Manganese-rich precursor, preparation method thereof and cathode material

Abstract

The application discloses a kind of manganese-rich precursors and preparation method and positive electrode material thereof, and is related to lithium ion battery material technical field.The preparation method includes that metal salt solution, precipitant and complexing agent are simultaneously added to reaction kettle by metering pump and carry out coprecipitation reaction, and hydrogen peroxide solution is pumped into reaction system by metering pump in stages during reaction process and carries out liquid phase micro-oxidation treatment.The prepared precursor is spherical secondary particle, and is composed of nanoscale particle and interwoven sheet-shaped primary particle.The method utilizes the direct and uniform oxidation effect of hydrogen peroxide in liquid phase, and in-situ constructs stable high-valence manganese oxide on the surface of precursor, so that the prepared positive electrode material simultaneously has excellent electrochemical kinetics and structural stability.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials technology, and in particular to a manganese-rich precursor, its preparation method, and a cathode material. Background Technology

[0002] Lithium-rich manganese-based cathode materials (xLi₂MnO₃·(1-x)LiMO₂, M=Ni, Co, Mn) are key materials for next-generation high-energy-density lithium-ion batteries due to their ultra-high specific capacity and high operating voltage. However, their commercial application is limited by significant capacity decay and voltage drop during cycling. These problems are closely related to the structural degradation of the material, especially its poor electrochemical kinetics (such as slow lithium-ion diffusion rate) and structural instability during cycling (such as transition metal dissolution and phase transition).

[0003] The performance of lithium-rich manganese-based cathode materials is highly dependent on the properties of their precursors. While traditional co-precipitation processes under inert atmospheres can ensure compositional uniformity, the lack of controllable methods results in coarse primary precursor particles and low tap density, directly leading to high ion transport impedance in the final material. More importantly, the unstable low-valence manganese (such as Mn) on its surface... 3+ During subsequent sintering and electrochemical cycling, manganese readily undergoes disproportionation reactions, leading to manganese ion dissolution and oxygen loss, which becomes the core failure mechanism for the rapid decay of material capacity and voltage. Therefore, developing a preparation method that can precisely control the surface manganese valence state and microstructure while maintaining high tap density and bulk composition uniformity of the precursor is of great significance for overcoming the performance bottleneck of lithium-rich manganese-based cathode materials and promoting their practical application. Summary of the Invention

[0004] One of the objectives of this invention is to provide a micro-oxidation manganese-rich precursor with specific morphology and surface characteristics. This precursor has high tap density and high-valence manganese particles on the surface, in order to solve the shortcomings of existing lithium-rich manganese-based cathode materials in terms of electrochemical kinetic performance and structural stability, thereby meeting the requirements of high energy density and long cycle life.

[0005] The second objective of this invention is to provide a method for preparing the manganese-rich precursor.

[0006] The third objective of this invention is to provide a cathode material prepared from the manganese-rich precursor.

[0007] The fourth objective of this invention is to provide a lithium-ion battery including the positive electrode material.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0009] In a first aspect, the present invention provides a manganese-rich precursor having the general chemical formula Mn x Ni y Co 1-x-y (OH)₂, where 0.3≤x≤1, 0≤y≤0.6; and has the following characteristics:

[0010] (1) The microstructure of the manganese-rich precursor consists of spherical secondary particles formed by the accumulation of primary particles. The primary particles are composed of nano-sized ellipsoidal particles and lamellar structures interwoven. The nano-sized ellipsoidal particles are located at the edge of the lamellar structure to form high-valence manganese compound particles.

[0011] Furthermore, the manganese-rich precursor also possesses at least one of the following characteristics:

[0012] (2) The D50 particle size of the secondary particles is 2-20 μm;

[0013] (3) The tap density of the manganese-rich precursor is 1.0-2.0 g / cm³. 3 ;

[0014] (4) The specific surface area of ​​the manganese-rich precursor is 5-50 m². 2 / g;

[0015] (5) The thickness of the primary particles in the lamellar structure is 10-200 nm; the size of the nano-sized ellipsoidal particles is 20-500 nm.

