Sodium ion battery positive electrode material and preparation method thereof, sodium ion battery

Abstract

The present invention discloses a sodium ion battery positive electrode material and a preparation method thereof, and a sodium ion battery. The sodium ion battery comprises a layered positive electrode material core and a coating layer; the core material is Na x1 Ni x Fe y Mn z R 1‑x‑y‑z O2, and the coating layer comprises a polyelectrolyte layer and a hydroxyapatite layer. The present invention utilizes a layer-by-layer self-assembly method to modify the hydroxyapatite / polyelectrolyte interface layer on the surface of a layered cathode material, achieving tight connections between different interface layers and between the interface layer and the core cathode material. The thickness of the coating layer is controlled by controlling the number of assembly steps. The resulting layered cathode material is then calcined to resist internal pressure and reduce the generation of internal cracks. This effectively improves interfacial stability, reduces specific surface area and interfacial impedance, and enhances the rapid migration of sodium ions, resulting in a sodium-ion battery cathode material with a long cycle life.

Description

Technical Field

[0001] The present invention relates to the field of sodium ion battery materials, and in particular to a sodium ion battery positive electrode material and a preparation method thereof, and a sodium ion battery. Background Art

[0002] Since the resources of Na element in the earth's crust are very rich and its energy storage mechanism is similar to that of mature lithium-ion batteries (LIB), but with lower cost and higher safety, it has become the focus of research in the scientific and industrial circles. Among the reported positive electrode materials for sodium-ion batteries, layered transition metal oxide materials (Na x TMO2) is considered to have the greatest commercial potential due to its simple structure, high working potential and ease of synthesis. x During the sodium ion deintercalation process, TMO2 exhibits cathode-electrolyte interface side reactions, excessive metal dissolution, the formation of rock salt phase, and multiple phase transitions (hexagonal O3→O3+monoclinic O'3→hexagonal P3→monoclinic P'3→hexagonal P3'→hexagonal O3'), which shortens its cycle life. x The residual sodium on the surface of TMO2 easily reacts with carbon dioxide and water in the air to form residual alkali, resulting in poor material stability, difficult coating, unstable surface density, and a rapid decline in the electrochemical performance of the battery at high rates. At the same time, it induces the degradation of the later material structure and causes rapid failure of the battery cell. Summary of the Invention

[0003] In response to the deficiencies in the prior art, the present invention provides a sodium ion battery cathode material, a preparation method thereof, and a sodium ion battery. A layer-by-layer self-assembly method is used to modify a hydroxyapatite (HAP) / polyelectrolyte interface layer on the surface of a layered cathode material. Electrostatic force is used as a driving force to tightly connect different interface layers and between the interface layer and the core cathode material. Simultaneously, the number of assemblies is controlled to regulate the thickness of the coating layer, and then a layered cathode material with a uniform surface coating is obtained by calcination. The coating method of the present invention produces a uniform surface coating layer, effectively improving the surface stability of the layered cathode material, reducing interfacial impedance, and enhancing the rapid migration of sodium ions, resulting in a sodium ion battery cathode material with a long cycle life.

[0004] To achieve the above object, the present invention is implemented through the following technical solutions:

[0005] First, the present invention provides a sodium ion positive electrode material, comprising a layered positive electrode material core and a coating layer;

[0006] The core of the layered positive electrode material is Na x1 Ni x Fe y Mnz R 1-x-y-z O2, wherein 0.8≤x1≤1, 0.1≤x≤0.5, 0.1≤y≤0.5, 0.1≤z≤0.5, and R is at least one of Al, Ti, Mg, Zr, W, Mo, Ta, Nb, Y, Co, Sr, B, Ce, La, Li, K, Cu, Ce, and Sm;

[0007] The coating layer is a polyelectrolyte layer and a hydroxyapatite layer coated outside the core of the layered structure positive electrode material;

[0008] Wherein, in the sodium ion battery positive electrode material, the mass percentage of the coating layer is 0.1-5%. First, the present invention provides a method for preparing a sodium ion battery positive electrode material, which comprises the following steps:

[0009] (1) Preparation of precursor cathode materials

[0010] After uniformly mixing the ternary precursor, dopant and sodium source in a certain proportion, sintering in an oxygen atmosphere, cooling to room temperature and crushing to obtain a sodium ion battery positive electrode precursor material;

[0011] (2) Preparation of coating solution

[0012] Dissolve the polyelectrolyte in the solvent, stir and mix uniformly to obtain solution A; dissolve the hydroxyapatite in the solvent, stir and mix uniformly to obtain solution B;

[0013] (3) Coating

[0014] The sodium ion battery positive electrode precursor material is immersed in solution A for a certain time, washed, and dried, and then immersed in solution B for a certain time, washed, and dried; this step is repeated n times to obtain a coating material, where n is an integer between 1 and 20;

[0015] (4) The coated material is calcined to obtain a positive electrode material for a sodium ion battery.

