Composite cathode material, preparation method thereof and sodium ion battery

Abstract

The application relates to the field of sodium ion battery materials, and discloses a composite positive electrode material, a preparation method thereof and a sodium ion battery. The composite positive electrode material comprises an O3 type layered oxide core and a P2 type layered oxide shell coated on the surface of the core, and cations in a transition metal layer in the P2 type layered oxide shell are in a disordered distribution; wherein the chemical composition of the O3 type layered oxide core satisfies a chemical formula Na x A m D n O2; the chemical composition of the P2 type layered oxide shell satisfies a chemical formula Na y E u G v O2; and the weight ratio of the O3 type layered oxide core to the P2 type layered oxide shell is 1:(0.05-0.2). The positive electrode material has the characteristics of low residual alkali, high capacity, excellent rate performance and cycle performance, has a high cycle retention rate under high voltage conditions, and still has excellent cycle performance under a high voltage of 4.2 V.

Description

Technical Field

[0001] This invention relates to the field of cathode materials for sodium-ion batteries, specifically to a composite cathode material, its preparation method, and a sodium-ion battery. Background Technology

[0002] Sodium-ion batteries possess electrochemical performance similar to lithium-ion batteries, and sodium resources are abundant and inexpensive, making them promising candidates for energy storage and backup power applications. Sodium-ion layered oxide cathode materials have attracted significant attention due to their high specific capacity, low cost, and simple preparation methods. Based on their structure, layered oxide cathode materials can be mainly classified into O3 and P2 types. O3-type layered oxides have a higher initial sodium content, resulting in a higher specific capacity, while P2-type layered oxides have a lower initial sodium content but wider sodium ion transport channels, leading to less structural change during extraction and insertion, thus exhibiting low residual alkali and better rate and cycle performance. However, with increasing charging voltage, harmful phase transitions in both O3 and P2-type sodium-ion layered oxides intensify, leading to significant volume changes and structural degradation, thereby accelerating capacity and cycle retention decline. To address structural degradation, one approach is to lower the upper charging voltage limit, thereby suppressing harmful phase transitions at high voltages, but this sacrifices some capacity. On the other hand, ion doping can suppress harmful phase transitions and improve the structural and air stability of materials. However, inert ion doping can significantly reduce capacity and cause the precipitation of electrochemically inactive impurity phases in the material system, thereby affecting rate capability and cycling performance. Constructing an O3 and P2 composite phase structure is an effective strategy to improve the structural stability and electrochemical performance of materials, and it usually exhibits better electrochemical performance than single-phase structures.

[0003] CN116014119A discloses a hybrid sodium-ion battery cathode material and its preparation method. This hybrid sodium-ion battery cathode material is prepared by resting the O3-type layered oxide, a product of a primary sintering process, in humid air with a humidity of 55%-75%. The rested material is then added to a manganese source, and a second sintering is performed to obtain P2-type Na. x MnO y While coated sodium-ion battery cathode materials improve air stability and reduce residual alkali content, and exhibit high capacity and cycle retention within a voltage range of 2-4.05V, they suffer from poor electrochemical and structural stability. This makes it difficult to guarantee excellent rate and cycle performance under long-term cycling and high voltage conditions. Furthermore, their performance is affected by factors such as space, ambient humidity, and material stacking height when stored in humid air, which is not conducive to mass production.

[0004] CN116435508A discloses a P2-structured material-coated O3-structured layered metal oxide sodium-ion battery cathode material and its preparation method. By mixing the O3-type layered oxide produced in the first sintering with sodium, nickel, and manganese sources and then performing a second sintering, the material's air stability and cycle performance are improved to some extent, but the capacity is significantly reduced. Furthermore, the ordered arrangement of cations in the transition metal layer of the P2-structured coating material easily causes changes in the transition metal layer structure, leading to structural stress and decreased electrochemical performance. Consequently, the material cannot exhibit excellent electrical performance under long cycles and high voltages.

[0005] There is an urgent need to develop an O3 / P2 composite phase cathode material with low residual alkali, stable structure, long cycle life, and excellent high voltage performance. Summary of the Invention

[0006] This invention addresses the problems of poor structural stability, unsatisfactory capacity and cycle retention under high voltage conditions in existing layered oxide sodium-ion battery cathode materials by providing a composite cathode material, its preparation method, and a sodium-ion battery.

[0007] To achieve the above objectives, the first aspect of the present invention provides a composite cathode material, the composite cathode material comprising: an O3-type layered oxide core and a P2-type layered oxide shell covering the surface of the core, wherein the cations in the transition metal layer of the P2-type layered oxide shell are randomly distributed.

[0008] The chemical composition of the O3-type layered oxide core satisfies the chemical formula Na x A m D n O2; wherein element A is selected from at least two of Ni, Fe, Mn, Zn, Cu, Co and Li; element D is selected from at least one of Al, Ti, Mg, Zr, Ca, Sr, Y, W, Nb, K and Sn; 0.8≤x≤1.05, 0.5<m<1, 0.01≤n≤0.15, and m+n=1;

[0009] The chemical composition of the P2-type layered oxide shell satisfies the chemical formula Na. y E u G v O2; wherein element E is selected from at least one of Ni, Fe, Cu and Cr; element G is selected from at least one of Mn, Mg, Ti, Zr, Nb and Sb; 0.5≤y≤0.7, 0.1<u<0.6, 0.4≤v≤0.8, u+v=1, and u / v is not equal to 1: (1.75-2);

[0010] The weight ratio of the O3-type layered oxide core to the P2-type layered oxide shell is 1:(0.05-0.2).

[0011] A second aspect of the present invention provides a method for preparing a composite cathode material, comprising:

[0012] (1) The first sodium source, element A source and element D source are mixed for the first time, followed by the first sintering and the first crushing to obtain the O3 type layered oxide core.

