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

Abstract

The invention provides a positive active material and a preparation method thereof, a positive pole piece, a battery and electric equipment, the positive active material comprises a bulk phase and a coating phase located on at least part of the surface of the bulk phase, the bulk phase comprises Nax1Mny1XzO2 + delta1, the Nax1Mny1XzO2 + delta1 comprises an O '3 phase, 0.8 < = x1 < = 1, 0.8 < = y1 < = 1, 0 < = z < = 0.2,-0.1 < = delta1 < = 1, and X comprises one or more of Ti, Zr, Ge and Sn; the coating phase comprises Nax2Mny2XzO2 + delta2, the Nax2Mny2XzO2 + delta2 comprises a P2 phase, 0.4 < = x2 < = 0.7, 0.85 < = y2 < = 1, and-0.1 < = delta2 < = 1. Therefore, the air stability of the positive electrode active material is improved, and the cycle stability of the battery is improved.

Description

Technical Field

[0001] The present application belongs to the field of battery technology, and specifically relates to positive electrode active materials and preparation methods, positive electrode sheets, batteries, and electrical equipment. Background Art

[0002] Secondary batteries, represented by sodium batteries, have been applied in energy storage power systems (such as hydropower, thermal power, wind power and solar power stations, etc.), as well as electric vehicles, aerospace and other fields. Compared with lithium batteries, sodium batteries have cost advantages in terms of raw materials, especially the sodium salts that are the main components of sodium battery positive electrode active materials. The reserves are more abundant, and the price of sodium salts is much lower than that of lithium salts used in lithium battery positive electrode active materials. This makes the cost of sodium battery positive electrode active materials lower than that of lithium batteries. However, the poor electrochemical performance of sodium batteries has limited their practical applications. Summary of the Invention

[0003] The purpose of this application is to provide a positive electrode active material and a preparation method thereof, a positive electrode plate, a battery and an electrical device, wherein the positive electrode active material has excellent air stability and can improve the cycle stability of the battery.

[0004] In a first aspect, the present application provides a positive electrode active material, comprising a bulk phase and a coating phase located at at least a portion of its surface, wherein the bulk phase comprises Na x1 Mn y1 X z O 2+δ1 , the Na x1 Mn y1 X z O 2+δ1 Including O'3 phase, 0.8≤x1≤1, 0.8≤y1≤1, 0≤z≤0.2, -0.1≤δ1≤1, X includes one or more of Ti, Zr, Ge, Sn; the coating phase includes Na x2 Mn y2 X z O 2+δ2 , the Na x2 Mn y2 X z O 2+δ2 The coating phase comprises a P2 phase, 0.4≤x2≤0.7, 0.85≤y2≤1, and -0.1≤δ2≤1. Thus, by forming a coating phase on at least a portion of the surface of the positive electrode active material, the coating phase can, on the one hand, reduce the probability of sodium in the bulk phase coming into contact with air and reacting by "coating"; on the other hand, the coating phase itself lacks sodium and has a low probability of reacting with air, thereby improving the air stability of the positive electrode active material and the cycle stability of the battery.

[0005] According to some embodiments of the present application, the volume average particle size D of the positive electrode active material is V 50 is 0.2 μm-3 μm. As a result, the conduction distance of sodium ions in the positive electrode active material is short and the surface side reaction is reduced, which promotes the positive electrode active material to exert its specific capacity and improves the capacity retention rate of the battery containing it.

[0006] According to some embodiments of the present application, the space groups of the O'3 phase and the P2 phase are C2 / m and P63 / mmc, respectively. As a result, the formed O'3 phase has a high sodium content, which can increase the capacity of the battery; and the formed P2 phase has a large interlayer spacing, which can improve the rate performance and cycle performance of the battery.

[0007] According to some embodiments of the present application, the 001 peak intensity in the X-ray diffraction spectrum of the O'3 phase is S1, the 002 peak intensity in the X-ray diffraction spectrum of the P2 phase is S2, and S1 and S2 satisfy 2≤S1 / S2≤6; the 2θ value corresponding to the 001 peak in the X-ray diffraction spectrum is 15.8°-16.8°, and the 2θ value corresponding to the 002 peak is 15.3°-16.3°. This improves the specific capacity of the positive electrode active material, increases the thickness and uniformity of the coating phase, and improves the air stability of the positive electrode active material.

[0008] According to some embodiments of the present application, the 001 peak intensity in the X-ray diffraction spectrum of the O'3 phase is S1, the 002 peak intensity in the X-ray diffraction spectrum of the P2 phase is S2, and S1 and S2 satisfy 3≤S1 / S2≤4.5; the 2θ value corresponding to the 001 peak in the X-ray diffraction spectrum is 15.8°-16.8°, and the 2θ value corresponding to the 002 peak is 15.3°-16.3°. This improves the specific capacity of the positive electrode active material, increases the thickness and uniformity of the coating phase, and improves the air stability of the positive electrode active material.

