Cobalt-free lithium-rich manganese-based oxide material for lithium-ion batteries and preparation method thereof

Abstract

The present invention discloses a cobalt-free lithium-rich manganese-based oxide material for lithium-ion batteries and a preparation method thereof, comprising: mixing a preset ratio of lithium source and a precursor and ball milling to obtain a mixture, and then performing a first calcination on the mixture to obtain a first reactant; soaking the first reactant in a citric acid ethanol solution, while performing magnetic stirring, and then performing a second calcination on the soaked first reactant to obtain a second reactant with a surface coated with a spinel phase; mixing a preset ratio of the second reactant and an aluminum source and stirring, and performing a third calcination on the stirred second reactant to allow aluminum elements to enter the lattice structure of the second reactant to obtain a third reactant; calcining the carbon source and the third reactant together to obtain a cobalt-free lithium-rich manganese-based oxide material for lithium-ion batteries coated with a carbon layer. The cobalt-free lithium-rich manganese-based oxide material for lithium-ion batteries obtained by the above method exhibits better cycle stability.

Description

Technical Field

[0001] The present invention relates to the technical field of positive electrode material preparation, and in particular to a cobalt-free lithium-rich manganese-based oxide material for lithium-ion batteries and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are widely used in consumer electronics, energy storage devices, new energy vehicles and other fields due to their high energy density, long cycle life and excellent charge and discharge performance. Among them, the positive electrode material is one of the key factors affecting the overall performance of lithium-ion batteries. Traditional lithium-ion battery positive electrode materials mainly include layered structure lithium cobalt oxide (LiCoO 2 ); However, the scarcity of cobalt resources and environmental issues limit the large-scale application of commercial lithium cobalt oxide materials. In contrast, lithium-rich manganese-based oxides have become a hot topic of research in recent years due to their high specific capacity, low cost, cobalt-free and environmentally friendly advantages.

[0003] However, in actual applications, it was found that lithium-rich manganese-based oxides will undergo irreversible layered structural phase changes during the charge and discharge process, leading to the formation of lithium vacancies and the migration of transition metals (such as Mn and Ni); in this process, it will trigger lattice oxygen release, electrolyte decomposition and voltage decay, resulting in obvious capacity decay and voltage decay in lithium batteries, significantly reducing the battery's cycle stability. Summary of the invention

[0004] The purpose of the present invention is to provide a cobalt-free lithium-rich manganese-based oxide material for lithium-ion batteries and a preparation method thereof, so as to solve the technical problem that lithium-rich manganese-based oxides in the prior art cause significant capacity decay and voltage decay in lithium batteries.

[0005] To achieve this object, the present invention adopts the following technical solutions:

[0006] A method for preparing a cobalt-free lithium-rich manganese-based oxide material for a lithium-ion battery, comprising:

[0007] Step S1, mixing a lithium source and a precursor in a preset ratio and ball-milling to obtain a mixture, and then performing a first calcination on the mixture to obtain a first reactant;

[0008] Step S2, soaking the first reactant in a citric acid ethanol solution while performing magnetic stirring, and then performing a second calcination on the soaked first reactant to obtain a second reactant with a surface coated with a spinel phase;

[0009] Step S3, mixing and stirring the second reactant and the aluminum source in a preset ratio, and performing a third calcination on the stirred second reactant to allow the aluminum element to enter the lattice structure of the second reactant to obtain a third reactant;

[0010] Step S4: calcining the carbon source and the third reactant together to obtain a cobalt-free lithium-rich manganese-based oxide material for lithium-ion batteries coated with a carbon layer.

[0011] Optionally, the step S1 includes:

[0012] Step S11, mixing the lithium source and the precursor at a first preset molar ratio to obtain a mixture, and ball milling the mixture in a ball mill until the particle size of the mixture reaches a target particle size;

[0013] Step S12, placing the mixture in a box furnace, and pre-calcining the mixture at 450-600° C. for 4-6 hours;

[0014] Step S13, calcining the mixture at 850-920° C. for 10-12 hours.

[0015] Optionally, the lithium source is LiOH·H 2 O, the precursor is Ni 0.2 Mn 0.6 (OH) 3 , the first preset molar ratio is (1.2~1.8):1.

