Lithium nickel manganese oxide positive electrode active material and preparation method therefor, positive electrode sheet, and battery

Abstract

A lithium nickel manganese oxide positive electrode active material and a preparation method therefor, a positive electrode sheet, and a battery. An X-ray diffraction pattern of the lithium nickel manganese oxide positive electrode active material satisfies: 0.13≤Ih / Iw≤0.28, wherein Iw=I(111)+I(311)+I(400), Ih=I(331)+I(511)+I(531), I(111) is the diffraction peak intensity of a crystal plane (111), I(311) is the diffraction peak intensity of a crystal plane (311), I(400) is the diffraction peak intensity of a crystal plane (400), I(331) is the diffraction peak intensity of a crystal plane (331), I(511) is the diffraction peak intensity of a crystal plane (511), and I(531) is the diffraction peak intensity of a crystal plane (531).

Description

Lithium nickel manganese oxide positive electrode active material, preparation method thereof, positive electrode sheet and battery TECHNICAL FIELD

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

[0002] The positive electrode active material is a key component of a battery, determines the energy density and cycle life of the entire battery, and is also the most costly part in the battery. The spinel-type lithium nickel manganese oxide material is developed on the basis of spinel-type lithium manganate, has the advantages of abundant resources, environmental friendliness and low cost, has a three-dimensional framework structure, the lithium ion transmission path is stable and efficient, and the working voltage window is wide, so that the battery including the spinel-type lithium nickel manganese oxide positive electrode active material has a high energy density, and therefore has great development prospects. However, the spinel phase has crystal self-limitation, and the conventional spinel-type lithium nickel manganese oxide has a sharp-edged octahedral structure, the octahedral sharp corners are easily crushed in the rolling process, and there is a risk of piercing the aluminum foil in the battery cell manufacturing process, in addition, the material has Jahn-Teller effect, Mn 3+ is easily dissolved out at the sharp corners, which is not conducive to the electrochemical performance of the battery. SUMMARY

[0003] The present application provides a lithium nickel manganese oxide positive electrode active material, and an X-ray diffraction spectrum of the lithium nickel manganese oxide positive electrode active material satisfies: 0.13≤I h / I w ≤0.28, wherein, I w =I (111) +I (311) +I (400) , I h =I (331) +I (511) +I (531) , I (111) is the diffraction peak intensity of the crystal face (111), I (311) is the diffraction peak intensity of the crystal face (311), I (400) is the diffraction peak intensity of the crystal face (400), I (331) is the diffraction peak intensity of the crystal face (331), I (511) is the diffraction peak intensity of the crystal face (511), and I (531)The intensity of the diffraction peak on crystal plane (531) is given. Therefore, the lithium nickel manganese oxide cathode active material proposed in this application is a mixed type of spherical and truncated octahedral lithium nickel manganese oxide particles. Compared to single spherical or truncated octahedral lithium nickel manganese oxide particles, the presence of spherical single-crystal particles reduces the risk of lithium nickel manganese oxide breaking or puncturing aluminum foil during rolling, thereby increasing the compaction density of the cathode sheet and improving the energy density of the battery. The presence of truncated octahedral particles can also reduce the Mn content in lithium nickel manganese oxide. 3+ The probability of dissolution is increased, and the (111), (100) and / or (110) crystal planes are exposed simultaneously, thereby improving the energy density and cycle performance of the battery.

[0004] According to some embodiments of this application, the number of spherical particles in the lithium nickel manganese oxide positive electrode active material is n, and the roundness of the spherical particles is R, satisfying: 0.75≤R≤1, 10%≤n≤40%. This reduces the risk of lithium nickel manganese oxide breaking or puncturing aluminum foil during the rolling process, increases the compaction density of the lithium nickel manganese oxide powder, and improves the energy density of the battery.

[0005] According to some embodiments of this application, the lithium nickel manganese oxide cathode active material satisfies at least one of the following conditions: 0.9 ≤ R ≤ 1; 15% ≤ n ≤ 25%. This improves the roundness of the spherical single-crystal particles, increases the compaction density of the lithium nickel manganese oxide powder, reduces the number of spherical single-crystal particles, decreases the hardness of the lithium nickel manganese oxide material, and lowers the processing cost of crushing.

[0006] According to some embodiments of this application, the lithium nickel manganese oxide positive electrode active material includes: Li (1+a) (Ni 0.5 Mn 1.5 ) (1-a-b-c) M b N c O4, wherein -0.3≤a≤0.3, 0<b≤0.002, 0≤c≤0.003, and M includes at least one of B, W, P, Nb, Mo, Ta, Si, and Ce, and N includes at least one of Y, Cr, and Co. Therefore, doping lithium nickel manganese oxide (NMC) materials with M and N elements affects the morphology of the NMC cathode material particles. M promotes the formation of spherical morphology in NMC particles, while N promotes the formation of truncated / side-octahedral morphology, thereby improving the energy density and cycle performance of the battery.

[0007] According to some embodiments of the present application, the nickel-manganese lithium acid positive electrode active material satisfies at least one of the following conditions: the M includes at least one of B, Nb; the N includes Y. In this way, single-crystal nickel-manganese lithium acid particles of a mixed type of spherical particles and truncated octahedral particles are obtained, the compaction density of the material is improved, and the energy density and cycle performance of the battery are improved.

