Double-coated lithium cobalt oxide cathode material, preparation method thereof and lithium cobalt oxide battery

Abstract

The present application relates to the technical field of lithium battery, in particular to a double-coated lithium cobaltate positive electrode material, a preparation method thereof and a lithium cobaltate battery. The double-coated lithium cobaltate positive electrode material comprises a lithium cobaltate core and a double-layer coating layer coated outside the core, the double-layer coating layer comprises a doped-element-containing Mxene coating layer and a doped-element-containing graphite-phase carbon nitride coating layer, the doped-element-containing Mxene coating layer is coated outside the lithium cobaltate core, the doped-element-containing graphite-phase carbon nitride coating layer is coated outside the doped-element-containing Mxene coating layer, and the doped element is selected from any one of nitrogen, phosphorus or sulfur. The problem that the cycle performance of the lithium cobaltate positive electrode material at high voltage will rapidly decay is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and more specifically, to a double-coated lithium cobalt oxide cathode material, its preparation method, and a lithium cobalt oxide battery. Background Technology

[0002] There are many types of lithium-ion batteries on the market. Lithium cobalt oxide batteries, as one of the earliest commercially available batteries, are widely used in 3C electronic products due to their advantages such as high energy density, long cycle life, and good safety.

[0003] While lithium cobalt oxide batteries offer numerous advantages, their cycle performance rapidly degrades during long-term cycling at high voltages. This is due to two main reasons: First, as lithium ions continuously escape from the lithium cobalt oxide cathode material under high voltage, an irreversible phase transition occurs in its crystal structure, leading to capacity decay. Second, with the continued loss of lithium ions, the surface lattice oxygen activity increases to a certain level, causing oxygen evolution. This results in decreased cobalt atom stability, forming unstable, high-valence cobalt ions that dissolve in the electrolyte, leading to surface side reactions.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a double-coated lithium cobalt oxide cathode material, its preparation method, and a lithium cobalt oxide battery. The double-coated lithium cobalt oxide cathode material provided by this invention solves one of the aforementioned problems, thereby improving the issue of rapid degradation of the cycling performance of lithium cobalt oxide cathode materials under high voltage.

[0006] This invention is implemented as follows:

[0007] In a first aspect, the present invention provides a double-coated lithium cobalt oxide cathode material, comprising a lithium cobalt oxide core and a double-layer coating layer covering the core. The double-layer coating layer comprises a doped Mxene coating layer and a doped graphitic carbon nitride coating layer. The doped Mxene coating layer covers the lithium cobalt oxide core, and the doped graphitic carbon nitride coating layer covers the doped Mxene coating layer. The doping element is selected from any one of nitrogen, phosphorus, or sulfur.

[0008] In an optional embodiment, the dopant content in the doped Mxene coating is 10%-40% of all dopant elements, and the dopant content in the doped graphite phase carbon nitride coating is 60%-90% of all dopant elements.

[0009] Preferably, the doped Mxene coating layer covers all or part of the lithium cobalt oxide core;

[0010] Preferably, the doped Mxene coating layer completely covers the lithium cobalt oxide core;

[0011] Preferably, the graphitic carbon nitride coating layer containing doped elements covers all or part of the Mxene coating layer containing doped elements.

[0012] Preferably, the doped graphite phase carbon nitride coating layer completely covers the outside of the doped Mxene coating layer.

[0013] Secondly, the present invention provides a method for preparing the double-coated lithium cobalt oxide cathode material described in the foregoing embodiments, see [link to previous document]. Figure 1 This includes: a doped Mxene coating layer and a doped graphitic carbon nitride coating layer sequentially coated around the lithium cobalt oxide core.

[0014] In an optional embodiment, the method includes: mixing the lithium cobalt oxide core with Mxene material uniformly and then performing a second sintering to form an undoped Mxene coating layer, wherein the undoped Mxene coating layer covers the lithium cobalt oxide core.

[0015] In an optional embodiment, the Mxene material comprises transition metal carbides and / or transition metal carbonitrides;

[0016] Preferably, it is at least one of Ti3C2Tx, TiCTx, V2CTx, Ti3CNTx, and Nb2CTx; more preferably, it is Ti3C2Tx and / or TiCTx.

[0017] Preferably, the mass of Mxene material in the undoped Mxene coating layer is 0.01%-0.05% of the total mass of the raw materials forming the double-coated lithium cobalt oxide cathode material;

[0018] Preferably, the conditions for the second sintering include: a temperature of 500℃-650℃ and a time of 10-15h.

