Perovskite lanthanum cobaltate coated lithium cobaltate composite material and preparation method thereof

Abstract

The invention relates to the technical field of battery materials, and discloses a perovskite lanthanum cobaltate coated lithium cobaltate composite material, a preparation method thereof, a positive plate and a lithium battery. The preparation method comprises the following steps: mixing a solution in which a divalent cobalt metal salt and a trivalent lanthanum metal salt are dissolved and a solution in which lithium cobalt oxide and sodium hydroxide are dispersed, then carrying out a hydrothermal reaction, centrifuging a product of the hydrothermal reaction, then carrying out vacuum drying on the product obtained by centrifuging, and then carrying out calcination treatment, so as to obtain the perovskite lanthanum cobalt oxide coated lithium cobalt oxide composite material. The perovskite coated lithium cobalt oxide composite material can be obtained. The perovskite lanthanum cobalt oxide coated lithium cobalt oxide composite material provided by the invention has excellent conductivity, rate capability and cycle performance.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of batteries, in particular to a perovskite cobaltite-lanthanum cobaltate coated lithium cobaltate composite material, a preparation method thereof, a positive plate and a lithium battery. BACKGROUND

[0002] LiCoO2 is a first-generation commercial lithium ion battery layered oxide positive material, which belongs to a hexagonal crystal system and has an R-3m layered structure. LiCoO2 has the advantages of simple preparation method, high working voltage, stable discharge, high filling density, good cycle performance and suitability for large-current discharge, but the global proven cobalt reserves are only more than 7 million tons, so the use cost is high, which limits the application of LiCoO2 material in batteries to some extent. LiCoO2 has a theoretical capacity of up to 274 mAh.g -1 -1 , but in actual application, the actual discharge capacity is only about 140 mAh.g -1 -1 , the reason is that when charged to above 4.2V, the lithium ion extraction amount is more than 50%, which causes the reversible capacity to decrease rapidly, thereby causing the capacity of LiCoO2 to rapidly decrease. In addition, the dangling bonds and unsaturated coordination on the surface of the LiCoO2 positive material significantly increase the surface reactivity, so that it is more prone to severe interface reactions. In order to improve the cycle stability of LiCoO2 and reduce the interface side reaction, coating is an effective and simple method. Surface coating can separate the positive material from the conductive agent and the electrolyte, thereby reducing the internal resistance and polarization phenomenon of the battery and improving the cycle stability and charge-discharge performance of the battery. ABO3 type all-inorganic perovskite oxides have excellent electrical conductivity and good structural stability in a wide range of oxidation-reduction conditions. This advantage mainly depends on the selection of constituent elements at A and B sites. Generally speaking, alkali metals or rare earth elements with large ionic radii usually occupy the 12-coordinated A site, and transition metals with smaller ionic radii tend to occupy the 6-coordinated B site. Therefore, the rare earth element lanthanum (La) becomes an ideal A-site element selection due to its special electronic configuration (4f n-1 5d 0，1 6s 2 , where n is 1-15), and when lanthanum and transition metals such as nickel (Ni), cobalt (Co) or manganese (Mn) jointly construct a perovskite structure, the composite oxide formed usually exhibits good electrochemical stability and conductivity. SUMMARY

[0003] The application aims to provide a perovskite lanthanum cobaltate coated lithium cobaltate composite material, a preparation method thereof, a positive plate and a lithium battery.

[0004] To achieve the above-mentioned purpose, the technical scheme of the application is as follows:

[0005] In the first aspect of the application, a preparation method of a perovskite lanthanum cobaltate coated lithium cobaltate composite material is provided, characterized in that: a reaction liquid 1 and a reaction liquid 2 are mixed to perform a hydrothermal reaction, and a solid-liquid mixture is obtained after the reaction; the reaction liquid 1 has dissolved therein a divalent cobalt metal salt and a trivalent lanthanum metal salt; the reaction liquid 2 has dispersed therein lithium cobaltate and sodium hydroxide; and the solid-liquid mixture is subjected to hydrothermal treatment, centrifugation, vacuum drying and high-temperature calcination, thereby obtaining a lithium cobaltate material coated with a perovskite lanthanum cobaltate shell.

