A lithium selenite / selenium dioxide bilayer coated ternary material and its preparation method

Abstract

This disclosure proposes a lithium selenite / selenium dioxide bilayer-coated ternary material, wherein the chemical formula of the lithium selenite / selenium dioxide bilayer-coated ternary material is LiNi. a Co b Mn c O2·xLi2SeO3·ySeO2, where Li2SeO3 is the inner coating layer and SeO2 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.

Description

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

[0002] The new energy electric vehicle industry in China is developing rapidly. The production and sales of new energy vehicles maintain a steady growth trend, and exports also show a strong momentum, continuously serving as a bright spot in the development of the automotive industry. With the popularization of new energy vehicles, the demand for positive materials such as lithium cobaltate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide is also gradually increasing. How to improve the electrochemical performance of the positive material is the key research direction of the lithium ion battery industry.

[0003] Ternary positive 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 materials usually have a specific capacity of more than 200 mAh / g due to their high nickel content. However, with the increase of nickel content, multiple phase changes occur during charging and discharging, especially the H2-H3 phase change with poor reversibility and the resulting severe volume change, resulting in poor cycle performance of the material. In addition, the increase of nickel content will lead to the increase of residual lithium compounds. LiOH reacts with HF generated by the decomposition of electrolyte to form LiF, which continuously corrodes the positive material, while Li2CO3 will cause gas production during the charging and discharging process of the battery, causing safety problems.

[0004] Doping and coating modification is a common means to improve the performance of high-nickel ternary positive materials. Coating can on the one hand hinder the direct contact of the positive material with the electrolyte and alleviate the occurrence of side reactions, and on the other hand, a good electronic / ionic conductance of the coating layer is conducive to improving the electrical performance of the material. For example, the prior art describes a method for modifying lithium ion battery positive materials with Li2SeO4 fast ion conductor. The Li2SeO4 formed by this method can inhibit the corrosion of the electrolyte on the electrode and improve the long cycle performance of the positive material, but the single-layer coating effect is limited and cannot be used as a large-scale production method. SUMMARY

[0005] The present disclosure aims to at least solve one of the technical problems existing in the 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 has a lithium selenite inner layer and a selenium dioxide outer layer, thereby improving the cycle performance and thermal stability of the ternary material.

[0006] According to a first aspect of the present disclosure, a lithium selenite / selenium dioxide double-layer coated ternary material is provided, and the chemical formula of the lithium selenite / selenium dioxide double-layer coated ternary material is LiNi a Co b Mn cO2·xLi2SeO3·ySeO2, wherein Li2SeO3 is the inner coating layer and SeO2 is the 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.

[0007] 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, 0<c<0.2.

[0008] In some embodiments, the particle size of the lithium selenite / selenium dioxide double-layer coated ternary material is 2-10 μm. The particle size of the ternary material is adjusted according to the particle size of the precursor. A too large particle size indicates that the particles are agglomerated together due to residual lithium during the sintering process. A too small particle size indicates that the material is excessively crushed and the performance is reduced.

[0009] In some embodiments, the thickness of the inner coating layer is 1-20 nm. A certain thickness of lithium selenite can improve the conductivity of the material. A too thin coating layer has no obvious improvement effect. A too thick coating layer can easily increase the difficulty of lithium insertion and extraction in the material, thereby reducing the capacity.

[0010] In some embodiments, the thickness of the outer coating layer is 1-20 nm. A certain thickness of the selenium dioxide coating layer can prevent the material from being corroded by the electrolyte during the charging and discharging process. A too thin coating layer has no protective effect. A too thick coating layer can easily increase the difficulty of lithium insertion and extraction in the material, thereby increasing the resistance and reducing the capacity.

[0011] According to a second aspect of the present disclosure, a preparation method of the ternary material according to the first aspect of the present disclosure is provided, comprising the following steps:

[0012] S1: mixing the ternary material substrate with a lithium selenite solution, and drying to obtain a single-layer coated ternary material;

[0013] S2: mixing the single-layer coated ternary material with a selenium dioxide powder, and calcining to obtain a lithium selenite / selenium dioxide double-layer coated ternary material.

