Lithium selenite / selenium dioxide double-layer coated ternary material and preparation method therefor

Abstract

The present invention provides a lithium selenite / selenium dioxide double-layer coated ternary material. The chemical formula of the lithium selenite / selenium dioxide double-layer coated ternary material is LiNiaCobMncO2·xLi2SeO3·ySeO2, wherein Li2SeO3 is an inner coating layer, SeO2 is an outer coating layer, a+b+c=1, 0.6<a<1, 0<b+c<0.4, 0<x<0.3, 0<y<0.1, and 0<x+y<0.4.

Description

A lithium selenite / selenium dioxide double-layer coated ternary material and its preparation method Technical Field

[0001] The present disclosure belongs to the technical field of lithium-ion batteries, and particularly relates to a lithium selenite / selenium dioxide double-layer coated ternary material and a preparation method thereof. Background Art

[0002] my country's new energy electric vehicle industry is developing rapidly, with production and sales of new energy vehicles maintaining steady growth. Exports are also showing strong momentum, continuing to be a bright spot in the automotive industry's development. With the promotion of new energy vehicles, demand for cathode materials such as lithium cobalt oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide is also increasing. Improving the electrochemical performance of cathode materials is a key research area in the lithium-ion battery industry.

[0003] Ternary positive electrode materials have great development prospects and have the advantages of low cost, large discharge capacity, and good cycle performance. Among them, high-nickel ternary positive electrode materials have a high specific capacity of more than 200mAh / g due to their high nickel content. However, as the nickel content increases, multiple phase changes will occur during the charge and discharge process, especially the H2-H3 phase change with poor reversibility and the resulting severe volume changes, resulting in poor cycle performance of the material. Secondly, an increase in nickel content will lead to an increase in residual lithium compounds. LiOH reacts with HF produced by the decomposition of the electrolyte to form LiF, which continuously corrodes the positive electrode material, while Li2CO3 will cause gas production during the battery charge and discharge process, causing safety problems.

[0004] Doping and coating modification are common methods to improve the performance of high-nickel ternary positive electrode materials. On the one hand, coating can prevent the positive electrode material from directly contacting the electrolyte and alleviate the occurrence of side reactions. On the other hand, the good electronic / ionic conductivity of the coating layer is conducive to improving the electrical performance of the material. For example, the prior art describes a method for modifying the positive electrode material of lithium-ion batteries with a Li2SeO4 fast ion conductor. The Li2SeO4 formed by this method can inhibit the electrolyte from corroding the electrode and improve the long-cycle ability of the positive electrode material. However, the effect of single-layer coating is limited and it cannot be used as a method for large-scale production.

[0005] Summary of the Invention

[0006] The present disclosure aims to address at least one of the technical problems existing in the aforementioned prior art. To this end, the present disclosure proposes a lithium selenite / selenium dioxide double-layer coated ternary material and a preparation method thereof. The double-layer coated ternary material comprises an inner layer of lithium selenite and an outer layer of selenium dioxide, thereby improving the cycling performance and thermal stability of the ternary material.

[0007] According to the first aspect of the present disclosure, a lithium selenite / selenium dioxide double-layer coated ternary material is proposed. The chemical formula of the lithium selenite / selenium dioxide double-layer coated ternary material is LiNi aCo b Mn c O2·xLi2SeO3·ySeO2, wherein Li2SeO3 is an inner coating layer and SeO2 is an outer coating layer; wherein a+b+c=1, 0.8≤a<1, 0<x<0.1, 0<y<0.05, 0<x+y<0.15.

[0008] In some embodiments, in the chemical formula of the lithium selenite / selenium dioxide double-layer coated ternary material, 0.8<a<1, 0<b<0.2, and 0<c<0.2.

[0009] In some embodiments, the particle size of the lithium selenite / selenium dioxide double-layer coated ternary material is 2 to 10 μm. The particle size of the ternary material is adjusted based on the particle size of the precursor. A particle size that is too large indicates that the particles are agglomerated due to residual lithium during the sintering process, while a particle size that is too small indicates that the material is over-crushed, causing material damage and reduced performance.

[0010] In some embodiments, the thickness of the inner coating layer is 1 to 20 nm. A certain thickness of lithium selenite can improve the conductivity of the material. A coating layer that is too thin has no significant improvement effect, while a coating layer that is too thick easily makes it more difficult to insert and remove lithium from the material, thereby reducing the capacity.

[0011] In some embodiments, the thickness of the outer coating is 1 to 20 nm. A certain thickness of selenium dioxide coating can prevent the material from being corroded by the electrolyte during charging and discharging. A thinner coating has no protective effect, while a thicker coating can easily make it more difficult for lithium to be inserted and removed from the material, increasing resistance and reducing capacity.

