Manganese tetraoxide for lithium ion battery and preparation method thereof

Abstract

The invention relates to the technical field of metal oxides, in particular to manganous-manganic oxide for a lithium ion battery and a preparation method of the manganous-manganic oxide. According to the technology, a double-ligand synergistic complexing system of citric acid-p-phenylenediamine-glutamic acid diacetic acid ammonium salt and citric acid-trioxa-tridecane diamine-glutamic acid diacetic acid ammonium salt is introduced, and coprecipitation is carried out by dropwise adding ammonium bicarbonate in a sectional mode under the conditions that the pH is controlled to be 6 and the temperature is controlled to be 60 DEG C. After precipitation, strict washing is performed, and nitrogen atmosphere prebaking and air roasting are performed to finally obtain manganous-manganic oxide compact spherical particles with high sphericity degree, high tap density and narrow particle size distribution. According to the technology, the bottlenecks of wide particle size distribution, poor sphericity, ion pollution, insufficient densification and the like in the traditional process are solved, the nucleation and crystallization controllability and the secondary agglomeration compactness of the material are remarkably improved, and the coating defect and the dispersion of the material are reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal oxides, and particularly relates to a trimanganese tetraoxide for a lithium ion battery and a preparation method thereof. BACKGROUND

[0002] With the rapid development of new energy automobile industry and the increasing demand of energy storage system, the performance requirements of lithium ion battery as the main electrochemical energy storage device are increasingly stringent. Trimanganese tetraoxide (Mn3O4) as an important battery material precursor plays a key role in the preparation of lithium manganate and other positive electrode materials. Its physical and chemical properties directly affect the electrochemical performance, cycle stability and safety characteristics of the final battery material.

[0003] The traditional preparation methods of trimanganese tetraoxide mainly include solid phase method, coprecipitation method, sol-gel method, etc. Among them, the coprecipitation method is widely used because of its relatively simple process and low cost. However, there are many technical bottlenecks in the existing technology, which seriously restricts the industrial production of high-performance trimanganese tetraoxide.

[0004] Firstly, the difficulty of morphology control is the main challenge currently faced. The ideal trimanganese tetraoxide particles should have high sphericity, uniform particle size distribution and dense internal structure to ensure good flowability, high tap density and excellent compaction performance. However, the nucleation and growth process in the traditional precipitation process is difficult to accurately control, and irregular morphology, internal loose and porous particles are easily formed, resulting in low tap density, wide particle size distribution, poor sphericity and other problems.

[0005] Secondly, the crystal face directional growth regulation technology is not mature. The crystal structure characteristics of trimanganese tetraoxide determine that the surface energy of different crystal faces is significantly different, and under the condition of disordered nucleation, anisotropic growth is easily formed, producing rod-shaped, sheet-shaped and other non-spherical morphologies. Lack of effective crystal face regulator and directional induction mechanism, it is difficult to realize the equiaxed crystal growth and the dense aggregation of secondary particles.

[0006] Thirdly, the ion pollution control problem is prominent. In the traditional preparation process, precipitants and complexing agents containing alkali metals such as sodium and potassium are often used. These alkali metal ions are difficult to completely remove in the subsequent washing process, forming solid solution or interface segregation, which seriously affects the electrochemical stability of the material. Especially sodium ions, which will compete with lithium ions for insertion sites during the operation of lithium ion batteries, resulting in capacity attenuation and cycle performance deterioration.

[0007] In addition, the precipitation kinetics control precision is insufficient. The existing precipitation process mostly adopts the way of single precipitant one-time addition, the nucleation rate and the growth rate are difficult to independently control, and it is easy to appear fine particles and loose agglomeration caused by instantaneous nucleation, or coarse particles and uneven distribution caused by insufficient nucleation. Lack of staged and gradual precipitation kinetics design, it is impossible to establish the ideal "slow nucleation-dense growth-ordered agglomeration" reaction window.

[0008] Finally, the post-processing process is not optimized enough. The washing end point control, drying condition selection, calcination atmosphere design and other post-processing links have a decisive influence on the quality of the final product, but the existing technology often ignores the accurate control of these detailed parameters. Insufficient washing leads to the residual of soluble impurities, and improper calcination conditions cause the increase of internal pores or surface defects of the particles, which finally affects the tap density, flowability and electrochemical performance of the material.

[0009] The above technical defects are manifested in industrial application as follows: the prepared trimanganese tetraoxide has low tap density, poor sphericity, wide particle size distribution and serious tail drag, and it is easy to appear rheological instability, high coating defect rate and poor compaction uniformity in the slurry preparation and coating process, which seriously affects the yield and consistency of battery manufacturing, and becomes an important bottleneck restricting the industrialization of high-performance lithium-ion batteries. SUMMARY

[0010] Therefore, the purpose of the present application is to provide a trimanganese tetraoxide for lithium-ion batteries and a preparation method thereof, so as to realize the preparation of dense spherical particles with high tap density, high sphericity and narrow particle size distribution by precise crystal face orientation control and staged precipitation kinetics design, and to meet the strict requirements of high tap density lithium manganate mass production process on raw material quality.

[0011] Based on the above purpose, the present application provides a trimanganese tetraoxide for lithium-ion batteries, which is prepared from manganese sulfate monohydrate in a double-ligand system containing citric acid-p-phenylenediamine-ammonium glutamate diacetate and citric acid-trioxatridecanediamine-ammonium glutamate diacetate, under the conditions of pH 6 and 60℃, by two-stage equal-volume addition of 1mol / L ammonium bicarbonate aqueous solution for precipitation, washing, drying, and then pre-calcination in nitrogen atmosphere and calcination in air atmosphere; wherein the ammonium bicarbonate aqueous solution is subjected to maturation treatment after two-stage equal-volume addition, and the washing is carried out until the conductivity of the filtrate is ≤50μS / cm.

[0012] Further, the citric acid-p-phenylenediamine-ammonium glutamate diacetate is synthesized from p-phenylenediamine and di-tert-butyl carbonate to obtain a single-end protected body, then grafted with citric acid to obtain a citric acid-p-phenylenediamine intermediate, and then deprotected from the p-phenylenediamine end and grafted with glutamic acid diacetate, and then purified by dialysis.

