CN114684874B - Doped high-magnification 5-series single crystal precursor and preparation method thereof - Google Patents

Abstract

The invention discloses a doped high-magnification 5-series single crystal precursor and a preparation method thereof. The general molecular formula of the precursor is LiNi _0.5(1-x-y) Co _0.2(1-x-y) Mn _{0.3 (1‑x‑y)} Ir _x Zr _y (OH) ₂ , where, 3.5×10 ^‑4 ≤ x+y≤3.0×10 ^‑3 , 4.8×10 ^‑5 ＜x＜3.9×10 ^‑4 , 3× 10 ^‑4 <y<3×10 ^‑3 , by making the ternary salt solution, the first accompanying liquid, the second accompanying liquid, preparing liquid alkali and ammonia water, and preparing the bottom liquid of the reaction kettle, the main metal ions and the doped Heteroelement ion co-precipitation reaction, when the particles reach the target particle size, filter to form a filter cake, the filter cake is washed, dried, sieved, and demagnetized to obtain the precursor. The layered structure of the precursor prepared by this method has high stability, good sphericity, porosity, primary particle crystal morphology and high rate performance. This preparation method is conducive to the precision control of the final doping element content.

Description

A doped high-magnification 5-series single crystal precursor and its preparation method

technical field

The invention relates to a doped high-magnification 5-series single crystal precursor, in particular to a high-magnification 5-series single crystal precursor doped with Ir and Zr at the same time and a preparation method thereof.

Background technique

The molar ratio of nickel in the metal composition of the 5-series monocrystalline precursor is about 0.5, the capacity is guaranteed, and the compaction density is also high. In addition, due to its single crystal structure, the expansion and contraction of the prepared positive electrode material can maintain equiaxed changes during the charge and discharge process, so it has a high layered structure stability, and the cycle life is extended, and the charge and discharge cut-off voltage and high temperature cycle Performance has also been improved. Therefore, it is an excellent research method to prepare positive electrode materials with 5-series single crystal precursors.

However, due to the cation mixing effect between nickel ions and lithium ions in the ternary cathode material, that is, the ionic radius of Ni ²⁺ is close to 0.69nm and 0.76nm of Li ⁺ , it is easy to occupy Ni during the actual cycle. The Li position causes Ni/Li mixing problem. One nickel hinders the entry of Li ⁺ at 7 positions, which leads to battery capacity attenuation, and the capacity and cycle performance of the material will gradually decrease, especially during high-rate charge and discharge processes. How to further improve its cycle performance under high magnification is a direction that researchers are currently developing.

Many researchers have modified cathode materials by doping in order to reduce cation mixing and improve the electrochemical performance of materials.

The mainstream doping elements are Ti, Mg, Al, etc. These doping elements can replace the position of the main elements in the material, and some of them increase the unit cell parameters of _LiNix Co _y Mn _z O ₂ , thereby increasing the crystal structure. The interlayer spacing reduces the migration resistance of Li ⁺ ; some elements can enhance the stability of the crystal structure of the material or increase the capacity, and finally improve the capacity, rate performance and thermal stability of the material. However, most of the above doping is achieved by mixing the precursor with TiO ₂ or MgO, and Li ₂ CO ₃ evenly and then sintering in the reaction furnace. The uniformity of doping inside the actual particles is uncontrollable, which affects the electrochemical performance of the positive electrode. performance.

Based on this, some researchers mixed doping elements into the material by co-precipitation during the precursor preparation stage. Since the precursor synthesis is carried out in a solution state, the uniformity of doping can be greatly improved. Especially for the doping of large particle precursors, it is very difficult to do it through the process of sintering the positive electrode. It is possible that after sintering and doping, there is no doping element at the center of the particle. In addition to the mainstream doping elements, researchers have also tried other element doping. For example, in the Chinese patent CN112794370A, the doping elements are selected from Sr, Ba, Al, Mg, Zr, Ca, La, Ce, Ti, Si, Hf One or more of , Y, Nb, W and Ta; one or more of Mg, W, Mo, Ag, Cu, Zr, La, Bi, Sn, Y, Sr in Chinese patent CN111547780B; In Chinese patent CN113582249A, at least one selected from beryllium, scandium, titanium, vanadium, aluminum, yttrium, zirconium, niobium, molybdenum, copper, zinc, gallium, indium, tantalum and tungsten; researchers also tried Cr, Zr , Zn, W, Nb, Ta, V, Mo, Ru, Ir, Ca, Sr, etc., and achieved certain expected results in doping uniformity. However, not all doping can be carried out in the precursor preparation stage. Some metal elements cannot effectively co-precipitate with the main metal elements or cannot form precipitates in an alkaline environment, but exist in the form of soluble salts or complex incompatible salts. This is not suitable for doping during the precursor preparation stage.

To sum up, it is an urgent need for those skilled in the art to find one or more doping metals to reduce the cation mixing effect, stabilize the crystal structure, realize the uniformity of the actual doping inside the particle, and then improve the electrochemical performance of the positive electrode material. Solved technical problems.

Contents of the invention

Obviously, among the many doping elements, there is no research on the technical issues of co-doping Ir and Zr to reduce the cation mixing effect and control the actual doping uniformity inside the particles. What ratio and method should be used to combine the two It is not mentioned that the rate performance of the material can be improved more effectively, so the present invention provides a high-rate 5-series single crystal precursor product with a specific Ir and Zr doping ratio and a preparation method thereof.

