A high-nickel cathode material for sodium-ion batteries, its preparation method and application

Abstract

The present invention provides a high-nickel cathode material for a sodium-ion battery, a preparation method thereof, and an application thereof. The high-nickel cathode material for a sodium-ion battery includes a core and a shell. The core includes Na u A v Li w Ni 1‑x‑y Fe x Mn y D t O 2+α , 0.9 ≤ u ≤ 1.0, 1.02 ≤ u + nv ≤ 1.05, where n is the valence of element A, 0.1x ≤ w ≤ 0.2x, 0.1 ≤ x ≤ 0.2, 0.1 ≤ y ≤ 0.4, 0.01 ≤ t ≤ 0.05, 0.02 ≤ α ≤ 0.2, the ionic valence of A is ≤ +2, the ionic radius is ≥ 0.065 nm, the ionic valence of D is ≥ +3, and the D-O bond energy > 400 kJ / mol; the shell includes an inorganic substance with a coefficient of thermal expansion of 4 × 10 ‑6 ~10 × 10 ‑6 / °C. Through the regulation of lattice anchoring, slip passivation, migration inhibition, and interfacial entropy control, the present invention realizes the collaborative optimization of high capacity and long cycle life.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and relates to a high-nickel cathode material for sodium-ion batteries, a preparation method thereof, and an application thereof. Background Art

[0002] Due to the high abundance of sodium resources and significant cost advantages, sodium-ion batteries have become a supplementary technical route for lithium-ion batteries and show great application prospects in the field of large-scale energy storage. However, its industrialization process faces technical bottlenecks in the cathode material system, that is, the current mainstream layered oxide cathodes have core defects of low reversible capacity (generally lower than 150 mAh / g) and insufficient cycle stability, and it is difficult to balance the requirements of high energy density and long cycle life.

[0003] Moreover, the O3-type sodium-ion layered oxide material is prone to multiple irreversible phase transitions of O3→P3→OP2 during high-voltage charge and discharge. Among them, the P3→OP2 phase transition will cause a significant deterioration of reversibility due to the sudden change of the kinetic energy barrier, which will further lead to lattice shear distortion and ion migration path mismatch. Under the condition of a high cut-off voltage of 4.25 V, the lattice oxygen participates in charge compensation to form a metastable OP2 phase, which has a high sodium vacancy concentration and a severe deviation of the interlayer slip angle from the initial value, resulting in an increase in the reconstruction resistance of the layered framework and the capacity decay rate. In addition, the relatively large ionic radius of sodium ions (1.02 Å) is prone to cause lattice stress accumulation during repeated deintercalation and intercalation processes, leading to the progressive destruction of the layered structure framework and the splitting of the bulk electron transport network. Although the increase in the nickel content in the transition metal layer and the charge and discharge voltage can activate multiple redox couples (Ni 2+ / Ni 4+ 、O 2- / O - )to increase the specific capacity to exceed 175 mAh / g, the high nickel content will also increase the driving force of the P3→OP2 phase transition.

[0004] Based on the above research, it is necessary to provide a high-nickel cathode material for sodium-ion batteries. The high-nickel cathode material for sodium-ion batteries breaks through the capacity-life trade-off bottleneck of traditional high-nickel sodium-ion materials through multi-dimensional collaborative optimization of the bulk and surface. Summary of the Invention

[0005] The purpose of the present invention is to provide a high-nickel cathode material for sodium-ion batteries, a preparation method thereof, and an application thereof. The high-nickel cathode material for sodium-ion batteries realizes the collaborative optimization of the high-capacity characteristics and long cycle life of the high-nickel cathode material through multi-level collaborative regulation strategies such as lattice anchoring to prevent structure collapse, interlayer slip passivation, ion migration barrier optimization, and interfacial entropy engineering to stabilize the electrode / electrolyte interface.

[0006] To achieve the purpose of the present invention, the following technical solutions are adopted:

[0007] In a first aspect, the present invention provides a high-nickel cathode material for a sodium-ion battery, and the high-nickel cathode material for a sodium-ion battery includes a core and a shell on the surface of the core;

[0008] The chemical general formula of the core is Na u A v Li w Ni 1-x-y Fe x Mn y D t O 2+α , where 0.9 ≤ u ≤ 1.0, 1.02 ≤ u + nv ≤ 1.05, n is the valence of element A, 0.1x ≤ w ≤ 0.2x, 0.1 ≤ x ≤ 0.2, 0.1 ≤ y ≤ 0.4, 0.01 ≤ t ≤ 0.05, 0.02 ≤ α ≤ 0.2, the valence of the metal ion corresponding to element A ≤ +2, and the corresponding metal ion radius ≥ 0.065 nm, the valence of the metal ion corresponding to element D ≥ +3, and the D-O bond energy > 400 kJ / mol;

[0009] The shell includes an inorganic substance with a coefficient of thermal expansion of 4 × 10 -6 / °C to 10 × 10 -6 / °C.

