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

Abstract

The invention discloses a positive active material and a preparation method thereof, a positive pole piece, a battery and an electric device. The positive electrode active material comprises a sodium manganese oxide, the sodium manganese oxide comprises a first phase and a second phase, the first phase comprises first sodium ion layers and first transition metal layers which are sequentially alternated, the interlayer spacing of the two adjacent first transition metal layers in the first phase in the direction perpendicular to the (001) crystal face is 0.550-0.565 nm, and the first phase comprises doping element fluorine; the second phase comprises second sodium ion layers and second transition metal layers which are sequentially alternated, and the interlayer spacing between the two adjacent second transition metal layers in the second phase in the direction perpendicular to the (001) crystal face is 0.530 nm to 0.545 nm. Therefore, cracks of the positive electrode active material in the charge-discharge cycle process can be obviously inhibited, and the cycle stability of the positive electrode active material 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 devices. Background Art

[0002] Secondary batteries 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 such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. Sodium-ion batteries, a type of secondary battery, primarily rely on the movement of sodium ions between the positive and negative electrodes to operate. Sodium-ion layered oxides are a common positive electrode active material in sodium-ion batteries. With the development of today's society, people's demands for batteries are becoming increasingly demanding.

[0003] Public content

[0004] In view of the technical problems existing in the background technology, the present application provides a positive electrode active material, which aims to inhibit the generation of cracks in the positive electrode active material during the cycle process and improve the cycle stability of the positive electrode.

[0005] In order to achieve the above-mentioned object, the first aspect of the present application provides a positive electrode active material, which includes sodium manganese oxide, and the sodium manganese oxide includes:

[0006] A first phase, wherein the first phase comprises alternating first sodium ion layers and first transition metal layers, wherein an interlayer spacing between two adjacent first transition metal layers in a direction perpendicular to a (001) crystal plane in the first phase is 0.550 nm to 0.565 nm, and the first phase comprises a doping element, fluorine;

[0007] The second phase includes a second sodium ion layer and a second transition metal layer alternating in sequence, and the interlayer spacing between two adjacent second transition metal layers in the second phase in a direction perpendicular to the (001) crystal plane is 0.530nm to 0.545nm.

[0008] The positive electrode active material of the first aspect of the present application has at least the following beneficial effects: there is stress and lattice mismatch between the first phase and the second phase at the two-phase interface and the position of the transition metal layer of the two phases, which is conducive to alleviating the lattice changes in the process of sodium ion insertion and extraction between the two phases, reducing the generation of cracks, and improving the cycle stability.

[0009] In some embodiments of the present application, the first phase includes a P2 phase, and the space group includes P63 / mmc; the second phase includes an O3 phase, and the space group includes The greater stacking difference of the layered structures in the P2 phase and the O3 phase helps to further enhance the lattice mismatch and “interlocking” effect between the first and second phases.

[0010] In some embodiments of the present application, the minimum distance between two adjacent transition metal ions in the same first transition metal layer is a1, and the minimum distance between two adjacent transition metal ions in the same second transition metal layer is a2, where a2-a1≥5 μm. As a result, the lattice mismatch between the first phase and the second phase in the transition metal layer is large, which helps further enhance the "interlocking" effect of the layered structure of the sodium manganese oxide on crystal plane slip during the process of sodium insertion and extraction, thereby further helping to further reduce the lattice changes of the crystal structure of the sodium manganese oxide during charge and discharge cycles, thereby reducing the occurrence of cracks.

[0011] In some embodiments of the present application, a2-a1 is 5pm to 15pm.

[0012] In some embodiments of the present application, the difference between the interlayer spacing between two adjacent first transition metal layers in the first phase in a direction perpendicular to the (001) crystal plane and the interlayer spacing between two adjacent second transition metal layers in the second phase in a direction perpendicular to the (001) crystal plane is 0.01 nm to 0.02 nm. This allows for a better "interlocking" effect in the interlayer spacing during the contraction and expansion of the sodium manganese oxide layered structure, thereby further suppressing the generation of cracks in the positive electrode active material during charge and discharge cycles.

[0013] In some embodiments of the present application, the first phase includes: Na x1 Mn y1 Fe a1 Ni b1 M1 c1 O 2+δ1-e F e , 0.5≤x1≤0.8, y1+a1+b1+c1=1, 0≤a1≤0.6, 0≤b1≤0.6, 0≤c1≤0.4, -0.1≤δ1≤0.1, 0<e≤0.1, M1 includes one or more elements selected from Sb, La, Ce, Co, In, Ga, Ta, W, Ba, Cu, Li, Ti, Zr, K, Nb, Mg, Ca, Mo, Zn, Cr, W, Bi, Sn, Ge, Al, Si, and B. As a result, it is beneficial to take into account both the specific capacity and cycle stability of the positive electrode active material.

[0014] In some embodiments of the present application, the second phase includes: Na x2 Mn y2 Fe a2 Ni b2 M2 c2 O 2+δ2, 0.7≤x2≤1, y2+a2+b2+c2=1, 0.1≤a2≤0.6, 0.1≤b2≤0.6, 0≤c2≤0.4, -0.1≤δ2≤0.1, M2 includes one or more elements selected from Sb, La, Ce, Co, In, Ga, Ta, W, Ba, Cu, Li, Ti, Zr, K, Nb, Mg, Ca, Mo, Zn, Cr, W, Bi, Sn, Ge, Al, Si, and B. As a result, it is beneficial to take into account both the specific capacity and cycle stability of the positive electrode active material.

[0015] In some embodiments of the present application, y1≥0.6, which is beneficial to further improve the cycle stability.

[0016] In some embodiments of the present application, 0.03≤e≤0.08. This is beneficial for further suppressing cracks in the crystal structure of the sodium manganese oxide during charge-discharge cycles, improving cycle stability, and reducing the risk of impurity phase formation due to high fluorine doping, which leads to a decrease in specific capacity.

[0017] In some embodiments of the present application, M1 includes one or more elements selected from Zn, Mg, Sn, and Ti. This is beneficial for causing strain in the local lattice of the first phase, increasing the lattice mismatch between the first and second phases, and enhancing the "interlocking" effect of the layered structure of the sodium manganese oxide during the process of sodium insertion and extraction, thereby further suppressing the generation of cracks in the positive electrode active material.

[0018] In some embodiments of the present application, M2 includes one or more elements of Cu, Zn, Ti, Mg, Co, and Al.

[0019] In some embodiments of the present application, at least one of the following conditions is met: 0.2≤y2≤0.5, 0.2≤a2≤0.35, and 0.2≤b2≤0.35. This not only facilitates further charge compensation during the sodium insertion and extraction process, thereby increasing the specific capacity, but also helps reduce the risk of Fe and Ni adjacent oxygen being easily activated, causing loss or side reactions, thereby balancing the specific capacity and cycle stability of the positive electrode active material.