[0016] Furthermore, in step (1), the molar ratio of the ternary precursor, the sodium source, and the dopant is 0.5:1-1.5:0.001-0.5; the ternary precursor is Ni 0.4 Fe 0.2 Mn 0.4 (OH)2、Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2、Ni 0.5 Fe 0.2 Mn 0.3 (OH)2、Ni 0.6 Fe 0.2 Mn 0.2(OH)2, the Dv50 particle size of the ternary precursor is 2μm~30μm; the dopant is one or more of aluminum oxide, titanium oxide, copper oxide, magnesium oxide, niobium oxide, and strontium oxide; the sodium source is one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide or sodium sulfate.

[0017] Furthermore, in step (1), the sintering process is: heating to 900-1000°C at a heating rate of 1-3°C / min, then cooling to 100°C at a cooling rate of 1-5°C / min, and then cooling to room temperature; the pulverization is carried out by using a rotary mill and a mechanical pulverizer in sequence.

[0018] Furthermore, in step (2), the polyelectrolyte is one or more of polydiallyldimethylammonium chloride, polyethyleneimine (PEI), polyhexamethylenedimethylammonium bromide (PB), chitosan, polyhydroxyethyl cellulose ether quaternary ammonium salt (PQN), ammonium polyphosphate (APP) or polylysine; the Dv50 particle size of the hydroxyapatite is 5 to 200 nm; and the solvent is one or more of dimethyl ether, ethyl ether, carbon tetrachloride, petroleum ether, ethanol, propanol, isopropanol, acetone, dimethylformamide, dimethylacetamide, and N-methylpyrrolidone.

[0019] Furthermore, in step (2), the concentration of solution A is 0.1 to 5 g / mL, and the concentration of solution B is 0.01 to 0.2 g / mL.

[0020] Furthermore, in step (3), the soaking time is 1 to 100 minutes.

[0021] Furthermore, in step (4), the calcination temperature is 400-800° C., and the holding time is 1-3 hours.

[0022] Third, the present invention provides a sodium ion battery, which includes a positive electrode material, a negative electrode material and an electrolyte, wherein the positive electrode material is the above-mentioned sodium ion battery positive electrode material or the sodium ion positive electrode material prepared by the above-mentioned method for preparing the sodium ion battery positive electrode material.

[0023] The beneficial effects of the present invention are:

[0024] (1) The core of the layered structure positive electrode material of the present invention is Na x1 Ni x Fe y Mn z R 1-x-y-z O2, among which Ni element can increase the capacity of the material, Mn element can reduce the material cost and improve the safety and stability of the material, Fe element can improve the high temperature resistance and cycle life of the material, and M doping element can also improve the structural stability of the material, so that it can inhibit phase change in a high sodium removal state.

[0025] (2) The present invention adopts a layer-by-layer self-assembly method to modify the hydroxyapatite / polyelectrolyte interface layer on the surface of the layered positive electrode material. On the one hand, hydroxyapatite has a low dielectric loss (1.73) and a high dielectric constant (εr=296.6), which not only effectively promotes the dissociation of sodium salt (NaPF6) in the electrolyte to form more free sodium ions, but also increases the migration number of sodium ions; on the other hand, electrostatic force is used as the driving force to ensure close connection between different interface layers and between the interface layer and the core positive electrode material; on the third hand, the number of assemblies is controlled to regulate the thickness of the coating layer, and then a layered positive electrode material with a uniform surface coating is obtained by calcination.

[0026] (3) The coating method of the present invention is used to obtain a uniform interface layer, which resists internal pressure to reduce the generation of internal cracks and effectively improves the interface stability. At the same time, the surface area is reduced, the contact area between the core positive electrode material and the electrolyte is smaller, and side reactions are also reduced. At the same time, the interfacial impedance is reduced, the rapid migration of sodium ions is improved, and a sodium ion battery positive electrode material with a long cycle life is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the XRD pattern of the sample provided in Example 1. DETAILED DESCRIPTION

[0028] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0029] The reagents and instruments used in the present invention without manufacturer indication are all conventional products that can be purchased from the market.