[0016] Optionally, step S2 includes:

[0017] Step S21, soaking the first reactant in a citric acid ethanol solution of a preset concentration;

[0018] Step S22, magnetically stirring the first reactant immersed in the citric acid ethanol solution;

[0019] Step S23, filtering the first reactant soaked in the citric acid ethanol solution, removing impurities by filtering, and then drying to obtain a dried reactant;

[0020] Step S24, calcining the dried reactant at 400° C. for 5 hours to obtain a second reactant having a surface covered with a spinel phase through high temperature calcination.

[0021] Optionally, the preset concentration of the citric acid ethanol solution is 1.2~1.5 mol / L.

[0022] Optionally, step S3 includes:

[0023] Step S31, mixing the second reactant and the aluminum source according to a second preset molar ratio, and stirring;

[0024] Step S32, heating the stirred second reactant to 300-400° C. at a rate of 2-5° C. / min and maintaining the temperature for 1-2 h; then heating the stirred second reactant to 850-950° C. at a rate of 2-5° C. / min and maintaining the temperature for 6-8 h to obtain a third reactant;

[0025] Step S33, naturally cooling the third reactant and washing the third reactant.

[0026] Optionally, the aluminum source is Al(NO 3 ) 3 9H 2 O, the second preset molar ratio is Al:Mn=(0.01-0.05):1.

[0027] Optionally, step S4 includes:

[0028] Step S41, mixing dopamine hydrochloride with deionized water to obtain a dopamine hydrochloride solution of a preset concentration, and immersing the third reactant in the dopamine hydrochloride solution and stirring;

[0029] Step S42, calcining the immersed third reactant at a temperature of 400-500° C. to obtain a cobalt-free lithium-rich manganese-based oxide material for lithium-ion batteries based on an aluminum-doped spinel phase and coated with a carbon layer.

[0030] Optionally, the preset concentration of the dopamine hydrochloride solution is 1.3-1.5 mol / L.

[0031] A cobalt-free lithium-rich manganese-based oxide material for lithium-ion batteries is prepared by the method for preparing the cobalt-free lithium-rich manganese-based oxide material for lithium-ion batteries as described above.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The cobalt-free lithium-rich manganese-based oxide material for lithium-ion batteries provided by the present invention and the preparation method thereof are as follows: a first reactant is calcined with a citric acid ethanol solution to obtain a second reactant with a surface-coated spinel phase, wherein the spinel phase provides a more efficient three-dimensional channel for the diffusion of lithium ions; then, an aluminum element is added to form an Al-O bond to inhibit the phase change of the layered structure; at the same time, before aluminum doping, the crystal structure of the material itself becomes more stable through the coating of the spinel phase, thereby ensuring that aluminum doping can more effectively enter the lattice and play its role in enhancing structural stability and cycle performance; finally, the cobalt-free lithium-rich manganese-based oxide material for lithium-ion batteries obtained, the spinel phase of which improves the ion diffusion efficiency and provides a surface protection layer by forming a more efficient three-dimensional channel, thereby improving the rate performance and the first coulomb efficiency; and aluminum doping enhances the long-term stability on the basis of the spinel phase, reduces the release of oxygen and the migration of metal ions, avoids the lithium battery from obvious capacity decay and voltage decay, and exhibits better cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0035] The structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with this technology. They are not used to limit the conditions under which the present invention can be implemented, and therefore have no substantive technical significance. Any structural modification, change in proportion or adjustment of size, without affecting the effects and purposes that can be achieved by the present invention, should still fall within the scope of the technical contents disclosed by the present invention.

[0036] Figure 1 A schematic flow chart of a method for preparing a cobalt-free lithium-rich manganese-based oxide material for a lithium-ion battery provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] In the description of the present invention, it should be understood that the terms "upper", "lower", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. It should be noted that when a component is considered to be "connected" to another component, it may be directly connected to the other component or there may be a centrally arranged component at the same time.

[0039] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0040] The present embodiment provides a method for preparing a cobalt-free lithium-rich manganese-based oxide material for a lithium-ion battery. The preparation method is used to prepare a cobalt-free lithium-rich manganese-based oxide material, specifically a cobalt-free lithium-rich manganese-based oxide positive electrode material. The present embodiment improves the preparation method so that the charge and discharge performance and cycle performance of the cobalt-free lithium-rich manganese-based oxide material for a lithium-ion battery are improved.