[0010] Since the high-nickel cathode material for a sodium-ion battery can significantly increase the density of redox active sites by increasing the proportion of transition metal nickel and activate lattice oxygen to participate in charge compensation in the high-voltage range, thereby releasing a higher specific capacity. However, under high-voltage conditions, the material undergoes a multi-stage phase transition process, and the formation of the OP2 phase is accompanied by a significant contraction of the sodium layer spacing in the c-axis direction, resulting in irreversible structural defects when restoring the O3 phase. At the same time, the dynamic expansion and contraction of the a-b plane lattice induces interlayer displacement, and the migration of Fe 3+ and the Jahn-Teller distortion act synergistically, which will cause local stress accumulation and ultimately lead to progressive structural collapse.

[0011] The present invention solves the problems faced by the above high-nickel cathode material through a four-dimensional cooperative regulation strategy, specifically including: (1) Lattice anchoring: introducing a low-valence cation (element A with a metal ion radius ≥ 0.065 nm) into the sodium layer to construct a sodium layer site support network, reducing the volatility of the Na layer spacing, and supporting a stable sodium layer spacing; (2) Slip passivation: by doping an element D with a metal ion valence ≥ +3 and a D-O bond energy > 400 kJ / mol, constructing a metal-oxygen bond buffer zone with a high-valence strong bond energy in the transition metal layer to increase the slip resistance of the crystal plane; (3) Ion locking: incorporating with the dual-site migration characteristics of the sodium / transition metal layer to increase the migration barrier and limit Fe 3+Migration; (4) Interfacial entropy control: Coating a shell with thermodynamic properties matching those of the matrix, that is, coating with an inorganic substance having a coefficient of thermal expansion slightly lower than that of the matrix, to relieve the structural volume strain and buffer the stress caused by the volume change. Therefore, through multi-dimensional collaborative optimization, the present invention realizes the synergistic improvement of high specific capacity and excellent cycle stability in high-pressure cycling, breaking through the capacity-life trade-off bottleneck of traditional high-nickel sodium battery materials.

[0012] The chemical general formula of the core is Na u A v Li w Ni 1-x-y Fe x Mn y D t O 2+α , where 0.9 ≤ u ≤ 1.0, for example, it can be 0.9, 0.92, 0.94, 0.96, 0.98 or 1.0, 1.02 ≤ u + nv ≤ 1.05, for example, it can be 1.02, 1.025, 1.03, 1.035, 1.04, 1.045 or 1.05, n is the valence of element A, 0.1x ≤ w ≤ 0.2x, for example, it can be 0.1x, 0.12x, 0.14x, 0.16x, 0.18x or 0.2x, 0.1 ≤ x ≤ 0.2, for example, it can be 0.1, 0.12, 0.14, 0.16, 0.18 or 0.2, 0.1 ≤ y ≤ 0.4, for example, it can be 0.1, 0.2, 0.3 or 0.4, 0.01 ≤ t ≤ 0.05, for example, it can be 0.01, 0.02, 0.03, 0.04 or 0.05, 0.02 ≤ α ≤ 0.2, for example, it can be 0.02, 0.05, 0.1, 0.15 or 0.2, the valence state of the metal ion corresponding to element A ≤ +2, for example, it can be +2 or +1, and the corresponding metal ion radius ≥ 0.065 nm, for example, it can be 0.065 nm, 0.07 nm, 0.075 nm, 0.08 nm, 0.085 nm or 0.09 nm, the valence state of the metal ion corresponding to element D ≥ +3, for example, it can be +3, +4, +5 or +6, and the D-O bond energy > 400 kJ / mol, for example, it can be 450 kJ / mol, 500 kJ / mol, 550 kJ / mol, 600 kJ / mol or 650 kJ / mol, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0013] In the chemical general formula of the core of the present invention, according to the four-dimensional collaborative regulation strategy, the contents of different elements are matched with each other, such as The function is to increase the migration barrier to limit Fe 3+Migration, so 0.1x ≤ w ≤ 0.2x; for another example, element A is doped in the sodium layer to support a stable sodium layer spacing, so 1.02 ≤ u + nv ≤ 1.05.

