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 substrate, and at least part of the surface of the substrate is provided with a coating layer; wherein the matrix comprises NayNiaMnbFecXdO2 + delta, X comprises one or more of Zn, Cu and Co, y is more than or equal to 0.8 and less than or equal to 1, a is more than or equal to 0.22 and less than or equal to 0.45, b is more than or equal to 0.33 and less than or equal to 0.45, c is more than or equal to 0.2 and less than or equal to 0.35, d is more than 0 and less than or equal to 0.15, a + b + c + d = 1, and delta is more than or equal to-0.1 and less than or equal to 1; the coating layer comprises perovskite, the perovskite comprises ABO3, A comprises one or more of Ca, La, Sr, Al, Gd and Y, and B comprises one or more of Ni, Mn, Fe and X. Therefore, gas production of the battery is reduced, 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 thereof, 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 sheet, a battery and an electrical device.

[0004] The first aspect of the present application provides a positive electrode active material, the positive electrode active material includes a substrate, at least part of the surface of the substrate has a coating layer; wherein the substrate includes Na y Ni a Mn b Fe c X d O 2+δ , X includes one or more of Zn, Cu, and Co, 0.8≤y≤1, 0.22≤a≤0.45, 0.33≤b≤0.45, 0.2≤c≤0.35, 0<d≤0.15, a+b+c+d=1, and -0.1≤δ≤1; the coating layer includes perovskite, the perovskite includes ABO3, A includes one or more of Ca, La, Sr, Al, Gd, and Y, and B includes one or more of Ni, Mn, Fe, and X. Thus, at least a portion of the surface of the positive electrode active material matrix has a coating layer, which can reduce the probability of gas generation due to side reactions of the matrix in contact with the electrolyte. Even if oxygen evolution occurs on the surface of the matrix, the oxygen vacancies in the perovskite structure of the coating layer can capture oxygen atoms, reducing the probability of oxygen atoms on the surface of the matrix combining with each other to form oxygen, thereby reducing battery gas production and improving battery cycle stability.

[0005] According to some embodiments of the present application, a transition layer is further included between the substrate and the coating layer, and the transition layer includes the Na doped with the ABO3 y Ni a Mn b Fe c X d O2+δ As a result, the lattice constants between the substrate and the transition layer, and between the transition layer and the coating layer are more matched, and the structural stability of the coating layer is improved during the cycle.

[0006] According to some embodiments of the present application, the ratio of the thickness of the transition layer to the coating layer is 1:(10-50). Thus, the transition layer includes both element A and element B as well as the material forming the matrix. The transition layer can act as a "pillar" to reduce the volume change of the material during charge and discharge, thereby reducing the impact on the electrode structure.

[0007] According to some embodiments of the present application, the molar ratio of Na atoms to A atoms in the positive electrode active material is 1:(0.005-0.02). This forms a uniform coating on the surface of the substrate, while increasing the substrate content in the positive electrode active material, thereby reducing battery gas production and increasing the battery's energy density.

[0008] According to some embodiments of the present application, in the perovskite, A includes Ca and La, and the molar ratio of Ca atoms to La atoms is 0.25-4. This is beneficial to valence balance and improves the structural stability of the perovskite.

[0009] According to some embodiments of the present application, the volume average particle size D of the positive electrode active material is V 50 is 3 μm-10 μm. As a result, the volume average particle size of the positive electrode active material is small, which can reduce the migration path of sodium ions and improve the rate performance of the battery.

[0010] The second aspect of the present application provides a method for preparing a positive electrode active material, comprising: mixing a positive electrode active material matrix with a source A, and first sintering to allow the source A to react with at least a portion of the surface of the positive electrode active material matrix to form a coating layer comprising perovskite; the matrix comprises Na y Ni a Mn b Fe c X d O 2+δ , X includes one or more of Zn, Cu, and Co, 0.8≤y≤1, 0.22≤a≤0.45, 0.33≤b≤0.45, 0.2≤c≤0.35, 0<d≤0.15, a+b+c+d=1, -0.1≤δ≤1; the perovskite includes ABO3, A includes one or more of Ca, La, Sr, Al, Gd, and Y, and B is the Na in the reaction y Ni a Mn b Fe c X d O 2+δThe metal elements provided include one or more of Ni, Mn, Fe, and X. Thus, the positive electrode active material prepared by this method possesses all the characteristics and advantages of the aforementioned positive electrode active materials, which will not be elaborated here. In general, perovskite can be formed in situ on at least a portion of the surface of the substrate, reducing battery gas production under high pressure conditions and improving battery cycle stability.

[0011] According to some embodiments of the present application, the A source includes one or more of a calcium source and a lanthanum source, thereby facilitating valence state balance and improving the structural stability of the perovskite.

[0012] According to some embodiments of the present application, the calcium source includes one or more of calcium oxide, calcium carbonate, calcium hydroxide, calcium nitrate, calcium chloride, and calcium sulfate; the lanthanum source includes one or more of lanthanum oxide, lanthanum hydroxide, lanthanum nitrate, and lanthanum chloride.