[0009] The second aspect of the present application provides a method for preparing a positive electrode active material, comprising: mixing a sodium source and a manganese source, and performing a first sintering in an inert atmosphere to form a bulk phase; performing a second sintering on the bulk phase in an oxygen-containing atmosphere to form a coating phase on at least a portion of the surface of the bulk phase; wherein the bulk phase comprises Na x1 Mn y1 O 2+δ1 , the Na x1 Mn y1 O 2+δ1 Including O'3 phase, 0.8≤x1≤1, 0.8≤y1≤1, -0.1≤δ1≤1; the coating phase includes Na x2 Mn y2 O 2+δ2 , the Na x2 Mn y2 O 2+δ2Including P2 phase, 0.4≤x2≤0.7, 0.85≤y2≤1, -0.1≤δ2≤1; or, mixing a sodium source, a manganese source, and an X source, performing a first sintering in an inert atmosphere to form a bulk phase; performing a second sintering in an oxygen-containing atmosphere to form a coating phase on at least a portion of the surface of the bulk phase; wherein the bulk phase includes Na x1 Mn y1 X z O 2+δ1 , the Na x1 Mn y1 X z O 2+δ1 Including O'3 phase, 0.8≤x1≤1, 0.8≤y1≤1, 0<z≤0.2, -0.1≤δ1≤1, X includes one or more of Ti, Zr, Ge, Sn; the coating phase includes Na x2 Mn y2 X z O 2+δ2 , the Na x2 Mn y2 X z O 2+δ2 The P2 phase comprises a P2 phase, 0.4≤x2≤0.7, 0.85≤y2≤1, and -0.1≤δ2≤1. Thus, a coating phase is formed on at least a portion of the surface of the bulk phase through secondary sintering. On the one hand, the coating phase can reduce the probability of sodium in the bulk phase reacting with air by "encapsulating" it. On the other hand, the coating phase itself has a low sodium content and a low probability of reacting with air, thereby improving the air stability of the positive electrode active material and the cycle stability of the battery.

[0010] According to some embodiments of the present application, the first sintering conditions include: a temperature of 800° C. to 1000° C. and a time of 12 hours to 18 hours, thereby forming sufficient O'3 phase and improving the specific capacity of the positive electrode active material.

[0011] According to some embodiments of the present application, the first sintering conditions include: a temperature of 850° C. to 950° C. and a time of 13 h to 17 h, thereby forming sufficient O'3 phase and improving the specific capacity of the positive electrode active material.

[0012] According to some embodiments of the present application, the oxygen-containing atmosphere includes oxygen or air. 3+ Oxidized to Mn by oxygen 4+ , while the surface part Na + The surface of the bulk phase forms a P2 phase with less sodium content, Na x MnO2 structure, thereby improving the air stability of the positive electrode active material.

[0013] According to some embodiments of the present application, the second sintering conditions include: a temperature of 900°C to 1000°C and a time of 8 hours to 15 hours. Thus, by setting the temperature and time of the second sintering within the above ranges, a uniform coating phase can be formed on the surface of the bulk phase of the positive electrode active material, thereby improving the air stability of the positive electrode active material.

[0014] According to some embodiments of the present application, the second sintering conditions include a temperature of 900°C-950°C and a time of 9-12 hours. Thus, by setting the temperature and time of the second sintering within the above ranges, a uniform coating phase can be formed on the surface of the bulk phase of the positive electrode active material, thereby improving the air stability of the positive electrode active material.

[0015] According to some embodiments of the present application, the method satisfies one or more of the following conditions: the sodium source includes one or more of Na2CO3, NaHCO3, NaOH, and Na2O2; and the manganese source includes one or more of Mn2O3, Mn3O4, MnO, and MnO2. Thus, the specific capacity of the positive electrode active material is increased.

[0016] According to some embodiments of the present application, the amounts of the sodium source and the manganese source are such that the atomic molar ratio of Na to Mn is 1:0.8-1.2.

[0017] A third aspect of the present application provides a positive electrode sheet 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. Thus, the positive electrode active material has excellent air stability, which can improve the structural stability of the positive electrode sheet and reduce the impact of the reaction between the positive electrode active material and air on the positive electrode sheet.

[0018] 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 cycle stability.

[0019] The fifth aspect of the present application provides an electrical device, including the battery provided by the fourth aspect of the present application.

[0020] 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

[0021] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings. The drawings are only for the purpose of illustrating the embodiments and are not to be considered as limiting the present application.

[0022] Figure 1 Schematic diagram of the structure of the positive electrode active material according to one embodiment of the present application.

[0023] Figure 2 It is a schematic diagram of the process of preparing positive electrode active materials according to one embodiment of the present application.

[0024] Figure 3 Schematic diagram of a battery according to one embodiment of the present application.

[0025] Figure 4 yes Figure 3 An exploded view of a battery according to an embodiment of the present application is shown.

[0026] Figure 5 Schematic diagram of a battery module according to one embodiment of the present application.

[0027] Figure 6 Schematic diagram of a battery pack according to one embodiment of the present application.

[0028] Figure 7 yes Figure 6 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0029] Figure 8 Schematic diagram of an electrical device using a battery as a power source according to one embodiment of the present application.

[0030] Figure 9 This is the XRD test pattern of the positive electrode active material in Example 1.

[0031] Figure 10 This is the XRD test pattern of the positive electrode active material in Comparative Example 1.

[0032] Figure 11 3 is a comparison chart of the XRD test results of the positive electrode active materials in Example 1 and Comparative Example 1.

[0033] Figure 12 This is a SEM test image of the positive electrode active material in Example 1 after being placed at room temperature for 10 days.

[0034] Figure 13 This is a SEM test image of the positive electrode active material in Comparative Example 1 after being placed at room temperature for 10 days.

[0035] Description of reference numerals:

[0036] 1: Battery; 2: Battery module; 3: Battery pack; 4: Upper case; 5: Lower case; 51: Shell; 52: Electrode assembly; 53: Cover; 11: Positive electrode active material; 111: Bulk phase; 112: Coating phase. DETAILED DESCRIPTION

[0037] The present application will be further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and are not used to limit the scope of the present application.

[0038] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the 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 in this application may be combined with other embodiments.

[0039] " Scope " disclosed in the present application is limited in the form of lower limit and / or upper limit, and given range is limited by selecting a lower limit and / or an upper limit, and the selected lower limit and / or 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 be combined with any upper limit to form a scope that is not clearly recorded, and any lower limit can be combined with other lower limits to form a scope that is not clearly recorded, and any upper limit can be combined with any other upper limit to form a scope that is not clearly recorded. In addition, each separately disclosed point or single numerical value itself can be combined with any other point or single numerical value as a lower limit or upper limit or form a scope that is not clearly recorded with other lower limits or upper limits.

[0040] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0041] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of this application.