[0019] In an optional embodiment, the method includes: mixing an intermediate with an undoped Mxene coating layer covering the lithium cobalt oxide core with graphite phase carbon nitride and raw materials containing doped elements, and then performing a third sintering to form a doped Mxene coating layer and a doped graphite phase carbon nitride coating layer, wherein the doped Mxene coating layer and the doped graphite phase carbon nitride coating layer are sequentially coated on the outside of the lithium cobalt oxide core.

[0020] In an optional embodiment, the mass of the dopant element in the doped Mxene coating layer is 0.05-0.1% of the total mass of the raw materials forming the double-coated lithium cobalt oxide cathode material;

[0021] The mass of the doped element in the graphite-phase carbon nitride coating layer containing doped elements is 0.4-1% of the total mass of the raw materials forming the double-coated lithium cobalt oxide cathode material;

[0022] The mass of the graphite phase carbon nitride in the doped graphite phase carbon nitride coating layer is 0.5-2% of the total mass of the raw materials forming the double-coated lithium cobalt oxide cathode material;

[0023] Preferably, the conditions for the third sintering are: a temperature of 400-550℃, more preferably 450℃-500℃; and a sintering time of 11-15 hours.

[0024] Preferably, the raw material containing the doped element is selected from any one of elemental sulfur, urea, and phosphorus oxide.

[0025] In an optional embodiment, the preparation steps of the lithium cobalt oxide core include: mixing a cobalt source and a lithium source and then performing a first sintering to form the lithium cobalt oxide core.

[0026] In an optional embodiment, the cobalt source is selected from at least one of cobalt salts, cobalt hydroxides, and cobalt oxides; preferably, it is selected from at least one of cobalt tetroxide, cobalt sulfate, cobalt chloride, cobalt carbonate, cobalt oxalate, and cobalt hydroxide.

[0027] Preferably, the lithium source is selected from at least one of lithium salts and lithium hydroxides; more preferably, it is selected from at least one of lithium carbonate and lithium hydroxide.

[0028] Preferably, the molar ratio of the cobalt source to the lithium source is 1:(1.1-1.2);

[0029] Preferably, the conditions for the first sintering include: a temperature of 700℃-1100℃ and a time of 9h-13h.

[0030] Thirdly, the present invention provides a lithium cobalt oxide battery, which includes the double-coated lithium cobalt oxide cathode material described in the foregoing embodiments.

[0031] The present invention has the following beneficial effects: In the embodiments of the present invention, by using a doped Mxene coating layer as the first coating layer for the lithium cobalt oxide core, the conductivity of the lithium cobalt oxide material and the suppression of surface side reactions can be improved. The doped graphitic carbon nitride coating layer, used as the second coating layer for the lithium cobalt oxide core, not only suppresses direct contact between the lithium cobalt oxide cathode material and the electrolyte, but also reduces the exposure of metal atoms on the Mxene surface and the resulting oxidation reaction, further improving the stability of the Mxene material. Simultaneously, the doping of the doped elements in both coating layers further improves the ionic conductivity and stability of the coating layers. In summary, the dual-coated lithium cobalt oxide cathode material provided by the embodiments of the present invention, by using these two materials for coating, can effectively suppress the dissolution of high-valence cobalt and the occurrence of surface side reactions in the lithium cobalt oxide cathode material under high voltage, thereby improving the cycle stability of the material. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a process flow diagram of the preparation process of the double-coated lithium cobalt oxide cathode material provided in the embodiments of the present invention;

[0034] Figure 2 The XRD pattern of the double-coated lithium cobalt oxide cathode material provided in the embodiments of the present invention;

[0035] Figure 3 This is a SEM image of the double-coated lithium cobalt oxide cathode material provided in an embodiment of the present invention. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0037] In a first aspect, the present invention provides a double-coated lithium cobalt oxide cathode material, comprising a lithium cobalt oxide core and a double-layer coating layer covering the core. The double-layer coating layer comprises a doped Mxene coating layer and a doped graphitic carbon nitride coating layer (hereinafter referred to as a doped g-C3N4 coating layer), wherein the doped Mxene coating layer serves as the first coating layer covering the lithium cobalt oxide core, and the doped graphitic carbon nitride coating layer serves as the second coating layer covering the doped Mxene coating layer.

[0038] This invention utilizes a doped Mxene coating layer as the first coating layer for the lithium cobalt oxide core, which improves the conductivity of the lithium cobalt oxide material and suppresses surface side reactions. A doped graphitic carbon nitride coating layer, used as the second coating layer for the lithium cobalt oxide core, not only inhibits direct contact between the lithium cobalt oxide cathode material and the electrolyte, but also reduces the exposure of metal atoms on the Mxene surface, thus reducing oxidation and further improving the stability of the Mxene material. Furthermore, the doping of both coating layers further enhances their ionic conductivity and stability.

