A lithium nickel manganese oxide cathode material, a preparation method and application thereof

Abstract

The application provides a lithium nickel manganese oxide positive electrode material and a preparation method and application thereof. The preparation method comprises the following steps: mixing lithium nickel manganese oxide pre-sintered material and a coating source, and performing microwave coating on the obtained mixture to obtain the lithium nickel manganese oxide positive electrode material, and the surface of the lithium nickel manganese oxide positive electrode material is coated with LiCoPO4; the coating source comprises a formula amount of a coating lithium source, a coating phosphorus source and a coating cobalt source. The lithium nickel manganese oxide positive electrode material is obtained by microwave coating, can realize uniform coating layer distribution, improves the structural stability of the positive electrode material, improves the serious gas production problem in the charging and discharging process of the soft package full battery, and can also avoid the problem of reduced discharge platform voltage caused by coating.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and relates to a lithium nickel manganese oxide positive electrode material, in particular to a lithium nickel manganese oxide positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] Spinel lithium nickel manganese oxide LiNi 0.5 Mn 1.5 O4 material (LNMO) is a high-voltage material prepared by replacing Mn in LiMn2O4 with Ni, and has a theoretical specific capacity of 147 mAh / g, a discharge platform of more than 130 mAh / g at 0.1 C under 4.7 V (vs. Li + / Li), and good cycle stability. Compared with ternary materials, LNMO has a low Li content, and its price advantage is highlighted when the price of Li fluctuates greatly. In addition, LNMO has excellent rate performance, a rich content of manganese and small price fluctuation, and good safety, and has attracted widespread attention.

[0003] Currently, there are some technical problems in the application of the spinel lithium nickel manganese oxide positive electrode material. Firstly, oxygen evolution during high-voltage charging leads to material safety problems. This is not only a problem encountered by spinel lithium nickel manganese oxide, but also a problem encountered by other positive electrode materials such as high-voltage lithium cobalt oxide, ternary materials, and high-nickel materials during high-voltage charging. Therefore, it is also a common problem in the positive electrode material field. In the prior art, methods for oxygen evolution and inhibition of high-nickel materials under large-current overcharging conditions have been studied. It is found that when overcharged to about 5.5 V, oxygen release mainly occurs in the near-surface and grain boundary regions of polycrystalline primary particles and generates voids. Therefore, single-crystal high-nickel materials with fewer grain boundaries and no agglomeration morphology can inhibit oxygen release. However, single-crystal high-nickel materials are difficult to synthesize.

[0004] Secondly, a series of side reactions occur at the interface between the electrolyte and the positive electrode material under high voltage. This can lead to the decomposition of the electrolyte to produce CH4, H2, CO2 and other gases during high-voltage charging and discharging, resulting in serious gas production in the battery and poor processing performance. Currently, the prior art discloses a method for coating lithium nickel manganese oxide with TaO5 material to inhibit the etching of lithium nickel manganese oxide positive electrode material by HF, a product of electrolyte decomposition. However, the discharge platform of lithium nickel manganese oxide positive electrode material coated with TaO5 is significantly reduced, and the energy density of the material is also reduced.

[0005] Based on the above research, it is necessary to provide a lithium nickel manganese oxide positive electrode material that can inhibit oxygen evolution during high-voltage charging through a reasonable coating modification method, improve the safety performance of the lithium nickel manganese oxide positive electrode material, and at the same time inhibit the problem of reduction of the high-voltage discharge platform to improve the energy density of the lithium nickel manganese oxide positive electrode material. SUMMARY

[0006] The application aims to provide a lithium nickel manganese oxide positive electrode material, a preparation method and application thereof.

[0007] To achieve the application purposes, the application adopts the following technical solutions.

[0008] In the first aspect, the application provides a preparation method of a lithium nickel manganese oxide positive electrode material, which comprises the following steps:

[0009] The lithium nickel manganese oxide positive electrode material is obtained by mixing the lithium nickel manganese oxide one-time calcined material and the coating source and performing microwave coating on the obtained mixture.

[0010] The coating source comprises a formula amount of a coating lithium source, a coating phosphorus source and a coating cobalt source.