[0030] Example 1

[0031] The preparation process of sodium ion battery positive electrode materials is as follows:

[0032] Ni with a Dv50 of 5 μm 0.4 Fe 0.2 Mn 0.4 The (OH)2 ternary precursor, sodium hydroxide and magnesium oxide were mixed evenly in a molar ratio of 1:1.03:0.01. The mixture was placed in an oxygen atmosphere furnace with an oxygen volume ratio of 95%, and heated to 970°C at a heating rate of 3°C / min, and kept warm for 15h; then the temperature was reduced to 100°C at a rate of 5°C / min, and cooled to room temperature. The mixture was crushed in turn by a rotary mill and a mechanical crusher, and passed through a 325 mesh sieve to obtain NaNi 0.39 Fe 0.2 Mn 0.4 Mg 0.01O2 material.

[0033] Polydiallyldimethylammonium chloride (PDDA) was dissolved in petroleum ether and stirred to prepare a 0.2 g / mL solution; hydroxyapatite (HAP) was dispersed in petroleum ether to obtain a 0.1 g / mL solution.

[0034] NaNi 0.39 Fe 0.2 Mn 0.4 Mg 0.01 The O2 material was immersed in polydiallyldimethylammonium chloride (PDDA) solution for 5 minutes to allow it to self-assemble on the NaNi 0.39 Fe 0.2 Mn 0.4 Mg 0.01 The outer surface of the O2 material is cleaned and dried to obtain a NaNi surface covered with a PDDA (positively charged) layer. 0.39 Fe 0.2 Mn 0.4 Mg 0.01 O2 material; NaNi coated with a PDDA (positively charged) layer on the surface 0.39 Fe 0.2 Mn 0.4 Mg 0.01 The O2 material was immersed in hydroxyapatite solution for 5 minutes to allow it to self-assemble on the outer surface of the cationic layer. After cleaning and drying, NaNi 0.39 Fe 0.2 Mn 0.4 Mg 0.01 O2@(PDDA / HAP)1;

[0035] NaNi 0.39 Fe 0.2 Mn 0.4 Mg 0.01 O2@(PDDA / HAP)1 was placed in an atmosphere furnace, introduced with dry air, kept at 500°C for 3 hours, and then cooled to room temperature to obtain a self-assembled coated sodium ion battery positive electrode material.

[0036] Example 2

[0037] The preparation process of sodium ion battery positive electrode materials is as follows:

[0038] Ni with a Dv50 of 5 μm 0.4 Fe 0.2 Mn 0.4The (OH)2 ternary precursor, sodium carbonate and copper oxide were mixed evenly in a molar ratio of 1:1.03:0.01. The mixture was placed in an oxygen atmosphere furnace with an oxygen volume ratio of 95%, and heated to 970°C at a heating rate of 3°C / min, and kept warm for 15h; then the temperature was reduced to 100°C at a rate of 5°C / min, and cooled to room temperature. The mixture was crushed in turn by a rotary mill and a mechanical crusher, and passed through a 325 mesh sieve to obtain NaNi 0.39 Fe 0.2 Mn 0.4 Cu 0.01 O2 material.

[0039] Polydiallyldimethylammonium chloride (PDDA) was dissolved in petroleum ether and stirred to prepare a 0.2 g / mL solution; hydroxyapatite (HAP) was dispersed in petroleum ether to obtain a 0.1 g / mL solution.

[0040] NaNi 0.39 Fe 0.2 Mn 0.4 Cu 0.01 The O2 material was immersed in polydiallyldimethylammonium chloride (PDDA) solution for 5 minutes to allow it to self-assemble on the NaNi 0.39 Fe 0.2 Mn 0.4 Cu 0.01 The outer surface of the O2 material is cleaned and dried to obtain a NaNi surface covered with a PDDA (positively charged) layer. 0.39 Fe 0.2 Mn 0.4 Cu 0.01 O2 material; NaNi coated with a PDDA (positively charged) layer on the surface 0.39 Fe 0.2 Mn 0.4 Cu 0.01 The O2 material was immersed in hydroxyapatite solution for 5 minutes to allow it to self-assemble on the outer surface of the cationic layer. After cleaning and drying, NaNi 0.39 Fe 0.2 Mn 0.4 Cu 0.01 O2@(PDDA / HAP)1;

[0041] NaNi 0.39 Fe 0.2 Mn 0.4 Cu 0.01 O2@(PDDA / HAP)1 was placed in an atmosphere furnace, introduced with dry air, kept at 500°C for 3 hours, and then cooled to room temperature to obtain a self-assembled coated sodium ion battery positive electrode material.

