A double-layer coated sodium-ion battery cathode material, a preparation method thereof and a battery

Abstract

The application discloses a kind of double-layer coated sodium-ion battery positive electrode material and its preparation method and battery, belong to electrochemical energy storage field.The application can improve the stability of electrode material in electrolyte, reduce transition metal element dissolution and precipitation, and improve the cycle stability and electrochemical performance of material by twice coating of layered oxide, while enhancing the conductivity of electrode material.The material after secondary coating is assembled into a battery, and the initial charge-discharge specific capacity can reach 173mAh·g ‑1 Within the voltage range of 1.5-4.1V and at a rate of 0.1C, the battery has good cycle performance due to stable structure during the charge-discharge process, and the capacity retention rate can reach 96% after 50 cycles at a rate of 1C, and the electrode and electrolyte side reactions are reduced.The secondary coated layered oxide material exhibits excellent electrochemical performance.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage, specifically relating to a double-layer coated sodium-ion battery cathode material, its preparation method, and the battery. Background Technology

[0002] With societal development, energy has garnered increasing attention. Lithium-ion batteries, due to their high specific capacity, high voltage, and good safety performance, are widely used in products such as mobile phones, cameras, laptops, power tools, electric bicycles, and electric vehicles. However, the ever-growing lithium-ion battery market inevitably leads to lithium resource shortages and rising lithium prices. Sodium-ion battery systems, with their abundant resources, low cost, environmental friendliness, and similar electrochemical properties to lithium-ion batteries, have received widespread attention in recent years, providing a new option for electrochemical energy storage. The working principle of sodium-ion batteries is similar to that of lithium-ion batteries, but compared to lithium-ion batteries, sodium-ion batteries offer advantages such as abundant resources, low cost, and high safety, making them highly favored by researchers. Despite their similar working principle, the large radius of sodium ions makes mature cathode materials for lithium-ion batteries unsuitable for sodium-ion battery systems. Furthermore, the large ionic radius and slow kinetic rate of sodium ions are major factors restricting the development of energy storage materials. Developing high-performance sodium-intercalated cathode materials is key to improving the specific energy of sodium-ion batteries and promoting their application. Therefore, developing high-performance electrode materials capable of rapid and stable sodium storage is particularly important.

[0003] Current research on cathode materials for sodium-ion batteries includes transition metal oxides, polyanionic materials, Prussian blue compounds, organic molecules and polymers, and amorphous materials. Based on their structure, transition metal oxides can be divided into tunnel oxides and layered oxides. Layered metal oxides offer high capacity and charge / discharge voltage, but their structure is unstable. Tunnel metal oxides, while structurally stable, suffer from poor reversible capacity and cycle performance. Polyanionic compounds also exhibit structural stability, but low electronic conductivity and volumetric energy density. Prussian blue compounds offer high voltage and reversible capacity, and low cost, but poor cycle stability and susceptibility to decomposition at high temperatures. Finally, organic compounds and polymers offer high theoretical specific capacity, abundant raw materials, environmental friendliness, low cost, and flexible structural design, but suffer from low voltage, easy solubility in electrolytes, and poor cycle stability. This demonstrates that it is difficult to obtain excellent performance characteristics from a single material.

[0004] In existing technologies, common methods to improve the electrochemical performance of sodium-intercalated cathode materials include structural doping and surface coating modifications. However, simple coating and doping of a single sodium-intercalated cathode material usually does not achieve satisfactory results, and the cost of modifying a single sodium-intercalated cathode material is relatively high. Currently, it is still far from large-scale production and final industrialization.

[0005] In industry, it is common practice to directly mix and coat two or more cathode materials onto the electrode sheet according to specific needs. This leverages the complementary advantages of two or more different materials to optimize various electrochemical indicators and save costs. However, the drawback of this method is that the multiple cathode materials coated on the electrode sheet are independent and only macroscopically mixed, which may lead to inhomogeneities in various performance indicators, potentially resulting in failure to meet expectations. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a double-layer coated sodium-ion battery cathode material, its preparation method, and the battery itself. The material has two coating layers on its surface, which can significantly improve electronic conductivity, suppress volume phase transitions during charging and discharging, reduce the dissolution of transition metal ions in the material, and improve cycle stability.

