Spinel type lithium nickel manganese oxide positive electrode material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of lithium battery positive electrode materials, and particularly discloses a spinel type lithium nickel manganese oxide positive electrode material and a preparation method and application thereof.The preparation method comprises the following steps that a lithium source and a nickel manganese hydroxide precursor are evenly mixed, pre-calcined at the temperature of 650-850 DEG C and then calcined at the temperature of 850-1050 DEG C, and the spinel type lithium nickel manganese oxide positive electrode material is obtained; cooling, crushing, sieving, uniformly mixing with a lithium-containing additive I, calcining at 750-950 DEG C, cooling, crushing, sieving, uniformly mixing with a lithium-containing additive II, nano molybdenum oxide and nano lanthanum oxide, calcining at 300-650 DEG C, cooling, crushing, and sieving; according to the invention, the initial lithium ratio of the material is reduced, the inner core is formed through first sintering, then the transition layer coated with high-temperature lithium is formed through subsequent second sintering, and the layered lanthanum lithium molybdate outermost layer is formed through third sintering; and finally, the spinel type lithium nickel manganese oxide positive electrode material with high capacity and good cycle performance and rate capability at high working voltage is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery positive electrode materials, in particular to a spinel-type lithium nickel manganese oxide positive electrode material and a preparation method and application thereof. Background Art

[0002] The theoretical capacity of spinel nickel manganese oxide is as high as 146.7mAh / g, which is higher than the 113mAh / g of lithium cobalt oxide. At the same time, its cycle life is long, which can meet the needs of high-quality batteries and has a significant competitive advantage in the field of lithium-ion batteries. Moreover, spinel nickel manganese oxide is cobalt-free and nickel-free, and is environmentally friendly. At the same time, it is inexpensive, has good thermal stability and overcharge safety performance, and can effectively reduce the safety risks of batteries. Therefore, it is widely used in new energy vehicles, energy storage and other fields. However, at high operating voltages, spinel nickel manganese oxide is prone to electrolyte system decomposition and reduced corrosion resistance. These interfacial reactions lead to reduced first efficiency of the battery and poor cycle performance, which greatly restricts its practical application. Moreover, in order to make up for the capacity disadvantage of spinel nickel manganese oxide, the existing technology adopts a higher lithium ratio, but excessive lithium embedding itself will lead to increased strain and stress in the crystal structure of the material, an increase in grain boundaries and excessive reduction of manganese elements, thereby exacerbating interfacial reactions and further deteriorating cycle performance and rate performance.

[0003] How to explore a more effective method to improve the cycle performance and rate performance of spinel nickel manganese oxide positive electrode materials at high working voltage without affecting the capacity is a technical problem that needs to be solved at present. Summary of the Invention

[0004] In view of the above-mentioned shortcomings of the prior art, the present invention provides a spinel-type lithium nickel manganese oxide positive electrode material and a preparation method and application thereof.

[0005] In order to achieve the above objectives, the main technical solutions adopted by the present invention include:

[0006] First, the present invention provides a method for preparing a spinel-type lithium nickel manganese oxide positive electrode material, comprising the following steps:

[0007] S1, mixing the lithium source and nickel manganese hydroxide precursor uniformly;

[0008] S2, pre-calcining the mixed powder obtained in S1 at 650-850°C, and then calcining at 850-1050°C, which is the first sintering operation, and then pulverizing and sieving after cooling to obtain a lithium nickel manganese oxide intermediate product;

[0009] S3, mixing the lithium nickel manganese oxide intermediate product obtained in the previous step with the lithium-containing additive I;

[0010] S4, calcining the mixed powder obtained in S3 at 750-950°C, which is the second sintering operation, and crushing and sieving after cooling to obtain a primary product of lithium nickel manganese oxide;

[0011] S5. Evenly mix the primary lithium nickel manganese oxide obtained in the previous step with the lithium-containing additive II, nano-molybdenum oxide, and nano-lanthanum oxide;

[0012] S6. calcining the mixed powder obtained in the previous step at 300-650°C. This operation is the third sintering. After cooling, crushing and sieving to obtain the final product.

[0013] It should be noted that:

[0014] (1) Steps S2, S4, and S6 all use a programmed temperature increase method with a heating rate of 2-5°C / min.

[0015] (2) In steps S2, S4, and S6, the pre-calcination or calcination is carried out in an air atmosphere or an oxygen atmosphere, preferably in an oxygen atmosphere.