[0008] According to some embodiments of the present application, at least one of the following conditions is satisfied: 0.0003≤b≤0.001; 0.0005≤c≤0.0015, c>b.

[0009] According to some embodiments of the present application, the compaction density of the nickel-manganese lithium acid positive electrode active material is 2.9 g / cm 3 -3.4 g / cm 3 , and optionally 3.1 g / cm 3 -3.3 g / cm 3 . In this way, the compaction density of the positive electrode sheet of the battery is improved, and the energy density of the battery is improved.

[0010] The second aspect of the present application provides a method for preparing a nickel-manganese lithium acid positive electrode active material, the method comprising: mixing a nickel source, a manganese source, a lithium source, an M source, and an N source according to stoichiometric ratios to obtain a mixture; heating the mixture to a first temperature for sintering, then cooling to a second temperature for annealing, and cooling to obtain a bulk nickel-manganese lithium acid; and crushing the bulk nickel-manganese lithium acid. In this way, by doping M elements and N elements in the process of preparing nickel-manganese lithium acid, uniformly full single-crystal large particles are obtained after constant-temperature sintering, and then defects in the nickel-manganese lithium acid reaction process are repaired through annealing, thereby forming single-crystal nickel-manganese lithium acid particles of a mixed type of spherical particles and truncated octahedral particles. The compaction density of the material is improved, the energy density and cycle performance of the battery are improved, the hardness of the single-crystal nickel-manganese lithium acid particles is reduced, and the process cost of later crushing is reduced.

[0011] According to some embodiments of the present application, the method further comprises: mixing a nickel-manganese precursor, the lithium source, the M source, and the N source according to stoichiometric ratios. In this way, the uniformity of the distribution of N elements in the single-crystal nickel-manganese lithium acid particles is improved, and segregation of elements is reduced.

[0012] According to some embodiments of the present application, the first temperature is T1, the second temperature is T2, and 250℃≤T1-T2≤500℃ is satisfied.

[0013] According to some embodiments of the present application, the method satisfies at least one of the following conditions: 850℃≤T1≤1100℃; 600℃≤T2≤800℃. Thus, by making the temperature of the isothermal sintering in the above range, more uniform and full single crystal large particles can be obtained; by making the temperature of the annealing in the above range, defects generated during the reaction of lithium nickel manganese oxide can be repaired, the content of Mn 3+ is controlled, the generation of oxygen vacancies is reduced, and the cycle performance of the battery is further improved.

[0014] According to some embodiments of the present application, the cooling rate from the first temperature to the second temperature is 1℃ / min-4℃ / min. Thus, by making the cooling rate in the above range, the content of Mn 3+ is reduced, the repair effect on the surface of the lithium nickel manganese oxide positive active material is improved, and the process cost is reduced.

[0015] According to some embodiments of the present application, the holding time of the mixture heated to the first temperature is t1, the holding time of the mixture cooled to the second temperature is t2, and at least one of the following conditions is satisfied: 6h≤t1≤12h, optionally, 8h≤t1≤10h; 2h≤t2≤6h, optionally, 3.5h≤t2≤4h. Thus, by making the holding time of the isothermal sintering in the above range, more uniform and full single crystal large particles can be obtained; by making the holding time of the annealing in the above range, defects generated during the reaction of lithium nickel manganese oxide can be repaired, the content of Mn 3+ is controlled, the generation of oxygen vacancies is reduced, and the cycle performance of the battery is further improved.

[0016] According to some embodiments of the present application, the sintering and the annealing are respectively independently carried out in an air or oxygen atmosphere. Thus, the process cost is reduced.

[0017] According to some embodiments of the present application, the sintering is carried out in an oxygen atmosphere. Thus, the lithium source is fully reacted between other raw materials, and then single crystal lithium nickel manganese oxide particles of a mixed type of spherical particles and truncated octahedral particles are more easily obtained.

[0018] According to some embodiments of the present application, the nickel manganese precursor satisfies at least one of the following conditions: 3μm≤Dv50≤5μm, where Dv50 is the volume distribution average particle size of the nickel manganese precursor; 0.8≤(Dv90-Dv10) / Dv50≤1.2, where Dv10 is the particle size corresponding to the particle size volume distribution percentage of 10% of the nickel manganese precursor, and Dv90 is the particle size corresponding to the particle size volume distribution percentage of 90% of the nickel manganese precursor. Thus, the particle size distribution of the nickel manganese precursor is narrow, and the uniformity of the single crystal lithium nickel manganese oxide particles can be improved.

[0019] The third aspect of the present application provides a positive electrode sheet, comprising the lithium nickel manganese acid positive electrode active material provided by the first aspect of the present application. In this way, the compaction density of the positive electrode sheet is improved, and the energy density of the battery is improved.

[0020] The fourth aspect of the present application provides a battery, comprising the positive electrode sheet provided by the third aspect of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0021] The above and / or additional aspects and advantages of the present application will become apparent and be readily appreciated from the following description, including the appended drawings, wherein:

[0022] FIG. 1 shows a flowchart of a method for preparing a lithium nickel manganese acid material according to an embodiment of the present application.

[0023] FIG. 2 shows an SEM image of a lithium nickel manganese acid material prepared according to Example 11 of the present application.

[0024] FIG. 3 shows an SEM image of a lithium nickel manganese acid material prepared according to Example 3 of the present application.

[0025] FIG. 4 shows an SEM image of a lithium nickel manganese acid material prepared according to Example 9 of the present application.

