Manganese-rich hydroxide precursor, preparation method thereof, cathode material and sodium ion battery

Abstract

This invention controls reaction conditions at different stages of co-precipitation. In the early stage of the reaction, the (011) crystal plane is preferentially grown to form primary nanosheets dominated by the (011) crystal plane. Then, the crystals are oriented along the (011) crystal plane to avoid cross-penetration of the sheet-like primary particles, synthesizing a spherical manganese-rich hydroxide precursor with dense subparticle packing and high tap density. The incorporation of metals with a valence below +2 will reduce the Mn content in the cathode material. 3+ The proportion of Mn can alleviate the Jahn-Teller effect and the disproportionation reaction of manganese, and inhibit the Mn content. 2+ It dissolves in the electrolyte, and the M atom can form a stable M-O bond with the O atom, inhibiting the extraction of lattice oxygen and improving structural stability. The corresponding cathode material has a good crystal structure, an ordered arrangement of transition metal layers, can suppress irreversible phase transitions under high voltage, and has good electrochemical performance, strong structural air stability, high redox potential, high specific capacity, and low cost.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a manganese-rich hydroxide precursor and its preparation method, a cathode material, and a sodium-ion battery. Background Technology

[0002] In recent years, countries around the world have been accelerating the development of renewable energy and new energy vehicle industries to address the increasingly serious energy crisis and environmental problems. Many cathode materials can be used in sodium-ion batteries, such as layered oxides, polyanionic materials, and Prussian blue compounds. Among these cathode materials, layered transition metal oxides have attracted much attention due to their high theoretical capacity and low cost.

[0003] Currently, manganese-rich (Mn≥0.8) layered transition metal oxide cathode materials have attracted much attention due to their high capacity, low cost, and environmental friendliness. However, the preparation of these materials using traditional solid-state sintering and sol-gel methods still faces numerous challenges, such as low tap density and non-uniform secondary particle size. These issues lead to severe irreversible structural damage during charge-discharge processes, resulting in sodium-deficient structures, limiting the discharge capacity of the cathode materials, and causing rapid volume changes, ultimately leading to structural collapse. This severely impacts their long-term cycle performance and air stability, and also results in low energy density. In contrast, the co-precipitation method produces precursors with high tap density and uniform particle size. The layered transition metal oxide cathode materials synthesized using these precursors through high-temperature calcination exhibit stable layered structures. However, the significant differences in solubility products among metal ions such as nickel, iron, manganese, and magnesium make it difficult to achieve uniform precipitation of all elements using existing co-precipitation processes. This results in porous precursor morphology and structural collapse, significantly increasing the complexity of the synthesis process.

[0004] When the molar proportion of manganese in the cathode material is greater than 0.8, structural decay caused by the extraction of lattice oxygen occurs simultaneously with the Jahn-Teller effect during electrochemical processes. At the same time, the disproportionation reaction of manganese induced by the Jahn-Teller effect causes a large number of manganese ions to convert to Mn²⁺. 2+ The form dissolves in the electrolyte, causing a sharp decline in the material's electrochemical performance. Summary of the Invention

[0005] The first objective of this invention is to provide a manganese hydroxide precursor; the second objective of this invention is to provide a method for preparing the manganese hydroxide precursor; the third objective of this invention is to provide a cathode material; and the fourth objective of this invention is to provide a sodium-ion battery.

[0006] To achieve the above objectives, the following technical solution is proposed:

[0007] A manganese-rich hydroxide precursor, the chemical formula of the manganese-rich hydroxide precursor is (Ni a Fe b Mn c M d )(OH)2, where 0 < a + d ≤ 0.1, 0 ≤ b ≤ 0.1, 0.8 ≤ c ≤ 1, a + b + c + d = 1, M is a metal element with a valence of ≤ +2, and the solubility product of the M hydroxide is 8×10 -6 ~1×10 -21 .

[0008] Preferably, it has nano-sheet primary particles, and the nano-sheet primary particles are cross-connected into spherical or quasi-spherical secondary particles, and the particle size D50 of the secondary particles is 7 - 12.3 μm; the secondary particles grow mainly on the (011) crystal plane;

[0009] The tap density of the precursor is 1.1 - 2.5 g / cm 3 ; the specific surface area is 0.1 - 10 m 2 / g.

[0010] Preferably, M is selected from one or more of Mg, Ca, Zn, Cu, and Cr.

[0011] As a general inventive concept, the present invention also provides a preparation method of a manganese-rich hydroxide precursor, including:

[0012] (1) Prepare salt solutions of Ni, Fe, Mn, and M; prepare a precipitant solution; prepare a complexing agent solution; M is a metal element with a valence of ≤ +2;

[0013] (2) Introduce the salt solution, the precipitant solution, and the complexing agent solution into the bottom liquid of the reaction kettle and flow them in, and carry out a coprecipitation reaction until a precursor slurry with the required particle size is obtained; the coprecipitation is divided into two stages, and the concentration of the complexing agent in the reaction system in the second stage is higher than that in the first stage, and the stirring speed of the reaction system in the second stage is higher than that in the first stage;

[0014] (3) Post-treat the obtained precursor slurry to obtain a manganese-rich hydroxide precursor (Ni a Fe b Mn c M d )(OH)2, where 0 < a + d ≤ 0.1, 0 ≤ b ≤ 0.1, 0.8 ≤ c ≤ 1, a + b + c + d = 1.

[0015] Preferably, in step (2), during the coprecipitation reaction, the pH of the reaction system is 9 - 11, and the reaction temperature is 50 - 70 °C;

[0016] The stirring speed in the first stage is 300 - 500 rpm; the stirring speed in the second stage is 700 - 1000 rpm;

[0017] In the first stage, the concentration of the complexing agent solution introduced is 0.25 - 0.5 mol / L; in the second stage, the concentration of the complexing agent solution introduced is 0.51 - 1 mol / L;

[0018] The concentration of the complexing agent solution introduced in the second stage is 1.5 - 2.8 times that of the complexing agent solution introduced in the first stage;

[0019] The flow rate of the complexing agent introduced in the first stage and the second stage is the same.

