WO2022083120A1 - Positive electrode material of lithium ion battery, and preparation method therefor - Google Patents

Abstract

A positive electrode material, and a preparation method therefor. The preparation method comprises performing sintering twice; when performing sintering for the first time, the ratio of components of residual alkali on the surface of a sintered product can be adjusted by adjusting an oxygen concentration, and part of doped elements enter particle crystal lattices, and part of doped elements are present on the surface of secondary particles and the surface of interior primary particles, and when performing sintering for the second time, a new coating element reacts with the elements present on the surface and residual alkali on the surface of particles, so as to form a composite fast-ionic conductor coating the surface of the secondary particles and the surface of the interior primary particles. The positive electrode material has loose and porous morphology, and has through holes, a large specific surface area, and a large area in contact with electrolyte, reducing the material reaction resistance; in addition, the coating can reach the interior of particles through the through holes, so that the surface of primary particles inside particles can also be coated with a fast-ionic conductor, further widening the migration path of lithium ions.

Description

A kind of lithium ion battery cathode material and preparation method thereof technical field

The invention belongs to the technical field of lithium-ion battery materials, and particularly relates to a high-power lithium-ion battery positive electrode material and a preparation method thereof.

Background technique

The raw materials of lithium-ion batteries mainly include cathode materials, anode materials, electrolytes, separators and packaging materials. In batteries, the performance of cathode materials must be considered first. Cathode materials are often used as confinement electrodes in lithium-ion batteries, which need to provide sufficient lithium for the charging and power generation process. Therefore, the positive electrode needs to be able to provide a high enough specific capacity to ensure that the lithium-ion battery has an objective energy density. As the limiting electrode, the performance of the cathode material directly affects the overall performance of the battery. In response to market demand, lithium-ion battery cathode materials mainly use doping, coating, and optimizing synthesis processes to improve performance. Coating technology is one of the most widely used and effective methods at present, that is, coating a layer of coating material on the surface of the positive electrode material. In recent years, the coating of fast ion conductors has gradually become a hot spot for the coating of cathode materials for lithium-ion batteries.

The patent with the announcement number CN107706390B discloses a preparation method of a lithium ion battery ternary positive electrode material double modified by a fast ion conductor and a conductive polymer. The fast ion conductor is coated on the ternary positive electrode material by phase method, and then the conductive polymer and the ternary positive electrode material coated with the fast ion conductor are mixed and ball-milled, and the conductive polymer is coated on the ternary positive electrode material covered by the fast ion conductor. on the positive electrode material. In this patent, the synthesized fast ion conductor is mixed with the matrix material for coating, while the commercially available fast ion conductor cannot adjust the composition ratio according to its own material characteristics, and the fast ion conductor cannot react with the residual alkali on the surface of the matrix material. Reducing the residual alkali in the material has no effect, and the cost is high.

The patent application with publication number CN110690435A discloses a high-nickel ternary positive electrode material coated with a fast ion conductor and a preparation method thereof. Mixing solution; adding high-nickel ternary precursor to the mixed solution, and then stirring, drying and grinding to obtain high-nickel ternary precursor powder coated with fast ion conductor; mixing the obtained precursor powder with lithium salt uniformly, sintering Then a high-nickel ternary positive electrode material coated with a fast ion conductor is obtained. In this patent application, the fast ion conductor is synthesized by itself, and the matrix is added and coated in the synthesis stage. There are two methods for synthesizing fast ionic conductors: wet synthesis and dry synthesis. Wet synthesis needs to be carried out in a solution environment, which has many difficulties in process control, is not easy to operate, and has great side effects on materials; dry synthesis first solidifies It is impossible to characterize the synthesis state of the fast ion conductor by mixing the phases to form a fast ion conductor, and then adding it to the matrix, and requires a large variety of raw materials, which is easy to introduce other impurities.

SUMMARY OF THE INVENTION

In view of the problems existing in the prior art, the present invention provides a ternary positive electrode material for lithium ion batteries which is coated and has a low residual alkali concentration on the surface of the base material and a preparation method thereof.

