Cathode material, preparation method and application thereof

Abstract

The application provides a positive electrode material and a preparation method and application thereof. The positive electrode material comprises a core and a coating layer coated on the surface of the core. The core comprises a layered oxide, and the coating layer comprises a sodium superionic conductor. Both the core and the coating layer have metal-doped elements. In the core, the mass content of the metal-doped elements gradually increases in the direction from the core to the coating layer. The core and the coating layer of the positive electrode material provided by the application both have metal-doped elements, and the mass content of the metal-doped elements gradually increases in the direction from the core to the coating layer. The metal-doped elements are enriched on the surface layer of the core, which improves the structural stability and conductivity of the positive electrode material, enhances the cycle performance and electrochemical performance of the positive electrode material, and is beneficial to the application of the positive electrode material.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of batteries, in particular to a positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] Currently, the layered oxide positive electrode material has excellent electrochemical performance and is a positive electrode material with application potential. However, in the charging and discharging process, the layered oxide positive electrode material will undergo ion migration, leading to irreversible transformation of the layered structure of the positive electrode material, and loss of active oxygen in the positive electrode material, which will cause decomposition of the electrolyte and deterioration of performance, and further cause the positive electrode material to be eroded by electrolyte decomposition by-products, resulting in a substantial capacity attenuation of the positive electrode material and a decrease in the electrochemical performance of the battery. In the related art, the loss of active oxygen can be improved by coating the layered oxide positive electrode material with an oxide. However, the oxide coating layer will lead to low electrochemical activity of the layered oxide positive electrode material, hinder ion migration, and be difficult to improve the electrochemical performance of the positive electrode material. Therefore, a positive electrode material with good cycle performance and excellent electrochemical performance is needed. SUMMARY

[0003] In view of this, the present application provides a positive electrode material and a preparation method and application thereof. The positive electrode material uses a sodium superionic conductor as a coating layer material to coat the inner core of the layered oxide, and both the inner core and the coating layer have metal-doped elements, while the metal-doped elements are controlled to be enriched on the surface layer of the inner core, which is beneficial to improve the structural stability and conductivity of the positive electrode material and to improve the cycle performance of the positive electrode material.

[0004] In a first aspect, the present application provides a positive electrode material, which comprises an inner core and a coating layer coated on the surface of the inner core, the inner core comprises a layered oxide, the coating layer comprises a sodium superionic conductor, and both the inner core and the coating layer have metal-doped elements; in the inner core, the mass content of the metal-doped elements gradually increases in the direction from the inner core to the coating layer.

[0005] Optionally, in the inner core, the mass content of the metal-doped elements increases from 0.1% to N in the direction from the inner core to the coating layer, and the value of N ranges from 0.5% to 15%.

[0006] Optionally, the metal-doped elements include at least one of titanium, vanadium, zirconium, chromium, and aluminum.

[0007] Optionally, the chemical formula of the layered oxide is Na x1 Ni x2 Fe x3 Mn x4 M x5O2, M is the metal-doped element, 0.6≤x1≤1.1, 0

[0008] Optionally, the chemical formula of the sodium superionic conductor is Na y1 M y2 (PO4) y3 , M is the metal-doped element, 0

[0009] Optionally, the D50 particle size of the positive electrode material is 0.5-20 μm.

[0010] Optionally, the thickness of the coating layer is 1-15 nm.

[0011] Optionally, in the positive electrode material, the mass percentage of the coating layer is 0.05%-10%, and the mass percentage of the inner core is 90%-99.5%.

[0012] The coating layer and the inner core of the positive electrode material provided in the application have a metal-doped element, and the metal-doped element is enriched on the surface layer of the inner core, thereby improving the structural stability and electrical conductivity of the positive electrode material and being conducive to the wide application of the positive electrode material.

[0013] In a second aspect, the application provides a preparation method of the positive electrode material of the first aspect, comprising:

[0014] dispersively mixing a metal-doped element source, a phosphorus source containing a phosphate radical, and a layered oxide precursor to obtain a first mixture;

[0015] mixing the first mixture with a sodium source, and obtaining the positive electrode material after sintering.

[0016] Optionally, the metal-doped element source comprises at least one of a sulfate containing a doped metal, a nitrate containing a doped metal, a chloride containing a doped metal, and an ammonium salt containing a doped metal.

[0017] Optionally, the phosphorus source containing a phosphate radical comprises at least one of phosphoric acid, ammonium dihydrogen phosphate, and dihydrogen ammonium phosphate.

[0018] Optionally, the layered oxide precursor comprises at least one of a hydroxide, an oxide, a carbonate, and an oxalate.

[0019] Optionally, the sodium source comprises at least one of sodium carbonate, sodium nitrate, and sodium hydroxide.

[0020] Optionally, the molar ratio of the metal-doped element source, the phosphorus element in the phosphorus source containing phosphate and the layered oxide precursor is (0.001-0.25):(0.001-0.45):1.

[0021] Optionally, the molar ratio of the layered oxide precursor and the sodium element in the sodium source is 1:(0.55-1.55).

[0022] Optionally, the sintering temperature is 700-1000 DEG C, and the sintering time is 10-18 hours.

[0023] The preparation method of the positive electrode material provided by the application is novel, the preparation process is simple, the positive electrode material prepared has high structural stability and good cycle performance.