[0042] Example 3

[0043] The preparation process of sodium ion battery positive electrode materials is as follows:

[0044] Ni with a Dv50 of 5 μm 0.4 Fe 0.2 Mn 0.4 The (OH)2 ternary precursor, sodium hydroxide and copper oxide were mixed evenly in a molar ratio of 1:1.03:0.01. The mixture was placed in an oxygen atmosphere furnace with an oxygen volume ratio of 95%, and heated to 970°C at a heating rate of 3°C / min, and kept warm for 15h; then the temperature was reduced to 100°C at a rate of 5°C / min, and cooled to room temperature. The mixture was crushed in turn by a rotary mill and a mechanical crusher, and passed through a 325 mesh sieve to obtain NaNi 0.39 Fe 0.2 Mn 0.4 Cu 0.01 O2 material.

[0045] Polydiallyldimethylammonium chloride (PDDA) was dissolved in petroleum ether and stirred to prepare a 0.2 g / mL solution; hydroxyapatite (HAP) was dispersed in petroleum ether to obtain a 0.1 g / mL solution.

[0046] NaNi 0.39 Fe 0.2 Mn 0.4 Cu 0.01 The O2 material was immersed in polydiallyldimethylammonium chloride (PDDA) solution for 5 minutes to allow it to self-assemble on the NaNi 0.39 Fe 0.2 Mn 0.4 Cu 0.01 The outer surface of the O2 material is cleaned and dried to obtain a NaNi surface covered with a PDDA (positively charged) layer. 0.39 Fe 0.2 Mn 0.4 Cu 0.01 O2 material; NaNi coated with a PDDA (positively charged) layer on the surface 0.39 Fe 0.2 Mn 0.4 Cu 0.01 The O2 material was immersed in hydroxyapatite solution for 5 minutes to allow it to self-assemble on the outer surface of the cationic layer. After cleaning and drying, NaNi 0.39 Fe 0.2 Mn 0.4 Cu 0.01 O2@(PDDA / HAP)1; repeat this process twice to obtain NaNi 0.39 Fe 0.2 Mn 0.4 Cu 0.01 O2@(PDDA / HAP)3.

[0047] NaNi 0.39 Fe 0.2 Mn 0.4 Cu 0.01 O2@(PDDA / HAP)3 was placed in an atmosphere furnace, introduced with dry air, kept at 500°C for 3 hours, and then cooled to room temperature to obtain a self-assembled coated sodium ion battery positive electrode material.

[0048] Example 4

[0049] The preparation process of sodium ion battery positive electrode materials is as follows:

[0050] Ni with a Dv50 of 5 μm 0.4 Fe 0.2 Mn 0.4 The (OH)2 ternary precursor, sodium hydroxide and copper oxide were mixed evenly in a molar ratio of 1:1.03:0.01. The mixture was placed in an oxygen atmosphere furnace with an oxygen volume ratio of 95%, and heated to 970°C at a heating rate of 3°C / min, and kept warm for 15h; then the temperature was reduced to 100°C at a rate of 5°C / min, and cooled to room temperature. The mixture was crushed in turn by a rotary mill and a mechanical crusher, and passed through a 325 mesh sieve to obtain NaNi 0.39 Fe 0.2 Mn 0.4 Cu 0.01 O2 material.

[0051] Polyethyleneimine (PEI) was dissolved in ethanol and stirred to prepare a 0.2 g / mL solution; hydroxyapatite (HAP) was dispersed in ethanol to obtain a 0.1 g / mL solution.

[0052] NaNi 0.39 Fe 0.2 Mn 0.4 Cu 0.01 The O2 material was immersed in polyethyleneimine (PEI) solution for 5 minutes to allow it to self-assemble on the NaNi 039 Fe 02 Mn 04 Cu 001 The outer surface of the O2 material is cleaned and dried to obtain NaNi coated with a PEI (positively charged) layer. 0.39 Fe 0.2 Mn 0.4 Cu 0.01 O2 material; NaNi coated with a PEI (positively charged) layer on the surface 0.39 Fe 0.2 Mn 0.4 Cu 0.01 The O2 material was immersed in hydroxyapatite solution for 5 minutes to allow it to self-assemble on the outer surface of the cationic layer. After cleaning and drying, NaNi 0.39 Fe0.2 Mn 0.4 Cu 0.01 O2@(PEI / HAP)1; repeat this process twice to obtain NaNi 0.39 Fe 0.2 Mn 0.4 Cu 0.01 O2@(PEI / HAP)3.

[0053] NaNi 0.39 Fe 0.2 Mn 0.4 Cu 0.01 O2@(PEI / HAP)3 was placed in an atmosphere furnace, dry air was introduced, the temperature was kept at 500°C for 3 hours, and then cooled to room temperature to obtain a self-assembled coated sodium ion battery positive electrode material.

