Positive electrode active material precursor and preparation method thereof, positive electrode active material and preparation method thereof, positive electrode and lithium ion secondary battery

Abstract

The present application relates to a positive electrode active material precursor, the general chemical molecular formula of which is Ni 0.5‑x Mn 1.5‑y‑s A s (PO4) z (B) u , wherein A is a non-lithium metal element and / or a metalloid element, and B is OH ‑ or CO3 2‑ , ‑0.2≤x≤0.2, ‑0.2≤y≤0.2, 0≤s≤0.1, 0.003≤z≤0.07 and 1.8≤u≤4.4, the P element in the positive active material precursor is unevenly distributed. The present application also relates to a method for preparing a positive active material precursor, by adding a water-soluble phosphate and a water-soluble nickel salt and a manganese salt into a reactor, controlling the reaction conditions, and co-precipitating phosphorus with nickel and manganese metal ions. Further, the present application also relates to a positive active material and a method for preparing the same.

Description

Technical Field

[0001] The present application relates to the field of lithium-ion batteries, and in particular to a positive electrode active material precursor and a preparation method thereof, a positive electrode active material and a preparation method thereof, a positive electrode of a lithium-ion secondary battery, and a lithium-ion secondary battery. Background Art

[0002] Compared with other rechargeable battery systems, lithium-ion secondary batteries have the advantages of high operating voltage, light weight, small size, no memory effect, low self-discharge rate, long cycle life, and high energy density. They are currently widely used in mobile terminal products such as mobile phones, laptops, and tablet computers. In recent years, due to environmental protection considerations, electric vehicles have been rapidly developed under the promotion of governments and automobile manufacturers, and lithium-ion secondary batteries have become the ideal power source for the new generation of electric vehicles with their excellent performance. At present, the positive active materials of lithium-ion secondary batteries that people are concerned about can be roughly divided into three categories: layered materials represented by lithium cobalt oxide (LiCoO2), olivine materials represented by lithium iron phosphate (LiFePO4), and spinel structure materials represented by lithium manganese oxide (LiMn2O4). Among these materials, spinel structure materials are widely studied because of their advantages such as environmentally friendly raw materials, low cost, simple process, high safety and good rate capability.

[0003] Spinel high-voltage materials are considered to be the most likely cathode active materials for the next generation of high-performance lithium batteries as an advanced cathode active material. In particular, the theoretical specific capacity of spinel-structured lithium nickel manganese oxide is 146.7 mAh / g and the operating voltage is 4.7 V vs. Li / Li. + The theoretical capacity density can reach 695Wh / kg, making it an ideal material for lithium-ion secondary batteries for future electric vehicles.

[0004] During the cycle of high-voltage spinel positive electrode active materials, due to the interaction between traditional carbonate electrolytes and positive electrode active materials, the positive electrode active material surface loses oxygen, which in turn dissolves the surface structure of the material. At the same time, the surface defects will gradually extend to the bulk phase, causing particle rupture, and ultimately leading to a rapid decline in battery performance. In order to solve this technical problem, people have proposed to modify the positive electrode active materials by element doping. The doped elements can form new chemical bonds inside and on the surface of the material to stabilize the lattice oxygen in the bulk phase and on the surface, and solve the stability problem of the interface and bulk phase of the positive electrode active material. For example, the positive electrode active material is modified by doping with phosphorus. The traditional phosphorus modification method is to mix the nickel-manganese precursor synthesized by the coprecipitation method with the phosphorus source and the lithium source, and sinter at high temperature. It is difficult for phosphorus to modify the nickel-manganese oxide lithium positive electrode material very uniformly. The traditional method cannot achieve precise control of the doping of phosphorus in specific areas, and has great limitations. Summary of the invention

[0005] Based on this, it is necessary to provide a positive electrode active material precursor and a preparation method thereof, a positive electrode active material and a preparation method thereof, a positive electrode of a lithium ion secondary battery and a lithium ion secondary battery.

[0006] The present application provides a positive electrode active material precursor, whose chemical molecular formula is Ni 0.5-x Mn 1.5-y-s A s (PO4) z (B) u , wherein A is a non-lithium metal element, a metalloid element, or a combination of a non-lithium metal element and a metalloid element, and B is OH - or CO3 2- , -0.2≤x≤0.2, -0.2≤y≤0.2, 0≤s≤0.1, 0.003≤z≤0.07 and 1.8≤u≤4.4, the P element in the positive electrode active material precursor is unevenly distributed.

[0007] In some embodiments, the P element in the positive electrode active material precursor is unevenly distributed along the radial direction of particles of the positive electrode active material precursor.

[0008] In some embodiments, the positive electrode active material precursor has a chemical molecular formula of Ni 0.5-x Mn 1.5-y- s A s (PO4) z (B) u , wherein A is a non-lithium metal element, a metalloid element, or a combination of a non-lithium metal element and a metalloid element, and B is OH - , −0.2≤x≤0.2, −0.2≤y≤0.2, 0≤s≤0.1, 0.003≤z≤0.07 and 3.6≤u≤4.4.

[0009] In some embodiments, the positive electrode active material precursor has a chemical molecular formula of Ni 0.5-x Mn 1.5-y- s A s (PO4) z (B) u , wherein A is a non-lithium metal element, a metalloid element, or a combination of a non-lithium metal element and a metalloid element, and B is CO3 2- , −0.2≤x≤0.2, −0.2≤y≤0.2, 0≤s≤0.1, 0.003≤z≤0.07 and 1.8≤u≤2.2.

[0010] In some embodiments, in the radial direction of the particles of the positive electrode active material precursor, there is at least one region in which the content of the P element decreases or increases gradually from the center to the outer surface of the particles of the positive electrode active material precursor.

[0011] In some embodiments, in the radial direction of the particles of the positive electrode active material precursor, there are at least two different regions with a P element concentration difference exceeding 10%.

[0012] In some embodiments, in different regions where the P element concentration difference exceeds 10%, the ratio of the distribution length of each region in the radial direction of the positive electrode active material precursor particle to the total radial length of the positive electrode active material precursor particle is 0.001-1.

[0013] In some embodiments, in the positive electrode active material precursor, s is 0, and the molar ratio of the elements Ni, Mn and P is 1:(2.5-3.5):(0.006-0.2).

[0014] In some embodiments, the non-lithium metal element is selected from at least one of alkaline earth metal elements, metalloid elements, transition metal elements and Al.

[0015] In some embodiments, A is selected from at least one of Al, Mg, Zn, Fe, Co, Ti, Y, Sc, Ru, Cu, Mo, Ge, W, Zr, Ca, Nb, Ta, Ni, Mn, and Sr.

[0016] In some embodiments, A is selected from at least one of Y, W, Ti, Mg, Cu, Ca, and Al.

[0017] In some embodiments, in the positive electrode active material precursor, the molar ratio of the elements Ni, Mn, A and P is 1: (2.5-3.5): (0.2-0.001): (0.006-0.2).

[0018] In some embodiments, the particle size of the positive electrode active material precursor particles is 0.1-30 microns.