[0026] FIG. 5 shows an SEM image of a lithium nickel manganese acid material prepared according to Comparative Example 1 of the present application.

[0027] FIG. 6 shows an XRD pattern of a lithium nickel manganese acid material prepared according to Example 11 of the present application. DETAILED DESCRIPTION

[0028] Embodiments of the present application are described in detail below with reference to the accompanying drawings, in which like or similar elements are denoted by the same or similar reference numerals, and examples of the embodiments are described in detail below with reference to the accompanying drawings, in which like or similar elements are denoted by the same or similar reference numerals, and the embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application.

[0029] The first aspect of the present application provides a lithium nickel manganese acid positive electrode active material, wherein the X-ray diffraction pattern of the lithium nickel manganese acid positive electrode active material satisfies: 0.13≤I h / I w ≤0.28,

[0030] wherein, I w =I (111) +I (311) +I (400) , I h =I (331) +I (511) +I (531) , I (111) is the diffraction peak intensity of the crystal face (111), I (311)I(400) is the intensity of the diffraction peak of the crystal face (400), (400) I(400) is the intensity of the diffraction peak of the crystal face (400), (331) I(331) is the intensity of the diffraction peak of the crystal face (331), (511) I(511) is the intensity of the diffraction peak of the crystal face (511), (531) I(531) is the intensity of the diffraction peak of the crystal face (531). Specifically, the crystal face (111), the crystal face (311) and the crystal face (400) are low-index energy crystal faces, and the crystal face (331), the crystal face (511) and the crystal face (531) are high-index energy crystal faces. The conventional spinel-type lithium nickel manganese oxide is a well-angled octahedral structure, and the (111) crystal face is fully exposed.

[0031] The present application improves the ratio of I h to I w in the above range, increases the proportion of spherical particles in the mixed nickel manganese oxide particles, reduces the risk of nickel manganese oxide breaking and piercing the aluminum foil during the rolling process, improves the compaction density of the positive electrode sheet, and improves the energy density of the battery. At the same time, the presence of truncated octahedral particles can also reduce the probability of Mn 3+ dissolution in the nickel manganese oxide, and expose the (111) crystal face, the (100) crystal face and / or the (110) crystal face. The (111) crystal face has low surface energy, which is beneficial to the performance of the battery cycle. If the ratio of I h to I w is too small, the number of spherical particles in the mixed nickel manganese oxide is too small, which increases the risk of the material piercing the aluminum foil during the rolling process; if the ratio of I h to I w is too large, the hardness of the mixed nickel manganese oxide particles is too large, which is difficult to break and dissociate, and will increase the process cost of breaking.

[0032] In the present application, the X-ray diffraction of the lithium nickel manganese oxide positive electrode active material is tested by an XRD-6000 type X-ray powder diffractometer (Japan Shimadzu). The test conditions of the XRD are as follows: Cu target, Kα ray (wavelength λ = 0.154 nm), tube voltage 40 kV, tube current 200 mA, and scanning speed 10° (2θ) / min.

[0033] As an example, I h / I w may be 0.13, 0.15, 0.17, 0.19, 0.21, 0.23, 0.25 or 0.28, etc., or can be a range composed of any of the above values.

[0034] According to some embodiments of the present application, the number ratio of the spherical particles in the lithium nickel manganese oxide positive electrode active material is n, the roundness of the spherical particles is R, and 0.75≤R≤1 and 10%≤n≤40% are satisfied. That is, the spherical particles refer to particles with a roundness R satisfying 0.75≤R≤1. By making the number of spherical particles in the above range, the risk of particle breakage and aluminum foil puncture during the rolling process is reduced, the hardness of the lithium nickel manganese oxide particles is reduced, and the breakage is more beneficial, thereby reducing the cost of breakage.

[0035] In the present application, R can be tested by a scanning electron microscope (SEM). Specifically, the length of the longest diagonal of a single crystal particle in the SEM is R1, the equivalent area circle diameter of a single crystal particle is R2, and R=R1 / R2. The closer R is to 1, the more round and regular the morphology of the spherical particles is.

[0036] For example, R can be 0.75, 0.8, 0.85, 0.9, 0.95, or 1, or can be a range composed of any of the above values. In this way, the roundness of the spherical particles is improved, the risk of particle breakage and aluminum foil puncture during the rolling process is reduced, the compaction density of the positive electrode sheet is improved, and the energy density of the battery is improved. According to some specific embodiments of the present application, 0.9≤R≤1.

[0037] For example, n can be 10%, 15%, 20%, 25%, 30%, 35%, or 40%, or can be a range composed of any of the above values. According to some specific embodiments of the present application, 15%≤n≤25%. In this way, lithium nickel manganese oxide particles with high powder compaction density and moderate hardness are obtained.

[0038] In the present application, the number ratio n of the spherical particles can be tested by SEM. Specifically, n is the ratio of the number of spherical particles identified in the SEM photograph to the total number of particles.

[0039] It should be noted that when counting the number of spherical particles in the present application, the sum of the spherical particles that exist alone without being bonded to other particles and the spherical particles that are bonded to other particles is counted.