[0014] The outer shell includes an inorganic substance with a coefficient of thermal expansion of 4×10 -6 / °C to 10×10 -6 / °C, for example, it can be 4×10 -6 / °C, 5×10 -6 / °C, 6×10 -6 / °C, 7×10 -6 / °C, 8×10 -6 / °C, 9×10 -6 / °C or 10×10 -6 / °C, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0015] Preferably, the thickness of the outer shell is T (unit: nm), and T is calculated by the following formula: w coating ={[π(r + T) 2 (h + 2T) - πr 2 h]ρ shell} / {πr 2 hρ core + [π(r + T) 2 (h + 2T) - πr 2 h]ρ shell} × 100%;

[0016] where, w coating is the mass percentage content of the outer shell (unit: %), r is the radius of the inner core (unit: μm), h is the height of the inner core (unit: μm), ρ shell is the density of the outer shell (unit: g / cm 3 ), ρ core is the density of the inner core (unit: g / cm 3 ).

[0017] The values on both sides of the equation of the present invention satisfy the formula for calculating T.

[0018] The morphology of the inner core of the present invention is quasi-cylindrical, r is the bottom radius of the quasi-cylindrical inner core, and h is the height of the quasi-cylindrical inner core.

[0019] The thickness of the outer shell of the present invention can be calculated by the above formula to effectively solve the problem of characterizing the influence of the coating amount on the material properties. Moreover, this formula creatively calculates the coating thickness of the "cylindrical-like" morphology material, which is completely different from the calculation method of the traditional "spherical" material. This formula is only applicable to the core material type of the present invention because the core of this material can be approximately regarded as a set of cylindrical-like rather than a set of spheres, and this formula is also designed based on the cylindrical core.

[0020] Preferably, the mass percentage content w of the outer shell coating is 0.5% - 2%, for example, it can be 0.5%, 0.7%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8% or 2%, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0021] The mass percentage content of the outer shell of the present invention in the high-nickel cathode material of the sodium-ion battery is preferably within the above range. On the one hand, adding too little is avoided to prevent the effective function of the outer shell from being affected, and at the same time, adding too much is avoided to prevent the influence on ion transport and the sharp increase in interfacial impedance. On the other hand, when w of the present invention coating is within the above range, a continuous and dense interfacial layer can be formed, significantly reducing the electrolyte corrosion and the excessive growth of the CEI film (cathode electrolyte interface film), effectively alleviating the volume strain during the phase change process, and also reducing the error between the calculated thickness T of the outer shell and the actually measured thickness, improving the accuracy of the calculated thickness T of the outer shell.

[0022] Preferably, the radius r of the core is 2 μm - 14 μm, for example, it can be 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm or 14 μm, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0023] Preferably, the height h of the core is 0.1 μm - 2 μm, for example, it can be 0.1 μm, 0.5 μm, 1 μm, 1.5 μm or 2 μm, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0024] Preferably, the density ρ of the outer shell shell is 0.5 g / cm 3 ~1.8 g / cm 3 , for example, it can be 0.5 g / cm 3 , 1 g / cm 3 , 1.5 g / cm 3 or 1.8 g / cm 3 , but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0025] Preferably, the density ρ of the corecore is 1.8 g / cm 3 ~2.2 g / cm 3 , for example, it can be 1.8 g / cm 3 , 2.0 g / cm 3 or 2.2 g / cm 3 , but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0026] Preferably, in the chemical general formula of the core, A includes K + , Ca 2+ , Sr 2+ , Ba 2+ , Cd 2+ , Zn 2+ , Cu 2+ or Mg 2+ or a combination of any one or at least two of them.

[0027] Preferably, in the chemical general formula of the core, D includes Al 3+ , Zr 4+ , Y 3+ , Ti 4+ , Sb 5+ , Cr 6+ , Co 3+ , Ga 3+ , Sc 3 + , Nb 5+ , Ta 5+ , W 6+ , V 5+ , Sn 4+ , Hf 4+ or Mo 6+ or a combination of any one or at least two of them, preferably Sb 5+ , Cr 6+ , Nb 5 + , Ta 5+ , W 6+ , V 5+ or Mo 6+ or a combination of any one or at least two of them.

[0028] Preferably, the valence state of the metal ion corresponding to element D in the present invention is ≥ +5, which can further enhance the lattice rigidity to resist slip deformation.

[0029] Preferably, the outer shell includes any one or a combination of at least two of ZrSiO4, Al2SiO5, MgSiO3, ZrP2O7, Al2TiO5 or MgAl2O4, preferably any one or a combination of at least two of ZrSiO4, Al2TiO5 or MgSiO3.

