Positive electrode material having concentration gradient, and preparation method therefor

Abstract

A positive electrode material having a concentration gradient, and a preparation method therefor. The positive electrode material having a concentration gradient comprises a core and a coating layer. The structural formula of the core is LiNixCoyMn1-x-yO2, and the structural formula of the coating layer is mLiaMebOc, wherein 0<x<1, 0<y<1, 0<m<1, 0.2<a≤6, 1≤b<10, and 1≤c<4; and Me is a metal. The core comprises a permeation layer; and the ratio of the number of Co atoms in the permeation layer to the total number of Ni, Co and Mn atoms is gradually reduced. The coating layer can reduce the corrosion effect of an electrolyte on the positive electrode material and reduce the occurrence of side reactions, thereby improving the cycle performance of the positive electrode material, and reducing cracks or breakage of the material after cycling. The cobalt element in the core has a concentration gradient, which is beneficial to improving the high voltage performance of the positive electrode material.

Description

Positive electrode material with concentration gradient and preparation method thereof

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure claims priority to Chinese patent application number 202311422707.7, filed with the Chinese Patent Office on October 30, 2023, entitled “Cathode Material with Concentration Gradient and Preparation Method Thereof,” the entire contents of which are incorporated by reference into this disclosure. Technical Field

[0003] The present disclosure relates to the technical field of lithium-ion battery positive electrode materials, and in particular to a positive electrode material with a concentration gradient and a preparation method thereof. Background Art

[0004] In recent years, ternary lithium batteries have gradually become the mainstream of the market due to their high energy density, good cycle stability and low cost. From the perspective of morphology, ternary materials can be divided into single crystal and polycrystalline. The single crystal system not only has high energy density, but also has better performance in terms of safety and cycle. In particular, single crystal gradient materials with better roundness have fewer side reactions, low impedance, long cycle life and high thermal stability during the cycle. When preparing single crystal ternary material precursors by the traditional co-precipitation method, the element distribution is uneven due to the difference in the solubility product of the ions. In addition, due to the small particle size of the single crystal precursor, the synthesized precursor has poor sphericity and the occurrence of twins and supernumerary balls, resulting in serious agglomeration of the primary sintered particles. During crushing, the particles are forcibly opened, resulting in sharp edges. Such sharp edges will increase the specific surface area of ​​the material and increase the side reactions between the material and the electrolyte. In addition, such sharp edges will cause uneven internal stress caused by uneven charging and discharging of the material during the battery cycle, causing strong polarization and cracks, resulting in particle breakage during the cycle and rapid degradation of battery life.

[0005] Chinese invention patent: CN 114291855 A discloses a method for preparing a full concentration gradient cathode material precursor, a full concentration gradient cathode material and a preparation method thereof, wherein a nickel-poor solution is added to a nickel-rich solution, and a metal salt solution, a precipitant and a complexing agent are added to a base solution containing the precipitant and the complexing agent, and the pH and the concentration of the complexing agent in the reaction system are controlled to gradually decrease as the nickel concentration in the added metal salt solution decreases; a cathode material with excellent electrical properties is prepared by a programmed temperature control method, but due to differences in the Ksp of different metal solutions and the concentration of the salt solution during the co-precipitation process, a slight deviation in the feeding speed control may result in the secondary balls having primary particles that are too large or too small, resulting in a low ball formation rate, irregular morphology, segregation of elements within the co-precipitate, and difficulty in quality control; and due to differences in nickel content, the temperature is difficult to control during the primary sintering, resulting in lithium and nickel mixing, and the originally designed concentration gradient distribution tends to be uniform, thereby losing its structural advantage.

[0006] In view of this, the present disclosure is hereby provided.

[0007] Summary of the Invention

[0008] The purpose of the present disclosure is to provide a cathode material with a concentration gradient and its preparation method, so as to improve the cycling performance of the material.

[0009] The present disclosure is implemented as follows:

[0010] In a first aspect, the present disclosure provides a cathode material with a concentration gradient, including a core and a coating layer. The structural formula of the core is LiNi , , c , a , , , ,

[0013] ,

[0017] ,

[0016] , b ,

[0015] ,

[0014] Co y Mn 1-x-y O2, and the structural formula of the coating layer is mLi a Me b O c , where 0 < x < 1, 0 < y < 1, 0 < m < 1, 0.2 < a ≤ 6, 1 ≤ b < 1​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​In a second aspect, the present disclosure provides a method for preparing a positive electrode material having a concentration gradient as described in any one of the aforementioned embodiments, comprising:

[0018] placing a mixture of nickel-cobalt-manganese ternary cathode material and a cobalt source in an oxygen-containing atmosphere for a second sintering to obtain a core;

[0019] The mixture of the core, the lithium source and the Me source is sintered for a third time to obtain the positive electrode material with the concentration gradient.