[0020] Preferably, the preparation of the salt solution in step (1), the coprecipitation reaction in step (2), and the post - treatment in step (3) are all carried out under an inert atmosphere or a nitrogen atmosphere;

[0021] The precipitating agent is NaOH and / or KOH;

[0022] The complexing agent is ammonia water and / or ammonium - containing compounds;

[0023] M is selected from one or more of Mg, Ca, Zn, Cu, Cr;

[0024] The salts of Ni, Fe, Mn, and M are soluble salts.

[0025] The present invention also provides a cathode material, which is obtained by mixing the aforementioned precursor or the precursor prepared by the aforementioned preparation method with a sodium salt and then sintering.

[0026] Preferably, the chemical formula of the cathode material is Na x Ni a Fe b Mn c M d O2, where 0.45 ≤ x ≤ 1, 0 < a + d ≤ 0.1, 0 ≤ b ≤ 0.1, 0.8 ≤ c ≤ 1, a + b + c + d = 1; the particle size D50 of the cathode material is 6.8 - 12.5 μm; the tap density is 1.1 - 2.9 g / cm 3 ; the specific surface area is 0.1 - 9 m 2 / g, and the phase structure presents a P2 or O3 phase.

[0027] Preferably, the sintering includes: heating to 800 - 1100 °C and sintering for 10 - 24 h; or pre - sintering at 450 - 500 °C for 3 - 8 h, and then heating to 700 - 1000 °C and sintering for 10 - 16 h.

[0028] The present invention also provides a sodium-ion battery, comprising the aforementioned positive electrode material.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] ① This invention uses a co-precipitation method to prepare a manganese-rich hydroxide precursor. By controlling the reaction conditions at different stages of the co-precipitation reaction, an appropriate amount of NH4 can be obtained in the early stage of the reaction. + Adsorbed onto the (011) crystal plane, the (011) crystal plane preferentially grows, forming primary particle nanosheets with complex ions growing mainly on the (011) crystal plane. Then, in the later growth stage and even during the aggregation stage, the crystals are oriented to grow along the (011) crystal plane to avoid cross-piercing of the sheet-like primary particles, thereby synthesizing a spherical manganese-rich hydroxide precursor with subparticle close packing and high tap density. After using this precursor to prepare a cathode material, a good crystal structure and an ordered transition metal layer arrangement are formed, which is beneficial to suppressing the irreversible phase transition of the material under high voltage. The layered cathode material of sodium-ion batteries has good electrochemical performance, strong structural air stability, high redox potential, high specific capacity, and low cost.

[0031] ② The solubility products of the hydroxides of element M are similar to those of the hydroxides of Ni, Fe, and Mn. This method enables uniform co-precipitation of all elements, resulting in a shorter process compared to traditional high-temperature solid-phase doping, more precise control over the content of element M, and a more uniform distribution within the material. The valence state of element Mn in the material is Mn. 3+ / Mn 4+ Coexistence, due to the charge compensation mechanism, the incorporation of M metal elements with a valence of ≤+2 will reduce the Mn content in the cathode material. 3+ The proportion of Mn is used to mitigate the Jahn-Teller effect and manganese disproportionation reaction in the cathode material during cycling, and to suppress Mn 2+ It dissolves in the electrolyte, improving the capacity and cycle performance of the material; and the M atom can form a stable MO bond with the O atom in the material, inhibiting the release of lattice oxygen during the material cycling process and improving the structural stability of the material. Attached Figure Description

[0032] Figure 1 This is a SEM image of the early stage of the reaction for preparing the manganese-rich hydroxide precursor in Example 1.

[0033] Figure 2 The images show the XRD patterns of the manganese-rich hydroxide precursors prepared in the various examples and comparative examples.

[0034] Figure 3 This is a SEM image of the manganese-rich hydroxide precursor prepared in Example 1.

[0035] Figure 4Graph showing the rate performance test results of the sodium-ion battery cathode materials prepared in each embodiment and comparative example.

[0036] Figure 5 Scanning electron microscope image of the precursor prepared in Comparative Example 1. Detailed implementation manners

[0037] The present invention provides a manganese-rich hydroxide precursor, and the chemical formula of the manganese-rich hydroxide precursor is (Ni a Fe b Mn c M d )(OH)2, where 0 < a + d ≤ 0.1, 0 ≤ b ≤ 0.1, 0.8 ≤ c ≤ 1, a + b + c + d = 1, M is a metal element with a valence of ≤ +2, and the solubility product of the M hydroxide is 8×10 -6 ~1×10 -21 . Doping of metal M element: ① The solubility products of the M hydroxide and the hydroxides of Ni, Fe, and Mn are similar, enabling uniform coprecipitation. ② Due to the charge compensation mechanism, the proportion of Mn in the cathode material is reduced, alleviating the Jahn-Teller effect and the disproportionation reaction of manganese, and inhibiting the dissolution of Mn 3+ into the electrolyte. 2+

[0038] In some preferred specific implementation manners, there are nano-sheet primary particles, and the nano-sheet primary particles are cross-connected into spherical or quasi-spherical secondary particles. This precursor has a sheet-like dense structure and regular morphology, which is beneficial to improving the cycle performance and rate performance of the cathode material.

[0039] In some preferred specific implementation manners, the secondary particles are mainly grown on the (011) crystal plane. The X-ray diffraction test results of the precursor grown on the (011) crystal plane show that the (011) peak and the (001) peak are the main peaks in its diffraction peaks, and the (011) peak is the peak with the strongest intensity; the particles grown on the (011) crystal plane are beneficial to forming a good crystal structure and an ordered arrangement of the transition metal layer to inhibit the irreversible phase transformation under high voltage to stabilize the material structure and improve the cycle stability, and the cathode material prepared from the precursor grown on the (011) crystal plane has good electrochemical performance. Among them, the peak intensity ratio I001 / I011 of the 001 peak and the 011 peak is 0.35 - 0.55, such as 0.36, 0.37, 0.38, 0.39, 0.40, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, etc.