[0014] The present disclosure uses a liquid phase method and a solid phase method to perform single-layer coating on the ternary material in a lithium selenite solution, consumes residual lithium, and forms a fast ion conductor lithium selenite on the surface of the ternary material to increase the conductivity of the material. Then, the lithium selenite is mixed with a selenium dioxide powder and sintered to form a second coating layer, i.e., a physical barrier layer of selenium dioxide. Compared with a single solid phase method, the present disclosure has a more obvious effect of reducing residual lithium, improves the conductivity, and protects the material from air. The method has universality, low cost, and is suitable for large-scale production.

[0015] In some embodiments, the ternary material substrate is prepared by calcining a ternary material precursor with a lithium source, wherein the chemical formula of the ternary material precursor is Ni. a Co b Mn c (OH)2, where 0.8 < a < 1, 0 < b < 0.2, 0 < c < 0.2.

[0016] In some embodiments, the molar ratio of the ternary material precursor to the lithium source is 1:(1.01 to 1.09).

[0017] In some embodiments, the lithium source is at least one of lithium hydroxide, lithium carbonate, lithium acetate, or lithium nitrate.

[0018] In some embodiments, the ternary material precursor and the lithium source are calcined in an oxygen atmosphere at a temperature of 600–900°C for a time of 12–24 hours.

[0019] In some embodiments, in step S1, the ternary material substrate is pulverized before being mixed with the selenite solution, and the particle size D of the ternary material substrate after pulverization is... 50 The size ranges from 2 to 10 μm.

[0020] In some embodiments, in step S1, the selenite solution is prepared by dissolving selenium dioxide powder in water, and the mass of the selenium dioxide powder is 0.5% to 5% of the mass of the ternary material substrate. The amount of selenium dioxide is selected according to the residual lithium in the ternary material. An excessively concentrated selenite solution is acidic and can easily damage the structure of the ternary material.

[0021] In some embodiments, in step S1, the selenite solution is prepared by dissolving selenium dioxide powder in water at 0–10°C. Excessively high water temperatures can easily cause lithium from the material to dissolve into the solution, resulting in material damage.

[0022] In some embodiments, in step S1, the liquid-to-solid ratio of the selenite 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 in the ternary material. Excessive selenite solution, being acidic, can easily damage the structure of the ternary material.

[0023] In some embodiments, in step S1, the ternary material substrate is mixed with the selenite solution for 1 to 3 minutes. During this mixing time, the selenite acid reacts fully with the residual lithium in the ternary material substrate to form lithium selenite, while preventing lithium precipitation from the material due to excessive mixing time, which could damage the material.

[0024] In some embodiments, the stirring speed for mixing the ternary material substrate with the selenite solution is 80 to 120 rpm.

[0025] In some embodiments, in step S2, the mass ratio of the monolayer coated ternary material to the selenium dioxide powder is 1:0.01 to 0.03. Selenium dioxide is non-conductive; excessive selenium dioxide can easily lead to increased material resistance and reduced capacity and cycle performance.

[0026] In some embodiments, the selenium dioxide powder is prepared by mixing industrial selenium powder with nitric acid of 30% to 50% by mass and heating it once. After solid-liquid separation, the solid phase is heated a second time to obtain the powder.

[0027] In some embodiments, the purity of the selenium dioxide powder is ≥99.9%.

[0028] In some embodiments, the solid-liquid ratio of the industrial selenium powder to the nitric acid is 1:4 to 6 g / mL.

[0029] In some embodiments, in step S2, the specific process of mixing the single-layer coated ternary material with selenium dioxide powder is as follows: mixing at 800-1000 rpm for 20-30 minutes.

[0030] In some embodiments, in step S2, the calcination is carried out in an oxygen atmosphere.

[0031] 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 its melting point and fully coat the material.

[0032] In some embodiments, step S2 further includes sieving the lithium selenite / selenium dioxide double-layer coated ternary material through a sieve with a mesh size of 200 to 400.

[0033] According to a third aspect of this disclosure, a positive electrode is provided, comprising a lithium selenite / selenium dioxide bilayer coated ternary material as described in the first aspect of this disclosure.

[0034] According to a fourth aspect of this disclosure, a lithium-ion battery is proposed, comprising a positive electrode as described in a third aspect of this disclosure.