[0012] According to a second aspect of the present disclosure, a method for preparing the ternary material as described in the first aspect of the present disclosure is proposed, comprising the following steps:

[0013] S1: mixing the ternary material substrate with a selenious acid solution, and drying the mixture to obtain a single-layer coated ternary material;

[0014] S2: mixing the single-layer coated ternary material with selenium dioxide powder, and calcining the mixture to obtain a lithium selenite / selenium dioxide double-layer coated ternary material.

[0015] The present invention uses a liquid-phase method and a solid-phase method to coat the ternary material with a single layer in a selenious acid solution, consuming residual lithium and forming a fast ion conductor, lithium selenite, on the surface of the ternary material to increase the material's electrical conductivity. The material is then mixed with selenium dioxide powder and sintered to form a second coating layer, i.e., a physical barrier layer of selenium dioxide. Compared to the single solid-phase method, the present invention is more effective in reducing residual lithium, improving electrical conductivity and protecting the material from air. The method is universal, uses a conventional wet method, is low-cost, and is suitable for large-scale production.

[0016] In some embodiments, the ternary material substrate is prepared by mixing and calcining a ternary material precursor and a lithium source, wherein the chemical formula of the ternary material precursor is Ni a Co b Mn c (OH)2, wherein 0.8<a<1, 0<b<0.2, 0<c<0.2.

[0017] In some embodiments, the molar ratio of the ternary material precursor to the lithium source is 1:(1.01-1.09).

[0018] In some embodiments, the lithium source is at least one of lithium hydroxide, lithium carbonate, lithium acetate, or lithium nitrate.

[0019] In some embodiments, the ternary material precursor and the lithium source are calcined in an oxygen atmosphere at a temperature of 600 to 900° C. and for a time of 12 to 24 hours.

[0020] In some embodiments, in step S1, the ternary material substrate is crushed before being mixed with the selenious acid solution. After the crushing process, the particle size D of the ternary material substrate is 50 2~10μm.

[0021] In some embodiments, in step S1, the selenious acid solution is prepared by dissolving selenium dioxide powder in water, wherein the mass of the selenium dioxide powder is 0.5-5% of the mass of the ternary material substrate. The amount of selenium dioxide is selected based on the residual lithium content of the ternary material. An overly concentrated selenious acid solution, due to its acidity, can easily destroy the structure of the ternary material.

[0022] In some embodiments, in step S1, the selenious acid solution is prepared by dissolving selenium dioxide powder in water at 0-10° C. Excessively high water temperature can easily cause lithium in the material to dissolve into the solution, causing damage to the material.

[0023] In some embodiments, in step S1, the liquid-to-solid ratio of the selenious acid solution to the ternary material substrate is 0.5-5:1 mL / g. The amount of selenium dioxide is selected based on the residual lithium content of the ternary material. Excessive selenious acid solution is acidic and can easily destroy the ternary material structure.

[0024] In some embodiments, in step S1, the ternary material substrate and the selenious acid solution are mixed for 1 to 3 minutes. During this mixing time, the selenious acid and the residual lithium in the ternary material substrate fully react to form lithium selenite, while preventing lithium precipitation in the material from being damaged by excessive mixing.

[0025] In some embodiments, the stirring speed of the mixing of the ternary material substrate and the selenious acid solution is 80-120 rpm.

[0026] In some embodiments, in step S2, the mass ratio of the single-layer coated ternary material to the selenium dioxide powder is 1:0.01 to 0.03. Selenium dioxide is not conductive, and excessive selenium dioxide can easily increase material resistance and reduce capacity and cycle performance.

[0027] In some embodiments, the selenium dioxide powder is prepared by mixing industrial selenium powder with nitric acid having a mass concentration of 30% to 50%, heating the mixture once, separating the solid and the liquid, and then heating the solid phase twice.

[0028] In some embodiments, the purity of the selenium dioxide powder is ≥99.9%.

[0029] In some embodiments, the solid-to-liquid ratio of the industrial selenium powder to the nitric acid is 1:4-6 g / mL.

[0030] In some embodiments, in step S2, the specific process of mixing the single-layer coated ternary material with selenium dioxide powder is: mixing at 800-1000 rpm for 20-30 minutes.

[0031] In some embodiments, in step S2, the calcination is performed under an oxygen atmosphere.

[0032] In some embodiments, in step S2, the calcination temperature is 250-350° C. and the calcination time is 8-12 hours. The purpose of calcination is to allow selenium dioxide to reach the melting point and fully coat the material.

[0033] In some embodiments, step S2 further includes a process of screening the lithium selenite / selenium dioxide double-layer coated ternary material, and the mesh size of the screening sieve is 200-400 meshes.