[0054] Example 5

[0055] The preparation process of sodium ion battery positive electrode materials is as follows:

[0056] Ni with a Dv50 of 5 μm 0.4 Fe 0.2 Mn 0.4 The (OH)2 ternary precursor, sodium hydroxide and copper oxide were mixed evenly in a molar ratio of 1:1.03:0.01. The mixture was placed in an oxygen atmosphere furnace with an oxygen volume ratio of 95%, and heated to 970°C at a heating rate of 3°C / min, and kept warm for 15h; then the temperature was reduced to 100°C at a rate of 5°C / min, and cooled to room temperature. The mixture was crushed in turn by a rotary mill and a mechanical crusher, and passed through a 325 mesh sieve to obtain NaNi 0.39 Fe 0.2 Mn 0.4 Cu 0.01 O2 material.

[0057] Polydiallyldimethylammonium chloride (PDDA) was dissolved in petroleum ether and stirred to prepare a 0.2 g / mL solution; hydroxyapatite (HAP) was dispersed in petroleum ether to obtain a 0.1 g / mL solution.

[0058] NaNi 0.39 Fe 0.2 Mn 0.4 Cu 0.01 The O2 material was immersed in polydiallyldimethylammonium chloride (PDDA) solution for 5 minutes to allow it to self-assemble on the NaNi 0.39 Fe 0.2 Mn 0.4 Cu 0.01 The outer surface of the O2 material is cleaned and dried to obtain a NaNi surface covered with a PDDA (positively charged) layer. 0.39 Fe 0.2 Mn0.4 Cu 0.01 O2 material; NaNi coated with a PDDA (positively charged) layer on the surface 0.39 Fe 0.2 Mn 0.4 Cu 0.01 The O2 material was immersed in hydroxyapatite solution for 5 minutes to allow it to self-assemble on the outer surface of the cationic layer. After cleaning and drying, NaNi 0.39 Fe 0.2 Mn 0.4 Cu 0.01 O2@(PDDA / HAP)1; repeat this process 6 times to obtain NaNi 0.39 Fe 0.2 Mn 0.4 Cu 0.01 O2@(PDDA / HAP)7.

[0059] NaNi 0.39 Fe 0.2 Mn 0.4 Cu 0.01 O2@(PDDA / HAP)7 was placed in an atmosphere furnace, introduced with dry air, kept at 500°C for 3 hours, and then cooled to room temperature to obtain a self-assembled coated sodium ion battery positive electrode material.

[0060] Comparative Example 1

[0061] Ni with a Dv50 of 5 μm 0.4 Fe 0.2 Mn 0.4 The (OH)2 ternary precursor and sodium hydroxide were mixed evenly in a molar ratio of 1:1.03. The mixture was placed in an oxygen atmosphere furnace with an oxygen volume ratio of 95%, and heated to 970°C at a heating rate of 3°C / min, and kept warm for 15h; then the temperature was reduced to 100°C at a rate of 5°C / min, cooled to room temperature, and powdered and sieved to obtain NaNi 0.4 Fe 0.2 Mn 0.4 O2 material.

[0062] Polydiallyldimethylammonium chloride (PDDA) was dissolved in petroleum ether and stirred to prepare a 0.2 g / mL solution; hydroxyapatite (HAP) was dispersed in petroleum ether to obtain a 0.1 g / mL solution.

[0063] NaNi 0.4 Fe 0.2 Mn 0.4 The O2 material was immersed in polydiallyldimethylammonium chloride (PDDA) solution for 5 minutes to allow it to self-assemble on the NaNi 0.4 Fe 0.2 Mn 0.4The outer surface of the O2 material is cleaned and dried to obtain a NaNi surface covered with a PDDA (positively charged) layer. 0.4 Fe 0.2 Mn 0.4 O2 material; NaNi coated with a PDDA (positively charged) layer on the surface 0.4 Fe 0.2 Mn 0.4 The O2 material was immersed in hydroxyapatite solution for 5 minutes to allow it to self-assemble on the outer surface of the cationic layer. After cleaning and drying, NaNi 0.4 Fe 0.2 Mn 0.4 O2@(PDDA / HAP)1;

[0064] NaNi 0.4 Fe 0.2 Mn 0.4 O2@(PDDA / HAP)1 was placed in an atmosphere furnace, introduced with dry air, kept at 500°C for 3 hours, and then cooled to room temperature to obtain a self-assembled coated sodium ion battery positive electrode material.