[0011] The application successfully overcomes the defects of the lithium nickel manganese oxide positive electrode material by using a specific coating method and coating material. Specifically, the lithium nickel manganese oxide positive electrode material is mixed with the coating source, and the synthesis coating is performed under the microwave condition, so that the lithium nickel manganese oxide positive electrode material with uniformly and completely coated LiCoPO4 on the surface is obtained. The microwave coating method can make the coating layer and the core more closely combined, and the coating material is dense and uniform. Compared with other traditional high-temperature sintering coating methods, the microwave coating method can obtain a uniformly distributed coating layer. On the other hand, the lithium nickel manganese oxide one-time calcined material after the microwave treatment is beneficial to improving the tap density and electrochemical performance of the lithium nickel manganese oxide. In addition, the raw material for coating in the application is the coating lithium source, the coating phosphorus source and the coating cobalt source, instead of directly using LiCoPO4, so that the coating source can directly generate uniform and dense LiCoPO4 on the surface of the lithium nickel manganese oxide, thereby making the coating layer and the core more closely combined.

[0012] The LiCoPO4 coated on the surface of the lithium nickel manganese oxide positive electrode material is a high-voltage material, and the microwave method can be used to coat the coating source on the surface of the positive electrode material. The discharge platform of the LiCoPO4 at 0.1C is 4.7V-4.8V (vs. Li +LiCoPO4, also a kind of polyanionic 5V high-voltage positive electrode material, has a theoretical specific capacity of 167 mAh / g, has the same olivine structure as LiFePO4, belongs to the orthorhombic system, has good safety performance, does not reduce the high-voltage discharge platform of the lithium nickel-manganese acid positive electrode material compared with other coating materials, at the same time, improves the energy density of the lithium nickel-manganese acid positive electrode material, suppresses the gas production problem of the lithium nickel-manganese acid positive electrode material at high voltage, and avoids the side reaction of the lithium nickel-manganese acid positive electrode material with the electrolyte.

[0013] Preferably, the microwave coating frequency is 2-10 GHz, for example, it can be 2 GHz, 3 GHz, 4 GHz, 5 GHz, 6 GHz, 7 GHz, 8 GHz, 9 GHz or 10 GHz, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0014] The coating described in the application is only carried out at a specific microwave frequency, that is, the coating can be achieved, and is not assisted by high temperature, which not only reduces energy consumption, but also enables the coating source to be directly generated on the surface of the lithium nickel-manganese acid, thereby improving the bonding strength of the lithium nickel-manganese acid and the coating layer.

[0015] Preferably, the microwave coating time is 0.5-3 h, for example, it can be 0.5 h, 0.75 h, 1 h, 1.25 h, 1.5 h, 1.75 h, 2 h, 2.25 h, 2.5 h, 2.75 h or 3 h, but is not limited to the listed values, and other values not listed in the value range are also applicable, preferably 1-3 h, and further preferably 2-3 h.

[0016] When the microwave coating time of the application is less than 0.5 h, the coating effect is poor, and when the coating time is too long, the coating effect is reduced.

[0017] Preferably, the microwave coating temperature is 100-500 DEG C, for example, it can be 100 DEG C, 200 DEG C, 250 DEG C, 300 DEG C, 350 DEG C, 400 DEG C or 500 DEG C, but is not limited to the listed values, and other values not listed in the value range are also applicable, preferably 200-400 DEG C.

[0018] Preferably, the microwave coating atmosphere includes a nitrogen atmosphere and / or an inert atmosphere.

[0019] The microwave coating described in the application is carried out in a nitrogen atmosphere or an inert atmosphere, which can ensure that the valence of Co in the finally prepared coated material LiCoPO4 is positive two.

[0020] Preferably, the inert atmosphere includes any one or a combination of at least two of argon, helium, neon, krypton or radon, and typical but non-limiting combinations include a combination of argon and helium, or a combination of neon and krypton.

[0021] Preferably, the mixing comprises solid phase mixing.

[0022] Preferably, the coating amount of LiCoPO4 is 0.001-5wt% of the lithium nickel manganese oxide as-fired, for example, it can be 0.001wt%, 0.01wt%, 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt% or 5wt%, but is not limited to the listed values, other values not listed in the value range are also applicable, preferably 0.1-3wt%, further preferably 0.2-2wt%.