The technical solution adopted by the present invention to solve the technical problem is: a doped high-magnification 5-series single crystal precursor, characterized in that its molecular formula is LiNi _0.5(1-xy) Co _0.2(1-xy) Mn _0.3(1-xy) Ir _x Zr _y (OH) ₂ , where, 3.5×10 ^-4 ≤x+y≤3.0×10 ^-3 , where 4.8×10 ^-5 <x<3.9×10 ^-4 , 3 ×10 ^-4 <y<3×10 ^-3 , the doped metals are Ir and Zr, and the precursor is secondary spherical or quasi-spherical particles formed by vertically stacking elongated hexagonal primary particles; wherein, The primary particles are 0.5-1.5 μm in length and 0.05-0.2 μm in width, the secondary spherical particles or quasi-spherical particles have a particle size of 3.3-3.8 μm, and the pore size is 0.1-0.5 μm; the mass of Ir and Zr respectively account for the precursor 0.01% to 0.08% and 0.03% to 0.3% of the total mass of the body.

Preferably, when Ir accounts for 0.03% of the total mass of the precursor and Zr accounts for 0.072% of the total mass of the precursor, the rate performance of the positive electrode prepared by the precursor is most obviously improved. This may be due to the fact that when these two elements are embedded in the precursor to replace some of the main metal elements, Ir ⁴⁺ balances the anti-site defects caused by Ni ²⁺ and can inhibit the further migration of Ni ²⁺ to the lithium layer. The mixing of cations is reduced, thereby improving the integrity and stability of the crystal structure of the material. Compared with Ni-O, Co-O, and Mn-O bonds, the Zr-O bond formed by Zr is more stable, which can stabilize the crystal structure of the material. However, when there are too many doping elements, the generation of antisite defects in the layered structure of the precursor will be induced, and the amount of antisite defects generated has a linear relationship with the doping amount. An appropriate amount of antisite defects can improve the structural stability of the material, but excessive doping will reduce the performance of the material.

The preparation method of the above-mentioned doped high-magnification 5-series single crystal precursor comprises the following steps:

(1) Prepare solution: prepare Ni, Co, Mn ternary salt solution according to the design ratio; prepare the salt solution of Ir as the first accompanying liquid; prepare the salt solution of Zr as the second accompanying liquid; prepare alkali solution; prepare ammonia aqueous solution;

(2) Prepare the bottom liquid of the reaction tank: under an inert gas environment, pure water, alkali solution, and ammonia solution are prepared into the bottom liquid;

(3) Co-precipitation reaction: uniformly pump the ternary salt solution, the first accompanying liquid and the second accompanying liquid, and alkali solution and ammonia water into the reactor for coprecipitation reaction until the particles reach the target particle size;

(4) Post-treatment: filter the precipitated slurry generated by the reaction to form a filter cake, and then wash, dry, sieve, and demagnetize the filter cake to obtain the precursor;

Wherein, the metal Ir concentration of the first accompanying liquid is 0.3-2.4 g/L, and the metal Zr concentration of the second accompanying liquid is 1.2-12 g/L. This concentration is selected for the convenience of adapting to the size of the equipment and the flow rate setting. Certainly. Because of the small amount of doping, the concentration of the first companion liquid and the second companion liquid should not be too high, otherwise they cannot coordinate with the flow of the ternary salt solution. At this concentration, the first accompanying liquid and the second accompanying liquid can enter the reactor with the ternary salt solution at a flow rate of 160ml to 600ml/h, and the flow rate of the first accompanying liquid and the second accompanying liquid are the same as The flow ratio of the ternary salt solution is controlled between 1:2.5 and 50, and the final mixture is more uniform.

The first co-feeding solution is to add IrCl ₄ ·xH ₂ O to the pure aqueous solution containing SO ₂ to form a solution with a metal Ir concentration of 0.3-2.4 g/L, wherein, the addition method of IrCl ₄ ·xH ₂ O is It can be one or more times, and the Ir content in the solution is detected after adding IrCl ₄ ·xH ₂ O each time. In the formula, because IrCl ₄ is easy to absorb water, x has no definite value, and the manufacturer is also expressed by x in the product label of the purchased reagent.

The second accompanying solution is to add ZrOCl ₂ ·8H ₂ O into the pure aqueous solution containing SO ₂ to form a solution with a metal Zr concentration of 1.2-12 g/L, wherein the addition method of ZrOCl ₂ ·8H ₂ O can be It is one or more times, and the Zr content in the solution is detected after adding ZrOCl ₂ ·8H ₂ O each time.

The above-mentioned _SO2 is slowly passed into pure water. It can be prepared at one time _. The pure aqueous solution containing _SO2 is divided into two parts and then used to prepare the first companion liquid and the second companion liquid respectively. Pass it into 50L pure water, the amount of feeding is 9L, and then divide it into two parts of 4.5L respectively for the preparation of the first companion liquid and the second companion liquid; it can also be divided into two parts to prepare pure SO ₂ Aqueous solution, and then prepare the first accompanying solution and the second accompanying solution, for example, slowly inject SO ₂ into 25L pure water twice, the amount of introduction is 4.5L, and prepare two parts containing SO ₂ pure aqueous solution.

