WO2022105696A1

WO2022105696A1 - Positive electrode active material precursor and preparation method therefor, positive electrode active material and preparation method therefor, positive electrode of lithium ion secondary battery, and lithium ion secondary battery

Info

Publication number: WO2022105696A1
Application number: PCT/CN2021/130504
Authority: WO
Inventors: 武怿达; 黄学杰; 詹元杰; 马晓威
Original assignee: 松山湖材料实验室
Priority date: 2020-11-17
Filing date: 2021-11-15
Publication date: 2022-05-27

Abstract

The present application relates to a positive electrode active material precursor, the chemical molecular general formula thereof being Ni_0.5-xMn_1.5-y-sA_s(PO₄)_z(B)_u, wherein A is a non-lithium metal element and/or a metalloid element, 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, 1.8 ≤ u ≤ 4.4, and the phosphorus in the positive electrode active material precursor is uniformly or non-uniformly distributed. The present invention further relates to a preparation method for a positive electrode active material precursor, where a water soluble phosphate along with a water soluble nickel salt and a manganese salt are added into a reaction vessel, a reaction condition is controlled, and co-precipitation of phosphorus with nickel and manganese metal ions is achieved. Further, the present application also relates to a positive electrode active material and a preparation method therefor, a positive electrode, and a lithium ion secondary battery.

Description

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

Related applications

This application requires the application filed on November 17, 2020, the application number is 202011286686.7, the name is "positive electrode active material precursor and its preparation method, and the positive electrode active material" and the application filed on November 5, 2021, the application number is 202111308255.0, the name It is the priority of the Chinese patent application for "positive electrode active material precursor and its preparation method, positive electrode active material and its preparation method, positive electrode and lithium ion secondary battery", which is hereby incorporated by reference in its entirety.

technical field

The present application relates to the field of lithium ion batteries, 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 technique

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. Mobile terminal products such as mobile phones, notebook computers, and tablet computers. In recent years, due to the consideration of environmental protection, electric vehicles have been rapidly developed under the impetus of governments and automakers, and lithium-ion secondary batteries have become an ideal power source for a new generation of electric vehicles due to their excellent performance. . At present, the positive active materials of lithium ion secondary batteries that people pay attention to can be roughly divided into three categories: layered materials represented by lithium cobalt oxide (LiCoO ₂ ), and olivine represented by lithium iron phosphate (LiFePO ₄ ). type materials and spinel structure materials represented by lithium manganate (LiMn ₂ O ₄ ). Among these materials, spinel-structured materials have been widely studied due to their advantages of environmentally friendly raw materials, low cost, simple process, high safety and good rate capability.

High-voltage materials with spinel structure, as an advanced cathode active material, are considered to be the most likely cathode active materials for next-generation high-performance lithium batteries. In particular, the theoretical specific capacity of lithium nickel manganese oxide with spinel structure is 146.7mAh/g, the working voltage is 4.7V vs. Li/Li ⁺ , and the theoretical capacity density can reach 695Wh/kg, which is the lithium for future electric vehicles. Ideal material for ion secondary batteries.

During the cycle of the high-pressure spinel positive active material, due to the interaction between the traditional carbonate electrolyte and the positive active material, the surface of the positive active material loses oxygen, thereby dissolving the surface structure of the material, and the surface defects will gradually extend. to the bulk phase, resulting in particle breakage, which eventually leads to a rapid decline in battery performance. In order to solve this technical problem, it is proposed to use element doping to modify the positive electrode active material. Doping elements can form new chemical bonds inside and on the surface of the material to stabilize the bulk phase and surface lattice oxygen, and solve the problem of the interface and the surface of the positive electrode active material. Phase stability issues. For example, the positive electrode active material is modified by doping with phosphorus element. The traditional modification method of phosphorus element is to mix the nickel-manganese precursor synthesized by co-precipitation method with phosphorus source and lithium source for high temperature sintering. It is difficult for phosphorus element to modify the lithium nickel manganate cathode material very uniformly. At the same time, traditional methods cannot achieve precise control of doping in specific regions of phosphorus element, which has great limitations.

SUMMARY OF THE INVENTION

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 for a lithium ion secondary battery and a lithium ion secondary battery.

The present application provides a positive electrode active material precursor, the general chemical formula of which is Ni _0.5-x _Mn _1.5-ys As (PO ₄ ) _z (B) _u , wherein A is a non-lithium metal element, a metalloid element or Combination of non-lithium metal elements and metalloid elements, B is OH ^- or CO ₃ ^2- , -0.2≤x≤0.2, -0.2≤y≤0.2, 0≤s≤0.1, 0.003≤z≤0.07 and 0.8≤u ≤4.4.

The present application also provides a positive electrode active material precursor, the general chemical formula of which is Ni _0.5-x _Mn _1.5-ys As (PO ₄ ) _z (B) _u , wherein A is a non-lithium metal element or a metalloid element Or a combination of a non-lithium metal element and a metalloid element, 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 present application also provides a positive electrode active material precursor, the general chemical formula of which is Ni _0.5-x _Mn _1.5-ys As (PO ₄ ) _z (B) _u , wherein A is a non-lithium metal element or a metalloid element Or a combination of non-lithium metal elements and metalloid elements, B is CO ₃ ^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 present application also provides a positive electrode active material precursor, the general chemical formula of which is Ni _0.5-x _Mn _1.5-ys As (PO ₄ ) _z (B) _u , wherein A is a non-lithium metal element or a metalloid element Or a combination of non-lithium metal elements and metalloid elements, 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, so The P element in the positive electrode active material precursor is unevenly distributed along the radial direction of the precursor particles.

The present application also provides a positive electrode active material precursor, the general chemical formula of which is Ni _0.5-x _Mn _1.5-ys As (PO ₄ ) _z (B) _u , wherein A is a non-lithium metal element or a metalloid element Or a combination of non-lithium metal elements and metalloid elements, B is CO ₃ ^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 cathode active material precursor is unevenly distributed along the radial direction of the precursor particles.

The present application also provides a positive electrode active material precursor, the general chemical formula of which is Ni _0.5-x _Mn _1.5-ys As (PO ₄ ) _z (B) _u , wherein A is a non-lithium metal element or a metalloid element Or a combination of non-lithium metal elements and metalloid elements, B is OH ^- or CO ₃ ^2- , -0.2≤x≤0.2, -0.2≤y≤0.2, 0≤s≤0.1, 0.003≤z≤0.07 and 0.8≤ u≤2.2, the P element in the positive electrode active material precursor is uniformly distributed.