[0013] Preferably, the weight ratio of the p-phenylenediamine, di-tert-butyl carbonate, citric acid and glutamic acid diacetate is 10:10:10:27.

[0014] Further, the citric acid-trioxatridecanediamine-glutamic acid diacetate ammonium salt is synthesized from 4,7,10-trioxa-1,13-tridecanediamine and di-tert-butyl carbonate to form a single end protection body, then grafted with citric acid to obtain a citric acid-trioxatridecanediamine intermediate, and then the trioxatridecanediamine end is deprotected and grafted with glutamic acid diacetate, and then purified by dialysis.

[0015] Preferably, the weight ratio of the 4,7,10-trioxa-1,13-tridecanediamine, di-tert-butyl carbonate, citric acid and glutamic acid diacetate is 12:6:10:27.

[0016] Preferably, the citric acid-p-phenylenediamine-glutamic acid diacetate ammonium salt is 6.25-7.78 parts by mass and the citric acid-trioxatridecanediamine-glutamic acid diacetate ammonium salt is 6.88-8.89 parts by mass based on 100 parts by mass of manganese sulfate monohydrate.

[0017] Preferably, the amount-of-substance ratio of the ammonium bicarbonate to the manganese sulfate monohydrate is 0.47-0.53:1.

[0018] Preferably, the pre-baking temperature in a nitrogen atmosphere is 500℃, and the holding time is 1.5-3.0h; the baking temperature in an air atmosphere is 650℃, and the holding time is 3-5h.

[0019] Preferably, the particle size distribution of the trimanganese tetraoxide for lithium ion batteries has a D10 of 5-6μm, a D50 of 9-10μm, and a D90 of 14-15μm; the tap density is 3.15-3.30g / cm 3 ; and the sphericity is 0.94-0.95.

[0020] Preferably, the glutamic acid diacetate is obtained by converting a glutamic acid diacetate tetrasodium aqueous solution through a cation exchange resin column.

[0021] Preferably, the cation exchange resin is DOWEX 50WX8, and the sample injection flow rate is 80-120mL / h.

[0022] Further, the application also provides a preparation method of the trimanganese tetraoxide for lithium ion batteries, comprising the following steps: dissolving manganese sulfate monohydrate in deionized water to obtain a solution, adding citric acid-p-phenylenediamine-glutamic acid diacetate ammonium salt and citric acid-trioxatridecanediamine-glutamic acid diacetate ammonium salt, adjusting the pH to 6 with ammonia water after stirring for 30 min, and keeping the temperature at 60 DEG C; adding ammonium bicarbonate aqueous solution in two equal volumes, the first stage is added for 40-50 min, matured for 10-20 min, the second stage is added for 10-20 min, and matured again for 25-40 min, filtered, washed with deionized water until the conductivity of the filtrate is less than or equal to 50 mu S / cm, dried at 80 DEG C for 8 h, and then sequentially pre-baked in a nitrogen atmosphere and baked in an air atmosphere to obtain the trimanganese tetraoxide for lithium ion batteries.

[0023] The application realizes a plurality of significant technical advantages by constructing a citric acid-p-phenylenediamine-glutamic acid diacetate and citric acid-trioxatridecanediamine-glutamic acid diacetate double-ligand synergistic complexing system, combining a segmented ammonium bicarbonate precipitation and a two-stage baking process. The crystal face directional growth is precisely controlled. In the double-ligand system, the rigid aromatic fragment containing p-phenylenediamine provides a stable pi-pi stacking effect to adjust the surface energy of a specific crystal face; the flexible ether segment containing trioxatridecanediamine realizes dynamic coordination adjustment through multi-point chelation. The multi-dentate coordination network formed by the two types of ligands and glutamic acid diacetate selectively adsorbs on the high-energy crystal face of the trimanganese tetraoxide crystal under the condition of pH 6, effectively inhibits anisotropic growth, induces the formation of equiaxed crystals, and realizes the improvement of sphericity.

[0024] The secondary particle dense agglomeration mechanism is optimized. Through the segmented precipitant addition strategy, the first stage slowly adds ammonium bicarbonate to establish uniform and fine crystal nucleus distribution, and the short-time maturation stabilizes the primary phase; the second stage promotes the dense growth of the crystal nucleus by rapid supplement, and the extended maturation time drives the secondary agglomeration reconstruction. The organic coordination bridge formed by the double-ligand molecules on the particle surface guides the ordered arrangement and dense accumulation of the crystal grains, and significantly improves the tap density.

[0025] Ion pollution is effectively eliminated. The glutamic acid diacetate tetrasodium is pretreated into an acid type by using ion exchange resin to eliminate the introduction of sodium ions from the source; ammonium bicarbonate is selected instead of sodium bicarbonate as a precipitant to avoid additional alkali metal pollution; the washing endpoint is strictly controlled to less than or equal to 50 mu S / cm to ensure that the soluble impurities are fully removed. This series of measures completely solves the ion pollution problem in the traditional process.

[0026] The particle size distribution is narrowed and the uniformity is improved. The double-ligand synergistic complexing inhibits a large number of instantaneous nucleation, the segmented precipitation realizes the time and space separation of nucleation and growth, effectively compresses the particle size distribution range, and controls D10-D90 in a narrow range, eliminating the coarse particle tail phenomenon in the traditional process.

[0027] The structure is improved by optimizing the calcination process. The mild decomposition of organic ligands and ammonium salt in the nitrogen pre-calcination stage avoids internal pores caused by violent gas release; the air atmosphere calcination completes the removal of sulfate and lattice perfection, ensuring the internal density and surface integrity of the particles.

[0028] The process applicability and stability are significantly improved. The prepared trimanganese tetraoxide exhibits excellent rheological stability during slurry preparation, and the coating defect rate is reduced to 7%-8%; the pressing piece density uniformity is greatly improved, and the dispersion coefficient is controlled at 1.5%-2.3%, which is much better than the traditional process level of 4.0%-6.5%.

[0029] The industrial application value is outstanding. The trimanganese tetraoxide prepared by the present application has high tap density, excellent sphericity, uniform distribution and low impurity content, fully meeting the strict requirements of high compaction density lithium manganate production line, providing reliable raw material guarantee for improving battery manufacturing yield and product consistency, and having important industrialization popularization value. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the present application or prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description.

