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

Abstract

The present invention provides a sodium ion positive electrode material and a preparation method thereof, and a sodium ion battery. The sodium ion positive electrode material comprises a manganese-based positive electrode material and a coating layer coated on the manganese-based positive electrode material. The chemical formula of the manganese-based positive electrode material is Na x Mn y M 1‑y O2, wherein M is selected from any one of Cu, Fe, Co, and Ni, and 0.5≤x≤1, 0.5≤y≤1, and the coating layer is a lithium-containing ternary material, and the general chemical formula of the lithium-containing ternary material is LiNi a Co b Mn c O2,0

Description

Technical Field

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

[0002] Lithium-ion batteries are widely used in energy storage due to their high energy density and long cycle life. However, lithium resources are relatively low in abundance and unevenly distributed in the Earth's crust. As demand for batteries in the energy storage sector grows, the cost of lithium-ion batteries continues to rise. Sodium, which has similar physical and chemical properties to lithium and is abundant and inexpensive, operates on similar principles to lithium-ion batteries. Therefore, sodium-ion batteries are considered a new generation of high-performance, low-cost secondary battery technology.

[0003] Manganese-based layered materials have attracted widespread attention due to their advantages such as simple preparation, environmental friendliness, and high specific capacity. However, manganese-based cathode materials are susceptible to electrolyte corrosion during the charge and discharge process, which can alter the material structure and severely affect their cycling performance. Furthermore, sodium-ion batteries currently have a lower energy density than lithium-ion batteries. When using hard carbon as the negative electrode, the formation of the SEI film during the formation process consumes a large amount of sodium source, further reducing the active sodium source and energy density, thus limiting the further application of manganese-based materials.

[0004] In terms of improving the consumption of sodium sources by forming the SEI film, there are two methods: positive electrode sodium supplementation and negative electrode sodium supplementation. Usually, negative electrode pre-sodiumization is used to improve the consumption of sodium sources. Pre-sodiumization refers to the introduction of exogenous sodium into the battery system in a suitable manner and form. Negative electrode pre-sodiumization is divided into direct addition of exogenous sodium, active additive pre-sodiumization, electrochemical pre-sodiumization and chemical pre-sodiumization according to the pre-sodiumization method. The above methods all involve further processing of the coated negative electrode sheet, and even require direct use of metallic sodium for pre-sodiumization. These methods have high requirements for the workshop environment and equipment, and require a long time, which is not conducive to commercial application. Positive electrode sodium supplementation, such as coating with inactive substances to isolate the manganese-based layered material from the corrosion of the electrolyte, improves the cycle performance of the material, but at the same time affects its energy density. Summary of the Invention

[0005] The main purpose of the present invention is to provide a sodium ion positive electrode material and a preparation method thereof, and a sodium ion battery, so as to solve the problem of low capacity and poor cycle performance of the sodium ion positive electrode material in the prior art due to the consumption of sodium source in the first cycle.

[0006] In order to achieve the above object, according to one aspect of the present invention, a sodium ion positive electrode material is provided, which comprises a manganese-based positive electrode material and a coating layer coated on the manganese-based positive electrode material. The chemical formula of the manganese-based positive electrode material is Na x Mny M 1-y O2, wherein M is selected from any one of Cu, Fe, Co, and Ni, and 0.5≤x≤1, 0.5≤y≤1, and the coating layer is a lithium-containing ternary material, and the general chemical formula of the lithium-containing ternary material is LiNi a Co b Mn c O2,0 <a<1,0<b<1,0<c<1,a+b+c=1。

[0007] Furthermore, the coating layer is 5 to 20 wt % of the manganese-based positive electrode material, preferably 10 to 20 wt %, and further preferably 12 to 17 wt %.

[0008] Furthermore, the particle size of the sodium ion positive electrode material is 0.2 to 1 μm.

[0009] According to another aspect of the present invention, a method for preparing the aforementioned sodium ion positive electrode material is provided, the preparation method comprising: step S1, mixing and heating raw materials including a manganese-based positive electrode material, a lithium source, a nickel source, a cobalt source, a manganese source and a complexing agent to obtain a gel; step S2, sintering the gel in an oxygen-containing atmosphere to obtain a sodium ion positive electrode material.

