Sodium-ion battery positive electrode precursor and preparation method thereof

Abstract

The application discloses a sodium ion battery positive electrode precursor and a preparation method thereof. x Mn (1‑x‑y) M1 y (OH)2, M1 is a low-valence transition metal, 0.1<=x<0.5, 0.1<=y<0.5; the chemical formula of the shell layer is Ni a Mn (1‑a‑b) M2 b (OH)2, M2 is a high-valence transition metal, 0.6<=a<0.9, 0.01<=b<0.5, a+b<1. The application effectively solves the problems of structural instability of a sodium ion positive electrode material, slow sodium ion embedding / extraction speed and formation of particle microcracks in a long cycle process by adopting a low-valence transition metal to replace part of nickel and manganese to form a low-nickel core layer and by introducing a high-valence transition metal to replace part of nickel and manganese to form a high-nickel shell layer arranged in a radial manner, thereby improving the rate performance and cycle stability of the sodium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, and particularly relates to a sodium-ion battery positive electrode precursor and its preparation method. Background Technology

[0002] In recent years, my country's energy demand has continued to grow rapidly. Although renewable energy sources such as solar and wind power can meet current needs to some extent, their availability depends on climate and geographical changes and they are difficult to store. Therefore, energy storage systems are attracting increasing attention. Currently, lithium-ion batteries are the most widely used energy storage device. However, the low abundance of lithium in the Earth's crust makes them insufficient to meet the ever-growing future demand. Sodium batteries, on the other hand, have attracted significant attention due to their abundant resources, low cost, high energy density, and similar energy storage mechanism to lithium-ion batteries. To accelerate the commercialization of sodium-ion batteries, exploring advanced cathode materials with superior battery performance is crucial.

[0003] Currently, sodium-ion cathode materials mainly include layered oxides, multi-anion compounds, and Prussian blue analogs. Among them, layered transition metal oxides have attracted widespread attention due to their advantages such as large specific capacity, high operating potential, simple synthesis, and environmental friendliness. Unfortunately, the sodium ion radius... It is the radius of lithium ions The sodium ion cathode material has a 1.3 times larger size, which leads to a larger volume change during charge and discharge, thus reducing the stability of the electrode material structure. At the same time, from a kinetic point of view, the insertion / deintercalation rate of the larger sodium ions in the anode material is slower. In addition, during long-term cycling, fatigue strain caused by lattice contraction / expansion will inevitably generate microcracks, which will lead to more active surface exposure, exacerbate the side reactions between the electrode and electrolyte, and further lead to the deterioration of capacity and rate performance.

[0004] Therefore, there is an urgent need for a sodium-ion battery cathode precursor and its preparation method to address the shortcomings of existing technologies. Summary of the Invention

[0005] The purpose of this invention is to provide a sodium-ion battery cathode precursor that has good structural stability and can improve the rate performance and cycle stability of sodium-ion batteries.

[0006] Another objective of this invention is to provide a method for preparing a sodium-ion battery cathode precursor, through which the above-mentioned sodium-ion battery cathode precursor can be obtained.

[0007] To achieve the above objectives, this invention provides a sodium-ion battery cathode precursor. The precursor is a spherical or near-spherical particle composed of a core layer and a shell layer. The chemical formula of the core layer is Ni. x Mn 1-x-y M1 y (OH)₂, M₁ is a low-valence transition metal, 0.1≤x<0.5, 0.1≤y<0.5; the shell's chemical formula is Ni. a Mn 1-a-b M2 b (OH)2, M2 is a high-valence transition metal, 0.6≤a≤0.9, 0.01≤b<0.5, a+b<1.

[0008] Compared with existing technologies, this invention uses low-valence transition metals to replace part of nickel and manganese to form a low-nickel core layer. This helps reduce the Jameer-Taylor effect of manganese and suppresses the phase transition of sodium ions during insertion / extraction, thereby reducing the volume change of the electrode material during charge and discharge and improving the structural stability of the electrode material. Simultaneously, replacing part of nickel and manganese with low-valence transition metals can also effectively improve the electronic conductivity of the material, reduce polarization during charge and discharge, and further improve the structural stability of the sodium-ion battery electrode material. Furthermore, by introducing high-valence transition metals to replace part of nickel and manganese to induce a radially arranged primary grain precursor, the radially arranged high-nickel shell facilitates the direct diffusion of sodium ions from the particle center to the surface, shortening the diffusion path and reducing crossing of grain boundaries, thereby improving its rate performance. In addition, the radially ordered primary grains have a consistent crystal orientation, which can significantly reduce the intergranular stress induced by volume change through synergistic expansion and contraction, thereby significantly suppressing the formation of microcracks in the particles and promoting cycle stability.