The purpose of introducing SO ₂ into the pure aqueous solution is to make the solution a weakly acidic solution, to inhibit the hydrolysis of IrCl ₄ xH ₂ O and ZrOCl ₂ 8H ₂ O, and to avoid the hydrolysis of doping elements in the form of tiny water insoluble substances. After entering the reactor, it is not embedded into the precursor particles by co-precipitation, but is attached to the surface of the precursor particles or suspended in the slurry, and these non-co-precipitated doping elements are processed by washing, drying, etc. will lose. The Ir and Zr accompanying liquids are configured in a weak acid environment, so that the doping elements tend to remain in an ionic state before entering the reactor, which is conducive to the precision control of the final precipitation element content. Under the same flow control, the content of doping elements is closer to the design value.

The molar ratio of Ni, Co, and Mn in the ternary salt solution is Ni:Co:Mn=5:2:3, and the Ni, Co, and Mn salts used in the ternary salt solution are NiSO ₄ ·6H ₂ O, CoSO ₄ ·7H ₂ O, MnSO ₄ ·H ₂ O, the corresponding main metal concentration of the ternary salt solution is 100-130g/L. Certainly, the molar ratio of Ni, Co, and Mn can also adopt other ratios, such as: 5:2.5::2.5, 5:1:4, etc.

The alkali solution has a concentration of 6 to 12 mol/L, the ammonia solution has a concentration of 6 to 10 mol/L, and the alkali solution is prepared by dissolving NaOH precipitant with pure water;

The preparation method of the bottom liquid of the reaction kettle is as follows: inject 60% of the volume of pure water into the reaction kettle, start stirring at 600-900rpm, heat up to 45-65°C, and then continuously blow _N2 with a purity of 99.99% into the kettle Gas, then add ammonia solution and alkali solution until the ammonia concentration of the system is 0.1-0.2mol/L, and the pH value is 11.8-11.9.

In the co-precipitation reaction, the Ir:Zr molar ratio is 1:3-6, and the preferred molar ratio is 1:5.

In the co-precipitation reaction, the feed flow rate of the ternary salt solution is 1.5-6 L/h, and the feed flow rates of the first accompanying liquid and the second accompanying liquid are 2-10 ml/min.

In the co-precipitation reaction, the flow rate of the ammonia solution 1 hour before the reaction is controlled to be 70-100ml/h, the flow rate of the alkali solution is controlled to be 600-900ml/h, the pH value is kept within the range of 11.85±0.05, and the ammonia value is 0.1-0.2 The nucleation reaction is carried out in the range of mol/L. From 1h, increase the ammonia flow rate by 20-40ml per hour, reduce the alkali flow rate by 40-80ml, increase the ammonia value by 0.05-0.1mol/L per hour, and reduce the pH value by 0.03-0.08 per hour, and the reaction will proceed to 6 After ~9 hours, the ammonia value reaches 0.35~0.45mol/L, the pH value of the solution reaches 11.5~11.6, and then the stable ammonia concentration is 0.4±0.05mol/L, and the stable pH is 11.55±0.05, so that the system enters the stable synthesis stage. The above-mentioned technology of controlling ammonia value and PH is the data that has been summed up through many tests before the present invention researches. This method can ensure that particles with good initial crystallization state can be formed in the initial stage nucleation reaction process, and the growth in the middle and later stages can be guaranteed. The process is capable of forming particles with a certain sphericity, morphology, compaction and specificity.

In the co-precipitation reaction, when the particle size reaches 2.0-2.5 μm, the N ₂ gas flow rate is reduced from 0.8-1m ³ /h to 0.4-0.6m ³ /h, and the flow rate is 5-15L/h. Air, continue to react until the particles reach 3.3-3.8μm; this control can refine the particles once, and can make the precursor particles produce a certain porosity.

In the post-treatment, the precipitated slurry generated by the precipitation reaction is pumped to the filter device, dried to form a filter cake, and the filter cake is centrifugally washed with an alkali solution with a concentration of 0.5-2 mol/L, and then washed with pure water. After the impurity content of the filter cake reaches Na≤200ppm and S≤1800ppm, it is dried, sieved, and demagnetized to obtain precursor product particles.

In the post-treatment, the drying temperature is 90-140° C., and the sieve mesh is 300-400 mesh.

The beneficial effects of the present invention are:

1. After the present invention incorporates Ir and Zr at the same time, the positive electrode prepared by the precursor has a more stable rate performance, especially when the molar ratio of Ir:Zr is 1:5, Ir and Zr respectively account for the total mass of the precursor The ratio is 0.03%, and the rate performance improvement is more obvious when it is 0.072%, as shown in Figure 11; this is because the Ir and Zr elements replace the position of the main element in the precursor, which makes the layered structure of the precursor more stable. At the same time, the Ir There may be a role similar to Ni, which can provide a little capacity for the material by changing the price.

2. In the present invention, Ir and Zr are simultaneously mixed in the precursor synthesis stage, and its element distribution is more uniform than that of conventional sintering doping, as shown in Figure 7; at the same time, the micro-oxidation and the control of reaction parameters in the middle and later stages of synthesis make the precursor It has good sphericity, porosity and primary particle crystal morphology, see Figure 5, Figure 6, and Figure 8.

3. In general, the dissolution process of metal salts in pure water is accompanied by hydrolysis, for example If the dopant element is hydrolyzed too much before the reaction, it will enter the reactor in the form of tiny water-incompatible substances, and eventually it will not be embedded into the interior of the precursor particles by co-precipitation, but attached to the surface of the precursor particles or suspended in the slurry middle. These non-co-precipitated dopant elements are lost by washing, drying, etc. In the process of preparing the first accompanying liquid and the second accompanying liquid, the present invention is all fed into _SO to form a weak acid environment, which can inhibit hydrolysis, so that the doping elements tend to maintain an ion state before entering the reactor, which is beneficial The precision control of the final precipitation element content. In the case of the same flow control, the content of doping elements is closer to the design value, see Table 6.

