Rock salt phase coated full concentration gradient positive electrode material, preparation method and application thereof

Abstract

This invention provides a rock-salt phase-coated full-concentration gradient cathode material, its preparation method, and its application. The preparation method includes: first, adding an ultra-high nickel salt solution A to a mixing container; then, introducing ultra-high nickel salt solution A and a high nickel salt solution B into the mixing container to obtain a mixed solution; simultaneously, introducing the mixed solution, along with a complexing agent solution and a precipitant solution, into a bottom liquid at a third flow rate to perform a co-precipitation reaction, obtaining a precursor material; mixing and sintering a lithium source and the precursor material to obtain a rock-salt phase-coated full-concentration gradient cathode material; wherein the molar content of lithium ions in the lithium source is n1, the molar content of total metal ions in the precursor material is n2, and n1 / n2≤1. The preparation method of this invention can improve the structural stability of the cathode material and enhance its cycle performance. Furthermore, the gradient change in metal ion content from the core to the surface in the cathode material can prevent the generation of microcracks, further improving the material's cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a rock salt phase coated full concentration gradient cathode material, its preparation method and application. Background Technology

[0002] With the increasing demands for energy density in power batteries, high-nickel ternary cathode materials have attracted widespread attention due to their higher theoretical capacity. However, the increased nickel content on the surface of high-nickel ternary cathode materials leads to a significant increase in their reactivity, which in turn triggers more severe electrode / electrolyte interface side reactions. This process not only promotes the dissolution of transition metal ions but also induces surface inactive phase transitions, severely affecting material performance. More critically, in the deep lithium insertion / extraction state, the accumulation of heterogeneous stress within the particles can cause microcracks or even structural collapse, while the newly exposed active surface further exacerbates interface side reactions. This vicious cycle ultimately leads to a significant decrease in the capacity retention and cycle performance of high-nickel ternary cathode materials.

[0003] Currently, the commonly used modification strategies for addressing the above problems mainly include doping and coating. Although doping can significantly improve the intrinsic properties of materials by introducing a small amount of dopant elements, it inevitably reduces the proportion of active material, thus affecting the specific capacity. While coating can effectively isolate the electrode from direct contact with the electrolyte, it faces technical bottlenecks such as insufficient ionic conductivity of the coating layer and easy detachment during cycling.

[0004] Based on the above research, there is a need to provide a cathode material with a stable structure that can solve the problem caused by excessive nickel content on the surface of high-nickel ternary cathode materials, which leads to excessively high reactivity. Summary of the Invention

[0005] The purpose of this invention is to provide a rock salt phase-coated full concentration gradient cathode material, its preparation method, and its application. The rock salt phase-coated full concentration gradient cathode material can improve the structural stability of the cathode material and improve its cycle performance. At the same time, the metal ion content in the cathode material changes in a gradient from the core to the surface, which can avoid the generation of microcracks and further improve the cycle performance of the material.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a rock salt phase-coated full-concentration gradient cathode material, the preparation method comprising the following steps:

[0008] (1) First, add ultra-high nickel salt solution A to the mixing container, then pass ultra-high nickel salt solution A and high nickel salt solution B into the mixing container at the first flow rate and the second flow rate to obtain a mixed solution. At the same time as passing ultra-high nickel salt solution A and high nickel salt solution B, pass the mixed solution into the bottom liquid at the third flow rate to carry out a co-precipitation reaction and obtain the precursor material.

[0009] Wherein, the second flow velocity is greater than the first flow velocity;

[0010] (2) The lithium source and the precursor material described in step (1) are mixed and sintered to obtain the full concentration gradient cathode material coated with the rock salt phase;

[0011] Wherein, the molar content of lithium ions in the lithium source is n1, the molar content of total metal ions in the precursor material is n2, and n1 / n2≤1.

[0012] This invention constructs a progressively changing material structure by reducing the lithium source content. Since the precursor material is a full concentration gradient material, the manganese and cobalt contents increase sequentially from the core to the surface. The surface region is rich in Mn and Co and low in nickel. Under low lithium conditions, the surface region is more likely to form a structurally stable rock salt phase, while the nickel-rich internal region forms a layered phase material. The intermediate natural transition layer may also form a spinel phase material. The method for constructing the full concentration gradient in this invention involves first introducing a portion of ultra-high nickel salt solution A during co-precipitation, then introducing both ultra-high nickel salt solution A and high nickel salt solution B to obtain a mixed solution. Simultaneously, this mixed solution is introduced into the co-precipitation system for co-precipitation. Because the second flow rate of the high nickel salt solution B is greater than the first flow rate of the ultra-high nickel salt solution A, the ion concentration in the mixed solution dynamically changes, with the nickel content gradually decreasing and the cobalt and manganese contents gradually increasing. This results in a precursor material with gradually decreasing nickel content and gradually increasing manganese and cobalt contents. In other words, the method for preparing the full concentration gradient in this invention ensures a uniform gradient change in metal ions and avoids abrupt changes in metal ion concentration.