[0020] In some embodiments of the present application, the mass ratio of the first phase to the second phase is 5:95 to 30:70. This not only helps the positive electrode active material have high specific capacity, rate performance, and average voltage, but also allows the two to play a good "interlocking" role, thereby achieving better cycle stability.

[0021] The second aspect of the present application provides a method for preparing the positive electrode active material of the first aspect of the present application, comprising:

[0022] Sodium manganese oxide comprising a first phase and sodium manganese oxide comprising a second phase are mixed and calcined, wherein:

[0023] The first phase includes alternating first sodium ion layers and first transition metal layers, the interlayer spacing between two adjacent first transition metal layers in the first phase in a direction perpendicular to the (001) crystal plane is 0.550nm to 0.565nm, and the first phase includes doped element fluorine; the second phase includes alternating second sodium ion layers and second transition metal layers, the interlayer spacing between two adjacent second transition metal layers in the second phase in a direction perpendicular to the (001) crystal plane is 0.530nm to 0.545nm.

[0024] The method for preparing a positive electrode active material according to the second aspect of the present application has at least the following beneficial effects: The two-phase positive electrode active materials are mixed and calcined, and the first phase is controlled to be doped with fluorine, so that the two phases form a good "interlocking" effect, thereby effectively suppressing the lattice changes of the two phases during the sodium ion insertion and extraction process, reducing the generation of cracks, and improving the cyclic stability of the material. As a result, the positive electrode active material prepared by this method can significantly suppress the generation of cracks during the charge and discharge cycle, thereby improving the cyclic stability of the battery.

[0025] In some embodiments of the present application, the calcination temperature is 500° C. to 1200° C., the calcination time is 0.5 h to 20 h, and the atmosphere is an oxygen-containing atmosphere.

[0026] The third aspect of the present application provides a positive electrode plate, which includes: the positive electrode active material of the first aspect of the present application, or the positive electrode active material prepared by the method of the second aspect of the present application.

[0027] The fourth aspect of the present application provides a battery, which includes: the positive electrode plate of the third aspect of the present application.

[0028] The fifth aspect of the present application provides an electrical device, which includes: the battery described in the fourth aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] 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, in which:

[0030] Figure 1 It is a schematic structural diagram of a battery according to one embodiment of the present application.

[0031] Figure 2 It is a schematic structural diagram of a battery module according to one embodiment of the present application.

[0032] Figure 3 It is a schematic structural diagram of a battery pack according to one embodiment of the present application.

[0033] Figure 4 yes Figure 3 Exploded diagram of .

[0034] Figure 5 It is a schematic diagram of an embodiment of an electrical device using a battery as a power source of the present application.

[0035] Figure 6 This is a scanning electron microscope image of the positive electrode active material prepared in Example 1 of the present application after 50 charge and discharge cycles.

[0036] Figure 7 This is a scanning electron microscope image of the positive electrode active material prepared in Comparative Example 1 of the present application after 50 charge and discharge cycles.

[0037] Description of reference numerals:

[0038] 1: Battery; 2: Battery module; 3: Battery pack; 4: Upper case; 5: Lower case. DETAILED DESCRIPTION

[0039] 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.

[0040] 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.

[0041] " 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 the rear 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 the scope of not clearly recording, and any lower limit can be combined with other lower limits to form the scope of not clearly recording, and any upper limit can be combined with any other upper limit to form the scope of not clearly recording. In addition, each separately disclosed point or single numerical value itself can be used as lower limit or upper limit and any other point or single numerical value combination or with other lower limit or upper limit combination to form the scope of not clearly recording.

[0042] 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.

[0043] 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.

[0044] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps S1 and S2, which means that the method may include steps S1 and S2 performed sequentially, or may include steps S2 and S1 performed sequentially. For example, the method may further include step S3, which means that step S3 may be added to the method in any order, for example, the method may include steps S1, S2, and S3, or may include steps S1, S3, and S2, or may include steps S3, S1, and S2, etc.

[0045] 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.

[0046] In this application, the terms "plurality" and "multiple" refer to two or more.

[0047] 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).

[0048] At present, sodium-ion batteries used as secondary batteries mainly rely on the movement of sodium ions between the positive and negative electrodes to work. Commonly used positive electrode active materials for sodium-ion batteries include sodium-ion layered oxides. Among them, sodium-ion layered oxides will deintercalate sodium ions during the charge and discharge process, causing large lattice changes and generating more cracks, which increases the area of ​​contact with the electrolyte, exacerbates the side reactions between the sodium-ion layered oxide and the electrolyte, and thus deteriorates its cycle stability. Therefore, how to suppress the generation of cracks in the layered oxide during the charge and discharge cycle has an important impact on improving the cycle stability of the positive electrode and extending the service life of the battery.

[0049] In response to the above problems, the present application proposes a positive electrode active material including sodium manganese oxide, which includes a first phase and a second phase. The first phase includes a first sodium ion layer and a first transition metal layer that alternate in sequence. The interlayer spacing between two adjacent first transition metal layers in the first phase in the direction perpendicular to the (001) crystal plane is 0.550nm to 0.565nm, and the first phase includes doped element fluorine; the second phase includes a second sodium ion layer and a second transition metal layer that alternate in sequence. The interlayer spacing between two adjacent second transition metal layers in the second phase in the direction perpendicular to the (001) crystal plane is 0.530nm to 0.545nm. The first phase and the second phase have stress and lattice mismatch at the interface between the two phases, which is conducive to alleviating the lattice change in the process of sodium ion insertion and extraction between the two phases, such as Figure 6 As shown, the generation of obvious cracks is suppressed; fluorine doping is introduced into the first phase with a larger interlayer spacing to reduce the distance between the transition metal elements in the transition metal layer of the first phase. In this way, the second phase and the first phase also have a lattice mismatch in the position of the transition metal layer, which is beneficial to further suppress the lattice changes of the two phases during the process of sodium ion insertion and extraction, and reduce the generation of cracks.

[0050] The inventors speculate that the above technical solution can suppress the generation of cracks because the first phase and the second phase that meet the interlayer spacing range do not undergo completely synchronous structural changes when sodium is inserted and removed. The first phase and the second phase that meet the given interlayer spacing conditions are simultaneously introduced into the positive electrode active material. During the contraction and expansion process of the sodium manganese oxide layered structure, stress and lattice mismatch exist at the interface between the two phases, which is conducive to the formation of an "interlocking" effect on the interlayer spacing and crystal plane slip, thereby making the layered structure of the sodium manganese oxide less stressed and strained during the process of sodium insertion and removal, thereby helping to reduce defects in the crystal structure caused by large strain. The fluorine doping method can reduce the appearance of cracks and cracks, thereby improving the stability of the positive electrode active material during the charge and discharge cycle. Moreover, by introducing fluorine doping into the first phase with a large interlayer spacing, the distance between the transition metal elements in the transition metal layer of the first phase can be reduced, thereby increasing the lattice mismatch between the two phases at the transition metal layer. This further enhances the "interlocking" effect of the layered structure of the sodium manganese oxide on the crystal plane slip during the process of sodium insertion and deintercalation, thereby reducing the stress and strain of the crystal structure of the sodium manganese oxide during the charge and discharge cycle, inhibiting the generation of cracks in the crystal structure, and improving the stability of the positive electrode active material during the charge and discharge cycle. In turn, it is beneficial for the positive electrode active material to have both a high specific capacity and a long cycle life.