[0042] Unless otherwise specified, the term "and / or" in this application simply describes an association between related objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Furthermore, the character " / " in this document generally indicates that the related objects are in an "or" relationship.

[0043] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and any variations thereof are intended to cover non-exclusive inclusions. Unless otherwise specified, the terms used in this application have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0044] Currently, market developments indicate that batteries are increasingly being used. They are not only used in energy storage systems such as hydropower, thermal, wind, and solar power plants, but are also widely used in electric vehicles like electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. As battery applications continue to expand, market demand is also growing.

[0045] Sodium is abundant in resources, widely distributed, and relatively low in cost. Furthermore, sodium-ion batteries (SIBs) share similar operating principles to lithium-ion batteries, and as such, have gradually attracted widespread attention and research. Among the positive electrode active materials for SIBs, the O'3 phase of manganese-based layered oxides offers the advantages of high specific capacity and low cost. However, due to the high sodium content in the O'3 phase, sodium easily accumulates on the surface of the SIB during preparation. When exposed to air, the sodium readily precipitates and reacts with carbon dioxide and water in the air, forming sodium carbonate and sodium hydroxide on the surface of the SIB. This results in a high residual alkali content in the SIB, which then readily reacts with carbon dioxide and water in the air, resulting in poor air stability.

[0046] The present application proposes a positive electrode active material, wherein the bulk phase includes an O'3 phase with a high sodium content, and at least part of the surface of the bulk phase has a coating phase, which is a sodium-deficient P2 phase. On the one hand, the coating phase can reduce the probability of sodium in the bulk phase reacting with air by "coating". On the other hand, the coating phase itself lacks sodium, which can reduce the probability of sodium reacting with air, reduce the content of residual alkali generated on the surface of the positive electrode active material due to the reaction of sodium with carbon dioxide and water in the air, thereby reducing the risk of further reaction of the residual alkali with air, improving the air stability of the positive electrode active material, and thus improving the cycle stability of the battery.

[0047] The positive electrode active material proposed in this application can be used in a battery, and the battery can be used in an electrical device that uses the battery as a power source or various energy storage systems that use the battery as an energy storage element. Electrical devices may include, but are not limited to, mobile phones, tablets, laptops, electric toys, electric tools, battery cars, electric cars, ships, spacecraft, and the like. Among them, electric toys may include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, and the like, and spacecraft may include airplanes, rockets, space shuttles, and spacecraft, and the like.

[0048] The first aspect of the present application proposes a positive electrode active material, referring to Figure 1 The positive electrode active material 11 includes a bulk phase 111 and a coating phase 112 located on at least a portion of its surface, wherein the bulk phase includes Na x1 Mn y1 X z O 2+δ1 , the Na x1 Mn y1 X z O 2+δ1 Including O'3 phase, 0.8≤x1≤1, 0.8≤y1≤1, 0≤z≤0.2, -0.1≤δ1≤1, X includes one or more of Ti, Zr, Ge, Sn; the coating phase includes Na x2 Mn y2 X z O 2+δ2 , the Na x2 Mn y2 X z O 2+δ2 Including P2 phase, 0.4≤x2≤0.7, 0.85≤y2≤1, -0.1≤δ2≤1.

[0049] The positive electrode active material proposed in this application has a sodium-deficient coating phase on at least part of the surface of the bulk phase. On the one hand, the coating phase can reduce the probability of the sodium in the bulk phase reacting with carbon dioxide and water in the air by "coating"; on the other hand, the sodium content in the P2 phase is relatively low. Compared with the surface of the O'3 phase as the surface of the positive electrode active material, the P2 phase as the surface of the positive electrode active material can form a "sodium-deficient" surface on the positive electrode active material. The reduction in the sodium content on the surface of the positive electrode active material can reduce the probability of sodium reacting with carbon dioxide and water in the air, thereby improving the air stability of the positive electrode active material and the cycle stability of the battery. The larger interlayer spacing of the P2 phase can increase the diffusion rate of sodium ions, thereby improving the rate performance of the battery.

[0050] The phase test method in this application is as follows: in a dry room or glove box, grind the sample to be tested in an agate mortar and then pass it through a 350 mesh sieve. Take an appropriate amount of the sieved sample and put it into the middle of the groove of the sample holder so that the loose sample powder is slightly higher than the plane of the sample holder; take a glass slide and gently press the surface of the sample to make the sample surface flat and consistent with the plane of the frame, and scrape off the excess powder. After the sample is prepared, use a Brucker D8A_A25 X-ray powder diffractometer from Brucker AxS, Germany, with CuK α The ray is the radiation source, and the wavelength of the ray is The scanning 2θ angle range is 5°-60° and the scanning rate is 4° / min for testing. The phase state of the positive electrode active material is determined according to the position of the characteristic peak in the XRD pattern. The characteristic peak in the scanning 2θ angle range of 42° to 43° indicates that the positive electrode active material is O'3 phase, and the characteristic peak in the scanning 2θ angle range of 48° to 50° indicates that the positive electrode active material is P2 phase.

[0051] In this application, the O'3 phase positive electrode active material refers to: sodium ions are octahedrally coordinated, the minimum number of repeated layers of TMO6 octahedral layers of oxygen ions stacked is 3, ABCABC, and it belongs to the C2 / m space group; the P2 phase positive electrode active material refers to: sodium ions are triangular prism coordinated, the minimum number of repeated layers of TMO6 octahedral layers of oxygen ions stacked is 2, ABAB, and it belongs to the P63 / mmc space group.

[0052] According to some embodiments of the present application, 0.8≤x1≤1, for example, x1 can be 0.8, 0.82, 0.84, 0.86, 0.88, 0.9, 0.92, 0.94, 0.96, 0.98, or 1, or can be any range of the above values, thereby increasing the capacity of the battery.