[0023] When the content of the coating material LiCoPO4 is too low, the coating material on the surface of the lithium nickel manganese oxide as-fired is less, and cannot inhibit the oxygen precipitation. As the content of the coating material gradually increases, the inhibition of gas production of the prepared positive electrode material is obvious. If the content of the coating material continues to increase, when the content is higher than 5wt%, the impedance will increase, which will deteriorate the electrochemical performance of the lithium nickel manganese oxide positive electrode material. Therefore, ensuring that the coating amount of LiCoPO4 is within a reasonable range can make the finally prepared positive electrode material have the effect of reducing gas production and maintaining the electrochemical performance.

[0024] Preferably, the coating lithium source comprises any one or a combination of at least two of lithium carbonate, lithium hydroxide, lithium oxide, lithium sulfate, lithium nitrate or lithium acetate, typically but not limited to a combination of lithium carbonate and lithium hydroxide, a combination of lithium oxide and lithium sulfate, or a combination of lithium nitrate and lithium acetate.

[0025] Preferably, the coating cobalt source comprises any one or a combination of at least two of cobalt hydroxide, cobalt carbonate, cobalt phosphate or cobalt oxide, typically but not limited to a combination of cobalt hydroxide and cobalt carbonate, or a combination of cobalt phosphate and cobalt oxide, wherein the cobalt ion is divalent.

[0026] Preferably, the coating phosphorus source comprises any one or a combination of at least two of H3PO4, NH4H2PO4 or (NH4)2HPO4, typically but not limited to a combination of H3PO4 and NH4H2PO4, or a combination of (NH4)2HPO4 and H3PO4.

[0027] Preferably, the preparation process of the lithium nickel manganese oxide as-fired comprises: calcining a nickel manganese precursor with a lithium source to obtain the lithium nickel manganese oxide as-fired.

[0028] Preferably, the temperature of the calcination is 700-1000℃, for example, it can be 700℃, 750℃, 800℃, 850℃, 900℃, 950℃ or 1000℃, but is not limited to the listed values, other values not listed in the range of values are also applicable, preferably 800-900℃, further preferably 850-900℃.

[0029] Preferably, the time of the calcination is 5-30h, for example, it can be 5h, 8h, 10h, 12h, 15h, 17h, 20h, 22h, 25h, 27h or 30h, but is not limited to the listed values, other values not listed in the range of values are also applicable, preferably 10-25h, further preferably 10-20h.

[0030] The calcination temperature in the preparation process of the lithium nickel manganese oxide calcined material is too high, or the calcination time is too long, which may promote the secondary crystallization of the material, so that the particle size of the final prepared positive electrode material is too large, the specific surface area of the positive electrode material is reduced, and the discharge specific capacity is reduced; if the calcination temperature is too low, or the calcination time is too short, the crystal structure of the positive electrode material will not grow completely, the crystallinity will be reduced, the structure stability in the charging and discharging process will be poor, and the structure will be easy to collapse, so that the cycle retention rate is reduced.

[0031] Preferably, the atmosphere of the calcination is air atmosphere or oxygen atmosphere, preferably air atmosphere.

[0032] Preferably, the calcination further comprises a crushing and grading step.

[0033] Preferably, the frequency of the grading is 10-30Hz, for example, it can be 10Hz, 15Hz, 20Hz, 25Hz or 30Hz, but is not limited to the listed values, other values not listed in the range of values are also applicable, preferably 20Hz.

[0034] Preferably, the median particle size of the lithium nickel manganese oxide calcined material obtained after the grading is below 20μm, for example, it can be 20μm, 18μm, 16μm, 15μm, 13μm, 10μm, 8μm, 6μm, 4μm, 2μm or 1μm, but is not limited to the listed values, other values not listed in the range of values are also applicable, preferably 1-15μm.

[0035] Preferably, in the nickel manganese precursor, the molar ratio of manganese element to nickel element is (2-4):1, for example, it can be 2:1, 2.5:1, 3:1, 3.5:1 or 4:1, but is not limited to the listed values, other values not listed in the range of values are also applicable, preferably (2.5-3.5):1, further preferably (2.85-3.15):1.