[0065] Comparative Example 2

[0066] The preparation process of sodium ion battery positive electrode materials is as follows:

[0067] Ni with a Dv50 of 5 μm 0.4 Fe 0.2 Mn 0.4 The (OH)2 ternary precursor, sodium hydroxide and magnesium oxide were mixed evenly in a molar ratio of 1:1.03:0.01. The mixture was placed in an oxygen atmosphere furnace with an oxygen volume ratio of 95%, and heated to 970°C at a heating rate of 3°C / min, and kept warm for 15h; then the temperature was reduced to 100°C at a rate of 5°C / min, cooled to room temperature, and powdered and sieved to obtain NaNi 0.39 Fe 0.2 Mn 0.4 Mg 0.01 O2 material.

[0068] Comparative Example 3

[0069] The preparation process of sodium ion battery positive electrode materials is as follows:

[0070] Ni with a Dv50 of 5 μm 0.4 Fe 0.2 Mn 0.4The (OH)2 ternary precursor, sodium hydroxide and magnesium oxide were mixed evenly in a molar ratio of 1:1.03:0.01. The mixture was placed in an oxygen atmosphere furnace with an oxygen volume ratio of 95%, and heated to 970°C at a heating rate of 3°C / min, and kept warm for 15h; then the temperature was reduced to 100°C at a rate of 5°C / min, cooled to room temperature, and powdered and sieved to obtain NaNi 0.39 Fe 0.2 Mn 0.4 Mg 0.01 O2 material.

[0071] Dissolve polydiallyldimethylammonium chloride (PDDA) in petroleum ether and stir to prepare a 0.2 g / mL solution.

[0072] NaNi 0.39 Fe 0.2 Mn 0.4 Mg 0.01 The O2 material was immersed in polydiallyldimethylammonium chloride (PDDA) solution for 5 minutes to allow it to self-assemble on the NaNi 0.39 Fe 0.2 Mn 0.4 Mg 0.01 The outer surface of the O2 material is cleaned and dried to obtain a NaNi surface covered with a PDDA (positively charged) layer. 0.39 Fe 0.2 Mn 0.4 Mg 0.01 O2 material, namely NaNi 0.39 Fe 0.2 Mn 0.4 Mg 0.01 O2@PDDA.

[0073] NaNi 0.39 Fe 0.2 Mn 0.4 Mg 0.01 O2@PDDA was placed in an atmosphere furnace, introduced with dry air, kept at 500°C for 3 hours, and then cooled to room temperature to obtain a self-assembled coated sodium ion battery positive electrode material.

[0074] Comparative Example 4

[0075] The preparation process of sodium ion battery positive electrode materials is as follows:

[0076] Ni with a Dv50 of 5 μm 0.4 Fe 0.2 Mn 0.4The (OH)2 ternary precursor, sodium hydroxide and magnesium oxide were mixed evenly in a molar ratio of 1:1.03:0.01. The mixture was placed in an oxygen atmosphere furnace with an oxygen volume ratio of 95%, and heated to 970°C at a heating rate of 3°C / min, and kept warm for 15h; then the temperature was reduced to 100°C at a rate of 5°C / min, cooled to room temperature, and powdered and sieved to obtain NaNi 0.39 Fe 0.2 Mn 0.4 Mg 0.01 O2 material.

[0077] Hydroxyapatite (HAP) was dispersed in petroleum ether to obtain a 0.1 g / mL solution.

[0078] NaNi 0.39 Fe 0.2 Mn 0.4 Mg 0.01 The O2 material was immersed in hydroxyapatite solution for 5 minutes to allow it to self-assemble on the NaNi 0.39 Fe 0.2 Mn 0.4 Mg 0.01 The outer surface of the O2 material is cleaned and dried to obtain NaNi coated with hydroxyapatite. 0.39 Fe 0.2 Mn 0.4 Mg 0.01 O2 material, namely NaNi 0.39 Fe 0.2 Mn 0.4 Mg 0.01 O2@HAP.

[0079] NaNi 0.39 Fe 0.2 Mn 0.4 Mg 0.01 O2@HAP was placed in an atmosphere furnace, introduced with dry air, kept at 500°C for 3 hours, and then cooled to room temperature to obtain a self-assembled coated sodium ion battery positive electrode material.

[0080] Figure 1 NaNi synthesized in Example 1 0.39 Fe 0.2 Mn 0.4 Mg 0.01 The XRD pattern of O2@(PDDA / HAP)1 shows that the diffraction peaks of the sample are clear and sharp, without any impurity peaks, and are a hexagonal O3 structure, indicating that the Na and Mg elements are uniformly introduced into the crystal lattice of the precursor.