[0013] According to some embodiments of the present application, the source A includes a calcium source and a lanthanum source, and the molar ratio of the calcium source to the lanthanum source, calculated as Ca and La, is 0.25-4. This is beneficial to the valence balance of the formed perovskite and improves the structural stability of the perovskite.

[0014] According to some embodiments of the present application, the molar ratio of the matrix to the A source, calculated as Na, is 1:(0.005-0.02). This allows a uniform coating to be formed on the surface of the matrix while increasing the matrix content in the positive electrode active material, thereby reducing battery gas production and increasing the battery's energy density.

[0015] According to some embodiments of the present application, the method satisfies one or more of the following conditions: the temperature of the first sintering is 400°C-1000°C, and the time of the first sintering is 2h-24h; the temperature of the second sintering is 700°C-1000°C, and the time of the second sintering is 6h-15h.

[0016] According to some embodiments of the present application, the method satisfies one or more of the following conditions: the temperature of the first sintering is 600°C-900°C, and the time of the first sintering is 4h-18h; the temperature of the second sintering is 720°C-850°C, and the time of the second sintering is 7h-10h.

[0017] Therefore, by setting the first sintering temperature within the above range, a uniform coating layer can be formed on the surface of the substrate while reducing the risk of sodium precipitation in the substrate; by setting the second sintering temperature and time within the above range, the content of the substrate in the positive electrode active material is increased, and the specific capacity of the positive electrode active material is increased.

[0018] The third aspect of the present application provides a positive electrode plate, comprising the positive electrode active material provided in the first aspect of the present application or the positive electrode active material prepared by the method provided in the second aspect of the present application.

[0019] The fourth aspect of the present application provides a battery, comprising the positive electrode plate provided in the third aspect of the present application.

[0020] The fifth aspect of the present application provides an electrical device, including the battery provided by the fourth aspect of the present application.

[0021] 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

[0022] 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.

[0023] Figure 1 Schematic diagram of the structure of the positive electrode active material in one embodiment of the present application.

[0024] Figure 2 Schematic diagram of the structure of the positive electrode active material in another embodiment of the present application.

[0025] Figure 3 It is a schematic diagram of the process of preparing positive electrode active materials according to one embodiment of the present application.

[0026] Figure 4 Schematic diagram of a battery according to one embodiment of the present application.

[0027] Figure 5 yes Figure 4 An exploded view of a battery according to an embodiment of the present application is shown.

[0028] Figure 6 Schematic diagram of a battery module according to one embodiment of the present application.

[0029] Figure 7 Schematic diagram of a battery pack according to one embodiment of the present application.

[0030] Figure 8 yes Figure 7 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0031] Figure 9 Schematic diagram of an electrical device using a battery as a power source according to one embodiment of the present application.

[0032] Figure 10This is a SEM image of the positive electrode active material of Example 1 of the present application.

[0033] Figure 11 This is the SEM image of the positive electrode active material of Comparative Example 1.

[0034] Figure 12 This is the XPS graph of the positive electrode active material of Example 1.

[0035] Figure 13 This is the XRD pattern of the positive electrode active material of Example 1.

[0036] Figure 14 This is the XRD pattern of the positive electrode active material of Comparative Example 1.

[0037] Description of reference numerals:

[0038] 1: battery pack; 2: upper case; 3: lower case; 4: battery module; 5: battery; 51: casing; 52: electrode assembly; 53: cover plate; 11: positive electrode active material; 111: substrate; 112: coating layer; 113: transition layer. DETAILED DESCRIPTION

[0039] The following embodiments of the technical solution of the present application are described in detail. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only used as examples and are not intended to limit the scope of protection of the present application.

[0040] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0041] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0042] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0043] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[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 share a similar operating principle to lithium-ion batteries. Therefore, sodium-ion batteries have gradually attracted widespread attention and research. Manganese-based sodium-ion battery quaternary cathode active materials offer the advantages of high specific capacity, good structural stability, and low cost. However, at high voltages, the oxygen in the cathode active material's lattice is easily oxidized. On the one hand, the oxidized oxygen on the surface of the cathode active material easily combines with each other to form oxygen gas. On the other hand, the oxidized oxygen on the surface of the cathode active material easily reacts with the electrolyte to produce oxygen gas, resulting in an increase in the volume of gas produced within the battery and a decrease in battery cycle performance.

[0046] This application proposes a positive electrode active material having a coating layer on at least part of the surface of a substrate. On the one hand, the coating layer can reduce the probability of gas production due to side reactions of the substrate with the electrolyte. On the other hand, the coating layer includes perovskite. The ABO3 structure of the perovskite contains oxygen vacancies. When the positive electrode active material undergoes lattice oxygen evolution, the ABO3 can capture oxygen atoms, reducing the probability of oxygen atoms on the surface of the positive electrode active material combining to form oxygen, thereby reducing the gas production within the battery at high voltage and improving the battery's cycle life. The perovskite structure in the coating layer has a good lattice constant match with the Ni-Mn-Fe-X quaternary system in the substrate, and can also improve the structural stability of the positive electrode active material during battery cycling.