[0051] The positive electrode active material disclosed in the embodiments of the present application is suitable for secondary batteries, and the battery disclosed in the embodiments of the present application can be used in electrical devices that use batteries as power sources or various energy storage systems that use batteries as energy storage elements. Electrical devices may include but are not limited to mobile phones, tablets, laptops, electric toys, power tools, battery cars, electric cars, ships, spacecraft, etc. Among them, electric toys may include fixed or mobile electric toys, for example, game consoles, electric car toys, electric ship toys and electric airplane toys, etc., and spacecraft may include airplanes, rockets, space shuttles and spacecraft, etc.

[0052] The first aspect of the present application provides a positive electrode active material, which includes sodium manganese oxide, and the sodium manganese oxide includes: a first phase, the first phase includes first sodium ion layers and first transition metal layers alternating in sequence, and the interlayer spacing between two adjacent first transition metal layers in the first phase in a direction perpendicular to the (001) crystal plane is 0.550nm~0.565nm, and the first phase includes doping element fluorine; the second phase includes second sodium ion layers and second transition metal layers alternating in sequence, and the interlayer spacing between two adjacent second transition metal layers in the second phase in a direction perpendicular to the (001) crystal plane is 0.530nm~0.545nm.

[0053] Illustratively, the interlayer spacing between two adjacent first transition metal layers in the first phase in the direction perpendicular to the (001) crystal plane can be 0.550 nm, 0.552 nm, 0.554 nm, 0.556 nm, 0.558 nm, 0.560 nm, 0.562 nm, 0.564 nm, 0.565 nm, etc., or can be a range consisting of any of the above numerical values; the interlayer spacing between two adjacent second transition metal layers in the second phase in the direction perpendicular to the (001) crystal plane can be 0.530 nm, 0.532 nm, 0.534 nm, 0.536 nm, 0.538 nm, 0.540 nm, 0.542 nm, 0.544 nm, 0.545 nm, etc., or can be a range consisting of any of the above numerical values.

[0054] The positive electrode active material of the first aspect of the present application has at least the following beneficial effects: significantly suppressing cracking of the material during charge and discharge cycles, improving cycle stability, and further enabling the positive electrode active material to have both a high specific capacity and a long cycle life.

[0055] According to an embodiment of the present invention, the interlayer spacing of the transition metal layers in the first phase and the second phase in the direction perpendicular to the (001) crystal plane, as well as the elemental composition of the positive electrode active material, can be obtained using conventional methods and conventional instruments in the art. For example, the test method for the interlayer spacing of the transition metal layers in the first phase and the second phase in the direction perpendicular to the (001) crystal plane includes, but is not limited to, X-ray diffraction (XRD) method, transmission electron microscopy (TEM) characterization, etc.; the test method for the elemental composition of the positive electrode active material includes, but is not limited to, inductively coupled plasma atomic emission spectrometry (specifically, the instrument standard can refer to EPA6010D-2014 "Inductively Coupled Plasma Atomic Emission Spectrometry", the specific operation is: after the sample to be tested is treated by a chemical method to be digested into a solution, it is atomized into a plasma and excited to produce characteristic spectral lines of the elements, and the element content is qualitatively and quantitatively analyzed based on the wavelength and intensity (proportional to the concentration) of the spectral lines). The elemental composition of each of the first phase and the second phase in the positive electrode active material (such as whether it contains sodium, manganese, fluorine, etc.) can be obtained by ion polishing the cross section of the sample to be tested and then performing elemental analysis on the particles of different phases.

[0056] In addition, it should be noted that, in the first phase and the second phase described in the present application, "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of phases included in the first phase or the second phase. In the present application, the first phase should be understood as a general term for all phases of sodium manganese oxide in the positive electrode active material that meet the said interlayer spacing range and include fluorine doping, and the second phase should be understood as a general term for all phases of sodium manganese oxide in the positive electrode active material that meet the said interlayer spacing range. For example, the first phase may include but is not limited to the fluorine-doped P2 phase, and the second phase may include but is not limited to the O3 phase.

[0057] Furthermore, the positive electrode active material of the first aspect of the present application may optionally satisfy one or more of the following conditions in addition to satisfying the above conditions.

[0058] In some embodiments of the present application, the first phase may include a P2 phase, and the space group may include P63 / mmc; the second phase may include an O3 phase, and the space group may include The inconsistent arrangement of the oxygen layers in the P2 and O3 phases, coupled with greater differences in layer stacking, further enhances the "interlocking" effect between the first and second phases, thereby further improving the cycling stability of the cathode active material. The presence of the P2 and O3 phases and their space group testing can also be confirmed through XRD characterization.

[0059] For example, in this application, the phase state, interlayer spacing and space group test of the positive electrode active material can be carried out according to the following method: XRD test can be carried out on the positive electrode active material, using CuKα radiation as the radiation source, and the radiation wavelength is The scanning 2θ angle range can be 5° to 60°, and the scanning rate can be 4° / min for testing. After the test is completed, the interlayer spacing of the selected crystal plane can be obtained by the angle corresponding to the selected crystal plane, according to the Bragg equation 2d·sinθ=λ, and each unit cell of the selected crystal plane contains three layers of transition metal layers, and then the interlayer spacing of the two adjacent transition metal layers in the corresponding phase in the direction perpendicular to the (001) crystal plane can be obtained. 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. For example, for the first phase (such as P2 phase), after the XRD test is completed, the interlayer spacing d of the 002 crystal plane can be obtained by the angle corresponding to the 002 crystal plane (for the P2 phase, the 2θ angle peak is generally within 15° to 17°), according to the Bragg equation 2dsinθ=λ, and each unit cell of the 002 crystal plane contains three layers of the first transition metal layer. 002 For the second phase (such as O3 phase), after the test is completed, the angle corresponding to the 003 crystal plane is obtained (for the O3 phase, the 2θ angle peak is generally within 15°~17°). According to the Bragg equation 2dsinθ=λ, and each unit cell of the 003 crystal plane contains three layers of the second transition metal layer, the interlayer spacing d of the 003 crystal plane can be obtained. 003 , d 002 and d 003 That is, it corresponds to the interlayer spacing between adjacent transition metal layers in the first phase and the second phase in the direction perpendicular to the (001) crystal plane.