[0013] Furthermore, the method of the present invention avoids the problem of reduced capacity caused by the introduction of impurities, while being simple to operate, cost-controllable, and suitable for industrial-scale promotion and use.

[0014] It is understood that the nickel content in the ultra-high nickel salt solution is higher than the nickel content in the high nickel salt solution B, while the cobalt and manganese content is lower than the cobalt and manganese content in the high nickel salt solution B.

[0015] The molar content of lithium ions in the lithium source is n1, and the molar content of total metal ions in the precursor material is n2, where n1 / n2 ≤ 1. For example, it can be 1, 0.99, 0.98, 0.97, 0.96, 0.95, 0.94, 0.93, 0.92, 0.91, or 0.90, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 0.9-0.98, and more preferably 0.93-0.98.

[0016] That is, the present invention preferably uses a lithium to metal ratio of less than 1, which makes it easier to construct a rock salt phase coating layer under lithium-deficient conditions. If the lithium to metal ratio changes, it will affect the content of the rock salt phase coating layer. If the lithium to metal ratio is too low and the lithium content is too low, lithiation will be insufficient, and a thicker rock salt phase will be formed under lithium-deficient conditions. If the lithium to metal ratio is too high and the lithium content is too high, the residual alkali on the surface of the sintered cathode material will be too high, which will deteriorate the processing performance, aggravate the interfacial side reactions, shorten the cycle life and deteriorate the rate performance.

[0017] Preferably, the lithium source in step (2) includes any one or a combination of at least two of lithium carbonate, lithium hydroxide, lithium sulfate, or lithium phosphate.

[0018] Preferably, in the later stage of sintering in step (2), a doping source gas is introduced, the doping source gas including NF3 and / or a boron source; exemplaryly, the boron source includes any one or a combination of at least two of trimethylborane, triethylborane or boron ethane.

[0019] This invention introduces doping elements into the rock salt phase coating layer using a gas phase doping method. Compared with traditional doping methods, it achieves high doping uniformity and excellent doping effect.

[0020] Preferably, the sintering in step (2) includes performing a first stage sintering and a second stage sintering in an oxygen-containing gas, and then performing a third stage sintering in a doped source gas.

[0021] Preferably, the sintering temperature of the third stage is 650-800℃, for example, 650℃, 700℃, 750℃ or 800℃, the holding time is 2-5h, for example, 2h, 3h, 4h or 5h, and the heating rate is 2-5℃ / min, for example, 2℃ / min, 3℃ / min, 4℃ / min or 5℃ / min, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] Preferably, the sintering temperature of the second stage is 650-800℃, for example, 650℃, 700℃, 750℃ or 800℃, the holding time is 10-20h, for example, 10h, 12.5h, 15h, 17.5h or 20h, and the heating rate is 2-5℃ / min, for example, 2℃ / min, 3℃ / min, 4℃ / min or 5℃ / min, but not limited to the listed values, other unlisted values ​​within the range are also applicable.

[0023] Preferably, the sintering temperature of the first stage is 450-550℃, for example, 450℃, 500℃ or 550℃, the holding time is 2-6h, for example, 2h, 4h or 6h, and the heating rate is 2-5℃ / min, for example, 2℃ / min, 3℃ / min, 4℃ / min or 5℃ / min, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] Preferably, the oxygen-containing gas includes any one or a combination of at least two of oxygen, compressed air, or nitrogen dioxide.

[0025] Preferably, in the ultra-high nickel salt solution A described in step (1), the molar ratio of nickel ions, manganese ions, and cobalt ions is x:y:z, where x+y+z=1, x=0.90-1.00, for example, it can be 0.90, 0.92, 0.94, 0.96, 0.98 or 1, y=0.00-0.10, for example, it can be 0, 0.02, 0.04, 0.06, 0.08 or 0.1, and z=0.00-0.10, for example, it can be 0, 0.02, 0.04, 0.06, 0.08 or 0.1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] Preferably, in the high-nickel salt solution B described in step (1), the molar ratio of nickel ions, manganese ions, and cobalt ions is x':y':z', where x'+y'+z'=1, x'=0.6-0.89, for example, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, or 0.89, y'=0.11-0.40, for example, 0.11, 0.2, 0.3, or 0.4, and z'=0.11-0.40, for example, 0.11, 0.2, 0.3, or 0.4, but not limited to the listed values; other unlisted values ​​within the range are also applicable.

[0027] Preferably, the volume of the mixing container in step (1) is 10%-100% of the total volume of the mixed solution required for the coprecipitation reaction. For example, it can be 10%, 30%, 50%, 70%, 90% or 100%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 20-40%.