[0019] The present application further provides a method for preparing a positive electrode active material precursor, comprising the following steps:

[0020] Providing an aqueous solution of a complexing agent and an aqueous solution of an alkaline precipitating agent, and configuring part of the aqueous solution of the complexing agent and part of the aqueous solution of the alkaline precipitating agent into a reaction kettle bottom liquid;

[0021] Mixing a water-soluble nickel salt, a water-soluble manganese salt and water to form a mixed solution; the mixed solution optionally further contains at least one water-soluble non-lithium metal salt, at least one water-soluble metalloid element salt, or a combination of at least one water-soluble non-lithium metal salt and at least one water-soluble metalloid element salt;

[0022] Under the protection of inert gas, the mixed solution and the water-soluble phosphate solution are respectively added to the reactor containing the reactor bottom liquid, and the feeding speed and / or concentration of the mixed solution and the water-soluble phosphate solution are controlled so that the concentration and / or feeding speed of the water-soluble phosphate solution changes with time, and a coprecipitation reaction is carried out under stirring, and at the same time, the remaining amount of the aqueous solution of the complexing agent and the remaining amount of the aqueous solution of the alkaline precipitant are also added, and the pH of the reaction system and the concentration of the complexing agent are controlled by controlling the feeding amount of the aqueous solution of the complexing agent and the feeding amount of the aqueous solution of the alkaline precipitant, and the reaction is terminated to obtain a mixed slurry; and

[0023] The mixed slurry is aged, centrifuged, washed and dried to obtain a positive electrode active material precursor with specific phosphorus doping distribution.

[0024] In some embodiments, the non-lithium metal salt is any one or more of a sulfate, chloride, and nitrate of any one of the metal elements Al, Mg, Zn, Fe, Co, Ti, Y, Sc, Ru, Cu, Mo, W, Zr, Ca, Nb, Ta, and Sr.

[0025] In some embodiments, the metalloid salt is any one or more of a sulfate, a chloride, and a nitrate of Ge.

[0026] In some embodiments, the phosphate ion concentration in the water-soluble phosphate solution is 0.0025 mol / L to 0.3 mol / L, and the water-soluble phosphate is at least one of sodium phosphate, potassium phosphate, ammonium phosphate, sodium dihydrogen phosphate, lithium dihydrogen phosphate, ammonium monohydrogen phosphate, and ammonium dihydrogen phosphate.

[0027] In some embodiments, the complexing agent is at least one of hydrazine hydrate, crown ether, ammonia water, oxalic acid, ammonium bicarbonate, ethylenediamine, and ethylenediaminetetraacetic acid, and the molar concentration of the complexing agent is 2 mol / L to 8 mol / L.

[0028] In some embodiments, the precipitant is at least one of NaOH, KOH, Ba(OH)2, Na2CO3, Li2CO3, K2CO3 or LiOH, and the molar concentration of the precipitant is 2 mol / L to 6 mol / L.

[0029] In some embodiments, the pH of the reaction kettle bottom liquid is 10-12.5, and the concentration of the complexing agent in the reaction kettle bottom liquid is 15 g / L-20 g / L.

[0030] In some embodiments, the pH of the reactor bottom liquid is 12 to 12.5.

[0031] In some embodiments, the reaction temperature of the coprecipitation reaction is 40°C to 70°C, the pH of the reaction system is 10 to 12.5, the concentration of the complexing agent is 15 g / L to 25 g / L, the stirring speed is 200 rpm to 250 rpm, and the reaction time is 5 h to 120 h.

[0032] In some embodiments, the pH of the reaction system is 11.5-12.

[0033] In some embodiments, the total molar concentration of metal ions in the mixed solution is 1 mol / L to 3 mol / L, the water-soluble nickel salt is at least one of nickel sulfate, nickel chloride, and nickel nitrate, and the water-soluble manganese salt is at least one of manganese sulfate, manganese chloride, and manganese nitrate.

[0034] In some embodiments, the feed rate of the mixed solution and the water-soluble phosphate is 0.1L / h to 100L / h, the feed rate of the aqueous solution of the complexing agent is 0.1L / h to 100L / h, and the feed rate of the aqueous solution of the alkaline precipitant is 0.1L / h to 100L / h.

[0035] In some embodiments, the feed concentration or rate of the aqueous phosphate solution may be increased or decreased over time.

[0036] The present application further provides a positive electrode active material prepared from the positive electrode active material precursor or the positive electrode active material precursor obtained by the method for preparing the positive electrode active material precursor.

[0037] The present application further provides a method for preparing a positive electrode active material, comprising the following steps:

[0038] Mixing the positive electrode active material precursor or the positive electrode active material precursor obtained by the method for preparing the positive electrode active material precursor with a lithium source;

[0039] In an oxygen-containing atmosphere, sinter at 600°C to 1200°C for 5 to 10 hours.

[0040] The present application further provides a positive electrode of a lithium ion secondary battery, comprising a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode active material described above.

[0041] The present application further provides a lithium-ion secondary battery, characterized in that it comprises the above-mentioned positive electrode, negative electrode, separator and electrolyte, wherein the negative electrode comprises a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0042] The positive electrode active material precursor and its preparation method, as well as the positive electrode active material and its preparation method provided by the present application, maintain the original properties of the nickel-manganese precursor and do not affect the element ratio, so that the phosphorus element reaches a controllable distribution state inside the precursor. This controllability can be controllable at the nanoscale. The use of the precursor with this composition structure solves the problem of difficult controllable regional doping of phosphorus while doping lithium using the high-temperature solid-phase method in the later traditional method. By improving the performance of the positive electrode active material precursor, a positive electrode active material and a lithium-ion battery with superior performance are prepared. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 The laser ion beam cutting image of the gradient phosphorus-doped positive electrode active material precursor prepared in Example 7 is shown.

[0044] Figure 2 A schematic diagram showing a line scan of the radial region of the gradient phosphorus-doped positive electrode active material precursor prepared in Example 7 is shown. DETAILED DESCRIPTION

[0045] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present application are given in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present application belongs. The terms used herein in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0047] Except as shown in the operating examples or otherwise indicated, all numbers used in the specification and claims to indicate the amount of ingredients, physicochemical properties, etc. are understood to be adjusted by the term "about" in all cases. For example, therefore, unless otherwise indicated, the numerical parameters listed in the above specification and the attached claims are approximate values, and those skilled in the art can use the teachings disclosed herein to seek to obtain the desired properties and appropriately change these approximate values. The use of numerical ranges expressed as endpoints includes all numbers within the range and any range within the range, for example, 1 to 5 includes 1, 1.1, 1.3, 1.5, 2, 2.75, 3, 3.80, 4 and 5, etc.

[0048] The present invention provides a positive electrode active material precursor, the chemical molecular formula of which is Ni 0.5-x Mn 1.5-y-s A s (PO4) z (B) u , wherein A is a non-lithium metal element and / or a metalloid element, and B is OH - or CO3 2- , -0.2≤x≤0.2, -0.2≤y≤0.2, 0≤s≤0.1, 0.003≤z≤0.07 and 1.8≤u≤4.4. The P element in the positive electrode active material precursor is non-uniformly distributed in a specific area.