[0060] In some embodiments of the present application, the minimum distance between two adjacent transition metal ions in the same first transition metal layer is a1, the minimum distance between two adjacent transition metal ions in the same second transition metal layer is a2, and a2-a1≥5pm.

[0061] For example, the value of a2-a1 can be 5pm, 6pm, 7pm, 8pm, 9pm, 10pm, 11pm, 12pm, 13pm, 15pm, 18pm, etc. Among them, the values ​​of a2 and a1 can be obtained by XRD characterization, and then the difference between the two is obtained. When a2-a1≥5pm, the lattice mismatch between the first phase and the second phase at the transition metal layer is large, which is beneficial to further improve the "interlocking" effect of the layered structure of sodium manganese oxide on the crystal plane slip during the process of sodium insertion and extraction, and further helps to further reduce the lattice change of the crystal structure of sodium manganese oxide during the charge and discharge cycle, reduce the generation of cracks, and improve the stability of the positive electrode active material during the charge and discharge cycle.

[0062] In some embodiments of the present application, a2-a1 may be 5 pm to 15 pm. For example, a2-a1 may be 5 pm to 10 pm. This is beneficial for reducing the fluorine doping content while improving the stability of the positive electrode active material during charge and discharge cycles.

[0063] In some embodiments of the present application, the difference between the interlayer spacing between two adjacent first transition metal layers in the first phase in a direction perpendicular to the (001) crystal plane (denoted as d1) and the interlayer spacing between two adjacent second transition metal layers in the second phase in a direction perpendicular to the (001) crystal plane (denoted as d2) can be 0.01nm to 0.02nm. That is, the value of d1-d2 can be 0.01nm to 0.02nm, for example, 0.01nm, 0.012nm, 0.014nm, 0.016nm, 0.018nm, 0.02nm, etc. The difference between d1 and d2 satisfies the given range relationship, which can play a good "interlocking" role in the interlayer spacing during the contraction and expansion process of the sodium manganese oxide layered structure, thereby further reducing the stress and strain of the sodium manganese oxide crystal structure during the charge and discharge cycle, inhibiting the generation of cracks in the crystal structure, and improving the stability of the positive electrode active material during the charge and discharge cycle.

[0064] In some embodiments of the present application, the first phase may include: Na x1 Mn y1 Fe a1 Ni b1 M1 c1 O 2+δ1-e F e , 0.5≤x1≤0.8, y1+a1+b1+c1=1, 0≤a1≤0.6, 0≤b1≤0.6, 0≤c1≤0.4, -0.1≤δ1≤0.1, 0<e≤0.1, M1 can include one or more elements of Sb, La, Ce, Co, In, Ga, Ta, W, Ba, Cu, Li, Ti, Zr, K, Nb, Mg, Ca, Mo, Zn, Cr, W, Bi, Sn, Ge, Al, Si, and B.

[0065] For example, the value of x1 can be 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, etc.; the value of a1 can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, etc.; the value of y1 can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, etc.; the value of b1 can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, etc.; c1 can be 0, 0.1, 0.2, 0.3, 0.4, etc.; δ1 can be -0.1, -0.08, -0.05, -0.02, 0, 0.02, 0.05, 0.08, 0.1, etc.; e can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, etc. Fe and Ni are active metal elements that can provide charge compensation in the process of sodium insertion and extraction, increasing the Na x1 Mn y1 Fe a1 Ni b1 M1 c1 O 2+δ1-e F e The specific capacity of Fe and Ni is high, while Fe and Ni are easily activated by oxygen nearby, resulting in loss or side reactions. Mn is beneficial to improve Na x1 Mn y1 Fe a1 Ni b1 M1 c1 O 2+δ1-e F e In terms of structural stability during the charge and discharge cycle, increasing the Mn element content is beneficial to stabilizing the situation where Fe and Ni are easily activated and lost or react with side reactions. In addition, the introduction of fluorine doping is beneficial to reducing the distance between two adjacent transition metal ions in the transition metal layer in the first phase, improving the lattice mismatch between the first phase and the second phase at the transition metal layer, and improving the "interlocking" effect of the layered structure of sodium manganese oxide on the crystal plane slip during the process of sodium insertion and extraction, thereby inhibiting the crystal structure of sodium manganese oxide from cracking during the charge and discharge cycle. Moreover, controlling the fluorine doping amount to meet the given range is also beneficial to reducing the risk of forming an impurity phase due to a high fluorine doping amount, which leads to a decrease in specific capacity. Therefore, by controlling the Na x1 Mn y1 Fe a1 Ni b1 M1 c1 O 2+δ1- e F e The content of each element satisfies the given range, which is beneficial to taking into account both the specific capacity and cycle stability of the positive electrode active material.

[0066] In some embodiments of the present application, the second phase may include: Na x2 Mn y2 Fe a2 Ni b2 M2 c2 O 2+δ2 , 0.7≤x2≤1.2, y2+a2+b2+c2=1, 0.1≤a2≤0.6, 0.1≤b2≤0.6, 0≤c2≤0.4, -0.1≤δ2≤0.1, M2 includes one or more elements of Sb, La, Ce, Co, In, Ga, Ta, W, Ba, Cu, Li, Ti, Zr, K, Nb, Mg, Ca, Mo, Zn, Cr, W, Bi, Sn, Ge, Al, Si, and B.

[0067] For example, the value of x2 can be 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, etc.; the value of y2 can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, etc.; the value of a2 can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, etc.; the value of b2 can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, etc.; the value of c2 can be 0, 0.05, 0.1, 0.2, 0.3, 0.4, etc.; the value of δ2 can be -0.1, -0.08, -0.05, -0.02, 0, 0.02, 0.05, 0.08, 0.1, etc. The second phase Na x2 Mn y2 Fe a2 Ni b2 M2 c2 O 2+δ2 The sodium ion content in the cathode is relatively high, and the interlayer spacing is small. Controlling the content of each element to meet the given range is beneficial to taking into account the specific capacity, cycle stability and first coulombic efficiency of the cathode active material. In addition, Fe and Ni are active metal elements that can provide charge compensation in the process of sodium insertion and extraction, increasing the Na x2 Mn y2 Fe a2 Ni b2 M2 c2 O 2+δ2 The specific capacity of Fe and Ni is high, and Fe and Ni are easily activated by oxygen, resulting in loss or side reactions. Increasing the Mn content is beneficial to stabilizing this situation. x2 Mn y2 Fe a2 Ni b2 M2 c2 O 2+δ2The content of each element in satisfies the given range, which is beneficial to taking into account the specific capacity, cycle stability and coulombic efficiency of the positive electrode active material. x1 Mn y1 Fe a1 Ni b1 M1 c1 O 2+δ1-e F e , the second phase may include Na x2 Mn y2 Fe a2 Ni b2 M2 c2 O 2+δ2 Mixing the two not only helps to achieve a better "interlocking" effect between the first phase and the second phase, thereby further improving the cycle stability of the positive electrode active material, but also helps to obtain a higher specific capacity.