[0034] According to a third aspect of the present disclosure, a positive electrode sheet is proposed, comprising the lithium selenite / selenium dioxide double-layer coated ternary material as described in the first aspect of the present disclosure.

[0035] According to a fourth aspect of the present disclosure, a lithium-ion battery is provided, comprising the positive electrode sheet as described in the third aspect of the present disclosure.

[0036] According to one embodiment of the present disclosure, there are at least the following beneficial effects:

[0037] The lithium selenite / selenium dioxide double-layer coated ternary material disclosed herein has an outer layer of selenium dioxide that can inhibit the precipitation and conversion of lattice lithium, and at the same time acts as a physical barrier to reduce electrolyte corrosion of the electrode; the inner layer provides a fast ion conductor lithium selenite to increase the lithium ion insertion and extraction rate, thereby improving the cycle performance and thermal stability of the positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The present disclosure is further described below with reference to the accompanying drawings and embodiments, wherein:

[0039] FIG1 is a 50,000-fold magnified SEM image of the lithium selenite / selenium dioxide double-layer coated high-nickel ternary material positive electrode material prepared in Example 1 of the present disclosure.

[0040] FIG2 is a SEM image of the lithium selenite / selenium dioxide double-layer coated high nickel ternary material positive electrode material obtained in Example 1 of the present disclosure, magnified 10,000 times.

[0041] FIG3 is a SEM image of the high-nickel ternary positive electrode material coated with lithium selenite prepared in Comparative Example 3 of the present disclosure, magnified 50,000 times.

[0042] FIG4 is a SEM image of the high-nickel ternary positive electrode material coated with lithium selenite prepared in Comparative Example 3 of the present disclosure, magnified 10,000 times.

[0043] FIG5 is a SEM image of the high-nickel ternary material positive electrode material prepared in Comparative Example 1 of the present disclosure, magnified 50,000 times.

[0044] FIG6 is a SEM image of the high-nickel ternary material positive electrode material prepared in Comparative Example 1 of the present disclosure, magnified 10,000 times.

[0045] FIG7 is a cycle diagram of Examples 1-2 and Comparative Examples 1-3 of the present disclosure. DETAILED DESCRIPTION

[0046] The following will clearly and completely describe the concept and technical effects of the present disclosure in conjunction with embodiments to fully understand the purpose, features and effects of the present disclosure.

[0047] The preparation method of the selenium dioxide powder used in the following examples and comparative examples is as follows:

[0048] Weigh 500 g of industrial selenium powder (≥98%) and 2 L of 30% nitric acid solution in a glass beaker, heat while stirring, heat to 70°C, stir for 16 hours, then heat to 90°C in a fume hood and evaporate until the solution is completely evaporated. Place the powder in a drying oven (110°C) and dry for 8 hours to obtain selenium dioxide powder with a purity of ≥99.9%.

[0049] Example 1

[0050] A lithium selenite / selenium dioxide double-layer coated ternary material with the chemical formula LiNi 0.95 Co 0.03 Mn 0.02 O2·0.01Li2SeO3·0.01SeO2, lithium selenite is the inner coating layer, and selenium dioxide is the outer coating layer.

[0051] A method for preparing the lithium selenite / selenium dioxide double-layer coated ternary material as described above comprises the following steps:

[0052] (1) Weigh 10 kg of Ni 0.95 Co 0.03 Mn 0.02 (OH)2 and 4.8 kg of LiOH·H2O were mixed in a high-speed mixer at 500 rpm for 120 min. After being mixed evenly, the mixture was put into a sagger and put into a box furnace. An oxygen atmosphere (oxygen concentration ≥ 90) was introduced and the temperature was raised to 500°C at a heating rate of 3°C / min and kept for 5 h. The temperature was then raised to 700°C at a heating rate of 3°C / min and kept for 16 h. After sintering, the mixture was cooled naturally and crushed to obtain a particle size of D 50 The ternary cathode material LiNi is 8.21μm 0.95 Co 0.03 Mn 0.02 O2.

[0053] (2) Add 80g of selenium dioxide powder and 16L of deionized cold water (5℃) into the reactor and stir at 95rpm until dissolved. Then slowly pour in 8kg of ternary cathode material, wash for 2min, centrifuge and dry to obtain 5.45kg of ternary cathode material LiNi 0.95 Co 0.03 Mn 0.02 O2·0.01Li2SeO3.

[0054] (3) 4 kg of the washed ternary cathode material and 40 g of selenium dioxide powder were mixed in a high-speed mixer at 800 rpm for 25 min. The mixture was calcined at 275°C under an oxygen atmosphere for 9 h. After cooling, it was passed through a 200-mesh sieve to obtain a lithium selenite / selenium dioxide double-layer coated high-nickel ternary cathode material.