[0035] According to one embodiment of this disclosure, at least the following beneficial effects are achieved:

[0036] The disclosed lithium selenite / selenium dioxide bilayer coated ternary material has an outer layer of selenium dioxide that can suppress the precipitation and conversion of lithium in the lattice and at the same time act as a physical barrier to reduce electrolyte corrosion of the electrode; the inner layer provides a fast ion conductor lithium selenite to improve the lithium ion insertion and extraction rate, thereby improving the cycle performance and thermal stability of the cathode material. Attached Figure Description

[0037] The present disclosure will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0038] Figure 1 This is a 50,000x magnified SEM image of the high-nickel ternary cathode material with lithium selenite / selenium dioxide double-layer coating prepared in Example 1 of this disclosure.

[0039] Figure 2 This is a 10,000x magnified SEM image of the high-nickel ternary cathode material with lithium selenite / selenium dioxide double-layer coating prepared in Example 1 of this disclosure.

[0040] Figure 3 This is a 50,000x magnified SEM image of the high-nickel ternary cathode material coated with lithium selenite prepared in Comparative Example 3 of this disclosure.

[0041] Figure 4 This is a 10,000x magnified SEM image of the high-nickel ternary cathode material coated with lithium selenite prepared in Comparative Example 3 of this disclosure.

[0042] Figure 5 This is a 50,000x magnified SEM image of the high-nickel ternary cathode material prepared in Comparative Example 1 of this disclosure.

[0043] Figure 6 This is a 10,000x magnified SEM image of the high-nickel ternary cathode material prepared in Comparative Example 1 of this disclosure.

[0044] Figure 7 This is a cycle diagram of Embodiments 1-2 and Comparative Examples 1-3 of this disclosure. Detailed Implementation

[0045] The following will describe the concept and technical effects of this disclosure clearly and completely with reference to the embodiments, so as to fully understand the purpose, features and effects of this disclosure.

[0046] The preparation methods of the selenium dioxide powder used in the following examples and comparative examples are as follows:

[0047] Weigh 500g of industrial selenium powder (≥98%) and 2L of 30% nitric acid solution into a glass beaker. Heat and stir simultaneously until the temperature reaches 70℃ and the mixture is stirred for 16 hours. Then, heat the mixture in a fume hood to 90℃ to evaporate until the solution is completely evaporated. Place the powder in a drying oven (110℃) and dry for 8 hours to obtain selenium dioxide powder with a purity of ≥99.9%.

[0048] Example 1

[0049] A lithium selenite / selenium dioxide bilayer coated ternary material with the chemical formula LiNi 0.95 Co 0.03Mn 0.02 The coating consists of O2·0.01Li2SeO3·0.01SeO2, with lithium selenite as the inner coating layer and selenium dioxide as the outer coating layer.

[0050] A method for preparing a lithium selenite / selenium dioxide bilayer coated ternary material as described above includes the following steps:

[0051] (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 uniform mixing, the mixture was placed in a sagger and then into a box furnace. An oxygen atmosphere (oxygen concentration ≥ 90%) was introduced, and the temperature was increased to 500℃ at a rate of 3℃ / min and held for 5 h. Then, the temperature was increased to 700℃ at a rate of 3℃ / min and held for 16 h. After sintering, the mixture was allowed to cool naturally and then pulverized to obtain a particle size D. 50 LiNi, a ternary cathode material with a thickness of 8.21 μm 0.95 Co 0.03 Mn 0.02 O2.

[0052] (2) Add 80g of selenium dioxide powder and 16L of deionized cold water (5℃) to the reactor, 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.

[0053] (3) Take 4 kg of washed ternary cathode material and 40 g of selenium dioxide powder and mix them in a high-speed mixer at 800 rpm for 25 min. Calcinate the mixture at 275 °C for 9 h in an oxygen atmosphere, cool it and pass it through a 200-mesh sieve to obtain a high-nickel ternary cathode material with lithium selenite / selenium dioxide double-layer coating.

