode active material precursor to Na2CO3 and Nb2O5 is different from that in embodiment 1. 0.33 Fe 0.33 Mn 0.33 ) 0.9 Nb 0.1 O2.

[0135] Example 8

[0136] This embodiment is basically the same as embodiment 1, except that the molar ratio of the second metal salt to the first metal salt added in step 1) of this embodiment is different from that of the embodiment, the molar ratio of each metal salt in the first metal salt is different from that of embodiment 1; the molar ratio of the positive electrode active material precursor to Na2CO3 and Nb2O5 is different from that of embodiment 1. The positive electrode active material Na(Ni 0.4 Fe 0.2 Mn 0.4 ) 0.98 Nb 0.02 O2.

[0137] Example 9

[0138] This embodiment is basically the same as embodiment 1, except that the ball milling process in this embodiment is to increase the rotation speed to 400 rpm, reduce the ball milling time to 40 min, and sieve through 1200 mesh.

[0139] Example 10

[0140] This embodiment is basically the same as embodiment 1, except that the ball milling process in this embodiment is to reduce the rotation speed to 200 rpm, increase the ball milling time to 80 min, and sieve through 800 mesh.

[0141] Example 11

[0142] This embodiment is basically the same as embodiment 1, except that the ball milling process in this embodiment is to increase the rotation speed to 1000 rpm, reduce the ball milling time to 30 min, and sieve through 2000 mesh.

[0143] Example 12

[0144] This embodiment is basically the same as embodiment 1, except that the ball milling process in this embodiment is to reduce the rotation speed to 100 rpm, increase the ball milling time to 2 h, and sieve through 500 mesh.

[0145] Example 13

[0146] This embodiment is basically the same as embodiment 1, except that at least part of the surface of the positive electrode active material of this embodiment has a coating layer, which is Al2O3. The specific method is to coat the positive electrode active material (Na(Ni 0.33 Fe 0.33 Mn 0.33 ) 0.98 Nb 0.02 After mixing with Al2O3 (1wt%), the mixture was dried at 120°C for 6h and put into a ball mill. After ball milling at 200rpm for 40min, the mixture was heated to 500°C at a heating rate of 5°C / min in air atmosphere and kept warm for 2h. Then, the mixture was heated to 900°C at a heating rate of 3°C / min and kept warm for 3h, and passed through an 800-mesh sieve.

[0147] Example 14

[0148] This embodiment is basically the same as embodiment 1, except that the first metal salt added in this embodiment includes Cr(NO3)3, and the raw material of the Q source added in step 2) is K2CO3, and the positive electrode active material KCr is obtained. 0.98 Nb 0.02 O2.

[0149] Example 15

[0150] This embodiment is basically the same as embodiment 1, except that the M source in this embodiment is only added in step 1).

[0151] Example 16

[0152] This embodiment is basically the same as embodiment 1, except that the amount of Na2CO3 added in this embodiment is less.

[0153] Comparative Example 1

[0154] This comparative example is basically the same as Example 1, except that the M element is not doped in this comparative example.

[0155] Comparative Example 2

[0156] This comparative example is basically the same as Example 1, except that the second metal salt solution added in this comparative example is Mg(NO3)2 solution; the raw material of the M source added in step 2) is MgO2. The positive electrode active material obtained is Na(Ni 0.33 Fe 0.33 Mn 0.33 ) 0.98 Mg 0.02 O2.

[0157] Comparative Example 3

[0158] This comparative example is basically the same as Example 1, except that the molar ratio of the second metal salt to the first metal salt added in step 1) of this example is different from that of the example; the molar ratio of the positive electrode active material precursor to Na2CO3 and Nb2O5 is different from that of Example 1. 0.33 Fe 0.33 Mn 0.33 ) 0.998 Nb 0.002 O2.

[0159] Comparative Example 4

[0160] This comparative example is basically the same as Example 1, except that the molar ratio of the second metal salt to the first metal salt added in step 1) of this example is different from that of Example 1; the molar ratio of the positive electrode active material precursor to Na2CO3 and Nb2O5 is different from that of the example. 0.33 Fe 0.33 Mn 0.33 ) 0.8 Nb 0.2 O2.