[0049] The positive electrode active material precursor provided in the embodiment of the present application has a specific distribution of phosphorus elements inside the precursor at the atomic and molecular scales, and the precursor maintains the properties and element ratios of the traditional nickel-manganese precursor. The precursor with this composition structure solves the problem that it is difficult to accurately control the doping of phosphorus elements when doping lithium with phosphorus using the high-temperature solid-phase method in the later traditional method. Specifically, phosphorus doping in the later stage will face three major problems. First, lithium salts will react with phosphorus sources to generate substances such as lithium phosphate, which will affect the activity of lithium salts during the entire sintering process; secondly, phosphorus elements diffuse very slowly in lithium nickel manganese oxide materials, and it is difficult to achieve uniform distribution of phosphorus elements on the surface of the synthesized lithium nickel manganese oxide material after the final sintering by simple mixing between solid particles; the last point is that when the particle size distribution range of the precursor is large, this completely outside-to-inside doping will inevitably lead to uneven distribution of phosphorus elements between different particles. The embodiments of the present application have achieved precise control of the final synthesized lithium nickel manganese oxide positive electrode material by precisely controlling the phosphorus content and distribution in the lithium nickel manganese oxide positive electrode material precursor, thereby ultimately improving the performance of the positive electrode active material precursor and preparing positive electrode active materials and lithium ion batteries with superior performance.

[0050] In some embodiments, the P element in the positive electrode active material precursor is unevenly distributed in the radial direction of particles of the positive electrode active material precursor.

[0051] In some embodiments, in at least a portion of the radial direction of the particles of the positive electrode active material precursor, the content of the P element decreases or increases gradually from the center to the outer surface of the particles of the positive electrode active material precursor, or first decreases and then increases, or first increases and then decreases.

[0052] In some embodiments, in the radial direction of the particles of the positive electrode active material precursor, there are at least two different regions with a P element concentration difference exceeding 10%.

[0053] In some embodiments, in different regions where the difference in P element concentration exceeds 10%, the ratio of the distribution length of each region in the radial direction of the positive electrode active material precursor particle to the total radial length of the positive electrode active material is 0.001-1.

[0054] In some embodiments, s is 0, and the chemical molecular formula of the positive electrode active material precursor is Ni 0.5-x Mn 1.5-y (PO4) z (B) u , wherein A is a non-lithium metal element and / or a metalloid element, and B is OH - or CO3 2- , where −0.2≤x≤0.2, −0.2≤y≤0.2, 0.005≤z≤0.05 and 1.8≤u≤4.4.

[0055] Optionally, in the above-mentioned positive electrode active material precursor, the molar ratio of the elements Ni, Mn and P can be any ratio between 1: (2.5-3.5): (0.006-0.2).

[0056] In other embodiments, s is not 0, and the non-lithium metal element A is selected from at least one of alkaline earth metal elements, transition metal elements and Al.

[0057] Optionally, A is selected from at least one of Al, Mg, Zn, Fe, Co, Ti, Y, Sc, Ru, Cu, Mo, Ge, W, Zr, Ca, Nb, Ta, Sr, B, and Si. In some embodiments, A is selected from at least one of Y, W, Ti, Mg, Cu, Ca, and Al.

[0058] Furthermore, in the above-mentioned cathode active material precursor, the molar ratio of the elements Ni, Mn, A and P can be any ratio between 1: (2.5-3.5): (0.2-0.001): (0.006-0.2).

[0059] The present application also provides a method for preparing a positive electrode active material precursor, comprising the following steps:

[0060] Step a, providing an aqueous solution X of a complexing agent and an aqueous solution Y of an alkaline precipitant, and configuring part of the aqueous solution X of the complexing agent and part of the aqueous solution Y of the alkaline precipitant to form a reaction kettle bottom liquid;

[0061] Step b, mixing a water-soluble nickel salt, a water-soluble manganese salt and water to form a mixed solution; the mixed solution optionally further contains at least one water-soluble non-lithium metal salt and / or metalloid element salt;

[0062] Step c, under the protection of inert gas, respectively adding the mixed solution and the water-soluble phosphate solution into the reactor containing the reactor bottom liquid, and controlling the feeding speed and / or concentration of the mixed solution and the water-soluble phosphate solution, and performing a coprecipitation reaction under stirring, and simultaneously adding the remaining amount of the complexing agent aqueous solution X and the remaining amount of the alkaline precipitant aqueous solution Y, and controlling the pH of the reaction system and the concentration of the complexing agent by controlling the feeding amount of X and Y, and completing the reaction to obtain a mixed slurry;

[0063] Step d: the mixed slurry is aged, centrifuged, washed and dried to obtain a positive electrode active material precursor uniformly doped with phosphorus.

[0064] In some embodiments, in the process of adding the mixed solution and the water-soluble phosphate solution to the reactor, the mixed solution and the water-soluble phosphate solution are added to the reactor according to the time and concentration set in advance, and / or the feeding rate and / or concentration of the water-soluble phosphate solution changes with time, and the feeding rate of the mixed solution remains constant, or also changes with time. The preparation method of the positive electrode active material precursor provided in the present application adopts a co-precipitation method to uniformly precipitate the three elements of nickel, manganese and phosphorus in the form of nickel hydroxide, manganese hydroxide and phosphate at the same time or unevenly precipitate with a specific element distribution to form a positive electrode active material precursor. The phosphorus element is unevenly distributed in the positive electrode active material precursor in a specific way inside the positive electrode active material precursor.

[0065] The preparation principle of the positive electrode active material precursor of the present application is: water-soluble phosphate, water-soluble nickel salt, and water-soluble manganese salt are added to the reactor, and the reaction conditions are controlled to achieve co-precipitation of phosphorus with nickel and manganese metal ions. The water-soluble phosphate provides phosphate radicals and nickel and manganese ions to produce precipitation. The reaction conditions must be strictly controlled during the preparation process, and the positive electrode active material precursor is obtained through reaction, aging, centrifugation, washing, and drying.

[0066] In some embodiments, the non-lithium metal salt may be a water-soluble sulfate, chloride or nitrate of any one of alkaline earth metal elements, transition metal elements and Al. Optionally, the non-lithium metal salt is any one or more of a water-soluble sulfate, chloride and nitrate of at least one of Al, Mg, Zn, Fe, Co, Ti, Y, Sc, Ru, Cu, Mo, Ge, W, Zr, Ca, Nb, Ta, Sr, B and Si. In some embodiments, the non-lithium metal salt is any one or more of a water-soluble sulfate, chloride and nitrate of any one of Y, W, Ti, Mg, Cu, Ca and Al.

[0067] In some embodiments, the metalloid salt is any one or more of a sulfate, a chloride, and a nitrate of Ge.

[0068] The complexing agent can be at least one of hydrazine hydrate, crown ether, ammonia water, oxalic acid, ammonium bicarbonate, ethylenediamine, and ethylenediaminetetraacetic acid, and in some embodiments, ammonia water. The molar concentration of the complexing agent in the aqueous solution X of the complexing agent can be any value between 2mol / L and 8mol / L, for example, 3mol / L, 4mol / L, 5mol / L, 6mol / L, 7mol / L, and 7.5mol / L.

[0069] The precipitant may be at least one of NaOH, KOH, Ba(OH)2, Na2CO3, Li2CO3, K2CO3 or LiOH. NaOH may be selected.

[0070] The molar concentration of the precipitant in the aqueous solution Y of the alkaline precipitant can be any value between 2 mol / L and 6 mol / L, for example, it can also be 2.5 mol / L, 3 mol / L, 3.2 mol / L, 3.5 mol / L, 3.8 mol / L, 4 mol / L, 4.2 mol / L, 4.5 mol / L, 4.8 mol / L, 5 mol / L, 5.5 mol / L.