[0040] According to some embodiments of the present application, the lithium nickel manganese oxide positive electrode active material comprises: Li (1+a) (Ni 0.5 Mn 1.5 ) (1-a-b-c) M b N cO4, wherein -0.3≤a≤0.3, 0 + The surface energy of the dominant crystal faces (100) and (110) is reduced to achieve a truncated corner effect, which cuts off the top of the octahedron, exposing the (100) crystal face (corresponding to the (400) crystal face in the XRD pattern), and cutting the octahedron from the edge, exposing the (110) crystal face (corresponding to the (310) crystal face in the XRD pattern), thereby forming a truncated octahedral particle. In addition, the doping element N occupies part of the trivalent manganese site, reducing the content of Mn 3+ in lithium nickel manganese oxide, which can reduce the probability of Mn 3+ reduction and the generation of Mn 2+ The reduction of Mn 2+ content can further improve the cycle stability of lithium nickel manganese oxide.

[0041] As an example, a can be -0.3, -0.25, -0.15, -0.1, -0.05, 0.05, 0.1, 0.15, 0.2, 0.25, or 0.3, etc., or can be a range consisting of any of the above values.

[0042] As an example, b can be 0.0002, 0.0005, 0.001, 0.0015, or 0.002, etc., or can be a range consisting of any of the above values. According to some embodiments of the present application, 0.0003≤b≤0.001. Thus, by doping the above content of M element in lithium nickel manganese oxide, the number of spherical particles in lithium nickel manganese oxide is increased, and the risk of breakage of lithium nickel manganese oxide particles and piercing of aluminum foil during rolling is reduced.

[0043] As an example, c can be 0, 0.0003, 0.0005, 0.001, 0.002, or 0.003, etc., or can be a range consisting of any of the above values. According to some embodiments of the present application, 0.0005≤c≤0.0015, c>b. Thus, by doping the above content of N element in lithium nickel manganese oxide, truncated octahedral lithium nickel manganese oxide particles are formed, and the cycle performance of the battery is improved. By making c>b, the N element doping can play a dominant role, which is beneficial to the specific capacity.

[0044] According to some embodiments of the present application, M comprises at least one of B and Nb. In this way, during the formation of lithium nickel manganese oxide, the fusion of primary particles is promoted, and the surface energy of high-index crystal planes is reduced.

[0045] According to some embodiments of the present application, M comprises Y elements.

[0046] According to some embodiments of the present application, the tap density of the lithium nickel manganese oxide positive electrode active material can be 2.9 g / cm 3 -3.4 g / cm 3 , for example, can be 2.9 g / cm 3 , 3 g / cm 3 , 3.1 g / cm 3 , 3.2 g / cm 3 , 3.3 g / cm 3 , or 3.4 g / cm 3 , etc., or can be a range composed of any of the above values. In this way, after the lithium nickel manganese oxide positive electrode active material is coated on the positive electrode sheet, the tap density of the positive electrode sheet can be improved, and the energy density of the battery can be improved. According to some specific embodiments of the present application, the tap density of the lithium nickel manganese oxide positive electrode active material can be 3.1 g / cm 3 -3.3 g / cm 3 .

[0047] In the present application, the tap density of the lithium nickel manganese oxide positive electrode active material can be tested by a tap density tester of BT-30 model of Bette Company.

[0048] The second aspect of the present application provides a method for preparing the lithium nickel manganese oxide positive electrode active material provided in the first aspect of the present application, the method comprising: mixing a nickel source, a manganese source, a lithium source, a M source, and a N source according to stoichiometric ratios to obtain a mixture; heating the mixture to a first temperature for sintering, then cooling to a second temperature for annealing, and cooling to obtain a bulk lithium nickel manganese oxide; and crushing the bulk lithium nickel manganese oxide.

[0049] In the process of preparing lithium nickel manganese oxide in the present application, on the one hand, M elements and N elements are doped, the doped M elements have a fluxing effect, which can promote the fusion of primary particles during the formation of lithium nickel manganese oxide, and can also effectively reduce the surface energy of high-index crystal planes to form multiple high-index crystal planes on the surface of lithium nickel manganese oxide particles, so that the particles are polyhedral, and after high-temperature and long-keeping, the crystal planes are fused to achieve the effect of spheroidization; the doped N elements are uniformly distributed inside the crystal structure of lithium nickel manganese oxide, and the N-O bond formed between N elements and O elements has higher bond energy, which can reduce the diffusion of Li +The surface energy of the dominant crystal faces (100) and (110) reaches the effect of particle truncated corner, the octahedral top is truncated, and the exposed face is (100) crystal face (corresponding to (400) crystal face in XRD pattern), the octahedral is cut from the edge, and the exposed is (110) crystal face (corresponding to (310) crystal face in XRD pattern), thereby forming a truncated octahedral particle; in addition, the doping element N occupies part of the trivalent manganese site, reduces the content of Mn 3+ in lithium nickel manganese oxide, and can reduce the occurrence probability of Mn 3+ disproportionation reaction to generate Mn 2+ . The reduction of Mn 2+ content can further improve the cycle stability of lithium nickel manganese oxide. On the other hand, after forming lithium nickel manganese oxide doped with M elements and N elements, annealing treatment is performed, the annealing process can repair the defects generated in the reaction process of lithium nickel manganese oxide, regulate the content of Mn 3+ , reduce the generation of oxygen vacancies, and further improve the cycle performance.

[0050] The method proposed in the present application will be described in detail below. Referring to FIG. 1, the method comprises:

[0051] S10: mixing a nickel source, a manganese source, a lithium source, an M source and an N source according to a stoichiometric ratio to obtain a mixture.