[0041] A method for preparing a cobalt-free lithium-rich manganese-based oxide material for a lithium-ion battery in this embodiment includes:

[0042] Step S1, mixing a lithium source and a precursor in a preset ratio and ball-milling to obtain a mixture, and then performing a first calcination on the mixture to obtain a first reactant;

[0043] Step S2, soaking the first reactant in a citric acid ethanol solution while performing magnetic stirring, and then performing a second calcination on the soaked first reactant to obtain a second reactant with a surface coated with a spinel phase;

[0044] Step S3, mixing and stirring the second reactant and the aluminum source in a preset ratio, and performing a third calcination on the stirred second reactant to allow the aluminum element to enter the lattice structure of the second reactant to obtain a third reactant;

[0045] Step S4: calcining the carbon source and the third reactant together to obtain a cobalt-free lithium-rich manganese-based oxide material for lithium-ion batteries coated with a carbon layer.

[0046] It can be understood that the preparation method of the cobalt-free lithium-rich manganese-based oxide material for lithium-ion batteries provided by the present invention is to calcine a citric acid ethanol solution with a first reactant to obtain a second reactant with a surface-coated spinel phase, wherein the spinel phase provides a more efficient three-dimensional channel for the diffusion of lithium ions; then, by adding aluminum elements, Al-O bonds are formed to inhibit the phase change of the layered structure; at the same time, before aluminum doping, the crystal structure of the material itself becomes more stable through the coating of the spinel phase, thereby ensuring that aluminum doping can more effectively enter the lattice and play its role in enhancing structural stability and cycle performance; finally, the cobalt-free lithium-rich manganese-based oxide material for lithium-ion batteries obtained, the spinel phase of which improves the ion diffusion efficiency and provides a surface protection layer by forming a more efficient three-dimensional channel, thereby improving the rate performance and the first coulomb efficiency; and aluminum doping enhances the long-term stability on the basis of the spinel phase, reduces the release of oxygen and the migration of metal ions, avoids obvious capacity decay and voltage decay of the lithium battery, and exhibits better cycle stability.

[0047] Specifically, step S1 includes:

[0048] Step S11, mixing the lithium source and the precursor at a first preset molar ratio (1.2-1.8):1 to obtain a mixture, and ball milling the mixture in a ball mill until the particle size of the mixture reaches a target particle size, and the target particle size is 100-400 nm;

[0049] LiOH·H can be used as the lithium source 2 O or Li 2 CO 3 , the precursor can be Ni 0.2 Mn 0.6 (OH) 2 or Ni 0.2 Mn 0.6 (OH) 3 In this embodiment, LiOH·H 2 O and Ni 0.2 Mn 0.6 (OH) 3 A combination of the above, after mixing and ball milling, obtains a mixture;

[0050] Step S12: placing the mixture in a box furnace and pre-calcining the mixture at 450-600° C. for 4-6 hours to make LiOH·H 2 O is fully decomposed to release H 2 O, promotes the initial solid phase reaction and forms a transition phase;

[0051] Step S13, calcining the mixture at 850-920°C for 10-12 hours to obtain the first reactant Li 1.2 Ni 0.2Mn 0.6 O 2 This step promotes the solid phase reaction between Ni, Mn and Li to form a stable Li 1.2 Ni 0.2 Mn 0.6 O 2 The structure forms a complete layered structure and improves crystallinity.

[0052] Specifically, step S2 includes:

[0053] Step S21, immersing the first reactant in a citric acid ethanol solution of a preset concentration; the citric acid ethanol solution is prepared by mixing citric acid and ethanol, and the preset concentration is 1.2-1.5 mol / L. The use of this higher concentration of citric acid solution helps to more effectively react with the surface of the first reactant, thereby forming a spinel phase after high-temperature calcination and improving the rate performance and the first coulombic efficiency, thereby improving the overall electrical performance of the lithium-ion battery;

[0054] Step S22, magnetically stirring the first reactant immersed in the citric acid ethanol solution; the magnetic stirring is achieved by a magnetic stirrer, the stirring speed is set to 300-600 r / min, and a straight bar stirrer is selected. The specific structure of the magnetic stirrer is well known to those skilled in the art and is not specifically described in this embodiment;

[0055] Step S23, filtering the first reactant soaked in the citric acid ethanol solution, removing impurities by filtering, and then drying to obtain a dried reactant;

[0056] Step S24, calcining the dried reactant at 400°C for 5 hours to obtain a second reactant with a surface-coated spinel phase through high-temperature calcination; in this step, citric acid and the surface substance undergo a chemical reaction to form a spinel phase, which helps to improve the ion diffusion and electrochemical properties of the material.