[0020] In an optional embodiment, the cobalt source is at least one of cobalt hydroxide, cobalt oxide, and cobalt trioxide;

[0021] And / or, the lithium source is at least one of lithium hydroxide, lithium carbonate and lithium fluoride;

[0022] And / or, the Me source is an oxide containing Me or a salt containing Me.

[0023] In an optional embodiment, the mass ratio of the nickel-cobalt-manganese ternary positive electrode material to the cobalt source is 1:0.01-1:0.5.

[0024] In an optional embodiment, the mass ratio of the core, the lithium source and the Z source is (4-6):1:(0.1-10).

[0025] In an optional embodiment, the temperature of the second sintering is 500° C.-800° C., and the time is 3 h-12 h, and the temperature of the third sintering is 300° C.-700° C., and the time is 3 h-12 h.

[0026] In an optional embodiment, the mixture of the nickel-cobalt-manganese ternary positive electrode material and the cobalt source is placed in an oxygen-containing atmosphere for a second sintering to obtain the core, and the preparation of the nickel-cobalt-manganese ternary positive electrode material is also included: using nickel hydroxide particles as a carrier, sodium hydroxide solution as a precipitant, and ammonia water as a chelating agent, in an inert gas atmosphere, manganese and cobalt are precipitated onto the carrier to obtain a nickel-cobalt-manganese precursor, and then the mixture of the nickel-cobalt-manganese precursor and the lithium source is sintered for the first time to obtain the nickel-cobalt-manganese ternary positive electrode material.

[0027] In an optional embodiment, in the step of preparing the nickel-cobalt-manganese ternary positive electrode material, the pH of the manganese and cobalt precipitation is 10-12, and the temperature of the first sintering is 500°C-1200°C.

[0028] The present disclosure has the following beneficial effects:

[0029] The cathode material with a concentration gradient disclosed herein comprises a coating and a core. The coating can reduce the corrosion of the electrolyte on the cathode material and the occurrence of side reactions, thereby improving the cycling performance of the cathode material and reducing cracking or breakage after cycling. The core disclosed herein has a cobalt concentration gradient, which is beneficial for improving the high-voltage performance of the cathode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0031] FIG1 is a SEM image of the positive electrode material having a concentration gradient obtained in Example 2;

[0032] FIG2 is a SEM image of the positive electrode material with a concentration gradient obtained in Comparative Example 1;

[0033] FIG3 is a SEM image of the positive electrode material with a concentration gradient obtained in Example 2 after cycling;

[0034] FIG4 is a SEM image of the positive electrode material with a concentration gradient obtained in Comparative Example 1 after cycling;

[0035] FIG5 shows the capacity retention rate of the positive electrode material with a concentration gradient obtained in Example 2 and Comparative Example 1;

[0036] FIG6 shows the DCR growth rate of the positive electrode materials with concentration gradient obtained in Example 2 and Comparative Example 1;

[0037] FIG7 is an XRD diagram of the positive electrode materials with concentration gradient obtained in Example 2 and Comparative Example 1. DETAILED DESCRIPTION

[0038] To make the purpose, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer were followed. Reagents or instruments used where the manufacturer is not specified are conventional products that can be purchased commercially.

[0039] In the first aspect, the present disclosure provides a positive electrode material with a concentration gradient, comprising a core and a coating layer, wherein the core structure is LiNi x Co y Mn 1-x-y O2, the structural formula of the coating layer is mLi a Meb O c where 0 < x < 1, 0 < y < 1, 0 < m < 1, 0.2 < a ≤ 6, 1 ≤ b < 10, 1 ≤ c < 4; Me is a metal;

[0040] The core includes a penetration layer, and the ratio of the number of Co atoms from the outside to the inside in the penetration layer gradually decreases with respect to the total number of Ni, Co, and Mn atoms.