[0068] It should be noted that in the positive electrode sheet, battery, or electrical device, sodium ions will be consumed during the battery formation and cycling process, so the measured sodium content x in the positive electrode active material may be less than 1. In addition, the battery will be accompanied by the deintercalation and consumption of Na during the charge and discharge process, and the molar content of Na will fluctuate when the battery is discharged to different states. In addition, during the preparation process of the first and second phases of the positive electrode active material, the oxygen content will also vary due to different process controls such as oxygen content or factors such as lattice oxygen release. In the enumeration of the first and second phases of the positive electrode active material in this application, the molar content of oxygen is only a theoretical value, and the actual molar content of oxygen will fluctuate.

[0069] In some embodiments of the present application, y1≥0.6. For example, the value of y1 can be 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, etc. The first phase Na x1 Mn y1 Fe a1 Ni b1 M1 c1 O 2+δ1-e F e By further controlling the element contents of Mn, Fe and Ni to meet the given range, it is beneficial to further improve its cycle stability while taking into account its specific capacity.

[0070] In some embodiments of the present application, 0.03≤e≤0.08. For example, the value of e can be 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, etc. The first phase Na x1 Mn y1 Fe a1 Ni b1 M1c1 O 2+δ1-e F e Increasing the fluorine doping level helps to further reduce the distance between two adjacent transition metal ions in the transition metal layer in the first phase, improve the lattice mismatch between the two phases at the transition metal layer, and enhance the "interlocking" effect of the layered structure of sodium manganese oxide on crystal plane slip during the process of sodium insertion and extraction. Therefore, controlling the fluorine doping level to meet the given range is beneficial for further reducing the stress and strain of the crystal structure of sodium manganese oxide during the charge and discharge cycle, thereby further suppressing the formation of cracks in the crystal structure, improving the stability of the positive electrode active material during the charge and discharge cycle, and also helping to reduce the risk of impurity phase formation due to high fluorine doping, which leads to a decrease in specific capacity.

[0071] In some embodiments of the present application, M1 may include one or more elements selected from the group consisting of Zn, Mg, Sn, and Ti. x1 Mn y1 Fe a1 Ni b1 M1 c1 O 2+δ1-e F e In the embodiment, when M1 is selected from one or more of Zn, Mg, Sn, and Ti, these metal elements are more likely to migrate to the sodium ion layer during the sodium removal process, causing strain in the local lattice of the first phase, increasing the lattice mismatch between the first phase and the second phase, and improving the "interlocking" effect of the layered structure of sodium manganese oxide in the process of sodium insertion and removal, which is beneficial to further inhibit the generation of cracks in the positive electrode active material during the charge and discharge cycle and improve the cycle stability of the positive electrode active material.

[0072] In some embodiments of the present application, M2 may include one or more elements of Cu, Zn, Ti, Mg, Co, and Al.

[0073] In some embodiments of the present application, at least one of the following conditions is satisfied: 0.2≤y2≤0.5, 0.2≤a2≤0.35, 0.2≤b2≤0.35. x2 Mn y2 Fe a2 Ni b2 M2 c2 O 2+δ2 In the process of sodium insertion and extraction, controlling the contents of Mn, Fe and Ni to meet the given range is beneficial to further provide charge compensation and increase Na x2 Mn y2 Fe a2 Ni b2 M2 c2 O 2+δ2The specific capacity of the positive electrode active material is improved, and it is also beneficial to reduce the risk of Fe and Ni adjacent oxygen being easily activated, resulting in loss or side reactions, thereby further balancing the specific capacity and cycle stability of the positive electrode active material.

[0074] In some embodiments of the present application, the first phase Na in the positive electrode active material can be determined by ion polishing the cross section of the sample to be tested and combining the elemental analysis of particles of different phases with conventional instruments such as X-ray diffraction (XRD), transmission electron microscope (TEM), energy dispersive spectrometer (EDS), etc. x1 Mn y1 Fe a1 Ni b1 M1 c1 O 2+δ1-e F e and the second phase Na x2 Mn y2 Fe a2 Ni b2 M2 c2 O 2+δ2 The presence of, as well as the composition of the elements in the two phases (such as the presence of Mn, Fe, Ni, F, etc. or the types of M1 and M2, etc.) and subscripts.

[0075] In some embodiments of the present application, x1≤x2. The interlayer spacing and specific capacity of sodium manganese oxide are both affected by the sodium content of the first phase. x1 Mn y1 Fe a1 Ni b1 M1 c1 O 2+δ1-e F e and the second phase Na x2 Mn y2 Fe a2 Ni b2 M2 c2 O 2+δ2 The sodium content in the medium meets the given conditions, which is beneficial for the positive electrode active material to have both higher specific capacity and better cycle stability.

[0076] In some embodiments of the present application, the mass ratio of the first phase to the second phase can be 5:95 to 3:7. For example, the mass ratio of the first phase to the second phase can be 5 / 95, 1 / 9, 1.5 / 8.5, 2 / 8, 2.5 / 7.5, 3 / 7, etc. Compared with the first phase, the second phase has a relatively higher specific capacity and a relatively lower ion diffusion rate and average voltage. By controlling the mass ratio of the first phase to the second phase to meet the given range, it is beneficial for the positive electrode active material to have a higher specific capacity, rate performance and average voltage, and it can also make the two play a better "interlocking" role, thereby obtaining better cycle stability.

[0077] The second aspect of the present application provides a method for preparing the positive electrode active material of the first aspect of the present application, comprising: mixing and calcining a sodium manganese oxide including a first phase and a sodium manganese oxide including a second phase, wherein: the first phase comprises a first sodium ion layer and a first transition metal layer alternating in sequence, and the interlayer spacing between two adjacent first transition metal layers in the first phase in a direction perpendicular to the (001) crystal plane is 0.550nm~0.565nm, and the first phase comprises doping element fluorine; the second phase comprises a second sodium ion layer and a second transition metal layer alternating in sequence, and the interlayer spacing between two adjacent second transition metal layers in the second phase in a direction perpendicular to the (001) crystal plane is 0.530nm~0.545nm.

[0078] The method for preparing the positive active material of the second aspect of the present application has at least the following beneficial effects: calcining the first phase and the second phase after mixing is also beneficial to shortening the difference in interlayer spacing between the two phases, increasing the interaction force between the two phases, obtaining an enhanced "interlocking" effect, thereby reducing the generation of cracks and improving the cycle performance. The mechanism of the above effect is likely to be because the first phase and the second phase with different interlayer spacing do not change their structures completely synchronously when deintercalating sodium, so that there is stress and lattice mismatch at the interface between the two phases, forming an "interlocking" effect, effectively suppressing the lattice change of the two phases in the process of deintercalating sodium ions, reducing the generation of cracks, and thus increasing the cycle stability; at the same time, introducing fluorine doping into the first phase with a larger interlayer spacing can also reduce the distance between the transition metals in the transition metal layer in the first phase, thereby causing the two phases to produce lattice mismatch at the transition metal layer, which is beneficial to further suppress the lattice change of the two phases in the process of deintercalating sodium ions and reducing the generation of cracks. Thus, the positive active material prepared by this method can significantly suppress the generation of cracks during the charge and discharge cycle and improve its cycle stability.