[0016] (6) The area ratio of nano-sized ellipsoidal particles in secondary particles is 0.1%-100%.

[0017] Secondly, the present invention provides a method for preparing the above-mentioned manganese-rich precursor, comprising the following steps:

[0018] (1) Add pure water and complexing agent to the container to prepare the base solution;

[0019] (2) The metal salt solution, precipitant and complexing agent are added to the bottom liquid at the same time to carry out co-precipitation reaction; during the co-precipitation reaction, an aqueous solution of oxidizing substance is pumped into the container in stages at intervals of 3-5 hours. The mass concentration of the oxidizing substance in the aqueous solution of oxidizing substance is 5%-30%, and the amount pumped in at one time is 0.1%-10.0% of the total slurry volume of the reaction system.

[0020] (3) Stop the reaction when the particle size D50 of the precipitated slurry grows to 2-20 μm;

[0021] (4) The precipitated slurry is aged, centrifuged, washed and dried to obtain a manganese-rich precursor.

[0022] Preferably, in step (1), the ammonia concentration in the bottom solution is 0.2 mol / L, and a precipitant is added to adjust the pH of the bottom solution to 9-13, preferably 10.5-11.5;

[0023] Preferably, the complexing agent in step (1) is one or more selected from ammonia, disodium ethylenediaminetetraacetate, aqueous solution of ammonium bicarbonate, and aqueous solution of ammonium carbonate;

[0024] Preferably, the precipitant in step (2) is one or more selected from sodium hydroxide aqueous solution and potassium hydroxide aqueous solution.

[0025] Preferably, in step (2), the oxidizing substance is one or more of hydrogen peroxide, sodium hypochlorite, ammonium persulfate, and potassium permanganate, with hydrogen peroxide being the most preferred.

[0026] Preferably, in step (2), the total concentration of metal ions in the metal salt solution is 1-4 mol / L, the concentration of the precipitant is 2-8 mol / L, and the concentration of the complexing agent is 1-8 mol / L.

[0027] Preferably, in step (2), the metal salt includes nickel salt, cobalt salt and manganese salt; the nickel salt is selected from one or more of nickel sulfate, nickel chloride, nickel nitrate and nickel acetate; the cobalt salt is selected from one or more of cobalt sulfate, cobalt chloride, cobalt nitrate and cobalt acetate; the manganese salt is selected from one or more of manganese sulfate, manganese chloride, manganese nitrate and manganese acetate; the molar ratio of Mn, Ni and Co is x:y:1-xy, where 0.3≤x≤1 and 0≤y≤0.6.

[0028] Preferably, in step (2), the conditions for the coprecipitation reaction include: a reaction temperature of 50-70℃, a stirring speed of 500-1000rpm, a reaction time of 10-30 h; and controlling the pH of the reaction system to be 10-12 and the ammonia concentration to be 0.2mol / L.

[0029] Preferably, in step (4), the aging temperature is 40-60℃ and the aging time is 1-8h; the drying temperature is 100-120℃ and the drying time is 10-15h.

[0030] The method of this invention utilizes the ·OH free radicals generated by the decomposition of hydrogen peroxide in an alkaline coprecipitation environment, which can instantly remove some of the Mn in the solution near the reaction interface. 2+ Oxidation to a higher oxidation state (Mn) 3+ / Mn 4+ These high-valence manganese ions rapidly hydrolyze, forming in situ colloidal particles of high-valence manganese oxides or hydroxides (such as MnOOH, MnO2) with nanoscale (typically <30 nm) sizes.

[0031] Thirdly, the present invention provides a cathode material, which is prepared by sintering the above-mentioned manganese-rich precursor with a lithium source.

[0032] Fourthly, the present invention provides a lithium-ion battery comprising the above-mentioned positive electrode material.