[0016] The preparation method proposed in the present invention optimizes the lithium addition sequence while maintaining the total lithium content unchanged. First, a lithium source and a nickel manganese hydroxide precursor are sintered for the first time to form an inner core. Then, a lithium-containing additive I is added and sintered for a second time to form a transition layer on the outer surface of the inner core. When the transition layer is formed, part of the lithium penetrates into the inner core to replenish a small amount of lithium for the inner core. The presence of the transition layer is more conducive to lithium ion deintercalation and alleviates the problem of low capacity. Finally, lithium-containing additive II, nano-molybdenum oxide, and nano-lanthanum oxide are added and sintered for a third time to form the outermost layer of lithium lanthanum molybdate on the outer surface of the transition layer, realizing the transformation from a spinel structure to a layered structure. The protective barrier formed by the layered structure enables the positive electrode material to more effectively resist corrosion from the electrolyte, ensures effective deintercalation of lithium ions, and achieves the purpose of simultaneously optimizing cycle performance and rate.

[0017] Preferably, in step S1, the lithium source and the nickel manganese hydroxide precursor are uniformly mixed according to the ratio of the molar amount of the lithium element to the sum of the molar amounts of the nickel element and the manganese element of 0.2-0.4, and the ratio of the molar amount of the lithium element to the sum of the molar amounts of the nickel element and the manganese element is more preferably 0.3-0.4; in step S3, the added concentration of the lithium element is 500-20000ppm; in step S5, the added concentration of the lithium element is 500-8000ppm, the added concentration of the molybdenum element is 500-4000ppm, and the added concentration of the lanthanum element is 500-4000ppm.

[0018] In this embodiment, lithium elements in the cathode material are added in three times. Most of the lithium is located in the core formed by the lithium nickel manganese oxide intermediate product, a small part is located in the transition layer formed in Step 4, and a small part is located on the outer surface of the transition layer, i.e., the outermost layer, which avoids excessive accumulation of lithium on the surface of the cathode material, relieves the lattice pressure on the surface, and then promotes the optimization of the cycle performance and rate performance.

[0019] Preferably, in Step S2, pre-calcination is carried out for 2 - 5 h and calcination is carried out for 8 - 15 h, and in both Step S4 and Step S6, calcination is carried out for 4 - 6 h.

[0020] The length of the calcination time affects both the doping degree and uniformity of lithium and the crystal structure and morphology of the material. Within the pre-calcination and calcination times defined in this embodiment, the reactions between various substances are more sufficient, lithium elements can diffuse more fully to form uniform doping, and a complete crystal structure and regular particle morphology are formed. If the time is too short, the doping of lithium elements may be incomplete, resulting in a decline in the electrochemical performance of the cathode material; if the time is too long, it may cause excessive growth of the material particles or even abnormal grain growth, which is also not conducive to the electrochemical performance of the cathode material.

[0021] Preferably, in Step S2, Step S4, and Step S6, pre-calcination or calcination is carried out in an oxygen atmosphere. The oxygen intake in Step S2 and Step S4 is 3 - 5 m 3 / h, and there is no special restriction on the oxygen intake in Step S6, and it can be within 1 - 10 m 3 / h.

[0022] As an oxidizing atmosphere, oxygen helps to promote the oxidation and doping of lithium during the calcination process. An appropriate oxygen concentration can ensure sufficient reaction between the lithium source and nickel manganese hydroxide. If the oxygen concentration is too low, it may lead to incomplete oxidation of lithium and affect the doping effect; if the oxygen concentration is too high, it may accelerate the volatilization of lithium or form other lithium-containing compound impurities; both too high and too low oxygen concentrations may lead to a decline in the electrochemical performance of the material. In this embodiment, in Step S2 and Step S4, under the defined oxygen intake, it helps to finally form a high-performance lithium nickel manganese oxide cathode material.

[0023] Preferably, in Step S1, the chemical formula of the nickel manganese hydroxide precursor is Ni x Mn 1-x (OH)2, where 0.1 < x ≤ 0.3; its specific surface area is a, the tapped density is b, and the median particle size is D50, and a, b, and D50 satisfy: 10 m 2 / g < a < 30 m 2 / g, 1 g / cm 3 < b < 2 g / cm 3 , 3 μm ≤ D50 ≤ 7 μm.

[0024] In order to obtain positive electrode materials with excellent performance, the specific surface area, tap density and median particle size of the nickel manganese hydroxide precursor have corresponding requirements.