[0055] The SEM image of the lithium selenite / selenium dioxide double-layer coated high-nickel ternary positive electrode material magnified 50,000 times is shown in Figure 1, and the SEM image of the lithium selenite / selenium dioxide double-layer coated high-nickel ternary positive electrode material magnified 10,000 times is shown in Figure 2.

[0056] Example 2

[0057] A lithium selenite / selenium dioxide double-layer coated ternary material with the chemical formula LiNi 0.95 Co 0.03 Mn 0.02 O2·0.02Li2SeO3·0.03SeO2, lithium selenite is the inner coating layer, and selenium dioxide is the outer coating layer.

[0058] A method for preparing the lithium selenite / selenium dioxide double-layer coated ternary material as described above comprises the following steps:

[0059] (1) Weigh 10 kg of Ni 0.95 Co 0.03 Mn 0.02 (OH)2 and 4.8 kg of LiOH·H2O were mixed in a high-speed mixer at 500 rpm for 120 min. After being mixed evenly, the mixture was put into a sagger and put into a box furnace. An oxygen atmosphere (oxygen concentration ≥ 90) was introduced and the temperature was raised to 500°C at a heating rate of 3°C / min and kept for 5 h. The temperature was then raised to 700°C at a heating rate of 3°C / min and kept for 16 h. After sintering, the mixture was cooled naturally and crushed to obtain a particle size of D 50 The ternary cathode material LiNi is 8.21μm 0.95 Co 0.03 Mn 0.02 O2.

[0060] (2) Add 160g of selenium dioxide powder and 16L of deionized cold water (5°C) into the reactor and stir at 95rpm until dissolved. Then slowly pour in 8kg of ternary positive electrode material, wash for 2min, centrifuge and dry to obtain 5.84kg of ternary positive electrode material LiNi 0.95 Co 0.03 Mn 0.02 O2·0.02Li2SeO3.

[0061] (3) 4 kg of the washed ternary cathode material and 120 g of selenium dioxide powder were mixed in a high-speed mixer at 800 rpm for 25 min. The mixture was calcined at 275°C under an oxygen atmosphere for 9 h. After cooling, it was passed through a 200-mesh sieve to obtain a lithium selenite / selenium dioxide double-layer coated high-nickel ternary cathode material.

[0062] Example 3

[0063] A lithium selenite / selenium dioxide double-layer coated ternary material with the chemical formula LiNi 0.8 Co 0.1 Mn 0.1 O2·0.02Li2SeO3·0.02SeO2, lithium selenite is the inner coating layer, and selenium dioxide is the outer coating layer.

[0064] A method for preparing the lithium selenite / selenium dioxide double-layer coated ternary material as described above comprises the following steps:

[0065] (1) Weigh 10 kg of Ni 0.8 Co 0.1 Mn 0.1(OH)2 and 4.8 kg of LiOH·H2O were mixed in a high-speed mixer at 500 rpm for 120 min. After being mixed evenly, the mixture was put into a sagger and put into a box furnace. An oxygen atmosphere (oxygen concentration ≥ 90) was introduced and the temperature was raised to 500°C at a heating rate of 3°C / min and kept for 5 h. The temperature was then raised to 700°C at a heating rate of 3°C / min and kept for 16 h. After sintering, the mixture was cooled naturally and crushed to obtain a particle size of D 50 The ternary cathode material LiNi is 8.47μm 0.8 Co 0.1 Mn 0.1 O2.

[0066] (2) Add 160g of selenium dioxide powder and 16L of deionized cold water (5°C) into the reactor and stir at 95rpm until dissolved. Then slowly pour in 8kg of ternary cathode material, wash for 2min, centrifuge and dry to obtain 6.28kg of ternary cathode material LiNi 0.95 Co 0.03 Mn 0.02 O2·0.06Li2SeO3.

[0067] (3) 4 kg of washed ternary cathode material and 80 g of selenium dioxide powder were mixed in a high-speed mixer at 800 rpm for 25 min. The mixture was calcined at 275°C under an oxygen atmosphere for 9 h. After cooling, it was passed through a 200-mesh sieve to obtain a lithium selenite / selenium dioxide double-layer coated high-nickel ternary cathode material.

[0068] Example 4

[0069] A lithium selenite / selenium dioxide double-layer coated ternary material with the chemical formula LiNi 0.8 Co 0.1 Mn 0.1 O2·0.03Li2SeO3·0.02SeO2, lithium selenite is the inner coating layer, and selenium dioxide is the outer coating layer.