[0039] It should be noted that (1) the lithium cobalt oxide core can be a conventional lithium cobalt oxide core without modified elements, or a lithium cobalt oxide core with modified elements. The embodiments of the present invention will be described using a lithium cobalt oxide core without modified elements as an example.

[0040] The two coatings mentioned above can be partial or complete coatings; that is, the doped Mxene coating layer completely or partially covers the lithium cobalt oxide core, and the doped graphitic carbon nitride coating layer completely or partially covers the doped Mxene coating layer. For excellent stability and conductivity, both coatings are complete coatings, meaning the doped Mxene coating layer completely covers the lithium cobalt oxide core, and / or, the doped graphitic carbon nitride coating layer completely covers the doped Mxene coating layer.

[0041] Furthermore, the dopant content in the doped Mxene coating is 10%-40% of the total dopant content, for example, any value between 10%-40% such as 40%, 30%, 20%, and 10%. The dopant content in the doped graphitic carbon nitride coating is 60%-90% of the total dopant content, for example, any value between 60%-90% such as 60%, 70%, 80%, and 90%.

[0042] It should be noted that the doping element content in the Mxene coating layer is 100% the same as that in the graphite phase carbon nitride coating layer.

[0043] The doping element is selected from any one of nitrogen, phosphorus and sulfur, preferably sulfur.

[0044] Secondly, the present invention provides a method for preparing the double-coated lithium cobalt oxide cathode material described in the foregoing embodiments, comprising: sequentially coating the lithium cobalt oxide core with a doped Mxene coating layer and a doped graphite-phase carbon nitride coating layer.

[0045] The specific process is as follows:

[0046] S1. Preparation of lithium cobalt oxide core;

[0047] The lithium cobalt oxide core is formed by mixing cobalt and lithium sources and then performing a first sintering. Specifically, the cobalt and lithium sources are mixed in a certain molar ratio and then sintered once in an oxygen-containing atmosphere to obtain lithium cobalt oxide powder, i.e., the lithium cobalt oxide core.

[0048] It should be noted that the above-mentioned oxygen-containing atmosphere includes, but is not limited to, air, pure oxygen gas, a mixture of oxygen and nitrogen, or any other gas containing oxygen.

[0049] The cobalt source is selected from at least one of cobalt salts, cobalt hydroxides, and cobalt oxides; preferably, at least one of cobalt tetroxide, cobalt sulfate, cobalt chloride, cobalt carbonate, cobalt oxalate, and cobalt hydroxide. The lithium source is selected from at least one of lithium salts and lithium hydroxides; more preferably, at least one of lithium carbonate and lithium hydroxide. The selection of the above-mentioned lithium and cobalt sources in this embodiment of the invention ensures the formation of a lithium cobalt oxide core and is beneficial to ensuring the performance of the subsequently formed double-coated lithium cobalt oxide cathode material.

[0050] Furthermore, the molar ratio of cobalt source to lithium source is 1:(1.1-1.2); for example, any value between 1:(1.1-1.2), such as 1:1.1, 1:1.11, 1:1.12, 1:1.13, 1:1.14, 1:1.15, 1:1.16, 1:1.17, 1:1.18, 1:1.19, and 1:1.2. A higher lithium source molar ratio can compensate for lithium loss during subsequent sintering, which is beneficial for the formation of a lithium cobalt oxide core and improves the performance of the formed double-coated lithium cobalt oxide cathode material.

[0051] The conditions for the first sintering include: a temperature of 700℃-1100℃ and a time of 9h-13h. For example, the temperature can be any value between 700℃ and 1100℃, such as 700℃, 800℃, 900℃, 1000℃, and 1100℃; and the time can be any value between 9h and 13h, such as 9h, 10h, 11h, 12h, and 13h.

[0052] Sintering within this temperature and time range allows for a more complete reaction between the cobalt and lithium sources, resulting in more stable lithium cobalt oxide.

[0053] S2, Forming an undoped Mxene coating layer;

[0054] After the lithium cobalt oxide core formed in S1 is uniformly mixed with the Mxene material, a second sintering is performed to form an undoped Mxene coating layer, and the undoped Mxene coating layer covers the outside of the lithium cobalt oxide core.

[0055] Since the raw material used in this calcination is Mxene material, which does not contain any doping elements, it only forms an Mxene coating layer to coat the lithium cobalt oxide core. This Mxene coating layer does not contain any doping elements.