[0036] Preferably, the molar ratio of the metal elements in the nickel-manganese precursor to the lithium elements in the lithium source is (0.1-1):1, which can be 0.1:1, 0.3:1, 0.5:1, 0.7:1, 0.9:1 or 1:1, but is not limited to the listed values, and other values not listed in the value range are also applicable, preferably (0.4-0.6):1, and further preferably (0.45-0.55):1.

[0037] Preferably, the nickel-manganese precursor comprises any one or a combination of at least two of nickel-manganese-containing hydroxides, carbonates or oxides, and typical but non-limiting combinations include a combination of hydroxides and carbonates, a combination of carbonates and oxides, and preferably nickel-manganese-containing hydroxides and / or carbonates.

[0038] Preferably, the median particle size of the nickel-manganese precursor is below 20 μm, which can be 20 μm, 18 μm, 16 μm, 15 μm, 13 μm, 10 μm, 8 μm, 6 μm, 4 μm, 2 μm or 1 μm, but is not limited to the listed values, and other values not listed in the value range are also applicable, preferably 1-15 μm.

[0039] Preferably, the lithium source comprises any one or a combination of at least two of lithium-containing carbonates, hydroxides, oxides, sulfates or nitrates, and typical but non-limiting combinations include a combination of carbonates and hydroxides, or a combination of oxides and sulfates.

[0040] As a preferred technical solution of the preparation method, the preparation method comprises the following steps:

[0041] (1) mixing the nickel-manganese precursor and the lithium source, calcining at a temperature of 700-1000°C for 5-30 h in an air atmosphere or an oxygen atmosphere, crushing the calcined material, and grading at a frequency of 10-30 Hz to obtain a lithium nickel-manganese oxide monocalcined material with a median particle size below 20 μm;

[0042] The median particle size of the nickel-manganese precursor is below 20 μm, and the molar ratio of manganese elements to nickel elements is (2-4):1; the molar ratio of the metal elements in the nickel-manganese precursor to the lithium elements in the lithium source is (0.1-1):1.

[0043] (2) solid-phase mixing the coating source and the lithium nickel-manganese oxide monocalcined material of step (1), and microwave coating the obtained mixture at a temperature of 200-400°C in a nitrogen atmosphere and / or an inert atmosphere at a frequency of 2-10 GHz for 0.5-3 h to obtain the lithium nickel-manganese oxide positive electrode material, the surface of the lithium nickel-manganese oxide positive electrode material is coated with LiCoPO4, and the coating amount of the LiCoPO4 is 0.001-5 wt% of the mass of the lithium nickel-manganese oxide monocalcined material;

[0044] The coating source includes a formula amount of a coated lithium source, a coated phosphorus source and a coated cobalt source.

[0045] In a second aspect, the present application provides a lithium nickel manganese oxide positive electrode material, which is obtained by the preparation method of the first aspect.

[0046] In a third aspect, the present application provides a lithium ion battery, which includes the lithium nickel manganese oxide positive electrode material of the second aspect.

[0047] Compared with the prior art, the present application has the following beneficial effects:

[0048] (1) The present application uses a microwave method for coating, which can overcome the application defects of the lithium nickel manganese oxide positive electrode material, and obtain LiCoPO4 that can uniformly and completely coat the surface of the lithium nickel manganese oxide, compared with other traditional high-temperature sintering coating methods, the coating layer of the present application is tightly combined with the core, is dense, and is uniformly distributed;

[0049] (2) The lithium nickel manganese oxide positive electrode material obtained by the present application effectively inhibits the oxygen precipitation problem in the 5V high-voltage charging and discharging process, improves the structural stability of the positive electrode material, and effectively improves the poor processing performance caused by serious gas production;

[0050] (3) The specific coating material of the present application can solve the problem of voltage platform reduction after other coating materials are used to coat the lithium nickel manganese oxide material, and improve the energy density of the lithium nickel manganese oxide positive electrode material, and the discharge platform retention rate can reach 99.1% at 25℃ normal temperature for 100 cycles. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 is a scanning electron microscope image of the lithium nickel manganese oxide positive electrode material of the present application embodiment 1;

[0052] Figure 2 is an EDS spectrum of the surface Ni element distribution of the lithium nickel manganese oxide positive electrode material of the present application embodiment 1;

[0053] Figure 3 is an EDS spectrum of the surface Mn element distribution of the lithium nickel manganese oxide positive electrode material of the present application embodiment 1;

[0054] Figure 4 is an EDS spectrum of the surface Co element distribution of the lithium nickel manganese oxide positive electrode material of the present application embodiment 1;

[0055] Figure 5 is an EDS spectrum of the surface P element distribution of the lithium nickel manganese oxide positive electrode material of the present application embodiment 1. DETAILED DESCRIPTION

[0056] The technical solutions of the present application are further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations on the present application.