[0010] Furthermore, the above-mentioned step S1 includes: step S11, mixing the raw materials to obtain a mixed solution; step S12, adjusting the pH value of the mixed solution to obtain a sol; step S13, heating the sol to obtain a gel; preferably the pH value is 7-8, the preferred heating temperature is 70-90°C, and the preferred heating method is water bath heating. The preferred mixing process includes: first mixing the manganese-based positive electrode material, lithium source, nickel source, cobalt source, manganese source and water to form a first solution; second mixing the complexing agent and water to form a second solution; dropwise adding the second solution to the first solution to obtain a mixed solution; preferably adjusting the pH value of the mixed solution by ammonia water, preferably the stirring speed of the first mixing is 400-600 r / min, preferably the stirring time of the first mixing is 3-5h, preferably the stirring speed of the second mixing is 300-500 r / min, and preferably the stirring time of the second mixing is 1-2h.

[0011] Furthermore, the molar ratio of the manganese-based positive electrode material, nickel source, cobalt source, and manganese source in the above-mentioned manganese-based positive electrode material, nickel source, cobalt source, and manganese source is 23-28:1.6-6.4:0.5-2:0.5-2:0.5-2, preferably 23-28:3.2-6.4:1-2:1-2:1-2, and more preferably 23-28:3.84-5.44:1.2-1.7:1.2-1.7:1.2-1.7; preferably, the lithium source is lithium carbonate and / or lithium hydroxide, preferably, the nickel source is selected from any one or more of nickel acetate, nickel sulfate, and nickel chloride, preferably, the cobalt source is selected from any one or more of cobalt acetate, cobalt sulfate, and cobalt chloride, and preferably, the manganese source is selected from any one or more of manganese acetate, manganese sulfate, and manganese chloride.

[0012] Furthermore, based on the transition metal ions contained in each component, the total molar number of the nickel source, the cobalt source, and the manganese source is n, and the ratio of the molar number of the complexing agent to n is 1 to 1.1:1. Preferably, the complexing agent is selected from any one or more of citric acid, glycolic acid, and acetic acid.

[0013] Furthermore, the sintering temperature is 800-1000° C., the sintering time is preferably 10-14 h, and the sintering heating rate is preferably 5-10° C. / min.

[0014] Furthermore, before the sintering, the gel is dried at a temperature of 400 to 450° C., and preferably for a drying time of 4 to 7 hours.

[0015] According to another aspect of the present invention, a sodium ion battery is provided, comprising a positive electrode and a negative electrode, wherein the positive electrode comprises a positive electrode material, and the positive electrode material is the aforementioned sodium ion positive electrode material.

[0016] By applying the technical solution of the present invention, the present invention addresses the problem that manganese-based positive electrode materials are easily corroded by the electrolyte and the problem of sodium source consumption during the formation of the SEI film. A lithium-containing ternary material with a larger capacity is used as a coating layer to coat the sodium ion positive electrode material. On the one hand, the coating layer reduces the corrosion of the manganese-based positive electrode material by the electrolyte. On the other hand, during the formation process, the lithium source of the lithium-containing ternary material is used as a sacrificial agent to generate a partial SEI film, thereby reducing the loss of active sodium source in the manganese-based positive electrode material, thereby improving the electrical properties of the sodium ion positive electrode material, such as the reversible capacity and cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0018] Figure 1 A schematic diagram of the first cycle charge and discharge curve of the cylindrical sodium ion battery of Example 1 at 2-4.1V is shown. DETAILED DESCRIPTION

[0019] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0020] As analyzed in the background art, the prior art has the problem that the sodium source consumption in the first cycle of the sodium ion positive electrode material leads to low capacity and poor cycle performance. To solve this problem, the present invention provides a sodium ion positive electrode material and a preparation method thereof, and a sodium ion battery.

[0021] In a typical embodiment of the present application, a sodium ion positive electrode material is provided, which includes a manganese-based positive electrode material and a coating layer coated on the manganese-based positive electrode material. The chemical formula of the manganese-based positive electrode material is Na x Mn y M 1-y O2, wherein M is selected from any one of Cu, Fe, Co, and Ni, and 0.5≤x≤1, 0.5≤y≤1, and the coating layer is a lithium-containing ternary material, the chemical formula of which is LiNi a Co b Mn c O2,0 <a<1,0<b<1,0<c<1,a+b+c=1。

[0022] The present invention addresses the problems of manganese-based positive electrode materials being easily corroded by the electrolyte and the problem of sodium source consumption during the formation of the SEI film. A lithium-containing ternary material with a larger capacity is used as a coating layer to coat the sodium ion positive electrode material. On the one hand, the coating layer reduces the corrosion of the manganese-based positive electrode material by the electrolyte. On the other hand, during the formation process, the lithium source of the lithium-containing ternary material is used as a sacrificial agent to generate a partial SEI film, thereby reducing the loss of active sodium source in the manganese-based positive electrode material, thereby improving the electrical properties of the sodium ion positive electrode material, such as the reversible capacity and cycle performance.