[0081] The electrochemical performance of the sodium ion battery positive electrode materials of Examples 1-5 and Comparative Examples 1-4 was tested, and the test results are shown in Tables 1 and 2.

[0082] Electrochemical performance test: The sodium ion battery positive electrode material is mixed with conductive carbon black and polyvinylidene fluoride binder in a mass ratio of 95:2.5:2.5, and an appropriate amount of N-methylpyrrolidone solution is added until a slurry is formed in a dry environment at room temperature; the prepared slurry is evenly coated on the aluminum foil of the current collector, and after initial drying, it is compacted and cut into circular electrodes with a diameter of 12 mm; the circular electrodes are dried at 120°C under vacuum conditions for 12 hours and then transferred to a glove box for use.

[0083] Assembly was performed in an argon-filled glove box, using the sodium-ion battery cathode materials obtained in Examples 1-5 and Comparative Examples 1-3 as the positive electrode, metallic sodium as the negative electrode, and glass fiber as the separator. The electrolyte consisted of a 1 mol·L⁻¹ NaClO⁻¹ mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and propylene carbonate (PC) (volume ratio 1:1:1), supplemented with 5% by volume of fluoroethylene carbonate (FEC). All materials were placed in a glove box filled with high-purity argon (O₂ <0.1 ppm, H₂O <0.1 ppm), assembled into CR2032 button cells, and sealed using a sealing machine. Finally, the assembled CR2032 button cells were left to activate at room temperature for 10 hours before use.

[0084] Charge and discharge tests were performed at a current density of 0.1C within the voltage range of 2.0-4.0V. Using the constant current charge and discharge mode, the charge and discharge tests were performed at a rate of 0.1C / 0.1C within the voltage window of 2.0V-4.0V to obtain the initial discharge specific capacity. The test results are shown in Table 1 below.

[0085] The test conditions for the 100-cycle cycle retention rate are as follows: the sodium-ion battery is first formed, then charged to 3.5V at a constant current of 0.01C at 40°C, then charged to 4.0V at a constant current of 0.2C, then charged to 0.05C at a constant voltage, left to stand for 10 minutes, and then discharged to 2.0V at 0.1C at 30±0.5°C. The 100-cycle capacity retention rate is calculated using the following formula:

[0086] 100-cycle capacity retention rate = discharge capacity after 100 cycles / initial discharge capacity × 100%.

[0087] Table 1 Test results of powder

[0088]

[0089] Table 2 Battery test results

[0090]

[0091] The present invention uses a layer-by-layer self-assembly method to modify the hydroxyapatite / organic compound interface layer on the surface of the layered positive electrode material. First, hydroxyapatite has a low dielectric loss (1.73) and a high dielectric constant (εr = 296.6), which not only effectively promotes the dissociation of sodium salt (NaPF6) in the electrolyte, forming more free sodium ions, but also increases the sodium ion migration number. Second, electrostatic force is used as a driving force to achieve close connections between different interface layers and between the interface layer and the core positive electrode material. Third, the number of assembly times is controlled to regulate the thickness of the coating layer, and then calcination is performed to obtain a ternary positive electrode material with a uniform surface coating. The coating method of the present invention produces a uniform interface layer to resist internal pressure and reduce the occurrence of internal cracks, effectively improving interface stability. At the same time, the specific surface area is reduced, the contact area between the core positive electrode material and the electrolyte will be smaller, and side reactions will also be reduced. At the same time, the interfacial impedance is reduced, the rapid migration of sodium ions is improved, and a sodium ion battery positive electrode material with a long cycle life is obtained.

[0092] Based on the disclosure of the above description, those skilled in the art may also make appropriate changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and any modifications and variations of the present invention should also fall within the scope of protection of the claims of the present invention. In addition, although certain specific terms are used in this description, these terms are merely for convenience of description and do not constitute any limitation to the present invention.