In some embodiments, the particle size of the particles of the cathode active material precursor is 0.1-30 microns.

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 difference in P element concentration exceeding 10%.

In some embodiments, in a partial region in the radial direction of the particles of the cathode active material precursor, the content of the P element has a gradient decrease or gradient from the center to the outer surface of the particles of the cathode active material precursor at least one of the increments.

In some embodiments, in different regions where the P element concentration difference in the radial direction of the particles of the positive electrode active material precursor exceeds 10%, the distribution length of each region in the radial direction of the particles of the positive electrode active material precursor accounts for the positive electrode active material. The ratio of the total radial length of the precursor particles is 0.001-1.

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

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.

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

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

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

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

An aqueous solution of a complexing agent and an aqueous solution of an alkaline precipitating agent are provided, and part of the aqueous solution of the complexing agent and part of the aqueous solution of the alkaline precipitating agent is configured as the bottom liquid of the reactor;

Mix water-soluble nickel salt, water-soluble manganese salt and water to form a mixed solution; the mixed solution optionally also contains at least one water-soluble non-lithium metal salt, at least one water-soluble metalloid element salt or at least one water-soluble metalloid element salt. A combination of a water-soluble non-lithium metal salt and at least one water-soluble salt of a metalloid element;

Under the protection of inert gas, the mixed solution and the water-soluble phosphate solution are respectively added to the reaction kettle containing the reaction kettle bottom liquid, and the coprecipitation reaction is carried out under stirring, and the aqueous solution of the remaining amount of the complexing agent is also added at the same time. With the aqueous solution of the alkaline precipitating agent of surplus, the pH of the reaction system and the concentration of the complexing agent are controlled by controlling the feed amount of the aqueous solution of the complexing agent and the aqueous solution of the alkaline precipitating agent, and the reaction finishes to obtain mixed slurry; and

The mixed slurry is aged, centrifuged, washed and dried to obtain a uniformly phosphorus-doped positive electrode active material precursor.

In some embodiments, in the step of separately adding the mixed solution and the water-soluble phosphate solution into the reaction kettle containing the reaction kettle bottom liquid, the mixed solution and the water-soluble phosphate solution are controlled Separate and simultaneous feeds were made at the same feed rate. In some embodiments, in the step of separately adding the mixed solution and the water-soluble phosphate solution into the reaction kettle containing the reaction kettle bottom liquid, the mixed solution and the water-soluble phosphate solution are controlled At least one of the feeding speed and concentration of the water-soluble phosphate solution changes with time, so that the particle size of the phosphorus element in the process of the growth of the precursor particles Uneven distribution upwards.

In some embodiments, the non-lithium metal salt is any one of Al, Mg, Zn, Fe, Co, Ti, Y, Sc, Ru, Cu, Mo, W, Zr, Ca, Nb, Ta and Sr Any one or more of sulfates, chlorides and nitrates of metal elements.

In some embodiments, the metalloid element salt is any one or more of Ge sulfate, chloride and nitrate.

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

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 2mol/L～8mol/L.

In some embodiments, the precipitating agent is at least one of NaOH, KOH, Ba(OH) ₂ , Na ₂ CO ₃ , Li ₂ CO ₃ , K ₂ CO ₃ or LiOH, and the molar concentration of the precipitating agent is It is 2mol/L～6mol/L.

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

In some embodiments, the pH of the reaction kettle bottom liquid is 12-12.5.

In some embodiments, the reaction temperature of the co-precipitation reaction is 40 ℃～70 ℃, the pH of the reaction system is 10～12.5, the concentration of the complexing agent is 15g/L～25g/L, and the stirring speed is 200rpm～250rpm, The reaction time is 5h～120h.

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

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 The water-soluble manganese salt is at least one of manganese sulfate, manganese chloride, and manganese nitrate.

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

In some embodiments, the feed rate of the water-soluble phosphate salt increases or decreases with time for a certain period of time throughout the dropping cycle.

In some embodiments, the concentration of the water-soluble phosphate increases or decreases with time for a certain period of time throughout the dripping cycle.

The present application further provides a positive electrode active material prepared from the positive electrode active material precursor obtained by 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.

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

mixing 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 with a lithium source;

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

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 on the positive electrode current collector, the positive electrode active material layer comprising the above-mentioned positive electrode active material.

The present application further provides a lithium ion secondary battery, including a positive electrode, a negative electrode, a separator and an electrolyte. The negative electrode includes a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector.

The positive electrode active material precursor and its preparation method provided by the present application, as well as the positive electrode active material and its preparation method, on the basis of maintaining the original properties of the nickel-manganese precursor and not affecting the element ratio, the phosphorus element in the precursor can reach Controllable distribution state. This kind of controllability can be controlled at the nanoscale. Using the precursor of this composition structure, the problem that the later traditional method uses high-temperature solid-phase method for lithium doping and phosphorus doping at the same time is difficult to dope uniform and controllable region doping problem. . By improving the performance of the cathode active material precursor, the cathode active material and the lithium ion battery with better performance are prepared.

Description of drawings

FIG. 1 is a SEM cross-sectional view of the positive electrode active material precursor prepared in Example 1. FIG.

Fig. 2 is the SEM mapping distribution diagram of the cross section of the positive electrode active material precursor prepared in Example 1.

Fig. 3 is the SEM mapping distribution diagram of the cross-section of the positive electrode active material precursor prepared in Example 2.

FIG. 4 shows a picture of laser ion beam cutting of the gradient phosphorus-doped cathode active material precursor prepared in Example 8.

FIG. 5 shows a schematic diagram of a line scan performed on the radial region of the gradient phosphorus-doped cathode active material precursor prepared in Example 8. FIG.

Detailed ways

In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the related drawings. The preferred embodiments of the present application are shown in the accompanying drawings. However, the application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that a thorough and complete understanding of the disclosure of this application is provided.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs. The terms used herein in the specification of the application are for the purpose of describing specific embodiments only, and are not intended to limit the application. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Except as shown in the working examples or otherwise indicated, all numbers used in the specification and claims indicating amounts, physicochemical properties, etc. of ingredients are understood to be adjusted in all cases by the term "about". For example, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that those skilled in the art can seek to obtain the desired properties using the teachings disclosed herein, as appropriate Change these approximations. The use of numerical ranges by endpoints includes all numbers within that range and any range within that range, eg, 1 to 5 includes 1, 1.1, 1.3, 1.5, 2, 2.75, 3, 3.80, 4, and 5, etc. .