[0024] In a third aspect, the application provides a positive electrode tab, which comprises a positive electrode current collector and a positive electrode active material layer arranged on the surface of the positive electrode current collector, and the positive electrode active material layer comprises the positive electrode material of the first aspect or the positive electrode material prepared by the preparation method of the second aspect.

[0025] The positive electrode tab provided by the application has good specific capacity, high safety performance, long service life and good product competitiveness.

[0026] In a fourth aspect, the application provides a battery, which comprises a negative electrode tab and the positive electrode tab of the third aspect.

[0027] The battery provided by the application has high capacity and excellent cycle performance, which is conducive to the wide application of the battery.

[0028] In a fifth aspect, the application provides an electric device, which comprises the battery of the fourth aspect.

[0029] The electric device provided by the application has long service life and excellent electrochemical performance. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. The specific embodiments described herein are only used to explain the application and not used to limit the application.

[0031] Figure 1 A cross-sectional schematic view of the positive electrode material provided by an embodiment of the application is shown in the figure;

[0032] Figure 2 A cross-sectional schematic view of the positive electrode material provided by another embodiment of the application is shown in the figure;

[0033] Figure 3A flow chart of a preparation method of a positive electrode material according to an embodiment of the present application is provided.

[0034] Figure 4 A cross-sectional schematic diagram of a positive electrode tab according to an embodiment of the present application is provided. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present application will be clearly and completely described in connection with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0036] Please refer to Figure 1 A cross-sectional schematic diagram of a positive electrode material according to an embodiment of the present application is provided. The positive electrode material 100 includes a core 10 and a coating layer 20 coated on the surface of the core 10. The core 10 includes a layered oxide, the coating layer 20 includes a sodium superionic conductor, and the core 10 and the coating layer 20 have metal-doped elements. In the core 10, the mass content of the metal-doped elements gradually increases in the direction from the core 10 to the coating layer 20. In the present application, the core includes a layered oxide, which is conducive to improving the capacity of the positive electrode material; the coating layer can isolate the core from the electrolyte to avoid the occurrence of side reactions, which is conducive to improving the capacity and safety of the positive electrode material; the coating layer includes a sodium superionic conductor (NASICON), which has high structural stability and can accelerate the rapid migration of ions and / or electrons, which is conducive to improving the stability and cycle performance of the positive electrode material; both the core and the coating layer have metal-doped elements, and in the coating layer, the metal-doped elements can improve the electrical conductivity of the positive electrode material; in the core, the mass content of the metal-doped elements gradually increases in the direction from the core to the coating layer, that is, the mass content of the metal-doped elements on the surface of the core is greater than that of the metal-doped elements inside the core, and the metal-doped elements are enriched on the surface layer of the core, which can stabilize the oxygen ions in the layered oxide of the core, reduce the loss of oxygen, improve the potential barrier of the migration of other metal components, and improve the structural stability and service life of the positive electrode material. The positive electrode material provided in the present application has good structural stability, high electrical conductivity, and excellent cycle performance, which is conducive to the wide application of the positive electrode material.

[0037] In the present application, the core includes a layered oxide, which has a special crystal structure and can provide more ion deintercalation sites, which is conducive to improving the capacity and ion transmission rate of the positive electrode material. Specifically, the layered oxide can be but is not limited to one of an O2-type layered oxide, an O3-type layered oxide, a P2-type layered oxide, or a P3-type layered oxide. In an embodiment of the present application, the layered oxide can be an O3-type layered oxide, which can further improve the capacity and cycle performance of the positive electrode material.

[0038] In an embodiment of the present application, in the core, the mass content of the metal-doped element increases from 0.1% to N, and N ranges from 0.5% to 15%. Specifically, N can be, but is not limited to, 0.5%, 1%, 2%, 5%, 8%, 10%, 12%, or 15%, etc. In some embodiments, the mass content of the metal-doped element at the center of the core is the lowest, which is 0.1%; the closer to the cladding layer, the higher the mass content of the metal-doped element, and the position where the core and the cladding layer meet is the surface of the core, at which the mass content of the metal-doped element can be 15%. In an embodiment of the present application, in the core, the mass content of the metal-doped element can increase from 0.1% to 5% along the direction from the core to the cladding layer. In another embodiment of the present application, in the core, the mass content of the metal-doped element can increase from 0.1% to 10% along the direction from the core to the cladding layer. In yet another embodiment of the present application, in the core, the mass content of the metal-doped element increases from 0.1% to 1% along the direction from the core to the cladding layer. In some embodiments, the positive electrode material is cut by a focused ion beam (FIB) to obtain a cross section of the positive electrode material, and the cross section of the positive electrode material is scanned by an elemental line scanning analysis (EDS) to obtain the mass content distribution of the metal-doped element in the positive electrode material from the core to the cladding layer.

[0039] In an embodiment of the present application, in the core, the mass content of the metal-doped element gradually increases in the direction of the core pointing to the cladding layer, that is, the mass content of the metal-doped element at the surface layer of the core is greater than that at the inside of the core, and the metal-doped element is enriched at the surface layer of the core. Specifically, at any position in the core along the direction from the core to the cladding layer, the mass content of the metal-doped element can be, but is not limited to, 0.1%, 1%, 2%, 3%, 5%, 8%, 10%, or 14%, etc. In the present application, the gradual increase can be linear or non-linear, such as gradient increase, parabolic increase, etc. Specifically, the metal-doped element includes, but is not limited to, at least one of titanium, vanadium, zirconium, chromium, and aluminum. In an embodiment of the present application, the metal-doped element is titanium. In another embodiment of the present application, the metal-doped element is aluminum and vanadium.