[0056] The Mxene material includes transition metal carbides and / or transition metal carbonitrides; for example, including but not limited to at least one of Ti3C2Tx, TiCTx, V2CTx, Ti3CNTx, and Nb2CTx; preferably Ti3C2Tx and / or TiCTx.

[0057] The mass of Mxene material in the undoped Mxene coating is 0.1%-0.5% of the total mass of the raw materials forming the double-coated lithium cobalt oxide cathode material; for example, any value between 0.1% and 0.5%, such as 0.1%, 0.2%, 0.3%, 0.4%, and 0.5%.

[0058] The conditions for the second sintering include: a temperature of 500℃-650℃ and a time of 10-15 hours. For example, temperatures can be any value between 500℃ and 650℃, such as 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, 600℃, 610℃, 620℃, 630℃, 640℃, and 650℃. The time can be any value between 10 hours and 15 hours, such as 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, and 15 hours.

[0059] Using the above conditions ensures the effectiveness of the second calcination, preventing the Mxene material from undergoing a phase transition, which is beneficial for the formation of the Mxene coating layer and its coating of the lithium cobalt oxide core.

[0060] Mxene materials have metal-like conductivity. By forming an Mxene coating layer as the first coating layer, the conductivity of lithium cobalt oxide materials can be improved and the occurrence of surface side reactions can be suppressed.

[0061] S3. Form and coat the doped Mxene coating layer and the doped graphite phase carbon nitride coating layer;

[0062] The intermediate, which is an undoped Mxene coating layer covering the lithium cobalt oxide core, is mixed with graphitic carbon nitride and raw materials containing doped elements and then subjected to a third sintering to form a doped Mxene coating layer and a doped graphitic carbon nitride coating layer. The doped Mxene coating layer and the doped graphitic carbon nitride coating layer are sequentially coated on the outside of the lithium cobalt oxide core.

[0063] The raw material containing the doped element is selected from any one of elemental sulfur, urea, and phosphorus oxide. The mass of the doped element in the Mxene coating layer is 0.05-0.1% of the total mass of the raw materials forming the double-coated lithium cobalt oxide cathode material; for example, any value between 0.05-0.1% such as 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, and 0.1%.

[0064] The mass of the doped element in the graphite phase carbon nitride coating layer containing the doped element is 0.4-1% of the total mass of the raw materials forming the double-coated lithium cobalt oxide cathode material; for example, any value between 0.4-1% such as 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, and 1.0%.

[0065] The mass of graphite phase carbon nitride in the doped graphite phase carbon nitride coating layer is 0.5-2% of the total mass of the raw materials forming the double-coated lithium cobalt oxide cathode material; for example, any value between 0.5% and 2.0%, such as 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, and 2.0%.

[0066] Using the above-mentioned material content is more conducive to the doping of doping elements, which in turn helps the double-coated lithium cobalt oxide cathode material to exert its function.

[0067] The conditions for the third sintering are: a temperature of 400-550℃ and a sintering time of 11-15 hours. For example, the temperature can be any value between 400-550℃, such as 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, 510℃, 520℃, 530℃, 540℃, and 550℃, preferably 450℃-500℃. The sintering time can be any value between 11-15 hours, such as 11 hours, 12 hours, 13 hours, 14 hours, and 15 hours.

[0068] The above conditions not only facilitate the formation of the graphitic carbon nitride coating, but also promote the doping of the graphitic carbon nitride coating and the Mxene coating by doping elements. Specifically, if the calcination temperature is too high, all the raw materials containing doping elements will vaporize, resulting in an excessively low doping element content in the graphitic carbon nitride coating and the Mxene coating. Conversely, if the calcination temperature is too low, the doping element content in the graphitic carbon nitride coating and the Mxene coating will be excessively high.

[0069] In this embodiment of the invention, g-C3N4 is used to form a second coating layer outside the lithium cobalt oxide core. g-C3N4 possesses good conductivity and excellent electrochemical stability. The graphitic carbon nitride coating layer formed by g-C3N4 inhibits direct contact between the lithium cobalt oxide cathode material and the electrolyte. Simultaneously, its placement as a second coating layer outside the first coating layer (Mxene) reduces the exposure of metal atoms on the Mxene surface, thus reducing oxidation and further improving the stability of the Mxene material. Furthermore, this embodiment of the invention improves the ionic conductivity of the material by doping the two coating layers. In particular, during the sulfur powder gasification process, a porous structure is formed in the g-C3N4 coating layer, providing diffusion channels for lithium ions and effectively improving the rate performance of the material.