[0070] A method for preparing the lithium selenite / selenium dioxide double-layer coated ternary material as described above comprises the following steps:

[0071] (1) Weigh 10 kg of Ni 0.8 Co 0.1 Mn 0.1 (OH)2 and 4.8 kg of LiOH·H2O were mixed in a high-speed mixer at 500 rpm for 120 min. After being mixed evenly, the mixture was put into a sagger and put into a box furnace. An oxygen atmosphere (oxygen concentration ≥ 90) was introduced and the temperature was raised to 500°C at a heating rate of 3°C / min and kept for 5 h. The temperature was then raised to 700°C at a heating rate of 3°C / min and kept for 16 h. After sintering, the mixture was cooled naturally and crushed to obtain a particle size of D 50The ternary cathode material LiNi is 8.47μm 0.8 Co 0.1 Mn 0.1 O2.

[0072] (2) Add 240g of selenium dioxide powder and 16L of deionized cold water (5°C) into the reactor and stir at 95rpm until dissolved. Then slowly pour in 8kg of ternary cathode material, wash for 2min, centrifuge and dry to obtain 6.63kg of ternary cathode material LiNi 0.95 Co 0.03 Mn 0.02 O2·0.03Li2SeO3.

[0073] (3) 4 kg of washed ternary cathode material and 80 g of selenium dioxide powder were mixed in a high-speed mixer at 800 rpm for 25 min. The mixture was calcined at 275°C under an oxygen atmosphere for 9 h. After cooling, it was passed through a 200-mesh sieve to obtain a lithium selenite / selenium dioxide double-layer coated high-nickel ternary cathode material.

[0074] Comparative Example 1

[0075] A ternary material with the chemical formula LiNi 0.95 Co 0.03 Mn 0.02 O2.

[0076] A method for preparing the coated ternary material as described above differs from Example 1 only in that no selenium dioxide powder is added in steps (2) and (3). The specific steps are as follows:

[0077] (1) Weigh 10 kg of Ni 0.8 Co 0.1 Mn 0.1 (OH)2 and 4.8 kg of LiOH·H2O were mixed in a high-speed mixer at 500 rpm for 120 min. After being mixed evenly, the mixture was put into a sagger and put into a box furnace. An oxygen atmosphere (oxygen concentration ≥ 90) was introduced and the temperature was raised to 500°C at a heating rate of 3°C / min and kept for 5 h. The temperature was then raised to 700°C at a heating rate of 3°C / min and kept for 16 h. After sintering, the mixture was cooled naturally and crushed to obtain a particle size of D 50 The ternary cathode material LiNi is 8.47μm 0.8 Co 0.1 Mn 0.1 O2.

[0078] (2) Add 16 L of deionized cold water (5 ° C) to the reactor and stir at 95 rpm. Then slowly pour in 8 kg of ternary positive electrode material, wash for 2 minutes, centrifuge and dry.

[0079] (3) 4 kg of the washed ternary positive electrode material was calcined at 275° C. for 9 h in an oxygen atmosphere, and after cooling, it was sieved through a 200-mesh sieve to obtain a high-nickel ternary positive electrode material.

[0080] The SEM image of the high-nickel ternary material positive electrode material magnified 50,000 times is shown in FIG5 , and the SEM image of the high-nickel ternary material positive electrode material magnified 10,000 times is shown in FIG6 .

[0081] Comparative Example 2

[0082] A coated ternary material with the chemical formula LiNi 0.95 Co 0.03 Mn 0.02 O2·0.01SeO2.

[0083] A method for preparing the coated ternary material as described above differs from Example 1 only in that no selenium dioxide powder is added in step (2). The specific steps are as follows:

[0084] (1) Weigh 10 kg of Ni 0.95 Co 0.03 Mn 0.02 (OH)2 and 4.8 kg of LiOH·H2O were mixed in a high-speed mixer at 500 rpm for 120 min. After being mixed evenly, the mixture was put into a sagger and put into a box furnace. An oxygen atmosphere (oxygen concentration ≥ 90) was introduced and the temperature was raised to 500°C at a heating rate of 3°C / min and kept for 5 h. The temperature was then raised to 700°C at a heating rate of 3°C / min and kept for 16 h. After sintering, the mixture was cooled naturally and crushed to obtain a particle size of D 50 The ternary cathode material LiNi is 8.21μm 0.95 Co 0.03 Mn 0.02 O2.

[0085] (2) Add 16 L of deionized cold water (5 ° C) to the reactor and stir at 95 rpm. Then slowly pour in 8 kg of ternary positive electrode material, wash for 2 minutes, centrifuge and dry.

[0086] (3) 4 kg of the washed ternary cathode material and 40 g of selenium dioxide powder were mixed in a high-speed mixer at 800 rpm for 25 min. The mixture was calcined at 275°C under an oxygen atmosphere for 9 h. After cooling, it was passed through a 200-mesh sieve to obtain a selenium dioxide-coated high-nickel ternary cathode material.