[0040] In an embodiment of the present application, the chemical formula of the layered oxide is Na x1 Ni x2 Fe x3 Mn x4 M x5O2, 0.6≤x1≤1.1, 0<x2<1, 0<x3<1, 0<x4<1, 0<x5≤0.2, and x2+x3+x4+x5=1. Specifically, the value of x1 can be, but is not limited to, 0.6, 0.7, 0.8, 0.9, 1, or 1.1, etc., and the value of x5 can be, but is not limited to, 0.01, 0.05, 0.1, 0.15, 0.18, or 0.2, etc., 0<x2<1, 0<x3<1, 0<x4<1, and x2+x3+x4+x5=1. In one embodiment of this application, the value of x5 is 0.005-0.03, which can further improve the structural stability and capacity of the cathode material. In another embodiment of this application, when x1 is 0.7 and x5 is 0.15, the chemical formula of the layered oxide can be, but is not limited to, Na. 0.7 Ni 0.25 Fe 0.25 Mn 0.35 M 0.15 O2, Na 0.7 Ni 0.2 Fe 0.4 Mn 0.25 M 0.15 O2, Na 0.7 Ni 0.3 Fe 0.4 Mn 0.15 M 0.15 O2, Na 0.7 Ni 0.5 Fe 0.25 Mn 0.1 M 0.15 O2, Na 0.7 Ni 0.1 Fe 0.3 Mn 0.45 M 0.15 O2, etc., for example, the chemical formula of layered oxides can be Na. 0.7 Ni 0.3 Fe 0.4 Mn 0.15 M 0.15 O2.

[0041] In this application, the core has a metal dopant element M, which can improve the stability of oxygen anions in the layered structure and reduce oxygen loss in the cathode material; at the same time, it also increases the potential barrier for the migration of other metal components in the layered oxide, prevents the loss of other metal components in the layered oxide, and improves the capacity and structural stability of the cathode material.

[0042] In the present application, the coating layer comprises a sodium super ionic conductor. The sodium super ionic conductor (NASICON) has a unique crystal structure, high ionic conductivity and excellent structural stability, which is beneficial to improve the conductivity and electrochemical stability of the positive electrode material. In an embodiment of the present application, the chemical formula of the sodium super ionic conductor is Na y1 M y2 (PO4) y3 , 0 < y1 < 4, 0 < y2 < 4, 0 < y3 < 4, specifically, the value of y1 can be but is not limited to 0.1, 0.5, 1, 1.5, 2, 3, 3.5 or 3.9, etc.; the value of y2 can be but is not limited to 0.1, 0.5, 1, 1.5, 2, 3, 3.5 or 3.9, etc.; the value of y3 can be but is not limited to 0.1, 0.5, 1, 1.5, 2, 3, 3.5 or 3.9, etc. In an embodiment of the present application, the value of y1 can be 0.1-2.3, the value of y2 can be 0.1-2.3, and the value of y3 can be 2-3.9. In another embodiment of the present application, the value of y1 can be 2-3.5, the value of y2 can be 1.5-3.8, and the value of y3 can be 2-3.9.

[0043] In an embodiment of the present application, the coating layer comprises a metal-doped element, and the metal-doped element of the coating layer and the inner core is the same, which is beneficial to improve the conductivity of the positive electrode material. Specifically, the metal-doped element comprises at least one of titanium, vanadium, zirconium, chromium and aluminum. In an embodiment of the present application, the metal-doped element can be titanium. In another embodiment of the present application, the metal-doped element can be vanadium.

[0044] In an embodiment of the present application, the D50 particle size of the positive electrode material is 0.5-20 μm, which is beneficial to improve the compaction density of the positive electrode sheet. Specifically, the D50 particle size of the positive electrode material can be but is not limited to 0.5 μm, 1 μm, 5 μm, 8 μm, 10 μm, 15 μm, 18 μm or 20 μm, etc. In an embodiment of the present application, the D50 particle size of the positive electrode material is 0.5-10 μm. In another embodiment of the present application, the D50 particle size of the positive electrode material can be 8-20 μm. In some embodiments, the shape of the positive electrode material can be spherical or spheroidal.

[0045] In an embodiment of the present application, the thickness of the coating layer is 1-15 nm. Specifically, the thickness of the coating layer can be but is not limited to 1 nm, 2 nm, 4 nm, 8 nm, 10 nm, 12 nm or 15 nm, etc. In an embodiment of the present application, the thickness of the coating layer can be 1-5 nm, which can improve the structural stability and conductivity of the positive electrode material. In another embodiment of the present application, the thickness of the coating layer can be 4-15 nm.

[0046] Please refer to Figure 2The cross-sectional schematic diagram of the positive electrode material provided by another embodiment of the present application is shown in FIG. 4. The positive electrode material 100 includes the core 10 and the coating layer 20 coated on the surface of the core 10. As can be seen, the shape of the coating layer 20 of the positive electrode material 100 is irregular. That is, the thickness of the coating layer at different positions in the same positive electrode material particle can be different, so as to increase the contact area between the positive electrode materials, improve the electron conductivity, and improve the electrical conductivity of the positive electrode material.