[0071] The pH of the reactor bottom liquid may be any value between 10 and 12.5, and in some embodiments, it is between 12 and 12.5.

[0072] The concentration of the complexing agent in the reactor bottom liquid can be any value between 15 g / L and 20 g / L, for example, it can also be 16 g / L, 17 g / L, 18 g / L, or 19 g / L.

[0073] The water-soluble nickel salt may be at least one of nickel sulfate, nickel chloride, and nickel nitrate.

[0074] The water-soluble manganese salt may be at least one of manganese sulfate, manganese chloride and manganese nitrate.

[0075] The water-soluble phosphate may be at least one of sodium phosphate, sodium monohydrogen phosphate, potassium dihydrogen phosphate, diammonium hydrogen phosphate, potassium phosphate, ammonium phosphate, sodium dihydrogen phosphate, lithium dihydrogen phosphate, ammonium monohydrogen phosphate, phosphoric acid, and ammonium dihydrogen phosphate.

[0076] The total molar concentration of metal ions in the mixed solution is 1 mol / L to 3 mol / L.

[0077] The phosphate ion concentration in the water-soluble phosphate solution is 0.0025 mol / L to 0.3 mol / L.

[0078] In step c, the feeding rate of the mixed solution and the water-soluble phosphate is 0.1mL / h to 100mL / h, the feeding rate of the aqueous solution X of the complexing agent is 0.1mL / h to -100mL / h, and the feeding rate of the aqueous solution Y of the alkaline precipitant is 0.1mL / h to 100mL / h.

[0079] During the coprecipitation reaction, the reaction temperature can be 40°C to 70°C, the pH of the reaction system is controlled to be 10 to 12.5, and in some embodiments, 11.5 to 12, the concentration of the complexing agent is controlled to be 15 g / L to 25 g / L, the stirring speed can be 200 rpm to 250 rpm, and the reaction time can be 80 h to 120 h.

[0080] In some embodiments, the feed rate or concentration of the water-soluble phosphate increases over time or decreases over time.

[0081] Furthermore, during the coprecipitation reaction, the pH of the reaction system can be controlled to be 12.

[0082] The inert gas may be nitrogen.

[0083] In step d, the aging time of the mixed slurry can be 20 hours to 24 hours, and the aging temperature can be 15° C. to 80° C.

[0084] The present application further provides a positive electrode active material prepared from the positive electrode active material precursor or the positive electrode active material precursor obtained by the preparation method of the positive electrode active material precursor.

[0085] The positive electrode active material precursor and its preparation method provided by the present application maintain the original properties of the lithium nickel manganese oxide precursor, and can make the phosphorus element distributed in a specific form through regulation, and unevenly distributed in the positive electrode active material precursor. This specific distribution form will help to further regulate the distribution of phosphorus elements in the bulk and surface of the final synthesized lithium nickel manganese oxide material under the premise of realizing the comprehensive modification of the lithium nickel manganese oxide material by phosphorus elements, and at the same time, it can also adjust the morphology of the synthesized lithium nickel manganese oxide material. For example, when the phosphorus content of the lithium nickel manganese oxide precursor gradually increases from the inside to the surface, in the process of sintering lithium nickel manganese oxide using the precursor, the high content of phosphorus on the surface of the precursor will inhibit the mutual fusion process of the lithium nickel manganese oxide precursor during the sintering process, and the final synthesized lithium nickel manganese oxide material has a smaller particle size and a more uniform particle size distribution. In the cycle process, such a material has a smaller particle size and a narrower particle size distribution, so the polarization of the battery is smaller and the rate performance is better. For another example, when the phosphorus content of the lithium nickel manganese oxide precursor gradually decreases from the surface of the lithium nickel manganese oxide precursor to the inside, in the process of synthesizing the lithium nickel manganese oxide material, the less phosphorus content on the surface of the precursor is more conducive to the fusion, absorption and growth between the lithium nickel manganese oxide precursors. In this way, the final synthesized lithium nickel manganese oxide material can obtain a larger material particle size and a better distribution of large and small particles on the basis of phosphorus doping, thereby obtaining a lithium nickel manganese oxide material with a higher tap density, thereby improving the volume energy density of the final lithium nickel manganese oxide battery product. In summary, we will find that by adjusting the distribution form of phosphorus in the positive electrode active material precursor, we can flexibly control the physical and electrochemical properties of the positive electrode active material obtained after the final sintering, and obtain a comprehensive performance far higher than that of the lithium nickel manganese oxide material uniformly doped with phosphorus.

[0086] In the present application, phosphorus doping of the lithium nickel manganese oxide precursor is a more flexible doping method. In particular, phosphorus doping of the precursor is selected in the process of synthesizing the lithium nickel manganese oxide precursor by coprecipitation. In this process, by adjusting the phosphorus content and addition speed and other conditions, the distribution of phosphorus in the lithium nickel manganese oxide precursor can be well and accurately regulated to obtain excellent battery performance in all aspects. Due to the complexity of the battery, it is usually difficult to take into account the comprehensive indicators of the high and low temperature cycle, mass energy density, volume energy density, rate performance, etc. of the battery. However, through a series of systematic studies, the inventor first found that uneven phosphorus doping in the precursor can ultimately greatly improve the comprehensive performance of the synthesized lithium nickel manganese oxide material, and design a lithium nickel manganese oxide material with excellent specific performance. Further, by adjusting the distribution of phosphorus content in the lithium nickel manganese oxide material, it is possible to achieve the regulation of some physical properties of the lithium nickel manganese oxide material itself, such as particle size, particle size distribution, and the overall phosphorus distribution of the final synthesized lithium nickel manganese oxide material. These all utilize the different characteristics brought about by the distribution of phosphorus in the lithium nickel manganese oxide precursor and in the final lithium nickel manganese oxide material to stabilize the surface of the lithium nickel manganese oxide material, making it reach the state of commercial application.

[0087] Specifically, for the precursor of the positive electrode material of lithium nickel manganese oxide, within a certain range of phosphorus content and sintering conditions, the higher the surface phosphorus distribution, the less conducive it is to the final synthesis of large-particle lithium nickel manganese oxide materials; the narrower the particle size distribution of lithium nickel manganese oxide, the more stable the surface of the final synthesized lithium nickel manganese oxide material. Therefore, when a lithium nickel manganese oxide material precursor with a small particle size but a more stable surface and a narrower particle size distribution is needed, it is most appropriate to synthesize a lithium nickel manganese oxide positive electrode precursor with a higher surface phosphorus distribution. Compared with the lithium nickel manganese oxide precursor with uniform phosphorus distribution, this type of precursor can save costs well, and finally synthesize a lithium nickel manganese oxide positive electrode material that meets the requirements with the same content of phosphorus source. On the other hand, the lower the surface phosphorus distribution, the more conducive it is to the final synthesis of large-particle lithium nickel manganese oxide materials, the more small-particle lithium nickel manganese oxide, and the greater the tap density of the final synthesized lithium nickel manganese oxide material. In fact, the radially uneven distribution of phosphorus in the lithium nickel manganese oxide precursor brings about rich and diverse adjustments to the properties of the final synthesized lithium nickel manganese oxide material. People have not noticed this in the past. The inventors have studied the properties of the interaction between phosphorus and the lithium nickel manganese oxide precursor through a large number of experiments. For the first time, they discovered that this property can ultimately affect the synthesized lithium nickel manganese oxide material. At the same time, this method has also been used to synthesize a variety of lithium nickel manganese oxide positive electrode materials with different properties. Each material has its own unique advantages. The phosphorus doping of the lithium nickel manganese oxide positive electrode precursor achieved by the method provided in the present application is simple, ingenious and practical.