[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 provides a positive electrode active material 11, referring to Figure 1 The positive electrode active material 11 includes a substrate 111, and at least part of the surface of the substrate 111 has a coating layer 112; wherein the substrate 111 includes Na y Ni a Mn b Fe c X d O 2+δ , X includes one or more of Zn, Cu, and Co, 0.8≤y≤1, 0.22≤a≤0.45, 0.33≤b≤0.45, 0.2≤c≤0.35, 0<d≤0.15, a+b+c+d=1, -0.1≤δ≤1; the coating layer 112 includes perovskite, the perovskite includes ABO3, A includes one or more of Ca, La, Sr, Al, Gd, and Y, and B includes one or more of Ni, Mn, Fe, and X.

[0049] The positive electrode active material proposed in this application has a coating layer on at least part of the surface of the substrate. On the one hand, the coating layer can reduce the probability of the substrate producing gas due to side reactions caused by contact with the electrolyte; on the other hand, the coating layer includes perovskite. There are oxygen vacancies in the ABO3 structure of the perovskite. When the positive electrode active material undergoes lattice oxygen evolution, the ABO3 can capture oxygen atoms, reducing the probability of oxygen atoms on the surface of the positive electrode active material combining with each other to form oxygen, thereby reducing the gas production inside the battery under high voltage and improving the cycle life of the battery. The perovskite structure is an excellent sodium ion conductor with high ionic conductivity. It can increase the migration rate of sodium ions in the coating layer and improve the rate performance of the battery. The matrix in the positive electrode active material is a Ni-Mn-Fe-X quaternary system, which has high stability and a lattice constant that is more compatible with the perovskite structure. It can improve the structural stability of the positive electrode active material during battery cycling. In addition, the coating layer formed by perovskite has strong rigidity, which can slow down the volume change of the positive electrode active material during the charging process, reduce the probability of cracking of the positive electrode active material, and improve the cycle stability of the positive electrode active material.

[0050] In this application, the perovskite detection method is as follows: in a dry room or glove box, the sample to be tested is ground in an agate mortar and then passed through a 350 mesh sieve. An appropriate amount of the sieved sample is taken and placed 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; a glass slide is taken to gently press the surface of the sample to make the sample surface flat and consistent with the plane of the frame, and the excess powder is scraped off. After the sample is prepared, a Brucker D8A_A25 X-ray powder diffractometer from Brucker AxS, Germany, is used to measure the 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. After the test is completed, the XRD diffraction peak of the sample is compared with the standard card of the XRD analysis software to confirm whether the sample still has ABO3.

[0051] According to some embodiments of the present application, X includes copper. Thus, the matrix material includes Ni, Mn, Fe, and Cu, which improves the air stability of the positive electrode active material.

[0052] According to some embodiments of the present application, 0.8≤y≤1, for example, 0.8, 0.84, 0.88, 0.92, 0.96, or 1, or any range thereof, thereby increasing the specific capacity of the positive electrode active material.

[0053] According to some embodiments of the present application, 0.22≤a≤0.45, for example, a may be 0.22, 0.26, 0.3, 0.34, 0.38, 0.42, or 0.45, or may be within a range consisting of any of the above values, thereby increasing the specific capacity of the positive electrode active material.

[0054] According to some embodiments of the present application, 0.33 ≤ b ≤ 0.45, for example, 0.33, 0.35, 0.37, 0.39, 0.41, 0.43, or 0.45, or a range consisting of any of the above values. Thus, the specific capacity of the positive electrode active material is increased and the cost of the positive electrode active material is reduced.

[0055] According to some embodiments of the present application, 0.2≤c≤0.35, for example, can be 0.2, 0.22, 0.24, 0.26, 0.28, 0.3, 0.32, or 0.35, or can be a range consisting of any of the above values. Thus, by adjusting the Fe content within the above range, the specific capacity of the positive electrode active material can be increased, and the structural stability of the positive electrode active material can be improved.

[0056] According to some embodiments of the present application, 0 < d ≤ 0.15, for example, 0.01, 0.03, 0.05, 0.07, 0.09, 0.11, 0.13, or 0.15, or any range thereof. Thus, by setting the value of d within the above range, the probability of X precipitating on the surface of the positive electrode active material to form an impurity phase can be reduced.

[0057] According to some embodiments of the present application, -0.1≤δ≤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.

[0058] It should be noted that, as the battery undergoes cycles and other processes, the oxygen element in the matrix is ​​lost, so the measured oxygen content in the matrix may be less than 2.

[0059] According to some embodiments of the present application, reference Figure 2 A transition layer 113 may be further included between the substrate 111 and the coating layer 112. The transition layer 113 includes the Na doped with the ABO3 y Ni a Mn b Fe c X d O 2+δ Therefore, compared with forming a coating layer directly on the surface of the substrate, the presence of the transition layer can make the lattice constants between the substrate and the transition layer, and between the transition layer and the coating layer more matched. During the battery cycle, the structural stability of the coating layer can be improved and the risk of the coating layer falling off can be reduced.

[0060] In the present application, the matrix, transition layer and coating layer in the positive electrode active material can be identified by scanning electron microscopy, or elemental analysis by X-ray photoelectron spectroscopy (XPS) can be performed to verify the presence of the transition layer.