Description of drawings

Fig. 1 is the particle morphology of product A in Example 1 (Ir:Zr=1:3, containing Ir0.02%).

Fig. 2 is the particle morphology of product B in Example 1 (Ir:Zr=1:4, containing Ir0.02%).

Fig. 3 is the particle morphology of product C in Example 1 (Ir:Zr=1:5, containing Ir0.02%).

Fig. 4 is the particle morphology of product D in Example 1 (Ir:Zr=1:6, containing Ir0.02%).

Fig. 5 is the particle morphology of product E in Example 2 (Ir:Zr=1:5, containing Ir0.01%).

Fig. 6 is the particle morphology of product F in Example 2 (Ir:Zr=1:5, containing Ir0.03%).

FIG. 7 is a distribution diagram of Zr and Ir elements of product F particles in Example 2. FIG.

Fig. 8 is the particle morphology of product G in Example 2 (Ir:Zr=1:5, containing Ir0.06%).

Fig. 9 is the particle morphology of the Fn product in Comparative Example 1 (Ir:Zr=1:5, containing 0.03% Ir).

Figure 10 is the particle morphology of the Fm product in Comparative Example 2 (undoped).

Figure 11 is a comparison of the rate performance after the product is made as a positive electrode and tested.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Example 1:

The ternary salt is made into a concentration of 2mol/L with pure water, and the Ni:Co:Mn molar ratio is a ternary salt solution of 5:2:3, and the Ni, Co, and Mn salts used in the ternary salt solution are NiSO ₄ 6H ₂ O, CoSO ₄ 7H ₂ O, MnSO ₄ .H ₂ O, the main metal concentration _of the ternary salt solution is 100~130g/L; ₂ After the pure aqueous solution is equally divided, add the IrCl ₄ ·xH ₂ O and ZrOCl ₂ ·8H ₂ O salts into two 25L pure aqueous solutions containing SO ₂ three times, and detect the element content after each addition to make the Ir salt concentration The first accompanying liquid is 0.6g/L and the second accompanying liquid is 3g/L Zr salt concentration.

Prepare the NaOH precipitating agent with pure water into an alkaline solution with a concentration of 10 mol/L, and then dilute the ammonia water to a 9.5 mol/L solution.

Inject 60% of the volume of pure water into the reactor, start stirring at 900rpm, raise the temperature to 60°C, and then blow _N2 gas with a purity of 99.99% into the reactor.

After bubbling nitrogen gas for 2 hours, ammonia solution and alkali solution were added until the ammonia concentration of the system was 0.2 mol/L and the pH value was 11.85. Divided into four experiments, according to the requirement that the mass of Ir accounted for 0.02% of the total mass of the precursor, and the molar ratio of Ir:Zr was 1:3, 1:4, 1:5, 1:6, the ternary salt solution, the first The flow rate of the first co-feeding liquid and the second co-feeding liquid, the flow rate of the ammonia solution and the flow of the alkali solution are set according to the nucleation and growth requirements, and the ternary salt solution, the first co-feeding liquid, the second co-feeding liquid, the ammonia solution, the alkali The solution is uniformly pumped into the reactor to carry out the synthesis reaction. Among them, the feed flow rate of the ternary salt solution is 1.5-6L/h, the feed flow rate of the first accompanying liquid and the second accompanying liquid is 2-10ml/min; the flow rate of the ternary salt solution is 1.5- 2L/h, 4-6L/h in the stable synthesis stage, when adjusting the flow rate of the ternary salt solution, increase the flow rate of the first companion liquid and the second companion liquid synergistically to ensure that the Ir content in each stage is 0.02% by mass . The four experiments were synthesized with the same flow rate of the ternary salt solution and the flow rate of the first co-feeding liquid, and the flow rate of the second co-feeding liquid was adjusted according to the different moles of Ir:Zr. The process time node, process ammonia value, PH value, etc. are all kept uniform.

The flow rate of the ammonia solution 1h before the synthesis reaction is controlled to be 70-100ml/h, the flow rate of the alkali solution is controlled to be 600-900ml/h, the ammonia value is kept within the range of 0.1-0.2mol/L, and the pH value is within the range of 11.85±0.05. nuclear reaction. From 1h, increase the flow rate of ammonia solution by 20-40ml per hour, reduce the flow rate of alkali solution by 40-80ml, increase the ammonia value by 0.05-0.1mol/L per hour, and reduce the pH value by 0.03-0.08 per hour, and the reaction will proceed. At 6 to 9 hours, the ammonia value reaches 0.35 to 0.45 mol/L, the pH value of the solution reaches 11.5 to 11.6, and then the ammonia concentration is stabilized at 0.4±0.05 mol/L, and the stable pH is 11.55±0.05, so that the system enters the stable synthesis stage. Since the system enters the stable and forming stage, the ternary salt flow rate is increased every 4 hours, and each adjustment node is increased by 1 to 2 L/h. At the same time, the flow rate of the first companion liquid and the second companion liquid are adjusted synchronously according to the process design until The flow rate of the ternary salt solution reaches 5-6L/h, and the flow rate of the inflow liquid reaches 3-8ml/min, that is, the stable flow rate. When the liquid level reaches 85%-90% of the tank body, it starts to carry out dense clearing and batch reaction.