[0087] Comparative Example 3

[0088] A coated ternary material with the chemical formula LiNi 0.95 Co 0.03 Mn 0.02 O2·0.06Li2SeO3.

[0089] A method for preparing the coated ternary material as described above differs from Example 1 only in that no selenium dioxide powder is added in step (3). The specific steps are as follows:

[0090] (1) Weigh 10 kg of Ni 0.95 Co 0.03 Mn 0.02 (OH)2 and 4.8 kg of LiOH·H2O were mixed in a high-speed mixer at 500 rpm for 120 min. After being mixed evenly, the mixture was put into a sagger and put into a box furnace. An oxygen atmosphere (oxygen concentration ≥ 90) was introduced and the temperature was raised to 500°C at a heating rate of 3°C / min and kept for 5 h. The temperature was then raised to 700°C at a heating rate of 3°C / min and kept for 16 h. After sintering, the mixture was cooled naturally and crushed to obtain a particle size of D 50 The ternary cathode material LiNi is 8.21μm 0.95 Co 0.03 Mn 0.02 O2.

[0091] (2) Add 120 g of selenium dioxide powder and 16 L of deionized cold water (5°C) into the reactor and stir at 95 rpm until dissolved. Then slowly pour in 8 kg of ternary cathode material, wash for 2 min, centrifuge and dry.

[0092] (3) 4 kg of the washed ternary positive electrode material was calcined at 275° C. for 9 h in an oxygen atmosphere, and after cooling, the material was sieved through 200 mesh to obtain a lithium selenite-coated high-nickel ternary positive electrode material.

[0093] The SEM image of the lithium selenite-coated high-nickel ternary positive electrode material magnified 50,000 times is shown in FIG3 , and the SEM image of the lithium selenite-coated high-nickel ternary positive electrode material magnified 10,000 times is shown in FIG4 .

[0094] Comparative Example 4

[0095] A ternary material with the chemical formula LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0096] A method for preparing the coated ternary material as described above differs from Example 3 only in that no selenium dioxide powder is added in steps (2) and (3). The specific steps are as follows:

[0097] (1) Weigh 10 kg of Ni 0.8 Co 0.1 Mn 0.1(OH)2 and 4.8 kg of LiOH·H2O were mixed in a high-speed mixer at 500 rpm for 120 min. After being mixed evenly, the mixture was put into a sagger and put into a box furnace. An oxygen atmosphere (oxygen concentration ≥ 90) was introduced and the temperature was raised to 500°C at a heating rate of 3°C / min and kept for 5 h. The temperature was then raised to 700°C at a heating rate of 3°C / min and kept for 16 h. After sintering, the mixture was cooled naturally and crushed to obtain a particle size of D 50 The ternary cathode material LiNi is 8.47μm 0.8 Co 0.1 Mn 0.1 O2.

[0098] (2) Add 16 L of deionized cold water (5 ° C) to the reactor and stir at 95 rpm. Then slowly pour in 8 kg of ternary positive electrode material, wash for 2 minutes, centrifuge and dry.

[0099] (3) 4 kg of the washed ternary positive electrode material was calcined at 275 ° C for 9 h in an oxygen atmosphere, and after cooling, it was passed through a 200-mesh sieve to obtain a lithium selenite / selenium dioxide double-layer coated high-nickel ternary material positive electrode material.

[0100] Comparative Example 5

[0101] A coated ternary material with the chemical formula LiNi 0.8 Co 0.1 Mn 0.1 O2·0.02SeO2.

[0102] A method for preparing the coated ternary material as described above differs from Example 3 only in that no selenium dioxide powder is added in step (2). The specific steps are as follows:

[0103] (1) Weigh 10 kg of Ni 0.8 Co 0.1 Mn 0.1 (OH)2 and 4.8 kg of LiOH·H2O were mixed in a high-speed mixer at 500 rpm for 120 min. After being mixed evenly, the mixture was put into a sagger and put into a box furnace. An oxygen atmosphere (oxygen concentration ≥ 90) was introduced and the temperature was raised to 500°C at a heating rate of 3°C / min and kept for 5 h. The temperature was then raised to 700°C at a heating rate of 3°C / min and kept for 16 h. After sintering, the mixture was cooled naturally and crushed to obtain a particle size of D 50 The ternary cathode material LiNi is 8.47μm 0.8 Co 0.1 Mn 0.1 O2.

[0104] (2) Add 16 L of deionized cold water (5 ° C) to the reactor and stir at 95 rpm. Then slowly pour in 8 kg of ternary positive electrode material, wash for 2 minutes, centrifuge and dry.