[0061] According to some embodiments of the present application, the thickness ratio of the transition layer to the coating layer can be 1:(10-50). For example, it can be 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, or 1:50, or a range of any of the above values. Thus, the transition layer includes both element A and element B as well as the material forming the matrix. The transition layer can act as a "pillar" to reduce the volume change of the material during charging and discharging, thereby reducing the impact on the electrode structure.

[0062] In this application, the thickness of the transition layer and the coating layer is tested by XPS. Specifically, the test can be carried out in accordance with GB / T33502-2017.

[0063] According to some embodiments of the present application, the thickness of the transition layer may be 1 nm-6 nm, for example, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm or 6 nm, or may be within a range consisting of any of the above values.

[0064] According to some embodiments of the present application, the thickness of the coating layer may be 10 nm-60 nm, for example, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm or 60 nm, or may be within a range consisting of any of the above values.

[0065] Therefore, by making the thickness of the transition layer thinner and the thickness of the coating layer thicker, both the specific capacity and the air stability of the positive electrode active material can be taken into account.

[0066] According to some embodiments of the present application, in the positive electrode active material, the molar ratio of Na atoms to A atoms can be 1:(0.005-0.02). For example, it can be 1:0.005, 1:0.01, 1:0.015 or 1:0.02, etc., or it can be a range composed of any of the above values. Thus, by making the molar ratio of Na atoms to A atoms within the above range, a uniform coating layer is formed on the surface of the substrate, thereby improving the oxygen capture effect, reducing the volume of gas generated in the battery, and improving the cycle life of the battery. At the same time, the mass proportion of the substrate in the positive electrode active material is increased, and the specific capacity of the positive electrode active material is increased.

[0067] In this application, the molar ratio of Na atoms to A atoms is tested by an ICP-OES: turn on the ignition, prepare a standard solution with a gradient concentration, run the analysis in sequence, check the resulting spectrum, ensure that the spectral peaks are free of interference, the spectral lines are linear, and the correlation coefficient is greater than 0.999; then test and analyze the sample after microwave digestion.

[0068] According to some embodiments of the present application, in the perovskite, A includes Ca and La, and the molar ratio of Ca atoms to La atoms can be 0.25-4. For example, it can be 0.25, 0.3, 0.35, or 0.4, or can be a range consisting of any of the above values. Thus, A includes Ca and La, and the ionic radius of Ca ions and La ions is closer to that of Na ions, making it easier to form a transition layer, thereby reducing the volume change of the positive electrode active material during charge and discharge.

[0069] In the present application, the molar ratio of Ca and La can be tested by ICP-OES. Specifically, the machine is turned on and ignited, a standard solution with a gradient concentration is prepared, the analysis is run in sequence, and the resulting spectrum is checked to ensure that the spectral peaks are free of interference, the spectral lines are linear, and the correlation coefficient is greater than 0.999; and then the sample after microwave digestion is tested and analyzed.

[0070] 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 3 μm-10 μm. For example, it can be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 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.

[0071] In this application, D v 50 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.

[0072] The second aspect of the present application provides a method for preparing a positive electrode active material, comprising: mixing a positive electrode active material matrix with a source A, and first sintering to allow the source A to react with at least a portion of the surface of the positive electrode active material matrix to form a coating layer comprising perovskite; the matrix comprises Na y Ni a Mn b Fe c X d O 2+δ , X includes one or more of Zn, Cu, and Co, 0.8≤y≤1, 0.22≤a≤0.45, 0.33≤b≤0.45, 0.2≤c≤0.35, 0<d≤0.15, a+b+c+d=1, -0.1≤δ≤1; the perovskite includes ABO3, A includes one or more of Ca, La, Sr, Al, Gd, and Y, and B is the Na in the reaction y Ni a Mn b Fe c X d O 2+δThe provided metal elements include one or more of Ni, Mn, Fe, and X. Thus, in the positive electrode active material prepared by this method, a coating is formed in situ on at least a portion of the surface of the substrate. On the one hand, the coating can reduce the probability of gas production due to side reactions of the substrate with the electrolyte. On the other hand, the coating includes perovskite. The ABO3 structure of the perovskite contains oxygen vacancies. When the positive electrode active material undergoes lattice oxygen evolution, the ABO3 can capture oxygen atoms, reducing the probability of oxygen atoms on the surface of the positive electrode active material combining to form oxygen, thereby reducing gas production within the battery at high voltage and improving the battery's cycle life. The perovskite structure is an excellent sodium ion conductor with high ionic conductivity, which can increase the migration rate of sodium ions within the coating layer and improve the battery's rate performance. The matrix in the positive electrode active material is a Ni-Mn-Fe-X quaternary system, which has high stability and a lattice constant that is more compatible with the perovskite structure, which can improve the structural stability of the positive electrode active material during battery cycling. In addition, the coating layer formed by perovskite has strong rigidity, which can slow down the volume change of the positive electrode active material during the charging process, reduce the probability of cracking of the positive electrode active material, and improve the cycle stability of the positive electrode active material.