[0053] According to some embodiments of the present application, 0.8≤y1≤1, for example, can be 0.8, 0.82, 0.84, 0.86, 0.88, 0.9, 0.92, 0.94, 0.96, 0.98, or 1, or can be a range consisting of any of the above values. Thus, by adjusting the manganese content within the above range, the structural stability of the O'3 phase layered material can be improved, the risk of active metal ion overflow in the positive electrode active material can be reduced, and the cycle stability of the positive electrode active material can be improved.

[0054] According to some embodiments of the present application, 0≤z≤0.2, for example, can be 0, 0.04, 0.08, 0.12, 0.16, or 0.2, or can be a range consisting of any of the above values. Thus, doping the bulk phase with different contents of the element X can form a bulk phase having an O'3 phase, thereby increasing the specific capacity of the positive electrode active material.

[0055] According to some embodiments of the present application, -0.1≤δ1≤1, for example, it can be -0.1, -0.05, 0, 0.1, 0.3, 0.5, 0.7, 0.9 or 1, etc., or it can be a range consisting of any of the above values.

[0056] It should be noted that, as the battery undergoes cycling and other processes, the oxygen element in the bulk phase is lost, so the measured oxygen element content 2+δ1 in the bulk phase may be less than 2.

[0057] According to some embodiments of the present application, 0.4 ≤ x2 ≤ 0.7, for example, can be 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, or 0.7, or can be a range consisting of any of the above values. Thus, by setting the sodium content in the P2 phase within the above range, the probability of sodium reacting with carbon dioxide and water in the air is reduced, the air stability of the positive electrode active material is improved, and the battery capacity is increased.

[0058] According to some embodiments of the present application, 0.85≤y2≤1, for example, y2 can be 0.85, 0.87, 0.89, 0.91, 0.93, 0.95, 0.97, 0.99, or 1, or can be a range consisting of any of the above values. Thus, by adjusting the manganese content within the above range, the structural stability of the P2 phase layered material can be improved, the risk of active metal ion overflow in the positive electrode active material can be reduced, and the cycle stability of the positive electrode active material can be improved.

[0059] According to some embodiments of the present application, -0.1≤δ2≤1, for example, it can be -0.1, -0.05, 0, 0.1, 0.3, 0.5, 0.7, 0.9 or 1, etc., or it can be a range consisting of any of the above values.

[0060] It should be noted that, as the battery undergoes cycling and other processes, the oxygen element in the coating phase is lost, so the measured oxygen element content 2+δ2 in the P2 phase may be less than 2.

[0061] 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 0.2 μm-3 μm. For example, it can be 0.2 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm or 3 μm, or can be a range consisting of any of the above values. As a result, the conduction distance of sodium ions in the positive electrode active material is short and the surface side reactions are reduced, which promotes the positive electrode active material to exert its specific capacity and improves the capacity retention rate of the battery containing it.

[0062] In this application, D v50 refers to the particle size corresponding to the cumulative volume distribution percentage reaching 50%, as measured, for example, using a laser particle size analyzer (Malvern Master Size 2000) in accordance with the standard GB / T 19077-2016 / ISO 13320:2009. The specific testing procedure is as follows: Take an appropriate amount of the sample to be tested (ensure the sample concentration is 8%-12% obscuration), add 20ml of deionized water, and ultrasonicate for 5 minutes (53kHz / 120W) to ensure complete dispersion of the sample. The sample is then measured according to the GB / T 19077-2016 / ISO 13320:2009 standard.

[0063] According to some embodiments of the present application, the space groups of the O'3 phase and the P2 phase are C2 / m and P63 / mmc, respectively. As a result, the formed O'3 phase has a high sodium content, which can increase the battery capacity; the formed P2 phase has a large interlayer spacing, which can increase the diffusion rate of sodium ions and thus improve the battery's rate performance.

[0064] According to some embodiments of the present application, the 001 peak intensity in the X-ray diffraction spectrum of the O'3 phase is S1, and the 002 peak intensity in the X-ray diffraction spectrum of the P2 phase is S2, with S1 and S2 satisfying 2≤S1 / S2≤6; the 2θ value corresponding to the 001 peak in the X-ray diffraction spectrum is 15.8°-16.8°, and the 2θ value corresponding to the 002 peak is 15.3°-16.3°. For example, S1 / S2 can be 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, or 6, or can be a range consisting of any of the above values. Thus, on the one hand, the content of the bulk phase in the positive electrode active material is increased, thereby increasing the specific capacity of the material; on the other hand, the content of the P2 phase in the positive electrode active material is increased, a uniform P2 phase is formed on the surface of the bulk phase, the coating effect of the P2 phase is improved, and the air stability of the positive electrode active material is improved. According to some specific embodiments of the present application, 3≤S1 / S2≤4.5.

[0065] 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 mixing a sodium source and a manganese source, performing a first sintering in an inert atmosphere to form a bulk phase; performing a second sintering on the bulk phase in an oxygen-containing atmosphere to form a coating phase on at least a portion of the surface of the bulk phase; wherein the bulk phase comprises Na x1 Mn y1 O 2+δ1 , the Na x1 Mn y1 O 2+δ1 Including O'3 phase, 0.8≤x1≤1, 0.8≤y1≤1, -0.1≤δ1≤1; the coating phase includes Na x2 Mn y2 O 2+δ2, the Na x2 Mn y2 O 2+δ2 Including P2 phase, 0.4≤x2≤0.7, 0.85≤y2≤1, -0.1≤δ2≤1; or, mixing a sodium source, a manganese source, and an X source, performing a first sintering in an inert atmosphere to form a bulk phase; performing a second sintering in an oxygen-containing atmosphere to form a coating phase on at least a portion of the surface of the bulk phase; wherein the bulk phase includes Na x1 Mn y1 X z O 2+δ1 , the Na x1 Mn y1 X z O 2+δ1 Including O'3 phase, 0.8≤x1≤1, 0.8≤y1≤1, 0<z≤0.2, -0.1≤δ1≤1, X includes one or more of Ti, Zr, Ge, Sn; the coating phase includes Na x2 Mn y2 X z O 2+δ2 , the Na x2 Mn y2 X z O 2+δ2 The P2 phase comprises a P2 phase, 0.4≤x2≤0.7, 0.85≤y2≤1, and -0.1≤δ2≤1. Thus, a coating phase is formed on at least a portion of the surface of the bulk phase through secondary sintering. On the one hand, the coating phase can reduce the probability of sodium in the bulk phase reacting with air by "encapsulating" it. On the other hand, the coating phase itself has a low sodium content and a low probability of reacting with air, thereby improving the air stability of the positive electrode active material and the cycle stability of the battery.

