Monocrystal lithium nickel manganese oxide positive electrode material and preparation method and application thereof

Abstract

The invention discloses a monocrystal lithium nickel manganese oxide positive electrode material for a lithium ion battery as well as a preparation method and application of the monocrystal lithium nickel manganese oxide positive electrode material. The method comprises the following steps: preparing a spherical hydroxide precursor composed of nanosheet crystal grains, converting the spherical hydroxide precursor into a stable biphase mixture of Mn2O3 and MnNiO3, and sintering the biphase mixture with a lithium source in an oxygen atmosphere at 950-1100 DEG C to generate single crystal lithium nickel manganese oxide LiNi < x > Mn < 2-x > O < 4 >, xlt; and 0.6. The monocrystal lithium nickel manganese oxide prepared by the method is of a square or octahedral structure, the grain size is 1-11 microns, the capacity is more than 134mAh / g, the rate and cycle performance are excellent, high energy density and high power density can be realized at the same time, and the service life is long.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery materials, and relates to a single-crystal lithium nickel manganate cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] The power density of a lithium-ion battery is mainly determined by the discharge voltage platform and rate performance of the cathode material. Single-crystal spinel lithium nickel manganate has a high tap density, which can improve the volumetric energy density, and it has a discharge voltage platform of 4.7V and excellent rate performance. It is a potential cathode material that can simultaneously meet the requirements of high energy density and high power density.

[0003] Single-crystal spinel lithium nickel manganate is mainly prepared by conventional processes such as high-temperature solid-phase method, co-precipitation method, sol-gel method, etc. For example, Patent CN113178566A discloses a preparation method of a spinel-type single-crystal cobalt-free high-voltage lithium nickel manganate cathode material, which includes the following steps: A) Under the action of a precipitant, ammonia water and a complexing agent, a nickel source and a manganese source are added to carry out a co-precipitation reaction to obtain a Ni 0.5 Mn 1.5 (OH)4 binary precursor; B) Mix the Ni 0.5 Mn 1.5 (OH)4 binary precursor with a lithium source, carry out high-temperature calcination, then carry out low-speed annealing and heat preservation, and finally naturally cool to obtain a single-crystal LiNi 0.5 Mn 1.5 O4 cathode material in the combination of regular octahedron and truncated octahedron.

[0004] However, the single-crystal lithium nickel manganate prepared by the above conventional process methods usually has a small size, less than 5μm; a low capacity, mostly less than 130 mAh / g; and low rate and cycle performance, which cannot meet the requirements of high energy density and long life. Summary of the Invention

[0005] Aiming at the above problems existing in the prior art, one of the purposes of the present invention is to provide a single-crystal lithium nickel manganate cathode material.

[0006] Another purpose of the present invention is to provide a preparation method of a single-crystal lithium nickel manganate cathode material. The method of the present invention prepares a nanosheet hydroxide precursor through a co-precipitation reaction, and then mixes lithium and sinters to obtain a single-crystal lithium nickel manganate material, which has excellent electrochemical performance.

[0007] Another purpose of the present invention is to provide a lithium-ion battery.

[0008] To achieve the above purposes, the present invention provides the following specific technical solutions.

[0009] The chemical formula of the single-crystal lithium nickel manganate cathode material is LiNix Mn 2-x O4, where 0.3 < x < 0.6, has a cubic or octahedral structure, and the grain size is 1 - 11 μm.

[0010] Furthermore, 0.4 ≤ x ≤ 0.5.

[0011] A method for preparing a single - crystal lithium nickel manganese oxide cathode material includes the following steps: (1) Under a protective atmosphere, a mixed solution of Ni salt and Mn salt, a precipitant solution, and a complexing agent solution are introduced into the bottom liquid of the reaction kettle and flow - through, and a coprecipitation reaction is carried out; wherein, the molar ratio of Ni:Mn in the mixed solution of Ni salt and Mn salt is x / 2:1 - x / 2; (2) When the D50 of the reaction slurry reaches the target value, the reaction is stopped, the reaction slurry is filtered, washed, and the solid phase is dried to obtain the precursor Ni x / 2 Mn 1-x / 2 (OH)2; (3) Convert Ni x / 2 Mn 1-x / 2 (OH)2 into a biphasic mixture of Mn2O3 and MnNiO3; (4) The biphasic mixture of Mn2O3 and MnNiO3 is mixed evenly with a lithium source and then sintered in an oxygen atmosphere at a temperature of 950 - 1100 °C to obtain the single - crystal lithium nickel manganese oxide cathode material; Wherein, 0.3 < x < 0.6.