[0088] The present application provides a method for preparing a positive electrode active material precursor, wherein phosphorus elements are distributed in a specific and uneven manner to form a positive electrode active material precursor. It should be particularly emphasized that the positive electrode active material precursor of the present application has a general chemical molecular formula of Ni 0.5-x Mn 1.5-y-s A s (PO4) z (B) u The distribution of manganese, nickel and element A in the positive electrode active material precursor is not restricted in the molecule. The nickel, manganese and element A in the molecular formula can be evenly distributed or unevenly distributed, for example, with a gradient increasing or decreasing distribution from the center of the precursor particle to the outer surface.

[0089] The gradient increase or decrease mentioned in this application refers to the tendency of the phosphorus content in a certain part of the precursor radial direction to increase or decrease, and this tendency of increase or decrease does not need to have a fixed slope. The characteristics of the synthetic material of this application can be detected by the most commonly used methods in the industry, such as cutting the synthetic material by methods such as focused laser ion beam, and determining the increasing or decreasing distribution of phosphorus or the ratio of phosphorus content in different regions by various electron microscope line scans. In addition, other methods reported in the industry and literature can also be used for discrimination.

[0090] In the present application, water-soluble phosphate and water-soluble nickel salt and manganese salt are added to a reactor, and the reaction conditions are controlled to achieve co-precipitation of phosphorus and nickel and manganese metal ions. The water-soluble phosphate provides phosphate radicals and nickel and manganese ions to produce precipitation.

[0091] The present application further provides a method for preparing the positive electrode active material, comprising the following steps:

[0092] Mixing the positive electrode active material precursor or the positive electrode active material precursor obtained by the method for preparing the positive electrode active material precursor with a lithium source;

[0093] In an oxygen-containing atmosphere, sinter at 600°C to 1200°C for 5 to 10 hours.

[0094] The lithium source is lithium carbonate or lithium hydroxide, and in some embodiments, is lithium carbonate.

[0095] The sintering can be carried out in an oxygen atmosphere such as oxygen or air. Optionally, the specific operation of the sintering process is: heating to 600°C to 1200°C at a heating rate of 0.5 to 10°C / min, then sintering for 0.5 to 10 hours, and then cooling to room temperature at a cooling rate of 0.5 to 10°C / min.

[0096] The above-mentioned positive electrode active material precursor contains phosphorus. The positive electrode active material precursor contained in this application can be cut by laser ion beam cutting, and the content and distribution of phosphorus in the positive electrode active material can be characterized by SEM mapping, TEM-mapping, ion beam etching combined with XPS photoelectron imaging or secondary ion mass spectrometry, so as to further determine the characteristics of the positive electrode active material precursor contained in this patent.

[0097] The present application also provides a positive electrode of a lithium-ion secondary battery, comprising a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode active material mentioned above.

[0098] The positive electrode current collector may be a conductive element formed of a highly conductive metal used in the positive electrode of a lithium ion secondary battery of the related art. For example, the positive electrode current collector may use aluminum or an alloy including aluminum as a main component. The shape of the positive electrode current collector is not particularly limited and may vary depending on the shape of the lithium ion secondary battery, etc. For example, the positive electrode current collector may have various shapes, such as a rod shape, a plate shape, a sheet shape, and a foil shape.

[0099] The positive electrode active material layer further includes a conductive additive and a binder.

[0100] The conductive additive may be a conventional conductive additive in the art, and the present application has no particular limitation thereto. In some embodiments, the conductive additive is carbon black (eg, acetylene black or Ketjen black).

[0101] The adhesive may be a conventional adhesive in the art, and the present application has no particular limitation thereto, and may be composed of polyvinylidene fluoride (PVDF), or may be composed of carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR). In some embodiments, the adhesive is polyvinylidene fluoride (PVDF).

[0102] The present application also provides a lithium-ion secondary battery, comprising:

[0103] A positive electrode as described above;

[0104] A negative electrode, comprising a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector;

[0105] Diaphragm and electrolyte.

[0106] As the negative electrode current collector,

[0107] The negative electrode, separator and electrolyte may adopt conventional negative electrode current collector, separator and electrolyte materials in the art, and the present application has no particular limitation on them.

[0108] The negative electrode current collector may be copper, and the shape of the negative electrode current collector is also not particularly limited, and may be rod-shaped, plate-shaped, sheet-shaped, and foil-shaped, and may vary depending on the shape of the lithium-ion secondary battery. The negative electrode active material layer includes a negative electrode active material, a conductive additive, and a binder. The negative electrode active material, the conductive additive, and the binder are also conventional materials in the art. In some embodiments, the negative electrode active material is metallic lithium. The conductive additive and the binder are as described above and will not be repeated here.

[0109] The separator can be selected from separators commonly used in lithium-ion secondary batteries, including microporous membranes made of polyethylene and polypropylene; multilayer membranes of porous polyethylene and polypropylene; non-woven fabrics formed of polyester fibers, aramid fibers, glass fibers, etc.; and base membranes formed by ceramic particles such as silicon dioxide, aluminum oxide, and titanium dioxide attached to their surfaces, etc. In some embodiments, the separator is a three-layer membrane of PP / PE / PP coated with aluminum oxide on both sides.

[0110] The electrolyte may include an electrolyte and a non-aqueous organic solvent. The electrolyte may be selected from LiPF6, LiBF4, LiSbF6, and LiAsF6. The non-aqueous organic solvent may be a carbonate, an ester, and an ether. In some embodiments, carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) may be used. In some embodiments, the electrolyte is an ethylene carbonate (EC) / dimethyl carbonate (DMC) non-aqueous electrolyte having a LiPF6 concentration of 1 mol / L, wherein the volume ratio of EC to DMC is 1:1.

[0111] The following are specific embodiments, which are intended to further explain the present application in detail to help the technical personnel and researchers in the field to further understand the present application. The relevant technical conditions do not constitute any limitation to the present application. Any form of modification made within the scope of the claims of the present application is within the scope of protection of the claims of the present application.

[0112] The following are examples, which are intended to further explain the present application in detail to help the technical personnel and researchers in the field to further understand the present application. The relevant technical conditions do not constitute any limitation to the present application. Any form of modification made within the scope of the claims of the present application is within the scope of protection of the claims of the present application.

[0113] Example 1

[0114] (1) Prepare a sodium hydroxide solution with a concentration of 5 mol / L and an ammonia solution with a concentration of 6 mol / L, take part of the sodium hydroxide solution and the ammonia solution and mix them to prepare a solution with a pH of 12 and an ammonia concentration of 15 g / L as the bottom liquid of the reactor.

[0115] (2) Nickel sulfate, manganese sulfate and ammonium dihydrogen phosphate were weighed in a molar ratio of Ni:Mn:P of 1:3:0.02, and the nickel sulfate and manganese sulfate were dissolved in water to prepare a mixed solution with a total metal ion concentration of 1 mol / L, and the ammonium dihydrogen phosphate was dissolved in water to prepare a water-soluble phosphate solution with a phosphate ion concentration of 0.02 mol / L.