The invention provides a ternary positive electrode material for a lithium ion battery, which is loose and porous inside, a large gap between primary particles on the outside, and some through-holes that can directly reach the inside of the particles; the general chemical formula of the positive electrode material is Li _a Ni _x Co _y M _z O _2±b , where 0.9≤a≤1.4, 0.3≤x≤1, 0≤y≤0.4, 0≤z≤0.4, 0≤b≤0.1; M is Mn, Mg, Al, Ti, Zr, W, One or more of Sr, B, La, Y, Nb. The residual alkali content on the surface of the material is lower than 4000 ppm, and the specific surface area of the positive electrode material is 0.3-3.0 m ² /g.

The surface residual alkali content is the sum of Li content in Li ₂ CO ₃ and LiOH.

The preparation method of the above-mentioned lithium ion battery ternary positive electrode material comprises the following steps:

In step S1, a Ni _x Co _y M _z (OH) ₂ precursor is synthesized by a co-precipitation method, wherein 0.3≤x≤1, 0≤y≤0.4, 0≤z≤0.4, x+y+z=1; M is one or more of Mn, Mg, Al, Ti, Zr, W, Sr, B, La, Y, Nb;

The synthesis of the precursor includes nucleation and inner core growth stage and shell growth stage;

In step S2, the Ni _x Co _y M _z (OH) ₂ precursor synthesized in step S1 is mixed with lithium salt according to a certain mass ratio, and doping elements are added at the same time, and the mixture is uniformly sintered in a high-temperature furnace; the doping elements are Mg, One or more of Al, Ti, Zr, W, Sr, B, La, Y, Nb;

The heating rate during sintering is 3-10℃/min, the sintering temperature is 700-1000℃, and the temperature is kept for 4-24h;

In step S3, the sintered product obtained in step S2 is uniformly mixed with the coating agent, and the second sintering is performed at 400°C-900°C, and the sintering time is 4h-12h to obtain a coated ternary cathode material for lithium ion batteries;

The coating agent is one or more of Mg, Al, Ti, Sr, Zr compounds, or one or more of W, B, La, Y, Nb, Mo, Ta compounds;

According to the type of coating agent in step S3, adjust the oxygen concentration of the atmosphere in the sintering process of step S2:

When the coating agent is one or more of the compounds of Mg, Al, Ti, Sr, and Zr, the volume concentration of oxygen in the atmosphere during the sintering process of step S2 ranges from 18% to 79%;

When the coating agent is one or more of W, B, La, Y, Nb, Mo, and Ta compounds, the volume concentration of oxygen in the atmosphere in the sintering process of step S2 ranges from 30% to 99%.

Further, in step S2, the mass ratio of the precursor and the lithium salt is 1.5-3:1, and the mass percentage of the doping element in the positive electrode material is 0.01%-2%.

Further, in step S3, the mass percentage of the coating element in the positive electrode material is 0.01%-2%.

The principle of the present invention is as follows:

During the first sintering, by adjusting the oxygen concentration, the composition ratio of the residual alkali on the surface of the sintered product can be adjusted. The surface residual base is mainly composed of Li ₂ CO ₃ and LiOH, in which the content of LiOH increases with the increase of oxygen concentration, and the opposite is true for Li ₂ CO ₃ . When the coating element reacts with the residual alkali, some elements will preferentially react with LiOH, and some elements will react with Li ₂ CO ₃ and LiOH at the same time. If the reaction with LiOH is preferred, the content of residual alkali LiOH in the material needs to be high, so that the residual alkali value of the final product will be effectively reduced.

During the first sintering, part of the doped element will enter the particle lattice, and part will exist on the surface of the secondary particle and the inner surface of the primary particle; during the second sintering, the new coating element will exist with this part on the surface The elements react with the residual alkali on the surface of the particles to form a composite fast ion conductor covering the surface of the secondary particles and the surface of the inner primary particles.

Compared with the prior art, the present invention has the following technical effects:

1. The positive electrode material has a loose and porous appearance, and there are through holes. The material has a large specific surface area and a large contact area with the electrolyte, which can reduce the reaction resistance of the material; and the coating can reach the inside of the particle through the through hole. The surface of the particles can also be coated with fast ion conductors, which further broadens the migration path of lithium ions. The material has the advantages of high power, low resistance, and high cycle performance.