[0013] (2) The O3-type layered oxide core, the second sodium source, the element E source and the element G source are mixed for the second time, and then sintered for the second time, so that the surface of the O3-type layered oxide core forms a P2-type layered oxide shell, and then crushed for the second time to obtain a composite cathode material.

[0014] The amounts of the first sodium source, element A source, and element D source are such that the chemical composition of the O3-type layered oxide core satisfies the chemical formula Na. x A m D n O2; wherein element A is selected from at least two of Ni, Fe, Mn, Zn, Cu, Co and Li; element D is selected from at least one of Al, Ti, Mg, Zr, Ca, Sr, Y, W, Nb, K and Sn; 0.8≤x≤1.05, 0.5<m<1, 0.01≤n≤0.15, and m+n=1;

[0015] The amounts of the second sodium source, element E source, and element G source are such that the chemical composition of the P2-type layered oxide shell satisfies the chemical formula Na. y E u G v O2; wherein element E is selected from at least one of Ni, Fe, Cu and Cr; element G is selected from at least one of Mn, Mg, Ti, Zr, Nb and Sb; 0.5≤y≤0.7, 0.1<u<0.6, 0.4≤v≤0.8, u+v=1, and u / v is not equal to 1: (1.75-2);

[0016] The amount of each raw material fed is such that the weight ratio of the O3 type layered oxide core to the P2 type layered oxide shell is 1:(0.05-0.2).

[0017] A third aspect of the present invention provides a composite cathode material prepared by the method described in the second aspect above.

[0018] A fourth aspect of the present invention provides a sodium-ion battery comprising the positive electrode material described in the first or third aspect above.

[0019] This invention coats the surface of an O3-type layered oxide core with a P2-type layered oxide shell, in which the cations in the transition metal layer of the shell are randomly distributed, significantly improving the structural stability and electrochemical performance of the coating layer. This results in a cathode material with low residual alkali, high capacity, excellent rate performance and cycle performance, especially with high cycle retention under high voltage conditions, and excellent cycle performance even at a high voltage of 4.2V. Attached Figure Description

[0020] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0021] Figure 1 The image shows the XRD pattern of the composite cathode material L1 prepared in Example 1 of this invention. Detailed Implementation

[0022] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] The first aspect of the present invention provides a composite cathode material, the composite cathode material comprising: an O3-type layered oxide core and a P2-type layered oxide shell covering the surface of the core, wherein the cations in the transition metal layer of the P2-type layered oxide shell are randomly distributed.

[0024] The chemical composition of the O3-type layered oxide core satisfies the chemical formula Na x A m D n O2; wherein element A is selected from at least two of Ni, Fe, Mn, Zn, Cu, Co and Li; element D is selected from at least one of Al, Ti, Mg, Zr, Ca, Sr, Y, W, Nb, K and Sn; 0.8≤x≤1.05, 0.5<m<1, 0.01≤n≤0.15, and m+n=1;

[0025] The chemical composition of the P2-type layered oxide shell satisfies the chemical formula Na. y E u G vO2; wherein element E is selected from at least one of Ni, Fe, Cu and Cr; element G is selected from at least one of Mn, Mg, Ti, Zr, Nb and Sb; 0.5≤y≤0.7, 0.1<u<0.6, 0.4≤v≤0.8, u+v=1, and u / v is not equal to 1: (1.75-2);

[0026] The weight ratio of the O3-type layered oxide core to the P2-type layered oxide shell is 1:(0.05-0.2).

[0027] The composite cathode material provided by this invention has an O3 / P2 composite phase structure. Specifically, the composite cathode material includes an O3-type layered oxide core and a P2-type layered oxide shell covering the surface of the core. The O3-type layered oxide core satisfies the above-mentioned chemical composition, providing high capacity. The P2-type layered oxide shell satisfies the above-mentioned chemical composition, reducing residual alkali on the material surface, improving material structural stability, and enhancing rate performance and cycle performance. Furthermore, the cations in the transition metal layer (containing elements E and G) of the shell are randomly distributed, manifested in its chemical composition Na. y E u G v In O2, u+v=1, and u / v ≠ 1:(1.75-2). A stable transition metal layer can be constructed using a disordered cation distribution method, preventing rapid capacity and cycle decay caused by changes in the sodium layer structure and size due to transition metal unit slippage. This significantly improves the structural stability and electrochemical performance of the coating layer. The combined effect of the O3-type layered oxide core and the P2-type layered oxide shell results in a cathode material with low residual alkali, high capacity, excellent rate performance, and superior cycle performance. It exhibits particularly high cycle retention under high voltage conditions, maintaining excellent cycle performance even at a high voltage of 4.2V.

[0028] According to the present invention, for the composite cathode material, the chemical composition of the O3-type layered oxide core is Na x A m D n In O2, preferably, element A can be selected from at least two of Ni, Fe, Mn and Zn; element D can be selected from at least one of Al, Ti, Ca and Sn; 0.9≤x≤1.0, 0.8<m<1, 0.01≤n≤0.05, and m+n=1. Using this preferred elemental composition and proportions enables the O3-type layered oxide core to have a higher capacity.

[0029] According to the present invention, for the composite cathode material, the chemical composition of the P2-type layered oxide shell is Na y Eu G v In O2, preferably, element E is selected from Ni and / or Fe; element G is selected from Mn and / or Ti; 0.6≤y≤0.7, 0.3<u<0.5, 0.5≤v≤0.7, u+v=1, and u / v is not equal to 1:(1.55-2). Using this preferred elemental composition and ratio, the P2-type layered oxide shell can have a lower residual alkali content, higher structural stability, and better improved rate performance and cycling performance under high voltage conditions.

[0030] According to the present invention, in the composite cathode material, the O3-type layered oxide core and the P2-type layered oxide shell, while satisfying the above-mentioned weight ratio range, preferably have a weight ratio of O3-type layered oxide core to P2-type layered oxide shell of 1:(0.08-0.12), which enables the composite cathode material to have higher capacity, better rate performance and cycle stability under high voltage conditions.