[0116] (3) nitrogen is introduced into the reactor containing the base liquid. Under the protection of nitrogen, the mixed solution in step (2) and the water-soluble phosphate solution are added into the reactor at a feeding rate of 0.5 L / h, the sodium hydroxide solution is added at a feeding rate of 0.5 L / h, and the ammonia water is added at a feeding rate of 0.5 L / h. The feed can be fed by a metering pump. During the feeding process, the pH of the reaction system is controlled to be 12 and the ammonia concentration is controlled to be 15 g / L. The coprecipitation reaction is carried out at 40° C. and a stirring speed of 200 rpm for 100 h to obtain a mixed slurry.

[0117] (4) The mixed slurry is transferred to an aging tank for aging, centrifugation, washing, and drying to obtain a positive electrode active material precursor uniformly doped with phosphorus, wherein the aging temperature is 70° C. and the aging time is 80 h.

[0118] Example 2

[0119] Take 10 g of the precursor synthesized in Example 1 and 2.169 g of lithium carbonate, grind and mix them, place them in a furnace at 950° C. for high-temperature calcination for 20 h, with a heating rate of 3° C. / min and a cooling rate of 5° C. / min to obtain a sintered phosphorus-doped lithium nickel manganese oxide positive electrode material.

[0120] Example 3

[0121] (1) Prepare a sodium hydroxide solution with a concentration of 5 mol / L and an ammonia solution with a concentration of 6 mol / L, take part of the sodium hydroxide solution and the ammonia solution and mix them to prepare a solution with a pH of 12 and an ammonia concentration of 15 g / L as the bottom liquid of the reactor.

[0122] (2) Nickel sulfate, manganese sulfate and ammonium dihydrogen phosphate were weighed in a molar ratio of Ni:Mn:P of 1:3:0.02, and the nickel sulfate and manganese sulfate were dissolved in water to prepare a mixed solution with a total metal ion concentration of 1 mol / L, and the ammonium dihydrogen phosphate was dissolved in water to prepare a water-soluble phosphate solution with a phosphate ion concentration of 0.02 mol / L.

[0123] (3) nitrogen is introduced into the reactor containing the base liquid. Under the protection of nitrogen, the mixed solution in step (2) and the water-soluble phosphate solution are added to the reactor at a feeding rate of 0.2 L / h, the sodium hydroxide solution is added at a feeding rate of 0.5 L / h, and the ammonia water is added at a feeding rate of 0.5 L / h. The feed can be fed by a metering pump. During the feeding process, the pH of the reaction system is controlled to be 12 and the ammonia concentration is 15 g / L. The coprecipitation reaction is carried out at 40° C. and a stirring speed of 200 rpm. The total reaction time is 100 h, wherein the dripping speed of the water-soluble phosphate solution is increased by 0.1 L / h every 20 h. During the process, the dripping speeds of the sodium hydroxide and the ammonia water are finely adjusted to meet the stability of the pH of the entire reaction system and the stability of the ammonia water concentration. After the reaction is completed, a mixed slurry is finally obtained.

[0124] (4) The mixed slurry is transferred to an aging tank for aging, centrifugation, washing, and drying to obtain a positive electrode active material precursor, wherein the aging temperature is 70° C. and the aging time is 80 h.

[0125] Example 4

[0126] (1) Prepare a sodium hydroxide solution with a concentration of 5 mol / L and an ammonia solution with a concentration of 6 mol / L, take part of the sodium hydroxide solution and the ammonia solution and mix them to prepare a solution with a pH of 12 and an ammonia concentration of 15 g / L as the bottom liquid of the reactor.

[0127] (2) Nickel sulfate, manganese sulfate and ammonium dihydrogen phosphate were weighed in a molar ratio of Ni:Mn:P of 1:3:0.02, and the nickel sulfate and manganese sulfate were dissolved in water to prepare a mixed solution with a total metal ion concentration of 1 mol / L, and the ammonium dihydrogen phosphate was dissolved in water to prepare a water-soluble phosphate solution with a phosphate ion concentration of 0.02 mol / L.

[0128] (3) nitrogen is introduced into the reactor containing the base liquid. Under the protection of nitrogen, the mixed solution in step (2) and the water-soluble phosphate solution are added to the reactor at a feeding rate of 0.8 L / h, the sodium hydroxide solution is added at a feeding rate of 0.5 L / h, and the ammonia water is added at a feeding rate of 0.5 L / h. The feed can be fed by a metering pump. During the feeding process, the pH of the reaction system is controlled to be 12 and the ammonia concentration is 15 g / L. The coprecipitation reaction is carried out at 40° C. and a stirring speed of 200 rpm. The total reaction time is 100 h, wherein the dripping speed of the water-soluble phosphate solution is reduced by 0.1 L / h every 20 h. During the process, the dripping speeds of the sodium hydroxide and the ammonia water are finely adjusted to meet the stability of the pH of the entire reaction system. After the reaction is completed, a mixed slurry is finally obtained.

[0129] (4) The mixed slurry is transferred to an aging tank for aging, centrifugation, washing, and drying to obtain a positive electrode active material precursor, wherein the aging temperature is 70° C. and the aging time is 80 h.

[0130] Example 5

[0131] Take 10 g of the precursor synthesized in Example 3 and 2.169 g of lithium carbonate, grind and mix them, place them in a furnace at 950°C for high temperature calcination for 20 h, with a heating rate of 3°C / min and a cooling rate of 5°C / min to obtain a sintered phosphorus-doped lithium nickel manganese oxide positive electrode material.

[0132] Example 6

[0133] Take 10 g of the precursor synthesized in Example 4 and 2.169 g of lithium carbonate, grind and mix them, place them in a furnace at 950°C for high temperature calcination for 20 h, with a heating rate of 3°C / min and a cooling rate of 5°C / min to obtain a sintered phosphorus-doped lithium nickel manganese oxide positive electrode material.

[0134] Example 7

[0135] (1) Prepare a sodium carbonate solution with a concentration of 4 mol / L and an ammonia solution with a concentration of 5 mol / L, and take part of the sodium hydroxide solution and the ammonia solution and mix them to a pH of 11.

[0136] (2) Nickel sulfate, manganese sulfate and ammonium dihydrogen phosphate were weighed in a molar ratio of Ni:Mn:P of 1:3:0.02, and the nickel sulfate and manganese sulfate were dissolved in water to prepare a mixed solution with a total metal ion concentration of 1 mol / L, and the ammonium dihydrogen phosphate was dissolved in water to prepare a water-soluble phosphate solution with a phosphate ion concentration of 0.02 mol / L.

[0137] (3) nitrogen is introduced into the reactor containing the base liquid. Under the protection of nitrogen, the mixed solution in step (2) and the water-soluble phosphate solution are added to the reactor at a feeding rate of about 0.2 L / h, the sodium carbonate solution is added at a feeding rate of 0.5 L / h, and the ammonia water is added at a feeding rate of 0.4 L / h. The feed can be fed by a metering pump. During the feeding process, the pH of the reaction system is controlled to be 11. The coprecipitation reaction is carried out at 40° C. and a stirring speed of 200 rpm. The total reaction time is 100 h, wherein the dripping rate of the water-soluble phosphate solution is increased by 0.1 L / h every 20 h. During the process, the dripping rates of sodium carbonate and ammonia water are fine-tuned to meet the stability of the pH of the entire reaction system and the stability of the ammonia concentration. After the reaction is completed, a mixed slurry is finally obtained.

