Nickel-manganese positive electrode active material, preparation method and application thereof

Abstract

The application belongs to the technical field of lithium ion battery cathode material, and particularly relates to a nickel-manganese cathode active material and a preparation method and application thereof. The nickel-manganese cathode active material comprises a matrix and a coating layer coated on the surface of the matrix, the coating layer comprises an aromatic compound, the aromatic compound is an aromatic acid with multiple carboxyl groups and / or an aromatic acid lithium salt with multiple carboxylate groups, and the mass content of the aromatic compound in the nickel-manganese cathode active material is 0.1% to 0.5%. The nickel-manganese cathode active material obtained by the modification method has better cycle performance, a lower capacity attenuation rate, better rate performance and a lower DCIR.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material technology, specifically relating to a nickel-manganese cathode active material, its preparation method, and its application. Background Technology

[0002] Current lithium-ion batteries are basically composed of lithium iron phosphate (LFP) with an olivine structure, lithium cobalt oxide (LCO) with a layered structure, lithium nickel cobalt manganese oxide (NCM), and lithium nickel cobalt aluminum oxide (NCA). Among them, lithium iron phosphate has relatively high safety performance and good cycle performance, but low energy density and poor low-temperature performance; the layered NCM / NCA has higher energy density, but its widespread use is limited due to the high cost of cobalt and nickel, as well as toxicity and safety issues.

[0003] LiNi 0.5 Mn 1.5 Cobalt-free high-voltage cathode materials such as O4 (LNMO) are gradually becoming known and used due to their high lithium-ion diffusion rate, high voltage plateau and energy density, good thermal stability and low cost. These excellent properties of LNMO will make it an economical and promising cathode material.

[0004] Conventional LNMO materials exhibit poor cycle life and rapid capacity decay at high temperatures. To address these issues, cation and anion doping techniques are typically employed to occupy lattice vacancies, suppress irreversible two-phase reactions, reduce metal (TM) ion dissolution and lattice distortion, and stabilize the crystal structure. Chinese patent application CN104828878A discloses a method for preparing graphene-coated lithium nickel manganese oxide (LNMO) materials. Specifically, graphene is added during the LNMO precursor stage to form in-situ graphene coating. However, adding graphene during the LNMO precursor stage results in the graphene reacting with oxygen during high-temperature sintering, which also reduces some of the Mn. 4+ Transform into Mn 3+ Thus, it is largely consumed, reducing its coating effect. 3+ The formation of these pollutants degrades the cycling performance of the material, significantly increasing costs and causing a rapid decline in capacity retention during high-voltage cycling, making large-scale application difficult. Existing technologies using aromatic compounds to coat LNMO involve large coating amounts and complex coating processes, increasing production costs and making them unsuitable for large-scale application. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a nickel-manganese cathode active material, its preparation method, and its applications.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides a nickel-manganese cathode active material, the nickel-manganese cathode active material comprising a matrix and a coating layer covering the surface of the matrix, the coating layer comprising an aromatic compound, wherein the mass content of the aromatic compound in the nickel-manganese cathode active material is 0.1%-0.5% (e.g., 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%).

[0008] In the above-mentioned nickel-manganese cathode active material, as a preferred embodiment, the aromatic compound has a centrosymmetric or axially symmetric molecular formula; preferably, the aromatic compound is an aromatic acid having multiple carboxyl groups and / or an aromatic lithium salt having multiple carboxyl groups; preferably, the aromatic acid having multiple carboxyl groups has 2 to 4 carboxyl groups, and the aromatic lithium salt having multiple carboxyl groups has 2 to 4 carboxyl groups; preferably, the aromatic compound is at least one of o-benzoic acid, lithium o-benzoate, terephthalic acid, lithium terephthalate, trimesic acid, and lithium trimesicate.

[0009] In the above-mentioned nickel-manganese cathode active material, as a preferred embodiment, the matrix is ​​lithium nickel manganese oxide, and the chemical formula of lithium nickel manganese oxide is LiNi. x Mn y M z O4, where 0.2≤x<0.6, 1.2≤y<1.8, 0.01≤z<0.1, and M is one or more combinations of Al, Zr, W, Mg, Ta, Ti, Nb, and B.