[0041] The core in this embodiment is a nickel-cobalt-manganese ternary cathode material, and the core includes a core layer with a relatively constant concentration and a penetration layer with a concentration gradient, or the core only includes a penetration layer with a concentration gradient. Among them, the core layer may or may not exist. The content of Co atoms in the penetration layer gradually decreases from the outside to the inside. In this embodiment, the content and distribution of cobalt in the core have a great influence on the material performance.

[0042] The cathode material with a concentration gradient in this embodiment includes a coating layer and a core. The coating layer can reduce the corrosion of the electrolyte on the cathode material and reduce the occurrence of side reactions, thereby improving the cycling performance of the cathode material and reducing cracks or fragmentation phenomena generated after material cycling. The cobalt element in the core in this disclosure has a concentration gradient, which is beneficial to slowing down the severity of the reaction between the material interface and the electrolyte after increasing the voltage, thereby reducing the metal dissolution rate, alleviating the generation of surface cracks and material cycling dives, and enhancing the high-voltage performance of the cathode material.

[0043] In an alternative embodiment, the structural formula of the cathode material with a concentration gradient is LiNi x Co y Mn 1-x-y O2@mLi[[ID=X]] a [[ID=Y]] b [[ID=Z]] c O, and 0 < m < 1; Although the coating layer can improve the cycling performance of the material in this embodiment, too high content of the coating layer will reduce the capacity of the material. Therefore, the amount of the coating layer should not be too much.

[0044] In an alternative embodiment, Me is at least one of B, Al, Co, W, Ti, Zr, Si, Sr, Mo, Ce, Mg. In this embodiment, using the above elements for the Me metal in the coating layer can reduce side reactions between the electrolyte and the cathode material and improve the ionic conductivity and electronic conductivity of the material.

[0045] In an alternative embodiment, the rate performance of the cathode material is improved by doping Co in the cathode material. [[ID=X]] [[ID=Y]]

[0046] ]]In an alternative embodiment, the ratio of the number of Co atoms on the surface of the core to the total number of Ni, Co, and Mn atoms is 0.5 - 1, which is beneficial to improving the rate performance and significantly reducing the material resistance. ​​

[0047] In an optional embodiment, the ratio of the number of Co atoms to the total number of Ni, Co, and Mn atoms at a distance z nm from the core surface is greater than 0.5, where z / r = 0.1 to 0.3, and r is the average radius of the core in nm. This is beneficial for maintaining structural stability of the positive electrode material during deep discharge and improving high-voltage performance.

[0048] In an optional embodiment, the average radius of the core is 1 μm-5 μm, and the thickness of the coating is 10 nm-500 nm. If the coating is too thin, it will not improve the cycle performance of the positive electrode material or the effect will be insignificant. If the coating is too thick, it may affect the migration of lithium ions and reduce the material capacity. In this embodiment, due to the large difference between the average radius of the coating and the core, in some cases, the average radius of the positive electrode material with a concentration gradient can be regarded as the average radius of the core.

[0049] In a second aspect, the present disclosure provides a method for preparing a positive electrode material having a concentration gradient as described in any one of the aforementioned embodiments, comprising:

[0050] placing a mixture of nickel-cobalt-manganese ternary cathode material and a cobalt source in an oxygen-containing atmosphere for a second sintering to obtain a core;

[0051] The mixture of the core, the lithium source and the Me source is sintered for a third time to obtain the positive electrode material with the concentration gradient.

[0052] In this example, the nickel-cobalt-manganese ternary cathode material and a cobalt source are first mixed, followed by a second sintering process. This allows the cobalt element in the cobalt source to migrate into the core, gradually decreasing the cobalt concentration from the surface layer to the inner layer, thereby obtaining the core. The core and the raw materials for the coating layer (including the lithium source and the Z source) are then mixed and calcined a third time to obtain the coating layer.

[0053] In an optional embodiment, the cobalt source is at least one of cobalt hydroxide, cobalt oxide and cobalt trioxide.

[0054] In an optional embodiment, the lithium-containing source is at least one of lithium hydroxide, lithium carbonate and lithium fluoride.

[0055] In an optional embodiment, the Me source is an oxide or hydroxide containing Me, specifically at least one of boric acid, aluminum oxide, cobalt oxide, tungsten oxide, titanium oxide, zirconium oxide, cerium oxide, molybdenum oxide, cesium oxide, strontium oxide and magnesium oxide.

