Positive electrode material and preparation method thereof

Abstract

The invention discloses a positive electrode material and a preparation method, the chemical formula of the positive electrode material is Li [Ni < x > Mn < 1-x-y > Cry] O < 2 >, 1.0, 0 lt; y is less than or equal to 0.05, and the positive electrode material is of a pseudo-single crystal structure with the diameter of 2-4 microns. According to the positive electrode material disclosed by the invention, the chromium ions are introduced into a high-nickel cobalt-free positive electrode material system structure in situ, so that the energy density of the cobalt-free positive electrode material is remarkably improved, and the cycling stability of the positive electrode material under high voltage and high-temperature working conditions is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery materials, and more specifically, to a cathode material and a preparation method thereof. Background Art

[0002] The high-nickel layered oxide ternary (nickel-cobalt-manganese, nickel-cobalt-aluminum) cathode material has a relatively high energy density and a relatively mature production process, and is currently the mainstream commercial cathode material. However, with the continuous consumption of global cobalt resources, the price of cobalt has been rising in recent years, seriously restricting the development of high-nickel cobalt-containing cathode materials. However, due to the unique role of cobalt in the ternary material structure system, it can stabilize the layered structure of the material and promote the transmission of lithium ions between layers during charge and discharge. Removing cobalt from the ternary material system will inevitably cause a certain degree of decline in material performance. Summary of the Invention

[0003] An object of the present invention is to provide a new technical solution for a cathode material and a preparation method thereof.

[0004] According to one aspect of the present invention, there is provided a cathode material, which is a compound represented by the chemical formula Li[Ni x Mn 1-x-y Cr y O2, wherein in terms of molar ratio, 0.8 ≤ x < 1.0, 0 < y ≤ 0.05, the cathode material is a quasi-single crystal structure, and the diameter of the cathode material is 2 - 4 μm.

[0005] Optionally, the chemical formula is Li[Ni 0.8 Mn 0.19 Cr 0.01 O2.

[0006] According to another aspect of the present invention, there is provided a preparation method of a cathode material, and the preparation method includes the following steps:

[0007] (1) Take soluble nickel salt, manganese salt, and chromium salt, add deionized water, and stir evenly to form a mixed salt solution;

[0008] (2) Add the mixed salt solution to a reaction kettle in a nitrogen atmosphere at a rate of 2.5 - 5 L / h, add a sodium hydroxide solution with a concentration of 2 - 4 mol / L to the reaction kettle as a precipitating agent, and add an ammonia water solution with a concentration of 1 - 4 mol / L as a complexing agent to carry out a coprecipitation reaction to obtain a solid-liquid mixture;

[0009] (3) Centrifuge, wash, dry, and screen out iron from the solid-liquid mixture to obtain a [Ni x Mn 1-x–y Cr y (OH)2 precursor;

[0010] (4) The precursor powder is fully mixed with battery-grade lithium hydroxide and placed in a tube furnace for high-temperature sintering in an oxygen atmosphere to obtain a positive electrode material Li[Ni x Mn 1-x–y Cr y ]O2.

[0011] Optionally, the diameter of the precursor is 3-4 μm, and the diameter of the positive electrode material is 2-4 μm.

[0012] Optionally, the soluble nickel salt, manganese salt and chromium salt in step (1) have a stoichiometric ratio of nickel:manganese:chromium=80:19:1.

[0013] Optionally, the chromium salt in step (1) is one of chromium sulfate, chromium nitrate and chromium halide.

[0014] Optionally, the process conditions of the coprecipitation reaction process in step (2) are as follows: in the reactor, the ammonia concentration is 4-12 g / L, the solution pH is 10-12, the rotation speed of the reactor is 300-450 rpm, and the duration of the coprecipitation reaction is 20-50 h.

[0015] Optionally, the stoichiometric ratio of the precursor to the battery-grade lithium hydroxide in step (4) is 1:(1.05-1.1).

[0016] Optionally, the oxygen concentration in step (4) is not less than 95%.

[0017] Optionally, the high temperature sintering in step (4) is first sintering at 500-600°C for 4-6h, and then sintering at 800-900°C for 10-16h, with a heating rate of 1-3°C / min throughout the process.

[0018] According to the positive electrode material of the present invention, by in-situ introducing chromium ions into the system structure of the cobalt-free high-nickel positive electrode material, based on the fact that the valence electrons of the chromium ions occupy a lower energy level, the electrochemical reaction potential of the high-nickel system can be effectively improved, thereby exerting more capacity under high voltage and significantly improving the energy density of the cobalt-free high-nickel positive electrode material.

[0019] Further features and advantages of the present invention will become apparent from the following detailed description of exemplary embodiments of the present invention with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0021] Figure 1This is a SEM image of the precursor obtained in Example 1 of the present invention.