[0031] Figure 1 The infrared spectra of citric acid-p-phenylenediamine-ammonium glutamate diacetate salt and citric acid-trioxa-tridecanediamine-ammonium glutamate diacetate salt in Example 2 of the present application; Figure 2 The viscosity-shear rate curve of the slurry prepared by the trimanganese tetraoxide in Example 1-3 of the present application; Figure 3 The viscosity-shear rate curve of the slurry prepared by the trimanganese tetraoxide in Example 2 and Comparative Examples 1-7 of the present application. DETAILED DESCRIPTION In order to make the purpose, technical scheme and advantages of the present application more clear, the following will further describe the present application in combination with specific embodiments.

[0032] Example 1: (1) Dissolve 73.6 g of tetrasodium glutamate diacetate in 500 mL of deionized water to prepare a tetrasodium glutamate diacetate solution, load 750 mL of cation exchange resin DOWEX 50WX8 into an ion exchange column, wash with 2 mol / L hydrochloric acid until the effluent pH is less than 2.0, and then wash with deionized water until the effluent conductivity is less than 10 μS / cm, pass the tetrasodium glutamate diacetate solution through the ion exchange column at a flow rate of 80 mL / h, collect the effluent until the pH stabilizes at 2.2, and concentrate the effluent under reduced pressure to 500 mL to obtain a glutamate diacetate solution; (2) Take 10 g of p-phenylenediamine and add it to 100 mL of anhydrous ethanol in an ice bath. Slowly add 10 g of di-tert-butyl dicarbonate and stir for 2 hours to obtain a single-tert-butoxycarbonyl-protected p-phenylenediamine ethanol solution. Take another 10 g of citric acid and add it to 120 mL of deionized water in an ice bath. Then, add 12 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 6 g of N-hydroxysuccinimide in sequence, and adjust the pH to 5 with an aqueous hydrochloric acid solution (concentration 1 mol / L). Stir for 30 minutes to activate, then slowly add the single-tert-butoxycarbonyl-protected p-phenylenediamine ethanol solution, and adjust the pH to 6 with ammonia water (concentration 2 mol / L). Stir at room temperature for 10 hours to obtain a citric acid-p-phenylenediamine intermediate mixture solution; (3) Take 20 mL of anhydrous ethanol hydrochloric acid solution (concentration 4 mol / L) and add it to the citric acid-p-phenylenediamine intermediate mixture solution prepared in step (2). Stir for 1 hour to remove the tert-butoxy carbonyl protection, then add 200 mL of deionized water and remove the ethanol under reduced pressure. Adjust the pH to 5 with ammonia water (concentration 2 mol / L) to obtain a citric acid-p-phenylenediamine free amine salt solution; (4) Take 250 mL of glutamic acid diacetic acid solution and place it in an ice bath. Then, add 12 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 6 g of N-hydroxysuccinimide in sequence, and adjust the pH to 5 with an aqueous hydrochloric acid solution (concentration 1 mol / L). Stir for 30 minutes to activate, then slowly add the citric acid-p-phenylenediamine free amine salt solution prepared in step (3), and adjust the pH to 6 with ammonia water (concentration 2 mol / L). Stir at room temperature for 14 hours. After the reaction is complete, adjust the pH to 3 with an aqueous hydrochloric acid solution (concentration 1 mol / L). After standing for 1 hour, filter out the insoluble material. Take the filtrate and place it in a molecular weight cutoff value 500 Da dialysis bag in deionized water for dialysis for 48 hours. Replace the deionized water every 8 hours until the conductivity is less than 100 μS / cm. Adjust the pH to 7 with ammonia water (concentration 2 mol / L) and freeze-dry to obtain a citric acid-p-phenylenediamine-glutamic acid diacetic acid ammonium salt; (5) Take 12 g of 4,7,10-trioxa-1,13-tridecanediamine and add it to 100 mL of anhydrous ethanol in an ice bath. Slowly add 6 g of di-tert-butyl dicarbonate and stir for 2 hours to obtain a single-tert-butoxycarbonyl-protected trioxa-tridecanediamine ethanol solution. Take another 10 g of citric acid and add it to 120 mL of deionized water in an ice bath. Then, add 12 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 6 g of N-hydroxysuccinimide in sequence, and adjust the pH to 5 with an aqueous hydrochloric acid solution (concentration 1 mol / L). Stir for 30 minutes to activate, then slowly add the single-tert-butoxycarbonyl-protected trioxa-tridecanediamine ethanol solution, and adjust the pH to 6 with ammonia water (concentration 2 mol / L). Stir at room temperature for 10 hours to obtain a citric acid-trioxa-tridecanediamine intermediate mixture solution; (6) Take 20 mL of hydrochloric acid anhydrous ethanol solution (concentration 4 mol / L) and add it to the citric acid-trioxatridecanediamine intermediate mixed solution prepared in step (5), stir for 1 h to remove the tert-butyloxy carbonyl protection, then add 200 mL of deionized water and remove the ethanol under reduced pressure, adjust the pH to 5 with ammonia water (concentration 2 mol / L) to obtain a citric acid-trioxatridecanediamine free amine salt solution; (7) Take 250 mL of glutamic acid diacetic acid solution and place it in an ice bath, then take 12 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 6 g of N-hydroxysuccinimide and add them in sequence, and adjust the pH to 5 with hydrochloric acid aqueous solution (concentration 1 mol / L), stir and activate for 30 min, slowly drop the citric acid-trioxatridecanediamine free amine salt solution prepared in step (6) and adjust the pH to 6 with ammonia water (concentration 2 mol / L), stir at room temperature for 14 h, after the reaction is completed, adjust the pH to 3 with hydrochloric acid aqueous solution (concentration 1 mol / L), stand for 1 h, then filter and discard the insoluble matter, take the filtrate and load it into a molecular weight cut-off value 500 Da dialysis bag in deionized water and dialyze for 48 h, replace the deionized water every 8 h until the conductivity is less than 100 μS / cm, adjust the pH to 7 with ammonia water (concentration 2 mol / L) and freeze-dry to obtain citric acid-trioxatridecanediamine-glutamic acid diacetic acid ammonium salt; (8) Take 160 g of manganese sulfate monohydrate, add deionized water to make the total volume 1000 mL and stir to dissolve to obtain a manganese sulfate solution, take 10 g of citric acid-p-phenylenediamine-glutamic acid diacetic acid ammonium salt and 11 g of citric acid-trioxatridecanediamine-glutamic acid diacetic acid ammonium salt, add them to the manganese sulfate solution and stir for 30 min, then adjust the pH to 6 with ammonia water (concentration 2 mol / L), heat to 60°C and maintain the temperature, add 250 mL of ammonium bicarbonate aqueous solution (concentration 1 mol / L) at a uniform speed of 50 min, maintain the temperature at 60°C, stir and mature for 10 min, then add 250 mL of ammonium bicarbonate aqueous solution (concentration 1 mol / L) at a fast speed of 20 min, maintain the temperature at 60°C, stir and mature for 25 min, filter the obtained slurry and wash it with deionized water until the conductivity of the filtrate is less than 50 μS / cm, take the wet filter cake and place it in a vacuum oven, dry it at 80°C for 8 h, heat it at 500°C for 1.5 h under a nitrogen atmosphere and then heat it at 650°C for 3 h under an air atmosphere to obtain manganese sesquioxide for lithium ion batteries.