The embodiments of the present application provide a positive electrode active material precursor, the general chemical formula of which is Ni _0.5-x _Mn _1.5-ys As (PO ₄ ) _z (B) _u , wherein A is a non-lithium metal element and/or Metalloid element, B is OH ^- or CO ₃ ^2- , -0.2≤x≤0.2, -0.2≤y≤0.2, 0≤s≤0.1, 0.003≤z≤0.07 and 0.8≤u≤4.4. The P element in the positive electrode active material precursor is uniformly distributed or non-uniformly distributed in a specific area.

In the cathode active material precursor provided by the embodiment of the present application, phosphorus element is uniformly distributed at the atomic level inside the precursor, and at the same time, the precursor maintains the properties and element ratio of the traditional nickel-manganese precursor. The precursor of the composition structure solves the problem that the later traditional method uses the high-temperature solid-phase method to dope lithium and it is difficult to dope uniformly with phosphorus. Specifically, phosphorus doping will face three major problems in the later stage. First, the lithium salt will react with the phosphorus source to generate lithium phosphate and other substances, which will affect the activity of the lithium salt during the whole sintering process; secondly, the phosphorus element is in the lithium nickel manganate material. Diffusion is extremely slow, and it is difficult to achieve uniform distribution of phosphorus elements on the surface of the synthesized lithium nickel manganate material after final sintering by simple mixing between solid and solid particles; the last point is that when the particle size distribution range of the precursor is large, This complete doping from the outside to the inside will inevitably lead to the uneven distribution of phosphorus among different particles. The examples of the present application have achieved the precise control of the final synthesis of the lithium nickel manganate cathode material through the precise control of the phosphorus element content and distribution in the lithium nickel manganate cathode material precursor, and finally improved the performance of the cathode active material precursor. A cathode active material with better performance and a lithium ion battery are prepared.

In some embodiments, the P element is uniformly distributed in the cathode active material precursor.

In some embodiments, the P element is not uniformly distributed in the cathode active material precursor.

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

In some embodiments, in different regions where the P element concentration difference in the radial direction of the particles of the positive electrode active material precursor exceeds 10%, the distribution length of each region in the radial direction of the positive electrode active material accounts for the total radial length of the positive electrode active material The ratio is 0.001-1.

In some embodiments, s is 0, and the general chemical formula of the positive active material precursor is Ni _0.5-x Mn _1.5-y (PO ₄ ) _z (B) _u , wherein A is a non-lithium metal element and /or metalloid element, B is OH ^- or CO ₃ ^2- , wherein -0.2≤x≤0.2, -0.2≤y≤0.2, 0.005≤z≤0.05 and 0.8≤u≤4.4.

Optionally, in the foregoing cathode active material precursor, the molar ratio of elements Ni, Mn and P may be any ratio between 1:(2.5-3.5):(0.006-0.2).

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.

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

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

In some embodiments, B is OH ^- or CO ₃ ^2- , 0.8≤u≤2.2, and the P element is uniformly distributed in the cathode active material precursor.

In some embodiments, B is OH ⁻ , 3.6≤u≤4.4, and the P element in the cathode active material precursor is unevenly distributed along the radial direction of the particles of the cathode active material precursor.

In some embodiments, B is CO ₃ ²⁻ , 1.8≤u≤2.2, and the P element in the cathode active material precursor is unevenly distributed along the radial direction of the particles of the cathode active material precursor.

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

Step a, provide the aqueous solution X of the complexing agent and the aqueous solution Y of the alkaline precipitating agent, and configure the aqueous solution X of part of the complexing agent and the aqueous solution Y of part of the alkaline precipitating agent into the bottom liquid of the reactor;

Step b, mixing water-soluble nickel salt, water-soluble manganese salt and water to form a mixed solution; optionally also containing at least one water-soluble non-lithium metal salt and/or metalloid element salt in the mixed solution;

Step c, under the protection of inert gas, the mixed solution and the water-soluble phosphate solution are respectively added to the reactor containing the bottom liquid of the reactor, and the feeding speed of the mixed solution and the water-soluble phosphate solution is controlled. Or concentration, carry out co-precipitation reaction under stirring, also add the remaining amount of the aqueous solution X of the complexing agent and the remaining amount of the aqueous solution Y of the alkaline precipitant, and control the pH and the pH of the reaction system by controlling the feeding amounts of X and Y. The concentration of the complexing agent, the reaction finishes to obtain a mixed slurry;

In step d, the mixed slurry is aged, centrifuged, washed and dried to obtain a positive electrode active material precursor uniformly doped with phosphorus.

In this application "simultaneously" means that the time periods in which the two or more solutions to be added to the reactor are added to the reactor at least partially overlap. In some embodiments, "simultaneously" means that the two or more solutions are added to the reaction kettle at the same starting time.

In some embodiments, the mixed solution and the water-soluble phosphate solution are added to the reaction kettle at the same time, and the mixed solution and the water-soluble phosphate solution are fed at the same feed rate.

In other embodiments, during the process of adding the mixed solution and the water-soluble phosphate solution to the reaction kettle, the mixed solution and the water-soluble phosphate solution are not added to the reaction kettle at the same time, that is, The time at which the mixed solution and the water-soluble phosphate solution are added to the reactor only partially overlaps; and/or the feed rate of the water-soluble phosphate solution varies with time, and the feed rate of the mixed solution or The concentration is always constant, or also varies with time.

More specifically, in the process of adding the mixed solution and the water-soluble phosphate solution to the reactor, at least one condition in the feeding speed and concentration of the mixed solution and the water-soluble phosphate solution is controlled, At least one of the concentration of the water-soluble phosphate solution and the feed rate is changed with time, so that the phosphorus element is not uniformly distributed in the radial direction of the precursor particles during the growth of the precursor particles. In some embodiments, the feed rate of the water-soluble phosphate salt increases or decreases with time for a certain period of time throughout the dropping cycle. In other embodiments, the concentration of the water-soluble phosphate increases or decreases with time for a certain period of time throughout the dropping period.

In the preparation method of the positive electrode active material precursor provided by the present application, the three elements of nickel, manganese and phosphorus are uniformly precipitated simultaneously in the form of nickel hydroxide, manganese hydroxide and phosphate by co-precipitation method or in different distributions of specific elements. The uniform precipitation constitutes the cathode active material precursor. The phosphorus element is uniformly distributed inside the positive electrode active material precursor or non-uniformly distributed in the positive electrode active material precursor in a specific manner.