[0022] Figure 2 This is a TEM image of the positive electrode material obtained in Example 1 of the present invention.

[0023] Figure 3 It is an XRD comparison diagram of the materials prepared in Example 1 of the present invention and Comparative Example 1.

[0024] Figure 4 It is a comparison diagram of differential capacity curves during charging process of the material prepared in Example 1 of the present invention and the material prepared in Comparative Example 1.

[0025] Figure 5 It is a comparison chart of the discharge capacity of the material prepared in Example 1 of the present invention and the material prepared in Comparative Example 1. DETAILED DESCRIPTION

[0026] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present invention unless otherwise specifically stated.

[0027] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses.

[0028] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered as part of the specification.

[0029] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0030] It should be noted that like reference numerals and letters refer to similar items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0031] Lithium batteries with a nickel content of more than 80% are called high-nickel lithium batteries, which have the advantages of high energy density and high power output. Products with relatively low cost sensitivity will use more positive electrode materials with high nickel and high cobalt content to achieve higher performance, while areas that focus more on cost and cycle life tend to use low-cobalt or cobalt-free material systems.

[0032] According to one embodiment of the present invention, a positive electrode material is provided, wherein the positive electrode material is a positive electrode material having a chemical formula of Li[Ni x Mn 1-x-y Cry The compound shown in ]O2, where 0.8 ≤ x < 1.0 and 0 < y ≤ 0.05 in molar ratio. The nickel element content in the positive electrode material of the present invention is above 80%, belonging to a cobalt-free high-nickel ternary positive electrode material. The present invention removes cobalt elements from the high-nickel ternary positive electrode material and introduces chromium elements, which is beneficial to improving the cycle stability of the cobalt-free high-nickel positive electrode material under high voltage and high-temperature working conditions.

[0033] The positive electrode material of the present invention has a quasi-single crystal structure, and the diameter of the positive electrode material is 2 - 4 μm. As a battery positive electrode material, the quasi-single crystal structure has significant advantages compared with the polycrystalline structure. Compared with the polycrystalline structure, the quasi-single crystal structure has higher lattice order and fewer defects. Serious microcracks will occur in the polycrystalline high-nickel positive electrode material during long-term cycling, resulting in rapid capacity decay. The cobalt-free high-nickel positive electrode material of the present invention has a quasi-single crystal structure and a small grain size, which can effectively inhibit crack formation and extend the cycle life of the material.

[0034] Optionally, the chemical formula is Li[Ni 0.8 Mn 0.19 Cr 0.01 O2. Under this composition, the cobalt-free high-nickel ternary positive electrode material increases the content of manganese in the ternary material, and more manganese ions that are electrochemically inert in the system can effectively stabilize the layered structure of the material, enabling the positive electrode material to have a high energy density and a long cycle life.

[0035] According to another embodiment of the present invention, a preparation method of a positive electrode material is provided. The preparation method includes the following steps:

[0036] (1) Take soluble nickel salt, manganese salt, and chromium salt, add deionized water, and stir evenly to form a mixed salt solution;

[0037] (2) Add the mixed salt solution to a reaction kettle under a nitrogen atmosphere at a rate of 2.5 - 5 L / h, add a sodium hydroxide solution with a concentration of 2 - 4 mol / L to the reaction kettle as a precipitating agent, and add an ammonia water solution with a concentration of 1 - 4 mol / L as a complexing agent to carry out a coprecipitation reaction to obtain a solid-liquid mixture;

[0038] (3) Centrifuge, wash, dry, and screen to remove iron from the solid-liquid mixture to obtain a [Ni x Mn 1-x–y Cr y (OH)2 precursor;

[0039] (4)充分混合后置于管式炉内,在氧气气氛下高温烧结,得到正极材料Li[Ni x Mn 1-x–y Cr y It should be noted that there seems to be an incomplete sentence in step (4). Please check and correct it if necessary.]O2.

[0040] Optionally, the diameter of the precursor is 3-4 μm, and the diameter of the positive electrode material is 2-4 μm.

[0041] Optionally, the soluble nickel salt, manganese salt and chromium salt in step (1) are in a stoichiometric ratio of nickel: manganese: chromium = 80:19:1. The so-called stoichiometric ratio refers to the molar ratio between reactants and products calculated according to the chemical reaction stoichiometric equation in a chemical reaction. The nickel salt, manganese salt and chromium salt are prepared into a metal salt solution according to the stoichiometric ratio to obtain a positive electrode material precursor with a high manganese content, and then a positive electrode material with a high manganese content can be obtained. Increasing the manganese content in the ternary material will increase the electrochemically inert manganese ions in the system, which is beneficial to stabilize the layered structure of the material, thereby ensuring that the positive electrode material has a high energy density and a long cycle life.