[0007] The technical solution of the present invention is as follows:

[0008] This invention provides a method for preparing a double-layer coated sodium-ion battery cathode material, comprising the following steps:

[0009] (1) The metal salt and sodium ion layered oxide Na x Mn a Fe b Ni c Ti d O2 is thoroughly mixed to obtain mixture 1;

[0010] (2) After wet ball milling of the mixture 1 in step (1), the mixture is dried and calcined to obtain a layer of coated positive electrode material;

[0011] (3) Preparation of core-shell structured sodium-based polymer: Disperse the layer of coated positive electrode material obtained in step (2) in water, add polyvinyl alcohol, pass in an inert gas, then add sodium acrylate, styrene, magnesium acrylate and initiator, heat and react, and filter to obtain core-shell structured sodium-based polymer.

[0012] (4) Mix the coated cathode material obtained in step (2) with the core-shell structured sodium-based polymer obtained in step (3) thoroughly to obtain mixture 2;

[0013] (5) After wet ball milling of the mixture 2 in step (4), the mixture is dried and calcined under an inert gas to obtain a double-layer coated sodium-ion battery cathode material.

[0014] Among them, sodium ion layered oxide Na x Mn a Fe b Ni c Ti d In O2, 0.6<x≤0.8, a+b+c+d=1.

[0015] Preferably, the metal salt mentioned in step (1) is an aluminum salt, a magnesium salt, or a titanium salt.

[0016] More preferably, the metal salt mentioned in step (1) is aluminum nitrate, magnesium nitrate or titanium nitrate.

[0017] The specific steps of wet ball milling in steps (2) and (4) are as follows: the mixture and the ball milling beads are added to the ball milling jar at a mass ratio of 1:2, and anhydrous ethanol of the same mass as the mixture is added as a dispersant. Wet ball milling is carried out. During the ball milling process, the ball mill speed is 500-800 rpm / min and the ball milling time is 4-8h.

[0018] Specifically, the roasting conditions in step (2) are: roasting temperature of 500-600℃ and roasting time of 5-10h; the roasting conditions in step (5) are: roasting temperature of 500-600℃ and roasting time of 5-10h, and the inert gas is nitrogen or argon.

[0019] Preferably, the initiator in step (3) is azobisisobutyronitrile; the heating reaction conditions are 60°C with stirring for 6 hours. The mass ratio of the coated positive electrode material, polyvinyl alcohol, sodium acrylate, styrene, magnesium acrylate, initiator and water is 100:0.2-2:5-9:15-21:2-5:0.2-2:1000-1200.

[0020] Preferably, the mass ratio of the metal salt, the core-shell structured sodium-based polymer, and the sodium ion layered oxide is 1-10:1-10:100.

[0021] The present invention also provides a double-layer coated sodium-ion battery cathode material prepared by the aforementioned preparation method.

[0022] The present invention also provides a sodium-ion battery positive electrode, wherein the sodium-ion battery positive electrode comprises the aforementioned double-layer coated sodium-ion battery positive electrode material.

[0023] The present invention also provides a sodium-ion battery, wherein the sodium-ion battery includes the sodium-ion battery positive electrode.

[0024] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0025] This invention enhances the conductivity of electrode materials and improves their stability in electrolytes by double-coating layered oxides, while reducing the dissolution and leaching of transition metal elements, thereby improving the material's cycle stability and electrochemical performance. When the double-coated material is assembled into a battery, the initial charge-discharge specific capacity can reach up to 173 mAh·g within a voltage range of 1.5–4.1 V and at a rate of 0.1 C. -1 During charge and discharge, it exhibits good cycle performance due to its stable structure; after 50 cycles at 0.1C, the capacity retention rate can reach 96%, and the side reactions between the electrode and the electrolyte are reduced. The secondary-coated layered oxide material demonstrates excellent electrochemical performance. Attached Figure Description

[0026] Figure 1 This is a TEM image of the double-layered coated layered oxide material obtained in Example 1.