[0040] In some preferred embodiments, the particle size D50 of the secondary particles is 7~12.3 μm; the tap density of the precursor is 1.1~2.5 g / cm³. 3 Specific surface area: 0.1~10 m² 2 / g. The precursor has good particle size uniformity, high tap density, and high specific surface area.

[0041] In some preferred embodiments, M is selected from one or more of Mg, Ca, Zn, Cu, and Cr. The MO bonds formed by these elements are strong and can suppress the release of lattice oxygen from the material, thereby making its crystal structure stable and less prone to collapse during charging and discharging.

[0042] This invention also provides a method for preparing a manganese-rich hydroxide precursor, comprising:

[0043] (1) Prepare salt solutions of Ni, Fe, Mn and M; prepare precipitant solutions; prepare complexing solutions; wherein M is a metallic element with a valence of ≤+2;

[0044] (2) Add the bottom liquid of the reactor to the reactor and keep the reactor stirring. Introduce nitrogen or inert gas into the reactor for a period of time. Then, introduce salt solution, precipitant solution and complexing agent solution into the bottom liquid of the reactor in parallel to carry out co-precipitation reaction until the precursor slurry with the required particle size is obtained. The co-precipitation is divided into two stages, and the concentration of complexing agent in the second stage reaction system is higher than that in the first stage. The stirring speed of the second stage reaction system is higher than that in the first stage.

[0045] (3) The obtained precursor slurry was aged, subjected to solid-liquid separation, washed and dried to obtain a manganese-rich hydroxide precursor (Ni a Fe b Mn c M d (OH)2, where 0 <a+d≤0.1,0≤b≤0.1,0.8≤c≤1,a+b+c+d=1。

[0046] In some preferred embodiments, in step (2), during the coprecipitation reaction, the pH of the reaction system is 9~11, such as 9.5, 10, 10.5, etc., and the reaction temperature is 50~70 ℃, more preferably 52~60 ℃, such as 53, 54, 55, 56, 57, 58, 59 ℃, etc.

[0047] In some preferred embodiments, in step (2), the stirring speed in the first stage is 300~500 rpm; and the stirring speed in the second stage is 700~1000 rpm.

[0048] To achieve uniform precipitation of elements with different Ksp, different complexing agent concentrations are controlled at different stages. Specifically, this invention can be achieved by preparing complexing agent solutions of different concentrations in two stages, or by preparing complexing agent solutions of the same concentration, and then adjusting the inflow rate of the complexing agent solutions at different stages.

[0049] In some embodiments, in order to achieve NH4 in the reaction system at different stages + To control the concentration, two complexing agent solutions with different molar concentrations were prepared. The first complexing agent had a concentration of 0.25–0.5 mol / L, designated as complexing agent number one; the second complexing agent had a concentration of 0.51–1 mol / L, designated as complexing agent number two. More preferably, the concentration of complexing agent number two was controlled to be 1.5–2.8 times that of complexing agent number one, for example, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, or 2.8 times. The flow rate of the complexing agent solutions in both the first and second stages was the same.

[0050] In some embodiments, the flow rates of the mixed salt solution in the first and second stages are also the same.

[0051] To avoid excessive NH4 due to high ammonia concentration in the initial stage of the reaction. + Adsorbed on the (011) crystal plane, hindering the adsorption and growth of each element along the (011) crystal plane, different concentrations of ammonia water were pumped into the reaction system in batches. In the first stage of the coprecipitation reaction, the mixed salt solution and the first complexing agent were pumped into the reactor at flow rates of 50~200 mL / min and 15~60 mL / min, respectively, for the coprecipitation reaction. In the second stage of the coprecipitation reaction, the mixed salt solution and the second complexing agent were pumped into the reactor at flow rates of 50~200 mL / min and 15~60 mL / min, respectively, for the coprecipitation reaction. In the early stage of the reaction, a low concentration of NH4 was used. + Through adsorption, various elements can pass through NH4 + After complexation, it grows along the (011) crystal plane, but due to NH4 + At low concentrations, the primary nanosheet particles cannot grow oriented along the (011) crystal plane. Continuous use of the first complexing agent will inevitably cause the (011) crystal plane to gradually grow along the side of the nanosheet as the reaction time increases. As a result, the primary nanosheet particles eventually grow gradually along the radial direction of the spherical secondary particles and penetrate from the center to the surface, leading to a loose morphology, low tap density, and inability of elements to precipitate uniformly. The role of the second complexing agent is to increase the amount of NH4 in the later stages of primary particle growth and agglomeration. + The adsorption of complexed metal ions onto the (011) crystal plane causes them to grow in a directional manner, forming spherical secondary particles with a compact morphology and high tap density.

[0052] In some preferred embodiments, the preparation of the salt solution in step (1), the co-precipitation reaction in step (2), and the aging in step (3) are all carried out under an inert atmosphere or a nitrogen atmosphere, and specifically can be carried out in a glove box filled with inert gas;

[0053] In some preferred embodiments, the precipitant is NaOH and / or KOH; the concentration of the precipitant solution is 1 - 3 mol / L;

[0054] In some preferred embodiments, the complexing agent is ammonia and / or ammonium-containing compound; more preferably ammonia water.

[0055] In some preferred embodiments, M is selected from one or more of Mg, Ca, Zn, Cu, Cr; the salts of Ni, Fe, Mn, M are soluble salts;

[0056] The total molar concentration of Ni, Fe, Mn, M in the salt solution is 1 - 4 mol / L.

[0057] In some preferred embodiments, the bottom liquid of the reaction kettle is an ammonia water solution with a concentration of 9 - 11 g / L.