[0057] Example 1

[0058] The present embodiment provides a preparation method of a lithium nickel manganese oxide positive electrode material, which comprises the following steps:

[0059] (1) Ni 0.25 Mn 0.75 (OH)2is mixed with lithium carbonate, and the calcined material obtained after calcination at a temperature of 900°C for 20h in an air atmosphere is crushed and graded at a frequency of 20Hz to obtain lithium nickel manganese oxide one-shot material with a median particle size of 10μm;

[0060] The median particle size of the Ni 0.25 Mn 0.75 (OH)2is 10μm, and the molar ratio of the metal elements in the Ni 0.25 Mn 0.75 (OH)2to the lithium elements in the lithium carbonate is 0.55:1;

[0061] (2) 1.2g of lithium carbonate, 3.8g of CoCO3, 3.7g of NH4H2PO4, and 5kg of the lithium nickel manganese oxide one-shot material of step (1) are solid-phase mixed, and the obtained mixture is microwave coated at a frequency of 3GHz for 1h at a temperature of 300°C in an argon atmosphere to obtain the lithium nickel manganese oxide positive electrode material, the surface of the lithium nickel manganese oxide positive electrode material is coated with LiCoPO4, and the coating amount of the LiCoPO4 is 0.1wt% of the mass of the lithium nickel manganese oxide one-shot material;

[0062] The scanning electron microscope image of the lithium nickel manganese oxide positive electrode material of the present embodiment is shown in Figure 1 , the EDS spectrum of the surface Ni element distribution is shown in Figure 2 , the EDS spectrum of the surface Mn element distribution is shown in Figure 3 , the EDS spectrum of the surface Co element distribution is shown in Figure 4 , the EDS spectrum of the surface P element distribution is shown in Figure 5 , and the white area in Figures 2-5 is the scattering of the corresponding elements, which can prove that the obtained positive electrode material has Co and P elements uniformly distributed on the surface, and there is no element agglomeration phenomenon, and the coating elements are uniformly distributed, thus proving that LiCoPO4 is uniformly coated on the surface of the core.

[0063] Example 2

[0064] The present embodiment provides a preparation method of a lithium nickel manganese oxide positive electrode material, which comprises the following steps:

[0065] (1) Ni 0.25 Mn 0.75 (OH)2 mixed with lithium carbonate, the calcined material obtained after calcination at a temperature of 850°C for 20h under air atmosphere is crushed, and fractionated at a frequency of 20Hz to obtain lithium nickel manganese oxide one-shot material with a median particle size of 20μm;

[0066] the median particle size of the Ni 0.25 Mn 0.75 (OH)2 is 4μm; the molar ratio of the metal elements in the Ni 0.25 Mn 0.75 (OH)2 to the lithium elements in lithium carbonate is 0.5:1;

[0067] (2) 12g of lithium carbonate, 30g of Co(OH)2, 37g of NH4H2PO4 and 5kg of the lithium nickel manganese oxide one-shot material of step (1) are solid-phase mixed, the obtained mixture is microwave coated at a frequency of 5GHz for 2h at a temperature of 200°C under nitrogen atmosphere to obtain the lithium nickel manganese oxide positive electrode material, the surface of the lithium nickel manganese oxide positive electrode material is coated with LiCoPO4, and the coating amount of the LiCoPO4 is 1wt% of the mass of the lithium nickel manganese oxide one-shot material.