[0027] Figure 2 This is a SEM image of the double-layered coated layered oxide material obtained in Example 1.

[0028] Figure 3 The graphs show the initial charge-discharge curves at 0.1C for the materials prepared in Example 1 and Comparative Example 1.

[0029] Figure 4 The graph shows the capacity retention of the coin cells in the materials prepared in Example 1 and Comparative Example 1.

[0030] Figure 5 The graph shows the change in the amount of metal ions dissolved in the electrolyte after 100 cycles for the examples and comparative samples. Detailed Implementation

[0031] Example 1

[0032] 1) Weigh out 3g of aluminum nitrate and 100g of layered oxide Na 0.67 Mn 0.47 Fe 0.17 Ni 0.24 Ti 0.12 O2, mix thoroughly to obtain mixture 1;

[0033] 2) Add mixture 1 and milling beads into a milling jar at a mass ratio of 1:2, add anhydrous ethanol of the same mass as mixture 1 as a dispersant, and perform wet milling at a speed of 500 rpm / min for 5 h. After milling, take out the mixture, dry it, and place it in a muffle furnace at 500℃ for 3 h. After cooling and grinding, the alumina-coated cathode material is obtained.

[0034] 3) Disperse 10g of alumina-coated cathode material into 100g of water, add 0.1g of polyvinyl alcohol, introduce nitrogen gas, add 0.5g of sodium acrylate, 2g of styrene, 0.35g of magnesium acrylate, and 0.1g of initiator (azobisisobutyronitrile), heat and stir at 60℃ for 6h, filter, and dry to obtain a core-shell structured sodium-based polymer.

[0035] 4) Weigh 5g of core-shell structured sodium-based polymer and 20g of alumina-coated cathode material according to the ratio, mix them thoroughly to obtain mixture 2;

[0036] 5) Add mixture 2 and the ball milling beads into a ball milling jar at a mass ratio of 1:2, add anhydrous ethanol of the same mass as mixture 2 as a dispersant, and perform wet ball milling at a speed of 800 rpm / min for 3 hours. After ball milling, take out the material, dry it thoroughly, place it in a tube furnace, and calcine it at 600℃ for 2 hours with high-purity nitrogen as a protective gas. After cooling and grinding, a double-layer coated sodium-ion battery cathode material is obtained.

[0037] TEM and SEM images of the double-layer coated sodium-ion battery cathode material prepared in Example 1 are shown below. Figure 1 and Figure 2 As shown.

[0038] Example 2

[0039] 1) Weigh out 1g of aluminum nitrate and 100g of layered oxide Na 0.67 Mn 0.52 Fe 0.15 Ni 0.23 Ti 0.10 O2, mix thoroughly to obtain mixture 1;

[0040] 2) Add mixture 1 and milling beads into a milling jar at a mass ratio of 1:2, add anhydrous ethanol of the same mass as mixture 1 as a dispersant, and perform wet milling at a speed of 800 rpm / min for 5 h. After milling, take out the mixture, dry it, and place it in a muffle furnace at 500℃ for 3 h. After cooling and grinding, the alumina-coated cathode material is obtained.

[0041] 3) Disperse 10g of alumina-coated cathode material into 100g of water, add 0.02g of polyvinyl alcohol, purge with nitrogen, add 0.5g of sodium acrylate, 1.5g of styrene, 0.2g of magnesium acrylate, and 0.02g of initiator (azobisisobutyronitrile), heat and stir at 60℃ for 6h, filter, and dry to obtain a core-shell structured sodium-based polymer.