[0030] The outer shell described in the present invention comprises inorganic salts and / or composite oxides, and preferably the above compounds, which can not only further enhance the function of the coating layer, but also be more suitable for the calculation formula of the thickness T of the outer shell, and the accuracy of the calculated T is higher.

[0031] In a second aspect, the present invention provides a method for preparing a high-nickel cathode material for a sodium-ion battery as described in the first aspect, and the preparation method comprises the following steps:

[0032] (1) According to the formula amount, mix a sodium source, a nickel-iron-manganese precursor, a source A, a source D and a lithium source, and perform a first sintering to obtain a first-sintered material;

[0033] (2) Mix the first-sintered material described in step (1) with an outer shell coating source and perform a second sintering to obtain the high-nickel cathode material for the sodium-ion battery.

[0034] Preferably, the temperature of the first sintering in step (1) is 900 °C to 1250 °C, for example, it can be 900 °C, 950 °C, 1000 °C, 1050 °C, 1100 °C, 1150 °C or 1200 °C, the heat preservation time is 10 h to 20 h, for example, it can be 10 h, 12 h, 14 h, 16 h, 18 h or 20 h, and the heating rate is 3 °C / min to 6 °C / min, for example, it can be 3 °C / min, 4 °C / min, 5 °C / min or 6 °C / min, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0035] Preferably, the atmosphere of the first sintering in step (1) comprises an oxygen-containing atmosphere, such as an air atmosphere or an oxygen atmosphere.

[0036] Preferably, the nickel-iron-manganese precursor in step (1) comprises Ni 1-x-y Fe x Mn y (OH)2, where 0.1 ≤ x ≤ 0.2, for example, it can be 0.1, 0.12, 0.14, 0.16, 0.18 or 0.2, 0.1 ≤ y ≤ 0.4, for example, it can be 0.1, 0.2, 0.3 or 0.4, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0037] Preferably, the sodium source in step (1) comprises any one or a combination of at least two of sodium carbonate, sodium bicarbonate or sodium hydroxide.

[0038] Preferably, the lithium source in step (1) comprises any one or a combination of at least two of lithium carbonate, lithium bicarbonate or lithium hydroxide.

[0039] Preferably, after the first sintering in step (1), a crushing and sieving treatment is also carried out to obtain the first-sintered material.

[0040] Preferably, the temperature of the second sintering in step (2) is 600 °C to 850 °C, for example, it can be 600 °C, 700 °C, 800 °C or 850 °C, and the heat preservation time is 5 h to 10 h, for example, it can be 5 h, 7 h, 9 h or 10 h, but it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0041] Preferably, the atmosphere of the second sintering in step (2) includes an oxygen-containing atmosphere.

[0042] Preferably, after the second sintering in step (2), a cooling, crushing and sieving treatment is also carried out.

[0043] Preferably, after the second sintering in step (2), the temperature is decreased at a rate of 1 °C / min to 6 °C / min, for example, it can be 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min or 6 °C / min, but it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0044] In the third aspect, the present invention provides a sodium-ion battery, and the sodium-ion battery includes the high-nickel cathode material for sodium-ion battery as described in the first aspect.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] The present invention solves the problems faced by the above high-nickel cathode material through a four-dimensional collaborative regulation strategy, specifically including (1) lattice anchoring: introducing a low-valence cation (element A with a metal ion radius ≥ 0.065 nm) into the sodium layer to construct a sodium layer site support network, reducing the volatility of the Na layer spacing, and supporting a stable sodium layer spacing; (2) slip passivation: doping an element D with a metal ion valence ≥ +3 and a D-O bond energy > 400 kJ / mol to construct a metal-oxygen bond buffer zone with a high valence and strong bond energy in the transition metal layer, so as to increase the slip resistance of the crystal plane; (3) ion locking: incorporating , by increasing the migration barrier to limit the migration of Fe 3+ migration; (4) interface entropy control: coating a shell that matches the thermodynamic properties of the matrix, that is, coating an inorganic substance with a coefficient of thermal expansion slightly lower than that of the matrix, so as to relieve the excessive structural volume strain and buffer the stress caused by the volume change. Therefore, through multi-dimensional collaborative optimization, the present invention enables the material to achieve a synergistic improvement of high specific capacity and excellent cycle stability in high-voltage cycling, breaking through the capacity-life trade-off bottleneck of traditional high-nickel sodium battery materials. Description of the Drawings

[0047] Figure 1 Morphology diagram of the high-nickel cathode material for sodium-ion batteries described in Embodiment 1 of the present invention.

[0048] Figure 2 Charge-discharge curve graph of the battery prepared from the high-nickel cathode material for sodium-ion batteries described in Embodiment 1 of the present invention.