2. The composition ratio of residual alkali on the surface of the material is adjusted by adjusting the oxygen concentration. This method is easy to implement and simple to operate. LiOH in the residual alkali is sensitive to the sintering atmosphere, and the difference in oxygen concentration will directly lead to the difference in the LiOH content; the type of residual alkali consumed by coating different fast ion conductors is different, so in the first sintering stage, adjust the residual alkali according to the needs. The ratio of alkali is conducive to the smooth progress of subsequent coating.

3. The fast ion conductor is formed by the reaction between the added element and the residual alkali on the surface of the material, and the element added during the primary sintering and the element added in the secondary sintering can produce a composite reaction, and the resulting fast ion conductor has more Li ⁺ diffusion channel. This method can not only achieve the effect of the commercially available fast ion conductor, but also consume the residual alkali of the material.

Description of drawings

1 is a cross-sectional electron microscope view of the positive electrode material prepared in Example 1.

FIG. 2 is an XRD pattern of the positive electrode material prepared in Example 1. FIG.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings. The description in this part is only exemplary and explanatory, and should not have any limiting effect on the protection scope of the present invention.

Example 1:

Preparation of cathode material for lithium ion battery:

First, the Ni _0.5 Co _0.2 Mn _0.3 (OH) ₂ precursor was synthesized by co-precipitation method. The synthesis of the precursor includes nucleation and inner core growth stage and shell growth stage. Sulfate, preparation total metal ion concentration is 2mol/L mixed metal salt solution, the molar ratio of nickel cobalt manganese is 5: 2: 3, preparation concentration is 4mol/L sodium hydroxide solution and ammonium ion concentration are 5mol/ L of aqueous ammonia solution, pure water is used as the bottom liquid in the reactor, the pH in the bottom liquid of the reactor is adjusted to 12.0 with sodium hydroxide, no ammonia water (guaranteed that the ammonium ion concentration is 0), and then mixed metal salt solution, The sodium hydroxide solution was fed into the reaction kettle through a metering pump to carry out the reaction. During the reaction, the reaction temperature was 45°C, the rotational speed was 600 r/min, the pH of the reaction kettle was controlled at 9.5-13.0, and nitrogen was continuously fed into the reaction kettle; During the growth phase of the inner core, ammonia water was not introduced, and after the particle size of the material grew to 0.8 μm, the ammonium concentration of the reaction system was adjusted to 15 g/L, and the shell growth was carried out until the particle size grew to 3.8 μm. After the precipitate obtained by the reaction is subjected to solid-liquid separation, aging, washing and drying, the Ni _0.5 Co _0.2 Mn _0.3 (OH) ₂ precursor is obtained.

The Ni _0.5 Co _0.2 Mn _0.3 (OH) ₂ precursor synthesized above is mixed with lithium carbonate in a mass ratio of 1.8:1, and doping elements are added at the same time, and the mixture is uniformly sintered in a high-temperature furnace; the doping elements are Mg and Sr, The doping content of Mg and Sr respectively accounts for 0.2% of the mass ratio of the positive electrode material; the heating rate during sintering is 8 °C/min, the sintering temperature is 900 °C, and the temperature is kept for 12 h; the volume concentration of oxygen in the atmosphere during the sintering process is 18. -50%;

Continue to mix the above-mentioned sintered product with Al and Ti oxides uniformly, and carry out the second sintering at 600 ° C for 12 hours. A coated ternary positive electrode material for lithium ion batteries is obtained.

FIG. 1 is a cross-sectional electron microscope view of the positive electrode material prepared in Example 1. It can be seen from the figure that the material is loose and porous inside, and there are certain through holes that can pass into the interior from the outside. FIG. 2 is an XRD pattern of the positive electrode material prepared in Example 1. FIG.

Comparative Example 1:

The synthesis process of the precursor is the same as that in Example 1, and the final synthesis product is Ni _0.5 Co _0.2 Mn _0.3 (OH) ₂ . The Ni _0.5 Co _0.2 Mn _0.3 (OH) ₂ precursor synthesized above and lithium carbonate are in a mass ratio of 1.8:1 Mixing, adding doping elements at the same time, mixing uniformly and then sintering in a high temperature furnace; the doping elements are Mg and Sr, and the doping amount of Mg and Sr respectively accounts for 0.2% of the mass ratio of the positive electrode material; the heating rate during sintering is 8 ℃ /min, the sintering temperature is 900 °C, and the temperature is kept for 12 hours; the volume concentration of oxygen in the atmosphere during the sintering process is 18-50%;

The difference from Example 1 is that in Comparative Example 1, only one sintering was performed, and subsequent coating was not performed.