[0070] Thirdly, the present invention provides a lithium cobalt oxide battery, which includes the double-coated lithium cobalt oxide cathode material described in the foregoing embodiments.

[0071] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0072] Example 1

[0073] This invention provides a method for preparing a double-coated lithium cobalt oxide cathode material, comprising:

[0074] Step 1: Add 1.5 kg of cobalt tetroxide and 1.75 kg of lithium carbonate to a high-speed mixer and mix for 15 minutes. After mixing evenly, heat the mixture to 900°C at a heating rate of 10°C / min and calcine for 10 hours. Then cool to room temperature (around 25°C) at a cooling rate of 5°C to obtain lithium cobalt oxide powder.

[0075] Step 2: Mix 700g of lithium cobalt oxide powder obtained in Step 1 with 3g of TiCTx material until homogeneous. Then, heat the mixture to 550℃ at a rate of 10℃ / min and calcine for 10h. Subsequently, cool it to room temperature (around 25℃) at a rate of 5℃ to obtain TiCTx-coated lithium cobalt oxide powder.

[0076] Step 3: Mix 300g of TiCTx-coated lithium cobalt oxide powder, 4g of g-C3N4, and 2g of sulfur powder obtained in Step 2 evenly, and then put them into a tube furnace and introduce nitrogen gas. Heat the mixture to 450℃ at a heating rate of 10℃ / min; calcine for 11h, and then cool to room temperature (about 25℃) to obtain the double-coated lithium cobalt oxide cathode material.

[0077] Example 2

[0078] This invention provides a method for preparing a double-coated lithium cobalt oxide cathode material, comprising:

[0079] Step 1: Add 1.5 kg of cobalt tetroxide and 1.75 kg of lithium carbonate to a high-speed mixer and mix for 15 minutes. After mixing evenly, heat the mixture to 900°C at a heating rate of 10°C / min and calcine for 10 hours. Then cool to room temperature (around 25°C) at a cooling rate of 5°C to obtain lithium cobalt oxide powder.

[0080] Step 2: Mix 700g of lithium cobalt oxide powder obtained in Step 1 with 4g of TiCTx material until homogeneous. Then, heat the mixture to 550℃ at a rate of 10℃ / min and calcine for 10h. Subsequently, cool it to room temperature (around 25℃) at a rate of 5℃ to obtain TiCTx-coated lithium cobalt oxide powder.

[0081] Step 3: Mix 300g of TiCTx-coated lithium cobalt oxide powder, 4g of g-C3N4, and 2g of sulfur powder obtained in Step 2 evenly, and then put them into a tube furnace and introduce nitrogen gas. Heat the mixture to 450℃ at a heating rate of 10℃ / min; calcine for 11h, and then cool to room temperature (about 25℃) to obtain the double-coated lithium cobalt oxide cathode material.

[0082] The XRD and SEM images of the double-coated lithium cobalt oxide cathode material are shown in [reference 1]. Figure 2 and Figure 3 .

[0083] Example 3

[0084] This invention provides a method for preparing a double-coated lithium cobalt oxide cathode material, comprising:

[0085] Step 1: Add 1.5 kg of cobalt tetroxide and 1.75 kg of lithium carbonate to a high-speed mixer and mix for 15 minutes. After mixing evenly, heat the mixture to 900°C at a heating rate of 10°C / min and calcine for 10 hours. Then cool to room temperature (around 25°C) at a cooling rate of 5°C to obtain lithium cobalt oxide powder.

[0086] Step 2: Mix 700g of lithium cobalt oxide powder obtained in Step 1 with 3g of TiCTx material until homogeneous. Then, heat the mixture to 600℃ at a rate of 10℃ / min and calcine for 10h. Subsequently, cool it to room temperature (around 25℃) at a rate of 5℃ to obtain TiCTx-coated lithium cobalt oxide powder.

[0087] Step 3: Mix 300g of TiCTx-coated lithium cobalt oxide powder, 4g of g-C3N4, and 2g of sulfur powder obtained in Step 2 evenly, and then put them into a tube furnace and introduce nitrogen gas. Heat the mixture to 450℃ at a heating rate of 10℃ / min; calcine for 11h, and then cool to room temperature (about 25℃) to obtain the double-coated lithium cobalt oxide cathode material.

[0088] Example 4

[0089] This invention provides a method for preparing a double-coated lithium cobalt oxide cathode material, comprising:

[0090] Step 1: Add 1.5 kg of cobalt tetroxide and 1.75 kg of lithium carbonate to a high-speed mixer and mix for 15 minutes. After mixing evenly, heat the mixture to 900°C at a heating rate of 10°C / min and calcine for 10 hours. Then cool to room temperature (around 25°C) at a cooling rate of 5°C to obtain lithium cobalt oxide powder.