[0105] (3) 4 kg of washed ternary cathode material and 80 g of selenium dioxide powder were mixed in a high-speed mixer at 800 rpm for 25 min. The mixture was calcined at 275°C under an oxygen atmosphere for 9 h. After cooling, it was passed through a 200-mesh sieve to obtain a selenium dioxide-coated high-nickel ternary cathode material.

[0106] Comparative Example 6

[0107] A coated ternary material with the chemical formula LiNi 0.8 Co 0.1 Mn 0.1 O2·0.06Li2SeO3.

[0108] A method for preparing the coated ternary material as described above differs from Example 3 only in that no selenium dioxide powder is added in step (3). The specific steps are as follows:

[0109] (1) Weigh 10 kg of Ni 0.8 Co 0.1 Mn 0.1 (OH)2 and 4.8 kg of LiOH·H2O were mixed in a high-speed mixer at 500 rpm for 120 min. After being mixed evenly, the mixture was put into a sagger and put into a box furnace. An oxygen atmosphere (oxygen concentration ≥ 90) was introduced and the temperature was raised to 500°C at a heating rate of 3°C / min and kept for 5 h. The temperature was then raised to 700°C at a heating rate of 3°C / min and kept for 16 h. After sintering, the mixture was cooled naturally and crushed to obtain a particle size of D 50 The ternary cathode material LiNi is 8.47μm 0.8 Co 0.1 Mn 0.1 O2.

[0110] (2) Add 120 g of selenium dioxide powder and 16 L of deionized cold water (5°C) into the reactor and stir at 95 rpm until dissolved. Then slowly pour in 8 kg of ternary cathode material, wash for 2 min, centrifuge and dry.

[0111] (3) 4 kg of the washed ternary positive electrode material was calcined at 275° C. for 9 h in an oxygen atmosphere, and after cooling, it was passed through a 200-mesh sieve to obtain a lithium selenite-coated high-nickel ternary material positive electrode material.

[0112] Test example

[0113] Battery assembly and testing: Lithium-ion button cells were assembled in a glove box (argon atmosphere, H2O < 0.1ppm, O2 < 0.1ppm). The high-nickel ternary positive electrode materials, conductive agents, and binders prepared in Examples 1-2 and Comparative Examples 1-8 were mixed evenly in a ratio of 90:5:5, and dimethylformamide (DMF) solvent was added and stirred to form a slurry before coating. The slurry was then baked at 105°C for 2 hours and punched out. The slurry was then dried again in a vacuum oven at 105°C for 5 hours to assemble the button cells. The electrolyte used was LiPF6 dissolved in a mixed solvent of propylene carbonate and diethyl carbonate, the diaphragm was a polyimide film, and the negative electrode was a lithium metal sheet. After assembly, the battery was allowed to stand for 3 hours for the first cycle test. The test conditions were 25°C to test the charge and discharge capacity and the first efficiency at 0.1C. The cycle performance test used a fully electric button cell, replaced the lithium metal negative electrode with a carbon material, and tested the battery cycle stability under 1C conditions. The methods provided in Examples 1-4 can well synthesize coating materials with double coatings, significantly reduce residual lithium, and improve the electrochemical performance and stability of the materials. The effects of the present invention are specifically described below in conjunction with comparative examples and examples.

[0114] LiOH content, Li2CO3 content and residual Li content of high nickel ternary positive electrode materials of Examples 1-4 and Comparative Examples 1-6 + The contents are shown in Table 1 and Table 2, where LiOH content and Li2CO3 content are the amounts of LiOH and Li2CO3 substances respectively, and the residual lithium is the amount of Li + The sum of the amounts of substances shows that the residual alkali on the surface of the materials of Examples 1-2 is significantly lower than that of Comparative Examples 1-3. Similarly, the residual alkali on the surface of the materials of Examples 3-4 is significantly lower than that of Comparative Examples 4-6. This is attributed to the fact that the lithium selenite produced by the reaction of lithium selenite and residual lithium in the solution coats the material and the selenium dioxide added for the second mixing coats the material, reducing the contact between the material and the air. The first cycle charge and discharge capacity data of the high nickel ternary positive electrode materials in Examples 1-4 and Comparative Examples 1-6 under 4.3V / 0.1C are shown in Table 3. It can be seen that the discharge specific capacity of the materials obtained in Example 1-2 is improved compared with that of Comparative Examples 1-3. This is attributed to the fact that the lithium selenite produced by the reaction of selenite and residual lithium is an excellent ion conductor. The cycle performance comparison of Example 1-2 and Comparative Examples 1-3 is shown in Figure 7, where the capacity retention rates of Example 1-2 and Comparative Examples 1-3 after 80 cycles are 80.55%, 77.11%, 70.50%, 74.97% and 75.18%, respectively. The examples and comparative examples show that double-layer coating improves performance more than single-layer coating and uncoated samples. Examples 1 and 2 show that the amount of lithium selenate / selenium dioxide coating can be appropriately increased based on the amount of residual lithium to further reduce residual lithium, but a higher coating amount will affect product performance to some extent.