[0028] Preferably, the mixing container in step (1) includes a mixing tank with a stirrer.

[0029] Preferably, the agitator contains a double-layered blade.

[0030] Preferably, in step (1), an ultra-high nickel salt solution A is first added to the mixing container, wherein the volume of the ultra-high nickel salt solution A added is 20%-100% of the volume of the mixing container, for example, it can be 20%, 40%, 60%, 80% or 100%, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0031] Preferably, the first flow rate in step (1) is 0.05-0.25 L / h, for example, it can be 0.05 L / h, 0.1 L / h, 0.15 L / h, 0.2 L / h or 0.25 L / h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the second flow rate in step (1) is 0.2-0.35 L / h, for example, it can be 0.2 L / h, 0.25 L / h, 0.30 L / h or 0.35 L / h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Preferably, the third flow rate in step (1) is 0.4-0.6 L / h, for example, it can be 0.4 L / h, 0.5 L / h or 0.6 L / h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] Preferably, the coprecipitation reaction in step (1) is carried out in a reaction vessel equipped with a double-layer impeller stirrer, temperature and pH sensors, and heated by an external mold temperature controller in a water bath.

[0035] Preferably, the pH of the coprecipitation reaction in step (1) is 9.5-10.5, for example, 9.5, 10 or 10.5, and the temperature is 50-70℃, for example, 50℃, 60℃ or 70℃, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] Preferably, in the coprecipitation reaction system described in step (1), the concentration of the complexing agent is 1-3 g / L, for example, it can be 1 g / L, 1.5 g / L, 2 g / L, 2.5 g / L or 3 g / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Preferably, the coprecipitation reaction in step (1) is carried out in a protective gas, which includes any one or a combination of at least two of argon, nitrogen or helium, with a flow rate of 10 to 400% of the reactor volume per hour, for example, 10%, 50%, 100%, 200%, 300% or 400%, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] Preferably, the coprecipitation reaction in step (1) results in a particle size D50 of 9-11 μm, for example, 9 μm, 9.5 μm, 10 μm, 10.5 μm or 11 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] Preferably, the concentration of the complexing agent solution in step (1) is 10-40 wt%, for example, it can be 10 wt%, 20 wt%, 30 wt% or 40 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0040] Preferably, the complexing agent solution in step (1) comprises any one or a combination of at least two of ammonia, oxalic acid, citric acid, sodium carbonate, or ammonium bicarbonate.

[0041] Preferably, the concentration of the precipitant solution in step (1) is 10-40 wt%, for example, it can be 10 wt%, 20 wt%, 30 wt% or 40 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0042] Preferably, the precipitant solution in step (1) comprises any one or a combination of at least two of sodium hydroxide, potassium hydroxide, or lithium hydroxide.

[0043] Preferably, the pH of the base solution in step (1) is 11.0-12.0, for example, it can be 11.0, 11.2, 11.4, 11.6, 11.8 or 12.0, and the concentration of the complexing agent is 1.0-9.0 g / L, for example, it can be 1.0 g / L, 3.0 g / L, 5.0 g / L, 7.0 g / L or 9.0 g / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0044] In a second aspect, the present invention provides a rock salt phase coated full concentration gradient cathode material prepared by the preparation method described in the first aspect, wherein the rock salt phase coated full concentration gradient cathode material includes a rock salt phase coating layer.

[0045] The full-concentration gradient cathode material coated with rock salt phase exhibits a gradual decrease in nickel content and a gradual increase in cobalt and manganese content from the core to the surface.

[0046] The rock salt phase coating layer of this invention not only acts as a physical barrier to isolate internal active materials and electrolytes and suppress interfacial side reactions, but also, due to the stable properties of the rock salt phase, it can alleviate the dissolution of transition metals, the escape of lattice oxygen, and further phase transitions on the surface of cathode particles, maintaining the structural stability of the cathode material and improving cycle performance. Furthermore, the full concentration gradient cathode material coated with the rock salt phase of this invention exhibits a gradual decrease in nickel content and a gradual increase in cobalt and manganese content from the core to the surface, effectively mitigating microcracks caused by anisotropic stress accumulation due to lattice volume changes caused by lithium-ion deintercalation / intercalation during charge-discharge cycles, thereby improving the cycle performance of the cathode material.

[0047] The core of the rock salt phase-coated full-concentration gradient cathode material of the present invention comprises a layered structure, and a spinel phase structure material may also be included between the core and the rock salt phase coating layer.