[0031] According to the present invention, in the composite cathode material, the average particle size (D50) of the O3-type layered oxide core is 5-7 μm, which can bring higher capacity and cycle retention rate.

[0032] In this invention, the particle size of the O3-type layered oxide core can be determined by a laser particle size analyzer after the core is prepared.

[0033] According to the present invention, the average particle size (D50) of the composite cathode material is 5.5-8 μm, which is beneficial to the high capacity and long cycle characteristics.

[0034] In this invention, the particle size of the composite cathode material can be determined by a laser particle size analyzer.

[0035] According to the present invention, the residual alkali content on the surface of the composite cathode material is low. Preferably, the residual alkali content on the surface of the cathode material is 100-3000 ppm.

[0036] According to the present invention, the residual alkali content on the surface of the composite cathode material refers to the residual alkali content on the surface of the freshly prepared composite cathode material (which has not been in contact with the surrounding air environment for a long time). In the present invention, the residual alkali content can be determined by potentiometric titration according to GB / T 41704-2022, wherein residual NaOH and Na2CO3 are tested using anhydrous ethanol and deionized water, respectively, and the residual alkali content on the surface is expressed as the content of free Na.

[0037] According to a particularly preferred embodiment of the present invention, in the composite cathode material, the chemical composition of the O3-type layered oxide core satisfies the chemical formula Na x A m D nO2; wherein element A is Ni, Fe, Mn and Zn; element D is Ti and Ca; 0.95≤x≤1.0, 0.95<m<1, 0.01≤n≤0.05, and m+n=1; the chemical composition of the P2 type layered oxide shell satisfies the chemical formula Na y E u G v O2; wherein element E is Fe; element G is Mn; 0.62≤y≤0.67, 0.35<u<0.45, 0.55≤v≤0.65, u+v=1, and u / v ≠ 1:(1.55-2); the weight ratio of the O3-type layered oxide core to the P2-type layered oxide shell is 1:(0.08-0.12). The composite cathode material with this structure and composition exhibits further improved high capacity, high rate capability, and long cycle life.

[0038] A second aspect of the present invention provides a method for preparing a composite cathode material, comprising:

[0039] (1) The first sodium source, element A source and element D source are mixed for the first time, followed by the first sintering and the first crushing to obtain the O3 type layered oxide core.

[0040] (2) The O3-type layered oxide core, the second sodium source, the element E source and the element G source are mixed for the second time, and then sintered for the second time, so that the surface of the O3-type layered oxide core forms a P2-type layered oxide shell, and then crushed for the second time to obtain a composite cathode material.

[0041] The amounts of the first sodium source, element A source, and element D source are such that the chemical composition of the O3-type layered oxide core satisfies the chemical formula Na. x A m D n O2; wherein element A is selected from at least two of Ni, Fe, Mn, Zn, Cu, Co and Li; element D is selected from at least one of Al, Ti, Mg, Zr, Ca, Sr, Y, W, Nb, K and Sn; 0.8≤x≤1.05, 0.5<m<1, 0.01≤n≤0.15, and m+n=1;

[0042] The amounts of the second sodium source, element E source, and element G source are such that the chemical composition of the P2-type layered oxide shell satisfies the chemical formula Na. y E u G vO2; wherein element E is selected from at least one of Ni, Fe, Cu and Cr; element G is selected from at least one of Mn, Mg, Ti, Zr, Nb and Sb; 0.5≤y≤0.7, 0.1<u<0.6, 0.4≤v≤0.8, u+v=1, and u / v is not equal to 1: (1.75-2);

[0043] The amount of each raw material fed is such that the weight ratio of the O3 type layered oxide core to the P2 type layered oxide shell is 1:(0.05-0.2).

[0044] According to the present invention, in the method for preparing the composite cathode material, the first sodium source and the second sodium source provide element Na in the composite cathode material. The first sodium source and the second sodium source may be the same or different, but preferably the same.

[0045] According to the present invention, the types of substances for the first sodium source and the second sodium source are broadly defined, and the sodium source selection can be the conventional method used in the preparation of sodium-ion battery cathode materials. Preferably, each of the first sodium source and the second sodium source is independently selected from at least one of sodium carbonate, sodium bicarbonate, sodium oxide, sodium peroxide, and sodium hydroxide, and more preferably sodium carbonate.

[0046] According to the present invention, the average particle size (D50) of the first sodium source and the second sodium source is independently 5-8 μm, preferably 5.5-6.5 μm, which is beneficial to the uniform mixing of materials and at the same time improves the reactivity.

[0047] According to the present invention, the method for preparing the composite cathode material has a relatively wide range of material types for the element A source, element D source, element E source, and element G source, and can employ materials that provide the corresponding elements as conventionally used in the preparation of sodium-ion battery cathode materials. Preferably, each group of element A source, element D source, element E source, and element G source is independently selected from one of the oxides, hydroxides, and carbonates of the corresponding element, with oxides of the corresponding element being more preferred.

[0048] According to the present invention, the average particle size (D50) of the element A source, element D source, element E source and element G source is independently 0.02-3 μm, preferably 0.02-2 μm, which is beneficial to the uniform mixing of materials, improves the reaction activity, and facilitates the generation of single crystal particles with more uniform morphology.

[0049] According to the present invention, in the preparation method of the composite cathode material, in step (1), the first mixing is not particularly limited, and the raw material mixing method used in the conventional preparation of sodium-ion battery cathode materials can be adopted, as long as the raw materials can be fully and uniformly mixed.

[0050] According to the present invention, in the preparation method of the composite cathode material, in step (1), preferably, the conditions for the first sintering include: a heating rate of 1-5℃ / min, a sintering temperature of 800-1050℃, a sintering time of 6-12h, and a sintering atmosphere of air and / or oxygen. Performing the first sintering under these conditions is more conducive to forming single-crystal particles with lower residual alkali content, uniform morphology dispersion, and suitable particle size.