Example 2:

Preparation of cathode material for lithium ion battery:

The precursor synthesis process is the same as that in Example 1, and the final synthesis product is Ni _0.33 Co _0.33 Mn _0.33 (OH) ₂ . Mix the precursor and lithium carbonate at a mass ratio of 2.0:1, add doping elements at the same time, and sinter in a high-temperature furnace after mixing evenly; the doping element is Zr, accounting for 0.5% of the mass of the positive electrode material, and the heating rate during sintering The sintering temperature is 5°C/min, the sintering temperature is 880°C, and the temperature is kept for 15h; the volume concentration of oxygen in the atmosphere during the sintering process is 70-99%;

Continue to mix the above-mentioned sintered product with oxides of B and W evenly, and perform the second sintering at 400°C for 5 hours. A coated ternary positive electrode material for lithium ion batteries is obtained.

Comparative Example 2-1:

The precursor synthesis process is the same as that in Example 1, and the final synthesis product is Ni _0.33 Co _0.33 Mn _0.33 (OH) ₂ . Mix the precursor and lithium carbonate at a mass ratio of 2.0:1, add doping elements at the same time, and sinter in a high-temperature furnace after mixing evenly; the doping element is Zr, accounting for 0.5% of the mass of the positive electrode material, and the heating rate during sintering The sintering temperature is 5°C/min, the sintering temperature is 880°C, and the temperature is kept for 15h; the volume concentration of oxygen in the atmosphere during the sintering process is 70-99%;

The difference from Example 2 is that in Comparative Example 2, only one sintering was performed, and subsequent coating was not performed.

Comparative Example 2-2:

Preparation of cathode material for lithium ion battery:

The precursor synthesis process is the same as that in Example 1, and the final synthesis product is Ni _0.33 Co _0.33 Mn _0.33 (OH) ₂ . Mix the precursor and lithium carbonate at a mass ratio of 2.0:1, add doping elements, and sinter in a high-temperature furnace after mixing evenly; the doping element is Zr, accounting for 0.5% of the mass of the positive electrode material, and the heating rate during sintering The sintering temperature is 5°C/min, the sintering temperature is 880°C, and the temperature is kept for 15h; the volume concentration of oxygen in the atmosphere during the sintering process is 18% to 40%;

Continue to mix the above-mentioned sintered product with oxides of B and W evenly, and perform the second sintering at 400°C for 5 hours. A coated ternary positive electrode material for lithium ion batteries is obtained.

Example 3:

Preparation of cathode material for lithium ion battery:

The precursor synthesis process is the same as that in Example 1, and the final synthesis product is Ni _0.6 Co _0.2 Mn _0.2 (OH) ₂ . Mix this precursor with lithium hydroxide in a mass ratio of 2.4:1, add doping elements at the same time, and sinter in a high-temperature furnace after mixing evenly; The mass percentage is 0.5% and 0.3%, the heating rate during sintering is 4°C/min, the sintering temperature is 860°C, and the temperature is kept for 18h; the volume concentration of oxygen in the atmosphere during the sintering process is 40-70%;

Continue to mix the above product with Ti and Zr oxides uniformly, and carry out the second sintering at 700°C for 8h.

Comparative Example 3:

The precursor synthesis process is the same as that in Example 1, and the final synthesis product is Ni _0.6 Co _0.2 Mn _0.2 (OH) ₂ . The precursor and lithium hydroxide were mixed at a mass ratio of 2.4, and doping elements were added at the same time, and the mixture was uniformly sintered in a high-temperature furnace; the doping elements were W and Al, and the doping amounts of W and Al respectively accounted for the mass percentage of the positive electrode material. 0.5% and 0.3%, the heating rate during sintering is 4°C/min, the sintering temperature is 860°C, and the temperature is kept for 18h; the volume concentration of oxygen in the atmosphere during sintering is 40-70%;

The difference from Example 3 is that in Comparative Example 3, only one sintering was performed, and subsequent coating was not performed.