[0048] Preferably, the chemical formula of the rock salt phase-coated full-concentration gradient cathode material is LiNi. a Co b Mn c O2, where a+b+c=1, a is 0.8-0.96, for example, it can be 0.8, 0.85, 0.9, 0.92, 0.94 or 0.96, b is 0.02-0.1, for example, it can be 0.02, 0.05, 0.075 or 0.1, and c is 0.02-0.1, for example, it can be 0.02, 0.05, 0.075 or 0.1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0049] Preferably, the rock salt phase coating layer contains doping elements, including B and / or F.

[0050] The rock salt phase coating layer of the present invention also includes B and / or fluorine doping elements, which can improve the ionic conductivity and structural stability of the rock salt phase coating layer and improve the diffusion rate of lithium ions.

[0051] Preferably, in the full concentration gradient cathode material coated with rock salt phase, the content of the doping element is 0.5-1.5 wt%, for example, it can be 0.5 wt%, 0.75 wt%, 1 wt%, 1.25 wt%, or 1.5 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0052] Preferably, in the full concentration gradient cathode material coated with rock salt phase, the thickness of the rock salt phase coating layer is 5-30 nm, for example, it can be 5 nm, 10 nm, 15 nm, 20 nm, 25 nm or 30 nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0053] The thickness of the rock salt phase coating layer in this invention affects the performance of the material. If the thickness of the rock salt phase structure material is too small, the structural stability of the material will decrease and the physical barrier effect will decrease. However, if the thickness of the rock salt phase coating layer is too high, it will reduce the proportion of active material in the cathode material, reduce the specific capacity of the cathode material, and the excessively thick rock salt phase will also hinder lithium ion diffusion and deteriorate the rate performance of the cathode material.

[0054] Thirdly, the present invention provides a lithium-ion battery comprising a full-concentration gradient cathode material coated with a rock salt phase as described in the first aspect.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] This invention constructs a progressively changing material structure by reducing the lithium source content. Since the precursor material is a full concentration gradient material, the manganese and cobalt contents increase sequentially from the core to the surface. The surface region is rich in Mn, and under low lithium conditions, the surface region is more likely to form a structurally stable rock salt phase. The nickel-rich internal region forms a layered phase material, and a spinel phase material may also form naturally in the intermediate transition. The method for constructing the full concentration gradient in this invention involves first introducing a portion of ultra-high nickel salt solution A during co-precipitation, then introducing both ultra-high nickel salt solution A and high nickel salt solution B to obtain a mixed solution. Simultaneously, this mixed solution is introduced into the co-precipitation system for co-precipitation. Because the second flow rate of the high nickel salt solution B is greater than the first flow rate of the ultra-high nickel salt solution A, the ion concentration in the mixed solution changes dynamically, with the nickel content gradually decreasing and the cobalt and manganese contents gradually increasing. This results in a precursor material with gradually decreasing nickel content and gradually increasing manganese and cobalt contents. In other words, the method for preparing the full concentration gradient in this invention ensures a uniform gradient change in metal ions and avoids abrupt changes in metal ion concentration. Detailed Implementation

[0057] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0058] Example 1

[0059] This embodiment provides a rock salt phase-coated full concentration gradient cathode material, which includes a rock salt phase coating layer containing doping elements, including F, and the content of the doping elements in the rock salt phase-coated full concentration gradient cathode material is 1 wt%; wherein, the thickness of the rock salt phase coating layer is 15 nm.

[0060] The rock salt phase-coated full-concentration gradient cathode material exhibits a gradual decrease in nickel content and a gradual increase in cobalt and manganese content from the core to the surface. The chemical formula of the rock salt phase-coated full-concentration gradient cathode material, excluding the doping elements, is LiNi. 0.88 Co 0.06 Mn 0.06 O2;

[0061] The preparation method of the rock salt phase-coated full-concentration gradient cathode material includes the following steps:

[0062] (1) Solution preparation: Weigh NiSO4·6H2O, CoSO4·7H2O and MnSO4·H2O in a molar ratio of Ni:Co:Mn = 96:2:2, and prepare ultra-high nickel salt solution A with pure water. The total metal ion concentration in ultra-high nickel salt solution A is 2 mol / L. Weigh NiSO4·6H2O, CoSO4·7H2O and MnSO4·H2O in a molar ratio of Ni:Co:Mn = 8:1:1, and prepare high nickel salt solution B with pure water. The total metal ion concentration in high nickel salt solution B is 2 mol / L.

[0063] Prepare a 16 wt% ammonia solution as a complexing agent solution; prepare a 32 wt% NaOH solution as a precipitating agent solution.

[0064] (2) Synthesis of precursor cores with full concentration gradient structure: A base solution consisting of pure water, complexing agent solution and precipitant solution was added to the reactor. The pH of the base solution was 11.80 and the ammonia content was 2.0 g / L.