[0051] According to the present invention, in the preparation method of the composite cathode material, in step (1), the first crushing results in an average particle size (D50) of 5-7 μm for the O3-type layered oxide core. This size range of cores allows the composite cathode material to possess high capacity and excellent cycle performance.

[0052] In this invention, the particle size of the O3-type layered oxide core is determined by a laser particle size analyzer.

[0053] According to the present invention, in the preparation method of the composite cathode material, in step (1), the surface residual alkali content of the O3-type layered oxide core is 100-10000ppm.

[0054] According to the present invention, in the preparation method of the composite cathode material, in step (2), the amount of the second sodium source, element E source and element G source to be fed can be calculated and determined according to the specific chemical composition and weight ratio of the O3 type layered oxide core and the P2 type layered oxide shell in the target composite cathode material, as well as the weight of the O3 type layered oxide core obtained in step (1) and the measured residual alkali on its surface (calculated as free Na), and the O3 type layered oxide core obtained in step (1) is mixed with the second sodium source, element E source and element G source in a second mixing.

[0055] According to the present invention, in the preparation method of the composite cathode material, step (2) does not have any particular limitation on the second mixing. The raw material mixing method used in the conventional preparation of sodium-ion battery cathode materials can be adopted, as long as the raw materials can be fully and uniformly mixed.

[0056] According to the present invention, in the preparation method of the composite cathode material, in step (2), by controlling the feeding ratio of the element E source and the element G source, the P2 type layered oxide shell formed after sintering has a specific chemical composition Na. y E u G vO2, where u+v=1 and u / v ≠ 1: (1.75-2), enables the disordered distribution of cations in the transition metal layer of the P2-type layered oxide shell, thus constructing a stable transition metal layer. This prevents the rapid capacity and cycling decay caused by changes in the structure and size of the sodium layer due to slippage of the transition metal units, and can significantly improve the structural stability and electrochemical performance of the coating layer (shell).

[0057] According to the present invention, in the preparation method of the composite cathode material, in step (2), preferably, the conditions for the second sintering include: a heating rate of 1-5℃ / min, a sintering temperature of 600-800℃, a sintering time of 5-10h, and a sintering atmosphere of air and / or oxygen. Under these conditions, the second sintering is more conducive to forming a uniformly distributed coating layer on the core surface, thereby improving the structural stability of the material.

[0058] According to the present invention, in the preparation method of the composite cathode material, in step (2), the second crushing makes the average particle size of the composite cathode material 5.5-8μm, which is beneficial to exert high capacity and long cycle characteristics.

[0059] In this invention, the first and second crushing are not particularly limited, and conventional material or product crushing methods used in the preparation of sodium-ion battery cathode materials can be adopted, such as air jet milling, mechanical milling, etc.

[0060] The composite cathode material preparation method provided by this invention first prepares an O3-type layered oxide with a specific chemical composition using a first sodium source, element A source, and element D source. Then, it is mixed and sintered with a second sodium source, element E source, and element G source. By controlling the feeding ratio of element E source and element G source, a P2-type layered oxide shell with a specific chemical composition and disordered cation distribution in the transition metal layer is achieved on the surface of the O3-type layered oxide. This can significantly improve the structural stability and electrochemical performance of the coating layer. The resulting cathode material has the characteristics of low residual alkali, high capacity, excellent rate performance and cycle performance, especially high cycle retention rate under high voltage conditions.

[0061] A third aspect of the present invention provides a composite cathode material prepared by the method described in the second aspect above.

[0062] In this invention, the composite cathode material prepared by the method described in the second aspect above has the same chemical composition, structure and properties as the composite cathode material described in the first aspect above, and will not be repeated here.

[0063] A fourth aspect of the present invention provides a sodium-ion battery comprising the composite cathode material described in the first or third aspect above.

[0064] According to the present invention, the sodium-ion battery using the composite cathode material provided by the present invention has the characteristics of high capacity, excellent rate performance and cycle performance compared with the battery using conventional O3 / P2 composite phase structure cathode material. It has a high cycle retention rate under high voltage conditions and can still have excellent cycle performance at a high voltage of 4.2V.

[0065] The present invention will be described in detail below through examples. Unless otherwise specified, the following examples and comparative examples are all conventional methods; the reagents and materials mentioned are commercially available unless otherwise specified.

[0066] In the following examples and comparative examples, the weight ratio of each component in the obtained cathode material was calculated by the amount of raw materials fed.

[0067] Example 1

[0068] (1) Weigh Na2CO3, NiO, Fe2O3, MnO2, ZnO, CaO, and TiO2 according to the designed stoichiometric ratio, mix them evenly in a high-speed mixer, then transfer the mixture to a kiln, heat it at a rate of 2℃ / min, and sinter it at 1010℃ for 10h in an air atmosphere. After removing it from the kiln, crush it to obtain the O3-type layered oxide core (Na2CO3). 0.98 Ni 0.28 Fe 0.32 Mn 0.33 Zn 0.05 Ca 0.01 Ti 0.01 O2 (D50 is 6.93 μm), the residual alkali content on the surface (calculated as free Na) was 3105 ppm as determined by potentiometric titration.

[0069] (2) Based on the chemical composition and component ratio of the target composite cathode material, as well as the weight of the O3-type layered oxide core obtained in step (1) and the measured residual alkali content on its surface (calculated as free Na), weigh Na2CO3, Fe2O3 and MnO2, mix them evenly in a high-speed mixer, then transfer the mixture to a kiln, heat it at a rate of 2℃ / min, sinter it at 600℃ for 8 hours in an air atmosphere, crush it after it comes out of the kiln, and obtain the composite cathode material (denoted as L1).