[0057] As another optional implementation, step S2 includes:

[0058] Step S25, taking out a portion of the first reactant as a sample and soaking it in an ethanol solution, and adding a citric acid solution dropwise to the ethanol solution soaked with the sample;

[0059] Step S26, when the ethanol solution soaked with the sample becomes turbid and changes color, record the dripping ratio of the citric acid solution to the ethanol solution; prepare a citric acid ethanol solution of a preset concentration according to the dripping ratio, and soak the first reactant in the citric acid ethanol solution of the preset concentration; wherein, when the preset concentration is prepared according to the dripping ratio, first calculate the limit concentration of the citric acid ethanol solution by the dripping ratio, and multiply the limit concentration by 0.8 to obtain the preset concentration;

[0060] It can be understood that when turbidity occurs, it means that the citric acid concentration begins to approach its upper limit. When color changes occur, citric acid forms a complex with the calculated metal ions in the sample, thereby determining the limit concentration, and adding a safety factor of 0.8 to obtain the preset concentration; thereby, excessive corrosion caused by excessively high citric acid concentrations and insufficient reactions caused by too low citric acid concentrations can be avoided;

[0061] Step S22, magnetically stirring the first reactant immersed in the citric acid ethanol solution; the magnetic stirring is achieved by a magnetic stirrer, the stirring speed is set to 300-600 r / min, and a straight bar stirrer is selected. The specific structure of the magnetic stirrer is well known to those skilled in the art and is not specifically described in this embodiment;

[0062] Step S23, filtering the first reactant soaked in the citric acid ethanol solution, removing impurities by filtering, and then drying to obtain a dried reactant;

[0063] Step S24, calcining the dried reactant at 400° C. for 5 hours to obtain a second reactant with a surface covered with a spinel phase through high temperature calcination;

[0064] Specifically, step S3 includes:

[0065] Step S31, mixing the second reactant and the aluminum source according to a second preset molar ratio and stirring; the second preset molar ratio is Al:Mn = (0.01-0.05): 1; in this embodiment, the aluminum source is Al(NO 3 ) 3 9H 2 O, the solvent can be deionized water or anhydrous ethanol, correspondingly, per 100g Li 1.2 Ni 0.2 Mn 0.6 O 2 0.34~1.7g Al(NO 3 ) 3 9H 2 O;

[0066] Step S32, heating the stirred second reactant to 300-400°C at a rate of 2-5°C / min and maintaining for 1-2h; then heating to 850-950°C at a rate of 2-5°C / min and maintaining for 6-8h to obtain a third reactant; air or oxygen atmosphere is used in the calcination process of this step;

[0067] Step S33, naturally cool the third reactant and wash the third reactant; specifically, after cooling, wash it with deionized water 2 to 3 times, using 100 to 200 mL of water / 50 g of material each time, stirring for 15 to 30 minutes and then filtering to remove residual NO3 groups and unreacted aluminum source.

[0068] Specifically, in this embodiment, the carbon source is dopamine hydrochloride, and step S4 includes:

[0069] Step S41, mixing dopamine hydrochloride with deionized water to obtain a dopamine hydrochloride solution of a preset concentration, and immersing the third reactant in the dopamine hydrochloride solution and stirring; the preset concentration of the dopamine hydrochloride solution is 1.3~1.5mol / L. Among them, the dopamine hydrochloride solution is used as a carbon source in this step. In other optional embodiments, the carbon source can also be other carbon sources such as glucose. Dopamine hydrochloride has good reducibility and can release a large amount of carbon elements during high-temperature calcination to form a carbon layer covering the surface of the positive electrode material; in the process of decomposition of dopamine hydrochloride, nitrogen groups and chlorine groups contained in dopamine participate in the reduction reaction, and a part of the manganese ions are reduced to a low-valent state, which can increase the capacity and rate performance of the material;