When the particle size reaches 2.0-2.5μm, reduce the N ₂ gas flow rate from 0.8-1m ³ /h to 0.4-0.6m ³ /h, feed air at a fixed flow rate of 5-15L/h, and continue to react until the particle size Reach 3.3 ~ 3.8μm.

The four kinds of slurry A (Ir:Zr=1:3), B(Ir:Zr=1:4), C (Ir:Zr=1:5), D (Ir:Zr=1:6) generated by the reaction ) into an aging kettle for aging for 4 hours, then pumped to a centrifuge and dried to form a filter cake, which was centrifugally washed with 8 times the weight of 1mol/L alkali solution, and then centrifugally washed with 6 times the weight of pure water for several Second, after the impurity content reaches Na≤200ppm and S≤1800ppm, it is sent to an oven at 130°C for drying. After the moisture is qualified, it is screened with a 300-mesh sieve tray, and finally it is demagnetized with a 12000GS iron remover to obtain A, B, C, and D four kinds of precursors, and their product appearances are shown in Figure 1, Figure 2, Figure 3, and Figure 4, respectively. It can be seen from the figure that the crystalline forms of A, B, C, and D particles are similar, and the primary particles are elongated, with good sphericity and relatively uniform porosity. Because product A is the first test, the process control is not complete and meticulous, so the sphericity is not as good as the other three products, and the pore size is not very uniform. From the charge-discharge cycle, it can be seen that the rate performance of the four products is higher than that of the undoped product, indicating that the doping of Ir and Zr can improve the structural stability of the precursor and reduce the cation mixing effect to a certain extent.

The general molecular formula of the four products is LiNi _0.5(1-xy) Co _0.2(1-xy) Mn _0.3(1-xy) Ir _{x Zry} (OH) ₂ , wherein,

3.5×10 ^-4 ≤x+y≤3.0×10 ^-3 , where 4.8×10 ^-5 ＜x＜3.9×10 ^-4 , 3×10 ^-4 ＜y＜3×10 ^-3 , all of which are slender The secondary spherical particles or quasi-spherical particles formed by vertically stacking hexagonal primary particles, among which, the particle indexes of the four products are as follows in Table 1.

Table 1: A, B, C, D four product particle index table

According to the molar ratio of Li ₂ CO ₃ excess of 4% to 8%, the above-mentioned A, B, C, D precursors and lithium sources were sintered in a sintering furnace for 2 hours. Take out, grind and disperse, then calcinate at 750°C for 12h, the heating rate is 25°C/min, take out and pulverize after cooling, and finally obtain positive electrode materials A1, B1, C1, D1, and then assemble them into coin cells for rate performance test. The results show that the rate performance is optimal when the molar ratio is Ir:Zr=1:5.

Further, the mass of Ir is respectively selected to account for 0.01%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, and 0.08% of the total mass of the precursor, according to the Ir:Zr molar ratio of 1:3, 1:4, The requirements of 1:5 and 1:6 are respectively prepared according to the above method to prepare the precursor and the positive electrode material. The morphology of the prepared precursor particles is similar to the above A, B, C, and D. The positive electrode prepared with these particles is assembled into The result of the rate performance test of the coin cell is also similar.

Example 2:

Further, according to the molar ratio of Ir:Zr=1:5, the mass of Ir accounts for 0.01%, 0.03%, and 0.06% of the total mass of the precursor to prepare the precursor according to the method in Example 1, respectively.

Three kinds of slurry E (Ir0.01%, Zr0.024%) that reaction generates, F (Ir0.03%, Zr0.072%), G (Ir0.06%, Zr0.144%), put into old The kettle is aged for 4 hours, then pumped to a centrifuge and dried to form a filter cake, which is centrifugally washed with 8 times the weight of 1mol/L alkali solution, and then centrifugally washed several times with 6 times the weight of pure water to remove impurities After the content reaches the standard, it is sent to an oven at 130°C for drying; after the moisture is qualified, it is screened with a 300-mesh sieve plate, and finally demagnetized with a 12000GS iron remover to obtain three precursors of E, F, and G. The morphology is shown in Figure 5, Figure 6, and Figure 8, respectively. It can be seen from the figures that the three products of E, F, and G have similar crystallization shapes, and the primary particles are elongated, with good sphericity and relatively uniform porosity. In addition, it can also be observed from Figure 7 that the Zr and Ir elements in the F product are evenly distributed on the spherical particles.

The molecular formulas of the three products are LiNi _0.5(1-xy) Co _0.2(1-xy) Mn _0.3(1-xy) Ir _{x Zry} (OH) ₂ , where 3.5×10 ^-4 ≤x+y≤ 3.0×10 ^-3 , in which 4.8×10 ^-5 <x<3.9×10 ^-4 , 3×10 ^-4 <y<3×10 ^-3 , all of which are formed by longitudinal stacking of elongated hexagonal primary particles Formed secondary spherical particles or quasi-spherical particles, wherein the particle indexes of the three products are shown in Table 2 below.

Table 2: E, F, G three product particle index table

According to the molar ratio of Li ₂ CO ₃ excess of 4% to 8%, the above-mentioned E, F, G precursors and lithium sources were sintered in a sintering furnace for 2 hours. The first sintering temperature was 400°C, and the heating rate was 15°C/min; Disperse, and then calcined at 750°C for 12h with a heating rate of 25°C/min. After cooling, they were taken out and pulverized to finally obtain positive electrode materials E1, F1, and G1, and then assembled into coin cells for rate performance testing. The results show that the rate performance is the best when the mass proportion of Ir is 0.03%.