[0047] In an embodiment of the present application, the coating layer covers the entire surface or part of the surface of the core. The coating rate of the coating layer can be 40%-100%. Specifically, the coating rate of the coating layer can be, but is not limited to, 40%, 50%, 60%, 70%, 80%, 90%, or 100%, etc. In an embodiment of the present application, the coating rate of the coating layer can be 100%, which is beneficial to improve the structural stability and electrical conductivity of the positive electrode material.

[0048] In an embodiment of the present application, the mass percentage of the coating layer in the positive electrode material is 0.05%-10%. Specifically, the mass percentage of the coating layer in the positive electrode material can be, but is not limited to, 0.05%, 0.1%, 1%, 2%, 4%, 6%, 8%, 9%, or 10%, etc. In an embodiment of the present application, the mass percentage of the coating layer in the positive electrode material can be 0.05%-2%, which can improve the electrical conductivity and capacity of the positive electrode material. In another embodiment of the present application, the mass percentage of the coating layer in the positive electrode material can be 3%-10%.

[0049] In an embodiment of the present application, the mass percentage of the core in the positive electrode material is 90%-99.5%. Specifically, the mass percentage of the core can be, but is not limited to, 90%, 92%, 94%, 96%, 98%, 99%, or 99.5%, etc. In an embodiment of the present application, the mass percentage of the core in the positive electrode material can be 90%-96%. In another embodiment of the present application, the mass percentage of the core in the positive electrode material can be 94%-99.5%.

[0050] Please refer to Figure 3 The preparation method flowchart of the positive electrode material provided by an embodiment of the present application is shown in FIG. 5, which includes the following steps.

[0051] S101: dispersing and mixing a metal-doped element source, a phosphorus source containing a phosphate radical, and a layered oxide precursor to obtain a first mixture;

[0052] S102: mix the first mixture with a sodium source, and obtain the positive electrode material after sintering, the positive electrode material comprises an inner core and a coating layer coated on the surface of the inner core, the inner core comprises a layered oxide, the coating layer comprises a sodium super ionic conductor, and the inner core and the coating layer both have metal doping elements; in the inner core, the mass content of the metal doping elements gradually increases in the direction from the inner core to the coating layer. The preparation method provided in the application is novel, simple in process, and can form the coating layer in situ on the surface of the inner core precursor, thereby improving the bonding force between the coating layer and the inner core, and the positive electrode material prepared by the method is not easy to fall off in long-term cyclic use, has high structural stability, good cyclic performance, high conductivity and excellent capacity. The positive electrode material described in any one of the embodiments can be prepared by the preparation method.

[0053] In the application, the metal doping element source and the phosphorus source containing phosphate are coated on the surface of the layered oxide precursor by using a dissolution-recrystallization method. In the sintering process, sodium ions in the sodium source combine with metal doping elements in the metal doping element source and phosphorus elements in the phosphorus source containing phosphate to form a sodium super ionic conductor coating layer on the surface of the layered oxide precursor. After further sintering, the remaining sodium ions and metal doping elements diffuse and embed into the interior of the layered oxide precursor, and an inner core layered oxide having metal doping elements is obtained, and the mass content of the metal doping elements is lower closer to the center of the inner core. The metal doping elements in the coating layer are uniformly distributed, and the mass content of the metal doping elements on the surface of the inner core is higher than that in the interior of the inner core, which is beneficial to improving the structural stability of the positive electrode material.

[0054] In an embodiment of the application, the metal doping element source provides doping metal elements to the inner core and the coating layer of the positive electrode material, which is beneficial to improving the structural stability and conductivity of the positive electrode material. Specifically, the metal doping element source includes but is not limited to at least one of a doping metal-containing sulfate, a doping metal-containing nitrate, a doping metal-containing chloride and a doping metal-containing ammonium salt. In an embodiment of the application, when the metal doping element is titanium, the metal doping element source can be a titanium-containing sulfate. In another embodiment of the application, when the metal doping element is zirconium, the metal doping element source can be a zirconium-containing nitrate.

[0055] In an embodiment of the application, the phosphorus source containing phosphate can form the coating layer of the positive electrode material. Specifically, the phosphorus source containing phosphate includes but is not limited to at least one of phosphoric acid, ammonium dihydrogen phosphate and di-ammonium hydrogen phosphate. In an embodiment of the application, the phosphorus source containing phosphate can be phosphoric acid, and the coating layer prepared thereby has high purity, which is beneficial to improving the conductivity of the positive electrode material. In another embodiment of the application, the phosphorus source containing phosphate can be ammonium dihydrogen phosphate, and the ammonium ion is converted into ammonia gas and volatilized in the preparation process, thereby avoiding the entry of impurity elements into the coating layer and improving the electrochemical performance of the positive electrode material.

[0056] In an embodiment of the present application, the layered oxide precursor provides a core of the positive electrode material. Specifically, the layered oxide precursor can include, but is not limited to, at least one of a hydroxide, an oxide, a carbonate and an oxalate. In an embodiment of the present application, the layered oxide precursor can be a hydroxide. In another embodiment of the present application, the layered oxide precursor can be a carbonate.