[0054] The SEM image of the lithium selenite / selenium dioxide bilayer coated high-nickel ternary cathode material, magnified 50,000 times, is shown below. Figure 1 As shown, a 10,000x magnified SEM image of the lithium selenite / selenium dioxide bilayer coated high-nickel ternary cathode material is shown below. Figure 2 As shown.

[0055] Example 2

[0056] A lithium selenite / selenium dioxide bilayer coated ternary material with the chemical formula LiNi 0.95 Co 0.03 Mn 0.02The coating consists of O2·0.02Li2SeO3·0.03SeO2, with lithium selenite as the inner coating layer and selenium dioxide as the outer coating layer.

[0057] A method for preparing a lithium selenite / selenium dioxide bilayer coated ternary material as described above includes the following steps:

[0058] (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 uniform mixing, the mixture was placed in a sagger and then into a box furnace. An oxygen atmosphere (oxygen concentration ≥ 90%) was introduced, and the temperature was increased to 500℃ at a rate of 3℃ / min and held for 5 h. Then, the temperature was increased to 700℃ at a rate of 3℃ / min and held for 16 h. After sintering, the mixture was allowed to cool naturally and then pulverized to obtain a particle size D. 50 LiNi, a ternary cathode material with a thickness of 8.21 μm 0.95 Co 0.03 Mn 0.02 O2.

[0059] (2) Add 160g of selenium dioxide powder and 16L of deionized cold water (5℃) to the reactor, stir at 95rpm until dissolved, then slowly pour in 8kg of ternary cathode material, wash for 2min, centrifuge and dry to obtain 5.84kg of ternary cathode material LiNi. 0.95 Co 0.03 Mn 0.02 O2·0.02Li2SeO3.

[0060] (3) Take 4 kg of washed ternary cathode material and 120 g of selenium dioxide powder and mix them in a high-speed mixer at 800 rpm for 25 min. Calcinate the mixture at 275 °C for 9 h in an oxygen atmosphere, cool it and pass it through a 200-mesh sieve to obtain a high-nickel ternary cathode material with lithium selenite / selenium dioxide double-layer coating.

[0061] Example 3

[0062] A lithium selenite / selenium dioxide bilayer coated ternary material with the chemical formula LiNi 0.8 Co 0.1 Mn 0.1 The coating consists of O2·0.02Li2SeO3·0.02SeO2, with lithium selenite as the inner coating layer and selenium dioxide as the outer coating layer.

[0063] A method for preparing a lithium selenite / selenium dioxide bilayer coated ternary material as described above includes the following steps:

[0064] (1) Weigh 10 kg of Ni 0.8 Co0.1 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 uniform mixing, the mixture was placed in a sagger and then into a box furnace. An oxygen atmosphere (oxygen concentration ≥ 90%) was introduced, and the temperature was increased to 500℃ at a rate of 3℃ / min and held for 5 h. Then, the temperature was increased to 700℃ at a rate of 3℃ / min and held for 16 h. After sintering, the mixture was allowed to cool naturally and then pulverized to obtain a particle size D. 50 LiNi, a ternary cathode material with a thickness of 8.47 μm 0.8 Co 0.1 Mn 0.1 O2.

[0065] (2) Add 160g of selenium dioxide powder and 16L of deionized cold water (5℃) to the reactor, 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.

[0066] (3) Take 4 kg of washed ternary cathode material and 80 g of selenium dioxide powder and mix them in a high-speed mixer at 800 rpm for 25 min. Calcinate the mixture at 275 °C for 9 h in an oxygen atmosphere, cool it and pass it through a 200-mesh sieve to obtain a high-nickel ternary cathode material with lithium selenite / selenium dioxide double-layer coating.

[0067] Example 4

[0068] A lithium selenite / selenium dioxide bilayer coated ternary material with the chemical formula LiNi 0.8 Co 0.1 Mn 0.1 The coating consists of O2·0.03Li2SeO3·0.02SeO2, with lithium selenite as the inner coating layer and selenium dioxide as the outer coating layer.