[0049] Figure 3 Cycle retention rate graph of the battery prepared from the high-nickel cathode material for sodium-ion batteries described in Embodiment 1 of the present invention. Detailed implementation manners

[0050] The technical solutions of the present invention will be further described below through specific implementation manners. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0051] Embodiment 1

[0052] This embodiment provides a high-nickel cathode material for sodium-ion batteries. The high-nickel cathode material for sodium-ion batteries includes a core and a shell on the surface of the core; the chemical formula of the core is Na 0.95 Ca 0.04 Li 0.02 Ni 0.6 Fe 0.15 Mn 0.25 Sb 0.0 3O 2.1 , (wherein, the ionic radius of Ca 2+ is 0.099 nm, and the bond energy of Sb-O is 480 kJ / mol);

[0053] The shell includes ZrSiO4 (the coefficient of thermal expansion is 4.5×10 -6 / °C); the thickness of the shell is T, and the T is 16 nm, which is calculated by the following formula:

[0054] w coating ={[π(r + T) 2 (h + 2T) - πr 2 h]ρ shell} / {πr 2 hρ core +[π(r + T) 2 (h + 2T) - πr 2 h]ρ shell}×100%; wherein, w coating is the mass percentage content of the shell (specifically 1.2%), r is the radius of the core (specifically 8.5 μm), h is the height of the core (specifically 1.08 μm), ρ shell is the density of the shell (specifically 0.72 g / cm 3), ρ core is the density of the core (specifically 1.98 g / cm 3 );

[0055] The preparation method of the high-nickel cathode material for sodium-ion batteries in this embodiment includes the following steps:

[0056] (1) According to the formula amount, mix sodium carbonate, nickel-iron-manganese precursor, calcium oxide, antimony oxide and lithium carbonate, and then in an oxygen atmosphere, heat up to 1050 °C at a heating rate of 5 °C / min for the first sintering for 15 h. After pulverization and sieving, a first-sintered material is obtained;

[0057] (2) Mix the first-sintered material obtained in step (1) with ZrSiO4, and then in an oxygen atmosphere, perform the second sintering at a temperature of 750 °C for 8 h, and finally cool down to room temperature at a rate of 3 °C / min. After pulverization and sieving, the high-nickel cathode material for sodium-ion batteries is obtained. The morphology diagram of the high-nickel cathode material for sodium-ion batteries is as Figure 1 shown.

[0058] Example 2

[0059] This embodiment provides a high-nickel cathode material for sodium-ion batteries. The high-nickel cathode material for sodium-ion batteries includes a core and a shell on the surface of the core; the chemical formula of the core is Na 0.9 Sr 0.06 Li 0.04 Ni 0.65 Fe 0.2 Mn 0.15 Cr 0.0 1O 2.06 , (where the ionic radius of Sr 2+ is 0.112 nm and the Cr-O bond energy is 580 kJ / mol);

[0060] The shell includes Al2TiO5 (the thermal expansion coefficient is 9.5×10 -6 / °C); the thickness of the shell is T, and the T is 5.2 nm, which is calculated by the following formula:

[0061] w coating ={[π(r + T) 2 (h + 2T) - πr 2 h]ρ shell} / {πr 2 hρ core + [π(r + T) 2 (h + 2T) - πr 2 h]ρ shell}×100%; where w coatingis the mass percentage of the outer shell (specifically 0.5%), r is the radius of the inner core (specifically 11.2 μm), h is the height of the inner core (specifically 1.56 μm), ρ shell is the density of the outer shell (specifically 1.4 g / cm 3 ), ρ core is the density of the inner core (specifically 2.1 g / cm 3 );

[0062] The preparation method of the high-nickel cathode material for sodium-ion batteries in this embodiment includes the following steps:

[0063] (1) According to the formula amount, mix sodium carbonate, nickel-iron-manganese precursor, strontium oxide, chromium oxide and lithium carbonate, and then in an oxygen atmosphere, heat up to 1250 °C at a heating rate of 6 °C / min for the first sintering for 10 h. After pulverization and sieving, a first-fired material is obtained;

[0064] (2) Mix the first-fired material described in step (1) with Al2TiO5, and then in an oxygen atmosphere, perform the second sintering at a temperature of 600 °C for 10 h, and finally cool down to room temperature at a rate of 1 °C / min. After pulverization and sieving, the high-nickel cathode material for sodium-ion batteries is obtained.