[0065] 10 L of ultra-high nickel salt solution A was added to a mixing tank equipped with a stirrer. Ultra-high nickel salt solution A and high nickel salt solution B were pumped into the mixing tank at flow rates of 0.15 L / h and 0.25 L / h respectively, and stirred until homogeneous. Simultaneously, the mixed solution in the mixing tank was pumped into the reaction vessel at a flow rate of 0.5 L / h, along with the complexing agent solution and the precipitant solution, for a co-precipitation reaction under a nitrogen atmosphere. During the reaction, the temperature was maintained at 55℃, the pH was gradually decreased to 10.0 and then maintained, and the ammonia value was maintained at 2.0 g / L. The precursor particle size was monitored using a Malvern particle size analyzer throughout the reaction. The reaction proceeded only after both ultra-high nickel salt solution A and high nickel salt solution B were consumed simultaneously and the precursor particles reached the target particle size (D). 50 The reaction was stopped when the particle size reached 10.0 μm; after filtration, washing with NaOH solution and pure water, drying, sieving, and demagnetization, the Ni precursor with a full concentration gradient structure was obtained. 0.88 Co 0.06 Mn 0.06 (OH)2;

[0066] (3) High-temperature sintering: The above precursor and LiOH·H2O are mixed evenly at a metal ion molar ratio of 1:0.96, and then placed in a ceramic boat and put into a tube furnace. Under an oxygen atmosphere, the temperature is first raised at 2℃ / min and held at 500℃ for 5h, then raised to 750℃ at a rate of 2℃ / min and held for 10h, and then held at 750℃ for 3h in an NF3 atmosphere. After cooling in the furnace, the full concentration gradient cathode material coated with rock salt phase is obtained.

[0067] Example 2

[0068] This embodiment provides a rock salt phase-coated full concentration gradient cathode material, which includes a rock salt phase coating layer containing a dopant element, including F, and the dopant element content in the rock salt phase-coated full concentration gradient cathode material is 0.5 wt%; wherein, the thickness of the rock salt phase coating layer is 5 nm.

[0069] The rock salt phase-coated full-concentration gradient cathode material exhibits a gradual decrease in nickel content and a gradual increase in cobalt and manganese content from the core to the surface. The chemical formula of the rock salt phase-coated full-concentration gradient cathode material, excluding the doping elements, is LiNi. 0.84 Co 0.08 Mn 0.08 O2;

[0070] The preparation method of the rock salt phase-coated full-concentration gradient cathode material includes the following steps:

[0071] (1) Solution preparation: Weigh NiSO4·6H2O, CoSO4·7H2O and MnSO4·H2O in a molar ratio of Ni:Co:Mn = 92:4:4, and prepare ultra-high nickel salt solution A with pure water. The total metal ion concentration in ultra-high nickel salt solution A is 2 mol / L. Weigh NiSO4·6H2O, CoSO4·7H2O and MnSO4·H2O in a molar ratio of Ni:Co:Mn = 7:1.5:1.5, and prepare high nickel salt solution B with pure water. The total metal ion concentration in high nickel salt solution B is 2 mol / L.

[0072] Prepare a 40 wt% ammonia solution as a complexing agent solution; prepare a 20 wt% NaOH solution as a precipitating agent solution.

[0073] (2) Synthesis of precursor cores with full concentration gradient structure: A base solution consisting of pure water, complexing agent solution and precipitant solution was added to the reactor. The pH of the base solution was 11.0 and the ammonia content was 9.0 g / L.

[0074] 10 L of ultra-high nickel salt solution A was added to a mixing tank equipped with a stirrer. Ultra-high nickel salt solution A and high nickel salt solution B were pumped into the mixing tank at flow rates of 0.05 L / h and 0.2 L / h respectively, and stirred until homogeneous. Simultaneously, the mixed solution in the mixing tank was pumped into the reaction vessel at a flow rate of 0.4 L / h, along with the complexing agent solution and the precipitant solution, in a co-precipitation reaction under a nitrogen atmosphere. During the reaction, the temperature was maintained at 70℃, the pH was gradually decreased to 9.5 and then maintained, and the ammonia value was maintained at 3 g / L. The precursor particle size was monitored using a Malvern particle size analyzer throughout the reaction. The reaction proceeded only after both ultra-high nickel salt solution A and high nickel salt solution B were consumed simultaneously and the precursor particles reached the target particle size (D). 50 The reaction was stopped when the concentration of Ni was 9 μm. After filtration, washing with NaOH solution and pure water, drying, sieving, and demagnetization, a Ni precursor with a full concentration gradient structure was obtained. 0.84 Co 0.08 Mn 0.08 (OH)2;

[0075] (3) High-temperature sintering: The above precursor and LiOH·H2O are mixed evenly at a metal ion molar ratio of 1:0.98, and then placed in a ceramic boat and put into a tube furnace. Under an oxygen atmosphere, the temperature is first raised at 550℃ for 2h at a heating rate of 5℃ / min, then raised to 800℃ for 10h at a heating rate of 3℃ / min, and then held at 800℃ for 2h in an NF3 atmosphere. After cooling in the furnace, the full concentration gradient cathode material coated with rock salt phase is obtained.