[0057] In an embodiment of the present application, the molar ratio of the metal-doped element source, the phosphorus element in the phosphorus source containing phosphate and the layered oxide precursor is (0.001-0.25):(0.001-0.45):1. Specifically, the molar ratio of the metal-doped element source, the phosphorus element in the phosphorus source containing phosphate and the layered oxide precursor can include, but is not limited to, 0.001:0.001:1, 0.001:0.01:1, 0.01:0.01:1, 0.05:0.05:1, 0.1:0.1:1, 0.2:0.2:1, 0.25:0.25:1, 0.25:0.3:1, 0.25:0.35:1, 0.2:0.4:1 or 0.25:0.45:1, etc. In an embodiment of the present application, the molar ratio of the metal-doped element source, the phosphorus element in the phosphorus source containing phosphate and the layered oxide precursor can be (0.01-0.2):(0.01-0.25):1. In another embodiment of the present application, the molar ratio of the metal-doped element source, the phosphorus element in the phosphorus source containing phosphate and the layered oxide precursor can be (0.1-0.25):(0.2-0.45):1.

[0058] In an embodiment of the present application, the metal-doped element source, the phosphorus source containing phosphate and the layered oxide precursor are dispersed and mixed to obtain a first mixture, and the first mixture further includes a solvent which can promote the dispersion of the components. Specifically, the solvent can include, but is not limited to, at least one of water, ethanol and ethylene glycol. In an embodiment of the present application, the solvent can be ethanol. In another embodiment of the present application, the solvent can be water and ethanol.

[0059] In an embodiment of the present application, the mass ratio of the layered oxide precursor and the solvent is 1:(2-45), which can promote the dispersion of the layered oxide precursor. Specifically, the mass ratio of the layered oxide precursor and the solvent can include, but is not limited to, 1:2, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40 or 1:45, etc. In an embodiment of the present application, the mass ratio of the layered oxide precursor and the solvent can be 1:(2-27). In another embodiment of the present application, the mass ratio of the layered oxide precursor and the solvent can be 1:(20-45).

[0060] In an embodiment of the present application, the heating treatment is further included after the dispersion mixing of the metal doping element source, the phosphate-containing phosphorus source and the layered oxide precursor, and the heating temperature is 60-120℃, which is beneficial to promote the volatilization of the solvent in the first mixed solution. Specifically, the heating temperature can be but is not limited to 60℃, 70℃, 80℃, 90℃, 100℃, 110℃ or 120℃, etc. In an embodiment of the present application, the heating temperature can be 80-110℃, which can further accelerate the volatilization of the solvent.

[0061] In an embodiment of the present application, the heating is followed by heat preservation, and the heat preservation time is 1-12h, which is beneficial to promote the uniform dispersion of the components. Specifically, the heat preservation time can be but is not limited to 1h, 2h, 4h, 6h, 8h, 10h or 12h, etc. In an embodiment of the present application, the heat preservation time can be 1-7h. In another embodiment of the present application, the heat preservation time can be 6-12h.

[0062] In an embodiment of the present application, stirring is required during the heating treatment and heat preservation, and the stirring speed is 200-800r / min, which is beneficial to promote the dispersion of the components and accelerate the volatilization of the solvent. Specifically, the stirring speed can be but is not limited to 200r / min, 300r / min, 400r / min, 500r / min, 600r / min, 700r / min or 800r / min, etc. In an embodiment of the present application, the stirring speed can be 200-550r / min. In another embodiment of the present application, the stirring speed can be 500-800r / min.

[0063] In an embodiment of the present application, the sodium source can promote the formation of sodium superionic conductor structure of the coating layer, and improve the stability and electrochemical performance of the positive electrode material. Specifically, the sodium source can be but is not limited to at least one of sodium carbonate, sodium nitrate and sodium hydroxide. In an embodiment of the present application, the sodium source can be sodium carbonate.

[0064] In an embodiment of the present application, the number of moles of sodium element in the sodium source is 100%-155% of the required stoichiometric ratio, and the required stoichiometric ratio is calculated according to the layered oxide chemical formula Na x1 Ni x2 Fe x3 Mn x4 M x5 O2, and the number of moles of x1 obtained is calculated. Specifically, the number of moles of sodium element in the sodium source can be but is not limited to 100%, 102%, 104%, 106%, 108%, 110%, 120%, 130%, 140%, 150% or 155% of the required stoichiometric ratio, etc. For example, according to the layered oxide chemical formula Na x1 Ni x2 Fex3 Mn x4 M x5 In O2, the calculated number of moles of x1 is 1 mol, and the number of moles of sodium element in the sodium source can be 1 mol-1.55 mol. In an embodiment of the present application, the molar mass of the sodium source can be 100%-125% of the required stoichiometric ratio. In another embodiment of the present application, the molar mass of the sodium source can be 120%-155% of the required stoichiometric ratio.

[0065] In an embodiment of the present application, the molar ratio of sodium element in the layered oxide precursor and the sodium source is 1:(0.55-1.55). Specifically, the molar ratio of sodium element in the layered oxide precursor and the sodium source can be, but is not limited to, 1:0.55, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.2, 1:1.4, or 1:1.55, etc. In an embodiment of the present application, specifically, the molar ratio of sodium element in the layered oxide precursor and the sodium source can be 1:(0.55-1). In another embodiment of the present application, specifically, the molar ratio of sodium element in the layered oxide precursor and the sodium source can be 1:(0.95-1.55).

[0066] In an embodiment of the present application, the sintering temperature is 700℃-1000℃, which can promote the formation of the positive electrode material. Specifically, the sintering temperature can be, but is not limited to, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, or 1000℃. In an embodiment of the present application, the sintering temperature can be 700℃-900℃. In another embodiment of the present application, the sintering temperature can be 800℃-1000℃. In some embodiments, the sintering is carried out in an oxygen atmosphere, which can promote the formation of the coating layer, improve the structural stability of the coating layer, and be beneficial to improving the electrochemical performance of the positive electrode material.