[0070] Step S42, calcining the immersed third reactant at a temperature of 400-500°C to obtain a cobalt-free lithium-rich manganese-based oxide material for lithium-ion batteries based on an aluminum-doped spinel phase and wrapped with a carbon layer; during the decomposition of dopamine hydrochloride, a portion of manganese ions will be reduced to form a large number of oxygen vacancies, thereby improving the electrochemical properties of the material and increasing the capacity and rate performance of the material; at the same time, a carbon layer doped with nitrogen and chlorine is formed on the surface of the aluminum-doped spinel phase; in addition, nitrogen and chlorine groups can combine with aluminum or other metal ions to form a stable coordination structure, thereby improving the structural stability of the material, especially in the aluminum-doped material, nitrogen and chlorine groups can combine with aluminum ions to enhance the high temperature resistance and structural stability of the material.

[0071] Through step S41 and step S42, dopamine hydrochloride not only provides a carbon protective layer for the surface of the aluminum-doped spinel phase, reducing the contact between the active material and the electrolyte, but also inhibits the dissolution of transition metals, improves the rate performance and first coulombic efficiency of the lithium-ion battery, and improves the cycle stability.

[0072] This embodiment also provides a cobalt-free lithium-rich manganese-based oxide material for a lithium-ion battery. The cobalt-free lithium-rich manganese-based oxide material for a lithium-ion battery is prepared by the above preparation method.

[0073] This embodiment also provides a lithium-ion battery, which includes the above-mentioned cobalt-free lithium-rich manganese-based oxide material for lithium-ion batteries.

[0074] Embodiment 1:

[0075] LiOH·H 2 O and Ni 0.2 Mn 0.6 (OH)3 The mixture is mixed at a first preset molar ratio of 1.5:1 to obtain a mixture, and the mixture is ball-milled in a ball mill until the particle size of the mixture reaches a target particle size, which is 100 nm; the mixture is placed in a box furnace, and the mixture is pre-calcined at 450° C. for 4 hours; the mixture is high-temperature calcined at 850° C. for 10 hours to obtain the first reactant Li 1.2 Ni 0.2 Mn 0.6 O 2 ;

[0076] The first reactant is immersed in a 1.2 mol / L citric acid ethanol solution; the first reactant immersed in the citric acid ethanol solution is magnetically stirred; the magnetic stirring is achieved by a magnetic stirrer, the stirring speed is set to 300 r / min, and a straight bar stirrer is selected; the dried reactant is calcined at 400° C. for 5 hours, and a second reactant with a surface coated with a spinel phase is obtained by high temperature calcination;

[0077] The second reactant is reacted with Al(NO 3 ) 3 9H 2 O is mixed according to Al: Mn = 0.05: 1, and stirred; the stirred second reactant is heated to 300°C at a rate of 2°C / min and maintained for 1 hour; then, the temperature is raised to 850°C at a rate of 2°C / min and maintained for 6 hours to obtain a third reactant; the third reactant is naturally cooled and washed; specifically, after cooling, it is washed 3 times with deionized water, each time using 200mL water / 50g material, and filtered after stirring for 15 minutes;

[0078] Dopamine hydrochloride is mixed with deionized water to obtain a 1.5 mol / L dopamine hydrochloride solution, and a third reactant is immersed in the dopamine hydrochloride solution and stirred; the immersed third reactant is calcined at a temperature of 400° C. to obtain a cobalt-free lithium-rich manganese-based oxide material for lithium-ion batteries based on an aluminum-doped spinel phase and coated with a carbon layer.