[0161] Test example

[0162] The positive electrode active materials prepared in the above examples and comparative examples were mixed with carbon black and PVDF in a ratio of (8:1:1) to form a slurry. The mixture was then coated on aluminum foil and dried in an oven to obtain a positive electrode sheet. In an argon-filled glove box, a half-cell was assembled using sodium metal as the negative electrode and glass fiber as the separator. The half-cell was activated by three cycles of 0.1C constant current charge and discharge at a voltage range of 2.0-4.0V at room temperature (25°C). Cycling tests were then performed at rates of 0.1C, 0.2C, 0.5C, 1C, 2C, and 3C. The test results are shown in Table 2.

[0163] The sodium ion diffusion coefficient of the positive electrode active materials prepared in the examples and comparative examples was obtained by GITT test, and the specific steps were as follows:

[0164] 1) The positive electrode active material was mixed with a conductive agent (Super P) and a binder (PVDF) in a mass ratio of 8:1:1, coated on aluminum foil, and then punched into electrodes after drying. A 2032-type button cell was then assembled using sodium metal as the counter electrode, glass fiber as the separator, and 1M NaPF6 / EC / DEC as the electrolyte, and allowed to stand for 24 hours.

[0165] 2) The above battery is tested in the voltage range of 2.0-4.0V vs.Na + / Na (if Q element is Na element, K element, Li element can be applied to the above range), pulse current is 0.05, pulse time is 15min, constant current charge / discharge pulse is performed (that is, first use a constant current of 0.05 to charge the battery until the voltage reaches 4.0V, and then use a pulse current of 0.05C to discharge the battery. Record the voltage change curve over time, and the voltage difference after the pulse charge and discharge is recorded as ΔE s , and the SOC curve is also drawn). After each pulse time, the battery is allowed to relax (the voltage difference after relaxation is recorded as ΔE t ), that is, the battery current is interrupted and the battery is allowed to stand for 1 hour until the voltage curve is stable. Then the above steps are repeated until the battery voltage reaches the set range (2 to 4V). The ion diffusion coefficient (D) is calculated as:

[0166]

[0167] Where, i: current density; V m :Material molar volume (30-40cm 3 / mol); Z: ionic charge number (lithium, sodium, and potassium are 1); F: Faraday constant (96485 C / mol); S: effective electrode contact area (1.5-2 cm 2 ); ΔE s : voltage change caused by pulse; ΔEt : voltage change at the end of relaxation; τ: relaxation time; t: pulse time. The test results are shown in Table 1

[0168] Battery cycle performance test: The battery cycle performance test was performed on the half-cell including the positive electrode active materials of the embodiment and the comparative example. The test method is as follows:

[0169] Cyclic performance test: At 25°C, charge to 4V at a constant current of 0.1C, then discharge to 2V at a constant voltage of 0.1C, and repeat for 3 cycles. Discharge to 4V at a discharge rate of 0.5C, then discharge to 2V at a constant voltage of 0.5C, and repeat this charge and discharge cycle 500 times. Measure the discharge capacity Q1 at the first cycle (starting from the first cycle at 0.5C rate) and the discharge capacity Q at the 500th cycle. 500 The capacity retention rate after 500 cycles is Q = Q 500 / Q1×100%. (The number of cycles of potassium ion battery is 200)

[0170] Rate performance test: At 25°C, the battery was charged at a constant current of 0.1C to 4V, then discharged at a constant voltage of 0.1C to 2V for three cycles. Four charge and discharge cycles were then performed at current densities of 0.1C, 0.2C, 0.5C, 1C, 2C, and 3C, respectively. The test results are shown in Table 2.

[0171] Table 1

[0172]

[0173] “ / ” means that the substance is not contained.

[0174] Table 2

[0175]

[0176] As can be seen from the table, compared with comparative examples 1-4, the embodiments of the present invention dope the positive electrode active material with a metal element having a valence greater than or equal to +4 and control the element ratio of each part in the positive electrode active material, which is beneficial for the active metal ions in the positive electrode active material to diffuse in the form of ODH, which is beneficial for improving the rate performance and cycle performance of the battery. Compared with Example 8, Example 1 of the present invention further controls the molar ratio of Ni, Mn, and Fe in the positive electrode active material to be the same, so that the battery further takes into account high rate performance and cycle performance. Compared with Examples 11 and 12, the embodiment of the present invention further controls the particle size of the positive electrode active material to be 3 to 5 μm, so that the rate performance and cycle performance of the battery are further improved.

