A sodium ion battery positive electrode material and preparation method thereof

Abstract

The present invention discloses a sodium ion battery positive electrode material, comprising a core material, a first carbon layer coated on the outside of the core material, a second carbon layer coated on the outside of the first carbon layer, a gap between the first carbon layer and the second carbon layer, and a molecular formula of the core material is Na4Fe 2.4 Ni 0.6 (PO4)2P2O7, with an orthorhombic core and space group Pn21a. This material exhibits excellent rapid charge and discharge performance at room and low temperatures and cycling stability at high current densities. The present invention also discloses a method for preparing the material.

Description

Technical Field

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

[0002] In today's world, the development and utilization of renewable energy has become a research hotspot. Sodium-ion batteries are considered a major breakthrough in the field of future energy storage due to their significant cost-effectiveness and environmentally friendly characteristics. Sodium is abundant in nature and more readily available than lithium resources, which makes the production cost of sodium-ion batteries much lower than that of lithium-ion batteries. However, this battery technology still faces many challenges in practical application, including low battery energy density, limited cycle life, and low charge and discharge efficiency. Therefore, in order to improve the performance of sodium-ion batteries, it is necessary to develop high-efficiency and long-life cathode materials.

[0003] In this regard, Na4Fe3(PO4)2P2O7 has an advantage in the field of cathode materials due to its high theoretical capacity, good charge-discharge stability and structural integrity. However, its practical application has been hindered by problems such as poor conductivity and slow ion diffusion kinetics. Summary of the Invention

[0004] The present invention aims to provide a sodium ion battery cathode material having good rapid charge and discharge performance at room temperature and low temperature and cycle stability at high current density.

[0005] In order to solve the above problems, the present invention adopts the following technical solutions:

[0006] A sodium ion battery positive electrode material comprises a core material, a first carbon layer coated on the outside of the core material, a second carbon layer coated on the outside of the first carbon layer, a gap between the first carbon layer and the second carbon layer, and the molecular formula of the core material is Na4Fe 2.4 Ni 0.6 (PO4)2P2O7, the core material is orthorhombic crystal system, and the space group is Pn21a.

[0007] The sodium ion battery positive electrode material is spherical, with a particle size of 1-8 microns, and a gap between the first carbon layer and the second carbon layer of 80-150 nanometers.

[0008] The present invention also provides a method for preparing the above-mentioned sodium ion battery positive electrode material, comprising the following steps:

[0009] A carbon source, a sodium source, an iron source, a nickel source and a phosphorus source are dissolved in water according to the stoichiometric ratio of the molecular formula, and then spray-dried to obtain a precursor. The precursor is placed in a protective atmosphere and pre-sintered at 200-350° C. for 3-5 hours, and then sintered at 500-650° C. for 9-12 hours to obtain the sodium ion battery positive electrode material.

[0010] Optionally, the carbon source is at least two of citric acid, glucose, sucrose, oxalic acid, ascorbic acid, and polyvinyl pyrrolidone; the sodium source is at least one of sodium carbonate, sodium bicarbonate, sodium acetate, sodium oxalate, sodium dihydrogen phosphate, and sodium citrate; the iron source is at least one of ferrous acetate, ferric nitrate, ferric oxalate, ferric sulfate, and iron powder; the nickel source is at least one of nickel nitrate and nickel acetate; and the phosphorus source is at least one of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, and phosphoric acid.

[0011] Preferably, the carbon source is citric acid and polyvinyl pyrrolidone, the sodium source is sodium bicarbonate; the iron source is ferric nitrate; the nickel source is nickel nitrate; and the phosphorus source is ammonium dihydrogen phosphate; the molar ratio of citric acid to the total amount of ferric nitrate and nickel nitrate is 3-5:3, and the mass ratio of citric acid to polyvinyl pyrrolidone is 7-9:1.

[0012] Preferably, the molar ratio of the citric acid to the total amount of ferric nitrate and nickel nitrate is 4:3, and the mass ratio of citric acid to polyvinyl pyrrolidone is 8.4:1.

[0013] Preferably, the protective atmosphere is one or more of argon, nitrogen or a hydrogen-argon mixture.

[0014] The present invention utilizes the different decomposition rates of two carbon sources during the sintering process to coat the positive electrode core material with a double carbon layer with gaps. This double carbon layer is permeable to the electrolyte and significantly improves the material's electronic and ionic conductivity, mitigating the adverse effects of volume expansion during charge and discharge. The carbon layer provides a highly conductive network, helping to reduce the contact resistance between the electrode core material and the electrolyte, thereby increasing the battery's energy and power density. Furthermore, the carbon layer effectively prevents the electrode core material from being directly exposed to the electrolyte, further improving the material's cycle stability and corrosion resistance, and extending the battery's service life.

[0015] By partially doping metallic Ni into Fe sites, the material's lattice parameters can be adjusted, expanding ion diffusion channels and thereby increasing ion diffusion rates. Ni doping can also regulate the material's electronic structure, improving intrinsic electronic conductivity, effectively increasing the number of active sites and enhancing the electrochemical reaction activity of the electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Na4Fe prepared in Example 1 2.4 Ni 0.6 X-ray diffraction (XRD) pattern of (PO4)2P2O7 positive electrode material.