[0065] Example 3

[0066] This embodiment provides a high-nickel cathode material for sodium-ion batteries. The high-nickel cathode material for sodium-ion batteries includes an inner core and an outer shell on the surface of the inner core; the chemical formula of the inner core is NaCa 0.025 Li 0.01 Ni 0.7 Fe 0.1 Mn 0.2 Sb 0.0 5O 2.155 , (where the ionic radius of Ca 2+ is 0.099 nm and the bond energy of Sb-O is 480 kJ / mol);

[0067] The outer shell includes ZrSiO4 (the thermal expansion coefficient is 4.5×10 -6 / °C); the thickness of the outer shell is T, and the T is 20 nm, which is calculated by the following formula:

[0068] w coating ={[π(r + T) 2 (h + 2T) - πr 2 h]ρ shell} / {πr 2 hρ core + [π(r + T) 2 (h + 2T) - πr 2 h]ρshell}(× 100%); where w coating is the mass percentage content of the said outer shell (specifically 2%), r is the radius of the said inner core (specifically 7.2 μm), h is the height of the said inner core (specifically 0.82 μm), ρ shell is the density of the said outer shell (specifically 0.72 g / cm 3 ), ρ core is the density of the said inner core (specifically 1.92 g / cm 3 );

[0069] The preparation method of the high-nickel cathode material for sodium-ion batteries in this embodiment includes the following steps:

[0070] (1) According to the formula amount, mix sodium carbonate, nickel-iron-manganese precursor, calcium oxide, antimony oxide and lithium carbonate, and then in an oxygen atmosphere, heat up to 900 °C at a heating rate of 3 °C / min for the first sintering for 20 h. After pulverizing and sieving, a first-sintered material is obtained;

[0071] (2) Mix the first-sintered material described in step (1) with ZrSiO4, and then in an oxygen atmosphere, perform the second sintering at a temperature of 850 °C for 10 h, and finally cool down to room temperature at a rate of 6 °C / min. After pulverizing and sieving, the high-nickel cathode material for sodium-ion batteries is obtained.

[0072] Example 4

[0073] This embodiment provides a high-nickel cathode material for sodium-ion batteries. Except that w coating is 0.1%, causing the thickness T of the outer shell to change adaptively, the rest are the same as those in Example 1.

[0074] Example 5

[0075] This embodiment provides a high-nickel cathode material for sodium-ion batteries. Except that w coating is 2.5%, causing the thickness T of the outer shell to change adaptively, the rest are the same as those in Example 1.

[0076] Example 6

[0077] This embodiment provides a high-nickel cathode material for sodium-ion batteries. Except that in the chemical formula of the said inner core, Al is used to replace Sb in an equimolar amount, causing the chemical formula of the inner core to change adaptively, the rest are the same as those in Example 1.

[0078] Example 7

[0079] This embodiment provides a high-nickel cathode material for a sodium-ion battery. Except that in the chemical formula of the inner core, Zr is used to replace Sb in an equimolar amount, causing an adaptive change in the chemical formula of the inner core, the rest is the same as in Embodiment 1.

[0080] Comparative Example 1

[0081] This comparative example provides a high-nickel cathode material for a sodium-ion battery. Except that it does not include the outer shell, the rest is the same as in Embodiment 1;

[0082] The preparation method of the high-nickel cathode material for the sodium-ion battery is the same as that in Embodiment 1 except that ZrSiO4 is not added during the mixing in step (2).

[0083] Comparative Example 2

[0084] This comparative example provides a high-nickel cathode material for a sodium-ion battery. Except that the chemical formula of the inner core is Na 0.95 Ca 0.04 Ni 0.6 Fe 0.15 Mn 0.25 Sb 0.03 O 2.09 otherwise, the rest is the same as in Embodiment 1;

[0085] The preparation method of the high-nickel cathode material for the sodium-ion battery is the same as that in Embodiment 1 except that it is adaptively changed according to the formula amount.

[0086] Comparative Example 3

[0087] This comparative example provides a high-nickel cathode material for a sodium-ion battery. Except that the chemical formula of the inner core is Na 0.95 Ca 0.04 Li 0.06 Ni 0.6 Fe 0.15 Mn 0.25 Sb 0.03 O 2.12 otherwise, the rest is the same as in Embodiment 1;

[0088] The preparation method of the high-nickel cathode material for the sodium-ion battery is the same as that in Embodiment 1 except that it is adaptively changed according to the formula amount.

[0089] Comparative Example 4

[0090] This comparative example provides a high-nickel cathode material for a sodium-ion battery. Except that the chemical formula of the inner core is Na 0.95 Li 0.02 Ni0.6 Fe 0.15 Mn 0.25 Sb 0.03 O 2.06 Except for the above, the rest are the same as in Example 1;

[0091] The preparation method of the high-nickel cathode material for sodium-ion batteries is the same as that in Example 1 except for the adaptive change according to the formula amount.