[0033] Example 2: (1) Take 73.6 g of tetrasodium glutamate diacetate and dissolve it in 500 mL of deionized water to prepare a tetrasodium glutamate diacetate solution. Load 750 mL of cation exchange resin DOWEX 50WX8 into an ion exchange column, wash it with 2 mol / L hydrochloric acid until the pH of the effluent is less than 2.0, and then wash it with deionized water until the conductivity of the effluent is less than 10 μS / cm. Pass the tetrasodium glutamate diacetate solution through the ion exchange column at a flow rate of 100 mL / h, collect the effluent until the pH stabilizes at 2.2, and then concentrate the effluent under reduced pressure to 500 mL to obtain a glutamate diacetate solution; (2) Take 10 g of p-phenylenediamine and add it to 100 mL of anhydrous ethanol in an ice bath. Slowly add 10 g of di-tert-butyl carbonate and stir for 2 h to obtain a single-tert-butoxycarbonyl-protected p-phenylenediamine ethanol solution. Take 10 g of citric acid and add it to 120 mL of deionized water in an ice bath. Then, sequentially add 12 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 6 g of N-hydroxysuccinimide, and adjust the pH to 5 with a hydrochloric acid aqueous solution (concentration 1 mol / L). Stir for 30 min to activate, slowly add the single-tert-butoxycarbonyl-protected p-phenylenediamine ethanol solution, and adjust the pH to 6 with ammonia water (concentration 2 mol / L). Stir at room temperature for 12 h to obtain a citric acid-p-phenylenediamine intermediate mixture solution; (3) Take 20 mL of a hydrochloric acid anhydrous ethanol solution (concentration 4 mol / L) and add it to the citric acid-p-phenylenediamine intermediate mixture solution prepared in step (2). Stir for 1 h to remove the tert-butoxycarbonyl protection, then add 200 mL of deionized water and remove the ethanol under reduced pressure. Adjust the pH to 5 with ammonia water (concentration 2 mol / L) to obtain a citric acid-p-phenylenediamine free amine salt solution; (4) Take 250 mL of the glutamate diacetate solution and place it in an ice bath. Then, sequentially add 12 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 6 g of N-hydroxysuccinimide, and adjust the pH to 5 with a hydrochloric acid aqueous solution (concentration 1 mol / L). Stir for 30 min to activate, slowly add the citric acid-p-phenylenediamine free amine salt solution prepared in step (3), and adjust the pH to 6 with ammonia water (concentration 2 mol / L). Stir at room temperature for 16 h. After the reaction is complete, adjust the pH to 3 with a hydrochloric acid aqueous solution (concentration 1 mol / L). After standing for 1 h, filter and discard the insoluble material. Take the filtrate, load it into a molecular weight cutoff value 500 Da dialysis bag, dialyze it in deionized water for 48 h, replace the deionized water every 8 h until the conductivity is less than 100 μS / cm, adjust the pH to 7 with ammonia water (concentration 2 mol / L), and then freeze-dry to obtain a citric acid-p-phenylenediamine-glutamate diacetate ammonium salt; (5) Take 12g of 4,7,10-trioxo-1,13-tridecanediamine and add it to 100mL of anhydrous ethanol and place it in an ice bath. Then take 6g of di-tert-butylcarbonic anhydride and slowly add it dropwise while stirring for 2h to obtain a trioxatridecanediamine ethanol solution protected by a single-terminal tert-butyloxycarbonyl group. Take 10g of citric acid and add it to 120mL of deionized water and place it in an ice bath. Then take 12g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 6g of N-hydroxysuccinimide and add them in sequence. Adjust the pH to 5 with hydrochloric acid aqueous solution (concentration 1mol / L), stir and activate for 30min. Slowly add the trioxatridecanediamine ethanol solution protected by a single-terminal tert-butyloxycarbonyl group and adjust the pH to 6 with ammonia water (concentration 2mol / L). Stir at room temperature for 12h to obtain a citric acid-trioxatridecanediamine intermediate mixture. (6) Take 20 mL of hydrochloric acid anhydrous ethanol solution (concentration 4 mol / L) and add it to the citric acid-trioxadecanediamine intermediate mixture prepared in step (5). Stir for 1 h to remove the tert-butyloxycarbonyl protection. Then add 200 mL of deionized water and remove the ethanol under reduced pressure. Adjust the pH to 5 with ammonia water (concentration 2 mol / L) to obtain the citric acid-trioxadecanediamine free amine salt solution. (7) Take 250 mL of glutamic acid diacetic acid solution and place it in an ice bath. Then take 12 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 6 g of N-hydroxysuccinimide and add them in sequence. Adjust the pH to 5 with hydrochloric acid aqueous solution (concentration 1 mol / L), stir and activate for 30 min. Slowly add the citrate-trioxadecanediamine free amine salt solution prepared in step (6) and adjust the pH to 6 with ammonia water (concentration 2 mol / L). Stir at room temperature for 16 h. After the reaction is completed, take hydrochloric acid aqueous solution (concentration 1 mol / L) and adjust the pH to 3. After standing for 1 h, filter and discard the insoluble matter. Take the filtrate and put it into a dialysis bag with a molecular weight cutoff of 500 Da and dialyze it in deionized water for 48 h. Change the deionized water every 8 h until the conductivity is less than 100 μS / cm. Adjust the pH to 7 with ammonia water (concentration 2 mol / L) and freeze dry to obtain citrate-trioxadecanediamine-glutamic acid diacetic acid ammonium salt. (8) Take 169 g of manganese sulfate monohydrate and add deionized water to make up to a total volume of 1000 mL and stir to dissolve, obtaining a manganese sulfate solution. Take 12 g of citric acid-p-phenylenediamine-glutamic acid diacetate ammonium salt and 13 g of citric acid-trioxa-tridecanediamine-glutamic acid diacetate ammonium salt and add to the manganese sulfate solution and stir for 30 min. Then use ammonia water (concentration 2 mol / L) to adjust the pH to 6, heat to 60°C and maintain the temperature, and add 250 mL of ammonium bicarbonate aqueous solution (concentration 1 mol / L) at a uniform speed of 45 min, maintain the temperature at 60°C, and stir for 15 min. Then add 250 mL of ammonium bicarbonate aqueous solution (concentration 1 mol / L) at a fast speed of 15 min, maintain the temperature at 60°C, and stir for 30 min. Take the obtained slurry and filter and wash with deionized water until the conductivity of the filtrate is less than 50 μS / cm. Take the wet filter cake and place it in a vacuum oven, dry at 80°C for 8 h, heat at 500°C under nitrogen atmosphere for 2 h, and then heat at 650°C under air atmosphere for 4 h, to obtain manganese sesquioxide for lithium ion batteries.