[0073] The following is a detailed description of each step of this application. Figure 3 , the method comprising:

[0074] S100: Mixing the positive electrode active material matrix with source A

[0075] According to some embodiments of the present application, the matrix of the positive electrode active material includes Na y Ni a Mn b Fe c X d O 2+δ , X includes one or more of Zn, Cu, and Co, 0.8≤y≤1, 0.22≤a≤0.45, 0.33≤b≤0.45, 0.2≤c≤0.35, 0<d≤0.15, a+b+c+d=1, and -0.1≤δ≤1.

[0076] According to some embodiments of the present application, the method for preparing the matrix may include mixing a sodium source, a Ni source, a Mn source, an Fe source, and an X source, and performing a second sintering to obtain the matrix of the positive electrode active material.

[0077] According to some embodiments of the present application, the temperature of the second sintering may be 700° C.-1000° C., and the time of the second sintering may be 6 h-15 h.

[0078] As an example, the second sintering temperature may be 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, or 1000°C, or may be within a range of any of the above values. According to some specific embodiments of the present application, the second sintering temperature may be 720°C-850°C.

[0079] As an example, the second sintering time can be 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours or 18 hours, 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 7 hours to 10 hours.

[0080] Therefore, by setting the temperature and time of the second sintering within the above ranges, the content of the matrix in the positive electrode active material is increased, thereby increasing the specific capacity of the positive electrode active material.

[0081] According to some embodiments of the present application, the A source includes one or more of a calcium source and a lanthanum source. Thus, the perovskite in the prepared positive electrode active material includes Ca and La, which is beneficial to valence balance and improves the structural stability of the perovskite.

[0082] According to some embodiments of the present application, the calcium source includes one or more of calcium oxide, calcium carbonate, calcium hydroxide, calcium nitrate, calcium chloride, and calcium sulfate.

[0083] According to some embodiments of the present application, the lanthanum source includes one or more of lanthanum oxide, lanthanum hydroxide, lanthanum nitrate, and lanthanum chloride.

[0084] According to some embodiments of the present application, the A source includes a calcium source and a lanthanum source, and the molar ratio of the calcium source to the lanthanum source, calculated as Ca to La, is 0.25-4. Thus, the molar ratio of Ca atoms to La atoms in the prepared positive electrode active material is 0.25-4, which is beneficial to valence balance and improves the structural stability of the perovskite.

[0085] According to some embodiments of the present application, the molar ratio of the substrate to the A source calculated as Na is 1:

[0086] (0.005-0.02). As a result, a uniform coating layer is formed on the surface of the substrate, while increasing the content of the substrate in the positive electrode active material, thereby reducing battery gas production and increasing the energy density of the battery.

[0087] S200: performing a first sintering on the substrate and the A source to obtain the positive electrode active material.

[0088] According to some embodiments of the present application, in this step, the A source is reacted with at least a portion of the surface of the positive electrode active material matrix by the first sintering to form a coating layer comprising perovskite, wherein the perovskite comprises ABO3, A comprises one or more of Ca, La, Sr, Al, Gd, and Y, and B is the Na in the reaction. y Ni a Mn b Fe c X d O 2+δ The metal elements provided include one or more of Ni, Mn, Fe, and X. Thus, through the first sintering, a perovskite structure is formed in situ on at least a portion of the surface of the substrate, and the perovskite structure captures the oxidized oxygen atoms on the surface of the substrate in situ, reducing the probability of the oxidized oxygen atoms on the surface of the material combining with each other to form oxygen, thereby reducing the gas production of the battery and improving the cycle stability of the battery.

[0089] According to some embodiments of the present application, the temperature of the first sintering may be 400° C.-1000° C., and the time of the first sintering may be 2 hours-24 hours.

[0090] As an example, the first sintering temperature may be 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, or 1000°C, or may be within a range of any of the above values. According to some specific embodiments of the present application, the first sintering temperature may be 600°C-900°C.

[0091] As an example, the first sintering time may be 2 hours to 24 hours, for example, 2 hours, 6 hours, 10 hours, 14 hours, 18 hours, 22 hours or 24 hours, or may be within a range of any of the above values. According to some specific embodiments of the present application, the first sintering time may be 4 hours to 18 hours.

[0092] Thus, by setting the temperature and time of the first sintering process within the above ranges, a uniform coating is formed on the surface of the substrate, enhancing oxygen capture, reducing gassing of the positive electrode active material, and improving the battery's cycling stability. Furthermore, the coating reduces the risk of sodium precipitation in the substrate and improves the structural stability of the positive electrode active material.

[0093] The third aspect of the present application provides a positive electrode plate, comprising the positive electrode active material provided in the first aspect of the present application or the positive electrode active material prepared by the method provided in the second aspect of the present application.

[0094] 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.

[0095] 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.

[0096] 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 at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0097] 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.

[0098] 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.

[0099] The fourth aspect of the present application provides a battery comprising the positive electrode sheet described in the third aspect of the present application.

[0100] 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.

[0101] [Negative electrode]

[0102] 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.

[0103] 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.

[0104] In the present application, the negative electrode material may include negative electrode active materials for secondary batteries known in the art. For example, the negative electrode active material may include at least one 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 at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include at least one of elemental tin, tin oxides, and tin alloys.