[0042] Optionally, the chromium salt in step (1) is one of chromium sulfate, chromium nitrate and chromium halide. Chromium sulfate, chromium nitrate, and chromium halide such as chromium chloride, chromium bromide, etc. are all common forms of chromium salts and are easy to obtain.

[0043] Optionally, the process conditions of the coprecipitation reaction process in step (2) are as follows: in the reactor, the ammonia concentration is 4-12 g / L, the pH value of the solution is 10-12, the rotation speed of the reactor is 300-450 rpm, and the duration of the coprecipitation reaction is 20-50 h.

[0044] The concentration of ammonia water has a certain influence on the morphology and performance of the precursor. In the present invention, the ammonia concentration is preferably controlled at 9.5-11.5 g / L to obtain a precursor material with a smooth particle surface and good dispersion between particles.

[0045] The pH value of the solution can be adjusted and controlled by adding sodium hydroxide and ammonia water. The present invention uses a higher pH value to facilitate the formation of crystal nuclei and control the particles to be more round. The pH value can be further selected to be 10.7, 11.2 or 11.5.

[0046] The reaction kettle is used as an agitator, and the speed of the reaction kettle is set at 300-450 revolutions per minute, so that the materials in the kettle can be fully mixed and kept uniform, ensuring the safety and efficiency of the reaction process in the kettle. The reaction time of the coprecipitation reaction to prepare the precursor is relatively long, and the growth time of particles of different particle sizes of the product is different. The duration of the coprecipitation reaction of the present invention is 20-50 hours, and the final [Ni x Mn 1-x–y Cr y ](OH)2 precursor.

[0047] Optionally, the stoichiometric ratio of the precursor to the battery-grade lithium hydroxide in step (4) is 1:(1.05-1.1). Lithium hydroxide is one of the key raw materials for preparing positive electrode materials for batteries. The high quality, high purity and stable chemical properties of battery-grade lithium hydroxide are the guarantee of the preparation effect and safety of positive electrode materials. The chemical formula of the battery-grade lithium hydroxide of the present invention is LiOH·H2O.

[0048] Optionally, the oxygen atmosphere in step (4) refers to an oxygen-containing atmosphere, and the gas used may be a mixture of oxygen and nitrogen. Furthermore, the oxygen concentration of the oxygen-containing atmosphere is preferably not less than 95%.

[0049] Optionally, the high temperature sintering in step (4) adopts two-stage high temperature sintering, specifically, sintering at 500-600°C for 4-6h first, and then sintering at 800-900°C for 10-16h. During each stage of sintering, the temperature is controlled constant to reduce fluctuations, and the temperature adjustment process is also relatively stable to avoid affecting the control accuracy due to excessive temperature changes. In the two-stage sintering step of the present invention, the whole heating rate is 1-3°C / min, and further 2°C / min can be selected.

[0050] According to the positive electrode material of the present invention, by in-situ introducing chromium ions into the system structure of the cobalt-free high-nickel positive electrode material, based on the fact that the valence electrons of the chromium ions occupy a lower energy level, the electrochemical reaction potential of the high-nickel system can be effectively improved, thereby exerting more capacity under high voltage and significantly improving the energy density of the cobalt-free high-nickel positive electrode material.

[0051] The preparation method of the positive electrode material of the present invention and the obtained positive electrode material are described in conjunction with specific examples. The examples cited are only used to explain the present invention and are not used to limit the scope of the present invention.

[0052] Example 1

[0053] A method for preparing a positive electrode material is specifically prepared by the following steps:

[0054] (1) First, a mixed salt solution containing nickel sulfate, manganese sulfate and chromium nitrate is prepared, wherein the molar ratio of nickel ion, manganese ion and chromium ion is 80:19:1 (the sum of the concentrations of nickel ion, manganese ion and chromium ion in the mixed salt solution is 2 mol / L). Then, 40 L of the mixed salt solution is added to a nitrogen atmosphere reactor at a rate of 5 L / h, and a sodium hydroxide solution with a concentration of 4 mol / L and an ammonia solution with a concentration of 4 mol / L are added to the reactor for coprecipitation reaction to obtain a solid-liquid mixture. The ammonia concentration in the reactor is maintained at 7-8 g / L, the reaction time is 30 h, the pH of the solution is maintained at 11.2-12 during the reaction, and the speed of the agitator is 400 rpm. Then, the solid-liquid mixture is centrifuged, washed, dried, and sieved to remove iron in turn to obtain a chemical formula of [Ni 0.8 Mn 0.19 Cr 0.01 ](OH)2 precursor, the drying temperature is 140℃ and the drying time is 8h.