[0010] Secondly, the present invention provides a method for preparing a nickel-manganese positive electrode active material, the method comprising the following steps in sequence:

[0011] S1. Prepare an organic solution by dissolving aromatic compounds in an organic solvent;

[0012] S2. Add lithium nickel manganese oxide to the organic solution obtained in step S1, mix evenly, and then perform low-temperature heat treatment to obtain the nickel manganese positive electrode active material.

[0013] The aromatic compound is an aromatic acid having multiple carboxyl groups and / or an aromatic lithium salt having multiple carboxyl groups.

[0014] In this invention, low-temperature heat treatment is used for coating, which in the early stage of coating is conducive to forming a more coating-compatible "honeycomb" grid structure with organic molecules, making the coating more uniform.

[0015] In the above-mentioned method for preparing nickel-manganese positive electrode active material, as a preferred embodiment, the lithium nickel manganese oxide in step S2 is prepared according to the following steps:

[0016] Sa, take the nickel-manganese precursor and lithium source and mix them evenly to obtain a mixture;

[0017] Sb, the mixture obtained in step Sa is subjected to calcination and annealing treatment in sequence to obtain lithium nickel manganese oxide.

[0018] In this invention, commercially available lithium nickel manganese oxide can be used as a matrix for coating organic matter, or it can be prepared using the preparation method in the preferred embodiment. The lithium nickel manganese oxide prepared by the method of this invention has a higher specific capacity and lower residual alkali content than commercially available lithium nickel manganese oxide.

[0019] In the above-mentioned method for preparing nickel-manganese positive electrode active material, as a preferred embodiment, the lithium source in step Sa is at least one of lithium carbonate, anhydrous lithium hydroxide, or lithium hydroxide monohydrate.

[0020] In the above-mentioned method for preparing nickel-manganese positive electrode active material, as a preferred embodiment, the nickel-manganese precursor in step Sa is Ni. a Mn b (OH)4, where 0.25 < a < 0.75, 0.5 < b < 1.

[0021] In the above-mentioned method for preparing nickel-manganese positive electrode active material, as a preferred embodiment, the organic solvent in step S1 is an alcohol or an ether; preferably, the alcohol is at least one of methanol, ethanol or isopropanol; preferably, the ether is diethyl ether and / or propylene oxide.

[0022] In the above-mentioned method for preparing nickel-manganese positive electrode active material, as a preferred embodiment, in step S1, the molecular formula of the aromatic compound is a centrosymmetric structure or an axially symmetric structure; preferably, the number of carboxyl groups in the aromatic acid having multiple carboxyl groups is 2 to 4, and the number of carboxyl groups in the aromatic lithium salt having multiple carboxyl groups is 2 to 4; preferably, the aromatic compound is at least one of o-benzoic acid, lithium o-benzoate, terephthalic acid, lithium terephthalate, trimesic acid, and lithium trimesicate.

[0023] In the above-mentioned method for preparing nickel-manganese cathode active material, as a preferred embodiment, the mass content of the aromatic compound in the nickel-manganese cathode active material is 1000ppm-5000ppm.

[0024] In the above-mentioned method for preparing nickel-manganese cathode active materials, as a preferred embodiment, the lithium nickel manganese oxide obtained in step Sb has the chemical formula LiNi. x Mn y M zO4, where 0.2≤x<0.6, 1.2≤y<1.8, 0.01≤z<0.1, and M is one or more combinations of Al, Zr, W, Mg, Ta, Ti, Nb, and B.

[0025] In the above-mentioned method for preparing nickel-manganese cathode active material, as a preferred embodiment, the molar ratio of lithium element in the lithium source in step Sa to the sum of nickel and manganese elements in the nickel-manganese precursor is (1.0~1.1):2.

[0026] In the above-mentioned method for preparing nickel-manganese positive electrode active material, as a preferred embodiment, the calcination atmosphere in step Sb is air; preferably, the calcination temperature is 900-1200℃ (e.g., 950℃, 1000℃, 1050℃, 1100℃, 1150℃); preferably, the calcination time is 18-24h (e.g., 19h, 20h, 21h, 22h, 23h).