[0105] In some embodiments, the negative electrode film layer may further optionally include a binder. The binder may include, for example, at least one 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).

[0106] In some embodiments, the negative electrode film layer may further optionally include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0107] 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).

[0108] 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.

[0109] [Electrolyte]

[0110] 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, at least one of NaPF6, NaClO4, NaBCl4, NaSO3CF3, and Na(CH3)C6H4SO3. The organic solvent includes, but is not limited to, at least one 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).

[0111] 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 but are not limited to 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).

[0112] [Isolation film]

[0113] 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 at least one 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.

[0114] In some embodiments, a ceramic coating and / or a metal oxide coating is further provided on the isolation membrane.

[0115] 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.

[0116] 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 4 The battery 5 is a square structure as an example.

[0117] In some embodiments, reference Figure 5 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.

[0118] 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.

[0119] Figure 6 4 is an example of a battery module. Figure 6 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.

[0120] 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.

[0121] 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.

[0122] Figure 7 and Figure 8 The battery pack 1 is used as an example. Figure 7 and Figure 8 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.

[0123] 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.

[0124] As the electrical device, a battery, a battery module or a battery pack can be selected according to its usage requirements.

[0125] Figure 9 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.

[0126] 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.

[0127] 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.

[0128] Example 1

[0129] First, sodium source (Na2CO3), manganese source (Mn2O3), nickel source (NiO) and copper source (CuO) were mixed evenly in proportion, and then placed in a sagger in a box furnace and sintered at 850℃ for 15h. After sintering, it was cooled to room temperature and crushed to obtain the matrix NaNi 0.3 Mn 0.3 Fe 0.3 Cu 0.1 O2.

[0130] The calcium source (CaO) and the lanthanum source (La2O3) were mixed uniformly in a ball mill at a molar ratio of 1:1.25 to obtain a coating raw material.

[0131] The coating raw material and the substrate were mixed evenly in a mixing device according to the molar ratio of Na / (Ca+La) of 1:0.01. The mixed materials were placed in a muffle furnace and sintered at 750℃ for 8h, and dry air was passed through the process. After the sintering was completed, the materials were naturally cooled to room temperature to obtain the positive electrode active material. The coating layer was Ca 0.4 La 0.6 MnO3.

[0132] Example 2

[0133] A manganese-based sodium electrical material was prepared according to the method of Example 1, except that during mixing, the molar ratio of Na / (Ca+La) was adjusted to 1:0.005.

[0134] Example 3

[0135] A manganese-based sodium electrical material was prepared according to the method of Example 1, except that during mixing, the molar ratio of Na / (Ca+La) was adjusted to 1:0.004.

[0136] Example 4

[0137] A manganese-based sodium electrical material was prepared according to the method of Example 1, except that during mixing, the molar ratio of Na / (Ca+La) was adjusted to 1:0.02.

[0138] Example 5

[0139] A manganese-based sodium electrical material was prepared according to the method of Example 1, except that during mixing, the molar ratio of Na / (Ca+La) was adjusted to 1:0.03.

[0140] Example 6

[0141] The manganese-based sodium electric material was prepared according to the method of Example 1, except that the first sintering temperature during the formation of perovskite was adjusted to 350°C.

[0142] Example 7

[0143] A manganese-based sodium electric material was prepared according to the method of Example 1, except that the first sintering temperature during the formation of perovskite was adjusted to 400°C.

[0144] Example 8

[0145] Manganese-based sodium electric materials were prepared according to the method of Example 1, except that the first sintering temperature during the formation of perovskite was adjusted to 600°C.

[0146] Example 9

[0147] Manganese-based sodium electric materials were prepared according to the method of Example 1, except that the first sintering temperature during the formation of perovskite was adjusted to 900°C.

[0148] Example 10

[0149] Manganese-based sodium electric materials were prepared according to the method of Example 1, except that the first sintering temperature during the formation of perovskite was adjusted to 1000°C.

[0150] Example 11

[0151] The manganese-based sodium electric material was prepared according to the method of Example 1, except that the sodium source (Na2CO3), manganese source (Mn2O3), nickel source (NiO) and zinc source (ZnO) were mixed uniformly in proportion, then placed in a sagger in a box furnace, sintered at 850°C for 15h, cooled to room temperature after sintering, and crushed to obtain the matrix NaNi 0.3 Mn 0.3 Fe 0.3 Zn 0.1 O2.

[0152] Example 12

[0153] A manganese-based sodium electrolytic material was prepared according to the method of Example 1, except that the molar ratio of the calcium source (CaO) to the lanthanum source (La2O3) was 1:5.

[0154] Example 13

[0155] A manganese-based sodium electrolytic material was prepared according to the method of Example 1, except that the molar ratio of the calcium source (CaO) to the lanthanum source (La2O3) was 1:4.

[0156] Example 14

[0157] A manganese-based sodium electrolytic material was prepared according to the method of Example 1, except that the molar ratio of the calcium source (CaO) to the lanthanum source (La2O3) was 1:0.25.