[0042] 4) Weigh 1g of core-shell structured sodium-based polymer and 10g of alumina-coated cathode material according to the ratio, mix them thoroughly to obtain mixture 2;

[0043] 5) Add mixture 2 and the ball milling beads into a ball milling jar at a mass ratio of 1:2, add anhydrous ethanol of the same mass as mixture 2 as a dispersant, and perform wet ball milling at a speed of 800 rpm / min for 3 hours. After ball milling, take out the material, dry it thoroughly, place it in a tube furnace, and calcine it at 600℃ for 2 hours with high-purity nitrogen as a protective gas. After cooling and grinding, a double-layer coated sodium-ion battery cathode material is obtained.

[0044] Example 3

[0045] 1) Weigh out 10g of titanium nitrate and 100g of layered oxide Na 0.70 Mn 0.41 Fe 0.17 Ni 0.30 Ti 0.12 O2, mix thoroughly to obtain mixture 1;

[0046] 2) Add mixture 1 and milling beads into a milling jar at a mass ratio of 1:2, add anhydrous ethanol of the same mass as mixture 1 as a dispersant, and perform wet milling at a speed of 500 rpm / min for 5 h. After milling, take out the mixture, dry it, and place it in a muffle furnace at 500℃ for 3 h. After cooling and grinding, titanium oxide-coated cathode material is obtained.

[0047] 3) Disperse 12g of titanium dioxide-coated cathode material into 120g of water, add 0.2g of polyvinyl alcohol, introduce nitrogen gas, add 0.9g of sodium acrylate, 2.1g of styrene, 0.5g of magnesium acrylate, and 0.2g of initiator (azobisisobutyronitrile), heat and stir at 70℃ for 4h, filter, and dry to obtain a core-shell structured sodium-based polymer.

[0048] 4) Weigh 10g of core-shell structured sodium-based polymer and 20g of titanium dioxide-coated cathode material according to the proportion, mix them thoroughly to obtain mixture 2;

[0049] 5) Add mixture 2 and milling beads to a milling jar at a mass ratio of 1:2, add anhydrous ethanol of the same mass as mixture 2 as a dispersant, and perform wet milling at a speed of 500 rpm / min for 3 hours. After milling, remove the material, dry it thoroughly, place it in a tube furnace, and calcine it at 600℃ for 2 hours with high-purity nitrogen as a protective gas. After cooling and grinding, a double-layer coated sodium-ion battery cathode material is obtained.

[0050] Comparative Example 1

[0051] 1) Weigh out 3g of aluminum nitrate and 100g of layered oxide Na 0.67 Mn 0.47 Fe 0.17 Ni 0.24 Ti 0.12 O2, mix thoroughly to obtain mixture 1;

[0052] 2) Add mixture 1 and milling beads into a milling jar at a mass ratio of 1:2, add anhydrous ethanol of the same mass as mixture 1 as a dispersant, and perform wet milling at a speed of 500 rpm / min for 5 h. After milling, take out the mixture, dry it, and place it in a muffle furnace at 500℃ for 3 h. After cooling and grinding, the alumina-coated cathode material is obtained.

[0053] Test Example 1

[0054] The sodium-ion battery cathode materials prepared in each embodiment and comparative example were mixed with conductive agent SP and binder PVDF (polyvinylidene fluoride) at a mass ratio of 7:2:1, and an appropriate amount of NMP was added until a slurry with suitable viscosity was formed by thorough stirring in a drying room. The prepared slurry was uniformly coated on the aluminum foil of the current collector, dried, and then punched into a circular electrode sheet of suitable size. After the suitable circular electrode sheet was fully baked under vacuum conditions, it was immediately transferred to a glove box for later use.

[0055] Battery Assembly: Battery assembly was performed in an Ar atmosphere glove box, using a sodium metal sheet as the negative electrode, glass fiber as the separator, and a 1 mol / L NaPF6 EC / DMC (volume ratio 1:1) solution as the electrolyte to assemble CR2032 coin cells. Constant current charge-discharge mode was used, and charge-discharge tests were conducted at a current density of 0.1C. The test conditions were: discharge cut-off voltage of 1.5V and charge cut-off voltage of 4.1V.