[0017] Figure 2 Na4Fe prepared in Example 1 2.4 Ni 0.6Scanning electron microscope (SEM) image of (PO4)2P2O7 positive electrode material.

[0018] Figure 3 Na4Fe prepared in Example 1 2.4 Ni 0.6 Transmission electron microscopy (TEM) image of (PO4)2P2O7 positive electrode material.

[0019] Figure 4 Na4Fe prepared in Example 1 2.4 Ni 0.6 High-resolution transmission electron microscopy (HRTEM) image of (PO4)2P2O7 cathode material.

[0020] Figure 5 Na4Fe prepared in Example 1 2.4 Ni 0.6 Element mapping distribution diagram of (PO4)2P2O7 positive electrode material.

[0021] Figure 6 Na4Fe prepared in Example 1 2.4 Ni 0.6 Cycling performance diagram of sodium-ion battery assembled with (PO4)2P2O7 positive electrode material at 1C rate.

[0022] Figure 7 Na4Fe prepared in Example 1 2.4 Ni 0.6 The charge and discharge voltage-capacity curve of the sodium-ion battery assembled with (PO4)2P2O7 positive electrode material at a 1C rate.

[0023] Figure 8 Na4Fe prepared in Example 1 2.4 Ni 0.6 Rate performance diagram of sodium ion battery assembled with (PO4)2P2O7 cathode material;

[0024] Figure 9 Na4Fe prepared in Example 1 2.4 Ni 0.6 Cycling performance diagram of sodium ion battery assembled with (PO4)2P2O7 cathode material at -20℃ 1C and 5C rates;

[0025] Figure 10 Na4Fe prepared in Example 1 2.4 Ni 0.6 Rate performance diagram of sodium ion battery assembled with (PO4)2P2O7 positive electrode material at -20℃. DETAILED DESCRIPTION

[0026] Example 1

[0027] First, 0.020 mol C6H8O7·H2O (4.2 g), 0.012 mol Fe(NO3)3·9H2O, 0.003 mol nickel nitrate hexahydrate, and 0.020 mol NaH2PO4 were dissolved in deionized water. After complete dissolution, 0.5 g polyvinyl pyrrolidone was added. After the solution became clear, stirring was continued for 0.5 h. Subsequently, the precursor powder was spray-dried at 120 ° C to obtain a precursor powder. The obtained precursor powder was pre-sintered at a heating rate of 5 ° C / min to 300 ° C in an atmosphere of argon-hydrogen mixed gas for 3 h, and then calcined at 550 ° C for 10 h to obtain Na4Fe 2.4 Ni 0.6 (PO4)2P2O7 is a sodium ion battery positive electrode material coated with an interstitial double carbon layer.

[0028] The XRD patterns of the prepared sodium ion battery cathode materials are as follows: Figure 1 As shown, the core material is confirmed to be Na4Fe 2.4 Ni 0.6 (PO4)2P2O7, high purity and uniform phase, is an orthorhombic crystal system with a space group of Pn21a. Figure 2 As shown in Figure 1, it is a regular spherical structure with a particle size of 1-8 μm. Figure 3 As shown in Figure 2, the gap between the two carbon layers is 80-150 nanometers. Figure 4 As shown in Figure 2, its lattice spacing of 0.52nm corresponds to the 002 crystal plane. Figure 5 As shown in Figure 1, Fe, Ni, Na, C, N, P and O elements are evenly distributed on the surface of the material. The sodium ion battery cathode material and sodium sheet were assembled into a button-type sodium ion battery, and the electrochemical performance was tested at room temperature and low temperature of -20°C. At room temperature, the test results of the button-type battery cycle performance are shown in Figure 1. Figure 6 As shown. Figure 6 It can be seen that the discharge capacity of the sodium ion battery prepared by this cathode material reaches 117.6 mAh g after 100 cycles at 1C rate. -1 .according to Figure 7 From the charge and discharge voltage-capacity curve, we can see that the voltage of the material can reach 3.2V. Figure 8 This is the rate performance diagram of the positive electrode material. It can be seen that even at an ultra-high current density of 25C, there is still 86.4mAh g -1 The discharge capacity of Figure 9 As shown, it was first pre-cycled at 1C rate for 100 times to improve the electrode stability, and then it could still provide 43.6 mAh g after 2500 cycles at 5C rate. -1The discharge specific capacity and capacity retention rate are 65.2%, which shows that it has good low temperature tolerance. Figure 10 The rate capability of the electrode was demonstrated at -20 °C, achieving high discharge specific capacities (ranging from 89.58 mAh g) at current densities from 1C to 10C. -1 to 44.28mAh g -1 ), showing excellent low-temperature fast charging and discharging capabilities.