[0033] Beneficial effects:

[0034] (1) This invention achieves the regulation of precursor morphology and surface element valence state by controlling the oxidation atmosphere during the co-precipitation process. This method enables the in-situ formation of high-valence manganese particles on the precursor surface. These particles act as heterogeneous nucleation centers, refining the lamellar primary particles (thickness 20-500 nm) and promoting the formation of dense secondary spheres, thus significantly increasing the precursor tap density (≥1.5 g / cm³). 3 The precursor primary particles consist of a dense microstructure composed of interwoven nano-sized particles and sheet-like primary particles, providing abundant channels for lithium-ion transport, thereby significantly improving the electrochemical kinetics of the final cathode material and enhancing rate performance.

[0035] (2) The preparation method of the present invention integrates morphology control and surface stabilization into a one-step coprecipitation process, which is achieved by precisely controlling a single parameter. The process is simple, the control is reliable, and it is easy to scale up for industrial production.

[0036] The present invention has been described in detail above; however, the above embodiments are merely illustrative in nature and are not intended to limit the invention. Furthermore, this document is not limited to the foregoing prior art or the invention itself, or to any theory described in the following embodiments. Attached Figure Description

[0037] Figure 1 A scanning electron microscope (SEM) image of the manganese-rich precursor prepared in Example 1 is shown;

[0038] Figure 2 A scanning electron microscope (SEM) image of the manganese-rich precursor prepared in Example 2 is shown;

[0039] Figure 3 A scanning electron microscope (SEM) image of the manganese-rich precursor prepared in Example 3 is shown;

[0040] Figure 4 A scanning electron microscope (SEM) image of the manganese-rich precursor prepared in Comparative Example 1 is shown.

[0041] Figure 5 A scanning electron microscope (SEM) image of the manganese-rich precursor prepared in Comparative Example 2 is shown.

[0042] Figure 6A scanning electron microscope (SEM) image of the manganese-rich precursor prepared in Comparative Example 3 is shown. Detailed Implementation

[0043] The present invention will be further described below with reference to the embodiments. It should be noted that the following embodiments are provided for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0044] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art.

[0045] Example 1

[0046] A manganese-rich precursor, its preparation method, and a cathode material thereof, comprising the following steps:

[0047] (1) Weigh out nickel sulfate, cobalt sulfate and manganese sulfate according to the molar ratio of Ni, Co and Mn of 0.30:0.06:0.64, and prepare a mixed salt solution with a total concentration of 2 mol / L; prepare a 4 mol / L NaOH solution as a precipitant; and prepare a 1 mol / L ammonia solution as a complexing agent.

[0048] (2) Add pure water and ammonia to the reactor to make the ammonia concentration 0.2 mol / L, and stir to dissolve. Add precipitant to adjust the pH of the bottom solution to 11.0.

[0049] (3) The mixed salt solution, precipitant and complexing agent were added dropwise to the reactor at the same time. The salt injection rate was controlled at 300 ml / h, the reaction temperature at 50℃, the stirring speed at 800 rpm, and the pH was maintained at 10.5. At the same time, nitrogen gas was continuously introduced into the reactor, and the nitrogen flow rate was controlled at 0.5 L / min and the ammonia concentration at 0.2 mol / L. During the reaction, a 20% hydrogen peroxide solution was pumped into the reactor every 4 hours through a metering pump. The single pumping volume was 0.2% of the total volume of the slurry. The reaction was stopped when the slurry D50 grew to about 6.5 μm. The slurry was aged at 50℃ for 6 hours.

[0050] (4) Centrifuge and wash the aged slurry, and dry it at 110°C for 12 hours to obtain a manganese-rich precursor.

[0051] Its SEM images are as follows Figure 1 As shown in the figure, the morphology of the obtained manganese-rich precursor is composed of spherical secondary particles formed by the accumulation of primary particles, and the primary particles are composed of nanoscale ellipsoidal particles and lamellar structures interwoven.

[0052] Example 2

[0053] The difference between this embodiment and Embodiment 1 is that the single pumping volume in step (3) is 0.5% of the total slurry volume; otherwise, it is the same as Embodiment 1. Its SEM image is shown below. Figure 2 As shown.