[0012] Furthermore, 0.4 ≤ x ≤ 0.5.

[0013] Furthermore, in step (1), the protective atmosphere is a nitrogen or argon atmosphere. The introduction of the protective gas can avoid the problems that Mn 2+ ions are easily oxidized and the particles are not easy to form spheres and grow during the coprecipitation of hydroxides; Furthermore, in step (1), the total concentration of metal ions in the mixed solution of Ni salt and Mn salt is 0.5 - 2 mol / L.

[0014] Furthermore, in step (1), the concentration of the precipitant solution is 1 - 8 mol / L. It is further preferred that the precipitant is a NaOH solution.

[0015] Furthermore, in step (1), the concentration of the complexing agent solution is 0.1 - 0.6 mol / L. It is further preferred that the complexing agent is an NH3·H2O solution.

[0016] Furthermore, in step (1), the bottom liquid of the reaction kettle is 0.05 - 0.2 mol / L ammonia water.

[0017] Further, in step (1), the feeding rate of the mixed solution of Ni salt and Mn salt is 50 - 250 ml / h.

[0018] Further, in step (1), the temperature of the reaction system is 50 - 60 °C.

[0019] Further, in step (1), the stirring speed is 300 - 800 rpm.

[0020] Further, in step (1), the pH value of the reaction system is in the range of 9.5 - 12.0; more preferably, during the reaction process, the pH value is controlled to fluctuate within the range of a certain value ± 0.1.

[0021] Further, in step (2), when the D50 of the reaction slurry > 6 μm, the reaction is stopped.

[0022] Further, in step (2), the drying method is low-temperature vacuum drying.

[0023] Due to Ni x / 2 Mn 1-x / 2 (OH)2 is unstable under normal temperature and pressure and is prone to spontaneous conversion to Mn3O4, forming a mixture of Ni x / 2 Mn 1-x / 2 (OH)2 and Mn3O4 with an uncertain and continuously changing proportion, and the valence states of Mn are inconsistent, which is not conducive to accurately calculating the lithium doping amount of single-crystal lithium nickel manganate LiNi x Mn 2-x O4. In this application, Ni x / 2 Mn 1-x / 2 (OH)2 is converted into a stable and single-phase mixture of Mn2O3 and MnNiO3.

[0024] Preferably, step (3) is specifically as follows: Ni x / 2 Mn 1-x / 2 (OH)2 is dried at low temperature under vacuum conditions and then heated at a temperature of 60 - 100 °C under vacuum to be converted into Ni x / 2 Mn 1-x / 2 OOH; Ni x / 2 Mn 1-x / 2 (OH)2 and / or Ni x Mn 1-x / 2 OOH is sintered in an O2 atmosphere at a temperature of 650 - 750 °C for 1 - 6 h to be converted into a two-phase mixture of Mn2O3 and MnNiO3.

[0025] Preferably, step (3) is specifically as follows: Ni x / 2 Mn 1-x / 2(OH)2 is sintered at 650 - 750 °C for 1 - 6 h in an O2 atmosphere to be converted into a biphasic mixture of Mn2O3 and MnNiO3.

[0026] This invention uses a single chemical formula (Ni x / 2 Mn 1-x / 2 )2O3 to represent this biphasic mixture for the convenience of calculating the lithium doping amount. That is: the (Ni x / 2 Mn 1-x / 2 )2O3 in this invention is a biphasic mixture of Mn2O3 and MnNiO3 converted from Ni x / 2 Mn 1-x / 2 (OH)2.