[0158] Example 15

[0159] A manganese-based sodium electrolytic material was prepared according to the method of Example 1, except that the molar ratio of the calcium source (CaO) to the lanthanum source (La2O3) was 1:0.22.

[0160] Comparative Example 1

[0161] The matrix NaNi of Example 1 0.3 Mn 0.3 Fe 0.3 Cu 0.1 O2 is used as the positive electrode active material.

[0162] Test Case

[0163] 1. Morphology characterization

[0164] SEM testing: Field emission scanning electron microscopy (Zeiss Gemini360) was used for testing in accordance with the JY / T010-1996 standard.

[0165] 2. Crystalline phase characterization

[0166] 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°-60° and the scanning rate is 4° / min. After the test is completed, the XRD diffraction peak of the sample is compared with the standard card of the XRD analysis software to confirm whether the sample contains a perovskite structure.

[0167] 3. Elemental analysis

[0168] The instrument standard refers to EPA 6010D-2014, Inductively Coupled Plasma Atomic Emission Spectrometry. The sample is chemically treated and dissolved into a solution. This solution is then atomized and injected into the plasma, where it is excited to produce characteristic elemental spectral lines. The wavelength and intensity of these spectral lines (which are proportional to concentration) are used to qualitatively and quantitatively analyze the elemental content.

[0169] 4. Gas production

[0170] The volume change of the battery after 500 cycles was tested using the drainage method.

[0171] 5. Cycle performance

[0172] At 25°C, the layered oxide positive electrode active material was prepared into a button cell and charged to 4.3V at a current density of 10mA / g. It was then discharged to 2V at a current density of 10mA / g to obtain the discharge specific capacity C0 of the button cell. Subsequently, the charge and discharge were cycled at a current density of 10mA / g for 50 cycles, and the discharge specific capacity C1 at the 50th cycle was obtained. The capacity retention rate of the layered oxide positive electrode active material after 50 cycles = (C1 / C0) × 100%

[0173] The button cell is prepared according to the following steps.

[0174] 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.

[0175] Negative electrode: Sodium metal sheet.

[0176] 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.

[0177] Isolation membrane: porous polyethylene membrane is used as the isolation membrane.

[0178] 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.

[0179] The preparation methods of the batteries in Examples 1 to 15 and Comparative Example 1 are the same as those in Example 1, with the differences detailed in Table 1.

[0180] Table 1

[0181]

[0182]

[0183] The test results of the batteries in Examples 1 to 15 and Comparative Example 1 are shown in Table 2.

[0184] Table 2

[0185] Serial number Specific capacity (mAh / g) Gas volume after 500 cycles / mL Cycle capacity retention rate / % Example 1 189 2.3 92 Example 2 186 2.5 83 Example 3 182 8.4 82 Example 4 183 2.4 91 Example 5 181 8.8 80 Example 6 183 8.0 83 Example 7 180 6.8 80 Example 8 184 2.9 90 Example 9 183 3.0 89 Example 10 176 4.0 82 Example 11 187 2.5 91 Example 12 185 4.7 85 Example 13 186 2.8 88 Example 14 183 2.7 89 Example 15 184 5.0 83 Comparative Example 1 188 9.3 76

[0186] Conclusion: Comparison of Examples 1-15 with Comparative Example 1 shows that the cathode active materials proposed in this application, when prepared into batteries, can reduce the volume of gas produced after battery cycling and improve the battery's cycle capacity retention. This indicates that forming a perovskite coating on at least a portion of the surface of the cathode active material can reduce the probability of gas production due to side reactions between the substrate and the electrolyte. The perovskite can also capture oxygen atoms, reducing the probability of oxygen atoms on the surface of the cathode active material combining to form oxygen, thereby reducing gas production within the battery at high voltage.

[0187] It can be seen from Examples 1 to 5 that by adjusting the molar ratio of Na / (Ca+La) in the positive electrode active material, the gas production volume after the battery cycle can be reduced and the cycle capacity retention rate of the battery can be improved. This shows that by adjusting the molar ratio of Na / (Ca+La), a uniform coating layer can be formed on the surface of the positive electrode active material, thereby improving the effect of isolating the substrate and the electrolyte and improving the oxygen capture effect.

[0188] It can be seen from Examples 6 to 10 that by adjusting the temperature during the first sintering, the gas production volume after the battery cycle can be reduced and the cycle capacity retention rate of the battery can be improved. This shows that by controlling the first sintering temperature within the protection scope of this application, the uniformity of the coating layer formed on the surface of the positive electrode active material can be improved, thereby improving the effect of isolating the substrate and the electrolyte and improving the ability to capture oxygen.

[0189] It can be seen from Examples 12 to 15 that by adjusting the molar ratio of the calcium source (CaO) and the lanthanum source (La2O3), the gas production volume after the battery cycle can be reduced and the cycle capacity retention rate of the battery can be improved. This shows that by adjusting the molar ratio of Ca and La, the structural stability of the coating layer can be improved, thereby improving the oxygen capture effect.