[0054] Example 3

[0055] The difference between this embodiment and Embodiment 1 is that in step (3), the single pumping volume is 1% of the total slurry volume; otherwise, it is the same as Embodiment 1. Its SEM image is shown below. Figure 3 As shown.

[0056] Comparative Example 1

[0057] A method for preparing a manganese-rich precursor includes the following steps:

[0058] (1) Weigh out nickel sulfate, cobalt sulfate and manganese sulfate according to the molar ratio of Ni, Co and Mn of 0.30:0.06:0.64, and prepare a mixed salt solution with a total concentration of 2 mol / L; prepare a 4 mol / L NaOH solution as a precipitant; and prepare a 1 mol / L ammonia solution as a complexing agent.

[0059] (2) Add pure water and ammonia to the reactor to make the ammonia concentration 0.2 mol / L, and stir to dissolve. Add precipitant to adjust the pH of the bottom solution to 11.0.

[0060] (3) Add the mixed salt solution, precipitant and complexing agent dropwise into the reactor at the same time, control the salt injection rate to be 300 ml / h, the reaction temperature to be 50℃, the stirring speed to be 800 rpm, maintain pH=10.5, and continuously introduce nitrogen into the reactor at the same time, control the nitrogen flow rate to be 0.5 L / min and the ammonia concentration to be 0.2 mol / L. Stop the reaction when the slurry D50 grows to about 6.5 μm, and age at 50℃ for 6 hours.

[0061] (4) The aged slurry was centrifuged, washed, and dried at 110℃ for 12 hours to obtain the manganese-rich precursor. Its SEM image is shown below. Figure 4 As shown.

[0062] Comparative Example 2

[0063] A method for preparing a manganese-rich precursor includes the following steps:

[0064] (1) Weigh out nickel sulfate, cobalt sulfate and manganese sulfate according to the molar ratio of Ni, Co and Mn of 0.30:0.06:0.64, and prepare a mixed salt solution with a total concentration of 2 mol / L; prepare a 4 mol / L NaOH solution as a precipitant; and prepare a 1 mol / L ammonia solution as a complexing agent.

[0065] (2) Add pure water and ammonia to the reactor to make the ammonia concentration 0.2 mol / L, and stir to dissolve. Add precipitant to adjust the pH of the bottom solution to 11.0.

[0066] (3) Add the mixed salt solution, precipitant and complexing agent dropwise into the reactor at the same time. Control the salt injection rate to 300 ml / h, the reaction temperature to 50°C, the stirring speed to 800 rpm, and maintain pH=10.5. At the same time, continuously introduce nitrogen into the reactor, control the nitrogen flow rate to 0.5 L / min, the ammonia concentration to 0.2 mol / L, and introduce air into the reactor at 0.2 L / h for 0.5 h every 4 hours. Stop the reaction when the slurry D50 grows to about 6.5 μm, and age at 50°C for 6 hours.

[0067] (4) The aged slurry was centrifuged, washed, and dried at 110℃ for 12 hours to obtain the manganese-rich precursor. Its SEM image is shown below. Figure 5 As shown.

[0068] Comparative Example 3

[0069] A manganese-rich precursor, its preparation method, and a cathode material thereof, comprising the following steps:

[0070] (1) Weigh out nickel sulfate, cobalt sulfate and manganese sulfate according to the molar ratio of Ni, Co and Mn of 0.30:0.06:0.64, and prepare a mixed salt solution with a total concentration of 2 mol / L; prepare a 4 mol / L NaOH solution as a precipitant; and prepare a 1 mol / L ammonia solution as a complexing agent.

[0071] (2) Add pure water and ammonia to the reactor to make the ammonia concentration 0.2 mol / L, and stir to dissolve. Add precipitant to adjust the pH of the bottom solution to 11.0.