[0079] In some embodiments of the present application, the calcination temperature can be 500°C to 1200°C, the time can be 0.5h to 20h, and the atmosphere can be an oxygen-containing atmosphere. For example, when the first phase and the second phase are mixed and calcined, the temperature can be 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, 1200°C, etc., and the time can be 0.5h, 1h, 3h, 5h, 8h, 10h, 12h, 15h, 18h, 20h, etc. The atmosphere can include but is not limited to an air atmosphere, or a mixed atmosphere of oxygen and nitrogen or an inert gas. It should be noted that the phase composition, space group, distance relationship between transition metal ions in the transition metal layer, interlayer spacing difference, specific type of sodium manganese oxide, fluorine doping content and transition metal element doping type in the first phase, Ni and Fe doping amount range in the second phase, mass ratio of the first phase and the second phase, etc., have been described in detail in the previous section and will not be repeated here. In addition, the sodium manganese oxide including the first phase and the sodium manganese oxide including the second phase can be independently obtained by conventional methods in the art, and the relevant process parameters can be flexibly selected according to actual needs.

[0080] In some embodiments of the present application, before calcining the sodium manganese oxide including the first phase and the sodium manganese oxide including the second phase, the process may further include: grinding and / or ball milling the two sodium manganese oxides separately or the mixture thereof to improve the mixing uniformity of the raw material components and the calcination efficiency.

[0081] The third aspect of the present application provides a positive electrode plate, which includes: the positive electrode active material of the first aspect of the present application, or the positive electrode active material prepared by the method of the second aspect of the present application.

[0082] In a battery, a positive electrode sheet generally includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material.

[0083] The positive electrode current collector may be a conventional metal foil or a composite current collector (a metal material may be disposed on a polymer substrate to form a composite current collector). As an example, the positive electrode current collector may include at least one of copper foil, aluminum foil, nickel foil, stainless steel foil, stainless steel mesh, and carbon-coated aluminum foil.

[0084] The positive electrode active material layer may also optionally include at least one of a binder, a conductive agent, and other optional auxiliary agents. Among them, the binder, conductive agent, and auxiliary agent can all be conventionally selected in the art. For example, the conductive agent can include but is not limited to one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The binder can include but is not limited to one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB). These materials can all be obtained through commercial channels.

[0085] The fourth aspect of the present application provides a battery, which includes: the positive electrode plate of the third aspect of the present application.

[0086] A battery is a battery that can be recharged to activate the active materials after discharge and continue to be used.

[0087] It is understandable that the battery proposed in this application can be a sodium ion battery.

[0088] Typically, a battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The separator is placed between the positive and negative electrodes to isolate them. The electrolyte conducts ions between the positive and negative electrodes.

[0089] [Negative electrode]

[0090] In a battery, the negative electrode plate typically includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material. The negative electrode current collector can be a conventional metal foil or a composite current collector (for example, a metal material disposed on a polymer substrate to form a composite current collector). As an example, the negative electrode current collector can be copper foil. The negative electrode active material layer typically also optionally includes a binder and a conductive agent. The conductive agent is used to improve the conductivity of the negative electrode active material layer, and the binder is used to firmly bond the negative electrode active material and the binder to the negative electrode current collector. This application does not specifically limit the types of conductive and binder agents used in the negative electrode plate; they can be selected based on actual needs. As examples, the conductive agent may include, but is not limited to, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. As examples, the binder may include, but is not limited to, at least one of styrene-butadiene rubber (SBR), styrene-butadiene rubber (SBCs), water-based acrylic resin, and carboxymethyl cellulose (CMC).

[0091] The negative electrode active material layer may also optionally include a thickener, such as carboxymethyl cellulose (CMC), etc. However, the present application is not limited thereto, and the present application may also use other materials that can be used as thickeners for sodium ion battery negative electrode sheets.

[0092] In some embodiments of the present application, the battery of the fourth aspect of the present application may be a sodium metal battery. In this case, the negative electrode active material may include, but is not limited to, metallic sodium. For example, the negative electrode active material may also be an alloy of metallic sodium and various other metal or non-metal elements.

[0093] In some embodiments of the present application, the battery of the fourth aspect of the present application can also be a negative electrode-free sodium metal battery. In this case, the negative electrode is composed of only a metal foil current collector, and there is no sodium metal on its surface. During the cycle, only the sodium in the positive electrode is used, and it is precipitated and stripped in the form of sodium metal on the negative electrode side.

[0094] [Electrolyte]

[0095] The electrolyte solution may include an electrolyte salt and a solvent.

[0096] As an example, the electrolyte sodium salt may include but is not limited to at least one of sodium hexafluorophosphate, sodium difluorooxalatoborate, sodium tetrafluoroborate, sodium bisoxalatoborate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, and sodium bis(trifluoromethylsulfonyl)imide.

[0097] As an example, the solvent may include, 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).

[0098] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0099] [Isolation film]

[0100] As the above-mentioned isolation membrane, the present application has no special restrictions and any known porous structure isolation membrane with electrochemical stability and mechanical stability can be selected according to actual needs, for example, it can include but is not limited to a single-layer or multi-layer film containing at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0101] The embodiment of the present application has no particular limitation on the shape of the battery, which can be cylindrical, square or any other shape. Figure 1 The battery 1 is a square structure as an example.

[0102] In some embodiments, the battery may include an outer packaging for encapsulating the positive electrode sheet, the negative electrode sheet, and the electrolyte.

[0103] In some embodiments, the outer packaging may include a housing and a cover. The housing may include a bottom plate and side plates connected to the bottom plate, with the bottom plate and side plates enclosing a receiving cavity. The housing may have an opening communicating with the receiving cavity, and the cover may be positioned over the opening to seal the receiving cavity.

[0104] The positive electrode sheet, negative electrode sheet, and separator can be wound or laminated to form an electrode assembly. The electrode assembly is encapsulated in the housing. The number of electrode assemblies in a battery can include one or more, which can be adjusted according to needs.

[0105] In some embodiments, the outer packaging of the battery may include a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell.

[0106] The outer packaging of the battery may also include a soft bag, such as a bag-type soft bag. The material of the soft bag may be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0107] In some embodiments, the battery may be either a single battery cell or a battery module or battery pack assembled from battery cells. The battery module or battery pack may contain multiple batteries, and the specific number may be adjusted according to the application and capacity of the battery module.