[0027] In the above-mentioned method for preparing nickel-manganese positive electrode active material, as a preferred embodiment, the annealing atmosphere in step Sb is air; preferably, the annealing temperature is 500-700℃ (e.g., 550℃, 600℃, 650℃); preferably, the annealing time is 2-6h (e.g., 3h, 4h, 5h).

[0028] In the above-mentioned method for preparing nickel-manganese positive electrode active material, as a preferred embodiment, in step S1, the organic solvent and the aromatic compound are mixed uniformly at a mass ratio of 1:(0.2-0.4).

[0029] In the above-mentioned method for preparing nickel-manganese positive electrode active material, as a preferred embodiment, in step S2, the lithium nickel manganese oxide and the organic solution are mixed evenly with a mass ratio of lithium element in the lithium nickel manganese oxide to aromatic compound in the organic solution of 1:(0.04-0.12) (e.g., 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.09, 1:0.1, 1:0.11).

[0030] In the above-mentioned method for preparing nickel-manganese positive electrode active material, as a preferred embodiment, in step S2, the low-temperature heat treatment is carried out under an inert atmosphere; preferably, the low-temperature heat treatment temperature is 80-100℃ (e.g., 85℃, 90℃, 95℃), and the low-temperature heat treatment time is 4-8h (e.g., 5h, 6h, 7h).

[0031] In this invention, if the temperature of the low-temperature heat treatment is too high, the ethanol will evaporate too quickly, which will destroy the "honeycomb" grid structure formed by the ethanol molecules and organic molecules and reduce the uniformity of the coating.

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

[0033] 1. Compared with existing technologies, batteries prepared using the nickel-manganese cathode active material coated with aromatic compounds according to this invention retain approximately 90% of their capacity after 400 cycles of 1C charge-discharge within a voltage range of 3.6-4.8V at room temperature (25°C). In contrast, batteries prepared using uncoated nickel-cobalt-manganese oxide material retain only about 40% of their capacity under the same conditions. The nickel-manganese cathode active material modified by the method of this invention exhibits better cycle performance, less capacity decay, better rate performance, and lower DCIR.

[0034] 2. Compared with the prior art, the preparation process of the nickel-manganese positive electrode active material of the present invention is simple, the cost is low, it saves energy and reduces emissions, and it is conducive to large-scale promotion.

[0035] 3. Compared with the prior art, the aromatic compounds of the present invention are uniformly coated on the substrate surface with a mass content of only 0.1%-0.5%, which improves the electrochemical performance of the nickel-manganese cathode active material. At the same time, the preparation process is simplified. The aromatic compounds can be uniformly coated on the substrate surface without complex ball milling and other processes to form a "honeycomb" grid structure, thereby achieving the effect of stabilizing LNMO materials. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of pyromellitic acid in ethanol;

[0037] Figure 2 These are the specific capacity change curves of the batteries prepared with the positive electrode active materials of Example 2 and Comparative Example 1 during the 1C constant current charge-discharge cycle.

[0038] Figure 3 The curves show the capacity retention rate changes of batteries prepared with the positive electrode active materials of Example 2 and Comparative Example 1 during a constant current charge-discharge cycle at 0.1C.

[0039] Figure 4 These are the capacity retention rate curves of batteries prepared with the positive electrode active materials of Example 2 and Comparative Example 1 during the 3C constant current charge-discharge cycle.

[0040] Figure 5 The results are DCIR test results of the batteries prepared with the positive electrode active materials of Example 2 and Comparative Example 1. Detailed Implementation

[0041] This invention employs aromatic compounds to surface-modify LNMO (lithium nickel manganese oxide). The aromatic compounds used for coating can form a honeycomb-like molecular network on the material surface. This molecular network has relatively large inter-cell gaps, providing smooth channels for lithium ions and facilitating their diffusion. Furthermore, the honeycomb-like network structure coating the material surface can stabilize the structure. Preferably, the organic compound used for coating is an aromatic acid with multiple carboxyl groups or its lithium salt (an aromatic lithium salt with multiple carboxyl groups). Figure 1 This is a schematic diagram of the structure of a triple-symmetric pyromellitic acid molecule in anhydrous ethanol.