[0029] Comparative Example 1

[0030] First, 0.020 mol of C6H8O7·H2O, (0.015 mol)Fe(NO3)3·9H2O, and 0.020 mol of NaH2PO4 were dissolved in deionized water. After complete dissolution, 0.5 g of polyvinyl pyrrolidone was added. After the solution became clear and transparent, stirring was continued for 0.5 h. Then, the precursor powder was spray-dried at 120 ° C to obtain a precursor powder. The obtained precursor powder was pre-sintered at 300 ° C for 3 h at a heating rate of 5 ° C / min in an atmosphere of argon-hydrogen mixed gas, and then continued to calcine at 550 ° C for 10 h to obtain Na4Fe3(PO4)2P2O7 sodium ion battery positive electrode material. The sodium ion battery positive electrode material prepared in this comparative example was assembled into a button battery with a sodium sheet. At a rate of 1C, the discharge capacity after 100 cycles reached 94.9 mAh g -1 g is lower than the discharge specific capacity of Example 1.

[0031] Comparative Example 2

[0032] First, 0.020 mol of C6H8O7·H2O, (0.0135 mol) of Fe(NO3)3·9H2O, (0.0015 mol) of nickel nitrate hexahydrate, and 0.020 mol of NaH2PO4 were dissolved in deionized water. After complete dissolution, 0.5 g of polyvinyl pyrrolidone was added. After the solution became clear, stirring was continued for 0.5 h. Subsequently, the precursor powder was spray-dried at 120 ° C to obtain a precursor powder. The obtained precursor powder was pre-sintered at 300 ° C for 3 h at a heating rate of 5 ° C / min in an atmosphere of argon-hydrogen mixed gas, and then calcined at 550 ° C for 10 h to obtain Na4Fe 2.7 Ni 0.3 (PO4)2P2O7 sodium ion battery positive electrode material. The sodium ion battery positive electrode material prepared in this comparative example was assembled with sodium sheets into a button battery. At a 1C rate, the discharge capacity reached 99.7 mAh g after 100 cycles. -1 , which is lower than the discharge specific capacity of Example 1.

[0033] Comparative Example 3

[0034] First, 0.020 mol of C6H8O7·H2O, (0.0105 mol) of Fe(NO3)3·9H2O, (0.0045 mol) of nickel nitrate hexahydrate, and 0.020 mol of NaH2PO4 were dissolved in deionized water. After complete dissolution, 0.5 g of polyvinyl pyrrolidone was added. After the solution became clear, stirring was continued for 0.5 h. Subsequently, the precursor powder was spray-dried at 120 ° C to obtain a precursor powder. The obtained precursor powder was pre-sintered at 300 ° C for 3 h at a heating rate of 5 ° C / min in an atmosphere of argon-hydrogen mixed gas, and then calcined at 550 ° C for 10 h to obtain Na4Fe 2.1 Ni 0.9 (PO4)2P2O7 sodium ion battery positive electrode material. The sodium ion battery positive electrode material prepared in this comparative example was assembled with sodium sheets into a button battery. At a 1C rate, the discharge capacity reached 83.4 mAh g after 100 cycles. -1 , which is lower than the discharge specific capacity of Example 1.

Claims

1. A sodium ion battery cathode material, comprising a core material, a first carbon layer coated on the outside of the core material, a second carbon layer coated on the outside of the first carbon layer, a gap between the first carbon layer and the second carbon layer, wherein the molecular formula of the core material is Na4Fe 2.4 Ni 0.6 (PO4)2P2O7, the core material is orthorhombic, the space group is Pn21a The sodium ion battery positive electrode material is spherical with a particle size of 1-8 microns, and the gap between the first carbon layer and the second carbon layer is 80-150 nanometers.

2. The method for preparing a positive electrode material for a sodium ion battery according to claim 1, wherein The steps include: A carbon source, a sodium source, an iron source, a nickel source, and a phosphorus source are dissolved in water in a stoichiometric ratio according to the molecular formula, and then spray-dried to obtain a precursor. The precursor is placed in a protective atmosphere and pre-sintered at 200-350 ° C for 3-5 hours, and then sintered at 500-650 ° C for 9-12 hours to obtain the sodium ion battery positive electrode material; the carbon source is citric acid and polyvinyl pyrrolidone.

3. The preparation method according to claim 2, wherein: The sodium source is at least one of sodium carbonate, sodium bicarbonate, sodium acetate, sodium oxalate, sodium dihydrogen phosphate, and sodium citrate; The iron source is at least one of ferrous acetate, ferric nitrate, ferric oxalate, and ferric sulfate; The nickel source is at least one of nickel nitrate and nickel acetate; The phosphorus source is at least one of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, and phosphoric acid.

4. The preparation method according to claim 2, wherein The sodium source is sodium bicarbonate; the iron source is ferric nitrate; the nickel source is nickel nitrate; and the phosphorus source is ammonium dihydrogen phosphate. The molar ratio of citric acid to the total amount of ferric nitrate and nickel nitrate is 3-5:3, and the mass ratio of citric acid to polyvinyl pyrrolidone is 7-9:

1.

5. The preparation method according to claim 4, wherein The molar ratio of the citric acid to the total amount of ferric nitrate and nickel nitrate is 4:3, and the mass ratio of citric acid to polyvinyl pyrrolidone is 8.4:

1.

6. The preparation method according to claim 2, wherein The protective atmosphere is one of argon, nitrogen or hydrogen-argon mixed gas.

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