[0079] Embodiment 2:

[0080] The difference between Example 2 and Example 1 is that the concentration of citric acid ethanol solution and Al(NO 3 ) 3 9H 2 ODifferent ratios;

[0081] LiOH·H 2 O and Ni 0.2 Mn 0.6 (OH) 3The mixture is mixed at a first preset molar ratio of 1.2:1 to obtain a mixture, and the mixture is ball-milled in a ball mill until the particle size of the mixture reaches a target particle size, which is 100 nm; the mixture is placed in a box furnace, and the mixture is pre-calcined at 450° C. for 4 hours; the mixture is high-temperature calcined at 850° C. for 10 hours to obtain the first reactant Li 1.2 Ni 0.2 Mn 0.6 O 2 ;

[0082] The first reactant is immersed in a 1.5 mol / L citric acid ethanol solution; the first reactant immersed in the citric acid ethanol solution is magnetically stirred; the magnetic stirring is achieved by a magnetic stirrer, the stirring speed is set to 300 r / min, and a straight bar stirrer is selected; the dried reactant is calcined at 400° C. for 5 hours, and a second reactant with a surface coated with a spinel phase is obtained by high temperature calcination;

[0083] The second reactant is reacted with Al(NO 3 ) 3 9H 2 O is mixed according to Al: Mn = 0.01: 1, and stirred; the stirred second reactant is heated to 300°C at a rate of 2°C / min and maintained for 1 hour; then, the temperature is raised to 850°C at a rate of 2°C / min and maintained for 6 hours to obtain a third reactant; the third reactant is naturally cooled and washed; specifically, after cooling, it is washed 3 times with deionized water, each time using 200mL water / 50g material, and filtered after stirring for 15 minutes;

[0084] Dopamine hydrochloride is mixed with deionized water to obtain a 1.5 mol / L dopamine hydrochloride solution, and the third reactant is immersed in the dopamine hydrochloride solution and stirred; the immersed third reactant is calcined at a temperature of 400° C. to obtain a cobalt-free lithium-rich manganese-based oxide material.

[0085] Embodiment three:

[0086] The difference between Example 2 and Example 1 is that the concentration of citric acid ethanol solution and Al(NO 3 ) 3 9H 2 ODifferent ratios;

[0087] LiOH·H 2 O and Ni 0.2 Mn 0.6 (OH) 3The mixture is mixed at a first preset molar ratio of 1.5:1 to obtain a mixture, and the mixture is ball-milled in a ball mill until the particle size of the mixture reaches a target particle size, which is 100 nm; the mixture is placed in a box furnace, and the mixture is pre-calcined at 450° C. for 4 hours; the mixture is high-temperature calcined at 850° C. for 10 hours to obtain the first reactant Li 1.2 Ni 0.2 Mn 0.6 O 2 ;

[0088] The first reactant is immersed in a 1.5 mol / L citric acid ethanol solution; the first reactant immersed in the citric acid ethanol solution is magnetically stirred; the magnetic stirring is achieved by a magnetic stirrer, the stirring speed is set to 300 r / min, and a straight bar stirrer is selected; the dried reactant is calcined at 400° C. for 5 hours, and a second reactant with a surface coated with a spinel phase is obtained by high temperature calcination;

[0089] The second reactant is reacted with Al(NO 3 ) 3 9H 2 O is mixed according to Al: Mn = 0.01: 1, and stirred; the stirred second reactant is heated to 300°C at a rate of 2°C / min and maintained for 1 hour; then, the temperature is raised to 850°C at a rate of 2°C / min and maintained for 6 hours to obtain a third reactant; the third reactant is naturally cooled and washed; specifically, after cooling, it is washed 3 times with deionized water, each time using 200mL water / 50g material, and filtered after stirring for 15 minutes;

[0090] Dopamine hydrochloride is mixed with deionized water to obtain a 1.5 mol / L dopamine hydrochloride solution, and the third reactant is immersed in the dopamine hydrochloride solution and stirred; the immersed third reactant is calcined at a temperature of 400° C. to obtain a cobalt-free lithium-rich manganese-based oxide material.

[0091] Comparative Example 1:

[0092] LiOH·H 2 O and Ni 0.2 Mn 0.6 (OH) 3 The mixture is mixed at a first preset molar ratio of 1.5:1 to obtain a mixture, and the mixture is ball-milled in a ball mill until the particle size of the mixture reaches a target particle size, which is 100 nm; the mixture is placed in a box furnace, and the mixture is pre-calcined at 450° C. for 4 hours; the mixture is high-temperature calcined at 850° C. for 10 hours to obtain the first reactant Li 1.2 Ni 0.2 Mn0.6 O 2 .