[0009] Preferably, in this invention, 0.2≤x≤0.45, 0.1≤y≤0.35, 0.5≤x+y≤0.7; 0.6≤a≤0.9, 0.01≤b≤0.1, 0.61≤a+b≤0.9. Specifically, the molar ratio of Ni:Mn:M1 is 20~45:30~50:10~35, and the molar ratio of Ni:Mn:M2 is 60~90:10~39:1~10.

[0010] Preferably, the precursor of the present invention has a particle size D50 of 3–14 μm and a specific surface area of ​​8–50 m². 2 / g, tap density is 0.8~2.4g / cm³ 3 .

[0011] Preferably, the core layer of the present invention has a particle size D50 of 2–11 μm, and the shell layer has a particle size D50 of 1–3 μm. The core layer of the present invention is low-nickel, and the shell layer is relatively thin and high-nickel, which makes it easier to form a radial structure, which is beneficial to improving the rate performance and cycle stability of sodium-ion batteries.

[0012] Preferably, the low-valence transition metal of the present invention is at least one of iron (Fe), copper (Cu), magnesium (Mg) and zinc (Zn), and the high-valence transition metal is at least one of vanadium (V), niobium (Nb) and molybdenum (Mo).

[0013] To achieve the above objectives, the present invention also provides a method for preparing a sodium-ion battery cathode precursor, comprising the following steps:

[0014] (1) Prepare core metal salt solutions and shell metal salt solutions respectively. In the core metal salt solution, the molar ratio of Ni, Mn, and M1 is x:1-xy:y, and the total molar concentration of Ni, Mn, and M1 ions is controlled at 1-3 mol / L. In the shell metal salt solution, the molar ratio of Ni, Mn, and M2 is a:1-ab:b, and the total molar concentration of Ni, Mn, and M2 ions is controlled at 0.1-2 mol / L.

[0015] (2) Under a protective atmosphere, the first complexing agent, the first precipitant, and the core layer metal salt solution are added to the bottom liquid to carry out a core layer coprecipitation reaction to obtain core layer precursor particles with the first target particle size;

[0016] (3) Under a protective atmosphere, the second complexing agent, the second precipitant, and the shell metal salt solution are added to the system after the reaction in step (2) to carry out a shell coprecipitation reaction to obtain core-shell precursor particles with the second target particle size.

[0017] (4) The core-shell precursor particles are post-processed to obtain the sodium-ion battery cathode precursor.

[0018] Compared with the prior art, the preparation method of the present invention uses a low-valence transition metal to replace part of nickel and manganese to form a low-nickel core layer, and introduces a high-valence transition metal to replace part of nickel and manganese to form a radially arranged high-nickel shell layer. This effectively solves the problems of structural instability of sodium ion cathode materials, slow sodium ion insertion / deintercalation speed, and particle microcrack formation during long cycling.

[0019] Preferably, the preparation of the base liquid of the present invention includes: adding a first complexing agent and a first precipitant to pure water under a protective atmosphere, adjusting the pH to 9.00 to 13.00 and heating to 30 to 70°C.

[0020] Preferably, the first complexing agent and the second complexing agent of the present invention are each independently selected from at least one of ammonia, ammonium bicarbonate, and ammonium carbonate, and the first precipitant and the second precipitant are each independently selected from at least one of sodium hydroxide, potassium hydroxide, and sodium carbonate. More preferably, the first complexing agent and the second complexing agent of the present invention are both ammonia, and the first precipitant and the second precipitant are both sodium hydroxide. More specifically, the mass fraction of ammonia is 2-16%, and the concentration of sodium hydroxide is 2-10 mol / L.

[0021] Preferably, step (2) of the present invention includes: under a protective atmosphere, adding the first complexing agent, the first precipitant, and the core layer metal salt solution to the base liquid at a flow rate of 10-100 mL / min to carry out a core layer coprecipitation reaction to obtain core layer precursor particles of 2-11 μm; wherein the pH value of the core layer coprecipitation reaction is 8-13, the temperature is 30-70°C, and the stirring speed is 400-800 r / min.

[0022] Preferably, step (3) of the present invention includes: under a protective atmosphere, adding the second complexing agent, the second precipitant, and the shell metal salt solution to the system after the reaction in step (2) at a flow rate of 10-100 mL / min to carry out a shell coprecipitation reaction to obtain core-shell precursor particles of 3-14 μm; wherein the pH value of the shell coprecipitation reaction is 8-13, the temperature is 30-70℃, and the stirring speed is 400-800 r / min. The present invention can induce a radially arranged primary grain precursor by introducing a high-valence transition metal to replace part of nickel and manganese and adjusting the reaction parameters (such as pH) of the shell coprecipitation.