[0069] A method for preparing a lithium selenite / selenium dioxide bilayer coated ternary material as described above includes the following steps:

[0070] (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 uniform mixing, the mixture was placed in a sagger and then into a box furnace. An oxygen atmosphere (oxygen concentration ≥ 90%) was introduced, and the temperature was increased to 500℃ at a rate of 3℃ / min and held for 5 h. Then, the temperature was increased to 700℃ at a rate of 3℃ / min and held for 16 h. After sintering, the mixture was allowed to cool naturally and then pulverized to obtain a particle size D.50 LiNi, a ternary cathode material with a thickness of 8.47 μm 0.8 Co 0.1 Mn 0.1 O2.

[0071] (2) Add 240g of selenium dioxide powder and 16L of deionized cold water (5℃) to the reactor, 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.

[0072] (3) Take 4 kg of washed ternary cathode material and 80 g of selenium dioxide powder and mix them in a high-speed mixer at 800 rpm for 25 min. Calcinate the mixture at 275 °C for 9 h in an oxygen atmosphere, cool it and pass it through a 200-mesh sieve to obtain a high-nickel ternary cathode material with lithium selenite / selenium dioxide double-layer coating.

[0073] Comparative Example 1

[0074] A ternary material with the chemical formula LiNi 0.95 Co 0.03 Mn 0.02 O2.

[0075] A method for preparing a coated ternary material as described above differs from Example 1 only in that selenium dioxide powder is not added in steps (2) and (3). The specific steps are as follows:

[0076] (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 uniform mixing, the mixture was placed in a sagger and then into a box furnace. An oxygen atmosphere (oxygen concentration ≥ 90%) was introduced, and the temperature was increased to 500℃ at a rate of 3℃ / min and held for 5 h. Then, the temperature was increased to 700℃ at a rate of 3℃ / min and held for 16 h. After sintering, the mixture was allowed to cool naturally and then pulverized to obtain a particle size D. 50 LiNi, a ternary cathode material with a thickness of 8.47 μm 0.8 Co 0.1 Mn 0.1 O2.

[0077] (2) Add 16L of deionized cold water (5℃) to the reactor, stir at 95rpm, then slowly pour in 8kg of ternary cathode material, wash for 2min, centrifuge and dry.

[0078] (3) Take 4 kg of washed ternary cathode material and calcine it at 275°C for 9 h in an oxygen atmosphere. After cooling, pass it through a 200-mesh sieve to obtain high-nickel ternary cathode material.

[0079] The SEM image of the high-nickel ternary cathode material magnified 50,000 times is shown below. Figure 5 As shown, the SEM image of the high-nickel ternary cathode material magnified 10,000 times is as follows. Figure 6 As shown.

[0080] Comparative Example 2

[0081] A coated ternary material with the chemical formula LiNi 0.95 Co 0.03 Mn 0.02 O2·0.01SeO2.

[0082] A method for preparing a coated ternary material as described above differs from Example 1 only in that selenium dioxide powder is not added in step (2). The specific steps are as follows:

[0083] (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 uniform mixing, the mixture was placed in a sagger and then into a box furnace. An oxygen atmosphere (oxygen concentration ≥ 90%) was introduced, and the temperature was increased to 500℃ at a rate of 3℃ / min and held for 5 h. Then, the temperature was increased to 700℃ at a rate of 3℃ / min and held for 16 h. After sintering, the mixture was allowed to cool naturally and then pulverized to obtain a particle size D. 50 LiNi, a ternary cathode material with a thickness of 8.21 μm 0.95 Co 0.03 Mn 0.02 O2.

[0084] (2) Add 16L of deionized cold water (5℃) to the reactor, stir at 95rpm, then slowly pour in 8kg of ternary cathode material, wash for 2min, centrifuge and dry.

[0085] (3) Take 4 kg of washed ternary cathode material and 40 g of selenium dioxide powder and mix them in a high-speed mixer at 800 rpm for 25 min. Calcinate the mixture at 275 °C for 9 h in an oxygen atmosphere, cool it and pass it through a 200 mesh sieve to obtain selenium dioxide-coated high-nickel ternary cathode material.

[0086] Comparative Example 3

[0087] A coated ternary material with the chemical formula LiNi 0.95 Co 0.03 Mn 0.02O2·0.06Li2SeO3.