[0070] L1 has an O3-type layered oxide core (Na) 0.98 Ni 0.28 Fe 0.32 Mn 0.33 Zn 0.05 Ca 0.01 Ti 0.01 O2 (D50 is 6.93 μm), and a P2-type layered oxide shell (Na) covering the surface of the core. 0.65 Fe0.4 Mn 0.6 O2, in which the cations in the transition metal layer are randomly distributed; wherein, the weight ratio of the O3 type layered oxide core to the P2 type layered oxide shell is 1:0.1.

[0071] The D50 of L1 is 7.26 μm.

[0072] The residual alkali content (calculated as free Na) on the L1 surface was determined to be 1145 ppm by potentiometric titration.

[0073] L1 was subjected to XRD testing, and the results are as follows: Figure 1 As shown in the figure (O3-NaFeO2 is the standard card of the O3 phase, numbered JCPDS NO. 82-1495, P2-Na...), 0.65 Cr 0.4 Mn 0.6 O2 is the standard card for the P2 phase (JCPDS NO. 54-0894). Figure 1 The prepared cathode material has an O3 / P2 dual-phase structure and no other impurities.

[0074] Example 2

[0075] (1) Weigh Na2CO3, NiO, Fe2O3, MnO2, ZnO, Al2O3, and TiO2 according to the designed stoichiometric ratio, mix them evenly in a high-speed mixer, then transfer the mixture to a kiln, heat it at a rate of 2℃ / min, and sinter it at 1010℃ for 10h in an air atmosphere. After removing it from the kiln, crush it to obtain the O3-type layered oxide core (Na2CO3). 0.98 Ni 0.28 Fe 0.31 Mn 0.34 Zn 0.05 Al 0.01 Ti 0.01 O2 (D50 is 6.81 μm), the residual alkali content on the surface (calculated as free Na) was 4381 ppm as determined by potentiometric titration.

[0076] (2) Based on the chemical composition and component ratio of the target composite cathode material, as well as the weight of the O3-type layered oxide core obtained in step (1) and the measured residual alkali content on its surface (calculated as free Na), weigh Na2CO3, NiO and MnO2, mix them evenly in a high-speed mixer, then transfer the mixture to a kiln, heat it at a rate of 2℃ / min, sinter it at 600℃ for 8 hours in an air atmosphere, and crush it after it comes out of the kiln to obtain the composite cathode material (denoted as L2).

[0077] L2 has an O3-type layered oxide core (Na) 0.98 Ni 0.28 Fe0.31 Mn 0.34 Zn 0.05 Al 0.01 Ti 0.01 O2 (D50 is 6.81 μm), and a P2-type layered oxide shell (Na) covering the surface of the core. 0.65 Ni 0.4 Mn 0.6 O2, in which the cations in the transition metal layer are randomly distributed; wherein, the weight ratio of the O3 type layered oxide core to the P2 type layered oxide shell is 1:0.1.

[0078] The D50 of L2 is 7.09 μm.

[0079] The residual alkali content (calculated as free Na) on the L2 surface was determined to be 1515 ppm by potentiometric titration.

[0080] Example 3

[0081] (1) Weigh Na2CO3, NiO, Fe2O3, MnO2, CuO, Al2O3, and Nb2O5 according to the designed stoichiometric ratio, mix them evenly in a high-speed mixer, then transfer the mixture to a kiln, heat it at a rate of 2℃ / min, and sinter it at 1010℃ for 10h in an air atmosphere. After removing it from the kiln, crush it to obtain the O3-type layered oxide core (Na2CO3). 1.02 Ni 0.28 Fe 0.30 Mn 0.33 Cu 0.03 Al 0.03 Nb 0.03 O2 (D50 is 6.90 μm), the residual alkali content on the surface (calculated as free Na) was 4018 ppm as determined by potentiometric titration.

[0082] (2) Based on the chemical composition and component ratio of the target composite cathode material, as well as the weight of the O3 type layered oxide core obtained in step (1) and the measured residual alkali content on its surface (calculated as free Na), weigh Na2CO3, Cr2O3 and TiO2, mix them evenly in a high-speed mixer, then transfer the mixture to a kiln, heat it at a rate of 2℃ / min, sinter it at 600℃ for 8 hours in an air atmosphere, crush it after it comes out of the kiln, and obtain the composite cathode material (denoted as L3).

[0083] L3 has an O3-type layered oxide core (Na) 1.02 Ni 0.28 Fe 0.30 Mn 0.33 Cu 0.03 Al 0.03 Nb 0.03O2 (D50 is 6.90 μm), and a P2-type layered oxide shell (Na) covering the surface of the core. 0.58 Cr 0.38 Ti 0.62 O2, in which the cations in the transition metal layer are randomly distributed; wherein, the weight ratio of the O3 type layered oxide core to the P2 type layered oxide shell is 1:0.1.

[0084] The D50 of L3 is 7.17 μm.

[0085] The residual alkali content (calculated as free Na) on the L3 surface was determined to be 1952 ppm by potentiometric titration.

[0086] Example 4

[0087] (1) Weigh Na2CO3, NiO, Fe2O3, MnO2, CuO, Al2O3, and MgO according to the designed stoichiometric ratio, mix them evenly in a high-speed mixer, then transfer the mixture to a kiln, heat it at a rate of 2℃ / min, and sinter it at 1010℃ for 10h in an air atmosphere. After removing it from the kiln, crush it to obtain the O3-type layered oxide core (Na). 1.02 Ni 0.28 Fe 0.30 Mn 0.34 Cu 0.02 Al 0.03 Mg 0.03 O2 (D50 is 6.77 μm), the residual alkali content on the surface (calculated as free Na) was 4355 ppm as determined by potentiometric titration.

[0088] (2) Based on the chemical composition and component ratio of the target composite cathode material, as well as the weight of the O3-type layered oxide core obtained in step (1) and the measured residual alkali content on its surface (calculated as free Na), weigh Na2CO3, Cr2O3 and Nb2O5, mix them evenly in a high-speed mixer, then transfer the mixture to a kiln, heat it at a rate of 2℃ / min, sinter it at 600℃ for 8 hours in an air atmosphere, crush it after it comes out of the kiln, and obtain the composite cathode material (denoted as L4).