[0091] Step 2: Mix 700g of lithium cobalt oxide powder obtained in Step 1 with 3g of TiCTx material until homogeneous. Then, heat the mixture to 550℃ at a rate of 10℃ / min and calcine for 10h. Subsequently, cool it to room temperature (around 25℃) at a rate of 5℃ to obtain TiCTx-coated lithium cobalt oxide powder.

[0092] Step 3: Mix 300g of TiCTx-coated lithium cobalt oxide powder, 6g of g-C3N4, and 2g of sulfur powder obtained in Step 2 evenly, and then put them into a tube furnace and introduce nitrogen gas. Heat the mixture to 450℃ at a heating rate of 10℃ / min; calcine for 11h, and then cool to room temperature (around 25℃) to obtain the double-coated lithium cobalt oxide cathode material.

[0093] Example 5

[0094] This invention provides a method for preparing a double-coated lithium cobalt oxide cathode material, comprising:

[0095] Step 1: Add 1.5 kg of cobalt tetroxide and 1.75 kg of lithium carbonate to a high-speed mixer and mix for 15 minutes. After mixing evenly, heat the mixture to 900°C at a heating rate of 10°C / min and calcine for 10 hours. Then cool to room temperature (around 25°C) at a cooling rate of 5°C to obtain lithium cobalt oxide powder.

[0096] Step 2: Mix 700g of lithium cobalt oxide powder obtained in Step 1 with 3g of TiCTx material until homogeneous. Then, heat the mixture to 550℃ at a rate of 10℃ / min and calcine for 10h. Subsequently, cool it to room temperature (around 25℃) at a rate of 5℃ to obtain TiCTx-coated lithium cobalt oxide powder.

[0097] Step 3: Mix 300g of TiCTx-coated lithium cobalt oxide powder, 4g of g-C3N4, and 2g of sulfur powder obtained in Step 2 evenly, and then put them into a tube furnace and introduce nitrogen gas. Heat the mixture to 550℃ at a heating rate of 10℃ / min; calcine for 11h, and then cool to room temperature (around 25℃) to obtain the double-coated lithium cobalt oxide cathode material.

[0098] Example 6

[0099] This invention provides a method for preparing a double-coated lithium cobalt oxide cathode material, comprising:

[0100] Step 1: Add 1.5 kg of cobalt tetroxide and 1.75 kg of lithium carbonate to a high-speed mixer and mix for 15 minutes. After mixing evenly, heat the mixture to 900°C at a heating rate of 10°C / min and calcine for 10 hours. Then cool to room temperature (around 25°C) at a cooling rate of 5°C to obtain lithium cobalt oxide powder.

[0101] Step 2: After uniformly mixing the 700 cobalt oxide powder obtained in Step 1 with 3g of TiCTx material, the mixture is heated to 550℃ at 10℃ / min and calcined for 10h. Then, it is cooled to room temperature (around 25℃) at a cooling rate of 5℃ to obtain TiCTx-coated lithium cobalt oxide powder.

[0102] Step 3: Mix 400g of TiCTx-coated lithium cobalt oxide powder, 4g of g-C3N4, and 3g of sulfur powder obtained in Step 2 evenly, and then put them into a tube furnace and introduce nitrogen gas. Heat the mixture to 500℃ at a heating rate of 10℃ / min; calcine for 11h, and then cool to room temperature (about 25℃) to obtain the double-coated lithium cobalt oxide cathode material.

[0103] Example 7

[0104] This invention provides a method for preparing a double-coated lithium cobalt oxide cathode material, comprising:

[0105] Step 1: Add 1.5 kg of cobalt tetroxide and 1.75 kg of lithium carbonate to a high-speed mixer and mix for 15 minutes. After mixing evenly, heat the mixture to 900°C at a heating rate of 10°C / min and calcine for 10 hours. Then cool to room temperature (around 25°C) at a cooling rate of 5°C to obtain lithium cobalt oxide powder.

[0106] Step 2: Mix 700g of lithium cobalt oxide powder obtained in Step 1 with 3g of TiCTx material until homogeneous. Then, heat the mixture to 550℃ at a rate of 10℃ / min and calcine for 10h. Subsequently, cool it to room temperature (around 25℃) at a rate of 5℃ to obtain TiCTx-coated lithium cobalt oxide powder.