[0058] In some embodiments, in step (3), the aging can be a conventional aging process; the solid-liquid separation can be pressure filtration, centrifugal filtration, etc.; the washing can use water or other conventional cleaning agents, as long as it can remove the impurities in the precursor and will not introduce new impurities to the final precursor product; the drying is carried out under vacuum and can adopt a conventional vacuum drying process, as long as the required drying effect can be achieved.

[0059] The present invention also provides a cathode material, which is obtained by mixing the aforementioned precursor or the precursor prepared by the aforementioned preparation method with a sodium salt and then sintering.

[0060] In some preferred embodiments, the chemical formula of the cathode material is Na x Ni a Fe b Mn c M d O2, where 0.45 ≤ x ≤ 1, more preferably 0.6 ≤ x ≤ 1, 0 < a + d ≤ 0.1, 0 ≤ b ≤ 0.1, 0.8 ≤ c ≤ 1, a + b + c + d = 1; the particle size D50 of the cathode material is 6.8 - 12.5 μm; the tapped density is 1.1 - 2.9 g / cm 3 ; the specific surface area is 0.1 - 9 m 2 / g, and the phase structure presents P2 or O3 phase.

[0061] In some preferred embodiments, the sodium salt is one or more of sodium carbonate, sodium hydroxide, sodium bicarbonate, sodium nitrate, and sodium oxalate, and the precursor and sodium salt are in a molar ratio of sodium to precursor of 0.5 to 1.1:1, more preferably 0.6 to 1.1:1.

[0062] To prevent oxygen precipitation from the material lattice from damaging its structural stability, the precursor is mixed with sodium salt and then sintered in a tube furnace with a single oxygen tube inserted. The tube furnace is placed in a glove box filled with inert gas or nitrogen, ensuring that the material is completely isolated from air.

[0063] In some embodiments, the mixing of the manganese-rich hydroxide precursor and the sodium source is achieved by thoroughly grinding the manganese-rich hydroxide precursor and the sodium source to obtain a mixture.

[0064] In some preferred embodiments, the sintering process involves pre-setting the material in a tube furnace filled with inert gas for 1-5 hours to remove residual air components and prevent unnecessary side reactions in the early stages of sintering. After setting, oxygen is pre-purified for a period of time, and then the temperature is increased to 800-1100°C at a rate of 1-10°C / min for sintering for 10-24 hours. After the reaction is complete, the oxygen valve is closed, and the material is then placed in an inert gas environment for 1-2 hours. Alternatively, the material is first settling in a tube furnace filled with inert gas for 1-5 hours, and after setting, oxygen is pre-purified for a period of time, and then the temperature is increased to 450-500°C for pre-sintering for 3-8 hours. Then, the temperature is increased to 700-1000°C at a rate of 1-10°C / min for sintering for 10-16 hours. After the reaction is complete, the oxygen valve is closed, and the material is then placed in an inert gas environment for 1-2 hours. The purpose of this process is to stabilize the structure of the cathode material after high-temperature sintering and to avoid the generation of impurities. Control the oxygen flow rate to 0.5~5 L / min.

[0065] In some embodiments, the method further includes a step of grinding the sintered cathode material, wherein the grinding is carried out in a dry atmosphere.

[0066] The present invention also provides a sodium-ion battery, comprising the aforementioned positive electrode material.

[0067] The sodium-ion battery cathode material prepared in this manner exhibits high specific capacitance, first-cycle coulombic efficiency, and cycle stability, along with good safety performance and low cost. Furthermore, the sodium-ion battery cathode material used in this process possesses advantages such as high energy density, strong air stability, and low cost.

[0068] The present invention will be further described below with reference to specific embodiments and accompanying drawings, but the present invention is not limited to the following embodiments. Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention.

[0069] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0070] Example 1:

[0071] A method for preparing a sodium-ion cathode material precursor by multi-element co-precipitation includes:

[0072] Step 1: Prepare an aqueous solution of Ni, Fe, and Mn sulfates in a glove box filled with inert gas, stir and seal, wherein the molar ratio of Ni, Fe, and Mn is 1:1:8 and the total metal molar concentration is 1 mol / L;

[0073] Prepare a sodium hydroxide solution with a molar concentration of 2 mol / L as a precipitant;

[0074] Prepare ammonia complexing agent No. 1 with a concentration of 0.25 mol / L and ammonia complexing agent No. 2 with a concentration of 0.6 mol / L respectively;

[0075] Prepare an ammonia solution with a concentration of 10 g / L as the bottom liquid of the reaction vessel;

[0076] Step 2: Pour the base liquid into the reaction vessel and keep the agitator running. Introduce nitrogen or inert gas into the reaction vessel at a flow rate of 0.5 L / min for 30 min. Pump the salt solution and complexing agent No. 1 from Step 1 into the reaction vessel at flow rates of 50 mL / min and 15 mL / min, respectively, for co-precipitation. During the reaction, maintain the pH at 10 by pumping in sodium hydroxide solution. The stirring speed in the reaction vessel is 300 rpm, and the reaction temperature is maintained at 54.4 ℃. Continue the reaction until the complexing agent No. 1 is completely consumed. Take samples during the reaction for SEM analysis. Figure 1 As shown in the figure, the precursor is in a loose state at this time and needs to be agglomerated and regenerated. Then, while adding the second complexing agent, the rotation speed is increased to 700 rpm. The pH, temperature, salt solution and flow rate of the complexing agent in the reactor remain unchanged. After the second complexing agent is consumed, the rotation speed is reduced to 100 rpm and the aging treatment is carried out for 4 hours to complete the reaction.