[0089] L4 has an O3-type layered oxide core (Na) 1.02 Ni 0.28 Fe 0.30 Mn 0.34 Cu 0.02 Al 0.03 Mg 0.03 O2 (D50 is 6.77 μm), and a P2-type layered oxide shell (Na) covering the surface of the core. 0.58 Cr 0.37 Nb 0.63O2, in which the cations in the transition metal layer are randomly distributed; wherein, the weight ratio of the O3 type layered oxide core to the P2 type layered oxide shell is 1:0.1.

[0090] The D50 of L4 is 6.91 μm.

[0091] The residual alkali content (calculated as free Na) on the L4 surface was determined to be 2674 ppm by potentiometric titration.

[0092] Example 5

[0093] (1) Weigh Na2CO3, NiO, Fe2O3, MnO2, ZnO, CaO, and TiO2 according to the designed stoichiometric ratio, mix them evenly in a high-speed mixer, then transfer the mixture to a kiln, heat it at a rate of 2℃ / min, and sinter it at 1010℃ for 10h in an air atmosphere. After removing it from the kiln, crush it to obtain the O3-type layered oxide core (Na2CO3). 0.98 Ni 0.28 Fe 0.32 Mn 0.33 Zn 0.05 Ca 0.01 Ti 0.01 O2 (D50 is 6.93 μm), the residual alkali content on the surface (calculated as free Na) was 3105 ppm as determined by potentiometric titration.

[0094] (2) Based on the chemical composition and component ratio of the target composite cathode material, as well as the weight of the O3 type layered oxide core obtained in step (1) and the measured residual alkali content on its surface (calculated as free Na), weigh Na2CO3, Fe2O3 and MnO2, mix them evenly in a high-speed mixer, then transfer the mixture to a kiln, heat it at a rate of 2℃ / min, sinter it at 600℃ for 8 hours in an air atmosphere, crush it after it comes out of the kiln, and obtain the composite cathode material (denoted as L5).

[0095] L5 has an O3-type layered oxide core (Na) 0.98 Ni 0.28 Fe 0.32 Mn 0.33 Zn 0.05 Ca 0.01 Ti 0.01 O2 (D50 is 6.93 μm), and a P2-type layered oxide shell (Na) covering the surface of the core. 0.65 Fe 0.4 Mn 0.6 O2, in which the cations in the transition metal layer are randomly distributed; wherein, the weight ratio of the O3 type layered oxide core to the P2 type layered oxide shell is 1:0.05.

[0096] The D50 of L5 is 7.11 μm.

[0097] The residual alkali content (calculated as free Na) on the L5 surface was determined to be 2079 ppm by potentiometric titration.

[0098] Example 6

[0099] (1) Weigh Na2CO3, NiO, Fe2O3, MnO2, ZnO, CaO, and TiO2 according to the designed stoichiometric ratio, mix them evenly in a high-speed mixer, then transfer the mixture to a kiln, heat it at a rate of 2℃ / min, and sinter it at 1010℃ for 10h in an air atmosphere. After removing it from the kiln, crush it to obtain the O3-type layered oxide core (Na2CO3). 0.98 Ni 0.28 Fe 0.32 Mn 0.33 Zn 0.05 Ca 0.01 Ti 0.01 O2 (D50 is 6.93 μm), the residual alkali content on the surface (calculated as free Na) was 3105 ppm as determined by potentiometric titration.

[0100] (2) Based on the chemical composition and component ratio of the target composite cathode material, as well as the weight of the O3-type layered oxide core obtained in step (1) and the measured residual alkali content on its surface (calculated as free Na), weigh Na2CO3, Fe2O3 and MnO2, mix them evenly in a high-speed mixer, then transfer the mixture to a kiln, heat it at a rate of 2℃ / min, sinter it at 600℃ for 8 hours in an air atmosphere, crush it after it comes out of the kiln, and obtain the composite cathode material (denoted as L6).

[0101] L6 has an O3-type layered oxide core (Na) 0.98 Ni 0.28 Fe 0.32 Mn 0.33 Zn 0.05 Ca 0.01 Ti 0.01 O2 (D50 is 6.93 μm), and a P2-type layered oxide shell (Na) covering the surface of the core. 0.65 Fe 0.365 Mn 0.635 O2, in which the cations in the transition metal layer are randomly distributed; wherein, the weight ratio of the O3 type layered oxide core to the P2 type layered oxide shell is 1:0.1.

[0102] The D50 of L6 is 7.20 μm.

[0103] The residual alkali content (calculated as free Na) on the L6 surface was determined to be 1772 ppm by potentiometric titration.

[0104] Example 7

[0105] (1) Weigh Na2CO3, NiO, Fe2O3, MnO2, CuO, MgO, and ZrO2 according to the designed stoichiometric ratio, mix them evenly in a high-speed mixer, then transfer the mixture to a kiln, heat it at a rate of 2℃ / min, and sinter it at 1010℃ for 10h in an air atmosphere. After removing it from the kiln, crush it to obtain the O3-type layered oxide core (Na). 0.98 Ni 0.28 Fe 0.32 Mn 0.33 Cu 0.05 Mg 0.01 Zr 0.01 O2 (D50 is 6.84 μm), the residual alkali content on the surface (calculated as free Na) was 3463 ppm as determined by potentiometric titration.

[0106] (2) Based on the chemical composition and component ratio of the target composite cathode material, as well as the weight of the O3-type layered oxide core obtained in step (1) and the measured residual alkali content on its surface (calculated as free Na), weigh Na2CO3, Fe2O3 and MnO2, mix them evenly in a high-speed mixer, then transfer the mixture to a kiln, heat it at a rate of 2℃ / min, sinter it at 600℃ for 8 hours in an air atmosphere, crush it after it comes out of the kiln, and obtain the composite cathode material (denoted as L7).