Claims

1. A sodium ion battery cathode material, characterized in that: It includes a core and a coating layer of a layered positive electrode material; The core of the layered positive electrode material is Na x1 Ni x Fe y Mn z R 1-x-y-z O2, wherein 0.8≤x1≤1, 0.1≤x≤0.5, 0.1≤y≤0.5, 0.1≤z≤0.5, and R is at least one of Al, Ti, Mg, Zr, W, Mo, Ta, Nb, Y, Co, Sr, B, Ce, La, Li, K, Cu, Ce, and Sm; The coating layer is a polyelectrolyte layer and a hydroxyapatite layer coated outside the core of the layered structure positive electrode material; Wherein, in the sodium ion battery positive electrode material, the mass percentage of the coating layer is 0.1 to 5%; The preparation method of the sodium ion battery positive electrode material comprises the following steps: After uniformly mixing the ternary precursor, dopant and sodium source in proportion, sintering in an oxygen atmosphere, cooling to room temperature and crushing to obtain a sodium ion battery positive electrode precursor material; Dissolve the polyelectrolyte in the solvent, stir and mix uniformly to obtain solution A; dissolve the hydroxyapatite in the solvent, stir and mix uniformly to obtain solution B; The sodium ion battery positive electrode precursor material is immersed in solution A for a certain time, washed, and dried, and then immersed in solution B for a certain time, washed, and dried; this step is repeated n times to obtain a coating material, where n is an integer between 1 and 20; The coated material is calcined to obtain a positive electrode material for a sodium ion battery.

2. A method for preparing a positive electrode material for a sodium ion battery according to claim 1, characterized in that: The following steps are involved: (1) Preparation of precursor cathode materials After uniformly mixing the ternary precursor, dopant and sodium source in a certain proportion, sintering in an oxygen atmosphere, cooling to room temperature and crushing to obtain a sodium ion battery positive electrode precursor material; (2) Preparation of coating solution Dissolve the polyelectrolyte in the solvent, stir and mix uniformly to obtain solution A; dissolve the hydroxyapatite in the solvent, stir and mix uniformly to obtain solution B; (3) Coating The sodium ion battery cathode precursor material is immersed in solution A for a certain period of time, washed, and dried, and then immersed in solution B for a certain period of time, washed, and dried; Repeat this step n times to obtain a coating material, wherein n is an integer between 1 and 20; (4) The coated material is calcined to obtain a positive electrode material for a sodium ion battery.

3. The method for preparing a positive electrode material for a sodium ion battery according to claim 2, wherein: In step (1), the molar ratio of the ternary precursor, the sodium source, and the dopant is 0.5-1:1-1.5:0.001-0.5; The ternary precursor is Ni 0.4 Fe 0.2 Mn 0.4 (OH)2、Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2、Ni 0.5 Fe 0.2 Mn 0.3 (OH)2、Ni 0.6 Fe 0.2 Mn 0.2 (OH)2, the Dv50 particle size of the ternary precursor is 2μm to 30μm; The sodium source is one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide or sodium sulfate; The dopant is one or more of aluminum oxide, titanium oxide, copper oxide, magnesium oxide, niobium oxide, and strontium oxide.

4. The method for preparing a positive electrode material for a sodium ion battery according to claim 2, wherein: In step (1), the sintering process is: heating to 900-1000°C at a heating rate of 1-3°C / min, then cooling to 100°C at a cooling rate of 1-5°C / min, and then cooling to room temperature; the pulverization is carried out by using a rotary mill and a mechanical pulverizer in sequence.

5. The method for preparing a positive electrode material for a sodium ion battery according to claim 2, wherein: In step (2), the polyelectrolyte is one or more of polydiallyldimethylammonium chloride, polyethyleneimine (PEI), polyhexamethylenedimethylammonium bromide (PB), chitosan, polyhydroxyethyl cellulose ether quaternary ammonium salt (PQN), ammonium polyphosphate (APP) or polylysine; The Dv50 particle size of the hydroxyapatite is 5 to 200 nm.

6. The method for preparing a positive electrode material for a sodium ion battery according to claim 2, wherein: In step (2), the solvent is one or more of dimethyl ether, ethyl ether, carbon tetrachloride, petroleum ether, ethanol, propanol, isopropanol, acetone, dimethylformamide, dimethylacetamide, and N-methylpyrrolidone.

7. The method for preparing a positive electrode material for a sodium ion battery according to claim 2, wherein: In step (2), the concentration of solution A is 0.1 to 5 g / mL, and the concentration of solution B is 0.01 to 0.2 g / mL.

8. The method for preparing a positive electrode material for a sodium ion battery according to claim 2, wherein: In step (3), the soaking time is 1 to 100 minutes.

9. The method for preparing a positive electrode material for a sodium ion battery according to claim 2, wherein: In step (4), the calcination temperature is 400-800° C., and the holding time is 1-3 hours.

10. A sodium ion battery comprising a positive electrode material, a negative electrode material, and an electrolyte, characterized in that: The positive electrode material includes the sodium ion battery positive electrode material according to claim 1 or the sodium ion positive electrode material prepared by the preparation method of the sodium ion battery positive electrode material according to any one of claims 2 to 9.

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