[0055] (2) Using a high energy mixer, [Ni 0.8 Mn 0.19 Cr 0.01 ](OH)2 precursor powder and battery-grade lithium hydroxide LiOH·H2O are fully mixed at a molar ratio of 1:1.07. Then, the mixture is placed in a tube furnace, heated to 600°C and sintered for 5 hours, and then heated to 820°C and sintered for another 12 hours. The heating rate is maintained at 2°C / min throughout the process, and the oxygen concentration in the tube furnace is maintained at ≥95%. The chemical formula is LiNi 0.8 Mn 0.19 Cr 0.01 O2 positive electrode material.

[0056] The above LiNi 80 Cr1Mn 19 The O2 positive electrode material, the conductive agent acetylene black (AB), and the binder polyvinylidene fluoride (PVDF) were mixed uniformly in a mass ratio of 8:1:1, and then N-methylpyrrolidone (NMP) was used as a solvent. The mixture was placed in a small beaker and stirred at a speed of 800r / min for 2h to obtain a black slurry; the slurry was then coated on the current collector aluminum foil using an automatic coating machine, placed flat on tempered glass and transferred to a vacuum drying oven at 85°C for drying for 4h; the punched sheets were taken out to prepare pole pieces with a diameter of 12mm and then dried in a vacuum drying oven at 105°C for 4h; the pole pieces were placed in a glove box filled with argon atmosphere with a water content and oxygen content both lower than 0.1ppm for 4h to reduce the moisture adsorbed by the pole pieces during the transfer process; finally, the CR2032 button batteries were assembled in the glove box. A circular lithium metal sheet with a diameter of 14 mm was used as the negative electrode, 1 mol / L LiPF6 (EC / DMC=1:1) was used as the electrolyte, and a polyolefin porous membrane with a diameter of 16 mm was used as the separator.

[0057] The precursor and cathode material obtained in this example were characterized and tested.

[0058] The SEM image of the precursor is as follows Figure 1 As shown, the precursor is a hydrangea-like structure with a diameter of 3-4 μm, which is conducive to realizing a conductive channel for rapid electron transfer and effective mass transfer.

[0059] SEM images of positive electrode materials are shown in Figure 2. Figure 2 As shown, the positive electrode material is a quasi-single crystal structure with a diameter of 2-4 μm.

[0060] Figure 3 The XRD analysis result of the positive electrode material shows that the positive electrode material of the present invention is a typical α-NaFeO2 phase layered structure. The α-NaFeO2 phase layered structure has high structural stability and chemical stability. The stability of this structure enables α-NaFeO2 to maintain structural integrity under high temperature and high pressure environments, so that it can be applied to energy conversion and storage devices under various extreme conditions. In lithium-ion batteries, α-NaFeO2, as a positive electrode material, realizes charge storage and release by embedding and de-embedding lithium ions. Compared with traditional lithium-ion batteries, α-NaFeO2 has higher specific capacity and longer cycle life, which can greatly improve the performance and service life of the battery.

[0061] The differential capacitance curve of the positive electrode material of this embodiment is as follows: Figure 4 As shown, the differential capacity curve (dQ / dV curve) of the charging process at 4.3V and 4.6V upper cut-off voltages, respectively, at a rate of 0.1C at 55°C. The dQ / dV curve is obtained by calculating the change in battery capacity within a constant voltage interval. For lithium battery positive electrode materials, it usually has one or more voltage platforms. This means that a smaller fluctuation in lithium battery voltage within the platform range corresponds to a larger capacity, which is displayed as a characteristic peak on the dQ / dV curve. The peak point represents the phase change point of the material, and the area enclosed by the curve and the horizontal axis represents the capacity charged or released during the phase change process. Figure 4 It can be seen that when the upper cutoff voltage is 4.6V, the charge and discharge capacity of the positive electrode material of this embodiment is higher than when the upper cutoff voltage is 4.3V.

[0062] The cycle performance of the positive electrode material of this embodiment under high temperature / high voltage conditions is as follows Figure 5 As shown in the figure, the discharge capacity curve is operated at 55℃ at 1C rate at 4.6V upper cut-off voltage. Figure 5It can be seen that the initial discharge specific capacity of the positive electrode material of the present invention is 195.1 mAh / g, and the discharge specific capacity is still 150 mAh / g after 200 cycles. The capacity retention rate after 200 cycles is 76.9%.

[0063] Combination Figure 4 As can be seen from Figure 5, the present invention significantly improves the reaction potential platform of the cobalt-free high-nickel material by in-situ introduction of heterogeneous Cr ions with low valence electron energy levels, and combines the construction of a single crystal structure to obtain higher energy density and cycle stability at high voltage.