[0107] L7 has an O3-type layered oxide core (Na) 0.98 Ni 0.28 Fe 0.32 Mn 0.33 Cu 0.05 Mg 0.01 Zr 0.01 O2 (D50 is 6.84 μm), and a P2-type layered oxide shell (Na) covering the surface of the core. 0.65 Fe 0.4 Mn 0.6 O2, in which the cations in the transition metal layer are randomly distributed; wherein, the weight ratio of the O3 type layered oxide core to the P2 type layered oxide shell is 1:0.1.

[0108] The D50 of L7 is 7.09 μm.

[0109] The residual alkali content (calculated as free Na) on the L7 surface was determined to be 1837 ppm by potentiometric titration.

[0110] Comparative Example 1

[0111] The method of Example 1 is followed, except that in step (2), the amount of Na2CO3, Fe2O3 and MnO2 is changed, while the other steps and conditions are the same as in Example 1, and the positive electrode material (denoted as DL1) is obtained.

[0112] DL1 has an O3-type layered oxide core (Na) 0.98 Ni 0.28 Fe 0.32 Mn 0.33 Zn 0.05 Ca 0.01 Ti 0.01 O2 (D50 is 6.93 μm), and a P2-type layered oxide shell (Na) covering the surface of the core. 0.65 Fe 0.4 Mn 0.6 O2, in which the cations in the transition metal layer are randomly distributed; wherein, the weight ratio of the O3 type layered oxide core to the P2 type layered oxide shell is 1:0.025.

[0113] The D50 of DL1 is 7.11 μm.

[0114] The residual alkali content (calculated as free Na) on the DL1 surface was determined to be 2553 ppm by potentiometric titration.

[0115] Comparative Example 2

[0116] The method of Example 1 is followed, except that in step (2), the amount of Na2CO3, Fe2O3 and MnO2 is changed, while the other steps and conditions are the same as in Example 1, and the positive electrode material (denoted as DL2) is obtained.

[0117] DL2 has an O3-type layered oxide core (Na) 0.98 Ni 0.28 Fe 0.32 Mn 0.33 Zn 0.05 Ca 0.01 Ti 0.01 O2 (D50 is 6.93 μm), and a P2-type layered oxide shell (Na) covering the surface of the core. 0.65 Fe 1 / 3 Mn 2 / 3 O2, in which the cations in the transition metal layer are distributed in an ordered manner; wherein, the weight ratio of the O3 type layered oxide core to the P2 type layered oxide shell is 1:0.1.

[0118] The D50 of DL2 is 7.34 μm.

[0119] The residual alkali content (calculated as free Na) on the DL2 surface was determined to be 2033 ppm by potentiometric titration.

[0120] Comparative Example 3

[0121] (1) Weigh Na2CO3, NiO, Fe2O3, MnO2, TiO2, La2O3, and SiO2 according to the designed stoichiometric ratio, mix them evenly in a high-speed mixer, then transfer the mixture to a kiln, heat it at a rate of 2℃ / min, and sinter it at 1010℃ for 10h in an air atmosphere. After removing it from the kiln, crush it to obtain the O3-type layered oxide core (Na2CO3). 0.98 Ni 0.28 Fe 0.32 Mn 0.33 Ti 0.05 La 0.01 Si 0.01 O2 (D50 is 6.16 μm), the residual alkali content on the surface (calculated as free Na) was 8907 ppm as determined by potentiometric titration.

[0122] (2) Based on the chemical composition and component ratio of the target composite cathode material, as well as the weight of the O3 type layered oxide core obtained in step (1) and the measured residual alkali content on its surface (calculated as free Na), weigh Na2CO3, Fe2O3 and MnO2, mix them evenly in a high-speed mixer, then transfer the mixture to a kiln, heat it at a rate of 2℃ / min, sinter it at 600℃ for 8 hours in an air atmosphere, crush it after it comes out of the kiln, and obtain the composite cathode material (denoted as DL3).

[0123] DL3 has an O3-type layered oxide core (Na) 0.98 Ni 0.28 Fe 0.32 Mn 0.33 Ti 0.05 La 0.01 Si 0.01 O2 (D50 is 6.16 μm), and a P2-type layered oxide shell (Na) covering the surface of the core. 0.65 Fe 0.4 Mn 0.6 O2, in which the cations in the transition metal layer are randomly distributed; wherein, the weight ratio of the O3 type layered oxide core to the P2 type layered oxide shell is 1:0.1.

[0124] The D50 of DL3 is 6.37 μm.

[0125] The residual alkali content (calculated as free Na) on the L3 surface was determined to be 7045 ppm by potentiometric titration.

[0126] Test case

[0127] The sodium-ion battery was fabricated and assembled using the cathode materials L1-L7 and DL1-DL3 prepared above, as follows:

[0128] The above-mentioned positive electrode materials L1-L7 and DL1-DL3, conductive carbon black, and polyvinylidene fluoride were mixed in a weight ratio of 90:5:5. After uniform mixing, N-methylpyrrolidone was added to prepare a slurry. The slurry was coated on aluminum foil, vacuum dried, and cut to obtain the positive electrode sheet. Using a sodium metal sheet as the negative electrode, glass fiber as the separator, and NaPF6 solution (1 mol / L, EC / DEC / DMC = 1:1:1) as the electrolyte, the negative electrode shell, sodium metal sheet, separator, electrolyte, positive electrode sheet, gasket, spring, and positive electrode shell were pressed and sealed in sequence to assemble a button sodium-ion battery (denoted as B1-B7 and DB1-DB3 respectively).