[0072] (3) The mixed salt solution, precipitant and complexing agent were added dropwise to the reactor at the same time. The salt inlet rate was controlled at 300 ml / h, the reaction temperature at 50℃, the stirring speed at 800 rpm, and the pH was maintained at 10.5. At the same time, nitrogen gas was continuously introduced into the reactor, and the nitrogen flow rate was controlled at 0.5 L / min and the ammonia concentration at 0.2 mol / L. During the reaction, a 20% hydrogen peroxide solution was continuously pumped into the reactor through a metering pump, and the hydrogen peroxide inlet rate was controlled at 30 ml / h. The reaction was stopped when the slurry D50 grew to about 6.5 μm, and the slurry was aged at 50℃ for 6 hours.

[0073] (4) The aged slurry was centrifuged, washed, and dried at 110℃ for 12 hours to obtain the manganese-rich precursor. Its SEM image is shown below. Figure 6 As shown.

[0074] Table 1. Properties of the precursor-rich precursors prepared in the examples and comparative examples.

[0075]

[0076] The above-mentioned physical property testing methods are as follows:

[0077] SEM image: obtained by field emission scanning electron microscopy;

[0078] Specific surface area: obtained by measuring the specific surface area.

[0079] Tap density: obtained by measuring with a tap density meter;

[0080] D50: Measured by a laser particle size analyzer;

[0081] The area ratio of small particles was obtained from statistics using the image processing software ImageJ.

[0082] The present invention provides a cathode material, which is prepared by sintering the above-mentioned manganese-rich precursor and lithium carbonate.

[0083] The manganese-rich precursors prepared in the examples and comparative examples were mixed with lithium carbonate at a molar ratio of transition metal to lithium of 1:1.4. The mixtures were placed in a muffle furnace and heated to 500°C at a heating rate of 5°C / min in air atmosphere and held for 5 hours. Then the temperature was increased to 900°C and held for 12 hours. Finally, the mixtures were allowed to cool naturally to room temperature to prepare lithium-rich manganese-based cathode materials.

[0084] The products prepared in the examples and comparative examples were subjected to coin cell performance tests. The test method for battery performance testing was as follows: the positive electrode materials prepared in the above examples and comparative examples were respectively mixed with conductive carbon black and binder PVDF (polyvinylidene fluoride) in a ratio of 8:1:1 to form a slurry, which was then coated on aluminum foil to form a positive electrode sheet. The negative electrode sheet was a lithium metal sheet, and the electrolyte was 1 mol / L LiPF6 / EC:DMC (volume ratio 1:1). The battery case, positive electrode sheet, negative electrode sheet, separator, and spring gasket were assembled into a coin cell in a vacuum glove box.

[0085] At room temperature, the charge and discharge tests of the coin cells were performed using the Land battery testing system, employing constant current and constant voltage charge and discharge testing. The tests were conducted at room temperature (25°C), with a charge and discharge voltage range of 2.0~4.6V and a current density of 1C=200mA / g. Specific test data are shown in Table 2.

[0086] Table 2 Battery discharge capacity test data

[0087]

[0088] A comparison of Examples 1-3 and Comparative Example 1 reveals that micro-oxidation using pumped hydrogen peroxide significantly improves the electrochemical performance of both the precursor and the final cathode material. The conditions in Example 2 (20% concentration, 0.5% volume) exhibit the best overall performance. This indicates that oxidation using liquid-phase hydrogen peroxide is an effective and controllable modification method.

[0089] Compared to Example 2, the manganese-rich hydroxide in Comparative Example 2 is a loose spherical aggregate composed of stacked sheet-like secondary structures with larger gaps between the stacks. The overall structure is significantly looser than that of Example 2, and the battery discharge capacity retention rate is lower.

[0090] Compared to Example 2, Comparative Example 3 is a dense spherical aggregate with a surface composed of stacked nanoparticles. The secondary structure is mainly composed of particle clusters, and the number of nanoparticles is significantly higher than that in Example 2. This indicates that the oxidation degree of Comparative Example 3 is higher, resulting in slightly lower capacity and capacity retention of the prepared battery.

[0091] The above embodiments are merely illustrative of the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and substance defined by the claims of the present invention; and such modifications or substitutions are still within the scope defined by the claims of the present invention.