[0077] Step 3: The co-precipitated product from Step 2 is subjected to pressure filtration, washing, and drying to obtain the sodium ion cathode material precursor. The chemical formula of the product is (Ni0.1 Fe 0.1 Mn 0.8 (OH)₂; D50 is 8.3 μm, tap density is 1.59 g / cm³. 3 Its specific surface area is 7.12 m². 2 / g, its XRD pattern is as follows Figure 2 As shown, from Figure 2 It can be seen that the precursor has (011) and (001) peaks as the main peaks, and the (011) main peak is sharp, indicating good crystallinity. The intensity ratio of the (001) peak to the (011) peak, I001 / I011, is 0.447. From this figure, it can be analyzed that the secondary particles grow mainly on the (011) crystal plane. Its SEM image is shown below. Figure 3 As shown in the figure, the nanosheet-like primary particles of the precursor are fully formed and tightly connected, interlocking to form spherical secondary particles without any cross-piercing. Combined with the tap density data, it can be seen that the precursor has a high tap density. Analysis suggests this may be due to controlling the reaction conditions at different stages of the co-precipitation reaction, allowing for the appropriate amount of NH4+ to be present in the early stages of the reaction. + Adsorbed on the (011) crystal plane, the (011) crystal plane preferentially grows to form complex ions that grow primarily on the (011) crystal plane, resulting in primary particle nanosheets that achieve uniform precipitation at the atomic level for elements with large differences in solubility products. Then, in the later stages of growth and even during the aggregation stage, the crystal is oriented to grow along the (011) crystal plane to avoid cross-penetration of the sheet-like primary particles, thereby synthesizing a spherical manganese-rich hydroxide precursor with tightly packed primary particles and high tap density.

[0078] Step 4: Mix the precursor described in Step 3 with Na2CO3 at a molar ratio of precursor to sodium of 1:0.7035 until homogeneous. Place the mixture in a tube furnace filled with inert gas and let it stand for 1 hour. Then, pre-purge with oxygen for 30 minutes, heat at a rate of 5 °C / min to 950 °C, and hold at that temperature for 12 hours. After that, close the oxygen valve and allow the material to remain in an inert gas environment for 1 hour to obtain the sodium ion cathode material Na. 0.67 [Ni 0.1 Fe 0.1 Mn 0.8 O2.

[0079] Step 5: The positive electrode material Na obtained in Step 4... 0.67 [Ni 0.1 Fe 0.1 Mn 0.8 O2 was thoroughly ground for 20 min under a dry atmosphere.

[0080] The above-prepared positive electrode material Na 0.67 [Ni 0.1 Fe 0.1 Mn 0.8O2, acetylene black, and polyvinylidene fluoride (PVDF) (mass ratio 8:1:1) were mixed in n-methyl-2-pyrrolidone (NMP) to form a slurry. After coating and drying, a positive electrode containing the target product was obtained. Sodium foil was used as the negative electrode, and glass fiber was used as the separator. CR2025 button batteries were assembled in a glove box filled with argon and oxygen with a moisture content of less than 0.1 ppm. Charge-discharge tests were conducted with a test voltage window of 1.5~4.3 V, a current density of 0.1~5 C, and a test temperature of 30 ℃. The initial discharge capacity was 233 mAh / g (0.05C). The battery rate performance was as follows: Figure 5 As shown, the obtained cathode material has good electrochemical performance and cycle stability. The analysis suggests that this may be because the precursor particles are mainly grown with the (011) crystal plane. After being prepared into cathode material, the hexagonal channels on the (011) crystal plane not only provide storage sites for sodium ions, but also help to suppress irreversible phase transitions under high pressure to stabilize the material structure.

[0081] Example 2

[0082] Step 1: Prepare an aqueous solution of Ni, Fe, Mn, and Cu sulfates in a glove box filled with inert gas, stir and seal, wherein the molar ratio of Ni, Fe, Mn, and Cu is 0.05:0.1:0.8:0.05, and the total metal molar concentration is 2 mol / L;

[0083] Prepare a sodium hydroxide solution with a molar concentration of 2 mol / L as a precipitant;

[0084] Prepare ammonia complexing agent No. 1 with a concentration of 0.5 mol / L and ammonia complexing agent No. 2 with a concentration of 1 mol / L respectively;

[0085] Prepare an ammonia solution with a concentration of 10 g / L as the bottom liquid of the reaction vessel;

[0086] Step 2: Pour the base liquid into the reactor and keep the reactor stirred. Introduce nitrogen or inert gas into the reactor at a flow rate of 0.5 L / min for 30 min. Pump the salt solution and complexing agent No. 1 from Step 1 into the reactor at flow rates of 50 mL / min and 15 mL / min, respectively, for co-precipitation reaction. During the reaction, maintain the pH at 10 by pumping in sodium hydroxide solution. The stirring speed of the reactor is 300 rpm, and the reaction temperature is maintained at 55 ℃. Continue the reaction until the complexing agent No. 1 is consumed. Then, add the complexing agent No. 2 while increasing the stirring speed to 700 rpm. Keep the pH, temperature, flow rate of the salt solution and complexing agent in the reactor constant. After the complexing agent No. 2 is consumed, reduce the stirring speed to 100 rpm and age for 4 hours to complete the reaction.

[0087] Step 3: The co-precipitated product from Step 2 is subjected to pressure filtration, washing, and drying to obtain the sodium ion cathode material precursor. The chemical formula of the product is (Ni 0.05 Fe 0.1 Mn 0.8 Cu 0.05 (OH)₂; D50 is 10.7 μm, tap density is 1.68 g / cm³ 3 Its specific surface area is 6.11 m². 2 / g, its XRD pattern is as follows Figure 2 As shown, from Figure 2 It can be seen that the precursor has a sharp (011) main peak and good crystallinity. The ratio of the 001 peak intensity to the 011 peak intensity, I001 / I011, is 0.473. From this figure, it can be analyzed that the secondary particles grow mainly on the (011) crystal plane.