Table 1 Residual base value and rate performance of embodiment and comparative example

	Li2CO3 %	LiOH%	Total residual base value ppm	5C/1C	10C/1C
Example 1	0.23	0.06	600	93%	90%

Comparative Example 1	0.41	0.07	990	91%	88%
Example 2	0.3	0.03	650	95%	92%
Comparative Example 2-1	0.26	0.14	880	94%	89%
Comparative Example 2-2	0.45	0.01	850	94%	89%
Example 3	0.37	0.19	1200	92%	89%
Comparative Example 3	0.41	0.24	1500	90%	87%

It can be seen from the data of each example and each comparative example in Table 1 that after coating with fast ions, the total residual base value of the sample is reduced, and the rate performance is improved.

It can be seen from Example 2 and Comparative Example 2-2 that the correct adjustment of the oxygen concentration in the sintering process is beneficial to the reduction of the residual alkali value in the positive electrode material and the improvement of the rate performance.

Moreover, by adjusting the oxygen concentration in the sintering atmosphere, and by coating with fast ions, the residual alkali value of the positive electrode material is greatly reduced, and the rate performance is significantly improved.

The above are only the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the principles of the present invention, several improvements and modifications can be made. It should be regarded as the protection scope of the present invention.

Claims (5)

1. A ternary positive electrode material for lithium ion batteries, characterized in that the interior is loose and porous, the outer primary particle gap is large, and there are some through holes that can directly reach the interior of the particles; the general chemical formula of the positive electrode material is Li _a Ni _x Co _y M _z O _2±b , where 0.9≤a≤1.4, 0.3≤x≤1, 0≤y≤0.4, 0≤z≤0.4, 0≤b≤0.1; M is Mn, Mg, Al, Ti, Zr, W , one or more of Sr, B, La, Y, and Nb; the residual alkali content on the surface of the positive electrode material is lower than 4000 ppm, and the specific surface area of the positive electrode material is 0.3-3.0 m ² /g.
2. The ternary positive electrode material for lithium ion batteries according to claim 1, wherein the surface residual alkali content is the sum of Li content in Li ₂ CO ₃ and LiOH.
3. A preparation method of a lithium ion battery ternary positive electrode material as claimed in claim 1 or 2, comprising the following steps:

   In step S1, a Ni _x Co _y M _z (OH) ₂ precursor is synthesized by a co-precipitation method, wherein 0.3≤x≤1, 0≤y≤0.4, 0≤z≤0.4, x+y+z=1; M is one or more of Mn, Mg, Al, Ti, Zr, W, Sr, B, La, Y, Nb;

   The synthesis of the precursor includes nucleation and inner core growth stage and shell growth stage;

   In step S2, the Ni _x Co _y M _z (OH) ₂ precursor synthesized in step S1 is mixed with lithium salt according to a certain mass ratio, and doping elements are added at the same time, and the mixture is uniformly sintered in a high-temperature furnace; the doping elements are Mg, One or more of Al, Ti, Zr, W, Sr, B, La, Y, Nb;

   The heating rate during sintering is 3-10℃/min, the sintering temperature is 700-1000℃, and the temperature is kept for 4-24h;

   In step S3, the sintered product obtained in step S2 is uniformly mixed with the coating agent, and the second sintering is performed at 400°C-900°C, and the sintering time is 4h-12h to obtain a coated ternary cathode material for lithium ion batteries;

   The coating agent is one or more of Mg, Al, Ti, Sr, Zr compounds, or one or more of W, B, La, Y, Nb, Mo, Ta compounds;

   According to the type of coating agent in step S3, adjust the oxygen concentration of the atmosphere in the sintering process of step S2:

   When the coating agent is one or more of the compounds of Mg, Al, Ti, Sr, and Zr, the volume concentration of oxygen in the atmosphere during the sintering process of step S2 ranges from 18% to 79%;

   When the coating agent is one or more of W, B, La, Y, Nb, Mo, and Ta compounds, the volume concentration of oxygen in the atmosphere during the sintering process of step S2 ranges from 30% to 99%.
4. The preparation method according to claim 3, wherein in step S2, the mass ratio of the precursor and the lithium salt is 1.5-3:1, and the mass percentage of the doping element in the positive electrode material is 0.01%-2%.
5. The preparation method according to claim 3, wherein in step S3, the mass percentage of the coating element in the positive electrode material is 0.01%-2%.

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