[0027] Furthermore, in step (4), the lithium source is LiOH.

[0028] Furthermore, in step (4), the amount of the lithium source is added in a molar ratio of Li:(Ni + Mn)=1.0 - 1.02:2.0. Furthermore, in step (4), the sintering duration is 10 - 30 h; Furthermore, in step (4), during the sintering process, the oxygen flow rate is 50 - 200 sccm; Furthermore, in step (4), the heating rate is controlled at 3 - 6 °C / min, and the cooling rate is controlled at 1 - 3 °C / min.

[0029] This invention also discloses a lithium-ion battery, and the lithium-ion battery includes the single-crystal lithium nickel manganese oxide cathode material described above.

[0030] Compared with the prior art, the beneficial effects of this invention are as follows: (1) The method of this invention prepares a nanosheet hydroxide precursor through the coprecipitation method, converts the unstable hydroxide precursor Ni x / 2 Mn 1-x / 2 (OH)2 into a stable biphasic mixture of Mn2O3 and MnNiO3 as the precursor. This biphasic mixture can be represented by a single chemical formula (Ni x / 2 Mn 1-x / 2 )2O3, which can accurately formulate the Li content required for sintering. Sintering is carried out at a relatively high lithium-doping sintering temperature to obtain a single-crystal lithium nickel manganese oxide cathode material with a cubic or octahedral structure. The capacity of this cathode material is above 134 mAh / g, the grain size is 1 - 11 μm, and it has excellent rate and cycling performance, can simultaneously achieve high energy density and high power density, and has a long service life.

[0031] (2) In the co-precipitation reaction process of the method of the present invention, by controlling the fluctuation range of the pH value to be ±0.1, the influence of the pH value fluctuation on the nucleation and growth of the hydroxide precursor can be avoided, the growth of the precursor particles can be ensured, and in cooperation with the control of the feeding rate, the growth rate of the precursor can be regulated, and a hydroxide precursor with a nanosheet structure can be generated. Description of the Drawings

[0032] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification, and are used to explain the present invention together with the embodiments of the present invention, and do not constitute a limitation to the present invention. In the drawings: Figure 1 Morphology diagram of the Ni 0.25 Mn 0.75 OOH precursor prepared in Example 1.

[0033] Figure 2 Morphology diagram of the LiNi 0.5 Mn 1.5 O4 prepared in Example 1.

[0034] Figure 3 (a) Ni 0.25 Mn 0.75 OOH and (b) LiNi 0.5 Mn 1.5 XRD diagram of the phase structure of O4, and the inset in Figure (a) is the fitting diagram of the (002) peak.

[0035] Figure 4 Electrochemical performance of the LiNi 0.5 Mn 1.5 O4 prepared in Example 1: (a) 1C charge-discharge curve, (b) rate performance, (c) 2C charge 5C discharge cycle performance; 1C is calculated as 140 mA / g.

[0036] Figure 5 Morphology diagram of the Ni 0.25 Mn 0.75 OOH precursor prepared in Example 2.

[0037] Figure 6 Morphology diagram of the LiNi 0.5 Mn 1.5 O4 prepared in Example 2.

[0038] Figure 7 (a) Ni 0.25 Mn 0.75 OOH and (b) LiNi 0.5 Mn 1.5 XRD diagram of the phase structure of O4, and the inset in Figure (a) is the fitting diagram of the (002) peak.

[0039] Figure 8 Electrochemical performance of LiNi 0.5 Mn 1.5 O4 prepared in Example 2: (a) 1C charge-discharge curve, (b) rate performance, (c) 2C charge 5C discharge cycle performance; 1C is calculated at 140 mA / g.

[0040] Figure 9 Morphology diagram of Ni 0.2 Mn 0.8 OOH precursor prepared in Example 3.

[0041] Figure 10 Morphology diagram of LiNi 0.4 Mn 1.6 O4 prepared in Example 3.