The preparation principle of the positive electrode active material precursor of the present application is as follows: water-soluble phosphate, water-soluble nickel salt and water-soluble manganese salt are added to the reaction kettle, and the reaction conditions are controlled to realize co-precipitation of phosphorus, nickel and manganese metal ions. Water-soluble phosphates provide precipitation of phosphate and nickel-manganese ions. In the preparation process, the reaction conditions need to be strictly controlled, and the positive electrode active material precursor is obtained through reaction, aging, centrifugation, washing and drying.

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

The complexing agent can be at least one of hydrazine hydrate, crown ether, ammonia water, oxalic acid, ammonium bicarbonate, ethylenediamine, 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～8mol/L, such as 3mol/L, 4mol/L, 5mol/L, 6mol/L, 7mol/L, 7.5mol/L.

The precipitant may be at least one of NaOH, KOH, Ba(OH) ₂ , Na ₂ CO ₃ , Li ₂ CO ₃ , K ₂ CO ₃ or LiOH. Optionally NaOH.

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, 3.8mol/L, 4mol/L, 4.2mol/L, 4.5mol/L, 4.8mol/L, 5mol/L, 5.5mol/L.

The pH of the reaction kettle bottom liquid can be any value between 10 and 12.5, and in some embodiments, it is 12 to 12.5.

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

The water-soluble nickel salt can be at least one of nickel sulfate, nickel chloride, and nickel nitrate.

The water-soluble manganese salt can be at least one of manganese sulfate, manganese chloride, and manganese nitrate.

The water-soluble phosphate can be 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, phosphoric acid at least one of ammonium dihydrogen.

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

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

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

In the co-precipitation reaction process, the reaction temperature can be 40 ℃～70 ℃, the pH of the reaction system is controlled at 10～12.5, in some embodiments, it is 11.5～12, and the concentration of the complexing agent is controlled at 15g/L～25g/L, The stirring speed can be 200rpm～250rpm, and the reaction time can be 80h～120h.

In some embodiments, the feed rate or concentration of the water-soluble phosphate increases or decreases with time.

Further, during the co-precipitation reaction, the pH of the reaction system can be controlled to be 12.

The inert gas may be nitrogen.

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

The present application further provides a positive electrode active material prepared from the above-mentioned positive electrode active material precursor or the positive electrode active material precursor obtained by the above-mentioned preparation method of the positive electrode active material precursor.

The positive electrode active material precursor and its preparation method provided by the present application, while maintaining the original properties of the lithium nickel manganate precursor, through regulation, the phosphorus element can be distributed in a specific form, uniformly or unevenly distributed in the positive electrode active material precursor. in the body. This specific distribution form will help to further regulate the distribution of phosphorus elements in the bulk phase and surface of the final synthesized lithium nickel manganate material under the premise of realizing the comprehensive modification of the lithium nickel manganate material by phosphorus elements, and at the same time It can also adjust the morphology of the synthesized lithium nickel manganate materials. For example, when the phosphorus content of the lithium nickel manganate precursor gradually increases from the inside to the surface, the high content of phosphorus on the surface of the precursor will inhibit the lithium nickel manganate sintering process using the precursor. In the process of mutual fusion of the precursors during the sintering process, the final synthesized lithium nickel manganate material has a smaller particle size and a more uniform particle size distribution. During the cycling process of such materials, due to the smaller particle size and narrower particle size distribution of the material, the polarization of the battery is smaller and the rate performance is better. For another example, when the content of phosphorus in the lithium nickel manganate precursor gradually decreases from the surface of the lithium nickel manganate precursor to the inside, in the process of synthesizing the lithium nickel manganate material, the content of phosphorus on the surface of the precursor is less, which is more conducive to Fusion, absorption and growth between NiMnO precursors. In this way, the final synthesized lithium nickel manganate material can obtain a larger material particle size and better particle size distribution on the basis of doping with phosphorus element, and then obtain a lithium nickel manganate material with a higher tap density. Then, the volume energy density of the finally obtained lithium nickel manganate battery product is improved.

In the present application, the doping of phosphorus element to the lithium nickel manganate precursor is a more flexible doping method. In particular, the precursor is doped with phosphorus during the co-precipitation synthesis of the lithium nickel manganate precursor. In this process, by adjusting the content of phosphorus and the addition rate, the concentration of phosphorus in nickel can be precisely regulated. The distribution in the lithium manganate precursor is not only the synthesis of uniform phosphorus element doped nickel lithium manganate precursor 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 battery's high and low temperature cycling, mass energy density, volume energy density, and rate performance. However, through a series of systematic studies, the inventor first found that doping the precursor with phosphorus element can ultimately greatly improve the comprehensive performance of the synthesized lithium nickel manganate material. Further, by adjusting the distribution of phosphorus element content in the lithium nickel manganate material, some physical properties of the lithium nickel manganate material itself can be adjusted, such as particle size, particle size distribution, and the overall composition of the final synthesized lithium nickel manganate material. Phosphorus distribution. All of these utilize the different characteristics brought about by the distribution of phosphorus in the lithium nickel manganate precursor and the final distribution in the final lithium nickel manganate material to stabilize the surface of the lithium nickel manganate material, enabling it to achieve commercial application. status.

Specifically, for the precursor of lithium nickel manganate cathode material, under a certain range of phosphorus element content and sintering conditions, the higher the distribution of phosphorus element on the surface, the less conducive to the final synthesis of large particle size lithium nickel manganate material; nickel manganese The narrower the particle size distribution of lithium oxide, the more stable the surface of the final synthesized lithium nickel manganate material. Therefore, when a lithium nickel manganate material precursor with a small particle size but a more stable surface and a narrower particle size distribution is required, it is most suitable to synthesize a lithium nickel manganate cathode precursor with a higher surface phosphorus distribution. . Compared with the lithium nickel manganate precursor with uniform distribution of phosphorus element, this type of precursor can save cost very well, and the same content of phosphorus source is used to finally synthesize a more satisfactory lithium nickel manganate cathode material. On the other hand, the lower the distribution of phosphorus elements on the surface, the more favorable the final synthesis of large particle size lithium nickel manganate material, the more small particle size lithium nickel manganese oxide, and the greater the tap density of the final synthesized lithium nickel manganate material. . In fact, the uniform and non-uniform distribution of phosphorus element in the lithium nickel manganate precursor brings rich and diverse adjustments to the properties of the final synthesized lithium nickel manganate material. People have not noticed this in the past. A large number of experiments have studied the properties of the interaction between phosphorus and lithium nickel manganate precursors. For the first time, it is found that this property can ultimately affect the synthesis of lithium nickel manganate materials. At the same time, a variety of Different properties of lithium nickel manganate cathode materials, each material has its own unique advantages, the phosphorus element doping of the lithium nickel manganate cathode precursor realized by the method provided in this application is simple, ingenious and practical.