[0088] Step 4: Mix the precursor described in Step 3 with Na2CO3 at a molar ratio of precursor to sodium of 1:0.7035 until homogeneous. Place the mixture in a tube furnace filled with inert gas and let it stand for 1.5 h. Then, pre-purge with oxygen for 30 min, heat at a rate of 5 °C / min to 1000 °C, and hold at that temperature for 12 h. After that, close the oxygen valve and allow the material to remain in an inert gas environment for 1.5 h to obtain the sodium ion cathode material Na. 0.67 [Ni 0.05 Fe 0.1 Mn 0.8 Cu 0.05 O2.

[0089] Step 5: The positive electrode material Na obtained in Step 4... 0.67 [Ni 0.05 Fe 0.1 Mn 0.8 Cu 0.05 O2 was thoroughly ground for 20 min under a dry atmosphere.

[0090] The above-prepared positive electrode material Na 0.67 [Ni 0.05 Fe 0.1 Mn 0.8 Cu 0.05O2, acetylene black, and polyvinylidene fluoride (PVDF) (mass ratio 8:1:1) were mixed in n-methyl-2-pyrrolidone (NMP) to form a slurry. After coating and drying, a positive electrode containing the target product was obtained. Sodium foil was used as the negative electrode, and glass fiber was used as the separator. CR2025 button batteries were assembled in a glove box filled with argon and oxygen with a moisture content of less than 0.1 ppm. Charge-discharge tests were conducted with a test voltage window of 1.5~4.3 V, a current density of 0.1~5 C, and a test temperature of 30 ℃. The initial discharge capacity was 230 mAh / g (0.05C). The battery rate performance was as follows: Figure 4 As shown in the figure, compared with the product of Example 1, the electrochemical performance of the Cu-doped product is significantly improved. Analysis suggests this may be due to the reduction of Mn by adding an appropriate amount of Cu. 3+ The ratio inhibits the disproportionation reaction of manganese, and the strong Cu-O bond inhibits the extraction of oxygen from the lattice, thus stabilizing the material's lattice structure.

[0091] Example 3

[0092] Step 1: Prepare an aqueous solution of Ni, Fe, Mn, and Mg sulfates in a glove box filled with inert gas, stir and seal, wherein the molar ratio of Ni, Fe, Mn, and Mg is 0.05:0.1:0.8:0.05, and the total metal molar concentration is 2 mol / L;

[0093] Prepare a sodium hydroxide solution with a molar concentration of 2 mol / L as a precipitant;

[0094] Prepare ammonia complexing agent No. 1 with a concentration of 0.3 mol / L and ammonia complexing agent No. 2 with a concentration of 0.55 mol / L respectively;

[0095] Prepare an ammonia solution with a concentration of 10 g / L as the bottom liquid of the reaction vessel;

[0096] Step 2: Pour the base liquid into the reactor and keep the reactor stirred. Introduce nitrogen or inert gas into the reactor at a flow rate of 0.5 L / min for 30 min. Pump the salt solution and complexing agent No. 1 from Step 1 into the reactor at flow rates of 200 mL / min and 50 mL / min, respectively, for co-precipitation reaction. During the reaction, maintain the pH at 11 by pumping in sodium hydroxide solution. The reactor stirring speed is 300 rpm, and the reactor temperature is maintained at 55 ℃. Continue the reaction until complexing agent No. 1 is consumed. Then, add complexing agent No. 2 while increasing the stirring speed to 700 rpm. Keep the pH, temperature, and flow rates of the salt solution and complexing agent in the reactor constant. After complexing agent No. 2 is consumed, reduce the stirring speed to 100 rpm and age for 4 h to complete the reaction.

[0097] Step 3: The co-precipitated product from Step 2 is subjected to pressure filtration, washing, and drying to obtain the sodium ion cathode material precursor. The chemical formula of the product is (Ni 0.05 Fe 0.1 Mn 0.8 Mg 0.05 (OH)₂; D50 is 12.1 μm, tap density is 1.75 g / cm³. 3 Its specific surface area is 5.46 m². 2 / g, its XRD pattern is as follows Figure 2 As shown, from Figure 2 It can be seen that the precursor has a sharp (011) main peak and good crystallinity. The ratio of the 001 peak intensity to the 011 peak intensity, I001 / I011, is 0.528. From this figure, it can be analyzed that the secondary particles grow mainly on the (011) crystal plane.

[0098] Step 4: Mix the precursor described in Step 3 with Na2CO3 at a molar ratio of precursor to sodium of 1:0.7035 until homogeneous. Place the mixture in a tube furnace filled with inert gas and let it stand for 1 hour. Then, pre-purge with oxygen for 30 minutes, heat at a rate of 5 °C / min to 1050 °C, and hold at that temperature for 12 hours. After that, close the oxygen valve and allow the material to remain in an inert gas environment for 1 hour to obtain the sodium ion cathode material Na. 0.67 [Ni 0.05 Fe 0.1 Mn 0.8 Mg 0.05 O2.

[0099] Step 5: The positive electrode material Na obtained in Step 4... 0.67 [Ni 0.05 Fe 0.1 Mn 0.8 Mg 0.05 O2 was thoroughly ground for 20 min under a dry atmosphere.

[0100] The above-prepared positive electrode material Na 0.67 [Ni 0.05 Fe 0.1 Mn 0.8 Mg 0.05 O2, acetylene black, and polyvinylidene fluoride (PVDF) (mass ratio 8:1:1) were mixed in n-methyl-2-pyrrolidone (NMP) to form a slurry. After coating and drying, a positive electrode containing the target product was obtained. Sodium foil was used as the negative electrode, and glass fiber was used as the separator. The CR2025 button cell was assembled in a glove box filled with argon and oxygen and with a moisture content of less than 0.1 ppm. Charge-discharge tests were conducted with a test voltage window of 1.5~4.3 V, a current density of 0.1~5 C, and a test temperature of 30 ℃. The initial discharge capacity was 220 mAh / g (0.05C).