[0042] Figure 11 XRD diagrams of the phase structures of (a) Ni 0.25 Mn 0.75 OOH and (b) LiNi 0.5 Mn 1.5 O4 prepared in Example 3. The inset in Figure (a) is the fitting diagram of the (002) peak.

[0043] Figure 12 Electrochemical performance of LiNi 0.5 Mn 1.5 O4 prepared in Example 3: (a) 1C charge-discharge curve, (b) rate performance, (c) 2C charge 5C discharge cycle performance; 1C is calculated at 140 mA / g.

[0044] Figure 13 Morphology diagram of LiNi 0.4 Mn 1.6 O4 prepared in Example 4.

[0045] Figure 14 XRD diagram of the phase structure of LiNi 0.4 Mn 1.6 O4 prepared in Example 5.

[0046] Figure 15 Electrochemical performance of LiNi 0.5 Mn 1.5 O4 prepared in Example 6: (a) 1C charge-discharge curve, (b) rate performance, (c) 2C charge 5C discharge cycle performance; 1C is calculated at 140 mA / g. Detailed implementation manners

[0047] For the convenience of understanding the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings of the specification and preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0048] Unless otherwise defined, all technical terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0049] Example 1 This example provides a method for preparing a single-crystal lithium nickel manganese oxide cathode material, comprising the following steps: (1) Prepare 1 L of a mixed solution A of NiSO4·6H2O and MnSO4·4H2O with a molar ratio of Ni:Mn = 25:75 at 2 mol / L, 1 L of a 4 mol / L NaOH solution B, and 1 L of a 0.25 mol / L ammonia water solution C. Mix solution B and C to form solution D.

[0050] (2) Add 5 L of a 0.06 mol / L dilute ammonia water bottom solution to a 50 L reactor, heat it to 55 °C and maintain the temperature, introduce nitrogen to exclude the air in the reactor below the liquid level, and keep the nitrogen flow rate at 500 sccm.

[0051] (3) Start stirring the reactor, maintain the rotation speed at 700 rpm, control the feeding rate of solution A at 60 ml / h, and control the initial feeding rate of solution D at 120 ml / h. Fine-tune the feeding rate of solution D to maintain the pH of the reaction system in the reactor at 9.7, with the pH fluctuation controlled within the range of ±0.1.

[0052] (4) After reacting for 8 hours, when the spherical particles in the reactor have a D50 > 10 μm and are evenly distributed, start discharging the solution in the reactor, filter, wash with deionized water until the pH of the filtrate < 8, and then dry under vacuum at 50 °C to obtain Ni 0.25 Mn 0.75 (OH)2.

[0053] (5) Heat Ni 0.25 Mn 0.75 (OH)2 under vacuum at 60 °C to obtain Ni 0.25 Mn 0.75 OOH; Heat Ni 0.25 Mn 0.75 OOH in an O2 atmosphere at 700 °C for 5 hours to convert it into a biphasic mixture of Mn2O3 and MnNiO3, which is reserved as a precursor.

[0054] Here, the biphasic mixture of Mn2O3 and MnNiO3 is converted from Ni 0.25 Mn 0.75 OOH and can be denoted as (Ni 0.25 Mn 0.75 )2O3 for facilitating subsequent lithium doping.

[0055] (6) Manually grind the prepared precursor (Ni 0.25 Mn 0.75 )2O3 and LiOH evenly. The amount of LiOH is in a molar ratio of Li:(Ni + Mn) of 1.01. Sinter at 950 °C for 20 h in an oxygen atmosphere. The oxygen flow rate is 100 sccm, the heating rate is controlled at 5 °C / min, and the cooling rate is controlled at 2 °C / min. After cooling to 300 °C, cool with the furnace and then take out the sample LiNi 0.5 Mn 1.5 O4 and store it in vacuum for standby.