[0076] Example 3

[0077] This embodiment provides a rock salt phase-coated full concentration gradient cathode material, which includes a rock salt phase coating layer containing doping elements, including F, and the content of the doping elements in the rock salt phase-coated full concentration gradient cathode material is 1.5 wt%; wherein, the thickness of the rock salt phase coating layer is 30 nm.

[0078] The rock salt phase-coated full-concentration gradient cathode material exhibits a gradual decrease in nickel content and a gradual increase in cobalt and manganese content from the core to the surface. The chemical formula of the rock salt phase-coated full-concentration gradient cathode material, excluding the doping elements, is LiNi. 0.92 Co 0.04 Mn 0.04 O2;

[0079] The preparation method of the rock salt phase-coated full-concentration gradient cathode material includes the following steps:

[0080] (1) Solution preparation: Weigh NiSO4·6H2O, CoSO4·7H2O and MnSO4·H2O in a molar ratio of Ni:Co:Mn = 98:1:1, and prepare ultra-high nickel salt solution A with pure water. The total metal ion concentration in ultra-high nickel salt solution A is 2 mol / L. Weigh NiSO4·6H2O, CoSO4·7H2O and MnSO4·H2O in a molar ratio of Ni:Co:Mn = 0.65:0.175:0.175, and prepare high nickel salt solution B with pure water. The total metal ion concentration in high nickel salt solution B is 2 mol / L.

[0081] Prepare a 10 wt% ammonia solution as a complexing agent solution; prepare a 40 wt% NaOH solution as a precipitating agent solution.

[0082] (2) Synthesis of precursor cores with full concentration gradient structure: A base solution consisting of pure water, complexing agent solution and precipitant solution was added to the reactor. The pH of the base solution was 12.0 and the ammonia content was 1.0 g / L.

[0083] 10 L of ultra-high nickel salt solution A was added to a mixing tank equipped with a stirrer. Ultra-high nickel salt solution A and high nickel salt solution B were pumped into the mixing tank at flow rates of 0.25 L / h and 0.35 L / h respectively, and stirred until homogeneous. Simultaneously, the mixed solution in the mixing tank was pumped into the reaction vessel at a flow rate of 0.6 L / h, along with the complexing agent solution and the precipitant solution, for a co-precipitation reaction under a nitrogen atmosphere. During the reaction, the temperature was maintained at 50℃, the pH was gradually decreased to 10.5 and then maintained, and the ammonia value was maintained at 1 g / L. The precursor particle size was monitored using a Malvern particle size analyzer throughout the reaction. The reaction proceeded only after both ultra-high nickel salt solution A and high nickel salt solution B were consumed simultaneously and the precursor particles reached the target particle size (D). 50The reaction was stopped when the particle size reached 11 μm; after filtration, washing with NaOH solution and pure water, drying, sieving, and demagnetization, the Ni precursor with a full concentration gradient structure was obtained. 0.92 Co 0.04 Mn 0.04 (OH)2;

[0084] (3) High-temperature sintering: The above precursor and LiOH·H2O are mixed evenly at a metal ion molar ratio of 1:0.93, and then placed in a ceramic boat and put into a tube furnace. Under an oxygen atmosphere, the temperature is first raised at 5℃ / min and held at 450℃ for 6h, then raised to 700℃ at a rate of 5℃ / min and held for 20h, and then held at 700℃ for 5h in an NF3 atmosphere. After cooling in the furnace, the full concentration gradient cathode material coated with rock salt phase is obtained.

[0085] Example 4

[0086] This embodiment provides a rock salt phase-coated full concentration gradient cathode material. Except for the preparation method in which the precursor and LiOH·H2O are mixed at a metal ion molar ratio of 1:0.90 to adapt the rock salt phase-coated full concentration gradient cathode material to changes, the rest of the preparation method is the same as in Example 1.

[0087] Example 5

[0088] This embodiment provides a rock salt phase-coated full concentration gradient cathode material. Except for the preparation method in which the precursor and LiOH·H2O are mixed in a 1:1 ratio of metal ions to make the rock salt phase-coated full concentration gradient cathode material adaptable to changes, the rest is the same as in Example 1.

[0089] Example 6

[0090] This embodiment provides a rock salt phase-coated full concentration gradient cathode material. Except for the preparation method in which ultra-high nickel salt solution A is directly introduced into the reactor containing the bottom liquid at a flow rate of 0.15 L / h and high nickel salt solution B at a flow rate of 0.25 L / h to make the obtained rock salt phase-coated full concentration gradient cathode material adaptable to changes, the rest is the same as in Example 1.