[0023] In order to further improve the protective effect of the coating layer on the manganese-based positive electrode material and reduce the loss of active sodium source, the coating layer is 5-20wt% of the manganese-based positive electrode material, preferably 10-20wt%, and further preferably 12-17wt%.

[0024] The particle size of the sodium ion positive electrode material is preferably 0.2 to 1 μm, so as to be more suitable for the use requirements of current positive electrode materials.

[0025] In another typical embodiment of the present application, a method for preparing the above-mentioned sodium ion positive electrode material is provided, which comprises: step S1, mixing and heating raw materials including a manganese-based positive electrode material, a lithium source, a nickel source, a cobalt source, a manganese source and a complexing agent to obtain a gel; step S2, sintering the gel in an oxygen-containing atmosphere to obtain a sodium ion positive electrode material.

[0026] In step S1 of the present application, after the raw materials are mixed, a low-viscosity solution is first formed in the solvent, thereby obtaining a molecular-level uniform sol in a short period of time. After heating, a molecular-level uniformly mixed gel is further formed. The preparation conditions of this sol-gel method are mild, the components are easy to control, the reaction time is short, and the temperature is controllable. The resulting particles are small and uniform in size. The gel is then sintered to obtain a sodium ion positive electrode material with uniform coating and uniform particles.

[0027] In order to improve the efficiency of sol forming gel, the above-mentioned step S1 preferably includes: step S11, mixing the raw materials to obtain a mixed solution; step S12, adjusting the pH value of the mixed solution to obtain a sol; step S13, heating the sol to obtain a gel; preferably the pH value is 7-8, the heating temperature is preferably 70-90°C, and the heating method is preferably water bath heating. The preferred mixing process includes: first mixing the manganese-based positive electrode material, lithium source, nickel source, cobalt source, manganese source and water to form a first solution; second mixing the complexing agent and water to form a second solution; dropwise adding the second solution to the first solution to obtain a mixed solution; preferably adjusting the pH value of the mixed solution by ammonia water, preferably the stirring speed of the first mixing is 400-600 r / min, preferably the stirring time of the first mixing is 3-5h, preferably the stirring speed of the second mixing is 300-500 r / min, and preferably the stirring time of the second mixing is 1-2h.

[0028] A manganese-based cathode material, a lithium source, a nickel source, a cobalt source, a manganese source, and water are first mixed to obtain a uniform first solution; a complexing agent is second mixed with water to form a uniform second solution; and the second solution is then dripped into the first solution to obtain a uniform mixed solution. The preferred stirring speed and time are conducive to obtaining uniform low-viscosity first and second solutions, and the dripping method of the second solution into the first solution helps to prevent the viscosity of the mixed solution from suddenly increasing too much, thereby facilitating the formation of a uniformly mixed gel sol at the molecular level. After heating and evaporating the water, a uniformly mixed gel at the molecular level is further formed. The gel is then sintered to obtain a uniformly coated, uniformly particle-sized sodium ion cathode material. The sol-gel method has mild preparation conditions, easy control of the components, short reaction time, and controllable temperature, and the resulting particles are small and uniform in size.

[0029] In one embodiment of the present application, the molar ratio of the manganese-based positive electrode material, the nickel source, the cobalt source, and the manganese source is 23-28:1.6-6.4:0.5-2:0.5-2:0.5-2, preferably 23-28:3.2-6.4:1-2:1-2:1-2, and more preferably 23-28:3.84-5.44:1.2-1.7:1.2-1.7:1.2-1.7; preferably, the lithium source is lithium carbonate and / or lithium hydroxide, the nickel source is preferably selected from any one or more of nickel acetate, nickel sulfate, and nickel chloride, the cobalt source is preferably selected from any one or more of cobalt acetate, cobalt sulfate, and cobalt chloride, and the manganese source is preferably selected from any one or more of manganese acetate, manganese sulfate, and manganese chloride.