[0025] A moderate specific surface area helps to uniformly diffuse lithium elements and optimize the performance of positive electrode materials. A specific surface area that is too large may lead to excessively high surface energy of the material, making it easy to agglomerate and affecting the sintering effect; a specific surface area that is too small may reduce the diffusion efficiency of lithium elements and affect the electrochemical properties of the positive electrode material.

[0026] The size of the tap density directly affects its filling and processing performance. A higher tap density is conducive to the close stacking of nickel manganese hydroxide during the sintering process, thereby improving the volume energy density of the positive electrode material. In addition, good filling properties also help reduce voids and defects during the preparation process. Too low a tap density may lead to excessive voids between materials during the sintering process, affecting the diffusion of lithium elements and the structural stability of the positive electrode material.

[0027] A moderate median particle size can ensure the uniform diffusion of lithium elements and the structural stability of the positive electrode material during the sintering process. A median particle size that is too large may cause the lithium element diffusion path to be too long, affecting the sintering effect and the electrochemical properties of the positive electrode material; while a median particle size that is too small may increase the agglomeration phenomenon during the preparation process and reduce the filling and processing performance of the material.

[0028] Through several experiments, the present invention found that the specific surface area a, tap density b, and median particle size D50 of the nickel manganese hydroxide precursor meet the above requirements, which can ensure that the nickel manganese hydroxide precursor can form a good structure and performance during the sintering process, thereby meeting the application requirements of lithium batteries.

[0029] Preferably, in order to promote better mixing of molybdenum oxide, lanthanum oxide and lithium nickel manganese oxide matrix and then uniform dispersion to form a relatively dense and stable outermost layer, the particle size of nano-molybdenum oxide and nano-lanthanum oxide is appropriately controlled at 20-50nm. If it is smaller than this particle size range, nano-molybdenum oxide and nano-lanthanum oxide are easy to agglomerate, thereby affecting the distribution effect; if it is larger than this particle size range, the larger particle size may cause the doping source to be unevenly distributed on the surface, making it difficult to form a uniform layered structure. After a long period of circulation, the outermost layer is easy to fall off or break, resulting in capacity decay and poor cycle stability. In addition, excessively large particle size may also block the lithium ion diffusion channel and reduce the ionic conductivity of the positive electrode material.

[0030] Preferably, the lithium source, lithium-containing additive I, and lithium-containing additive II are each selected from at least one of lithium hydroxide, lithium carbonate, and lithium acetate. The lithium source, lithium-containing additive I, and lithium-containing additive II may be the same, different, or partially the same, as long as the amount of lithium element added therein meets the addition concentration required by the preparation method.

[0031] Compared with the prior art, the preparation method proposed in the present invention has at least the following beneficial effects:

[0032] (1) The lithium element is added through three sintering steps and is distributed in different materials. Compared with the method of simply distributing the lithium element on the surface of the same material, the present invention has a better dispersion effect, which can achieve uniform distribution without causing excessive lithiation on the surface, thus not significantly affecting the crystal structure of the material. The obtained product has high capacity at a high lithium ratio and excellent cycle performance and rate performance at a low lithium ratio.

[0033] (2) The second sintering adopts a relatively high temperature, which promotes the full reaction of the lithium nickel manganese oxide intermediate product and the lithium-containing additive I without causing significant impact on the physical and chemical indicators of the material, so that part of the lithium is burned into the inner core, and the other part remains on the surface of the core to form a transition layer. The design of the transition layer is more conducive to the deintercalation of lithium ions and replenishes a small amount of lithium to the core, thereby alleviating the defect of low capacity.

[0034] (3) The outermost layer is formed into a layered lithium lanthanum molybdate by doping lithium-containing additive II, molybdenum oxide, and lanthanum oxide, which helps to further resist the corrosion of the electrolyte and improve the cycle performance.

[0035] Secondly, the present invention proposes a spinel-type lithium nickel manganese oxide positive electrode material prepared according to the above preparation method. The positive electrode material has a large capacity and also has good cycle performance and rate performance at high operating voltage.

[0036] Thirdly, the present invention provides a positive electrode sheet, which comprises the above-mentioned spinel-type lithium nickel manganese oxide positive electrode material.