[0052] According to some embodiments of the present application, the nickel source, the manganese source, the lithium source, the M source and the N source are weighed according to the stoichiometric ratio and placed in a high-speed mixer for mixing to obtain the mixture.

[0053] According to some embodiments of the present application, the nickel manganese precursor, the lithium source, the M source and the N source are mixed according to a stoichiometric ratio.

[0054] For example, the M source includes an M-containing compound. For example, when M is B element, the M source can be boric acid. When M is Nb element, the M source can be Nb2O5.

[0055] For example, the N source includes an N-containing compound. For example, when N is Y element, the N source can be yttrium oxide.

[0056] According to some embodiments of the present application, the volume average particle size Dv50 of the nickel manganese precursor satisfies: 3 μm≤Dv50≤5 μm, for example, can be 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm, etc., or can be a range consisting of any of the above values. In this way, the particle size distribution of the nickel manganese precursor is narrow, and the uniformity of the lithium nickel manganese oxide single crystal particles can be improved.

[0057] According to some embodiments of the present application, the Dv10, Dv50 and Dv90 of the nickel-manganese precursor satisfy: 0.8≤(Dv90-Dv10) / Dv50≤1.2, wherein Dv10 is the particle size corresponding to the 10% of the particle size volume distribution percentage of the nickel-manganese precursor, Dv90 is the particle size corresponding to the 90% of the particle size volume distribution percentage of the nickel-manganese precursor, for example, can be 0.8, 0.9, 1.0, 1.1 or 1.2, or can be a range consisting of any of the above values. In this way, the particle size distribution of the nickel-manganese precursor is narrow, and the uniformity of the lithium nickel-manganese oxide single crystal particles can be improved.

[0058] In the present application, the Dv10, Dv50 and Dv90 of the nickel-manganese precursor can be tested by a Hydro 3000mu model laser particle size analyzer of Marvern Company.

[0059] S20: heating the mixture to a first temperature for sintering, then cooling to a second temperature for annealing, and cooling to obtain a blocky lithium nickel-manganese oxide.

[0060] According to some embodiments of the present application, the mixture is heated to increase the temperature of the mixture from room temperature to a first temperature, and then the mixture is naturally cooled to a second temperature for annealing, and then cooled to room temperature after a certain time of constant temperature, to obtain a blocky lithium nickel-manganese oxide.

[0061] According to some embodiments of the present application, the time for increasing the temperature from room temperature to the first temperature can be 2h-9h, for example, can be 2h, 4h, 6h, 8h or 9h, or can be a range consisting of any of the above values. According to some specific embodiments of the present application, the time for increasing the temperature from room temperature to the first temperature can be 2h-4h. In this way, the lithium source is fully melted to quickly complete the synthesis reaction of lithium nickel-manganese oxide.

[0062] According to some embodiments of the present application, the temperature increasing from room temperature to the first temperature can be carried out in an air atmosphere or an oxygen atmosphere.

[0063] According to some embodiments of the present application, the temperature increasing from room temperature to the first temperature can be carried out in an oxygen atmosphere. In this way, the melting rate of the lithium source is improved, and the reaction rate of the nickel source, the manganese source, the lithium source, the M source and the N source to form lithium nickel-manganese oxide crystals is improved.

[0064] According to some embodiments of the present application, the first temperature is T1, and satisfies 850℃≤T1≤1100℃, for example, can be 850℃, 900℃, 950℃, 1000℃, 1050℃ or 1100℃, or can be a range consisting of any of the above values.

[0065] According to some embodiments of the present application, the time for temperature rising to the first temperature for isothermal sintering can be t1, and satisfies: 6h≤t1≤12h, for example, can be 6h, 8h, 10h or 12h, or can be a range consisting of any of the above values. According to some specific embodiments of the present application, 8h≤t1≤10h.

[0066] Thus, by making the temperature and holding time of isothermal sintering in the above range, a uniform and full single crystal large particle can be obtained.

[0067] According to some embodiments of the present application, the isothermal sintering can be performed in an air atmosphere or an oxygen atmosphere.

[0068] According to some specific embodiments of the present application, the isothermal sintering can be performed in an air atmosphere. Thus, the reaction cost is reduced.

[0069] According to some embodiments of the present application, the second temperature is T2, and satisfies: 250℃≤T1-T2≤500℃. For example, can be 250℃, 300℃, 350℃, 400℃, 450℃ or 500℃, or can be a range consisting of any of the above values.

[0070] According to some embodiments of the present application, the cooling rate from the first temperature to the second temperature is 1℃ / min-4℃ / min. For example, can be 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min or 4℃ / min, or can be a range consisting of any of the above values. Thus, by making the cooling rate in the above range, the content of Mn 3+ is reduced, the repairing effect on the surface of the lithium nickel-manganese acid positive electrode active material is improved, and the process cost is reduced.

[0071] According to some embodiments of the present application, the time for cooling from the first temperature to the second temperature can be 1h-5h, for example, can be 1h, 2h, 3h, 4h or 5h, or can be a range consisting of any of the above values.

[0072] According to some embodiments of the present application, the cooling process can be performed in an air atmosphere or an oxygen atmosphere.

[0073] According to some specific embodiments of the present application, the cooling process can be performed in an air atmosphere. Thus, the reaction cost is reduced.