[0129] Performance tests were conducted on batteries B1-B7 and DB1-DB3. The first-cycle discharge specific capacity was tested at voltages of 2.0-4.0V and 2.0-4.2V, at 0.1C / 0.1C. The rate retention was tested by cycling the batteries sequentially at 0.5C / 0.2C, 0.5C / 0.5C, 0.5C / 1C, 0.5C / 2C, and 0.5C / 5C at 2.0-4.0V. The rate retention was tested after 100 cycles at voltages of 2.0-4.0V and 2.0-4.2V, at 1C / 1C. The results are shown in Table 1.

[0130] Table 1

[0131]

[0132]

[0133] As can be seen from the above embodiments and the results in Table 1, the composite cathode material provided by the present invention has low surface residual alkali, high specific capacity, excellent rate performance, and good cycle stability under normal pressure and high pressure.

[0134] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A composite cathode material, characterized in that, The composite cathode material comprises: an O3-type layered oxide core and a P2-type layered oxide shell covering the surface of the core, wherein the cations in the transition metal layer of the P2-type layered oxide shell are randomly distributed. The chemical composition of the O3-type layered oxide core satisfies the chemical formula Na x A m D n O2; wherein element A is selected from at least two of Ni, Fe, Mn, Zn, Cu, Co and Li; element D is selected from at least one of Al, Ti, Mg, Zr, Ca, Sr, Y, W, Nb, K and Sn; 0.8≤x≤1.05, 0.5<m<1, 0.01≤n≤0.15, and m+n=1; The chemical composition of the P2-type layered oxide shell satisfies the chemical formula Na. y E u G v O2; wherein element E is selected from at least one of Ni, Fe, Cu and Cr; element G is selected from at least one of Mn, Mg, Ti, Zr, Nb and Sb; 0.5≤y≤0.7, 0.1<u<0.6, 0.4≤v≤0.8, u+v=1, and u / v is not equal to 1: (1.75-2); The weight ratio of the O3-type layered oxide core to the P2-type layered oxide shell is 1:(0.05-0.2).

2. The composite cathode material according to claim 1, wherein, Chemical formula Na x A m D n In O2, element A is selected from at least two of Ni, Fe, Mn and Zn; element D is selected from at least one of Al, Ti, Ca and Sn; 0.9≤x≤1.0, 0.8<m<1, 0.01≤n≤0.05, and m+n=1; And / or, chemical formula Na y E u G v In O2, element E is selected from Ni and / or Fe; element G is selected from Mn and / or Ti; 0.6≤y≤0.7, 0.3<u<0.5, 0.5≤v≤0.7, u+v=1, and u / v is not equal to 1: (1.55-2).

3. The composite cathode material according to claim 1 or 2, wherein, The weight ratio of the O3-type layered oxide core to the P2-type layered oxide shell is 1:(0.08-0.12).

4. The composite cathode material according to any one of claims 1-3, wherein, The average particle size of the O3-type layered oxide core is 5-7 μm; And / or, the average particle size of the composite cathode material is 5.5-8 μm.

5. The composite cathode material according to any one of claims 1-4, wherein, The residual alkali content on the surface of the composite cathode material is 100-3000 ppm.

6. A method for preparing a composite cathode material, characterized in that, The method includes: (1) The first sodium source, element A source and element D source are mixed for the first time, followed by the first sintering and the first crushing to obtain the O3 type layered oxide core. (2) The O3-type layered oxide core, the second sodium source, the element E source and the element G source are mixed for the second time, and then sintered for the second time, so that the surface of the O3-type layered oxide core forms a P2-type layered oxide shell, and then crushed for the second time to obtain a composite cathode material. The amounts of the first sodium source, element A source, and element D source are such that the chemical composition of the O3-type layered oxide core satisfies the chemical formula Na. x A m D n O2; wherein element A is selected from at least two of Ni, Fe, Mn, Zn, Cu, Co and Li; element D is selected from at least one of Al, Ti, Mg, Zr, Ca, Sr, Y, W, Nb, K and Sn; 0.8≤x≤1.05, 0.5<m<1, 0.01≤n≤0.15, and m+n=1; The amounts of the second sodium source, element E source, and element G source are such that the chemical composition of the P2-type layered oxide shell satisfies the chemical formula Na. y E u G v O2; wherein element E is selected from at least one of Ni, Fe, Cu and Cr; element G is selected from at least one of Mn, Mg, Ti, Zr, Nb and Sb; 0.5≤y≤0.7, 0.1<u<0.6, 0.4≤v≤0.8, u+v=1, and u / v is not equal to 1: (1.75-2); The amount of each raw material fed is such that the weight ratio of the O3 type layered oxide core to the P2 type layered oxide shell is 1:(0.05-0.2).

7. The preparation method according to claim 6, wherein, The first sodium source and the second sodium source are each independently selected from at least one of sodium carbonate, sodium bicarbonate, sodium oxide, sodium peroxide and sodium hydroxide, preferably sodium carbonate; And / or, each of the element A source, element D source, element E source, and element G source is independently selected from one of the oxides, hydroxides, and carbonates of the corresponding element, preferably oxides of the corresponding element.

8. The preparation method according to claim 7 or 8, wherein, In step (1), the conditions for the first sintering include: a heating rate of 1-5℃ / min, a sintering temperature of 800-1050℃, a sintering time of 6-12h, and a sintering atmosphere of air and / or oxygen. And / or, in step (1), the first crushing results in an average particle size of 5-7 μm for the O3-type layered oxide core; And / or, in step (1), the surface residual alkali of the O3-type layered oxide core is 100-10000 ppm; And / or, in step (2), the conditions for the second sintering include: a heating rate of 1-5℃ / min, a sintering temperature of 600-800℃, a sintering time of 5-10h, and a sintering atmosphere of air and / or oxygen. And / or, in step (2), the second crushing results in an average particle size of 5.5-8 μm for the composite cathode material.

9. A composite cathode material prepared by the preparation method according to claim 7 or 8.

10. A sodium-ion battery comprising the positive electrode material according to any one of claims 1-5 and 9.

Images