[0023] Preferably, the protective atmosphere of the present invention is an atmosphere in which a protective gas is formed. Specifically, the protective gas may be, but is not limited to, nitrogen, helium, or argon.

[0024] Specifically, the core metal salt solution of the present invention is a mixed solution composed of nickel salt, manganese salt and M1 salt, and the shell metal salt solution is a mixed solution composed of nickel salt, manganese salt and M2 salt. The specific types of nickel salt, manganese salt, M1 salt and M2 salt are not particularly limited. For example, nickel salt can be at least one of nickel nitrate, nickel sulfate and nickel chloride; manganese salt can be at least one of manganese nitrate, manganese sulfate and manganese chloride; M1 salt can be at least one of ferric sulfate, ferrous sulfate, ferric chloride, ferrous chloride, ferric nitrate, ferrous nitrate, copper sulfate, copper chloride, copper nitrate, magnesium sulfate, magnesium chloride, magnesium nitrate, zinc sulfate, zinc chloride and zinc nitrate; M2 salt can be a sodium vanadate solution prepared by dissolving vanadium pentoxide or ammonium metavanadate in an alkaline solution (sodium hydroxide or sodium carbonate); M2 salt can also be a sodium niobate solution prepared by dissolving niobium pentoxide in an alkaline solution (sodium hydroxide or sodium carbonate); M2 salt can also be at least one of molybdenum nitrate, molybdenum chloride, ammonium molybdate, niobium pentachloride, niobium oxalate and niobium nitrate.

[0025] Preferably, both the core-shell coprecipitation reaction and the shell-shell coprecipitation reaction of the present invention are carried out in a reaction vessel.

[0026] Preferably, the post-processing in step (4) of the present invention includes, in sequence, aging, pressure filtration, washing and drying. Attached Figure Description

[0027] Figure 1 This is a CP diagram of the sodium-ion battery positive electrode precursor of Example 1 of the present invention. Detailed Implementation

[0028] To further understand the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] The sources of all raw materials used in this invention are not particularly limited; they can be purchased commercially or prepared using conventional methods well-known to those skilled in the art. The purity of all raw materials used in this invention is not particularly limited; however, analytical grade or conventional purity levels used in the field of sodium-ion batteries are preferred.

[0030] Example 1

[0031] This embodiment provides a sodium-ion battery cathode precursor. The precursor is a spherical or near-spherical particle composed of a core layer and a shell layer. The chemical formula of the core layer is Ni. 0.33 Mn 0.34 Fe 0.33 (OH)₂; the chemical formula of the shell is Ni 0.8 Mn 0.1 Nb 0.1 (OH)2.

[0032] The method for preparing the sodium-ion battery cathode precursor in this embodiment includes the following steps:

[0033] (1) Weigh out nickel nitrate, manganese nitrate and ferric nitrate according to the molar ratio of Ni:Mn:Fe of 33:34:33, and dissolve them together in water to prepare a core metal salt solution. The total molar concentration of Ni, Mn and Fe ions is 2 mol / L. Weigh out nickel nitrate, manganese nitrate and sodium niobate according to the molar ratio of Ni:Mn:Nb of 80:10:10, and dissolve them together in water to prepare a shell metal salt solution. The total molar concentration of Ni, Mn and Nb ions is 1 mol / L.

[0034] (2) Under nitrogen protection, 6% ammonia water, 4 mol / L sodium hydroxide and pure water were added to the reactor to obtain a bottom liquid with a pH of 9.0. The reactor was then heated to 40°C and stirred at 200 r / min. 6% ammonia water, 4 mol / L sodium hydroxide and core layer metal salt solution were then added to the bottom liquid at a flow rate of 50 mL / min to carry out a core layer coprecipitation reaction to obtain core layer precursor particles with a particle size of 4 μm. The pH of the core layer coprecipitation reaction was 8.5-9.0, the temperature was 40°C and the stirring speed was 500 r / min.

[0035] (3) Under a protective atmosphere, 8% ammonia water, 4 mol / L sodium hydroxide and shell metal salt solution were added to the system after the reaction in step (2) at a flow rate of 50 mL / min to carry out shell coprecipitation reaction to obtain core-shell precursor particles with a particle size of 6 μm; wherein the pH value of the shell coprecipitation reaction was 9.0 to 9.5, the temperature was 40℃ and the stirring speed was 500 r / min;

[0036] (4) The core-shell precursor particles are sequentially aged, filtered, washed and dried to obtain sodium-ion battery cathode precursor.