In the preparation method of the positive electrode active material precursor provided by the present application, the phosphorus element enters the positive electrode active material precursor in a uniform form or forms the positive electrode active material precursor unevenly in a specific distribution. What needs to be emphasized here is the positive electrode active material precursor of the present application, the general chemical formula of which is Ni _0.5-x _Mn _1.5-ys As (PO ₄ ) _z (B) _u , and the positive electrode active material precursor in the molecule is The distribution of manganese and nickel in the body is also not limited. The nickel or manganese in the formula can be uniformly distributed or non-uniformly distributed, for example, the gradient increases or decreases gradually from the center of the precursor particle to the outer surface.

The increasing or decreasing gradient mentioned in this application means that the phosphorus content has a tendency to increase or decrease in a certain part of the radial direction of the precursor, and this increasing or decreasing trend does not need to have a fixed slope. The characteristics of the synthetic materials of the present application can be detected by the most common methods in the industry, such as cutting the synthesized materials by means of a focused laser ion beam, etc., and determining the increasing or decreasing distribution of phosphorus elements or different regions through various electron microscope line scans. The ratio of the internal phosphorus content. In addition, other methods reported in the industry and literature can also be used for discrimination.

In the present application, by adding water-soluble phosphate, water-soluble nickel salt and manganese salt into the reaction kettle, and controlling the reaction conditions, co-precipitation of phosphorus, nickel and manganese metal ions is achieved. Water-soluble phosphates provide precipitation of phosphate and nickel-manganese ions.

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

The lithium source is lithium carbonate or lithium hydroxide, in some embodiments lithium carbonate.

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

The above-mentioned positive electrode active material precursor contains phosphorus element, and the positive electrode active material precursor contained in this application can be cut out by a laser ion beam cutting method, and combined with XPS by SEM mapping, TEM-mapping, ion beam etching Photoelectron imaging or secondary ion mass spectrometry and other methods are used to characterize the content and distribution of phosphorus elements in the positive electrode active material, and further determine the characteristics of the positive electrode active material precursor contained in this patent.

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 on the positive electrode current collector, wherein the positive electrode active material layer includes the above-mentioned positive electrode active material.

The positive electrode current collector may be a conductive member 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 and the like of the lithium ion secondary battery. 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.

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

The conductive additive may be a conventional conductive additive in the art, which is not particularly limited in the present application. In some embodiments, the conductive additive is carbon black (eg, acetylene black or Ketjen black).

The adhesive may be a conventional adhesive in the art, which is not particularly limited in the present application, and may be composed of polyvinylidene fluoride (PVDF), or may be composed of carboxymethyl cellulose (CMC) and butylbenzene Made of rubber (SBR). In some embodiments, the binder is polyvinylidene fluoride (PVDF).

The application also provides a lithium-ion secondary battery, comprising:

A positive electrode as described above;

a negative electrode comprising a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector;

Diaphragm and electrolyte.

As a negative current collector,

The negative electrode, separator and electrolyte can use conventional negative electrode current collector, separator and electrolyte materials in the art, which are not particularly limited in the present application.

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 and the like. The negative electrode active material layer includes a negative electrode active material, a conductive additive and a binder. Negative active materials, conductive additives and binders are also conventional materials in the art. In some embodiments, the negative active material is metallic lithium. The conductive additives and binders are described above and will not be repeated here.

The separator can be selected from those commonly used in lithium ion secondary batteries, including microporous films made of polyethylene and polypropylene; porous polyethylene films and polypropylene multi-layer films; Nonwoven fabrics formed of aramid fibers, glass fibers, etc.; and base films formed by adhering ceramic particles such as silica, alumina, and titania to their surfaces, and the like. In some embodiments, the separator is a triple-layer film of PP/PE/PP coated with alumina on both sides.

The electrolytic solution may include an electrolyte and a non-aqueous organic solvent. The electrolyte can be selected from LiPF ₆ , LiBF ₄ , LiSbF ₆ , and LiAsF ₆ . The non-aqueous organic solvent can be carbonate, ester and ether. In some embodiments, carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethylmethyl carbonate (EMC) may be employed. In some embodiments, the electrolyte is an ethylene carbonate (EC)/dimethyl carbonate (DMC) non-aqueous electrolyte with a concentration of LiPF ₆ of 1 mol/L, wherein the volume ratio of EC to DMC is 1: 1.

The following are specific examples, which are intended to further describe the application in detail to help those skilled in the art and researchers to further understand the application, and the relevant technical conditions and the like do not constitute any limitation to the application. Any modifications made within the scope of the claims of the present application are all within the protection scope of the claims of the present application.

The following examples are intended to further describe the application in detail to help those skilled in the art and researchers to further understand the application, and the relevant technical conditions and the like do not constitute any limitation to the application. Any modifications made within the scope of the claims of the present application are all within the protection scope of the claims of the present application.

Example 1

(1) preparation concentration is that the sodium hydroxide solution of 5mol/L and the ammoniacal liquor that concentration is 6mol/L, get part sodium hydroxide solution and ammoniacal liquor to mix and be mixed to be pH=12, the solution that ammonia concentration is 15g/L is used as the bottom of the reactor liquid.

(2) Weigh nickel sulfate, manganese sulfate and ammonium dihydrogen phosphate according to the molar ratio Ni:Mn:P of 1:3:0.02, dissolve nickel sulfate and manganese sulfate in water to make the total concentration of metal ions to be 1mol/L The mixed solution of ammonium dihydrogen phosphate was dissolved in water to prepare a water-soluble phosphate solution with a phosphate ion concentration of 0.02 mol/L.

(3) feed nitrogen into the reactor equipped with bottom liquid, under nitrogen protection, in step (2), mixing solution and water-soluble phosphate solution are at the feed rate of 0.5L/h, and sodium hydroxide solution is at 0.5 L/h The feed rate of L/h and ammonia water are added to the reaction kettle at the feed rate of 0.5L/h. The feed can be fed through a metering pump. During the feeding process, the pH of the control reaction system is 12, and the ammonia concentration is 15g/ L, the co-precipitation reaction was carried out at 40° C. and a stirring speed of 200 rpm, and the reaction time was 100 h to obtain a mixed slurry.