[0138] (4) The mixed slurry is transferred to an aging tank for aging, centrifugation, washing, and drying to obtain a positive electrode active material precursor, wherein the aging temperature is 70° C. and the aging time is 80 h.

[0139] Figure 1 The laser ion beam cutting image of the gradient phosphorus-doped positive electrode active material precursor prepared in Example 7 is shown.

[0140] Figure 2 The schematic diagram of the line scan of the radial area of ​​the gradient phosphorus-doped positive active material precursor prepared in Example 7 is shown. The black line represents the line scan area. By analyzing the intensity of the phosphorus element in the solid frame part and the dashed frame part on the line scan area, we can obtain I(solid frame) / I(dashed frame)=1.84, wherein I(solid frame) is the phosphorus element signal intensity obtained at the line scan collection point in the solid frame, and I(dashed frame) is the phosphorus element signal intensity obtained at the line scan collection point in the dashed frame.

[0141] Example 8

[0142] Take 10 g of the precursor synthesized in Example 7 and 1.594 g of lithium carbonate, grind and mix them, place them in a furnace at 950°C for high temperature calcination for 20 h, with a heating rate of 3°C / min and a cooling rate of 5°C / min to obtain a sintered phosphorus-doped lithium nickel manganese oxide positive electrode material.

[0143] Comparative Example 1

[0144] Take 10g of Ni 0.5 Mn 1.5 (OH)4, 0.064g of diammonium hydrogen phosphate and 2.169g of lithium carbonate were ground and mixed, and placed in a furnace at 950°C for high temperature calcination for 20h, with a heating rate of 3°C / min and a cooling rate of 5°C / min to obtain a nickel manganese oxide positive electrode material doped with the same phosphorus content as in Example 3 after sintering.

[0145] Comparative Example 2

[0146] Take 10g of Ni 0.5 Mn 1.5 (CO3)2, 0.064g of diammonium hydrogen phosphate and 1.594g of lithium carbonate were ground and mixed, and placed in a furnace at 950°C for high temperature calcination for 20 hours, with a heating rate of 3°C / min and a cooling rate of 5°C / min to obtain a nickel manganese oxide positive electrode material doped with the same phosphorus content as in Example 3 after sintering.

[0147] The positive electrode active materials prepared in Examples 2, 5, 6, 8, Comparative Examples 1 and 2 were assembled into button cells according to the following steps.

[0148] (1) Preparation of positive electrode sheet

[0149] The positive electrode active material prepared in the embodiment and carbon black as a conductive additive and a binder were mixed uniformly at a weight ratio of 80:10:10 to prepare a uniform positive electrode slurry. The uniform positive electrode slurry was evenly coated on an aluminum foil current collector with a thickness of 15 μm, dried at 55°C to form a pole piece with a thickness of 100 μm, and the pole piece was placed under a roller press (pressure of about 1 MPa×1.5 cm 2 ), cut into pieces with a diameter of The wafer was placed in a vacuum oven and baked at 120°C for 6 hours. After natural cooling, it was taken out and placed in a glove box for use as a positive electrode.

[0150] (2) Assembly of lithium-ion secondary batteries

[0151] In a glove box filled with an inert atmosphere, metallic lithium is used as the negative electrode of the battery, a three-layer film of PP / PE / PP coated with aluminum oxide on both sides is placed between the positive electrode and the negative electrode as a separator, a commonly used carbonate electrolyte is added dropwise, and the positive electrode sheet prepared in step (1) is used as the positive electrode to assemble a button battery of model CR2032.

[0152] High temperature cycle test:

[0153] After the prepared button battery was left to stand at room temperature (25°C) for 10 hours, the button battery was charged and discharged for activation, and then the button battery prepared above was subjected to a charge and discharge cycle test using a Blue Electric Battery Charge and Discharge Tester. First, at room temperature (25°C), the battery was cycled at a rate of 0.1C for 1 week, and then continued to cycle at a rate of 0.2C for 4 weeks, wherein the charge and discharge voltage range of the battery was controlled to be 3.5V to 4.9V. Then, the button battery was transferred to a high temperature environment of 55°C and continued to cycle at a rate of 0.2C for 50 weeks, while the charge and discharge voltage range of the battery was still controlled to be 3.5V to 4.9V.

[0154] Table 1. Electrochemical properties of the positive electrode active materials of Example 6, Example 7 and Comparative Example 1

[0155]

[0156] It can be seen from Table 1 that the positive electrode active material prepared from the precursor material prepared in Example 5 has an electrochemical performance that is significantly better than other lithium nickel manganese oxide positive electrode materials.

[0157] Table 3. Physical performance indicators of the positive electrode active materials synthesized in Example 5, Example 6 and Example 2

[0158]

[0159] It can be seen from Table 3 that the positive electrode active material prepared from the precursor material prepared in Example 6 has the highest tap density.

[0160] Table 4. Electrochemical properties of the positive electrode active materials of Example 8 and Comparative Example 2

[0161]

[0162] It can be seen from Table 4 that the electrochemical performance of the positive electrode active material prepared in Example 8 is significantly better than that of the lithium nickel manganese oxide positive electrode material prepared in Comparative Example 2.

[0163] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0164] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims.

Claims

1. A positive electrode active material precursor, characterized in that: Its chemical molecular formula is Ni 0.5-x Mn 1.5-y-s A s (PO4) z (B) u , wherein A is a non-lithium metal element, a metalloid element, or a combination of a non-lithium metal element and a metalloid element, and B is OH - or CO3 2- , -0.2≤x≤0.2, -0.2≤y≤0.2, 0≤s≤0.1, 0.003≤z≤0.07 and 1.8≤u≤4.4, the P element in the positive electrode active material precursor is unevenly distributed along the radial direction of the particles of the positive electrode active material precursor; In at least one region, the content of the P element increases gradually from the center to the outer surface of the particles of the positive electrode active material precursor.

2. A positive electrode active material precursor, characterized in that: Its chemical molecular formula is Ni 0.5-x Mn 1.5-y-s A s (PO4) z (B) u , wherein A is a non-lithium metal element, a metalloid element, or a combination of a non-lithium metal element and a metalloid element, and B is OH - , -0.2≤x≤0.2, -0.2≤y≤0.2, 0≤s≤0.1, 0.003≤z≤0.07 and 3.6≤u≤4.4, the P element in the positive electrode active material precursor is unevenly distributed along the radial direction of the particles of the positive electrode active material precursor; In at least one region, the content of the P element increases gradually from the center to the outer surface of the particles of the positive electrode active material precursor.

3. A positive electrode active material precursor, characterized in that: Its chemical molecular formula is Ni 0.5-x Mn 1.5-y-s A s (PO4) z (B) u , wherein A is a non-lithium metal element, a metalloid element, or a combination of a non-lithium metal element and a metalloid element, and B is CO3 2- , -0.2≤x≤0.2, -0.2≤y≤0.2, 0≤s≤0.1, 0.003≤z≤0.07 and 1.8≤u≤2.2, the P element in the positive electrode active material precursor is unevenly distributed along the radial direction of the particles of the positive electrode active material precursor; In at least one region, the content of the P element increases gradually from the center to the outer surface of the particles of the positive electrode active material precursor.