[0037] The obtained sodium-ion battery cathode precursor has a particle size D50 of 6.2 μm and a specific surface area of ​​11.5 m². 2 / g, tap density is 1.6g / cm³ 3 .

[0038] Example 2

[0039] This embodiment provides a sodium-ion battery cathode precursor. The precursor is a spherical or near-spherical particle composed of a core layer and a shell layer. The chemical formula of the core layer is Ni. 0.25 Mn 0.40 Fe 0.35 (OH)₂; the chemical formula of the shell is Ni 0.8 Mn 0.1 Nb 0.1 (OH)2.

[0040] The method for preparing the sodium-ion battery cathode precursor in this embodiment includes the following steps:

[0041] (1) Weigh out nickel nitrate, manganese nitrate and ferric nitrate according to the molar ratio of Ni:Mn:Fe of 25:40:35, and dissolve them together in water to prepare a core metal salt solution. The total molar concentration of Ni, Mn and Fe ions is 2 mol / L. Weigh out nickel nitrate, manganese nitrate and sodium niobate according to the molar ratio of Ni:Mn:Nb of 80:10:10, and dissolve them together in water to prepare a shell metal salt solution. The total molar concentration of Ni, Mn and Nb ions is 1 mol / L.

[0042] (2) Under nitrogen protection, 6% ammonia water, 4 mol / L sodium hydroxide and pure water were added to the reactor to obtain a bottom liquid with a pH of 9. The reactor was then heated to 40°C and stirred at 200 r / min. 6% ammonia water, 4 mol / L sodium hydroxide and core layer metal salt solution were then added to the bottom liquid at a flow rate of 50 mL / min to carry out a core layer coprecipitation reaction to obtain core layer precursor particles with a particle size of 4 μm. The pH of the core layer coprecipitation reaction was 8.2-8.5, the temperature was 40°C and the stirring speed was 500 r / min.

[0043] (3) Under a protective atmosphere, 8% ammonia water, 4 mol / L sodium hydroxide and shell metal salt solution were added to the system after the reaction in step (2) at a flow rate of 50 mL / min to carry out shell coprecipitation reaction to obtain core-shell precursor particles with a particle size of 6 μm; wherein the pH value of the shell coprecipitation reaction was 8.5-9.0, the temperature was 40℃, and the stirring speed was 500 r / min;

[0044] (4) The core-shell precursor particles are sequentially aged, filtered, washed and dried to obtain sodium-ion battery cathode precursor.

[0045] The obtained sodium-ion battery cathode precursor has a particle size D50 of 6.5 μm and a specific surface area of ​​10.8 m². 2 / g, tap density is 1.6g / cm³ 3 .

[0046] Example 3

[0047] This embodiment provides a sodium-ion battery cathode precursor. The precursor is a spherical or near-spherical particle composed of a core layer and a shell layer. The chemical formula of the core layer is Ni. 0.33 Mn 0.34 Fe 0.33 (OH)₂; the chemical formula of the shell is Ni 0.8 Mn 0.15 V 0.05 (OH)2.

[0048] The method for preparing the sodium-ion battery cathode precursor in this embodiment includes the following steps:

[0049] (1) Weigh out nickel nitrate, manganese nitrate and ferric nitrate according to the molar ratio of Ni:Mn:Fe of 33:34:33, and dissolve them together in water to prepare a core metal salt solution. The total molar concentration of Ni, Mn and Fe ions is 2 mol / L. Weigh out nickel nitrate, manganese nitrate and sodium vanadate according to the molar ratio of Ni:Mn:V of 80:15:5, and dissolve them together in water to prepare a shell metal salt solution. The total molar concentration of Ni, Mn and V ions is 0.5 mol / L.

[0050] (2) Under nitrogen protection, 8% ammonia water, 5 mol / L sodium hydroxide and pure water were added to the reactor to obtain a bottom liquid with a pH of 10. The reactor was then heated to 40°C and stirred at 300 r / min. 10% ammonia water, 5 mol / L sodium hydroxide and core layer metal salt solution were added to the bottom liquid at a flow rate of 60 mL / min to carry out a core layer coprecipitation reaction to obtain core layer precursor particles with a particle size of 10 μm. The pH of the core layer coprecipitation reaction was 9.2-9.6, the temperature was 40°C and the stirring speed was 600 r / min.