[0088] A method for preparing a coated ternary material as described above differs from Example 1 only in that selenium dioxide powder is not added in step (3). The specific steps are as follows:

[0089] (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 uniform mixing, the mixture was placed in a sagger and then into a box furnace. An oxygen atmosphere (oxygen concentration ≥ 90%) was introduced, and the temperature was increased to 500℃ at a rate of 3℃ / min and held for 5 h. Then, the temperature was increased to 700℃ at a rate of 3℃ / min and held for 16 h. After sintering, the mixture was allowed to cool naturally and then pulverized to obtain a particle size D. 50 LiNi, a ternary cathode material with a thickness of 8.21 μm 0.95 Co 0.03 Mn 0.02 O2.

[0090] (2) Add 120g of selenium dioxide powder and 16L of deionized cold water (5℃) to the reactor, stir at 95rpm until dissolved, then slowly pour in 8kg of ternary cathode material, wash for 2min, centrifuge and dry.

[0091] (3) Take 4 kg of washed ternary cathode material and calcine it at 275°C for 9 h in an oxygen atmosphere. After cooling, sieve it through a 200-mesh sieve to obtain high-nickel ternary cathode material coated with lithium selenite.

[0092] The SEM image of the lithium selenite-coated high-nickel ternary cathode material, magnified 50,000 times, is shown below. Figure 3 As shown, a 10,000x magnified SEM image of the lithium selenite-coated high-nickel ternary cathode material is shown below. Figure 4 As shown.

[0093] Comparative Example 4

[0094] A ternary material with the chemical formula LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0095] The preparation method of the ternary material coated as described above differs from Example 3 only in that selenium dioxide powder is not added in steps (2) and (3). The specific steps are as follows:

[0096] (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 uniform mixing, the mixture was placed in a sagger and then into a box furnace. An oxygen atmosphere (oxygen concentration ≥ 90%) was introduced, and the temperature was increased to 500℃ at a rate of 3℃ / min and held for 5 h. Then, the temperature was increased to 700℃ at a rate of 3℃ / min and held for 16 h. After sintering, the mixture was allowed to cool naturally and then pulverized to obtain a particle size D. 50 LiNi, a ternary cathode material with a thickness of 8.47 μm 0.8 Co 0.1 Mn 0.1 O2.

[0097] (2) Add 16L of deionized cold water (5℃) to the reactor, stir at 95rpm, then slowly pour in 8kg of ternary cathode material, wash for 2min, centrifuge and dry.

[0098] (3) Take 4 kg of washed ternary cathode material and calcine it at 275°C for 9 h in an oxygen atmosphere. After cooling, pass it through a 200-mesh sieve to obtain high-nickel ternary cathode material with lithium selenite / selenium dioxide double-layer coating.

[0099] Comparative Example 5

[0100] A coated ternary material with the chemical formula LiNi 0.8 Co 0.1 Mn 0.1 O2·0.02SeO2.

[0101] A method for preparing a coated ternary material as described above differs from Example 3 only in that selenium dioxide powder is not added in step (2). The specific steps are as follows:

[0102] (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 uniform mixing, the mixture was placed in a sagger and then into a box furnace. An oxygen atmosphere (oxygen concentration ≥ 90%) was introduced, and the temperature was increased to 500℃ at a rate of 3℃ / min and held for 5 h. Then, the temperature was increased to 700℃ at a rate of 3℃ / min and held for 16 h. After sintering, the mixture was allowed to cool naturally and then pulverized to obtain a particle size D. 50 LiNi, a ternary cathode material with a thickness of 8.47 μm 0.8 Co 0.1 Mn 0.1 O2.

[0103] (2) Add 16L of deionized cold water (5℃) to the reactor, stir at 95rpm, then slowly pour in 8kg of ternary cathode material, wash for 2min, centrifuge and dry.

[0104] (3) Take 4 kg of washed ternary cathode material and 80 g of selenium dioxide powder and mix them in a high-speed mixer at 800 rpm for 25 min. Calcinate the mixture at 275 °C for 9 h in an oxygen atmosphere, cool it and pass it through a 200 mesh sieve to obtain selenium dioxide-coated high-nickel ternary cathode material.

[0105] Comparative Example 6

[0106] A coated ternary material with the chemical formula LiNi 0.8 Co 0.1 Mn 0.1 O2·0.06Li2SeO3.