[0107] Step 3: Mix 300g of TiCTx-coated lithium cobalt oxide powder, 4g of g-C3N4, and 2g of phosphorus pentoxide obtained in Step 2 evenly, place the mixture in a tube furnace, introduce nitrogen gas, and heat to 550℃ at a heating rate of 10℃ / min; calcine for 11h, and then cool to room temperature (around 25℃) to obtain the double-coated lithium cobalt oxide cathode material.

[0108] Comparative Example 1:

[0109] The lithium cobalt oxide cathode material provided in Comparative Example 1 is the lithium cobalt oxide powder without any coating material prepared in step one of Example 1.

[0110] Comparative Example 2:

[0111] The lithium cobalt oxide cathode material provided in Comparative Example 2 is the undoped Mxene-coated lithium cobalt oxide cathode material prepared in step two of Example 1.

[0112] Comparative Example 3:

[0113] The preparation method of the lithium cobalt oxide cathode material in Comparative Example 3 is basically the same as that in Example 1, with the only difference being:

[0114] Step 2: Mix 700g of lithium cobalt oxide powder obtained in Step 1 of Example 1 with 2g of sulfur powder and 3g of TiCTx until homogeneous. Heat the mixture to 550℃ at 10℃ / min and calcine for 10h. Then cool it to room temperature (around 25℃) at a cooling rate of 5℃ to obtain TiCTx-coated lithium cobalt oxide powder, which is the lithium cobalt oxide cathode material of Comparative Example 3.

[0115] Step 3 is no longer performed for Example 3.

[0116] Comparative Example 4:

[0117] The preparation method of the lithium cobalt oxide cathode material in Comparative Example 4 is basically the same as that in Example 1, with the only difference being:

[0118] Step two is not performed in Comparative Example 4.

[0119] Step 3: Mix the 300 g lithium cobalt oxide powder, 4 g g-C3N4, and 2 g sulfur powder obtained in Step 1 evenly, place them in a tube furnace, introduce nitrogen gas, and heat to 450°C at a heating rate of 10°C / min; calcine for 11 h, and then cool to room temperature (around 25°C) to obtain g-C3N4 coated lithium cobalt oxide powder, which is the lithium cobalt oxide cathode material of Comparative Example 4.

[0120] Comparative Example 5:

[0121] The preparation method of the lithium cobalt oxide cathode material in Comparative Example 5 is basically the same as that in Example 1, with the only difference being:

[0122] Step two is not performed for Comparative Example 5.

[0123] Step 3: Mix 300g of lithium cobalt oxide powder and 4g of g-C3N4 obtained in Step 1 evenly, place them in a tube furnace, introduce nitrogen gas, and heat to 450℃ at a heating rate of 10℃ / min; calcine for 11h, and then cool to room temperature (about 25℃) to obtain g-C3N4 coated lithium cobalt oxide powder, which is the lithium cobalt oxide cathode material of Comparative Example 5.

[0124] Comparative Example 6

[0125] The preparation method of the lithium cobalt oxide cathode material in Comparative Example 6 is basically the same as that in Example 1, with the only difference being:

[0126] Step 3: Mix 300g of TiCTx-coated lithium cobalt oxide powder and 4g of g-C3N4 evenly in a tube furnace, introduce nitrogen gas, and heat to 450℃ at a heating rate of 10℃ / min; calcine for 11h, and then cool to room temperature (around 25℃) to obtain g-C3N4-coated lithium cobalt oxide powder, which is the lithium cobalt oxide cathode material of Comparative Example 6.

[0127] Detection example

[0128] The double-coated lithium cobalt oxide cathode materials of Examples 1-6 and Comparative Examples 1-6 were respectively fabricated into cathode plates, and assembled into batteries with anode plates, ceramic separators, and LiPF6 electrolyte for electrochemical performance testing. The results are shown in Table 1.

[0129] Table 1 Electrochemical performance test of various lithium cobalt oxide cathode materials at 0.1C

[0130]

[0131]

[0132] As shown in Table 1, the lithium cobalt oxide cathode materials prepared in each embodiment of the present invention still have high initial coulombic efficiency and excellent capacity retention at 0.1C. Different material ratios, sintering temperatures, and sintering times all affect the electrochemical performance of the lithium cobalt oxide cathode materials.

[0133] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A double-coated lithium cobalt oxide cathode material, characterized in that, The device includes a lithium cobalt oxide core and a double-layer coating layer covering the core. The double-layer coating layer includes a doped Mxene coating layer and a doped graphitic carbon nitride coating layer. The doped Mxene coating layer covers the lithium cobalt oxide core, and the doped graphitic carbon nitride coating layer covers the doped Mxene coating layer. The doping element is selected from any one of nitrogen, phosphorus, or sulfur.