[0093] Comparative Example 2:

[0094] LiOH·H 2 O and Ni 0.2 Mn 0.6 (OH) 3 The mixture is mixed at a first preset molar ratio of 1.5:1 to obtain a mixture, and the mixture is ball-milled in a ball mill until the particle size of the mixture reaches a target particle size, which is 100 nm; the mixture is placed in a box furnace, and the mixture is pre-calcined at 450° C. for 4 hours; the mixture is high-temperature calcined at 850° C. for 10 hours to obtain the first reactant Li 1.2 Ni 0.2 Mn 0.6 O 2 ;

[0095] The first reactant is immersed in a 1.5 mol / L citric acid ethanol solution; the first reactant immersed in the citric acid ethanol solution is magnetically stirred; the magnetic stirring is achieved by a magnetic stirrer, the stirring speed is set to 300 r / min, and a straight bar stirrer is selected; the dried reactant is calcined at 400°C for 5 hours, and a Li-ion battery with a surface-coated spinel phase is obtained by high-temperature calcination. 1.2 Ni 0.2 Mn 0.6 O 2 ;

[0096] Dopamine hydrochloride is mixed with deionized water to obtain a 1.5 mol / L dopamine hydrochloride solution, and the reactants are immersed in the dopamine hydrochloride solution and stirred; the immersed reactants are calcined at a temperature of 400° C. to obtain a cobalt-free lithium-rich manganese-based oxide material.

[0097] Application method: Use Li 1.2 Ni 0.2 Mn 0.6 O 2As the positive electrode material, a conventional lithium-ion battery negative electrode material (such as graphite) and a standard electrolyte (such as 1 mol / L LiPF6 / EC+DMC) are selected. After the electrode is prepared, it is assembled into a CR2032 button cell. The constant current charge and discharge (Galvanostatic) method is adopted, the voltage window is set to 2.0V~4.8V, and the cycle is 100 times and 200 times, and the charge and discharge are performed at a rate of 0.1 C, 1 C and 5 C respectively. The capacity and voltage decay after each charge and discharge are recorded, and the first coulomb efficiency, reversible specific capacity, capacity retention rate, voltage decay and other parameters are recorded. The acquisition and recording methods of the above parameters are well known to those skilled in the art and are not described in detail in this embodiment.

[0098] Table 1 is a description of the parameters of Examples 1 to 3 and Comparative Examples 1 and 2:

[0099]

[0100] From the results of the first coulombic efficiency, it can be seen that the first coulombic efficiency of Example 1 is the highest, reaching 95.4%, which is significantly better than Comparative Examples 1 and 2, indicating that the combination of high-concentration citric acid and high-concentration aluminum source can effectively reduce the irreversible loss during the first charge and discharge process, and significantly improve the first coulombic efficiency; the treatment of citric acid forms a good surface coating, and the introduction of the aluminum source not only inhibits the change of the spinel phase structure by enhancing the stability of the Al-O bond, but also reduces the irreversible loss during the lithium ion deintercalation, and further reduces the side reactions of the electrolyte during the redox process. At the same time, the reversible specific capacity of Example 1 at 0.1 C is 292 mAh·g-1, which is compared with Comparative Examples 2 and 1, indicating that the combination of high-concentration citric acid and high-concentration aluminum source improves the lithium ion storage capacity and conductivity of the material through more effective surface modification, especially enhances the high capacity utilization rate and long-term stability of the material.

[0101] Example 1 shows the best cycle stability, and its capacity retention rate after 200 cycles is 93.4%, which is much higher than that of Comparative Examples 1 and 2. This shows that the combination has a significant improvement in the cycle stability of the battery and can effectively inhibit the capacity decay of the battery. At the same time, the data of Comparative Example 2 are close to those of Comparative Example 1, and even more serious than that of Comparative Example 1 in terms of voltage decay, indicating that if there is no aluminum addition, the high concentration of citric acid will affect the long-term operation of the positive electrode material. In terms of voltage decay, the voltage decay of Example 1 is significantly lower than that of Comparative Examples 1 and 2; low voltage decay means that the structure of the material is more stable during the cycle, and has higher stability and longer service life during long-term use.

[0102] Through the above data analysis, the lithium-ion battery prepared by the preparation method of the cobalt-free lithium-rich manganese-based oxide material for lithium-ion batteries has significant advantages, especially in the first coulombic efficiency, reversible specific capacity, cycle stability and voltage decay.