[0107] A method for preparing a coated ternary material as described above differs from Example 3 only in that selenium dioxide powder is not added in step (3). The specific steps are as follows:

[0108] (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 uniform mixing, the mixture was placed in a sagger and then into a box furnace. An oxygen atmosphere (oxygen concentration ≥ 90%) was introduced, and the temperature was increased to 500℃ at a rate of 3℃ / min and held for 5 h. Then, the temperature was increased to 700℃ at a rate of 3℃ / min and held for 16 h. After sintering, the mixture was allowed to cool naturally and then pulverized to obtain a particle size D. 50 LiNi, a ternary cathode material with a thickness of 8.47 μm 0.8 Co 0.1 Mn 0.1 O2.

[0109] (2) Add 120g of selenium dioxide powder and 16L of deionized cold water (5℃) to the reactor, stir at 95rpm until dissolved, then slowly pour in 8kg of ternary cathode material, wash for 2min, centrifuge and dry.

[0110] (3) Take 4 kg of washed ternary cathode material and calcine it at 275°C for 9 h in an oxygen atmosphere. After cooling, pass it through a 200-mesh sieve to obtain high-nickel ternary cathode material coated with lithium selenite.

[0111] Test case

[0112] Battery Assembly and Testing: Lithium-ion coin cells were assembled in a glove box (argon atmosphere, H2O < 0.1 ppm, O2 < 0.1 ppm). The high-nickel ternary cathode materials, conductive agents, and binders prepared in Examples 1-2 and Comparative Examples 1-8 were mixed uniformly at a ratio of 90:5:5. Dimethylformamide (DMF) solvent was added and stirred to form a slurry, which was then coated. After baking at 105°C for 2 hours, the slabs were punched and dried again in a vacuum oven at 105°C for 5 hours. Coin cells were then assembled. The electrolyte was LiPF6 dissolved in a mixed solvent of propylene carbonate and diethyl carbonate. The separator was a polyimide membrane, and the negative electrode was a lithium metal sheet. After assembly, the cells were allowed to stand for 3 hours before the first cycle test. The test conditions were 25°C and 0.1C for charge / discharge capacity and initial efficiency. Cycle performance testing was performed using all-electric coin cells, with the lithium metal negative electrode replaced by carbon material. The cycle stability of the cells was tested under 1C conditions. The methods provided in Examples 1-4 can effectively synthesize coated materials with dual coatings, significantly reduce residual lithium, and improve the electrochemical performance and stability of the materials. The effects of the present invention will be specifically explained below in conjunction with comparative examples and examples.

[0113] The LiOH content, Li2CO3 content, and residual Li content of the high-nickel ternary cathode materials in Examples 1-4 and Comparative Examples 1-6 + The contents are shown in Tables 1 and 2, where the LiOH content and Li2CO3 content are the amounts of LiOH and Li2CO3, respectively, and the residual lithium is the sum of the amounts of the two. + The total amount of substance shows that the residual alkali on the surface of the materials in Examples 1-2 is significantly lower than that in Comparative Examples 1-3. Similarly, the residual alkali on the surface of the materials in Examples 3-4 is significantly lower than that in Comparative Examples 4-6. This is attributed to the coating of the materials by lithium selenite produced by the reaction of lithium selenite with residual lithium in the solution, and the coating by the selenium dioxide added in the second mixing, which reduces the contact between the materials and air. The first charge-discharge capacity data of the high-nickel ternary cathode materials in Examples 1-4 and Comparative Examples 1-6 under the condition of 4.3V / 0.1C are shown in Table 3. It can be seen that the discharge specific capacity of the materials obtained in Examples 1-2 is higher than that of Comparative Examples 1-3. This is attributed to the fact that lithium selenite produced by the reaction of selenite with residual lithium is an excellent ionic conductor. The cycle performance comparison between Examples 1-2 and Comparative Examples 1-3 is as follows: Figure 7 As shown, the capacity retention rates of Examples 1-2 and Comparative Examples 1-3 after 80 cycles were 80.55%, 77.11%, 70.50%, 74.97%, and 75.18%, respectively. The examples and comparative examples demonstrate that double-layer coating significantly improves performance compared to 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 residual lithium content to further reduce residual lithium; however, a higher coating amount can negatively impact product performance to some extent.