[0056] In this example, the morphology of the precursor Ni 0.25 Mn 0.75 OOH prepared in step (5) is as shown in Figure 1 , and it has a nanosheet structure. The LiNi 0.5 Mn 1.5 O4 prepared in step (6) is as shown in Figure 2 , and it is generally an octahedral single crystal with a grain size of about 2 μm. The XRD of the phase structures of Ni 0.25 Mn 0.75 OOH and LiNi 0.5 Mn 1.5 O4 is as shown in Figure 3 . By fitting the (002) peak of Ni 0.25 Mn 0.75 OOH, the thickness of the nanosheet is obtained to be about 30 nm, and LiNi 0.5 Mn 1.5 O4 has a spinel structure.

[0057] According to the mass ratio of active material: carbon black: PVDF = 8:1:1, manually grind 1.2 g of the prepared sample, 0.15 g of carbon black, and 3.75 g of a 4% wt. PVDF solution in NMP evenly. After passing through a 200# sieve, coat it on carbon-coated aluminum foil, dry, cut into pieces, weigh, and assemble a button battery. As shown in Figure 4 , the discharge capacity of the obtained 1C charge and discharge is 134 mAh / g, the 15C discharge capacity is 121 mAh / g, and the capacity retention rate after 200 cycles of 2C charge and 5C discharge is 96%.

[0058] Example 2 This example is basically the same as Example 1, except that: The C solution in step (1) is 0.5 mol / L ammonia water.

[0059] The bottom liquid in step (2) is 0.1 mol / L ammonia water.

[0060] In step (3), the feeding rate of solution A is controlled at 120 ml / h, and the initial feeding rate of solution D is controlled at 240 ml / h. Fine-tune the feeding rate of solution D to maintain the pH of the reaction system in the reaction kettle at 10.1, with the pH fluctuation controlled within the range of ±0.1.

[0061] In this embodiment, the precursor Ni 0.25 Mn 0.75 OOH has a morphology as Figure 5 shown, which is a nanosheet structure. The LiNi 0.5 Mn 1.5 O4 prepared in Example 2 is as Figure 6 shown, generally being an octahedral single crystal with a grain size of about 2 μm. The Ni 0.25 Mn 0.75 OOH and LiNi 0.5 Mn 1.5 O4 of Example 2 have a phase structure XRD as Figure 7 shown. By fitting the (002) peak of Ni 0.25 Mn 0.75 OOH, the thickness of the nanosheet is obtained to be about 50 nm, and LiNi 0.5 Mn 1.5 O4 is a spinel structure.

[0062] According to the mass ratio of active material: carbon black: PVDF = 8:1:1, 1.2 g of the prepared sample, 0.15 g of carbon black, and 3.75 g of a 4% wt. PVDF solution in NMP are manually ground evenly, passed through a 200# sieve, then coated on carbon-coated aluminum foil, dried, cut into pieces, weighed, and assembled into a button battery. As Figure 8 shown, the discharge capacity of the obtained 1C charge and discharge is 134 mAh / g, the 15C discharge capacity is 120 mAh / g, and the capacity retention rate after 200 cycles of 2C charge and 5C discharge is 99%.

[0063] Example 3 This example is basically the same as Example 2, except that: In step (1), solution A is a mixed solution of NiSO4·6H2O and MnSO4·4H2O with a molar ratio of Ni:Mn = 0.2:0.8 at a concentration of 2 mol / L.

[0064] The precursor Ni 0.2 Mn 0.8 OOH prepared in Example 3 has a morphology as Figure 9 shown, which is a nanosheet structure. The LiNi 0.4 Mn 1.6 O4 prepared in Example 3 is as Figure 10 shown, generally being a block-shaped single crystal with a grain size of about 2 μm. The Ni0.2 Mn 0.8 OOH and LiNi 0.4 Mn 1.6 The XRD of the phase structure of Figure 11 LiNi 0.2 Mn 0.8 OOH is as follows. By fitting the (002) peak of 0.4 LiNi 1.6 Mn

[0065] O4, the thickness of the nanosheets is obtained to be about 50 nm, and Figure 12 LiNi

[0066] Example 4 This example is basically the same as Example 3, except that: (6) The above-prepared precursor 0.2 LiNi 0.8 Mn 0.4 OOH and LiOH are manually ground evenly, and the amount of LiOH is 1.01 in terms of the molar ratio of Li:(Ni + Mn). Sinter at 1050 °C for 20 h in an oxygen atmosphere. The oxygen flow rate is 100 sccm, the heating rate is controlled at 5 °C / min, and the cooling rate is controlled at 2 °C / min. After cooling to 300 °C, cool with the furnace and then take out the sample 1.6 LiNi

[0067] The 0.4 LiNi 1.6 Mn Figure 13 O4 prepared in Example 4 is as shown in 0.4 LiNi 1.6 Mn Figure 14 O4 is of spinel structure.