[0006] At least one of the following features (1) to (13) is further included:

[0007] (1) In the perovskite coated lithium cobaltate material, the mass ratio of the perovskite lanthanum cobaltate to the lithium cobaltate is 0.01 to 0.05:1, and preferably 0.03:1;

[0008] (2) The concentration of the divalent cobalt metal salt in the reaction liquid 1 is 0.05 to 0.1 mol / L, and preferably 0.1 mol / L;

[0009] (3) The concentration of the trivalent lanthanum metal salt in the reaction liquid 1 is 0.05 to 0.1 mol / L, and preferably 0.1 mol / L;

[0010] (4) The lithium cobaltate and the sodium hydroxide are dispersed in the reaction liquid 2, and the reaction liquid 1 and the reaction liquid 2 are mixed to perform the reaction in the following manner: the reaction liquid 1 is added to the reaction liquid 2 under vigorous stirring;

[0011] (5) The concentration of the sodium hydroxide in the reaction liquid 2 is 0.1 to 0.2 mol / L, and preferably 0.15 mol / L;

[0012] (6) The lithium cobaltate is dispersed in the reaction liquid 2, and the configuration method comprises the following steps: the lithium cobaltate is added to deionized water and then crushed in an ultrasonic cell disruptor, and the crushing power is set to 80 to 100%, and the crushing time is 2 to 3 hours;

[0013] (7) The divalent cobalt metal salt in the reaction liquid 1 is at least one of cobalt chloride, cobalt carbonate, cobalt sulfate, cobalt nitrate, cobalt oxalate and cobalt hydroxide, and preferably cobalt chloride;

[0014] (8) the trivalent lanthanum metal salt in the reaction solution 1 is at least one of lanthanum chloride, lanthanum sulfate, lanthanum phosphate, lanthanum oxalate, lanthanum nitrate, and lanthanum carbonate, and is preferably lanthanum chloride;

[0015] (9) the particle size of the lithium cobaltate dispersed in the reaction solution 2 is 0.5-2 μm, and is preferably 1 μm;

[0016] (10) the temperature of the hydrothermal reaction is 160-240℃, and the time is 10-20 h, and is preferably 12 h;

[0017] (11) the rotation speed of the centrifugation operation is 5000-10000 rpm, and the time is 5-10 min, and is preferably 8000 rpm;

[0018] (12) the temperature of the vacuum drying is 60-100℃, and the time is 10-15 h, and is preferably 80℃, and 12 h;

[0019] (13) the conditions of the high-temperature calcination are calcination in an air or oxygen atmosphere, the temperature is 500-700℃, and the time is 5-8 h, and is preferably 600℃, and 6 h.

[0020] The solvent in the reaction solution 1 or the reaction solution 2 is at least one of deionized water, anhydrous methanol, anhydrous ethanol, ethylene glycol, and glycerol, and is preferably anhydrous ethanol and deionized water.

[0021] In a second aspect, the application provides a perovskite lanthanum cobaltate coated lithium cobaltate composite material prepared by the method of any one of the preceding embodiments.

[0022] In a third aspect, the application provides a positive electrode sheet, the active material of which comprises the perovskite lanthanum cobaltate coated lithium cobaltate composite material prepared by the method of any one of the preceding embodiments.

[0023] In a fourth aspect, the application provides a lithium battery comprising the positive electrode sheet prepared by the method of any one of the preceding embodiments.

[0024] Compared with the prior art, the application has the following advantages:

[0025] (1) The application prepares a perovskite lanthanum cobaltate coated lithium cobaltate composite material. The preparation process of the material is simple, and the cycle and rate performance of the lithium cobaltate can be improved.