[0056] Figure 3 The first-week charge-discharge curves for Example 1 and Comparative Example 1 are shown. Example 1 exhibits a certain improvement in gram capacity compared to Comparative Example 1; within a voltage range of 1.5–4.1 V and at a 0.1C rate, the highest initial charge-discharge gram capacity reaches 173 mAh·g. -1 .

[0057] Figure 4 The capacity retention rates for Example 1 and Comparative Example 1 after 100 cycles are compared, with Example 1 showing a higher capacity retention rate; after 50 cycles at 0.1C, the capacity retention rate reaches 96%.

[0058] Figure 5 The figure represents the amount of transition metal ions dissolved in the electrolyte of Example 1 and Comparative Example 1 after 100 cycles. The amount of transition metal ions dissolved in Example 1 is less than that in the comparative example. After double-layer coating, there are fewer side reactions between the electrode and the electrolyte, and the electrode stability is improved, which is beneficial to the subsequent lifespan improvement.

Claims

1. A method for preparing a double-coated sodium-ion battery cathode material, characterized in that, Includes the following steps: (1) Mix the metal salt and sodium ion layered oxide Na x Mn a Fe b Ni c Ti d O2 well to obtain mixture 1; (2) After wet ball milling of the mixture 1 in step (1), it is dried and calcined to obtain a layer of coated positive electrode material; the calcination temperature is 500-600℃ and the calcination time is 5-10 h. (3) Preparation of core-shell structured sodium-based polymer: Disperse the layer of coated positive electrode material obtained in step (2) in water, add polyvinyl alcohol, pass in an inert gas, then add sodium acrylate, styrene, magnesium acrylate and initiator, heat and react, and filter to obtain core-shell structured sodium-based polymer. The initiator is azobisisobutyronitrile; the heating reaction conditions are: heating and stirring at 60°C for 6 hours. The mass ratio of the coated cathode material, polyvinyl alcohol, sodium acrylate, styrene, magnesium acrylate, initiator and water is 100:0.2-2:5-9:15-21:2-5:0.2-2:1000-1200. (4) The coated cathode material obtained in step (2) is thoroughly mixed with the core-shell structured sodium-based polymer obtained in step (3) to obtain mixture 2; (5) After wet ball milling of the mixture 2 in step (4), dry it and calcine it under an inert atmosphere to obtain a double-layer coated sodium-ion battery cathode material; the calcine temperature is 500-600℃, the calcine time is 5-10 h, and the inert atmosphere is nitrogen or argon. Na x Mn a Fe b Ni c Ti d 0.6 < x < 0.8, a + b + c + d = 1 The mass ratio of the metal salt, the core-shell structured sodium-based polymer, and the sodium ion layered oxide is 1-10:1-10:

100.

2. The production method according to claim 1, wherein The metal salt mentioned in step (1) is an aluminum salt, a magnesium salt, or a titanium salt.

3. The production method according to claim 1, wherein The specific steps of wet ball milling in steps (2) and (5) are as follows: the mixture and the ball milling beads are added to the ball milling jar at a mass ratio of 1:2, and anhydrous ethanol of the same mass as the mixture is added as a dispersant. Wet ball milling is carried out. During the ball milling process, the ball mill speed is 500-800 rpm / min and the ball milling time is 4-8h.

4. The double-layer coated sodium-ion battery cathode material prepared by the preparation method according to any one of claims 1 to 3.

5. A sodium-ion battery cathode, characterized in that, The sodium-ion battery cathode comprises the double-layer coated sodium-ion battery cathode material as described in claim 4.

6. A sodium-ion battery, characterized in that, The sodium-ion battery includes the sodium-ion battery positive electrode as described in claim 5.

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