[0067] In an embodiment of the present application, the sintering time is 10h-18h. Specifically, the sintering time can be, but is not limited to, 10h, 12h, 15h, 16h, 17h, or 18h, etc. In an embodiment of the present application, the sintering time can be 10h-15h. In another embodiment of the present application, the sintering time can be 14h-18h.

[0068] Please refer to Figure 4 , the cross-sectional schematic diagram of the positive electrode tab provided in an embodiment of the present application. The positive electrode tab 200 includes a positive electrode current collector 30 and a positive electrode active material layer 40 disposed on the surface of the positive electrode current collector 30, and the positive electrode active material layer 40 includes the positive electrode material described in any one of the embodiments. Due to the high structural stability, good electrical conductivity, excellent cycle performance, and high capacity of the positive electrode material, the positive electrode tab has high energy density and good cycle performance, which is beneficial to the wide application of the positive electrode material.

[0069] In an embodiment of the present application, the positive current collector can be, but is not limited to, at least one of copper, aluminum, nickel and stainless steel. In an embodiment of the present application, the positive current collector can be an aluminum foil.

[0070] In an embodiment of the present application, the positive active material layer further comprises a positive conductive agent. The positive conductive agent can increase the conductivity between the active materials and improve the electronic conductivity of the positive electrode sheet. Specifically, the positive conductive agent can be, but is not limited to, at least one of graphite, carbon black, acetylene black and graphene. In an embodiment of the present application, the positive conductive agent can be graphite. In another embodiment of the present application, the positive conductive agent can be carbon black.

[0071] In an embodiment of the present application, the positive active material layer further comprises a positive binder. The positive binder can improve the binding ability of the components in the positive active material layer and improve the binding ability between the positive active material layer and the positive current collector. Specifically, the positive binder can be, but is not limited to, one or more of polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, polystyrene, polybutadiene, acrylic resin, epoxy resin, polyethylene oxide, sodium carboxymethyl cellulose and butadiene-styrene latex. In an embodiment of the present application, the positive binder can be polyvinylidene fluoride.

[0072] In an embodiment of the present application, the mass ratio of the positive active material, the positive conductive agent and the positive binder is (90-98):(1-5):(1-5). Specifically, the mass ratio of the positive active material, the positive conductive agent and the positive binder can be, but is not limited to, 92:4:6, 90:5:5, 94:3:3, 96:3:1, 97:1:2 or 98:1:1, etc. In an embodiment of the present application, the mass ratio of the positive active material, the positive conductive agent and the positive binder can be (90-96):(1-5):(1-3). In another embodiment of the present application, the mass ratio of the positive active material, the positive conductive agent and the positive binder can be (94-98):(2-5):(3-5).

[0073] The present application also provides a battery comprising a negative electrode sheet and a positive electrode sheet provided by any one of the embodiments described above. The positive electrode sheet has high energy density, high cycle performance and good conductivity, which improves the battery capacity of the battery, improves the cycle performance of the battery and is conducive to the wide application of the battery.

[0074] In an embodiment of the present application, the negative electrode tab includes a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector. Specifically, the negative electrode current collector can include, but is not limited to, at least one of copper, aluminum, nickel, and stainless steel. In an embodiment of the present application, the negative electrode current collector can be a copper foil. In an embodiment of the present application, the negative electrode active material layer includes a negative electrode active material, which can include, but is not limited to, at least one of silicon, tin, germanium, lithium, alloys thereof, and carbon materials. The carbon material can include, but is not limited to, at least one of non-graphitized carbon, graphite, pyrolytic carbon, coke, and activated carbon. In an embodiment of the present application, the negative electrode active material can be a carbon material. In another embodiment of the present application, the negative electrode active material can be a silicon material.

[0075] In an embodiment of the present application, the negative electrode active material layer further includes a negative electrode conductive agent. The negative electrode conductive agent can increase the conductivity between the active materials and improve the electronic conductivity. Specifically, the negative electrode conductive agent can include, but is not limited to, at least one of graphite, carbon black, acetylene black, and graphene. In an embodiment of the present application, the negative electrode conductive agent can be graphite. In another embodiment of the present application, the negative electrode conductive agent can be carbon black.

[0076] In an embodiment of the present application, the negative electrode active material layer further includes a negative electrode binder. The negative electrode binder can improve the binding ability of the components in the negative electrode active material layer and the binding ability between the negative electrode active material layer and the negative electrode current collector. Specifically, the negative electrode binder can include, but is not limited to, one or more of polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, polystyrene, polybutadiene, acrylic resin, epoxy resin, polyethylene oxide, sodium carboxymethyl cellulose, and butadiene-styrene latex. In an embodiment of the present application, the negative electrode binder can be polyvinylidene fluoride.

[0077] In an embodiment of the present application, the battery further includes an electrolyte. At least part of the positive electrode tab and at least part of the negative electrode tab are soaked in the electrolyte. The electrolyte of the present application is not particularly limited and can include, but is not limited to, substances that can be used as electrolytes of batteries in the art.