[0068] According to the mass ratio of active material: carbon black: PVDF = 8:1:1, 1.2 g of the prepared sample, 0.15 g of carbon black, and 3.75 g of a 4% wt. PVDF solution in NMP are manually ground evenly, passed through a 200# sieve, then coated on carbon-coated aluminum foil, dried, cut into pieces, weighed, and assembled into a button battery. AsFigure 15 As shown, the discharge capacity of the 1C charge and discharge test is 140 mAh / g, the 15C discharge capacity is 125 mAh / g, and the capacity retention rate of the 2C charge and 5C discharge cycle for 200 cycles is 99%.

[0069] Example 5 This example is basically the same as Example 1, except that: (6) Manually grind the prepared precursor (Ni 0.25 Mn 0.75 )2O3 and LiOH evenly. The amount of LiOH is in a molar ratio of Li:(Ni + Mn) of 1.01. Sinter at 1000 °C for 25 h in an oxygen atmosphere. The oxygen flow rate is 100 sccm, the heating rate is controlled at 5 °C / min, the cooling rate is controlled at 2 °C / min. After cooling to 300 °C, cool with the furnace, and then take out the sample LiNi 0.5 Mn 1.5 O4 and store it in vacuum for standby.

[0070] According to the mass ratio of active material: carbon black: PVDF = 8:1:1, manually grind 1.2 g of the prepared sample, 0.15 g of carbon black, and 3.75 g of a 4% wt. PVDF solution in NMP evenly. After passing through a 200# sieve, coat it on the carbon-coated aluminum foil, dry, cut into pieces, weigh, and assemble a button battery.

[0071] After testing, in this example, sintered at 1000 °C, the morphology of LiNi 0.5 Mn 1.5 O4 shows an octahedral single crystal, and the phase shows a spinel structure, with better rate performance and capacity.

[0072] Comparative Example 1 This example is basically the same as Example 2, except that: (6) Manually grind the prepared precursor (Ni 0.25 Mn 0.75 )2O3 and LiOH evenly. The amount of LiOH is in a molar ratio of Li:(Ni + Mn) of 1.01. Sinter at 900 °C for 20 h in an oxygen atmosphere. The oxygen flow rate is 100 sccm, the heating rate is controlled at 5 °C / min, the cooling rate is controlled at 2 °C / min. After cooling to 300 °C, cool with the furnace, and then take out the sample LiNi 0.5 Mn 1.5 O4 and store it in vacuum for standby.

[0073] Prepare a sample of 1.2 g, carbon black of 0.15 g, and a solution of 3.75 g of 4% wt. PVDF in NMP, and manually grind them evenly according to the mass ratio of active material: carbon black: PVDF = 8:1:1. After passing through a 200# sieve, coat them on the carbon-coated aluminum foil, dry, cut into pieces, weigh, and assemble button cells.

[0074] After testing, this comparative example was sintered at a temperature of 900 °C. The temperature was too low, and the crystallization was insufficient to form single crystals, seriously affecting the rate performance and capacity.

[0075] Comparative Example 2 This example is basically the same as Example 2, except that: (6) Manually grind the prepared precursor (Ni 0.25 Mn 0.75 )2O3 and LiOH evenly. The amount of LiOH is in a molar ratio of Li:(Ni + Mn) of 1.01. Sinter at 1200 °C for 20 h in an oxygen atmosphere. The oxygen flow rate is 100 sccm, the heating rate is controlled at 5 °C / min, and the cooling rate is controlled at 2 °C / min. After cooling to 300 °C, cool with the furnace, and then take out the sample LiNi 0.5 Mn 1.5 O4 and store it in vacuum for later use.