[0042] In a preferred embodiment of the present invention, the aromatic compound used for coating is uniformly mixed with anhydrous ethanol, and then uniformly mixed with LNMO in a certain proportion. Then, it is subjected to low-temperature heat treatment under nitrogen protection to finally obtain LNMO with the surface coated with aromatic compound, thereby achieving surface modification of LNMO material.

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0044] The embodiments of the present invention are implemented under the premise of the technical solution of the present invention, and detailed implementation methods and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The process parameters in the following embodiments that do not specify specific conditions are generally in accordance with conventional conditions.

[0045] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0046] In this invention, unless otherwise specified and / or stated, all values ​​relating to component amounts are in parts by weight throughout. Process parameters in the following examples that do not specify particular conditions are generally performed under conventional conditions.

[0047] Example 1

[0048] (1) Ni manganese precursor Ni 0.5 Mn 0.75(OH)4 is mixed with lithium carbonate to obtain a mixture in which the molar ratio of the sum of nickel and manganese elements in the nickel-manganese precursor to the molar ratio of lithium elements in the lithium carbonate is 2:1.05.

[0049] (2) The mixture obtained in step (1) was calcined at 1100℃ for 22h in air atmosphere, then cooled to 600℃ for 2h at a rate of 2℃ / min. After cooling, it was pulverized and passed through a 400-mesh sieve to obtain lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5 O4;

[0050] (3) Mix anhydrous ethanol and trimesic acid in a mass ratio of 1:0.38 to prepare a trimesic acid solution.

[0051] (4) The lithium nickel manganese oxide obtained in step (2) is added to the trimesic acid solution obtained in step (3) and mixed evenly. The mass ratio of lithium element to trimesic acid in lithium nickel manganese oxide is 1:0.06. Then, it is dried at 80°C for 8 hours under nitrogen protection to finally obtain trimesic acid-coated lithium nickel manganese oxide, which is the nickel manganese positive electrode active material of the present invention (wherein the mass content of trimesic acid is about 0.23%).

[0052] Example 2

[0053] (1) Ni manganese precursor Ni 0.5 Mn 0.75 (OH)4 and lithium carbonate are mixed to obtain a mixture in which the molar ratio of the sum of nickel and manganese elements in the nickel-manganese precursor to the molar ratio of lithium elements in the lithium carbonate is 2:1.05.

[0054] (2) The mixture obtained in step (1) was calcined at 1100℃ for 22h in air atmosphere, then cooled to 600℃ for 2h at a rate of 2℃ / min. After cooling, it was pulverized and passed through a 400-mesh sieve to obtain lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5 O4;

[0055] (3) Mix anhydrous ethanol and trimesic acid in a mass ratio of 1:0.38 to prepare a trimesic acid solution.

[0056] (4) The lithium nickel manganese oxide obtained in step (2) is added to the trimesic acid solution obtained in step (3) and mixed evenly. The mass ratio of lithium element to trimesic acid in lithium nickel manganese oxide is 1:0.08. The mixture is then kept at 80°C for 4 hours under nitrogen protection to finally obtain trimesic acid-coated lithium nickel manganese oxide, which is the nickel manganese positive electrode active material of the present invention (wherein the mass content of trimesic acid is about 0.3%).

[0057] Example 3

[0058] (1) Ni manganese precursor Ni0.5 Mn 0.75 (OH)4 and lithium carbonate are mixed to obtain a mixture in which the molar ratio of the sum of nickel and manganese elements in the nickel-manganese precursor to the molar ratio of lithium elements in the lithium carbonate is 2:1.05.

[0059] (2) The mixture obtained in step (1) was calcined at 1100℃ for 22h in air atmosphere, then cooled to 600℃ for 2h at a rate of 2℃ / min. After cooling, it was pulverized and passed through a 400-mesh sieve to obtain lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5 O4;

[0060] (3) Mix anhydrous ethanol and trimesic acid in a mass ratio of 1:0.38 to prepare a solution containing trimesic acid.