[0068] Example 3

[0069] The present example provides a preparation method of a lithium nickel manganese oxide positive electrode material, which comprises the following steps:

[0070] (1) Ni 0.25 Mn 0.75 CO3 mixed with lithium hydroxide, the calcined material obtained after calcination at a temperature of 850°C for 10h under air atmosphere is crushed, and fractionated at a frequency of 20Hz to obtain lithium nickel manganese oxide one-shot material with a median particle size of 20μm;

[0071] the median particle size of the Ni 0.25 Mn 0.75 CO3 is 4μm; the molar ratio of the metal elements in the Ni 0.25 Mn 0.75 CO3 to the lithium elements in lithium hydroxide is 0.5:1;

[0072] (2) 23g of lithium carbonate, 92g of CoC2O4, 73g of NH4H2PO4 and 5kg of the lithium nickel manganese oxide one-shot material of step (1) are solid-phase mixed, the obtained mixture is microwave coated at a frequency of 8GHz for 3h at a temperature of 400°C under nitrogen atmosphere to obtain the lithium nickel manganese oxide positive electrode material, the surface of the lithium nickel manganese oxide positive electrode material is coated with LiCoPO4, and the coating amount of the LiCoPO4 is 2wt% of the mass of the lithium nickel manganese oxide one-shot material.

[0073] Example 4

[0074] The present example provides a preparation method of a lithium nickel manganese oxide cathode material, which is the same as example 1 except that the coating amount of LiCoPO4 is 0.0005wt% of the lithium nickel manganese oxide as-fired material by adjusting the mass of the coating source.

[0075] Example 5

[0076] The present example provides a preparation method of a lithium nickel manganese oxide cathode material, which is the same as example 1 except that the coating amount of LiCoPO4 is 5.5wt% of the lithium nickel manganese oxide as-fired material by adjusting the mass of the coating source.

[0077] Example 6

[0078] The present example provides a preparation method of a lithium nickel manganese oxide cathode material, which is the same as example 1 except that the frequency of the microwave coating in step (2) is 1GHz.

[0079] Example 7

[0080] The present example provides a preparation method of a lithium nickel manganese oxide cathode material, which is the same as example 1 except that the frequency of the microwave coating in step (2) is 12GHz.

[0081] Comparative Example 1

[0082] The present comparative example provides a preparation method of a lithium nickel manganese oxide cathode material, which is the same as example 3 except that no coating source lithium carbonate, CoC2O4 and NH4H2PO4 is added in step (2).

[0083] Comparative Example 2

[0084] The present comparative example provides a preparation method of a lithium nickel manganese oxide cathode material, which comprises the following steps:

[0085] (1) Ni 0.25 Mn 0.75 CO3 is mixed with lithium hydroxide, and the calcined material obtained after calcination at a temperature of 850℃ for 10h in an air atmosphere is crushed, and fractionated at a frequency of 20Hz to obtain lithium nickel manganese oxide as-fired material with a median particle size of 20μm;

[0086] The median particle size of the Ni 0.25 Mn 0.75 CO3 is 4μm; and the median particle size of the Ni 0.25 Mn 0.75The molar ratio of the metal element in CO3 to the lithium element in lithium hydroxide is 0.5:1;

[0087] (2) 23 g of lithium carbonate, 92 g of CoC2O4, 73 g of NH4H2PO4, and 5 kg of the lithium nickel-manganese phosphate one-burnt material of step (1) are subjected to solid-phase mixing, and the obtained mixture is sintered at a temperature of 600°C for 3 h under a nitrogen atmosphere to obtain the lithium nickel-manganese phosphate positive electrode material, the surface of the lithium nickel-manganese phosphate positive electrode material is coated with LiCoPO4, and the coating amount of the LiCoPO4 is 2 wt% of the lithium nickel-manganese phosphate one-burnt material.

[0088] The 2032 type button cells made of the lithium nickel-manganese phosphate positive electrode materials provided in the above examples and comparative examples are subjected to electrochemical performance testing at 25°C and 2.5C, wherein the charge and discharge cutoff voltage is 3.0-4.95 V, and the discharge platform voltage obtained by testing is shown in Table 1; the 1 Ah P405060 type soft package cells made of the lithium nickel-manganese phosphate positive electrode materials provided in the above examples and comparative examples are subjected to gas production testing at 25°C and 1C, wherein the charge and discharge cutoff voltage is 3.0-4.9 V, and the 200 cycle gas production amount obtained by testing is shown in Table 1.