[0115] Figures 1-6 show the morphologies of the positive electrode materials of Example 1, Comparative Example 3, and Comparative Example 1, respectively. Specifically, Figures 1-2 are SEM images of Example 1, Figures 3-4 are SEM images of Comparative Example 3, and Figures 5-6 are SEM images of Comparative Example 1. As can be seen from Figures 5-6, the ternary material is completely uncoated, and the primary particles are clearly visible; as can be seen from Figures 3-4, Comparative Example 3, which has undergone the first coating, has an obvious thin layer of coating; as can be seen from Figures 1-2, after undergoing double-layer coating, the primary particles are clearly visible.

[0116] Example 1 has a more obvious and thicker coating layer, and the coating layer is more uniform, with no obvious material exposed.

[0117] Table 1

[0118] Table 2

Claims

1. A lithium selenite / selenium dioxide double-layer coated ternary material, characterized in that, The chemical formula of the lithium selenite / selenium dioxide double-layer coated ternary material is LiNi a Co b Mn c O 2 ·xLi 2 SeO 3 ·ySeO 2 , where Li 2 SeO 3 is the inner coating layer, and SeO 2 is the outer coating layer; where a + b + c = 1, 0.6 < a < 1, 0 < b + c < 0.4, 0 < x < 0.3, 0 < y < 0.1, 0 < x + y < 0.

4.

2. The lithium selenite / selenium dioxide double-layer coated ternary material according to claim 1, characterized in that, The chemical formula of the lithium selenite / selenium dioxide double-layer coated ternary material is LiNi a Co b Mn c O 2 ·xLi 2 SeO 3 ·ySeO 2 , where 0.8 < a < 1 and 0 < b + c < 0.

2.

3. The lithium selenite / selenium dioxide double-layer coated ternary material according to claim 1 or 2, characterized in that, The chemical formula of the lithium selenite / selenium dioxide double-coated ternary material is LiNi a Co b Mn c O 2 ·xLi 2 SeO 3 ·ySeO 2 , where 0.005 < x < 0.05, 0.01 < y < 0.03, and 0.015 < x + y < 0.

08.

4. The lithium selenite / selenium dioxide double-layer coated ternary material according to claim 1, characterized in that, the Dv50 particle size of the lithium selenite / selenium dioxide double-layer coated ternary material is 2 - 10 μm.

5. The lithium selenite / selenium dioxide double-layer coated ternary material according to claim 1, characterized in that, the thickness of the inner coating layer is 1 - 20 nm.

6. The lithium selenite / selenium dioxide double-layer coated ternary material according to claim 1, characterized in that, the thickness of the outer coating layer is 1 - 20 nm.

7. A preparation method of the lithium selenite / selenium dioxide double-layer coated ternary material according to any one of claims 1 - 6, characterized in that, comprises the following steps: S1: Mix the ternary material substrate with selenious acid solution, and obtain a single-layer coated ternary material after drying; S2: Mix the single-layer coated ternary material with selenium dioxide powder, and obtain the lithium selenite / selenium dioxide double-layer coated ternary material after calcination.

8. The preparation method according to claim 7, characterized in that, in step S1, the selenious acid solution is prepared by dissolving selenium dioxide powder in water, and the mass of the selenium dioxide powder is 0.5 - 5% of the mass of the ternary material substrate.

9. The preparation method according to claim 8, characterized in that, the selenious acid solution is prepared by dissolving selenium dioxide powder in water at 0 - 10 °C.

10. The preparation method according to claim 7, characterized in that, in step S1, the liquid-solid ratio of the selenious acid solution to the ternary material substrate is 0.5 - 5:1 mL / g.

11. The preparation method according to claim 7, characterized in that, in step S1, the mixing time of the ternary material substrate and the selenious acid solution is 1 - 3 min.

12. The preparation method according to claim 7, characterized in that, in step S2, the mass ratio of the single-layer coated ternary material to the selenium dioxide powder is 1:0.01 - 0.

03.

13. The preparation method according to claim 7, characterized in that, in step S2, the calcination temperature is 250 - 350 °C, and the calcination time is 8 - 12 h.

14. A positive electrode sheet, characterized in that, comprises the lithium selenite / selenium dioxide double-layer coated ternary material according to any one of claims 1 - 6.

15. A lithium-ion battery, characterized in that, comprises the positive electrode sheet according to claim 14.

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