[0030] The above ratio of raw materials and their types are conducive to their uniform dispersion in the solvent and obtain manganese-based positive electrode materials Na with excellent performance. x Mn y M 1-y O2 and lithium-containing ternary material LiNi coated on the manganese-based positive electrode material a Co b Mn c The amount of the O2 coating layer varies with the molar ratio of the lithium source, nickel source, cobalt source, and manganese source. The preferred molar ratio of the manganese-based positive electrode material, lithium source, nickel source, cobalt source, and manganese source is more conducive to the formation of Na x Mn y M 1-y LiNi with excellent O2 coating a Co b Mn c In the O2 coating layer, during the sintering process of the gel, the lithium source volatilizes and causes a small amount of loss, so a slightly excessive amount of lithium source is added.

[0031] In order to improve the complexing effect of the complexing agent with the metal ions in the raw materials, based on the transition metal ions contained in each component, the total molar number of the nickel source, the cobalt source, and the manganese source is n, and the ratio of the molar number of the complexing agent to n is 1 to 1.1:1. Preferably, the above-mentioned complexing agent is selected from any one or more of citric acid, glycolic acid, and acetic acid. Among them, although a slightly excessive amount of the complexing agent will not lead to a decrease in the electrical properties of the sodium ion positive electrode material, it will cause its waste, thereby increasing the cost.

[0032] In order to take into account both the sintering efficiency and the uniformity of the coating layer as much as possible, the sintering temperature is preferably 800-1000° C., the sintering time is preferably 10-14 h, and the sintering heating rate is preferably 5-10° C. / min.

[0033] In one embodiment of the present application, the gel is dried before the sintering, the drying temperature is 400-450° C., and the drying time is preferably 4-7 hours.

[0034] Drying the gel before sintering is beneficial to eliminate the interference of moisture in the gel on the sintering process.

[0035] In another typical embodiment of the present application, a sodium ion battery is provided, comprising a positive electrode and a negative electrode, wherein the positive electrode comprises a positive electrode material, and the positive electrode material is the above-mentioned sodium ion positive electrode material.

[0036] The sodium ion battery including the sodium ion positive electrode material of the present application has higher reversible capacity and longer life.

[0037] Among them, sodium-ion batteries mainly include: positive electrode, negative electrode, separator, electrolyte and shell.

[0038] In order to further improve the performance of sodium ion batteries, the preferred method for preparing the positive electrode includes:

[0039] Add a binder (polyvinylidene fluoride, sodium alginate, etc.) into N-methylpyrrolidone to prepare a glue solution with a concentration of 6%.

[0040] The sodium ion positive electrode material and the conductive agent (any one or more of graphite, carbon black, acetylene black, and graphene) prepared above in the present application are added to the glue and stirred evenly to obtain a slurry with a viscosity of 4500 to 6500 mPas·s. The slurry is coated on an aluminum foil, the solvent is removed at high temperature, and the positive electrode is obtained after roller pressing and slitting. The mass ratio of the above-mentioned sodium ion positive electrode material, conductive agent, and binder is 97:2:1.

[0041] The preferred method for preparing the negative electrode includes:

[0042] Hard carbon, thickener CMC, and binder SBR were added to deionized water in proportion to prepare a slurry, which was then coated on copper foil. The solvent was removed at high temperature, and the negative electrode was obtained after roller pressing and slitting. The mass ratio of hard carbon: CMC: SBR was 97:1.5:1.5.

[0043] The sodium salt in the electrolyte is any one or more of NaClO4, NaPF6, and NaTFSI, and the organic solvent in the electrolyte is any one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate.

[0044] The beneficial effects of the present application will be described below with reference to specific embodiments and comparative examples.

[0045] Example 1

[0046] Will Na 0.67MnO2, lithium carbonate, nickel acetate, cobalt acetate, manganese acetate (Na 0.67 MnO2, nickel acetate, cobalt acetate, manganese acetate (calculated as transition metal ions in each component, lithium carbonate (calculated as lithium ions)) are dissolved in water in a molar ratio of 26:4.48:1.4:1.4:1.4 to form a first solution. 0.67 The molar ratio of MnO2 to citric acid is 26:4.2) and added to water for a second mixing to form a second solution, and the second solution is dripped into the first solution to obtain a mixed solution. Among them, the stirring speed of the first mixing is 600r / min, the stirring time of the first mixing is 3h, the stirring speed of the second mixing is 500r / min, and the stirring time of the second mixing is 1h. The pH value of the mixed solution is adjusted to between 7 and 8 with ammonia water to obtain a sol. The sol water bath is heated to 80°C, and the water is removed to obtain a gel. The gel is dried at 450°C for 5 hours. The gel is then sintered at 900°C (heating rate of 5-10°C / min) for 12 hours to obtain LiNi a Co b Mn c The first cycle charge and discharge curve of the sodium ion positive electrode material with an O2 coating amount of 14wt% at 2~4.1V is as follows Figure 1 As shown, its charge capacity is 103 mAh / g and its discharge capacity is 84.5 mAh / g.