[0101] Example 4

[0102] Step 1: Prepare an aqueous solution of Ni, Fe, Mn, and Zn sulfates in a glove box filled with inert gas, stir and seal, wherein the molar ratio of Ni, Fe, Mn, and Zn is 0.05:0.1:0.8:0.05, and the total metal molar concentration is 2 mol / L;

[0103] Prepare a sodium hydroxide solution with a molar concentration of 2 mol / L as a precipitant;

[0104] Prepare ammonia complexing agent No. 1 with a concentration of 0.4 mol / L and ammonia complexing agent No. 2 with a concentration of 0.7 mol / L respectively;

[0105] Prepare an ammonia solution with a concentration of 10 g / L as the bottom liquid of the reaction vessel;

[0106] Step 2: Pour the base liquid into the reactor and keep the reactor stirred. Introduce nitrogen or inert gas into the reactor at a flow rate of 0.5 L / min for 30 min. Pump the salt solution and complexing agent No. 1 from Step 1 into the reactor at flow rates of 100 mL / min and 25 mL / min, respectively, for co-precipitation reaction. During the reaction, maintain the pH at 10.5 by pumping in sodium hydroxide solution. The reactor stirring speed is 300 rpm, and the reactor reaction temperature is maintained at 55 ℃. Continue the reaction until complexing agent No. 1 is consumed. Then, add complexing agent No. 2 while increasing the stirring speed to 900 rpm. Keep the pH, temperature, salt solution, and complexing agent flow rates of the reactor constant. After complexing agent No. 2 is consumed, reduce the stirring speed to 100 rpm and age for 4 h to complete the reaction.

[0107] Step 3: The co-precipitated product from Step 2 is subjected to pressure filtration, washing, and drying to obtain the sodium ion cathode material precursor. The chemical formula of the product is (Ni 0.05 Fe 0.1 Mn 0.8 Zn 0.05 (OH)₂; D50 is 9.3 μm, tap density is 1.60 g / cm³. 3 Its specific surface area is 6.83 m². 2 / g, its XRD pattern is as follows Figure 2 As shown, from Figure 2 It can be seen that the precursor has a sharp (011) main peak and good crystallinity. The ratio of the 001 peak intensity to the 011 peak intensity, I001 / I011, is 0.479. From this figure, it can be analyzed that the secondary particles grow mainly on the (011) crystal plane.

[0108] Step 4: Mix the precursor described in Step 3 with Na2CO3 at a molar ratio of precursor to sodium of 1:0.7035 until homogeneous. Place the mixture in a tube furnace filled with inert gas and let it stand for 1 hour. Then, pre-purge with oxygen for 30 minutes, heat at a rate of 5 °C / min to 1200 °C, and hold at that temperature for 12 hours. After that, close the oxygen valve and allow the material to remain in an inert gas environment for 1 hour to obtain the sodium ion cathode material Na. 0.67 [Ni 0.05 Fe 0.1 Mn 0.8 Zn 0.05 O2.

[0109] Step 5: The positive electrode material Na obtained in Step 4... 0.67 [Ni 0.05 Fe 0.1 Mn 0.8 Zn 0.05 O2 was thoroughly ground for 20 min under a dry atmosphere.

[0110] The above-prepared positive electrode material Na 0.67 [Ni 0.05 Fe 0.1 Mn 0.8 Zn 0.05 O2, acetylene black, and polyvinylidene fluoride (PVDF) (mass ratio 8:1:1) were mixed in n-methyl-2-pyrrolidone (NMP) to form a slurry. After coating and drying, a positive electrode containing the target product was obtained. Sodium foil was used as the negative electrode, and glass fiber was used as the separator. The CR2025 button cell was assembled in a glove box filled with argon and oxygen and with a moisture content of less than 0.1 ppm. Charge-discharge tests were conducted with a test voltage window of 1.5~4.3 V, a current density of 0.1~5 C, and a test temperature of 30 ℃. The initial discharge capacity was 214 mAh / g (0.05C).

[0111] Comparative Example 1

[0112] Step 1: Prepare an aqueous solution of sulfate containing Ni, Fe, and Mn, wherein the total molar concentration of Ni, Fe, and Mn is 1 mol / L;

[0113] Prepare a sodium hydroxide solution with a molar concentration of 2 mol / L as a precipitant;

[0114] Prepare an ammonia solution with a molar concentration of 0.6 mol / L as a complexing agent;

[0115] Prepare an ammonia solution with a concentration of 10 g / L as the bottom liquid of the reaction vessel;

[0116] Step 2: Pour the bottom liquid into the reactor and keep the reactor stirred. Introduce nitrogen gas into the reactor at a flow rate of 0.5 L / min for 30 min. Pump the salt solution and complexing agent mentioned in Step 1 into the reactor at flow rates of 50 mL / min and 15 mL / min, respectively, to carry out the co-precipitation reaction. During the reaction, the pH is maintained at 10 by pumping in sodium hydroxide solution. The stirring speed of the reactor is 700 rpm, and the reaction temperature of the reactor is maintained at 54.4 ℃.

[0117] After reacting for 12 hours, the reactor speed was reduced to 100 rpm to age the slurry for 4 hours before the reaction was stopped.

[0118] Step 3: Filter, wash and dry the coprecipitated product from Step 2 to obtain the precursor.

[0119] Step 4: Mix the precursor described in Step 3 with Na2CO3 at a molar ratio of precursor to sodium of 1:0.7035 until homogeneous. Place the mixture in a tube furnace, introduce oxygen for 30 min, and heat to 950℃ at a rate of 5℃ / min for sintering for 12 h. Close the oxygen valve, then remove the material at high temperature and transfer it to a glove box. Vacuum cool to room temperature to obtain the sodium ion cathode material Na. 0.67 [Ni 0.1 Fe 0.1 Mn 0.8 O2.

[0120] Step 5: The positive electrode material Na obtained in Step 4... 0.67 [Ni 0.1 Fe 0.1 Mn 0.8 O2 was thoroughly ground for 20 minutes under a dry atmosphere.