[0034] Example 3: (1) Take 73.6 g of tetrasodium glutamate diacetate and dissolve in 500 mL of deionized water to prepare a tetrasodium glutamate diacetate solution. Load 750 mL of cation exchange resin DOWEX 50WX8 into an ion exchange column, wash with 2 mol / L hydrochloric acid until the effluent pH is less than 2.0, and then wash with deionized water until the conductivity of the effluent is less than 10 μS / cm. Pass the tetrasodium glutamate diacetate solution through the ion exchange column at a flow rate of 120 mL / h, collect the effluent until the pH stabilizes at 2.2, and concentrate the effluent under reduced pressure to 500 mL to obtain a glutamic acid diacetate solution; (2) Take 10 g of p-phenylenediamine and add to 100 mL of anhydrous ethanol in an ice bath, then slowly add 10 g of di-tert-butyl carbonate and stir for 2 h to obtain a single-tert-butoxycarbonyl-protected p-phenylenediamine ethanol solution. Take 10 g of citric acid and add to 120 mL of deionized water in an ice bath, then sequentially add 12 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 6 g of N-hydroxysuccinimide, and use an aqueous hydrochloric acid solution (concentration 1 mol / L) to adjust the pH to 5, stir for 30 min to activate, slowly add the single-tert-butoxycarbonyl-protected p-phenylenediamine ethanol solution, and use ammonia water (concentration 2 mol / L) to adjust the pH to 6, stir at room temperature for 14 h to obtain a citric acid-p-phenylenediamine intermediate mixture; (3) Take 20 mL of anhydrous ethanol hydrochloric acid solution (concentration 4 mol / L) and add to the citric acid-p-phenylenediamine intermediate mixture prepared in step (2), stir for 1 h to remove the tert-butoxycarbonyl protection, then add 200 mL of deionized water and remove the ethanol under reduced pressure, use ammonia water (concentration 2 mol / L) to adjust the pH to 5, and obtain a citric acid-p-phenylenediamine free amine salt solution; (4) Take 250 mL glutamic acid diacetic acid solution in an ice bath, then add 12 g 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 6 g N-hydroxysuccinimide in turn, and adjust pH to 5 with hydrochloric acid aqueous solution (concentration 1 mol / L), stir for 30 min, slowly add the citric acid-p-phenylenediamine free amine salt solution prepared in step (3), and adjust pH to 6 with ammonia water (concentration 2 mol / L), stir at room temperature for 18 h, after the reaction is completed, adjust pH to 3 with hydrochloric acid aqueous solution (concentration 1 mol / L), stand for 1 h, then filter and discard the insoluble substance, take the filtrate, load into a molecular weight cut-off value 500 Da dialysis bag, dialyze in deionized water for 60 h, replace the deionized water every 8 h until the conductivity is less than 100 μS / cm, adjust pH to 7 with ammonia water (concentration 2 mol / L), and freeze-dry to obtain citric acid-p-phenylenediamine-glutamic acid diacetic acid ammonium salt; (5) Take 12 g 4,7,10-trioxa-1,13-tridecanediamine, add 100 mL anhydrous ethanol in an ice bath, then slowly add 6 g di-tert-butyl carbonate and stir for 2 h to obtain a single-terminated tert-butyloxycarbonyl-protected trioxa-tridecanediamine ethanol solution, take 10 g citric acid, add 120 mL deionized water in an ice bath, then add 12 g 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 6 g N-hydroxysuccinimide in turn, and adjust pH to 5 with hydrochloric acid aqueous solution (concentration 1 mol / L), stir for 30 min, slowly add the single-terminated tert-butyloxycarbonyl-protected trioxa-tridecanediamine ethanol solution, and adjust pH to 6 with ammonia water (concentration 2 mol / L), stir at room temperature for 14 h to obtain a citric acid-trioxa-tridecanediamine intermediate mixture; (6) Take 20 mL hydrochloric acid anhydrous ethanol solution (concentration 4 mol / L) and add to the citric acid-trioxa-tridecanediamine intermediate mixture prepared in step (5), stir for 1 h to remove the tert-butyloxycarbonyl protection, then add 200 mL deionized water and remove ethanol under reduced pressure, and adjust pH to 5 with ammonia water (concentration 2 mol / L) to obtain a citric acid-trioxa-tridecanediamine free amine salt solution; (7) Take 250 mL glutamic acid diacetate solution into an ice bath, then take 12 g 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 6 g N-hydroxysuccinimide in turn, and adjust pH to 5 with hydrochloric acid aqueous solution (concentration 1 mol / L), stir for 30 min for activation, slowly drop the citric acid-trioxatridecanediamine free amine salt solution prepared in step (6), and adjust pH to 6 with ammonia water (concentration 2 mol / L), stir for 18 h at room temperature, after the reaction is completed, adjust pH to 3 with hydrochloric acid aqueous solution (concentration 1 mol / L), stand for 1 h, then filter and discard the insoluble substance, take the filtrate into a dialysis bag with a molecular weight cut-off value of 500 Da, dialyze in deionized water for 60 h, replace the deionized water every 8 h until the conductivity is less than 100 μS / cm, adjust pH to 7 with ammonia water (concentration 2 mol / L), and freeze-dry to obtain citric acid-trioxatridecanediamine-glutamic acid diacetate ammonium salt; (8) Take 180 g manganese sulfate monohydrate, add deionized water to make up to a total volume of 1000 mL, stir to dissolve, to obtain a manganese sulfate solution, take 14 g citric acid-p-phenylenediamine-glutamic acid diacetate ammonium salt and 16 g citric acid-trioxatridecanediamine-glutamic acid diacetate ammonium salt, add them into the manganese sulfate solution, stir for 30 min, then adjust pH to 6 with ammonia water (concentration 2 mol / L), heat to 60 ℃, drop 250 mL ammonium bicarbonate aqueous solution (concentration 1 mol / L) at a uniform speed of 40 min, maintain the temperature at 60 ℃, stir for 20 min, then drop 250 mL ammonium bicarbonate aqueous solution (concentration 1 mol / L) quickly at 10 min, maintain the temperature at 60 ℃, stir for 40 min, filter the obtained slurry and wash with deionized water until the conductivity of the filtrate is less than 30 μS / cm, take the wet filter cake into a vacuum oven, dry at 80 ℃ for 8 h, heat at 500 ℃ for 3 h in a nitrogen atmosphere, and then heat at 650 ℃ for 5 h in an air atmosphere, to obtain trimanganese tetraoxide for lithium ion batteries.