[0051] (3) Under a protective atmosphere, 10% ammonia water, 5 mol / L sodium hydroxide and shell metal salt solution were added to the system after the reaction in step (2) at a flow rate of 30 mL / min to carry out shell coprecipitation reaction to obtain core-shell precursor particles with a particle size of 12 μm; wherein the pH value of the shell coprecipitation reaction was 10.1 to 10.8, the temperature was 45℃, and the stirring speed was 700 r / min;

[0052] (4) The core-shell precursor particles are sequentially aged, filtered, washed and dried to obtain sodium-ion battery cathode precursor.

[0053] The obtained sodium-ion battery cathode precursor has a particle size D50 of 12.3 μm and a specific surface area of ​​10.3 m². 2 / g, tap density is 2.0g / cm³ 3 .

[0054] Comparative Example 1

[0055] This comparative example provides a sodium-ion battery cathode precursor. The precursor is a spherical or near-spherical particle composed of a core layer, the chemical formula of which is Ni. 0.33 Mn 0.34 Fe 0.33 (OH)2.

[0056] The preparation method of the sodium-ion battery cathode precursor in this comparative example includes the following steps:

[0057] (1) Weigh out nickel nitrate, manganese nitrate and ferric nitrate according to the molar ratio of Ni:Mn:Fe of 33:34:33. Dissolve nickel nitrate, manganese nitrate and ferric nitrate together in water to prepare a core layer metal salt solution. The total molar concentration of Ni, Mn and Fe ions is 2 mol / L.

[0058] (2) Under nitrogen protection, 6% ammonia water, 4 mol / L sodium hydroxide and pure water were added to the reactor to obtain a bottom liquid with a pH of 9.0. The reactor was then heated to 40°C and stirred at 200 r / min. 6% ammonia water, 4 mol / L sodium hydroxide and core layer metal salt solution were then added to the bottom liquid at a flow rate of 50 mL / min to carry out a core layer coprecipitation reaction to obtain core layer precursor particles with a particle size of 6 μm. The pH of the core layer coprecipitation reaction was 8.5–9.0, the temperature was 40°C and the stirring speed was 500 r / min.

[0059] (3) The core layer precursor particles are subjected to aging, pressure filtration, washing and drying processes in sequence to obtain sodium-ion battery cathode precursor.

[0060] The obtained sodium-ion battery cathode precursor has a particle size D50 of 6.3 μm and a specific surface area of ​​11.2 m². 2 / g, tap density is 1.4g / cm³ 3 .

[0061] Comparative Example 2

[0062] This comparative example provides a sodium-ion battery cathode precursor. The precursor is a spherical or near-spherical particle composed of a core layer and a shell layer. The chemical formula of the core layer is Ni. 0.8 Mn 0.1 Nb 0.1 (OH)₂, the chemical formula of the shell is Ni 0.33 Mn 0.34 Fe 0.33 (OH)2.

[0063] The preparation method of the sodium-ion battery cathode precursor in this comparative example includes the following steps:

[0064] (1) Weigh out nickel nitrate, manganese nitrate and ferric nitrate according to the molar ratio of Ni:Mn:Fe of 33:34:33, and dissolve them together in water to prepare a core metal salt solution. The total molar concentration of Ni, Mn and Fe ions is 2 mol / L. Weigh out nickel nitrate, manganese nitrate and sodium niobate according to the molar ratio of Ni:Mn:Nb of 80:10:10, and dissolve them together in water to prepare a shell metal salt solution. The total molar concentration of Ni, Mn and Nb ions is 1 mol / L.

[0065] (2) Under nitrogen protection, 6% ammonia water, 4 mol / L sodium hydroxide and pure water were added to the reactor to obtain a bottom liquid with a pH of 9.0. The reactor was then heated to 40°C and stirred at 200 r / min. 8% ammonia water, 4 mol / L sodium hydroxide and shell metal salt solution were added to the bottom liquid at a flow rate of 50 mL / min to carry out a core-layer coprecipitation reaction to obtain core-layer precursor particles with a particle size of 4 μm. The pH of the core-layer coprecipitation reaction was 9.0–9.5, the temperature was 40°C and the stirring speed was 500 r / min.

[0066] (3) Under a protective atmosphere, 6% ammonia water, 4 mol / L sodium hydroxide and core metal salt solution were added to the system after the reaction in step (2) at a flow rate of 50 mL / min to carry out a shell coprecipitation reaction to obtain core-shell precursor particles with a particle size of 6 μm; wherein the pH value of the shell coprecipitation reaction was 8.5-9.0, the temperature was 40℃, and the stirring speed was 500 r / min;

[0067] (4) The core-shell precursor particles are sequentially aged, filtered, washed and dried to obtain sodium-ion battery cathode precursor.