Further, according to the molar ratio of Ir:Zr=1:5, the mass of Ir is respectively selected to account for 0.02%, 0.04%, and 0.05% of the total mass of the precursor, and then the precursor and the positive electrode material are prepared according to the above methods respectively. The morphology of the prepared product particles is similar to the above-mentioned E, F, and G particles, and the positive electrode prepared with these particles is assembled into a button battery for rate performance test results.

Comparative example 1: The first co-feeding solution and the second co-feeding solution were not prepared and tested in a weak acid environment.

Add IrCl ₄ ·xH ₂ O and ZrOCl ₂ ·8H ₂ O to 50L of pure water when making the concomitant liquid, and make the first concomitant liquid with Ir salt concentration of 0.6g/L and Zr salt concentration of 3g respectively /L of the second companion liquid. The remaining operating steps are consistent with the "F" product (Ir:Zr=1:5, containing Ir0.03%) in "Example 2".

Put the slurry generated by the reaction into an aging tank for aging for 4 hours, then pump it to a centrifuge and dry it into a filter cake. The filter cake was centrifuged and washed with 8 times the weight of 1 mol/L alkaline solution, and then centrifuged and washed several times with 6 times the weight of pure water. After the impurity content reaches the standard, it is sent to an oven at 130°C for drying. After the moisture is qualified, use a 300-mesh sieve plate to sieve, and finally use a 12000GS iron remover to demagnetize to obtain the Fn precursor, and its appearance is shown in Figure 9. It can be seen from the figure that the appearance of Fn is similar to that of F product, the particle crystallization form is good, the primary particle is elongated, has better sphericity and more uniform porosity.

The molecular formula of Fn product particles is LiNi _0.5(1-xy) Co _0.2(1-xy) Mn _0.3(1-xy) Ir _{x Zry} (OH) ₂ , where 3.5×10 ^-4 ≤x+y≤ 3.0×10 ^-3 , in which 4.8×10 ^-5 <x<3.9×10 ^-4 , 3×10 ^-4 <y<3×10 ^-3 , all of which are formed by longitudinal stacking of elongated hexagonal primary particles Formed secondary spherical particles or quasi-spherical particles, wherein the Fn product particle indicators are shown in Table 3 below.

Table 3: Particle index table of Fn products

According to the molar ratio of Li ₂ CO ₃ excess of 4% to 8%, the above precursor and lithium source were sintered in a sintering furnace for 2h, the temperature of the first sintering was 400°C, and the heating rate was 15°C/min; It was calcined at ℃ for 12 hours, and the heating rate was 25 ℃/min. After cooling, it was taken out and pulverized to obtain the positive electrode material Fn1, which was then assembled into a button battery for rate performance test. The results show that the rate performance is also improved, but not optimal. Compared with the design value, the content of doping elements is slightly lower than that of the F product.

Comparative example 2: No concomitant feeding liquid is configured, and no doping test is performed.

The precursor was prepared according to the method in Example 1, and the preparation steps of the first concomitant liquid and the second concomitant liquid were omitted, that is, no doping was performed, and the precursor slurry was prepared.

Put the slurry generated by the reaction into an aging kettle for aging for 4 hours, then pump it to a centrifuge and dry it into a filter cake, wash the filter cake with 8 times the weight of 1mol/L alkali solution, and then use 6 times the weight After the impurity content reaches the standard, it is sent to an oven at 130°C for drying. After the moisture is qualified, it is sieved with a 300-mesh sieve plate, and finally it is demagnetized with a 12000GS iron remover to obtain the Fm precursor. , and its morphology is shown in Figure 10. The crystalline form of the particles is good, and the primary particles are elongated, with good sphericity and relatively uniform porosity.

The molecular formula of the Fm product particles is LiNi _0.5 Co _0.2 Mn _0.3 (OH) ₂ , which are secondary spherical particles or quasi-spherical particles formed by vertically stacking elongated hexagonal primary particles. Among them, the Fm product particle index See Table 4 below.

Table 4: Particle index table of Fm products

According to the molar ratio of Li ₂ CO ₃ excess of 4% to 8%, the above precursor and lithium source were sintered in a sintering furnace for 2h, the temperature of the first sintering was 400°C, and the heating rate was 15°C/min; It was calcined at ℃ for 12 hours, and the heating rate was 25 ℃/min. After cooling, it was taken out and pulverized to obtain the positive electrode material Fm1, which was then assembled into a button battery for rate performance test. The results show that its high-rate performance is significantly lower than that of doped cathode materials.

Detection method:

The nine positive electrode materials A1, B1, C1, D1, E1, F1, G1, Fn1, Fm1 prepared in Examples 1-2 and Comparative Examples 1-2 were mixed with conductive agent, dispersant, etc. according to a certain mass: 25g positive electrode material + 10g PVDF glue (17.18g NMP mixed with 1g KF9700) + 3.5g conductive agent slurry (10g XC-72 conductive agent, 7.5g dispersant + 50gNMP) + 0.05g maleic acid + 0.8g KS6L. After mixing evenly, it is a coatable material.