[0076] Prepare a sample of 1.2 g, carbon black of 0.15 g, and a solution of 3.75 g of 4% wt. PVDF in NMP, and manually grind them evenly according to the mass ratio of active material: carbon black: PVDF = 8:1:1. After passing through a 200# sieve, coat them on the carbon-coated aluminum foil, dry, cut into pieces, weigh, and assemble button cells.

[0077] After testing, this comparative example was sintered at a temperature of 1200 °C. The temperature was too high, resulting in too large grain sizes formed, affecting the rate performance and capacity.

[0078] Comparative Example 3 This comparative example is basically the same as Example 1, except that: Do not set step (5).

[0079] Specifically: (1) Prepare 1 L of a mixed solution A of 2 mol / L NiSO4·6H2O and MnSO4·4H2O with a molar ratio of Ni:Mn = 25:75, 1 L of 4 mol / L NaOH solution B, and 1 L of 0.25 mol / L ammonia water solution C. Mix solution B and C to form solution D.

[0080] (2) Add 5 L of 0.06 mol / L dilute ammonia water bottom liquid to a 50 L reaction kettle, heat up to 55 °C and maintain, introduce nitrogen to exclude the air in the kettle under the liquid surface, and keep the nitrogen flow rate at 500 sccm.

[0081] (3) Start the stirring of the reactor, maintain the rotation speed at 700 rpm, control the feeding rate of solution A at 60 ml / h, and control the initial feeding rate of solution D at 120 ml / h. Fine-tune the feeding rate of solution D to maintain the pH of the reaction system in the reactor at 9.7, with the pH fluctuation controlled within the range of ±0.1.

[0082] (4) After reacting for 8 hours, when the spherical particles in the reactor have D50 > 10 μm and are evenly distributed, start to discharge the solution in the reactor, filter it, wash it with deionized water until the pH of the filtrate < 8, and then dry it under vacuum by heating to 50 °C to obtain Ni 0.25 Mn 0.75 (OH)2.

[0083] (5) Manually grind Ni 0.25 Mn 0.75 (OH)2 and LiOH evenly. The amount of LiOH is in a molar ratio of Li:(Ni + Mn) of 1.01. Sinter at 950 °C for 20 h in an oxygen atmosphere. The oxygen flow rate is 100 sccm, the heating rate is controlled at 5 °C / min, the cooling rate is controlled at 2 °C / min. After cooling to 300 °C, cool it with the furnace, and then take out the sample LiNi 0.5 Mn 1.5 O4, and store it in vacuum for standby.

[0084] Since Ni 0.25 Mn 0.75 (OH)2 is unstable under normal temperature and pressure and is prone to spontaneously transform into Mn3O4, forming a mixture of Ni 0.25 Mn 0.75 (OH)2 and Mn3O4 with an uncertain and continuously changing proportion. That is, the precursor of this comparative example is composed of Ni 0.25 Mn 0.75 (OH)2 and Mn3O4 with an uncertain proportion. When calculating the lithium dosage, if the precursor is regarded as pure-phase Ni 0.25 Mn 0.75 (OH)2, it will lead to less lithium dosage and the inability to generate stoichiometric LiNi 0.5 Mn 1.5 O4. If lithium is dosed according to Mn3O4, then the lithium is in excess, and the sintered product is agglomerated and cannot be used. Moreover, Ni 0.25 Mn 0.75 (OH)2 will continuously and spontaneously transform into Mn3O4, and the lithium dosage cannot be estimated within a reasonable range, resulting in inaccurate lithium dosing. In industrial mass production, it will lead to a greater error and poor consistency between batches, and it is basically impossible to obtain consistent target products.

[0085] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the scope of the present invention.

Claims

1. A single-crystal lithium nickel manganese oxide cathode material, characterized in that, The chemical formula of the single-crystal lithium nickel manganate cathode material is LiNi x Mn 2-x O4, where 0.3 < x < 0.6; it has a cubic or octahedral structure, and the grain size is 1 - 11 μm.