[0037] The positive electrode sheet is obtained by coating a positive electrode slurry containing the above-mentioned spinel-type lithium nickel manganese oxide positive electrode material (the coating method is the existing technology, such as transfer coating, extrusion coating or gravure coating) on ​​a positive electrode current collector, drying and rolling. The positive electrode slurry also contains a conductive agent, a binder, and a solvent. The conductive agent, the binder, and the solvent are all prepared by conventional technical means in the field. For example, the conductive agent is selected from at least one of carbon black SP, acetylene black, carbon nanotubes CNTs, and graphene. For example, the binder is selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, nitrile rubber, styrene ethylene butylene styrene copolymer, polyacrylonitrile, styrene butadiene styrene copolymer, polyether ether ketone, lithium polyacrylate, and sodium polyacrylate. For example, the solvent is selected from one of deionized water, N-methylpyrrolidone NMP, dimethyl sulfoxide DMSO, tetrahydrofuran THF, and N,N-dimethylformamide DMF, with deionized water and NMP being the most common.

[0038] Fourthly, the present invention provides a lithium battery, which includes the above-mentioned positive electrode sheet.

[0039] In addition, the lithium battery also includes the necessary structural components of a conventional lithium battery, such as a negative electrode sheet, an electrolyte, and a separator. Except for the positive electrode sheet, the rest are all made of existing technology. For example, the negative electrode sheet is a lithium sheet. For example, the electrolyte includes a solvent, an electrolyte salt, and an additive. The solvent is selected from one or more of ethylene carbonate, fluoroethylene carbonate, propylene carbonate, fluoropropylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate. The electrolyte salt is selected from one or more of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluorosulfonyl)imide. The additive is selected from one or more of carbonate additives, nitrile additives, sulfur-containing additives, fluorine-containing additives, boron-containing additives, and phosphorus-containing additives. For example, the separator can be any one of a PP film, a PE film, an alumina coating separator, a polymer coating separator and a solid electrolyte coating separator.

[0040] In summary, the preparation method of the spinel-type lithium nickel manganese oxide positive electrode material proposed in the present invention reduces the initial lithium ratio of the material, and then forms a high-temperature lithium-coated transition layer through a second sintering and a layered lithium lanthanum molybdate outermost layer through a third sintering, which not only supplements the missing lithium ions but also does not affect the structure of the entire system, avoiding the risk of exacerbating over-lithiation, and finally obtains a spinel-type lithium nickel manganese oxide positive electrode material with high capacity and good cycle performance and rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0042] Figure 1 This is an SEM image of the spinel lithium nickel manganese oxide positive electrode material prepared in Example 1;

[0043] Figure 2 This is an SEM / EDS image of the spinel lithium nickel manganese oxide positive electrode material prepared in Example 1;

[0044] Figure 3 The charge and discharge curves of lithium-ion batteries assembled from the products obtained in Example 1, Comparative Example 1, and Comparative Example 2 are shown. DETAILED DESCRIPTION

[0045] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only some of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0046] It should be noted that the technical solutions not described in detail below all adopt conventional technical means in the art, and those skilled in the art can combine and use them without any creative effort.

[0047] In the following examples and comparative examples, the chemical formula of the nickel manganese hydroxide precursor is Ni 0.2 Mn 0.8 (OH)2, its specific surface area a is 22m 2 / g, and the tap density b is 1.6g / cm 3 The median particle size D50 is 4.5 μm. The particle size of nano-molybdenum oxide is 30-50 nm, and the particle size of nano-lanthanum oxide is 20-50 nm.

[0048] Example 1

[0049] The spinel-type lithium nickel manganese oxide positive electrode material was prepared as follows:

[0050] S1. Evenly mix lithium carbonate and nickel manganese hydroxide precursor, wherein the lithium carbonate and nickel manganese hydroxide precursor are evenly mixed according to a ratio of the molar amount of lithium element to the molar amount of nickel element and manganese element of 0.35;

[0051] S2: The mixed powder obtained in S1 was pre-calcined in an oxygen atmosphere at 700°C for 3.5 h, and then calcined at 950°C for 12 h with an oxygen intake of 4 m 3 / h, and after cooling, crushing and sieving to obtain the lithium nickel manganese oxide intermediate product;

[0052] S3, mixing the lithium nickel manganese oxide intermediate product obtained in the previous step with lithium carbonate, wherein the concentration of the added lithium element is 10000 ppm;

[0053] S4: calcine the mixed powder obtained in S3 at 850°C in an oxygen atmosphere for 5 h with an oxygen intake of 4 m 3 / h, and after cooling, crushing and sieving to obtain primary lithium nickel manganese oxide;

[0054] S5. The primary lithium nickel manganese oxide obtained in the previous step is mixed evenly with lithium carbonate, nano-molybdenum oxide, and nano-lanthanum oxide, wherein the concentration of lithium element added is 4000ppm, the concentration of molybdenum element added is 2000ppm, and the concentration of lanthanum element added is 2000ppm;

[0055] S6. The mixed powder obtained in the previous step was calcined at 450° C. for 5 h, and after cooling, it was crushed and sieved to obtain the final product.