[0061] (4) The lithium nickel manganese oxide obtained in step (2) is added to the trimesic acid solution obtained in step (3) and mixed evenly. The mass ratio of lithium element to trimesic acid in lithium nickel manganese oxide is 1:0.1. Then, it is kept at 80°C for 4 hours under nitrogen protection to finally obtain trimesic acid-coated lithium nickel manganese oxide, which is the nickel manganese positive electrode active material of the present invention (wherein the mass content of trimesic acid is about 0.38%).

[0062] Example 4

[0063] (1) Ni manganese precursor Ni 0.5 Mn 0.75 (OH)4 and lithium carbonate are mixed to obtain a mixture in which the molar ratio of the sum of nickel and manganese elements in the nickel-manganese precursor to the molar ratio of lithium elements in the lithium carbonate is 2:1.05.

[0064] (2) The mixture obtained in step (1) was calcined at 1100℃ for 22h in air atmosphere, then cooled to 600℃ for 2h at a rate of 2℃ / min. After cooling, it was pulverized and passed through a 400-mesh sieve to obtain lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5 O4;

[0065] (3) Mix anhydrous ethanol and terephthalic acid in a mass ratio of 1:0.38 to prepare a terephthalic acid solution.

[0066] (4) The lithium nickel manganese oxide obtained in step (2) is added to the terephthalic acid solution obtained in step (3) and mixed evenly. The mass ratio of lithium element to terephthalic acid in lithium nickel manganese oxide is 1:0.06. The mixture is then kept at 80°C for 4 hours under nitrogen protection to finally obtain lithium nickel manganese oxide coated with terephthalic acid, which is the nickel manganese positive electrode active material of the present invention (wherein the mass content of terephthalic acid is about 0.23%).

[0067] Example 5

[0068] This embodiment is basically the same as embodiment 2, except that lithium pyromellitic acid is used instead of pyromellitic acid in this embodiment.

[0069] Comparative Example 1

[0070] Ni manganese precursor Ni 0.5 Mn 0.75 (OH)4 and lithium carbonate were mixed to obtain a mixture in which the molar ratio of the sum of nickel and manganese elements in the nickel-manganese precursor to the lithium element in the lithium carbonate was 2:1.05. The resulting mixture was calcined at 1100℃ for 22 h in air, then annealed at 600℃ for 2 h at a rate of 2℃ / min. After cooling, it was pulverized through a 400-mesh sieve to obtain lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5 O4 (i.e., uncoated lithium nickel manganese oxide LiNi) 0.5 Mn 1.5 O4).

[0071] Comparative Example 2

[0072] This comparative example is basically the same as Example 2, except that in step (4) of this comparative example, the mass ratio of lithium element to pyromellitic acid in lithium nickel manganese oxide is 1:0.02.

[0073] The nickel-manganese cathode active material prepared in this comparative example (in which the mass content of trimesic acid is about 0.075%) has too low an amount of organic matter coating on its surface, which makes it impossible to form a "honeycomb" mesh structure, resulting in reduced coating uniformity and poor cycle performance.

[0074] Comparative Example 3

[0075] This comparative example is basically the same as Example 2, except that in step (4) of this comparative example, the mass ratio of lithium element to pyromellitic acid in lithium nickel manganese oxide is 1:0.18.

[0076] The nickel-manganese cathode active material prepared in this comparative example (containing approximately 0.67% trimellitic acid by mass) was used to prepare a battery according to the method described in Test Example 1 below, and then tested. At 25°C, a voltage range of 3.6-4.8V, and a 1C cycle rate, the initial discharge capacity was 134.5 mAh / g (see Table 1 below). In this comparative example, the excessive amount of trimellitic acid coating resulted in overly tight coating, hindering lithium-ion diffusion and causing a decrease in capacity and reduced cycle performance compared to Example 2.

[0077] Comparative Example 4

[0078] This comparative example is basically the same as Example 2, except that in step (4) of this comparative example, the mass ratio of lithium element to pyromellitic acid in lithium nickel manganese oxide is 1:0.82.

[0079] The nickel-manganese cathode active material prepared in this comparative example (containing approximately 3% trimesic acid by mass) was used to prepare a battery according to the method described in Test Example 1 below, and then tested. At 25°C, a voltage range of 3.6-4.8V, and a 1C cycle rate, the initial cycle discharge capacity was 130.1 mAh / g (see Table 1 below). This comparative example shows that further increasing the amount of coating material not only fails to further improve the cycle performance of the obtained nickel-manganese cathode active material, but also, due to the overly tight coating, hinders lithium-ion diffusion, resulting in a decrease in cycle performance compared to the 0.3% coating amount in Example 2.