[0074] According to some embodiments of the present application, 600℃≤T2≤800℃, for example, can be 600℃, 650℃, 700℃, 750℃ or 800℃, or can be a range consisting of any of the above values.

[0075] According to some embodiments of this application, the holding time for annealing the mixture at the second temperature can be t2, and satisfies 2h ≤ t2 ≤ 6h, for example, it can be 2h, 3h, 4h, 5h or 6h, or a range of any of the above values. According to some specific embodiments of this application, 3.5h ≤ t2 ≤ 4h.

[0076] Therefore, by keeping the annealing temperature and holding time within the above range, defects generated during the lithium nickel manganese oxide reaction can be repaired, and Mn can be controlled. 3+ This reduces the amount of oxygen vacancies, thereby improving the battery's cycle performance.

[0077] According to some embodiments of this application, the annealing process can be carried out in an air atmosphere or an oxygen atmosphere.

[0078] According to some specific embodiments of this application, the annealing process can be carried out in an air atmosphere. This reduces reaction costs.

[0079] S30: The blocky lithium nickel manganese oxide is crushed.

[0080] According to some embodiments of this application, the obtained blocky lithium nickel manganese oxide product is crushed and dissociated to obtain powdered spinel-type lithium manganese oxide.

[0081] In summary, the lithium nickel manganese oxide cathode active material and its preparation method proposed in this application have the following advantages:

[0082] (1) The lithium nickel manganese oxide positive electrode active material proposed in this application is a mixture of spherical particles and truncated octahedral particles. Compared with single particles, the mixed particles as positive electrode active material can reduce the risk of puncturing aluminum foil during the battery preparation process, increase the compaction density of the positive electrode sheet, and thus improve the energy density and safety of the battery.

[0083] (2) This application can obtain single crystal particles with two morphologies in one sintering process. Compared with the method of preparing spherical particles and truncated octahedral particles separately and then mixing them, the process is simpler and can significantly reduce production costs.

[0084] (3) The synthesis process of this application utilizes an oxygen atmosphere during the heating stage, which can accelerate the melting rate of lithium salt and quickly complete the synthesis reaction of lithium nickel manganese oxide. At the same time, the oxygen atmosphere can also make the reaction between Li and other raw materials more complete, thus making it easier to obtain spherical and octahedral morphological effects.

[0085] (4) In the synthesis process of this application, defects generated during the lithium nickel manganese oxide reaction are repaired by slow cooling and medium-temperature annealing during the cooling and annealing stages, which can regulate Mn. 3+ The content is reduced, the generation of oxygen vacancies is decreased, and the cycle performance is further improved.

[0086] (5) The constant temperature sintering stage, the cooling stage and the constant temperature annealing stage of the synthesis process of the application are all carried out in an air atmosphere, which can significantly reduce the production cost.

[0087] The third aspect of the application provides a positive electrode tab, which comprises the lithium nickel manganese acid positive electrode active material provided by the first aspect of the application or the lithium nickel manganese acid positive electrode active material prepared by the method provided by the second aspect of the application. Thus, the compaction density of the positive electrode tab can be improved while reducing the risk of the positive electrode active material piercing the aluminum foil, thereby improving the energy density and safety of the battery.

[0088] The fourth aspect of the application provides a battery comprising the positive electrode tab provided by the third aspect of the application. Thus, the battery has a high energy density and excellent cycle performance.

[0089] It should be noted that the shape of the battery in the application is not particularly limited and can include at least one of a soft pack battery, a cylindrical battery, a button battery and an aluminum shell square battery.

[0090] Although the embodiments of the application have been shown and described above, it should be understood that the above embodiments are exemplary and cannot be construed as limiting the application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the application.

[0091] Example 1

[0092] 1. The nickel-manganese precursor (the mass ratio of Ni and Mn is 25:75), lithium carbonate, yttrium oxide and boric acid were weighed according to the element mole ratio and added to a high-speed mixer for mixing to obtain a mixture, wherein the Dv10 of the nickel-manganese precursor is 3.17 μm, the Dv50 is 4.61 μm and the Dv90 is 6.94 μm;

[0093] 2. The mixture was added to an Al2O3 crucible and heated, and the mixture was heated to a first temperature T1 of 970℃ for constant temperature sintering in an oxygen atmosphere, the sintering atmosphere was oxygen, the sintering time t1 was 10 h, then the temperature was lowered to T2 of 500℃ for annealing in an air atmosphere, the annealing time t2 was 4 h, and then cooled to room temperature in an air atmosphere;

[0094] 3. The mixture was crushed to obtain Li(Ni 0.5 Mn 1.5 ) 0.998 B 0.0008 Y 0.0012 O4.

[0095] 4. Preparation of a positive electrode tab

[0096] Will Li(Ni 0.5 Mn 1.5 ) 0.998 B 0.0008 Y 0.0012 O4, conductive carbon black, and polyvinylidene fluoride (PVDF) were thoroughly mixed with an appropriate amount of N-methylpyrrolidone (NMP) at a mass ratio of 95%:2.5%:2.5% to form a homogenous slurry. This slurry was then coated onto aluminum foil and dried in a vacuum drying oven at 120°C for 12 hours. After drying, the slurry was pressed into shape using a pressure of 100 MPa to produce a positive electrode sheet with a diameter of 15.8 mm and a thickness of 3.2 mm. The areal density of the positive electrode sheet was 147.4 g / m³. 2 .