[0064] Example 2

[0065] In combination with a specific example, a high voltage positive electrode material and a preparation method thereof of the present invention are described, which are specifically prepared by the following steps:

[0066] (1) First, a mixed salt solution containing nickel sulfate, manganese sulfate and chromium nitrate is prepared, wherein the molar ratio of nickel ion, manganese ion and chromium ion is 80:19:1 (the sum of the concentrations of nickel ion, manganese ion and chromium ion in the mixed salt solution is 2 mol / L). Then, 40 L of the mixed salt solution is added to a nitrogen atmosphere reactor at a rate of 2.5 L / h, and a sodium hydroxide solution with a concentration of 4 mol / L and an ammonia solution with a concentration of 4 mol / L are added to the reactor for coprecipitation reaction to obtain a solid-liquid mixture. The ammonia concentration in the reactor is maintained at 7-8 g / L, the reaction time is 30 h, the pH of the solution is maintained at 11.2-12 during the reaction, and the speed of the agitator is 400 rpm. Then, the solid-liquid mixture is centrifuged, washed, dried, and sieved to remove iron in turn to obtain a chemical formula of [Ni 0.8 Mn 0.19 Cr 0.01 ](OH)2 precursor, the drying temperature is 140℃ and the drying time is 8h.

[0067] (2) Using a high energy mixer, [Ni 0.8 Mn 0.19 Cr 0.01 ](OH)2 precursor powder and battery-grade lithium hydroxide LiOH·H2O are fully mixed at a molar ratio of 1:1.1. Then, the mixture is placed in a tube furnace, heated to 500°C and sintered for 4 hours, and then heated to 830°C and sintered for 11.5 hours. The heating rate is maintained at 2°C / min throughout the process, and the oxygen concentration in the tube furnace is maintained at ≥95%. The chemical formula is LiNi 0.8 Mn 0.19 Cr 0.01 O2 positive electrode material.

[0068] Example 3

[0069] In combination with a specific example, a high voltage positive electrode material and a preparation method thereof of the present invention are described, which are specifically prepared by the following steps:

[0070] (1) First, a mixed salt solution containing nickel sulfate, manganese sulfate and chromium nitrate is prepared, wherein the molar ratio of nickel ion, manganese ion and chromium ion is 80:19:1 (the sum of the concentrations of nickel ion, manganese ion and chromium ion in the mixed salt solution is 2 mol / L). Then, 40 L of the mixed salt solution is added to a nitrogen atmosphere reactor at a rate of 4 L / h, and a sodium hydroxide solution with a concentration of 4 mol / L and an ammonia solution with a concentration of 4 mol / L are added to the reactor for coprecipitation reaction to obtain a solid-liquid mixture. The ammonia concentration in the reactor is maintained at 7-8 g / L, the reaction time is 30 h, the pH of the solution is maintained at 11.2-12 during the reaction, and the speed of the agitator is 400 rpm. Then, the solid-liquid mixture is centrifuged, washed, dried, and sieved for iron removal in sequence to obtain a chemical formula of [Ni 0.8 Mn 0.19 Cr 0.01 ](OH)2 precursor, the drying temperature is 140℃ and the drying time is 8h.

[0071] (2) Using a high energy mixer, [Ni 0.8 Mn 0.19 Cr 0.01 ](OH)2 precursor powder and battery-grade lithium hydroxide LiOH·H2O were fully mixed at a molar ratio of 1:1.06. Then, the mixture was placed in a tube furnace, heated to 520°C and sintered for 4.5 hours, and then heated to 850°C and sintered for 11 hours. The heating rate was maintained at 1°C / min throughout the process, and the oxygen concentration in the tube furnace was maintained at ≥95%, and the chemical formula was obtained. 0.8 Mn 0.19 Cr 0.01 O2 positive electrode material.

[0072] Example 4

[0073] In combination with a specific example, a high voltage positive electrode material and a preparation method thereof of the present invention are described, which are specifically prepared by the following steps:

[0074] (1) First, a mixed salt solution containing nickel sulfate, manganese sulfate and chromium nitrate is prepared, wherein the molar ratio of nickel ion, manganese ion and chromium ion is 80:19.5:0.5 (the sum of the concentrations of nickel ion, manganese ion and chromium ion in the mixed salt solution is 2 mol / L). Then, 40 L of the mixed salt solution is added to a nitrogen atmosphere reactor at a rate of 5 L / h, and a sodium hydroxide solution with a concentration of 4 mol / L and an ammonia solution with a concentration of 4 mol / L are added to the reactor for coprecipitation reaction to obtain a solid-liquid mixture. The ammonia concentration in the reactor is maintained at 7-8 g / L, the reaction time is 30 h, the pH of the solution is maintained at 11.2-12 during the reaction, and the speed of the agitator is 400 rpm. Then, the solid-liquid mixture is centrifuged, washed, dried, and sieved for iron removal in sequence to obtain a chemical formula of [Ni 0.8 Mn 0.195 Cr 0.005 ](OH)2 precursor, the drying temperature is 140℃ and the drying time is 8h.