[0026] (2) The positive electrode sheet provided by the application can be prepared by a simple coating process without special atmosphere protection. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 A scanning electron microscope image of the perovskite lanthanum cobaltate coated lithium cobaltate composite material prepared in Example 1 of the application;

[0028] Figure 2 Rate capability (a) and cycle performance (b) of batteries assembled with the perovskite LaCoO3-coated LiCoO2 composite material and commercial LiCoO2 in Example 2 of the present application. DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the present application will be described clearly and completely below in conjunction with specific embodiments and drawings. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. The embodiments described and shown in the drawings herein can be realized through various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of protection, but merely represents selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present application.

[0030] The present application does not have special restrictions on the sources of all raw materials used, and commercially available or self-made materials can be used. There are no special restrictions on the purity thereof.

[0031] Example 1

[0032] The present embodiment provides a preparation method of a perovskite LaCoO3-coated LiCoO2 composite material.

[0033] 0.06 mM of LaCl3·7H2O and 0.06 mM of CoCl2·6H2O were accurately weighed and dissolved in deionized water to prepare a reaction solution 1;

[0034] 0.97 g of LiCoO2 powder was dispersed in an appropriate amount of deionized water, and was fully mixed and uniformly mixed under magnetic stirring at room temperature. Subsequently, while continuously stirring, a 0.04 mM NaOH aqueous solution was slowly added dropwise, and the stirring was continued for about 30 min to prepare a reaction solution 2;

[0035] The reaction solution 2 was continuously stirred, and the reaction solution 1 was slowly added;

[0036] The obtained mixed suspension was transferred into a polytetrafluoroethylene-lined high-pressure reaction kettle, which was then placed in an oven preheated to 150°C after being sealed, and was subjected to hydrothermal reaction for 12 h;

[0037] After the reaction was completed, the obtained solid product was naturally cooled to room temperature, and was repeatedly washed with deionized water and centrifuged for 3 times, and then was washed with anhydrous ethanol and centrifuged for 3 times, at a speed of 8000 rpm, to remove residual ions and organic impurities;

[0038] After the washing was completed, the wet product was placed in a drying oven and was dried at 80°C for 12 h to a constant weight.

[0039] The precursor after drying is raised to 800℃ at a temperature raising rate of 5℃ / min, and calcined at this temperature for 6h, and cooled to room temperature to obtain the perovskite lanthanum cobaltate coated lithium cobaltate composite material.

[0040] Figure 1 The scanning electron microscope image of the perovskite lanthanum cobaltate coated lithium cobaltate composite material prepared in Example 1 is shown in the figure, and the lanthanum cobaltate is uniformly coated on the surface of the lithium cobaltate, which proves that the composite material is successfully prepared.

[0041] Example 2:

[0042] This example tests the rate and cycle performance of the lithium battery assembled by the positive electrode sheet based on the perovskite lanthanum cobaltate coated lithium cobaltate composite material.

[0043] The lithium battery is assembled in an argon-filled glove box using the perovskite lanthanum cobaltate coated lithium cobaltate composite material and the commercial lithium cobaltate material as the positive electrode, with the positive electrode sheet as the working electrode, lithium metal as the counter electrode, 1.0M LiPF6 in EC:DMC:EMC=1:1:1 Vol% as the electrolyte, and commercial polypropylene as the separator.

[0044] The preparation method of the positive electrode sheet is as follows: a mixture of lithium cobaltate powder, acetylene black and polyvinylidene fluoride (pvdf) in a mass ratio of 8:1:1 is added with an appropriate amount of N-methyl pyrrolidone (NMP). The mixture is magnetically stirred to obtain a slurry with moderate viscosity. The slurry is uniformly coated on a carbon-coated aluminum foil and vacuum dried at 80℃ overnight. After drying, the electrode is cut into a circular sheet with a diameter of 12mm, and the mass of each positive electrode sheet is weighed. The mass of the active material is calculated according to the proportion.

[0045] The preparation method of the lithium battery is as follows: in the glove box, a button cell with model CR2032 is assembled in the order of negative electrode shell, positive electrode sheet, separator, electrolyte, lithium metal, gasket, spring, and positive electrode shell, and then the electrochemical performance is tested on a battery test system.