[0108] Figure 2 2 is an example of a battery module. Figure 2 In the battery module 2, the multiple batteries 1 can be arranged in sequence along the length of the battery module 2. Of course, they can also be arranged in any other manner. The multiple batteries 1 can further be fixed by fasteners. The battery module 2 can also include a housing having a storage space, and the multiple batteries 1 are accommodated in the storage space. In some embodiments, the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0109] Figure 3 and 4 The battery pack 3 is used as an example. Figure 3 and 4 The battery pack 3 may include a battery box and multiple battery modules 2 disposed in the battery box. The battery box includes an upper box body 4 and a lower box body 5. The upper box body 4 can cover the lower box body 5 and form an enclosed space for accommodating the battery modules 2. The multiple battery modules 2 can be arranged in the battery box in any manner.

[0110] The fifth aspect of the present application provides an electrical device, which includes: the battery of the fourth aspect of the present application.

[0111] Specifically, the battery can serve as a power source or an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks), electric trains, ships, satellites, and energy storage systems.

[0112] Figure 5This is an example of an electrical device. This device includes a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. Another example of an electrical device may include a mobile phone, a tablet computer, or a laptop computer. These devices are typically required to be lightweight and thin, and may use batteries as a power source.

[0113] 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.

[0114] Example 1

[0115] (1) Preparation of batteries

[0116] (1) Preparation of positive electrode active materials for sodium ion batteries

[0117] To synthesize the first phase, weigh a total of 30 g of Na₂CO₃, Mn₂O₃, NiO, ZnO, and NaF at a molar ratio of Na:Mn:Ni:Zn:F of 0.75:0.7:0.25:0.05:0.05. This sample was pre-ground in an agate mortar and milled in a planetary ball mill for 1 hour to produce a precursor mixture. The resulting precursor mixture was evenly distributed in an open crucible and then heated in a muffle furnace from room temperature to 850°C at a rate of 5°C / min. The mixture was maintained at 850°C for 15 hours and allowed to cool naturally to yield the first phase of sodium magnesium oxide.

[0118] Synthesis of the second phase: Weigh a total of 30g of Na2CO3, Mn2O3, Fe2O3, NiO, and CuO at a molar ratio of Na:Mn:Fe:Ni:Cu of 0.9:0.4:0.25:0.25:0.1. The resulting sample was pre-ground in an agate mortar and milled in a planetary ball mill for 1 hour to obtain a precursor mixture. The resulting precursor mixture was evenly distributed in an open crucible and then heated from room temperature to 950°C in a muffle furnace at a heating rate of 5°C / min. The mixture was maintained at 950°C for 15 hours and allowed to cool naturally to obtain the second phase of sodium magnesium oxide.

[0119] Synthesize mixed phase: Combine the first phase and the second phase

[0120] A 30g sample of the first and second phases obtained above was prepared at a molar ratio of 1:4. This sample was pre-ground in an agate mortar and then ball-milled in a planetary ball mill for 1 hour to obtain a precursor mixture. The resulting precursor mixture was evenly placed in an open crucible and then heated from room temperature to 800°C in a muffle furnace at a heating rate of 5°C / min. The temperature was maintained at 800°C for 10 hours and allowed to cool naturally to obtain the mixed-phase layered oxide positive electrode active material.

[0121] (2) Preparation of positive electrode sheet

[0122] The obtained mixed-phase layered oxide positive electrode active material, conductive agent carbon black (Super P), and binder polyvinylidene fluoride (PVDF) were 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 was evenly coated on the surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, it was punched into a disc with a diameter of 14 mm to obtain a positive electrode sheet.

[0123] (3) Preparation of negative electrode sheet: The negative electrode sheet is made of metal sodium sheet.

[0124] (4) Preparation of 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.

[0125] (5) Isolation membrane: A porous polyethylene membrane is used as the isolation membrane.

[0126] (6) Preparation of button batteries

[0127] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to serve as an isolation. The prepared electrolyte is added to complete the preparation of the button battery.

[0128] Examples 2 to 10 and Comparative Examples 1 to 4

[0129] Examples 2-10 and Comparative Examples 1-4 differ from the Examples in that the compositions of the raw material components and the molar ratios of the relevant elements differ during the preparation of the positive electrode active materials, and / or the presence or absence of the first phase, second phase, and mixed phase synthesis operations, resulting in different compositions of the resulting positive electrode active materials (see Table 1 for details). Specifically, in the positive electrode active materials prepared in Examples 2-9 and Comparative Examples 1-3, MgO was used as the Mg source, TiO2 was used as the Ti source, Al2O3 was used as the Al source, and SnO2 was used as the Sn source.

[0130] Test method:

[0131] (1) Elemental composition test by inductively coupled plasma optical emission spectrometry

[0132] The elemental composition of the synthesized first and second phases was analyzed. The instrument standard referenced EPA 6010D-2014, Inductively Coupled Plasma Atomic Emission Spectrometry. The sample was chemically treated and dissolved into a solution. The atomized sample was then atomized into a plasma, where it was excited to produce characteristic spectral lines. The elemental content was qualitatively and quantitatively analyzed based on the wavelength and intensity of these lines (which are proportional to the concentration).

[0133] (2) Test of interlayer spacing of layered oxide positive electrode active materials and minimum spacing of transition metal ions in the same transition metal layer

[0134] 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 test was performed with a scanning 2θ angle range of 5° to 60° and a scanning rate of 4° / min.

[0135] Taking the second phase as an example, after the test is completed, the angle corresponding to the (003) crystal plane is obtained according to the Bragg equation 2d·sinθ=λ, and each unit cell of the (003) crystal plane contains three layers of transition metal layers, and the interlayer spacing d of the (003) crystal plane can be obtained. 003 , through d 003 That is, the interlayer spacing between adjacent transition metal layers in the corresponding second phase in the direction perpendicular to the (001) crystal plane can be obtained; the size of its a-axis can be calculated through the (104) crystal plane diffraction peak of the sample, that is, the minimum spacing between two transition metal ions in the same transition metal layer.

[0136] Note: For the first phase, the (002) crystal plane is taken, and for the second phase, the (003) crystal plane is taken. The 2θ angle peaks of the above two crystal planes are usually located within 15°~17°.

[0137] (3) 50-cycle capacity retention test

[0138] At 25 ° C, the layered oxide positive electrode active material was prepared into a button battery, which was charged to 4.1V at a current density of 10mA / g, and then discharged to 1.5V at a current density of 10mA / g to obtain the discharge capacity C0 of the button battery. Subsequently, the charge and discharge cycle was repeated at a current density of 10mA / g for 50 cycles, and the discharge capacity C0 at the 50th cycle was obtained. 50The capacity retention rate of the layered oxide positive electrode active material after 50 cycles = C1 / C0×100%.