[0190] Attachment Figure 10 This is the SEM image of the positive electrode active material of Example 1 of the present application, Figure 11 This is the SEM image of the positive electrode active material of Comparative Example 1. By comparison, it can be seen that Figure 10 The surface of the positive electrode active material is relatively rough and has a coating layer. Figure 11 The surface of the positive electrode active material is relatively smooth and no coating layer is formed.

[0191] Attachment Figure 12 This is the XPS graph of the positive electrode active material of Example 1. The peak around 830 is the characteristic peak of La. The peak intensity on the surface of the positive electrode active material is relatively high, indicating that there is a coating layer on the surface of the material. After etching 60 nm, the coating layer has been completely etched away, but the characteristic peak of La still exists, indicating the presence of a transition layer.

[0192] Attachment Figure 13 : This is the XRD pattern of the positive electrode active material of Example 1. The spectrum has characteristic peaks of perovskite, indicating that the positive electrode active material contains a coating layer formed by perovskite.

[0193] Attachment Figure 14 This is the XRD pattern of the positive electrode active material of Comparative Example 1. There is no characteristic peak of perovskite in the spectrum, indicating that there is no perovskite in the positive electrode active material.

[0194] 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 comprises a substrate, at least part of the surface of which has a coating layer; wherein, The matrix includes Na y Ni a Mn b Fe c X d O 2+δ , X includes one or more of Zn, Cu, and Co, 0.8≤y≤1, 0.22≤a≤0.45, 0.33≤b≤0.45, 0.2≤c≤0.35, 0<d≤0.15, a+b+c+d=1, -0.1≤δ≤1; The coating layer includes perovskite, the perovskite includes ABO3, A includes one or more of Ca, La, Sr, Al, Gd, and Y, and B includes one or more of Ni, Mn, Fe, and X.

2. The positive electrode active material according to claim 1, characterized in that A transition layer is further included between the substrate and the coating layer, and the transition layer includes the Na doped with the ABO3 y Ni a Mn b Fe c X d O 2+δ .

3. The positive electrode active material according to claim 2, characterized in that The thickness ratio of the transition layer to the coating layer is 1:(10-50).

4. The positive electrode active material according to any one of claims 1 to 3, characterized in that In the positive electrode active material, the molar ratio of Na atoms to A atoms is 1:(0.005-0.02).

5. The positive electrode active material according to any one of claims 1 to 4, characterized in that In the perovskite, A includes Ca and La, and the molar ratio of Ca atoms to La atoms is 0.25-4.

6. The positive electrode active material according to any one of claims 1 to 5, characterized in that The volume average particle size D of the positive electrode active material V 50 is 3μm-10μm.

7. A method for preparing a positive electrode active material, characterized in that: include: Mixing a positive electrode active material matrix with a source A and performing a first sintering process to allow the source A to react with at least a portion of the surface of the positive electrode active material matrix to form a coating layer comprising perovskite; The matrix includes Na y Ni a Mn b Fe c X d O 2+δ , X includes one or more of Zn, Cu, and Co, 0.8≤y≤1, 0.22≤a≤0.45, 0.33≤b≤0.45, 0.2≤c≤0.35, 0<d≤0.15, a+b+c+d=1, -0.1≤δ≤1; The perovskite includes ABO3, A includes one or more of Ca, La, Sr, Al, Gd, and Y, and B is the Na y Ni a Mn b Fe c X d O 2+δ The provided metal elements include one or more of Ni, Mn, Fe, and X.

8. The method according to claim 7, characterized in that The method includes: mixing a sodium source, a Ni source, a Mn source, an Fe source, and an X source, and performing a second sintering to obtain the matrix of the positive electrode active material.

9. The method according to claim 7 or 8, characterized in that The A source includes one or more of a calcium source and a lanthanum source.

10. The method according to claim 9, characterized in that The calcium source includes one or more of calcium oxide, calcium carbonate, calcium hydroxide, calcium nitrate, calcium chloride, and calcium sulfate; The lanthanum source includes one or more of lanthanum oxide, lanthanum hydroxide, lanthanum nitrate, and lanthanum chloride.

11. The method according to any one of claims 7 to 10, characterized in that: The A source includes a calcium source and a lanthanum source, and the molar ratio of the calcium source to the lanthanum source is 0.25-4 based on Ca and La.

12. The method according to any one of claims 7 to 11, characterized in that: The molar ratio of the substrate to the A source calculated in terms of Na is 1:(0.005-0.02).

13. The method according to any one of claims 8 to 12, characterized in that: One or more of the following conditions are met: The temperature of the first sintering is 400° C.-1000° C., and the time of the first sintering is 2 h-24 h; The temperature of the second sintering is 700° C.-1000° C., and the time of the second sintering is 6 hours-15 hours.

14. The method according to any one of claims 8 to 13, characterized in that: One or more of the following conditions are met: The temperature of the first sintering is 600° C.-900° C., and the time of the first sintering is 4 hours-18 hours; The temperature of the second sintering is 720° C.-850° C., and the time of the second sintering is 7 hours-10 hours.

15. A positive electrode plate, characterized in that: The invention comprises the positive electrode active material according to any one of claims 1 to 6 or the positive electrode active material prepared by the method according to any one of claims 7 to 14.

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

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

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