[0068] The obtained sodium-ion battery cathode precursor has a particle size D50 of 6.1 μm and a specific surface area of ​​10.0 m². 2 / g, tap density is 1.5g / cm³ 3 .

[0069] Comparative Example 3

[0070] This comparative example provides a sodium-ion battery cathode precursor. The precursor is a spherical or near-spherical particle composed of a core layer and a shell layer. The chemical formula of the core layer is Ni. 0.33 Mn 0.34 Fe 0.33 (OH)₂; the chemical formula of the shell is Ni 0.8 Mn 0.1 Fe 0.1 (OH)2.

[0071] The preparation method of the sodium-ion battery cathode precursor in this comparative example includes the following steps:

[0072] (1) Weigh out nickel nitrate, manganese nitrate and ferric nitrate according to the molar ratio of Ni:Mn:Fe of 33:34:33, and dissolve them together in water to prepare a core metal salt solution with a total molar concentration of Ni, Mn and Fe ions of 2 mol / L; Weigh out nickel nitrate, manganese nitrate and ferric nitrate according to the molar ratio of Ni:Mn:Fe of 80:10:10, and dissolve them together in water to prepare a shell metal salt solution with a total molar concentration of Ni, Mn and Fe ions of 1 mol / L;

[0073] (2) Under nitrogen protection, 6% ammonia water, 4 mol / L sodium hydroxide and pure water were added to the reactor to obtain a bottom liquid with a pH of 9.0. The reactor was then heated to 40°C and stirred at 200 r / min. 6% ammonia water, 4 mol / L sodium hydroxide and core layer metal salt solution were then added to the bottom liquid at a flow rate of 50 mL / min to carry out a core layer coprecipitation reaction to obtain core layer precursor particles with a particle size of 4 μm. The pH of the core layer coprecipitation reaction was 8.5–9.0, the temperature was 40°C and the stirring speed was 500 r / min.

[0074] (3) Under a protective atmosphere, 8% ammonia water, 4 mol / L sodium hydroxide and shell metal salt solution were added to the system after the reaction in step (2) at a flow rate of 50 mL / min to carry out shell coprecipitation reaction to obtain core-shell precursor particles with a particle size of 6 μm; wherein the pH value of the shell coprecipitation reaction was 9.0 to 9.5, the temperature was 40℃ and the stirring speed was 500 r / min;

[0075] (4) The core-shell precursor particles are sequentially aged, filtered, washed and dried to obtain sodium-ion battery cathode precursor.

[0076] The obtained sodium-ion battery cathode precursor has a particle size D50 of 6.0 μm and a specific surface area of ​​10.2 m². 2 / g, tap density is 1.5g / cm³ 3 .

[0077] Comparative Example 4

[0078] This comparative example provides a sodium-ion battery cathode precursor. The precursor is a spherical or near-spherical particle composed of a core layer and a shell layer. The chemical formula of the core layer is Ni. 0.33 Mn 0.34 Nb 0.33 (OH)₂; the chemical formula of the shell is Ni 0.8 Mn 0.1 Nb 0.1(OH)2.

[0079] The preparation method of the sodium-ion battery cathode precursor in this comparative example includes the following steps:

[0080] (1) Weigh out nickel nitrate, manganese nitrate, and sodium niobate according to the molar ratio of Ni:Mn:Nb of 33:34:33, and dissolve them together in water to prepare a core metal salt solution. The total molar concentration of Ni, Mn, and Nb ions is 2 mol / L. Weigh out nickel nitrate, manganese nitrate, and sodium niobate according to the molar ratio of Ni:Mn:Nb of 80:10:10, and dissolve them together in water to prepare a shell metal salt solution. The total molar concentration of Ni, Mn, and Nb ions is 1 mol / L.

[0081] (2) Under nitrogen protection, 6% ammonia water, 4 mol / L sodium hydroxide and pure water were added to the reactor to obtain a bottom liquid with a pH of 9.0. The reactor was then heated to 40°C and stirred at 200 r / min. 6% ammonia water, 4 mol / L sodium hydroxide and core layer metal salt solution were then added to the bottom liquid at a flow rate of 50 mL / min to carry out a core layer coprecipitation reaction to obtain core layer precursor particles with a particle size of 4 μm. The pH of the core layer coprecipitation reaction was 8.5–9.0, the temperature was 40°C and the stirring speed was 500 r / min.