[0097] 5. Preparation of negative electrode sheet

[0098] Use a lithium metal sheet with a diameter of 15.8 mm and a thickness of 1 mm.

[0099] 6. Separating membrane

[0100] A 25 μm thick polypropylene microporous membrane (Celgard 2325) was used.

[0101] 7. Preparation of electrolyte

[0102] The electrolyte is a mixture of equal volumes of 1 mol / L LiPF6, ethylene carbonate (EC), and diethyl carbonate (DEC).

[0103] 8. Fabrication of button cells

[0104] Assembly was carried out in a glove box under an argon atmosphere, where the water and oxygen content was <5ppm. After assembling the positive electrode, separator, negative electrode, and electrolyte into a CR2032 coin cell, the cell was left to stand for 6 hours.

[0105] The preparation methods of lithium nickel manganese oxide in Examples 2-17 and Comparative Example 1 are the same as those in Example 1, with the differences detailed in Table 1.

[0106] Performance testing

[0107] 1. Morphological testing

[0108] The results were obtained using a scanning electron microscope (SEM) of Hitachi S4800 from Japan, with the roundness R determined by SEM images.

[0109] 2. Compacted density of powder

[0110] The density was obtained by testing with a Baxter BT-30 tap density tester.

[0111] 3. Discharge specific capacity

[0112] The CR2032 button cell was subjected to electrochemical performance test by using Shenzhen Xinhui battery test system, the button voltage window was 3.5-4.95V, the nominal specific capacity was 120mAh / g, and after full charging and full discharging according to 0.1C current, the 0.1C first week discharge specific capacity Co was recorded.

[0113] 4. Capacity retention rate

[0114] The CR2032 button cell was subjected to electrochemical performance test by using Shenzhen Xinhui battery test system, the button voltage window was 3.5-4.95V, the nominal specific capacity was 120mAh / g, and after full charging and full discharging according to 0.1C current for two cycles, after 0.1C cycle for 2 cycles, the button cell was subjected to full charging and full discharging according to 1C current, the discharge specific capacity C1 of the first cycle was recorded, and the discharge specific capacity C100 of 100 cycles was recorded. 100 The capacity retention rate was calculated by C100 / C1x100%, and the cycle performance was evaluated by the capacity retention rate. 100

[0115] 5. Mn 3+ content ratio

[0116] The CR2032 button cell was subjected to electrochemical performance test by using Shenzhen Xinhui battery test system, the button voltage window was 3.5-4.95V, the nominal specific capacity was 120mAh / g, and after full charging and full discharging according to 0.1C current, the first charge-discharge curve was drawn, the discharge specific capacity Cm in the range of 3.5V-4.3V and the total discharge specific capacity Cn in the range of 3.5V-4.95V were recorded according to the first charge-discharge curve, and the Mn content=Cm / Cnx100%. 3+

[0117] The performance test results of the lithium nickel manganese oxide material and the battery in Example 1-Example 17 and Comparative Example 1-Comparative Example 3 are shown in Table 2.

[0118] Table 2

[0119] Conclusion: Compared with Example 1-Example 17 and Comparative Example 1, it can be seen that by making the ratio of I h / I w in the above range, the number of spherical particles in the lithium nickel manganese oxide positive active material can be increased, the compaction density of the lithium nickel manganese oxide positive active material can be improved, the discharge specific capacity and the cycle capacity retention rate of the battery can be improved, and it is indicated that by making the ratio of I h / I w in the above range, the energy density and the cycle performance of the battery can be improved. ​​

[0120] As can be seen from Example 1 to Example 5, by adjusting the temperature in the annealing process, the proportion of Mn 3+ at T2 = 700°C can be changed 3+ The proportion of Mn 3+ is the lowest, and the discharge specific capacity and capacity retention of the battery are improved.

[0121] As can be seen from Example 3 and Example 6, the faster the cooling rate in the cooling stage, the greater the proportion of Mn 3+ , and the discharge specific capacity and capacity retention of the battery are reduced.

[0122] As can be seen from Example 7 to Example 9, by adjusting the doping amount of M element in the lithium nickel manganese oxide positive electrode active material, the ratio of I h / I w can be adjusted, and the compaction density of the lithium nickel manganese oxide positive electrode active material is improved, and the discharge specific capacity and capacity retention of the battery are improved. However, when the doping amount of M element is too high (Example 10), the condition b < c is not met, and although the compaction density of the material is improved, the number of truncated octahedrons is reduced, and the discharge specific capacity and capacity retention of the battery are reduced.

[0123] As can be seen from Example 3 and Example 11, changing the type of M element doping can also meet the ratio requirement of I h / I w and the proportion range of spherical particles, and the discharge specific capacity and capacity retention of the battery are better.

[0124] As can be seen from Example 12 and Example 3, without N element doping, although the ratio requirement of I h / I w and the proportion range of spherical particles are met, the discharge specific capacity and capacity retention of the battery are reduced.

[0125] As can be seen from Example 13 to Example 14, increasing the doping amount of N element improves the discharge specific capacity and capacity retention of the battery, but compared with Example 3, the discharge specific capacity and capacity retention of the battery are poorer because the condition b < c is not met.

[0126] As can be seen from Example 15 and Example 3, when the content of c is too large, the ratio of I h / I w is reduced, the compaction density is reduced, the discharge specific capacity of the battery is poor, and the proportion of spherical particles is too small, which reduces the capacity retention of the battery, but the capacity retention is still higher than that of the comparative example.