Apply the material on the positive electrode sheet to make a positive electrode with an areal density of 12 mg/cm ² , and then cut it into a disc with a diameter of 14 mm. A CR2016 button battery was assembled in a glove box after drying with a lithium metal sheet as the negative electrode.

Cycling performance test: LiPF ₆ was used as solute, EC:DEC:DMC=1:1:1V% mixture was used as solvent to make 1M electrolyte, the button battery was charged and discharged twice at 0.1C, and charged and discharged twice at 0.5C. Charge and discharge once, then charge at 0.5C, and then discharge at 1.0C, 2.0C, 5.0C for activation. Finally, cycle 100 times under 0.1C, 0.5C, 1C, 2C, 5C magnification respectively, and the cut-off voltage is 4.5V. The discharge capacity at the 1st cycle and the discharge capacity at the 100th cycle were measured respectively, and the capacity retention rate was calculated. Calculation formula: 100 cycles capacity retention rate (%) = discharge capacity at the 100th cycle ÷ discharge capacity at the 1st cycle × 100%. The specific capacity and cycle retention of the material were obtained, and the electrochemical performance of the product after testing is shown in Table 5 and Figure 11.

Table 5: Product electrochemical test results table

The rate performance comparison after the product test is shown in Figure 11. According to the results in Table 1 and Figure 11, it can be seen that the high-rate 5-series single crystal precursor prepared by doping Ir and Zr in the present invention has a higher Fm than the undoped product. The magnification performance has been significantly improved. Product F1 has the best rate performance, and its corresponding precursor F is characterized by Ir:Zr=1:5, containing 0.03% Ir, containing 0.076% Zr, and its accompanying liquid is configured in a weak acidic environment; F product is more conventional operation The Fn product with liquid feeding is configured below, the Ir content of the two is 0.0308%, 0.0278%, and the Zr content is 0.0771%, 0.0682%, respectively. Obviously, the content of the doping elements of the F product is consistent with the design value (Ir: 0.03%, Zr : 0.076%) is closer, and the final doping content is more accurate, as shown in Table 6. The energy spectrum scanning of the precursor F shows that the doping of Ir and Zr in the preparation stage of the precursor can ensure the uniformity of element distribution.

Table 6: Comparison table of final doping content of F product and Fn product particles

Claims (23)