2. The double-coated lithium cobalt oxide cathode material according to claim 1, characterized in that, The doped element content in the Mxene coating layer is 10%-40% of the total doped elements, and the doped element content in the graphitic carbon nitride coating layer is 60%-90% of the total doped elements.

3. The double-coated lithium cobalt oxide cathode material according to claim 1, characterized in that, The doped Mxene coating layer covers all or part of the lithium cobalt oxide core.

4. The double-coated lithium cobalt oxide cathode material according to claim 1, characterized in that, The doped Mxene coating layer completely covers the lithium cobalt oxide core.

5. The double-coated lithium cobalt oxide cathode material according to claim 1, characterized in that, The doped graphite-phase carbon nitride coating layer covers all or part of the doped Mxene coating layer.

6. The double-coated lithium cobalt oxide cathode material according to claim 1, characterized in that, The doped graphitic carbon nitride coating layer completely covers the outside of the doped Mxene coating layer.

7. A method for preparing the double-coated lithium cobalt oxide cathode material according to claim 1, characterized in that, include: The lithium cobalt oxide core is sequentially coated with a doped Mxene coating layer and a doped graphitic carbon nitride coating layer.

8. The preparation method according to claim 7, characterized in that, include: After the lithium cobalt oxide core is mixed evenly with Mxene material, a second sintering is performed to form an undoped Mxene coating layer, which covers the outside of the lithium cobalt oxide core.

9. The preparation method according to claim 8, characterized in that, The Mxene material includes transition metal carbides and / or transition metal carbonitrides.

10. The preparation method according to claim 9, characterized in that, The Mxene material is at least one of Ti3C2Tx, TiCTx, V2CTx, Ti3CNTx, and Nb2CTx.

11. The preparation method according to claim 9, characterized in that, The Mxene material is Ti3C2Tx and / or TiCTx.

12. The preparation method according to claim 8, characterized in that, The mass of Mxene material in the undoped Mxene coating layer is 0.1%-0.5% of the total mass of the raw materials forming the double-coated lithium cobalt oxide cathode material.

13. The preparation method according to claim 9, characterized in that, The conditions for the second sintering include: a temperature of 500℃-650℃ and a time of 10-15h.

14. The preparation method according to claim 8, characterized in that, include: An intermediate containing an undoped Mxene coating layer is mixed with graphitic carbon nitride and raw materials containing doped elements and then subjected to a third sintering process to form a doped Mxene coating layer and a doped graphitic carbon nitride coating layer. The doped Mxene coating layer and the doped graphitic carbon nitride coating layer are sequentially coated on the outside of the lithium cobalt oxide core.

15. The preparation method according to claim 14, characterized in that, The mass of the dopant element in the Mxene coating layer is 0.05-0.1% of the total mass of the raw materials forming the double-coated lithium cobalt oxide cathode material; The mass of the doped elements in the graphitic carbon nitride coating layer is 0.4-1% of the total mass of the raw materials forming the double-coated lithium cobalt oxide cathode material; The mass of the graphite phase carbon nitride in the doped graphite phase carbon nitride coating is 0.5-2% of the total mass of the raw materials forming the double-coated lithium cobalt oxide cathode material; The conditions for the third sintering are: temperature of 400-550 ℃ and sintering time of 11-15 h.

16. The preparation method according to claim 15, characterized in that, The third sintering temperature is 450℃-500℃.

17. The preparation method according to claim 15, characterized in that, The raw materials containing doped elements are selected from any one of elemental sulfur, urea, and phosphorus oxide.

18. The preparation method according to claim 7, characterized in that, The preparation steps of the lithium cobalt oxide core include: mixing a cobalt source and a lithium source and then performing a first sintering to form the lithium cobalt oxide core.

19. The preparation method according to claim 18, characterized in that, The cobalt source is selected from at least one of cobalt salts, cobalt hydroxides, and cobalt oxides; The lithium source is selected from at least one of lithium salts and lithium hydroxides.

20. The preparation method according to claim 18, characterized in that, The cobalt source is at least one of cobalt tetroxide, cobalt oxide, cobalt chloride, cobalt carbonate, cobalt oxalate, and cobalt hydroxide. The lithium source is at least one of lithium carbonate and lithium hydroxide.

21. The preparation method according to claim 18, characterized in that, The molar ratio of the cobalt source to the lithium source is 1:(1.1-1.2). The conditions for the first sintering include: a temperature of 700℃-1100℃ and a time of 9h-13h.

22. A lithium cobalt oxide battery, characterized in that, It includes the double-coated lithium cobalt oxide cathode material as described in claim 1.

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