[0114] Figures 1-6The morphology of the cathode materials in Example 1, Comparative Example 3, and Comparative Example 1 are shown respectively. Specifically, Figures 1-2 This is the SEM image of Example 1. Figures 3-4 This is the SEM image for Comparative Example 3. Figures 5-6 This is the SEM image for Comparative Example 1. (From...) Figures 5-6 The ternary material, completely uncoated, is clearly visible, with primary particles clearly discernible; [The text abruptly ends here, likely due to an incomplete translation or source material.] Figures 3-4 As can be seen in Comparative Example 3, which underwent the first coating, there is a clear thin-layer coating; by Figures 1-2 As can be seen from Example 1 after double-layer coating, there is a more obvious and thicker coating layer, the coating layer is more uniform, and there is no obvious material exposure.

[0115] Table 1

[0116] % by content Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 LiOH 0.5624 0.5148 0.8671 0.7523 0.6213 Li2CO3 0.3194 0.3017 0.6814 0.4328 0.3946 Residual Li + ]]> 0.2230 0.2059 0.3793 0.2994 0.2542

[0117] Table 2

[0118] % by content Example 3 Example 4 Comparative Example 4 Comparative Example 5 Comparative Example 6 LiOH 0.3153 0.2921 0.6318 0.4209 0.4057 Li2CO3 0.1753 0.1612 0.3574 0.2357 0.2296 Residual Li + ]]> 0.1243 0.1149 0.2503 0.1663 0.1607

[0119] Table 3

[0120]

Claims

1. A lithium selenite / selenium dioxide double-shelled 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 O2·xLi2SeO3·ySeO2, wherein Li2SeO3 is an inner coating layer, and SeO2 is an outer coating layer; wherein a+b+c=1, 0.6 The lithium selenite is generated by the reaction of selenous acid and residual lithium on the surface of the ternary material.

2. The lithium selenite / selenium dioxide double-shelled ternary material of claim 1, wherein, The chemical formula of the lithium selenite / selenium dioxide double-layer coated ternary material is LiNi a Co b Mn c O2·xLi2SeO3·ySeO2, wherein 0.8 3. The lithium selenite / selenium dioxide double-shelled ternary material of claim 1 or 2, characterized in that, The chemical formula of the lithium selenite / selenium dioxide double-layer coated ternary material is LiNi a Co b Mn c O2·xLi2SeO3·ySeO2, wherein 0.005 O2·xLi2SeO3·ySeO2, wherein 0.005 O2·xLi2SeO3·ySeO2, wherein 0.005 4. The lithium selenite / selenium dioxide double-shelled ternary material of claim 1, wherein, 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-shelled ternary material of claim 1, wherein, The thickness of the inner coating layer is 1-20 nm.

6. The lithium selenite / selenium dioxide double-shelled ternary material of claim 1, wherein, The thickness of the outer coating layer is 1-20 nm.

7. A method for preparing lithium selenite / selenium dioxide double-coated ternary material according to any one of claims 1-6, characterized by, The method comprises the following steps: S1: mixing a ternary material substrate with a selenious acid solution, drying to obtain a single-layer coated ternary material; S2: mixing the single-layer coated ternary material with selenium dioxide powder, calcining to obtain a lithium selenite / selenium dioxide double-layer coated ternary material. 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.

8. The preparation method according to claim 7, characterized in that, The selenious acid solution is prepared by dissolving selenium dioxide powder in water at 0-10 ℃.

9. The preparation method according to claim 8, 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.

10. The preparation method according to claim 7, characterized in that, In step S1, the ternary material substrate is mixed with the selenious acid solution for 1-3 min.

11. 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.

12. The method of claim 7, wherein, In step S2, the calcining temperature is 250-350 ℃, and the calcining time is 8-12 h.

13. The preparation method according to claim 7, characterized in that, The lithium selenite / selenium dioxide double-layer coated ternary material of any one of claims 1-6.

14. A positive electrode sheet characterized by comprising: The positive electrode sheet of claim 14.

15. A lithium-ion battery, characterized by, ​

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