[0056] In an optional embodiment, the mass ratio of the nickel-cobalt-manganese ternary positive electrode material to the cobalt source is 1:0.01-1:0.5.

[0057] In an optional embodiment, the mass ratio of the core, lithium-containing source and Z source is (4-6):1:(0.1-10). Excessive lithium content in the coating layer will result in a high level of residual lithium on the surface, affecting the processing performance of the material. Excessive Me content will also cause the surface coating layer to be too thick, resulting in an increase in the migration path of internal lithium, a decrease in the conductivity of the material, affecting the migration of lithium ions, and reducing the capacity of the material. Therefore, the lithium and Me elements need to be within a reasonable range.

[0058] In an optional embodiment, the temperature of the second sintering is 500° C.-800° C., and the time is 3 h-12 h.

[0059] The purpose of the second sintering is to allow the cobalt element to penetrate into the core. In theory, the higher the sintering temperature and the longer the time, the more and farther the cobalt element will penetrate into the interior. However, too high a temperature or too long a sintering time may cause damage to the structure of the ternary material itself. Therefore, the temperature and time of the second sintering need to be based on the particle size of the core and the amount and depth of cobalt element penetration into the core, and the bearing capacity of the ternary material itself.

[0060] In an optional embodiment, the third sintering temperature is 300°C-700°C, and the duration is 3 hours-12 hours. The purpose of the third sintering is to form a coating layer, and to ensure that the coating layer is relatively tightly coated on the surface of the core. To ensure the best possible bond between the coating layer and the core, the third sintering temperature should not be too low, and the duration should not be too short.

[0061] In an optional embodiment, the preparation of a nickel-cobalt-manganese ternary positive electrode material is also included: using nickel hydroxide particles as a carrier, sodium hydroxide solution as a precipitant, and ammonia water as a chelating agent, manganese and cobalt are precipitated onto the carrier under an inert gas atmosphere to obtain a nickel-cobalt-manganese precursor, and then the mixture of the nickel-cobalt-manganese precursor and a lithium source is sintered for the first time to obtain a nickel-cobalt-manganese ternary positive electrode material.

[0062] In some preferred embodiments, in the step of preparing the nickel-cobalt-manganese ternary positive electrode material, the pH of the manganese and cobalt precipitation is 10-12, and the temperature of the first sintering is 500°C-1200°C.

[0063] The raw material nickel-cobalt-manganese ternary cathode material in this embodiment can be a conventional ternary cathode material. However, to obtain a precursor with better sphericity, loose, porous, small-particle nickel hydroxide can also be used as a carrier. Cobalt and manganese salt solutions are pumped into the reactor at preset rates, allowing manganese and cobalt to precipitate into the pores of the nickel hydroxide particles. The lithium source in this step can be the same as or different from the lithium source in the coating layer raw material.

[0064] This method can adjust the distribution of elements in the nickel-cobalt-manganese ternary positive electrode material as needed, for example, gradually reduce the concentration of cobalt from the surface to the inside, and use the coprecipitation method to obtain a core with a concentration gradient. However, due to the difference in the cobalt-manganese Ksp and salt solution concentrations during the coprecipitation process, the feeding speed control is slightly offset, and the secondary balls obtained may have internal element segregation of the coprecipitation, which makes quality control difficult. In addition, due to the difference in nickel content, the temperature is not easy to control during the first sintering, resulting in lithium-nickel mixing. The originally designed concentration gradient distribution tends to be uniform, thereby losing its structural advantage. Therefore, this embodiment does not adjust the concentration of cobalt during the coprecipitation process, and obtains a ternary material without a concentration gradient. Then, a second sintering is used to allow cobalt to penetrate into the interior of the ternary material without a concentration gradient, obtaining a permeation layer with a cobalt concentration gradient, strengthening the concentration gradient in the positive electrode material, and is more controllable than directly adjusting the concentration gradient of cobalt when preparing the nickel-cobalt-manganese ternary positive electrode material.

[0065] The features and performance of the present disclosure are further described in detail below with reference to the embodiments.

[0066] Example 1:

[0067] This embodiment provides a method for preparing a nickel-cobalt-manganese ternary positive electrode material, specifically comprising:

[0068] Preparation: The nickel salt is nickel hydroxide particles with a particle size of 1-5 μm and a porosity of 50%; the cobalt salt is an aqueous solution of CoSO4, and the molar concentration of cobalt in the cobalt salt solution is 1 mol / L; the manganese salt is MnSO4, and the molar concentration of manganese in the manganese salt solution is 1 mol / L; the lithium salt is LiOH.