1. A doped high-magnification 5-series single crystal precursor, characterized in that: its general molecular formula is LiNi _0.5(1-xy) Co _0.2(1-xy) Mn _0.3(1-xy) Ir _x Zr _y (OH) ₂ , where 3.5×10 ^-4 ≤x+y≤3.0×10 ^-3 , where 4.8×10 ^-5 <x<3.9×10 ^-4 , 3×10 ^-4 <y<3×10 ^{- 3.} The doping metals are Ir and Zr, and the precursor is secondary spherical or quasi-spherical particles formed by vertically stacking elongated hexagonal primary particles. 2. The doped high-magnification 5-series single crystal precursor according to claim 1, characterized in that: the primary particles are 0.5-1.5 μm long and 0.05-0.2 μm wide, and the secondary spherical particles or quasi-spherical particles The particle size is 3.3~3.8μm, and the pore size is 0.1~0.5μm. 3. The doped high-magnification 5-series single crystal precursor according to claim 1, wherein the mass of Ir and Zr account for 0.01%-0.08% and 0.03%-0.3% of the total mass of the precursor, respectively . 4. The doped high-magnification 5-series single crystal precursor according to claim 1, wherein the mass of Ir and Zr account for 0.03% and 0.072% of the total mass of the precursor, respectively. 5. The preparation method of the doped type high-magnification 5-series single crystal precursor according to claim 1, 2, 3 or 4, comprising the steps of: Prepare solution: prepare Ni, Co, Mn ternary salt solution according to the design ratio; prepare Ir salt solution as the first accompanying solution; prepare Zr salt solution as the second accompanying solution; prepare alkali solution; prepare ammonia solution; Prepare the bottom liquid of the reaction kettle: under an inert gas environment, prepare the bottom liquid of the reaction kettle with pure water, alkali solution, and ammonia solution; Co-precipitation reaction: uniformly pump the ternary salt solution, the first co-feeding liquid and the second co-feeding liquid, as well as alkali solution and ammonia water into the reactor for co-precipitation reaction until the particles reach the target particle size; Post-processing: filter the precipitated slurry generated by the reaction to form a filter cake, and then wash, dry, sieve, and demagnetize the filter cake to obtain the precursor; It is characterized in that: the metal Ir concentration of the first accompanying liquid is 0.3-2.4g/L, the metal Zr concentration of the second accompanying liquid is 1.2-12g/L, and in the co-precipitation reaction, the first accompanying liquid The ratios of the flow rate of the liquid and the flow rate of the second accompanying liquid to the flow rate of the ternary salt solution are all controlled between 1:2.5~50. 6. The preparation method of the doped high-magnification 5-series single crystal precursor according to claim 5, characterized in that: the first companion liquid is to add IrCl ₄ ·xH ₂ O to the SO ₂ Formed in pure aqueous solution, the second accompanying liquid is formed by adding ZrOCl ₂ 8H ₂ O to pure aqueous solution containing SO ₂ , and the pure aqueous solution containing _{SO 2 is} slowly introduced into pure water Formed in , and divided into two equal parts to prepare the first companion liquid and the second companion liquid respectively. 7. The preparation method of the doped high-magnification 5-series single crystal precursor according to claim 5, characterized in that: the first companion liquid is to add IrCl ₄ ·xH ₂ O to the pure aqueous solution containing SO ₂ A solution with a metal Ir concentration of 0.3-2.4g/L is formed, wherein IrCl ₄ ·xH ₂ O is added once or multiple times, and the Ir content in the solution is detected after each addition of IrCl ₄ ·xH ₂ O. 8. The preparation method of the doped high-magnification 5-series single crystal precursor according to claim 5, characterized in that: the second accompanying solution is to add ZrOCl ₂ 8H ₂ O to the pure aqueous solution containing SO ₂ A solution with a metal Zr concentration of 1.2-12g/L is formed, wherein ZrOCl ₂ ·8H ₂ O is added once or several times, and the Zr content in the solution is detected after each addition of ZrOCl ₂ ·8H ₂ O. 9. The preparation method of the doped high-magnification 5-series single crystal precursor according to claim 7, characterized in that: the pure aqueous solution containing _SO2 is formed by slowly injecting _SO2 into 25L pure water Yes, the injected volume is 4.5L. 10. The preparation method of doped high-magnification 5-series single crystal precursor according to claim 8, characterized in that: the pure aqueous solution containing _SO2 is formed by slowly passing _SO2 into 25L pure water Yes, the injected volume is 4.5L. 11. The preparation method of the doped high-magnification 5-series single crystal precursor according to claim 5, characterized in that: the molar ratio of Ni, Co, and Mn in the ternary salt solution is Ni: Co: Mn = 5:2:3. 12. The preparation method of the doped high-magnification 5-series single crystal precursor according to claim 5, characterized in that: the Ni, Co, and Mn salts used in the ternary salt solution are NiSO ₄ ·6H ₂ O, CoSO ₄ .7H ₂ O, MnSO ₄ .H ₂ O. 13. The preparation method of the doped high-magnification 5-series single crystal precursor according to claim 5, characterized in that: the concentration of the alkali solution is 6-12mol/L, and the concentration of the ammonia solution is 6-10mol /L. 14. The method for preparing the doped high-magnification 5-series single crystal precursor according to claim 13, wherein the alkaline solution is prepared by dissolving NaOH precipitant with pure water. 15. The preparation method of the doped high-magnification 5-series single crystal precursor according to claim 5, characterized in that: the preparation method of the reaction kettle bottom liquid is: injecting 60% of the kettle volume of pure water, start stirring at 600~900rpm, heat up to 45~65°C, then continuously blow _N2 gas with a purity of 99.99% into the kettle, then add ammonia solution and alkali solution until the ammonia concentration of the system is 0.1~0.2mol/L, pH The value is 11.8~11.9. 16. The method for preparing the doped high-magnification 5-series single crystal precursor according to claim 5, wherein the molar ratio of Ir:Zr in the co-precipitation reaction is 1:3~6. 17. The method for preparing the doped high-magnification 5-series single crystal precursor according to claim 16, wherein the molar ratio of Ir:Zr in the co-precipitation reaction is 1:5. 18. The preparation method of the doped high-magnification 5-series single crystal precursor according to claim 5, characterized in that: in the co-precipitation reaction, the feed flow rate of the ternary salt solution is 1.5~6L/h , The feed flow rate of the first accompanying liquid and the second accompanying liquid is 2~10mL/min. 19. The preparation method of the doped high-magnification 5-series single crystal precursor according to claim 5, characterized in that: in the co-precipitation reaction, the flow rate of the ammonia solution 1 h before the reaction is controlled to 70-100 mL/h, The flow rate of the alkaline solution is controlled at 600~900mL/h, the pH value is kept in the range of 11.85±0.05, the ammonia value is in the range of 0.1-0.2mol/L for nucleation reaction, and the ammonia flow rate is increased by 20~40mL per hour starting from 1h. Reduce the alkali flow rate by 40~80mL, increase the ammonia value by 0.05~0.1mol/L per hour, and reduce the pH value by 0.03~0.08 per hour, and the ammonia value reaches 0.35~0.45mol/L when the reaction is carried out for 6~9 hours. The pH value of the solution reaches 11.5~11.6, then the ammonia concentration is stabilized at 0.4±0.05mol/L, and the pH is stabilized at 11.55±0.05, so that the system enters the stable synthesis stage. 20. The preparation method of the doped high-magnification 5-series single crystal precursor according to claim 5, characterized in that: in the co-precipitation reaction, when the particle size reaches 2.0-2.5 μm, the _N2 gas flow Reduce from 0.8~1m ³ /h to 0.4~0.6m ³ /h, feed air at a fixed flow rate of 5~15L/h, and continue to react until the particles reach the target particle size. 21. The method for preparing the doped high-magnification 5-series single crystal precursor according to claim 20, characterized in that: the target particle size is 3.3-3.8 μm. 22. The preparation method of the doped high-magnification 5-series single crystal precursor according to claim 5, characterized in that: in the post-treatment, the precipitation slurry generated by the co-precipitation reaction is pumped to the filter device, Dried to form a filter cake, centrifuge and wash the filter cake with an alkali solution with a concentration of 0.5~2mol/L, and then wash the filter cake with pure water. After the impurity content reaches Na≤200ppm, S≤1800ppm, then dry and sieve Separation and demagnetization treatment to obtain precursor product particles. 23. The preparation method of the doped high-magnification 5-series single crystal precursor according to claim 5, characterized in that: in the post-treatment, the drying temperature is 90-140°C, and the sieving mesh It is 300~400 mesh.