[0035] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that citric acid-trioxatridecanediamine-glutamic acid diacetate ammonium salt is not added, and only 25 g of citric acid-p-phenylenediamine-glutamic acid diacetate ammonium salt (equivalent to the total amount of two ligands in Example 2) is added, and the other conditions are the same as those in Example 2.

[0036] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that citric acid-p-phenylenediamine-glutamic acid diacetate ammonium salt is not added, and only 25 g of citric acid-trioxatridecanediamine-glutamic acid diacetate ammonium salt (equivalent to the total amount of two ligands in Example 2) is added, and the other conditions are the same as those in Example 2.

[0037] Comparative Example 3: Comparative Example 3 differs from Example 2 in that step (1) is not ion-exchanged to remove sodium, and 73.6 g of tetrasodium glutamate diacetate solution is used directly without acid conversion, and the rest of the conditions are consistent with Example 2.

[0038] Comparative Example 4: Comparative Example 4 differs from Example 2 in that the precipitant is replaced by 1 mol / L sodium bicarbonate aqueous solution instead of 1 mol / L ammonium bicarbonate aqueous solution, and the volume, staged dropping time sequence and ripening time remain the same, and the rest of the conditions are consistent with Example 2.

[0039] Comparative Example 5: Comparative Example 5 differs from Example 2 in that 1 mol / L ammonium bicarbonate aqueous solution is retained as the precipitant, but the two-stage dropping is changed to a single stage: 500 mL is added at a constant speed within 60 min at 60°C, and there is no intermediate and end ripening time, and the rest of the conditions are consistent with Example 2.

[0040] Comparative Example 6: Comparative Example 6 differs from Example 2 in that the calcination procedure is changed to single-stage calcination at 650°C in air for 4 h, and the nitrogen pre-calcination stage is cancelled, and the rest of the conditions are consistent with Example 2.

[0041] Comparative Example 7: Comparative Example 7 differs from Example 2 in that the end point of washing is relaxed from filtrate conductivity < 50 μS / cm to 200 μS / cm, and the rest of the conditions are consistent with Example 2.

[0042] Performance test: Infrared spectrum test: Fourier infrared spectrometer is used for testing, and the results are shown in Figure 1 .

[0043] Tap density: GB / T 1479.1-2011 is executed, standard tap density cylinder is used, and tap frequency is 1x10 3 Stable value is obtained, ambient temperature is 23±2℃, relative humidity is 50±5%, and the results are shown in Table 1.

[0044] Sphericity and particle size distribution: sphericity is tested according to GB / T 25915.1-2010 and GB / T 25915.2-2010, ≥1000 particles are counted in a representative field of view, and sphericity is calculated; particle size distribution is tested according to GB / T 19077-2016, deionized water is used as dispersion medium, ultrasonic dispersion is performed for 2 min, D10 / D50 / D90 is recorded, and the results are shown in Table 1.

[0045] Rheology and coating defect rate: The slurry of 70wt% solid content of trimanganese tetraoxide was prepared by using water-based system (mass ratio of CMC:SBR (based on solid content) 1:1, total gum amount accounting for 3wt% of solid (active material + conductive agent + binder solid)), and was defoamed by planetary stirring. The viscosity-shear rate curve was tested by using Brookfield DV2T at 25°C, at a speed of 0.5-20rpm, as shown in Figure 2 and Figure 3 The slurry of 70wt% solid content of trimanganese tetraoxide was prepared by using water-based system (mass ratio of CMC:SBR (based on solid content) 1:1, total gum amount accounting for 3wt% of solid (active material + conductive agent + binder solid)), and was defoamed by planetary stirring. The slurry was coated on aluminum foil (12μm thick) by using an experimental coater (wet film thickness 100μm), and was dried (80°C, 10min). The pinhole, bubble, and flow mark defect rates (defect number / m 2 ) were recorded, and the results are shown in Table 1.

[0046] Compaction performance and sheet density uniformity: The powder was directly pressed into a standard circular sheet (diameter 12mm). The sheet density was measured after static pressing at 200MPa for 30s. Ten sheets were prepared for each sample, and the sheet density dispersion coefficient (RSD) was recorded, and the results are shown in Table 1.