[0046] Figure 2 The rate (a) and cycle performance (b) of the lithium battery assembled using the perovskite lanthanum cobaltate coated lithium cobaltate composite material and the commercial lithium cobaltate material in Example 2 of the present application. The results show that the lithium battery assembled using the perovskite lanthanum cobaltate coated lithium cobaltate composite material has a capacity of about 132.82-135.22mAh·g -1 at a current density of 10C (1C=160mAhg -1 ), while the lithium battery assembled using the commercial lithium cobaltate material has a capacity of only about 89mAh g -1capacity of 130.63 mAh g-1 at a current density of 1C after 100 cycles, while the lithium battery assembled using the commercial lithium cobalt oxide material has a capacity of only 98 mAh g-1 at a current density of 1C after 100 cycles. -1 capacity of 130.63 mAh g-1 at a current density of 1C after 100 cycles, while the lithium battery assembled using the commercial lithium cobalt oxide material has a capacity of only 98 mAh g-1 at a current density of 1C after 100 cycles. -1 The cycle stability of the lithium battery assembled using the perovskite lanthanum cobalt oxide coated lithium cobalt oxide composite material is obviously higher than that of the lithium battery assembled using the commercial lithium cobalt oxide material (b).

[0047] The above description is merely preferred embodiments of the application, but not to limit the application. Any modification, equivalent replacement and improvement made within the spirit and principle of the application shall fall within the protection scope of the application.

Claims

1. A method for preparing a perovskite lanthanum cobalt oxide coated lithium cobalt oxide composite material, characterized in that, Reaction solution 1 and reaction solution 2 are mixed and subjected to a hydrothermal reaction. After the reaction is completed, a solid-liquid mixture is obtained. Reaction solution 1 contains divalent cobalt metal salt and trivalent lanthanum metal salt, while reaction solution 2 contains lithium cobalt oxide and sodium hydroxide. The solid-liquid mixture is subjected to hydrothermal, centrifugal, vacuum drying and high-temperature calcination operations to obtain lithium cobalt oxide material with a perovskite lanthanum cobalt oxide shell.

2. The perovskite-coated lithium cobalt oxide composite material according to claim 1, characterized in that, It also includes at least one of the following features (1) to (13): (1) In the perovskite-coated lithium cobalt oxide material, the mass ratio of perovskite lanthanum cobalt oxide to lithium cobalt oxide is 0.01 to 0.05:1; (2) The concentration of divalent cobalt metal salt in the reaction solution 1 is 0.05-0.1 mol / L; (3) The concentration of trivalent lanthanum metal salt in the reaction solution 1 is 0.05-0.1 mol / L; (4) The lithium cobalt oxide and sodium hydroxide are dispersed in the reaction solution 2. The reaction solution 1 and the reaction solution 2 are mixed and reacted by adding the reaction solution 1 to the reaction solution 2 under vigorous stirring. (5) The concentration of sodium hydroxide in reaction solution 2 is 0.1-0.2 mol / L; (6) The lithium cobalt oxide is dispersed in the reaction solution 2. The preparation method includes: adding lithium cobalt oxide to deionized water and then placing it in an ultrasonic cell disruptor for pulverization, with the pulverization power set to 80-100% and the pulverization time to be 2-3 hours. (7) The divalent cobalt metal salt in the reaction solution 1 is at least one of cobalt chloride, cobalt carbonate, cobalt sulfate, cobalt nitrate, cobalt oxalate, and cobalt hydroxide; (8) The trivalent lanthanum metal salt in the reaction solution 1 is at least one of lanthanum chloride, lanthanum sulfate, lanthanum phosphate, lanthanum oxalate, lanthanum nitrate, and lanthanum carbonate; (9) The particle size of lithium cobalt oxide dispersed in the reaction solution 2 is 0.5-2 μm; (10) The temperature of the hydrothermal reaction is 160-240℃ and the time is 10-20h; (11) The centrifugation operation is performed at a speed of 5000-10000 rpm for 5-10 min; (12) The vacuum drying temperature is 60-100℃ and the time is 10-15h; (13) The conditions for high-temperature calcination are calcination in an air or oxygen atmosphere, at a temperature of 500-700°C, and for a time of 5-8 hours.

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