[0092] Comparative Example 5

[0093] This comparative example provides a high-nickel cathode material for sodium-ion batteries. Except that the chemical formula of the inner core is Na 0.95 Ca 0.1 Li 0.02 Ni 0.6 Fe 0.15 Mn 0.25 Sb 0.03 O 2.16 Except for the above, the rest are the same as in Example 1;

[0094] The preparation method of the high-nickel cathode material for sodium-ion batteries is the same as that in Example 1 except for the adaptive change according to the formula amount.

[0095] Comparative Example 6

[0096] This comparative example provides a high-nickel cathode material for sodium-ion batteries. Except that the chemical formula of the inner core is Na 0.95 Ca 0.04 Li 0.02 Ni 0.6 Fe 0.15 Mn 0.25 O 2.025 Except for the above, the rest are the same as in Example 1;

[0097] The preparation method of the high-nickel cathode material for sodium-ion batteries is the same as that in Example 1 except for the adaptive change according to the formula amount.

[0098] Comparative Example 7

[0099] This comparative example provides a high-nickel cathode material for sodium-ion batteries. Except that the chemical formula of the inner core is Na 0.95 Ca 0.04 Li 0.02 Ni 0.6 Fe 0.15 Mn 0.25 Sb 0.1 O 2.275 Except for the above, the rest are the same as in Example 1;

[0100] The preparation method of the high-nickel cathode material for the sodium-ion battery is the same as that of Example 1 except for the adaptive change according to the formula amount.

[0101] The shell thickness T calculated from the above examples and comparative examples and the measured shell thickness T are shown in Table 1. Among them, the method for measuring the shell thickness T includes observation and measurement by transmission electron microscopy; the high-nickel cathode material for the sodium-ion battery obtained from the above examples and comparative examples and the negative sodium sheet are prepared into a battery, and then the electrochemical performance of the battery is tested. The test conditions are 0.1C discharge in the first week under 2~4.25V, and then 1C discharge and cycle for 50 weeks. The test results are shown in Table 1. Among them, the charge-discharge curve of the battery prepared from the high-nickel cathode material for the sodium-ion battery described in Example 1 is as Figure 2 shown, and the cycle retention rate diagram is as Figure 3 shown. It can be seen from Figure 2 and Figure 3 that the battery prepared from the high-nickel cathode material for the sodium-ion battery described in Example 1 has excellent electrochemical performance.

[0102] Table 1

[0103]

[0104] It can be seen from Table 1 that:

[0105] From Examples 1-3 and Comparative Example 1, it can be seen that the present invention uses an inorganic substance with a specific coefficient of thermal expansion as the shell for coating, which can buffer the stress caused by volume change, thereby improving the cycle performance of the battery; from Examples 1-3 and Comparative Examples 2-3, it can be seen that the high-nickel cathode material for the sodium-ion battery described in the present invention is also doped with lithium ions to increase the migration barrier to limit Fe 3+Migration is carried out to improve the capacity and cycling performance of the battery. However, the doping amount of doped lithium ions should not be excessive. If there is too much lithium ion doping, Li2O remaining on the material surface reacts with the electrolyte to form LiF and NaF deposition layers, increasing the interfacial impedance. It can be seen from Examples 1-3 and Comparative Examples 4-5 that the present invention preferably further dopes a low-valence A element at the sodium site for lattice anchoring to improve battery performance. However, when there is too much doped low-valence A element, it preferentially occupies the sodium layer vacancies, and the reversible deintercalation capacity loss rate of sodium ions increases. It can be seen from Examples 1-3 and Comparative Examples 6-7 that the present invention preferably dopes a high-valence D element at the transition metal site for slip passivation to improve the stability of the material and thus improve the battery performance. However, when there is too much doped high-valence D element, the excessive D element occupies the transition metal sites, resulting in lattice contraction and causing excessive local stress concentration. This distortion will hinder the interlayer diffusion of sodium ions. It can be seen from Example 1 and Examples 4-5 that the present invention preferably has the outer shell within a specific content range to further enhance the matching effect between the outer shell and the inner core and improve battery performance. It can be seen from Example 1 and Examples 6-7 that the valence of the doped D element in the present invention is preferably ≥ +5, so as to further promote the D element to play the slip passivation effect and further improve the capacity and cycling performance of the battery.