(4) The mixed slurry is transferred to an aging tank for aging, centrifugation, washing and drying to obtain a uniform phosphorus-doped cathode active material precursor, wherein the aging temperature is 70°C and the aging time is 80h.

FIG. 1 shows a picture of laser ion beam cutting of the uniformly phosphorus-doped cathode active material precursor prepared in this example.

Figure 2 is a SEM element mapping distribution diagram of a uniform phosphorus-doped cathode active material precursor obtained after laser ion beam cutting. As can be seen from Figure 2, phosphorus is uniformly distributed inside the precursor.

Example 2

(1) preparation concentration is that the sodium hydroxide solution of 5mol/L and concentration are the ammoniacal liquor of 6mol/L, get part sodium hydroxide solution and ammoniacal liquor and mix and be mixed and be mixed to pH=10.8, and ammonia concentration is that the solution of 15g/L is used as the bottom of the reactor liquid.

(3) feed nitrogen into the reactor equipped with bottom liquid, under nitrogen protection, mixing solution and water-soluble phosphate solution are at the feed rate of 0.5L/h, and sodium hydroxide solution is at the feed rate of 0.5L/h The feed rate and ammonia water are added to the reaction kettle at a feed rate of 0.5L/h. The feed can be fed through a metering pump. During the feeding process, the pH of the reaction system is controlled to be 10.8, and the ammonia concentration is 15g/L. And the co-precipitation reaction was carried out at a stirring speed of 200 rpm, and the reaction time was 100 h to obtain a mixed slurry.

(4) The mixed slurry is transferred to an aging tank for aging, centrifugation, washing, and drying to obtain a uniform phosphorus-doped cathode active material precursor, wherein the aging temperature is 60° C. and the aging time is 20 hours.

FIG. 3 is a scanning electron microscope element mapping distribution diagram of the uniform phosphorus-doped cathode active material precursor obtained after laser ion beam cutting. It can be seen from Figure 3 that phosphorus is uniformly distributed inside the precursor.

Example 3

Take 10 g of the precursor synthesized in Example 1 and 2.169 g of lithium carbonate for grinding and mixing, and place it 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 sintered phosphorus. Element-doped lithium nickel manganate cathode material.

Example 4

(3) feed nitrogen into the reactor equipped with bottom liquid, under nitrogen protection, in step (2), mixing solution and water-soluble phosphate solution are at the feed rate of 0.2L/h, and sodium hydroxide solution is at 0.5 The feed rate of L/h and ammonia water are jointly added to the reaction kettle with the feed rate of 0.5L/h, and the feed can be fed by a metering pump, and the pH of the control reaction system in the feeding process is 12, and the ammonia concentration is 15g/ L, the co-precipitation reaction was carried out at 40 °C and a stirring speed of 200 rpm. The total reaction time was 100 h, and the dropping rate of the water-soluble phosphate solution was increased by 0.1 L/h every 20 h. The acceleration is fine-tuned to meet the pH stability of the entire reaction system and the stability of the ammonia concentration. After the reaction is completed, a mixed slurry is finally obtained.

(4) The mixed slurry is transferred to an aging tank for aging, centrifugation, washing, and drying, to obtain a positive active material precursor with a gradually increasing content of phosphorus from the inside to the outside. The aging temperature is 70°C, and the aging time is 80h. .

Example 5

(3) feed nitrogen into the reactor equipped with bottom liquid, under nitrogen protection, in step (2), mixing solution and water-soluble phosphate solution are at the feed rate of 0.8L/h, and sodium hydroxide solution is at 0.5 The feed rate of L/h and ammonia water are added to the reaction kettle at the feed rate of 0.5L/h. The feed can be fed through a metering pump. During the feeding process, the pH of the control reaction system is 12, and the ammonia concentration is 15g/ L, the co-precipitation reaction was carried out at 40 °C and a stirring speed of 200 rpm. The total reaction time was 100 h, and the dropping rate of the water-soluble phosphate solution was reduced by 0.1 L/h every 20 h. The acceleration is fine-tuned to meet the pH stability of the entire reaction system, and the mixed slurry is finally obtained after the reaction is completed.

(4) The mixed slurry is transferred to an aging tank for aging, centrifugation, washing, and drying to obtain a cathode active material precursor with a gradually decreasing content of phosphorus from the inside to the outside. The aging temperature is 70°C and the aging time is 80h. .

Example 6

Take 10 g of the precursor synthesized in Example 4 and 2.169 g of lithium carbonate for grinding and mixing, and place it 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 the phosphorus after sintering. Element-doped lithium nickel manganate cathode material.

Example 7

Take 10 g of the precursor synthesized in Example 5 and 2.169 g of lithium carbonate for grinding and mixing, and place it 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 sintered phosphorus. Element-doped lithium nickel manganate cathode material.

Example 8

(1) the sodium carbonate solution that the preparation concentration is 4mol/L and the ammoniacal liquor that the concentration is 5mol/L, get a part of sodium hydroxide solution and ammoniacal liquor and mix and prepare pH=11.

(3) feed nitrogen into the reactor equipped with bottom liquid, under nitrogen protection, in step (2), mixing solution and water-soluble phosphate solution are about with the feed rate of 0.2L/h, sodium carbonate solution with 0.5 The feed rate of L/h and ammonia water are added to the reaction kettle at a feed rate of 0.4L/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, at 40°C and 200rpm. The co-precipitation reaction was carried out under the stirring speed of 100 h, the total reaction time was 100 h, and the dripping rate of the water-soluble phosphate solution was increased by 0.1 L/h every 20 h. During the process, the dripping rate of sodium carbonate and ammonia water was fine-tuned to meet the whole reaction The pH of the system is stable and the concentration of ammonia water is stable, and the mixed slurry is finally obtained after the reaction is completed.

5 shows a schematic diagram of a line scan performed on the radial region of the gradient phosphorus-doped positive active material precursor prepared in Example 8. The black line represents the line scan region. Intensity analysis of some phosphorus elements, we can get I (solid line box) / I (dotted line box) = 1.84, where I (solid line box) is the signal intensity of phosphorus element obtained from the line scan collection point in the solid line box, I (dotted line) Box) is the signal intensity of phosphorus element obtained by scanning the collection points in the dotted box.