[0075] (2) Using a high energy mixer, [Ni 0.8 Mn 0.195 Cr 0.005 ](OH)2 precursor powder and battery-grade lithium hydroxide LiOH·H2O were fully mixed at a molar ratio of 1:1.07. Then, the mixture was placed in a tube furnace, heated to 540°C and sintered for 5.5 hours, and then heated to 860°C and sintered for 10.2 hours. The heating rate was maintained at 1°C / min throughout the process, and the oxygen concentration in the tube furnace was maintained at ≥95%. The chemical formula was LiNi 0.8 Mn 0.195 Cr 0.005 O2 positive electrode material.

[0076] Example 5

[0077] In combination with a specific example, a high voltage positive electrode material and a preparation method thereof of the present invention are described, which are specifically prepared by the following steps:

[0078] (1) First, a mixed salt solution containing nickel sulfate, manganese sulfate and chromium nitrate is prepared, wherein the molar ratio of nickel ion, manganese ion and chromium ion is 80:18:2 (the sum of the concentrations of nickel ion, manganese ion and chromium ion in the mixed salt solution is 2 mol / L). Then, 40 L of the mixed salt solution is added to a nitrogen atmosphere reactor at a rate of 5 L / h, and a sodium hydroxide solution with a concentration of 4 mol / L and an ammonia solution with a concentration of 4 mol / L are added to the reactor for coprecipitation reaction to obtain a solid-liquid mixture. The ammonia concentration in the reactor is maintained at 7-8 g / L, the reaction time is 30 h, the pH of the solution is maintained at 11.2-12 during the reaction, and the speed of the agitator is 400 rpm. Then, the solid-liquid mixture is centrifuged, washed, dried, and sieved for iron removal in sequence to obtain a chemical formula of [Ni 0.8 Mn 0.18 Cr 0.02 ](OH)2 precursor, the drying temperature is 140℃ and the drying time is 8h.

[0079] (2) Using a high energy mixer, [Ni 0.8 Mn 0.18 Cr 0.02 ](OH)2 precursor powder and battery-grade lithium hydroxide LiOH·H2O were fully mixed at a molar ratio of 1:1.08. Then, the mixture was placed in a tube furnace, heated to 560°C and sintered for 4.6 hours, and then heated to 810°C and sintered for 10 hours. The heating rate was maintained at 3°C / min throughout the process, and the oxygen concentration in the tube furnace was maintained at ≥95%. The chemical formula was LiNi 0.8 Mn 0.18 Cr 0.02 O2 positive electrode material.

[0080] Example 6

[0081] In combination with a specific example, a high voltage positive electrode material and a preparation method thereof of the present invention are described, which are specifically prepared by the following steps:

[0082] (1) First, a mixed salt solution containing nickel sulfate, manganese sulfate and chromium nitrate is prepared, wherein the molar ratio of nickel ion, manganese ion and chromium ion is 80:16:4 (the sum of the concentrations of nickel ion, manganese ion and chromium ion in the mixed salt solution is 2 mol / L). Then, 40 L of the mixed salt solution is added to a nitrogen atmosphere reactor at a rate of 4 L / h, and a sodium hydroxide solution with a concentration of 4 mol / L and an ammonia solution with a concentration of 4 mol / L are added to the reactor for coprecipitation reaction to obtain a solid-liquid mixture. The ammonia concentration in the reactor is maintained at 7-8 g / L, the reaction time is 30 h, the pH of the solution is maintained at 11.2-12 during the reaction, and the speed of the agitator is 400 rpm. Then, the solid-liquid mixture is centrifuged, washed, dried, and sieved for iron removal in sequence to obtain a chemical formula of [Ni0.8 Mn 0.16 Cr 0.04 ](OH)2 precursor, the drying temperature is 140℃ and the drying time is 8h.

[0083] (2) Using a high energy mixer, [Ni 0.8 Mn 0.16 Cr 0.04 ](OH)2 precursor powder and battery-grade lithium hydroxide LiOH·H2O are fully mixed at a molar ratio of 1:1.09. Then, the mixture is placed in a tube furnace, heated to 580°C and sintered for 6 hours, and then heated to 880°C and sintered for 15 hours. The heating rate is maintained at 2°C / min throughout the process, and the oxygen concentration in the tube furnace is maintained at ≥95%. The chemical formula is LiNi 0.8 Mn 0.16 Cr 0.04 O2 positive electrode material.