[0091] Example 7

[0092] This embodiment provides a rock salt phase coated full concentration gradient cathode material. Except that the rock salt phase coating layer does not contain doping elements, the rock salt phase coated full concentration gradient cathode material is the same as that in Embodiment 1.

[0093] The preparation method of the full concentration gradient positive electrode material coated with rock salt phase described in this embodiment is the same as that in Example 1, except that the step of holding at 750°C for 3 hours in an NF3 atmosphere is not performed.

[0094] Comparative Example 1

[0095] This comparative example provides a cathode material. Except for the preparation method, in which a mixed metal salt solution with a molar ratio of nickel ions, cobalt ions, and manganese ions of 88:12:12 is directly pumped into a reactor containing a base liquid at a flow rate of 0.5 L / h along with a complexing agent solution and a precipitant solution, so as to change the adaptability of the obtained cathode material, the cathode material is otherwise the same as in Example 1.

[0096] Comparative Example 2

[0097] This comparative example provides a cathode material. Except for the preparation method in which the precursor and LiOH·H2O are mixed in a metal ion molar ratio of 1:1.1 to change the adaptability of the obtained cathode material, the cathode material is otherwise the same as in Example 1.

[0098] The cathode materials prepared in all the above examples and comparative examples were mixed with SP and PVDF at a mass ratio of 97:1.5:1.5 to prepare a cathode sheet. The cathode sheet was then matched with lithium metal to assemble a lithium-ion battery. The battery was tested at 25°C and within a voltage range of 2.5V to 4.3V. First, it was charged and discharged for 3 cycles at a rate of 0.1C, and then charged and discharged for 100 cycles at 1C. The electrochemical performance was then tested, and the test results are shown in Table 1.

[0099] Table 1

[0100] Example 1 186.4 93.1 Example 2 184.2 92.7 Example 3 188.1 90.4 Example 4 179.5 89.7 Example 5 184.2 86.2 Example 6 184.3 84.7 Example 7 184.8 91.9 Comparative Example 1 184.1 83.9 Comparative Example 2 184.9 83.2

[0101] As can be seen from Table 1 above:

[0102] As shown in Example 1 and Comparative Example 1, the construction of a full concentration gradient in the material of the present invention can effectively alleviate the generation of microcracks in the material, improve the cycle performance of the material, and help to construct the specific structure of the material of the present invention. As shown in Example 1 and Comparative Example 2, when preparing the cathode material, it is difficult to construct the rock salt phase coating layer when the lithium content is sufficient, thereby reducing the stability of the cathode material and decreasing the electrochemical performance of the battery. As shown in Example 1 and Examples 4-5, the lithium source content during the preparation of the cathode material will affect the content of the rock salt phase coating layer, thereby affecting the performance of the material. As shown in Example 1 and Example 6, the present invention preferably uses a specific method to prepare a full concentration gradient structure, thereby improving the uniform distribution of ion content and further improving the performance of the material. As shown in Example 1 and Example 7, the present invention preferably contains doped elements in the rock salt phase coating layer, which can further improve the ionic conductivity of the material and improve the rate performance of the battery.

[0103] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a rock salt phase-coated full-concentration gradient cathode material, characterized in that, The preparation method includes the following steps: (1) First, add ultra-high nickel salt solution A to the mixing container, then pass ultra-high nickel salt solution A and high nickel salt solution B into the mixing container at the first flow rate and the second flow rate to obtain a mixed solution. At the same time as passing ultra-high nickel salt solution A and high nickel salt solution B, pass the mixed solution into the bottom liquid at the third flow rate to carry out a co-precipitation reaction to obtain the precursor material. Wherein, the second flow velocity is greater than the first flow velocity; (2) The lithium source and the precursor material described in step (1) are mixed and sintered to obtain the full concentration gradient cathode material coated with the rock salt phase; Wherein, the molar content of lithium ions in the lithium source is n1, the molar content of total metal ions in the precursor material is n2, and n1 / n2≤1.

2. The preparation method according to claim 1, characterized in that, The n1 / n2 ratio in step (2) is 0.9-0.

98.

3. The preparation method according to claim 1, characterized in that, The n1 / n2 ratio in step (2) is 0.93-0.

98.

4. The preparation method according to claim 1, characterized in that, The lithium source in step (2) includes any one or a combination of at least two of lithium carbonate, lithium hydroxide, lithium sulfate or lithium phosphate.

5. The preparation method according to claim 1 or 2, characterized in that, In step (2), a doping source gas is introduced during the later stage of sintering, and the doping source gas includes NF3 and / or a boron source.