[0047] Table 1 Performance test results

[0048] Data analysis: As can be seen from the data of Examples 1-3 in Table 1, the trimanganese tetraoxide prepared by the present application has high and stable stacking and morphology characteristics as a whole, the coating defect number is about 7-8 / m 2 , the sheet density is about 3.70-3.82g / cm 3 , and the dispersion coefficient is about 1.5-2.3%. The possible mechanism is that the multi-dentate coordination network formed by citric acid-p-phenylenediamine, citric acid-trioxa-tridecanediamine, and glutamic acid diacetate inhibits transient nucleation and induces crystal face orientation at a pH of about 6; the segmented addition of ammonium bicarbonate provides a kinetic window of slow nucleation-dense growth-agglomeration reconstruction; and strict washing reduces the soluble salt source, and the two-stage calcination gradually removes organic and ammonium salts, thereby reducing the porosity, and thus the high tap density, good rheology, and low coating defects are achieved.

[0049] From the data of Example 2 and Comparative Example 1 in Table 1, it can be seen that: Example 2 is more advantageous in tap density, sphericity, coating defect rate, tablet density and dispersion coefficient, and the particle size is concentrated and the two sides are controlled. It shows that the coexistence of citric acid-p-phenylenediamine-glutamic acid diacetate and citric acid-trioxatridecanediamine-glutamic acid diacetate in Example 2, through the bridging of multi-dentate coordination and flexible chain segment, jointly restricts the growth orientation of crystal nucleus surface and promotes the isotropic dense aggregation of secondary particles; only one coordination path of rigid aromatic diamine is reserved, the coordination environment tuning ability decreases, it is difficult to establish a stable slow nucleation-dense growth window, and it is easy to appear loose aggregation and increase of pores, thereby reducing the packing efficiency and enlarging the tablet density fluctuation.

[0050] From the data of Example 2 and Comparative Example 2 in Table 1, it can be seen that: the particle size distribution parameters of the two are close, but the tap density and tablet density of Example 2 are more excellent than those of Comparative Example 2, at the same time, the sphericity and coating defect rate are also more excellent, and the dispersion coefficient is lower. Under the premise of similar particle size, the density and uniformity can still be improved, which may be due to the introduction of rigid fragments containing p-phenylenediamine and flexible chain segments containing trioxatridecanediamine, which together construct a coordination network with glutamic acid diacetate, achieving synergy in crystal orientation, particle surface rearrangement and secondary aggregation densification, further reducing internal porosity and making morphology closer to equiaxed, thereby improving packing and compaction and reducing coating defects without changing the particle size window.

[0051] From the data of Example 2 and Comparative Example 3 in Table 1, it can be seen that: Example 2 is more excellent in tap density, sphericity, D90, coating defect rate and tablet density dispersion coefficient, indicating that the large particle tail and irregular morphology are effectively inhibited. It is speculated that when sodium is not fully removed, the ionic strength and charge shielding of the solution may weaken the multi-dentate complexation of organic ligands, causing more intense instantaneous nucleation and aggregation coarsening during the precipitation stage, which is manifested as D90 expansion, sphericity decrease and internal pore increase; after desodium, the coordination-nucleation is more controllable, which is beneficial to narrower distribution and higher packing density.

[0052] From the data of Example 2 and Comparative Example 4 in Table 1, it can be seen that: the tap density, sphericity and tablet density of Example 2 are better than those of Comparative Example 4, the coating defect rate and dispersion coefficient are lower, and the particle size distribution is also more concentrated. It shows the criticality of the choice of precipitant: ammonium bicarbonate releases ammonia and forms a mild buffer at 60°C and pH about 6, gradually supplying carbonate and ammonia, which is conducive to controllable nucleation and growth; sodium bicarbonate may produce a relatively high alkaline microenvironment locally and introduce sodium, which not only intensifies instantaneous precipitation and morphology fragmentation, but also brings about the residual of exogenous soluble salt, leading to secondary loose aggregation and elongation of tail particles, and thus weakening the packing and coating stability.

[0053] From the data of Example 2 and Comparative Example 5 in Table 1, it can be seen that: Example 2 is more superior in tap density, sphericity, coating defect rate, tablet density and coefficient of variation. And D90 is smaller. The trend is related to the process window of segmented dropwise addition combined with double ripening: slow dropwise addition and short ripening provide time for uniform and fine crystal nucleus, and rapid supplement and re-ripening promote dense growth and secondary agglomeration reconstruction, which overall compresses the particle size distribution and improves the sphericity; single-stage uniform addition without ripening may cause nucleation and growth to compete with each other, resulting in wide particle size distribution, insufficient structure densification and increased tablet density fluctuation, thereby increasing the exposure of coating defects.

[0054] From the data of Example 2 and Comparative Example 6 in Table 1, it can be seen that: the particle size distribution parameters of the two are similar, but Example 2 is significantly superior to Comparative Example 6 in tap density, sphericity, tablet density, coating defect rate and coefficient of variation. The difference in density and morphology under the condition of similar particle size is due to the roasting atmosphere and temperature trajectory: pre-roasting at medium temperature in nitrogen can mildly decompose organic and ammonium salts and promote structural rearrangement, followed by stable phase and removal of sulfate in air, reducing sintering hole source and improving crystal face integrity; if directly roasting in air, oxidation decomposition and outgassing may form pores inside the particles or edge collapse, although the particle size does not change, but the effective packing and compaction are damaged, leading to the decrease of coating stability.

[0055] From the data of Example 2 and Comparative Example 7 in Table 1, it can be seen that: the tap density and sphericity of Example 2 are obviously superior to those of Comparative Example 7, the tail of particle size distribution is effectively compressed, and the coating defect rate and tablet density coefficient of variation are lower. It shows that the control of washing endpoint has a decisive influence on the final microstructure: when the filtrate conductivity is strictly controlled at a low level, the soluble sulfate and residual sodium, ammonium, etc. are removed, the outgassing and side reaction source during roasting is significantly reduced, which is conducive to the formation of dense primary crystals and stable secondary agglomerates; insufficient washing may induce pores and agglomeration coarsening during heating, which is manifested as long particle size tail, reduced packing efficiency and increased coating defects.