[0078] The present application also provides a power-consuming device including the battery of any one of the embodiments described above. The power-consuming device provided by the present application has high energy density, good cycle performance, high safety performance, excellent comprehensive electrochemical performance, and strong market competitiveness. The power-consuming device includes a mobile phone, a tablet, a watch, a VR glasses, a vehicle, and the like. In an embodiment of the present application, the battery can be used in a vehicle, which can improve the safety of power consumption of the vehicle and prolong the service life of the battery of the vehicle. In another embodiment of the present application, the battery can also be applied to a mobile phone, which can increase the capacity of the battery of the mobile phone and improve the service life and safety of the battery.

[0079] The effects of the technical solutions of the present application are further described below through specific examples.

[0080] Example 1

[0081] 90 mg of a metal-doped element source (NH4VO3) and 38 mg of a phosphate-containing phosphorus source (ammonium dihydrogen phosphate) were dispersed in 200 ml of water, 5 g of a layered oxide material precursor (Ni 0.4 Mn 0.3 Fe 0.3 (OH)2) was added, heated and stirred, the heating temperature was 90°C, the stirring speed was 800 r / min, until the solvent was completely evaporated, to obtain a first mixture.

[0082] The first mixture was ground and mixed with a sodium source (sodium carbonate), the number of moles of sodium in the sodium source was 103% of the required stoichiometric ratio, and the mass of the sodium source was 3.08 g, and after mixing, sintering was performed in an oxygen atmosphere, the sintering temperature was 800°C, and the sintering time was 13 h, to obtain a positive electrode material.

[0083] Example 2

[0084] The difference from Example 1 is that the stirring speed was 300 r / min.

[0085] Example 3

[0086] The difference from Example 1 is that the number of moles of sodium in the sodium source was 100% of the required stoichiometric ratio, and the mass of the sodium source was 2.99 g.

[0087] Example 4

[0088] The difference from Example 1 is that the sintering time was 10 h.

[0089] Example 5

[0090] The difference from Example 1 is that the sintering time was 18 h.

[0091] Example 6

[0092] The difference from Example 1 is that the metal-doped element source (NH4VO3) was excessive, and the mass of the metal-doped element source was 2 g.

[0093] Example 7

[0094] The difference from Example 1 is that the phosphate-containing phosphorus source was excessive, and the mass of the phosphate-containing phosphorus source was 380 mg.

[0095] Example 8

[0096] The difference from Example 1 is that the number of moles of sodium element in the sodium source is 52% of the required stoichiometric ratio, and the mass of the sodium source is 1.555 g.

[0097] Example 9

[0098] The difference from Example 1 is that the sintering temperature is 500°C.

[0099] Example 10

[0100] The difference from Example 1 is that the sintering temperature is 1000°C.

[0101] Example 11

[0102] The difference from Example 1 is that the sintering atmosphere is argon.

[0103] Comparative Example 1

[0104] The difference from Example 1 is that 3.02 g of a sodium source is added, and no metal-doped element source (NH4VO3) and phosphorus source containing phosphate (ammonium dihydrogen phosphate) is added, and the positive electrode material does not include a coating layer and a metal-doped element.

[0105] Comparative Example 2

[0106] The difference from Example 1 is that 3.02 g of a sodium source is added, and 25 mg of a metal-doped element source (NH4VO3) is added, and the core does not include a metal-doped element.

[0107] Comparative Example 3

[0108] The difference from Example 1 is that 65 mg of a metal-doped element source (NH4VO3) is added, and no phosphorus source containing phosphate (ammonium dihydrogen phosphate) is added, and the positive electrode material does not include a coating layer.

[0109] Performance detection

[0110] The positive electrode materials prepared in Examples 1-11 and Comparative Examples 1-3 above were subjected to XRD testing, and the testing process was as follows: the positive electrode material was subjected to XRD testing, and the mass percentage of the core and the coating layer was obtained by refining the XRD results, and the results are shown in Table 1.

[0111] The positive electrode materials prepared in Examples 1-11 and Comparative Examples 1-3 above, a positive electrode binder (polyvinylidene fluoride), and a positive electrode conductive agent (conductive carbon black) were mixed in a mass ratio of 94:3:3, and then the mixed powder was added to an N-methyl pyrrolidone (NMP) solution and stirred uniformly to obtain a positive electrode slurry.

[0112] The positive electrode slurry was uniformly coated on the positive electrode current collector (aluminum foil) using a coater, and then the electrode piece was placed in a vacuum drying oven at a temperature of 120°C for vacuum drying for 12 hours, and then roll-pressed to form a positive electrode piece.

[0113] CR-2025 button-type sodium ion batteries were assembled in an argon-filled glove box, with a sodium sheet as the negative electrode, a polypropylene separator as the separator, and an electrolyte with a solute of 1 mol of sodium hexafluorophosphate (NaPF6) and a solvent of a mixed solution of ethylene carbonate (EC) and methyl ethyl carbonate (EMC) in a volume ratio of 1:1.

[0114] The button-type sodium ion batteries prepared in Examples 1-11 and Comparative Examples 1-3 above were subjected to electrochemical performance testing using a blue light Landt 2001A.

[0115] The button-type sodium ion batteries prepared in Examples 1-11 and Comparative Examples 1-3 above were subjected to first cycle coulombic efficiency testing, and the testing process was as follows: 0.1C constant current charging to 4.0V, then constant voltage charging with a cutoff current of 0.02C, followed by 0.1C constant current discharging to 2.0V, and the test results are shown in Table 2.