[0106] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A high-nickel cathode material for sodium-ion batteries, characterized in that The high-nickel cathode material for the sodium-ion battery comprises a core and a shell on the surface of the core; The chemical general formula of the core is Na u A v Li w Ni 1-x-y Fe x Mn y D t O 2+α , where 0.9 ≤ u ≤ 1.0, 1.02 ≤ u + nv ≤ 1.05, n is the valence of element A, 0.1x ≤ w ≤ 0.2x, 0.1 ≤ x ≤ 0.2, 0.1 ≤ y ≤ 0.4, 0.01 ≤ t ≤ 0.05, 0.02 ≤ α ≤ 0.2, the valence state of the metal ion corresponding to element A ≤ +2, and the corresponding metal ion radius ≥ 0.065 nm, the valence state of the metal ion corresponding to element D ≥ +3, and the D-O bond energy > 400 kJ / mol; The housing includes an inorganic substance with a coefficient of thermal expansion of 4×10 -6 / °C to 10×10 -6 / °C.

2. The high-nickel cathode material for sodium-ion batteries according to claim 1, wherein The thickness of the shell is T, and T is calculated by the following formula: w coating ={[π(r + T) 2 (h + 2T)-πr 2 h]ρ shell} / {πr 2 hρ core +[π(r + T) 2 (h + 2T)-πr 2 h]ρ shell}×100%; wherein, w coating is the mass percentage of the outer shell, r is the radius of the inner core, h is the height of the inner core, ρ shell is the density of the outer shell, ρ core is the density of the inner core.

3. The high-nickel cathode material for sodium-ion battery according to claim 2, wherein The mass percentage of the said outer shell w coating is 0.5% - 2%.

4. The high-nickel cathode material for sodium-ion battery according to claim 2 or 3, characterized in that The radius r of the core is 2 μm to 14 μm; and / or, the height h of the core is 0.1 μm to 2 μm; and / or, the density ρ of the housing shell is 0.5 g / cm 3 ~1.8 g / cm 3 ; and / or, the density ρ of the core core is 1.8 g / cm 3 ~2.2 g / cm 3 .

5. The high-nickel cathode material for sodium-ion batteries according to any one of claims 1-3, characterized in that In the chemical general formula of the said kernel, A includes K + , Ca 2+ , Sr 2+ , Ba 2+ , Cd 2+ , Zn 2+ , Cu 2+ or Mg 2+ or a combination of any one or at least two of them; And / or, in the chemical general formula of the core, D includes Al 3+ , Zr 4+ , Y 3+ , Ti 4+ , Sb 5+ , Cr 6+ , Co 3+ , Ga 3+ , Sc 3+ , Nb 5 + , Ta 5+ , W 6+ , V 5+ , Sn 4+ , Hf 4+ or Mo 6+ Any one or a combination of at least two of them; and / or, the shell comprises any one or a combination of at least two of ZrSiO4, Al2SiO5, MgSiO3, ZrP2O7, Al2TiO5 or MgAl2O4.

6. The high-nickel cathode material for sodium-ion batteries according to claim 5, characterized in that, In the chemical general formula of the core, D includes Sb 5+ , Cr 6+ , Nb 5+ , Ta 5+ , W 6+ , V 5+ or Mo 6+ or a combination of any one or at least two of them; and / or, the shell comprises any one or a combination of at least two of ZrSiO4, Al2TiO5 or MgSiO3.

7. A method for preparing a high-nickel cathode material for a sodium-ion battery according to any one of claims 1-6, characterized in that, The preparation method comprises the following steps: (1) According to the formula amount, mix a sodium source, a nickel-iron-manganese precursor, an A source, a D source and a lithium source and perform a first sintering to obtain a first-sintered material; (2) Mix the first-sintered material obtained in step (1) with a shell coating source and perform a second sintering to obtain the high-nickel cathode material for the sodium-ion battery.

8. The preparation method according to claim 7, characterized in that, The temperature of the first sintering in step (1) is 900 °C to 1250 °C, the heat preservation time is 10 h to 20 h, and the heating rate is 3 °C / min to 6 °C / min; and / or, the atmosphere of the first sintering in step (1) comprises an oxygen-containing atmosphere.

9. The preparation method according to claim 7 or 8, characterized in that, The temperature of the second sintering in step (2) is 600 °C to 850 °C, and the heat preservation time is 5 h to 10 h; and / or, the atmosphere of the second sintering in step (2) comprises an oxygen-containing atmosphere; and / or, after the second sintering in step (2), cool down at a rate of 1 °C / min to 6 °C / min.

10. A sodium-ion battery, characterized in that, The sodium-ion battery comprises the high-nickel cathode material for the sodium-ion battery according to any one of claims 1-6.

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