[0082] (3) Under a protective atmosphere, 8% ammonia water, 4 mol / L sodium hydroxide and shell metal salt solution were added to the system after the reaction in step (2) at a flow rate of 50 mL / min to carry out shell coprecipitation reaction to obtain core-shell precursor particles with a particle size of 6 μm; wherein the pH value of the shell coprecipitation reaction was 9.0 to 9.5, the temperature was 40℃ and the stirring speed was 500 r / min;

[0083] (4) The core-shell precursor particles are sequentially aged, filtered, washed and dried to obtain sodium-ion battery cathode precursor.

[0084] The obtained sodium-ion battery cathode precursor has a particle size D50 of 6.0 μm and a specific surface area of ​​8.0 m². 2 / g, tap density is 1.4g / cm³ 3 .

[0085] Figure 1 The CP diagram of the sodium-ion battery cathode precursor prepared in Example 1 is shown. Figure 1 It can be clearly seen that the sodium-ion battery cathode precursor has a core-shell structure, and the shell layers are arranged radially.

[0086] The sodium-ion battery positive electrode precursors prepared in Examples 1-3 and Comparative Examples 1-4 were mixed with sodium carbonate at a molar ratio of 1:1.05 and heated to 650°C in a box furnace at a heating rate of 2°C / min, held for 5 hours, then heated to 900°C and held for 11 hours. After cooling to room temperature, the mixture was crushed by a jaw crusher, air crushed, and sieved to obtain sodium-ion battery positive electrode material. The sodium-ion battery positive electrode material was mixed with conductive carbon black and polyvinylidene fluoride binder at a mass ratio of 95:2.5:2.5, and an appropriate amount of N-methylpyrrolidone solution was added until a slurry was formed in a dry environment at room temperature. The slurry was evenly coated onto aluminum foil with a scraper, vacuum dried for 12 hours, and then cut into round sheets to obtain the tested positive electrode sheet. The assembly was carried out in a glove box under an argon atmosphere. A positive electrode sheet was used as the positive electrode, metallic sodium as the counter electrode, and glass fiber as the separator. Ethylene carbonate (EC) / dimethyl carbonate (DMC) / propylene carbonate (PC) in a volume ratio of 1 mol / L NaClO4 was used as the solvent, and 5% by volume of fluoroethylene carbonate (FEC) was added as the electrolyte. The CR2032 coin cell sodium-ion battery was assembled.

[0087] Ratio performance test:

[0088] After the sodium-ion battery completed its first charge-discharge test, it was charged to 4V at 1C, and then discharged to 0.01V at currents of 0.1C, 1C, and 2C respectively. The discharge capacity at different rates was tested, and the results are shown in Table 1. Long-cycle performance test:

[0089] After the sodium-ion battery completes its first charge-discharge test, it is charged with constant current and constant voltage (1C) to 4V, discharged with constant current (1C) to 0.01V, and cycled for 100 cycles. The ratio of the capacity at 0.01V in the 100th cycle to the capacity at 0.01V in the 1st cycle is the 100-cycle retention rate. The results are shown in Table 1.

[0090] Table 1. Test results of rate performance and long-cycle performance

[0091]

[0092] As shown in Table 1, the sodium-ion battery cathode precursors of Examples 1-3 have good rate performance and cycle stability. This indicates that by replacing some nickel and manganese with low-valence transition metals to form a low-nickel core layer, and by introducing high-valence transition metals to replace some nickel and manganese to form a radially arranged high-nickel shell layer, the problems of structural instability of sodium-ion cathode materials, slow sodium-ion insertion / deintercalation speed, and particle microcrack formation during long-cycle processes can be effectively solved.

[0093] Comparing Example 1 and Comparative Example 1, it can be seen that if the sodium-ion battery cathode precursor does not contain a radially arranged high-nickel shell, it is detrimental to improving the rate performance and cycle stability of the sodium-ion battery. This is because the radially arranged high-nickel shell facilitates the direct diffusion of sodium ions from the particle center to the surface, shortening the diffusion path and reducing the crossing of grain boundaries, thereby improving its rate performance. In addition, the radially ordered primary grains have a consistent crystal orientation, which can significantly reduce the intergranular stress induced by volume change through synergistic expansion and contraction, thereby significantly suppressing the formation of microcracks in the particles and promoting cycle stability.

[0094] Comparing Example 1 and Comparative Example 2, it can be seen that if the core layer is high-nickel and the shell layer is low-nickel, it is not conducive to improving the rate performance of sodium-ion batteries. In addition, the higher raw material cost when the core layer is high will also reduce the economics of sodium-ion batteries.