[0047] Example 2

[0048] The difference between Example 2 and Example 1 is that:

[0049] Na 0.67 MnO2, lithium carbonate, nickel acetate, cobalt acetate, manganese acetate (Na 0.67 The molar ratio of MnO2, nickel acetate, cobalt acetate, and manganese acetate (calculated as the transition metal ions contained in each component, and lithium carbonate (calculated as lithium ions)) is 26:3.84:1.2:1.2:1.2, Na 0.67 The molar ratio of MnO2 to citric acid is 26:3.6, and a sodium ion positive electrode material with a coating amount of 12wt% is finally obtained.

[0050] Example 3

[0051] The difference between Example 3 and Example 1 is that:

[0052] Na 0.67 MnO2, lithium carbonate, nickel acetate, cobalt acetate, manganese acetate (Na 0.67 The molar ratio of MnO2, nickel acetate, cobalt acetate, and manganese acetate (calculated as transition metal ions in each component, and lithium carbonate (calculated as lithium ions)) is 26:5.44:1.7:1.7:1.7, Na0.67 The molar ratio of MnO2 to citric acid is 26:5.1, and a sodium ion positive electrode material with a coating amount of 17wt% is finally obtained.

[0053] Example 4

[0054] The difference between Example 4 and Example 1 is that,

[0055] Na 0.67 MnO2, lithium carbonate, nickel acetate, cobalt acetate, manganese acetate (Na 0.67 The molar ratio of MnO2, nickel acetate, cobalt acetate, and manganese acetate (calculated as transition metal ions in each component, and lithium carbonate (calculated as lithium ions)) is 26:3.2:1:1:1, Na 0.67 The molar ratio of MnO2 to citric acid is 26:3, and a sodium ion positive electrode material with a coating amount of 10wt% is finally obtained.

[0056] Example 5

[0057] The difference between Example 5 and Example 1 is that,

[0058] Na 0.67 MnO2, lithium carbonate, nickel acetate, cobalt acetate, manganese acetate (Na 0.67 The molar ratio of MnO2, nickel acetate, cobalt acetate, and manganese acetate (calculated as transition metal ions in each component, and lithium carbonate (calculated as lithium ions)) is 26:6.4:2:2:2, Na 0.67 The molar ratio of MnO2 to citric acid is 26:6, and a sodium ion positive electrode material with a coating amount of 20% is finally obtained.

[0059] Example 6

[0060] The difference between Example 6 and Example 1 is that:

[0061] Na 0.67 MnO2, lithium carbonate, nickel acetate, cobalt acetate, manganese acetate (Na 0.67 The molar ratio of MnO2, nickel acetate, cobalt acetate, and manganese acetate (calculated as transition metal ions in each component, and lithium carbonate (calculated as lithium ions)) is 26:1.6:0.5:0.5:0.5, Na 0.67 The molar ratio of MnO2 to citric acid is 26:1.5, and a sodium ion positive electrode material with a coating amount of 5% is finally obtained. Its first cycle charge and discharge curve at 2-4.1V shows that its charge capacity is 89.3mAh / g and its discharge capacity is 71.2mAh / g.

[0062] Example 7

[0063] The difference between Example 7 and Example 1 is that

[0064] Na0.67 MnO2, lithium chloride, nickel chloride, cobalt chloride, manganese chloride (Na 0.67 The molar ratio of MnO2, nickel chloride, cobalt chloride, and manganese chloride (calculated as transition metal ions contained in each component, and lithium chloride (calculated as lithium ions)) is 26:4.48:1.4:1.4:1.4, and a sodium ion positive electrode material with a coating amount of 14% is finally obtained.

[0065] Example 8

[0066] The difference between Example 8 and Example 1 is that,

[0067] The complexing agent is glycolic acid, and a sodium ion positive electrode material with a coating amount of 14 wt% is finally obtained.