[0177] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode active material, characterized in that Including Q x T z M y O2, Q includes one or more elements selected from the group consisting of Na, K, and Li; T includes one or more elements selected from the group consisting of Ni, Mn, Fe, and Ti; and M includes one or more metal elements having a valence greater than or equal to +4. Among them, x>0; z>0; 0.01≤y≤0.1; z+y=1.

2. The positive electrode active material according to claim 1, characterized in that The Na ion diffusion coefficient of the positive electrode active material is ≥1*10 -9 cm 2 / s; Or, the K ion diffusion coefficient of the positive electrode active material is ≥1*10 -10 cm 2 / s; Or, the Li ion diffusion coefficient of the positive electrode active material is ≥1*10 -8 cm 2 / s.

3. The positive electrode active material according to claim 1 or 2, characterized in that The Na ion diffusion coefficient of the positive electrode active material is 1*10 -9 ~4*10 -9 cm 2 / s; Or, the K ion diffusion coefficient of the positive electrode active material is 1*10 -10 ~1*10 -9 cm 2 / s; Or, the Li ion diffusion coefficient of the positive electrode active material is 1*10 -8 ~1*10 -7 cm 2 / s.

4. The positive electrode active material according to any one of claims 1 to 3, characterized in that The M element is selected from one or more elements of Zr, Nb, Mo, Ru and W.

5. The positive electrode active material according to any one of claims 1 to 4, characterized in that 0.9≤x≤1； and / or, 0.9≤z≤0.

99.

6. The positive electrode active material according to any one of claims 1 to 5, characterized in that A coating layer is provided on a portion of the surface of the positive electrode active material, and the coating layer includes at least one of NaAlPO 4 , Na 2 SiO 3 , NaCaPO 4 , and Al 2 O 3 .

7. The positive electrode active material according to any one of claims 1 to 6, characterized in that The T element includes a plurality of elements, and the molar number of each of the T elements in the positive electrode active material is the same.

8. The positive electrode active material according to claim 7, characterized in that The T element includes Ni, Mn and Fe.

9. The positive electrode active material according to claims 1 to 8, characterized in that The particle size of the positive electrode active material is 3-5 μm.

10. A method for preparing a positive electrode active material, characterized in that: The method for preparing the positive electrode active material according to any one of claims 1 to 9 comprises the following steps: co-precipitating a metal salt solution including a T source and a portion of an M source to obtain a positive electrode active material precursor; The positive electrode active material precursor is sintered with raw materials including a Q source, an O source, and a remaining M source to obtain the positive electrode active material.

11. The method for preparing a positive electrode active material according to claim 10, characterized in that: The molar ratio of the part of the M source to the remaining M source is (0.1~2):

1.

12. The method for preparing a positive electrode active material according to claim 10 or 11, characterized in that: The sintering process includes a primary sintering process and a secondary sintering process; The heating rate of the primary sintering treatment is 1-10°C / min, the treatment temperature is 100-600°C, and the treatment time is 1-20h; The secondary sintering treatment has a heating rate of 1-10°C / min, a treatment temperature of 600-1100°C, and a treatment time of 1-20h.

13. The method for preparing a positive electrode active material according to any one of claims 10 to 12, characterized in that: Before the sintering process, the raw materials including the Q source, the O source, part of the M source, and the positive electrode active material precursor are subjected to ball milling; The ball milling process is performed at a rotation speed of 50 to 1000 rpm and a processing time of 0.1 to 5 hours. 14 . A positive electrode sheet, comprising the positive electrode active material according to claim 1 or the positive electrode active material prepared by the method for preparing the positive electrode active material according to claim 10 .

15. A battery, characterized in that: Including the positive electrode sheet according to claim 14.

16. A battery pack, characterized in that: Including the battery according to claim 15.

17. An electrical device, characterized in that: Comprising the battery according to claim 15 or the battery pack according to claim 16.

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