Example 9

Take 10 g of the precursor synthesized in Example 8 and 1.594 g of lithium carbonate for grinding and mixing, and place it 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 the phosphorus after sintering. Element-doped lithium nickel manganate cathode material.

Example 10

(3) feed nitrogen into the reactor equipped with bottom liquid, under nitrogen protection, in step (2), mixing solution and water-soluble phosphate solution are about with the feed rate of 0.5L/h, and sodium carbonate solution is about 0.5L/h The feed rate of L/h and ammonia water are added to the reaction kettle at a feed rate of 0.4L/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, at 40°C and 200rpm. The co-precipitation reaction was carried out at the stirring speed of 100 h, and the total reaction time was 100 h. During the process, the dropping speed of sodium carbonate and ammonia water was fine-tuned to meet the stability of pH and ammonia concentration of the whole reaction system. After the reaction was completed, a mixed slurry was finally obtained. material.

(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 hours.

Example 11

Take 10 g of the precursor synthesized in Example 10 and 1.594 g of lithium carbonate, grind and mix, and place it 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 the phosphorus after sintering. Element-doped lithium nickel manganate cathode material.

Comparative Example 1

Take 10g of Ni _0.5 Mn _1.5 (OH) ₄ , 0.064g of diammonium hydrogen phosphate and 2.169g of lithium carbonate for grinding and mixing, and place it 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 3°C. The temperature is 5°C/min, to obtain the lithium nickel manganate cathode material doped with the same phosphorus content as in Example 3 after sintering.

Comparative Example 2

Take 10g of Ni _0.5 Mn _1.5 (CO ₃ ) ₂ , 0.064g of diammonium hydrogen phosphate and 1.594g of lithium carbonate for grinding and mixing, and place it in a furnace at 950°C for calcination at high temperature for 20h, the heating rate is 3°C/min, and the temperature is lowered. The rate is 5°C/min, and the sintered lithium nickel manganate cathode material is obtained.

The positive electrode active materials prepared in Examples 3, 6, 7, 9, 11 and Comparative Examples 1 and 2 were assembled into coin cells according to the following steps.

(1) Preparation of positive electrode pieces

The positive electrode active material and carbon black prepared in the examples were used as conductive additives and binders, and were uniformly mixed according to a weight ratio of 80:10:10 to prepare a uniform positive electrode slurry. The uniform positive electrode slurry was evenly coated on the aluminum foil current collector with a thickness of 15 μm, and 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 for rolling (pressure about 1MPa). ×1.5cm ² ), cut into a circle with a diameter of φ14mm, and then placed in a vacuum oven at 120° C. for 6 hours. After natural cooling, it was taken out and placed in a glove box to be used as a positive pole piece.

(2) Assembly of lithium ion secondary battery

In a glove box filled with an inert atmosphere, metal lithium is used as the negative electrode of the battery, and a triple-layer film of PP/PE/PP coated with alumina on both sides is placed between the positive electrode and the negative electrode as a separator, and commonly used carbonates are added dropwise. The electrolyte solution is assembled into a button battery with a model of CR2032, using the positive electrode plate prepared in step (1) as the positive electrode.

High temperature cycle test:

After standing the prepared button battery at room temperature (25°C) for 10 hours, the button battery was activated by charging and discharging, and then the button battery prepared above was charged and discharged using a blue battery charge and discharge tester. Loop test. First, cycle at room temperature (25°C) at a rate of 0.1C for 1 week, and then continue to cycle at a rate of 0.2C for 4 weeks, wherein the charge-discharge voltage range of the control battery is 3.5V-4.9V. Then, the button battery was transferred to a high temperature environment of 55°C, and the cycle was continued for 50 cycles at a rate of 0.2C, while the charge-discharge voltage range of the control battery was still 3.5V to 4.9V.

Table 1. Electrochemical performance of positive active materials of Example 3 and Comparative Example 1

It can be seen from Table 1 that the electrochemical performance of the cathode active material prepared from the precursor material prepared in Example 1 is significantly better than that of the lithium nickel manganate cathode material doped with the same phosphorus content in Comparative Example 1.

Table 2. Electrochemical properties of cathode active materials synthesized in Example 6, Example 7 and Comparative Example 1

As can be seen from Table 2, the positive electrode active material prepared in Example 6 has the best electrochemical performance, the positive electrode active material prepared in Example 7 has the second highest electrochemical performance, and the positive electrode active material prepared in Comparative Example 1 has the best electrochemical performance. The electrochemical performance is the worst.

Table 3. Physical property indexes of the cathode active materials synthesized in Example 6, Example 7 and Example 3

It can be seen from Table 3 that the positive electrode active material prepared from the precursor material prepared in Example 7 has the highest tap density.

Table 4. Electrochemical performance of positive active materials of Example 9, Example 11 and Comparative Example 2

It can be seen from Table 4 that the electrochemical performance of the cathode active materials prepared in Examples 9 and 11 is significantly better than that of the lithium nickel manganate cathode material prepared in Comparative Example 2.

The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity, all possible combinations of the technical features in the above-described embodiments are not described. However, as long as there is no contradiction between the combinations of these technical features, All should be regarded as the scope described in this specification.

The above-mentioned embodiments only represent several embodiments of the present application, and the descriptions thereof are relatively specific and detailed, but should not be construed as a limitation on the scope of the patent application. It should be pointed out that for those skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which all belong to the protection scope of the present application. Therefore, the scope of protection of the patent of the present application shall be subject to the appended claims.