[0056] From Figure 1 it can be seen that: both double-ligand ammonium salt samples appear a broad O-H / N-H stretching band in the 3500-3300 cm -1 interval; at 1660±5 cm -1 and 1546±3 cm -1 , there appear paired strong absorption of amide I (C=O) and amide II (N-H bending / C-N), respectively, while the COO -1 symmetric stretching peak at ~1410 cm - has high intensity, indicating that the amide bond and carboxylate structure in the target product have been formed. Further comparison shows that the citric acid-trioxatridecanediamine-glutamic acid diaminium salt appears at 1145 / 1110 / 1060 cm -1The C-O-C stretching peak group is continuous and has higher relative intensity; while the citric acid-p-phenylenediamine-gluconic acid ammonium salt has more prominent absorption of aromatic ring C=C at 1600 cm -1 and para-substituted out-of-plane bending at 830 / 765 cm -1 , which proves the successful synthesis of the two kinds of double-ligand ammonium salts.

[0057] It can be seen from Figure 2 that the slurries of the three examples all have typical shear thinning (pseudoplastic) characteristics. With the increase of shear rate, the viscosity continuously decreases and tends to be stable in the medium-high shear rate range, indicating that the system has good viscosity reduction and leveling ability under actual coating shear.

[0058] It can be seen from Figure 3 that under the same conditions, the curve of Example 2 is located in a lower viscosity region as a whole, especially in the medium-high shear rate range related to actual coating, which is significantly lower than each comparative example, showing more sufficient shear thinning and better coating adaptability.

[0059] It should be understood by those skilled in the art that the above discussion of any of the embodiments is only exemplary and is not intended to imply that the scope of the present application is limited to these examples; under the idea of the present application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other changes of different aspects of the present application as described above. In order to be brief, they are not provided in details.

Claims

1. A manganese tetroxide for use in lithium-ion batteries, characterized in that, Manganese sulfate monohydrate was prepared by adding 1 mol / L ammonium bicarbonate aqueous solution dropwise in two stages at pH 6 and 60°C in a dual-ligand system containing citric acid-p-phenylenediamine-glutamic acid diacetate and citric acid-trioxadecanediamine-glutamic acid diacetate, followed by precipitation, washing, drying, and subsequent pre-baking under nitrogen atmosphere and calcination under air atmosphere. The ammonium bicarbonate aqueous solution was added dropwise in two equal volumes and then subjected to aging treatment, and washed until the conductivity of the filtrate was ≤50μS / cm; The citrate-p-phenylenediamine-glutamic acid diacetate ammonium salt is obtained by synthesizing a single-end protected form of p-phenylenediamine and di-tert-butyl carbonate anhydride, then grafting it with citric acid to obtain a citrate-p-phenylenediamine intermediate, then deprotecting the p-phenylenediamine end, grafting it with glutamic acid diacetate, and dialysis purification. The citrate-trioxatridecanediamine-glutamic acid diacetate ammonium salt is synthesized from a single-end protected form of 4,7,10-trioxa-1,13-tridecanediamine and di-tert-butylcarbonic anhydride, which is then grafted with citric acid to obtain a citrate-trioxatridecanediamine intermediate. The trioxatridecanediamine end is then deprotected, grafted with glutamic acid diacetate, and purified by dialysis.

2. The manganese tetroxide for lithium-ion batteries according to claim 1, characterized in that, The weight ratio of p-phenylenediamine, di-tert-butylcarbonic anhydride, citric acid, and glutamic acid diacetic acid in the raw materials for preparing the citric acid-p-phenylenediamine-glutamic acid diacetic acid salt is 10:10:10:

27.

3. The manganese tetroxide for lithium-ion batteries according to claim 1, characterized in that, The weight ratio of 4,7,10-trioxatridecanediamine, di-tert-butylcarbonic anhydride, citric acid, and glutamic acid diacetic acid in the raw materials for preparing citric acid-trioxatridecanediamine-glutamic acid diacetic acid is 12:6:10:

27.

4. The manganese tetroxide for lithium-ion batteries according to claim 1, characterized in that, Based on 100 parts by weight of manganese sulfate monohydrate, the citric acid-p-phenylenediamine-glutamic acid diacetate ammonium salt is 6.25-7.78 parts by weight, and the citric acid-trioxadecanediamine-glutamic acid diacetate ammonium salt is 6.88-8.89 parts by weight.

5. The manganese tetroxide for lithium-ion batteries according to claim 1, characterized in that, The molar ratio of ammonium bicarbonate to manganese sulfate monohydrate is 0.47-0.53:

1.

6. The manganese tetroxide for lithium-ion batteries according to claim 1, characterized in that, The nitrogen atmosphere pre-baking temperature is 500℃ and the holding time is 1.5-3.0h; the air atmosphere calcination temperature is 650℃ and the holding time is 3-5h.

7. The manganese tetroxide for lithium-ion batteries according to claim 1, characterized in that, The particle size distribution of the manganese tetroxide used in lithium-ion batteries is as follows: D10 is 5-6 μm, D50 is 9-10 μm, and D90 is 14-15 μm; the tap density is 3.15-3.30 g / cm³. 3 The sphericity is 0.94-0.

95.

8. The manganese tetroxide for lithium-ion batteries according to claim 1, characterized in that, The glutamic acid diacetic acid was obtained by converting a tetrasodium glutamic acid diacetate aqueous solution through a cation exchange resin column.

9. The manganese tetroxide for lithium-ion batteries according to claim 8, characterized in that, The cation exchange resin is DOWEX 50WX8, and the injection flow rate of the tetrasodium glutamate diacetate aqueous solution is 80-120 mL / h.

10. A method for preparing manganese tetroxide for lithium-ion batteries according to any one of claims 1-9, comprising the following steps: Manganese sulfate monohydrate was dissolved in deionized water to prepare a solution. Citric acid-p-phenylenediamine-glutamic acid diacetate ammonium salt and citric acid-trioxadecanediamine-glutamic acid diacetate ammonium salt were added. After stirring for 30 min, the pH was adjusted to 6 with ammonia water and kept at 60℃. Ammonium bicarbonate aqueous solution was added dropwise in two equal volumes. The first dropwise addition lasted 40-50 min, followed by aging for 10-20 min. The second dropwise addition lasted 10-20 min, followed by aging for another 25-40 min. The solution was filtered and washed with deionized water until the conductivity of the filtrate was ≤50 μS / cm. After drying at 80℃ for 8 h, the solution was pre-calcined under nitrogen atmosphere and then calcined under air atmosphere to obtain manganese tetroxide for lithium-ion batteries.

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