Claims

1. A manganese-rich precursor, characterized in that, Its general chemical formula is Mn x Ni y Co 1-x-y (OH)₂, where 0.3≤x≤1, 0≤y≤0.6; and has the following characteristics: (1) The microstructure of the manganese-rich precursor consists of spherical secondary particles formed by the accumulation of primary particles. The primary particles are composed of nano-sized ellipsoidal particles and lamellar structures interwoven. The nano-sized ellipsoidal particles are located at the edges of the lamellar structures to form Mn-containing structures. 3+ or Mn 4+ Oxides or hydroxides; (2) The D50 particle size of the secondary particles is 2-20 μm; (3) The tap density of the manganese-rich precursor is 1.0-2.0 g / cm³. 3 ; (4) The specific surface area of ​​the manganese-rich precursor is 5-50 m². 2 / g; (5) The thickness of the primary particles in the lamellar structure is 10-200 nm; the size of the nano-sized ellipsoidal particles is 20-500 nm. (6) The area ratio of nano-sized ellipsoidal particles in secondary particles is 0.1%-100%.

2. A method for preparing the manganese-rich precursor according to claim 1, characterized in that, Includes the following steps: (1) Add pure water and complexing agent to the container to prepare the base solution; (2) The metal salt solution, precipitant and complexing agent are added to the bottom liquid at the same time to carry out co-precipitation reaction; during the co-precipitation reaction, an aqueous solution of oxidizing agent is pumped into the container in stages at intervals of 3-5 hours. The mass concentration of the oxidizing agent in the aqueous solution is 5%-30%, and the amount pumped in at one time is 0.1%-10.0% of the total slurry volume of the reaction system; the oxidizing agent is hydrogen peroxide; (3) Stop the reaction when the particle size D50 of the precipitated slurry grows to 2-20 μm; (4) The precipitated slurry is aged, centrifuged, washed and dried to obtain a manganese-rich precursor.

3. The preparation method according to claim 2, characterized in that, In step (1), the ammonia concentration in the bottom solution is 0.2 mol / L, and a precipitant is added to adjust the pH of the bottom solution to 9-13; In step (1), the complexing agent is one or more selected from ammonia, disodium ethylenediaminetetraacetate, ammonium bicarbonate aqueous solution, and ammonium carbonate aqueous solution.

4. The preparation method according to claim 2, characterized in that, In step (2), the precipitant is one or more selected from sodium hydroxide aqueous solution and potassium hydroxide aqueous solution.

5. The preparation method according to claim 2, characterized in that, In step (2), the total concentration of metal ions in the metal salt solution is 1-4 mol / L, the concentration of the precipitant is 2-8 mol / L, and the concentration of the complexing agent is 1-8 mol / L. In step (2), the metal salts include nickel salts, cobalt salts, and manganese salts; the nickel salt is selected from one or more of nickel sulfate, nickel chloride, nickel nitrate, and nickel acetate; the cobalt salt is selected from one or more of cobalt sulfate, cobalt chloride, cobalt nitrate, and cobalt acetate; the manganese salt is selected from one or more of manganese sulfate, manganese chloride, manganese nitrate, and manganese acetate; the molar ratio of Mn, Ni, and Co is x:y:1-xy, where 0.3≤x≤1 and 0≤y≤0.

6.

6. The preparation method according to claim 2, characterized in that, In step (2), the conditions for the coprecipitation reaction include: a reaction temperature of 50-70℃, a stirring speed of 500-1000rpm, a reaction time of 10-30 h; and controlling the pH of the reaction system to be 10-12 and the ammonia concentration to be 0.2mol / L.

7. The preparation method according to claim 2, characterized in that, In step (4), the aging temperature is 40-60℃ and the aging time is 1-8h; the drying temperature is 100-120℃ and the drying time is 10-15h.

8. A positive electrode material, characterized in that, The manganese-rich precursor prepared by the method described in claim 1 or any one of claims 2-7 is mixed with a lithium source and sintered.

9. A lithium-ion battery comprising the positive electrode material as described in claim 8.

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