[0066] refer to Figure 2 , the following is a detailed description of each step of this application:

[0067] S100: Sodium source and manganese source are mixed for the first sintering to prepare the bulk phase

[0068] According to some embodiments of the present application, in this step, the sodium source and the manganese source are mixed and sintered for the first time in an inert atmosphere to form a bulk phase, wherein the bulk phase includes Na x1 Mn y1 O 2+δ1 , the Na x1 Mn y1 O 2+δ1 Including O'3 phase, 0.8≤x1≤1, 0.8≤y1≤1, -0.1≤δ1≤1.

[0069] According to some embodiments of the present application, a sodium source, a manganese source, and an X source are mixed and sintered for the first time in an inert atmosphere to form a bulk phase, wherein the bulk phase includes Na x1 Mn y1 X z O 2+δ1 , the Na x1 Mn y1 X z O 2+δ1 The invention comprises an O'3 phase, 0.8≤x1≤1, 0.8≤y1≤1, 0<z≤0.2, -0.1≤δ1≤1, and X comprises one or more of Ti, Zr, Ge, and Sn.

[0070] According to some embodiments of the present application, the conditions for the first sintering include: a temperature of 800° C.-1000° C. and a time of 12 hours-18 hours.

[0071] As an example, the temperature of the first sintering can be 800°C, 850°C, 900°C, 950°C or 1000°C, or any range thereof. According to some specific embodiments of the present application, the temperature of the first sintering can be 850°C-950°C.

[0072] As an example, the first sintering time can be 12h, 13h, 14h, 15h, 16h, 17h or 18h, or can be any range of the above values. According to some specific embodiments of the present application, the first sintering time can be 13h-17h.

[0073] Therefore, by setting the temperature and time of the first sintering within the above ranges, the content of the O'3 phase in the positive electrode active material is increased, thereby increasing the specific capacity of the positive electrode active material.

[0074] According to some embodiments of the present application, the inert atmosphere may include an inert gas or nitrogen.

[0075] According to some embodiments of the present application, the sodium source includes one or more of Na2CO3, NaHCO3, NaOH, and Na2O2.

[0076] According to some embodiments of the present application, the manganese source includes one or more of Mn2O3, Mn3O4, MnO, and MnO2.

[0077] According to some embodiments of the present application, the amounts of the sodium source and the manganese source are such that the atomic molar ratio of Na to Mn is 1:0.8-1.2. For example, the ratio may be 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, or any range thereof. This reduces the volatilization of the sodium source during high-temperature sintering and, at the same time, reduces the residual alkali content on the surface of the positive electrode active material.

[0078] S200: Sinter the bulk phase for the second time to prepare the coating phase

[0079] According to some embodiments of the present application, the bulk phase prepared in S100 is sintered for a second time in an oxygen-containing atmosphere to form a coating phase on at least a portion of the surface of the bulk phase, wherein the coating phase includes Na x2 Mn y2 X z O 2+δ2 , the Na x2 Mn y2 X z O 2+δ2 The P2 phase comprises a P2 phase, 0.4≤x2≤0.7, 0.85≤y2≤1, 0≤z≤0.2, -0.1≤δ2≤1, and X comprises one or more of Ti, Zr, Ge, and Sn. Thus, on the one hand, the "coating" of the coating phase can reduce the probability of sodium in the bulk phase reacting with air. On the other hand, the coating phase itself lacks sodium and has a lower probability of reacting with air, thereby improving the air stability of the positive electrode active material and the cycle stability of the battery.

[0080] According to some embodiments of the present application, the conditions for the second sintering include: a temperature of 900° C.-1000° C. and a time of 8 h-15 h.

[0081] As an example, the temperature of the second sintering can be 900°C, 920°C, 940°C, 960°C, 980°C or 1000°C, or can be a range of any of the above values. According to some specific embodiments of the present application, the temperature of the second sintering can be 900°C-950°C.

[0082] As an example, the second sintering time can be 8h, 9h, 10h, 11h, 12h, 13h, 14h or 15h, or can be a range of any of the above values. According to some specific embodiments of the present application, the second sintering time can be 9h-12h.

[0083] Therefore, by setting the temperature and time of the second sintering within the above ranges, a uniformly coated coating phase is formed on the surface of the bulk phase, thereby enhancing the air isolation effect of the coating phase and improving the air stability of the positive electrode active material.

[0084] According to some embodiments of the present application, the oxygen-containing atmosphere includes oxygen or air.

[0085] A third aspect of the present application provides a positive electrode sheet 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. Thus, the positive electrode active material has excellent air stability, which can improve the structural stability of the positive electrode sheet and reduce the impact of the reaction between the positive electrode active material and air on the positive electrode sheet.

[0086] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, and the positive electrode film layer contains the positive electrode active material.

[0087] In the present application, the positive electrode current collector may be, for example, a metal foil or a composite current collector. The metal foil may be, for example, aluminum foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one side of the polymer base layer. The metal layer may be made of, but is not limited to, aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The polymer material of the polymer base layer may be, for example, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and the like.