6. The preparation method according to claim 5, characterized in that, The sintering in step (2) includes first-stage sintering and second-stage sintering in oxygen-containing gas, and then third-stage sintering in doped source gas.

7. The preparation method according to claim 6, characterized in that, The sintering temperature of the third stage is 650-800℃, the holding time is 2-5h, and the heating rate is 2-5℃ / min.

8. The preparation method according to claim 6, characterized in that, The second sintering temperature is 650-800℃, the holding time is 10-20h, and the heating rate is 2-5℃ / min.

9. The preparation method according to claim 6, characterized in that, The sintering temperature of the first stage is 450-550℃, the holding time is 2-6h, and the heating rate is 2-5℃ / min.

10. The preparation method according to claim 6, characterized in that, The oxygen-containing gas includes any one or a combination of at least two of oxygen, compressed air, or nitrogen dioxide.

11. The preparation method according to claim 1, characterized in that, In step (1), the molar ratio of nickel ions, manganese ions and cobalt ions in the ultra-high nickel salt solution A is x:y:z, where x+y+z=1, x=0.90-1.00, y=0.00-0.10, and z=0.00-0.

10.

12. The preparation method according to claim 1, characterized in that, In step (1), the molar ratio of nickel ions, manganese ions and cobalt ions in the high nickel salt solution B is x':y':z', where x'+y'+z'=1, x'=0.6-0.89, y'=0.11-0.40, and z'=0.11-0.

40.

13. The preparation method according to claim 1, characterized in that, The volume of the mixing container in step (1) is 10%-100% of the total volume of the mixed solution required for the coprecipitation reaction.

14. The preparation method according to claim 1, characterized in that, The volume of the mixing container in step (1) is 20-40% of the total volume of the mixed solution required for the coprecipitation reaction.

15. The preparation method according to claim 1, characterized in that, In step (1), an ultra-high nickel salt solution A is first added to the mixing container, wherein the volume of the ultra-high nickel salt solution A added is 20%-100% of the volume of the mixing container.

16. The preparation method according to claim 1, characterized in that, Step (1) The first flow rate is 0.05-0.25 L / h.

17. The preparation method according to claim 1, characterized in that, Step (1) The second flow rate is 0.2-0.35 L / h.

18. The preparation method according to claim 1, characterized in that, The third flow rate in step (1) is 0.4-0.6 L / h.

19. The preparation method according to claim 1, characterized in that, The pH of the coprecipitation reaction in step (1) is 9.5-10.5 and the temperature is 50-70℃.

20. The preparation method according to claim 1, characterized in that, In the coprecipitation reaction system described in step (1), the concentration of the complexing agent is 1-3 g / L.

21. The preparation method according to claim 1, characterized in that, The coprecipitation reaction in step (1) is carried out in a protective gas, which includes any one or a combination of at least two of argon, nitrogen or helium.

22. The preparation method according to claim 1, characterized in that, The coprecipitation reaction in step (1) is carried out until the particle size D50 is 9-11 μm.

23. The preparation method according to claim 1, characterized in that, The concentration of the complexing agent solution in step (1) is 10-40 wt%.

24. The preparation method according to claim 1, characterized in that, The concentration of the precipitant solution in step (1) is 10-40 wt%.

25. The preparation method according to claim 1, characterized in that, The pH of the base solution in step (1) is 11.0-12.0, and the concentration of the complexing agent is 1.0-9.0 g / L.

26. A full-concentration gradient cathode material coated with rock salt phase prepared by the preparation method according to any one of claims 1-25, characterized in that, The rock salt phase-coated full concentration gradient cathode material includes a rock salt phase coating layer; The full-concentration gradient cathode material coated with rock salt phase exhibits a gradual decrease in nickel content and a gradual increase in cobalt and manganese content from the core to the surface.

27. The rock salt phase-coated full-concentration gradient cathode material according to claim 26, characterized in that, The chemical general formula of the rock salt phase coated full-concentration gradient positive material is LiNi a Co b Mn c O2, wherein a+b+c=1, a is 0.8-0.96, b is 0.02-0.1, and c is 0.02-0.

1.

28. The rock salt phase-coated full-concentration gradient cathode material according to claim 26, characterized in that, The rock salt phase coating contains doping elements, including B and / or F.

29. The rock salt phase-coated full-concentration gradient cathode material according to claim 28, characterized in that, In the full concentration gradient cathode material coated with rock salt phase, the content of the doping element is 0.5-1.5 wt%.

30. The rock salt phase-coated full-concentration gradient cathode material according to claim 26, characterized in that, The thickness of the rock salt phase coating layer is 5-30 nm.

31. A lithium-ion battery, characterized in that, The lithium-ion battery includes a full-concentration gradient cathode material coated with a rock salt phase as described in any one of claims 26-30.