[0139] (4) SEM test

[0140] The test was carried out using a field emission scanning electron microscope (Zeiss Gemini360) according to the JY / T010-1996 standard.

[0141] The above-mentioned related tests were carried out on Examples 1 to 10 and Comparative Examples 1 to 4. The test results are shown in Table 1. Figure 6 and Figure 7 .

[0142]

[0143] Results and Conclusions:

[0144] Combining Examples 1 to 9, Comparative Examples 1 to 3, and Table 1, it can be seen that the sodium manganese oxide positive electrode active material with a mixed phase prepared in the above examples of the present application has good cycle stability and a high specific capacity. Figure 6 This is a scanning electron microscope image of the positive electrode active material prepared in Example 1 after 50 charge and discharge cycles. Figure 7 This is a scanning electron microscope image of the positive electrode active material prepared in Comparative Example 1 after 50 charge and discharge cycles. It can be seen from the figure that there are obvious cracks on the surface of the positive electrode active material prepared in Comparative Example 1, while there are no obvious cracks on the surface of the positive electrode active material prepared in Example 1. This further illustrates that the cycle stability of the positive electrode active material prepared in Example 1 is improved. The main reason for this is that fluorine doping is introduced into the first phase, which increases the lattice mismatch at the interface between the two phases and the transition metal layer, improves the interlocking effect of the two phases, can better inhibit the generation of cracks in the crystal structure, and improves the stability of the positive electrode active material during the charge and discharge cycle. Furthermore, in combination with Examples 1 to 4, it can be seen that with the increase of the fluorine doping content in the first phase, the improvement effect on the cycle performance of the positive electrode active material including the first phase and the second phase generally shows a trend of first increasing and then decreasing; in addition, in combination with the various embodiments and comparative examples, it can be seen that an increase in the difference between the minimum distance a2 between two adjacent transition metal ions in the second identical transition metal layer and the minimum distance a1 between two adjacent transition metal ions in the first identical transition metal layer is beneficial to improving the cycle stability of the positive electrode active material. Optionally, a2-a1≥5pm.

[0145] 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 Comprising sodium manganese oxide, the sodium manganese oxide comprising: A first phase, wherein the first phase comprises alternating first sodium ion layers and first transition metal layers, wherein an interlayer spacing between two adjacent first transition metal layers in a direction perpendicular to a (001) crystal plane in the first phase is 0.550 nm to 0.565 nm, and the first phase comprises a doping element, fluorine; The second phase includes a second sodium ion layer and a second transition metal layer alternating in sequence, and the interlayer spacing between two adjacent second transition metal layers in the second phase in a direction perpendicular to the (001) crystal plane is 0.530nm to 0.545nm.

2. The positive electrode active material according to claim 1, characterized in that The first phase includes a P2 phase, and the space group includes P63 / mmc; the second phase includes an O3 phase, and the space group includes 3. The positive electrode active material according to claim 1 or 2, characterized in that The minimum distance between two adjacent transition metal ions in the same first transition metal layer is a1, and the minimum distance between two adjacent transition metal ions in the same second transition metal layer is a2, where a2-a1≥5pm.

4. The positive electrode active material according to claim 1 or 2, characterized in that a2-a1 is from 5pm to 15pm.

5. The positive electrode active material according to any one of claims 1 to 4, characterized in that The difference between the interlayer spacing between two adjacent first transition metal layers in the first phase in the direction perpendicular to the (001) crystal plane and the interlayer spacing between two adjacent second transition metal layers in the second phase in the direction perpendicular to the (001) crystal plane is 0.01nm to 0.02nm.

6. The positive electrode active material according to any one of claims 1 to 5, characterized in that The first phase includes: Na x1 Mn y1 Fe a1 Ni b1 M1 c1 O 2+δ1-e F e , 0.5≤x1≤0.8, y1+a1+b1+c1=1, 0≤a1≤0.6, 0≤b1≤0.6, 0≤c1≤0.4, -0.1≤δ1≤0.1, 0<e≤0.1, M1 includes one or more elements selected from Sb, La, Ce, Co, In, Ga, Ta, W, Ba, Cu, Li, Ti, Zr, K, Nb, Mg, Ca, Mo, Zn, Cr, W, Bi, Sn, Ge, Al, Si, and B; and / or, The second phase includes: Na x2 Mn y2 Fe a2 Ni b2 M2 c2 O 2+δ2 , 0.7≤x2≤1.2, y2+a2+b2+c2=1, 0.1≤a2≤0.6, 0.1≤b2≤0.6, 0≤c2≤0.4, -0.1≤δ2≤0.1, M2 includes one or more elements of Sb, La, Ce, Co, In, Ga, Ta, W, Ba, Cu, Li, Ti, Zr, K, Nb, Mg, Ca, Mo, Zn, Cr, W, Bi, Sn, Ge, Al, Si, and B.

7. The positive electrode active material according to claim 6, characterized in that y1≥0.6。 8. The positive electrode active material according to claim 6 or 7, characterized in that 0.03≤e≤0.08。 9. The positive electrode active material according to any one of claims 6 to 8, characterized in that M1 includes one or more elements of Zn, Mg, Sn, and Ti; and / or, M2 includes one or more elements of Cu, Zn, Ti, Mg, Co, and Al.

10. The positive electrode active material according to any one of claims 6 to 9, characterized in that At least one of the following conditions is satisfied: 0.2≤y2≤0.5, 0.2≤a2≤0.35, 0.2≤b2≤0.

35.

11. The positive electrode active material according to any one of claims 6 to 10, characterized in that x1≤x2.

12. The positive electrode active material according to any one of claims 1 to 11, characterized in that The mass ratio of the first phase to the second phase is 5:95 to 30:

70.

13. A method for preparing the positive electrode active material according to any one of claims 1 to 12, characterized in that: include: Sodium manganese oxide comprising a first phase and sodium manganese oxide comprising a second phase are mixed and calcined, wherein: The first phase includes alternating first sodium ion layers and first transition metal layers, the interlayer spacing between two adjacent first transition metal layers in the first phase in a direction perpendicular to the (001) crystal plane is 0.550nm to 0.565nm, and the first phase includes doped element fluorine; the second phase includes alternating second sodium ion layers and second transition metal layers, the interlayer spacing between two adjacent second transition metal layers in the second phase in a direction perpendicular to the (001) crystal plane is 0.530nm to 0.545nm.

14. The method according to claim 13, characterized in that The calcination temperature is 500° C. to 1200° C., the calcination time is 0.5 h to 20 h, and the atmosphere is an oxygen-containing atmosphere.

15. A positive electrode plate, characterized in that: include: The positive electrode active material according to any one of claims 1 to 12, and / or the positive electrode active material prepared by the method according to any one of claims 13 to 14.

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

17. An electrical device, characterized in that: include: The battery according to claim 16.

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