[0089] Table 1

[0090]

[0091] The following points can be seen from Table 1:

[0092] (1) As can be seen from Examples 1-7 and Comparative Examples 1-2, the lithium nickel-manganese phosphate positive electrode material prepared by the microwave coating method of the application has excellent electrochemical performance, effectively solves the problem of voltage platform reduction caused by coating other coating materials on the lithium nickel-manganese phosphate material, improves the energy density of the lithium nickel-manganese phosphate positive electrode material, and the highest retention rate of the discharge platform after 100 cycles at room temperature is 99.1%, the 200 cycle gas production amount is significantly reduced, effectively inhibits the oxygen precipitation problem in the high voltage charge and discharge process, improves the structural stability of the positive electrode material, and improves the poor processing performance caused by serious gas production; and from Figures 1-5 It can be proved that the positive electrode material prepared by the microwave coating method of the application can uniformly distribute the coating elements on the surface of the core.

[0093] (2) As can be seen from Example 1 and Examples 4-5, the coating amount of the coating material will affect the performance of the obtained positive electrode material, too low coating amount cannot inhibit oxygen precipitation, as the content of the coating material gradually increases, the gas production inhibition effect is obvious, but when the coating amount is too high, the impedance of the material will be increased, which will deteriorate the electrochemical performance of the lithium nickel-manganese phosphate positive electrode material; as can be seen from Example 1 and Examples 6-7, the frequency during microwave coating will affect the coating effect, and the material needs a specific coating frequency to achieve the technical effect of the application.

[0094] (3)From Example 3 and Comparative Example 1, it can be seen that Comparative Example 1 adopts the same preparation process, but no coating source is added, and the uncoated lithium nickel manganese oxide positive electrode material obtained has a decline in various electrochemical performances, and the gas production problem is particularly serious; from Example 3 and Comparative Example 2, it can be seen that the difference between Comparative Example 2 and Example 3 is only in the coating method, and Comparative Example 2 adopts the traditional high-temperature sintering coating method, and the coating effect, the uniformity of the coating layer and the bonding strength with the core are all declined, so that the electrochemical performance of the positive electrode material obtained is also declined accordingly.

[0095] In summary, the lithium nickel manganese oxide positive electrode material, the preparation method and the application thereof provided by the present application have excellent electrochemical performance, and the discharge platform retention rate of the battery prepared by using the lithium nickel manganese oxide positive electrode material prepared by the microwave coating method is 99.1% after 100 cycles at room temperature, the gas production amount is obviously reduced after 200 cycles, the structural stability of the positive electrode material is improved, the problem of poor processing performance caused by serious gas production in the charging and discharging process of the soft package full battery is improved, and the problem of the decrease of the discharge platform voltage caused by coating can also be avoided.

[0096] The above merely describes the specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and those skilled in the art should understand that any changes or replacements within the technical scope disclosed by the present application can be easily thought of by those skilled in the art, and all fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for preparing a lithium nickel manganese oxide cathode material, characterized in that, The preparation method comprises the following steps: The preparation method comprises the following steps: The coating source comprises a formula amount of a coating lithium source, a coating phosphorus source and a coating cobalt source. The microwave coating frequency is 2-10 GHz. The microwave coating time is 0.5-3 h. The microwave coating temperature is 100-500 ℃. The coating amount of LiCoPO4 is 0.001-5 wt% of the mass of the lithium nickel manganese oxide one-fired material.

2. The production method according to claim 1, characterized by, The microwave coating time is 1-3 h.

3. The production method according to claim 2, characterized by, The microwave coating time is 2-3 h.

4. The production method according to claim 1, characterized by, The microwave coating temperature is 200-400 ℃.

5. The method of claim 1, wherein, The microwave coating atmosphere comprises a nitrogen atmosphere and / or an inert atmosphere.

6. The method of claim 1, wherein, The mixing comprises solid-phase mixing.

7. The preparation method according to claim 1, characterized in that, The coating amount of LiCoPO4 is 0.1-3 wt% of the mass of the lithium nickel manganese oxide one-fired material.

8. The preparation method according to claim 7, characterized in that, The coating amount of LiCoPO4 is 0.2-2 wt% of the mass of the lithium nickel manganese oxide one-fired material.

9. The method of claim 1, wherein, The coating lithium source comprises any one or a combination of at least two of lithium carbonate, lithium hydroxide, lithium oxide, lithium sulfate, lithium nitrate or lithium acetate.