[0069] Preparation: The nickel hydroxide particles are placed in a reactor as a carrier, the temperature in the reactor is controlled at 50 degrees Celsius, the pH value is 11, the atmosphere is nitrogen, a 2 mol / L sodium hydroxide solution is added as a precipitant, and a 0.5 mol / L ammonia solution is added as a complexing agent; the manganese salt solution is pumped into the reactor at a rate of 50 mL / min, and the cobalt salt solution is pumped into the reactor at a rate of 50 mL / min, so that the manganese salt and the cobalt salt are deposited in the pores of the nickel hydroxide particles to synthesize a precursor; the synthesized precursor is mixed with lithium hydroxide and calcined at 800°C for 10 hours to obtain LiNi 0.63 Mn 0.28 Co 0.09 O2 nickel-cobalt-manganese ternary positive electrode material.

[0070] Example 2:

[0071] This embodiment provides a method for preparing a positive electrode material with a concentration gradient, comprising the following steps:

[0072] S1, the nickel-cobalt-manganese ternary cathode material obtained in Example 1 and nano-cobalt hydroxide are uniformly mixed in a mass ratio of 1:0.5, and placed in an oxygen atmosphere for a second sintering at a temperature of 600° C. for 10 hours to obtain a core;

[0073] S2, the core, lithium hydroxide and tungsten oxide are uniformly mixed in a mass ratio of 1:0.2:0.25 and then sintered for a third time at a sintering temperature of 600° C. for 12 h to obtain a positive electrode material with a concentration gradient.

[0074] Example 3:

[0075] This embodiment provides a method for preparing a positive electrode material with a concentration gradient, comprising the following steps:

[0076] S1, the nickel-cobalt-manganese ternary cathode material obtained in Example 1 and nano-cobalt hydroxide are uniformly mixed in a mass ratio of 1:0.3, and placed in an oxygen atmosphere for a second sintering at a temperature of 600° C. for 10 hours to obtain a core;

[0077] S2, uniformly mixing the core, lithium hydroxide and tungsten oxide in a mass ratio of 1:0.2:0.25 and then sintering for a third time at a sintering temperature of 600° C. for 12 h to obtain the positive electrode material with a concentration gradient.

[0078] Example 4:

[0079] This embodiment provides a method for preparing a positive electrode material with a concentration gradient, comprising the following steps:

[0080] S1, the nickel-cobalt-manganese ternary cathode material obtained in Example 1 and nano-cobalt hydroxide are uniformly mixed in a mass ratio of 1:0.5, and placed in an oxygen atmosphere for a second sintering at a temperature of 700° C. for 12 hours to obtain a core;

[0081] S2, uniformly mixing the core, lithium hydroxide and tungsten oxide in a mass ratio of 1:0.3:0.25 and then sintering for a third time at a sintering temperature of 600° C. for 6 hours to obtain the positive electrode material with a concentration gradient.

[0082] Example 5:

[0083] The only difference from Example 2 is that tungsten oxide is replaced by an equimolar amount of Al2O3.

[0084] Comparative Example 1:

[0085] Nickel sulfate, cobalt sulfate, manganese sulfate and aluminum sulfate are prepared into a uniform mixed solution according to a certain molar ratio of Ni:Co:Mn, and the total molar number of the three transition metal ions of Ni, Co and Mn is 0.5 mol / L. Then, 2 mol / L NaOH solution, 0.5 mol / L transition metal ion solution and 2 mol / L ammonia water are added to a batch reaction vessel at the same time. The feeding rates of ammonia water, NaOH solution and transition metal ion solution are controlled to be 200 ml / h, 100 ml / h and 50 ml / h respectively, and the power of the stirring device obtained per unit volume is controlled to be 1.3 kW / m 3 The pH value of the reaction system was controlled to be 11, the reaction temperature was 60 ° C, and the reaction was terminated when the crystals grew to a certain size. The obtained precipitate was filtered, washed, and dried at 120 ° C for 12 hours to obtain a precursor. The synthesized precursor was mixed with lithium hydroxide and calcined at 800 ° C for 10 hours to obtain LiNi 0.63 Mn 0.28 Co 0.09 O2 nickel-cobalt-manganese ternary positive electrode material.