[0088] In some embodiments, the positive electrode active material is a positive electrode active material in the positive electrode film layer. In addition to the positive electrode active material, the positive electrode film layer may optionally contain a conductive agent and / or a binder. 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 include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0089] This application does not particularly limit the preparation method of the positive electrode sheet, and the preparation method can refer to existing methods. For example, the positive electrode slurry is coated on the positive electrode current collector, dried, and cold pressed to form the positive electrode sheet. The positive electrode slurry can be formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and other components in a solvent (e.g., N-methylpyrrolidone) and stirring them uniformly.

[0090] In addition, the positive electrode sheet of the present application does not exclude other additional functional layers in addition to the positive electrode film layer. For example, the positive electrode sheet may also include a conductive primer layer (e.g., composed of a conductive agent and a binder) disposed between the positive electrode current collector and the positive electrode film layer. For another example, the positive electrode sheet may also include a protective layer covering the surface of the positive electrode film layer.

[0091] The fourth aspect of the present application provides a battery comprising the positive electrode sheet described in the third aspect of the present application.

[0092] In some embodiments, the battery further comprises a negative electrode, a separator, and an electrolyte. During the battery's charge and discharge processes, active ions are intercalated and released between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, disposed between the positive and negative electrodes, prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0093] [Negative electrode]

[0094] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode material.

[0095] In some embodiments, the negative electrode current collector may include a metal foil or a composite current collector. The metal foil is, for example, copper foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one side of the polymer base layer. The material of the metal layer includes, but is not limited to, copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, and the polymer material of the polymer base layer includes, but is not limited to, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and the like.

[0096] In the present application, the negative electrode material may include negative electrode active materials for secondary batteries well known in the art. For example, the negative electrode active material includes one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include one or more of elemental tin, tin oxides, and tin alloys.

[0097] In some embodiments, the negative electrode film layer may further optionally include a binder. The binder may include, for example, one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0098] In some embodiments, the negative electrode film layer may further optionally include a conductive agent. For example, the conductive agent may include one or more of superconducting carbon, acetylene black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0099] In some embodiments, the negative electrode film layer may further optionally contain other additives, such as a thickener. Specific examples of thickeners include, but are not limited to, sodium carboxymethyl cellulose (CMC-Na).

[0100] The present application does not particularly limit the preparation method of the negative electrode sheet, and the negative electrode sheet can be prepared by referring to existing methods. For example, the negative electrode components, such as the negative electrode material, conductive agent, and binder, are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry; the negative electrode slurry is then coated on a negative electrode current collector, and the negative electrode sheet is obtained by drying and cold pressing.

[0101] [Electrolyte]

[0102] In this application, the electrolyte can be selected with reference to existing secondary batteries. In some embodiments, the electrolyte comprises an organic solvent, a sodium salt, and an optional additive. The sodium salt includes, but is not limited to, one or more of NaPF6, NaClO4, NaBCl4, NaSO3CF3, and Na(CH3)C6H4SO3. The organic solvent includes, but is not limited to, one or more of 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), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0103] In some embodiments, the additives in the electrolyte may include negative electrode film-forming additives and positive electrode film-forming additives; they may also include additives that can improve certain performance of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high temperature or low temperature performance of the battery, etc. As an example, the additives may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), vinyl sulfate (DTD), propylene sulfate, vinyl sulfite (ES), 1,3-propane sultone (PS), 1,3-propene sultone (PST), sulfonate cyclic quaternary ammonium salt, succinic anhydride, succinonitrile (SN), adiponitrile (AND), tris(trimethylsilyl) phosphate (TMSP) and tris(trimethylsilyl) borate (TMSB). One or more.

[0104] [Isolation film]

[0105] In the present application, the isolation membrane is arranged between the positive electrode plate and the negative electrode plate, and mainly plays the role of preventing the positive and negative electrodes from short-circuiting, while allowing active ions to pass through. The present application has no particular restrictions on the type of isolation membrane, and various porous structure isolation membranes well known in the art can be selected. In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. In addition, the isolation membrane can be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer are the same or different.

[0106] In some embodiments, a ceramic coating and / or a metal oxide coating is further provided on the isolation membrane.

[0107] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0108] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0109] In some embodiments, the battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0110] In some embodiments, the battery outer packaging may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the battery outer packaging may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0111] The present application has no particular restrictions on the shape of the battery, which can be cylindrical, square or any other shape. For example, Figure 3 The battery 5 is a square structure as an example.

[0112] In some embodiments, reference Figure 4 The outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0113] In some embodiments, batteries may be assembled into a battery module. The number of batteries contained in the battery module may be one or more. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0114] Figure 5 4 is an example of a battery module. Figure 5 In the battery module 4, the multiple batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other manner. Further, the multiple batteries 5 can be fixed by fasteners.

[0115] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of batteries 5 are received in the receiving space.

[0116] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0117] Figure 6 and Figure 7 The battery pack 1 is used as an example. Figure 6 and Figure 7 The battery pack 1 may include a battery box and multiple battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner in the battery box.

[0118] In addition, the present application also provides an electric device, which includes at least one of the batteries, battery modules, or battery packs provided in the present application. The battery, battery module, or battery pack can be used as a power source for the electric device, or as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0119] As the electrical device, a battery, a battery module or a battery pack can be selected according to its usage requirements.

[0120] Figure 8 This is an example of an electric device. This electric device is 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 the electric device, a battery pack or battery module can be used.

[0121] Another example device may be a mobile phone, a tablet computer, a laptop computer, etc. Such a device is usually required to be light and thin, and may use a battery as a power source.

[0122] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0123] Example 1

[0124] The corresponding sodium source (Na2CO3) and manganese source (Mn2O3) were weighed according to the Na:Mn (molar ratio) = 1:1, and mechanically ball milled at 400 rpm for 2 hours. The resulting mixture was placed in a muffle furnace and heated to 900°C at 5°C / min under argon protection, kept warm for 15 hours, and naturally cooled to room temperature to obtain O'3 phase material.

[0125] Subsequently, the O'3 phase material was heated to 900°C at 5°C / min in an air atmosphere, kept at this temperature for 10 h, and naturally cooled to room temperature to obtain a positive electrode active material.