[0068] Example 9

[0069] The difference between Example 9 and Example 1 is that

[0070] Na 0.67 MnO2, lithium carbonate, nickel acetate, cobalt acetate, manganese acetate (Na 0.67 The molar ratio of MnO2, nickel acetate, cobalt acetate, and manganese acetate (calculated as transition metal ions in each component, and lithium carbonate (calculated as lithium ions)) is 23:4.48:1.4:1.4:1.4, Na 0.67 The molar ratio of MnO2 to citric acid is 26:4.62, and a sodium ion positive electrode material with a coating amount of 14% is finally obtained.

[0071] Example 10

[0072] The difference between Example 10 and Example 1 is that

[0073] Na 0.67 MnO2, lithium carbonate, nickel acetate, cobalt acetate, manganese acetate (Na 0.67 The molar ratio of MnO2, nickel acetate, cobalt acetate, and manganese acetate (calculated as transition metal ions in each component, and lithium carbonate (calculated as lithium ions)) is 28:4.48:1.4:1.4:1.4, Na 0.67 The molar ratio of MnO2 to citric acid is 26:3.78, and a sodium ion positive electrode material with a coating amount of 14% is finally obtained.

[0074] Example 11

[0075] The difference between Example 11 and Example 1 is that

[0076] Na 0.67 MnO2, lithium carbonate, nickel acetate, cobalt acetate, manganese acetate (Na 0.67The molar ratio of MnO2, nickel acetate, cobalt acetate, and manganese acetate (calculated as transition metal ions in each component, and lithium carbonate (calculated as lithium ions)) is 30:4.48:1.4:1.4:1.4, Na 0.67 The molar ratio of MnO2 to citric acid is 26:6.3, and a sodium ion positive electrode material with a coating amount of 14% is finally obtained.

[0077] Example 12

[0078] The difference between Example 12 and Example 1 is that

[0079] The sol water bath was heated to 70° C. to remove moisture to obtain a gel, and finally a sodium ion positive electrode material with a coating amount of 14 wt % was obtained.

[0080] Example 13

[0081] The difference between Example 13 and Example 1 is that

[0082] The sol water bath was heated to 90° C. to remove moisture to obtain a gel, and finally a sodium ion positive electrode material with a coating amount of 14 wt % was obtained.

[0083] Example 14

[0084] The difference between Example 14 and Example 1 is that

[0085] The sol water bath was heated to 60° C. to remove moisture to obtain a gel, and finally a sodium ion positive electrode material with a coating amount of 14% was obtained.

[0086] Example 15

[0087] The difference between Example 15 and Example 1 is that

[0088] Ammonia water is used to adjust the pH value of the mixed solution to between 8 and 9 to obtain a sol, and finally a sodium ion positive electrode material with a coating amount of 14% is obtained.

[0089] Example 16

[0090] The difference between Example 16 and Example 1 is that

[0091] The gel was dried at 400° C. for 7 hours to finally obtain a sodium ion positive electrode material with a coating amount of 14%.

[0092] Example 17

[0093] The difference between Example 17 and Example 1 is that

[0094] The gel was sintered at 1000°C for 10 hours to finally obtain a sodium ion positive electrode material with a coating amount of 14%.

[0095] Example 18

[0096] The difference between Example 18 and Example 1 is that

[0097] The gel was sintered at 800°C for 14 hours to finally obtain a sodium ion positive electrode material with a coating amount of 14%.

[0098] Example 19

[0099] The difference between Example 19 and Example 1 is that

[0100] The gel was sintered at 750°C for 12 hours to finally obtain a sodium ion positive electrode material with a coating amount of 14%.

[0101] Example 20

[0102] The difference between Example 20 and Example 1 is that

[0103] Manganese-based cathode materials are Na 0.67 Mn 0.67 Ni 0.33 O2, and finally a sodium ion positive electrode material with a coating amount of 14% was obtained.

[0104] Example 21

[0105] The difference between Example 21 and Example 1 is that

[0106] The stirring speed of the first mixing was 400 r / min, and the stirring time of the first mixing was 5 h, and finally a sodium ion positive electrode material with a coating amount of 14% was obtained.

[0107] Example 22

[0108] The difference between Example 22 and Example 1 is that

[0109] The stirring speed of the first mixing was 350 r / min, and the stirring time of the first mixing was 3 h, and finally a sodium ion positive electrode material with a coating amount of 14% was obtained.

[0110] Example 23

[0111] The difference between Example 23 and Example 1 is that

[0112] The stirring speed of the first mixing was 300 r / min, and the stirring time of the first mixing was 2 h, and finally a sodium ion positive electrode material with a coating amount of 14% was obtained.