[0086] Comparative Example 2:

[0087] The only difference from Example 2 is that in step S1, the sintering temperature is 700° C. and the sintering time is 12 h.

[0088] Comparative Example 3:

[0089] The only difference from Example 2 is that in step S1, the sintering temperature is 700° C. and the sintering time is 8 hours.

[0090] Test Case

[0091] The positive electrode material, conductive carbon and binder obtained in the above examples and comparative examples were mixed in a ratio of 90:5:5 to prepare a slurry. The slurry was then coated on aluminum foil, dried, rolled, slit and die-cut, and finally assembled with a graphite negative electrode into a 5AH soft-pack battery with a formation voltage of 2.84.4V and a formation rate of 0.33C. The capacity retention rate and DCR growth rate of the soft-pack battery were tested, and the results are shown in the table below.

[0092] Electrical Performance Tests 1) Gram Capacity Test: The obtained positive electrode material was made into a 5AH soft-pack battery. After preparation, conventional formation was performed at a formation voltage of 3.04.4V and a formation rate of 0.33C to obtain gram capacity data. The results are shown in the table below.

[0093] 2) DCR performance test: The obtained positive electrode material is made into a 5AH soft pack battery. After the preparation is completed, conventional formation is carried out and a room temperature DCR test is carried out. The room temperature DCR test process is as follows: the formed battery is fully charged at a 1 / 3C rate within a voltage range of 3.04.4V at room temperature 25°C, allowed to stand, and then discharged at a 1 / 3C rate for different SOCs, allowed to stand, and then a 2.5C pulse is applied for 18s. The voltage changes before and after the pulse are recorded, and the DCR data at different SOCs at room temperature are obtained according to the calculation formula DCR = (voltage after pulse discharge at the end of standing) / pulse current. The results are shown in the table below;

[0094] Cycling performance test: The obtained positive electrode material was made into a 5AH soft-pack battery. After preparation, conventional formation was performed. The formed battery was charged and discharged at a 1C rate at 25°C in the voltage range of 2.84.4V. The capacity retention rate was recorded after 600 cycles. The results are shown in the table below.

[0095] Cyclic DCR growth test: During the cycling process, the voltage and discharge current after the first, 100th, and 200th cycle, as well as the voltage after 30 seconds, are selected to calculate the DCR value and DCR growth rate.

[0096] Figures 1 and 3 in the present disclosure are respectively SEM images of the positive electrode material with a concentration gradient obtained in Example 2 before and after the cycle test. It can be seen from the figures that the primary particles of the positive electrode material with a concentration gradient obtained in Example 2 have better roundness, and no microcracks occur in the cross-section after the cycle; Figures 2 and 4 are respectively SEM images of the positive electrode material with a concentration gradient obtained in Comparative Example 1 before and after the cycle test. It can be seen from the figures that the primary particles of the positive electrode material with a concentration gradient obtained in Comparative Example 1 have sharp edges and corners, relatively poor particle roundness, and microcracks appear in the particle cross-section after the cycle.

[0097] Figures 5-7 are comparisons of the capacity retention rate, DCR growth rate and XRD diagram of the positive electrode material with concentration gradient obtained in Example 2 and Comparative Example 1, respectively. It can be seen from the figures that, compared with Comparative Example 1, Example 2 has better cycle retention rate, lower cycle DCR growth rate, higher peak intensity and better crystallinity.

[0098] The foregoing description is merely a preferred embodiment of the present disclosure and is not intended to limit the present disclosure. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present disclosure shall be included within the scope of protection of the present disclosure. Industrial Applicability

[0099] The disclosed cathode material with a concentration gradient comprises a coating and a core. The coating reduces electrolyte corrosion and side reactions, thereby improving the cycling performance of the cathode material and reducing cracking or breakage after cycling. The core of the disclosed cathode material has a cobalt concentration gradient, which helps improve the high-voltage performance of the cathode material.

Claims

1. A positive electrode material having a concentration gradient, characterized in that: It includes a core and a coating layer. The structural formula of the core is LiNi x Co y Mn 1-x-y O2. The structural formula of the coating layer is Li a Me b O c , where 0 < x < 1, 0 < y < 1, 0.2 < a ≤ 6, 1 ≤ b < 10, 1 ≤ c < 4; Me is a metal; the core includes a penetration layer, and in the penetration layer, the ratio of the number of Co atoms from the outside to the inside to the total number of Ni, Co, and Mn atoms gradually decreases.