[0056] Example 2

[0057] Compared with Example 1, in step S1, the ratio of the molar amount of lithium element to the molar amount of nickel and manganese elements in the lithium source and the nickel manganese hydroxide precursor is 0.2, the concentration of lithium element added in step S3 is 500 ppm, the concentration of lithium element added in step S5 is 500 ppm, the concentration of molybdenum element added is 500 ppm, and the concentration of lanthanum element added is 500 ppm. The rest are consistent with Example 1.

[0058] Example 3

[0059] Compared with Example 1, in step S1, the ratio of the molar amount of lithium element to the molar amount of nickel and manganese elements in the lithium source and the nickel manganese hydroxide precursor is 0.4, the concentration of lithium element added in step S3 is 20000 ppm, the concentration of lithium element added in step S5 is 8000 ppm, the concentration of molybdenum element added is 4000 ppm, and the concentration of lanthanum element added is 4000 ppm. The rest are consistent with Example 1.

[0060] Example 4

[0061] Compared with Example 1, the addition ratio of raw materials in each step is the same, but the pre-calcination, calcination and air intake in step S2, step S4 and step S6 are adjusted, specifically:

[0062] S2: The mixed powder obtained in S1 was pre-calcined in an oxygen atmosphere at 850°C for 4 h and then calcined at 950°C for 8 h with an oxygen intake of 5 m3. 3 / h, cooling, crushing and sieving to obtain lithium nickel manganese oxide intermediate product;

[0063] S4: calcine the mixed powder obtained in S3 at 750°C in an oxygen atmosphere for 4 h with an oxygen intake of 5 m3 / min. 3 / h, and after cooling, crushing and sieving to obtain primary lithium nickel manganese oxide;

[0064] S6. The mixed powder obtained in the previous step was calcined at 500° C. for 6 h, and after cooling, it was crushed and sieved to obtain the final product.

[0065] Example 5

[0066] Compared with Example 1, the addition ratio of raw materials in each step is the same, but the pre-calcination, calcination and air intake in step S2, step S4 and step S6 are adjusted, specifically:

[0067] S2: The mixed powder obtained in S1 was pre-calcined in an oxygen atmosphere at 650°C for 5 h, and then calcined at 900°C for 15 h with an oxygen intake of 4 m3. 3 / h, cooling, crushing and sieving to obtain lithium nickel manganese oxide intermediate product;

[0068] S4: calcine the mixed powder obtained in S3 at 800°C in an oxygen atmosphere for 5 h with an oxygen intake of 4 m 3 / h, and after cooling, crushing and sieving to obtain primary lithium nickel manganese oxide;

[0069] S6. The mixed powder obtained in the previous step was calcined at 300° C. for 4 h, and after cooling, it was crushed and sieved to obtain the final product.

[0070] Example 6

[0071] Compared with Example 1, the addition ratio of raw materials in each step is the same, but the pre-calcination, calcination and air intake in step S2, step S4 and step S6 are adjusted, specifically:

[0072] S2: The mixed powder obtained in S1 was pre-calcined in an oxygen atmosphere at 750°C for 2 h, and then calcined at 1050°C for 10 h with an oxygen intake of 3 m 3 / h, cooling, crushing and sieving to obtain lithium nickel manganese oxide intermediate product;

[0073] S4: calcine the mixed powder obtained in S3 at 950°C in an oxygen atmosphere for 6 h with an oxygen intake of 3 m 3 / h, and after cooling, crushing and sieving to obtain primary lithium nickel manganese oxide;

[0074] S6. The mixed powder obtained in the previous step was calcined at 650° C. for 5 h, and after cooling, it was crushed and sieved to obtain the final product.

[0075] Example 7

[0076] Compared with Example 1, the pre-calcination temperature of step S2 is adjusted to 650° C. and the calcination temperature is adjusted to 850° C., and the rest are consistent with Example 1.

[0077] Example 8

[0078] Compared with Example 1, the pre-calcination temperature of step S2 is adjusted to 850° C. and the calcination temperature is adjusted to 1050° C., and the rest are consistent with Example 1.