4. The positive electrode active material precursor according to any one of claims 1 to 3, characterized in that: The particle size of the positive electrode active material precursor particles is 0.1-30 microns.

5. The positive electrode active material precursor according to any one of claims 1 to 3, characterized in that: In the radial direction of the positive electrode active material precursor particle, there are at least two different regions with a P element concentration difference exceeding 10%.

6. The positive electrode active material precursor according to claim 5, characterized in that: In different regions where the difference in P element concentration exceeds 10%, the ratio of the distribution length of each region in the radial direction of the positive electrode active material precursor particle to the total radial length of the positive electrode active material precursor particle is 0.001-1.

7. The positive electrode active material precursor according to any one of claims 1 to 3, characterized in that: In the positive electrode active material precursor, s is 0, and the molar ratio of the elements Ni, Mn and P is 1:(2.5-3.5):(0.006-0.2).

8. The positive electrode active material precursor according to any one of claims 1 to 3, characterized in that: The non-lithium metal element is selected from at least one of alkaline earth metal elements, transition metal elements and Al.

9. The positive electrode active material precursor according to any one of claims 1 to 3, characterized in that: The A is selected from at least one of Al, Mg, Zn, Fe, Co, Ti, Y, Sc, Ru, Cu, Mo, Ge, W, Zr, Ca, Nb, Ta, Ni, Mn and Sr.

10. The positive electrode active material precursor according to any one of claims 1 to 3, characterized in that: In the positive electrode active material precursor, the molar ratio of the elements Ni, Mn, A and P is 1: (2.5-3.5): (0.2-0.001): (0.006-0.2).

11. A method for preparing a positive electrode active material precursor according to any one of claims 1 to 10, characterized in that: The following steps are involved: Providing an aqueous solution of a complexing agent and an aqueous solution of an alkaline precipitating agent, and configuring part of the aqueous solution of the complexing agent and part of the aqueous solution of the alkaline precipitating agent into a reaction kettle bottom liquid; Mixing a water-soluble nickel salt, a water-soluble manganese salt and water to form a mixed solution; the mixed solution optionally contains at least one water-soluble non-lithium metal salt, at least one water-soluble metalloid element salt, or a combination of at least one water-soluble non-lithium metal salt and at least one water-soluble metalloid element salt; Under the protection of inert gas, the mixed solution and the water-soluble phosphate solution are respectively added to the reactor containing the reactor bottom liquid, and the feeding speed and / or concentration of the mixed solution and the water-soluble phosphate solution are controlled so that the concentration and / or feeding speed of the water-soluble phosphate solution change with time, so as to achieve the uneven distribution of phosphorus element in the radial direction of the particles during the growth of the precursor particles, and a coprecipitation reaction is carried out under stirring, and at the same time, the remaining amount of the aqueous solution of the complexing agent and the remaining amount of the aqueous solution of the alkaline precipitant are also added, and the pH of the reaction system and the concentration of the complexing agent are controlled by controlling the feeding amount of the aqueous solution of the complexing agent and the feeding amount of the aqueous solution of the alkaline precipitant, and the reaction is terminated to obtain a mixed slurry; and The mixed slurry is aged, centrifuged, washed and dried to obtain a non-uniformly phosphorus-doped positive electrode active material precursor.

12. The method for preparing a positive electrode active material precursor according to claim 11, characterized in that: The non-lithium metal salt is any one or more of the sulfate, chloride and nitrate of any one of the metal elements of Al, Mg, Zn, Fe, Co, Ti, Y, Sc, Ru, Cu, Mo, W, Zr, Ca, Nb, Ta and Sr, and the metalloid element salt is any one or more of the sulfate, chloride and nitrate of Ge; the phosphate ion concentration in the water-soluble phosphate solution is 0.0025 mol / L to 0.3 mol / L, and the water-soluble phosphate is at least one of sodium phosphate, sodium monohydrogen phosphate, potassium dihydrogen phosphate, potassium phosphate, ammonium phosphate, sodium dihydrogen phosphate, lithium dihydrogen phosphate, ammonium monohydrogen phosphate, phosphoric acid and ammonium dihydrogen phosphate.

13. The method for preparing a positive electrode active material precursor according to claim 11, characterized in that: The complexing agent is at least one of hydrazine hydrate, crown ether, ammonia water, oxalic acid, ammonium bicarbonate, ethylenediamine, and ethylenediaminetetraacetic acid, and the molar concentration of the complexing agent is 2mol / L to 8mol / L; the precipitating agent is at least one of NaOH, KOH, Ba(OH)2, Na2CO3, Li2CO3, K2CO3 or LiOH, and the molar concentration of the precipitating agent is 2mol / L to 6mol / L.

14. The method for preparing a positive electrode active material precursor according to claim 11, characterized in that: The pH of the reaction kettle bottom liquid is 10-12.5, and the concentration of the complexing agent in the reaction kettle bottom liquid is 15g / L-20g / L.

15. The method for preparing a positive electrode active material precursor according to claim 11, characterized in that: The pH of the reaction kettle bottom liquid is 12 to 12.

5.

16. The method for preparing a positive electrode active material precursor according to claim 11, characterized in that: The reaction temperature of the coprecipitation reaction is 40° C. to 70° C., the pH of the reaction system is 10 to 12.5, the concentration of the complexing agent is 15 g / L to 25 g / L, the stirring speed is 200 rpm to 250 rpm, and the reaction time is 5 h to 120 h.

17. The method for preparing a positive electrode active material precursor according to claim 11, characterized in that: The total molar concentration of metal ions in the mixed solution is 1 mol / L to 3 mol / L, the water-soluble nickel salt is at least one of nickel sulfate, nickel chloride, and nickel nitrate, and the water-soluble manganese salt is at least one of manganese sulfate, manganese chloride, and manganese nitrate.

18. The method for preparing a positive electrode active material precursor according to claim 11, characterized in that: The feed rates of the mixed solution and the water-soluble phosphate are 0.1L / h to 100L / h, the feed rate of the aqueous solution of the complexing agent is 0.1L / h to 100L / h, and the feed rate of the aqueous solution of the alkaline precipitant is 0.1L / h to 100L / h.

19. A positive electrode active material prepared from the positive electrode active material precursor according to any one of claims 1 to 10 or the positive electrode active material precursor prepared by the method for preparing the positive electrode active material precursor according to any one of claims 11 to 18.

20. A method for preparing a positive electrode active material, comprising the following steps: Mixing a positive electrode active material precursor according to any one of claims 1 to 10 or a positive electrode active material precursor obtained by the method for preparing a positive electrode active material precursor according to any one of claims 11 to 18 with a lithium source; In an oxygen-containing atmosphere, sinter at 600°C to 1200°C for 5 to 10 hours.

21. A positive electrode of a lithium ion secondary battery, characterized in that: The invention comprises a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode active material as claimed in claim 19.

22. A lithium ion secondary battery, characterized in that: include: The positive electrode as claimed in claim 21; A negative electrode, comprising a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector; Diaphragm and electrolyte.

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