2. The positive electrode material with concentration gradient according to claim 1, characterized in that The positive electrode material with concentration gradient has a structural formula of LiNi x Co y Mn 1-x-y O2@mLi a Me b O c , and 0<m<1.

3. The positive electrode material with concentration gradient according to claim 2, characterized in that: Me is at least one of B, Al, Co, W, Ti, Zr, Si, Sr, Mo, Ce, and Mg.

4. The positive electrode material with concentration gradient according to claim 1, characterized in that The ratio of the number of Co atoms on the surface of the core to the total number of Ni, Co and Mn atoms is 0.5-1.

5. The positive electrode material with concentration gradient according to claim 4, characterized in that: The ratio of the number of Co atoms to the total number of Ni, Co and Mn atoms at a distance of z nm from the core to the core surface is greater than 0.5, wherein z / r=0.1-0.3, and r is the average radius of the core, in nm.

6. The positive electrode material with concentration gradient according to claim 1, characterized in that The average radius of the core is 1 μm-5 μm, and the thickness of the coating layer is 10 nm-500 nm.

7. The positive electrode material with concentration gradient according to claim 1, characterized in that Satisfies at least one of the following characteristics ag: a.0.33C discharge capacity is 194mAh / g-196.68mAh / g; b.1C rate discharge capacity is 187.7mAh / g-190.22mAh / g, 1C / 0.33C rate discharge retention is 96.75%-96.71%; c. 2C rate discharge capacity is 185.81mAh / g-186.75mAh / g, 2C / 0.33C rate discharge retention rate is 95.78%-94.95%; d. 3C rate discharge capacity is 185.37mAh / g-186.16mAh / g, 3C / 0.33C rate discharge The retention rate is 95.55%-94.65%; e.4C rate discharge capacity is 176.05mAh / g-185.82mAh / g, 4C / 0.33C rate discharge retention rate is 90.74%-94.48%; f. DCR is 10.90mΩ-12.99mΩ at 50% SOC; g. After 600 cycles, the DCR is 13.91mΩ-30.69mΩ.

8. A method for preparing a positive electrode material with a concentration gradient according to any one of claims 1 to 7, characterized in that: include: placing a mixture of nickel-cobalt-manganese ternary positive electrode material and a cobalt source in an oxygen-containing atmosphere for a second sintering to obtain a core; The mixture of the core, the lithium source and the Z source is sintered for the third time to obtain the positive electrode material with the concentration gradient.

9. The method for preparing a positive electrode material with a concentration gradient according to claim 8, characterized in that: The mass ratio of the nickel-cobalt-manganese ternary positive electrode material to the cobalt source is 1:0.01-1:0.

5.

10. The method for preparing a positive electrode material with a concentration gradient according to claim 8, characterized in that: The mass ratio of the core, the lithium source and the Z source is (4-6):1:(0.1-10).

11. The method for preparing a positive electrode material with a concentration gradient according to claim 8, characterized in that: The temperature of the second sintering is 500° C.-800° C., and the time is 3 h-12 h. The temperature of the third sintering is 300° C.-700° C., and the time is 3 h-12 h.

12. The method for preparing a positive electrode material with a concentration gradient according to claim 8, characterized in that: The method further includes placing the mixture of the nickel-cobalt-manganese ternary positive electrode material and the cobalt source in an oxygen-containing atmosphere for a second sintering to obtain the core, and also includes the preparation of the nickel-cobalt-manganese ternary positive electrode material: using nickel hydroxide particles as a carrier, sodium hydroxide solution as a precipitant, and ammonia water as a complexing agent, in an inert gas atmosphere, manganese and cobalt are precipitated on the carrier to obtain a nickel-cobalt-manganese precursor, and then the mixture of the nickel-cobalt-manganese precursor and the lithium source is sintered for the first time to obtain the nickel-cobalt-manganese ternary positive electrode material.

13. The method for preparing a positive electrode material with a concentration gradient according to claim 8, characterized in that in the step of preparing the nickel-cobalt-manganese ternary positive electrode material, the pH of manganese and cobalt precipitation is 10-12, and the temperature of the first sintering is 500°C-1200°C.

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