[0079] Example 9

[0080] Compared with Example 1, the calcination temperature of step S4 is adjusted to 750° C., and the calcination temperature of step S6 is adjusted to 300° C.; the rest are the same as in Example 1.

[0081] Example 10

[0082] Compared with Example 1, the calcination temperature of step S4 is adjusted to 950° C., and the calcination temperature of step S6 is adjusted to 650° C.; the rest are the same as in Example 1.

[0083] Example 11

[0084] Compared with Example 1, the oxygen intake volume in step S2 and step S4 is adjusted to 3m 3 / h, and the rest are consistent with Example 1.

[0085] Example 12

[0086] Compared with Example 1, the oxygen intake volume in step S2 and step S4 is adjusted to 5m 3 / h, and the rest are consistent with Example 1.

[0087] Example 13

[0088] Compared with Example 1, the pre-calcination time in step S2 is 5 hours and the calcination time is 15 hours, the calcination time in step S4 and step S6 is 6 hours, and the rest is consistent with Example 1.

[0089] Example 14

[0090] Compared with Example 1, the pre-calcination time in step S2 is 2 hours and the calcination time is 8 hours, the calcination time in step S4 and step S6 is 4 hours, and the rest is consistent with Example 1.

[0091] Comparative Example 1

[0092] Compared with Example 1, the addition amounts of lithium carbonate and nickel manganese hydroxide precursor in step S1 are the same, and the lithium carbonate equivalent to that in step S3 and the lithium carbonate equivalent to that in step S5 are added to step S1. Then, the mixture is pre-calcined at 750°C in an oxygen atmosphere for 3.5h and then calcined at 1000°C for 12h. The oxygen intake is 4m 3 / h, and then crush and sieve to obtain the product after cooling.

[0093] Comparative Example 2

[0094] Compared with Example 1, no molybdenum element and lanthanum element are added in step S5. The rest are the same as Example 1.

[0095] Comparative Example 3

[0096] Compared with Example 1, the concentration of the added molybdenum element and the concentration of the added lanthanum element in step S5 are both 300 ppm.

[0097] Comparative Example 4

[0098] Compared with Example 1, the concentration of the added molybdenum element and the concentration of the added lanthanum element in step S5 are both 4500 ppm.

[0099] Comparative Example 5

[0100] Compared with Example 1, the pre-calcination temperature of step S2 is adjusted to 600° C. and the calcination temperature is adjusted to 800° C., and the rest are consistent with Example 1.

[0101] Comparative Example 6

[0102] Compared with Example 1, the pre-calcination temperature of step S2 is adjusted to 1000° C. and the calcination temperature is adjusted to 1200° C., and the rest are consistent with Example 1.

[0103] Comparative Example 7

[0104] Compared with Example 1, the calcination temperature of step S4 is adjusted to 650° C., and the calcination temperature of step S6 is adjusted to 200° C.; the rest are the same as in Example 1.

[0105] Comparative Example 8

[0106] Compared with Example 1, the calcination temperature of step S4 is adjusted to 1050° C., and the calcination temperature of step S6 is adjusted to 750° C.; the rest are the same as in Example 1.

[0107] Comparative Example 9

[0108] Compared with Example 1, the oxygen intake volume in step S2 and step S4 is adjusted to 2m 3 / h, and the rest are consistent with Example 1.

[0109] Comparative Example 10

[0110] Compared with Example 1, the oxygen intake volume in step S2 and step S4 is adjusted to 6m 3 / h, and the rest are consistent with Example 1.

[0111] Comparative Example 11

[0112] Compared with Example 1, the pre-calcination time in step S2 is 1 hour and the calcination time is 6 hours, the calcination time in step S4 and step S6 is 3 hours, and the rest is consistent with Example 1.

[0113] Comparative Example 12

[0114] Compared with Example 1, the pre-calcination time in step S2 is 6 hours and the calcination time is 16 hours, the calcination time in step S4 and step S6 is 7 hours, and the rest is consistent with Example 1.

[0115] The main preparation conditions of each embodiment and comparative example are shown in Table 1 below. For ease of description, in Table 1: Example 1 is represented by S1, Example 2 is represented by S2, and so on; Comparative Example 1 is represented by D1, Comparative Example 2 is represented by D2, and so on; during the first sintering, the pre-calcination temperature is represented by T1a, the pre-calcination time is represented by t1a, the calcination temperature is represented by T1b, the calcination time is represented by t1b, and the oxygen intake is represented by V1; during the second sintering, the calcination temperature is represented by T2, the calcination time is represented by t2, and the oxygen intake is represented by V2; during the third sintering, the calcination temperature is represented by T3, and the calcination time is represented by t3.