[0116] The button-type sodium ion batteries prepared in Examples 1-11 and Comparative Examples 1-3 above were subjected to rate performance testing, and the testing process was as follows: 0.1C constant current charging to 4.0V, then constant voltage charging with a cutoff current of 0.02C, followed by 0.1C constant current discharging to 2.0V, and the discharge specific capacity at 0.1C was recorded, and after repeating the above steps three times, 4.0V was charged using 0.5C, then constant voltage charging with a cutoff current of 0.02C, followed by 10C constant current discharging to 2.0V, and the discharge specific capacity at 10C was recorded, and the test results are shown in Table 2.

[0117] The button-type sodium ion batteries prepared in Examples 1-11 and Comparative Examples 1-3 above were subjected to cycle performance testing, and the testing process was as follows: 0.1C constant current charging to 4.0V, then constant voltage charging with a cutoff current of 0.02C, followed by 0.1C constant current discharging to 2.0V, and after repeating the above steps three times, charging and discharging cycles were performed using a current density of 1C, with a charging and discharging interval of 2.0-4.0V, and the first discharge capacity was recorded as C1, and the discharge capacity after 100 cycles was recorded as C100, and the 100 cycle capacity retention rate was calculated as (C100 / C1) x 100%, and the test results are shown in Table 2.

[0118] Table 1 Performance of positive electrode material

[0119]

[0120]

[0121] Table 2 Electrochemical performance test results

[0122]

[0123] According to the data of Examples 1-11 and Comparative Examples 1-3, it can be seen that the positive electrode material provided by the present application has good cycle performance and excellent electrochemical performance. According to Examples 1 and Comparative Examples 1-3, it can be seen that coating a sodium superionic conductor outside the core of a layered oxide and doping metal elements can improve the electrochemical performance of the positive electrode material, and improve the initial efficiency, discharge specific capacity and cycle performance of the battery. According to Examples 1 and Examples 2-11, it can be seen that suitable stirring speed, doping element content, content of the coating layer, sintering temperature, sintering atmosphere and sintering time are conducive to improving the electrochemical performance of the positive electrode material, and further improving the cycle stability and capacity of the battery.

[0124] The above describes the preferred embodiments of the present application, but should not be construed as limiting the scope of the present application. It should be noted that for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, which are also considered within the scope of protection of the present application.

Claims

1. A positive electrode material, characterized in that, The positive electrode material comprises a core and a coating layer covering the surface of the core. The core comprises a layered oxide, and the coating layer comprises a sodium superionic conductor. Both the core and the coating layer have metal dopant elements. In the core, the mass content of the metal dopant element gradually increases along the direction from the core to the coating layer. The chemical formula of the layered oxide is Na. x1 Ni x2 Fe x3 Mn x4 M x5 O2, M is the metal doping element, 0.6≤x1≤1.1, 0<x2<1, 0<x3<1, 0<x4<1, 0<x5≤0.2, and x2+x3+x4+x5=1.

2. The cathode material as described in claim 1, characterized in that, In the core, along the direction from the core to the cladding layer, the mass content of the metal dopant element increases from 0.1% to N, where N ranges from 0.5% to 15%.

3. The positive electrode material as described in claim 1, characterized in that, The metal doping element includes at least one of titanium, vanadium, zirconium, chromium, and aluminum.

4. The positive electrode material as described in claim 1, characterized in that, The chemical formula of the sodium superionic conductor is Na. y1 M y2 (PO4) y3 M is the metal dopant element, 0 < y1 < 4, 0 < y2 < 4, 0 < y3 < 4.

5. The positive electrode material as described in claim 1, characterized in that, The D50 particle size of the cathode material is 0.5μm-20μm; the thickness of the coating layer is 1nm-15nm.

6. The positive electrode material as described in claim 1, characterized in that, In the cathode material, the mass percentage of the coating layer is 0.05%-10%, and the mass percentage of the core is 90%-99.5%.

7. A method for preparing a positive electrode material as described in any one of claims 1-6, characterized in that, include: The metal doping element source, the phosphorus source containing phosphate, and the layered oxide precursor are dispersed and mixed to obtain the first mixture; The first mixture was mixed with a sodium source and sintered to obtain a cathode material.

8. The preparation method according to claim 7, characterized in that, The metal doping element source includes at least one of the following: sulfate containing doped metal, nitrate containing doped metal, chloride containing doped metal, and ammonium salt containing doped metal. The phosphorus source containing phosphate includes at least one of phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate. The layered oxide precursor includes at least one of hydroxide, oxide, carbonate and oxalate; The sodium source includes at least one of sodium carbonate, sodium nitrate, and sodium hydroxide.

9. The preparation method according to claim 7, characterized in that, The molar ratio of phosphorus in the metal doping source, the phosphorus source containing phosphate, and the layered oxide precursor is (0.001-0.25):(0.001-0.45):1; the molar ratio of sodium in the layered oxide precursor and the sodium source is 1:(0.55-1.55).

10. The preparation method according to claim 7, characterized in that, The sintering temperature is 700℃-1000℃, and the sintering time is 10h-18h.

11. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive current collector and a positive active material layer disposed on the surface of the positive current collector. The positive active material layer includes the positive electrode material according to any one of claims 1-6 or the positive electrode material prepared by the preparation method according to any one of claims 7-10.

12. A battery, characterized in that, The battery includes a negative electrode and a positive electrode as described in claim 11.

13. An electrical appliance, characterized in that, The electrical device includes the battery as described in claim 12.

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