[0127] As can be seen from Example 16 and Example 3, changing the type of N element doping can also meet the ratio requirement of I h / I wThe ratio of I / I and the proportion of spherical particles are slightly better, and the discharge specific capacity and capacity retention rate of the battery are better.

[0128] It can be seen from the comparison between Example 17 and Example 3 that, compared with isothermal sintering in an air atmosphere, isothermal sintering in an oxygen atmosphere can obtain spherical particles with higher sphericity and proportion, I h / I w The ratio of I / I is slightly better, and the discharge specific capacity and capacity retention rate of the battery are better.

[0129] As can be seen from FIGS. 2-4, the lithium nickel manganese oxide positive electrode active material particles prepared in the embodiments of the present application are uniform, and include spherical particles and truncated octahedral particles.

[0130] As can be seen from FIG. 5, the lithium nickel manganese oxide positive electrode active material prepared in the comparative example 1 of the present application has no spherical particle morphology.

[0131] In the XRD data of FIG. 6, the ratio of I / I h / I w is within the protection scope of the present application.

[0132] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

Claims

1. A lithium nickel manganese oxide cathode active material, wherein, The X-ray diffraction spectrum of the nickel-manganese lithium acid positive electrode active material satisfies: 0.13≤I h / I w ≤0.28, wherein I w = I (111) + I (311) + I (400) , I h = I (331) + I (511) + I (531) , I (111) is the diffraction peak intensity of the crystal face (111), I (311) is the diffraction peak intensity of the crystal face (311), I (400) is the diffraction peak intensity of the crystal face (400), I (331) is the diffraction peak intensity of the crystal face (331), I (511) is the diffraction peak intensity of the crystal face (511), I (531) is the diffraction peak intensity of the crystal face (531).

2. The lithium nickel manganese oxide cathode active material of claim 1, wherein, The number of spherical particles in the nickel-manganese lithium acid positive electrode active material accounts for n, the roundness of the spherical particles is R, and satisfies: 0.75≤R≤1, 10%≤n≤40%.

3. The lithium nickel manganese oxide cathode active material of claim 2, wherein, At least one of the following conditions is satisfied: 0.9≤R≤1; 15%≤n≤25%.

4. The lithium nickel manganese oxide cathode active material according to any one of claims 1 to 3, wherein, Comprising: Li (1+a) (Ni 0.5 Mn 1.5 ) (1-a-b-c) M b N c O4, wherein -0.3≤a≤0.3, 0 5. The lithium nickel manganese oxide cathode active material of claim 4, wherein, At least one of the following conditions is satisfied: The M includes at least one of B, Nb; The N includes Y.

6. The lithium nickel manganese oxide cathode active material of claim 4, wherein, At least one of the following conditions is satisfied: 0.0003≤b≤0.001; 0.0005≤c≤0.0015, c>b.

7. The lithium nickel manganese oxide cathode active material according to any one of claims 1 to 3, wherein, The compacted density of the nickel-manganese lithium acid positive active material is 2.9 g / cm 3 - 3.4 g / cm 3 , optionally 3.1 g / cm 3 - 3.3 g / cm 3 .

8. A method for preparing the nickel-manganese lithium acid positive electrode active material of any one of claims 1-7, comprising: Mixing a nickel source, a manganese source, a lithium source, an M source, and an N source according to a stoichiometric ratio to obtain a mixture; Heating the mixture to a first temperature for sintering, then cooling to a second temperature for annealing, and cooling to obtain a bulk nickel-manganese lithium acid; Crushing the bulk nickel-manganese lithium acid.

9. The method of claim 8, wherein, The method further comprises mixing a nickel-manganese precursor, the lithium source, the M source, and the N source according to a stoichiometric ratio.

10. The method of claim 9, wherein, The first temperature is T1, and the second temperature is T2, and satisfy 250℃≤T1-T2≤500℃.

11. The method of claim 10, wherein, At least one of the following conditions is satisfied: 850℃≤T1≤1100℃; 600℃≤T2≤800℃.

12. The method of claim 8, wherein, The cooling rate from the first temperature to the second temperature is 1℃ / min-4℃ / min.

13. The method of claim 12, wherein, The holding time of the mixture heated to the first temperature is t1, and the holding time of the mixture cooled to the second temperature is t2, and at least one of the following conditions is satisfied: 6h≤t1≤12h, optionally, 8h≤t1≤10h; 2h≤t2≤6h, optionally, 3.5h≤t2≤4h.

14. The method of claim 8, wherein, The sintering and the annealing are independently carried out in an air or oxygen atmosphere.

15. The method of claim 14, wherein, The sintering is carried out in an oxygen atmosphere.

16. The method of claim 9, wherein, The nickel-manganese precursor satisfies at least one of the following conditions: 3μm≤Dv50≤5μm, wherein Dv50 is the volume average particle size of the nickel-manganese precursor particles; 0.8≤(Dv90-Dv10) / Dv50≤1.2, wherein Dv10 is the particle size corresponding to the particle size volume distribution percentage of 10% of the nickel-manganese precursor particles, and Dv90 is the particle size corresponding to the particle size volume distribution percentage of 90% of the nickel-manganese precursor particles.

17. A positive electrode sheet, wherein, The nickel-manganese lithium acid positive electrode active material of any one of claims 1-7.

18. A battery, wherein, The positive electrode sheet of claim 17.

Images