[0116] Table 1 Main preparation conditions of each embodiment and comparative example

[0117]

[0118]

[0119] The products obtained in each embodiment and each comparative example were used as positive electrode active materials to prepare positive electrode sheets. The specific operation was as follows: first, the positive electrode active material, the conductive agent SP, and the binder PVDF were uniformly mixed in a mass ratio of 90:5:5, and then NMP was added in an amount of about 40% by weight of the positive electrode material. The mixture was stirred at a stirring rate of 2000 rpm for 30 minutes to obtain a positive electrode slurry. The positive electrode slurry was then evenly applied to a clean aluminum foil and the thickness was controlled to 200 μm with a scraper. The slurry was then placed in an 80°C oven for drying for 1 hour. Finally, the dried aluminum foil was placed on a 200nm roller press and rolled. The electrode sheets of Φ12 were cut out and placed in a 60°C oven for drying for 8 hours for later use.

[0120] The obtained positive electrode sheets are then assembled into half-cells for electrochemical performance testing. The specific assembly operations are as follows: lithium sheets are selected for the negative electrode, and are installed in the order of negative electrode shell, lithium sheet, diaphragm, electrolyte, positive electrode sheet, gasket, spring, and positive electrode shell. After being pressed using an electric press, it is confirmed that the button battery has no obvious dents and is then loaded into the cabinet for testing.

[0121] Electrochemical performance testing included capacity testing, high-voltage cycling performance testing, and rate performance testing. The capacity test involved two cycles at 3.0-4.95V @ 0.1C, with a nominal specific capacity of 130 mAh / g. The cycling performance test involved 100 cycles at 3.0-4.95V @ 1C, comparing the discharge capacity ratio of the 100 cycles to the discharge capacity ratio of the first cycle. The rate performance test involved two cycles at 3.0-4.95V @ 0.1C, followed by another cycle at 3.0-4.95V @ 1C, comparing the discharge capacity ratio of the first cycle at 1C to that at 0.1C. The specific test results are shown in Table 2 below.

[0122] Table 2 Electrochemical performance test results of each embodiment and comparative example

[0123]

[0124]

[0125] As shown in Table 1, Table 2, Figure 1 、 Figure 2 、 Figure 3 Commonly shown:

[0126] (1) From Figure 1 and Figure 2 As can be seen, in the product obtained in Example 1, the La and Mo elements are evenly distributed, with no obvious coating marks on the surface of the product, indicating that the La and Mo elements have entered the interior of the spinel-type lithium nickel manganese oxide positive electrode material. There is no obvious accumulation of the La and Mo elements, indicating that the La and Mo elements within the spinel-type lithium nickel manganese oxide positive electrode material form a stable compound, lithium lanthanum molybdate. The structures and elemental distributions of the products obtained in the remaining examples are similar to those in Example 1 and are therefore not included separately.

[0127] (2) As shown in Table 2, the 1C first-cycle discharge capacity of the products obtained in Examples 1 to 14 is 130.25-131.53 mAh / g, and the discharge capacity after 100 cycles is 126.88-128.78 mAh / g, with a cycle retention rate as high as 97.32%-97.91%. It can be seen that the products prepared according to the preparation method proposed in the present invention have good structural stability at high rates and are not prone to phase change or lattice collapse during rapid lithium ion deintercalation.

[0128] (3) From the comparison of the test results of Example 1 and Comparative Example 1, it can be seen that: compared with the traditional method of adding lithium element once, the present invention increases the cycle retention rate of the obtained product 1C, 100 cycles from 95.85% to 97.91% by adding lithium element three times, and the rate performance is also significantly improved, and the capacity is higher. From the comparison of the test results of Example 1 and Comparative Example 2, it can be seen that: if only the method of adding lithium element is improved without introducing molybdenum and lanthanum, the obtained product cannot effectively resist the corrosion of the electrolyte due to the lack of the outermost layer with a barrier effect, resulting in poor cycle performance and rate performance. Figure 3 It can be seen that Example 1 has both high capacity and high cycle stability, and has the best comprehensive performance.

[0129] (4) From the comparison of the test results of Comparative Examples 3 to 12 with those of Example 1, it can be seen that the concentrations of Mo and La, the temperature / time of the three sinterings, and the oxygen intake during the first and second sinterings have a relatively obvious influence on the rate performance and cycle performance of the product. The preparation conditions shown in Example 1 are the most preferred preparation conditions.