[0095] Comparing Example 1 and Comparative Example 3, it can be seen that if a low-valence transition metal is introduced to replace part of the nickel and manganese to form a high-nickel shell, it is not conducive to improving the rate performance and cycle stability of sodium-ion batteries. This is because when the niobium salt in the shell metal salt solution is replaced with iron salt, it is difficult for the shell to form a radial structure.

[0096] Comparing Example 1 and Comparative Example 4, it can be seen that replacing part of nickel and manganese with high-valence transition metals to form a low-nickel core layer is also not conducive to improving the rate performance and cycle stability of sodium-ion batteries. This is because replacing iron salts in the core layer metal salt solution with niobium salts results in a higher molar ratio, and niobium is more easily precipitated.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A sodium-ion battery positive electrode precursor, characterized in that, The precursor is a spherical or near-spherical particle composed of a core layer and a shell layer, wherein the chemical formula of the core layer is Ni. x Mn (1-x-y) M1 y (OH)₂, M₁ is a low-valence transition metal, 0.2≤x≤0.45, 0.1≤y≤0.35, 0.5≤x+y≤0.7; the chemical formula of the shell is Ni. a Mn (1-a-b) M2 b (OH)2, M2 is a high-valence transition metal, 0.6≤a≤0.9, 0.01≤b≤0.1, 0.61≤a+b≤0.9, the shell is arranged radially, the low-valence transition metal is at least one of iron, copper, magnesium and zinc, and the high-valence transition metal is at least one of vanadium, niobium and molybdenum.

2. The sodium-ion battery positive electrode precursor as described in claim 1, characterized in that, The precursor has a particle size D50 of 3~14μm and a specific surface area of ​​8~50m². 2 / g, tap density is 0.8~2.4g / cm³ 3 .

3. A method for preparing a sodium-ion battery cathode precursor as described in any one of claims 1 to 2, characterized in that the step... include: (1) Prepare core metal salt solutions and shell metal salt solutions respectively. In the core metal salt solution, the molar ratio of Ni, Mn, and M1 is x:1-xy:y, 0.2≤x≤0.45, 0.1≤y≤0.35, 0.5≤x+y≤0.7, and the total molar concentration of Ni, Mn, and M1 ions is controlled at 1~3 mol / L. In the shell metal salt solution, the molar ratio of Ni, Mn, and M2 is a:1-ab:b, 0.6≤a≤0.9, 0.01≤b≤0.1, 0.61≤a+b≤0.9, and the total molar concentration of Ni, Mn, and M2 ions is controlled at 0.1~2 mol / L. (2) Under a protective atmosphere, the first complexing agent, the first precipitant, and the core layer metal salt solution are added to the bottom liquid to carry out a core layer coprecipitation reaction to obtain core layer precursor particles with the first target particle size; (3) Under a protective atmosphere, the second complexing agent, the second precipitant, and the shell metal salt solution are added to the system after the reaction in step (2) to carry out a shell coprecipitation reaction to obtain core-shell precursor particles with the second target particle size; wherein the pH value of the shell coprecipitation reaction is 8~13, the temperature is 30~70℃, and the stirring speed is 400~800r / min. (4) The core-shell precursor particles are post-processed to obtain sodium-ion battery cathode precursor.

4. The method for preparing the sodium-ion battery cathode precursor as described in claim 3, characterized in that, The first complexing agent and the second complexing agent are each independently selected from at least one of ammonia, ammonium bicarbonate and ammonium carbonate, and the first precipitant and the second precipitant are each independently selected from at least one of sodium hydroxide, potassium hydroxide and sodium carbonate.

5. The method for preparing the sodium-ion battery cathode precursor as described in claim 3, characterized in that, The preparation of the base solution includes: adding the first complexing agent and the first precipitant to pure water under a protective atmosphere, adjusting the pH to 9 to 13.00 and heating to 30 to 70°C.

6. The method for preparing the sodium-ion battery cathode precursor as described in claim 3, characterized in that, Step (2) includes: under a protective atmosphere, adding the first complexing agent, the first precipitant, and the core layer metal salt solution to the bottom liquid at a flow rate of 10-100 mL / min to carry out a core layer coprecipitation reaction to obtain core layer precursor particles of 2-11 μm; wherein the pH value of the core layer coprecipitation reaction is 8-13, the temperature is 30-70℃, and the stirring speed is 400-800 r / min.

7. The method for preparing the sodium-ion battery cathode precursor as described in claim 3, characterized in that, Step (3) includes: under a protective atmosphere, adding the second complexing agent, the second precipitant, and the shell metal salt solution to the system after the reaction in step (2) at a flow rate of 10~100 mL / min to carry out a shell coprecipitation reaction to obtain core-shell precursor particles of 3~14 μm.

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