Claims

A positive active material precursor, characterized in that its general chemical formula is Ni 0.5-x Mn 1.5-ys As (PO 4 ) z (B) u , wherein A is a non-lithium metal element or a metalloid element Or a combination of non-lithium metal elements and metalloid elements, B is OH - or CO 3 2- , -0.2≤x≤0.2, -0.2≤y≤0.2, 0≤s≤0.1, 0.003≤z≤0.07 and 0.8≤ u≤4.4.
The positive electrode active material precursor according to claim 1, wherein B is OH - or CO 3 2- , 0.8≤u≤2.2, and the P element in the positive electrode active material precursor is uniformly distributed.
The cathode active material precursor according to claim 1, wherein B is OH − , 3.6≤u≤4.4, and the P element in the cathode active material precursor is along the particles of the cathode active material precursor. The radial direction is unevenly distributed.
The positive electrode active material precursor according to claim 1, wherein B is CO 3 2- , 1.8≤u≤2.2, and the P element in the positive electrode active material precursor is along the positive electrode active material precursor. The particles are not uniformly distributed in the radial direction.
The positive electrode active material precursor according to any one of claims 1-4, wherein the particle size of the positive electrode active material precursor is 0.1-30 microns.
The positive electrode active material precursor according to claims 3-4, characterized in that, 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%.
The positive electrode active material precursor according to claim 3-4, characterized in that, in at least one region, the content of the P element has a gradient decrease or gradient from the center to the outer surface of the particles of the positive electrode active material precursor at least one of the increments.
The positive electrode active material precursor according to claims 3-7, characterized in that, in different regions where the P element concentration difference exceeds 10%, the distribution length of each region in the radial direction of the particles of the positive electrode active material precursor accounts for The ratio of the total radial length of the particles of the positive electrode active material precursor is 0.001-1.
The positive electrode active material precursor according to any one of claims 1-8, wherein, in the positive electrode active material precursor, s is 0, and the molar ratio of elements Ni, Mn and P is 1:(2.5～ 3.5): (0.006～0.2).
The positive electrode active material precursor according to any one of claims 1-9, wherein the non-lithium metal element is selected from at least one of alkaline earth metal elements, transition metal elements and Al.
The positive electrode active material precursor according to any one of claims 1-10, wherein the A is selected from the group consisting of Al, Mg, Zn, Fe, Ti, Y, Sc, Ru, Cu, Mo, Ge, W , at least one of Zr, Ca, Nb, Ta, Ni, Mn and Sr; preferably, the A is selected from at least one of Y, W, Ti, Mg, Cu, Ca and Al.
The positive electrode active material precursor according to any one of claims 1-12, wherein in the positive electrode active material precursor, the molar ratio of elements Ni, Mn, A and P is 1:(2.5-3.5) : (0.2 to 0.001): (0.006 to 0.2).
A method for preparing a positive electrode active material precursor, comprising the following steps:

An aqueous solution of a complexing agent and an aqueous solution of an alkaline precipitating agent are provided, and part of the aqueous solution of the complexing agent and part of the aqueous solution of the alkaline precipitating agent is configured as the bottom liquid of the reactor;

Mix water-soluble nickel salt, 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 at least one water-soluble metalloid element salt. A water-soluble non-lithium metal salt in combination with at least one water-soluble salt of a metalloid element;

Under the protection of inert gas, the mixed solution and the water-soluble phosphate solution are respectively added to the reaction kettle containing the reaction kettle bottom liquid, and the coprecipitation reaction is carried out under stirring, and the aqueous solution of the remaining amount of the complexing agent is also added at the same time. With the aqueous solution of the alkaline precipitating agent of surplus, the pH of the reaction system and the concentration of the complexing agent are controlled by controlling the feed amount of the aqueous solution of the complexing agent and the aqueous solution of the alkaline precipitating agent, and the reaction finishes to obtain mixed slurry; and

The mixed slurry is aged, centrifuged, washed and dried to obtain a uniformly phosphorus-doped positive electrode active material precursor.
The method for preparing a positive electrode active material precursor according to claim 13, wherein in the step of adding the mixed solution and the water-soluble phosphate solution to the reaction kettle containing the reaction kettle bottom liquid, respectively , control the mixed solution and the water-soluble phosphate solution to feed separately and simultaneously at the same feed rate.
The method for preparing a positive electrode active material precursor according to claim 13, wherein in the step of adding the mixed solution and the water-soluble phosphate solution to the reaction kettle containing the reaction kettle bottom liquid, respectively , control at least one condition in the feed rate and concentration of the mixed solution and the water-soluble phosphate solution, so that at least one condition in the concentration and feed rate of the water-soluble phosphate solution changes with time, to The non-uniform distribution of phosphorus element in the radial direction of the precursor particles during the growth of the precursor particles.
The method for preparing a positive electrode active material precursor according to any one of claims 13-15, wherein the non-lithium metal salt is Al, Mg, Zn, Fe, Co, Ti, Y, Sc, Ru, Any one or more of sulfate, chloride and nitrate of any one metal element in Cu, Mo, W, Zr, Ca, Nb, Ta and Sr, and the metalloid element salt is Ge sulfuric acid any one or more of salts, chlorides and nitrates;

The phosphate ion concentration in the water-soluble phosphate solution is 0.0025mol/L～0.3mol/L, and the water-soluble phosphate is sodium phosphate, sodium monohydrogen phosphate, potassium dihydrogen phosphate, diammonium hydrogen phosphate, potassium phosphate , at least one of ammonium phosphate, sodium dihydrogen phosphate, lithium dihydrogen phosphate, ammonium monohydrogen phosphate, phosphoric acid, and ammonium dihydrogen phosphate;

Described complexing agent is at least one in hydrazine hydrate, crown ether, ammonia water, oxalic acid, ammonium bicarbonate, ethylenediamine, ethylenediaminetetraacetic acid, and the molar concentration of described complexing agent is 2mol/L～8mol/ L;

The precipitant is at least one of NaOH, KOH, Ba(OH) 2 , Na 2 CO 3 , Li 2 CO 3 , K 2 CO 3 or LiOH, and the molar concentration of the precipitant is 2mol/L～6mol /L;

The pH of the reaction kettle bottom liquid is 10 to 12.5, and the concentration of the complexing agent in the reaction kettle bottom liquid is 15 g/L to 20 g/L;

The reaction temperature of the co-precipitation reaction is 40℃～70℃, the pH of the reaction system is 10～12.5, the concentration of the complexing agent is 15g/L～25g/L, the stirring speed is 200rpm～250rpm, and the reaction time is 5h～120h .
A positive electrode active material prepared from the positive electrode active material precursor according to any one of claims 1-12 or the positive electrode active material precursor obtained by the method for preparing a positive electrode active material precursor according to any one of claims 13-16.
A preparation method of a positive electrode active material, comprising the following steps:

Mixing the positive electrode active material precursor according to any one of claims 1-12 or the positive electrode active material precursor obtained by the preparation method of the positive electrode active material precursor according to any one of claims 13-16 and the lithium source;

In an oxygen-containing atmosphere, sinter at 600°C to 1200°C for 5 hours to 10 hours.
A positive electrode for a lithium ion secondary battery is characterized by comprising a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, the positive electrode active material layer comprising the positive electrode active material according to claim 17 .
A lithium-ion secondary battery, comprising:

The positive electrode of claim 19;

a negative electrode comprising a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector;

Diaphragm and electrolyte.