[0130] In summary: The preparation method of the spinel-type lithium nickel manganese oxide positive electrode material proposed in the present invention reduces the initial lithium ratio of the material, and then forms a high-temperature lithium-coated transition layer through a second sintering and a layered lithium lanthanum molybdate outermost layer through a third sintering, which not only supplements the missing lithium ions but also does not affect the structure of the entire system, avoiding the risk of exacerbating over-lithiation, and finally obtains a spinel-type lithium nickel manganese oxide positive electrode material with high capacity and good cycle performance and rate performance.

[0131] Although embodiments of the present invention have been shown and described above, it should be understood that the above embodiments are illustrative and are not to be construed as limiting the present invention. Those skilled in the art may alter, modify, replace, and modify the above embodiments within the scope of the present invention. Furthermore, those skilled in the art may combine and incorporate the various embodiments or examples described in this specification, as well as features thereof, without conflicting requirements.

Claims

1. A method for preparing a spinel-type lithium nickel manganese oxide positive electrode material, characterized in that: The steps are as follows: S1, mixing the lithium source and nickel manganese hydroxide precursor uniformly; S2, pre-calcining the mixed powder obtained in S1 at 650-850°C, then calcining at 850-1050°C, cooling, crushing, and sieving to obtain a lithium nickel manganese oxide intermediate product; S3, mixing the lithium nickel manganese oxide intermediate product obtained in the previous step with the lithium-containing additive I; S4, calcining the mixed powder obtained in S3 at 750-950° C., cooling, crushing, and sieving to obtain a primary product of lithium nickel manganese oxide; S5. Evenly mix the primary lithium nickel manganese oxide obtained in the previous step with the lithium-containing additive II, nano-molybdenum oxide, and nano-lanthanum oxide; S6. calcining the mixed powder obtained in the previous step at 300-650° C., cooling it, crushing it, and sieving it to obtain the final product.

2. The method for preparing the spinel-type lithium nickel manganese oxide positive electrode material according to claim 1, characterized in that: In step S1, the lithium source and the nickel manganese hydroxide precursor are uniformly mixed according to a ratio of the molar amount of the lithium element to the sum of the molar amounts of the nickel element and the manganese element of 0.2-0.4; In step S3, the concentration of lithium added is 500-20000 ppm; In step S5, the concentration of lithium added is 500-8000 ppm, the concentration of molybdenum added is 500-4000 ppm, and the concentration of lanthanum added is 500-4000 ppm.

3. The method for preparing the spinel-type lithium nickel manganese oxide positive electrode material according to claim 1, characterized in that: In step S2, the pre-calcination is performed for 2-5 hours and the calcination is performed for 8-15 hours. In step S4 and step S6, the calcination is performed for 4-6 hours.

4. The method for preparing the spinel-type lithium nickel manganese oxide positive electrode material according to claim 1, characterized in that: Step S2, step S4, and step S6 are pre-calcined or calcined in an oxygen atmosphere. The oxygen intake volume of step S2 and step S4 is 3-5m 3 / h.

5. The method for preparing the spinel-type lithium nickel manganese oxide positive electrode material according to claim 1, characterized in that: In step S1, the chemical formula of the nickel manganese hydroxide precursor is Ni x M n 1-x (OH)2, where 0.1 < x ≤ 0.3; its specific surface area is a, the tapped density is b, and the median particle size is D50. a, b, and D50 satisfy: 10 m 2 / g < a < 30 m 2 / g, 1 g / cm 3 < b < 2 g / cm 3 , 3 μm ≤ D50 ≤ 7 μm.

6. The method for preparing the spinel-type lithium nickel manganese oxide positive electrode material according to claim 1, characterized in that: In step S5, the particle sizes of nano-molybdenum oxide and nano-lanthanum oxide are both 20-50 nm.

7. The method for preparing the spinel-type lithium nickel manganese oxide positive electrode material according to claim 1, characterized in that: The lithium source, lithium-containing additive I and lithium-containing additive II are each selected from at least one of lithium hydroxide, lithium carbonate and lithium acetate.

8. A spinel-type lithium nickel manganese oxide positive electrode material prepared according to the preparation method according to any one of claims 1 to 7.

9. A positive electrode sheet, characterized in that: The positive electrode sheet comprises the spinel-type lithium nickel manganese oxide positive electrode material as claimed in claim 8.

10. A lithium battery, characterized in that: The lithium battery includes the positive electrode sheet as claimed in claim 9.

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