[0084] The process path and process parameters for preparing button-type batteries from positive electrode materials in Example 2-Example 6 are the same as those in Example 1. The battery materials and performances of Example 2-Example 6 are analyzed and tested using the same test conditions and test parameters as in Example 1. The process parameters and analysis and test results of each example are shown in Tables 1 and 2.

[0085] Comparative Example 1

[0086] (1) preparing a mixed salt solution containing nickel sulfate and manganese sulfate, wherein the molar ratio of nickel ion to manganese ion is 80:20 (the sum of the concentrations of nickel ion and manganese ion in the mixed salt solution is 2 mol / L); adding 40 L of the mixed salt solution to a nitrogen atmosphere reactor at a rate of 5 L / h, and simultaneously adding sodium hydroxide solution and ammonia solution to the reactor for coprecipitation reaction to obtain a solid-liquid mixture (the concentration of the sodium hydroxide solution is 4 mol / L, the concentration of the ammonia solution is 4 mol / L, the ammonia concentration in the reactor is maintained at 7-8 g / L, the pH of the reaction solution is maintained at 11.2-12, the reaction time is 30 h, and the stirrer speed is 400 rpm); then centrifuging the solid-liquid mixture, washing, drying, and sieving to remove iron, to obtain a solid-liquid mixture with a chemical formula of [Ni 0.8 Mn 0.2 ](OH)2 precursor (drying temperature is 140℃, drying time is 8h).

[0087] (2) [Ni 0.8 Mn 0.2](OH)2 precursor powder and battery-grade lithium hydroxide LiOH·H2O are fully mixed at a molar ratio of 1:1.07; the mixture is placed in a tube furnace, heated to 600°C and sintered for 5 hours, and then heated to 820°C and sintered for 12 hours. The heating rate is maintained at 2°C / min throughout the process, and the oxygen concentration in the tube furnace is maintained at ≥95%, thereby obtaining LiNi 0.8 Mn 0.2 O2 modified positive electrode material.

[0088] LiNi 0.8 Mn 0.2 The O2 material, the conductive agent acetylene black (AB), and the binder polyvinylidene fluoride (PVDF) were mixed evenly in a mass ratio of 8:1:1, and then N-methylpyrrolidone (NMP) was used as a solvent. The mixture was placed in a small beaker and stirred at a speed of 800r / min for 2h to obtain a black slurry; the slurry was then coated on the current collector aluminum foil using an automatic coating machine, placed flat on tempered glass and transferred to a vacuum drying oven at 85°C for drying for 4h; the punched sheets were taken out to prepare pole pieces with a diameter of 12mm and then dried in a vacuum drying oven at 105°C for 4h; the pole pieces were placed in a glove box filled with argon atmosphere with a water content and oxygen content both lower than 0.1ppm for 4h to reduce the moisture adsorbed by the pole pieces during the transfer process; finally, the CR2032 button batteries were assembled in the glove box. A circular lithium metal sheet with a diameter of 14 mm was used as the negative electrode, 1 mol / L LiPF6 (EC / DMC=1:1) was used as the electrolyte (lithium hexafluorophosphate electrolyte, LiPF6 was the lithium salt, EC and DMC were the solvent), and a polyolefin porous membrane with a diameter of 16 mm was used as the separator.

[0089] The positive electrode material obtained in this comparative example was characterized and tested, and the differential capacitance curve of the positive electrode material was as follows: Figure 4 As shown, the cycle performance of the positive electrode material under high temperature / high voltage conditions is as follows Figure 5 As shown, the initial discharge specific capacity is 196.6 mAh / g, the discharge specific capacity after 100 cycles is 107.7 mAh / g, and the capacity retention rate is 54.8%.

[0090] Effect comparison

[0091] The process parameter comparison table of Examples 1 to 6 and Comparative Example 1 is shown in Table 1.

[0092] Table 1

[0093]

[0094] The detection and analysis results of each embodiment are shown in Table 2.

[0095] Table 2

[0096]

[0097]

[0098] refer to Figure 4 , the voltage differential capacity curve comparison diagram of the positive electrode material prepared in Example 1 and the positive electrode material prepared in Comparative Example 1, the differential capacity curve (dQ / dV curve) of the charging process at an upper cut-off voltage of 4.3V and a rate of 0.1C at 55°C, it can be seen that compared with the positive electrode material prepared in Comparative Example 1, the positive electrode material prepared in Example 1 obviously has a larger charge and discharge capacity (the area enclosed by the curve and the horizontal axis).

[0099] Figure 4 The charge and discharge capacities of the positive electrode material battery prepared in Example 1 at an upper cutoff voltage of 4.3V and an upper cutoff voltage of 4.6V are also given. It can be seen that the positive electrode material battery of the present invention has a larger capacity at a higher voltage (4.6V).