[0126] Example 2

[0127] A manganese-based sodium electrical material was prepared according to the method of Example 1, except that the second sintering temperature was adjusted to 850°C.

[0128] Example 3

[0129] A manganese-based sodium electrical material was prepared according to the method of Example 1, except that the second sintering temperature was adjusted to 950°C.

[0130] Example 4

[0131] A manganese-based sodium electrical material was prepared according to the method of Example 1, except that the second sintering time was adjusted to 7 h.

[0132] Example 5

[0133] A manganese-based sodium electrical material was prepared according to the method of Example 1, except that the second sintering time was adjusted to 9 hours.

[0134] Example 6

[0135] A manganese-based sodium electrical material was prepared according to the method of Example 1, except that the second sintering time was adjusted to 12 h.

[0136] Example 7

[0137] A manganese-based sodium electrical material was prepared according to the method of Example 1, except that the corresponding sodium source (Na2CO3) and manganese source (Mn2O3) were weighed according to Na:Mn (molar ratio) = 0.85:1.

[0138] Example 8

[0139] A manganese-based sodium electrical material was prepared according to the method of Example 1, except that the corresponding sodium source (Na2CO3), manganese source (Mn2O3) and titanium source (TiO2) were weighed according to Na:Mn:Ti=1:0.9:0.1.

[0140] Comparative Example 1

[0141] The corresponding sodium source (Na2CO3) and manganese source (Mn2O3) were weighed according to the Na:Mn (molar ratio) = 1:1, and mechanically ball milled at 400 rpm for 2 hours. The resulting mixture was placed in a muffle furnace and heated to 900°C at 5°C / min under argon protection, kept warm for 15 hours, and naturally cooled to room temperature to obtain O'3 phase material with the chemical formula NaMnO2.

[0142] Test Case

[0143] 1. Morphology characterization

[0144] Testing using SEM images: Field emission scanning electron microscope (Zeiss Gemini360) was used for testing in accordance with JY / T010-1996 standard.

[0145] 2. Crystalline phase characterization

[0146] In a dry room or glove box, grind the sample to be tested in an agate mortar and pass it through a 350 mesh sieve. Take an appropriate amount of the sieved sample and place it in the middle of the groove of the sample holder so that the loose sample powder is slightly higher than the plane of the sample holder. Take a glass slide and gently press the sample surface until the sample surface is flattened and aligned with the frame plane, and scrape off the excess powder. After the sample is prepared, use a Brucker D8A_A25 X-ray powder diffractometer from BruckerAxS, Germany, with CuK α The ray is the radiation source, and the wavelength of the ray is The scanning 2θ angle range is 5° to 60°, and the scanning rate is 4° / min. After the test is completed, the space group of the sample can be confirmed by comparing the XRD diffraction peak of the sample with the standard card of the XRD analysis software.

[0147] 3. Air stability test

[0148] The positive electrode active material was placed in humid air (humidity>60%) at room temperature for 10 days and then subjected to XRD and SEM tests.

[0149] 4. Capacity retention rate test after 50 cycles

[0150] At 25°C, a button cell prepared from the layered oxide cathode active material was charged to 4.3 V at a constant current density of 10 mA / g, and then discharged to 2 V at a constant current density of 10 mA / g. The battery's discharge specific capacity (C0) was obtained. The battery was then subjected to 50 cycles of constant charge and discharge at a current density of 10 mA / g, with the discharge specific capacity (C1) at the 50th cycle being obtained. The capacity retention ratio of the layered oxide cathode active material after 50 cycles is calculated as C1 / C0.

[0151] The button cell is prepared according to the following steps.

[0152] Preparation of positive electrode sheets: The layered oxide positive electrode active material, conductive agent carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are thoroughly stirred and mixed in an appropriate amount of solvent NMP at a mass ratio of 80:15:5 to form a uniform positive electrode slurry; the positive electrode slurry is evenly coated on the surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, it is punched into a disc with a diameter of 14 mm to obtain a positive electrode sheet.

[0153] Negative electrode: Sodium metal sheet.

[0154] Preparation of the electrolyte: Ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in equal volumes to obtain an organic solvent, and then NaClO4 was dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0155] Isolation membrane: porous polyethylene membrane is used as the isolation membrane.

[0156] Preparation of button battery: stack the above-mentioned positive electrode sheet, separator, and negative electrode sheet in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, add the above-prepared electrolyte, and the preparation of the button battery is completed.

[0157] The structures of the positive electrode active materials in Examples 1 to 9 and Comparative Example 1 and the test results of the batteries are shown in Table 1.

[0158] Table 1

[0159]

[0160] Conclusion: It can be seen from the comparison of Examples 1 to 8 with Comparative Example 1 that the cycle capacity retention rate of the battery proposed in the present application is significantly higher than that of the comparative example, indicating that the present application can reduce the probability of sodium reacting with carbon dioxide and water in the air by forming a coating phase on at least part of the surface of the bulk phase, thereby improving the air stability of the positive electrode active material.

[0161] From the comparison of Examples 1 to 6, it can be seen that by adjusting the temperature and time of the second sintering, it is expected to increase the content of the coating phase on the surface of the bulk phase, form a uniform coating phase on the surface of the bulk phase, thereby improving the coating effect and improving the air stability of the positive electrode active material.

[0162] It can be seen from the comparison between Example 1 and Example 7 that by adjusting the mass ratio of the sodium source to the manganese source, the element content of the bulk phase and the coating phase can be adjusted, thereby improving the air stability of the positive electrode active material.

[0163] It can be seen from Example 8 that when the bulk phase and the coating phase contain doping elements, the coating phase can also reduce the probability of sodium reacting with carbon dioxide and water in the air, thereby improving the air stability of the positive electrode active material.