[0113] Example 24

[0114] The difference between Example 24 and Example 1 is that

[0115] The stirring speed of the first mixing was 250 r / min, and the stirring time of the first mixing was 1 h, and finally a sodium ion positive electrode material with a coating amount of 14% was obtained.

[0116] Example 25

[0117] The difference between Example 25 and Example 1 is that

[0118] The second solution is directly mixed with the first solution to obtain a mixed solution, and finally a sodium ion positive electrode material with a coating amount of 14% is obtained.

[0119] Comparative Example 1

[0120] The difference between Comparative Example 1 and Example 1 is that

[0121] The manganese-based positive electrode material is Na 0.67 MnO2 is directly used as the sodium ion positive electrode material.

[0122] Comparative Example 2

[0123] The difference between Comparative Example 2 and Example 20 is that,

[0124] The manganese-based positive electrode material is Na 0.67 Mn 0.67 Ni 0.33 O2 is directly used as the sodium ion positive electrode material.

[0125] The first cycle charge and discharge curve of the cylindrical sodium ion battery of Comparative Example 1 at 2-4.1V shows that its charge capacity is 85 mAh / g, discharge capacity is 67 mAh / g, and irreversible capacity is 18 mAh / g. 0.67 The charge capacity of MnO2 is 85 mAh / g, and the charge capacity of the sodium ion positive electrode material in Example 1 is 103 mAh / g. It can be seen that the coating performance of the manganese-based positive electrode material in this application can better compensate for the irreversible capacity loss in the first cycle.

[0126] The chemical formula of the coating layer of the sodium ion positive electrode material obtained in Examples 1 to 25 is LiNi 1 / 3 Co 1 / 3 Mn 1 / 3O2, the particle size of sodium ion positive electrode materials is basically in the range of 0.2 to 1 μm.

[0127] N-methylpyrrolidone was added in a ratio of sodium ion positive electrode material: Super P: PVDF = 97:2:1, wherein the solid content was 65%, and the mixture was stirred evenly to obtain a positive electrode slurry. The positive electrode slurry was coated on an aluminum foil with a thickness of 15 μm and dried to obtain a positive electrode.

[0128] N-methylpyrrolidone was added in a ratio of hard carbon: Super P: PVDF = 94:3:3 with a solid content of 52%, and stirred evenly to obtain a negative electrode slurry. The negative electrode slurry was coated on a copper foil with a thickness of 8 μm and dried to obtain a negative electrode.

[0129] Battery assembly: The positive electrode, negative electrode, and separator are wound together, and then the electrolyte (the sodium salt is NaClO4, and the organic solvent in the electrolyte is ethylene carbonate, propylene carbonate, and dimethyl carbonate in a volume ratio of 1:1:1) is injected to obtain a cylindrical sodium ion battery.

[0130] The initial discharge capacity, the residual capacity after 100 cycles, and the capacity retention rate after 100 cycles of the cylindrical sodium ion batteries of Examples 1 to 25, Comparative Example 1, and Comparative Example 2 were tested under 0.5C conditions, as shown in Table 1.

[0131] Table 1

[0132]

[0133]

[0134] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0135] The present invention addresses the problems of manganese-based positive electrode materials being easily corroded by the electrolyte and the problem of sodium source consumption during the formation of the SEI film. A lithium-containing ternary material with a larger capacity is used as a coating layer to coat the sodium ion positive electrode material. On the one hand, the coating layer reduces the corrosion of the manganese-based positive electrode material by the electrolyte. On the other hand, during the formation process, the lithium source of the lithium-containing ternary material is used as a sacrificial agent to generate a partial SEI film, thereby reducing the loss of active sodium source in the manganese-based positive electrode material, thereby improving the electrical properties of the sodium ion positive electrode material, such as the reversible capacity and cycle performance.