[0103] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a cobalt-free lithium-rich manganese-based oxide material for lithium-ion batteries, characterized in that: include: Step S1, mixing a lithium source and a precursor in a preset ratio and ball-milling to obtain a mixture, and then performing a first calcination on the mixture to obtain a first reactant; Step S2, soaking the first reactant in a citric acid ethanol solution, while performing magnetic stirring, and then performing a second calcination on the soaked first reactant to obtain a second reactant with a surface coated with a spinel phase, wherein the preset concentration of the citric acid ethanol solution is 1.2-1.5 mol / L; Step S3, mixing and stirring the second reactant and the aluminum source in a preset ratio, and performing a third calcination on the stirred second reactant to allow the aluminum element to enter the lattice structure of the second reactant to obtain a third reactant; Step S4, calcining the carbon source and the third reactant together to obtain a cobalt-free lithium-rich manganese-based oxide material for a lithium-ion battery coated with a carbon layer; The step S3 comprises: Step S31, mixing the second reactant and the aluminum source according to a second preset molar ratio and stirring, wherein the second preset molar ratio is Al:Mn = (0.01-0.05): 1; Step S32, heating the stirred second reactant to 300-400° C. at a rate of 2-5° C. / min and maintaining the temperature for 1-2 h; then heating the stirred second reactant to 850-950° C. at a rate of 2-5° C. / min and maintaining the temperature for 6-8 h to obtain a third reactant; Step S33, naturally cooling the third reactant and washing the third reactant.

2. The method for preparing a cobalt-free lithium-rich manganese-based oxide material for a lithium-ion battery according to claim 1, characterized in that: The step S1 comprises: Step S11, mixing the lithium source and the precursor at a first preset molar ratio to obtain a mixture, and ball milling the mixture in a ball mill until the particle size of the mixture reaches a target particle size; Step S12, placing the mixture in a box furnace, and pre-calcining the mixture at 450-600° C. for 4-6 hours; Step S13, calcining the mixture at 850-920° C. for 10-12 hours.

3. The method for preparing a cobalt-free lithium-rich manganese-based oxide material for a lithium-ion battery according to claim 2, characterized in that: The lithium source is LiOH·H2O, and the precursor is Ni 0.2 Mn 0.6 (OH)3, the first preset molar ratio is (1.2~1.8):

1.

4. The method for preparing a cobalt-free lithium-rich manganese-based oxide material for a lithium-ion battery according to claim 1, characterized in that: The step S2 comprises: Step S21, soaking the first reactant in a citric acid ethanol solution of a preset concentration; Step S22, magnetically stirring the first reactant immersed in the citric acid ethanol solution; Step S23, filtering the first reactant soaked in the citric acid ethanol solution, removing impurities by filtering, and then drying to obtain a dried reactant; Step S24, calcining the dried reactant at 400° C. for 5 hours to obtain a second reactant having a surface covered with a spinel phase through high temperature calcination.

5. The method for preparing a cobalt-free lithium-rich manganese-based oxide material for a lithium-ion battery according to claim 1, characterized in that: The aluminum source is Al(NO3)3·9H2O.

6. The method for preparing a cobalt-free lithium-rich manganese-based oxide material for a lithium-ion battery according to claim 1, characterized in that: The step S4 comprises: Step S41, mixing dopamine hydrochloride with deionized water to obtain a dopamine hydrochloride solution of a preset concentration, and immersing the third reactant in the dopamine hydrochloride solution and stirring; Step S42, calcining the immersed third reactant at a temperature of 400-500° C. to obtain a cobalt-free lithium-rich manganese-based oxide material for lithium-ion batteries based on an aluminum-doped spinel phase and coated with a carbon layer.

7. The method for preparing a cobalt-free lithium-rich manganese-based oxide material for lithium-ion batteries according to claim 6, characterized in that: The preset concentration of the dopamine hydrochloride solution is 1.3-1.5 mol / L.

8. A cobalt-free lithium-rich manganese-based oxide material for lithium-ion batteries, characterized in that: The method for preparing the cobalt-free lithium-rich manganese-based oxide material for lithium-ion batteries as claimed in claim 7 is used for preparing the cobalt-free lithium-rich manganese-based oxide material.

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