[0164] Figure 9 is the XRD test result of Example 1, Figure 10 is the XRD test result of Comparative Example 1, Figure 11 3 is a comparison chart of the XRD test results of Example 1 and Comparative Example 1. The XRD peak intensity of Example 1 is higher than that of Comparative Example 1, and Comparative Example 1 has more new miscellaneous peaks, indicating that the bulk structure is damaged.

[0165] Figure 12 This is the SEM image of the positive electrode active material in Example 1 after being placed at room temperature for 10 days. Figure 13 This is an SEM image of the positive electrode active material in Comparative Example 1 after being placed at room temperature for 10 days. By comparison, it can be seen that the surface of the positive electrode active material in Example 1 is relatively smooth and basically has no cracks; the surface of the positive electrode active material in Comparative Example 1 has products after reaction with air, and the material has many cracks, indicating that the positive electrode active material in Example 1 has better stability in air.

[0166] 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, characterized in that It includes a bulk phase and a coating phase located on at least a portion of its surface, wherein the bulk phase includes Na x1 Mn y1 X z O 2+δ1 , the Na x1 Mn y1 X z O 2+δ1 Including O'3 phase, 0.8≤x1≤1, 0.8≤y1≤1, 0≤z≤0.2, -0.1≤δ1≤1, X includes one or more of Ti, Zr, Ge, Sn; the coating phase includes Na x2 Mn y2 X z O 2+δ2 , the Na x2 Mn y2 X z O 2+δ2 Including P2 phase, 0.4≤x2≤0.7, 0.85≤y2≤1, -0.1≤δ2≤1.

2. The positive electrode active material according to claim 1, characterized in that The volume average particle size D of the positive electrode active material V 50 is 0.2μm-3μm.

3. The positive electrode active material according to claim 1 or 2, characterized in that The space groups of the O'3 phase and the P2 phase are C2 / m and P63 / mmc, respectively.

4. The positive electrode active material according to any one of claims 1 to 3, characterized in that The 001 peak intensity in the X-ray diffraction spectrum of the O'3 phase is S1, the 002 peak intensity in the X-ray diffraction spectrum of the P2 phase is S2, and S1 and S2 satisfy 2≤S1 / S2≤6; The 2θ value corresponding to the 001 peak of the X-ray diffraction spectrum is 15.8°-16.8°, and the 2θ value corresponding to the 002 peak is 15.3°-16.3°.

5. The positive electrode active material according to any one of claims 1 to 4, characterized in that The 001 peak intensity in the X-ray diffraction spectrum of the O'3 phase is S1, the 002 peak intensity in the X-ray diffraction spectrum of the P2 phase is S2, and S1 and S2 satisfy 3≤S1 / S2≤4.5; The 2θ value corresponding to the 001 peak of the X-ray diffraction spectrum is 15.8°-16.8°, and the 2θ value corresponding to the 002 peak is 15.3°-16.3°.

6. A method for preparing a positive electrode active material, characterized in that: include: The sodium source and the manganese source are mixed and sintered for the first time in an inert atmosphere to form a bulk phase; The bulk phase is sintered for a second time in an oxygen-containing atmosphere to form a coating phase on at least a portion of the surface of the bulk phase; wherein the bulk phase includes Na x1 Mn y1 O 2+δ1 , the Na x1 Mn y1 O 2+δ1 Including O'3 phase, 0.8≤x1≤1, 0.8≤y1≤1, -0.1≤δ1≤1; the coating phase includes Na x2 Mn y2 O 2+δ2 , the Na x2 Mn y2 O 2+δ2 Including P2 phase, 0.4≤x2≤0.7, 0.85≤y2≤1, -0.1≤δ2≤1; or, The sodium source, manganese source and X source are mixed and sintered for the first time in an inert atmosphere to form a bulk phase; The bulk phase is sintered for a second time in an oxygen-containing atmosphere to form a coating phase on at least a portion of the surface of the bulk phase; wherein the bulk phase includes Na x1 Mn y1 X z O 2+δ1 , the Na x1 Mn y1 X z O 2+δ1 Including O'3 phase, 0.8≤x1≤1, 0.8≤y1≤1, 0<z≤0.2, -0.1≤δ1≤1, X includes one or more of Ti, Zr, Ge, Sn; the coating phase includes Na x2 Mn y2 X z O 2+δ2 , the Na x2 Mn y2 X z O 2+δ2 Including P2 phase, 0.4≤x2≤0.7, 0.85≤y2≤1, -0.1≤δ2≤1.

7. The method according to claim 6, characterized in that The conditions for the first sintering include: a temperature of 800° C.-1000° C. and a time of 12 hours-18 hours.

8. The method according to claim 6 or 7, characterized in that The conditions for the first sintering include: a temperature of 850° C.-950° C. and a time of 13 h-17 h.

9. The method according to any one of claims 6 to 8, characterized in that The oxygen-containing atmosphere includes oxygen or air.

10. The method according to any one of claims 6 to 9, characterized in that: The conditions for the second sintering include: a temperature of 900° C.-1000° C. and a time of 8 h-15 h.

11. The method according to any one of claims 6 to 10, characterized in that: The conditions for the second sintering include: a temperature of 900° C.-950° C. and a time of 9 hours-12 hours.

12. The method according to any one of claims 6 to 11, characterized in that: The method satisfies one or more of the following conditions: The sodium source includes one or more of Na2CO3, NaHCO3, NaOH, and Na2O2. The manganese source includes one or more of Mn2O3, Mn3O4, MnO, and MnO2.

13. The method according to any one of claims 6 to 12, characterized in that: The amounts of the sodium source and the manganese source are such that the atomic molar ratio of Na to Mn is 1:0.8-1.

2.

14. A positive electrode plate, characterized in that: The invention comprises: the positive electrode active material according to any one of claims 1 to 5 or the sodium secondary positive electrode active material prepared by the method according to any one of claims 6 to 13.

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

16. An electrical device, characterized in that: Including the battery according to claim 15.

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