[0080] Detection Example 1:

[0081] The nickel-manganese positive electrode active materials (90wt%) prepared in Examples 1-5 and Comparative Examples 2-4, and the lithium nickel manganese oxide (90wt%) prepared in Comparative Example 1 were uniformly mixed with SuperP (5wt%) and PVDF (5wt%), respectively. After slurry preparation, coating, and drying, positive electrode sheets were obtained. The negative electrode sheet was a lithium metal sheet. The electrolyte was 1.15mol / L LiPF6, and the electrolyte solvent was EC+DEC+EMC (volume ratio 1:1:1), wherein the additive DFP≤2%. The separator was a battery-grade polypropylene microporous film with a thickness of 12μm. The battery was prepared as a CR2032 model and tested in a charging cabinet at a temperature of 25℃ and a voltage range of 3.6-4.8V. It was charged and discharged at constant currents of 1C, 0.1C, and 3C, respectively. The electrochemical performance test results are shown in Table 1 below.

[0082] Appendix Figure 2 The specific capacity change curves of CR2032 batteries prepared using the positive electrode active materials prepared in Example 2 and Comparative Example 1 during constant current charge-discharge cycles are shown. The temperature is 25°C, the voltage range is 3.6-4.8V, and the current is 1C.

[0083] Appendix Figure 3 The curves show the capacity retention rate of CR2032 batteries prepared using the positive electrode active materials prepared in Example 2 and Comparative Example 1 during constant current charge-discharge cycles. The temperature was 25°C, the voltage range was 3.6-4.8V, and the current was 0.1C.

[0084] Appendix Figure 4 The curves show the capacity retention rate of CR2032 batteries prepared using the positive electrode active materials prepared in Example 2 and Comparative Example 1 during constant current charge-discharge cycles. The temperature was 25°C, the voltage range was 3.6-4.8V, and the current was 3C.

[0085] Table 1

[0086]

[0087]

[0088] Detection Example 2:

[0089] DCIR detection method:

[0090] Following the method described in Example 1, CR2032 coin cells were prepared using the nickel-manganese positive electrode active material from Example 2 and the lithium nickel-manganese oxide from Comparative Example 1. Then, at 25°C and a voltage range of 3.6-4.8V, the cells were cycled with a 0.5C charge and 1C discharge rate. The internal resistance of the cells was measured after every 50 cycles. The test results are as follows: Figure 5 As shown.

[0091] The method for detecting battery internal resistance is as follows:

[0092] 1. Let stand for 10 hours;

[0093] 2. Constant current and constant voltage charging (first charge at a constant current of 0.1C to 4.8V, then charge at a constant voltage of 4.8V, with a cutoff current of 0.01C); discharge at a 1C rate to the cutoff voltage of 3.6V;

[0094] 3. Let stand for 5 hours;

[0095] 4. (i) 4.8V constant voltage charging, cutoff current 0.01C; (ii) 5C rate discharge for 3s (cycle 5C rate discharge for 3s for a total of 9 times); (iii) 1C rate discharge to cutoff voltage 3.6V.

[0096] The formula for calculating internal resistance is: R = (U1 - U2) / (I1 - I2)

[0097] In the formula: U1 is the voltage at the end of the 1C rate discharge in step 4 above, in volts (V);

[0098] U2 is the voltage at the start of the first 5C rate discharge in step 4 above, in volts (V);

[0099] I1 is the 1C rate discharge current in step 4 above, in amperes (A).

[0100] I2 is the 5C rate discharge current in step 4 above, in amperes (A).

[0101] The results of Examples 1 and 2 above show that, at room temperature (25°C), the battery prepared using LNMO material without aromatic compound coating (Comparative Example 1) retained approximately 40% of its capacity after 400 cycles. Under the same conditions, the battery prepared using LNMO material coated with aromatic compounds (Example 1) retained 90% of its capacity after 400 cycles. Coating with aromatic compounds significantly improves the cycling performance of LNMO. The aromatic compound coating reduces the dissolution of transition metal cations, ensuring the stability of the material structure under long-term cycling conditions. Compared to uncoated LNMO, LNMO coated with aromatic compounds exhibits better cycling performance, less capacity decay, better rate performance, and lower DCIR.