[0121] The obtained positive electrode material Na 0.67 [Ni 0.1 Fe 0.1 Mn 0.8 O2, acetylene black, and polyvinylidene fluoride (PVDF) (mass ratio 8:1:1) are mixed in n-methyl-2-pyrrolidone (NMP) to form a slurry. After coating and drying, a positive electrode containing the target product is obtained. Sodium foil is used as the negative electrode and glass fiber is used as the separator. The CR2025 button cell is assembled in a glove box filled with argon and oxygen and with a moisture content of less than 0.1 ppm.

[0122] The morphology of the precursor obtained in Comparative Example 1 is as follows Figure 5 As shown in the figure, the obtained precursor has primary particles that are flaky and cross-pierced, and small particles are attached to the surface of the primary particles, resulting in a loose and irregular morphology; the XRD pattern of the obtained precursor is shown in the figure. Figure 2As shown in the figure, it can be seen that the (011) main peak of the precursor is no longer sharp and the crystallinity is worse. The ratio of the 001 peak intensity to the 011 peak intensity, I001 / I011, is 0.967. From this figure, it can be analyzed that the secondary particles no longer grow mainly on the (011) crystal plane.

[0123] Table 1 Characterization parameters of precursors in Examples 1-4

[0124]

[0125] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A manganese-rich hydroxide precursor, characterized in that, The chemical formula of the manganese-rich hydroxide precursor is (Ni a Fe b Mn c M d )(OH)₂, where 0 < a + d ≤ 0.1, 0 ≤ b ≤ 0.1, 0.8 ≤ c < 1, a + b + c + d = 1, M is a metal element with a valence of ≤ +2, and the solubility product of the M hydroxide is 8×10 -6 ~1×10 -21 ; the manganese-rich hydroxide precursor has nano-sheet primary particles, and the nano-sheet primary particles are cross-connected into spherical or quasi-spherical secondary particles; the secondary particles grow mainly with the (011) crystal plane as the dominant; the peak intensity ratio I(001) / I(011) of the peak of the (001) crystal plane to the peak of the (011) crystal plane is 0.35 - 0.

55.

2. The manganese-rich hydroxide precursor as described in claim 1, characterized in that, The secondary particles have a particle size D50 of 7–12.3 μm; the tap density of the precursor is 1.1–2.5 g / cm³. 3 Specific surface area: 0.1~10 m² 2 / g.

3. The manganese-rich hydroxide precursor as described in claim 1, characterized in that, M is selected from one or more of Mg, Ca, Zn, Cu, and Cr.

4. The method for preparing the manganese-rich hydroxide precursor according to any one of claims 1 to 3, characterized in that, include: (1) Prepare a mixed salt solution of Ni, Fe, Mn and M; Prepare the precipitant solution; Preparation of complexing agent solution; Where M is a metallic element with a valence of ≤+2; the solubility product of the hydroxide of M is 8×10⁻⁶. -6 ~1×10 -21 ; (2) A mixed salt solution, a precipitant solution, and a complexing agent solution are introduced concurrently into the bottom liquid of the reactor to carry out a co-precipitation reaction until a precursor slurry with the desired particle size is obtained. During the co-precipitation reaction, the pH of the reaction system is 9-11. The co-precipitation is divided into two stages, and the concentration of the complexing agent in the second stage reaction system is higher than that in the first stage. The stirring speed of the second stage reaction system is higher than that in the first stage. The concentration of the complexing agent solution introduced in the second stage is 1.5-2.8 times that of the complexing agent solution introduced in the first stage. The flow rate of the complexing agent solution in the first and second stages is the same. The stirring speed in the first stage is 300-500 rpm. The stirring speed in the second stage is 700-1000 rpm. (3) The obtained precursor slurry was aged, separated into solid and liquid components, washed, and dried to obtain a manganese-rich hydroxide precursor (Ni). a Fe b Mn c M d (OH)2, where 0 <a+d≤0.1,0≤b≤0.1,0.8≤c<1,a+b+c+d=1。 5. The method of producing a manganese-rich hydroxide precursor according to claim 4, wherein In step (2), the reaction temperature during the coprecipitation reaction is 50~70 ℃; In the first stage, the concentration of the complexing agent solution introduced is 0.25~0.5 mol / L; in the second stage, the concentration of the complexing agent solution introduced is 0.51~1 mol / L.

6. The method of producing a manganese-rich hydroxide precursor according to claim 4, wherein The preparation of the salt solution in step (1), the coprecipitation reaction in step (2), and the aging in step (3) are carried out under an inert atmosphere or a nitrogen atmosphere; the drying in step (3) is carried out under a vacuum. The precipitant is NaOH and / or KOH; The complexing agent is ammonia and / or an ammonium-containing compound; M is selected from one or more of Mg, Ca, Zn, Cu, and Cr; Salts of Ni, Fe, Mn, and M are soluble salts.

7. A positive electrode material, characterized in that, The precursor prepared by any one of the precursors described in claims 1 to 3 or by any one of the preparation methods described in claims 4 to 6 is mixed with sodium salt and then sintered.

8. The cathode material as described in claim 7, characterized in that, The chemical formula of the positive electrode material is Na x Ni a Fe b Mn c M d O2, where 0.45 ≤ x ≤ 1, 0 < a + d ≤ 0.1, 0 ≤ b ≤ 0.1, 0.8 ≤ c ≤ 1, and a + b + c + d = 1; the particle size D50 of the positive electrode material is 6.8 - 12.5 μm; the tapped density is 1.1 - 2.9 g / cm 3 ; the specific surface area is 0.1 - 9 m 2 / g, and the phase structure presents a P2 or O3 phase.

9. The cathode material of claim 7, wherein, The sintering process includes: sintering at 800~1100 ℃ for 10~24 h; or pre-sintering at 450~500 ℃ for 3~8 h, followed by sintering at 700~1000 ℃ for 10~16 h.

10. A sodium-ion battery, characterized in that, Includes the cathode material as described in any one of claims 7 to 9.

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