10. The method of claim 1, wherein, The coating cobalt source comprises any one or a combination of at least two of cobalt hydroxide, cobalt carbonate, cobalt phosphate or cobalt oxide, wherein the cobalt ion is divalent.

11. The method of claim 1, wherein, The coating phosphorus source comprises any one or a combination of at least two of H3PO4, NH4H2PO4 or (NH4)2HPO4.

12. The method of claim 1, wherein, The preparation process of the lithium nickel manganese oxide one-fired material comprises calcining a lithium nickel manganese precursor and a lithium source to obtain the lithium nickel manganese oxide one-fired material.

13. The method of claim 12, wherein, The calcination temperature is 700-1000 ℃.

14. The method of claim 13, wherein, The calcination temperature is 800-900 ℃.

15. The method of claim 14, wherein, The calcination temperature is 850-900 ℃.

16. The method of claim 12, wherein, The calcination time is 5-30 h.

17. The method of claim 16, wherein, The calcination time is 10-25 h.

18. The method of claim 17, wherein, The calcination time is 10-20 h.

19. The method of claim 12, wherein, The calcination atmosphere is an air atmosphere or an oxygen atmosphere.

20. The method of claim 19, wherein, The calcination atmosphere is an air atmosphere.

21. The method of claim 12, wherein, The calcination is followed by a crushing and grading step.

22. The method of claim 21, wherein, The grading frequency is 10-30 Hz.

23. The preparation method according to claim 21, characterized in that, The median particle size of the lithium nickel manganese oxide one-fired material obtained after the grading is below 20 μm.

24. The method of claim 23, wherein, The median particle size of the lithium nickel manganese oxide one-fired material obtained after the grading is 1-15 μm.

25. The method of claim 12, wherein, In the lithium nickel manganese precursor, the molar ratio of manganese to nickel is (2-4):

1.

26. The method of claim 12, wherein, The molar ratio of metal elements in the lithium nickel manganese precursor to lithium elements in the lithium source is (0.1-1):

1.

27. The method of claim 12, wherein, The lithium nickel manganese precursor comprises any one or a combination of at least two of a nickel manganese-containing hydroxide, carbonate or oxide.

28. The method of claim 12, wherein, The median particle size of the lithium nickel manganese precursor is below 20 μm.

29. The method of claim 28, wherein, The median particle size of the lithium nickel manganese precursor is 1-15 μm.

30. The method of claim 12, wherein, The lithium source comprises any one or a combination of at least two of a lithium-containing carbonate, hydroxide, oxide, sulfate or nitrate.

31. The method of claim 1, wherein, The preparation method comprises the following steps: (1) crushing the calcined material obtained by mixing nickel-manganese precursor with lithium source, calcining at a temperature of 700-1000℃ for 5-30h under air or oxygen atmosphere, and grading at a frequency of 10-30Hz to obtain lithium nickel-manganese oxide one-fired material with a median particle size of below 20μm; the nickel-manganese precursor has a median particle size of below 20μm, and the molar ratio of manganese element to nickel element is (2-4):1; the molar ratio of metal elements in the nickel-manganese precursor to lithium element in the lithium source is (0.1-1):1; (2) coating the lithium nickel-manganese oxide one-fired material obtained in step (1) with a coating source by solid phase mixing, and microwave coating the obtained mixture at a frequency of 2-10GHz for 0.5-3h at a temperature of 200-400℃ under nitrogen and / or inert atmosphere to obtain the lithium nickel-manganese oxide positive electrode material, wherein the surface of the lithium nickel-manganese oxide positive electrode material is coated with LiCoPO4, and the coating amount of LiCoPO4 is 0.001-5wt% of the mass of the lithium nickel-manganese oxide one-fired material; the coating source comprises a formula amount of coating lithium source, coating phosphorus source and coating cobalt source.

32. A lithium nickel manganese oxide cathode material, characterized in that, The lithium nickel-manganese oxide positive electrode material is obtained by the preparation method according to any one of claims 1-31.

33. A lithium-ion battery, characterized by, The lithium ion battery comprises the lithium nickel-manganese oxide positive electrode material according to claim 32. The lithium ion battery comprises the lithium nickel-manganese oxide positive electrode material according to claim 32.

Images