[0136] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a sodium ion positive electrode material, characterized in that: The preparation method comprises: Step S1, mixing and heating raw materials including a manganese-based positive electrode material, a lithium source, a nickel source, a cobalt source, a manganese source and a complexing agent to obtain a gel; Step S2, sintering the gel in an oxygen-containing atmosphere to obtain the sodium ion positive electrode material; The step S1 comprises: step S11, mixing the raw materials to obtain a mixed solution; step S12, adjusting the pH value of the mixed solution to obtain a sol; step S13, heating the sol to obtain the gel; The heating temperature is 70-90°C; the pH value is 7-8; the sintering temperature is 800-1000°C; and the sintering time is 10-14 hours; The mixing process includes: first mixing the manganese-based positive electrode material, the lithium source, the nickel source, the cobalt source, the manganese source and water to form a first solution; second mixing the complexing agent and water to form a second solution; and dripping the second solution into the first solution to obtain the mixed solution; The stirring speed of the first mixing is 400-600 r / min; the stirring time of the first mixing is 3-5 h; The sodium ion positive electrode material comprises a manganese-based positive electrode material and a coating layer coated on the manganese-based positive electrode material. The chemical formula of the manganese-based positive electrode material is Na x Mn y M 1-y O2, wherein M is selected from any one of Cu, Fe, Co, and Ni, and 0.5≤x≤1, 0.5≤y≤1, and the coating layer is a lithium-containing ternary material, and the general chemical formula of the lithium-containing ternary material is LiNi a Co b Mn c O2,0 <a<1,0<b<1,0<c<1,a+b+c=1; The coating layer is 5-20 wt% of the manganese-based positive electrode material.

2. The method for preparing a sodium ion positive electrode material according to claim 1, wherein The coating layer is 10-20 wt% of the manganese-based positive electrode material.

3. The method for preparing a sodium ion positive electrode material according to claim 1, wherein: The coating layer is 12-17 wt % of the manganese-based positive electrode material.

4. The method for preparing a sodium ion positive electrode material according to any one of claims 1 to 3, characterized in that: The particle size of the sodium ion positive electrode material is 0.2-1 μm.

5. The preparation method according to claim 1, characterized in that The heating method is water bath heating.

6. The preparation method according to claim 1, characterized in that The pH value of the mixed solution is adjusted by using aqueous ammonia.

7. The preparation method according to claim 1, characterized in that The stirring speed of the second mixing is 300-500 r / min.

8. The preparation method according to claim 1, characterized in that The stirring time of the second mixing is 1 to 2 hours.

9. The preparation method according to claim 1, characterized in that The molar ratio of the manganese-based positive electrode material, the nickel source, the cobalt source, and the manganese source is 23-28:1.6-6.4:0.5-2:0.5-2:0.5-2 in terms of the transition metal ions contained in each component, and the molar ratio of the lithium source is 23-28:1.6-6.4:0.5-2:0.5-2:0.5-2 in terms of the lithium ions contained in each component.

10. The preparation method according to claim 9, characterized in that The molar ratio of the manganese-based positive electrode material, the nickel source, the cobalt source, and the manganese source is 23~28:3.2~6.4:1~2:1~2:1~2, calculated based on the transition metal ions contained in each component, and the lithium source is calculated based on the lithium ions.

11. The preparation method according to claim 9, characterized in that The molar ratio of the manganese-based positive electrode material, the nickel source, the cobalt source, and the manganese source is 23~28:3.84~5.44:1.2~1.7: 1.2~1.7: 1.2~1.7, calculated based on the transition metal ions contained in each component, and the lithium source is calculated based on the lithium ions.

12. The preparation method according to claim 1, characterized in that The lithium source is lithium carbonate and / or lithium hydroxide; And / or, the nickel source is selected from any one or more of nickel acetate, nickel sulfate, and nickel chloride; And / or, the cobalt source is selected from any one or more of cobalt acetate, cobalt sulfate, and cobalt chloride; And / or, the manganese source is selected from any one or more of manganese acetate, manganese sulfate, and manganese chloride.

13. The preparation method according to claim 1, characterized in that Based on the transition metal ions contained in each component, the total molar number of the nickel source, the cobalt source, and the manganese source is n, and the ratio of the molar number of the complexing agent to n is 1-1.1:

1.

14. The preparation method according to claim 13, characterized in that The complexing agent is selected from any one or more of citric acid, glycolic acid and acetic acid.

15. The preparation method according to claim 1, characterized in that The heating rate of the sintering is 5-10°C / min.

16. The preparation method according to claim 1, characterized in that Before the sintering, the gel is dried at a temperature of 400-450°C.

17. The preparation method according to claim 16, characterized in that The drying time is 4 to 7 hours.

18. A sodium ion battery comprising a positive electrode and a negative electrode, wherein the positive electrode comprises a positive electrode material, characterized in that: The positive electrode material is a sodium ion positive electrode material obtained by the preparation method according to any one of claims 1 to 17.

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