2. A method for preparing a single-crystal lithium nickel manganese oxide cathode material, characterized in that, It includes the following steps: (1) Under a protective atmosphere, a mixed solution of Ni salt and Mn salt, a precipitant solution, and a complexing agent solution are introduced into the bottom liquid of the reaction kettle in parallel to carry out a coprecipitation reaction; wherein, the molar ratio of Ni:Mn in the mixed solution of Ni salt and Mn salt is x / 2:1 - x / 2; (2)When the D50 of the reaction slurry reaches the target value, stop the reaction, filter the reaction slurry, wash it, and dry the solid phase to obtain the precursor Ni x / 2 Mn 1-x / 2 (OH)2; (3) Convert Ni x / 2 Mn 1-x / 2 (OH)2 into a biphasic mixture of Mn2O3 and MnNiO3; (4) The biphasic mixture of Mn2O3 and MnNiO3 is mixed evenly with a lithium source and then sintered at a temperature of 950 - 1100 °C in an oxygen atmosphere to obtain a single crystal lithium nickel manganate cathode material; Wherein, 0.3 < x < 0.6; more preferably 0.4 ≤ x ≤ 0.

5.

3. The preparation method according to claim 2, characterized in that, In step (1): the total metal ion concentration in the mixed solution of Ni salt and Mn salt is 0.5 - 2 mol / L; Preferably, the concentration of the precipitant solution is 1 - 8 mol / L; Preferably, the concentration of the complexing agent solution is 0.1 - 0.6 mol / L. The bottom liquid of the reaction kettle is ammonia water with a concentration of 0.05 - 0.2 mol / L.

4. The preparation method according to claim 2, characterized in that, In step (1), the pH value of the reaction system is in the range of 9.5 - 12.0; Preferably, during the reaction process, the pH value is controlled to fluctuate within the range of a certain value ±0.

1.

5. The preparation method according to claim 2, characterized in that, In step (1), the feeding rate of the mixed solution of Ni salt and Mn salt is 50 - 250 ml / h; Preferably, the temperature of the reaction system is 50 - 60 °C; Preferably, the stirring speed is 300 - 800 rpm.

6. The preparation method according to claim 2, characterized in that, In step (2), when D50 of the reaction slurry > 6 μm, the reaction is stopped.

7. The preparation method according to claim 2, characterized in that, Step (3) specifically is: Ni x / 2 Mn 1-x / 2 (OH)2 is dried at low temperature under vacuum conditions and then heated at a temperature of 60 - 100 °C under vacuum to be converted into Ni x / 2Mn 1-x / 2 OOH; Ni x / 2 Mn 1-x / 2 (OH)2 and / or Ni x / 2 Mn 1-x / 2 OOH is sintered for 1 - 6 h at a temperature of 650 - 750 °C in an O2 atmosphere to be converted into a two-phase mixture of Mn2O3 and MnNiO3.

8. The preparation method according to claim 2, characterized in that, Step (3) specifically is: Mix Ni x / 2 and Mn 1-x / 2 (OH)2 is sintered for 1 - 6 h at 650 - 750 °C in an O2 atmosphere to be converted into a two-phase mixture of Mn2O3 and MnNiO3.

9. The preparation method according to claim 2, characterized in that, In step (4): The lithium source is LiOH; Preferably, the amount of the lithium source is added in a molar ratio of Li:(Ni + Mn) = 1.0 - 1.02:2.0; Preferably, the sintering duration is 10 - 30 h; Preferably, during the sintering process, the oxygen flow rate is 50 - 200 sccm; Preferably, the heating rate is controlled at 3 - 6 °C / min, and the cooling rate is controlled at 1 - 3 °C / min.

10. A lithium-ion battery, characterized in that, A single crystal lithium nickel manganate cathode material prepared by the preparation method according to any one of claims 2 - 9 or the single crystal lithium nickel manganate cathode material according to claim 1.

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