[0102] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. However, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a nickel-manganese cathode active material, characterized in that, The method consists of the following steps in sequence: S1. Prepare an organic solution by dissolving aromatic compounds in an organic solvent; S2. Add lithium nickel manganese oxide to the organic solution obtained in step S1, mix evenly, and then perform low-temperature heat treatment to obtain the nickel manganese positive electrode active material. The aromatic compound is an aromatic acid having multiple carboxyl groups and / or an aromatic lithium salt having multiple carboxyl groups; In step S2, the low-temperature heat treatment is carried out under an inert atmosphere, the low-temperature heat treatment temperature is 80~100℃, and the low-temperature heat treatment time is 4~8h. In the nickel-manganese positive electrode active material, the mass content of the aromatic compound is 1000ppm-5000ppm; The lithium nickel manganese oxide described in step S2 is prepared according to the following steps: Sa, take the nickel-manganese precursor and lithium source and mix them evenly to obtain a mixture; Sb, the mixture obtained in step Sa is subjected to calcination and annealing treatment in sequence to obtain lithium nickel manganese oxide; In step Sb, the annealing atmosphere is air, the annealing temperature is 500~700℃, and the annealing time is 2~6h.

2. The preparation method according to claim 1, characterized in that, The lithium source mentioned in step Sa is at least one of lithium carbonate, anhydrous lithium hydroxide, or lithium hydroxide monohydrate; And / or, the nickel-manganese precursor mentioned in step Sa is Ni a Mn b (OH)4, where 0.25 < a < 0.75, 0.5 < b < 1; And / or, the organic solvent in step S1 is an alcohol or an ether; And / or, in step S1, the molecular formula of the aromatic compound is a centrosymmetric structure or an axially symmetric structure; And / or, in step S1, the aromatic acid having multiple carboxyl groups has 2 to 4 carboxyl groups, and the aromatic lithium salt having multiple carboxyl groups has 2 to 4 carboxyl groups; And / or, in step S1, the aromatic compound is at least one of o-benzoic acid, lithium o-benzoate, terephthalic acid, lithium terephthalate, trimesic acid, and lithium trimesic acid. And / or, the lithium nickel manganese oxide obtained in step Sb has the chemical formula LiNi. x Mn y M z O4, where 0.2≤x<0.6, 1.2≤y<1.8, 0.01≤z<0.1, and M is one or more combinations of Al, Zr, W, Mg, Ta, Ti, Nb, and B; And / or, the molar ratio of lithium in the lithium source in step Sa to the sum of nickel and manganese in the nickel-manganese precursor is (1.0~1.1):2; And / or, in step Sb, the calcination atmosphere is air, the calcination temperature is 900~1200℃, and the calcination time is 18~24h; And / or, in step S1, the organic solvent and the aromatic compound are mixed uniformly in a mass ratio of 1:(0.2~0.4); And / or, in step S2, the lithium nickel manganese oxide is mixed evenly with the organic solution, with the mass ratio of lithium element in the lithium nickel manganese oxide to aromatic compound in the organic solution being 1:(0.04~0.12).

3. The preparation method according to claim 2, characterized in that, The alcohol is at least one of methanol, ethanol or isopropanol, and the ether is diethyl ether and / or propylene oxide.

4. The application of the nickel-manganese cathode active material prepared by the preparation method according to any one of claims 1-3 in lithium battery cathode materials.

5. A nickel-manganese cathode material, characterized in that, The nickel-manganese positive electrode active material prepared by the preparation method according to any one of claims 1-3, as well as the conductive agent and binder.

6. A lithium-ion battery, the battery comprising the nickel-manganese positive electrode material of claim 5, the battery further comprising a battery casing and a positive electrode, a separator and a negative electrode located within the battery casing, the positive electrode comprising a positive electrode current collector and a positive electrode material located on the positive electrode current collector.

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