[0100] refer to Figure 5 , the cycle performance comparison diagram of the positive electrode material of Example 1 and the material of Comparative Example 1 under high temperature / high voltage conditions shows that under high temperature / high voltage conditions, the initial discharge specific capacity of the positive electrode material prepared in Example 1 is equivalent to that of the positive electrode material prepared in Comparative Example 1, but the positive electrode material prepared in Example 1 has a more excellent subsequent cycle performance, and its capacity retention rate after 100 or even 200 cycles is higher. The excellent cycle performance of the positive electrode material battery of the present invention can be clearly seen from the performance data of each embodiment in Table 2. The initial discharge specific capacity of the positive electrode material of the present invention is 194-197 mAh / g, and the discharge specific capacity is still 145-155 mAh / g after 200 cycles. The capacity retention rate after 200 cycles is more than 76%. However, for the material battery of Comparative Example 1, the positive electrode material of the embodiment of the present invention has a considerable initial discharge specific capacity. After only 100 cycles, the discharge specific capacity is rapidly reduced to less than 100 mAh / g, and the capacity retention rate is less than 55%, which is much lower than the discharge specific capacity retention rate of the positive electrode material battery of the present invention after 200 cycles.

[0101] It can be seen that the present invention significantly improves the reaction potential platform of cobalt-free high-nickel materials by in-situ introduction of heterogeneous Cr ions with low-valence electron energy levels, and combines the construction of single crystal structure to obtain higher energy density and cycle stability at high voltage.

[0102] Although some specific embodiments of the present invention have been described in detail by way of example, it will be appreciated by those skilled in the art that the above examples are for illustration only and are not intended to limit the scope of the present invention. It will be appreciated by those skilled in the art that the above embodiments may be modified without departing from the scope and spirit of the present invention. The scope of the present invention is defined by the appended claims.

Claims

1. A positive electrode material, characterized in that: The chemical formula of the positive electrode material is Li[Ni x Mn 1-x–y Cr y O2, where, in terms of molar ratio, 0.8 ≤ x < 1.0, 0 < y ≤ 0.05, the positive electrode material is a quasi-single crystal structure, and the diameter of the positive electrode material is 2 - 4 μm.

2. The positive electrode material according to claim 1, characterized in that The chemical formula is Li[Ni 0.8 Mn 0.19 Cr 0.01 ]O2.

3. A method for preparing a positive electrode material, characterized in that: The preparation method comprises the following steps: (1) taking soluble nickel salt, manganese salt and chromium salt, adding deionized water, and stirring to form a mixed salt solution; (2) adding the mixed salt solution into a reactor in a nitrogen atmosphere at a rate of 2.5-5 L / h, adding a sodium hydroxide solution with a concentration of 2-4 mol / L as a precipitant, and adding an ammonia solution with a concentration of 1-4 mol / L as a complexing agent into the reactor to perform a coprecipitation reaction to obtain a solid-liquid mixture; (3) The solid-liquid mixture is centrifuged, washed, dried, and sieved to remove iron to obtain [Ni x Mn 1-x–y Cr y ](OH)2 precursor; (4) The precursor powder is fully mixed with battery-grade lithium hydroxide and placed in a tube furnace for high-temperature sintering in an oxygen atmosphere to obtain a positive electrode material Li[Ni x Mn 1-x–y Cr y ]O2.

4. The preparation method according to claim 3, characterized in that: The diameter of the precursor is 3-4 μm, and the diameter of the positive electrode material is 2-4 μm.

5. The preparation method according to claim 3, characterized in that: The soluble nickel salt, manganese salt and chromium salt described in step (1) have a stoichiometric ratio of nickel:manganese:chromium=80:19:

1.

6. The preparation method according to claim 3, characterized in that: The chromium salt in step (1) is one of chromium sulfate, chromium nitrate and chromium halide.

7. The preparation method according to claim 3, characterized in that: The process conditions of the coprecipitation reaction process in step (2) are as follows: in the reactor, the ammonia concentration is 4-12 g / L, the solution pH value is 10-12, the rotation speed of the reactor is 300-450 rpm, and the duration of the coprecipitation reaction is 20-50 h.

8. The preparation method according to claim 3, characterized in that: The stoichiometric ratio of the precursor to the battery-grade lithium hydroxide in step (4) is 1:(1.05-1.1).

9. The preparation method according to claim 3, characterized in that: The oxygen concentration in step (4) is not less than 95%.

10. The preparation method according to claim 3, characterized in that: The high temperature sintering in step (4) is first sintering at 500-600°C for 4-6h, and then sintering at 800-900°C for 10-16h, with a heating rate of 1-3°C / min throughout the process.

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